摘要:

Consider a long hollow cylinder which is radially split along its entire length. When such a cylinder is heated, its inner radius undergoes a change &dgr;a. The cylinder is called stable if &dgr;a≤0. An approximate solution for &dgr;ais derived and is used to determine conditions for stability. The pressure against the inner surface required to prevent the contraction &dgr;ais also derived.

ISSN:0021-8979    

DOI:10.1063/1.1721194

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A general formula is derived for the spectrum of a multiply‐periodic, amplitude modulated sequence of pulses. The result is used to show that a function which lies in a frequency band (W0,W0+W) is completely determined by its values at a properly chosen set of points of density 2W. This verifies a supposition commonly accepted in communication theory.The well‐known, exact interpolation formula for a functionf(t) in a band (O, W) isf(t)=&Sgr;nf(n/2W)sin&pgr;(2Wt−n)&pgr;(2Wt−n).The function is thus determined by its values at a set of evenly spaced points ½Wapart.For a functionf(t) in a band (W0,W0+W) it is shown that an exact interpolation formula isf(t)=&Sgr;n[f(n/W)s(t−n/W)+f(n/W+k)s(n/W+k−t)]in whichkis subject to weak restrictions ands(t)=cos[2&pgr;(W0+W)t−(r+1)&pgr;Wk]−cos[2&pgr;(rW−W0)t−(r+1)&pgr;WK]2&pgr;Wtsin(r+1)&pgr;WK+cos[2&pgr;(rW−W0)t−r&pgr;Wk]−cos[2&pgr;W0t−r&pgr;Wk]2&pgr;Wtsinr&pgr;Wk.Thus, the function is determined by its values at a set of points of density 2W, but the points consist of two similar groups with spacing 1/W, shifted with respect to each other.

ISSN:0021-8979    

DOI:10.1063/1.1721195

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A discussion of the effect of variation of the total absorption coefficient on gamma‐ray transmission probabilities is given, which leads to estimates of the build‐up factors for a material of arbitrary atomic numberZ.Estimates are made of the photon and energy densities arising from a plane of sources, a line of sources, and a point source in an infinite homogeneous medium, where the material of the medium is (1) iron and (2) lead.

ISSN:0021-8979    

DOI:10.1063/1.1721196

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Many infinite two‐dimensional electromagnetic‐scattering problems are strictly equivalent to the configuration obtained from the image principle by placing a finite‐scattering obstacle between two parallel, infinite, and perfectly conducting planes and illuminating it with a plane or cylindrical incident wave confined to the parallel‐plate region.An experimental approximation to this arrangement is described for use in the 3‐centimeter wavelength region. Finite rectangular parallel metal plates support a transverse incident electromagnetic wave with the electric field oriented perpendicular to the plates. Absorbing wedges at the boundary of the region reduce reflections from this discontinuity. The electromagnetic field scattered from any particular obstacle may be investigated by means of a dipole probe introduced into the region through a moveable section of one of the plates.The success of this technique is demonstrated by comparing measurements of the total field scattered by infinite conducting wedges of included angle 0, 45, and 90 degrees with the known theoretical expressions, for perpendicular incidence. Agreement with theory is good.The effect of finite thickness of the diffracting screen (case of 0° wedge) in increasing the amplitude of the scattered wave is noted and compared to theoretical results derived for scattering from a thin conducting half‐plane with a cylinder superimposed on the edge.

ISSN:0021-8979    

DOI:10.1063/1.1721197

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

We have not yet obtained a perfect theory of bubble formation. In this paper the perfect theory of the formation of bubbles in the case where the bubbles of vapor are nucleated spontaneously in pure liquid is presented. This is done by the systematization of the classical theory of M. Volmer (Kinetik der Phasenbildung, 1939) and the theory of D. Turnbull and J. C. Fisher [J. Chem. Phys.17, 71 (1949)] and it coincides satisfactorily with the experiment of K. L. Wismer [J. Phys. Chem.26, 301 (1922)].Theory must be advanced further so as to afford a perfect explanation of the processes of boiling, cavitation and the critical phenomena of the movement of soil moisture [S. Takagi,Monographs on Theoretical Soil Physics; Theoretical Considerations on the Thermodynamical and Kinematic Properties of Soil Moisture(not yet published)]. To effect this object, the author has calculated the rate of formation of bubbles at a surface. The theoretical value, however, of the negative pressure at which the liquid fractures does not coincide by any means with the atmospheric pressure in the process of boiling. This is true also in the process of cavitation and in the process of critical phenomena of the movement of soil moisture. Some other factors must be introduced in order to bring the theory to a state of practical value.

ISSN:0021-8979    

DOI:10.1063/1.1721198

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

Schwinger's variational methods are applied to a resistance problem with mixed boundary conditions. By the use of two formulations, both upper and lower bounds to the resistance are obtained. Results are given for a cylinder subject to given boundary conditions for a number of values of the relevant parameters.

ISSN:0021-8979    

DOI:10.1063/1.1721199

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

An approximation technique for computing the space charge limited current between electrodes of unusual and complicated geometry that cannot be treated rigorously is discussed and applied to several electrode systems involving both cylindrical and sphreical emitters. This method was originally suggested by Matricon and Trouve´ and by O'Neill. All that is required is a knowledge of the electrostatic capacitance of the system concerned. Many electrode systems of practical importance which were heretofore not susceptible of calculation are amenable to this technique.

ISSN:0021-8979    

DOI:10.1063/1.1721200

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

In current aeronautical research, rapidly‐responding thermocouples and hot‐wire anemometers are required. The use of oxide cylinders coated with more or less thin layers of metal effects substantial improvements in rates of instrument response. The theory and results of numerical calculations for six typical situations are given. It is shown that for ratios of metal thickness to over‐all radius of 0.1, response amplitude gains of the order of 4 or 5 are to be expected as compared with typical gains of the order of 10 or more for infinitesimal shells (surface layers).

ISSN:0021-8979    

DOI:10.1063/1.1721201

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

The present paper seeks to describe the shapes of liquid floating zones between solid rods of silicon and of germanium and to discuss stability conditions. The shapes were deduced from the equation given by Laplace,p=&ggr;(1/R1+1/R2),wherepindicates the pressure difference across the surface membrane of a liquid at any point,R1andR2are the principal radii of curvature at that point, and &ggr; is the surface tension of the liquid.The floating liquid zone is analyzed within a wide stability range. Its dimensions were theoretically determined and experimentally confirmed.

ISSN:0021-8979    

DOI:10.1063/1.1721202

出版商:AIP    

年代:1953

数据来源: AIP

摘要:

A new method is described for preparation ofp — njunctions in single‐crystal semiconductors: the upper part of a slice cut from a single‐crystal semiconductor is melted by radiation. Impurities of the opposite type than those present in the crystal are introduced into the melt. Upon slow solidification of the melt a single crystal is obtained with ap — njunction at the original position of the solid‐liquid interface. The method is capable of producing multiple junctions.The influence of (a) heater temperature, (b) forced cooling, and (c) thickness of the slice on the position of the solid liquid interface is calculated for a one‐dimensional model, assuming that the temperature difference between bottom and top of the semiconductor is small compared to the melting temperature of the semiconductor. The time constant characterizing the rate of reaching equilibrium conditions after a sudden small change in heater temperature is estimated.

ISSN:0021-8979    

DOI:10.1063/1.1721203

出版商:AIP    

年代:1953

数据来源: AIP