bluuebunny/crossref_metadata_2025_split huggingface dataset:
Diffraction by Apertures
Authors: Huang Chaang , Kodis Ralph D. , Levine Harold 
Published: April 2005

The diffraction of plane electromagnetic waves by apertures in a plane screen which is infinitesimally thin and perfectly conducting is studied both theoretically and experimentally. The theoretical analysis employs a dyadic Green's function to develop vector formulas for the scattered fields, and from these formulas integral equations are obtained for the aperture distributions. The vector representation makes possible a compact demonstration of the electromagnetic form of Babinet's principle by means of which one may extend the aperture analysis to complementary disks. The integral equations are then used to construct a variational principle for the aperture transmission coefficient.
Detailed analysis and numerical computations are carried out for two configurations. For the circular aperture a first-order vector trial function with frequency dependent coefficients is chosen for the aperture distribution. The approximate transmission coefficient is found to agree closely with the exact value in the region 2πa/λ≤3. For elliptical apertures a zeroth-order approximation is evaluated using a one-component trial function. Numerical results are given for minor-to-major axis ratios of ½ and ⅓.
Transmission coefficient measurements were carried out in the 24 000 megacycle band (λ=1.25 cm) using an image plane technique. The apparatus was first calibrated with the exact solution of the circular aperture. The approximate results calculated for elliptical apertures are then seen to be in good agreement with the measurements over the accessible range.
On Power Spectra and the Minimum Detectable Signal in Measurement Systems
Authors: Freeman J. J. 
Published: April 2005

A least upper bound for the minimum detectable signal of a receiving system whose input is a periodic wave form plus interference is specified in terms of the first and second moments of the rectified output. Also, it is shown that the power spectrum of the rectified output (together with the impedance characteristic of the output meter) serves to establish the first and second moments of the meter deflection for either of the following two cases:
(1) The rectified output operates a meter, and the difference in meter readings with the signal on and off constitutes the observation from which the message is inferred.
(2) The rectified output feeds a synchronous detector whose meter reading is directly proportional to the message. Here we require that there be no input noise which is modulated at the synchronous frequency.
Acceleration of Slender Bodies of Revolution through Sonic Velocity
Authors: Cole J. D. 
Published: April 2005

The linearized theory of slender bodies in arbitrary motion at zero angle of attack has been worked out. The results have been applied to a smooth body accelerating uniformly through sonic velocity. The results theory can be used to estimate the nonlinear or transonic effects.
For an accelerating body, the parameter (bl/c2)½ is important where 2b = acceleration, 2l = length of body, c = sound speed at infinity. For sufficiently high (bl/c2)½, transonic effects can be neglected. Using linearized theory to estimate the ratio of nonlinear terms in the differential equation gives λ=nonlinear termssignificant linear terms=34(γ+1)δ2(bl/c2)12{log2δ2(c2bl)12−94},where δ = thickness ratio of body. The result above is evaluated at the maximum thickness of a symmetric parabolic arc body at the instant it passes through sonic velocity. For λ&lt;1 transonic effects can be neglected while for λ&gt;1 they begin to dominate. For practical applications the result shows that there is a possibility of a sufficiently long and slender missile accelerating fast enough to avoid transonic effects (e.g., 50 feet long, 5 percent thick, 3g acceleration). For conventional aircraft, transonic effects will dominate. An interesting side result is that when the acceleration is sufficiently large so that transonic effects do not matter the drag coefficient near sonic speed is independent of the acceleration (CD≐3δ2 for parabolic arc body).
Silicon Solar Energy Converters
Authors: Prince M. B. 
Published: April 2005

Theory is given for the design of silicon solar energy converters commonly known as the Bell Solar Battery. Values are given for the various parameters in the design theory. Experimental data are presented and compared with the theoretical relations based on a simple model.
It is found that with present techniques, units can be made with up to 6 percent efficiency in the conversion of solar radiant energy to electrical energy. An important factor in obtaining such high efficiencies is the reduction of the series resistance of the cell to as low a value as possible.
Nyquist's and Thevenin's Theorems Generalized for Nonreciprocal Linear Networks
Authors: Twiss R. Q. 
Published: April 2005

It is shown that an N-node nonreciprocal linear network, with a system of internal thermal noise generators at temperature T, is equivalent to the source-free network together with a set of correlated nodal current generators, with infinite internal impedance, such that 〈iris*〉Avdν=2kT(yrs+ysr*)dν where yrs is an element of the network admittance matrix and ir is the rth nodal noise current with frequency v. The noise sources can also be represented by a system of nodal voltage generators, with infinite internal admittance, such that 〈vrvs*〉Avdν=2kT(zrs+zsr*)dν.
The application of these results to a system of coupled antennas in an equi-thermal enclosure is noted and necessary conditions for the realizability of passive nonreciprocal networks are derived.
Short-Time Stress Relaxation Behavior of Plastics
Authors: Watson M. T. , Kennedy W. D. , Armstrong G. M. 
Published: April 2005

An apparatus for measuring stress relaxation of plastics at constant strain in the time range of 0.01 to 2.5 sec after load application is described. Experimental results obtained indicate that rigid plastics at room temperature may be classified as either brittle or ductile. Brittle plastics sustain only low strains without fracture at the testing speed of the apparatus and undergo little relaxation of stress in this time range; ductile plastics sustain higher strains and undergo considerable relaxation of stress. The factors affecting relaxation behavior are briefly discussed. Increasing the strain, temperature, or plasticizer content generally increases the relaxation rate.
Many of the results yield a linear plot of stress vs logarithmic time, as has been reported in the literature for various materials tested at longer times. By application of one form of the Eyring absolute rate theory, an average free energy of activation for the relaxation process can be calculated. The value thus calculated for polymethyl methacrylate is in the range reported in the literature for other polymers.
An empirical measure of ``toughness'' can be based on these results. For many plastics this measurement is in accord with service performance.
Microwave Diffraction by Apertures of Various Shapes
Authors: Buchsbaum S. J. , Milne A. R. , Hogg D. C. , Bekefi G. , Woonton G. A. 
Published: April 2005

Experimental results of the near zone diffraction field of circular and elliptical apertures and of the infinite slit are presented. The investigations were made on apertures which were illuminated by a plane polarized electromagnetic wave and whose characteristic dimensions were varied over a considerable range with respect to the wavelength of the incident radiation.
Most of the measurements are compared with predictions from recently published approximate theories and in a few cases with exact solutions. In general the agreement between theory and experiment is found to be satisfactory. Some of the discrepancies are discussed.
Electrical Breakdown in High Vacuum
Authors: Boyle W. S. , Kisliuk P. , Germer L. H. 
Published: April 2005

Currents preceding breakdown have been measured between closely spaced tungsten electrodes in high vacuum. It is found that field emission currents sufficient to evaporate anode metal flow before breakdown. These currents follow the Fowler-Nordheim equation when field magnification due to surface irregularities on the cathode is taken into account. The field magnification is a function of distance at electrode separations less than 4×10−4 cm.
Explanation of the observed breakdown at low voltage and small spacing requires an unusually high yield of electrons at the cathode per ion formed in the gap. Furthermore there is no measurable direct enhancement of the current by ionization even at higher voltages. The high electron yield must therefore exist over the entire observed range of breakdown voltages. This high yield is satisfactorily accounted for by the increase in field emission due to the positive ion space charge, which in turn increases the positive ion current density until there is breakdown. It is shown that breakdown occurs when the field emission current is increased by only 65 percent. This condition is reached with the ion current density much smaller than the electron current density.
Theory of Non-Newtonian Flow. II. Solution System of High Polymers
Authors: Ree Taikyue , Eyring Henry 
Published: April 2005

The authors' theory developed in the preceding paper I is applied to solutions of polystyrene, polyisobutylene, X-518 GR-S rubber, and lime base grease with good agreement with experiment. The parameters, xn/αn and βn (see the abstract of the paper I), were calculated, and are tabulated; these parameters are proportional to the surface concentration and the relaxation time of the nth group of flow units, respectively. The effects of the molecular weights of polymers, concentration, solvent, and temperature on these parameters were studied. Our results establish the following facts:
(1) The heterogeneity of flow units increases with increasing molecular weight.
(2) In the range of low concentration, βn (relaxation time) is independent of concentration, while the areal concentration of non-Newtonian units increases more rapidly than proportional to the bulk concentration of a polymer.
(3) A ``good'' solvent increases the concentration of non-Newtonian units, while the contrary is true for a ``poor'' solvent.
(4) In poor solvent solutions, the concentration of non-Newtonian units increases with increasing temperature, while the concentration is independent of temperature in good solvents.
Influence of Space Charge on the Potential Distribution in Mass Spectrometer Ion Sources
Authors: Brubaker W. M. 
Published: April 2005

The role of space charge as a factor influencing the potentials and potential gradients in a mass spectrometer ion source of the electron bombardment type is calculated. Planar equipotential surfaces are assumed, and the analysis then becomes that of a plane parallel positive ion diode. The ``cathode'' of the ion diode may be either emission-limited or space-charged-limited. The analysis considers the charge of the electrons in the ionizing sheet and the charge of the positive ions in the diode.
At a critical gas pressure the influences of the positive and negative charges on the potential of the ionizing region are equal and opposite, for small ionizing current. This concept leads to a pressure normalization in terms of the critical pressure. For a given source geometry and electron bombarding energy one can construct universal curves which give the potentials and the potential gradients as a function of the normalized gas pressure and the ratio of the ionizing electron current density to the repeller voltage. Experimental data are in agreement with the predictions of the theory.
Rectification Properties of Metal Semiconductor Contacts
Authors: Borneman E. H. , Schwarz R. F. , Stickler J. J. 
Published: April 2005

Metal semiconductor contacts of a number of different metals were made on n- and p-type germanium using jet etching and plating techniques. Current voltage curves taken on 12 of these metals on 5 ohm-cm n-type germanium showed rectification which follows the diode equation J=J0(eqV/kT−1). No correlation was found between the reverse saturation current densities of these diodes and such properties of the metals as work function, electromotive force, etc. For those metal contacts possessing the lowest saturation current densities, calculations indicated the current crossing the contact was to a large percent hole current and that the magnitude of the hole current was controlled primarily by the geometry of the diode. All metals plated on 5 ohm-cm p-type germanium produced ohmic contacts of resistivity comparable to the spreading resistance expected for the diode geometry used.
For indium diodes, a study of rectification versus resistivity indicated that the barrier produced on both n- and p-type germanium with plated contacts is one to electron flow rather than hole flow. When the assumption of only hole current crossing the barrier was made, it was shown that the I–V curves calculated from the diode theory, for different resistivities of germanium, were in qualitative agreement with the measured curves. Curves of zero voltage conductance versus temperature for different resistivities of germanium were also found to be in good agreement with those calculated on the assumption of all hole current.
Measurement of Excess Ba in Practical Oxide Coated Cathodes
Authors: Wooten L. A. , Moore George E. , Guldner W. G. 
Published: April 2005

These papers, designated I and II, discuss measurements of excess Ba (and/or Sr) in practical oxide coated cathodes. More than 300 cathodes of various designs were prepared, aged for periods up to 50 000 hours, tested thermionically, and then analyzed chemically.
Despite its great importance, the accurate measurement of excess Ba in practical cathodes is a problem whose complexity has not been adequately realized. Although the methods of the present experiments avoided many difficulties, limitations still exist. The difficulties and limitations, as well as the capabilities, can best be discussed in terms of typical measurements; we emphasize this aspect in I.
Excess Ba Content of Practical Oxide Coated Cathodes and Thermionic Emission
Authors: Moore George E. , Wooten L. A. , Morrison J. 
Published: April 2005

Using methods given in paper I, emission and Ba content are given on (a) 125 coated cathodes, (b) 15 coated filaments; H2 evolution by 19 uncoated cathodes was also measured. For analysis, each was isolated from the remainder of its tube. Coatings varied in composition from pure SrO to pure BaO and in density from 1 to 5 mg per cm2. Ba was also measured in cathode coatings removed from their support metal. Essentially all cathodes contained excess Ba, but no cathode structure gave any correlation between Ba content and emission.
These experiments contribute the following toward understanding practical oxide cathodes: If excess Ba (or Sr) is important, the significant amounts are probably less than one atom of Ba in 106 molecules of (BaSr)O. Because essentially all cathodes, including some with extremely low emission, contained at least this amount, we believe that performance is seldom limited by excess Ba. The concentration of Ba (or Sr) was not affected by using pure BaO or SrO coatings or Pt supports, although each of these steps led to very low emission; the highest emissions were obtained by operating at relatively low temperature during life, but this retained no more Ba in the coat. These major effects require interpretation.
On the Reflection of Shock Waves from an Open End of a Duct
Authors: Rudinger George 
Published: April 2005

The readjustment of the mean exit pressure to its steady-flow equilibrium level, following the arrival of a shock wave at an open end of a duct, has been investigated. For a cylindrical duct in which the gas is initially at rest, a solution based on acoustic theory was obtained in the form of a Fourier integral. The nature of this solution was established as a series of damped harmonic oscillations superposed on an exponential pressure decay. The actual pressure decay curve was obtained by numerical integrations. The same problem was also attacked experimentally using a shock tube of 3.23 inches i.d. From pressure records taken some distance from the open end, the ``effective'' exit pressure was derived.
It was found that the exit pressure deviates appreciably from its steady-flow equilibrium value during a time in which a sound wave could travel about three duct diameters. Satisfactory agreement between theory and experiment was observed for shock pressure ratios up to about 1.9 (in air) although, near this limit, significant deviations owing to wall friction were observed toward the end of the pressure decay region. For still stronger shocks, the influence of the decay time on the phenomena inside the duct becomes unimportant while friction effects dominate. The possible significance of the lag in the establishment of steady-flow boundary conditions in practical applications is discussed, in particular, for cases where the acceleration of the gas by the reflected expansion wave may be of importance.
X-Ray Diffraction Studies of Crystallization in Elastomers
Authors: Alexander Leroy E. , Ohlberg Stanley , Taylor G. Russell 
Published: April 2005

In general, extension of an elastomer results in a degree of preferred orientation of the molecular chains composing the amorphous phase. Therefore the amorphous fraction of a partially crystalline elastomer must be related to the integrated intensity of the amorphous diffraction halo rather than to the intensity at any one azimuth. A noteworthy exception is natural rubber, for which simple meridional measurements suffice.
A Geiger-counter apparatus with beam monitor and temperature-controlling accessories is described for making accurate measurements of the x-ray intensities scattered at any azimuth and at small or moderate Bragg angles. Measurements of crystallinity in natural rubber are in essential agreement with the findings of previous workers. When polybutadiene is extended at room temperature, molecular orientation occurs, but little if any crystallization. Measurements at lowered temperatures show that the crystalline fraction becomes appreciable at about 0°C and that it increases with further reduction in temperature and with increasing extension ratio. Preferred orientation of the crystalline regions in extended polybutadiene has been measured quantitatively with the object of providing jointly with birefringence measurements a value of the birefringence of a single crystal of polybutadiene.
Friction of Teflon Sliding on Teflon
Authors: Flom D. G. , Porile N. T. 
Published: April 2005

The low coefficient of friction for Teflon sliding on Teflon, as observed previously by others, has been found in this study to hold only if low sliding speeds and newly prepared surfaces are used. At high sliding speed, the nature of the surface is irreversibly changed such that subsequent sliding at low speed reveals a two- to threefold increase in the friction coefficient.
In addition to the effect of high speed sliding, there are reversible changes in the friction of Teflon on Teflon dependent in part on temperature. As the temperature of Teflon is increased from below room temperature, a sharp and pronounced increase in the coefficient of friction is observed in the vicinity of 20°C. The existence of a phase transition in Teflon at this temperature indicates a close correlation between the frictional and the structural properties of this material.
Unilateral Compression of Rubber
Authors: Forster Michael J. 
Published: April 2005

One-dimensional compression measurements have been made on samples of natural rubber gum stock. The experimental stress-strain curve and the theoretical relation f=G(L−1/L2) agreed quite well over the entire range (0%–32%) studied. No hysteresis loop was evident.
The friction at the faces of the sample was eliminated by a new method of lubrication. The sample essentially floated between two thin films of a liquid which flowed under pressure between the sample and compressing plates allowing uniform lateral expansion of the sample.
Plasma Oscillations at Extremely High Frequencies
Authors: Lampert Murray A. 
Published: April 2005

Plasma oscillations are here treated for a frequency range having application not only to gaseous discharges but also to solids such as impurity semiconductors.
Amplification of longitudinal electrostatic waves in a plasma may be achieved through energy exchange with a synchronously traveling electron beam, this being the same mechanism which underlies amplification in the traveling-wave tube. The dispersion equation describing this beam-plasma interaction, first derived by Bohm and Gross, is studied systematically to obtain the characteristics of the growth-in-time, ω vs κ, of standing plasma waves and the complex propagation constant κ vs ω for traveling plasma waves, at extremely high frequencies (high plasma densities). The problem of collision damping is also discussed. The possible application of plasma oscillations to the solution of the problem of the generation of millimeter wave power is considered, both for plasmas in gaseous discharges and for the thermally generated plasmas in impurity semiconductors.
Dynamic Elastic Moduli of Iron, Aluminum, and Fused Quartz
Authors: Hughes D. S. , Maurette Christian 
Published: April 2005

The dynamic elastic constants of Armco iron, pure aluminum, and fused quartz have been measured with a supersonic pulse technique as functions of pressure and temperature over the range 1 to 9000 bars and 25°C to 300°C (200°C for quartz).
Within the experimental accuracy the dynamic elastic moduli of these materials can be represented by linear functions of pressure and temperature.
The isothermal bulk moduli of other observers have been used to compute the equivalent adiabatic moduli by use of the thermodynamic relations. Comparison shows that at high pressures the dynamic moduli agree with the adiabatic moduli within the experimental accuracy for iron and aluminum. At low pressure the dynamic modulus of Armco iron is less than the adiabatic. The deviation is small but is about four times the estimated probable error.
Viscoelastic Properties of Ice
Authors: Jellinek H. H. G. , Brill R. 
Published: April 2005

An apparatus has been constructed for the study of deformation under tension of single and polycrystalline ice. Deformations down to 10−5 cm could be measured. Deformation of single and polycrystals was investigated as a function of time, stress, and temperature. Whereas the strain rate for polycrystalline ice decreases with time, that for single glacier ice increases linearly with time. The deformation for fine-grained polycrystalline ice consists of an instantaneous elastic deformation, a transient creep and a steady state creep. Deformation curves can be represented by empirical equations. The recovery curves on removal of the loads have also been investigated and the plastic flow has been deduced from the residual deformation after complete recovery. This plastic flow was found to be Newtonian within the range of stresses investigated and the viscosity coefficients can be represented by an exponential relationship as follows: η1 = 7.5·e+16100/RT poises, where 16 100 calories is the energy of activation for the plastic flow. The total deformation can be represented satisfactorily by a large number of Voigt units representing a distribution of retardation times, in series with a Maxwell unit.
The experimental results are further discussed in the light of current theories of dislocations and tentative mechanisms for the deformation of single and polycrystalline ice are proposed.