摘要:

Measurements of the integrated intensity of the superstructure reflections 100 and 110 from powders and a single crystal of CuAu3give a long‐range order parameterS=0.87±0.04 for a temperature belowTcnot well defined. At the composition CuAu3,Tc=199°C. With decreasing Au content,Tcincreases. Compositions richer in Au than CuAu3could not be ordered. No annealing treatment was found which would sharpen the superstructure reflections. The breadths correspond to antiphase domains about 50 A in size. Measurements of the diffuse intensity from a single crystal of CuAu3quenched from 285°C, or held at temperatures of 250°C and 320°C, gave short‐range order coefficients qualitatively similar to those for Cu3Au. Compared with Cu3Au, CuAu3shows a weaker first neighbor and a stronger second neighbor ordering.

ISSN:0021-8979    

DOI:10.1063/1.1722802

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The microwave breakdown electric field has been measured for pure air uncontaminated by discharge products (presumably oxides of nitrogen), and for nitrogen and oxygen separately. The breakdown field for pure air is significantly higher than that previously observed, in which cases such contamination could be suspected.The breakdown field for pure air lies between those for nitrogen and oxygen. A calculation of the high‐frequency breakdown field in air is made from dc data, using the measured Townsend ionization coefficient, electron attachment coefficient, and average electron energy. The present data agree well with this calculation.

ISSN:0021-8979    

DOI:10.1063/1.1722803

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A new technique is described for measuring the charge distribution of an electron beam in a magnetic field. The method is especially applicable to the long, thin, high‐current beams commonly used in traveling wave tubes and backward wave oscillators. It consists of making the beam trace out its own characteristics by sweeping it across a pinhole in crossed electric and magnetic fields. The data are presented in the form of oscilloscope pictures of the actual charge distribution. Quantitative measurements of the charge distribution are also obtainable.

ISSN:0021-8979    

DOI:10.1063/1.1722804

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

The field diffracted by an aperture of any shape is evaluated asymptotically for small wavelengths on the basis of several approximate diffraction theories. These are the Kirchhoff method, its two customary modifications, and W. Braunbek's new modification. In each case, a double integral over the aperture is evaluated asymptotically, and contributions from interior stationary points, edge stationary points, and corners of the edge are obtained. The contributions from points of each type, according to all the theories examined are exactly of the form recently deduced by J. B. Keller using his geometrical theory of diffraction. The edge stationary points and the corners correspond respectively to rays singly diffracted from edges and from corners. For edge‐diffracted rays the Braunbek diffraction coefficients alone coincide with those given by the geometrical theory of diffraction, but the Braunbek method does not apply to corner diffraction. None of these methods takes account of multiple diffraction as does the geometrical theory of diffraction.

ISSN:0021-8979    

DOI:10.1063/1.1722805

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Plots of flux tubes in axially symmetric static field problems are ordinarily obtained by rather tedious methods from plots of the equipotentials. The differential equation for the flux function in circular cylindrical coordinates does not have the same form as Laplace's equation. Hence, an ordinary wedge‐shaped electrolytic tank cannot be used directly to plot flux tubes in an axially symmetric potential field. A direct method is described making use of a coordinate system in which Laplace's equation has the same form as the flux equation in the cylindrical system. An electrolytic tank can then be set up which makes use of this coordinate system in plotting equipotentials which are the analog of the flux tubes in an axially symmetric problem.

ISSN:0021-8979    

DOI:10.1063/1.1722806

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Uniform thin films of carbon in the thickness range 100 to 2300 A have been prepared by arc‐evaporation in vacuum. Evaporation rates were about 50 A/sec. The electrical properties of these films suggest that unannealed arc‐evaporated carbon had less long‐range order and was, therefore, more truly amorphous in structure than any other form of carbon yet obtained. After the films had been heated to 1200°K, however, their properties were similar to ordinary fine‐particle carbon blacks, apparently as a result of increased ordering. The electrical resistivity of unannealed films followed Ohm's law, was not photosensitive, and could be well represented in the temperature range 77°K to 300°K by the equationR=AT−b, whereb=5. When the carbon films were heated above room temperature, the resistivity and the exponentbwere both decreased substantially. After the films had been annealed at 1200°K, the resistivity was reduced by a factor exceeding 800, and could be best represented, in the temperature range 77°K to 1200°K, by the equationR=&agr;—&bgr;T. The values of the resistivity, temperature coefficient of resistivity, and thermoelectric power of the annealed films were then more nearly in agreement with the corresponding values for ordinary fine‐particle carbon blacks. Other properties and applications of the films are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1722807

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Bombardment of a silica‐soda‐lime glass (nD=1.5246) by more than 5×1016A+ions/cm2with an energy of 33.5 kev reduces the reflection coefficient to 0.36 of its normal value for light of wavelength &lgr;=0.6 &mgr;. The change in reflection coefficient is attributed to the formation of an altered glass layer. For a bombardment by 40‐kev A+ions, the layer has a thickness of 0.095 &mgr; and an effective refractive index of 1.343. The depth of the layer is determined by the ion energy and agrees approximately with the theoretical range of the incident ions. The refractive index of the altered layer is determined by the integrated flux of positive ions and the type of ion. The magnitude of the positive ion flux employed here is shown to be orders of magnitude larger than the flux of primary ``knocked‐on'' atoms produced by fast neutron bombardment in a reactor.

ISSN:0021-8979    

DOI:10.1063/1.1722808

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A hydrodynamic theory for the flow of a viscoelastic fluid is formulated and applied. The viscoelasticity is specified in terms of the conventional and well‐known relaxation and retardation spectra. Time dependent recoverable strains are defined with respect to convected rotating coordinate axes. The theory is linear to the extent that these strains are small although the over‐all displacement gradients of the fluid may be large. The theory is applied to two‐dimensional steady‐state simple shear flow to predict the variation of the apparent viscosity and the steady‐state elastic compliance with shear rate. Pressure flow through a pipe of circular cross section has also been treated.Previous work of a similar nature is reviewed.

ISSN:0021-8979    

DOI:10.1063/1.1722809

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

A theoretical treatment of space charge effects in beam‐type magnetron amplifiers and oscillators is given. It is assumed that the beam is relatively thin and that the magnetic field is large. The ``cyclotron waves'' are not treated. A space charge parameter appears in this theory of magnetron‐type traveling‐wave interaction in a manner which is analogous to the manner in whichQCappears in ordinary traveling‐wave interaction. A distinctive feature of the space charge waves in the magnetron case is that one increases along the beam and the other decreases along the beam. A simple physical explanation of this effect is given.This theory is then used to determine the starting conditions of anM‐type backward wave oscillator. It is found that when the tube is long in space charge wavelengths there is an appreciable reduction of starting current. When the space charge parameter approaches zero, the solutions found here reduce to the usual two‐wave solutions.

ISSN:0021-8979    

DOI:10.1063/1.1722810

出版商:AIP    

年代:1957

数据来源: AIP

摘要:

Tetragonal BaTiO3is transformed into cubic BaTiO3as a result of irradiation with fast neutrons at a temperature of approximately 100°C. Sufficient atomic displacements are produced by bombardment with an integrated fast neutron flux of 1.8×1020n/cm2so that tetragonal single crystals (c0=4.0349 A anda0=3.9923 A) expand anisotropically to form perovskite‐type cubic single crystals witha0=4.0824 A. The irradiated material remains cubic to the lowest temperature of measurement, 78°K, showing none of the low temperature phase transitions of unirradiated BaTiO3, and after annealing at 1000°C the crystal remains cubic but with a reduced lattice parameter. X‐ray, thermal, and optical methods were employed in studying these effects.

ISSN:0021-8979    

DOI:10.1063/1.1722811

出版商:AIP    

年代:1957

数据来源: AIP