摘要:

High‐speed photographs have been obtained of the fracture of glass produced by the detonation of a high explosive charge. Using photoelastic methods, the shock waves set up in the glass can also be photographed. In addition to providing a high intensity loading method, the explosive also serves as a convenient time base for determination of the rates of propagation of shock waves and cracking.The results presented in this paper extend those obtained by other investigators who used low energy impacts to produce fracture.

ISSN:0021-8979    

DOI:10.1063/1.1701977

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The M.I.T. linear electron accelerator consists of a circular wave guide fitted with uniformly spaced irises, and sustains a standing‐wave, transverse magnetic &pgr;‐mode oscillation at a resonant frequency of 2800 Mc/sec. The phase velocity is equal to the velocity of light. Electrons are injected into the accelerating tube at an energy of 2 Mev by a standard Van de Graaff generator. Acceleration up to an energy of at least 18 Mev has been obtained, using the 21‐foot length of the accelerator. Peak accelerated currents of the order of 10 ma, and average currents of the order of 1 &mgr;a, are obtained. The accelerator is fed by 21 tunable magnetrons (Raytheon RK5586), phased in synchronism. In this paper, the principles of design, constructional features, and operation are discussed. The accelerator is now being used for nuclear experimentation.

ISSN:0021-8979    

DOI:10.1063/1.1701978

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Hamilton's equations for the motion of an electron in a linear accelerator are integrated to find the final kinetic energy and phase of an electron injected with arbitrary initial kinetic energy and phase, after traveling down a fixed length of accelerator. The results are expressed in the form of a map of the initial energy‐phase space onto a final energy‐phase space. This map proves in practice to be very convenient for discussing the actual operation of the accelerator. The curves presented are calculated for numerical values appropriate for the M.I.T. accelerator.

ISSN:0021-8979    

DOI:10.1063/1.1701979

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

It is shown that the frequency of a resonant electromagnetic cavity is perturbed by inserting a metallic sphere, needle, or disk of dimensions small compared to a wavelength by an amount depending upon the local electric and magnetic field at the position of the perturbing object. This perturbation is calculated for ellipsoidal objects of needle‐shaped, spherical, and disk‐shaped form. The perturbations by the different objects depend upon different components of electric and magnetic fields, and by combining measurements with all three, it is in theory possible to measure all the field components. Experimental checks of the calculations are described, resulting in satisfactory agreement between theory and experiment except with the needles, in which the perturbation is very sensitive to the precise shape of the object, and the needles used were not accurate enough ellipsoids to give satisfactorily quantitative results.

ISSN:0021-8979    

DOI:10.1063/1.1701980

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

One theoretical and two experimental methods are described for finding the accelerating field in the M.I.T. linear accelerator cavity, in terms of the input power. One of the experimental methods is based on measuring the power leaking out through a calibrated hole in an end wall closing the cavity, the hole being located where the field strength is to be determined. The other method is based on the perturbation of the resonant frequency of the cavity by a small conducting sphere located on the axis. All three methods of determination check satisfactorily. In terms of the resulting relations, we discuss the probable field actually existing in the accelerator under operating conditions.

ISSN:0021-8979    

DOI:10.1063/1.1701982

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

An approximate theory is given for the vibrations of piezoelectric crystal plates in thickness‐shear and flexural modes, including the interaction between the elastic and electric fields. The problem of the rectangular, AT, quartz plate is solved and computed frequencies are compared with measurements by Sykes. Algebraic formulas are obtained relating resonant frequencies with dimensions, elastic and electric constants, and orientation of cut.

ISSN:0021-8979    

DOI:10.1063/1.1701983

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Young's modulus and the shear modulus of grade SA‐25 molded graphite and grade AUF extruded graphite were measured as functions of temperature in the range from 25°C to 2000°C. In the case of the extruded material, variations of the two moduli with position and direction relative to the axis of extrusion were also investigated. The moduli were found to increase with temperature, a behavior in contrast with that exhibited by most materials. Maxima in the low frequency shear modulus values and increases in the internal friction of both graphites observed in the range from 1550–1750°C may possibly be interpreted in terms of grain boundary relaxation. The bulk modulus and Poisson's ratio at room temperature were calculated from the data for the nominally isotropic SA‐25 graphite to be 6×1010dynes/cm2and 0.27, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1701984

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

A solution in successive approximations is presented for the heat diffusion across a spherical boundary with radial motion. The approximation procedure converges rapidly provided the temperature variations are appreciable only in a thin layer adjacent to the spherical boundary. An explicit solution for the temperature field is given in the zero order when the temperature at infinity and the temperature gradient at the spherical boundary are specified. The first‐order correction for the temperature field may also be found. It may be noted that the requirements for rapid convergence of the approximate solution are satisfied for the particular problem of the growth or collapse of a spherical vapor bubble in a liquid when the translational motion of the bubble is neglected.

ISSN:0021-8979    

DOI:10.1063/1.1701985

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

Smoothed values for the viscosities of water and mercury, as reported in the literature, show surprisingly large percentage deviations from the experimental data. Because water is frequently used as the calibrating fluid in viscometry, it was of interest to apply expressions, suggested by the theory of Eyring, for smoothing experimental data. It was of further interest to apply the Arrhenius expression for the variation of viscosity with temperature to the data for both water and mercury and to compare the closeness of fit with that obtained by the use of the aforementioned expressions. As judged by the Gaussian criterion of fit, an expression suggested by the Eyring theory provides smoothed values for the viscosities of both water and mercury which are believed to be more reliable than those in common use. This is especially true for the viscosity of water, for which relative viscosity data were first smoothed and then pinned to the recent value of 10.019±0.003 millipoises at 20°C as reported by Swindells and Coe.From other empirical equations relating densities and energies of vaporization to temperature, equations are derived for expressing the activation energies for viscous flow as a function of temperature.

ISSN:0021-8979    

DOI:10.1063/1.1701986

出版商:AIP    

年代:1952

数据来源: AIP

摘要:

The intuitive concept of a changing spectrum is discussed. Theinstantaneous power spectrumis defined mathematically and used to make the intuitive concepts more precise. It depends upon the past history of a signal, but not upon the future.Integration of the instantaneous power spectrum over time yields the conventional energy spectrum. The instantaneous power spectrum of a random function may be averaged over the ensemble of functions, with a resulting stochastic average instantaneous power spectrum that is equal to the conventional time average power spectrum of a stochastic process.

ISSN:0021-8979    

DOI:10.1063/1.1701949

出版商:AIP    

年代:1952

数据来源: AIP