Westinghouse Electric (United States)

Communication Systems and Information Theory. A Measure of Information. Coding for Discrete Sources. Discrete Memoryless Channels and Capacity. The Noisy-Channel Coding Theorem. Techniques for Coding and Decoding. Memoryless Channels with Discrete Time. Waveform Channels. Source Coding with a Fidelity Criterion. Index.

article Free Access`` Direct Search'' Solution of Numerical and Statistical Problems Authors: Robert Hooke Wesinghouse Research Laboratories, Pittsburgh, Pennsylvania Wesinghouse Research Laboratories, Pittsburgh, PennsylvaniaView Profile , T. A. Jeeves Wesinghouse Research Laboratories, Pittsburgh, Pennsylvania Wesinghouse Research Laboratories, Pittsburgh, PennsylvaniaView Profile Authors Info & Claims Journal of the ACMVolume 8Issue 2April 1961 pp 212–229https://doi.org/10.1145/321062.321069Published:01 April 1961Publication History 2,930citation8,393DownloadsMetricsTotal Citations2,930Total Downloads8,393Last 12 Months769Last 6 weeks95 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteeReaderPDF

A phenomenological model is developed to facilitate calculation of lattice thermal conductivities at low temperatures. It is assumed that the phonon scattering processes can be represented by frequency-dependent relaxation times. Isotropy and absence of dispersion in the crystal vibration spectrum are assumed. No distinction is made between longitudinal and transverse phonons. The assumed scattering mechanisms are (1) point impurities (isotopes), (2) normal three-phonon processes, (3) umklapp processes, and (4) boundary scattering. A special investigation is made of the role of the normal processes which conserve the total crystal momentum and a formula is derived from the Boltzmann equation which gives their contribution to the conductivity. The relaxation time for the normal three-phonon processes is taken to be that calculated by Herring for longitudinal modes in cubic materials. The model predicts for germanium a thermal conductivity roughly proportional to ${T}^{\ensuremath{-}\frac{3}{2}}$ in normal material, but proportional to ${T}^{\ensuremath{-}2}$ in single-isotope material in the temperature range 50\ifmmode^\circ\else\textdegree\fi{}-100\ifmmode^\circ\else\textdegree\fi{}K. Magnitudes of the relaxation times are estimated from the experimental data. The thermal conductivity of germanium is calculated by numerical integration for the temperature range 2-100\ifmmode^\circ\else\textdegree\fi{}K. The results are in reasonably good agreement with the experimental results for normal and for single-isotope material.

A theory is presented which describes the development of surface grooves at the grain boundaries of a heated polycrystal. The mechanisms of evaporation-condensation and surface diffusion are discussed with the use of the Gibbs-Thompson formula and the assumption that the properties of an interface do not depend on its orientation. For the idealized case in which only one of the mechanisms is operative, the groove profile is shown to have a time-independent shape whose linear dimensions are proportional to t½ for evaporation-condensation, and to t½ for surface diffusion. The proportionality constants are evaluated, and criteria are developed which permit one to estimate which process predominates in practice. Order of magnitude agreement is obtained with estimates of actual grooving speeds and profiles.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text S. Timoshenko, "Analysis of Bi-Metal Thermostats," J. Opt. Soc. Am. 11, 233-255 (1925) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

A method is described for determining the position of an atom in a molecule from spectroscopic measurements on two isotopic species of the molecule. The method is applied to various types of molecules; explicit expressions are derived for linear, symmetric top, planar, and nonplanar asymmetric top molecules. The number of isotopic species on which measurements must be made to complete the structural determination, i.e., determine the position of every atom in the molecule, is discussed for various types of molecules. An application of the method to the determination of mass difference ratios is also considered.

It is known that resonance quanta are highly absorbable by normal atoms of the emitting gas; hence, under suitable conditions of gas density the eventual escape of these quanta from a gas-filled enclosure may require a large number of repeated absorptions and emissions. This "radiative" transport of excitation is determined essentially by the probability, $T(\ensuremath{\rho})$, that a quantum traverses a layer of gas of thickness, $\ensuremath{\rho}$, without being absorbed; the dependence of $T(\ensuremath{\rho})$ on the frequency distribution of the resonance line is investigated, and explicit expressions are derived for the cases of Doppler and dispersion broadening. The general transport problem is formulated in terms of a Boltzmann-type integro-differential equation involving $T(\ensuremath{\rho})$; the variational method of obtaining steady-state solutions of this equation is discussed. The theory is then applied to the evaluation of the rate of decay of excitation in an infinite slab; the results are compared with Zemansky's measurements of the decay of radiation from an enclosure of mercury vapor. Finally, the application of the theory to a number of problems concerning excited atoms is discussed briefly.

First Page

A model-reference adaptive system (MRAS) for the estimation of induction motor speed from measured terminal voltages and currents is described. The estimated speed is used as feedback in a vector control system, thus achieving moderate bandwidth speed control without the use of shaft-mounted transducers. This technique is less complex and more stable than previous MRAS tacholess drives. It has been implemented on a 30 hp laboratory drive, where its effectiveness has been verified.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A device is described which permits high- <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> frequency selection to be incorporated into silicon integrated circuits. It is essentially an electrostatically excited tuning fork employing field-effect transistor "readout." The device, which is called the resonant gate transistor (RGT), can be batch-fabricated in a manner consistent with silicon technology. Experimental RGT's with gold vibrating beams operating in the frequency range 1 kHz < f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> < 100 kHz are described. As an example of size, a 5-kHz device is about 0.1 mm long (0.040 inch). Experimental units possessing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</tex> 's as high as 500 and overall input-output voltage gain approaching + 10 dB have been constructed. The mechanical and electrical operation of the RGT is analyzed. Expressions are derived for both the beam and the detector characteristic voltage, the device center frequency, as well as the device gain and gain-stability product. A batch-fabrication procedure for the RGT is demonstrated and theory and experiment corroborated. Both single- and multiple-pole pair band pass filters are fabricated and discussed. Temperature coefficients of frequency as low as 90- 150 ppm/°C for the finished batch-fabricated device were demonstrated.

Abstract For a number of metallic polycrystalline aggregates, it is shown experimentally that [sgrave]f, the flow stress at constant strain, is related to the grain diameter l by where [sgrave]0 and k are constants. This has the same form as the relationship between the lower yield point, when this occurs, and grain size. An explanation is given by an extension of Taylor's theory to allow for the resistance at the grain boundary to the formation of a slip band. Dislocation-locking and a small number of slip systems are shown to favour a strong grain-size dependence of [sgrave]f and this explains the variation of this dependence amongst the common metals and alloys.

An expression is derived from perturbation theory for the lifetime of an optical phonon decaying into two acoustical phonons, and its temperature dependence. The strength of the interaction is expressed in terms of the Gr\"uneisen constant and the effect of a strain, equivalent to the instantaneous strain of an optical mode, on the frequency spectrum of a linear chain with alternating force constants. This interaction depends on the ratio of the acoustical and optical mode frequencies at the zone boundary. Fitting the theory to silicon, the optical mode at k = 0 has a calculated half-width at 300\ifmmode^\circ\else\textdegree\fi{}K of about 1.2% of its frequency. This result is compared with experimental data.

To represent ideal grain boundary motion in two dimensions, a rule of motion of plane curves is considered whereby any given point of a curve moves toward its center of curvature with a speed that is proportional to the curvature. A general theorem is deduced concerning the change of area enclosed by such a curve. Three families of curves are found that obey the curvature rule of motion while undergoing the shape preserving transformations of uniform magnification, translation, and rotation respectively. Pieces of these curves represent the steady shapes of idealized grain boundaries under certain symmetrical conditions.

First Page

The abstract of the paper is to outline the technical and economical factors which characterise the uniform, all solid-state power-flow controller approach for real-time controlled, flex ible AC transmission systems.The unified power-flow controller in its general form can provide simultaneous, real-time control of all basic power system parameters (transmission voltage, impedance, and phase angle), or any combinations thereof, determining the transmitted power. The parameters selected for control can be changed without hardware alterations, e.g. the function of the controller can be changed from that of a phase-shifter to that of a series line compensator, or vice versa, with or without additional terminal voltage regulation and shunt VAr compensation, to adapt to particular short term contingencies or future system modifications.

This paper is a continuation of an earlier paper which treated the decay of resonance radiation in optically excited gases for the case of doppler-broadened radiation in plane-parallel enclosures. The treatment is here extended to a second type of enclosure geometry---infinite cylinders---and to a variety of spectral line shapes.

This paper shows that the unified power flow controller (UPFC) is able to control both the transmitted real power and, independently, the reactive power flows at the sending- and the receiving-end of the transmission line. The unique capabilities of the UPFC in multiple line compensation are integrated into a generalized power flow controller that is able to maintain prescribed, and independently controllable, real power and reactive power flow in the line. The paper describes the basic concepts of the proposed generalized P and Q controller and compares it to the more conventional, but related power flow controllers, such as the thyristor-controlled series capacitor and thyristor-controlled phase angle regulator. The paper also presents results of computer simulations showing the performance of the UPFC under different system conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The one-phonon differential scattering cross section for the coherent scattering of thermal neutrons by an anharmonic Bravais crystal is obtained correct to the lowest nonvanishing order in the anharmonic force constants. Cubic and quartic anharmonic terms are retained in the crystal's Hamiltonian. It is found that the $\ensuremath{\delta}$-function peaks in the energy distribution of the scattered neutrons for a fixed momentum transfer (which occur at the unperturbed phonon energies) in the harmonic approximation are broadened and their positions are shifted in an anharmonic crystal. Some numerical results for the magnitudes of the phonon widths and shifts are obtained for a simple model of a face-centered cubic crystal.

The relaxation of a nearly plane surface to flatness is discussed under the assumption that all surface properties are independent of orientation. A general solution is obtained for the combined action of the transport processes of viscous flow, evaporation-condensation (in a closed system), volume diffusion, and surface diffusion. Green's function solutions are developed for each of the transport processes separately, and criteria are obtained to decide which process dominates. The initial forms of these solutions represent point concentrations (particles), or line concentrations (wires) of material set upon an infinite plane. The progressive topographical developments described by the formulas are idealized representations of the latter stages of the sintering of small wires and particles to a plane.

The development of anisotropy in an initially isotropie spectrum is studied numerically for two-dimensional magnetohydrodynamic turbulence. The anisotropy develops through the combined effects of an externally imposed d.c. magnetic field and viscous and resistive dissipation at high wavenumbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wavenumbers.