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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 1,621 records · Page 90
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Come for predictions, stay for complexity: synthesis and experimental probing of ionic conductivity in Li 9 B 19 S 33

Lithium thioborates, despite their potential cost-effectiveness and low density, have received considerably less attention as solid electrolytes compared to their thiophosphate counterparts. A primary obstacle to their widespread investigation has been the inherent challenge in synthesizing single-phase materials. Computational studies have predicted several lithium thioborate phases exhibiting high ionic conductivity, with Li 9 B 19 S 33 notably predicted to reach 80 mS cm −1 . However, experimental validation of these theoretical predictions remains absent. This work addresses this gap by detailing a successful synthesis of the previously elusive Li 9 B 19 S 33 phase, facilitated by in situ temperature dependent powder X-ray diffraction. Our findings reveal the peritectic nature of phase formation, necessitating an excess of boron sulfide in the reaction mixture. We further present a comprehensive structural characterization of Li 9 B 19 S 33 utilizing spectroscopic techniques like NMR, FT-IR, and diffuse reflectance and report on its ionic conductivity. Solid-state 6 Li NMR line narrowing experiments revealed an ion mobility activation energy of 0.26 eV whereas activation energies derived from impedance spectroscopy measurements were significantly higher, resulting in lower than theoretically predicted ionic conductivity.

Oppong, Richeal A. [Iowa State Univ., Ames, IA (Un↗
DOE OSTI2018

Structural insights into lethal contractural syndrome type 3 (LCCS3) caused by a missense mutation of PIP5Kγ

Signaling molecule phosphatidylinositol 4,5-bisphosphate is produced primarily by phosphatidylinositol 4-phosphate 5-kinase (PIP5K). PIP5K is essential for the development of the human neuronal system, which has been exemplified by a recessive genetic disorder, lethal congenital contractural syndrome type 3, caused by a single aspartate-to-asparagine mutation in the kinase domain of PIP5Kγ. So far, the exact role of this aspartate residue has yet to be elucidated. As such, we conducted structural, functional and computational studies on a zebrafish PIP5Kα variant with a mutation at the same site. Compared with the structure of the wild-type (WT) protein in the ATP-bound state, the ATP-associating glycine-rich loop of the mutant protein was severely disordered and the temperature factor of ATP was significantly higher. Both observations suggest a greater degree of disorder of the bound ATP, whereas neither the structure of the catalytic site nor the Km toward ATP was substantially affected by the mutation. Microsecond molecular dynamics simulation revealed that negative charge elimination caused by the mutation destabilized the involved hydrogen bonds and affected key electrostatic interactions in the close proximity of ATP. Taken together, our data indicated that the disease-related aspartate residue is a key node in the interaction network crucial for effective ATP binding. This work provides a paradigm of how a subtle but critical structural perturbation caused by a single mutation at the ATP-binding site abolishes the kinase activity, emphasizing that stabilizing substrate in a productive conformational state is crucial for catalysis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Capacity Design Method for Integrated Convective/Radiant Terminals to Guarantee Overall and Local Environment

To achieve energy efficiency in the operation of heating devices and ensure thermal comfort in indoor environments, the integrated convective/radiant terminals have become an important development direction for heating systems. This study selected a 14 m 2 bedroom hot summer and cold winter region in China as a case study. Computational Fluid Dynamics (CFD) methodology was used to investigate the design of integrated convective/radiant terminals to ensure thermal comfort for both the entire room and partial space. The results indicate that focusing on partial space during the steady-state stage can achieve energy savings of 31.1% compared to guaranteeing the entire room. Additionally, during the start-up stage, there is a significant reduction of convective unit capacity by 17.6% when the start-up time is 15 minutes. These findings provide data support for the design and engineering applications of products of integrated convective/radiant terminals. Besides, the excess convection ratios for the entire room and partial space are specified as 0.69 to 0.80 and 0.73 to 0.83, respectively.

Chi, Junjie↗
DOE OSTI2013

Modeling oscillatory dynamics in brain microcircuits as a way to help uncover neurological disease mechanisms: A proposal

There is an undisputed need and requirement for theoretical and computational studies in Neuroscience today. Furthermore, it is clear that oscillatory dynamical output from brain networks is representative of various behavioural states, and it is becoming clear that one could consider these outputs as measures of normal and pathological brain states. Although mathematical modeling of oscillatory dynamics in the context of neurological disease exists, it is a highly challenging endeavour because of the many levels of organization in the nervous system. This challenge is coupled with the increasing knowledge of cellular specificity and network dysfunction that is associated with disease. Recently, whole hippocampus in vitro preparations from control animals have been shown to spontaneously express oscillatory activities. In addition, when using preparations derived from animal models of disease, these activities show particular alterations. These preparations present an opportunity to address challenges involved with using models to gain insight because of easier access to simultaneous cellular and network measurements, and pharmacological modulations. We propose that by developing and using models with direct links to experiment at multiple levels, which at least include cellular and microcircuit, a cycling can be set up and used to help us determine critical mechanisms underlying neurological disease. We illustrate our proposal using our previously developed inhibitory network models in the context of these whole hippocampus preparations and show the importance of having direct links at multiple levels.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Hydrogen evolution from water through metal sulfide reactions

Transition metal sulfides play an important catalytic role in many chemical reactions. In this work, we have conducted a careful computational study of the structures, electronic states, and reactivity of metal sulfide cluster anions M{sub 2}S{sub X}{sup −} (M = Mo and W, X = 4–6) using density functional theory. Detailed structural analysis shows that these metal sulfide anions have ground state isomers with two bridging sulfide bonds, notably different in some cases from the corresponding oxides with the same stoichiometry. The chemical reactivity of these metal sulfide anions with water has also been carried out. After a thorough search on the reactive potential energy surface, we propose several competitive, energetically favorable, reaction pathways that lead to the evolution of hydrogen. Selectivity in the initial water addition and subsequent hydrogen migration are found to be the key steps in all the proposed reaction channels. Initial adsorption of water is most favored involving a terminal metal sulfur bond in Mo{sub 2}S{sub 4}{sup −} isomers whereas the most preferred orientation for water addition involves a bridging metal sulfur bond in the case of W{sub 2}S{sub 4}{sup −} and M{sub 2}S{sub 5}{sup −} isomers. In all the lowest energy H{sub 2} elimination steps, the interacting hydrogen atoms involve a metal hydride and a metal hydroxide (or thiol) group. We have also observed a higher energy reaction channel where the interacting hydrogen atoms in the H{sub 2} elimination step involve a thiol (–SH) and a hydroxyl (–OH) group. For all the reaction pathways, the Mo sulfide reactions involve a higher barrier than the corresponding W analogues. We observe for both metals that reactions of M{sub 2}S{sub 4}{sup −} and M{sub 2}S{sub 5}{sup −} clusters with water to liberate H{sub 2} are exothermic and involve modest free energy barriers. However, the reaction of water with M{sub 2}S{sub 6}{sup −} is highly endothermic with a considerable barrier due to saturation of the local bonding environment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Ab initio modeling of graphene layer functionalized with boron and nitrogen

We present a computational study of the phenomenon of opening the band gap in graphene by means of functionalization with boron and nitrogen atoms. For most of the considered structures, we observe a nonzero energy gap with the width slightly dependent on the concentration of the substituent atoms. Additionally, elastic properties for graphene functionalized with B/N atoms for concentrations of 2% and 4% have been predicted. N-substitution almost does not influence the elastic moduli of graphene, while changes caused by B-substitution are more remarkable.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Phonon dispersion and thermal conductivity of nanocrystal superlattices using three-dimensional atomistic models

A computational study of thermal conductivity and phonon dispersion of gold nanocrystal superlattices is presented. Phonon dispersion curves, reported here for the first time from combined molecular dynamics and lattice dynamics calculations, show multiple phononic band gaps and consist of many more dispersion branches than simple atomic crystals. Fully atomistic three dimensional molecular dynamics calculations of thermal conductivity using the Green Kubo method are also performed for the first time on these materials. Thermal conductivity is observed to increase for increasing nanocrystal core size and decrease for increasing surface ligand density. Our calculations predict values in the range 0.1–1 W/m K that are consistent with reported experimental results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Theoretical study of defect formation during the initial stages of native-oxide growth on GaSb (001)

The formation of defects during the initial stages of native-oxide growth on the GaSb (001)-α(4 × 3) surface has been studied computationally using spin-unrestricted density functional theory. It is found that insertion into a Ga-Sb adatom dimer to form a peroxo Ga-O-O-Sb bridge is the most energetically favorable process with insertion into Ga-Sb back-bonds being somewhat less so. A Ga-O-O-Ga bridge between dimers is also favorable, but Sb-O-O-Sb bridges show little if any stability. In the course of analyzing molecular adsorption, a particularly reactive site has been identified that leads to O{sub 2} dissociation with little or no barrier. This process is initiated in the vicinity of an Sb-Sb dimer in the terminating layer and leads to sub-surface Ga and Sb defect sites (i.e., coordinatively unsaturated atoms) and to strained Ga-Sb bonds that may be susceptible to further O{sub 2} attack. However, the defects formed in these reactions do not produce states in the gap.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Titanium embedded cage structure formation in Al{sub n}Ti{sup +} clusters and their interaction with Ar

Recently, Ar physisorption was used as a structural probe for the location of the Ti dopant atom in aluminium cluster cations, Al{sub n}Ti{sup +} [Lang et al., J. Am. Soc. Mass Spectrom. 22, 1508 (2011)]. As an experiment result, the lack of Ar complexes for n > n{sub c} determines the cluster size for which the Ti atom is located inside of an Al cage. To elucidate the decisive factors for the formation of endohedrally Al{sub n}Ti{sup +}, experimentalists proposed detailed computational studies as indispensable. In this work, we investigated, using the density functional theory, the structural and electronic properties of singly titanium doped cationic clusters, Al{sub n}Ti{sup +} (n = 16–21) as well as the adsorption of an Ar atom on them. The first endohedral doped cluster, with Ti encapsulated in a fcc-like cage skeleton, appears at n{sub c} = 21, which is the critical number consistent with the exohedral-endohedral transition experimentally observed. At this critical size the non-crystalline icosahedral growth pattern, related to the pure aluminium clusters, with the Ti atom in the surface, changes into a endohedral fcc-like pattern. The map of structural isomers, relative energy differences, second energy differences, and structural parameters were determined and analyzed. Moreover, we show the critical size depends on the net charge of the cluster, being different for the cationic clusters (n{sub c} = 21) and their neutral counterparts (n{sub c} = 20). For the Al {sub n} Ti {sup +} · Ar complexes, and for n < 21, the preferred Ar adsorption site is on top of the exohedral Ti atom, with adsorption energy in very good agreement with the experimental value. Instead, for n = 21, the Ar adsorption occurs on the top an Al atom with very low absorption energy. For all sizes the geometry of the Al{sub n}Ti{sup +} clusters keeps unaltered in the Ar-cluster complexes. This fact indicates that Ar adsorption does not influence the cluster structure, providing support to the experimental technique used. For n{sub c} = 21, the smallest size of endohedral Ti doped cationic clusters, the Ar binding energy decreases drastically, whereas the Ar-cluster distance increases substantially, point to Ar physisorption, as assumed by the experimentalists. Calculated Ar adsorption energies agree well with available experimental binding energies.

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

Potential of mean force analysis of the self-association of leucine-rich transmembrane α-helices: Difference between atomistic and coarse-grained simulations

Interaction of transmembrane (TM) proteins is important in many biological processes. Large-scale computational studies using coarse-grained (CG) simulations are becoming popular. However, most CG model parameters have not fully been calibrated with respect to lateral interactions of TM peptide segments. Here, we compare the potential of mean forces (PMFs) of dimerization of TM helices obtained using a MARTINI CG model and an atomistic (AT) Berger lipids-OPLS/AA model (AT{sup OPLS}). For helical, tryptophan-flanked, leucine-rich peptides (WL15 and WALP15) embedded in a parallel configuration in an octane slab, the AT{sup OPLS} PMF profiles showed a shallow minimum (with a depth of approximately 3 kJ/mol; i.e., a weak tendency to dimerize). A similar analysis using the CHARMM36 all-atom model (AT{sup CHARMM}) showed comparable results. In contrast, the CG analysis generally showed steep PMF curves with depths of approximately 16–22 kJ/mol, suggesting a stronger tendency to dimerize compared to the AT model. This CG > AT discrepancy in the propensity for dimerization was also seen for dilauroylphosphatidylcholine (DLPC)-embedded peptides. For a WL15 (and WALP15)/DLPC bilayer system, AT{sup OPLS} PMF showed a repulsive mean force for a wide range of interhelical distances, in contrast to the attractive forces observed in the octane system. The change from the octane slab to the DLPC bilayer also mitigated the dimerization propensity in the CG system. The dimerization energies of CG (AALALAA){sub 3} peptides in DLPC and dioleoylphosphatidylcholine bilayers were in good agreement with previous experimental data. The lipid headgroup, but not the length of the lipid tails, was a key causative factor contributing to the differences between octane and DLPC. Furthermore, the CG model, but not the AT model, showed high sensitivity to changes in amino acid residues located near the lipid-water interface and hydrophobic mismatch between the peptides and membrane. These findings may help interpret CG and AT simulation results on membrane proteins.

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

Vibrationally specific photoionization cross sections of acrolein leading to the Χ{sup ~}A{sup '} ionic state

The vibrational branching ratios in the photoionization of acrolein for ionization leading to the Χ{sup ~}A{sup '} ion state were studied. Computed logarithmic derivatives of the cross section and the corresponding experimental data derived from measured vibrational branching ratios for several normal modes (ν{sub 9}, ν{sub 10}, ν{sub 11}, and ν{sub 12}) were found to be in relatively good agreement, particularly for the lower half of the 11–100 eV photon energy range considered. Two shape resonances have been found near photon energies of 15.5 and 23 eV in the photoionization cross section and have been demonstrated to originate from the partial cross section of the A{sup ′} scattering symmetry. The wave functions computed at the resonance complex energies are delocalized over the whole molecule. By looking at the dependence of the cross section on the different normal mode displacements together with the wave function at the resonant energy, a qualitative explanation is given for the change of the cross sections with respect to changing geometry.

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

The thermodynamics of proton hydration and the electrochemical surface potential of water

The free energy change for transferring a single ion across the water liquid/vapor interface includes an electrochemical surface potential contribution. Since this potential is not directly accessible to thermodynamic measurement, several extra-thermodynamic approaches have been employed to infer its sign and magnitude, with a resulting wide spread of values. Here, we examine further the thermodynamics of proton hydration and the electrochemical surface potential of water along three directions: (1) a basic relation of interfacial electrostatics and experimental results on ion distributions near a water/organic interface are employed to infer a solvent contribution to the electrochemical surface potential, (2) a re-analysis is performed of the existing bulk and cluster ion hydration data, and (3) extensive computational modeling is conducted to examine the size dependence of hydration enthalpy differences for the NaF ion pair between the small cluster and the converged bulk limits. The computational studies include classical polarizable models and high-level quantum chemical methods. The new theoretical analysis of existing experimental data and the combined classical/quantum modeling lead to results consistent with our previously derived proton hydration quantities.

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

Stereo-selective partitioning of translation-to-internal energy conversion in gas ensembles

A recent computational study of translation-to-internal energy transfer to H{sub 2} (v = 0,j = 0), hereinafter denoted H{sub 2} (0;0), in a bath of H atoms [A. J. McCaffery and R. J. Marsh, J. Chem. Phys. 139, 234310 (2013)] revealed an unexpected energy partitioning in which the H{sub 2} vibrational temperature greatly exceeds that of rotation. This occurs despite rotation and vibration distributions being close to Boltzmann from early in ensemble evolution. In this work, the study is extended to include H{sub 2} (0;0), O{sub 2} (0;0), and HF (0;0) in a wide range of atomic bath gases comprising some 22 ensembles in all. Translation-to-internal energy conversion in the systems studied was found to be relatively inefficient, falling approximately with (√μ′){sup −1} as bath gas mass increases, where μ′ is the reduced mass of the diatomic–bath gas pair. In all 22 systems studied, T{sub v} exceeds T{sub r} – by a factor > 4 for some pairs. Analysis of the constraints that influence (0;0) → (1;j) excitation for each diatomic–atom pair in momentum–angular momentum space demonstrates that a vibrational preference results from energy constraints that limit permitted collision trajectories to those of low effective impact parameter, i.e., to those that are axial or near axial on impact with the Newton surface. This implies that a steric constraint is an inherent feature of vibration-rotation excitation and arises because momentum and energy barriers must be overcome before rotational states may be populated in the higher vibrational level.

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

On readout of vibrational qubits using quantum beats

Readout of the final states of qubits is a crucial step towards implementing quantum computation in experiment. Although not scalable to large numbers of qubits per molecule, computational studies show that molecular vibrations could provide a significant (factor 2–5 in the literature) increase in the number of qubits compared to two-level systems. In this theoretical work, we explore the process of readout from vibrational qubits in thiophosgene molecule, SCCl{sub 2}, using quantum beat oscillations. The quantum beats are measured by first exciting the superposition of the qubit-encoding vibrational states to the electronically excited readout state with variable time-delay pulses. The resulting oscillation of population of the readout state is then detected as a function of time delay. In principle, fitting the quantum beat signal by an analytical expression should allow extracting the values of probability amplitudes and the relative phases of the vibrational qubit states. However, we found that if this procedure is implemented using the standard analytic expression for quantum beats, a non-negligible phase error is obtained. We discuss the origin and properties of this phase error, and propose a new analytical expression to correct the phase error. The corrected expression fits the quantum beat signal very accurately, which may permit reading out the final state of vibrational qubits in experiments by combining the analytic fitting expression with numerical modelling of the readout process. The new expression is also useful as a simple model for fitting any quantum beat experiments where more accurate phase information is desired.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Probing ground and low-lying excited states for HIO{sub 2} isomers

We present a computational study on HIO{sub 2} molecules. Ground state properties such as equilibrium structures, relative energetics, vibrational frequencies, and infrared intensities were obtained for all the isomers at the coupled-cluster with single and double excitations as well as perturbative inclusion of triples (CCSD(T)) level of theory with the aug-cc-pVTZ-PP basis set and ECP-28-PP effective core potential for iodine and the aug-cc-pVTZ basis set for hydrogen and oxygen atoms. The HOIO structure is confirmed as the lowest energy isomer. The relative energies are shown to be HOIO < HOOI < HI(O)O. The HO(O)I isomer is only stable at the density functional theory (DFT) level of theory. The transition states determined show interconversion of the isomers is possible. In order to facilitate future experimental identification, vibrational frequencies are also determined for all corresponding deuterated species. Vertical excitation energies for the three lowest-lying singlet and triplet excited states were determined using the configuration interaction singles, time-dependent density functional theory (TD-DFT)/B3LYP, TD-DFT/G96PW91, and equation of motion-CCSD approaches with the LANL2DZ basis set plus effective core potential for iodine and the aug-cc-pVTZ basis set for hydrogen and oxygen atoms. It is shown that HOIO and HOOI isomers have excited states accessible at solar wavelengths (<4.0 eV) but these states have very small oscillator strengths (<2 × 10{sup −3})

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

Understanding neutron production in the deuterium dense plasma focus

The deuterium Dense Plasma Focus (DPF) can produce copious amounts of MeV neutrons and can be used as an efficient neutron source. However, the mechanism by which neutrons are produced within the DPF is poorly understood and this limits our ability to optimize the device. In this paper we present results from a computational study aimed at understanding how neutron production occurs in DPFs with a current between 70 kA and 500 kA and which parameters can affect it. A combination of MHD and kinetic tools are used to model the different stages of the DPF implosion. It is shown that the anode shape can significantly affect the structure of the imploding plasma and that instabilities in the implosion lead to the generation of large electric fields at stagnation. These electric fields can accelerate deuterium ions within the stagnating plasma to large (>100 keV) energies leading to reactions with ions in the cold dense plasma. It is shown that the electromagnetic fields present can significantly affect the trajectories of the accelerated ions and the resulting neutron production.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Spatial filter based light-sheet laser interference technique for three-dimensional nanolithography

We propose a laser interference technique for the fabrication of 3D nano-structures. This is possible with the introduction of specialized spatial filter in a 2π cylindrical lens system (consists of two opposing cylindrical lens sharing a common geometrical focus). The spatial filter at the back-aperture of a cylindrical lens gives rise to multiple light-sheet patterns. Two such interfering counter-propagating light-sheet pattern result in periodic 3D nano-pillar structure. This technique overcomes the existing slow point-by-point scanning, and has the ability to pattern selectively over a large volume. The proposed technique allows large-scale fabrication of periodic structures. Computational study shows a field-of-view (patterning volume) of approximately 12.2 mm{sup 3} with the pillar-size of 80 nm and inter-pillar separation of 180 nm. Applications are in nano-waveguides, 3D nano-electronics, photonic crystals, and optical microscopy.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Thermodynamic and morphological analysis of large silicon self-interstitial clusters using atomistic simulations

We study computationally the formation of thermodynamics and morphology of silicon self-interstitial clusters using a suite of methods driven by a recent parameterization of the Tersoff empirical potential. Formation free energies and cluster capture zones are computed across a wide range of cluster sizes (2 < N{sub i} < 150) and temperatures (0.65 < T/T{sub m} < 1). Self-interstitial clusters above a critical size (N{sub i} ∼ 25) are found to exhibit complex morphological behavior in which clusters can assume either a variety of disordered, three-dimensional configurations, or one of two macroscopically distinct planar configurations. The latter correspond to the well-known Frank and perfect dislocation loops observed experimentally in ion-implanted silicon. The relative importance of the different cluster morphologies is a function of cluster size and temperature and is dictated by a balance between energetic and entropic forces. The competition between these thermodynamic forces produces a sharp transition between the three-dimensional and planar configurations, and represents a type of order-disorder transition. By contrast, the smaller state space available to smaller clusters restricts the diversity of possible structures and inhibits this morphological transition.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗