摘要:

The thermodynamic theory of irreversible processes as developed by Onsager, de Groot, and Callen is used to derive in a straightforward way the partial differential equation for the stationary temperature distribution in an electrically heated, chemically inhomogeneous conductor. It is shown that the form of this differential equation given in 1900 by Diesselhorst (for homogeneous media) in terms of the electrical potential gradient∇·&kgr;∇T+&sgr;&tgr;∇T·∇&phgr;+&sgr;(∇&phgr;)2=0, is incorrect. Diesselhorst's equation reads∇&phgr;in which &kgr; is the thermal conductivity (for zero electrical current),Tthe temperature, &sgr; the isothermal electrical conductivity, and &tgr; the Thomson coefficient. The correct form of the equation, for the special case of a chemically homogeneous conductor, is∇·&kgr;∇T+(1/&sgr;)J2−&tgr;J·∇T=0, whereJis the electrical current density. The correct form can be obtained from Diesselhorst's equation by substitution of the ``isothermal Ohm's law''J=−&sgr;∇&phgr;, which, however, is not valid in a nonisothermal medium. The apparent difficulty is resolved by the method of Onsager‐de Groot‐Callen, and it is shown that the correct differential equation expressed in terms of electrical potential is much more complicated than the form given by Diesselhorst.

ISSN:0021-8979    

DOI:10.1063/1.1721551

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A sensitive instrument for the measurement of the viscoelastic properties of dilute polymer solutions is described. It makes use of torsion pendulums with resonant frequencies in the range between 200 cps and 2300 cps. The test liquid is contained in a hollow oscillating disk. The shearing stress which is exerted at the liquid‐metal interface alters the frequency and rate of decay of the free oscillations of the pendulum. By means of an optical system, the oscillations of the pendulum are caused to modulate the light striking the cathode of a phototube. The frequency and the rate of decay of the resulting alternating voltage are measured electronically.The operation of the instrument and the factors affecting the precision of measurement are analyzed.

ISSN:0021-8979    

DOI:10.1063/1.1721552

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

This paper gives the solution to the torsion problem for a near‐cylindrical shaft of circular section having a toroidal cavity. Since the interpretation of the axially symmetric problem as a flow problem in 5 dimensions is well known, the first part of the paper is devoted to developing a method for handling the flow problem about anndimensional ring‐shaped body of general cross section. In the second part of the paper this method is applied to the case of anndimensional torus ring. The casen=3 then yields the solution to the classical flow problem, andn=5 gives the solution to the torsion problem under consideration.

ISSN:0021-8979    

DOI:10.1063/1.1721553

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Equations governing the coupled thickness‐shear and flexural vibrations of isotropic, elastic plates are solved for the case of a circular disk with free edges. The results of computations are given for the resonant frequencies analogous to those which would be excited in an AT‐cut quartz disk with full electrode coating. A marked difference is observed between the frequency spectrum of the disk and the spectrum of cylindrical vibrations of a rectangular plate. The difference is due to the presence of thickness‐twist modes of motion, in the disk, which, along with the thickness‐shear modes, are coupled to the flexural modes.

ISSN:0021-8979    

DOI:10.1063/1.1721554

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The use of low‐energy (10–250 ev) electron diffraction as a method of studying the chemisorption of gases on metal single crystals is described. The apparatus permits controlling the temperature of the crystal in the range from liquid nitrogen to room temperatures during observation. Outgassing the crystal is effected by strong heating using electron bombardment. The residual gas structures on the (100) faces of copper and nickel single crystals are determined to be: (1) a monolayer with a single‐spaced square array, found on both copper and nickel after heating at temperatures slightly below the minimum temperature for observable evaporation; and (2) a double‐spaced, face‐centered square array, found after heating at or above this temperature. Nitrogen adsorbs on the (100) face of a copper single crystal at 25°C and −78°C into an incomplete single‐spaced square array. Most of the adsorption at 25°C occurs in a pressure range of 10−4to 10−1mm Hg in a ten‐minute interval, with little change occurring between 10−1and 8 mm Hg. At −78°C, the corresponding pressure range is 10−4to 10−3mm Hg with little adsorption occurring between 10−3and 1 mm. At room temperature, oxygen adsorbs into a complete, single‐spaced, square array at a pressure of 2×10−3mm Hg in a ten‐minute interval. At higher pressures, additional oxygen adsorbs into a thicker layer of no regular structure.

ISSN:0021-8979    

DOI:10.1063/1.1721555

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

It is shown that a large amount of flicker noise is generated in tubes that have developed a high‐resistance interface layer between the cathode‐nickel and the oxide coating. The equivalent noise resistanceRnof this effect can be represented by the equationRn=KIp2Ri2/f&agr;, whereKis a constant,Ipthe plate current,Rithe interface resistance, andfthe frequency whereas &agr; varies between 1.1 (for lowRi) and 1.5 (for highRi). All evidence suggests that the noise is generated in the interface layer; this was subsequently proved by a direct experiment. The current dependence suggests that the noise is caused by spontaneous fluctuations in the resistanceRi. Experiments up to 1.5 mc indicate a change in the exponent &agr; from 1.1 to 1.6 at high frequencies, indicating that the interface impedance cannot be represented by a fixed resistanceRiand a fixed capacitanceCiin parallel.

ISSN:0021-8979    

DOI:10.1063/1.1721556

出版商:AIP    

年代:1954

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721558

出版商:AIP    

年代:1954

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721559

出版商:AIP    

年代:1954

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721560

出版商:AIP    

年代:1954

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721561

出版商:AIP    

年代:1954

数据来源: AIP