摘要:

Observation of the deformation of thin aluminum specimens inside the transmission electron microscope has revealed the intimate connection between deformation and the nucleation and motion of dislocations. Nucleation, slip propagation, and the progress of deformation to the point of rupture have been observed visually on the fluorescent screen and photographed by both ``still'' and motion pucture techniques. In this way even the detailed predictions of the dislocation theory of deformation have been confirmed, and the new phenomena of grain boundaries acting as ``donors'' or ``acceptors'' of dislocations have been discovered.

ISSN:0021-8979    

DOI:10.1063/1.1735089

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The thermoelectric figure of meritz=&agr;2/&rgr;&kgr; is calculated for an extrinsic semiconductor with mixed acoustic‐mode lattice scattering and ionized‐impurity scattering. The result is compared to the value for pure acoustic‐mode scattering. As the amount of ionized‐impurity scattering is increased, the figure of merit increases by less than 10% and then falls slowly.

ISSN:0021-8979    

DOI:10.1063/1.1735090

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The rocket optimization formulation of B.D. Fried is modified slightly to facilitate the study of maximum accuracy trajectories. Various illustrative special solutions are obtained, particularly perturbation results valid for small thrust. For surface‐to‐surface rockets in a Kepler field, optimal thrust programs are obtained numerically, their accuracy is studied quantitatively, and comparison of range and of accuracy is made with rockets using a constant‐angle thrust program. Optimization leads to only a slight increase in range but to a substantial gain in accuracy. The possible application of rocket optimization methods to the focusing of charged particles is also suggested.

ISSN:0021-8979    

DOI:10.1063/1.1735091

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Quantitative data are presented which show the relative contributions of wall motion and domain rotation to the magnetization reversal process in thin ferromagnetic films for driving fields ranging from the coercivity to many times the anisotropy field. Also, an equation for the total magnetization reversal time is developed. This expression consists of two distinct components: one represents wall motion reversal time and the other reversal time due to domain rotation. The equation is similar to one published previously but contains a more realistic and more suitable wall nucleation distribution function.

ISSN:0021-8979    

DOI:10.1063/1.1735092

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The characteristics of a germanium surface barrier diode operated at room temperature make it particularly useful as an alpha‐particle spectrometer. The small size, stability, energy resolution, and relative insensitivity to &bgr; and &ggr; radiation of the units suggest applications in medical and nuclear research. Studies were made on Au&sngbnd;Ge and Au&sngbnd;Si surface barriers with a barrier width (≅1 &mgr;) less than the range of the incident alpha particles. In the germanium units, the pulse‐height response to alpha particles increased linearly with energy up to 7.5 Mev and then increased monotonically but more slowly as the energy rose to 12 Mev. In silicon the deviation from linearity occurred around 6 Mev. The observed linearity between pulse height and energy depends simply on the fact that the number of carriers excited is proportional to the particle energy and that the time for the carriers to be collected at the barrier is less than the circuit time constant. The general theory of the transient response of the diode was developed and the calculated response compared with the observed behavior. The observed values of the energy required to create a hole‐electron pair, measured over the energy range of linear response of the junction, were &egr;(Ge)=2.96±0.1 ev and &egr;(Si)=3.9±0.3 ev.

ISSN:0021-8979    

DOI:10.1063/1.1735093

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The breakdown characteristics of two types of siliconp‐njunctions are studied. In the first type of junction which is commonly encountered, the breakdown occurs in many localized regions, the characteristic being determined by the aggregate effect of the localized regions; in the second type of junction the geometry is such that only one localized breakdown region occurs. Whereas the simple avalanche theory can explain the onset of breakdown for both types of junctions, the shape of theV‐Icurve in the breakdown region cannot be explained without the inclusion of another variable in the theory. Experimental evidence obtained by the use of pulse techniques indicates that this variable is the temperature rise due to the current flowing through the junction. It is found that this self‐heating is the most important single factor in determining the shape of theV‐Icurve and that almost the entire dynamic resistance in this region is due to this effect. A method is given for determining the temperature rise of the junctions, provided that theV‐Icharacteristic is known.

ISSN:0021-8979    

DOI:10.1063/1.1735094

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

Experiments and theory are described concerning the rupture of soap films and the continuous formation, by impinging jets, of quasi‐stationary liquid sheets.

ISSN:0021-8979    

DOI:10.1063/1.1735095

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The method previously used to calculate the magnetization curve of an infinite cylinder is applied to the new Meiklejohn and Bean material which is made of Co particles in a CoO shell. It is assumed that the interface of the ferromagnetic and antiferromagnetic materials is held parallel to the cylindrical axis and does not change its direction for any value of the applied field. The crystal anisotropy is neglected.It is shown that the easiest nucleation mode for small radii is buckling and for large radii is curling. The transition from buckling to curling is at aboutRIsA−½=2, whereRis the radius of the cylinder,Isis the saturation magnetization andAis the exchange constant.Numerical solution of the nonlinear equations involved, yields two branches in the magnetization curve, which are both stable with respect to curling perturbations. The general stability is not tested.A similar calculation is carried out for an infinite slab with the spins on the surface held at a fixed direction and with the crystal anisotropy neglected.

ISSN:0021-8979    

DOI:10.1063/1.1735096

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

The course of &khgr;″ at resonanceversusapplied power is traced for various ratios of intrinsic to scattering line widths. It is assumed that the line width contribution from thermal spin‐wave agitation is negligible.

ISSN:0021-8979    

DOI:10.1063/1.1735097

出版商:AIP    

年代:1959

数据来源: AIP

摘要:

X‐ray powder and rotation patterns of six cubic substances (W, Si, Cr, TiO, Al, and V) using specimens of different thickness were made; the patterns were measured, the lattice constants calculated and plotted against the &thgr; angle or against the Nelson and Riley function. Such curves for thin mounts, semitransparent to x‐rays (below 0.2 mm in diam), consist of two parts: a region of high slope (due to absorption) and one approaching a zero slope at high Bragg angles. The latter, varying in extent with the size and nature of the mount, indicates that due to the rapid decrease in absorption, the lines in this region are shifted, little if any, from their correct positions. Hence, lattice constants calculated from the reflections of the high &thgr; angles lying on the horizontal portion of the curve need not be corrected for absorption. The constant, with negligible error, can be calculated from a single last strong &agr;1or &bgr; reflection. If an extrapolation is applied, the curve must be traced through points in the high back reflection region. Otherwise any extrapolation, disregarding the horizontal part, would lead to lattice constants too high in value. The amount of line displacement due to absorption in thin samples (below 0.2 mm in diam) agrees with the geometrical concept of Hadding and Buerger.

ISSN:0021-8979    

DOI:10.1063/1.1735098

出版商:AIP    

年代:1959

数据来源: AIP