bluuebunny/crossref_metadata_2025 huggingface dataset:
Curie Temperature of Some Garnets by the Differential Thermal Analysis Technique
Authors: Aharoni A. , Frei E. H. , Scheidlinger Z. , Schieber M.
Published: April 2005

The differential thermal analysis (DTA) technique is used to measure the Curie temperature of yttrium iron garnets, and of the garnets obtained by partially substituting Sm, Nd, Pr, or La for the Y. The accuracy of the method is within about 1°C. It is found that in all the above substitutions the Curie point is increased more or less linearily in the rare-earth contents, with the largest slope for Pr, somewhat less for Nd and Sm. For La, only the compound Y2.5La0.5Fe5O12 could be prepared and it did not show any measurable change from the Curie point of pure yttrium iron garnet. Two possible explanation are suggested to the increase in Curie point by Sm substitution, which does not change the magnetization of the garnet.
Paramagnetic Resonance of Defects Introduced Near the Surface of Solids by Mechanical Damage
Authors: Walters G. K. , Estle T. L.
Published: April 2005

Electron spin resonance characteristics of a number of materials subjected to violent mechanical treatment are reported. A line with g=2.0055 observed in silicon is attributed to defects introduced near the surface by mechanical damage. The resonance properties are uninfluenced by interactions of the silicon surface with atmospheric gases. Similar lines appear in germanium, silicon carbide, and diamond. The dominant line produced by mechanical damage to MgO is attributed to F centers. Similar lines are observed in other II-VI compounds. Results are also reported for a number of other materials. Similarity between defects produced mechanically and by fast neutrons is noted.
Modification of the Koehler-Granato-Lücke Dislocation Damping Theory
Authors: Swartz J. C. , Weertman J.
Published: April 2005

The dislocation damping theory of Koehler, Granato, and Lücke is modified for metals with high stacking fault energy. It is assumed that the most abundant impurity atom species interacts only with the edge component of each dislocation. For this model the hysteretic, or frequency independent damping initially increases linearly with stress amplitude and approaches the Granato-Lücke amplitude dependence at higher stresses. The influence of a second, less abundant impurity atom species which can interact with both screw and edge components also is considered. When the glide distance of a dislocation after breakaway becomes comparable with the mean spacing of the second type of impurity, the hysteretic damping becomes amplitude independent. This modification is best suited for application to the damping of bcc metals containing a higher concentration of substitutional impurities than interstitial impurities.
Energy of a Crossed Grid of Screw Dislocations
Authors: Li James C. M.
Published: April 2005

The strain energy of a crossed grid of screw dislocations is calculated using isotropic elasticity theory. It is found that a distortion from the stable structure requires a large amount of strain energy. It is indicated that long-range stresses can exist in metastable dislocation networks without a long pile-up of like dislocations. Possible rearrangements of dislocation networks in both fcc and bcc metals are shown.
Generation and Distribution of Dislocations by Solute Diffusion
Authors: Prussin S.
Published: April 2005

The stress introduced by solute lattice contraction of boron and phosphorus in silicon is shown to be sufficient to generate dislocations in silicon wafers. Such dislocations were observed. Expressions for the density distribution and for the total number of dislocations generated are derived and a mechanism of dislocation generation and distribution during the diffusion process is postulated. The dislocation distribution is shown to be highly dependent upon the nature of the diffusion process, expressions being derived for the conditions of (1) constant surface concentration of solute and (2) diffusion from a finite source. An expression for and means to determine the residual stresses in diffused silicon wafers are given.
Behavior of Exploding Gold Wires
Authors: Tucker T. J.
Published: April 2005

A square-wave generator current source was used to study the behavior of gold wires exploded by current densities in the range of 0.25×108 to 3.26×108 amp/cm2. Measurements of wire resistance vs cumulative energy and action at various current densities are compared with a simple theoretical exploding wire model and the results of Kerr cell photographic studies. Experimentally, the total energy input to the time of maximum wire resistance increases with current density and may exceed by threefold the normal vaporization energy. Also, the instantaneous wire resistance at any point is smaller with a larger current density. The resistance depression is first apparent in the region following vaporization. At higher current densities, the effect is observed to occur at progressively earlier phases up to and including the point at which melting occurs.
Microwave Harmonic Generation by Ferrimagnetic Crystals
Authors: Douthett D. D. , Kaufman I. , Risley A. S.
Published: April 2005

The experimental behavior of isotropic ferrimagnetic insulators in second harmonic generation at microwave frequencies has been investigated and compared with the behavior predicted by the equations of motion with Landau-Lifshitz and with Bloch-Bloem-bergen damping. In general, a close agreement between experiment and theory was found. The experiments were carried out with small samples of single-crystal manganese ferrite, YIG, and other ferrimagnetic materials. Since harmonic generation results from asymmetries in the precessional orbit, measurements were made with disk-shaped specimens in which the demagnetizing fields create the asymmetry. The technique employed a cavity simultaneously resonant to 8.5 and 17 kMc. Absolute values of field intensities and magnetizations were computed from absolute power measurements. A figure of merit F for a ferrimagnet is defined. In a practical 2ω generator the output power P2ω is expected to vary as the product F2Pi2, where Pi is the input ω power. In comparing materials at ferrimagnetic resonance (FMR), F should vary as χ0″. This was verified experimentally, even at high drive levels. At constant frequency and drive level F should be nearly independent of Hdc. Only slight deviations from this were found at low drive levels.
Mechanism of Chemisorption, Place Exchange, and Oxidation on a (100) Nickel Surface
Authors: Farnsworth H. E. , Madden Hannibal H.
Published: April 2005

Results obtained by low-energy electron-diffraction and photoelectric work-function measurements indicate that the following features result from exposure to oxygen at room temperature. Initial adsorption occurs in an amorphous molecular form. Some of the adsorbed molecules diffuse over the surface to lattice-defect sites where they dissociate. The resulting atoms form in a lattice structure surrounding the defect site. With continued exposure to oxygen, a place exchange between some oxygen and nickel atoms occurs to form a single-spaced simple-square structure with a slight increase in the lattice constant. This place exchange immediately precedes, in exposure, the formation of the oxide structure of the rock-salt type. The work function of clean (100) nickel depends on the type of anneal. φ=5.08 ev after argon ion bombardment, φ=5.12 ev after a small anneal, φ=5.22 ev after a more complete anneal.
On the Wear of Sapphire
Authors: Steijn R. P.
Published: April 2005

The wear resistance of single crystals of sapphire was determined as a function of crystallographic orientation with respect to plane of wear and rubbing direction. Distinct anisotropy was found. Evidence of plastic flow at the wear surface on both basal and prismatic slip systems was obtained. In bulk deformation tests, these systems do not become operative until a temperature of 1000°C is reached for basal slip, 1800°C for prismatic slip. The resistance against wear correlates in a qualitative way with the relative ease of operation of the two slip systems involved. When the orientation is such that both basal and prismatic slip are blocked, a brittle type of wear occurs that is characterized by conchoidal fracture. All results confirm that plastic flow during rubbing is a governing factor in, if not an integral part of, the wear process for even such a hard material as sapphire.
Specific Heat of Superparamagnetic Particles
Authors: Livingston J. D. , Bean C. P.
Published: April 2005

The specific heat of an assembly of independent superparamagnetic particles has been calculated with the methods of statistical mechanics. The cases of isotropic particles in an applied field and anisotropic particles in the absence of a field have been considered. The specific heat calculated is temperature dependent and is of the order of k per particle at low temperatures. A smaller contribution varying linearly with temperature can also appear, thereby affecting the linear temperature coefficient of specific heat usually associated with the electronic specific heat. Conditions are discussed under which these effects should be experimentally observable.
Majority Carrier Magnetosurface Effect
Authors: Larrabee Robert D.
Published: April 2005

In semiconductors with extremely low majority carrier densities, the conductivity of the surface space charge region can be very different from the conductivity of the bulk. This paper demonstrates that the conductivity of this surface space charge region can be materially altered by the application of a magnetic field which is perpendicular to the direction of current flow. A tentative prototype model of this effect is presented which not only illustrates the mechanisms of importance, but also is sufficiently accurate to enable one to estimate the order of magnitude of the effect for certain experimental conditions. This model suggests that this effect may find application in magnetoresistance and/or negative resistance devices and might prove useful in the measurement of surface parameters.
Preparation of Monocrystalline Cuprous Oxide
Authors: Ebisuzaki Yukiko
Published: April 2005

A method is described for preparing large single crystals of cuprous oxide by oxidation of monocrystalline copper. The initial oxidation is performed slowly at low oxygen pressure and temperature, to promote oriented growth of the oxide film. The cuprous oxide crystals obtained from the oxidation process showed subgrain boundaries which were removed by subsequent annealing.
Conductivity of Seeded Atmospheric Pressure Plasmas
Authors: Frost L. S.
Published: April 2005

The electrical conductivity is calculated for some typical seeded gases of magnetohydrodynamic interest. The electron density is obtained using Saha's equation. A method is developed for calculating electron mobility in gas mixtures, taking account of the variation of the scattering cross section with energy. Scattering by ions is also considered. Results are presented for several gases seeded with small amounts of Cs or K in the temperature range from 2000° to 4000°K.
Electron Microscope Investigation on the Nature of Tracks of Fission Products in Mica
Authors: Bonfiglioli Guido , Ferro Andrea , Mojoni Adriana
Published: April 2005

Specimens of biotite, muscovite, artificial fluorophlogopite, and muscovite annealed at 900°C were examined using an electron microscope after having been covered with a uranium layer and irradiated in a reactor. Tracks due to fission products appeared on every specimen except biotite, and the respective diameters were put into correspondence with the resistance of the various micas to thermal decomposition. The tracks were larger in muscovite (240 A), thinner in fluorophlogopite (150 A), and still more in dehydrated muscovite (115 A). The writers believe that the mechanism of damage has its origin in the heat released by the heavy ionizing particles. Peculiar recovery effects were often observed.
Magnetic Investigation of Pure Manganese and of Several of its Alloys
Authors: Cooper H. W. , Arrott A. S. , Paxton H. W.
Published: April 2005

Arrott, Coles, and Goldman have shown that a parasitic ferromagnetism can be induced at low temperatures in antiferromagnetic α manganese by pickling in nitric acid, and that this effect can be subsequently removed by a vacuum anneal. We have confirmed this result. Furthermore, we have eliminated as possible sources for this effect the presence of hydrogen or nitrogen in solid solution and the formation of nitrides or hydrides. However, strains arising upon transforming from the β phase to the α phase can induce this parasitic ferromagnetism. These results fit well with Li's hypothesis of antiferromagnetic domain boundaries giving rise to parasitic ferromagnetism. According to Li, strains should serve well to stabilize the domain boundaries.
Growth of Refractory Crystals Using the Induction Plasma Torch
Authors: Reed Thomas B.
Published: April 2005

Apparatus is described for growing refractory crystals using the induction plasma torch in a Verneuil-type geometry. The plasma torch makes possible crystal growth at higher temperatures than can be achieved with flames and in inert or reactive atmospheres. Conditions are given for growth of sapphire, stabilized zirconia, and niobium crystals.
A cw Solid State, Push-Pull Maser in the 5 to 6 Millimeter Wavelength Region
Authors: Carter David L.
Published: April 2005

Cw maser oscillation from 49 to 57 kMc was achieved with 0.12% Fe3+-doped rutile, using push-pull pumping at 78.2 kMc. A short experiment on cross-relaxation effects was also performed.
A Comparison of Theory and Experiment for a Thermoelectric Cooler
Authors: Norwood M. H.
Published: April 2005

The performance of single-stage Peltier thermocouples was calculated using the experimentally measured values of thermoelectric power, electrical resistivity, and thermal conductivity as functions of temperature. These calculations were made by solving numerically the differential equation for the temperature distributions in the thermoelements. The boundary conditions were the hot junction temperature and the heat flow at the cold junction. The calculated behavior of the thermocouples agreed well with the measured performance in the three cases studied. The measured thermocouple figure of merit agreed with that calculated from the material properties.

The effect of temperature variations of the material properties on thermocouple performance was studied by comparing exact calculations with calculations involving one temperature-averaged constant material property. This type of calculation showed that the Thomson effect caused about 4°K of the maximum ΔT of 66°K for one couple studied. The temperature variation of resistivity was found to be the major cause of disagreement between exact calculations and the simpler theory (Ioffe equations).
Hardening of Lithium Fluoride Crystals by Irradiation
Authors: Nadeau J. S. , Johnston W. G.
Published: April 2005

The very soft, pure crystals of LiF that are now commercially available are unsuitable for some experimental work because they suffer accidental plastic deformation during cleavage and tend to split on (110) planes. Irradiation with gamma rays produces harder crystals that can be cleaved and handled without much damage. The radiation-induced hardening and the color centers produced by moderate irradiation can be completely removed by annealing for several hours at 450°C. This method for handling very soft crystals may be useful for other types of crystals, and various types of irradiation can be employed.
Motion of c Domain Centers in BaTiO3
Authors: Link G. L.
Published: April 2005

A novel effect has been observed in BaTiO3. By applying a biased alternating field to a BaTiO3 crystal which contains an a domain, one can observe a large number of small dots which move in straight lines. The dots are shown to be small c domains, and their motion can be accounted for by the electric field perturbation caused by the a domain.
Momentum and Energy of Waves
Authors: Pierce J. R.
Published: April 2005

Elementary arguments of conservation of energy and momentum are used to derive expressions for what Sturrock terms the ``formal'' momentum, angular momentum, and energy of a plane wave in a moving medium. If E is the energy per unit length, p the momentum per unit length, q the angular momentum per unit length, vf the phase velocity, and if the angular variation of a circulatory polarized wave is as exp(—jnθ), p=E/vf,q=nE/ω.If E0 is the energy per unit length observed moving with the medium, and then if the medium moves past the observer with a velocity u and the observer measures a phase velocity vf, he observes an energy per unit length E, E=E0/(1−u/vf). When p, q, and E are not the physical momenta and energy, they lead to the correct power and force for sinusoidal sources moving with respect to the medium.
Magnetic Domain Patterns in Cr-Modified Mn2Sb
Authors: Wolf J. D. , Hanlon J. E.
Published: April 2005

The relationship between microstructure and the magnetic properties of Cr-modified Mn2Sb has been studied using the Bitter pattern technique. The solid solution formed when Cr is substituted for Mn in Mn2Sb exhibits a ferrimagnetic to antiferromagnetic first order phase transformation which occurs at about room temperature for 5 at.% Cr. In the transformation temperature range, we have followed the initiation and growth of the ferrimagnetic phase by observing the associated domain patterns. In addition, the Bitter pattern technique has been used to examine precipitates with magnetic properties differing from the matrix.
Harmonic Generation and Frequency Mixing in Ferromagnetic Insulators
Authors: Jepsen R. L.
Published: April 2005

When a transverse rf magnetic field is applied to a ferromagnetic insulator, a second harmonic frequency term arises in mz (the axial or longitudinal component of the rf magnetization). If in addition an axial component of the rf field is applied, then a second harmonic frequency term appears in mt (the transverse component of the rf magnetization) as well. It happens further that mt exhibits two dc magnetic field resonances. One resonance occurs when the material is biased to the fundamental, and the other arises when the material is biased to the second harmonic.

In a similar way, application of two frequencies having both axial and transverse components results in sum and difference frequency terms appearing in mt, in addition to the usual mz. The mixed frequency terms in mz are resonant for the two values of dc magnetic field corresponding to the two applied frequencies. The mixed frequency terms in mt exhibit additional resonances for dc magnetic fields corresponding to the sum and difference frequencies.

The present paper describes calculations of second harmonic generation and second-order frequency mixing under the assumption of uniform precession of the magnetization, for small and ellipsoidally shaped samples of material and with loss included in the Landau-Lifshitz form. A simple case of third harmonic generation is also discussed. Results of the calculations are applied to a simple example of second harmonic generation. The detailed calculations and results are contained elsewhere in a rather lengthy report.
A Method for Measuring the Conductivity in a High Electron Density Plasma
Authors: Persson K. B.
Published: April 2005

The interaction between the solenoidal electric field and a circular cylindrical plasma column is used as the basis for the design of a pulse-operated bridge suitable for transient measurements of the electrical conductivity in the high-electron density plasma. The solenoidal electric field is generated in a single layer solenoid with a special shield preventing the axial electric field from interacting with the plasma, thereby avoiding the electric polarization and associated effects. The time varying magnetic field generated by the solenoid and the induced electric field are then the only fields interacting with the plasma, and these fields penetrate essentially unperturbed into the plasma as long as the skin depth of the plasma is large in comparison with its radius. The upper limit for the measurable conductivity is determined by the skin depth of the plasma, while the lower limit is determined by the noise level in and the maximum allowed signal on the bridge. The maximum allowed signal on the bridge is either determined by the fact that the solenoidal electric field must be sufficiently small so it does not disturb the thermal state of the plasma to a measurable degree, or else that the amplitude of the electron cyclotron frequency corresponding to the amplitude of the time varying, but essentially uniform, magnetic field must be negligible in comparison with the electron collision frequency vm so that nonlinear magnetic field effects are avoided. This makes the bridge most useful in the high pressure range (vm>ω) where the ratio between the upper and lower limits for the measurable conductivity in a typical afterglow plasma can be approximated as 1013p/ω, while the upper limit as determined by the skin depth is 1010/ω ohm−1 cm−1 for a plasma with 1 cm radius. A Gaussianlike pulse with a width of approximately 1 μsec is applied to the solenoids which are close to critically damped in the corresponding frequency range, resulting in a time resolution of less than ⅓ of a μsec for the conductivity measurement.
Effect of Residual Gases on the Properties of Indium Films
Authors: Caswell Hollis L.
Published: April 2005

Indium films have been deposited at pressures less than 10−9 mm Hg and at higher pressures of specific residual gases. N2, H2, CH4, A, CO, and CO2 were found to have no measurable effect on the electrical or superconducting properties of these films when present in partial pressures of 10−5 mm Hg. For oxygen, a pronounced effect was observed when K (the ratio of oxygen molecules to indium atoms striking the substrate) exceeded 3%. The room temperature resistivity increased from 9.0 μohm-cm to 14 μohm-cm, the critical temperature decreased from (3.402±0.005)°K to (3.389±0.002)°K, the effective magnetic penetration depth increased from 630±100 A to over 1000 A. For 10−3<K<3×10−2, a larger apparent penetration depth was observed for films deposited through a mask due to edge effects. It was shown that indium films could be deposited at 100 A/sec on clean, baked substrates at 10−5 mm Hg with characteristics indistinguishable from those of films deposited in ultrahigh vacuum provided the partial pressures of oxygen and water vapor were below 10−7 and 10−5 mm Hg, respectively.
Voltage Dependence of Microplasma Density in p-n Junctions in Silicon
Authors: Goetzberger A. , Stephens C.
Published: April 2005

The voltage distribution of breakdown spots in p—n junctions was measured. A junction in silicon which was uniform in its crystallographic properties, and had an impurity gradient of 1022 cm−4, showed two kinds of microplasmas. One type is characterized by bright light emission and low breakdown voltage, and the other has less light emission and higher breakdown voltage. Both have broad distribution of breakdown voltages of the order of several volts. Samples containing a grain boundary show a line of light emitting spots having a minimum spacing of 7000 A versus a 40-A spacing of dislocations along the grain boundary.
Friction and Adhesion of Clean and Contaminated Mica Surfaces
Authors: Bailey Anita I.
Published: April 2005

In order to determine the shear strength of boundary lubricants it is essential to use a substrate which is smooth on a molecular scale. An apparatus is described in which it is possible to apply normal and tangential loads to sheets of mica covered with monomolecular layers of boundary lubricant. The shear strength obtained from these experiments explains in part why frictional force and pickup are not reduced proportionately, in the presence of a boundary lubricant. The remaining difference is probably due to elastic hysteresis losses in the sliding solids. The surface energy of mica in air has also been measured by determining the force necessary to propagate a crack in the material. Cycles of opening and closing the crack have been performed and the difference in energy which is observed is attributed to the adsorption and migration of an interfacial film of air or water vapor. An electronmicrographic study of the structure of monolayers deposited by retraction from nonpolar solution is also described. This indicates that the area covered by the monolayer is only about ⅓ the total surface area. This poor coverage arises from incorporation of solvent molecules in the monolayer, which later evaporate.
Recent Work on Solid Friction at the Research Laboratory for the Physics and Chemistry of Solids
Authors: Bailey Anita I.
Published: April 2005

This paper is a review of some of the recent work which has been done in the Research Laboratory for the Physics and Chemistry of Solids, University of Cambridge. Three main topics are discussed: (a) The friction and wear of materials at very high rates of sliding. When a ball, spinning at high velocity, is brought into contact with a flat surface of a material such as bismuth, very rapid wear occurs as a result of melting on a large scale. For this to occur, the material should have a low melting point and a low thermal conductivity, as these properties together influence the rate at which the melted zone penetrates the solid. (b) Elastic hysteresis losses and rolling friction. A cylinder rolling over the surface of rubber causes the material under the roller to be subjected to a complex deformation cycle, partly torsion and partly tension. Experiments to investigate the hysteresis losses in such complex cycles are described and used in the interpretation of rolling friction results. (c) The effect of combined stresses and contamination on the growth of junctions between metal surfaces. The simple theory of friction treats the mean yield pressure and the maximum shear stress as independent strength properties. Plasticity theory suggests that the yielding of a junction should occur as the result of their combined action. The theory has been confirmed by experiment and used to explain the fact that small traces of contamination can reduce the very high values of friction observed with outgassed metals to normal values of 1 or 2.
Single Contacts and Multiple Encounters
Authors: Archard J. F.
Published: April 2005

The analysis of wear experiments suggests that most of the events which occur in rubbing are contacts between protuberances which are deformed elastically and which separate without damage; an asperity encounter with damage is a relatively rare event. Apparatus for the study of isolated single contacts is described. A single contact which is deformed elastically does not obey Amontons's law, but an assembly of such contacts (multiple contact conditions) should do so. It is shown that under multiple contact conditions the load which can be borne by elastic deformation of the protuberances may be as much as a million times larger than that which can be borne by each individual asperity contact. Reflection electron microscopy shows that many irregularities on worn surfaces must bear their share of the load without plastic flow. Recent experiments suggest that, although a worn particle is produced very infrequently, it is nevertheless the direct consequence of the many preceding encounters which occurred without apparent damage.
Electron Spin Resonance in Neutron-Irradiated Quartz
Authors: Silsbee Robert H.
Published: April 2005

The electron spin resonance of one of the defects produced by fast neutron irradiation of crystalline quartz is analyzed. The g tensor and hyperfine tensors deduced from these results imply that the defect electron is in a nonbonding tetrahedral hybrid orbital on a silicon. It is suggested that the instability of the lattice at high doses results in part from the presence of these defects.
Shock Wave Compression of Hardened and Annealed 2024 Aluminum
Authors: Fowles G. R.
Published: April 2005

Measurements of the Hugoniot equations of state of hardened and annealed 2024 aluminum at pressures below 50 kbar are presented. The major aim of the experiments was to determine the validity of elastic-plastic theory, which predicts that, at a given compression, the stress normal to the shock front is larger than the hydrostatic pressure necessary to produce the same compression by an amount equal to two-thirds the yield strength in simple tension. Oblique shock geometry was employed. Shock and free-surface velocities were recorded with a streak camera by means of a light-reflection technique employing the principle of the optical level. This technique provides continuous recording of free-surface motion with time, an essential requirement because of the existence of a double shock system. The observed elastic wave amplitudes (5.4±0.2 kbar and 0.9±0.2 kbar for hardened and annealed material, respectively) agree within experimental precision with values predicted from static tensile specimen data. The shock wave data, in the range 25–50 kbar, yield one-dimensional strain isotherms which, while significantly different for the two different hardness conditions, agree within experimental precision with semitheoretical curves based on Bridgman's hydrostatic data to 30 kbar and on simple tension stress-strain data. No significant strain rate effects are evident. It is concluded that elastic-plastic theory is valid for the description of plane shock waves in this material.
Low-Angle X-Ray Diffraction of Crystalline Nonoriented Polyethylene and Its Relation to Crystallization Mechanisms
Authors: Mandelkern L. , Posner A. S. , Diorio A. F. , Roberts D. E.
Published: April 2005

X-ray diffraction maxima at low angles have been observed in crystalline but nonoriented linear polyethylene, the crystallization process being conducted from the melt of the pure undiluted polymer. Several orders of diffraction are observed in favorable cases, and the spacings corresponding to the first-order reflections range from 150–850 A. The values of the maxima depend on the mode of crystallization. Previous assertions that in such systems the maxima are limited to 100–200 A are shown to be very restrictive and typical only of crystallization processes conducted at very large undercooling. Major attention is focused on the properties of specimens crystallized isothermally at relatively low values of the undercooling. The spacings are very sensitive to the crystallization temperature in this range. The highest values are observed at low undercooling, and substantial decreases occur as the temperature is lowered. Concomitantly, the density observed after isothermal crystallization significantly decreases with a lowering of the crystallization temperature.

The fact that a periodicity can be developed in such systems, the magnitude of the maxima, and their dependence on the crystallization temperature, is explicable by the application of nucleation theory. It is assumed that subsequent to the formation of critical-size nuclei from a bundle of polymer chains, crystal growth along the chain direction is severely retarded, while in the transverse direction essentially unimpeded crystallization occurs. From the observed temperature coefficient of the low-angle spacings, the ratio of the excess free energy (resulting from the junction of crystalline and amorphous regions at the crystallite ends) to the bulk enthalpy of fusion is found to be 2.6. The magnitude of this ratio receives confirmation from another type of experiment.
An Approximate Solution of Fick's Diffusion Equation
Authors: Tsang T.
Published: April 2005

An approximate method of solving Fick's diffusion equation (or the heat conduction equation) with variable diffusion coefficients is discussed. Simple solutions may be obtained. In one example, the result appears to be in good agreement with the more elaborate numerical calculations by Crank.
Experimental Study of Arc Stability. II. An Investigation of Mercury Arc Stability
Authors: Farrall G. A. , Reiling G. H.
Published: April 2005

The duration of an arc struck on a mercury pool has been studied under a variety of arc currents and vapor pressures. It is shown that at temperatures greater than −38°C the distribution of arc lifetimes follows an exponential decay law over the entire current range studied, whereas a distinct departure from this distribution occurs between −57° and −195°C. Over the current range 0.02–2.0 amp the mean arc lifetime varies from a few microseconds to 0.1 sec on a mercury cathode at 23.5°C. This study extends previous work and establishes that there is a sudden change in arc stability at the melting point. The data demonstrate, contrary to experience with liquid mercury, that an arc can be struck for very low currents in the case of solid mercury and, once struck, will burn for a finite length of time given by τ=τ0+KI, where τ0 is a residual lifetime for almost zero current. It is shown, however, that as the current is reduced, the probability of drawing an arc becomes diminishingly small.
Orientation-Dependent Dissolution of Lithium Fluoride
Authors: Ives M. B.
Published: April 2005

It is shown that the etch rate of lithium fluoride crystals in both a modified CP-4 etchant and a dilute aqueous solution of ferric fluoride is a function only of crystallographic orientation. This conclusion is reached by comparing experimental observations with the results of a recent topographical theory of crystal dissolution.
Lattice Parameter Determinations with an X-Ray Spectrogoniometer by the Debye-Scherrer Method and the Effect of Specimen Condition
Authors: Otte Henry M.
Published: April 2005

It is shown that the Debye-Scherrer method can be used successfully on an x-ray spectrogoniometer by removing the bisecting mechanism. Complete profiles of the diffraction lines have been recorded and the center of gravity (CG) determined with an accuracy of ±0.005°2θ. Monochromated CuKα1 radiation was employed and the complete x-ray unit housed in a room maintained at constant temperature to within ±1°C. The lattice constant was calculated from each reflection and plotted against the Nelson-Riley function; a straight line could be drawn through all the points. The limiting factors in the accuracy of the lattice constant determination are the uncertainties in the correction for vertical divergence, monochromatization, and tail effects in measuring the CG (and in the x-ray wavelength). Solid rods as well as compacts made of filings were examined after annealing and after deformation. The lattice constant of pure Al was found to be unaffected (within ±0.00005 A) by the condition in which it was examined, contrary to observations by certain other investigators. However, the lattice constants of single-phase alloys are in general quite sensitive to their state of preparation. The influence of short-range ordering, stacking faults, solute clustering, quenching stresses, etc., are discussed and their relative importance assessed.
Single-Crystal Tin Films
Authors: Vook Richard W.
Published: April 2005

High-purity tin films have been made in ultrahigh vacuum by evaporation on (001) faces of NaCl at liquid nitrogen temperature and 0°C. An evaporation rate of approximately 50 A/sec was used. Film thicknesses ranged from 1000 to 3600 A. The films were allowed to warm to room temperature before they were removed from the vacuum system and examined by the techniques of electron diffraction and electron microscopy. Single-crystal films were obtained when the substrates were at liquid nitrogen temperature and when cleaved surfaces and short successive evaporation times were used. If the substrates were at 0°C, or one continuous evaporation of more than about 10 sec was made, the resulting film was polycrystalline and (100) oriented. Grain growth in all the polycrystalline films could be produced by electron-beam bombardment in the electron microscope. Some of the factors influencing grain growth are discussed.
Optimization of Emission-Limited Thermionic Generators
Authors: Schock Alfred
Published: April 2005

Equations are derived describing the performance of space-charge neutralized thermionic converters with negligible transport effects. For a given anode work function and cathode temperature, optimization of the other system parameters leads to an expression for the maximum attainable conversion efficiency, in terms of the fundamental physical constants e, m, c, and k. The calculated results, presented graphically, suggest several distinct modes of high-efficiency operation, and lead to a number of interesting conclusions about converters with cesium coated cathodes. With electrodes having a thermal emissivity equal to that of hot tungsten, efficiencies in excess of 30% are shown to be possible.
Dislocation Etch Pit Formation in Sodium Chloride
Authors: Mendelson S.
Published: April 2005

Dislocation etch pits can be formed on (100) surfaces of NalC crystals by etching in a solution of FeCl3 in glacial acetic acid. Observations and arguments are enumerated to illustrate the reliability of the etching technique to reveal dislocations at positions where they intersect the crystal surface. The difference in shape of etch pits at edge and screw dislocations is consistent with that expected due to their different angles of inclination. Etch pit formation depends on variables of the etching solution and procedure. Insufficient FeCl3 in solution results in wide, indistinctly shaped pits, whereas excessive FeCl3 results in small pits with rounded corners. NaCl in the solution decreases the etching rate, while the presence of water increases the etching rate and results in more shallow pits. The added salt in the solution is believed to act as an inhibitor which poisons the dissolution process in the same manner as that proposed by Gilman et al. [J. J. Gilman, W. G. Johnston, and G. W. Sears, J. Appl. Phys. 29, 747 (1958)] for LiF. Agitation increases the size of the pits for a given etching time.
Study of Electron Bombardment of Thin Films
Authors: Gilbert G. B. , Poehler T. O. , Miller C. F.
Published: April 2005

An experimental study has been made of methods by which the physical properties of thin metallic films may be changed. In particular, emphasis has been placed on investigating alterations of the crystal structure of certain films subjected to electron bombardment. The films, after being vapor deposited on amorphous substrates, were bombarded by a 35-kev electron beam in a zone recrystallization process. X-ray diffraction photographs and photomicrographs indicate substantial crystal growth in films of indium, bismuth, and germanium.
X-Ray Diffraction Study of Interdiffusion in Cu–Ni Powder Compacts
Authors: Fisher Bertina , Rudman P. S.
Published: April 2005

Interdiffusion in Cu–Ni powder compacts was studied by x-ray diffraction line shape analysis. Analogues to concentration-penetration plots are obtained. Results obtained at 750°, 850°, 950°, and 1050°C are compared with the conclusion that a single diffusion mechanism dominates in the range 750–950°C with an activation energy of about 26 kcal/mole, and it is concluded that the dominant mechanism is grain boundary diffusion. At 1050°C a new mechanism with a higher activation energy dominates, and it is concluded to be bulk diffusion. Metallographic observation revealed that prior to appreciable interdiffusion, the Cu, presumably by surface diffusion, envelops the Ni particles with subsequent interdiffusion between the Ni-rich core and the Cu-rich shell. This configuration is idealized to a concentric spheres model permitting rigorous solution of the diffusion equation for constant diffusion coefficient. The result of the calculation according to this new model and according to other authors' models are compared with the experimental results with the general certification of the concentric spheres model. The concentric spheres model is shown to predict that the rate of homogenization in the Cu–Ni system should be independent of the Cu particle size.
Surface Layer in BaTiO3 Single Crystals
Authors: Fatuzzo Ennio , Merz Walter J.
Published: April 2005

The switching time and the coercive field in ferroelectric BaTiO3 are known to depend on crystal thickness. A model along the following lines is proposed to explain the experimental results: on the crystal surface there is a thin layer of electrically biased and mechanically strained BaTiO3 which has a much smaller dielectric constant than the bulk. It is proposed that the electrical bias and the mechanical strains in the surface are caused by a Schottky exhaustion layer. This model and the model proposed by Drougard and Landauer are discussed and their predictions are compared with experimental results.
Effect of Gaseous Ambients upon 1/f Noise in Germanium Filaments
Authors: Noble V. E. , Thomas J. E.
Published: April 2005

The variation of 1/f noise in thin, single crystal germanium filaments was investigated by using gaseous ambients to change the surface potential of the sample. The noise samples, having a thickness of only 4 μ, were extremely sensitive to variations in the surface potential and exhibited large fractional changes of the total sample conductance as a result of the surface conductance fluctuations which were interpreted as the 1/f noise. These experimental results showed a definite noise minimum when the sample surface potential corresponded to the sample conductance minimum. The rms conductance fluctuation varied roughly linearly with ΔG, where ΔG is the increase of the sample conductance with respect to the minimum value. The slope of the curve for the condition of an accumulation layer on the sample surface was an order of magnitude less than that for the inversion layer. The amplitude of the accumulation noise agreed (within a factor of two) with the prediction of McWhorter's majority carrier trapping effect, but the inversion noise was an order of magnitude greater.
Application of the Three-Parameter Stress Function to Natural Rubbers of Widely Different Hardness
Authors: Carmichael A. J. , Holdaway H. W.
Published: April 2005

The previously reported three-parameter stress function has been applied to natural rubbers similar to those used for engineering purposes. These rubbers were selected to cover a harness range from 30 to 80 British Standard Degrees. A suitable choice of values for the parameters A, B, and β was found to give a good description of the stress-strain characteristics in pure shear, and positive and negative stretch squeeze. This agreement applied up to the maximum possible strains. Unique functional relationships were found to exist between the three parameters and rubber hardness. Theoretically, it would be possible to reduce the three-parameter stress function to a single-parameter stress function. As previously reported, this confirms and hence is indirectly confirmed by Blackwell's results [Trans. I. R. I. 28, 75 (1952)].
Effect of Pressure on the Energy Gap of Bi2Te3
Authors: Li Che-Yu , Ruoff A. L. , Spencer C. W.
Published: April 2005

The effect of hydrostatic pressure on the energy gap of Bi2Te3 has been investigated in the pressure range one to 30 000 atm. From resistivity measurements as a function of temperature and pressure, it has been determined that the energy gap decreases from 0.171 ev at one atmosphere to 0.104 ev at 30 000 atm, corresponding to ∂Eg(0)/∂p=−2×10−6 ev/atm.
Generalized Coupled Mode Theory
Authors: Pease M. C.
Published: April 2005

The pairwise coupling of modes in distributed systems such as the traveling-wave parametric electron-beam amplifier and many other types is shown to permit only two types of interaction. One type, called β coupling, results in the periodic interchange of the signal between the modes, as typified in the Kompfner-null coupler. The other, γ coupling, results in the exponential growth of the mode, as in the TWT and in the pump section of a parametric amplifier. The nature of the resultant interaction is a direct consequence of the underlying relations contained in the conservation law that applies throughout the system, i.e., in the separate parts of the system and that is independent of the various coupling coefficients. The ``rank'' and ``signature'' of the metric that expresses this conservation law is sufficient to determine the type of behavior. The direction of flow of energy in the coupled modes imposes a duality on these relations. Where modes of opposite directionality are coupled, β coupling causes system amplification, while γ coupling causes system interchange. These relations are generalizations of effects that have been studied in detail for many specific systems. They are not, however, consequences of the details of the system but are, rather, the only alternatives possible under assumptions that are broad in scope and generally applicable to devices of interest.
Thermorheological Simplicity in Extrusion Flow Curves of High Polymers
Authors: Ito Katsuhiko
Published: April 2005

Thermorheological simplicity is available for the extrusion flow curves of polymers in a way similar to the case of creep or stress relaxation. The true consistency curves for acrylic resin which were obtained from the extrusion flow curves at various extrusion temperatures by the help of the end-correction factor ξ are superimposed by shifting along the log Dw′ (where Dw′ is apparent maximum shear rate at the die wall). Thus the consistency curves by extrusion which are useful for evaluating the viscoelastic behavior of amorphous linear polymers can easily be determined over a sufficiently wide range of shear rates by the change of extrusion temperature.
Nonbasal Glide in Dislocation-Free Cadmium Crystals. II. The (112̄2) [1̄1̄23] System
Authors: Price P. B.
Published: April 2005

The (112̄2) [1̄1̄23] glide system was studied in thin, dislocation-free cadmium platelets by transmission electron microscopy and compared with observations on zinc platelets. Screw dislocations with a ⅓<1̄1̄23> Burgers vector were formed at the edges of the crystal and moved primarily on {112̄2} planes. Elongated, sessile dislocation loops were formed on basal planes when screws developed large jogs during cross-glide. Smaller numbers of secondary ⅓<1̄1̄20> dislocations were also formed and moved on basal planes. Observations in the temperature range −150° to +25°C showed that the behavior of the long loops and of the other dislocations in cadmium and zinc varied with temperature as follows: (1) At temperatures lower than ∼−120° in Cd and ∼−80° in Zn, the long loops were stable and practically no recovery took place. High densities of loops and networks of secondary dislocations were built up and hardened the crystal. (2) In the intermediate temperature range −120° to −40° for Cd and −80° to +10° for Zn, the long loops split up into rows of circular loops, which were then stable. The process involved the pipe-diffusion of material around the long loops and required a lower activation energy than that for climb. Some of the circular loops were found to contain stacking faults. (3) At high temperature, above ∼−40° for Cd and ∼+10° for Zn, circular loops annealed out by climb with an activation energy ∼0.8 ev for Cd and ∼0.95 ev for Zn; secondary dislocation networks dispersed by climb; and the dislocation density, and therefore the work-hardening, was small.

At high beam intensities dislocation loops often grew by climb, probably as a result of the formation of point defects by ion bombardment, the ions being formed by the interaction between electrons and residual gas molecules.
Acoustical Study of Quench-Aging in α Cu-Al Alloys
Authors: Koppenaal T. J. , Fine M. E.
Published: April 2005

Young's modulus at 21°C in quenched α Cu-Al alloys increases with time. This correlates with a decrease in resistivity which has been attributed to vacancy-enhanced diffusion and short-range ordering [M. S. Wechsler and R. H. Kernohan, Acta Met. 7, 599 (1959); R. H. Kernohan and M. S. Wechsler, J. Phys. Chem. Solids 18, 175 (1961)]. The total change in modulus during aging increases with Al content and quenching speed and is also a function of the quenching temperature. An effective activation energy of 0.69 ev was determined 38 min after quenching. This is an effective energy of motion for the point defects involved in the diffusion process at this point in the reaction.