Search NASA⌕ Search

SEARCH · Search NASA

Results for “Sample entropy”

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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Gradient cell–structured high-entropy alloy with exceptional strength and ductility

We report that similar to conventional materials, most multicomponent high-entropy alloys (HEAs) lose ductility as they gain strength. In this study, we controllably introduced gradient nanoscaled dislocation cell structures in a stable single-phase HEA with face-centered cubic structure, thus resulting in enhanced strength without apparent loss of ductility. Upon application of strain, the sample-level structural gradient induces progressive formation of a high density of tiny stacking faults (SFs) and twins, nucleating from abundant low-angle dislocation cells. Furthermore, the SF-induced plasticity and the resultant refined structures, coupled with intensively accumulated dislocations, contribute to plasticity, increased strength, and work hardening. These findings offer a promising paradigm for tailoring properties with gradient dislocation cells at the nanoscale and advance our fundamental understanding of the intrinsic deformation behavior of HEAs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Prediction of Magnetocaloric Effect in La{sub 0.67}Pb{sub 0.33}(Mn{sub 1−x}Co{sub x})O{sub 3} Compounds (x = 0.01, 0.06, 0.1 and 0.15)

The magnetocaloric properties for the Co-doped La{sub 0.67}Pb{sub 0.33}(Mn{sub 1−x}Co{sub x})O{sub 3} samples with x= 0.01, 0.06, 0.1 and 0.15 under a 0.005 T magnetic field have been theoretically investigated and compared with experimental results. It has been found that the Co doping in this system decreases lightly the magnetocaloric properties. Moreover, the results of Co doping indicate that the magnetocaloric effect in this system is tunable, which is beneficial for manipulating magnetocaloric refrigeration that occurs in various temperature ranges. This makes the La{sub 0.67}Pb{sub 0.33}(Mn{sub 1−x}Co{sub x})O{sub 3} samples potential candidates for practical applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Multiple magnetic interactions and large inverse magnetocaloric effect in TbSi and TbSi 0.6 Ge 0.4

We present a comprehensive investigation of the electronic structure, magnetization, specific heat, and crystallography of TbSi (FeB structure type) and TbSi 0.6 ⁢Ge 0.4 (CrB structure type) compounds. Both TbSi and TbSi 0.6 ⁢Ge 0.4 exhibit two antiferromagnetic (AFM) transitions at T N⁢1 ≈ 58 and 57 K, and T N⁢2 ≈ 36 and 44 K, respectively, along with an onset of weak metamagneticlike transition around 6 T between T N⁢1 and T N⁢2 . High-resolution specific heat (C P ) measurements show the second- and first-order nature of the magnetic transition at T N⁢1 and T N⁢2 , respectively, for both samples. However, in the case of TbSi, the low-temperature (LT) AFM to high-temperature (HT) AFM transition takes place via an additional AFM phase at the intermediate temperature (IT), where both LT to IT AFM and IT to HT AFM phase transitions exhibit a first-order nature. Both TbSi and TbSi 0.6 ⁢Ge 0.4 manifest significant magnetic entropy changes (Δ⁢S M ) of 9.6 and 11.6 J/kg-K, respectively, for Δ⁢μ 0 ⁢H=7 T, at T N⁢2 . The HT AFM phase of TbSi 0.6 ⁢Ge 0.4 is found to be more susceptible to the external magnetic field, causing a significant broadening in the peaks of Δ⁢S M curves at higher magnetic fields. Temperature- and field-dependent specific-heat data have been utilized to construct the complex HT phase diagram of these compounds. As a result, temperature-dependent x-ray diffraction measurements demonstrate substantial magnetostriction and anisotropic thermal expansion of the unit cell in both samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Next Steps for Compressively Sensed Video in Transmission Electron Microscopy

Here, compressive sensing (CS) is a fast-emerging approach for improving data throughput by taking advantage of the inherent compressibility of real world data—the same kind of compressibility that allows millions of users to stream full-screen video without breaking the internet. Transmission electron microscope (TEM) users regularly collect multi-GB data sets and then use aggressive data reduction strategies to draw out the tiny residual of Shannon entropy that answers the question they wanted to ask. Much of the raw-byte-count information in an acquisition is random, redundant, or irrelevant, yet its collection still represents substantial cost in terms of instrumentation bandwidth and sample damage.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

True randomness from an incoherent source

Quantum random number generators (QRNGs) harness the intrinsic randomness in measurement processes: the measurement outputs are truly random, given the input state is a superposition of the eigenstates of the measurement operators. In the case of trusted devices, true randomness could be generated from a mixed state ρ so long as the system entangled with ρ is well protected. We propose a random number generation scheme based on measuring the quadrature fluctuations of a single mode thermal state using an optical homodyne detector. By mixing the output of a broadband amplified spontaneous emission (ASE) source with a single mode local oscillator (LO) at a beam splitter and performing differential photo-detection, we can selectively detect the quadrature fluctuation of a single mode output of the ASE source, thanks to the filtering function of the LO. Experimentally, a quadrature variance about three orders of magnitude larger than the vacuum noise has been observed, suggesting this scheme can tolerate much higher detector noise in comparison with QRNGs based on measuring the vacuum noise. The high quality of this entropy source is evidenced by the small correlation coefficients of the acquired data. A Toeplitz-hashing extractor is applied to generate unbiased random bits from the Gaussian distributed raw data, achieving an efficiency of 5.12 bits per sample. Furthermore, the output of the Toeplitz extractor successfully passes all the NIST statistical tests for random numbers.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Comparison of Thaumarchaeotal populations from four deep sea basins

The nitrogen cycle in the marine environment is strongly affected by ammonia-oxidizing Thaumarchaeota. In some marine settings, Thaumarchaeotes can comprise a large percentage of the prokaryotic population. To better understand the biogeographic patterns of Thaumarchaeotes, we sought to investigate differences in their abundance and phylogenetic diversity between geographically distinct basins. Samples were collected from four marine basins (The Caspian Sea, the Great Australian Bight, and the Central and Eastern Mediterranean). The concentration of bacterial and archaeal 16S rRNA genes and archaeal amoA genes were assessed using qPCR. Minimum entropy decomposition was used to elucidate the fine-scale diversity of Thaumarchaeotes. We demonstrated that there were significant differences in the abundance and diversity of Thaumarchaeotes between these four basins. The diversity of Thaumarchaeotal oligotypes differed between basins with many oligotypes only present in one of the four basins, which suggests that their distribution showed biogeographic patterning. There were also significant differences in Thaumarchaeotal community structure between these basins. This would suggest that geographically distant, yet geochemically similar basins may house distinct Thaumarchaeaotal populations. In conclusion, these findings suggest that Thaumarchaeota are very diverse and that biogeography in part contributes in determining the diversity and distribution of Thaumarchaeotes.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

Spin dynamics and a nearly continuous magnetic phase transition in an entropy-stabilized oxide antiferromagnet

In this work, the magnetic order and the spin dynamics in the antiferromagnetic entropy-stabilized oxide (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )O (MgO-ESO) have been studied using muon spin relaxation (μSR) and inelastic neutron scattering. We find that antiferromagnetic order develops gradually in the sample volume as it is cooled below 140 K, becoming fully ordered around 100 K. The spin dynamics show a critical slowing down in the vicinity of the transition, and the magnetic order parameter grows continuously in the ordered state. These results indicate that the antiferromagnetic transition is continuous but proceeds with a Gaussian distribution of ordering temperatures. Additionally, the magnetic contribution to the specific heat determined from inelastic neutron scattering likewise shows a broad feature centered around 120 K. High-resolution inelastic neutron scattering further reveals an initially gapped spectrum at low temperature which sees an increase in a quasielastic contribution upon heating until the ordering temperature.

36 MATERIALS SCIENCE↗
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 NTRS1979

Stochastic control and the second law of thermodynamics

The second law of thermodynamics is studied from the point of view of stochastic control theory. We find that the feedback control laws which are of interest are those which depend only on average values, and not on sample path behavior. We are lead to a criterion which, when satisfied, permits one to assign a temperature to a stochastic system in such a way as to have Carnot cycles be the optimal trajectories of optimal control problems. Entropy is also defined and we are able to prove an equipartition of energy theorem using this definition of temperature. Our formulation allows one to treat irreversibility in a quite natural and completely precise way.

Brockett, R. W.↗
NASA NTRS2002

Diurnal Cycle of Convection in the East Pacific ITCZ during EPIC-2001

During the last three weeks of September 2001, the EPIC-2001 intensive field campaign focused on studies of deep convection in the ITCZ over the Mexican warm pool region (10N, 95W) of the East Pacific. This study focuses on the pronounced observed diurnal cycle of environmental and convective parameters within the experiment domain. Data from three primary sources are examined: the R/V Ronald H. Brown C-band weather radar, 4-hourly soundings from the Brown and the Global Atmospherics, Inc. National Lightning Detection Network (long range product). Satellite data from TRMM, GOES and OV-1 are also used. The domain boundary layer shows a robust daily evolution of moist enthalpy (as reflect by equivalent potential temperature, theta-e, or wet bulb potential temperature, theta-w), with contributions from changes in both dry and moist entropy. Peak theta-w is found after local nightfall; the average diurnal range of theta-w is approximately 1 deg C. A composite diurnal cycle of convective properties was derived from the C-band volume scans, sampled continuously through the experiment at 10 minute updates. Products derived from the volumetric data include a surface PPI, 15 and 30 dBZ echo top height, vertically integrated liquid, and 6 km (mixed phase region) reflectivity CAPPIs. For almost all products, the parameter means showed virtually no diurnal cycle. However, for the upper-level products, the parameter spectra showed a clear peak in the occurrence of deep/vigorous convection (the "tail end of the distribution") between 7-9 UTC (1-3 AM local), while overall frequency of occurrence peaked later, from 12-15 UTC (6-9 AM local). This represents a daily "outbreak" of isolated deep cells a couple of hours after sunset and subsequent growth, organization and decay through the nighttime hours. The coherence of the diurnal cycle of the convective spectrum is impressive given the wide variety of convective organization observed during the experiment, and given the modulation by passage of 3-5 day easterly waves. While earlier satellite OLR composites suggested an offshore coastal migration of storms into the domain at night, examination of the 150 km and 300 km range radar products showed little evidence of such organization; almost all convection developed "in-place" within the analysis domain. Consistent with the diurnal thermodynamic and microphysical evolution, a clear cycle in cloud-to-ground (CG) lightning occurrence was observed. The local CG diurnal cycle is significantly stronger than the satellite-derived tropical ocean diurnal cycle of total (IC+CG) lightning. Flash rates of 3-4 fl/min were often visually observed after nightfall; these are fairly 'healthy' flash rates for tropical ocean storms, and the domain was qualitatively noted to be unusually lightning-productive by the R/V Brown crew (also consistent with satellite-based climatologies).

Boccippio, Dennis J.↗
DOE OSTI2025

Experimental and computational studies on high-entropy carbide MoNbTaVWC 5 under high pressures

High-entropy carbide, MoNbTaVWC 5 , was synthesized from oxide precursors of the constituent metals, mixed with graphite powder in a microwave-generated hydrogen plasma at 26.66 kPa and 2100 °C. Ambient x-ray diffraction analysis confirms the full conversion of oxide precursors into a single-phase, face-centered cubic structure with a lattice parameter a = 4.3309 Å. Nanoindentation measured a hardness of 24.5 ± 1.3 GPa and an elastic modulus of 386 ± 22 GPa. The synthesized sample, mixed with a copper pressure marker, was studied by the radial x-ray diffraction technique with beryllium gasketing in a diamond anvil cell up to 70 GPa. The experimentally measured pressure–volume curve and shear strength were compared with theoretical predictions using the special quasi-random structure technique and density functional theory. MoNbTaVWC 5 achieved a 12% volume compression at 70 GPa and exhibited a high shear strength of 6.6 GPa. The present study demonstrates that the high-entropy carbide MoNbTaVWC 5 exhibits exceptional incompressibility and high strength under extreme conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Evidence for Galaxy Dynamics Tracing Background Cosmology Below the de Sitter Scale of Acceleration

Galaxy dynamics probe weak gravity at accelerations below the de Sitter scale of acceleration a{sub dS}=cH, where c is the velocity of light and H is the Hubble parameter. Low- and high-redshift galaxies hereby offer a novel probe of weak gravity in an evolving cosmology, satisfying H(z)=H{sub 0}√(1+ω{sub m}(6z+12z{sup 2}+12z{sup 3}+6z{sup 4}+(6/5)z{sup 5}))/(1+z) with matter content ω{sub m}=0.2808±0.028 sans tension to H {sub 0} in surveys of the local universe. Galaxy rotation curves show anomalous galaxy dynamics in weak gravity a{sub N}<a{sub dS} across a transition radius r{sub t}=4.7 kpc M{sub 11}{sup 1/2}(H{sub 0}/H){sup (1/2)} in galaxies of mass M=10{sup 11} M{sub ⊙}M{sub 11}, where a {sub N} is the Newtonian acceleration based on baryonic matter content. We identify this behavior with a holographic origin of inertia from entanglement entropy, which introduces a C {sup 0} onset across a{sub N}=a{sub dS} with asymptotic behavior described by a Milgrom parameter satisfying a{sub 0}=ω{sub 0}/2π, where ω{sub 0}=√(1−q)H is a fundamental eigenfrequency of the cosmological horizon. Extending an earlier confrontation with data covering 0.003≲a{sub N}/a{sub dS}≲1 at redshift z∼0 in Lellie et al., the modest anomalous behavior in the Genzel et al. sample at redshifts 0.854⩽z⩽2.282 is found to be mostly due to clustering 0.36≲a{sub N}/a{sub dS}≲1 close to the C {sup 0} onset to weak gravity and an increase of up to 65% in a {sub 0}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Glass Transition Characteristics and Thermodynamic Functions of (1–x)(0.75TeO{sub 2}–0.25WO{sub 3}) + xLa{sub 2}O{sub 3} Glasses

The temperature-dependent heat capacity of three high-purity (1–x)(0.75TeO{sub 2}–0.25WO{sub 3}) + xLa{sub 2}O{sub 3} tellurite glass samples (x = 0.02, 0.04, and 0.06) has been determined by dynamic calorimetry in the range 320–1000 K. The experimental devitrification and heat capacity data have been used to evaluate standard thermodynamic functions: C{sub p}{sup o}(T), enthalpy, entropy, and Gibbs energy in glassy and supercooled liquid states. We have demonstrated model-parameter similarity of properties in a statistical approach and found correlation relationships for parameters as functions of composition, which make it possible to predict the thermodynamic functions of unexplored glasses of this series. We have identified crystallization-resistant compositions of (1–x)(0.75TeO{sub 2}–0.25WO{sub 3}) + xLa{sub 2}O{sub 3} glasses as a basis for the development of optically active elements.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A JWST Survey of the Supernova Remnant Cassiopeia A

We present initial results from a James Webb Space Telescope (JWST) survey of the youngest Galactic core-collapse supernova remnant, Cassiopeia A (Cas A), made up of NIRCam and MIRI imaging mosaics that map emission from the main shell, interior, and surrounding circumstellar/interstellar material (CSM/ISM). We also present four exploratory positions of MIRI Medium Resolution Spectrograph integral field unit spectroscopy that sample ejecta, CSM, and associated dust from representative shocked and unshocked regions. Surprising discoveries include (1) a weblike network of unshocked ejecta filaments resolved to ~0.01 pc scales exhibiting an overall morphology consistent with turbulent mixing of cool, low-entropy matter from the progenitor's oxygen layer with hot, high-entropy matter heated by neutrino interactions and radioactivity; (2) a thick sheet of dust-dominated emission from shocked CSM seen in projection toward the remnant's interior pockmarked with small (~1'') round holes formed by ≲0$^"_•$1 knots of high-velocity ejecta that have pierced through the CSM and driven expanding tangential shocks; and (3) dozens of light echoes with angular sizes between ~0$^"_•$1 and 1' reflecting previously unseen fine-scale structure in the ISM. NIRCam observations place new upper limits on infrared emission (≲20 nJy at 3 μm) from the neutron star in Cas A's center and tightly constrain scenarios involving a possible fallback disk. These JWST survey data and initial findings help address unresolved questions about massive star explosions that have broad implications for the formation and evolution of stellar populations, the metal and dust enrichment of galaxies, and the origin of compact remnant objects.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

Image reconstruction of IRAS survey scans

The IRAS survey data can be used successfully to produce images of extended objects. The major difficulties, viz. non-uniform sampling, different response functions for each detector, and varying signal-to-noise levels for each detector for each scan, were resolved. The results of three different image construction techniques are compared: co-addition, constrained least squares, and maximum entropy. The maximum entropy result is superior. An image of the galaxy M51 with an average spatial resolution of 45 arc seconds is presented, using 60 micron survey data. This exceeds the telescope diffraction limit of 1 minute of arc, at this wavelength. Data fusion is a proposed method for combining data from different instruments, with different spacial resolutions, at different wavelengths. Data estimates of the physical parameters, temperature, density and composition, can be made from the data without prior image (re-)construction. An increase in the accuracy of these parameters is expected as the result of this more systematic approach.

Bontekoe, Tj. Romke↗
NASA NTRS1990

Image construction from the IRAS survey and data fusion

The IRAS survey data can be used successfully to produce images of extended objects. The major difficulty, viz. non-uniform sampling, different response functions for each detector, and varying signal-to-noise levels for each detector for each scan, were resolved. The results of three different image construction techniques are compared: co-addition, constrained least squares, and maximum entropy. The maximum entropy result is superior. An image of the galaxy M51 with an average spatial resolution of 45 arc seconds, is presented using 60 micron survey data. This exceeds the telescope diffraction limit of 1 minute of arc, at this wavelength. Data fusion is a proposed method for combining data from different instruments, with different spatial resolutions, at different wavelengths. Direct estimates of the physical parameters, temperature, density and composition, can be made from the data without prior images (re-)construction. An increase in the accuracy of these parameters is expected as the result of this more systematic approach.

Bontekoe, Tj. R.↗
NASA NTRS1991

Image construction from the IRAS survey

IRAS survey data can be used successfully to produce images of extended objects. The major difficulties, i.e., nonuniform sampling, different response functions for each detector, and varying signal-to-noise levels for each detector for each scan, have been resolved. The results of three different image construction techniques are compared: coaddition, constrained least-squares, and maximum entropy. The maximum entropy result is superior. An image of the galaxy M51 with an average spatial resolution of 45 arcsecods, using 60 microns survey data is presented. This exceeds the telescope diffraction limit of about 1 minute of arc at this wavelength.

Bontekoe, T. R.↗
DOE OSTI2023

Nanolamellar phase transition in an additively manufactured eutectic high-entropy alloy under high pressures

Much is unknown about how phase transitions link to micro-/nano-structures in high-entropy systems, especially under extreme pressure and temperature conditions. This work studies the evolution of dual-phase nanolamellar eutectic high-entropy alloy phases of AlCoCrFeNi 2.1 generated by laser powder-bed fusion (L-PBF) for pressures up to 42 GPa. We compare quasi-hydrostatic high pressure synchrotron x-ray diffraction studies on L-PBF printed cylindrical samples up to 5.5 GPa (large-volume Paris–Edinburgh cell) to those carried out on an L-PBF printed foil in a diamond anvil cell where the pressure reached 42 GPa. Our results show that the initially alternating face-centered cubic (FCC) and body-centered cubic (BCC) nanolamellar structure of AlCoCrFeNi 2.1 transformed into single-phase FCC nanolamellae under high pressure with BCC–FCC phase transformation completion at 21 ± 3 GPa. Our results indicate a diffusionless BCC–FCC transformation in this additively manufactured far-from-equilibrium microstructure and demonstrate that the FCC phase is stable up to very high pressures. The measured equation of state for the FCC phase of AlCoCrFeNi 2.1 is presented up to 42 GPa and shows excellent agreement between the data obtained in large-volume press and diamond anvil cell experiments.

36 MATERIALS SCIENCE↗