bluuebunny/crossref_metadata_2025 huggingface dataset:
Stimulated Brillouin scattering of laser radiation in a piezoelectric semiconductor in the presence of a magnetic field
Authors: M Salimullah  , R R Sharma  , V K Tripathi
Published: July 2002

The authors investigated the stimulated Brillouin scattering of right-handed circularly polarised (RHCP) laser radiation in a piezoelectric semiconductor when laser radiation propagates (i) in the direction of the applied magnetic field and (ii) perpendicular to the magnetic field. The nonlinearity in the low-frequency ion-acoustic wave arises due to the equation of motion of electrons and in the high-frequency scattered sideband through the equation of continuity. Typically for T0 approximately=77K, Bs approximately=1 kG, n0
0 approximately=1014 cm-3, scattering anglue theta approximately=30 degrees , laser power density corresponding to a CO2 laser approximately=10 kW cm-2, the growth rate for longitudinal propagation in n-InSb turns out to be approximately=107 s-1. For transverse propagation the growth rate is one order of magnitude smaller than for longitudinal propagation.
The free recovery of wall-stabilised arcs with imposed laminar and turbulent flows
Authors: R J Hill  , G R Jones
Published: July 2002

Voltage probe measurements are presented for the free recovery period of wall-stabilised arcs subjected to an axial flow of nitrogen. Results are reported for 15, 25 and 45 A arcs in a 2.5 mm radius stabilising bore and for 30 and 50 A arcs in a 5 mm radius bore with mass flow rates in the range 0-0.6 g s-1. The measurements show that the conductance decay rate increases with mass flow rate and that, although this increase is most pronounced in the flow entrainment region, a significant increase is also observed in the fully developed column region. The observed experimental trends are explained in terms of a boundary layer arc model which includes turbulent diffusion effects.
Temperature determination for arcs in sulphur hexafluoride accounting for demixing
Authors: E Schulz-Gulde
Published: July 2002

Methods of temperature determination for arcs in sulphur hexafluoride (SF6) are presented for the temperature range from 9000 to 20000K. Temperatures are derived from combinations of measured S I, S II, F I and F II absolute line intensities and computed equilibrium plasma composition data by means of iterative procedures. Demixing effects are accounted for as both the temperature and the fluorine to sulphur concentration ratio M are determined from the measured data. The methods are applied to experimental line intensity data obtained from steady-state wall-stabilised arcs in SF6at atmospheric pressure, at axis temperatures of about 15000K. Simple approximation formulae are given for calculating the various partition functions at a pressure of p=1 bar for M=6, 12, 24 and 48; and at p=2, 4, 8 and 16 bar for M=6.
Flexural strength of polygranular carbon and graphite materials after various heat treatments and their correlation with porosity
Authors: E Fitzer  , K -H Kochling  , G Schwarz
Published: July 2002

Concerns the changes of flexural strength of fine grained extruded carbon and graphite materials caused by heat treatment between 1800 and 3000K. Measurements of flexural strength, bulk density and pore size distribution were performed at room temperature after heat treatment, whereas the thermal (reversible and irreversible) bulk expansion was measured in situ with a pushrod dilatometer up to 2700K. A correlation of all data points measured is discussed to explain the strength changed during heat treatment. A distinction is made between geometric effects, caused by isotropic bulk dilatation or shrinkage during heat treatment, and quality effects, consisting mainly of crystalline rearrangement processes. Special emphasis is given to 'sulphur-puffing and its influence on strength and porosity of the samples.
A critical analysis of ionising wave propagation mechanisms in breakdown
Authors: I Abbas  , P Bayle
Published: July 2002

The formation and propagation of ionising waves in impulsive overvolted gas discharges for parallel plane electrode geometry is studied. The spatio-temporal evolution of the electronic and ionic densities together with the space-charge distorted field was thoroughly examined for different initial electron distributions. The study elucidates the important role of the electrons present ahead of both the anode and cathode ionising waves and shows particularly how the wavefront profile evolves during its propagation. In all cases, provided that the discharge gap is sufficiently large, the wavefront is transformed into an electron shock wave defined by a shock zone of extremely high electronic density and field gradients. This limits the domain of validity of the gas discharge models that neglect both the thermal diffusion of charge carriers and gas photoionisation of photodetachment.
Optimum conditions for testing electrical fuses. II. Maximisation of total arcing energy
Authors: C B Wheeler
Published: July 2002

For pt.I see ibid., vol.9, no.12, p.1809-16 (1976). The total arcing energy for a fuse link of uniform cross-section in an AC circuit of known power factor is evaluated assuming adiabatic heating of the link and a constant voltage fuse arcing characteristic. It is shown that this energy maximises for optimum values of the closing angle and prospective current. The maximum and optimum parameters are expressed in units involving the supply voltage and fuse link properties and presented as a function of fuse arcing voltage and circuit power factor. In particular, for fuse testing applications, the tolerance on closing angle and prospective current is determined in order that the arcing energy should be at least 95% of its maximum value.
Spark-gap-triggered RLC circuits
Authors: W N Hugrass  , B L Jessup  , A A Pugatschew
Published: July 2002

There is always a voltage drop between the electrodes of a triggered gas-filled spark gap. It is shown that the magnitude of this voltage, its form and frequency, can have a dramatic effect on the damping of a triggered RLC circuit. Energy can be fed to such an oscillating circuit by externally controlling the frequency of the spark gap voltage drop waveform. The dependence of this energy transfer on the amplitude, frequency and polarity of the gap voltage drop is examined experimentally and theoretically with the aid of numerical calculations. The conclusions of this study are applied to reducing the damping influence of a spark gap and to the construction of a circuit to generate pulses of RF oscillations.
Electroluminescence effects associated with the field emission of electrons from a carbon fibre micropoint emitter
Authors: R V Latham  , D A Wilson
Published: July 2002

It has been observed that the field emission of electrons from a micropoint carbon fibre cathode is accompanied by the emission of optical photons. Image intensifier techniques have been used both to record the visible spectrum of this radiation and to show that the dependence of its intensity on the applied voltage is consistent with it being electroluminescent in origin. The phenomenon has been qualitatively interpreted in terms of an emission mechanism involving a composite microregime consisting of a metallic-like substrate overlayed by a thin insulating medium.
The negative end of cold cathode glow discharges
Authors: K G Emeleus
Published: July 2002

Recent developments in basic knowledge of the negative end of anomalous (abnormal) cold cathode discharges are discussed. The following features are considered: the cathode fall space, the negative glow, the boundary zone between fall space and negative flow. Some details of the role of the cathode glow (erste Kathodenschicht) and of the effect of the wall charges near the negative glow are uncertain. Otherwise there are no obvious outstanding problems, at least for tubes with simple geometry, if the gas composition is shown. Where quantitative data for discharge parameters do not already exist, methods are available for measuring them with confidence, as well as reliable theoretical techniques for predicting them.
Repetitively pulsed iodine laser with thermal gas flow cycle
Authors: H J Baker  , T A King
Published: July 2002

The 1.315 mu m atomic iodine laser has been developed for repetitively pulsed operation by the use of a thermally driven fast gas flow and replenishment system. The flow, produced by thermal evaporation and condensation, removes the molecular iodine formed by photolysis which acts as a strong laser quenching agent. An all-glass construction of the laser and flow system gives long life sealed-off operation, and no iodine corrosion problems. Fluorocarbon buffer gases have been evaluated for use in providing flexibility in the operation of temperatures of the flow system in projected larger aperture oscillator systems, and for enhancing energy storage capability by pressure broadening the laser linewidth in Q-switched oscillators and amplifiers.
The ultrasonic stress distribution in the fatigue dumb-bell specimen
Authors: C H Green
Published: July 2002

With ultrasonic fatigue-cycling, a dumb-bell design of specimen is commonly used, some being of a shape for which the well-known stress equations pertaining to a stub dumb-bell would only give a poor approximation to the actual stress endured. In cases where the gauge-fillets are too large to be ignored theoretically, the stress distribution is examined in detail and expressions are found for the maximum stress amplitude S and resonant half-length l. Special requirements for S and l leading to optimum specimen design are also found.
The electron optics of high-voltage magnetically-focused image converters. II. Aberrations and the effects of transverse fields
Authors: C I Coleman
Published: July 2002

In pt.I (ibid., vol.7, p.1877, 1974) concerning the electron optics of high-voltage image converters using homogeneous coaxial electric and magnetic fields, it was shown that a relativistic treatment leads to a rather small deviation from the 'classical' focus condition. Here, it is shown that aberrations resulting from non-uniformity of the fields, and also image displacements caused by deliberately applied transverse electric or magnetic fields, are reduced by several per cent compared with those calculated using non-relativistic formulae. Methods are presented which enable the results of existing classical treatments to be simply corrected to account for relativistic effects.
Direct measurement of photoabsorption cross-sections: application to UV laser photolysis of OCSe and Se2+CO
Authors: M C Gower  , S Rolt  , C E Webb
Published: July 2002

Demonstrates a new method for directly measuring absorption cross-sections. The technique involves measuring the saturation energy fluence for short pulse propagation through strongly absorbing media, and is applied to the case of an ArF laser pulse propagating through OCSe. Pulsed saturation effects have also been studied in ArF laser photolysis of Se2+CO gas mixtures.
An investigation into the origin of frequency sweeping in a hybrid TEA CO2 laser
Authors: D V Willetts  , M R Harris
Published: July 2002

An analysis of the sources of the intrapulse frequency modulation in the hybrid TEA CO2 laser is presented. Two principal effects predominate: the falling frequency at the start of the pulse is shown to be due to plasma effects, while the increasing frequency during the remainder of the pulse arises from a laser induced refractive index perturbation. The significance of these results to the design of high stability pulsed lasers is discussed.
A novel treatment of Trichel-type phenomena with possible application to stepped-leader phenomena
Authors: M M Kekez  , P Savic  , G D Lougheed
Published: July 2002

A simple theory for Trichel discharges in gases is proposed, in which the corona region is assumed to be describable in terms of a Townsend generation-recombination mechanism, while the outer drift region is deemed subject to photoionisation-attachment processes, together with displacement current effects. The pair of first-order nonlinear differential equations is examined with a linearising 'small signal' procedure, yielding stability limits, frequency and damping coefficients. A numerical treatment of the full equations gives the development of pulse shapes, as well as large-signal modifications of the stability limits. Good qualitative agreement with observation is established, especially with the well-known proportionality between average current and pulse frequency. An extension of the theory to stepped-leader phenomena is proposed and it is shown that the agreement with observation is quite acceptable, even though the parameters involved here are of a different order of magnitude when compared with Trichel discharges.
The modelling of hydrothermal aging in glass fibre reinforced epoxy composites
Authors: B Dewimille  , A R Bunsell
Published: July 2002

The usefulness of two diffusion models of differing complexity has been examined in the case of hydrothermal aging of a unidirectional glass fibre reinforced epoxy composite. It has been shown that water absorption in this material under immersion conditions cannot be explained on the basis of simple single-free-phase diffusion into the resin and that a more complex description is needed.
Improved point-contact diodes using rare earths
Authors: P G Frayne  , M W Booton  , N Chandler
Published: July 2002

The voltage responsitivity of low output resistance point-contact metal-insulator-metal detectors can be increased by selection of electrode materials. This is shown to be consistent with a theoretical model of the point-contact junction developed to simulate the observed properties. The voltage responsivity of a tungsten-gadolinium diode was an order of magnitude better than those using aluminium or gold planar electrodes and only half an order lower than tungsten-silicon. The combination of good responsivity and low output resistance is attractive for fast-response detection.
The magnetostatic energies of ellipsoidal particles which contain a reverse domain and a nonmagnetic inclusion
Authors: J E Coleman
Published: July 2002

A superposition method is used to obtain expressions for the changes of magnetostatic energy when a reverse domain is formed either adjacent to or surrounding a nonmagnetic inclusion. It is shown that such inclusions may lower the energy barriers to the nucleation of reverse domains and may also hinder the achievement of true saturation.
Theoretical description of gas discharges containing excited atoms at low pressures
Authors: H -B Valentini
Published: July 2002

For low-pressure gas discharges a theory is established taking into account excited atoms, in particular metastable atoms, and stepwise ionisation processes. A macroscopic boundary condition for the outward-directed drift velocity of the excited atoms is derived. Using this condition the concentration of metastable atoms can be calculated. At a low degree of ionisation and low gas density the drift considerably reduces the density of the metastables. Saturation of the concentration of the metastables occurs as the electron density is increased. For argon the spatial distributions of the particle densities and of the drift velocities of the metastable atoms and of the charge carriers are calculated. The influence of the metastable atoms and of the stepwise ionisation on the electron temperature is discussed.
Diagnostics and modelling of a methane plasma used in the chemical vapour deposition of amorphous carbon films
Authors: K Tachibana  , M Nishida  , H Harima  , Y Urano
Published: July 2002

In an RF-discharge methane plasma, the dissociation rate of CH4in collisions with electrons has been measured using a laser absorption technique. The measured rate increases as the RF power increases and as the gas pressure decreases. The electron energy distribution function f( epsilon ) and the electron density nehave also been measured by a heated electrical probe. The measured f( epsilon ) is quite different from the Maxwellian distribution and rather close to the Druyvesteynian distribution. The dissociation rate constant deduced from f( epsilon ) and the reported cross-section when multiplied by the measured neis consistent with the results of the laser absorption method. Based on these measurements a modelling of the plasma has been performed using a set of rate equations for CH4and the various neutral and ionic species produced in the plasma. The calculated degree of dissociation for CH4in the plasma agrees well with the measured results. The most abundant neutral radical in the plasma predicted by the model is CH3, while CH5+is the most abundant ionic species.
The interfacial friction of compacted maize powders
Authors: B J Briscoe  , M S D Fernando
Published: July 2002

This paper describes an experimental study of the friction generated between compacted maize and smooth ridge counterfaces. The influence of compaction conditions and the normal load is presented for a hemispherical compact in contact with a smooth rigid plane. The data are analysed using the approaches which have been widely adopted to interpret the friction of rough solid bodies. The compact surface is an interesting and structurally simple case of a rough solid surface. These analyses are shown to provide a good prediction of the friction and its load dependence.
High magnetoresistance in bipolar semiconductors by impurity concentration optimisation
Authors: A G Kollyukh  , V K Malyutenko  , V B Sukhorebry  , A Chovet  , S Cristoloveanu
Published: July 2002

The well known two carrier transverse magnetoresistance in semiconductors is analysed in order to show that a high magnetoresistance coefficient can be reached for an impurity concentration which closely depends on the electron-hole mobility ratio and the magnetic field intensity. The condition for a strong magnetoresistance is shown to be quite different from that leading to a null Hall field. Experiments in InSb crystals fully confirm the analysis and outline the possibility to use this effect for magnetic or temperature sensors.
Ionization coefficients in nitrogen containing radioactive impurities
Authors: J Jones
Published: July 2002

Values of the Townsend coefficients α and ω/α have been obtained over the range 100 <E/p0 < 510 v cm−1torr−1for contaminated nitrogen samples; the contaminants used were the radioactive isotopes tritium and krypton-85. Two impurity concentrations were used for each contaminant: 6 μCi cm−3and 60 μCi cm−3respectively. Values obtained for the primary coefficients in these contaminated samples were significantly higher than those in pure nitrogen. This increase in α/pwas attributed to the preferential ionization of long-lived metastable states of nitrogen, which were produced by the decay radiations of the included isotopes. This conclusion was supported by the breakdown of the similarity principle found to occur for Paschen curves during the present work. No significant difference in the secondary coefficients for the pure and contaminated nitrogen was observed.
Thermoelectric properties of the molten silver chloride-silver iodide eutectic mixture
Authors: K Cornwell  , R W Dyson
Published: July 2002

The silver chloride-silver iodide equilibrium diagram has been constructed. The eutectic temperature is 259°C and the eutectic composition is 47 mole% silver chloride. The mean thermoelectric potential of this mixture between 260 and 960°C has been measured as -0·498 mv degK−1. Values of electrical conductivity of silver chloride-silver iodide mixtures are available in the literature, and the mean specific conductivity of the eutectic mixture between 260 and 960°C has been estimated as 2·91 Ω−1cm−1. The thermal conductivity has been measured as 1·83 × 10−3 W cm−1 degK−1 at 300°C. These values yield an approximate mean figure of merit for thermoelectric generation between 260 and 960°C of 0·4 × 10−3 degK−1. This is a threefold increase over the estimated figures of merit for the pure components.
Reply to Comments of Holland
Authors: K Kanaya  , K Shimizu  , Y Ishikawa
Published: July 2002

Polymer films may grow on ion bombarded surfaces due to cross-linking
of hydrocarbon molecules adsorbed from a vacuum atmosphere. Electron-induced
polymer formation has been studied intensively, but only limited information exists on the role of ions (their mass and energy) in promoting the growth of similar films. Attention is drawn to a recent paper in the journal, and it is suggested that polymer growth during argon ion bombardment may have arisen also from secondary electrons returned to the target.
Electrical conduction in polycrystalline CdS films. II. Comparison of theory and experiment
Authors: M V Garcia-Cuenca  , J L Morenza  , E Bertran  , A Lousa
Published: July 2002

For pt.I see ibid., vol.20, p.951-57 (1987). The electrical conduction in polycrystalline In doped CdS films has been studied over the temperature range 77-300 K using Hall effect and conductivity measurements. In the preceding paper a model for the electrical conduction in polycrystalline CdS has been developed. The comparison of the model to the experimental data gives a satisfactory interpretation of the transport parameters in the In doped CdS films. The conduction is limited by the energy barriers, even at high dopant densities, and tunnelling transport becomes predominant. The trap state density increases with increasing dopant density.
The correlation of turbulent electric fields in a magnetised positive column
Authors: H Satoh  , M Matsumoto
Published: July 2002

In positive columns of H2, He and Ne gases, the statistical properties of turbulent fields Eperpendicular to (r,t) perpendicular to strong magnetic fields B have been investigated experimentally. It is found that the correlation times tau of Eperpendicular to (r,t) and the mean square value (Eperpendicular to
2(r)) correlate very well with the averaged ion saturation currents (ips(r)).
A strange attractor and its dimension of ionisation instability
Authors: K Ohe  , H Tanaka
Published: July 2002

Strange attractors are plotted for the ionisation instability excited in the weakly ionised positive columns of helium glow discharges. The transition to the turbulent state is experimentally observed. On calculating the correlation integral the periodic instability is revealed to have a low dimension and the turbulent one to have a high but finite dimension.
Investigation of I-V characteristics in polycrystalline BaTiO3
Authors: W Osak  , K Tkacz
Published: July 2002

Polarisation currents were investigated in polycrystalline BaTiO3in order to investigate its I-V characteristics. All but one of the measurements were performed at temperatures below the Curie point, for voltages between 1 V and 1000 V. The experimental curves consist of three parts of different shape: a region in which Ohm's law is valid, a region in agreement with the Fridkin-Kreher theory and a region showing a rapid increase in current for the highest applied fields. Comparison of the SCLC theory for ferroelectrics with the results obtained allows an estimate to be made of the temperature dependence of the carrier mobility in the sample. It increases from 10-8cm V-1s-1at 25 degrees C to 10-5cm V-1s-1at 140 degrees C.
NMR of oriented polymers: the effects of molecular motion on the second and fourth moments of drawn polyoxymethylene
Authors: V J McBrierty  , I R McDonald
Published: July 2002

An expression is derived for the motionally averaged NMR fourth moment of a partially oriented polymer. This result, taken together with expressions previously obtained for the second moment, makes it possible to study quantitatively the effects of different types of molecular motion. The case of drawn polyoxymethylene is used to show how the theory may be applied. Detailed comparisons are made with the previous experimental results of Olf and Peterlin. For this system it is found that the experimental data at room temperature may be accounted for by a model in which the chains are oscillating about the helical axis with an amplitude of 42°. At a higher temperature (100°C) it is necessary to assume, in addition, that the chains are undergoing rapid translational motion which has the effect of greatly reducing the intermolecular contributions to the moments.
The calculation of electron energy distributions and attachment coefficient for electron swarms in oxygen
Authors: J Lucas  , D A Price  , J L Moruzzi
Published: July 2002

Electron energy distributions have been calculated for electron swarms in oxygen for 15 less-than-or-eq, slantE/Nless-than-or-eq, slant 152 Td. These distributions satisfy the experimentally measured values of both drift velocity and the diffusion coefficient, and allowed the theoretical value of the rate of attachment (ηv) to be calculated to an accuracy of ±3%.

The calculated values of η/Nare dependent upon the measured values of the drift velocity, but since the latter show a large variation, the η/Nvalues have been represented by two limiting curves. The important feature of these curves is that η/Nquickly rises to its maximum value at aboutE/N=30 Td, from which it only gradually reduces asE/Nincreases. It has also been possible to obtain values of the momentum transfer cross section in oxygen for electron energies up to 10 eV. This cross section was found to have a simple form and to be very close in value to the total cross section.
Tensile failure of liquids under dynamic stressing
Authors: D C F Couzens  , D H Trevena
Published: July 2002

This paper contains an account of various experiments associated with the propagation of a pressure pulse up a vertical column of liquid. When such a pulse reaches the upper free surface of the liquid it is reflected downwards as a pulse of tension. This method therefore provides a means of subjecting the liquid to tension under dynamic conditions of stressing. If the value of the tension at any depth exceeds a certain critical value the liquid will cavitate. Values of this critical tensionTwere measured for liquids of varying viscosities η and it was found that the empirical relationT=kη0.1holds. Secondly, pulse propagation across the interface between two immiscible liquids was studied, and it was found that the maximum tension which could be sustained by an interface separating silicone oil and water is less than the tension which produces cavitation in either of these two liquids. Thirdly, it has been found that the cavitation produced shows several cycles of growth and collapse, a phenomenon which has been observed photographically by previous workers.
An interferometric method for the direct evaluation of principal stresses in plane-stress fields
Authors: P S Theocaris  , E Gdoutos
Published: July 2002

If a monochromatic and coherent light beam is normally incident on a thin plate under generalized plane-stress conditions, it is analysed into two plane-polarized bundles, whose directions of oscillation coincide with the principal stress directions. The plane-polarized rays are retarded when traversing the plate according to the Neumann-Maxwell law. The absolute variations of the optical paths depend on the thickness and the refractive index variations. Interference of the two primary reflections from the front and rear faces of the plate yields a contour map of the thickness and refractive index in the unloaded state, while the variation of the interference pattern express the variations of these quantities due to loading. If the incident light is successively polarized along either of the principal directions, the interference pattern of the reflected light rays along each direction yields the values of principal stresses. Loading of the specimen creates a displacement of the interference fringes along the field. By counting the number of fringes passing across each point, we can evaluate separately the two principal stresses. This pointwise method is much more sensitive and accurate than classical photoelasticity, since it measures absolute variations of the optical path. The method was applied to a concrete problem of elasticity and compared with other similar methods.
New data on the creep discharge at the surface of a dielectric
Authors: J S Brzosko  , A Konarzewski  , A Wojewodzka  , E Zukowski  , J Grudzinski
Published: July 2002

Discharge energy spectra were measured in air at the surface of a dielectric placed in an electric field of intensity V=V0sin (2 pi nu t), where V0is of the order of 103V mm-1and nu =50 Hz. The creep discharges were studied on the surface of a Seignette salt and an organic glass. An intensive group of discharges of energy of the order of 1 MeV was observed. This high-energy part is of lower intensity in the case of the ferroelectric material (Seignette salt). This fact is inconsistent with the interpretations given by authors who relate the discharges on the ferroelectric material surface to the domain surface.
Ionization growth in carbon dioxide
Authors: V J Conti  , A W Williams
Published: July 2002

Current growth measurements have been carried out in carbon dioxide for E/N (electric field/gas number density) values between 84*10-17and 166*10-17V cm2and N values between 4.5*1017and 220*1017cm-3. Ionization and attachment coefficients have been obtained which agree with the results of other workers at the lower pressures while the higher pressure results provide new data for carbon dioxide. The results of sparking potential measurements indicate Paschen's Law is obeyed and secondary ionization coefficients have been calculated. A decrease in the initial photoelectric current with increasing E/N and N has been observed.
Ionization and breakdown in oxygen
Authors: D T Blair  , H W Whittington
Published: July 2002

Measurements are reported of uniform-field breakdown voltages and of effective primary and secondary ionization coefficients in oxygen in the range 0.825*1018<or=N<or=9.90*1018cm-3, 1.1*10-15<or=E/N<or=2.1*10-15V cm-2, where N is the gas number density and E is the electric field strength. Oscillographic observations show that, over the range covered, the secondary electrons are produced only by photoelectric processes. Also reported are theoretical values of the secondary ionization coefficient, calculated using a one-dimensional model. The results show that for N=0.825*1018cm-3the secondary process can be described in terms of a single radiation component with an absorption coefficient of 38 cm-1(at N=25.1*1018cm-3). The secondary process appears to be mainly cathode photoemission but photo-ionization of the gas also plays a significant part. For N=3.30*1018cm-3, on the other hand, the calculated and measured secondary coefficients differ considerably and additional radiation components must be assumed to be active.
Scattering of 2-20 keV electrons in aluminium
Authors: A J Green  , R C G Leckey
Published: July 2002

An investigation of the major scattering processes involved when an incident electron suffers an appreciable change of momentum in a metal has been undertaken. The results of this study have been incorporated within a Monte Carlo framework, allowing calculations of energy and angular distributions of electrons, both transmitted and backscattered from films, to be made. The advantage of this treatment of the problem over earlier Monte Carlo work is that fundamental scattering processes are used rather than invoking mean energy-loss approximations, thus allowing an investigation to be made of the shortcomings of the theoretical treatments of the individual collision types.
Stresses and displacements in lamellar composites. II
Authors: R G C Arridge  , M W B Lock
Published: July 2002

For pt.I see ibid., vol.8, p.34 (1975). The two-dimensional problem in infinitesimal elasticity of a series of rectangular blocks of two different materials interleaved in a stack of infinite extent, loaded along its axis is solved by two complementary techniques. These are (i) a Fourier series solution of the Airy stress function and (ii) a finite element calculation. Tables and graphs of representative calculations are given. The shape of the distorted layers is of barrel and pincushion type and the positions of the maximum stresses differ from the predictions of more elementary calculations. The analysis is applied to the prediction of elastic moduli and failure mechanisms in real lamellar polymers modelled by long strips, such as oriented linear polyethylene, oriented polychloroprene, and cis-polyisoprene and 'elastic-hard' fibres.
The instability of electric arcs burning axially in accelerated flow
Authors: A M Howatson  , D R Topham
Published: July 2002

Experiments with electric arcs in an expansion tube fitted with a plane-symmetric converging nozzle section have demonstrated that the arc in accelerating flow is inherently unstable. An axisymmetric disturbance is generated which tends to develop into a helical mode in downstream regions. The evidence suggests that the source of instability is the shear layer between the cold flow and the hot, more highly accelerated arc column. For flows at low Reynolds number (<100) the arc column may be regarded as stable and its measured properties then lie close to the theoretical steady-state characteristic.
Apparatus for the measurement of Seebeck coefficient in solid biopolymers
Authors: D D Eley  , N C Lockhart  , C N Richardson
Published: July 2002

The design and evaluation of an improved apparatus for the sensitive detection of small thermoelectric effects in insulating samples are reported.
Compton scattering with synchrotron radiation
Authors: R S Holt  , M Cooper  , K R Lea
Published: July 2002

Compton scattering spectra from various metallic and ionic crystals have been measured at three energies in the range 40-80 keV using monochromated radiation from the 5 GeV electron synchrotron NINA. Good statistical accuracy was obtained with thin samples in short measurement periods. This indicates that Compton profile studies of the electron momentum density with synchrotron radiation are not only practicable but also currently offer the best method of minimising parasitic multiple scattering effects.
Application of Deschamps' method to the measurement at microwave frequencies of permittivities of liquids
Authors: M Levij  , P Bordewijk
Published: July 2002

The method first suggested by Deschamps (1953) for the determination of the scattering parameters of microwave junctions, is applied to the measurements of dielectric permittivities of liquids. This involves the use of a cell with two windows. Using the appropriate correction formula for these windows, the method permits determination of the permittivity of non-polar liquids with an accuracy better than 0.2%.
Fundamentals of ion motion in electric radio-frequency multipole fields
Authors: M H Friedman  , A L Yergey  , J E Campana
Published: July 2002

The fundamentals of ion motion in electromagnetic fields are reviewed in detail with a special emphasis on electric radio-frequency (RF) fields which are used frequently in dynamic mass spectrometry. Forces and effects on ions in electromagnetic fields which are typically neglected, but which may be important in practical applications are reviewed and discussed for completeness. A method, based on complex variable theory, is developed for finding the potential function of 'ideal multipole electromagnetic fields'. Application of this method for the determination of potential functions and differential equations of ion motion is demonstrated with reference to the electric radio-frequency dipole, quadrupole, hexapole, octupole and decapole fields. This is the first time that these topics have been addressed in one unified and fundamental literature presentation. The results and implications of this preliminary communication and tutorial are of importance in ion physics and dynamic mass spectrometry.
A 40 T pulsed field de Haas-van Alphen spectrometer
Authors: A P J van Deursen  , A R de Vroomen
Published: July 2002

A pulsed field system is described, dedicated to de Haas-van Alphen experiments. Owing to the high field a good sensitivity is obtained, expressed in terms of a maximum allowable value for m*TD. This strongly relaxes the condition on the quality of single crystals for a Fermi surface study. Among the examples given the authors mention the observation of quantum oscillations from the neck orbit in the alloy Au1-xAgxfor a concentration x of 15%. The system is online coupled to a minicomputer. The data are handled quickly and signal averaging is possible.
An erosion technique for the measurement of the shear stress field on a flat plate
Authors: D X Viegas  , A R Janeiro Borges
Published: July 2002

A simple technique for the measurement of the shear stress field on a flat surface is presented. The technique is based on a correlation established between the erosion patterns of fine grains spread on a horizontal smooth plate and the known shear stress values obtained by conventional, well established, means for the flow produced by a round jet perpendicular to a flat plate. The critical shear stress values are found to be practically independent of the overall flow configuration and properties, and depend on the particle distribution and characteristics. Various granular materials of different sizes, shapes and densities were used at varying surface concentration and flow conditions. The experimental scatter of the results is small enough to make the erosion technique useful for quantitative assessment of wall shear stresses with an accuracy compatible with most practical applications. Furthermore it combines simplicity with promptness, given that in each run a curve of constant shear stress is obtained instead of a single local value.
Measurement of surface temperature with a thermally compensated probe
Authors: K Kalliomaki  , P Wallin
Published: July 2002

An electronically controlled differential transducer using microthermocouples (diameter <30 mu m) has been developed. The transducer is suitable for measuring the surface temperature of a small area (<1 mm2) when the thermal conductivity of the surface is low. The contact pressure of the transducer is very low, so that it is possible, for example, to measure a corneal temperature without causing irritation. It is accurate to less than 0.5 degrees C and reproduces to 0.1 degrees C. The transducer operates when the air speed is from 0 to 10 m s-1 and the ambient temperature is as low as -25 degrees C.
A method for determining photoconductive response times
Authors: Z Hurych  , C Wang
Published: July 2002

It is shown how the photoconductive response time tau 0 can be readily determined from the phase shift between the exciting radiation and the photocurrent using a lock-in amplifier technique.
Frequency modulated NMR spectrometer for measuring of internal magnetic fields
Authors: F I Toth  , K Tompa  , G Gruner
Published: July 2002

A Robinson-type oscillator with an automatic frequency control circuit suitable for the measurement of internal magnetic fields, is described. An AFC circuit ensures that the tuning of the tank circuit is such that the first harmonic of the modulation frequency is kept at a minimum in the detector output. Cascade amplifier states permit operation at higher frequencies with a better signal-to-noise ratio and larger sweep amplitudes than with other types of amplifiers. The use of the equipment is demonstrated by measuring the 57Fe NMR signal in iron and iron-cobalt alloys.
Measurement of vapour density pulses
Authors: D R Airey  , J H Bach
Published: July 2002

A method is described for measuring rapid (1-10 ms) changes in vapour density close to the plasma in a high current arc discharge at pressures of 1-10 mTorr. A high pressure ionization gauge is used with a fast emission current stabilization circuit. Using the gauge a figure has been derived for the pulsed vapour emission from an anchored mercury cathode of 3.8*1016 molecules C-1 which is within the range of values given in previous data for steady state emission.
Secondary electron detector, with an extended life, for use in a scanning electron microscope
Authors: D C Marshall  , J Stephen
Published: July 2002

The plastic scintillator tip used as the secondary electron detector of a scanning microscope has a limited working life particularly with high electron beam currents. A detector with an extended life and capable of working up to beam currents of 3*10-6 A has been made by replacing the plastic scintillator tip with one made of a lithium glass scintillator.
A system of disc-stabilized DC arc and solution nebulization device for the investigation of multicomponent plasmas
Authors: H Raab
Published: July 2002

A disc-stabilized plasma jet with a solution nebulization device was developed for the spectroscopy of aqueous solutions of sample concentrations smaller than 1000 ppm and for the investigation of multicomponent plasmas. The technical assembly of the arc and the nebulization device are described and the various applications of the apparatus are discussed. The enrichment of the sample in the aerosol produced in the introduction system can be explained by heating the spray chamber and subsequent cooling of the aerosol.
Fast driver stage in a high-voltage discharge pulser
Authors: H Stori  , T D Mark  , M Langenwalter  , M Pahl
Published: July 2002

A fast transistor driver circuit with rise and decay times <50 ns is described. This driver was developed to be employed in a high-voltage discharge pulser.
The direct linearisation approach to hierarchies of integrable PDEs in 2 + 1 dimensions: I. Lattice equations and the differential-difference hierarchies
Authors: Nijhoff F W , Capel H W
Published: July 2002

Using the direct linearising transform (DLT) method a systematic study is undertaken of hierarchies of nonlinear evolution equations. The starting point is a general class of integrable equations on a three-dimensional lattice where the variables take values in the algebra of N*N matrices. From these lattice equations by performing suitable continuum limits the authors obtain hierarchies of integrable differential-difference and partial differential equations in successive steps. They restrict themselves to continuum limits leading to equations with one continuous (time) variable and two discrete lattice evolution variables.
The Nanomanufacturing Programme at the National
Science Foundation
Authors: Haris Doumanidis
Published: July 2002

This paper describes the new Nanomanufacturing
programme at the National Science Foundation (NSF). This programme
focuses on up-scaling fabrication and synthesis of functional
nanoscale structures, devices and systems. It also emphasizes
integration across multiple dimensional scales,
multi-functionality across several energetic domains, and new
design and manufacturing approaches such as biomimetics. The
paper elaborates on key issues to this goal, including research
in precursor nanomaterials and nanoparticles; fabrication,
analysis and synthesis processes; instrumentation and equipment
for characterization and processing; theory, modelling,
simulation and control; design and integration of nanodevices
and systems; and nanomanufacturing education and dissemination
strategies. The discussion suggests a number of outstanding
research issues and topics, and illustrates them with current
research projects in nanomaterials processing, nanomachines and
metrology, nanosystems and design etc supported by the NSF.
Open subgroups of 𝐺 and almost periodic functionals on 𝐴(𝐺)
Authors: Hu Zhiguo
Published: July 2002

Let

G
G

be a locally compact group and let

C

δ

∗

(
G
)

C_{\delta }^{*}(G)

denote the

C

∗

C^{*}

-algebra generated by left translation operators on

L

2

(
G
)

L^{2}(G)

. Let

A
P
(

G
^

)

AP(\hat {G})

and

W
A
P
(

G
^

)

WAP(\hat {G})

be the spaces of almost periodic and weakly almost periodic functionals on the Fourier algebra

A
(
G
)

A(G)

, respectively. It is shown that if

G
G

contains an open abelian subgroup, then (1)

A
P
(

G
^

)
=

C

δ

∗

(
G
)

AP(\hat {G}) = C_{\delta }^{*}(G)

if and only if

A
P
(

G
^

)

c

AP(\hat {G})_{c}

is norm dense in

A
P
(

G
^

)

AP(\hat {G})

; (2)

W
A
P
(

G
^

)

WAP(\hat {G})

is a

C

∗

C^{*}

-algebra if

W
A
P
(

G
^

)

c

WAP(\hat {G})_{c}

is norm dense in

W
A
P
(

G
^

)

WAP(\hat {G})

, where

X

c

X_{c}

denotes the set of elements in

X
X

with compact support. In particular, for any amenable locally compact group

G
G

which contains an open abelian subgroup,

G
G

has the dual Bohr approximation property and

W
A
P
(

G
^

)

WAP(\hat {G})

is a

C

∗

C^{*}

-algebra.
A co-Frobenius Hopf algebra with a separable Galois extension is finite
Authors: Beattie M. , Dăscălescu S. , Raianu Ş.
Published: July 2002

If

H
H

is a co-Frobenius Hopf algebra over a field, having a Galois

H
H

-object

A
A

which is separable over

A

c
o
H

A^{coH}

, its ring of coinvariants, then

H
H

is finite dimensional.
Asymptotically isometric copies of ℓ^{∞} in Banach spaces and a theorem of Bessaga and Pelczynski
Authors: Dowling Patrick , Randrianantoanina Narcisse
Published: July 2002

We introduce the notion of a Banach space containing an asymptotically isometric copy of

ℓ
∞

\ell ^\infty

. A well known result of Bessaga and Pełczyński states a Banach space

X
X

contains a complemented isomorphic copy of

ℓ
1

\ell ^1

if and only if

X
∗

X^*

contains an isomorphic copy of

c
0

c_0

if and only if

X
∗

X^*

contains an isomorphic copy of

ℓ
∞

\ell ^\infty

. We prove an asymptotically isometric analogue of this result.
Analytic linearizability of some resonant vector fields
Authors: Basto-Gonçalves J. , Cruz I.
Published: July 2002

A method allowing the linearization of vector fields with resonant eigenvalues is presented, the admissible nonlinearities being characterized by conditions that are easy to check.
Finiteness of polyhedral decompositions of cusped hyperbolic manifolds obtained by the Epstein-Penner’s method
Authors: Akiyoshi Hirotaka
Published: July 2002

Epstein and Penner give a canonical method of decomposing a cusped hyperbolic manifold into ideal polyhedra. The decomposition depends on arbitrarily specified weights for the cusps. From the construction, it is rather obvious that there appear at most a finite number of decompositions if the given weights are slightly changed. However, since the space of weights is not compact, it is not clear whether the total number of such decompositions is finite. In this paper we prove that the number of polyhedral decompositions of a cusped hyperbolic manifold obtained by the Epstein-Penner’s method is finite.
Compact operators whose real and imaginary parts are positive
Authors: Bhatia Rajendra , Zhan Xingzhi
Published: July 2002

Let

T
T

be a compact operator on a Hilbert space such that the operators

A
=

1
2

(
T
+

T

∗

)

A = \frac {1}{2} (T + T^{*})

and

B
=

1

2
i

(
T
−

T

∗

)

B = \frac {1}{2i}(T-T^{*})

are positive. Let

{

s

j

}

\{ s_{j}\}

be the singular values of

T
T

and

{

α

j

}
,
{

β

j

}

\{ \alpha _{j}\} , \{ \beta _{j}\}

the eigenvalues of

A
,
B

A,B

, all enumerated in decreasing order. We show that the sequence

{

s

j

2

}

\{ s^{2}_{j}\}

is majorised by

{

α

j

2

+

β

j

2

}

\{ \alpha ^{2}_{j} + \beta ^{2}_{j}\}

. An important consequence is that, when

p
≥
2
,
 
‖
T

‖

p

2

p \ge 2, ~\| T\| ^{2}_{p}

is less than or equal to

‖
A

‖

p

2

+
‖
B

‖

p

2

\| A\| ^{2}_{p} + \| B\| ^{2}_{p}

, and when

1
≤
p
≤
2
,

1\le p \le 2,

this inequality is reversed.
Realisation of special Kähler manifolds as parabolic spheres
Authors: Baues Oliver , Cortés Vicente
Published: July 2002

We prove that any simply connected special Kähler manifold admits a canonical immersion as a parabolic affine hypersphere. As an application, we associate a parabolic affine hypersphere to any nondegenerate holomorphic function. We also show that a classical result of Calabi and Pogorelov on parabolic spheres implies Lu’s theorem on complete special Kähler manifolds with a positive definite metric.
A characterization of heat balls by a mean value property for temperatures
Authors: Suzuki Noriaki , Watson Neil
Published: July 2002

We discuss an inverse mean value property of solutions of the heat equation. We show that, under certain conditions, a volume mean value identity characterizes heat balls.