Showing papers by "Ames Research Center published in 2018"
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629 citations
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TL;DR: In this paper, the authors proposed the task of sampling from the output distribution of random quantum circuits as a demonstration of quantum supremacy and showed that this sampling task must take exponential time in a classical computer.
Abstract: A critical question for quantum computing in the near future is whether quantum devices without error correction can perform a well-defined computational task beyond the capabilities of supercomputers. Such a demonstration of what is referred to as quantum supremacy requires a reliable evaluation of the resources required to solve tasks with classical approaches. Here, we propose the task of sampling from the output distribution of random quantum circuits as a demonstration of quantum supremacy. We extend previous results in computational complexity to argue that this sampling task must take exponential time in a classical computer. We introduce cross-entropy benchmarking to obtain the experimental fidelity of complex multiqubit dynamics. This can be estimated and extrapolated to give a success metric for a quantum supremacy demonstration. We study the computational cost of relevant classical algorithms and conclude that quantum supremacy can be achieved with circuits in a two-dimensional lattice of 7 × 7 qubits and around 40 clock cycles. This requires an error rate of around 0.5% for two-qubit gates (0.05% for one-qubit gates), and it would demonstrate the basic building blocks for a fault-tolerant quantum computer. As a benchmark for the development of a future quantum computer, sampling from random quantum circuits is suggested as a task that will lead to quantum supremacy—a calculation that cannot be carried out classically.
567 citations
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TL;DR: Nine superconducting qubits are used to demonstrate a promising path toward quantum supremacy and the scaling of errors and output with the number of qubits is explored in a five- to nine-qubit device.
Abstract: A key step toward demonstrating a quantum system that can address difficult problems in physics and chemistry will be performing a computation beyond the capabilities of any classical computer, thus achieving so-called quantum supremacy. In this study, we used nine superconducting qubits to demonstrate a promising path toward quantum supremacy. By individually tuning the qubit parameters, we were able to generate thousands of distinct Hamiltonian evolutions and probe the output probabilities. The measured probabilities obey a universal distribution, consistent with uniformly sampling the full Hilbert space. As the number of qubits increases, the system continues to explore the exponentially growing number of states. Extending these results to a system of 50 qubits has the potential to address scientific questions that are beyond the capabilities of any classical computer.
419 citations
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Peking University1, University of Arizona2, Leiden University3, University of Leicester4, University of Cambridge5, University of Milan6, Vassar College7, Smith College8, University of Grenoble9, University of Victoria10, Chinese Academy of Sciences11, Max Planck Society12, Rice University13, University of Paris14, European Southern Observatory15, University of Chicago16, INAF17, Space Telescope Science Institute18, Ames Research Center19
TL;DR: In this article, the authors identify the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, and measure their properties to investigate how they form, including axisymmetric rings and gaps.
Abstract: Rings are the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, but their origin is still hotly debated. In this paper, we identify dust substructures in 12 disks and measure their properties to investigate how they form. This subsample of disks is selected from a high-resolution ($\sim0.12''$) ALMA 1.33 mm survey of 32 disks in the Taurus star-forming region, which was designed to cover a wide range of sub-mm brightness and to be unbiased to previously known substructures. While axisymmetric rings and gaps are common within our sample, spiral patterns and high contrast azimuthal asymmetries are not detected. Fits of disk models to the visibilities lead to estimates of the location and shape of gaps and rings, the flux in each disk component, and the size of the disk. The dust substructures occur across a wide range of stellar mass and disk brightness. Disks with multiple rings tend to be more massive and more extended. The correlation between gap locations and widths, the intensity contrast between rings and gaps, and the separations of rings and gaps could all be explained if most gaps are opened by low-mass planets (super-Earths and Neptunes) in the condition of low disk turbulence ($\alpha=10^{-4}$). The gap locations are not well correlated with the expected locations of CO and N$_2$ ice lines, so condensation fronts are unlikely to be a universal mechanism to create gaps and rings, though they may play a role in some cases.
395 citations
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Space Telescope Science Institute1, Ames Research Center2, Search for extraterrestrial intelligence3, California Institute of Technology4, Massachusetts Institute of Technology5, Bishop's University6, Harvard University7, Space Science Institute8, University of Texas at Austin9, Villanova University10, Princeton University11, Goddard Space Flight Center12, University of Birmingham13, Aarhus University14, Principia College15, Lowell Observatory16, University of California, Berkeley17, Brigham Young University18, University of Nevada, Las Vegas19, San Diego State University20, Pennsylvania State University21
TL;DR: The Robovetter and the metrics it uses to decide which TCEs are called planet candidates in the DR25 KOI catalog are discussed and a value called the disposition score is discussed which provides an easy way to select a more reliable, albeit less complete, sample of candidates.
Abstract: We present the Kepler Object of Interest (KOI) catalog of transiting exoplanets based on searching 4 yr of Kepler time series photometry (Data Release 25, Q1–Q17). The catalog contains 8054 KOIs, of which 4034 are planet candidates with periods between 0.25 and 632 days. Of these candidates, 219 are new, including two in multiplanet systems (KOI-82.06 and KOI-2926.05) and 10 high-reliability, terrestrial-size, habitable zone candidates. This catalog was created using a tool called the Robovetter, which automatically vets the DR25 threshold crossing events (TCEs). The Robovetter also vetted simulated data sets and measured how well it was able to separate TCEs caused by noise from those caused by low signal-to-noise transits. We discuss the Robovetter and the metrics it uses to sort TCEs. For orbital periods less than 100 days the Robovetter completeness (the fraction of simulated transits that are determined to be planet candidates) across all observed stars is greater than 85%. For the same period range, the catalog reliability (the fraction of candidates that are not due to instrumental or stellar noise) is greater than 98%. However, for low signal-to-noise candidates between 200 and 500 days around FGK-dwarf stars, the Robovetter is 76.7% complete and the catalog is 50.5% reliable. The KOI catalog, the transit fits, and all of the simulated data used to characterize this catalog are available at the NASA Exoplanet Archive.
356 citations
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University of California, Riverside1, Virtual Planetary Laboratory2, Ames Research Center3, Goddard Institute for Space Studies4, Columbia University5, University of Maryland, Baltimore6, Arizona State University7, Goddard Space Flight Center8, NASA Astrobiology Institute9, University of Washington10, University of Edinburgh11, German Aerospace Center12, Cornell University13, University of St Andrews14, California Institute of Technology15
TL;DR: A comprehensive overview of the current understanding of potential exoplanet biosignatures, including gaseous, surface, and temporal signatures, can be found in this article, with a focus on recent advances in assessing biosignature plausibility.
Abstract: In the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. Life on Earth, through its gaseous products and reflectance and scattering properties, has left its fingerprint on the spectrum of our planet. Aided by the universality of the laws of physics and chemistry, we turn to Earth's biosphere, both in the present and through geologic time, for analog signatures that will aid in the search for life elsewhere. Considering the insights gained from modern and ancient Earth, and the broader array of hypothetical exoplanet possibilities, we have compiled a comprehensive overview of our current understanding of potential exoplanet biosignatures, including gaseous, surface, and temporal biosignatures. We additionally survey biogenic spectral features that are well known in the specialist literature but have not yet been robustly vetted in the context of exoplanet biosignatures. We briefly review advances in assessing biosignature plausibility, including novel methods for determining chemical disequilibrium from remotely obtainable data and assessment tools for determining the minimum biomass required to maintain short-lived biogenic gases as atmospheric signatures. We focus particularly on advances made since the seminal review by Des Marais et al. The purpose of this work is not to propose new biosignature strategies, a goal left to companion articles in this series, but to review the current literature, draw meaningful connections between seemingly disparate areas, and clear the way for a path forward.
320 citations
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TL;DR: Direct and definitive evidence for surface-exposed water ice in the lunar polar regions is found and the observation of spectral features of H2O confirms that water ice is trapped and accumulates in permanently shadowed regions of the Moon and in some locations, it is exposed at the modern optical surface.
Abstract: Water ice may be allowed to accumulate in permanently shaded regions on airless bodies in the inner solar system such as Mercury, the Moon, and Ceres [Watson K, et al. (1961) J Geophys Res 66:3033–3045]. Unlike Mercury and Ceres, direct evidence for water ice exposed at the lunar surface has remained elusive. We utilize indirect lighting in regions of permanent shadow to report the detection of diagnostic near-infrared absorption features of water ice in reflectance spectra acquired by the Moon Mineralogy Mapper [M (3)] instrument. Several thousand M (3) pixels (∼280 × 280 m) with signatures of water ice at the optical surface (depth of less than a few millimeters) are identified within 20° latitude of both poles, including locations where independent measurements have suggested that water ice may be present. Most ice locations detected in M (3) data also exhibit lunar orbiter laser altimeter reflectance values and Lyman Alpha Mapping Project instrument UV ratio values consistent with the presence of water ice and also exhibit annual maximum temperatures below 110 K. However, only ∼3.5% of cold traps exhibit ice exposures. Spectral modeling shows that some ice-bearing pixels may contain ∼30 wt % ice that is intimately mixed with dry regolith. The patchy distribution and low abundance of lunar surface-exposed water ice might be associated with the true polar wander and impact gardening. The observation of spectral features of H2O confirms that water ice is trapped and accumulates in permanently shadowed regions of the Moon, and in some locations, it is exposed at the modern optical surface.
317 citations
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TL;DR: The spectral properties of ultra hot Jupiters were investigated in this article, where the authors used the SPARC/MITgcm spectral model to model the atmospheres of the four ultra hot supergiants and discussed more thoroughly the case of WASP-121b.
Abstract: Context A new class of exoplanets has emerged: the ultra hot Jupiters, the hottest close-in gas giants. The majority of them have weaker-than-expected spectral features in the 1.1−1.7 μm bandpass probed by HST/WFC3 but stronger spectral features at longer wavelengths probed by Spitzer. This led previous authors to puzzling conclusions about the thermal structures and chemical abundances of these planets. Aims We investigate how thermal dissociation, ionization, H− opacity, and clouds shape the thermal structures and spectral properties of ultra hot Jupiters. Methods We use the SPARC/MITgcm to model the atmospheres of four ultra hot Jupiters and discuss more thoroughly the case of WASP-121b. We expand our findings to the whole population of ultra hot Jupiters through analytical quantification of the thermal dissociation and its influence on the strength of spectral features. Results We predict that most molecules are thermally dissociated and alkalies are ionized in the dayside photospheres of ultra hot Jupiters. This includes H2O, TiO, VO, and H2 but not CO, which has a stronger molecular bond. The vertical molecular gradient created by the dissociation significantly weakens the spectral features from H2O while the 4.5 μm CO feature remains unchanged. The water band in the HST/WFC3 bandpass is further weakened by the continuous opacity of the H− ions. Molecules are expected to recombine before reaching the limb, leading to order of magnitude variations of the chemical composition and cloud coverage between the limb and the dayside. Conclusions Molecular dissociation provides a qualitative understanding of the lack of strong spectral features of water in the 1−2 μm bandpass observed in most ultra hot Jupiters. Quantitatively, our model does not provide a satisfactory match to the WASP-121b emission spectrum. Together with WASP-33b and Kepler-33Ab, they seem the outliers among the population of ultra hot Jupiters, in need of a more thorough understanding.
294 citations
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25 Jun 2018TL;DR: This paper will serve as a starting point to develop a framework for NASA’s Urban Air Mobility airspace integration research and development efforts with partners and stakeholders that could include fast-time simulations, human-in-the-loop simulations, and flight demonstrations.
Abstract: Urban Air Mobility (UAM) - defined as safe and efficient air traffic operations in a metropolitan area for manned aircraft and unmanned aircraft systems - is being researched and developed by industry, academia, and government. Significant resources have been invested toward cultivating an ecosystem for Urban Air Mobility that includes manufacturers of electric vertical takeoff and landing aircraft, builders of takeoff and landing areas, and researchers of the airspace integration concepts, technologies, and procedures needed to conduct Urban Air Mobility operations safely and efficiently alongside other airspace users. This paper provides high-level descriptions of both emergent and early expanded operational concepts for Urban Air Mobility that NASA is developing. The scope of this work is defined in terms of missions, aircraft, airspace, and hazards. Past and current Urban Air Mobility operations are also reviewed, and the considerations for the data exchange architecture and communication, navigation, and surveillance requirements are also discussed. This paper will serve as a starting point to develop a framework for NASA's Urban Air Mobility airspace integration research and development efforts with partners and stakeholders that could include fast-time simulations, human-in-the-loop (HITL) simulations, and flight demonstrations.
264 citations
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University of Washington1, Virtual Planetary Laboratory2, Georgia Institute of Technology3, NASA Astrobiology Institute4, Goddard Space Flight Center5, Ames Research Center6, California Institute of Technology7, German Aerospace Center8, University of Maryland, Baltimore9, Cornell University10, University of Tokyo11, University of California, Riverside12
TL;DR: The coevolution of life with the early Earth's environment is examined to identify how the interplay of sources and sinks may have suppressed O2 release into the atmosphere for several billion years, producing a false negative for biologically generated O2.
Abstract: We describe how environmental context can help determine whether oxygen (O2) detected in extrasolar planetary observations is more likely to have a biological source. Here we provide an in...
241 citations
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TL;DR: The NASA Ames Stereo Pipeline is a suite of free and open source automated geodesy and stereogrammetry tools designed for processing stereo images captured from satellites, robotic rovers, aerial cameras, and historical images, with and without accurate camera pose information.
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Leibniz Association1, Kapteyn Astronomical Institute2, Durham University3, University of Oslo4, Tartu Observatory5, Stanford University6, Ames Research Center7, National Autonomous University of Mexico8, University of Los Andes9, Pontifical Catholic University of Chile10, Institute of Cosmology and Gravitation, University of Portsmouth11, University of Zielona Góra12, Hebrew University of Jerusalem13, Spanish National Research Council14, University of La Laguna15, Autonomous University of Madrid16, University of Kansas17, University of Western Australia18, University of Lorraine19, Institut d'Astrophysique de Paris20
TL;DR: In this paper, a variety of different methods have been devised to classify the cosmic web, depending on the data at hand, be it numerical simulations, large sky surveys or other.
Abstract: The cosmic web is one of the most striking features of the distribution of galaxies and dark matter on the largest scales in the Universe. It is composed of dense regions packed full of galaxies, long filamentary bridges, flattened sheets and vast low-density voids. The study of the cosmic web has focused primarily on the identification of such features, and on understanding the environmental effects on galaxy formation and halo assembly. As such, a variety of different methods have been devised to classify the cosmic web – depending on the data at hand, be it numerical simulations, large sky surveys or other. In this paper, we bring 12 of these methods together and apply them to the same data set in order to understand how they compare. In general, these cosmic-web classifiers have been designed with different cosmological goals in mind, and to study different questions. Therefore, one would not a priori expect agreement between different techniques; however, many of these methods do converge on the identification of specific features. In this paper, we study the agreements and disparities of the different methods. For example, each method finds that knots inhabit higher density regions than filaments, etc. and that voids have the lowest densities. For a given web environment, we find a substantial overlap in the density range assigned by each web classification scheme. We also compare classifications on a halo-by-halo basis; for example, we find that 9 of 12 methods classify around a third of group-mass haloes (i.e. Mhalo ∼ 1013.5 h−1 M⊙) as being in filaments. Lastly, so that any future cosmic-web classification scheme can be compared to the 12 methods used here, we have made all the data used in this paper public.
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25 Jun 2018TL;DR: A number of candidate concept aircraft are presently being designed to meet a set of UAM requirements, in order to quantify the tradeoffs and performance targets necessary for practical implementation of the UAM vision.
Abstract: The current push for Urban Air Mobility (UAM) is predicated on the feasibility of novel aircraft types, which will be enabled by the near-term availability of mature technology for high performance subsystems. A number of candidate concept aircraft are presently being designed to meet a set of UAM requirements, in order to quantify the tradeoffs and performance targets necessary for practical implementation of the UAM vision. In examining these vehicles, performance targets and recurring technology themes emerge, which may guide investments in research and development within NASA, other government agencies, academia, and industry.
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TL;DR: The Kepler Pipeline has been modified to support the TESS Mission which will commence in 2018, and the DV architecture and diagnostic tests, and a brief overview of the data products are described.
Abstract: The Kepler Mission was designed to identify and characterize transiting planets in the Kepler Field of View and to determine their occurrence rates. Emphasis was placed on identification of Earth-size planets orbiting in the Habitable Zone of their host stars. Science data were acquired for a period of four years. Long-cadence data with 29.4 min sampling were obtained for approx. 200,000 individual stellar targets in at least one observing quarter in the primary Kepler Mission. Light curves for target stars are extracted in the Kepler Science Data Processing Pipeline, and are searched for transiting planet signatures. A Threshold Crossing Event is generated in the transit search for targets where the transit detection threshold is exceeded and transit consistency checks are satisfied. These targets are subjected to further scrutiny in the Data Validation (DV) component of the Pipeline. Transiting planet candidates are characterized in DV, and light curves are searched for additional planets after transit signatures are modeled and removed. A suite of diagnostic tests is performed on all candidates to aid in discrimination between genuine transiting planets and instrumental or astrophysical false positives. Data products are generated per target and planet candidate to document and display transiting planet model fit and diagnostic test results. These products are exported to the Exoplanet Archive at the NASA Exoplanet Science Institute, and are available to the community. We describe the DV architecture and diagnostic tests, and provide a brief overview of the data products. Transiting planet modeling and the search for multiple planets on individual targets are described in a companion paper. The final revision of the Kepler Pipeline code base is available to the general public through GitHub. The Kepler Pipeline has also been modified to support the Transiting Exoplanet Survey Satellite (TESS) Mission which is expected to commence in 2018.
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TL;DR: The parameter landscape is numerically investigated and it is shown that it is a simple one in the sense of having no local optima, which greatly simplifies numerical search for the optimal values of the parameters.
Abstract: Farhi et al. recently proposed a class of quantum algorithms, the Quantum Approximate Optimization Algorithm (QAOA), for approximately solving combinatorial optimization problems. A level-p QAOA circuit consists of steps in which a classical Hamiltonian, derived from the cost function, is applied followed by a mixing Hamiltonian. The 2p times for which these two Hamiltonians are applied are the parameters of the algorithm. As p increases, however, the parameter search space grows quickly. The success of the QAOA approach will depend, in part, on finding effective parameter-setting strategies. Here, we analytically and numerically study parameter setting for QAOA applied to MAXCUT. For level-1 QAOA, we derive an analytical expression for a general graph. In principle, expressions for higher p could be derived, but the number of terms quickly becomes prohibitive. For a special case of MAXCUT, the Ring of Disagrees, or the 1D antiferromagnetic ring, we provide an analysis for arbitrarily high level. Using a Fermionic representation, the evolution of the system under QAOA translates into quantum optimal control of an ensemble of independent spins. This treatment enables us to obtain analytical expressions for the performance of QAOA for any p. It also greatly simplifies numerical search for the optimal values of the parameters. By exploring symmetries, we identify a lower-dimensional sub-manifold of interest; the search effort can be accordingly reduced. This analysis also explains an observed symmetry in the optimal parameter values. Further, we numerically investigate the parameter landscape and show that it is a simple one in the sense of having no local optima.
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Massachusetts Institute of Technology1, University of Texas at Austin2, Princeton University3, University of Southern Queensland4, University of California, Riverside5, Harvard University6, Ames Research Center7, Search for extraterrestrial intelligence8, University of Geneva9, NASA Exoplanet Science Institute10, University of Maryland, College Park11, Johns Hopkins University12, Lehigh University13, Hungarian Academy of Sciences14, Eötvös Loránd University15, Vanderbilt University16, INAF17, Aarhus University18, Yale University19, Goddard Space Flight Center20, University of Chicago21, Technical University of Denmark22, Konkoly Thege Miklós Astronomical Institute23, Tokyo Institute of Technology24, Cornell University25, Spanish National Research Council26, Carnegie Institution for Science27, University of Florida28
TL;DR: The detection of a transiting planet around π Men (HD 39091), using data from the Transiting Exoplanet Survey Satellite (TESS), is reported, confirming the existence of the planet and leading to a mass determination of 4.82±0.85 M ⊕.
Abstract: We report the detection of a transiting planet around π Men (HD 39091), using data from the Transiting Exoplanet Survey Satellite (TESS). The solar-type host star is unusually bright (V = 5.7) and was already known to host a Jovian planet on a highly eccentric, 5.7-year orbit. The newly discovered planet has a size of 2.04 ± 0.05 R⊕ and an orbital period of 6.27 days. Radial-velocity data from the HARPS and AAT/UCLES archives also displays a 6.27-day periodicity, confirming the existence of the planet and leading to a mass determination of 4.82±0.85 M⊕. The star's proximity and brightness will facilitate further investigations, such as atmospheric spectroscopy, asteroseismology, the Rossiter-McLaughlin effect, astrometry, and direct imaging.
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California Institute of Technology1, Goddard Space Flight Center2, University of Michigan3, York University4, Ames Research Center5, Spanish National Research Council6, Luleå University of Technology7, Carnegie Institution for Science8, Jacobs Engineering Group9, Cooperative Institute for Research in Environmental Sciences10, Pennsylvania State University11, Open University12, National Autonomous University of Mexico13, Space Science Institute14, Southwest Research Institute15, Finnish Meteorological Institute16, Texas A&M University17
TL;DR: In situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover show large seasonal variation in the background and occurrences of higher temporary spikes that are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.
Abstract: Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.
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TL;DR: In this article, a version of the AM4.0/LM 4.0 atmosphere/land model that will serve as a base for a new set of climate and Earth system models (CM4 and ESM4) is presented.
Abstract: In Part II of this two-part paper, documentation is provided of key aspects of a version of the AM4.0/LM4.0 atmosphere/land model that will serve as a base for a new set of climate and Earth system models (CM4 and ESM4) under development at NOAA's Geophysical Fluid Dynamics Laboratory (GFDL). The quality of the simulation in AMIP (Atmospheric Model Intercomparison Project) mode has been provided in Part I. Part II provides documentation of key components and some sensitivities to choices of model formulation and values of parameters, highlighting the convection parameterization and orographic gravity wave drag. The approach taken to tune the model's clouds to observations is a particular focal point. Care is taken to describe the extent to which aerosol effective forcing and Cess sensitivity have been tuned through the model development process, both of which are relevant to the ability of the model to simulate the evolution of temperatures over the last century when coupled to an ocean model.
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TL;DR: In this paper, the authors developed neuro-transistors by integrating dynamic pseudo-memcapacitors as the gates of transistors to produce electronic analogs of the soma and axon of a neuron, with leaky integrate-and-fire dynamics augmented by a signal gain on the output.
Abstract: Experimental demonstration of resistive neural networks has been the recent focus of hardware implementation of neuromorphic computing. Capacitive neural networks, which call for novel building blocks, provide an alternative physical embodiment of neural networks featuring a lower static power and a better emulation of neural functionalities. Here, we develop neuro-transistors by integrating dynamic pseudo-memcapacitors as the gates of transistors to produce electronic analogs of the soma and axon of a neuron, with “leaky integrate-and-fire” dynamics augmented by a signal gain on the output. Paired with non-volatile pseudo-memcapacitive synapses, a Hebbian-like learning mechanism is implemented in a capacitive switching network, leading to the observed associative learning. A prototypical fully integrated capacitive neural network is built and used to classify inputs of signals.
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Ames Research Center1, University of Arizona2, Chesapeake Energy3, Lunar and Planetary Institute4, California Institute of Technology5, University of Guelph6, Imperial College London7, Carnegie Institution for Science8, Purdue University9, University of Nantes10, Goddard Space Flight Center11, Planetary Science Institute12
TL;DR: The results suggest that dioctahedral smectite formed via near-surface chemical weathering driven by fluctuations in lake level and atmospheric infiltration, a process leading to the redistribution of nutrients and potentially influencing the cycling of gases that help regulate climate.
Abstract: Clay minerals provide indicators of the evolution of aqueous conditions and possible habitats for life on ancient Mars. Analyses by the Mars Science Laboratory rover Curiosity show that ~3.5–billion year (Ga) fluvio-lacustrine mudstones in Gale crater contain up to ~28 weight % (wt %) clay minerals. We demonstrate that the species of clay minerals deduced from x-ray diffraction and evolved gas analysis show a strong paleoenvironmental dependency. While perennial lake mudstones are characterized by Fe-saponite, we find that stratigraphic intervals associated with episodic lake drying contain Al-rich, Fe^(3+)-bearing dioctahedral smectite, with minor (3 wt %) quantities of ferripyrophyllite, interpreted as wind-blown detritus, found in candidate aeolian deposits. Our results suggest that dioctahedral smectite formed via near-surface chemical weathering driven by fluctuations in lake level and atmospheric infiltration, a process leading to the redistribution of nutrients and potentially influencing the cycling of gases that help regulate climate.
18 May 2018
TL;DR: This paper demonstrates the use of convolutional neural networks on color fundus images for the recognition task of diabetic retinopathy staging, and discovers that preprocessing with contrast limited adaptive histogram equalization and ensuring dataset fidelity by expert verification of class labels improves recognition of subtle features.
Abstract: Diabetic retinopathy is a leading cause of blindness among working-age adults. Early detection of this condition is critical for good prognosis. In this paper, we demonstrate the use of convolutional neural networks (CNNs) on color fundus images for the recognition task of diabetic retinopathy staging. Our network models achieved test metric performance comparable to baseline literature results, with validation sensitivity of 95%. We additionally explored multinomial classification models, and demonstrate that errors primarily occur in the misclassification of mild disease as normal due to the CNNs inability to detect subtle disease features. We discovered that preprocessing with contrast limited adaptive histogram equalization and ensuring dataset fidelity by expert verification of class labels improves recognition of subtle features. Transfer learning on pretrained GoogLeNet and AlexNet models from ImageNet improved peak test set accuracies to 74.5%, 68.8%, and 57.2% on 2-ary, 3-ary, and 4-ary classification models, respectively.
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Liverpool John Moores University1, University of Hamburg2, Monash University, Clayton campus3, University of Western Australia4, University of St Andrews5, Cardiff University6, University of Edinburgh7, Ames Research Center8, University of New South Wales9, University of the Western Cape10, Max Planck Society11, University of Bonn12, Australian Astronomical Observatory13, University of Sussex14, Vanderbilt University15, Durham University16, Macquarie University17, Swinburne University of Technology18, University of Nottingham19, University of Sydney20, University of Bristol21, Australian National University22, European Space Research and Technology Centre23, University of Louisville24, Leiden University25, University of Copenhagen26, Queen Mary University of London27, European Southern Observatory28
TL;DR: The Galaxy And Mass Assembly (GAMA) survey as discussed by the authors is a spectroscopic redshift and multiwavelength photometric survey in three equatorial regions each of 60.0, G12, and G15.
Abstract: We describe data release 3 (DR3) of the Galaxy And Mass Assembly (GAMA) survey. The GAMA survey is a spectroscopic redshift and multiwavelength photometric survey in three equatorial regions each of 60.0 deg2 (G09, G12, and G15), and two southern regions of 55.7 deg2 (G02) and 50.6 deg2 (G23). DR3 consists of: the first release of data covering the G02 region and of data on H-ATLAS (Herschel – Astrophysical Terahertz Large Area Survey) sources in the equatorial regions; and updates to data on sources released in DR2. DR3 includes 154 809 sources with secure redshifts across four regions. A subset of the G02 region is 95.5 per cent redshift complete to r < 19.8 mag over an area of 19.5 deg2, with 20 086 galaxy redshifts, that overlaps substantially with the XXL survey (X-ray) and VIPERS (redshift survey). In the equatorial regions, the main survey has even higher completeness (98.5 per cent), and spectra for about 75 per cent of H-ATLAS filler targets were also obtained. This filler sample extends spectroscopic redshifts, for probable optical counterparts to H-ATLAS submillimetre sources, to 0.8 mag deeper (r < 20.6 mag) than the GAMA main survey. There are 25 814 galaxy redshifts for H-ATLAS sources from the GAMA main or filler surveys. GAMA DR3 is available at the survey website (www.gama-survey.org/dr3/).
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Cooperative Institute for Research in the Atmosphere1, California Institute of Technology2, University of Toronto3, University of Colorado Boulder4, Earth System Research Laboratory5, Centre national de la recherche scientifique6, University of Oklahoma7, University of Edinburgh8, Los Alamos National Laboratory9, University of Wollongong10, Karlsruhe Institute of Technology11, Ames Research Center12, University of Bremen13, Belgian Institute for Space Aeronomy14, University of Paris15
TL;DR: The Atmospheric Carbon Observations from Space (ACOS) algorithm has been applied to greenhouse gas observations from the GOSAT satellite since 2009, with modifications necessary for OCO-2.
Abstract: . Since September 2014, NASA's Orbiting Carbon Observatory-2 (OCO-2)
satellite has been taking measurements of reflected solar spectra and using
them to infer atmospheric carbon dioxide levels. This work provides details
of the OCO-2 retrieval algorithm, versions 7 and 8, used to derive the
column-averaged dry air mole fraction of atmospheric CO2
( X CO 2 ) for the roughly 100 000 cloud-free measurements recorded
by OCO-2 each day. The algorithm is based on the Atmospheric Carbon
Observations from Space (ACOS) algorithm which has been applied to
observations from the Greenhouse Gases Observing SATellite (GOSAT) since
2009, with modifications necessary for OCO-2. Because high accuracy,
better than 0.25 %, is required in order to accurately infer carbon
sources and sinks from X CO 2 , significant errors and regional-scale
biases in the measurements must be minimized. We discuss efforts to filter
out poor-quality measurements, and correct the remaining good-quality
measurements to minimize regional-scale biases. Updates to the radiance
calibration and retrieval forward model in version 8 have improved many
aspects of the retrieved data products. The version 8 data appear to have
reduced regional-scale biases overall, and demonstrate a clear improvement
over the version 7 data. In particular, error variance with respect to TCCON
was reduced by 20 % over land and 40 % over ocean between versions 7
and 8, and nadir and glint observations over land are now more consistent.
While this paper documents the significant improvements in the ACOS
algorithm, it will continue to evolve and improve as the CO2 data
record continues to expand.
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TL;DR: This paper suggests that DL-based methods can open up a complementary avenue toward knowledge discovery in hydrologic sciences, and suggests that integrating process-based models with DL models will help alleviate data limitations.
Abstract: . Recently, deep learning (DL) has emerged as a revolutionary and
versatile tool transforming industry applications and generating new and
improved capabilities for scientific discovery and model building. The
adoption of DL in hydrology has so far been gradual, but the field is now
ripe for breakthroughs. This paper suggests that DL-based methods can open up a
complementary avenue toward knowledge discovery in hydrologic sciences. In
the new avenue, machine-learning algorithms present competing hypotheses that
are consistent with data. Interrogative methods are then invoked to interpret
DL models for scientists to further evaluate. However, hydrology presents
many challenges for DL methods, such as data limitations, heterogeneity
and co-evolution, and the general inexperience of the hydrologic field with
DL. The roadmap toward DL-powered scientific advances will require the
coordinated effort from a large community involving scientists and citizens.
Integrating process-based models with DL models will help alleviate data
limitations. The sharing of data and baseline models will improve the
efficiency of the community as a whole. Open competitions could serve as the
organizing events to greatly propel growth and nurture data science education
in hydrology, which demands a grassroots collaboration. The area of
hydrologic DL presents numerous research opportunities that could, in turn,
stimulate advances in machine learning as well.
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University of St Andrews1, University of Western Australia2, Australian National University3, Ames Research Center4, University of Sydney5, University of Edinburgh6, University of New South Wales7, University of Bristol8, University of the Western Cape9, University of Nottingham10, Cardiff University11, University of Louisville12, Australian Astronomical Observatory13, Astrophysics Research Institute14, University of Sussex15, University of Hamburg16, University of Hull17, Johns Hopkins University18, University of Central Lancashire19, Swinburne University of Technology20, Netherlands Institute for Space Research21
TL;DR: In this paper, the energy-balance code MAGPHYS was used to determine stellar and dust masses, and dust corrected star-formation rates for over 200,000 GAMA galaxies, 170, 000 G10-COSMOS galaxies and 200, 000 3D-HST galaxies.
Abstract: We use the energy-balance code MAGPHYS to determine stellar and dust masses, and dust corrected star-formation rates for over 200,000 GAMA galaxies, 170,000 G10-COSMOS galaxies and 200,000 3D-HST galaxies. Our values agree well with previously reported measurements and constitute a representative and homogeneous dataset spanning a broad range in stellar mass (10^8---10^12 Msol), dust mass (10^6---10^9 Msol), and star-formation rates (0.01---100 Msol per yr), and over a broad redshift range (0.0 < z < 5.0). We combine these data to measure the cosmic star-formation history (CSFH), the stellar-mass density (SMD), and the dust-mass density (DMD) over a 12 Gyr timeline. The data mostly agree with previous estimates, where they exist, and provide a quasi-homogeneous dataset using consistent mass and star-formation estimators with consistent underlying assumptions over the full time range. As a consequence our formal errors are significantly reduced when compared to the historic literature. Integrating our cosmic star-formation history we precisely reproduce the stellar-mass density with an ISM replenishment factor of 0.50 +/- 0.07, consistent with our choice of Chabrier IMF plus some modest amount of stripped stellar mass. Exploring the cosmic dust density evolution, we find a gradual increase in dust density with lookback time. We build a simple phenomenological model from the CSFH to account for the dust mass evolution, and infer two key conclusions: (1) For every unit of stellar mass which is formed 0.0065---0.004 units of dust mass is also formed; (2) Over the history of the Universe approximately 90 to 95 per cent of all dust formed has been destroyed and/or ejected.
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Peking University1, University of Arizona2, Leiden University3, University of Leicester4, University of Cambridge5, University of Milan6, Vassar College7, Smith College8, University of Grenoble9, University of Victoria10, Chinese Academy of Sciences11, Max Planck Society12, Rice University13, University of Paris14, European Southern Observatory15, University of Chicago16, INAF17, Space Telescope Science Institute18, Ames Research Center19
TL;DR: In this article, the authors identify the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, and measure their properties to investigate how they form, including axisymmetric rings and gaps.
Abstract: Rings are the most frequently revealed substructure in ALMA dust observations of protoplanetary disks, but their origin is still hotly debated. In this paper, we identify dust substructures in 12 disks and measure their properties to investigate how they form. This subsample of disks is selected from a high-resolution ($\sim0.12''$) ALMA 1.33 mm survey of 32 disks in the Taurus star-forming region, which was designed to cover a wide range of sub-mm brightness and to be unbiased to previously known substructures. While axisymmetric rings and gaps are common within our sample, spiral patterns and high contrast azimuthal asymmetries are not detected. Fits of disk models to the visibilities lead to estimates of the location and shape of gaps and rings, the flux in each disk component, and the size of the disk. The dust substructures occur across a wide range of stellar mass and disk brightness. Disks with multiple rings tend to be more massive and more extended. The correlation between gap locations and widths, the intensity contrast between rings and gaps, and the separations of rings and gaps could all be explained if most gaps are opened by low-mass planets (super-Earths and Neptunes) in the condition of low disk turbulence ($\alpha=10^{-4}$). The gap locations are not well correlated with the expected locations of CO and N$_2$ ice lines, so condensation fronts are unlikely to be a universal mechanism to create gaps and rings, though they may play a role in some cases.
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Technical University of Berlin1, Washington State University2, University of Potsdam3, Tufts University4, Imperial College London5, London Metropolitan University6, German Aerospace Center7, Leibniz Association8, Instituto Nacional de Técnica Aeroespacial9, University of Lorraine10, University of Duisburg-Essen11, Ames Research Center12, Free University of Berlin13, University of Antofagasta14, University of Westminster15, Johns Hopkins University16, University of Tübingen17, University of California, Davis18, Heidelberg University19, University of Bremen20
TL;DR: It is shown that even the hyperarid Atacama Desert can provide a habitable environment for microorganisms that allows them to become metabolically active following an episodic increase in moisture and that once it decreases, so does the activity of the microbiota.
Abstract: Traces of life are nearly ubiquitous on Earth. However, a central unresolved question is whether these traces always indicate an active microbial community or whether, in extreme environments, such as hyperarid deserts, they instead reflect just dormant or dead cells. Although microbial biomass and diversity decrease with increasing aridity in the Atacama Desert, we provide multiple lines of evidence for the presence of an at times metabolically active, microbial community in one of the driest places on Earth. We base this observation on four major lines of evidence: (i) a physico-chemical characterization of the soil habitability after an exceptional rain event, (ii) identified biomolecules indicative of potentially active cells [e.g., presence of ATP, phospholipid fatty acids (PLFAs), metabolites, and enzymatic activity], (iii) measurements of in situ replication rates of genomes of uncultivated bacteria reconstructed from selected samples, and (iv) microbial community patterns specific to soil parameters and depths. We infer that the microbial populations have undergone selection and adaptation in response to their specific soil microenvironment and in particular to the degree of aridity. Collectively, our results highlight that even the hyperarid Atacama Desert can provide a habitable environment for microorganisms that allows them to become metabolically active following an episodic increase in moisture and that once it decreases, so does the activity of the microbiota. These results have implications for the prospect of life on other planets such as Mars, which has transitioned from an earlier wetter environment to today's extreme hyperaridity.
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TL;DR: The results suggest that the support vector regression model can outperform the life usage model on the evaluation measures of sample standard deviation, median error, median absolute error, and percentage error and the generalized linear model provides an effective approach for predictive maintenance with comparable results to the baseline.
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Princeton University1, Massachusetts Institute of Technology2, Lyon Observatory3, University of Bologna4, Ames Research Center5, Université de Montréal6, Durham University7, Masaryk University8, Hiroshima University9, Eötvös Loránd University10, INAF11, University of Alabama in Huntsville12, Harvard University13, University of Waterloo14, Max Planck Society15, Beijing Normal University16, University of Trieste17, University of Valencia18
TL;DR: In this paper, the authors propose a novel method to constrain turbulence and bulk motions in massive galaxies, galaxy groups, and clusters, exploring both simulations and observations, and show that all phases are tightly linked in terms of the ensemble (wide-aperture) velocity dispersion along the line of sight.
Abstract: We propose a novel method to constrain turbulence and bulk motions in massive galaxies, galaxy groups, and clusters, exploring both simulations and observations. As emerged in the recent picture of top-down multiphase condensation, hot gaseous halos are tightly linked to all other phases in terms of cospatiality and thermodynamics. While hot halos (~107 K) are perturbed by subsonic turbulence, warm (~104 K) ionized and neutral filaments condense out of the turbulent eddies. The peaks condense into cold molecular clouds (<100 K) raining in the core via chaotic cold accretion (CCA). We show that all phases are tightly linked in terms of the ensemble (wide-aperture) velocity dispersion along the line of sight. The correlation arises in complementary long-term AGN feedback simulations and high-resolution CCA runs, and is corroborated by the combined Hitomi and new Integral Field Unit measurements in the Perseus cluster. The ensemble multiphase gas distributions (from the UV to the radio band) are characterized by substantial spectral line broadening (σ v,los ≈ 100–200 $\mathrm{km}\,{{\rm{s}}}^{-1}$) with a mild line shift. On the other hand, pencil-beam detections (as H i absorption against the AGN backlight) sample the small-scale clouds displaying smaller broadening and significant line shifts of up to several 100 $\mathrm{km}\,{{\rm{s}}}^{-1}$ (for those falling toward the AGN), with increased scatter due to the turbulence intermittency. We present new ensemble σ v,los of the warm Hα+[N ii] gas in 72 observed cluster/group cores: the constraints are consistent with the simulations and can be used as robust proxies for the turbulent velocities, in particular for the challenging hot plasma (otherwise requiring extremely long X-ray exposures). Finally, we show that the physically motivated criterion C ≡ t cool/t eddy ≈ 1 best traces the condensation extent region and the presence of multiphase gas in observed clusters and groups. The ensemble method can be applied to many available spectroscopic data sets and can substantially advance our understanding of multiphase halos in light of the next-generation multiwavelength missions.
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TL;DR: In this article, the authors develop quantum algorithms that run on two-dimensional qubit lattices with nearest-neighbor interactions, to simulate strongly correlated fermions, avoiding the parity problem in mapping fermionic operators to qubit operators, with hardly any overhead.
Abstract: Physical systems with strongly correlated electrons (fermions) are notoriously difficult to study using traditional computers. Meanwhile, as programmable $q\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}m$ computers become a reality, efficient (and preferably general) quantum algorithms are needed, in the face of limited qubit-qubit connectivity in the near term. Addressing both problems, the authors develop quantum algorithms that run on two-dimensional qubit lattices with nearest-neighbor interactions, to simulate strongly correlated fermions. Their approach avoids the parity problem in mapping fermionic operators to qubit operators, with hardly any overhead, and can be used for a whole class of problems.