摘要:

The rate of bubble evolution, and hence the rate of mass transport across a curved liquid‐gas interface, has been examined both theoretically and experimentally. A single gas bubble is contained in approximately 1.3 cc of a liquid‐gas solution that is closed to mass transport. This condition provides the mechanism by which the gas bubble may be placed initially in a state of stable equilibrium, and thus allow an accurate determination of the system parameters. A stirred liquid condition is achieved by rotating a micro‐stir bar within the volume, and the resultant flow pattern is characterized with laser‐doppler anemometry. Through an experimental examination on the complete dissolution of nitrogen‐gas bubbles in water, the mechanism of mass transport is shown to be consistent with a model comprised of two processes: (1) the primary and rate‐limiting process is modelled by the diffusion of gas through an unstirred liquid‐boundary layer whose thickness varies with bubble radius; and (2) a second‐order limitation is due to the nonequilibrium transport of gas across the phase boundary as predicted by a statistical rate theory expression. The theoretical model is then applied to predict the evolution of a bubble towards a state of stable equilibrium.

ISSN:0021-8979    

DOI:10.1063/1.331741

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The magnetic‐field dependence of the Hall factor is investigated theoretically and experimentally. The theory includes arbitrary band structure, carrier degeneracy, and wave functions assuming isotropic media and carriers behaving as spinless Fermions without energy‐level quantization. Comparisons between theory and experiments on high‐purity GaAs from the low magnetic‐field limit to the classical high magnetic‐field limit agree to within 0.7 percent.

ISSN:0021-8979    

DOI:10.1063/1.331735

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A method for separating hydrogenic isotopes particularly directed at separating tritium from deuterium in the civilian energy context is outlined. An atomically dissociated deuterium/tritium flow—the feedstock—is subject to radiation from an electrical discharge containing pure tritium gas. The tritium atoms in the feedstock selectively absorb line radiation from the discharge light source, are excited to high lying levels and are subsequently ionized. The tritium ions are then trapped in solids present within the light‐absorption zone—either as wires or as entrained particles— and are removed from the system. Energy requirements for separation of tritium from deuterium for a typical fusion feedstock are found to be on the order of approximately 300 eV/T.

ISSN:0021-8979    

DOI:10.1063/1.331722

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A new type of negative deuterium ion source for the neutral particle injection in the fusion research is proposed. The element of the ion source is made of a bilayer of vanadium or palladium metal and a silicon semiconductor. The D−ions are formed with the cascade processes which involve the dissociation of D2’s when they are dissolved into the element, the electronic resonance transition from the Si surface to D(1s) diffusing through the element, and the detachment of the resultant D−ion from the surface. The estimations show that in an ideal case, the obtainable current density of D−ions is about 27 mA/cm2and that the neutral component leaving the surface is about 18.5% of the D−ion current.

ISSN:0021-8979    

DOI:10.1063/1.331730

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Emission signals at 8758 A˚ were observed when bismuth atom vapor was introduced into a supersonic flow of electronically excited nitrogen fluoride, NF (a1&Dgr;). A correlation of thermal and pressure data with the appearance of the chemiluminescence, along with a computer analysis of the IRTV observations at two wavelengths, is presented. On the basis of an analysis of these data, it is concluded that the observed emission results from the production of an excited‐state bismuth atom density, Bi(2D3/2), on the order of >1013atoms cm−3by collisional transfer with NF (a1&Dgr;).

ISSN:0021-8979    

DOI:10.1063/1.331700

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

As an aid to the study of coupling microstrip structures, this paper analyzes and computes the radial dependence, along the dielectric substrate, of the magnetic field Green’s function of a horizontal magnetic dipole. The analysis is based on the contour integration of the exact spectral Green’s function. From the results, it is observed that the radial dependence can easily be approximated by the corresponding free‐space Green’s function with a small correction term.

ISSN:0021-8979    

DOI:10.1063/1.331707

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A class of nuclear pumped lasers (excited by reactor‐produced thermal neutrons) in which the laser levels are populated by negative ion‐positive ion neutralization is proposed and an analysis of two particular systems,3He/N2O/O2and3He/N2O/N2, is performed. Laser action is predicted in atomic oxygen and nitrogen as a result of O−‐O+and O−‐N+neutralizations. The source of negative ions is dissociative attachment to N2O. A threshold neutron flux of ≊1015cm−2 s−1, peak power of >500 W/cm2, and a fission power to laser power conversion efficiency of ≊0.4% may be possible in these systems. This is as a result of efficient utilization of the large thermal electron density in the attachment process, and the highly selective nature of the ion‐ion neutralization in producing product‐excited states.

ISSN:0021-8979    

DOI:10.1063/1.331718

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

Operation of a pulsed, multikilohertz‐repetition‐rate, supersonic HF chemical laser is described. Continuously flowing reactants are premixed and then expanded through a supersonic nozzle to the laser cavity where a pulsed electrical discharge initiates the chemical reaction producing the lasing species. An average power of 12 W has been obtained from a hydrogen/sulfur‐hexafluoride/helium mixture. It is suggested that this apparatus can be used to overcome some of the inherent problems in achieving quasi‐continuous laser operation based on a chain reaction in fluorine/hydrogen mixtures.

ISSN:0021-8979    

DOI:10.1063/1.331684

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

InGaAsP/InP double heterostructure lasers with buried rib waveguide structure in whichp‐quaternary rib waveguide layers surrounded byn‐InP are formed adjacent to the active layers, are proposed for the 1.5–1.6 &mgr;m wavelength range and have been successfully fabricated by two‐step liquid phase epitaxial methods combined with a controlled mesa etching technique. In this structure, the rib waveguide layer can provide carrier confinement as well as lateral optical confinement. The low threshold current of 50 mA was obtained with the external differential quantum efficiencies of about 42% and 36% under pulsed and cw operation, respectively. Stable fundamental transverse mode operation was achieved up to three times the threshold current, and single longitudinal mode cw operation was also observed up to 1.5 times threshold current.

ISSN:0021-8979    

DOI:10.1063/1.331685

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An rf‐sputtered thin film of LiNbO3on a sapphire substrate was used as a waveguide for optical frequency doubling. Employing a Nd:YAG laser and a tunable dye laser, whose output was used to pump a stimulated Raman cell, the TM&ohgr;0 → TM2&ohgr;2up‐conversion process was investigated in detail, and the phase‐matched nature of this process was demonstrated. The conversion efficiency was estimated to be about 10−3.

ISSN:0021-8979    

DOI:10.1063/1.331686

出版商:AIP    

年代:1983

数据来源: AIP