摘要:

We report absolute cross sections for Hg(63P1)+Hg(63P0) associative ionization and Hg+2Hg+2+e−dissociative recombination in mercury vapor, following saturation of the 253.7‐nm transition using pulsed laser excitation. The quantitative time dependencies of all relevant species were determined by combining this information with measurements of the total Hg(63P1) density and the total electron current following the laser pulse. The electron temperature associated with our measurement ofkDRis 298 K. The measured values ofkAIkAI= (2.5 ± 0.6) × 10−8cm3 s−1andkDR= (4.4 ± 1.1) × 10−6cm3 s−1are 3.5 times smaller and 10.5 times larger, respectively, than those previously reported in cw and discharge flow studies.

ISSN:0021-8979    

DOI:10.1063/1.347386

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The wavelength of semiconductor lasers generally increases with increased output power due to changes in laser gain with current and temperature. Time‐resolved studies of the optical spectrum during the write‐pulse train clearly depicted the quasirandom mode hopping that occurred. In optically dispersive systems, the wavelength shifts caused significant write‐spot displacements down at the recording surface and affected mark lengths. Thermal modeling studies successfully duplicated the salient features of this effect and provided explanations for some of the experimental observations.

ISSN:0021-8979    

DOI:10.1063/1.347387

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

For the general oblique incidence for which the grating vector is inclined to the plane of incidence, the diffraction of a plane wave by a plane grating is treated by a perturbation technique. The transverse electric mode and the transverse magnetic mode incidences are investigated. The copolarized and the cross‐polarized parts of the diffraction efficiencies are evaluated, and their dependencies on the direction of incidence are examined.

ISSN:0021-8979    

DOI:10.1063/1.347388

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The temperature dependence of the laser threshold and the slope efficiency of a YAG:Er laser operated at 2.94 &mgr;m have been measured. With a reduction of the temperature from 55 to 4 °C the output of the YAG:Er laser can be increased by a factor of 2.8. From the above measurements the relative populationNuof the4I11/2andNlof the4I13/2levels are determined, leading to further insight into the mechanism of this laser system.

ISSN:0021-8979    

DOI:10.1063/1.347389

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A numerical method for the analysis of thickness modes in piezoelectric plates with full account of the electromechanical coupling is presented. Numerical data for the main electroacoustical characteristics of some highly efficient piezoelectric crystals are given. Some inconsistencies with the available theoretical models are discussed.

ISSN:0021-8979    

DOI:10.1063/1.347390

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A theoretical analysis of the electromechanical coupling properties of piezoelectric transducers and resonators in the general thickness‐multimode case is presented. A new concept for material characterization usingthreemode thickness resonator geometries is discussed. The insertion loss function of the piezoelectric transducer is derived and numerically analyzed for arbitrary polarizations of the excited modes.

ISSN:0021-8979    

DOI:10.1063/1.347391

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The second law of thermodynamics is presented in terms of the heat accumulation function. The meaning of the heat accumulation functions is illustrated by a practical example. The optimization problem of heat engines is formulated with the aid of the heat accumulation function at a very general level. As an example, we have studied a heat engine process where the heat input and output changes are limited by the finite heat capacity of the combustion air. We have obtained formulas for estimating the maximum efficiency for heat engines as a function of the ratio of the combustion heat and the heat capacity of the combustion air. Representative numerical examples are presented.

ISSN:0021-8979    

DOI:10.1063/1.347392

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The influence of a nonuniform electric field (ac or dc) on heat transfer from an electrically heated platinum wire immersed inn‐hexane was investigated. The platinum wire was concentrically mounted in a closed copper cylinder filled with the test liquid. The copper cylinder was placed horizontally in a constant temperature bath. Heat transfer coefficients for natural convection were obtained to serve as a reference for the electric field measurements. The electric field results showed an increase in the heat transfer rate from the wire over free convection for both ac and dc fields. The electric Nusselt numbers in ac fields were a factor of 4 higher than corresponding results in dc fields. This behavior differed from results reported in the literature forn‐hexane, which was further demonstrated by replotting some of the raw data using the same physical and electrical properties employed to reduce the present experimental data.

ISSN:0021-8979    

DOI:10.1063/1.347393

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The coefficient of restitutioneis usually defined as an empirically determined constant of proportionality that relates normal components of incident and rebound relative velocity for contact points CPiof colliding rigid bodies. Assuming thaterepresents inelastic behavior, this definition results in calculated kinetic energy increases during eccentric (noncollinear) collisions for some conditions of contact point slip. These paradoxical energy increases arise only in noncollinear collisions where slip at CPiis opposed by friction. In this caseemust also depend on the slip process and friction, but then the ‘‘impact law’’ is valid for only a vanishingly small range of incident velocities. To resolve this paradox, we propose a new definition whereeis independent of friction; thenceespecifically represents internal dissipation by irreversible deformation processes. This definition clearly separates frictional and nonfrictional sources of energy dissipation. The two definitions are only equivalent in the case of nonfrictional or central (collinear) collisions.

ISSN:0021-8979    

DOI:10.1063/1.348922

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A new soft x‐ray source has been developed and investigated. Argon is injected into a plasma focus through a hole in the anode. The pinch emits several Joules per shot of soft x rays at &lgr;<0.5 nm from multiple micropinches well aligned along the axis of symmetry. When viewed end‐on the pinch appears as a small source of 700 &mgr;m diam. The micropinches have the following characteristics: Range of size 40–250 &mgr;m (depending on radiation wavelength), density 1028m−3, temperature 1.5 keV, and lifetime typically less than 1 ns. The helium‐like emission from single micropinches lasts for 250 ps only, which is much shorter than previously reported.

ISSN:0021-8979    

DOI:10.1063/1.347394

出版商:AIP    

年代:1991

数据来源: AIP