Showing papers in "Journal of Physics D in 1993"
TL;DR: In this paper, the Lissajous figure of voltage-electric charges and current pulse shapes are used as a method of distinguishing between the atmospheric pressure glow plasma and the silent electric discharge.
Abstract: Unusual glow discharges in air, argon, oxygen and nitrogen at atmospheric pressure can be produced using a 50 Hz source. This technique is introduced on the basis of the idea of a lower dielectric breakdown voltage gas. The electrode system, which is composed of a fine metal wire mesh of specified radius and a dielectric substance, is very useful for plasma surface processes and for chemical reactions in the plasma bulk. The observations of the Lissajous figure of voltage-electric charges and of the current pulse shapes are proposed as a method of distinguishing between the atmospheric pressure glow plasma and the silent electric discharge.
451 citations
AeA1
TL;DR: In this article, the authors reviewed the application of this unique ultrasonic source with particular emphasis on the application in non-destructive testing and determination of candle flame parameters, and possible future applications are also outlined.
Abstract: The laser generation of ultrasound in solids is reviewed with particular emphasis on the application of this unique ultrasonic source. Three regimes for the generation of ultrasound in solids using lasers in the visible near infrared wavelength region exist: thermoelastic, plasma and constrained surface source regimes. The mechanism for ultrasonic generation in each of these regimes is given. Recent experimental investigations into laser-generated ultrasound are also described, including a description of a different mechanism for the generation of ultrasound in solids using a CO2 laser. Finally, the many applications of laser-generated ultrasound are reviewed. These applications range from nondestructive testing to the determination of candle flame parameters. Possible future applications are also outlined.
348 citations
TL;DR: In this paper, a stable discharge was produced in atmospheric air using water as a cathode and spectral lines of elements dissolved in tap water could be observed, and it was demonstrated that the appearance of these spectral lines is a consequence of cathode sputtering of water during the discharge.
Abstract: A stable discharge was produced in atmospheric air using water as a cathode. Spectral lines of elements dissolved in tap water could be observed. It is demonstrated that the appearance of these spectral lines is a consequence of cathode sputtering of water during the discharge. The intensity of the lines was found to depend strongly on the acidity of the water. This kind of discharge gives a possibility for continuous analysis of water and waste water solutions.
260 citations
TL;DR: In this paper, a transparent anode imaging technique was used to monitor the spatial distribution of the individual emission centres of a diamond-coated Mo electrode and a bulk carbon graphite electrode.
Abstract: Details are given of an experimental study of field emission characteristics of diamond-coated Mo electrodes: in particular, a transparent anode imaging technique was used to monitor the spatial distribution of the individual emission centres. This study has revealed the important fact that substantial emission can be obtained at fields as low as 5 MV m-1. In order to investigate the physical nature of the emission process, a comparative study has been made of emission obtained from a diamond-coated electrode and a bulk carbon graphite electrode. Significantly, it was found that both the graphite-rich diamond film and the diamond-rich graphite electrode shared a similar high-emissivity characteristic, with a high surface density of emission sites. It has also been noted that CVD diamond films have two important properties that are favourable to low-field cold electron emission, namely their negative electron affinity and the presence of graphite inclusions.
242 citations
TL;DR: The finding that particles trapped in potential energy wells under the action of negative dielectrophoresis can be more easily removed from the electrode structure than those trapped under positive dielectophoresis was verified for mixtures of viable and non-viable yeast cells.
Abstract: The potential energy surfaces generated by microelectrodes of polynomial and interdigitated castellated geometry have been calculated for particles experiencing both positive and negative dielectrophoretic forces. The resulting forms of particle collection at these electrodes are governed by the locations of the potential energy wells, and the theoretical predictions of the modes of collection for particles experiencing positive and negative dielectrophoretic forces are verified using mixtures of viable and non-viable yeast cells, as well as of bacteria and blood cells. An important result for the interdigitated electrodes is the finding that particles trapped in potential energy wells under the action of negative dielectrophoresis can be more easily removed from the electrode structure (e.g. by fluid flow or gravitational forces) than those trapped under positive dielectrophoresis. This was verified for mixtures of bacteria and blood cells, viable and non-viable yeast cells.
233 citations
TL;DR: In this article, the properties of magnetic field sensors based on semiconductors such as Hall generators and magnetoresistors, and on magnetic metals such as permalloy and the recently discovered 'giant magnetoresistance' metallic multilayers are discussed.
Abstract: Discusses the properties of magnetic field sensors based on semiconductors such as Hall generators and magnetoresistors, and on magnetic metals, such as permalloy and the recently discovered 'giant magnetoresistance' metallic multilayers. Some emphasis is placed on the comparison between sensors made using these different technologies. Applications of magnetic field sensors in magnetic recording technology and in position sensing are discussed briefly. Typically a sensor has to detect the difference between a high and a low value of field, around an average, which is of the order of 10-3 T in recording applications, but can exceed 0.1 T in position sensors.
229 citations
TL;DR: The paper introduces the time-reversal approach in a discussion of the techniques used in optics for focusing through inhomogeneous media to ultrasonic pulsed fields where adaptive time delay focusing and TRM focusing are the main techniques of interest.
Abstract: Time-reversal of ultrasonic fields allows a very efficient approach to focus pulsed ultrasonic waves through inhomogeneous media. Time-reversal mirrors (TRMS) are made of large transducer arrays, allowing the incident acoustic field to be sampled, time-reversed and re-emitted. The paper introduces the time-reversal approach in a discussion of the techniques used in optics for focusing through inhomogeneous media. The discussion is extended to ultrasonic pulsed fields where adaptive time delay focusing and TRM focusing are the main techniques of interest. Time reversal focusing of a pulsed wave is optimal in comparison with time delay focusing in the sense that it realizes the spatiotemporally matched filter to the inhomogeneous propagation transfer function between the array and the target. Time-reversal processing also permits choice of any temporal window to be time-reversed, allowing operation in an iterative mode. In multi-target media, such a process converges on the most reflective target. In the case of an extended target, automatic resonances can be achieved. Applications of TRM are numerous and include medical applications (imaging, lithotripsy and hyperthermia) as well as non-destructive testing (NDT) and underwater acoustics. Experimental results obtained with 64 and 128 channel TRMS demonstrate the efficiency of this technique.
208 citations
TL;DR: Suspensions of yeast cells were used as model systems to investigate the electrokinetic behaviour of colloidal particles subjected to travelling electric fields generated using microelectrodes and dielectrophoresis and electrorotation measurements were made to provide a further understanding of the observed effects.
Abstract: Suspensions of yeast cells (Saccharomyces cerevisiae) were used as model systems to investigate the electrokinetic behaviour of colloidal particles subjected to travelling electric fields generated using microelectrodes. Measurements were made over the frequency range 1 kHz to 10 MHz and for suspending medium conductivities in the range 6-260 mS m-1. A theoretical model is developed to provide a good description of the dependence of the observed translational motion, termed travelling-wave dielectrophoresis (TWD), on the dielectric properties of the particle and suspending medium, on the size of the particle, and on the magnitude and frequency of the applied field. Unlike conventional dielectrophoresis, the TWD effect is found to be related to the imaginary, rather than to the real, component of the induced dipole moment. Dielectrophoresis and electrorotation measurements were made to provide a further understanding of the observed effects and to support the theoretical model.
168 citations
TL;DR: In this paper, the deformation, interaction and freezing during substrate impact of molten droplets in plasma spray processes are numerically investigated, and the numerical results reveal that a droplet spreads and solidifies into a splat of diameter 1.6 to 3.8 times the initial droplet diameter within a time of 0.12 to 0.44 mu s.
Abstract: In the present study, deformation, interaction and freezing during substrate impact of molten droplets in plasma spray processes are numerically investigated. The numerical simulation is conducted on the basis of the full Navier-Stokes equations and the volume of fluid (VOF) function by using a two-domain method for the thermal field and freezing problem and a two-phase flow continuum model for the flow problem with a growing solid layer. Important processing parameters, such as droplet temperature, substrate temperature and droplet velocity are considered and their effects on flattening and freezing are discussed. The numerical results reveal that a droplet spreads and solidifies into a splat of diameter 1.6 to 3.8 times the initial droplet diameter within a time of 0.12 to 0.44 mu s. The droplet liquid separates from the solid/liquid interface when freezing occurs. Increasing initial droplet velocity and enhancing substrate temperature can significantly enhance the flattening extent of droplet. A fully liquid droplet impinging on a solid substrate may generate good contact between the splat and the substrate; a fully liquid droplet striking on another flattening splat produces ejection of the liquid; a fully liquid ring colliding with a flattening splat causes bounce of the liquid and formation of voids. A combination of a liquid droplet condition at a high initial velocity with a semi-solid or solid surface condition may produce good adhesion in sprayed deposits or coatings.
153 citations
TL;DR: In this paper, the transfer of heat through a cellular material is considered, taking into account conduction in the solid and gas phases, but excluding radiation and convection, and various published methods of reaching such a conclusion are critically reviewed and compared.
Abstract: The transfer of heat through a cellular material is considered, taking into account conduction in the solid and gas phases, but excluding radiation and convection Formulae are derived which relate the apparent conductivity of the material to the conductivities of the component phases and to the density Some published methods of reaching such a conclusion are critically reviewed and compared It is shown by binomial expansion that the various formulae tend to the same approximate result for foams of low density
145 citations
TL;DR: In this article, the stability of a cylindrical keyhole was investigated using the energy and pressure balance, and a threshold for the laser power per thickness of the workpiece was found above which the formation of a stable keyhole commences.
Abstract: The stability of a cylindrical keyhole is investigated using the energy and pressure balance. Non-equilibrium evaporation from the keyhole surface, surface tension, hydrostatic and hydrodynamic pressure in the melt as well as heat conduction into the workplace are considered. In contrast to former investigations, the temperature at the keyhole wall and the radius of the keyhole adjust themselves self-consistently. A threshold for the laser power per thickness of the workpiece is found above which the formation of a stable keyhole commences. For iron, this threshold is 790 W mm-1. The temperature at the keyhole wall exceeds evaporation temperature by approximately 100 K. The keyhole radius exceeds the radius of the laser beam and is at least 1.7 times the laser radius.
TL;DR: In this article, the authors analyzed various estimators for characterizing synthetic aperture radar clutter textures and compared their predicted performance with the maximum likelihood estimates in a search for robust, optimum texture estimators.
Abstract: This paper analyses various estimators for characterizing synthetic aperture radar clutter textures. First, we consider maximum likelihood estimators, which require specific knowledge of the form of the probability distribution of the data but would be expected to yield the best performance. Both K- and Weibull-distributed clutter models, which are often applied to characterize natural SAR clutter, are considered. Though a full maximum likelihood solution is impossible for the K distribution, we derive an approximate one for the multi-look case. We next derive expressions for limiting errors in a variety of direct texture estimators and compare their predicted performance with the maximum likelihood estimates in a search for robust, optimum texture estimators.
TL;DR: In this article, a modification of an earlier technique, to measure the distribution of space charge in the insulation of a coaxial cable, under both DC and AC electric fields, is described.
Abstract: A modification of an earlier technique, to measure the distribution of space charge in the insulation of a coaxial cable, under both DC and AC electric fields, is described. The mathematical analysis is developed on the basis of acoustic waves propagating in media with cylindrical geometry. In order to measure the charge distribution in AC electric fields at any phase angle, a phase shift technique has been employed. The method of calibration of charge density is given, and the charge distribution in the insulation (2 mm in thickness) of XLPE cable has been measured under DC voltages (+or-40 kV, at room temperature) and AC voltage (17 kV peak, at 24 degrees C and 105 degrees C).
TL;DR: In this article, the effect of solvent in crystallization of polymorphs has been studied using the drug sulphathiazole as a model compound, and it is considered that the solvent acts by selective adsorption to certain faces of some polymorphs and thereby either inhibits their nucleation or retards their growth to the advantage of others.
Abstract: The effect of solvent in crystallization of polymorphs has been studied using the drug sulphathiazole as a model compound. The solubilities of the four polymorphic forms of sulphathiazole were determined as a function of temperature in various solvents. Within the temperature ranges studied, the rank order of solubility of the polymorphs was the same in all solvent systems. On the basis of this knowledge of the temperature dependence of the solubilities, recrystallization experiments, in which the supersaturation was systematically varied, were carried out in an endeavour to isolate each of the polymorphic forms from each solvent system. These recrystallization experiments reveal that not all of the know polymorphic forms can be crystallized from any given solvent by varying the supersaturation. Indeed some solvents selectively favour the crystallization of a particular form of forms. The authors conclude that thermodynamic effects are not responsible for the selective behaviour of a solvent. A kinetic mechanism is proposed. It is considered that the solvent acts by selective adsorption to certain faces of some of the polymorphs, and thereby either inhibits their nucleation or retards their growth to the advantage of others.
TL;DR: In this article, the authors derived theoretical relationships to link the dielectric properties of a suspension of colloidal particles to both dielectrophoretic (DEP) and electrorotation (ROT) behaviour exhibited by a single suspended particle.
Abstract: New theoretical relationships are derived to link the dielectric properties of a suspension of colloidal particles to both the dielectrophoretic (DEP) and electrorotation (ROT) behaviour exhibited by a single suspended particle. It is found that the relaxation frequencies that characterize the dielectric spectrum of a colloidal suspension are close to, but different from, those that characterize the DEP and ROT responses. The extent of this difference is dependent on particle volume fraction and the intrinsic dielectric properties of both particle and suspending medium. Experimental results obtained for yeast cells in the frequency range from 1 kHz to 10 MHz provide confirmation of the theory.
TL;DR: In this article, the power loss owing to heat conduction in laser cutting and welding of metals is calculated analytically using the model of a cylinder-type heat source, and the theoretically predicted power loss into the cut workpiece is confirmed by measurements of the temperature rise within the metal sheet within the laser cutting experiments.
Abstract: Using the model of a cylinder-type heat source, the power loss owing to heat conduction in laser cutting and welding of metals is calculated analytically. The case of laser cutting is described by taking into account the influence of the generated cutting kerf using numerical calculations. Both the analytical and the numerical solution for the power loss deposited into the material are well described by approximative formulae. The theoretically predicted power loss into the cut workpiece is confirmed by measurements of the temperature rise within the metal sheet in laser cutting experiments.
TL;DR: In this article, the authors reported the inclusion of protein molecules in growing crystals of trans-sinapic acid (trans-3,5-dimethoxy-4-hydroxy-cinnamic acid).
Abstract: The authors report on the inclusion of protein molecules in growing crystals of trans-3,5-dimethoxy-4-hydroxy-cinnamic acid (trans-sinapic acid). This material is important as the 'matrix' compound in matrix-assisted lasar desorption, a promising new ion source for heavy molecule mass spectrometry. The crystal structure of trans-sinapic acid was determined. It belongs to the space group P21/n and has a structure in which the planar trans-sinapic acid molecules are hydrogen bonded into extended sheets. Dyes were used to follow protein incorporation into growing trans-sinapic crystals. The staining pattern obtained demonstrated that protein molecules were included only on crystal faces parallel to these extended sheets. This result is the first demonstration that proteins can be incorporated into a growing crystal by a selective interaction with one of the crystal faces. The structure of the crystal plane that interacts with the protein was consistent with a 'hydrophobic' bonding of the protein to the crystal face.
TL;DR: In this article, the authors calculated the net emission coefficient of Ar-Cu, N2-Cu and SF6-Cu mixtures for homogeneous and isothermal plasmas at atmospheric pressure in the temperature range between 3000 and 25000 K.
Abstract: The net emission coefficient of Ar-Cu, N2-Cu, SF6-Cu and Ar-Fe mixtures was calculated for homogeneous and isothermal plasmas at atmospheric pressure in the temperature range between 3000 and 25000 K. The increase in power radiated due to the presence of metal vapours depends on the vapour itself (the net emission is higher with iron than with copper) and on the type of gas. The influence of pressure was calculated for the SF6-Cu mixture. In the last part of the paper the values of the net emission coefficient were used to calculate the temperature profile in stationary arc in Ar-Cu and N2-Cu mixtures. The influence of copper on radiation is preponderant on the temperature field at higher currents whereas the effect on electrical conductivity is important at lower currents.
TL;DR: In this article, the relationship between polymorphism, structure-property relations and crystal growth is discussed, and representative systems which illustrate the intimate connections between polymorphisms, structure properties, and growth are presented.
Abstract: Understanding the role of structure in determining the properties of materials is a crucial aspect of the design of new materials. The existence of polymorphic crystal structures provides a unique opportunity to study structure-property relationships, since the only variable among polymorphic forms is that of structure, and variation in properties must be due to differences in structure. Systematic characterization of the polymorphic forms and acquisition of the ability to grow crystals of a desired form are additional elements in the design strategy of new materials. The conditions and techniques required to obtain a particular polymorph, combined with knowledge of the crystal structures, can also provide information on the relative stability of the different structures. Studies of representative systems which illustrate the intimate connections between polymorphism, structure-property relations and crystal growth are presented.
TL;DR: In this article, an experimental study of the inception of positive streamers in point-to-plane geometry under pulsed voltage was performed in two liquids, cyclohexane and pentane, where the roles of the tip radius, voltage pulse rise time, gap distance and hydrostatic pressure were investigated.
Abstract: This paper presents an experimental study of the inception of positive streamers in point-to-plane geometry under pulsed voltage. The different pre-breakdown events (slow and filamentary streamers) are characterized via sensitive transient current recordings, obtained using a new differential measurement technique described in the text. The roles of the tip radius, voltage pulse rise time, gap distance and hydrostatic pressure are systematically investigated in two liquids, cyclohexane and pentane. We found two parameters to characterize inception of both streamer types in a liquid: a unique initiation field for slow and filamentary streamers (depending slightly on the point tip radius of curvature); and a threshold propagation voltage for filamentary streamers (depending on the gap distance). There is also a critical point-tip radius above which no slow streamers are observed. It is shown that the initiation field and the propagation threshold can be accurately determined only in very specific conditions, namely below the critical point-tip radius and with fast rise time voltage impulses (about 10 ns). The presence of a gaseous phase in the initiation process is identified via the influence of hydrostatic pressure. Finally, the significance of the critical point-tip radius and that of the propagation voltage of filamentary streamers are discussed by comparison between the streamer and a conducting filament.
TL;DR: In this article, a non-equilibrium one-dimensional model for the plasma sheaths near the electrodes of electric arcs where the cathode is a thermionic emitter is proposed.
Abstract: A non-equilibrium one-dimensional model is proposed for the plasma sheaths near the electrodes of electric arcs where the cathode is a thermionic emitter. Three coupled equations are solved: (a) the charge continuity equation, which accounts for ambipolar diffusion, recombination and ionization, (b) a form of Ohm's law relating the effective electrical conductivity with a local electric field and (c) the energy balance equation, accounting for thermal conduction, Ohmic heating, plasma radiation and the effects which occur at the electrode surface, i.e. thermionic cooling, ion heating, radiative heating from the plasma and radiative cooling by thermal emission. The three equations give distributions of temperature, electric field and charge density within the sheath. Results are given for the sheath at the thoriated-tungsten cathode and anode for a 200 A arc in argon. Calculations have also been made of sheath properties for various electrode materials to determine the critical current density sustainable by a cathode without cathode melting. Critical current densities for anode melting are less than for cathode melting because of the cooling effect at the cathode of thermionic emission. The authors find that the effect of ion heating tends to keep the cathode temperature near to the temperature for which the current density from thermionic emission equals the imposed current density.
TL;DR: In this paper, stable negative ions containing up to sixteen silicon atoms have been measured by mass spectrometry in RF power-modulated silane plasmas for amorphous silicon deposition.
Abstract: Stable negative ions containing up to sixteen silicon atoms have been measured by mass spectrometry in RF power-modulated silane plasmas for amorphous silicon deposition. These hydrogenated silicon cluster ions reach much higher masses than the positive ions, which have no more then six silicon atoms. This supports the view that negative ions are the precursors to particulate formation in silane plasmas. The time-dependent fluxes of positive and negative ions from the plasma are shown with a 5 mu s time resolution. Possible cluster reaction sequences are discussed and the effect of visible light on the negative ion signal is commented upon.
TL;DR: In this article, the results of an experimental investigation of a DC glow discharge in fast air flow at a pressure of up to two atmospheres are presented, and a high efficiency in the production of chemically active palticles is achieved in this kind of discharge.
Abstract: The results of an experimental investigation of a DC glow discharge in fast air flow at a pressure of up to two atmospheres are presented. A high efficiency in the production of chemically active palticles is achieved in this kind of discharge. For dry air the ozone yield was as high as 80 g kwh" at a concentration of 0.05%. The resuits of a successful application of this discharge for SO2 and NO removal from polluted air are described. A full kinetic model for the glow discharge at atmospheric pressure of dry air has been developed which explains experimental results with satisfactory accuracy.
TL;DR: In this paper, the dynamic behavior of a keyhole in laser welding is studied theoretically, where the recoil pressure from ablating particles is in equilibrium with the surface tension at the keyhole wall, and the collapse time due to a sudden laser shutdown is calculated.
Abstract: The dynamic behaviour of a keyhole in laser welding is studied theoretically. Starting from the stationary state, where the recoil pressure from ablating particles is in equilibrium with the surface tension at the keyhole wall, the collapse time due to a sudden laser shut-down is calculated. The characteristic time constant (r03 rho / gamma )1/2 of the system (r0 is the initial keyhole radius, rho is the density of the melt, gamma is the gamma coefficient of surface tension) which is approximately 0.1 ms for Al, Fe and Cu turns out to be a lower limit of the keyhole closing time. Linear stability analysis of the stationary state reveals that under conditions relevant in practice, the keyhole is expected to perform oscillations with frequencies of several hundred Hertz. The results of this investigation are particularly important for pulsed laser applications.
TL;DR: In this paper, the Nottingham effect and the thermo-field emission current were calculated for a wide range of temperatures, field strengths and the work function of the emitter, and it was shown that simple approximation formulae commonly used may give incorrect results to several orders of magnitude.
Abstract: The thermo-field emission current and Nottingham effect are calculated for a wide range of temperatures (
Abstract: VHF glow discharges are employed for high-rate a-Si:H deposition, maintaining good optoelectronic properties. A more efficient radical generation, either due to higher electron densities or an enhanced high-energy electron tail, is generally assumed as the mechanism. A VHF a-Si:H depositing plasma was investigated between 40 and 250 MHz by optical emission spectroscopy, mass spectroscopy, ion energy measurements and electrical impedance analysis. The present study shows that the increase of deposition rate with frequency is essentially due to enhanced ion flux to the growth surface, such that models of deposition kinetics taking into account only neutral species and neglecting the role of ions impinging on the substrate can therefore not be applied to VHF plasma deposition.
TL;DR: In this article, the electron and vibrational kinetics in an N2-H2 glow discharge have been analyzed using a self-consistent theoretical approach valid in the conditions of a low-pressure moderate current, positive column.
Abstract: The electron and vibrational kinetics in an N2-H2 glow discharge have been analysed using a self-consistent theoretical approach valid in the conditions of a low-pressure moderate current, positive column. This model is based on the solutions to the homogeneous Boltzmann equation and the two systems of rate balance equations for the vibrational levels N2(X1 Sigma g+, v) and H2(X1 Sigma g+, v'), which take into account e-V, V-V, and V-T processes for the N2-N2 and H2-H2 systems as well as those involving N2-H2 collisions. The paper presents a large amount of calculated data on the vibrational distribution functions of N2(X,v) and H2(X,v') molecules, electron energy distribution function, rate of dissociation and electron rate coefficients for excitation. This formulation provides a relationship between the characteristic vibrational temperatures Tv(N2) and Tv(H2) and a dependence of Tv(N2) on the fractional H2 concentration, which are in satisfactory agreement with measurements by emission spectroscopy and by CARS. The model also predicts the strong decrease of the rate of dissociation of N2 as it is observed in flowing discharges when a few per cent of H2 is added to N2.
TL;DR: In this article, the authors used dynamic mechanical and dielectric thermal analyses together with infrared spectroscopy to identify molecular motions in polyaniline films cast from emeraldine base powder dissolved in the solvent N-methyl-2-pyrrolidinone (NMP).
Abstract: The authors used dynamic mechanical and dielectric thermal analyses together with infrared spectroscopy to identify molecular motions in polyaniline films cast from emeraldine base powder dissolved in the solvent N-methyl-2-pyrrolidinone (NMP). These relaxations include a librational ring motion at around -80 degrees C and a glass transition (Tg) centred at 100 degrees C. They have also observed a permanent film hardening process at around 180 degrees C which is ascribed to polymer chain crosslinking, both physical (associated with chain entanglements) and more importantly chemical (chain-chain chemical bonding). Chemical crosslinking can be further identified with chain defects and residual impurities in the polymeric material. The importance of precise control of polyaniline synthesis and processing is therefore strongly emphasised. These results have clear implications for the thermal orientation process in polyaniline.
TL;DR: In this article, the electron swarm behavior in SF6 gas is re-analysed over the E/N range 141-7000 Td by a six-term Boltzmann equation method and by a Monte Carlo simulation considering the latest cross section data, in particular, that of the elastic momentum transfer cross section.
Abstract: The electron swarm behaviour in SF6 gas is re-analysed over the E/N range 141-7000 Td by a six-term Boltzmann equation method and by a Monte Carlo simulation considering the latest cross section data, in particular, that of the elastic momentum transfer cross section. The Boltzmann equation analysis shows that the present set of cross sections gives the values of swarm parameters such as ionization and electron attachment coefficients, drift velocity, longitudinal and transverse diffusion coefficients in excellent agreement with the respective measurements for a wide range of E/N. The swarm parameters calculated by the six-term approximation analysis agree well with those by Monte Carlo calculation. Furthermore, the Monte Carlo simulation confirms the results of a previous computer simulation study for correspondence between experimental and theoretical electron drift velocities; that is, the drift velocity deduced from Schlumbohm's experiment (1965) assumes a value close to but slightly larger than Wm and the drift velocity deduced from Frommhold's experiment (1959) assumes a value represented by (Wr+Wm)/2, where Wm and Wr are the mean arrival time and the centre-of-mass electron drift velocities, respectively.
TL;DR: In this article, a systematic study of the thermoluminescence emission spectra of thirty feldspars covering the whole composition range from high potassium (orthoclase) through high sodium (albite) to high calcium (anorthite).
Abstract: The paper describes a systematic study of the thermoluminescence emission spectra of thirty feldspars covering the whole composition range from high potassium (orthoclase) through high sodium (albite) to high calcium (anorthite). The study was stimulated by the need to understand the properties of feldspars in connection with the application of thermoluminescence to the dating of sediments. The data were obtained with a high-sensitivity Fourier transform spectrometer, which allows measurements at the low light levels found in natural samples. Three-dimensional displays in which intensity is plotted as a function of photon energy and temperature assist identification of a wide range of spectral features. A number of common features are found: an emission at 3.1 eV is strong in alkali feldspars with more than 80 mole.% orthoclase and occurs with lower intensity in most other alkali feldspars and some plagioclases; a broad band with a flat maximum near 2.6 eV is found in all alkali feldspars at temperatures near 200 degrees C when artificially irradiated, and at higher temperatures in some natural samples. Emission at 2.2 and 4.4 eV is characteristic of plagioclases with more than 75 mole.% of albite. Plagioclases with more than 50 mole.% anorthite, and alkali feldspars with less than 50 mole.% orthoclase, emit mainly in the range 1.5-2 eV. These features can be identified with luminescence centres suggested by previous workers. The application to practical thermoluminescence dating is discussed.