bluuebunny/crossref_metadata_2025 huggingface dataset:
The Detection of Weak Signals by Correlation Methods
Authors: Rudnick Philip
Published: April 2005

A procedure involving autocorrelation is described which, for long averaging time and incoming signals with continuous spectrum, has a detection threshold equal to that of a corresponding conventional system consisting of band pass filter, rectifier, and low pass filter. The autocorrelation procedure is quite complex; a full autocorrelation function is computed and then subjected to a ``filtering'' operation. A simpler procedure, such as computing autocorrelation coefficients for only one or a few delay times, will in general be less effective. A third process, involving multiplication by a local sinusoidal signal, is also discussed and shown to be closely parallel to the conventional system.
The Nature of the Coefficient of Friction
Authors: Burwell J. T. , Rabinowicz E.
Published: April 2005

The modern theory of the friction between dry metal surfaces ascribes it to local minute welds or adhesions between the surfaces and suggests that for a given pair of surfaces the friction force is uniquely defined by the normal load alone. Herein it is demonstrated that this cannot in general be true and that some further condition of operation must also be defined. Experiments are reported indicating that one such possible condition is the sliding speed so that the friction force is actually a function of the normal load and the sliding speed. It is pointed out that the speed can influence the friction force in two ways—one, by the resulting shear strain rate in the vicinity of the welded junction, and the other by the length of time taken for a junction of full strength to form.
Hall Effect Modulators and ``Gyrators'' Employing Magnetic Field Independent Orientations in Germanium
Authors: Mason W. P. , Hewitt W. H. , Wick R. F.
Published: April 2005

Three uses for the Hall effect in germanium crystals are described. These are (1) use of Hall effect probes in measuring magnetic flux, (2) use of Hall effect in crystals to produce a pure product modulator, and (3) use of Hall effect in germanium crystals to produce a nonreciprocal transmission. If the resistances are shunted around such gyrators, the transmission can be made zero in one direction and finite in the other. In all these applications, use is made of a crystal orientation for which the cross magneto-resistance effects are zero and the Hall effect constant does not vary with field by more than 2 percent out to a flux density of 20 000 gausses. This orientation was located by making a phenomenological study of the magneto-resistance and Hall effect corrections for a cubic crystal and evaluating constants experimentally. Correction terms to fourth and fifth powers of the magnetic field have been obtained.
Analog Computer Elements for Solving Nonlinear Differential Equations
Authors: Ludeke Carl A. , Morrison Cohn L.
Published: April 2005

The authors present the design and construction of an analog computer unit which is particularly well adapted for solving nonlinear differential equations. The units are readily combined to solve simultaneous nonlinear differential equations. The unit is carefully checked by using it to solve some nonlinear differential equations for which known solutions exist. Finally the unit is used to find the solution to some nonlinear differential equations whose solutions are not given in the literature.
The Detection of a Sine Wave in Gaussian Noise
Authors: Reich Edgar , Swerling Peter
Published: April 2005

This paper deals with the problem of finding the ``optimum'' method of detecting a sine wave of known frequency and amplitude in the presence of noise. The type of noise considered is the so-called Gaussian process, which is obtained when thermal noise is passed through an arbitrary linear passive device.

The analysis takes into account the fact that in practice only a finite sample of observed signal is available.

The optimum detection method is defined as that which maximizes the probability of recognizing the presence of a sine wave if one has actually appeared; while the probability of falsely announcing the presence of a sine wave, if none has actually appeared, does not exceed some prechosen value.

It is shown that when the noise has a flat spectrum, all the relevant information is contained in the amplitude and phase of the Fourier transform of the received sample at the frequency of the sine wave. Almost the same result holds in the case where the noise has an exponentially decaying autocorrelation, except that in this case the values of the observed sample at the end points of the sample also play a role.
On the New Method of Measuring Dielectric Constant and Loss Angles of Semiconductors
Authors: Ichijō Bunjirō
Published: April 2005

In the following, the author explains the principle of the double resonant circuit method as used in measuring the electrical characteristics of extremely poor insulating materials such as wood or textile containing much moisture. The characteristics of the measuring circuit and the results obtained thereby are studied.
Analysis of the Linear RF Mass Spectrometer
Authors: Redhead P. A. , Crowell C. R.
Published: April 2005

The linear rf mass spectrometer previously described is analyzed for small signal operation. The results are obtained in a closed form for any entrance phase where previously only a graphical solution for an optimized entrance phase was obtained. Expressions for resolving power and current efficiency are derived for both sine wave and square wave operation. It is shown that although high resolving power may be more readily obtained with square wave operation, the product of resolving power and efficiency is approximately the same for sine or square waves. Loss of resolving power caused by the thermal energies of the ions is shown to be less troublesome with square wave operation.
On the Zeros of Polynomials and the Degree of Stability of Linear Systems
Authors: Koenig J. Frank
Published: April 2005

A method is presented for finding the zeros of any nth degree real or complex polynomial as its coefficients (or their parameters) are varied. Several new theorems are presented. The method is based on new theorems, some concerning determinants, and on known theorems. It is applied to characteristic equations of linear physical systems with or without feedback. Root trajectories in the complex plane can be visualized without plotting them from ``root trajectory diagrams'' which show curve families for real or complex roots of a polynomial equation in a plane having two coefficients of the polynomial equation as coordinates. The diagrams can be used in the converse manner to determine the coefficient values corresponding to a desired dominant complex pair or real root.
Arc Drop and Deionization Time in Inert Gas Thyratrons
Authors: Pakswer S. , Meyer R.
Published: April 2005

The energy balance is discussed and a semi-empirical equation for recovery time is derived; the discussion is based on diffusion alone without consideration of cumulative ionization and metastable states. Corroborating the theoretical considerations, measurements were made of arc drop and recovery time in thyratrons filled with mixtures of Xe with Ar, Ne, and He. The spectral emission lines in these discharges were photographed in the visible range. It was found that the arc drop remained fairly constant down to low concentrations of Xe and then increased steeply. Lines of the gas other than Xe also appeared only at low concentrations of Xe. The recovery time is a monotone declining function of the mixture of the heavy and the light components. The spectral lines are tabulated.
Null Characteristics of the Rotating Adcock Antenna System
Authors: Holbrook James G.
Published: April 2005

It has been the usual practice when designing a rotating Adcock antenna system to allow a spacing of one-half wavelength between opposite dipoles at the highest intended frequency of operation. A mathematical analysis of this antenna system is presented, and it is shown that an optimum spacing for the most clearly defined nonmultiple nulls approaches a full wavelength. Useful design formulas are developed and typical response curves are presented graphically.
A Method for the Quantitative Determination of Preferred Orientation
Authors: Jetter L. K. , Borie B. S.
Published: April 2005

A new method for the study of preferred orientation in polycrystalline materials with a Geiger counter x-ray spectrometer is described. The unique feature of the method is that a spherical diffraction specimen is employed. Sufficient data for the construction of a complete pole figure may be obtained, and the observed intensities may be plotted directly on a stereographic net without geometry or absorption corrections. The method may be used satisfactorily with the heavy metals since x-rays are not transmitted through the specimen. A technique for accurately machining and electroetching spherical specimens is given, and the special goniometer used with the spectrometer is described. Sample data are given and their interpretation discussed. The method is compared with other recently developed techniques for the study of preferred orientation.
Free Space Radiation Impedance of Rhombic Antenna
Authors: Chaney Jesse Gerald
Published: April 2005

The expression for the driving point impedance of a generalized electric circuit as vizualized by the author is partially integrated, and the physical significance of certain terms is discussed in connection with their application to antenna problems. Upon postulating an unattenuated traveling wave as a first approximation to the current along either a terminated rhombic or Vee antenna, a formula is derived for the free space radiation impedance of each. The expression radiation impedance is used for that portion of the driving point impedance which may be determined from the complex power into the external fields. The resistive component of the impedance for the rhombic antenna checks with the radiation resistance as listed by Leonard Lewin in a discussion of a paper by Donald Foster, with Lewin apparently obtaining his formula by the solid angle Poynting vector method.
The Effect of a Soller Slit on the Diffraction of X-Rays by Deformed Crystals
Authors: Cullity B. D. , Julien Carl A.
Published: April 2005

In the application of the Guinier-Tennevin focusing Laue method to the study of crystal distortion, it is found that the use of a Soller slit in the incident beam produces striations in reflections from certain crystals. The diffraction geometry of a beam so modified is examined in detail, and it is shown that the striations are due to torsion of the crystal. The relation between the amount of torsion and the slope and spacing of the striations is treated quantitatively. There results a useful extension of the focusing Laue method by which not only the bending, but also the torsion, of a crystal may be measured.
Current Element Near the Edge of a Conducting Half-Plane
Authors: Harrington Roger F.
Published: April 2005

The two-dimensional problem of the Maxwellian field from a line source of current adjacent to a conducting half-plane is treated by a transform method of solution. Expressions in the form of contour integrals are given for the current induced in the conductor and for the radiated field.
Spectral Emissivities of Graphite and Carbon
Authors: Thorn R. J. , Simpson O. C.
Published: April 2005

The spectral emissivities of graphite and carbon have been determined at a wavelength of 0.653μ in the temperature range of 1285 to 2035°K and have been found to be temperature dependent in accordance with a prediction from a relation between reflectivity and resistivity. For polished graphite of high purity having a resistivity of about 1120 microhm-cm the value obtained is 0.78; the value obtained for a polished high density graphite having a resistivity of 1740 microhm-cm is 0.78; and that for polished spectroscopic carbon having a resistivity of 5080 microhm-cm is 0.79. If graphite is sublimed from a polished surface, the latter becomes roughened, so that the emissivity increases. In one particular experiment it attained a value of 0.90.
The Electric Permittivity of a Dilute Suspension of Membrane-Covered Ellipsoids
Authors: Fricke Hugo
Published: April 2005

This theoretical paper deals with the low frequency permittivity (ε) of a dilute suspension (conductivity σ, volume concentration ρ), in a conducting medium (conductivity σs, permittivity εs), of ellipsoidal particles (major axis 2a) each composed of a conducting core covered with a nonconducting surface membrane (thickness t, permittivity εm). The quantity [ε−(σ/σs)εs]/(ρaεm/t) is expressed in terms of Weierstrass' elliptic functions of the axial ratios, for parallel and random arrangement of the ellipsoidal axis. A table of its numerical values is given.
Dynamic Mechanical Properties of Polyisobutylene
Authors: Fitzgerald Edwin R. , Grandine Lester D. , Ferry John D.
Published: April 2005

Values of complex shear compliance (and rigidity) have been obtained for a sample of polyisobutylene of viscosity-average molecular weight 1.35×106 at 22 temperatures from −45 to 100°C and at about 20 frequencies from 30 to 5000 cps. Measurements were made by means of the transducer method of Fitzgerald and Ferry with a precision of ±2 percent and are estimated to be accurate to within ±3 percent as evidenced by agreement obtained between 7 different samples of widely varying dimensions. Values of the real part of the complex shear compliance J′ vary from 3.1×10−7 cm2/dyne at 99.9°C to 1.0×10−10 cm2/dyne at −44.6°C. The frequency dependence of the loss tangent J″/J′ indicates the presence of a low, broad maximum of 1.7 at −10 to −5°C and a second, smaller maximum at lower temperatures. This second maximum is also evident in a plot of J″/J′ at a fixed frequency against temperature. The wide temperature and frequency ranges of the measurements have provided an essentially complete experimental description of the dispersion region in polyisobutylene corresponding to the transition from a rubber-like elasticity to that of a hard glass.
Dynamic Mechanical Properties of the System Polystyrene-Decalin
Authors: Grandine Lester D. , Ferry John D.
Published: April 2005

The dynamic rigidities and viscosities of solutions of polystyrene (number-average molecular weight 197 000) in decalin have been measured by three experimental methods over ranges of concentration from 10 to 62 percent, of temperature from −5° to 50°C, and of frequency from 30 to 2000 cps. Similar measurements were made on the undiluted polystyrene from 115° to 133°C and 30 to 2800 cps. The data for the solutions, when reduced to a reference state of unit density and viscosity at a standard temperature, provide single composite curves for dynamic rigidity and viscosity. The distribution function of relaxation times calculated from these curves overlaps that previously derived from stress relaxation measurements on this system, and the combined function covers a range of time scale of ten powers of ten. It shows the three characteristic regions previously identified in the relaxation distribution function of polyisobutylene; there are no obvious anomalies associated with the fact that decalin is a very poor solvent for polystyrene. The data for the undiluted polymer, when reduced to a standard temperature, provide single composite curves for dynamic rigidity and viscosity. The temperature reduction factors provide apparent energies of activation for relaxation which agree with those for viscous flow obtained by Fox and Flory. The relaxation distribution function of the undiluted polymer is similar in shape to, but somewhat sharper than, those for other polymers in the transition from soft to glassy consistency. When reduced to a reference state of unit density and viscosity, the distribution function of the undiluted polymer lies near that reduced from data on solutions, but is considerably sharper than the latter.
Signal-to-Noise Ratios in Band-Pass Limiters
Authors: Davenport W. B.
Published: April 2005

A general analysis is made of the relations between output signal and noise powers and input signal and noise powers for band-pass limiters having odd symmetry in their limiting characteristics. Specific results are given for the case where the limiter has an nth root characteristic, and they include the ideal symmetrical limiter (or clipper) as a limiting case. This analysis shows that, for the band-pass limiter, the output signal-to-noise power ratio is essentially directly proportional to the input signal-to-noise power ratio for all values of the latter. This result is due to the band-pass characteristics rather than to the symmetrical limiting action.
Simplification for Mutual Impedance of Certain Antennas
Authors: Chaney Jesse Gerald
Published: April 2005

The formula for mutual impedance by the generalized circuit method is reduced to a form which greatly reduces the number of integrations required in determining the mutual impedance of various combinations of open wire and terminated wire antennas. The application is illustrated by finding the mutual impedance of the legs of an open wire X-antenna, the latter being equivalent to the radiation impedance of a biconical antenna, and for small angle cones reduces to a form from which Schelkunoff's inverse terminal impedance may be determined.
Slot Coupling of Rectangular and Spherical Wave Guides
Authors: Felsen L. B. , Marcuvitz N.
Published: April 2005

A dominant-mode wave guide radiating through a slot into a half-space may be regarded from a network viewpoint, with the half-space represented by a number of spherical transmission lines, the wave-guide feed by a single uniform transmission line and the slot by a coupling network. This paper contains (a) an investigation of how many spherical transmission lines are necessary to represent adequately the far field (gain pattern) of the slot antenna, and (b) an approximate theoretical evaluation (by a variational calculation) and experimental check of the equivalent circuit parameters of a slot-coupled junction of a rectangular and spherical wave guide, when the far field can be well represented by the dominant spherical mode. The results are useful in connection with a method of measuring the electromagnetic scattering properties of obstacles located in a half-space illuminated by a wave-guide-fed slot antenna.
Charged Disk in Cylindrical Box
Authors: Smythe W. R.
Published: April 2005

The mixed boundary value problem of the potential inside a cylindrical conducting box of radius a and height 2c in which is mounted coaxially and concentrically a thin flat charged conducting disk of radius b is solved approximately. A formula for the coefficients in the Bessel function potential series is derived which is valid for c>¼a and b<¾a. The boundary conditions are met rigorously except that the disk is not quite flat. Figures show its deviation for twelve parameter values. A formula for narrow gaps is derived. Upper and lower limits for the capacitance for twelve parameter values are tabulated.
Experiments on Radiation by Fast Electron Beams
Authors: Motz H. , Thon W. , Whitehurst R. N.
Published: April 2005

The results of some experiments on millimeter wave and light generation by means of an undulator are described. After a brief survey of the theoretical background the design of a magnet system is discussed. An experiment is described in which a 100-Mev electron beam from the Stanford linear accelerator passed through the undulator. Light radiated by the beam was observed and the plane of polarization determined. A small linear accelerator with good bunching action was used for an experiment on millimeter wave generation. At a beam energy of 3 Mev, radiation in a wavelength band below 1.9 millimeters was observed. A peak power output of the order of one watt was obtained. Millimeter waves generated in the accelerator tube were also observed.
A Theorem on the Impedance-Transforming Properties of Reactive Networks
Authors: Storch Leo
Published: April 2005

Complex impedance-matching problems are simplified substantially when they are studied in terms of appropriate circle transformations in the R-X impedance plane. The geometric approach yields valuable insight into the behavior of specific networks and leads to the interesting Circle-Locus Theorem which applies to any arbitrary, linear, reactive, two-terminal-pair network with lumped or distributed parameters (or a combination of both).
The Equivalence of Optimum Transducers and Sufficient and Most Efficient Statistics
Authors: Preston Glenn W.
Published: April 2005

The problem of the design of transducers for the purpose of restoring the fidelity of a signal (which has been corrupted by noise), while preserving information in the sense of Shannon is shown to be a particular though unusual one of statistical inference and to be amendable to the methods of mathematical statistics.

Adopting the view that the inference of the approximate form of a function s(t) (the signal) from the available mixture of the signal and the noise time series n(t) is the natural limiting case of inference from discrete series of random variables, it is seen that the transducer under discussion is the physical analog of a ``statistic''—in the sense of Fisher—and that the properties of the optimum transducer are equivalent to the statistical properties of sufficiency (preservation of information) and efficiency (maximization of fidelity).

The case of a Gaussian signal to which Gaussian noise has been added is considered in detail. Using the probability density functional of the Gaussian time series, the maximum likelihood estimate (which in this case is efficient, hence sufficient) of the signal is derived, and it's physical analog is identified as the smoothing filter of Wiener with infinite lag.
Convection Currents in Porous Media. V. Variational Form of the Theory
Authors: Rogers F. T.
Published: April 2005

A theory for the mean thermal gradient at the onset of convective flow of a fluid in a porous medium and heated from below, is given in variational form. Thermal equilibrium is not assumed, nor is viscosity assumed to be constant. An approximate solution is given for the theory, and is shown to agree quite well with published data. No attempt is made to maintain complete mathematical rigor in the derivations.
Probe Studies of Energy Distributions and Radial Potential Variations in a Low Pressure Mercury Arc
Authors: Howe R. M.
Published: April 2005

Probe measurements were made in the plasma of a low pressure mercury arc. The electron-energy distributions showed depletions from a Maxwellian distribution in the high energy range. Coupling effects between adjacent probes were investigated and were found to be quite small but in the proper direction to agree with the Langmuir-Tonks theory. Drift-current distortion of the random electron-energy distributions was measured with a bidirectional probe and compared with theory. A multisection probe extending from tube axis to tube wall allowed a determination of radial potential and density variations. Results over a pressure range from 3.4 microns to 35 microns showed good agreement with the ambipolar diffusion theory based on cumulative ionization. A direct calculation of ionization rate in the plasma was made from the ionization probability for a one-step ionizing process; comparison of this calculation with the observed ionization rate at 1.7 microns indicated that at that pressure the ionization is half direct, half cumulative. For higher arc pressures cumulative ionization evidently predominates.
A Certain Problem in Heat Conduction
Authors: Zatzkis Henry
Published: April 2005

A homogeneous sphere is surrounded by an infinite homogeneous medium. Heat is generated inside the sphere at a prescribed rate. The temperature distribution inside and outside the sphere is computed.
The Relaxation Distribution Function of Polyisobutylene in the Transition from Rubber-Like to Glass-Like Behavior
Authors: Ferry John D. , Grandine Lester D. , Fitzgerald Edwin R.
Published: April 2005

The steady flow viscosity of a sample of polyisobutylene of viscosity-average molecular weight 1.35 million, distributed by the National Bureau of Standards, has been measured from 15° to 100°C. Its logarithm is a linear function of 1/T2. Application of the method of reduced variables to dynamic mechanical data from −45° to 100°, previously reported for this polyisobutylene, yields composite curves reduced to 25°C for the real and imaginary parts of the complex compliance and complex shear modulus; the real part of the complex dynamic viscosity; and the mechanical loss tangent. The latter exhibits a broad and peculiarly asymmetric maximum. The reduced time scale extends from 1 to 10−9 sec. The reduction factors aT obtained in this way are slightly higher than those derived either from the viscosity or from stress relaxation measurements of Tobolsky and associates. The distribution functions of relaxation and retardation times have been calculated by second approximation methods and their detailed shapes are defined in the transition region between rubber-like and glass-like behavior. The relaxation distribution function is compared with the idealized distribution of Tobolsky.
Reflection of Sound in the Ocean from Temperature Changes
Authors: Carhart Richard R.
Published: April 2005

When the temperature of the ocean changes with depth within a horizontal layer, it is accompanied by a change in the velocity of sound. The reflection of sound from such a transition layer depends on the incident angle and wavelength of the sound, the thickness of the layer, the manner in which the velocity changes, and the total amount of the change. The usual formula for reflection assumes a transition layer of negligible thickness. The reflection coefficient then depends only on the incident angle and the total velocity change. This case is treated and numerical values are given for the reflection coefficient under conditions of practical interest. It is then shown that for a gradual velocity change which corresponds to certain temperature data, the reflection coefficient for small glancing angles of incidence changes gradually with increasing layer thickness and may be approximated very closely by the usual formula. Quantitative comparison of the cases is made and the general applicability of the approximation is discussed.
The Nature of Solutions of a Rayleigh-Type Forced Vibration Equation with a Large Coefficient of Damping
Authors: Brock Paul
Published: April 2005

In this paper, the author considers an approximation to the Rayleigh equation, y¨+ε(13ẏ3−ẏ)+y=A cosωt, and its equivalent form under the transformation ẏ=v,y=εξ. A cubic function 13v3−v+ξ that appears in the altered equation is replaced by a piecewise linear function. For large ε, the existence of periodic solutions of the approximating equation is demonstrated. Strong orbital stability properties of neighboring solutions is also shown.
Diffusion of Barium in an Oxide-Coated Cathode
Authors: Bever Renate S.
Published: April 2005

The diffusion of Ba through activated BaO–SrO cathode coatings was studied as a function of temperature. Most of the radioactive tracer material diffused according to a dependence of log10D vs 1/T similar to that obtained by Redington for diffusion of Ba in single crystals of BaO. The activation energy was 4.1±0.6 ev above 1280°K and 0.40±0.07 ev below that temperature.
Degradation of Polyisobutylenes on Shearing in Solution
Authors: Bestul A. B. , Belcher H. V.
Published: April 2005

The decrease of viscosity on shearing in a capillary at 37.8°C and a nominal rate of shear of 65 000 sec−1 has been measured for 5, 10, and 15 weight-percent solutions in o-dichlorobenzene of 10 polyisobutylenes having viscosity-average molecular weights from 40 000 to 2 300 000. Very little, if any, viscosity decrease was observed for polymers having molecular weights below 500 000, but marked decreases were observed for polymers with molecular weights above 500 000. The observed decreases were not recovered on standing and correspond to appreciable decreases in the molecular weights of the polymers. The molecular weight reduction can be explained on the basis of polymer chain rupture if the mechanical energy developed in a volume less than that enveloping a single polymer molecule can be concentrated into a single bond.
Measurement of Particle Size of Fine Ferromagnetic Powders
Authors: Franklin A. D. , Campbell R. , Weinman J.
Published: April 2005

The particle sizes of four Fe and two Fe–Co powders with diameters ranging from 200 to 600 angstroms have been determined using electron microscope, x-ray line broadening, and nitrogen adsorption techniques. Reasonable agreement was found between the electron microscope and the x-ray methods, while the sizes determined through nitrogen adsorption were in every case larger. A method of dispersing single-domain ferromagnetic powders for electron microscopy is described.
A Replica Technique in the Study of Chemical Precipitation Processes
Authors: Fischer Robert B. , Ellinger Joseph P.
Published: April 2005

A replica technique has been developed for the electron microscope study of particles of precipitates formed by mixing solutions of chemical reagents. The replica is formed thermally in a thin film of parlodion. A one-step, shadowed replica has been found most satisfactory. The technique has been found suitable for studies of the effect of conditions of observation upon the specimen materials, studies of precipitates such as silver chloride which are known to be unstable during direct observation, studies of precipitates as they exist in the mother liquid; and studies which require detailed observation of surfaces.
Methods of Measuring the Properties of Ionized Gases at High Frequencies. IV. A Null Method of Measuring the Discharge Admittance
Authors: Gould Lawrence , Brown Sanborn C.
Published: April 2005

The admittance of a gas discharge may be obtained from measuring the ratio of the transmitted power through a microwave cavity to the incident power as a function of signal frequency near the cavity resonance. The method involves balancing the transmitted and incident signals to zero at the cavity resonance after they have passed through two separate receiving systems. When the signal frequency is changed, an attenuator is used to rebalance the two signals. The change in frequency from resonance and the corresponding change in attenuation gives the necessary data which will plot as a straight line whose slope yields the desired information.
Electrical Properties of Liquid Selenium I
Authors: Henkels H. W. , Maczuk J.
Published: April 2005

The thermoelectric power of liquid selenium has been measured in the range 250–500°C. Values of activation energies calculated from the temperature dependences of thermoelectric powers and resistivities agree. This activation energy taken as the intrinsic activation energy (or the energy to break the Se–Se bond) is 2.31 ev calculated from data given by Henkels. The mobility of holes in the intrinsic region exceeds that of electrons and has a value (8.4×106)/T32 cm2/volt sec, assuming electronic mass.

As a further check of the electronic nature of the conduction in the liquid and of theories of conduction in the hexagonal form, preliminary measurements of the thermoelectric power of pure selenium doped with small percentages of As, Sb, and Bi up to 4 percent were made. In the intrinsic region the specimens exhibited p type conduction, but at lower temperatures the sign of the thermoelectric powers reversed and values became quite large but negative. The crossover point depended qualitatively on the amount of impurity in the correct manner. The n type conduction is tentatively attributed to donor levels introduced by the normal trivalence of Group Vb elements. Two p electrons are considered bound in the selenium chain, the third ionized at high temperature.
The Formation of Black Carbon
Authors: Grisdale R. O.
Published: April 2005

Electron microscopic evidence is presented in support of the hypothesis that black carbon resulting from pyrolysis of gaseous hydrocarbons is produced through the intermediate formation of droplets of complex hydrocarbons. Electron diffraction studies further confirm this hypothesis if, as has been found for particles of carbon blacks, the droplets consist in part of graphitic nuclei arranged with their basal planes tangential to the droplet surface. The carbonization of small solid spherules of highly cross-linked organic polymers is described, and it is shown that the morphology of the carbonization products is wholly analogous to those for pyrolytic carbon and carbon blacks. It is suggested, therefore, that the formation of carbon by the carbonization of solids and by deposition from the gas phase occurs through similar mechanisms and that the two processes are simply two extremes in an infinite series of processes which are all fundamentally alike.
Effect of Stiffness and Nonuniformity on Vibroscopic Determination of Filament Cross-Sectional Area
Authors: Montgomery D. J.
Published: April 2005

The presence of stiffness in a stretched string vibrating between fixed supports raises all the natural frequencies over those for a perfectly flexible string. The presence of nonuniformity in cross-sectional area along the string changes some or all of the frequencies from those for a perfectly uniform string, the amount and direction of change depending on the form of the nonuniformity. These changes in frequency may introduce error into the calculation of the average cross-sectional area of a fiber by means of the vibroscopic technique, wherein the mechanical resonance of a stretched fiber is observed under oscillating mechanical or electrostatic forces. In this paper the natural frequencies are calculated with both the stiffness and the nonuniformity taken into account to first-order terms. The relation between the average cross-sectional area and the natural frequencies is analyzed. Consideration is given to the manner in which the changes in frequency and shifts of the nodes, due to nonuniformity, determine the detailed form of the area variation. The characterization of nonuniformities in terms of certain arbitrary parameters is shown to lead to the possibility of calculating the average area by measuring the natural frequencies in only the first and second modes and of calculating the maximum or minimum area by measuring also the nodal shift in the second mode.
Radioactive Charging Effects with a Dielectric Medium
Authors: Rappaport P. , Linder E. G.
Published: April 2005

A process is described in which radioactive radiation traverses a solid dielectric medium to charge a collector electrode. This process offers a simple method of studying effects of radiation on matter such as bombardment-induced conductivity, secondary emission, charge soakage, and radiation absorption. Typical data are given. Possible application of this process for the construction of a current or voltage source for use in electronic devices is discussed.
Diffraction of Electromagnetic Waves by an Aperture in a Large Screen
Authors: Bekefi G.
Published: April 2005

It has been shown that an approximate solution for the diffraction of an electromagnetic wave by an aperture in a plane conducting screen can be obtained from a single component of the Hertz vector and that the results can be applied to calculating the field of apertures which are sufficiently large as compared to the wavelength of the incident radiation. The solution rests upon an evaluation of an inhomogeneous scalar boundary-value problem. An infinitesimal wavelength approximation leads to a simple Kirchhoff-like formula which is found to be identical to that obtained by Neugebauer who derived it from geometrical optics as first approximation. The special case of diffraction by a circular aperture is treated in detail, and experimental measurements by which the theory was checked are cited.
Reactor Simulators
Authors: O'Meara F. E.
Published: April 2005

Reactor kinetic equations are given together with the equations for fission product poisoning and temperature effects. A conceptual design of a reactor simulator is presented and the numerical values of the coefficients are listed.
Crystallographic Variations of Field Emission from Tungsten
Authors: Wilkinson M. K.
Published: April 2005

A photometric method has been developed and used to measure field-emission electron currents as a function of the crystallographic directions found in a tungsten single crystal emission point. Data obtained indicate that the appearance of bright and dark areas on the pattern of a field-emission projection tube can be explained by the differences in the work functions of the various crystallographic directions. The experiments also suggest that the value of the exponent of the work function needed to relate the field-emission equation to observed data is (32) as predicted by theory. The method of analysis is independent of the need for high accuracy of electric field determination. However, it does depend on a knowledge of the electric field distribution about the surface of the emission point. In these experiments, the field distribution was an assumption based on experimental data.

To insure the constancy of the electron emission required for measurement it was necessary to maintain an excellent vacuum. A method is given for the attainment and maintenance of a pressure in the region of 10−12 mm of Hg.
Laminar Flow in Channels with Porous Walls
Authors: Berman Abraham S.
Published: April 2005

The Navier-Stokes equations have been solved to obtain a complete description of the fluid flow in a channel having a rectangular cross section and two equally porous walls. The scope has been limited to two-dimensional incompressible steady-state laminar flow.

The solution of the flow equations leads to detailed expressions for the dependence of the velocity components and the pressure on position coordinates, channel dimensions, and fluid properties.
Electrical Properties of Selenium. III. Microcrystalline Selenium Metal Doped
Authors: Henkels H. W. , Maczuk J.
Published: April 2005

The thermoelectric powers and dc and 200-mc resistivities of pure and metal-doped selenium have been studied as functions of temperature. The properties of materials in the two important microstructures (colony and equiaxed) were distinguished. The influences of the metals Na, Cu, Ag, Mg, Zn, Cd, Hg, Ga, In, Tl, Pb, Sb, Bi, Te, Fe, Ni, Co, and Ce were noted.

A working model of the selenium semiconductor was developed. In this model there is an acceptor level <0.15 ev from the full band caused by nonmetals and possibly lattice defects. In strained crystals or material in the colony structure a second acceptor level 0.27 ev from the full band is postulated from the behavior of dc and ac resistivity curves as a function of temperature. The density of the first level varies in the range 1014/cm3 to 6×1016/cm3 with amount of nonmetal impurity. The density of the second level depends on the crystal structure, decreasing as the colony structure recrystallizes to the equiaxed. In the specimens crystallized at 110°C the density was about 2×1016/cm3. Both metals and non-metals are largely segregated at grain boundaries. Metals produce effective donor levels at these places.

The dc properties reflect the presence of internal barriers produced by the segregation. The donor levels enhance barriers existing in the purest selenium tested increasing resistivities and thermoelectric powers.

With increase in temperature >160°C the density of acceptor levels decreases as defects are removed by structural changes in the lattice.
Field Emission Current-Density Distribution
Authors: Dyke W. P. , Trolan J. K. , Dolan W. W. , Grundhauser F. J.
Published: April 2005

A quantitative measurement of the current-density distribution over the surface of monocrystalline tungsten field emitters is obtained by densitometric analysis of calibrated photographic negatives of emission patterns observed with a modified Mueller projection tube. Analysis of distributions thus obtained permits an improved evaluation of average field current density and a confirmation of the surface distribution of electric field previously derived; an earlier comparison of experiment with field emission theory is thus strengthened. Current-density ratios for various crystal faces of the emitter confirm recent values of the work function for those faces. Emission patterns were viewed on an aluminum backed phosphor, the advantages and fabrication of which are discussed. Relative light output from such phosphors is presented for excitation by field currents at various values of the applied potential for both steady state and microsecond operation.
On Reciprocity Theorems in Electromagnetic Theory
Authors: Crowley T. H.
Published: April 2005

Various forms of the reciprocity theorem arise in electromagnetic theory because of differences in the source of the fields. Five different types of sources are discussed briefly and the corresponding reciprocity theorem given.
Thickness-Shear Vibrations of Piezoelectric Crystal Plates with Incomplete Electrodes
Authors: Mindlin R. D. , Deresiewicz H.
Published: April 2005

In this paper the influence of length of electrodes on thickness-shear frequencies of piezoelectric crystal plates is investigated.
Suppression of Overtones of Thickness-Shear and Flexural Vibrations of Crystal Plates
Authors: Mindlin R. D. , Deresiewicz H.
Published: April 2005

It is shown how electrodes, coated on the surfaces of thickness-shear plates, may be shaped so that, when the driving frequency coincides with a particular resonant frequency, only that resonant mode is excited.
Effect of Gas Slip on Unsteady Flow of Gas Through Porous Media
Authors: Aronofsky J. S.
Published: April 2005

A numerical method is presented for describing either the one-dimensional or radial transient flow of gases through a porous medium in which the initial and terminal pressures and/or rates are specified. The purpose of this investigation was to evaluate the effect on transient gas flow of a pressure-sensitive gas permeability resulting from gas-slip effects. The gas-slip permeability or apparent permeability is assumed to vary as a linear function with the reciprocal pressure. The computations were carried out by means of punch card machines.

The results demonstrate that under certain conditions, the transient flow system is greatly influenced by gas-slip permeability. However, the results also indicate that the effect of gas slip on transient flow behavior is negligible for pressure conditions usually associated with gas or petroleum reservoirs, and would be of most importance in the conduct and analysis of gas flow experiments in the laboratory. A specific laboratory application of the calculations is a possible transient method for the determination of porosity and/or gas-slip corrected permeability.
The Effect of Inelastic Collisions on the Slowing-Down Length of Neutrons in a Hydrogenous Mixture
Authors: Volkin Howard C.
Published: April 2005

An expression for the slowing-down length of neutrons in a hydrogenous mixture in which inelastic collisions occur is derived from the rigorous transport equation under the assumptions that (1) the masses of the nonhydrogen nuclei are infinite and (2) the inelastic scattering is of the type in which only discrete well-defined energy levels of the target nucleus are involved. The result is applied to an iron-water mixture.
On the Stability of Fluid Flows with Spherical Symmetry
Authors: Plesset M. S.
Published: April 2005

The conditions for the stability or instability of the interface between two immiscible incompressible fluids in radial motion are deduced. The stability conditions derived by Taylor for the interface of two fluids in plane motion do not apply to spherical flows without significant modifications.
Studies of Rubberlike Polymers by Nuclear Magnetism
Authors: Honnold V. R. , McCaffrey F. , Mrowca B. A.
Published: April 2005

The actual width of the proton resonance line in uncured natural rubber has been determined at room temperature to be 0.06 gauss. Curing of polymers increases the line width at a given temperature. The small increase in natural rubber is possibly compatible with a physical bonding rather than the usually assumed cross linking. For a butadiene-styrene copolymer the increase in line width due to cure is somewhat larger. Carbon black loading increases the line width to a lesser degree than cure. This is compatible with the concept of physical bonding between the blacks and the polymer chain molecules. Variations in line width caused by changes in chemical composition and copolymerization were also investigated. Polypropylene and polypropylene oxide of roughly the same average molecular weight are compared. The polypropylene oxide exhibits a greater degree of ``rotation'' about its C–O bonds than polypropylene does about its C–C bonds. Two butadiene-acrylonitrile copolymers also have been studied as a function of temperature. Finally, spin-lattice relaxation time vs temperature studies are reported for a butadiene-acrylonitrile copolymer and for raw butyl, over the temperature range from −-50°C to 70°C. Estimates of the magnitude of the barriers hindering ``rotation'' are made.
Theory of Orientation and Double Refraction in Polymers
Authors: Gurnee Edward F.
Published: April 2005

Orientation and birefringence in linearly oriented amorphous polymers are discussed with particular emphasis on polystyrene type chains. A system of completely uncoiled parallel zigzag chains is defined as 100 percent orientation. The variation of birefringence with orientation is assumed to follow the same expression as that for the variation of polarization anisotropy with extension for a single random coil chain. With these assumptions and reasonable models for the completely uncoiled polystyrene chain it is possible to express any given birefringence as a percentage orientation.

Methods are developed for the experimental determination of the birefringence at a particular point in an oriented monofilament instead of the usual determination of an average birefringence through the monofilament. The application of these methods to actual examples leads to reasonable values of the orientation.
Transformation of Scattering Cross Sections
Authors: Zweifel P. F. , Hurwitz H.
Published: April 2005

A simple method is presented for the calculation of the transformation matrices between the Legendre polynomial expansion coefficients of the scattering cross section in the laboratory and center-of-mass systems. Approximate expressions for the matrices are given. Applications to transport problems involving the elastic scattering of neutrons are discussed.
Radiation from a Point Dipole Located at the Tip of a Prolate Spheroid
Authors: Hatcher E. C. , Leitner A.
Published: April 2005

The radiation patterns of prolate spheroidal conductors, excited by an electric dipole in its tip, are calculated, for a number of spheroids of varying thickness, the wavelengths being equal to roughly π, π/2, and π/3 times their major axes.