摘要:

Within a certain range of composition spiral defects were observed on etched soda‐lime‐silica glasses. The patterns described spirals of Archimedes and appeared to originate from interstitial defects in the glass. Mutual stress influence effects were observed. The hypothesis of an existing torque field around the interstitial defects was useful in explaining the spiral mechanism. Application of mechanical torque stresses produced the spiral effect. In some cases it appeared feasible to apply stress energy relationships developed from dislocation theories to these minute flaw patterns.A dynamic spherical indenter technique was developed to study structural variations in these glasses. The lengths of flaws produced by a rolling indenter were found to be sensitive to changes in the silica content of the glasses and less affected by variations in the soda‐lime ratio. The effects of heating and crystallization were also studied.

ISSN:0021-8979    

DOI:10.1063/1.1735855

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The values reported for the characteristic energy losses of electrons in carbon vary by as much as 50%. In an attempt to resolve this discrepancy the electron energy losses have been remeasured for evaporated carbon and natural graphite, and it is found that there is a large difference for these two forms of carbon. Electron diffraction patterns of evaporated carbon show it to be highly amorphous. Annealing of the films causes growth of the crystallites, and also an increase of the energy loss toward the loss values for graphite. It is shown by calculation that the difference in the energy losses for the two forms is due to a difference in density, and that annealing increases the density of the evaporated carbon and, therefore, the energy loss value.

ISSN:0021-8979    

DOI:10.1063/1.1735856

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The ultrasonic cw resonance technique was used to measure the adiabatic elastic constants of single‐crystal aluminum antimonide at 27°C. The values for the elastic stiffness constants, in units of 1011d/cm2, are:c11= 8.939,c12= 4.427, andc44= 4.155. A theoretical density of 4.36 g/cc was used. The values ofc11andc44for single crystal GaSb obtained by the cw resonance technique are compared with previous values obtained by pulse‐echo techniques.

ISSN:0021-8979    

DOI:10.1063/1.1735857

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Specimens ofN‐type GaAs were found to becomeP‐type or less stronglyN‐type as a result of heat treatment. The heat treatment was carried out in small quartz tubes, of two grades of purity. The magnitude of the changes was much less in high‐purity quartz. The effect in ordinary quartz was shown to be due in part to copper contamination, the copper originating in the quartz; the changes could be reduced by annealing.

ISSN:0021-8979    

DOI:10.1063/1.1735858

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A rolling‐ball analogue for the motion of electrons in a high‐frequency longitudinal field has been developed in which the balls, injected at regular time intervals, plotted photographically a family of graphs of distance against time, indicated the electron bunching, velocity modulation, and density modulation. From these graphs the current densities were found as a function of time for a series of equally spaced positions between cathode and anode, and the plate current induced by the electron stream was computed. Graphs of conductance against transit angle revealed that the conductance was independent of the size of signal for indices of modulation 0.25, 0.50, and 0.75. When the transit angle was 2&pgr; the induced plate current was almost pure first harmonic plus dc. When the transit angle was 3&pgr; the first harmonic disappeared.

ISSN:0021-8979    

DOI:10.1063/1.1735859

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

An investigation has been made of the motion of a plasma under the action of a rapidly varying magnetic field from a stationary coil. The analysis has been done for two cases: (1) the plasma is assumed completely diamagnetic so that the ionization history of the plasma may be ignored and (2) the nondiamagnetic case where the ionization process is considered in detail. For the diamagnetic case the analysis yields a coupled set of nonlinear ordinary differential equations which have been put in similarity form and solved for a wide range of the similarity parameters. An illustrative example is given to show how to use the results to obtain detailed information for a given physical system. The calculations indicate that, for field frequencies of about one megacycle, velocities of the order 107cm/sec may be attained, but the efficiency of conversion of stored energy into kinetic energy is rather low (about 5–10%) and cannot be varied much by possible changes in the physical and geometrical parameters of the system.Because of the complexity of the analysis, a systematic series of solutions has not been made for the nondiamagnetic case. Instead, a typical example has been worked out to indicate the major differences to be expected. The results show that the nondiamagnetic plasma yields an efficiency slightly less than that obtained for the corresponding diamagnetic plasma. The ionization process inside the plasma levels off very rapidly so that the electron density increases by only a few percent during the motion of the plasma, but the amount of ionization has very little effect upon the efficiency of the system. The indications are that the efficiency of a plasma driven by a magnetic field from a stationary coil is probably too low for practical applications.

ISSN:0021-8979    

DOI:10.1063/1.1735860

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A theory is given for a new type of parametric amplifier which uses a gas discharge plasma as a nonlinear propagating medium. This theory is based on a zero‐temperature plasma assumption. The nonlinear coupling between traveling waves passing through the plasma is determined by taking second‐order terms in the velocity into account. A simplified normal mode theory is used to describe the effect on the propagation constants of the individual modes due to coupling between them. The theory is carried out in detail for a plasma in an infinite magnetic field and for a plasma in a zero magnetic field. The final propagation equation for the traveling waves is found in terms of the fields in the plasma of the small‐signal pumping wave, signal wave, and idler wave. In the Appendix the theory is extended to cover the case of beam‐type parametric amplifiers. It is shown that the theory is applicable both to beam‐type amplifiers which use space‐charge waves for all three modes of propagation or to waves which are partially those of a circuit and of the beam itself. The results obtained are in agreement with the theory of Louisell and Quate for the principal waves of a space‐charge wave parametric amplifier.

ISSN:0021-8979    

DOI:10.1063/1.1735861

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Electron microscopy has been applied to the problem of characterizing the distribution of preferred sites for nucleation and growth on clean surfaces of evaporated films of magnesium metal. The films were deposited, platinum‐shadowed, and carbon‐backed in the same system under ultra‐high vacuum conditions to minimize surface contamination and to improve the fidelity of surface replication. Upon examination of both clean and oxidized films in the electron microscope, the distribution of the platinum deposit was observed to be markedly influenced by the vacuum conditions used in the replication procedure. In addition, the particle size and separation of the platinum grains and their distribution, with relation to the substrate, indicated an enhanced surface mobility on cleaved mica and an apparent reaction on magnesium. These observations may have bearing on both the surface properties of metal deposits and on the development of high‐resolution replication techniques.

ISSN:0021-8979    

DOI:10.1063/1.1735862

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The plasmas of the negative glow region of a cold‐cathode discharge in helium and neon are examined for their ability to supply free electrons for operation of a ``vacuum'' amplifier tube. The plasma replaces the conventional oxide‐coated hot cathode in a tube with closely‐spaced fine‐mesh grids. At gas pressures ∼1‐mm Hg the volt‐ampere characteristics of the amplifier portion of the total discharge tube are essentially the same as found in the high‐vacuum, hot‐cathode counterpart.The noise content of the plate current of the ``glow‐cathode'' tube, defined by equivalent noise‐diode current, was examined from 50 kc to 50 Mc. At the lower frequency this equivalent current is ∼10 times the actual plate current flowing. At frequencies approaching 50 Mc the equivalent current drops to a factor ∼0.5 and may be considerably lower for unexamined frequencies above 50 Mc.

ISSN:0021-8979    

DOI:10.1063/1.1735863

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A method of producing permanent magnets, which is believed to be novel, is briefly described. The method consists of drawing a compact containing parallel iron wires spaced by a copper alloy matrix until the iron wires become extremely small.Intrinsic coercive forces of 400 oe have been measured in samples drawn from compacts in which the initial spacing between the iron wires corresponded to an iron packing fractionpof about 0.45. Annealing of cold‐drawn samples generally increased both the coercive force and the squareness of the demagnetizing curve.

ISSN:0021-8979    

DOI:10.1063/1.1735864

出版商:AIP    

年代:1960

数据来源: AIP