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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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Temperature dependent dielectric function in the near-infrared to vacuum-ultraviolet ultraviolet spectral range of alumina and yttria stabilized zirconia thin films

The dielectric function of nano-/polycrystalline alumina and yttria stabilised zirconia thin films has been investigated in a wide spectral range from 1.0 eV to 7.5 eV and temperatures between 10 K and room temperature. In the near band-edge spectral range, we found a broad distribution of optical transitions within the band gap, the so-called Urbach absorption tail which is typical for amorphous or polycrystalline materials due to the lack of long range order in the crystal structure. The coupling properties of the electronic system to the optical phonon bath and thermal lattice vibrations strongly depend on the ratio of the spectral extent of these disorder states to the main phonon energy, which we correlate with the different crystalline structure of our samples. The films have been grown at room temperature and 650 °C by pulsed laser deposition.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Dynamic structural disorder in supported nanoscale catalysts

We investigate the origin and physical effects of “dynamic structural disorder” (DSD) in supported nano-scale catalysts. DSD refers to the intrinsic fluctuating, inhomogeneous structure of such nano-scale systems. In contrast to bulk materials, nano-scale systems exhibit substantial fluctuations in structure, charge, temperature, and other quantities, as well as large surface effects. The DSD is driven largely by the stochastic librational motion of the center of mass and fluxional bonding at the nanoparticle surface due to thermal coupling with the substrate. Our approach for calculating and understanding DSD is based on a combination of real-time density functional theory/molecular dynamics simulations, transient coupled-oscillator models, and statistical mechanics. This approach treats thermal and dynamic effects over multiple time-scales, and includes bond-stretching and -bending vibrations, and transient tethering to the substrate at longer ps time-scales. Potential effects on the catalytic properties of these clusters are briefly explored. Model calculations of molecule-cluster interactions and molecular dissociation reaction paths are presented in which the reactant molecules are adsorbed on the surface of dynamically sampled clusters. This model suggests that DSD can affect both the prefactors and distribution of energy barriers in reaction rates, and thus can significantly affect catalytic activity at the nano-scale.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Tuning the magnetic ground state of a triangular lattice system

The anisotropic triangular lattice of the crednerite system Cu(Mn$_{1-x}$Cu$_{x}$)O$_{2}$ is used as a basic model for studying the influence of spin disorder on the ground state properties of a two-dimensional frustrated antiferromagnet. Neutron diffraction measurements show that the undoped phase (x=0) undergoes a transition to antiferromagnetic long-range order that is stabilized by a frustration-relieving structural distortion. Small deviation from the stoichiometric composition alters the magnetoelastic characteristics and reduces the effective dimensionality of the magnetic lattice. Upon increasing the doping level, the interlayer coupling changes from antiferromagnetic to ferromagnetic, while the structural distortion is fully suppressed. Concomitantly, the long-range magnetic order is gradually transformed into a two-dimensional order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Relaxation dynamics of vortex lines in disordered type-II superconductors following magnetic field and temperature quenches

We study the effects of rapid temperature and magnetic field changes on the nonequilibrium relaxation dynamics of magnetic vortex lines in disordered type-II superconductors by employing an elastic line model and performing Langevin molecular dynamics simulations. In a previously equilibrated system, either the temperature is suddenly changed or the magnetic field is instantaneously altered which is reflected in adding or removing flux lines to or from the system. Here, the subsequent aging properties are investigated in samples with either randomly distributed pointlike or extended columnar defects, which allows us to distinguish the complex relaxation features that result from either type of pinning centers. One-time observables such as the radius of gyration and the fraction of pinned line elements are employed to characterize steady-state properties, and two-time correlation functions such as the vortex line height autocorrelations and their mean-square displacement are analyzed to study the nonlinear stochastic relaxation dynamics in the aging regime.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Powder Diffraction Crystallography : 98 Years as Plan B?

A historical essay written in 2014 to accompany a talk in the Transactions Symposium "100 Years of Crystallography" at the 2014 American Crystallographic Association Annual Meeting (talk at https://history.amercrystalassn.org/h-brian-toby-videos). Abstract: Powder diffraction patterns were used for structure solution almost contemporaneously with the Bragg’s initial single-crystal determinations. Structures have continued to be determined from powders, in the subsequent century. There has been a nearly explosive growth in this technique since the 1970’s. This was initially driven by neutron diffraction, which prompted the invention of Rietveld analysis, but synchrotrons have gone on to have at least as large an impact. There is no apparent upper limit to the scale of systems that can be structurally studied with powder diffraction; novel protein structures have been determined. When short-range ordering or disordered regions of a material are of interest, the Fourier transform of a powder diffraction pattern, the pair distribution function can be modeled.

Toby, Brian H.↗
DOE OSTI2017

Holography, Gravity and Condensed Matter

Over the five years of funding from this grant, I produced 26 publications. These include a book-long monograph on "Holographic Quantum Matter" that is currently in press with MIT press. The remainder were mostly published in Physical Review Letters, the Journal of High Energy Physics, Nature Physics, Classical and Quantum Gravity and Physical Review B. Over this period, the field of holography applied to condensed matter physics developed from a promising theoretical approach to a mature conceptual and practical edifice, whose ideas were realized in experiments. My own work played a central role in this development. In particular, in the final year of this grant, I co-authored two experimental papers in which ideas that I had developed in earlier years were shown to usefully describe transport in strongly correlated materials — these papers were published in Science and in the Proceedings of the National Academy of Sciences (obviously my contribution to these papers was theoretical). My theoretical work in this period developed several new directions of research that have proven to be influential. These include (i) The construction of highly inhomogeneous black hole event horizons, realizing disordered fixed points and describing new regimes of classical gravity, (ii) The conjecture of a bound on diffusivities that could underpin transport in strongly interacting media — an idea which may be proven in the near future and has turned out to be intimately connected to studies of quantum chaos in black holes and strongly correlated media, (iii) The characterization of new forms of hydrodynamic transport, e.g. with phase-disordered order parameters. These studies pertain to key open questions in our understanding of how non-quasiparticle, intrinsically strongly interacting systems can behave. In addition to the interface between holography and strongly interacting condensed matter systems, I made several advances on understanding the role of entanglement in quantum gravity. These included the first computation of holographic entanglement beyond the bulk classical limit as well understanding short distance entanglement in the emergent spacetime of the c=1 matrix quantum mechanics. The objective here is ultimately to understanding how a priori non-local degrees of freedom can re-arrange themselves quantum mechanically to support emergent local dynamics. Much of work funded by this grant involved collaboration with postdocs and graduate students, several of which were directly funded by the grant. These students have now successfully graduated to postdoctoral positions and in one case to high tech industry. The ideas developed in this work have directly fed into my current research in which I am aiming to prove fundamental bounds on entropy production and transport from quantum mechanics and statistical physics. As often, as with much of my previous work, black hole physics can be an inspiration for extreme dynamics such as fundamental bounds, but ultimately one hopes to prove them using more general tools of quantum field theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1980

Mechanisms for vestibular disorders in space flight. Facts and hypotheses

This article discusses the vestibular disorders associated with space flight. It is found there is still no complete understanding of the changes occurring in the sensory systems of the body during weightlessness. Results of studies are presented, including results of a ground model.

Matsnev, E. I.↗
NASA NTRS1999

The Effects of Gravity on the Circadian Timing System

All vertebrates have a physiological control system that regulates the timing of the rhythms of their daily life. Dysfunction of this system, the circadian timing system (CTS), adversely affects an organism's ability to respond to environmental challenges and has been linked to physiological and psychological disorders. Exposure to altered gravitational environments (the microgravity of space and hyperdynamic environments produced via centrifugation) produces changes in both the functioning of the CTS and the rhythmic variables it controls. The earliest record of primate rhythms in a spaceflight environment come from Biosatellite III. The subject, a pig-tailed macaque, showed a loss of synchronization of the body temperature rhythm and a fragmented sleep-wake cycle. Alterations in the rhythm of body temperature were also seen in rhesus macaques flown on COSMOS 1514. Squirrel monkeys exposed to chronic centrifugation showed an initial decrease in the amplitude and mean of their body temperature and activity rhythms. In a microgravity environment, Squirrel monkeys on Spacelab-3 showed a reduction in the mean and amplitude of their feeding rhythms. Since 1992 we have had the opportunity to participate on three US/Russian sponsored biosatellite missions on which a total of six juvenile male rhesus macaques were flown. These animals uniformly exhibited delays in the phasing of their temperature rhythms, but not their heart rate or activity rhythms during spaceflight. There was also a tendency for changes in waveform mean and amplitude. These data suggest that the spaceflight environment may have a differential effect on the different oscillators controlling different rhythmic variables. Ongoing studies are examining the effects of +G on the CTS. The long-term presence of humans in space highlights the need for effective countermeasures to gravitational effects on the CTS.

Fuller, Charles A.↗
DOE OSTI2015

Correlated rattling-ion origins of dielectric properties in reentrant dipole glasses BaTiO{sub 3}-BiScO{sub 3}

The local structure of the pseudo-cubic solid solution 0.6BaTiO{sub 3}-0.4BiScO{sub 3}, which exhibits reentrant dipole-glass behavior, has been determined using the Reverse Monte Carlo method to simultaneously fit (1) neutron and X-ray total scattering data (including the corresponding real-space pair-distribution functions), (2) Bi and Sc extended X-ray absorption fine structure, and (3) patterns of diffuse scattering in electron diffraction. These structural refinements revealed the multi-site probability density distributions for both Bi (14-sites) and Ti (8 sites), whereas Ba and Sc featured normal unimodal distributions. Bi atoms are displaced along both the 〈111〉 and 〈100〉 directions, while Ti atoms are shifted along 〈111〉. Correlated dynamic hopping of Bi and Ti over their corresponding split sites combined with chemical disorder is proposed as the origin of the strong frequency dispersion observed in dielectric measurements. The existence of split sites also explains the reentrant dipole-glass behavior reported for this system.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

MODELING THE DYNAMICS OF MATERIALS PROCESSING AND ELECTROCHEMICAL SYSTEMS FOR ENERGY STORAGE APPLICATIONS

To realize the promise of electric vehicles, personal electronics, and renewable energy sources, improvements in energy storage technology are crucial. However, avenues for improvement such as designing superior electrode materials or modifying the battery electrolyte and separator are difficult without sufficient understanding of the materials and processes used to produce them. One such process is electrospinning, which uses high voltage to produce polymer nanofibers cheaply and continuously. To examine the effect of electrospinning on material morphology, the placement of nanoparticles within lamella-forming polymer blends and block copolymers is simulated using molecular dynamics under planar elongational flow. Then, extensional flow is combined with cylindrical confinement to simulate a block copolymer-filled cylinder with a constantly shrinking diameter, which is a better model for electrospinning. The appearance of ordered or disordered morphologies is found to be connected to a Weissenberg number relating the deformation and self-assembly time scales. A second approach towards understanding energy storage systems is to simulate the battery’s electrochemical performance. Of particular interest is the lithium-sulfur (Li-S) battery, which aims to replace lithium-ion batteries due to its higher specific capacity and cheaper material costs. However, well-known challenges such as polysulfide crossover, large volume changes during cycling, and deposition of insulating lithium sulfide limit the capacity and capacity retention of Li-S batteries. Using a continuum-level numerical simulation which includes reaction, mass transport, adsorption, and nucleation, these challenges are investigated in order to explain the mechanisms underlying Li-S discharge behavior. The model is used to explain the end-of-discharge failure behavior of liquid and gel electrolyte systems, finding that insufficient mass transport of polysulfides is the cause. In addition, the effects of adsorptive materials, cathode passivation with insulating lithium sulfide, and spherical carbon cathode particle geometry is investigated. It is found that adsorptive materials can greatly improve battery performance when the location of lithium sulfide deposition is considered in the model. Finally, the model suggests that different cathode processing techniques in experiment can lead to different end-of-discharge failure mechanisms.

25 ENERGY STORAGE↗
DOE OSTI2022

Case studies of robots and automation as health/safety interventions in small manufacturing enterprises

This article reviews the experiences of 63 case studies of small businesses (<250 employees) with manufacturing automation equipment acquired through a health/safety intervention grant program. The review scope included equipment technologies classified as industrial robots (n = 17), computer numerical control (CNC) machining (n = 29), or other programmable automation systems (n = 17). Descriptions of workers' compensation (WC) claim injuries and identified risk factors that motivated the acquisition of the equipment were extracted from grant applications. Other aspects of the employer experiences, including qualitative and quantitative assessment of effects on risk factors for musculoskeletal disorders (MSD), effects on productivity, and employee acceptance of the intervention were summarized from the case study reports. Case studies associated with a combination of large reduction in risk factors, lower cost per affected employee, and reported increases in productivity were CNC stone cutting system, CNC/vertical machining system, automated system for bottling, CNC/routing system for plastics products manufacturing, and a CNC/Cutting system for vinyl/carpet. Six case studies of industrial robots reported quantitative reductions in MSD risk factors in these diverse manufacturing industries: snack foods; photographic film, paper, plate, and chemical; machine shops; leather goods and allied products; plastic products; and iron and steel forging. Furthermore, this review of health/safety intervention case studies indicates that advanced (programmable) manufacturing automation, including industrial robots, reduced workplace musculoskeletal risk factors, and improved process productivity in most cases.

42 ENGINEERING↗
DOE OSTI2021

Nanoparticle-Induced Disorder at Complex Liquid–Liquid Interfaces: Effects of Curvature and Compositional Synergy on Functional Surfaces

The self-assembly of surfactant monolayers at interfaces plays a sweeping role in tasks ranging from household cleaning to the regulation of the respiratory system. The synergy between different nanoscale species at an interface can yield assemblies with exceptional properties, which enhance or modulate their function. However, understanding the mechanisms underlying coassembly, as well as the effects of intermolecular interactions at an interface, remains an emerging and challenging field of study. Herein, we study the interactions of gold nanoparticles striped with hydrophobic and hydrophilic ligands with phospholipids at a liquid–liquid interface and the resulting surface-bound complexes. We show that these nanoparticles, which are themselves minimally surface active, have a direct concentration-dependent effect on the rapid reduction of tension for assembling phospholipids at the interface, implying molecular coassembly. Through the use of sum frequency generation vibrational spectroscopy, we reveal that nanoparticles impart structural disorder to the lipid molecular layers, which is related to the increased volumes that amphiphiles can sample at the curved surface of a particle. The results strongly suggest that hydrophobic and electrostatic attractions imparted by nanoparticle functionalization drive lipid–nanoparticle complex assembly at the interface, which synergistically aids lipid adsorption even when lipids and nanoparticles approach the interface from opposite phases. The use of tensiometric and spectroscopic analyses reveals a physical picture of the system at the nanoscale, allowing for a quantitative analysis of the intermolecular behavior that can be extended to other systems.

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

New insights into the mechanism governing the elasticity of calcium silicate hydrate gels exposed to high temperature: A molecular dynamics study

When exposed to fire, the integrity of cement-based materials is governed by thermally-induced changes in the mechanical properties of their binding phase, i.e., the calcium–silicate–hydrate (C–S–H) gel. However, the effect of temperature on the structure, density, and mechanical properties of C–S–H remains only partially known. Here, based on reactive molecular dynamics simulations, we reveal the nature of thermally-induced damage in C–S–H gels. In general, we show that, at the atomic scale, exposure to high temperature results in partial dehydration, volumetric shrinkage, disordering, and stiffening in the C–S–H grains. However, we show that the thermal response of C–S–H strongly depends on its chemical composition, wherein C–S–H systems associated with lower Ca/Si molar ratios are able to undergo higher temperatures before amorphization. Based on these results, we demonstrate that the stiffness of C–S–H gels (i.e., including porosity—as probed by nanoindentation) is governed by a competition between the stiffening of the grains and the decrease in packing density—wherein the latter eventually become predominant.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Effect of disorder on the charge-carrier dynamics in {kappa}-(D{<_8}-ET){<_2}Cu[N(CN){<_2}]Br.

We have applied resistance fluctuation spectroscopy to study the intrinsic low-frequency dynamics of the charge carriers in the system {kappa}-(D{sub 8}-ET){sub 2}Cu[N(CN){sub 2}]Br for two different cooling rates. A strong increase of both the resistance and the noise level is observed below the thermodynamic glass-transition temperature T{sub g}. Surprisingly, the data of the normalized spectral weight <({delta}R){sup 2}>/R{sup 2} fall on top of each other for both cooling rates except for temperatures near the Mott critical point (T{sub 0} {approx_equal} 35 K) and below 28 K. The suppression of the peak in <({delta}R){sup 2}>/R{sup 2} associated with the Mott transition suggests that disorder is an additional parameter in the generalized phase diagram. The enhanced noise level below 28 K might be explained by a disorder-induced staggered magnetic moment in the metallic state close to the antiferromagnetic Mott insulator.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

A Critical Review of Existing Criteria for the Prediction of Pyrochlore Formation and Stability

Depending on intrinsic (e.g., radius ratio rule r Ln / r Zr ) and extrinsic factors (e.g., processing conditions), pyrochlore-type Ln 2 Zr 2 O 7 oxides achieve variable degrees of structural disorder. In this paper we report on a systematic study of the structural and microstructural characteristics of the Gd 2– x Ln x Zr 2 O 7 system, exploring the effect of replacing Gd with a wide range of homovalent lanthanide ions (Ln = Nd, Sm, Dy, Ho, Y, and Er; x = 0.20 and 0.80). All compositions were prepared via a mechanochemical reaction between the corresponding oxides and characterized by X-ray diffraction (standard and synchrotron sources) using the Rietveld method, as well as by Raman spectroscopy. Irrespective of chemical composition, this study reveals that all compositions exhibit a fluorite-like structure. Furthermore, by firing each sample at 800 and 1400 °C, we are able to analyze the transition to pyrochlore-like structures, featuring different degrees of disorder, in all but Gd 1.20 Y 0.80 Zr 2 O 7 , which retains the fluorite structure even after heating. The structural data are used to assess the existing criteria for predicting the formation and stability of the pyrochlore structure; according to this analysis, the simple radius ratio rule ( r Ln / r Zr ), provides a useful and sufficiently robust criterion. Because the pyrochlore structure has a strong tendency to disorder, it is not possible to define an empirical index similar to the Goldschmidt tolerance factor for perovskite.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Periodic ordering of clusters and stripes in a two-dimensional lattice model. I. Ground state, mean-field phase diagram and structure of the disordered phases

The short-range attraction and long-range repulsion between nanoparticles or macromolecules can lead to spontaneous pattern formation on solid surfaces, fluid interfaces, or membranes. In order to study the self-assembly in such systems we consider a triangular lattice model with nearest-neighbor attraction and third-neighbor repulsion. At the ground state of the model (T = 0) the lattice is empty for small values of the chemical potential μ, and fully occupied for large μ. For intermediate values of μ periodically distributed clusters, bubbles, or stripes appear if the repulsion is sufficiently strong. At the phase coexistences between the vacuum and the ordered cluster phases and between the cluster and the lamellar (stripe) phases the entropy per site does not vanish. As a consequence of this ground state degeneracy, disordered fluid phases consisting of clusters or stripes are stable, and the surface tension vanishes. For T > 0 we construct the phase diagram in the mean-field approximation and calculate the correlation function in the self-consistent Brazovskii-type field theory.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Configurational entropy of hydrogen-disordered ice polymorphs

The configurational entropy of several H-disordered ice polymorphs is calculated by means of a thermodynamic integration along a path between a totally H-disordered state and one fulfilling the Bernal-Fowler ice rules. A Monte Carlo procedure based on a simple energy model is used, so that the employed thermodynamic path drives the system from high temperatures to the low-temperature limit. This method turns out to be precise enough to give reliable values for the configurational entropy s{sub th} of different ice phases in the thermodynamic limit (number of molecules N → ∞). The precision of the method is checked for the ice model on a two-dimensional square lattice. Results for the configurational entropy are given for H-disordered arrangements on several polymorphs, including ices Ih, Ic, II, III, IV, V, VI, and XII. The highest and lowest entropy values correspond to ices VI and XII, respectively, with a difference of 3.3% between them. The dependence of the entropy on the ice structures has been rationalized by comparing it with structural parameters of the various polymorphs, such as the mean ring size. A particularly good correlation has been found between the configurational entropy and the connective constant derived from self-avoiding walks on the ice networks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Light-induced dilation in nanosheets of charge-transfer complexes

We observe a sizable photostrictive effect of 5.7% with fast, submillisecond response times, arising from a light-induced lattice dilation of a molecular nanosheet, composed of the molecular charge-transfer compound dibenzotetrathiafulvalene (DBTTF) and C 60 . An interfacial self-assembly approach is introduced for the thickness-controlled growth of the thin films. From photoabsorption measurements, molecular simulations, and electronic structure calculations, we suggest that photostriction within these films arises from a transformation in the molecular structure of constituent molecules upon photoinduced charge transfer, as well as the accommodation of free charge carriers within the material. Additionally, we find that the photostrictive properties of the nanosheets are thickness-dependent, a phenomenon that we suggest arises from surface-induced conformational disorder in the molecular components of the film. Moreover, because of the molecular structure in the films, which results largely from interactions between the constituent π-systems and the sulfur atoms of DBTTF, the optoelectronic properties are found to be anisotropic. This work enables the fabrication of 2D molecular charge-transfer nanosheets with tunable thicknesses and properties, suitable for a wide range of applications in flexible electronic technologies.

2D nanosheets↗