Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “large array”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

On-Sky Performance of the SPT-3G Frequency-Domain Multiplexed Readout

Frequency-domain multiplexing (fMux) is an established technique for the readout of large arrays of transition-edge sensor (TES) bolometers. Each TES in a multiplexing module has a unique AC voltage bias that is selected by a resonant filter. This scheme provides for the operation and readout of multiple bolometers on a single pair of wires, reducing thermal loading onto sub-Kelvin stages. The current receiver on the South Pole Telescope, SPT-3G, uses a 68x fMux system to operate its large-format camera of ~16,000 TES bolometers. We present here the successful implementation and performance of the SPT-3G readout as measured on-sky. Characterization of the noise reveals a median pair-differenced 1/f knee frequency of 33 mHz, indicating that low-frequency noise in the readout will not limit SPT-3G’s measurements of sky power on large angular scales. Measurements further show that the median readout white noise level in each of the SPT-3G observing bands is below the expectation for photon noise, demonstrating that SPT-3G is operating in the photon-noise-dominated regime.

47 OTHER INSTRUMENTATION↗
DOE OSTI2016

WEAK AND COMPACT RADIO EMISSION IN EARLY HIGH-MASS STAR-FORMING REGIONS. I. VLA OBSERVATIONS

We present a high-sensitivity radio continuum survey at 6 and 1.3 cm using the Karl G. Jansky Very Large Array toward a sample of 58 high-mass star-forming regions. Our sample was chosen from dust clumps within infrared dark clouds with and without IR sources (CMC–IRs and CMCs, respectively), and hot molecular cores (HMCs), with no previous, or relatively weak radio continuum detection at the 1 mJy level. Due to the improvement in the continuum sensitivity of the Very Large Array, this survey achieved map rms levels of ∼3–10 μ Jy beam{sup −1} at sub-arcsecond angular resolution. We extracted 70 continuum sources associated with 1.2 mm dust clumps. Most sources are weak, compact, and prime candidates for high-mass protostars. Detection rates of radio sources associated with the millimeter dust clumps for CMCs, CMC–IRs, and HMCs are 6%, 53%, and 100%, respectively. This result is consistent with increasing high-mass star formation activity from CMCs to HMCs. The radio sources located within HMCs and CMC–IRs occur close to the dust clump centers, with a median offset from it of 12,000 au and 4000 au, respectively. We calculated 5–25 GHz spectral indices using power-law fits and obtained a median value of 0.5 (i.e., flux increasing with frequency), suggestive of thermal emission from ionized jets. In this paper we describe the sample, observations, and detections. The analysis and discussion will be presented in Paper II.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

Microstrip reflectarray antenna for the SCANSCAT radar application

This publication presents an antenna system that has been proposed as one of the candidates for the SCANSCAT (Scanned Scatterometer) radar application. It is the mechanically steered planar microstrip reflectarray. Due to its thin, lightweight structure, the antenna's mechanical rotation will impose minimum angular momentum for the spacecraft. Since no power-dividing circuitry is needed for its many radiating microstrip patches, this electrically large array antenna demonstrates excellent power efficiency. In addition, this fairly new antenna concept can provide many significant advantages over a conventional parabolic reflector. The basic formulation for the radiation fields of the microstrip reflectarray is presented. This formulation is based on the array theory augmented by the Uniform Geometrical Theory of Diffraction (UTD). A computer code for analyzing the microstrip reflectarray's performances, such as far-field patterns, efficiency, etc., is also listed in this report. It is proposed here that a breadboard unit of this microstrip reflectarray should be constructed and tested in the future to validate the calculated performance. The antenna concept presented here can also be applied in many other types of radars where a large array antenna is needed.

Huang, John↗
DOE OSTI2014

Development of a He{sup 3}−He{sup 4} sub Kelvin active magnetic regenerative refrigerator (AMRR) with no moving parts

Current state of the art particle and photon detectors such as Transition Edge Sensors (TES) and Microwave Kinetic Inductance Detectors (MKID) use large arrays of sensors or detectors for space science missions. As the size of these space science detectors increases, future astrophysics missions will require sub-Kelvin cooling over larger areas. This leads to not only increased cooling power requirements, but also a requirement for distributed sub-Kelvin cooling. We propose an active Magnetic Regenerative Refrigerator (AMRR) that uses a Superfluid Magnetic Pump (SMP) to circulate liquid He{sup 3}−He{sup 4} through a magnetic regenerator to provide the necessary cooling at sub-Kelvin temperatures. Such system will be capable of distributing the cooling load to a relatively large array of objects. One advantage of using a fluid for heat transfer in such systems is to isolate components such as the superconducting magnets from detectors that are sensitive to magnetic fields. Another advantage of the proposed tandem AMRR is that it does not need Gas Gap Heat Switches (GGHS) to transfer heat during various stages of the magnetic cooling. Our proposed system consists of four superconducting magnets, one superleak, and three heat exchangers. It will operate continuously with no moving parts and it will be capable of providing the necessary cooling at sub-Kelvin temperatures for future space science applications.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

PRESAGE: Protecting Structured Address Generation against Soft Errors

Modern computer scaling trends in pursuit of larger component counts and power efficiency have, unfortunately, lead to less reliable hardware and consequently soft errors escaping into application data ("silent data corruptions"). Techniques to enhance system resilience hinge on the availability of efficient error detectors that have high detection rates, low false positive rates, and lower computational overhead. Unfortunately, efficient detectors to detect faults during address generation (to index large arrays) have not been widely researched. We present a novel lightweight compiler-driven technique called PRESAGE for detecting bit-flips affecting structured address computations. A key insight underlying PRESAGE is that any address computation scheme that flows an already incurred error is better than a scheme that corrupts one particular array access but otherwise (falsely) appears to compute perfectly. Enabling the flow of errors allows one to situate detectors at loop exit points, and helps turn silent corruptions into easily detectable error situations. Our experiments using PolyBench benchmark suite indicate that PRESAGE-based error detectors have a high error-detection rate while incurring low overheads.

Sharma, Vishal C.↗
DOE OSTI2016

iPTF SEARCH FOR AN OPTICAL COUNTERPART TO GRAVITATIONAL-WAVE TRANSIENT GW150914

The intermediate Palomar Transient Factory (iPTF) autonomously responded to and promptly tiled the error region of the first gravitational-wave event GW150914 to search for an optical counterpart. Only a small fraction of the total localized region was immediately visible in the northern night sky, due both to Sun-angle and elevation constraints. Here, we report on the transient candidates identified and rapid follow-up undertaken to determine the nature of each candidate. Even in the small area imaged of 126 deg{sup 2}, after extensive filtering, eight candidates were deemed worthy of additional follow-up. Within two hours, all eight were spectroscopically classified by the Keck II telescope. Curiously, even though such events are rare, one of our candidates was a superluminous supernova. We obtained radio data with the Jansky Very Large Array and X-ray follow-up with the Swift satellite for this transient. None of our candidates appear to be associated with the gravitational-wave trigger, which is unsurprising given that GW150914 came from the merger of two stellar-mass black holes. This end-to-end discovery and follow-up campaign bodes well for future searches in this post-detection era of gravitational waves.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Metabolic and spatio-taxonomic response of uncultivated seafloor bacteria following the Deepwater Horizon oil spill

The release of 700 million liters of oil into the Gulf of Mexico over a few months in 2010 produced dramatic changes in the microbial ecology of the water and sediment. Here in this work, we reconstructed the genomes of 57 widespread uncultivated bacteria from post-spill deep-sea sediments, and recovered their gene expression pattern across the seafloor. These genomes comprised a common collection of bacteria that were enriched in heavily affected sediments around the wellhead. Although rare in distal sediments, some members were still detectable at sites up to 60 km away. Many of these genomes exhibited phylogenetic clustering indicative of common trait selection by the environment, and within half we identified 264 genes associated with hydrocarbon degradation. Alkane degradation ability was near ubiquitous among candidate hydrocarbon degraders, whereas just three harbored elaborate gene inventories for the degradation of alkanes and aromatic and polycyclic aromatic hydrocarbons (PAHs). Differential gene expression profiles revealed a spill-promoted microbial sulfur cycle alongside gene upregulation associated with PAH degradation. Gene expression associated with alkane degradation was widespread, although active alkane degrader identities changed along the pollution gradient. Finally, analyses suggest that a broad metabolic capacity to respond to oil inputs exists across a large array of usually rare indigenous deep-sea bacteria.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2016

Radio follow-up of gravitational-wave triggers during advanced LIGO O1

We present radio follow-up observations carried out with the Karl G. Jansky Very Large Array during the first observing run (O1) of the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO). A total of three gravitational-wave triggers were followed-up during the ≈4 months of O1, from 2015 September to 2016 January. Two of these triggers, GW150914 and GW151226, are binary black hole (BH) merger events of high significance. A third trigger, G194575, was subsequently declared as an event of no interest (i.e., a false alarm). Our observations targeted selected optical transients identified by the intermediate Palomar Transient Factory in the Advanced LIGO error regions of the three triggers, and a limited region of the gravitational-wave localization area of G194575 not accessible to optical telescopes due to Sun constraints, where a possible high-energy transient was identified. No plausible radio counterparts to GW150914 and GW151226 were found, in agreement with expectations for binary BH mergers. We show that combining optical and radio observations is key to identifying contaminating radio sources that may be found in the follow-up of gravitational-wave triggers, such as emission associated with star formation and active galactic nuclei. We discuss our results in the context of the theoretical predictions for radio counterparts to gravitational-wave transients, and describe our future plans for the radio follow-up of Advanced LIGO (and Virgo) triggers.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Radio observations of a sample of broad-line type Ic supernovae discovered by PTF/IPTF: a search for relativistic explosions

Long duration γ-ray bursts are a rare subclass of stripped-envelope core-collapse supernovae (SNe) that launch collimated relativistic outflows (jets). All γ-ray-burst-associated SNe are spectroscopically Type Ic, with broad-lines, but the fraction of broad-lined SNe Ic harboring low-luminosity γ-ray bursts remains largely unconstrained. Some SNe should be accompanied by off-axis γ-ray burst jets that initially remain invisible, but then emerge as strong radio sources (as the jets decelerate). However, this critical prediction of the jet model for γ-ray bursts has yet to be verified observationally. Here, we present K. G. Jansky Very Large Array observations of 15 broad-lined SNe of Type Ic discovered by the Palomar Transient Factory in an untargeted manner. Most of the SNe in our sample exclude radio emission observationally similar to that of the radio-loud, relativistic SN 1998bw. We constrain the fraction of 1998bw-like broad-lined SNe Ic to be ≲41% (99.865% confidence). Most of the events in our sample also exclude off-axis jets similar to GRB 031203 and GRB 030329, but we cannot rule out off-axis γ-ray bursts expanding in a low-density wind environment. Three SNe in our sample are detected in the radio. PTF11qcj and PTF14dby show late-time radio emission with average ejecta speeds of ≈0.3–0.4 c, on the dividing line between relativistic and “ordinary” SNe. The speed of PTF11cmh radio ejecta is poorly constrained. We estimate that ≲85% (99.865% confidence) of the broad-lined SNe Ic in our sample may harbor off-axis γ-ray bursts expanding in media with densities in the range probed by this study.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Measuring photometric redshifts for high-redshift radio source surveys

With the advent of deep, all-sky radio surveys, the need for ancillary data to make the most of the new, high-quality radio data from surveys like the Evolutionary Map of the Universe (EMU), GaLactic and Extragalactic All-sky Murchison Widefield Array survey eXtended, Very Large Array Sky Survey, and LOFAR Two-metre Sky Survey is growing rapidly. Radio surveys produce significant numbers of Active Galactic Nuclei (AGNs) and have a significantly higher average redshift when compared with optical and infrared all-sky surveys. Thus, traditional methods of estimating redshift are challenged, with spectroscopic surveys not reaching the redshift depth of radio surveys, and AGNs making it difficult for template fitting methods to accurately model the source. Machine Learning (ML) methods have been used, but efforts have typically been directed towards optically selected samples, or samples at significantly lower redshift than expected from upcoming radio surveys. This work compiles and homogenises a radio-selected dataset from both the northern hemisphere (making use of Sloan Digital Sky Survey optical photometry) and southern hemisphere (making use of Dark Energy Survey optical photometry). We then test commonly used ML algorithms such as k-Nearest Neighbours (kNN), Random Forest, ANNz, and GPz on this monolithic radio-selected sample. We show that kNN has the lowest percentage of catastrophic outliers, providing the best match for the majority of science cases in the EMU survey. We note that the wider redshift range of the combined dataset used allows for estimation of sources up to z = 3 before random scatter begins to dominate. When binning the data into redshift bins and treating the problem as a classification problem, we are able to correctly identify ≈ 76% of the highest redshift sources—sources at redshift z > 2.51 —as being in either the highest bin (z > 2.51) or second highest (z = 2.25).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

The Two-sided Jet Structures of NGC 1052 at Scales from 300 to 4 × 10{sup 7} Schwarzschild Radii

We investigated the jet width profile with distance along the jet in the nearby radio galaxy NGC 1052 at radial distances between ∼300 and 4 × 10{sup 7} Schwarzschild radii (R {sub S}) from the central engine on both their approaching and receding jet sides. The width of jets was measured in images obtained with the Very Long Baseline Interferometry (VLBI) Space Observatory Programme, the Very Long Baseline Array, and the Very Large Array. The jet width profiles of receding jets are apparently consistent with those of approaching jets throughout the measuring distance ranges, indicating symmetry at least up to the sphere of gravitational influence of the central black hole. The power-law index a of the jet width profile (w {sub jet} ∝ r {sup a}, where w {sub jet} is the jet width, r is the distance from the central engine in the unit of R {sub S}) apparently shows a transition from a ∼ 0 to a ∼ 1, i.e., the cylindrical-to-conical jet structures, at a distance of ∼1 × 10{sup 4} R {sub S}. The cylindrical jet shape at small distances is reminiscent of the innermost jets in 3C 84. Both the central engines of NGC 1052 and 3C 84 are surrounded by dense material, part of which is ionized and causes heavy free–free absorption.

79 ASTRONOMY AND ASTROPHYSICS↗