bluuebunny/crossref_metadata_2025 huggingface dataset:
An Extension of Saint-Venant's Principle, with Applications
Authors: Goodier J. N.
Published: January 2005

Simple energy considerations, which have previously been employed to provide a rational basis for the principle of Saint-Venant, are shown to lead to the conclusion that forces applied in the neighborhood of a rigidly fixed portion of an elastic solid can cause only local stress and strain. This principle indicates useful features of certain problems encountered in engineering, and is used here in the calculation of the stiffness of a thin layer of elastic material confined between rigid plates, under any kind of load applied to the plates.
On Relaxation Effects in Amorphous Media
Authors: Simha Robert
Published: January 2005

The Maxwell relaxation theory leading to the concept of a viscous-elastic body is briefly stated. Extensions to systems built up from several such viscous-elastic components with different relaxation times are discussed. In the case of high molecular weight materials, it is more appropriate to assume a continuous distribution of relaxation rates. Equations are formulated whose solution gives the distribution function in terms of the rate of deformation and of the applied stress or the elongation in terms of the two other quantities. The connection with the corresponding distribution of dielectric relaxation times, molecular inhomogeneity and chain branching, and effects at mechanical frequencies large compared with the relaxation rates, are pointed out.
Frictional Phenomena. VIII
Authors: Gemant Andrew
Published: January 2005

GEL formation in colloidal systems causes the viscosity of such systems to vary with the stress: these are called non-Newtonian liquids. Because the physical cause of such behavior is related to the gel structure, the phenomenon is called structural viscosity. Three particular features are observed with such systems: a non-linearity of the rate of shear vs. stress relation in the case of stationary flow; a finite relaxation process for suddenly applied stresses or deformations; and a frequency dependent dynamic viscosity in the case of alternating processes. The chief experimental facts in these three fields are presented, together with certain semitheoretical equations best suited to describe the experiments.
A New Approach to the Study of Arcback
Authors: White John E.
Published: January 2005

The generally employed methods of investigating arcback in mercury arc rectifiers are incapable of uncovering some of the important characteristics of the phenomenon. A new method of study has shown that arcback probability varies with time after the appearance of negative voltage, in a surprising and hitherto unsuspected manner. Theoretical implications of this effect are discussed.
Transient Temperatures in the Anode of an X-Ray Tube
Authors: Abbott F. R.
Published: January 2005

The rapid heating and cooling cycle of the focal area of a high speed radiographic x-ray tube anode results in short life, although maximum temperatures produced are not excessive. Some objections are found to earlier theoretical investigations of temperature distributions beneath such focal areas. An operational solution is obtained in terms of Bessel functions. From the calculated temperature distribution the mechanism of disruption is explainable.
Human Trajectories
Authors: Oldenburger Rufus
Published: January 2005

It is proved that a human being M falling from a ledge A through the air to the ground below will attain the greatest range if M falls forward while standing upright. If M was found on the ground at a position B beyond this range of fall, M furnished energy himself to attain B. An analysis of trajectories from A to the ground due to an effort on the part of M is made. If the kinetic energy which M must produce to reach B is much greater than that which M can furnish after loss of balance, M made the trip from A to B by a premeditated jump. Such analyses are important for determining suicides.
Energy and Energy Flow in the Electromagnetic Field
Authors: Slepian J.
Published: January 2005

A new method for deriving the usual Poynting vector is given. This method also yields other equally valid energy flow vectors with the same or other equally valid postulated electromagnetic energy densities. Examples of such alternative Poynting vectors with their associated energy densities are given. A definition is given which distinguishes between the conduction and displacement currents in matter. It is shown that by addition of a term, the postulated energy flow widely used by electrical power engineers and based on wattmeter readings becomes a valid alternative Poynting vector.
The Use of a Mechanical Synthesizer to Solve Trigonometric and Certain Types of Transcendental Equations, and for the Double Summations Involved in Patterson Contours
Authors: Brown S. Leroy , Wheeler Lisle L.
Published: January 2005

A method is shown whereby equations in trigonometric form and types of transcendental equations, which can be expanded into rapidly converging series, may be solved by a mechanical and graphical process. A mechanical and graphical method is also shown which effects the double summation of Fourier series used in the Patterson method for the determination of interatomic distances in crystals. Graphs are given to illustrate each of the processes discussed.
Two New Hot-Filament Resistances
Authors: Minter Clarke C.
Published: January 2005

This report gives the results of attempts to produce a gaseous atmosphere in which the thermal conductivity increases with increasing ambient temperature much more rapidly than the normal, thereby causing a hot filament mounted in such an atmosphere to behave as if it had a negative temperature coefficient of resistance. There is also described a means of producing a gaseous atmosphere the thermal conductivity of which decreases very rapidly as the ambient temperature is increased, so that a hot filament mounted in such an atmosphere behaves as though it had a positive temperature coefficient of resistance three to four times as great as normal.
Rheological Properties of Colloidal Solutions, Pigment Suspensions, and Oil Mixtures
Authors: Weltmann R. N. , Green H.
Published: January 2005

The law of Arrhenius which correlates the viscosity of a colloidal solution logarithmically to the volume percent concentration of solid matter has previously been tested only for dilute suspensions which appeared to the investigators to behave like true Newtonians. Similar suspensions have been tested at higher concentrations of solid matter and the authors found that although Arrhenius' law could not be checked, a similar exponential law evolved, which, however, is correct only within the tested region of viscosity. The authors realized that with the increase of solid matter the suspension can become plastic or pseudo-plastic and may also show thixotropic behavior. Therefore it was considered as a major part of this investigation to determine the validity of Arrhenius' law in that region of concentration, where plasticity occurs. Although Arrhenius' law was not found to be applicable for plastic materials, two exponential laws, similar to Arrhenius' law, have been established between the plastic viscosity and the volume percent of pigment content of a plastic suspension on the one hand, and between the yield value and the volume percent of pigment content of a plastic suspension on the other hand. The two constants in the exponents of the two equations have been shown to be logarithmically related to the average diameter, d3, of the pigment particles contained in the suspension. Oil mixtures with the same and with different type constituents have been tested below a certain rate of shear, called ``the limiting rate of shear,'' where they are Newtonian liquids, and also above this limiting rate of shear where they behave like thixotropic plastics. Their Newtonian viscosities, obtained at rates of shear below the limiting rate of shear, have been found to increase logarithmically with the volume percent of one of the oils contained in the mixture, which is in agreement with Arrhenius' exponential law. However, above the limiting rate of shear, oil mixtures deviate from the exponential law, which is logically expected, since their limiting rate of shear depends on the Newtonian viscosity and therefore is different for each oil mixture.
Magnification Calibration of the Electron Microscope
Authors: Fullam Ernest F.
Published: January 2005

A method is proposed for the magnification calibration of the electron microscope to compensate for the calibration errors caused by mechanical and electrical variations of the instrument. This method uses microscopic glass spheres of predetermined size, mounted directly on the specimen supporting film. A single calibrating sphere is then exposed on the same photographic plate with the sample. Any change, therefore, in the magnification of the specimen also causes a corresponding change in the magnification of the sphere, thus eliminating errors in calculating magnification arising from instrumental variations. The spheres are graded to a given size by controlled levigation and calibrated internally on a grating replica at a low magnification with a very low electron-beam intensity. By the use of low intensity of the beam, deformation of the replica of the grating is avoided. Also at the lower magnification many more lines of the grating replica may be included in the field for greater accuracy in determining the calibrating magnification. The spheres are placed on the specimen supporting film by evaporation from a water suspension. It is estimated that an accuracy of about ±3.0 percent is attained by the measurement of the image of the calibrated sphere on the same plate as the sample.
Two-Dimensional Boundary Value Problems in Potential Theory
Authors: Sokolnikoff I. S. , Specht R. D.
Published: January 2005

A solution of the problem of Dirichlet for a two-dimensional region that can be mapped conformally on a circle is given by the formula of Schwarz. This formula is specialized to yield a complete solution of the torsion problem of St. Venant, and it is demonstrated that the results obtained formally by R. M. Morris are deducible rigorously from the general results of N. Muschelisvili. It is shown that the solution of the torsion problem for a prism whose cross section is the inverse of an ellipse, offered by T. J. Higgins, can be obtained more easily by utilizing the method outlined in this paper rather than by following the procedure of R. M. Morris.
Probable X-Ray Mass Absorption Coefficients for Wave-Lengths Shorter Than the K Critical Absorption Wave-Length
Authors: Victoreen John A.
Published: January 2005

Absorption coefficients of all elements may be calculated, from short wave-lengths up to the K critical absorption wave-length by the expression: μ/ρ=αλ3Z2(2Z/A)−βλ4Z5(2Z/A)+σeN0(Z/A). This formula holds for all elements when suitable values for α and β are chosen. Factors α and β are related to the atomic number, Z, by the expressions α=(aZ2+bZ−c), and β=(dZ2−eZ+f). Different values of the constants a, b, c, d, e, and f are required for each side of the critical absorption wave-lengths and for either side of Z=5, and are given for the short wave-length side of the K critical absorption wave-lengths. The values of αZ2(2Z/A) and βZ5(2Z/A) computed for all elements, are shown in the tables. The calculated mass absorption coefficients of a few elements are also furnished together with comparison of calculated mass absorption coefficients with published experimental data. No anomalies were found and the average agreement is of the order of 1 to 2 percent for all elements and all wave-lengths on the short wave-length side of the K critical absorption wave-length. Values for the region between the K and L1 critical absorption wave-lengths will be published later.
The Penetrometer Method for Determining the Flow Properties of High Viscosity Fluids
Authors: Pendleton Wesley W.
Published: January 2005

A review of the literature has shown that there was no reliable method of measuring the flow properties of fluids in the range of viscosity 106 to 1012 poises where the flow is ``generally viscous.'' The theory of the penetrometer has been developed in this paper to a point where absolute viscosities may be determined both for viscous flow (viscosity independent of rate of shear) and generally viscous flow (viscosity dependent on rate of shear). The new penetrometer method was checked (1) with the capillary viscometer for viscous flow using coal tar pitch, and (2) with the revised axially moving cylinder method for generally viscous flow using a high melting blown asphalt. For any one temperature, the flow properties of a generally viscous material are defined by the straight line relationship between log shearing stress and log rate of shear. From this relationship viscosity may be calculated at any desired rate of shear. The slope n of this line is required in the calculation of rate of shear both for the penetrometer method and for any other type of standard viscometer method. An independent means for observing n was developed for the penetrometer and for the moving cylinder method. It is shown that earlier formulas for standard instruments based on viscous flow are invalid when applied to fluids showing generally viscous flow properties. The power function law relating shearing stress and rate of shear has been found to hold for the asphalt studied over the range of rate of shear from 10−5 to 10 reciprocal seconds. In addition to speed of operation and precision, the penetrometer has the advantages of minimizing the elastic effects and reproducibility without extensive heat treatment and preworking. Entire shearing stress-rate of shear curves can be determined with one load and one penetration using a succession of time intervals.
New Formulas for the Inductance and Reactance of Square Tubular Conductors
Authors: Higgins Thomas James
Published: January 2005

Formulas are derived for the inductance per unit length of square tubular conductors. A numerical example illustrates use of these formulas. A comparison is effected with other formulas advanced earlier by Dwight and Wang.
Studies in Lubrication. XI. Temperature Behavior of Journal Bearing Systems
Authors: Muskat M. , Morgan F.
Published: January 2005

Transient bearing temperature and friction data have been obtained for a journal bearing system operating under thick film conditions. The journal speed was varied from 1.5 to 11.0 r.p.s., and tests were made with five different lubricants. Equilibrium values of temperature and friction were determined by exponential extrapolation of data taken over time intervals of three to six hours. By inversion of the Petroff formula, average film temperatures were calculated from the friction data. These were in all cases greater than the directly measured bearing temperatures, although the excess was in general less than 10°F. The equilibrium temperature data for the various lubricants and speeds were correlated on the basis of heat balance considerations by the formula: μN2=const (T−Ta)1.35,the film viscosity μ and temperature T referring to equilibrium conditions, Ta denoting the ambient temperature, and N the journal speed. This relation permits the calculation of the equilibrium conditions for a journal bearing system of the type used here for any lubricant and journal speed. The asymptotic rate of approach to equilibrium was also quantitatively correlated to the final equilibrium conditions. For Gulflube 10 the equilibrium frictional force was found to increase monotonically with the journal speed, the rate of increase quickly tapering off for speeds greater than 4 r.p.s. Its value at 11 r.p.s. is only 0.14 of that to be expected if there were no fall in film viscosity. For Gulflube 30 the friction force curve rises to a maximum at 3 r.p.s. and then falls slowly for greater speeds. The value at 11 r.p.s. is here only 0.04 of that for a constant film viscosity system.
A Tension-Compression Device for Quantitative X-Ray Diffraction Evaluation of Strain in Metals and a Calibrated Series of Aluminum Alloys
Authors: Clark George L. , Pish George , Seabury Ralph
Published: January 2005

An easily constructed apparatus is described for applying tension and compression stresses to metal and alloy samples while being subjected to x-ray diffraction analysis. The back reflection technique is employed in which diffraction patterns can be photographed in five minutes or less. The apparatus and technique have been developed because of the increasing interest in the measurement of strain in a variety of metallurgical materials of primary war interest. A series of patterns on a familiar aluminum alloy under calibrated tension stresses is reproduced as an example by means of which evaluation of residual strains in large castings can be non-destructively evaluated.
Use of an Electron Diffraction Camera as an Ultraoscilloscope, and Suggested Application to Contact Erosion
Authors: Lander J. J.
Published: January 2005

A high speed oscilloscope, obtained by adaptation of an electron diffraction camera, is described and a preliminary account is given of the use of this oscilloscope in a study of the ``short arc'' which occurs on opening mechanical contacts under certain conditions.
Properties of a Long Antenna
Authors: Hallén Erik
Published: January 2005

Although exact integral expressions for the outgoing current waves on a long antenna have long existed, they have never been brought in such a form that a numerical or graphical description of the wave has been possible. The author shows how to transform them into good series expansions valid for all distances from the feeding point. Graphs show the result. The traveling current waves can also be extracted from the author's expression for the current on a finite transmitting antenna published in Nova Acta Upsal, 1938. Both ways give identical series.
A Technique for Quantitative Determination of Texture of Sheet Metals
Authors: Norton John T.
Published: January 2005

A method is described for making a pole figure of rolled sheet employing an x-ray unit equipped with a G-M counter for measuring intensities. Small rods are cut from the sheet with their axes parallel to the plane of the sheet and making various angles with the rolling direction. With the counter tube set at the correct diffraction angle for the desired crystallographic plane, each rod in turn is placed in the beam and rotated continuously about its axis. The recorder chart, synchronized with the rod rotation, plots a curve of intensity vs. angular position. Thus the record for each rod provides information for a specific diameter of the pole figure and all have a common point at the center. Since all rods are cylindrical and of the same diameter, there is no absorption correction to be applied. Contours for the pole figures may be drawn as closely together as desired. For special purposes where the complete pole figure is not required but quantitative comparisons are to be made between specimens, certain simplified techniques based on the same principle have proved useful.
On the Investigation of Specimen Contamination in the Electron Microscope
Authors: Hillier James
Published: January 2005

A number of experiments directed toward determining the nature and cause of deposits which occur on electron microscope specimens under electron bombardment are described. From these the conclusion is drawn that the material is a result of chemical reaction, occurring at any surface simultaneously bombarded by electrons and organic molecules. The organic vapors are shown to arise in two ways: (1) by diffusion out of the metal walls, gaskets, and greases exposed to the vacuum, (2) by the outgassing of metal parts of the instrument exposed to electron bombardment. To eliminate the effect both sources must be removed.
Simple Relations for Calculating Certain Transient Responses
Authors: Cunningham W. J.
Published: January 2005

The response of a linear transmission system to a step or an impulse is related directly to its steady-state response to a sinusoidal signal of variable frequency. Several very simple relations between these two types of response for low pass systems are collected here. These equations are empirical in nature, but generally may be expected to be in error no more than ±25 percent. Such equations may be useful in preliminary design work where great accuracy is not required, or in checking the results of exact but tedious calculations.
A Determination of the Elastic Constants for Beta-Quartz
Authors: Kammer E. W. , Pardue T. E. , Frissel H. F.
Published: January 2005

The complete set of adiabatic elastic constants for beta-quartz have been obtained for a series of temperatures ranging from 580°C to 800°C. The elastic moduli were computed from the elastic constants and are compared with the adiabatic and isothermal values which have been determined by others.
Viscous Slip Along Grain Boundaries and Diffusion of Zinc in Alpha-Brass
Authors: Kê T'ing-Sui
Published: January 2005

The viscous behavior of the grain boundaries in 70–30 alpha-brass was demonstrated by anelastic measurements. It was shown that the grain boundaries cannot sustain permanently a shear stress and have a coefficient of viscosity decreasing with an increase of temperature. Using the same alpha-brass specimen, the activation energy associated with the stress-induced preferential orientation of pairs of zinc atoms in alpha-brass (which is a diffusion process) was determined. This activation energy was found to be identical, within experimental error, to the activation energy associated with the grain boundary slip in alpha-brass. This finding indicates that the grain boundary slip in alpha-brass is a diffusion process and the diffusion mechanism is similar to the volume diffusion in alpha-brass.
An Electronic Simultaneous Equation Solver
Authors: Goldberg Edwin A. , Brown George W.
Published: January 2005

An analogy device for directly solving simultaneous linear equations (without resorting to successive approximation methods) is described in this paper. It utilizes a number of high gain amplifiers interconnected by networks whose elements bear definite relationships to the known coefficients and constants of the system of equations. The stability criterion for such a system, and its application to an equation solver are described. Since the device produces the answers to a system of equations without delay, it is readily adaptable to problems of synthesis as well as those of analysis.
The Head-On Collision of a Shock Wave and a Rarefaction Wave in One Dimension
Authors: Moses H. E.
Published: January 2005

A procedure for investigating the strengthening of a shock which collides head-on with a rarefaction wave is suggested and is carried through for the case in which the entropy jump across the shock is small enough to be negligible.
Measurements of Dielectric Constant and Dipole Moment of Gases by the Beat-Frequency Method
Authors: Jelatis J. G.
Published: January 2005

The beat-frequency method for measuring the dielectric constant and dipole moment of gases is critically investigated. It appears that the wide discrepancies in the data of previous observers are due in part, at least, to the neglect of certain stray components in the circuits involved. An apparatus taking these factors into consideration is described, and a method for the ``absolute'' standardization of the equipment is given. Results of dielectric constant and dipole moment measurements for several gases are presented and compared with previous data.
Separation of quadrupolar and chemical/paramagnetic shift interactions in two-dimensional H2 (I=1) nuclear magnetic resonance spectroscopy
Authors: Antonijevic Sasa , Wimperis Stephen
Published: January 2005

A novel two-dimensional H2 (spin I=1) nuclear magnetic resonance technique is introduced for determination of both quadrupole and chemical/paramagnetic shift tensors and their relative orientation. The new method is based upon the well-known quadrupolar-echo experiment and is designed to refocus the quadrupolar interaction at the end of the t1 evolution period while retaining the modulation introduced by the shift interaction. As a result, a projection of the resulting two-dimensional spectrum onto its F1 dimension yields a shift anisotropy powder lineshape free from any quadrupolar broadening. The chemical/paramagnetic shifts appear in both F1 and F2 dimensions and are thus spread along a +1 frequency gradient; hence, a projection orthogonal to this gradient yields the pure quadrupolar powder lineshape, free from all shift interaction effects. The relative orientation of the quadrupole and shift tensors can be obtained by analysis of the full two-dimensional correlation lineshape. Unlike the well-known double-quantum experiment, the new method is, in principle, equally effective for all values of the quadrupolar splitting, including zero. The properties of the new technique are demonstrated using computer simulation and methods for the extraction of quadrupole and shift tensor parameters are described. The new technique is applied to (diamagnetic) benzoic acid-d1 (C6H5CO2D) and (paramagnetic) copper(II) chloride dihydrate-d4 (CuCl2⋅2D2O).
Line strengths and transition dipole moment of the ν2 fundamental band of the methyl radical
Authors: Stancu G. D. , Röpcke J. , Davies P. B.
Published: January 2005

The line strengths of nine Q-branch lines in the ν2 fundamental band of the methyl radical in its ground electronic state have been measured by diode laser absorption spectroscopy. The vibration–rotation spectrum of methyl was recorded in a microwave discharge in ditertiary butyl peroxide heavily diluted in argon. The absolute concentration of the radical was determined by measuring its kinetic decay when the discharge was extinguished. The translational, rotational, and vibrational temperatures, also required to relate the line strengths to the transition dipole moment, were determined from relative integrated line intensities and from the Doppler widths of the lines after allowing for instrumental factors. The line strengths of the nine Q-branch lines were used to derive a more accurate value of the transition dipole moment of this band, μ2=0.215(25) D. Improved accuracy over earlier measurements of μ2 (derived from line strengths of single lines) was obtained by integrating over the complete line profile instead of measuring the peak absorption and assuming a Doppler linewidth to deduce the concentration. In addition, a more precise value for the rate constant for methyl radical recombination than available earlier was employed. The new value of μ2 is in very good agreement with high-quality ab initio calculations. Furthermore, the ratio of the transition dipole moments of the ν2 and ν3 fundamental bands in the gas phase is now in highly satisfactory agreement with the ratio determined for the condensed phase.
O 18 tracer diffusion in Pb(Zr,Ti)O3 thin films: A probe of local oxygen vacancy concentration
Authors: Wang Ruey-Ven , McIntyre Paul C.
Published: January 2005

A series of O18 tracer in-diffusion experiments have been conducted on state-of-the-art metal organic chemical vapor deposition–grown Pb(Zr,Ti)O3 (PZT) films. Prior to O18 incorporation, samples were preequilibrated in O216 at the same temperature and total pressure used for the following O218 isotope exchange anneal. The final O18 depth profiles were obtained using secondary ion mass spectroscopy (SIMS), which provides a depth resolution of 3–5Å. The SIMS results indicate that the O18 tracer diffusivity varies as a function of depth from the PZT film surface in a way that is inconsistent with a combined grain boundary and lattice diffusion mechanism. Based on a previously-developed model for point defect equilibrium in metal titanate thin films, simulations of O18 tracer diffusion into PZT thin films that are consistent with the experimental results are described.
One-dimensional reaction coordinates for diffusive activated rate processes in many dimensions
Authors: Berezhkovskii Alexander , Szabo Attila
Published: January 2005

For multidimensional activated rate processes controlled by diffusive crossing of a saddle point region, we show that a one-dimensional reaction coordinate can be constructed even when the diffusion anisotropy is arbitrary. The rate constant, found using the potential of mean force along this coordinate, is identical to that predicted by the multidimensional Kramers–Langer theory. This reaction coordinate minimizes the one-dimensional rate constant obtained using a trial reaction coordinate and is orthogonal to the stochastic separatrix, the transition state that separates reactants from products.
A molecular dynamics computer simulation study of room-temperature ionic liquids. I. Equilibrium solvation structure and free energetics
Authors: Shim Y. , Choi M. Y. , Kim Hyung J.
Published: January 2005

Solvation in 1-ethyl-3-methylmidazolium chloride and in 1-ethyl-3-methylimidazolium hexafluorophosphate near equilibrium is investigated via molecular dynamics computer simulations with diatomic and benzenelike molecules employed as probe solutes. It is found that electrostriction plays an important role in both solvation structure and free energetics. The angular and radial distributions of cations and anions become more structured and their densities near the solute become enhanced as the solute charge separation grows. Due to the enhancement in structural rigidity induced by electrostriction, the force constant associated with solvent configuration fluctuations relevant to charge shift and transfer processes is also found to increase. The effective polarity and reorganization free energies of these ionic liquids are analyzed and compared with those of highly polar acetonitrile. Their screening behavior of electric charges is also investigated.
Modeling of microcrystalline silicon film deposition in a capacitively coupled radio-frequency plasma reactor
Authors: Satake Koji , Kobayashi Yasuyuki
Published: January 2005

We present a numerical model of plasma-enhanced chemical-vapor deposition of hydrogenated microcrystalline silicon (μc-Si:H) film from SiH4 and H2 gas mixtures in a capacitively coupled radio-frequency plasma reactor. The model takes into account electron-impact, gas-phase, and surface reactions within a well-mixed reactor model. Plasma parameters such as the electron density, the electron temperature, and the electron-impact reaction rates are determined through a discharge model and used as inputs for the reactor model. The gas-phase reactions include electron-impact and neutral–neutral reactions. Some of the surface reaction rates are determined using quantum chemical calculations and transition state theory. In the reactor model, concentrations of each chemical species are calculated at steady state using mass conservation equation uniformed throughout the reactor. Numerical results of the deposition rate as a function of the plasma reactor operating parameters show good agreement with experiments. Based on the model, the correlation between μc-Si:H properties, such as the crystal grain orientation and the hydrogen content, and deposition operating parameters has been studied using a design of experiment. Finally, optimal operating parameters are investigated using optimization techniques.
Light-induced changes in the gap states above midgap of hydrogenated amorphous silicon
Authors: Kounavis P.
Published: January 2005

The energy dependence of the capture coefficients and the density of states (DOS) above midgap of hydrogenated amorphous silicon (a-Si:H) in annealed and light exposed states are examined by modulated photocurrent experiments. In the annealed and light exposed states, the electrons are found to interact with two different kinds of gap states through trapping and thermal release. The densities of both gap state distributions at trap depths shallower than 0.67eV below the conduction band decrease rapidly during the initial stage of light degradation. The DOS of the annealed and light exposed states are found to cross at about 0.67eV. In addition, a parallel increase in the capture coefficients of the gap states at trap depths lower than 0.67eV is observed indicating a light-induced disorder. The above behavior is explained with the conversion of strained Si–Si and Si–H–Si bonds, which become highly strained during illumination, into dangling bonds near midgap.
Toward a robust and general molecular simulation method for computing solid-liquid coexistence
Authors: Eike David M. , Brennecke Joan F. , Maginn Edward J.
Published: January 2005

A rigorous and generally applicable method for computing solid-liquid coexistence is presented. The method overcomes some of the technical difficulties associated with other solid-liquid simulation procedures and can be implemented within either a molecular dynamics or Monte Carlo framework. The method consists of three steps: First, relative Gibbs free energy curves are created for the solid and liquid phases using histogram reweighting. Next, the free energy difference between the solid and liquid phases is evaluated at a single state point by integrating along a pseudosupercritical transformation path that connects the two phases. Using this result, the solid and liquid free energy curves are referenced to a common point, allowing a single coexistence point to be determined. Finally, Gibbs-Duhem integration is used to determine the full coexistence curve. To evaluate its utility, this method is applied to the Lennard-Jones and NaCl systems. Results for solid-liquid coexistence agree with previous calculations for these systems. In addition, it is shown that the NaCl model does not correctly describe solid-liquid coexistence at high pressures. An analysis of the accuracy of the method indicates that the results are most sensitive to the transformation free energy calculation.
Coulomb potentials in two and three dimensions under periodic boundary conditions
Authors: Tyagi Sandeep
Published: January 2005

A method to sum over logarithmic potential in two-dimensions (2D) and Coulomb potential in three dimensions (3D) with periodic boundary conditions in all directions is given. We consider the most general form of unit cells, the rhombic cell in 2D and the triclinic cell in 3D. For the 3D case, this paper presents a generalization of Sperb’s work [R. Sperb, Mol. Simulation 22, 199 (1999)]. The expressions derived in this work converge extremely fast in all region of the simulation cell. We also obtain results for slab geometry. Furthermore, self-energies for both 2D as well as 3D cases are derived. Our general formulas can be employed to obtain Madelung constants for periodic structures.
Theoretical studies on hydroquinone-benzene clusters
Authors: Manojkumar T. K. , Kim Dongwook , Kim Kwang S.
Published: January 2005

High-level ab initio calculations were carried out to evaluate the interaction between the hydroquinone and benzene molecules. The intermolecular interaction energy was calculated using the Møller–Plesset second-order perturbation theory at the complete basis set limit and also at the coupled cluster theory with single, double, and perturbatively triple excitations. The calculated binding energy is larger than the benzene dimer interaction energy. The T-shaped cluster (T-a) and the parallel conformation (P-a) are calculated to be nearly isoenergetic. Owing to the large energy gain in the attraction by electron correlation, the dispersion interaction is important for the attraction.
Photodetachment microscopy of the P, Q, and R branches of the OH−(v=0) to OH(v=0) detachment threshold
Authors: Goldfarb Fabienne , Drag Cyril , Chaibi Walid , Kröger Sophie , Blondel Christophe , Delsart Christian
Published: January 2005

A photodetachment experiment is performed on the v=0→v=0 OH− detachment threshold. The weak O and S branches provide a signal strong enough to make amplitude measurements on all five O, P, Q, R, and S branches possible, which are used to fix the formulas for their relative intensities. Photodetachment microscopy is applied to 15 different thresholds of the P, Q, and R branches. The quantitative analysis of the interference patterns obtained does not show any effect of the dipole moment of OH, but yields a new measurement of the rotational parameters of OH−(v=0) and of the electron affinity of the molecule. The new recommended value for the electron affinity of O116H is 14 740.982(7) cm−1 or 1.827 648 7(11) eV.
Directional dispersion in absorbance spectra of oligothiophene crystals
Authors: Spearman P. , Borghesi A. , Campione M. , Laicini M. , Moret M. , Tavazzi S.
Published: January 2005

Due to the large oscillator strength of the first molecular transition in oligothiophenes, a strong directional dispersion of the bu exciton transition is expected originating from the macroscopic polarization field. Examining such dispersion unambiguously usually requires different faces to be accessible for the optical measurements. Alternatively, measurements carried out at different angles of incidence are met with intrinsic limits due to the peculiarities of wave propagation in such anisotropic systems. In order to demonstrate these limits along with the experimental difficulties involved, we examine refraction and absorption of light in these crystals and discuss the effects of directional dispersion on the absorbance spectra of quaterthiophene crystals.
Field-theoretic simulations of polymer solutions: Finite-size and discretization effects
Authors: Alexander-Katz Alfredo , Moreira André G. , Sides Scott W. , Fredrickson Glenn H.
Published: January 2005

In this work we analyze the finite-size and discretization effects that occur in field-theoretic polymer simulations. Following our previous work, we study these effects for a polymer solution in the canonical ensemble confined to a slit (with nonadsorbing walls) of width L, and focus on the behavior of two quantities: the chemical potential μ, and the correlation length ξ. Our results show that the finite-size effects disappear for both quantities once the lateral size of the system L is larger than ∼2ξ. On the other hand, the chemical potential is dominated by the lattice discretization Δx. The origins of this dependence are discussed in detail, and a scheme is proposed in which this effect is avoided. Our results also show that the density profiles do not depend on the lattice discretization if Δx≲ξ/4. This implies that the correlation length ξ, extracted from the density profiles, is free of lattice size and lattice discretization artifacts once L≳2ξ and Δx≲ξ/4.
In situ real-time spectroscopic ellipsometry study of HfO2 thin films grown by using the pulsed-source metal-organic chemical-vapor deposition
Authors: Zheng Yangdong , Mizuta Hiroshi , Tsuchiya Yoshishige , Endo Masato , Sato Daisuke , Oda Shunri
Published: January 2005

The HfO2 thin-film growth process is investigated by using in situ real-time spectroscopic ellipsometry (SE) technique combined with the first-principles molecular-orbital (MO) calculations of the electronic states. The HfO2 films are grown on the silicon substrate by using the pulsed-source metal-organic chemical-vapor deposition method. Particular attention is paid to the formation of an interfacial layer at the early stage of the growth process by monitoring energy-dependent dielectric constants of the film. The energy dependence of the electronic polarizabilities and dielectric constants is calculated for the amorphous HfO2, SiO2, and HfSiO4 films based on the electronic states and density of states obtained using the discrete-variational Xα MO method with the unit cluster model. The measured SE spectra show that the average dielectric constants of the film vary gradually from those for SiO2 to those for HfO2 when the number of deposition cycles increases. By comparing the varied dielectric constants during the film growth with the calculated results, we find that the HfO2 film growth process can be divided into two stages with different growth mechanisms: SiO2 and HfxSiyOz layers are grown at the first stage, which are regarded as the interfacial layers, and the HfO2 layer formation becomes predominant at the second stage.
Quantum trajectories in elastic atom-surface scattering: Threshold and selective adsorption resonances
Authors: Sanz A. S. , Miret-Artés S.
Published: January 2005

The elastic resonant scattering of He atoms off the Cu(117) surface is fully described with the formalism of quantum trajectories provided by Bohmian mechanics. Within this theory of quantum motion, the concept of trapping is widely studied and discussed. Classically, atoms undergo impulsive collisions with the surface, and then the trapped motion takes place covering at least two consecutive unit cells. However, from a Bohmian viewpoint, atom trajectories can smoothly adjust to the equipotential energy surface profile in a sort of sliding motion; thus the trapping process could eventually occur within one single unit cell. In particular, both threshold and selective adsorption resonances are explained by means of this quantum trapping considering different space and time scales. Furthermore, a mapping between each region of the (initial) incoming plane wave and the different parts of the diffraction and resonance patterns can be easily established, an important issue only provided by a quantum trajectory formalism.
Dynamics from picoseconds to nanoseconds of trehalose in aqueous solutions as seen by quasielastic neutron scattering
Authors: Köper I. , Bellissent-Funel M.-C. , Petry W.
Published: January 2005

We present a study of the dynamical behavior of trehalose, a cryoprotecting agent, in concentrated aqueous solutions. Dynamics in a wide time range from picoseconds to nanoseconds has been observed using both neutron time of flight and neutron spin-echo techniques. Fast dynamics has been described using a simple diffusion model, while dynamical processes at longer times show a more complex behavior, described by a stretched exponential decay. Obtained relaxation times show a good agreement with data from viscosity measurements on aqueous trehalose solutions by Magazu et al. [Branca, Magazu, Maisano et al., J. Phys.: Condens. Matter 11, 3823 (1999)]. Experimental data provide us with some insight into the cryoprotecting properties and processes of trehalose. We conclude that an increase of the solvent viscosity in embedded biological material due to the production or the presence of trehalose might prevent biomolecules from damage.
Comparing the short and ultrashort pulsed laser ablation of LiF
Authors: Henley Simon J. , Fuge Gareth M. , Ashfold Michael N. R.
Published: January 2005

Pulsed laser ablation of LiF was studied using both nanosecond (ns) and femtosecond (fs) pulses at 248nm. Optical emission from electronically excited Li and F atoms in the plume of ejected material was investigated by wavelength, time and spatially resolved imaging methods. Careful analysis of images of species selected optical emission yielded estimates of the mean velocities of the Li+ ions arising in both excitation schemes (∼11 and ∼13km∕s, respectively), and highlighted the dramatic effects of radiation trapping, most notably by the reabsorption of Li(2p→2s) emission by ground state Li atoms in the ns ablation studies. Plumes formed by fs excitation are found to contain a higher fraction of energetic∕electrically excited components, including excited F atoms and ions, indicative of an explosive boiling mechanism, whereas the ablation plume resulting from ns ablation is deduced to arise primarily from thermal evaporation of the transiently heated target surface. The amount of target material removed per shot is significantly less in the case of fs excitation. The density (and size) of unwanted droplets in films grown by fs ablation is much smaller than in the case of ns ablation, especially on substrates mounted in an off-axis ablation geometry, implying that hydrodynamic sputtering is much reduced by the use of short pulses and that fs ablation must be the preferred route to forming very thin LiF coatings.
Conical intersections and semiclassical trajectories: Comparison to accurate quantum dynamics and analyses of the trajectories
Authors: Jasper Ahren W. , Truhlar Donald G.
Published: January 2005

Semiclassical trajectory methods are tested for electronically nonadiabatic systems with conical intersections. Five triatomic model systems are presented, and each system features two electronic states that intersect via a seam of conical intersections (CIs). Fully converged, full-dimensional quantum mechanical scattering calculations are carried out for all five systems at energies that allow for electronic de-excitation via the seam of CIs. Several semiclassical trajectory methods are tested against the accurate quantum mechanical results. For four of the five model systems, the diabatic representation is the preferred (most accurate) representation for semiclassical trajectories, as correctly predicted by the Calaveras County criterion. Four surface hopping methods are tested and have overall relative errors of 40%–60%. The semiclassical Ehrenfest method has an overall error of 66%, and the self-consistent decay of mixing (SCDM) and coherent switches with decay of mixing (CSDM) methods are the most accurate methods overall with relative errors of ∼32%. Furthermore, the CSDM method is less representation dependent than both the SCDM and the surface hopping methods, making it the preferred semiclassical trajectory method. Finally, the behavior of semiclassical trajectories near conical intersections is discussed.
Geometry optimization of molecular clusters and complexes using scaled internal coordinates
Authors: Maslen P. E.
Published: January 2005

Scaled internal coordinates are introduced for use in the geometry optimization of systems composed of multiple fragments, such as solvated molecules, clusters, and biomolecular complexes. The new coordinates are related to bond lengths, bond angles and torsion angles by geometry-dependent scaling factors. The scaling factors serve to expedite the optimization of complexes containing outlying fragments, without hindering the optimization of the intramolecular degrees of freedom. Trial calculations indicate that, at asymptotic separations, the scaling factors improve the rate of convergence by a factor of 4 to 5.
Fatigue studies in compensated bulk lead zirconate titanate
Authors: Verdier Cyril , Morrison Finlay D. , Lupascu Doru C. , Scott James F.
Published: January 2005

Impedance analysis studies were carried out on compensated bulk lead zirconate titanate samples. Fatigue is concomitant with the onset of dielectric loss. This is shown to be dominantly due to an irreversibly modified near-surface layer that can be polished off. The highly compensated nature of these samples minimizes the role of oxygen vacancies.
Luminescence and spectroscopic behavior of Eu3+-doped Y2O3 and Lu2O3 epitaxial films grown by pulsed-laser deposition
Authors: Pradhan A. K. , Zhang Kai , Mohanty S. , Dadson J. , Hunter D. , Loutts G. B. , Roy U. N. , Cui Y. , Burger A. , Wilkerson A. L.
Published: January 2005

We report on the fabrication of highly epitaxial Y2O3:Eu3+ and Lu2O3:Eu3+ films on sapphire and Si single crystalline, and quartz substrates under different growth and optimization conditions using pulsed-laser deposition technique. The films were characterized using x rays, microstructure, and spectroscopic measurements. Our results demonstrate superior spectroscopic performance on the films grown on sapphire substrates due to the high quality and epitaxial nature of the film. The surface morphology of the epitaxial films controls the photoluminescence property of these phosphors film.