摘要:

A procedure is described whereby nonresonant polarized and depolarized Rayleigh, electronic Raman, and Thomson scattering are used as a diagnostic tool for high‐pressure nonhomogeneous plasmas. The method is applied to 0.1–3 atm Ne, Ar, and Xe arcs, with currents not exceeding 3 A. Polarized Rayleigh scattering is dominant in these cases. Radial gas temperature and density distributions, an axis electron density, and upper limits of excited state and electron densities are obtained. The temperature range covered extends from about 350 K (near the wall) up to 4500 K (at the axis of a 2‐A 3‐atm Ne arc). A comparison with spectroscopically obtained temperatures is shown to yield interesting information on the deviations from local thermodynamic equilibrium.

ISSN:0021-8979    

DOI:10.1063/1.1663067

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A general theory is developed to determine the dynamic characteristics and stability of a gas cavity situated in viscoelastic liquids whose rheological state is described by the generalized model of the Kelvin or Maxwell type. The characteristic function of the bubble‐liquid system is obtained by the first‐order perturbation method, including the effects of surface tension, vapor pressure, and thermodynamic behavior of the gas confined in the cavity. The zeros of the characteristic function determine the types of bubble growth, bound on unbound. The Hurwitz (or Routh) stability is employed to determine the conditions for the onset of incipient cavitation. The applications of the theory are demonstrated in some liquids having simpler shear‐stress‐shear‐strain relationship.

ISSN:0021-8979    

DOI:10.1063/1.1663068

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Significant surface‐temperature decreases may be achieved by generating a corona discharge near a heated object. We demonstrate that this electrocooling phenomenon may be ascribed to an electric wind which results from ionic drag and which produces a convective heat‐transfer coefficient that is proportional to the fourth root of corona current.

ISSN:0021-8979    

DOI:10.1063/1.1663069

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Polycrystalline bismuth specimens were impacted in plane‐wave experiments at stresses of 2.3–2.9 GPa (29 kbar) and for initial temperatures ranging from room temperature to 523 °K. These impact stresses are sufficient to produce final states in the solid II phase of bismuth. For initial temperatures below 435 °K, the Hugoniot in the solid I phase of bismuth intersects the solid I‐solid II phase boundary; the dynamic measurements of the solid I‐solid II transition pressure over this temperature range and the quasistatic measurements of the phase boundary are in good agreement. For initial temperatures above 435 °K, the Hugoniot intersects the melt boundary and melting can occur during shock compression. It is found that there are no discontinuities in the wave profiles, as expected from hydrodynamic predictions for instantaneous melting. Instead, the wave profiles are highly dispersive for initial temperatures near melt. Nevertheless, melting is inferred from the present measurements by comparing the stress states attained during the shock compression with the known phase diagram for bismuth. The present data also show that deviatoric stresses are present for initial states within 20 °K of ambient melt.

ISSN:0021-8979    

DOI:10.1063/1.1663070

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The effect on PTFE of crystallization conditions and subsequent tensile deformation have been examined by Fourier analysis of the shapes of diffraction peaks. Crystal perfection increases with decreasing rate of cooling from the melt. During deformation, the crystallite size is reduced drastically in the range of strain from 35 to 185%. The microstrains are not altered over this range, implying crystal breakup rather than distortion within crystallites. It is in this range that previous studies with the same specimens have indicate a sharp transition in texture. The fact that root‐mean‐square (rms) microstrains increase due to elongation suggests that the crystalline regions not only break up but that they are also deforming plastically. Electron microscopic investigation indicate that the striation spacing on crystals in the fracture faces is much smaller than the crystallite size measured with x‐rays; thus the striations do not represent alternating crystalline and amorphous regions.

ISSN:0021-8979    

DOI:10.1063/1.1663071

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A theoreticalP,v,E,Tequation of state has been derived for the secondary explosive TATB. From this it has been found that the pressures generated within TATB and similar secondary explosives, when they are compressed, should be relatively insensitive to temperature changes at constant volume. For TATB this means that the shock Hugoniot of the nonporous material should remain close to the room‐temperature isotherm up to pressures of about 200 kbar.

ISSN:0021-8979    

DOI:10.1063/1.1663072

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An analytic and experimental investigation on the dependence of gas temperature on flow and discharge characteristics is presented. The entire range of slow‐ to fast‐flowing coaxial CO2electric lasers is considered. As is known, at low flow rates the gas temperature is proportional to the electric power input per unit length, while at high flow rates the gas end temperature is proportional to the ratio of total electric power and gas mass flow rate. In addition, gas pressure and entrance Mach number were found to have a noticeable effect on gas temperature; the temperature tends to increase with increasing pressure and to decrease with increasing Mach number. The agreement between theory and experiment is fairly good, so that estimates of gas temperature at given flow and discharge conditions can be obtained. Also presented is an experimental correlation between laser power output (or efficiency) and gas temperature. Finally, scaling laws for temperature‐limited coaxial flow CO2electric lasers are proposed.

ISSN:0021-8979    

DOI:10.1063/1.1663073

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Previously reported annealing effects on the carrier density and free‐carrier absorption are correlated with photoluminescence and localized vibrational mode infrared absorption measurements of annealed samples of heavily doped GaAs: Si. Annealing in the range 400≤TA≤750 °C produces the following qualitative changes: (i) a major reduction in the free‐carrier concentrationne, (ii) an increase in the carrier absorption cross section, (iii) a reduction of the SiGalocalized mode absorption band, and (iv) the introduction of a new photoluminescence band at 0.98 eV. A defect model is proposed which is consistent with the observed changes. There is a major reduction in [SiGa], the Si donor concentration, which is a function of the anneal temperature between 400 and 750 °C. The reduction is probably through the formation of (SiGa−VGa) pairs. There is little change if any in [SiAs] the Si acceptor concentration. When TA= 400°C thene= [SiGa] −[SiAs]. WhenTA= 600 and 750°C, a new acceptor is formed having concentrations ≃3 to 4×1018cm−3, in samples having [Si]≃4×1019cm−3, andne≠[SiGa] − [SiAs]. The new acceptor defect is a Si complex with an acceptor state ≃0.54 eV above the valence band. There is no evidence for SiGa→ SiAssite transfer after annealing at anyTAin the 400–750°C range. Annealing at 1100 °C removes all the lower‐temperature annealing effects including the new acceptors and againne=[SiGa] − [SiAs].

ISSN:0021-8979    

DOI:10.1063/1.1663074

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The temperature range of Ohmic contact formation to ZnSe, ZnS0.5Se0.5, and ZnS is presented. New experiments show contacts are formed by cooldown rather than by heatup and that contacts can be formed and removed reversibly by cyclic cooling and heating. This and other evidence suggest contact formation by liquid‐phase epitaxy, as had been shown in group‐IV and ‐III‐V semiconductors, rather than diffusion. The role of wetting, which is necessary but not equivalent to contact formation, is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1663075

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The photoluminescence spectra of CuGaS2crystals doped with Cd or Zn vary continuously from a green emission (0.51 &mgr;) to an orange emission (∼ 0.59 &mgr;) depending upon the concentrations of Cd and Zn. The room‐temperature internal quantum efficiency is reproducibly 0.2%. The electroluminescent efficiencies of CuGaS2: CdS heterojunction LEDs fabricated by using these substrates are not appreciably higher than the best efficiencies reported earlier.

ISSN:0021-8979    

DOI:10.1063/1.1663076

出版商:AIP    

年代:1974

数据来源: AIP