Showing papers by "Raytheon published in 2019"
Proceedings Article•
10 Jul 2019
TL;DR: This paper presents the experiences designing and operating CloudLab for four years, serving nearly 4,000 users who have run over 79,000 experiments on 2,250 servers, switches, and other pieces of datacenter equipment, and draws lessons organized around two themes.
Abstract: Given the highly empirical nature of research in cloud computing, networked systems, and related fields, testbeds play an important role in the research ecosystem. In this paper, we cover one such facility, CloudLab, which supports systems research by providing raw access to programmable hardware, enabling research at large scales, and creating a shared platform for repeatable research.
We present our experiences designing CloudLab and operating it for four years, serving nearly 4,000 users who have run over 79,000 experiments on 2,250 servers, switches, and other pieces of datacenter equipment. From this experience, we draw lessons organized around two themes. The first set comes from analysis of data regarding the use of CloudLab: how users interact with it, what they use it for, and the implications for facility design and operation. Our second set of lessons comes from looking at the ways that algorithms used "under the hood," such as resource allocation, have important-- and sometimes unexpected--effects on user experience and behavior. These lessons can be of value to the designers and operators of IaaS facilities in general, systems testbeds in particular, and users who have a stake in understanding how these systems are built.
254 citations
TL;DR: In this article, the current status of weather radar polarimetry, discuss the issues and limitations of PRD usage, and explore potential approaches to more efficiently use PRD for quantitative precipitation estimation and forecasting based on statistical retrieval with physical constraints.
Abstract: After decades of research and development, the WSR-88D (NEXRAD) network in the United States was upgraded with dual-polarization capability, providing polarimetric radar data (PRD) that have the potential to improve weather observations, quantification, forecasting, and warnings. The weather radar networks in China and other countries are also being upgraded with dual-polarization capability. Now, with radar polarimetry technology having matured, and PRD available both nationally and globally, it is important to understand the current status and future challenges and opportunities. The potential impact of PRD has been limited by their oftentimes subjective and empirical use. More importantly, the community has not begun to regularly derive from PRD the state parameters, such as water mixing ratios and number concentrations, used in numerical weather prediction (NWP) models. In this review, we summarize the current status of weather radar polarimetry, discuss the issues and limitations of PRD usage, and explore potential approaches to more efficiently use PRD for quantitative precipitation estimation and forecasting based on statistical retrieval with physical constraints where prior information is used and observation error is included. This approach aligns the observation-based retrievals favored by the radar meteorology community with the model-based analysis of the NWP community. We also examine the challenges and opportunities of polarimetric phased array radar research and development for future weather observation.
53 citations
TL;DR: In this paper, the options, challenges, and techniques associated with the development of embedded thermal management technology (TMT) have been discussed, and a modified Johnson's figure-of-merit (JFOM-k) was introduced to reflect the near-junction thermal limitation.
Abstract: Successful utilization of the inherent capability of wide bandgap materials and architectures for radio frequency (RF) power amplifiers (PAs) necessitates the creation of an alternative thermal management paradigm. Recent “embedded cooling” efforts in the aerospace industry have focused on overcoming the near-junction thermal limitations of conventional electronic materials and enhancing removal of the dissipated power with on-chip cooling. These efforts, focusing on the use of diamond substrates and microfluidic jet impingement, are ushering in a new generation (Gen3) of thermal packaging technology. Following the introduction of a modified Johnson's figure-of-merit (JFOM-k), which includes thermal conductivity to reflect the near-junction thermal limitation, attention is turned to the options, challenges, and techniques associated with the development of embedded thermal management technology (TMT). Record GaN-on-Diamond transistor linear power of 11 W/mm, transistor power fluxes in excess of 50 kW/cm2, and heat fluxes, above 40 kW/cm2, achieved in Defense Advanced Research Projects Agency (DARPA)'s near-junction thermal transport (NJTT) program, are described. Raytheon's ICECool demonstration monolithic microwave integrated circuits (MMICs), which achieved 3.1× the CW RF power output and 4.8× the CW RF power density relative to a baseline design, are used to illustrate the efficacy of Gen3 embedded cooling.
46 citations
TL;DR: This review surveyed potential testing systems published from 1989 to 2017 and analyzed their performances in terms of robustness, sensitivity, clinical relevance, and suitability for POC diagnostics, and introduces bubble plots to facilitate the analysis.
25 citations
TL;DR: In this article, the authors present a detailed analysis of the galaxy environment within which Coma P resides and conclude that the available data are best fit by a distance of 5.5 Mpc.
Abstract: We present Hubble Space Telescope (HST) observations of the low surface brightness (SB) galaxy Coma P. This system was first discovered in the Arecibo Legacy Fast ALFA H i survey and was cataloged as an (almost) dark galaxy because it did not exhibit any obvious optical counterpart in the available survey data (e.g., Sloan Digital Sky Survey). Subsequent WIYN pODI imaging revealed an ultra-low SB stellar component located at the center of the H i detection. We use the HST images to produce a deep color–magnitude diagram of the resolved stellar population present in Coma P. We clearly detect a red stellar sequence that we interpret to be a red giant branch and use it to infer a tip of the red giant branch distance of ${5.50}_{-0.53}^{+0.28}$ Mpc. The new distance is substantially lower than earlier estimates and shows that Coma P is an extreme dwarf galaxy. Our derived stellar mass is only 4.3 × 105 M ⊙, meaning that Coma P has an extreme H i-to-stellar mass ratio of 81. We present a detailed analysis of the galaxy environment within which Coma P resides. We hypothesize that Coma P formed within a local void and has spent most of its lifetime in a low-density environment. Over time, the gravitational attraction of the galaxies located in the void wall has moved it to the edge, where it had a recent "fly-by" interaction with M64. We investigate the possibility that Coma P is at a farther distance and conclude that the available data are best fit by a distance of 5.5 Mpc.
24 citations
TL;DR: In this paper, the authors used simulated photometry to investigate the dependency of the red giant branch (TRGB) luminosity on stellar age and metallicity as a function of wavelength (475 nm - 4.5 micron).
Abstract: The tip of the red giant branch (TRGB) is a well-established standard candle used to measure distances to nearby galaxies. The TRGB luminosity is typically measured in the I-band, where the luminosity has little dependency on stellar age or stellar metallicity. As the TRGB is brighter at wavelengths redder than the I-band, observational gains can be made if the TRGB luminosity can be robustly calibrated at longer wavelengths. This is of particular interest given the infrared capabilities that will be available with the James Webb Space Telescope and an important calibration consideration for using TRGB distances as part of an independent measurement of the Hubble constant. Here, we use simulated photometry to investigate the dependency of the TRGB luminosity on stellar age and metallicity as a function of wavelength (475 nm - 4.5 micron). We find intrinsic variations in the TRGB magnitude to increase from a few hundredths of a magnitude at 800-900 nm to ~0.6 mag by 1.5 micron. We show that variations at the longer infrared wavelengths can be reduced to 0.02-0.05 mag (1-2% accuracy in distance) with careful calibrations that account for changes in age and metal content. These represent the minimum uncertainties; observational uncertainties will be higher. Such calibration efforts may also provide independent constraints of the age and metallicity of stellar halos where TRGB distances are best measured. At 3.6 and 4.5 micron, the TRGB magnitude is predicted to vary up to ~0.15 mag even after corrections for stellar age and metallicity, making these wavelengths less suitable for precision distances.
23 citations
TL;DR: In this article, the ages of the young, resolved stellar populations at the locations of 237 optically-identified supernova remnants in M83 were determined using resolved stellar photometry of seven archival WFC3/UVIS fields in F336W, F438W, and F814W.
Abstract: We determine the ages of the young, resolved stellar populations at the locations of 237 optically-identified supernova remnants in M83. These age distributions put constraints on the progenitor masses of the supernovae that produced 199 of the remnants. The other 38 show no evidence for having a young progenitor and are therefore good Type Ia SNR candidates. Starting from Hubble Space Telescope broadband imaging, we measured resolved stellar photometry of seven archival WFC3/UVIS fields in F336W, F438W, and F814W. We generate color-magnitude diagrams of the stars within 50 pc of each SNR and fit them with stellar evolution models to obtain the population ages. From these ages we infer the progenitor mass that corresponds to the lifetime of the most prominent age that is $ $15 M$_{\odot}$, and 5 of these are $>$15 M$_{\odot}$ at 84% confidence. This is the largest collection of high-mass progenitors to date, including our highest-mass progenitor inference found so far, with a constraint of $<$8 Myr. Overall, the distribution of progenitor masses has a power-law index of $-3.0^{+0.2}_{-0.7}$, steeper than Salpeter initial mass function ($-2.35$). It remains unclear whether the reason for the low number of high-mass progenitors is due to the difficulty of finding and measuring such objects or because only a fraction of very massive stars produce supernovae.
22 citations
TL;DR: A self-oscillating boost converter with a blocking diode is proposed to meet the desire for simple, cost-effective, high performance, and highly efficient LED drivers and demonstrates several appealing advantages including design simplicity, robustness, soft-switching characteristics, tight current regulation, and high efficiency over a wide line/load range.
Abstract: In this paper, a self-oscillating boost converter with a blocking diode is proposed to meet the desire for simple, cost-effective, high performance, and highly efficient LED drivers. As compared with traditional self-oscillating converters, the proposed converter demonstrates several appealing advantages including design simplicity, robustness, soft-switching characteristics (zero-voltage switching and zero-current switching), tight current regulation, and high efficiency over a wide line/load range. The control stage is implemented with a compact and low-cost industry standard controller, which assumes multiple roles in switching and LED current regulation. A type III compensator with anti-windup is designed to limit the maximum LED current at startup and to achieve tight LED current regulation at steady state. The efficiency and desired transient/steady-state performances are verified with SPICE simulation and a prototype circuit, which demonstrate a maximum efficiency of 95.9% and 2.3% ripple factor for the LED current. The robustness of the proposed driver is verified under a range of power supply voltage and different numbers of LEDs at the load side. In addition, the circuit is modified to implement high efficiency pulsewidth modulation dimming between 5% and 95%.
22 citations
University of California, Berkeley1, Raytheon2, Max Planck Society3, University of Strasbourg4, University of Surrey5, University of Edinburgh6, University of Sydney7, Australian National University8, Herzberg Institute of Astrophysics9, University of California, Los Angeles10, University of Minnesota11
TL;DR: In this article, the authors presented new horizontal branch (HB) distance measurements to 17 of the faintest known M31 satellites (−6 ≲ MV ≲ −13) based on deep Hubble Space Telescope (HST) imaging.
Abstract: We present new horizontal branch (HB) distance measurements to 17 of the faintest known M31 satellites (−6 ≲ MV ≲ −13) based on deep Hubble Space Telescope (HST) imaging. The colour–magnitude diagrams extend ∼1–2 mag below the HB, which provides for well-defined
HBs, even for faint galaxies in which the tip of the red giant branch (TRGB) is sparsely populated. We determine distances across the sample to an average precision of 4 per cent (∼30 kpc at 800 kpc).We find that the majority of these galaxies are in good agreement, though
slightly farther (0.1–0.2 mag) when compared to recent ground-based TRGB distances. Two galaxies (And IX and And XVII) have discrepant HST and ground-based distances by ∼0.3 mag (∼150 kpc), which may be due to contamination from Milky Way foreground stars and/or
M31 halo stars in sparsely populated TRGB regions. We use the new distances to update the luminosities and structural parameters for these 17 M31 satellites. The new distances do not substantially change the spatial configuration of the M31 satellite system. We comment on
future prospects for precise and accurate HB distances for faint galaxies in the Local Group and beyond.
22 citations
TL;DR: Experimental results from metal 3D printed parts confirm that the proposed boundary slope-based formulation is effective for controlling part self-support during printing and for affecting surface roughness of the printed parts.
Abstract: This paper studies how to control boundary slope of optimized parts in density-based topology optimization for additive manufacturing (AM). Boundary slope of a part affects the amount of support structure required during its fabrication by additive processes. Boundary slope also has a direct relation with the resulting surface roughness from the AM processes, which in turn affects the heat transfer efficiency. By constraining the minimal boundary slope, support structures can be eliminated or reduced for AM, and thus, material and postprocessing costs are reduced; by constraining the maximal boundary slope, high-surface roughness can be attained, and thus, the heat transfer efficiency is increased. In this paper, the boundary slope is controlled through a constraint between the density gradient and the given build direction. This allows us to explicitly control the boundary slope through density gradient in the density-based topology optimization approach. We control the boundary slope through two single global constraints. An adaptive scheme is also proposed to select the thresholds of these two boundary slope constraints. Numerical examples of linear elastic problem, heat conduction problem, and thermoelastic problems demonstrate the effectiveness and efficiency of the proposed formulation in controlling boundary slopes for additive manufacturing. Experimental results from metal 3D printed parts confirm that our boundary slope-based formulation is effective for controlling part self-support during printing and for affecting surface roughness of the printed parts.
22 citations
TL;DR: In this article, the effects of rotation on the color-magnitude diagram (CMD) of the Magellanic Clouds and the Milky Way were examined in the young to intermediate age clusters.
Abstract: The extended main sequence turn offs (eMSTOs) of several young to intermediate age clusters are examined in the Magellanic Clouds and the Milky Way. We explore the effects of extended star formation (eSF) and a range of stellar rotation rates on the behavior of the color-magnitude diagram (CMD), paying particular attention to the MSTO. We create synthetic stellar populations based on MESA stellar models to simulate observed Hubble Space Telescope and Gaia star cluster data. We model the effect of rotation as a non-parametric distribution, allowing for maximum flexibility. In our models the slow rotators comprise the blueward, and fast rotators the redward portion of the eMSTO. We simulate data under three scenarios: non-rotating eSF, a range of rotation rates with a single age, and a combination of age and rotation effects. We find that two of the five clusters (the youngest and oldest) favor an age spread, but these also achieve the overall worst fits of all clusters. The other three clusters show comparable statistical evidence between rotation and an age spread. In all five cases, a rotation rate distribution alone is capable of qualitatively matching the observed eMSTO structure. In future work, we aim to compare our predicted Vsin(i) with observations in order to better constrain the physics related to stellar rotation.
Patent•
24 Jan 2019TL;DR: In this paper, a virtual training system includes a computing processor, a virtual reality (VR) headset and a sensor to determine a VR hand position, and the processor is configured according to computing instructions in a memory device for displaying a first VR scene that includes a VR object.
Abstract: A virtual training system includes a computing processor, a virtual reality (VR) headset and a sensor to determine a VR hand position. The processor is configured according to computing instructions in a memory device for displaying a first VR scene that includes a first VR object. A second VR scene is displayed within a visual portal in the first VR scene that includes a second VR object. A user VR hand image is displayed in at least one of the first VR scene and the second VR scene based upon the determined VR hand position.
TL;DR: In this article, the effects of rotation on the color-magnitude diagram of the Magellanic clouds and the Milky Way were explored, with particular attention to the extended main-sequence turn off (eMSTO) of several young to intermediate age clusters.
Abstract: The extended main-sequence turn offs (eMSTOs) of several young to intermediate age clusters are examined in the Magellanic Clouds and the Milky Way. We explore the effects of extended star formation (eSF) and a range of stellar rotation rates on the behavior of the color–magnitude diagram, paying particular attention to the MSTO. We create synthetic stellar populations based on MESA stellar models to simulate observed Hubble Space Telescope and Gaia star cluster data. We model the effect of rotation as a nonparametric distribution, allowing for maximum flexibility. In our models the slow rotators comprise the blueward, and fast rotators the redward portion of the eMSTO. We simulate data under three scenarios: nonrotating eSF, a range of rotation rates with a single age, and a combination of age and rotation effects. We find that two of the five clusters (the youngest and oldest) favor an age spread, but these also achieve the overall worst fits of all clusters. The other three clusters show comparable statistical evidence between rotation and an age spread. In all five cases, a rotation-rate distribution alone is capable of qualitatively matching the observed eMSTO structure. In future work, we aim to compare our predicted $V\sin i$ with observations in order to better constrain the physics related to stellar rotation.
02 Jun 2019
TL;DR: In this article, the authors leverage the enhanced polarization properties of ScAlN lattice-matched to Gallium Nitride (GaN) to produce heterostructures that support very large carrier densities (>3.0×1013 /cm2).
Abstract: We report on recent progress on the development of Scandium Aluminum Nitride (ScAlN) based heterostructure field effect transistors (HFETs). We are leveraging the enhanced polarization properties of ScAlN lattice-matched to Gallium Nitride (GaN) to produce heterostructures that support very large carrier densities (>3.0×1013 /cm2). We have successfully grown device-quality ScAlN/GaN heterostructures by molecular beam epitaxy (MBE). Using these wafers we have fabricated low resistance contacts for ScAlN barrier HFETs and demonstrated transistors which simultaneously achieve high current density (>3 A/mm), large breakdown voltage (>60 V), and good mm-wave small signal gain (>13 dB at 30 GHz). The high current density coupled with the large breakdown field strength of GaN enables both current and voltage scaling of ScAlN/GaN HFETs and enables design of transistors that overcome the Bode-Fano bandwidth limitations.
17 Jun 2019
TL;DR: The runtime overhead is found to be insignificant both for checkpoint-restart within a single host, and when comparing a local MPI computation that was migrated to a remote cluster against an ordinary MPI computations running natively on that same remote cluster.
Abstract: Transparently checkpointing MPI for fault tolerance and load balancing is a long-standing problem in HPC. The problem has been complicated by the need to provide checkpoint-restart services for all combinations of an MPI implementation over all network interconnects. This work presents MANA (MPI-Agnostic Network-Agnostic transparent checkpointing), a single code base which supports all MPI implementation and interconnect combinations. The agnostic properties imply that one can checkpoint an MPI application under one MPI implementation and perhaps over TCP, and then restart under a second MPI implementation over InfiniBand on a cluster with a different number of CPU cores per node. This technique is based on a novel "split-process" approach, which enables two separate programs to co-exist within a single process with a single address space. This work overcomes the limitations of the two most widely adopted transparent checkpointing solutions, BLCR and DMTCP/InfiniBand, which require separate modifications to each MPI implementation and/or underlying network API. The runtime overhead is found to be insignificant both for checkpoint-restart within a single host, and when comparing a local MPI computation that was migrated to a remote cluster against an ordinary MPI computation running natively on that same remote cluster.
University of California, Berkeley1, University of Tasmania2, Raytheon3, University of Minnesota4, University of Washington5, University of Texas at Austin6, University of California, Irvine7, California Institute of Technology8, Max Planck Society9, Massachusetts Institute of Technology10, University of California, Davis11
TL;DR: Albers et al. as discussed by the authors measured the star formation history (SFH) of the isolated Local Group dwarf galaxy Wolf-Lundmark-Melotte (WLM) measured from color-magnitude diagrams (CMDs) constructed from deep Hubble Space Telescope imaging.
Abstract: Author(s): Albers, SM; Weisz, DR; Cole, AA; Dolphin, AE; Skillman, ED; Williams, BF; Boylan-Kolchin, M; Bullock, JS; Dalcanton, JJ; Hopkins, PF; Leaman, R; McConnachie, AW; Vogelsberger, M; Wetzel, A | Abstract: We present the star formation history (SFH) of the isolated (D ∼ 970 kpc) Local Group dwarf galaxy Wolf-Lundmark-Melotte (WLM) measured from colour-magnitude diagrams (CMDs) constructed from deep Hubble Space Telescope imaging. Our observations include a central (0.5 rh) and outer field (0.7 rh) that reach below the oldest main-sequence turn-off. WLM has no early dominant episode of star formation: 20 per cent of its stellar mass formed by ∼12.5 Gyr ago (z ∼ 5). It also has an SFR that rises to the present with 50 per cent of the stellar mass within the most recent 5 Gyr (z l 0.7). There is evidence of a strong age gradient: the mean age of the outer field is 5 Gyr older than the inner field despite being only 0.4 kpc apart. Some models suggest such steep gradients are associated with strong stellar feedback and dark-matter core creation. The SFHs of real isolated dwarf galaxies and those from the Feedback in Realistic Environment suite are in good agreement for M*(z = 0) ∼ 107-109M☉, but in worse agreement at lower masses (M*(z = 0) ∼ 105-107 M☉). These differences may be explainable by systematics in the models (e.g. reionization model) and/or observations (HST field placement). We suggest that a coordinated effort to get deep CMDs between HST/JWST (crowded central fields) and WFIRST (wide-area halo coverage) is the optimal path for measuring global SFHs of isolated dwarf galaxies.
University of California, Berkeley1, Max Planck Society2, University of Strasbourg3, University of Arizona4, Raytheon5, University of Surrey6, University of Sydney7, Australian National University8, Herzberg Institute of Astrophysics9, University of California, Los Angeles10, University of Minnesota11
TL;DR: In this article, the star formation histories (SFHs) of 20 faint M31 satellites were measured by modeling sub-horizontal branch (HB) depth color-magnitude diagrams constructed from Hubble Space Telescope (HST) imaging.
Abstract: We present the star formation histories (SFHs) of 20 faint M31 satellites ($-12 \lesssim M_V \lesssim -6$) that were measured by modeling sub-horizontal branch (HB) depth color-magnitude diagrams constructed from Hubble Space Telescope (HST) imaging. Reinforcing previous results, we find that virtually all galaxies quenched between 3 and 9 Gyr ago, independent of luminosity, with a notable concentration $3-6$ Gyr ago. This is in contrast to the Milky Way (MW) satellites, which are generally either faint with ancient quenching times or luminous with recent ($<3$ Gyr) quenching times. We suggest that systematic differences in the quenching times of M31 and MW satellites may be a reflection of the varying accretion histories of M31 and the MW. This result implies that the formation histories of low-mass satellites may not be broadly representative of low-mass galaxies in general. Among the M31 satellite population we identify two distinct groups based on their SFHs: one with exponentially declining SFHs ($\tau \sim 2$ Gyr) and one with rising SFHs with abrupt quenching. We speculate how these two groups could be related to scenarios for a recent major merger involving M31. The Cycle 27 HST Treasury survey of M31 satellites will provide well-constrained ancient SFHs to go along with the quenching times we measure here. The discovery and characterization of M31 satellites with $M_V \gtrsim -6$ would help quantify the relative contributions of reionization and environment to quenching of the lowest-mass satellites.
University of California, Berkeley1, Max Planck Society2, University of Strasbourg3, Raytheon4, University of Arizona5, University of Surrey6, University of Sydney7, Australian National University8, Herzberg Institute of Astrophysics9, University of California, Los Angeles10, University of Minnesota11
TL;DR: In this article, the star formation histories (SFHs) of 20 faint M31 satellites were measured by modeling sub-horizontal branch depth color-magnitude diagrams constructed from Hubble Space Telescope (HST) imaging.
Abstract: We present the star formation histories (SFHs) of 20 faint M31 satellites (−12 ≲ M V ≲ −6) that were measured by modeling sub-horizontal branch depth color–magnitude diagrams constructed from Hubble Space Telescope (HST) imaging. Reinforcing previous results, we find that virtually all galaxies quenched between 3 and 9 Gyr ago, independent of luminosity, with a notable concentration 3–6 Gyr ago. This is in contrast to the Milky Way (MW) satellites, which are generally either faint with ancient quenching times or luminous with recent (<3 Gyr) quenching times. We suggest that systematic differences in the quenching times of M31 and MW satellites may be a reflection of the varying accretion histories of M31 and the MW. This result implies that the formation histories of low-mass satellites may not be broadly representative of low-mass galaxies in general. Among the M31 satellite population we identify two distinct groups based on their SFHs: one with exponentially declining SFHs (τ ~ 2 Gyr) and one with rising SFHs with abrupt quenching. We speculate how these two groups could be related to scenarios for a recent major merger involving M31. The Cycle 27 HST Treasury survey of M31 satellites will provide well-constrained ancient SFHs to go along with the quenching times we measure here. The discovery and characterization of M31 satellites with M V ≳ −6 would help quantify the relative contributions of reionization and environment to quenching of the lowest-mass satellites.
Proceedings Article•
01 Jan 2019TL;DR: In this article, a hierarchical attention-based temporal convolutional network (HA-TCN) was proposed for myotonic dystrohpy diagnosis from handgrip time series data.
Abstract: Myotonia, which refers to delayed muscle relaxation after contraction, is the main symptom of myotonic dystrophy patients. We propose a hierarchical attention-based temporal convolutional network (HA-TCN) for myotonic dystrohpy diagnosis from handgrip time series data, and introduce mechanisms that enable model explainability. We compare the performance of the HA-TCN model against that of benchmark TCN models, LSTM models with and without attention mechanisms, and SVM approaches with handcrafted features. In terms of classification accuracy and F1 score, we found all deep learning models have similar levels of performance, and they all outperform SVM. Further, the HA-TCN model outperforms its TCN counterpart with regards to computational efficiency regardless of network depth, and in terms of performance particularly when the number of hidden layers is small. Lastly, HA-TCN models can consistently identify relevant time series segments in the relaxation phase of the handgrip time series, and exhibit increased robustness to noise when compared to attention-based LSTM models.
TL;DR: In this paper, the ages of the young, resolved stellar populations at the locations of 237 optically-identified supernova remnants in M83 were determined using resolved stellar photometry of seven archival WFC3/UVIS fields in F336W, F438W, and F814W.
Abstract: We determine the ages of the young, resolved stellar populations at the locations of 237 optically-identified supernova remnants in M83. These age distributions put constraints on the progenitor masses of the supernovae that produced 199 of the remnants. The other 38 show no evidence for having a young progenitor and are therefore good Type Ia SNR candidates. Starting from Hubble Space Telescope broadband imaging, we measured resolved stellar photometry of seven archival WFC3/UVIS fields in F336W, F438W, and F814W. We generate color-magnitude diagrams of the stars within 50 pc of each SNR and fit them with stellar evolution models to obtain the population ages. From these ages we infer the progenitor mass that corresponds to the lifetime of the most prominent age that is $ $15 M$_{\odot}$, and 5 of these are $>$15 M$_{\odot}$ at 84% confidence. This is the largest collection of high-mass progenitors to date, including our highest-mass progenitor inference found so far, with a constraint of $<$8 Myr. Overall, the distribution of progenitor masses has a power-law index of $-3.0^{+0.2}_{-0.7}$, steeper than Salpeter initial mass function ($-2.35$). It remains unclear whether the reason for the low number of high-mass progenitors is due to the difficulty of finding and measuring such objects or because only a fraction of very massive stars produce supernovae.
TL;DR: In this paper, the integrated phase technique based on laser interferometry was used to measure the dynamic dipole polarizability of metal atoms in a vacuum and to generate a radial expanding gas cylinder surrounded by low-density plasma corona.
Abstract: The fast electrical explosion of fine metal wires in a vacuum will produce calibrated gas cylinders of metal atoms surrounded by a low-density corona. For fully vaporized wires, the integrated-phase technique, based on laser interferometry, provides the dynamic dipole polarizability of metal atoms. A fast-rising current of $\ensuremath{\sim}1\phantom{\rule{0.16em}{0ex}}\mathrm{kA}/\mathrm{ns}$ will vaporize thin 12.7-\textmu{}m-diameter Au and Cu wires in a vacuum and generate a radial-expanding gas cylinder surrounded by low-density plasma corona. Employing the integrated-phase technique on fast-exploding Au and Cu wires, we find that the dynamic dipole polarizability of Au atoms is $8.3\ifmmode\pm\else\textpm\fi{}0.8\phantom{\rule{0.16em}{0ex}}{\AA{}}^{3}$ for 532 nm and $7.0\ifmmode\pm\else\textpm\fi{}0.7\phantom{\rule{0.16em}{0ex}}{\AA{}}^{3}$ for 1064 nm. Measurements collected from exploding Cu wire provide dynamic dipole polarizability of $10.2\ifmmode\pm\else\textpm\fi{}1\phantom{\rule{0.16em}{0ex}}{\AA{}}^{3}$ for 532 nm and $6.5\ifmmode\pm\else\textpm\fi{}0.7\phantom{\rule{0.16em}{0ex}}{\AA{}}^{3}$ for 1064 nm. All experimental values correspond to theoretical predictions based on quantum-mechanical calculations.
20 Jul 2019
TL;DR: The Appreciative Inquiry approach provides a method for systems engineering practitioners to more readily identify complexity when they encounter it, and to deal more effectively with this complexity once it has been identified.
Abstract: Complex systems have characteristics that challenge traditional systems engineering processes and methods. These characteristics have been defined in various ways. INCOSE has previously identified characteristics of complex systems and potential methods to deal with complexity in system development. The purpose of this paper is to provide definitions and describe distinguishing characteristics of complexity using example systems to illustrate approaches to assessing the extent of complexity. The paper applies Appreciative Inquiry to identify and assess complex system characteristics. The characteristics are used to examine several different examples of systems to illuminate areas of complexity. These examples range from seemingly simple systems to complicated systems to complex systems. Different tiers of complexity are identified as a result of the assessment. The paper also identified and introduces topics on managing complexity and the integrating system perspective that represent new directions for the engineering of complex systems. The Appreciative Inquiry approach provides a method for systems engineering practitioners to more readily identify complexity when they encounter it, and to deal more effectively with this complexity once it has been identified.
TL;DR: In this paper, the authors demonstrate that the thermal activation energy of the photocurrent density, as a function of the applied bias voltage, can be a very sensitive probe of the valence band features and identify and measure two types of impediments, the hole-block due to a band misalignment and the localization sites formed by fluctuations in the superlattice layer thicknesses.
Abstract: Mid-wavelength infrared detectors have been fabricated in the nBn configuration using the InAs/InAsSb superlattice as the absorber. Possible impediments in the valence band can interfere with the transport of holes that represent the signal. We demonstrate that the thermal activation energy of the photocurrent density, as a function of the applied bias voltage, can be a very sensitive probe of the valence band features. We identify and measure two types of impediments, the hole-block due to a band misalignment and the localization sites formed by fluctuations in the superlattice layer thicknesses. The latter are found to dominate the temperature dependence of the hole mobility. Our inferred localization characteristics are consistent with published results obtained by other techniques.
TL;DR: The method is applied to U.S. Army application showing the ease of the practical use and is a tool for enterprise architects to easily assess the complexity of enterprises of interest.
Abstract: In this paper, an application of cyclomatic complexity to enterprise scale is proposed. Enterprise architecture frameworks are introduced as a standard way to document enterprises. A specific enterprise architecture framework is selected for the implementation of the proposed cyclomatic complexity application. A candidate implementation shows how the cyclomatic complexity of an enterprise documented in an enterprise architecture framework is estimated. Results from manual analysis of the enterprise elements comprising enterprise cyclomatic complexity are compared to results of the proposed extension, showing the two approaches are equivalent. The method is applied to U.S. Army application showing the ease of the practical use. The result is a tool for enterprise architects to easily assess the complexity of enterprises of interest.
TL;DR: In this paper, the functionality of a nanowire integrated into a superconducting transmission line acting as a single pole single throw switch is demonstrated, and the switch has an instantaneous bandwidth from 2 to 8 GHz with more than 10 dB of isolation between the open and closed states.
Abstract: The functionality of a nanowire integrated into a superconducting transmission line acting as a single pole single throw switch is demonstrated. The switch has an instantaneous bandwidth from 2 to 8 GHz with more than 10 dB of isolation between the open and closed states. The switch consumes no power in the closed state and $\approx 15~\rm{nW}$ in the open state. The rise and fall response time between open and closed states is approximately $370~\rm{ps}$.
TL;DR: In this article, the authors used simulated photometry to investigate the dependency of the red giant branch (TRGB) luminosity on stellar age and metallicity as a function of wavelength (475 nm - 4.5 micron).
Abstract: The tip of the red giant branch (TRGB) is a well-established standard candle used to measure distances to nearby galaxies. The TRGB luminosity is typically measured in the I-band, where the luminosity has little dependency on stellar age or stellar metallicity. As the TRGB is brighter at wavelengths redder than the I-band, observational gains can be made if the TRGB luminosity can be robustly calibrated at longer wavelengths. This is of particular interest given the infrared capabilities that will be available with the James Webb Space Telescope and an important calibration consideration for using TRGB distances as part of an independent measurement of the Hubble constant. Here, we use simulated photometry to investigate the dependency of the TRGB luminosity on stellar age and metallicity as a function of wavelength (475 nm - 4.5 micron). We find intrinsic variations in the TRGB magnitude to increase from a few hundredths of a magnitude at 800-900 nm to ~0.6 mag by 1.5 micron. We show that variations at the longer infrared wavelengths can be reduced to 0.02-0.05 mag (1-2% accuracy in distance) with careful calibrations that account for changes in age and metal content. These represent the minimum uncertainties; observational uncertainties will be higher. Such calibration efforts may also provide independent constraints of the age and metallicity of stellar halos where TRGB distances are best measured. At 3.6 and 4.5 micron, the TRGB magnitude is predicted to vary up to ~0.15 mag even after corrections for stellar age and metallicity, making these wavelengths less suitable for precision distances.
TL;DR: In this paper, the authors describe two new methods for calibrating large-scale phased arrays, namely, the mobile Fourier gauge (MFG) and satellite-based calibration (SatCal), that permit rapid calibration of large phased arrays on site and that remove the need for expensive near field facility testing that limits the size of the array sections that can be RF aligned.
Abstract: One challenge in fielding large-scale phased array antennas is calibration of the antenna system, so that RF radiated beams can be accurately formed and steered. Here, we describe two new methods for calibrating large phased arrays, namely, the mobile Fourier gauge (MFG) and satellite-based calibration (SatCal) that permit rapid calibration of large phased arrays on site and that remove the need for expensive near-field facility testing that limits the size of the array sections that can be RF aligned. The MFG utilizes a known short RF line source that can be sequentially moved across the array using an existing crane; RF coupling measurements between this RF line source and the array elements made at different RF line source positions are vector summed, so as to form a known virtual RF line source that stretches the length of the array. A second independent method, SatCal, is presented that uses reflections from orbiting satellites to calibrate the array, either at the subarray or radiating element level. These calibration methods have been demonstrated on a large ${S}$ -band phased array and have resulted in array calibrations equivalent to within 5°, 0.7 dB rms (element level), or 4°, 0.6 dB rms (subarray level).
Patent•
31 Dec 2019TL;DR: In this paper, a thermochroic membrane that becomes highly reflective at temperatures above a certain threshold is applied over at least some of the microbolometer pixels to prevent the pixels from being damaged by excessive heat.
Abstract: Methods and apparatus for preventing solar damage, and other heat-related damage, to uncooled microbolometer pixels. In certain examples, a thermochroic membrane that becomes highly reflective at temperatures above a certain threshold is applied over at least some of the microbolometer pixels to prevent the pixels from being damaged by excessive heat.
TL;DR: In this article, the authors used the HST images to produce a deep color-magnitude diagram (CMD) of the resolved stellar population present in Coma P and inferred a red stellar sequence that they interpret to be a red giant branch, and use it to infer a tip of the red giant branches (TRGB) distance of 5.5 Mpc.
Abstract: We present Hubble Space Telescope (HST) observations of the low surface brightness (SB) galaxy Coma P. This system was first discovered in the Arecibo Legacy Fast ALFA HI survey and was cataloged as an (almost) dark galaxy because it did not exhibit any obvious optical counterpart in the available survey data (e.g., Sloan Digital Sky Survey). Subsequent WIYN pODI imaging revealed an ultra-low SB stellar component located at the center of the HI detection. We use the HST images to produce a deep color-magnitude diagram (CMD) of the resolved stellar population present in Coma P. We clearly detect a red stellar sequence that we interpret to be a red giant branch, and use it to infer a tip of the red giant branch (TRGB) distance of 5.50$^{+0.28}_{-0.53}$ Mpc. The new distance is substantially lower than earlier estimates and shows that Coma P is an extreme dwarf galaxy. Our derived stellar mass is only 4.3 $\times$ 10$^5$ $M_\odot$, meaning that Coma P has an extreme HI-to-stellar mass ratio of 81. We present a detailed analysis of the galaxy environment within which Coma P resides. We hypothesize that Coma P formed within a local void and has spent most of its lifetime in a low-density environment. Over time, the gravitational attraction of the galaxies located in the void wall has moved it to the edge, where it had a recent "fly-by" interaction with M64. We investigate the possibility that Coma P is at a farther distance and conclude that the available data are best fit by a distance of 5.5 Mpc.