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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

G11.92–0.61-MM2: A BONAFIDE MASSIVE PRESTELLAR CORE?

Core accretion models of massive star formation require the existence of stable massive starless cores, but robust observational examples of such objects have proven elusive. We report subarcsecond-resolution Submillimeter Array (SMA) 1.3 mm, 1.1 mm, and 0.88 mm and Very Large Array 1.3 cm observations of an excellent massive starless core candidate, G11.92–0.61-MM2, initially identified in the course of studies of GLIMPSE Extended Green Objects (EGOs). Separated by ∼7.''2 from the nearby MM1 protostellar hot core, MM2 is a strong, compact dust continuum source (submillimeter spectral index α = 2.6 ± 0.1), but is devoid of star formation indicators. In contrast to MM1, MM2 has no masers, no centimeter continuum, and no (sub)millimeter wavelength line emission in ∼24 GHz of bandwidth observed with the SMA, including N{sub 2}H{sup +}(3-2), HCO{sup +}(3-2), and HCN(3-2). Additionally, there is no evidence for an outflow driven by MM2. The (sub)millimeter spectral energy distribution of MM2 is best fit with a dust temperature of ∼17-19 K and luminosity of ∼5-7 L {sub ☉}. The combined physical properties of MM2, as inferred from its dust continuum emission, are extreme: M ≳ 30 M {sub ☉} within a radius <1000 AU, N{sub H{sub 2}}>10{sup 25} cm{sup –2} and n{sub H{sub 2}} >10{sup 9} cm{sup –3}. Comparison of the molecular abundance limits derived from our SMA observations with gas-grain chemical models indicates that extremely dense (n(H) >> 10{sup 8} cm{sup –3}), cold (<20 K) conditions are required to explain the lack of observed (sub)millimeter line emission, consistent with the dust continuum results. Our data suggest that G11.92–0.61-MM2 is the best candidate for a bonafide massive prestellar core found to date, and a promising target for future higher-sensitivity observations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Techno-Economic Modelling of Tidal Energy Converter Arrays in the Tacoma Narrows

Hydrokinetic tidal energy converter (TEC) technology is yet to become cost competitive with other renewable energy sources. Understanding the interaction between energy production and the costs incurred harvesting that energy may unlock the economic potential of this technology. Although hydrodynamic simulation of TEC arrays has matured over time, including demonstration of how small and large arrays affect the resource, integration of cost modelling is often limited. The advanced ocean energy array techno-economic modelling tool ‘DTOcean’ enables designers to calculate and improve the levelised cost of energy (LCOE) of an array through parametric simulation of the energy extraction, design of the electrical network, moorings and foundations, and simulation of the installation and lifetime operations and maintenance of the array. This work presents a verification of DTOcean’s ability to simulate the techno-economic performance of TEC arrays by reproducing the hypothetical RM1 reference model, a semi-analytical model of a TEC array based in the Tacoma Narrows of Washington state, U.S.A. It is demonstrated that DTOcean can produce a reasonable estimate to the LCOE predicted by the reference model, giving (in Euro cents per kiloWatt hour) 36.69 ¢/kWh against the reference model’s 34.612 ¢/kWh for 10 TECs, while for 50 TECs, DTOcean calculated 20.34 ¢/kWh compared to 17.34 ¢/kWh for the reference model.

Topper, Mathew B. R. (ORCID:0000000347324347)↗
DOE OSTI2016

The detection of diffuse extended structure in 3C 273: implications for jet power

We present deep Very Large Array imaging of 3C 273 in order to determine the diffuse, large scale radio structure of this famous radio-loud quasar. Diffuse extended structure (radio lobes) is detected for the first time in these observations as a consequence of high dynamic range in the 327.5 and 1365 MHz images. This emission is used to estimate a time averaged jet power, 7.2 × 10{sup 43} erg s{sup −1} < Q-bar < 3.7 × 10{sup 44} erg s{sup −1}. Brightness temperature arguments indicate consistent values of the time variability Doppler factor and the compactness Doppler factor for the inner jet, δ ≳ 10. Thus, the large apparent broadband bolometric luminosity of the jet, ∼3 × 10{sup 46} erg s{sup −1}, corresponds to a modest intrinsic luminosity ≳10{sup 42} erg s{sup −1}, or ∼1% of Q-bar . In summary, we find that 3C 273 is actually a “typical” radio-loud quasar contrary to suggestions in the literature. The modest Q-bar is near the peak of the luminosity distribution for radio-loud quasars and it is consistent with the current rate of dissipation emitted from millimeter wavelengths to gamma rays. The extreme core-jet morphology is an illusion from a near pole-on line of sight to a highly relativistic jet that produces a Doppler enhanced glow that previously swamped the lobe emission. 3C 273 apparently has the intrinsic kpc scale morphology of a classical double radio source, but it is distorted by an extreme Doppler aberration.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

(abstract) Scaling Nominal Solar Cell Impedances for Array Design

This paper discusses a task the objective of which is to characterize solar cell array AC impedance and develop scaling rules for impedance characterization of large arrays by testing single solar cells and small arrays. This effort is aimed at formulating a methodology for estimating the AC impedance of the Mars Pathfinder (MPF) cruise and lander solar arrays based upon testing single cells and small solar cell arrays and to create a basis for design of a single shunt limiter for MPF power control of flight solar arrays having very different inpedances.

solar cells solar arrays AC impedance Mars Pathfin↗
NASA NTRS2002

Ultralow-Background Large-Format Bolometer Arrays

In the coming decade, work will commence in earnest on large cryogenic far-infrared telescopes and interferometers. All such observatories - for example, SAFIR, SPIRIT, and SPECS - require large format, two dimensional arrays of close-packed detectors capable of reaching the fundamental limits imposed by the very low photon backgrounds present in deep space. In the near term, bolometer array architectures which permit 1000 pixels - perhaps sufficient for the next generation of space-based instruments - can be arrayed efficiently. Demonstrating the necessary performance, with Noise Equivalent Powers (NEPs) of order 10-20 W/square root of Hz, will be a hurdle in the coming years. Superconducting bolometer arrays are a promising technology for providing both the performance and the array size necessary. We discuss the requirements for future detector arrays in the far-infrared and submillimeter, describe the parameters of superconducting bolometer arrays able to meet these requirements, and detail the present and near future technology of superconducting bolometer arrays. Of particular note is the coming development of large format planar arrays with absorber-coupled and antenna-coupled bolometers.

Benford, Dominic↗
DOE OSTI2014

Accretion disks in the IRAS 23151+5912 region

We present observations of radio continuum emission at 1.3 and 3.6 cm and H{sub 2}O masers toward the high-mass star-forming region IRAS 23151+5912 carried out with the Very Large Array-Expanded Very Large Array (in transition phase) in configuration A. We detected one continuum source at 1.3 cm in the region, but the counterpart of this radio continuum source at 3.6 cm was not detected at a level of 3σ. We also detected 13 water maser spots toward IRAS 23151+5912, which are distributed in three groups aligned along the northeast-southwest direction. Our results suggest that the 1.3 cm emission is consistent with a hypercompact H II region, probably with an embedded zero-age main-sequence star of type B2. In particular, we find that this young star is spatially associated with a maser group, which is tracing a disk-like structure of about 460 AU. We also find that the masers of the second group are probably describing a circumstellar disk of about 86 AU, whose central protostar, still undetected, should have a mass of ∼11 M {sub ☉}. We also suggest that the third water maser group is possibly associated with the SiO outflow and the undetected driving source of the system. Finally, we noted that the 1.3 cm continuum source and the three maser groups are aligned in the northeast-southwest direction, similar to the elongation of the large ionized region, which probably is the result of shock-wave induced star formation on the densest region of the medium.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Search for in-band transitions in the candidate superdeformed band in Si 28

Background: Superdeformed (SD) bands are suggested by theory around Ca 40 and in lighter alpha-conjugate nuclei such as Mg 24 , Si 28 , and S 32 . Such predictions originate from a number of theoretical models including mean-field models and antisymmetrized molecular dynamics (AMD) calculations. While SD bands have been identified in Ca 40 and its near neighbors, evidence of their existence in the lighter, midshell nuclei is circumstantial at best. Additionally, the key evidence of superdeformation would be the observation of transitions with high B ( E 2 ) transition strengths connecting states in a rotational sequence. This is challenging information to obtain since the bands lie at a high excitation energy and competition from out-of-band decay is dominant. Purpose: The purpose of the present study is to establish a new methodology to circumvent the difficulties in identifying and quantifying in-band transitions through directly populating candidate states in the SD band in Si 28 through inelastic alpha scattering, selecting such states with a spectrometer, and measuring their gamma-ray decay with a large array of high-purity germanium detectors, allowing direct access to electromagnetic transition strengths. Methods: Excited states in Si 28 were populated in the Si 28 ( α , α ' ) reaction using a 130-MeV He 4 beam from the K140 AVF cyclotron at the Research Center for Nuclear Physics. Outgoing alpha particles were analyzed using the Grand Raiden spectrometer positioned at an angle of 9 . 1 ° to favor the population of states with J ≈ 4 . Coincident gamma rays were detected with the CAGRA array of 12 HPGe clover detectors augmented by a set of four large LaBr 3 detectors. Results: Data analysis showed that it was possible to identify additional low-energy transitions in competition with high-energy decays from excited states in Si 28 in the vicinity of 10 MeV. However, while the candidate 4 + SD state at 10.944 MeV was populated, a 1148-keV transition to the candidate 2 + SD state at 9.796 MeV was not observed, and only an upper limit for its transition strength of B ( E 2 ) < 43 W.u. could be established. This contradicts AMD predictions of ≈ 200 W.u. for such a transition. Conclusion: The present study strongly rejects the hypothesis that the candidate set of states identified in Si 28 represents an SD band, which demonstrates the potential of the methodology devised here.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Probing the Impact of Radio-mode Feedback on the Properties of the Cool Circumgalactic Medium

We explore the influence of radio-mode feedback on the properties of the cool circumgalactic medium (CGM). To this end, we assemble a statistical sample of approximately 30,000 radio galaxies with background quasars by combining optical spectroscopic measurements of luminous red galaxies and quasars from the year 1 data set of the Dark Energy Spectroscopic Instrument and radio sources from the LOw-Frequency ARray Two-metre Sky Survey (LoTSS) DR2 catalog and the Very Large Array Sky Survey (VLASS) quick-look catalog. Galaxies with similar optical properties but with no radio counterparts in LoTSS and VLASS are selected as the control group. We measure the cool CGM properties of radio galaxies and their control samples traced by Mg ii absorption lines, including covering fraction, rest equivalent width, and gas kinematics. Our results show no significant difference in the properties of gas around radio galaxies and their control sample, indicating that the operating radio-mode feedback of massive galaxies does not produce detectable effects on the properties of the cool CGM. Finally, we show that the CGM of radio galaxies contains a nonnegligible amount of cool gas with approximately 10 10 M ⊙ . This abundance can place a stringent constraint on the radio-mode feedback models.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Quantum Versus Classical Switching Dynamics of Driven Dissipative Kerr Resonators

Here, we report a first-principles study of the driven dissipative dynamics for Kerr oscillators in the mesoscopic regime. This regime is characterized by large Kerr nonlinearity, realized here using the nonlinear kinetic inductance of a large array of Josephson junctions. The experimentally measured nonlinear resonance lineshapes of the junction array modes show significant deviations from steady-state numerical predictions, and necessitate time-dependent numerical simulations indicative of strong measurement-induced dephasing in the system arising from the large cross-Kerr effect between array modes. Analytical and numerical calculations of switching rate corroborate this by showing the emergence of a slow time scale, which is much longer than the linear decay rate and is set by fluctuation-induced switching times in the bistable regime. Furthermore, our analysis shows that the usual quantum-activated escape treatment is inadequate for prediction of the switching rates at large frequency shifts caused by strong nonlinearities, necessitating a quantum treatment that utilizes the full system Liouvillian. Based on our analysis, we identify a universal crossover parameter that delineates the regimes of validity of semiclassical and quantum descriptions, respectively. Our work shows how dynamical switching effects in strongly nonlinear systems provide a platform to study quantum-to-classical transitions.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1979

Phase conjugation method and apparatus for an active retrodirective antenna array

An active retrodirective antenna array wherein a reference array element is used to generate a phase reference which is replicated at succeeding elements of the array. Each element of the array is associated with a phase regeneration circuit and the phase conjugation circuitry of an adjacent element. In one implementation, the phase reference circuit operates on the input signal at the reference element, a voltage controlled oscillator (VCO) output signal and the input pilot signal at the next array element received from a transmission line. By proper filtering and mixing, a phase component may be produced to which the VCO may be locked to produce the phase conjugate of the pilot signal at the next array element plus a transmission line delay. In another implementation, particularly suited for large arrays in space, two different input pilot frequencies are employed.

Tausworthe, R. C.↗
NASA NTRS1992

Report of the Working Design Group

The engineering study group in the LOUISA workshop was responsible for producing a preliminary general design for an optical synthetic aperture telescope on the Moon. This design is intended to be a test case for focusing continuing design studies. The scope of the design included consideration of the array geometry, individual telescopes, metrology, site attributes, and construction. However, no attempt was made to go into further depth in the design than to cover the essential characteristics of the instrument. The starting point for the array design was the lunar optical array discussed by Burke (1985). His array geometry followed the design and correlation procedure of the 27-element Very Large Array (VLA) radio telescopes near Socorro, New Mexico.

Source record↗
DOE OSTI2020

Particle Response of Antenna-Coupled TES Arrays: Results from SPIDER and the Laboratory

Future mm-wave and sub-mm space missions will employ large arrays of multiplexed transition-edge-sensor (TES) bolometers. Such instruments must contend with the high flux of cosmic rays beyond our atmosphere that induce ‘glitches’ in bolometer data, which posed a challenge to data analysis from the Planck bolometers. Future instruments will face the additional challenges of shared substrate wafers and multiplexed readout wiring. Here, we explore the susceptibility of modern TES arrays to the cosmic ray environment of space using two data sets: the 2015 long-duration balloon flight of the SPIDER cosmic microwave background polarimeter, and a laboratory exposure of SPIDER flight hardware to radioactive sources. We find manageable glitch rates and short glitch durations, leading to minimal effect on SPIDER analysis. We constrain energy propagation within the substrate through a study of multi-detector coincidences and give a preliminary look at pulse shapes in laboratory data.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1985

Planning for VLA/DSN arrayed support to the Voyager at Neptune

Preplanning for the use of the National Radio Astronomy Observatory's Very Large Array (VLA) in support of Voyager at Neptune has been underway since early 1982. When arrayed with the Deep Space Network (DSN) antennas at Goldstone, CA, the VLA more than doubles the potential data return over the American longitude for the 1989 Voyager encounter. The background, rationale and current status of planning for VLA-DSN Arrayed Support to the Voyager at Neptune are discussed.

Layland, J. W.↗
DOE OSTI2016

44 GHZ CLASS I METHANOL (CH{sub 3}OH) MASER SURVEY IN THE GALACTIC CENTER

We report on a large 44 GHz (7{sub 0}–6{sub 1} A {sup +}) methanol (CH{sub 3}OH) maser survey of the Galactic Center. The Karl G. Jansky Very Large Array was used to search for CH{sub 3}OH maser emission covering a large fraction of the region around Sgr A. In 25 pointings, over 300 CH{sub 3}OH maser sources (>10 σ ) were detected. The majority of the maser sources have a single peak emission spectrum with line of sight velocities that range from about −13 to 72 km s{sup −1}. Most maser sources were found to have velocities around 35−55 km s{sup −1}, closely following velocities of neighboring interacting molecular clouds (MCs). The full width at half-maximum of each individual spectral feature is very narrow (∼0.85 km s{sup −1} on average). In the north, where Sgr A East is known to be interacting with the 50 km s{sup −1} MC, more than 100 44 GHz CH{sub 3}OH masers were detected. In addition, three other distinct concentrations of masers were found, which appear to be located closer to the interior of the interacting MCs. It is possible that a subset of masers is associated with star formation, although conclusive evidence is lacking.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Numerical modeling of the effects of wave energy converter characteristics on nearshore wave conditions

Modeled nearshore wave propagation was investigated downstream of simulated wave energy converters (WECs) to evaluate overall near- and far-field effects of WEC arrays. Model sensitivity to WEC characteristics and WEC array deployment scenarios was evaluated using a modified version of an industry standard wave model, Simulating WAves Nearshore (SWAN), which allows the incorporation of device-specific WEC characteristics to specify obstacle transmission. The sensitivity study illustrated that WEC device type and subsequently its size directly resulted in wave height variations in the lee of the WEC array. Wave heights decreased up to 30% between modeled scenarios with and without WECs for large arrays (100 devices) of relatively sizable devices (26 m in diameter) with peak power generation near to the modeled incident wave height. Other WEC types resulted in less than 15% differences in modeled wave height with and without WECs, with lesser influence for WECs less than 10 m in diameter. Wave directions and periods were largely insensitive to changes in parameters. Furthermore, additional model parameterization and analysis are required to fully explore the model sensitivity of peak wave period and mean wave direction to the varying of the parameters.

16 TIDAL AND WAVE POWER↗
DOE OSTI2017

Aces4: A Platform for Computational Chemistry Calculations with Extremely Large Block-Sparse Arrays

Aces4 is a parallel programming platform comprising a DSL for Computational Chemistry and its runtime system. It offers a convenient way to express parallelism together with extensive support for extremely large, possibly sparse, distributed arrays. It aids scientists in the creation of performant, scalable, massively parallel programs that can effectively take advantage of leadership class computing systems to address important scientific questions. Aces4 has enabled the development and implementation of new methods in electronic structure theory which are breaking new ground in their ability to perform highly accurate calculations on ever larger molecular systems. In this paper the design of Aces4, which is based on the the Super Instruction Architecture approach, is described. Experimental scaling results for Molecular Cluster Perturbation Theory, a new method enabled by Aces4, and CCSD, a widely used computational chemistry method are given.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Mass assembly of stellar systems and their evolution with the SMA (MASSES). multiplicity and the physical environment in L1448N

We present continuum and molecular line observations at 230 and 345 GHz from the Submillimeter Array (SMA) toward three protostars in the Perseus L1448N region. The data are from the large project “Mass Assembly of Stellar Systems and their Evolution with the SMA.” Three dust continuum sources, Source B, Source NW, and Source A, are detected at both frequencies. These sources have corresponding emission peaks in C{sup 18}O (J=2→1), {sup 13}CO (J=2→1), and HCO{sup +} (J=4→3), and have offsets with N{sub 2}D{sup +} (J=3→2) peaks. High angular resolution data from a complementary continuum survey with the Karl G. Jansky Very Large Array show that Source B is associated with three 8 mm continuum objects, Source NW with two, and Source A remains single. These results suggest that multiplicity in L1448N exists at different spatial scales from a few thousand AU to <100 AU. Velocity gradients in each source obtained from two-dimensional fits to the SMA C{sup 18}O emission are found to be perpendicular to within 20° of the outflow directions as revealed by {sup 12}CO (J=2→1). We have observed that Sources B and NW with multiplicity have higher densities than Source A without multiplicity. This suggests that thermal Jeans fragmentation can be relevant in the fragmentation process. However, we have not observed a difference in the ratio between rotational and gravitational energy between sources with and without multiplicity. We also have not observed a trend between non-thermal velocity dispersions and the level of fragmentation. Our study has provided the first direct and comprehensive comparison between multiplicity and core properties in low-mass protostars, although based on small number statistics.

79 ASTRONOMY AND ASTROPHYSICS↗