摘要:

Experiments on the neutrons produced in deuterium gas during a high‐current pulsed discharge are described. With 15 kv applied to a straight discharge tube 30 cm long, neutrons are produced during a 0.1 &mgr;sec pulse ∼1.4 &mgr;sec after gas breakdown. The yield of 107to 108neutrons per discharge depends on gas purity and the discharge tube wall material. The axial asymmetry in neutron energy indicates that the neutrons are produced in reactions whose center of mass moves preferentially towards the cathode.

ISSN:0021-8979    

DOI:10.1063/1.1723390

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Wire probe contacts are found to be diodic upon first touching CdS, but can be permanently changed from diodic to ohmic by the passage of a moderately intense electric current pulse. This result obtained for ten metals, which work‐function‐wise bracket CdS, supports the idea that an exhaustion barrier exists on the surface and contradicts proposals that ohmic contact is solely dependent upon the relative metal and CdS work functions. It is postulated that the current pulse punctures the exhaustion barrier, thereby permitting electrons to tunnel more freely and in greater numbers.

ISSN:0021-8979    

DOI:10.1063/1.1723391

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Cinematographic observations have been made of crack propagation under well‐defined boundary conditions in rubbers at speeds up to 30 m/sec. The fracture‐markings showed resemblances to those obtained with metals, plastics, and glass, and could be related directly to the corresponding speed of fracture‐propagation. In close analogy with Schardin's observations on glass, a noncrystallizing rubber (GR‐S) showed a mode of crack propagation in which the fractured surfaces were visually smooth and the speed was about one quarter of the speed of longitudinal elastic waves. A crystallizing rubber (natural rubber) did not show this mode of propagation under the present test conditions. It is suggested that the modes of solid fracture can be usefully classified in three categories: (i) slow propagation, generally with smooth surfaces, obtained by careful control of the boundary conditions; (ii) propagation at intermediate rates with rough surfaces, involving correspondingly greater energy consumption; and (iii) fast propagation with smooth surfaces, the rate of propagation being limited by the speed of elastic waves in the material in accord with Mott's theory.

ISSN:0021-8979    

DOI:10.1063/1.1723392

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The ion‐bombardment cleaning method has been successfully applied to the (100) faces of germanium, silicon, and nickel, and to the (0001) face of titanium. Conditions and precautions necessary for the production of clean surfaces are described. Tests have been made for contamination from the ambient during the cleaning procedure for germanium. It has been shown that contamination approximating one‐half monolayer does not occur under the conditions which were obtained, and that the method is capable of producing surfaces which are atomically clean.Results for clean (100), (111), and (110) germanium faces and the (100) silicon face indicate that the atomic positions in the surface planes are not the same as the corresponding positions in the bulk structure. For (100) nickel and (0001) titanium, the positions of the atoms in the surface planes are in agreement with x‐ray data. In the case of titanium, an unidentified surface structure was present until after several cycles of alternate heating and ion bombardment. In the case of nickel, a double‐spaced surface monolayer and in some cases a single‐spaced, simple‐square structure, attributed to carbon, was present until after several cycles of alternate heating and ion bombardment.

ISSN:0021-8979    

DOI:10.1063/1.1723393

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The adsorption of oxygen, carbon monoxide, and nitrogen on a tungsten ribbon filament at 300°K has been measured by means of the flash filament technique. An omegatron rf mass spectrometer has been used to measure pressure. It is shown that oxygen pressures cannot be measured satisfactorily with ionization gauges of the hot‐tungsten‐filament type. The total amounts of gases adsorbed by tungsten are 5.7×1014molecules/cm2for oxygen, 5.8×1014for carbon monoxide, and 1.8×1014for nitrogen. The sticking probabilities of these gases on the uncovered surface are 0.65 for oxygen, 0.62 for carbon monoxide, and 0.42 for nitrogen. All of the carbon monoxide and nitrogen desorb from the heated filament as the gases CO and N2; less than 1 percent of the oxygen desorbs as O2. The filament pumps oxygen at a rate of 9 liters/cm2sec at temperatures above 2000°K.

ISSN:0021-8979    

DOI:10.1063/1.1723394

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A distribution of surface asperities is proposed for the case in which both mating surfaces are rough and asperities are in the form of right circular cones. The assumption of this particular asperity form is suggested by roughness measurements of ground steel, brass, and aluminum which yielded similar results for stylus traversing parallel, 45°, and perpendicular to lay. Considering the mating cones perfectly plastic and distributed in the proposed manner, bulk deformation‐load is related to compliance.The essential finding is that the load‐compliance characteristics for mating surfaces having comparable roughness have slopes much steeper than those predictable by previous theories, all of which involve the assumption that one of the surfaces is smooth and rigid. A simple experiment is described in which load and compliance are measured. Results seem to support the plausibility of the proposed theory. Moreover, this plausibility shows promise of the calculation of other bulk‐quantities such as frictional resistance.

ISSN:0021-8979    

DOI:10.1063/1.1723395

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Two simple formulas are given which enable the total mass absorption coefficient of air to be readily calculated. These formulas, which are derived from published theoretical values of the total coefficient, are applicable to the energy ranges 0.01 to 100 Mev and 0.05 to 10 Mev, and yield results which agree with the theoretical values to within about 5% and 1%, respectively. Comparison is made with values calculated from existing empirical formulas which cover energies up to about 1 Mev.

ISSN:0021-8979    

DOI:10.1063/1.1723396

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

If the surface area of a liquid is large compared to its volume, the normal freezing temperature of the liquid will be altered. In a porous material a liquid can therefore exist in equilibrium, below its normal freezing temperature. However, such a liquid will be unstable with respect to bulk solid. This instability provides the driving force for frost heave in soils.

ISSN:0021-8979    

DOI:10.1063/1.1723397

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Some of the more interesting effects of nonuniform electric fields are described in this report. Experimental and theoretical studies show the effects to be rather striking for particles larger than molecular size. The results show that the effect can be used to produce a fairly efficient pumping action of nonconducting liquids, to cause continuous and easily measureable separations in coarse suspensions, to cause selective precipitation, and to produce mixing.By this means, liquids may be thrown several feet into the air with an electromechanical efficiency of about 25%. A separation factor of at least 2.5 in continuous separatory operation may be produced in a suspension of polyvinyl chloride in carbon tetrachloride‐benzene mixture. Suspensions of polar materials in less polar liquids may be either dispersed or precipitated. In one interesting ``demonstration'' type experiment, drops were ``hung'' in mid‐air.

ISSN:0021-8979    

DOI:10.1063/1.1723398

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

This paper discusses the effect of pressure‐diffusion flux upon the concentration distribution of gas mixtures in flow fields. The equation of concentration is formulated for a binary gas mixture in which the mass ratio is large and the concentration of the lighter gas is very small. An asymptotic solution to the steady‐state equation of concentration is given for an irrotational and incompressible flow.As an illustration, the diffusive separation (i.e., deviation from the original homogeneous state) of a mixture of helium and nitrogen along streamlines at the entrance to a long straight channel is calculated. It is assumed that the pressure inside the channel is 90% of that in the free stream, and that the diffusion coefficient of the mixture corresponds with the atmospheric conditions at 80‐km altitude.

ISSN:0021-8979    

DOI:10.1063/1.1723399

出版商:AIP    

年代:1958

数据来源: AIP