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At least 1,477 records · Page 82
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Water Structure at Hematite-Water Interfaces

The atomic-level structure of water at mineral surfaces is an important controlling factor in interfacial reactions such as foreign ion incorporation, crystal growth and dissolution, and redox reactions. Molecular dynamics simulations with four different models based on interatomic potentials have been carried out to determine the atomic-level structure of three hematite-water interfaces. In addition, for each of the three surfaces, different terminations or protonation schemes were considered. The availability of surface X-ray scattering data for the surfaces considered here allowed for an extensive comparison with experimental data. Qualitatively, with the exception of one termination with one model, all models predict the correct arrangement of water molecules at the interface. Quantitatively, the agreement with experimental positions, distances, and layer occupancies is good to excellent, especially given the range of values reported in published experimental studies. Therefore, this study provides further evidence that interatomic potential models can be used to reliably predict the structure of mineral-water interfaces. In addition, molecular simulations are a valuable source of information to complement surface X-ray scattering experiments owing to their ability to directly determine the position of hydrogen atoms and to yield three-dimensional predicted structures at no added cost, as demonstrated in this work. Indeed, the molecular dynamics trajectories were analyzed to determine the surface structural controls on the interfacial water structure. Each of the three surface functional groups present at the surfaces considered in this work, namely, triply-coordinated oxo, doubly-coordinated hydroxo, and singly-coordinated aquo groups, was found to form similar hydrogen bond configurations with adsorbed water molecules at all surfaces. Oxo groups accept long-lasting and linear hydrogen bonds from adsorbed water molecules; hydroxo groups can form hydrogen bonds with other surface functional groups as well as with adsorbed water molecules; and aquo groups normally only donate hydrogen bonds to other surface groups or adsorbed water molecules. Additionally, the majority of adsorbed water molecules were found to adopt multiple configurations and orientations. This information was used to evaluate three-dimensional structural models of the interfaces, which were previously derived experimentally from one-dimensional electron density profiles and steric considerations.

08 HYDROGEN↗
DOE OSTI2016

Reduced dislocation density in Ga x In 1–x P compositionally graded buffer layers through engineered glide plane switch

In this work we develop control over dislocation glide dynamics in Ga x In 1-x P compositionally graded buffer layers (CGBs) through control of CuPt ordering on the group-III sublattice. The ordered structure is metastable in the bulk, so any glissile dislocation that disrupts the ordered pattern will release stored energy, and experience an increased glide force. Here we show how this connection between atomic ordering and dislocation glide force can be exploited to control the threading dislocation density (TDD) in Ga x In 1-x P CGBs. When ordered Ga x In 1-x P is graded from the GaAs lattice constant to InP, the order parameter ..eta.. decreases as x decreases, and dislocation glide switches from one set of glide planes to the other. This glide plane switch (GPS) is accompanied by the nucleation of dislocations on the new glide plane, which typically leads to increased TDD. We develop control of the GPS position within a Ga x In 1-x P CGB through manipulation of deposition temperature, surfactant concentration, and strain-grading rate. We demonstrate a two-stage Ga x In 1-x P CGB from GaAs to InP with sufficiently low TDD for high performance devices, such as the 4-junction inverted metamorphic multi-junction solar cell, achieved through careful control the GPS position. Here, experimental results are analyzed within the context of a model that considers the force balance on dislocations on the two competing glide planes as a function of the degree of ordering.

14 SOLAR ENERGY↗
DOE OSTI2016

Pronounced Dielectric and Hydration/Dehydration Behaviors of Monopolar Poly( N -alkylglycine)s in Aqueous Solution

Poly(N-methylglycine) (NMG n ) and poly(N-ethylglycine) (NEG n ) obtained by polymerization reactions initiated by benzylamine have no carboxy termini, such as those in normal polyamides, but have only amino termini, which exist primarily as cations in aqueous media at a pH value of ca. 9.5, observed in aqueous solutions without any buffer reagents. Therefore, polypeptoids, such as NMG n and NEG n , possessing a degree of polymerization (DP) higher than a certain value behave as cationic monopolar polymeric chain molecules in aqueous solution. It has not been clarified so far whether such a monopolar chain molecule exhibits dielectric relaxation (DR) behavior resulting from its molecular motions in aqueous media as dipolar chain molecules. DR measurements revealed that NMG 19 and NEG 17 , possessing DPs of 19 and 17, respectively, dissolved in pure water clearly demonstrated pronounced DR behavior caused by fluctuating molecular motions of cationic termini at relaxation times of ca. 4 and 9 ns at 10 °C (283 K). The hydration numbers of NMG 19 and NEG 17 per monomeric residue (nm) in aqueous solution were also evaluated via DR data as functions of temperature, and the nm value of ca. 4.5 at 10 °C showed a remarkable reduction to ca. 2.0 around 40 °C (313 K) and 30 °C (303 K), depending on differences in the substituted group: methyl and ethyl groups. Furthermore, this temperature-dependent hydration/dehydration behavior found in NMG 19 and NEG 17 slightly influenced the sizes and molecular dynamics of the monopolar chain molecules in aqueous solution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Oxidation of the para-Tolyl Radical by Molecular Oxygen under Single-Collison Conditions: Formation of the para-Toloxy Radical

Crossed molecular beam experiments were performed to elucidate the chemical dynamics of the para-tolyl (CH 3 C 6 H 4 ) radical reaction with molecular oxygen (O 2 ) at an average collision energy of 35.3 ± 1.4 kJ mol –1 . Combined with theoretical calculations, the results show that para-tolyl is efficiently oxidized by molecular oxygen to para-toloxy (CH 3 C 6 H 4 O) plus ground-state atomic oxygen via a complex forming, overall exoergic reaction (experimental, -33 ± 16 kJ mol –1 ; computational, -42 ± 8 kJ mol –1 ). Finally, the reaction dynamics are analogous to those observed for the phenyl (C 6 H 5 ) plus molecular oxygen system which suggests the methyl group is a spectator during para-tolyl oxidation and that application of phenyl thermochemistry and reaction rates to para-substituted aryls is likely a suitable approximation.

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

Investigating Morphology and Diffusion in Simulations of Precise Anion-Conducting Polymers

Using atomistic molecular dynamics simulations, we investigate the morphology and transport properties of a new class of polymers which are functionalized with quaternary ammonium groups for use as anion exchange membranes. The polymers are precision polyolefins with either a trimethylammonium (p5CNMe3) or a dimethyl-hexyl ammonium (p5CNMe2Hx) pendant group at every fifth carbon along a polyethylene backbone. Simulations are performed at hydration levels of 5, 10, 15, and 20 water molecules per ammonium group. The hydrated polymers form nanoscale, percolated hydrophilic domains (water channels) in the hydrophobic polymer matrix that become wider with increasing water content. Water and hydroxide anion diffusion coefficients also increase with increasing water content. The morphology of the water domains is similar in both polymers, while the diffusion coefficients are somewhat lower in p5CNMe2Hx at fixed water content. Furthermore, the diffusion coefficients in both polymers fall on the same curve as a function of the fractal dimension of the percolated water channels, which appears to be a useful scalar measure of the effects of the nanoscale morphology on water and hydroxide anion transport.

Anion exchange membrane↗
DOE OSTI2020

Here aqueous solubilization of hydrophobic tetrapyrrole macrocycles by attachment to an amphiphilic single-chain nanoparticle (SCNP)

Solubilization of hydrophobic tetrapyrrole macrocycles and other fluorophores in aqueous solution has been achieved by covalent attachment to the terminus of an amphiphilic polymer, thereby affording a single-fluorophore–single-chain nanoparticle (SCNP). The polymer is a heterotelechelic random polyacrylate/polyacrylamide copolymer bearing hydrophobic and hydrophilic pendant groups. The polymer has a folded unimeric morphology (~13 nm hydrodynamic diameter) in 1 M NaCl aqueous solution as indicated by dynamic light-scattering spectroscopy. Five hydrophobic organic fluorophores (coumarin, perylene, two chlorins, one phthalocyanine) have been synthesized with a conjugatable tether. Covalent conjugation of the fluorophore–maleimide to the polymer terminus via thiol–maleimide reaction was carried out in DMF. The resulting fluorophore–SCNP in 1 M NaCl aqueous solution exhibited retained spectral features and fluorescence quantum yield comparable to those of the respective hydrophobic benchmark in toluene. This single-fluorophore–single-polymer strategy simplifies the challenging and often idiosyncratic syntheses of water-soluble tetrapyrrole macrocycles by using the polymer as a general aqueous solubilization package, and in so doing opens up opportunities for the application of hydrophobic fluorophores in the life sciences.

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

Computational insights of water droplet transport on graphene sheet with chemical density

Surface gradient has been emerging as an intriguing technique for nanoscale particle manipulation and transportation. Owing to its outstanding and stable chemical properties, graphene with covalently bonded chemical groups represents extraordinary potential for the investigation of nanoscale transport in the area of physics and biology. Here, we employ molecular dynamics simulations to investigate the fundamental mechanism of utilizing a chemical density on a graphene sheet to control water droplet motions on it. Simulation results have demonstrated that the binding energy difference among distinct segment of graphene in terms of interaction between the covalently bonded oxygen atoms on graphene and the water molecules provides a fundamental driving force to transport the water droplet across the graphene sheet. Also, the velocity of the water droplet has showed a strong dependence on the relative concentration of oxygen atoms between successive segments. Furthermore, a multi-direction channel provides insights to guide the transportation of objects towards a targeted position, separating the mixtures with a system of specific chemical functionalization. Our findings shed illuminating lights on the surface gradient method and therefore provide a feasible way to control nanoscale motion on the surface and mimic the channelless microfluidics.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

Quantization of systems with temporally varying discretization. I. Evolving Hilbert spaces

A temporally varying discretization often features in discrete gravitational systems and appears in lattice field theory models subject to a coarse graining or refining dynamics. To better understand such discretization changing dynamics in the quantum theory, an according formalism for constrained variational discrete systems is constructed. While this paper focuses on global evolution moves and, for simplicity, restricts to flat configuration spaces R{sup N}, a Paper II [P. A. Höhn, “Quantization of systems with temporally varying discretization. II. Local evolution moves,” J. Math. Phys., e-print http://arxiv.org/abs/arXiv:1401.7731 [gr-qc].] discusses local evolution moves. In order to link the covariant and canonical picture, the dynamics of the quantum states is generated by propagators which satisfy the canonical constraints and are constructed using the action and group averaging projectors. This projector formalism offers a systematic method for tracing and regularizing divergences in the resulting state sums. Non-trivial coarse graining evolution moves lead to non-unitary, and thus irreversible, projections of physical Hilbert spaces and Dirac observables such that these concepts become evolution move dependent on temporally varying discretizations. The formalism is illustrated in a toy model mimicking a “creation from nothing.” Subtleties arising when applying such a formalism to quantum gravity models are discussed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

The Wendelstein Weak Lensing (WWL) pathfinder: accurate weak lensing masses for Planck clusters

We introduce results from the Wendelstein Weak Lensing (WWL) pathfinder project, in which we have observed three intermediate-redshift Planck clusters of galaxies with the new 30 arcmin × 30 arcmin wide field imager at the 2 m Fraunhofer Telescope at Wendelstein Observatory. We investigate the presence of biases in our shear catalogues and estimate their impact on our weak lensing mass estimates. The overall calibration uncertainty depends on the cluster redshift and is below 8.1–16 per cent for z ≈ 0.27–0.77. It will decrease with improvements on the background sample selection and the multiplicative shear bias calibration. This work shows the first weak lensing mass estimates for PSZ1 G109.88+27.94 and PSZ1 G139.61+24.20, two Sunyaev-Zeldovich (SZ)-selected cluster candidates. Based on Wendelstein colours and SDSS (Sloan Digital Sky Survey) photometry, we find that the redshift of PSZ1 G109.88+27.94 has to be corrected to z ≈ 0.77. We investigate the influence of line-of-sight structures on the weak lensing mass estimates and find upper limits for two groups in each of the fields of PSZ1 G109.88+27.94 and PSZ1 G186.98+38.66. We compare our results to SZ and dynamical mass estimates from the literature, and in the case of PSZ1 G186.98+38.66 to previous weak lensing mass estimates. We conclude that our pathfinder project demonstrates that weak lensing cluster masses can be accurately measured with the 2 m Fraunhofer Telescope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Light chiral dark sector

An interesting possibility for dark matter is a scalar particle of mass of order 10 MeV-1 GeV, interacting with a U(1) gauge boson (dark photon) which mixes with the photon. We present a simple and natural model realizing this possibility. The dark matter arises as a composite pseudo-Nambu-Goldstone boson (dark pion) in a non-Abelian gauge sector, which also gives a mass to the dark photon. For a fixed non-Abelian gauge group, SU(N), and a U(1) charge of the constituent dark quarks, the model has only three free parameters: the dynamical scale of the non-Abelian gauge theory, the gauge coupling of the dark photon, and the mixing parameter between the dark and standard model photons. In particular, the gauge symmetry of the model does not allow any mass term for the dark quarks, and the stability of the dark pion is understood as a result of an accidental global symmetry. The model has a significant parameter space in which thermal relic dark pions comprise all of the dark matter, consistently with all experimental and cosmological constraints. In a corner of the parameter space, the discrepancy of the muon g-2 between experiments and the standard model prediction can also be ameliorated due to a loop contribution of the dark photon. Smoking-gun signatures of the model include a monophoton signal from the e + e - collision into a photon and a "dark rho meson." Observation of two processes in e + e - collision - the mode into the dark photon and that into the dark rho meson - would provide strong evidence for the model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Fast Rotational Diffusion of Water Molecules in a 2D Hydrogen Bond Network at Cryogenic Temperatures

Individual water molecules or small clusters of water molecules contained within microporous minerals present an extreme case of confinement where the local structure of hydrogen bond networks are dramatically altered from bulk water. In the zinc silicate hemimorphite, the water molecules form a two-dimensional hydrogen bond network with hydroxyl groups in the crystal framework. Here in this paper, we present a combined experimental and theoretical study of the structure and dynamics of water molecules within this network. The water molecules undergo a continuous phase transition in their orientational configuration analogous to a two-dimensional Ising model. The incoherent dynamic structure factor reveals two thermally activated relaxation processes, one on a subpicosecond timescale and another on a 10–100 ps timescale, between 70 and 130 K. The slow process is an in-plane reorientation of the water molecule involving the breaking of hydrogen bonds with a framework that, despite the low temperatures involved, is analogous to rotational diffusion of water molecules in the bulk liquid. The fast process is a localized motion of the water molecule with no apparent analogs among known bulk or confined phases of water.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Evaluating the Effectiveness of Soil Profile Rehabilitation for Pluvial Flood Mitigation Through Two-Dimensional Hydrodynamic Modeling

Pluvial flooding, driven by increasingly impervious surfaces and intense storm events, presents a growing challenge for urban areas worldwide. In Baltimore City, MD, USA, climate change, rapid urbanization, and aging stormwater infrastructure are exacerbating flooding impacts, resulting in significant socio-economic consequences. This study evaluated the effectiveness of a soil profile rehabilitation scenario using a 2D hydrodynamic modeling approach for the Tiffany Run watershed, Baltimore City. This study utilized different extreme storm events, a high-resolution (1 m) LiDAR Digital Terrain Model (DTM), building footprints, and hydrological soil data. These datasets were integrated into a fully coupled 2D hydrodynamic model, the City Catchment Analysis Tool (CityCAT), to simulate urban flood dynamics. The pre-soil rehabilitation simulation revealed a maximum water depth of 3.00 m in most areas, with hydrologic soil groups C and D, especially downstream of the study area. The post-soil rehabilitation simulation was targeted at vacant lots and public parcels, accounting for 33.20% of the total area of the watershed. This resulted in a reduced water depth of 2.50 m. Additionally, the baseline runoff coefficient of 0.49 decreased to 0.47 following the rehabilitation, and the model consistently recorded a peak runoff reduction rate of 4.10 across varying rainfall intensities. The validation using a contingency matrix demonstrated true-positive rates of 0.75, 0.50, 0.64, and 0 for the selected events, confirming the model’s capability at capturing real-world flood occurrences.

Baltimore City↗
DOE OSTI2024

Collaborative Design of Robust Adaptation Pathways for Urban Flooding Resilience in Baltimore

Urban pluvial flooding poses a growing threat to the city of Baltimore, driven by changes in climate and rainfall, increased impervious area, aging infrastructure, and severe social inequity. Adaptations to urban flooding should strengthen community-scale resilience while navigating the uncertainties associated with future actions. However, the highly uncertain future climate and conflicting stakeholder objectives complicate the selection of effective and socially acceptable strategies. This study addresses these challenges through a community-informed Multi Objective Robust Decision Making (MORDM) process, coupled with Dynamic Adaptation Policy Pathways (DAPP). Community stakeholders are engaged on a large scale through community partnerships, including priority identification sessions, focus groups, and metric identification workshops. The combination of community partnership, MORDM, and DAPP will create an original set of adaptation pathways which are aligned with community goals and values, and furthermore are adjustable under changing future constraints and conditions. This framework will enhance the city's capacity to respond to evolving pluvial flood conditions while accounting for diverse stakeholder interests and will provide guidance for addressing both the immediate and long-term challenges of urban flooding in Baltimore.

BSEC↗
NASA NTRS1973

A high resolution study in time, position, intensity, and frequency of a radio event on 14 January 1971

High resolution position and spectrum measurements were made of a complex solar radio activity on January 14, 1971, from 1120 to 1130 UT. Positions were measured with 169 MHz Nancay E-W Radioheliograph, while dynamic spectra and polarization were observed with the 60-channel radiospectrograph of Nera. The radio event consisted of two closely similar groups of type 3 bursts and type 2-like details, and a stationary type 4 continuum, including some very clear pulsating structures. The general aspect of this activity is presented.

Caroubalos, C.↗
NASA NTRS1981

Influence of display and control compatibility on pilot-induced oscillations

The differences in techniques used by seven pilots to acquire information from an advanced display for instrument approaches to and landings on a runway were investigated. A fixed base simulator programmed with dynamics resembling the terminal configured vehicle (TCV) was studied. It is shown that the seven pilots can be divided into two groups which used the display with distinctly different strategies for controlling the airplane. A related pattern of performance differences resulted. It is found that pilots who primarily use raw flight path information experience longitudinal oscillations while pilots using attitude information did not.

Waller, M. C.↗
NASA NTRS1983

A method for static and dynamic load analysis of standard and modified spur gears

The mesh stiffness and dynamic load characteristics for several cases of the Normal Contract Ratio and High Contact ratio gearing. The considered contact ratios were grouped in the general range of 1.7,2.0, and 2.3. The HCR gearing is defined by contact ratios equal to or greater than 2.0. The HCR gearing is represented by a group of small pressure angle, fine pitch, and long addendum gearing.

Kasuba, R.↗
NASA NTRS1991

Integrated Analysis Capability Program

Integrated Analysis Capability (IAC) software system intended to provide highly effective, interactive analysis tool for integrated design of large structures. Supports needs of engineering analysis groups concerned with interdisciplinary problems. Developed to serve as software interface between computer programs from fields of structures, thermodynamics, controls, and dynamics of systems on one hand and executive software system and data base on other hand to yield highly efficient multi-disciplinary system. Special attention given to such users' requirements as handling data and online assistance with operational features and ability to add new modules of user's choice at future date. Written in FORTRAN 77.

Vos, R. G.↗