摘要:

Using a repetitively pulsed nitrogen laser of 100‐kW peak power and 10‐nsec duration, the Raman scattering cross sections at 3371 Å for various gas species relative to that of molecular nitrogen have been measured by a gated photon counting technique. The gases studied include N2, O2, CO, CO2, NO, SO2, C3H6, and C3H8. A statistical correction formula has been derived and applied to the apparent count rate to avoid possible errors due to the finite recovery time of the counter and its inability to distinguish between single‐ and multiple‐photon arrival events within the very short time gate. The resultant accuracy of the present measurements is accordingly estimated to be better than ± 5%.

ISSN:0021-8979    

DOI:10.1063/1.1662746

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The utility of laser interference fringe microscopy is demonstrated in a variety of electric contact problems. The technique is used for quantitative surface topography, measurement of load‐bearing areas, lubricant film characterization, wetting angle measurements, and particulate contaminant size determinations.

ISSN:0021-8979    

DOI:10.1063/1.1662747

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The results of a study of the plasma produced by focused TEA‐CO2laser radiation on aluminum foil targets are presented. Streak photography, interferometry, and charge collection measurements are used to describe the time and space evolution of the plasma. A maximum plasma temperature of 30 eV, deduced from the ion expansion energy, was obtained for an incident flux of 1010W/cm2. The electron density remained below cutoff throughout the interaction. For thick targets the plasma production can be described by using a self‐regulating process. For thin foils the plasma becomes transparent during the laser pulse and the hydrodynamic expansion can influence the results. In this latter case temperature scaling laws based on an integrated inhomogeneous spherical model give good agreement with the experiment.

ISSN:0021-8979    

DOI:10.1063/1.1662748

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

High‐speed ground vehicles magnetically suspended above a continuous aluminum guideway by superconducting coils can have a clearance of 0.1–0.3 m. To take full advantage of the large clearance, a propulsion system with a comparable clearance is needed. Two such systems based upon physically moving static magnetic fields produced by superconducting coils are proposed. With the use of a prime mover such as a gas turbine or a diesel engine, these systems avoid power collection problems and should result in a lower‐weight propulsion unit. A numerical analysis of each has been made to determine the thrust, the lift force, and the efficiency as a function of various parameters. The mechanical efficiency of the paddle wheel appears to have a maximum of ∼60% at 483 km/h (300 mph), while that of the superconducting screw is (1‐slip) for an infinitely long machine. End effects will degrade the efficiency somewhat for a screw of finite length.

ISSN:0021-8979    

DOI:10.1063/1.1662749

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

This report shows that magnetically isotropic and anisotropic compacts of BaFe12O19or SrFe12O19sinter to high density with controlled microstructure in the presence of a liquid phase. The liquid‐phase compositions are in the systemsMO&sngbnd;SiO2andMO&sngbnd;Al2O3&sngbnd;SiO2,M=Ba, Sr. Further, it is shown that systems containingMB2O4as an additional component will give similar results at significantly lower temperatures. The resultant magnetic properties meet or exceed the appropriate magnet industry criteria for hard ferrite magnets.

ISSN:0021-8979    

DOI:10.1063/1.1662750

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Experimental evidence is presented in support of a simple model, containing one adjustable parameter, which accounts for the dependence of the limiting frequency of single bubble propagation on bias field, rotating field intensity, and circuit period. The parameter, which characterizes the design of the overlay, is defined as the magnetic pole strength per unit of in‐plane field. Having the dimensions of area, it is referred to as the cross section &sgr;. Data taken on the same circuit designs at different periods (&lgr;) confirm the expectation that &sgr; is proportional to &lgr;2. We found &sgr;/&lgr;2=0.016 for T‐X circuits, 0.014 for T‐Bar circuits, and 0.012 for a 3‐bar chevron design.

ISSN:0021-8979    

DOI:10.1063/1.1662751

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

It is shown that a Josephson junction, biased at a voltageV0and driven simultaneously by two monochromatic sources at the frequencies &ohgr;1and &ohgr;2, produces an output power at the frequency &ohgr;3= &ohgr;1—n&ohgr;2and that this frequency is independent of the Josephson frequency &ohgr;0= 2eV0/ℏ. The power output depends upon the dc bias, showing fine structure with a voltage periodicity of ℏ&ohgr;2/2e.

ISSN:0021-8979    

DOI:10.1063/1.1662752

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

By detecting the oscillation of a tuned circuit resonant at frequencyv0coupled to a shunted superconducting point contact we have observed oscillations not only at the Josephson voltageV=&phgr;0v0, where &phgr;0is the flux quantum, but also at voltagesVn=gn(T)&phgr;0v0, wheregn(T)is a continuous monotonic function of temperature. For most temperaturesgn(T)=N(T)/n, whereNandnare integers, however there are ranges of temperature over whichg1(T) varies rapidly through nonintegral values and the voltagesVnare not harmonically related. The level of oscillation of the tuned circuit was used to measure the power spectrum of the voltage waveform at the point contact and the linewidths were found to be oscillatory functions of temperature with minima whenV1=N&phgr;0v0and maxima whenV1=(N+1/2)&phgr;0v0. The Josephson oscillation of the shunted point contact consists of pulses ofNflux quanta (N&phgr;0) crossing the point contact at a repetition frequencyv0. The temperature dependencies are interpreted in terms of fluctuations inN. The relationship between these results and some temperature dependent features observed on theI‐Vcurves of point contacts and some implications for noise thermometry are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1662753

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Flat braids partially soldered together with a soft nonsuperconducting alloy have superior electrical stability and mechanical properties as compared to braids made from fully insulated superconducting wires. Eddy currents induced by a changing field, however, may cause undesirable field shape changes and power loss in magnets. An analysis of these eddy currents for the case of constant rate of change of field is presented, and comparisons made with observed field distortions or power loss in two magnets.

ISSN:0021-8979    

DOI:10.1063/1.1662754

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

It has been shown that effective uniaxial anisotropy fieldsHk″of epitaxial magnetic‐garnet bubble materials can be found from an optical measurement of the sample's easy‐axis susceptibility. The susceptibility is influenced by the cubic anisotropy which the materials possess in addition to their induced uniaxial anisotropy. This paper examines in detail how the optical measurements are affected by various ratios of cubic and uniaxial anisotropies. In particular, it is found thatHk″can be found accurately using this technique for a wide range of material parameters which includes bubble materials. A procedure which corrects for sample misalignment is presented along with a method by which the cubic and uniaxial anisotropy constants for a material can be calculated from measurements of itsHk″and magnetization.

ISSN:0021-8979    

DOI:10.1063/1.1662755

出版商:AIP    

年代:1973

数据来源: AIP