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At least 343 records · Page 19

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NASA NTRS1976

Dynamic polarizabilities of two-electron atoms, with rigorous upper and lower bounds

Methods are described for calculating rigorous upper and lower bounds to dynamic dipole polarizabilities for frequencies up to and beyond the first excitation threshold, even when (as usual) the field-free problem cannot be solved exactly. These methods were employed to calculate rigorous bounds to the dynamic polarizabilities of the two-electron atoms H(-), He, and Li(+), using well correlated trial wavefunctions up to 135 terms in length. The majority of previous theoretical and experimental results for these atoms can thereby be ruled out, including the highly precise Starkschall-Gordon values, which had heretofore appeared to be the most accurate available.

Glover, R. M.↗

NASA NTRS1977

Dynamic polarizabilities of metastable 2/1,3S/ excited states of He and Li/+/, with rigorous upper and lower bounds

Methods previously described for calculating rigorous upper and lower bounds to dynamic dipole polarizabilities are applied to the metastable 2(1S) and 2(2S) excited states of He and Li(+), using highly correlated variational trial functions. For each of these species, the bounds rigorously establish the values of the frequency-dependent dipole polarizability to within about 1% and appear to represent the first determination of this property at frequencies above the first excitation threshold.

Glover, R. M.↗

NASA NTRS1978

The Lovasz bound and some generalizations

The zero error capacity of a discrete memoryless channel is defined as the largest rate at which information can be transmitted over the channel with zero error probability. One channel with five inputs and outputs whose zero capacity remained unsolved until very recently is considered. An extremely powerful and general technique phased in terms of graph theory, for studying combinatorial packing problems is presented. In particular, Delsarte's linear programming bound for cliques in association schemes appears as a special case of the Lovasz bound.

Mceliece, R. J.↗

NASA NTRS1978

Semirigorous bounds for the dipole moments and transition moments of the LiH molecule

Semirigorous error limits for the dipole moments and transition moments of LiH at R = 3.015 bohr are reported. Weinhold's formula for the upper and lower bounds to transition moments is extended to include transitions between states of the same symmetry, and Chong's (1976) semirigorous expression for the lower bound to the overlap between the approximate and the true wavefunctions is applied to the calculation. The semirigorous theory of Chong was also generalized in the sense that the zeroth-order wavefunction was allowed to contain many configuration state functions instead of just the Hartree-Fock or first natural configuration state function.

Langhoff, S. R.↗

NASA NTRS1980

A bounds on the resonant frequency of rectangular microstrip antennas

The calculation of currents induced by a transverse electric plane wave normally incident upon an infinite strip embedded in a grounded dielectric slab is used to infer a lower bound on the resonant frequency (or resonant-E-plane dimension) for rectangular microstrip antennas. An upper bound is provided by the frequency for which the E-plane dimension is a half-wavelength.

Bailey, M. C.↗

NASA NTRS1981

Numerical optimization techniques for bound circulation distribution for minimum induced drag of Nonplanar wings: Computer program documentation

A two dimensional advanced panel far-field potential flow model of the undistorted, interacting wakes of multiple lifting surfaces was developed which allows the determination of the spanwise bound circulation distribution required for minimum induced drag. This model was implemented in a FORTRAN computer program, the use of which is documented in this report. The nonplanar wakes are broken up into variable sized, flat panels, as chosen by the user. The wake vortex sheet strength is assumed to vary linearly over each of these panels, resulting in a quadratic variation of bound circulation. Panels are infinite in the streamwise direction. The theory is briefly summarized herein; sample results are given for multiple, nonplanar, lifting surfaces, and the use of the computer program is detailed in the appendixes.

Kuhlman, J. M.↗

NASA NTRS1982

Quantitation of chlorpromazine-bound calmodulin during chlorpromazine inhibition of gravitropism

The regulatory protein, calmodulin (CaM), controls the activity of a plasma membrane localized ATPase in plants which serves to pump calcium out of cells. Recent data are consistent with the hypothesis that activation of this pump is one of the early steps necessary for gravitropism. Chlorpromazine (CPZ), a CaM antagonist, reversibly inhibits gravitropism in oat coleoptiles at concentrations which permit normal growth rates. C-14-labeled CPZ was used to photo-affinity label endogenous CaM in vivo to learn whether the drug is actually binding to some portion of endogenous CaM when it inhibits gravitropism. Under conditions in which CPZ inhibits gravitropism for over an hour, at least 11% of the CaM in gravitropically stimulated coleoptiles is bound to CPZ. In a given CPZ experiment the degree of inhibition of gravitropism correlates well with the amount of CaM bound to CPZ.

Roux, S. J.↗

NASA NTRS1984

Upper and lower bounds for semi-Markov reliability models of reconfigurable systems

This paper determines the information required about system recovery to compute the reliability of a class of reconfigurable systems. Upper and lower bounds are derived for these systems. The class consists of those systems that satisfy five assumptions: the components fail independently at a low constant rate, fault occurrence and system reconfiguration are independent processes, the reliability model is semi-Markov, the recovery functions which describe system configuration have small means and variances, and the system is well designed. The bounds are easy to compute, and examples are included.

White, A. L.↗

NASA NTRS1983

An upper bound on the radius of a highly electrically conducting lunar core

Parker's (1980) nonlinear inverse theory for the electromagnetic sounding problem is converted to a form suitable for analysis of lunar day-side transfer function data by: (1) transforming the solution in plane geometry to that in spherical geometry; and (2) transforming the theoretical lunar transfer function in the dipole limit to an apparent resistivity function. The theory is applied to the revised lunar transfer function data set of Hood et al. (1982), which extends in frequency from 10 to the -5th to 10 to the -3rd Hz. On the assumption that an iron-rich lunar core, whether molten or solid, can be represented by a perfect conductor at the minimum sampled frequency, an upper bound of 435 km on the maximum radius of such a core is calculated. This bound is somewhat larger than values of 360-375 km previously estimated from the same data set via forward model calculations because the prior work did not consider all possible mantle conductivity functions.

Hobbs, B. A.↗

NASA NTRS1984

Solitons in superfluid (He-3)-A - Bound states on domain walls

The effects of solitons on the spectrum of fermion excitations in superfluid (He-3)-A are investigated. It is found that there is a two-dimensional manifold of bound states with energies within the gap of the bulk superfluid. The bound-state spectrum lacks inversion symmetry parallel to the wall.

Ho, T. L.↗

NASA NTRS1984

A Very Efficient Transfer Function Bounding Technique on Bit Error Rate for Viterbi Decoded, Rate 1/N Convolutional Codes

For rate 1/N convolutional codes, a recursive algorithm for finding the transfer function bound on bit error rate (BER) at the output of a Viterbi decoder is described. This technique is very fast and requires very little storage since all the unnecessary operations are eliminated. Using this technique, we find and plot bounds on the BER performance of known codes of rate 1/2 with K 18, rate 1/3 with K 14. When more than one reported code with the same parameter is known, we select the code that minimizes the required signal to noise ratio for a desired bit error rate of 0.000001. This criterion of determining goodness of a code had previously been found to be more useful than the maximum free distance criterion and was used in the code search procedures of very short constraint length codes. This very efficient technique can also be used for searches of longer constraint length codes.

Lee, P. J.↗

NASA NTRS1985

Reliability bounds for fault-tolerant systems with competing responses to component failures

Bounds are established on the probability of system failure for fault-tolerant systems of the type used, for example, in aviation control. Event series leading to system failure are assumed to follow a semi-Markov model in which the potential sojourn times associated with component failures have exponential distributions and those associated with system responses have distributions with unspecified form. A product form of the bounds is derived by using a model that provides for multiple competing system responses to component failures.

Lee, L. D.↗

NASA NTRS1985

Synthetic bounds for semi-Markov reliability models

Upper and lower bounds are derived for the probability of failure for a class of highly reliable process control computers. The bounds are synthetic in the sense that the descriptions of component failure and system recovery are assumed to be obtained from different sources. The reliability model is constructed under the assumption that the processes are independent.

White, A. L.↗

NASA NTRS1986

Reliability bounds for fault-tolerant systems with competing responses to component failures

Lee, L. D.↗

NASA NTRS1986

Cramer-Rao bounds for signal-to-noise ratio and combiner weight estimation

Cramer-Rao lower bounds on estimator variance are calculated for arbitrary unbiased estimates of signal-to-noise ratio and combiner weight parameters. Estimates are assumed to be based on a discrete set of observables obtained by matched filtering of a biphase modulated signal. The bounds are developed first for a problem model based on one observable per channel symbol period, and then extended to a more general problem in which subperiod observables are also available.

Dolinar, S. J.↗

NASA NTRS1987

Computable optimal value bounds for generalized convex programs

It has been shown by Fiacco that convexity or concavity of the optimal value of a parametric nonlinear programming problem can readily be exploited to calculate global parametric upper and lower bounds on the optimal value function. The approach is attractive because it involves manipulation of information normally required to characterize solution optimality. A procedure is briefly described for calculating and improving the bounds as well as its extensions to generalized convex and concave functions. Several areas of applications are also indicated.

Fiacco, Anthony V.↗

NASA NTRS1987

Dynamic optimization problems with bounded terminal conditions

Bounded terminal conditions of nonlinear optimization problems are converted to equality terminal conditions via Valentine's device. In so doing, additional unknown parameters are introduced into the problem. The transformed problems can still be easily solved using the sequential gradient-restoration algorithm (SGRA) via a simple augmentation of the unknown parameter vector pi. Three example problems with bounded terminal conditions are solved to verify this technique.

Lee, A. Y.↗

NASA NTRS1987

WHAMII - An enumeration and insertion procedure with binomial bounds for the stochastic time-constrained traveling salesman problem

This paper presents an algorithm (WHAMII) designed to solve the Artificial Intelligence Design Challenge at the 1987 AIAA Guidance, Navigation and Control Conference. The problem under consideration is a stochastic generalization of the traveling salesman problem in which travel costs can incur a penalty with a given probability. The variability in travel costs leads to a probability constraint with respect to violating the budget allocation. Given the small size of the problem (eleven cities), an approach is considered that combines partial tour enumeration with a heuristic city insertion procedure. For computational efficiency during both the enumeration and insertion procedures, precalculated binomial probabilities are used to determine an upper bound on the actual probability of violating the budget constraint for each tour. The actual probability is calculated for the final best tour, and additional insertions are attempted until the actual probability exceeds the bound.

Dahl, Roy W.↗