bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Generation of Vacancies and Substitutional Sites in Crystalline Polymers
Authors: Eby R. K.
Published: April 2005

It is proposed that differences between the thermal expansion of the macroscopic and crystal lattice volumes of crystalline polymers might be attributed to thermal generation of new substitutional sites. Consideration of the molecular arrangements suggests that vacancies can be generated within the lamellae at molecular folds and ends and at any point along some helical molecules. Part of the displaced molecule can be transported by point defects to the crystal surface where new sites are formed. Analysis of the available data for polyethylene shows the concentration of new sites (Δn/n) to be 2.2×10−2 at 100°C with an energy of creation of 0.2 eV and an entropy of creation of 5.3×10−4 eV/°K per site. It is pointed out that the phenomenon could account for the so-called glass transitions and is, therefore, closely related to the ``amorphous'' relaxations observed in crystalline polymers. The need for additional experiments is discussed.
Statistical Stability of the Preisach Diagram for Particles of γ-Fe2O3
Authors: Bate G.
Published: April 2005

An experiment is described that enables the statistical stability of the Preisach diagram for interacting ferromagnetic particles to be tested. The samples used were of γ—Fe2O3 dispersed in a nonferromagnetic matrix to a nominal packing density of 20% by volume. Both oriented and nonoriented samples were examined. In every case the diagram was found to be stable over most of the area bounded by the major remanence loop. The region of departure from stability occurred at the higher levels of remanent intensity. A method of calculating the diagrams using only dc measurements is given. They are then used to predict accurately the ascending remanence curve after ac demagnetization for each sample. Finally, it is shown how the experimental ascending and descending remanence curves, which could not be explained by Wohlfarth's relations [J. Appl. Phys. 29, 595 (1958)] based on noninteracting particles, can be completely described in terms of the Preisach diagram.
Climb-Barrier to Dislocation Glide in fcc Crystals
Authors: Hirth J. P.
Published: April 2005

A dislocation interaction in fcc crystals is considered which yields a barrier dislocation extended in the glide direction. The barrier consists of a high-energy stacking fault bounded by two partial dislocations. The barrier stability is discussed in relation to both work hardening and quench hardening.
Characteristics and a New Application of High-Field Superconductors
Authors: Swartz Paul S. , Rosner Carl H.
Published: April 2005

This paper presents a simple physical and mathematical model and experimental support of the manner in which magnetic flux penetrates into a high-field superconductor. Based on this model a new device using high-field superconductors in their bulk form called a superconducting magnetic flux compressor is proposed. Present theory suggests that magnetic field strengths approaching the critical field strength of a high-field superconductor (> 100 kOe) should be attainable using the apparatus and techniques described. It was found experimentally with the particular high-field superconductors tested that compressed field strengths of 15 kOe could be achieved. Beyond this value anomalous magnetic flux jumping occurred that limited the field strengths obtainable. The characteristic conditions under which magnetic flux jumping is found are discussed. The experimental results also suggest that heat is generated when a high-field superconductor is exposed to an alternating magnetic field well below the critical field strength.
Zeeman Effect in Gaseous Helium-Neon Optical Maser
Authors: Statz H. , Paananen R. , Koster G. F.
Published: April 2005

The strongest emission in the helium-neon gas maser corresponds to transitions between the 2s2 and 2p4 states of neon which have angular momenta of 1 and 2, respectively. These levels split up in a magnetic field and the maser output contains differently polarized radiations of slightly different frequencies. In particular, for a small magnetic field parallel to the maser axis two circularly polarized components of different frequency are emitted. Their superposition may be described as linearly polarized light where the plane of polarization is rotating at half the difference frequency. A polarizer in the beam gives rise to amplitude modulated light. Interesting effects may be observed when the various Zeeman components resonate in different cavity modes of the Fabry-Perot interferometer.
Initiating and Maintaining a Discharge by a Transfer Mechanism
Authors: Hansen Lorin K. , Mackenzie K. R.
Published: April 2005

A new discharge is described which is radially contained by a magnetic field and is not sustained by electron emission from any surface. Two positive anodes of arbitrary but similar shape are lined up along the magnetic field. A control electrode, at a lower potential, is placed between them and creates a potential barrier and two positive potential wells in the vicinity of each anode. Electrons are axially trapped in these wells. An rf voltage in the megacycle range is applied, out of phase, to the two anodes and causes the trapped electrons to alternately spill across the barrier and pick up energy from the rf field. During each half-cycle they make many oscillations in the potential well which is most positive and make ionizing collisions. Every ion pair yields an electron which can gain energy in the same way. The process is very efficient and is characterized by rf breakdown voltages that approach the ionization potential of the gas.
High-Temperature X-Ray Diffraction Study of the Order-Disorder Transition in a Cu-32.2 Atomic Percent Gold Alloy
Authors: Yakel Harry L.
Published: April 2005

The order-disorder transition in a polycrystalline specimen of Cu-32.2 at.% Au has been investigated by means of a high-temperature x-ray diffraction method. The experiment confirms the existence of an equilibrium Cu3Au II-type phase in a temperature interval from 313±3°C to 328±3°C. Diffraction data from this phase are not in conflict with a previously described structure at 31.6 at.% Au based upon an ordered Cu3Au I-type superlattice in which strictly periodic antiphase domain boundaries occur parallel to any one of the three possible cube faces. Antiphase periods ranging from 18 to 16 are found for the Cu3Au II-type phase. There is an indication that this period may change as a function of temperature and that periods which are not integral multiples of cubic subcell edges may exist. A two-phase field between the Cu3Au II-type and disordered single-phase regions has been located on the basis of fundamental reflection broadening. Unambiguous evidence for a similar field was not found between the Cu3Au I and Cu3Au II-type single-phase fields.
Effect of a Phase Transformation on the Vapor Phase Growth of Single-Crystal HgS
Authors: Curtis O. L.
Published: April 2005

Attempts have been made to grow single-crystal HgS using a vapor phase growth technique. The lack of success led to the discovery of a phase transformation which occurs between the temperature of deposition and room temperature. The crystals were deposited in the cubic meta-cinnabar form and transformed to the hexagonal cinnabar form upon cooling, with a resultant destruction of the deposited crystals. There is a large supercooling effect which seems to depend upon particle size. Upon heating cinnabar in an atmosphere of air the transformation to meta-cinnabar occurs at 335°±10°C. Possibilities for the use of other techniques in the growth of single-crystal HgS are considered.
Quantitative Measurement of Semiconductor Homogeneity from Plasma Edge
Authors: Edwards David F. , Maker Paul D.
Published: April 2005

The carrier concentration homogeneity in a semiconductor can be quantitatively measured from the position of the plasma edge. This has been demonstrated for an InAs sample for which changes of homogeneity of about 0.5% have been measured. This plasma edge method for measuring carrier concentration inhomogeneities is at least an order of magnitude more sentitive than other methods reported to date and can be applied for any semiconductor that has a well-defined plasma edge.
Highly Ionized Hollow Cathode Discharge
Authors: Lidsky L. M. , Rothleder S. D. , Rose D. J. , Yoshikawa S. , Michelson C. , Mackin R. J.
Published: April 2005

A hollow cathode discharge (HCD) is described that produces a highly ionized steady-state plasma (ne≈1013−1014/cm3) at a temperature 1–10 eV, in a volume as large as 104 cm3, with background neutral gas density ≈1013/cm3. The HCD is generated by the prescription: gas flow (H2, He, A, or N2) 0.05–2 cc STP/sec through a refractory metal hollow cathode tube into a vacuum; any anode; 20–200 V dc applied. An axial induction 100–1000 G is used to collimate the discharge and to aid in starting by rf excitation. The HCD runs from the cathode interior, deep enough that p0d≈1 cm×mm Hg. Current range is 2.0–300 A. Various electrode configurations and a wide range of operating parameters have been studied. The external plasma density and temperature were measured by Langmuir probes. A discussion is given of the confinement mechanism and of the energy balance, both in the external plasma and in the region of the cathode itself.
Annealing Effects in Evaporated InSb Films
Authors: Dale E. Brock , Senecal Gerard
Published: April 2005

The conductivity and Hall coefficient of evaporated InSb films 550 to 3750 Å thick have been monitored while the films were being annealed. It is found that the conductivity passes through a maximum during annealing, if the temperature is above 130°C. The Hall coefficient remains very small while films are annealed at temperatures below 200°C, but it rises rather abruptly at a fixed higher temperature, approaching some asymptotic value after several hours. Evidences of free In and Sb shown by electron and x-ray diffraction of unannealed films are no longer present after the films are annealed at 130°C. Electron microscope examination of carbon replicas reveals no gross differences between the surfaces of annealed and unannealed films and shows that the films are continuous. Annealed films of both conductivity types have been observed. At room temperature, carrier concentrations lie between 6×1015 and 4×1019/cm3 and Hall mobilities between 10 and 500 cm2/V sec. The mobility increases with increasing temperature over most of the range from 100 to 500°K; in a few cases it has passed through a maximum near the high temperature limit.
Anisotropy of the Electrical Conductivity and the Seebeck Coefficient of Bi8Te7S5
Authors: Soonpaa H. H.
Published: April 2005

Electrical conductivity and the Seebeck coefficient of Bi8Te7S5 have been measured in the two main crystallographic directions of the rhombohedral lattice, parallel and perpendicular to the hexagonal (basal) plane. The ratio of the two electrical conductivities has a value of 7.56 at liquid nitrogen temperature. The Hall effect along the basal plane has been measured. The properties change with temperature in a manner that indicates a complicated degenerate conduction band.
Propagation of Electromagnetic Step Functions over a Conducting Medium
Authors: Mijnarends P. E.
Published: April 2005

A theoretical treatment is presented of the behavior of various components of the electromagnetic field generated by a horizontal electric dipole, embedded in a homogeneous conducting half-space, and excited by a step-function current. Displacement currents are neglected, thereby limiting the validity of the treatment to frequencies that are not too high, while the results for the transient response are only valid for sufficiently large times after the application of the step function to the dipole. The treatment is based on Laplace transform theory. Besides the electric and magnetic components in the conducting medium, also the vertical electric field in air e0z at points at the interface is examined. Since the expressions obtained are rather involved, numerical results are given only for e0z and a horizontal magnetic component in the conducting medium h1x. The response of e0z is a pulse with a rise time proportional to the square of the antenna depth but independent of horizontal distance, and a long trailing edge. The magnetic component h1x rises slowly to a stationary value; its rise time increases with increasing horizontal distance. It is shown that there is a marked difference in attenuation with depth, and sometimes also with horizontal distance, between transient and sinusoidal signals.
Direct Observation of Longitudinal Modes in the Output of Optical Masers
Authors: Duncan R. C. , Kiss Z. J. , Wittke J. P.
Published: April 2005

Longitudinal modes in the output of pulsed U: CaF2 and ruby optical masers have been observed directly by means of a high resolution, high-dispersion grating spectrometer. The mode spacings are in reasonable agreement with the expected values. The linewidth of the individual modes is instrument-limited at about 0.05 cm−1. Maser action is observed to occur simultaneously in the various modes.
Radio-Frequency Noise of an Immersed Langmuir Probe
Authors: Sears Robert D. , Brophy J. J.
Published: April 2005

The rf noise power spectrum at a Langmuir probe in a cold-cathode neon discharge is observed over a 50-kc to 10-Mc range. The statistical noise amplitude distribution function is found to be Gaussian and the probe noise can be analyzed in terms of shot noise of the probe electron and ion currents using a substantially constant probe sheath impedance at different probe potentials. The noise current spectral density increases at low frequencies in agreement with hot-cathode discharge probe observations, has a minimum at about the shot noise current level, and has a high-frequency increase corresponding to that observed by Shimada [K. Shimada, Proc. I.R.E. 49, 632 (1961)]. It is believed that freedom from wall effects can be attained, since relative insensitivity of the noise to discharge pressure, current, and purity is observed. The introduction of stationary striations does not influence the power spectrum other than to superimpose very sharp oscillatory peaks which are easily altered by changing discharge current or pressure. Low-frequency fluctuations in the plasma can be largely eliminated by using large diameter discharge tubes.
Increase in Dielectric Constant during Switching in Barium Titanate and Triglycine Sulfate
Authors: Fatuzzo Ennio
Published: April 2005

The increase in dielectric constant and losses during switching was measured in barium titanate and triglycine sulfate (TGS) at frequencies up to 2 Gc. These measurements revealed the presence of two relaxations, one at low frequencies (described by Landauer, Young, and Drougard) and a new one at higher frequencies. The relaxation frequency of this new relaxation is 100 Mc in the case of triglycine sulfate and higher than 2 Gc in the case of BaTiO3. The value of Δε′ at the relaxation frequency is 2 for triglycine sulfate and 1.2 for BaTiO3.

A model which explains the experimental facts is given. The increase in dielectric constant and losses is attributed to oscillations of the ``side'' walls of the ferroelectric domains in the case of the high frequency relaxation. The low-frequency relaxation is believed to be due to oscillations of ``front'' walls of the newly formed domains.
Diffusion of Vacancies during Quenching of Ge and Si
Authors: Melngailis J. , O'Hara S.
Published: April 2005

The diffusion of vacancies in Ge and Si during quenching from the melting point is examined mathematically. In typical dendrites of either material (0.01-cm-thick ribbons), cooling after growth is slow enough so that only 10−3 of the concentration of vacancies at the melting point φ0 can be trapped. For this calculation vacancies are considered as the only defects present, and surfaces are considered as the only vacancy sinks. For Ge samples of larger dimensions (approximately 0.1 cm) cooled by radiation alone the concentration trapped can be 34[open phi]0 with surfaces acting as the only sinks. However, if dislocations in excess of 104 per cm2 are present acting as vacancy sinks of 10−7-cm radius, the concentration quenched-in drops very rapidly with increasing dislocation density. At 105 per cm2 only 10−2 φ0 are quenched-in. Thus, if samples contain more than 105 dislocations per cm2, vacancies would probably not be observed in radiation quenching experiments. Existing theory combined with the present calculation indicates that the formation of dislocation loops in growing Ge dendrites is unlikely.
Silicon Surface-Barrier Photocells
Authors: Ahlstrom E. , Gärtner W. W.
Published: April 2005

This paper describes the properties of surface-barrier photocells on silicon. In particular, data are given on photocurrent versus light intensity, photocurrent versus reverse bias voltage, open-circuit photovoltage versus light intensity, open-circuit photovoltage versus wavelength of light, open-circuit photovoltage versus temperature, and photocurrent versus temperature. An interesting multiplication effect of optically excited carriers is observed at lower temperatures. The theory of the surface-barrier photoeffect is further generalized.
Overshoot in Photoconductivity of Lead Oxide
Authors: Haq Kazi E.
Published: April 2005

The overshoot in the photoconductivity of lead oxide has been studied. It has been concluded to be due to build-up of space charge in the bulk of the material, rather than to any blocking at the electrode. The overshoot vanishes both at temperatures above +70°C and below −50°C. A physical model, which can explain these results, has been discussed.
Experimental Procedure and Its Influence on the Value of α in the Vacuum Breakdown Equation V = Cxα
Authors: Maitland A.
Published: April 2005

From the results published by previous investigators using uniform or nearly uniform macroscopic fields, the value of α in the equation V = Cxα has been shown to range over the values 0.1 to 1.1. In general, the highest values of α were observed at the smallest gaps of an experimental range. The present experiments demonstrate two causes of the variations in the value of α. The first arises from the discharges of an investigation which are shown to produce effects which make the experimental procedure an important cause of the high values of α; and the second from spark conditioning at constant gap. This is shown to produce a state such that a discontinuity in the value of α occurs at the chosen gap. Some consequences of the α-variations are discussed in relation to interpretation of results.
Boron Induced Dislocations in Silicon
Authors: Miller Donald P. , Moore James E. , Moore C. R.
Published: April 2005

Electron microscopy, x-ray diffraction, and chemical etch techniques have been used to study the induction of dislocations in silicon by boron. Boron at low doping levels clusters in silicon to form highly strained vacancy regions. As the doping level is raised, the clusters condense into dislocation loops. As the doping level is increased, loop formation increases. The silicon between these point defects contracts until at a boron level of about 8×1018 atoms cm−3 the lattice stress is sufficient to induce edge dislocation generation from loop interaction. As the dislocation density increases the lattice strain is relieved and the lattice constant approaches that of a Vegard alloy.
An Approximate Relation Between Elastic Moduli and Thermal Expansivities
Authors: Barker R. E.
Published: April 2005

A large number of polycrystalline and amorphous materials ranging from pure metals to glassy polymers have been found to obey the relations α2E=150 [dyn cm−2°K−2]s at normal temperatures. The linear coefficient of expansion is denoted by α, Young's modulus by E, and s is a dimensionless spread factor (0.5<s<2). The spread of about ±0.3 decade is small compared to the three-decade range of E covered by the data. Notable exceptions to the relation are certain alloys, some inorganic glasses, cellular materials (e.g., wood), granular materials (e.g., cement), and rubbery materials. The variations with temperature of α, E, and heat capacity Cp are compared for representative materials and implications of the α2E relation are discussed. An empirical approach in which generalized Grüneisen numbers are utilized and a preliminary statistical mechanical attempt to relate α to Cv and the elastic properties of polymers are discussed. Both lead to the conclusion that for polymers, perhaps even more so than for metals, it would be of interest to make separate measurements to very low temperatures of α, Cp, and various elastic moduli.
Right-Angle Bends in Thin Strip Conductors
Authors: Hagedorn F. B. , Hall P. M.
Published: April 2005

Current density and resistance expressions are obtained by means of a conformal transformation for a strip conductor which contains a right-angle bend. The approach, similar to that applied by Cockcroft to the problem of rectangular coaxial capacitors, is sufficiently general to take into account the effects arising both from a width change at the bend and from a small radius on the inside corner. It is suggested that the current density expressions can be applied in some cases to superconducting thin film strips, and the effect of a right-angle bend on the supercurrent-carrying capacity of such a strip is discussed. A typical result is that the critical current of a bent superconducting strip may be only 1/6 that of a similar but straight strip if the radius of the inside corner of the bend is 1% of the strip width. A specially shaped right-angle bend is then described, the critical current for which is identical to the corresponding straight strip. Current density nonuniformity somewhat away from the corner is also discussed. For example, a 4% variation across the strip is found two strip widths from the corner. The design of a thin film cryotron gate element is then discussed in the context of these current density results. The resistance expression, which naturally applies only to normal conductors, relates the resistance of the bent film strip to the strip dimensions and the bulk resistivity. It is shown that a radius on the inside corner as large as several percent of the strip width will decrease the resistance by an amount which is generally negligible.
Photoconductivity in CdSe
Authors: Stupp Edward H.
Published: April 2005

The photoconductivity in cadmium selenide single crystals is investigated to determine if the Klasens picture properly describes the electronic phenomena in this material. It is found that the simple two-state model is inadequate and at least three recombination centers, and possibly four, are needed for consistency. It is furthermore found that for the model to be acceptable, it must be assumed that activation occurs at impurity levels below that available in the purest material. Some of the limitations of using sintered photoconductors in a study of this type are also described.
Theory of Galvano-Thermomagnetic Energy Conversion Devices. III. Generators Constructed from Anisotropic Materials
Authors: Harman T. C. , Honig J. M.
Published: April 2005

Phenomenological equations in the partially inverted form have been derived for anisotropic materials. Tensor components relate entropy flux and gradient of electrochemical potential to gradient of temperature and electrical current. Using these equations, the characteristics for galvano-thermomagnetic Nernst generators operating under isothermal conditions have been formulated. In this case, the efficiency η is no longer exclusively determined by the figure of merit as is the case for isotropic generators. Rather, η depends on an anisotropy factor r in such a way that, as |r| → 0, the figure of merit required to reach Carnot efficiency becomes increasingly smaller.
Radiation Damage and the Ferroelectric Effect in Rochelle Salt
Authors: Krueger Helmut H. A. , Cook William R. , Sartain C. C. , Yockey Hubert P.
Published: April 2005

Rochelle salt 45° X-cut square plates were exposed to Co60 radiation of 8.6×103 to 2.6×107 R and reactor radiation up to 2.4×106 R gamma plus 3.5×1015 neutrons/cm2. Measurements were made over a temperature range including both Curie points (−30° to +30°C) of dielectric constant and loss, elastic stiffness coefficients c44D, and mechanical Q. In addition, double-crystal x-ray rocking curves were made above the upper Curie point to check line broadening. All the data indicate an initial improvement in crystal perfection (Curie points are sharper, linewidths narrower) up to 8.6×104 R, with subsequent degradation (Curie point and linewidth broadening: finally coalescence of Curie points) including elimination of the ferroelectric phase after 2.6×106 R Co60 radiation or 2.4×106 R gamma plus 3.5×1015 neutrons/cm2 reactor radiation. The Q rose with radiation dosage as the ferroelectric phase disappeared, dropping only at the highest dosage. Destruction of the ferroelectric phase by radiation is compared to similar effects due to substitution of NH4 for K in the Rochelle salt lattice.
Point Contact Diodes Utilizing Single-Crystal Reduced Rutile Titanium Dioxide
Authors: Davis Goebel , Grannemann W. W.
Published: April 2005

Point contact diodes were made by utilizing reduced single-crystal rutile TiO2. No indication of minority carrier holes injection was experimentally detectable. The diode volt-ampere characteristics were fitted to different theoretical mathematical models of diode operation for noninjecting contacts. The resultant fits indicate (for both diode and diffusion theory) that the rectification phenomena is most likely attributable to a Mott-type barrier in which the image forces reduce the effective barrier height in the reverse direction.
Solubility and Diffusion of Zinc in Gallium Phosphide
Authors: Allison Herbert W.
Published: April 2005

The solubility and diffusion coefficient of zinc in gallium phosphide have been determined over a temperature range of 700–1300°C. The maximum solubility of Zn in GaP is about 4×1020 atoms cm−3, and occurs at approximately 1200°C. The diffusion is similar to that of Zn in GaAs and can be represented by the equation: D=1.0 exp[−2.1/kT]. The mechanism of diffusion evidently involves interstitial Zn as well as Zn on substitutional sites.
Crystalline and Paracrystalline Order in High Polymers
Authors: Hosemann Rolf
Published: April 2005

The mathematical treatment of light scattering by regular and random arrays of points is outlined. The diffraction patterns of two-dimensional models are compared with patterns from ideal crystals, imperfect crystals, and paracrystalline lattices. The effects of various types of crystalline imperfections and paracrystalline order on the diffraction pattern are analyzed and examples are presented. It is shown that both natural and synthetic polymers can be treated as paracrystalline materials. The diffraction patterns of polyethylene after various thermal and mechanical treatments are discussed. A detailed model of the structure of polyethylene is presented and various features of the structure of other polymers are pointed out.
Order and Flow of Liquid Crystals: The Nematic Mesophase
Authors: Porter Roger S. , Johnson Julian F.
Published: April 2005

Liquid crystals offer a unique opportunity for physical studies. The nematic mesophase is an aggregate, yet fluid state, which consists of anisometric, rodlike structures. The flow of three nematic-forming compounds, p-azoxyanisole, anisaldazine, and p-anisal-p-aminoazobenzene, was studied in both their isotropic and anisotropic states. Studies were made with capillary viscometers and with a high-shear concentric cylinder viscometer. New density, coefficient of expansion, and transition temperature data are also given. The instrumentation used is described. The results add definition to the viscosity and density anomalies at nematic-isotropic transitions. The data for p-anisal-p-aminoazobenzene are entirely new. Values for anisaldazine establish previous viscosity and density results on an absolute basis. New results on p-azoxyanisole contribute a temperature and shear rate extension to previous studies.
Order and Flow of Liquid Crystals: The Cholesteric Mesophase
Authors: Porter Roger S. , Johnson Julian F.
Published: April 2005

The flow properties of three cholesteryl esters have been studied in both their liquid crystal and isotropic ranges. Tests were made with low-shear capillary viscometers and with a high-shear rotational concentric cylinder instrument. Measurements on cholesteryl acetate are compared with relative viscosities given by Ostwald. Ostwald's viscosity data on cholesteryl propionate and butyrate are reevaluated. New flow data are also given for cholesteryl palmitate and stearate. Viscosity and flow activation energy are reported as a function of temperature, shear, and ester molecular weight. Results indicate that all cholesteryl esters show Newtonian flow in their isotropic states and non-Newtonian flow in their respective cholesteric liquid crystal phases. New transition temperature and density data are also given for the three esters. These values and earlier density data for the benzoate ester are discussed in terms of the aggregate size of liquid crystals. Comparisons are made between the major types of mesophase.
Rhe-Optical Properties of Polymers. III. Dynamic Polarized Light Scattering
Authors: LeGrand D. G. , Erhardt P. F.
Published: April 2005

In a recent paper on the dynamic strain-optical coefficient for polyethylene, it was reported that the strain-optical coefficient displayed a relaxation-dispersion effect. Experiments have now been carried out to measure the dynamic scattering strain-optical coefficient as a function of frequency. Preliminary results are presented and interpreted in terms of the motion of domains within the specimen under dynamic conditions.
Dynamic Birefringence of High Polymers II
Authors: Stein R. S. , Onogi S. , Sasaguri K. , Keedy D. A.
Published: April 2005

The time-dependence of birefringence was investigated in experiments involving relaxation at constant strain, extension at constant rate of strain, and periodically varying strain. The results of constant strain relaxation are calculated from the other two types of experiments using the linear phenomenological theory of birefringence relaxation. Strain-optical coefficient spectra are calculated for a number of low- and high-density polyethylenes and characteristics of the spectra are correlated with sample density. A simple molecular theory is presented. The time-dependence of birefringence is believed to principally arise from the finite relaxation time for crystal orientation.
On Maser Rate Equations and Transient Oscillations
Authors: Tang C. L.
Published: April 2005

Masers exhibit interesting transient behavior that cannot be completely understood on the basis of the rate equations. The use of the rate equations in most transient analyses is usually justified on a more or less intuitive basis and the implied assumptions are not always clear. In this paper, the macroscopic maser rate equations are derived systematically from the Boltzmann equation for the density matrix of the atomic systems and Maxwell's equations for the radiation fields. When the coherence linewidth (T2−1) of the atomic systems is much larger than the cavity linewidth and the natural linewidth (T1−1) of the atomic emission, and with a WKB approximation, in the lowest order of approximation one obtains the two widely used, coupled first-order nonlinear rate equations of Statz and deMars. On the other hand, if the cavity linewidth is much larger than the atomic linewidths (T1−1 and T2−1), one can use the so-called ``reaction-field principle'' of Anderson and obtain, again, two coupled first-order rate equations; however, only one of the equations is nonlinear. The ranges of validity of both approaches are discussed in some detail.
Electrical Conductivity of Cesium-Seeded Atmospheric Pressure Plasmas near Thermal Equilibrium
Authors: Harris Lawson P.
Published: April 2005

Measurements have been made of the electrical conductivities of gaseous mixtures formed by the addition of small fractions of cesium vapor to nitrogen, helium, neon, or argon. The mixtures were maintained near thermal equilibrium at temperatures in the 1500°–2000°K range and a total pressure of one atmosphere. The cesium vapor pressures ranged over two decades, from 0.1 to 10 Torr.

The apparatus consists, in essence, of two heated zones connected by a slow flow. The first zone is a low-temperature (200°–400°C) oven where the body-gas flow picks up the cesium vapor. The second zone is a small electrically heated furnace (1250°–1850°C) containing a diode test section.

The principal measurements taken were the seeding temperature, furnace temperature, and voltages and currents in the test section.

The results exhibit variations with temperature, seeding pressure, and gas species that correlate reasonably well with simple theory and values for electron collision frequencies and cross sections taken from the literature.
Ultrasonic-Diffraction Shutters for Optical Maser Oscillators
Authors: DeMaria A. J.
Published: April 2005

The ultrasonic-diffraction effect was utilized as a shutter to gate and amplitude modulate the output of a ruby optical maser (laser) by regulating the optical feedback within the Fabry-Perot interferometer. In addition, an oscillation resembling limit cycle operation was induced in the ruby laser by an ultrasonic-progressive wave that periodically changed the optical path length between the interferometer reflectors by varying the refractive index.
Study of the Cathode-Fall Region in a Pulsed Glow Discharge
Authors: Nahemow M. , Wainfan N.
Published: April 2005

Time-resolved optical studies were made of the cathode-fall region of a wall-bounded pulsed discharge in hydrogen. The temporal variation and spatial configuration of the electric fields within the cathode-fall region are presented as a function of the experimental parameters. The short cathode-fall region formed within 0.1 μsec and remained stable for the duration of the applied-voltage pulse. This rapid formation requires that the positive-ion space-charge cloud near the cathode face be formed locally. It is speculated that a fast initial breakdown wave leaves behind a low-density plasma, which then goes into the equilibrium configuration by an over-damped plasma oscillation mode.
New Type of Two-Stream Plasma Instability
Authors: Tosima S. , Hirota R.
Published: April 2005

The stability of one of the low-frequency plasma oscillation modes is examined from the standpoint of two-fluid theory. It is found that when the scattering time is short enough, a density perturbation may actually grow at the frequency of one of the acoustic modes. In this short scattering time regime, the phase difference between the electron and hole perturbation velocities can lead to a net growth of the perturbation. If the damping effects of diffusion and recombination of excess carriers can be overcome by the growing mechanism, the net result would be a growing instability. The results presented are applicable to both gaseous and solid-state plasmas. Some discussion is given on which solid-state materials might exhibit this new instability. It is found that InSb is best, but that bismuth might also be suitable.
Linewidth and Conditions for Steady Oscillation in Single and Multiple Element Lasers
Authors: Fleck J. A.
Published: April 2005

A derivation is given for the linewidth of an optical maser at steady power, taking into account its peculiar physical configuration and mode structure. Two limiting cases are considered: one in which the number of back and forth reflections between the end plates is not sufficient to establish a mode in the sense of Fox and Li, the other in which such a mode is established. The linewidth for the latter case may be interpreted as the ``theoretical lower limit.'' It is pointed out, however, that this limit could not be attained even if all other sources of noise in the maser system could be eliminated. General conditions are also developed for the oscillation of a system consisting of any combination of laser and mirror elements.
A Correlation of Mechanical Properties and Microstructure of Polytetrafluoroethylene at Various Temperatures
Authors: Speerschneider C. J. , Li C. H.
Published: April 2005

Mechanical properties and microstructure of PTFE at various temperatures were correlated through the effects of temperature and band size on the flow stress and microstructure deformation. Electron microscopic examination of deformed microstructure showed that at low temperatures the crystalline deformation modes (kinking and bowing) were favored, whereas noncrystalline modes (sliding and rotation) were predominant at high temperatures. At low temperatures PTFE showed a crystalline size effect and stress drop phenomenon in its flow-stress relations not manifested at high temperatures.
Hypervelocity Impact of Radioactive Projectiles into Stainless Steel and Aluminum
Authors: Rolsten R. F. , Schmitt R. A.
Published: April 2005

Radioactive, cylindrical, steel projectiles were explosively accelerated into plates of stainless steel and aluminum. The amounts of radioisotopes Fe59 and Cr51 in the projectile prior to acceleration and in the crater in plate were measured in order to determine the fraction of the original projectile remaining in the crater.

Impact experiments with steel plates showed that 3.4 to 7.8% of the original projectile remained in the crater of the steel plate; 3.6 to 7.5% of the original projectile remained in the crater of the aluminum plate. Data on any given crater, obtained by the measurement of both Fe59 and Cr51, are in good concordance. The fraction of the projectile remaining in the crater is independent of the impact velocity over the range of 12 000 to 14 900 ft/sec (3600 to 4540 m/sec).
Modulation of Carrier Surface Lifetime and the Time Constants of Surface States in Si
Authors: Alexanderakis G. C. , Dousmanis G. C.
Published: April 2005

The effects of ac fields on the surface potential (φs) and recombination velocity (s) (or surface lifetime) of carriers in Si surfaces have been studied by means of a method used earlier in Ge. The field is applied normally to the ``back surface'' of large area p-n junctions and its effects on the surface are detected by means of changes in the reverse saturation current of the diode. The study yielded the following results: The range of the equlibrium values of φs at 300°K is about ±0.5 V. Mainly one recombination energy level is found at ±16 kT from mid-gap. The effectiveness of the modulation of s is a measure of surface response. The data are compared with frequency response curves derived for some specific distributions of time constants for the surface states. The response to applied fields is much larger in the higher frequency range (5 to 50 kc/sec) rather than at 10–1000 cps. The time constants for the Si surface states involved in this behavior are ≈10−4 sec, one to two orders to magnitude shorter than in Ge, and this may account for the difficulties encountered earlier in modulating φs in Si at the low frequencies used in Ge. These surface states, that inhibit modulation at low frequencies, may be the usual states on the outside of the oxide (``slow'' states), part of the ``fast'' states at the semiconductor-oxide interface, or may be spread in the space-charge region.
Evidence for the Existence of Overlapping Valence and Conduction Bands in SnTe
Authors: Damon D. H. , Martin C. R. , Miller R. C.
Published: April 2005

Measurements of the magnetic field dependence of the Seebeck coefficient of a sample of SnTe provide evidence for the existence of overlapping valence and conduction bands in this material.
Growth Mechanisms in Germanium Dendrites: Three Twin Dendrites; Experiments on and Models for the Entire Interface
Authors: Seidensticker R. G. , Hamilton D. R.
Published: April 2005

The measured growth velocity of three twin germanium dendrites has been related to melt undercooling and to one of the twin spacings, and can be explained by the theory for two twin dendrites of this spacing. Three twin dendrites differed from two twin dendrites in that they grew at lower undercoolings, and, when propagation was possible, grew as fast or faster in the reverse or [2̄11] directions as in forward or [21̄1̄]'s. Irrespective of twin structure, the theory of Horvay and Cahn fitted parabolic decanted interfaces, provided the undercooling was taken to be that apparent at the tip and not that of the melt. Calculations from a model show layer nucleation to be possible on part of the interface and provide a rational for the understanding of H-arm growth. The spacing of certain facets is found to agree moderately well with predictions of the theory of Mullins and Sekerka on morphological instabilities.
Pressure Dependence of Creep in Zn and Cd
Authors: DeVries K. L. , Gibbs P.
Published: April 2005

Bending creep in Zn is reported as a function of hydrostatic confining pressure P up to 8 kbars. The ratio of activation volume for creep to atomic volume, ΔV‡/V0=0.65−0.044 P (P in kbars), is essentially independent of temperature between 27° and 57°C. The ratio ΔV‡/V0=0.63−0.035 P for creep of Cd is independent of temperature between 0° to 57°C. ΔV‡/V0 for Zn at a given pressure was 5 to 15% higher for creep than for self-diffusion in the basal plane reported by Liu and Drickamer.
Calcium Niobate Ca(NbO3)2—A New Laser Host Crystal
Authors: Ballman A. A. , Porto S. P. S. , Yariv A.
Published: April 2005

Large single crystals of calcium niobate Ca(NbO3)2, grown by the Čzochralski technique, are transparent and can be doped with rare earth or transition metal ions. Laser action has been observed in calcium niobate doped with trivalent neodymium, holmium, praseodymium, erbium, and thulium.
Dipole Resonances of a Plasma in a Magnetic Field
Authors: Crawford F. W. , Kino G. S. , Cannara A. B.
Published: April 2005

It has been known for many years that cylindrical plasma columns subjected to a transverse electric field exhibit dipole resonance effects. Very little attention has been given to the modification of this phenomenon by a magnetic field. This paper gives a theory for the splitting of the resonance that occurs under these conditions and describes experiments carried out using mercury-vapor discharges at a pressure of about 1 μ Hg to verify the theoretical prediction. Good agreement was obtained for magnetic fields giving an electron cyclotron frequency up to about half the geometric mean-resonant frequency, and it is suggested that the effect provides a useful diagnostic technique for the measurement of mean electron density and magnetic field in discharge columns.
Calculation of Axially Symmetric Electrostatic Fields for Two Coaxial Equidiameter Cylinders
Authors: Morikawa Minoru
Published: April 2005

A method is given for calculating the potential distribution of a system consisting of two coaxial cylinders, each of unit radius, separated by a distance of 2a along the axis. The potentials of the left- and right-hand cylinders are taken as −1 and +1, respectively. The problem can be solved if the potential φ(1,z) on r = 1 or its inverse Fourier sine transform A(λ) is obtained. The dual integral equations for A(λ) are derived from the boundary condition on the cylinders and the continuity condition of the potential and of its normal derivative on the gap (r = 1, |z|≤a) between the cylinders. The solution A(λ) is expressed by the following series: A(λ)=2πJ0(λa)λ+ ∑ n=1∞anJ2n(λa)λ. The coefficients an in this series satisfy an infinite set of linear equations. The values of an for several values of the half-gap length a are calculated by successive approximations and are shown in a table.
Improved Thermionic Emitter Using Uniaxially Oriented Tungsten
Authors: Weissman Ira , Kinter M. L.
Published: April 2005

Emission from most practical electron sources is nonuniform over the emitting area. Ordinary metallic surfaces are polycrystalline and their emission comes from many different small crystal facets whose work functions can vary over a wide range of values. As an example, the range of work functions of tungsten goes from a low of 4.3 eV for the (116) face to a high of 5.9 eV for the (110) face. Substantially improved uniformity of work function and current density would result if the entire emitting surface contained only a single-crystal plane. The use of a single crystal as a means of obtaining such a surface is costly and wasteful since its unique bulk properties are superfluous and do not in any way contribute towards the improved performance. Even more important, using a single crystal inherently limits one to planar geometries.

Many polycrystalline materials of arbitrary shape, among them the refractory metals, when prepared by chemical vapor deposition can be made to exhibit a high degree of uniaxial crystal orientation with their preferred axis centered about the direction of growth. Given proper treatment after deposition, the surface of such materials predominantly consists of a single-crystal plane.

In this paper, X-ray, optical, and thermionic-emission measurements are described which were made on vapor-deposited tungsten prepared by the hydrogen reduction of tungsten hexafluoride. By comparing volt-ampere characteristics of high-vacuum diodes, one of which contains a conventional tungsten filament and the other a chemically vapor deposited one, of identical dimensions, it is found that there is an expected improvement in emission uniformity due to the uniaxial grain orientation in the latter.

By a similar comparison of cesium-neutralized energy-converter diodes, it is shown that the improved surface uniformity results in significantly improved power quadrant characteristics.
Steady-State Output Power of a Laser as a Function of the Single-Pass Gain
Authors: Tobias Irwin
Published: April 2005

An expression for the output power of a laser in terms of the measured single-pass gain is discussed for two cases: homogeneously and inhomogeneously broadened spectral lines. The results are applied to the 6328-Å laser line in the helium-neon mixture, but only an order-of-magnitude calculation is possible because of the lack of data. Finally, several of the assumptions made during the derivation are discussed.
Near-Ultraviolet Light Scattering for the Determination of Molecular Dimensions
Authors: Krigbaum W. R. , Smith P. , Mark F. G.
Published: April 2005

Modification of a conventional light-scattering photometer for measurements in the near ultraviolet is described. As a test of the instrument, unperturbed dimensions are determined for a series of polystyrene fractions covering a thirtyfold range of molecular weight. Values of the Flory hydrodynamic parameter are found to be nearly independent of molecular weight, averaging 10−21 Φ = 2.65±0.24, but there is a fairly definite indication that the polystyrene chain is non-Gaussian for molecular weights below 3×105. Use of a 313-mμ wavelength extends the measurement of radii of gyration of coiling molecules down to 100 Å, which is about the upper limit which has been achieved by low-angle x-ray diffraction.
Power Spectrum of the Barkhausen Noise of Various Magnetic Materials
Authors: Mazzetti P. , Montalenti G.
Published: April 2005

This work describes a simple apparatus used to measure power spectra of Barkhausen noise in an analysis frequency band between 25 and 104 cps. Because previous work by the authors showed that when the specimen is in the form of a closed magnetic circuit and unlaminated the intensity of the noise has but small dependence on the core dimensions, unlaminated ring-shaped samples were used in this work. Spectra obtained with a magnetizing field frequency of 0.1 cps are given for iron, 6% silicon iron, grain-oriented silicon iron, ultraperm, mumental, nickel, and Permalloy C. It is observed that the intensity of the noise depends to a large extent on the nature of the ferromagnetic material. No interpretation of this fact is given, as it appears very complicated to understand.
One-Sided Multipactor Discharge Modes
Authors: Vance Edward F.
Published: April 2005

Modes of multipactor discharge occurring in a biased gap are described in which secondary emission from only one electrode is required to sustain the discharge. An analysis of these modes and an experimental corroboration of the theory are presented.