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All about Graphene

2013-10-07T06:06:00.000-07:00

a. Fabrication and Characteristics

Graphene is two-dimensional crystalline form of carbon: a single layer of carbon atoms arranged in hexagons, like a honeycomb, with sp² bonding, unlike diamond and amorphous carbon materials as having sp³ bonding. Chemical functionalization of the main graphene sheet (not the edges) is achieved by either covalent or non-covalent methods. Covalent functionalization requires the breaking of sp² bonds and can be achieved using a wide range of reactions. Non-covalent functionalization relies on van der Waals forces often due to pi-pi stacking between aromatic molecules and the graphene lattice. Regarding its electronic properties, a good approximation to the band structure of mono-layer graphene can be obtained from a simple nearest neighbor tight-binding calculation. Inspection of this band structure immediately reveals three electronic properties of mono-layer graphene which have excited such interest in this material: the vanishing carrier density at the Dirac points, the existence of pseudo-spin and the relativistic nature of carriers [1]. In case of magnetic properties of graphene, weak paramagnetism at low temperatures is reported for relatively defect free graphene, and the use of ion irradiation to add vacancies can increase the paramagnetism [2].

Manufacturing process of graphene can be done by several methods in which each method shows different characteristics of the obtained graphene including crystallite size, sample size, and charge carrier mobility. As reported by Novoselov et al [3], the summary of graphene`s fabrication methods is shown as following table.

Table 1 | Properties of graphene obtained by different methods

Method	Description	Characteristics
Method	Description	Crystallite Size (μm)	Sample Size (mm)	Charge Carrier Mobility (at ambient temperature) (cm² V^-1 s^-1)
Mechanical Exfoliation	The weathering of a graphite structure by freeze/thaw cycles or temperature differentials between the graphite surface and interior, then physically scrubbed.	>1000	>1	>2.10^5 and >10^6 at low temperature
Liquid-Phase Chemical Exfoliation	Sonication-aided exposure of the materials to a non-aqueous solvent (or aqueous solutions with surfactant) with a surface tension that favors an increase in the total area of graphite crystallites [4]	<=0.1	Infinite as a layer of overlapping flakes	100 (for a layer of overlapping flakes)
Chemical Exfoliation via Graphene Oxide	Oxidizing graphite pellets and then ultrasonically exfoliated in an aqueous solution [5]	around 100	Infinite as a layer of overlapping flakes	1 (for a layer of overlapping flakes)
CVD	Large-area uniform polycrystalline graphene films are grown on copper foils and films by deposition [6]	1000	around 1000	10000
SiC	Graphitic layers can be grown either on the silicon or carbon faces of a SiC wafer at high temperature (1000) by sublimating Si atoms, thus leaving a graphitized surface [7]	50	100	10000

b. Application and Current Situation (Issues and Challenges)

Due to its unique characteristic, graphene has possibility to be implemented in various fields, especially in electronics devices. Semiconductor industry may rely on silicon technology such for CMOS fabrication, but silicon devices have a physical limit such quantum tunneling of electrons across the insulator into the gate which increases the power consumption. The promise of graphene as replacement of semiconductor in CMOS may beat this silicon limit. Here, the summary of other possible application of graphene, followed with current challenges and issues are presented in below table [3].

Table 2 | Applications of graphene

Field	Application	Drivers and Challenges	Issues
Photonics	Tunable fiber mode-locked laser	Wide spectral range of graphene	The requirement of a cost-effective graphene-transferring technology
	Solid-state mode-locked laser	Graphene-saturable absorber would be cheaper and easy to integrate into laser system
	Photo-detector	Graphene can provide bandwidth per wavelength of 640 GHz for chip to chip or inter-chip communication in which IV or III-IV detectors are not compatible)	The necessary to increase responsivity which might require a new structure and/or doping control in which the modulator bandwidth must also follow suit.
	Polarization Controller	Current polarization controlling devices are difficult to integrate, but graphene is easy integrate with silicon	The necessary to gain full control of parameters of high-quality graphene
	Optical Modulator	Graphene could increase operating speed where Si operation bandwidth is limited to about 50 GHz, thus avoiding the use of complicated III-IV epitaxial growth or bonding on SI	The requirement of high-quality graphene with low sheet resistance to increase bandwidth to over 100 GHz
	Isolator	Graphene can provide both compact and integrated isolators on Si substrate, dramatically aiding miniaturization.	The necessity of magnetic field strength decrement and process architecture optimization
	Passively mode-locked semiconductor laser	Core-to-core and core-to-memory bandwidth increase requires a dense wavelength-division-multiplexing optical interconnect with over 50 wavelength in which not achievable with a laser array, but a graphene-saturable absorber can provide.	The necessity of low power consumption of interconnect architecture using graphene
Electronics	Touch screen	Graphene has better endurance	Requirement of better control od contact resistance and low sheet resistance
	E-paper	High transmittance of monolayer graphene could provide visibility
	Foldable OLED	High-quality graphene provides bendability of below 5 mm. atomically flat-surface of graphene avoid electrical short and leakage current.	The necessary of low sheet resistance and conformal coverage of 3D structure
	High-frequency transistor	No producible solution for InP high-electron mobility transistor after 2021.	Need to achieve current saturation, 850 GHz of cut-off frequency and 1200 GHz of maximum oscillating frequency
	Logic transistor	High mobility	The necessary of new structure to resolve band gap-mobility trade off and an on/off ratio larger than 10⁶
Energy Generation and Storage	Transparent electrodes of solar cell	Uniform absorption over a broad spectrum but low intrinsic optical absorption.	Requirement of complex interferometry or plasmonic enhance structure
	Electrodes for Lithium Batteries	High thermal and electrical conductivity	Mass production technology
	Supercapacitor	Combination of a high-surface-area activated carbon material and a nanoscopic charge separation at the electrode–electrolyte interface.	Necessary to reduce high irreversible capacitance of graphene-based supercapacitor
	Support material for platinum catalysts for fuel cells	Strong interaction between the platinum atoms and graphene decreases the platinum particle size to under nanometer order	Applicable on only direct methanol fuel cells
Composite Materials, coating and paints	Reinforcement component	High Young`s modulus of graphene	Chemical modification of graphene to provide adhesion properties is necessary
Composite Materials, coating and paints	Coatings and Paints	Graphene is highly inert, and so can act as a corrosion barrier against water and oxygen diffusion	Durability assessment is necessary
Sensor	Strain-gauge transducer	Graphene is the only crystal which can be stretched by 20%,	Good electrical and/or optical readouts of sensor
Sensor	Gas sensor	Extremely high sensitivity	Low selectivity and poisoning by water are main issues
Bio-application	Drug delivery vehicles	Large surface area and delocalized p electrons and lipophilic of graphene	Necessary to understand the bio-distribution, biocompatibility and acute and chronic toxicity of graphene under conditions that are relevant to exposure during manufacture and subsequent use

As unique crystal which combines many superior properties from electronic to mechanical, graphene and its full ability will only can be realized in very new application designed specially with this material rather than replacing other materials in existing applications. Recent development in printable and flexible electronics, flexible solar cells, and supercapacitor gives such an opportunity in very soon. Hopefully, for next few years, graphene-based devices will come to the end-users, the customers

c. Graphene on Devices

Relating to the previous section about the possible applications of graphene, three different applications of graphene are pointed out according its electrical, chemical and optical properties. High conductivity, chemical responsivity, and photo-sensitivity of graphene are used to develop new OLED, biosensor and photodetector, respectively. Here, table 3 summarizes some ideas to apply graphene in those three applications.

Table 3 | Idea to apply graphene in electronic devices

Device	Schematic Design	Description
OLED [8]		High work function (WF) and low sheet resistance-modified graphene has possibility to be used as anode for OLED. It is reported that the efficiency was beyond Indium tin oxide-based OLED both for fluorescence and phosphorescence. The method that was used to increase WF and reduce sheet resistance was by using conducting polymer to modify the surface thus creating a WF gradient from graphene to the over lying organic layer, and by doping of p-dopant.
Field Effect Transistor -based Bio-sensor [9]		High sensitivity and excellent selectivity of graphene toward biomolecules become the reason to combine graphene with CMOS platform to provide direct, label-free and real-time electrical detection of biomolecules. The ability of graphene-FETs biosensor to detect single molecule or single cell-level has been reported, but yet to be mass produced due to the difficulty of controlling layer number and surface cleanness of graphene. System integration also becomes a challenge since it was reported in most of studies that sample delivery system was used.
Photo-detector [10]		Owing to unique band structure, graphene shows remarkable response in photocurrent generation near metal/graphene interfaces. This was followed by utilizing graphene as photo-detectors which could be operated at hundreds GHz level. It was reported that in graphene-FET photodetector, the internal electric fields which are responsible for separation of photo-generated carriers near electrode/graphene interfaces leads to band bending, while the absence of strong electric in the bulk graphene sheet allows carrier recombination. By using interdigitated metal finger, large, high electric field-light detection area could be created.

References

[1] J. M. Warner, F. Schäffel, A. Bachmatiuk, M. H. Rümmeli, Graphene: Fundamentals and Emergent Applications 1^st edition, ISBN 978-0-12-394593-8

[2] R. R. Nair, M. Sepioni, I-Ling Tsai, O. Lehtinen, J. Keinonen, A. V. Krasheninnikov, T. Thomson, A. K. Geim and I. V. Grigorieva, Nat. Phys. 8 (2012) 199–202

[3] K. S. Novoselov, V. I. Fal`ko, L. Colombo, P. R. Gellert, M. G. Schwab & K. Kim, Nature 490 (2012) 192–200

[4] Y. Hernandez, V. Nicolosi, M. Lotya, F. M. Blighe, Z. Sun, S. De, T. McGovern, B. Holland, M. Byrne, Y. K. Gun`ko, J. J. Boland, P. Niraj, G. Duesberg, S. Krishnamurthy, R. Goodhue, J. Hutchison, V. Scardaci, A. C. Ferrari, J. N. Coleman, Nature Nanotechnology. 3 (2008), 563–568

[5] X. S. Li, W. W. Cai, J. H. An, S. Y. Kim, J. H. Nah, D. X. Yang, R. Piner, A. Vemalakanni, I. H. Jung, E. Tutuc, S. K. Banarjee, L. Colombo, R. S. Ruoff, Science 324 (2009) 1312–1314

[6] D. R., Dreyer, R. S. Ruoff, & C. W. Bielawski, Angew. Chem. Int. Ed. 49 (2010) 9336–9344.

[7] I. Fourbeaux, J. M. Themlin, J. M. Debever, Phys. Rev. B 58 (1998) 16396-16406

[8] T. H. Han, Y. Lee, M. R. Choi, S. H. Woo, S. H. Bae, B. H. Hong, J. H. Ahn and T. W. Lee, Nature Photonics 6 (2012) 105-110

[9] S. Liu, X. Guo, NPG Asia Materials 4 (2012), e23;

[10] T. Mueller, F. Xia, P. Avouris, Nature Photonics 4 (2010) 297 - 301

Semiconductor Physics and Devices: Solar Cell

2013-10-04T05:48:00.002-07:00

Solar cells are devices that convert photon energy into electricity. There are several types of solar cells regarding the materials which are used. The common structure of solar cell is configured by p-n junction where electron-hole pair generation takes place, and electrodes to transfer the electrons. There are other components installed in some solar cells in order to improve efficiency such as inserting intrinsic semiconductor in enlarge the area of photocurrent generation or reflector to enhance photon energy. The example of organic and inorganic solar cells is presented in Fig. 1. The mechanism of power generation of solar cells is due to photovoltaic effect which explains that light of certain wavelengths is able to ionize the atoms in semiconductor materials and the internal electric field produced by the p-n junction separates some of the positive charges ("holes") from the negative charges (electrons) which then are transferred to the electrodes. Here, the band gap between p-type and n-type semiconductors determines the specific absorbance of light.

a. Structure, Mechanism, and Energy Loss Factor of Solar Cell

Fig. 1 The example of organic solar cell using semiconducting polymers (a) [1] and silicon based-solar cell (b) [2].

Regarding the overall energy conversion efficiency in solar cell, several possible losses should be considered such as losses due to non-absorption of long wave length , thermalization of the excess energy of photon total reflection , incomplete absorption due to finite thickness , electron-hole recombination, electrode coverage (shading losses), voltage factor, and fill factor.

It can be expressed as

Fig.2 Typical I-V characteristic of nanowire dye-sensitized solar cell [3]

Experimentally, the efficiency of solar cells is defined from I-V measurement result, as depicted in Fig. 2 which contains direct information about fill factor. The maximum power generated by a solar cell is dependent on this value. In a practical solar cell, the FF is lower than the ideal value due to voltage drop both by series resistance and current leakage.

b. High Efficiency-Solar Cells

Basically, solar cells can be categorized at least into 5 categories in which each type has efficiency limit regarding recent progress. There are emerging photovoltaic system (such as dye sensitized cell), thin film solar cells (such as amorphous Si:H solar cells), c-Si solar cells, single-junction GaAs, and multi-junctions solar cells. The researches progress for achieving higher conversion efficiency for different category of solar cell is summarized in below table.

Table 1 | Researches toward high efficiency solar cell

Type	Schematic Devices	Descriptions
Emerging Photo-Voltaic Cells	Dye-sensitized Solar Cell (DSSC) [4]	DSSC is similar with photosynthesis in the use of a dye as the light harvester to produce excited electrons, TiO₂ replacing carbon dioxide as the electron acceptor, iodide/tri-iodide (I^-/I^3-) replacing water and oxygen as the electron donor and oxidation product and a multilayer structure (similar to the thylakoid membrane) to enhance both the light absorption and electron collection efficiency. It was reported that the efficiency has reached about 11.4 % [5] by improving the open circuit potential with introduction of co-absorber to avoid dye aggregation and reduce the charge recombination.
Thin film solar cells	Si:H based solar cells [6]	Thin film solar cell is made by depositing one or more thin layers of photovoltaic material on a substrate. The thickness range of such a layer is wide and varies from a few nanometers to tens of micrometers. Reductions in the requisite thickness are a pathway to reduce costs for most solar cell materials, as well as a route to higher open circuit voltages due to decreased bulk recombination. But, offsetting the reduced photocurrent is necessary which can be done by light trapping [6]. In case of aSi:H based solar cell the highest stable efficiency so far is 13.4% [7]
c-Si solar cells	Passivized Emitter Rear Localized (PERL) Cell [8]	As being the largest market share of solar cell business, the crystalline silicon PV cell is essentially a diode with a semiconductor structure. Representative example of high-efficiency mono-crystalline silicon PV cells is PERL cell. The highest energy conversion efficiency for PERL cell reported so far is 25% [8]. This value is below the single crystal Si based solar cell which was reported to have 27.6 % of conversion efficiency [9].
Single-junction GaAs Solar cells	Single Junction GaAs Solar Cell [10]	Owing to its direct band gap and high electron mobility, gallium arsenide (GaAs) based compound semiconductor has advantages over silicon. In case of photovoltaic application, limiting the emission angle of a high-quality GaAs solar cell becomes a feasible route to achieving power conversion efficiencies above 38% with a single junction [11]. But, experimentally, it was found that highest efficiency was about 28.8% using thin film crystal [12].
Multi-junction solar cells	Schematic diagram of a multi-junction (MJ) solar cell [13]	The highest conversion efficiency among 5 types of solar cells being discussed here is multi-junction solar cell which has reached 44 % using terrestrial concentrator [12]. In MJ solar cell, semiconductors with different band gaps convert different portions of the solar spectrum to reduce thermalization losses. Light-management architectures are also applicable for reaching ultrahigh efficiency [14].

c. Low-cost Solar Cells

As mentioned in previous section, mainly the solar cell that can be categorized as lowest-cost one is emerging PV especially dye-sensitized solar cell. In case both fabrication method and cost, this type does not require complicated manufacturing process compared to silicon based solar cell and even some of examples can be made by home industry. The issues and challenges are the conversion efficiency and durability for long-term use. Several improvements have been done to reach better efficiency as described in Table 2.

Table 2 | Researches toward low-cost solar cell

Improvements	Nanomaterial Design	Remark
Better nanostructure design for better collection of charges and higher surface roughness factor for higher dye loading capacity	Hierarchical TiO₂ tubular macrochannel arrays (HTTMAs) [15]	229.6 m²g^-1 high surface area of HTTMA showed 8.1 % of energy conversion efficiency, a better efficiency than TiO₂ nanoparticles based DSSC. HTTMAs were produced by one step hydrothermal method without template or electric filed assistant. This method was the simplification of common alkaline hydrothermal method which requires anodic aluminum oxide template or anodic oxidation.
Low electron recombination rates by optimizing active layer thickness of electrolyte layers	Schematic of thin DSSC [16]	Trapping/detrapping processes and electrons exchange between semiconductor and electrolyte in DSSC determine recombination rates. Low electron recombination rates and high electron generation is expected to achieve good conversion efficiency. It was shown that increasing active layer of DSSC and decreasing bulk electrolyte layer would further increase the cell efficiency thus defined the optimum thickness of DSSC.
Low electron recombination rates by increasing energy barrier between ZnO and TiO₂	Schematic band structure of DSSC using additional energy barrier [17]	Another way to increase transportation rates of electrons toward decreasing the recombination of electrons in dye or electrolyte is by creating energy barrier in the working electrode. ZnO-coated TiO₂electrode was chosen as part of it. This working electrode was fabricated by using simple dip coating method and the efficiency calculation showed the increase from 5.45 % (without ZnO coating) to 6.62 % (with ZnO coating).
Better ligand exchange process to increase hydrophility and anchoring-sites for dyes	TEM image of acetic acid-treated TiO₂ photo anode [18]	The efficiency of DSSC is also directly related to the quantity of the adsorbed dye on the photo-anode layer. Thus, TiO2 photo-anode should have lots of anchoring sites for dyes. The acetic acid treatment on photo electrode was reported to increase hydrophility which was advantageous for the adsorption of dye molecules. The result showed there was optimum concentration that suited for DSSC.
Adding new functional parts: reflectors to reduce the energy losses caused by the inactive areas	Sketch of reflector [19]	The energy losses caused by the inactive areas decrease the overall efficiency of DSSC. The application of reflectors to collect more photons so that energy losses due to inactive areas decreased has been reported. Increasing the reflectance from 0 to 0.9 increased the total area efficiency around 1.12 %.

References

[1] M. A. Rahman, A. Rahim, Md. Maniruzzaman, K. Yang, C. Lee, H. Nam, H. Soh, J. Lee, Solar Energy Materials & Solar Cells 95 (2011) 3573–3578

[2] H. Cui, S. Pillai, P. Campbell, M. Green, Solar Energy Materials & Solar Cells 109 (2013) 233–239

[3] M. Law, L. E. Greene, J. C. Johnson, R. Saykally and P. Yang, Nature Materials 4 (2005)455 - 459

[4] M.R. Narayan. Renewable and Sustainable Energy Reviews 16 (2012) 208-215

[5] L. Han, A. Islam, H. Chen, C. Malapaka, B. Chiranjeevi, S. Zhang, X. Yang and M. Yanagida, Energy Environ. Sci. 5 (2012) 6057

[6] V. E. Ferry, IEEE 35^th Photovoltaic Specialists Conference (PVSC), 2010

[7] K. Söderström, G. Bugnon, R. Biron, C. Pahud, F.Meillaud, J. Appl. Phys. 112 (2012) 114503

[8] M. A. Green, Prog. Photovoltaics 17 (2009) 183–189

[9] A. Slade and V. Garboushian, Proc. of the 15^thInt. Photovoltaic Science and Engineering Conf. (2005) pp. 701–703

[10] J. S. Yoon, S. J. Jo, I. S. Chun, I. H. Jung, H. S. Kim, M. Meitl, E. Menard, X. L. Li, J. J. Coleman, U. Paik & J.A. Rogers, Nature 4652010329–333

[11] E. D, Kosten, J. H. Atwater, J. Parsons, A. Polman and H. A. Atwater, Light: Science & Applications 2 (2013) e45;

[12] M. A. Green, K. Emery, Y. Hishikawa, W. Warta and E.D. Dunlop, Prog. Photovolt: Res. Appl. 21 (2013) 1-11

[13] U.S. Naval Research Laboratory http://www.nrl.navy.mil/media/news-releases/2013/nrl-designs-multi-junction-solar-cell-to-break-efficiency-barrier (2013)

[14] A. Polman and H. A. Atwater, Nature Materials 11 (2012) 174-177

[15] X. Wang, H. Li, Y. Liu, W. Zhao, C. Liang, H. Huang, D. Mo, Z. Liu, X. Yu, Y. Deng, H. Shen, Applied Energy 99(2012) 198-205

[16] M. Filipic, M. Berginc, F. Smole, M. Topic, Current Applied Physics 12 (2012) 238-246

[17] C. S. Chou, F.C. Chou, J. Y. Kang, Powder Technology 215-216 (2012) 38–45

[18] H. G. Bang, J. K. Chung, R. Y. Jung, S. Y. Park, Ceramics International 38S (2012) S511–S515

[19] Y. D. Zhang, X. M. Huang, D. M. Li, Y. H. Luo, Q. B. Meng, Solar Energy Materials & Solar Cells 98 (2012) 417–423

QA on Delectric Materials

2013-08-24T09:26:00.000-07:00

Q1. Describe the definition of dielectric materials

Dielectric materials are electrical insulators which can be easily polarized by external electric field. The presence of electric field results in charges re-arrangement in which the positive charges are displaced toward the field whereas negative charges are in opposite direction so called dielectric polarization. They are categorized as electrical insulator since there is no field induced-charges flow as it happens on conductor. This is due to large energy band gap and no free electron exists at conduction band. Closely seeing to the atomic model, the external electric field will distort electron cloud surrounding nucleus and give rise to electric dipole.

Q2. Categorize dielectric materials and describe their features individually

Category	Illustration/Features
Piezoelectric Materials	In piezoelectric materials, applying mechanical forces/stresses will induce spontaneous polarization inside materials due to ionic displacement (direct piezoelectric effect), or oppositely applying electric field will cause structural deformation (inverse piezoelectric effect)
Pyroelectric Materials	In pyroelectric materials, temporary voltage due to spontaneous polarization will be generated when the materials are heated or cooled. The change in temperature slightly modifies the atomic position within crystal structure.
Ferroelectric Materials	In ferroelectric materials, spontaneous electric polarization can be reversed by the application of external electric field. The reversibility of spontaneous polarization is observed as hysteresis in P-E curve.

Q3. Describe the real application of dielectric materials to electric devices

Applications	Descriptions
Motion sensor (Passive Infra Red) PIR sensor	PIRs are basically made of a pyroelectric sensor (the round metal can with a rectangular crystal in the center), which can detect levels of infrared radiation. Everything emits some low level radiation, and the hotter something is, the more radiation is emitted. That is why PIR sensors allow us to sense motion,　and they are almost always used to detect whether a human has moved in or out of the sensors range.
Piezoelectric Sounder	Basically, the sound source of a piezoelectric sounder is a piezoelectric diaphragm. A piezoelectric diaphragm consists of a piezoelectric ceramic plate which has electrodes on both sides and a metal plate. Applying D.C. voltage between electrodes of a piezoelectric diaphragm causes mechanical distortion due to the piezoelectric effect. When AC voltage is applied across electrodes, the bending is repeated and producing sound waves in the air.
FRAM (Ferroelectric Random Access Memory) with RFID (Radio Frequency Identity) interface	F-RAM performs reads and writes like a RAM. It provides reliable data retention for 20 years while eliminating the complexities, overhead, and system level reliability problems caused by EEPROM and other nonvolatile memories, combined with RFID to enable traceability through monitoring. Large amounts of information can be stored with each individual product, for example historical records and other tracking information as well as ID.

Introduction to Biosensor

2011-08-15T23:47:00.000-07:00

A biosensor is defined as a detecting device that combines a transducer with a biologically sensitive and selective component. When a specific target molecule interacts with the biological component, a signal is produced, at transducer level, proportional to the concentration of the substance. Therefore biosensors can measure compounds present in the environment, chemical processes, food and human body at low cost if compared with traditional analytical techniques. According to the receptor type, biosensors can be classified as enzymatic biosensors, genosensors, immunosensors, etc. Biosensors can be also divided into several categories based on the transduction process, such as electrochemical, optical, piezoelectric, and thermal/calorimetric biosensors.

Biosensor can be broken down into several components, namely; analyte, sample handling, bioreceptor, and tranducer. Analyte is what we want to be detected, such molecule of protein, toxin, peptide, vitamin, sugar, or metal ion. Sample handling is how to deliver analyte to the sensitive region (bioreceptor). It can be done for example by microfluidics and filtration. Bioreceptor is aimed to specifically recognize the analyte. There are some type of bioreceptors, such antibody with Fc and Fab, enzyme with active site, cell with membrane receptor, and polymer/hydrogel with competitive binding. Then, transducer will convert detection into specific variable (eletroactive substance, pH change, heat, light, or mass change).

Due to recognition pattern, there are 3 kinds of signals probably being generated, signal from specific recognition, non-specific recognition and false specific recognition. Since the signal is very small corresponding to the size of molecules, an improving performance is added. Such magnetic bead, fluorescent dye, enzyme etc. will increase detection signal even though the signal error may occur. The common signal error source can be from inhomogenous sample, bubbles/flow artifacts, temperature, electromagnetic interferance, electronic unstability, and unstable chip/detection layer.

Same with other sensors, biosensor has some main basic characteristics. Linearity, linearity of the sensor should be high for the detection of high substrate concentration. Sensitivity, sensitivity is value of the electrode response per substrate concentration. Selectivity, chemicals interference must be minimized for obtaining the correct result. Response time, response time is time necessary for having 95% of the response. Those characteristics highly depend on parts of biosensor. Therefore, to design a biosensor, analyte, sample handling, bioreceptor and transducer must be wisely chosen.

Fourier’s Smart Tool: Altering a Problem to be Easily Solved

2011-05-23T02:53:00.000-07:00

Linear transforms, especially Fourier and Laplace transforms are widely used in solving problems in science and engineering, The Fourier transform is used in linear systems analysis, antenna studies, optics, random process modeling, probability theory, quantum physics, and boundary value problems and has been very successfully applied to restoration of astronomical data. The Fourier transform, a pervasive and versatile tool is used in many fields of science as a mathematical or physical tool to alter a problem into one that can be more easily solved. Some scientists understand Fourier theory as a physical phenomenon not simply as a mathematical tool. In some branches of science the Fourier transform of one function may yield another physical function.

The Fourier transform, in essence, decomposes or separates a waveform or function into sinusoids of different frequency which sum to the original waveform. It identifies or distinguishes the different frequency sinusoids and their respective amplitudes. The Fourier transform of f(x) is defined as:

Since the Fourier transform F(s) is a frequency domain representation of a function f(x) the s characterizes the frequency of the decomposed co-sinusoids and sinusoids and is equal to the number of cycles per unit of x. If a function or waveform is not periodic, then the Fourier transform of the function will be a continuous function of frequency.

Fourier Transform Properties

It is often useful to think of functions and their transforms as occupying two domains. These domains are referred to as the upper and the lower domains in older texts as if functions circulated at ground level and their transforms in the underworld. They are also referred to as the function and transform domains, but in most physics applications they are called the time and frequency domains respectively.

Operations performed in one domain have corresponding operations in the other. For example, as will be shown below, the convolution operation in the time domain becomes a multiplication operation in the frequency domain, that is f(x)Äg(x) = F(s).G(s).The reverse is also true, F(s)ÄG(s) = f(x).g(x). Such theorems allow one to move between domains so that operations can be performed where they are easiest or most advantageous.

Scaling Properties From time scaling property, it is an evident that if the width of a function is decreased while its height is kept constant, then its Fourier transform becomes wider and shorter. If its width is increased, its transform becomes narrower and taller
Shifting Properties This time shifting property states that the Fourier transform of a shifted function is just the transform of the un-shifted function multiplied by an exponential factor having a linear phase.
Convolution Theorem As previously mentioned, the Fourier transform of a product is given by the convolution of the individual transforms, and so it works reversely. Fourier transform of a convolution is given by product of the individual transforms.
Correlation Theorem The correlation integral, like the convolution integral is important in theoretical and practical applications. This is the statement of the correlation theorem. If f(x) and g(x) are the same function. The integral above is normally called the autocorrelation function and the cross-correlation if they differ.

Material Surface Analysis with X-Ray Photoelectron Spectroscopy (XPS)

2011-05-10T09:09:00.000-07:00

The XPS technique is used to investigate the chemistry at the surface of a sample. The basic mechanism behind an XPS instrument is illustrated in below picture, where photons of a specific energy are used to excite the electronic states of atoms below the surface of the sample. Electrons ejected from the surface are energy filtered via a hemispherical analyzer (HSA) before the intensity for a defined energy is recorded by a detector. Since core level electrons in solid-state atoms are quantized, the resulting energy spectra exhibit resonance peaks characteristic of the electronic structure for atoms at the sample surface. While the x-rays may penetrate deep into the sample, the escape depth of the ejected electrons is limited. That is, for energies around 1400 eV, ejected electrons from depths greater than 10nm have a low probability of leaving the surface without undergoing an energy loss event, and therefore contribute to the background signal rather than well defined primary photoelectric peaks.

In principle, the energies of the photoelectric lines are well defined in terms of the binding energy of the electronic states of atoms. Further, the chemical environment of the atoms at the surface result in well defined energy shifts to the peak energies. In the case of conducting samples, for which the detected electron energies can be referenced to the Fermi energy of the spectrometer, an absolute energy scale can be established, thus aiding the identification of species.

However, for non-conducting samples the problem of energy calibration is significant. Electrons leaving the sample surface cause a potential difference to exist between the sample and the spectrometer resulting in a retarding field acting on the electrons escaping the surface. Without redress, the consequence can be peaks shifted in energy by as much as 150 eV. Charge compensation designed to replace the electrons emitted from the sample is used to reduce the influence of sample charging on insulating materials, but nevertheless identification of chemical state based on peak positions requires careful analysis.

XPS is a quantitative technique in the sense that the number of electrons recorded for a given transition is proportional to the number of atoms at the surface. The chemical shifts seen in XPS data are a valuable source of information about the sample. Tilting the sample with respect to the axis of the analyzer results in changing the sampling depth for a given transition and therefore data collected at different angles vary due to the differing composition with depth.

Chemical shift in X-ray spectroscopy

The chemical shift reflects the influence of the chemical bonds with neighboring atoms. The chemical shift in the X-ray spectra is caused by changes in the electron binding energies. The more specific reason is about the electro-negativity effect in the presence of another atom. For example, in the C-O bond, due to the electro-negativity of oxygen, C 2p electron in valence level will be attracted by atom O, and C 1s electron in core level will tend to be attracted by carbon nucleus so that the binding energy of C 1s electron will shift to higher binding energy. Therefore we shall here consider different ways of calculating the electron binding energy of an atom or a molecule, methods that can also be used to evaluate chemical shifts.

From Force to Energy: Evolution of Classical Mechanics

2011-05-02T01:26:00.000-07:00

Newtonian mechanics is mathematically fairly straightforward, and can be applied to a wide variety of problems. It took the Apollo astronauts to the moon and the voyager spacecraft to the far reaches of the solar system. It is not a unique formulation of mechanics, however; other formulations are possible. Here we will look at two common alternative formulations of classical mechanics: Lagrangian mechanics and Hamiltonian mechanics.

Its original prescription rested on two principles. First, we should try to express the state of the mechanical system using the minimum representation possible and which reflects the fact that the physics of the problem is coordinate-invariant. Second, a mechanical system tries to optimize its action from one split second to the next; often this corresponds to minimizing its total energy as it evolves from one state to the next. These notes are intended as an elementary introduction into these ideas and the basic prescription of Lagrangian and Hamiltonian mechanics.

It is important to understand that all of these formulations of mechanics equivalent. In principle, any of them could be used to solve any problem in classical mechanics. The reason they’re important is that in some problems one of the alternative formulations of mechanics may lead to equations that are much easier to solve than the equations that arise from Newtonian mechanics. Unlike Newtonian mechanics, neither Lagrangian nor Hamiltonian mechanics requires the concept of force; instead, these systems are expressed in terms of energy. The equations of Lagrangian and Hamiltonian mechanics are also expressed in the language of partial differential equations.

Lagrangian Mechanics

The first alternative to Newtonian mechanics we will look at is Lagrangian mechanics. Using Lagrangian mechanics instead of Newtonian mechanics is sometimes advantageous in certain problems, where the equations of Newtonian mechanics would be quite difficult to solve. In Lagrangian mechanics, we begin by defining a quantity called the Lagrangian (L), which is defined as the difference between the kinetic energy K and the potential energy U:

Since the kinetic energy is a function of velocity v and potential energy will typically be a function of position x, the Lagrangian will (in one dimension) be a function of both x and v: L(x,v). The motion of a particle is then found by solving Lagrange’s equation; in one dimension it is;

Hamiltonian Mechanics

The second formulation we will look at is Hamiltonian mechanics. In this system, in place of the Lagrangian we define a quantity called the Hamiltonian, to which Hamilton’s equations of motion are applied. While Lagrange’s equation describes the motion of a particle as a single second-order differential equation, Hamilton’s equations describe the motion as a coupled system of two first-order differential equations.

One of the advantages of Hamiltonian mechanics is that it is similar in form to quantum mechanics, the theory that describes the motion of particles at very tiny (subatomic) distance scales. An understanding of Hamiltonian mechanics provides a good introduction to the mathematics of quantum mechanics. The Hamiltonian H is defined to be the sum of the kinetic and potential energies:

Here the Hamiltonian should be expressed as a function of position x and momentum p (rather than x and v, as in the Lagrangian), so that H = H(x, p). This means that the kinetic energy should be written as K = p^2/2m, rather than K = ½mv^2. Hamilton’s equations in one dimension have the elegant nearly-symmetrical form;

Revolution in Equation of State: Van der Waals’s Correction for Ideal Gas Equation

2011-04-25T03:23:00.000-07:00

The perfect gas equation of state PV = nRT is manifestly incapable of describing actual gases at low temperatures, since they undergo a discontinuous change of volume and become liquids. Van der Waals equation comes up to recognize the molecules that interact with each other. The equation puts two parameters to mimic this interaction. The first, an attractive intermolecular force at long distances, helps draw the gas together and therefore reduces the necessary outside pressure to contain the gas in a given volume (the gas is a little thinner near the walls). The second is to take account of the finite molecular volume. A real gas cannot be compressed indefinitely (it becomes a liquid, for all practical purposes incompressible).

Where p is the pressure, V is the volume, T is the temperature, n is the number of moles of gas present, R is the gas constant, and a and b are constants that depend upon the gas. In the usual situation, a and b are known and can be found in tables. One must watch the units used though. This rather crude approximation does in fact give sets of isotherms representing the basic physics of a phase transition quite well.

Van der Waals’s equation is approximate and quantitatively describes the properties of real gases only in regions of high temperatures and low pressures. However, it permits the qualitative description of the behavior of a gas at high pressures, the condensation of a gas into a liquid, and the critical state. Based on above picture, at low temperatures all three roots are real, but above a specific temperature Tc, called the critical temperature. Physically, this means that for T > Tc the substance can exist in only one state (the gaseous), and below Tc, in three states (two stable liquid ⊽1 and gaseous ⊽g and one unstable). This is expressed graphically in the following way: for T < Tc the isotherm has three points of intersection with the straight line ac, parallel to the volume axis. The points of the straight line ac correspond to the equilibrium of liquid and its saturated vapor.

Under the equilibrium conditions, for example, in the state corresponding to point b, the relative amounts of liquid and vapor are determined by the ratio of the segments bc/ba (the “rule of moments”). The saturated vapor pressure psy and the volume interval from ⊽1 to ⊽g correspond to the phase equilibrium at a specific temperature. At lower pressures (to the right of ⊽g), the isotherm characterizes the properties of the gas. To the left, the almost vertical part of the isotherm indicates a very low compressibility of the liquid. Segments ad and ec belong to superheated liquid and super-cooled vapor respectively (meta-stable states). Segment de is physically unrealized because here there is a volume increase with an increase in pressure. The set of points a, a’, a’’, … and c, c’, c’’, … determines a curve, called a bi-nodal, which outlines the region of simultaneous existence of gas and liquid. At the critical point-C the temperature, pressure, and volume (Tc, pc, and ⊽c) have values that are characteristic of each substance. However, if the relative values T/Tc, p/pc, and ⊽/⊽c are introduced into Van der Waals’s equation, then it is possible to obtain the so-called reduced Van der Waals’s equation, it does not depend on the individual properties of the substance.

With reduced quantities:

Schrodinger and Wave Mechanics

2011-04-20T22:40:00.000-07:00

In mathematical physics, the Schrodinger equation, are the most fundamental equations in non-relativistic quantum mechanics, playing the same role as Hamilton’s laws of motion in non-relativistic classical mechanics. The Schrodinger equation has two ‘forms’, one in which time explicitly appears, and so describes how the wave function of a particle will evolve in time. In general, the wave function behaves like a wave, and so the equation is often referred to as the time dependent Schrodinger wave equation. The other is the equation in which the time dependence has been ‘removed’ and hence is known as the time independent Schrodinger equation and is found to describe, amongst other things, what the allowed energies are of the particle. These are not two separate, independent equations – the time independent equation can be derived readily from the time dependent equation.

Time dependent Schrodinger wave equation:

Time independent Schrodinger equation:

The Finite Potential Well

The infinite potential well is a valuable model since, with the minimum amount of fuss, it shows immediately the way that energy quantization as potentials do not occur in nature. However, for electrons trapped in a block of metal, or gas molecules contained in a bottle, this model serves to describe very accurately the quantum character of such systems. In such cases the potential experienced by an electron as it approaches the edges of a block of metal, or as experienced by a gas molecule as it approaches the walls of its container are effectively infinite as far as these particles are concerned, at least if the particles have sufficiently low kinetic energy compared to the height of these potential barriers.

But, of course, any potential well is of finite depth, and if a particle in such a well has energy comparable to the height of the potential barriers that define the well, there is the prospect of the particle escaping from the well. This is true both classically and quantum mechanically, though, as you might expect, the behavior in the quantum mechanical case is not necessarily consistent with our classical physics based expectations. Thus we now proceed to look at the quantum properties of a particle in a finite potential well. To find the wave function for a particle of energy E, we have to solve three equations, one for each of the regions:

The Potential Barrier

In quantum mechanics, it is possible for the particle to be confined to a limited region in space, in which boundary condition is enough to yield the quantization of energy. Although a particle hypothetically behaving as a point mass would be reflected, a particle actually behaving as a matter wave has a finite probability that it will penetrate the barrier and continue its travel as a wave on the other side in case of rectangular potential barrier.

From the ilustration result, we note that the incident and reflected waves have the same ‘intensity’ and hence they have the same amplitude. This suggests that the incident de Broglie wave is totally reflected, i.e. that the particle merely travels towards the barrier where it ‘bounces off’, as would be expected classically. There is a non-zero probability of finding the particle in the region x > 0 where, classically, the particle has no chance of ever reaching. The distance that the particle can penetrate into this ‘forbidden’ region is given roughly by 1/2% which, for a subatomic particle can be a few nanometers, while for a macroscopic particle, this distance is immeasurably small.

春が来てある時、咲いている桜は綺麗になる。

2011-04-11T00:32:00.000-07:00

日本では他の亜熱帯の国と同じ、四季があります。夏、秋、冬そして春と言うことですが、春は一番待たれる季節になりそうです。大変な冬が消えた後、天気は以前よりどんどん温かくになってきます。しかも、色々綺麗な花は咲いています。今度はお花見と言うことをされています。食事を食べたり、友達と喋ったり，写真を撮ったり、風景を描いたりにして、人々は桜の下に座っています。家族に一緒に来て、友達と歩いて、皆さんは本当に春を楽しむようです。

花見の歴史と言えば、花見は奈良時代の貴族の行事が起源だと言われています。奈良時代には中国から伝来したばかりの梅が鑑賞されていましたが、平安時代に桜と変わってきました。その存在感の移り変わりは歌にも現れており『万葉集』において桜を詠んだ歌は40首、梅を詠んだ歌は100首程度だが、平安時代の『古今和歌集』ではその数が逆転します。また「花」といえば桜を意味するようになるのもこの頃からであるようです　「www.ja.wikipedia.org」。

一つの日本での花見を楽しむ場所は新宿御苑です。その公園では、色々桜があります。新宿駅から、２０分ぐらいの歩くにかかります。咲いている桜を見ている時はいつでもありませんが、春にはしかありませんから、そろそろ花を見てくださいね。それでは、これの詩を歌いましょう。

誰の為にふる桜の花

上を見て歩くたびに散る桜

時を重ねて咲き誇れ

音は聞こえない

姿は見えない

空は全て桜色に

零れた涙さえ桜は隠してくれる

誰の為に咲く桜の花

誰の為でも咲き誇れ

If You Want To Start Your Business, Just Learn From Konosuke Matsushita

2011-04-06T05:13:00.000-07:00

Everything on the world goes under the law of nature. Even a management of an enterprise also cannot disregard the existence of nature’s will. Constant circle of birth, growth, development and transformation affects all aspects of the world by the time passes away. Konosuke Matsushita, the founder of Panasonic Corporation said that even if the running out of natural resources become present fear to be predicted only few decades can be used by human race, even if certain fuels such as petroleum, coal and natural gas will become rare in the future, but humanity will survive and continue to develop. Human knowledge will lead the new way to use fuel wisely, or new discovery of other reliable resources because it is how the nature works.

As insensibly or consciously known, nature has taught us how to survive within its. The law of nature becomes essential to be understood, especially for people who want run their own business. I, as Indonesian people who has an eager to make better civilization, also want to make a dynasty industry just like him. If the sacred management of Konosuke Matsushita based on the principle of tap water says that manufacturers should produce commodities for daily life as much as tap water in order to supply the customers at the lowest price, but I would like also to use the principle of bees as my true management philosophy that serves the costumers with best quality product which has many merits

Inspiring by Konosuke Matsushita in building a great corporation, understanding the law of nature as the foundation of management is not the only the one aspect that must be considered for running an enterprise, such social corporate responsibility, customer awareness, self-reliance, worst case planning, politics awareness, self understanding, innovation and creativity are also important parts of successful business. Perhaps, for peoples who have many capital sources, it is easy to build new business. They only must concern in managing their business. But, for ones who do not have much money, both capital crisis and management problem will be faced on, just learn from Konosuke Matsushita, starting his business together with his family from small workshop into Multinational Corporation. “Believe in success”, he also taught us.

Finally, how great the enterprise are, the most important measurement point of the successful business is how they fulfill their social mission, how they serve to give customers the satisfaction because the business activities we have done or we will do are closely connected to the public service and society itself. This is the real meaning of the existence of an enterprise.

Are We Safe from Nuclear Radiation?

2011-03-17T09:47:00.000-07:00

In about a week ago, we were surprised by nuclear crisis on Fukushima Daiichi Complex, Japan since hit by earthquake 8.9 R.S. It is worried if the radiation of radioactive substances will blow up and contaminate many people affecting the health. But, basically we are exposed to nuclear radiation every day of our lives. Some of this radiation is from natural sources, and some results from human activity. Natural sources include cosmic radiation from space, radiation from lighter, unstable nuclei produced by the bombardment of the atmosphere by cosmic radiation, and radiation from heavy, unstable nuclei produced by the decay of a few long-lived nuclides in the earth’s crust. Artificial sources include medical procedures, commercial products that contain radioactive materials, and fallout from nuclear testing.

Nuclear radiation can cause biological damage because it is highly energetic. In passing through matter, nuclear radiation loses its energy by causing ionization in the absorbing material. For this reason, nuclear radiation is called ionizing radiation. In the ionization process, neutral atoms in the absorbing material lose electrons, forming positive ions. Frequently, the ejected electron possesses sufficient energy to cause ionizations in other atoms. The average amount of energy required to ionize an atom is about 35 electron volts (an electron volt is the amount of energy acquired by an electron accelerated in an electric field of 1 volt). The energy of a single particle from a nuclear decay can be as high as 8 million electron volts (8 MeV). This energy is dissipated by producing ions, and an 8-MeV particle can produce 2 × 10E5 ions.

The magnitude of radioactivity in a sample of radioactive material is expressed using several different units (Table 1). One type of unit focuses on the number of decaying nuclei and is called the activity. Activity is expressed in terms of disintegrations per time. The most common unit of activity is the curie (abbreviated as Ci).

It is defined as 3.7 × 10E10 disintegrations per second. This happens to be the activity of 1 gram of Ra-224, which was discovered by Marie Curie. The SI unit of activity is the becquerel, which is 1 disintegration per second. The other units of radioactivity focus on the effects of radiation on the surroundings. The exposure expresses the amount of ionization caused by radioactive material. The common unit of exposure is the roentgen, which is defined as the amount of radiation that produces, in 1 cm3 of dry air, ions having a total charge of 1 electrostatic unit. In SI units, the roentgen is equivalent to 2.58 × 10E-4 Coulomb/kg of air. The absorbed dose of radioactivity expresses the amount of energy absorbed by a substance exposed to ionizing radiation. One such absorbed dosage unit is the radiation absorbed dose, rad, which is 1 × 10E-5 Joule/g. Different kinds of radiation will cause different biological effects for the same amount of energy absorbed. For this reason, the unit called the roentgen equivalent in man, or rem, was introduced. The rem is equal to the rad multiplied by a factor, Q, which accounts for the relative biological effect of radiation on humans. For β and γ radiation (and for X-rays) Q.1, while for α particles and fast neutrons, Q.20.

The ionizing power of radiation depends on the type of radiation. An alpha particle, which is relatively massive, is quite efficient at producing ions, ionizing virtually every atom in its path. Alpha particles lose most of their energy after traveling only a few centimeters in air or less than 0.005 mm in aluminum. A beta particle, which is relatively light, ionizes only a fraction of the atoms in its path. Beta particles travel more than a meter in air or several millimeters in aluminum.

We should also point out that the location of the radiation’s origin is important, too. If the radiation is emanating from outside of your body, then you worry about how penetrating the radiation is. As we have just discussed, alpha radiation can be blocked from entering your body by a thin sheet of paper. Gamma radiation has a much greater likelihood of getting into your body and being absorbed in this case. However, if the radiation is emanating from inside your body, then alpha particles are going to have a much tougher time to not be absorbed by something in your body. In this case, gamma has a much greater likelihood of not being absorbed and getting out of your body.

Most radiation produced by nuclear decay falls within a category called ionizing radiation. Because of its charge and/or its energy, this type of radiation has the ability to turn neutral atoms into ions. This, in and of itself, is not necessarily a bad thing. Ions are found throughout nature and are essential to many physical and biological processes. However, if this ion is created in or near certain parts of the cells in your body, it can be quite hazardous. For instance, if the ionizing radiation where to hit one of the atoms that comprise the DNA in one of your cells, it could change the bonding properties of the atom, and thereby, physically change the DNA. If this cell and DNA were to survive, it will have undergone a mutation, which could be either harmless or lethal, depending upon where in the DNA molecule it occurs.

How the Particles Enter Cell?

2011-03-12T00:09:00.000-08:00

An alternative solution of cancer treatment is the cellular treatment that allows the medicine invades into cancer cell and disturbs metabolism to kill the cell. In magnetic hyperthermia cancer treatment, the nanoparticles are injected into the abnormal tissue, by subjected with high frequency AC magnetic field, the cancer cells are heated. This kind of cellular treatment will be more effective if the amounts of nanoparicles that enter the cells are bigger. Since the amounts are greater, the heat generated by superparamagnetism effect of magnetic nanoparticles increases and will be uniformly distributed inside the cell.

Molecules and particles will enter the cell via cell membrane. The size also determines how they can pass through the membrane. If the diameter of nanoparticles is big, they cannot enter passively, and only stay in interstitial fluid. Although the hyperthermia process will still go on, the effect is less effective than the nanoparticles stay in plasma cell. Since the transport via cell membrane becomes one of many considerations in nanomagnetic design, the review about cellular membrane transport is needed.

There are two principal mechanisms of outer cellular membrane transport. The transport mechanisms are passive transport and active transport. Passive transport permits the substance entering the cell via simple diffusion, facilitated diffusion and osmosis. Whereas, the active transport allows the particles pass via membrane by using energy to activate the protein gate.
Diffusion is the net passive movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration. It continues until the concentration of substances is uniform throughout. High Diffusion Rate depends on short distance, large surface area, big concentration difference (Fick’s Law). High temperatures will increase diffusion; large molecules will slow diffusion.

Fick's first law relates the diffusive flux to the concentration field, by postulating that the flux goes from regions of high concentration to regions of low concentration, with a magnitude that is proportional to the concentration gradient (spatial derivative). In one (spatial) dimension, this is

where

J is the diffusion flux in dimensions of [(amount of substance) length−2 time−1], example mol/(m^2)s. J measures the amount of substance that will flow through a small area during a small time interval.

D is the diffusion coefficient or diffusivity in dimensions of [length2 time−1], example m^2/s.

(for ideal mixtures) is the concentration in dimensions of [(amount of substance) length−3], example mol/m^3

x is the position [length], example m

D is proportional to the squared velocity of the diffusing particles, which depends on the temperature, viscosity of the fluid and the size of the particles according to the Stokes-Einstein relation. In dilute aqueous solutions the diffusion coefficients of most ions are similar and have values that at room temperature are in the range of 0.6x10−9 to 2x10−9 m2/s. For biological molecules the diffusion coefficients normally range from 10−11 to 10−10 m2/s.

In two or more dimensions we must use , the del or gradient operator, which generalizes the first derivative, obtaining

And for second law is:

Facilitated diffusion is the movement of specific molecules down a concentration gradient, passing through the membrane via a specific carrier protein. Thus, rather like enzymes, each carrier has its own shape and only allows one molecule (or one group of closely related molecules) to pass through. Selection is by size; shape; charge. Common molecules entering/leaving cells this way include glucose and amino-acids. It is passive and requires no energy from the cell. If the molecule is changed on entering the cell (glucose + ATP → glucose phosphate + ADP), then the concentration gradient of glucose will be kept high, and there will a steady one-way traffic.

Osmosis is a special example of diffusion. It is the diffusion of water through a partially permeable membrane from a more dilute solution to a more concentrated solution – down the water potential gradient (Note: diffusion and osmosis are both passive, i.e. energy from ATP is not used). A partially permeable membrane is a barrier that permits the passage of some substances but not others; it allows the passage of the solvent molecules but not some of the larger solute molecules. Cell membranes are described as selectively permeable because not only do they allow the passage of water but also allow the passage of certain solutes. The presence of particular solutes stimulates the membrane to open specific channels or trigger active transport mechanisms to allow the passage of those chemicals across the membrane.

Active transport is the energy-demanding transfer of a substance across a cell membrane against its concentration gradient, i.e., from lower concentration to higher concentration. Special proteins within the cell membrane act as specific protein ‘carriers’. The energy for active transport comes from ATP generated by respiration (in mitochondria). Major examples of active transport are re-absorption of glucose, amino acids and salts by the proximal convoluted tubule of the nephron in the kidney, sodium/potassium pump in cell membranes (especially nerve cells).

In order to make nanoparticles pass through cell membrane easily, some nanoparticles are designed by embedding with special protein, encapsulating with liposome, or just designed in very small sized (3-5 nm) to make them freely diffused.

Image Processing: Getting Some Information From An Image (Part 2)

2011-03-10T10:40:00.000-08:00

Pixel operation is operation of an image where each pixel's intensity value is modified. The modification/transformation depends solely on its previous value, regardless of its position and other pixels value. Some image operation in this category is brightness modification, contrast enhancement, color inversion (negation), and thresholding operation.

Pixel operation is done by transforming each pixel value to new value according to a transformation function, known as gray-scale transformation (GST) function. This function maps the gray-level input (Ki) to a new gray-level output (Ko). In general, a GST function can be expressed as:

Ko=f(Ki)

The mapping of typical GST function can presented as transformation curve, as shown in above figure. The function can be linear or non-linear. In a true color image, GST function is applied to each RGB elements. Each function for each color element can take the same form or different depends on the application.

RGB to Grayscale conversion

Intensity of an image is the average of the three color elements, so the gray scale image that represent the original color image can be computed as:

I0=(Ri+Gi+Bi)/3

Io is the output intensity, Ri, Gi, and Bi are the red, green, and the blue element intensity. The formula for more realistic result is by adding different weight for each R,G, and B element. We normally percept green color brighter that red color, and red color brighter than blue color. That's why we usually set the weight higher for red and higher for green.

Io=(0.299Ri + 0.587Gi + 0.144Bi)/3

Actually there is no absolute reference for each weight values because it depends on the display technology that might change in the future. The above formula is standardized by NTSC (National Television System Committee), and its usage is common in computer imaging.

Color Inversion

Color inversion in digital image processing is done by inverting all color elements. For monochrome image, the dark pixel in the original image will be the bright pixel in the inversed image. The effect show horizontal mirroring in the histogram.

The GST function is simple, the Intensity of the output Io=Imax-Ii, where Imax is the maximum Intensity value, and Ii is the input pixel's intensity. The maximum intensity value is 255 for 8bit monochrome or 24bit true color. For 24 bit true color, each RGB elements is operated independently.

Contrast Enhancement

Contrast in an image is the difference between pixels values. Without contrast we can't see anything because everything will be white or black, or just gray. If an image has a low contrast, it means that different objects in the image have low luminosity difference, and it'll be difficult to separate them in our perception. Contrast enhancement will be helpful in increasing the visibility of an image. Figure below show two images with different contrast and their histogram.

Contrast enhancement can be done using various gray scale transformation (GST) formulas. The following is one of contrast enhancement GST formula:

Po=G(Pi-C)+C

Which G is contrast gain, and C is the center for contrasting reference. At point C the pixel value is not modified, at above C point the pixels values is increased, and below C they're decreased.

Image Processing: Getting Some Information From An Image (Part 1)

2011-03-07T10:01:00.000-08:00

In infrared imaging, images are source of primary data processed to obtain useful information of temperature distribution. In some cases, the data gathering is not about single sampling but continuous sampling that shows temperature varying in unit time. To analyze and get the correspondence between image and temperature distribution, image processing method is used. Image processing deals with color manipulation, pixel-by-pixel operation, even frame-by-frame operation that can be associated in degree of temperature.

Many types of image processing can be classified into some categories:

Pixel operation is an operation of pixels that each pixel in an image is operated independently, means that the value of the pixel is not affected by other pixels value. It depends solely on its previous value and the operation parameters. Brightness and contrast manipulation are the examples.
Global operation, when a global characteristic of an image is used to deduct the parameter to operate each pixel. The global characteristic is usually determined using statistical method, for example is automatic brightness and contrast equalization, where the histogram is redistributed for a better distribution.
Multi-frame operation, where an image is operated with other images to get a result. For example is the generation of transitional image of subsequent slow motion picture. When a 20 fps (frames per second) movie will be played back four times slower, it looks smoother if we show them in 20 fps with 3 additional transition frames between the two original frames, rather than show only the original frames by 5 fps.
Geometric operation, where the shape, size, or the orientation is modified. Resizing and skewing are some examples.
Neighboring pixels operation, where the result of a pixel operation depends not only on its previous value but also on other surrounding pixels values. Smoothing and sharpening operation are some examples.
Morphologic operation, is operation that is focused on specific image region. This operation is closely related to image analysis, because it deals with object/morph detection algorithm.

There are many program software used for image processing, and Delphi is one of them. Delphi doesn't provide image processing component, but uses processing algorithm. To learn image processing in Delphi by directly coding the algorithm, GUI (graphical user interface) is made to load an image, view, process, and show the result.

Image histogram (gray level histogram) is one of simple and easy statistical tool for image analysis. From the histogram, many useful information of an image can be represented from an image. Image histogram is easy and fast to compute. Gray level histogram is a function that shows how many pixels for every gray level exist in an image. The x-axis is the gray level, and the y-axis is the numbers of pixels that have certain level appear on an image.

Above figure shows an image and its histogram. The histogram shows that the pixels values (the gray level values) is distributed only on the middle part of the available level, at levels from 100-200. It is said that the image doesn't maximize the usage of the available bit-depth (0-255). Using image processing techniques, the image can be manipulated to equalize the histogram, to have a better picture.

Image histogram analysis is very useful in image processing, some of the purposes are:

Selecting appropriate digitizing parameter. Histogram can be used to visually judge if an image is in an appropriate range of gray level. Ideally, digital image should use all available gray scale range, from minimum to maximum. This is important to optimize the display and other imaging devices to use all their potential capability. The imaging devices will be optimum if they display (or print) the image data that contain optimum usage of its format (for example 0-255 for 8bit monochrome image).
Selection of Thresholding Level. One of image processing technique is thresholding, where all pixels above certain brightness level are maximized to the maximum value and others are minimized to the minimum value. Thresholding in image processing is used to convert a gray scale image to binary format, where only two values are possible for the pixel, zero or one. Thresholding can be viewed as the simplest method of image segmentation.

Thresholding is common step in an image analysis, where we need to differentiate the pixel area by two different brightness areas, for example between object and the background. This is very useful in object and background separation if there is significant difference between an object and its background on an image.

Seeing Throughout Blood Circulatory to Understand Drugs Delivery System

2011-03-05T13:10:00.000-08:00

それが十回と言われているように、ナノ粒子は生物医学アプリケーション内の多くの利点があります。薬物送達アプリケーションでは、ナノ粒子はテレサと、キャリアと、薬自体となることができます。

Studying drug delivery system will combine some basic knowledge in Physics, Chemistry and Biology as interdisciplinary of science and engineering. Targeting medicines into specific tissue or part of body needs some considerations such as in which way the drugs will be delivered, what kind of media that ensures the drugs reaching the their destination, drugs biocompatibility to not be detected as “alien or invader” by immune system, etc. So, it becomes necessity to understand blood circulatory since blood is main “transporter” in our body.

As a living creature, human has specialized system to control blood circulatory called cardiovascular system. The cardiovascular system is an elaborate network that performs two major tasks: It delivers oxygen and nutrients to body organs and removes waste products of metabolism from tissue cells. Its major components are the heart “a hollow muscular pump” and a circulatory system of large and small elastic vessels or conduits that transport blood throughout the body. The circulatory system is an intricate network of vessels that supplies blood to all body organs and tissues. The part of the network that delivers blood to all parts of the body except the lungs is called the systemic circulation, while the flow of blood through the lungs is referred to as the pulmonary circulation.

Blood that has been oxygenated in the lungs is pumped out of the heart through the aorta which branches off into numerous arteries that deliver oxygen-rich blood to various tissues. The arteries are further subdivided into smaller tubes, the arterioles, which in turn branch off into even smaller vessels, the capillaries. It is in the capillaries that the exchange of substances between the blood and the tissues takes place. The capillaries carrying blood that now has lower oxygen content merge to form the venules, which in turn converge into successively larger veins. Then, venous blood enters to heart and is pumped to lungs, performing next circulation.

The lymph system is an accessory to the circulation functioning to return excess fluid filtered into the interstitial space back to the circulation. The lymph system also contains lymph nodes and other tissue in which mature lymphocytes proliferate.

Mean blood pressure is greatest in aorta and the large elastic arteries. They also experience the greatest pulse pressure. Pulse pressure and average pressure decline as the blood enters the smaller muscular arteries and disappears within the arterioles. The capillaries have no pulse pressure. Capillary pressure is highest at their arterial ends and declines precipitously to their venous end. In the venous system, the slope of decline ebbs and lowest pressure is seen in the vena cave. In fact, the pressure goes below zero (a negative or pulling pressure) when the ventricle relaxes.

Based on Starlings law, hydrostatic pressure is greatest at the arterial end of capillaries. This forces water and dissolved substances out into the interstitial fluid. Net filtration pressure (NFP = Hydrostatic Pressure –Osmotic Pressure) is 10 mmHg. As fluid is lost, the hydrostatic pressure decreases, becoming only 17 mmHg at the venous end. The osmotic pressure is not remaining same, there is now an inward pressure of 8 mmHg, (NFP = -8). This returns most, but not all of the lost fluid to the circulation. The remainder must be collected and returned by the lymphatic system.

Cross sectional area is the greatest in the capillary component producing the slowest velocity. This facilitates transport from capillaries to interstitial fluid. Cross sectional areas are lower, and velocities are higher in the arteries and veins, since cross sectional area corresponds geometrically to the surface area, about 50 m2 in both the systemic tissues and the lungs.

By understanding how the blood being circulated, hopefully gives information used as a consideration in designing nanomedicine and how its delivery system goes on. Parts of body is not like a hard drive that we can access as much as we want since they have specific register address (almost zero error communication). But, every organ is connected by vessels containing blood as media transport of essential substances and as protector from hazardous materials that may disturb parts of body. The drugs may be removed, relocated or destroyed before they reach their destination

A Great Instrument To Atomize Liquid: Ultrasonic Vibrator

2011-03-04T02:01:00.000-08:00

Now, in nanotechnology era, the smallest sized thing is regarded. In domain of about 10^-9 m or 10 Å size, material becomes unique. We have already known the implementation of SPIO (small particle iron oxides which have size distribution up to 10 nm) in biomedical application such magnetic hyperthermia, because they have unique size effect called superparamagnetism. Since size becomes important parameter in nanomaterial design, the researchers are urged to find best method to obtain finest result of nanomaterial synthesis, throughout chemical approaches, mechanical approaches even acoustical approaches. One of the best methods is ultrasonic atomization.

The applications of ultrasonic atomization for the generation of aerosol sprays are growing due to its capability for producing very small droplets with very narrow size distributions. The droplet size depends on the ultrasonic frequency, and hence it is possible to generate droplets in the micron range by using MHz-order driving frequencies. With higher frequencies, capillary waves are excited on the free surface primary drop at shorter wavelengths; destabilization of these waves then results in smaller atomized droplets. Nevertheless, ultrasonic atomizers are limited by a maximum frequency of around 1 MHz, due to the limitations of the piezoelectric material.

Ultrasonic atomizing is carried out by focusing ultrasonic energy on a liquid surface and by scattering liquid particles by the energy. As shown in figure, when an ultrasonic vibrator is placed toward a liquid surface, a high intensity ultrasound is omitted. Waves arise at the center of the area with higher acoustic pressure and successive water columns are formed by focused ultrasonic energy. At this moment, surface waves are generated on the surface of the water columns. A stationary wave of the surface waves is very fine wave called a capillary wave. From the end of the wave or wave head, liquid particles are scattered away. This is the principle of the phenomenon of atomization.

In atomization by an ultrasound particle size and volume can be controlled independently. Practically, an electrical input intensity can control the volume of atomization, while an ultrasonic frequency can control particle size. Generally an ultrasound of a higher frequency makes a smaller size of particles. The mean diameter, D of particles generated by using ultrasonic vibrators can be estimated from Lang’s equation wherein y and p are the surface tension and the density of the liquid, respectively, and f is the applied frequency.

It’s already said above that ultrasonic vibrator has limitation in generated frequency. It is said up to 1 MHz in maximum. It is however possible to circumvent this limitation by employing surface acoustic waves (SAWs), which are nanometer order amplitude elastic waves that propagate along the surface of a piezoelectric substrate, wherein it is possible to obtain working frequencies in the MHz-GHz range. The SAW atomization device essentially comprises a single inter-digital transducer (IDT) consisting of pairs of straight aluminum electrodes sputter-deposited onto a 127.68° yx-cut lithium niobate (LiNbO3) single crystal piezoelectric substrate. When a sinusoidal electrical signal matching the operating frequency is applied to the IDT, x-propagating Rayleigh waves are generated. A Rayleigh wave has an elliptical displacement on the surface due to the combination of its two mechanical acoustic components: a longitudinal component along the direction of propagation, and a transverse one perpendicular to the surface.

How Can Magnetic Fields Interfere?

2011-03-03T19:57:00.000-08:00

It’s obvious whether we can also treat magnetic fields as a common wave. As doubtlessly known, two propagated waves can be interfered each other. Wave interference is the phenomenon that occurs when two waves meet while traveling along the same medium. The interference of waves causes the medium to take on a shape resulted from the net effect of the two individual waves upon the particles of the medium.

Consider two waves that are in phase, sharing the same frequency and with amplitudes A₁ and A₂. Their troughs and peaks line up and the resultant wave will have amplitude A = A₁ + A₂. This is known as constructive interference. If the two waves are π radians, or 180°, out of phase, then one wave's crests will coincide with another waves' troughs and so will tend to cancel it out. The resultant amplitude is A = |A₁ − A₂|. If A₁ = A₂, the resultant amplitude will be zero. This is known as destructive interference.

When two sinusoidal waves superimpose, the resulting waveform depends on the frequency (or wavelength) amplitude and relative phase of the two waves. If the two waves have the same amplitude A and wavelength the resultant waveform will have amplitude between 0 and 2A depending on whether the two waves are in phase or out of phase.

A magnetic field is a field of force produced by moving electric charges, by electric fields that vary in time, and by the 'intrinsic' magnetic field of elementary particles associated with the spin of the particle. As a field of force, magnetic field has both direction and amplitude as a common wave has. But, magnetic field’s direction is different with common wave. In term of magnetism, a magnet, source of magnetic field, has an entity called magnetic moment.

The sources of magnetic moments in materials can be represented by poles in analogy to electrostatics. Consider a bar magnet which has magnetic poles of equal magnitude but opposite polarity. Each pole is the source of magnetic force which weakens with distance. Since magnetic poles always come in pairs, their forces partially cancel each other because while one pole pulls, the other repels. This cancellation is greatest when the poles are close to each other i.e. when the bar magnet is short. The magnetic force produced by a bar magnet, at a given point in space, therefore depends on two factors: on both the strength p of its poles, and l on the vector separating them. The moment is defined as u = pl.

A longitudinal wave from a point source propagates in all direction until its energy runs out. But, magnetic field with the possession of magnetic moment, the direction always comes from “+” poles (north pole) to “–“poles (south pole), called magnetic field lines. This phenomenon is just like a flow, a wave flow acting on magnetic field. So, can we categorize magnetic field as a wave? It becomes interesting question since there is diversity in similarity.

Interference and diffraction are specific characters of a wave, especially light wave. Double slit experiment by Young has shown those phenomena. Does it happen to magnetic field? If we place 2 magnet bar by parallel mounting with the same pole side to side (analogy of Young’s experiment reconstruction), the magnetic field contour can be described as follow:

There is no such superposition, but changing in flux density and field intensity in middle region between those magnets. “Magnetic field waves” do not construct or destruct each other, since they have no phase. This changing can be said as interference effect of magnetic field.

Let's Do Experiment Using XRD: How to Interpret the Diffractogram

2011-03-02T08:45:00.000-08:00

Basically, XRD (X-Ray Powder Diffraction), as a nondestructive technique has some functions for identifying crystalline phases and orientation, determining structural properties (lattice parameters, strain, grain size, phase composition, thermal expansion, etc), measuring thickness of thin films and multi layers, determining atomic arrangement. Thus, XRD is most widely used for the identification of unknown crystalline materials (e.g. minerals, inorganic compounds). Determination of unknown solids is critical to studies in geology, environmental science, material science, engineering and biology.

In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals. Informally, two crystals tend to be in the same crystal system if they have similar symmetries, though there are many exceptions to this. Space groups and crystals are divided into 7 crystal systems according to their point groups, and into 7 lattice systems according to their Bravais lattices. Five of the crystal systems are essentially the same as five of the lattice systems, but the hexagonal and trigonal crystal systems differ from the hexagonal and rhombohedral lattice systems.

Doing experiment using XRD takes some procedural activities to achieve the objectives. Collecting, analyzing, and interpreting activities should be done by the researchers.

Data Collection

The intensity of diffracted X-rays is continuously recorded as the sample and detector rotate through their respective angles. A peak in intensity occurs when the mineral contains lattice planes with d-spacings appropriate to diffract X-rays at that value of θ. Although each peak consists of two separate reflections (Kα1 and Kα2), at small values of 2θ the peak locations overlap with Kα2 appearing as a hump on the side of Kα1. Greater separation occurs at higher values of θ. Typically these combined peaks are treated as one. The 2λ position of the diffraction peak is typically measured as the center of the peak at 80% peak height.

Data Reduction

Results are commonly presented as peak positions at 2θ and X-ray counts (intensity) in the form of a table or an x-y plot (shown above). Intensity (I) is either reported as peak height intensity, that intensity above background, or as integrated intensity, the area under the peak. The relative intensity is recorded as the ratio of the peak intensity to that of the most intense peak (relative intensity = I/I1 x 100).

Determination of an Unknown

The d-spacing of each peak is then obtained by solution of the Bragg equation for the appropriate value of λ. Once all d-spacings have been determined, automated search/match routines compare the ds of the unknown to those of known materials. Because each mineral has a unique set of d-spacings, matching these d-spacings provides an identification of the unknown sample. A systematic procedure is used by ordering the d-spacings in terms of their intensity beginning with the most intense peak. Files of d-spacings for hundreds of thousands of inorganic compounds are available from the International Centre for Diffraction Data as the Powder Diffraction File (PDF). Many other sites contain d-spacings of minerals such as the American Mineralogist Crystal Structure Database.

Determination of Unit Cell Dimensions

For determination of unit cell parameters, each reflection must be indexed to a specific hkl known as Miller indices. Miller indices is a notation system in crystallographic for planes and direction in crystal (Bravais) lattices. They are written (hkl), and each index denotes a plane orthogonal to a direction (h, k, l) in the basis of the reciprocal lattice vectors. By convention, negative integers are written with a bar, as in 3 for −3. The integers are usually written in lowest terms, i.e. their greatest common divisor should be 1. Miller index 100 represents a plane orthogonal to direction ℓ; index 010 represents a plane orthogonal to direction m, and index 001 represents a plane orthogonal to n.

The crystallographic directions are fictitious lines linking nodes (atoms, ions or molecules) of a crystal. Similarly, the crystallographic planes are fictitious planes linking nodes. Some directions and planes have a higher density of nodes; these dense planes have an influence on the behavior of the crystal such as optical properties, absorption and reactivity, surface tension, and dislocations (plastic deformation). For all these reasons, it is important to determine the planes and thus to have a notation system.

As summary, in order to do phase identification, one of the most important uses of XRD, there are several steps. We can conclude as obtaining XRD pattern, measuring d-spacings, obtaining integrated intensities, and comparing data with known standards in the ICDD file formerly known as JCPDS. In the last step, we can use JCPDS Card. The card contain file number (1), three strongest lines (2), lowest angle line (3), chemical formula (4), data on diffraction method used (5), crystallographic data (6), optical and other data (7), data on specimen (8), and data on diffraction pattern (9). Commonly this information is an integral portion of the software that comes with the instrumentation.

Nanoparticles Characterization Using AFM

2011-03-01T14:53:00.000-08:00

Nanoparticles, a unique subset of the broad field of nanotechnology, include any type of particle with at least one dimension of less than 500 nanometers. Nanoparticles play an important role in a wide variety of fields including advanced materials, pharmaceuticals, and environmental detection and monitoring.
The atomic force microscope (AFM) is ideally suited for characterizing nanoparticles. It offers the capability of 3D visualization and both qualitative and quantitative information on many physical properties including size, morphology, surface texture and roughness. Statistical information, including size, surface area, and volume distributions, can be determined as well. A wide range of particle sizes can be characterized in the same scan, from 1 nanometer to 8 micrometers. In addition, the AFM can characterize nanoparticles in multiple mediums including ambient air, controlled environments, and even liquid dispersions.

While nanoparticles are important in a diverse set of fields, they can generally be classified as one of two types: engineered or nonengineered. Engineered nanoparticles are intentionally designed and created with physical properties tailored to meet the needs of specific applications. They can be end products in and of themselves, as in the case of quantum dots or pharmaceutical drugs, or they can be components later incorporated into separate end products, such as carbon black in rubber products. Either way, the particle’s physical properties are extremely important to their performance and the performance of any product into which they are ultimately incorporated.
Nonengineered nanoparticles, on the other hand, are unintentionally generated or naturally produced, such as atmospheric nanoparticles created during combustion. With nonengineered nanoparticles, physical properties also play an important role as they determine whether or not ill effects will occur as a result of the presence of these particles. Depending on the application of interest, nanoparticles may be known by a number of alternative and trade-specific names, including particulate matter, aerosols, colloids, nanocomposites, nanopowders, and nanoceramics.

Qualitative Analysis

Using the AFM, individual particles and groups of particles can be resolved. Microscope images are essential in research and development projects and can be critical when troubleshooting quality control issues. The AFM offers visualization in three dimensions. Resolution in the vertical, or Z, axis is limited by the vibration environment of the instrument: whereas resolution in the horizontal, or X-Y, axis is limited by the diameter of tip utilized for scanning. Typically, AFM instruments have vertical resolutions of less than 0.1 nm and X-Y resolutions of around 1 nm. In material sensing mode, the AFM can distinguish between different materials, providing spatial distribution information on composite materials with otherwise uninformative topographies.

Quantitative Analysis

Software-based image processing of AFM data can generate quantitative information from individual nanoparticles and between groups of nanoparticles. For individual particles, size information (length, width, and height) and other physical properties (such as morphology and surface texture) can be measured. Statistics on groups of particles can also be measured through image analysis and data processing. Commonly desired ensemble statistics include particle counts, particle size distribution, surface area distribution and volume distribution. With knowledge of the material density, mass distribution can be easily calculated. Whenever data from single-particle techniques is processed to provide statistical information, the concern over statistical significance exists. It is easy to attain greater statistical significance in AFM by combining data from multiple scans to obtain information on the larger population.

Experimental Media

AFM can be performed in liquid or gas mediums. This capability can be very advantageous for nanoparticle characterization. For example, with combustion-generated nanoparticles, major component of the particles are volatile components that are only present in ambient conditions. Dry particles can be scanned in both ambient air and in controlled environments, such as nitrogen or argon gas. Liquid dispersions of particles can also be scanned, provided the dispersant is not corrosive to the probe tip and can be anchored to the substrate. Particles dispersed in a solid matrix can also be analyzed by topographical or material sensing scans of cross-sections of the composite material. Such a technique is useful for investigating spatial nanocomposites.

Size

In many industries, the ability to scan from the nanometer range into the micron range is important. With AFM, particles anywhere from 1nm to 5μm in height can be measured in a single scan. It is important to note that AFM scanning is done with a physical probe in either direct contact or near contact. Therefore, particles must be anchored to the sample surface during the scan. Multiple scans can be performed, however, to provide greater statistical accuracy.

Sample Preparation for AFM Nanoparticle Characterization

Nanoparticles typically fall into one of two categories when it comes to sample preparation. The first category is nanoparticles rigidly attached to a solid structure. The second category is nanoparticles with weak adhesion to the substrate, such as dispersions of nanoparticles in liquid or dry mediums. A good example of the first category is nanoparticles imbedded a solid matrix, as in the case of nanocomposites or nanoprecipitates3. In such cases, typically a cross-section of the composite material is scanned to determine such properties as average particle size and spatial distribution.

Examples of nanoparticles in the second category are quantum dots, diesel soot particles, carbon black, and colloidal suspensions.4 Sample preparation for the second category of nanoparticles involves the stable attachment of particles onto the substrate. Because the AFM works by scanning a mechanical probe across the sample surface, any structure being imaged must have greater affinity to the flat surface than to probe tip. When nanoparticles do accidentally attach to the probe, the resulting images typically show reduced resolution. Streaking will occur in the images if nanoparticles are not rigidly attached to the flat surface while scanning in contact mode. To avoid such artifacts, close contact mode (near contact) or CFM (crystal sensing) is strongly recommended for such samples.

Be Systematic, and You’ll Find the Red Line across Your Physics Problems

2011-02-22T18:46:00.000-08:00

We should know that learning productivity is not marked as achieved value. But, the true meaning is put on ourselves that we can say as thinking satisfaction. Have you ever questioned yourself about your achievement, does it impress you? Or does it represent your competence? Sometimes we just neglect it by said “whatever, but I got a good mark”, short sentence that can shut up the rebellion inside our mind.

Successful learning or productive learning can be obtained when we’re able to transfer our knowledge to the others, by meaning of self-understanding about the subject we learned. In education world, the term of evaluation is introduced, both as test and quiz or other assignment. Evaluation becomes transfer medium of information and knowledge from student to teacher. How much understanding that student have, will be evaluated by teacher via general examination, with the mark of 60, 75, 90, 100, or A, B, C, D as quantitative benchmark that shows final result.

As succinctly described above, we know that the key of evaluation process is how to transfer our knowledge with objective appraisal. It is simply said that student who answer the question systematically will be highly regarded than the student who answer the question practically.

Talking about systematic thinking, we should also do the same thing in order to learn Physics. In Physics, there are a lot of problems describing natural phenomenon and its circumstances that must be solved. Sometimes we feel dizzy, what kind of equation we should put off, or generally how we can solve them. Basically, if we think systematically and write down the problem systematically, we will be able to find the answers at least we can transfer the problem we face on to the reader. That’s why the systematic answer in Physics problem has advantages both the answerer and the reader.

Here, the steps are:

* Given : (Attaching all data provide in problem set).

* Find : (Re-writing the main question)

* Schematic : (Illustrating the problem into sketch/diagram physics)

* Assumptions : (Writing down the problem circumstances)

* Solution:

- Basic theories : (Showing up all theories used in solving problem)

- Analysis : (Corresponding the data, main question, diagram physic, and problem circumstances with basic theories to find out the solution)

- Comments : (Giving some notes to the answer)

A Basic Chemical Reaction, REDOX

2011-02-21T06:46:00.000-08:00

化学反応（かがくはんのう）とは、原子間の結合の生成、あるいは切断によって異なる物質を生成する変化のことである。Any chemical reaction in which the oxidation numbers (oxidation states) of the atoms are changed is an oxidation - reduction reaction. Such reactions are also known as redox reactions, which is shorthand for reduction-oxidation reactions.

Oxidation and Reduction

Oxidation involves an increase in oxidation number, while reduction involves a decrease in oxidation number. Usually the change in oxidation number is associated with a gain or loss of electrons, but there are some redox reactions (e.g., covalent bonding) that do not involve electron transfer. Depending on the chemical reaction, oxidation and reduction may involve any of the following for a given atom, ion, or molecule:

· Oxidation - involves the loss of electrons or hydrogen OR gain of oxygen OR increase in oxidation state

· Reduction - involves the gain of electrons or hydrogen OR loss of oxygen OR decrease in oxidation state

Reactions involving oxidation and reduction processes are very important in our everyday world. They make batteries work and cause metal to corrode (or help to prevent their corrosion). They enable us to obtain heat by burning fuels--in factories and in our bodies.

Many redox reactions are complex. However, combustion and synthesis (from elements) are two ordinary examples which require very little description. Just a little more involved is the displacement reactions. These processes are divided into three categories: hydrogen displacement, metal displacement, halogen displacement.

Example of an Oxidation Reduction Reaction

The reaction between hydrogen and fluorine is an example of an oxidation-reduction reaction:

H₂ + F₂ → 2 HF

The overall reaction may be written as two half-reactions:

H₂ → 2 H⁺ + 2 e⁻ (the oxidation reaction)

F₂ + 2 e⁻ → 2 F⁻ (the reduction reaction)

There is no net change in charge in a redox reaction so the excess electrons in the oxidation reaction must equal the number of electrons consumed by the reduction reaction. The ions combine to form hydrogen fluoride:

H₂ + F₂ → 2 H⁺ + 2 F⁻ → 2 HF

Importance of Redox Reactions

Oxidation-reduction reactions are vital for biochemical reactions and industrial processes. The electron transfer system in cells and oxidation of glucose in the human body are examples of redox reactions. Redox reactions are used to reduce ores to obtain metals, to produce electrochemical cells, to convert ammonia into nitric acid for fertilizers, and to coat compact discs.

Infrared Thermal Imaging: See The Unseen

2011-02-18T21:28:00.000-08:00

Infrared thermography also called infrared thermal imaging uses thermal imagers or Infrared imaging cameras. This technique is widely used in many application fields, such as analyzing component stress in PCB, surveillance affairs, monitoring body temperature etc. Infrared thermal imaging becomes effective method as monitoring tool since every matter radiates thermal energy. In bioengineering application, this method can be used to monitor the temperature distribution of human body in hyperthermia treatment. By monitoring, the researcher can control heat distribution to specific localization in disease area.

The Spectrum

When the sun goes down and the other sources of illumination are removed, there is no light to be reflected and most mammals, especially, cannot see anything. The unaided human eye cannot see infrared radiation, but the radiation is always present. It is heat or thermal radiation in a portion of the Electromagnetic (EM) spectrum to which our eyes do not respond. Our bodies respond to infrared, if it is intense enough, by feeling warmed, or sometimes, cooled.

The illustration above depicts the EM spectrum ordered in terms of wavelength given in centimeters. There are 100 centimeters in one meter and 10,000 microns in one centimeter. (Most of the terminology used in infrared imaging discusses wavelength in units of micrometers, also called microns). Also shown are the common names given to the different portions of the spectrum.

The IR or infrared portion occupies roughly the region between 10 to the minus 4 to 10 to the minus 3 centimeters, or, from about 1 micron to about 100 microns. But most commercial equipment comes designed to operate in portions of the region, for a number of reasons (lower atmospheric absorption of IR radiation -or IR "atmospheric windows", detector availability at reasonable cost). Commercial IR thermography equipment comes in in the following wavelength bands and their filtered sub-bands. Common jargon follows approximately the terminology listed below:

· The Near IR region and band is from about 0.7 to 1.7 microns,

· The short wave or SW band is from about 1.8 to 2.4 microns,

· The medium wave or MW band is from about 2.4 to 5 microns, and the

· Long wave or LW band is from about 8 to 14 microns.

The two principle properties of this radiation are:

1. All types travel at the speed of light in a vacuum, although they may differ in speed or not travel at all through or in some materials and,

2. Their physical interactions with various materials can be described mathematically in terms of transverse (electromagnetic) waves (TEM) or, in many cases as uncharged particles each particle having an energy of h*(nu), where (nu) is the frequency and h is a constant number known as Planck's constant (its value differs slightly with the unit system used, but in the International System of Units (System International or SI units) it is: 6.6260693 x E-34 Joule seconds (E-34 is 10 to the -34th power or 1/1,000,000,000,000,000,000,000,000,000,000,000).

Every object at temperatures above Absolute Zero (0 K or -273.15 °C) emits thermal radiation, much in the infrared portion of the EM spectrum. Many objects that are very hot emit thermal radiation that is in the visible and even the ultraviolet portion of the EM spectrum as well as the infrared, e.g. an incandescent light bulb or our local star that we call the Sun. See the hand-sketched graph below of thermal radiation intensity versus wavelength from several objects including the Sun; note the range of visible wavelengths. Note, too, that here the units of wavelength are in nanometers; 1000 nanometers = 1 micrometer (micron). That is a common variant found in physics courses.

What is invisible to humans, particularly when only thermal infrared is present, can be "seen" by a thermal imager, or more precisely, a thermal imaging camera, especially at night. It works in daylight, too, and one can easily see the surprising differences in appearance of any object from emitted thermal "light" to reflected visible light. The shape will be the same but the brightness distribution and shadows look very different even in black and white and more pronounced when viewed in false colors.

Faraday’s Law of Induction and The Correlation between Biot-Savart Concept

2011-02-17T04:50:00.000-08:00

Faraday’s Law and Biot-Savart equation become 2 basic concepts respectively in designing electric generator or magnetic generator that have been used in many application field, for example, producing electric power by power generator to supply town’s electricity or especially producing high frequency AC magnetic field to cause heat loss in super paramagnetic magnetic nanoparticle for hyperthermia treatment. We’ve already learned about the Biot-Savart’s equation that simply said if the magnetic field can be produced along wire carrying an electric current. Now, Faraday’s concept tells reversely.

Any change of magnetic environment in a coil of a wire will cause a voltage (Electromotive Force: EMF) to be induced in the coil. No matter the change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving magnet toward or away from the coil, moving the coil into or out the magnetic field, rotating the coil relative to the magnet, etc.

Faraday’s law is fundamental relationship which comes from Maxwell’s equation. It serves as a succinct summary of the ways a voltage (or EMF) may be generated by changing magnetic environment. The induced EMF in a coil is equal to the negative of the rate of change in magnetic flux times the number of turns in the coil. It involves the interaction of charge with magnetic field.

Understanding Faraday's law requires understanding the concept of magnetic flux. The magnetic flux is a way of measuring the total amount of magnetic field over a surface or a surface area. An example might be the area of the coil of wire in the above experiments. If the magnetic field direction is perpendicular to the surface, then the magnetic flux is the magnetic field multiplied by the surface area. If the magnetic field is not perpendicular, then this product must also be multiplied by the cosine of the angle between the magnetic field direction and the outward pointing line perpendicular to the surface. This line perpendicular to the surface is called the normal.

じゃあ、Faraday's Law のことが分かてしまいましたか。

Understanding Standard Laboratory Procedures for Better Experiments

2011-02-16T04:57:00.000-08:00

Despite the fact that laboratory work is done in a seemingly endless amount of fields, with often vastly different equipment and varying goals, there are some generalized standard laboratory procedures to be followed no matter the nature of the work. Individual laboratories will likely have specific testing methods or standard operation procedures (SOPs) that both complement and enhance general operations.

意義 (Significance), implementing guidelines for lab work is done for different reasons. A primary goal of standard operating procedures is to ensure human safety and protect equipment as well as chemicals from being mishandled. Maintaining standards for quality assurance and quality control (QA/QC), so that valid data may be obtained is also a significant goal of standard procedures. Individual tests may have different and specific QA/QC procedures.

労働安全衛生管理 (Standard OSHA Procedures), the Occupational Safety and Health Administration set standards to protect both workers and the public from potentially dangerous practices. There are specific requirements dealing with labs that use chemicals. As part of these requirements, as stated in OSHA standards 29CFR, there are specific action levels based on the concentration of exposure to a particular chemical that kick in other requirements such as medical monitoring.

精度(Accuracy), it’s a component of QA/QC monitoring, which basically means the ability of a test to give data that is correct. When considering accuracy it is useful to think of a bull’s eye. An arrow that hits the middle of the bull’s-eye is completely accurate. Using known values of a substance to make sure they indeed exhibit these values when tested is a method to determine accuracy. This is mathematically calculated as tested value--known value/ known value x100= the percentage of error.

精密(Precision), tracking precision is also a necessary part of QA/QC and standard laboratory procedures. Precision is sometimes referred to as the "repeatability" of a test. Going back to the bull’s eye analogy, a grouping of arrows in any part of the target is displaying precision. If the grouping is outside of the center of the target, the arrows are still precise but are not accurate. Mathematically, precision can be represented by the relative percent difference of samples. This is done by taking sample one-sample two, dividing this by the mean of the two samples and multiplying by 100.

考慮(Considerations), while each individual experiment generally has its own SOP which will guide the tester through the procedure, it is often necessary that the tester be qualified in order to follow the steps correctly. As pointed out by the California EPA Air Resources Board SOPs are often written so that an experienced technician can get the same results as would another experienced technician. Attention to detail and the ability to follow directions is a must for any lab technician.

Moreover, to achieve those standards, at least there is knowledge of test equipments used in research. So, it becomes a must to study and understand their manual or instruction book, before doing the research. Specifically, in order to conduct a research in magnetic nano-material development field, because there are many types of equipment needed to obtain some valid data, such as PPMS (Physical Properties Measurement System), SEM (Scanning Electron Microscope), TEM (Transmission electron Microscope), AFM (Atomic Force Microscope), FIB (Focused Ion Beam), VSM (Vibrating Sample Magnetometer) etc, researcher must know how they work and how they can be safely operated.

PPMS	SEM
TEM	AFM
FIB	VSM