摘要:

The effects of structural and chemical defects on the low‐temperature (30–50°K) annealing peak in low‐temperature reactor‐irradiated aluminum and copper were studied. From the fact that the density of reactor‐induced defects did not affect the annealing kinetics, it was possible to conclude that the low‐temperature annealing process was of the first order without a unique activation energy. The fact fact that both oversized and undersized atoms could suppress this annealing peak led to the conclusion that the radiation‐induced defects were more complicated than simple point defects. The suggestion is made that a defect similar to a crowdion must be created by low‐temperature neutron irradiation. This data also supports to some degree the viewpoint that a radiation‐induced defect, possibly a crowdion, has sufficient knock‐on energy to migrate several hundred atomic distances. The experiments also contain evidence which rule out all forms of vacancy‐interstitial annihilation.

ISSN:0021-8979    

DOI:10.1063/1.1722822

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Experimental measurements on the transverse velocity distribution in cylindrically symmetric electron beams emergent from magnetically shielded cathodes are reported. For strong magnetic fields the transverse velocity distribution at the beam center has been found to be composed of discrete classes. These results are explained on the basis of a beam model with nonlaminar flow in which thermal velocities and space charge are neglected. The mechanism depends on the periodic passage of electrons through or very near the beam axis and the fact that the wavelength of this periodicity is a decreasing function of the distance between the point of entry into the magnetic field and the axis.When the space charge and magnetic forces are comparable, no discrete transverse velocity distribution was observed. It is shown, however, that the beam should still be in the same type of nonlaminar flow as above.

ISSN:0021-8979    

DOI:10.1063/1.1722823

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Single crystals of copper were deformed at 4.2°K and 77.3°K. At 4.2°K, after a large strain produced by normal slip, jerky flow (discontinuous slip) occurs. From the study of reactor irradiated crystals, it was deduced that a packet of 30 slip lines, each containing 104dislocations, was released to form each jerk of the discontinuous flow. For samples of certain orientation the region of discontinuous flow was followed by a region of deformation twinning. The fact that deformation twinning was taking place was verified by x‐ray methods. The twinning elements were determined to be the (111) plane and the [112] direction. At 77.3°K, discontinuous slip was not observed. In a limited range of orientations, twinning has been observed at 77.3°K. The effects of reactor irradiations on discontinuous slip and on twinning were also studied and it was determined that the occurrence of twinning was unaffected by the irradiations.

ISSN:0021-8979    

DOI:10.1063/1.1722824

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A general method of correcting for the finite magnetic modulation amplitude in line shape analyses of paramagnetic or nuclear magnetic resonance lines is described. The method consists of determining the proper ``folding'' function for the detection system. Once this has been determined, the numerical ``unfolding'' procedure of A. R. Stokes can be used to compute the true line shape from the observed shape of an arbitrary experimental line.

ISSN:0021-8979    

DOI:10.1063/1.1722825

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The purpose of this investigation was to measure the limits with regard to currents and time duration of the glow and arc modes for the low current discharge at atmospheric pressure. In addition, some indications were obtained as to the conditions at the cathode which lead to such transitions. Accurate measurements in the normally unstable transition region were made possible through the use of a current stabilized power supply, together with special instrumentation for determining the magnitude and duration of the arc or glow voltage for periods as short as 0.02 microsecond.It is shown that glow‐arc transitions can occur for currents as low as 0.002 amp and for currents at least as high as 1.0 amp in the atmospheric pressure argon discharge. The duration of the arc mode at low currents is usually less than 5 microseconds. These low current transitions occur only when an oxide film is present on the cathode and are caused by the action of high fields created by positive ions across the bulk of the thin oxide films.

ISSN:0021-8979    

DOI:10.1063/1.1722826

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Surface waves in crystals are investigated for surface orientations and directions of propagation which preclude waves of plane strain. These waves are of importance in the study of very high frequency vibrations of certain crystal plates. It is shown that, in theATcut of quartz, one and only one surface wave can propagate along the digonal axis. By reduction to the case of orthorhombic symmetry, it is shown that the surface wave is the result of coupling between a surface wave of plane strain and either a face‐shear mode or a transverse thickness‐shear mode. The former combination is associated with flexural and the latter with extensional vibrations ofATplates. Computation of the wave velocity requires the simultaneous solution of algebraic equations of the third and fifth degrees as opposed to a single cubic equation in the case of waves of plane strain.

ISSN:0021-8979    

DOI:10.1063/1.1722827

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

One of the simplest trajectory programs for the powered flight of a missile through the atmosphere is the ``gravity turn,'' which results from simply keeping the propulsive thrust always parallel to the vector velocity. However, even for a ``point mass'' missile, in a uniform gravitational field with constant thrust and no aerodynamic forces, the differential equations for the motion are nonlinear and require numerical integration. To avoid the necessity of doing this computation anew for each missile preliminary design, a method has been found for integrating the equations for the singular case of zero initial velocity. When expressed in terms of appropriate dimensionless variables, the resulting solutions are ``universal'' in the sense that they constitute a good approximation to any gravity turn with a small, nearly vertical, initial velocity. The solutions depend upon two parameters, the initial thrust to weight ratio &eegr; and a parameterkwhich corresponds to the initial ``kick angle'' of nonsingular gravity turns.

ISSN:0021-8979    

DOI:10.1063/1.1722828

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A method for calculating the criticality conditions for spatially disconnected fissile regions based on the multiplication constantkis presented. To illustrate the method, the case of two interacting infinite water‐tamped fissile slabs containing solutions of pure U235in water is considered.

ISSN:0021-8979    

DOI:10.1063/1.1722829

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Experiments on the angular intensity distribution of x‐rays scattered by porous materials (hole structures) in the range of small angles are described. It is shown that the scattering can be characterized by anexponential correlation functionin the case of a distribution of holes of random shape and size in solid; a theoretical derivation of the exponential function is given for this case. When the correlation function is an exponential, the rule holds that the reciprocal square root of the scattered intensity is a linear function of the square of the scattering angle. The specific surface of the material is determined by the slope of this straight line. Specific surfaces of a number of compositions are calculated from their experimental correlation functions and compared to surfaces based on adsorption measurements.

ISSN:0021-8979    

DOI:10.1063/1.1722830

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The size spectrum of isotropic fluctuations in the troposphere's dielectric constant is related to quantities measured by radio means. Two classes of experiments are analyzed: (1) line‐of‐sight phase and amplitude instability and (2) refractometer measurements of dielectric fluctuations. This analysis is independent of models for the dielectric fluctuations and provides a system from which the spectrum can be estimated from experimental data. The measured quantities are expressed as weighted integrals of the spectrum, many of which may be inverted to give the spectrum directly in terms of the data. Aerial smoothing by the receivers and finite data sample effects are studied, in addition to the basic propagation mechanisms.

ISSN:0021-8979    

DOI:10.1063/1.1722831

出版商:AIP    

年代:1957

数据来源: AIP