摘要:

Recently derived improved boundary conditions for the reflection of weak shock waves from an open end of a duct can be well approximated by a centered expansion wave if the center of the later is located on the leading characteristic of the reflected wave and some distanceeoutside the duct. A relation is derived betweene/D(Dis the duct diameter), the shock pressure ratiop1/p0, and &ggr; (the ratio of specific heats). This relationship is represented with sufficient accuracy by the empirical formulaeD=0.90+0.677(p1/p0)−1(&ggr;+1.08)−3.8.This result makes it possible to apply the improved boundary conditions without losing the convenience of of the customarily used wave diagram procedure.

ISSN:0021-8979    

DOI:10.1063/1.1721904

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

It is assumed that the velocity of the domain wall is proportional to the difference between the magnetic field intensity at the wall and the coercive force. The local magnetic field, which is not equal to the external field, is calculated from the eddy‐current equations. The rate of change of the magnetic flux as a function of time is determined. The total switching time is expressed in terms of two phenomenological constants: the retardation constant &agr; mentioned above, and a delay time &tgr;, the duration of the formative phase during which the plane walls are formed.

ISSN:0021-8979    

DOI:10.1063/1.1721905

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Compression waves generated by paper pistons accelerated by shock waves in a shock tube have been reflected from a symmetrical wedge. Studies of the density fields in the interaction region have been made with an interferometer, and the parameters, ``wave age,'' distance up the wedge, and angle of incidence have been investigated over a range of incidence angles from 25° to 80° and ``effective shock strengths'' from &xgr;=1.1 to &xgr;=2.0. The limit of regular reflection for this type of wave is shown to exist theoretically, and this limit has been verified experimentally. Beyond this limit a type of Mach reflection occurs.

ISSN:0021-8979    

DOI:10.1063/1.1721906

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The second derivative of the current‐voltage relationship of an ideal plane diode is calculated from the Epstein‐Fry‐Langmuir analysis. From this analysis it is shown that for the large saturation emission characteristic of oxide‐coated cathodes at normal operating temperatures, the current at the inflection point (i.e., the zero of the second derivative) is a sensitive measure of the saturation emission and is unaffected by the existence of a linear interface impedance. It is also shown that the general features of the results apply to cylindrical diodes.

ISSN:0021-8979    

DOI:10.1063/1.1721907

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

If the forward current through ap‐njunction suddenly ceases, an emf appears due to nonequilibrium carrier concentrations at the junction barrier. Measurements of the barrier emf have been made with a wide range of injection currents and yield currentvsbarrier voltage characteristic curves. The open circuit case of voltage decay across ap‐njunction in the rangeV≫kT/qis discussed. The voltage decay is observed to be linear with time with a slopekT/q&tgr;. It follows from an analysis based on a simple model that the excess minority carrier concentrations decrease exponentially with the time constant &tgr;. The floating emitter and collector voltages,VE(t) andVC(t), ofp‐n‐ptransistors are observed to decay like the open circuit voltage across ap‐njunction, and it is noted thatVE(t) ≈VC(t) in the rangeV≫kT/q. The transient response of a semiconductor rectifier connected in parallel with a large external capacitance is analyzed. The response calculated for large negative excursions of voltage gives a simple relation by which the saturation current may be determined. Measurements are presented and discussed.

ISSN:0021-8979    

DOI:10.1063/1.1721908

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Absolute photoelectric yields of Ni, Cu, Pt, Au, W, Mo, Ag, and Pd are presented for the spectral region from 1400 to 473 A. Measurements were obtained for commercially pure polycrystalline surfaces which were treated in various ways including heat treatmentin vacuoand in various gas atmospheres at reduced pressures. Surfaces, heat treatedin vacuo, gave reproducible yields ranging from 10−3electrons per photon at 1400 A to 10−1electrons per photon at 500 A. Although untreated samples exhibited a maximum in the region studied, this maximum disappeared after heat treatment resulting in most cases in a broad plateau extending from 1000 A to 500 A. At wavelengths longer than 1000 A a decrease in yield was observed. Representative experiments with a Ni cathode, heat treatedin vacuothen exposed to O2at reduced pressures, indicated that the maxima for untreated surfaces were caused by adsorbed gases and metallic oxide formation. The absolute error in the values of the photoyields was estimated to be within ±15%.

ISSN:0021-8979    

DOI:10.1063/1.1721909

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The transmission of gamma rays through slabs of various shielding materials has been calculated by a random sampling method in which the path lengths between interactions are deliberately chosen larger than those which occur naturally. Results for the case of normal incidence compare reasonably with values obtained by Goldstein and Wilkins for transmission in infinite media. The present results for the case of obliquely incident photons show the same general behavior as noted experimentally by Kirn,et al.In particular, the transmission plotted against slant path length shows a crossover, in the region of 1 or 2 mean free paths, of the curves corresponding to different incident angles. Angular and spectral distributions were obtained in the form of histograms, and it was found that the photons assume spatial equilibrium after one or two mean free paths, as evidenced by the constancy of the flux‐to‐current ratio. The relative contribution to the total penetration arising from the first, second, etc. scattering has been found to have the same general trend as noted earlier by Peebles. The biased sampling method which was used enables one to use the same set of photon case histories in treating a number of slab thicknesses.

ISSN:0021-8979    

DOI:10.1063/1.1721910

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

An experiment has been devised whereby excess noise is measured along various different directions in a germanium filament after the directions of current flow for the majority and minority carriers had been altered by a magnetic field. From this experiment it is possible to determine that whereas shot noise is caused by both majority and minority carrier fluctuation, 1/fnoise is essentially produced only by majority carrier fluctuation.

ISSN:0021-8979    

DOI:10.1063/1.1721911

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A treatment is given of the hysteresis loops of dilute mixtures of various sizes of ferromagnetic particles. Three ranges of particle size are considered: very small particles called ``super‐paramagnetic'' which are single domain and equilibrate resulting from thermal vibrations, single domain particles which are large enough that they do not equilibrate, and particles large enough to contain many domains in equilibrium. The results are compared to experiment.

ISSN:0021-8979    

DOI:10.1063/1.1721912

出版商:AIP    

年代:1955

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721914

出版商:AIP    

年代:1955

数据来源: AIP