摘要:

The thermoelectric powers and dc and 200‐mc resistivities of pure and metal‐doped selenium have been studied as functions of temperature. The properties of materials in the two important microstructures (colony and equiaxed) were distinguished. The influences of the metals Na, Cu, Ag, Mg, Zn, Cd, Hg, Ga, In, Tl, Pb, Sb, Bi, Te, Fe, Ni, Co, and Ce were noted.A working model of the selenium semiconductor was developed. In this model there is an acceptor level <0.15 ev from the full band caused by nonmetals and possibly lattice defects. In strained crystals or material in the colony structure a second acceptor level 0.27 ev from the full band is postulated from the behavior of dc and ac resistivity curves as a function of temperature. The density of the first level varies in the range 1014/cm3to 6×1016/cm3with amount of nonmetal impurity. The density of the second level depends on the crystal structure, decreasing as the colony structure recrystallizes to the equiaxed. In the specimens crystallized at 110°C the density was about 2×1016/cm3. Both metals and non‐metals are largely segregated at grain boundaries. Metals produce effective donor levels at these places.The dc properties reflect the presence of internal barriers produced by the segregation. The donor levels enhance barriers existing in the purest selenium tested increasing resistivities and thermoelectric powers.With increase in temperature >160°C the density of acceptor levels decreases as defects are removed by structural changes in the lattice.

ISSN:0021-8979    

DOI:10.1063/1.1721489

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

An approximate method is devised for calculating frequencies of thickness‐shear and flexural vibrations of crystal plates of varying thickness. Applications are made to plates having the shape of a double wedge and to plates with beveled edges.

ISSN:0021-8979    

DOI:10.1063/1.1721494

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

In this paper the influence of length of electrodes on thickness‐shear frequencies of piezoelectric crystal plates is investigated.

ISSN:0021-8979    

DOI:10.1063/1.1721514

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

It is shown how electrodes, coated on the surfaces of thickness‐shear plates, may be shaped so that, when the driving frequency coincides with a particular resonant frequency, only that resonant mode is excited.

ISSN:0021-8979    

DOI:10.1063/1.1721515

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The equations of motion for ions in an idealized two‐dimensional Omegatron are solved for the general case of arbitrary initial velocity and arbitrary starting time. A simple picture of the paths is obtained by use of a rotating coordinate system.

ISSN:0021-8979    

DOI:10.1063/1.1721516

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A magnetically confined sheet electron beam filling the space between two plane parallel electrodes is discussed. It is assumed that the average electron space charge is not neutralized by positive ions so that the potential at the center is depressed, and the beam is inhomogeneous in velocity and charge density. The objective of this theoretical treatment is to determine whether or not exponentially growing space charge waves can be supported by such a beam.For small inhomogeneity and continuous behavior of all quantities as functions of the inhomogeneity, it is shown that growing waves are not possible. This conclusion is supported by discussion of the analogous adjacent beam problem and the analogous velocity distributed filamentary beam. Although the adjacent beams can support growing waves, it is argued that the analogy is not valid because the adjacent beams cannot be obtained by a continuous perturbation of a single homogeneous beam. The analogy of the velocity distributed beam does not suffer from this deficiency. In this case it is shown that growing space charge waves cannot exist unless the distribution function has more than one relative maximum.

ISSN:0021-8979    

DOI:10.1063/1.1721517

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

It is shown that all the normals drawn from any point in the plane to the members of a family of equiangular spirals may be simply located geometrically. The locus of all the end points of the normals is a circle. It is also shown that the standing wave pattern in a uniformly attenuating medium may in simple cases (as with an attenuating transmission line) be represented by a vector diagram using a symmetrical pair of spirals. Then the foregoing theorem makes it possible to determine the voltage and current maxima and minima by constructing the locus circle referred to. This is illustrated by several examples. Finally it is pointed out that the locus circle may also be projected into the ``Smith Chart.''

ISSN:0021-8979    

DOI:10.1063/1.1721518

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A numerical method is presented for describing either the one‐dimensional or radial transient flow of gases through a porous medium in which the initial and terminal pressures and/or rates are specified. The purpose of this investigation was to evaluate the effect on transient gas flow of a pressure‐sensitive gas permeability resulting from gas‐slip effects. The gas‐slip permeability or apparent permeability is assumed to vary as a linear function with the reciprocal pressure. The computations were carried out by means of punch card machines.The results demonstrate that under certain conditions, the transient flow system is greatly influenced by gas‐slip permeability. However, the results also indicate that the effect of gas slip on transient flow behavior is negligible for pressure conditions usually associated with gas or petroleum reservoirs, and would be of most importance in the conduct and analysis of gas flow experiments in the laboratory. A specific laboratory application of the calculations is a possible transient method for the determination of porosity and/or gas‐slip corrected permeability.

ISSN:0021-8979    

DOI:10.1063/1.1721519

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Taylor's analysis of the intense spherical explosion has been extended to the cylindrical case. It is found that the radiusRof a strong cylindrical shock wave produced by a sudden release of energyEper unit length grows with timetaccording to the equationR=S(&ggr;)(E/&rgr;0)1/4t1/2, where &rgr;0is the atmospheric density andS(&ggr;) is a calculated function of the specific heat ratio &ggr;. For &ggr;=1.4,S(&ggr;) is found to be approximately unity. For this case, the pressurep1behind the shock wave decays with radiusRaccording to the relationp1=0.216E/R2. Applying the results of this analysis to the case of hypersonic flight, it can be shown that the shock envelope behind a meteor or a high‐speed missile is approximately a paraboloid given byR=(D/&rgr;0)1/4(x/V)1/2whereDandVdenote the total drag and the velocity of the missile, respectively, andxis the distance behind the missile.

ISSN:0021-8979    

DOI:10.1063/1.1721520

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

A modified A˚ngstro¨m method for measuring thermal diffusivity and hence thermal conductivity of metals has been developed. Like previously reported dynamic methods, this method uses a heat source, whose temperature varies sinusoidally with time, located at one end of an effectively infinite rod. Unlike these methods, only one period of the heat pulse is required to eliminate the unknown coefficient determining the heat lost by radiation since both velocity and amplitude decrement of the heat pulse are measured. In addition to providing greater reliability at high temperatures by using only one period, the new method is faster in taking data and simpler in computation. The thermoelectric potentials from two thermojunctions are amplified and plotted on a Brown electronic recorder in order to obtain a permanent record of all necessary data for computing the thermal diffusivity. Results for copper, nickel, and thorium over the temperature range 0–500°C are given.

ISSN:0021-8979    

DOI:10.1063/1.1721521

出版商:AIP    

年代:1954

数据来源: AIP