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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Ge atom distribution in buried dome islands

Laser-assisted atom probe tomography microscopy is used to provide direct and quantitative compositional measurements of tri-dimensional Ge distribution in Ge dome islands buried by Si. Sub-nanometer spatial resolution 3D imaging shows that islands keep their facets after deposition of the Si cap, and that the island/substrate/Si cap interfaces are abrupt. The core of the domes contains 55% of Ge, while the island shell exhibits a constant composition of 15% of Ge. The {l_brace}113{r_brace} facets of the islands present a Ge enrichment up to 35%. The wetting layer composition is not homogeneous, varying from 9.5% to 30% of Ge.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Localization of electrons in dome-shaped GeSi/Si islands

We report on intraband photocurrent spectroscopy of dome-shaped GeSi islands embedded in a Si matrix with n{sup +}-type bottom and top Si layers. An in-plane polarized photoresponse in the 85–160 meV energy region has been observed and ascribed to the optical excitation of electrons from states confined in the strained Si near the dome apexes to the continuum states of unstrained Si. The electron confinement is caused by a modification of the conduction band alignment induced by inhomogeneous tensile strain in Si around the buried GeSi quantum dots. Sensitivity of the device to the normal incidence radiation proves a zero-dimensional nature of confined electronic wave functions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Nanoscale heat transport from Ge hut, dome, and relaxed clusters on Si(001) measured by ultrafast electron diffraction

The thermal transport properties of crystalline nanostructures on Si were studied by ultra-fast surface sensitive time-resolved electron diffraction. Self-organized growth of epitaxial Ge hut, dome, and relaxed clusters was achieved by in-situ deposition of 8 monolayers of Ge on Si(001) at 550 °C under UHV conditions. The thermal response of the three different cluster types subsequent to impulsive heating by fs laser pulses was determined through the Debye-Waller effect. Time resolved spot profile analysis and life-time mapping was employed to distinguish between the thermal response of the different cluster types. While dome clusters are cooling with a time constant of τ = 150 ps, which agrees well with numerical simulations, the smaller hut clusters with a height of 2.3 nm exhibit a cooling time constant of τ = 50 ps, which is a factor of 1.4 slower than expected.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2011

PHOTOMETRY OF VARIABLE STARS FROM DOME A, ANTARCTICA

Dome A on the Antarctic plateau is likely one of the best observing sites on Earth thanks to the excellent atmospheric conditions present at the site during the long polar winter night. We present high-cadence time-series aperture photometry of 10,000 stars with i < 14.5 mag located in a 23 deg{sup 2} region centered on the south celestial pole. The photometry was obtained with one of the CSTAR telescopes during 128 days of the 2008 Antarctic winter. We used this photometric data set to derive site statistics for Dome A and to search for variable stars. Thanks to the nearly uninterrupted synoptic coverage, we found six times as many variables as previous surveys with similar magnitude limits. We detected 157 variable stars, of which 55% were unclassified, 27% were likely binaries, and 17% were likely pulsating stars. The latter category includes {delta} Scuti, {gamma} Doradus, and RR Lyrae variables. One variable may be a transiting exoplanet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Pulsations and period changes of the non-Blazhko RR lyrae variable Y oct observed from Dome A, Antarctica

During the operation of the Chinese Small Telescope Array (CSTAR) in Dome A of Antarctica in the years 2008, 2009, and 2010, large amounts of photometric data have been obtained for variable stars in the CSTAR field. We present here the study of one of six RR Lyrae variables, Y Oct, observed with CSTAR in Dome A, Antarctica. Photometric data in the i band were obtained in 2008 and 2010, with a duty cycle (defined as the fraction of time representing scientifically available data to CSTAR observation time) of about 44% and 52%, respectively. In 2009, photometric data in the g and r bands were gathered for this star, with a duty cycle of 65% and 60%, respectively. Fourier analysis of the data in the three bands only shows the fundamental frequency and its harmonics, which is characteristic of the non-Blazhko RR Lyrae variables. Values of the fundamental frequency and the amplitudes, as well as the total pulsation amplitude, are obtained from the data in the three bands separately. The amplitude of the fundamental frequency and the total pulsation amplitude in the g band are the largest, and those in the i band the smallest. Two-hundred fifty-one times of maximum are obtained from the three seasons of data, which are analyzed together with 38 maximum times provided in the GEOS RR Lyrae database. A period change rate of −0.96 ± 0.07 days Myr{sup −1} is then obtained, which is a surprisingly large negative value. Based on relations available in the literature, the following physical parameters are derived: [Fe/H] = −1.41 ± 0.14, M{sub V} = 0.696 ± 0.014 mag, V−K = 1.182 ± 0.028 mag, logT{sub eff} = 3.802 ± 0.003 K, logg = 2.705 ± 0.004, logL/L{sub ⊙} = 1.625 ± 0.013, and logM/M{sub ⊙} = −0.240 ± 0.019.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DOME-SHAPED EUV WAVES FROM ROTATING ACTIVE REGIONS

Recent STEREO observations enabled the study of the properties of EUV waves in more detail. They were found to have a three-dimensional (3D) dome-shaped structure. We investigate, by means of 3D MHD simulations, the formation of EUV waves as the result of the interaction of twisted coronal magnetic loops. The numerical simulation is initialized with an idealized dipolar active region and is performed under coronal (low {beta}) conditions. A sheared rotational motion is applied to the central parts of both the positive and negative flux regions at the photosphere so that the flux tubes in between them become twisted. We find that the twisting motion results in a dome-shaped structure followed in space by a dimming and in time by an energy release (flare). The rotation of the sunspots is the trigger of the wave which initially consists of two fronts that later merge together. The resulting EUV wave propagates nearly isotropically on the disk and {approx}2 times faster in the upward direction. The initial stage of the evolution is determined by the driver, while later the wave propagates freely with a nearly Alfvenic speed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Thermodynamic signatures of an antiferromagnetic quantum critical point inside a superconducting dome

Recent experiments in unconventional superconductors, and in particular iron-based materials, have reported evidence of an antiferromagnetic quantum critical point (AFM-QCP) emerging inside the superconducting dome of the phase diagram. Fluctuations associated with such an AFM-QCP are expected to promote unusual temperature dependencies of thermodynamic quantities. Here, we compute the T dependence of the specific heat C(T) deep inside a fully gapped s +– superconducting state as the AFM-QCP is approached. We find that at the AFM-QCP, the specific heat C(T) vanishes quadratically with temperature, as opposed to the typical exponential suppression seen in fully gapped BCS superconductors. This robust result is due to a nonanalytic contribution to the free energy arising from the general form of the bosonic (AFM) propagator in the SC state. Away from the AFM-QCP, as temperature is lowered, C(T) shows a crossover from a T2 behavior to an exponential behavior, with the crossover temperature scale set by the value of the superconducting gap and the distance to the QCP. As a result, we argue that these features in the specific heat can be used to unambiguously determine the existence of AFM-QCPs inside the superconducting domes of iron-based and other fully gapped unconventional superconductors.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Superconducting Dome in Nd 1-x Sr x NiO 2 Infinite Layer Films

We show the phase diagram of Nd 1-x Sr x NiO 2 infinite layer thin films grown on SrTiO 3 . A superconducting dome spanning 0.125 < x < 0.25 is found, remarkably similar to cuprates, albeit over a narrower doping window. However, while cuprate superconductivity is bounded by an insulator for underdoping and a metal for overdoping, here we observe weakly insulating behavior on either side of the dome. Furthermore, the normal state Hall coefficient is always small and proximate to a continuous zero crossing in doping and in temperature, in contrast to the ~ 1/x dependence observed for cuprates. This suggests the presence of both electronlike and holelike bands, consistent with band structure calculations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Ferromagnetic order beyond the superconducting dome in a cuprate superconductor

According to conventional wisdom, the extraordinary properties of the cuprate high-temperature superconductors arise from doping a strongly correlated antiferromagnetic insulator. The highly overdoped cuprates—whose doping lies beyond the dome of superconductivity—are considered to be conventional Fermi liquid metals. We report the emergence of itinerant ferromagnetic order below 4 kelvin for doping beyond the superconducting dome in thin films of electron-doped La 2– x Ce x CuO 4 (LCCO). The existence of this ferromagnetic order is evidenced by negative, anisotropic, and hysteretic magnetoresistance, hysteretic magnetization, and the polar Kerr effect, all of which are standard signatures of itinerant ferromagnetism in metals. This surprising result suggests that the overdoped cuprates are strongly influenced by electron correlations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Noise Reduction Capability of the Trampoline Fabric Wind Dome

Low frequency sound below 20 Hz, also known as infrasound, is generated by both natural and anthropogenic sources. Local surface winds also generate signals within this frequency band and can dominate signals. Effectively monitoring sources of interest requires filtering out the influence of wind. Recently, the National Center for Physical Acoustics developed a 1 m fabric dome made from trampoline material that can serve as a wind filter for temporary field deployments. We assess the performance of this new dome by quantifying its overall noise reduction and show that it is an acceptable wind filter for temporary infrasound field deployments.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2016

STELLAR VARIABILITY AND FLARE RATES FROM DOME A, ANTARCTICA, USING 2009 AND 2010 CSTAR OBSERVATIONS

The Chinese Small Telescope Array (CSTAR) carried out high-cadence time-series observations of ∼20.1 square degrees centered on the South Celestial Pole during the 2008, 2009, and 2010 winter seasons from Dome A in Antarctica. The nearly continuous six months of dark conditions during each observing season allowed for >10{sup 6} images to be collected through gri and clear filters, resulting in the detection of >10{sup 4} sources over the course of three years of operation. The nearly space-like conditions in the Antarctic plateau are an ideal testbed for the suitability of very small-aperture (<20 cm) telescopes to detect transient events, variable stars, and stellar flares. We present the results of a robust search for such objects using difference image analysis of the data obtained during the 2009 and 2010 winter seasons. While no transients were found, we detected 29 flaring events and find a normalized flaring rate of 5 ± 4 × 10{sup −7} flare hr{sup −1} for late-K dwarfs, 1 ± 1 × 10{sup −6} flare hr{sup −1} for M dwarfs and 7 ± 1 × 10{sup −7} flare hr{sup −1} for all other stars in our sample. We suggest future small-aperture telescopes planned for deployment at Dome A would benefit from a tracking mechanism, to help alleviate effects from ghosting, and a finer pixel scale, to increase the telescope's sensitivity to faint objects. We find that the light curves of non-transient sources have excellent photometric qualities once corrected for systematics, and are limited only by photon noise and atmospheric scintillation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Assessments of Ali, Dome A, and Summit Camp for mm-wave Observations Using MERRA-2 Reanalysis

NASA's latest MERRA-2 reanalysis of the modern satellite measurements has made atmospheric data easily accessible with unprecedented uniformity, fidelity, and completeness. In this paper, these data are used to evaluate five sites for millimeter-wave (mm-wave) observations. These include two established sites (South Pole and Chajnantor, Atacama), and three new sites (Ali in Tibet, Dome A in Antarctica, and Summit Camp in Greenland). Atmospheric properties including precipitable water vapor (PWV), sky brightness temperature fluctuations, and ice and liquid water paths are derived and compared. Dome A emerges to be the best among those evaluated, with PWV and fluctuations smaller than the second-best site, South Pole, by more than a factor of 2. It is found that the higher site in Ali (6100 m) is on par with Cerro Chajnantor (5612 m) in terms of transmission and stability. The lower site in Ali (5250 m) planned for the first stage of observations at 90/150 GHz provides conditions comparable to those on the Chajnantor Plateau. These analyses confirm Ali to be an excellent mm-wave site in the Northern Hemisphere that will complement well-established Southern sites. According to MERRA-2 data, the observing conditions at Summit Camp are also comparable to Cerro Chajnantor. Furthermore, it is more affected by the presence of liquid water clouds.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1978

Imbrian-age highland volcanism on the moon - The Gruithuisen and Mairan domes

The Gruithuisen and Mairan domes on the moon represent morphologically and spectrally distinct nonmare extrusive volcanic features of Imbrian age. The composition, morphology, and age relationships of the domes indicate that nonmare extrusive volcanism in the northern Procellarum region of the moon continued until about 3.3 x 10 to the 9th to 3.6 x 10 to the 9th years ago and was partially contemporaneous with the emplacement of the main sequence of mare deposits.

Head, J. W., III↗
NASA NTRS1980

Topographic domes on Ganymede - Ice vulcanism or isostatic upwarping

Two formation processes are considered for two gently sloping domeshaped features on the surface of Ganymede, lying on grooved terrain and having diameters of roughly 250 km: (1) water vulcanism, triggered by a major impact, and (2) the isostatic upwarping of a crater formed in a thin crust. Numerical simulations show the volume of the domes to be consistent with eruption through fractures created by an impact that excavates partly through a thin crust. Isostatic upwarp rates calculated as a function of effective crustal temperature indicate that upwarping could also create such a dome if the impact excavated to a depth where the crust was sufficiently warm and mobile. Morphologic evidence suggests that both processes may have been important and, if either of the proposed models is correct, it is strongly implied that grooved terrain formation occurred prior to the thickening and stiffening of Ganymede's crust.

Squyres, S. W.↗
NASA NTRS1985

The Geology of East Butte, a Rhyolitic Volcanic Dome on the Eastern Snake River Plain, Idaho

East Butte is a prominent volcanic dome located on the eastern Snake River Plain. It is situated 51 km west of Idaho Fallls in the southeast corner of the Idaho National Engineering facility. East Butte rises 350 meters above the Quaternary basalt flows which encircle its 2.4 kilometer diameter base. Its maximum elevation is 2003 meters above sea level. East Butte is composed dominantly of rhyolite. Armstrong and others (1975) determined a K-Ar age of 0.6 +/- m.y. for a rhyolite sample from East Butte. Detailed geologic mapping revealed East Butte to be a single, large cumulo-dome composed dominantly of rhyolite. Major element geochemical analyses indicate that the rhyolite of East Butte is mildly peralkaline (molecular excess of Na2O and K2O over Al2O3 and compositionally homogeneous. Color variations in the East Butte rhyolite result from varying amounts of chemical and physical weathering and to the degree of devitrification that the glass in the groundmass of the rhyolite underwent.

Bretches, J. E.↗
NASA NTRS1989

Characteristics, distribution and geologic/terrain associations of small dome-like hills on Venus

Approximately 22,000 small dome-like hills were recognized on the northern 20 percent of the surface of Venus imaged by Verera 15/16. These features were described as generally circular in planimetric outline, with a range in basal diameter from the effective resolution of the Venera images (1 to 2 km) up to 20 km. The General Characteristics, Dome Distribution and Terrain Unit and Geologic Feature Associations are discussed.

Aubele, J. C.↗
NASA NTRS1989

Volcanism on Venus: Large shields and major accumulations of small domes

The outer layers of the Venusian lithosphere appear to dissipate heat from the interior through mantle-driven thermal anomalies (hot spots, swells). As a result, Venus exhibits diverse forms of thin-skin tectonism and magmatic transfer to and extrusion from countless numbers of volcanic centers (e.g., shields, paterae, domes) and volcano-tectonic complexes (e.g., coronae, arachnoids). What is known about the distribution and morphologies of major Venusian shields is summarized, and the evidence for possible structural control of major accumulations as long as 5000 km of small volcanic domes is described.

Schaber, Gerald G.↗