摘要:

Contrary to the conclusions of previous researchers who found the drag coefficients of small bubbles in water to coincide with those expected for solid spheres, we found the drag coefficients of small bubbles in water (Reynolds numbers from 2 to 40) to be significantly less than those expected for solid spheres and close to what we expect are the drag coefficients for ideal fluid spheres. The difference between the present results and those of previous workers is ascribed to velocity measurements nearer to the point of formation, thus giving the surface of a bubble less time to age and collect surfactants.

ISSN:0021-8979    

DOI:10.1063/1.1663630

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An experimental study of a microwave reflection arrangement used to measure changes in the conductivity of semiconductor samples is presented. A germanium sample with associated microwave circuitry acts as a highly sensitive system whereby in the null condition almost complete absorption occurs. Changes in conductivity from the null point will cause a sharp increase in reflected microwave power. This technique will allow electrodeless measurements of both bulk and thick‐film semiconductor properties and may have application as a large‐area detector of infrared radiation.

ISSN:0021-8979    

DOI:10.1063/1.1663631

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A large zero‐bias anomaly has been observed in the point contact tunnel junctions made between a degeneratep‐type GaAs and Mo. The anomaly corresponds to a resistance peak centered at zero bias. The junction resistance at zero bias is a strong function of temperature, increasing with decreasing temperature. A quantitative study of the voltage and temperature dependence of the zero‐bias anomaly has been made. No effect of the magnetic field up to 12 kG was found. When the temperature was lowered below the transition temperature of Mo, the superconducting energy gap of Mo was observed, which indicated that the mechanism of current flow is by electron tunneling.

ISSN:0021-8979    

DOI:10.1063/1.1663632

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

New procedures are described for analyzing diffusion length measurements obtained by using several methods which, in the past, have shown inconsistent results. These procedures consist of a microwave photoconductive decay method and three techniques in which carriers, generated by &ggr; rays, 1‐MeV electrons, or ir light, are collected by ap‐njunction. Special attention is given to measurements of solar cells in which the sample thickness may be comparable to the diffusion length. A theoretical analysis of each method is presented, as well as the results of a study in which a set of solar cells with a wide range of diffusion lengths was measured. It is shown that results from all methods are consistent over the entire range. A discussion of the advantages and disadvantages of the various methods is also included.

ISSN:0021-8979    

DOI:10.1063/1.1663633

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Experimental values of the standard deviation &sgr;sof fluctuations of surface potential are discussed. A comparison is made between the experiments and the theory of Nicollian and Goetzberger recently generalized by the mathematical model of Brews. We conclude that Brews's model adequately represents most of the data, provided both positive and negative fixed charges are assumed to be present simultaneously in our devices.

ISSN:0021-8979    

DOI:10.1063/1.1663634

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A new monolithic structure for solid‐state traveling‐wave amplifiers is proposed, which promises efficient interaction between a drifting charge carrier stream and a slow electromagnetic wave component. The suggested configuration is potentially suitable for operation in the far‐ir frequency regime. A one‐dimensional analysis of the interaction between the electromagnetic waveguide mode and the carrier current is presented, including the loss contribution due to the nonsynchronous space harmonics of the electromagnetic mode.

ISSN:0021-8979    

DOI:10.1063/1.1663635

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Vacuum‐deposited thin films of B, C, Mg, Al, Si, Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Zr, Mo, Ag, In, Sn, Sb, Pt, Au, Pb, and Bi in several thicknesses, confined between glass substrates, were irradiated by a uniformQ‐switched ruby laser beam. The laser pulse was 15 ns in duration, with a maximum energy of 5 J in an area 6.35 mm in diameter. The stress waves were studied using the piezoelectric response of X‐cut quartz‐crystal disks of the same diameter. The peak stresses are presented as a function of the energy fluence, with possible interpretations of the phenomenon.

ISSN:0021-8979    

DOI:10.1063/1.1663636

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

An electron‐beam‐initiated high‐pressure CO2laser discharge is investigated. It is assumed that initially the discharge current flows along the vacuum electric field direction. The resulting distortion of the electric field is calculated by a linearization of the continuity equation. We have computed the solution for the special case of a finite electron beam and infinite planar electrodes. The predicted variation of the sustainer current and distortions of the applied voltage are compared with experimental results.

ISSN:0021-8979    

DOI:10.1063/1.1663637

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Picosecond pulses generated by a mode‐locked neodymium‐glass laser have been compressed down to 0.5 psec with a repetition rate up to 3 × 1011Hz by the insertion of a glass flat inside the laser cavity. The reduction in pulse width is attributed to a frequency‐dependent transit time on transmission through the glass flat.

ISSN:0021-8979    

DOI:10.1063/1.1663638

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Theoretical expressions based on the Boltzmann transport equation, nondegenerate statistics, and Poisson's equation are derived for the electrical conductivity of extrinsic semiconductor films. The theoretical conductivity is presented as a function of film thickness and Fuch's scattering indices for the nondegeneraten‐ orp‐type semiconducting films. The analysis predicts that the conductivity of thin films having quasisymmetrical space‐charge layers at the surfaces should be strongly dependent upon the excess carrier density in these layers even under conditions of specular surface scattering. The limited amount of conductivity data reported for epitaxial germanium films are interpreted using the extrinsic film model. Universal curves are presented for normalized film conductivity as a function of normalized film thickness for accumulatedn‐ andp‐type films and depletedn‐ andp‐type films having specularly scattering surfaces. The general case analysis yields the symmetrical and flat‐band results as previously reported. The symmetrical‐field case is briefly reviewed as an aid for comparison.

ISSN:0021-8979    

DOI:10.1063/1.1663639

出版商:AIP    

年代:1974

数据来源: AIP