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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 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Discerning the thermodynamic feasibility of the spontaneous coexistence of multiple functional vegetation groups

Can the Second Law of Thermodynamics explain why ecosystems naturally organize into a complex structure composed of multiple vegetation species and functional groups? Ecosystem structure, which refers to the number and type of plant functional groups, is the result of self-organization, or the spontaneous emergence of order from random fluctuations. By considering ecosystems as open thermodynamic systems, we model and study these fluctuations of throughput signatures on short timescales to determine the drivers and characteristics of ecosystem structure. This diagnostic approach allows us to use fluxes of energy and entropy to calculate an ecosystem’s estimated work and understand the thermodynamic behavior of the system. We use a multi-layer canopy-root-soil model to calculate the energy and entropy fluxes of different scenarios for field sites across various climates. At each site, scenarios comprised of native individual plant functional groups and a coexisting multi-group composition scenario including all functional groups observed at the site are compared. Ecosystem-scale calculations demonstrate that entropy fluxes and work efficiency—the work performed for the amount of radiation entering the ecosystem—are greatest in the multi-group scenario when its leaf area is significantly larger than each of its individual functional groups. Thus, we conclude that ecosystems self-organize towards the vegetation structure with the greatest outgoing entropy flux and work efficiency, resulting in the coexistence of multiple functional groups and performing the maximum amount of work within the constraints of locally available energy, water, and nutrients.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1987

Maximum Entropy/Optimal Projection (MEOP) control design synthesis: Optimal quantification of the major design tradeoffs

The underlying philosophy and motivation of the optimal projection/maximum entropy (OP/ME) stochastic modeling and reduced control design methodology for high order systems with parameter uncertainties are discussed. The OP/ME design equations for reduced-order dynamic compensation including the effect of parameter uncertainties are reviewed. The application of the methodology to several Large Space Structures (LSS) problems of representative complexity is illustrated.

Hyland, D. C.↗
DOE OSTI2016

SU-F-R-45: The Prognostic Value of Radiotherapy Based On the Changes of Texture Features Between Pre-Treatment and Post-Treatment FDG PET Image for NSCLC Patients

Purpose: The purpose of this research is investigating which texture features extracted from FDG-PET images by gray-level co-occurrence matrix(GLCM) have a higher prognostic value than the other texture features. Methods: 21 non-small cell lung cancer(NSCLC) patients were approved in the study. Patients underwent 18F-FDG PET/CT scans with both pre-treatment and post-treatment. Firstly, the tumors were extracted by our house developed software. Secondly, the clinical features including the maximum SUV and tumor volume were extracted by MIM vista software, and texture features including angular second moment, contrast, inverse different moment, entropy and correlation were extracted using MATLAB.The differences can be calculated by using post-treatment features to subtract pre-treatment features. Finally, the SPSS software was used to get the Pearson correlation coefficients and Spearman rank correlation coefficients between the change ratios of texture features and change ratios of clinical features. Results: The Pearson and Spearman rank correlation coefficient between contrast and SUV maximum is 0.785 and 0.709. The P and S value between inverse difference moment and tumor volume is 0.953 and 0.942. Conclusion: This preliminary study showed that the relationships between different texture features and the same clinical feature are different. Finding the prognostic value of contrast and inverse difference moment were higher than the other three textures extracted by GLCM.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2011

Thermodynamic functions of degenerate magnetized electron gas

The Fermi energy, pressure, internal energy, entropy, and heat capacity of completely degenerate relativistic electron gas are calculated by numerical methods. It is shown that the maximum admissible magnetic field on the order of 10{sup 9} G in white dwarfs increases the pressure by a factor of 1.06 in the central region, where the electron concentration is {approx}10{sup 33} cm{sup -3}, while the equilibrium radius increases by approximately a factor of 1.03, which obviously cannot be observed experimentally. A magnetic field of {approx}10{sup 8} G or lower has no effect on the pressure and other thermodynamic functions. It is also shown that the contribution of degenerate electron gas to the total pressure in neutron stars is negligible compared to that of neutron gas even in magnetic fields with a maximum induction {approx}10{sup 17} G possible in neutron stars. The neutron beta-decay forbiddeness conditions in a superstrong magnetic field are formulated. It is assumed that small neutron stars have such magnetic fields and that pulsars with small periods are the most probable objects that can have super-strong magnetic fields.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Magnetocaloric Effect in BiFe{sub 1−x}Zn{sub x}O{sub 3} Multiferroics

Ceramic BiFe{sub 1−x}Zn{sub x}O{sub 3} multiferroic samples were prepared by the solid combustion method for x = 0.1, 0.15, and 0.2. Structural, magnetic, and magnetocaloric properties of the multiferroics have been studied. For all samples, an antiferromagnetic phase transition is observed in the region of 630 K. With increase in x, the reduction in magnitude of magnetization and Neel temperature is observed. The magnetocaloric properties, entropy, relative cooling power, and heat capacity have been calculated within the framework of thermodynamic theory. It has been established that the maximum changes of magnetocaloric properties of multiferroics are observed in the region of magnetic phase transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1990

Turbulence measurements and noise generation in a transonic cryogenic wind tunnel

A high-frequency combination probe was used to measure dynamic flow quality in the test section of the NASA Langley 0.3-m Transonic Cryogenic Tunnel. The probe measures fluctuating stagnation (total) temperature and pressure, static pressure, and flow angles in two orthogonal planes. Simultaneous measurements of unsteady total temperature and pressure were also made in the settling chamber of the tunnel. The data show that the stagnation temperature fluctuations remain constant, and the stagnation pressure fluctuations increase by a factor of two, as the flow accelerates from the settling chamber to the test section. In the test section, the maximum rms value of the normalized fluctuating velocity is 0.7 percent. Correlation coefficients failed to show vorticity, entropy, or sound as the dominant mode of turbulence in the tunnel.

Ng, W. F.↗
DOE OSTI2015

Table-like magnetocaloric effect in Gd{sub 56}Ni{sub 15}Al{sub 27}Zr{sub 2} alloy and its field independence feature

In order to obtain “table-like” magnetocaloric effect (MCE), multiple-phase Gd{sub 56}Ni{sub 15}Al{sub 27}Zr{sub 2} alloy was prepared by arc-melting followed by suck-casting method. Powder x-ray diffraction and calorimetric measurements reveal that the sample contains both glassy and crystalline phases. The fraction of the glassy phase is about 62%, estimated from the heat enthalpy of the crystallization. The crystalline phases, Gd{sub 2}Al and GdNiAl further broadened the relatively wider magnetic entropy change (−ΔS{sub M}) peak of the amorphous phase, which resulted in the table-like MCE over a maximum temperature range of 52.5 K to 77.5 K. The plateau feature of the MCE was found to be nearly independent of the applied magnetic field from 3 T to 5 T. The maximum −ΔS{sub M} value of the MCE platforms is 6.0 J/kg K under applied magnetic field change of 5 T. Below 3 T, the field independence of the table-like feature disappears. The relatively large constant values of −ΔS{sub M} for the respective applied magnetic fields have promising applications in magnetic refrigeration using regenerative Ericsson cycle.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Optimation of cooled shields in insulations

A method to optimize the location, temperature, and heat dissipation rate of each cooled shield inside an insulation layer was developed. The method is based on the minimization of the entropy production rate which is proportional to the heat leak across the insulation. It is shown that the maximum number of shields to be used in most practical applications is three. However, cooled shields are useful only at low values of the overall, cold wall to hot wall absolute temperature ratio. The performance of the insulation system is relatively insensitive to deviations from the optimum values of the temperature and location of the cooling shields. Design curves for rapid estimates of the locations and temperatures of cooling shields in various types of insulations, and an equation for calculating the cooling loads for the shields are presented.

Chato, J. C.↗
DOE OSTI2014

Partial Spin Ordering and Complex Magnetic Structure in BaYFeO4: A Neutron Diffraction and High Temperature Susceptibility Study

The novel iron-based compound, BaYFeO4, crystallizes in the Pnma space group with two distinct Fe3+ sites, that are alternately corner-shared [FeO5]7 square pyramids and [FeO6]9 octahedra, forming into [Fe4O18]24 rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of shortrange magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and hightemperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, 1/3), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, 0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe3+ are only of the order 3.0 B, smaller than the expected values near 4.5 B, indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at 550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the observed complex magnetic structure.

Thompson, Corey↗
DOE OSTI2014

Magnetic and magnetocaloric properties of La{sub 0.85}(Na{sub 1−x}K{sub x}){sub 0.15}MnO{sub 3} ceramics produced by reactive spark plasma sintering

La{sub 0.85}(Na{sub 1−x}K{sub x}){sub 0.15}MnO{sub 3} (0 ≤ x ≤ 1) ceramics were synthesized from the raw La(OH){sub 3}, NaOH, KOH, and MnO{sub 2} powders using Reactive Spark Plasma Sintering. All the compounds were obtained as pure, dense, and ultrafine grained pellets. The Rietveld refinement of the X-Ray powder diffraction shows that all our synthesized samples are single phase and crystallize in the distorted rhombohedral system with R-3c space group. The thermal variation of their magnetization under a magnetic applied field of 50 mT shows a paramagnetic to ferromagnetic transition at a Curie temperature very close to room temperature. The magnetic entropy change, deduced from magnetization measurements versus magnetic applied field up to 5 T at several temperatures exhibits a maximum |ΔS{sub M}|{sub max} which slightly increases with increasing K content. The relative cooling power values, inferred from the |ΔS{sub M}| vs T peak broadening, vary slightly with the potassium content, reaching, values between 316 and 289 Jkg{sup −1}, in an applied magnetic field of 5 T, when x increases from 0 to 1. Technically, these large values make the prepared materials very promising for domestic magnetic refrigeration.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1993

Entropy and climate. I - ERBE observations of the entropy production of the earth

An approximate method for estimating the global distributions of the entropy fluxes flowing through the upper boundary of the climate system is introduced, and an estimate of the entropy exchange between the earth and space and the entropy production of the planet is provided. Entropy fluxes calculated from the Earth Radiation Budget Experiment measurements show how the long-wave entropy flux densities dominate the total entropy fluxes at all latitudes compared with the entropy flux densities associated with reflected sunlight, although the short-wave flux densities are important in the context of clear sky-cloudy sky net entropy flux differences. It is suggested that the entropy production of the planet is both constant for the 36 months of data considered and very near its maximum possible value. The mean value of this production is 0.68 x 10 exp 15 W/K, and the amplitude of the annual cycle is approximately 1 to 2 percent of this value.

Stephens, G. L.↗
NASA NTRS1994

Energy and maximum norm estimates for nonlinear conservation laws

We have devised a technique that makes it possible to obtain energy estimates for initial-boundary value problems for nonlinear conservation laws. The two major tools to achieve the energy estimates are a certain splitting of the flux vector derivative f(u)(sub x), and a structural hypothesis, referred to as a cone condition, on the flux vector f(u). These hypotheses are fulfilled for many equations that occur in practice, such as the Euler equations of gas dynamics. It should be noted that the energy estimates are obtained without any assumptions on the gradient of the solution u. The results extend to weak solutions that are obtained as point wise limits of vanishing viscosity solutions. As a byproduct we obtain explicit expressions for the entropy function and the entropy flux of symmetrizable systems of conservation laws. Under certain circumstances the proposed technique can be applied repeatedly so as to yield estimates in the maximum norm.

Olsson, Pelle↗
DOE OSTI2021

Structure-property correlations and scaling in the magnetic and magnetocaloric properties of GdCrO 3 particles

The structure, magnetic, and magnetocaloric (MC) properties of orthorhombic nanocrystalline GdCrO 3 with six particle sizes: < d > = 87, 103, 145, 224, 318, and 352 nm are reported. The particle size was tailored by annealing under different temperatures and estimated by scanning electron microscopy. With increase in < d >, Goldschmidt tolerance factor t, orthorhombic strain s, and out-of-plane Cr–O 1 –Cr bond angle first decrease, reaching minimum values for < d > = 224 nm, and then increase for sample with < d > = 318 nm and 352 nm, thus showing a V-shaped variation. Temperature dependence of the magnetization (M) reveals an antiferromagnetic transition at ${T}_{\text{N}}^{\text{Cr}}\sim 168$ K for < d > ≥ 224 nm and ${T}_{\text{N}}^{\text{Cr}}\sim 167$ K for < d > < 224 nm and an essentially d-independent spin-reorientation at T SR = 9 K. M measured at 5 K and 7 T first increases with increase in < d >, reaching maximum value for sample with < d > = 224 nm, and then decreases for samples with < d > = 318 nm and 352 nm, showing an inverted-V variation with < d >. Similar < d >-dependence is observed for the magnetic entropy change (MEC) and relative cooling power (RCP) showing a close relationship between the structural and magnetic properties of GdCrO 3 nanoparticles investigated here. The 224 nm sample with the minimum values of t, s, and Cr–O 1 –Cr bond angle exhibits the maximum value of MEC (–ΔS) = 37.8 J kg –1 K –1 at 5 K under a field variation (ΔH) of 7 T and its large estimated RCP of 623.6 J Kg –1 is comparable with those of typical MC materials. Both (–ΔS) and RCP are shown to scale with the saturation magnetization MS, suggesting that MS is the crucial factor controlling their magnitudes. Assuming (–ΔS) ~ (ΔH) n , the temperature dependence of n for the six samples are determined, n varying between 1.3 at 5 K to n = 2.2 at 130 K in line with its expected magnitudes based on mean-field theory. Furthermore, these results on structure-property correlations and scaling in GdCrO 3 suggest that its MC properties are tunable for potential low-temperature magnetic refrigeration applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Quantum and Classical Ergotropy from Relative Entropies

The quantum ergotropy quantifies the maximal amount of work that can be extracted from a quantum state without changing its entropy. Given that the ergotropy can be expressed as the difference of quantum and classical relative entropies of the quantum state with respect to the thermal state, we define the classical ergotropy, which quantifies how much work can be extracted from distributions that are inhomogeneous on the energy surfaces. A unified approach to treat both quantum as well as classical scenarios is provided by geometric quantum mechanics, for which we define the geometric relative entropy. The analysis is concluded with an application of the conceptual insight to conditional thermal states, and the correspondingly tightened maximum work theorem.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Magnetocaloric effect in manganites

The magnetocaloric effect (MCE) in La{sub 1-x}Sr{sub x}MnO{sub 3}, Sm{sub 0.55}Sr{sub 0.45}MnO{sub 3}, and PrBaMn{sub 2}O{sub 6} compounds is studied. The maximum values of MCE ({Delta}T{sub max}) determined by a direct method in the second and third compositions and in La{sub 0.9}Sr{sub 0.1}MnO{sub 3} are found to be much lower than those calculated from the change of the magnetic part of entropy in the Curie temperature (T{sub C}) and the Neel temperature (T{sub N}) range. The negative contribution of the antiferromagnetic (AFM) part of a sample in the La{sub 1-x}Sr{sub x}MnO{sub 3} system at 0.1 {<=} x {<=} 0.3 decreases {Delta}T{sub max} and changes the {Delta}T(T) curve shape, shifting its maximum 20-40 K above T{sub C}. Lower values of {Delta}T{sub max} are detected in the range T{sub C} = 130-142 K in polycrystalline and single-crystal Sm{sub 0.55}Sr{sub 0.45}MnO{sub 3} samples cooled in air. If such samples were cooled in an oxygen atmosphere (which restores broken Mn-O-Mn bonds and, thus, increases the volume of CE-type AFM clusters), the maximum in the temperature dependence of MCE is located at T{sub N} (243 K) for CE-type AFM clusters. A magnetic field applied to a sample during the MCE measurements transforms these clusters into a ferromagnetic (FM) state, and both types of clusters decompose at T = T{sub N}. The PrBaMn{sub 2}O{sub 6} composition undergoes an AFM-FM transition at 231 K, and the temperature dependence of its MCE has a sharp minimum at T = 234 K, where MCE is negative, and a broad maximum covering T{sub C}. The absolute values of MCE at both extrema are several times lower than those calculated from the change in the magnetic entropy. These phenomena are explained by the presence of a magnetically heterogeneous FM-AFM state in these manganites.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Warping wormholes with dust: a metric construction of the Python’s Lunch

We show how wormholes in three spacetime dimensions can be customizably warped using pressureless matter. In particular, we exhibit a large new class of solutions in (2 + 1)-dimensional general relativity with energy-momentum tensor describing a negative cosmological constant and positive-energy dust. From this class of solutions, we construct wormhole geometries and study their geometric and holographic properties, including Ryu- Takayanagi surfaces, entanglement wedge cross sections, mutual information, and outer entropy. Finally, we construct a Python’s Lunch geometry: a wormhole in asymptotically anti-de Sitter space with a local maximum in size near its middle.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Quantum magic and computational complexity in the neutrino sector

We consider the quantum magic in systems of dense neutrinos undergoing coherent flavor transformations, relevant for supernova and neutron-star binary mergers. Mapping the three-flavor-neutrino system to qutrits, the evolution of quantum magic is explored in the single scattering angle limit for a selection of initial tensor-product pure states for 𝑁 𝜈 ≤ 8 neutrinos. For |𝜈𝑒⟩ ⊗𝑁𝜈 initial states, the magic, as measured by the 𝛼 = 2 stabilizer Renyi entropy ℳ 2 , is found to decrease with radial distance from the neutrino sphere, reaching a value that lies below the maximum for tensor-product qutrit states. Further, the asymptotic magic per neutrino, ℳ 2 /𝑁 𝜈 , decreases with increasing 𝑁 𝜈 . In contrast, the magic evolving from states containing all three flavors reaches values only possible with entanglement, with the asymptotic ℳ 2 /𝑁 𝜈 increasing with 𝑁 𝜈 . These results highlight the connection between the complexity in simulating quantum physical systems and the parameters of the Standard Model.

computational complexity↗
NASA NTRS1994

An adaptive technique to maximize lossless image data compression of satellite images

Data compression will pay an increasingly important role in the storage and transmission of image data within NASA science programs as the Earth Observing System comes into operation. It is important that the science data be preserved at the fidelity the instrument and the satellite communication systems were designed to produce. Lossless compression must therefore be applied, at least, to archive the processed instrument data. In this paper, we present an analysis of the performance of lossless compression techniques and develop an adaptive approach which applied image remapping, feature-based image segmentation to determine regions of similar entropy and high-order arithmetic coding to obtain significant improvements over the use of conventional compression techniques alone. Image remapping is used to transform the original image into a lower entropy state. Several techniques were tested on satellite images including differential pulse code modulation, bi-linear interpolation, and block-based linear predictive coding. The results of these experiments are discussed and trade-offs between computation requirements and entropy reductions are used to identify the optimum approach for a variety of satellite images. Further entropy reduction can be achieved by segmenting the image based on local entropy properties then applying a coding technique which maximizes compression for the region. Experimental results are presented showing the effect of different coding techniques for regions of different entropy. A rule-base is developed through which the technique giving the best compression is selected. The paper concludes that maximum compression can be achieved cost effectively and at acceptable performance rates with a combination of techniques which are selected based on image contextual information.

Stewart, Robert J.↗