摘要:

The ideal flow predicted for an inviscid adiabatic shock tube is not realized in experiments. A correction of the ideal theory for the viscous stresses and heat losses arising from the interaction of the gas flow with the tube walls is calculated. The boundary layer is regarded as a distribution of sinks of energy and momentum. The actual distribution is approximated by that behind a constant strength shock front and is calculated for laminar flows. The change in shock strength caused by a single sink located at a fixed distance behind the shock front is determined and this result is integrated over the distribution previously calculated. Interactions between the expanding compression chamber gas and the wall are neglected. It is shown by comparison with experiment that the interactions treated account for the major part of the attenuation of the shock front. It is pointed out that more data are required to evaluate precisely the assumptions used in the calculation.

ISSN:0021-8979    

DOI:10.1063/1.1722352

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Hydrogen‐oxygen and hydrogen‐air mixtures were ignited by converging cylindrical shock waves using the apparatus devised by Perry and Kantrowitz [J. Appl. Phys.22, 878–886 (1951)], and the minimum strength shock wave necessary for ignition was determined. The enthalpy increase in the wake of the shock wave within a cylinder of diameter equal to the quenching distance and of unit height was calculated and found to be comparable with the minimum spark ignition energy divided by the quenching distance. An analysis of the unsteady heat conduction problem lends support to the choice of the quenching distance as the significant dimension of the region over which heat addition is effective in causing ignition.

ISSN:0021-8979    

DOI:10.1063/1.1722354

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The problem of two‐dimensional steady‐state laminar flow in channels with porous walls has been extended to the case of moderate to high suction or injection velocity at the walls. An exact solution of the Navier‐Stokes equations, reduced to a third‐order nonlinear differential equation with appropriate boundary conditions, is obtained. The velocity components, the pressure, and the coefficient of wall friction are expressed as functions of velocity through the porous walls, the average axial velocity of Poiseuille's flow, the coordinates and dimensions of the channel, and the physical properties of the fluid.

ISSN:0021-8979    

DOI:10.1063/1.1722355

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Extensive wave shape data are presented for various (effectively) unconfined explosives over wide ranges of diameterd, lengthL, density &rgr;1, and physical conditions. Observed wave fronts were invariably spherical segments with radii of curvatureRincreasing at first directly withL(R=L), but eventually becoming steady at a constant valueRm/dbetween 0.5 and 4 depending on the charge diameter primarily through the ratioa0/d(a0=reaction zone length). At the critical diameter of propagation (largea0/d)Rm/dapproached 0.5, and at large diameter (smalla0/d) it approached or leveled off at the upper limit of about four. The upper limit (Rm/d∼4) is apparently a restriction imposed by the fundamental nature of detonation of solid explosives with free boundaries.

ISSN:0021-8979    

DOI:10.1063/1.1722356

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Photoconductive (PC) and photoelectromagnetic (PEM) effects have been observed inp‐type InSb single crystals of high purity at 77°K (extrinsic range) and 301°K (intrinsic range). Because of the large electron mobilities in InSb, and because the variation of the PEM response with magnetic field was found to be strongly dependent on surface treatment, it was necessary to develop a new theoretical model to describe the PEM effect, permitting the evaluation of bulk lifetime and both electron and hole mobilities. In addition, the model affords an interpretation of Hall and magnetoresistance effects in intrinsic InSb. When the PEM effect is analyzed using impurity or thermal scattering, assuming Boltzmann statistics, the result does not fit the data so well as the simple model presented here.

ISSN:0021-8979    

DOI:10.1063/1.1722357

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Measurements have been made on a system composed of two parallel planar cathodes so arranged that their surfaces may be pressed together or separated by a small gap. Low‐field conductivity measurements show that above approximately 700°K, the conductance of the system does not depend on physical contact between the cathode surfaces. This result supports the theory that the high‐temperature conductivity is a property of the electron gas in the cathode pores. The ratio of conductivity to thermionic emission was measured under conditions designed to preserve the state of activation of the cathode surface. The results agreed with the theoretically predicted ratio and demonstrate that the higher values previously reported were caused by a lower activation on the surface than in the interior of the cathode.

ISSN:0021-8979    

DOI:10.1063/1.1722358

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Propagation of compressive waves generated by high explosive in Armco iron may, under certain conditions, occur with three stable shocks, which are characterized by abrupt and possibly quasi‐discontinuous change of pressure. The characteristics of these have been investigated experimentally and found to be consistent with the hypothesis of a polymorphic transition in iron at about 0.13 megabar. The same phenomenon has been observed in mild steel.

ISSN:0021-8979    

DOI:10.1063/1.1722359

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Experiments on surface breakdown at reverse‐biased germaniumn+palloyed junctions are described, and the results related to a new model for surface breakdown that takes explicit account of semiconductor surface charge and fringing field. The experiments show (i) that surface breakdown, like body breakdown, is an avalanche process; (ii) that multiplication sets in first at a particular spot. The experiments serve also to confirm conclusions already reached from device experience: (i) that high breakdown voltage is promoted by that sign of surface charge which tends towards the formation of a ``channel'' over the material of the higher resistivity side, and low breakdown voltage by the opposite sign of surface charge; (ii) that the breakdown voltage is increased by surrounding the material by a medium of high dielectric constant. The theory accounts for all these observations and leads, when the calculations are carried out for an equivalent one‐dimensional structure, to a quantitative prediction of the relation between breakdown voltage, surface charge, resistivity, and the dielectric constant of the surrounding medium. The evidence for the validity of this relation is discussed briefly.

ISSN:0021-8979    

DOI:10.1063/1.1722360

出版商:AIP    

年代:1956

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722363

出版商:AIP    

年代:1956

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1722364

出版商:AIP    

年代:1956

数据来源: AIP