摘要:

Absorption curves for neutrons and &ggr;‐radiation produced by 16‐Mev protons on beryllium are measured in absorber blocks of various concrete mixtures to obtain information on their shielding properties. It is shown that a mixture of cement, scrap iron, and limonite ore is as efficient as water in slowing down and capturing neutrons and, in addition, has sufficient density (&rgr;=3.5 g/cm3) to be an effective absorber for &ggr;‐radiation. Compared to ordinary concrete, a three‐foot wall of iron and limonite concrete is superior by a factor of 280 for neutrons and by a factor of 20 for &ggr;‐radiation. Boron is shown to be of little value in this type of shielding. Mechanical properties of the scrap iron‐limonite concrete are satisfactory for structural purposes. From the practical cost standpoint, a concrete made entirely of limonite ore is shown to be a reasonable compromise.

ISSN:0021-8979    

DOI:10.1063/1.1699669

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

The tensile strength and Young's modulus of Johns‐Manville experimental drawn glass fibers were measured by a bending method which consists of twisting a loop in a fiber and pulling the ends until the loop breaks. The tensile strength observed by this method was two to three times higher than observed by the conventional straight fiber method, while Young's modulus was practically unchanged. These results may be accounted for by the presence of flaws, since the probability is small that the weakest flaw will occur in the loop, while the straight fiber will always break at the weakest flaw. The apparatus used, a modified Chainomatic balance, is described and the equation of the looped fiber is derived. The method is used to measure the maximum tensile stress and strain attained at the point of minimum radius of curvature of the loop as well as the breaking tensile stress and strain at the actual break point of the fiber. The stress at the break point was found to be as small as one‐half the maximum attained in the loop, showing that the strength of the fiber was not uniform.

ISSN:0021-8979    

DOI:10.1063/1.1699670

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A method is described and equations are presented which permit the calculation of the magnetic field characteristics of large cross‐section air core coils. The method is applied to the determination of the field non‐uniformities on the median plane to be expected with annular cloud‐chamber coils of rectangular cross section. The field non‐uniformity results are provided in graph form to facilitate the design of cloud‐chamber coils.

ISSN:0021-8979    

DOI:10.1063/1.1699671

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

A series of cylinders of annealed, extruded, pure magnesium and medium soft steel were subjected to a sequence of compressive stresses at room temperature and their respective coefficients of linear thermal expansion in the direction of stress application were determined for the range 20° to 100°C. The cylinders were then heat treated to permit either recovery or recrystallization and the changes in length were measured. Characteristic curves are given for each metal in which the coefficient of linear thermal expansion and length changes are plotted as a function of the true compressive stress. It is shown that these properties may be used to determine the stress history of a test specimen for which characteristic curves are available. It is suggested that this stress analysis technique may find application in the study of rock deformation and in the investigation of metals, both before and after failure.

ISSN:0021-8979    

DOI:10.1063/1.1699672

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Spenke's discussion of thermal noise from the point of view of the electron theory leads to a result which differs from Nyquist's original formula at frequencies &ngr; such thath&ngr;/kT≧1. This discrepancy is due to the assumptions which Spenke made in his analysis.

ISSN:0021-8979    

DOI:10.1063/1.1699673

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Semiconductive particles in a colloidal suspension, when subjected to an electric polarizing field, form semiconductive chains. Once the suspension is polarized, its conductivity increases with increasing fields because the forces of electrostatic attraction press the individual particles together, thus strengthening the transition contacts along the chains. Both effects result in an over‐all electric non‐linearity that is the subject of extensive investigation.The non‐linear characteristics of such colloidal resistors are oscillographed and described in relation to the polarizing field strength by means of simple formulas based on field coefficients of the first and second order.In addition to a true rectification, resulting from the curved characteristics, a ``pseudo‐rectification'' occurs which corresponds to an average pre‐polarization by stronger alternating fields. The alternating forces of electrostatic attraction assure a high frequency response, so that non‐linear Lissajous‐figures and harmonics, up to radiofrequencies, are produced.

ISSN:0021-8979    

DOI:10.1063/1.1699674

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

In connection with the study of the internal friction peak (versustemperature) associated with the viscous behavior of grain boundaries in metals, some other effects were observed at higher temperatures causing an additional internal friction in superposition with the high temperature branch of this internal friction peak. This additional internal friction at high temperatures was found to have its origins in some effects of cold‐working introduced in the interior of the grains which remains even after the complete recrystallization of the cold‐worked specimens. It increases with the amount of cold‐work the specimen was subjected to before and after recrystallization; it decreases with annealing at successively higher temperatures until a stable value is reached; and it increases with the precipitated impurity content in the specimen. This high temperature internal friction was found to be very high in an aged specimen of high purity aluminum alloyed with 4 percent of copper. These observations are consistent with the viewpoint that this internal friction is caused by the presence of dislocations in the interior of the specimen although the mechanism of giving rise to the internal friction is unknown. It is pointed out that a study of high temperature creep under very low stress may be conveniently carried out through the internal friction measurements described.

ISSN:0021-8979    

DOI:10.1063/1.1699675

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

Very small recrystallized grains of a large variety of orientations were produced locally in lightly rolled high purity aluminum crystals. The rate of growth of these small grains varied greatly, depending on their relative orientation with respect to the matrix crystal. Grains with an orientation corresponding to a [111] rotation of about 40° showed by far the highest rate of growth. These results indicate that recrystallization textures developing in the spontaneous recrystallization of deformed single crystals can be accounted for by the orientation dependence of the rate of growth.

ISSN:0021-8979    

DOI:10.1063/1.1699676

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

An earth heat pump was set in operation to abstract heat from soil assumed to be in thermal equilibrium. Temperature‐time graphs of the antifreeze and of the soil at distances of six, twelve, and eighteen inches below the center of the antifreeze line were plotted from experimental data. From these graphs data are obtained from which the thermal diffusivity of the soil is calculated. The soil was analyzed and found to fall in the general Casagrande classification of lean clay (CL) with low plasticity.

ISSN:0021-8979    

DOI:10.1063/1.1699677

出版商:AIP    

年代:1950

数据来源: AIP

摘要:

TheE‐plane radiation patterns of two horn radiators have been measured in the laboratory with a metal lens by the same method that is used in optical diffraction pattern measurements. Comparison of patterns measured outdoors, by standard methods, with the lens measurements shows little deterioration in precision over the angular interval between ±15 degrees, for horns of aperture width 32 cm, measured by a lens of aperture 110 cm, at a wave‐length of 3.2 cm. It was found that a stepped lens was unsatisfactory for this purpose, possibly because of diffraction caused by the steps.

ISSN:0021-8979    

DOI:10.1063/1.1699678

出版商:AIP    

年代:1950

数据来源: AIP