Fola Jokes Villa

THE ALMA TELESCOPE

2013-03-15T02:26:00.001-07:00

SAN PEDRO DE ATACAMA — The largest astronomical project in history, the ALMA telescope arrayin Chile’s northern desert, has officially begun operations in a ceremony involving leaders of the scientific community, swarms of reporters from international media outlets, and the President of the Republic. “This is undoubtedly the most powerful telescope in the world,” President Piñera said. “It will allow us to expand the frontiers of knowledge, bring us closer to our ancestors, and likelybring us closer to the secrets of the origin of the universe.” ALMA will indeed help us understand the world in which we are living, our origins, how our planet and our galaxy was formed, and what exactly surrounds us in the universe. ALMA can peer into nebulae, giant clouds of gas where stars are born, in order to understand their formation and those of planets that may eventually orbit them. ALMA is able to capture the light of the universe at millimeter and submillimeter wavelengths, about a thousand times longer than the wavelengths of visible light. The observation of these long wavelengths allow astronomers to study very cold objects in space, such as the thick clouds of cosmic dust and gas where stars and planets are being formed and also very distant objects in the early universe. That differentiates this complex from the optical and infrared telescopes. The set of synchronized antennas functionsas a single giant telescope, so that the images of the universe itcaptures are quite different fromthose we know. ALMA is based on an international partnership between Europe ( ESO ), North America ( NRAO ), and East Asia ( NAOJ ), in cooperation with the Republic of Chile. These international organizations helped Chile finance, build, and direct operations in the project. In total, 20 countries and over 500 people work on it. “ALMA is like a window to the knowledge of the universe, to discover what’s surrounding us. This is like opening a window never opened before in a house, and see what’s hiding behind it,”astronomer Gianni Marconi says.

URINE POWERED GENERATOR

2012-11-08T05:58:00.001-08:00

14-year-old Duro-Aina Adebola, Akindele Abiola, and Faleke Oluwatoyin, together with 15-yearold Bello Eniola showcased their unique innovation at this year’s Maker Faire Africa held in Lagos, Nigeria. The system works by pouring urine into an electrolytic cell to separate the hydrogen. The filtered hydrogen then goes into awater filter for purification where it then be pushed into a gas cylinder. Afterwards, the gas cylinder pushes hydrogen into a cylinder of liquid borax in order toremove the moisture from the hydrogen gas. Lastly, the purified hydrogen gas is then pushed into the generator to provide power to the bulb. The girls claim that one liter of urine is enough to power the generator for six hours. Not bad for an alternative source of electricity! The urine-powered generator could prove to be useful, especially in Africa, where power shortages are rampant.

THE CANCER DETECTING BRA

2012-11-06T11:39:00.003-08:00

Preliminary studies with First Warning Systems were conducted in more than 650 women, resulting in an average detection of at least 90 percent. Compared with the standard mammogram, the tests averaged 70 percent accuracy. In a release, Lifeline Biotechnologies, the medical technology company licensing thebra observed that the First Warning System is capable not only identifying breast tissue abnormalities at their earliest stages, but can also identify the general location of such abnormalities in three dimensionsto each of the four quadrants of each breast. “It is, therefore, not intended as an additional step in the breast cancer screening process, but as an accurate identifier of early breast abnormalities which generate heat via the presence of new blood vessels that nourish the area in question.” The bra, which would be worn at a physician’s office, has 16 colour-coded sensors that are taped to the patient’s breast. The sensors would then measure temperatures at programmed times over a predetermined testing period. The data is then stored in a recording device wornby the patient. Once the test period is over, the patient then submits the device to their doctor.The sensors are removed; the data is downloaded and then analyzed. Once a report is returned to the physician, the patient will be called in to discuss any clinical recommendations. Based on what is described as “disruptive technology” and tissue health science, the new breast cancer detector could become a major breakthrough in making testing easier for women, however, medical experts say more studies are required before being actively used. In a statement, Dr. Ted Gansler, Director of Medical Content for theAmerican Cancer Society said: “Most investigational medicines and medical devices, even those based on sound scientific and technical principles do not end upbeing adopted into clinical practice. He adds that the main reason is that once these new products are rigorously tested in clinical trials, the result of the study is that they are less effectivethan current practices. But Gansler also explains that disregarding mammography would have harmful, serious effects. “A woman who chooses any breast cancer screening test based on thermography instead of mammography would be making a serious mistake that could have fatal consequences. Major medical and public health organizations all recommend mammography and none recommend thermography or anyother tests based on temperature measurements for early detection of breast cancer.” Dr. Michele Doughty, who has conducted extensive research on how breast cancer affects womenof various races differently, thinks the bra could be used as part of an overall test without replacing mammography. “There needs to be more researchand studies on the long term effects of the bra because they must contain some kind of ultraviolet ray component or chemical component,” says Doughty. “Mammograms and the bra just screen for breast cancer. The only way to actually detect breast cancer is through a biopsy where the specimen is found in the lab.”

THE NEW PLANET (SUPPER EARTH)

2012-10-25T08:55:00.001-07:00

Scientists have discovered a planet made of diamonds. The strange alien world is roughlytwice the size of Earth, eight timesits mass and is orbiting a (relatively) near star. "This is our first glimpse of a rocky world with a fundamentally different chemistry from Earth," said lead researcher Nikku Madhusudhan, from Yale . "The surface of this planet is likely covered in graphite and diamond rather than water and granite." The planet is called 55 Cancri E, and is one of five worlds in the system located just 40 light years from Earth in the constellation of Cancer. Its composition was discovered after new details about its orbit - a year lasts just 18 hours on 55 Cancri E - and conditions on the planet (a super-hot 3,9000 degrees Fahrenheit) came to light. Researchers are able to estimate its mass, and infer its chemical make-up from this and other information. They now say it is mainly made of carbon (as graphite and diamond), iron and silicon carbide. The discovery is not the first diamond planet to be discovered. A similar find was made in 2011, and there are likely many other worlds with a similar composition. But the discovery will still force researchers to think differently about how alien worlds are made,the study said. "The identification of a carbon-rich super-Earth means that distant rocky planets can no longer be assumed to have chemical constituents, interiors, atmospheres, or biologies similar to those of Earth," the researchersreported. "This 'diamond-rich super-Earth' is likely just one example of the rich sets of discoveries that await us as we begin to explore planets around nearby stars."

THE BRAIN

2012-09-12T10:33:00.002-07:00

The brain is the most complex organ in the body. It is the organ that allows us to think, have emotions, move, and even dream. Given this complexity, it should not be surprising that there are many ways to separate the parts of the brain. Brain parts can be separated on the basis of what they look like to the naked eye, under a microscope, or by what certain brain parts do. The brain and spinal cord make up the central nervous system and all of the nerves found in our body make up the peripheral nervous system.
When you see a picture of the brain you probably think of a wrinkled gray blob. Well, the wrinkles are called cortex and it is where the majority of brain cells or neurons reside. The cortex can be divided into four main lobes. The frontal lobe, where you do your heavy thinking, pondering and planning your actions; temporal cortex, where you process sounds and form memories; occipital cortex, where you process all the things that you see; and parietal cortex, where you integrate or makes sense of all of the different bits of information that are bombarding your brain.

The Hindbrain

Having evolved hundreds of millions of years ago, the Hindbrain or the Reptillian Brain is the oldest part of the human brain. As you might guess from it's name, it's a piece of brain anatomy that we share with reptiles and is the most primitive. Likewise it's in charge of our primal instincts and most basic functions. Things like the instincts of survival, dominance, mating and the basic functions of respiration, heartbeat all come from this area of the brain. Located in the Hindbrain are:

The Spinal Cord

The Medulla Oblongata

The Pons

The Cerebellum

The Limbic System

The Limbic System sometimes called the "emotional brain" or "Old Mammalian Brain" is the next part of the brain to have evolved in the more primitive mammals about 150 million years ago. This is where our emotions reside, where memory begins and where these two functions combine together to mark behaviours with positive or negative feelings. It's where mostly unconcious value judgements are made. Information going through the Limbic System are filed under "agreeable or disagreeable". It also plays a role in salience (what grabs your attention), spontaneity and creativity. Located in the Limbic System are:

The Amygdala

The Hippocampus

The Hypothalamus

Hyper

The Thalamus

The Neocortex

The last and most advanced brain to evolve to date is called the Neocortex, neomammalian or rational brain. We share this part of our brain with other higher level mammals like the primates and dolphins, although in humans the neocortex is the largest. It takes up 2/3's of the human brain. This is where we find the brain power to develop language, abstract thought, conciousness and imagination. Let there be no doubt, this is what grants us our status on the food chain and allows us to be human.
The Neocortex is divided into two hemispheres, right and left. The right side of the brain controls the left side of the body and vice versa. Also the hemispheres are divided in terms of what kind of thought they process or produce. The right being more concerned with the artistic, spatial and musical. While the left is more concerned with the colder, linear, rational and verbal aspects. Located in the Neocortex are:

The Frontal Lobe

The Parietal Lobe

The Temporal Lobe

The Occipital Lobe

Broca's Area

The Corpus Callosum

MICROSOFT WORD

2012-08-24T10:52:00.001-07:00

Microsoft Word

Article Contents

Translations

Translations of this article are available in:

German - External Link - courtesy of SEO Matrix - External Link

Introduction

Microsoft Word is currently the most common word processor on the market. Because it is so common, the .doc (and to a lesser extent, .docx) format has become the de facto format for text documents. Word is often used to create files that end up in PDF and HTML. This article will cover several things that you can do to make web content created in Word more accessible.

Create Accessible Word Documents

Headings

A good heading structure is probably the most important accessibility consideration in most Word documents. Headings will allow screen reader users to navigate through the page easily and will make the page more usable for everyone. Many people do not use true styles in Word. For example, when creating a heading, they simply change the font, enlarge the font size, make it bold, etc. If this is done, the document has no real structure that can be discerned by a screen reader. In Word, the correct way to provide structure is to use Word styles. This section will outline how to add and edit headings in all common versions of Word. You can also add 1st, 2nd, or 3rd level headings using Ctrl + Alt + 1, 2, or 3 (Cmd + Option on a Mac).

Word 2000-2003

The drop-down styles list allows you to create true headings, as well as apply any previously-created custom style.

There are a couple of advantages of having true structure in Word documents. First, when the file is exported to HTML, it will retain the structure, making it accessible to screen readers. Second, the structure will also be retained when exported to PDF. In both cases, the added structure increases the readability of the document for people using screen readers.

Word 2007 and 2010

Word 2007 and later does a good job of encouraging the use of proper styles. About half of the default toolbar is devoted to styles. To change a block of text, select the text and click on the appropriate style.

Word for Mac

Styles on Word for Mac are available in the Formatting palette. The Styles dropdown list is similar to the list found in Word 2000-2003 for Windows.

Alternative text for images

Images can be given appropriate alternative text in Word. This alt text will be read by a screen reader in a Word file and should remain intact when exporting to HTML or PDF.

Notes

Embedded charts should be given a text description within the context of the document itself. The data that is used to create the chart will be accessible in the original file (it is basically a simple spreadsheet), but will not be included in a PDF or HTML version.
"Word art" is actually converted to an image in Office 2003-2007 and must be given alt text. It remains text in Office 2010.
There is no way to add alt text to images in Word 2004 or 2008 for Mac.

Word 2000-2003

To provide alternative text, Right-click on the image, then select Format Picture....

A dialog box will appear. Select the Web tab and then add the appropriate alternative text.

Word 2007

Adding alt text to images is less intuitive in Word 2007. To add alternative text, right-click on the picture and select Size....

A dialog box will appear. Select the Alt Text tab. You will notice that the image filename is entered into the field by default. The filename is never appropriate alternative text. This functionality will almost certainly result in misuse of the alt attribute.

Replace the filename with appropriate alternative text. For this image, it would be something like "WebAIM - Web Accessibility in Mind".

Word 2010

Word 2010 moved the alt text field back to an intuitive place, but made things even more confusing by creating two fields for alt text. To add alt text to an image, Select the Format Picture... option.

With the Format Picture menu open, select the option for Alt Text in the sidebar. Two fields will appear, one labeled Title and one labeled Description. For best results, add appropriate alt text to the Description field, not the Title field. Information in the Title field will not be saved as alt text when the file is saved as HTML.

If you want to be extra safe, you can duplicate the alt text in both the Title and Description fields.

Data tables and accessibility issues

There is no way to assign table headers or <th> elements to a table created in Word. You can indicate that a row should Repeat as header on the top of each page; in the Table Properties menu. When saved as PDF, the cells in the first row are detected as table headers, though the headers are not maintained if the file is saved as HTML. Instead, the cells will all be contained in a <thead> element. The <thead>, <tfoot>, and <tbody> are used to divide the tables into the three main parts of a data table. While the inclusion of the <thead> element poses no problems, it does not replace the need for the <th> elements for all table headers. There is no way to add row headers (headers across the side of a table) in Word.

Links

Hyperlinks are usually created in Word by pasting the full url into a page (e.g., http://webaim.org/techniques/word/) and hitting space, Enter, or some other key. This automatically creates a link. It's simple, but the URL may not make sense to the reader. To change the hyperlink text, select a link, right click and select Edit Hyperlink, or select Ctrl + K (Cmd + K on a Mac). Change the URL in the Text to display field to something more descriptive.

If you are creating a Word document that may be both printed and read electronically, you may want to include the URL and a description in the link text - "WebAIM article on Creating accessible documents in Word (webaim.org/techniques/word)."

Other principles

In addition to the principles addressed above, most web accessibility principles can also be applied to files created in Word. The following is a list of a few other important accessibility principles:

Use true numbered and bulleted lists.
Ensure that font size is sufficient, usually around 12 points or more.
Provide sufficient contrast.
Don't use color as the only way to convey content.
Use true columns, not tables or columns created by hand with the Tab key.
Provide a table of contents, especially for long documents. If you have a good heading structure, creating a table of contents is easy.
Use simple language.

Word 2010 Accessibility Checker

Word 2010 includes a new accessibility checker that allows you to check for accessibility problems. This is an excellent resource and one of the best accessibility features to come along in a long time. The accessibility checker makes it much easier to identify and repair accessibility issues. This is an excellent resource.
To run the accessibility checker, select File > Info > Check for Issues > Check Accessibility.

This will start the accessibility checker.

The checker presents accessibility errors (e.g., images with no alt text), warnings (e.g., unclear link text) and tips (e.g., skipping from a first level heading to a third level heading). Feedback about the importance of each item, as well as tips on how to repair it, are included. Selecting an item in the report will select the corresponding item in the document.

Docx Format

The "docx" format is the default file format for documents created in Word 2007 and newer. The format has some advantages (such as smaller file size), but is not as widely supported as the old "doc" format. Although there is a free download that allows users to open the newer format in older versions of Word, some content will be lost in the conversion process - external link. If the Word file is going to end up on the web, or if your going to send it to someone and are not doing anything that relies on the newer docx format, consider saving files as Word 97-2003 Document (*.doc) in Office 2007 and 2010.

Convert Word to HTML

Save as HTML in Word

When saving a Word document as HTML, the structure and alt text will be retained in the final document. To save as HTML, select File > Save as Web Page.... In Word 2007, select the Word logo in the upper right corner and then select Save As.

In Office XP or later, there are two options for exporting to HTML:

Save as Web Page
Save as Web Page, Filtered

The advantage of the Web Page option is that the page will look almost exactly like the printed document. The advantage of the Web Page, Filtered option is that the underlying code is much cleaner, the file size is significantly smaller, and most, if not all, of the look and feel of the original document is retained.
In terms of accessibility, both options are acceptable, as long as the source file was created with structure and with alternative text for images, the document does not contain any data tables, and other accessibility principles are applied. Because of the reduced amounts of Internet Explorer-specific markup, Filtered web pages are more likely to be supported and compatible in various web browsers.

"Paste Special" into Dreamweaver

If you are using Dreamweaver to author your web content, you can import Word content using the Paste Special option. Select all the content in your Word Document and Copy it to the clipboard. Then open an empty page in Dreamweaver, right-click and select Paste Special..., or Ctrl + Shift + V.

A dialog box will appear with four options:

Text only
Text with structure (paragraphs, lists, tables, etc.)
Text with structure plus basic formatting (bold, italic)
Text with structure plus full formatting (bold, italic, styles).

There are also options to Retain line breaks (if there are any) and Clean up Word paragraph spacing. Using any of the results will provide cleaner HTML than if you save as HTML in Word. Text with structure or Text with structure plus basic formatting is usually the best option.

Virtual508.com Accessible Web Publishing Wizard

A Word Document can also be converted to HTML with the Virtual508.com Accessible Web Publishing Wizard - external link for Microsoft Office. It is only available for the Windows operating system and requires the .NET framework. It should work with Office 2000-2007. The Wizard is not a free tool, but there is a demonstration version available that allows conversion of a limited number of pages or slides. The Office conversion tool is probably better suited for PowerPoint presentations. There is a Best Practices for Microsoft Word - external link reference manual that will inform you how to mark up the document so that the Word to HTML conversion process will be smoother.

Convert Word to PDF

Many Word documents end up as PDF files. It is a convenient way to preserve formatting and accessibility information, assuming the file is converted correctly. Read more on converting a Word document to accessible PDF in our Acrobat/PDF article.

CHARACTERISTICS OF ORGANISM USED FOR GENETICS STUDIES

2012-08-15T11:05:00.000-07:00

Characteristics Of Organisms Used For Genetic Studies

General Features of an Organism Used for Genetic Studies
- good genetic background
- easy to grow
- controlled matings possible
- can be genetically engineered
- funding available
Viruses
- easily grown in culture
- rapid generation time
- encode only a few the proteins, which permit a detailed analysis of well-defined system
- some viruses have control mechanisms found in eukaryotic species
- can be genetically engineered
- lack organized chromosome
- not all genetic features can be extrapolated to other organisms
Escherichia coli
- easily grown in culture
- rapid generation time
- many mutants available
- many genes involved
- life cycle very well defined
- relatively simple to generate new mutants
- can be genetically engineered
- contain a rudimentary chromosome
- not all genetic features can be extrapolated to higher organisms
Human
- intense public interest and funding available
- relatively well-mapped for most eukaryotic species
- many diseases (mutant phenotypes) understood clinically
- well-defined cytogenetic system
- long generation time
- many traits can only be studied in cell culture
- cannot make controlled crosses
- cannot be genetically engineered
Drosophila
- short generation time for a eukaryotic organisms (two weeks)
- availability of many mutants controlling specific phenotypes
- large chromosomes with well-defined cytogenetic system
- survives well in the lab and matings are easily performed
- currently, the best organism to study developmental genetics
- transposable elements can be manipulated to clone genes
- can be genetically engineered
Maize
- best mapped plant species
- many mutants are available that control seed traits
- well-defined cytogenetic system
- transposable elements well understood and can be used to clone genes
- matings tedious, but produce many (hundreds) of progeny
- only three generations per year
- cannot be easily genetically engineered
- not well funded
Arabidopsis thaliana
- small genome with little repetitive DNA
- short generation time (six weeks)
- many mutants rapidly becoming available
- matings tedious, but produce many (thousands) of progeny
- currently, an intensely investigated organisms; the Drosophila of plant species
- can be easily genetically engineered

Although these species have been studied intensely, these are by no means the only species analyzed for genetic studies. Mouse has been used for many genetic studies because it is a mammal that is a relatively good model for human gene expression. A good example is the globin genes, protein that carry oxygen in blood cells. The genetic and molecular organization of the mouse and human genes are quite similar: they have the same number of exons and have the introns located at the same amino acid residue in the transcript. Furthermore, the order of the multigene family is conserved. Yeast has also been well studied. Although this species is a good model system, this is not the reason that it was first investigated. The primary reason was because of its role in brewing.

In addition many plant species have relatively well-defined genetic systems. Tomato, next to corn, is the best mapped plant species. Tobacco has become a valuable tool to study plant molecular genetics because of the ease in which it can be genetically engineered at the whole plant level. This permits the molecular analysis of many genes in the functioning organism, rather than in a cellular condition as is the case with animal systems.

The genetic systems of many other plant species have been analyzed by plant breeders who need to understand how specific traits are genetically controlled. This information is important so that the traits can be successfully manipulated in a breeding program. This ability to manipulate crop plants is not a recent discovery. That native Americans were aware of the concept of heredity is evidenced by their deliberate attempts to maintain specific lines of their crops that were adapted to or superior in their environment.

THE SCIENCE OF GENETICS

2012-08-15T10:55:00.001-07:00

Scientific Method Fields of Genetics
Genetic Organisms
Study Questions
Science of Genetics Overheads
Science of Genetics WWW Links Genetic Topics

The Fields Of Genetics

As was mentioned it is important to place a genetics observation in a conceptual framework. To do this it is important to understand the breadth of the science of genetics. The three primary areas and the topics that are relevant to each are listed below (modified from Principles of Genetics, 3rd Edition; R. Tamarin; 1991; Wm. C. Brown Publishers, Dubuque, IA). Classical Genetics (based on Mendel's 1st and 2nd laws)

Mendel's first and second laws of inheritance
Meiosis and mitosis
Somatic and sex chromosome mapping
Extrachromosomal inheritance
Cytogenetics (changes in chromosome number and structure)
Quantitative genetics

Molecular Genetics (based on the Central Dogma of Molecular Genetics)

Structure of nuclear and organelle DNA
Chemistry and replication of DNA
Transcription and translation
DNA cloning
Control of gene expression
Mutation and the repair of DNA

Evolutionary Genetics (based on the theory of Natural Selection proposed by Darwin)

Hardy-Weinberg equilibrium
Evolution
Speciation
Population genetics

The next step in a genetic experiment is to obtain the correct experimental material for the experiments you which to perform. Each of the three areas of genetics has its own requirements for experimentation. For Classical Genetics, genetic stocks that contain the alternate alleles that you will be studying are required. When performing an experiment in molecular genetics, you will need a genetic stock containing the specific allele that you want to study at the molecular level, and a probe to identify and analyze the specific allele. For many studies, the allele to be studied is the wild type allele. Finally, a population with varying gene frequencies is necessary for a successful experiment in the field of evolutionary genetics. To determine what type of genetic stock or population is best for your specific experiments, it is necessary to understand the advantages and disadvantages of the different biological species that are used as test organisms.

GREEN HOUSE EFFECT AND CAUSES

2012-08-09T11:17:00.000-07:00

According to some recent reports (e.g. PlanetArk; The Guardian), the public concern about global warming may be declining. It’s not clear whether this is actually true: a poll conducted by researchers at Stanford suggests otherwise. In any case, the science behind climate change has not changed (also see America’s Climate Choices), but there certainly remains a problem in communicating the science to the public.
This makes me think that perhaps a new simple mental picture of the situation is needed. We can look at climate models, and they tell us what we can expect, but it is also useful to have an idea of why increased greenhouse gas concentrations result in higher surface temperatures. The saying “Everything should be made as simple as possible, but not simpler” has been attributed to Albert Einstein, which also makes me wonder if we – the scientists – need to reiterate the story of climate change in a different way.
Gavin has already discussed this (also see here and here), but it may be necessary to tell story over again, with a slightly different slant. So how can we explain how the greenhouse effect (GHE) work in both simple terms and with a new angle? I also want to explain why the middle atmosphere cools with increasing greenhouse gas concentrations associated with an increased GHE. Here I will try to present a conceptual and comprehensive picture of GHE, explaining both the warming in the lower part of the atmosphere as well as the cooling aloft, and where only the most central features are included. Also, it is important to provide a good background, and we need to start with some very fundamental facts.

Four main physical aspects
Several factors are involved, and hence it may be useful to write a simple recipe for the GHE. This recipe then involves four main ingredients: (i) the relationship between temperature and light, (ii) the planetary energy balance, (iii) the distance light travels before being absorbed, and (iv) the relationship between temperature and altitude.
(i) Temperature and light
Energy can be transmitted in many different ways, involving photons (light or electromangetic radiation), conduction, and motion. Most of these require a medium, such as a gas, fluid, or a solid, but space is basically a void through which photons represent virtually the only form for energy transfer. Hence, planets tend to gain or lose energy to space in the form of photons, and we often refer to the energy loss as ‘radiative heat loss’.
A fundamental law of physics, known as the Planck’s law, says that radiative heat loss from any object depends on its temperature. Planck’s law also explains the colour of the light, or its wavelength, and hence explains why iron gets red hot when heated sufficiently.

Figure 1. Illustration of Planck's law, where the different curves represent objects with different temperature. The y-axis is marks the intensity and the x-axis the wave length (colour) of the light emitted by bodies with a given temperature (PDF-version and R-script generating the figure.)

Planck’s law predicts that the light from an object with a temperature of 6000K – such as the solar surface – produces light that is visible, whereas objects with a temperature of 288K produce light with a wavelength that our eyes are not able to see (infra red). This is illustrated in Figure 1 showing how the light intensity (y-axis; also referred to as ‘flux density‘) and the colour of the light (wave length) vary for objects with different temperatures (here represented by different curves). The yellow curve in the figure represents the solar surface and the light blue curve the earth.
(ii) The planetary energy balance
The planetary energy balance says that our planet loses heat at the same rate as it receives energy from the sun (otherwise it would heat or cool over time). This is because energy cannot just be created or destroyed (unless it involves nuclear reactions or takes place on quantum physics scales).
The planets’ distance from the sun and the brightness of its surface dictates how much energy it receives from the sun, as the light gets dimmer when it spreads out in space, as described by Gauss’ theorem.

Figure 2. A schematic of the solar system, where the energy received by the earth is the sunlight intercepted by its cross-section, and where the heat loss on average is due to thermal emission from the whole surface area of the planet. As the sunlight travels away from the sun, it spreads out over larger space and gets dimmer.

The energy flowing from the sun is intercepted by the earth with energy density described by the ‘solar constant‘ (S₀=1366W/m²), and the amount of energy intercepted is the product between this flux density and the earth’s disc (minus the reflected light due to the planet’s albedo: A ~0.3). The average heat loss is given by the product of earth’s surface and its black body radiation:
S₀/4 (1-A) = σT⁴,
where σ=5.67 x 10^-8W/(m² K⁴) is the Stefan-Boltzman constant. This gives a value of 255K, known as the emission temperature.
Figure 3 shows a comparison between observed surface temperature and calculated emission temperature for the planets in the solar system, based on the balance between energy from the sun and heat loss due to black body emission. In these simple calculations, the greenhouse effect is neglected, and the black body radiation can be derived from Planck’s law. The calculations agree quite well with the observations for most of the objects in our solar system, except for Venus which is known to harbour a strong GHE and has a hotter surface than Mercury despite being about twice as far away from the sun.

Figure 3. Comparison between calculated emission temperature and the observed surface temperatures for planets and moons in our solar system. The calculations estimate the reduction in the energy flux density with distance away from the sun (Gauss' theorem) and the black body radiation describing the rate of planetary heat loss. Here, the greenhouse effect has been neglected in the calculations, but the GHE does affect the observed surface temperatures. Venus is a bright planet (high albedo) with a thick atmosphere mostly made up of CO₂, which explains higher surface temperature than inferred from a pure energy balance (PDF-version and R-script generating the figure).

(iii) Light absorption
It is also clear that our planet is largely heated at the surface because the light from the sun – which is visible for our eyes – penetrates the atmosphere without much absorption (hence we can see the sun from the ground). However, the atmosphere is a medium of gas and particles that can absorb and scatter light, depending on their wavelength (hence explain why the sky is blue and sunsets orange).
The distance light travels before being absorbed – optical depth – can vary with the light’s wavelength and the medium through which is travels. The optical depth in our atmosphere is different for visible and infra-red light.
Infra-red light is absorbed by molecules, which in turn get more energetic, and the excited molecules will eventually re-emit more infra-red light in any random direction or transfer excess energy to other molecules through collisions. In a optically thick (opaque) atmosphere, there will be a cascade of absorption and re-emission.
Hence, whereas the planet is heated at the surface, it’s main heat loss takes place from a height about 5.5 km above the ground, where most of the radiation is free to escape out to space. The optical depth dictates how deep into the planet’s atmosphere the origin is for most of the planet’s infra-red light (the main planetary heat loss) that can be seen from space. Furthermore, it is the temperature at this level that dictates the magnitude of the heat loss (Planck’s law), and the vertical temperature change (lapse rate) is of course necessary for a GHE. The temperature at this level is the emission temperature, not to be confused by the surface temperature.
We know that the optical depth is affected by CO₂ – in fact, this fact is the basis for measuring CO₂ concentrations with infra-red gas analysers. Molecules composed of three or more atoms tend to act as greenhouse gases because they can possess energy in terms of rotation and vibrations which can be associated with the energy of photons at the infra-red range. This can be explained by theory and be demonstrated in lab experiments. Other effects are present too, such as pressure and Doppler broadening, however, these are secondary effects in this story.
(iv) The relationship between temperature and altitude
There is a well-known relationship between temperature and height in the troposphere, known as the ‘lapse rate‘ (the temperature decreases with height at a rate -6K/km). The relationship between temperature and altitude can also be seen in the standard atmosphere. The lapse rate can be derived from theory for any atmosphere that is the hydrostatically stable condition with maximum vertical temperature gradient, but it is also well-known within meteorology. Thus, given the height and value of the emission temperature, we can get a simple estimate for the surface temperature: 255K + 5.5km * 6K/km = 288K (=15^oC; close to the global mean estimated from observations given by NCDC of ~14^oC).
Enhanced greenhouse effect
The term known as the ‘enhanced greenhouse effect’ describes a situation where the atmosphere’s becomes less transparent to infra-red light (
reduced
increased optical depth), and that the heat loss must take place at higher levels. Moreover, an observer in space cannot see the infra-red light from as deep levels as before because the atmosphere has become more opaque.

Figure 4. A simple schematic showing how the planet is heated at the surface, how the temperature (blue) decreases with height according to the lapse rate, and how infra-red light (wiggly arrows) is absorbed and re-emitted at various stages on its way up through the atmosphere. Energy is also transferred through vertical motion (convection), evaporation, and condensation too (latent heat), but that doesn't affect this picture, as they all act to restore the vertical structure toward the hydrostatically stable lapse rate in the long run. At the top of the atmosphere, the infra-red light escapes freely out to space, and this is where the planet's main heat loss takes place. This level is determined by the optical depth, and the heat loss depends on the temperature here. (click on figure for animation)

The effect of heightened level of heat loss on the surface temperature is illustrated in Figure 4, where the emission temperature and lapse rate are given if we assume an energy balance and a hydrostatically stable atmosphere on average (a generally hydrostatically unstable atmosphere would be bad news).
Hence, a
reduced
increased optical depth explains why atmospheres are not easily ‘saturated‘ and why planets such as Venus have surface temperatures that are substantially higher than the emission temperature. Planets with a thin atmosphere and insignificant greenhouse effect, on the other hand, have a surface temperature that is close
the
to the estimates from the planetary energy balance model (Figure 3).
Feedback processes
The way the atmosphere reacts to changes in the optical depth is more complicated, due to a number of different feedback mechanisms taking place. But to get a simple overview, it is useful to keep in mind that the optical depth is sensitive to how much water vapour (humidity) there is in the air, and that the lapse rate is sensitive to the composition of the atmosphere (i.e. humidity). Furthermore, the albedo A is affected by clouds, snow, ice, and vegetation, all of which affect the way the earth receives energy from the sun.
In our simple picture, feedback processes affect changes in the height of the level where most heat loss takes place, the slope of the lapse rate, and heating at the surface (and hence the emission temperature).
So why is the upper atmosphere cooled then?
The upper atmosphere, comprising the stratosphere and mesosphere, is expected to cool during an AGW, as shown by the GCMs. So what is happening there? This is when the picture becomes more complicated.
Since CO₂ mostly absorbs/re-emits infra-red light at around 14 microns, an increased concentration in the troposphere will reduce the upward infra-red radiation at this band. The total energy is roughly constant, but it is made up from increased emissions at other bands because it’s warmer. There is less absorption by CO₂ of upwelling infra-red light above the troposphere, but increased emission as a function of increased concentrations. Thus there is a cooling.
Controversy?
Can this picture be falsified, e.g. if other factors were to play a role too? For instance, can this situation be altered by changes in the sun?
Changes in the sun can of course affect the amount of energy received by the earth through changes in its output, variations in the intensity of UV-light, or perhaps even clouds through galactic cosmic rays. But it’s hard to see any systematic long-term trend in the level of solar activity over the last 50 years, and it is difficult to see how solar activity may have an effect while other factors, such as GHGs, don’t. Gavin and I recently published a study on the response to both solar activity and GHGs, and found similar magnitude for both forcings in both observations and the GISS GCM.
There have been claims of negative feedbacks, such as the “iris effect“. One would expect negative feedbacks in general to dampen the response to most forcings, unless they involve a particular process that is active for a particular forcing. In other word, why would a negative feedback act for GHGs but not for solar forcing? Many feedbacks, such as changes in atmospheric moisture, cloudiness, and atmospheric circulation should be similar for most forcings.
Another question is why we do see a global warming trend if the negative feedbacks were most important (Figure 5). Negative feedbacks usually imply quiet conditions in a complex system, whereas positive feedbacks tend to lead to instabilities, often manifested as internal and spontaneous oscillations (see Figure 5). It is reasonable to expect the feedback processes to affect natural variations as well as forced changes such as an enhanced GHE, orbital changes, volcanoes, or changes in the sun.

Figure 5. Estimates of the global and annual mean temperature based on a number of different data sets, including both traditional analyses as well as re-analyses (also see the last 15 years).

The point about negative feedback also brings up another interesting issue: Negative feedbacks usually act to restore a system to a particular zero-level state. What would the zero-state be for our climate? No greenhouse effect or some preferred level of greenhouse warming? There is already a natural GHE that, together with other atmospheric effects, can account for about 32^oC higher global mean surface temperature. What makes this state so special, and can we explain the present natural GHE in the presence of negative feedbacks (consider starting from a state with no GHE)?
Hence, claims of negative feedback is controversial because all these tough questions then need to be addressed. We can write down a simple recipe for the GHE, but it is indeed challenging to reconcile a presence of a negative feedback with our observations, or explain the current observed global warming in any other terms.

GREEN HOUSE EFFECT

2012-08-09T10:59:00.000-07:00

The "greenhouse effect" often gets a bad rap because of its association with global warming, but the truth is we couldn't live without it.
What Causes the Greenhouse Effect?
Life on earth depends on energy from the sun. About 30 percent of the sunlight that beams toward Earth is deflected by the outer atmosphere and scattered back into space. The rest reaches the planet's surface and is reflected upward again as a type of slow-moving energy called infrared radiation.
The heat caused by infrared radiation is absorbed by "greenhouse gases" such as water vapor, carbon dioxide, ozone and methane, which slows its escape from the atmosphere.
Although greenhouse gases make up only about 1 percent of the Earth's atmosphere, they regulate our climate by trapping heat and holding it in a kind of warm-air blanket that surrounds the planet.
This phenomenon is what scientists call the "greenhouse effect." Without it, scientists estimate that the average temperature on Earth would be colder by approximately 30 degrees Celsius (54 degrees Fahrenheit), far too cold to sustain our current ecosystem.
How Do Humans Contribute to the Greenhouse Effect?
While the greenhouse effect is an essential environmental prerequisite for life on Earth, there really can be too much of a good thing.
The problems begin when human activities distort and accelerate the natural process by creating more greenhouse gases in the atmosphere than are necessary to warm the planet to an ideal temperature.

Burning natural gas, coal and oil -including gasoline for automobile engines-raises the level of carbon dioxide in the atmosphere.
Some farming practices and land-use changes increase the levels of methane and nitrous oxide.
Many factories produce long-lasting industrial gases that do not occur naturally, yet contribute significantly to the enhanced greenhouse effect and "global warming" that is currently under way.
Deforestation also contributes to global warming. Trees use carbon dioxide and give off oxygen in its place, which helps to create the optimal balance of gases in the atmosphere. As more forests are logged for timber or cut down to make way for farming, however, there are fewer trees to perform this critical function.
Population growth is another factor in global warming, because as more people use fossil fuels for heat, transportation and manufacturing the level of greenhouse gases continues to increase. As more farming occurs to feed millions of new people, more greenhouse gases enter the atmosphere.

Ultimately, more greenhouse gases means more infrared radiation trapped and held, which gradually increases the temperature of the Earth's surface and the air in the lower atmosphere.
The Average Global Temperature is Increasing Quickly
Today, the increase in the Earth's temperature is increasing with unprecedented speed. To understand just how quickly global warming is accelerating, consider this:
During the entire 20th century, the average global temperature increased by about 0.6 degrees Celsius (slightly more than 1 degree Fahrenheit).
Using computer climate models, scientists estimate that by the year 2100 the average global temperature will increase by 1.4 degrees to 5.8 degrees Celsius (approximately 2.5 degrees to 10.5 degrees Fahrenheit).
Not All Scientists Agree
While the majority of mainstream scientists agree that global warming is a serious problem that is growing steadily worse, there are some who disagree. John Christy, a professor and director of the Earth System Science Center at the University of Alabama in Huntsville is a respected climatologist who argues that global warming isn't worth worrying about.

Christy reached that opinion after analyzing millions of measurements from weather satellites in an effort to find a global temperature trend. He found no sign of global warming in the satellite data, and now believes that predictions of global warming by as much as 10 degrees Fahrenheit by the end of the 21st century are incorrect.

THE TRANSFORMER

2012-07-21T11:21:00.001-07:00

DISCOVERY OF HE TRANSFORMER Faraday's experiment with induction between coils of wire[1] The principle behind the operation of a transformer, electromagnetic induction, was discovered independently by Michael Faraday and Joseph Henry in 1831. However, Faraday was the first to publish the results of his experiments and thus receive credit for the discovery.[2] The relationship between electromotive force (EMF) or "voltage" and magnetic flux was formalized in an equation now referred to as "Faraday's law of induction": |\mathcal{E}| = \left|{{d\Phi_B} \over dt}\right|. where |\mathcal{E}| is the magnitude of the EMF in volts and ΦB is the magnetic flux through the circuit in webers.[3] Faraday performed the first experiments on induction between coils of wire, including winding a pair of coils around an iron ring, thus creating the first toroidal closed-core transformer.[4] However he only applied individual pulses of current to his transformer, and never discovered the relation between the turns ratio and EMF in the windings INDUCTION COIL Faraday's ring transformer The first type of transformer to see wide use was the induction coil, invented by Rev. Nicholas Callan of Maynooth College, Ireland in 1836. He was one of the first researchers to realize that the more turns the secondary winding has in relation to the primary winding, the larger is the increase in EMF. Induction coils evolved from scientists' and inventors' efforts to get higher voltages from batteries. Since batteries produce direct current (DC) rather than alternating current (AC), induction coils relied upon vibrating electrical contacts that regularly interrupted the current in the primary to create the flux changes necessary for induction. Between the 1830s and the 1870s, efforts to build better induction coils, mostly by trial and error, slowly revealed the basic principles of transformers. ELECTRIC POWER DISTRIBUTION Before the transformer was developed, long-distance direct-current electric power distribution required the use of spinning motor-generator systems to step a high transmission voltage down to utility voltage for lighting. [5] G = power plant generator, M/D = motor-generator at customer's location, L = lights Before the development of the transformer, electric power distribution primarily used direct current. It was difficult for a DC utility-power generation station to be more than a few kilometers from the user, because up until about 1897, light bulbs could only be effectively designed to operate at up to 110 volts maximum,[6], and up to 220 volts by 1917.[7]. It is expensive to send energy long distances at utility voltage (100-250 volts) due to the very high amperage of many customers, and the need for very thick transmission wires capable of handling the current. It was understood that high voltages allowed long distance transmission with low amperage (250 volts at 5000 amps = 25000 volts at 50 amps) so the transmission wires can be smaller and less expensive, but it still needed to be stepped back down to utility voltage at the customer's location. At the time the only way to efficiently convert DC from one voltage to another was with a spinning motor-generator device, and this would be needed at each customer site. Each motor-generator has brushes constantly rubbing on a commutator, and axle bearings that need lubrication. The brushes wear out and need to be periodically replaced, and the commutator wears down and needs to be resurfaced, then the whole machine is rebuilt when the commutator wears too thin. By the 1870s, efficient generators that produced alternating current (alternators) were available, and it was found that alternating current could power an induction coil directly, without an interrupter. In 1876, Russian engineer Pavel Yablochkov invented a lighting system based on a set of induction coils where the primary windings were connected to a source of alternating current and the secondary windings could be connected to several "electric candles" (arc lamps) of his own design. [8] [9] The coils Yablochkov employed functioned essentially as transformers.[8] In 1878, the Ganz Company in Hungary began manufacturing equipment for electric lighting and, by 1883, had installed over fifty systems in Austria-Hungary. Their systems used alternating current exclusively and included those comprising both arc and incandescent lamps, along with generators and other equipment.[10] Lucien Gaulard and John Dixon Gibbs first exhibited a device with an open iron core called a "secondary generator" in London in 1882, then sold the idea to the Westinghouse company in the United States.[11] They also exhibited the invention in Turin, Italy in 1884, where it was adopted for an electric lighting system.[12] However, the efficiency of their open-core bipolar apparatus remained very low.[12] Induction coils with open magnetic circuits are inefficient for transfer of power to loads. Until about 1880, the paradigm for AC power transmission from a high voltage supply to a low voltage load was a series circuit. Open-core transformers with a ratio near 1:1 were connected with their primaries in series to allow use of a high voltage for transmission while presenting a low voltage to the lamps. The inherent flaw in this method was that turning off a single lamp affected the voltage supplied to all others on the same circuit. Many adjustable transformer designs were introduced to compensate for this problematic characteristic of the series circuit, including those employing methods of adjusting the core or bypassing the magnetic flux around part of a coil.[12] Efficient, practical transformer designs did not appear until the 1880s, but within a decade, the transformer would be instrumental in the "War of Currents", and in seeing AC distribution systems triumph over their DC counterparts, a position in which they have remained dominant ever since. [13] CLOSED-CORE TRANSFORMERS AD PARALLE POWER DISTRIBUTOR; Shell-form transformer. Sketch used by Uppenborn to describe Z.B.D. engineers' 1885 patents and earliest articles.[12] Core-form, front; shell-form, back. Earliest specimens of Z.B.D.-designed high-efficiency constant-potential transformers manufactured at the Ganz factory in 1885. Stanley's 1886 design for adjustable gap open-core induction coils[14] In the autumn of 1884, Károly Zipernowsky, Ottó Bláthy and Miksa Déri (Z.B.D.), three engineers associated with the Ganz factory, had determined that open-core devices were impracticable, as they were incapable of reliably regulating voltage.[15] In their joint 1885 patent applications for novel transformers (later called Z.B.D. transformers), they described two designs with closed magnetic circuits where copper windings were either a) wound around iron wire ring core or b) surrounded by iron wire core.[12] The two designs were the first application of the two basic transformer construction types in common use to this day which can as a class all be termed as either core-form or shell-form (or alternatively, core-type or shell-type), as in a) or b), respectively (see images).[16][17][18][19] The Ganz factory had also in the autumn of 1884 made delivery of the world's first five high-efficiency AC transformers, the first of these units having been shipped on September 16, 1884.[20] This first unit had been manufactured to the following specifications: 1,400 W, 40 Hz, 120:72 V, 11.6:19.4 A, ratio 1.67:1, one-phase, shell-form.[20] In both designs, the magnetic flux linking the primary and secondary windings traveled almost entirely within the confines of the iron core, with no intentional path through air (see 'Toroidal cores' below). The new transformers were 3.4 times more efficient than the open core bipolar devices of Gaulard and Gibbs.[21] Their patents included two other major interrelated innovations: one concerning the use of parallel connected, instead of series connected, utilization loads, the other concerning the ability to have high turns ratio transformers such that the supply network voltage could be much higher (initially 1,400 to 2,000 V) than the voltage of utilization loads (100 V initially preferred). [22][23] When they employed them in parallel connected electric distribution systems, closed-core transformers finally made it technically and economically feasible to provide electric power for lighting in homes, businesses and public spaces.[24][25] Bláthy had suggested the use of closed-cores, Zipernowsky the use of parallel shunt connections, and Déri had performed the experiments;[26] Transformers in use today are designed based on principles discovered by the three engineers. They also popularized the word "transformer" to describe a device for altering the EMF of an electric current,[24][27] although the term had already been in use by 1882.[28][29] In 1886, the Z.B.D. engineers designed, and the Ganz factory supplied electrical equipment for, the world's first power station that used AC generators to power a parallel-connected common electrical network, the steam-powered Rome-Cerchi power plant.[30] Although George Westinghouse had bought Gaulard and Gibbs' patents in 1885, the Edison Electric Light Company held an option on the U.S. rights for the Z.B.D. transformers, requiring Westinghouse to pursue alternative designs on the same principles. He assigned to William Stanley the task of developing a device for commercial use in United States.[31] Stanley's first patented design was for induction coils with single cores of soft iron and adjustable gaps to regulate the EMF present in the secondary winding (see image).[14] This design[32] was first used commercially in the U.S. in 1886[13] but Westinghouse was intent on improving the Stanley design to make it (unlike the Z.B.D. type) easy and cheap to produce.[32] Westinghouse, Stanley and a few other associates had soon developed a core consisting of a stack of thin "E‑shaped" iron plates, separated individually or in pairs by thin sheets of paper or other insulating material. Prewound copper coils could then be slid into place, and straight iron plates laid in to create a closed magnetic circuit. Westinghouse applied for a patent for the new design in December 1886; it was granted in July 1887.[26][33] OTHER EARLY TRANSFORMER In 1889, Russian-born engineer Mikhail Dolivo-Dobrovolsky developed the first three-phase transformer at the Allgemeine Elektricitäts-Gesellschaft ("General Electricity Company") in Germany.[34] In 1891, Nikola Tesla invented the Tesla coil, an air-cored, dual-tuned resonant transformer for generating very high voltages at high frequency.[35] [36] Audio frequency transformers ("repeating coils") were used by early experimenters in the development of the telephone.BASIC PRICIPLES An ideal transformer. The secondary current arises from the action of the secondary EMF on the (not shown) load impedance. The transformer is based on two principles: first, that an electric current can produce a magnetic field (electromagnetism) and second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil. An ideal transformer is shown in the adjacent figure. Current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron, so that most of the magnetic flux passes through both the primary and secondary coils. If a load is connected to the secondary winding, the load current and voltage will be in the directions indicated, given the primary current and voltage in the directions indicated (each will be alternating current in practice). Induction law The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states that: V_\text{s} = N_\text{s} \frac{\mathrm{d}\Phi}{\mathrm{d}t}, where Vs is the instantaneous voltage, Ns is the number of turns in the secondary coil and Φ is the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicularly to the magnetic field lines, the flux is the product of the magnetic flux density B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer,[37] the instantaneous voltage across the primary winding equals V_\text{p} = N_\text{p} \frac{\mathrm{d}\Phi}{\mathrm{d}t}. Taking the ratio of the two equations for Vs and Vp gives the basic equation[38] for stepping up or stepping down the voltage \frac{V_\text{s}}{V_\text{p}} = \frac{N_\text{s}}{N_\text{p}}. Np/Ns is known as the turns ratio, and is the primary functional characteristic of any transformer. In the case of step-up transformers, this may sometimes be stated as the reciprocal, Ns/Np. Turns ratio is commonly expressed as an irreducible fraction or ratio: for example, a transformer with primary and secondary windings of, respectively, 100 and 150 turns is said to have a turns ratio of 2:3 rather than 0.667 or 100:150. Ideal power equation The ideal transformer as a circuit element If the secondary coil is attached to a load that allows current to flow, electrical power is transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly efficient. All the incoming energy is transformed from the primary circuit to the magnetic field and into the secondary circuit. If this condition is met, the input electric power must equal the output power: P_\text{incoming} = I_\text{p} V_\text{p} = P_\text{outgoing} = I_\text{s} V_\text{s},\! giving the ideal transformer equation \frac{V_\text{s}}{V_\text{p}} = \frac{N_\text{s}}{N_\text{p}} = \frac{I_\text{p}}{I_\text{s}}. This formula is a reasonable approximation for most commercial built transformers today. If the voltage is increased, then the current is decreased by the same factor. The impedance in one circuit is transformed by the square of the turns ratio.[37] For example, if an impedance Zs is attached across the terminals of the secondary coil, it appears to the primary circuit to have an impedance of (Np/Ns)2Zs. This relationship is reciprocal, so that the impedance Zp of the primary circuit appears to the secondary to be (Ns/Np)2Zp. Detailed operation The simplified description above neglects several practical factors, in particular, the primary current required to establish a magnetic field in the core, and the contribution to the field due to current in the secondary circuit. Models of an ideal transformer typically assume a core of negligible reluctance with two windings of zero resistance.[39] When a voltage is applied to the primary winding, a small current flows, driving flux around the magnetic circuit of the core.:[39] The current required to create the flux is termed the magnetizing current. Since the ideal core has been assumed to have near-zero reluctance, the magnetizing current is negligible, although still required, to create the magnetic field. The changing magnetic field induces an electromotive force (EMF) across each winding.[40] Since the ideal windings have no impedance, they have no associated voltage drop, and so the voltages VP and VS measured at the terminals of the transformer, are equal to the corresponding EMFs. The primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the "back EMF".[41] This is in accordance with Lenz's law, which states that induction of EMF always opposes development of any such change in magnetic field. Practical considerations Leakage flux Main article: Leakage inductance Leakage flux of a transformer The ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it outside the windings.[42] Such flux is termed leakage flux, and results in leakage inductance in series with the mutually coupled transformer windings.[41] Leakage results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply. It is not directly a power loss (see "Stray losses" below), but results in inferior voltage regulation, causing the secondary voltage to not be directly proportional to the primary voltage, particularly under heavy load.[42] Transformers are therefore normally designed to have very low leakage inductance. Nevertheless, it is impossible to eliminate all leakage flux because it plays an essential part in the operation of the transformer. The combined effect of the leakage flux and the electric field around the windings is what transfers energy from the primary to the secondary.[43] In some applications increased leakage is desired, and long magnetic paths, air gaps, or magnetic bypass shunts may deliberately be introduced in a transformer design to limit the short-circuit current it will supply.[41] Leaky transformers may be used to supply loads that exhibit negative resistance, such as electric arcs, mercury vapor lamps, and neon signs or for safely handling loads that become periodically short-circuited such as electric arc welders.[44] Air gaps are also used to keep a transformer from saturating, especially audio-frequency transformers in circuits that have a direct current component flowing through the windings.[45] Leakage inductance is also helpful when transformers are operated in parallel. It can be shown that if the "per-unit" inductance of two transformers is the same (a typical value is 5%), they will automatically split power "correctly" (e.g. 500 kVA unit in parallel with 1,000 kVA unit, the larger one will carry twice the current).[citation needed] Effect of frequency Transformer universal EMF equation If the flux in the core is purely sinusoidal, the relationship for either winding between its rms voltage Erms of the winding, and the supply frequency f, number of turns N, core cross-sectional area a and peak magnetic flux density B is given by the universal EMF equation:[39] E_\text{rms} = {\frac {2 \pi f N a B_\text{peak}} {\sqrt{2}}} \! \approx 4.44 f N a B If the flux does not contain even harmonics the following equation can be used for half-cycle average voltage Eavg of any waveshape: E_\text{avg}= 4 f N a B_\text{peak} \! The time-derivative term in Faraday's Law shows that the flux in the core is the integral with respect to time of the applied voltage.[46] Hypothetically an ideal transformer would work with direct-current excitation, with the core flux increasing linearly with time.[47] In practice, the flux rises to the point where magnetic saturation of the core occurs, causing a large increase in the magnetizing current and overheating the transformer. All practical transformers must therefore operate with alternating (or pulsed direct) current.[47] The EMF of a transformer at a given flux density increases with frequency.[39] By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation and fewer turns are needed to achieve the same impedance. However, properties such as core loss and conductor skin effect also increase with frequency. Aircraft and military equipment employ 400 Hz power supplies which reduce core and winding weight.[48] Conversely, frequencies used for some railway electrification systems were much lower (e.g. 16.7 Hz and 25 Hz) than normal utility frequencies (50 – 60 Hz) for historical reasons concerned mainly with the limitations of early electric traction motors. As such, the transformers used to step down the high over-head line voltages (e.g. 15 kV) were much heavier for the same power rating than those designed only for the higher frequencies. Operation of a transformer at its designed voltage but at a higher frequency than intended will lead to reduced magnetizing current. At a lower frequency, the magnetizing current will increase. Operation of a transformer at other than its design frequency may require assessment of voltages, losses, and cooling to establish if safe operation is practical. For example, transformers may need to be equipped with "volts per hertz" over-excitation relays to protect the transformer from overvoltage at higher than rated frequency. One example of state-of-the-art design is transformers used for electric multiple unit high speed trains, particularly those required to operate across the borders of countries using different electrical standards. The position of such transformers is restricted to being hung below the passenger compartment. They have to function at different frequencies (down to 16.7 Hz) and voltages (up to 25 kV) whilst handling the enhanced power requirements needed for operating the trains at high speed. Knowledge of natural frequencies of transformer windings is necessary for the determination of winding transient response and switching surge voltages. Energy losses An ideal transformer would have no energy losses, and would be 100% efficient. In practical transformers, energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 98%.[49] Experimental transformers using superconducting windings achieve efficiencies of 99.85%.[50] The increase in efficiency can save considerable energy, and hence money, in a large heavily loaded transformer; the trade-off is in the additional initial and running cost of the superconducting design. Losses in transformers (excluding associated circuitry) vary with load current, and may be expressed as "no-load" or "full-load" loss. Winding resistance dominates load losses, whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The no-load loss can be significant, so that even an idle transformer constitutes a drain on the electrical supply and a running cost. Designing transformers for lower loss requires a larger core, good-quality silicon steel, or even amorphous steel for the core and thicker wire, increasing initial cost so that there is a trade-off between initial cost and running cost (also see energy efficient transformer).[51] Transformer losses are divided into losses in the windings, termed copper loss, and those in the magnetic circuit, termed iron loss. Losses in the transformer arise from: Winding resistance Current flowing through the windings causes resistive heating of the conductors. At higher frequencies, skin effect and proximity effect create additional winding resistance and losses. Hysteresis losses Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the loss is proportional to the frequency, and is a function of the peak flux density to which it is subjected.[52] Eddy currents Ferromagnetic materials are also good conductors and a core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness.[53] Eddy current losses can be reduced by making the core of a stack of plates electrically insulated from each other, rather than a solid block; all transformers operating at low frequencies use laminated or similar cores. Magnetostriction Magnetic flux in a ferromagnetic material, such as the core, causes it to physically expand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This produces the buzzing sound commonly associated with transformers[38] that can cause losses due to frictional heating. This buzzing is particularly familiar from low-frequency (50 Hz or 60 Hz) mains hum, and high-frequency (15,734 Hz (NTSC) or 15,625 Hz (PAL)) CRT noise. Mechanical losses In addition to magnetostriction, the alternating magnetic field causes fluctuating forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the buzzing noise and consuming a small amount of power.[54] Stray losses Leakage inductance is by itself largely lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat.[55] There are also radiative losses due to the oscillating magnetic field but these are usually small. Dot convention Main article: Dot convention It is common in transformer schematic symbols for there to be a dot at the end of each coil within a transformer, particularly for transformers with multiple primary and secondary windings. The dots indicate the direction of each winding relative to the others. Voltages at the dot end of each winding are in phase; current flowing into the dot end of a primary coil will result in current flowing out of the dot end of a secondary coil. Core form and shell form transformers Core form = core type; shell form = shell type As first mentioned in regard to earliest ZBD closed-core transformers, transformers are generally considered to be either core form or shell form in design depending on the type of magnetic circuit used in winding construction (see image). That is, when winding coils are wound around the core, transformers are termed as being of core form design; when winding coils are surrounded by the core, transformers are termed as being of shell form design. Shell form design may be more prevalent than core form design for distribution transformer applications due to the relative ease in stacking the core around winding coils.[16] Core form design tends to, as a general rule, be more economical, and therefore more prevalent, than shell form design for high voltage power transformer applications at the lower end of their voltage and power rating ranges (less than or equal to, nominally, 230 kV or 75 MVA). At higher voltage and power ratings, shell form transformers tend to be more prevalent.[19][16][56][57] Shell form design tends to be preferred for extra high voltage and higher MVA applications because, though more labor intensive to manufacture, shell form transformers are characterized as having inherently better kVA-to-weight ratio, better short-circuit strength characteristics and higher immunity to transit damage.[57] Equivalent circuit .The physical limitations of the practical transformer may be brought together as an equivalent circuit model (shown below) built around an ideal lossless transformer.[58] Power loss in the windings is current-dependent and is represented as in-series resistances Rp and Rs. Flux leakage results in a fraction of the applied voltage dropped without contributing to the mutual coupling, and thus can be modeled as reactances of each leakage inductance Xp and Xs in series with the perfectly coupled region. Iron losses are caused mostly by hysteresis and eddy current effects in the core, and are proportional to the square of the core flux for operation at a given frequency.[59] Since the core flux is proportional to the applied voltage, the iron loss can be represented by a resistance RC in parallel with the ideal transformer. A core with finite permeability requires a magnetizing current Im to maintain the mutual flux in the core. The magnetizing current is in phase with the flux. Saturation effects cause the relationship between the two to be non-linear, but for simplicity this effect tends to be ignored in most circuit equivalents.[60] With a sinusoidal supply, the core flux lags the induced EMF by 90° and this effect can be modeled as a magnetizing reactance (reactance of an effective inductance) Xm in parallel with the core loss component, Rc. Rc and Xm are sometimes together termed the magnetizing branch of the model. If the secondary winding is made open-circuit, the current I0 taken by the magnetizing branch represents the transformer's no-load current.[58] The secondary impedance Rs and Xs is frequently moved (or "referred") to the primary side after multiplying the components by the impedance scaling factor (Np/Ns)2. Transformer equivalent circuit, with secondary impedances referred to the primary side The resulting model is sometimes termed the "exact equivalent circuit", though it retains a number of approximations, such as an assumption of linearity.[58] Analysis may be simplified by moving the magnetizing branch to the left of the primary impedance, an implicit assumption that the magnetizing current is low, and then summing primary and referred secondary impedances, resulting in so-called equivalent impedance. The parameters of equivalent circuit of a transformer can be calculated from the results of two transformer tests: open-circuit test and short-circuit test. Types For more details on this topic, see Transformer types. A wide variety of transformer designs are used for different applications, though they share several common features. Important common transformer types are described below. Autotransformer Main article: Autotransformer A variable autotransformer In an autotransformer portions of the same winding act as both the primary and secondary. The winding has at least three taps where electrical connections are made. An autotransformer can be smaller, lighter and cheaper than a standard dual-winding transformer, but it does not provide electrical isolation. As an example of the material saving an autotransformer can provide, consider a double wound 2 kVA transformer designed to convert 240 volts to 120 volts. Such a transformer would require 8 amp wire for the 240 volt primary and 16 amp wire for the secondary. If constructed as an autotransformer, the output is a simple tap at the centre of the 240 volt winding. Even though the whole winding can be wound with 8 amp wire, 16 amps can nevertheless be drawn from the 120 volt tap. This comes about because the 8 amp 'primary' current is of opposite phase to the 16 amp 'secondary' current and thus it is the difference current that flows in the common part of the winding (8 amps). There is also considerable potential for savings on the core material as the apertures required to hold the windings are smaller. The advantage is at its greatest with a 2:1 ratio transformer and becomes smaller as the ratio is greater or smaller. Autotransformers are often used to step up or down between voltages in the 110-117-120 volt range and voltages in the 220-230-240 volt range, e.g., to output either 110 or 120V (with taps) from 230V input, allowing equipment from a 100 or 120V region to be used in a 230V region. A variable autotransformer is made by exposing part of the winding coils and making the secondary connection through a sliding brush, giving a variable turns ratio.[61] Such a device is often referred to by the trademark name Variac. It resembles, but is different from, a potentiometer. Three-phase step-down transformer mounted between two utility poles Screenshot of a FEM simulation of the magnetic flux inside a three-phase power transformer (full animation) Polyphase transformers For more details on this topic, see Three-phase electric power. For three-phase supplies, a bank of three individual single-phase transformers can be used, or all three phases can be incorporated as a single three-phase transformer. In this case, the magnetic circuits are connected together, the core thus containing a three-phase flow of flux.[62] A number of winding configurations are possible, giving rise to different attributes and phase shifts.[63] One particular polyphase configuration is the zigzag transformer, used for grounding and in the suppression of harmonic currents.[64] Leakage transformers Leakage transformer A leakage transformer, also called a stray-field transformer, has a significantly higher leakage inductance than other transformers, sometimes increased by a magnetic bypass or shunt in its core between primary and secondary, which is sometimes adjustable with a set screw. This provides a transformer with an inherent current limitation due to the loose coupling between its primary and the secondary windings. The output and input currents are low enough to prevent thermal overload under all load conditions—even if the secondary is shorted. Uses Leakage transformers are used for arc welding and high voltage discharge lamps (neon lights and cold cathode fluorescent lamps, which are series-connected up to 7.5 kV AC). It acts then both as a voltage transformer and as a magnetic ballast. Other applications are short-circuit-proof extra-low voltage transformers for toys or doorbell installations. Resonant transformers For more details on this topic, see Resonant inductive coupling. A resonant transformer is a kind of leakage transformer. It uses the leakage inductance of its secondary windings in combination with external capacitors, to create one or more resonant circuits. Resonant transformers such as the Tesla coil can generate very high voltages, and are able to provide much higher current than electrostatic high-voltage generation machines such as the Van de Graaff generator.[65] One of the applications of the resonant transformer is for the CCFL inverter. Another application of the resonant transformer is to couple between stages of a superheterodyne receiver, where the selectivity of the receiver is provided by tuned transformers in the intermediate-frequency amplifiers.[66] Audio transformers Audio transformers are those specifically designed for use in audio circuits. They can be used to block radio frequency interference or the DC component of an audio signal, to split or combine audio signals, or to provide impedance matching between high and low impedance circuits, such as between a high impedance tube (valve) amplifier output and a low impedance loudspeaker, or between a high impedance instrument output and the low impedance input of a mixing console. Such transformers were originally designed to connect different telephone systems to one another while keeping their respective power supplies isolated, and are still commonly used to interconnect professional audio systems or system components. Being magnetic devices, audio transformers are susceptible to external magnetic fields such as those generated by AC current-carrying conductors. "Hum" is a term commonly used to describe unwanted signals originating from the "mains" power supply (typically 50 or 60 Hz). Audio transformers used for low-level signals, such as those from microphones, often include magnetic shielding to protect against extraneous magnetically-coupled signals. Output transformer Early audio amplifiers used transformers for coupling between stages, i.e., for transferring signal without connecting different operating voltages together. It was realised that transformers introduced distortion; furthermore they produced significant frequency-dependent phase shifts, particularly at higher frequencies. The phase shift was not problematical in itself, but made it difficult to introduce distortion-cancelling negative feedback, either over a transformer-coupled stage or the whole amplifier. Where they were used as a convenient way to isolate stages while coupling signals, transformers could be eliminated by using capacitor coupling. The transformer coupling the output of the amplifier to the loudspeaker, however, had the important requirement to couple the high impedance of the output valves with the low impedance of the loudspeakers. With the 1940s Williamson amplifier as a much-quoted early example, audio amplifiers with hitherto unprecedentedly low distortion were produced, using designs with only one transformer, the output transformer, and large overall negative feedback. Some attempts to design transformerless amplifiers were made, for example using very-low-impedance power triodes (such as the 6080, originally designed for power regulation), but were not widely used. The design of output transformers became a critical requirement for achieving low distortion, and carefully-designed, expensive components were produced with minimal inherent distortion and phase shift. Blumlein's Ultra-Linear transformer design was used in conjunction with Williamson's principles, allowing pentode or beam tetrode output devices to produce the higher power of a pentode than a triode, and lower distortion than either type. Some early junction transistor amplifiers used transformers in the signal path, both interstage and output, but solid-state designs were rapidly produced with suitably low impedance to drive loudspeakers without using transformers, allowing very large amounts of feedback to be applied without instability. Since the replacement of thermionic by solid-state electronics, signal transformers, including output transformers, are rarely or never used in modern audio designs. A few very expensive valve audio amplifiers are produced for vacuum-tube audio enthusiasts, and they require well-designed output transformers. Instrument transformers Instrument transformers are used for measuring voltage and current in electrical power systems, and for power system protection and control. Where a voltage or current is too large to be conveniently used by an instrument, it can be scaled down to a standardized low value. Instrument transformers isolate measurement, protection and control circuitry from the high currents or voltages present on the circuits being measured or controlled. Current transformers, designed for placing around conductors A current transformer is a transformer designed to provide a current in its secondary coil proportional to the current flowing in its primary coil.[67] Voltage transformers (VTs), also referred to as "potential transformers" (PTs), are designed to have an accurately known transformation ratio in both magnitude and phase, over a range of measuring circuit impedances. A voltage transformer is intended to present a negligible load to the supply being measured. The low secondary voltage allows protective relay equipment and measuring instruments to be operated at a lower voltages.[68] Both current and voltage instrument transformers are designed to have predictable characteristics on overloads. Proper operation of over-current protective relays requires that current transformers provide a predictable transformation ratio even during a short-circuit. Classification Electrical machines are generally understood to include not only rotating and linear electro-mechanical machines but transformers as well. Transformers can be further classified according to such key parameters as follow: Power capacity: from a fraction of a volt-ampere (VA) to over a thousand MVA; Duty of a transformer: continuous, short-time, intermittent, periodic, varying; Frequency range: power-, audio-, or radio frequency; Voltage class: from a few volts to hundreds of kilovolts; Cooling type: (dry and liquid-immersed) self-cooled, forced air-cooled; (liquid-immersed) forced oil-cooled, water-cooled; Application: such as power supply, impedance matching, output voltage and current stabilizer or circuit isolation; Purpose: distribution, rectifier, arc furnace, amplifier output, etc.; Basic magnetic form: core form, shell form; Constant-potential transformer descriptor: power, step-up, step-down, isolation, high-voltage, low voltage; Three phase winding configuration: autotransformer, delta, wye, zigzag;[69] Rectifier input phase-shift configuration: (n-winding -> p-pulse) 2-wdg -> 6-p, 3-wdg -> 12-p, . . . n-wdg -> [n-1]*6-p; polygon; etc.) System characteristics: ungrounded, solidly grounded, high or low resistance grounded, reactance grounded; Efficiency, losses and regulation: excitation, impedance & total losses, resistance, reactance & impedance drop, regulation. Construction Cores Laminated steel cores Laminated core transformer showing edge of laminations at top of photo Transformers for use at power or audio frequencies typically have cores made of high permeability silicon steel.[70] The steel has a permeability many times that of free space and the core thus serves to greatly reduce the magnetizing current and confine the flux to a path which closely couples the windings.[71] Early transformer developers soon realized that cores constructed from solid iron resulted in prohibitive eddy-current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires.[11] Later designs constructed the core by stacking layers of thin steel laminations, a principle that has remained in use. Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation.[62] The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation. The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so reduce their magnitude. Thinner laminations reduce losses,[72] but are more laborious and expensive to construct.[73] Thin laminations are generally used on high frequency transformers, with some types of very thin steel laminations able to operate up to 10 kHz. Laminating the core greatly reduces eddy-current losses One common design of laminated core is made from interleaved stacks of E-shaped steel sheets capped with I-shaped pieces, leading to its name of "E-I transformer".[73] Such a design tends to exhibit more losses, but is very economical to manufacture. The cut-core or C-core type is made by winding a steel strip around a rectangular form and then bonding the layers together. It is then cut in two, forming two C shapes, and the core assembled by binding the two C halves together with a steel strap.[73] They have the advantage that the flux is always oriented parallel to the metal grains, reducing reluctance. A steel core's remanence means that it retains a static magnetic field when power is removed. When power is then reapplied, the residual field will cause a high inrush current until the effect of the remaining magnetism is reduced, usually after a few cycles of the applied alternating current.[74] Overcurrent protection devices such as fuses must be selected to allow this harmless inrush to pass. On transformers connected to long, overhead power transmission lines, induced currents due to geomagnetic disturbances during solar storms can cause saturation of the core and operation of transformer protection devices.[75] Distribution transformers can achieve low no-load losses by using cores made with low-loss high-permeability silicon steel or amorphous (non-crystalline) metal alloy. The higher initial cost of the core material is offset over the life of the transformer by its lower losses at light load.[76] Solid cores Powdered iron cores are used in circuits such as switch-mode power supplies that operate above mains frequencies and up to a few tens of kilohertz. These materials combine high magnetic permeability with high bulk electrical resistivity. For frequencies extending beyond the VHF band, cores made from non-conductive magnetic ceramic materials called ferrites are common.[73] Some radio-frequency transformers also have movable cores (sometimes called 'slugs') which allow adjustment of the coupling coefficient (and bandwidth) of tuned radio-frequency circuits. Toroidal cores Small toroidal core transformer Toroidal transformers are built around a ring-shaped core, which, depending on operating frequency, is made from a long strip of silicon steel or permalloy wound into a coil, powdered iron, or ferrite.[77] A strip construction ensures that the grain boundaries are optimally aligned, improving the transformer's efficiency by reducing the core's reluctance. The closed ring shape eliminates air gaps inherent in the construction of an E-I core.[78] The cross-section of the ring is usually square or rectangular, but more expensive cores with circular cross-sections are also available. The primary and secondary coils are often wound concentrically to cover the entire surface of the core. This minimizes the length of wire needed, and also provides screening to minimize the core's magnetic field from generating electromagnetic interference. Toroidal transformers are more efficient than the cheaper laminated E-I types for a similar power level. Other advantages compared to E-I types, include smaller size (about half), lower weight (about half), less mechanical hum (making them superior in audio amplifiers), lower exterior magnetic field (about one tenth), low off-load losses (making them more efficient in standby circuits), single-bolt mounting, and greater choice of shapes. The main disadvantages are higher cost and limited power capacity (see "Classification" above). Because of the lack of a residual gap in the magnetic path, toroidal transformers also tend to exhibit higher inrush current, compared to laminated E-I types. Ferrite toroidal cores are used at higher frequencies, typically between a few tens of kilohertz to hundreds of megahertz, to reduce losses, physical size, and weight of a switched-mode power supply. A drawback of toroidal transformer construction is the higher labor cost of winding. This is because it is necessary to pass the entire length of a coil winding through the core aperture each time a single turn is added to the coil. As a consequence, toroidal transformers are uncommon above ratings of a few kVA. Small distribution transformers may achieve some of the benefits of a toroidal core by splitting it and forcing it open, then inserting a bobbin containing primary and secondary windings. Air cores A physical core is not an absolute requisite and a functioning transformer can be produced simply by placing the windings near each other, an arrangement termed an "air-core" transformer. The air which comprises the magnetic circuit is essentially lossless, and so an air-core transformer eliminates loss due to hysteresis in the core material.[41] The leakage inductance is inevitably high, resulting in very poor regulation, and so such designs are unsuitable for use in power distribution.[41] They have however very high bandwidth, and are frequently employed in radio-frequency applications,[79] for which a satisfactory coupling coefficient is maintained by carefully overlapping the primary and secondary windings. They're also used for resonant transformers such as Tesla coils where they can achieve reasonably low loss in spite of the high leakage inductance. Windings Windings are usually arranged concentrically to minimize flux leakage. The conducting material used for the windings depends upon the application, but in all cases the individual turns must be electrically insulated from each other to ensure that the current travels throughout every turn.[80] For small power and signal transformers, in which currents are low and the potential difference between adjacent turns is small, the coils are often wound from enamelled magnet wire, such as Formvar wire. Larger power transformers operating at high voltages may be wound with copper rectangular strip conductors insulated by oil-impregnated paper and blocks of pressboard.[81] Cut view through transformer windings. White: insulator. Green spiral: Grain oriented silicon steel. Black: Primary winding made of oxygen-free copper. Red: Secondary winding. Top left: Toroidal transformer. Right: C-core, but E-core would be similar. The black windings are made of film. Top: Equally low capacitance between all ends of both windings. Since most cores are at least moderately conductive they also need insulation. Bottom: Lowest capacitance for one end of the secondary winding needed for low-power high-voltage transformers. Bottom left: Reduction of leakage inductance would lead to increase of capacitance. High-frequency transformers operating in the tens to hundreds of kilohertz often have windings made of braided Litz wire to minimize the skin-effect and proximity effect losses.[46] Large power transformers use multiple-stranded conductors as well, since even at low power frequencies non-uniform distribution of current would otherwise exist in high-current windings.[81] Each strand is individually insulated, and the strands are arranged so that at certain points in the winding, or throughout the whole winding, each portion occupies different relative positions in the complete conductor. The transposition equalizes the current flowing in each strand of the conductor, and reduces eddy current losses in the winding itself. The stranded conductor is also more flexible than a solid conductor of similar size, aiding manufacture.[81] For signal transformers, the windings may be arranged in a way to minimize leakage inductance and stray capacitance to improve high-frequency response. This can be done by splitting up each coil into sections, and those sections placed in layers between the sections of the other winding. This is known as a stacked type or interleaved winding. Power transformers often have internal connections or taps at intermediate points on the winding, usually on the higher voltage winding side, for voltage regulation control purposes. Such taps are normally manually operated, automatic on-load tap changers being reserved, for cost and reliability considerations, to higher power rated or specialized transformers supplying transmission or distribution circuits or certain utilization loads such as furnace transformers. Audio-frequency transformers, used for the distribution of audio to public address loudspeakers, have taps to allow adjustment of impedance to each speaker. A center-tapped transformer is often used in the output stage of an audio power amplifier in a push-pull circuit. Modulation transformers in AM transmitters are very similar. Certain transformers have the windings protected by epoxy resin. By impregnating the transformer with epoxy under a vacuum, one can replace air spaces within the windings with epoxy, thus sealing the windings and helping to prevent the possible formation of corona and absorption of dirt or water. This produces transformers more suited to damp or dirty environments, but at increased manufacturing cost.[82] Cooling Cutaway view of oil-filled power transformer. The conservator (reservoir) at top provides oil-to-atmosphere isolation. Tank walls' cooling fins provide required heat dissipation balance. Though it is not uncommon for oil-filled transformers to have today been in operation for over fifty years[83] high temperature damages winding insulation,[84] the accepted rule of thumb being that transformer life expectancy is halved for every 8 degree C increase in operating temperature.[85] At the lower end of the power rating range, dry and liquid-immersed transformers are often self-cooled by natural convection and radiation heat dissipation. As power ratings increase, transformers are often cooled by such other means as forced-air cooling, force-oil cooling, water-cooling, or a combinations of these.[86] The dielectic coolant used in many outdoor utility and industrial service transformers is transformer oil that both cools and insulates the windings.[87] Transformer oil is a highly refined mineral oil that inherently helps thermally stabilize winding conductor insulation, typically paper, within acceptable insulation temperature rating limitations. However, the heat removal problem is central to all electrical apparatus such that in the case of high value transfomer assets, this often translates in a need to monitor, model, forecast and manage oil and winding conductor insulation temperature conditions under varying, possibly difficult, power loading conditions. Indoor liquid-filled transformers are required by building regulations in many jurisdictions to either use a non-flammable liquid or to be located in fire-resistant rooms.[88] Air-cooled dry transformers are preferred for indoor applications even at capacity ratings where oil-cooled construction would be more economical, because their cost is offset by the reduced building construction cost. The oil-filled tank often has radiators through which the oil circulates by natural convection. Some large transformers employ electric-operated fans or pumps for forced-air or forced-oil cooling or heat exchanger-based water-cooling.[87] Oil-filled transformers undergo prolonged drying processes to ensure that the transformer is completely free of water vapor before the cooling oil is introduced. This helps prevent electrical breakdown under load. Oil-filled transformers may be equipped with Buchholz relays, which detect gas evolved during internal arcing and rapidly de-energize the transformer to avert catastrophic failure.[74] Oil-filled transformers may fail, rupture, and burn, causing power outages and losses. Installations of oil-filled transformers usually includes fire protection measures such as walls, oil containment, and fire-suppression sprinkler systems. Polychlorinated biphenyls have properties that once favored their use as a dielectic coolant, though concerns over their environmental persistence led to a widespread ban on their use.[89] Today, non-toxic, stable silicone-based oils, or fluorinated hydrocarbons may be used where the expense of a fire-resistant liquid offsets additional building cost for a transformer vault.[84][88] Before 1977, even transformers that were nominally filled only with mineral oils may also have been contaminated with polychlorinated biphenyls at 10-20 ppm. Since mineral oil and PCB fluid mix, maintenance equipment used for both PCB and oil-filled transformers could carry over small amounts of PCB, contaminating oil-filled transformers.[90] Some "dry" transformers (containing no liquid) are enclosed in sealed, pressurized tanks and cooled by nitrogen or sulfur hexafluoride gas.[84] Experimental power transformers in the 2 MVA range have been built with superconducting windings which eliminates the copper losses, but not the core steel loss. These are cooled by liquid nitrogen or helium.[91] Insulation drying Construction of oil-filled transformers requires that the insulation covering the windings be thoroughly dried before the oil is introduced. There are several different methods of drying. Common for all is that they are carried out in vacuum environment. The vacuum makes it difficult to transfer energy (heat) to the insulation. For this there are several different methods. The traditional drying is done by circulating hot air over the active part and cycle this with periods of hot-air vacuum (HAV) drying. More common for larger transformers is to use evaporated solvent which condenses on the colder active part. The benefit is that the entire process can be carried out at lower pressure and without influence of added oxygen. This process is commonly called vapour-phase drying (VPD). For distribution transformers, which are smaller and have a smaller insulation weight, resistance heating can be used. This is a method where current is injected in the windings to heat the insulation. The benefit is that the heating can be controlled very well and it is energy efficient. The method is called low-frequency heating (LFH) since the current is injected at a much lower frequency than the nominal of the grid, which is normally 50 or 60 Hz. A lower frequency reduces the effect of the inductance in the transformer, so the voltage needed to induce the current can be reduced.[92] The LFH drying method is also used for service of older transformers.[93] Terminals Very small transformers will have wire leads connected directly to the ends of the coils, and brought out to the base of the unit for circuit connections. Larger transformers may have heavy bolted terminals, bus bars or high-voltage insulated bushings made of polymers or porcelain. A large bushing can be a complex structure since it must provide careful control of the electric field gradient without letting the transformer leak oil.[94] Applications Image of an electrical substation in Melbourne, Australia showing 3 of 5 220kV/66kV transformers, each with a capacity of 185MVA A major application of transformers is to increase voltage before transmitting electrical energy over long distances through wires. Wires have resistance and so dissipate electrical energy at a rate proportional to the square of the current through the wire. By transforming electrical power to a high-voltage (and therefore low-current) form for transmission and back again afterward, transformers enable economical transmission of power over long distances. Consequently, transformers have shaped the electricity supply industry, permitting generation to be located remotely from points of demand.[95] All but a tiny fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer.[55] Image of transformer at the Limestone Generating Station in Manitoba, Canada Transformers are also used extensively in electronic products to step down the supply voltage to a level suitable for the low voltage circuits they contain. The transformer also electrically isolates the end user from contact with the supply voltage. Signal and audio transformers are used to couple stages of amplifiers and to match devices such as microphones and record players to the input of amplifiers. Audio transformers allowed telephone circuits to carry on a two-way conversation over a single pair of wires. A balun transformer converts a signal that is referenced to ground to a signal that has balanced voltages to ground, such as between external cables and internal circuits. The principle of open-circuit (unloaded) transformer is widely used for characterisation of soft magnetic materials, for example in the internationally standardised Epstein frame method.[96]

THE DAY THE EARTH STOOD STILL

2012-07-21T10:17:00.000-07:00

An extraterrestrial flying saucer is tracked flying around the Earth until it lands on the President's Park Ellipse in Washington, D.C.. Klaatu (Michael Rennie) emerges, announcing that he has come from outer space on a goodwill mission. When he takes out and opens a small device, Klaatu is shot and wounded by a nervous soldier. In response, Gort, a large humanoid robot, emerges from the ship and begins disintegrating the weapons present with a ray coming from a visor like structure on its head. Gort continues until Klaatu orders him to stop. Klaatu explains that the now destroyed object was a viewing device, a gift for the President. Klaatu is taken to an army hospital, where he is found to be physically human, but stuns the doctors with the quickness of his healing. Meanwhile the military attempts to enter Klaatu's ship, finding it impregnable. Gort stands by, mute and unmoving. Klaatu reveals to the President's secretary, Harley (Frank Conroy), that he bears a message so momentous and urgent that it must be revealed to all the world's leaders simultaneously. Harley tells him that it would be impossible to get all of the world leaders to agree to meet. Klaatu wants to get to know the ordinary people. Harley forbids it and leaves Klaatu locked up under guard. Klaatu escapes and lodges at a boarding house, assuming the alias "Mr. Carpenter," the name he finds on the cleaners tag on the suit he "borrowed." Among the residents are Helen Benson (Patricia Neal), a World War II widow, and her son Bobby (Billy Gray). At breakfast the next morning, during alarming radio reports, Klaatu takes in his fellow boarders' suspicions and speculations about the alien visit. While Helen and her boyfriend Tom Stephens (Hugh Marlowe) go on a day trip, Klaatu babysits Bobby. The boy takes Klaatu on a tour of the city, including a visit to his father's grave in Arlington National Cemetery, where Klaatu is dismayed to learn that most of those buried there were killed in wars. The two visit the heavily guarded spaceship and the Lincoln Memorial. Klaatu, impressed by the Gettysburg Address inscription, queries Bobby for the greatest person living in the world. Bobby suggests a leading American scientist, Professor Jacob Barnhardt (Sam Jaffe), who lives in Washington, D.C. Bobby takes Klaatu to Barnhardt's home, but the professor is absent. Klaatu enters and adds a key mathematical equation to an advanced problem on the professor's blackboard, and then leaves his contact information with the suspicious housekeeper. Later, government agents escort Klaatu to see Barnhardt. Klaatu introduces himself and warns the professor that the people of the other planets have become concerned for their own safety after human beings developed atomic power. Klaatu declares that if his message goes unheeded, "Planet Earth will be eliminated." Barnhardt agrees to arrange a meeting of scientists at Klaatu's ship and suggests that Klaatu give a demonstration of his power. Klaatu returns to his spaceship the next evening to implement the idea, unaware that Bobby has followed him. Bobby tells the unbelieving Helen and Tom what has transpired, but not until Tom finds a diamond on the floor of Klaatu's room do they begin to accept his story. When Tom takes the diamond for appraisal, the jeweler informs him it is unlike any other on Earth. Klaatu finds Helen at her workplace. She leads him to an unoccupied elevator which mysteriously stops at noon, trapping them together. Klaatu admits he is responsible, tells Helen his true identity, and asks for her help. A montage sequence shows that Klaatu has neutralized all electric power everywhere around the planet except in situations that would compromise human safety, such as hospitals and airplanes. After the thirty-minute blackout ends, the manhunt for Klaatu intensifies and Tom informs authorities of his suspicions. Helen is very upset by Tom's betrayal of Klaatu and breaks off their relationship. Helen and Klaatu take a taxi to Barnhardt's home; en route, Klaatu instructs Helen that, should anything happen to him, she must tell Gort "Klaatu barada nikto". When they are spotted, Klaatu is shot by military personnel. Helen heads to the spaceship. Gort awakens and kills two guards before Helen can relay Klaatu's message. Gort gently deposits her in the spaceship, then goes to fetch Klaatu's corpse. Gort then revives Klaatu while the amazed Helen watches. Klaatu explains that his revival is only temporary; even with their advanced technology, they cannot truly overcome death, that power being reserved for the "Almighty Spirit."[2] Klaatu steps out of the spaceship and addresses the assembled scientists, explaining that humanity's penchant for violence and first steps into space have caused concern among other inhabitants of the universe who have created and empowered a race of robot enforcers including Gort to deter such aggression. He warns that if the people of Earth threaten to extend their violence into space, the robots will destroy Earth, adding, "The decision rests with you." He enters the spaceship and departs.

JOSEPH HENRY'S: WORK WITH MAGNETS

2012-07-18T09:32:00.004-07:00

BIOGRAPHY OF JOSEPH HENRY

Joseph Henry was a researcher in the field of electricity whose work inspired inventors. Joseph Henry Biography In 1799, Joseph Henry was born in Albany, New York. He was educated at Albany Academy (now Princeton University). Intending to become a doctor, he studied natural sciences. In 1824, Joseph Henry was employed as an assistant engineer on a survey team for a State road, three hundred miles long, between the Hudson River and Lake Erie. The experience changed the course of his career; he decided to study civil and mechanical engineering instead of medicine. WORK WITH MAGNETS: Joseph Henry's first discovery was that the power of a magnet could be immensely strengthened by winding it with insulated wire. He was the first person to make a magnet that could lift thirty-five hundred pounds of weight. Joseph Henry showed the difference between "quantity" magnets composed of short lengths of wire connected in parallel and excited by a few large cells; and "intensity" magnets wound with a single long wire and excited by a battery composed of cells in series. This was an original discovery, greatly increasing both the immediate usefulness of the magnet and its possibilities for future experiments. Michael Faraday, William Sturgeon, and other inventors were quick to recognize the value of Joseph Henry's discoveries. Sturgeon magnanimously said, "Professor Joseph Henry has been enabled to produce a magnetic force which totally eclipses every other in the whole annals of magnetism; and no parallel is to be found since the miraculous suspension of the celebrated Oriental imposter in his iron coffin." SELF INDUCTION: Joseph Henry discovered the phenomena of self induction and mutual induction. In his experiment, a current sent through a wire in the second story of the building induced currents through a similar wire in the cellar two floors below. TELEGRAPH: A telegraph was an early invention that communicated messages at a distance over a wire using electricity that was later replaced by the telephone. The word telegraphy comes from the Greek words tele which means faraway and grapho which means write. The first attempts to send signals by electricity (telegraph) had been made many times before Joseph Henry became interested in the problem. William Sturgeon's invention of the electromagnet encouraged researchers in England to experiment with the electromagnet. The experiments failed and only produced current that weakened after a few hundred feet. Basis For the Electric Telegraph: However, Joseph Henry strung a mile of fine wire, placed an "intensity" battery at one end, and made the armature strike a bell at the other. Joseph Henry discovered the essential mechanics behind the electric telegraph. This discovery was made in 1831, a full year before Samuel Morse invented the telegraph. There is no controversy as to who invented the first telegraph machine. That was Samuel Morse's achievement, but the discovery which motivated and allowed Morse to invent the telegraph was Joseph Henry's achievement. In Joseph Henry's own words: "This was the first discovery of the fact that a galvanic current could be transmitted to a great distance with so little a diminution of force as to produce mechanical effects, and of the means by which the transmission could be accomplished. I saw that the electric telegraph was now practicable. I had not in mind any particular form of telegraph, but referred only to the general fact that it was now demonstrated that a galvanic current could be transmitted to great distances, with sufficient power to produce mechanical effects adequate to the desired object." MAGNETIC ENGINE
Joseph Henry next turned to designing a magnetic engine and succeeded in making a reciprocating-bar motor, on which he installed the first automatic pole changer, or commutator, ever used with an electric battery. He did not succeed in producing direct rotary motion. His bar oscillated like the walking beam of a steamboat. Joseph Henry - Professor of Natural Philosophy In 1839, Joseph Henry was appointed as the Professor of Natural Philosophy at Princeton University. There he repeated his old experiments on a larger scale. He confirmed Steinheil's experiment of using the earth as return conductor, showed how a feeble current would be strengthened, and how a small magnet could be used as a circuit maker and breaker, the principles later used for the telegraph relay and the dynamo. Joseph Henry - RESEARCHER VS INVENTOR: Joseph Henry was more of a researcher, rather than an inventor. He stated that "I never myself attempted to reduce the principles to practice, or to apply any of my discoveries to processes in the arts. My whole attention exclusive of my duties to the College, was devoted to original scientific investigations, and I left to others what I considered of subordinate importance, the application of my discoveries to useful purposes in the arts." Joseph Henry was also uninterested in applying for any patents. Smithsonian Institution: The Smithsonian Institution was founded in Washington in 1846, and Joseph Henry was its chief executive officer until his death in 1878. Joseph Henry - Other Achievements Joseph Henry made meteorology into a science and made the first weather map. He issued forecasts of the weather based upon definite knowledge rather than upon signs. He improved maritime lights and fog signals today. Even though Joseph Henry was drawn into a controversy with Samuel Morse over credit for the invention of the telegraph, he used his influence to protect Morse's patent. Joseph Henry advised Alexander Graham Bell, when Bell first had the idea that electric wires might be able carry the human voice. Henry encouraged Bell to proceed with his experiments. Alexander Graham Bell wrote that Joseph Henry thought Bell's ideas were the beginning of a great invention. Bell told Henry that he faced mechanical difficulties and that he lacked the electrical knowledge necessary to overcome those difficulties. Joseph Henry's advise was "Get It!"

DISCOVERY OF MAGNETS

2012-07-16T09:48:00.003-07:00

As with all great discoveries, the discovery of magnet is very interesting and very colorful too. THE SHEPHERD MAGNESE The most popular legend accounting for the discovery of magnets is that of an elderly Cretan shepherd named Magnes. Legend has it that Magnes was herding his sheep in an area of Northern Greece called Magnesia, about 4,000 years ago. Suddenly both, the nails in his shoes and the metal tip of his staff became firmly stuck to the large, black rock on which he was standing. To find the source of attraction he dug up the Earth to find lodestones (load = lead or attract). Lodestones contain magnetite, a natural magnetic material Fe3O4. This type of rock was subsequently named magnetite, after either Magnesia or Magnes himself. THE GREEK AND THE CHINESE The earliest discovery of the properties of lodestone was either by the Greeks or Chinese. Stories of magnetism date back to the first century B.C in the writings of Lucretius and Pliny the Elder (23-79 AD Roman). Pliny wrote of a hill near the river Indus that was made entirely of a stone that attracted iron. He mentioned the magical powers of magnetite in his writings. For many years following its discovery, magnetite was surrounded in superstition and was considered to possess magical powers, such as the ability to heal the sick, frighten away evil spirits and attract and dissolve ships made of iron! People believed that there were whole islands of a magnetic nature that could attract ships by virtue of the iron nails used in their construction. Ships that thus disappeared at sea were believed to have been mysteriously pulled by these islands. Archimedes is purported to have used loadstones to remove nails from enemy ships thus sinking them. People soon realized that magnetite not only attracted objects made of iron, but when made into the shape of a needle and floated on water, magnetite always pointed in a north-south direction creating a primitive compass. This led to an alternative name for magnetite, that of lodestone or "leading stone". For many years following the discovery of lodestone magnetism was just a curious natural phenomenon. The Chinese developed the mariner's compass some 4500 years ago. The earliest mariner's compass comprised a splinter of loadstone carefully floated on the surface tension of water. EARLY DISCOVERIES Peregrinus & Gilbert Peter Peregrinus is credited with the first attempt to separate fact from superstition in 1269. Peregrinus wrote a letter describing everything that was known, at that time, about magnetite. It is said that he did this while standing guard outside the walls of Lucera which was under siege. While people were starving to death inside the walls, Peter Peregrinus was outside writing one of the first 'scientific' reports and one that was to have a vast impact on the world. However, significant progress was made only with the experiments of William Gilbert in 1600 in the understanding of magnetism. It was Gilbert who first realized that the Earth was a giant magnet and that magnets could be made by beating wrought iron. He also discovered that heating resulted in the loss of induced magnetism. Oersted & Maxwell In 1820 Hans Christian Oersted (1777-1851 Danish) demonstrated that magnetism was related to electricity by bringing a wire carrying an electric current close to a magnetic compass which caused a deflection of the compass needle. It is now known that whenever current flows there will be an associated magnetic field in the surrounding space, or more generally that the movement of any charged particle will produce a magnetic field. Eventually it was James Clerk Maxwell (1831-1879 Scottish) who established beyond doubt the inter-relationships between electricity and magnetism and promulgated a series of deceptively simple equations that are the basis of electromagnetic theory today. What is more remarkable is that Maxwell developed his ideas in 1862 more than thirty years before J. Thomson discovered the electron in 1897, the particle that is so fundamental to the current understanding of both electricity and magnetism. The term magnetism was thus coined to explain the phenomenon whereby lodestones attracted iron. Today, after hundreds of years of research we not only know the attractive and repulsive nature of magnets, but also understand MIR scans in the field of medicine, computers chips, television and telephones in electronics and even that certain birds, butterflies and other insects have a magnetic sense of direction. The term magnetism was coined to explain the phenomenon. whereby loadstone attracts iron. Today, after hundred of years of research we not only know the attractive and repulsive nature of magnets but also understands THE MIR scans in the field of medicine, computer chips, television and telephone and even that certain birds, insects and butterflies have a magnetic sense of direction.

Fola Jokes Villa

THE ALMA TELESCOPE

URINE POWERED GENERATOR

THE CANCER DETECTING BRA

THE NEW PLANET (SUPPER EARTH)

THE BRAIN

The Hindbrain

The Spinal Cord

The Medulla Oblongata

The Pons

The Cerebellum

The Limbic System

The Amygdala

The Hippocampus

The Hypothalamus

The Thalamus

The Neocortex

The Frontal Lobe

The Parietal Lobe

The Temporal Lobe

The Occipital Lobe

Broca's Area

The Corpus Callosum

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CHARACTERISTICS OF ORGANISM USED FOR GENETICS STUDIES

Characteristics Of Organisms Used For Genetic Studies

THE SCIENCE OF GENETICS

The Fields Of Genetics

GREEN HOUSE EFFECT AND CAUSES

GREEN HOUSE EFFECT

THE TRANSFORMER

THE DAY THE EARTH STOOD STILL

JOSEPH HENRY'S: WORK WITH MAGNETS

BIOGRAPHY OF JOSEPH HENRY

DISCOVERY OF MAGNETS