bluuebunny/crossref_metadata_2025 huggingface dataset:
Criteria for partial LTE in an argon thermal discharge at atmospheric pressure; validity of the spectroscopically measured electronic temperature
Authors: A M Gomes
Published: July 2002

A collisional-radiative (C-R) model is used to obtain the population number densities of the excited levels of neutral and singly charged ions in argon for 6000K<Tc<13000K for P=1 atm; radiative processes, atomic and electronic collisions altogether with diffusive phenomena are taken into consideration. The threshold value nethfor the electronic density, corresponding to a Saha equilibrium for the lower-lying excited levels, is determined for each Tevalue. A simplified model allows evaluation of the influence of each process on the density of the set of metastable and pseudo-metastable atomic excited levels of the 3p54s electronic configuration. For the different zones of the discharge, the Saha and Boltzmann temperatures, which can be experimentally obtained, are compared to the electronic temperature Tc.
Departures from CLTE composition in a nitrogen arc at atmospheric pressure. II. Interpretation of departures from CLTE
Authors: J Bacri  , M Lagreca
Published: July 2002

For pt.I see ibid., vol.16, 829-40 (1983). Departures from chemical equilibrium and from Boltzmann's distribution for excited level populations expected with the assumption of CLTE in a nitrogen plasma at atmospheric pressure are explained by means of a collisional-radiative model taking into account both monatomic and diatomic species, in which transport processes are treated by a parametric approach.
Transport properties of SnTe epitaxial films: two-circuit model
Authors: S Santhanam  , A K Chaudhuri
Published: July 2002

The transport properties of SnTe epitaxial films of different thicknesses deposited on mica substrates at a substrate temperature of 448K have been studied at 300K. Thermoelectric power, conductivity and Hall data confirm the presence of inhomogeneity in the SnTe film-substrate interface. The data obtained from these measurements have been analysed with a two-circuit model and the thickness of the interface layer is calculated to be 600 AA.
Power transmitted by different modes in an optical-fibre waveguide and behaviour as cut-off is approached
Authors: H M Barlow
Published: July 2002

Traces the flow of power in both the core and the cladding of a step-index fibre. Particular attention is focused on behaviour as cut-off is approached, where the power in the cladding rises very rapidly, extending outwards over the whole cross-section of the fibre to the surface of the cladding. Cut-off must be accompanied by collapse of the field of the mode concerned and release of the energy stored in that field, to give radiation and/or conversion to another guided wave.
Dispersive transport of charge carriers in polycrystalline pentacene layers
Authors: V I Arkhipov  , V A Kolesnikov  , A I Rudenko
Published: July 2002

This paper presents an experimental study of carrier drift in polycrystalline pentacene layers under small-signal conditions. The shape of the transient current, caused by pulsed bulk carried generation, and the transit time field-dependence are analysed in detail for various temperatures. The data obtained indicate a dispersive transport regime. A theory of dispersive transport with bulk generation is formulated in order to explain the experimental results. The theory is based on the concept of transport controlled by carrier trapping on localised levels distributed over a wide energy region. Particular attention is given to the exponential and Gaussian models of trap energy distribution. The Gaussian model seems more realistic for interpretation of experimental data on polycrystalline pentacene layers.
Monte Carlo and Boltzmann calculations of the density gradient expanded energy distribution functions of electron swarms in gases
Authors: B M Penetrante  , J N Bardsley  , L C Pitchford
Published: July 2002

The authors have developed an arbitrary-collision sampling technique for Monte Carlo calculations of the diffusion term in the density gradient expanded energy distribution functions. The technique is shown to provide for an alternative and accurate Monte Carlo calculation of the diffusion coefficients. Comparisons of the diffusion distribution function for the cases of electron swarm transport in the ramp model gas and CH4show excellent agreement with the results obtained by the Boltzmann method of Pitchford and Phelps (1982). However, there remains a discrepancy for the case of N2.
Precise modelling of tunnelling transmission probability and surface potential in a MIST structure
Authors: A K Duong  , A G Nassibian
Published: July 2002

A precise model deriving electron tunnel current in a metal-tunnel insulator-semiconductor thyristor (MIST) is presented, taking into account the effect of fast interface states. The model is then used to determine the tunnelling transmission probability and the surface potential in the thyristor for various oxide thicknesses. It is found that the tunnelling transmission probability is very sensitive to the oxide thickness and is dependent on the voltage drop across the oxide layer. The surface potential is increased with increasing bias voltage, but becomes saturated at a value corresponding to (Egs/2q)+ theta Fn.
Plasma generation by mechanical compression of argon by piston compressor: determination of kinematic data, pressures and temperatures
Authors: H Kasimir  , H J Kusch
Published: July 2002

High-pressure argon plasmas have been generated by mechanical gas compression. Experimentally determined values for kinematic data: minimum volume, time of piston motion, piston speed as well as for the pressure of the test gas are compared with the results of theoretical approaches. Temperatures up to 11000K are derived from spectroscopic measurements of the continuous emission by applying a multichannel spectrometer, and at lower conditions optical depth determinations were also carried out. The comparison with theoretical results shows that radiation losses and boundary layers may not be neglected.
The time-dependent temperature distribution in a cylindrical conductor with Joule heating and temperature-dependent properties
Authors: V T Morgan  , N G Barton
Published: July 2002

The time-dependent distribution of the temperature within a circular cylinder carrying an alternating current is studied. It is assumed that the temperature distribution is axially symmetric; the resistivity, thermal conductivity, density and specific heat capacity are all linearly dependent on the temperature; and the heat transfer at the surface boundary is axially symmetric and non-linear with the temperature rise above ambient temperature. The variables in the heat equation are non-dimensionalised, and the equation is solved numerically for particular solid and stranded aluminium conductors.
Role of local temperature rise in stress channel production due to ⩾350 keV proton implantation on Mylar surface
Authors: V Shrinet  , U K Chaturvedi  , A K Nigam
Published: July 2002

The production of radial stress channels in the unimplanted zone but along the boundary of the circular beam spot of Mylar surface implanted at H+ ion energy >or=350 keV has been explained on the basis of severe local temperature rise due to beam heating. On account of this temperature rise the irradiated zone melts and the radial channels are generated due to radial compressive stress along the boundary on cooling. The sharp decrease in the critical dose for the onset of blistering with a beam energy is attributed to the increase in gaseous diffusivity of evolved gases with local temperature rise which results in a faster coalescence of gas and earlier blistering.
A study of casein hydration by the thermally stimulated depolarisation currents method
Authors: A Anagnostopoulou-Konsta  , P Pissis
Published: July 2002

The dielectric behaviour of bound water in compressed casein pellets has been studied using the thermally stimulated depolarisation currents method over the temperature range from 77 to 300 K and the hydration range from 1 to 24% w/w. Two distinct relaxation regions are obtained: one in the range of T from 100 to 170 K attributed to the reorientation of loosely bound water molecules, and a second one in the range 190-290 K interpreted mainly in terms of water-assisted relaxation of the protein polar groups. The fact that both relaxations are very markedly influenced by the presence of water for hydration contents, h, higher than 9%, strongly suggests that all water molecules sorbed up to this value are irrotationally bound to the protein macromolecules. Comparison with results obtained by other investigators by a variety of methods, as well as calculation of the primary sorption sites at the molecular level, give further support to the above interpretation.
A model of amorphous silicon deposition in DC glow discharge in silane
Authors: Y Yamaguchi  , A Sumiyama  , R Hattori  , Y Morokuma  , T Makabe
Published: July 2002

The structure of the cylindrical DC glow discharge in SiH4is presented by solving a basic set of equations, consisting of the electron, ion, gas molecule and radical continuity equations, and Poisson's equation. The electron swarm parameters are then obtained up to an E/N of 6*10-14V cm2from the analysis of the Boltzmann equation using the available cross-sectional information, and considering the local non-equilibrium at the cathode fall region. The spatial distribution of the radical is shown to have a maximum of 1012cm-3at the boundary between the sheath and plasma bulk. The production rate profile is also studied. The deposition rate of the radicals to the inner electrode is calculated from the diffusion flux of the radical molecule in space. The evaluated deposition rate of a-Si:H in the DC discharge in SiH4is consistent with previous experimental results within a factor of 0.5. The role of the negative ion and the influence of the non-equilibrium region in front of the cathode are also discussed.
A study of electron swarms in nitrogen gas by the voltage transient technique
Authors: P H Purdie  , J Fletcher
Published: July 2002

The voltage transient technique has traditionally been limited to high-pressure (p>500 Torr) discharges so that electron diffusion can be neglected. In much previous work image terms have also been omitted from the analysis of the experimental data. An analysis of the voltage transient has been developed which includes all image terms and both electron and ion diffusion. This analysis is applied to data in nitrogen gas, and the results have been compared with previous values obtained by other techniques. It is established that the measurement of voltage transients can be used to obtain electron transport parameters over a wide range of gas pressure and of E/N so long as the present full analysis is used.
Beam deflection in electron beam welding by thermoelectric eddy currents
Authors: J Paulini  , G Simon  , I Decker
Published: July 2002

A model of the thermoelectric eddy currents occurring in the electron beam and laser welding of two dissimilar metals is presented, based on irreversible thermodynamics. The distribution of eddy currents and the magnetic field generated are computed and the resulting deflection of the electron beam is calculated, approximately. The model predicts large thermoelectric currents in the workpiece and a deflection of the electron beam that is in good agreement with experiment.
Measurements of very small angle scattering of medium energy electrons in gases
Authors: R G Lord
Published: July 2002

The total scattering cross sections of helium, nitrogen and argon for 13, 23 and 43 kV electrons have been measured in the angular range up to 6 mrad. The results are compared with theoretical cross sections based on Hartree and Hartree-Fock atomic models. Agreement is found to be quite good for helium but for the other two gases the measured cross sections are smaller than predicted on the basis of the Raman-Compton theory of inelastic scattering. This is believed to be due to the neglect of exchange terms in calculating the inelastic cross sections.
Flow modes in shock tubes with electromagnetic driving sections
Authors: G J Pert
Published: July 2002

The stability of the shock front under free-flow down the expansion tube of an electromagnetically driven shock tube is investigated. The results of a wide range of experiments covering different electrode geometries, ambient gas pressures and front velocities in hydrogen, helium and argon are analysed. It is found that a condition for stability can be found in terms of a critical hydrodynamic Reynold's number of about 9000 for the flow. The implications of this result are discussed.
The viscosity of carbon dioxide and acetylene at atmospheric pressure
Authors: B J Bailey
Published: July 2002

The viscosities of carbon dioxide and acetylene have been determined to temperatures of 700 and 600 K respectively using the method of capillary flow. The viscometer was a continuous-flow instrument incorporating a differential mercury manometer and a soap-film flow meter. A determination of the constantmin the kinetic energy term of the Hagen-Poiseuille equation, showed it to have a mean value of 1·064 and to be independent of Reynolds number over the range 150 to 600. The viscosity of carbon dioxide was found to differ from the previously accepted capillary values, being 3% higher at 700 K. It was, however, in good agreement with recent oscillating disk data. In the case of acetylene the data reported here is in good agreement with existing data at 300 K but is 3% higher at 500 K. The precision of the determinations is estimated at 0·4% for carbon dioxide and 0·6% for acetylene.
The plume of electron and laser pulses
Authors: B Steverding  , A H Werkheiser
Published: July 2002

When powerful radiation bursts interact with solid targets the ejected material escapes in a peculiar sheet-like form with hyperthermal velocity. An attempt is made to explain this phenomenon by the action of a thermomechanical shock wave which is generated in the target and ejects the heated surface layer with twice the particle velocity of the shock. The theory has been tested for electron pulses for which a simple one-dimensional approach is possible. Extension of the presented theory to laser pulses gives the proper order of magnitude for the plume velocity and other observed phenomena.
Thermomechanical damage by pulsed lasers
Authors: B Steverding
Published: July 2002

Equipment is under development to generate powerful laser pulses capable of producing fracture in metals. Since laser energy - in a continuous mode of operation - can also be used to induce thermal damage, the laser provides an excellent model to assess thermal as against mechanical damage potential. A simple one-dimensional theory is presented which combines energy absorption, shock formation and dynamic fracture phenomena in order to predict failure of metals in relation to laser characteristics. Conditions are indicated under which the destructive power of a pulsed laser becomes maximal.
Dislocation damage by spark cutting in cadmium single crystals
Authors: C Luke  , K E Puttick
Published: July 2002

A method is described for estimating dislocation damage in crystals as a result of spark cutting. The method allows direct comparison of dislocation arrangement in the same area before and after cutting and is applied to estimate the maximum depth of damage (mdd) in cadmium single crystals using a dislocation etch on the (101bar above 0) plane.

The investigation suggests that previous work on other metals has underestimated the mdd and in addition shows:

The moving-wire cutter commonly used to section metal crystals frequently makes mechanical contact with the workpiece, with resultant shorting and mechanical abrasion.

A simple fixed-wire cutter produces a more satisfactory and damage-free cut than the moving wire.

Using this fixed wire, the mdd is a function of the diameter of the wire.

Using the lowest available spark energy and a wire of 0·001 inch diameter, the maximum depth of damage in cadmium can be reduced to 0·1 mm.
The drift and diffusion of electrons in oxygen containing traces of hydrogen
Authors: I A Fleming  , D R Gray  , J A Rees
Published: July 2002

Measurements of the drift velocity and lateral diffusion of electrons in oxygen containing traces of hydrogen are reported for values ofE/Nup to 20 × 10−17V cm2. Complications due to the production of negative oxygen ions were removed through an associative detachment process by the addition of the hydrogen. By comparison with other available data for pure oxygen, it appears that relatively large concentrations (similar 10%) of hydrogen can be added without producing significant changes in the transport coefficients at a givenE/Nover the range ofE/Nstudied.
Quantitative analysis of electron microscope images recorded on thin polymer films
Authors: Koichi Kanaya  , Hisazo Kawakatsu  , Nobufumi Atoda  , Haruo Yotsumoto  , Akishige Ono
Published: July 2002

A quantitative procedure for the evaluation of object mass-thickness in electron microscopy by the use of a new recording method is described on the basis of single and plural scattering theories. With this method, recorded images can be observed as colour images, and the difference in mass-thickness of a specimen is estimated directly from the observed colours as well as from the photographic density. Because of the high contrast, the detectable limit of difference in thickness is found to be about ten times smaller than that with usual emulsions.
Measurement of the flexural damping capacity and dynamic Young's modulus of metals and reinforced plastics
Authors: R D Adams  , D G C Bacon
Published: July 2002

An apparatus is described which is suitable for measuring the flexural damping and dynamic Young's modulus of beam specimens at stress levels up to 200 MN m−2. Symmetric free-free flexural modes of vibration are excited by a coil/magnet pair, the coil being attached to the midpoint of the beam. Extraneous sources of damping have been reduced to a low level despite the difficulties of producing high-amplitude vibration. Low-damping specimens must be testedin vacuo(0·5 Torr was usually sufficient) if the effects of air damping are not to be significant. Specific damping capacities from 0·1 to 50% can be accurately measured over a frequency range of 100 to 800 Hz and a temperature range -50 to +200°C.
An appraisal of the mass spectrometer diagnostic technique in the study of afterglow plasmas
Authors: D Smith  , I C Plumb
Published: July 2002

An appraisal is presented of the mass spectrometer diagnostic technique as applied to the sampling of positive and negative ions diffusing towards an orifice probe located at the boundary of an afterglow plasma. The report is largely based on the results obtained from detailed studies over several years in these laboratories of time-resolved (or stationary) afterglow plasmas, together with reported observations of other workers. Several specific plasma situations are discussed and illustrated with data, including diffusion- and recombination-controlled positive-ion/electron plasmas and positive-ion/negative-ion plasmas. These examples emphasize the importance of spatial charge density distributions, space-charge sheaths and electric fields in both the vicinity of the sampling orifice and in the body of the plasma. Data are also presented which graphically illustrate the serious effects which can result from contamination of the sampling electrode in the region of the orifice. The problem of collisional break-up of weakly bound `cluster' ions in the sampling system is also briefly discussed. It is suggested that the serious discrepancies which exist between reported values of a large number of reaction rate coefficients obtained from afterglow studies are due at least in part to a lack of appreciation of some of these important physical phenomena. Throughout the paper, attempts are made to indicate the experimental conditions which must exist if valid data are to be obtained using the mass spectrometer sampling technique.
Studies of plasma production at hypervelocity microparticle impact
Authors: D Smith  , N G Adams
Published: July 2002

This paper is concerned with an investigation of the plasma generated during the impact of hypervelocity microparticles with a metal target. A laboratory source of hypervelocity micron-sized iron particles is first described which utilizes a 2 MV Van de Graaff generator, followed by a discussion of the techniques used to determine the mass and velocity of the particles. On impact of the iron projectiles on a slatted molybdenum target, charge is generated, extracted from the region of impact by suitably biasing a gridded electrode, and subsequently detected using a conventional wideband electronic amplifier or an electron multiplier. It is shown statistically that during impact equal numbers of electrons and positive ions are produced - indicating plasma generation - and that the total charge released (Q) may be described empirically in terms of the mass (m) and velocity (v) of the particle by a simple power law relationship of the kindQαmαvβ, with β = 3·2 ± 0·1 over the complete velocity range investigated (0·05 to 10 km s−1) and with α = 0·85 forv>1 km s−1and 1·33 forv<1 km s−1. It is also shown that the charge extracted from the plasma reaches a maximum a few microseconds after impact and subsequently decays exponentially with a time constant of several micro-seconds.

A crude mass analysis of the positive ions generated during the impact using a simple time-of-flight mass spectrometer has indicated that, over the velocity range investigated, the dominant ions in the spectrum are characteristic of the projectile and not the target material. From considerations of the relative abundance of the metal ions in the spectra, together with the known relative metal atom concentrations in the iron projectiles, the temperatures of the plasmas have been estimated (from Saha equilibrium considerations) to be of the order of several thousands of degrees Kelvin.

In a detailed discussion, attempts are made to consider how the kinetic energy of the projectile is dissipated - eventually producing plasma - in terms of available theoretical models of hypervelocity impact. It is shown that the most satisfactory model of this very complex interaction appears to be one in which the relative importance of shock-wave propagation into the projectile and target materials is considered. Finally, a discussion of the properties and the temporal behaviour of the impact-produced plasma is presented in order to assess the relative importance of diffusion and recombination processes, thus to assist in the interpretation of the experimental results obtained in this study.
Experimental and theoretical study of a stationary high-current arc in a supersonic nozzle flow
Authors: W Hermann  , U Kogelschatz  , L Niemeyer  , K Ragaller  , E Schade
Published: July 2002

In a previous paper (Hermannet al1974) a detailed experimental and theoretical investigation of an arc in a supersonic nozzle flow was initiated by discussing the high-pressure arc section near the stagnation point.

This paper is a continuation of this work for the section further downstream, especially within the nozzle. Extensive measurements of temperature, flow velocity, pressure and electric field strength are described. Theoretical results are obtained by a two-zone model.

A detailed comparison between theory and experiment allows for the first time a complete quantitative discussion of all effects influencing the arc and the flow. Compared with the arc in the high-pressure section the influence of radiative energy transfer decreases. Instead, flow turbulence becomes the dominating exchange mechanism.
Application of the dusty-gas model to the permeability of a porous medium to a dissociating gas in local chemical equilibrium
Authors: P G Wright
Published: July 2002

The dusty-gas model is employed to obtain expressions for the flow of a dissociating gas (in local chemical equilibrium) through a porous medium, or a capillary tube. The resulting equations can be expressed in a manner that is formally similar to those for the flow of a single nonreacting gas, but with a viscous term involving a dependence of viscosity on pressure, and a diffusive term which involves not only Knudsen diffusion coefficients but also the binary mutual diffusion coefficientD1vfor interdiffusion of dissociated and associated species.

For an isomerizing gas, however, these complications virtually disappear. The equilibrium composition, and therefore the viscosity, no longer varies with pressure; and the dependence on the binary mutual diffusion coefficient (to a good approximation) is removed by a cancellation of terms.

The effect of flow in an adsorbed layer is considered.
Microwave radiometric investigation of the positive column instability in pulsed nitrogen discharges
Authors: Omesh Sahni  , W C Jennings
Published: July 2002

A microwave radiometric technique has been used to study the positive column instability in pulsed nitrogen discharges. The technique involves monitoring the effective temperature of microwave radiation as a function of the longitudinal magnetic field. The critical magnetic fieldBcfor the onset of the instability is found to be dependent on both the discharge current and the duration of the excitation pulse. The experimental results are consistent with an explanation based on significant cumulative ionization.

The plasma became turbulent at progressively lower values of magnetic field aboveBcas the discharge current was increased. Further increase in current led to the unstable regime beyondBcreverting back to stability on progressively increasing the magnetic field.
A hypersonic interpretation of the development of the spark channel in gases
Authors: M M Kekez  , P Savic
Published: July 2002

A new mechanism for the development of the spark channel in gases is proposed, in which it is assumed that the shock wave, known to exist after the channel is complete (Freeman and Craggs 1969), actually develops while the channel is still in formation. The paraboloidal shock is thought to derive its power from the transfer of energy only from the electrons pre-heated in front of the developing channel by field concentration to the neutrals and ions behind it (detonation wave mechanism). Neutral gas in front of the channel is considered to be cold. Analytical expressions for the velocity and position of the detonation wave are derived, and experiments by the authors and by previous workers tend to confirm the mechanism for certain low-density gases. The `radiation overshoot' characteristic of shock transmission through some gases has been observed, suggesting that a shock indeed exists prior to completion of the spark channel.
Constriction of a high-pressure glow discharge in hydrogen
Authors: P Suleebka  , M R Barrault  , J D Craggs
Published: July 2002

An image converter was used as a fast streak camera to study the glow-to-arc transition in a uniform field hydrogen discharge gap (160-460 Torr pressure). The maximum discharge current was about 850 A. For the first 20-30 shots or so, with stainless steel electrodes, the constriction of the glow always started at the cathode irrespective of pressure and overvoltage. When the electrodes became conditioned, i.e. after about 100 shots, the constriction was initiated at the anode for overvoltages up to a critical value depending on the gas pressure. Above the critical overvoltage the constriction began at the cathode, and at the critical overvoltage the constriction was initiated in mid-gap and propagated in both directions.
On the theory of flux jumps in hard superconductors
Authors: R G Mints  , A L Rakhmanov
Published: July 2002

The critical state stability against flux jumps in hard superconductors is considered by means of the WKBJ method. The universal stability criterion for an arbitrary critical state model is obtained.
Consistent theory of electron scattering with atoms in electron microscopes
Authors: K Kanaya  , S Ono
Published: July 2002

The potential function consisting of the power and exponential forms as a function of a screened atomic radius is proposed, by which the electron scattering amplitude is a complex quantity and involves the effects of energy dependence. An empirical relation is used for the exponent, and the cross sections of elastically and inelastically scattered electrons with atoms thus obtained are shown to be in good agreement with previous exact numerical calculations. The energy losses are in good agreement with experiments over the energy range 10-1000 keV. A small fitting factor is required in the range 1-10 keV.
The limits of measurement with mass spectroscopy
Authors: R A Saunders
Published: July 2002

The methods of measurement of nuclidic mass and isotopic abundance by mass spectroscopy are reviewed. The various factors that limit the accuracy of these measurements are considered. Also studied are those factors that limit the sensitivity of the mass spectroscope. The ways in which mass and abundance measurements are used when a mass spectroscope is used for chemical analyses are discussed and the limitations of the various methods are considered.
Apparatus for RE plasma zone melting
Authors: Y Kumashiro  , N Yazawa  , S Misawa  , A Itoh
Published: July 2002

The characteristics of a newly developed RF plasma jet for the crystal growth of nitrides with high dissociation pressures are described. Firstly, a newly designed ammeter utilising DC conversion is used to clarify the electrical behaviour of the RF plasma jet. Secondly, the value of RF plasma melting for the crystal growth of nitrides is confirmed by melting VN rods under the optimum conditions of 53.2 kPa (400 Torr) in Ar-N2plasma to indicate that the nitrogen/vanadium ratio is almost equivalent to that obtained by RF induction heating under 1.01 MPa (10 atm) of nitrogen.
A general digital linearising method for transducers
Authors: W T Bolk
Published: July 2002

A practical three-point interpolation algorithm is presented which corrects for manufacturing tolerances, zero offset, scaling errors and nonlinearity of transducers and signal conditioners. The algorithm is applicable to data-acquisition systems which make use of a microprocessor. Each measuring channel requires three parameters. One simple universal routine using these parameters calculates the value of each measurand. Results are given for eight temperature transducers.
Detection of deviations from Ohm's law by a phase-resolved microwave harmonic mixing technique
Authors: W Mayr  , A Philipp  , K Seeger
Published: July 2002

A nonlinear current-voltage characteristic gives rise to a DC voltage proportional to the deviation from Ohm's law when microwave radiation of frequency omega and its second harmonic 2 omega are applied to a sample. The principles of this method and the microwave apparatus are described in detail and the advantages of this method are discussed. As an example, some results on NbSe3 in the temperature range between 4.2 and 300K are presented.
Sensor materials
Authors: W E Duckworth
Published: July 2002

For the first two thirds of the 20th century the
development of new materials has been dominated by three
major requirements - physical transportation, power generation
and armament production. These three motivators have now
lost their force: intellectual communication is expanding more
rapidly than physical transportation: energy conservation has
assumed more importance than power generation; the materials
intensity of armaments has declined dramatically.
Information technology in all is now the main driving force
behind material development, and here the prime requirement is
for materials that can convert the analogue signals of nature into
the digital form required by electronic manipulators. These
sensors are required in physical, chemical, metallurgical and
engineering environments. Examples will be given in all four and
future needs outlined.
A microcomputer-based image processing system for studies of transmission electron micrographs of stacking faults
Authors: A H G El-Dhaher  , A A Farhat  , K Z Botros  , A N Abu-Rezeq
Published: July 2002

A microcomputer-based image processing system was constructed to acquire, process and display images of transmission electron micrographs. The system hardware consisted of a video camera, microcomputer unit, video digitiser and frame buffer boards. The software developed consisted of powerful functions for image display, saving and image manipulation. Other functions such as filtering and contrast enhancement were also included. The user is offered a friendly interactive environment, and no previous experience in image processing or computer programming is needed to operate the system. Development of an efficient program allowed many functions to be executed with the limited resources available on the microcomputer unit. Calculated theoretical images created by the system are compared with experimental images taken by the video camera. Images are displayed on the video monitor which are more meaningful to human eyes than conventional hard copy printouts. Also, the use of contrast enhancement techniques allows hidden information to be extracted from experimental images. Preliminary studies of identifying stacking faults in transmission electron microscopy using this system were very encouraging.
Design considerations in multiprobe roundness measurement
Authors: D Moore
Published: July 2002

The author examines current practice in the multiprobe method of roundness measurements, and derives design strategies for improved measurement accuracy and reliability. The multiprobe method eliminates variable centring errors by combining displacement measurements made simultaneously at several points about the periphery of the workpiece. Discrete signal processing methods for reconstruction of the workpiece profile are described, and design guidelines are established to eliminate the detrimental effects of aliasing from the reconstruction process. The harmonic response of a three-probe arrangement is investigated, and methods are developed to avoid the unwanted suppression of harmonics. The advantages of a more complex multiprobe arrangement are discussed, and a novel harmonic reconstruction method used to avoid suppression, and to allow the detection of incorrect measurements by a redundancy technique.
Analysis of back scattered ions as a technique for the study of surfaces
Authors: D G Armour  , G Carter
Published: July 2002

When energetic ions strike a surface, a fraction, depending upon the ion energy and other parameters, penetrate the surface, whilst the remainder are reflected or backscattered. This review shows how studies of the energy and angular distribution of backscattered ions is being used to investigate the composition of the surface and near surface of a solid, the location of impurities in a lattice and the orientation and crystallinity of solids. The apparent limitations and prospects for development of this technique, as a precise analytical tool, are discussed.
Cathode cap for the EM6 microscope suitable for use with pointed filaments
Authors: M J Bowman  , D I Hardie
Published: July 2002

A design is presented for a cathode cap for the AEI-EM6 microscope suitable for use with pointed filaments. Experimental results indicate that an increase in brightness by a factor of ten and coherence by a factor of two may be obtained with the cap over that using the standard apparatus.
Temperature effects on hot wire anemometer calibrations
Authors: F A Koch  , I S Gartshore
Published: July 2002

Calibrations of a miniature DISA hot wire anemometer probe over a range of wire temperatures and a narrow range of ambient temperatures have been correlated by a simple expression (Ne)(Tm/To)a=A+B(Re)n. Values of a and n, which are expected to remain roughly constant for wires of similar geometry, were found to be 0.67 and 0.45 respectively. The value of a is different from that found by Collis and Williams, an effect due mainly to the difference in aspect ratio between the wires tested. An alternative expression which replaces the term (Tm/T0) by one involving the overheat resistance ratio is suggested, which collapses the data as completely as the expression involving the temperature ratio. Using the alternative representation, the coefficients necessary for a measurement of temperature and velocity fluctuations are derived.
X-ray safety systems for use with Philips PW1016 and PW1316 tube shields
Authors: C F Sampson
Published: July 2002

Protective systems designed to safeguard the users of a variety of X-ray diffraction equipments are reported. In particular, mechanical interlocks have been fitted to Philips PW1016 and PW1316 X-ray tube shields and the necessary camera modifications for both single crystal and powder cameras are described. Environmental enclosures surround the tube shield and crystallographic instruments to form part of the interlock system.
A hot wire technique for continuous measurement in unsteady concentration fields of binary gaseous mixtures
Authors: D Adler
Published: July 2002

A new technique for the measurement of concentration in binary gaseous mixtures is described. Due to the high frequency response of the hot wire equipment used this technique is suitable for measurements in rapidly varying processes. The instrument developed can be used as a concentration probe, interference with the measured phenomenon being kept to a minimum by the small size of the sampling tube used and the small sampling flow rate required. The theoretical basis of the instrument is discussed and the governing equations are numerically analysed to indicate the effect of the main instrument parameters on its sensitivity. Experimental results are given and compared with theory.
Ion beam milling of silica for IR transmission
Authors: H Bach  , R Haspel  , N Neuroth
Published: July 2002

Ion beam etching is applied to produce specimens less than 1 mu m thick with a free aperture of 4 mm in diameter. Plane specimens which have the same chemical composition and structure as the bulk material can be obtained. Infrared transmission spectra were obtained from fused silica samples Herasil and Suprasil W. The shapes of these transmission spectra are discussed. The absorption bands in the region 5-7 mu m have the same intensity for both glasses independent of the OH content of the silica. They are supposed to be overtones of the basic Si-O vibrations at 9.4 mu m and 12.4 mu m.
Characterizations of the Gelfand-Shilov spaces via Fourier transforms
Authors: Chung Jaeyoung , Chung Soon-Yeong , Kim Dohan
Published: July 2002

We give symmetric characterizations, with respect to the Fourier transformation, of the Gelfand-Shilov spaces of (generalized) type

S
S

and type

W
W

. These results explain more clearly the invariance of these spaces under the Fourier transformations.
Perturbing polynomials with all their roots on the unit circle
Authors: Mossinghoff Michael , Pinner Christopher , Vaaler Jeffrey
Published: July 2002

Given a monic real polynomial with all its roots on the unit circle, we ask to what extent one can perturb its middle coefficient and still have a polynomial with all its roots on the unit circle. We show that the set of possible perturbations forms a closed interval of length at most

4
4

, with

4
4

achieved only for polynomials of the form

x

2
n

+
c

x
n

+
1

x^{2n}+cx^n+1

with

c
c

in

[
−
2
,
2
]

[-2,2]

. The problem can also be formulated in terms of perturbing the constant coefficient of a polynomial having all its roots in

[
−
1
,
1
]

[-1,1]

. If we restrict to integer coefficients, then the polynomials in question are products of cyclotomics. We show that in this case there are no perturbations of length

3
3

that do not arise from a perturbation of length

4
4

. We also investigate the connection between slightly perturbed products of cyclotomic polynomials and polynomials with small Mahler measure. We describe an algorithm for searching for polynomials with small Mahler measure by perturbing the middle coefficients of products of cyclotomic polynomials. We show that the complexity of this algorithm is

O
(

C

d

)

O(C^{\sqrt {d}})

, where

d
d

is the degree, and we report on the polynomials found by this algorithm through degree 64.
Annihilation Theorem and Separation Theorem for basic classical Lie superalgebras
Authors: Gorelik Maria
Published: July 2002

In this article we prove that for a basic classical Lie superalgebra the annihilator of a strongly typical Verma module is a centrally generated ideal. For a basic classical Lie superalgebra of type I we prove that the localization of the enveloping algebra by a certain central element is free over its centre.
A set-theoretic approach to database searching and clustering.
Authors: Krause A , Vingron M
Published: July 2002

MOTIVATION: In this paper, we introduce an iterative method of database searching and apply it to design a database clustering algorithm applicable to an entire protein database. The clustering procedure relies on the quality of the database searching routine and further improves its results based on a set-theoretic analysis of a highly redundant yet efficient to generate cluster system. RESULTS: Overall, we achieve unambiguous assignment of 80% of SWISS-PROT sequences to non-overlapping sequence clusters in an entirely automatic fashion. Our results are compared to an expert-generated clustering for validation. The database searching method is fast and the clustering technique does not require time-consuming all-against-all comparison. This allows for fast clustering of large amounts of sequences. AVAILABILITY: The resulting clustering for the PIR1 (Release 51) and SWISS-PROT (Release 34) databases is available over the Internet from http://www.dkfz-heidelberg.de/tbi/services/modest/b rowsesysters.pl. CONTACT: a.krause@dkfz-heidelberg.de; m.vingron@dkfz-heidelberg.de
Fast assignment of protein structures to sequences using the
Intermediate Sequence Library PDB-ISL
Authors: Teichmann Sarah A. , Chothia Cyrus , Church George M. , Park Jong
Published: July 2002

Motivation: For large-scale structural assignment to sequences, as in computational structural genomics, a fast yet sensitive sequence search procedure is essential. A new approach using intermediate sequences was tested as a shortcut to iterative multiple sequence search methods such as PSI-BLAST.

Results: A library containing potential intermediate sequences for proteins of known structure (PDB-ISL) was constructed. The sequences in the library were collected from a large sequence database using the sequences of the domains of proteins of known structure as the query sequences and the program PSI-BLAST. Sequences of proteins of unknown structure can be matched to distantly related proteins of known structure by using pairwise sequence comparison methods to find homologues in PDB-ISL. Searches of PDB-ISL were calibrated, and the number of correct matches found at a given error rate was the same as that found by PSI-BLAST. The advantage of this library is that it uses pairwise sequence comparison methods, such as FASTA or BLAST2, and can, therefore, be searched easily and, in many cases, much more quickly than an iterative multiple sequence comparison method. The procedure is roughly 20 times faster than PSI-BLAST for small genomes and several hundred times for large genomes.

Availability: Sequences can be submitted to the PDB-ISL servers at http://stash.mrc-lmb.cam.ac.uk/PDB˙ISL/or http://cyrah.ebi.ac.uk:1111/Serv/PDB˙ISL/and can be downloaded from ftp://stash.mrc-lmb.cam.ac.uk/pub/PDB˙ISL/or ftp://ftp.ebi.ac.uk/pub/contrib/jong/PDB˙ISL/

Contact: sat@mrc-lmb.cam.ac.ukand jong@ebi.ac.uk
Taxonomic markup language: applying XML to systematic data
Authors: Gilmour R.
Published: July 2002

Summary: An XML document type definition (DTD) is provided for the description of taxonomic relationships between organisms. Two XSL stylesheets for the graphical presentation of simple taxonomic trees are also provided.

Availability: The DTD and stylesheets along with sample files are available at http://www.albany.edu/~gilmr/pubxml/.

Contact: gilmr@cnsvax.albany.edu
Validating clustering for gene expression data
Authors: Yeung K. Y. , Haynor D. R. , Ruzzo W. L.
Published: July 2002

Motivation: Many clustering algorithms have been proposed for the analysis of gene expression data, but little guidance is available to help choose among them. We provide a systematic framework for assessing the results of clustering algorithms. Clustering algorithms attempt to partition the genes into groups exhibiting similar patterns of variation in expression level. Our methodology is to apply a clustering algorithm to the data from all but one experimental condition. The remaining condition is used to assess the predictive power of the resulting clusters—meaningful clusters should exhibit less variation in the remaining condition than clusters formed by chance.

Results: We successfully applied our methodology to compare six clustering algorithms on four gene expression data sets. We found our quantitative measures of cluster quality to be positively correlated with external standards of cluster quality.

Availability: The software is under development.

Contact: kayee@cs.washington.edu

Supplementary information: http://www.cs.washington.edu/homes/kayee/cluster or http://www.cs.washington.edu/homes/ruzzo/cluster

* To whom correspondence should be addressed.