M@storo Blog

Helical MFCG for Driving a High Inductance Load

2015-10-08T01:18:00.001-07:00

Title	:	Helical MFCG for Driving a High Inductance Load
Authors	:	Andreas A. Neuber, Juan-Carlos Hernandez, James C. Dickens, Magne Kristiansen
		Electromagnetic Phenomena, V. 3, No.3 (11), 2003

Abstract

Even at small dimensions of less than 0.5 meter in length end-initiated helical magnetic flux compression generators (MFCG) have at least one order of magnitude higher energy density (by weight or volume) than capacitive energy storage with similar discharge time characteristics. However, simple MFCGs with a single helix produce high output energy only into low inductance loads, thus producing several 100 kA of current at a voltage level of less than 10 kV. Many pulsed power devices require less current but a considerably higher voltage level. For effectively driving a high inductance load of several μH, a multistage MFCG design has been suggested. We successfully tested a dual stage MFCG with a total length of 250 mm, a helix inner diameter of 51 mm, which is wound with Teflon insulated stranded wire of different sizes in the range from AWG 12 to AWG 22. We have presently achieved an energy gain of ~13 into a 3 μH load and will discuss the generator performance based on experimental current/voltage waveforms and specify the observed losses.

PDF: Helical MFCG for Driving a High Inductance Load

Explosive Shocks and Impedance Mismatch in Armatures

2015-10-08T01:18:00.000-07:00

Title	:	Explosive Shocks and Impedance Mismatch in Armatures
Authors	:	Jason Baird
		Electromagnetic Phenomena, V. 3, No.3 (11), 2003

Abstract

This investigation presents and discusses the influence of impedance mismatch on the explosive expansion of multilayer armature tubes, as an adjunct to helical flux-compression generator research at the University of Missouri-Rolla, directly affecting the understanding of flux cut-off and high strain-rate changes in generator armatures.
A previous investigation, reported elsewhere, studied longitudinal fractures that characteristically developed in single-layer armatures at smaller expansion ratios than predicted by classical analysis. The current study examines shock-produced tensile stresses in the armature skin, and the effects on those tensile stresses caused by density variations within layers of multi-layer armatures. In the original investigation, these tensile stresses produced cracks that occurred within two diameters of the detonator end of the armature, but did not extend when the tubing expanded under explosive pressurization. Such cracks appear to cause magnetic flux cut-off, and flux losses seriously affect energy conversion efficiency. The current study utilizes a two-dimensional Lagrangian finitedifference numerical model, classical impedance-matching calculations, and explosives-loaded multi-layer armature testing to analyze the effect of detonation waves on multi-layer armatures of different compositions. As an extension of the original work, this study further isolates shock wave effects during armature expansion.

PDF: Explosive Shocks and Impedance Mismatch in Armatures

Evaluating the Limits of Shock Wave Magnetic Flux Compression in Solids

2015-10-06T01:18:00.000-07:00

Title	:	Evaluating the Limits of Shock Wave Magnetic Flux Compression in Solids
Authors	:	S.V. Kolosenok, V.S. Soukhomlinov, Yu.A. Tolmachev, L.L. Altgilbers, D.J. Hemmert
		Electromagnetic Phenomena, V. 8, No.1 (19), 2008

Abstract

In this paper we present the results of an investigation of the interaction of ionizing shock waves in solids with strong magnetic fields in the Shock Wave Magnetic Flux Compression (SWMFC) generator. Deceleration of the ionizing shock waves by magnetic pressure is calculated for cesium iodide (CsI). It will be shown that it is possible to evaluate the limiting magnetic pressure for the SWMFC by a relatively simple and clearly understandable method.

PDF: Evaluating the Limits of Shock Wave Magnetic Flux Compression in Solids

Dynamical Process of Liner Implosion in the Electromagnetic Flux Compression for Ultra-high Magnetic Fields

2015-10-05T01:04:00.000-07:00

Title	:	Dynamical Process of Liner Implosion in the Electromagnetic Flux Compression for Ultra-high Magnetic Fields
Authors	:	D Nakamura, H Sawabe, Y H Matsuda and S Takeyama

Abstract

The spatial distribution of magnetic fields that are generated by the electromagnetic flux compression technique is investigated, with emphasis on the dynamical processes of an imploding liner. By comparing with the results of computer simulations, we found that the non-uniform implosion of a liner is important in order to explain the magnetic field’s distribution during the liner’s implosion. In addition, our results suggest that the initial inwards compressing spool-like motion of the liner subsequently turns out to be outwards stretching barrel-like motion along the magnetic field axis.

PDF: Dynamical Process of Liner Implosion in the Electromagnetic Flux Compression for Ultra-high Magnetic Fields

Development of Small, Tapered Stator Helical Magnetic Flux Compression Generators

2015-10-03T01:04:00.000-07:00

Title	:	Development of Small, Tapered Stator Helical Magnetic Flux Compression Generators
Authors	:	Bruce L. Freeman, Larry L. Altgilbers, Alvin D. Luginbill, James C. Rock
		"Electromagnetic Phenomena", V.3, 3 (11), 2003

Abstract

For some applications of magnetic flux compression generators, shorter pulse widths, with associated higher voltages and power levels, are required.We have developed a family of small, tapered stator generators that begin to address these requirements. Specifically, the three versions of these FCGs developed use stator angles of 100, 120, and 130 with respect to the generator axis. These three respective angles resulted in increasingly larger phased closure velocities. The armature diameter is 2.54 cm, and the armature expansion ratio is about 2:1. The shortest dI/dt pulse, in terms of Full-Width-Half-Maximum (FWHM), produced is 398 ns in the current derivative. The peak value for dI/dt is about 3.5 × 10¹⁰ amps/sec.

PDF: Development of Small, Tapered Stator Helical Magnetic Flux Compression Generators

Completely Explosive Autonomous High-Voltage Pulsed-Power System Based on Shockwave Ferromagnetic Primary Power Source and Spiral Vector Inversion Generator

2015-10-01T01:04:00.000-07:00

Title	:	Completely Explosive Autonomous High-Voltage Pulsed-Power System Based on Shockwave Ferromagnetic Primary Power Source and Spiral Vector Inversion Generator
Authors	:	Sergey I. Shkuratov, Evgueni F. Talantsev, Jason Baird, Millard F. Rose, Zachary Shotts, Zack Roberts, Larry L. Altgilbers, Allen H. Stults
		IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 34, NO. 5, OCTOBER 2006

Abstract

Novel explosive and conventional pulsed-power technologies were combined, and a series of explosive-driven high–voltage power supplies was designed, built, and tested. The power supply contained an explosive-driven high-voltage primary power source based on the fundamental physical effect of shockwave demagnetization of Nd2Fe14B high-energy ferromagnet and a power-conditioning stage. The volume of the energy-carrying ferromagnetic elements in the shockwave ferromagnetic generators (FMGs) was 8.75 cm3. The power-conditioning stage was based on the spiral vector inversion generator (VIG). The combined FMG–VIG system demonstrated successful operation and good performance. The output-voltage pulse amplitude of the combined FMG–VIG system exceeded 40 kV, with a rise time of 6.2 ns. The methodology was developed for digital simulation of the operation of completely explosive FMG–VIG system. Experimental results obtained are in a good agreement with the results of digital calculations performed.

PDF: Completely Explosive Autonomous High-Voltage Pulsed-Power System Based on Shockwave Ferromagnetic Primary Power Source and Spiral Vector Inversion Generator

Physical Modeling of Magneto Hydrodynamic Explosive Munition and Detonation Control

2015-09-29T01:04:00.000-07:00

Title	:	Physical Modeling of Magneto Hydrodynamic Explosive Munition and Detonation Control
Authors	:	Yun Lei Shi, Shao Jie Ma, He Zhang, Lin Gu
		Applied Mechanics and Materials Vols 300-301 (2013) pp 1448-1453

Abstract

Definition of magneto hydrodynamic explosive munition is introduced. The technology that magneto hydrodynamic loaded EFP is presented. The magneto hydrodynamic power is generated by MFCG. The physical model of magneto hydrodynamic explosive munition using ferroelectric ceramics as primary source is established. The equivalent circuit of primary source, MFCG and magneto hydrodynamic accelerating model is analyzed by current transfer process. The security system is designed for the new ammunition, and its initiation timing is analyzed. A microsecond detonation control method is also given.

PDF: Physical Modeling of Magneto Hydrodynamic Explosive Munition and Detonation Control

Advances in Planar Lipid Bilayers and Liposomes, Volume 13 [Ales Iglic, 2011]

2015-09-28T10:05:00.000-07:00

Title	:	Advances in Planar Lipid Bilayers and Liposomes, Volume 13
Editor	:	Ales Iglic

Advances in Planar Lipid Bilayers and Liposomes volumes cover a broad range of topics, including main arrangements of the reconstituted system, namely planar lipid bilayers as well as spherical liposomes. The invited authors present the latest results of their own research groups in this exciting multidisciplinary field.

Incorporates contributions from newcomers and established and experienced researchers
Explores the planar lipid bilayer systems and spherical liposomes from both theoretical and experimental perspectives
Serves as an indispensable source of information for new scientists

PDF: Advances in Planar Lipid Bilayers and Liposomes, Volume 13 [Ales Iglic, 2011]

A dictionary of behavioral motifs reveals clusters of genes affecting Caenorhabditis elegans locomotion

2015-09-26T10:05:00.000-07:00

Title	:	A dictionary of behavioral motifs reveals clusters of genes affecting Caenorhabditis elegans locomotion
Authors	:	André E X Brown, Eviatar I Yemini, Laura J Grundy, Tadas Jucikas, and William R Schafer

Visible phenotypes based on locomotion and posture have played a critical role in understanding the molecular basis of behavior and development in Caenorhabditis elegans and othermodel organisms. However, it is not known whether these human-defined features capture the most important aspects of behavior for phenotypic comparison or whether they are sufficient to discover new behaviors. Here we show that four basic shapes, or eigenworms, previously described for wild-type worms, also capture mutant shapes, and that this representation can be used to build a dictionary of repetitive behavioral motifs in an unbiased way. By measuring the distance between each individual’s behavior and the elements in the motif dictionary,wecreate a fingerprint that can be used to compare mutants to wild type and to each other. This analysis has revealed phenotypes not previously detected by real-time observation and has allowed clustering of mutants into related groups. Behavioral motifs provide a compact and intuitive representation of behavioral phenotypes.

PDF: A dictionary of behavioral motifs reveals clusters of genes affecting Caenorhabditis elegans locomotion

A conserved NAD+ binding pocket that regulates protein-protein interactions during aging

2015-09-24T10:05:00.000-07:00

Title	:	A conserved NAD+ binding pocket that regulates protein-protein interactions during aging
Authors	:	Jun Li, Michael S Bonkowski, Sébastien Moniot, Dapeng Zhang, Basil P Hubbard, Alvin J Y Ling, Luis A Rajman, Bo Qin, Zhenkun Lou, Vera Gorbunova, L Aravind, Clemens Steegborn, David A Sinclair

DNA repair is essential for life, yet its efficiency declines with age for reasons that are
unclear. Numerous proteins possess Nudix homology domains (NHDs) that have no
known function. We show that NHDs are NAD+ (oxidized form of nicotinamide adenine
dinucleotide) binding domains that regulate protein-protein interactions. The binding
of NAD+ to the NHD domain of DBC1 (deleted in breast cancer 1) prevents it from
inhibiting PARP1 [poly(adenosine diphosphate–ribose) polymerase], a critical DNA repair
protein. As mice age and NAD+ concentrations decline, DBC1 is increasingly bound to
PARP1, causing DNA damage to accumulate, a process rapidly reversed by restoring the
abundance of NAD+. Thus, NAD+ directly regulates protein-protein interactions, the
modulation of which may protect against cancer, radiation, and aging.

PDF: A conserved NAD+ binding pocket that regulates protein-protein interactions during aging

Electron Acceleration for X-ray Production Using Paired Pyroelectric Crystals

2015-09-19T08:35:00.000-07:00

Title	:	Electron Acceleration for X-ray Production Using Paired Pyroelectric Crystals
Authors	:	Jeffrey Geuther, Yaron Danon, Frank Saglime, Bryndol Sones

Abstract

The exposure of pyroelectric crystals to a heating cycle in near-vacuum conditions has been shown to be a viable method of producing x-rays. The z-negative face of the crystal forms a positive charge as the crystal heats, and a negative charge as it cools. The opposite is true for the z-positive face. Literature has shown that this charge is great enough to accelerate electrons to energies of up to 170 keV. This phenomenon can be used to create small X-ray, electron and charged particle sources. X-rays are produced when the electrons in the ambient gas are accelerated by this field toward a target (when the exposed face of the crystal is negatively charged) or toward the crystal itself (when the exposed face is positively charged).

In this experiment, z-cut lithium tantalate crystals with 5 mm x 5 mm surface area and thicknesses of 1, 2, 4, and 10 mm were placed in a vacuum and subjected to a thermal cycle. A 10 x10 x 0.5 mm crystal was also tested. The counts per thermal cycle and maximum energy of the x-ray spectra were shown to increase with crystal thickness. In addition, a system was explored in which two 10 mm crystals were arranged in series. This system was shown to double the maximum x-ray energy. Additional crystal thicknesses and system geometries that may further increase maximum x-ray energy and yield are currently under investigation..

PDF: Electron Acceleration for X-ray Production Using Paired Pyroelectric Crystals

Deuterated target comparison for pyroelectric crystal D–D nuclear fusion experiments

2015-09-17T08:35:00.000-07:00

Title	:	Deuterated target comparison for pyroelectric crystal D–D nuclear fusion experiments
Authors	:	Donald J. Gillich, Andrew Kovanen, Yaron Danon
	:	Journal of Nuclear Materials 405 (2010) 181–185

Abstract
Different target materials were investigated to determine which ones are favorable to increasing the theoretical neutron yield using pyroelectric crystal D–D nuclear fusion. Calculations show that deuterated polyethylene (CD2) will potentially yield the highest number of neutrons compared to the other targets investigated. However, deuterated plastic targets have been found to erode over the course of experiments.

PDF: Deuterated target comparison for pyroelectric crystal D–D nuclear fusion experiments

Effect of amino acid doping on the dielectric properties of triglycine sulphate (TGS) crystals

2015-09-15T08:35:00.001-07:00

Title	:	Effect of amino acid doping on the dielectric properties of triglycine sulphate (TGS) crystals
Authors	:	Jeyaprakash Manoharan, Joseph John, Revathi, Rajendran and Andavan
	:	Indian Journal of Science and Technology; Vol. 4 No. 6 (June 2011)

Abstract
Effect of amino acid (proline) doping on the dielectric properties of triglycine sulphate has been studied. Pure and proline doped triglycine sulphate (TGS) were grown from aqueous solution by solution growth technique at room temperature. The dielectric studies were carried out to identify the phase transition temperature and the dielectric behavior. The present study shows that there is an increase in the Curie temperature for the doped crystals.

PDF: Effect of amino acid doping on the dielectric properties of triglycine sulphate (TGS) crystals

Development of pyroelectric neutron source for calibration of neutrino and dark matter detectors

2015-09-14T08:35:00.000-07:00

Title	:	Development of pyroelectric neutron source for calibration of neutrino and dark matter detectors
Authors	:	A S Chepurnov, V Y Ionidi, M B Gromov, M A Kirsanov, A S Klyuyev, A S Kubankin, A N Oleinik, A V Shchagin, and K A Vokhmyanina
	:	IOP Conf. Series: Journal of Physics: Conf. Series 798 (2017)

Abstract.
The laboratory experimental setup for development of pyroelectric neutron generator for calibration of neutrino and dark matter detectors for direct search of Weakly Interacting Massive Particles (WIMP) has been developed. The setup allows providing and controlling the neutrons generation process realized during d-d nuclear fusion. It is shown that the neutrons with energy 2.45 MeV can be generated starting from a level of electric potential generated by pyroelectric crystal about 30 kV, in contrast to the typical neutron tubes which need the applied outer high voltage level about 100 kV

PDF: Determinants of Financial Sustainability of Small Holder Sugarcane Farming Systems in Tanzania

Comparative analysis of organic and non-organic farming systems: A critical assessment of farm profitability

2015-09-07T09:17:00.000-07:00

Title	:	Comparative analysis of organic and non-organic farming systems: A critical assessment of farm profitability
Authors	:	Noémi Nemes
	:	Food and Agriculture Organization of the United Nations; June 2009

Executive summary

The last decades have seen a proliferation of economic studies that have compared the economic performance of organic and non-organic farming systems. Several criticisms were formulated questioning the validity of such comparisons, partly because of the inherent difference between the two systems (in terms of complexity, diversity and objectives other than yield maximalisation), and partly due to the difficulty in excluding ’non-system’ determined factors that also have an influence on profitability. Furthermore, the adequate selection of a reference group for comparisons has proved to be fundamental for relative profitability: which organic farms are put on the profit measuring scale by researchers with which conventional farms determine the outcome.

The list of profitability studies compiled in this paper involve more than 50 different cases, mostly from U.S.A, where several universities started long-term experimental field studies in the eighties and from European countries. Just over a dozen shorter-term studies have been collected from developing countries on high-value export crops. Most studies have used a casestudy approach selecting between five up to hundreds of farms for the collection of data on farm economics.

PDF: Comparative analysis of organic and non-organic farming systems: A critical assessment of farm profitability

Determinants of Financial Sustainability of Small Holder Sugarcane Farming Systems in Tanzania

2015-09-06T09:17:00.000-07:00

Title	:	Determinants of Financial Sustainability of Small Holder Sugarcane Farming Systems in Tanzania
Authors	:	Ally S. Mushi and Deus D. Ngaruko
	:	African Journal of Economic Review, Volume III, Issue 2, July 2015

Abstract:
The study investigated the impact of farming systems on determinants of smallholder sugarcane farmers (SSFs) financial sustainability (FS) between Block Farming (BF) and Traditional Farming (TF) systems. FS was analyzed by assessing profitability of the farming system. Semi structured questionnaires were administered to a random sample of SSFs and officials of block farms within Kilombero valley in Morogoro region in the south eastern Tanzania. 1040 observations from 394 respondents for SSFs’ FS have been analyzed at significance level of p = 0.05. Two sample t-Tests, one way ANOVA and Tobit regression analysis performed revealed that effects of the two farming systems on the hypothesized factors differs significantly. Yield, price and cost have been found to have significant effects on financial sustainability, whereas the effect of land size and sucrose were not significant.BF has been found to be significantly more effective than TF system in ensuring profitability of the farmers. Profitability through BF is 0.56 (56%) as compared to 0.39 (39%) through TF.

PDF: Determinants of Financial Sustainability of Small Holder Sugarcane Farming Systems in Tanzania

Restricting Pesticide Use: The Impact on Profitability by Farm Size

2015-09-05T09:17:00.000-07:00

Title	:	Restricting Pesticide Use: The Impact on Profitability by Farm Size
Authors	:	Gerald Whittaker, Biing-Hwan Lin, Utpal Vasavada
	:	J Agr. and Applied Econ. 27 (2), December, 1995:352-362

A sample of 226 cash grain farms in the Lake States-Corn Belt region are analyzed to estimate the impact of restricting pesticide use on profits. These 226 farms are classified into small, medkun, and large farms according to their sale revenues. The results suggest the existence of pest management practices that could substantially reduce pesticide use without incurring economic losses. The reductions in profits associated with gradual reductions in pesticide expenditure appear to increase with farm size.

PDF: Restricting Pesticide Use: The Impact on Profitability by Farm Size

A Treatise on the Differential Geometry of Curves and Surfaces

2015-09-04T10:35:00.000-07:00

Title	:	A Treatise on the Differential Geometry of Curves and Surfaces
Authors	:	Luther Pfahler Eisenhart
	:	1910

This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project to make the world’s books discoverable online. It has survived long enough for the copyright to expire and the book to enter the public domain. Whether a book is in the public domain may vary country to country. Make non-commercial use of the files.

PDF: A Treatise on the Differential Geometry of Curves and Surfaces

Elementary Differential Geometry: Curves and Surfaces; Edition 2008

2015-09-03T10:35:00.000-07:00

Title	:	Elementary Differential Geometry: Curves and Surfaces; Edition 2008
Authors	:	Martin Raussen
	:	DEPARTMENT OF MATHEMATICAL SCIENCES, AALBORG UNIVERSITY

Plane and Space: Linear Algebra and Geometry
1. Vectors and Products
2. Description of Lines and Planes
3. Orthogonal Projections, Distances and Angles
4. Change of Coordinate Systems

Curves in plane and space
1. Vector functions in one variable
2. Parametrized Curves
3. Curvature
4. Space Curves: Moving Frames and Torsion
5. How to use the geometric laboratory - an example

Chapter 3. Regular Surfaces
1. Parametrizations of surfaces
2. Measurement in curved coordinates: the 1. fundamental form
3. Normal sections and normal curvature
4. Normal and geodesic curvature; the second fundamental form
5. Principal curvatures, Gaussian curvature, and Mean curvature
6. Special surfaces
7. The geometric labotatory for surfaces

PDF: Elementary Differential Geometry: Curves and Surfaces; Edition 2008

Differential Geometry: A First Course in Curves and Surfaces

2015-09-02T10:35:00.000-07:00

Title	:	Differential Geometry: A First Course in Curves and Surfaces
Authors	:	Theodore Shifrin
	:	Preliminary Version; Fall, 2015

CURVES

Examples, Arclength Parametrization
Local Theory: Frenet Frame
Some Global Results

SURFACES: LOCAL THEORY

Parametrized Surfaces and the First Fundamental Form
The Gauss Map and the Second Fundamental Form
The Codazzi and Gauss Equations and the Fundamental Theorem of Surface Theory
Covariant Differentiation, Parallel Translation, and Geodesics

SURFACES: FURTHER TOPICS

Holonomy and the Gauss-Bonnet Theorem
An Introduction to Hyperbolic Geometry
Surface Theory with Differential Forms
Calculus of Variations and Surfaces of Constant Mean Curvature

PDF: Differential Geometry: A First Course in Curves and Surfaces

Differential Geometry of Curves and Surfaces: A Concise Guide

2015-09-01T10:35:00.000-07:00

Title	:	Differential Geometry of Curves and Surfaces: A Concise Guide
Authors	:	Victor Andreevich Toponogov
	:	2006 Birkhauser Boston

The study of curves and surfaces forms an important part of classical differential geometry. Differential Geometry of Curves and Surfaces: A Concise Guide presents traditional material in this field along with important ideas of Riemannian geometry. The reader is introduced to curves, then to surfaces, and finally to more complex topics. Standard theoretical material is combined with more difficult theorems and complex problems, while maintaining a clear distinction between the two levels.

Key topics and features:

Covers central concepts including curves, surfaces, geodesics, and intrinsic geometry
Substantive material on the Aleksandrov global angle comparison theorem, which the author generalized for Riemannian manifolds (a result now known as the celebrated Toponogov Comparison Theorem, one of the cornerstones of modern Riemannian geometry)
Contains many nontrivial and original problems, some with hints and solutions
Standard theoretical material is combined with more difficult theorems and complex problems, while maintaining a clear distinction between the two levels

This rigorous exposition, with well-motivated topics, is ideal for advanced undergraduate, first-year graduate students seeking to enter the fascinating world of geometry, and students specializing in geometry. The material is given in two parallel streams.

Download: Differential Geometry of Curves and Surfaces: A Concise Guide [PDF]

Handbook of Industrial Drying, Third Edition

2015-09-01T08:53:00.000-07:00

Title	:	Handbook of Industrial Drying, Third Edition
Authors	:	Arun S. Mujumdar (editor)
	:	CRC, 2006

Drying is a highly energy-intensive operation and is encountered in nearly all industrial sectors. With rising energy costs and consumer demands for higher quality dried products, it is increasingly important to be aware of the latest developments in industrial drying technologies. For two decades, Mujumdar’s industry-standard Handbook of Industrial Drying has been the quintessential source of state-of-the-art information in the field, and this third edition is no exception.

Features

Provides comprehensive coverage of conventional, emerging, and potential drying technologies worldwide
Traces the latest industrial trends along with the technologies and practices designed to follow them
Covers drying technologies from all industrial sectors as well as safety, energy efficiency, cost, and control aspects
Includes new and extensively rewritten chapters as well as updated material throughout the book
Compiles the work of leading international experts from 20 countries along with references to the most current literature

Providing important data along with the experience, insight, and practical know-how contributed by experts from around the world, the Handbook of Industrial Drying, Third Edition remains the definitive reference to the complete spectrum of current and emerging industrial drying technologies.

Download: Handbook of Industrial Drying, Third Edition [PDF]

A new metal-dielectric cathode with long lifetime

2015-09-01T01:04:00.000-07:00

Title	:	A new metal-dielectric cathode with long lifetime
Authors	:	Ping Wu, Jun Sun, Guozhi Liu, Zhanfeng Yang, Shaofei Huo, Wenyuan Liu
		Applied Mechanics and Materials Vols 300-301 (2013) pp 1448-1453

Abstract

Explosive emission cathodes are widely used in high power microwave generation. Conventional metallic cathodes have the disadvantages of bad emission uniformity and short lifetime. In order to improve the emission property of metallic cathodes, a new metal-dielectric cathode is fabricated with the plasma spraying technology. Unlike previous metal-dielectric cathodes, our metaldielectric cathode adopts a ferroelectric ceramic which possesses a large permittivity. The results of lifetime experiments show the metal-dielectric cathode presents just slight performance deterioration within 2.5105 pulses and thus has a much longer lifetime than the normal copper cathode.
The morphology observation demonstrates that the good emission property of the metal-dielectric cathode may benefit from the appearance of irregularities on the dielectric surface, which will have large microscopic field enhancement factors with the help of large permittivity of the ferroelectric material.

PDF: A new metal-dielectric cathode with long lifetime

Notes on Assessing Speaking

2015-08-29T00:50:00.004-07:00

Title	:	Notes on Assessing Speaking
Authors	:	Barry O’Sullivan

With all language skill testing, it is necessary to clearly state the specifications before beginning to write the test (just as the previous sections have stated). In his very pragmatic ‘Understanding and Developing Language Tests’ Cyril Weir (1993) presents an approach to skills testing which calls for the identification of a series of language operations which the skill in question will entail. In addition to this list, Weir suggests that we need a set of conditions under which the task will be performed. Together these will allow the test writer to establish the parameters of the task or tasks to be employed in the test. Weir (2005) updated his original ideas and this later framework adds greatly to our conceptualisation of how all four skills can be tested and validated. In the following sections we will be looking at the testing of the four language skills in terms of Weir’s 2005 framework.

Download: Notes on Assessing Speaking [PDF]

An examination of the rating process in the revised IELTS Speaking Test

2015-08-29T00:50:00.003-07:00

Title	:	An examination of the rating process in the revised IELTS Speaking Test
Authors	:	Annie Brown
	:	IELTS, Grant awarded Round 9, 2003

Abstract:

In 2001 the IELTS interview format and criteria were revised. A major change was the shift from a single global scale to a set of four analytic scales focusing on different aspects of oral proficiency. This study is concerned with the validity of the analytic rating scales. Through a combination of stimulated verbal report data and questionnaire data, this study seeks to analyse how IELTS examiners interpret the scales and how they apply them to samples of candidate performance.

This study addresses the following questions:

How do examiners interpret the scales and what performance features are salient to their judgements?
How easy is it for examiners to differentiate levels of performance in relation to each of the scales?
What problems do examiners identify when attempting to make rating decisions?

Experienced IELTS examiners were asked to provide verbal reports after listening to, and rating a set of the interviews. Each examiner also completed a detailed questionnaire about their reactions to the approach to assessment. The data were transcribed, coded and analysed according to the research questions guiding the study.

Findings showed that, in contrast with their use of the earlier holistic scale (Brown, 2000), the examiners adhered closely to the descriptors when rating. In general, the examiners found the scales easy to interpret and apply. Problems that they identified related to overlap between the scales, a lack of clear distinction between levels, and the inference-based nature of some criteria. Examiners reported the most difficulty with the Fluency and Coherence scale, and there were concerns that the Pronunciation scale did not adequately differentiate levels of proficiency.

Download: An examination of the rating process in the revised IELTS Speaking Test [PDF]