bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Basic Theory of the Mercury Cathode Spot
Authors: Hull A. W. 
Published: April 2005

Most writers about the cathode spot have concluded that it is too complicated for valid conclusions. There is presented here a simple theory, which can be called basic, since it is founded on the single assumption that the electron emission is field emission.
It follows immediately from this assumption that the positive ion current density must be about 5×105 A/cm2 to supply the necessary field of 2.7×107 V/cm; and this, with an allowance of 20 electrons per ion for the two-stage ionization, determines an electron current density of 107 A/cm2.
This large ion current and the resultant heating of the spot precludes an energy balance, which would require temperatures and pressures far above the critical to dissipate the heat by conduction and evaporation.
Such a balance would never be reached, however, because of a mechanical balance between the forces of surface tension and vapor pressure, which limits the pressure and temperature to much lower values; namely a pressure of about 1 atm and the temperature of the order of 400°C. The balance is given by the simple equation p=(2γ/r) dyn/cm2,where γ is the surface tension in dyn/cm, and r the radius of the spot in cm. A table is given for the calculated pressure and temperature for different currents.
This maximum temperature determines the velocity of (random) motion of the spot, which is just its diameter divided by the time to heat a new spot to this temperature. The calculated velocities are included in the table.
Retrograde motion of the spot in a magnetic field is explained by a drift of slow ``residual'' electrons parallel to the surface in the ``correct'' direction, thus weakening the electric field drawing ions to the surface. A theory of drift of slow electrons by Tonks, makes possible a calculation of the drift angle, which determines the change from retrograde to ``correct'' motion as the magnetic field and vapor pressure are changed. The calculated values are in good agreement with experiment.
There are no measurements of pressure on a free spot, but the theory predicts correctly the height to which mercury droplets are thrown, assuming the erupted droplets to be the same diameter as the spot.
Observed pressures for anchored spots are much higher, but these depend on an entirely different mechanism.
The observed velocities of retrograde motion are much less than those calculated; but it is pointed out that the motion may be largely random, rather than in a straight line, which would make agreement with the theory possible.
Evidence is given that the limiting current of 30 A per spot is due to the IR potential drop in the mercury, which leaves insufficient energy for ionization if this current is exceeded.
A few values of pressure and temperature are calculated for other low-boiling-point metal arcs, assuming that the same theory applies to them.
Double-Cantilever Cleavage Mode of Crack Propagation
Authors: Gillis Peter P. , Gilman J. J. 
Published: April 2005

The quantitative cleavage method for determining specific surface energies of solids is subject to several possible sources of error. Some of these are investigated analytically in this study, and a general expression for the surface energy is derived from beam theory for a linearly elastic material. The exact equation of motion for the propagating crack is derived but not solved.
Errors associated with each term of the general expression are assessed. The ratio of shear to bending strain energy is small if the initial crack length is long compared with the specimen depth. The term arising from strains in the specimen past the tip of the crack is not developed, but is estimated; and a procedure is outlined for determining this term experimentally.
Comparison of simple beam theory with more exact elasticity theory shows that in the main spans the difference is small because it involves only the shear strain energy. Also, restriction of anticlastic curvature near the crack tip is unimportant if the initial crack length is long compared with the specimen width. Elastic anisotropy is unimportant when shear can be neglected, provided the appropriate modulus is used.
For nonlinear elastic material, as the crack propagates a small amount, the work increment is either zero or double the strain energy increment. A surface energy expression is developed in terms of Timoshenko's ``reduced modulus,'' and upper and lower bounds are fixed.
For plastic materials the analysis is based on pseudoinstantaneous plastic response. Justification of this assumption is difficult to defend or deny. Therefore, an important conclusion is that whenever possible specimens should be designed to remain grossly within the elastic limit of the material.
Superposition of large axial forces is a potential source of large errors in surface energy determinations, and possible eccentricities in the application of such forces makes even the sign of these errors difficult to determine. Hence, this method for stabilizing the crack plane is not recommended.
Two Photomechanical Effects in Alkali Halide Crystals
Authors: Nadeau J. S. 
Published: April 2005

Two photomechanical effects, observed in alkali halide crystals containing color centers, appear as sudden reversible changes in flow stress when a crystal is illuminated. Both effects are related to optical transitions of the F center. In potassium chloride, intensely illuminated at 175°K, hardening appears to be caused by the F → F′ process. Below 80°K, in KCl, even more severe hardening is caused upon illumination, by transport of the F-center electron to an unspecified trap lying very close to the conduction band; decay of the hardening after extinction of the exciting light requires several seconds and may be caused by dislocation—point defect interactions.
The effects have been observed in nine of the alkali halides. Flow stress increases and decreases were both observed, depending upon the particular alkali halide.
Future Developments in Large Magnetic Film Memories
Authors: Raffel Jack I. 
Published: April 2005

Some judgments are formulated about memory organization, fabrication techniques and cell structures which are generally applicable to improving the speed-cost ratio of static magnetic storage devices.
More specifically, for magnetic films, techniques for realizing simultaneously high bit density and simple fabrication are discussed.
Based on very rough estimates, it is proposed that for a million-word memory, a cost reduction of almost two orders of magnitude over present day stores with speeds of approximately one microsecond or less should be feasible with films.
Alternative cell configurations and areas of engineering compromise are discussed. Experimental results with etched cells having dimensions as small as 2 mils (0.05 mm) for both quasiclosed and open structures have been obtained.
Both multiword readout and a method for sharing sense amplifiers by ``band switching'' are considered.
Magnetic Behavior of High-Field Superconductors
Authors: Bean Charles P. 
Published: April 2005

Homogeneous superconductors have reversible magnetic properties. We distinguish two types of superconductors, type I and type II. The type I superconductor (most pure superconducting elements are of this type) has a particularly simple magnetic behavior.1 In a macroscopic specimen, the flux density is zero for fields less than the critical field, Hc, that marks the limit of the superconducting state. Above this field the specimen has all the properties of a normal metal including the property that the flux density is essentially equal to the applied field. So, in summary, the type I superconductor is either completely superconducting or completely normal. (This statement is strictly true only for a long thin specimen in a field that is parallel to the axis of the specimen. In other geometries one finds a gross mixture of superconducting and normal regions called the intermediate state that is created by the field concentrations associated with specimen shape.) In recent years it has been appreciated that there is another class of superconductor—usually an alloy or compound—in which the flux in a bulk specimen is completely excluded for fields less than Hc1, but above this field flux penetration is partial and increases with applied field until flux penetration is complete at an upper critical field, Hc2. Since this field is generally larger than the equivalent Hc of type I superconductor, these type II superconductors are known as high-field superconductors. The region between Hc1 and Hc2 is known as the mixed state which is not to be confused with the shape-dependent intermediate state mentioned earlier.
The present conception of the mixed state2 pictures the flux as entering in the form of quantized current vortices. The total flux contained in each vortex is 2×10−7 G-cm2. In equilibrium these vortices repel one another to form a lattice that compresses as the field is increased from Hc1 to Hc2 and finally all flux variation smoothly disappears at Hc2. Experimental magnetization curves on homogeneous alloys show good agreement with this theory.3
If the type II is inhomogeneous, there may be impediments to the motion of these flux lines. In this event there will be a gradient of flux as the flux is driven into the specimen.4 This gradient of flux lines is equivalent to a macroscopic current density by Ampere's law, curl H=4πJ/10.4 This behavior allows one to calculate the magnetic behavior of these superconductors in terms of only one parameter, the critical current density, Jc(H)5—the same critical current density that is measured in current transport measurements. The magnetic behavior includes size-dependent magnetization and a hysteresis loop that is the precise diamagnetic equivalent of the Rayleigh hysteresis loop for ferromagnets.
Magnetic Properties of an Iron—Nickel Single Crystal Ordered by Neutron Bombardment
Authors: Néel L. , Pauleve J. , Pauthenet R. , Laugier J. , Dautreppe D. 
Published: April 2005

It has been shown that a new ordered structure can be obtained in an Fe-Ni (50%–50%) alloy, by irradiating it with neutrons below 320°C. This ordered structure is tetragonal (AuCu type) and leads to a very high magnetic anisotropy. We have studied the magnetic properties of a single-crystal disk irradiated with neutrons at 295°C, with an applied magnetic field along the [100] direction. The x-ray superlattice lines show that after irradiation the sample is made of small ordered crystallites with their tetragonal axes distributed along a [100], [010], or [001] direction. The study of the anisotropy energy in the sample plane [011], and the magnetization curves drawn for different directions, show that this sample presents the characteristics of a uniaxial substance. But if we express, in a classical way, the anisotropy energy by K1 sin2θ+K2 sin4θ, we find experimentally K1=3.2·106 ergs/cm3 and K2=2.3·106 ergs/cm3.
This high value of K2 is not in agreement with the conception of independent crystallites. One of us (L.N.) has made a theory taking into account the exchange interaction between the crystallites which are in fact smaller than the magnetic domains. The formulas obtained in this way give a good agreement with the experimental results.
Irradiation of Iron and 5–79 Mo Permalloy with 2-MeV Electrons
Authors: Gordon D. I. , Sery R. S. 
Published: April 2005

Large changes in the structure-sensitive magnetic properties of bulk polycrystalline 5–79 Mo Permalloy resulted from irradiation with 2-MeV electrons at ∼1017 electrons/cm2 at temperatures ranging from 60° to 170°C. These changes showed an approximately linear dependence on sample thickness from 0.10 to 0.25 mm. In addition, extreme rectangularities in the magnetization curves and hysteresis loops were obtained. For example, the maximum slope of the magnetization curve for a 0.10-mm sample increased from ΔB/ΔH=0.3×106 to ΔB/ΔH=4.3×106. This unusual steepness is evidence of the effectiveness of electron irradiation in influencing order in 5–79 Mo Permalloy at temperatures well below the ordering temperature, and without an applied magnetic field.
Iron, irradiated under the same conditions, showed no changes in its magnetic properties.
The range of 2-MeV electrons in these materials is ∼1.3 mm, well beyond the maximum sample thickness used. The calculated fractional number of atoms displaced is ∼5.3×10−6, which decreases slightly with thickness, unless one considers the difference between the actual path length of the electron in the sample (due to multiple scattering) and the actual sample thickness. If this difference between the average path length and sample thickness is calculated according to the theory of Yang, then the fractional number of atoms displaced increases linearly with sample thickness, in agreement with the thickness dependence of the radiation induced magnetic properties changes observed.
Flux Jumping in Nb +25% Zr Wire
Authors: Lubell M. S. , Mallick G. T. , Chandrasekhar B. S. 
Published: April 2005

Flux jumping has been investigated in both cold-worked and heat-treated (1 h at 700°C) 0.025-cm-diam Nb+25% Zr wire wound into solenoids and noninductive coils of approximate dimensions: i.d.=0.3 cm, o.d.=1.2 cm, length=2.6 cm. The measurements taken at 4.2°K were: (1) The induced voltage pulses vs applied magnetic field with both I=0 and a preset transport current. (2) The induced voltage pulses vs coil current for H=0 and with a preset uniform external field.
For the case with no transport current in the coil (I=0) when the external field was increased smoothly from zero, a squence of very sharp voltage pulses (flux jumps) were induced in the coil, and recorded simultaneously on both an X-Y recorder and an oscilloscope. These flux jumps had the following general characteristics for all the cases discussed in this paper: (1) Starting from well defined initial conditions, the pulse always appeared at about the same place in the field sweeping cycle. (2) The polarity of the pulses is reversed when the direction of field change is reversed. (3) The pattern of these pulses was essentially unchanged when the field sweep rate was increased from 7 to 340 G/sec.
As a result of these measurements, we have obtained new insight into both the multilevel transitions of noninductive coils and the phenomenon known as degradation of solenoids. Two successful methods are described for partially overcoming the excessive degradation of a solenoid made from heat treated wire. The flux jumps are interpreted according to an extension of a model proposed by both Bean and London.
Ferromagnetic Europium Compounds
Authors: McGuire T. R. , Shafer M. W. 
Published: April 2005

Ferromagnetism has been found in several divalent europium compounds. Some of these materials are particularly simple in both crystal and magnetic structure and are ideal for experimental and theoretical study. The materials we have investigated can be divided into three groups, europium chalcogenides, europium halogens, and europium silicates. Magnetic information on these compounds are summarized and theoretical results reviewed.
The europium chalcogenide series all have the rocksalt structure, the oxide, sulfide, and selenide being ferromagnetic, and it is on these materials that the most work has been done. This is especially true of EuS where detailed moment, specific heat, and nuclear magnetic resonance measurements are available. The oretical analysis indicates that there is positive exchange between nearest-neighbor europium atoms which decreases with increasing atom spacings. There is also a weaker negative superexchange via the anions in these compounds which is responsible for antiferromagnetism in EuTe. The EuTe magnetic ordering has been studied by neutron diffraction at Brookhaven and the sublattice magnetization-temperature behavior is found to be somewhat anomalous. EuSe is ferromagnetic but reveals low-field magnetization curves that have an unusual shape. In view of this, EuS seems to be the simplest of the group so that fundamental parameters obtained from analyzing the data are probably the most reliable.
In the halogen group, EuI2 appears to be ferromagnetic while EuF2 is apparently antiferromagnetic. The latter behavior is somewhat unexpected from interatomic distance considerations which hold for the chalcogenides. Of three silicates prepared, two were ferromagnetic. The most interesting was Eu2SiO4 which was obtained as transparent single crystals. Magneto-optical studies show this compound to have a Verdet constant higher than any other previously reported.
Effect of Crystallization Conditions and Heat Treatment on Polyethylene: Lamellar Thickness, Melting Temperature, and Density
Authors: Brown R. G. , Eby R. K. 
Published: April 2005

Lamellar thickness, melting temperature, and density were measured for bulk polyethylene crystallized by the application of a fixed pressure to molten polymer at different temperatures. Melting temperature varied from 135.2° to 139.2°C, and density varied from 0.9759 to 0.9842 g/cc. Small-angle x-ray diffraction yields two maxima which apparently are not first and second orders of diffraction. Electron micrographs of fracture surfaces exhibit lamellae, which support the suggestion that the lamellar thickness is the shorter of the two dimensions (469≤L1≤981 Å and 193≤L2≤440 Å) corresponding to the diffraction maxima. However, the functional relationship of both dimensions to melting temperature and density are in accord with existing or easily derived equations. Analysis of these data, together with the result obtained from paraffin data, yields an equilibrium melting temperature of 141.9±1.7°C. Dimensions of the unit cell did not vary with lamellar thickness.
Single crystals of polyethylene were collected into mats and heated at a fixed temperature under various pressures. The observed effect of pressure was to limit the fold period attained during heat treatment. The data suggest that the refolding process follows a relationship which describes crystallization from the melt.
Variable-State Methods of Measuring the Thermal Properties of Solids
Authors: Harmathy T. Z. 
Published: April 2005

Two variable-state methods have been developed which both offer the advantage of producing negligible thermal disturbance in a solid during measurement. The first is a curve-fitting method. It makes use of the fact that the initial temperature rise, due to a constant flux plane heat source, at points within a certain region of a finite solid is essentially the same as that in an infinite solid. Temperature records obtained from such points thus can be analyzed with the assumption of linear heat flow, and used for calculating all thermal properties of the solid.
The second is a pulse method. If a hot or cold pulse is applied to a plane surface of a specimen, the rise or drop of temperature at some distance from the surface will pass through a maximum; from the time of the maximum the thermal diffusivity can be calculated. The main advantage of this method is the ease of specimen preparation.
Dynamic Response of Aluminum
Authors: Barker L. M. , Lundergan C. D. , Herrmann Walter 
Published: April 2005

The dynamic stress-strain relation of aluminum was measured in compression to a stress of 22 kbar using plate impacts to induce uniaxial strain. The results were compared to a uniaxial strain curve constructed from elastic moduli and quasistatically determined stress-strain curves. The dynamically determined stress-strain relation was not unique in that it varied as a function of the magnitude of the induced stress and was offset from the quasistatic curve. These small deviations are attributed to strain rate effects. The rate effects were further demonstrated by observing the transmission of an elastic compression stress wave in aluminum after the aluminum was dynamically stressed beyond the yield point and held at constant strain for a period of approximately 2 μsec.
The dynamic stress-strain relation was measured upon the release of a shock induced compressive stress of 10.5 kbar to a tension of −9 kbar by observing the effects of tensile stress waves. The deviation of the unloading stress-strain relation from that predicted by simple elastic-plastic theory is attributed to strain rate and Bauschinger effects.
Elastic Constants of CsBr and CsI from 4.2°K to Room Temperature
Authors: Vallin J. , Beckman O. , Salama K. 
Published: April 2005

The elastic constants of pure single crystals of CsBr and CsI have been measured at liquid-helium, liquid-nitrogen, and room temperatures. For CsBr, the values of c11, c12, and c44 at 4.2°K are 3.437, 1.035, and 0.999 in units of 1010 N/m2. The corresponding values of CsI at 4.2°K are 2.737, 0.793, and 0.825·1010 N/m2.
The elastic constants give the Debye temperature 148.8°K for CsBr and 125.6°K for CsI.
The infrared resonance frequencies calculated from compressibility data are in agreement with those obtained from infrared spectroscopy.
Vocabulary of Surface Crystallography
Authors: Wood Elizabeth A. 
Published: April 2005

The recent increase of activity in the field of slow-electron diffraction has resulted in a need for agreement on conventions of terminology in the description of a diperiodic surface structure relative to a triperiodic substrate. Vector description of the surface structure net in terms of the substrate surface net is suggested. Fractional Miller indices result when the surface structure mesh is larger than the substrate surface mesh. The surface structure may be either that of a deposit or that of the selvedge of the substrate.
With the relaxation of one of the diffraction conditions in the diperiodic structure the reciprocal lattice becomes a set of parallel rods intersecting the Ewald sphere continuously with change of wavelength of the incident radiation or change of orientation of the crystal.
The paper discusses the applicability of the seventeen two-dimensional space groups and the eighty diperiodic groups in three dimensions to these diperiodic structures. A comparison is made between the different effects of surface symmetry on etch pits and epitaxial deposits on the cleavage face of muscovite.
Effect of Temperature and Environment on the Structure of Thin Single-Crystal Nickel Films
Authors: Alessandrini E. I. 
Published: April 2005

Annealing experiments under varying conditions of temperature and pressure have been carried out along with transmission electron diffraction from thin single-crystal films of nickel. The single-crystal films were epitaxially grown by vapor deposition on heated, freshly cleaved (100) faces of rocksalt, and the annealing experiments were carried out in the diffraction instrument after the films had been floated off the rocksalt and mounted on Ni grids. The diffraction patterns of the as-grown films indicated that the Ni was a {001}-oriented single crystal with faulting that resulted in streaking in all four [111] directions. The {111} faults were removed by annealing above 500°C for 1 h at less than 1×10−5 Torr. At 400°C and vacuum pressures controlled by leaking air into the diffraction unit, structural changes were observed. At 1×10−5 Torr, the film remained single crystal; at 3×10−5 Torr, the electron diffraction patterns indicated faults in the [111] directions; and as the pressure increased to 5×10−5 Torr, Ni plus the previously reported metastable Ni+O phase appeared. A new complex two-phase structure of Ni plus Ni+O occurred at 7×10−5 Torr; and at 1×10−4 Torr, only the equilibrium NiO phase was observed. At higher temperatures and a constant pressure of 3×10−5 Torr, there was an absence of any transition phases.
Experiments were repeated with argon under similar conditions and no structural changes were observed. The changes are attributed to an increasing oxygen content in the film during the annealing conditions. The transformations are interpreted to be dependent upon a complex type of precipitation in which the oxygen fault interpretation postulated by Heidenreich et al. may be the first stage in the precipitation of NiO in the film.