bluuebunny/crossref_metadata_2025 huggingface dataset:
EPR SPECTRA OF PAIRS OF INTERACTING RARE-EARTH IONS
Authors: Baker J. M. , Mau A. E.
Published: April 2011

The EPR spectra of interacting pairs of Dy3+, Tb3+, and Ho3+ ions in rare-earth ethyl sulfates have been studied in order to determine the nature and magnitude of the interactions. The departures from dipole–dipole interaction are mostly rather small, except for the interaction between a pair of Dy3+ ions, one of which is in the ground doublet and the other in the first excited doublet at 16 cm−1. A discussion is given of the difficulties of differentiating between the effects of electric quadrupole–quadrupole interaction and virtual phonon exchange interaction.
ION–ION RECOMBINATION COEFFICIENT: I. CORRECTION FOR ION DISTRIBUTION AND DIFFUSION LOSSES IN PLANE PARALLEL ION CHAMBERS
Authors: McGowan S.
Published: April 2011

Correction factors to measured values of the ion–ion recombination coefficient, which are required because of nonuniform ion density and diffusion losses, are calculated from computer solutions to the differential equation for simultaneous recombination and diffusion. Results for plane-parallel ion chambers are given as a function of ion age for an initially uniform ion distribution over a considerable range of ion density and electrode spacing, and for a collimated distribution for two particular combinations of ion density and electrode spacing. Corrections to be applied to some reported experimental ion–ion recombination coefficients are estimated.
DISLOCATION MOVEMENT THROUGH RANDOM ARRAYS OF OBSTACLES
Authors: Foreman A. J. E. , Makin M. J.
Published: April 2011

A computer program that determines the stress required to move a dislocation through an array of obstacles distributed at random on a slip plane has been written. This program has been used to measure the critical shear stress of random arrays of (a) obstacles of various equal strengths, (b) obstacles with two differing strengths, (c) obstacles with a square spectrum of strengths, and (d) circular prismatic loops lying on {110} planes in a face-centered cubic crystal.
SLIP BEHAVIOR IN COPPER CRYSTALS PREVIOUSLY DEFORMED ON ANOTHER SLIP SYSTEM
Authors: Sharp J. V. , Makin M. J.
Published: April 2011

An electron-microscope study has been made of the nature of the dislocation arrangements produced during the second deformation of a copper single crystal previously deformed on another slip system. Two features are commonly observed. First, the second deformation commences by fine slip within the cell structure produced by the first deformation. This process, however, appears to be capable of accommodating only a limited strain, which depends markedly on the cell size, being much larger for larger cell sizes. At higher strains, coarse slip bands form, and it is suggested that these occur by the mutual annihilation of piled-up groups of positive and negative dislocations on opposite sides of cell walls, and thus creating softened regions which spread across the crystal.
THE EFFECT OF SOLUTE ON SLIP AND MECHANICAL TWINNING IN IRON ALLOYS
Authors: Bolling G. F. , Richman R. H.
Published: April 2011

The effects of solute type and concentration upon the nature of, and stresses for, plastic flow in polycrystalline iron solid solutions have been examined. An extensive study was made using Al, Be, Ge, P, Si, and Sn; limited examples with Co, Sb, and Ti are also included. Three experimental observations stand out: (i) At room temperature and lower solute concentration the flow stress for slip increases monotonically with the parameter c|ln km|. Here c is the solute concentration, and the solid–liquid distribution coefficient, km, differentiates the solute type, (ii) At room temperature, there is a transition in the deformation mode from slip to twinning at a concentration that decreases with increasing |ln km|. The actual stresses for mechanical twinning can be compared with those at 77 °K; they are higher and provide a second measure for the deformation-mode transition, (iii) At 77 °K the initial deformation mode is predominantly mechanical twinning, and, below concentrations producing atomic ordering, the initial flow stresses are independent of solute concentration and type.When these observations are accompanied by tests for the propagation-controlled phenomenon of continual mechanical twinning, we deduce the following: (i) and (ii) show that solute promotes mechanical twinning as a consequence of its effect on dislocation behavior, most likely by requiring fast-moving individual dislocations, while (iii) shows that a threshold stress exists for the nucleation of mechanical twins that cannot easily be explained by existing twin-nucleation mechanisms.
DISLOCATION PILEUPS AND THE HALL–PETCH RELATION
Authors: Chou Y. T.
Published: April 2011

The strength of a linear dislocation pileup depends on the nature of its barrier. Analysis is given for the case in which the barrier is a second-phase particle and for that in which the barrier is a locked dislocation with a different Burgers vector.In the first case, where pileups lie in front of hard inclusions, it is shown that the Hall–Petch relation is valid and that the Petch slope increases as the ratio of the inclusion/matrix shear moduli increases. For a screw dislocation pileup, the Petch slope increases by a factor of about 2 for a modulus ratio of 3 and by about a factor of 3 for a ratio of 7. The increase for edge pileups is somewhat higher.In the second case, where the barrier is a locked dislocation with a different Burgers vector, the Petch slope may be increased (or decreased) by a factor of √m, where m is the ratio of the Burgers vector of the locked dislocation resolved in the slip plane to that of the free dislocations in the pileup.
THE LINEAR HARDENING OF CADMIUM
Authors: Risebrough N. R. , Teghtsoonian E.
Published: April 2011

It has been observed that in polycrystalline cadmium regions of linear hardening insensitive to temperature and strain rate occur at temperatures below 150 °K. The extent of this region increases as the temperature decreases. The hardening coefficients of single crystals are also independent of temperature below 150 °K.The rate of hardening at 77 °K is a function of the grain size and has been shown to vary linearly with the inverse square root of the grain size. The hardening rate obtained on extrapolating [Formula: see text] to zero is that of the tensile hardening rate during stage B deformation of single crystals when the latter is associated with a heavily twinned structure. The grain-size dependence of hardening is due mainly to the amount of [Formula: see text][Formula: see text] slip. It was observed that the Cottrell–Stokes Law is obeyed only in the linear hardening regions. The rate-controlling process is probably one of dislocation intersection with the force–distance curve being independent of grain size. A grain-size dependence of the value of Δσ/σ is interpreted in terms of a change in the relative contributions of the components of the athermal stress τG.
ON THE MECHANISM OF WORK HARDENING IN f.c.c. METALS
Authors: Kronmüller Helmut
Published: April 2011

A review of the methods applied for the investigation of long-range stresses in deformed single crystals is given. The results found by magnetic methods are discussed in some detail; slip-line data and transmission microscopy are mentioned briefly. The effect of internal stresses on the flow stress is discussed and it is shown that the elastic interaction between the primary dislocations determines the flow stress almost completely. Secondary dislocations are found to be incapable of relaxing the stress fields of the primary dislocations appreciably.
WORK HARDENING IN EASY GLIDE
Authors: Hazzledine P. M.
Published: April 2011

A theory of single-slip work hardening is proposed, in which the flow stress is controlled by the stress required for one group of dislocations to pass another group with the same Burgers vector but with opposite sign on a parallel slip plane. The strain and the details of the slip-line pattern are calculated as a function of stress from the known properties of edge-dislocation multipoles. The predictions of the theory are compared with experimental measurements on Mg and are found to be in fair agreement.The theory presented is a highly simplified first version, and various possible developments of it are discussed.
THE PLASTIC DEFORMATION OF THIN COPPER SINGLE CRYSTALS: II. AN ELECTRON MICROSCOPE STUDY OF THE SURFACE STRUCTURE
Authors: Fourie J. T.
Published: April 2011

A comparison is made between the slip-line structure of two copper single crystals, where the glide path length of edge dislocations is 1.44 mm and 0.066 mm, respectively. No significant difference is found. This leads to the conclusion that dislocations that escape at the surface of a crystal are generated very close to it.Stress–strain experiments on thin layers of crystal from the surface and from the center of previously deformed crystals confirm that slip lines are not representative of the bulk deformation. They also show that a flow-stress gradient exists between the surface and the center of the crystal. It is argued that the existence of such a gradient can be used to explain the dependence of the extent of stage I on the glide path length of edge dislocations.
THE STACKING-FAULT ENERGY IN α-SILVER – TIN ALLOYS
Authors: Ruff Jr. A. W. , Ives L. K.
Published: April 2011

Direct measurements by transmission electron microscopy on extended dislocation nodes in alloys of tin in silver have led to values for the intrinsic stacking-fault energy. The values decreased smoothly from 23 erg/cm2 for pure silver to 4.2 erg/cm2 for 7.8 at.% tin. The results are compared with previous determinations in other silver-base alloys.
GLIDE OF JOGGED DISLOCATIONS
Authors: Hirth J. P. , Lothe J.
Published: April 2011

The glide of jogged dislocations is considered. Rate equations are presented to describe the motion of dislocations containing interstitial-producing jogs in both the low-stress, quasi-equilibrium regime of behavior and the high-stress, thermally activated regime. The concept of point forces acting at pinning points is introduced. Extended jogs are considered and are shown to always dissociate such that the sessile jog partial is in trailing position. Sessile jogs in edge dislocations are found to be predominantly vacancy producing. Mechanisms are presented for stacking-fault tetrahedron formation at jogs.
THE INFLUENCE OF POINT DEFECT ORIENTATION UPON DISLOCATION MOBILITY IN KCl
Authors: Nadeau John S.
Published: April 2011

Point defects having less than cubic symmetry are known to be much more effective solution-hardening agents in cubic materials than those possessing such symmetry. Solution-hardening theories predict that for certain relative orientations of the dislocation Burgers vector and the anisotropic defect the hardening effectiveness should be reduced or entirely absent. The theory was tested by measuring the solution hardening in KCl:Ag irradiated at liquid nitrogen temperature. The principal hardening agents are Cl2− defects most of which can be aligned parallel to a chosen crystal direction by irradiation with polarized light. The experiments showed that the hardening effectiveness of the defects was about 20% less when they were aligned than when they were randomly distributed. This finding is in qualitative agreement with the theory, but etching experiments failed to confirm the directional character to the dislocation point defect interaction.
THE STRESSES PRODUCED BY A SCREW DISLOCATION PILEUP AT A CIRCULAR INCLUSION OF FINITE RIGIDITY
Authors: Barnett D. M. , Tetelman A. S.
Published: April 2011

The method of continuously distributed dislocations is used to obtain the exact solution for the distribution of screw dislocations in a linear array of length L piled up against a circular inclusion of radius R and finite shear modulus. The solution presented is valid for 0 < G2/G1 < ∞, where G2 is the shear modulus of the inclusion and G1 is the matrix shear modulus.The solution enables one to study simultaneously the effects of second-phase size and rigidity upon N, the number of dislocations in the pileup, and upon the local stresses induced in the second phase. In the second phase close to the pileup tip it is shown that the local stresses vary as: (1) (2L/ρ)g, when the inclusion diameter is much greater than the slip line length; [Formula: see text], when the particle diameter is much less than the slip line length, ρ is the radial distance from the pileup tip, and g is a function only of the shear moduli ratio, G2/G1, with 0 < g < 1. The effects of varying second-phase size and rigidity upon the magnitude of the local stresses is explained in terms of image dislocation forces generated by the presence of the inhomogeneity ahead of the pileup.
FATIGUE IN COPPER SINGLE CRYSTALS AND A NEW MODEL OF FATIGUE IN FACE-CENTERED CUBIC METALS
Authors: Nine H. D. , Kuhlmann-Wilsdorf D.
Published: April 2011

The fatigue process has been studied in copper single crystals cycled in torsion at constant total shear strain. A discontinuity in the slope of the S–N curve of [Formula: see text] axially oriented specimens and a step discontinuity in the S–N curve of [Formula: see text] oriented specimens dividing the curves into a low-amplitude and high-amplitude region, together with metallographic changes, are interpreted as evidence that mechanisms of fatigue failure are dependent on amplitude. In the low-amplitude range the distributions of fatigue striations have been compared with the resolved shear stresses plotted as a function of azimuthal angle. This comparison shows that repeated cross-slip models do not account for the observed striation distribution but, instead, high stresses on both the primary slip system and another slip system in the primary plane are important. A new model of fatigue striation formation is proposed according to which the interaction of dislocations of at least two different Burgers vectors in the primary plane forms sequences of cells whose sides are twist boundaries parallel to the primary plane separated by a relatively dislocation-free interior. Slip is believed to concentrate between the twist boundaries giving rise to striations. The model is shown to be in good accord with available experimental evidence. At high strain amplitudes slip on intersecting planes will account for the change in macroscopic appearance and fracture behavior from those observed at low amplitudes.
THE THEORETICAL STRENGTHS OF CRYSTALS AND THE TIP OF A CRACK
Authors: Kelly A. , Tyson W. R. , Cottrell A. H.
Published: April 2011

Calculations of the cleavage strength σmax and of the shear strength τmax of ideally perfect crystals have been reviewed by Kelly (1966), and Tyson (1966) has carried out some accurate calculations using a computer. We have used these calculations in an attempt to predict the modes of failure at the tip of a crack.
THE INTERPRETATION OF TERMINATING DISLOCATIONS
Authors: Eshelby J. D. , Laub T.
Published: April 2011

A physical meaning is suggested for Li's terminating dislocation, based on Heaviside's interpretation of the magnetic field, which the formula of Biot and Savart gives when applied to an incomplete circuit.
DEFORMATION PROPERTIES OF NIOBIUM SINGLE CRYSTALS
Authors: Bowen D. K. , Christian J. W. , Taylor G.
Published: April 2011

Vacuum-purified niobium crystals of various orientations have been tested in tension and compression, mainly at room temperature and 158 °K. The observed slip planes were almost always of the {101} or {211} type, and the asymmetry of the stress for slip on {211} has been confirmed at both temperatures. The critical resolved shear stress was approximately constant at room temperature, but a strong orientation dependence of both the macroyield and the microyield stress was found at 158 °K. Three-stage work-hardening curves were found for both the {101} and {211} single-slip orientations at room temperature; there was also a pronounced stage 0 and large overshoot for {101} slip, but not for {211} slip.Dislocation distributions in stage I consisted mainly of long slip-plane clusters containing edge dislocations, and in stage II complex, densely packed obstacles built up into a cell structure. The secondary dislocation density was very high in stage II. After deformation at 158 °K, the structure contained a fairly uniform distribution of screw dislocations and small loops.Current ideas on the effects of impurities, the origin of the friction stress, the significance of asymmetry, and the orientation dependence are reviewed.
SLIP AND THE CONCEPTION OF SPLITTING OF DISLOCATIONS IN b.c.c. METALS
Authors: Kroupa F. , Vítek V.
Published: April 2011

The specific features of the slip geometry in b.c.c. metals are reviewed. The properties of sessile and glissile splittings of screw dislocations on both {110} and {112} planes are then discussed and a dislocation theory of the slip geometry in b.c.c. metals, based on thermally activated sessile–glissile transformations of screw dislocations to different {110} and {112} planes, is introduced.
A CRITICAL REVIEW OF THE PEIERLS MECHANISM
Authors: Guyot Pierre , Dorn John E.
Published: April 2011

A thorough review is made of the application of the Peierls model to the macroscopic plastic deformation of ionic crystals, metals, alloys, and covalently bonded crystals. The effects of the shape of the Peierls hill, kink–kink energies, and the frequency terms on the stress–temperature and activation volume–stress relationships are extended and discussed. Theory is compared with experimental results, giving special emphasis to recent advances. Single-crystal data for [Formula: see text] {110} thermally activated slip in Ta and Mo at low temperatures agree well with the dictates of the Peierls mechanism. Deformation characteristics of polycrystalline Fe alloys containing either 2 wt.% Mn or 11 at.% Mo agree with expectations based on the Peierls mechanism only at temperatures below about 200 °K. At higher temperatures, the effective stress decreases more slowly and the activation volume increases more rapidly with increasing temperature than can be accounted for by the Peierls mechanism. Over this higher temperature range, however, the experimental data are in good agreement with Escaig's mechanism based on the recombination of dissociated screw dislocations. It is also shown that low-temperature [Formula: see text] {123} slip in AgMg, prismatic slip in Ag plus 33 at.% Al, and in Mg plus 6–12 at.% Li occurs by the Peierls mechanism.
MECHANICAL PROPERTIES OF SOME TANTALUM ALLOYS
Authors: Mitchell T. E. , Raffo P. L.
Published: April 2011

The mechanical properties of a series of Ta–Re alloys and some Ta–Mo and Ta–W alloys have been investigated by deforming single crystals in compression. Experimental results on slip-line observations, stress–strain curves, yield stresses and anisotropic elastic constants are presented. Slip occurs on the {110} planes; twinning is never observed and the alloys become increasingly brittle as the solute concentration is increased or the temperature is decreased. Yield stress versus composition curves show a minimum at low temperatures. It is suggested that this is due to a reduction in the intrinsic lattice friction stress of the pure metal by alloying, before alloy hardening is able to increase the yield stress again. The alloy hardening has been analyzed and the yield stress τ, the solute concentration c, and the temperature T are related by an expression [Formula: see text], where k and T0 are constants and μ is the shear modulus. Such a relationship has been derived by Fleischer for interactions of dislocations with tetragonal distortions. It is unlikely that this implies that tetragonal defects (for example, solute pairs) are important in tantalum alloys; presumably elastic interactions with single solute atoms can also give such a temperature and concentration dependence of the yield stress. Comparisons with other b.c.c. alloys have been made and it is found that the rate of alloy hardening is directly proportional to the atomic size misfit in most of the alloys where data are available for single crystals.
PLASTIC ANISOTROPY OF TANTALUM, NIOBIUM, AND MOLYBDENUM
Authors: Sherwood P. J. , Guiu F. , Kim H. C. , Pratt P. L.
Published: April 2011

The stress–strain behavior of single crystals of tantalum, niobium, and molybdenum has been studied in both tension and compression in the temperature range 4.2–400 °K. The crystals were stressed in both the [Formula: see text] and the [Formula: see text] directions.At high temperatures, the yield stress of all three metals is independent of the direction and sense of the applied stress. At low temperatures, the yield stress depends markedly on the orientation of the crystals and the sense of the applied stress. This anisotropic behavior cannot be satisfactorily explained in terms of any of the mechanisms proposed so far, such as the mobility of jogs in screw dislocations, or the dissociation of a/2 [Formula: see text] screw dislocations on {112} planes.
ORIENTATION DEPENDENCE OF YIELD IN BODY-CENTERED CUBIC METALS
Authors: Hull D. , Byron J. F. , Noble F. W.
Published: April 2011

Recent observations relating to the critical resolved shear stress for slip in tantalum and tungsten are reported. The results of tensile and compressive deformation are discussed in terms of the operative slip systems and the possible asymmetry of {112} [Formula: see text] slip. It is concluded that the asymmetry hypothesis is unable to account satisfactorily for anomalies in the deformation behavior of these materials.
DISLOCATION STRUCTURES IN COPPER SINGLE CRYSTALS DEFORMED IN HIGH TEMPERATURE CREEP
Authors: Gupta V. P. , Strutt P. R.
Published: April 2011

The etch-pit technique has been used to study dislocations and substructures in copper single crystals deformed in primary, and into secondary creep at 550 °C at a CRSS of 250 g.mm−2. Etch-pit structures in crept specimens were observed parallel to the primary (111) plane and also the (111) plane to reveal "forest dislocations" and primary and other dislocations. In the initial stage of primary creep, the dislocations formed well-defined cells. Subboundaries began to form later on in primary creep. When a steady-state creep ensued, a well-developed subboundary structure was evident, with a random distribution of dislocations within the subgrains. The mean subgrain diameter was approximately twice that of the original cells and the dislocation density decreased by a factor of 2 during primary creep. Since the general form of the dislocation structure changes during primary creep, it is concluded that the decreasing strain rate cannot be ascribed to any one particular mechanism. However, the high initial strain rate probably results from the escape of dislocations from the cell walls in the initial type of structure.
INVESTIGATIONS ON SOME DEFORMATION MODES OF BERYLLIUM
Authors: Poirier J. P. , Antolin J. , Dupouy J. M.
Published: April 2011

Single crystals of beryllium, compressed along the c axis, above 400 °C, undergo a deformation which can be ascribed to the climb of c dislocation loops possibly created by Bardeen–Herring sources. Observation of twins have given evidence supporting the theory of twinning by dislocations. Also, numerous stacking faults have been found in twins, resulting from the condensation of vacancies created during twinning.
ACOUSTIC WAVES AND THEIR EFFECTS ON ANTENNA IMPEDANCE
Authors: Carlin J. , Mittra R.
Published: April 2011

Expressions have been derived for the terminal admittance of a biconical dipole encased in a dielectric sphere which is immersed in a warm plasma. A linearized hydrodynamic description is used for the plasma. For thin-angle cones an exact expression is derived. For thick-angle cones the terminal admittance is related to the aperture fields at the spherical boundary of the cones by means of a variational expression. The admittance was found to be strongly dependent on the ratio of the velocity of light in free space to the acoustic velocity in the plasma. Compressibility effects seem to be quite significant if the acoustical "phase length" of the antenna is between approximately 0.5 and 10.
INFINITE RANGE CORRELATION AND LARGE EIGENVALUES OF THE 2-MATRIX
Authors: Coleman A. J.
Published: April 2011

A simple energy argument indicates that the existence of an eigenvalue of order N−1 in the second-order reduced density matrix, or 2-matrix, implies macroscopic correlation characterized by the corresponding eigengeminal.
EFFECTS OF PAIRING IN THE 20Ne NUCLEUS
Authors: Kalman C. S. , Bernier J.-P. , Harvey M.
Published: April 2011

An investigation is made into the effects of a perturbing pairing force on the structure of the 20Ne nucleus described primarily by a quadrupole–quadrupole force (SU3 model). It is shown that such a perturbation cannot explain simultaneously the observed deviations from the SU3 predictions of energy and the B(E2) systematics in the "ground-state band".
TREATMENT OF SINGULARITIES IN SCATTERING FROM PERFECTLY CONDUCTING POLYGONAL CYLINDERS—A NUMERICAL TECHNIQUE
Authors: Abdelmessih S. , Sinclair G.
Published: April 2011

Certain field components become infinite at sharp edges, causing difficulties in computation when solving scattering problems for polygonal cylinders by numerical methods. Since the field behavior near an edge is known, it is possible to devise appropriate functions to represent the singularities at the edges. By suitably representing the induced current and using an integral equation for it, it is possible to obtain a set of simultaneous linear equations which can be solved by a high-speed digital computer. In this way, an explicit analytical expression for the induced current including the singularities from which the other field components can be derived, is obtained. Numerical results are shown for square and triangular cylinders of various sizes, for an incident plane wave polarized parallel to the axis of the cylinders.
THE 4 550 Å BAND SYSTEM OF GLYOXAL: I. ROTATIONAL ANALYSES OF THE (0–0) BANDS FOR C2H2O2, C2HDO2, AND C2D2O2
Authors: Paldus J. , Ramsay D. A.
Published: April 2011

Rotational analyses of the (0–0) bands of the 4 550 Å band system of C2H2O2 (glyoxal), C2HDO2, and C2D2O2 have been performed. The analyses show unambiguously that the bands have type C structures, in agreement with the assignment to a 1Au–1Ag, (or1A″–1A′), π*–n transition. Rotational constants, A, B, C, and DK have been determined for each isotope and probable structures for the molecule in the ground and excited states have been determined. The CO bond is longer and the CC bond shorter in the excited state, in agreement with the predictions of molecular orbital theory.
THE 1Πu ← 1Δg ELECTRONIC SPECTRUM OF NCN
Authors: Kroto H. W.
Published: April 2011

The analysis of a new electronic absorption spectrum observed during the flash photolysis of cyanogen azide, NCN3, in the region 3 327 Å indicates that the spectrum belongs to a 1Πu–1Δg transition of NCN. The 1Δg state is metastable with respect to the [Formula: see text] ground state. The bond distance in the 1Δg state is 1.228 5 Å. The value of the Renner splitting parameter, εω2, for the 1Πu state has been determined as −84.2 cm−1.
A MODEL FOR THE DECAY OF AN UNSTABLE STATE
Authors: Razavy M.
Published: April 2011

A nonrelativistic model for the decay of an unstable system, in which the mean energy of the unstable state and the rate of decay are finite, is discussed.
LOCALIZED MAGNETIC MOMENTS IN IMPURITY-BANDED SEMICONDUCTORS
Authors: Hedgcock F. T.
Published: April 2011

Using existing magnetoresistivity data and assuming that the occurrence of negative magnetoresistivity is a result of the presence of localized magnetic moments in impurity-banded semiconducting material, a method for deriving values of local moments is presented. The concentration and temperature dependence of the moments is also estimated and compared with the Anderson criteria for the occurrence of magnetic moments in conductors.
A COMPARISON OF SPIN-ORBIT PARAMETERS
Authors: Froese Charlotte
Published: April 2011

Hartree–Fock results for some spin-orbit parameters are presented. The calculations are based on the Blume and Watson (1962) expression for the spin-orbit parameter, derived on the assumption that the atomic wave function is antisymmetric.The results are compared with experimental values and it is shown that the earlier conclusions concerning the accuracy of the spin-orbit parameter for 3p and 3d electrons are not valid. The results are also compared with Hartree–Fock–Slater values based on a simplified definition.
SEMICLASSICAL THEORY OF PROTON TRANSPORT IN ICE
Authors: Kim Dong-Yun , Schmidt V. Hugo
Published: April 2011

A method is described for calculating proton or other ion mobility which is applicable if mobility is limited by lattice scattering rather than by barrier jumping. The Boltzmann transport equation is used, with the collision term calculated from the electrostatic interactions between the mobile ion and the vibrating lattice. In particular the proton mobility in ice is calculated. The lattice vibrations are approximated by a Debye spectrum for translational vibrations of water molecules, plus an Einstein spectrum for modes in which protons vibrate almost as independent particles. Scattering by phonons somewhat below the Debye cutoff frequency is of the greatest importance in determining the mobility, and the proton modes have negligible effect. The calculated mobility agrees reasonably well with the experimental value.
TUNNELING MEASUREMENTS ON SUPERCONDUCTORS WITH ISOTROPIC ENERGY GAPS
Authors: Walmsley D. G. , Campbell C. K.
Published: April 2011

The energy-gap anisotropy found in bulk superconductors is considerably reduced in thin films whose thickness, d, is much less than the range of coherence, ξ0, of the pure metal from which they are fabricated. By preparing such thin films of tin, indium, and lead, we have been able to examine the temperature dependence of the energy gap in each above 1.2 °K, using the tunneling technique. Values of the energy-gap parameter 2Δ(0)/kTe are given as 3.67 ± 0.07 and 3.87 ± 0.08, for tin and indium respectively, while the energy gap for lead is estimated to be 2ΔPb(0) = 2.70 ± 0.02 meV.
THE ASSOCIATION OF PHASE CHANGES OF IONOSPHERE-PROPAGATING RADIO WAVES AND GEOMAGNETIC VARIATIONS
Authors: Lewis T. J.
Published: April 2011

Classification of Doppler frequency changes of ionosphere-propagating radio waves has been made with special emphasis on their possible relationships with simultaneous geomagnetic variations. The Doppler frequency changes are suitably divided into two classes: rapid variations and slow changes, according to whether or not the time scale of a change is shorter than about 4 minutes. The overall coincidence between geomagnetic variations and Doppler frequency changes is poor. However, it is found that rapid geomagnetic variations such as sudden impulses and pi 2 micropulsations accompany a Doppler frequency change with a high degree of probability. The correspondence between the two is activity-wise in most cases. Peak-to-peak correspondence has been observed, however, in some cases, when the Doppler frequency changes amount to a few tenths of a c.p.s. for magnetic variations of unit strength (1γ in the south–north component). The coincidence is also very good for sudden commencements of magnetic storms. The ratio of the main positive frequency change to the magnetic-field variation in the south–north component is about one order smaller than that for the above-mentioned group. The correspondence is, in most cases, indefinite for geomagnetic bays. When a clear coincidence is seen, the ratio of the change of frequency to magnetic variation is of the order of a few hundredths of a c.p.s. per γ.
ELECTRON DECAY FOLLOWING d-c. DISCHARGE IONIZATION IN NO AND NO–Ne MIXTURES
Authors: Mentzoni Michael H. , Donohoe James
Published: April 2011

The time dependence of the electron density, Ne(t), and radiation temperature, Te(t), has been measured in d-c. discharge afterglows of NO and NO–Ne mixtures. Microwave wave-guide transmission and noise-sampling techniques were used. In pure NO the experimental results were compared with those computed for a recombination–attachment controlled plasma using Gunton and Shaw's values, and good agreement was found. In the NO–Ne mixtures p(Ne) was about 20 Torr, and p(NO) was varied from 0.5 × 10−3 to 0.10 Torr. It was found that 1/Ne(t) was linear over extensive ranges of Ne(t) indicating two-body electron–ion recombination. The results yield [Formula: see text] and the three-body attachment coefficient K = 2.2 × 10−31 cm6sec−1 for Te = Tgas = 300 °K. Te(t) decayed nonexponentially varying with p(NO) indicating that Penning ionization takes place together with other collision processes which are briefly discussed.
NONLINEAR GENERATION OF COMBINATION FREQUENCIES IN A HOMOGENEOUS MAGNETOPLASMA
Authors: Mittal R. S. , Kaw P. K.
Published: April 2011

In this paper, the authors have derived explicit expressions for the combination frequency components of the current density in a homogeneous magnetoplasma due to two alternating electric fields. While deriving these expressions, all the important contributions arising from the various isotropic and anisotropic parts of the distribution function have been taken into account. An interesting result is that, in the general case, when the applied electric fields are in the form of pure modes of two fundamental waves, only the opposite modes of the combination frequency components are generated in the current density. Some numerical results depicting the phenomenon of resonances for some simple interesting situations have also been presented at the end.
COMPLEX DIELECTRIC CONSTANT OF CIS-DICHLOROETHYLENE IN THE MICROWAVE-FREQUENCY REGION
Authors: Srivastava G. P. , Mathur P. C.
Published: April 2011

The relaxation time and dipole moment of cis-dichloroethylene has been determined in the X-band microwave-frequency region from its dilute solutions in a nonpolar solvent. The dielectric loss tangent δ is found to vary linearly with concentration only for very dilute solutions.
MASS DEPENDENCE IN GRAVITATIONAL COLLAPSE OF STELLAR CORES
Authors: Arnett David
Published: April 2011

The mass dependence of the behavior of a stellar core undergoing gravitational collapse is examined, using an improved equation of state and improved mean-free path for energy transfer by neutrinos and antineutrinos. Energy loss due to the escape of muon-type neutrinos is included. For [Formula: see text] and [Formula: see text] there is explosive mass ejection. A neutron-star remnant of [Formula: see text] is left in the [Formula: see text] case, while in the [Formula: see text] case the remnant mass is [Formula: see text]. Upon cooling, the latter remnant may not be able to remain stable because of general relativistic effects. For [Formula: see text] and [Formula: see text] the models were too opaque to electron-type neutrinos to eject matter. In both cases they cooled by copious muon-type neutrino emission (to which they were transparent) and developed dense [Formula: see text] central regions in which general relativistic effects became important. It appears that highly evolved stars with [Formula: see text] may not be able to avoid the Schwarzschild singularity of general relativity.
HARTREE–FOCK WAVE FUNCTIONS FOR EXCITED STATES: III. DIPOLE TRANSITIONS IN THREE-ELECTRON SYSTEMS
Authors: Cohen Maurice , Kelly Paul S.
Published: April 2011

Hartree–Fock wave functions for a number of S, P, and D states of the lithium isoelectronic sequence have been calculated, using a simplified procedure described in an earlier paper. Transition matrix elements for all permitted dipole transitions between these states have been computed using both the dipole length and the dipole velocity formulations. The results are in good agreement with earlier calculations.
IDEAL RESISTIVITY OF PLATINUM BELOW 20 °K
Authors: Berry R. J.
Published: April 2011

An improved estimate for the electrical resistivity of ideally pure platinum is derived for the 3–20 °K region from highly accurate measurements on a specimen of thermometric-grade Pt. The two-band model is used to correct for the small, but significant, impurity scattering. The temperature dependency of this "ideal" resistivity function is compared with theory and previous work. Certain discrepancies are noted.
LIFETIMES AND g FACTORS OF RARE-GAS RESONANCE STATES
Authors: Wilkinson P. G.
Published: April 2011

The mean lifetimes, τ, and ratios, 3τ/1τ of rare gas (Xe, Kr, Ar, Ne) resonance levels, as determined experimentally and theoretically, are intercompared. A new relationship was found connecting τ and the Landé g factor, g: 1/τ = a − bg. For [Formula: see text]: a = 1.80, b = 1.26; for [Formula: see text]: a = 1.40, b = 0.94, in 109 sec−1 units. Unexplained deviations are revealed for Ne(3τ/1τ) and [Formula: see text].
THE MECHANISM OF THE ARGON EMISSION CONTINUUM IN THE VACUUM ULTRAVIOLET. I
Authors: Wilkinson P. G.
Published: April 2011

The spectral intensity, Iem, of the microwave excited continuous emission in molecular argon has been investigated from 1 060 to 1 450 Å as a function of pressure (pAr) with the result:[Formula: see text]The Ar2 continuum, like Xe2, Kr2, and Ne2 (X2), exhibits a sharp short wavelength limit corresponding energetically to the 3p54s3P0 resonance configuration and two intensity maxima at 1 080 and 1 265 Å. The integrated intensities of the rare-gas continua compare as follows:[Formula: see text]with (Iem)Ne expected to be weaker still. The pressure dependence and the short wavelength limit suggest a two-body collision process involving 3P0 atoms as the controlling step to produce [Formula: see text] molecules responsible for the continuum.Although the lifetimes of the 3P0 atoms do play a kinetic role in the continuum production, it is concluded that the molecular transition probabilities, [Formula: see text] predominate and decrease, as expected in the direction Xe2* to Ne2* in the approach (weaker spin-orbit coupling) to Hund's case b.
A REFORMULATED BOUNDARY PERTURBATION THEORY IN ELECTROMAGNETISM AND ITS APPLICATION TO A SPHERE
Authors: Burrows M. L.
Published: April 2011

The classical method of solving electromagnetic field problems involving boundary perturbations is reformulated in a way that is both more general and simpler. The new formulation makes it easier to apply the theory to the class of boundaries amenable to the classical formulation, and shows that it can also be applied to other boundary shapes. As an example, the perfectly conducting sphere with surface perturbations has been treated, using the methods appropriate only for boundaries in the classical class and also using those applicable to the larger class. Some experimental results which appear to support the theory are reported.
ROCKET OBSERVATIONS OF ELECTRON PITCH-ANGLE DISTRIBUTIONS DURING AURORAL SUBSTORMS
Authors: McDiarmid I. B. , Budzinski E. E. , Whalen B. A. , Sckopke N.
Published: April 2011

Electron angular distributions obtained from three rocket flights during auroral substorms are described. Pitch-angle distributions of the incident electrons vary from isotropic to strongly peaked at pitch angles near 90°. Isotropic distributions are sometimes maintained for times at least of the order of minutes with very little change in intensity. When an anisotropic distribution persists for some time, the particle intensity is usually observed to decay.Following an intensity increase the angular distribution generally becomes more isotropic. The degree of isotropy attained following an intensity increase does not appear to depend on the magnitude of the increase but rather on the degree of isotropy before the increase.The intensity of upward moving electrons (pitch angles 90–180°) can in most cases be accounted for by atmospheric scattering and mirroring in the undisturbed geomagnetic field. A few cases are observed in which the electron intensity in the pitch-angle range 90–180° is probably larger than can be accounted for by normal scattering and mirroring. The effect of an ionospheric current on the intensity of upward moving electrons is considered.
DIFFERENCE FREQUENCY HARMONIC ION HEATING
Authors: James C. R. , Thompson W. B.
Published: April 2011

The heating of a magnetized hot diffuse plasma using the difference frequency signal generated from two high-frequency (35 GHz) transverse waves is examined. The plasma is described by the cold plasma model and a series expansion of harmonics is used to obtain a solution to the equations. It is shown that the energy absorbed by the ions can be made inversely proportional to the collision frequency and the fourth power of the driven frequency and proportional to the fourth power of the driven electric field intensity. An investigation of the sensitivity of the heating process to fluctuations in frequency, density, and d-c. magnetic field is carried out.
SOLITARY DISPERSION
Authors: Scheidegger A. E.
Published: April 2011

The Buckley–Leverett and the diffusivity equations are shown to be two limiting forms of the continuity equation formulated for the independent dispersion of a single substance in a mixture containing a great number of other substances ("solitary dispersion"). The Buckley–Leverett equation is obtained if the deviation from mean flow depends phenomenologically only on the instantaneous saturation itself, the diffusivity equation if it depends on the saturation gradient. The physical implications, in terms of statistical mechanics, of the two limiting cases are investigated, and it is shown that both types of transport equations can be deduced from fluctuation theory, in analogy with thermodynamics, by assuming the appropriate microscopic decay law.
MULTIPLE IONIZATION OF THE RARE GASES BY SUCCESSIVE ELECTRON IMPACTS (0–250 eV): I. APPEARANCE POTENTIALS AND METASTABLE ION FORMATION
Authors: Redhead P. A.
Published: April 2011

Multiple ionization of the rare gases has been examined in a mass spectrometer with a trapped-ion source. Ions with charge multiplicity up to n = 2 (He), n = 5 (Ne), n = 6 (Ar), n = 7 (Kr), and n = 10 (Xe) were observed with electron energies less than 250 eV. For He and Ne the thresholds agree with spectroscopic values of the ionization potentials, indicating a process of the form eN/ee(N + 1), where N represents an ion of charge multiplicity n. For Ar, Kr, and Xe, processes involving metastable states of the ion are also observed, eN/eNm; eNm/ee(N + 1). The estimated energies of the metastable levels of Ar+, Kr+, Xe+, Ar2+, and Xe2+ are in agreement with spectroscopic values. The energies of the metastable states of Ar+, Kr+, and Xe+ are in agreement with measurements of Auger electron emission from metals by metastable ions. The metastable levels estimated for the more highly charged ions (up to n = 5 for Ar, n = 6 for Kr, and n = 8 for Xe) have not been observed previously. The excitation functions of the metastable levels of Ar+, Kr+, and Xe+ are very similar and show a very sharp maximum near threshold.
NUCLEAR g FACTOR OF THE FIRST EXCITED STATE IN 106Pd AND THE INTERNAL FIELD ON PALLADIUM IN NICKEL
Authors: Murray J. , McMath T. A. , Cameron J. A.
Published: April 2011

The nuclear g factor of the first excited state in 106Pd has been measured by the method of perturbed angular correlations. The perturbing fields used were the internal fields on palladium in dilute iron and cobalt alloys. By comparing the rotation caused by these alloys with the rotation observed when nickel was the host, a measurement of the internal field on palladium in nickel has been obtained.The g factor of the first excited state in 106Pd has been determined to be +0.35 ± 0.03. The internal field on palladium in nickel at room temperature was found to be −174 ± 13 kOe.
THEORY OF COHERENT RESONANT ABSORPTION AND EMISSION AT INFRARED AND OPTICAL FREQUENCIES
Authors: Freedhoff Helen , Kranendonk J. Van
Published: April 2011

The theory of the line shape in coherent resonant absorption and emission in the infrared and optical region is developed. The Dicke spin model and the Lorentz oscillator model of a radiating molecule are discussed in detail, and the complications arising for degenerate levels are analyzed. The absorption and emission spectra are expressed in terms of the damped normal modes of the system of equivalent oscillators interacting via the retarded dipole–dipole interaction, and the results are shown to be identical with those derived using Heitler's quantum theory of radiation damping. The theory is applied to small clusters and linear chains of molecules. For a chain that is small compared with the wavelength, the natural line width is proportional to the total number of molecules, whereas for a long chain the width approaches a constant value. The discussion of three-dimensional systems, and the application to the zero-phonon lines in the infrared spectrum of solid hydrogen will be given in a separate paper.
ACOUSTIC WHISPERING-GALLERY PHENOMENA IN CIRCULAR CYLINDERS
Authors: Wait James R.
Published: April 2011

An early analysis of whispering-gallery modes due to Lord Rayleigh (J. W. Strutt) is extended to cylindrical geometry where the axial wave number h is nonzero. The model is an infinitely long homogeneous fluid cylinder surrounded by another homogeneous fluid with differing properties. It is shown that the modes are leaky if the external wave number k2 > h even where there is no dissipation. An expression is derived for the circumferential attenuation rate in this case. It is also demonstrated that there is no attenuation when h > k2 provided the media are lossless.
SPECIFIC HEATS OF POTASSIUM IODIDE BY A MODIFIED SHELL MODEL
Authors: Deo R. G. , Dayal B.
Published: April 2011

The shell model of Woods et al. has been modified to include the effect of the many-body interaction in the ionic crystals in a simple phenomenological way. This is based on the work of Lowdin, Lundqvist, and Verma and Dayal. In the new model which the authors refer to as the modified shell model, it is assumed that the volume-dependent potential is due to the interaction between the cores of the ions only. This introduces additional parameters in the model which have been derived from the elastic and dielectric properties of the crystal. The variation of the specific heat with temperature of potassium iodide has been studied by the original model of Woods et al. as well as by the new model. It is seen that the theoretical specific heats and dispersion curves given by both the models are in fair agreement with the experimental results. However, the shell model fails to account for the Cauchy discrepancy in this crystal, whereas the new model removes this difficulty.
SURFACE CURRENT EXCITATION ON AN INHOMOGENEOUSLY SHEATHED PLASMA-IMMERSED CYLINDER BY ELECTROMAGNETIC AND ELECTROKINETIC WAVES
Authors: Miller Edmund K.
Published: April 2011

A theoretical investigation is described which analyzes the effect of an inhomogeneous sheath on the surface currents and scattering cross section of an infinitely long, perfectly conducting, circular cylinder immersed in an isotropic collisionless, compressible plasma by plane electromagnetic (EM) and electrokinetic (EK) waves incident at an arbitrary angle with respect to the cylinder axis. The linearized fluid equations are used in the analysis, with the inhomogeneous sheath taken to extend a finite distance into the plasma from the cylinder surface, on the order of 10 electron Debye lengths, beyond which the plasma is uniform. The numerical results for the surface currents obtained from the inhomogeneous sheath analysis are compared with those obtained when the sheath is replaced by a free-space region, called the vacuum sheath. It is found that for EM wave incidence, the surface currents are practically independent of the sheath and the finite plasma temperature. For EK wave incidence, the sheath has an attenuating effect on the currents produced, compared with the sheathless case, with the attenuating effect of the vacuum sheath being greater than that of the inhomogeneous sheath. The scattering cross sections for EM wave incidence are, for the scattered fields with the same polarization as the incident wave, also independent of the sheath and finite plasma temperature. The scattered fields with polarization different from that of the incident wave have cross sections generally less than 10−2 of the scattered fields with the incident wave polarization.