摘要:

A procedure has been developed for the exact calculation of the efficiency of thermoelectric generators and cooling devices in which the parameters of the materials have arbitrary temperature dependence. High speed computer techniques are found necessary. Approximate methods are reviewed and their discussion extended. A number of examples are worked out by both the exact and approximate methods. Comparison of these results show that the approximate methods agree with the exact method to about 5% in the case of power generation and to about 15% in the case of the refrigeration coefficient of performance. However, in the case of the maximum heat pumping rate deviations as large as a factor of 2 are found.

ISSN:0021-8979    

DOI:10.1063/1.1735380

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The waves on a filamentary electron beam in a longitudinal dc magnetic field, and their interaction with a transverse‐field slow‐wave circuit, are studied in detail. All quantities are expressed in terms of circular polarization, with the circuit fields having arbitrary polarization. The beam is found to carry four waves: a positively polarized negative‐energy slow cyclotron wave, a negatively polarized positive‐energy fast cyclotron wave, and two synchronous (&bgr;=&bgr;e) waves, one with positive polarization and positive energy, one with negative polarization and negative energy. The coupling of these waves to the circuit is described both in the manner of Pierce's longitudinal traveling wave tube (TWT) analysis and in a coupled‐mode description. For the two special cases of positive or negative circularly polarized fields, only the appropriately polarized beam waves couple. A third special case of linear polarization is more complicated, but essentially only the two cyclotron waves couple. In each of the three cases one positive‐energy and one negative‐energy beam wave is involved. In each case the equations can be made identical with the longitudinal TWT equations. As one example, a positively polarized circuit can be used as a fast‐wave coupler for an Adler‐type parametric amplifier, and its design becomes formally identical with the longitudinal Kompfner dip problem. Published Kompfner dip data can be used. The beam‐circuit interaction is found to be correctly described by considering only the apparent transverse motion of the beam's position, although the actual interaction mechanism involves both the true transverse interaction with the actual transverse electron velocities, and the longitudinal interaction of the dc beam velocity with the longitudinal ac fields off the dc beam axis. The latter leads to changes in longitudinal dc velocity of the electrons and thus accounts for the negative rf energies of two of the waves.

ISSN:0021-8979    

DOI:10.1063/1.1735394

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Electron‐microscope photographs of a germanium single crystal surface subjected to prolonged argon‐ion bombardment under conditions used for surface cleaning disclosed etch patterns of a type completely different from those observed after chemical etching alone. The dimensions and distribution of the bombardment‐induced pits were such that the patterns were not detectable either with an optical microscope or by low‐energy electron diffraction. Approximately 95% of the surface remained undamaged. Bombardment of silicon and germanium at 500 ev for prolonged periods at higher current densities produced a different type of etching which may be associated with screw‐type dislocations.

ISSN:0021-8979    

DOI:10.1063/1.1735413

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The dipole mode of minority carrier diffusion about a spherical emitter is presented. The current‐voltage relationship, and frequency characteristics of this mode are determined. Compared with the unipole mode, which has been treated extensively, the dipole mode offers superior high‐frequency performance, which is partially offset by an inferior dc characteristic curve. A representative numerical example gives 40 m&mgr;sec mean response time with the unipole mode and 0.5 m&mgr;sec with the dipole mode. It is proposed that the reproducibility of special diode characterictics might be improved by designing diodes to suppress either the unipole or dipole mode. Methods are suggested for the suppression of either mode.

ISSN:0021-8979    

DOI:10.1063/1.1735414

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Hexagonal zinc sulfide crystals were obtained by controlled cooling of melted zinc sulfide. Both pure and activated zinc sulfide powders were used. The density of pure melt grown crystals was found to be higher than that of natural zinc blende crystals or crystals grown by evaporation. The stability of the pure hexagonal crystals towards transformation to the cubic zinc‐blende structure in the interval of temperature 700–1150°C was investigated. A full conversion to the cubic phase was never observed. The experimental evidence indicates the transition point to be above 1150°C.

ISSN:0021-8979    

DOI:10.1063/1.1735415

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

Evacuated mats of glass fiber made up of fibers of proper size and orientation are capable of supporting a compressive mechanical loading of at least one atmosphere and yet maintain a thermal conductivity of less than 10 microcalories/cm°C sec. The use of such a glass fiber mat as a filler makes possible an evacuated flat‐panel thermal insulation which is comparable to a Dewar flask in insulation efficiency. The rate of heat transfer through a Dewar flask wall was reduced several‐fold at liquid nitrogen temperatures and below by adding a 2‐cm‐thick layer of orientated and evacuated glass fiber mat to the outer surface.This investigation showed that in evacuated glass fiber mats, supporting external atmospheric loading, the fiber to fiber contact area is less than 10−4the mat area, making the contact pressure about 15 000 kg/cm2. The effective length of the thermal conduction paths along the fibers is about four times the mat thickness. The mean pore size for gas molecule motion in the mat was found to be about 54×10−4cm and 2×10−4cm for mean fiber sizes of 14×10−4cm and 0.2×10−4cm, respectively. The radiation mean free paths for the same fiber sizes were found to be 150×10−4cm and 52×10−4cm, respectively. The thermal diffusivity is about 10−4cm2/sec, which is much smaller than any other insulating material.

ISSN:0021-8979    

DOI:10.1063/1.1735416

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

A flow system used for continuous measurement of the gases evolved from aluminized glass during bombardment with 20 kev electrons is described. The system is also suitable for gettering measurements. A cathode‐ray tube containing the samples is sealed directly to the source of a mass spectrometer. Calibration of the first flow system built revealed the gettering of oxygen by the graphite‐silicate conductive coating and the hot metal parts of the electron gun of the cathode‐ray tube. This gettering was minimized in a second flow system. It was found that oxygen constitutes at least 95% of the gas evolved from each of five types of glasses investigated. Also, a graphite‐silicate coating can play a dual role in a cathode‐ray tube; when not bombarded by electrons it is an active getter for oxygen, but when bombarded it is a source of oxygen, carbon monoxide, and carbon dioxide.

ISSN:0021-8979    

DOI:10.1063/1.1735417

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The magnetic coating of recording tape is assumed to be composed of an assemblage of small, single‐domain particles. Each particle is assumed to have a symmetrical, square hysteresis loop when the reversible component of magnetization is neglected and when the particle is not influenced by the fields of neighboring particles. When influenced by the fields of its neighbors, the particle may exhibit an asymmetrical loop when the loop is plotted relative to an external applied field. In this case the positive and negative switching fields for the particle are not equal, and their difference gives an indication of the particle interaction. While it is not possible to measure the switching fields of a single particle on the recording tape, the distribution of switching fields in the assemblage of particles and the associated magnetic moment can be measured. The two switching fields and the magnetic moment define a 3‐dimensional distribution function which describes the magnetic properties of the tape, and in terms of which both dc and anhysteretic magnetization processes may be described.The distribution functions have been measured for two recording tapes. While the functions for the two tapes are markedly different in detail, both show that particle interaction is very appreciable in recording tapes and that it is a significant factor in determining the bulk magnetic properties and the recording performance of tapes.

ISSN:0021-8979    

DOI:10.1063/1.1735418

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

An improved method is presented for determining those three molecular field coefficients which yield essentially the best agreement between the Ne´el theory and the experimental curve of saturation moment per unit mass (&sgr;)versustemperature (T) in a given ferrimagnetic material. This method is analytical, and for a given accuracy it is more rapid than previously used trial‐and‐error methods. Experimental data on &sgr;vs Tare presented for monocrystals of lithium ferrite and two compositions of magnesium‐iron ferrite. One of the latter ferrites was measured in two states of ionic distribution which were obtained by varying the heat treatment. Application of the analytical method to these data shows that the agreement between the Ne´el theory and experiment is somewhat better than that expected on the basis of previous work. The present method is particularly useful for determining the temperature dependence of the sublattice magnetizations. Accurate values of these magnetizations are required, for example, in calculations of the temperature dependence of magnetocrystalline anisotropy by means of crystalline field theory.

ISSN:0021-8979    

DOI:10.1063/1.1735419

出版商:AIP    

年代:1960

数据来源: AIP

摘要:

The seemingly anomalous results obtained by Graham for the temperature dependence of magnetic anisotropy in iron are interpreted on the basis of Zener's theory, with the effect of thermal expansion included.

ISSN:0021-8979    

DOI:10.1063/1.1735420

出版商:AIP    

年代:1960

数据来源: AIP