摘要:

Beams consisting of charged particles which are all directed towards a given virtual focus will generally not reach this focus but, due to their mutual repulsion, they will pass through a waist and then become divergent. Ray tracing shows that either positive or negative spherical aberration is introduced in a beam passing through a waist. This aberration is caused by the interaction of the electrons; its sign depends on voltage, current, and on the angle of initial convergence of the beam. For sufficiently high voltages or low currents, waist formation no longer occurs, but the electron rays cross the axis of the beam. With decreasing current density, the transition from waist to crossover is found to occur first for the inner rays of the beam while the outer rays still form a waist. All experimental results are found to be in approximate agreement with theoretical predictions.

ISSN:0021-8979    

DOI:10.1063/1.1721932

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Equation of state data for Duralumin in the pressure range from 0.1 to 0.3 megabar have been determined dynamically by measuring shock and free surface velocity electrically in a plate of 24 ST Duralumin that has been stressed by a high explosive detonation. A theory is presented which allows comparison with data obtained by other experimenters, and which yields the relationship between pressure and compression either at constant entropy or constant temperature. The empirical form chosen for the equation of state (p=&agr;&mgr;+&bgr;&mgr;2) expresses the pressure as a quadratic function of the compression. Experimental techniques are described in detail. Five points are given for the equation of state of Duralumin in the pressure range from approximately 0.15 megabar to 0.33 megabars. Some data are also presented for cadmium and steel.

ISSN:0021-8979    

DOI:10.1063/1.1721933

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The properties of the dynamic hysteresis loop of ac‐domain BaTiO3single crystal are examined as a function of temperature. Experimental results indicate that the coercivity and hysteresis losses decrease sharply as the crystal passes through a phase transition to a lower order of symmetry. This occurs without a substantial loss in loop rectangularity. The properties of a theoretical model for the hysteresis loop are derived from the Devonshire thermodynamic equations and previously defined experimental parameters. In the tetragonal and orthorhombic crystal phases, good agreement is obtained between the behavior predicted for the theoretical model and the experimental observations made on ac‐domain.

ISSN:0021-8979    

DOI:10.1063/1.1721934

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The heat transferred by radiation was measured between surfaces at room temperature and liquid‐nitrogen temperature. The surfaces used were various combinations of electroplated gold and silver and polished copper sheet. From the test data, the approximate total emissivities of the room‐temperature surfaces and the total absorptivities of the liquid‐nitrogen surfaces were computed.The results of these tests indicated that electroplated silver surfaces have lower emissivities and absorptivities than equivalently treated electroplated gold surfaces in this temperature range. The best surface tested was a special, bright, unbuffed silver‐plated surface. This surface is known to the trade as ``silver lume.'' The room‐temperature emissivity of this surface was approximately 0.017, and the absorptivity at 77.3°K for radiation from a 300°K surface was about 0.0083. These are the lowest values at these temperatures of which we have knowledge.It was found that the electroplated surfaces were best used without buffing or any mechanical working of the surface. It is believed that cold working of the metal surface increases its emissivity and absorptivity by increasing its electrical resistivity.

ISSN:0021-8979    

DOI:10.1063/1.1721935

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Titanium metal has been studied as a getter for oxygen, nitrogen, carbon dioxide, air, water vapor, hydrogen, and methane. Titanium above 700°C will getter oxygen, nitrogen, and carbon dioxide. Hydrogen is absorbed by titanium in the temperature range of 25 to 400°C. Water vapor and methane are readily sorbed when the metal is operated at both elevated and reduced temperatures. Large quantities of gases can be sorbed; sorption of ten to ninety atomic percent is possible. When saturated with gas, the metal becomes brittle and is easily fractured. Hydrogen gas is the only gas which can be released by heating after it has been sorbed by titanium.

ISSN:0021-8979    

DOI:10.1063/1.1721936

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Two types of tests were performed on the uniaxial compression of snow; experiments at constant strain rate and at constant load. The strain rate can be represented as the product of functions of density, stress, temperature, and time. For densities between &ggr;≃0.3 g/cc and &ggr;≃0.6 g/cc the strain rate is proportional to (&ggr;ice−&ggr;)/&ggr; to the fourth power. The strain rate varies linearly with stress for low stresses (2<&sgr;<100 g/cm2) but increases to an approximately cubic relationship at higher stresses (1<&sgr;<5 kg/cm2). An activation energy of about 14 000 cal/mole can be derived from the temperature dependence. In the constant load tests the strain is proportional to the time to a power of about 0.8. The effect of snow type is small, being less than the relatively large experimental scatter encountered.

ISSN:0021-8979    

DOI:10.1063/1.1721937

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Two methods of determining the variation of real and complex modulus with frequency from vibrating reed test results are detailed. One is based on measurements of the relative amplitude and phase lag of the motion of the free and driven ends of the reed, the other on amplitude resonance measurements only. The analysis is based on a general linear viscoelastic law, and takes into account the influence of the frequency dependent moduli of the material on the frequency and amplitude of the resonance peaks. This influence has not been correctly accounted for in previous analyses which have included the assumption that the material behaves according to a particular, simple viscoelastic law, which will in general not be borne out by the final results.The method is applied to a series of tests. For the material and frequency range used the imaginary part of the complex modulus was small compared with the real part, and the influence mentioned in the foregoing was small. A simpler method of analysis might thus be justified, but in other cases it will be necessary to carry out the complete analysis in order to obtain a satisfactory interpretation of test results.

ISSN:0021-8979    

DOI:10.1063/1.1721938

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

A method is given for calculating, within the framework of the moment‐method of Spencer and Fano, the angular distribution of radiation from a plane isotropic source. Essential use is made of the simplification introduced by a geometrical feature of radiation from such a source. Sample calculations are presented for a 1‐Mev source in water.

ISSN:0021-8979    

DOI:10.1063/1.1721939

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

The general expressions for the x‐ray absorption corrections in the reflection region for flat sheets in any orientation are derived. These equations contain, as special cases, the correction factors of previously reported pole figure techniques and also correction factors for a new method, permitting a rapid and accurate determination of complete quantitative pole figures of flat sheets using one sample and one sample holder. For the outer regions of the polar net a low‐order Bragg reflection is used with the technique of Decker, Asp, and Harker; and for the center region a higher order Bragg reflection from the same set of planes is used with a different set of correction factors. Pole figures, obtained by this method, for cold rolled aluminum and magnesium are presented.

ISSN:0021-8979    

DOI:10.1063/1.1721940

出版商:AIP    

年代:1955

数据来源: AIP

摘要:

Donor densities in the base material of fused junction diodes, inferred from capacitance data, are used to calculate majority carrier mobilities. The dependence of capacitance on reverse bias at very low biases is found to be given by the sum of two terms, a space charge capacitance and a capacitance due to the flow of holes as given by Shockley's low levelp‐njunction theory.

ISSN:0021-8979    

DOI:10.1063/1.1721941

出版商:AIP    

年代:1955

数据来源: AIP