Search NASA⌕ Search

SEARCH · Search NASA

Results for “Rearrangement”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Systolic VLSI array for implementing the Kalman filter algorithm

A method and apparatus for processing signals representative of a complex matrix/vector equation. More particularly, signals representing an orderly sequence of the combined matrix and vector equation, known as a Kalman filter algorithm, are processed in real time in accordance with the principles of this invention. The Kalman filter algorithm is rearranged into a Faddeeva algorithm, which is a matrix-only algorithm that is modified to represent both the matrix and vector portions of the Kalman filter algorithm. The modified Faddeeva algorithm is embodied into electrical signals which are applied as inputs to a systolic array processor. The processor performs triangulation and nullification on the input signals, and delivers an output signal which is a real-time solution to the input signals.

Jaw J Chang↗
NASA NTRS1989

Design of laminated plates for maximum buckling load

The buckling load of laminated plates having midplane symmetry is maximized for a given total thickness. The thicknesses of the layers are taken as the design variables. Buckling analysis is carried out using the finite element method. The optimality equations are solved by a homotopy method which permits tracing optima as a function of total thickness. It is shown that for any design with a given stacking sequence of ply orientations, there exists a design associated with any other stacking sequence which possesses the same bending stiffness matrix and same total thickness. Hence, from the optimum design for a given stacking sequence, one can directly determine the optimum design for any rearrangement of the ply orientations, and the optimum buckling load is independent of the stacking sequence.

Shin, Yung S.↗
NASA NTRS1990

Search for resonances in positron-atom systems

No one likes to see a scattering cross section curve that is too smooth; it is much more interesting to find bumps and wiggles and most interesting if it is possible to understand their cause. Several types of resonances were clearly established in positron-containing systems: those lying just below a degenerate threshold (like 2s-2p in hydrogenic atoms or ions) and those representing Coulomb bound states in a rearranged channel (like Ps + H reversing positron +H(-)). Recently, two new sorts of resonances have been reported for which the resonant mechanism is not clear. The first is a very low lying resonance in the e-Ps system (obtained by an adiabatic expansion method), and the second is a similarly low lying two channel resonance in the positron -H system (obtained by a close-coupling technique.) These developments encouraged the examination of such systems using the standard methods of stabilization and complex rotation. Most of the results are negative; the low lying resonances in either system are verified. Some indication of new resonances in the e(+)-He(+) system is found; this may be caused by the attraction between Ps in the n=2 state and the He(++) nucleus.

Bhatia, A. K.↗
NASA NTRS1990

On the bonding of La(+) and La(2+) to C2H2, C2H4, and C3H6

The interaction of La(+) and La(2+) with C2H2, C2H4, and C3H6 is studied using electronic structure calculations that include correlation. The calculations show that the bonding in the dication is electrostatic in origin, and the computed binding energies are in good agreement with experiment. The La(+) forms two chemical bonds with the hydrocarbons. Since the pi bond is weaker for C2H2 than C2H4, the La(+)-C2H2 binding energy is larger than for La(+)-C2H4, LaC3H6(+) rearranges to yield a stronger bond than in LaC2H4(+) even though both hydrocarbons have a double bond.

Rosi, Marzio↗
NASA NTRS1990

Demand Assignment in the ACTS LBR System

On the Advanced Communications Technology Satellite (ACTS) being developed at NASA Lewis, low-burst-rate (LBR) traffic stations will access the ACTS multibeam package via two hopping beams that can be directed at certain areas in the continental U.S. An onboard baseband processor (BBP) demodulates uplink traffic, switches it between uplink and downlink beams at baseband, and then remodulates it for retransmission at 20 GHz. This study describes the demand-assigned operation of the ACTS LBR system, where the onboard switch is remote from both traffic stations and master control station (MCS). Network control uses inbound and outbound orderwire channels and a BBP control channel, allowing the MCS to coordinate assignment of individual 64-kb/s spacecraft channels. Models are developed to simulate the dynamics of the assignment process and verify the call blocking behavior, to predict control channel loads, and to evaluate algorithms for burst time plan rearrangement.

White, Lawrence W.↗
NASA NTRS1991

Processor Reformats Data For Transmission In Bursts

Data-processor-and-buffer electronic system receives audio signals digitized in first standard format at relatively low data rate, rearranges data for transmission in bursts in second standard format at relatively high rate, stores second-format bursts, and releases them at higher rate upon request. Conceived for asynchronous, one-way transmission of digitized speech in outer-space communications, concept of system applied in other digital communication systems in which data transmitted from low-rate sources to high-rate sinks not synchronized with sources.

Steele, Glen F.↗
NASA NTRS1990

A review of nonlinear constitutive models for metals

Over the past two decades a number of thermomechanical constitutive theories have been proposed for viscoplastic metals. These models are in most cases similar in that they utilize a set of internal state variables which provide locally averaged representations of microphysical phenomena such as dislocation rearrangement and grain boundary sliding. The state of development of several of these models is now at the point where accurate theoretical solutions can be obtained for a wide variety of structural problems at elevated temperatures. The fundamentals of viscoplasticity are briefly reviewed and a general framework is outlined. Several of the more prominent models are reviewed, and predictions from models are compared to experimental results.

Allen, David H.↗
NASA NTRS1989

Matrix isolation as a tool for studying interstellar chemical reactions

Since the identification of the OH radical as an interstellar species, over 50 molecular species were identified as interstellar denizens. While identification of new species appears straightforward, an explanation for their mechanisms of formation is not. Most astronomers concede that large bodies like interstellar dust grains are necessary for adsorption of molecules and their energies of reactions, but many of the mechanistic steps are unknown and speculative. It is proposed that data from matrix isolation experiments involving the reactions of refractory materials (especially C, Si, and Fe atoms and clusters) with small molecules (mainly H2, H2O, CO, CO2) are particularly applicable to explaining mechanistic details of likely interstellar chemical reactions. In many cases, matrix isolation techniques are the sole method of studying such reactions; also in many cases, complexations and bond rearrangements yield molecules never before observed. The study of these reactions thus provides a logical basis for the mechanisms of interstellar reactions. A list of reactions is presented that would simulate interstellar chemical reactions. These reactions were studied using FTIR-matrix isolation techniques.

Ball, David W.↗
NASA NTRS1991

High-temperature, flexible, thermal barrier seal

This device seals the sliding interfaces between structural panels that are roughly perpendicular to each other or whose edges are butted against one another. The nonuniformity of the gap between the panels requires significant flexibility along the seal length. The seal is mounted in a rectangular groove in a movable structural panel. A plurality of particles or balls is densely packed in an outer sheathing. The balls are laterally preloaded to maintain sealing contact with the adjacent wall using a pressurized linear bellows. Distortions in the adjacent panel are accommodated by rearrangement of the particles within the outer sheathing. Leakage through the seal is minimized by densely compacting the internal particles and by maintaining positive preload along the back side of the seal. The braid architecture of the outer sheathing is selected to minimize leakage through the seal and to resist mechanical abrasion.

Sirocky, Paul J.↗
NASA NTRS1990

Atomic-oxygen induced structural changes in polyphosphazene films and coatings

Various polymers were exposed to atomic oxygen O(3P) and comparisons made of their stability. The rates of reaction and mass removal for polyphosphazenes exposed to atomic oxygen were found to be significantly lower than for other polymers evaluated in this study. Surface analysis of polyphosphazene films indicated that O(3P) induces rearrangements in the phosphorus-nitrogen backbone of the polymer, resulting in cross-linking and cleavage of some pendant groups that are then replaced by oxygen.

Fewell, Larry L.↗
NASA NTRS1991

Theoretical study of the bonding of Sc, Y, and La singly charged and dipositive ions to C2H2, C2H4, and C3H6

The interaction of the Sc and Y singly-charged and dipositive ions with C2H2, C2H4, and C3H6 is studied using electronic structure calculations that include high levels of electron correlation. These results are compared with comparable calculations performed previously for La(+) and La(2+). For C2H2 and C2H4, all three metal ions insert into the C-C pi bond, making a three-membered ring. The optimal structures for the MC3H6(+) ions all involve rearrangement to make a four-membered ring. The strength of the metal-ligand bond for the singly charged ions follows the order La greater than Sc equal to about Y. In contrast, the bonds involving the dipositive ions are electrostatic, so that the binding energy increases as the size of the ion decreases, leading to the trend Sc greater than Y greater than La.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1991

Alteration of the UV-visible reflectance spectra of H2O ice by ion bombardment

Satellite in the Jovian and Saturnian system exhibit differences in reflectivity between their 'leading' and 'trailing' surfaces which can affect the local vapor pressure. Since these differences are thought to be due to differences in the flux of bombarding magnetospheric ions, the influence of ion impact on the UV-visible reflectance of water ice surfaces (20-90 K) by keV ion bombardment was studied. An observed decrease in reflectance in the UV is attributed to rearrangement processes that affect the physical microstructure and surface 'roughness'. The ratio in reflectance of bombarded to freshly deposited films is compared to the ratio of the reflectance of the leading and trailing hemispheres for Europa and Ganymede.

Sack, N. J.↗
NASA NTRS1992

Preventing Integrator Windup In A Control System

Design concept for control system addresses how to prevent control inputs to plant from exceeding electrical limits imposed by mechanical limits of control actuators in plant, and prevent windup in integrators in control system. Concept consists of two parts. First, to rearrange terms of control equation to move integrators into output path of control system. Second, involves limiting inputs to integrators when one control input of plant reaches its limit. Concept applicable to control systems typical of aircraft autopilot systems.

Kaminer, Isaac↗
NASA NTRS1991

Report on carbon and nitrogen abundance studies

The aim of the proposal was to determine the nitrogen to carbon abundance ratios from transition layer lines in stars with different T(sub eff) and luminosities. The equations which give the surface emission line fluxes and the measured ratio of the NV to CIV emission line fluxes are presented and explained. The abundance results are compared with those of photospheric abundance studies for stars in common with the photospheric investigations. The results show that the analyses are at least as accurate as the photospheric determinations. These studies can be extended to F and early G stars for which photospheric abundance determinations for giants are hard to do because molecular bands become too weak. The abundance determination in the context of stellar evolution is addressed. The N/C abundance ratio increases steeply at the point of evolution for which the convection zone reaches deepest. Looking at the evolution of the rotation velocities v sin i, a steep decrease in v sin i is related to the increasing depth of the convection zone. It is concluded that the decrease in v sin i for T(sub eff) less than or approximately = 5800 K is most probably due to the rearrangement of the angular momentum in the stars due to deep convective mixing. It appears that the convection zone is rotating with nearly depth independent angular momentum. Other research results and ongoing projects are discussed.

Boehm-Vitense, Erika↗
NASA NTRS1991

Carbohydrates as a source of energy and matter for the origin of life

Recently, we proposed a new model of early glycolysis in which the oxidation of glyceraldehyde self-hemiacetals yielded energy rich polyglyceric acid instead of energy rich thioesters. In this model, polyglyceric acid not only acts as an energy source for phosphoanhydride synthesis, but also as an autocatalyst that can replicate the sequence of D and L residues in its structure. We began our investigation of this new hypothesis - the triose model - by developing a thermal method for the racemization-free synthesis of polyglyceric acid. The hydrolytic stability and the role of chirality in interactions of polyglyceric acid were studied using this thermal polymer. Next, we established that the 2- and 3-glycerol esters of polyglyceric acid are energy rich by measuring the Gibbs free energy change of hydrolysis of the 2- and 3-glycerol esters of 2 and 3-O-L glyceroyl-glyceric acid methyl ester - a model of polyglyceric acid. Recently, we discovered that glyceraldehyde is bound and oxidized to glyceric acid on the surface of ferric hydroxide and that soluble ferric ion catalyzes the rearrangement of glyceraldehyde to lactic acid. We are exploring the possibility that these reactions could yield polyglyceric acid and polylactic acid under plausible prebiotic conditions.

Weber, A. L.↗
NASA NTRS1992

Microgravity vestibular investigations (10-IML-1)

Our perception of how we are oriented in space is dependent on the interaction of virtually every sensory system. For example, to move about in our environment we integrate inputs in our brain from visual, haptic (kinesthetic, proprioceptive, and cutaneous), auditory systems, and labyrinths. In addition to this multimodal system for orientation, our expectations about the direction and speed of our chosen movement are also important. Changes in our environment and the way we interact with the new stimuli will result in a different interpretation by the nervous system of the incoming sensory information. We will adapt to the change in appropriate ways. Because our orientation system is adaptable and complex, it is often difficult to trace a response or change in behavior to any one source of information in this synergistic orientation system. However, with a carefully designed investigation, it is possible to measure signals at the appropriate level of response (both electrophysiological and perceptual) and determine the effect that stimulus rearrangement has on our sense of orientation. The environment of orbital flight represents the stimulus arrangement that is our immediate concern. The Microgravity Vestibular Investigations (MVI) represent a group of experiments designed to investigate the effects of orbital flight and a return to Earth on our orientation system.

Reschke, Millard F.↗
NASA NTRS1991

Clathrate hydrate formation in amorphous cometary ice analogs in vacuo

Experiments conducted in clathrate hydrates with a modified electron microscope have demonstrated the possibility of such compounds' formation during the warming of vapor-deposited amorphous ices in vacuo, through rearrangements in the solid state. Subsolidus crystallization of compositionally complex amorphous ices may therefore be a general and ubiquitous process. Phase separations and microporous textures thus formed may be able to account for such anomalous cometary phenomena as the release of gas at large radial distances from the sun and the retention of volatiles to elevated temperatures.

Blake, David↗
NASA NTRS1992

Evaluation of tests for vestibular function

Vestibular testing methodologies are examined in terms of their clinical value and applicability to the assessment of astronaut candidates and human responses to microgravity. Classical and novel testing approaches are examined in terms of nine functions such as otolith organs, vestibular neural processing, and ocular motor systems. The tests reviewed include the basic vestibular-function test battery, postural stability testing, visual-vestibular interaction, reactions to off-axis rotation, and vestibular evoked responses. The basic test battery is shown to be essential for astronaut and inertial-environment baseline-data evaluations, whereas the newer and research tests are only recommended in special cases. Stimulus rearrangement and motion-sickness tests are indicated for testing adaptation to inertial environments. Postural stability and visual-vestibular interaction are recommended for evaluating one's suitability for being an astronaut.

Source record↗