摘要:

The elastic‐wave scattering by a flat crack can be represented by an integral expression involving displacement and strain on the surface of the crack. We have explored the use of a modified static solution as an approximation to the displacement field of a penny‐shape crack in the long‐wavelength regime and then studied numerically how well it connects with the low‐freqency limit of the diffraction regime. Comparisons between this and several other existing approximations are made. We conclude that this quasistatic approximation is useful practically in both the long‐wavelength and beginning diffraction regime.

ISSN:0021-8979    

DOI:10.1063/1.325202

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Deuterium enrichments are reported for flowing methane/hydrogen mixtures subjected to a glow discharge at low temperatures. Dependence of the enrichment factor on initial D/H ratios, flow rates, system pressure, discharge energies, and translational temperature of the reacting gas mixture was studied. In addition to enrichment measurements, details of the estimate of energy requirements for enrichment of deuterium from natural abundance are included.

ISSN:0021-8979    

DOI:10.1063/1.325203

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The molecular stopping cross sections of butyraldehyde, acetone, 2‐butanone, and 3‐pentanone have been measured for 0.3–2.0‐MeV He+ions with probable random errors of 0.6–0.7&percent;. The stopping cross sections of cyclopropane and ethylene have also been remeasured in order that the stopping cross sections of oxygen in aldehydes and ketones [&egr;DB(O)] and in epoxides [&egr;RING(O)] can be extracted. It is found that &egr;DB(O) ≳&egr;RING(O) ≳&egr;SB(O) forE<0.7 MeV, where the subscripts DB, RING, and SB refer to oxygen in a double bond, in a three‐membered ring, and in a straight‐chained single bond, respectively.

ISSN:0021-8979    

DOI:10.1063/1.325204

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The resistive phase of self‐breaking water‐dielectric spark gaps in a high‐current relativistic electron‐beam accelerator is investigated experimentally. For gaps that withstand voltagesV?1.8 MV and mean electric fields between 2×107and 5×107V/m, both the current rise time and the energy dissipated in the discharge are adequately described by the semiempirical relations of Martin. In contrast to the results reported in lower‐energy experiments, no evidence was found of a slowly varying resistive phase with a gap resistance comparable to the circuit impedance aftert=2.5&tgr;r. Approximately 8±3&percent; of the energy dissipated in the gap is coupled into a shock wave generated by the discharge. Light emission from the arc channels indicated that the light was strongly filtered by the highly excited water surrounding the channel, and the light emission cannot be analyzed to determine the plasma properties of the arc channel unambiguously.

ISSN:0021-8979    

DOI:10.1063/1.325205

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The statistical equilibrium model for the electrostatic spraying of liquids, previously described by the author, is compared with the available experimental data for Woods’s metal, octoil, and glycerine. The model’s Lagrangian multipliers &agr;′, &bgr;′, and &dgr;′ have been evaluated for these fluids. In the two instances where the ratio &agr;′/&bgr;′ could be determined (Woods’s metal and octoil), the same value −10−17±15&percent; J was obtained. A tentative expression for this ratio is presented and it is proposed that all practical electrostatic‐spray systems are dominated by electron‐emission‐limited processes. Discontinuities in mean specific charge as a function of droplet radius are predicted and shown to be consistent with the available data. Best correspondence with limited data indicates &agr;′ to be proportional to an inverse fluid property capillary number. In addition, an expression for the pulsed system Lagrangian multiplier &dgr;′ is developed for steady‐state systems. The detailed characteristics of a pulsed benzene spray appropriate for use in internal‐combustion engines are described.

ISSN:0021-8979    

DOI:10.1063/1.325154

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Processes have been developed for producing stripe-geometry planar DH lasers and channeled substrate buried DH lasers where lateral-current confinement is obtained with reverse-biasedn-pjunctions on both sides of the active layer. These current-confinement schemes lead to current flow only through the two superimposed top and bottom stripe windows in otherwise completely reverse-biasedn-pjunctions. The structures are composed only of as-grown liquid-phase-epitaxy multilayers. These lasers have low threshold current densities, clean stable optical-mode patterns, and excellent linearity in the light-current curves. In addition, the channeled substrate buried DH lasers have optical and carrier confinement in both transverse directions, while also achieving efficient lateral-injection-current confinement. Results from a theoretical analysis, which describes the dependence of the threshold current densityJsthof DH lasers upon stripe widthS, are compared to the measured dependence and excellent agreement is obtained.

ISSN:0021-8979    

DOI:10.1063/1.325206

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Measurements of the emission from Pb+in the afterglow of a pulsed He : Pb discharge in a large‐bore tube and of the intensities of Pb+and Pb emission lines in a small‐bore dc discharge tube have been made to clarify the excitation mechanism of the He : Pb laser. In both He :  pure Pb and He : Pb containing a low concentration of Cd to act as a probe, the rate constants for the decay of the Pb+and Cd+emission lines obtained using the large‐bore tube indicated that the only excitation mechanism was thermal charge exchange between2S1/2He+and ground‐state Pb atoms. The collision cross section for the He+‐Pb reaction was determined to be 4.0×10−16cm2from measurements of the variations of the decay rates of the 5608.8‐A Pb+, 4386.4‐A Pb+, and 5378‐A Cd+emission lines with Pb concentration. The variation of the rate constant of the 4416‐A Cd+line indicated that the collision cross section for the 2s3S1He‐Pb Penning ionization is 14.8×10−16cm2. In a small‐bore tube, Penning ionization was verified to be the dominant excitation mechanism for the 4245‐A˚ Pb+emission line but not the 5608‐A˚ Pb+laser line. The change in the relative importance of the various excitation mechanisms with the discharge‐tube diameter, and its ramifications regarding other metal‐vapor laser systems, is discussed.

ISSN:0021-8979    

DOI:10.1063/1.325207

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

The results of a theoretical investigation of the discharge excitation of the CdHg* excimer are presented. Estimates are obtained for the efficiency of production of CdHg*, which has potential as an energy‐storage medium for the amplification of light pulses at 470 nm. A time‐independent analysis using a Boltzmann code was performed on a Cd, Hg mixture with an argon buffer. Seven atomic levels were considered in both Cd and Hg. A very high efficiency is obtained for excitation of the Cd(3P0,1,2) manifold from which the CdHg* excimer forms. The optimumE/Nvalue for the mixture Cd : Hg : Ar=1 : 4 : 20 is 8×10−17V cm2. The small value of the calculated Townsend coefficient at thisE/Nvalue required the consideration of an electron beam as the primary source of ionization. A detailed kinetic model was constructed which included electronic transition rates three‐body association rates, dissociative recombination, biexcimer mixing, and biexcimer quenching. The kinetic equations were solved using the time‐dependent solution of the Boltzmann equation for the electronic distribution function with a source term to account for the production of slow secondary (∼1‐eV) electrons by ionization collisions of the fast (∼100‐keV) primary electrons from the sustainer electron beam with the neutral atoms of the gas mixture. The effects of superelastic and inelastic collisions were explicitly included in the evaluation of the distribution function. In the case of a Cd : Hg : Ar mixture of 1 : 4 : 20 and Cd density of 5×1017atoms/cm3, 40&percent; of the discharge energy was deposited after 1 &mgr;sec into the molecular manifold of CdHg*. The sustainer ionization rate was 3.61×1020electrons/cm3/sec, and theE/Nvalue was 8×10−17V cm2. The stored‐energy density was 7 J/l. A molecular potential diagram for CdHg is given which indicates that 50&percent; of the stored energy could be available for the amplification of subnanosecond optical pulses at 470 nm.

ISSN:0021-8979    

DOI:10.1063/1.325208

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

Optical gain has been observed on the 470‐nm continuum band of CdHg following the flashlamp excitation of vapor mixtures of Cd and Hg. An argon ion laser was used to monitor gain signals at wavelengths ranging from 457.9 to 514.5 nm.

ISSN:0021-8979    

DOI:10.1063/1.325182

出版商:AIP    

年代:1978

数据来源: AIP

摘要:

We have measured the time dependence of the concentration of copper atoms in the ground and metastable states in a pulsed CuCl laser by monitoring the absorption of atomic copper lines. We found that the ground‐state population rises from a very small value at the end of the dissociation pulse to a maximum and decreases slowly after about 160 &mgr;sec. The metastable population reaches a maximum after about 40 &mgr;sec and then decreases relatively rapidly. We conclude that the minimum and optimum delay times in a double‐pulse copper halide laser are determined primarily by the slow buildup of the copper‐atom ground‐state concentration. This concentration then decays by recombination.

ISSN:0021-8979    

DOI:10.1063/1.325183

出版商:AIP    

年代:1978

数据来源: AIP