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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Reevaluating uncertainties in $\overline{B}$→ X s γ decay

The rare decay $\overline{B}$→ X s γ is an important probe of physics beyond the standard model. The largest uncertainty on the total rate and the CP asymmetry arises from resolved photon contributions. These appear first at order 1/m b and are related to operators other than Q 7γ in the effective weak Hamiltonian. One of the three leading contributions, Q${q}\atop1$- Q 7γ , is described by a non-local function whose moments are related to HQET parameters. We use recent progress in our knowledge of these parameters to reevaluate the resolved photon contribution to $\overline{B}$→ X s γ total rate and CP asymmetry.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Southern Ocean Precipitation Characteristics Observed From CloudSat and Ground Instrumentation During the Macquarie Island Cloud & Radiation Experiment (MICRE): April 2016 to March 2017

A 1-year blended surface precipitation data set using Parsivel disdrometer, surface W-band radar, and tipping bucket measurements is produced for the Macquarie Island Cloud and Radiation Experiment (MICRE) and compared with retrievals from CloudSat (spaceborne 94 GHz radar). Surface precipitation was observed 44% ± 4% of the time between April 2016 and March 2017. Precipitation composed primarily of small particles (diameter <1 mm) occurred about 36% ± 2% of the time, constituting 10% of total accumulation. Remaining precipitation contained enough large particles such that the disdrometer could be used to identify the precipitation type as rain, ice, snow or wet snow. Seasonal and annual statistics on frequency of occurrence and accumulation for each precipitation type observed during MICRE are presented. Most ice and mixed phase precipitation was shallow, originating at a height of 3 km or lower, and occurred most often when Macquarie Island was to the northwest of the nearest cyclonic low-pressure center. In contrast, rain was more often deep and occurred most frequently when the island was to the southeast of cyclonic lows. A weak diurnal cycle in frequency and mean rate was present with a minimum between 12:00 and 14:00 local time and maximum between 03:00 and 06:00 local time. The CloudSat 2C-Precip-Column product missed the lightest precipitation (because the near-surface reflectivity is <-15 dBZ) and overestimated total liquid precipitation and occurrence of mixed phase precipitation, but captured reasonably well the distribution of rain rates for rates >0.5 mm/hr.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Discovery of charge density wave in a kagome lattice antiferromagnet

A hallmark of strongly correlated quantum materials is the rich phase diagram resulting from competing and intertwined phases with nearly degenerate ground state energies. A well-known example is the copper oxides, where a charge density wave (CDW) is ordered well above and strongly coupled to the magnetic order to form spin-charge separated stripes that compete with superconductivity. Recently, such rich phase diagrams have also been revealed in correlated topological materials. In two-dimensional kagome lattice metals consisting of corner-sharing triangles, the geometry of the lattice can produce flat bands with localized electrons, non-trivial topology, chiral magnetic order, superconductivity and CDW order. While CDW has been found in weakly electron correlated nonmagnetic AV 3 Sb 5 (A = K, Rb, Cs), it has not yet been observed in correlated magnetic ordered kagome lattice metals. Here we report the discovery of CDW within the antiferromagnetic (AFM) ordered phase of kagome lattice FeGe. The CDW in FeGe occurs at wavevectors identical to that of AV 3 Sb 5 , enhances the AFM ordered moment, and induces an emergent anomalous Hall effect. Furthermore, our findings suggest that CDW in FeGe arises from the combination of electron correlations-driven AFM order and van Hove singularities-driven instability possibly associated with a chiral flux phase, in stark contrast to strongly correlated copper oxides and nickelates, where the CDW precedes or accompanies the magnetic order.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Structure, dielectric, and magnetic properties of Sr{sub 2}TiMnO{sub 6} ceramics

Sr{sub 2}TiMnO{sub 6}, a double perovskite associated with high degree of B-site cation disorder was investigated in detail for its structural, magnetic, and dielectric properties. Though x-ray powder diffraction analysis confirms its cubic structure, first order Raman scattering and infrared reflectivity spectra indicate a breaking of the local cubic symmetry. The magnetization study reveals an anomaly at 14 K owing to a ferrimagnetic/canted antiferromagneticlike ordering arising from local Mn-O-Mn clusters. Saturated M-H hysteresis loops obtained at 5 K also reflect the weak ferromagnetic exchange interactions present in the system and an approximate estimation of Mn{sup 3+}/Mn{sup 4+} was done using the magnetization data for the samples sintered at different temperatures. The conductivity and dielectric behavior of this system has been investigated in a broad temperature range of 10 to 300 K. Intrinsic permittivity was obtained only below 100 K whereas giant permittivity due to conductivity and Maxwell-Wagner polarization was observed at higher temperatures. X-ray photoemission studies further confirmed the presence of mixed oxidation states of Mn and the valence band spectra analysis was carried out in detail.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Mechanics of cantilever beam: Implementation and comparison of FEM and MLPG approach

Two weak form solution approaches for partial differential equations, the well known meshbased finite element method and the newer meshless local Petrov Galerkin method are described and compared on a standard test case - mechanics of cantilever beam. The implementation, solution accuracy and calculation complexity are addressed for both approaches. We found out that FEM is superior in most standard criteria, but MLPG has some advantages because of its flexibility that results from its general formulation.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

SPECTROSCOPIC ANALYSIS OF INTERACTION BETWEEN AN EXTREME-ULTRAVIOLET IMAGING TELESCOPE WAVE AND A CORONAL UPFLOW REGION

We report a spectroscopic analysis of an EUV Imaging Telescope (EIT) wave event that occurred in active region 11081 on 2010 June 12 and was associated with an M2.0 class flare. The wave propagated nearly circularly. The southeastern part of the wave front passed over an upflow region near a magnetic bipole. Using EUV Imaging Spectrometer raster observations for this region, we studied the properties of plasma dynamics in the wave front, as well as the interaction between the wave and the upflow region. We found a weak blueshift for the Fe XII {lambda}195.12 and Fe XIII {lambda}202.04 lines in the wave front. The local velocity along the solar surface, which is deduced from the line-of-sight velocity in the wave front and the projection effect, is much lower than the typical propagation speed of the wave. A more interesting finding is that the upflow and non-thermal velocities in the upflow region are suddenly diminished after the transit of the wave front. This implies a significant change of magnetic field orientation when the wave passed. As the lines in the upflow region are redirected, the velocity along the line of sight is diminished as a result. We suggest that this scenario is more in accordance with what was proposed in the field-line stretching model of EIT waves.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Spatial confinement of the IBEX Ribbon: A dominant turbulence mechanism

The narrow ribbon of enhanced energetic neutral atom flux observed by the Interstellar Boundary Explorer spacecraft has prompted numerous ideas to explain its structure and properties. One of these ideas is the 'neutral solar wind' scenario, which identifies the source particles as pickup protons in the local interstellar medium originating in solar wind charge-exchange interactions. This scenario has been thought to require unrealistically weak pitch-angle scattering of the pickup protons to explain the narrow structure. Recently, Schwadron and McComas suggested that this structure could result from a spatial retention of the pickup protons, rather than from a restricted pitch-angle distribution. Here, we present a physically motivated, quantitative mechanism to produce such a spatial configuration. This mechanism is based on the 'dominant turbulence' assumption, which can be applied where the production of new pickup protons is slow, and has been used to successfully explain the level of turbulent heating observed in the outer solar wind. This formalism predicts a pickup isotropization process which adds or subtracts energy from the ambient turbulent fluctuations, depending on the initial pitch angle of the pickup protons. We show that a simple model of this process can yield a ribbon structure in qualitative agreement with the observations. The results of this simple model are not yet quantitatively satisfactory, but we suggest several improvements which may reduce the quantitative discrepancy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Learning how structures form in drift-wave turbulence

Drift-wave turbulence produces anomalous transport via cross-correlations between fluctuations. This transport has profound implications for confinement, structure formation, and virtually all aspects of the non-linear turbulent dynamics. Herein, we use a data-driven method based on deep learning in order to study turbulent transport in the 2D Hasegawa–Wakatani system and infer a reduced mean-field model from numerical solution. In addition to the usual turbulent diffusion, we find an effect which couples the particle flux to the local gradient of vorticity, which tends to modulate the density profile. The direct coupling to the shear is relatively weak. In addition, the deep learning method finds a model for spontaneous zonal flow generation by negative viscosity, stabilized by non-linear and hyperviscous terms. We compare these results to analytic calculations using quasilinear theory and wave kinetics, finding qualitative agreement, though the calculations miss certain higher-order effects. A simplified, 1-D model for the evolution of the profile, flow, and intensity based on the deep learning results is solved numerically and compared to previous models for staircasing based on bistability. We see that the physics uncovered by the deep learning method provided simple explanations for the formation of zonal structures in the density, flow, and turbulence fields. We highlight the important role of symmetry in the deep learning method and speculate on the portability of the method to other applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2011

CONVERGENT FLOWS AND LOW-VELOCITY SHOCKS IN DR21(OH)

DR21(OH) is a pc-scale massive, {approx}7000 M{sub sun} clump hosting three massive dense cores (MDCs) at an early stage of their evolution. We present a high angular resolution mosaic, covering {approx}70'' x 100'', with the IRAM Plateau de Bure Interferometer at 3 mm to trace the dust continuum emission and the N{sub 2}H{sup +} (J = 1-0) and CH{sub 3}CN (J = 5-4) molecular emission. The cold, dense gas traced by the compact emission in N{sub 2}H{sup +} is associated with the three MDCs and shows several velocity components toward each MDC. These velocity components reveal local shears in the velocity fields which are best interpreted as convergent flows. Moreover, we report the detection of weak extended emission from CH{sub 3}CN at the position of the N{sub 2}H{sup +} velocity shears. We propose that this extended CH{sub 3}CN emission is tracing warm gas associated with the low-velocity shocks expected at the location of convergence of the flows where velocity shears are observed. This is the first detection of low-velocity shocks associated with small (subparsec) scale convergent flows which are proposed to be at the origin of the densest structures and of the formation of (high-mass) stars. In addition, we propose that MDCs may be active sites of star formation for more than a crossing time as they continuously receive material from larger scale flows as suggested by the global picture of dynamical, gravity-driven evolution of massive clumps which is favored by the present observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Role of degeneracy, hybridization, and nesting in the properties of multiorbital systems

To understand the role that degeneracy, hybridization, and nesting play in the magnetic and pairing properties of multiorbital Hubbard models we here study numerically two types of two-orbital models, both with holelike and electron-like Fermi surfaces (FS s) that are related by nesting vectors ( ,0) and (0, ). In one case the bands that determine the FS s arise from strongly hybridized degenerate dxz and dyz orbitals, while in the other the two bands are determined by nondegenerate and nonhybridized s-like orbitals. Using a variety of techniques, in the weak-coupling regime it is shown that only the model with hybridized bands develops metallic magnetic order, while the other model exhibits an ordered excitonic orbital-transverse spin state that is insulating and does not have a local magnetization. However, both models display similar insulating magnetic stripe ordering in the strong-coupling limit. These results indicate that nesting is a necessary but not sufficient condition for the development of ordered states with finite local magnetization in multiorbital Hubbard systems; the additional ingredient appears to be that the nested portions of the bands need to have the same orbital flavor. This condition can be achieved via strong hybridization of the orbitals in weak coupling or via the FS reconstruction induced by the Coulomb interactions in the strong-coupling regime. This effect also affects the pairing symmetry as demonstrated by the study of the dominant pairing channels for the two models.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1993

Mars: Noachian hydrology by its statistics and topology

Discrimination between fluvial features generated by surface drainage and subsurface aquifer discharges will provide clues to the understanding of early Mars' climatic history. Our approach is to define the process of formation of the oldest fluvial valleys by statistical and topological analyses. Formation of fluvial valley systems reached its highest statistical concentration during the Noachian Period. Nevertheless, they are a scarce phenomenom in Martian history, localized on the craterized upland, and subject to latitudinal distribution. They occur sparsely on Noachian geological units with a weak distribution density, and appear in reduced isolated surface (around 5 x 10(exp 3)(sq km)), filled by short streams (100-300 km length). Topological analysis of the internal organization of 71 surveyed Noachian fluvial valley networks also provides information on the mechanisms of formation.

Cabrol, N. A.↗
DOE OSTI2014

Weak ferromagnetism and nanodimensional ferroelectric domain structure stabilized in the polar phase of Bi{sub 1−x}Nd{sub x}FeO{sub 3} multiferroics via Ti doping

Crystal structure, microstructure, local ferroelectric, and magnetic properties of the Bi{sub 0.9}Nd{sub 0.1}Fe{sub 1−x}Ti{sub x}O{sub 3} samples have been investigated at room temperature to reveal the effect of Ti{sup 4+} doping on the multiferroic behavior of the lanthanide-modified compound representing a polar (space group R3c) antiferromagnetic phase of the Bi{sub 1−x}Ln{sub x}FeO{sub 3} perovskites. Ti doping results in a gradual suppression of the rhombohedral distortions, however, symmetry of the crystal structure remains the same in the entire concentration range allowing the single-phase perovskites to be obtained (x ≤ 0.08). The doping tends to reduce existing lone-pair cation-driven polar displacements, thus giving rise to a decrease of the ferroelectric polarization in the Bi{sub 0.9}Nd{sub 0.1}Fe{sub 1−x}Ti{sub x}O{sub 3} (x→0.08) series. A drastic (from ∼10 μm for x = 0 to ∼1 μm for 0.02 ≤ x ≤ 0.08) decrease of the average grain size induced by the doping is accompanied by the formation of a ferroelectric domain structure with the average domain width of ∼40 nm. Finally, the doping was shown to induce an antiferromagnetic to weak ferromagnetic transformation. The maximum remanent magnetization observed in the Bi{sub 0.9}Nd{sub 0.1}Fe{sub 1−x}Ti{sub x}O{sub 3} series at x ∼ 0.05 coincides with the locked magnetization releasing upon the magnetic field-induced suppression of the magnetic cycloid in pure BiFeO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Longitudinal singular response of dusty plasma medium in weak and strong coupling limits

The longitudinal response of a dusty plasma medium in both weak and strong coupling limits has been investigated in detail using analytic as well as numerical techniques. In particular, studies on singular response of the medium have been specifically investigated here. A proper Galilean invariant form of the generalized hydrodynamic fluid model has been adopted for the description of the dusty plasma medium. For weak non-linear response, analytic reductive perturbative approach has been adopted. It is well known that in the weak coupling regime for the dusty plasma medium, such an analysis leads to the Korteweg-de Vries equation (KdV) equation and predicts the existence of localized smooth soliton solutions. We show that the strongly coupled dust fluid with the correct Galilean invariant form does not follow the KdV paradigm. Instead, it reduces to the form of Hunter-Saxton equation, which does not permit soliton solutions. The system in this case displays singular response with both conservative as well as dissipative attributes. At arbitrary high amplitudes, the existence and spontaneous formation of sharply peaked cusp structures in both weak and strong coupling regimes has been demonstrated numerically.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS2005

Phase control of electromagnetically induced transparency and its applications to tunable group velocity and atom localization

We show that, by simple modifications of the usual three-level lambda-type scheme used in electromagnetically induced transparency (EIT) schemes, phase dependence in the response of the atomic medium to a weak probe field can be introduced. This gives rise to phase dependent susceptibility. By properly controlling phase and amplitudes of the drive fields we obtain variety of interesting effects. On one hand we obtain phase control of the group velocity of a probe field passing through medium to the extend that continuous tuning of the group velocity from subluminal to superluminal and back is possible. While on the other hand, by choosing one of the drive fields to be a standing wave field inside a cavity, we obtain sub-wavelength localization of moving atoms passing through the cavity field.

Zubairy, M. Suhail↗
DOE OSTI2015

Synergy and destructive interferences between local magnetic anisotropies in binuclear complexes

Magnetic anisotropy is responsible for the single molecule magnet behavior of transition metal complexes. This behavior is characterized by a slow relaxation of the magnetization for low enough temperatures, and thus for a possible blocking of the magnetization. This bistable behavior can lead to possible technological applications in the domain of data storage or quantum computing. Therefore, the understanding of the microscopic origin of magnetic anisotropy has received a considerable interest during the last two decades. The presentation focuses on the determination of the anisotropy parameters of both mono-nuclear and bi-nuclear types of complexes and on the control and optimization of the anisotropic properties. The validity of the model Hamiltonians commonly used to characterize such complexes has been questioned and it is shown that neither the standard multispin Hamiltonian nor the giant spin Hamiltonian are appropriate for weakly coupled ions. Alternative models have been proposed and used to properly extract the relevant parameters. Rationalizations of the magnitude and nature of both local anisotropies of single ions and the molecular anisotropy of polynuclear complexes are provided. The synergy and interference effects between local magnetic anisotropies are studied in a series of binuclear complexes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

CANDELS: THE CORRELATION BETWEEN GALAXY MORPHOLOGY AND STAR FORMATION ACTIVITY AT z {approx} 2

We discuss the state of the assembly of the Hubble sequence in the mix of bright galaxies at redshift 1.4 < z {<=} 2.5 with a large sample of 1671 galaxies down to H{sub AB} {approx} 26, selected from the HST/ACS and WFC3 images of the GOODS-South field obtained as part of the GOODS and CANDELS observations. We investigate the relationship between the star formation properties and morphology using various parametric diagnostics, such as the Sersic light profile, Gini (G), M{sub 20}, concentration (C), asymmetry (A), and multiplicity ({Psi}) parameters. Our sample clearly separates into massive, red, and passive galaxies versus less massive, blue, and star-forming ones, and this dichotomy correlates very well with the galaxies' morphological properties. Star-forming galaxies show a broad variety of morphological features, including clumpy structures and bulges mixed with faint low surface brightness features, generally characterized by disky-type light profiles. Passively evolving galaxies, on the other hand, very often have compact light distribution and morphology typical of today's spheroidal systems. We also find that artificially redshifted local galaxies have a similar distribution with z {approx} 2 galaxies in a G-M{sub 20} plane. Visual inspection between the rest-frame optical and UV images show that there is a generally weak morphological k-correction for galaxies at z {approx} 2, but the comparison with non-parametric measures show that galaxies in the rest-frame UV are somewhat clumpier than rest-frame optical. Similar general trends are observed in the local universe among massive galaxies, suggesting that the backbone of the Hubble sequence was already in place at z {approx} 2.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Hybrid SERS platform by adapting both chemical mechanism and electromagnetic mechanism enhancements: SERS of 4-ATP and CV by the mixture with GQDs on hybrid PdAg NPs

Surface-enhanced Raman spectroscopy (SERS) is a versatile analytical technique widely adapted for the identification of target analytes even at an extremely low concentration. Herein, a unique hybrid SERS platform is demonstrated by utilizing the graphene quantum dots (GQDs) and hybrid PdAg NPs for the detection of 4-amino-thiophenol (4-ATP) and crystal violet (CV). GQDs offer the rich charge transfer to the LUMO and HOMO of 4-ATP and CV by the CM enhancement. A significant EM enhancement is achieved by the strong localized surface plasmon resonance (LSPR) of uniquely designed hybrid core-shell PdAg NP, possessing the narrow nano-gaps with the highly dense small Ag NPs and Pd core Ag shell configuration. As a result, orders of enhancement of originally weak 4-ATP and CV Raman signal is witnessed by the combination of electromagnetic mechanism (EM) and chemical mechanism (CM) enhancements on a single SERS substrate. The hybrid GQD/HNP SERS substrate demonstrates significantly improved hot spots and strongly localized electromagnetic fields as confirmed by the finite-difference time-domain (FDTD) simulations. There for a proper mixture ratio of GQDs and probe molecules presents largely enhanced SERS signals by a strong adsorption of probe molecules through π - π interaction and the enhancement factors vary by the mixture ratio depending on the adsorption kinetics and Raman cross-section of molecules.

36 MATERIALS SCIENCE↗