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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Some elements of a theory of multidimensional complex variables. I - General theory. II - Expansions of analytic functions and application to fluid flows

The paper introduces a new theory of N-dimensional complex variables and analytic functions which, for N greater than 2, is both a direct generalization and a close analog of the theory of ordinary complex variables. The algebra in the present theory is a commutative ring, not a field. Functions of a three-dimensional variable were defined and the definition of the derivative then led to analytic functions.

Martin, E. Dale↗
NASA NTRS1988

A 'transient' automated mapping procedure for complex geometries

A numerical procedure is presented which is applicable to the general curvilinear mappings of complex geometries and is unrestricted by slow convergence or strong dependence on the initial conditions of physical space. The scheme, employing a time-dependent factored-implicit scheme, is shown to be general and robust. In the illustrative applications presented, complex, closed geometries are routinely mapped even when they begin with unreasonable initial conditions created through the analytical and computer graphics inputs. Due to the natural damping introduced into the governing equations, fast convergence is achieved and high stability is observed.

Raad, Peter E.↗
NASA NTRS1990

Complex permittivity of lanthanum aluminate in the 20 to 300 K temperature range from 26.5 to 40.0 GHz

Dielectric constants of microwave substrates are required in the design of superconducting microwave circuits at various temperatures. In this paper, the results are reported of a study of the complex permittivity of the newly developed lanthanum aluminate (LaAlO3) substrate, in the 20 to 300 K temperature range at frequencies from 26.5 to 40.0 GHz. The value of the complex permittivity was obtained by measuring the sample scattering parameters using a microwave waveguide technique. It is observed that, while the dielectric constant did not change appreciably with frequency, its value decreased by approximately 14 percent from room temperature to 20 K.

Miranda, F. A.↗
NASA NTRS1990

Development of realtime connected element interferometry at the Goldstone Deep Space Communications Complex

Connected-element interferometry (CEI) has the potential to provide high-accuracy angular spacecraft tracking on short baselines by making use of the very precise phase delay observable. Within the Goldstone Deep Space Communications Complex (DSCC), one of three tracking complexes in the NASA Deep Space Network, baselines of up to 21 km in length are available. Analysis of data from a series of short-baseline phase-delay interferometry experiments are presented to demonstrate the potential tracking accuracy on these baselines. Repeated differential observations of pairs of angularly close extragalactic radio sources were made to simulate differential spacecraft-quasar measurements. Fiber-optic data links and a correlation processor are currently being developed and installed at Goldstone for a demonstration of real-time CEI in 1990.

Edwards, C. D.↗
NASA NTRS1990

Modified Hilbert transform pair and Kramers-Kronig relations for complex permittivities

Modified versions of the Hilbert transform pair and the Kramers-Kronig relations are derived for the complex permittivity of a plasma/dielectric medium which is singular at the frequency of the applied electric field equal to 0. Such a complex permittivity exists when the plasma/dielectric model allows a loss term but no restoring term. Permittivity, in which both loss and restoring terms are included, is shown to satisfy the standard Hilbert transform pair and, thus, the Kramers-Kronig relations.

Cockrell, C. R.↗
NASA NTRS1989

Distribution of dust in W31 complex

W31 is a H II region/molecular cloud complex in the galactic plane at a distance of 6 Kpc. This complex consists of two prominent radio continuum sources (G10.2-0.3 and G10.3-0.1) representing H II regions. An extended region covering both these H II regions was mapped in the Far IR (FIR) using the TIFR 1 m balloon-borne telescope with an angular resolution of approx. 1 min and a dynamic range of 100. The resulting flux density distribution at an effective wavelength of 160 microns is presented. The coadded IRAS survey scan data at 60 and 100 microns were deconvolved using a maximum entropy method to generate the flux density maps of the same region. These 60 and 100 micron maps are given and are briefly discussed.

Ghosh, Swarna Kanti↗
NASA NTRS1987

A NASA initiative: Software engineering for reliable complex systems

The objective is the development of methods, technology, and skills that will enable NASA to cost-effectively specify, build, and manage reliable software which can evolve and be maintained over an extended period. The need for such software is rooted in the increasing integration of software and computing components into NASA systems. Current NASA Software Engineering expertise was applied toward some of the largest reliable systems including: shuttle launch; ground support; shuttle simulation; minor control; satellite tracking; and scientific data systems. Unfortunately, no theory exists for reliable complex software systems. NASA is seeking to fill this theoretical gap through a number of approaches. One such approach is to conduct research on theoretical foundations for managing complex software systems. It includes: communication models, new and modified paradigms, and life-cycle models. Another approach is research in the theoretical foundations for reliable software development and validation. It focuses upon formal specifications, programming languages, software engineering systems, software reuse, formal verification, and software safety. Further approaches involve benchmarking a NASA software environment, experimentation within the NASA context, evolution of present NASA methodology, and transfer of technology to the space station software support environment.

Holcomb, Lee B.↗
NASA NTRS1989

Fractal applications to complex crustal problems

Complex scale-invariant problems obey fractal statistics. The basic definition of a fractal distribution is that the number of objects with a characteristic linear dimension greater than r satisfies the relation N = about r exp -D where D is the fractal dimension. Fragmentation often satisfies this relation. The distribution of earthquakes satisfies this relation. The classic relationship between the length of a rocky coast line and the step length can be derived from this relation. Power law relations for spectra can also be related to fractal dimensions. Topography and gravity are examples. Spectral techniques can be used to obtain maps of fractal dimension and roughness amplitude. These provide a quantitative measure of texture analysis. It is argued that the distribution of stress and strength in a complex crustal region, such as the Alps, is fractal. Based on this assumption, the observed frequency-magnitude relation for the seismicity in the region can be derived.

Turcotte, Donald L.↗
NASA NTRS1991

IRAS detection of very cold dust in the Lynds 134 cloud complex

IRAS maps at 60 and 100 microns of the complex of dark clouds containing L1345, L183, and L1780 are presented and discussed. Extended regions are apparent where the 60 micron emission is very low compared to the 100 micron emission. The 60-100 micron flux ratio has a constant value of 0.2 in the outer diffuse parts of the clouds but suddenly drops to less than 0.03 in the opaque cloud centers. A geometrical model is used to show that the drop occurs in a narrow transition layer that has not been resolved by IRAS. The observations provide direct evidence for dust temperatures colder than 15 K in dark clouds. A number of 60 micron-deficient regions are defined using the quantity Delta I(100) = I(60)/Theta, where Theta is the ratio I(60)/I(100) in the diffuse parts of the complex. Delta I(100) is highly proportional to extinction and (C-13)O column density. The relationships indicate that the dust temperature must be constant over a large fraction of the volume sampled by Delta I(100). An upper limit of 4.8 g/sq cm is obtained for the mass absorption coefficient of dust at 100 microns.

Laureijs, R. J.↗
NASA NTRS1990

Impeller response calculation due to complex pressure loading

An analysis technique is described to calculate the harmonic response of the first-stage impeller of the Space Shuttle Main Engine high pressure fuel turbopump. The excitation is a complex pressure loading at various locations on the impeller blades. The pressure loading was predicted using computational fluid dynamic techniques and was given as a Fourier series at 48 different locations on each of the three impeller blade types. The analysis consisted of mapping the pressures onto a three-dimensional finite element model, then converting these pressure loads to complex nodal force vectors at specified equal time intervals. The resulting vectors were then converted to modal force time histories that were then transformed into the frequency domain where the frequency response was calculated directly. This technique resulted in an improvement to the previously used direct integration technique and in a substantial analysis cost reduction.

Wellstein, Carl↗
NASA NTRS1992

Three-Component Laser Velocimetry Of Complex Flows

Since aeronautical research community depends on computations, to extent that predictions of flow-field behavior used without supporting data, question arises whether predictions of complex flow fields represent real world. In experiment, laser velocimetry used to validate computed predictions of complex flow fields. Results demonstrated capabilities of orthogonal three-component laser velocimeter to obtain data necessary to validate computational codes used.

Meyers, James F.↗
NASA NTRS1992

Potential Flows From Three-Dimensional Complex Variables

Report presents investigation of several functions of three-dimensional complex variable, with emphasis on potential-flow fields computed from these functions. Part of continuing research on generalization of well-established two-dimensional complex analysis to three and more dimensions.

Martin, E. Dale↗
NASA NTRS1992

Optical Correlator With Complex Holographic Filter

Experimental real-time optical correlator includes complex-valued holographic filter computed from one of two input scenes. Made more tolerant of errors in patterns to be recognized. Filter function essentially coded hologram computed by Burchhardt's method, in which complex value of each pixel of fast Fourier transform of image represented by three real, nonnegative numbers. In generating optical correlator according to method, phasor of each pixel in Fourier transform represented by intensities in three adjacent pixels.

Chao, Tien-Hsin↗
NASA NTRS1989

Some fast elliptic solvers on parallel architectures and their complexities

The discretization of separable elliptic partial differential equations leads to linear systems with special block triangular matrices. Several methods are known to solve these systems, the most general of which is the Block Cyclic Reduction (BCR) algorithm which handles equations with nonconsistant coefficients. A method was recently proposed to parallelize and vectorize BCR. Here, the mapping of BCR on distributed memory architectures is discussed, and its complexity is compared with that of other approaches, including the Alternating-Direction method. A fast parallel solver is also described, based on an explicit formula for the solution, which has parallel computational complexity lower than that of parallel BCR.

Gallopoulos, E.↗
NASA NTRS1989

Optimal Chebyshev polynomials on ellipses in the complex plane

The design of iterative schemes for sparse matrix computations often leads to constrained polynomial approximation problems on sets in the complex plane. For the case of ellipses, we introduce a new class of complex polynomials which are in general very good approximations to the best polynomials and even optimal in most cases.

Fischer, Bernd↗
NASA NTRS1991

Photosynthetic reaction center complexes from heliobacteria

The goal of this project is to understand the early evolutionary development of photosynthesis by examining the properties of reaction centers isolated from certain contemporary organisms that appear to contain the simplest photosynthetic reaction centers. The major focus of this project is the family of newly discovered strictly anaerobic photosynthetic organisms known as Heliobacteria. These organisms are the only known photosynthetic organisms that are grouped with the gram-positive phylum of bacteria. The properties of these reaction centers suggest that they might be the decendants of an ancestor that also gave rise to Photosystem 1 found in oxygen-evolving photosynthetic organisms. Photoactive reaction center-core antenna complexes have been isolated from the photosynthetic bacteria Heliobacillus mobilis and Heliobacterium gestii. The absorption and fluorescence properties of membranes and reaction centers are almost identical, suggesting that a single pigment-protein complex serves as both antenna and reaction center. Experiments in progress include sequence determination of the 48,000 Mr reaction center protein, and evolutionary comparisons with other reaction center proteins.

Trost, J. T.↗
NASA NTRS1991

Photosynthetic reaction center complexes from heliobacteria

Photosynthetic reaction centers are pigment-protein complexes that are responsible for the transduction of light energy into chemical energy. Considerable evidence indicates that photosynthetic organisms were present very early in the evolution of life on Earth. The goal of this project is to understand the early evolutionary development of photosynthesis by examining the properties of reaction centers isolated from certain contemporary organisms that appear to contain the simplest photosynthetic reaction centers. The major focus is on the family of newly discovered strictly anaerobic photosynthetic organisms that are grouped with the gram-positive phylum of bacteria. The properties of these reactions centers suggest that they may be the descendants of an ancestor that also gave rise to Photosystem 1 found in oxygen-evolving photosynthetic organisms. Photoactive reaction center-core antenna complexes were isolated from the photosynthetic bacteria, Heliobacillus mobilis and Heliobacterium gestii, by extraction of membranes with Deriphat 160C followed by differential centrifugation and sucrose density gradient centrifugation. Other aspects of this investigation are briefly discussed.

Trost, J. T.↗
NASA NTRS1991

Design of 3-dimensional complex airplane configurations with specified pressure distribution via optimization

A subcritical panel method applied to flow analysis and aerodynamic design of complex aircraft configurations is presented. The analysis method is based on linearized, compressible, subsonic flow equations and indirect Dirichlet boundary conditions. Quadratic dipol and linear source distribution on flat panels are applied. In the case of aerodynamic design, the geometry which minimizes differences between design and actual pressure distribution is found iteratively, using numerical optimization technique. Geometry modifications are modeled by surface transpiration concept. Constraints in respect to resulting geometry can be specified. A number of complex 3-dimensional design examples are presented. The software is adopted to personal computers, and as result an unexpected low cost of computations is obtained.

Kubrynski, Krzysztof↗