bluuebunny/crossref_metadata_2025 huggingface dataset:
New Formulas for Calculating Short-Circuit Stresses in Bus Supports for Rectangular Tubular Conductors
Authors: Higgins Thomas James
Published: January 2005

New and simple formulas are derived for calculating short-circuit stress in bus supports for rectangular tubular conductors. A numerical example illustrates their use and advantages.
Electrostatic Electron Microscopy. III
Authors: Bachman C. H. , Ramo Simon
Published: January 2005

This article, the final one of a series on the design of electrostatic electron microscopes, contains a description of an instrument which illustrates the principles previously discussed. The microscope described is believed to be the first constructed with the object of providing the greatest of simplicity in construction, operation, and maintenance with the design parameters balanced to give a particular range of resolving power. The range chosen is about ten times the light microscope. The instrument is permanently aligned and utilizes external photography. The over-all size and weight of the instrument, as well as the number and complexity of components, are materially less than previously described instruments.
Transient Analysis of Linear Systems
Authors: Osborne M. F. M.
Published: January 2005

A method is suggested for determining either the indicial admittance of a linear system, when the response to a known transient is observed, or the shape of the transient, when the admittance is known. A method is also outlined for obtaining the impedance operators, and in particular the impedance coefficients (stiffness, resistance, and inertia). Corrections due to the reaction of the instrument used in measuring the response of the system, or of a restraint to insure stability of the system, can be taken into account when appreciable. Suggested applications are to acoustical and aerodynamical problems.
Formulas for the Geometric Mean Distances of Rectangular Areas and of Line Segments
Authors: Higgins Thomas James
Published: January 2005

Formulas are derived, by direct integration of the defining definite integrals, for the general geometric mean distance between (i) a point and a line segment; (ii) a point and a rectangular area; (iii) two parallel line segments; (iv) two orthogonal line segments; (v) a line segment and a parallel-sided rectangular area; (vi) two parallel-sided rectangular areas. Certain useful identities of the formula for the last-named case are presented.
Flow and Recovery Properties of Viscose Rayon Yarn
Authors: Press Jack J.
Published: January 2005

A series of flow and recovery tests are used as a basis for describing and interpreting the elastic, viscous, and tensile properties of a typical solid linear high polymer. Extensions of viscose rayon at 70°F and 65 percent R.H. are given under loads of 0.1 to 1.0 grams per denier (1900 to 19,000 lb. per sq. inch) for times up to 106 seconds. Recoveries at 70°F are given for times up to 106 seconds at 65 percent R.H. and also after wetting and reconditioning to remove internal strains. The data are interpreted in terms of changes in modulus, viscosity, restoring forces, viscous flow, crystallization, and internal load distribution.
The Fundamental Problem of the Theory of Viscous Fluids
Authors: Putman Henri
Published: January 2005

A theorem is proved, giving the value of d(▿·v̄)/dt for viscous fluids. With the known value of dw̄/dt, it gives a theoretical method of studying the fundamental problem of viscous fluids.
The Viscosity of Dilute Solutions of Long-Chain Molecules. V. Dependence on the Solvent
Authors: Huggins Maurice L.
Published: January 2005

Staudinger's relation between ηsp/c and the molecular weight of a chain molecule solute should theoretically apply only if the chain molecules are kinked in a purely random way. With actual solutions, one would expect the kinked chains to be more or less tightly coiled than for purely random kinking, depending on whether the average cohesive energy density between like units (solvent molecules and solute submolecules) is greater or less than that between unlike units. The tighter the coiling, the less is the specific viscosity, for a given solute molecule chain length. This cohesive energy density difference is closely related to μ1, the constant, characteristic of a given solute-solvent system, which enters into the equations recently derived by the author for the activities of the components and for related quantities, such as osmotic pressures, solubilities, and precipitabilities. From this relationship, it has been shown that the ηsp/c values for solutions of a given polymer in different solvents should, in general, be symbatic with the proportion of a poor solvent which is required to produce precipitation of a solid phase. Data from the literature on polystyrene and polybutene solutions are in agreement with this conclusion.
Frictional Phenomena. XIV
Authors: Gemant Andrew
Published: January 2005

IN this chapter technical applications of the solid friction concept in four different fields are discussed. These are: (1) mechanical engineering, (a) damping of unwanted vibrations in machinery—for instance, crank-shaft vibrations, (b) vibrations excited by internal friction—for instance, whirl of rotating shafts; (2) metallurgy in which damping measurement promises to be a useful new tool; (3) rubber technology, as applied to automobile tires with regard to the heat generated therein; and (4) electrical engineering, specifically dielectric losses in electrical insulating materials.
On Torsion Combined with Compression
Authors: Bridgman P. W.
Published: January 2005

If a rod is twisted while subjected to longitudinal compression it will support without fracture angles of twist many-fold greater and maximum torques somewhat greater than is possible in the absence of load. Under compressional load the curve of shearing stress against shearing strain rises to a maximum and then sinks with a long drawn out tail to an approximate asymptote. Fracture is never complete, but some coherence always remains, probably due to cold welding. The maximum torque is not marked by any visible beginning of fracturing or other discontinuity. The strain hardening curve in torsion, therefore, under proper circumstances passes through a maximum. The whole mechanism of strain hardening appears to be different in torsion and in tension, and reasons are given for anticipating such a difference because of the difference of the atomic kinetics in torsion and tension. It is shown in particular that the method of correlating tension and torsion through the ``octahedral'' coordinates which is applicable for small strains is not applicable to the large strains which are the subject of the present discussion. It is shown that the equations of conventional plasticity theory correctly reproduce certain qualitative aspects of the secondary longitudinal and radial flow which accompany twisting, but it is possible to establish large failures of isotropy not covered by the elementary theory. With regard to fracture, it is necessary to distinguish sharply between fracture in tension and in shear. The latter is not clean cut and it is probably possible to realize a continuous gradation of atomic disorganizations, culminating under proper conditions in complete shearing fracture.
Studies on the Structure of Thin Metallic Films by Means of the Electron Microscope
Authors: Picard Robert G. , Duffendack O. S.
Published: January 2005

A study was made of thin films of aluminum, cadmium, copper, gold, magnesium, and zinc using an RCA electron microscope capable of 30A resolving power. The films were formed by evaporation and condensation on collodion substrates in vacuum. An evaporating chamber was devised that permitted control of the temperature of the condensing surface. Photographs of the surfaces show that all the films are made of agglomerates of the metals separated by interstices of various widths. All evidence leads to the conclusion that the surface structure is explainable by assuming migration of the atoms over the surface. The observed structure can be used to explain the electrical conductivity, the optical reflectivity, and adsorptivity of thin films. Electron microscopic studies also provide a ready means of classifying surfaces according to the mobility of the atoms comprising them, and thus enable a rough estimate of the potential distribution over the surface to be made.
A Note on the Mutual Impedance of Antennas
Authors: Harrison Charles W.
Published: January 2005

An expression is derived for the mutual impedance of a symmetrical center-driven antenna in proximity to an untuned parasitic element, when the wires are parallel, and are not displaced in length. An integral, frequently occurring in antenna problems, is evaluated graphically over the range required in the present analysis.
Interpretation of Electron Micrographs of Silica Surface Replicas
Authors: Heidenreich Robert D.
Published: January 2005

Experiments are described for investigating the interpretation of polystyrene-silica surface replicas. It is demonstrated on a polished and etched stainless steel 18–8 specimen that the light microscope and electron microscope pictures are strikingly similar with corresponding regions easily recognized. The great value of stereo-pictures in determining relative surface elevations is demonstrated with a comparison of the topography as shown by the light microscope using oblique illumination. The question of resolution is discussed and a method of quantitatively determining the practical limiting resolution of replicas is described. A shape limitation factor, α, is defined and evaluated for both silica and Formvar replicas. With α = 1 being perfect reproduction, the values obtained were α∼1.3 for silica and α∼3.8 for Formvar. The value α∼3.8 is valid only for the surface employed in its determination while the value of α∼1.3 is realized on any surface to which the polystyrene-silica method can be applied.
Time Lag of Impulse Breakdown at High Pressures
Authors: Cobine J. D. , Easton E. C.
Published: January 2005

Experiments were conducted to determine the variation of time lag of spark breakdown as a function of gas pressure. All tests were made in pre-purified nitrogen using 1.250-inch diameter spheres of copper, aluminum and nickel with a gap spacing of 0.0125 inch. The voltage applied to the gap was in the form of a surge which reached its maximum value in one quarter of a microsecond and which decayed slowly to 97 percent of its maximum value in 5000 microseconds. Most of the recorded lags lay in the range from 5 to 5000 microseconds. The maximum value of the applied voltage was varied from 14 to 128 percent above the static breakdown value, while the gas pressure was varied from 7 to 100 pounds per square inch absolute. The most probable time lag was found to vary greatly with pressure, changing rather abruptly from a large value (10−2 sec.) to a small value (10−5−10−6 sec.) at certain critical conditions of pressure and overvoltage. The change appears to occur under conditions at which the ions normally present in the gas begin to produce free electrons by negative-ion disintegration, or by positive-ion bombardment of the cathode. The distribution of time lags was found to vary with cathode material and condition of cathode surface. The nickel spheres quickly developed a heavy coating when sparked in nitrogen. The copper and aluminum spheres became only slightly discolored. The time lag distribution curves for copper and aluminum were of the same type, but different from that for nickel. The observations suggest methods for speeding the action of spark plugs and protective gaps, as well as for increasing the reliability of gas-insulated apparatus. Apparatus operated below the critical conditions can withstand surges which on the average are one thousand times as long as those which would cause the apparatus to fail when operated in the short time lag region. Similarly, a protective gap or spark plug which is to operate on very short surges can be made to break down more consistently by operating at an overvoltage and a gas pressure in the short time lag region.
Some Applications of the High Resolving Power of the Electron Microscope
Authors: Green Henry , Fullam Ernest F.
Published: January 2005

The high resolving power attained with the electron microscope has extended the field of pigment microscopy to cover particles falling within the range of 0.20–0.004 micron. High resolving power also brings into view many particles that would otherwise be invisible, and shows definite shape in particles that with optical instruments appear simply as diffraction disks.
Surge-Generator Circuits
Authors: Fisher Edward
Published: January 2005

Formulas are developed for the free periods and damping factors of high voltage surge-generator circuits in discharge that contain a large number of meshes. The approximations used are based on an actual case, a generator in the High Voltage Laboratory of the National Bureau of Standards.
Breakdown of Thixotropic Structure as Function of Time
Authors: Weltmann Ruth N.
Published: January 2005

Measurements of the thixotropic breakdown of structure with time of agitation were performed at different rates of shear on a number of pigment suspensions and on various oils in a rotational viscometer. The product of rate of breakdown in thixotropic structure and time of agitation at any rate of shear was found to be a constant for each material. It is called ``the time coefficient of thixotropic breakdown'' and is independent of the rate of shear, which is applied to agitate the sample. The time coefficient of thixotropic breakdown is measured in absolute units, having the dimensions of viscosity (dynes sec./cm2). The equilibrium time—the time necessary to break the thixotropic structure down to its minimum at a specified rate of shear—was also found to be independent of the rate of shear applied while agitating.
Concerning the Roots of Jn′(x)Nn′(kx)−Jn′(kx)Nn′(x)=0
Authors: Truell Rohn
Published: January 2005

The relation Jn′(x)Nn′(kx)−Jn′(kx)Nn′(x)=0 arises in certain resonant cavity problems having cylindrical symmetry. The first roots of this relation are presented here as a function of k for n = 1, 2, 3, 4. The M'Mahon relation does not allow calculation of the first roots despite statements to the contrary in several places. It is shown that the functions Jn′(x)/Nn′(x) have relative maxima at x = n except for n = 0.
Electrical Circuit Analysis of Torsional Oscillations
Authors: Pipes Louis A.
Published: January 2005

The equivalence between the torsional oscillations of a general dynamical system and those of a certain electrical circuit is considered. This equivalence makes it possible to compute the behavior of the dynamical system by making use of some well-known results of electrical circuit theory. It also makes it possible to determine the critical speeds and the response of the mechanical system by simple electrical measurements of the equivalent system. The forced oscillations of a damped multi-disk system and those of continuous shafts are studied. The results may be applied by a mere change in notation to the analysis of the longitudinal oscillations of linear spring and mass systems as well as to that of the longitudinal oscillations of prismatic bars.
The Vibration Characteristics of ``Free-Free'' Circularly Curved Bars
Authors: Pliskin W. A. , Edwards J. E. , Bundy F. P.
Published: January 2005

The positions of the nodal points and the values of the frequencies of vibration have been determined for the first five or six modes of parallel and transverse vibration of circularly curved bars of uniform cross section with central angles ranging from 356° to 60°. For vibration in the plane of curvature (parallel) the relative positions of the nodal points are the same for the same central angles, regardless of the type of cross section. Also, for the parallel vibration the frequency in the nth mode is given by the expression, fn=θ2K(n,θ)L2(Bm)12,where θ is the half central angle in radians, L is the length, B is the bending stiffness of the cross section about an axis perpendicular to the plane of the ring, m is the mass per unit length, and K is a ``frequency constant'' which depends upon n and θ. For n>1 or 2, K may be expressed accurately as, K(n,θ)=S2(θ)[n−g(θ)]2K(1,θ). Graphs of S(θ), g(θ), and K(1, θ) are presented. For vibrations transverse to the plane of curvature the relative positions of the nodal points depend only upon the central angle. The frequency in the nth mode of transverse vibration is given by the expression, fn=θ2ψ(n,θ,A/C)L2(Am)12,where θ, L, and m are the same as defined above, A is the bending stiffness of the cross section about an axis in the radial direction, and ψ is a ``frequency constant'' which depends upon n, θ, and the A/C ratio. For n>2, ψ may be expressed quite accurately as, ψ(n,θ,A/C)=Q2(θ,A/C)[n−q(θ,A/C)]2ψ(1,θ,A/C). Graphs of Q(θ, A/C), q(θ, A/C), and ψ(1, θ, A/C) are presented.
A Spectrophotometric Method for the Analysis of Multicomponent Mixtures and Its Infra-Red Application
Authors: Brattain R. Robert , Rasmussen R. S. , Cravath A. M.
Published: January 2005

A general method has been developed for spectrophotometric analysis of multicomponent mixtures. The method is based on the assumption that the optical density of a mixture equals the sum of the optical densities of the components, although the transmissions of the individual components may not follow Beer's law. The application of the method to infra-red absorption of vapor samples is described in detail. The results of tests using a six-component C4 hydrocarbon mixture are given. The method is especially useful for the rapid routine analysis of large numbers of samples containing the same components, and therefore is well suited for plant control purposes.
Radiosulfur Tracer Study of Sulfurized Lubrication Addition Agents
Authors: Clark George L. , Gallo S. George , Lincoln Bert H.
Published: January 2005

Radioactive tracer techniques have been used to ascertain the concentration of sulfurized addition agent in lubricating oil blends on metallic surfaces, the active element being radiosulfur prepared with the cyclotron and introduced into the olefin molecules. Film formation seems to be quite general, having been tested on seven different types of commercial metallic bearings as well as on glass. The film is transparent and very thin. In the extreme cases, it imparts a faint opalescence to the bright surface. The organic molecules may form a loose molecular compound with the metal or a polymerized film, sufficiently adherent, however, to resist the solvent action of benzene and carbon disulfide. The rate of film formation has been established at 88°C (190°F) and at room temperature for a typical bearing composition. It has been found that the rate though several times slower than at 88°C at room temperature is still quite appreciable and favorable from the standpoint of engine protection. The mechanism of oxidation inhibition and thus retardation of corrosion and sludging with this addition agent seems to embrace both alteration of surface character of catalyzing metals and bulk or liquid phase inhibition in the oil. The adherent organic film is probably involved in ``oiliness'' (film strengthening and prevention of complete oil drainage from motor bearings and walls by anchoring through polar molecules) since engine tests have shown that the oiliness of straight mineral oil is appreciably improved by addition of sulfurized olefins.
Distribution of Light Intensity within a Scattering Medium
Authors: Newton Robert R.
Published: January 2005

An integral-differential equation is developed which gives the intensity within a scattering medium as a function of position and direction. The scattering properties of an infinitesimal volume of the medium are assumed known, but no special assumption is made concerning their nature. The equation is put in a form suitable for numerical solution.
Applications of the Operational Calculus to the Theory of Structures
Authors: Pipes Louis A.
Published: January 2005

The differential equations governing the deflection of structural elements such as loaded cords and beams freely suspended or resting on an elastic foundation are solved operationally. The operational method simplifies the analysis because it reduces the number of arbitrary constants to be determined and enables the effect of concentrated loads or applied couples to be determined directly.
Radioactive Mercury in Mercury-Vapor Measurements
Authors: Irvine John W. , Goodman Clark
Published: January 2005

Radioactive mercury, Hg197, was prepared by deuteron bombardment of gold. This isotope was used as a tracer to establish an average concentration of 0.01 mg Hg per m3 of air in a particular industrial operation suspected of causing chronic mercurialism. Mercury in quantities of 10−8 g was detected, and the method offers possibilities of higher sensitivity and more general application.
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.
Drag Coefficients of Steel Spheres Entering Water Vertically
Authors: May Albert , Woodhull Jean C.
Published: January 2005

Drag coefficients have been determined from high speed motion pictures for ¼-inch to 1½-inch steel spheres shot into water vertically with speeds from 25 to 208 ft./sec. These drag coefficients correspond to the entrance cavity phase and to the v-squared-law drag forces only, the immediate effects on the spheres of other forces being eliminated in the calculations. It is found that CD is a function of both the Reynolds and Froude Numbers. Within the range investigated, the dependence may be expressed by CD=0.0174 ln(RF½).
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 Dissipation of Heat by Free Convection from Vertical and Horizontal Cylinders
Authors: Elenbaas W.
Published: January 2005

This paper gives a simpler deduction of formulas given previously [W. Elenbaas, Physica 9, 285, 665, (1942)] for the dissipation of heat of horizontal and vertical cylinders with natural cooling.
On the Theory of Biconical Antennas
Authors: Tai C. T.
Published: January 2005

The investigation contained in this paper gives a general treatment of the theory of biconical antennas based upon Smith's formulation of the problem. For the case of small-angle cones, an expression of the effective load admittance is obtained which is the same one that Schelkunoff derived based upon two rather ingenious methods, both of which, however, are not as rigorous as the present one. As an illustration of another application of the analysis, a treatment is given of the characteristics of biconical antennas where the space between the cones is filled with a dielectric other than air.
Measurement by Radioactive Tracers of Diffusion in Liquids
Authors: Gemant Andrew
Published: January 2005

A method, using a radioactive tracer technique, for the measurement of diffusion coefficients in liquids is described. Results for uranyl nitrate solutions, revealing the diffusion of Th-234, in water and dioxane are presented.
Physical Limitations of Omni-Directional Antennas
Authors: Chu L. J.
Published: January 2005

The physical limitations of omni-directional antennas are considered. With the use of the spherical wave functions to describe the field, the directivity gain G and the Q of an unspecified antenna are calculated under idealized conditions. To obtain the optimum performance, three criteria are used, (1) maximum gain for a given complexity of the antenna structure, (2) minimum Q, (3) maximum ratio of G/Q. It is found that an antenna of which the maximum dimension is 2a has the potentiality of a broad band width provided that the gain is equal to or less than 4a/λ. To obtain a gain higher than this value, the Q of the antenna increases at an astronomical rate. The antenna which has potentially the broadest band width of all omni-directional antennas is one which has a radiation pattern corresponding to that of an infinitesimally small dipole.
A Microflash Unit for Ballistic Photography
Authors: McCormick W. W. , Madansky L. , Fairbanks A. F.
Published: January 2005

A flash unit has been developed for photographing large projectiles in flight. The light source combines high intensity with short duration. Details of the geometry and processing of the lamp are given, together with a discussion of the methods of measuring intensity and duration. Several of the units described have been in use at the Aberdeen Proving Ground and some photographs taken there are reproduced.
Possible Fluctuations in Electron Streams Due to Ions
Authors: Pierce J. R.
Published: January 2005

The equations for low amplitude space-charge waves in an electron stream containing heavy positive ions are considered. At frequencies a little below the ion plasma frequency there should be a wave which increases in amplitude as it travels (negative attenuation). Ion motion tends to limit the rate of increase. In a beam filling a conducting cylinder and confined by a uniform magnetic field there should be an increasing wave at frequencies near the ion cyclotron frequency. Such waves might explain observed fluctuations in long electron beams.
Application of the Laplace Transform in the Solution of Linear Integral Equations
Authors: Robinson Lawrence Baylor
Published: January 2005

Integral equations are defined and references are given to the Laplace transform technique. Most of the operations used are illustrated through a solution of Abel's integral equation. It is shown that the Liouville-Neumann series follows logically from an operational solution of Volterra's integral of the second kind. Whittaker obtained solutions to the integral equation with the kernel expressed in the last three forms. His procedure was quite involved and it is shown here that the same solutions are obtained more directly through the operational calculus based on the Laplace transform.
Response of Linear Resonant Systems to Excitation of a Frequency Varying Linearly with Time
Authors: Hok Gunnar
Published: January 2005

A general solution of this problem is obtained by means of Laplacian transforms. The resulting complex function is evaluated numerically, and universal response curves are presented in order to facilitate the application of the solution to simple or complicated electrical networks as well as to other resonant systems represented by equivalent networks.
On Creep and Relaxation. II.
Authors: Gross B.
Published: January 2005

A phenomenological theory of the elastic aftereffect can be formulated with the aid of the principle of superposition. In a previous paper the theory of the transient effects, caused by the sudden application of a constant load or a constant deformation, has been developed. In the present paper the theory of the steady-state behavior under alternating load and deformation is given. Relations are established between the loss factor, the storage factor, the distribution functions, and the Laplace transforms of the creep—and the relaxation—function.
Dark-Field Electron Microscopy: II. Studies of colloidal carbon
Authors: Hall C. E.
Published: January 2005

Several commercial carbon blacks were examined with dark-field illumination in the electron microscope. Anomalous intensities in the dark-field images are interpreted as resulting from coherent scattering by parallel layer groups of graphitic planes, which were previously identified by Biscoe and Warren using x-ray diffraction. The dark-field micrographs indicate that in a nonreinforcing and a semireinforcing black, the parallel layer groups near the surface of the roughly spherical particles are oriented with their representative vector approximately normal to the surface. No definite evidence was obtainable for such an arrangement in a reinforcing channel black with average particle diameter about 300A. After prolonged heat treatment to the point where graphitization occurs the channel black exhibits numerous diffraction images in darkfield, indicating the presence of crystals with dimensions in the range 20 to 90A.
Mass Emissivity of Powder Gases in Solid Fuel Rockets
Authors: Penner S. S.
Published: January 2005

An analysis has been carried out to determine an upper limit for the effective mass emissivity of the radiating gases in a solid fuel rocket motor. The calculations depend upon a comparison between experimentally observed performance data relating to a rocket motor and theoretical results based on a theory for the effect of radiation on the performance of solid fuel rocket motors. A simplified treatment is developed for correlating the rate of burning of the powder with the temperature rise of a powder grain caused by the absorption of radiant energy.
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.
Gyrograms for Simple Harmonic Systems Subjected to External Forces
Authors: Rojansky V.
Published: January 2005

A graphical method is described for the approximate integration of equations of the form md2x/dt2+kx=f(t), which arise in several branches of physics and engineering. The graphs, named ``gyrograms,'' are an extension of the familiar ``reference circle'' used in representing simple harmonic motion. The method is applicable whenever f(t) can be adequately approximated by a step function having a few steps.
Large Plastic Flow and the Collapse of Hollow Cylinders
Authors: Bridgman P. W.
Published: January 2005

The collapse of heavy steel cylinders under external pressures running up to 412,000 p.s.i. was studied during the war under contract with the Watertown Arsenal. The distortions are so large that the conventional small strain analysis is not adequate. The presence of large strains is recognized in the analysis by writing the stress equations of equilibrium in terms of the final displaced positions of the particles instead of in terms of the initial positions. The conventional assumption of negligible volume change is retained. Attention is called to a purely geometrical condition on the strains. In the experiments the cylinders showed no change of length. The generality of the conditions under which this may be expected is examined. A linear relation was found experimentally between collapsing pressure and log (rext/rint). Furthermore, P/log(rext/rint) is not constant but rises continually with increasing collapsing pressure. These results indicate that the strain hardening increases continually with increasing distortion, but at a rate two- or threefold less than would be given by experiments in simple tension. The collapse was pushed experimentally to such extremes that the geometrical symmetry was lost because of the grain structure. This limits the region of applicability of any simple theory.
Self-Excited Mechanical Oscillations
Authors: Minorsky N.
Published: January 2005

This paper deals with a phenomenon of self-excitation observed in an electromechanical system. It is shown that this phenomenon is expressible in terms of a difference-differential equation, having a frequency spectrum that depends on a parameter. The linear theory fails to give an answer to the question of stability of oscillations. It is necessary for this purpose to make use of the equations of the first approximation of the non-linear theory. Expressions for a stable stationary amplitude and frequency obtained on that basis show an agreement with the observed features of these self-excited oscillations.
Surface Waves from an Underwater Explosion
Authors: Kirkwood J. G. , Seeger R. J.
Published: January 2005

A general expression has been derived theoretically for the pressure due to surface waves produced by an underwater explosion. The integrals involved have been evaluated in terms of dimensionless variables over a range of practical interest. A specific formula is given for the pressure on the bottom of the water due to the first pulsation of the gas globe from a TNT explosion originating also on the bottom.
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.
Measurement of Carbon Black Particles by the Electron Microscope and Low Temperature Nitrogen Adsorption Isotherms
Authors: Anderson R. B. , Emmett P. H.
Published: January 2005

Electron micrographs and nitrogen adsorption isotherms have been compared on six commercial carbon blacks as methods for obtaining particle size and surface area values of finely divided materials. Good agreement between the two procedures was obtained for four of the backs: Grade 6, P 33, acetylene black, and lampblack. For two blacks known to be porous, Mogul and after-treated lampblack, the areas, as measured by the nitrogen isotherms, were 5 to 7 times as large as one would calculate from the electron microscope results.
The Visco-Elastic Behavior of a Highly Plasticized Nitrocellulose in Compression under Constant Load
Authors: Doyle George J. , Badger Richard M.
Published: January 2005

The behavior of a highly plasticized nitrocellulose in compression under constant load has been investigated over a rather wide range of load and temperature. The load dependence appears to require the assumption of non-Newtonian viscosity. Though the observations are not quantitatively accounted for by the Tobolsky-Eyring model, the load and temperature dependence of the rate of compression appear to have some relation to the predictions of these authors.
An Oxide Replica Technique for the Electron Microscope Examination of Stainless Steel and High Nickel Alloys
Authors: Mahla E. M. , Nielsen N. A.
Published: January 2005

An oxide replica method has been developed which is suitable for the electron microscope examination of the surfaces of stainless steel, nickel, and high nickel alloys. The oxide film is produced on the metal surface by oxidation in a molten nitrate solution and is chemically stripped from the base metal by a bromine-methanol solution. Replicas of this type have been used to study deep-etched structures, preferential etch attack, and secondary phases in austenitic and ferritic stainless steel and in nickel.
Preferred Orientation Determination Using a Geiger Counter X-Ray Diffraction Goniometer
Authors: Decker B. F. , Asp E. T. , Harker D.
Published: January 2005

A simple and accurate method of determining pole figures by using a special sample mount with a Geiger counter x-ray diffraction goniometer is described and examples given. Also, a correction formula is derived which takes into account absorption change and change in diffracting volume as the sample changes position with respect to the x-ray beam.
Effect of Radiation on the Rate of Burning of Solid Fuel Rocket Propellants
Authors: Penner S. S.
Published: January 2005

The temperature rise of powder grains in different rocket motors, resulting from the absorption of radiant energy, has been computed by the method of Avery. The calculated results show that more radiant energy is absorbed by the powder grains in large service rockets than in small experimental test motors. The increase in powder temperature before burning, associated with the absorption of radiant energy, leads to an increase in the average rate of burning of the solid fuel charge. The differences in burning rate produced by the absorption of radiant energy amount to less than four percent for the rocket motors commonly employed. Thus burning rate results obtained in small test motors may be applied to predict the approximate behavior of the same propellant in a large service rocket.
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.
The Stresses in a Plate Containing an Overlapped Circular Hole
Authors: Ling Chih-Bing
Published: January 2005

This paper deals with the stresses in a plate containing a hole whose rim is composed of two equal circular arcs. The stress function concerned is constructed by means of an even integral solution of biharmonic equation expressed in bipolar coordinates. The parameters involved in the solution are determined from the given boundary conditions with the aid of Fourier transforms. Three fundamental stress systems are discussed. Expressions of the stress along the rim of hole are derived and, in particular, values of the maximum stress are calculated. The results are then plotted in conjunction with those of a plate containing two equal circular holes, which are obtained by the present author in a previous paper. It may be interesting to compare the the methods used in both solutions.
Minimum Detectable Absorption in Microwave Spectroscopy and an Analysis of the Stark Modulation Method
Authors: Hershberger W. D.
Published: January 2005

It is shown that the minimum detectable absorption coefficient for an isolated spectral line as measured in a matched wave guide of optimum length is [4kTNΔf/(P0/e)]αc,where N is the noise factor and Δf the band width of the receiver, αc is the attenuation constant for the wave guide, and P0/e is the average microwave power available at the receiver. The equivalence between cavity and wave guide methods is developed. The Stark modulation method of Hughes and Wilson is analyzed, assuming a quadratic Stark effect, and expressions are developed for the modulation factor of a microwave at twice and four times the frequency of the Stark field. For a matched guide the modulation factor is αgl/4. Also the shift in line position is calculated, and finally, the directions in which improvement in sensitivity may be expected are indicated.
Infrared spectroscopy of acetone-methanol liquid mixtures: Hydrogen bond network
Authors: Max Jean-Joseph , Chapados Camille
Published: January 2005

Acetone and methanol mixtures covering the whole solubility range are studied by Fourier transform infrared attenuated total reflectance spectroscopy. The strong bathochromic shifts observed on methanol OH and acetone CO stretch IR bands are related to hydrogen bonds between these groups. Factor analysis separates the spectra into four acetone and four methanol principal factors. A random molecular model developed for the acetone-water system [Max and Chapados, J. Chem. Phys. 119, 5632 (2003); 120, 6625 (2004)] was modified for the acetone-methanol system. This model, which takes into account H bonds accepted by methanol and acetone, is made up of 12 methanol and 11 acetone species. The 23 species abundances are regrouped according to evolving patterns or spectral similarities to compare them to the eight experimental factors. Methanol acetone mixtures are almost but not exactly random: the methanol oxygen atoms have stronger capacities than acetone to accept H bonds from methanol in the proportion 1.5 to 1. Since oxygen atoms are in excess, all labile hydrogen atoms will form H bonds. As acetone is added to methanol, its OH stretch band blueshifts as the number of accepted H bonds decreases. When methanol gives one H bond and accepts one, an H-bonding network is formed that was coined “chained organization.” However, the acetone molecules do not sequester any methanol molecules by breaking or increasing the H-bond methanol network. Similarly, the methanol molecules do not sequester any acetone molecules. Consequently no acetone-methanol complex is formed in the mixtures. Gaussian simulation of the four principal factors in the methanol OH stretch region gave three distinct absorption regimes consisting of the OH stretch bands and their satellites that are identified as MeOH1, MeOH2, and MeOH3 (subscript indicates the number of H, covalent and H bond, which surround the oxygen). These regimes are related to those identified in the water-acetone system as OH2, OH3, and OH4.
High-level ab initio studies of unimolecular dissociation of the ground-state N3 radical
Authors: Zhang Peng , Morokuma Keiji , Wodtke Alec M.
Published: January 2005

A comprehensive study of the unimolecular dissociation of the N3 radical on the ground doublet and excited quartet potential energy surfaces has been carried out with multireference single and double excitation configuration interaction and second-order multireference perturbation methods. Two forms of the N3 radical have been located in the linear and cyclic region of the lowest doublet potential energy surface with an isomerization barrier of 62.2 kcal/mol above the linear N3. Three equivalent C2v minima of cyclic N3 are connected by low barrier, meaning the molecule is free to undergo pseudorotation. The cyclic N3 is metastable with respect to ground state products, N(4S)+N2, and dissociation must occur via intersystem crossing to a quartet potential energy surface. Minima on the seams of crossing between the doublet and quartet potential surfaces are found to lie substantially higher in energy than the cyclic N3 minima. This strongly suggests that cyclic N3 possesses a long collision-free lifetime even if formed with substantial internal excitation.
Correlated photon pairs from single (In,Ga)As∕GaAs quantum dots in pillar microcavities
Authors: Benyoucef M. , Ulrich S. M. , Michler P. , Wiersig J. , Jahnke F. , Forchel A.
Published: January 2005

We demonstrate the triggered generation of photon pairs by the cascaded biexciton-exciton emission from a single (In,Ga)As∕GaAs quantum dot (QD) in a pillar microcavity. Photon cross-correlation measurements between the biexciton and exciton decay reveal highly asymmetric features under continuous wave excitation and a bunching effect under pulsed excitation due to the cascaded nature of the process. An enhancement of the QD photoluminescence (PL) intensity by a factor of 40 was found for pillar microcavities (0.6μm diameter) compared to the excitonic PL intensity in bulk semiconductors, thus reflecting the enhanced photon collection effect out of the cavity structure. The observed pillar mode structure is well understood on the basis of an extended transfer-matrix method.