bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Thickness Measurement of Thin Films by Multiple Beam Interferometry
Authors: Scott G. D. , McLauchlan T. A. , Sennett R. S. 
Published: April 2005

A method is described for the measurement of the thickness of thin films using the multiple beam interference techniques. Only simple equipment is required, but reduction of the order of interference to as low as one makes possible the measurement of average thicknesses down to 10A. Applications have been made to evaporated films of six different metals and the method appears to be useful for all stable thin films in thicknesses up to several microns.
Possible errors in the method and the precautions which may be taken to avoid them are discussed.
Some Effects of Nozzle Design on the Diffraction of Electrons by Gases
Authors: Harvey R. B. , Keidel F. A. , Bauer S. H. 
Published: April 2005

An evaluation has been made of some of the errors introduced into the electron diffraction of gases by failure of the sample to be localized, and by secondary and higher order scattering.
The degree to which poor nozzle design may contribute to these factors was investigated experimentally by measurements of the pressure in the camera and absorption measurements of the main electron beam when a small volume of gas was allowed to expand into the camera; and theoretically for the cumulative effects of higher order scattering on the final picture. This evidence was complemented by density measurements on photographic plates taken under similar conditions. The effect of using liquid air cooled surfaces around the nozzle was tested.
Of the nozzles tested, better ``image to background'' ratios were obtained with the ``hydrodynamic'' and ``comparison'' nozzles than with the ``conventional'' nozzle, but the gas must be admitted slowly enough so that less than about 10 percent of the main beam is appreciably scattered. The ``image to background'' ratios were always higher using adequate cooling on the condensing surfaces surrounding the nozzle. In the case of pressure and electron beam absorption measurements short exposures were advantageous, where secondary scattering was not directly considered, and high camera pumping speeds were always advantageous.
On the basis of these results some general design suggestions for electron diffraction cameras, and requirements for good efficiency in nozzles can be made. A nozzle design is proposed which would reduce materially the errors normally encountered in electron diffraction work.
Applications of Potential Theory to the Design of Linear Arrays
Authors: Taylor Thomas T. , Whinnery John R. 
Published: April 2005

The polynomial formulation of the linear array problem introduced by Schelkunoff is studied from the point of view of potential theory. An electrical analogy results which is not only very helpful in qualitative thinking about the problem, but which also makes possible the construction of an analog computer for the synthesis of arrays to produce a desired radiation pattern, and for the evaluation of existing arrays. Such a computer has been built, and tested on known patterns with remarkable success.
Several theorems concerning the effect of the roots of the polynomial on the magnitude and phase of the space factor of an array are given. Some of the most important consequences of these are the lack of uniqueness in the array synthesis problem, and the evaluation of known methods of synthesis which consider only constant-phase patterns.
A method of analysis is sketched which in principle does the same thing as the computer, and the difficulties in applying this are described. It is concluded that the computer would be preferable for a wide range of practical problems.
A Theory of the Dynamic Plastic Deformation of a Thin Diaphragm
Authors: Hudson G. E. 
Published: April 2005

The theory presented in this article was developed in an attempt to describe the observed motion and plastic deformation of clamped metal diaphragms used in certain underwater explosion experiments and in certain mechanical gauges. The theoretical attack on this problem enables one to set up certain equations of motion, which may be solved in finite form under certain conditions. The solutions enable one to specify, for instance, the final deformed diaphragm profile, the distribution of thickness after deformation, the swing-time, which is the total time for deformation to take place, and many other quantities.
The simplest case, termed the ``elementary approximation,'' turns out, except for relatively minor details, to describe adequately for many purposes the motion and final shape of the diaphragm; it is found that the deformed diaphragm shape is conical, the thickness distribution shows a marked dimpling at the center of the diaphragm, and the swing-time ts is, to this order of approximation tS=a/c, where a is the radius of the diaphragm, and c is the square root of the ratio of the ``yield stress'' to the density. These results are all in good agreement with experimental facts.
Certain Refractory Compounds as Thermionic Emitters
Authors: Goldwater D. L. , Haddad R. E. 
Published: April 2005

Several refractories of the nitride, boride, and carbide families are investigated as sources of thermionic electrons. An activation pattern qualitatively common to several of the compounds is observed. Emission data for the final state of activation are presented. Data concurrently obtained for thoria are also given for comparison.
True temperature used in the Richardson equation is obtained by correction from brightness temperature. Temperature correction curves have been obtained. These curves can be satisfactorily represented in the region of thermionic emission by one value of spectral emissivity, which values are listed for the materials studied.
Secondary Emission of Nickel-Barium Mixtures and Rhenium When Bombarded by Electrons with Energies from 50 to 8000 Electron-Volts
Authors: Farnsworth H. E. , Lun M. J. 
Published: April 2005

The experimental tube contains a contamination-free gun which directs an electron beam at normal incidence onto a small thin sheet target which may be heated by conduction. The target is located at the center of a conducting sphere to permit a measure of the secondary current, and also of the energy distribution of the secondary electrons by means of the retarding potential method.
The maximum value of δ, the secondary emission ratio, for a cast alloy of nickel containing 1.5 percent barium is 2.8 and occurs at 800 to 900 volts after a critical amount of previous heat treatment of target. The value of δmax increases with heat treatment of target, subsequent to baking of tube, to the above value and then decreases with further heating. For the critical condition the value of δ above 4000 volts is sensitive to the amount of previous electron bombardment of the target. A δmax of 1.3 for rhenium after thorough out-gassing was obtained at 900 volts.
The most probable energy of low speed secondary electrons from rhenium is approximately 5 ev.
Electrical Properties of Selenium. II. Microcrystalline Selenium
Authors: Henkels H. W. 
Published: April 2005

The electrical properties of selenium have been studied in their dependence on history of preparation, i.e., as functions of temperature of initial liquid selenium, quench procedure, nucleation procedure, temperature of crystallization, and time of crystallization.
The electrical properties of melt single crystals and the microcrystalline matrix of these crystals have been compared.
The influence of nonmetals S, O2, I2, in small quantities on the electrical properties has been determined.
Carrier densities and effective mobilities as functions of temperature of measurement have been estimated from data on thermoelectric powers and resistivities. The order of the carrier densities have been checked by measurements of the voltage dependence of capacity of completely vacuum prepared rectifiers.
The frequency dependence of resistivity has been determined to gain insight into the nature of the effective mobilities.
Scattering of Plane Waves by Soft Obstacles. II. Scattering by Cylinders, Spheroids, and Disks
Authors: Montroll Elliott W. , Hart Robert W. 
Published: April 2005

Approximate closed form analytical expressions are derived for the total and differential scattering cross sections of cylindrical, prolate spheroidal, and disk-shaped scatterers which subject scalar plane waves to only a small phase shift.
When a plane wave excites a sphere or infinite cylinder, the internal field of these objects can be expressed as an infinite series of bessel functions. By making an approximation in coefficient of the nth bessel function which is valid for either 2πa/λ0»n (a = sphere or cylinder radius, λ0 = wavelength of incident plane wave) or |m−1| «1 (m = λ0/λ1, λ1 = wavelength of plane wave in medium composed of material of scatterer), it is possible to obtain a closed form expression for the series. The scattered field is obtained by integrating over these internal fields.
The scattered fields for long but finite cylinders and prolate spheroids are calculated by approximating their internal fields by those of infinite cylinders of the same radius. The scattered fields of thin disks are obtained by assuming the internal fields to be that of an infinite flat plate of the same thickness.
General Theory of Electromagnetic Horns
Authors: Stevenson A. F. 
Published: April 2005

Exact equations for the propagation of electromagnetic waves in a perfectly conducting horn of arbitrary shape are given. They take the form of an infinite set of simultaneous ordinary linear differential equations, and can be interpreted as the equations of propagation of a system of coupled E- and H-waves. If the coupling is neglected, we need only consider a single differential equation for each E- and H-wave, which can be solved approximately by the W.K.B. method. This approximate solution brings out the distinction between ``transmission regions'' and ``attenuation regions'' of the horn, as found by Barrow and Chu for the sectoral horn.
It is shown that the error due to neglect of coupling is, in general, of the order of the square of the flare angle as far as the variation of the field along the horn is concerned, but is of the first order in the flare angle as regards the variation of the field over the cross section. The coupling cannot, however, be neglected between modes of propagation which have the same cut-off frequency for all cross sections. The propagation characteristics of several special shapes of horn are discussed in detail.
Deceleration and Ionizing Efficiency of Radar Meteors
Authors: McKinley D. W. R. 
Published: April 2005

Improved instrumentation of the radar system has permitted a more accurate analysis of range-time records of meteor echoes and enabled the meteor deceleration to be determined in a few special cases. Three illustrative examples are described in which the measured mean decelerations were −0.48, −1.1, and −1.5 km sec−2. Velocity data from a continuous wave Doppler system were also available for these meteors and are compared with the radar data.
Using existing atmospheric density values and Lovell's scattering formula, it is computed that the ionizing efficiency, or the fraction of the kinetic energy of the meteor converted to ionization, is 10−6 for a 60-km/sec meteor and 10−8 for a 20-km/sec meteor. If lower values of the air density are adopted, the efficiency figures are increased and at the same time the gap is narrowed between the rates of electron production deduced from loss of mass considerations and the rates calculated from the radar data. More statistical data on radar meteors and further information on the ionizing properties of 1000 electron-volt atoms are required before definite conclusions can be drawn.
Electron Optical Exploration of Space Charge in a Cut-Off Magnetron
Authors: Reverdin D. L. 
Published: April 2005

The main effort in the work described has been directed towards the measurement of the electric field distribution in a cut-off magnetron, based on the electron optical shadow method. The space charge distribution can be determined qualitatively from the measured electric field distribution. The first objective is the development of a convenient method for such a study. In this work an elementary magnetron was investigated by sending an electron beam axially through the tube.
The conclusions of the study are that the space charge distribution does not conform to Hull's classical theory (which predicts that the space charge density is approximately constant out to a well-defined radius and zero beyond this cloud radius). Three different space charge distributions have been observed. One distribution has a sharp maximum near the cloud radius. Another falls off gradually toward the cathode; a third is time-variant. The shape of the space charge distribution is closely related to the symmetry of the magnetron.
A Correlating Modulus for Fluid Resistance in Accelerated Motion
Authors: Iversen H. W. , Balent R. 
Published: April 2005

The resistance to accelerating movement of objects in a fluid is normally evaluated with a mass term in the equation of motion that is greater than the actual mass of the object by an added mass described as a constant times the displaced mass of fluid. This added mass has been evaluated by numerous investigators for different body shapes from potential flow considerations. Published experimental results, mostly with oscillating systems with small amplitudes of motion, show an added mass constant that is higher than that derived from potential flow with values that are dependent upon the fluid and the object size. A few previous experiments on resistance in unidirectional accelerated motion indicate that the added mass is variable and depends upon the state of motion.
The present investigation includes a development from model law considerations that results in a resistance equation of the form F=C12ρV2S. This is identical with the normal resistance equation for steady state except for the coefficient C which, in addition to being a function of Reynolds' modulus, Froude's modulus, and the geometry, is also a function of a modulus, AL/V2, where A is the acceleration, L is a characteristic length, and V is the velocity.
Experiments with circular disks moving perpendicular to the plane of the disk under the action of approximate constant driving forces show this resistance coefficient to be correlated by the modulus AL/V2.
Kerr Cell Photography of High Speed Phenomena
Authors: Pugh E. M. , Heine-Geldern R.v. , Foner S. , Mutschler E. C. 
Published: April 2005

Visible light photographs have been obtained of metal jets squirted from the lined conical cavities of high explosive charges. Since these jets travel through air at nearly meteoric velocities (7 to 12×105 cm/sec), their front ends are heated to incandescense and vaporized. The remainder of the jet is relatively nonluminous and is photographed by synchronizing a Kerr cell shutter (exposure time &lt;1 μsec) and an exploding wire light source (peak intensity 4×108 candlepower) with the phenomenon. Schlieren type photography cannot be used because of the luminosity accompanying the phenomenon. Detail is obtained in the photographs by using a large lens with a seven-in. focal length. To maintain the effective aperture at f/4 requires a large Kerr cell which in turn requires a 25,000 volt pulse for its operation.
The technique is used in studying the action of these jets on steel, water, glass, and Plexiglas. The technique is also used in studying the propagation of shock waves in solids and liquids when these phenomena are due to the action of the metal jets or to the more direct action of explosives.
Electromagnetic Scattering from Spheres with Sizes Comparable to the Wavelength
Authors: Aden A. L. 
Published: April 2005

By using suitably defined logarithmic derivative functions and the recurrence formulas due to Infeld, the problem of obtaining numerical answers for the scattering of a plane electromagnetic wave by a sphere can be simplified. This is particularly true if the sphere has a complex index of refraction. The nature of these logarithmic derivative functions is shown for one special case involving water spheres.
Experimental results are given for the back-scattering cross sections of water spheres in the electrical size region 0.74≤2πa/λ≤5.90. These results were obtained at a wavelength of 16.230 cm using the standing-wave method of measurement. It is believed that these were the first laboratory measurements of the back-scattering cross section made on individual water spheres in this critical size region.
Comparison is made between the experimental and theoretical results.
A New X-Ray Diffraction Method for Studying Imperfections of Crystal Structure in Polycrystalline Specimens
Authors: Reis Alfred J. , Slade Jerome J. , Weissmann Sigmund 
Published: April 2005

A new double spectrometer method for the study of polycrystalline materials is developed. From intensity data of the diffracted spots and known angular settings of the specimen, the angular range of reflection of the misaligned scattering regions in a crystallite is determined statistically.
The instrument and the technique of the multiple exposure method is described. The statistical evaluation of the data is discussed and a mathematical treatment introducing correction terms as functions of the azimuth and of the Bragg angle is presented.
A commercial silicon powder specimen was investigated. The average angular range of reflection was found to be nearly the same for all (hkl)-reflections with exception of (111), (333), and (444).
The study of broadening effects with the same instrument has been started.
The new double spectrometer method for polycrystalline specimens described in this paper is based on the examination of numerous microscopic spots reflected by individual crystallites. The small spots on the diagram facilitate the detection and measurement of small broadening effects. Independently, the pattern of angular misalignment of the same reflecting crystallite can be accurately determined. For both broadening and misalignment, the method offers statistical information which is representative of the specimen and which can be compared for different (hkl)-reflections.
The total information on imperfections obtained in this manner may serve to correlate experimental observation with the theory of dislocations and hence, may be useful in the understanding of structure-sensitive properties of solids.
Visco-Elasticity of Rubber
Authors: Blizard Robert B. 
Published: April 2005

A theory has been obtained for the visco-elastic behavior of rubber in the frequency range above that at which creep is important and below that at which it behaves like a hard solid. The rubber chains are treated as springs in a viscous medium, and a general expression is obtained for the contribution to modulus of a single section of chain as a function of its length and terminations. A statistical estimate is made of the number of chain segments having given length and terminations. A modulus function is found for the group of chains with each kind of termination and these are added in the proper amounts to give the form of the modulus vs frequency curve for any amount of cross-linking.
Measurements of shear modulus were made on one apparatus at frequencies between 0.0125 and 750 cps. Agreement is good if a pure viscosity is added to the theory. However, at low frequencies the imaginary part of modulus does not decrease as much as predicted.
Three-Dimensional Photoelasticity
Authors: O'Rourke R. C. 
Published: April 2005

The classical Sommerfeld-Runge method for deriving the laws of geometric optics in isotropic inhomogeneous media from Maxwell's equations is applied to problems in ``weakly'' anisotropic and inhomogeneous media. This leads to a generalized Hamilton-Jacobi partial differential equation for the phases of the two waves (eikonals) which can propagate with finite velocity in such a medium. If one restricts oneself to a limited class of stress distributions, one derives a very powerful method of solving axially and spherically symmetric problems which would be very difficult to treat by the direct solution of the classical equations of elasticity. The Maxwell-Neumann law is derived in variational form so that, in principle, one can estimate in any given case the error involved in the conventional assumption that the paths are straight lines instead of the actual Fermat paths.
The last section treats the so-called general problem of photoelasticity in which the principal stress directions in the plane of the wave front rotate arbitrarily as the latter propagates through the medium. Again the Sommerfeld-Runge method gives one a solution which claims that if the rate of rotation is small in a wavelength one can ignore the contributions of the rotation to the integrated phase. An experiment is proposed to check this claim.
Current and Charge Distributions on Antennas and Open-Wire Lines
Authors: Angelakos D. J. 
Published: April 2005

An experimental investigation has been made of the distributions of current and charge amplitude and phase on cylindrical antennas and on the driving lines. The presence of a stub support modifies the distributions on the antenna only near the junction of the antenna, line, and stub; however, for antenna loads near antiresonance, the distributions on the line as well as the impedances of the structure are altered considerably.
A corrective network is defined for the terminal region of the junction. Impedances of theoretical models of antennas, the network, and conventional transmission line equations may then be used to predict the apparent impedances of the structure.
Instantaneous Power Spectra
Authors: Page Chester H. 
Published: April 2005

The intuitive concept of a changing spectrum is discussed. The instantaneous power spectrum is 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.
Simulation of Trajectories of Charged Particles in Magnetic Fields
Authors: Vineyard George H. 
Published: April 2005

A ball rolling on a rotating surface is shown to simulate the motion of a charged particle in a magnetic field. The theory is given for the case of a warped surface undergoing arbitrary rotation about a fixed axis and translation perpendicular thereto, while the system from which the ball is observed partakes of similar but independent motion. With approximations based on not too large departure of the surface from flatness, the following cases can be simulated: (a) The magnetic field is homogeneous and constant. The electric field is perpendicular to the magnetic field, and irrotational, but otherwise arbitrarily spatially dependent, and arbitrarily time dependent within certain limits. (b) The magnetic field is homogeneous but arbitrarily time dependent. The electric field is perpendicular to the magnetic field and may have a variety of space and time dependences, including a part which encircles the axis and has just the right magnitude to produce acceleration in a circular orbit as in the betatron.
Results of rudimentary experiments are presented which indicate that the method is capable of good accuracy.