摘要:

The following straight‐line relationship between the stacking‐fault probability &agr; and alloying concentration has been obtained by fitting published data:ln&agr;=ln&agr;0+K&agr; [C/(1+C)].In this expression,C=X/X*, whereXis the alloying concentration andX* is the solubility limit (both in atomic percent) at either the peritectic or the eutectic temperature, &agr;0is the stacking‐fault probability for pure silver andK&agr;is an experimental constant. The value of &agr;0, obtained by extrapolation, is 3.13±0.14×10−3;K&agr;is usually within the range 6.2±0.5, but is lower in those binary systems alloyed with the hcp elements Mg, Zn, and Cd. Similarly, an analytical expression relating stacking‐fault energy &ggr; and alloying concentration may be written asln&ggr;=ln&ggr;0+K&ggr; [C/(1+C)]2,where &ggr;0is the stacking‐fault energy of silver. The value ofK&ggr;for the Ag&sngbnd;Sn, Ag&sngbnd;In, and Ag&sngbnd;Al systems ranges from −10.0 to −10.5, but is −6.5 in the Ag&sngbnd;Zn system. The relationship between &agr; and &ggr; is discussed on the basis of these equations.

ISSN:0021-8979    

DOI:10.1063/1.1660734

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A detailed program for the optimization of the ultrasoft x‐ray reflectivity and resolution of multilayer soap crystals is described which is based on classical x‐ray diffraction theory and fundamental data concerning monolayer films. New measurements of the conversion factor (fraction of fatty acid converted to soap in a monolayer formed on a liquid substrate containing metal ions) as a function of the metal‐ion concentration and liquid substrate pH have been used as the basis of a logical optimization procedure. Full optimization parameters are given for the lead soaps of melissic, lignoceric, stearic, myristic, and lauric acids which have 2dinterplanar spacings of 159.6, 131.5, 100.4, 80.5, and 70.0±0.1 Å, respectively. These crystals have a reproducibility of about 10% (mean deviation from mean reflectivity), except in the case of lead stearate where it is 5%. For each soap the optimum lead concentration in the liquid substrate is 3×10−5M, the pH of this solution is 6.0, and the dipping speed is 0.2 cm sec−1. The resultant crystal is 100% soap and contains no unconverted acid. The necessary surface pressure and temperature are dependent upon the particular soap being produced. The optimum values which give good reproducibility and high reflectivity, for the acids mentioned above, are (1) temperature: 30, 20, 18, 12, and 12°C; (2) pressure: 40, 35, 32, 20, and 15 dyn cm−1, respectively. The relative reflectivity of crystals containing varying amounts of lead are in agreement with diffraction theory. The absolute reflectivities for different thicknesses of all the optimized crystals are presented for various ultrasoft x‐ray emission lines and are shown to be in qualitative, but not quantitative, agreement with theory. Crystals of thickness in excess of about 150 monolayers (75 lattice planes) proved impossible to build. The diffraction half‐widths of the crystals are found to be in agreement with theory, and the spectral resolution of the crystals has thus been estimated. In general, this is equal to the effective number of diffracting planes and is thus limited by crystal absorption. Resolving powers of 30–60 can be obtained in the 20–120‐Å region for the thickest crystals grown. The peak and integrated reflectivities of these crystals were of the order of 1–5% and 1–4×10−4rad. Detailed measurements are given for all crystals and a variety of emission lines. Reflectivity data is also presented for beryl and potassium acid phthalate (KAP) crystals and a comparison is made between soap crystals and other possible dispersive elements in the ultrasoft x‐ray region. Data is presented on peak‐to‐background ratios, high‐order spectra intensity, and the use of mixed fatty acids to achieve intermediate spacing crystals. Because the optimized crystals contain no unconverted acid, they are shown to be particularly stable to a vacuum environment and rises in temperature up to at least 100°C. Spectra are presented to illustrate the use of multilayer soap crystals in ultrasoft x‐ray spectrometry.

ISSN:0021-8979    

DOI:10.1063/1.1660735

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Calculations are presented for various mechanisms by which two‐wave and three‐wave mixing of far‐infrared and millimeter‐wave signals in high‐purity GaAs might occur. The emphasis is on low IF, about 1 MHz, as detected by photoconductivity. The energy dependence of the carrier‐energy relaxation time and the carrier‐recombination time is found to be important, but for three‐wave mixing, in addition, the hydrogenic donor levels allow mixing by means of photoexcitation and modulation of the level densities, followed by thermal ionization that carries the modulation to the carrier density and the photocurrent.

ISSN:0021-8979    

DOI:10.1063/1.1660736

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The extrapolated rangeRexand the projected rangeRprof 4‐ to 24‐MeV electrons in Be, Al, Cu, Ag, and Au have been determined from the experimental data for the charge‐deposition distribution produced by the electrons in the effectively semiinfinite absorber. While the results forRexshow no significant difference from the data obtained by Harder and Poschet and by Ebertet al.for the absorber configuration of finite slab, the present values ofRprfor the absorbers of high atomic number are slightly smaller than the results of Harder and Poschet. In the energy region considered here,Rexhas been found to obey an empirical equation of the formRex=A(E0−B)C, whereA, B, andCare expressed by simple functions of atomic number, andE0is the incident kinetic energy of the electron. A semiempirical relation previously found betweenRprand the continuous slowing‐down approximation rangeR0has been modified so as to show a better agreement with the present data.

ISSN:0021-8979    

DOI:10.1063/1.1660737

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The comparison between the observed cathode damage in a short arc (20–100 nsec duration; 0.3 mm long), as observed by a scanning electron microscope, and a model of cathode erosion employing ionic bombardment as the main erosion source leads to the evaluation of the current density in the individual craters comprising the cathode spot. Only order‐of‐magnitude calculations were possible; however, the main feature was that the current density was found to remain almost constant at a value of 1.9×107A cm−2for craters of radius between 0.3 and 1.0 &mgr;. The ratio of the ionic to electronic currents was found to be significantly higher than previously published values for cathode spots.

ISSN:0021-8979    

DOI:10.1063/1.1660738

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

It was found that arc potential rises discontinously when the separation between two electrodes reaches a critical distance which has a certain functional dependence on the ambient gas pressure and the arc current. This phenomenon is discussed quantitatively as being caused by diffusion of metal vapor from the cathode spot to the surrounding gas in hemispherical geometry.

ISSN:0021-8979    

DOI:10.1063/1.1660739

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The gas temperature has been measured at the axis of the positive column of a number of discharges commonly used for CO2lasers. The measurements have been made with an interferometer. For the first series of measurements the tube is filled initially with 2‐Torr CO2and 4‐Torr N2. Next, He is added in steps. In the second series the gas mixture also contains a small amount of H2O vapor. If the power input into the column is kept constant the gas temperature decreases when He is added.

ISSN:0021-8979    

DOI:10.1063/1.1660740

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A transparent solid and liquid were chosen to study the thermomigration of liquid droplets through solids. Irreversible processes associated with the transfer of atoms between the solid and the liquid phases at the solid‐liquid interface of the droplet were found to have a profound influence on the migration behavior of the liquid droplets. For large droplets, these interface kinetics cause the droplet to disintegrate in a thermal gradient. In smaller droplets where the containing effects of surface tension are relatively greater, the droplets experience a prolonged transient period of thermomigration during which there is a monotonic increase in the velocity of the droplet and a gradual distortion of the droplet shape. Following this transient period, the smaller drops enter a steady‐state period during which both their shape and velocity remain constant. The steady‐state velocity of droplets in this region decreases with decreasing droplet volume and falls to zero below a critical droplet size. This variation of droplet velocity with size produces an increased rate of collision and coalescence of droplets during thermomigration.

ISSN:0021-8979    

DOI:10.1063/1.1660741

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The electrical conduction of polyvinyl chloride was measured from low electric field to high field near breakdown below, in, and above a glass transition region. Ionic conduction was found to hold up to the field near breakdown. The estimated jump distance of a charge carrier changes considerably in the glass transition region, while it remains constant (12 Å) at a temperature fairly below the glass transitionTg(=87°C) and seems to reach a saturation value (30 Å) aboveTg. The elongation of substantial jump distance may be explained by the change in the shape and height of potential barriers against ionic migration due to the liberation of micro‐Brownian motion of main chains in the glass transition region.

ISSN:0021-8979    

DOI:10.1063/1.1660742

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The expansion of a hot mixture of CO2, N2, and H2O through a Laval nozzle is analyzed. Mixtures appropriate to the stoichiometric combustion of acetylene and propane are used. The calculations indicate that, despite the large quantities of water vapor present, the expansion will result in a population inversion on the CO2laser transition for both fuels. The predicted maximum gain for these conditions is 3 dB/m which occurs for a reservoir temperature of 2000 °K. Design curves for this type of laser are given.

ISSN:0021-8979    

DOI:10.1063/1.1660743

出版商:AIP    

年代:1971

数据来源: AIP