bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypo-Elastic Shear
Authors: Truesdell C.
Published: April 2005

Part I reproduces the lecture given at the meeting of the Society of Rheology and furnishes a nonmathematical introduction to the theory of hypo-elasticity. Hypo-elasticity is a smooth, simple theory of elastic response based on time rates. For small strains it agrees with the classical linear theory of elasticity. To determine stress-strain relations for large deformation is a mathematical problem, the answer to which varies from one special case to another. Simple shear is taken as an example. Here it turns out that hypo-elastic materials may soften or stiffen in shear, depending on the value of a dimensionless constant which has no effect when the strain is small. For bodies which soften, a theoretical prediction of ``hypo-elastic yield'' is obtained.

Part II concerns a new special type of hypo-elastic body in some ways more general, in other ways more special than that considered in Part I. According to this theory, yield of the von Mises type appears to follow if the stress intensity is sufficiently great. The equations of this theory are solved for the case of simple shear. It is shown that if von Mises yield occurs, hypo-elastic yield must occur at a lesser stress. For large values of a certain parameter, von Mises yield is imaginary and only hypo-elastic yield occurs. For moderate values of the parameter, hypo-elastic yield appears as primary yield, with von Mises yield as secondary yield at infinite strain. For small values of the parameter, hypo-elastic yield and von Mises yield are indistinguishable, and the stress-strain curve is similar to the idealized forms assumed at the outset in the conventional Prandtl-Reuss theory.
Fracture in the Extrusion of Amorphous Polymers through Capillaries
Authors: Tordella J. P.
Published: April 2005

In the extrusion of an amorphous, un-cross-linked polymer through a capillary, there is a critical stress at and beyond which the emerging stream becomes irregular in shape. This effect appears to originate in the approach to the capillary rather than within the capillary. Tearing or fracture of the molten polymer appears to occur in this region.
Viscometric Analysis of Dispersions at Small Shear Stresses
Authors: Myers Raymond R. , Miller John C. , Zettlemoyer A. C.
Published: April 2005

The flow behavior of certain dispersions at small shear stresses has been studied in a rotational viscometer. Criteria which were used in analyzing the dispersions are the relative viscosity and its temperature dependence, the ratio of viscosities at infinite and zero shear, sedimentation rates, and the existence of a critical volume concentration for the occurrence of non-Newtonian behavior.
Technique for Making Surface Replicas from Comparatively Small Objects
Authors: Feng I-Ming
Published: April 2005

A simple replica technique for making surface replicas from small objects is described and illustrated with electron micrographs taken from replicas prepared by these techniques from glass fibers of 8μ diam and 36 grit Al2O3 grains.
Radioactive Isotope Study of the Dissociation of Barium Oxide under Electron Bombardment
Authors: Yoshida S. , Shibata N. , Igarashi Y. , Arata H.
Published: April 2005

The evolution of Ba from BaO was detected by using radioactive Ba140, and the rate was measured for various electron bombardment conditions. The following results were obtained: (1) When the bombarding voltage was fixed, the rate of evolution increased linearly with the number of primary electrons, provided the temperature of the oxide remained constant. (2) The rate of evolution increased exponentially with temperature; the activation energy was about 0.7 ev. (3) The efficiency of 500 ev electrons was far less than of 150 ev electrons at constant bombarding power. (4) The efficiency was around 3.9×10−7 atom per primary electron at 150 ev and 710°K. A simple mechanism of the electron bombardment dissociation is proposed.
Transient Behavior in a Ferroresonant Circuit
Authors: Skalnik J. G.
Published: April 2005

Several physical systems are described approximately by Duffing's equation d2φdt2+adφdt+bφ+cφ3=Fcosω1t,where a, b, and c are constants of the system and F and ω1 are constants of the applied forcing function. This is a second-order nonlinear differential equation whose complete exact solution is unknown.

Approximate solutions for the steady-state behavior of the systems represented by the above equation are well known. The present work investigates the transient behavior in the region of the steady-state response. The theory developed is supported by solutions using an analog computer and by experiment with an actual electrical circuit whose behavior is approximated by the foregoing equation.
p-n Junction Theory by the Method of δ Functions
Authors: Reiss Howard
Published: April 2005

This article describes a concise new method for calculating current-voltage phenomena in structures involving p-n junctions. In fact, the problem of the current-voltage characteristics of any one-dimensional p-n junction structure with any number of junctions and contacts is solved in a form general enough so that one only needs to insert the physical parameters of the structure into the formulas to write down its characteristics.
Flicker Noise in Secondary Emission Tubes and Multiplier Phototubes
Authors: Schwantes R. C. , Hannam H. J. , Van Der Ziel A.
Published: April 2005

Flicker noise with a 1/f frequency dependence has been observed in the secondary emission process. No flicker noise was observed in multiplier phototubes which means that a possible flicker noise component caused by the photoemission or secondary emission process is small in comparison with the shot noise of the tube. The secondary emission flicker noise resistance, measured for Philips EFP60 tubes, increases with increasing primary current and also increases with increasing primary energy. The results are interpreted in terms of a fluctuating work function.
Effect of Cathode Roughness on the Maximum Current Density in an Electron Beam
Authors: Preston Glenn W.
Published: April 2005

A discussion is presented of the limitation of current density by random irregularities of the cathode surface in an electron beam which is focused by a static electromagnetic field. The Langmuir-Pierce law for the maximum attainable current density is profoundly altered by the effects of cathode roughness. It is found that the minimum beam diameter attainable in typical cathode-ray tubes is unaffected by change of cathode temperature or proportional change in the potentials of all electrodes.
Mechanism of Electrical Breakdown in Saturated Hydrocarbon Liquids
Authors: Lewis T. J.
Published: April 2005

There have been several investigations of the electrical breakdown strength of hydrocarbon liquids in a high state of purity in which attempts have been made to correlate the strength with density or chain length. A simple relationship between these quantities did not exist when branched-chain isomers of the n-paraffins were included. The present paper develops the theory of breakdown outlined by the author in a previous publication in which molecular vibrations in these liquids can provide an energy barrier to ionization by electrons and final breakdown. It is suggested that three major processes occur, namely, electron emission from the cathode, energy loss to molecular vibrations, and ionization of the liquid. The instability which marks breakdown is then induced by positive ions which result from ionization. Provided a suitable test procedure is employed it is possible to compare the energy-loss mechanism in the various liquids by comparing their electric strengths. The nature of the molecular vibrations is discussed, and it is suggested that the infrared frequencies of the CH3, CH2, and CH groups undergoing bond stretching are excited by the electron motion. Such a frequency, characteristic of the carbon-hydrogen bond would be common to all hydrocarbon liquids. Collision cross sections for these groups can then be assigned and a breakdown criterion set up which is analogous to that proposed by von Hippel for condensed phases. The general correctness of this theory is illustrated by reference to the measurements of Crowe, Sharbaugh, and Bragg and to new measurements obtained by the author. It is found to be possible to correlate not only the electric strength of straight-chain hydrocarbons but branched-chain isomers as well. Finally it is suggested that the current pulses frequently observed in conduction measurements in n-hexane are possibly associated with bond deformation vibrations.
Theory of the Non-Newtonian Rheology of Raw Rubbers Consisting of Supermolecular Rheological Units
Authors: Mooney M.
Published: April 2005

A theory of the viscosity of raw rubbers is developed on the postulate that raw rubbers, when subjected to continuous shear in the non-Newtonian region of flow, consist of microscopic rheological units which are semipermanent aggregates of many rubber molecules [M. Mooney and W. E. Wolstenholme, J. Appl. Phys. 25, 1098 (1954)]. The theory treats these units as tacky, elastic solids, whose relative movement and slippage constitute the macroscopic flow of the rubber. The resulting theoretical flow curve differs little from that given by H. M. Smallwood [J. Appl. Phys. 8, 505 (1937)], but the interpretation of the parameters is radically different. The new theory leads to expressions for the number of temporary point attachments per unit area between two touching rheological units and for the mean life of these attachments.

Agreement with experimental data is slightly better than in Smallwood. Two types of observed deviation from the theory can be interpreted as due to two plausible phenomena not included in the mathematical treatment.
Upper-Air Density and Temperature by the Falling-Sphere Method
Authors: Bartman F. L. , Chaney L. W. , Jones L. M. , Liu V. C.
Published: April 2005

Upper-atmosphere air densities and temperatures have been calculated from the measured trajectory data of a falling sphere. Densities were calculated from the equation for the drag force on the falling sphere, and temperatures were then obtained by using the hydrostatic equation and the equation of state of a perfect gas. The aerodynamic background and instrumentation are described; the method of calculation and the errors are discussed. The results of four rocket flights which carried the experiment are given. Comparison with the average of other rocket measurements indicates agreement with these results.
Some Recent Studies of Random Noise between Metals and Dielectrics
Authors: Reynolds S. I.
Published: April 2005

The purpose of these studies was to investigate the source of noise which is generated when thin dielectrics are subjected to relatively low dc voltages as reported by Boyer. It has been suggested by J. H. Mason that this phenomenon may be caused by the ionization in small voids due to poor electrode contact. Tests reported in this paper show that the application of 300 volts dc to dry films having a total resistance between test electrodes of 1.5×10 in. ohms was sufficient to give rise to a steady noise voltage if the electrodes were not in intimate contact. During some of the experimental work a two phase dielectric was subjected to dc voltage up to 1425 volts with no pulses. As expected, when the polarity was reversed, the dc current momentarily increased many-fold, and then during its decay, noise was measured simultaneously. The noise ceased when the dc current became constant. A similar phenomena has been observed during the decay of the hetero-change on a polarized dielectric. The test methods used provide a very sensitive method for detecting ionization in extremely small voids.
X-Ray Study of the Local Atomic Arrangement in Partially Ordered Cu3Au
Authors: Chipman D. R.
Published: April 2005

The atomic arrangement present in Cu3Au in a state of equilibrium partial long-range order has been investigated by measuring with x-ray techniques the short-range order existing below the critical temperature. A single crystal of Cu3Au, cut parallel to a (100) face was quenched into water from 380°C, just below the critical temperature for ordering. Using monochromated Cu Kα radiation and a Geiger counter spectrometer, the diffuse scattering from this crystal was measured in the (h1h20) plane of reciprical space. From these data, short-range order parameters and a first-neighbor size effect coefficient were obtained. The measurements show that there is a marked short-range order among the wrongly occupied sites below the critical temperature. It is shown that the measured short-range order parameters can be predicted by assuming that the wrongly occupied sites coalesce into tiny antiphase domains, and that these domains are one atomic plane in thickness, lie parallel to any one of the three sets of (100) planes in the crystal, and contain, on the average, about nine atoms each.
Formation of p-n Junctions in Semiconductors by the Variation of Crystal Growth Parameters
Authors: Bridgers Henry E.
Published: April 2005

The fluid transport theory of Burton et al. for the variation of the effective distribution coefficient with growth rate and stirring is applied to the growth of semiconductor crystals from a melt containing both donor and acceptor impurities. ``Rate growing,'' or the formation of p-n junctions by varying the growth rate, is considered and the importance of the ratio of melt concentrations is demonstrated. Junction formation by varying the degree of stirring in the melt, or ``stirring modulation'' is also described. General principles are derived and various applications are discussed.
High-Resolution Microradiography Using Low-Voltage X-Rays
Authors: Engström A. , Greulich R. C.
Published: April 2005

Mathematical considerations of the concept of extremely high resolution in microradiography have allowed the derivation of optimal conditions for studies of biological material. Specimen thickness must be kept below 4 microns, and as a consequence very low voltages over the x-ray tube are needed. Using a special method for preparing the specimen for analysis, it has been possible to obtain microradiograms at x-ray potentials of a few hundred volts. The absolute resolution of the x-ray image is comparable to that of the light microscope.
Theoretical Considerations Governing the Choice of the Optimum Semiconductor for Photovoltaic Solar Energy Conversion
Authors: Loferski Joseph J.
Published: April 2005

The theory of the photovoltaic effect is used to predict the characteristics of a semiconductor which would operate with an optimum efficiency as a photovoltaic solar energy converter. The existence of such an optimum material results from the interaction between the optical properties of the semiconductor which determine what fraction of the solar spectrum is utilized and its electrical properties which determine the maximum efficiency of conversion into electricity. Considerable attention is devoted to the effect of the forbidden energy gap (EG) of the semiconductor. It is shown that atmospheric absorption causes a shift in the solar spectrum which changes the value of the optimum forbidden energy gap between the limits 1.2 ev<EG <1.6 ev. Furthermore, plausible departures of the diode reverse saturation current (I0) from the parametric dependence predicted by Shockley are considered, and it is shown that such departures reduce the advantage of the optimum material over others in the range 1.1 ev<EG<2.0 ev. The relation between EG and the load impedance for maximum power transfer from the solar converter is discussed. Finally, I0 is computed from the published values of the semiconductor parameters of three intermetallic compounds, i.e., InP, GaAs, and CdTe, and it is shown that the efficiencies predicted for these materials are greater than those predicted for other materials which have been proposed, i.e., Si, CdS, Se, and AlSb.
Molecular Ringing
Authors: Bloom Stanley
Published: April 2005

Semiclassical radiation theory is used to describe the response of an assemblage of two-state molecules driven by an electromagnetic field. When the field is suddenly removed, the assemblage does not immediately become quiescent; it continues to radiate in diminishing amount. This coherent molecular-ringing radiation persists until the molecular populations return to the values they had at the beginning of the driving pulse. Depending upon the strength and duration of the driving pulse, the ringing radiation may exhibit a delayed peak.
Application of Dislocation Theory to Internal Friction Phenomena at High Frequencies
Authors: Granato A. , Lücke K.
Published: April 2005

A detailed discussion of data obtained over the past 15 years concerning the damping of mechanical vibrations in the kilocycle and megacycle range is given. The dependence of the decrement and modulus change on the variables of frequency and strain-amplitude and many other parameters is compared with predictions of the dislocation theory developed in an earlier paper. Although general agreement is obtained, and many interesting quantitative results are found, it is not possible to say that the theory agrees everywhere since not all the necessary parameters are known well enough theoretically. A number of new experiments are suggested which may permit stronger conclusions to be made. This part may be read independently of the earlier paper by the reader who does not wish to follow the development of the theory in detail.
Measurement of the Image Rotations Produced by the Lenses of a Magnetic Electron Microscope
Authors: Miller R. , Sharpe J. W.
Published: April 2005

A method of measuring the amount of rotation produced by the lenses of a three-stage electron microscope is described and the application of the results to stereo-electron microscopy discussed.
Diffraction by a Wide Slit
Authors: Karp S. N. , Russek A.
Published: April 2005

The problem of diffraction of scalar waves by an infinite conducting plane with a slit is investigated. Approximate expressions for the near and far fields, taking into account the interaction between the edges, are derived in terms of the well-known solutions for the field produced when an isolated conducting half-plane is excited by (a) a plane wave, and (b) a line source. Results of numerical calculation are given for the case of a plane wave normally incident on the slit. Twelve values of slit width ranging from 0.96 to 2.5 wavelengths are considered. A comparison of transmission coefficients is given. It is found that the new approximate solution agrees well with the exact solution, and provides a significant correction to the noninteraction solution. The accuracy increases with the slit width, so that the result is useful in the range where interaction cannot well be neglected but where the exact solution converges so slowly that computation is impracticable.
Avalanche Breakdown Voltage in Silicon Diffused p-n Junctions as a Function of Impurity Gradient
Authors: Veloric H. S. , Prince M. B. , Eder M. J.
Published: April 2005

A method is presented for controlling the reverse breakdown voltage (VB) in a silicon graded junction. The significant process parameters are shown to be resistivity, time of diffusion, and temperature of diffusion. For a constant resistivity, VB increases with the fourth root of the time of diffusion and with the square root of the depth of diffusion as predicted by theory. Statistical analysis shows that the mean breakdown voltage for a large group of units can be predicted within 2%. The method fails for very low or high resistivity material.
Two-Dimensional Motion of Idealized Grain Boundaries
Authors: Mullins W. W.
Published: April 2005

To represent ideal grain boundary motion in two dimensions, a rule of motion of plane curves is considered whereby any given point of a curve moves toward its center of curvature with a speed that is proportional to the curvature. A general theorem is deduced concerning the change of area enclosed by such a curve. Three families of curves are found that obey the curvature rule of motion while undergoing the shape preserving transformations of uniform magnification, translation, and rotation respectively. Pieces of these curves represent the steady shapes of idealized grain boundaries under certain symmetrical conditions.
Effect of Magnetic Field Strength During Condensation on the Coercivity and Form of Vapor-Deposited Iron
Authors: Griest A. J. , Libsch J. F. , Conard G. P.
Published: April 2005

The coercivity and form of iron deposited from the vapor were found to be influenced by the strength of a magnetic field applied during condensation. The intrinsic coercivities of powders deposited at −196°C and at −78°C in fields of 800 to 900 oersteds were about 120 oersteds. The greater fraction of particle diameters ranged from 10 to 20μ. No appreciable quantity of submicron particles was detected in several samples examined by electron microscopy. Line-broadening in the diffraction patterns of the vapor-deposited iron was attributed to strain, the magnitude of which was theoretically sufficient to account for the observed coercivities.
Solutions of the Reactor Kinetics Equations for Time Varying Reactivities
Authors: Ash Milton
Published: April 2005

The solutions of the reactor kinetics equations for constant (step-function) reactivities are straight-forward and well known. For time dependent reactivities, however, only approximate solutions (excluding machine results) peculiar to the individual need are generally available. To obtain solutions for time dependent reactivities, the reactor kinetics equations are combined into a single integral equation of the Volterra type. The kernel of the integral equation characterizes the particular reactor through the decay properties of the six groups of delayed neutrons plus the prompt neutron generation time. A simple iterative procedure for hand computation of the solutions for general time dependent reactivities is given. Curves for two types of such reactivities (linear and ≃∫0vtsin2kxdx) are included.
First Correction to the Geometric-Optics Scattering Cross Section from Cylinders and Spheres
Authors: Rubinow S. I. , Wu T. T.
Published: April 2005

The total scattering cross section in the short wavelength limit is considered in this paper. The problems treated include diffraction of a plane electromagnetic wave by a conducting cylinder (two possible polarizations) or a conducting sphere, acoustic scattering by a rigid sphere, and quantum-mechanical scattering by an impenetrable sphere. The first correction term to the geometric optics result is computed. In each case, this term is proportional to (ka)−2/3. The constant of proportionality depends on the specific geometry.
Neutron Flux Spectra in Air
Authors: Holland Samuel S. , Richards Paul I.
Published: April 2005

Application of the moment method of L. V. Spencer and U. Fano is made to the penetration and slowing down of neutrons in infinite media. General considerations are restricted mainly to those modifications of the method necessary for the neutron problem; in particular, a special technique is given for reducing the integral term of the neutron transport equation. Calculations are carried out for point isotropic monoenergic neutron sources of 1, 100, 500 kev, 1, 2, 5, and 14 Mev in an infinite atmosphere of air. Best available numerical values of the cross sections are used, and the effects of absorption, anisotropic angular distributions, and inelastic scattering are included. Distances out to 10 mean free paths are considered.
Investigations on Barium Ferrite Magnets
Authors: Sixtus K. J. , Kronenberg K. J. , Tenzer R. K.
Published: April 2005

Barium ferrite (BaO:6Fe2O3) has been investigated magnetically to test the predictions of fine particle theory in the region of grain sizes larger than the critical one for which no satisfactory theory exists as yet. Grain size and coercive force of polycrystalline magnets (nonoriented and crystal oriented) were closely related to sintering temperatures. A comparison of theoretical and observed temperature dependence of coercive force is made and shows a close fit when certain reasonable assumptions are made.

Susceptibilities showed values attributed to rotation of the magnetization vector for samples of high coercive force only (4000 oe), while wall movements contribute more or less to the susceptibility of all other samples.

Domain patterns show wall movements in applied fields on samples with particle thickness down to 10×10−4 cm. Patterns on grains below 5×10−4 cm thickness (IHC more than 2000 oe) indicate reversals of magnetization by the rotation process. On magnets of the transition particle size both processes can be observed side by side, the walls being less movable for higher coercive forces.
Monte Carlo Calculation of Noise Near the Potential Minimum of a High-Frequency Diode
Authors: Tien P. K. , Moshman J.
Published: April 2005

Noise near the potential-minimum of a high-frequency diode has been calculated in this paper using a high speed electronic, digital computer. Random numbers were generated and used to simulate the emission of electrons at the cathode. Electrons emitted were continuously fed into the calculating process and those collected on the anode or returned to the cathode were automatically erased. In this way the electron motions computed by numerical integration followed the actual operation of a one-dimensional space-charge limited diode.

The results of this paper are based upon data obtained in the course of 3000 unit time intervals. In each case current and velocity fluctuations near the potential minimum were computed. This basic information permitted the calculation of the reduction in noise current caused by space-charge smoothing. The results were then applied for a calculation of the minimum noise figure for microwave beam-type amplifiers and show a sharp minimum of less than 2 db around 2500 Mc and a maximum of about 7.5 db near 4000 Mc. At very low frequencies the noise figure is small and agrees with existing low-frequency theories. At very high frequencies it approaches the figure corresponding to full shot noise, namely 6.3 db. Within the accuracy of calculation, correlation between current and velocity fluctuations has not been found nor the smoothing in velocity fluctuation.
Kinematographic Study of Tensile Fracture in Polymers
Authors: Bueche A. M. , White A. V.
Published: April 2005

High speed motion pictures were taken of silicone rubber, irradiated polyethylene, Plexiglas II, and aluminum foil while they were being broken. Fractures started internally in some of the silicone samples but at the edges of all of the others. The rates of crack growth and the rates of retraction of the ends of the rubber samples were measured. The velocities with which the cracks grew were compared with the results of the theories of Poncelet, Yoffe, Mott, and Roberts and Wells. Their prediction, that the velocities should be about one half those of transverse waves in the media, was found to represent the data for materials with moduli differing by five decades. After fracture, the ends of the rubber samples contracted with velocities approximately equal to the velocities of longitudinal waves in these samples.
Secondary Waves of Electroluminescence
Authors: Haake C. H.
Published: April 2005

Secondary waves of electroluminescence exhibit specific trends with varying frequency and temperature. As has been assumed before, secondary waves are caused by effects of charge polarization inside the phosphor crystals; however, there has been no previous theoretical approach to this problem which leads to a description of the behavior of secondary waves with respect to frequency and temperature. An attempt has therefore been made to treat this phenomenon mathematically, using a simple model of charge polarization. During electroluminescent excitation conduction electrons are drawn to the anodic crystal parts where they become trapped. When the alternating field externally applied passes zero these electrons, under the influence of a polarization field, may return to luminescence centers and thus give rise to light emission. The return process depends on the trap depth, the temperature, the applied external field, and its frequency. This model can indeed describe the observed behavior, so that there seems to be little doubt as to the actual origin of secondary waves. As an interesting corollary of these considerations, the occurrence of secondary waves may be a means for determining electron trap depths and for detecting shallow traps where ``glow curves'' fail.
Network Synthesis for a Prescribed Impulse Response Using a Real-Part Approximation
Authors: Pucel Robert A.
Published: April 2005

A semigraphical scheme is presented for the synthesis of a linear, finite, discrete network, in which the desired network response is prescribed in the time domain. The method is based on the approximation of the real part of a desired system function by a sequence of impulses along a contour parallel to the imaginary axis of the complex-frequency plane. A simple scheme of error evaluation is proposed. Examples illustrating the synthesis procedure are also considered.
Influence of the Cathode Base on the Chemical Activation of Oxide Cathodes
Authors: Peterson R. W. , Anderson D. E. , Shepherd W. G.
Published: April 2005

By the use of radioactive tracer techniques it is shown that the strontium evolution from an oxide coated cathode provides a measure of the rate of reduction of the coating. For the cases of carbon, aluminum, manganese, and tungsten the results indicate that the rate of reduction of the coating is controlled by diffusion of the reducing agents from the base nickel. The rate at which common reducing agents (excluding carbon) reach the nickel-coating interface is proportional to t−½ for lifetimes up to 104 hours. For oxide coated cathodes operated without current drain the thermionic emission as measured by pulse means is observed to correlate with the rate of reduction of the coating. The development of thermionic activity can be understood in terms of a model in which the concentration of donors in the oxide particles is controlled by the surface concentration of the alkaline earth metals. This surface concentration is controlled by the rate of reduction of the coating, with the further postulate that there is a maximum effective surface concentration.
Permeation of Gases through Solids
Authors: Norton Francis J.
Published: April 2005

The permeation process consists of the steps: adsorption, solution, diffusion, and desorption. These are discussed for glasses, polymers, and metals. There are two generalizations: (1) All gases go through all polymers. (2) No rare gas permeates any metal. Criteria are given for measurements of the permeation process.

In glasses the permeation rate depends on atomic size and glass composition. Some special processes which may simulate permeation in vacuum devices are discussed: oxide dissociation, electrolysis in ceramic materials, nuclear reactions, and ionic impact.
Electron Microscopy of Aluminum Crystals Deformed at Various Temperatures
Authors: Noggle T. S. , Koehler J. S.
Published: April 2005

99.994% pure aluminum single crystals were deformed in tension at 4.2°K, 78°K, and 295°K. The deformation at 4.2°K produced fine slip, observed by electron microscopy, and gave rise to a linear stress strain curve. At 78°K at low strain one again observed fine slip and a linear stress strain curve; at large strains (resolved shear strain above about 0.25) a weak slip band structure developed progressively and the slope of the stress strain curve decreased. The stress strain curves were orientation dependent at all temperatures.
Flow in a Viscous Vortex
Authors: Pengelley C. Desmond
Published: April 2005

Equations have been derived for velocity, temperature, and pressure distribution in a two-dimensional compressible viscous vortex with a steady state component of radial flow. Radial velocity has been assumed small compared with the tangential component, and heat transfer has been neglected. The equations have been based upon the Navier-Stokes equation in its most general form, the First Law of Thermodynamics, and the Gas Laws. A reference radius has been defined where viscous stress is zero; from this, nondimensional forms have been set up and generalized charts prepared for ready visualization and numerical applications. Because of the classical concept of viscosity as used in the Navier-Stokes equation, results are strictly applicable to laminar flow only; a discussion is presented regarding possible application to turbulent flow.
Nuclear Magnetic Resonance Studies of Polyethylene
Authors: Rempel R. C. , Weaver H. E. , Sands R. H. , Miller R. L.
Published: April 2005

Nuclear magnetic resonance (NMR) studies of three polyethylenes have been made over the temperature range −190°C to 120°C. Two components of the NMR line are observed—a narrow one identified with the ``amorphous'' regions and a broad one identified with the ``crystalline'' regions. Differences between polyethylenes in the shape of the narrow component are observed and discussed.

The variation of line width of the two components with temperature indicates two motional transitions occurring in the ``amorphous'' regions and one in the ``crystalline'' regions over the temperature range studied. Energies of activation inferred for one of the ``amorphous'' transitions agree well with those determined from melt viscosity studies implying a similarity of molecular processes controlling the two measurements and allowing an interpretation of the one observed by NMR to be made.

The NMR data are used to interpret (in terms of molecular motions) the three dispersion regions observed by dynamic mechanical measurements, with the following results: in the vicinity of −100°C, the amorphous regions undergo a transition involving mainly the onset of rotation of linear segments of the polymer chains. Between −35°C and 0°C (depending on the sample), the motion of amorphous chain segments containing branch points leads to a transition. In the neighborhood of 60–100°C (depending on the sample), there are the beginnings of observable motion of the chain segments within crystallites.

Using a new method of decomposing the NMR line into its two components (based on the experimental line shape at low temperatures), the relative intensities of the two components (hence, the relative amounts of fixed and moving nuclei) are determined. This ratio, previously held to be identical with the ``percentage crystallinity,'' is shown to be inconsistent with this view and to support the molecular interpretation presented.
Photoelastic Properties of Polystyrene in the Glassy State. I. Effect of Molecular Orientation
Authors: Andrews R. D. , Rudd J. F.
Published: April 2005

The effect of molecular orientation on the stress-optical coefficient of polystyrene at room temperature (24°C) was measured using polystyrene monofilaments with different degrees of orientation. High degrees of orientation were obtained by cold-stretching. The optical measurements were made using a polarizing microscope fitted with a Sénarmont compensator. The stress-optical coefficient shows a strong dependence on molecular orientation, using birefringence as the index of molecular orientation. The stress-optical coefficient appears to decrease linearly vs birefringence, from a value of about +10 brewsters at zero birefringence to a value of about +4 brewsters at −0.04 birefringence. The elastic (Young's) modulus was also measured (in tension) as a function of orientation, and was found to increase nonlinearly with orientation (from 4.3×105 psi at zero birefringence to 6.1×105 psi at −0.04). A curve of strain-optical coefficient vs orientation was obtained by multiplying stress-optical and modulus values; this decreases nonlinearly and to a somewhat lesser extent than the stress-optical curve (from about +0.03 at zero birefringence to +0.017 at −0.04). The significance of these constants in photoelastic experiments is discussed.
Kinetics of Spherulite Growth in High Polymers
Authors: Burnett Bruce B. , McDevit W. F.
Published: April 2005

Spherulite growth rates have been measured in two polyamides, 66 and 6 nylon, at temperatures ranging from 38 to 141° below the melting points using a moving photomicrographic technique. At constant temperature, the spherulite radius increases at a constant rate. This isothermal growth rate constant is temperature dependent, having low values just below the melting point, passing through a maximum on further supercooling and decreasing to negligible values at room temperature. These facts indicate that spherulite growth is not a diffusion controlled process. A reasonable interpretation of the data has been obtained using the concept of growth by two-dimensional surface nucleation. A theoretical expression for the temperature dependence of the growth rate based on this concept has given good agreement with the experimentally determined values.
Lattice Energy of Crystalline Polyethylene
Authors: Billmeyer Fred W.
Published: April 2005

The heat of sublimation of linear paraffin chains from the crystalline form to the gas at 0°K is calculated from heats of fusion, heats of vaporization, and heat capacities of solid, liquid, and gaseous hydrocarbons. The heat of sublimation, which is defined as the lattice energy of the crystalline phase of linear polyethylene, is 1.84 kcal/mole of CH2 groups. The heat of fusion of crystalline linear polyethylene is 0.922 kcal/mole of CH2 groups.
Effect of Irradiation On Dynamic Mechanical Properties of 6–6 Nylon
Authors: Deeley C. W. , Woodward A. E. , Sauer J. A.
Published: April 2005

Measurements of elastic modulus and mechanical loss at audio-frequencies have been obtained on irradiated and nonirradiated specimens of polyhexamethylene adipamide over a broad temperature range extending from 80°K to 600°K. The irradiations were carried out at the Brookhaven and Penn State Reactors. The internal friction spectrum of unirradiated nylon 6–6 contains at least four peaks corresponding to different mechanisms being invoked as the temperature is raised. With irradiation doses from 0.3×1018 nvt to 5.5×1018 nvt, significant changes in the dispersion regions occur. At temperatures above the main softening region, an increase in modulus with temperature is found. This is evidence of rubber-like behavior and is accounted for by the introduction of cross-links resulting from ionization and free radical formation produced by the irradiation. At high irradiation doses the percent cross-linking appears to become independent of dose. The various effects found are discussed in terms of molecular forces and mobility of chain segments.
Experimental Gamma-Ray Collimator Sensitivity Patterns
Authors: Tomnovec F. M. , Mather R. L.
Published: April 2005

The spatial sensitivity pattern of a gamma-ray collimator and NaI scintillation detector was explored with small radiation sources of three gamma-ray energies (0.145 Mev, 1.12 Mev, 1.59 Mev). The collimator used was a cylindrical hole of ½ in. diam through 8 in. of lead. The results are compared with calculated patterns. The effects of penetration of the collimator edges are clearly shown.
Temperature-Dependent Equations of State of Solids
Authors: Gilvarry J. J.
Published: April 2005

An isothermal equation of state of a solid is considered, which contains as special cases the equations of Birch, Murnaghan, Bardeen, and others. The equation is generalized to arbitrary temperature by replacing two constants of the equation by temperature-dependent parameters, whose functional form is determined by considerations of thermodynamic consistency. The thermal properties of the solid implied by this equation of state are examined. It is shown that the generalized equation is consistent with the Mie-Grüneisen relation for the thermal pressure of the lattice, and that the corresponding Grüneisen parameter is only slightly dependent on temperature, in general. The form of the generalized equation of state at low temperature is exhibited as an explicit function of volume and temperature for a solid whose heat capacity obeys the Debye law. A comparison with pressure-volume data of Swenson for potassium at low temperatures shows excellent agreement of the generalized equation of state with experiment.
Reflection of Sound from a Surface of Saw-Tooth Profile
Authors: Proud J. M. , Tamarkin P. , Meecham W. C.
Published: April 2005

A variational method is used to calculate the energy diffracted into the various orders produced when a plane acoustic wave is incident on a periodic, pressure-release surface of saw-tooth shape. The results of companion experiments performed with a cork-covered surface, using techniques of underwater sound are also presented. The relative energies reflected in various orders are plotted as a function of the ratio of acoustic wavelength to spatial period of the surface for a range of angles of incidence. Theory and experiment agree within 10% for all angles of incidence examined and for a large part of the frequency range covered.
Electrical Conductivity of Plexiglas
Authors: Munick R. J.
Published: April 2005

The electrical conductivity of Plexiglas in an electric field of 2.6 kv/cm in the temperature range from 21° to 90°C was found to be represented by the sum of two exponentials, which have activation energies of 1.45 and 2.7 ev. At the higher temperatures the curves of current as a function of electric field strength from 2.6 to 29 kv/cm were resolved into the sum of a linear and an exponential term. The results suggest that ionic conduction dominates at low fields.
Fine Structure of Response Curves of Frequency Entrained Oscillations
Authors: Ludeke Carl A. , Blades John D.
Published: April 2005

By simulating with an electro-mechanical analog a forced van der Pol like system, it has been possible to observe some of the jump and hysteresis phenomena suggested by Cartwright. The dependence of entrainment band width on forcing amplitude, as suggested by Andronow and Witt, has also been observed.
Motion of an Arc in a Magnetic Field
Authors: Smith Charles G.
Published: April 2005

A magnetic field transverse to an arc tends to move the cathode spot in either the direction of the electromagnetic force (the Amperian sense) or in the opposite direction (the retrograde sense). The theory of A. E. Robson and A. von Engle assumes that an arc, bent over in the Amperian direction forms a loop in which the magnetic field of the arc opposes the applied field to yield the retrograde motion. Calculations herein presented indicate that the arc field is too weak to uphold the theory. Retrograde motion proceeds continuously against a blast of vapor, while Amperian motion proceeds in the direction of the blast and is often discontinuous. These phenomena are recalled in giving an alternative explanation of the data.

Examination of the ``ball of fire'' discharge, which can display retrograde motion, shows the excitation phenomena in the region between dark and bright plasma yields information about retrograde motion. Studies of the corresponding dark space and negative glow of an arc and a better knowledge of electron liberation at the cathode give promise of yielding information about the retrograde motion.
Dynamics of a Projectile Penetrating Sand. Part II
Authors: Allen William A. , Mayfield Earle B. , Morrison Harvey L.
Published: April 2005

Additional data are reported that confirm a theory presented in a previous paper for the penetration of a stable flat-nosed projectile in sand. The negative acceleration of the projectile can be expressed by the relations: −dv/dt=αv2, v0>v>vc; −dv/dt=βv2+γ, vc>v>0 where the coefficients α, β, γ are positive constants and v0 is the striking velocity. In the case where air is removed from the sand and the sand is loaded transverse to the trajectory by one atmosphere pressure, the coefficients α and β are characteristic of inelastic and elastic impact, respectively, where the flow process is regarded as Newtonian. An additional experiment has been performed where quartz powder produced by impact is plotted as a function of initial projectile energy. Although the powder production curve can be represented roughly as a straight line through the origin, there are small discontinuities in slope corresponding to the critical velocity v=vc. The velocity of sound in sand has been measured under the conditions of the experiments. Loading increases the velocity of sound markedly but has little effect on the critical velocity vc.
High-Speed Microwave Switching of Semiconductors
Authors: Garver R. V. , Spencer E. G. , LeCraw R. C.
Published: April 2005

The high-speed microwave semiconductor switch, employing an n-type germanium diode, has been further investigated to determine the ultimate switching speed. Data are presented which show that pulse rise and decay times are as fast as 3 mμsec. This limit is imposed by the capacitances and inductances of the equipment and is not intrinsic to the germanium diode. The ultimate rise and decay times are determined by relaxation processes in the germanium, and are expected to be faster than 1 mμsec.

Two switching pulses of variable spacing in time were employed to show that there are no essential residual processes in the germanium following the application of a pulse. Since there is then no measured dead time of switching, the pulse-repetition rate is limited by the rise times and decay times.

Measurements have been made on a series of semiconductor switches using different concentrations of donors. As the concentration is decreased, avalanche breakdown occurs at higher negative voltages which allows switching of higher microwave powers. Successful operation has been obtained with microwave powers as high as one watt impinging upon the semiconductor switch. In general, rise and decay times tend to increase as donors decrease. Thus, rise times and decay times of 10 mμsec were obtained at one watt of microwave power.
Simple Geometric Model for the Effect of Porosity on Material Constants
Authors: Euler Ferdinand
Published: April 2005

The effect of porosity on several material constants can be described by three types of empirical functions. One of these features linear increase from zero to unity of the relative bulk material constant when the relative density increases from π/6 to 1. An almost identical function results from application of a theoretical model with the following properties.

(1) The porous compact is divided into two systems: first, isolated pores in a continuous solid matrix; second, solid grains mixed with continuous voids.

(2) The geometry of both systems is assumed to be a cubic array of equal spheres. With this simplification, the relative bulk material constants of each system are calculated as functions of the relative density. The equations obtained are valid for those material constants which are ratios of corresponding fluxes and forces in the sense defined by Maxwell (e.g., the electric conductivity).

(3) Weight factors for the presence of either system are introduced.

(4) The weight factor for the system of isolated pores is assumed equal to the relative bulk material constant of the total compact for all values of relative density.

The implications of this model to the mechanism of sintering are discussed.
Effect of Oxygen on Etch-Pit Formation in Silicon
Authors: Logan R. A. , Peters A. J.
Published: April 2005

The etching behavior of as-grown and heat-treated silicon crystals has been studied using an etching procedure developed by Dash. The rate of chemical etching of silicon was found to decrease with increased concentration of dissolved oxygen. This effect impedes the formation of etch-pits. To explain the observed etching behavior after heat treatment it is necessary to assume that the rate of chemical etching increases with increased amount of precipitated oxygen in pulled crystals.