bluuebunny/crossref_metadata_2025 huggingface dataset:
Solution of the Boltzmann equation with ionisation and attachment: application to SF6
Authors: M Yousfi  , P Segur  , T Vassiliadis
Published: July 2002

A new method of solution of the Boltzmann equation, able to take into account the full anisotropy of the distribution function, is applied to the calculation of swarm parameters in certain reactive gases. The authors first checked the accuracy of the method on the model gas of Lucas and Saelee (1975) where comparisons can be made with results of other authors. Calculations are then carried out with the authors' method in SF6using three sets of cross-sections available in the literature. The results obtained are compared with those of the standard two-term approximation. It is seen that large differences occur, mainly for the determination of the attachment and transverse diffusion coefficients. Inconsistencies between the three sets of cross-sections used are demonstrated.
Dynamics and optics of oil hills and oilscapes
Authors: L H Tanner  , M V Berry
Published: July 2002

A pimple or dimple on an otherwise uniform oil film on a flat surface decays under the action of surface tension and viscosity. The process is followed analytically from the Navier-Stokes equation, and by optical experiments employing interferometry and the observation of caustics of refraction. Point or line disturbances give a range of recognisable oil hills and ridges, and the theory predicts their shapes and how these scale with time. If the surface is disturbed in a distributed random way, the interferometric contour map shows a random oilscape. The statistics of the oilscape develop self-similarly by changes in lateral and vertical scales which may be predicted and observed. The theory is well verified for the hills, ridges and oilscapes.
Interpretation of surface potential kinetics in HDPE by a trapping model
Authors: H von Berlepsch
Published: July 2002

This paper presents an empirical decay relationship containing five parameters depending on field strength and temperature for describing the isothermal surface potential kinetics of high-density polyethylene (HDPE) over a wide range of field strength and temperature for samples of different thickness subjected to positive or negative corona discharge. Based on a mathematical model describing the hopping mechanism, modulated by surface and bulk traps, of injected charge carriers, a theoretical explanation of the relationship is provided, the model parameters being determined by a fitting procedure. The transport parameters obtained, as charge carrier mobility, hopping distance, trap concentration, trap depth and attempt-to-escape frequency, are discussed.
The dielectric properties of muscovite mica along the cleavage planes
Authors: M A Chaudhry  , A K Jonscher  , R M Hill
Published: July 2002

The dielectric responses of mica along the cleavage planes has been measured in the frequency range between 0.01 Hz and 100 kHz and in the temperature range between 368K and 173K. The loss parallel to the planes is two to three orders of magnitude higher that that measured normal to the planes. The response is due to relaxation of ions along the cleavage planes, including interlaminal and surface water molecules.
Pressure and temperature dependence of dielectric properties of lithium potassium sulphate
Authors: S Fujimoto  , N Yasuda  , H Hibino
Published: July 2002

The pressure (p) and temperature (T) dependence of the dielectric and dilatometric properties of single crystal LiKSO4have been measured in the pressure range up to 8 kbar and over the temperature range -120 to +70 degrees C. The stability range of the intermediate phase II decreases as the pressure rises and phase II disappears at a triple point. This phase is stable over the range -84<T<-63 degrees C on cooling and -79<T<-22 degrees C on heating at atmospheric pressure. The triple point also varies with heating/cooling, being at -59.0+or-0.5 degrees C, 2.1+or-0.1 kbar on cooling or increasing pressure and 16.5+or-0.3 degrees C. 4.3+or-0.1 kbar on heating or decreasing pressure. The variation of permittivity and spontaneous polarisation with temperature is explained in terms of the free energy and the piezoelectric coupling.
A study of sorbed water on cellulose by the thermally stimulated depolarisation technique
Authors: P Pissis
Published: July 2002

The dielectric behaviour of compressed pellets of hydrated cellulose was studied by the thermally stimulated depolarisation (TSD) current technique in the temperature range of 77-300K in an attempt to determine the binding modes of water molecules. The water content was varied between 1.1 and 22.1%. Two broad dielectric dispersion bands were observed. The first dispersion band at lower temperatures is attributed to the reorientation of sorbed water molecules. A model is proposed which accounts for the different dielectric behaviour of water molecules in cellulose and in pure water. The second dispersion band at higher temperatures is complex. Its magnitude and position depend strongly on the water content.
Le microscope électronique 1·5 MV
Authors: G Dupouy
Published: July 2002

This paper deals with the high-voltage (1·5 MV) Toulouse electron microscope and contains some unpublished information about the objective lens and the column of the instrument. Some examples are given of the advantage of working at very high voltages; in particular the increase of resolving power and the spectacular reduction of chromatic aberration are pointed out. A few micrographs give an idea of the results obtained with this microscope.
Statistics of electron multiplication in the presence of primary and secondary ionisation processes
Authors: C J Evans
Published: July 2002

A theoretical study is made of the development of a gas discharge in which two ionisation processes are present: primary ionisation due to electron impact in the gas and secondary ionisation due to photo-electric emission at the cathode, with negligible delay. The discharge is allowed to develop continuously in time, in contrast to previous work in which the time was considered to progress in discrete steps. Equations are derived which give the probability of finding any number of electrons in the discharge at a given time. These are solved for the particular problem of finding the probability that the discharge should have become extinguished at any time. It is shown that the discrete-time model gives reasonable agreement with these calculations.
Laser heating versus resistive heating in the field-desorption mass spectrometry of organic polymers
Authors: A I Tottszer  , G M Neumann  , P J Derrick  , G D Willett
Published: July 2002

Laser heating of field-desorption emitters is evaluated against conventional resistive heating by comparing mass spectra of organic polymers (polypropylene glycol, polystyrene and polymethyl methacrylate). The temperature dependence of such spectra allows comparison at equivalent temperatures of the mass spectrometric sensitivities obtained with the two heating methods. No significant differences in sensitivity are observed. The power required for laser heating is 85% of that required using resistive heating to produce equivalent field desorption conditions.
Departures from equilibrium in a free-burning argon arc
Authors: L E Cram  , L Poladian  , G Roumeliotis
Published: July 2002

A magnetogasdynamic arc model due to Kovitya and Lowke has been combined with a collisional-radiative model of the argon atom to show how intense radiation from an arc can produce excited-state densities in the boundary of the arc which are far in excess of the densities corresponding to thermodynamic equilibrium. Quantitative predictions based on this model have been compared with measurements recently reported by Farmer and Haddad. There are encouraging similarities between theory and experiment, although it is suggested that the theory could be further improved by including the effect of resonance radiation which is scattered in the arc boundary.
A multiple scattering theoretical approach to the effective thermal conductivity of disordered solids and its dependence on phase geometry
Authors: T K Ballabh  , T R Middya  , A N Basu
Published: July 2002

The authors have estimated the effective thermal conductivity of a polycrystal with orthorhombic, hexagonal, trigonal and tetragonal symmetries, in terms of the principal thermal conductivities of an individual crystal, within the framework of multiple scattering theory. In addition the self-consistent values and different bounds for the effective thermal conductivity are computed for various shapes of the crystallites. It is found that the optical potential bounds depend strongly on the shape of the crystallite. It may be mentioned that the results computed for thermal conductivity are equally applicable to the electrical conductivity, magnetic permeability and dielectric constants for such a medium.
Application of the many-body theory of Dissado and Hill to the complex permittivity of 1,2,4-butanetriol at pressures to 1 GPa
Authors: H Forsman
Published: July 2002

The dielectric relaxation of 1,2,4-butanetriol in its supercooled liquid state has been studied at pressures up to 1 GPa. The frequency of the applied field is varied within the range from 1 mHz to 10 MHz. The automated and computer controlled dielectric spectroscopy measuring system is presented in detail. It is found that neither the dielectric relaxation spectra nor the static susceptibility can be accurately described within the theoretical framework which only considers the behaviour of non-interacting dipoles. Instead, the dielectric loss is described by the many-body correlated cluster theory of Dissado and Hill (1983). A relationship between the correlation parameters and the static susceptibility is discussed. The results are compared with previous findings on the homologues glycerol and 1,2,6-hexanetriol.
Dielectric breakdown of high-density polyethylene (HDPE) under high pressure
Authors: M Farkh  , Hoang-The-Giam  , R El Hayani  , Bui Ai  , B Dalle  , J Perret  , C Simon  , J Berdala
Published: July 2002

The dielectric strength of high-density polyethylene was measured under high hydrostatic pressure (50 to 500 bar) at temperatures of 30, 45 and 70 degrees C. Results have shown that the breakdown field Eb increases with pressure and decreases with temperature for short-time tests.
Theoretical basis for the statistics of dielectric breakdown
Authors: L A Dissado
Published: July 2002

The engineers' approach to dielectric breakdown has traditionally been one of testing leading to life prediction and material comparison. On the other hand, the scientist has attempted to understand the mechanism of specific breakdown processes. It is shown here that the former approach is prone to ambiguity and that a need exists to understand not just the physics of breakdown processes but also their resulting statistics. A number of statistical models are developed and discussed with the aid of experimental data. Finally it is shown how the general trends obtained can be used to aid the interpretation of the engineers' data.
Stress in silicon films deposited heteroepitaxially on insulating substrates with particular reference to corundum
Authors: Diana M Jefkins
Published: July 2002

The stresses in a thin silicon film deposited epitaxially on to a corundum substrate, arising from the differences in thermal expansion, are considered theoretically and the results are found to be in agreement with published experimental data. It is shown that the stress problem in such films cannot be overcome in the context of the two-layer system, though some alleviation can be obtained by the application of stringent dimensional conditions. Theoretical considerations show that the use of a third layer of material as a backing for the corundum substrate can reduce the stress at the silicon-corundum interface to zero and that at the silicon surface to a negligibly small value.
A theoretical consideration of some defects in electron optical images. A formulation of the problem for the incoherent case
Authors: R A Crick  , D L Misell
Published: July 2002

Expressions are derived for the resolution functions appropriate to chromatic and spherical aberration in electron microscopy. The resolution functions are given for the two components of the scattered electron beam (i.e. the elastic and inelastic components). The analysis given here for the elastic component is valid only in the case of incoherent radiation (i.e. using a large condenser aperture). The treatment of aberrations caused by inelastic scattering in the specimen assumes that the inelastically scattered radiation is incoherent, an assumption which is valid for amorphous specimens.

Numerical results are presented for the angular distributions for plural elastic and inelastic electron scattering in `amorphous' carbon films. It is shown that the contribution of the inelastic scattering to the intensity scattered within the objective aperture (semi-angle in the range 10−3-10−2rad) exceeds the elastic scattering by an order of magnitude for film thicknesses in the range 50-2000 Å and for incident electrons of energy 100 keV. The variation of the electron energy loss spectrum of carbon with the angle of scattering is given. The angular and energy distributions are used to calculate the spherical, chromatic and combined aberration functions appropriate to carbon specimens of thickness 50-1000 Å and for 100 keV electrons. In the incoherent approximation, it is concluded that for carbonaceous materials, inelastic electron scattering dominates all resolution considerations; in particular the chromatic aberration effect due to the inelastic scattering is far more significant than the contribution from spherical aberration.

The present treatment of aberrations would seem relevant to low voltage electron microscopy and to thick (about 1000 Å) films of carbonaceous materials at conventional voltages; in both these situations inelastic electron scattering determines the resolution attainable.
An arc column in forced axial convection
Authors: A M Howatson  , R D Rowe
Published: July 2002

Experimental results for an axial arc column in the steady flow behind the shock front in a shock tube are presented. Tests were made at currents between 5 A and 150 A for free-stream Mach numbers of 0·4, 0·7, 1·0 and 1·3 in nitrogen gas at a pressure of one atmosphere. A semi-empirical heat transfer theory is proposed and an excellent correlation of the voltage gradient to current data is found.
The determination of the optical constants of thin films from measurements of reflectance and transmittance at normal incidence
Authors: R E Denton  , R D Campbell  , S G Tomlin
Published: July 2002

The derivation of the componentsnandkof the complex refractive index of a thin film from measurements, at normal incidence, of reflectanceRand transmittanceTis complicated by the existence of multiple solutions of the relevant equations. It is shown that, although use of Tomlin's expressions for (1 ±R)/Trather than Heavens's explicit formulae forRandTseparately simplifies the problem, it is still necessary to consider very carefully the multiple solutions. A procedure is given for determining the correct solutions fornandk, and also for accurately fixing the film thickness, provided that the film is a homogeneous single layer on a substrate.

Some experimental results have not yielded to this treatment and in these cases it has been found necessary to assume the presence of a surface layer (often, but not necessarily, an oxide layer) and to make use of the equations in the preceding paper which relate to a double layer on a substrate. It is shown how this may be done in such a way as to obtain the correct dispersion curve for the material, together with its thickness, and that of the surface layer.
The accumulation of damage in a glass-reinforced plastic under tensile and fatigue loading
Authors: M J Owen  , R J Howe
Published: July 2002

Glass chopped strand mat/polyester resin specimens were subjected to tensile or fatigue loading. From examination of polished specimen edges fibre debonding and resin crack damage were quantified. The damage depended on the topography of the site observed, but by expressing damage as a fraction of that present at failure all the results could be reduced to single, nonlinear curves for debonding and cracking. Resin cracking damage and the loss of residual tensile strength of damaged specimens gave curves of similar quadratic form. It was concluded that the development of resin cracking was primarily responsible for the progressive loss of strength in a fatigue specimen. Damage depended on cycle ratio but not on fatigue stress. It was suggested that a suitable cumulative fatigue damage law would be nonlinear and stress-independent.
Cathode-ray-induced space and surface currents in wurtzite crystals
Authors: W Ehrenberg  , R P Shrivastava
Published: July 2002

Electric currents induced in wurtzite crystals by steady streams of cathode rays are studied experimentally, with the view to elucidating the electronic properties of these crystals. It is found that currents are carried in surface channels as well as through the bulk of the crystals, the range of the bulk currents being limited to about 200 μm. Crystals grown from the melt, from the vapour phase and naturally grown platelets are used. The platelets have built-in fields which influence the currents.
On the motion of small spheres in gases III. Drag and heat transfer
Authors: M M R Williams
Published: July 2002

From the general theory of a previous paper, formulae have been developed for the rate of change of momentum and the rate of energy transfer due to collisions of gas atoms with a massive sphere. The sphere has arbitrary gas-surface interaction properties, but must be small compared with the mean free path of a gas atom.

The drag coefficient, recovery temperature and modified Stanton number have been calculated for a number of surface scattering models including that of Kuscer and Cercignani. Results indicate that the type of surface can influence the integral parameters mentioned above to a considerable degree. It is also shown that the change in surface temperature of the sphere due to heat transfer can affect quite profoundly the drag forces at high Mach numbers. Neglect of these effects leads to an underestimate of the drag coefficientCDat high speeds of about 40%.

The equations of motion for a spherical dust grain moving in interstellar gas are set up and solved in the high- and low-velocity limits. Some estimates of the slowing-down times and stopping distances for these particles are obtained, and an extension of the work to non-uniform atmospheres is discussed.
Microscopic evolution of the ionizing collision frequency in Townsend avalanches
Authors: G Vidal  , J Lacaze  , J Maurel
Published: July 2002

Information obtained from the analysis of the spectra of the Townsend avalanche amplification provides the basis for the study of average microscopic behaviour of the electrons. The electrical fieldEis uniform, and the avalanches are triggered off at the cathode by a single primary electron. Experimental conditions are such that no secondary effects or space charge can take place. The results of these experiments (methane, 50<E/p<300 V cm−1Torr−1) prove that the multiplication process is a non-markovian one, and also that it rapidly attains asymptotic behaviour. When interpreted in the light of the age-dependent branching processes, the results enable one to determine some distribution functions: the distributiong(θ) of the time intervals θ between two ionizing collisions, the multiplication coefficienta(τ) characterizing the ionizing capacity of the electron as a function of its `age' τ.a(τ) describes the phenomenon more precisely than does the first Townsend coefficient. The application of this method whenE/pandpdare constant (prepresents gas pressure anddgap distance) shows that these distributions comply with the similarity principle.
The fracture toughness of a glass chopped-strand-mat/polyester-resin laminate
Authors: A W Holdsworth  , S Morris  , M J Owen
Published: July 2002

Measurements of the critical strain energy release rateGcand the critical crack tip stress intensity factorKchave been made on chopped-strand-mat/polyester-resin laminates using centre-notched specimens of constant width and varying initial crack length. In the determination ofGcallowance was made for irrecoverable energy due to progressive damage. TheGcvalues were converted toKcvalues using the relationshipKc2=EGc, whereEis the initial modulus of the material. The direct determination ofKcgave lower values. However, when Irwin's plastic-zone correction factor for metals was applied, using the resin cracking stress as an equivalent yield stress, the corrected values compared well with those obtained from theGcvalues. All the results showed a variation ofKcwith initial crack length.
Investigation of the straggling effect on characteristic X-ray emission in thick targets
Authors: J Henoc  , F Maurice
Published: July 2002

The energy straggling effect has been studied by Bishop (1965) in a Monte Carlo calculation to investigate the mean energy losses of electrons in a thick target. The authors incorporate the statistical energy losses of electrons in a Monte Carlo calculation of the depth distribution of characteristic X-ray production.
Theory of frequency optimisation for hot-film anemometers
Authors: P Freymuth
Published: July 2002

The two-parameter frequency optimisation theory which was originally developed for the constant-temperature hot-wire anemometer is extended to hot-film anemometers. It is found that the constant-temperature hot-film anemometer behaves as a control system of order5/2which allows for a two-parameter optimisation of its dynamic response. The cut-off frequency of the hot-film anemometer can be estimated by means of a sine-wave test. A combination of sine-wave and square-wave testing seems to be the best strategy for optimising the system.
The measurement of convective heat loss from a solid surface to an airstream
Authors: H Y Wong
Published: July 2002

A device capable of measuring the local convective heat transfer from a solid surface to an airstream is described. It has a novel feature in that it can operate in transient three-dimensional flow conditions and is therefore particularly suitable for measuring heat loss from most modern buildings having a relatively smooth surface. Its performance has been found satisfactory when comparing the results with those derived from the heat transfer equations for a flat plate.
Electron interferometry and interference electron microscopy
Authors: G F Missiroli  , G Pozzi  , U Valdre
Published: July 2002

A state-of-the-art review of electron interferometry and interference electron microscopy is given. The various types of interferometry device, interferometers and interference microscopes, which have been proposed and/or constructed are reviewed and commented upon. The electron biprism, by far the most successful interferometry device, is treated in some detail from both the experimental and theoretical (geometric and wave optics) points of view. The applications of electron interferometry are presented with particular reference to off-axis electron holography. Finally the future perspectives are indicated.
Optimisation of low-perveance electron gun by experimental and numerical methods
Authors: Z Maternia  , W Slowko
Published: July 2002

The paper presents a proposed method for improving the electron gun used for microscopes or similar electron beam devices. The electron gun has been divided into two zones: the high perveance cathode zone and the low perveance lens zone. The final virtual crossover of the gun is thus the image of the exit pupil of the cathode zone. This image is produced by the action of the lens zone. The basic assumption of this approach is that the electron brightness does not depend significantly on the lens zone electron-optical parameters. Based on this assumption the optimisation of the electrodes has been carried out. This has been done experimentally in the cathode zone and by means of numerical calculations in the lens zone. Results obtained for the scanning electron microscope gun are presented as an example of this approach.
Rapid recording of the characteristic parameters of the ferromagnetic hysteresis loop
Authors: W E Martin  , J Wieser
Published: July 2002

An apparatus has been developed to record rapidly and continuously fast changes of ferromagnetic parameters represented by the hysteresis loop, occurring e.g. under normal conditions in metal-hydrogen systems with the ferromagnetic component nickel. For ths application, the apparatus is capable of both continuous oscilloscopic tracing and automatic recording of the hysteresis loop by integrating analogue-to-digital conversion based on the Dual-Slope method with digital data readout at power frequencies of 50 Hz.
Sixty years of scientific instruments
Authors: A E Bailey
Published: July 2002

The first regular issue of the Journal of Scientific Instruments was published sixty years ago. This paper gives a brief account of the history of the Journal. which later became Journal of Physics E: Scientific Instruments, and discusses how developments in instrument science and technology have been reflected in its pages.
A microcomputer-controlled flow microcalorimeter
Authors: O Lopez-Mayorga  , P L Mateo  , J Mira  , M Cortijo
Published: July 2002

The connection of an LKB flow microcalorimetric unit. Model 2107, to a development system based on an M-6800 microcomputer is described. The microcalorimeter-microcomputer system can work under either open-loop or closed-loop control. The latter type of control results in the total automation of a whole set of isothermal measurements corresponding to a complete thermal or thermal-potentiometric titration. Two different configurations of commanded peristaltic pumps (or high precision syringes) to control the reagent concentrations within the calorimetric cell are shown. Some of the advantages of this automation, such as higher precision, less material required and time saving, are emphasised, particularly with regard to scarce biological materials. The thermal and potentiometric titration of Tris (tris(hydroxymethyl)-aminoethane) is included as a practical example.
Quantitative mass spectrometer analysis of very low impurity concentrations in gases
Authors: H J Christ  , D Schwanke  , Th Uihlein  , H G Sockel
Published: July 2002

An apparatus for the quantitative analysis of gas impurities by means of a quadrupole mass spectrometer is described. The goal-to be able to measure and record component concentrations down to 0.1 PPM-requires some special construction techniques and operating conditions in order to be realised. The special calibration and analysis procedures necessary for the quantitative measurement of small concentrations of gas components within a carrier gas are described. The usefulness of both the apparatus presented and the evaluation method is demonstrated by means of specific examples.
Biosensors
Authors: C R Lowe
Published: July 2002

This paper will commence with a general introduction
to the concepts and technology of biosensors including some
discussion of the need for sensors, the range of analytes that can
be measured, the areas of application, the construction of
sensors with a biological recognition/response system and the
range of transducer technologies that are potentially amenable
to sensor use. Examples of sensor technologies for the
monitoring of substrates, proteins and immunoanalytes will be
given. For example. the development will be described of a novel
amperometric sensor for glucose and other substrates which
incorporates oxidases in conducting organic polymers and of a
miniaturised surface conductivity device for monitoring analytes
such as urea. Devices capable of detecting proteinaceous
analytes based on optoelectronic, sensitised semiconductor,
conductimetric immunosensor and various sophisticated optical
techniques will also be discussed. Future trends in biosensor
research will be described.
Apparatus for the extraction of gases from blood and tissue samples
Authors: D E Evans  , V Flook  , W W Mapleson
Published: July 2002

An apparatus for vacuum extraction of gases from liquid or semi-solid samples is described. It has been used for the extraction of anaesthetic agents from blood and tissue samples. The performance is consistent with 100% extraction and 99% recovery of nitrous oxide, the standard deviation of the mean value for handling and extracting nitrus oxide from water being +or-1.8% of the mean. A theoretical assessment is described and demonstrates the changes in extraction procedure required for gas-sample combinations having Ostwald solubility coefficients greater than that of nitrous oxide in water (0.66 at 20 degrees C).
A versatile automatic X-ray diffractometer for the study of high vapour pressure liquids
Authors: R Causer  , S P Isherwood  , B R Orton  , R L T Street
Published: July 2002

An automatic, horizontal axis X-ray diffractometer is described employing Bragg-Brentano para-focusing geometry, with post diffraction monochromatization. The diffractometer is specially designed to examine either the top free surface or, in the present work, the lower surface of a liquid. The lower surface is irradiated through a beryllium window in the base of a cell. Measurements on liquid mercury at 23 degrees C indicate that the technique produces diffraction patterns in good agreement with those of other workers.
A rotary atomization technique for bulk splat cooling
Authors: H Jones  , M H Burden
Published: July 2002

An apparatus for the production of bulk quantities of splat- cooled material is described. The technique involves feeding liquid alloy into a rapidly revolving crucible from the lip of which the atomized metal is impelled on to a surrounding cooled substrate. The performance of the apparatus is discussed on the basis of experience with Al-Fe alloys.
Cryostats for vacuum ultraviolet spectroscopy
Authors: R A George  , I Roberts  , E G Wilson
Published: July 2002

Two cryostats for vacuum ultraviolet spectroscopy are described, one for temperatures between 77 and 300 K, the other for a temperature of 4.2 K. They are designed so as to reduce to a minimum the rate of condensation of a solid contaminant film on to the cold samples from the residual vacuum of the system. At the lowest rate obtained, the absorption of L alpha radiation (121.6 nm) by the growing film increases by only 0.2% per hour. The nature of the contaminants is discussed.
A thermoluminescent image storage panel
Authors: P Broadhead  , G A Newman
Published: July 2002

A thermoluminescent imaging device is described in which the phosphor layer and the heated layer are fully integrated into a single panel. The performance of this image storage panel is compared with that obtained from a commercially available luminescent imaging panel, and with an X-ray fluorescent screen.
Light collection in rectangular scintillation counters
Authors: T Smith  , B M Jasani
Published: July 2002

An expression is derived which can be used to calculate the quantity of light available for collection at one surface of a rectangular scintillation counter in which the total internal reflection method of light collection is used, and under conditions in which there is no loss of light by absorption. Methods of correcting the expression to allow for light absorption are applied in order to derive the theoretical response to scintillations at any position along the central axis and an extreme axis of a rectangular block (61 cm*40.5 cm*6.3 cm) of refractive index 1.5. Results obtained using an experimental model of the same dimensions are in good agreement with the theory. The value of the expression in counter design is discussed.
A pressure chamber for high resolution light microscopy
Authors: C J Coakley  , M E J Holwill
Published: July 2002

Apparatus for investigating by light microscopy the effects on biological systems of hydrostatic pressures in the range 1-1600 atm at temperatures between 0 and 40 degrees C is described. The system has good resolving power as demonstrated by observation and photography of flagella 0.2 mu m in diameter. Possible improvements to the system are discussed.
An automatic level controller for a double beam spectrophotometer
Authors: P J Beckwith
Published: July 2002

A simple electronic accessory for a double beam spectrophotometer is described which causes the instrument to be made insensitive to changes in signal strength over a range limited mainly by noise. High performance may be achieved at low cost.
A simple plateholder for on site wet processing of holograms in real-time holographic interferometry
Authors: B U Achia
Published: July 2002

An inexpensive and easy-to-build on-site hologram processing device is described. The plateholder has been successfully tested in a real-time holographic interferometer to give precisely located holograms. Liquid gate immersion yields a brighter and undistorted reconstructed image. Photographic processing is faster due to easier solution handling and elimination of the drying step.
A method of measuring internal strains within elastomeric materials using radioactive implants
Authors: J B Benzies
Published: July 2002

A method is described of measuring the internal strains, caused by externally applied stress within solid elastomeric materials. In principle the method consists of measuring the displacement of radioactive point sources which have previously been embedded into the material. Two methods of observation, one using a pinhole camera and the other a multichannel collimator are described. An example of the practical use of the method in the measurement of internal strains within small model tyres is presented.
Electrostatic cylinder lenses II: Three element einzel lenses
Authors: A Adams  , F H Read
Published: July 2002

For Pt. I see ibid., vol. 4, 625 of 1971 The potential distribution inside three equidiameter coaxial cylinders separated by finite distances has been used to calculate the focal lengths, mid focal lengths and spherical aberration coefficients of some triple cylinder einzel lenses. The lenses considered have the length of the middle cylinder equal to its diameter or to half its diameter. Data are presented for such lenses with the middle cylinder at either a higher or lower potential than the outer cylinders over a large range of voltage ratios.
Electrostatic cylinder lenses III: three element asymmetric voltage lenses
Authors: A Adams  , F H Read
Published: July 2002

For Pt. II see ibid., vol. 5, 150 of 1972. The potential distribution inside three equidiameter coaxial cylinders separated by finite distances has been derived and used to calculate the focal lengths, mid focal lengths and spherical aberration coefficients of some triple cylinder lenses having three different voltages applied to them. The lenses have the length of the central cylinder equal to its diameter or to half its diameter. Data are presented for such lenses with the middle potential both higher and lower than the outer potentials.
Improved dilatometric technique for the study of vacancies
Authors: E A Harrison  , P Wilkes
Published: July 2002

Two electrical transducer techniques are described for the dilatometric study of quenched-in point defects. The linear transducer gave a higher resolution than had previously been attained but with considerable scatter. The capacitance micrometer gave an extremely high resolution (<1AA) and was preferred. The results for aluminium specimens indicate that the annealing of quenched rods (3mm diameter) can be easily detected and give an Arrhenius plto close to that derived from equilibrium vacancy measurements. This can be interpreted tentatively to give a volume per vacancy in aluminium of 0.95 atomic volume.
Dual camera attachment for a scanning electron microscope
Authors: D C Marshall
Published: July 2002

Describes how a dual camera attachment may be fitted to a scanning electron microscope in order that Polaroid prints and 35 mm negatives can be produced quickly and efficiently.
Energy analysers for charged particle beams
Authors: W Steckelmacher
Published: July 2002

A review is given covering the retarding field and electrostatic deflection energy analyser types, since these are the most suitable for use with both ions and electrons. Deflection analysers are considered for various field configurations; the main lines of development are discussed, including a guide to the numerous recent publications dealing with their design and performance.
Study of a 40 kV multistage spark gap operated in air at atmospheric pressure
Authors: A Anvari  , O Steinvall
Published: July 2002

The electrical properties of a multistage spark gap have been studied and a compact 40 kV four-stage switch is described. The switch can be operated in atmospheric air with a 50 ns delay time and a +or-5 ns jitter, when triggered at breakdown voltage. Both these values are shorter, by a factor of 3, than those of similar two-electrode spark gap. The discharge gaps, besides the electrical connection, have been coupled to each other, optically, by means of an axial hole through the switch. This coupling, which gives rise to a simultaneous ignition in the gaps, is mainly responsible for reduction of the jitter and the delay time. The simultaneity of the gap ignitions has been shown by investigating the short light pulses (about 2 ns halfwidth) emitted from the spark of each gap. The switch is also capable to work with high repetition rate. More than 1200 Hz with a 4 kA peak current has been obtained, when operating the switch in air at atmospheric pressure.
A cryostat for metal-insulator-semiconductor studies
Authors: Y W Lam
Published: July 2002

A simple cryostat is described for the investigation of open MIS specimens. It overcomes the water condensation problem by continuous evaporation of liquid nitrogen which drives away the water vapour from the specimen. The copper housing also provides a good electrical shield for the prevention of noise signal pick-up.
Design principles in electron spectroscopy
Authors: B Wannberg  , U Gelius  , K Siegbahn
Published: July 2002

The factors which determine the resolution and sensitivity of electron spectrometers are discussed. Various types of instruments commonly used in X-ray or ultraviolet photoelectron spectroscopy are reviewed, mainly from an electron-optical point of view. The influence of fringing fields and preretardation on resolution and sensitivity is considered. Three different schemes for monochromatizing the exciting X-radiation are compared.
Modification of a transmission electron microscope to give energy-filtered images and diffraction patterns, and electron energy loss spectra
Authors: R F Egerton  , J G Philip  , P S Turner  , M J Whelan
Published: July 2002

A magnetic spectrometer of the Castaing-Henry type has been incorporated between the objective and intermediate lenses of a conventional 100 keV transmission electron microscope (AEI EM6). The electron optics of the spectrometer were adjusted to give semistigmatic focusing, allowing an overall energy resolution of 2 eV in spectra and energy selected images. Making use of the hysteresis properties of the magnetic circuit, energy-selected diffraction patterns are also obtained, with an energy window of about 8 eV. An electron counting system was incorporated to allow accurate recording of energy loss spectra. A simple Zener diode circuit is described, which provides calibration of the energy loss to within +or-0.2% for losses up to 690 eV.
Fast scan proton density imaging by NMR
Authors: P Mansfield  , A A Maudsley  , T Bains
Published: July 2002

A new fast scanning method of producing proton density images by NMR is described which could be useful for the examination of plants as well as biological tissue in vivo. Examples are given of images produced from small samples of plant and biological material. Calculations show that imaging equipment, if scaled to deal with objects of human proportions, could under ideal conditions produce pictures close to television quality in times ranging down to a few minutes by this method.
A simple ion source for H3+ions and molecular rare gas ions
Authors: G Lange  , B Huber  , K Wiesemann
Published: July 2002

A simple ion source producing H3+and different molecular rare gas ions is described. To stabilize the extracted ion current the discharge current is stabilized by regulating the gas flow. With hydrogen the extracted ion current consists of more than 95% of H3+ions. Thus a primary mass selection is not needed. In rare gases the content of molecular ions rises to about 1% to 4%.
Iterative optimization of auxiliary coils for stellarators
Authors: B.F. McMillan  , B.D. Blackwell  , J.H. Harris
Published: July 2002

A direct method is described for finding optimal coils, and `flexibility' coils are presented which have been determined by this method. The method proceeds straight to a coil design from the required vacuum magnetic configuration parameters for the desired plasma, rather than producing an intermediate `surface current' description. This allows engineering requirements to be faithfully reproduced. The method has been applied by implementing a perturbative vacuum rotational transform evaluator as an optimality criterion. The speed of this evaluation step allows a thorough exploration of the set of possible coil trajectories and permits a high degree of confidence in the optimality of the best candidate. It is shown that the flexible heliac winding is very near optimal for rotational transform generation.
Optimization of pellet scenarios for long pulse fuelling to high densities at JET*
Authors: P.T. Lang  , B. Alper  , L.R. Baylor  , M. Beurskens  , J.G. Cordey  , R. Dux  , R. Felton  , L. Garzotti  , G. Haas  , L.D. Horton  , S. Jachmich  , T.T.C. Jones  , P.J. Lomas  , A. Lorenz  , M. Maraschek  , H.W. Müller  , J. Ongena  , J. Rapp  , M. Reich  , K.F. Renk  , R. Sartori  , G. Schmidt  , M. Stamp  , W. Suttrop  , E. Villedieu  , EFDA-JET Work Programme Collaborators
Published: July 2002

Pellet injection was investigated for its fuelling capability to high densities in ELMy H mode discharges at JET. Applying the high field side launch system, optimized refuelling scenarios were developed on the basis of conventional discharge configurations withIp= 2.5 MA,Bt= 2.4 T, averaged triangularity ⟨δ⟩≈0.34 and mainly neutral beam heating at a level of approximately 17 MW. The accessible operational range was extended with respect to gas puff refuelling by the use of pellet injection. For example, H mode conditions could be maintained at densities beyond the Greenwald level. Plasma energy confinement was observed to become density independent at high densities. Deep pellet particle deposition made possible the uncoupling of edge and core density, allowing more peaked density profiles. When confinement deterioration due to pellet triggered MHD activity or parasitic pellet borne gas was avoided in appropriate pulse schedules, an enhanced particle inventory was achieved while maintaining the plasma pressure profile. In a technical assessment it was found that there is still room for further enhancement of the injection scenario by improved adaptation to high density plasma operation.
Transport barriers and bifurcation characteristics in stellarators
Authors: Akihide Fujisawa
Published: July 2002

Transport barriers in the present stellarators are reviewed in comparison with those in tokamaks. Peculiarities of stellarator plasma structures are introduced in order to obtain a unified view of the barrier formation mechanism. Particular attention is paid to neoclassical (-driven) internal transport barriers that are commonly observed in stellarators. Discussion is made about important aspects of structural formation; e.g. the formation or bifurcation mechanism of radial electric field and its causal link with the transport barrier, and effects of magnetic field configuration on the barrier formation.
Identification of genes by hybrid ribozymes that couple cleavage activity with the unwinding activity of an endogenous RNA helicase
Authors: Kawasaki Hiroaki , Taira Kazunari
Published: July 2002

Novel ribozymes that couple the cleavage activity of hammerhead ribozymes with the unwinding activity of RNA helicase eIF4AI were constructed. This leads to extremely efficient cleavage of the target mRNA, regardless of the secondary structure of the RNA, and eliminates one of the major problems: many target sites on the RNA were previously inaccessible to cleavage due to secondary and/or tertiary structure formation. Moreover, libraries of hybrid ribozymes with randomized binding arms were introduced into cells. This procedure made it possible to readily identify the relevant genes associated with phenotype. Specifically, four genes known to be in the Fas‐mediated apoptosis pathway were identified along with additional genes. This application of a randomized library of hybrid ribozymes represents a simple, powerful method for the identification of genes associated with specific phenotypes in the post‐genome era.
Electrochemistry of Copper in Aqueous Glycine Solutions
Authors: Aksu Serdar , Doyle Fiona M.
Published: July 2002

Potential-pH equilibria and potentiodynamic polarization studies were used to examine the electrochemical behavior of copper in aqueous glycine solutions. Potential-pH diagrams for the copper-water-glycine system were derived at different total copper

{

Cu

T

}

and glycine

{

L

T

}

activities. The diagrams show that glycine significantly extended the solubility range of copper. Polarization experiments were conducted in deaerated and aerated aqueous solutions of

10

−
2

M

glycine with

10

−
5

M

cupric nitrate and

10

−
1

M

glycine with

10

−
4

M

cupric nitrate at pH values between 9 and 12. The results of these experiments are discussed in terms of the relevant potential-pH diagrams. Good correlations were observed. © 2000 The Electrochemical Society. All rights reserved.
Zirconia-Based Potentiometric Sensors Using Metal Oxide Electrodes for Detection of Hydrocarbons
Authors: Hibino Takashi , Hashimoto Atsuko , Kakimoto Shiro , Sano Mitsuru
Published: July 2002

The non-Nernstian behavior of zirconia-based electrochemical cells with various metal oxide electrodes for 0–500 ppm C1-C4 hydrocarbons, hydrogen, and carbon monoxide was studied in the presence of 10% oxygen at 600°C. The cell using an

In

2

O

3

electrode exhibited a largely negative electromotive force (emf) for propene but gave moderately negative emfs for hydrogen and carbon monoxide. The addition of 0.1 wt %

MnO

2

to the

In

2

O

3

electrode significantly improved the selectivity of the parent electrode for propene over hydrogen and carbon monoxide. The negative emf of the cell using the

MnO

2

-containing

In

2

O

3

electrode for the hydrocarbons became enhanced as the carbon number of the hydrocarbon increased, the C-C linkage was unsaturated, and the chain structure was branched. This enhanced effect, as well as the addition effect of

MnO

2

,

was discussed on the basis of the measurements of the polarization curves of the

MnO

2

-containing

In

2

O

3

electrode for the hydrocarbons and oxygen and the nonelectrochemical oxidation of the hydrocarbons by oxygen. In addition, the

MnO

2

-containing

In

2

O

3

electrode for the hydrocarbons was compared with an Au electrode with respect to sensitivity to the hydrocarbons and reproducibility of the sensing properties. © 2000 The Electrochemical Society. All rights reserved.