摘要:

A theory formulated in 1916 by Horace Lamb predicting that plates may vibrate in up to an infinite number of modes is confirmed by a method described. The theory is extended to correlate experimental observations. Equations are developed relating phase velocity to frequency and plate thickness in terms of longitudinal and shear wave velocity. Families of curves are obtained for aluminum and zirconium. The distinguishing characteristics of the various modes are discussed in the light of potential nondestructive testing applications. It is shown that the interior particles are displaced in elliptical orbits, with vertical motions existing at the surfaces when the wave velocity is (2)½shear wave velocity, and horizontal surface motions existing for wave velocities equal to longitudinal wave velocity.

ISSN:0021-8979    

DOI:10.1063/1.1736196

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Measurements of the real (&egr;′) and imaginary (&egr;″) parts of the dielectric constant have been made on polyvinyl stearate at temperatures from −50° to +80°C and over a frequency range from 100 to 50 000 cps. Although no full relaxation dispersion region has been found in this frequency range, there are indications of the beginnings of a high‐frequency dispersion region just above the freezing point (49.1°C) in the liquid polymer. This dispersion cuts off or is ``frozen in'' rapidly as the sample freezes, giving evidence of a slight rotational freedom in the solid polymer near the freezing and melting points. Because of this ``freezing in'' of the dispersion mechanism it is supposed that the dipolar side chain is unable to rotate in the solid form because of the combined effects of the side‐chain crystalline field and angle which the C&sngbnd;O bond (between the main chain and side chain of the polymer) makes with the side‐chain axis. Specific volume measurements were made to supplement the above work. The measurements show that a quickly frozen sample will melt at a lower temperature (52.5°C) than a slowly frozen sample (55.0°C). Also, discontinuities in the slope of the specific volume vs temperature curve are related to changes in the imaginary part of the dielectric constant and to changes in mechanical dispersion data. The above results are compared with those for other polymers.

ISSN:0021-8979    

DOI:10.1063/1.1736197

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Experiments on the flow of gases through porous Pyrex disks at pressures in the range of a few mm Hg are described. For air, hydrogen, and carbon dioxide the specific flow is found to be given byQ=A(MT)12+B&eegr;Tp¯+CM12{1−exp[&agr;0−&bgr;T12]p¯}The significance of this result is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1736198

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

A statistical theory is presented to explain microplasma instability at the onset of avalanche in reversebiased silicon linearly graded and step junctions. An expression is derived which relates the turnoff probability of the microplasma to the differential resistance of the diode in its conducting state and to other physically measurable diode parameters. Measurements of the turnoff probability as a function of the pulse current are presented for several diodes and are shown to agree well with the derived theory. To explain the turnon probability, three expressions, each involving slightly different approximations, are derived for the probability that a carrier entering the breakdown region will initiate an avalanche. In each case, this probability is found to be proportional to the excess of the applied voltage over a uniquely definable sustaining voltageVs, in poor agreement with experiment. The various mechanisms which determine the diode's differential impedance in the conducting state are discussed and approximate expressions for the contributions of each mechanism to the differential impedance are derived. Multilevel pulses, previously interpreted as indicating more than one conducting state for a microplasma, are explained in terms of parallel breakdowns of more than one microplasma.

ISSN:0021-8979    

DOI:10.1063/1.1736199

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Single‐crystal TiC exhibits a positive temperature coefficient of resistivity with a resistivity in the [100] direction of 200±20 &mgr;ohm cm. The thermoelectric power &Dgr;V/&Dgr;Treferenced against copper at room temperature is 7.8±0.6 &mgr;v/°C and indicatesn‐type conduction. No hydrostatic piezoresistivity was observed. The predominant cleavage plane for single‐crystal TiC is {100}. It can be concluded fromPvsTand thermoelectric data that single‐crystal TiC has metallic‐type conduction, and the predominant charge carriers are electrons.

ISSN:0021-8979    

DOI:10.1063/1.1736200

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The imaginary part of the x‐ray scattering factor for germanium is calculated from dispersion theory and individual Hartree‐Fock electron scattering factors and is compared with Hunter's experimental values measured with anomalously transmitted x rays. The agreement is quite good and verifies the treatment of anomalous transmission by the dynamical theory of diffraction. It is shown that the imaginary part of the scattering factor can be related directly to the form factor of theLelectrons in germanium and it is concluded that their charge distribution in the solid is essentially the same as in the free atom.

ISSN:0021-8979    

DOI:10.1063/1.1736201

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

The characteristic equation determining the eigenfrequencies of the magnetostatic modes is derived from the equations of motion and the boundary conditions. The solutions may be classified as pertaining to surface and to volume modes. Surface‐mode solutions exist only for sufficiently small wave numbers, and their eigenfrequencies are larger than those of volume modes. The eigenfrequencies generally decrease with increasing wave number. Approximate, analytic expressions for the dependence of the eigenfrequencies on wave number have been obtained for the regions in which the wavelength is either much smaller or much larger than the cylinder radius. The approximate expressions are compared with numerical results obtained by means of an electronic computer.

ISSN:0021-8979    

DOI:10.1063/1.1736149

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Two methods of calculating the instability threshold are described. The first is a plane‐wave analysis which is strictly applicable only in an infinite medium. The second is a more rigorous theory in which the boundary conditions at the surface of the sample are taken into account. The refined theory admits instabilities at frequencies different from half the pump frequency, which are forbidden according to the less rigorous plane‐wave analysis. The general theory is applied to the magnetostatic modes of a long, circular cylinder, which is magnetized along its axis. It is concluded that: (a) Instability at half the pump frequency can occur only for those cases in which the magnetostatic potential is invariant under rotation around the cylinder axis (m=0). The instability threshold for these modes is identical to that deduced on the basis of the plane‐wave analysis, except that the frequencies now have to satisfy the characteristic equation derived from the boundary conditions. (b) Instabilities at frequencies different from half the pump frequency can occur, but generally have a higher threshold. (c) Pairs of surface modes (with frequencies higher than the highest plane‐wave frequency) are not subject to instability. (d) Instabilities involving a surface mode and a volume mode are not strictly forbidden. It is very likely, however, that such instabilities will be masked by the instability of spin waves of shorter wavelength.

ISSN:0021-8979    

DOI:10.1063/1.1736150

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Data are presented which show how the adsorption of carbon monoxide and oxygen on atomically clean germanium affect the process of Auger neutralization of He+and Ne+at the surface. Measurements of both total yield and kinetic‐energy distribution of ejected Auger electrons have been made. The effect of ion bombardment alone without subsequent anneal, including the presence of absorbed noble gas in the surface layers of the crystal, has been investigated. Photomicrographs of the germanium target surface are reproduced.

ISSN:0021-8979    

DOI:10.1063/1.1736151

出版商:AIP    

年代:1961

数据来源: AIP

摘要:

Data are presented which yield relative magnitudes of the initial, room‐temperature sticking probabilitiesS0of nitrogen on clean tungsten and oxygen on clean silicon and germanium. TakingS0to be 0.35 for N2on W, we obtain 1×10−2and 8×10−4forS0of O2on Si and Ge, respectively. Data are also given concerning the temperatures at which the atomically clean surface is thermally regenerated from the oxygenated surface for both Si and Ge.

ISSN:0021-8979    

DOI:10.1063/1.1736152

出版商:AIP    

年代:1961

数据来源: AIP