摘要:

By simulating with an electro‐mechanical analog a forced van der Pol like system, it has been possible to observe some of the jump and hysteresis phenomena suggested by Cartwright. The dependence of entrainment band width on forcing amplitude, as suggested by Andronow and Witt, has also been observed.

ISSN:0021-8979    

DOI:10.1063/1.1722643

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A magnetic field transverse to an arc tends to move the cathode spot in either the direction of the electromagnetic force (the Amperian sense) or in the opposite direction (the retrograde sense). The theory of A. E. Robson and A. von Engle assumes that an arc, bent over in the Amperian direction forms a loop in which the magnetic field of the arc opposes the applied field to yield the retrograde motion. Calculations herein presented indicate that the arc field is too weak to uphold the theory. Retrograde motion proceeds continuously against a blast of vapor, while Amperian motion proceeds in the direction of the blast and is often discontinuous. These phenomena are recalled in giving an alternative explanation of the data.Examination of the ``ball of fire'' discharge, which can display retrograde motion, shows the excitation phenomena in the region between dark and bright plasma yields information about retrograde motion. Studies of the corresponding dark space and negative glow of an arc and a better knowledge of electron liberation at the cathode give promise of yielding information about the retrograde motion.

ISSN:0021-8979    

DOI:10.1063/1.1722644

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Additional data are reported that confirm a theory presented in a previous paper for the penetration of a stable flat‐nosed projectile in sand. The negative acceleration of the projectile can be expressed by the relations: −dv/dt=&agr;v2,v0>v>vc; −dv/dt=&bgr;v2+&ggr;,vc>v>0 where the coefficients &agr;, &bgr;, &ggr; are positive constants andv0is the striking velocity. In the case where air is removed from the sand and the sand is loaded transverse to the trajectory by one atmosphere pressure, the coefficients &agr; and &bgr; are characteristic of inelastic and elastic impact, respectively, where the flow process is regarded as Newtonian. An additional experiment has been performed where quartz powder produced by impact is plotted as a function of initial projectile energy. Although the powder production curve can be represented roughly as a straight line through the origin, there are small discontinuities in slope corresponding to the critical velocityv=vc. The velocity of sound in sand has been measured under the conditions of the experiments. Loading increases the velocity of sound markedly but has little effect on the critical velocityvc.

ISSN:0021-8979    

DOI:10.1063/1.1722645

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The high‐speed microwave semiconductor switch, employing ann‐type germanium diode, has been further investigated to determine the ultimate switching speed. Data are presented which show that pulse rise and decay times are as fast as 3 m&mgr;sec. This limit is imposed by the capacitances and inductances of the equipment and is not intrinsic to the germanium diode. The ultimate rise and decay times are determined by relaxation processes in the germanium, and are expected to be faster than 1 m&mgr;sec.Two switching pulses of variable spacing in time were employed to show that there are no essential residual processes in the germanium following the application of a pulse. Since there is then no measured dead time of switching, the pulse‐repetition rate is limited by the rise times and decay times.Measurements have been made on a series of semiconductor switches using different concentrations of donors. As the concentration is decreased, avalanche breakdown occurs at higher negative voltages which allows switching of higher microwave powers. Successful operation has been obtained with microwave powers as high as one watt impinging upon the semiconductor switch. In general, rise and decay times tend to increase as donors decrease. Thus, rise times and decay times of 10 m&mgr;sec were obtained at one watt of microwave power.

ISSN:0021-8979    

DOI:10.1063/1.1722646

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

By reflecting 10‐cm microwaves from the trails of ultra‐speed pellets, the ion (electron) density in the trails was found to be from 109to 1013electrons per cm of path length. Column diameters were from 1.0 to 7.5 cm and pellet velocities ranged from 1.48 to 2.67 km/sec. The ions appeared to come from thermal ionization behind the pellet shock waves and from oxidation reactions involving material ablated from the pellets.

ISSN:0021-8979    

DOI:10.1063/1.1722647

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The effect of porosity on several material constants can be described by three types of empirical functions. One of these features linear increase from zero to unity of the relative bulk material constant when the relative density increases from &pgr;/6 to 1. An almost identical function results from application of a theoretical model with the following properties.(1) The porous compact is divided into two systems: first, isolated pores in a continuous solid matrix; second, solid grains mixed with continuous voids.(2) The geometry of both systems is assumed to be a cubic array of equal spheres. With this simplification, the relative bulk material constants of each system are calculated as functions of the relative density. The equations obtained are valid for those material constants which are ratios of corresponding fluxes and forces in the sense defined by Maxwell (e.g., the electric conductivity).(3) Weight factors for the presence of either system are introduced.(4) The weight factor for the system of isolated pores is assumed equal to the relative bulk material constant of the total compact for all values of relative density.The implications of this model to the mechanism of sintering are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722648

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Effective scattering cross sections for polystyrene in electron microscope specimens were measured through the microdensitometry of the images of polystyrene latex spheres recorded with an RCA Type EMU 3B electron microscope. Measurements were made at both 50 kv and 100 kv beam potential without an objective aperture, with a 40‐&mgr; aperture and with a 20‐&mgr; aperture. Cross sections per gram vary from 1.9 to 11×104cm2/g. The results are consistent with previous experimental data and are in reasonable agreement with theoretical calculations.

ISSN:0021-8979    

DOI:10.1063/1.1722649

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The surface photovoltage method uses the junction‐like properties of a semiconductor surface as a means for studying the decay of excess carriers. No more than capacitive contact with the specimen is required to detect the surface photovoltage which, in the millivolt range, is a linear function of the excess carrier density. Theoretically, the surface method yields exactly the same carrier decay constant as the photoconductivity method when the lowest diffusion mode prevails in the specimen. This has been quantitatively confirmed for Ge: only qualitative confirmation has been made with Si.For surfaces tending toward inversion, the surface method gives larger signals than the photoconductivity method, particularly for semiconductors with low intrinsic carrier density. On the other hand, for accumulation layer surfaces the surface method usually gives smaller output signals.

ISSN:0021-8979    

DOI:10.1063/1.1722650

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

In axially symmetric electron beams, the current density (as a function of radius) may be rather easily related to the current through a narrow slit (as a function of slit position) by means of an integral equation. A similar equation applies to scanning by a straightedge. In this paper, the solution of the integral equation is obtained and a simple technique for rapid numerical evaluation of the resulting ordinary equation is included. The relations derived are of particular interest in the large number of cases where the mechanical simplicity of slit or straightedge scanning makes these methods preferable to the more common pinhole method. The resolving powers for slit and pinhole scans are compared.

ISSN:0021-8979    

DOI:10.1063/1.1722651

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Experimental studies on the effects of contact materials and crystal surface preparation on the voltampere characteristics of contacts to CdS single crystals are presented. Rectifying contacts are influenced by the surface preparation prior to electrode application. An artificially roughened or naturally rough crystal surface tends to reduce the rectification ratio of a contact. Two kinds of current fluctuations that may be attributed to the contacts are observed.

ISSN:0021-8979    

DOI:10.1063/1.1722652

出版商:AIP    

年代:1957

数据来源: AIP