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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Threshold detection in an on-off binary communications channel with atmospheric scintillation

The optimum detection threshold in an on-off binary optical communications system operating in the presence of atmospheric turbulence was investigated assuming a poisson detection process and log normal scintillation. The dependence of the probability of bit error on log amplitude variance and received signal strength was analyzed and semi-emperical relationships to predict the optimum detection threshold derived. On the basis of this analysis a piecewise linear model for an adaptive threshold detection system is presented. Bit error probabilities for non-optimum threshold detection system were also investigated.

Webb, W. E.↗
NASA NTRS1973

Effect of solutes in binary columbium /Nb/ alloys on creep strength

The effect of seven different solutes in binary columbium (Nb) alloys on creep strength was determined from 1400 to 3400 F for solute concentrations to 20 at.%, using a new method of creep-strength measurement. The technique permits rapid determination of approximate creep strength over a large temperature span. All of the elements were found to increase the creep strength of columbium except tantalum. This element did not strengthen columbium until the concentration exceeded 10 at.%. Hafnium, zirconium, and vanadium strengthed columbium most at low temperatures and concentrations, whereas tungsten, molybdenum, and rhenium contributed more to creep strength at high temperatures and concentrations.

Klein, M. J.↗
NASA NTRS1973

A study of the reflection effect in close spectroscopic binary stars

Four W Ursae Majoris-type binaries were investigated using the simple model of blackbody solid spheres. Numerical computations were carried out for the rotationally broadened profiles of spectral lines Sr II (4077.7) and Ca I (4226.7) and the mean radial velocities. These mean velocities at different phases outside eclipses were compared with sinusoidal values of the radial velocity curve for point masses. Within the present accuracy of observations, the reflection effect is small and may be neglected in the analysis of radial velocity curves.

Chen, K.-Y.↗
NASA NTRS1974

On the fractional weight of distinct binary n-tuples

It is shown that the fraction p of ones in the Mn positions of M distinct binary n-tuples satisfies a given inequality. This inequality, which simplifies the derivation of the distance property of the Justesen codes, is proved using an elegant information-theoretic argument due to Kriz.

Massey, J. L.↗
NASA NTRS1974

LX Persei, an eclipsing binary with H and K emission

The masses and MK classes were calculated for the eclipsing spectroscopic binary LX Persei. Its spectrum shows strong H and K emission and doubled lines in the photographic region. The Ca II emission velocity shifts vary in phase with the secondary's absorption lines and are presumably associated with this component. The stars are tentatively classed as G0 V and K0 IV, and the cooler component is the more massive by a ratio of 0.96. The system has a period of 8.0 days.

Weiler, E. J.↗
NASA NTRS1974

Binary signaling over channels containing quadratic nonlinearities

This paper examines the transmission of binary data signals over channels which contain quadratic nonlinearities and additive Gaussian noise. We consider the case where the channel is nonlinear with memory and where the signal is passed through an input receiver filter and sampled once every signaling interval. The samples are represented by a discrete Volterra series and a special case where the received sample contains a single quadratic distortion term is examined. The optimum (maximum-likelihood) receiver (processor) is derived and upper and lower performance bounds obtained. The performance of a practical, suboptimum receiver is examined by means of computer simulation and is shown to be very close to the lower bound of the optimum receiver. Next we examine the case where the received sample contains two quadratic distortion terms. Again, upper and lower performance bounds are obtained.

Lawless, W. J.↗
NASA NTRS1974

The nature of Cygnus X-3 - A prototype for old population binary X-ray sources

Description of a model for Cyg X-3 based on a short-lived phase in the evolution of a U Geminorum-type binary where rapid mass transfer and mass loss occurs. X rays are generated by accretion on the white dwarf component, while both stars are enveloped in a thick stellar wind emanating from the red dwarf. Electron scattering in the cloud is responsible for the modulation of the X rays with the orbital period of 4.8 hours. Ultraviolet radiation and low-energy X rays absorbed in the cloud are reradiated in the optical and infrared, which, it is predicted, will display a 4.8-hr modulation in phase with the X-ray light curve. The X-ray absorption cutoff should also vary with phase, appearing at minimum energy when the source is at maximum light. The model also provides a framework in which certain aspects of the associated nonthermal radio source may be understood. Finally, it is suggested that the model may be applicable to Sco X-1 as well.

Davidsen, A.↗
NASA NTRS1974

Supergiant binary stars

It is pointed out that the energy radiated by HD 101584 (F2e Iap) at IR frequencies cannot be convincingly explained by thermal reradiation from atmospheric grains. It is theorized that this energy emission can be explained by assuming that the F supergiant has an M supergiant companion responsible for IR radiation. Other possible binaries containing an IR star are discussed.

Humphreys, R. M.↗
NASA NTRS1974

Infrared stars in binary systems

The peculiar F-type supergiant HD 101584, which has a large and unusual infrared excess, is discussed along with the possibility that the infrared radiation could be accounted for by a cool companion. The peculiar F supergiants 89 Her, v Sgr, and R CrB are also considered as possible binary systems containing an infrared star. It is pointed out that all four of these stars have infrared excesses with characteristics similar to the infrared radiation from several cool objects which are known single stars.

Humphreys, R. M.↗
NASA NTRS1975

Page composer to translate binary electrical data to optical form

Composer converts binary data to optical form for storage as hologram. Device consists of an array of deformable metal membranes controlled by MOSFET's. Device is fast, produces high contrast ratios, does not degrade with extended use, and can be addressed from diverse angles.

Bailey, G. A.↗
NASA NTRS1975

Investigation A: Numerical solutions of driven vortices of binary fluid in a cylindrical geometry

The steady state laminar motion of a viscous, incompressible and binary fluid is studied for a rotating flow in a cylindrical geometry. The mathematical model employed is a cold flow simulation of the fluid mechanics of the light-bulb concept of the gaseous core nuclear engine. A numerical treatment is developed for the rotating flow which includes a description of the nuclear fuel addition. The problem is formulated with the complete Navier-Stokes equations in order to show the interaction between the fuel addition, the main flow, and the boundary layer flow in an accurate manner. The results presented show holdup of the nuclear fuel for the case of steady fuel addition.

Shin, Y. W.↗
NASA NTRS1974

Investment and operating costs of binary cycle geothermal power plants

Typical investment and operating costs for geothermal power plants employing binary cycle technology and utilizing the heat energy in liquid-dominated reservoirs are discussed. These costs are developed as a function of reservoir temperature. The factors involved in optimizing plant design are discussed. A relationship between the value of electrical energy and the value of the heat energy in the reservoir is suggested.

Holt, B.↗
NASA NTRS1975

Threshold detection in an on-off binary communications channel with atmospheric scintillation

The optimum detection threshold in an on-off binary optical communications system operating in the presence of atmospheric turbulence was investigated assuming a poisson detection process and log normal scintillation. The dependence of the probability of bit error on log amplitude variance and received signal strength was analyzed and semi-empirical relationships to predict the optimum detection threshold derived. On the basis of this analysis a piecewise linear model for an adaptive threshold detection system is presented. The bit error probabilities for nonoptimum threshold detection systems were also investigated.

Webb, W. E.↗
NASA NTRS1975

Some long, rate one-half, binary convolutional codes with an optimum distance profile and the systematic versus nonsystematic code question

A tabulation is given of long systematic and long quick-look-in (QLI) nonsystematic rate R = 1/2 binary convolutional codes with an optimum distance profile (ODP). These codes appear attractive for use with sequential decoders. Simulations for two of the new codes are reported and confirm Massey's conjecture that systematic and non-systematic codes of the same rate yield nearly identical computational and error probability performance with sequential decoding when the number of digits transmitted in the tail of the encoded frame is the same for both codes.

Johannesson, R.↗
NASA NTRS1975

Langevin equation with stochastic damping - Possible application to critical binary fluid

We solve the familiar Langevin equation with stochastic damping to represent the motion of a Brownian particle in a fluctuating medium. A connection between the damping and the random driving forces is proposed which preserves quite generally the Einstein relation between the diffusion and mobility coefficients. We present an application to the case of a Brownian particle in a critical binary mixture.

Jasnow, D.↗
NASA NTRS1974

Binary stellar winds

Stellar winds from a binary star will interact with each other along a contact discontinuity. We discuss qualitatively the geometry of the flow and field resulting from this interaction in the simplest case where the stars and winds are identical. We consider the shape of the critical surface (defined as the surface where the flow speed is equal to the sound speed) as a function of stellar separation and the role of shock waves in the flow field. The effect of stellar spin and magnetic sectors on the field configuration is given. The relative roles of mass loss and magnetic torque in the evolution of orbital parameters are discussed.

Siscoe, G. L.↗
NASA NTRS1974

The structure of synchronously rotating close binaries built on polytropic model nu = 3

Mathematical procedures are developed which can provide an exact solution for the structure of synchronously rotating close binaries built on the polytropic model with nu equal to 3. Results are discussed for separations of centers of 10.0, 4.0, 3.0, and 2.8 solar radii. For the present discussion, both components are assumed to have the solar mass and, in the zeroth approximation, the solar radius. The present results are compared with those obtained by Chandrasekhar (1933) using first-order perturbation theory.

Green, L. C.↗