bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Growth Imperfections on the Strength of Aluminum Single Crystals
Authors: Lauriente Mike , Pond Robert B.
Published: April 2005

The effect of growth imperfections on the critical resolved shear stress is investigated for high-purity (99.99+%) aluminum single crystals as compared with strain-anneal crystals. An apparatus for measuring strains of the order of 0.2 μin. is described. Using etch pits as an index, the critical resolved shear stress is found to be inversely proportional to the growth imperfections for a range of etch pit density ρ of 5 to 25×104/cm2. An elastic range is demonstrated; and prior plastic deformation is found to lower Young's modulus. The results are interpreted in terms of dislocation theory.
Observations of Dislocation Glide and Climb in Lithium Fluoride Crystals
Authors: Gilman J. J. , Johnston W. G.
Published: April 2005

It is shown that reagent CP-4 plus ferric ions can be used to detect the positions of dislocations in LiF crystals. The technique is highly selective and both edge and screw (110) [11̄0] dislocations can be detected and distinguished. A double etching method is used to observe, for the first time, the glide and climb of individual dislocations in LiF.
Neutron Diffraction Study of Titanium-Zirconium System
Authors: Sidhu S. S. , Heaton LeRoy , Zauberis D. D. , Campos F. P.
Published: April 2005

Titanium and zirconium alloy system consists of a continuous series of random substitutional solid solutions of solvent and solute atoms. Titanium scatters thermal neutrons in the opposite phase from those scattered by zirconium, the scattering amplitudes being: bTi=−0.38×10−12 cm and bZr=0.62×10−12 cm. An alloy containing 62 atomic percent titanium and 38 atomic percent zirconium is developed that gives no coherent scattering reflections in its neutron diffraction pattern, and is extremely useful in constructing devices in which scattering of thermal neutrons is not desired. Based on negative and positive scattering amplitudes of different isotopes of the same element for thermal neutrons, development of isotopic alloys is suggested.
Effect of Pile Irradiation on the Dielectric Constant of Ceramic BaTiO3
Authors: Rogers F. T.
Published: April 2005

A specimen of ceramic BaTiO3, made of reagent-grade materials at a calcination temperature of 1250°C, was exposed to pile irradiation in the amount of nvt=2.1·1020 at Hanford, Washington. The original ceramic showed a peak in the dielectric constant versus temperature curve usually ascribed to ferroelectricity. After irradiation this peak essentially disappeared, and the dielectric constant was reduced to a nearly constant value over the temperature range 30°C to 140°C. This reduced value is about half of the room-temperature dielectric constant as determined before irradiation. Evidence is mentioned for a small residual peak in the dielectric constant of the irradiated specimen.
Measurement of Wall Shearing Stress in the Boundary Layer by Means of an Evaporating Liquid Film
Authors: Murphy James S. , Smith A. M. O.
Published: April 2005

A mass transfer method for measurement of local wall shear stress in laminar and turbulent flow is presented. A thin film of a suitable fluid is coated on the model surface and evaporation rate determined from film thickness measurements using light interference fringes. Application of the method to wall stress measurements in flat plate flow is presented and shows good correlation with theory. In the present state of development, the technique may be used for determining the shear stress distribution over a surface relative to the value at some reference station. The absolute magnitude of the shear stress at the reference station must be found by another method. In this respect the mass transfer method is similar to the interferometric method of measuring density distributions in high-speed flows.
Dynamic Properties of Various Rubbers at High Frequencies
Authors: Cunningham J. R. , Ivey D. G.
Published: April 2005

The shear wave velocity and attenuation of GR-S, Butyl, Hevea, Hycar, and Paracril rubbers have been measured in the frequency range 0.2–7 Mc/sec and the temperature range −60°C to 20°C. To minimize errors arising from interfaces in the acoustic path, a double path technique was used. By combining the shear wave data with bulk wave data the dynamic shear, bulk, and Young's moduli, and their associated viscosities, were calculated. The results were coupled with low-frequency Young's modulus data on the same materials to give information over many decades of logarithmic frequency, and from this the distribution of relaxation times was determined.

To a fair approximation, in the range investigated, it was found that the real and imaginary parts of the dynamic Young's modulus could be taken as equal to three times the corresponding values of the dynamic shear modulus. It was found that the classical Stokes assumption, that the bulk viscosity is negligible in comparison to the shear viscosity, was reasonable for some of the rubbers, but not for all of them.
Effect of Light Scattering upon the Refractive Index of Dispersed Colloidal Spheres
Authors: Nakagaki Masayuki , Heller Wilfried
Published: April 2005

The Zimm-Dandliker equation on the effect of light scattering upon the refractive index of colloidal dispersions of spheres is found to be in good agreement with experimental facts. It is transformed to give a new mixture rule from which the refractive index of colloidal spheres, to be expected in absence of light scattering, can be calculated. The latter is needed for particle size determinations in colloidal solutions from light-scattering measurements to be evaluated on the basis of the Mie theory. For the same purpose, a graphical method is worked out which is less time consuming and yields very accurate results. The graphical method allows one to obtain simultaneously both the refractive index and the diameter of the particles. The method is tested successfully against data obtained by alternate procedures used heretofore.
Flow Birefringence and Stress
Authors: Philippoff Wladimir
Published: April 2005

Simultaneous measurements of flow birefringence, shear and normal stresses on a 15% solution of polyisobutylene in decalin were performed. They proved that the extinction angle measured in birefringence is identical to the orientation of the principal tensile stress calculated from the normal stress measurements and that the birefringence was proportional to the difference in principal stresses in flow. A detailed discussion of the significance of this result is given with a possibility of a far-reaching generalization of the mechanical behavior of high polymer solutions.
Birefringence Changes During Retraction of Oriented Polystyrene Monofilaments. I. Changes of Average Birefringence
Authors: Andrews R. D. , Rudd J. F.
Published: April 2005

The changes in average birefringence during retraction have been measured at 85°C for four different oriented polystyrene monofilaments. The relationship between birefringence decay and length decrease is not linear: the birefringence decay is relatively more rapid than the length decrease, in all cases. Also, the birefringence-length relationship seems to be essentially independent of retraction temperature. Birefringence decay rate can be reduced by a factor of 1000 by not allowing the filament to retract. One of the filaments shows an interesting change in sign of the birefringence, from negative to positive, in the final stages of the retraction. The birefringence decay data for the four filaments could not be reduced to any universal curve by plotting either birefringence or relative birefringence against any simple functions of length or extension (all the filaments were made from the same polymer, so that a reduction to some such common basis should be possible). Analyzing the data in terms of a distribution of retardation times, by assuming that birefringence decay and length decrease are in some constant ratio for each retardation time (where the additional parameter, time, is introduced), also failed to reduce the data to a single common curve. Internal stress may be an essential parameter for a proper characterization of the birefringence.
Fabrication of Multiple Junctions in Semiconductors by Surface Melt and Diffusion in the Solid State
Authors: Lehovec K. , Levitas A.
Published: April 2005

Techniques are described for the preparation of multiple junction structures in semiconductors by solid state diffusion of impurities from a region of a doubly doped crystal into an adjacent region of different impurity concentrations. The change in impurity concentrations from one region to the other is achieved initially by surface melting and regrowth, and is later modified by diffusion. Conditions which must be imposed on the doping levels, segregation coefficients, and diffusion constants of the doping materials employed will be discussed. p-n-p, n-p-n, and n-p-n-p structures have been fabricated in germanium.
Electrical Resistances of Thin Metal Films before and after Artificial Aging by Heating
Authors: Belser Richard B.
Published: April 2005

The electrical resistances of thin films of 24 metals, deposited on glass substrates (near room temperature) by evaporation, sputtering, or electroplating, have been measured before and after artificial aging by heating in vacua. Reductions in resistance of 25 to 50% as a result of aging were commonly noted. Evaporated films were reduced from approximately 2ρb to 1.3ρb (resistivity of the bulk metal) and sputtered films from 4–10ρb to 1.5–1.8ρb. A preferred aging temperature, specific to each metal but influenced somewhat by film thickness, was noted. This temperature agreed closely with the temperature of recrystallization of the metal. Thin metal films, as usually deposited, appear to be in a state of strain not associated with the bulk metal as it crystallizes from the melt. The application of heat energy to the film promotes the removal of strains, occluded and adsorbed gas, and the growth of the crystallites of the film. These concurrent actions reduce the electrical resistance of films of 1000 A thickness to a value usually in the range 25–75% above that of the bulk metal.
Geometrical Representation of the Schrödinger Equation for Solving Maser Problems
Authors: Feynman Richard P. , Vernon Frank L. , Hellwarth Robert W.
Published: April 2005

A simple, rigorous geometrical representation for the Schrödinger equation is developed to describe the behavior of an ensemble of two quantum-level, noninteracting systems which are under the influence of a perturbation. In this case the Schrödinger equation may be written, after a suitable transformation, in the form of the real three-dimensional vector equation dr/dt=ω×r, where the components of the vector r uniquely determine ψ of a given system and the components of ω represent the perturbation. When magnetic interaction with a spin ½ system is under consideration, ``r'' space reduces to physical space. By analogy the techniques developed for analyzing the magnetic resonance precession model can be adapted for use in any two-level problems. The quantum-mechanical behavior of the state of a system under various different conditions is easily visualized by simply observing how r varies under the action of different types of ω. Such a picture can be used to advantage in analyzing various MASER-type devices such as amplifiers and oscillators. In the two illustrative examples given (the beam-type MASER and radiation damping) the application of the picture in determining the effect of the perturbing field on the molecules is shown and its interpretation for use in the complex Maxwell's equations to determine the reaction of the molecules back on the field is given.
Particle-Size Effects in Explosives at Finite and Infinite Diameters
Authors: Malin M. E. , Campbell A. W. , Mautz C. W.
Published: April 2005

The effect of particle-size variations on the detonation velocity of the two-component solid explosive, Composition B, has been studied at various diameters and shown to be important. An attempt has been made to apply the diameter-effect theory of Eyring and that of Jones to explain the experimental data, but without complete success.

Certain particle-size effects in Composition B have been shown to persist to infinite diameter, and a plausibility argument in terms of the Kirkwood-Wood theory has been offered.

The presence of large crystals in low-density RDX has been shown to lead to a ``super velocity'' which still prevails at infinite diameter. Experiments using large spheres of Composition B have been performed which also demonstrate a ``super velocity'' which may be related to the effect found in RDX.
Formation of High-Density Electron Beams
Authors: Brewer George R.
Published: April 2005

The physical principles underlying the design and performance of electron guns suitable for the generation of high-density electron beams (beam current density of the order of 200 amp/cm2) are discussed. Initiation of the flow of a cylindrical electron beam focused by a uniform magnetic field is described, with emphasis on the design of the electron gun. The principles underlying the Pierce design procedure for space-charge limited electron guns is treated, including the limitations and the modifications necessary when used for very high-density beams. Means are suggested for partial compensation of the electric field distortion due to the anode aperture of the gun. The effects on the beam and resulting limitations in gun design due to thermal velocities of emission are described.

The experimental techniques for study of gun and beam performance are described, together with some results of these studies. These techniques include detailed measurement of beam characteristics, such as current density and transverse velocity distributions, both with and without a magnetic field. These measurements illustrate a number of deviations of actual electron flow from that usually considered in the simple theories.
Effects of Size on the Microwave Properties of Ferrite Rods, Disks, and Spheres
Authors: Artman J. O.
Published: April 2005

The effects of sample size on the apparent properties of ferrites observed by microwave cavity perturbation methods are treated. Retardation effects associated with the propagation of electromagnetic waves in the specimen are considered. Results are given for the idealized cases of rods of infinite length and disks of infinite extent. Methods of adaptation to finite rods and disks are suggested. An approximate solution is given for the sphere which is in qualitative agreement with some aspects of the experimental observations. A formula relating the shift in resonance field to the sphere size is presented: HR−H0=4πMε·(16π2/45)(R/λ)2.
Semiempirical Determination of Mass Absorption Coefficients for the 5 to 50 Angstrom X-Ray Region
Authors: Henke Burton L. , White Richard , Lundberg Bruno
Published: April 2005

A semiempirical method for the determination of mass absorption coefficients for the very soft x-ray region of 5 to 50 A is described. A universal function for the absorption by K-shell electrons and another for absorption by L and extra-L shell electrons are given in table form to permit the calculation of mass absorption coefficients for elements of atomic number up to 36. Calculated and observed values from available absorption data are compared with those predicted by quantum theory. Tables are given for the mass absorption coefficients for nine useful wavelengths in the ultra-soft region, 8.34, 13.3, 17.6, 21.7, 23.7, 27.4, 31.6, 36.3, and 44 A.
Nuclear Magnetic Resonance, Radiation Damage, and Rigidity in Branched Polyethylene as a Function of Temperature
Authors: Fuschillo N. , Sauer J. A.
Published: April 2005

Molecular motions and microstructure are studied as a function of irradiation damage and temperature in branched polyethylene. The methods of proton magnetic resonance, specific volume and density percent crystallinity, mechanical rigidity and loss, and x-ray determined crystallinities are employed. The samples were subjected to irradiation doses ranging from 0 to 8.3×1018 nvt in the Brookhaven reactor. Significant changes in the proton resonance line shape at 295°K occur for an irradiation of 0.3×1018 nvt. Second moments and intensity ratios indicate that the first effect of irradiation on the line shape can be interpreted as due to the destruction of crystallinity or order. This effect however is offset at higher doses by the restrictive influence of radiation induced crosslinks on molecular chain motion. Estimates of the percent crosslinking aid in the interpretation of the temperature variation of proton resonance line shapes and allow some estimate to be made of the lengths of chain associated with a given type of molecular motion. Activation energies are calculated from NMR and mechanical loss data for these molecular motions.

With increasing temperature the proton resonance and mechanical properties are associated first with rotational oscillations, over energy barriers, of short segments (of the order four methylene groups in length) of a chain (activation energy ∼6 kcal/mole) and also with the γ peak of the mechanical loss data. At temperatures exceeding the ``glass transition temperature'' the molecular movements are also described by neo-Brownian diffusional motions involving chain lengths of about 10 methylene groups (activation energy ∼12 kcal/mole). These latter ``neo-Brownian'' motions are associated to some extent with the β peak of the mechanical loss data and probably also involve some branch point motion. The majority of the motion occurs principally in the amorphous regions of the branched polyethylene until temperatures above 290°K are reached and the microstructure begins to change due to the ``melting'' of crystallites.

The intensity ratio for the complex line shape exhibited by polyethylene at temperatures greater than 200°K are associated with the high-frequency rigidity of the sample.
Tridirectional X-Ray Patterns of Oriented Film at Wide and Small Angles
Authors: Statton W. O. , Godard Grace M.
Published: April 2005

Drawn, oriented film of polyethylene terephthalate was studied by means of an x-ray diffraction technique in which the x-ray beam was directed in three mutually perpendicular directions: (1) through the film, (2) and (3) in the plane of the film, parallel and normal to the direction of draw. Patterns were obtained in each of these directions for the diffractions occurring at both small and large angles. This combination of patterns provides a picture of the film's polymer texture with these parameters: size, orientation, and arrangement of crystallites; extent of amorphous material; shape of microvoids. In this film the crystallites have planar orientation and are 45 A wide in the plane. A long period of 125 A exists in the direction of draw and is comprised of 75-A crystallite length and 50-A amorphous material. There is evidence that the film is composed of lamellae about 60 A thick; these lamellae are stacked in a staggered arrangement such that the crystallites in one lamella are adjacent to the amorphous regions in the lamella below. The small angle diffraction evidence cannot be reconciled with the ``coiled ribbon'' arrangement recently proposed in the literature to explain off-meridional diffraction spots.
Temperature Consideration in Solar Battery Development
Authors: Halsted R. E.
Published: April 2005

Semiconductor materials of band gap appreciably greater than that of silicon may prove useful for photovoltaic solar energy converters operating at elevated temperatures. Such operation is of interest for applications where solar energy concentration can be employed to reduce the photovoltaic surface area required to produce a desired amount of electrical power.
Analysis of Multivelocity Electron Beams by the Density-Function Method
Authors: Siegman A. E.
Published: April 2005

Some mathematical techniques are presented which assist in the analysis of one-dimensional multivelocity accelerated electron streams by the density-function method. These techniques include methods for removing mathematical singularities from the equations. The correspondence between the density-function method and the usual single-velocity analysis is discussed; and a new definition of the equivalent ac voltage in terms of the density function is given. This definition is meaningful even for large velocity spread. The density-function method and the single-velocity theory agree for small velocity spread while, for a strongly multivelocity beam, no simple transmission-line type of equations are to be found. Because of the latter fact, a common assumption about the noise conservation properties of the low-voltage region of an electron gun is not valid, and the beam's ``noisiness'' is not invariant with distance in this region. These conclusions are verified by detailed noise calculations reported in an accompanying paper.
Density-Function Calculations of Noise Propagation on an Accelerated Multivelocity Electron Beam
Authors: Siegman A. E. , Watkins D. A. , Hsieh Hsung-Cheng
Published: April 2005

The propagation of noise current and voltage fluctuations through the multivelocity accelerating region immediately in front of the potential minimum has been calculated using the density-function method of analysis. Basic assumptions made include: (a) linearized one-dimensional analysis; (b) zero total ac current in the beam; (c) uncorrelated full shot noise in each velocity class at the minimum plane; (d) dc potential η(ξ) given by the Fry-Langmuir analysis. Starting at the minimum, the noise fluctuations were traced out towards positive ξ by a numerical forward-integration process using an IBM 650 electronic computer. Principal results of the computations are that Haus's noise parameters S and Π are found to vary significantly with distance between η=0 and η=4, contrary to previous assumption. The noise parameter S decreases to ∼0.7 of its initial value of kTc/2π, while the noise power Π rises from zero to ∼0.3 of the initial value of S. Exact results depend slightly on frequency. Beyond η=4 both noise parameters become invariant. The theoretical minimum noise figure of a beam type microwave amplifier, which is Fmin=1 +(2π/kT) (S-Π), is thus found to be reduced to ∼3½ db for a temperature-limited cathode instead of the commonly quoted value of 6½ db which is based on the values of S and Π at the cathode.
Characteristics of the Bayard-Alpert Ionization Gauge at Pressures above 10−5 mm Hg
Authors: Schulz G. J.
Published: April 2005

Bayard-Alpert ionization gauges were calibrated in the range from 10−5 to about 10−1 mm Hg for various gases. In this pressure range, it is necessary to operate with grid currents below 100 μa in order to minimize the effects of gauge pumping and to prevent space charge from affecting the operation of the gauge. The gauge becomes insensitive to pressure when the ion current reaches 20 to 30% of the electron current. However, linearity is preserved only up to an ion current of about two percent of the electron current. Some of the reasons for the high pressure behavior of the Bayard-Alpert gauge are discussed.
Effect of Irradiation on the Hole Lifetime of N-Type Germanium
Authors: Curtis O. L. , Cleland J. W. , Crawford J. H. , Pigg J. C.
Published: April 2005

The minority carrier lifetime of germanium is very sensitive to certain types of irradiation. The results of irradiating large single crystal samples of n-type germanium with fast neutrons and Co60 gamma rays are presented and discussed. Lifetime was determined from a transient measurement of the decay of holes following an injection pulse. The effect of initial carrier concentration has been considered. According to the James-Lark-Horovitz model, four energy levels are introduced by irradiation into the forbidden band of germanium, one above and three below the center of the band. Using the upper level, a one level recombination model serves to explain the experimental results approximately. The determination of the recombination level agrees well with the position of the first ionization level of the interstitial produced by irradiation at about 0.2 ev below the conduction band. On this basis, the effective cross section for hole capture by these recombination centers is found to be about 4×10−15 cm2 and 5×10−16 cm2 for neutron and gamma-irradiated germanium, respectively. A lower level may also be responsible for the recombination process.
Contribution to the Theory of the Contact between a Carbon Brush and a Copper Collector Ring
Authors: Holm Else
Published: April 2005

The main subject is the interpretation of the fluctuations, ΔU, (0.3 to 0.6 v), in the contact voltage U between a carbon brush sliding smoothly on a copper ring. A special method was used and proved very informative. Within a fraction of a second, voltage or current was varied from an initial value (often zero) to a higher value and back again. Thereby voltage vs current or time were registered by means of an oscilloscope. It is shown that the sudden negative ΔU's are essentially due to electrical breakdowns—frittings at about 1 v—of the collector films, which are necessary in order to let the current through. The proof is given with stationary as well as sliding contacts by comparing the features involved with those of model diagrams, the design of which is based on the concept of fritting. Besides typical frittings of the type studied earlier, the concept of widening the area of conducting spots (generated through the collector films) by frittings as the current is increased, has been worked out. It is shown that every fritting of the collector films leads to a metallic junction by proving that consecutive records with decreasing voltage exhibit the character prescribed by the electrical and thermal constants of the electrode material used.

Experimental proofs were obtained showing that ``frictional oxidation'' provided a noticeable contamination (of fritted spots) during one revolution between leaving the brush and meeting it again.
Steady-State Creep of Crystals
Authors: Weertman J.
Published: April 2005

An expression for the steady-state creep rate of crystals is derived for the case where dislocation climb is not rate controlling. Two rate-controlling processes are considered. In the first the dislocations are considered to move in a viscous manner, their velocity of motion being proportional to the force exerted on them. The second mechanism makes use of the Peierls stress. The Peierls stress mechanism can be used to explain the results of Gilman on creep by prismatic glide in high-purity zinc. At low stresses the analysis for both processes leads to a power law stress dependence for the creep rate. The value of the exponent of the stress is approximately equal to three.
Backscattering of 5–20 kev Electrons from Insulators and Metals
Authors: Holliday J. E. , Sternglass E. J.
Published: April 2005

Electron backscattering measurements were carried out on composite layers consisting of thin metal films deposited on base layers of widely different backscattering properties. At low primary energies the backscattered fraction η (energies >50 ev) is found to be characteristic of the surface film. When the electron energy is such that the range in the surface material is equal to twice its thickness, a marked change in η occurs. At sufficiently high energies, η approaches the value for the base layer. Measurements of η as a function of energy were made for layers of Al–Au, Al–Ag, and Al–C. These results led to a new method for measuring η for insulators using thin aluminum surface films (∼200 A) to avoid charging. Data on LiF, Zn3 (PO4)2, KCl, RbBr, and TlI above ∼5 kev indicated agreement with the known values for metals of the same average atomic number, demonstrating that backscattering in the kev range and above is an atomic characteristic independent of the crystal structure or the conduction properties of the solid.
Domain Effects in Polycrystalline Barium Titanate
Authors: Subbarao E. C. , McQuarrie M. C. , Buessem W. R.
Published: April 2005

Upon depoling ceramic barium titanate, up to 9% of the domains reorient by 90°, indicating that during poling at least this percentage of the domains was permanently reoriented by 90°. Ceramic barium titanate shows a strong anelastic effect in the ferroelectric state, presumably due to domain reorientations under stress. Application of tensile and compressive stresses causes up to 13% of the domains to change their orientation by 90°, but, unlike the electric case, no permenent domain reorientation is found. These domain switches are detected by x-ray intensity and strain measurements. The agreement between the percent domain switches computed from the x-ray data and that computed from the strain data is good in the case of mechanical compression, but not in the case of electrical and mechanical tension. In the latter case more domains appear to switch in the bulk than in the surface of the material. A space-charge effect at the surface of ferroelectric barium titanate is suggested as a reason for this anomaly. Experimental evidence of the effect of grinding, etching, and irradiation on the domain orientation in the surface layer of ceramic barium titanate is cited.
Theory of the Ferromagnetic Microwave Amplifier
Authors: Suhl H.
Published: April 2005

The theory of ferromagnetic microwave amplification is presented in detail. All three possible types of operation using, respectively, two electromagnetic cavity modes, two sample modes, and one sample and one cavity mode, are discussed. One especially simple case, that of a sphere in the first type of operation is treated separately. Thereafter all three cases are discussed in terms of scaler and vector potentials. An appendix deals with the gain-band-width problem and gives an expression for the equivalent ``negative Q'' of the sample.
Electron Multiplication Processes in High-Voltage Electrical Discharge in Vacuum
Authors: Bennett A. I.
Published: April 2005

The efficiency of a class of electron-multiplication processes previously considered to be possible initiators of high-voltage vacuum arcs has been studied as a function of applied voltage in the voltage range below about one hundred fifty kilovolts. This efficiency is found to be typically less than one part in ten thousand, in contrast to the unity or greater required for arc initiation by such processes. The variation of the efficiency with field is noted. The conclusion is drawn that this class of processes apparently plays no significant role in arc initiation, and the remaining possibilities are briefly discussed.
Ionization in the Trail of High-Velocity Pellets
Authors: Partridge William S. , Harris L. Dale
Published: April 2005

Aluminum, magnesium, and lithium-magnesium pellets were accelerated to velocities as high as 4.5 km/sec by means of an explosive. The ionization in the trails of these pellets was determined by measuring the reflection of a microwave signal from the trail. It was found that the ion density in the trail is an increasing function of the velocity and for the velocity range between 1 and 4.5 km/sec lies between 1010 and 1015 electrons per cm of path. It was observed that aluminum pellets do not produce ionization at velocities below approximately 2.9 km/sec, while magnesium leaves an ionized trail at velocities down to approximately 1.6 km/sec and lithium-magnesium alloy down to approximately 1.3 km/sec.
Study of Phase Transitions in WO3 with a High-Temperature X-Ray Diffractometer
Authors: Perri J. A. , Banks E. , Post B.
Published: April 2005

WO3 undergoes a phase transformation from monoclinic to orthorhombic at approximately 320°C and from orthorhombic to tetragonal at 720°C. A detailed study of the variation of the unit cell dimensions over the range from room temperature to 1000°C has been carried out using high-temperature x-ray diffraction techniques. Some unique features of the apparatus are described in this paper.

Between the 320°C and 720°C transformations, the a and c axes increase uniformly in length while the b axis decreases. There is a marked increase in the volume of the unit cell below the orthorhombic to tetragonal transformation; the volume decreases sharply in the transformation and resumes its ``normal'' increase above 720°C.
Solution of the Bloch Equations for Determination of Relaxation Times in Liquids
Authors: Hubbard P. S. , Rowland T. J.
Published: April 2005

A solution of the Bloch differential equations is given in which both audio modulation and linear variation of the external magnetic field are explicitly included. For the case of T1 approximately equal to T2 and (γH1)2T1T2»1, the solution assumes a simple form which agrees well with experiment. T1 can be determined by comparison of the predicted line shapes with those obtained experimentally.
Dimensional Changes Resulting from Dezincification of Alpha Brass
Authors: Cooley W. J. , Van Horn D. D.
Published: April 2005

Small sheet and wire samples of high purity 70–30 brass were dezincified in vacuo at various temperatures, and the dimensional changes were observed as a function of the amount of zinc removed. The fractional changes in the dimensions normal to the diffusion direction were comparable to the changes in the diffusion direction. The dimensional changes were directly proportional to the amount of zinc removed and were independent of the temperature. The observed dimensional changes are explained as a combination of a net loss of lattice sites from the sample and the substitution of vacancies for zinc atoms at some of the other lattice sites. From the observed dimensional changes can be calculated both the ratio of diffusivities of copper and zinc atoms in the lattice and the effective size of the vacancies introduced. The ratio DCu/DZn is found to be 0.0832, and the volume dilation (fractional expansion per lattice fraction vacancies introduced) is −0.120.
Time Lag between High-Speed Pellets and the Ionization in Their Trails
Authors: Davidson R. A. , Partridge W. S.
Published: April 2005

An investigation of the spatial relation between high-speed projectiles fired at velocities of from 1 to 2.5 km per sec shows that the ionization and light in their trail does not occur at a point along the projectile path at the same instant the projectile passes. The time lag has been measured by letting the projectile and ionization in its trail obstruct the transmission of microwaves through a short length of wave guide. The time lag between the pellet and the ionization was observed for magnesium, aluminum, and titanium projectiles, but attempts to obtain the same data for copper, steel, and zinc were unsuccessful because these materials did not seem to produce ionization in their flight at the velocities being investigated. Time lags of up to 1000 μsec were measured at the lower velocities for aluminum projectiles. At velocities of 2.5 km per sec no time lag was observed. That is, the ionization occurred immediately as the pellet passed. Measurements of the luminosity associated with these pellets by means of photocells indicated that the ionization and the luminous region occurred simultaneously. The variations of this time lag as a function of velocity is explained by some thermodynamic properties of the metal in the pellet.
Radiation Resulting from an Impulsive Current in a Vertical Antenna Placed on a Dielectric Ground
Authors: Pekeris C. L. , Alterman Z.
Published: April 2005

We consider the electromagnetic field generated by passing an impulsive current of the form of a delta function δ(t) through a vertical Dipole antenna placed on a dielectric ground. The problem is formulated in operational form, and the Hertzian potential Π is expressed as an integral over a Bessel function. This operational solution is then inverted, and the Hertzian potential Π(r,z,t) is expressed in terms of finite complex integrals over a fixed range. The integrals for Π were evaluated on the electronic computer of the Weizmann Institute, and the results for the case of a dielectric constant ε=9 are shown in Fig. 1. The field in the air starts with a finite value at the time of arrival of the wave front, and then increases in a monotone fashion towards the steady state value. In the ground, there is a cone of angle sin−1(1/ε) centered around the downward vertical, inside which the field starts again with a finite value and then decreases toward the steady state value. Outside this cone, the direct wave in the ground is preceded by a diffracted wave originating from secondary radiation emanating from the portion of the boundary where the air wave passed in advance of the ground wave. This diffracted wave starts with zero amplitude and increases thereafter, becoming logarithmically infinite at the time of arrival of the direct wave in the ground. After that the amplitude decreases continuously toward the steady-state value.
Absorption of Rayleigh Waves in Low-Loss Media
Authors: Press Frank , Healy John
Published: April 2005

Many materials are characterized by internal dissipation parameter 1/Q«1. An expression is derived for such media relating the Rayleigh wave absorption coefficient to compressional and shear wave absorption coefficients with the elastic velocities as parameters. Ultrasonic experiments are described in which the three absorption coefficients are measured in thin Plexiglas sheets. The theoretically derived expression satisfactorily relates the observed absorption coefficients.
Experimental Study of Electron Scattering in Electron Microscope Specimens
Authors: Hall C. E. , Inoue T.
Published: April 2005

Effective scattering cross sections for polystyrene in electron microscope specimens were measured through the microdensitometry of the images of polystyrene latex spheres recorded with an RCA Type EMU 3B electron microscope. Measurements were made at both 50 kv and 100 kv beam potential without an objective aperture, with a 40-μ aperture and with a 20-μ aperture. Cross sections per gram vary from 1.9 to 11×104 cm2/g. The results are consistent with previous experimental data and are in reasonable agreement with theoretical calculations.
Measurement of Minority Carrier Lifetimes with the Surface Photovoltage
Authors: Johnson E. O.
Published: April 2005

The surface photovoltage method uses the junction-like properties of a semiconductor surface as a means for studying the decay of excess carriers. No more than capacitive contact with the specimen is required to detect the surface photovoltage which, in the millivolt range, is a linear function of the excess carrier density. Theoretically, the surface method yields exactly the same carrier decay constant as the photoconductivity method when the lowest diffusion mode prevails in the specimen. This has been quantitatively confirmed for Ge: only qualitative confirmation has been made with Si.

For surfaces tending toward inversion, the surface method gives larger signals than the photoconductivity method, particularly for semiconductors with low intrinsic carrier density. On the other hand, for accumulation layer surfaces the surface method usually gives smaller output signals.
Electron Emission in Moderate Accelerating Fields
Authors: Juenker D. W.
Published: April 2005

Investigations of Schottky emission from metals, including some recent work, are summarized and discussed. The following are some of the conclusions: The surface barrier outside a uniform metal surface can be represented accurately by a mirror-image form for distances greater than about 20 A from the surface. Patch effects can be correlated to some extent with known surface properties. The dependence of photoelectric emission on applied field is in agreement with the Fowler theory adjusted for a Schottky-type field-dependent threshold. Periodic deviations from the thermionic Schottky effect are in full agreement with the mirror-image model for the extra-surface barrier, and can be used in determining the barrier form in the immediate vicinity of the emitter surface.
Transmission of Electrons through Metal Surfaces
Authors: Good R. H.
Published: April 2005

This paper is a review of recent developments in the theory of electron emission from metals. The main subjects discussed are the periodic deviations in the Schottky effect and the transition between thermionic and field emission. The indications are that each of these phenomena can be understood in terms of the free electron model for the metal and the transmission of the electrons through the image force barrier at the metal surface.
Effect of Heat Treatment upon the Electrical Properties of Silicon Crystals
Authors: Fuller C. S. , Logan R. A.
Published: April 2005

Studies have been made of the process in which donors are introduced into silicon by heating in the temperature range 300°–500°C and are caused to disappear on heating at higher temperature. This phenomena is shown to depend on the conditions of growth and the heat-treatment history of the crystal. Evidence is summarized which shows that oxygen is the impurity from which the donors are formed. The characteristics of the processes involved are described and possible mechanisms are discussed.
Explosive Induced Shock Waves. Part I. Plane Shock Waves
Authors: Drummond William E.
Published: April 2005

The explosive production of plane shock waves in solids is analyzed in the approximation that third and higher order terms in the shock strength can be neglected, and a procedure is developed for calculating the attenutation of the shocks. Application is made to the problem of determining the equation of state of the burned explosive gas.
Junction of Smooth Flared Wave Guides
Authors: Leonard D. J. , Yen J. L.
Published: April 2005

Stevenson's general theory of electromagnetic horns or flared wave guides, which is valid only for geometrical configurations whose cross sections are continuous along the direction of propagation together with their first and second derivatives, is generalized to include sudden jumps in the first derivatives of the cross sections. Thus the junction of wave guides with different flares and of arbitrary cross sections can be treated, provided that at the junction plane the cross sections on the two sides are identical. General expressions are derived for the reflection and transmission coefficients correct up to the second order in flare angle. Explicit results for a few configurations of practical interests are derived, including some second-order ones. In cases where special theories exist, comparisons are made with favorable results. In addition, an experimental check is performed.
Some New Aspects of the Reflection of Electromagnetic Waves on a Rough Surface
Authors: Biot M. A.
Published: April 2005

The reflection of a plane-electromagnetic wave from a rough perfect conductor is investigated. The roughness is represented by hemispherical bosses whose radii and mutual distances are small relative to the wavelength. This problem is solved taking into account the electromagnetic interaction of the bosses. Aside from throwing some light on the limitations of approximate methods, the present solution reveals some effects not known before. For grazing incidence and vertical polarization the interaction has a drastic influence in that it causes a complete phase reversal of the reflected wave, near a 45 degree incidence the influence of the roughness vanishes. These effects do not occur for horizontal polarization. An approximate treatment for the case of the imperfect conductor is indicated. The analogous case for the acoustic wave is also developed and shows similar behavior. The effect of the roughness is shown to be equivalent to a boundary condition for the wave equation. Extension of the method to a more general type of roughness, and to the case of statistical and asymmetric shapes and distributions, is briefly discussed.
Emissivities of Metallic Surfaces at 76°K
Authors: Fulk M. M. , Reynolds M. M.
Published: April 2005

Heat transport by radiation between surfaces at 300°K and 76°K was measured to evaluate the effective emissivities of a number of technical grade or commercially available metals with unknown metallurgical history. The surface with the lowest total hemispherical emissivity was an unbuffed silver-plated surface. It was found that the emissivity of surfaces was lowest when used without any mechanical working and that the ability to absorb radiant energy varied with the length of time the surface was kept cold, even at a pressure less than 10−6 mm Hg, indicating surface contamination by residual gases.
On the Mechanism of Operation of the Barium Aluminate Impregnated Cathode
Authors: Rittner E. S. , Rutledge W. C. , Ahlert R. H.
Published: April 2005

Emission and evaporation characteristics of a porous tungsten cathode impregnated with the composition 5BaO·2Al2O3 are presented and are interpreted in terms of the cathode mechanism. Barium necessary for activation is generated by the reaction, 23 Ba3Al2O6+13 W=13 BaWO4+23 BaAl2O4+Ba,and is transported through partially clogged pores, the length of which increases with time, predominantly via Knudsen flow. During transport, oxygen is acquired from the tungsten, leading to a substantial content of BaO in the evaporant. The BaAl2O4 component of the impregnant is inert. Emission is substantially lower than that of an L cathode, presumably because of release of a poisoning agent accompanying the activator.
Drift Mobility Measurements
Authors: Green Milton
Published: April 2005

Measurements of drift mobility have been made by observing the transit time t of a pulse of charge carriers over the distance x between the point of photoinjection and a ``point of detection.'' The detector point may be a reverse biased junction, a constriction in the cross-sectional area, a point contact electrode, or other electrically indicating semiconductor construction. The arrival of the injected pulse at the detector results in a relatively large change in the conductance of the specimen. A signal taken from a load resistor in series with the sample is observed on the CRO. The time t is plotted against x. The reciprocal slope of the curve gives pulse drift velocity which when divided by the field strength E(x) gives the corresponding mobility μ(x). For a junction, electron mobility is determined by injection in the p region; hole mobility is determined by injection in the n region.
Fields in Gap-Excited Rectangular Ducts
Authors: Van Bladel J.
Published: April 2005

The electromagnetic field in a rectangular wave guide, cut in two by a plane perpendicular to its longitudinal axis, is investigated. A voltage applied across the two halves of the guide generates the field structure, which is analyzed for several values of the frequency (between zero and cutoff) and of the aspect ratio of the cross section. The problem is of interest for the design of particle accelerators.
Calculation of Energy Dissipation by Gamma Radiation near the Interface between Two Media
Authors: Berger Martin J.
Published: April 2005

A Monte Carlo calculation was made of the energy dissipation by gamma radiation in a medium with the scattering properties of water which consists of two semi-infinite regions, one of which is much denser than the other. The calculations are for a 1.28-Mev point-isotropic source at or near the boundary plane separating the two regions. The results are presented in terms of boundary correction factors which express the change of energy dissipation compared to that prevailing at the same location in a medium of uniform density. The analysis of the results leads to the conclusion that the boundary effect is rather insensitive to the atomic number of the medium, and is mainly a function of the density change. The Monte Carlo results are in good agreement with an experiment of Soole on the propagation of radiation in the air above the ground, and an experiment by Titus on the dose distribution in iron.