bluuebunny/crossref_metadata_2025_split huggingface dataset:
Charge-Carrier Mobility in Polycrystalline Semiconducting Films Based on Bulk Single-Crystal Theory
Authors: Ramey R. L. , McLennan W. D. 
Published: January 2005

The temperature and thickness dependence of charge-carrier mobility in vacuum-deposited germanium films can be represented by the relation 1/μe=1/μL+1/μI+1/μd+1/μF,where the first three terms represent the lattice, impurity, and dislocation scattering in bulk material. The term μF is a function of the surface scattering of the carriers as well as of grain-boundary effects. Thus film-size effects are represented in a large part by the fourth term which satisfies the empirical relation 1/μF=A log(δ/a).For the films studied, this is the dominant term for polycrystalline films less than 5000 Å in thickness or single-crystal films less than 1800 Å in thickness.
The measured value of the coefficient A was 0.0219 V·sec·cm−2 for our polycrystalline films and 0.0176 for the single-crystal films of Sloope and Tiller. The characteristic thickness, δ, was found to be dependent upon grain-boundary scattering, having a value of 8000 Å for polycrystalline films as compared to 2000 Å for the single-crystal films.
Nickel Ferrite Thin Films: Microstructures and Magnetic Properties
Authors: Brook R. J. , Kingery W. D. 
Published: January 2005

Thin films of nickel ferrite (NiFe2O4) have been prepared by a reactive-sputtering technique using an iron-nickel alloy as the cathode and oxygen-argon mixtures as the reactive gas. Electron microscopy and electron-diffraction studies indicate that films deposited on substrates at temperatures below 0°C are noncrystalline whereas films deposited at higher temperatures are polycrystalline, the size of the crystallites increasing as the temperature is increased.
Measurements of electrical conductivity and magnetic susceptibility have been made on films prepared at various temperatures, and the results are interpreted in terms of film microstructure. In particular, the noncrystalline films show paramagnetic behavior, and the micropolycrystalline films show superparamagnetic behavior; ferrimagnetism is only found in films having a grain size greater than 150 Å and prepared at 400°C and above.
Structural Dependence of the Tracer-Level Diffusion of Thorium in Pyrolytic Carbons
Authors: Lonsdale H. K. , Graves J. N. 
Published: January 2005

Tracer-level diffusion studies have been carried out on laboratory-prepared samples of pyrolytic carbons of widely divergent microstructure. These samples are well characterized and contain no exposed layer-plane edges. Using a 228Th tracer, diffusion coefficients have been measured perpendicular to the plane of deposition over the temperature range 1600° to 2000°C. The diffusion coefficients were found to have a significant dependence on microstructure, the diffusion coefficient in a highly oriented, laminar pyrolytic carbon being more than an order of magnitude smaller than that in either isotropic or granular carbons. The diffusion coefficient D, in cm2/sec, of thorium perpendicular to the plane of deposition in granular, isotropic, and laminar pyrolytic carbons is given by D=7.1×104 exp(−152 000/RT)  (granular),D=15.5 exp(−114 000/RT)      (isotropic),D=1.2×104 exp(−157 000/RT)  (laminar).
The tracer-level diffusion coefficients for thorium in the laminar pyrolytic carbon were substantially smaller than the values that have been reported by others for diffusion in highly anisotropic, columnar pyrolytic carbon. Microstructural parameters, such as apparent crystallite size and anisotropy factor, are useful in correlating the present results but are of limited value in quantitatively rationalizing the large variations in diffusion coefficients.
Measurements of the tracer-level diffusion coefficient of thorium in a polycrystalline graphite were also performed.
Thermal Properties of Gold-Silicon Binary Alloy near the Eutectic Composition
Authors: Chen H. S. , Turnbull D. 
Published: January 2005

We have measured the specific heat Cp and the enthalpy of Au-18.6 at.% Si alloy in some of its various forms. Cp of the liquid form falls continuously with increasing temperature from 8.38±0.05 at 563°K, corresponding to an undercooling of 73°K, to 7.90±0.05 cal/gfw·°K, and it exhibits no singular behavior at the melting temperature Tm. It exceeds the heat capacity of the eutectic solid by 1.87 cal/gfw·°K at Tm. This high specific heat in the liquid state and its decrease with increasing temperature is attributed principally to the configurational entropy, as has been suggested for the pure liquid metals. Cp of the amorphous alloy, formed by rapidly chilling the liquid, was measured for the temperature range from 208° to 278°K. It rises slowly to 225°K, then falls, and then rises again with increasing temperature. It exceeds Cp of the eutectic solid by 0.2 to 0.4 cal/gfw·°K. Cp of the metastable intermetallic crystalline phase, formed when the liquid is less rapidly chilled, falls between the values for the eutectic and the amorphous solids.
The intermetallic phase melts at 631°K, which is only a little lower than the melting point, 636°K, found for the eutectic mixture. Its heat of fusion ΔHf is 1.59 kcal/gfw, while that of the eutectic mixture is found to be 2.35±0.1 kcal/gfw. The heat and excess entropy of mixing of the liquid elements to form the liquid alloy at 1336°K are evaluated to be −1.6±0.1 kcal/gfw and 0.39±0.17 cal/gfw·°K, respectively. The especially deep-lying eutectic exhibited by this system is attributed to the tendency for unlike atoms to associate when in the metallic state, in contrast with the strong tendency for phase separation in the solid state owing to the high stability of silicon in its covalent crystalline form.
Avalanche-Photodiode Frequency Response
Authors: Emmons R. B. 
Published: January 2005

The short-circuit photocurrent from an avalanche photodiode is calculated using an exact solution of the differential transport equations for the multiplication region. The dc electric field and the hole and electron velocities are assumed constant in the avalanche region into which photoelectrons are injected. It is shown that the electron- and hole-ionization coefficients α and β remain constant over a practical range of multiplied photocurrents. Computer studies of the solution show that avalanche multiplication does not reduce the device bandwidth as long as the dc multiplication M0 is less than the ratio of α and β, i.e., as long as M0&lt;α/β. The previously obtained frequency dependence of the multiplication, M(ω) = M0[1 + ω2M02τ12]−1/2, which indicates a constant-multiplication bandwidth product, is now shown to be valid only if M0&gt;α/β. The previously unspecified ``effective'' transit time, τ1, in this equation is approximately τ1 = N(β/α)τ, where N is a number varying slowly from ⅓ to 2 as β/α varies from 1 to 10−3, and τ is the multiplication-region transit time.
The complete solution of this problem thus shows that the widely different results previously obtained for β/α = 0 and β/α = 1 are continuously joined, and provides a simple criterion for judging the ranges of validity of the two limiting cases. The results emphasize the practical importance of obtaining the required multiplication at fields such that M0&lt;α/β where the multiplication does not affect the bandwidth. This also leads to minimum excess avalanche-region noise, and hence to the closest possible solid-state analog to the vacuum-tube photomultiplier.
Stresses in Freely Falling Chimneys and Columns
Authors: Bundy Francis P. 
Published: January 2005

A chimney or column is considered as a rigid rod, initially in a vertical position, and hinged at its base. The internal forces and stresses which are developed as the rod falls freely from the vertical position are calculated. It is shown that the inertial reaction forces produce a bending moment which results in a tension on the leading side and a compression in the trailing side of the rod. This tension in the leading side has its maximum value at roughly 0.3 to 0.5 the height of the rod, depending upon its shape and the angle of inclination from the vertical. This tension usually produces a transverse rupture in large falling chimneys or columns, though not always. These transverse ruptures should occur at the point of maximum tension.
It is shown that in very tall columns or chimneys the vertical shear stress near the base is sufficient to produce a tension rupture there—and usually does. The positions of these latter ruptures cannot be predicted accurately in actual cases because of the greatly variable conditions which may exist at the point of support after dynamiting.
Calculations are given for the cases of solid columns of uniform cross section, solid columns of uniformly tapered cross section, and uniformly tapered chimneys of constant wall thickness. Photographs of actual falling chimneys are presented to check the theory.
A Theory of Large Elastic Deformation
Authors: Mooney M. 
Published: January 2005

It is postulated that (A) the material is isotropic, (B) the volume change and hysteresis are negligible, and (C) the shear is proportional to the traction in simple shear in a plane previously deformed, if at all, only by uniform dilatation or contraction. It is deduced that the general strain-energy function, W, has the form W=G4 ∑ i=13(λi−1λi)2+H4 ∑ t=13(λi2−1λi2),where the λi's are the principal stretches (1+principal extension), G is the modulus of rigidity, and H is a new elastic constant not found in previous theories. The differences between the principal stresses are σi[minus]σi=λi∂ W/∂λi[minus]λi∂ W/∂λi.
Calculated forces agree closely with experimental data on soft rubber from 400 percent elongation to 50 percent compression.
The Solution of A.C. Circuit Problems
Authors: Pipes Louis A. 
Published: January 2005

Starting with the set of linear equations that determine the complex currents of a general n-mesh circuit, a method is presented for the numerical solution of the equations to determine the various mesh currents of the system.
The method presented has computational advantages over the conventional methods usually used in that only real numbers are involved in the various numerical operations and only the evaluation of second-order determinants is involved. The operations required are those of matrix multiplication and are most conveniently performed with a calculating machine. The paper is concluded by the solution of a general Y-Y circuit with a neutral return as an example of the method presented.
Fatigue of Fabrics
Authors: Busse W. F. , Lessig E. T. , Loughborough D. L. , Larrick L. 
Published: January 2005

The effect of temperature and time of application of load on the growth and the apparent ``tensile strength'' of fabrics was studied with a number of new tests. The results gave considerable information about the mechanism of failure of mechanical fabrics at low loads in service which could not be obtained with standard textile tests.
A ``fatigue'' test was developed which measured the lives of samples at elevated temperatures when subjected to a constant average load and a superimposed cyclic stress. The change in life with temperature on this test is enormously greater than the change of tensile strength with temperature. Over a considerable range the logarithm of the life under a given load is a linear function of the reciprocal of the absolute temperature, showing that the failure depends on a viscous or plastic flow within the fibers. Calculated activation energies for this flow process increase for different fibers in the order rayon, cotton, Nylon. The construction of the fabric affects the absolute life, but not the calculated activation energy. When creep is negligible, a loaded cord contracts when the temperature is raised, analogous to the Joule effect in rubber.
Large Scale Extraction of Polonium from Active Lead and Formation of Radioactive Electrode Alloys
Authors: Dillon J. H. , Street J. N. 
Published: January 2005

Various possible sources of Po for industrial use are discussed and reasons for selection of active lead salts for this purpose are given. Methods of measurement of the amounts of Po present on plated metal foils and in electrode alloy are described. The RaD/Pb ratio was found to vary from 1.2×10−8 to 1.9×10−8 for various samples of active lead from the Great Bear Lake region. Methods for extraction of Po from active lead salts are discussed and a large scale plating method is described. Results of experiments on the rate of Po-plating from boiling solutions of active lead salts as related to the acid concentration, exposed foil area, foil composition, etc., are presented. Chemical methods for producing soluble active lead salts are described.
A method of introducing Po into electrode alloy is described. In a typical experiment, it was found that 94 percent of the Po introduced into the melt was retained in the final alloy. Contact radiographs of electrode alloy samples showing the affect of various heat treatments and surface condition are presented.
The American Institute of Physics Building. I. Early History of the Building
Authors: Hutchisson Rose V. 
Published: January 2005

A HOME office for the American Institute of Physics, as well as a national headquarters for its member societies and for the physicists of America is no longer a dream but a definite accomplished fact. At a fraction of its former value, the Institute has obtained a building eminently suited to its needs. Because of the durable construction and fire-proof nature of the building, upkeep costs will be reasonably low. This fact together with the tax-free status of the Institute makes ``home-ownership'' decidedly a matter of good business.
The suitability of the building for the purposes of the Institute has been emphasized in the appeal for funds. The dignified entrance hall will make physicists proud of ``their building.'' The large member's room on the second floor will provide a place for physicists visiting New York to read, write, telephone, and meet people. In addition, this room will make an excellent board room and meeting place for small groups. The other rooms on the second, third, and fourth floors will provide adequate space for the Director, Publications Manager, and other officers of the Institute, and for the publications staff. Fortunately there is room for the expansion of the activities of the Institute which is sure to come in the near future.
Many of the interior photographs in this issue of the Journal show the furnishings of the building when used as a residence. Naturally when used as an office some of the elegance will be sacrificed for utility. The Institute will of necessity carry out gradually interior decorations adapted to its new use. Since the building has not been used for several years minor repairs and a thorough cleaning will be in order first of all. Although the present appearance of the building inside and out is not as bright as the pictures used here indicate the architectural details are in sound condition underneath the grime.
Dr. Barton has pointed out that the goal of $75,000 which must be raised if this building is to be owned by the Institute free-of-debt has not yet been reached. Physicists are asked to send in their contributions soon. Every physicist will want to own a small part of this building. It is to be hoped that everyone will make a contribution even if it must be small so that the Institute will know that physicists are unanimously back of its carefully formulated program for the future of organized physics in America. Great credit is due to the Governing Board and the War Policy Committee, but those close to the Institute know that were it not for the hard work and unbounded enthusiasm of the Director and the Publications Manager, a national headquarters for physicists would not have been possible for a long time to come.
So that physicists may become better acquainted with their new headquarters, a series of articles describing the building is planned. The first of these is concerned with its early history and follows below.—The Editor
Transformations in Organic Pigments
Authors: Hamm F. A. , Van Norman Earl 
Published: January 2005

Organic pigments are often recrystallized in various ways to effect purification and to control the particle size of the new crop of crystals. Copper phthalocyanine and indanthrene blue RS have been observed to yield crystals of varying shades, ranging from a light greenish blue to a dark reddish blue (purple). These shades have in the past been attributed only to differences in particle size because the elementary analyses strongly indicated that the samples were chemically identical. This investigation shows that both these pigments are polymorphic, and each can exist in at least two different physical forms. The shade differences, therefore, may be due to the differences in the light absorption exhibited by the structurally different polymorphic forms.
The polymorphic transformations can, for both pigments, be readily observed to take place in the electron microscope. The new form of both pigments, completely stable to the illuminating beam after the transformation, can be seen to grow from the vapor state at the expense of the original metastable solid material. The ``red'' shade of indanthrene blue RS and the ``hard'' powder of copper phthalocyanine have been labeled ``metastable'' because they transform in the electron microscope. The ``red'' shade of indanthrene blue RS can also be made to transform during its molecular distillation; the ``blue'' shade did not transform under any circumstances. The ``hard'' and ``soft'' powders of copper phthalocyanine can both be made to transform during their molecular distillations (not in the electron microscope) to give the same new form which is identical with the form that grew in the electron microscope at the expense of the original ``hard'' powder.
Electron diffraction patterns prove that the newly formed phases are structurally different from the original samples. Both these commercially important pigments are therefore at least dimorphic.
Homing and Navigational Courses of Automatic Target-Seeking Devices
Authors: Yuan Luke Chia-Liu 
Published: January 2005

A graphical and mathematical analysis of homing and navigational courses of automatic target-seeking devices is presented.
Homing courses for a seeker-to-target speed ratio of over two are likely to be impractical for target interception.
A method for obtaining a constant bearing course (navigational course) is developed. Some special cases of navigational courses have been studied graphically. It is shown that an optimum navigational ratio exists between that which leads to too slow an approach to the desired course and that which leads to instability.
Graphical analysis of navigational courses for straight as well as circular target motion is also given.
Dielectric Measurement Methods for Solids at Microwave Frequencies
Authors: Surber W. H. , Crouch G. E. 
Published: January 2005

An experimental method of measuring the dielectric constants of solids is described for the case of medium and high loss materials. The dielectric sample is enclosed within a section of wave guide terminated by a reflecting plane, and measurements are made of the standing wave ratio and position of the voltage minimum for both a short-circuit and an open-circuit termination. The equations for the dielectric properties of the substance may then be expressed in a relatively simple form in terms of elementary functions for media having tanδ ≥ 0.03.
In order to obtain reasonable accuracy for the determination of the loss factor of low loss materials using only standard wave-guide components, it was found to be necessary to adjust the operating conditions to obtain maximum power absorption by the dielectric sample. A frequency variation method of obtaining this maximum loss sensitivity is described, the apparatus being the same as that used for the medium and high loss materials.
A set of experimental values is given for the dielectric constants of a group of common plastics at 24,000 mega-cycles. A brief analysis of the effect of certain of the equipment losses is included.
The Plastic Flow of Thick-Walled Tubes with Large Strains
Authors: MacGregor C. W. , Coffin L. F. , Fisher J. C. 
Published: January 2005

The theory for the plastic flow of thick-walled tubes is discussed for a material having an arbitrary true stress-strain curve, loaded by any combination of internal pressure, external pressure, and end load, where the strains may become large necessitating the use of finite true strain definitions.
Comparisons are made of the finite strain theory, the infinitesimal strain theory, and experimental results for the special case of a closed end thick-walled tube of aluminum. The comparison shows that the infinitesimal strain theory is considerably in error even at moderate strain values. The finite strain theory appears to be satisfactory even for strains somewhat beyond the value for the local bulging of thick-walled tubes.
Calculation of the Temperature Development in a Contact Heated in the Contact Surface, and Application to the Problem of the Temperature Rise in a Sliding Contact
Authors: Holm Ragnar 
Published: January 2005

I. A circular area on a semi-infinite body is assumed to be heated at a constant rate from the time t=0 on. The development of the temperature in this area and in its surroundings is calculated with certain simplifications.
II. In a sliding contact the heat generated by friction is limited at every point to the time of contact. The temperature reached by the contact surface is calculated by aid of Part I and with assumptions about the size of the contact surface, which are based on earlier investigations of the author.
Observations on the temperatures in bimetallic sliding contacts, indicating the contact temperature rise by means of a thermoelectric current, are compared with calculations partly according to the deduced theory partly according to an earlier published theory by Jaeger. A fairly good agreement is found with one exception.
Observations on Arc Discharges at Low Pressures
Authors: Kofoid M. J. 
Published: January 2005

It has been observed in these laboratories (J. Slepian and E. J. Haverstick, Phys. Rev. 33, 52 (1929); J. Slepian, W. E. Berkey, and M. J. Kofoid, J. App. Phys. 13, 113 (1942)) that in a certain range of pressures, of the order of millimeters, short arcs burn with low apparent cathode current densities. The melting of the electrodes is then greatly reduced.
In this paper are described spectrographic tests to determine the presence of electrode material in the arc. It was found that as the gas pressure was increased, for an arc of given current and length, at a critical pressure the amount of cathode metal in the arc, as indicated by spectral line density, suddenly increased. Presumably, boiling of the cathode metal took place at this pressure. This critical pressure was found to increase as the arc length was reduced.
In this range where melting of the cathode occurred, it was found that the molten spot was at the center of the cathode for magnetic cathode material but at the edge of the cathode for non-magnetic material.