bluuebunny/crossref_metadata_2025 huggingface dataset:
Statistical Analysis of Thermal Shock in Disks (Flat Faces Insulated)
Authors: Wilson Fred L.
Published: February 2004

A statistical analysis of failure of brittle materials subjected to a thermal shock by cooling is made. A thin circular disk with the flat faces insulated is used in the analysis. Numerical results are given for the tangential stress in the disk as a function of time and radial coordinate. The probability of fracture is defined relative to the volume under stress. Numerical results are obtained for the probability of fracture as a function of time. It is found that this probability is maximum for θ=0.0400 (θ is dimensionless time). From this analysis it is shown that the thermal shock resistance is a function of the geometry of the solid as well as other mechanical properties.
An Analysis of Total Gamma-Ray Cross Sections in Al, Cu, and Pb
Authors: Parthasaradhi K.
Published: February 2004

Experimental gamma-ray cross sections in the energy region 145–662 keV, in the elements Al, Cu, and Pb are evolved utilizing most of the available experimental data with suitable errors attached to them on a statistical basis. Agreement is observed with the theoretical total gamma-ray cross sections within the range of errors. With these values using the ``subtraction technique,'' studies are made on (a) photoelectric cross sections, (b) scattering cross sections, and (c) S(q, Z) function. Within the range of errors, agreement is observed between theory and experiment, deferring the existing discrepancies in this region and in these elements. A systematic measurement of total gamma-ray cross sections is suggested, so that there should be repeatability of the experimental results by any experimenter within the range of specified accuracy to draw better conclusions on the existing discrepancies between theory and experiment in the region and in these elements.
Fluorescence Corrections to X-Ray Absorption in a Sphere
Authors: Veigele Wm. J. , Balogh J.
Published: February 2004

Photoelectric absorption or absorption resulting from incoherent scattering of x rays may produce secondary (fluorescent) radiation which, by escaping the absorbing material, will reduce the actual energy absorbed. This is described by reductions in linear photoelectric and incoherent scattering absorption coefficients which are functions of the incident photon energy only. For fluorescent radiation which does not escape the absorbing material, additional energy- and geometry-dependent corrections are required. These corrections are derived for a sphere. Values are calculated for a gold sphere of 0.1-cm diam, and the energy- and geometry-dependent correction terms are compared.
Electron-Microprobe Determination of the Angular Distribution of Sputtered Aluminum Atoms
Authors: Hasseltine E. H. , Olson N. Thomas , Smith Harold P.
Published: February 2004

A technique for the determination of relative surface densities of very thin films with an electron microprobe was developed and applied to the measurement of the angular distrubution of aluminum atoms sputtered from a monocrystalline aluminum target by 5–10 keV cesium ions. In all measurements the ion beam was normal to the target surface and the (100) crystallographic plane. Peaks in the distribution were noted at polar angles to the incident beam of 27° and 45°. The distribution exhibited no temperature dependence between 77° and 475°K.
Microdeformation of Solids
Authors: Gane N. , Bowden F. P.
Published: February 2004

A technique is described for observing and measuring the deformation of solids on a very small scale. A very fine stylus (approx 1000 Å in diameter) is pressed against the surface of a metal crystal with a load which can be as small as 10−4 g, and the deformation observed simultaneously by performing the experiment in a scanning electron microscope. Measurements were made on crystals of gold, copper, and aluminium. The behavior under these conditions of microdeformation was unusual in that no penetration occured until a critical load was reached. This critical load was frequently very high and corresponded to a shear strength which approached the theoretical shear strength of metals. Microfriction experiments could also be performed by allowing the stylus to slide over the crystal and the nature of the surface deformation could be examined during the sliding process.
Effects of Diffusion and Thermal Generation on Double Injection in Semiconductors
Authors: Baron R.
Published: February 2004

The theoretical treatment of the double-injection semiconductor regime has been extended to include first diffusion and then both diffusion and thermal generation. When only diffusion is included, the results parallel earlier results for the insulator regime. Large deviations from the simple Lampert theory are found even when the sample length L is as great as 50 times the ambipolar diffusion length La. The electric field distribution is characterized by exponentially increasing regions from the boundaries in which ε∝ exp |x/La|, merging into a central region which approximates the Lampert distribution ε∝(x—x0)1/2. The current—voltage characteristic approximately follows a I∝V2+s law, where s is a monotonically increasing function of La/L, the magnitude of the current being larger than predicted by Lampert. The inclusion of thermal generation leads to a very large transition region between the Ohmic and high-level regimes. For values of the ratio τl/τ≳10 between low-level and high-level lifetimes, this region extends over currents from 10-2-106 times the transition current between the Ohmic and high-level regimes. A portion of this transition region (for τl/τ≳1) has an almost exact I∝V2 current—voltage characteristic over about two orders of magnitude of current, which may be easily mistaken for high-level behavior. In this region the effective-length approximation has its greatest validity, current being the Lampert expression times (L/Leff)3, where Leff=L—Q(2La), and Q is independent of I and is only a slowly varying function of L/La. Parallel results were found for the inclusion of both diffusion and thermal generation into the insulator regime.
Surface-Barrier Diodes on Silicon Carbide
Authors: Hagen S. H.
Published: February 2004

Metal—semiconductor Schottky barrier contacts on SiC have been made both by cleaving single crystals of SiC (6H and 15R polytype) in ultrahigh vacuum in a stream of evaporating metal, and by evaporating metal onto etched surfaces. Results of capacitance and photoresponse measurements on n-type and p-type samples are presented. The barrier height on n-type samples is 1.45(±0.10) eV, independent of the work function of the metals (Au, Ag, Al). Nearly the same value is found for Al contacts on p-type SiC. When Au contacts are used, the barriers on heavily doped p-type crystals spread from 0.90–1.25 eV. The results for the purer n-type samples show that the Fermi level at the interface is fixed by surface states at the middle of the energy gap.
Computer Simulation of Field-Ion Microscopy of Interstitial Solid Solutions
Authors: Perry A. J.
Published: February 2004

The distribution of atomic bonding in computer-simulated field-ion images of interstitial solid solutions has been determined. The consequences of relaxation of the surface interstitial atoms are discussed in terms of the thin shell model of Moore and the bond-number criterion introduced by Perry and Brandon.
Thermally Activated Dislocation Depinning in Dilute Copper Alloys
Authors: Saul Robert H. , Bauer Charles L.
Published: February 2004

Internal friction and Young's modulus measurements have been performed on a series of dilute copper—silicon, copper—germanium, and copper—tin alloys at temperatures ranging from 4° to 300°K in order to determine the extent of thermally activated dislocation depinning from solute atoms. Specimens are in the form of singel-crystal bars, and are excited piezoelectrically in their fundamental longitudinal mode of vibration at 80 kHz.

For temperatures in excess of 180°K, the amplitude-dependent internal friction is characterized by an Arrhenius temperature dependence with an activation energy that varies linearly with the stress amplitude. A low-temperature modification of the Granato—Lücke theory accounts for the temperature dependence of the internal friction below about 120°K; however, the stress dependence is contradictory to that predicted theoretically. In general, thermal depinning is enhanced at high temperatures and stress levels, and in crystals containing long dislocation segment lengths and solute atoms of low pinning strength.
A Moments Method for Describing the Diffusion of Radiation from a Cavity. II
Authors: Pomraning G. C.
Published: February 2004

In an earlier paper the diffusion of radiation from a cavity was treated in the case that the transport of energy is purely radiative and the radiation mean free path in the cavity is infinite. In this paper we reconsider the same problem allowing for a finite mean free path in the cavity. For short times this problem admits a similarity transformation and the resulting equations are solved by a combination of series expansion and perturbation theory methods. Comparison with exact numerical results in special cases shows that a second-order calculation gives quite good accuracy. These short-time results, together with the known long-time results, are incorporated into a moments-method solution of the cavity problem valid for all times. Typical numerical results are presented which confirm the expectation that the improved model presented here differs from the earlier model mainly in its predictions of the short-time characteristics of the solution.
Perturbations of Microwave Cavity Fields by Time-Varying Xenon Laser Discharges
Authors: Weaver L. A. , Freiberg R. J.
Published: February 2004

The effects of a time-varying complex dielectric constant upon the resonant characteristics of a cylindrical microwave cavity are presented. The cavity resonance equations are developed to consider the influence of small periodic changes in resonant frequency, bandwidth, and cavity-coupling coefficient upon the microwave power density within the cavity as a function of the probing microwave frequency. Expressions are derived which enable the separate contributions of periodic changes in cavity power density to be extracted from measurements at several microwave frequencies. It is shown that for high-Q cavities, variations in the sampled microwave cavity fields are due predominantly to shifts in the cavity resonant frequency. By repetitively interrupting the mirror cavity of a 3.51-μ xenon laser with a mechanical chopping wheel, very small periodic changes are induced in the electron density and collision frequency of the xenon dc discharge due to changes in the laser field strength. The resultant changes in microwave power level within a cylindrical cavity enclosing the discharge are measured as a function of probing frequency and compared with theoretical values, yielding excellent agreement for high-Q cavity conditions. Where cavity loading severely degrades the Q, good agreement is obtained within the cavity half-power frequencies. A microwave-frequency compensation technique is employed which permits accurate direct measurement of small electron-number density changes (Δne/ne∼3×10-5) along the discharge-tube length.
Deposition of Permalloy with Varying Degrees of Anisotropy
Authors: Landler P. F. J.
Published: February 2004

Some of the physical properties of 81/19 Permalloy films with different degrees of uniaxial anisotropy have been studied. Such films were produced by vacuum deposition in rotating magnetic fields with varying ellipticity, keeping all other deposition parameters constant during one test series. Substrate temperatures were 300°, 200°, 100°C, and room temperature. Explanations for the observed dependence of angular anisotropy dispersion and easy-axis coercivity on uniaxial anisotropy and substrate temperature are presented.
Critical Analysis of the Theory of the Double Cantilever Method of Measuring Fracture-Surface Energies
Authors: Wiederhorn S. M. , Shorb A. M. , Moses R. L.
Published: February 2004

This paper presents a critical discussion of the double cantilever method of measuring fracture-surface energies. It was found that the equation developed by Gillis and Gilman is valid for crack lengths greater than 1.5 times the crack arm height. The constants in this equation were evaluated and were found to be practically independent of the elastic constants of the material for which they were evaluated, suggesting that the equation could be used on any material. The Gilman and Gillis approach to the double cantilever problem was found to be consistent with the approach used by Gross and Srawley.
Optical Properties of Tellurium as an Isoelectronic Trap in Cadmium Sulfide
Authors: Cuthbert J. D. , Thomas D. G.
Published: February 2004

Optical fluorescence and absorption associated with tellurium, an isoelectronic trap in CdS, are described. At low temperatures two fluorescence bands can appear: one, with a peak near 6000 Å, occurs in lightly doped crystals containing less than 1019 Te atoms/cm3; the other, with a peak near 7300 Å, occurs in more heavily doped crystals. The temperature dependencies of the fluorescence decay times of both bands were measured and compared with various models for the recombination mechanisms. It is concluded that the 6000-Å band arises from bound hole-electron recombination at isolated tellurium atoms on sulfur sites, while the 7300-Å band is probably associated with recombination at pairs of tellurium atoms on nearest neighbor sulfur sites. At room temperature, the quantum efficiency for electron-beam excited fluorescence of of 7300-Å band can be near unity. The reasons for the high efficiency are discussed.
Influence of Dielectric Films on the Resistance of Vacuum-Deposited Chromium Films
Authors: Milgram Alvin A. , Lu Chih-shun
Published: February 2004

The resistance of vacuum-deposited chromium films was found to decrease when over-coated with insulating films. The cause of this effect was investigated. It was shown that the effect could be explained as being due to a change in the surface tension of the metallic film. The experimental results are in agreement with this concept.
Structural Characterization of and Phase Separation in Vanadate Glasses
Authors: Anderson Gordon Wood , Luehrs Fred U.
Published: February 2004

Structural characterization of vanadate glasses, an essential but often neglected step in studying physical properties of nonperiodic solids, has been carried out in the composition range 70.0–87.5 mole % V2O5, the remainder being P2O5, by bright-field, dark-field, and diffraction electron microscopy. Replicas and powdered chips of bulk samples gave inconclusive results, and thinning techniques were not attempted due to difficulties associated with the water solubility of the material. Blown, thin films were suitable for electron microscope study, any crystals occurring in the films being of dimension 20 Å or less and not readily detectable. Liquid-liquid immiscible regions, possibly due to phase separation by the spinodal mechanism, were observed in the 87.5 mole % V2O5 films but not in films of other compositions.
Strong Proximity Effects in Cu: Superconductivity of a Fine Nb–Cu Composite
Authors: Strauss B. P. , Rose R. M.
Published: February 2004

The magnetic behavior of composites of very fine (less than 1000 Å) niobium wires in copper matrices has been measured at temperatures below 10°K. Three Meissner effects were observed, two of which were apparently due to strong proximity effects in the copper. The temperature dependence of the magnetization curve and measurements of the real and imaginary components of zero-field ac susceptibility agree. The geometry and properties of the composite, which are known in some detail, are used together with current models for proximity effects to develop an adequate explanation of the data.
Effect of Heat Treatment with Excess Arsenic Pressure on Photoluminescence of p-Type GaAs
Authors: Hwang C. J.
Published: February 2004

Photoluminescence measurements at 20°, 77°, and 300°K are used to investigate radiative recombination via the near gap transition in p-type GaAs after heat treatment with excess arsenic pressure, PAs4. The heat treatments are performed at 800°C for 24 h. For heavily doped crystals of Zn acceptor concentration NA≃5×1018 cm−3, the intensity of the Zn photoluminescent line, I(hv1), is independent of PAs4 up to pressures as high as 3 atm. For lightly doped materials of NA+ND≃8×1016 cm−3, I(hv1) ∝ (PAs4)−1/4 for PAs4 >2×10−1 atm. These results can be attributed to Ga vacancies or associates of Ga vacancies with other defects which dominate the nonradiative recombination at low acceptor concentration and to acceptor impurities which dominate the nonradiative recombination at high acceptor concentration. The transitions corresponding to shallow defect levels at 1.480 eV are found to disappear after heat treatment.
New Vitreous Semiconductors
Authors: Schottmiller J. C. , Bowman D. L. , Wood C.
Published: February 2004

Coevaporation with vapor quenching has been used to combine metallic and nonmetallic elements into new vitreous semiconductors. These binary glasses, formed with an excess of nonmetal over a wide range of compositions exhibit semiconducting and optical properties differing from the corresponding properties of either component alone or of any known crystalline compound formed between the components. Detailed investigation of the vitreous Bi–Se system indicates that an intermediate temperature region of the equilibrium phase diagram has been retained at room temperature. Variation of bandgap, resistivity, and photo-sensitivity with composition are presented and interpreted in terms of the equilibrium existing at ∼620°C.
Low-Frequency Noise in Gas Discharges
Authors: Hanson D. G. , van der Ziel A.
Published: February 2004

It is shown with the help of probe measurements that the low-frequency noise in relatively quiet, cold-cathode gas discharges is caused by a distributed noise source. The spectrum is constant at low frequencies and varies as 1/fα, with α near 1.5 or near 2, at high frequencies. The noise in the positive column can be interpreted as diffusion-limited generation-recombination noise. The noise in the Faraday dark space seems to indicate volume recombination limited generation-recombination noise, but we have difficulty in interpreting the observed time constant of the noise. The noise in the negative glow region seems to have more than one time constant and we have no satisfactory interpretation of the observed data.
Effects of Space Charge on Mobility, Diffusion, and Recombination of Minority Carriers
Authors: Scales J. L. , Ward A. L.
Published: February 2004

A computer has been used to solve the coupled nonlinear equations, including space charge, that govern the motion of pulses of minority carriers in semiconductors. The advantages of using the computer are that one does not have to assume space-charge neutrality, and one can treat drift, diffusion, and recombination simultaneously. The use of a mass action recombination law enabled the calculation of the decrease of life-time with increase in pulse size. The electric field due to a pulse of uncompensated minority carriers was found to decay initially with the dielectric relaxation time, but a small field distortion was found to persist. This space charge influenced the mobility and diffusion of minority carriers. It was found that the decrease in mobility with large pulse size was less severe than predicted by the conventional theory based on charge neutrality. There were indications that diffusion, in the presence of space charge, was also less than that predicted by conventional theory.
Plane Collisionless Sheaths between Field-Modified Emitting Electrodes and Thermally Ionized Plasmas Exemplified by Cesium
Authors: Morris James F.
Published: February 2004

This paper describes a theory for plane collisionless sheaths separating plasmas ionized by thermal electrons from emitting electrodes affected by sheath fields. Examples for cesium plasmas and thermionic-diode configurations show sheath effects over ranges of conditions: temperatures from 1400° to 2400°K for electrodes, from 1600° to 2400°K for plasma atoms and ions, and from 1700° to 2700°K for plasma electrons; plasma-electron number densities from 1012 to 1015 cm−3; and work functions from 1.5 to 5 V. Sheath drops from 0 to 2.1.V and net currents from 0 to over 100 A cm−2 result. Over-all sheath characteristics correlate with work function minus plasma potential, plasma-electron concentration (Nep), electrode temperature (TE), and an emission Debye length λDE≈6.9(TE/Nep)1/2. Effective sheath widths range from 1.7 to 2.6 emission Debye lengths.
Anisotropic Energy-Gap Measurements on Superconducting Niobium Single Crystals by Tunneling
Authors: MacVicar M. L. A. , Rose R. M.
Published: February 2004

Nb-oxide-In tunneling junctions were constructed on the as-grown surfaces of Nb single crystals at controlled orientations. The energy gap was observed to be anisotropic for crystals with resistivity ratios of 178 or greater. The lowest gap, 2.84 mV, was observed for the 〈100〉 direction. Local gap maxima were observed at the 〈311〉 and 〈111〉 directions, where the gap was about 3.19 mV. No anisotropy was observed in crystals having resistivity ratios of 65, presumably due to impurity scattering. Some coincidence of the energy gap anisotropy with main features of the proposed group V transition metal Fermi surface is noted.
Properties of Thin Metal Films at Microwave Frequencies
Authors: Ramey R. L. , Lewis T. S.
Published: February 2004

The power transmission, reflection, and absorption coefficients of thin metal films positioned in the transverse plane of a rectangular waveguide are investigated. The results are presented as a function of film thickness for iron, nickel, and silver at 9800 MHz using (a) theoretical expressions for conductivity as a function of film thickness, and (b) measured values of conductivity. Experimental transmission data were obtained and compare favorably with theory.
Spectrographic Measurements of a Pulsed Arc
Authors: Barach John Paul
Published: February 2004

A Kerr cell shutter has been used with a photographic spectrograph to do time-resolved studies of an arc discharge in 2.5 Torr of helium with air impurity. The arc had a peak current of 40 kA and a period of 40 μsec. Temperatures were obtained from line intensity ratios of NII, NIII, OII, CII, CIII, and electron densities from Stark broadening measurements. Plasma temperatures were found to reach a peak in the first few μsec and decline thereafter. For an unconfined arc, Ne declined in time, whereas for a confined arc (tube diam 8–13 mm) the initial temperature was higher (as much as 3.8 eV), and its decline was accompanied by an increase in Ne (from 1017 to 1018 cm−3) due to wall erosion. The intensity of He I 5876 was anomalously low at first. This is interpreted as a temperature deficiency in neutral helium which decreases as time goes on, reaching equilibrium in some 30 μsec.
Effects of Radiation-Induced Cross-Links on the Low-Temperature Thermal Properties of Polystyrene
Authors: Reese W. , Higgins P. J. , Rostine G. W.
Published: February 2004

Measurements of the thermal conductivity and heat capacity in the liquid-helium temperature range of polystyrene which was cross linked by exposure to an 80-MeV electron beam are reported. The measurements were performed over a range of cross-linking coefficient from 0 to 12. No significant change in the thermal conductivity was observed, but about a 25% reduction in the heat capacity occurred. The thermal conductivity results are compatible with the existing theory of the thermal conductivity of amorphous polymers, while the heat capacity result is taken to indicate a significant reduction in the ``excess heat capacity'' associated with nonacoustic, low-frequency modes.
Temperature Dependence of Dispersed Barrier Hardening
Authors: Ono Kanji
Published: February 2004

This paper examines the temperature dependence predicted by theories of dispersed barrier hardening. Most of interaction potentials employed in the theories are similar. It is not possible to select one of several interaction potentials on the basis of an experimentally obtained stress-temperature relationship. This paper discusses limitations of the theories and clarifies several misconceptions on the theories.
Photothermoelectric and Thermally Stimulated Thermoelectric Effects: Techniques in Photoelectronic Analysis
Authors: Lawrance Robert , Bube Richard H.
Published: February 2004

Thermoelectric power measurements have seldom been used to investigate the photoelectronic properties of semiconductor crystals. This paper presents the results of an exploratory investigation of thermoelectric power in three different specific situations: (1) the effect on thermoelectric power of extrinsic photoexcitation involving imperfection states in the crystal, (2) the effect on thermoelectric power of optical quenching of photoconductivity, and (3) thermally stimulated thermoelectric power, associated with the emptying of electron and hole traps in the crystal. The increased sensitivity of the thermoelectric effect to two-carrier phenomena as compared to the Hall effect, makes it a valuable effect for investigating the contribution of electrons and holes to photoelectronic behavior. The results obtained with single-crystal CdS suggest that: (1) The thermoelectric effect is quite useful in imperfection-level spectroscopy, (2) Sensitizing imperfections for photoconductivity have a complex dipole-like structure, and (3) Holes play a larger role in photo-electronic effects than commonly attributed. Further investigations of the techniques using thermoelectric power are certainly indicated.
Small-Angle X-Ray Scattering from Glassy Carbon
Authors: Rothwell W. S.
Published: February 2004

Samples of glassy carbon prepared from two different resins and given different heat treatments have been studied with small-angle x-ray scattering to determine pore structure and concentration. The results of the study are described and discussed after an initial section in which the analytical methods used are defined and developed. The Warren method of measuring absolute intensity was used and checked by obtaining scattering data on known concentrations of type AS Ludox. It was concluded that with heat treatment to 3000°C, the voids in glassy carbon approach a spherical shape nearly uniform in size, about 50 Å in diameter. Also, the total volume concentration of these voids was about one-third and accounted for the difference of the glassy carbon density from the theoretical value.
Spectroscopic Observations on Induction-Coupled Plasma Flames in Air and Argon
Authors: Eckert H. U. , Kelly F. L. , Olsen H. N.
Published: February 2004

Plasma flames in argon and air have been maintained at atmospheric pressure by rf induction in a 100-mm-wide quartz tube for extended times with only forced air required for tube cooling. For air, a rotational temperature of 6300°K at the central point of the induction zone was determined from intensity ratios of both sextet components and unresolved sextets in the 0, 0 band of the N2(2+) system. Absolute intensity measurements in this band and in the 0, 0 band of the N2+(1−) system yielded probabilities of 1.34×107 sec−1±14% for the C 3πu→B 3πg transition and 1.15×107 sec−1±14% for the B 2Σu+→X 2Σg+ transition, which agree well with values in the literature. Under the assumption of local thermal equilibrium (LTE) in the plasma, radial temperature distributions at the coil midsection were derived for both systems. Results agree within 7%, which supports the validity of the above values for transition probabilities and indicates that deviations from LTE are less than 10%. Average electron densities were determined for argon and air at the coil midsection from Stark broadening of the Hβ line. For air a value of 5×1014 cm−3 has been found which is slightly above the equilibrium value. The value for argon is 1.7×1015 cm−3. It correlates well with data from other sources which indicate that the average electron density in argon is inversely proportional to the tube radius.
Measurements of the Time-Averaged Potentials in Low-Pressure, rf Discharges using an Ion-Beam Probe
Authors: Miller A. , Bruce C. W. , Kregel M. D.
Published: February 2004

A positive-ion-beam probe has been used to examine the approximate static electric-field distribution in low-pressure rf discharges. Analysis of deflection data has yielded a picture of the way in which the potential distributions vary as one moves from the multipacting type of discharge up to the modes in which dark-sheath rf plasmoids can be observed. The measurements confirm that the multipacting discharge creates a well for positive ions; furthermore they show that the dark-sheath in plasmoidal discharges represents a narrow region in which the static electric field is much larger than either that in the center of the discharge or between the dark sheath and the walls.
Fracture Behavior of Tubular Bombs
Authors: Hoggatt Chester R. , Recht Rodney F.
Published: February 2004

The plastic deformation behavior and modes of fracture exhibited by tubular bomb casings are greatly influenced by the stress state imposed by explosive and inertial forces. These forces combine to produce triaxial compression over a varying inner portion of the tube wall. Noting that compressive hoop stresses would exist over a portion of the wall, Taylor has previously developed a hypothesis for prediction of fracture radius, assuming a radial fracture mode. This paper introduces hypotheses related to the influences of stress state and thermoplasticity upon fracture mode as well as fracture radius. The resulting prediction model closely predicts fracture radius and explains the development of commonly observed shear-lip fractures. It illustrates why radial fractures are typical only when detonation pressures are relatively low, and why shear fractures are typical when detonation pressures are high.
Guided Wave Propagation in Gyromagnetic Media as Applied to the Theory of Exchange Spin-Wave Excitation
Authors: Vasile Carmine F. , LaRosa Richard
Published: February 2004

Source-excited propagation in a narrow, lossless, ferrite-filled parallel-plate waveguide is analyzed. The effect of an inhomogeneous bias field is considered. A new, linear theory of exchange spin-wave excitation is presented, and its relation to the theory of Schlömann is discussed. Several previously unpublished aspects of the dispersion relation and the solution of a corresponding fourth-order partial differential equation are presented.
Influence of Deposition Parameters on the Coalescence Stage of Growth of Metal Films
Authors: Chopra K. L. , Randlett M. R.
Published: February 2004

Growth of vapor-deposited films by coalescence processes in the post-nucleation stage is discussed. It is shown that increasing values of the parameters of rate of deposition, rate of evaporation from the vapor source, substrate temperature, and angle-of-incidence of vapors should produce increasing agglomeration (that is, islands smaller in number but larger in size), characteristic of high surface mobility. These predictions have been verified by the electrical and electron microscope studies on gold and silver films prepared under controlled conditions of rate of evaporation and rate of deposition. The critical thickness tc at which films become electrically continuous increases with increasing agglomeration. An exponential dependence of tc on the inverse of the reciprocal of substrate temperature yields two activation energies of 0.26 and 0.85 eV. The smaller activation energy obtained for temperatures below 450°K may be ascribed to thermal diffusion of adatoms, while the higher value is tentatively proposed to be due to the diffusion of subcritical nuclei resulting from thermal motion as well as the momentum transfer from the impinging energetic vapor. Oblique deposition enhances agglomeration. The growth and distribution of islands is found to be isotropic in the plane of the film for angles of incidence of up to 80°. Anisotropic (columnar) growth in the direction of the incident vapor occurs due to self-shadowing only after the film becomes physically continuous.
Multiple Transitions in Polyalkyl Methacrylates
Authors: Haldon Robert A. , Simha Robert
Published: February 2004

A series of polyalkyl methacrylates, two hydroxylated methacrylates, polymethoxy ethyl methacrylate, and polymethyl acrylate have been studied by linear expansion and torsion-pendulum measurements, in the temperature range from −180°C to just above the respective glass transition temperatures. The length-temperature data (L-T) were analyzed by a least-squares differentiation procedure, based on moving arcs, to give directly the thermal expansion coefficients as a function of temperature. The L-T measurements suggest the existence of two Tgg transitions (Tg−100<Tgg<Tg) in the polymers with the more flexible side chains, and one transition for polymers with bulky side groups. There is also evidence of a third Tgg transition at about −120° to −90°C, which may be associated with adsorbed water molecules. In similar fashion to that of Tg, the location of the Tgg transitions decreases upon increasing the length of the n-alkyl side chain. The hydroxylated polymers have higher Tg's than the corresponding alkyl samples, and have thermal expansion coefficients only about one-half as large, both features being a result of interchain hydrogen bonds. Torsion-pendulum measurements indicate only one clear-cut Tgg transition region; hence, it seems that the two Tgg transitions observed in the expansion studies cannot be unequivocally resolved by dynamic measurements. Expansion coefficients of the n-alkyl series suggest the retention of some excess free volume below Tg for side chains larger than ethyl. Substitution of 3α′g″, the expansion coefficient below our second Tgg transition, into the Simha-Boyer equation (αl-αg) Tg gives a value close to their empirical constant. This supports their suggestion that polymers with pronounced subgroup motions exist in an iso-free volume state below the subgroup transition temperature.
Mobility Anisotropy and Piezoresistance in Silicon p-Type Inversion Layers
Authors: Colman D. , Bate R. T. , Mize J. P.
Published: February 2004

The Hall mobility of holes in silicon p-type inversion layers has been measured as a function of gate voltage (perpendicular electric field), inversion layer orientation [(100), (110), and (111) surfaces], direction of current flow within an inversion layer, and temperature. It has been shown that hole mobility in silicon inversion layers depends not only on the crystalline orientation of the inverted surface, but also on the azimuthal direction of current flow within the inversion layer. Thus, on the (110) silicon surface at room temperature, the inversion-layer hole mobility is 40% higher in the[l̄10] direction than in the [001] direction. Room-temperature piezoresistance tensors have been experimentally determined for inversion layers on the (100), (110), and (111) surfaces of silicon. It is found that, in general, the piezoresistance coefficients are not the same as those for the same directions in bulk silicon and that they depend on the orientation of the surface. The existence of these anomalous effects can be understood in terms of quantization of the carrier wavefunction in the surface channel, which is narrow compared with the carrier wavelength in bulk silicon. This quantization tends to depopulate that part of the Brillouin zone within which k⊥, the component of wavevector perpendicular to the surface, is small. If the dependence of energy on k is not quadratic, as is true for the valence band of silicon, the effective masses for conduction in the plane of the surface can be complicated functions of k⊥. The mass anisotropies estimated from the cyclotron resonance parameters for the valence band of bulk silicon are in qualitative agreement with the experimental mobility values.
Epitaxial GaAs Films Deposited by Vacuum Evaporation
Authors: Davey John E. , Pankey Titus
Published: February 2004

Epitaxial films of GaAs have been vacuum-deposited onto GaAs and Ge single-crystal substrates by a modified three-temperature-zone technique. The film properties have been investigated by reflection electron diffraction (RED) and also optically. At a deposition temperature of 375°C the films possess [100] fiber textures; below 375°C, the film properties follow those deposited on amorphous substrates. At 400°C the films become epitaxial with twinning on all (111) planes. Between 425° and 450°C, the films are highly ordered, twin free, on the b faces of GaAs and on Ge; in the same temperature range, thick films (> 10 000 Å) and films deposited on a faces of GaAs exhibit extra reflections in RED and departures from the expected optical behavior. Films deposited above 450°C, under conditions for which excess Ga may exist, grow in an hcp modification; the reflectivity of these films agrees with bulk zinc blende GaAs.
Self and Mutual Inductances of Superconducting Structures
Authors: Sass A. R. , Stewart W. C.
Published: February 2004

The self and mutual inductances of London superconductor structures, of completely generalized geometry, have been derived in terms of London fluxoids. The final expressions for superconducting systems are analogous in form to the inductance expressions found for normal conductors. It is shown, however, that the ``fine wire'' approximation and the concept of ``partial linkages'' needed for normal conductors are not necessary when treating superconducting structures.
Eigenvectors of Configuration (2p)5(3p) and Relative Probabilities of 2s-2p Transitions for NeI
Authors: She C. Y.
Published: February 2004

Eigenvectors of configuration (2p)5(3p) of NeI are determined and expressed in terms of the j1-l2 basic states. A considerable mixing among the j1-l2 states is seen and a slight change in the assignment of Racah designations to the energy levels is suggested. Based on these eigenvectors, the relative probabilities for NeI 2s-2p transitions are evaluated. An improvement over the previous calculation is evident in the present result.
Positive-Ion and Electron Emission from Fe in the Region of the α⇌γ Transformation
Authors: Antypas G. A. , Tinder R. F. , Donaldson E. E.
Published: February 2004

The behavior of the positive-ion and electron current was studied as a high-purity Fe filament passed through the α⇌γ structural transformation. Maxima in the positive-ion current that were coincident with the transformation could be effectively eliminated by continued heating, which exhausted the Fe filament of surface-ionizable impurities. When an exhausted filament, passing through the α⇌γ transformation, was bombarded by an external source of surface-ionizable impurities from a tungsten filament, it was observed that the α→γ transformation produced a maximum in the positive-ion current, while the γ→α transformation produced a minimum. The electron current emitted as the filament passed through the transformation varied in the opposite manner. Richardson and Saha-Langmuir plots made in the region of the transformation provided values for the work function eφ and the quantity e(φ−I). Small stresses up to 25 g/mm2, which were externally applied to an almost exhausted filament, did not influence the positive-ion or electron currents as the filament was passed through the transformation. Various mechanisms that affect the positive-ion and electron current behavior are discussed. These include transient structural and heating effects, and changes in the work function due to stresses produced during the transformation.
The Lattice Softening in V3Si
Authors: Vance E. R. , Finlayson T. R.
Published: February 2004

Elasticity measurements have been made on several polycrystalline samples which contained various amounts of second phase. The results suggest that the superconducting transition is not directly related to the lattice softening in V3Si. The relationship between the lattice softening and the martensitic transformation is briefly discussed. For all samples, magnetization vs field characteristics at 4.2°K have been measured to investigate the effect of second phase with respect to the lattice softening of the samples.
Modulation Broadening of the Shape of Unsaturated Gaussian Magnetic Resonance Absorption Lines
Authors: Buckmaster H. A.
Published: February 2004

An expression is derived for the Fourier coefficients anG of a modulation-broadened, unsaturated Gaussian absorption lineshape.
Preparation and Optical Properties of AlxGa1−xP
Authors: Merz J. L. , Lynch R. T.
Published: February 2004

Aluminum-doped GaP has been grown from solution with concentrations up to 30% Al. The crystals are stable and do not corrode in air. Evidence that the system is forming an Al–Ga alloy is provided by an observed shift of the absorption edge and photoluminescence from those of GaP by 0.10 eV to higher energies. The green photoluminescence peaking at 2.306 eV (4.2°K) is studied and identified as pair emission. A weak band at 1.92 eV is also seen, analogous to the highly efficient Zn–O red band at 1.82 eV in Al-free GaP. The implications of this shift in photoluminescence energy are discussed.
Electrocaloric Effects in Some Ferroelectric and Antiferroelectric Pb(Zr, Ti)O3 Compounds
Authors: Thacher P. D.
Published: February 2004

Variations of sample temperature arising from the electrocaloric effect, antiferroelectric to ferroelectric transitions, and hysteresis-loss heating have been recorded together with the hysteresis loops for four different ceramic ferroelectrics near room temperature. Both the electric-field dependence and the temperature dependence of the electrocaloric effect were accurately predicted by the usual thermodynamic expression for the effect. Values for the heat capacity and the pyroelectric constant were also obtained from the data. The sample temperature of one composition which becomes antiferroelectric under zero applied field near 40°C was monitored at various temperatures as antiferroelectric to ferroelectric transitions were forced by an electric field. Above 55°C, the temperature change at the transition could be fitted with a theory originally developed for the field-enforced antiferroelectric to ferroelectric transition in PbZrO3.
On Diffusion of Electrons Across a Magnetic Field
Authors: Mouthaan K. , Fulop W.
Published: February 2004

A recent theory for electron transport in the smooth-bore magnetron [K. Mouthaan and C. Süsskind, J. Appl. Phys. 37, 2598 (1966)] is tested for agreement with results of an experiment [W. Fulop, J. Electron. Control 5, 531 (1958)] in which thermal emission velocities of the electrons are greater than average E × B drift velocities. The theory is found to yield correct results in that case only if the square of the E × B drift velocity in the expression for the diffusion coefficient, D = (3g/2ωc) (E/B)2, is replaced by the mean-square thermal velocity. This result adds substance to the observation made previously [K. Mouthaan, Phys. Fluids 8, 1715 (1965)] that the experimental diffusion coefficient for enhanced diffusion in ionized gases can be obtained from the theoretical diffusion coefficient for electrons in crossed fields in that manner.
Diffusion in Silicon. III. Generation of Excess Vacancies at Climbing Diffusion-Induced Dislocations, and Dislocation-Enhanced Diffusion in (001) Crystals
Authors: Parker T. J.
Published: February 2004

In Part I a simple dislocation-enhanced diffusion model was proposed to explain the anomalous diffusion of phosphorus and boron in (111)-oriented silicon crystals. Consideration was given to jogs created by dislocation intersections which undergo climb and emit vacancies as they are carried into the crystal on gliding diffusion-induced dislocations, and it was shown that this can result in a considerably increased rate of impurity diffusion. We show here that a significant contribution to the total vacancy concentration is also produced by the emission of vacancies by climbing diffusion-induced dislocations. This contribution also results in a considerable increase in the rate of diffusion. The results are extended to the case of diffusion in (001) crystals in which the mechanisms of dislocation propagation are different. It is shown that the mechanisms of vacancy generation at dislocations operate with approximately equal efficiency in (001) and (111) crystals.
Residual Resistivity and Kohler's Rule in Nickel
Authors: Schwerer F. C. , Silcox J.
Published: February 2004

Measurements have been made of the magnetoresistance of nickel polycrystalline foils. The specimens have been treated to form particular sets, each of which is thought to contain predominantly one kind of scattering center, e.g., chromium impurity atoms, dislocations, etc. The data from any one set obey Kohler's rule provided the magnetic induction B is the relevant field and the reducing resistivity ρ0B is taken as ρ at B=0. A novel extrapolation procedure is described for finding ρ0B. The internal field 4πM8 gives rise to a correction to the residual resistance at zero applied field which for high-purity samples can be large, comparable to the residual resistance itself.
Translational Energy Distribution of Electrons and Positive Ions in the Plasma of Microwave and High-Frequency Discharges of He, Ne, and Ar
Authors: Franklin J. L. , Studniarz Stanley A. , Ghosh P. K.
Published: February 2004

The mean electron energy, mean positive-ion energy, and sheath potentials in the plasma of microwave discharges were measured by extracting the positive ions and electrons through a small hole in a metal probe and subjecting the effused particles to a retarding electric field. The electron and positive-ion translational energy distribution fitted the Maxwellian distribution function The mean electron energy was independent of the input power to the cavity and position of visible plasma sampled along the axis of the discharge tube The electric field in the sheath in front of the probe orifice was mapped and approximate values of the sheath thickness are given. The variations of the sheath potential and electron density with pressure and power input and sheath potential profiles along the axis of the discharge tube are given.
Magnetoelastic Parametric Interaction due to the ΔE Effect
Authors: Lord A. E.
Published: February 2004

A calculation is presented for the instability of elastic waves parametrically pumped by a time-varying elastic modulus in long, thin nickel rods or tubes at kilocycle frequencies. The modulus is varied by varying the biasing magnetic field according to the ΔE effect. The instability has been observed in nickel tubes (but not in rods) by driving the parametric magnetic pump at twice the fundamental mechanical resonant frequency of the tube, and observing that the vibrations corresponding to fundamental resonance of the tube set in at a very definite value of the pump amplitude, i.e., the threshold value. The form of the curves of threshold amplitude vs dc bias field in annealed tubes is in agreement with theory, using the previously measured modulus vs field curves. The observed threshold amplitudes are in satisfactory agreement with the theoretical estimate. The form of the above curves and threshold amplitudes are quite different in tubes which presumably still retain some of the effects of cold work experienced in fabrication.