bluuebunny/crossref_metadata_2025 huggingface dataset:
Microwave Properties of Nonstoichiometric Polycrystalline Yttrium Iron Garnet
Authors: Seiden P. E. , Kooi C. F. , Katz J. M.
Published: April 2005

An investigation has been made of the microwave properties of nonstoichiometric yttrium iron garnet ranging from 31% iron excess through stoichiometric to 12% yttrium excess. No ion substitution in the garnet lattice is observed. All material in excess of stoichiometric proportions goes into ceramic second phases. The phases observed are perovskite (YFeO3) for yttrium excess, hematite (Fe2O3) for iron-excess samples fired in oxidizing atmospheres, and magnetite (Fe3O4) for iron-excess samples fired in neutral atmospheres.

On the basis of the assumption that all excess material goes into the appropriate ceramic second phase, we may account for the behavior of the saturation magnetization, spectroscopic splitting factor, and linewidth as a function of composition.

It is found that the linewidth is strongly narrowed by the large magnetization as predicted by Geschwind and Clogston. The behavior of the dielectric constant can be explained, at least qualitatively, by a theory of Wagner and Sillars which considers particles of one dielectric material imbedded in a matrix of another. The behavior of the dielectric loss tangent is not understood and cannot be accounted for by this theory.
Current Noise due to Ohmic Contacts on Cadmium Sulfide
Authors: Brophy James J. , Robinson Robert J.
Published: April 2005

Current noise measurements on the same lightly doped cadmium sulfide crystal having indium soldered contacts of different quality are used to demonstrate the strong influence of contacts on the observed noise spectra. The results suggest the presence of shallow trapping states distributed in energy and located near the electrodes. The concentration of these states depends on the quality of the contact. These effects are not contact noise in the usual sense since the shape of the noise spectra is only moderately affected; however, the noise level may change by orders of magnitude.
Thermal Expansion Coefficients of Bismuth
Authors: Cave E. F. , Holroyd L. V.
Published: April 2005

The linear thermal expansion coefficients of the a and c axes of bismuth have been measured from 80°K to 540°K by mechanical means. These same coefficients were determined over a more limited range of temperatures by single crystal and powder x-ray methods. The mechanical and x-ray values did not differ significantly. The expansion coefficient for the c axis was found to be 16.6±0.4×10−6 (C°)−1 at 100°K, 17.3±0.2×10−6 (C°)−1 at 150°K, and 17.6±0.2×10−6 (C°)−1 at 540°K. For the a axis the expansion coefficient was 10.8±0.3×10−6 (C°)−1 at 100°K, 11.6±0.2×10−6 (C°)−1 at 150°K, and 11.8±0.2×10−6 (C°)−1 at 540°K.
Dislocations in Silicon Carbide
Authors: Amelinckx S. , Strumane G. , Webb W. W.
Published: April 2005

The dislocation structure of type 6H hexagonal silicon carbide has been studied by etching combined with optical microscopy and by x-ray diffraction microscopy. The validity of the conventional etching technique for identification of the sites of the intersection of dislocations with (0001) surfaces has been established. However, high densities of dislocations lying in (0001) planes and hence heretofore undetected by etching techniques were often observed by diffraction microscopy. Dislocations with [112̄0] vectors have now been found with evidence for slip both on basal planes and on a ``puckered'' pyramidal plane. Pileups formed by slip and dislocation walls formed by climb were also observed. Silicon carbide shows many of the characteristics of more conventional plastically deformable materials.
Stress Waves in Solids
Authors: Cassity C. R.
Published: April 2005

Several experimental tests dealing with the effects of stress waves initiated in solids by high explosives or by impacts are described. The tests indicate that stress waves which are initiated solely as compression commonly acquire tensile components which are not due to reflections.
Forces on Ion-Bombarded Electrodes in a Low-Pressure Plasma
Authors: Wehner G. K.
Published: April 2005

Forces arising on ion-bombarded electrodes have been measured with a torsion balance immersed in a low-pressure Hg plasma. The force curves obtained for 22 metals in the range of 20 to 300 ev bombarding energy indicate that Hg+-ions are completely accommodated (α=1) on clean metal surfaces and the forces originate essentially from the ejection of sputtered atoms. On comparing the forces with the sputtering yields, one obtains information on the average ejection velocities of sputtered atoms which are found to be much higher than those of thermally evaporated atoms. Oxide-covered surfaces exhibit a quite different behavior inasmuch as the accommodation coefficient for Hg+-ions seems to be less than unity.
Contribution of Anode Emission to Space Charge in Thermionic Power Converters
Authors: Dugan Anthony F.
Published: April 2005

The space charge theory of Langmuir has been extended to include the effects of anode emission on the performance of a vacuum thermionic power converter. The basic equation is similar to Langmuir's ξ—η equation, but it involves two additional parameters which depend on the temperatures and thermionic properties of the electrodes. An iterative technique is described for obtaining solutions in specific cases, and some sample calculations based on hypothetical diodes are presented. The calculations indicate that the effect of the anode temperature is considerably more pronounced if the cathode-anode work function difference is large.
Electromagnetic Theory of dc Effects in Ferromagnetic Resonance
Authors: Juretschke H. J.
Published: April 2005

Effects of magnetoresistance and extraordinary Hall effect on the propagation of electromagnetic waves through very thin sheets of ferromagnetic conductors are studied. These contributions to the conductivity produce electric fields varying like products of current and magnetization and introduce nonlinear interactions, which are particularly large in the neighborhood of ferromagnetic resonance. Detailed first-order dc electric fields are obtained for the configuration of a very thin ferromagnetic sheet very close to a conducting wall. The results predict signals strictly proportional to incident microwave power, and mostly inversely proportional to film thickness, becoming independent of thickness for the thinnest films. Their magnetic field or frequency dependence gives typical resonance curves modulated by slowly varying amplitudes. The maxima and zeros of these amplitudes are very sensitive to the local field configuration. Once this latter is well known, however, these effects can be employed to study conveniently the high-frequency conduction and magnetic properties of the thinnest films.
Thermal Conductivity of Eight Halide Crystals in the Temperature Range 220°K to 390°K
Authors: McCarthy Kathryn A. , Ballard Stanley S.
Published: April 2005

The thermal conductivity of eight halide crystals has been measured over the temperature range 220°K to 390°K. The thermal conductivities of potassium bromide, potassium chloride, and sodium chloride vary inversely with temperature for the lower part of this temperature range, and are nearly independent of temperature for the higher temperatures of the range measured. The thermal conductivities of cesium bromide, cesium iodide, and silver chloride are nearly independent of temperature throughout the entire temperature range. The thermal conductivities of barium fluoride and calcium fluoride vary more rapidly with temperature than anticipated from a T−1 relationship; however, the accuracy of the data is not sufficient to establish the exact form of the variation of the thermal conductivity with temperature. The comparative method used for these measurements is described.
Spiral Dislocations on Glass Fracture Surfaces
Authors: Levengood W. C. , Vong T. S.
Published: April 2005

Within a certain range of composition spiral defects were observed on etched soda-lime-silica glasses. The patterns described spirals of Archimedes and appeared to originate from interstitial defects in the glass. Mutual stress influence effects were observed. The hypothesis of an existing torque field around the interstitial defects was useful in explaining the spiral mechanism. Application of mechanical torque stresses produced the spiral effect. In some cases it appeared feasible to apply stress energy relationships developed from dislocation theories to these minute flaw patterns.

A dynamic spherical indenter technique was developed to study structural variations in these glasses. The lengths of flaws produced by a rolling indenter were found to be sensitive to changes in the silica content of the glasses and less affected by variations in the soda-lime ratio. The effects of heating and crystallization were also studied.
Heat Treatment of Gallium Arsenide
Authors: Edmond J. T.
Published: April 2005

Specimens of N-type GaAs were found to become P-type or less strongly N-type as a result of heat treatment. The heat treatment was carried out in small quartz tubes, of two grades of purity. The magnitude of the changes was much less in high-purity quartz. The effect in ordinary quartz was shown to be due in part to copper contamination, the copper originating in the quartz; the changes could be reduced by annealing.
Plasma Propulsion by a Rapidly Varying Magnetic Field
Authors: Klein Milton M. , Brueckner Keith A.
Published: April 2005

An investigation has been made of the motion of a plasma under the action of a rapidly varying magnetic field from a stationary coil. The analysis has been done for two cases: (1) the plasma is assumed completely diamagnetic so that the ionization history of the plasma may be ignored and (2) the nondiamagnetic case where the ionization process is considered in detail. For the diamagnetic case the analysis yields a coupled set of nonlinear ordinary differential equations which have been put in similarity form and solved for a wide range of the similarity parameters. An illustrative example is given to show how to use the results to obtain detailed information for a given physical system. The calculations indicate that, for field frequencies of about one megacycle, velocities of the order 107 cm/sec may be attained, but the efficiency of conversion of stored energy into kinetic energy is rather low (about 5–10%) and cannot be varied much by possible changes in the physical and geometrical parameters of the system.

Because of the complexity of the analysis, a systematic series of solutions has not been made for the nondiamagnetic case. Instead, a typical example has been worked out to indicate the major differences to be expected. The results show that the nondiamagnetic plasma yields an efficiency slightly less than that obtained for the corresponding diamagnetic plasma. The ionization process inside the plasma levels off very rapidly so that the electron density increases by only a few percent during the motion of the plasma, but the amount of ionization has very little effect upon the efficiency of the system. The indications are that the efficiency of a plasma driven by a magnetic field from a stationary coil is probably too low for practical applications.
Parametric Amplifier Theory for Plasmas and Electron Beams
Authors: Kino G. S.
Published: April 2005

A theory is given for a new type of parametric amplifier which uses a gas discharge plasma as a nonlinear propagating medium. This theory is based on a zero-temperature plasma assumption. The nonlinear coupling between traveling waves passing through the plasma is determined by taking second-order terms in the velocity into account. A simplified normal mode theory is used to describe the effect on the propagation constants of the individual modes due to coupling between them. The theory is carried out in detail for a plasma in an infinite magnetic field and for a plasma in a zero magnetic field. The final propagation equation for the traveling waves is found in terms of the fields in the plasma of the small-signal pumping wave, signal wave, and idler wave. In the Appendix the theory is extended to cover the case of beam-type parametric amplifiers. It is shown that the theory is applicable both to beam-type amplifiers which use space-charge waves for all three modes of propagation or to waves which are partially those of a circuit and of the beam itself. The results obtained are in agreement with the theory of Louisell and Quate for the principal waves of a space-charge wave parametric amplifier.
Effect of Cu Precipitation on Dislocation Etch Pits in Ge
Authors: Savage Howard
Published: April 2005

Measured quantities of copper were introduced into n-type germanium single crystals by diffusion. Subsequently, both quenching and annealing heat treatments were performed on the samples. The effect on etch pit sizes and resistivity was recorded. It is shown that saturation with copper does not inhibit completely the formation of etch pits, although they are altered in size.
Diffusion of Deuterium in Deuteron-Irradiated Copper
Authors: Robinson Mark T. , Southern A. L. , Willis William R.
Published: April 2005

The rate of diffusion of deuterium in metals can be studied by measuring the counting rate of neutrons from the D (d,n) He3 reaction occurring in metals irradiated with low energy deuterons. A method of analyzing the time-dependence of the observed neutron counting rate is presented and applied to experiments on Cu in the temperature range −46° to +20°C. It is concluded from the results that grain boundary diffusion is primarily responsible for the movement of deuterium in polycrystalline Cu in this temperature range. The apparent activation energy for diffusion of deuterium in polycrystalline 99.999% Cu is found to be 0.12±0.02 ev/atom. Chemical purity appears to play an influential role in deuterium diffusion in Cu, the rate in OFHC Cu being significantly lower than that in the more pure material. A surface resistance effect, independent of the crystallinity of the specimen but proportional to the deuteron beam current, was found to be of major importance in determining the rate of escape of deuterium from the targets.
Statistics of the Occupation of Dislocation Acceptors (One-Dimensional Interaction Statistics)
Authors: Broudy R. M. , McClure J. W.
Published: April 2005

It is known that dislocations in semiconductors can act as acceptors. This effect has been explained by noting that dislocations with edge components can have unpaired electrons at the terminating half-plane which act as acceptors; thus a dislocation contains a line of uniformly spaced acceptors only a few angstroms apart. In n-type materials the dislocation line becomes negatively charged and a positive space charge develops around the line. The occupation statistics are strongly modified by the electrostatic energies involved. Certain approximate solutions to this problem have already been given by W. T. Read. This paper derives improved statistics which, in addition, explicitly take into account interactions between nearest-neighbor electrons; the results are valid over the complete range of occupation. The statistics are given in terms of two functions which occur in the form of infinite series; the series have been evaluated over a considerable range of occupation and are herein tabulated. Techniques for use of the results are presented. Our theory was applied to a specific problem originally chosen by Read. The results fall between his most accurate approximations for this problem. Statistics have also been derived which take into account the proper spin degeneracy of acceptor states.
Ion-Bombardment Etching of Synthetic Fibers
Authors: Anderson Franklin R. , Holland V. F.
Published: April 2005

An ion-bombardment etching method was used to prepare synthetic fiber samples for study in the electron microscope. Reproductible results were obtained by bombardment in a constantly changing argon atmosphere at a pressure of 1–2 cm Hg for 2–5 min. The etch patterns produced by this method were characteristic of the orientation of the fiber samples which were investigated.
Some Electrical Properties of Amorphous Selenium Films
Authors: Fotland Richard A.
Published: April 2005

The dark current and photocurrent characteristics of amorphous selenium and arsenic-selenium alloy films have been investigated. One millisecond after the application of an electric field, the dark current (neglecting capacitance charging) is several orders of magnitude higher than the steady-state dark current. A hysteresis effect is observed in the dark volt-ampere curves with the descending voltage branch exhibiting an exponential volt-ampere relationship. The voltage of a charged Se plate in the dark discharges logarithmically with time as anticipated from the exponential volt-ampere relationship. Upon admitting air to a freshly evaporated Se plate, a negative surface potential of 150 mv is observed. The phenomenon of ``fatigue'' (i.e., the temporary increase in dark current following an exposure to illumination) obtained with highly absorbed radiation indicates surface barrier effects exert a large measure of control over dark currents. Photogenerated holes and electrons in Se films are trapped with trapping parameters such that the hole range/unit field is on the order of 10−8 cm2/v, and the electron range is less than 10−9 cm3/v. The addition of As to the Se greatly increases the electron effective lifetime. Trapped holes are eliminated in the dark exponentially with time through a process having an activation energy of 0.77 ev. A 40-mv negative surface photovoltage is observed in Se films upon illumination. This voltage may be accounted for by hole diffusion away from the surface. The addition of As to Se extends the spectral response into the red end of the spectrum, results in the initiation of secondary photocurrent effects, intensifies fatigue effects, and increases the softening temperature of the film.
Crystallography and Domain Walls in Antiferromagnetic NiO Crystals
Authors: Slack Glen A.
Published: April 2005

Twin-domain walls in large crystals of antiferromagnetic NiO have been observed by specular reflection in optically polished and annealed crystals. These walls can be moved in annealed crystals by small mechanical stresses (<106 d/cm2) or by moderate magnetic fields (<25 000 oe) to yield completely untwinned crystals. The ease with which a twin wall moves appears to be limited by a spin-rotation energy loss. Crystallographic measurements of the rhombohedral distortion agree with the x-ray data, and verify the [111] antiferromagnetic contraction. The anisotropy in the magnetic susceptibility vs field has been measured for untwinned crystals, and is compared with earlier work.
Surface Cleaning by Cathode Sputtering
Authors: Yonts O. C. , Harrison Don E.
Published: April 2005

Evidence is presented to indicate that surface recontamination from background gases may be a significant factor in quantitative sputtering measurements, even for beam current densities of 0.1 ma/cm2 and operating pressures of 5×10−5 mm of Hg. An oversimplified mechanism is discussed which leads to criteria for a cleansurface sputtering experiment.
Negative Hydrogen and Deuterium Ion Beams
Authors: Philp Sanborn F.
Published: April 2005

The charge state of a monoenergetic beam of hydrogen atomic and molecular ions traversing a hydrogen gas target has been measured as a function of the energy of the beam and the thickness of the gas target. The yield of negative ions from protons has a maximum of 1.5% at 13 kev. From diatomic and triatomic molecular ions the maximum yields were 3.0% and 4.5% at 26 and 39 kev, respectively. The experiments have also been performed with deuterium ions traversing the hydrogen gas target. The deuterium results are almost identical with those of hydrogen if the energy scale for the hydrogen data is multiplied by two.
High-Frequency Breakdown of Air
Authors: Kelly Donald , Margenau Henry
Published: April 2005

Kinetic theory is applied to the problem of ionization breakdown of the air surrounding a high-speed vehicle. It is found that electrons are removed primarily by being swept out of the field of the moving antenna, and that in the interesting cases this action predominates over diffusion losses. Breakdown voltages are plotted against altitude for frequencies of 225 Mc, 1 kMc, and 10 kMc. The theory may offer an explanation of some types of signal loss during missile flights.
Bounds on the Nonlinear Diffusion Controlled Growth Rate of Spherical Precipitates
Authors: Morrison J. A. , Frisch H. L.
Published: April 2005

This paper considers a nonlinear diffusion problem in which there is a change of phase. The physical situation is e.g., the diffusion of solute in a crystal towards a growing precipitate. The nonlinear-diffusion coefficient is a function of the local concentration of solute. A radially symmetric precipitate which grows at a rate proportional to the square root of the time is considered in n dimensions (n=1, 2, 3); thus ρ=s(D0t)½, where ρ is the radius, D0 is a constant having dimensions of area/time and s is a number, the quantity of particular interest. A comparison theorem is established which, in part, states that s increases with increasing diffusion coefficient. A consequence of the theorem is that a unique value of s is associated with a prescribed diffusion coefficient. The comparison theorem also leads to bounds on s. Some other bounds, involving functionals of the diffusion coefficient, are also obtained for s.
Photovoltaic Effect Derived from the Carnot Cycle
Authors: Rose A.
Published: April 2005

An expression for the maximum power derivable from any photovoltaic device is developed in terms of the incident light intensity measured in units of black body radiation. The expression shows the linear dependence of photovoltage on light intensity at low light levels, the logarithmic dependence at intermediate light levels and the saturation at high light levels. The analysis is used to resolve a paradox proposed by W. Shockley.
Walker Modes in Large Ferrite Samples
Authors: Auld B. A.
Published: April 2005

The modes of resonance for a ferrite strip and a ferrite post resonator between conducting planes are found by taking appropriate combinations of uniform plane-wave solutions. It is shown that magnetostatic resonances (Walker modes) may exist even when the resonator dimensions are arbitrarily large, provided the mode indices satisfy certain restrictions.
Etch Pits in Pyrolytic Graphite
Authors: Tarpinian Aram , Gazza George E.
Published: April 2005

The observation of etch pits in pyrolytic graphite after ion-bombardment etching is described and their similarity to dislocation etch pits is speculated. Evidence of etch-pit multiplication in the form of slip-line segments and low-angle tilt boundaries is presented.
Optical Observations Concerning the Polymorphic Transition in the Potassium Halides
Authors: Wiederhorn S. , Drickamer H. G.
Published: April 2005

At approximately 20 000 atm the potassium halides undergo a phase transition from the FCC (NaCl) structure to the SC (CsCl) structure. Using optical equipment developed in this laboratory various optical effects were observed including the rate of cutoff of the light and the wavelength dependence of the scattered light. The phase transition is apparently initiated by shear involving a large cutoff of light with little or no volume change. At the beginning and end of the transition the scattering is largely small particle scattering, with large particles dominating the middle region. Rb+ impurity has little effect on the transition. Na+ impurity apparently inhibits the nucleation strongly, and, to some extent, the growth.

From the absorption spectra of Pb++ ion impurity it is apparent the nuclei consist of hundreds of ions, rather than smaller units.
Production of Single-Crystal Copper Films at Low Temperatures
Authors: Yelon Arthur , Hoffman R. W.
Published: April 2005

A method is described for the production of single-crystal films of copper at temperatures as low as −40°C. This method utilizes the epitaxy of copper on rocksalt. A thin layer of copper is evaporated on a single crystal of salt at 350°C. Then a thick layer is evaporated at the low temperature.

Films grown by this method have been examined using x-ray and etching techniques. It was found that some of these films had single-crystal regions of 1 mm diameter and larger. These crystallites had [100] directions within 1° to a normal to the film surface.
Effect of Li-B Ion Pairing on Li+ Ion Drift in Si
Authors: Pell E. M.
Published: April 2005

When Li+ and B− ions are present simultaneously in Si, relatively immobile Li-B ion pairs are formed. Only those Li+ ions which have not become paired with B− are free to diffuse through the Si, and measurement of the effective diffusion rate of the Li+ can thus be used to determine the fraction of Li+ paired. Such measurements have been made in the range 2°–100°C using the method of ion drift in a pn junction. The results agree well with the Reiss model for ion pairing, yielding a distance of closest approach between Li+ and B− of 2.5–2.7 A. This value is larger than given by the sum of Li+ and B− radii; it is roughly equal to the distance from a lattice-atom site to the next-nearest interstitial site (2.72 A). The kinetics of the ion-pairing reaction have been investigated by the same technique. The resulting value for the capture radius of the B− ion agrees satisfactorily with theory.
Influence of Crystallographic Orientation on the Charge Formation during Phase Changes in Solids
Authors: Mascarenhas S. , Freitas L. G.
Published: April 2005

The effect of charge separation during phase changes (Costa Ribeiro effect) is studied with naphthalene single crystals. By properly seeding the melt the authors showed that the effect is dependent on crystallographic orientation. Values of the trapped charge are 32×10−9 C/g for growth normal to cleavage plane, 2.5×10−9 C/g for growth along b axis, and 2.9×10−9 C/g for growth along a axis. If the effect is due to selective ionic trapping in the solid phase this observation may be important in zone refining techniques. If it is due to an electronic effect this points out to an orientation dependent double-layer at the solid-liquid interface.
The Near Ultraviolet Absorption of Substituted Benzenes
Authors: Sklar A. L.
Published: April 2005

The intensification of ultraviolet absorption in substituted over unsubstituted benzene is here attributed to the destruction of the sixfold symmetry of the benzene by the partial migration of an electron to the ring or out of it. Toluene, aniline, phenol, and fluorobenzene are treated. The electric moment produced by a migration of an electron from the radical into the benzene ring is calculated by the method of antisymmetric molecular orbitals and the extent of migration by a minimum condition. The results are in agreement with empirical data. It is concluded that a radical will produce a large intensification of the absorption if it has a low ionization potential, a pair of nonbonding P electrons, and a not too large ring-radical distance. On this basis the SH group is predicted to be very effective.
The Infra-Red Absorption by Hydrogen Selenide, Deuterium Selenide and Deutero-Hydrogen Selenide
Authors: Cameron Donald M. , Sears William C. , Nielsen Harald H.
Published: April 2005

The infra-red spectra of H2Se, D2Se and HDSe have been measured and the positions of the three fundamental frequencies for each molecule have been determined. These are; for H2Se v1 = 2260 cm—1, v2 = 1074 cm—1, v3 = 2350 cm—1; for D2Se, v1 = 1630 cm—1, v2 = 745 cm—1, v3 = 1696 cm—1; for HDSe, v1 = 1691 cm—1, v2 = 905 cm—1 and v3 = 2352 cm—1. Interpretation of the observed data has led to the adoption of an obtuse model where the H–Se–H bond angle is slightly in excess of 90°. The H–Se distances are evaluated to be 1.6A and the H–H distance is equal to 2.3A. The product relations of Redlich are made use of as a verification of a correct assignment of frequencies and for a correct determination of the band centers.
Hecke transformation and the generalized theta function
Authors: Biswas Indranil , Raina A. K.
Published: April 2005

We describe the behavior of the generalized theta function with respect to the Hecke transformations. Let E be a holomorphic vector bundle over rank r and degree r(g−1) over a compact Riemann surface X of genus g. Let P(E) [respectively, P(E)] be the space of all lines (respectively, hyperplanes) in the fibers of E. Certain Zariski open subsets of P(E)××P(E) and P(E)×P(E)×P(E)×P(E) parametrize holomorphic families of vector bundles over X of rank r and degree r(g−1). We describe the generalized theta line bundle for these families.
Topography of molecular scalar fields. II. An appraisal of the hierarchy principle for electron momentum densities
Authors: Balanarayan P. , Gadre Shridhar R.
Published: April 2005

The previously observed hierarchy principle for nondegenerate critical points (CPs) of the electron momentum density (EMD) of molecules [Kulkarni, Gadre, and Pathak, Phys. Rev. A. 45, 4399 (1992)] is verified at a reliable level of theory. Application of Morse inequalities and the Poincaré–Hopf relation to EMD leads to some rigorous results viz (i) for total number of CPs, NCP=3,7,11,15,… there must be either a (3,+3) or a (3,−1) CP at the center of symmetry, (ii) for NCP=1,5,9,13,… there must be either a (3,−3) or a (3,+1) CP at the center of symmetry. A single directional maximum on every ray, starting from p=0 has been observed for all the test molecules and is suggested as a working topographical principle in p space. This working principle is shown to satisfy the sufficiency condition for the hierarchy principle.
Gear formalism of the always stable predictor-corrector method for molecular dynamics of polarizable molecules
Authors: Kolafa Jiří
Published: April 2005

The recently proposed always stable predictor-corrector method for molecular dynamics of polarizable molecules [J. Kolafa, J. Comput. Chem. 25, 335 (2004)] is rewritten in the Gear formalism. This equivalent form simplifies an implementation if the Newton equations of motion are integrated by the Gear method and also enables a variable integration step. Algorithms are presented for both the original and new versions and tested on a pair of polarizable ions exhibiting anharmonic vibrations.
Partial averaging and the centroid virial estimator for stereographic projection path-integral simulations in curved spaces
Authors: Avilés Michael W. , Curotto E.
Published: April 2005

We develop and test three different partial averaging theories for the stereographic projection path integral in curved spaces. Additionally, we adapt and test the centroid virial estimator for the kinetic energy in curved spaces. We tested both a confining as well as a nonconfining potential for the particle in a ring. All three partial averaging theories are demonstrated to converge linearly in the asymptotic region with kmax−2, the number of Fourier coefficients. We use an error estimator to determine the optimal parameters for an extrapolation to infinite kmax. We verify that the centroid virial estimator (derived from the primitive DeWitt path-integral formula) converges to the kinetic energy for both confining and nonconfining potentials.
A coherent discrete variable representation method for multidimensional systems in physics
Authors: Yu Hua-Gen
Published: April 2005

A coherent discrete variable representation (ZDVR) is proposed for constructing a multidimensional potential-optimized DVR basis. The multidimensional quadrature pivots are obtained by diagonalizing a complex coordinate operator matrix in a finite basis set, which is spanned by the lowest eigenstates of a two-dimensional reference Hamiltonian. Here a c-norm condition is used in the diagonalization procedure. The orthonormal eigenvectors define a collocation matrix connecting the localized ZDVR basis functions and the finite basis set. The method is applied to two vibrational models for computing the lowest bound states. Results show that the ZDVR method provides exponential convergence and accurate energies. Finally, a zeroth-order approximation method is also derived.
Theory of the GaN crystal diode: Negative mass negative differential resistance
Authors: Ridley B. K. , Schaff W. J. , Eastman L. F.
Published: April 2005

The classical description of the electric properties of the vacuum diode is modified to be applicable to the diode structure in a semiconductor crystal when scattering is negligible. The principal modification is the introduction of the effect of the conduction-band structure, and a simple model band structure is assumed. This introduces states with negative effective mass and the Bloch frequency into the problem. A small-signal analysis of the ideal case of ballistic transport in GaN describes conditions for the appearance of a negative differential resistance (NDR) associated with the negative effective mass and yields explicit expressions for the components of the impedance. We show that injection at a finite energy is necessary for NDR, which is present in the frequency range 0 to about 30 THz. An analysis incorporating space charge is also presented and the components of the impedance are calculated explicitly as a function of frequency.
Interrelation between nonlinear elastic surface pulses and dynamic fracture
Authors: Lomonosov Alexey M. , Hess Peter
Published: April 2005

Initiation of impulsive fracture near the source of a nonlinear surface acoustic wave (SAW) pulse, launched by laser-based transient pressure shocks, is investigated. A numerical method is developed that solves the problem of nonlinear SAW generation, the propagation of SAW pulses in nonlinear media, and the initiation and growth of cracks by such pulses. The characteristic features of SAW profiles in linear media, nonlinear media with quadratic nonlinearity, and nonlinear media with crack induction provide a tool to determine the critical stress of dynamic fracture. Former discrepancies between theoretical and experimental pulse shapes were eliminated by taking into account the effects of fracture. Good agreement was obtained with experiments in isotropic fused quartz. By calculating the stress field of the nonlinear SAW pulse modified by the interaction with a crack and by applying the condition of vanishing shear stress at the crack tip, the angle of crack penetration into the solid was estimated. At a depth of 7.1μm, for example, this angle was approximately 50° to the surface normal, in reasonable agreement with previous measurements in isotropic fused quartz.
Oscillatory behavior of C60-nanotube oscillators: A molecular-dynamics study
Authors: Liu P. , Zhang Y. W. , Lu C.
Published: April 2005

The mechanical oscillatory behavior of a C60 molecule tunneling through a carbon nanotube induced by van der Waals interaction are investigated by molecular-dynamics simulations. It is found that the C60 performs a decaying oscillation with a gradual decrease of the oscillatory amplitude and a gradual decrease of the oscillatory frequency. It is shown that this decay is due to the transformation of thermal energy and is sensitive to the change in the diameter and the degree of the helicity of the nanotube. In addition, the nanotube length can be used to tune the oscillation frequency of the C60-nanotube oscillators.
Molecular-dynamics model of energetic fluorocarbon-ion bombardment on SiO2 I. Basic model and CF2+-ion etch characterization
Authors: Smirnov V. V. , Stengach A. V. , Gaynullin K. G. , Pavlovsky V. A. , Rauf S. , Stout P. J. , Ventzek P. L. G.
Published: April 2005

A molecular-dynamics-based model has been developed to understand etching of amorphous SiO2, with and without a fluorocarbon reactive layer, by energetic fluorocarbon (CFx+) ions. The model includes a representation of the solid and a set of interatomic potentials required for the SiO2–CFx interaction system. Two- and three-body pseudopotentials have either been obtained from published literature or computed using ab initio techniques. The Stillinger–Weber potential construct is used to represent potentials in our model and particle trajectories are advanced using the velocity-Verlet algorithm. The model is validated by comparing computed bond lengths and energies with published experimental results. Computed yield for Ar+ ion sputtering of SiO2 is also compared with published data. In the computational results described in this article, the model SiO2 test structure (with a thin fluorocarbon reactive layer) is prepared by starting with α-quartz ([001] orientation) and bombarding it with 50-eV CF2+ ions. Energetic CF2+ ions with different energies and angles of impact are then bombarded on this test structure to determine ion etch characteristics. Results show that etch yield increases with ion energy for all angles of impact. Etch yield, however, exhibits a nonlinear dependence on angle of impact with a peak around 60°. This nonlinear behavior is attributed to the balance among fraction of incident ion energy deposited in the material, ion energy deposition depth, and direction of scattering during secondary interaction events. Si in the lattice is primarily etched by F atoms and the primary Si-containing etch by-products are SiFx and SiOxFy radicals. However, oxygen either leaves the test structure as atomic O or in combination with C. While fragments of the energetic incident ion retain a substantial fraction of incident ion energy on ejection from the surface, etch by-products that have their origin in test structure atoms only have a few eV of energy on exit. Etch results are sensitive to fluorocarbon layer characteristics and etch yields decrease as the fluorocarbon reactive layer thickens.
A revised reverse gated-diode technique for determining generation parameters in thin-film silicon-on-insulator devices and its application at high temperatures
Authors: Rudenko T. , Kilchytska V. , Dessard V. , Flandre D.
Published: April 2005

In this paper the reverse gated-diode technique is examined for determining the carrier generation lifetime and surface generation velocities in thin-film silicon-on-insulator (SOI) devices. Using the modeling of the gate-controlled volume and surface generation components, SOI-specific aspects of the technique are highlighted. A reliable approach for extracting generation parameters in thin-film SOI devices from reverse gated-diode measurements is proposed and validated for high temperatures. The technique is demonstrated on the devices fabricated on two different SOI materials (zone-melt recrystallized and Unibond®), as examples of volume- and surface-dominated generation current behaviors. Finally, the technique is applied to characterize Unibond® SOI devices operating in the temperature range 100–300 °C to demonstrate the model and technique applicability at high temperatures.
Formation and oxidation of Si nanoclusters in Er-doped Si-rich SiOx
Authors: Pi X. D. , Zalloum O. H. Y. , Wojcik J. , Knights A. P. , Mascher P. , Todd A. D. W. , Simpson P. J.
Published: April 2005

The mechanisms for the formation and oxidation of Si nanoclusters (Si-ncls) are elucidated by means of the study of their effects on the photoluminescence of Er in Er-doped Si-rich SiOx (x<2) films. We find that the light emission of Er is the most intense in films with a Si concentration of ∼40% after annealing at 875°C in an argon ambient, which yields an optimum Si-ncl size. The nucleation rate of Si-ncls increases with temperature, however, they stabilize around a critical size which increases with annealing temperature. We determine that the activation energy for the formation of Si-ncls is 1.4±0.5eV. During annealing in an oxygen ambient Si-ncls are oxidized. The resultant oxide reduces the efficiency of energy transfer from them to Er ions and thus the light emission of Er. The activation energy for the oxidation is 1.06±0.03eV.
Residual stress evolution in multilayer ceramic capacitors corresponding to layer increase and its correlation to the dielectric constant
Authors: Park Jong-Sung , Kim Sujin , Shin Hyunho , Jung Hyun Suk , Hong Kug Sun
Published: April 2005

The residual thermal stress in multilayer ceramic capacitors (MLCCs) with varying number of layers was analyzed using finite element analysis, in order to find the links among the dielectric constant, the number of layers, and the stress state. In the active region of the MLCC, the in-plane stresses in a ceramic layer, σ11 and σ22, were compressive while the out-of-plane stress, σ33, was mostly tensile. Changes in the dielectric constant were related to the reinforcement of the compressive in-plane stress components for small numbers of layers, while out-of-plane tensile stress was attributed to the increased dielectric constant when the number of layers was large. In the intermediate regime, in-plane stress components and out-of-plane components both affected the dielectric constant.
Optical calibration of pressure sensors for high pressures and temperatures
Authors: Goncharov Alexander F. , Zaug Joseph M. , Crowhurst Jonathan C. , Gregoryanz Eugene
Published: April 2005

We present the results of Raman-scattering measurements of diamond (C12) and of cubic boron nitride, and fluorescence measurements of ruby, Sm:yttrium aluminum garnet (Sm:YAG), and SrB4O7:Sm2+ in the diamond anvil cell at high pressures and temperatures. These measurements were accompanied by synchrotron x-ray-diffraction measurements on gold. We have extended the room-temperature calibration of Sm:YAG in a quasihydrostatic regime up to 100 GPa. The ruby scale is found to systematically underestimate pressure at high pressures and temperatures compared with all the other sensors. On this basis, we propose an alternative high-temperature ruby pressure scale that is valid to at least 100 GPa and 850 K.
Influence of the annealing field strength on exchange bias and magnetoresistance of spin valves with IrMn
Authors: Kerr Emma , van Dijken Sebastiaan , Coey J. M. D.
Published: April 2005

We report on field annealing effects in spin valves with an IrMn pinning layer and spin valves with a synthetic antiferromagnet. The exchange bias field and magnetoresistance of spin valves with an IrMn∕CoFe bilayer at the bottom improve drastically upon annealing in large magnetic fields. The evolution of the exchange bias field with annealing field strength shows a rapid increase up to an applied field of 0.5 T, which is followed by a more gradual improvement up to an annealing field of 5.5 T. The increase of the exchange bias field in large magnetic fields indicates that the interfacial spin structure of the IrMn layer is directly influenced by the annealing field strength.
Assessing the effects of atmospheric stability on the fine structure of surface layer turbulence using local and global multiscale approaches
Authors: Shi Bin , Vidakovic Brani , Katul Gabriel G. , Albertson John D.
Published: April 2005

The conceptual framework for modeling the inertial subrange is strongly influenced by the Richardson cascade, now the subject of various reinterpretations. One apparent departure from the Richardson cascade is attributed to boundary conditions influencing large-scale motion, which in turn, can directly interact with smaller scales thereby destroying the universal statistical scaling attributes of the inertial subrange. Investigating whether boundary conditions and inertial subrange eddies interact continues to be an active research problem in contemporary turbulence research. Using longitudinal u, lateral v, and vertical w velocities colocated with temperature T time series measurements collected in the atmospheric surface layer, we evaluate whether the inertial subrange is influenced by different stability regimes. The different stability regimes are proxies for different boundary conditions, as upper boundary condition forces the mechanical shear and lower boundary condition forces the surface heating and buoyancy. The novelty of the present work lies in its combined use of global and local scaling properties (e.g., quasi-Hurst exponent, distributional properties of the wavelet coefficients, and Tsallis’s thermostatic entropy measures) to assess whether atmospheric stability impacts both local and global inertial subrange scaling for velocity and temperature.
Discrete and continuous cosine transform generalized to Lie groups SU(2)×SU(2) and O(5)
Authors: Patera J. , Zaratsyan A.
Published: April 2005

We develop and describe continuous and discrete transforms of class functions on compact semisimple Lie group G as their expansions into series of uncommon special functions, called here C-functions in recognition of the fact that the functions generalize cosine to any dimension n<∞. A uniform discretization of the problem on lattices of any density is described. Continuous and discrete orthogonality of C-functions is shown. Discrete transform is known in the case n=1 as the cosine transform. Continuous extension of the discrete transform is described. In general, C-functions are the contributions to irreducible characters from just one orbit of the Weyl group of G. Their products are fully decomposable to the sums of C-functions, so are the reductions to subgroups of the Lie group. They are eigenfunctions of Laplace operator, satisfying Neumann conditions at the boundary of the fundamental region of G, etc. A ready-to-use presentation is made of two of the four variants of the two-dimensional transforms. Both variants have in common exploitation of square lattices for the discrete version of the transforms. They are based on the compact Lie groups SU(2)×SU(2) and O(5), or, equivalently, Sp(4). Remaining two groups, SU(3) and G(2), involve triangular lattices. They are considered separately. Processing digital data, sampled on square lattices, is our motivating application.
Geometry of contours and Peierls estimates in d=1 Ising models with long range interactions
Authors: Cassandro Marzio , Ferrari Pablo Augusto , Merola Immacolata , Presutti Errico
Published: April 2005

Following Fröhlich and Spencer, we study one dimensional Ising spin systems with ferromagnetic, long range interactions which decay as ∣x−y∣−2+α, 0⩽α⩽1∕2. We introduce a geometric description of the spin configurations in terms of triangles which play the role of contours and for which we establish Peierls bounds. This in particular yields a direct proof of the well-known result by Dyson about phase transitions at low temperatures.
Multispecies extension of the solvable partially asymmetric reaction–diffusion processes
Authors: Alimohammadi M. , Naimi Y.
Published: April 2005

By considering the master equation of the partially asymmetric diffusion process on a one-dimensional lattice, the most general boundary condition (i.e., interactions) for the multispecies reaction–diffusion processes is considered. The resulting system has various interactions including diffusion to the left and right, two-particle interactions AαAβ→AγAδ, and the extended n-particle drop–push interactions to the left and right. We obtain three distinct new models. The conditions on reaction rates to ensure the solvability of the resulting models are obtained. The two-particle conditional probabilities are calculated exactly.