Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Disordered System”

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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Effects of Simulated Microgravity on a Host-Pathogen System

While it has been shown that decades of astronauts and cosmonauts suffer from immune disorders both during and after spaceflight, the underlying causes are still poorly understood, due in part to the fact that there are so many variables to consider when investigating the human immune system in a complex environment. Invertebrates have become popular models for studying human disease because they are cheap, highly amenable to experimental manipulation, and have innate immune systems with a high genetic similarity to humans. Fruit flies (Drosophila melanogaster) have been shown to experience a dramatic shift in immune gene expression following spaceflight, but are still able to fight off infections when exposed to bacteria. Furthermore, a recent spaceflight mission showed that flies are more susceptible to infection following exposure to microgravity conditions, compared to ground-reared flies from the same population. Additionally, the common bacterial pathogen Serratia marcescens was shown to become more lethal to fruit flies (both space- and ground-reared) after being cultured in space, suggesting that not only do we need to consider host changes in susceptibility, but also changes in the pathogen itself after spaceflight conditions. Being able to simulate spaceflight conditions in a controlled environment on the ground gives us the ability to not only evaluate the effects of microgravity on the host immune system, but also how the microorganisms that cause immune disorders are being affected by these drastic environmental shifts. In this study, I use both spaceflight and ground-based (simulated microgravity) environments to examine the genetic changes associated with increased S. marcescens virulence in order to understand how microgravity is affecting this pathogen, as well as to evaluate how these genetic changes influence and interact with the host immune system. This study will provide us with more directed approaches to studying the effects of spaceflight on human beings, with the ultimate goal of being able to ameliorate human immune dysfunction in future space exploration.

Immunology↗
DOE OSTI2020

Stochastically Realized Observables for Excitonic Molecular Aggregates

In this work, we show that a stochastic approach enables calculations of the optical properties of large 2-dimensional and nanotubular excitonic molecular aggregates. Previous studies of such systems relied on numerically diagonalizing the dense and disordered Frenkel Hamiltonian, which scales approximately as $\mathcal{O}$($N$ 3 ) for $N$ dye molecules. Our approach scales much more efficiently as $\mathcal{O}$($N$ log($N$)), enabling quick study of systems with a million of coupled molecules on the micrometer size scale. We calculate several important experimental observables, including the optical absorption spectrum and density of states, and develop a stochastic formalism for the participation ratio. Quantitative agreement with traditional matrix diagonalization methods is demonstrated for both small- and intermediate-size systems. The stochastic methodology enables the study of the effects of spatial-correlation in site energies on the optical signatures of large 2D aggregates. Our results demonstrate that stochastic methods present a path forward for screening structural parameters and validating experiments and theoretical predictions in large excitonic aggregates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2001

Animal model of neuropathic tachycardia syndrome

Clinically relevant autonomic dysfunction can result from either complete or partial loss of sympathetic outflow to effector organs. Reported animal models of autonomic neuropathy have aimed to achieve complete lesions of sympathetic nerves, but incomplete lesions might be more relevant to certain clinical entities. We hypothesized that loss of sympathetic innervation would result in a predicted decrease in arterial pressure and a compensatory increase in heart rate. Increased heart rate due to loss of sympathetic innervation is seemingly paradoxical, but it provides a mechanistic explanation for clinical autonomic syndromes such as neuropathic postural tachycardia syndrome. Partially dysautonomic animals were generated by selectively lesioning postganglionic sympathetic neurons with 150 mg/kg 6-hydroxydopamine hydrobromide in male Sprague-Dawley rats. Blood pressure and heart rate were monitored using radiotelemetry. Systolic blood pressure decreased within hours postlesion (Delta>20 mm Hg). Within 4 days postlesion, heart rate rose and remained elevated above control levels. The severity of the lesion was determined functionally and pharmacologically by spectral analysis and responsiveness to tyramine. Low-frequency spectral power of systolic blood pressure was reduced postlesion and correlated with the diminished tyramine responsiveness (r=0.9572, P=0.0053). The tachycardia was abolished by treatment with the beta-antagonist propranolol, demonstrating that it was mediated by catecholamines acting on cardiac beta-receptors. Partial lesions of the autonomic nervous system have been hypothesized to underlie many disorders, including neuropathic postural tachycardia syndrome. This animal model may help us better understand the pathophysiology of autonomic dysfunction and lead to development of therapeutic interventions.

NASA Discipline Regulatory Physiology↗
DOE OSTI2026

Reaching quantum critical point by adding nonmagnetic disorder in single crystals of superconductor (Ca 𝑥 ⁢Sr 1−𝑥 ) 3 ⁢Rh 4 ⁢Sn 13

The Remeika series superconductor, (Ca 𝑥 ⁢Sr 1−𝑥 ) 3 ⁢Rh 4 ⁢Sn 13 , shows a rare nonmagnetic quantum critical point (QCP) associated with the continuous charge-density wave (CDW) and structural transition under the “dome” of superconductivity achieved by tuning composition and applying pressure. Here, we use a nonmagnetic pointlike disorder induced by 2.5 MeV electron irradiation to suppress the CDW and drive the system to and even beyond the QCP. This conclusion is based on a clear evolution of temperature-dependent resistivity, 𝜌⁡(𝑇), from the Fermi liquid to the non-Fermi liquid regime with increasing amount of disorder. Starting on the CDW side, below the suggested QCP concentration of 𝑥 𝑐 =0.9, added disorder resulted in a progressively larger linear term and a reduced quadratic term in 𝜌⁡(𝑇). Nearly perfect 𝑇−linear dependence is observed at the dose at which long-range CDW order is suppressed to 𝑇=0, consistent with the expectations. We refine the QCP location in this system and place it in the interval between 𝑥=0.75 and 0.85. Our results strongly support the concept that the disorder can tune the system to the quantum critical regime and even beyond. It follows from the argument by Imry and Ma that any ordered phase is unstable toward quenched disorder. Introduced in a controlled way, this disorder becomes a nonthermal tuning parameter likely applicable to a variety of different systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1984

Nonauditory-system response to noise and effects on health

Continued exposure to noise in real life can be a source of physiological stress possibly capable of causing health disorders beyond that of direct damage to the auditory receptor system. Some theorists hold that some of these effects occur because of innate, reflexive responses to noise that cannot be prevented or, when suppressed, that require some effort that may itself become somewhat debilitting in time. An alternative theory is that the truly nonhabituating reflexive responses to noise are not sufficient in character to cause any ill health, and that those responses to noise that are or could be significant in this regard are not directly the result of exposure to noise but are responses to the emotional meanings conveyed by the sounds. Obviously, the degree to which noise can lead to harm to nonauditory physiological systems of the body are questions of utmost importance for the assessment of the need for noise control.

Source record↗
DOE OSTI2021

Structural and chemical disorder enhance point defect diffusion and atomic transport in Ni 3 Al-based γ' phase

The ordered L1 2 γ' Ni 3 Al intermetallic inclusions are routinely used as strengthening constituents in Ni-based superalloys and recent high-entropy alloys. As there are different metallic elements relative to the alloy matrix, the composition of γ' phase inclusions usually suffers some variations. In this work, we studied the elemental partition and its influence on atomic transport properties in a model (NiCo) 3 Al γ' phase with chemical and structural disorder. Combining the Monte Carlo and molecular static techniques, we first determined the elemental distribution in such compositionally-complexed γ' phase. The results suggest that Co tends to segregate, which profoundly influences defect energetics and diffusion properties. By modeling thermally activated diffusion by molecular dynamics, we found that chemical disorder induced by Co can enhance vacancy diffusion while significantly suppress diffusion via interstitial atom migration, as compared to the stoichiometric γ' Ni 3 Al. We further reveal that these observations are closely related to the defect energetics in these systems. Furthermore, our results explain the effects of disorder, long- and short-range orders on the diffusion properties in multicomponent intermetallic alloys, which helps to understand the stability and, thus, γ'-phase-assisted strengthening at different conditions including annealing and irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Chemical short-range order in derivative Cr–Ta–Ti–V–W high entropy alloys from the first-principles thermodynamic study

The development of high-entropy alloys (HEAs) focuses on exploring compositional regions in multi-component systems with all alloy elements in equal or near-equal atomic concentrations. Initially it was based on the main idea that high mixing configurational entropy contributions to the alloy free energy could promote the formation of a single solid solution phase. By using the ab-initio based Cluster Expansion (CE) Hamiltonian model constructed for the quinary bcc Cr–Ta–Ti–V–W system in combination with Monte Carlo (MC) simulations, we show that the phase stability and chemical short-range order (SRO) of the equiatomic quinary and five sub-quaternary systems, as well as their derivative alloys, can dramatically change the order–disorder transition temperatures (ODTT) as a function of alloy compositions. In particular, it has been found, that the equiatomic quaternary Ta–Ti–V–W and Cr–Ta–Ti–W alloys had the lowest order–disorder transition temperature (500 K) among all the analysed equiatomic compositions. In all investigated alloy systems, the strongest chemical ordering has been observed between Cr and V, which led to the conclusion that decreasing the concentration of either Cr or V might be beneficial in terms of decreasing the ODTT. It also predicts that increasing concentration of Ti significantly decreases the ODTT. Our analysis of chemical SRO as a function of alloy composition allows to understand the microstructure evolution of HEAs as a function of temperature in excellent agreement with available experimental observations. Importantly, our free energy of mixing and SRO calculations predict that the origin of precipitates formed by Cr- and V-rich in the sub-quaternary Cr–Ta–V–W system is driven by the thermodynamics. The modelling results are in an excellent agreement with experimental observation of Cr and V segregation in the W 0.38 Ta 0.36 Cr 0.15 V 0.11 alloy which in turns shows an exceptional radiation resistance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Flat band carrier confinement in magic-angle twisted bilayer graphene

Abstract Magic-angle twisted bilayer graphene has emerged as a powerful platform for studying strongly correlated electron physics, owing to its almost dispersionless low-energy bands and the ability to tune the band filling by electrostatic gating. Techniques to control the twist angle between graphene layers have led to rapid experimental progress but improving sample quality is essential for separating the delicate correlated electron physics from disorder effects. Owing to the 2D nature of the system and the relatively low carrier density, the samples are highly susceptible to small doping inhomogeneity which can drastically modify the local potential landscape. This potential disorder is distinct from the twist angle variation which has been studied elsewhere. Here, by using low temperature scanning tunneling spectroscopy and planar tunneling junction measurements, we demonstrate that flat bands in twisted bilayer graphene can amplify small doping inhomogeneity that surprisingly leads to carrier confinement, which in graphene could previously only be realized in the presence of a strong magnetic field.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Fluorinated cation-disordered rocksalt materials and methods of making thereof

This disclosure provides systems, methods, and apparatus related to lithium metal oxyfluorides. In one aspect, a method for manufacturing a lithium metal oxyfluoride having a general formula Li 1+x (MM′) z O 2-y F y , with 0.6 ≤ z ≤ 0.95, 0 < y ≤ 0.67, and 0.0 5 ≤ x ≤ 0.4, the lithium metal oxyfluoride having a cation-disordered rocksalt structure, includes: providing at least one lithium-based precursor; providing at least one redox-active transition metal-based precursor; providing at least one redox-inactive transition metal-based precursor; providing at least one fluorine-based precursor comprising a fluoropolymer; and mixing the at least one lithium-based precursor, the at least one redox-active transition metal-based precursor, the at least redox-inactive transition metal-based precursor, and the at least one fluorine-based precursor comprising a fluoropolymer to form a mixture.

Ahn, Juhyeon↗
DOE OSTI2024

Exploring the impact of the local environment on charge transfer states at molecular donor-acceptor heterojunctions

This program explored a broad range of charge transfer (CT) states in organic solar cells with the goal of understanding how molecular energetics, structure, and morphology influence CT state energy and dynamics, and how this in turn influences solar cell performance. We identified new types of delocalized CT states at ordered molecular heterojunctions, determined the factors that dictate CT state energetic disorder in bulk heterojunctions, determined that hot CT state dissociation is negligible for most systems, that the occupation of CT states is generally non-thermal in disordered heterojunctions, and that quasi-equilibrium generally does not hold in organic solar cells. These findings allowed us to demonstrate the lowest loss in potential of any organic solar cell to date and provide valuable guidance for designing higher efficiency organic solar cells in the future.

14 SOLAR ENERGY↗
DOE OSTI2021

Metal–insulator transition and low-density phases in a strongly-interacting two-dimensional electron system

Highlights: • Quantum phase transition observed in ultrahigh mobility SiGe/Si/SiGe quantum wells. • Metallic state observed in a strongly interacting spinless two-valley electron system. • Indication of band flattening at the Fermi level reported. • Transport evidence for a sliding two-dimensional quantum electron solid reported. We review recent experimental results on the metal–insulator transition and low-density phases in strongly-interacting, low-disordered silicon-based two-dimensional electron systems. Special attention is given to the metallic state in ultra-clean SiGe quantum wells and to the evidence for a flat band at the Fermi level and a quantum electron solid.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Floquet engineering with spatially nonuniform driving fields

In Floquet engineering, we apply a time-periodic modulation to change the effective behavior of a wave system. In this work, we generalize Floquet engineering to more fully exploit spatial degrees of freedom, expanding the scope of effective behaviors we can access. We develop a perturbative procedure to engineer space-time dependent driving forces that effectively transform broad classes of tight-binding systems into one another. We demonstrate several applications, including removing disorder, undoing Anderson localization, and enhancing localization to an extreme in spatially modulated waveguides. This procedure straightforwardly extends to other types of physical systems and different Floquet driving field implementations.

42 ENGINEERING↗
DOE OSTI2020

First-principles calculation of the configurational energy density of states for a solid-state ion conductor with a variant of the Wang and Landau algorithm

In this work, a variant of the Wang and Landau algorithm for calculation of the configurational energy density of states is proposed. The algorithm was developed for the purpose of using first-principles simulations, such as density functional theory, to calculate the partition function of disordered sublattices in crystal materials. The expensive calculations of first-principles methods make a parallel algorithm necessary for a practical computation of the configurational energy density of states within a supercell approximation of a solid-state material. The algorithm developed in this work is tested with the two-dimensional (2d) Ising model to bench mark the algorithm and to help provide insight for implementation to a materials science application. Tests with the 2d Ising model revealed that the algorithm has good performance compared to the original Wang and Landau algorithm and the 1/$\textit{t}$ algorithm, in particular the short iteration performance. Further, a proof of convergence is presented within an adiabatic assumption, and the analysis is able to correctly predict the time dependence of the modification factor to the density of states. The algorithm was then applied to the lithium and lanthanum sublattice of the solid-state lithium ion conductor Li 0.5 La 0.5 TiO 3 . This was done to help understand the disordered nature of the lithium and lanthanum. The results find, overall, that the algorithm performs very well for the 2d Ising model and that the results for Li 0.5 La 0.5 TiO 3 are consistent with experiment while providing additional insight into the lithium and lanthanum ordering in the material. The primary result is that the lithium and lanthanum become more mixed between layers along the c axis for increasing temperature. In part, the simulation of the disordered Li 0.5 La 0.5 TiO 3 system serves as a benchmark for what size systems are currently and in the near future practical to calculate with density functional theory methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Instability and evolution of the magnetic ground state in metallic perovskites GdRh 3 C 1-x B x

In this paper, we report investigations of the structural, magnetic, electrical transport and thermal properties of five compositions of the metallic perovskite GdRh 3 C 1–x B x (0.00 ≤ x ≤ 1.00). Our results show that all the five compositions undergo magnetic ordering at low temperatures, but the nature of the ordered state is significantly different in the carbon- and the boron-rich compositions, where the former shows signatures of an amplitude-modulated magnetic structure and the latter exhibits evidences of an equal-moment incommensurate antiferromagnetic ordering. We also observe a remarkable field-dependent evolution of conduction carrier polarization in the compositionally disordered compounds. The outcomes indicate that this system is energetically situated in proximity to a magnetic instability where small variations in the control parameter(s), such as lattice constant and/or electron density, lead to considerably different ground states.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Helical versus collinear antiferromagnetic order tuned by magnetic anisotropy in polar and chiral (Ni,Mn) 3 TeO 6

In this work, polar and chiral Ni 3 TeO 6 was found to exhibit a colossal magnetoelectric (ME) effect associated with collinear antiferromagnetic order. We have investigated the evolution of its magnetic state with the substitution of the Ni 2+ spins by isotropic Mn 2+ spins, namely (Ni, Mn) 3 TeO 6 (NMTO). The ground state of NMTO maintains an Ising nature, but a new phase with XY-type magnetic anisotropy is discovered at an intermediate temperature range. Neutron powder diffraction experiments reveal that (1) Mn ions tend to occupy a specific transition-metal site, consistent with the first-principle calculation, and (2) the intermediate phase is an incommensurate (IC) helical magnetic state propagating along the $\textit{c}$ axis with $\vec q_{\text{IC}}$ = (0, 0, 1.5 ± δ). We also found that the balance between these two magnetic states can be readily manipulated with magnetic fields, which results in significant ME effects. This selective site occupancy of NMTO allows for a unique competition between collinear and helical magnetic structures with minimal chemical disorder. Thus, NMTO serves as a model system to study site-specific chemical control of noncollinear magnetism and ME coupling.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Thermodynamically informed priors for uncertainty propagation in first-principles statistical mechanics

Here, this work demonstrates how first-principles statistical mechanics approaches within a Bayesian framework can quantify and propagate uncertainties to downstream thermodynamic calculations. To address the issue of Bayesian prior selection, knowledge of 0 K ground states in the material system of interest is incorporated into the prior. The effectiveness of this framework is shown by creating a phase diagram for the fcc zirconium nitride system, including confidence intervals on order-disorder transition temperatures.

Bayesian methods↗
NASA NTRS1971

An estimator for the standard deviation of a natural frequency. I.

A brief review of mean-square approximate systems is given. The case in which the masses are deterministic is considered first in the derivation of an estimator for the upper bound of the standard deviation of a natural frequency. Two examples presented include a two-degree-of-freedom system and a case in which the disorder in the springs is perfectly correlated. For purposes of comparison, a Monte Carlo simulation was done on a digital computer.

Schiff, A. J.↗
NASA NTRS1994

Formation Energy of Disordered Alloys form the Energetics of Ordered Compounds

The cluster expansion technique is used in combination with first-principles calculations of the total energy of ordered compounds to study the energetics of the disordered phase for a number of alloy systems. The effect of short-range order, as seen in the energy differences between an alloy with the configuration corresponding to finite temperature and the perfectly random one is studied. The role of relaxation due to large size mismatch is discussed in terms of an effective cluster volume approximation. Very good agreement with measured energies of formation is obtained when short-range order and relaxation effects are taken into account.

Amador, Carlos↗