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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 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

On stability of self-sustained volume discharge in working mixtures of non-chain electrochemical HF laser

Burning voltage of a self-sustained volume discharge (SSVD) is studied as a function of the specific energy deposition in SF{sub 5} with C{sub 2}-H{sub 6} and H{sub 2} mixtures, which are working media of a non-chain electrochemical HF laser. It is established that the voltage rises linearly with increasing the specific energy deposition, the relative voltage rise in the SF{sub 6}-C{sub 2}H{sub 6} mixtures being noticeably higher than in pure SF{sub 6} and SF{sub 6}-H{sub 2} mixtures. An assumption is suggested and substantiated on determining the role of molecule dissociation by the electron impact leading to the observed voltage rise. From experimental data we have found approximate energy expenditures of producing dissociation fragments including atomic fluorine in a discharge in pure SF{sub 6}: E-tilde {sub d}(F)= 5{+-}1 eV. The values of E{sub d} well agree with literature data obtained by other experimental methods. A conclusion is drawn that the dissociation process is the main mechanism limiting the current density, which implies SSVD realisation without preliminary gas ionisation in working mixtures of a non-chain HF laser and determines a higher stability of the volume discharge in mixtures of SF{sub 6} with hydrocarbons (deuterocarbons) as compared to mixtures with hydrogen (deuterium). A method is suggested and substantiated for numerical estimation of the limitation effect of the current density and its influence on the SSVD stability. (control of radiation parameters)

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Formation of high quality interference fringes from both sides of a suitably designed hololens in the laser Doppler anemometer measurement volume

We report, for the first time to the best of our knowledge, the formation of high quality, evenly spaced, undistorted fringes in the measurement volume of a laser Doppler anemometer from both sides of a suitably designed hololens. Experiments are performed for the analysis of fringes formed at the measurement volume by real time monitoring and actual fringe field analysis techniques. The results indicate the qualitative as well as quantitative improvement of 66.58% in overall average normalised standard deviations of the width of the fringes formed by the proposed imaging configuration than that of the conventional imaging configuration. (laser applications and other topics in quantum electronics)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2010

Large volume collapse observed in the phase transition in cubic PbCrO[subscript 3] perovskite

When cubic PbCrO{sub 3} perovskite (Phase I) is squeezed up to {approx}1.6 GPa at room temperature, a previously undetected phase (Phase II) has been observed with a 9.8% volume collapse. Because the structure of Phase II can also be indexed into a cubic perovskite as Phase I, the transition between Phases I and II is a cubic to cubic isostructural transition. Such a transition appears independent of the raw materials and synthesizing methods used for the cubic PbCrO{sub 3} perovskite sample. In contrast to the high-pressure isostructural electronic transition that appears in Ce and SmS, this transition seems not related with any change of electronic state, but it could be possibly related on the abnormally large volume and compressibility of the PbCrO{sub 3} Phase I. The physical mechanism behind this transition and the structural and electronic/magnetic properties of the condensed phases are the interesting issues for future studies.

36 MATERIALS SCIENCE↗
DOE OSTI2010

STELLAR TIDAL STREAMS IN SPIRAL GALAXIES OF THE LOCAL VOLUME: A PILOT SURVEY WITH MODEST APERTURE TELESCOPES

Within the hierarchical framework for galaxy formation, minor merging and tidal interactions are expected to shape all large galaxies to the present day. As a consequence, most seemingly normal disk galaxies should be surrounded by spatially extended stellar 'tidal features' of low surface brightness. As part of a pilot survey for such interaction signatures, we have carried out ultra deep, wide field imaging of eight isolated spiral galaxies in the Local Volume, with data taken at small (D = 0.1-0.5 m) robotic telescopes that provide exquisite surface brightness sensitivity ({mu}{sub lim}(V) {approx} 28.5 mag arcsec{sup -2}). This initial observational effort has led to the discovery of six previously undetected extensive (to {approx}30 kpc) stellar structures in the halos surrounding these galaxies, likely debris from tidally disrupted satellites. In addition, we confirm and clarify several enormous stellar over-densities previously reported in the literature, but never before interpreted as tidal streams. Even this pilot sample of galaxies exhibits strikingly diverse morphological characteristics of these extended stellar features: great circle-like features that resemble the Sagittarius stream surrounding the Milky Way, remote shells and giant clouds of presumed tidal debris far beyond the main stellar body, as well as jet-like features emerging from galactic disks. Together with presumed remains of already disrupted companions, our observations also capture surviving satellites caught in the act of tidal disruption. A qualitative comparison with available simulations set in a {Lambda}Cold Dark Matter cosmology (that model the stellar halo as the result of satellite disruption evolution) shows that the extraordinary variety of stellar morphologies detected in this pilot survey matches that seen in those simulations. The common existence of these tidal features around 'normal' disk galaxies and the morphological match to the simulations constitutes new evidence that these theoretical models also apply to a large number of other Milky Way-mass disk galaxies in the Local Volume.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

MORE GALAXIES IN THE LOCAL VOLUME IMAGED IN H{alpha}

We have carried out an H{alpha} flux measurement for 52 nearby galaxies as part of a general H{alpha} imaging survey for the Local Volume sample of galaxies within 10 Mpc. Most of the objects are probable members of the groups around Maffei 2/IC 342, NGC 672/IC 1727, NGC 784, and the Orion galaxy. The measured H{alpha} fluxes corrected for extinction are used to derive the galaxy star formation rate (SFR). We briefly discuss some basic scaling relations between SFR, hydrogen mass, and absolute magnitude of the Local Volume galaxies. The total SFR density in the local (z = 0) universe is estimated to be (0.019 {+-} 0.003)M{sub sun} yr{sup -1} Mpc{sup -3}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

THE ACS NEARBY GALAXY SURVEY TREASURY. VIII. THE GLOBAL STAR FORMATION HISTORIES OF 60 DWARF GALAXIES IN THE LOCAL VOLUME

We present uniformly measured star formation histories (SFHs) of 60 nearby (D {approx}< 4 Mpc) dwarf galaxies based on color-magnitude diagrams of resolved stellar populations from images taken with the Hubble Space Telescope and analyzed as part of the ACS Nearby Galaxy Survey Treasury program (ANGST). This volume-limited sample contains 12 dwarf spheroidal (dSph)/dwarf elliptical (dE), 5 dwarf spiral, 28 dwarf irregular (dI), 12 dSph/dI (transition), and 3 tidal dwarf galaxies. The sample spans a range of {approx}10 mag in M{sub B} and covers a wide range of environments, from highly interacting to truly isolated. From the best-fit SFHs, we find three significant results for dwarf galaxies in the ANGST volume: (1) the majority of dwarf galaxies formed the bulk of their mass prior to z {approx} 1, regardless of current morphological type; (2) the mean SFHs of dIs, transition dwarf galaxies (dTrans), and dSphs are similar over most of cosmic time, and only begin to diverge a few Gyr ago, with the clearest differences between the three appearing during the most recent 1 Gyr; and (3) the SFHs are complex and the mean values are inconsistent with simple SFH models, e.g., single bursts, constant star formation rates (SFRs), or smooth, exponentially declining SFRs. The mean SFHs show clear divergence from the cosmic SFH at z {approx}< 0.7, which could be evidence that low-mass systems have experienced delayed star formation relative to more massive galaxies. The sample shows a strong density-morphology relationship, such that the dSphs in the sample are less isolated than the dIs. We find that the transition from a gas-rich to gas-poor galaxy cannot be solely due to internal mechanisms such as stellar feedback, and instead is likely the result of external mechanisms, e.g., ram pressure and tidal stripping and tidal forces. In terms of their environments, SFHs, and gas fractions, the majority of the dTrans appear to be low-mass dIs that simply lack H{alpha} emission, similar to Local Group (LG) dTrans DDO 210. However, a handful of dTrans have remarkably low gas fractions, suggesting that they have nearly exhausted their gas supply, analogous to LG dTrans such as Phoenix. Finally, we have also included extensive exploration of uncertainties in the SFH recovery method, including the optimization of time resolution, the effects of photometric depth, and impact of systematic uncertainties due to the limitations in current stellar evolution models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

COHERENT BACKSCATTERING VERIFIED NUMERICALLY FOR A FINITE VOLUME OF SPHERICAL PARTICLES

We consider electromagnetic scattering by a spherical volume sparsely and randomly populated by spherical particles of equal size and optical properties. The far-field scattering matrix of the entire volume is computed using an exact method and an approximate method. The former is a direct computer solver of the Maxwell equations called the superposition T-matrix method (STMM). The latter is a solver based on numerical Monte Carlo integration of the ladder and cyclical diagrams appearing in the microphysical theory of radiative transfer and coherent backscattering (RT-CB). The quantitative agreement between the STMM and RT-CB computations provides verification of the RT-CB theory. Prominent backscattering features exhibited by the STMM data cannot be reproduced by keeping only the ladder diagrams of RT. Our results strongly support the CB explanation of opposition brightness and polarization phenomena observed for a class of atmosphereless solar-system objects. Further research is necessary to determine the range of quantitative applicability of the RT-CB theory to densely packed particulate media.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Large-volume flux closure during plasmoid-mediated reconnection in coaxial helicity injection

A large-volume flux closure during transient coaxial helicity injection (CHI) in NSTX-U is demonstrated through resistive magnetohydrodynamics (MHD) simulations. Several major improvements, including the improved positioning of the divertor poloidal field coils, are projected to improve the CHI start-up phase in NSTX-U. Simulations in the NSTX-U configuration with constant in time coil currents show that with strong flux shaping the injected open field lines (injector flux) rapidly reconnect and form large volume of closed flux surfaces. This is achieved by driving parallel current in the injector flux coil and oppositely directed currents in the flux shaping coils to form a narrow injector flux footprint and push the injector flux into the vessel. As the helicity and plasma are injected into the device, the oppositely directed field lines in the injector region are forced to reconnect through a local Sweet-Parker type reconnection, or to spontaneously reconnect when the elongated current sheet becomes MHD unstable to form plasmoids. In these simulations for the first time, it is found that the closed flux is over 70% of the initial injector flux used to initiate the discharge. Furthermore, these results could work well for the application of transient CHI in devices that employ super conducting coils to generate and sustain the plasma equilibrium.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2010

EMBEDDING REALISTIC SURVEYS IN SIMULATIONS THROUGH VOLUME REMAPPING

Connecting cosmological simulations to real-world observational programs is often complicated by a mismatch in geometry: while surveys often cover highly irregular cosmological volumes, simulations are customarily performed in a periodic cube. We describe a technique to remap this cube into elongated box-like shapes that are more useful for many applications. The remappings are one-to-one, volume-preserving, keep local structures intact, and involve minimal computational overhead.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Suggested reference values for regional blood volumes in children and adolescents

Estimates of regional blood volumes (BVs) in humans are needed in dosimetric models of radionuclides and radiopharmaceuticals that decay in the circulation to a significant extent. These values are also needed to refine models of tissue elemental composition in computational human phantoms of both patients and exposed members of the general public. The International Commission on Radiological Protection (ICRP) in its Publication 89 provides reference values for total blood content in the full series of their reference individuals, to include the male and female newborn, 1 year-old, 5 year-old, 10 year-old, 15 year-old, and adult. Furthermore, Publication 89 provides reference values for the percentage distribution of total blood volume in 27 different blood-filled organs and tissues of the reference adult male and adult female. However, no similar distribution values are provided for non-adults. The goal of the present paper is to present a volumetric scaling methodology to derive these values for the same organs and tissues at ages younger than the reference adult. Finally, literature data on organ-specific vascular growth in the brain, kidneys, and skeletal tissues are also considered.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2011

Doping the 1 kton Large Volume Detector with Gd

The Large Volume Detector (LVD) in the INFN Gran Sasso National Laboratory (LNGS), Italy, is a ν observatory which has been monitoring the Galaxy since June 1992 to study neutrinos from core collapse supernovae. The experiment in the present configuration is made by 840 scintillator detectors, for a total active mass of 1000 tons. The detector sensitivity to neutrino bursts due to a core collapse supernova has been already discussed in term of maximum detectable distance. In this paper we evaluate the improvements that LVD could obtain if all its active scintillator mass was doped with a small amount (0.14% in weight) of Gadolinium. We simulated neutron captures following ν-bar {sub e} inverse beta decay reactions in one LVD counter (1.2 ton) with Gd doped liquid scintillator obtaining an efficiency for the detection of this process of η{sub n}|{sub Gd} = 80% and a mean capture time τ = 25μs, in good agreement with the results obtained by the measures. This implies a gain of a factor ∼ 20 in the signal to noise ratio for neutron capture detection with respect to the undoped liquid scintillator. We discuss how the captures of neutrons from rock radioactivity on Gd modify the background conditions of the detector and we calculate the curves expressing the sensitivity to a ν-bar {sub e} burst from core collapse supernovae depending on the distance of the collapsing star. It results that doping the 1 kton Large Volume Detector with Gd would assure a 90% detection efficiency at the distance of the Large Magellanic Cloud (50 kpc), an achievement which is equivalent to that obtained by doubling the number of counters in LVD.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Inflationary spectra with inverse-volume corrections in loop quantum cosmology and their observational constraints from Planck 2015 data

We first derive the primordial power spectra, spectral indices and runnings of both scalar and tensor perturbations of a flat inflationary universe to the second-order approximations of the slow-roll parameters, in the framework of loop quantum cosmology with the inverse-volume quantum corrections. This represents an extension of our previous work in which the parameter σ was assumed to be an integer, where σ characterizes the quantum corrections and in general can take any of values from the range σ element of (0, 6]. Restricting to the first-order approximations of the slow-roll parameters, we find corrections to the results obtained previously in the literature, and point out the causes for such errors. To our best knowledge, these represent the most accurate calculations of scalar and tensor perturbations given so far in the literature. Then, fitting the perturbations to the recently released data by Planck (2015), we obtain the most severe constraints for various values of σ. Using these constraints as our referring point, we discuss whether these quantum gravitational corrections can lead to measurable signatures in the future cosmological observations. We show that, depending on the value of σ, the scale-dependent contributions to the relativistic inflationary spectra due to the inverse-volume corrections could be well within the range of the detectability of the forthcoming generations of experiments, such as the Stage IV experiments.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Symmetrically tuned large-volume conic shell-cavities for axion searches

In an earlier paper [1], a new class of thin-shell cavities were proposed to evade the steep frequency scaling of conventional axion haloscopes. In this follow-up work, we see that a generalized conic geometry enables robust frequency-tuning for these large-volume cm-wave cavities. The frequency-defining dimension of a conic shell-cavity changes symmetrically and uniformly during tuning, maintaining a high axion coupling efficiency (the "form factor") to an external solenoid field. It is further shown that such tunable geometry is not restricted to circular cones. A general prescription for arbitrary volume-filling conic shell-cavities is developed and direct solutions are obtained for the created numerical models. Additionally, the largest of the realized designs is a meandering "brain" cavity that is tunable over a frequency range of 20%. The scan rate of this cavity is three orders of magnitude larger than that of a scaled cylindrical cavity used in the current generation experiments. The prospects for such a large improvement in the scan rate should motivate R& D efforts in fabrication and other implementation techniques. If these engineering challenges can be met, cavity-based axion haloscopes can stay competitive at frequencies higher than a few GHz. We propose an experimental configuration at 20 GHz (~80 μeV) using an array of brain cavities and compare it with other proposals for similar frequencies.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Operational experience with the Proto-DUNE NP02 and NP04 large volume liquid argon cryostats and their cryogenic systems at CERN

The far Detector of the Deep Underground Neutrino Experiment (DUNE) will be housed in several large volume (about 12.500 m$^{3}$) liquid argon cryostats. The design principle of these large cryostats, and of the cryogenic system belonging to them, are investigated through the design, construction and operation of a series of prototype installations.The Neutrino Platform 02 (NP02) and 04 (NP04) cryostats, placed at CERN, contain DUNE proto-type detectors, each of them housed in an about 600 m$^{3}$ liquid argon bath. These cryostats, based on the membrane cryostat principle, and their cryogenic systems have been designed according to the DUNE principle. Measurements performed in these test stands shall confirm the foreseen heat loads into the cryostat systems entering via its walls, via detector cabling and via the cold electronics, shall confirm the low temperature gradient over the active detector volume and shall certify the liquid argon purification principle.This paper introduces the requirements for the NP02 and NP04 cryostats and their cryogenic systems, describes the design principle applied to these two systems and gives an overview of the different modes in which the two systems have been operating. The experimental results are presented and discussed, and “lessons learned” for future installations are dawn.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

THE HISTORY OF STAR FORMATION IN GALAXY DISKS IN THE LOCAL VOLUME AS MEASURED BY THE ADVANCED CAMERA FOR SURVEYS NEARBY GALAXY SURVEY TREASURY

We present a measurement of the age distribution of stars residing in spiral disks and dwarf galaxies. We derive a complete star formation history of the {approx}140 Mpc{sup 3} covered by the volume-limited sample of galaxies in the Advanced Camera for Surveys (ACS) Nearby Galaxy Survey Treasury (ANGST). The total star formation rate density history ({rho}{sub SFR}(t)) is dominated by the large spirals in the volume, although the sample consists mainly of dwarf galaxies. Our {rho}{sub SFR}(t) shows a factor of {approx}3 drop at z {approx} 2, in approximate agreement with results from other measurement techniques. While our results show that the overall {rho}{sub SFR}(t) has decreased since z {approx} 1, the measured rates during this epoch are higher than those obtained from other measurement techniques. This enhanced recent star formation rate appears to be largely due to an increase in the fraction of star formation contained in low-mass disks at recent times. Finally, our results indicate that despite the differences at recent times, the epoch of formation of {approx}50% of the stellar mass in dwarf galaxies was similar to that of {approx}50% of the stellar mass in large spiral galaxies (z {approx}> 2), despite the observed galaxy-to-galaxy diversity among the dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Activation volumes of oxygen self-diffusion in fluorite structured oxides

In this study, fluorite structured oxides are used in numerous applications and as such it is necessary to determine their materials properties over a range of conditions. In the present study we employ molecular dynamics calculations to calculate the elastic and expansivity data, which are then used in a thermodynamic model (the cBΩ model) to calculate the activation volumes of oxygen self-diffusion coefficient in ThO 2 , UO 2 and PuO 2 fluorite structured oxides over a wide temperature range. We present relations to calculate the activation volumes of oxygen self-diffusion coefficient in ThO 2 , UO 2 and PuO 2 for a wide range of temperature (300–1700 K) and pressure (–7.5 to 7.5 GPa).

36 MATERIALS SCIENCE↗
DOE OSTI2024

High-volume tunable resonator for axion searches above 7 GHz

In this research, we present results from an experimental demonstration of a tunable thin-shell axion haloscope whose geometry decouples its overall volume from its resonant frequency, thereby evading the steep sensitivity degradation at high frequencies. An aluminum 2.6-l (41⁢λ 3 ) prototype, which tunes from 7.1 to 8.0 GHz, was fabricated and characterized at room temperature. An axion-sensitive, straightforwardly tunable TM 010 mode is clearly identified with a room-temperature quality factor, Q, of approximately 5000. The on-resonance E-field distribution is mapped and found to agree with numerical calculations. Anticipating future cryogenic operation, we develop an alignment protocol relying only on rf measurements of the cavity, maintaining a form factor of 0.57 across the full tuning range. These measurements demonstrate the feasibility of cavity-based haloscopes with operating volume V $\gg$ λ 3 . We discuss plans for future development and the parameters required for a thin-shell haloscope exploring the postinflationary axion parameter space (approximately 4 to 30 GHz) at Dine-Fischler-Srednicki-Zhitnitsky sensitivity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Rainbow scars: From area to volume law

Quantum many-body scars (QMBS) constitute a new quantum dynamical regime in which rare “scarred” eigenstates mediate weak ergodicity breaking. One open question is to understand the most general setting in which these states arise. In this work, we develop a generic construction that embeds a new class of QMBS, rainbow scars, into the spectrum of an arbitrary Hamiltonian. Unlike other examples of QMBS, rainbow scars display extensive bipartite entanglement entropy while retaining a simple entanglement structure. Specifically, the entanglement scaling is volume-law for a random bipartition, while scaling for a fine-tuned bipartition is subextensive. When internal symmetries are present, the construction leads to multiple, and even towers, of rainbow scars revealed through distinctive non-thermal dynamics. Remarkably, certain symmetries can lead rainbow scars to arise in translation-invariant models. To this end, we provide an experimental road map for realizing rainbow scar states in a Rydberg-atom quantum simulator, leading to coherent oscillations distinct from the strictly sub-volume-law QMBS previously realized in the same system.

36 MATERIALS SCIENCE↗