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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Segmental relaxation of sequence defined polymers

For this work, the dynamical behavior of sequence defined polymers, P(C n EG 4 ), was studied using dielectric spectroscopy showing one segmental relaxation in addition to a secondary relaxation. In case of segmental relaxation, the relaxation times strongly depend on the molecular weight at low temperatures, while at higher temperatures, unlike to linear homo polymers, this effect levels out. With increasing length of C-units, the segmental relaxation accelerates. This is also reflected in the glass transition temperature, extracted from dielectric spectroscopy. With increasing length of C-units the glass transition temperature decreases, compatible with the accelerated segmental relaxation.

36 MATERIALS SCIENCE↗
NASA NTRS1984

The influence of rat suspension-hypokinesia on the gastrocnemius muscle

Hind-limb hypokinesia was induced in rats by the Morey method to characterize the response of the gastrocnemius muscle. A comparison of rats suspended for 2 weeks with weight, sex, and litter-matched control rats indicate no difference in gastrocnemius wet weight, contraction, or one-half relaxation times, but less contractile function as indicated by lowered dP/dt. Myosin ATPase staining identified uniform Type I (slow-twitch) and II (fast-twitch) atrophy in the muscles from 4 of 10 rats suspended for 2 weeks and 1 of 12 rats suspended for 4 weeks; muscles from three other rats of the 4-week group displayed greater Type I atrophy. Other histochemical changes were characteristic of a neuropathy. These data together with recently acquired soleus data (29) indicate the Morey model, like space flight, evokes greater changes in the Type I or slow twitch fibers of the gastrocnemius and soleus muscles.

Templeton, G. H.↗
NASA NTRS1991

A graph theoretic approach to scene matching

The ability to match two scenes is a fundamental requirement in a variety of computer vision tasks. A graph theoretic approach to inexact scene matching is presented which is useful in dealing with problems due to imperfect image segmentation. A scene is described by a set of graphs, with nodes representing objects and arcs representing relationships between objects. Each node has a set of values representing the relations between pairs of objects, such as angle, adjacency, or distance. With this method of scene representation, the task in scene matching is to match two sets of graphs. Because of segmentation errors, variations in camera angle, illumination, and other conditions, an exact match between the sets of observed and stored graphs is usually not possible. In the developed approach, the problem is represented as an association graph, in which each node represents a possible mapping of an observed region to a stored object, and each arc represents the compatibility of two mappings. Nodes and arcs have weights indicating the merit or a region-object mapping and the degree of compatibility between two mappings. A match between the two graphs corresponds to a clique, or fully connected subgraph, in the association graph. The task is to find the clique that represents the best match. Fuzzy relaxation is used to update the node weights using the contextual information contained in the arcs and neighboring nodes. This simplifies the evaluation of cliques. A method of handling oversegmentation and undersegmentation problems is also presented. The approach is tested with a set of realistic images which exhibit many types of sementation errors.

Ranganath, Heggere S.↗
NASA NTRS2000

High Order Discontinuous Gelerkin Methods for Convection Dominated Problems with Application to Aeroacoustics

This project is about the investigation of the development of the discontinuous Galerkin finite element methods, for general geometry and triangulations, for solving convection dominated problems, with applications to aeroacoustics. On the analysis side, we have studied the efficient and stable discontinuous Galerkin framework for small second derivative terms, for example in Navier-Stokes equations, and also for related equations such as the Hamilton-Jacobi equations. This is a truly local discontinuous formulation where derivatives are considered as new variables. On the applied side, we have implemented and tested the efficiency of different approaches numerically. Related issues in high order ENO and WENO finite difference methods and spectral methods have also been investigated. Jointly with Hu, we have presented a discontinuous Galerkin finite element method for solving the nonlinear Hamilton-Jacobi equations. This method is based on the RungeKutta discontinuous Galerkin finite element method for solving conservation laws. The method has the flexibility of treating complicated geometry by using arbitrary triangulation, can achieve high order accuracy with a local, compact stencil, and are suited for efficient parallel implementation. One and two dimensional numerical examples are given to illustrate the capability of the method. Jointly with Hu, we have constructed third and fourth order WENO schemes on two dimensional unstructured meshes (triangles) in the finite volume formulation. The third order schemes are based on a combination of linear polynomials with nonlinear weights, and the fourth order schemes are based on combination of quadratic polynomials with nonlinear weights. We have addressed several difficult issues associated with high order WENO schemes on unstructured mesh, including the choice of linear and nonlinear weights, what to do with negative weights, etc. Numerical examples are shown to demonstrate the accuracies and robustness of the methods for shock calculations. Jointly with P. Montarnal, we have used a recently developed energy relaxation theory by Coquel and Perthame and high order weighted essentially non-oscillatory (WENO) schemes to simulate the Euler equations of real gas. The main idea is an energy decomposition under the form epsilon = epsilon(sub 1) + epsilon(sub 2), where epsilon(sub 1) is associated with a simpler pressure law (gamma)-law in this paper) and the nonlinear deviation epsilon(sub 2) is convected with the flow. A relaxation process is performed for each time step to ensure that the original pressure law is satisfied. The necessary characteristic decomposition for the high order WENO schemes is performed on the characteristic fields based on the epsilon(sub l) gamma-law. The algorithm only calls for the original pressure law once per grid point per time step, without the need to compute its derivatives or any Riemann solvers. Both one and two dimensional numerical examples are shown to illustrate the effectiveness of this approach.

Shu, Chi-Wang↗
NASA NTRS1984

Influence of suspension hypokinesia on rat soleus muscle

Hindlimb hypokinesia was induced in rats by the Morey method to characterize the response of the soleus muscle. Rats suspended for 1-4 wk exhibited continuous and significant declines in soleus mass, function, and contractile duration. Soleus speeding was in part explained by an alteration in fiber type. The normal incidence of 70-90 percent type I fibers in the soleus muscle was reduced after 4 wk of suspension to 50 percent or less in 9 of 11 rats. A significant decline in type I myosin isozyme content occurred without a change in that of type II. Other observed histochemical changes were characteristic of denervation. Consistent with soleus atrophy, there was a significant increase in lysosomal (acid) protease activity. One week of recovery after a 2-wk suspension was characterized by a return to values not significantly different from control for muscle wet weights, peak contraction force, one-half relaxation time, and type I myosin. Persistent differences from control were observed in maximal rate of tension development, contraction time, and denervation-like changes.

Templeton, G. H.↗
NASA NTRS1997

Correlation of Chemical and Physical Test Data For the Environment Ageing of Coflon (PVDF)

This report aims to identify correlations between mechanical property changes and chemical/morphological structure changes for Coflon. It is intended both to illustrate the overall methodology and to indicate the testing that needs to be undertaken in order to obtain correlations. Many fluid exposures have now been carried out on Coflon during the project and many data generated as a result. The report summarises the changes observed in mechanical and physical properties and relates these as well as possible to the chemistry thought to be occurring during ageing. For this purpose, data have been collated from already-issued MERL and TRI technical and progress reports. Most of the mechanical testing of aged testpieces has been performed soon after the completion of the exposure; however, there is of necessity a delay in obtaining chemical analysis of the same testpieces, so that more physical than chemical data are shown. Three fluids have so far caused measurable deterioration of Coflon, these being: methanol (Fluid A), a methanol and amine mixture (Fluid G), and a mixture of methane, carbon dioxide gas and hydrogen sulphide gas plus aqueous amine (Fluid F). Only the effects of these fluids will be dealt with in any detail in this report, although other fluids are assessed to give relevant background information. Relevant test data collated here include: tensile modulus and related properties, mode of sample failure at break, fracture toughness, fatigue crack growth rate and resistance, stress relaxation rate, permeation coefficients, % crystallinity and molecular weight distributions together with changes in fluorine levels, and other observations where appropriate. However, not all of these were obtained for every ageing condition. Because of the wide range of tests employed, and the different ways in which their results are obtained, the following section has been included to serve as a background for making comparisons.

Morgan, G. J.↗
NASA NTRS2001

Viscosity Relaxation in Molten HgZnTe

Rotating cup measurements of the viscosity of the pseudo-binary melt, HgZnTe have shown that the isothermal liquid with zinc mole fraction 0.16 requires tens of hours of equilibration time before a steady viscous state can be achieved. Over this relaxation period, the viscosity at 790 C increases by a factor of two, while the viscosity at 810 C increases by 40%. Noting that the Group VI elements tend to polymerize when molten, we suggest that the viscosity of the melt is enhanced by the slow formation of Te atom chains. To explain the build-up of linear Te n-mers, we propose a scheme, which contains formation reactions with second order kinetics that increase the molecular weight, and decomposition reactions with first order kinetics that inactivate the chains. The resulting rate equations can be solved for the time dependence of each molecular weight fraction. Using these molecular weight fractions, we calculate the time dependence of the average molecular weight. Using the standard semi-empirical relation between polymer average molecular weight and viscosity, we then calculate the viscosity relaxation curve. By curve fitting, we find that the data imply that the rate constant for n-mer formation is much smaller than the rate constant for n-mer deactivation, suggesting that Te atoms only weakly polymerize in molten HgZnTe. The steady state toward which the melt relaxes occurs as the rate of formation of an n-mer becomes exactly balanced by the sum of the rate for its deactivation and the rate for its polymerization to form an (n+1)-mer.

Su, Ching-Hua↗
NASA NTRS1998

Real Gas Computation Using an Energy Relaxation Method and High-Order WENO Schemes

In this paper, we use a recently developed energy relaxation theory by Coquel and Perthame and high order weighted essentially non-oscillatory (WENO) schemes to simulate the Euler equations of real gas. The main idea is an energy decomposition into two parts: one part is associated with a simpler pressure law and the other part (the nonlinear deviation) is convected with the flow. A relaxation process is performed for each time step to ensure that the original pressure law is satisfied. The necessary characteristic decomposition for the high order WENO schemes is performed on the characteristic fields based on the first part. The algorithm only calls for the original pressure law once per grid point per time step, without the need to compute its derivatives or any Riemann solvers. Both one and two dimensional numerical examples are shown to illustrate the effectiveness of this approach.

Montarnal, Philippe↗
NASA NTRS1993

National Launch System: Structures and materials

The National Launch System provides an opportunity to realize the potential of Al-Li. Advanced structures can reduce weights by 5-40 percent as well as relax propulsion system performance specifications and reduce requirements for labor and materials. The effect on costs will be substantial. Advanced assembly and process control technologies also offer the potential for greatly reduced labor during the manufacturing and inspection processes. Current practices are very labor-intensive and, as a result, labor costs far outweigh material costs for operational space transportation systems. The technological readiness of new structural materials depends on their commercial availability, producibility and materials properties. Martin Marietta is vigorously pursuing the development of its Weldalite 049 Al-Li alloys in each of these areas. Martin Marietta is also preparing to test an automated work cell concept that it has developed using discrete event simulation.

Bunting, Jack O.↗
DOE OSTI2022

Joule heating in bad and slow metals

Heat supplied to a metal is absorbed by the electrons and then transferred to the lattice. In conventional metals energy is released to the lattice by phonons emitted from the Lindhard continuum. However in a 'bad' metal, with short mean free path, the low energy Lindhard continuum is destroyed. To describe energy transfer to the lattice in these cases we obtain a general Kubo formula for the energy relaxation rate in terms of the electronic density spectral weight \text{lm} \, G^R_{nn}(\omega_{k},k) lm G n n R ( ω k , k ) evaluated on the phonon dispersion \omega_k ω k . We apply our Kubo formula to the high temperature Hubbard model, using recent data from quantum Monte Carlo and experiments in ultracold atoms to characterize \text{lm} \, G^R_{nn}(\omega_{k},k) lm G n n R ( ω k , k ) . We furthermore use recent data from electron energy-loss spectroscopy to estimate the energy relaxation rate of the cuprate strange metal to a high energy optical phonon. As a second, distinct, application of our formalism we consider 'slow' metals. These are defined to have Fermi velocity less than the sound velocity, so that particle-hole pairs are kinematically unable to emit phonons. We obtain an expression for the energy relaxation rate of a slow metal in terms of the optical conductivity.

36 MATERIALS SCIENCE↗
NASA NTRS2022

Epoxy Resins with Reduced Viscoelastic Relaxation

The payloads of current space launch systems, e.g. rockets, are constrained to a small size due to aerodynamic, weight, and cost limitations. Deployable structures allow for a folded or stowed configuration during launch and deployment at the mission location. Polymer composites have shown both high weight savings over current metallic structure, as well as improved specific mechanical strengths overall. One issue encountered with polymer composite deployables, however, is stress relaxation of the polymer matrix in the stowed configuration. In this study, a range of different epoxy formulations were evaluated as potential matrix resins for deployable composites. A new multifunctional epoxy resin with a fortifying additive is predicted to show 70% less stress relaxation after 1 year as compared to a state-of-the-art aerospace epoxy matrix.

Ray S. Peterson↗
NASA NTRS1976

A summary of the application of active controls technology in the ATT system studies

The application of active controls technology to subsonic, long-range transport aircraft was investigated in three Advanced Transport Technology system studies. Relaxed stability requirements, maneuver and gust load alleviation, and active flutter suppression were the concepts considered. A different configuration was investigated for each of the three airframe manufacturers, and each had a somewhat different approach to the application of active controls technology. Consequently, the results varied in magnitude between the contractors, but several trends were noted. Relaxed stability requirements resulted in the largest benefits - reduced weight, increased return on investment, and decreased direct operating costs. Maneuver load alleviation, gust load alleviation, and flutter suppression resulted in much smaller benefits. Prior to application of active controls technology, a research and development program directed toward fulfilling data base requirements, establishing effective design techniques and criteria, improving systems maintainability and reliability, and demonstrating technology readiness must be completed.

Hood, R. V.↗
DOE OSTI2026

Dataset_for_Molecular_Motion_Below_the_Glass_Transition_A_Solid-State_NMR_Study_of_Siloxane_Polymer_Dynamics Study

This dataset contains solid-state 1H and 13C NMR relaxometry data, differential scanning calorimetry (DSC) data, and size exclusion chromatography (SEC/GPC) data supporting the study of sub-glass-transition (sub-Tg) molecular dynamics in a composition- and sequence-controlled series of diphenyl-substituted polysiloxanes (PDMS, 14Ph, 33Ph, 50Ph, 67Ph, and 100Ph; 0–100% diphenylsiloxane content by mole).All solid-state NMR data were acquired on a 200 MHz Bruker Avance III HD spectrometer using a static 7 mm HX probe or a 4 mm HX probe under 4 kHz magic-angle spinning. Raw Bruker TopSpin experiment folders are included for: (1) variable-temperature 1H lineshape measurements used to determine linewidth (FWHM) as a function of temperature across the glass transition; (2) 1H T1 (saturation recovery with solid-echo detection), probing nanosecond-scale dynamics near the 1H Larmor frequency; (3) 1H T1rho (direct spin-lock, 62.5 kHz), probing microsecond-scale segmental dynamics; (4) 13C-detected Lee–Goldburg cross-polarization 1H T1rho (LGCPH T1rho) for 33Ph and 50Ph, resolving aromatic and aliphatic proton environments; and (5) 13C T1 relaxation for 33Ph and 50Ph. Differential scanning calorimetry data (TA Instruments DSC 25, −150 to +120 °C, up to +300 °C for 100Ph, 10 °C/min) are included for all six compositions and support the glass-transition temperatures in Table 1 and Figure 1. Size exclusion chromatography data (Agilent 1200 Series, PL-Gel 300 mixed-C column, THF mobile phase, polystyrene calibration standards) are included for the three synthesized copolymers (33Ph, 50Ph, 67Ph) and support the number-average molecular weights in Table 1. Processed data include per-composition relaxation-time summaries (Excel), curve-fitting and Bloembergen-Purcell-Pound (BPP) model analysis notebooks (Jupyter/Python), and Igor Pro (.pxp) master files used to generate the manuscript's figures.

Bloembergen-Purcell-Pound theory↗
NASA NTRS1981

On the accuracy of pixel relaxation labeling

An analysis of pixel labeling by probabilistic relaxation techniques is presented to demonstrate that these labeling procedures degenerate to weighted averages in the vicinity of fixed points. A consequence of this is that undesired label conversions can occur, leading to a deterioration of labeling accuracy at a stage after an improvement has already been achieved. Means for overcoming the accuracy deterioration are suggested and used as the basis for a possible design strategy for using probabilistic relaxation procedures. The results obtained are illustrated using simple data sets in which labeling on individual pixels can be examined and also using Landsat imagery to show application to data typical of that encountered in remote sensing applications.

Richards, J. A.↗
NASA NTRS1976

NASA's present and future sensor technology developments

NASA's overall sensing, data acquisition, and instrumentation programs are reviewed. The review shows that the trends in advanced sensor technology involve increased use of solid-state sensors, multiapplication sensors, standardized instrumentation, and miniaturized detectors. Examples are given of several new technologies, showing how improvements in sensor operational capability (such as enhanced sensitivity and spectral range) derived from these advances have resulted in relaxed spacecraft stability requirements, mission time savings, and savings in weight, size, and power. The introduction of multiapplication sensors and standardized instrumentation will result in measurement cost reduction and improved compatibility with standardized spacecraft.

Rubin, B.↗
NASA NTRS1989

An improved algorithm for optimum structural design with multiple frequency constraints

An optimality criterion (OC) method for minimum-weight design of structures having multiple constraints on natural frequencies is presented. In this work a new resizing strategy is developed based on relaxation techniques. A computationally adaptive control parameter is used in conjunction with existing OC recursive formulae to promote convergence of optimum structural designs. Some considerations regarding the coupling of the modified Aitken accelerator with the OC method are discussed. Improved and rapidly converged minimum-weight designs are obtained when using an under-relaxed recursive scheme combined with the modified Aitken accelerator.

Mcgee, Oliver G.↗