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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Short-range order and its impact on the CrCoNi medium-entropy alloy

Traditional metallic alloys are mixtures of elements in which the atoms of minority species tend to be distributed randomly if they are below their solubility limit, or to form secondary phases if they are above it. The concept of multiple-principal-element alloys has recently expanded this view, as these materials are single-phase solid solutions of generally equiatomic mixtures of metallic elements. This group of materials has received much interest owing to their enhanced mechanical properties 1,2,3,4,5 . They are usually called medium-entropy alloys in ternary systems and high-entropy alloys in quaternary or quinary systems, alluding to their high degree of configurational entropy. However, the question has remained as to how random these solid solutions actually are, with the influence of short-range order being suggested in computational simulations but not seen experimentally 6,7 . In this paper we report the observation, using energy-filtered transmission electron microscopy, of structural features attributable to short-range order in the CrCoNi medium-entropy alloy. Increasing amounts of such order give rise to both higher stacking-fault energy and hardness. These findings suggest that the degree of local ordering at the nanometre scale can be tailored through thermomechanical processing, providing a new avenue for tuning the mechanical properties of medium- and high-entropy alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ab initio study of mechanical and thermal properties of GeTe-based and PbSe-based high-entropy chalcogenides

GeTe-based and PbSe-based high-entropy compounds have outstanding thermoelectric (TE) performance and crucial applications in mid and high temperatures. Recently, the optimization of TE performance of high-entropy compounds has been focused on reducing thermal conductivity by strengthening the phonon scattering process to improve TE performance. We report a first-principles investigation on nine GeTe-based high-entropy chalcogenide solid solutions constituted of eight metallic elements (Ag, Pb, Sb, Bi, Cu, Cd, Mn, and Sn) and 13 PbSe-based high-entropy chalcogenide solid solutions: Pb 0.99-y Sb 0.012 Sn y Se 1-2x Te x S x (x = 0.1, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and y = 0) and Pb 0.99-y Sb 0.012 Sn y Se 1-2x Te x S x (y = 0.05, 0.1, 0.15, 0.2, 0.25 and x = 0.25). We have investigated the mechanical properties focusing on Debye temperature (Θ D ), thermal conductivity (κ), Grüneisen parameter (γ α ), dominant phonon wavelength (λ dom ), and melting temperature (T m ). We find that the lattice thermal conductivity is significantly reduced when GeTe is alloyed into the following compositions: Ge 0.75 Sb 0.13 Pb 0.12 Te, Ge 0.61 Ag 0.11 Sb 0.13 Pb 0.12 Bi 0.01 Te, and Ge 0.61 Ag 0.11 Sb 0.13 Pb 0.12 Mn 0.05 Bi 0.01 Te. This reduction is due to the mass increase and strain fluctuations. The results also show that Ge 0.61 Ag 0.11 Sb 0.13 Pb 0.12 Bi 0.01 Te solid solution has the lowest Young’s modulus (30.362 GPa), bulk and shear moduli (18.626 and 12.359 GPa), average sound velocity (1653.128 m/sec), Debye temperature (151.689 K), lattice thermal conductivity (0.574 W.m –1 .K –1 ), dominant phonon wavelength (0.692 Å), and melting temperature (535.91 K). Moreover, Ge 0.61 Ag 0.11 Sb 0.13 Pb 0.12 Bi 0.01 Te has the highest Grüneisen parameter with a reduced and temperature-independent lattice thermal conductivity. The positive correlation between Θ D and κ is revealed. Alloying of PbSe-based high-entropy by Sb, Sn, Te, and S atoms at the Se and Pb sites resulted in much higher shear strains resulted in the reduction of phonon velocity, a reduced Θ D , and a lower lattice thermal conductivity.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2024

Entropy removal of medical diagnostics

Shannon entropy is a core concept in machine learning and information theory, particularly in decision tree modeling. To date, no studies have extensively and quantitatively applied Shannon entropy in a systematic way to quantify the entropy of clinical situations using diagnostic variables (true and false positives and negatives, respectively). Decision tree representations of medical decision-making tools can be generated using diagnostic variables found in literature and entropy removal can be calculated for these tools. This concept of clinical entropy removal has significant potential for further use to bring forth healthcare innovation, such as quantifying the impact of clinical guidelines and value of care and applications to Emergency Medicine scenarios where diagnostic accuracy in a limited time window is paramount. This analysis was done for 623 diagnostic tools and provided unique insights into their utility. For studies that provided detailed data on medical decision-making algorithms, bootstrapped datasets were generated from source data to perform comprehensive machine learning analysis on these algorithms and their constituent steps, which revealed a novel and thorough evaluation of medical diagnostic algorithms.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2023

Maximum entropy distributions of dark matter in ΛCDM cosmology

Context. Small-scale challenges to ΛCDM cosmology require a deeper understanding of dark matter physics. Aims. This paper aims to develop the maximum entropy distributions for dark matter particle velocity (denoted by X ), speed (denoted by Z ), and energy (denoted by E ) that are especially relevant on small scales where system approaches full virialization. Methods. For systems involving long-range interactions, a spectrum of halos of different sizes is required to form to maximize system entropy. While the velocity in halos can be Gaussian, the velocity distribution throughout the entire system, involving all halos of different sizes, is non-Gaussian. With the virial theorem for mechanical equilibrium, we applied the maximum entropy principle to the statistical equilibrium of entire system, such that the maximum entropy distribution of velocity (the X distribution) could be analytically derived. The halo mass function was not required in this formulation, but it did indeed result from the maximum entropy. Results. The predicted X distribution involves a shape parameter α and a velocity scale, v 0 . The shape parameter α reflects the nature of force ( α → 0 for long-range force or α → ∞ for short-range force). Therefore, the distribution approaches Laplacian with α → 0 and Gaussian with α → ∞. For an intermediate value of α , the distribution naturally exhibits a Gaussian core for v ≪ v 0 and exponential wings for v ≫ v 0 , as confirmed by N -body simulations. From this distribution, the mean particle energy of all dark matter particles with a given speed, v , follows a parabolic scaling for low speeds (∝ v 2 for v ≪ v 0 in halo core region, i.e., “Newtonian”) and a linear scaling for high speeds (∝ v for v ≫ v 0 in halo outskirt, i.e., exhibiting “non-Newtonian” behavior due to long-range gravity). We compared our results against N -body simulations and found a good agreement.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Empirical correlations between the function of entropy ( Z S ) and net artificial viscous work in a shock physics hydrocode

Entropy is a state variable that may be obtained from any thermodynamically complete equation of state (EOS). However, hydrocode calculations that output the entropy often contain numerical errors; this is not because of the EOS, but rather the solution techniques that are used in hydrocodes (especially Eulerian) such as convection, remapping, and artificial viscosity. Here, in this work, empirical correlations are investigated to reduce the errors in entropy without altering the solution techniques for the conservation of mass, momentum, and energy. Specifically, these correlations are developed for the function of entropy Z S , and they depend upon the net artificial viscous work, as determined via Sandia National Laboratories’ shock physics hydrocode CTH. These results are a continuation of a prior effort to implement the entropy-based CREST reactive burn model in CTH, and they are presented here to stimulate further interest from the shock physics community. Future work is planned to study higher-dimensional shock waves, shock wave interactions, and possible ties between the empirical correlations and a physical law.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Entropy of Strongly Correlated Electrons in a Partially Filled Landau Level

We use high-resolution chemical potential measurements to extract the entropy of monolayer and bilayer graphene in the quantum Hall regime via the Maxwell relation [(𝑑⁢𝜇)/(𝑑⁢𝑇)]| 𝑁 =−[(𝑑⁢𝑆)/(𝑑⁢𝑁)]| 𝑇 . Measuring the entropy from 𝑇 = 300 K down to 𝑇 = 200 mK, we identify the sequential emergence of quantum Hall ferromagnetism, fractional quantum Hall states, and various charge orders by comparing the measured entropy in different temperature regimes with theoretical models. At the lowest temperature of 𝑇 ≈ 200 mK we perform a detailed study of the entropy near even-denominator fractional quantum Hall states in bilayer graphene, and comment on the possible topological origin of the observed excess entropy.

Assouline, Alexandre [University of California, Sa↗
DOE OSTI2024

Evidence of ordering in Cu-Ni alloys from experimental electronic entropy measurements

Phase diagrams exhibiting extended solid-solution and lenslike melting are often reproduced using ideal solutions, where ideal mixing considers a fully random configurational entropy of mixing. In the field of irreversible thermodynamics, experimental measurements of the composition variation of high-temperature electronic transport and molten-state properties suggest, however, a strong role for short-range atomic ordering in these systems. Herein, measurements of the thermopower and resistivity are reported for Cu-Ni solid solutions as a function of temperature and composition. The electronic transport properties were interpreted with an irreversible thermodynamic framework, revealing a large electronic contribution to the entropy of mixing. By considering a cluster model for the configurational entropy that uses the electronic contribution to inform the existence of ordered associates, we rationalize such a contribution of the electronic entropy with the ideal entropy of mixing commonly used to model such systems. In conclusion, these results suggest that the short-range order of the atoms plays a significant role in both solid and liquid states, even when there are no dominant intermetallic compounds in these alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Entanglement entropy production in deep inelastic scattering

Deep inelastic scattering (DIS) samples a part of the wave function of a hadron in the vicinity of the light cone. Lipatov constructed a spin chain which describes the amplitude of DIS in leading logarithmic approximation. Kharzeev and Levin proposed the entanglement entropy as an observable in DIS [Phys. Rev. D 95, 114008 (2017)], and suggested a relation between the entanglement entropy and parton distributions. Here we represent the DIS process as a local quench in Lipatov’s spin chain and study the time evolution of the produced entanglement entropy. We show that the resulting entanglement entropy depends on time logarithmically, $\mathcal{S}(t) = 1/3 ln(t/τ)$ with $τ = 1/m for 1/m ≤ t ≤ (mx)^{–1}$, where m is the proton mass and $\textit{x}$ is the Bjorken $\textit{x}$. The central charge c of Lipatov’s spin chain is determined here to be $\textit{c}$ = 1; using the proposed relation between the entanglement entropy and parton distributions, this corresponds to the gluon structure function growing at small $\textit{x}$ as $xG(x) ~ 1/x^{1/3}$.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Vibrational Entropy Contribution to Mixing Free Energy of Ni-Rich LiNi 1- y Co y O 2

First principles density-functional-theory calculations are performed of the mixing free energy of the layered oxide LiNi 1-y Co y O 2 , a model Li-ion-battery cathode material, at 1000 K. Analysis of internal energy, LN exchange, configurational entropy and vibrational entropy are combined to obtain the net mixing free energy. The vibrational entropy requires a more indirect treatment than the other terms; analysis based on heat capacity is presented here, to show that the vibrational entropy is of comparable magnitude to the configurational entropy, and it tends to promote solid-solution behavior in LiNi 1-y Co y O 2 .

25 ENERGY STORAGE↗
DOE OSTI2023

PUF Entropy

This note discusses aspects of fuzzy extraction: in particular, how the interplay between PUF entropy and the revelation of helper data affects the entropy of the underlying secret. We examine the theory behind a scheme by Dodis et alii to develop exact formulas for the entropy of the given seed, given that an adversary knows the helper data. We also give a simple lower bound on the security of the Dodis scheme that is achieved exactly in many instances. By way of several examples, we quantify the amount of entropy that can be lost due to interactions between imperfect PUF implementations and given error correction methods. We repeatedly show that understanding the details of the error correction scheme and the interaction with the PUF response is crucial to being able to estimate the entropy of the system.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2025

Entropy-Assisted Quality Pattern Identification in Finance

Short-term patterns in financial time series form the cornerstone of many algorithmic trading strategies, yet extracting these patterns reliably from noisy market data remains a formidable challenge. In this paper, we propose an entropy-assisted framework for identifying high-quality, non-overlapping patterns that exhibit consistent behavior over time. We ground our approach in the premise that historical patterns, when accurately clustered and pruned, can yield substantial predictive power for short-term price movements. To achieve this, we incorporate an entropy-based measure as a proxy for information gain: patterns that lead to high one-sided movements in historical data yet retain low local entropy are more “informative” in signaling future market direction. Compared to conventional clustering techniques such as K-means and Gaussian Mixture Models (GMMs), which often yield biased or unbalanced groupings, our approach emphasizes balance over a forced visual boundary, ensuring that quality patterns are not lost due to over-segmentation. By emphasizing both predictive purity (low local entropy) and historical profitability, our method achieves a balanced representation of Buy and Sell patterns, making it better suited for short-term algorithmic trading strategies. This paper offers an in-depth illustration of our entropy-assisted framework through two case studies on Gold vs. USD and GBPUSD. While these examples demonstrate the method’s potential for extracting high-quality patterns, they do not constitute an exhaustive survey of all possible asset classes.

Physics↗
DOE OSTI2024

The SPT-Chandra BCG Spectroscopic Survey. I. Evolution of the Entropy Threshold for ICM Cooling and AGN Feedback in Galaxy Clusters over the Last 10 Gyr

Abstract We present a multiwavelength study of the brightest cluster galaxies (BCGs) in a sample of the 95 most massive galaxy clusters selected from the South Pole Telescope Sunyaev–Zeldovich (SZ) survey. Our sample spans a redshift range of 0.3 < z < 1.7, and is complete with optical spectroscopy from various ground-based observatories, as well as ground and space-based imaging from optical, X-ray, and radio wave bands. At z ∼ 0, previous studies have shown a strong correlation between the presence of a low-entropy cool core and the presence of both star formation and radio-loud active galactic nuclei in the central BCG. We show for the first time that the central entropy threshold for triggering star formation, which is universally seen in nearby systems, persists out to z ∼ 1, with only marginal (∼1 σ ) evidence for evolution in the threshold entropy value itself. In contrast, we do not find a similar high- z analog for an entropy threshold for feedback, but instead measure a strong evolution in the fraction of radio-loud BCGs in high-entropy cores, decreasing with increasing redshift. This could imply that the cooling-feedback loop was not as tight in the past, or that some other fuel source like mergers are fueling the radio sources more often with increasing redshift, making the radio luminosity an increasingly unreliable proxy for radio jet power. We also find that our SZ-based sample is missing a small (∼4%) population of the most luminous radio sources ( ν L ν > 10 42 erg s −1 ), likely due to radio contamination suppressing the SZ signal with which these clusters are detected.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1982

Pressure transfer function of a JT15D nozzle due to acoustic and convected entropy fluctuations

An acoustic transmission matrix analysis of sound propagation in a variable area duct with and without flow is extended to include convected entropy fluctuations. The boundary conditions used in the analysis are a transfer function relating entropy and pressure at the nozzle inlet and the nozzle exit impedance. The nozzle pressure transfer function calculated is compared with JT15D turbofan engine nozzle data. The one dimensional theory for sound propagation in a variable area nozzle with flow but without convected entropy is good at the low engine speeds where the nozzle exit Mach number is low (M=0.2) and the duct exit impedance model is good. The effect of convected entropy appears to be so negligible that it is obscured by the inaccuracy of the nozzle exit impedance model, the lack of information on the magnitude of the convected entropy and its phase relationship with the pressure, and the scatter in the data. An improved duct exit impedance model is required at the higher engine speeds where the nozzle exit Mach number is high (M=0.56) and at low frequencies (below 120 Hz).

Miles, J. H.↗
NASA NTRS1985

The numerical viscosity of entropy stable schemes for systems of conservation laws

Discrete approximations to hyperbolic systems of conservation laws are studied. The amount of numerical viscosity present in such schemes, is quantified and related to their entropy stability by means of comparison. To this end, conservative schemes which are also entropy conservative are constructed. These entropy conservative schemes enjoy second-order accuracy; moreover, they admit a particular interpretation within the finite-element frameworks, and hence can be formulated on various mesh configurations. It is then shown that conservative schemes are entropy stable if and only if they contain more viscosity than the mentioned above entropy conservative ones.

Tadmor, E.↗
NASA NTRS1987

The numerical viscosity of entropy stable schemes for systems of conservation laws. I

Discrete approximations to hyperbolic systems of conservation laws are studied. The amount of numerical viscosity present in such schemes is quantified and related to their entropy stability by means of comparison.To this end, conservative schemes which are also entropy-conservative are constructed. These entropy-conservative schemes enjoy second-order accuracy; moreover, they can be interpreted as piecewise-linear finite-element methods, and hence can be formulated on various mesh configurations. It is then shown that conservative schemes are entropy stable, if and (for three-point schemes) only they contain more viscosity than that present in the above-mentioned entropy-conservative ones.

Tadmor, Eitan↗
NASA NTRS1992

Discrete-time entropy formulation of optimal and adaptive control problems

The discrete-time version of the entropy formulation of optimal control of problems developed by G. N. Saridis (1988) is discussed. Given a dynamical system, the uncertainty in the selection of the control is characterized by the probability distribution (density) function which maximizes the total entropy. The equivalence between the optimal control problem and the optimal entropy problem is established, and the total entropy is decomposed into a term associated with the certainty equivalent control law, the entropy of estimation, and the so-called equivocation of the active transmission of information from the controller to the estimator. This provides a useful framework for studying the certainty equivalent and adaptive control laws.

Tsai, Yweting A.↗
NASA NTRS1993

Quantum entropy and uncertainty for two-mode squeezed, coherent and intelligent spin states

We compute the quantum entropy for monomode and two-mode systems set in squeezed states. Thereafter, the quantum entropy is also calculated for angular momentum algebra when the system is either in a coherent or in an intelligent spin state. These values are compared with the corresponding values of the respective uncertainties. In general, quantum entropies and uncertainties have the same minimum and maximum points. However, for coherent and intelligent spin states, it is found that some minima for the quantum entropy turn out to be uncertainty maxima. We feel that the quantum entropy we use provides the right answer, since it is given in an essentially unique way.

Aragone, C.↗
NASA NTRS1996

Conditional Entropy-Constrained Residual VQ with Application to Image Coding

This paper introduces an extension of entropy-constrained residual vector quantization (VQ) where intervector dependencies are exploited. The method, which we call conditional entropy-constrained residual VQ, employs a high-order entropy conditioning strategy that captures local information in the neighboring vectors. When applied to coding images, the proposed method is shown to achieve better rate-distortion performance than that of entropy-constrained residual vector quantization with less computational complexity and lower memory requirements. Moreover, it can be designed to support progressive transmission in a natural way. It is also shown to outperform some of the best predictive and finite-state VQ techniques reported in the literature. This is due partly to the joint optimization between the residual vector quantizer and a high-order conditional entropy coder as well as the efficiency of the multistage residual VQ structure and the dynamic nature of the prediction.

Kossentini, Faouzi↗