bluuebunny/crossref_metadata_2025_split huggingface dataset:
Magnetic Susceptibility and Free Energy of Graphite Bromide
Authors: Hennig G. R. , McClelland J. D. 
Published: April 2005

The magnetic susceptibility of graphite bromide residue compounds has been measured by a Faraday method. The addition of bromine decreased the diamagnetism of graphite. Fair agreement was obtained between the measured diamagnetism and values calculated by assuming an undistorted graphite band structure depleted in electrons due to the dissociation and ionization of two out of eleven bromine molecules.
It has also been shown that the transfer of electrons from the graphite bands to bromine can account for the observed pressure dependence of the graphite bromine equilibrium.
Pulse Technique for Measurement of the Probability of Formation and Mobility of Negative Ions
Authors: McAfee K. B. 
Published: April 2005

A new technique for measurement of the attachment coefficient of electrons to molecules has been devised. The technique involves production of a beam of electrons in an attaching gas. The transient current flowing after the initiation and termination of the electron beam is interpreted as a flow of negative ions produced by electron-molecule collisions. Analysis of the transient current which may last several milliseconds yields a value for the mobility of the negative ions thus formed. The ratio of the magnitude of the electron beam current to the negative ion current yields a direct measure of the attachment coefficient.
Preliminary results obtained with SF6 show a very large attachment coefficient. Values of α/p (the ratio of attachment coefficient to pressure) are considerably larger in SF6 than those obtained for O2 in studies elsewhere. As might be expected the mobility of negative ions formed in SF6 is much lower than that observed for other gases. This is attributed to the very large collision cross section resulting from (1) the interaction between the negative ion and neutral gas molecules comprising polarization attraction and hard sphere repulsion and (2) resonance or exchange interaction.
Adsorption of Strontium and of Barium on Tungsten
Authors: Moore George E. , Allison H. W. 
Published: April 2005

Sr or Ba was deposited on W ribbon receivers by evaporation from source filaments in which a chemical reaction produced the metal at least 99.7% pure. The receiving surfaces could be cleaned at will by heating to high temperatures; repeated tests were thus possible. By thermionic measurements, adsorption and desorption were observed independently under nonequilibrium conditions. By using radioactive Sr isotopes, the deposit corresponding to any thermionic activation was measured. For each ribbon, thermionic activation was apparently a reversible function of the amount adsorbed.
Our experimental methods give information on kinetics, rather than equilibria. The adsorption mechanism more nearly resembles that proposed in Langmuir's later papers rather than that of his earlier theories but treatment of desorption by the theory of absolute reaction rates is considerably more satisfactory. This accounts for desorption kinetics over the experimental temperature range by only two disposable constants, the activation energy for desorption, (a.e.d.), and a repulsive energy of interaction between adatoms.
The work function [open phi] for a monolayer of Sr is ∼2.2 v and for Ba is ∼1.9 v. The thermionic activation is explained in terms of polarized adatoms, rather than by the usual assumption of partial ionization, which has no experimental justification for Ba or Sr films. The theory proposed gives a reasonable value for the polarizability of Sr and of Ba, which when substituted into the theory of Prosen, Sachs, and Teller predicts a heat of physical desorption agreeing well with the observed a.e.d. This also agrees with the heat of desorption (h.d.) determined by the usual method of applying the Clapeyron equation to kinetics of this kind. We therefore believe that this adsorption should be called ``physical,'' rather than ``chemical,'' although the mean a.e.d.'s are, for Sr 77.4, and for Ba 80.7 kcal/mole, considerably larger than for most examples of chemisorption.
Energy Calculations of Multiple Hydrogen-Atom Systems by VB and MO Methods
Authors: Barker Roland S. , Snow Richard L. , Eyring Henry 
Published: April 2005

The equivalence of complete valence bond (VB) and of total configuration interaction molecular orbital (CIMO) methods has often been discussed. The two methods give identical expressions for H2. Treatment of H2 by the method of Coulson and Fischer also gives the same result. An extension of this method of semilocalized orbitals to the H3+ and H3 systems is attempted and found to be unsatisfactory. This indicates that a single configuration treatment, however general the molecular orbitals may be, is a poorer approximation than either the extended VB or CIMO treatments.
R. Taylor's exact integral (LCI) molecular orbital treatment for linear H4 is compared with the exact integral covalent bond (HL) method. A single structure of the latter method gave a ground-state energy of —57.02 ev while the two covalent structure treatment gave —58.59 ev. An energy of —55.64 ev is reported by Taylor using the best single MO configuration while he found an energy of only —56.40 ev using six of twelve possible MO ground-state configurations. It appears in view of the equivalence of the refined forms of the two treatments that the omitted higher energy configurations contribute more strongly to the ground-state energy than the lower energy ones. This indicates that low energy is not a good criterion for inclusion of configurations in a limited configuration interaction treatment. Recent work by A. Pullman on butadiene supports this conclusion.
Properties of Semi-Insulating GaAs
Authors: Gooch C. H. , Hilsum C. , Holeman B. R. 
Published: April 2005

Most samples of GaAs show properties similar to those of germanium and silicon, but it is possible to prepare GaAs with a resistivity at room temperature greater than 106 ohm-cm, and the electrical properties are then more like those of the wide band gap II–VI compounds, such as CdS. This form of material, known as semi-insulating GaAs, previously has not been studied thoroughly, partly because homogeneous samples were not available.
Measurements have now been made on semi-insulating GaAs, and results are reported for carrier concentration and mobility as a function of temperature. The interpretation of the results is sometimes complicated because even at room temperature the activation energy is about half of the intrinsic activation energy, and the carrier concentration can be close to the intrinsic concentration.
The dominant lattice scattering mechanism in GaAs is believed to be polar scattering, but even in the purest samples of semiconducting GaAs made thus far, impurity scattering is observed at room temperature. In a highly compensated material like semi-insulating GaAs, neither the Brooks-Herring nor the Conwell-Weisskopf theory of impurity scattering is likely to be valid. An initial study of carrier scattering has been made using measurements of transverse magnetoresistance and the field dependence of Hall coefficient. Some values for carrier lifetime are also reported.
Free Carrier Cyclotron Resonance, Faraday Rotation, and Voigt Double Refraction in Compound Semiconductors
Authors: Palik E. D. , Teitler S. , Wallis R. F. 
Published: April 2005

Measurements of cyclotron resonance absorption have been made in the far infrared spectral region from 25−150 μ on several III–V compounds at room and liquid-nitrogen temperatures using steady magnetic fields as high as 75 kgauss. For n-type InSb, InAs, InP, and GaAs, the data yield information concerning the conduction electron effective mass at the bottom of the band and its variation with magnetic field. Experiments have also been carried out on p-type InSb and corresponding information has been obtained for light holes. The dependence of the effective masses on both temperature and magnetic field can be satisfactorily interpreted in terms of Kane's theory for the band structure of these materials.
Measurements of Faraday rotation and Voigt double refraction have been made in the spectral region between 15 and 25 μ on a number of compound semiconductors at liquid-nitrogen temperatures. Either experiment gives the effective mass of the free carriers if their concentration is known. If both experiments can be performed, the results can be combined to give both the effective mass and carrier concentration directly without recourse to electrical measurements.
Electrical Properties of Lead Telluride
Authors: Kanai Yasuo , Nii Riro , Watanabe Naozo 
Published: April 2005

Samples of n-type PbTe crystals with different electron concentrations (n=2×1017∼5×1019/cc) were prepared by impurity doping or by heating in the vapor of lead. The electrical properties of these crystals were independent of the kind of impurities and depended only on the electron concentration. The electron mobilities of our samples were proportional to n−⅓ at 77°K, and to n−4/3 at 4.2°K. As the conduction electrons in our samples are degenerate at these temperatures, the experimental results mentioned above suggests that the conduction electrons in PbTe crystals are scattered mainly by acoustical mode at 77°K and by neutral imperfections at 4.2°K.
Since the electron mobility in PbTe becomes very large at 4.2°K (e.g., 1∼4×106 cm2/v-sec), this material is quite suitable for the experimental studies of the quantum transport phenomena. To investigate such phenomena, the Hall and magnetoresistive effects of n-type PbTe crystals were measured at 4.2°K in a pulsed magnetic field up to 170 kgauss. In the specimens with relatively low electron concentrations (e.g., n≃3×1017/cc), the magnetoresistive effect had a single minimum at about 77 kgauss in a transverse magnetic field, and at about 55 kgauss in a longitudinal field. This minimum should correspond to the situation where the Landau level with l = 1 coincides with the Fermi level in the PbTe crystals.
Self-Trapping and Drift Motion of an Electron
Authors: Toyozawa Y. 
Published: April 2005

The importance of the acoustical mode lattice vibration for self-trapping of an electron is emphasized in this paper. It is shown that when the coupling constant between the electron and the acoustical vibration exceeds a certain critical value, the effective mass of the electron changes discontinuously to such an enormous value that it is practically allowed to take a localized self-trapping state as an eigenstate, in contrast to the case of polar mode, in which the effective mass changes continuously with coupling constant. This difference is attributed to the different force range of the electron-lattice interaction in the two cases.
The self-trapping state as well as the activated state for the hopping motion are discussed within the framework of adiabatic approximation by making use of Koster-Slater's method. It is pointed out that drift motion is more probable than the hopping motion for the intermediate magnitude of coupling constant.
Polarization of Luminescence
Authors: Clark C. D. , Maycraft G. W. , Mitchell E. W. J. 
Published: April 2005

A brief review will be given of the methods of studying the polarization of luminescence and of the theory of the effect in relation to determining the electronic structure of centers. Reference will be made to the work on the alkali halides and diamond.
Detailed experimental results will be presented and discussed of the fluorescence of the 5032 A center in diamond which is formed by heat treatment after irradiation. In these experiments the polarization has been studied as a function of the energy of both the exciting and of the emitted light. Depolarization occurs if the system is excited above the lowest level in the excited electronic state, or decays to a level above the lowest level in the ground electronic state.
A comparison of the results will be given with those expected from centers having various electronic axes.
Disorder and Oxygen Transport in Cadmium Oxide
Authors: Haul R. , Just D. 
Published: April 2005

Oxygen-18 exchange between gaseous oxygen and cadmium oxide crystals has been studied in the temperature range 630° to 855°C. Since isotope equilibrium is not instantaneously established at the crystal surface an appropriate solution for this particular diffusion problem has been given. In this way it is possible to evaluate rate constants (K) of the phase boundary reaction as well as lattice diffusion constants (D): D=3.8·106exp(−92±4/RT);  K=1.3·102exp(−49±11/RT). The influence of the ambient oxygen pressure (D∼po2−1/5) indicates that a vacancy mechanism is operative in the diffusion of oxygen. This is substantiated by the finding that diffusion is enhanced by incorporation of Li2O. From experiments with doped crystals the fraction of vacancies can be estimated, e.g., 4.4·10−4 in ``pure'' CdO at 790°C and 0.16 atm O2. On the basis of thermodynamic considerations the energy of formation of defects can be estimated at 29 leaving 63 kcal/mole for the activation energy of the diffusion process proper.
The rate constant of the phase boundary reaction increases with decreasing oxygen pressure (K∼po2−⅓) as well as with increasing Li2O addition. These findings offer a possibility for the suggestion of a mechanism of the surface exchange process.
Superconducting Film Geometry With Strong Critical Current Asymmetry
Authors: Edwards H. H. , Newhouse V. L. 
Published: April 2005

It is shown that film critical current, defined as the maximum current for which a film shows no resistance, can be strongly increased in one direction and strongly decreased in the other by the field from two current carrying conductors placed parallel to the film edges.
The effect is shown to be due to mutual cancellation of the magnetic fields normal to the film created by the wire currents and the film current. It appears to make a flat film superconductive rectifier possible.
It is proved that the symmetrical increase of critical current due to the proximity of a superconducting ``shield'' plane is due to a similar mechanism, and that fields normal to the film surface are largely responsible for the broad current induced transition of flat ``unshielded'' films.
It is also shown that with mutually opposed wire currents the variation of critical current with wire current exhibits a significant hysteresis. This effect may have applications to digital storage.
Effect of Noncrystallizable Components on the Crystallization Kinetics of Polymers
Authors: Gornick F. , Mandelkern L. 
Published: April 2005

The effects of chain irregularities, treated as randomly introduced copolymeric units and of added monomeric diluents, on the nucleation rate of crystallizing polymeric systems have been calculated. A marked attenuation in the nucleation rate is expected under certain conditions as a consequence of the varying composition of the melt. The decrease in the nucleation rate becomes more pronounced at the lower undercoolings and as the concentration of the noncrystallizing component increases.
The Avrami mathematical formulation for the kinetics of phase changes can be generalized to allow for nucleation and growth rates which vary with the amount of material transformed. The resulting isotherms for copolymers are no longer superposable, superposability being characteristic of crystallization under conditions of constant nucleation and growth. Possible error in the interpretation of crystallization kinetics utilizing the simplified version of Avrami's equation is pointed out, as is the extreme sensitivity of the crystallization process to the presence of small amounts of chain irregularities.
Hot-Electron Transport in Semiconductor-Metal-Semiconductor Structures
Authors: Sze S. M. , Crowell C. R. , Carey G. P. , LaBate E. E. 
Published: April 2005

The low-frequency common-base current transfer ratio α0 for hot-electron transport in semiconductor-metal-semiconductor point-contact-transistor structures has been measured as a function of metal film thickness and temperature. Measurements have been made possible by the use of a cantilever-beam mechanism capable of contact-separation adjustments as low as 10 Å. From these results, the ballistic mean free paths for electron transport in the metal base have been obtained as a function of temperature and electron energy.
Au, Ag, Pd, and Al have been used as the base metals; Ge, Si, GaAs, and GaP as the emitter semiconductors; and Ge, Si, GaAs, GaP, CdSe, and CdS as the collector semiconductors.
The measured values of α0 obey the simple expression α0=α* exp(−W/LB), where α* is the current gain extrapolated to zero metal-base thickness, and LB the ballistic mean free path. Of the structures investigated GaP-Au-Ge exhibits the highest α*, about 0.5. With≈100-Å base thickness, the highest α0 obtained is about 0.3 (for Si–Au/Ag–Ge and GaP–Au/Ag–Ge structures). The ballistic mean free paths for 1-eV electrons at room temperature are 265 Å for Ag, 220 Å for Au, 90 Å for Pd, and ≈100 Å for Al. The results are in reasonable agreement with theoretical expectations.
Temperature Dependence of Dielectric Breakdown of Potassium Chloride Crystals under dc and Pulse Voltages
Authors: Kaseta Francis W. , Li H. Tung 
Published: April 2005

The dielectric breakdown strength of a KCl single crystal in the temperature range 4.2°–425°K and of a mixed crystal (75/25 mole % KCl-RbCl) between 77° and 375°K was measured with dc voltage and with pulses of 1- and 10-μsec risetime. The dc strength lies below the pulse strength over the entire temperature range. Pulse and dc strengths gradually rise from 4° to 77°K. The temperature characteristic of the dc breakdown strength traverses a maximum that vanishes completely for 1-μsec risetime. The dc strength for the mixed crystal lies above that of pure KCl at low temperature and drops more sharply in the high temperature range.
Von Hippel's and Fröhlich's breakdown criteria are re-examined. The former is formulated quantitatively and its necessity demonstrated within the framework of the ``one-electron'' intrinsic breakdown theory. The experimental results are in substantial agreement with theoretical values, based on von Hippel's criterion and Callen's calculation.
Evidence by Lorentz Microscopy for Magnetically Active Stacking Faults in MnAl Alloy
Authors: Zijlstra H. , Haanstra H. B. 
Published: April 2005

In the ordered MnAl crystal containing magnetic atoms which are coupled ferromagnetically, stacking faults are postulated through which an antiferromagnetic coupling exists between the atoms on either side of the fault. These account for the anomalous magnetic behavior of fine MnAl powder. Such faults give rise to a domain structure the walls of which are strongly pinned to these crystallographic defects. A direct evidence for the occurrence of these stacking faults is obtained by using Lorentz electron microscopy, whereby shadow patterns of opaque MnAl particles show a characteristic distortion of their contours when the microscope is used out of focus. The distortion is interpreted in terms of stray fields due to the domain structure.
By using either the normal objective lens, which is an immersion lens, or the diffraction lens, the pattern can be studied with or without a strong applied field. Fields up to 9000 Oe could be applied. Domain structures were observed that showed a remarkable indifference for these fields. This rigidity is explained by assuming that the walls are pinned to stacking faults.
Domain structures with a high pole density on the walls were also observed. These structures are unfavorable owing to large magnetostatic energy. Their occurrence is also explained by the presence of stacking faults.
Thermionic Converters Operating in the Ignited Mode. Part II: A Quasi-Equilibrium Model for the Interelectrode Plasma
Authors: Wilkins Daniel R. , Gyftopoulos Elias P. 
Published: April 2005

A multistage ionization-recombination model is proposed to describe the formation and loss of atomic ions in low-energy cesium plasmas. Solutions of the ambipolar diffusion equation are investigated with due consideration given to these processes. The solutions indicate the existence of a state of quasi-equilibrium throughout most of a low-energy plasma in which the electron temperature is more than several hundred degrees above a critical ignition temperature.
The assumption of quasi-equilibrium in the interelectrode plasma of a thermionic converter operating in the collisional ignited mode is shown to result in a plasma model which correlates a wide variety of experimental data. Included in the successful correlations are electron random current density and temperature profiles as well as output-current characteristics.
The experimentally observed state of quasi-equilibrium in thermionic converter plasmas is found to be near the Saha-equilibrium limit. It is therefore concluded that the multistage ionization-recombination processes in these plasmas involve numerous excited states.
Transient changes in behaviour lead to heroin overdose: results from a case‐crossover study of non‐fatal overdose
Authors: Dietze Paul , Jolley Damien , Fry Craig , Bammer Gabriele 
Published: April 2005

ABSTRACTBackground and aims  Heroin overdose is a serious consequence of heroin use and one of the leading causes of premature death and illness in Australia. Despite considerable research effort little is known about the effects of transient changes in heroin user behaviour and the links to overdose. This research is the first to use a suitable methodology to allow such ephemeral changes and their effects on non‐fatal heroin overdose to be examined.Methods  A case‐crossover design was used in which non‐fatal heroin overdose survivors’ recall of risk behaviours in the 12 hours prior to overdose (hazard period) was compared to their recall of risk behaviours in the 12 hours prior to a selected non‐overdose heroin injection (control period).Results  A total of 155 participants were able to provide valid details of hazard and control periods. A dose–response relationship was observed between the self‐reported amount of heroin used and likelihood of overdose (e.g. > AUD50, OR 12.97, 95% CI 2.54–66.31). The use of benzodiazepines (OR 28, 95% CI 3.81–205.79) or alcohol (OR 2.88, 95% CI 1.29–6.43), during the hazard period was related to overdose risk, but the effect of alcohol was attenuated by the effect of benzodiazepines. Shifting from private to public locations between control and hazard periods was also related to increased risk of overdose (OR 3.63, 95% CI 1.66–7.93).Conclusions  We demonstrate the value of a new methodology to explore heroin overdose, as well as discussing its limitations and ways to overcome them in future. In terms of our findings, overdose prevention messages need to highlight the impact of these transient changes in behaviour and to emphasize the risks of using higher doses of heroin as well as continuing to emphasize the risks of combining heroin with other central nervous system (CNS) depressants. Safer environments for heroin use, such as injecting rooms, may also reduce the chances of overdose.