bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dislocation Velocities, Dislocation Densities, and Plastic Flow in Lithium Fluoride Crystals
Authors: Johnston W. G. , Gilman J. J. 
Published: April 2005

Velocities of individual dislocations have been measured in LiF, covering a range of twelve orders of magnitude in velocity, from 10−7 cm/sec to 105 cm/sec. The velocity is extremely sensitive to applied stress at low velocities, and for each crystal there exists a minimum stress for dislocation motion, below which dislocations do not move. The edge components of dislocation loops move considerably faster than the screw components. The upper limit for dislocation velocity appears to be the velocity of sound in the crystal. The effects of temperature, impurities, and radiation damage on dislocation velocity are described. These variables affect the dynamic resistance to motion encountered by a moving glide dislocation.
The growth of total dislocation density, the growth of individual glide bands, and the distribution of glide dislocations during plastic deformation are described.
The yield stress of LiF is determined by the resistance to motion encountered by a glide dislocation in moving through an otherwise dislocation-free region of the crystal. The yield stress is independent of the dislocations present in an undeformed crystal, and the state of pinning and geometrical arrangement of such dislocations do not affect the yield stress.
Stress-strain curves have been calculated from the data on dislocation mobility and dislocation density, and the calculated and measured curves are compared. At low strains the flow stress can be predicted from measured dislocation properties.
Small Angle X-Ray Scattering from Copper and Aluminum under Cyclic Stress
Authors: Grosskreutz J. C. , Rollins F. R. 
Published: April 2005

Copper and aluminum samples were subjected to cyclic stress and run to fatigue while being held in an x-ray beam. Small angle scattering intensities were recorded at various stages of the fatigue life. These intensities were found to increase with the number of elapsed stress cycles.
The observed angular dependence and intensity of the scattered radiation agrees most nearly with a double Bragg scattering mechanism. The relation of the fatigue mechanism to the formation of small angle subgrain boundaries responsible for the double Bragg scattering is not clear-cut. However, the evidence favors the view that the formation of subgrains, while probably necessary to the propagation of the fatigue crack, is not sufficient either for its formation or propagation. Complete annealing of the scattering was not possible, indicating that recrystallization does not take place following cyclic stress of the order of one-fourth the yield stress. No evidence exists for a widespread formation of voids in the fatigued specimen.
Form Effect in Linear Magnetostriction
Authors: Stauss H. E. 
Published: April 2005

The influence of the shape of the specimen upon the measured value of magnetostriction is a matter of importance. The classical thermodynamical calculation of Becker applies to specimens in like magnetic fields and consequently compares bodies with unlike intensities of magnetization. In the present paper use is made of the principle of virtual work to make a calculation of the form effect as dependent upon the intensity of magnetization. The form effect for an ellipsoid in an extended uniform field is found to be a constrictive strain of the magnitude ΔA11=−(1−2μ)ENI22, where ΔA11 is the form effect in strain, μ is Poisson's ratio, E is Young's modulus, N is the coefficient of self-demagnetization, and I the intensity of magnetization. Above saturation the form effect is ΔA11=−(1−2μ)ENIs22, where Is is the saturation value of I.
The meaning of the term form effect has been expanded to include not only the change in strain in the specimen resulting from the shape of the specimen itself, but also the change resulting from the position of the specimen relative to the magnetizing apparatus. A calculation of the form effect in this extended sense is made for two useful experimental arrangements; one where a specimen is sandwiched between two movable rods and the other where the specimen is situated in the fixed gap of a magnet. For the first case it is found that the form effect depends upon the self-demagnetization of the entire ferromagnetic arrangement and not of the specimen itself. In the second case, the form effect is dependent upon the ratio of gap energy to the volume of the ferromagnetic system and can be small, subject to the qualification that the form effect does not include the effects of any stresses that develop within the gap.
Temperature Dependence of Fractional Velocity Changes in a Silicon Single Crystal
Authors: Stein Frances , Einspruch Norman G. , Truell Rohn 
Published: April 2005

An ultrasonic interferometer technique for measuring the temperature dependence of the relative change in elastic constants is described in detail. Results are reported for measurements carried out as a function of frequency from 10 mc/sec to 170 mc/sec, for compressional wave propagation along the [100] axis of silicon over a temperature range of −60° to +15°C.
The mean value of (1/c11)(dc11/dT) obtained is 55.59±0.81×10−6 (°C)−1, and no frequency dependence of (1/c11)(dc11/dT) was found.
High-Energy Electron Irradiation of Germanium and Tellurium
Authors: Van Lint Victor A. J. , Roth Harold 
Published: April 2005

Tellurium samples in which current flowed parallel to the c axis were irradiated at 78°K with 20-Mev electrons. The conductivity increased linearly with a slope of 1.0×10−14 (ohm-cm)−1 per electron/cm2 up to at least 3×1014 electrons/cm2. Beyond 3×1015 electrons/cm2 the slope was approximately one tenth of the initial value. The reciprocal of the Hall coefficient decreased at first and then increased. Between 1×1013 and 5×1013 electrons/cm2 1/RH increases linearly from 3×10−5 to 6.3×10−5 coulomb/cm3. After irradiation, the samples showed no measurable conductivity changes during 14 hr at 78°K. After a day's anneal at 300°K the 78°K conductivity returned to its preirradiation value.
N-type germanium was irradiated with 20-Mev electrons at room temperature. Conductivity measurements indicated that the sample became intrinsic and then p type. However, the detailed dependence of conductivity on radiation dosage did not agree with a calculation based on four energy levels introduced into the gap. Carrier lifetime changes were also observed.
On the Macroscopic Analysis of the Conducting Electromechanical Solid with Application to Cylinders Subjected to Axial Electric Fields
Authors: Geldmacher R. C. 
Published: April 2005

In the present work, the ambient to melting phase of the problem has been examined from the standpoint of intercoupled electrical, thermal, and mechanical effects in order to establish the foundations for a theoretical solution, and to establish the intervals over which the solution is valid. Thermoelectric and electromagnetic effects were considered relative to their influence on the distribution of temperature and electric field within the conductor. Body forces resulting from the electromagnetic field were also considered and the corresponding stresses worked out.
The principal analytic result obtained is that for the nonlinear problem resulting from electrothermal coupling through temperature-dependent electrical conductivity. General solutions have been obtained for conditions of no heat loss at the boundary, radiation at the boundary (Newton's law of cooling), and the boundary fixed at the initial temperature.
Various examples of engineering interest have been worked out and the results are compared with solutions obtained assuming constant electrical conductivity.
It has been found that significant electromechanical body forces may be present under certain circumstances and it is shown that these body forces may play an important part in the breakup of wires subjected to large, suddenly applied fields.
Dislocation Contributions to the Modulus and Damping in Copper at Megacycle Frequencies
Authors: Alers G. A. , Thompson D. O. 
Published: April 2005

The three elastic moduli of 99.999+% pure copper and their associated internal frictions have been measured at Mc frequencies between 4.2 and 250°K both before and after fast neutron bombardment. The changes produced by the irradiation were used to determine the dislocation contributions to the damping and moduli as a function of frequency and temperature. The dislocation damping showed the maximum predicted by Granato and Lücke to arise from the heavily damped bowing of dislocation loops. By calculating the resolved shear stress factors and measuring the dislocation density by etch pit counts, it was possible to determine the coefficient B which describes the viscous drag on a moving dislocation as well as the effective loop length l. The factor B was found to be 8×10−4 d sec/cm2 at 300°K and to decrease linearly with decreasing temperature, as predicted by Leibfried. The effective loop length appeared temperature independent and had a value of 3×10−4 cm in the sample examined most carefully.
Cold-worked single crystals of the same copper were also studied. Two Bordoni type peaks in the damping vs temperature curves were located at 135 and 60°K at 10 Mc. Activation energies of 0.113 and 0.05 ev were determined by using low-frequency data taken from the literature.
Effects of Doping Additions on the Thermoelectric Properties of the Intrinsic Semiconductor Bi2Te2.1Se0.9
Authors: Bennett L. C. , Wiese J. R. 
Published: April 2005

An alloy of 70 mol % Bi2Te3−30 mol % Bi2Se3, or Bi2Te2.1Se0.9, is the intrinsic semiconductor of the pseudobinary system Bi2Te3–Bi2Se3. This V–VI alloy was doped with lead (Group IV) and iodine (Group VII) separately and together. The effects of the dopants are analogous to those produced by Group III or Group V impurities in Group IV elemental semiconductors, the lower Group impurity producing a p-type material and the higher Group impurity an n-type material. Plots of the Seebeck coefficient, electrical conductivity, and thermal conductivity are given as a function of impurity concentration and show that the separate effects of the impurities are countered when the impurities are in the lattice together in the same amount.
Doping was also done with silver and iodine, separately and together. The results indicate that the silver is in the lattice interstitially (lead and iodine substitutionally) and that the type material produced is dependent also on how the impurity atom enters the lattice.
Measurement of the Electrical Conductivity and Dielectric Constant without Contacting Electrodes
Authors: Ogawa Tomoya 
Published: April 2005

A method is developed whereby electrical conductivity and dielectric constant of semiconducting and dielectric materials without contacting electrodes can be measured. The principle of this method is that a specimen suspended in a rotating field with a fine fiber is rotated by the torque proportional to the electrical conductivity or the imaginary part of its complex dielectric constant, and the torque exerted on it by a linearly polarized field is proportional to the real part of its dielectric constant.
An analysis of the method and some preliminary measurements of conductivity, photoconductivity, the dielectric constant of cadmium sulphate crystals and the dielectric loss of the lamella containing CdS powder are presented. The latter shows the photodielectric effect.
Motion of 180° Domain Walls in BaTiO3 under the Application of a Train of Voltage Pulses
Authors: Miller Robert C. , Savage Albert 
Published: April 2005

A study has been made of the sidewise motion of 180° domain walls in single-crystal BaTiO3 under the application of a train of voltage pulses. Measurements of the sidewise wall velocity as a function of the pulse amplitude, pulse width, and pulse repetition rate can be explained in terms of a surface layer model recently proposed for BaTiO3. These data constitute the first experimental verification of some of the important phenomena consequent on the model. This model assumes that a surface charge density of 2Ps, where Ps is the spontaneous polarization, is deposited immediately behind an advancing 180° domain boundary on the interface between the bulk ferroelectric material and the anomalous surface layer. This charge distribution gives rise to an electric field Eb′ in the bulk of the material with a component opposite in direction to the field applied to move the wall. It is found that relaxation of Eb′ begins in about 0.3 msec and continues for times in excess of 1 sec. This relaxation is not due to a simple, single time-constant, mechanism. Any fast relaxation, if present, must take place in times less than 1 μsec. After a 180° wall is at rest sufficiently long so that relaxation of Eb′ has occurred, application of an external applied field results in a wall velocity which depends on the magnitude of the wall displacement. In particular, the wall velocity decreases (due to Eb′ which increases) with increasing wall displacement. Analyses of the data show that the lateral or sidewise range of the field from the elements of charge which give rise to Eb′ is of the order of 2000 A so that once the wall has moved this distance, the effect of Eb′ at the wall, and hence the wall velocity, becomes constant. With thin crystals in the absence of an external applied field, Eb′ gives rise to wall displacements of the order of 100 A in a direction opposite to that of the wall motion which produced Eb′. The decrease in wall velocity observed when the wall displacement per pulse is of the order of a unit cell is consistent with a nucleation-controlled mechanism proposed earlier for the wall motion.
Pulse data on crystals with different impurity concentrations and electrode materials show that the relaxation of Eb′ and the lateral range r, and hence the surface layers inferred from these data, are not markedly dependent on these parameters. Other data on the dc wall velocity indicate that for a velocity of 10−3 cm/sec, the potential drop across the surface layer is 1.0±0.1 v, and that it is independent of the crystal dopings and the electrode materials tested. These data indicate that the average field in the bulk required for a given wall velocity is not a constant independent of the type of electrode or the impurity concentration. The approximate constancy of the measured characteristics of the surface layers makes the dependence of the wall velocity on the impurity content and the electrode material difficult to explain in terms of the model considered.
A Phenomenological Theory of the Soret Diffusion
Authors: Bierlein James A. 
Published: April 2005

The classical Soret diffusion problem is solved analytically for the case of unrestricted composition in a binary liquid system, taking account of the temperature-variation of the density of the mixture. Previous treatments have neglected the phenomenon of thermal dilatation entirely and have not developed a unique general solution which applies both to dilute and to nondilute mixtures.
The rigorous solution derived in the present work is similar in form to de Groot's well-known equation for dilute mixtures, but contains additional parameters characterizing the initial composition of the system and its coefficient of thermal expansion. These parameters disappear in the asymptotic approximation for a vanishing temperature gradient, but this approximation differs from that proposed by de Groot, even for dilute solutions. The asymptotic expression has practical importance for estimating the Soret coefficient and the ordinary diffusion coefficient of a system from experimental data taken during the thermodiffusional unmixing period; some examples of its application in this connection are discussed.
Magnetic Susceptibility of Liquid Ozone-Oxygen Mixtures
Authors: Brown Callaway , Hersh Charles K. , Berger Abraham W. 
Published: April 2005

The data needed for analysis of liquid ozone-oxygen mixtures by measurement of magnetic susceptibility are presented. Volumetric preparation of liquid ozone-oxygen mixtures in equilibrium with the vapor phase is described. A permanent magnet at the temperature of the solutions provided the key for use of the Quincke (U-tube) method for magnetic susceptibility.
Results at — 195° and — 183°C show a linear relation between the magnetic susceptibility of the solutions and weight percent oxygen at low oxygen content. Above about 10 percent oxygen the specific susceptibility of oxygen in solution decreases significantly. At — 183°C, the ratio X8/X0 of specific susceptibility of oxygen in solution to that of pure liquid oxygen decreased from 1.30 at low concentrations to 1.13 at 27.6 percent oxygen, the two-liquid phase boundary. The limiting ratio at — 195°C was 1.42. The discontinuity in magnetic susceptibility was used to establish the compositions at the phase boundaries; 9.2 and 91 percent by weight oxygen at — 195°C, 27.6 and 70.2 percent at — 183°C.
C13 Isotope Effect in the Thermodecomposition of Ethyl Bromide
Authors: Friedman Henry L. , Bernstein Richard B. , Gunning Harry E. 
Published: April 2005

The C12—C13 fractionation factor in the decomposition of gaseous ethyl bromide has been measured from 350—450°C, using samples of natural isotope abundance. The rate constants are defined as follows: CH3CH2Br→CH2=CH2+HBrk1,CH3C*H2Br→CH2=C*H2+HBrk2,C*H3CH2Br→C*H2=CH2+HBrk3.At 400°C, the C12 enrichment of the first fraction of ethylene from decomposition of the ethyl bromide is S0≡1+ε0=2k1k2+k3=1.0079±0.0006,with a temperature coefficient of — 2.8×10-5/°C.
The primary and secondary isotope effects are defined, respectively, as β=k1/k2—1 and γ=k1/k3—1; thus, to a good approximation, β+γ=2ε0. According to theory, β&gt;γ≥0, so that ε0&lt;β≤2ε0 and ε0&gt;γ≥0. From the data of 400°C one then obtains as an upper limit (k1/k2)max≤1.0159±0.0012. This is significantly lower than the value k1/k2≥1.036 calculated for the rupture of an isolated C—Br bond. The present results, therefore, favor a mechanism involving the direct intramolecular elimination of HBr.
Spectroscopic Studies of Rotational Isomerism in Fluorinated Ethanes. I. 1,2-Difluoro-1,1,2,2-Tetrachloroethane
Authors: Kagarise R. E. , Daasch L. W. 
Published: April 2005

The Raman spectra of solid and liquid CFCl2–CFCl2 have been investigated, and the observed frequency shifts (Δν cm—), relative intensities, and depolarization factors are presented for the latter. The infrared absorption spectra of the liquid in the 2—36-μ region, and of the solid and vapor in the 2—22-μ region have also been studied.
The behavior of the infrared and Raman spectra as a function of temperature and upon solidification was anomalous in that no changes in the relative intensities of the spectral lines were observed.
Two possible explanations of the spectroscopic data are considered, neither of which is completely satisfactory. The assumption of a single molecular species, corresponding to a large energy difference, is apparently in conflict with the number of observed Raman frequencies, while the assumption of two forms of almost equal energy (ΔH&lt;300 calories/mole) is inconsistent with the persistence of all lines upon solidification.
Oxygen-18 Isotope Effect in the Reaction of Oxygen with Copper
Authors: Bernstein Richard B. 
Published: April 2005

The fractionation of oxygen-18 in the reaction of copper with oxygen of natural isotopic composition has been measured over the temperature range 68—256°C. The oxide films (estimated thicknesses varying from 150—2500 A) were removed for O18 assay by treatment with hydrogen at 350°C. Using the CO2 equilibration technique, the O18/O16 ratios for the resulting water samples were determined mass spectrometrically and compared with the ratio for a reference sample of water prepared from the original oxygen gas.
The direction of the fractionation indicated that O216 reacts preferentially compared to O16O18. The isotope effect appeared to be independent of the oxygen pressure over the limited range studied (2—25 cm Hg). The magnitude of the fractionation factor was 2.0% at 150°C, with a small negative temperature coefficient. From this it was possible to estimate a value of ΔEact=17 cal/mole, which may be compared with the calculated isotopic zero-point energy difference of 64 cal/mole. The theoretical implications of the experimental results are discussed.
Electronic Population Analysis on LCAO–MO Molecular Wave Functions. I
Authors: Mulliken R. S. 
Published: April 2005

With increasing availability of good all-electron LCAO MO (LCAO molecular orbital) wave functions for molecules, a systematic procedure for obtaining maximum insight from such data has become desirable. An analysis in quantitative form is given here in terms of breakdowns of the electronic population into partial and total ``gross atomic populations,'' or into partial and total ``net atomic populations'' together with ``overlap populations.'' ``Gross atomic populations'' distribute the electrons almost perfectly among the various AOs (atomic orbitals) of the various atoms in the molecule. From these numbers, a definite figure is obtained for the amount of promotion (e.g., from 2s to 2p) in each atom; and also for the gross charge Q on each atom if the bonds are polar. The total overlap population for any pair of atoms in a molecule is in general made up of positive and negative contributions. If the total overlap population between two atoms is positive, they are bonded; if negative, they are antibonded.
Tables of gross atomic populations and overlap populations, also gross atomic charges Q, computed from SCF (self-consistent field) LCAO-MO data on CO and H2O, are given. The amount of s-p promotion is found to be nearly the same for the O atom in CO and in H2O (0.14 electron in CO and 0.15e in H2O). For the C atom in CO it is 0.50e. For the N atom in N2 it is 0.26e according to calculations by Scherr. In spite of very strong polarity in the π bonds in CO, the σ and π overlap populations are very similar to those in N2. In CO the total overlap population for the π electrons is about twice that for the σ electrons. The most easily ionized electrons of CO are in an MO such that its gross atomic population is 94% localized on the carbon atom; these electrons account for the (weak) electron donor properties of CO. A comparison between changes of bond lengths observed on removal of an electron from one or another MO of CO and H2, and corresponding changes in computed overlap populations, shows good correlation. Several other points of interest are discussed.
Electronic Population Analysis on LCAO–MO Molecular Wave Functions. II. Overlap Populations, Bond Orders, and Covalent Bond Energies
Authors: Mulliken R. S. 
Published: April 2005

LCAO molecular orbital overlap populations give in general much more flexible and widely useful measures of the non-Coulombic parts of covalent bond energies than do LCAO bond orders. They are immediately applicable to both π and σ bonds, including bonds involving hybrid AOs of all kinds, and they take account directly of the effects of variations in bond length on bond strength. In the last section of this paper, a number of ways of defining LCAO bond orders are reviewed, and their advantages and disadvantages discussed.
If all LCAO parameters β are assumed proportional to corresponding overlap integrals S times suitable mean atomic ionization energies Ī, a simple general approximate formula for covalent resonance energies is obtained in terms of partial overlap populations and Ī's, including one or two empirical coefficients. This formula indicates that forced hybridization (see III of this series) due to inner shells should make important negative contributions to bond energies. The application of the formula to H2, CO, and H2O is discussed.
The assumption of proportionality of β values to SĪ values may be useful also in estimating unknown β values.