The Importance of High Frequency Observations for the SKA

NASA Astrophysics Data System (ADS)

Welch, William J.

2007-12-01

The plan for the Square Kilometer Array (SKA) is one or more very large arrays operating in two or more contiguous frequency bands: roughly 15 - 90 MHz, 120 - 500 MHz, and 500 MHz - 25 GHz. The last band may be further divided into roughly 500 MHz - 1.5 GHz and 1.5 - 25 GHz. Construction costs may delay or forgo one or more of these bands. We argue that the entire high frequency band is of special importance for astronomy both in the local universe and at great distances and early times. One of the Key Science Projects, the Cradle of Life, requires high sensitivity and resolution at frequencies up to 20 GHz for the study of forming disks around new stars with disk opacities too great for millimeter wave observations. The larger issue of star formation, a poorly understood area, will also benefit from high sensitivity observations at short cm wavelengths. Magnetic field measurements through the Zeeman effect in the densest star forming gas are best done using tracers such as CCS at frequencies of 11 and 22 GHz. The wide frequency range of the SKA permits the observation of multiple rotational transitions of long chain molecules, providing accurate measures of both gas densities and temperatures. The wide field of view will permit large scale surveys of entire star forming clouds revealing, at high resolution, the formation of clusters of pre-protostellar stars and class 0-2 protostars in line radiation. The continuum cm wave radiation will reveal the growth of grains in disks. On the larger scale, observations of CO at high redshifts will trace the evolution of star formation and the formation of metals back to the Epic of Reionization.

Cosmology with the Square Kilometre Array by SKA-Japan

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamauchi, Daisuke; Ichiki, Kiyotomo; Kohri, Kazunori

In the past several decades, the standard cosmological model has been established and its parameters have been measured to a high precision, while there are still many fundamental questions in cosmology; such as the physics in the very early universe, the origin of the cosmic acceleration, and the nature of dark matter. The forthcoming radio telescope, the Square Kilometre Array (SKA), which will be the world's largest, will be able to open a new frontier in cosmology and will be one of the most powerful tools for cosmology in the coming decade. The cosmological surveys conducted by the SKA wouldmore » have the potential not only to answer these fundamental questions but also deliver precision cosmology. In this article we briefly review the role of the SKA from the viewpoint of modern cosmology. Furthermore, the cosmological science led by the SKA-Japan Consortium (SKA-JP) Cosmology Science Working Group is also discussed.« less

Cosmology with the Square Kilometre Array by SKA-Japan

DOE PAGES

Yamauchi, Daisuke; Ichiki, Kiyotomo; Kohri, Kazunori; ...

2016-10-17

In the past several decades, the standard cosmological model has been established and its parameters have been measured to a high precision, while there are still many fundamental questions in cosmology; such as the physics in the very early universe, the origin of the cosmic acceleration, and the nature of dark matter. The forthcoming radio telescope, the Square Kilometre Array (SKA), which will be the world's largest, will be able to open a new frontier in cosmology and will be one of the most powerful tools for cosmology in the coming decade. The cosmological surveys conducted by the SKA wouldmore » have the potential not only to answer these fundamental questions but also deliver precision cosmology. In this article we briefly review the role of the SKA from the viewpoint of modern cosmology. Furthermore, the cosmological science led by the SKA-Japan Consortium (SKA-JP) Cosmology Science Working Group is also discussed.« less

Observation management challenges of the Square Kilometre Array

NASA Astrophysics Data System (ADS)

Bridger, Alan; Williams, Stewart J.; Nicol, Mark; Klaassen, Pamela; Thompson, Roger S.; Knapic, Cristina; Jerse, Giovanna; Orlati, Andrea; Messina, Marco; Valame, Snehal

2016-07-01

The Square Kilometre Array (SKA) will be the world's most advanced radio telescope, designed to explore some of the biggest questions in astronomy today, such as the epoch of re-ionization, the nature of gravity and the origins of cosmic magnetism. SKA1, the first phase of SKA construction, is currently being designed by a large team of experts world-wide. SKA1 comprises two telescopes: a 200-element dish interferometer in South Africa and a 130000-element dipole antenna aperture array in Australia. To enable the ground-breaking science of the SKA an advanced Observation Management system is required to support both the needs of the astronomical community users and the SKA Observatory staff. This system will ensure that the SKA realises its scientiffc aims and achieves optimal scientific throughput. This paper provides an overview of the design of the system that will accept proposals from SKA users, and result in the execution of the scripts that will obtain science data, taking in the stages of detailed preparation, planning and scheduling of the observations and onwards tracking. It describes the unique challenges of the differing requirements of two telescopes, one of which is very much a software telescope, including the need to schedule the data processing as well as the acquisition, and to react to both internally and externally discovered transient events. The scheduling of multiple parallel sub-array use is covered, along with the need to handle commensal observing - using the same data stream to satisfy the science goals of more than one project simultaneously. An international team from academia and industry, drawing on expertise and experience from previous telescope projects, the virtual observatory and comparable problems in industry, has been assembled to design the solution to this challenging but exciting problem.

The Australian SKA Pathfinder: project update and initial operations

NASA Astrophysics Data System (ADS)

Schinckel, Antony E. T.; Bock, Douglas C.-J.

2016-08-01

The Australian Square Kilometre Array Pathfinder (ASKAP) will be the fastest dedicated cm-wave survey telescope, and will consist of 36 12-meter 3-axis antennas, each with a large chequerboard phased array feed (PAF) receiver operating between 0.7 and 1.8 GHz, and digital beamforming prior to correlation. The large raw data rates involved ( 100 Tb/sec), and the need to do pipeline processing, has led to the antenna incorporating a third axis to fix the parallactic angle with respect to the entire optical system (blockages and phased array feed). It also results in innovative technical solutions to the data transport and processing issues. ASKAP is located at the Murchison Radio-astronomy Observatory (MRO), a new observatory developed for the Square Kilometre Array (SKA), 315 kilometres north-east of Geraldton, Western Australia. The MRO also hosts the SKA low frequency pathfinder instrument, the Murchison Widefield Array and will host the initial low frequency instrument of the SKA, SKA1-Low. Commissioning of ASKAP using six antennas equipped with first-generation PAFs is now complete and installation of second-generation PAFs and digital systems is underway. In this paper we review technical progress and commissioning to date, and refer the reader to relevant technical and scientific publications.

Constraints on the neutrino parameters by future cosmological 21 cm line and precise CMB polarization observations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oyama, Yoshihiko; Kohri, Kazunori; Hazumi, Masashi, E-mail: oyamayo@icrr.u-tokyo.ac.jp, E-mail: kohri@post.kek.jp, E-mail: masashi.hazumi@kek.jp

2016-02-01

Observations of the 21 cm line radiation coming from the epoch of reionization have a great capacity to study the cosmological growth of the Universe. Besides, CMB polarization produced by gravitational lensing has a large amount of information about the growth of matter fluctuations at late time. In this paper, we investigate their sensitivities to the impact of neutrino property on the growth of density fluctuations, such as the total neutrino mass, the effective number of neutrino species (extra radiation), and the neutrino mass hierarchy. We show that by combining a precise CMB polarization observation such as Simons Array withmore » a 21 cm line observation such as Square kilometer Array (SKA) phase 1 and a baryon acoustic oscillation observation (Dark Energy Spectroscopic Instrument:DESI) we can measure effects of non-zero neutrino mass on the growth of density fluctuation if the total neutrino mass is larger than 0.1 eV. Additionally, the combinations can strongly improve errors of the bounds on the effective number of neutrino species σ (N{sub ν}) ∼ 0.06−0.09 at 95 % C.L.. Finally, by using SKA phase 2, we can determine the neutrino mass hierarchy at 95 % C.L. if the total neutrino mass is similar to or smaller than 0.1 eV.« less

Spectral performance of Square Kilometre Array Antennas - II. Calibration performance

NASA Astrophysics Data System (ADS)

Trott, Cathryn M.; de Lera Acedo, Eloy; Wayth, Randall B.; Fagnoni, Nicolas; Sutinjo, Adrian T.; Wakley, Brett; Punzalan, Chris Ivan B.

2017-09-01

We test the bandpass smoothness performance of two prototype Square Kilometre Array (SKA) SKA1-Low log-periodic dipole antennas, SKALA2 and SKALA3 ('SKA Log-periodic Antenna'), and the current dipole from the Murchison Widefield Array (MWA) precursor telescope. Throughout this paper, we refer to the output complex-valued voltage response of an antenna when connected to a low-noise amplifier, as the dipole bandpass. In Paper I, the bandpass spectral response of the log-periodic antenna being developed for the SKA1-Low was estimated using numerical electromagnetic simulations and analysed using low-order polynomial fittings, and it was compared with the HERA antenna against the delay spectrum metric. In this work, realistic simulations of the SKA1-Low instrument, including frequency-dependent primary beam shapes and array configuration, are used with a weighted least-squares polynomial estimator to assess the ability of a given prototype antenna to perform the SKA Epoch of Reionisation (EoR) statistical experiments. This work complements the ideal estimator tolerances computed for the proposed EoR science experiments in Trott & Wayth, with the realized performance of an optimal and standard estimation (calibration) procedure. With a sufficient sky calibration model at higher frequencies, all antennas have bandpasses that are sufficiently smooth to meet the tolerances described in Trott & Wayth to perform the EoR statistical experiments, and these are primarily limited by an adequate sky calibration model and the thermal noise level in the calibration data. At frequencies of the Cosmic Dawn, which is of principal interest to SKA as one of the first next-generation telescopes capable of accessing higher redshifts, the MWA dipole and SKALA3 antenna have adequate performance, while the SKALA2 design will impede the ability to explore this era.

Modeling the neutral hydrogen distribution in the post-reionization Universe: intensity mapping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Villaescusa-Navarro, Francisco; Viel, Matteo; Datta, Kanan K.

We model the distribution of neutral hydrogen (HI) in the post-reionization era and investigate its detectability in 21 cm intensity mapping with future radio telescopes like the Square Kilometer array (SKA). We rely on high resolution hydrodynamical N-body simulations that have a state-of-the-art treatment of the low density photoionized gas in the inter-galactic medium (IGM). The HI is assigned a-posteriori to the gas particles following two different approaches: a halo-based method in which HI is assigned only to gas particles residing within dark matter halos; a particle-based method that assigns HI to all gas particles using a prescription based onmore » the physical properties of the particles. The HI statistical properties are then compared to the observational properties of Damped Lyman-α Absorbers (DLAs) and of lower column density systems and reasonable good agreement is found for all the cases. Among the halo-based method, we further consider two different schemes that aim at reproducing the observed properties of DLAs by distributing HI inside halos: one of this results in a much higher bias for DLAs, in agreement with recent observations, which boosts the 21 cm power spectrum by a factor ∼ 4 with respect to the other recipe. Furthermore, we quantify the contribution of HI in the diffuse IGM to both Ω{sub HI} and the HI power spectrum finding to be subdominant in both cases. We compute the 21 cm power spectrum from the simulated HI distribution and calculate the expected signal for both SKA1-mid and SKA1-low configurations at 2.4 ≤ z ≤ 4. We find that SKA will be able to detect the 21 cm power spectrum, in the non-linear regime, up to k ∼ 1 h/Mpc for SKA1-mid and k ∼ 5 h/Mpc for SKA1-low with 100 hours of observations. We also investigate the perspective of imaging the HI distribution. Our findings indicate that SKA1-low could detect the most massive HI peaks with a signal to noise ratio (SNR) higher than 5 for an observation time of about 1000 hours at z = 4, for a synthesized beam width of 2'. Detection at redshifts z≥2.4 with SKA1-mid would instead require a much longer observation time to achieve a comparable SNR level.« less

International Design Concepts for the SKA

NASA Astrophysics Data System (ADS)

Tarter, J.

2001-12-01

In August of 2000, representatives of eleven countries signed a Memorandum of Understanding to Establish the International Square Kilometre Array Steering Committee (ISSC). Arguably, the SKA could be built today, but without question it would be unaffordable. Increasing collecting area by a factor of 100 beyond today's largest array cannot be done cost effectively by simple extensions of what has been done before. New concepts, new designs, and new technologies will be required, as well as a paradigm shift. It will be necessary to heavily exploit emerging communications and consumer market technologies; to "hammer" them into shapes required to solve the SKA challenges, rather than inventing our own solutions from scratch. Or if we do invent ab initio solutions, we should look at creating consumer markets to embrace them, so that the full benefits of mass production and manufacturing can be realized. The strawman science goals of the SKA are extremely ambitious. Today there are six primary design concepts being studied that attempt to meet some or all of these goals; phased arrays of active elements embedded into flat tiles, "super Arecibo" antennas constructed in individual limestone karst sinkholes and arrayed together, large arrays of small, spherical (or hemispherical) Luneberg lenses, large deformable apertures with long focal ratios and aerostat-borne focal plane array receivers, arrays of large parabolic antennas constructed from steel "ropes," and large arrays of small parabolic dishes derived from the TVRO industry. This talk summarizes the strengths and weaknesses of these various designs in their current, incomplete state. In the US, the US SKA Consortium of 10 academic and research organizations has generated a roadmap to guide and assess the technology development that will be required to produce a successful SKA design, with well understood costs, performance, and minimal risk. The design and construction efforts for the ATA, LOFAR and the EVLA will provide essential opportunities for proofs-of-concept for portions of the preferred US design; a very large number of small elements configured into a Large-N number of stations. An aggressive timetable has been adopted for choosing a final (hybrid?) SKA design and the selection of a site, with a target date of 2005. The first, tentative steps have been taken to create an international project office capable of overseeing the development and construction of this facility, negotiating creative solutions to problems of radio frequency interference, and along the way, inventing the infrastructure and management appropriate to this "born international" venture.

The Square Kilometre Array

NASA Technical Reports Server (NTRS)

Huynh, Minh; Lazio, Joseph

2011-01-01

The Square Kilometre Array (SKA) will be the premier instrument to study radiation at centimetre and metre wavelengths from the cosmos, and in particular neutral hydrogen, the most abundant element in the universe. The SKA will probe the dawn of galaxy formation as well as allow advances in many other areas of astronomy, such as fundamental physics, astro-biology and cosmology. The SKA will have a collecting area of up to one million square metres spread over at least 3000 km, providing a collecting area more than twenty times greater than the current largest radio telescope. Its field of view on the sky will be several tens of square degrees with potentially several large (100 square degrees) independent beams at the lower frequencies, providing a survey speed many thousands of times greater than current facilities. This paper summarises the key science drivers of the SKA and provides an update on the international project.

Building contacts for the SKA

NASA Astrophysics Data System (ADS)

Bowler, Sue

2016-06-01

The Square Kilometre Array needs industrial expertise; SKA technology will, in turn, streamline big-data challenges for business and society. Or that's the idea: Sue Bowler reports on a day of networking designed to build industry-academia collaborations in the UK.

The Murchison Widefield Array: solar science with the low frequency SKA Precursor

NASA Astrophysics Data System (ADS)

Tingay, S. J.; Oberoi, D.; Cairns, I.; Donea, A.; Duffin, R.; Arcus, W.; Bernardi, G.; Bowman, J. D.; Briggs, F.; Bunton, J. D.; Cappallo, R. J.; Corey, B. E.; Deshpande, A.; deSouza, L.; Emrich, D.; Gaensler, B. M.; R, Goeke; Greenhill, L. J.; Hazelton, B. J.; Herne, D.; Hewitt, J. N.; Johnston-Hollitt, M.; Kaplan, D. L.; Kasper, J. C.; Kennewell, J. A.; Kincaid, B. B.; Koenig, R.; Kratzenberg, E.; Lonsdale, C. J.; Lynch, M. J.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Ord, S. M.; Pathikulangara, J.; Prabu, T.; Remillard, R. A.; Rogers, A. E. E.; Roshi, A.; Salah, J. E.; Sault, R. J.; Udaya-Shankar, N.; Srivani, K. S.; Stevens, J.; Subrahmanyan, R.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.; Wyithe, J. S. B.

2013-06-01

The Murchison Widefield Array is a low frequency (80 - 300 MHz) SKA Precursor, comprising 128 aperture array elements (known as tiles) distributed over an area of 3 km diameter. The MWA is located at the extraordinarily radio quiet Murchison Radioastronomy Observatory in the mid-west of Western Australia, the selected home for the Phase 1 and Phase 2 SKA low frequency arrays. The MWA science goals include: 1) detection of fluctuations in the brightness temperature of the diffuse redshifted 21 cm line of neutral hydrogen from the epoch of reionisation; 2) studies of Galactic and extragalactic processes based on deep, confusion-limited surveys of the full sky visible to the array; 3) time domain astrophysics through exploration of the variable radio sky; and 4) solar imaging and characterisation of the heliosphere and ionosphere via propagation effects on background radio source emission. This paper concentrates on the capabilities of the MWA for solar science and summarises some of the solar science results to date, in advance of the initial operation of the final instrument in 2013.

System engineering and science projects: lessons from MeerKAT

NASA Astrophysics Data System (ADS)

Kapp, Francois

2016-08-01

The Square Kilometre Array (SKA) is a large science project planning to commence construction of the world's largest Radio Telescope after 2018. MeerKAT is one of the precursor projects to the SKA, based on the same site that will host the SKA Mid array in the central Karoo area of South Africa. From the perspective of signal processing hardware development, we analyse the challenges that MeerKAT encountered and extrapolate them to SKA in order to prepare the System Engineering and Project Management methods that could contribute to a successful completion of SKA. Using the MeerKAT Digitiser, Correlator/Beamformer and Time and Frequency Reference Systems as an example, we will trace the risk profile and subtle differences in engineering approaches of these systems over time and show the effects of varying levels of System Engineering rigour on the evolution of their risk profiles. It will be shown that the most rigorous application of System Engineering discipline resulted in the most substantial reduction in risk over time. Since the challenges faced by SKA are not limited to that of MeerKAT, we also look into how that translates to a system development where there is substantial complexity in both the created system as well as the creating system. Since the SKA will be designed and constructed by consortia made up from the ten member countries, there are many additional complexities to the organisation creating the system - a challenge the MeerKAT project did not encounter. Factors outside of engineering, for instance procurement models and political interests, also play a more significant role, and add to the project risks of SKA when compared to MeerKAT.

Square Kilometre Array Telescope—Precision Reference Frequency Synchronisation via 1f-2f Dissemination

PubMed Central

Wang, B.; Zhu, X.; Gao, C.; Bai, Y.; Dong, J. W.; Wang, L. J.

2015-01-01

The Square Kilometre Array (SKA) project is an international effort to build the world’s largest radio telescope, with a one-square-kilometre collecting area. In addition to its ambitious scientific objectives, such as probing cosmic dawn and the cradle of life, the SKA demands several revolutionary technological breakthroughs, such as ultra-high precision synchronisation of the frequency references for thousands of antennas. In this report, with the purpose of application to the SKA, we demonstrate a frequency reference dissemination and synchronisation scheme in which the phase-noise compensation function is applied at the client site. Hence, one central hub can be linked to a large number of client sites, thus forming a star-shaped topology. As a performance test, a 100-MHz reference frequency signal from a hydrogen maser (H-maser) clock is disseminated and recovered at two remote sites. The phase-noise characteristics of the recovered reference frequency signal coincide with those of the H-maser source and satisfy the SKA requirements. PMID:26349544

SKA weak lensing - I. Cosmological forecasts and the power of radio-optical cross-correlations

NASA Astrophysics Data System (ADS)

Harrison, Ian; Camera, Stefano; Zuntz, Joe; Brown, Michael L.

2016-12-01

We construct forecasts for cosmological parameter constraints from weak gravitational lensing surveys involving the Square Kilometre Array (SKA). Considering matter content, dark energy and modified gravity parameters, we show that the first phase of the SKA (SKA1) can be competitive with other Stage III experiments such as the Dark Energy Survey and that the full SKA (SKA2) can potentially form tighter constraints than Stage IV optical weak lensing experiments, such as those that will be conducted with LSST, WFIRST-AFTA or Euclid-like facilities. Using weak lensing alone, going from SKA1 to SKA2 represents improvements by factors of ˜10 in matter, ˜10 in dark energy and ˜5 in modified gravity parameters. We also show, for the first time, the powerful result that comparably tight constraints (within ˜5 per cent) for both Stage III and Stage IV experiments, can be gained from cross-correlating shear maps between the optical and radio wavebands, a process which can also eliminate a number of potential sources of systematic errors which can otherwise limit the utility of weak lensing cosmology.

Development of the AuScope Australian Earth Observing System

NASA Astrophysics Data System (ADS)

Rawling, T.

2017-12-01

Advances in monitoring technology and significant investment in new national research initiatives, will provide significant new opportunities for delivery of novel geoscience data streams from across the Australian continent over the next decade. The AuScope Australian Earth Observing System (AEOS) is linking field and laboratory infrastructure across Australia to form a national sensor array focusing on the Solid Earth. As such AuScope is working with these programs to deploy observational infrastructure, including MT, passive seismic, and GNSS networks across the entire Australian Continent. Where possible the observational grid will be co-located with strategic basement drilling in areas of shallow cover and tied with national reflection seismic and sampling transects. This integrated suite of distributed earth observation and imaging sensors will provide unprecedented imaging fidelity of our crust, across all length and time scales, to fundamental and applied researchers in the earth, environmental and geospatial sciences. The AEOS will the Earth Science community's Square Kilometer Array (SKA) - a distributed telescope that looks INTO the earth rather than away from it - a 10 million SKA. The AEOS is strongly aligned with other community strategic initiatives including the UNCOVER research program as well as other National Collaborative Research Infrastructure programs such as the Terrestrial Environmental Research Network (TERN) and the Integrated Marine Observing System (IMOS) providing an interdisciplinary collaboration platform across the earth and environmental sciences. There is also very close alignment between AuScope and similar international programs such as EPOS, the USArray and EarthCube - potential collaborative linkages we are currently in the process of pursuing more fomally. The AuScope AEOS Infrastructure System is ultimately designed to enable the progressive construction, refinement and ongoing enrichment of a live, "FAIR" four-dimensional Earth Model for the Australian Continent and its immediate environs.

Exploring the performance of large-N radio astronomical arrays

NASA Astrophysics Data System (ADS)

Lonsdale, Colin J.; Doeleman, Sheperd S.; Cappallo, Roger J.; Hewitt, Jacqueline N.; Whitney, Alan R.

2000-07-01

New radio telescope arrays are currently being contemplated which may be built using hundreds, or even thousands, of relatively small antennas. These include the One Hectare Telescope of the SETI Institute and UC Berkeley, the LOFAR telescope planned for the New Mexico desert surrounding the VLA, and possibly the ambitious international Square Kilometer Array (SKA) project. Recent and continuing advances in signal transmission and processing technology make it realistic to consider full cross-correlation of signals from such a large number of antennas, permitting the synthesis of an aperture with much greater fidelity than in the past. In principle, many advantages in instrumental performance are gained by this 'large-N' approach to the design, most of which require the development of new algorithms. Because new instruments of this type are expected to outstrip the performance of current instruments by wide margins, much of their scientific productivity is likely to come from the study of objects which are currently unknown. For this reason, instrumental flexibility is of special importance in design studies. A research effort has begun at Haystack Observatory to explore large-N performance benefits, and to determine what array design properties and data reduction algorithms are required to achieve them. The approach to these problems, involving a sophisticated data simulator, algorithm development, and exploration of array configuration parameter space, will be described, and progress to date will be summarized.

A user interface framework for the Square Kilometre Array: concepts and responsibilities

NASA Astrophysics Data System (ADS)

Marassi, Alessandro; Brajnik, Giorgio; Nicol, Mark; Alberti, Valentina; Le Roux, Gerhard

2016-07-01

The Square Kilometre Array (SKA) project is responsible for developing the SKA Observatory, the world's largest radio telescope, with eventually over a square kilometre of collecting area and including a general headquarters as well as two radio telescopes: SKA1-Mid in South Africa and SKA1-Low in Australia. The SKA project consists of a number of subsystems (elements) among which the Telescope Manager (TM) is the one involved in controlling and monitoring the SKA telescopes. The TM element has three primary responsibilities: management of astronomical observations, management of telescope hardware and software subsystems, management of data to support system operations and all stakeholders (operators, maintainers, engineers and science users) in achieving operational, maintenance and engineering goals. Operators, maintainers, engineers and science users will interact with TM via appropriate user interfaces (UI). The TM UI framework envisaged is a complete set of general technical solutions (components, technologies and design information) for implementing a generic computing system (UI platform). Such a system will enable UI components to be instantiated to allow for human interaction via screens, keyboards, mouse and to implement the necessary logic for acquiring or deriving the information needed for interaction. It will provide libraries and specific Application Programming Interfaces (APIs) to implement operator and engineer interactive interfaces. This paper will provide a status update of the TM UI framework, UI platform and UI components design effort, including the technology choices, and discuss key challenges in the TM UI architecture, as well as our approaches to addressing them.

Pulsar-black hole binaries as a window on quantum gravity

NASA Astrophysics Data System (ADS)

Estes, John; Kavic, Michael; Lippert, Matthew; Simonetti, John H.

Pulsars (PSRs) are some of the most accurate clocks found in nature, while black holes (BHs) offer a unique arena for the study of quantum gravity. As such, PSR-BH binaries provide ideal astrophysical systems for detecting effects of quantum gravity. With the success of aLIGO and the advent of instruments like the Square Kilometer Array (SKA) and Evolved Laser Interferometer Space Antenna (eLISA), the prospects for discovery of such PSR-BH binaries are very promising. We argue that PSR-BH binaries can serve as ready-made testing grounds for proposed resolutions to the BH information paradox. We propose using timing signals from a PSR beam passing through the region near a BH event horizon as a probe of quantum gravitational effects. In particular, we demonstrate that fluctuations of the geometry outside a BH lead to an increase in the measured root-mean-square deviation of arrival times of PSR pulsar traveling near the horizon.

Active Galactic Nucleus Feedback with the Square Kilometre Array and Implications for Cluster Physics and Cosmology

NASA Astrophysics Data System (ADS)

Iqbal, Asif; Kale, Ruta; Majumdar, Subhabrata; Nath, Biman B.; Pandge, Mahadev; Sharma, Prateek; Malik, Manzoor A.; Raychaudhury, Somak

2017-12-01

Active Galactic Nuclei (AGN) feedback is regarded as an important non-gravitational process in galaxy clusters, providing useful constraints on large-scale structure formation. It modifies the structure and energetics of the intra-cluster medium (ICM) and hence its understanding is crucially needed in order to use clusters as high precision cosmological probes. In this context, particularly keeping in mind the upcoming high quality radio data expected from radio surveys like Square Kilometre Array (SKA) with its higher sensitivity, high spatial and spectral resolutions, we review our current understanding of AGN feedback, its cosmological implications and the impact that SKA can have in revolutionizing our understanding of AGN feedback in large-scale structures. Recent developments regarding the AGN outbursts and its possible contribution to excess entropy in the hot atmospheres of groups and clusters, its correlation with the feedback energy in ICM, quenching of cooling flows and the possible connection between cool core clusters and radio mini-halos, are discussed. We describe current major issues regarding modeling of AGN feedback and its impact on the surrounding medium. With regard to the future of AGN feedback studies, we examine the possible breakthroughs that can be expected from SKA observations. In the context of cluster cosmology, for example, we point out the importance of SKA observations for cluster mass calibration by noting that most of z>1 clusters discovered by eROSITA X-ray mission can be expected to be followed up through a 1000 hour SKA1-mid programme. Moreover, approximately 1000 radio mini halos and ˜ 2500 radio halos at z<0.6 can be potentially detected by SKA1 and SKA2 and used as tracers of galaxy clusters and determination of cluster selection function.

ON THE COMPLEMENTARITY OF PULSAR TIMING AND SPACE LASER INTERFEROMETRY FOR THE INDIVIDUAL DETECTION OF SUPERMASSIVE BLACK HOLE BINARIES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spallicci, Alessandro D. A. M., E-mail: spallicci@cnrs-orleans.fr

2013-02-20

Gravitational waves coming from supermassive black hole binaries (SMBHBs) are targeted by both the Pulsar Timing Array (PTA) and Space Laser Interferometry (SLI). The possibility of a single SMBHB being tracked first by PTA, through inspiral, and later by SLI, up to merger and ring-down, has been previously suggested. Although the bounding parameters are drawn by the current PTA or the upcoming Square Kilometer Array (SKA), and by the New Gravitational Observatory (NGO), derived from the Laser Interferometer Space Antenna (LISA), this paper also addresses sequential detection beyond specific project constraints. We consider PTA-SKA, which is sensitive from 10{sup -9}more » to p Multiplication-Sign 10{sup -7} Hz (p = 4, 8), and SLI, which operates from s Multiplication-Sign 10{sup -5} up to 1 Hz (s = 1, 3). An SMBHB in the range of 2 Multiplication-Sign 10{sup 8}-2 Multiplication-Sign 10{sup 9} M {sub Sun} (the masses are normalized to a (1 + z) factor, the redshift lying between z = 0.2 and z = 1.5) moves from the PTA-SKA to the SLI band over a period ranging from two months to fifty years. By combining three supermassive black hole (SMBH)-host relations with three accretion prescriptions, nine astrophysical scenarios are formed. They are then related to three levels of pulsar timing residuals (50, 5, 1 ns), generating 27 cases. For residuals of 1 ns, sequential detection probability will never be better than 4.7 Multiplication-Sign 10{sup -4} yr{sup -2} or 3.3 Multiplication-Sign 10{sup -6} yr{sup -2} (per year to merger and per year of survey), according to the best and worst astrophysical scenarios, respectively; put differently this means one sequential detection every 46 or 550 years for an equivalent maximum time to merger and duration of the survey. The chances of sequential detection are further reduced by increasing values of the s parameter (they vanish for s = 10) and of the SLI noise, and by decreasing values of the remnant spin. The spread in the predictions diminishes when timing precision is improved or the SLI low-frequency cutoff is lowered. So while transit times and the SLI signal-to-noise ratio (S/N) may be adequate, the likelihood of sequential detection is severely hampered by the current estimates on the number-just a handful-of individual inspirals observable by PTA-SKA, and to a lesser extent by the wide gap between the pulsar timing and space interferometry bands, and by the severe requirements on pulsar timing residuals. Optimization of future operational scenarios for SKA and SLI is briefly dealt with, since a detection of even a single event would be of paramount importance for the understanding of SMBHBs and of the astrophysical processes connected to their formation and evolution.« less

Advanced European Network of E-Infrastructures for Astronomy with the SKA

NASA Astrophysics Data System (ADS)

Massardi, Marcella

2017-11-01

Here, I present the AENEAS (Advanced European Network of E-infrastructures for Astronomy with the SKA) project has been funded in the Horizon 2020 Work Programme call "Research and Innovation Actions for International Co-operation on high-end e-infrastructure requirements" supporting the Square Kilometre Array (SKA). INAF is contributing to all the AENEAS working packages and leading the WP5 - Access and Knowledge Creation (WP leader M. Massardi IRA-ARC), participants from IRA (Brand, Nanni, Venturi) ,OACT(Becciani, Costa, Umana), OATS (Smareglia, Knapic, Taffoni)

Searching for Extraterrestrial Intelligence with the Square Kilometre Array

NASA Astrophysics Data System (ADS)

Siemion, A.; Benford, J.; Cheng-Jin, J.; Chennamangalam, J.; Cordes, J. M.; Falcke, H. D. E.; Garrington, S. T.; Garrett, M. A.; Gurvits, L.; Hoare, M.; Korpela, E.; Lazio, J.; Messerschmitt, D.; Morrison, I.; O'Brien, T.; Paragi, Z.; Penny, A.; Spitler, L.; Tarter, J.; Werthimer, D.

2015-04-01

The vast collecting area of the Square Kilometre Array (SKA), harnessed by sensitive receivers, flexible digital electronics and increased computational capacity, could permit the most sensitive and exhaustive search for technologically-produced radio emission from advanced extraterrestrial intelligence (SETI) ever performed. For example, SKA1-MID will be capable of detecting a source roughly analogous to terrestrial high-power radars (e.g. air route surveillance or ballistic missile warning radars, EIRP (EIRP = equivalent isotropic radiated power, ~10^17 erg sec^-1) at 10 pc in less than 15 minutes, and with a modest four beam SETI observing system could, in one minute, search every star in the primary beam out to ~100 pc for radio emission comparable to that emitted by the Arecibo Planetary Radar (EIRP ~2 x 10^20 erg sec^-1). The flexibility of the signal detection systems used for SETI searches with the SKA will allow new algorithms to be employed that will provide sensitivity to a much wider variety of signal types than previously searched for. Here we discuss the astrobiological and astrophysical motivations for radio SETI and describe how the technical capabilities of the SKA will explore the radio SETI parameter space. We detail several conceivable SETI experimental programs on all components of SKA1, including commensal, primary-user, targeted and survey programs and project the enhancements to them possible with SKA2. We also discuss target selection criteria for these programs, and in the case of commensal observing, how the varied use cases of other primary observers can be used to full advantage for SETI.

SKALA, a log-periodic array antenna for the SKA-low instrument: design, simulations, tests and system considerations

NASA Astrophysics Data System (ADS)

de Lera Acedo, E.; Razavi-Ghods, N.; Troop, N.; Drought, N.; Faulkner, A. J.

2015-10-01

The very demanding requirements of the SKA-low instrument call for a challenging antenna design capable of delivering excellent performance in radiation patterns, impedance matching, polarization purity, cost, longevity, etc. This paper is devoted to the development (design and test of the first prototypes) of an active ultra-wideband antenna element for the low-frequency instrument of the SKA radio telescope. The antenna element and differential low noise amplifier described here were originally designed to cover the former SKA-low band (70-450 MHz) but it is now aimed to cover the re-defined SKA-low band (50-350 MHz) and furthermore the antenna is capable of performing up to 650 MHz with the current design. The design is focused on maximum sensitivity in a wide field of view (+/- 45° from zenith) and low cross-polarization ratios. Furthermore, the size and cost of the element has to be kept to a minimum as millions of these antennas will need to be deployed for the full SKA in very compact configurations. The primary focus of this paper is therefore to discuss various design implications for the SKA-low telescope.

The SKA1 LOW telescope: system architecture and design performance

NASA Astrophysics Data System (ADS)

Waterson, Mark F.; Labate, Maria Grazia; Schnetler, Hermine; Wagg, Jeff; Turner, Wallace; Dewdney, Peter

2016-07-01

The SKA1-LOW radio telescope will be a low-frequency (50-350 MHz) aperture array located in Western Australia. Its scientific objectives will prioritize studies of the Epoch of Reionization and pulsar physics. Development of the telescope has been allocated to consortia responsible for the aperture array front end, timing distribution, signal and data transport, correlation and beamforming signal processors, infrastructure, monitor and control systems, and science data processing. This paper will describe the system architectural design and key performance parameters of the telescope and summarize the high-level sub-system designs of the consortia.

The Spanish participation in the SKA

NASA Astrophysics Data System (ADS)

Verdes-Montenegro, L.; Garrido, J.; González-García, M.

2017-03-01

The Square Kilometre Array (SKA) will be a radio interferometer aiming to answer fundamental questions in Astrophysics, Fundamental Physics, and Astrobiology. It will be composed of thousands of antennas distributed over distances of more than 3000 kilometres on both Africa and Australia. The SKA has been recently identified as a Landmark Project in the European Strategy Forum on Research Infrastructures (ESFRI) roadmap. Spain has been participating in SKA-related activities since the 1990s, coordinated since 2011 by the Instituto de Astrofísica de Andalucía (IAA-CSIC). Up to now, 21 researchers participate in 7 out of the 11 main SKA Science Working Groups, and a total of 119 researchers from 40 Spanish centres have participated in the Spanish SKA White Book, published in 2015. From a technological point of view, more than 20 research centres and companies are contributing to the design of the SKA as part of 7 international consortia. The Spanish contribution was estimated in 2M euro (2014), officially recognized by the SKA Organisation Director General in a letter to the Spanish Ministry of Economy and Competitiveness. In addition, the Spanish Astronomy Infrastructures Network (RIA from its Spanish initials) issued a recommendation on the interest of the scientific community and industry that Spain explores the possibility to join the SKA project as Full Member before the construction phase starts. In December 2015, the Spanish Secretary of State of Research, Development and Innovation sent a letter to the SKA Organisation Director General proposing to establish a dialogue in order to explore scenarios for Spain to join the SKA, what constitutes a further motivation for the Spanish community to continue its efforts.

MeerKAT Science: On the Pathway to the SKA

NASA Astrophysics Data System (ADS)

MeerKAT Science: On the Pathway to the SKA. MeerKAT is a next generation radio telescope under construction on the African SKA central site in the Karoo plateau of South Africa. When completed in 2017 MeerKAT will be a 64-element array of 13.5-m parabolic antennas distributed over an area with a diameter of 8 km. With a combination of wide bandwidth and field of view, with the large number of antennas and total collecting area, MeerKAT will be one of the world’s most powerful imaging telescopes operating at GHz frequencies. MeerKAT is a science and technology precursor of the SKA mid-frequency dish array, and following several years of operation as a South African telescope will be incorporated into the SKA phase-one facility. The MeerKAT science program will consist of a combination of key science, legacy-style, large survey projects, and smaller projects based on proposals for open time. This workshop, which took place in Stellenbosch in the Western Cape, was held to discuss and plan the broad range of scientific investigations that will be undertaken during the pre-SKA phase of MeerKAT. Topics covered included: technical development and roll out of the MeerKAT science capabilities, details of the large survey projects presented by the project teams, science program concepts for open time, commensal programs such as the Search for Extraterrestrial Intelligence, and the impact of MeerKAT on global Very Long Baseline Interferometry. These proceedings serve as a record of the scientific vision of MeerKAT in the year before its completion, foreshadowing a new era of radio astronomy on the African continent.

Self-Calibration in the Ska: Dealing with Inherently Strong Instrumental Polarization

NASA Astrophysics Data System (ADS)

Hamaker, Johan

The polarization properties of a phased-array SKA will depart radically from those we are familiar with. The E- and H-plane beams of a linear or planar dipole are very different and the primary beam formed by arrays of such dipoles is strongly polarized. The customary quasi-scalar description is inadequate: Polarization must be accounted for in a fundamental way. Once this is done, we must investigate whether or not a phased-array SKA will in principle be capable of achievements comparable to those of conventional synthesis arrays. Selfcal is crucial to these achievements. In this paper I address the vital question of its viability in the presence of arbitrary instrumental polarization. I introduce an interferometer description based on 2x2 matrices. I then propose a matrix-based self-calibration method that is entirely analogous to the scalar one. I show that the standard selfcal assumptions suppress spatial scattering in matrix selfcal like they do in scalar selfcal: Thus the basic condition for obtaining images with a high dynamic range is satisfied. However, matrix selfcal alone cannot guarantee the polarimetric fidelity of the image: It introduces an unknown polrotation of the Stokes (Q,U,V) brightness vector and an unknown polconversion between unpolarized and polarized brightness. Methods similar to those currently applied in quasi-scalar polarimetry must be applied to reduce these poldistorsions to an acceptable level.

A cyber infrastructure for the SKA Telescope Manager

NASA Astrophysics Data System (ADS)

Barbosa, Domingos; Barraca, João. P.; Carvalho, Bruno; Maia, Dalmiro; Gupta, Yashwant; Natarajan, Swaminathan; Le Roux, Gerhard; Swart, Paul

2016-07-01

The Square Kilometre Array Telescope Manager (SKA TM) will be responsible for assisting the SKA Operations and Observation Management, carrying out System diagnosis and collecting Monitoring and Control data from the SKA subsystems and components. To provide adequate compute resources, scalability, operation continuity and high availability, as well as strict Quality of Service, the TM cyber-infrastructure (embodied in the Local Infrastructure - LINFRA) consists of COTS hardware and infrastructural software (for example: server monitoring software, host operating system, virtualization software, device firmware), providing a specially tailored Infrastructure as a Service (IaaS) and Platform as a Service (PaaS) solution. The TM infrastructure provides services in the form of computational power, software defined networking, power, storage abstractions, and high level, state of the art IaaS and PaaS management interfaces. This cyber platform will be tailored to each of the two SKA Phase 1 telescopes (SKA_MID in South Africa and SKA_LOW in Australia) instances, each presenting different computational and storage infrastructures and conditioned by location. This cyber platform will provide a compute model enabling TM to manage the deployment and execution of its multiple components (observation scheduler, proposal submission tools, MandC components, Forensic tools and several Databases, etc). In this sense, the TM LINFRA is primarily focused towards the provision of isolated instances, mostly resorting to virtualization technologies, while defaulting to bare hardware if specifically required due to performance, security, availability, or other requirement.

SKA weak lensing- II. Simulated performance and survey design considerations

NASA Astrophysics Data System (ADS)

Bonaldi, Anna; Harrison, Ian; Camera, Stefano; Brown, Michael L.

2016-12-01

We construct a pipeline for simulating weak lensing cosmology surveys with the Square Kilometre Array (SKA), taking as inputs telescope sensitivity curves; correlated source flux, size and redshift distributions; a simple ionospheric model; source redshift and ellipticity measurement errors. We then use this simulation pipeline to optimize a 2-yr weak lensing survey performed with the first deployment of the SKA (SKA1). Our assessments are based on the total signal to noise of the recovered shear power spectra, a metric that we find to correlate very well with a standard dark energy figure of merit. We first consider the choice of frequency band, trading off increases in number counts at lower frequencies against poorer resolution; our analysis strongly prefers the higher frequency Band 2 (950-1760 MHz) channel of the SKA-MID telescope to the lower frequency Band 1 (350-1050 MHz). Best results would be obtained by allowing the centre of Band 2 to shift towards lower frequency, around 1.1 GHz. We then move on to consider survey size, finding that an area of 5000 deg2 is optimal for most SKA1 instrumental configurations. Finally, we forecast the performance of a weak lensing survey with the second deployment of the SKA. The increased survey size (3π steradian) and sensitivity improves both the signal to noise and the dark energy metrics by two orders of magnitude.

Science with the Square Kilometre Array

NASA Technical Reports Server (NTRS)

Lazio, Joseph; Huynh, Minh

2010-01-01

The Square Kilometre Array (SKA) is the centimeter- and meter-wavelength telescope for the 21st Century. Its Key Science Projects are (a) The end of the Dark Ages, involving searches for an H i signature and the first metalrich systems; (b) Testing theories of gravitation using an array of pulsars to search for gravitational waves and relativistic binaries to probe the strong-field regime; (c) Observations of H i to a redshift z 2 from which to study the evolution of galaxies and dark energy. (d) Astrobiology including planetary formation within protoplanetary disks; and (c) The origin and evolution of cosmic magnetism, both within the Galaxy and in intergalactic space. The SKA will operate over the wavelength range of at least 1.2 cm to 4 m (70 MHz to 25 GHz), providing milliarcsecond resolution at the shortest wavelengths.

Square Kilometre Array Science Data Processing

NASA Astrophysics Data System (ADS)

Nikolic, Bojan; SDP Consortium, SKA

2014-04-01

The Square Kilometre Array (SKA) is planned to be, by a large factor, the largest and most sensitive radio telescope ever constructed. The first phase of the telescope (SKA1), now in the design phase, will in itself represent a major leap in capabilities compared to current facilities. These advances are to a large extent being made possible by advances in available computer processing power so that that larger numbers of smaller, simpler and cheaper receptors can be used. As a result of greater reliance and demands on computing, ICT is becoming an ever more integral part of the telescope. The Science Data Processor is the part of the SKA system responsible for imaging, calibration, pulsar timing, confirmation of pulsar candidates, derivation of some further derived data products, archiving and providing the data to the users. It will accept visibilities at data rates at several TB/s and require processing power for imaging in range 100 petaFLOPS -- ~1 ExaFLOPS, putting SKA1 into the regime of exascale radio astronomy. In my talk I will present the overall SKA system requirements and how they drive these high data throughput and processing requirements. Some of the key challenges for the design of SDP are: - Identifying sufficient parallelism to utilise very large numbers of separate compute cores that will be required to provide exascale computing throughput - Managing efficiently the high internal data flow rates - A conceptual architecture and software engineering approach that will allow adaptation of the algorithms as we learn about the telescope and the atmosphere during the commissioning and operational phases - System management that will deal gracefully with (inevitably frequent) failures of individual units of the processing system In my talk I will present possible initial architectures for the SDP system that attempt to address these and other challenges.

Update on the SKA Offset Optics Design for the U.S. Technology Development Project

NASA Technical Reports Server (NTRS)

Imbriale, William A.; Cortes-Medellin, German; Baker, Lynn

2011-01-01

The U.S. design concept for the Square Kilometre Array (SKA) program is based on utilizing a large number of small-diameter dish antennas in the 12 to 15 meter diameter range. The Technology Development Project (TDP) is planning to design and build the first of these antennas to provide a demonstration of the technology and a solid base on which to estimate costs. The latest considerations for selecting both the optics and feed design are presented.

LUNASKA experiments using the Australia Telescope Compact Array to search for ultrahigh energy neutrinos and develop technology for the lunar Cherenkov technique

DOE Office of Scientific and Technical Information (OSTI.GOV)

James, C. W.; Protheroe, R. J.; Ekers, R. D.

2010-02-15

We describe the design, performance, sensitivity and results of our recent experiments using the Australia Telescope Compact Array (ATCA) for lunar Cherenkov observations with a very wide (600 MHz) bandwidth and nanosecond timing, including a limit on an isotropic neutrino flux. We also make a first estimate of the effects of small-scale surface roughness on the effective experimental aperture, finding that contrary to expectations, such roughness will act to increase the detectability of near-surface events over the neutrino energy-range at which our experiment is most sensitive (though distortions to the time-domain pulse profile may make identification more difficult). The aimmore » of our 'Lunar UHE Neutrino Astrophysics using the Square Kilometre Array' (LUNASKA) project is to develop the lunar Cherenkov technique of using terrestrial radio telescope arrays for ultrahigh energy (UHE) cosmic ray (CR) and neutrino detection, and, in particular, to prepare for using the Square Kilometre Array (SKA) and its path-finders such as the Australian SKA Pathfinder (ASKAP) and the Low Frequency Array (LOFAR) for lunar Cherenkov experiments.« less

Large-N correlator systems for low frequency radio astronomy

NASA Astrophysics Data System (ADS)

Foster, Griffin

Low frequency radio astronomy has entered a second golden age driven by the development of a new class of large-N interferometric arrays. The low frequency array (LOFAR) and a number of redshifted HI Epoch of Reionization (EoR) arrays are currently undergoing commission and regularly observing. Future arrays of unprecedented sensitivity and resolutions at low frequencies, such as the square kilometer array (SKA) and the hydrogen epoch of reionization array (HERA), are in development. The combination of advancements in specialized field programmable gate array (FPGA) hardware for signal processing, computing and graphics processing unit (GPU) resources, and new imaging and calibration algorithms has opened up the oft underused radio band below 300 MHz. These interferometric arrays require efficient implementation of digital signal processing (DSP) hardware to compute the baseline correlations. FPGA technology provides an optimal platform to develop new correlators. The significant growth in data rates from these systems requires automated software to reduce the correlations in real time before storing the data products to disk. Low frequency, widefield observations introduce a number of unique calibration and imaging challenges. The efficient implementation of FX correlators using FPGA hardware is presented. Two correlators have been developed, one for the 32 element BEST-2 array at Medicina Observatory and the other for the 96 element LOFAR station at Chilbolton Observatory. In addition, calibration and imaging software has been developed for each system which makes use of the radio interferometry measurement equation (RIME) to derive calibrations. A process for generating sky maps from widefield LOFAR station observations is presented. Shapelets, a method of modelling extended structures such as resolved sources and beam patterns has been adapted for radio astronomy use to further improve system calibration. Scaling of computing technology allows for the development of larger correlator systems, which in turn allows for improvements in sensitivity and resolution. This requires new calibration techniques which account for a broad range of systematic effects.

An innovative, highly sensitive receiver system for the Square Kilometre Array Mid Radio Telescope

NASA Astrophysics Data System (ADS)

Tan, Gie Han; Lehmensiek, Robert; Billade, Bhushan; Caputa, Krzysztof; Gauffre, Stéphane; Theron, Isak P.; Pantaleev, Miroslav; Ljusic, Zoran; Quertier, Benjamin; Peens-Hough, Adriaan

2016-07-01

The Square Kilometre Array (SKA) Project is a global science and engineering project realizing the next-generation radio telescopes operating in the metre and centimetre wavelengths regions. This paper addresses design concepts of the broadband, exceptionally sensitive receivers and reflector antennas deployed in the SKA1-Mid radio telescope to be located in South Africa. SKA1-Mid (350 MHz - 13.8 GHz with an option for an upper limit of 24 GHz) will consist of 133 reflector antennas using an unblocked aperture, offset Gregorian configuration with an effective diameter of 15 m. Details on the unblocked aperture Gregorian antennas, low noise front ends and advanced direct digitization receivers, are provided from a system design perspective. The unblocked aperture results in increased aperture efficiency and lower side-lobe levels compared to a traditional on-axis configuration. The low side-lobe level reduces the noise contribution due to ground pick-up but also makes the antenna less susceptible to ground-based RFI sources. The addition of extra shielding on the sub-reflector provides a further reduction of ground pick-up. The optical design of the SKA1-Mid reflector antenna has been tweaked using advanced EM simulation tools in combination with sophisticated models for sky, atmospheric and ground noise contributions. This optimal antenna design in combination with very low noise, partially cryogenic, receivers and wide instantaneous bandwidth provide excellent receiving sensitivity in combination with instrumental flexibility to accommodate a wide range of astronomical observation modes.

Dynamic scheduling and planning parallel observations on large Radio Telescope Arrays with the Square Kilometre Array in mind

NASA Astrophysics Data System (ADS)

Buchner, Johannes

2011-12-01

Scheduling, the task of producing a time table for resources and tasks, is well-known to be a difficult problem the more resources are involved (a NP-hard problem). This is about to become an issue in Radio astronomy as observatories consisting of hundreds to thousands of telescopes are planned and operated. The Square Kilometre Array (SKA), which Australia and New Zealand bid to host, is aiming for scales where current approaches -- in construction, operation but also scheduling -- are insufficent. Although manual scheduling is common today, the problem is becoming complicated by the demand for (1) independent sub-arrays doing simultaneous observations, which requires the scheduler to plan parallel observations and (2) dynamic re-scheduling on changed conditions. Both of these requirements apply to the SKA, especially in the construction phase. We review the scheduling approaches taken in the astronomy literature, as well as investigate techniques from human schedulers and today's observatories. The scheduling problem is specified in general for scientific observations and in particular on radio telescope arrays. Also taken into account is the fact that the observatory may be oversubscribed, requiring the scheduling problem to be integrated with a planning process. We solve this long-term scheduling problem using a time-based encoding that works in the very general case of observation scheduling. This research then compares algorithms from various approaches, including fast heuristics from CPU scheduling, Linear Integer Programming and Genetic algorithms, Branch-and-Bound enumeration schemes. Measures include not only goodness of the solution, but also scalability and re-scheduling capabilities. In conclusion, we have identified a fast and good scheduling approach that allows (re-)scheduling difficult and changing problems by combining heuristics with a Genetic algorithm using block-wise mutation operations. We are able to explain and eradicate two problems in the literature: The inability of a GA to properly improve schedules and the generation of schedules with frequent interruptions. Finally, we demonstrate the scheduling framework for several operating telescopes: (1) Dynamic re-scheduling with the AUT Warkworth 12m telescope, (2) Scheduling for the Australian Mopra 22m telescope and scheduling for the Allen Telescope Array. Furthermore, we discuss the applicability of the presented scheduling framework to the Atacama Large Millimeter/submillimeter Array (ALMA, in construction) and the SKA. In particular, during the development phase of the SKA, this dynamic, scalable scheduling framework can accommodate changing conditions.

Big Data Challenges for Large Radio Arrays

NASA Technical Reports Server (NTRS)

Jones, Dayton L.; Wagstaff, Kiri; Thompson, David; D'Addario, Larry; Navarro, Robert; Mattmann, Chris; Majid, Walid; Lazio, Joseph; Preston, Robert; Rebbapragada, Umaa

2012-01-01

Future large radio astronomy arrays, particularly the Square Kilometre Array (SKA), will be able to generate data at rates far higher than can be analyzed or stored affordably with current practices. This is, by definition, a "big data" problem, and requires an end-to-end solution if future radio arrays are to reach their full scientific potential. Similar data processing, transport, storage, and management challenges face next-generation facilities in many other fields.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lepori, Francesca; Viel, Matteo; Baccigalupi, Carlo

We investigate the Alcock Paczy'nski (AP) test applied to the Baryon Acoustic Oscillation (BAO) feature in the galaxy correlation function. By using a general formalism that includes relativistic effects, we quantify the importance of the linear redshift space distortions and gravitational lensing corrections to the galaxy number density fluctuation. We show that redshift space distortions significantly affect the shape of the correlation function, both in radial and transverse directions, causing different values of galaxy bias to induce offsets up to 1% in the AP test. On the other hand, we find that the lensing correction around the BAO scale modifiesmore » the amplitude but not the shape of the correlation function and therefore does not introduce any systematic effect. Furthermore, we investigate in details how the AP test is sensitive to redshift binning: a window function in transverse direction suppresses correlations and shifts the peak position toward smaller angular scales. We determine the correction that should be applied in order to account for this effect, when performing the test with data from three future planned galaxy redshift surveys: Euclid, the Dark Energy Spectroscopic Instrument (DESI) and the Square Kilometer Array (SKA).« less

Medicina array demonstrator: calibration and radiation pattern characterization using a UAV-mounted radio-frequency source

NASA Astrophysics Data System (ADS)

Pupillo, G.; Naldi, G.; Bianchi, G.; Mattana, A.; Monari, J.; Perini, F.; Poloni, M.; Schiaffino, M.; Bolli, P.; Lingua, A.; Aicardi, I.; Bendea, H.; Maschio, P.; Piras, M.; Virone, G.; Paonessa, F.; Farooqui, Z.; Tibaldi, A.; Addamo, G.; Peverini, O. A.; Tascone, R.; Wijnholds, S. J.

2015-06-01

One of the most challenging aspects of the new-generation Low-Frequency Aperture Array (LFAA) radio telescopes is instrument calibration. The operational LOw-Frequency ARray (LOFAR) instrument and the future LFAA element of the Square Kilometre Array (SKA) require advanced calibration techniques to reach the expected outstanding performance. In this framework, a small array, called Medicina Array Demonstrator (MAD), has been designed and installed in Italy to provide a test bench for antenna characterization and calibration techniques based on a flying artificial test source. A radio-frequency tone is transmitted through a dipole antenna mounted on a micro Unmanned Aerial Vehicle (UAV) (hexacopter) and received by each element of the array. A modern digital FPGA-based back-end is responsible for both data-acquisition and data-reduction. A simple amplitude and phase equalization algorithm is exploited for array calibration owing to the high stability and accuracy of the developed artificial test source. Both the measured embedded element patterns and calibrated array patterns are found to be in good agreement with the simulated data. The successful measurement campaign has demonstrated that a UAV-mounted test source provides a means to accurately validate and calibrate the full-polarized response of an antenna/array in operating conditions, including consequently effects like mutual coupling between the array elements and contribution of the environment to the antenna patterns. A similar system can therefore find a future application in the SKA-LFAA context.

Scalable, efficient ASICS for the square kilometre array: From A/D conversion to central correlation

NASA Astrophysics Data System (ADS)

Schmatz, M. L.; Jongerius, R.; Dittmann, G.; Anghel, A.; Engbersen, T.; van Lunteren, J.; Buchmann, P.

2014-05-01

The Square Kilometre Array (SKA) is a future radio telescope, currently being designed by the worldwide radio-astronomy community. During the first of two construction phases, more than 250,000 antennas will be deployed, clustered in aperture-array stations. The antennas will generate 2.5 Pb/s of data, which needs to be processed in real time. For the processing stages from A/D conversion to central correlation, we propose an ASIC solution using only three chip architectures. The architecture is scalable - additional chips support additional antennas or beams - and versatile - it can relocate its receiver band within a range of a few MHz up to 4GHz. This flexibility makes it applicable to both SKA phases 1 and 2. The proposed chips implement an antenna and station processor for 289 antennas with a power consumption on the order of 600W and a correlator, including corner turn, for 911 stations on the order of 90 kW.

Cosmological parameter forecasts for H I intensity mapping experiments using the angular power spectrum

NASA Astrophysics Data System (ADS)

Olivari, L. C.; Dickinson, C.; Battye, R. A.; Ma, Y.-Z.; Costa, A. A.; Remazeilles, M.; Harper, S.

2018-01-01

H I intensity mapping is a new observational technique to survey the large-scale structure of matter using the 21 cm emission line of atomic hydrogen (H I). In this work, we simulate BINGO (BAO from Integrated Neutral Gas Observations) and SKA (Square Kilometre Array) phase-1 dish array operating in autocorrelation mode. For the optimal case of BINGO with no foregrounds, the combination of the H I angular power spectra with Planck results allows w to be measured with a precision of 4 per cent, while the combination of the BAO acoustic scale with Planck gives a precision of 7 per cent. We consider a number of potentially complicating effects, including foregrounds and redshift-dependent bias, which increase the uncertainty on w but not dramatically; in all cases, the final uncertainty is found to be Δw < 8 per cent for BINGO. For the combination of SKA-MID in autocorrelation mode with Planck, we find that, in ideal conditions, w can be measured with a precision of 4 per cent for the redshift range 0.35 < z < 3 (350-1050 MHz) and 2 per cent for 0 < z < 0.49 (950-1421 MHz). Extending the model to include the sum of neutrino masses yields a 95 per cent upper limit of ∑mν < 0.24 eV for BINGO and ∑mν < 0.08 eV for SKA phase 1, competitive with the current best constraints in the case of BINGO and significantly better than them in the case of SKA.

Calibration and Stokes Imaging with Full Embedded Element Primary Beam Model for the Murchison Widefield Array

NASA Astrophysics Data System (ADS)

Sokolowski, M.; Colegate, T.; Sutinjo, A. T.; Ung, D.; Wayth, R.; Hurley-Walker, N.; Lenc, E.; Pindor, B.; Morgan, J.; Kaplan, D. L.; Bell, M. E.; Callingham, J. R.; Dwarakanath, K. S.; For, Bi-Qing; Gaensler, B. M.; Hancock, P. J.; Hindson, L.; Johnston-Hollitt, M.; Kapińska, A. D.; McKinley, B.; Offringa, A. R.; Procopio, P.; Staveley-Smith, L.; Wu, C.; Zheng, Q.

2017-11-01

The Murchison Widefield Array (MWA), located in Western Australia, is one of the low-frequency precursors of the international Square Kilometre Array (SKA) project. In addition to pursuing its own ambitious science programme, it is also a testbed for wide range of future SKA activities ranging from hardware, software to data analysis. The key science programmes for the MWA and SKA require very high dynamic ranges, which challenges calibration and imaging systems. Correct calibration of the instrument and accurate measurements of source flux densities and polarisations require precise characterisation of the telescope's primary beam. Recent results from the MWA GaLactic Extragalactic All-sky Murchison Widefield Array (GLEAM) survey show that the previously implemented Average Embedded Element (AEE) model still leaves residual polarisations errors of up to 10-20% in Stokes Q. We present a new simulation-based Full Embedded Element (FEE) model which is the most rigorous realisation yet of the MWA's primary beam model. It enables efficient calculation of the MWA beam response in arbitrary directions without necessity of spatial interpolation. In the new model, every dipole in the MWA tile (4 × 4 bow-tie dipoles) is simulated separately, taking into account all mutual coupling, ground screen, and soil effects, and therefore accounts for the different properties of the individual dipoles within a tile. We have applied the FEE beam model to GLEAM observations at 200-231 MHz and used false Stokes parameter leakage as a metric to compare the models. We have determined that the FEE model reduced the magnitude and declination-dependent behaviour of false polarisation in Stokes Q and V while retaining low levels of false polarisation in Stokes U.

Development of Very Long Baseline Interferometry (VLBI) techniques in New Zealand: Array simulation, image synthesis and analysis

NASA Astrophysics Data System (ADS)

Weston, S. D.

2008-04-01

This thesis presents the design and development of a process to model Very Long Base Line Interferometry (VLBI) aperture synthesis antenna arrays. In line with the Auckland University of Technology (AUT) Institute for Radiophysics and Space Research (IRSR) aims to develop the knowledge, skills and experience within New Zealand, extensive use of existing radio astronomical software has been incorporated into the process namely AIPS (Astronomical Imaging Processing System), MIRIAD (a radio interferometry data reduction package) and DIFMAP (a program for synthesis imaging of visibility data from interferometer arrays of radio telescopes). This process has been used to model various antenna array configurations for two proposed New Zealand sites for antenna in a VLBI array configuration with existing Australian facilities and a passable antenna at Scott Base in Antarctica; and the results are presented in an attempt to demonstrate the improvement to be gained by joint trans-Tasman VLBI observation. It is hoped these results and process will assist the planning and placement of proposed New Zealand radio telescopes for cooperation with groups such as the Australian Long Baseline Array (LBA), others in the Pacific Rim and possibly globally; also potential future involvement of New Zealand with the SKA. The developed process has also been used to model a phased building schedule for the SKA in Australia and the addition of two antennas in New Zealand. This has been presented to the wider astronomical community via the Royal Astronomical Society of New Zealand Journal, and is summarized in this thesis with some additional material. A new measure of quality ("figure of merit") for comparing the original model image and final CLEAN images by utilizing normalized 2-D cross correlation is evaluated as an alternative to the existing subjective visual operator image comparison undertaken to date by other groups. This new unit of measure is then used ! in the presentation of the results to provide a quantative comparison of the different array configurations modelled. Included in the process is the development of a new antenna array visibility program which was based on a Perl code script written by Prof Steven Tingay to plot antenna visibilities for the Australian Square Kilometre Array (SKA) proposal. This has been expanded and improved removing the hard coded fixed assumptions for the SKA configuration, providing a new useful and flexible program for the wider astronomical community. A prototype user interface using html/cgi/perl was developed for the process so that the underlying software packages can be served over the web to a user via an internet browser. This was used to demonstrate how easy it is to provide a friendlier interface compared to the existing cumbersome and difficult command line driven interfaces (although the command line can be retained for more experienced users).

The Square Kilometre Array Epoch of Reionisation and Cosmic Dawn Experiment

NASA Astrophysics Data System (ADS)

Trott, Cathryn M.

2018-05-01

The Square Kilometre Array (SKA) Epoch of Reionisation and Cosmic Dawn (EoR/CD) experiments aim to explore the growth of structure and production of ionising radiation in the first billion years of the Universe. Here I describe the experiments planned for the future low-frequency components of the Observatory, and work underway to define, design and execute these programs.

The future of Canada's radio astronomy

NASA Astrophysics Data System (ADS)

Gaensler, Bryan M.

2017-11-01

Through involvement in CHIME, ALMA, the Jansky VLA and the Murchison Widefield Array, Canada is well placed in current radio astronomy facilities and the future looks even brighter, with strategic interest in the SKA and the Next Generation VLA.

Source finding in linear polarization for LOFAR, and SKA predecessor surveys, using Faraday moments

NASA Astrophysics Data System (ADS)

Farnes, J. S.; Heald, G.; Junklewitz, H.; Mulcahy, D. D.; Haverkorn, M.; Van Eck, C. L.; Riseley, C. J.; Brentjens, M.; Horellou, C.; Vacca, V.; Jones, D. I.; Horneffer, A.; Paladino, R.

2018-03-01

The optimal source-finding strategy for linear polarization data is an unsolved problem, with many inhibitive factors imposed by the technically challenging nature of polarization observations. Such an algorithm is essential for Square Kilometre Array (SKA) pathfinder surveys, such as the Multifrequency Snapshot Sky Survey with the LOw Frequency ARray (LOFAR), as data volumes are significant enough to prohibit manual inspection. We present a new strategy of `Faraday Moments' for source-finding in linear polarization with LOFAR, using the moments of the frequency-dependent full-Stokes data (i.e. the mean, standard deviation, skewness, and excess kurtosis). Through simulations of the sky, we find that moments can identify polarized sources with a high completeness: 98.5 per cent at a signal to noise of 5. While the method has low reliability, rotation measure (RM) synthesis can be applied per candidate source to filter out instrumental and spurious detections. This combined strategy will result in a complete and reliable catalogue of polarized sources that includes the full sensitivity of the observational bandwidth. We find that the technique can reduce the number of pixels on which RM Synthesis needs to be performed by a factor of ≈1 × 105 for source distributions anticipated with modern radio telescopes. Through tests on LOFAR data, we find that the technique works effectively in the presence of diffuse emission. Extensions of this method are directly applicable to other upcoming radio surveys such as the POlarization Sky Survey of the Universe's Magnetism with the Australia Square Kilometre Array Pathfinder, and the SKA itself.

LEAP: An Innovative Direction Dependent Ionospheric Calibration Scheme for Low Frequency Arrays

NASA Astrophysics Data System (ADS)

Rioja, María J.; Dodson, Richard; Franzen, Thomas M. O.

2018-05-01

The ambitious scientific goals of the SKA require a matching capability for calibration of atmospheric propagation errors, which contaminate the observed signals. We demonstrate a scheme for correcting the direction-dependent ionospheric and instrumental phase effects at the low frequencies and with the wide fields of view planned for SKA-Low. It leverages bandwidth smearing, to filter-out signals from off-axis directions, allowing the measurement of the direction-dependent antenna-based gains in the visibility domain; by doing this towards multiple directions it is possible to calibrate across wide fields of view. This strategy removes the need for a global sky model, therefore all directions are independent. We use MWA results at 88 and 154 MHz under various weather conditions to characterise the performance and applicability of the technique. We conclude that this method is suitable to measure and correct for temporal fluctuations and direction-dependent spatial ionospheric phase distortions on a wide range of scales: both larger and smaller than the array size. The latter are the most intractable and pose a major challenge for future instruments. Moreover this scheme is an embarrassingly parallel process, as multiple directions can be processed independently and simultaneously. This is an important consideration for the SKA, where the current planned architecture is one of compute-islands with limited interconnects. Current implementation of the algorithm and on-going developments are discussed.

Wide field imaging problems in radio astronomy

NASA Astrophysics Data System (ADS)

Cornwell, T. J.; Golap, K.; Bhatnagar, S.

2005-03-01

The new generation of synthesis radio telescopes now being proposed, designed, and constructed face substantial problems in making images over wide fields of view. Such observations are required either to achieve the full sensitivity limit in crowded fields or for surveys. The Square Kilometre Array (SKA Consortium, Tech. Rep., 2004), now being developed by an international consortium of 15 countries, will require advances well beyond the current state of the art. We review the theory of synthesis radio telescopes for large fields of view. We describe a new algorithm, W projection, for correcting the non-coplanar baselines aberration. This algorithm has improved performance over those previously used (typically an order of magnitude in speed). Despite the advent of W projection, the computing hardware required for SKA wide field imaging is estimated to cost up to $500M (2015 dollars). This is about half the target cost of the SKA. Reconfigurable computing is one way in which the costs can be decreased dramatically.

Direct shear mapping - a new weak lensing tool

NASA Astrophysics Data System (ADS)

de Burgh-Day, C. O.; Taylor, E. N.; Webster, R. L.; Hopkins, A. M.

2015-08-01

We have developed a new technique called direct shear mapping (DSM) to measure gravitational lensing shear directly from observations of a single background source. The technique assumes the velocity map of an unlensed, stably rotating galaxy will be rotationally symmetric. Lensing distorts the velocity map making it asymmetric. The degree of lensing can be inferred by determining the transformation required to restore axisymmetry. This technique is in contrast to traditional weak lensing methods, which require averaging an ensemble of background galaxy ellipticity measurements, to obtain a single shear measurement. We have tested the efficacy of our fitting algorithm with a suite of systematic tests on simulated data. We demonstrate that we are in principle able to measure shears as small as 0.01. In practice, we have fitted for the shear in very low redshift (and hence unlensed) velocity maps, and have obtained null result with an error of ±0.01. This high-sensitivity results from analysing spatially resolved spectroscopic images (i.e. 3D data cubes), including not just shape information (as in traditional weak lensing measurements) but velocity information as well. Spirals and rotating ellipticals are ideal targets for this new technique. Data from any large Integral Field Unit (IFU) or radio telescope is suitable, or indeed any instrument with spatially resolved spectroscopy such as the Sydney-Australian-Astronomical Observatory Multi-Object Integral Field Spectrograph (SAMI), the Atacama Large Millimeter/submillimeter Array (ALMA), the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the Square Kilometer Array (SKA).

RF Design of a Wideband CMOS Integrated Receiver for Phased Array Applications

NASA Astrophysics Data System (ADS)

Jackson, Suzy A.

2004-06-01

New silicon CMOS processes developed primarily for the burgeoning wireless networking market offer significant promise as a vehicle for the implementation of highly integrated receivers, especially at the lower end of the frequency range proposed for the Square Kilometre Array (SKA). An RF-CMOS ‘Receiver-on-a-Chip’ is being developed as part of an Australia Telescope program looking at technologies associated with the SKA. The receiver covers the frequency range 500 1700 MHz, with instantaneous IF bandwidth of 500 MHz and, on simulation, yields an input noise temperature of < 50 K at mid-band. The receiver will contain all active circuitry (LNA, bandpass filter, quadrature mixer, anti-aliasing filter, digitiser and serialiser) on one 0.18 μm RF-CMOS integrated circuit. This paper outlines receiver front-end development work undertaken to date, including design and simulation of an LNA using noise cancelling techniques to achieve a wideband input-power-match with little noise penalty.

News and Views: Diamond is new head of SKA; Did you read our `A&G' mobile issue? BBC writer wins astro journalism prize; Kavli prize recognizes work on Kuiper Belt objects

NASA Astrophysics Data System (ADS)

2012-10-01

Philip Diamond will become director general of the Square Kilometre Array this month, moving from Australia to the new SKA headquarters at Jodrell Bank Radio Observatory. Technology writer Katia Moskvitch has won the first European Astronomy Journalism Prize for her series of articles on the Very Large Telescope at Paranal, Chile. Moskvitch will be the guest of the ESO at the inauguration of the Atacama Large Millimeter/submillimeter Array (ALMA) in the Atacama desert in March 2013. The 2012 Kavli Prize in Astrophysics is shared between David C Jewitt (University of California, USA), Jane X Luu (Massachusetts Institute of Technology, Lincoln Laboratory, USA), and Michael E Brown (California Institute of Technology, USA) “for discovering and characterizing the Kuiper Belt and its largest members, work that led to a major advance in the understanding of the history of our planetary system”.

Calibration of radio-astronomical data on the cloud. LOFAR, the pathway to SKA

NASA Astrophysics Data System (ADS)

Sabater, J.; Sánchez-Expósito, S.; Garrido, J.; Ruiz, J. E.; Best, P. N.; Verdes-Montenegro, L.

2015-05-01

The radio interferometer LOFAR (LOw Frequency ARray) is fully operational now. This Square Kilometre Array (SKA) pathfinder allows the observation of the sky at frequencies between 10 and 240 MHz, a relatively unexplored region of the spectrum. LOFAR is a software defined telescope: the data is mainly processed using specialized software running in common computing facilities. That means that the capabilities of the telescope are virtually defined by software and mainly limited by the available computing power. However, the quantity of data produced can quickly reach huge volumes (several Petabytes per day). After the correlation and pre-processing of the data in a dedicated cluster, the final dataset is handled to the user (typically several Terabytes). The calibration of these data requires a powerful computing facility in which the specific state of the art software under heavy continuous development can be easily installed and updated. That makes this case a perfect candidate for a cloud infrastructure which adds the advantages of an on demand, flexible solution. We present our approach to the calibration of LOFAR data using Ibercloud, the cloud infrastructure provided by Ibergrid. With the calibration work-flow adapted to the cloud, we can explore calibration strategies for the SKA and show how private or commercial cloud infrastructures (Ibercloud, Amazon EC2, Google Compute Engine, etc.) can help to solve the problems with big datasets that will be prevalent in the future of astronomy.

Potential Impact of Global Navigation Satellite Services on Total Power HI Intensity Mapping Surveys

NASA Astrophysics Data System (ADS)

Harper, Stuart E.; Dickinson, Clive

2018-06-01

Future total-power single-dish HI intensity mapping (HI IM) surveys have the potential to provide unprecedented insight into late time (z < 1) cosmology that are competitive with Stage IV dark energy surveys. However, redshifts between 0 < z < 0.2 lie within the transmission bands of global navigation satellite services (GNSS), and even at higher redshifts out-of-band leakage from GNSS satellites may be problematic. We estimate the impact of GNSS satellites on future single-dish HI IM surveys using realistic estimates of both the total power and spectral structure of GNSS signals convolved with a model SKA beam. Using a model of the SKA phase one array with 200 dishes we simulate a HI IM survey covering 30000 sq. deg. of sky. We compare the integrated GNSS emission on the sky with the expected HI signal. It is found that for frequencies >950 MHz the emission from GNSS satellites will exceed the expected HI signal for all angular scales to which the SKA is sensitive when operating in single-dish mode.

A generalized measurement equation and van Cittert-Zernike theorem for wide-field radio astronomical interferometry

NASA Astrophysics Data System (ADS)

Carozzi, T. D.; Woan, G.

2009-05-01

We derive a generalized van Cittert-Zernike (vC-Z) theorem for radio astronomy that is valid for partially polarized sources over an arbitrarily wide field of view (FoV). The classical vC-Z theorem is the theoretical foundation of radio astronomical interferometry, and its application is the basis of interferometric imaging. Existing generalized vC-Z theorems in radio astronomy assume, however, either paraxiality (narrow FoV) or scalar (unpolarized) sources. Our theorem uses neither of these assumptions, which are seldom fulfiled in practice in radio astronomy, and treats the full electromagnetic field. To handle wide, partially polarized fields, we extend the two-dimensional (2D) electric field (Jones vector) formalism of the standard `Measurement Equation' (ME) of radio astronomical interferometry to the full three-dimensional (3D) formalism developed in optical coherence theory. The resulting vC-Z theorem enables full-sky imaging in a single telescope pointing, and imaging based not only on standard dual-polarized interferometers (that measure 2D electric fields) but also electric tripoles and electromagnetic vector-sensor interferometers. We show that the standard 2D ME is easily obtained from our formalism in the case of dual-polarized antenna element interferometers. We also exploit an extended 2D ME to determine that dual-polarized interferometers can have polarimetric aberrations at the edges of a wide FoV. Our vC-Z theorem is particularly relevant to proposed, and recently developed, wide FoV interferometers such as Low Frequency Array (LOFAR) and Square Kilometer Array (SKA), for which direction-dependent effects will be important.

Prospects of Detecting HI using Redshifted 21-cm Radiation at z˜3

NASA Astrophysics Data System (ADS)

Gehlot, Bharat Kumar; Bagla, J. S.

2017-03-01

Distribution of cold gas in the post-reionization era provides an important link between distribution of galaxies and the process of star formation. Redshifted 21-cm radiation from the hyperfine transition of neutral hydrogen allows us to probe the neutral component of cold gas, most of which is to be found in the interstellar medium of galaxies. Existing and upcoming radio telescopes can probe the large scale distribution of neutral hydrogen via HI intensity mapping. In this paper, we use an estimate of the HI power spectrum derived using an ansatz to compute the expected signal from the large scale HI distribution at z˜3. We find that the scale dependence of bias at small scales makes a significant difference to the expected signal even at large angular scales. We compare the predicted signal strength with the sensitivity of radio telescopes that can observe such radiation and calculate the observation time required for detecting neutral hydrogen at these redshifts. We find that OWFA (Ooty Wide Field Array) offers the best possibility to detect neutral hydrogen at z˜3 before the SKA (Square Kilometer Array) becomes operational. We find that the OWFA should be able to make a 3 σ or a more significant detection in 2000 hours of observations at several angular scales. Calculations done using the Fisher matrix approach indicate that a 5 σ detection of the binned HI power spectrum via measurement of the amplitude of the HI power spectrum is possible in 1000 h (Sarkar et al. 2017).

Using low-frequency pulsar observations to study the 3-D structure of the Galactic magnetic field

NASA Astrophysics Data System (ADS)

Sobey, C.; LOFAR Collaboration; MWA Collaboration

2018-05-01

The Galactic magnetic field (GMF) plays a role in many astrophysical processes and is a significant foreground to cosmological signals, such as the Epoch of Reionization (EoR), but is not yet well understood. Dispersion and Faraday rotation measurements (DMs and RMs, respectively) towards a large number of pulsars provide an efficient method to probe the three-dimensional structure of the GMF. Low-frequency polarisation observations with large fractional bandwidth can be used to measure precise DMs and RMs. This is demonstrated by a catalogue of RMs (corrected for ionospheric Faraday rotation) from the Low Frequency Array (LOFAR), with a growing complementary catalogue in the southern hemisphere from the Murchison Widefield Array (MWA). These data further our knowledge of the three-dimensional GMF, particularly towards the Galactic halo. Recently constructed or upgraded pathfinder and precursor telescopes, such as LOFAR and the MWA, have reinvigorated low-frequency science and represent progress towards the construction of the Square Kilometre Array (SKA), which will make significant advancements in studies of astrophysical magnetic fields in the future. A key science driver for the SKA-Low is to study the EoR, for which pulsar and polarisation data can provide valuable insights in terms of Galactic foreground conditions.

S-ProvFlow: provenance model and tools for scalable and adaptive analysis pipelines in geoscience.

NASA Astrophysics Data System (ADS)

Spinuso, A.; Mihajlovski, A.; Atkinson, M.; Filgueira, R.; Klampanos, I.; Sanchez, S.

2017-12-01

The reproducibility of scientific findings is essential to improve the quality and application of modern data-driven research. Delivering such reproducibility is challenging in the context of systems handling large data-streams with sophisticated computational methods. Similarly, the SKA (Square Kilometer Array) will collect an unprecedented volume of radio-wave signals that will have to be reduced and transformed into derived products, with impact on space-weather research. This highlights the importance of having cross-disciplines mechanisms at the producer's side that rely on usable lineage data to support validation and traceability of the new artifacts. To be informative, provenance has to describe each methods' abstractions and their implementation as mappings onto distributed platforms and their concurrent execution, capturing relevant internal dependencies at runtime. Producers and intelligent toolsets should be able to exploit the produced provenance, steering real-time monitoring activities and inferring adaptations of methods at runtime.We present a model of provenance (S-PROV) that extends W3C PROV and ProvONE, broadening coverage of provenance to aspects related to distribution, scale-up and steering of stateful streaming operators in analytic pipelines. This is supported by a technical framework for tuneable and actionable lineage, ensuring its relevance to the users' interests, fostering its rapid exploitation to facilitate research practices. By applying concepts such as provenance typing and profiling, users define rules to capture common provenance patterns and activate selective controls based on domain-metadata. The traces are recorded in a document-store with index optimisation and a web API serves advanced interactive tools (S-ProvFlow, https://github.com/KNMI/s-provenance). These allow different classes of consumers to rapidly explore the provenance data. The system, which contributes to the SKA-Link initiative, within technology and knowledge transfer events, will be discussed in the context of an existing data-intensive service for seismology (VERCE), and the newly funded project DARE - Delivering Agile Research Excellence. A generic solution for extreme data and methods in geosciences that domain experts can understand, change and use effectively.

Multiple-Beam Detection of Fast Transient Radio Sources

NASA Technical Reports Server (NTRS)

Thompson, David R.; Wagstaff, Kiri L.; Majid, Walid A.

2011-01-01

A method has been designed for using multiple independent stations to discriminate fast transient radio sources from local anomalies, such as antenna noise or radio frequency interference (RFI). This can improve the sensitivity of incoherent detection for geographically separated stations such as the very long baseline array (VLBA), the future square kilometer array (SKA), or any other coincident observations by multiple separated receivers. The transients are short, broadband pulses of radio energy, often just a few milliseconds long, emitted by a variety of exotic astronomical phenomena. They generally represent rare, high-energy events making them of great scientific value. For RFI-robust adaptive detection of transients, using multiple stations, a family of algorithms has been developed. The technique exploits the fact that the separated stations constitute statistically independent samples of the target. This can be used to adaptively ignore RFI events for superior sensitivity. If the antenna signals are independent and identically distributed (IID), then RFI events are simply outlier data points that can be removed through robust estimation such as a trimmed or Winsorized estimator. The alternative "trimmed" estimator is considered, which excises the strongest n signals from the list of short-beamed intensities. Because local RFI is independent at each antenna, this interference is unlikely to occur at many antennas on the same step. Trimming the strongest signals provides robustness to RFI that can theoretically outperform even the detection performance of the same number of antennas at a single site. This algorithm requires sorting the signals at each time step and dispersion measure, an operation that is computationally tractable for existing array sizes. An alternative uses the various stations to form an ensemble estimate of the conditional density function (CDF) evaluated at each time step. Both methods outperform standard detection strategies on a test sequence of VLBA data, and both are efficient enough for deployment in real-time, online transient detection applications.

Radio weak lensing shear measurement in the visibility domain - I. Methodology

NASA Astrophysics Data System (ADS)

Rivi, M.; Miller, L.; Makhathini, S.; Abdalla, F. B.

2016-12-01

The high sensitivity of the new generation of radio telescopes such as the Square Kilometre Array (SKA) will allow cosmological weak lensing measurements at radio wavelengths that are competitive with optical surveys. We present an adaptation to radio data of lensfit, a method for galaxy shape measurement originally developed and used for optical weak lensing surveys. This likelihood method uses an analytical galaxy model and makes a Bayesian marginalization of the likelihood over uninteresting parameters. It has the feature of working directly in the visibility domain, which is the natural approach to adopt with radio interferometer data, avoiding systematics introduced by the imaging process. As a proof of concept, we provide results for visibility simulations of individual galaxies with flux density S ≥ 10 μJy at the phase centre of the proposed SKA1-MID baseline configuration, adopting 12 frequency channels in the band 950-1190 MHz. Weak lensing shear measurements from a population of galaxies with realistic flux and scalelength distributions are obtained after natural gridding of the raw visibilities. Shear measurements are expected to be affected by `noise bias': we estimate the bias in the method as a function of signal-to-noise ratio (SNR). We obtain additive and multiplicative bias values that are comparable to SKA1 requirements for SNR > 18 and SNR > 30, respectively. The multiplicative bias for SNR >10 is comparable to that found in ground-based optical surveys such as CFHTLenS, and we anticipate that similar shear measurement calibration strategies to those used for optical surveys may be used to good effect in the analysis of SKA radio interferometer data.

Mulibrey nanism: Two novel mutations in a child identified by Array CGH and DNA sequencing.

PubMed

Mozzillo, Enza; Cozzolino, Carla; Genesio, Rita; Melis, Daniela; Frisso, Giulia; Orrico, Ada; Lombardo, Barbara; Fattorusso, Valentina; Discepolo, Valentina; Della Casa, Roberto; Simonelli, Francesca; Nitsch, Lucio; Salvatore, Francesco; Franzese, Adriana

2016-08-01

In childhood, several rare genetic diseases have overlapping symptoms and signs, including those regarding growth alterations, thus the differential diagnosis is sometimes difficult. The proband, aged 3 years, was suspected to have Silver-Russel syndrome because of intrauterine growth retardation, postnatal growth retardation, typical facial dysmorphic features, macrocephaly, body asymmetry, and bilateral fifth finger clinodactyly. Other features were left atrial and ventricular enlargement and patent foramen ovale. Total X-ray skeleton showed hypoplasia of the twelfth rib bilaterally and of the coccyx, slender long bones with thick cortex, and narrow medullary channels. The genetic investigation did not confirm Silver-Russel syndrome. At the age of 5 the patient developed an additional sign: hepatomegaly. Array CGH revealed a 147 kb deletion (involving TRIM 37 and SKA2 genes) on one allele of chromosome 17, inherited from his mother. These results suggested Mulibrey nanism. The clinical features were found to fit this hypothesis. Sequencing of the TRIM 37 gene showed a single base change at a splicing locus, inherited from his father that provoked a truncated protein. The combined use of Array CGH and DNA sequencing confirmed diagnosis of Mulibrey nanism. The large deletion involving the SKA2 gene, along with the increased frequency of malignant tumours in mulibrey patients, suggests closed monitoring for cancer of our patient and his mother. Array CGH should be performed as first tier test in all infants with multiple anomalies. The clinician should reconsider the clinical features when the genetics suggests this. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Pulsar Observations with Radio Telescope FAST

NASA Astrophysics Data System (ADS)

Nan, Ren-Dong; Wang, Qi-Ming; Zhu, Li-Chun; Zhu, Wen-Bai; Jin, Cheng-Jin; Gan, Heng-Qian

2006-12-01

FAST, Five hundred meter Aperture Spherical Telescope, is the Chinese effort for the international project SKA, Square Kilometer Array. An innovative engineering concept and design pave a new road to realizing huge single dish in the most effective way. Three outstanding features of the telescope are the unique karst depressions as the sites, the active main reflector which corrects spherical aberration on the ground to achieve full polarization and wide band without involving complex feed system, and the light focus cabin driven by cables and servomechanism plus a parallel robot as secondary adjustable system to carry the most precise parts of the receivers. Besides a general coverage of those critical technologies involved in FAST concept, the progresses in demonstrating model being constructed at the Miyun Radio Observatory of the NAOC is introduced. Being the most sensitive radio telescope, FAST will enable astronomers to jumpstart many of science goals, for example, the natural hydrogen line surveying in distant galaxies, looking for the first generation of shining objects, hearing the possible signal from other civilizations, etc. Among these subjects, the most striking one could be pulsar study. Large scale survey by FAST will not only improve the statistics of the pulsar population, but also may offer us a good fortune to pick up more of the most exotic, even unknown types like a sub-millisecond pulsar or a neutron star -- black hole binary as the telescope is put into operation.

Definitive test of the Rh = ct universe using redshift drift

NASA Astrophysics Data System (ADS)

Melia, Fulvio

2016-11-01

The redshift drift of objects moving in the Hubble flow has been proposed as a powerful model-independent probe of the underlying cosmology. A measurement of the first- and second-order redshift derivatives appears to be well within the reach of upcoming surveys using as the Extremely Large Telescope high resolution spectrometer (ELT-HIRES) and the Square Kilometer Phase 2 Array (SKA). Here we show that an unambiguous prediction of the Rh = ct cosmology is zero drift at all redshifts, contrasting sharply with all other models in which the expansion rate is variable. For example, multiyear monitoring of sources at redshift z = 5 with the ELT-HIRES is expected to show a velocity shift Δv = -15 cm s-1 yr-1 due to the redshift drift in Planck ΛCDM, while Δv = 0 cm s-1 yr-1 in Rh = ct. With an anticipated ELT-HIRES measurement error of ±5 cm s-1 yr-1 after 5 yr, these upcoming redshift drift measurements might therefore be able to differentiate between Rh = ct and Planck ΛCDM at ˜3σ, assuming that any possible source evolution is well understood. Such a result would provide the strongest evidence yet in favour of the Rh = ct cosmology. With a 20-yr baseline, these observations could favour one of these models over the other at better than 5σ.

Application of Adaptive Beamforming to Signal Observations at the Mt. Meron Array, Israel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harris, D. B.

2010-06-07

The Mt. Meron array consists of 16 stations spanning an aperture of 3-4 kilometers in northern Israel. The array is situated in a region of substantial topographic relief, and is surrounded by settlements at close range (Figure 1). Consequently the level of noise at the array is high, which requires efforts at mitigation if distant regional events of moderate magnitude are to be observed. This note describes an initial application of two classic adaptive beamforming algorithms to data from the array to observe P waves from 5 events east of the array ranging in distance from 1100- 2150 kilometers.

Radio telescope search for the resonant conversion of cold dark matter axions from the magnetized astrophysical sources

NASA Astrophysics Data System (ADS)

Huang, Fa Peng; Kadota, Kenji; Sekiguchi, Toyokazu; Tashiro, Hiroyuki

2018-06-01

We study the conditions for the adiabatic resonant conversion of the cold dark matter (CDM) axions into photons in the astrophysically sourced strong magnetic fields such as those in the neutron star magnetosphere. We demonstrate the possibility that the forthcoming radio telescopes such as the SKA (Square Kilometre Array) can probe those photon signals from the CDM axions.

Dusty Star Forming Galaxies and Supermassive Black Holes at High Redshifts: In- Situ Coevolution

NASA Astrophysics Data System (ADS)

Mancuso, Claudia

2016-10-01

We have exploited the continuity equation approach and the star-formation timescales derived from the observed 'main sequence' relation (Star Formation Rate vs Stellar Mass), to show that the observed high abundance of galaxies with stellar masses ≥ a few 10^10 M⊙ at redshift z ≥ 4 implies the existence of a galaxy population featuring large star formation rates (SFRs) ψ ≥ 10^2 M⊙ yr^-1 in heavily dust-obscured conditions. These galaxies constitute the high-redshift counterparts of the dusty star-forming population already surveyed for z ≤ 3 in the Far-InfraRed (FIR) band by the Herschel space observatory. We work out specific predictions for the evolution of the corresponding stellar mass and SFR functions out to z ∼10, elucidating that the number density at z ≤ 8 for SFRs ψ ≥ 30 M⊙ yr^-1 cannot be estimated relying on the UltraViolet (UV) luminosity function alone, even when standard corrections for dust extinction based on the UV slope are applied. We compute the number counts and redshift distributions (including galaxy-scale gravitational lensing) of this galaxy population, and show that current data from AzTEC-LABOCA, SCUBA-2 and ALMA-SPT surveys are already digging into it. We substantiate how an observational strategy based on a color preselection in the far-IR or (sub-)mm band with Herschel and SCUBA-2, supplemented by photometric data via on-source observations with ALMA, can allow to reconstruct the bright end of the SFR functions out to z ≤ 8. In parallel, such a challenging task can be managed by exploiting current UV surveys in combination with (sub-)mm observations by ALMA and NIKA2. The same could be done with radio observations by SKA and its precursors. In particular we have worked out predictions for the radio counts of star-forming galaxies down to nJy levels, along with redshift distributions down to the detection limits of the phase 1 Square Kilometer Array MID telescope (SKA1-MID) and of its precursors. To do that we exploited our SFR functions with relations between SFR and radio (synchrotron and free-free) emission. Our results show that the deepest SKA1- MID surveys will detect high-z galaxies with SFRs two orders of magnitude lower compared to Herschel surveys. The highest redshift tails of the distributions at the detection limits of planned SKA1-MID surveys comprise a substantial fraction of strongly lensed galaxies. The SKA1-MID will thus provide a comprehensive view of the star formation history throughout the re-ionization epoch, unaffected by dust extinction. We have also provided specific predictions for the EMU/ASKAP and MIGHTEE/MeerKAT surveys. We finally provide a novel, unifying physical interpretation on the origin, the average shape, the scatter, and the cosmic evolution for the main sequences (MS) of star-forming galaxies and active galactic nuclei at high redshift z ≥ 1. We achieve this goal in a model-independent way by exploiting the redshift-dependent SFR functions, and the deterministic evolutionary tracks for the history of star formation and black hole accretion, gauged on a wealth of multiwavelength observations including the observed Eddington ratio distribution. We further validate these ingredients by showing their consistency with the observed galaxy stellar mass functions and active galactic nucleus (AGN) bolometric luminosity functions at different redshifts via, again, the continuity equation approach. Our analysis of the main sequence for high-redshift galaxies and AGNs highlights that the present data strongly support a scenario of in situ coevolution for star formation and black hole accretion, envisaging these as local, time coordinated processes.

Transient Phenomena: Opportunities for New Discoveries

NASA Technical Reports Server (NTRS)

Lazio, T. Joseph W.

2010-01-01

Known classes of radio wavelength transients range from the nearby (stellar flares and radio pulsars) to the distant Universe (gamma-ray burst afterglows). Hypothesized classes of radio transients include analogs of known objects, such as extrasolar planets emitting Jovian-like radio bursts and giant-pulse emitting pulsars in other galaxies, to the exotic, such as prompt emission from gamma-ray bursts, evaporating black holes and transmitters from other civilizations. Time domain astronomy has been recognized internationally as a means of addressing key scientific questions in astronomy and physics, and pathfinders and Precursors to the Square Kilometre Array (SKA) are beginning to offer a combination of wider fields of view and more wavelength agility than has been possible in the past. These improvements will continue when the SKA itself becomes operational. I illustrate the range of transient phenomena and discuss how the detection and study of radio transients will improve immensely.

Human Ska complex and Ndc80 complex interact to form a load-bearing assembly that strengthens kinetochore–microtubule attachments

PubMed Central

Zelter, Alex; Riffle, Michael; MacCoss, Michael J.; Asbury, Charles L.; Davis, Trisha N.

2018-01-01

Accurate segregation of chromosomes relies on the force-bearing capabilities of the kinetochore to robustly attach chromosomes to dynamic microtubule tips. The human Ska complex and Ndc80 complex are outer-kinetochore components that bind microtubules and are required to fully stabilize kinetochore–microtubule attachments in vivo. While purified Ska complex tracks with disassembling microtubule tips, it remains unclear whether the Ska complex–microtubule interaction is sufficiently strong to make a significant contribution to kinetochore–microtubule coupling. Alternatively, Ska complex might affect kinetochore coupling indirectly, through recruitment of phosphoregulatory factors. Using optical tweezers, we show that the Ska complex itself bears load on microtubule tips, strengthens Ndc80 complex-based tip attachments, and increases the switching dynamics of the attached microtubule tips. Cross-linking mass spectrometry suggests the Ska complex directly binds Ndc80 complex through interactions between the Ska3 unstructured C-terminal region and the coiled-coil regions of each Ndc80 complex subunit. Deletion of the Ska complex microtubule-binding domain or the Ska3 C terminus prevents Ska complex from strengthening Ndc80 complex-based attachments. Together, our results indicate that the Ska complex can directly strengthen the kinetochore–microtubule interface and regulate microtubule tip dynamics by forming an additional connection between the Ndc80 complex and the microtubule. PMID:29487209

DALiuGE: A graph execution framework for harnessing the astronomical data deluge

NASA Astrophysics Data System (ADS)

Wu, C.; Tobar, R.; Vinsen, K.; Wicenec, A.; Pallot, D.; Lao, B.; Wang, R.; An, T.; Boulton, M.; Cooper, I.; Dodson, R.; Dolensky, M.; Mei, Y.; Wang, F.

2017-07-01

The Data Activated Liu Graph Engine - DALiuGE- is an execution framework for processing large astronomical datasets at a scale required by the Square Kilometre Array Phase 1 (SKA1). It includes an interface for expressing complex data reduction pipelines consisting of both datasets and algorithmic components and an implementation run-time to execute such pipelines on distributed resources. By mapping the logical view of a pipeline to its physical realisation, DALiuGE separates the concerns of multiple stakeholders, allowing them to collectively optimise large-scale data processing solutions in a coherent manner. The execution in DALiuGE is data-activated, where each individual data item autonomously triggers the processing on itself. Such decentralisation also makes the execution framework very scalable and flexible, supporting pipeline sizes ranging from less than ten tasks running on a laptop to tens of millions of concurrent tasks on the second fastest supercomputer in the world. DALiuGE has been used in production for reducing interferometry datasets from the Karl E. Jansky Very Large Array and the Mingantu Ultrawide Spectral Radioheliograph; and is being developed as the execution framework prototype for the Science Data Processor (SDP) consortium of the Square Kilometre Array (SKA) telescope. This paper presents a technical overview of DALiuGE and discusses case studies from the CHILES and MUSER projects that use DALiuGE to execute production pipelines. In a companion paper, we provide in-depth analysis of DALiuGE's scalability to very large numbers of tasks on two supercomputing facilities.

Simulations for 21 cm radiation lensing at EoR redshifts

NASA Astrophysics Data System (ADS)

Romeo, Alessandro; Metcalf, Robert Benton; Pourtsidou, Alkistis

2018-02-01

We introduce simulations aimed at assessing how well weak gravitational lensing of 21cm radiation from the Epoch of Reionization (z ˜ 8) can be measured by a Square Kilometre Array (SKA)-like radio telescope. A simulation pipeline has been implemented to study the performance of lensing reconstruction techniques. We show how well the lensing signal can be reconstructed using the 3D quadratic lensing estimator in Fourier space assuming different survey strategies. The numerical code introduced in this work is capable of dealing with issues that cannot be treated analytically such as the discreteness of visibility measurements and the inclusion of a realistic model for the antennas distribution. This paves the way for future numerical studies implementing more realistic re-ionization models, foreground subtraction schemes, and testing the performance of lensing estimators that take into account the non-Gaussian distribution of HI after re-ionization. If multiple frequency channels covering z ˜ 7-11.6 are combined, Phase 1 of SKA-Low should be able to obtain good quality images of the lensing potential with a total resolution of ˜1.6 arcmin. The SKA-Low Phase 2 should be capable of providing images with high fidelity even using data from z ˜ 7.7 to 8.3. We perform tests aimed at evaluating the numerical implementation of the mapping reconstruction. We also discuss the possibility of measuring an accurate lensing power spectrum. Combining data from z ˜ 7 to 11.6 using the SKA2-Low telescope model, we find constraints comparable to sample variance in the range L < 1000, even for survey areas as small as 25 deg2.

Can Radio Telescopes Find Axions?

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2017-08-01

In the search for dark matter, the most commonly accepted candidates are invisible, massive particles commonly referred to as WIMPs. But as time passes and we still havent detected WIMPs, alternative scenarios are becoming more and more appealing. Prime among these is the idea of axions.A Bizarre ParticleThe Italian PVLAS is an example of a laboratory experiment that attempted to confirm the existence of axions. [PVLAS]Axions are a type of particle first proposed in the late 1970s. These theorized particles arose from a new symmetry introduced to solve ongoing problems with the standard model for particle physics, and they were initially predicted to have more than a keV in mass. For this reason, their existence was expected to be quickly confirmed by particle-detector experiments yet no detections were made.Today, after many unsuccessful searches, experiments and theory tell us that if axions exist, their masses must lie between 10-610-3 eV. This is minuscule an electrons mass is around 500,000 eV, and even neutrinos are on the scale of a tenth of an eV!But enough of anything, even something very low-mass, can weigh a lot. If they are real, then axions were likely created in abundance during the Big Bang and unlike heavier particles, they cant decay into anything lighter, so we would expect them all to still be around today. Our universe could therefore be filled with invisible axions, potentially providing an explanation for dark matter in the form of many, many tiny particles.Artists impression of the central core of proposed Square Kilometer Array antennas. [SKA/Swinburne Astronomy Productions]How Do We Find Them?Axions barely interact with ordinary matter and they have no electric charge. One of the few ways we can detect them is with magnetic fields: magnetic fields can change axions to and from photons.While many studies have focused on attempting to detect axions in laboratory experiments, astronomy provides an alternative: we can search for cosmological axions. Now scientists Katharine Kelley and Peter Quinn at ICRAR, University of Western Australia, have explored how we might use next-generation radio telescopes to search for photons that were created by axions interacting with the magnetic fields of our galaxy.Hope for Next-Gen TelescopesPotential axion coupling strengths vs. mass (click for a closer look). The axion mass is thought to lie between a eV and a meV; two theoretical models are shown with dashed lines. The plot shows the sensitivity of the upcoming SKA and its precursors, ASKAP and MEERKAT. [KelleyQuinn 2017]By using a simple galactic halo model and reasonable assumptions for the central galactic magnetic field even taking into account the time dependence of the field Kelley and Quinn estimate the radio-frequency power density that we would observe at Earth from axions being converted to photons within the Milky Ways magnetic field.The authors then compare this signature to the detection capabilities of upcoming radio telescope arrays. They show that the upcoming Square Kilometer Array and its precursors should have the capability to detect signs of axions across large parts of parameter space.Kelley and Quinn conclude that theres good cause for optimism about future radio telescopes ability to detect axions. And if we did succeed in making a detection, it would be a triumph for both particle physics and astrophysics, finally providing an explanation for the universes dark matter.CitationKatharine Kelley and P. J. Quinn 2017 ApJL 845 L4. doi:10.3847/2041-8213/aa808d

Big data challenges for large radio arrays

NASA Astrophysics Data System (ADS)

Jones, D. L.; Wagstaff, K.; Thompson, D. R.; D'Addario, L.; Navarro, R.; Mattmann, C.; Majid, W.; Lazio, J.; Preston, J.; Rebbapragada, U.

2012-03-01

Future large radio astronomy arrays, particularly the Square Kilometre Array (SKA), will be able to generate data at rates far higher than can be analyzed or stored affordably with current practices. This is, by definition, a "big data" problem, and requires an end-to-end solution if future radio arrays are to reach their full scientific potential. Similar data processing, transport, storage, and management challenges face next-generation facilities in many other fields. The Jet Propulsion Laboratory is developing technologies to address big data issues, with an emphasis in three areas: 1) Lower-power digital processing architectures to make highvolume data generation operationally affordable, 2) Date-adaptive machine learning algorithms for real-time analysis (or "data triage") of large data volumes, and 3) Scalable data archive systems that allow efficient data mining and remote user code to run locally where the data are stored.

Expression of Spindle and Kinetochore-Associated Protein 1 Is Associated with Poor Prognosis in Papillary Thyroid Carcinoma

PubMed Central

Dong, Chao; Wang, Xiao-li; Ma, Bin-lin

2015-01-01

Aim. Spindle and kinetochore-associated protein 1 (SKA1) is one subtype of SKA, whose protein can make spindle microtubules attach steadily to the kinetochore in the middle of mitosis. At present, there are fewer researches on the relationship between SKA1 expression and tumor development. Methods. In this study, immunohistochemical analysis was used to determine the expression of SKA1 in papillary thyroid carcinoma (PTC) and adjacent tissues. We used quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analysis to further verify the results. Results. We found that SKA1 expression was significantly higher in PTC tissues than normal adjacent tissues (P < 0.05). There existed a significant correlation among a higher SKA1 expression, including lymphoid node (P = 0.005), clinical stage (P = 0.015), and extrathyroid invasion (P = 0.004). Survival analysis showed high SKA1 expression in PTC patients more likely to relapse after surgery. Conclusion. High SKA1 expression is predictive of poor prognosis of PTC, implying that SKA1 may be a promising new target for targeted therapies for PTC. PMID:26063960

South African Student Constructed Indlebe Radio Telescope

NASA Astrophysics Data System (ADS)

McGruder, Charles H.; MacPherson, Stuart; Janse Van Vuuren, Gary Peter

2017-01-01

The Indlebe Radio Telescope (IRT) is a small transit telescope with a 5 m diameter parabolic reflector working at 21 cm. It was completely constructed by South African (SA) students from the Durban University of Technology (DUT), where it is located. First light occurred on 28 July 2008, when the galactic center, Sagittarius A, was detected. As a contribution to the International Year of Astronomy in 2009, staff members in the Department of Electronic Engineering at DUT in 2006 decided to have their students create a fully functional radio telescope by 2009. The specific project aims are to provide a visible project that could generate interest in science and technology in high school students and to provide a real world system for research in radio astronomy in general and an optimization of low noise radio frequency receiver systems in particular. These aims must be understood in terms of the SA’s government interests in radio astronomy. SA is a partner in the Square Kilometer Array (SKA) project, has constructed the Karoo Array Telescope (KAT) and MeerKat, which is the largest and most sensitive radio telescope in the southern hemisphere. SA and its partners in Africa are investing in the construction of the African Very Long Baseline Interferometry Network (AVN), an array of radio telescopes throughout Africa as an extension of the existing global Very Long Baseline Interferometry Network (VLBI). These projects will allow SA to make significant contributions to astronomy and enable astronomy to contribute to the scientific education and development goals of the country. The IRT sees on a daily basis the transit of Sag A. The transit time is influenced by precession, nutation, polar motion, aberration, celestial pole offset, proper motion, length of the terrestrial day and variable ionospheric refraction. Of these eight factors six are either predictable or measureable. To date neither celestial pole offset nor variable ionospheric refraction are predicable. Currently, we are comparing the observed transit times of Sag A with the calculable predications in order to obtain information over these two factors, with a view to better understanding them.

Taming the Data Deluge to Unravel the Mysteries of the Universe

NASA Astrophysics Data System (ADS)

Johnston-Hollitt, M.

2017-04-01

Modern Astrophysics is one of the most data intensive research fields in the world and is driving many of the required innovations in the "big data" space. Foremost in astronomy in terms of data generation is radio astronomy, and in the last decade an increase in global interest and investment in the field had led to a large number of new or upgraded facilities which are each currently generating petabytes of data per annum. The peak of this so-called 'radio renaissance' will be the Square Kilometre Array (SKA) - a global observatory designed to uncover the mysteries of the Universe. The SKA will create the highest resolution, fastest frame rate movie of the evolving Universe ever and in doing so will generate 160 terrabytes of data a second, or close to 5 zettabytes of data per annum. Furthermore, due to the extreme faintness of extraterrestrial radio signals, the telescope elements for the SKA must be located in radio quite parts of the world with very low population density. Thus the project aims to build the most data intensive scientific experiment ever, in some of the most remote places on Earth. Generating and serving scientific data products of this scale to a global community of researchers from remote locations is just the first of the "big data" challenges the project faces. Coordination of a global network of tiered data resources will be required along with software tools to exploit the vast sea of results generated. In fact, to fully realize the enormous scientific potential of this project, we will need not only better data distribution and coordination mechanisms, but also improved algorithms, artificial intelligence and ontologies to extract knowledge in an automated way at a scale not yet attempted in science. In this keynote I will present an overview of the SKA project, outline the "big data" challenges the project faces and discuss some of the approaches we are taking to tame the astronomical data deluge we face.

The Square Kilometre Array: a challenge for 2020 to which Spain can contribute in 2012

NASA Astrophysics Data System (ADS)

Verdes-Montenegro, L.; Dios Santander-Vela, J. D.

2013-05-01

The SKA, composed of several hundreds of three different types of antennas with separations up to 3.000 km, and up to 200 square degrees field of view, will be the largest, most sensitive radio telescope ever built. It will be able to provide fundamental answers in areas such as the dark era, when gas in galaxies was first turned into stars and the first black holes formed, star formation in nearby galaxies from stellar birth to death, faint extragalactic emission, magnetism in galaxies, extrasolar planets, or confrontation of Einstein predictions with pulsars and black hole observations. The technological challenges involved offer an unprecedented opportunity to collaborate in the development of hardware and software technologies. The energy requirements of the SKA provide an opportunity to accelerate technology development in scalable renewable energy generation, distribution, storage and demand monitoring and reduction. Data transport will reach over a hundred times the current global internet traffic data rates, delivering as much data as the full World Wide Web. Processing this data torrent in real time will require high-performance distributed computing as well as data storage and innovative retrieval technologies in the exascale. This way to do science, based on data-intensive interdisciplinary cooperation, is the base of the concept of e-Science, which necessarily includes outreach as an indissoluble part of the knowledge-based human progress. The scientific and technological challenges and opportunities that SKA can bring to the Spanish community will be described in this talk.

Small-scale effects of thermal inflation on halo abundance at high-z, galaxy substructure abundance, and 21-cm power spectrum

NASA Astrophysics Data System (ADS)

Hong, Sungwook E.; Zoe, Heeseung; Ahn, Kyungjin

2017-11-01

We study the impact of thermal inflation on the formation of cosmological structures and present astrophysical observables which can be used to constrain and possibly probe the thermal inflation scenario. These are dark matter halo abundance at high redshifts, satellite galaxy abundance in the Milky Way, and fluctuation in the 21-cm radiation background before the epoch of reionization. The thermal inflation scenario leaves a characteristic signature on the matter power spectrum by boosting the amplitude at a specific wave number determined by the number of e-foldings during thermal inflation (N_{bc}), and strongly suppressing the amplitude for modes at smaller scales. For a reasonable range of parameter space, one of the consequences is the suppression of minihalo formation at high redshifts and that of satellite galaxies in the Milky Way. While this effect is substantial, it is degenerate with other cosmological or astrophysical effects. The power spectrum of the 21-cm background probes this impact more directly, and its observation may be the best way to constrain the thermal inflation scenario due to the characteristic signature in the power spectrum. The Square Kilometre Array (SKA) in phase 1 (SKA1) has sensitivity large enough to achieve this goal for models with N_{bc} ≳ 26 if a 10000-hr observation is performed. The final phase SKA, with anticipated sensitivity about an order of magnitude higher, seems more promising and will cover a wider parameter space.

Genetic programming applied to RFI mitigation in radio astronomy

NASA Astrophysics Data System (ADS)

Staats, K.

2016-12-01

Genetic Programming is a type of machine learning that employs a stochastic search of a solutions space, genetic operators, a fitness function, and multiple generations of evolved programs to resolve a user-defined task, such as the classification of data. At the time of this research, the application of machine learning to radio astronomy was relatively new, with a limited number of publications on the subject. Genetic Programming had never been applied, and as such, was a novel approach to this challenging arena. Foundational to this body of research, the application Karoo GP was developed in the programming language Python following the fundamentals of tree-based Genetic Programming described in "A Field Guide to Genetic Programming" by Poli, et al. Karoo GP was tasked with the classification of data points as signal or radio frequency interference (RFI) generated by instruments and machinery which makes challenging astronomers' ability to discern the desired targets. The training data was derived from the output of an observation run of the KAT-7 radio telescope array built by the South African Square Kilometre Array (SKA-SA). Karoo GP, kNN, and SVM were comparatively employed, the outcome of which provided noteworthy correlations between input parameters, the complexity of the evolved hypotheses, and performance of raw data versus engineered features. This dissertation includes description of novel approaches to GP, such as upper and lower limits to the size of syntax trees, an auto-scaling multiclass classifier, and a Numpy array element manager. In addition to the research conducted at the SKA-SA, it is described how Karoo GP was applied to fine-tuning parameters of a weather prediction model at the South African Astronomical Observatory (SAAO), to glitch classification at the Laser Interferometer Gravitational-wave Observatory (LIGO), and to astro-particle physics at The Ohio State University.

The Breakthrough Listen Initiative and the Future of the Search for Intelligent Life

NASA Astrophysics Data System (ADS)

Enriquez, J. Emilio; Siemion, Andrew; Falcke, Heino; Croft, Steve; DeBoer, David R.; Gajjar, Vishal; Hickish, Jack; Isaacson, Howard T.; Lebofsky, Matt; MacMahon, David; Price, Danny C.; Tellis, Nate; Werthimer, Dan; ter Veen, Sander; Garrett, Michael A.; Hellbourg, Greg

2017-01-01

Unprecedented recent results in the fields of exoplanets and astrobiology have dramatically increased the interest in the potential existence of intelligent life elsewhere in the galaxy. Additionally, the capabilities of modern Searches for Extraterrestrial Intelligence (SETI) have increased tremendously. Much of this improvement is due to the ongoing development of wide bandwidth radio instruments and the Moore’s Law increase in computational power over the previous decades. Together, these instrumentation improvements allow for narrow band signal searches of billions of frequency channels at once.The Breakthrough Listen Initiative (BL) was launched on July 20, 2015 at the Royal Society in London, UK with a charge to conduct the most comprehensive and sensitive search for advanced life in humanity’s history. Here we detail important milestones achieved during the first year of the program, describe the key BL SETI surveys and briefly describe current facilities, including the Green Bank Telescope, the Automated Planet Finder and the Parkes Observatory.Complementary to the BL initiative (at a smaller scale), pioneering SETI work at low radio frequencies (20-250 MHz) is being undertaken with the LOw Frequency ARray (LOFAR). This program uses simple fixed-stationary antennas and multiple phased-array beams formed in a supercomputer to search many targets at once and will lay the groundwork for future searches with SKA1-low and mid frequency aperture array pathfinders. We will present the results of a volume complete sample of nearby stars (< 5pc) observed with LOFAR, searching for drifting narrow band signals with expected Doppler drifts covering a wide range of potential transmitter host planets.We conclude with a brief view towards future SETI searches with upcoming next-generation radio facilities such as SKA and ngVLA.

Tracking interstellar space weather toward timing-array millisecond pulsars

NASA Astrophysics Data System (ADS)

Bhat, N. D. R.; Ord, S. M.; Tremblay, S. E.; Shannon, R. M.; van Straten, W.; Kaplan, D. L.; Macquart, J.-P.; Kirsten, F.

2016-07-01

Recent LIGO detection of milli-Hertz gravitational wave (GW) signals from a black-hole merger event has further reinforced the important role of Pulsar timing array (PTA) experiments in the GW astronomy. PTAs exploit the clock-like stability of fast-spinning millisecond pulsars (MSPs) to make a direct detection of ultra-low frequency (nano-Hertz) gravitational waves. The science enabled by PTAs is thus highly complementary to that possible by LIGO-like detectors. PTAs are also a key science objective for the SKA. PTA efforts over the past few years suggest that interstellar propagation effects on pulsar signals may ultimately limit the detection sensitivity of PTAs unless they are accurately measured and corrected for in timing measurements. Interstellar medium (ISM) effects are much stronger at lower radio frequencies and therefore the MWA presents an exciting and unique opportunity to calibrate interstellar propagation delays. This will potentially lead to enhanced sensitivity and scientific impact of PTA projects. Since our first demonstration of ability to form a coherent (tied-array) beam by reprocessing the recorded VCS data (Bhat et al. 2016), we have successfully ported the full processing chain to the Galaxy cluster of Pawsey and demonstrated the value of high-sensitivity multi-band pulsar observations that are now possible with the MWA. Here we propose further observations of two most promising PTA pulsars that will be nightly objects in the 2016B period. Our main science driver is to characterise the nature of the turbulent ISM through high-quality scintillation and dispersion studies including the investigation of chromatic (frequency-dependent) DMs. Success of these efforts will define the breadth and scope of a more ambitious program in the future, bringing in a new science niche for the MWA and SKA-low.

On post-SKA radio astronomy

NASA Astrophysics Data System (ADS)

Parijskij, Yuri; Chernenkov, Vladimir

It is suggested that the development of the SKA will drastically change the face of radio astronomy in the 21st Century. A FAST-style SKA would admit observations of low contrast features, and would be the best design for studying the `dark ages' of the Universe (x>> 1) where sub-arcmin total power instruments can usefully be employed. To date there have been no proposals for post-SKA, billion square-metra instruments; we speculate that mobile communication systems can be used. In the very distant future, SKA multi-beam systems could be used to collect signals reflected by Solar system bodies such as the asteroid belt.

The Engineering Development Array: A Low Frequency Radio Telescope Utilising SKA Precursor Technology

NASA Astrophysics Data System (ADS)

Wayth, Randall; Sokolowski, Marcin; Booler, Tom; Crosse, Brian; Emrich, David; Grootjans, Robert; Hall, Peter J.; Horsley, Luke; Juswardy, Budi; Kenney, David; Steele, Kim; Sutinjo, Adrian; Tingay, Steven J.; Ung, Daniel; Walker, Mia; Williams, Andrew; Beardsley, A.; Franzen, T. M. O.; Johnston-Hollitt, M.; Kaplan, D. L.; Morales, M. F.; Pallot, D.; Trott, C. M.; Wu, C.

2017-08-01

We describe the design and performance of the Engineering Development Array, which is a low-frequency radio telescope comprising 256 dual-polarisation dipole antennas working as a phased array. The Engineering Development Array was conceived of, developed, and deployed in just 18 months via re-use of Square Kilometre Array precursor technology and expertise, specifically from the Murchison Widefield Array radio telescope. Using drift scans and a model for the sky brightness temperature at low frequencies, we have derived the Engineering Development Array's receiver temperature as a function of frequency. The Engineering Development Array is shown to be sky-noise limited over most of the frequency range measured between 60 and 240 MHz. By using the Engineering Development Array in interferometric mode with the Murchison Widefield Array, we used calibrated visibilities to measure the absolute sensitivity of the array. The measured array sensitivity matches very well with a model based on the array layout and measured receiver temperature. The results demonstrate the practicality and feasibility of using Murchison Widefield Array-style precursor technology for Square Kilometre Array-scale stations. The modular architecture of the Engineering Development Array allows upgrades to the array to be rolled out in a staged approach. Future improvements to the Engineering Development Array include replacing the second stage beamformer with a fully digital system, and to transition to using RF-over-fibre for the signal output from first stage beamformers.

Congressing kinetochores progressively load Ska complexes to prevent force-dependent detachment

PubMed Central

Auckland, Philip; Clarke, Nicholas I.

2017-01-01

Kinetochores mediate chromosome congression by either sliding along the lattice of spindle microtubules or forming end-on attachments to their depolymerizing plus-ends. By following the fates of individual kinetochores as they congress in live cells, we reveal that the Ska complex is required for a distinct substep of the depolymerization-coupled pulling mechanism. Ska depletion increases the frequency of naturally occurring, force-dependent P kinetochore detachment events, while being dispensable for the initial biorientation and movement of chromosomes. In unperturbed cells, these release events are followed by reattachment and successful congression, whereas in Ska-depleted cells, detached kinetochores remain in a futile reattachment/detachment cycle that prevents congression. We further find that Ska is progressively loaded onto bioriented kinetochore pairs as they congress. We thus propose a model in which kinetochores mature through Ska complex recruitment and that this is required for improved load-bearing capacity and silencing of the spindle assembly checkpoint. PMID:28495837

Vascular Reactivity Profile of Novel KCa3.1-Selective Positive-Gating Modulators in the Coronary Vascular Bed

PubMed Central

Oliván-Viguera, Aida; Valero, Marta Sofía; Pinilla, Estéfano; Amor, Sara; García-Villalón, Ángel Luis; Coleman, Nichole; Laría, Celia; Calvín-Tienza, Víctor; García-Otín, Ángel-Luis; Fernández-Fernández, José M.; Murillo, Ma Divina; Gálvez, José A.; Díaz-de-Villegas, María D.; Badorrey, Ramón; Simonsen, Ulf; Rivera, Luis; Wulff, Heike; Köhler, Ralf

2017-01-01

Opening of intermediate-conductance calcium-activated potassium channels (KCa3.1) produces membrane hyperpolarization in the vascular endothelium. Here, we studied the ability of two new KCa3.1-selective positive-gating modulators, SKA-111 and SKA-121, to (1) evoke porcine endothelial cell KCa3.1 membrane hyperpolarization, (2) induce endothelium-dependent and, particularly, endothelium-derived hyperpolarization (EDH)-type relaxation in porcine coronary arteries (PCA) and (3) influence coronary artery tone in isolated rat hearts. In whole-cell patch-clamp experiments on endothelial cells of PCA (PCAEC), KCa currents evoked by bradykinin (BK) were potentiated ≈7-fold by either SKA-111 or SKA-121 (both at 1 μM) and were blocked by a KCa3.1 blocker, TRAM-34. In membrane potential measurements, SKA-111 and SKA-121 augmented bradykinin-induced hyperpolarization. Isometric tension measurements in large- and small-calibre PCA showed that SKA-111 and SKA-121 potentiated endothelium-dependent relaxation with intact NO synthesis and EDH-type relaxation to BK by ≈2-fold. Potentiation of the BK response was prevented by KCa3.1 inhibition. In Langendorff-perfused rat hearts, SKA-111 potentiated coronary vasodilation elicited by BK. In conclusion, our data show that positive-gating modulation of KCa3.1 channels improves BK-induced membrane hyperpolarization and endothelium-dependent relaxation in small and large PCA as well as in the coronary circulation of rats. Positive-gating modulators of KCa3.1 could be therapeutically useful to improve coronary blood flow and counteract impaired coronary endothelial dysfunction in cardiovascular disease. PMID:26821335

SKA2 Methylation is Involved in Cortisol Stress Reactivity and Predicts the Development of Post-Traumatic Stress Disorder (PTSD) After Military Deployment

PubMed Central

Boks, Marco P; Rutten, Bart P F; Geuze, Elbert; Houtepen, Lotte C; Vermetten, Eric; Kaminsky, Zachary; Vinkers, Christiaan H

2016-01-01

Genomic variation in the SKA2 gene has recently been identified as a promising suicide biomarker. In light of its role in glucocorticoid receptor transactivation, we investigated whether SKA2 DNA methylation influences cortisol stress reactivity and is involved in the development of post-traumatic stress disorder (PTSD). Increased SKA2 methylation was significantly associated with lower cortisol stress reactivity in 85 healthy individuals exposed to the Trier Social Stress Test (B=−173.40, t=−2.324, p-value=0.023). Next, we observed that longitudinal decreases in SKA2 methylation after deployment were associated with the emergence of post-deployment PTSD symptoms in a Dutch military cohort (N=93; B=−0.054, t=−3.706, p-value=3.66 × 10−4). In contrast, exposure to traumatic stress during deployment by itself resulted in longitudinal increases in SKA2 methylation (B=0.037, t=4.173, p-value=6.98 × 10−5). Using pre-deployment SKA2 methylation levels and childhood trauma exposure, we found that the previously published suicide prediction rule significantly predicted post-deployment PTSD symptoms (AUC=0.66, 95% CI: 0.53–0.79) with an optimal sensitivity of 0.81 and specificity of 0.91. Permutation analysis using random methylation loci supported these findings. Together, these data establish the importance of SKA2 for cortisol stress responsivity and the development of PTSD and provide further evidence that SKA2 is a promising biomarker for stress-related disorders including PTSD. PMID:26361058

SKA2 Methylation is Involved in Cortisol Stress Reactivity and Predicts the Development of Post-Traumatic Stress Disorder (PTSD) After Military Deployment.

PubMed

Boks, Marco P; Rutten, Bart P F; Geuze, Elbert; Houtepen, Lotte C; Vermetten, Eric; Kaminsky, Zachary; Vinkers, Christiaan H

2016-04-01

Genomic variation in the SKA2 gene has recently been identified as a promising suicide biomarker. In light of its role in glucocorticoid receptor transactivation, we investigated whether SKA2 DNA methylation influences cortisol stress reactivity and is involved in the development of post-traumatic stress disorder (PTSD). Increased SKA2 methylation was significantly associated with lower cortisol stress reactivity in 85 healthy individuals exposed to the Trier Social Stress Test (B=-173.40, t=-2.324, p-value=0.023). Next, we observed that longitudinal decreases in SKA2 methylation after deployment were associated with the emergence of post-deployment PTSD symptoms in a Dutch military cohort (N=93; B=-0.054, t=-3.706, p-value=3.66 × 10(-4)). In contrast, exposure to traumatic stress during deployment by itself resulted in longitudinal increases in SKA2 methylation (B=0.037, t=4.173, p-value=6.98 × 10(-5)). Using pre-deployment SKA2 methylation levels and childhood trauma exposure, we found that the previously published suicide prediction rule significantly predicted post-deployment PTSD symptoms (AUC=0.66, 95% CI: 0.53-0.79) with an optimal sensitivity of 0.81 and specificity of 0.91. Permutation analysis using random methylation loci supported these findings. Together, these data establish the importance of SKA2 for cortisol stress responsivity and the development of PTSD and provide further evidence that SKA2 is a promising biomarker for stress-related disorders including PTSD.

Hydrogen Epoch of Reionization Array (HERA)

NASA Astrophysics Data System (ADS)

DeBoer, David R.; HERA

2015-01-01

The Hydrogen Epoch of Reionization Arrays (HERA - reionization.org) roadmap uses the unique properties of the neutral hydrogen (HI) 21cm line to probe our cosmic dawn: from the birth of the first stars and black holes, through the full reionization of the primordial intergalactic medium (IGM). HERA is a collaboration between the Precision Array Probing the Epoch of Reionization (PAPER - eor.berkeley.edu), the US-based Murchison Widefield Array (MWA - mwatelescope.org), and MIT Epoch of Reionization (MITEOR) teams along with the South African SKA-SA, University of KwaZulu Natal and the University of Cambridge Cavendish Laborabory. HERA has recently been awarded a National Science Foundation Mid-Scale Innovation Program grant to begin the next phase.HERA leverages the operation of the PAPER and MWA telescopes to explore techniques and designs required to detect the primordial HI signal in the presence of systematics and radio continuum foreground emission some four orders of magnitude brighter. With this understanding, we are now able to remove foregrounds to the limits of our sensitivity, culminating in the first physically meaningful upper limits. A redundant calibration algorithm from MITEOR improves the sensitivity of the approach.Building on this, the next stage of HERA incorporates a 14m diameter antenna element that is optimized both for sensitivity and for minimizing foreground systematics. Arranging these elements in a compact hexagonal grid yields an array that facilitates calibration, leverages proven foreground removal techniques, and is scalable to large collecting areas. HERA will be located in the radio quiet environment of the SKA site in the Karoo region of South Africa (where PAPER is currently located). It will have a sensitivity close to two orders of magnitude better than PAPER and the MWA to ensure a robust detection. With its sensitivity and broader frequency coverage, HERA can paint an uninterrupted picture through reionization, back to the end of the Dark Ages.This paper will present a summary of the current understanding of the signal characteristics and measurements and describe the funded and planned HERA telescope to be built to detect and characterize the EoR power spectrum.

Tracking and Navigation of Future NASA Spacecraft with the Square Kilometer Array

NASA Astrophysics Data System (ADS)

Resch, G. M.; Jones, D. L.; Connally, M. J.; Weinreb, S.; Preston, R. A.

2001-12-01

The international radio astronomy community is currently working on the design of an array of small radio antennas with a total collecting area of one square kilometer - more than a hundred times that of the largest existing (100-m) steerable antennas. An array of this size would provide obvious advantages for high data rate telemetry reception and for spacecraft navigation. Among these advantages are a two-orders-of-magnitude increase in sensitivity for telemetry downlink, flexible sub-arraying to track multiple spacecraft simultaneously, increased reliability through the use of large numbers of identical array elements, very accurate real-time angular spacecraft tracking, and a dramatic reduction in cost per unit area. NASA missions in many disciplines, including planetary science, would benefit from this increased ground-based tracking capability. The science return from planned missions could be increased, and opportunities for less expensive or completely new kinds of missions would be created.

Intensity Mapping of Hα, Hβ, [OII], and [OIII] Lines at z < 5

NASA Astrophysics Data System (ADS)

Gong, Yan; Cooray, Asantha; Silva, Marta B.; Zemcov, Michael; Feng, Chang; Santos, Mario G.; Dore, Olivier; Chen, Xuelei

2017-02-01

Intensity mapping is becoming a useful tool to study the large-scale structure of the universe through spatial variations in the integrated emission from galaxies and the intergalactic medium. We study intensity mapping of the {{H}}α 6563 \\mathringA , [O III] 5007 Å, [O II] 3727 Å, and {{H}}β 4861 \\mathringA lines at 0.8≤slant z≤slant 5.2. The mean intensities of these four emission lines are estimated using the observed luminosity functions (LFs), cosmological simulations, and the star formation rate density (SFRD) derived from observations at z≲ 5. We calculate the intensity power spectra and consider the foreground contamination of other lines at lower redshifts. We use the proposed NASA small explorer SPHEREx (the Spectro-Photometer for the History of the universe, Epoch of Reionization, and Ices Explorer) as a case study for the detectability of the intensity power spectra of the four emission lines. We also investigate the cross-correlation with the 21 cm line probed by the Canadian Hydrogen Intensity Mapping Experiment (CHIME), Tianlai experiment and the Square Kilometer Array (SKA) at 0.8≤slant z≤slant 2.4. We find both the auto and cross power spectra can be well measured for the Hα, [O III] and [O II] lines at z≲ 3, while it is more challenging for the Hβ line. Finally, we estimate the constraint on the SFRD from intensity mapping, and find we can reach an accuracy higher than 7% at z≲ 4, which is better than with the usual method of measurements using the LFs of galaxies.

Cross-correlation cosmography with intensity mapping of the neutral hydrogen 21 cm emission

NASA Astrophysics Data System (ADS)

Pourtsidou, A.; Bacon, D.; Crittenden, R.

2015-11-01

The cross-correlation of a foreground density field with two different background convergence fields can be used to measure cosmographic distance ratios and constrain dark energy parameters. We investigate the possibility of performing such measurements using a combination of optical galaxy surveys and neutral hydrogen (HI) intensity mapping surveys, with emphasis on the performance of the planned Square Kilometre Array (SKA). Using HI intensity mapping to probe the foreground density tracer field and/or the background source fields has the advantage of excellent redshift resolution and a longer lever arm achieved by using the lensing signal from high redshift background sources. Our results show that, for our best SKA-optical configuration of surveys, a constant equation of state for dark energy can be constrained to ≃8 % for a sky coverage fsky=0.5 and assuming a σ (ΩDE)=0.03 prior for the dark energy density parameter. We also show that using the cosmic microwave background as the second source plane is not competitive, even when considering a COrE-like satellite.

Gravitational Microlensing Events as a Target for the SETI project

NASA Astrophysics Data System (ADS)

Rahvar, Sohrab

2016-09-01

The detection of signals from a possible extrasolar technological civilization is one of the most challenging efforts of science. In this work, we propose using natural telescopes made of single or binary gravitational lensing systems to magnify leakage of electromagnetic signals from a remote planet that harbors Extraterrestrial Intelligent (ETI) technology. Currently, gravitational microlensing surveys are monitoring a large area of the Galactic bulge to search for microlensing events, finding more than 2000 events per year. These lenses are capable of playing the role of natural telescopes, and, in some instances, they can magnify radio band signals from planets orbiting around the source stars in gravitational microlensing systems. Assuming that the frequency of electromagnetic waves used for telecommunication in ETIs is similar to ours, we propose follow-up observation of microlensing events with radio telescopes such as the Square Kilometre Array (SKA), the Low Frequency Demonstrators, and the Mileura Wide-Field Array. Amplifying signals from the leakage of broadcasting by an Earth-like civilization will allow us to detect them as far as the center of the Milky Way galaxy. Our analysis shows that in binary microlensing systems, the probability of amplification of signals from ETIs is more than that in single microlensing events. Finally, we propose the use of the target of opportunity mode for follow-up observations of binary microlensing events with SKA as a new observational program for searching ETIs. Using optimistic values for the factors of the Drake equation provides detection of about one event per year.

Vascular Reactivity Profile of Novel KCa 3.1-Selective Positive-Gating Modulators in the Coronary Vascular Bed.

PubMed

Oliván-Viguera, Aida; Valero, Marta Sofía; Pinilla, Estéfano; Amor, Sara; García-Villalón, Ángel Luis; Coleman, Nichole; Laría, Celia; Calvín-Tienza, Víctor; García-Otín, Ángel-Luis; Fernández-Fernández, José M; Murillo, M Divina; Gálvez, José A; Díaz-de-Villegas, María D; Badorrey, Ramón; Simonsen, Ulf; Rivera, Luis; Wulff, Heike; Köhler, Ralf

2016-08-01

Opening of intermediate-conductance calcium-activated potassium channels (KC a 3.1) produces membrane hyperpolarization in the vascular endothelium. Here, we studied the ability of two new KC a 3.1-selective positive-gating modulators, SKA-111 and SKA-121, to (1) evoke porcine endothelial cell KC a 3.1 membrane hyperpolarization, (2) induce endothelium-dependent and, particularly, endothelium-derived hyperpolarization (EDH)-type relaxation in porcine coronary arteries (PCA) and (3) influence coronary artery tone in isolated rat hearts. In whole-cell patch-clamp experiments on endothelial cells of PCA (PCAEC), KC a currents evoked by bradykinin (BK) were potentiated ≈7-fold by either SKA-111 or SKA-121 (both at 1 μM) and were blocked by a KC a 3.1 blocker, TRAM-34. In membrane potential measurements, SKA-111 and SKA-121 augmented bradykinin-induced hyperpolarization. Isometric tension measurements in large- and small-calibre PCA showed that SKA-111 and SKA-121 potentiated endothelium-dependent relaxation with intact NO synthesis and EDH-type relaxation to BK by ≈2-fold. Potentiation of the BK response was prevented by KC a 3.1 inhibition. In Langendorff-perfused rat hearts, SKA-111 potentiated coronary vasodilation elicited by BK. In conclusion, our data show that positive-gating modulation of KC a 3.1 channels improves BK-induced membrane hyperpolarization and endothelium-dependent relaxation in small and large PCA as well as in the coronary circulation of rats. Positive-gating modulators of KC a 3.1 could be therapeutically useful to improve coronary blood flow and counteract impaired coronary endothelial dysfunction in cardiovascular disease. © 2016 Nordic Association for the Publication of BCPT (former Nordic Pharmacological Society).

Clusters of Galaxies and the Cosmic Web with Square Kilometre Array

NASA Astrophysics Data System (ADS)

Kale, Ruta; Dwarakanath, K. S.; Vir Lal, Dharam; Bagchi, Joydeep; Paul, Surajit; Malu, Siddharth; Datta, Abhirup; Parekh, Viral; Sharma, Prateek; Pandey-Pommier, Mamta

2016-12-01

The intra-cluster and inter-galactic media that pervade the large scale structure of the Universe are known to be magnetized at sub-micro Gauss to micro Gauss levels and to contain cosmic rays. The acceleration of cosmic rays and their evolution along with that of magnetic fields in these media is still not well understood. Diffuse radio sources of synchrotron origin associated with the Intra-Cluster Medium (ICM) such as radio halos, relics and mini-halos are direct probes of the underlying mechanisms of cosmic ray acceleration. Observations with radio telescopes such as the Giant Metrewave Radio Telescope, the Very Large Array and the Westerbork Synthesis Radio Telescope have led to the discoveries of about 80 such sources and allowed detailed studies in the frequency range 0.15-1.4 GHz of a few. These studies have revealed scaling relations between the thermal and non-thermal properties of clusters and favour the role of shocks in the formation of radio relics and of turbulent re-acceleration in the formation of radio halos and mini-halos. The radio halos are known to occur in merging clusters and mini-halos are detected in about half of the cool-core clusters. Due to the limitations of current radio telescopes, low mass galaxy clusters and galaxy groups remain unexplored as they are expected to contain much weaker radio sources. Distinguishing between the primary and the secondary models of cosmic ray acceleration mechanisms requires spectral measurements over a wide range of radio frequencies and with high sensitivity. Simulations have also predicted weak diffuse radio sources associated with filaments connecting galaxy clusters. The Square Kilometre Array (SKA) is a next generation radio telescope that will operate in the frequency range of 0.05-20 GHz with unprecedented sensitivities and resolutions. The expected detection limits of SKA will reveal a few hundred to thousand new radio halos, relics and mini-halos providing the first large and comprehensive samples for their study. The wide frequency coverage along with sensitivity to extended structures will be able to constrain the cosmic ray acceleration mechanisms. The higher frequency (>5 GHz) observations will be able to use the Sunyaev-Zel'dovich effect to probe the ICM pressure in addition to tracers such as lobes of head-tail radio sources. The SKA also opens prospects to detect the `off-state' or the lowest level of radio emission from the ICM predicted by the hadronic models and the turbulent re-acceleration models.

Impact of Simulated 1/f Noise for HI Intensity Mapping Experiments

NASA Astrophysics Data System (ADS)

Harper, S.; Dickinson, C.; Battye, R. A.; Roychowdhury, S.; Browne, I. W. A.; Ma, Y.-Z.; Olivari, L. C.; Chen, T.

2018-05-01

Cosmology has entered an era where the experimental limitations are not due to instrumental sensitivity but instead due to inherent systematic uncertainties in the instrumentation and data analysis methods. The field of HI intensity mapping (IM) is still maturing, however early attempts are already systematics limited. One such systematic limitation is 1/f noise, which largely originates within the instrumentation and manifests as multiplicative gain fluctuations. To date there has been little discussion about the possible impact of 1/f noise on upcoming single-dish HI IM experiments such as BINGO, FAST or SKA. Presented in this work are Monte-Carlo end-to-end simulations of a 30 day HI IM survey using the SKA-MID array covering a bandwidth of 950 and 1410 MHz. These simulations extend 1/f noise models to include not just temporal fluctuations but also correlated gain fluctuations across the receiver bandpass. The power spectral density of the spectral gain fluctuations are modelled as a power-law, and characterised by a parameter β. It is found that the degree of 1/f noise frequency correlation will be critical to the success of HI IM experiments. Small values of β (β < 0.25) or high correlation is preferred as this is more easily removed using current component separation techniques. Spectral index of temporal fluctuations (α) is also found to have a large impact on signal-to-noise. Telescope slew speed has a smaller impact, and a scan speed of 1 deg s-1 should be sufficient for a HI IM survey with the SKA.

Congressing kinetochores progressively load Ska complexes to prevent force-dependent detachment.

PubMed

Auckland, Philip; Clarke, Nicholas I; Royle, Stephen J; McAinsh, Andrew D

2017-06-05

Kinetochores mediate chromosome congression by either sliding along the lattice of spindle microtubules or forming end-on attachments to their depolymerizing plus-ends. By following the fates of individual kinetochores as they congress in live cells, we reveal that the Ska complex is required for a distinct substep of the depolymerization-coupled pulling mechanism. Ska depletion increases the frequency of naturally occurring, force-dependent P kinetochore detachment events, while being dispensable for the initial biorientation and movement of chromosomes. In unperturbed cells, these release events are followed by reattachment and successful congression, whereas in Ska-depleted cells, detached kinetochores remain in a futile reattachment/detachment cycle that prevents congression. We further find that Ska is progressively loaded onto bioriented kinetochore pairs as they congress. We thus propose a model in which kinetochores mature through Ska complex recruitment and that this is required for improved load-bearing capacity and silencing of the spindle assembly checkpoint. © 2017 Auckland et al.

SKA Telescope Manager (TM): status and architecture overview

NASA Astrophysics Data System (ADS)

Natarajan, Swaminathan; Barbosa, Domingos; Barraca, Joao P.; Bridger, Alan; Choudhury, Subhrojyoti R.; Di Carlo, Matteo; Dolci, Mauro; Gupta, Yashwant; Guzman, Juan; Van den Heever, Lize; Le Roux, Gerhard; Nicol, Mark; Patil, Mangesh; Smareglia, Riccardo; Swart, Paul; Thompson, Roger; Vrcic, Sonja; Williams, Stewart

2016-07-01

The SKA radio telescope project is building two telescopes, SKA-Low in Australia and SKA-Mid in South Africa respectively. The Telescope Manager is responsible for the observations lifecycle and for monitoring and control of each instrument, and is being developed by an international consortium. The project is currently in the design phase, with the Preliminary Design Review having been successfully completed, along with re-baselining to match project scope to available budget. This report presents the status of the Telescope Manager work, key architectural challenges and our approach to addressing them.

MIGHTEE: The MeerKAT International GHz Tiered Extragalactic Exploration

NASA Astrophysics Data System (ADS)

Taylor, A. Russ; Jarvis, Matt

2017-05-01

The MeerKAT telescope is the precursor of the Square Kilometre Array mid-frequency dish array to be deployed later this decade on the African continent. MIGHTEE is one of the MeerKAT large survey projects designed to pathfind SKA key science in cosmology and galaxy evolution. Through a tiered radio continuum deep imaging project including several fields totaling 20 square degrees to microJy sensitivities and an ultra-deep image of a single 1 square degree field of view, MIGHTEE will explore dark matter and large scale structure, the evolution of galaxies, including AGN activity and star formation as a function of cosmic time and environment, the emergence and evolution of magnetic fields in galaxies, and the magnetic counter part to large scale structure of the universe.

21-cm lensing and the cold spot in the cosmic microwave background.

PubMed

Kovetz, Ely D; Kamionkowski, Marc

2013-04-26

An extremely large void and a cosmic texture are two possible explanations for the cold spot seen in the cosmic microwave background. We investigate how well these two hypotheses can be tested with weak lensing of 21-cm fluctuations from the epoch of reionization measured with the Square Kilometer Array. While the void explanation for the cold spot can be tested with Square Kilometer Array, given enough observation time, the texture scenario requires significantly prolonged observations, at the highest frequencies that correspond to the epoch of reionization, over the field of view containing the cold spot.

GRAVITATIONAL MICROLENSING EVENTS AS A TARGET FOR THE SETI PROJECT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rahvar, Sohrab, E-mail: rahvar@sharif.edu

2016-09-01

The detection of signals from a possible extrasolar technological civilization is one of the most challenging efforts of science. In this work, we propose using natural telescopes made of single or binary gravitational lensing systems to magnify leakage of electromagnetic signals from a remote planet that harbors Extraterrestrial Intelligent (ETI) technology. Currently, gravitational microlensing surveys are monitoring a large area of the Galactic bulge to search for microlensing events, finding more than 2000 events per year. These lenses are capable of playing the role of natural telescopes, and, in some instances, they can magnify radio band signals from planets orbitingmore » around the source stars in gravitational microlensing systems. Assuming that the frequency of electromagnetic waves used for telecommunication in ETIs is similar to ours, we propose follow-up observation of microlensing events with radio telescopes such as the Square Kilometre Array (SKA), the Low Frequency Demonstrators, and the Mileura Wide-Field Array. Amplifying signals from the leakage of broadcasting by an Earth-like civilization will allow us to detect them as far as the center of the Milky Way galaxy. Our analysis shows that in binary microlensing systems, the probability of amplification of signals from ETIs is more than that in single microlensing events. Finally, we propose the use of the target of opportunity mode for follow-up observations of binary microlensing events with SKA as a new observational program for searching ETIs. Using optimistic values for the factors of the Drake equation provides detection of about one event per year.« less

The temporal distribution of seismic radiation during deep earthquake rupture

USGS Publications Warehouse

Houston, H.; Vidale, J.E.

1994-01-01

The time history of energy release during earthquakes illuminates the process of failure, which remains enigmatic for events deeper than about 100 kilometers. Stacks of teleseismic records from regional arrays for 122 intermediate (depths of 100 to 350 kilometers) and deep (depths of 350 to 700 kilometers) earthquakes show that the temporal pattern of short-period seismic radiation has a systematic variation with depth. On average, for intermediate depth events more radiation is released toward the beginning of the rupture than near the end, whereas for deep events radiation is released symmetrically over the duration of the event, with an abrupt beginning and end of rupture. These findings suggest a variation in the style of rupture related to decreasing fault heterogeneity with depth.The time history of energy release during earthquakes illuminates the process of failure, which remains enigmatic for events deeper than about 100 kilometers. Stacks of teleseismic records from regional arrays for 122 intermediate (depths of 100 to 350 kilometers) and deep (depths of 350 to 700 kilometers) earthquakes show that the temporal pattern of short-period seismic radiation has a systematic variation with depth. On average, for intermediate depth events more radiation is released toward the beginning of the rupture than near the end, whereas for deep events radiation is released symmetrically over the duration of the event, with an abrupt beginning and end of rupture. These findings suggest a variation in the style of rupture related to decreasing fault heterogeneity with depth.

Radio Continuum Surveys with Square Kilometre Array Pathfinders

NASA Astrophysics Data System (ADS)

Norris, Ray P.; Afonso, J.; Bacon, D.; Beck, Rainer; Bell, Martin; Beswick, R. J.; Best, Philip; Bhatnagar, Sanjay; Bonafede, Annalisa; Brunetti, Gianfranco; Budavári, Tamás; Cassano, Rossella; Condon, J. J.; Cress, Catherine; Dabbech, Arwa; Feain, I.; Fender, Rob; Ferrari, Chiara; Gaensler, B. M.; Giovannini, G.; Haverkorn, Marijke; Heald, George; Van der Heyden, Kurt; Hopkins, A. M.; Jarvis, M.; Johnston-Hollitt, Melanie; Kothes, Roland; Van Langevelde, Huib; Lazio, Joseph; Mao, Minnie Y.; Martínez-Sansigre, Alejo; Mary, David; Mcalpine, Kim; Middelberg, E.; Murphy, Eric; Padovani, P.; Paragi, Zsolt; Prandoni, I.; Raccanelli, A.; Rigby, Emma; Roseboom, I. G.; Röttgering, H.; Sabater, Jose; Salvato, Mara; Scaife, Anna M. M.; Schilizzi, Richard; Seymour, N.; Smith, Dan J. B.; Umana, Grazia; Zhao, G.-B.; Zinn, Peter-Christian

2013-03-01

In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telescopes and upgrades are already being built around the world. These include APERTIF (The Netherlands), ASKAP (Australia), e-MERLIN (UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), MeerKAT (South Africa), and the Murchison Widefield Array. Each of these new instruments has different strengths, and coordination of surveys between them can help maximise the science from each of them. A radio continuum survey is being planned on each of them with the primary science objective of understanding the formation and evolution of galaxies over cosmic time, and the cosmological parameters and large-scale structures which drive it. In pursuit of this objective, the different teams are developing a variety of new techniques, and refining existing ones. To achieve these exciting scientific goals, many technical challenges must be addressed by the survey instruments. Given the limited resources of the global radio-astronomical community, it is essential that we pool our skills and knowledge. We do not have sufficient resources to enjoy the luxury of re-inventing wheels. We face significant challenges in calibration, imaging, source extraction and measurement, classification and cross-identification, redshift determination, stacking, and data-intensive research. As these instruments extend the observational parameters, we will face further unexpected challenges in calibration, imaging, and interpretation. If we are to realise the full scientific potential of these expensive instruments, it is essential that we devote enough resources and careful study to understanding the instrumental effects and how they will affect the data. We have established an SKA Radio Continuum Survey working group, whose prime role is to maximise science from these instruments by ensuring we share resources and expertise across the projects. Here we describe these projects, their science goals, and the technical challenges which are being addressed to maximise the science return.

SPATIALLY EXTENDED 21 cm SIGNAL FROM STRONGLY CLUSTERED UV AND X-RAY SOURCES IN THE EARLY UNIVERSE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahn, Kyungjin; Xu, Hao; Norman, Michael L.

2015-03-20

We present our prediction for the local 21 cm differential brightness temperature (δT{sub b}) from a set of strongly clustered sources of Population III (Pop III) and II (Pop II) objects in the early universe, by a numerical simulation of their formation and radiative feedback. These objects are located inside a highly biased environment, which is a rare, high-density peak (“Rarepeak”) extending to ∼7 comoving Mpc. We study the impact of ultraviolet and X-ray photons on the intergalactic medium (IGM) and the resulting δT{sub b}, when Pop III stars are assumed to emit X-ray photons by forming X-ray binaries verymore » efficiently. We parameterize the rest-frame spectral energy distribution of X-ray photons, which regulates X-ray photon-trapping, IGM-heating, secondary Lyα pumping and the resulting morphology of δT{sub b}. A combination of emission (δT{sub b} > 0) and absorption (δT{sub b} < 0) regions appears in varying amplitudes and angular scales. The boost of the signal by the high-density environment (δ ∼ 0.64) and on a relatively large scale combines to make Rarepeak a discernible, spatially extended (θ ∼ 10′) object for 21 cm observation at 13 ≲ z ≲ 17, which is found to be detectable as a single object by SKA with integration time of ∼1000 hr. Power spectrum analysis by some of the SKA precursors (Low Frequency Array, Murchison Widefield Array, Precision Array for Probing the Epoch of Reionization) of such rare peaks is found to be difficult due to the rarity of these peaks, and the contribution only by these rare peaks to the total power spectrum remains subdominant compared to that by all astrophysical sources.« less

Scalable splitting algorithms for big-data interferometric imaging in the SKA era

NASA Astrophysics Data System (ADS)

Onose, Alexandru; Carrillo, Rafael E.; Repetti, Audrey; McEwen, Jason D.; Thiran, Jean-Philippe; Pesquet, Jean-Christophe; Wiaux, Yves

2016-11-01

In the context of next-generation radio telescopes, like the Square Kilometre Array (SKA), the efficient processing of large-scale data sets is extremely important. Convex optimization tasks under the compressive sensing framework have recently emerged and provide both enhanced image reconstruction quality and scalability to increasingly larger data sets. We focus herein mainly on scalability and propose two new convex optimization algorithmic structures able to solve the convex optimization tasks arising in radio-interferometric imaging. They rely on proximal splitting and forward-backward iterations and can be seen, by analogy, with the CLEAN major-minor cycle, as running sophisticated CLEAN-like iterations in parallel in multiple data, prior, and image spaces. Both methods support any convex regularization function, in particular, the well-studied ℓ1 priors promoting image sparsity in an adequate domain. Tailored for big-data, they employ parallel and distributed computations to achieve scalability, in terms of memory and computational requirements. One of them also exploits randomization, over data blocks at each iteration, offering further flexibility. We present simulation results showing the feasibility of the proposed methods as well as their advantages compared to state-of-the-art algorithmic solvers. Our MATLAB code is available online on GitHub.

Astronomy Education & Outreach in South Africa

NASA Astrophysics Data System (ADS)

Throop, Henry B.

2015-11-01

Although South Africa has evolved greatly in the 20 years since the end of apartheid, it remains a very divided country. The highest-performing students are comparable in ability to those in the US and Europe, but nearly all of these students are from priveleged Afrikaaner (European) backgrounds. The vast majority of students in the country are native African, and school standards remain very low across the country. It is common that students have no textbooks, teachers have only a high school education, and schools have no telephones and no toilets. By high school graduation, the majority of students have never used a web browser -- even students in the capital of Johannesburg. And while a few students are inspired by home-grown world-class projects such as the Square Kilometer Array (SKA) and Southern African Large Telescope (SALT), most remain unaware of their existence.Despite the poor state of education in the country, students work hard, are curious, and desire information from the outside world. Astronomy is one subject in which students in rural Africa often show exceptional interest. Perhaps astronomy serves as a 'gateway science,' linking the physically observable world with the exotic and unknown.Here I report on many visits I have made to both rural and urban schools in South Africa during the 2013-2015 period. I have interacted with thousands of grade 7-12 students at dozens of schools, as well as taught students who graduated from this system and enrolled in local universities. I will present an assessment of the state of science education in South Africa, as well as a few broader suggestions for how scientists and educators in developed countries can best make an impact in Southern Africa.

SKA2 Methylation is associated with Decreased Prefrontal Cortical Thickness and Greater PTSD Severity among Trauma-Exposed Veterans

PubMed Central

Sadeh, Naomi; Spielberg, Jeffrey M.; Logue, Mark W.; Wolf, Erika J.; Smith, Alicia K.; Lusk, Joanna; Hayes, Jasmeet P.; Sperbeck, Emily; Milberg, William P.; McGlinchey, Regina E.; Salat, David H.; Carter, Weleetka C.; Stone, Annjanette; Schichman, Steven A.; Humphries, Donald E.; Miller, Mark W.

2015-01-01

Methylation of the SKA2 gene has recently been identified as a promising biomarker of suicide risk. Based on this finding, we examined associations between SKA2 methylation, cortical thickness, and psychiatric phenotypes linked to suicide in trauma-exposed veterans. 200 trauma-exposed white non-Hispanic veterans of the recent conflicts in Iraq and Afghanistan (91% male) underwent clinical assessment and had blood drawn for genotyping and methylation analysis. 145 participants also had neuroimaging data available. Based on previous research, we examined DNA methylation at the CpG locus cg13989295 as well as DNA methylation adjusted for genotype at the methylation-associated SNP (rs7208505) in relationship to whole-brain cortical thickness, posttraumatic stress disorder symptoms (PTSD), and depression symptoms. Whole-brain vertex-wise analyses identified three clusters in prefrontal cortex that were associated with genotype-adjusted SKA2 DNA methylation (methylationadj). Specifically, DNA methylationadj was associated with bilateral reductions of cortical thickness in frontal pole and superior frontal gyrus, and similar effects were found in the right orbitofrontal cortex and right inferior frontal gyrus. PTSD symptom severity was positively correlated with SKA2 DNA methylationadj and negatively correlated with cortical thickness in these regions. Mediation analyses showed a significant indirect effect of PTSD on cortical thickness via SKA2 methylation status. Results suggest that DNA methylationadj of SKA2 in blood indexes stress-related psychiatric phenotypes and neurobiology, pointing to its potential value as a biomarker of stress exposure and susceptibility. PMID:26324104

Radio Frequency Interference Detection using Machine Learning.

NASA Astrophysics Data System (ADS)

Mosiane, Olorato; Oozeer, Nadeem; Aniyan, Arun; Bassett, Bruce A.

2017-05-01

Radio frequency interference (RFI) has plagued radio astronomy which potentially might be as bad or worse by the time the Square Kilometre Array (SKA) comes up. RFI can be either internal (generated by instruments) or external that originates from intentional or unintentional radio emission generated by man. With the huge amount of data that will be available with up coming radio telescopes, an automated aproach will be required to detect RFI. In this paper to try automate this process we present the result of applying machine learning techniques to cross match RFI from the Karoo Array Telescope (KAT-7) data. We found that not all the features selected to characterise RFI are always important. We further investigated 3 machine learning techniques and conclude that the Random forest classifier performs with a 98% Area Under Curve and 91% recall in detecting RFI.

New positive Ca2+-activated K+ channel gating modulators with selectivity for KCa3.1.

PubMed

Coleman, Nichole; Brown, Brandon M; Oliván-Viguera, Aida; Singh, Vikrant; Olmstead, Marilyn M; Valero, Marta Sofia; Köhler, Ralf; Wulff, Heike

2014-09-01

Small-conductance (KCa2) and intermediate-conductance (KCa3.1) calcium-activated K(+) channels are voltage-independent and share a common calcium/calmodulin-mediated gating mechanism. Existing positive gating modulators like EBIO, NS309, or SKA-31 activate both KCa2 and KCa3.1 channels with similar potency or, as in the case of CyPPA and NS13001, selectively activate KCa2.2 and KCa2.3 channels. We performed a structure-activity relationship (SAR) study with the aim of optimizing the benzothiazole pharmacophore of SKA-31 toward KCa3.1 selectivity. We identified SKA-111 (5-methylnaphtho[1,2-d]thiazol-2-amine), which displays 123-fold selectivity for KCa3.1 (EC50 111 ± 27 nM) over KCa2.3 (EC50 13.7 ± 6.9 μM), and SKA-121 (5-methylnaphtho[2,1-d]oxazol-2-amine), which displays 41-fold selectivity for KCa3.1 (EC50 109 nM ± 14 nM) over KCa2.3 (EC50 4.4 ± 1.6 μM). Both compounds are 200- to 400-fold selective over representative KV (KV1.3, KV2.1, KV3.1, and KV11.1), NaV (NaV1.2, NaV1.4, NaV1.5, and NaV1.7), as well as CaV1.2 channels. SKA-121 is a typical positive-gating modulator and shifts the calcium-concentration response curve of KCa3.1 to the left. In blood pressure telemetry experiments, SKA-121 (100 mg/kg i.p.) significantly lowered mean arterial blood pressure in normotensive and hypertensive wild-type but not in KCa3.1(-/-) mice. SKA-111, which was found in pharmacokinetic experiments to have a much longer half-life and to be much more brain penetrant than SKA-121, not only lowered blood pressure but also drastically reduced heart rate, presumably through cardiac and neuronal KCa2 activation when dosed at 100 mg/kg. In conclusion, with SKA-121, we generated a KCa3.1-specific positive gating modulator suitable for further exploring the therapeutical potential of KCa3.1 activation. Copyright © 2014 by The American Society for Pharmacology and Experimental Therapeutics.

SeaWiFS technical report series. Volume 4: An analysis of GAC sampling algorithms. A case study

NASA Technical Reports Server (NTRS)

Yeh, Eueng-Nan (Editor); Hooker, Stanford B. (Editor); Hooker, Stanford B. (Editor); Mccain, Charles R. (Editor); Fu, Gary (Editor)

1992-01-01

The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) instrument will sample at approximately a 1 km resolution at nadir which will be broadcast for reception by realtime ground stations. However, the global data set will be comprised of coarser four kilometer data which will be recorded and broadcast to the SeaWiFS Project for processing. Several algorithms for degrading the one kilometer data to four kilometer data are examined using imagery from the Coastal Zone Color Scanner (CZCS) in an effort to determine which algorithm would best preserve the statistical characteristics of the derived products generated from the one kilometer data. Of the algorithms tested, subsampling based on a fixed pixel within a 4 x 4 pixel array is judged to yield the most consistent results when compared to the one kilometer data products.

Epoch of Reionisation

NASA Astrophysics Data System (ADS)

Barry, N.; Beardsley, A.; Bowman, J.; Briggs, F.; Byrne, R.; Carroll, P.; Hazelton, B.; Jacobs, D.; Jordan, C.; Kittiwisit, P.; Lanman, A.; Lenc, E.; Li, W.; Line, J.; McKinley, B.; Mitchell, D.; Morales, M.; Murray, S.; Paul, S.; Pindor, B.; Pober, J.; Rahimi, M.; Riding, J.; Sethi, S.; Shankar, U.; Subrahmanyan, R.; Sullivan, I.; Takahashi, K.; Thyagarajan, N.; Tingay, S.; Trott, C.; Wayth, R.; Webster, R.; Wyithe, S.

2017-01-01

The Murchison Widefield Array is designed to measure the fluctuations in the 21cm emission from neutral hydrogen during the Epoch of Reionisation. The new hex configuration is explicitly designed to test the predicted increase in sensitivity of redundant baselines. However the challenge of the new array is to understand calibration with the new configuration. We have developed two new pipelines to reduce the hex data, and will compare the results with previous datasets from the Phase 1 array. We have now processed 80 hours of data refining the data analysis through our two established Phase 1 pipelines. This proposal requests as much observing time as possible in semester 2017-A to (1) obtain a comparable hex dataset to test the sensitivity and systematic limits with redundant arrays, (2) establish the optimal observing strategy for an EoR detection, and (3) continue to explore observational strategies in the three EoR fields to advise the design of SKA-low experiments. Due to the proposed changes in the array during the upcoming semester, we have not requested a specific number of hours, but will optimise our observing program as availability of the telescope becomes clear. We note that this observing proposal implements the key scientific program that can benefit from the new hex configuration.

Elucidating dark energy with future 21 cm observations at the epoch of reionization

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohri, Kazunori; Oyama, Yoshihiko; Sekiguchi, Toyokazu

2017-02-01

We investigate how precisely we can determine the nature of dark energy such as the equation of state (EoS) and its time dependence by using future observations of 21 cm fluctuations at the epoch of reionization (06.8∼< z ∼<1) such as Square Kilometre Array (SKA) and Omniscope in combination with those from cosmic microwave background, baryon acoustic oscillation, type Ia supernovae and direct measurement of the Hubble constant. We consider several parametrizations for the EoS and find that future 21 cm observations will be powerful in constraining models of dark energy, especially when its EoS varies at high redshifts.

Distributed agile software development for the SKA

NASA Astrophysics Data System (ADS)

Wicenec, Andreas; Parsons, Rebecca; Kitaeff, Slava; Vinsen, Kevin; Wu, Chen; Nelson, Paul; Reed, David

2012-09-01

The SKA software will most probably be developed by many groups distributed across the globe and coming from dierent backgrounds, like industries and research institutions. The SKA software subsystems will have to cover a very wide range of dierent areas, but still they have to react and work together like a single system to achieve the scientic goals and satisfy the challenging data ow requirements. Designing and developing such a system in a distributed fashion requires proper tools and the setup of an environment to allow for ecient detection and tracking of interface and integration issues in particular in a timely way. Agile development can provide much faster feedback mechanisms and also much tighter collaboration between the customer (scientist) and the developer. Continuous integration and continuous deployment on the other hand can provide much faster feedback of integration issues from the system level to the subsystem developers. This paper describes the results obtained from trialing a potential SKA development environment based on existing science software development processes like ALMA, the expected distribution of the groups potentially involved in the SKA development and experience gained in the development of large scale commercial software projects.

Recent highlights from IceCube

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kappes, A.; Collaboration: IceCube Collaboration

2014-11-18

The IceCube Neutrino Observatory, completed in December 2010, is located at the geographic South Pole and incorporates a one cubic kilometer neutrino detector buried in the deep ice and a one square kilometer air shower array, IceTop, sitting atop the glacial ice. This unique combination of neutrino and cosmic-ray detectors allows to investigate a wide variety of physics topics both in astrophysics and particle physics. Here, we discuss latest results from IceCube concentrating on astrophysical aspects.

The Australian SKA Pathfinder: operations management and user engagement

NASA Astrophysics Data System (ADS)

Harvey-Smith, Lisa

2016-07-01

This paper describes the science operations model for the Australian Square Kilometre Array Pathfinder (ASKAP) telescope. ASKAP is a radio interferometer currently being commissioned in Western Australia. It will be operated by a dedicated team of observatory staff with the support of telescope monitoring, control and scheduling software. These tools, as well as the proposal tools and data archive will enable the telescope to operate with little direct input from the astronomy user. The paper also discusses how close engagement with the telescope user community has been maintained throughout the ASKAP construction and commissioning phase, leading to positive outcomes including early input into the design of telescope systems and a vibrant early science program.

Implementation of a direct-imaging and FX correlator for the BEST-2 array

NASA Astrophysics Data System (ADS)

Foster, G.; Hickish, J.; Magro, A.; Price, D.; Zarb Adami, K.

2014-04-01

A new digital backend has been developed for the Basic Element for SKA Training II (BEST-2) array at Radiotelescopi di Medicina, INAF-IRA, Italy, which allows concurrent operation of an FX correlator, and a direct-imaging correlator and beamformer. This backend serves as a platform for testing some of the spatial Fourier transform concepts which have been proposed for use in computing correlations on regularly gridded arrays. While spatial Fourier transform-based beamformers have been implemented previously, this is, to our knowledge, the first time a direct-imaging correlator has been deployed on a radio astronomy array. Concurrent observations with the FX and direct-imaging correlator allow for direct comparison between the two architectures. Additionally, we show the potential of the direct-imaging correlator for time-domain astronomy, by passing a subset of beams though a pulsar and transient detection pipeline. These results provide a timely verification for spatial Fourier transform-based instruments that are currently in commissioning. These instruments aim to detect highly redshifted hydrogen from the epoch of reionization and/or to perform wide-field surveys for time-domain studies of the radio sky. We experimentally show the direct-imaging correlator architecture to be a viable solution for correlation and beamforming.

Strongly lensed neutral hydrogen emission: detection predictions with current and future radio interferometers

NASA Astrophysics Data System (ADS)

Deane, R. P.; Obreschkow, D.; Heywood, I.

2015-09-01

Strong gravitational lensing provides some of the deepest views of the Universe, enabling studies of high-redshift galaxies only possible with next-generation facilities without the lensing phenomenon. To date, 21-cm radio emission from neutral hydrogen has only been detected directly out to z ˜ 0.2, limited by the sensitivity and instantaneous bandwidth of current radio telescopes. We discuss how current and future radio interferometers such as the Square Kilometre Array (SKA) will detect lensed H I emission in individual galaxies at high redshift. Our calculations rely on a semi-analytic galaxy simulation with realistic H I discs (by size, density profile and rotation), in a cosmological context, combined with general relativistic ray tracing. Wide-field, blind H I surveys with the SKA are predicted to be efficient at discovering lensed H I systems, increasingly so at z ≳ 2. This will be enabled by the combination of the magnification boosts, the steepness of the H I luminosity function at the high-mass end, and the fact that the H I spectral line is relatively isolated in frequency. These surveys will simultaneously provide a new technique for foreground lens selection and yield the highest redshift H I emission detections. More near term (and existing) cm-wave facilities will push the high-redshift H I envelope through targeted surveys of known lenses.

Distinguishing models of reionization using future radio observations of 21-cm 1-point statistics

NASA Astrophysics Data System (ADS)

Watkinson, C. A.; Pritchard, J. R.

2014-10-01

We explore the impact of reionization topology on 21-cm statistics. Four reionization models are presented which emulate large ionized bubbles around overdense regions (21CMFAST/global-inside-out), small ionized bubbles in overdense regions (local-inside-out), large ionized bubbles around underdense regions (global-outside-in) and small ionized bubbles around underdense regions (local-outside-in). We show that first generation instruments might struggle to distinguish global models using the shape of the power spectrum alone. All instruments considered are capable of breaking this degeneracy with the variance, which is higher in outside-in models. Global models can also be distinguished at small scales from a boost in the power spectrum from a positive correlation between the density and neutral-fraction fields in outside-in models. Negative skewness is found to be unique to inside-out models and we find that pre-Square Kilometre Array (SKA) instruments could detect this feature in maps smoothed to reduce noise errors. The early, mid- and late phases of reionization imprint signatures in the brightness-temperature moments, we examine their model dependence and find pre-SKA instruments capable of exploiting these timing constraints in smoothed maps. The dimensional skewness is introduced and is shown to have stronger signatures of the early and mid-phase timing if the inside-out scenario is correct.

MiR-520d-3p antitumor activity in human breast cancer via post-transcriptional regulation of spindle and kinetochore associated 2 expression.

PubMed

Ren, Zhouhui; Yang, Tong; Ding, Jie; Liu, Weihong; Meng, Xiangyu; Zhang, Pingping; Liu, Kaitai; Wang, Ping

2018-01-01

MicroRNAs (miRNAs) play an important role in human tumorigenesis as oncogenes or tumor suppressors by directly binding to the 3'-untranslated region of their target mRNAs. MiR-520d-3p has been reported as a tumor suppressor gene in ovarian cancer and gastric cancer, while the function of miR-520d-3p in human breast cancers is still uninvolved. In this study, we initially identified that the expression of miR-520d-3p was significantly reduced in breast cancer specimens and cell lines. The restoration of miR-520d-3p expression not only reduced breast cancer cell viability by causing the accumulation of G2 phase and cell apoptosis, but also inhibited tumorigenicity in vivo . In addition, as a critical target of miR-520d-3p, the activity of spindle and kinetochore associated 2 (SKA2) was greatly inhibited by miR-520d-3p, and overexpression of miR-520d-3p decreased the expression of SKA2. SKA2 downregulation suppressed cell viability, whereas restoration of SKA2 expression significantly reversed the inhibitory effects of miR-520d-3p antitumor activity. Furthermore, SKA2 was frequently overexpressed in clinical specimens and cell lines, and the expression levels were statistically inversely correlated with miR-520d-3p expression. In conclusion, our data demonstrated that miR-520d-3p antitumor activity is achieved by targeting the SKA2 in human breast cancer cells, suggesting that miR-520d-3p may be a potential target molecule for the therapy.

Free radicals in the stratosphere - A new observational technique

NASA Technical Reports Server (NTRS)

Anderson, J. G.; Hazen, N. L.; Mclaren, B. E.; Rowe, S. P.; Schiller, C. M.; Schwab, M. J.; Solomon, L.; Thompson, E. E.; Weinstock, E. M.

1985-01-01

A new approach to in situ observations of trace reactive species in the stratosphere is described. A balloon-borne system, floating 40 kilometers above the earth's surface, successfully lowered and then retracted a cluster of instruments a distance of 12 kilometers on a filament of Kevlar. This instrument cluster is capable of detecting gas-phase free radicals at the part-per-trillion level. The suspended instrument array has excellent stability and has been used to measured atomic oxygen concentrations in the stratosphere.

Results from the Telescope Array Experiment

NASA Astrophysics Data System (ADS)

Jui, Charles C. H.; Telescope Array Collaboration

2016-04-01

The Telescope Array (TA) is the largest ultrahigh energy cosmic ray detector in the northern hemisphere. The experiment consists of three fluorescence stations viewing the air space over a surface array of 507 scintillation counters deployed over 700 square kilometers. TA has been in operation since 2008. The most recent results from TA, including that of composition studies and search for arrival direction anisotropy, will be presented. We will also report on the progress of the new TA low energy extension (TALE).

The Five-Hundred Aperture Spherical Radio Telescope (fast) Project

NASA Astrophysics Data System (ADS)

Nan, Rendong; Li, Di; Jin, Chengjin; Wang, Qiming; Zhu, Lichun; Zhu, Wenbai; Zhang, Haiyan; Yue, Youling; Qian, Lei

Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project to build the largest single dish radio telescope in the world. Its innovative engineering concept and design pave a new road to realize a huge single dish in the most effective way. FAST also represents Chinese contribution in the international efforts to build the square kilometer array (SKA). Being the most sensitive single dish radio telescope, FAST will enable astronomers to jump-start many science goals, such as surveying the neutral hydrogen in the Milky Way and other galaxies, detecting faint pulsars, looking for the first shining stars, hearing the possible signals from other civilizations, etc. The idea of sitting a large spherical dish in a karst depression is rooted in Arecibo telescope. FAST is an Arecibo-type antenna with three outstanding aspects: the karst depression used as the site, which is large to host the 500-meter telescope and deep to allow a zenith angle of 40 degrees; the active main reflector correcting for spherical aberration on the ground to achieve a full polarization and a wide band without involving complex feed systems; and the light-weight feed cabin driven by cables and servomechanism plus a parallel robot as a secondary adjustable system to move with high precision. The feasibility studies for FAST have been carried out for 14 years, supported by Chinese and world astronomical communities. Funding for FAST has been approved by the National Development and Reform Commission in July of 2007 with a capital budget ~ 700 million RMB. The project time is 5.5 years from the commencement of work in March of 2011 and the first light is expected to be in 2016. This review intends to introduce the project of FAST with emphasis on the recent progress since 2006. In this paper, the subsystems of FAST are described in modest details followed by discussions of the fundamental science goals and examples of early science projects.

LADUMA: Looking At the Distant Universe with the MeerKAT Array

NASA Astrophysics Data System (ADS)

Baker, Andrew J.; Blyth, Sarah; Holwerda, Benne W.; LADUMA team

2018-01-01

The cosmic evolution of galaxies' neutral atomic gas content is a major science driver for the Square Kilometre Array (SKA), as well as for its Australian (ASKAP) and South African (MeerKAT) precursors. Among the HI surveys planned for ASKAP and MeerKAT, the deepest and narrowest tier of the "wedding cake" will be defined by the approved 3424-hour Looking At the Distant Universe with the MeerKAT Array (LADUMA) survey, which will probe HI in emission within a single "cosmic vuvuzela" that extends to z = 1.4, when the universe was only a third of its present age. Through a combination of individual and stacked detections (the latter relying on extensive multiwavelength studies of the survey's target field), LADUMA will study the redshift evolution of the baryonic Tully-Fisher relation and the cosmic HI density, the variation of the HI mass function with redshift and environment, and the connection between HI content and the properties of galaxies' stars (mass, age, etc.). The survey will also build a sample of OH megamaser detections that can be used to trace the cosmic merger history. This talk will introduce the science potential of LADUMA and plans for its execution starting in 2018.

Analysis and Modeling of the Shear Waves Generated by Explosions at the San Andreas Fault Observatory at Depth

DTIC Science & Technology

2012-09-01

09NA29328 Proposal No. BAA09-69 ABSTRACT Using a deep deployment of an 80-element, 3-component borehole seismic array stretching from 1.5 to 2.3...Administration (NNSA). 14. ABSTRACT Using a deep deployment of an 80-element, 3-component borehole seismic array stretching from 1.5 to 2.3 kilometer (km) depth...in the lower half of the borehole array . The strong velocity discontinuity at 2.0 km depth gives rise to another converted S wave, best seen in

The small regulatory RNA FasX enhances group A Streptococcus virulence and inhibits pilus expression via serotype-specific targets

PubMed Central

Danger, Jessica L.; Cao, Tram N.; Cao, Tran H.; Sarkar, Poulomee; Treviño, Jeanette; Pflughoeft, Kathryn J.; Sumby, Paul

2015-01-01

Summary Bacterial pathogens commonly show intra-species variation in virulence factor expression and often this correlates with pathogenic potential. The group A Streptococcus (GAS) produces a small regulatory RNA (sRNA), FasX, which regulates the expression of pili and the thrombolytic agent streptokinase. As GAS serotypes are polymorphic regarding (a) FasX abundance, (b) the fibronectin, collagen, T-antigen (FCT) region of the genome, which contains the pilus genes (nine different FCT-types), and (c) the streptokinase-encoding gene (ska) sequence (two different alleles), we sought to test whether FasX regulates pilus and streptokinase expression in a serotype-specific manner. Parental, fasX mutant, and complemented derivatives of serotype M1 (ska-2, FCT-2), M2 (ska-1, FCT-6), M6 (ska-2, FCT-1), and M28 (ska-1, FCT-4) isolates were compared. While FasX reduced pilus expression in each serotype, the molecular basis differed, as FasX bound, and inhibited the translation of, different FCT-region mRNAs. FasX enhanced streptokinase expression in each serotype, although the degree of regulation varied. Finally, we established that the regulation afforded by FasX enhances GAS virulence, assessed by a model of bacteremia using human plasminogen-expressing mice. Our data are the first to identify and characterize serotype-specific regulation by an sRNA in GAS, and to show an sRNA directly contributes to GAS virulence. PMID:25586884

Surface Diversity

NASA Image and Video Library

2016-03-17

This enhanced color view of Pluto's surface diversity was created by merging Ralph/Multispectral Visible Imaging Camera (MVIC) color imagery (650 meters per pixel) with Long Range Reconnaissance Imager panchromatic imagery (230 meters per pixel). At lower right, ancient, heavily cratered terrain is coated with dark, reddish tholins. At upper right, volatile ices filling the informally named Sputnik Planum have modified the surface, creating a chaos-like array of blocky mountains. Volatile ice also occupies a few nearby deep craters, and in some areas the volatile ice is pocked with arrays of small sublimation pits. At left, and across the bottom of the scene, gray-white CH4 ice deposits modify tectonic ridges, the rims of craters, and north-facing slopes. The scene in this image is 260 miles (420 kilometers) wide and 140 miles (225 kilometers) from top to bottom; north is to the upper left. http://photojournal.jpl.nasa.gov/catalog/PIA20534

Gemini Follow-up of Two Massive H I Clouds Discovered with the Australian Square Kilometer Array Pathfinder

NASA Astrophysics Data System (ADS)

Madrid, Juan P.; Lee-Waddell, Karen; Serra, Paolo; Koribalski, Bärbel S.; Schirmer, Mischa; Spekkens, Kristine; Wang, Jing

2018-02-01

Using the Gemini Multi Object Spectrograph (GMOS) we search for optical counterparts of two massive (∼109 M ⊙) neutral hydrogen clouds near the spiral galaxy IC 5270, located in the outskirts of the IC 1459 group. These two H I clouds were recently discovered using the Australian Square Kilometer Array Pathfinder (ASKAP). Two low surface brightness optical counterparts to one of these H I clouds are identified in the new Gemini data that reaches down to magnitudes of ∼27.5 mag in the g-band. The observed H I mass-to-light ratio derived with these new data, {M}{{H}{{I}}}/{L}g=242, is among the highest reported to date. We are also able to rule out that the two H I clouds are dwarf companions of IC 5270. Tidal interactions and ram pressure stripping are plausible explanations for the physical origin of these two clouds.

Probing the nature of Dark Matter with the SKA

NASA Astrophysics Data System (ADS)

Colafrancesco, S.; Regis, M.; Marchegiani, P.; Beck, G.; Beck, R.; Zechlin, H.; Lobanov, A.; Horns, D.

2015-04-01

Dark Matter (DM) is a fundamental ingredient of our Universe and of structure formation, and yet its nature is elusive to astrophysical probes. Information on the nature and physical properties of the WIMP (neutralino) DM (the leading candidate for a cosmologically relevant DM) can be obtained by studying the astrophysical signals of their annihilation/decay. Among the various e.m. signals, secondary electrons produced by neutralino annihilation generate synchrotron emission in the magnetized atmosphere of galaxy clusters and galaxies which could be observed as a diffuse radio emission (halo or haze) centered on the DM halo. A deep search for DM radio emission with SKA in local dwarf galaxies, galaxy regions with low star formation and galaxy clusters (with offset DM-baryonic distribution, like e.g. the Bullet cluster) can be very effective in constraining the neutralino mass, composition and annihilation cross-section. For the case of a dwarf galaxy, like e.g. Draco, the constraints on the DM annihilation cross-section obtainable with SKA1-MID will be at least a factor $\\sim 10^3$ more stringent than the limits obtained by Fermi-LAT in the $\\gamma$-rays. These limits scale with the value of the B field, and the SKA will have the capability to determine simultaneously both the magnetic field in the DM-dominated structures and the DM particle properties. The optimal frequency band for detecting the DM-induced radio emission is around $\\sim 1$ GHz, with the SKA1-MID Band 1 and 4 important to probe the synchrotron spectral curvature at low-$\

Analysis of 21-cm tomographic data

NASA Astrophysics Data System (ADS)

Mellema, Garrelt; Giri, Sambit; Ghara, Raghuna

2018-05-01

The future SKA1-Low radio telescope will be powerful enough to produce tomographic images of the 21-cm signal from the Epoch of Reionization. Here we address how to identify ionized regions in such data sets, taking into account the resolution and noise levels associated with SKA1-Low. We describe three methods of which one, superpixel oversegmentation, consistently performs best.

Prospects for discovering pulsars in future continuum surveys using variance imaging

NASA Astrophysics Data System (ADS)

Dai, S.; Johnston, S.; Hobbs, G.

2017-12-01

In our previous paper, we developed a formalism for computing variance images from standard, interferometric radio images containing time and frequency information. Variance imaging with future radio continuum surveys allows us to identify radio pulsars and serves as a complement to conventional pulsar searches that are most sensitive to strictly periodic signals. Here, we carry out simulations to predict the number of pulsars that we can uncover with variance imaging in future continuum surveys. We show that the Australian SKA Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) survey can find ∼30 normal pulsars and ∼40 millisecond pulsars (MSPs) over and above the number known today, and similarly an all-sky continuum survey with SKA-MID can discover ∼140 normal pulsars and ∼110 MSPs with this technique. Variance imaging with EMU and SKA-MID will detect pulsars with large duty cycles and is therefore a potential tool for finding MSPs and pulsars in relativistic binary systems. Compared with current pulsar surveys at high Galactic latitudes in the Southern hemisphere, variance imaging with EMU and SKA-MID will be more sensitive, and will enable detection of pulsars with dispersion measures between ∼10 and 100 cm-3 pc.

Making the most of MBSE: pragmatic model-based engineering for the SKA Telescope Manager

NASA Astrophysics Data System (ADS)

Le Roux, Gerhard; Bridger, Alan; MacIntosh, Mike; Nicol, Mark; Schnetler, Hermine; Williams, Stewart

2016-08-01

Many large projects including major astronomy projects are adopting a Model Based Systems Engineering approach. How far is it possible to get value for the effort involved in developing a model that accurately represents a significant project such as SKA? Is it possible for such a large project to ensure that high-level requirements are traceable through the various system-engineering artifacts? Is it possible to utilize the tools available to produce meaningful measures for the impact of change? This paper shares one aspect of the experience gained on the SKA project. It explores some of the recommended and pragmatic approaches developed, to get the maximum value from the modeling activity while designing the Telescope Manager for the SKA. While it is too early to provide specific measures of success, certain areas are proving to be the most helpful and offering significant potential over the lifetime of the project. The experience described here has been on the 'Cameo Systems Modeler' tool-set, supporting a SysML based System Engineering approach; however the concepts and ideas covered would potentially be of value to any large project considering a Model based approach to their Systems Engineering.

Application of Rqd-Number and Rqd-Volume Multifractal Modelling to Delineate Rock Mass Characterisation in Kahang Cu-Mo Porphyry Deposit, Central Iran / Zastosowanie Metod Modelowania Numerycznego Oraz Modelowania Fraktalnego do Analizy JAKOŚCI SKAŁ W Celu OKREŚLENIA Charakterystyki GÓROTWORU W Obszarze ZŁOŻA Cu-Mo W Kahang, ŚRODKOWY Iran

NASA Astrophysics Data System (ADS)

Yasrebi, Amir Bijan; Wetherelt, Andrew; Foster, Patrick J.; Afzal, Peyman; Coggan, John; Ahangaran, Dariush Kaveh

2013-12-01

Identification of rock mass properties in terms of Rock Quality Designation (RQD) plays a significant role in mine planning and design. This study aims to separate the rock mass characterisation based on RQD data analysed from 48 boreholes in Kahang Cu-Mo porphyry deposit situated in the central Iran utilising RQD-Volume (RQD-V) and RQD-Number (RQD-N) fractal models. The log-log plots for RQD-V and RQD-N models show four rock mass populations defined by RQD thresholds of 3.55, 25.12 and 89.12% and 10.47, 41.68 and 83.17% respectively which represent very poor, poor, good and excellent rocks based on Deere and Miller rock classification. The RQD-V and RQD-N models indicate that the excellent rocks are situated in the NW and central parts of this deposit however, the good rocks are located in the most parts of the deposit. The results of validation of the fractal models with the RQD block model show that the RQD-N fractal model of excellent rock quality is better than the RQD-V fractal model of the same rock quality. Correlation between results of the fractal and the geological models illustrates that the excellent rocks are associated with porphyric quartz diorite (PQD) units. The results reveal that there is a multifractal nature in rock characterisation with respect to RQD for the Kahang deposit. The proposed fractal model can be intended for the better understanding of the rock quality for purpose of determination of the final pit slope. Identyfikacja właściwości górotworu odgrywa zasadniczą rolę w planowaniu wydobycia i projektowaniu kopalni. Praca niniejsza ma na celu określenie charakterystyki górotworu w oparciu o dane o jakości skał zebrane na podstawie próbek uzyskanych z 48 odwiertów wykonanych w złożu porfiru Cu-Mo w Kahang, zalegającym w środkowym Iranie przy użyciu modeli fraktalnych RQD-V - Rock Quality Determination-Volume [Określenie jakości skał-objętość]) i RQD-N (Rock Quality Determination-Number [Określenie jakości skał-liczba]). Wykresy logarytmiczne wykonane dla modeli RQD-V i RQD-N wykazują istnienie czterech populacji warstw górotworu, określonych na podstawie parametrów progowych: 3.55; 25.12; 89.12% oraz 10.47; 41.68 i 83.17%, odpowiadającym kolejno stopniom jakości: bardzo słaby, słaby, dobry i bardzo dobry, zgodnie z klasyfikacją skał Deere i Millera. Wyniki uzyskane przy zastosowaniu modeli RQD-V i RQD-N wskazują, że najlepsze skały zalegają w północno- zachodniej i centralnej części złoża, z kolei dobrej jakości skały znaleźć można w obrębie całego złoża. Walidacja modeli fraktalnych w oparciu o model blokowy (RQD block model) wskazuje, że model RQD-N dla bardzo dobrej jakości skał jest skuteczniejszy niż model RQD-V dla tej samej jakości skał. Wysoki stopień korelacji pomiędzy wynikami uzyskanymi w oparciu o modele fraktalne i geologiczne pokazuje, że najwyższej jakości skały związane są z obecnością porfirowego diorytu kwarcowego. Badanie wykazuje fraktalną naturę charakterystyki jakości skał w złożu Kahang. Zaproponowany model fraktalny wykorzystać można do lepszego poznania zagadnienia jakości skał w celu obliczenia nachylenia wyrobiska.

Investigation of the infrasound produced by geophysical events such as volcanoes, thunder, and avalanches: the case for local infrasound monitoring (Invited)

NASA Astrophysics Data System (ADS)

Johnson, J. B.; Marcillo, O. E.; Arechiga, R. O.; Johnson, R.; Edens, H. E.; Marshall, H.; Havens, S.; Waite, G. P.

2010-12-01

Volcanoes, lightning, and mass wasting events generate substantial infrasonic energy that propagates for long distances through the atmosphere with generally low intrinsic attenuation. Although such sources are often studied with regional infrasound arrays that provide important records of their occurrence, position, and relative magnitudes these signals recorded at tens to hundreds of kilometers are often significantly affected by propagation effects. Complex atmospheric structure, due to heterogeneous winds and temperatures, and intervening topography can be responsible for multi-pathing, signal attenuation, and focusing or, alternatively, information loss (i.e., a shadow zone). At far offsets, geometric spreading diminishes signal amplitude requiring low noise recording sites and high fidelity microphones. In contrast recorded excess pressures at local distances are much higher in amplitude and waveforms are more representative of source phenomena. We report on recent studies of volcanoes, thunder, and avalanches made with networks and arrays of infrasound sensors deployed local (within a few km) to the source. At Kilauea Volcano (Hawaii) we deployed a network of ~50 infrasound sensitive sensors (flat from 50 s to 50 Hz) to track the coherence of persistent infrasonic tremor signals in the near-field (out to a few tens of kilometers). During periods of high winds (> 5-10 m/s) we found significant atmospheric influence for signals recorded at stations only a few kilometers from the source. Such observations have encouraged us to conduct a range of volcano, thunder, and snow avalanche studies with networks of small infrasound arrays (~30 m aperture) deployed close to the source region. We present results from local microphone deployments (12 sensors) at Santiaguito Volcano (Guatemala) where we are able to precisely (~10 m resolution) locate acoustic sources from explosions and rock falls. We also present results from our thunder mapping acoustic arrays (15 sensors) in the Magdalena Mountains of New Mexico capable of mapping lightning channels more than 10 km in extent whose positions are corroborated by the radio wave detecting lightning mapping array. We also discuss the recent implementation of a network of snow avalanche detection arrays (12 sensors) in Idaho that are used to monitor and track and map infrasound produced by moving sources. We contend that local infrasound deployment is analogous to local seismic monitoring in that it enables precision localization and interpretation of source phenomena.

System Modeling of a large FPGA project: the SKA Tile Processing Module

NASA Astrophysics Data System (ADS)

Belli, C.; Comoretto, G.

Large projects like the SKA have an intrinsic complexity due to their scale. In this context, the application of a management design system becomes fundamental. For this purpose the SysML language, a UML customization for engineering applications, has been applied. As far as our work is concerned, we focused on the SKA Low Telescope - Tile Processing Module, designing diagrams at different detail levels. We designed a conceptual model of the TPM, primarily focusing on the main interfaces and the major data flows between product items. Functionalities are derived from use cases and allocated to hardware modules in order to guarantee the project's internal consistency and features. This model has been used both as internal documentation and as job specification, to commit part of the design to external entities.

Modelling the 21-cm Signal from the Epoch of Reionization and Cosmic Dawn

NASA Astrophysics Data System (ADS)

Choudhury, T. Roy; Datta, Kanan; Majumdar, Suman; Ghara, Raghunath; Paranjape, Aseem; Mondal, Rajesh; Bharadwaj, Somnath; Samui, Saumyadip

2016-12-01

Studying the cosmic dawn and the epoch of reionization through the redshifted 21-cm line are among the major science goals of the SKA1. Their significance lies in the fact that they are closely related to the very first stars in the Universe. Interpreting the upcoming data would require detailed modelling of the relevant physical processes. In this article, we focus on the theoretical models of reionization that have been worked out by various groups working in India with the upcoming SKA in mind. These models include purely analytical and semi-numerical calculations as well as fully numerical radiative transfer simulations. The predictions of the 21-cm signal from these models would be useful in constraining the properties of the early galaxies using the SKA data.

Gravitational wave as probe of superfluid dark matter

NASA Astrophysics Data System (ADS)

Cai, Rong-Gen; Liu, Tong-Bo; Wang, Shao-Jiang

2018-02-01

In recent years, superfluid dark matter (SfDM) has become a competitive model of emergent modified Newtonian dynamics (MOND) scenario: MOND phenomenons naturally emerge as a derived concept due to an extra force mediated between baryons by phonons as a result of axionlike particles condensed as superfluid at galactic scales; Beyond galactic scales, these axionlike particles behave as normal fluid without phonon-mediated MOND-like force between baryons, therefore SfDM also maintains the usual success of Λ CDM at cosmological scales. In this paper, we use gravitational waves (GWs) to probe the relevant parameter space of SfDM. GWs through Bose-Einstein condensate (BEC) could propagate with a speed slightly deviation from the speed-of-light due to the change in the effective refractive index, which depends on the SfDM parameters and GW-source properties. We find that Five hundred meter Aperture Spherical Telescope (FAST), Square Kilometre Array (SKA) and International Pulsar Timing Array (IPTA) are the most promising means as GW probe of relevant parameter space of SfDM. Future space-based GW detectors are also capable of probing SfDM if a multimessenger approach is adopted.

LIMITS ON THE EVENT RATES OF FAST RADIO TRANSIENTS FROM THE V-FASTR EXPERIMENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wayth, Randall B.; Tingay, Steven J.; Deller, Adam T.

2012-07-10

We present the first results from the V-FASTR experiment, a commensal search for fast transient radio bursts using the Very Long Baseline Array (VLBA). V-FASTR is unique in that the widely spaced VLBA antennas provide a discriminant against non-astronomical signals and a mechanism for the localization and identification of events that is not possible with single dishes or short baseline interferometers. Thus, far V-FASTR has accumulated over 1300 hr of observation time with the VLBA, between 90 cm and 3 mm wavelength (327 MHz-86 GHz), providing the first limits on fast transient event rates at high radio frequencies (>1.4 GHz).more » V-FASTR has blindly detected bright individual pulses from seven known pulsars but has not detected any single-pulse events that would indicate high-redshift impulsive bursts of radio emission. At 1.4 GHz, V-FASTR puts limits on fast transient event rates comparable with the PALFA survey at the Arecibo telescope, but generally at lower sensitivities, and comparable to the 'fly's eye' survey at the Allen Telescope Array, but with less sky coverage. We also illustrate the likely performance of the Phase 1 SKA dish array for an incoherent fast transient search fashioned on V-FASTR.« less

A FRAMEWORK FOR INTERPRETING FAST RADIO TRANSIENTS SEARCH EXPERIMENTS: APPLICATION TO THE V-FASTR EXPERIMENT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trott, Cathryn M.; Tingay, Steven J.; Wayth, Randall B.

2013-04-10

We define a framework for determining constraints on the detection rate of fast transient events from a population of underlying sources, with a view to incorporate beam shape, frequency effects, scattering effects, and detection efficiency into the metric. We then demonstrate a method for combining independent data sets into a single event rate constraint diagram, using a probabilistic approach to the limits on parameter space. We apply this new framework to present the latest results from the V-FASTR experiment, a commensal fast transients search using the Very Long Baseline Array (VLBA). In the 20 cm band, V-FASTR now has themore » ability to probe the regions of parameter space of importance for the observed Lorimer and Keane fast radio transient candidates by combining the information from observations with differing bandwidths, and properly accounting for the source dispersion measure, VLBA antenna beam shape, experiment time sampling, and stochastic nature of events. We then apply the framework to combine the results of the V-FASTR and Allen Telescope Array Fly's Eye experiments, demonstrating their complementarity. Expectations for fast transients experiments for the SKA Phase I dish array are then computed, and the impact of large differential bandwidths is discussed.« less

CONRAD Software Architecture

NASA Astrophysics Data System (ADS)

Guzman, J. C.; Bennett, T.

2008-08-01

The Convergent Radio Astronomy Demonstrator (CONRAD) is a collaboration between the computing teams of two SKA pathfinder instruments, MeerKAT (South Africa) and ASKAP (Australia). Our goal is to produce the required common software to operate, process and store the data from the two instruments. Both instruments are synthesis arrays composed of a large number of antennas (40 - 100) operating at centimeter wavelengths with wide-field capabilities. Key challenges are the processing of high volume of data in real-time as well as the remote mode of operations. Here we present the software architecture for CONRAD. Our design approach is to maximize the use of open solutions and third-party software widely deployed in commercial applications, such as SNMP and LDAP, and to utilize modern web-based technologies for the user interfaces, such as AJAX.

Pipeline Processing with an Iterative, Context-Based Detection Model

DTIC Science & Technology

2016-01-22

25: Teleseismic paths from earthquakes in Myanmar to three North American arrays. The path length to ILAR (the nearest array) is about 8950...kilometers. ................................. 57 Figure 26: Waveforms of Myanmar calibration event (left) and target event (right), recorded at ILAR...one Myanmar event (2007 5/16 8:56:16.0, Mw 6.3; 20.47°N 100.69°E) as a calibration for a second event occurring nearly 4 years later (2011 3/24 13:55

Results of the 1979 NASA/JPL balloon flight solar cell calibration program

NASA Technical Reports Server (NTRS)

Seaman, C. H.; Weiss, R. S.

1980-01-01

Calibration of solar cells to be used as reference standards in simulator testing of cells and arrays was accomplished. Thirty-eight modules were carried to an altitude of about 36 kilometers during the solar cell calibration balloon flight.

Clinical Effects of Posterior Limited Long-Segment Pedicle Instrumentation for the Treatment of Thoracolumbar Fractures.

PubMed

Liang, Chengmin; Liu, Bin; Zhang, Wei; Yu, Haiyang; Cao, Jie; Yin, Wen

2018-06-01

The purpose of this study was to assess the clinical effects of treating thoracolumbar fractures with posterior limited long-segment pedicle instrumentation (LLSPI). A total of 58 thoracolumbar fracture patients were retrospectively analyzed, including 31 cases that were fixed by skipping the fractured vertebra with 6 screws using LLSPI and 27 cases that were fixed by skipping the fractured vertebra with 4 screws using short-segment pedicle instrumentation (SSPI). Surgery time, blood loss, hospital stay, Oswestry disability index (ODI), neurological function, sagittal kyphotic Cobb angle (SKA), percentage of anterior vertebral height (PAVH), instrumentation failure, and the loss of SKA and PAVH were recorded before and after surgery. No significant differences were observed in either the surgery time or hospital stay (P < 0.05), while there were significant differences in blood loss between the two groups. At the final follow-up, both the ODI and the neurological status were notably improved compared to those at the preoperative state (P < 0.05), but the difference between the two groups was relatively small. Furthermore, the SKA and PAVH were notably improved at the final follow-up compared to postoperative values (P < 0.05), but no significant difference was observed between the two groups. During long-term follow-up, the loss of SKA and PAVH in the LLSPI group was significantly less than that in the SSPI group (P < 0.05). Based on strict criteria for data collection and analysis, the clinical effects of LLSPI for the treatment of thoracolumbar fractures were satisfactory, especially for maintaining the height of the fractured vertebra and reducing the loss of SKA and instrumentation failure rates.

Responses of a tall building with U.S. code-type instrumentation in Tokyo, Japan, to events before, during and after the Tohoku earthquake of 11 March 2011

USGS Publications Warehouse

Çelebi, Mehmet; Kashima, Toshihide; Ghahari, S. Farid; Abazarsa, Fariba; Taciroglu, Ertugrul

2016-01-01

The 11 March 2011 M 9.0 Tohoku earthquake generated long-duration shaking that propagated hundreds of kilometers from the epicenter and affected tall buildings in urban areas several hundred kilometers from the epicenter of the main shock. Recorded responses show that tall buildings were affected by long-period motions. This study presents the behavior and performance of a 37-story building in the Tsukuda area of Tokyo, Japan, as inferred from modal analyses of records retrieved for a time interval covering a few days before, during, and for several months after the main shock. The U.S. “code-type” array comprises three triaxial accelerometers deployed at three levels in the superstructure. Such a sparse array in a tall structure limits a reliable assessment, because its performance must be based on only the average drift ratios. Based on the inferred values of this parameter, the subject building was not structurally damaged.

R&D at JIVE: transforming the way VLBI is done

NASA Astrophysics Data System (ADS)

Szomoru, Arpad; van Langevelde, Huib

2015-08-01

Arpad Szomoru, Huib van Langevelde and the JIVE staffFor many years, the heart of operations at JIVE has been the MkIV hardware correlator, a custom-built high-performance data processor. At this time the MkIV has been replaced by the locally developed EVN software correlator (SFXC).This development has vastly improved the science capacity of the EVN, by providing higher spectral resolution and polarization accuracy, but most notably, by enabling completely new observing modes. Observing multiple simultaneous field centers has enabled wide-field imaging, while a phased-array mode has made it possible to do pulsar time series with the EVN. New algorithms have been developed for near-field VLBI, making it possible to focus on objects within our solar system. This has been used to track the RadioAstron satellite, and by applying the derived orbital parameters to improve subsequent space VLBI observations.New digital baseband convertors will allow higher observing bandwidths in the EVN. In anticipation of this, and of the even higher bandwidths of future mm-VLBI observations, added to the deployment of much larger arrays (including the AVN, the SKA precursors and the SKA itself), we are investigating more powerful and economical solutions. The JIVE UniBoard Correlator is the first FPGA-based EVN correlator; its scalability and flexibility are now under assessment. The new UniBoard2 project, also sponsored by the EC, will skip two generations of FPGA technology and deliver enormous processing power at lower power consumption.Maybe just as importantly, research is ongoing into software tools to enable the efficient handling of the vast data sets that the EVN and other current and future instruments will produce. New data processing pipelines are being designed that will be able to cache intermediate products, and upon changing parameters only re-calculate what is needed, as opposed to re-starting every time from scratch.Finally, we will discuss the development of time and frequency transfer via public networks, in the context of a new H2020 project aimed at the astronomy, astrophysics and astroparticle physics faciclities within the ESFRI roadmap .

Concorde sonic booms as an atmospheric probe.

PubMed

Balachandran, N K; Donn, W L; Rind, D H

1977-07-01

Infrasound generated by the sonic boom from the inbound Concorde supersonic transport is recorded at Palisades, New York (Lamont-Doherty Geological Observatory), as a series of impulses from distances varying from 165 to about 1000 kilometers. Refraction effects determined by temperature and wind conditions return the signal to the surface from both stratospheric (40 to 50 kilometers) and thermospheric (100 to 130 kilometers) levels. The frequency of the recorded signal is a function of the level of reflection; the frequency decreases from impulse stretching as the atmosphere becomes more rarified relative to the sound pressure. The horizontal trace velocity of the signal across the array of instruments is equal to the acoustic velocity at the reflection level. The sonic boom can thus be used to provide temperature-wind parameters at reflection levels estimated from the signal frequency. Daily observed signal variations have indicated significant variations in these parameters.

Seismomagnetic observation during the 8 July 1986 magnitude 5.9 North Palm Springs earthquake

USGS Publications Warehouse

Johnston, M.J.S.; Mueller, R.J.

1987-01-01

A differentially connected array of 24 proton magnetometers has operated along the San Andreas fault since 1976. Seismomagnetic offsets of 1.2 and 0.3 nanotesla were observed at epicentral distances of 3 and 9 kilometers, respectively, after the 8 July 1986 magnitude 5.9 North Palm Springs earthquake. These seismomagnetic observations are the first obtained of this elusive but long-anticipated effect. The data are consistent with a seismomagnetic model of the earthquake for which right-lateral rupture of 20 centimeters is assumed on a 16-kilometer segment of the Banning fault between the depths of 3 and 10 kilometers in a region with average magnetization of 1 ampere per meter. Alternative explanations in terms of electrokinetic effects and earthquake-generated electrostatic charge redistribution seem unlikely because the changes are permanent and complete within a 20-minute period.

SETI reloaded: Next generation radio telescopes, transients and cognitive computing

NASA Astrophysics Data System (ADS)

Garrett, Michael A.

2015-08-01

The Search for Extra-terrestrial Intelligence (SETI) using radio telescopes is an area of research that is now more than 50 years old. Thus far, both targeted and wide-area surveys have yet to detect artificial signals from intelligent civilisations. In this paper, I argue that the incidence of co-existing intelligent and communicating civilisations is probably small in the Milky Way. While this makes successful SETI searches a very difficult pursuit indeed, the huge impact of even a single detection requires us to continue the search. A substantial increase in the overall performance of radio telescopes (and in particular future wide-field instruments such as the Square Kilometre Array - SKA), provide renewed optimism in the field. Evidence for this is already to be seen in the success of SETI researchers in acquiring observations on some of the world's most sensitive radio telescope facilities via open, peer-reviewed processes. The increasing interest in the dynamic radio sky, and our ability to detect new and rapid transient phenomena such as Fast Radio Bursts (FRB) is also greatly encouraging. While the nature of FRBs is not yet fully understood, I argue they are unlikely to be the signature of distant extra-terrestrial civilisations. As astronomers face a data avalanche on all sides, advances made in related areas such as advanced Big Data analytics, and cognitive computing are crucial to enable serendipitous discoveries to be made. In any case, as the era of the SKA fast approaches, the prospects of a SETI detection have never been better.

Power monitoring and control for large scale projects: SKA, a case study

NASA Astrophysics Data System (ADS)

Barbosa, Domingos; Barraca, João. Paulo; Maia, Dalmiro; Carvalho, Bruno; Vieira, Jorge; Swart, Paul; Le Roux, Gerhard; Natarajan, Swaminathan; van Ardenne, Arnold; Seca, Luis

2016-07-01

Large sensor-based science infrastructures for radio astronomy like the SKA will be among the most intensive datadriven projects in the world, facing very high demanding computation, storage, management, and above all power demands. The geographically wide distribution of the SKA and its associated processing requirements in the form of tailored High Performance Computing (HPC) facilities, require a Greener approach towards the Information and Communications Technologies (ICT) adopted for the data processing to enable operational compliance to potentially strict power budgets. Addressing the reduction of electricity costs, improve system power monitoring and the generation and management of electricity at system level is paramount to avoid future inefficiencies and higher costs and enable fulfillments of Key Science Cases. Here we outline major characteristics and innovation approaches to address power efficiency and long-term power sustainability for radio astronomy projects, focusing on Green ICT for science and Smart power monitoring and control.

A procedure for sensory detection of androstenone in meat and meat products from entire male pigs: Development of a panel training.

PubMed

Garrido, Mª Dolores; Egea, Macarena; Linares, Mª Belén; Martínez, Beatriz; Viera, Ceferina; Rubio, Begoña; Borrisser-Pairó, Francesc

2016-12-01

This study represents a proposal for training sensory panels in androstenone (AND) perception in meat and meat products. The procedure consists of four main parts: (1) selection and training of a sensory panel (11 panelists) using standards with Vaseline oil media as carriers of AND and skatole (SKA); (2) developing a training method AND detection in meat; (3) dry cured meat product and (4) cooked meat product. All candidates were able to distinguish between AND, SKA and AND+SKA in Vaseline oil, order AND solutions with different concentrations and classify them in the three categories: low, medium and high. The panel was able to differentiate the meat in the three categories, but only the high level in meat products. Due to the individual features in AND perception, specific training for each type of product is required. Copyright © 2016 Elsevier Ltd. All rights reserved.

Results of the 1980 NASA/JPL balloon flight solar cell calibration program

NASA Technical Reports Server (NTRS)

Seaman, C. H.; Weiss, R. S.

1981-01-01

Thirty-eight modules were carried to an altitude of about 36 kilometers. In addition to the cell calibration program, an experiment to evaluate the calibration error versus altitude was performed. The calibrated cells can be used as reference standards in simulator testing of cells and arrays.

Detecting signatures of cosmological recombination and reionization in the cosmic radio background

NASA Astrophysics Data System (ADS)

Subrahmanyan, Ravi; Shankar Narayana Rao, Udaya; Sathyanarayana Rao, Mayuri; Singh, Saurabh

2015-08-01

Evolution of the baryons during the Epochs of cosmological Recombination and Reionization has left traces in the cosmic radio background in the form of spectral distortions (Sunyaev & Chluba 2008 Astron. Nachrichten, 330, 657; Pritchard & Loeb 2012 Rep Prog Phys 75(8):086901). The spectral signature depends on the evolution in the ionization state in hydrogen and helium and on the spin temperature of hydrogen. These probe the physics of energy release beyond the last scattering surface at redshifts exceeding 1090 and the nature of the first sources and gas evolution down to redshift about 6. The spectral distortions are sensitive to the nature of the first stars, ultra-dwarf galaxies, accreting compact objects, and the evolving ambient radiation field: X-rays and UV from the first sources. Detection of the all-sky or global spectral distortions in the radio background is hence a probe of cosmological recombination and reionization.We present new spectral radiometers that we have purpose designed for precision measurements of spectral distortions at radio wavelengths. New antenna elements include frequency independent and electrically small fat-dipole (Raghunathan et al. 2013 IEEE TAP, 61, 3411) and monopole designs. Receiver configurations have been devised that are self-calibratable (Patra et al. 2013 Expt Astron, 36, 319) so that switching of signal paths and of calibration noise sources provide real time calibration for systematics and receiver noise. Observing strategies (Patra et al. arXiv:1412.7762) and analysis methods (Satyanarayana Rao et al. arXiv:1501.07191) have been evolved that are capable of discriminating between the cosmological signals and the substantially brighter foregrounds. We have also demonstrated the value of system designs that exploit advantages of interferometer detection (Mahesh et al. arXiv:1406.2585) of global spectral distortions.Finally we discuss how the Square Kilometer Array stations may be outfitted with precision spectral radiometer outriggers (Subrahmanyan et al. arXiv:1501.04340) to provide the zero-spacing measurement sets, complement the interferometer visibilities and give the SKA a capability for measurements of cosmic radio background spectral distortions.

Automated detection of extended sources in radio maps: progress from the SCORPIO survey

NASA Astrophysics Data System (ADS)

Riggi, S.; Ingallinera, A.; Leto, P.; Cavallaro, F.; Bufano, F.; Schillirò, F.; Trigilio, C.; Umana, G.; Buemi, C. S.; Norris, R. P.

2016-08-01

Automated source extraction and parametrization represents a crucial challenge for the next-generation radio interferometer surveys, such as those performed with the Square Kilometre Array (SKA) and its precursors. In this paper, we present a new algorithm, called CAESAR (Compact And Extended Source Automated Recognition), to detect and parametrize extended sources in radio interferometric maps. It is based on a pre-filtering stage, allowing image denoising, compact source suppression and enhancement of diffuse emission, followed by an adaptive superpixel clustering stage for final source segmentation. A parametrization stage provides source flux information and a wide range of morphology estimators for post-processing analysis. We developed CAESAR in a modular software library, also including different methods for local background estimation and image filtering, along with alternative algorithms for both compact and diffuse source extraction. The method was applied to real radio continuum data collected at the Australian Telescope Compact Array (ATCA) within the SCORPIO project, a pathfinder of the Evolutionary Map of the Universe (EMU) survey at the Australian Square Kilometre Array Pathfinder (ASKAP). The source reconstruction capabilities were studied over different test fields in the presence of compact sources, imaging artefacts and diffuse emission from the Galactic plane and compared with existing algorithms. When compared to a human-driven analysis, the designed algorithm was found capable of detecting known target sources and regions of diffuse emission, outperforming alternative approaches over the considered fields.

Photovoltaic solar array technology required for three wide scale generating systems for terrestrial applications: rooftop, solar farm, and satellite

NASA Technical Reports Server (NTRS)

Berman, P. A.

1972-01-01

Three major options for wide-scale generation of photovoltaic energy for terrestrial use are considered: (1) rooftop array, (2) solar farm, and (3) satellite station. The rooftop array would use solar cell arrays on the roofs of residential or commercial buildings; the solar farm would consist of large ground-based arrays, probably in arid areas with high insolation; and the satellite station would consist of an orbiting solar array, many square kilometers in area. The technology advancement requirements necessary for each option are discussed, including cost reduction of solar cells and arrays, weight reduction, resistance to environmental factors, reliability, and fabrication capability, including the availability of raw materials. The majority of the technology advancement requirements are applicable to all three options, making possible a flexible basic approach regardless of the options that may eventually be chosen. No conclusions are drawn as to which option is most advantageous, since the feasibility of each option depends on the success achieved in the technology advancement requirements specified.

Designing Successful Next-Generation Instruments to Detect the Epoch of Reionization

NASA Astrophysics Data System (ADS)

Thyagarajan, Nithyanandan; Hydrogen Epoch of Reionization Array (HERA) team, Murchison Widefield Array (MWA) team

2018-01-01

The Epoch of Reionization (EoR) signifies a period of intense evolution of the Inter-Galactic Medium (IGM) in the early Universe caused by the first generations of stars and galaxies, wherein they turned the neutral IGM to be completely ionized by redshift ≥ 6. This important epoch is poorly explored to date. Measurement of redshifted 21 cm line from neutral Hydrogen during the EoR is promising to provide the most direct constraints of this epoch. Ongoing experiments to detect redshifted 21 cm power spectrum during reionization, including the Murchison Widefield Array (MWA), Precision Array for Probing the Epoch of Reionization (PAPER), and the Low Frequency Array (LOFAR), appear to be severely affected by bright foregrounds and unaccounted instrumental systematics. For example, the spectral structure introduced by wide-field effects, aperture shapes and angular power patterns of the antennas, electrical and geometrical reflections in the antennas and electrical paths, and antenna position errors can be major limiting factors. These mimic the 21 cm signal and severely degrade the instrument performance. It is imperative for the next-generation of experiments to eliminate these systematics at their source via robust instrument design. I will discuss a generic framework to set cosmologically motivated antenna performance specifications and design strategies using the Precision Radio Interferometry Simulator (PRISim) -- a high-precision tool that I have developed for simulations of foregrounds and the instrument transfer function intended primarily for 21 cm EoR studies, but also broadly applicable to interferometer-based intensity mapping experiments. The Hydrogen Epoch of Reionization Array (HERA), designed in-part based on this framework, is expected to detect the 21 cm signal with high significance. I will present this framework and the simulations, and their potential for designing upcoming radio instruments such as HERA and the Square Kilometre Array (SKA).

Imaging the redshifted 21 cm pattern around the first sources during the cosmic dawn using the SKA

NASA Astrophysics Data System (ADS)

Ghara, Raghunath; Choudhury, T. Roy; Datta, Kanan K.; Choudhuri, Samir

2017-01-01

Understanding properties of the first sources in the Universe using the redshifted H I 21 cm signal is one of the major aims of present and upcoming low-frequency experiments. We investigate the possibility of imaging the redshifted 21 cm pattern around the first sources during the cosmic dawn using the SKA1-low. We model the H I 21 cm image maps, appropriate for the SKA1-low, around the first sources consisting of stars and X-ray sources within galaxies. In addition to the system noise, we also account for the astrophysical foregrounds by adding them to the signal maps. We find that after subtracting the foregrounds using a polynomial fit and suppressing the noise by smoothing the maps over 10-30 arcmin angular scale, the isolated sources at z ˜ 15 are detectable with the ˜4σ-9σ confidence level in 2000 h of observation with the SKA1-low. Although the 21 cm profiles around the sources get altered because of the Gaussian smoothing, the images can still be used to extract some of the source properties. We account for overlaps in the patterns of the individual sources by generating realistic H I 21 cm maps of the cosmic dawn that are based on N-body simulations and a one-dimensional radiative transfer code. We find that these sources should be detectable in the SKA1-low images at z = 15 with a signal-to-noise ratio (SNR) of ˜14(4) in 2000 (200) h of observations. One possible observational strategy thus could be to observe multiple fields for shorter observation times, identify fields with SNR ≳ 3 and observe these fields for much longer duration. Such observations are expected to be useful in constraining the parameters related to the first sources.

Results from Dealing with Rock and Gas Outburst Prevention in The Czech Republic / Efekty Działań Mających Na Celu Zapobieganie Wybuchom Skał I Gazu, Podejmowanych W Republice Czeskiej

NASA Astrophysics Data System (ADS)

Hudeček, Vlastimil; Zapletal, Pavel; Stoniš, Milan; Sojka, Radislav

2013-09-01

In the Czech Republic, the prevention of rock and gas outbursts is carried out in the course of driving mine workings in seams and in sandstone and conglomerate beds classified into a category with the highest degree of rock and gas outburst hazard. It is a case of active methods that aim at prevention of rock and gas outbursts by creating a protection zone in front of and in sides of mine workings being driven and passive methods that mitigate the effects of outbursts (Hudeček et al., 2009, 2010). In this article, authors present recommendations and proposals for changes in rock and gas outburst prevention. These proposed changes should reflect in increased efficiency in coping with this anomalous geomechanical events. Działania w celu zapobiegania wybuchom skał i gazów w Republice czeskiej podejmowane są już na etapie drążenia wyrobisk w złożach oraz w piaskowcach oraz w pokładach zlepieńców sklasyfikowanych jako lokalizacje o najwyższym stopniu zagrożenia wybuchami skał i gazów. W tym przypadku mamy do dyspozycji metody aktywne, których celem jest zapobieżenie wybuchom skał i gazów poprzez stworzenie strefy ochronnej w części czołowej i bocznych częściach wyrobiska oraz metody bierne, mające na celu złagodzenie skutków wybuchu (Hudecek et al., 2009, 2010). W artykule autor rekomenduje i zaleca dokonanie pewnych zmian w systemie zapobiegania wybuchom skał i gazów. Proponowane zmiany skutkować powinny zwiększoną skutecznością działania w przypadku wystąpienia zjawisk geomechanicznych uznawanych za anomalie.

Antenna data storage concept for phased array radio astronomical instruments

NASA Astrophysics Data System (ADS)

Gunst, André W.; Kruithof, Gert H.

2018-04-01

Low frequency Radio Astronomy instruments like LOFAR and SKA-LOW use arrays of dipole antennas for the collection of radio signals from the sky. Due to the large number of antennas involved, the total data rate produced by all the antennas is enormous. Storage of the antenna data is both economically and technologically infeasible using the current state of the art storage technology. Therefore, real-time processing of the antenna voltage data using beam forming and correlation is applied to achieve a data reduction throughout the signal chain. However, most science could equally well be performed using an archive of raw antenna voltage data coming straight from the A/D converters instead of capturing and processing the antenna data in real time over and over again. Trends on storage and computing technology make such an approach feasible on a time scale of approximately 10 years. The benefits of such a system approach are more science output and a higher flexibility with respect to the science operations. In this paper we present a radically new system concept for a radio telescope based on storage of raw antenna data. LOFAR is used as an example for such a future instrument.

Portion of Pluto Sputnik Planum Sputnik Plain

NASA Image and Video Library

2015-07-17

This annotated view of a portion of Pluto's Sputnik Planum (Sputnik Plain), named for Earth's first artificial satellite, shows an array of enigmatic features. The surface appears to be divided into irregularly shaped segments that are ringed by narrow troughs, some of which contain darker materials. Features that appear to be groups of mounds and fields of small pits are also visible. This image was acquired by the Long Range Reconnaissance Imager (LORRI) on July 14 from a distance of 48,000 miles (77,000 kilometers). Features as small as a half-mile (1 kilometer) across are visible. The blocky appearance of some features is due to compression of the image. http://photojournal.jpl.nasa.gov/catalog/PIA19714

Results of the 1984 NASA/JPL balloon flight solar cell calibration program

NASA Technical Reports Server (NTRS)

Downing, R. G.; Weiss, R. S.

1984-01-01

The 1984 solar cell calibration balloon flight was successfully completed on July 19, meeting all objectives of the program. Thirty-six modules were carried to an altitude of 36.0 kilometers. The calibrated cells can now be used as reference standards in simulator testing of cells and arrays.

Results of the 1982 NASA/JPL balloon flight solar cell calibration program

NASA Technical Reports Server (NTRS)

Downing, R. G.; Weiss, R. S.

1983-01-01

The 1982 solar cell calibration balloon flight was successfully completed on July 21, meeting all objectives of the program. Twenty-eight modules were carried to an altitude of 36.0 kilometers. The calibrated cells can now be used as reference standards in simulator testing of cells and arrays.

47 CFR 73.154 - AM directional antenna partial proof of performance measurements.

Code of Federal Regulations, 2013 CFR

2013-10-01

... 47 Telecommunication 4 2013-10-01 2013-10-01 false AM directional antenna partial proof of...) BROADCAST RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.154 AM directional antenna... measurements are to be made within 3 to 15 kilometers from the center of the antenna array. When a monitoring...

47 CFR 73.154 - AM directional antenna partial proof of performance measurements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 47 Telecommunication 4 2012-10-01 2012-10-01 false AM directional antenna partial proof of...) BROADCAST RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.154 AM directional antenna... measurements are to be made within 3 to 15 kilometers from the center of the antenna array. When a monitoring...

47 CFR 73.154 - AM directional antenna partial proof of performance measurements.

Code of Federal Regulations, 2014 CFR

2014-10-01

... 47 Telecommunication 4 2014-10-01 2014-10-01 false AM directional antenna partial proof of...) BROADCAST RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.154 AM directional antenna... measurements are to be made within 3 to 15 kilometers from the center of the antenna array. When a monitoring...

47 CFR 73.154 - AM directional antenna partial proof of performance measurements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 47 Telecommunication 4 2011-10-01 2011-10-01 false AM directional antenna partial proof of...) BROADCAST RADIO SERVICES RADIO BROADCAST SERVICES AM Broadcast Stations § 73.154 AM directional antenna... measurements are to be made within 3 to 15 kilometers from the center of the antenna array. When a monitoring...

Calibration of the LHAASO-KM2A electromagnetic particle detectors using charged particles within the extensive air showers

NASA Astrophysics Data System (ADS)

Lv, Hongkui; He, Huihai; Sheng, Xiangdong; Liu, Jia; Chen, Songzhan; Liu, Ye; Hou, Chao; Zhao, Jing; Zhang, Zhongquan; Wu, Sha; Wang, Yaping; Lhaaso Collaboration

2018-07-01

In the Large High Altitude Air Shower Observatory (LHAASO), one square kilometer array (KM2A), with 5242 electromagnetic particle detectors (EDs) and 1171 muon detectors (MDs), is designed to study ultra-high energy gamma-ray astronomy and cosmic ray physics. The remoteness and numerous detectors extremely demand a robust and automatic calibration procedure. In this paper, a self-calibration method which relies on the measurement of charged particles within the extensive air showers is proposed. The method is fully validated by Monte Carlo simulation and successfully applied in a KM2A prototype array experiment. Experimental results show that the self-calibration method can be used to determine the detector time offset constants at the sub-nanosecond level and the number density of particles collected by each ED with an accuracy of a few percents, which are adequate to meet the physical requirements of LHAASO experiment. This software calibration also offers an ideal method to realtime monitor the detector performances for next generation ground-based EAS experiments covering an area above square kilometers scale.

Research on Wide-field Imaging Technologies for Low-frequency Radio Array

NASA Astrophysics Data System (ADS)

Lao, B. Q.; An, T.; Chen, X.; Wu, X. C.; Lu, Y.

2017-09-01

Wide-field imaging of low-frequency radio telescopes are subject to a number of difficult problems. One particularly pernicious problem is the non-coplanar baseline effect. It will lead to distortion of the final image when the phase of w direction called w-term is ignored. The image degradation effects are amplified for telescopes with the wide field of view. This paper summarizes and analyzes several w-term correction methods and their technical principles. Their advantages and disadvantages have been analyzed after comparing their computational cost and computational complexity. We conduct simulations with two of these methods, faceting and w-projection, based on the configuration of the first-phase Square Kilometre Array (SKA) low frequency array. The resulted images are also compared with the two-dimensional Fourier transform method. The results show that image quality and correctness derived from both faceting and w-projection are better than the two-dimensional Fourier transform method in wide-field imaging. The image quality and run time affected by the number of facets and w steps have been evaluated. The results indicate that the number of facets and w steps must be reasonable. Finally, we analyze the effect of data size on the run time of faceting and w-projection. The results show that faceting and w-projection need to be optimized before the massive amounts of data processing. The research of the present paper initiates the analysis of wide-field imaging techniques and their application in the existing and future low-frequency array, and fosters the application and promotion to much broader fields.

Analysing the 21 cm signal from the epoch of reionization with artificial neural networks

NASA Astrophysics Data System (ADS)

Shimabukuro, Hayato; Semelin, Benoit

2017-07-01

The 21 cm signal from the epoch of reionization should be observed within the next decade. While a simple statistical detection is expected with Square Kilometre Array (SKA) pathfinders, the SKA will hopefully produce a full 3D mapping of the signal. To extract from the observed data constraints on the parameters describing the underlying astrophysical processes, inversion methods must be developed. For example, the Markov Chain Monte Carlo method has been successfully applied. Here, we test another possible inversion method: artificial neural networks (ANNs). We produce a training set that consists of 70 individual samples. Each sample is made of the 21 cm power spectrum at different redshifts produced with the 21cmFast code plus the value of three parameters used in the seminumerical simulations that describe astrophysical processes. Using this set, we train the network to minimize the error between the parameter values it produces as an output and the true values. We explore the impact of the architecture of the network on the quality of the training. Then we test the trained network on the new set of 54 test samples with different values of the parameters. We find that the quality of the parameter reconstruction depends on the sensitivity of the power spectrum to the different parameters at a given redshift, that including thermal noise and sample variance decreases the quality of the reconstruction and that using the power spectrum at several redshifts as an input to the ANN improves the quality of the reconstruction. We conclude that ANNs are a viable inversion method whose main strength is that they require a sparse exploration of the parameter space and thus should be usable with full numerical simulations.

Algorithmic aspects for the reconstruction of spatio-spectral data cubes in the perspective of the SKA

NASA Astrophysics Data System (ADS)

Mary, D.; Ferrari, A.; Ferrari, C.; Deguignet, J.; Vannier, M.

2016-12-01

With millions of receivers leading to TerraByte data cubes, the story of the giant SKA telescope is also that of collaborative efforts from radioastronomy, signal processing, optimization and computer sciences. Reconstructing SKA cubes poses two challenges. First, the majority of existing algorithms work in 2D and cannot be directly translated into 3D. Second, the reconstruction implies solving an inverse problem and it is not clear what ultimate limit we can expect on the error of this solution. This study addresses (of course partially) both challenges. We consider an extremely simple data acquisition model, and we focus on strategies making it possible to implement 3D reconstruction algorithms that use state-of-the-art image/spectral regularization. The proposed approach has two main features: (i) reduced memory storage with respect to a previous approach; (ii) efficient parallelization and ventilation of the computational load over the spectral bands. This work will allow to implement and compare various 3D reconstruction approaches in a large scale framework.

Revolutionizing Our Understanding of AGN Feedback and its Importance to Galaxy Evolution in the Era of the Next Generation Very Large Array

NASA Astrophysics Data System (ADS)

Nyland, K.; Harwood, J. J.; Mukherjee, D.; Jagannathan, P.; Rujopakarn, W.; Emonts, B.; Alatalo, K.; Bicknell, G. V.; Davis, T. A.; Greene, J. E.; Kimball, A.; Lacy, M.; Lonsdale, Carol; Lonsdale, Colin; Maksym, W. P.; Molnár, D. C.; Morabito, L.; Murphy, E. J.; Patil, P.; Prandoni, I.; Sargent, M.; Vlahakis, C.

2018-05-01

Energetic feedback by active galactic nuclei (AGNs) plays an important evolutionary role in the regulation of star formation on galactic scales. However, the effects of this feedback as a function of redshift and galaxy properties such as mass, environment, and cold gas content remain poorly understood. The broad frequency coverage (1 to 116 GHz), high sensitivity (up to ten times higher than the Karl G. Jansky Very Large Array), and superb angular resolution (maximum baselines of at least a few hundred kilometers) of the proposed next-generation Very Large Array (ngVLA) are uniquely poised to revolutionize our understanding of AGNs and their role in galaxy evolution. Here, we provide an overview of the science related to AGN feedback that will be possible in the ngVLA era and present new continuum ngVLA imaging simulations of resolved radio jets spanning a wide range of intrinsic extents. We also consider key computational challenges and discuss exciting opportunities for multiwavelength synergy with other next-generation instruments, such as the Square Kilometer Array and the James Webb Space Telescope. The unique combination of high-resolution, large collecting area, and wide frequency range will enable significant advancements in our understanding of the effects of jet-driven feedback on sub-galactic scales, particularly for sources with extents of a few parsec to a few kiloparsec, such as young and/or lower-power radio AGNs, AGNs hosted by low-mass galaxies, radio jets that are interacting strongly with the interstellar medium of the host galaxy, and AGNs at high redshift.

Relativistic corrections and non-Gaussianity in radio continuum surveys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maartens, Roy; Zhao, Gong-Bo; Bacon, David

Forthcoming radio continuum surveys will cover large volumes of the observable Universe and will reach to high redshifts, making them potentially powerful probes of dark energy, modified gravity and non-Gaussianity. We consider the continuum surveys with LOFAR, WSRT and ASKAP, and examples of continuum surveys with the SKA. We extend recent work on these surveys by including redshift space distortions and lensing convergence in the radio source auto-correlation. In addition we compute the general relativistic (GR) corrections to the angular power spectrum. These GR corrections to the standard Newtonian analysis of the power spectrum become significant on scales near andmore » beyond the Hubble scale at each redshift. We find that the GR corrections are at most percent-level in LOFAR, WODAN and EMU surveys, but they can produce O(10%) changes for high enough sensitivity SKA continuum surveys. The signal is however dominated by cosmic variance, and multiple-tracer techniques will be needed to overcome this problem. The GR corrections are suppressed in continuum surveys because of the integration over redshift — we expect that GR corrections will be enhanced for future SKA HI surveys in which the source redshifts will be known. We also provide predictions for the angular power spectra in the case where the primordial perturbations have local non-Gaussianity. We find that non-Gaussianity dominates over GR corrections, and rises above cosmic variance when f{sub NL}∼>5 for SKA continuum surveys.« less

High redshift signatures in the 21 cm forest due to cosmic string wakes

NASA Astrophysics Data System (ADS)

Tashiro, Hiroyuki; Sekiguchi, Toyokazu; Silk, Joseph

2014-01-01

Cosmic strings induce minihalo formation in the early universe. The resultant minihalos cluster in string wakes and create a ``21 cm forest'' against the cosmic microwave background (CMB) spectrum. Such a 21 cm forest can contribute to angular fluctuations of redshifted 21 cm signals integrated along the line of sight. We calculate the root-mean-square amplitude of the 21 cm fluctuations due to strings and show that these fluctuations can dominate signals from minihalos due to primordial density fluctuations at high redshift (zgtrsim10), even if the string tension is below the current upper bound, Gμ < 1.5 × 10-7. Our results also predict that the Square Kilometre Array (SKA) can potentially detect the 21 cm fluctuations due to strings with Gμ ≈ 7.5 × 10-8 for the single frequency band case and 4.0 × 10-8 for the multi-frequency band case.

Cosmology and Astrophysics using the Post-Reionization HI

NASA Astrophysics Data System (ADS)

Sarkar, Tapomoy Guha; Sen, Anjan A.

2016-12-01

We discuss the prospects of using the redshifted 21-cm emission from neutral hydrogen in the post-reionization epoch to study our Universe. The main aim of the article is to highlight the efforts of Indian scientists in this area with the SKA in mind. It turns out that the intensity mapping surveys from SKA can be instrumental in obtaining tighter constraints on the dark energy models. Cross-correlation of the HI intensity maps with the Ly α forest data can also be useful in measuring the BAO scale.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tingay, S. J.; Wayth, R. B.; Hurley-Walker, N.

The Murchison Widefield Array (MWA) is a new low-frequency interferometric radio telescope, operating in the benign radio frequency environment of remote Western Australia. The MWA is the low-frequency precursor to the Square Kilometre Array (SKA) and is the first of three SKA precursors to be operational, supporting a varied science mission ranging from the attempted detection of the Epoch of Reionization to the monitoring of solar flares and space weather. In this paper we explore the possibility that the MWA can be used for the purposes of Space Situational Awareness (SSA). In particular we propose that the MWA can bemore » used as an element of a passive radar facility operating in the frequency range 87.5-108 MHz (the commercial FM broadcast band). In this scenario the MWA can be considered the receiving element in a bi-static radar configuration, with FM broadcast stations serving as non-cooperative transmitters. The FM broadcasts propagate into space, are reflected off debris in Earth orbit, and are received at the MWA. The imaging capabilities of the MWA can be used to simultaneously detect multiple pieces of space debris, image their positions on the sky as a function of time, and provide tracking data that can be used to determine orbital parameters. Such a capability would be a valuable addition to Australian and global SSA assets, in terms of southern and eastern hemispheric coverage. We provide a feasibility assessment of this proposal, based on simple calculations and electromagnetic simulations, that shows that the detection of sub-meter size debris should be possible (debris radius of >0.5 m to ∼1000 km altitude). We also present a proof-of-concept set of observations that demonstrate the feasibility of the proposal, based on the detection and tracking of the International Space Station via reflected FM broadcast signals originating in southwest Western Australia. These observations broadly validate our calculations and simulations. We discuss some significant challenges that need to be addressed in order to turn the feasible concept into a robust operational capability for SSA. The aggregate received power due to reflections off space debris in the FM band is equivalent to a <1 mJy increase in the background confusion noise for the long integrations needed for Epoch of Reionization experiments, which is insignificant.« less

The many facets of extragalactic radio surveys: towards new scientific challenges

NASA Astrophysics Data System (ADS)

2015-10-01

Radio continuum surveys are a powerful tool to detect large number of objects over a wide range of redshifts and obtain information on the intensity, polarization and distribution properties of radio sources across the sky. They are essential to answer to fundamental questions of modern astrophysics. Radio astronomy is in the midst of a transformation. Developments in high-speed digital signal processing and broad-band optical fibre links between antennas have enabled significant upgrades of the existing radio facilities (e-MERLIN, JVLA, ATCA-CABB, eEVN, APERTIF), and are leading to next-generation radio telescopes (LOFAR, MWA, ASKAP, MeerKAT). All these efforts will ultimately lead to the realization of the Square Kilometre Array (SKA), which, owing to advances in sensitivity, field-of-view, frequency range and spectral resolution, will yield transformational science in many astrophysical research fields. The purpose of this meeting is to explore new scientific perspectives offered by modern radio surveys, focusing on synergies allowed by multi-frequency, multi-resolution observations. We will bring together researchers working on wide aspects of the physics and evolution of extra-galactic radio sources, from star-forming galaxies to AGNs and clusters of galaxies, including their role as cosmological probes. The organization of this conference has been inspired by the recent celebration of the 50th anniversary of the Northern Cross Radio Telescope in Medicina (BO), whose pioneering B2 and B3 surveys provided a significant contribution to radio astronomical studies for many decades afterwards. The conference was organized by the Istituto di Radioastronomia (INAF), and was held at the CNR Research Area in Bologna, on 20-23 October 2015. This Conference has received support from the following bodies and funding agencies: National Institute for Astrophysics (INAF), ASTRON, RadioNet3 (through the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 283393) and the Ministry of Foreign Affairs and International Cooperation, Directorate General for the Country Promotion (under the Bilateral Grant Agreement ZA14GR02 - Mapping the Universe on the Pathway to SKA). Scientific Organizing Committee: I. Prandoni (INAF-IRA) co-chair R. Morganti (ASTRON) co-chair P. Best (ROE) A. Bonafede (Hamburg Univ.) R. Braun (SKA Org) L. Feretti (INAF-IRA) M. Jarvis (Western Cape/Oxford Univ.) E. Murphy (Caltech) R. Norris (CSIRO) M. Perez-Torres (IAA) L. Saripalli (Raman) T. Venturi (INAF-IRA) Local Organizing Committee: R. Cassano (co-chair) I. Prandoni (co-chair) A. Casoni D. Guidetti R. Lico R. Ricci M. Stagni

Expanding Coherent Array Processing to Larger Apertures Using Empirical Matched Field Processing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ringdal, F; Harris, D B; Kvaerna, T

2009-07-23

We have adapted matched field processing, a method developed in underwater acoustics to detect and locate targets, to classify transient seismic signals arising from mining explosions. Matched field processing, as we apply it, is an empirical technique, using observations of historic events to calibrate the amplitude and phase structure of wavefields incident upon an array aperture for particular repeating sources. The objective of this project is to determine how broadly applicable the method is and to understand the phenomena that control its performance. We obtained our original results in distinguishing events from ten mines in the Khibiny and Olenegorsk miningmore » districts of the Kola Peninsula, for which we had exceptional ground truth information. In a cross-validation test, some 98.2% of 549 explosions were correctly classified by originating mine using just the Pn observations (2.5-12.5 Hz) on the ARCES array at ranges from 350-410 kilometers. These results were achieved despite the fact that the mines are as closely spaced as 3 kilometers. Such classification performance is significantly better than predicted by the Rayleigh limit. Scattering phenomena account for the increased resolution, as we make clear in an analysis of the information carrying capacity of Pn under two alternative propagation scenarios: free-space propagation and propagation with realistic (actually measured) spatial covariance structure. The increase in information capacity over a wide band is captured by the matched field calibrations and used to separate explosions from very closely-spaced sources. In part, the improvement occurs because the calibrations enable coherent processing at frequencies above those normally considered coherent. We are investigating whether similar results can be expected in different regions, with apertures of increasing scale and for diffuse seismicity. We verified similar performance with the closely-spaced Zapolyarni mines, though discovered that it may be necessary to divide event populations from a single mine into identifiable subpopulations. For this purpose, we perform cluster analysis using matched field statistics calculated on pairs of individual events as a distance metric. In our initial work, calibrations were derived from ensembles of events ranging in number to more than 100. We are considering the performance now of matched field calibrations derived with many fewer events (even, as mentioned, individual events). Since these are high-variance estimates, we are testing the use of cross-channel, multitaper, spectral estimation methods to reduce the variance of calibrations and detection statistics derived from single-event observations. To test the applicability of the technique in a different tectonic region, we have obtained four years of continuous data from 4 Kazakh arrays and are extracting large numbers of event segments. Our initial results using 132 mining explosions recorded by the Makanchi array are similar to those obtained in the European Arctic. Matched field processing clearly separates the explosions from three closely-spaced mines located approximately 400 kilometers from the array, again using waveforms in a band (6-10 Hz) normally considered incoherent for this array. Having reproduced ARCES-type performance with another small aperture array, we have two additional objectives for matched field processing. We will attempt to extend matched field processing to larger apertures: a 200 km aperture (the KNET) and, if data permit, to an aperture comprised of several Kazakh arrays. We also will investigate the potential of developing matched field processing to roughly locate and classify natural seismicity, which is more diffuse than the concentrated sources of mining explosions that we have investigated to date.« less

Systems and context modeling approach to requirements analysis

NASA Astrophysics Data System (ADS)

Ahuja, Amrit; Muralikrishna, G.; Patwari, Puneet; Subhrojyoti, C.; Swaminathan, N.; Vin, Harrick

2014-08-01

Ensuring completeness and correctness of the requirements for a complex system such as the SKA is challenging. Current system engineering practice includes developing a stakeholder needs definition, a concept of operations, and defining system requirements in terms of use cases and requirements statements. We present a method that enhances this current practice into a collection of system models with mutual consistency relationships. These include stakeholder goals, needs definition and system-of-interest models, together with a context model that participates in the consistency relationships among these models. We illustrate this approach by using it to analyze the SKA system requirements.

Performance of a scintillation detector array operated with LHAASO-KM2A electronics

NASA Astrophysics Data System (ADS)

Wang, Zhen; Guo, Yiqing; Cai, Hui; Chang, Jinfan; Chen, Tianlu; Danzengluobu; Feng, Youliang; Gao, Qi; Gou, Quanbu; Guo, Yingying; Hou, Chao; Hu, Hongbo; Labaciren; Liu, Cheng; Li, Haijin; Liu, Jia; Liu, Maoyuan; Qiao, Bingqiang; Qian, Xiangli; Sheng, Xiangdong; Tian, Zhen; Wang, Qun; Xue, Liang; Yao, Yuhua; Zhang, Shaoru; Zhang, Xueyao; Zhang, Yi

2018-04-01

A scintillation detector array composed of 115 detectors and covering an area of about 20000 m2 was installed at the end of 2016 at the Yangbajing international cosmic ray observatory and has been taking data since then. The array is equipped with electronics from Large High Altitude Air Shower Observatory Square Kilometer Complex Array (LHAASO-KM2A) and, in turn, currently serves as the largest debugging and testing platform for the LHAASO-KM2A. Furthermore, the array was used to study the performance of a wide field-of-view air Cherenkov telescope by providing accurate information on the shower core, direction and energy, etc. This work is mainly dealing with the scintillation detector array. The experimental setup and the offline calibration are described in detail. Then, a thorough comparison between the data and Monte Carlo (MC) simulations is presented and a good agreement is obtained. With the even-odd method, the resolutions of the shower direction and core are measured. Finally, successful observations of the expected Moon's and Sun's shadows of cosmic rays (CRs) verify the measured angular resolution.

Advanced Land Observing Satellite (ALOS) Phased Array Type L-Band Synthetic Aperture Radar (PALSAR) mosaic for the Kahiltna terrane, Alaska, 2007-2010

USGS Publications Warehouse

Cole, Christopher J.; Johnson, Michaela R.; Graham, Garth E.

2015-01-01

The USGS has compiled a continuous, cloud-free 12.5-meter resolution radar mosaic of SAR data of approximately 212,000 square kilometers to examine the suitability of this technology for geologic mapping. This mosaic was created from Advanced Land Observing Satellite (ALOS) Phased Array type L-band Synthetic Aperture Radar (PALSAR) data collected from 2007 to 2010 spanning the Kahiltna terrane and the surrounding area. Interpretation of these data may help geologists understand past geologic processes and identify areas with potential for near-surface mineral resources for further ground-based geological and geochemical investigations.

KSC-97PC1127

NASA Image and Video Library

1997-07-24

Applied Physics Laboratory engineers and technicians from Johns Hopkins University test for true perpendicular solar array deployment of the Advanced Composition Explorer (ACE) in KSC’s Spacecraft Assembly and Encapsulation Facility-II (SAEF-II). The white magnetometer boom seen across the solar array panel will deploy the panel once in space. Scheduled for launch on a Delta II rocket from Cape Canaveral Air Station on Aug. 25, ACE will study low-energy particles of solar origin and high-energy galactic particles. The ACE observatory will be placed into an orbit almost a million miles (1.5 million kilometers) away from the Earth, about 1/100 the distance from the Earth to the Sun

KSC-97PC1128

NASA Image and Video Library

1997-07-24

An Applied Physics Laboratory engineer from Johns Hopkins University tests for true perpendicular solar array deployment of the Advanced Composition Explorer (ACE) in KSC’s Spacecraft Assembly and Encapsulation Facility-II (SAEF-II). The white magnetometer boom seen across the solar array panel will deploy the panel once in space. Scheduled for launch on a Delta II rocket from Cape Canaveral Air Station on Aug. 25, ACE will study low-energy particles of solar origin and high-energy galactic particles. The ACE observatory will be placed into an orbit almost a million miles (1.5 million kilometers) away from the Earth, about 1/100 the distance from the Earth to the Sun

Imprints of quasar duty cycle on the 21cm signal from the Epoch of Reionization

NASA Astrophysics Data System (ADS)

Bolgar, Florian; Eames, Evan; Hottier, Clément; Semelin, Benoit

2018-05-01

Quasars contribute to the 21-cm signal from the Epoch of Reionization (EoR) primarily through their ionizing UV and X-ray emission. However, their radio continuum and Lyman-band emission also regulates the 21-cm signal in their direct environment, potentially leaving the imprint of their duty cycle. We develop a model for the radio and UV luminosity functions of quasars from the EoR, and constrain it using recent observations. Our model is consistent with the recent discovery of the quasar J1342+0928 at redshift ˜7.5, and also predicts only a few quasars suitable for 21-cm forest observations (˜10 mJy) in the sky. We exhibit a new effect on the 21-cm signal observed against the CMB: a radio-loud quasar can leave the imprint of its duty cycle on the 21-cm tomography. We apply this effect in a cosmological simulation and conclude that the effect of typical radio-loud quasars is most likely negligible in an SKA field of view. For a ˜10mJy quasar the effect is stronger though hardly observable at SKA resolution. Then we study the contribution of the lyman band (Ly-α to Ly-β) emission of quasars to the Wouthuisen-Field coupling. The collective effect of quasars on the 21-cm power spectrum is larger than the thermal noise at low k, though featureless. However, a distinctive pattern around the brightest quasars in an SKA field of view may be observable in the tomography, encoding the duration of their duty cycle. This pattern has a high signal-to-noise ratio for the brightest quasar in a typical SKA shallow survey.

Silyl Ketene Acetals/B(C₆F₅)₃ Lewis Pair-Catalyzed Living Group Transfer Polymerization of Renewable Cyclic Acrylic Monomers.

PubMed

Hu, Lu; Zhao, Wuchao; He, Jianghua; Zhang, Yuetao

2018-03-15

This work reveals the silyl ketene acetal (SKA)/B(C₆F₅)₃ Lewis pair-catalyzed room-temperature group transfer polymerization (GTP) of polar acrylic monomers, including methyl linear methacrylate (MMA), and the biorenewable cyclic monomers γ-methyl-α-methylene-γ-butyrolactone (MMBL) and α-methylene-γ-butyrolactone (MBL) as well. The in situ NMR monitored reaction of SKA with B(C₆F₅)₃ indicated the formation of Frustrated Lewis Pairs (FLPs), although it is sluggish for MMA polymerization, such a FLP system exhibits highly activity and living GTP of MMBL and MBL. Detailed investigations, including the characterization of key reaction intermediates, polymerization kinetics and polymer structures have led to a polymerization mechanism, in which the polymerization is initiated with an intermolecular Michael addition of the ester enolate group of SKA to the vinyl group of B(C₆F₅)₃-activated monomer, while the silyl group is transferred to the carbonyl group of the B(C₆F₅)₃-activated monomer to generate the single-monomer-addition species or the active propagating species; the coordinated B(C₆F₅)₃ is released to the incoming monomer, followed by repeated intermolecular Michael additions in the subsequent propagation cycle. Such neutral SKA analogues are the real active species for the polymerization and are retained in the whole process as confirmed by experimental data and the chain-end analysis by matrix-assisted laser desorption/ionization time of flight mass spectroscopy (MALDI-TOF MS). Moreover, using this method, we have successfully synthesized well-defined PMMBL- b -PMBL, PMMBL- b -PMBL- b -PMMBL and random copolymers with the predicated molecular weights ( M n ) and narrow molecular weight distribution (MWD).

Glucocorticoid Receptor Related Genes: Genotype And Brain Gene Expression Relationships To Suicide And Major Depressive Disorder

PubMed Central

Pantazatos, Spiro P.; Huang, Yung-yu; Rosoklija, Gorazd B.; Dwork, Andrew J.; Burke, Ainsley; Arango, Victoria; Oquendo, Maria A.; Mann, J. John

2016-01-01

Introduction We tested the relationship between genotype, gene expression and suicidal behavior and MDD in live subjects and postmortem samples for three genes, associated with the hypothalamic-pituitary-adrenal axis, suicidal behavior and major depressive disorder (MDD); FK506 binding protein 5 (FKBP5), Spindle and kinetochore-associated protein 2 (SKA2) and Glucocorticoid Receptor (NR3C1). Materials and Methods Single-nucleotide polymorphisms (SNPs) and haplotypes were tested for association with suicidal behavior and MDD in a live (N=277) and a postmortem sample (N=209). RNA-seq was used to examine gene and isoform-level brain expression postmortem (Brodmann Area 9) (N=59). Expression quantitative trait loci (eQTL) relationships were examined using a public database (UK Brain Expression Consortium). Results We identified a haplotype within the FKBP5 gene, present in 47% of the live subjects, that was associated with increased risk of suicide attempt (OR=1.58, t=6.03, p=0.014). Six SNPs on this gene, three SNPs on SKA2 and one near NR3C1 showed before-adjustment association with attempted suicide, and two SNPs of SKA2 with suicide death, but none stayed significant after adjustment for multiple testing. Only the SKA2 SNPs were related to expression in the prefrontal cortex. One NR3C1 transcript had lower expression in suicide relative to non-suicide sudden death cases (b=-0.48, SE=0.12, t=-4.02, adjusted p=0.004). Conclusion We have identified an association of FKBP5 haplotype with risk of suicide attempt and found an association between suicide and altered NR3C1 gene expression in the prefrontal cortex. Our findings further implicate hypothalamic pituitary axis dysfunction in suicidal behavior. PMID:27030168

GLUCOCORTICOID RECEPTOR-RELATED GENES: GENOTYPE AND BRAIN GENE EXPRESSION RELATIONSHIPS TO SUICIDE AND MAJOR DEPRESSIVE DISORDER.

PubMed

Yin, Honglei; Galfalvy, Hanga; Pantazatos, Spiro P; Huang, Yung-Yu; Rosoklija, Gorazd B; Dwork, Andrew J; Burke, Ainsley; Arango, Victoria; Oquendo, Maria A; Mann, J John

2016-06-01

We tested the relationship between genotype, gene expression and suicidal behavior and major depressive disorder (MDD) in live subjects and postmortem samples for three genes, associated with the hypothalamic-pituitary-adrenal axis, suicidal behavior, and MDD; FK506-binding protein 5 (FKBP5), Spindle and kinetochore-associated protein 2 (SKA2), and Glucocorticoid Receptor (NR3C1). Single-nucleotide polymorphisms (SNPs) and haplotypes were tested for association with suicidal behavior and MDD in a live (N = 277) and a postmortem sample (N = 209). RNA-seq was used to examine gene and isoform-level brain expression postmortem (Brodmann Area 9; N = 59). Expression quantitative trait loci (eQTL) relationships were examined using a public database (UK Brain Expression Consortium). We identified a haplotype within the FKBP5 gene, present in 47% of the live subjects, which was associated with increased risk of suicide attempt (OR = 1.58, t = 6.03, P = .014). Six SNPs on this gene, three SNPs on SKA2, and one near NR3C1 showed before-adjustment association with attempted suicide, and two SNPs of SKA2 with suicide death, but none stayed significant after adjustment for multiple testing. Only the SKA2 SNPs were related to expression in the prefrontal cortex (pFCTX). One NR3C1 transcript had lower expression in suicide relative to nonsuicide sudden death cases (b = -0.48, SE = 0.12, t = -4.02, adjusted P = .004). We have identified an association of FKBP5 haplotype with risk of suicide attempt and found an association between suicide and altered NR3C1 gene expression in the pFCTX. Our findings further implicate hypothalamic pituitary axis dysfunction in suicidal behavior. © 2016 Wiley Periodicals, Inc.

MAPPING THE RELEASE OF VOLATILES IN THE INNER COMAE OF COMETS C/2012 F6 (LEMMON) AND C/2012 S1 (ISON) USING THE ATACAMA LARGE MILLIMETER/SUBMILLIMETER ARRAY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cordiner, M. A.; Milam, S. N.; Mumma, M. J.

2014-09-01

Results are presented from the first cometary observations using the Atacama Large Millimeter/Submillimeter Array (ALMA), including measurements of the spatially resolved distributions of HCN, HNC, H{sub 2}CO, and dust within the comae of two comets: C/2012 F6 (Lemmon) and C/2012 S1 (ISON), observed at heliocentric distances of 1.5 AU and 0.54 AU, respectively. These observations (with angular resolution ≈0.''5), reveal an unprecedented level of detail in the distributions of these fundamental cometary molecules, and demonstrate the power of ALMA for quantitative measurements of the distributions of molecules and dust in the inner comae of typical bright comets. In both comets, HCN ismore » found to originate from (or within a few hundred kilometers of) the nucleus, with a spatial distribution largely consistent with spherically symmetric, uniform outflow. By contrast, the HNC distributions are clumpy and asymmetrical, with peaks at cometocentric radii ∼500-1000 km, consistent with release of HNC in collimated outflow(s). Compared to HCN, the H{sub 2}CO distribution in comet Lemmon is very extended. The interferometric visibility amplitudes are consistent with coma production of H{sub 2}CO and HNC from unidentified precursor material(s) in both comets. Adopting a Haser model, the H{sub 2}CO parent scale length is found to be a few thousand kilometers in Lemmon and only a few hundred kilometers in ISON, consistent with the destruction of the precursor by photolysis or thermal degradation at a rate that scales in proportion to the solar radiation flux.« less

Frontiers of Radio Astronomy in the 2020s: The Next Generation Very Large Array

NASA Astrophysics Data System (ADS)

Murphy, Eric Joseph; ngVLA Project Office, ngVLA Science and Technical Advisory Councils, ngVLA Science Working Groups

2018-01-01

This talk will describe the current community-driven science goals, design, and planning status of a future large centimeter radio array: the ‘Next Generation Very Large Array’ (ngVLA). The ngVLA is being developed to observe at wavelengths between ALMA at submm wavelengths, and the future SKA-1 at few centimeter and longer wavelengths, opening a new window on the Universe through ultra-sensitive imaging of thermal line and continuum emission down to milliarcsecond resolution, and unprecedented broad band continuum polarimetric imaging of non-thermal processes. The current design for the array includes 10x more effective collecting area and 10x higher spatial resolution than the current JVLA or ALMA, carefully optimized for operation in the frequency range 10GHz to 50GHz, while still delivering world-leading sensitivity over the entire 1.2GHz to 116 GHz spectrum.With this array, new frontiers in modern astronomy can be reached, including direct imaging and chemical analysis of planet formation in the terrestrial-zone of nearby stars, studies of dust-obscured star formation and the cosmic baryon cycle down to pc-scales in the local Universe, and detailed imaging of molecular gas and galaxy formation into the epoch of reionization. Novel techniques for exploring temporal phenomena on timescales from milliseconds to years will also be implemented. The ngVLA will be situated in the desert southwest of the United States, centered on the current JVLA infrastructure, with multiple antennas anticipated in states/regions adjacent to NM, and in northern Mexico.A recently formed Project Office is working closely with the U.S. and international research community to design the array, and plan its construction beginning mid next decade. Recent significant funding for design and development brought forward by the NSF will enable detailed science case development and technology prototyping/risk reduction before the next U.S astronomy Decadal Survey.

First light from a kilometer-baseline Scintillation Auroral GPS Array.

PubMed

Datta-Barua, S; Su, Y; Deshpande, K; Miladinovich, D; Bust, G S; Hampton, D; Crowley, G

2015-05-28

We introduce and analyze the first data from an array of closely spaced Global Positioning System (GPS) scintillation receivers established in the auroral zone in late 2013 to measure spatial and temporal variations in L band signals at 100-1000 m and subsecond scales. The seven receivers of the Scintillation Auroral GPS Array (SAGA) are sited at Poker Flat Research Range, Alaska. The receivers produce 100 s scintillation indices and 100 Hz carrier phase and raw in-phase and quadrature-phase samples. SAGA is the largest existing array with baseline lengths of the ionospheric diffractive Fresnel scale at L band. With an initial array of five receivers, we identify a period of simultaneous amplitude and phase scintillation. We compare SAGA power and phase data with collocated 630.0 nm all-sky images of an auroral arc and incoherent scatter radar electron precipitation measurements, to illustrate how SAGA can be used in multi-instrument observations for subkilometer-scale studies. A seven-receiver Scintillation Auroral GPS Array (SAGA) is now at Poker Flat, Alaska SAGA is the largest subkilometer array to enable phase/irregularities studies Simultaneous scintillation, auroral arc, and electron precipitation are observed.

First light from a kilometer-baseline Scintillation Auroral GPS Array

PubMed Central

Datta-Barua, S; Su, Y; Deshpande, K; Miladinovich, D; Bust, G S; Hampton, D; Crowley, G

2015-01-01

We introduce and analyze the first data from an array of closely spaced Global Positioning System (GPS) scintillation receivers established in the auroral zone in late 2013 to measure spatial and temporal variations in L band signals at 100–1000 m and subsecond scales. The seven receivers of the Scintillation Auroral GPS Array (SAGA) are sited at Poker Flat Research Range, Alaska. The receivers produce 100 s scintillation indices and 100 Hz carrier phase and raw in-phase and quadrature-phase samples. SAGA is the largest existing array with baseline lengths of the ionospheric diffractive Fresnel scale at L band. With an initial array of five receivers, we identify a period of simultaneous amplitude and phase scintillation. We compare SAGA power and phase data with collocated 630.0 nm all-sky images of an auroral arc and incoherent scatter radar electron precipitation measurements, to illustrate how SAGA can be used in multi-instrument observations for subkilometer-scale studies. Key Points A seven-receiver Scintillation Auroral GPS Array (SAGA) is now at Poker Flat, Alaska SAGA is the largest subkilometer array to enable phase/irregularities studies Simultaneous scintillation, auroral arc, and electron precipitation are observed PMID:26709318

Coal Mining and Post-Metallurgic Dumping Grounds and Their Connections with Exploitation of Raw Materials in the Region of Ruda Śląska

NASA Astrophysics Data System (ADS)

Jonczy, Iwona; Gawor, Łukasz

2017-06-01

Characteristics of mining and metallurgical waste dumps in Ruda Śląska was presented in this article. Special attention was paid to the relationship of waste material accumulated on the dumps with resources exploited on studied area. The possibilities of dumps management were also traced and two directions were indicated. The first one is associated with forming a biological covering on the dumps and the second one - with the dumps liquidation and with recovery areas now occupied by the dumps and thus with the secondary use of material collected on them.

Prospects of detection of the first sources with SKA using matched filters

NASA Astrophysics Data System (ADS)

Ghara, Raghunath; Choudhury, T. Roy; Datta, Kanan K.; Mellema, Garrelt; Choudhuri, Samir; Majumdar, Suman; Giri, Sambit K.

2018-05-01

The matched filtering technique is an efficient method to detect H ii bubbles and absorption regions in radio interferometric observations of the redshifted 21-cm signal from the epoch of reionization and the Cosmic Dawn. Here, we present an implementation of this technique to the upcoming observations such as the SKA1-low for a blind search of absorption regions at the Cosmic Dawn. The pipeline explores four dimensional parameter space on the simulated mock visibilities using a MCMC algorithm. The framework is able to efficiently determine the positions and sizes of the absorption/H ii regions in the field of view.

Mps1 Regulates Kinetochore-Microtubule Attachment Stability via the Ska Complex to Ensure Error-Free Chromosome Segregation.

PubMed

Maciejowski, John; Drechsler, Hauke; Grundner-Culemann, Kathrin; Ballister, Edward R; Rodriguez-Rodriguez, Jose-Antonio; Rodriguez-Bravo, Veronica; Jones, Mathew J K; Foley, Emily; Lampson, Michael A; Daub, Henrik; McAinsh, Andrew D; Jallepalli, Prasad V

2017-04-24

The spindle assembly checkpoint kinase Mps1 not only inhibits anaphase but also corrects erroneous attachments that could lead to missegregation and aneuploidy. However, Mps1's error correction-relevant substrates are unknown. Using a chemically tuned kinetochore-targeting assay, we show that Mps1 destabilizes microtubule attachments (K fibers) epistatically to Aurora B, the other major error-correcting kinase. Through quantitative proteomics, we identify multiple sites of Mps1-regulated phosphorylation at the outer kinetochore. Substrate modification was microtubule sensitive and opposed by PP2A-B56 phosphatases that stabilize chromosome-spindle attachment. Consistently, Mps1 inhibition rescued K-fiber stability after depleting PP2A-B56. We also identify the Ska complex as a key effector of Mps1 at the kinetochore-microtubule interface, as mutations that mimic constitutive phosphorylation destabilized K fibers in vivo and reduced the efficiency of the Ska complex's conversion from lattice diffusion to end-coupled microtubule binding in vitro. Our results reveal how Mps1 dynamically modifies kinetochores to correct improper attachments and ensure faithful chromosome segregation. Copyright © 2017 Elsevier Inc. All rights reserved.

Model-independent constraints on modified gravity from current data and from the Euclid and SKA future surveys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taddei, Laura; Martinelli, Matteo; Amendola, Luca, E-mail: taddei@thphys.uni-heidelberg.de, E-mail: martinelli@lorentz.leidenuniv.nl, E-mail: amendola@thphys.uni-heidelberg.de

2016-12-01

The aim of this paper is to constrain modified gravity with redshift space distortion observations and supernovae measurements. Compared with a standard ΛCDM analysis, we include three additional free parameters, namely the initial conditions of the matter perturbations, the overall perturbation normalization, and a scale-dependent modified gravity parameter modifying the Poisson equation, in an attempt to perform a more model-independent analysis. First, we constrain the Poisson parameter Y (also called G {sub eff}) by using currently available f σ{sub 8} data and the recent SN catalog JLA. We find that the inclusion of the additional free parameters makes the constraintsmore » significantly weaker than when fixing them to the standard cosmological value. Second, we forecast future constraints on Y by using the predicted growth-rate data for Euclid and SKA missions. Here again we point out the weakening of the constraints when the additional parameters are included. Finally, we adopt as modified gravity Poisson parameter the specific Horndeski form, and use scale-dependent forecasts to build an exclusion plot for the Yukawa potential akin to the ones realized in laboratory experiments, both for the Euclid and the SKA surveys.« less

Astrophysics in Southern Africa

NASA Astrophysics Data System (ADS)

Whitelock, Patricia

2008-03-01

The government of South Africa has identified astronomy as a field in which their country has a strategic advantage and is consequently investing very significantly in astronomical infrastructure. South Africa now operates a 10-m class optical telescope, the Southern African Large Telescope (SALT), and is one of two countries short listed to host the Square Kilometre Array (SKA), an ambitious international project to construct a radio telescope with a sensitivity one hundred times that of any existing telescope. The challenge now is to produce an indigenous community of users for these facilities, particularly from among the black population which was severely disadvantaged under the apartheid regime. In this paper I briefly describe the observing facilities in Southern Africa before going on to discuss the various collaborations that are allowing us to use astronomy as a tool for development, and at the same time to train a new generation of astronomers who will be well grounded in the science and linked to their colleagues internationally.

New simulation of QSO X-ray heating during the Cosmic Dawn

NASA Astrophysics Data System (ADS)

Ross, Hannah E.; Dixon, Keri; Iliev, Ilian; Mellema, Garrelt

2018-05-01

The upcoming radio interferometer Square Kilometre Array is expected to directly detect the redshifted 21-cm signal from the Cosmic Dawn for the first time. In this era temperature fluctuations from X-ray heating of the neutral intergalactic medium can impact this signal dramatically. Previously, in Ross et al. (2017), we presented the first large-volume, 244 h-1 Mpc=349 Mpc a side, fully numerical radiative transfer simulations of X-ray heating. This work is a follow-up where we now also consider QSO-like sources in addition to high mass X-ray binaries. Images of the two cases are clearly distinguishable at SKA1-LOW resolution and have RMS fluctuations above the expected noise. The inclusion of QSOs leads to a dramatic increase in non-Gaussianity of the signal, as measured by the skewness and kurtosis of the 21-cm signal. We conclude that this increased non-Gaussianity is a promising signature of early QSOs.

A World of Hurt

NASA Technical Reports Server (NTRS)

2005-01-01

The most detailed images ever taken of Saturn's moon Mimas show it to be one of the most heavily cratered Saturnian moons, with little if any evidence for internal activity. Mimas has been so heavily cratered that new impacts can only overprint or even completely obliterate other older craters. Mimas is 397 kilometers or (247 miles) across.

The moon displays an unexpected array of crater shapes. The highest crater walls tower 6 kilometers (4 miles) above the floors and show signs of material sliding down slope. Indeed, many of the large craters -- more than 15 kilometers (10 miles) in diameter -- appear to be filled in with rough-surfaced material, likely the result of landslides triggered by subsequent impacts elsewhere on Mimas' surface. Some of these deposits have craters superimposed on them, demonstrating that the landslides themselves may be quite old.

Grooves, some of which are over a kilometer deep, cut across the surface for more than 100 kilometers (63 miles). These are some of the only indications that there might have once been internal activity under this ancient, battered surface.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Recent results from the Telescope Array Experiment

NASA Astrophysics Data System (ADS)

Abbasi, Rasha; Telescope Array Collaboration

2016-03-01

The Telescope Array (TA) is the largest ultrahigh energy cosmic rays detector in the northern hemisphere. TA is a hybrid detector comprised of three air fluorescence stations and a large surface array consisting of 507 scintillator counters. Each of the three fluorescence stations, located at the periphery of the ground array, views 108 degrees in azimuth and up to 30 degrees in elevation. The surface detectors are arranged in a square grid of 1.2 km spacing, covering over 700 square kilometers. TA has collected more than seven years of data. In this talk, we will present some of the main results on the cosmic rays composition and energy spectrum obtained by TA and its low energy extension (TALE). Finally, we will present our results from the search for arrival direction anisotropy, including the observed large excess of events at the highest energies, seen in the region of the northern sky centered on Ursa Major. Based on the current results, the ``hot spot'' in particular, TA is pursuing the expansion of the surface array to four times its current size.

Results of the 1978 NASA/JPL balloon flight solar cell calibration program

NASA Technical Reports Server (NTRS)

Seaman, C. H.; Sidwell, L. B.

1979-01-01

The 1978 scheduled solar cell calibration balloon flight was successfully completed. Thirty six modules were carried to an altitude of above 36 kilometers. Recovery of telemetry and flight packages was without incident. These calibrated standard cells are used as reference standards in simulator testing of cells and arrays with similar spectral response characteristics. The factors affecting the spectral transmission of the atmosphere at various altitudes are summarized.

Process Study of Oceanic Responses to Typhoons Using Arrays of EM-APEX Floats and Moorings

DTIC Science & Technology

2012-09-30

maximum potential intensity, structure , energy, trajectory, and dynamic evolution. The most energetic oceanic responses to tropical cyclone forcing are...during tropical cyclone passage will aid understanding of storm dynamics and structure . The ocean’s recovery after tropical cyclone passage depends...days). The wake was advected hundreds of kilometers from the storm track by a pre- existing mesoscale eddy. Its thermal structure could not be

Findings from NASA's 2015-2017 Electric Sail Investigations

NASA Technical Reports Server (NTRS)

Wiegmann, Bruce. M.

2017-01-01

Electric Sail (E-Sail) propulsion systems will enable scientific spacecraft to obtain velocities of up to 10 astronomical units per year without expending any on-board propellant. The E-Sail propulsion is created from the interaction of a spacecraft's positively charged multi-kilometer-length conductor/s with protons that are present in the naturally occurring hypersonic solar wind. The protons are deflected via natural electrostatic repulsion forces from the Debye sheath that is formed around a charged wire in space, and this deflection of protons creates thrust or propulsion in the opposite direction. It is envisioned that this E-Sail propulsion system can provide propulsion throughout the solar system and to the heliosphere and beyond. Consistent with the concept of a "sail," no propellant is needed as electrostatic repulsion interactions between the naturally occurring solar wind protons and a positively charged wire creates the propulsion. The basic principle on which the Electric Sail operates is the exchange of momentum between an "electric sail" and solar wind, which continually flows radially away from the sun at speeds ranging from 300 to 700 kilometers per second. The "sail" consists of an array of long, charged wires which extend radially outward 10 to 30 kilometers from a slowly rotating spacecraft. Momentum is transferred from the solar wind to the array through the deflection of the positively charged solar wind protons by a high voltage potential applied to the wires. The thrust generated by an E-Sail is proportional to the area of the sail, which is given by the product of the total length of the wires and the effective wire diameter. The wire is approximately 0.1 millimeters in diameter. However, the effective diameter is determined by the distance the applied electric potential penetrates into space around the wire (on the order of 10 meters at 1 astronomical unit). As a result, the effective area over which protons are repelled is proportional to the size of the region of electric potential, or the plasma sheath region, surround the wires of the array. A large sheath is, therefore, beneficial to the generation of thrust. However, this benefit must be balanced with the additional fact that electron collection is proportional to sheath size. Electrons collected by the wire array must be injected back into the solar wind in order to maintain the potential on the wires - which requires power. The primary power requirement for E-Sail operation is, therefore, also proportional to sheath size.

Local constraints on cosmic string loops from photometry and pulsar timing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pshirkov, M. S.; Tuntsov, A. V.; Sternberg Astronomical Institute, M.V. Lomonosov Moscow State University, 119992

2010-04-15

We constrain the cosmological density of cosmic string loops using two observational signatures--gravitational microlensing and the Kaiser-Stebbins effect. Photometry from RXTE and CoRoT space missions and pulsar timing from Parkes Pulsar Timing Array, Arecibo and Green Bank radio telescopes allow us to probe cosmic strings in a wide range of tensions G{mu}/c{sup 2}=10{sup -16} divide 10{sup -10}. We find that pulsar timing data provide the most stringent constraints on the abundance of light strings at the level {Omega}{sub s{approx}}10{sup -3}. Future observational facilities such as the Square Kilometer Array will allow one to improve these constraints by orders of magnitude.

Management competencies required in ambulatory care settings.

PubMed

Brooke, P P; Hudak, R P; Finstuen, K; Trounson, J

1998-01-01

A study was conducted to identify the most important competencies physician executives in medical groups and other ambulatory settings will need to have in the next five years. The specific job skills, knowledge, and abilities (SKA) that physician executives will need to acquire these competencies were also explored. The Delphi techniques were used to analyze responses from two surveys from members of the American College of Medical Practice Executives. The most important competencies were grouped into 13 management domains, each with specific SKAs. "Managing health care resources to create quality and value" and "fundamentals of business and finance" were rated as the most important competencies. The most frequently rated SKA was the "ability to build and maintain credibility and trust."

The Management, Storage, Utilization of Astronomical Data in the 21st Century Version 1.00

NASA Astrophysics Data System (ADS)

Hanisch, Bob; Quinn, Peter; Lawrence, Andy; Hanisch, Bob

2004-03-01

The costs and resources associated with the development of forefront astronomical research capabilities often greatly exceed the funding capacities of individual universities, research organizations, and nations (e.g., Atacama Large Millimeter Array [ALMA], The Square Kilometre Array [SKA], and Extremely Large (optical) Telescopes in the 30m-100m class [ELTs]). Collaborative alliances of organizations and nations are therefore being formed to build new, facility-class astronomical observatories across the globe. This expansion and globalization of the astronomical research effort raises a number of major issues that need to be confronted and solved by astronomers, research funding bodies, and governments. Some of these issues are being met by other sciences and some are unique to the research diversity inherent in exploring the Universe through multiple, complementary wavelength windows. In all cases, the challenges of managing, maximally utilizing, and collaboratively sharing the huge volume of digital information flowing from these new observatories is focusing and leading the discussion of critical issues for success. This discussion paper seeks to identify a number of these major issues, to highlight a new vision for a common research infrastructure that will enable some of these issues to be addressed, and further, to identify some of the practical and policy issues associated with long term solutions and the maximal return on a global research investments.

Chemistry and Star Formation: A Love-Hate Relationship

NASA Astrophysics Data System (ADS)

Jiménez-Serra, Izaskun; Zhang, Qizhou; Patel, Nimesh; Lu, Xing; Wang, Ke; Testi, Leonardo; Caselli, Paola; Martin-Pintado, Jesus

2014-06-01

The development of the broad bandwidth receivers at the Submillimeter Array (SMA) a decade ago opened up the possibility to observe tens of molecular lines at high angular resolution simultaneously. The unprecedented wealth of molecular line data provided by the SMA allowed for the first time detailed studies of the chemistry in star-forming regions. These studies have revealed that chemistry is a useful tool to pin down the internal physical structure and the physical processes involved in the process of low-mass and high-mass star formation. In this talk, I will review the most important advances in our understanding of the star-formation process through chemistry thanks to the SMA, and I will present the challenges that will be faced in the next decade in this field of research thanks to the advent of new instrumentation such as the Atacama Large Millimeter/Submillimeter Array and the Square Kilometer Array.

Results of the 1983 NASA/JPL balloon flight solar cell calibration program

NASA Technical Reports Server (NTRS)

Downing, R. G.; Weiss, R. S.

1984-01-01

The 1983 solar cell calibration balloon flight was successfully completed and met all objectives of the program. Thirty-four modules were carried to an altitude of 36.0 kilometers. The calibrated cells can now be used as reference standards in simulator testing of cells and arrays. Cell calibration data are tabulated as well as the repeatability of standard solar cell BFS-17A (35 flights over a 21-year period).

Arms Control and Nonproliferation Technologies, First Quarter 1994

DTIC Science & Technology

1994-01-01

earthquake show detectable signals PATWINGSPAC, U.S. Navy, (3) an array of the U.S. for magnitude 3 events at 320-360 kilometers. Initial Navy SOSUS system...30 explosions shots, in generating seismic signals at regional or greater than 50 tons, including one shot greater than teleseismic distances). These... general Rainier Mesa earthquakes from Rock Valley at NTS appear to be events (Area 12) of roughly the same yield had signif- intermediate between the

Intensity Interferometry: Imaging Stars with Kilometer Baselines

NASA Astrophysics Data System (ADS)

Dravins, Dainis

2018-04-01

Microarcsecond imaging will reveal stellar surfaces but requires kilometer-scale interferometers. Intensity interferometry circumvents atmospheric turbulence by correlating intensity fluctuations between independent telescopes. Telescopes connect only electronically, and the error budget relates to electronic timescales of nanoseconds (light-travel distances on the order of a meter), enabling the use of imperfect optics in a turbulent atmosphere. Once pioneered by Hanbury Brown and Twiss, digital versions have now been demonstrated in the laboratory, reconstructing diffraction-limited images from hundreds of optical baselines. Arrays of Cherenkov telescopes (primarily erected for gamma-ray studies) will extend over a few km, enabling an optical equivalent of radio interferometers. Resolutions in the tens of microarcseconds will resolve rotationally flattened stars with their circumstellar disks and winds, or possibly even the silhouettes of transiting exoplanets. Applying the method to mirror segments in extremely large telescopes (even with an incompletely filled main mirror, poor seeing, no adaptive optics), the diffraction limit in the blue may be reached.

Earth's interior. Dehydration melting at the top of the lower mantle.

PubMed

Schmandt, Brandon; Jacobsen, Steven D; Becker, Thorsten W; Liu, Zhenxian; Dueker, Kenneth G

2014-06-13

The high water storage capacity of minerals in Earth's mantle transition zone (410- to 660-kilometer depth) implies the possibility of a deep H2O reservoir, which could cause dehydration melting of vertically flowing mantle. We examined the effects of downwelling from the transition zone into the lower mantle with high-pressure laboratory experiments, numerical modeling, and seismic P-to-S conversions recorded by a dense seismic array in North America. In experiments, the transition of hydrous ringwoodite to perovskite and (Mg,Fe)O produces intergranular melt. Detections of abrupt decreases in seismic velocity where downwelling mantle is inferred are consistent with partial melt below 660 kilometers. These results suggest hydration of a large region of the transition zone and that dehydration melting may act to trap H2O in the transition zone. Copyright © 2014, American Association for the Advancement of Science.

ARC-1979-A79-7088

NASA Image and Video Library

1979-07-10

P-21760 BW This color image of the Jovian moon Europa, which is the size of our moon, is thought to have a crust of ice perhaps 100 kilometers thick which overlies the silicate crust. The complex array of streaks indicate that the crust has been fractured and filled by materials from the interior. The lack of relief, any visible mountains or craters, on its bright limb is consistent with a thick ice crust. In contrast to its icy neighbors, Ganymede and Callisto, Europa has very few impact craters. One possible candidate is the small feature near the center of this image with radiating rays and a bright circular interior. The relative absence of features and low topography suggests the crust is young and warm a few kilometers below the surface. The tidal heating process suggested for Io also may be heating Europa's interior at a lower rate.

ARC-1979-AC79-7088

NASA Image and Video Library

1979-07-10

P-21760 C This color image of the Jovian moon Europa, which is the size of our moon, is thought to have a crust of ice perhaps 100 kilometers thick which overlies the silicate crust. The complex array of streaks indicate that the crust has been fractured and filled by materials from the interior. The lack of relief, any visible mountains or craters, on its bright limb is consistent with a thick ice crust. In contrast to its icy neighbors, Ganymede and Callisto, Europa has very few impact craters. One possible candidate is the small feature near the center of this image with radiating rays and a bright circular interior. The relative absence of features and low topography suggests the crust is young and warm a few kilometers below the surface. The tidal heating process suggested for Io also may be heating Europa's interior at a lower rate.

Chronostratigraphical Subdivision of the Late Glacial and the Holocene for the Alaska Region

NASA Astrophysics Data System (ADS)

Michczynska, D. J.; Hajdas, I.

2009-04-01

Our work is a kind of so called data mining. The first step of our work was collection of the radiocarbon data for samples coming from Alaska. We construct data base using Radiocarbon Measurements Lists published by different radiocarbon laboratories (mainly in the journal 'Radiocaron'). The next step was careful analysis of collected dates. We excluded from our analysis all dates suspected of contamination by younger or older organic matter. Such fact could be stated, for instance, on the base of inconsistency of radiocarbon age and stratigraphy or palynology. Finally, we calibrated whole large set of chosen radiocarbon dates and construct probability density function (PDF). Analysis of the shape of PDF was the subject of the previous research (eg. Michczynska and Pazdur, 2004; Macklin et al., 2006; Starkel et al., 2006, Michczynska et al., 2007). In our analysis we take into account the distinct tendency to collect samples from specific horizons. It is a general rule to take samples for radiocarbon dating from places of visible sedimentation changes or changes in palynological diagram. Therefore the culminations of the PDF represent periods of environmental changes and could be helpful in identifying the chronostratigraphical boundaries on the calendar time scale. References: Michczyńska D.J., Pazdur A., 2004. A shape analysis of cumulative probability density function of radiocarbon dates set in the study of climate change in Late Glacial and Holocene. Radiocarbon 46(2): 733-744. Michczyńska D.J., Michczyński A., Pazdur A. 2007. Frequency distribution of radiocarbon dates as a tool for reconstructing environmental changes. Radiocarbon 49(2): 799-806. Macklin M.G., Benito G., Gregory K.J., Johnstone E., Lewin J., Michczyńska D.J., Soja R., Starkel L., Thorndycraft V.R., 2006. Past hydrological events reflected in the Holocene fluvial record of Europe. CATENA 66: 145-154. Starkel L., Soja R., Michczyńska D.J., 2006. Past hydrological events reflected in Holocene history of Polish rivers. CATENA 66: 24-33.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jacobson, Paul T; Hagerman, George; Scott, George

This project estimates the naturally available and technically recoverable U.S. wave energy resources, using a 51-month Wavewatch III hindcast database developed especially for this study by National Oceanographic and Atmospheric Administration's (NOAA's) National Centers for Environmental Prediction. For total resource estimation, wave power density in terms of kilowatts per meter is aggregated across a unit diameter circle. This approach is fully consistent with accepted global practice and includes the resource made available by the lateral transfer of wave energy along wave crests, which enables wave diffraction to substantially reestablish wave power densities within a few kilometers of a linear array,more » even for fixed terminator devices. The total available wave energy resource along the U.S. continental shelf edge, based on accumulating unit circle wave power densities, is estimated to be 2,640 TWh/yr, broken down as follows: 590 TWh/yr for the West Coast, 240 TWh/yr for the East Coast, 80 TWh/yr for the Gulf of Mexico, 1570 TWh/yr for Alaska, 130 TWh/yr for Hawaii, and 30 TWh/yr for Puerto Rico. The total recoverable wave energy resource, as constrained by an array capacity packing density of 15 megawatts per kilometer of coastline, with a 100-fold operating range between threshold and maximum operating conditions in terms of input wave power density available to such arrays, yields a total recoverable resource along the U.S. continental shelf edge of 1,170 TWh/yr, broken down as follows: 250 TWh/yr for the West Coast, 160 TWh/yr for the East Coast, 60 TWh/yr for the Gulf of Mexico, 620 TWh/yr for Alaska, 80 TWh/yr for Hawaii, and 20 TWh/yr for Puerto Rico.« less

A computer model of solar panel-plasma interactions

NASA Technical Reports Server (NTRS)

Cooke, D. L.; Freeman, J. W.

1980-01-01

High power solar arrays for satellite power systems are presently being planned with dimensions of kilometers, and with tens of kilovolts distributed over their surface. Such systems face many plasma interaction problems, such as power leakage to the plasma, particle focusing, and anomalous arcing. These effects cannot be adequately modeled without detailed knowledge of the plasma sheath structure and space charge effects. Laboratory studies of 1 by 10 meter solar array in a simulated low Earth orbit plasma are discussed. The plasma screening process is discussed, program theory is outlined, and a series of calibration models is presented. These models are designed to demonstrate that PANEL is capable of accurate self consistant space charge calculations. Such models include PANEL predictions for the Child-Langmuir diode problem.

Next Generation Astronomical Data Processing using Big Data Technologies from the Apache Software Foundation

NASA Astrophysics Data System (ADS)

Mattmann, Chris

2014-04-01

In this era of exascale instruments for astronomy we must naturally develop next generation capabilities for the unprecedented data volume and velocity that will arrive due to the veracity of these ground-based sensor and observatories. Integrating scientific algorithms stewarded by scientific groups unobtrusively and rapidly; intelligently selecting data movement technologies; making use of cloud computing for storage and processing; and automatically extracting text and metadata and science from any type of file are all needed capabilities in this exciting time. Our group at NASA JPL has promoted the use of open source data management technologies available from the Apache Software Foundation (ASF) in pursuit of constructing next generation data management and processing systems for astronomical instruments including the Expanded Very Large Array (EVLA) in Socorro, NM and the Atacama Large Milimetre/Sub Milimetre Array (ALMA); as well as for the KAT-7 project led by SKA South Africa as a precursor to the full MeerKAT telescope. In addition we are funded currently by the National Science Foundation in the US to work with MIT Haystack Observatory and the University of Cambridge in the UK to construct a Radio Array of Portable Interferometric Devices (RAPID) that will undoubtedly draw from the rich technology advances underway. NASA JPL is investing in a strategic initiative for Big Data that is pulling in these capabilities and technologies for astronomical instruments and also for Earth science remote sensing. In this talk I will describe the above collaborative efforts underway and point to solutions in open source from the Apache Software Foundation that can be deployed and used today and that are already bringing our teams and projects benefits. I will describe how others can take advantage of our experience and point towards future application and contribution of these tools.

H I observations of the nearest starburst galaxy NGC 253 with the SKA precursor KAT-7

NASA Astrophysics Data System (ADS)

Lucero, D. M.; Carignan, C.; Elson, E. C.; Randriamampandry, T. H.; Jarrett, T. H.; Oosterloo, T. A.; Heald, G. H.

2015-07-01

We present H I observations of the Sculptor group starburst spiral galaxy NGC 253, obtained with the Karoo Array Telescope (KAT-7). KAT-7 is a pathfinder for the Square Kilometre Array precursor MeerKAT, under construction. The short baselines and low system temperature of the telescope make it very sensitive to large-scale, low-surface-brightness emission. The KAT-7 observations detected 33 per cent more flux than previous Very Large Array observations, mainly in the outer parts and in the halo for a total H I mass of 2.1 ± 0.1 × 109 M⊙. H I can be found at large distances perpendicular to the plane out to projected distances of ˜9-10 kpc away from the nucleus and ˜13-14 kpc at the edge of the disc. A novel technique, based on interactive profile fitting, was used to separate the main disc gas from the anomalous (halo) gas. The rotation curve (RC) derived for the H I disc confirms that it is declining in the outer parts, as seen in previous optical Fabry-Perot measurements. As for the anomalous component, its RC has a very shallow gradient in the inner parts and turns over at the same radius as the disc, kinematically lagging by 100 km s-1. The kinematics of the observed extra-planar gas is compatible with an outflow due to the central starburst and galactic fountains in the outer parts. However, the gas kinematics shows no evidence for inflow. Analysis of the near-IR WISE data, shows clearly that the star formation rate is compatible with the starburst nature of NGC 253.

Characterising the Dense Molecular Gas in Exceptional Local Galaxies

NASA Astrophysics Data System (ADS)

Tunnard, Richard C. A.

2016-08-01

The interferometric facilities now coming online (the Atacama Large Millimetre Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA)) and those planned for the coming decade (the Next Generation Very Large Array (ngVLA) and the Square Kilometre Array (SKA)) in the radio to sub-millimetre regimes are opening a window to the molecular gas in high-redshift galaxies. However, our understanding of similar galaxies in the local universe is still far from complete and the data analysis techniques and tools needed to interpret the observations in consistent and comparable ways are yet to be developed. I first describe the Monte Carlo Markov Chain (MCMC) script developed to empower a public radiative transfer code. I characterise both the public code and MCMC script, including an exploration of the effect of observing molecular lines at high redshift where the Cosmic Microwave Background (CMB) can provide a significant background, as well as the effect this can have on well-known local correlations. I present two studies of ultraluminous infrared galaxies (ULIRGs) in the local universe making use of literature and collaborator data. In the first of these, NGC6240, I use the wealth of available data and the geometry of the source to develop a multi-phase, multi-species model, finding evidence for a complex medium of hot diffuse and cold dense gas in pressure equilibrium. Next, I study the prototypical ULIRG Arp 220; an extraordinary galaxy rendered especially interesting by the controversy over the power source of the western of the two merger nuclei and its immense luminosity and dust obscuration. Using traditional grid based methods I explore the molecular gas conditions within the nuclei and find evidence for chemical differentiation between the two nuclei, potentially related to the obscured power source. Finally, I investigate the potential evolution of proto-clusters over cosmic time with sub-millimetre observations of 14 radio galaxies, unexpectedly finding little to no evidence for cluster evolution.

HERA: Illuminating Our Early Universe

NASA Astrophysics Data System (ADS)

DeBoer, David

2014-06-01

The Hydrogen Epoch of Reionization Arrays (HERA) roadmap is a staged plan for using the unique properties of the 21cm line from neutral hydrogen to probe our cosmic dawn, from the birth of the first stars and black holes, through the full reionization of the primordial intergalactic medium (IGM). HERA is a collaboration between the Precision Array Probing the Epoch of Reionization (PAPER), US-Murchison Widefield Array (MWA), and MIT Epoch of Reionization (MITEOR) teams.The first phase of the HERA roadmap entailed the operation of the PAPER and MWA telescopes to explore techniques and designs required to detect the primordial HI signal in the presence of radio continuum foreground emission some four orders of magnitude brighter. Studies with PAPER and the MWA have led to a new understanding of the interplay of foreground and instrumental systematics in the context of a three-dimensional cosmological intensity-mapping experiment. We are now able to remove foregrounds to the limits of our sensitivity with these instruments, culminating in the first physically meaningful upper limits on the power spectrum of 2 cm emission from reionization.Building on this understanding, the next stage of HERA entails a new 14m diameter antenna element that is optimized both for sensitivity and for minimizing foreground systematics. Arranging these elements in a compact hexagonal grid yields an array that facilitates calibration, leverages proven foreground removal techniques, and is scalable to large collecting areas. The HERA phase II will be located in the radio quiet environment of the SKA site in Karoo, South Africa, and have a sensitivity close to two orders of magnitude better than PAPER and the MWA, with broader frequency coverage, HERA can paint an uninterrupted picture through reionization, back to the end of the Dark Ages.This paper will present a summary of the current understanding of the signal characteristics and measurements and describe this planned HERA telescope to be built to detect and characterize the EoR power spectrum.

New Surveys of the Universe with the Jansky Very Large Array (VLA) and the Very Long Baseline Array (VLBA)

NASA Astrophysics Data System (ADS)

Myers, Steven T.

2013-01-01

The Jansky Very Large Array is a recently completed upgrade to the VLA that has significantly expanded its capabilities through replacement of the receivers, electronics, signal paths, and correlator with cutting-edge technology. This enhancement provides significantly increased continuum sensitivity and spectral survey speeds (by factors of 100 or more in select cases) from 1-50 GHz and in key bands below 1 GHz. Concurrently, we are greatly enhancing the sensitivity of the Very Long Baseline Array. A suite of ever more ambitious radio sky survey programs undertaken with these new instruments address science goals central to answering the questions posed by Astro2010, and will undoubtedly incite new inquiries. The science themes of the Jansky VLA and the VLBA are: illuminating the obscured, probing the magnetic, sounding the transient, and charting the evolving Universe. New observations will allow us to image young stars in massive black holes in dust enshrouded environments, measure the strength and topology of the cosmic magnetic field, follow the rapid evolution of energetic phenomena, and to study the formation and evolution of stars, galaxies, AGN, and the Universe itself. We can follow the evolution of gas and galaxies and particles and fields through cosmic time to bridge the eras from cosmic dawn to the dawn of new worlds. I will describe the salient features of the Jansky VLA and the VLBA for cosmological survey work, and summarize the multi-wavelength aspects in regard to those with ALMA and next generation optical, infrared, X-ray and Gamma-ray telescopes. Example data taken from Janksy VLA and upgraded VLBA commissioning tests and early science will illustrate these features. I also describe evolution of the VLA and VLBA and their capabilities for future surveys that will lead towards the next decade, into the era of the LSST and the SKA.

Integrating Science Communication, Outreach and Awareness into the R&D Investment Framework of SKA in order to drive a knowledge economy

NASA Astrophysics Data System (ADS)

Raynard, Lorenzo; Garnier, William

2015-08-01

The emergence of the "knowledge society" has reshaped the context and content of public communication of science and technology. The construction and design of SKA and associated science research are increasingly characterised by the formation of large, multidisciplinary and multi-institute research teams. The integration of science communication into the scientific endeavour is key to building the foundations of a thriving knowledge-based economy identified by new technology investments, high-technology industries and highly skilled labour. Knowledge Economy Indicators profile, among others, the efficient and effective Management of Knowledge Assets. This presentation will explore the strategic trade and positioning of Knowledge Assets in order to drive and stimulate innovation.

Source Finding in the Era of the SKA (Precursors): Aegean 2.0

NASA Astrophysics Data System (ADS)

Hancock, Paul J.; Trott, Cathryn M.; Hurley-Walker, Natasha

2018-03-01

In the era of the SKA precursors, telescopes are producing deeper, larger images of the sky on increasingly small time-scales. The greater size and volume of images place an increased demand on the software that we use to create catalogues, and so our source finding algorithms need to evolve accordingly. In this paper, we discuss some of the logistical and technical challenges that result from the increased size and volume of images that are to be analysed, and demonstrate how the Aegean source finding package has evolved to address these challenges. In particular, we address the issues of source finding on spatially correlated data, and on images in which the background, noise, and point spread function vary across the sky. We also introduce the concept of forced or prioritised fitting.

Source and Path Calibration in Regions of Poor Crustal Propagation Using Temporary, Large-Aperture, High-Resolution Seismic Arrays (Postprint). Annual Report 3

DTIC Science & Technology

2012-06-04

central Tibetan Plateau. Automated hypocenter locations in south- central Tibet were finalized. Refinements included an update of the model used for... central Tibet. A subset of ~7,900 events with 25+ arrivals is considered well-located based on kilometer-scale differences relative to manually located...propagation in the Nepal Himalaya and the south- central Tibetan Plateau. The 2002–2005 experiment consisted of 233 stations along a dense 800 km linear

Fifty Years of Pulsar Candidate Selection: From simple filters to a new principled real-time classification approach

NASA Astrophysics Data System (ADS)

Lyon, R. J.; Stappers, B. W.; Cooper, S.; Brooke, J. M.; Knowles, J. D.

2016-06-01

Improving survey specifications are causing an exponential rise in pulsar candidate numbers and data volumes. We study the candidate filters used to mitigate these problems during the past fifty years. We find that some existing methods such as applying constraints on the total number of candidates collected per observation, may have detrimental effects on the success of pulsar searches. Those methods immune to such effects are found to be ill-equipped to deal with the problems associated with increasing data volumes and candidate numbers, motivating the development of new approaches. We therefore present a new method designed for on-line operation. It selects promising candidates using a purpose-built tree-based machine learning classifier, the Gaussian Hellinger Very Fast Decision Tree (GH-VFDT), and a new set of features for describing candidates. The features have been chosen so as to I) maximise the separation between candidates arising from noise and those of probable astrophysical origin, and II) be as survey-independent as possible. Using these features our new approach can process millions of candidates in seconds (˜1 million every 15 seconds), with high levels of pulsar recall (90%+). This technique is therefore applicable to the large volumes of data expected to be produced by the Square Kilometre Array (SKA). Use of this approach has assisted in the discovery of 20 new pulsars in data obtained during the LOFAR Tied-Array All-Sky Survey (LOTAAS).

Large depth high-precision FMCW tomography using a distributed feedback laser array

NASA Astrophysics Data System (ADS)

DiLazaro, Thomas; Nehmetallah, George

2018-02-01

Swept-source optical coherence tomography (SS-OCT) has been widely employed in the medical industry for the high resolution imaging of subsurface biological structures. SS-OCT typically exhibits axial resolutions on the order of tens of microns at speeds of hundreds of kilohertz. Using the same coherent heterodyne detection technique, frequency modulated continuous wave (FMCW) ladar has been used for highly precise ranging for distances up to kilometers. Distributed feedback lasers (DFBs) have been used as a simple and inexpensive source for FMCW ranging. Here, we use a bandwidth-combined DFB array for sub-surface volume imaging at a 27 μm axial resolution over meters of distance. 2D and 3D tomographic images of several semi-transparent and diffuse objects at distances up to 10 m will be presented.

Vision for Astronomy in South Africa and partnership with the US

NASA Astrophysics Data System (ADS)

Nemaungani, Takalani

2014-01-01

The 2002 National Research and Development Strategy identified astronomy as a national geographic advantage. This identification was based on the historical investments in optical and, to a lesser extent, radio astronomy up to that point and the realisation that the conditions prevailing in Sutherland were among the best in the world. Since then a number of astronomy initiatives have burgeoned in the Southern African region and these include the HESS, SKA and the AVN. Currently, investments in astronomy are by far the biggest investments being made by the Department of Science and Technology (DST). South Africa’s involvement in modern astronomy dates back to 1685 when a French Astronomer, Guy Tachard, setup an observatory at the southern tip of Africa to decipher the star charts of the extreme southern sky. In 1820, a permanent observatory - the Royal Observatory - was established outside of Cape Town and astronomy has been practised continuously since then. By the late 1980s, it became clear that for South African astronomers and astrophysicists to continue conducting first class research, the acquisition of a much larger, powerful and sophisticated telescope would be necessary. This provided the impetus for a new vision to construct the largest single optical telescope in the Southern Hemisphere, eventually known as the Southern African Large Telescope (SALT). Within the last decade, the African appetite for radio astronomy initiatives has increased exponentially. This has largely been spurred by the African bid to host the SKA project and the need for African countries to work in close partnership that consequently resulted in a successful bid to co-host the SKA project and the subsequent need to ensure its effective implementation. This partnership, and the interactions related thereto, has effectively enhanced awareness around the requirements for hosting radio astronomy instrumentation and the associated benefits that could be derived in making such commitments. Consequently, there have been concerted efforts in support of various radio astronomy initiatives that sit at the cusp of the continents ambitions for the hosting of the SKA.

A Multi-frequency analysis of dark matter annihilation interpretations of recent anti-particle and γ-ray excesses in cosmic structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beck, G.; Colafrancesco, S., E-mail: geoff.m.beck@gmail.com, E-mail: sergio.colafrancesco@wits.ac.za

2016-05-01

The Fermi-LAT observation of a γ-ray excess from the galactic-centre, as well as the PAMELA, AMS, and AMS-2 anti-particle excesses, and the recent indications of a Fermi-LAT γ-ray excess in the Reticulum II dwarf galaxy have all been variously put forward as possible indirect signatures of supersymmetric neutralino dark matter. These are of particular interest as the neutralino annihilation models which fit these observations must have observable consequences across the frequency spectrum, from radio to γ-ray emission. Moreover, since dark matter is expected to be a major constituent of cosmic structure, these multi-frequency consequences should be common to such structuresmore » across the mass spectrum, from dwarf galaxies to galaxy clusters. Thus, in this work we make predictions for the multi-frequency spectra of three well-known sources dominated by dark matter on cluster, galaxy and dwarf galaxy scales, e.g. the Coma cluster, the galaxy M81, and the Draco dwarf galaxy, using models favoured by dark matter interpretations of the aforementioned observations. We pay special attention to the consequences for these models when their cross-sections are renormalised to reproduce the recent γ-ray excess observed in the Reticulum II dwarf galaxy, as well as using cross-sections from the Fermi-LAT dwarf galaxy limits, which throw a dark matter interpretation of this excess into doubt. We find that the multi-frequency data of Coma and Draco are in conflict with the dark matter interpretation of the AMS, PAMELA and Fermi positron excess. Additionally, models derived from Fermi-LAT galactic centre observations, and AMS-2 re-analysis, present similar but less extensive conflicts. Using the sensitivity projections for the Square Kilometre Array, the Cherenkov Telescope Array, as well as the ASTROGAM and ASTRO-H satellites, we determine the detection prospects for a subset of neutralino models that remain consistent with Planck cosmological constraints. Although the SKA has the greatest sensitivity to dark matter models, we demonstrate that ASTRO-H is well positioned to probe the inverse-Compton scattering emissions from neutralino annihilation and identify characteristics of the spectra which contain information about the neutralino mass and annihilation channel. This means that, given environments with favourable X-ray backgrounds, multi-frequency observation with the next generation of experiments will allow for unprecedented sensitivity to the neutralino parameter space as well as offsetting the individual weaknesses of each observation mode. Finally we show that all of the studied models can be better tested with the SKA phase 1.« less

Europa During Voyager 2 Closest Approach

NASA Image and Video Library

1996-09-26

This color image of the Jovian moon Europa was acquired by NASA Voyager 2 during its close encounter on Jul. 9, 1979. Europa, the size of our moon, is thought to have a crust of ice perhaps 100 kilometers thick which overlies the silicate crust. The complex array of streaks indicate that the crust has been fractured and filled by materials from the interior. The lack of relief, any visible mountains or craters, on its bright limb is consistent with a thick ice crust. In contrast to its icy neighbors, Ganymede and Callisto, Europa has very few impact craters. One possible candidate is the small feature near the center of this image with radiating rays and a bright circular interior. The relative absence of features and low topography suggests the crust is young and warm a few kilometers below the surface. The tidal heating process suggested for Io also may be heating Europa's interior at a lower rate. http://photojournal.jpl.nasa.gov/catalog/PIA00459

Exploring EUV Spicules Using 304 Angstrom He II Data from SDO AIA

NASA Technical Reports Server (NTRS)

Snyder, Ian R.; Sterling, Alphonse C.; Falconer, David A.; Moore, Ron L.

2014-01-01

We present results from a statistical study of He II 304 Angstrom Extreme Ultraviolet (EUV) spicules at the limb of the Sun. We also measured properties of one macrospicule; macrospicules are longer than most spicules, and much broader in width than spicules. We use high-cadence (12 second) and high-resolution (0.6 arcseconds pixels) resolution data from the Atmospheric Imaging Array (AIA) instrument on the Solar Dynamic Observatory (SDO). All of the observed events occurred near the solar north pole, where quiet Sun or coronal hole environments ensued. We examined the maximum lengths, maximum rise velocities, and lifetimes of 33 Extreme Ultraviolet (EUV) spicules and the macrospicule. For the bulk of the Extreme Ultraviolet (EUV) spicules these quantities are, respectively, approximately 10,000-40,000 kilometers, 20-100 kilometers per second, and approximately 100- approximately 1000 seconds. For the macrospicule the corresponding quantities were respectively approximately 60,000 kilometers, approximately 130 kilometers per second, approximately 1800 seconds, which is typical of macrospicules measured by other workers. Therefore macrospicules are taller, longer-lived, and faster than most Extreme Ultraviolet (EUV) spicules. The rise profiles of both the spicules and the macrospicules match well a second-order ("parabolic" ) trajectory, although the acceleration was often weaker than that of solar gravity in the profiles fitted to the trajectories. Our macrospicule also had an obvious brightening at its base at birth, while such brightening was not apparent for the Extreme Ultraviolet (EUV) spicules. Most of the Extreme Ultraviolet (EUV) spicules remained visible during their descent back to the solar surface, although a small percentage of the spicules and the macrospicule faded out before falling back to the surface. Our sample of macrospicules is not yet large enough to determine whether their initiation mechanism is identical to that of Extreme Ultraviolet (EUV) spicules.

Probing primordial non-Gaussianity via iSW measurements with SKA continuum surveys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raccanelli, Alvise; Doré, Olivier, E-mail: alvise@jhu.edu, E-mail: olivier.dore@caltech.edu; Bacon, David J.

The Planck CMB experiment has delivered the best constraints so far on primordial non-Gaussianity, ruling out early-Universe models of inflation that generate large non-Gaussianity. Although small improvements in the CMB constraints are expected, the next frontier of precision will come from future large-scale surveys of the galaxy distribution. The advantage of such surveys is that they can measure many more modes than the CMB—in particular, forthcoming radio surveys with the Square Kilometre Array will cover huge volumes. Radio continuum surveys deliver the largest volumes, but with the disadvantage of no redshift information. In order to mitigate this, we use twomore » additional observables. First, the integrated Sachs-Wolfe effect—the cross-correlation of the radio number counts with the CMB temperature anisotropies—helps to reduce systematics on the large scales that are sensitive to non-Gaussianity. Second, optical data allows for cross-identification in order to gain some redshift information. We show that, while the single redshift bin case can provide a σ(f{sub NL}) ∼ 20, and is therefore not competitive with current and future constraints on non-Gaussianity, a tomographic analysis could improve the constraints by an order of magnitude, even with only two redshift bins. A huge improvement is provided by the addition of high-redshift sources, so having cross-ID for high-z galaxies and an even higher-z radio tail is key to enabling very precise measurements of f{sub NL}. We use Fisher matrix forecasts to predict the constraining power in the case of no redshift information and the case where cross-ID allows a tomographic analysis, and we show that the constraints do not improve much with 3 or more bins. Our results show that SKA continuum surveys could provide constraints competitive with CMB and forthcoming optical surveys, potentially allowing a measurement of σ(f{sub NL}) ∼ 1 to be made. Moreover, these measurements would act as a useful check of results obtained with other probes at other redshift ranges with other methods.« less

PULSE@Parkes, Engaging Students through Hands-On Radio Astronomy

NASA Astrophysics Data System (ADS)

Hollow, Robert; Hobbs, George; Shannon, Ryan M.; Kerr, Matthew

2015-08-01

PULSE@Parkes is an innovative, free educational program run by CSIRO Astronomy and Space Science (CASS) in which high school students use the 64m Parkes radio telescope remotely in real time to observe pulsars then analyse their data. The program caters for a range of student ability and introduces students to hands-on observing and radio astronomy. Students are guided by professional astronomers, educators and PhD students during an observing session. They have ample time to interact with the scientists and discuss astronomy, careers and general scientific questions. Students use a web-based module to analyse pulsar properties. All data from the program are streamed via a web browser and are freely available from the online archive and may be used for open-ended student investigations. The data are also used by the team for ongoing pulsar studies with two scientific papers published to date.Over 100 sessions have been held so far. Most sessions are held at CASS headquarters in Sydney, Australia but other sessions are regularly held in other states with partner institutions. The flexibility of the program means that it is also possible to run sessions in other countries. This aspect of the program is useful for demonstrating capability, engaging students in diverse settings and fostering collaborations. The use of Twitter (@pulseatparkes) during allows followers worldwide to participate and ask questions.Two tours of Japan plus sessions in the UK, Netherlands and Canada have reached a wide audience. Plans for collaborations in China are well underway with the possibility of use with other countries also being explored. The program has also been successfully used in helping to train international graduate students via the International Pulsar Timing Array Schools. We have identified strong demand and need for programs such as this for training undergraduate students in Asia and the North America in observing and data analysis techniques so one area of planned development is teaching materials and a package for students at this level. The program has also been used to inform the development of educational programs for new telescopes such as the Australian SKA Pathfinder (ASKAP) and the SKA.http://pulseatparkes.atnf.csiro.au/

The MeqTrees software system and its use for third-generation calibration of radio interferometers

NASA Astrophysics Data System (ADS)

Noordam, J. E.; Smirnov, O. M.

2010-12-01

Context. The formulation of the radio interferometer measurement equation (RIME) for a generic radio telescope by Hamaker et al. has provided us with an elegant mathematical apparatus for better understanding, simulation and calibration of existing and future instruments. The calibration of the new radio telescopes (LOFAR, SKA) would be unthinkable without the RIME formalism, and new software to exploit it. Aims: The MeqTrees software system is designed to implement numerical models, and to solve for arbitrary subsets of their parameters. It may be applied to many problems, but was originally geared towards implementing Measurement Equations in radio astronomy for the purposes of simulation and calibration. The technical goal of MeqTrees is to provide a tool for rapid implementation of such models, while offering performance comparable to hand-written code. We are also pursuing the wider goal of increasing the rate of evolution of radio astronomical software, by offering a tool that facilitates rapid experimentation, and exchange of ideas (and scripts). Methods: MeqTrees is implemented as a Python-based front-end called the meqbrowser, and an efficient (C++-based) computational back-end called the meqserver. Numerical models are defined on the front-end via a Python-based Tree Definition Language (TDL), then rapidly executed on the back-end. The use of TDL facilitates an extremely short turn-around time (hours rather than weeks or months) for experimentation with new ideas. This is also helped by unprecedented visualization capabilities for all final and intermediate results. A flexible data model and a number of important optimizations in the back-end ensures that the numerical performance is comparable to that of hand-written code. Results: MeqTrees is already widely used as the simulation tool for new instruments (LOFAR, SKA) and technologies (focal plane arrays). It has demonstrated that it can achieve a noise-limited dynamic range in excess of a million, on WSRT data. It is the only package that is specifically designed to handle what we propose to call third-generation calibration (3GC), which is needed for the new generation of giant radio telescopes, but can also improve the calibration of existing instruments.

Operational modes, health, and status monitoring

NASA Astrophysics Data System (ADS)

Taljaard, Corrie

2016-08-01

System Engineers must fully understand the system, its support system and operational environment to optimise the design. Operations and Support Managers must also identify the correct metrics to measure the performance and to manage the operations and support organisation. Reliability Engineering and Support Analysis provide methods to design a Support System and to optimise the Availability of a complex system. Availability modelling and Failure Analysis during the design is intended to influence the design and to develop an optimum maintenance plan for a system. The remote site locations of the SKA Telescopes place emphasis on availability, failure identification and fault isolation. This paper discusses the use of Failure Analysis and a Support Database to design a Support and Maintenance plan for the SKA Telescopes. It also describes the use of modelling to develop an availability dashboard and performance metrics.

The solar array is installed on ACE in SAEF-2

NASA Technical Reports Server (NTRS)

1997-01-01

Applied Physics Laboratory Engineer Cliff Willey (kneeling) and Engineering Assistant Jim Hutcheson from Johns Hopkins University install solar array panels on the Advanced Composition Explorer (ACE) in KSC's Spacecraft Assembly and Encapsulation Facility-II. Scheduled for launch on a Delta II rocket from Cape Canaveral Air Station on Aug. 25, ACE will study low-energy particles of solar origin and high-energy galactic particles for a better understanding of the formation and evolution of the solar system as well as the astrophysical processes involved. The ACE observatory will be placed into an orbit almost a million miles (1.5 million kilometers) away from the Earth, about 1/100 the distance from the Earth to the Sun. The collecting power of instrumentation aboard ACE is at least 100 times more sensitive than anything previously flown to collect similar data by NASA.

ROSS Skills, Knowledge, and Abilities Training Evaluation. Gaps and Recommendations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ala, Maureen; Gruidl, Jeremiah; Buddemeier, Brooke

2015-09-30

This document describes the development of the ROSS SKAs, the cross-mapping of the SKAs to the available training, identifies gaps in the SKA and training, and provides recommendations to address those gaps.

Could the IMS Infrasound Stations Support a Global Network of Small Aperture Seismic Arrays?

NASA Astrophysics Data System (ADS)

J, Gibbons, Steven; Kværna, Tormod; Mykkeltveit, Svein

2015-04-01

The infrasound stations of the International Monitoring System are arrays consisting of up to 15 sites and with apertures of up to 3 km. The arrays are distributed remarkably uniformly over the globe and provide excellent coverage of South America, Africa, and Antarctica. This is to say that there are many infrasound arrays in regions many thousands of kilometers from the closest seismic array. Several infrasound arrays are in the immediate vicinity of existing 3-component seismic stations and these provide us with examples of how typical seismic signals look at these locations. We can make idealized estimates of the predicted performance of seismic arrays, consisting of seismometers at each site of the infrasound arrays, by duplicating the signals from the 3-C stations at all sites of the array. However, the true performance of seismic arrays at these sites will depend both upon Signal-to-Noise Ratios of seismic signals and the coherence of both signal and noise between sensors. These properties can only be determined experimentally. Recording seismic data of sufficient quality at many of these arrays may require borehole deployments since the microbarometers in the infrasound arrays are often situated in vaults placed in soft sediments. The geometries of all the current IMS infrasound arrays are examined and compared and we demonstrate that, from a purely geometrical perspective, essentially all the array configurations would provide seismic arrays with acceptable slowness resolution for both regional and teleseismic phase arrivals. Seismic arrays co-located with the infrasound arrays in many regions would likely enhance significantly the seismic monitoring capability in parts of the world where only 3-component stations are currently available. Co-locating seismic and infrasound sensors would facilitate the development of seismic arrays that share the infrastructure of the infrasound arrays, reducing the development and operational costs. Hosting countries might find such added capabilities valuable from a national perspective. In addition, the seismic recordings may also help to identify the sources of infrasound signals with consequences for improved event screening and evaluating models of infrasound propagation and atmospheric properties.

IRIS Arrays: Observing Wavefields at Multiple Scales and Frequencies

NASA Astrophysics Data System (ADS)

Sumy, D. F.; Woodward, R.; Frassetto, A.

2014-12-01

The Incorporated Research Institutions for Seismology (IRIS) provides instruments for creating and operating seismic arrays at a wide range of scales. As an example, for over thirty years the IRIS PASSCAL program has provided instruments to individual Principal Investigators to deploy arrays of all shapes and sizes on every continent. These arrays have ranged from just a few sensors to hundreds or even thousands of sensors, covering areas with dimensions of meters to thousands of kilometers. IRIS also operates arrays directly, such as the USArray Transportable Array (TA) as part of the EarthScope program. Since 2004, the TA has rolled across North America, at any given time spanning a swath of approximately 800 km by 2,500 km, and thus far sampling 2% of the Earth's surface. This achievement includes all of the lower-48 U.S., southernmost Canada, and now parts of Alaska. IRIS has also facilitated specialized arrays in polar environments and on the seafloor. In all cases, the data from these arrays are freely available to the scientific community. As the community of scientists who use IRIS facilities and data look to the future they have identified a clear need for new array capabilities. In particular, as part of its Wavefields Initiative, IRIS is exploring new technologies that can enable large, dense array deployments to record unaliased wavefields at a wide range of frequencies. Large-scale arrays might utilize multiple sensor technologies to best achieve observing objectives and optimize equipment and logistical costs. Improvements in packaging and power systems can provide equipment with reduced size, weight, and power that will reduce logistical constraints for large experiments, and can make a critical difference for deployments in harsh environments or other situations where rapid deployment is required. We will review the range of existing IRIS array capabilities with an overview of previous and current deployments and examples of data and results. We will review existing IRIS projects that explore new array capabilities and highlight future directions for IRIS instrumentation facilities.

Results of the 1981 NASA/JPL balloon flight solar cell calibration program

NASA Technical Reports Server (NTRS)

Seaman, C. H.; Weiss, R. S.

1982-01-01

The calibration of the direct conversion of solar energy through use of solar cells at high altitudes by balloon flight is reported. Twenty seven modules were carried to an altitude of 35.4 kilometers. Silicon cells are stable for long periods of time and can be used as standards. It is demonstrated that the cell mounting cavity may be either black or white with equal validity in setting solar simulators. The calibrated cells can be used as reference standards in simulator testing of cells and arrays.

Science with a lunar low-frequency array: From the dark ages of the Universe to nearby exoplanets

NASA Astrophysics Data System (ADS)

Jester, Sebastian; Falcke, Heino

2009-05-01

Low-frequency radio astronomy is limited by severe ionospheric distortions below 50 MHz and complete reflection of radio waves below 10-30 MHz. Shielding of man-made interference from long-range radio broadcasts, strong natural radio emission from the Earth's aurora, and the opportunity to set up a large distributed antenna array make the lunar far side a supreme location for a low-frequency radio array. A number of new scientific drivers for such an array, such as the study of the dark ages and epoch of reionization, exoplanets, and ultra-high energy cosmic rays, have emerged and need to be studied in greater detail. Here we review the scientific potential and requirements of these new scientific drivers and discuss the constraints for various lunar surface arrays. In particular, we describe observability constraints imposed by the interstellar and interplanetary medium, calculate the achievable resolution, sensitivity, and confusion limit of a dipole array using general scaling laws, and apply them to various scientific questions. Of particular interest for a lunar array are studies of the earliest phase of the universe which are not easily accessible by other means. These are the epoch of reionization at redshifts z = 6-20, during which the very first stars and galaxies ionized most of the originally neutral intergalactic hydrogen, and the dark ages prior to that. For example, a global 21-cm wave absorption signature from primordial hydrogen in the dark ages at z = 30-50 could in principle be detected by a single dipole in an eternally dark crater on the moon, but foreground subtraction would be extremely difficult. Obtaining a high-quality power spectrum of density fluctuations in the epoch of reionization at z = 6-20, providing a wealth of cosmological data, would require about 103-105 antenna elements on the moon, which appears not unreasonable in the long term. Moreover, baryonic acoustic oscillations in the dark ages at z = 30-50 could similarly be detected, thereby providing pristine cosmological information, e.g., on the inflationary phase of the universe. With a large array also exoplanet magnetospheres could be detected through Jupiter-like coherent bursts. Smaller arrays of order 102 antennas over ˜100 km, which could already be erected robotically by a single mission with current technology and launchers, could tackle surveys of steep-spectrum large-scale radio structures from galaxy clusters and radio galaxies. Also, at very low frequencies the structure of the interstellar medium can be studied tomographically. Moreover, radio emission from neutrino interactions within the moon can potentially be used to create a neutrino detector with a volume of several cubic kilometers. An ultra-high energy cosmic ray detector with thousands of square kilometer area for cosmic ray energies >1020eV could in principle be realized with some hundred antennas. In any case, pathfinder arrays are needed to test the feasibility of these experiments in the not too distant future. Lunar low-frequency arrays are thus a timely option to consider, offering the potential for significant new insights into a wide range of today's crucial scientific topics. This would open up one of the last unexplored frequency domains in the electromagnetic spectrum.

EoR imaging with the SKA: the challenge of foreground removal

NASA Astrophysics Data System (ADS)

Bonaldi, Anna

2018-05-01

21-cm observations of the Cosmic dawn (CD) and Epoch of Reionization (EoR) are one of the high priority science objectives for SKA Low. One of the most difficult aspects of the 21-cm measurement is the presence of foreground emission, due to our Galaxy and extragalactic sources, which is about four orders of magnitude brighter than the cosmological signal. While end-to-end simulations are being produced to investigate in details the foreground subtraction strategy, it is useful to complement this thorough but time-consuming approach with simpler, quicker ways to evaluate performance and identify possible critical steps. In this work, I present a forecast method, based on Bonaldi et al. (2015), Bonaldi & Ricciardi (2011), to understand the level of residual contamination after a component separation step, and its impact on our ability to investigate CD and EoR.

Wanda Ossowska (1912-2001) and Stanisława Leszczyńska (1896-1974): Polish nurses working under Nazi occupation.

PubMed

Dobrowolska, Barbara; Hoch, Stefania; Jabkowska-Sochanska, Aniela; Benedict, Susan; Shields, Linda

2011-11-01

Poland was invaded by Nazi Germany on 1 September 1939 and World War II began on 3 September. Polish nurses have their place in this difficult history. In the first months of occupation, nurses focused on caring for wounded soldiers. In order to protect them from prisoner-of-war camps and execution, nurses sought safe havens for the wounded in private homes and transported them there. After their regular jobs, the nurses visited them, changed their dressings and provided them with civilian clothes so that soldiers could eventually escape. This paper describes the work of two of these nurses, Wanda Ossowska and Stanisława Leszczyńska. The first three authors (BD, SH, AJS) were nurses in Poland at that time and they present some of the information in this paper as primary source data.

JPL Big Data Technologies for Radio Astronomy

NASA Astrophysics Data System (ADS)

Jones, Dayton L.; D'Addario, L. R.; De Jong, E. M.; Mattmann, C. A.; Rebbapragada, U. D.; Thompson, D. R.; Wagstaff, K.

2014-04-01

During the past three years the Jet Propulsion Laboratory has been working on several technologies to deal with big data challenges facing next-generation radio arrays, among other applications. This program has focused on the following four areas: 1) We are investigating high-level ASIC architectures that reduce power consumption for cross-correlation of data from large interferometer arrays by one to two orders of magnitude. The cost of operations for the Square Kilometre Array (SKA), which may be dominated by the cost of power for data processing, is a serious concern. A large improvement in correlator power efficiency could have a major positive impact. 2) Data-adaptive algorithms (machine learning) for real-time detection and classification of fast transient signals in high volume data streams are being developed and demonstrated. Studies of the dynamic universe, particularly searches for fast (<< 1 second) transient events, require that data be analyzed rapidly and with robust RFI rejection. JPL, in collaboration with the International Center for Radio Astronomy Research in Australia, has developed a fast transient search system for eventual deployment on ASKAP. In addition, a real-time transient detection experiment is now running continuously and commensally on NRAO's Very Long Baseline Array. 3) Scalable frameworks for data archiving, mining, and distribution are being applied to radio astronomy. A set of powerful open-source Object Oriented Data Technology (OODT) tools is now available through Apache. OODT was developed at JPL for Earth science data archives, but it is proving to be useful for radio astronomy, planetary science, health care, Earth climate, and other large-scale archives. 4) We are creating automated, event-driven data visualization tools that can be used to extract information from a wide range of complex data sets. Visualization of complex data can be improved through algorithms that detect events or features of interest and autonomously generate images or video to display those features. This work has been carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Executive competencies in healthcare administration: preceptors of the Army-Baylor University Graduate Program.

PubMed

Finstuen, Kenn; Mangelsdorff, A David

2006-01-01

The purpose of this research was to identify the mentoring and executive competencies required among preceptors of the Army-Baylor University Graduate Program in Health and Business Administration, and to specify the requisite skills, knowledge, and abilities (SKAs) needed to achieve those competencies. In the first wave of inquiry, a list of 123 competencies and associated SKAs was elicited from a network of 80 current and past preceptor executives employing a Delphi methodology using e-mail. An expert panel, which consisted of seven past program directors, examined and sorted the list into four preceptor content domains, viz., Health Systems Management (HS Management), Leadership, Residency Administration, and Community Involvement. Frequency analyses showed that the HS Management domain constituted over half of the competencies, with particular emphasis on strategic thinking, planning, billing, finance, manpower, and contracting. In the second wave, the preceptor Delphi network reviewed the expertpanel list and made 7-pointSKA importance ratings on an 80-item structured questionnaire representative of the four domains. Findings indicated thataverage SKA ratings were reliable and agreed upon to a high degree among preceptors. Results, rank ordered by SKA item means within preceptor content domains and overall, suggested that the most important rated items centered on teamwork, negotiation, interpersonal skills, communication, leadership vision, and customer and healthcare business operations. Outcomes from the competency list are expected to be useful for preceptor mentoring, self-assessment, and for professional development. Additionally, specific SKAs can provide a means for developing job requirements and career performance criteria at a behavioral task level, and can contribute information for identifying continuing education and conference topical needs.

DOI/GTN-P climate and active-layer data acquired in the National Petroleum Reserve-Alaska and the Arctic National Wildlife Refuge

USGS Publications Warehouse

Urban, Frank E.; Clow, Gary D.

2014-01-01

This report provides data collected by the climate monitoring array of the U.S. Department of the Interior on Federal lands in Arctic Alaska over the period August 1998 to July 2013; this array is part of the Global Terrestrial Network for Permafrost, (DOI/GTN-P). In addition to presenting data, this report also describes monitoring, data collection, and quality-control methods. This array of 16 monitoring stations spans lat 68.5°N. to 70.5°N. and long 142.5°W. to 161°W., an area of approximately 150,000 square kilometers. Climate summaries are presented along with quality-controlled data. Data collection is ongoing and includes the following climate- and permafrost-related variables: air temperature, wind speed and direction, ground temperature, soil moisture, snow depth, rainfall totals, up- and downwelling shortwave radiation, and atmospheric pressure. These data were collected by the U.S. Geological Survey in close collaboration with the Bureau of Land Management and the U.S. Fish and Wildlife Service.

DOI/GTN-P Climate and active-layer data acquired in the National Petroleum Reserve–Alaska and the Arctic National Wildlife Refuge, 1998–2014

USGS Publications Warehouse

Urban, Frank E.; Clow, Gary D.

2016-03-04

This report provides data collected by the climate monitoring array of the U.S. Department of the Interior on Federal lands in Arctic Alaska over the period August 1998 to July 2014; this array is part of the Global Terrestrial Network for Permafrost (DOI/GTN-P). In addition to presenting data, this report also describes monitoring, data collection, and quality-control methods. The array of 16 monitoring stations spans lat 68.5°N. to 70.5°N. and long 142.5°W. to 161°W., an area of approximately 150,000 square kilometers. Climate summaries are presented along with quality-controlled data. Data collection is ongoing and includes the following climate- and permafrost-related variables: air temperature, wind speed and direction, ground temperature, soil moisture, snow depth, rainfall totals, up- and downwelling shortwave radiation, and atmospheric pressure. These data were collected by the U.S. Geological Survey in close collaboration with the Bureau of Land Management and the U.S. Fish and Wildlife Service.

DOI/GTN-P Climate and active-layer data acquired in the National Petroleum Reserve–Alaska and the Arctic National Wildlife Refuge, 1998–2015

USGS Publications Warehouse

Urban, Frank E.; Clow, Gary D.

2017-02-06

This report provides data collected by the climate monitoring array of the U.S. Department of the Interior on Federal lands in Arctic Alaska over the period August 1998 to July 2015; this array is part of the Global Terrestrial Network for Permafrost (DOI/GTN-P). In addition to presenting data, this report also describes monitoring, data collection, and quality-control methods. The array of 16 monitoring stations spans lat 68.5°N. to 70.5°N. and long 142.5°W. to 161°W., an area of approximately 150,000 square kilometers. Climate summaries are presented along with quality-controlled data. Data collection is ongoing and includes the following climate- and permafrost-related variables: air temperature, wind speed and direction, ground temperature, soil moisture, snow depth, rainfall totals, up- and downwelling shortwave radiation, and atmospheric pressure. These data were collected by the U.S. Geological Survey in close collaboration with the Bureau of Land Management and the U.S. Fish and Wildlife Service.

DOI/GTN-P climate and active-layer data acquired in the National Petroleum Reserve: Alaska and the Arctic National Wildlife Refuge, 1998-2011

USGS Publications Warehouse

Urban, Frank E.; Clow, Gary D.

2014-01-01

This report provides data collected by the climate monitoring array of the U.S. Department of the Interior on Federal lands in Arctic Alaska over the period August 1998 to July 2011; this array is part of the Global Terrestrial Network for Permafrost, (DOI/GTN-P). In addition to presenting data, this report also describes monitoring, data collection, and quality-control methodology. This array of 16 monitoring stations spans lat 68.5°N. to 70.5°N. and long 142.5°W. to 161°W., an area of approximately 150,000 square kilometers. Climate summaries are presented along with quality-controlled data. Data collection is ongoing and includes the following climate- and permafrost-related variables: air temperature, wind speed and direction, ground temperature and soil moisture, snow depth, rainfall, up- and downwelling shortwave radiation, and atmospheric pressure. These data were collected by the U.S. Geological Survey in close collaboration with the Bureau of Land Management and the U.S. Fish and Wildlife Service.

Fiber-Optic Network Observations of Earthquake Wavefields

NASA Astrophysics Data System (ADS)

Lindsey, Nathaniel J.; Martin, Eileen R.; Dreger, Douglas S.; Freifeld, Barry; Cole, Stephen; James, Stephanie R.; Biondi, Biondo L.; Ajo-Franklin, Jonathan B.

2017-12-01

Our understanding of subsurface processes suffers from a profound observation bias: seismometers are sparse and clustered on continents. A new seismic recording approach, distributed acoustic sensing (DAS), transforms telecommunication fiber-optic cables into sensor arrays enabling meter-scale recording over tens of kilometers of linear fiber length. We analyze cataloged earthquake observations from three DAS arrays with different horizontal geometries to demonstrate some possibilities using this technology. In Fairbanks, Alaska, we find that stacking ground motion records along 20 m of fiber yield a waveform that shows a high degree of correlation in amplitude and phase with a colocated inertial seismometer record at 0.8-1.6 Hz. Using an L-shaped DAS array in Northern California, we record the nearly vertically incident arrival of an earthquake from The Geysers Geothermal Field and estimate its backazimuth and slowness via beamforming for different phases of the seismic wavefield. Lastly, we install a fiber in existing telecommunications conduits below Stanford University and show that little cable-to-soil coupling is required for teleseismic P and S phase arrival detection.

Observations and Analyses of Heliospheric Faraday Rotation of a Coronal Mass Ejection (CME) Using the LOw Frequency ARray (LOFAR) and Space-Based Imaging Techniques

NASA Astrophysics Data System (ADS)

Bisi, Mario Mark; Jensen, Elizabeth; Sobey, Charlotte; Fallows, Richard; Jackson, Bernard; Barnes, David; Giunta, Alessandra; Hick, Paul; Eftekhari, Tarraneh; Yu, Hsiu-Shan; Odstrcil, Dusan; Tokumaru, Munetoshi; Wood, Brian

2017-04-01

Geomagnetic storms of the highest intensity are general driven by coronal mass ejections (CMEs) impacting the Earth's space environment. Their intensity is driven by the speed, density, and, most-importantly, their magnetic-field orientation and magnitude of the incoming solar plasma. The most-significant magnetic-field factor is the North-South component (Bz in Geocentric Solar Magnetic - GSM - coordinates). At present, there are no reliable prediction methods available for this magnetic-field component ahead of the in-situ monitors around the Sun-Earth L1 point. Observations of Faraday rotation (FR) can be used to attempt to determine average magnetic-field orientations in the inner heliosphere. Such a technique has already been well demonstrated through the corona, ionosphere, and also the interstellar medium. Measurements of the polarisation of astronomical (or spacecraft in superior conjunction) radio sources (beacons/radio frequency carriers) through the inner corona of the Sun to obtain the FR have been demonstrated but mostly at relatively-high radio frequencies. Here we show some initial results of true heliospheric FR using the Low Frequency Array (LOFAR) below 200 MHz to investigate the passage of a coronal mass ejection (CME) across the line of sight. LOFAR is a next-generation low-frequency radio interferometer, and a pathfinder to the Square Kilometre Array (SKA) - LOW telescope. We demonstrate preliminary heliospheric FR results through the analysis of observations of pulsar J1022+1001, which commenced on 13 August 2014 at 13:00UT and spanned over 150 minutes in duration. We also show initial comparisons to the FR results via various modelling techniques and additional context information to understand the structure of the inner heliosphere being detected. This observation could indeed pave the way to an experiment which might be implemented for space-weather purposes that will eventually lead to a near-global method for determining the magnetic field throughout the inner heliosphere.

High-resolution imaging of the low velocity layer in Alaskan subduction zone with scattered waves and interferometry

NASA Astrophysics Data System (ADS)

Kim, D.; Keranen, K. M.; Abers, G. A.; Kim, Y.; Li, J.; Shillington, D. J.; Brown, L. D.

2017-12-01

The physical factors that control the rupture process of great earthquakes at convergent plate boundaries remain incompletely understood. While recent developments in imaging using the teleseismic wavefield have led to marked advances at wavelengths of a couple kilometers to tens of kilometers, higher resolution imaging of the rupture zone would improve the resolution of imaging and thus provide improved parameter estimation, as the teleseismic wavefield is fundamentally limited by its low frequency content. This study compares and evaluates two seismic imaging techniques using the high-frequency signals from teleseismic coda versus earthquake scattered waves to image the subducting Yakutat oceanic plateau in the Alaska subduction zone. We use earthquakes recorded by the MOOS PASSCAL broadband deployment in southern Alaska. In our first method, we select local earthquakes that lie directly beneath and laterally near the recording array for imaging, and extract body wave information via a simple autocorrelation and stacking. Profiles analogous to seismic reflection profile are constructed using the near-vertically travelling waves. In our second method, we compute teleseismic receiver functions within the 0.02-1.0 Hz frequency band. Both results image interfaces that we associate with the subducting oceanic plate in Alaska-Aleutian system, with greater resolution than commonly used methods with teleseismic sources. Structural details from our results can further our understanding of the conditions and materials that characterize the subduction megathrusts, and the techniques can be employed in other regions along the Alaska-Aleutian system and at other convergent margins with suitable seismic arrays.

Status of LOFAR Data in HDF5 Format

NASA Astrophysics Data System (ADS)

Alexov, A.; Schellart, P.; ter Veen, S.; van der Akker, M.; Bähren, L.; Greissmeier, J.-M.; Hessels, J. W. T.; Mol, J. D.; Renting, G. A.; Swinbank, J.; Wise, M.

2012-09-01

The Hierarchical Data Format, version 5 (HDF5) is a data model, library, and file format for storing and managing data. It is designed for flexible and efficient I/O and for high volume, complex data. The Low Frequency Array (LOFAR) project is solving the challenge of data size and complexity using HDF5. Most of LOFAR's standard data products will be stored using HDF5; the beam-formed time-series data and transient buffer board data have already transitioned from project-specific binary format to HDF5. We report on our effort to pave the way towards new astronomical data encapsulation using HDF5, which can be used by future ground and space projects. The LOFAR project has formed a collaboration with NRAO, the Virtual Astronomical Observatory (VAO) and the HDF Group to obtain funding for a full-time staff member to work on documenting and developing standards for astronomical data written in HDF5. We hope our effort will enhance HDF5 visibility and usage within the community, specifically for LSST, the SKA pathfinders (ASKAP, MeerKAT, MWA, LWA), and other major new radio telescopes such as EVLA, ALMA, and eMERLIN.

Direct Shear Mapping: Prospects for Weak Lensing Studies of Individual Galaxy-Galaxy Lensing Systems

NASA Astrophysics Data System (ADS)

de Burgh-Day, C. O.; Taylor, E. N.; Webster, R. L.; Hopkins, A. M.

2015-11-01

Using both a theoretical and an empirical approach, we have investigated the frequency of low redshift galaxy-galaxy lensing systems in which the signature of 3D weak lensing might be directly detectable. We find good agreement between these two approaches. Using data from the Galaxy and Mass Assembly redshift survey we estimate the frequency of detectable weak lensing at low redshift. We find that below a redshift of z ~ 0.6, the probability of a galaxy being weakly lensed by γ ⩾ 0.02 is ~ 0.01. We have also investigated the feasibility of measuring the scatter in the M * - Mh relation using shear statistics. We estimate that for a shear measurement error of Δγ = 0.02 (consistent with the sensitivity of the Direct Shear Mapping technique), with a sample of ~50,000 spatially and spectrally resolved galaxies, the scatter in the M * - Mh relation could be measured. While there are currently no existing IFU surveys of this size, there are upcoming surveys that will provide this data (e.g The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), surveys with Hector, and the Square Kilometre Array (SKA)).

Multibeam Gpu Transient Pipeline for the Medicina BEST-2 Array

NASA Astrophysics Data System (ADS)

Magro, A.; Hickish, J.; Adami, K. Z.

2013-09-01

Radio transient discovery using next generation radio telescopes will pose several digital signal processing and data transfer challenges, requiring specialized high-performance backends. Several accelerator technologies are being considered as prototyping platforms, including Graphics Processing Units (GPUs). In this paper we present a real-time pipeline prototype capable of processing multiple beams concurrently, performing Radio Frequency Interference (RFI) rejection through thresholding, correcting for the delay in signal arrival times across the frequency band using brute-force dedispersion, event detection and clustering, and finally candidate filtering, with the capability of persisting data buffers containing interesting signals to disk. This setup was deployed at the BEST-2 SKA pathfinder in Medicina, Italy, where several benchmarks and test observations of astrophysical transients were conducted. These tests show that on the deployed hardware eight 20 MHz beams can be processed simultaneously for 640 Dispersion Measure (DM) values. Furthermore, the clustering and candidate filtering algorithms employed prove to be good candidates for online event detection techniques. The number of beams which can be processed increases proportionally to the number of servers deployed and number of GPUs, making it a viable architecture for current and future radio telescopes.

The solar array is installed on ACE in SAEF-2

NASA Technical Reports Server (NTRS)

1997-01-01

Applied Physics Laboratory engineers and technicians from Johns Hopkins University install solar array panels on the Advanced Composition Explorer (ACE) in KSC's Spacecraft Assembly and Encapsulation Facility-II. The panel on which they are working is identical to the panel (one of four) seen in the foreground on the ACE spacecraft. Scheduled for launch on a Delta II rocket from Cape Canaveral Air Station on Aug. 25, ACE will study low- energy particles of solar origin and high-energy galactic particles for a better understanding of the formation and evolution of the solar system as well as the astrophysical processes involved. The ACE observatory will be placed into an orbit almost a million miles (1.5 million kilometers) away from the Earth, about 1/100 the distance from the Earth to the Sun. The collecting power of instrumentation aboard ACE is at least 100 times more sensitive than anything previously flown to collect similar data by NASA.

So Long, C Ring

NASA Image and Video Library

2017-11-13

Saturn's C ring is home to a surprisingly rich array of structures and textures. Much of the structure seen in the outer portions of Saturn's rings is the result of gravitational perturbations on ring particles by moons of Saturn. Such interactions are called resonances. However, scientists are not clear as to the origin of the structures seen in this image which has captured an inner ring region sparsely populated with particles, making interactions between ring particles rare, and with few satellite resonances. In this image, a bright and narrow ringlet located toward the outer edge of the C ring is flanked by two broader features called plateaus, each about 100 miles (160 kilometers) wide. Plateaus are unique to the C ring. Cassini data indicates that the plateaus do not necessarily contain more ring material than the C ring at large, but the ring particles in the plateaus may be smaller, enhancing their brightness. This view looks toward the sunlit side of the rings from about 53 degrees above the ring plane. The image was taken in green light with the Cassini spacecraft narrow-angle camera on Aug. 14, 2017. The view was acquired at a distance of approximately 117,000 miles (189,000 kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 74 degrees. Image scale is 3,000 feet (1 kilometer) per pixel. The Cassini spacecraft ended its mission on Sept. 15, 2017. https://photojournal.jpl.nasa.gov/catalog/PIA21356

Ganymede in Visible and Infrared Light

NASA Technical Reports Server (NTRS)

2007-01-01

This montage compares New Horizons' best views of Ganymede, Jupiter's largest moon, gathered with the spacecraft's Long Range Reconnaissance Imager (LORRI) and its infrared spectrometer, the Linear Etalon Imaging Spectral Array (LEISA).

LEISA observes its targets in more than 200 separate wavelengths of infrared light, allowing detailed analysis of their surface composition. The LEISA image shown here combines just three of these wavelengths -- 1.3, 1.8 and 2.0 micrometers -- to highlight differences in composition across Ganymede's surface. Blue colors represent relatively clean water ice, while brown colors show regions contaminated by dark material.

The right panel combines the high-resolution grayscale LORRI image with the color-coded compositional information from the LEISA image, producing a picture that combines the best of both data sets.

The LEISA and LORRI images were taken at 9:48 and 10:01 Universal Time, respectively, on February 27, 2007, from a range of 3.5 million kilometers (2.2 million miles). The longitude of the disk center is 38 degrees west. With a diameter of 5,268 kilometers (3,273 miles), Ganymede is the largest satellite in the solar system.

Ionospheric Specifications for SAR Interferometry (ISSI)

NASA Technical Reports Server (NTRS)

Pi, Xiaoqing; Chapman, Bruce D; Freeman, Anthony; Szeliga, Walter; Buckley, Sean M.; Rosen, Paul A.; Lavalle, Marco

2013-01-01

The ISSI software package is designed to image the ionosphere from space by calibrating and processing polarimetric synthetic aperture radar (PolSAR) data collected from low Earth orbit satellites. Signals transmitted and received by a PolSAR are subject to the Faraday rotation effect as they traverse the magnetized ionosphere. The ISSI algorithms combine the horizontally and vertically polarized (with respect to the radar system) SAR signals to estimate Faraday rotation and ionospheric total electron content (TEC) with spatial resolutions of sub-kilometers to kilometers, and to derive radar system calibration parameters. The ISSI software package has been designed and developed to integrate the algorithms, process PolSAR data, and image as well as visualize the ionospheric measurements. A number of tests have been conducted using ISSI with PolSAR data collected from various latitude regions using the phase array-type L-band synthetic aperture radar (PALSAR) onboard Japan Aerospace Exploration Agency's Advanced Land Observing Satellite mission, and also with Global Positioning System data. These tests have demonstrated and validated SAR-derived ionospheric images and data correction algorithms.

Diffraction-limited Mid-infrared Integral Field Spectroscopy of Io's Volcanic Activity with ALES on the Large Binocular Telescope

NASA Astrophysics Data System (ADS)

Skrutskie, Michael F.; de Kleer, Katherine R.; Stone, Jordan; Conrad, Al; Davies, Ashley; de Pater, Imke; Leisenring, Jarron; Hinz, Philip; Skemer, Andrew; Veillet, Christian; Woodward, Charles E.; Ertel, Steve; Spalding, Eckhart

2017-10-01

The Arizona Lenslet for Exoplanet Spectroscopy (ALES) is an enhancement to the Large Binocular Telescope's mid-infrared imager, LMIRcam, that permits low-resolution (R~20) spectroscopy between 2.8 and 4.2 μm of every diffraction-limited resolution element in a 2.5"x2.5" field-of-view on a 2048x2048 HAWAII-2RG 5.2 μm-cutoff array. The 1" disk of Io, dotted with powerful self-luminous volcanic eruptions, provides an ideal target for ALES, where the single 8.4-meter aperture diffraction-limited scale for Io at opposition ranges from 240 kilometers (80 milliarcseconds) at 2.8 μm to 360 kilometers (120 milliarcseconds) at 4.2 μm. ALES provides the capability to assess the color temperature of each volcanic thermal emission site as well as map broadband absorbers such as SO2 frost. A monitoring campaign in the Spring 2017 semester provided two global snapshots of Io's volcanic activity with ALES as well as characterization of a new brightening episode at Loki Patera over four epochs between January and May 2017.

Design of the Longitudinal Dispersion Compensation System for the CHARA Array

NASA Astrophysics Data System (ADS)

Berger, D. H.; Bagnuolo, W. G.

2001-05-01

In recent years, the baselines of optical and infrared interferometers have been approaching half of a kilometer in length. With increased spatial layout comes new and challenging problems to solve. One common hurdle occurs when observing objects not perpendicular to the baseline. The result is one beam with added path length that must be added to the non-delayed beam such that identical phase fronts are combined together to produce fringes. For several interferometers without the addition of costly and logistically difficult evacuated delay lines, path length equalization occurs in long buildings through the ambient air medium. This causes a beam which is spectrally dispersed along the optical axis. The undesirable consequence is decreased fringe contrast. A solution is to disperse the uncompensated beam by inserting a block of glass to match the optical path lengths for all wavelengths within the observing waveband. A single glass solution is presented for the CHARA Array. Modeling, design and fabrication methods are also considered. The CHARA Array, a six-telescope O/IR interferometric array operated by Georgia State University on Mt. Wilson, California, was funded by the National Science Foundation, the W.M. Keck Foundation, the David and Lucile Packard Foundation, and Georgia State University. This research is also funded in part by the Michelson Fellowship Program sponsored by Jet Propulsion Laboratory.

Kilometer-Spaced GNSS Array for Ionospheric Irregularity Monitoring

NASA Astrophysics Data System (ADS)

Su, Yang

This dissertation presents automated, systematic data collection, processing, and analysis methods for studying the spatial-temporal properties of Global Navigation Satellite Systems (GNSS) scintillations produced by ionospheric irregularities at high latitudes using a closely spaced multi-receiver array deployed in the northern auroral zone. The main contributions include 1) automated scintillation monitoring, 2) estimation of drift and anisotropy of the irregularities, 3) error analysis of the drift estimates, and 4) multi-instrument study of the ionosphere. A radio wave propagating through the ionosphere, consisting of ionized plasma, may suffer from rapid signal amplitude and/or phase fluctuations known as scintillation. Caused by non-uniform structures in the ionosphere, intense scintillation can lead to GNSS navigation and high-frequency (HF) communication failures. With specialized GNSS receivers, scintillation can be studied to better understand the structure and dynamics of the ionospheric irregularities, which can be parameterized by altitude, drift motion, anisotropy of the shape, horizontal spatial extent and their time evolution. To study the structuring and motion of ionospheric irregularities at the sub-kilometer scale sizes that produce L-band scintillations, a closely-spaced GNSS array has been established in the auroral zone at Poker Flat Research Range, Alaska to investigate high latitude scintillation and irregularities. Routinely collecting low-rate scintillation statistics, the array database also provides 100 Hz power and phase data for each channel at L1/L2C frequency. In this work, a survey of seasonal and hourly dependence of L1 scintillation events over the course of a year is discussed. To efficiently and systematically study scintillation events, an automated low-rate scintillation detection routine is established and performed for each day by screening the phase scintillation index. The spaced-receiver technique is applied to cross-correlated phase and power measurements from GNSS receivers. Results of horizontal drift velocities and anisotropy ellipses derived from the parameters are shown for several detected events. Results show the possibility of routinely quantifying ionospheric irregularities by drifts and anisotropy. Error analysis on estimated properties is performed to further evaluate the estimation quality. Uncertainties are quantified by ensemble simulation of noise on the phase signals carried through to the observations of the spaced-receiver linear system. These covariances are then propagated through to uncertainties on drifts. A case study of a single scintillating satellite observed by the array is used to demonstrate the uncertainty estimation process. The distributed array is used in coordination with other measuring techniques such as incoherent scatter radar and optical all-sky imagers. These scintillations are correlated with auroral activity, based on all-sky camera images. Measurements and uncertainty estimates made over a 30-minute period are made and compared to a collocated incoherent scatter radar, and show good agreement in horizontal drift speed and direction during periods of scintillation for cases when the characteristic velocity is less than the drift velocity. The methods demonstrated are extensible to other zones and other GNSS arrays of varying size, number, ground distribution, and transmitter frequency.

What Eating at Pluto?

NASA Image and Video Library

2016-03-10

Scientists on NASA's New Horizons mission have discovered what looks like a giant bite-mark on the planet's surface. In this image, north is up. The southern portion of the left inset above shows the cratered plateau uplands informally named Vega Terra (note that all feature names are informal). This terrain is separated from the young, nearly uncratered, mottled plains of Piri Planitia in the center of the image by a generally north-facing jagged scarp called Piri Rupes. The scarp breaks up into isolated mesas in several places. Cutting diagonally across Piri Planitia is the long extensional fault of Inanna Fossa, which stretches eastward 370 miles (600 kilometers) from here to the western edge of the great nitrogen ice plains of Sputnik Planum. Compositional data from the New Horizons spacecraft's Ralph/Linear Etalon Imaging Spectral Array (LEISA) instrument, shown in the right inset, indicate that the plateau uplands south of Piri Rupes are rich in methane ice (shown in false color as purple). Scientists speculate that sublimation of methane may be causing the plateau material to erode along the face of the scarp cliffs, causing them to retreat south and leave the plains of Piri Planitia in their wake. Compositional data also show that the surface of Piri Planitia is more enriched in water ice (shown in false color as blue) than the plateau uplands, which may indicate that Piri Planitia's surface is made of water ice bedrock, on top of which the layer of retreating methane ice had been sitting. Because the surface of Pluto is so cold, the water ice behaves like rock and is immobile. The light/dark mottled pattern of Piri Planitia in the left inset is reflected in the composition map, with the lighter areas corresponding to areas richer in methane – these may be remnants of methane that have not yet sublimated away entirely. The inset at left shows about 650 feet (200 meters) per pixel; the image measures approximately 280 miles (450 kilometers) long by 255 miles (410 kilometers) wide. It was obtained by New Horizons at a range of approximately 21,100 miles (33,900 kilometers) from Pluto, about 45 minutes before the spacecraft's closest approach to Pluto on July 14, 2015.The LEISA data at right was gathered when the spacecraft was about 29,000 miles (47,000 kilometers) from Pluto; best resolution is 1.7 miles (2.7 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA20531

Electron-Muon Identification by Atmospheric Shower and Electron Beam in a New EAS Detector Concept

NASA Astrophysics Data System (ADS)

Iori, M.; Denizli, H.; Yilmaz, A.; Ferrarotto, F.; Russ, J.

2015-03-01

We present results demonstrating the time resolution and μ/e separation capabilities of a new concept for an EAS detector capable of measuring cosmic rays arriving with large zenith angles. This kind of detector has been designed to be part of a large area (several square kilometer) surface array designed to measure ultra high energy (10-200 PeV) τ neutrinos using the Earth-skimming technique. A criterion to identify electron-gammas is also shown and the particle identification capability is tested by measurements in coincidence with the KASKADE-GRANDE experiment in Karlsruhe, Germany.

Cosmology on a Mesh

NASA Astrophysics Data System (ADS)

Gill, Stuart P. D.; Knebe, Alexander; Gibson, Brad K.; Flynn, Chris; Ibata, Rodrigo A.; Lewis, Geraint F.

2003-04-01

An adaptive multi grid approach to simulating the formation of structure from collisionless dark matter is described. MLAPM (Multi-Level Adaptive Particle Mesh) is one of the most efficient serial codes available on the cosmological "market" today. As part of Swinburne University's role in the development of the Square Kilometer Array, we are implementing hydrodynamics, feedback, and radiative transfer within the MLAPM adaptive mesh, in order to simulate baryonic processes relevant to the interstellar and intergalactic media at high redshift. We will outline our progress to date in applying the existing MLAPM to a study of the decay of satellite galaxies within massive host potentials.

21-cm signature of the first sources in the Universe: prospects of detection with SKA

NASA Astrophysics Data System (ADS)

Ghara, Raghunath; Choudhury, T. Roy; Datta, Kanan K.

2016-07-01

Currently several low-frequency experiments are being planned to study the nature of the first stars using the redshifted 21-cm signal from the cosmic dawn and Epoch of Reionization. Using a one-dimensional radiative transfer code, we model the 21-cm signal pattern around the early sources for different source models, I.e. the metal-free Population III (PopIII) stars, primordial galaxies consisting of Population II (PopII) stars, mini-QSOs and high-mass X-ray binaries (HMXBs). We investigate the detectability of these sources by comparing the 21-cm visibility signal with the system noise appropriate for a telescope like the SKA1-low. Upon integrating the visibility around a typical source over all baselines and over a frequency interval of 16 MHz, we find that it will be possible to make a ˜9σ detection of the isolated sources like PopII galaxies, mini-QSOs and HMXBs at z ˜ 15 with the SKA1-low in 1000 h. The exact value of the signal-to-noise ratio (SNR) will depend on the source properties, in particular on the mass and age of the source and the escape fraction of ionizing photons. The predicted SNR decreases with increasing redshift. We provide simple scaling laws to estimate the SNR for different values of the parameters which characterize the source and the surrounding medium. We also argue that it will be possible to achieve an SNR ˜9 even in the presence of the astrophysical foregrounds by subtracting out the frequency-independent component of the observed signal. These calculations will be useful in planning 21-cm observations to detect the first sources.

Prospects of Measuring the Angular Power Spectrum of the Diffuse Galactic Synchrotron Emission with SKA1 Low

NASA Astrophysics Data System (ADS)

Ali, Sk. Saiyad; Bharadwaj, Somnath; Choudhuri, Samir; Ghosh, Abhik; Roy, Nirupam

2016-12-01

The Diffuse Galactic Syncrotron Emission (DGSE) is the most important diffuse foreground component for future cosmological 21-cm observations. The DGSE is also an important probe of the cosmic ray electron and magnetic field distributions in the turbulent interstellar medium (ISM) of our galaxy. In this paper we briefly review the Tapered Gridded Estimator (TGE) which can be used to quantify the angular power spectrum C ℓ of the sky signal directly from the visibilities measured in radio-interferometric observations. The salient features of the TGE are: (1) it deals with the gridded data which makes it computationally very fast, (2) it avoids a positive noise bias which normally arises from the system noise inherent to the visibility data, and (3) it allows us to taper the sky response and thereby suppresses the contribution from unsubtracted point sources in the outer parts and the side lobes of the antenna beam pattern. We also summarize earlier work where the TGE was used to measure the C ℓ of the DGSE using 150 MHz GMRT data. Earlier measurements of C ℓ are restricted to ℓ ≤ ℓ _{max } ˜ 103 for the DGSE, the signal at the larger ℓ values is dominated by the residual point sources after source subtraction. The higher sensitivity of the upcoming SKA1 Low will allow the point sources to be subtracted to a fainter level than possible with existing telescopes. We predict that it will be possible to measure the C ℓ of the DGSE to larger values of ℓ _{max } with SKA1 Low. Our results show that it should be possible to achieve ℓ _{max }˜ 104 and ˜105 with 2 minutes and 10 hours of observations respectively.

Discovery and replication of a peripheral tissue DNA methylation biosignature to augment a suicide prediction model.

PubMed

Clive, Makena L; Boks, Marco P; Vinkers, Christiaan H; Osborne, Lauren M; Payne, Jennifer L; Ressler, Kerry J; Smith, Alicia K; Wilcox, Holly C; Kaminsky, Zachary

2016-01-01

Suicide is the second leading cause of death among adolescents in the USA, and rates are rising. Methods to identify individuals at risk are essential for implementing prevention strategies, and the development of a biomarker can potentially improve prediction of suicidal behaviors. Prediction of our previously reported SKA2 biomarker for suicide and PTSD is substantially improved by questionnaires assessing perceived stress or anxiety and is therefore reliant on psychological assessment. However, such stress-related states may also leave a biosignature that could equally improve suicide prediction. In genome-wide DNA methylation data, we observed significant overlap between waking cortisol-associated and suicide-associated DNA methylation in blood and the brain, respectively. Using a custom bioinformatic brain to blood discovery algorithm, we derived a DNA methylation biosignature that interacts with SKA2 methylation to improve the prediction of suicidal ideation in our existing suicide prediction model across both blood and saliva data sets. This biosignature was independently validated in the Grady Trauma Project cohort and interacted with HPA axis metrics in the same cohort. The biosignature showed a relationship with immune status by its correlation with myeloid-derived cell proportions in all data sets and with IL-6 measures in a prospective postpartum depression cohort. Three probes showed significant correlations with the biosignature: cg08469255 ( DDR1 ), cg22029879 ( ARHGEF10 ), and cg24437859 ( SHP1 ), of which SHP1 methylation correlated with immune measures. We conclude that this biosignature interacts with SKA2 methylation to improve suicide prediction and may represent a biological state of immune and HPA axis modulation that mediates suicidal behavior.

Perception of managerial and administrative competencies of professional pharmacists in the U.S. Department of Defense.

PubMed

Meadows, Andrew B; Finstuen, Kenn; Hudak, Ronald P; Carrillo, Jorge D; Lawrence, Joseph B; Wright, Kevin

2003-01-01

To determine whether executive and junior pharmacists perceive skills, knowledge, and abilities (SKA) items differently. Two-factor split-plot analysis of variance (ANOVA) mixed design with repeated measures. U.S. Department of Defense (DoD). One hundred fifty-one active duty pharmacy officers in DoD, classified as either executive pharmacists (serving in the military grades of lieutenant colonel/commander [0-5] and colonel/captain [0-6], as well as pharmacists selected for promotion to those grades) or junior pharmacists (serving in the military grades of second lieutenant/ensign [0-1], first lieutenant/lieutenant junior grade [0-2], and captain/lieutenant [0-3], as well as pharmacists selected for promotion to those grades). Seven-point relative importance rating scales, with 1 = extremely unimportant to 7 = extremely important, were used to assess respondents' judgments of SKAs. Main effects of group membership (executive versus junior pharmacists), differences among items within eight specific domains, and assessment of potential interaction effects for the dependent variable of SKA item importance ratings. No main effects for overall rating differences between pharmacist groups were found for any of the eight domains; however, statistically significant and systematic within-main-effect differences were detected for SKA items in all domains. Additionally, statistically significant interaction effects emerged in five of the eight domains. The importance ratings given SKAs in the domains of human resources, pharmacy operations and business practices, drug therapy management, and leadership were highly similar between the two groups. However, executive pharmacists tended to place a much greater emphasis on the importance of SKAs within the financial resources and the pharmacy benefit management domains.

Strong Gravitational Lensing as a Probe of Gravity, Dark-Matter and Super-Massive Black Holes

NASA Astrophysics Data System (ADS)

Koopmans, L.V.E.; Barnabe, M.; Bolton, A.; Bradac, M.; Ciotti, L.; Congdon, A.; Czoske, O.; Dye, S.; Dutton, A.; Elliasdottir, A.; Evans, E.; Fassnacht, C.D.; Jackson, N.; Keeton, C.; Lasio, J.; Moustakas, L.; Meneghetti, M.; Myers, S.; Nipoti, C.; Suyu, S.; van de Ven, G.; Vegetti, S.; Wucknitz, O.; Zhao, H.-S.

Whereas considerable effort has been afforded in understanding the properties of galaxies, a full physical picture, connecting their baryonic and dark-matter content, super-massive black holes, and (metric) theories of gravity, is still ill-defined. Strong gravitational lensing furnishes a powerful method to probe gravity in the central regions of galaxies. It can (1) provide a unique detection-channel of dark-matter substructure beyond the local galaxy group, (2) constrain dark-matter physics, complementary to direct-detection experiments, as well as metric theories of gravity, (3) probe central super-massive black holes, and (4) provide crucial insight into galaxy formation processes from the dark matter point of view, independently of the nature and state of dark matter. To seriously address the above questions, a considerable increase in the number of strong gravitational-lens systems is required. In the timeframe 2010-2020, a staged approach with radio (e.g. EVLA, e-MERLIN, LOFAR, SKA phase-I) and optical (e.g. LSST and JDEM) instruments can provide 10^(2-4) new lenses, and up to 10^(4-6) new lens systems from SKA/LSST/JDEM all-sky surveys around ~2020. Follow-up imaging of (radio) lenses is necessary with moderate ground/space-based optical-IR telescopes and with 30-50m telescopes for spectroscopy (e.g. TMT, GMT, ELT). To answer these fundamental questions through strong gravitational lensing, a strong investment in large radio and optical-IR facilities is therefore critical in the coming decade. In particular, only large-scale radio lens surveys (e.g. with SKA) provide the large numbers of high-resolution and high-fidelity images of lenses needed for SMBH and flux-ratio anomaly studies.

Small aperture seismic arrays for studying planetary interiors and seismicity

NASA Astrophysics Data System (ADS)

Schmerr, N. C.; Lekic, V.; Fouch, M. J.; Panning, M. P.; Siegler, M.; Weber, R. C.

2017-12-01

Seismic arrays are a powerful tool for understanding the interior structure and seismicity across objects in the Solar System. Given the operational constraints of ground-based lander investigations, a small aperture seismic array can provide many of the benefits of a larger-scale network, but does not necessitate a global deployment of instrumentation. Here we define a small aperture array as a deployment of multiple seismometers, with a separation between instruments of 1-1000 meters. For example, small aperture seismic arrays have been deployed on the Moon during the Apollo program, the Active Seismic Experiments of Apollo 14 and 16, and the Lunar Seismic Profiling Experiment deployed by the Apollo 17 astronauts. Both were high frequency geophone arrays with spacing of 50 meters that provided information on the layering and velocity structure of the uppermost kilometer of the lunar crust. Ideally such arrays would consist of instruments that are 3-axis short period or broadband seismometers. The instruments must have a sampling rate and frequency range sensitivity capable of distinguishing between waves arriving at each station in the array. Both terrestrial analogs and the data retrieved from the Apollo arrays demonstrate the efficacy of this approach. Future opportunities exist for deployment of seismic arrays on Europa, asteroids, and other objects throughout the Solar System. Here we will present both observational data and 3-D synthetic modeling results that reveal the sensing requirements and the primary advantages of a small aperture seismic array over single station approach. For example, at the smallest apertures of < 1 m, we constrain that sampling rates must exceed 500 Hz and instrument sensitivity must extend to 100 Hz or greater. Such advantages include the improved ability to resolve the location of the sources near the array through detection of backazimuth and differential timing between stations, determination of the small-scale structure (layering, scattering bodies, density and velocity variations) in the vicinity of the array, as well as the ability to improve the signal to noise ratio of distant body waves by additive methods such as stacking and velocity-slowness analysis. These results will inform future missions on the surfaces of objects throughout the Solar System.

Ambient Noise Correlation Amplitudes and Local Site Response

NASA Astrophysics Data System (ADS)

Bowden, D. C.; Tsai, V. C.; Lin, F. C.

2014-12-01

We investigate amplitudes from ambient noise cross correlations in a spatially dense array. Our study of wave propagation effects and ambient noise is focused on the Long Beach Array, with more than 5000 single component geophones in an area of about 100 square kilometers, providing high resolution imaging of shallow crustal features. The method allows for observations of ground properties like site response and attenuation, which can well supplement traditional velocity models and simulations for seismic hazard. Traditional ambient noise cross correlations have proven to be an effective means of measuring velocity information about surface waves, but the amplitudes of such signals in traditional processing are often distorted. We discuss a method of signal processing which preserves relative amplitudes of signals within an array, and the subsequent processing to track wave motion across the array. Previous work showed promising correlation to known local structure, but did not represent a thorough application of tomographic methods. Now we extend the methodology to more robustly consider wavefront focusing and defocusing, interference with higher modes, and discuss the differing effects of local site response, attenuation, and scattering. Application of Helmholtz tomography and determination of local site amplification has previously been demonstrated using earthquake data on the continental scale with USArray, but the exploitation of the ambient noise field is required both for the higher frequencies needed by seismic hazard studies and for the short deployment time of a Long Beach scale array. We outline both the successes and shortcomings of the methodology, and show how it can be extended for use on future arrays.

Status of Foreground and Instrument Challenges for 21cm EoR experiments - Design Strategies for SKA and HERA

NASA Astrophysics Data System (ADS)

Thyagarajan, Nithyanandan

2018-05-01

Direct detection of the Epoch of Reionization (EoR) via redshifted 21 cm line of H i will reveal the nature of the first stars and galaxies as well as revolutionize our understanding of a poorly explored evolutionary phase of the Universe. Projects such as the MWA, LOFAR, and PAPER commenced in the last decade with the promise of high significance statistical detection of the EoR, but have so far only weakly constrained models owing to unforeseen challenges from bright foreground sources and instrument systematics. It is essential for next generation instruments like the HERA and SKA to have these challenges addressed. I present an analysis of these challenges - wide-field measurements, antenna beam chromaticity, reflections in the instrument, and antenna position errors - along with performance specifications and design solutions that will be critical to designing successful next-generation instruments in enabling the first detection and also in placing meaningful constraints on reionization models.

Quartz c-axis fabrics in constrictionally strained orthogneisses: implications for the evolution of the Orlica-Śnieżnik Dome, the Sudetes, Poland

NASA Astrophysics Data System (ADS)

Żelaźniewicz, Andrzej; Kromuszczyńska, Olga; Biegała, Natalia

2013-12-01

Żelaźniewicz, A., Kromuszczyńska, O. and Biegała, N. 2013. Quartz c-axis fabrics in constrictionally strained orthogneisses: implications for the evolution of the Orlica-Śnieżnik Dome, the Sudetes, Poland. Acta Geologica Polonica, 63(4), 697-722, Warszawa. The Orlica-Śnieżnik Dome (OSD), NE Bohemian Massif, contains in its core several gneiss variants with protoliths dated at ~500 Ma. In the western limb of the OSD, rodding augen gneisses (Spalona gneiss unit) are mainly L>S tectonites with a prominent stretching lineation. The few quartz LPO studies have produced somewhat discrepant results. Reexamination of these rocks revealed that texture formation was a protracted, multistage process that involved strain partitioning with changing strain rate and kinematics in a general shear regime at temperatures of the amphibolite facies (450-600°C). Quartz c-axis microfabrics show complex yet reproducible patterns that developed under the joint control of strain geometry and temperature; thus the LPOs are mixed features represented by pseudogirdle patterns. Domainal differences in quartz microfabrics (ribbons, tails, quartzo-feldspathic aggregate) are common in the Spalona orthogneisses but uncommon in the sheared migmatitic gneisses. In the latter rocks, the constrictional strain was imposed on the originally planar fabric defined by high-temperature migmatitic layering. The constrictional fabric of the Spalona gneisses may have developed in the hinge zones of kilometer-scale folds, where the elongation occurred parallel to the fold axes. Other occurrences of rodding gneisses throughout the Orlica-Śnieżnik Dome are thought to occupy similar structural positions, which would point to the significance of large-scale folds in the tectonic structure of the dome.

Seismic Imaging of a Prospective Geothermal Play, Using a Dense Geophone Array

NASA Astrophysics Data System (ADS)

Trow, A.; Pankow, K. L.; Wannamaker, P. E.; Lin, F. C.; Ward, K. M.

2017-12-01

In the summer of 2016 a dense array of 48 Nodal Seismic geophones was deployed near Beaver, Utah on the eastern flank of the Mineral Mountains. The array aperture was approximately 20 kilometers and recorded continuous seismic data for 30 days. Geophones were centered on a previously known shallow (5km depth) magnetolluric (MT) low-resistivity body. This region of low resistivity was interpreted to possibly contain hydrothermal/geothermal fluids and was targeted for further seismic investigation. The seismic array geometry was designed to optimize seismic event detection for small (magnitude of completeness zero) earthquakes and to facilitate seismic imaging at depths of 5 km and deeper. For the duration of the experiment, one ML 1 earthquake was detected underneath the array with 15 other earthquakes detected to the east and south in the more seismically active Pavant Range. Different passive imaging techniques, including ambient noise and earthquake tomography are being explored in order to produce a seismic velocity image. Understanding the subsurface, specifically the fracture network and fluid content of the bedrock is important for characterization of a geothermal prospect. If it is rich in fluids, it can be assumed that some fracture network is in place to accommodate such fluids. Both fractures and fluid content of the prospect will have an effect on the seismic velocities in the basement structure. These properties can help determine the viability of a geothermal system for power production.

On-line Machine Learning and Event Detection in Petascale Data Streams

NASA Astrophysics Data System (ADS)

Thompson, David R.; Wagstaff, K. L.

2012-01-01

Traditional statistical data mining involves off-line analysis in which all data are available and equally accessible. However, petascale datasets have challenged this premise since it is often impossible to store, let alone analyze, the relevant observations. This has led the machine learning community to investigate adaptive processing chains where data mining is a continuous process. Here pattern recognition permits triage and followup decisions at multiple stages of a processing pipeline. Such techniques can also benefit new astronomical instruments such as the Large Synoptic Survey Telescope (LSST) and Square Kilometre Array (SKA) that will generate petascale data volumes. We summarize some machine learning perspectives on real time data mining, with representative cases of astronomical applications and event detection in high volume datastreams. The first is a "supervised classification" approach currently used for transient event detection at the Very Long Baseline Array (VLBA). It injects known signals of interest - faint single-pulse anomalies - and tunes system parameters to recover these events. This permits meaningful event detection for diverse instrument configurations and observing conditions whose noise cannot be well-characterized in advance. Second, "semi-supervised novelty detection" finds novel events based on statistical deviations from previous patterns. It detects outlier signals of interest while considering known examples of false alarm interference. Applied to data from the Parkes pulsar survey, the approach identifies anomalous "peryton" phenomena that do not match previous event models. Finally, we consider online light curve classification that can trigger adaptive followup measurements of candidate events. Classifier performance analyses suggest optimal survey strategies, and permit principled followup decisions from incomplete data. These examples trace a broad range of algorithm possibilities available for online astronomical data mining. This talk describes research performed at the Jet Propulsion Laboratory, California Institute of Technology. Copyright 2012, All Rights Reserved. U.S. Government support acknowledged.

Hydrogen Epoch of Reionization Array (HERA)

NASA Astrophysics Data System (ADS)

DeBoer, David R.; Parsons, Aaron R.; Aguirre, James E.; Alexander, Paul; Ali, Zaki S.; Beardsley, Adam P.; Bernardi, Gianni; Bowman, Judd D.; Bradley, Richard F.; Carilli, Chris L.; Cheng, Carina; de Lera Acedo, Eloy; Dillon, Joshua S.; Ewall-Wice, Aaron; Fadana, Gcobisa; Fagnoni, Nicolas; Fritz, Randall; Furlanetto, Steve R.; Glendenning, Brian; Greig, Bradley; Grobbelaar, Jasper; Hazelton, Bryna J.; Hewitt, Jacqueline N.; Hickish, Jack; Jacobs, Daniel C.; Julius, Austin; Kariseb, MacCalvin; Kohn, Saul A.; Lekalake, Telalo; Liu, Adrian; Loots, Anita; MacMahon, David; Malan, Lourence; Malgas, Cresshim; Maree, Matthys; Martinot, Zachary; Mathison, Nathan; Matsetela, Eunice; Mesinger, Andrei; Morales, Miguel F.; Neben, Abraham R.; Patra, Nipanjana; Pieterse, Samantha; Pober, Jonathan C.; Razavi-Ghods, Nima; Ringuette, Jon; Robnett, James; Rosie, Kathryn; Sell, Raddwine; Smith, Craig; Syce, Angelo; Tegmark, Max; Thyagarajan, Nithyanandan; Williams, Peter K. G.; Zheng, Haoxuan

2017-04-01

The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to measure 21 cm emission from the primordial intergalactic medium (IGM) throughout cosmic reionization (z = 6-12), and to explore earlier epochs of our Cosmic Dawn (z ˜ 30). During these epochs, early stars and black holes heated and ionized the IGM, introducing fluctuations in 21 cm emission. HERA is designed to characterize the evolution of the 21 cm power spectrum to constrain the timing and morphology of reionization, the properties of the first galaxies, the evolution of large-scale structure, and the early sources of heating. The full HERA instrument will be a 350-element interferometer in South Africa consisting of 14 m parabolic dishes observing from 50 to 250 MHz. Currently, 19 dishes have been deployed on site and the next 18 are under construction. HERA has been designated as an SKA Precursor instrument. In this paper, we summarize HERA’s scientific context and provide forecasts for its key science results. After reviewing the current state of the art in foreground mitigation, we use the delay-spectrum technique to motivate high-level performance requirements for the HERA instrument. Next, we present the HERA instrument design, along with the subsystem specifications that ensure that HERA meets its performance requirements. Finally, we summarize the schedule and status of the project. We conclude by suggesting that, given the realities of foreground contamination, current-generation 21 cm instruments are approaching their sensitivity limits. HERA is designed to bring both the sensitivity and the precision to deliver its primary science on the basis of proven foreground filtering techniques, while developing new subtraction techniques to unlock new capabilities. The result will be a major step toward realizing the widely recognized scientific potential of 21 cm cosmology.

Key Science Goals for a Next-generation Very Large Array

NASA Astrophysics Data System (ADS)

Murphy, Eric Joseph; ngVLA Science Advisory Council and all ngVLA Science Working Groups

2018-01-01

Inspired by dramatic discoveries from the Jansky VLA and ALMA, a plan to pursue a large collecting area radio interferometer that will open new discovery space from proto-planetary disks to distant galaxies is being developed by NRAO and the science community. Building on the superb cm observing conditions and existing infrastructure of the VLA site, the current vision of the ngVLA will be an interferometric array with more than 10 times the effective collecting area and spatial resolution of the current VLA and ALMA, that will operating at frequencies spanning ~1.2. – 116 GHz. The ngVLA will be optimized for observations at wavelengths between the exquisite performance of ALMA at submm wavelengths, and the future SKA-1 at decimeter to meter wavelengths, thus lending itself to be highly complementary with these facilities. As such, the ngVLA will open a new window on the universe through ultra-sensitive imaging of thermal line and continuum emission down to milliarcecond resolution, as well as deliver unprecedented broad band continuum polarimetric imaging of non-thermal processes. The ngVLA will be the only facility in the world that can tackle a broad range of outstanding scientific questions in modern astronomy by simultaneously delivering the capability to: unveil the formation of Solar System analogues; probe the initial conditions for planetary systems and life with astrochemistry; characterize the assembly, structure, and evolution of galaxies from the first billion years to the present; use pulsars in the Galactic center as fundamental tests of gravity; and understand the formation and evolution of stellar and supermassive blackholes in the era of multi-messenger astronomy.

High-Tech 'Heart' of New-Generation Radio Telescope Passes First Test

NASA Astrophysics Data System (ADS)

2008-08-01

The Expanded Very Large Array (EVLA), part of the National Radio Astronomy Observatory (NRAO), took a giant step toward completion on August 7 with successful testing of advanced digital hardware designed to combine signals from its upgraded radio-telescope antennas to produce high resolution images of celestial objects. Successful Moment NRAO Crew Views Successful Computer Display Of WIDAR "First Fringes" Seated, front to back: Barry Clark, Ken Sowinski, Michael Rupen, Kevin Ryan. Standing, front to rear: Mark McKinnon, Rick Perley, Hichem Ben Frej. CREDIT: Dave Finley, NRAO/AUI/NSF Click on image for larger file. By upgrading the 1970s-era electronics of its original Very Large Array (VLA), NRAO is creating a major new radio telescope that is ten times more sensitive than before. Using the EVLA, astronomers will observe fainter and more-distant objects than previously possible and use vastly improved analysis tools to decipher their physics. The heart of the new electronics that makes this transformation possible is a high-performance, special-purpose supercomputer, called the WIDAR Correlator. It has been designed and is being built by the National Research Council of Canada at the Dominion Radio Astrophysical Observatory (DRAO) of the Herzberg Institute for Astrophysics, and serves as Canada's contribution to the EVLA project. The design of the correlator incorporates an NRC-patented new digital electronic architecture. The successful test, at the VLA site 50 miles west of Socorro, New Mexico, used prototype correlator electronics to combine the signals from two upgraded VLA antennas to turn them into a single, high-resolution telescope system, called an interferometer. The technical term for this achievement is called "first fringes." Each upgraded EVLA antenna produces 100 times more data than an original VLA antenna. When all 27 antennas are upgraded, they will pump data into the WIDAR correlator at a rate equal to 48 million digital telephone calls. To process this torrent of data, the correlator will make 10 million billion calculations per second. Powerful, multi-antenna imaging radio-telescope systems use pairs of antennas as their basic building blocks. Each of the VLA's 27 giant dish antennas is combined electronically with every other antenna to form a multitude of pairs. Each pair contributes unique information that is used to build a highly-detailed image of some astronomical object. The successful two-antenna test thus verifies the design of the new correlator. "This achievement marks the first time that the complete chain of electronics for the EVLA has worked together, and represents a huge milestone in the project. Our congratulations go to our Canadian colleagues and to the NRAO staff members participating in this project. This is a job well done," said Fred Lo, Director of the National Radio Astronomy Observatory. The VLA Expansion, a ten-year project approved in 2001, is funded by 55 million from the United States National Science Foundation (NSF) and 1.75 million from the Mexican government. The Canadian correlator represents a contribution of about $17 million to the project. Throughout the project, the VLA has continued to operate, using a mix of the old and new-style antennas to provide an ongoing research tool. Over its lifetime, the VLA has been the most scientifically-productive ground-based telescope in the history of astronomy. When completed in 2012, the EVLA will be the most powerful centimeter-wavelength radio telescope in the world. The technology developed for the EVLA will enable progress on the next generation radio telescope called the Square Kilometer Array (SKA). The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc. Plots of amplitude (top) and phase (bottom) from WIDAR correlator "first fringes" on August 7, 2008.

Central electrical utility power for a satellite ring city in low earth orbit space

NASA Technical Reports Server (NTRS)

Myers, Ira T.; Faymon, Karl A.; Patton, A. D.

1989-01-01

Information is given in viewgraph form on central electrical power for a satellite ring city, defined as a group of large free flyers of 10 to 20 units with perhaps 100 people in each unit, and organized in a circle so that power can be fed from a central location. The free flyers would be located at 300 to 700 miles in altitude, and spaced about a kilometer apart. Potential activities of a ring city are listed as well as the electrical power needs. Information is given on costs and individual and centralized solar arrays and nuclear reactor systems.

Magnetic shielding of large high-power-satellite solar arrays using internal currents

NASA Technical Reports Server (NTRS)

Parker, L. W.; Oran, W. A.

1979-01-01

Present concepts for solar power satellites involve dimensions up to tens of kilometers and operating internal currents up to hundreds of kiloamperes. A question addressed is whether the local magnetic fields generated by these strong currents during normal operation can shield the array against impacts by plasma ions and electrons (and from thruster plasmas) which can cause possible losses such as power leakage and surface erosion. One of several prototype concepts was modeled by a long narrow rectangular panel 2 km wide and 20 km long. The currents flow in a parallel across the narrow dimension (sheet current) and along the edge (wire currents). The wire currents accumulate from zero to 100 kiloamp and are the dominant sources. The magnetic field is approximated analytically. The equations of motion for charged particles in this magnetic field are analyzed. The ion and electron fluxes at points on the surface are represented analytically for monoenergetic distributions and are evaluated.

Long-range acoustic observations of the Eyjafjallajökull eruption, Iceland, April-May 2010

NASA Astrophysics Data System (ADS)

Matoza, Robin S.; Vergoz, Julien; Le Pichon, Alexis; Ceranna, Lars; Green, David N.; Evers, Läslo G.; Ripepe, Maurizio; Campus, Paola; Liszka, Ludwik; Kvaerna, Tormod; Kjartansson, Einar; Höskuldsson, Ármann

2011-03-01

The April-May 2010 summit eruption of Eyjafjallajökull, Iceland, was recorded by 14 atmospheric infrasound sensor arrays at ranges between 1,700 and 3,700 km, indicating that infrasound from modest-size eruptions can propagate for thousands of kilometers in atmospheric waveguides. Although variations in both atmospheric propagation conditions and background noise levels at the sensors generate fluctuations in signal-to-noise ratios and signal detectability, array processing techniques successfully discriminate between volcanic infrasound and ambient coherent and incoherent noise. The current global infrasound network is significantly more dense and sensitive than any previously operated network and signals from large volcanic explosions are routinely recorded. Because volcanic infrasound is generated during the explosive release of fluid into the atmosphere, it is a strong indicator that an eruption has occurred. Therefore, long-range infrasonic monitoring may aid volcanic explosion detection by complementing other monitoring technologies, especially in remote regions with sparse ground-based instrument networks.

Correlated Lightning Mapping Array (LMA) and Radar Observations of the Initial Stages of Florida Triggered Lightning Discharges

NASA Technical Reports Server (NTRS)

Hill, J. D.; Pilkey, J.; Uman, M, A.; Jordan, D. M.; Biggerstaff, M. I.; Rison, W.; Blakeslee, R.

2012-01-01

We characterize the geometrical and electrical characteristics of the initial stages of nine Florida triggered lightning discharges using a Lightning Mapping Array (LMA), a C-band SMART radar, and measured channel-base currents. We determine initial channel and subsequent branch lengths, average initial channel and branch propagation speeds, and channel-base current at the time of each branch initiation. The channel-base current is found to not change significantly when branching occurs, an unexpected result. The initial stage of Florida triggered lightning typically transitions from vertical to horizontal propagation at altitudes of 3-6 km, near the typical 0 C level of 4-5 km and several kilometers below the expected center of the negative cloud-charge region at 7-8 km. The data presented potentially provide information on thunderstorm electrical and hydrometeor structure and discharge propagation physics. LMA source locations were obtained from VHF sources of positive impulsive currents as small as 10 A, in contrast to expectations found in the literature.

Performance and Results from a Space Borne, Uncooled Microbolometer Array Spectral Radiometric Imager

NASA Technical Reports Server (NTRS)

Spinhirne, James M; Scott, V. Stan; Lancaster, Redgie S.; Manizade, Kathrine; Palm, Steven P.

2000-01-01

The Infrared Spectral Imaging Radiometer experiment was flown on a space shuttle mission as a shuttle hitchhiker experiment in August of 1997. The goals of the experiment were to test uncooled array detectors for infrared spectral imaging from space and to apply for the first time retrieval from space of brightness temperatures of cloud, land and sea along with direct laser measurements of cloud top height. The instrument operates in 3 narrow and one broad spectral band, all between 7 and 13 microns in either stare or time-delay and integration mode. The nominal spatial resolution was 1/4 kilometer. Using onboard calibrations along with periodic views of deep space, radiometric calibration of imagery was carried out and performance analyzed. The noise equivalent temperature difference and absolute accuracy reported here varied with operating mode, spectral band and scene temperature but were within requirements. This paper provides a description of the instrument, its operating modes, the method of brightness temperature retrieval, the method of spectral registration and results from the flight.

Acoustic Eaton lens array and its fluid application

NASA Astrophysics Data System (ADS)

Kim, Sang-Hoon; Sy, Pham-Van; Das, Mukunda P.

2017-03-01

A principle of an acoustic Eaton lens array and its application as a removable tsunami wall is proposed theoretically. The lenses are made of expandable rubber pillars or balloons and create a stop-band by rotating the incoming tsunami wave and reduce the pressure by canceling each other. The diameter of each lens is larger than the wavelength of the tsunami near the coast, that is, order of a kilometer. The impedance matching on the border of the lenses results in a little reflection. Before a tsunami, the balloons are buried underground in shallow water near the coast in folded or rounded form. Upon sounding of the tsunami alarm, water and air are pumped into the pillars, which expand and erect the wall above the sea level within a few hours. After the tsunami, the water and air are released from the pillars, which are then buried underground for reuse. Electricity is used to power the entire process. A numerical simulation with a linear tsunami model was carried out.

Mining the Sky for Explosive Optical Transients with Both Eyes Open

NASA Astrophysics Data System (ADS)

Vestrand, W. T.; Borozdin, K.; Casperson, D. J.; Davidoff, S.; Davis, H.; Fenimore, E.; Galassi, M.; McGowan, K.; Starr, D.; White, R. R.; Wozniak, P.; Wren, J.

2004-09-01

While it has been known for centuries that the optical sky is variable, monitoring the sky for optical transients with durations as short as a minute is an area of astronomical research that remains largely unexplored. Prompt follow-up observations of Gamma Ray Bursts have shown that bright, explosive, optical transients exist. However, there are many reasons to suspect the existence of explosive optical transients that cannot be located through sky monitoring by high-energy satellites. The RAPTOR sky monitoring system is an autonomous system of telescope arrays at Los Alamos National Laboratory that identifies fast optical transients as short as a minute and makes follow-up observations in real time. The core of the RAPTOR system is composed of two arrays of telescopes, separated by 38 kilometers, that stereoscopically monitor a field of about 1300 square degrees for transients down to about 12.5th magnitude in 30 seconds. Both arrays are coupled to real-time data analysis pipelines that are designed to identify transients on timescales of seconds. Each telescope array also contains a more sensitive higher resolution ``fovea'' telescope, capable of both measuring the light curve at a faster cadence and providing color information. In a manner analogous to human vision, each array is mounted on a rapidly slewing mount so that the ``fovea'' of the array can be rapidly directed for real-time follow-up observations of any interesting transient identified by the wide-field system. We discuss the first results from RAPTOR and show that stereoscopic imaging and the absence of measurable parallax is a powerful tool for distinguishing real celestial transients in the ``forest'' of false positives.

Mining the Sky for Explosive Optical Transients with Both Eyes Open

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vestrand, W.T.; Casperson, D.J.; Davis, H.

2004-09-28

While it has been known for centuries that the optical sky is variable, monitoring the sky for optical transients with durations as short as a minute is an area of astronomical research that remains largely unexplored. Prompt follow-up observations of Gamma Ray Bursts have shown that bright, explosive, optical transients exist. However, there are many reasons to suspect the existence of explosive optical transients that cannot be located through sky monitoring by high-energy satellites. The RAPTOR sky monitoring system is an autonomous system of telescope arrays at Los Alamos National Laboratory that identifies fast optical transients as short as amore » minute and makes follow-up observations in real time. The core of the RAPTOR system is composed of two arrays of telescopes, separated by 38 kilometers, that stereoscopically monitor a field of about 1300 square degrees for transients down to about 12.5th magnitude in 30 seconds. Both arrays are coupled to real-time data analysis pipelines that are designed to identify transients on timescales of seconds. Each telescope array also contains a more sensitive higher resolution 'fovea' telescope, capable of both measuring the light curve at a faster cadence and providing color information. In a manner analogous to human vision, each array is mounted on a rapidly slewing mount so that the 'fovea' of the array can be rapidly directed for real-time follow-up observations of any interesting transient identified by the wide-field system. We discuss the first results from RAPTOR and show that stereoscopic imaging and the absence of measurable parallax is a powerful tool for distinguishing real celestial transients in the 'forest' of false positives.« less

Distributed Acoustic Sensing (DAS) Array near a Highway for Traffic Monitoring and Near-Surface Shear-Wave Velocity Profiles

NASA Astrophysics Data System (ADS)

Wang, H. F.; Fratta, D.; Lancelle, C.; Ak, E. Ms; Lord, N. E.

2017-12-01

Monitoring traffic is important for many technical reasons. It allows for better design of future roads and assessment of the state of current roads. The number, size, weight, and speed of vehicles control deterioration rate. Also, real-time information supplies data to intelligent information systems to help control traffic. Recently there have been studies looking at monitoring traffic seismically as vibrations from traffic are not sensitive to weather and poor visibility. Furthermore, traffic noise can be used to image S-wave velocity distribution in the near surface by capturing and interpreting Rayleigh and Love waves (Nakata, 2016; Zeng et al. 2016). The capability of DAS for high spatial sampling (1 m), temporal sampling (up to 10 kHz), and distributed nature (tens of kilometers) allows for a closer look at the traffic as it passes and how the speed of the vehicle may change over the length of the array. The potential and difficulties of using DAS for these objectives were studied using two DAS arrays. One at Garner Valley in Southern California (a 700-meter array adjacent to CA Highway 74) and another in Brady Hot Springs, Nevada (an 8700-meter array adjacent to Interstate 80). These studies experimentally evaluated the use of DAS data for monitoring traffic and assessing the use of traffic vibration as non-localized sources for seismic imaging. DAS arrays should also be resilient to issues with lighting conditions that are problematic for video monitoring and it may be sensitive to the weight of a vehicle. This study along a major interstate provides a basis for examining DAS' potential and limitations as a key component of intelligent highway systems.

Survey parameters for detecting 21cm - Lyα emitter cross correlations with the Square Kilometre Array

NASA Astrophysics Data System (ADS)

Hutter, Anne; Trott, Cathryn M.; Dayal, Pratika

2018-06-01

Detections of the cross correlation signal between the 21cm signal during reionization and high-redshift Lyman Alpha emitters (LAEs) are subject to observational uncertainties which mainly include systematics associated with radio interferometers and LAE selection. These uncertainties can be reduced by increasing the survey volume and/or the survey luminosity limit, i.e. the faintest detectable Lyman Alpha (Lyα) luminosity. We use our model of high-redshift LAEs and the underlying reionization state to compute the uncertainties of the 21cm-LAE cross correlation function at z ≃ 6.6 for observations with SKA1-Low and LAE surveys with Δz = 0.1 for three different values of the average IGM ionization state (⟨χHI⟩≃ 0.1, 0.25, 0.5). At z ≃ 6.6, we find SILVERRUSH type surveys, with a field of view of 21 deg2 and survey luminosity limits of Lα ≥ 7.9 × 1042erg s-1, to be optimal to distinguish between an inter-galactic medium (IGM) that is 50%, 25% and 10% neutral, while surveys with smaller fields of view and lower survey luminosity limits, such as the 5 and 10 deg2 surveys with WFIRST, can only discriminate between a 50% and 10% neutral IGM.

Modeling and system design for the LOFAR station digital processing

NASA Astrophysics Data System (ADS)

Alliot, Sylvain; van Veelen, Martijn

2004-09-01

In the context of the LOFAR preliminary design phase and in particular for the specification of the Station Digital Processing (SDP), a performance/cost model of the system was used. We present here the framework and the trajectory followed in this phase when going from requirements to specification. In the phased array antenna concepts for the next generation of radio telescopes (LOFAR, ATA, SKA) signal processing (multi-beaming and RFI mitigation) replaces the large antenna dishes. The embedded systems for these telescopes are major infrastructure cost items. Moreover, the flexibility and overall performance of the instrument depend greatly on them, therefore alternative solutions need to be investigated. In particular, the technology and the various data transport selections play a fundamental role in the optimization of the architecture. We proposed a formal method [1] of exploring these alternatives that has been followed during the SDP developments. Different scenarios were compared for the specification of the application (selection of the algorithms as well as detailed signal processing techniques) and in the specification of the system architecture (selection of high level topologies, platforms and components). It gave us inside knowledge on the possible trade-offs in the application and architecture domains. This was successful in providing firm basis for the design choices that are demanded by technical review committees.

Music Preferences and Civic Activism of Young People

ERIC Educational Resources Information Center

Leung, Ambrose; Kier, Cheryl

2008-01-01

This study examines the relationship between music preferences and civic activism among 182 participants aged 14-24 years. Our analyses show that participants who regularly listened to certain music genres such as classical, opera, musicals, new age, easy listening, house, world music, heavy metal, punk, and ska were significantly more likely to…

The Ndc80 internal loop is required for recruitment of the Ska complex to establish end-on microtubule attachment to kinetochores.

PubMed

Zhang, Gang; Kelstrup, Christian D; Hu, Xiao-Wen; Kaas Hansen, Mathilde J; Singleton, Martin R; Olsen, Jesper V; Nilsson, Jakob

2012-07-01

The Ndc80 complex establishes end-on attachment of kinetochores to microtubules, which is essential for chromosome segregation. The Ndc80 subunit is characterized by an N-terminal region that binds directly to microtubules, and a long coiled-coil region that interacts with Nuf2. A loop region in Ndc80 that generates a kink in the structure disrupts the long coiled-coil region but the exact function of this loop, has until now, not been clear. Here we show that this loop region is essential for end-on attachment of kinetochores to microtubules in human cells. Cells expressing loop mutants of Ndc80 are unable to align the chromosomes, and stable kinetochore fibers are absent. Through quantitative mass spectrometry and immunofluorescence we found that the binding of the spindle and kinetochore associated (Ska) complex depends on the loop region, explaining why end-on attachment is defective. This underscores the importance of the Ndc80 loop region in coordinating chromosome segregation through the recruitment of specific proteins to the kinetochore.

Lensing convergence in galaxy clustering in ΛCDM and beyond

NASA Astrophysics Data System (ADS)

Villa, Eleonora; Di Dio, Enea; Lepori, Francesca

2018-04-01

We study the impact of neglecting lensing magnification in galaxy clustering analyses for future galaxy surveys, considering the ΛCDM model and two extensions: massive neutrinos and modifications of General Relativity. Our study focuses on the biases on the constraints and on the estimation of the cosmological parameters. We perform a comprehensive investigation of these two effects for the upcoming photometric and spectroscopic galaxy surveys Euclid and SKA for different redshift binning configurations. We also provide a fitting formula for the magnification bias of SKA. Our results show that the information present in the lensing contribution does improve the constraints on the modified gravity parameters whereas the lensing constraining power is negligible for the ΛCDM parameters. For photometric surveys the estimation is biased for all the parameters if lensing is not taken into account. This effect is particularly significant for the modified gravity parameters. Conversely for spectroscopic surveys the bias is below one sigma for all the parameters. Our findings show the importance of including lensing in galaxy clustering analyses for testing General Relativity and to constrain the parameters which describe its modifications.

Olminska and colleagues' study, "Conversion of the helical tomotherapy plans to the step-and-shoot IMRT plans for patients with hip prosthesis during radiotherapy for prostate cancer" was interesting to read.

PubMed

Cihan, Yasemin Benderli

2016-11-01

Olmińska and colleagues' study, Olmińska et al. (2016) was interesting to read [1]. While prasining the authors for their great work, I want to emphasize e few points. In the recent years, with the development of new device technology, Intensity Modulated Radiotherapy (IMRT) and complex treatment modalities such as stereotactic radiosurgery and helical tomotherapy were started to be implemented. Thus, due to increased local control of tumor growth and reduction of dose received by surrounding critical organs, serious complications were avoided. In this new treatment modality, while calculating appropriate dose, all the parameters such as patient anatomy and characteristics of radiation should be taken into account. Besides, during conformal radiotherapy, if hip prosthesis is located around or in the clinical target volume (CTV), type, thickness and density of biomaterial should be considered to avoid dose differences. Copyright © 2016 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.

Jansky Very Large Array: technology advancing science

NASA Astrophysics Data System (ADS)

Carilli, Christopher

2015-08-01

Over the last decade, the NRAO has completed on time, and on budget, a major reconstruction of the Very Large Array. Building on existing infrastructure to maximize efficiency, the entire VLA electronics system, including correlator, receivers, data transmission, and monitor and control, have been replaced with state of the art systems. This complete rebuild establishes the new Jansky VLA, operating between 75MHz and 50GHz, as the most powerful radio telescope in the world for the coming decade.I will review the technical improvements of the array, including:- Correlator: Increased bandwidth from 100MHz to 8GHz, with thousands of spectral channels.- Receivers: replaced the previous narrow bands with receivers covering the full frequency range from 1 GHz to 50GHz. New systems are also being tested to cover from 50MHz to 400MHz.- Data transmission: 8GHz over optical fiber out to 30km.I will then highlight some of the science enabled by these improvements, including:- Large cosmic volume searches for atomic and molecular gas, from the nearby Universe to the most distant galaxies, plus kpc-scale imaging of the cool gas in distant starburst galaxies.- High resolution studies of star and planet formation.- Innovative interferometric searches for transient phenomena.- The first radio continuum deep fields with sensitivities < 1uJy, with full polarization for Faraday tomography.- Imaging radio-mode feedback in galaxies and clusters, and delineating the complex plasma physical processes involved on scales from a few kpc to hundreds of kpc.I will conclude with a few words about the major challenges facing such a new instrument. These challenges are all on the critical path toward any successful development of future facilities, such as the next generation VLA and SKA:- Big data: data volumes and post-processing are currently major bottlenecks in the turn-over from observation to science publication. NRAO is developing calibration and imaging pipelines to provide science ready data products to the community.- Algorithmic development for ultra-deep, wide band, wide field polarimetric imaging.- Exploring the time domain with interferometers.

Radioastronomic signal processing cores for the SKA radio telescope

NASA Astrophysics Data System (ADS)

Comorett, G.; Chiarucc, S.; Belli, C.

Modern radio telescopes require the processing of wideband signals, with sample rates from tens of MHz to tens of GHz, and are composed from hundreds up to a million of individual antennas. Digital signal processing of these signals include digital receivers (the digital equivalent of the heterodyne receiver), beamformers, channelizers, spectrometers. FPGAs present the advantage of providing a relatively low power consumption, relative to GPUs or dedicated computers, a wide signal data path, and high interconnectivity. Efficient algorithms have been developed for these applications. Here we will review some of the signal processing cores developed for the SKA telescope. The LFAA beamformer/channelizer architecture is based on an oversampling channelizer, where the channelizer output sampling rate and channel spacing can be set independently. This is useful where an overlap between adjacent channels is required to provide an uniform spectral coverage. The architecture allows for an efficient and distributed channelization scheme, with a final resolution corresponding to a million of spectral channels, minimum leakage and high out-of-band rejection. An optimized filter design procedure is used to provide an equiripple response with a very large number of spectral channels. A wideband digital receiver has been designed in order to select the processed bandwidth of the SKA Mid receiver. The receiver extracts a 2.5 MHz bandwidth form a 14 GHz input bandwidth. The design allows for non-integer ratios between the input and output sampling rates, with a resource usage comparable to that of a conventional decimating digital receiver. Finally, some considerations on quantization of radioastronomic signals are presented. Due to the stochastic nature of the signal, quantization using few data bits is possible. Good accuracies and dynamic range are possible even with 2-3 bits, but the nonlinearity in the correlation process must be corrected in post-processing. With at least 6 bits it is possible to have a very linear response of the instrument, with nonlinear terms below 80 dB, providing the signal amplitude is kept within bounds.

A Method to have Multi-Layer Thermal Insulation Provide Damage Detection

NASA Technical Reports Server (NTRS)

Woodward, Stanley E.; Taylor, Bryant D.; Jones, Thomas W.; Shams, Qamar A.; Lyons, Frankel; Henderson, Donald

2007-01-01

Design and testing of a multi-layer thermal insulation system that also provides debris and micrometeorite damage detection is presented. One layer of the insulation is designed as an array of passive open-circuit electrically conductive spiral trace sensors. The sensors are a new class of sensors that are electrically open-circuits that have no electrical connections thereby eliminating one cause of failure to circuits. The sensors are powered using external oscillating magnetic fields. Once electrically active, they produce their own harmonic magnetic fields. The responding field frequency changes if any sensor is damaged. When the sensors are used together in close proximity, the inductive coupling between sensors provides a means of telemetry. The spiral trace design using reflective electrically conductive material provides sufficient area coverage for the sensor array to serves as a layer of thermal insulation. The other insulation layers are designed to allow the sensor s magnetic field to permeate the insulation layers while having total reflective surface area to reduce thermal energy transfer. Results of characterizing individual sensors and the sensor array s response to punctures are presented. Results of hypervelocity impact testing using projectiles of 1-3.6 millimeter diameter having speeds ranging from 6.7-7.1 kilometers per second are also presented.

Distributed sensing of ionospheric irregularities with a GNSS receiver array

NASA Astrophysics Data System (ADS)

Su, Yang; Datta-Barua, Seebany; Bust, Gary S.; Deshpande, Kshitija B.

2017-08-01

We present analysis methods for studying the structuring and motion of ionospheric irregularities at the subkilometer scale sizes that produce L band scintillations. Spaced-receiver methods are used for Global Navigation Satellite System (GNSS) receivers' phase measurements over approximately subkilometer to kilometer length baselines for the first time. The quantities estimated by these techniques are plasma drift velocity, diffraction anisotropy magnitude and orientation, and characteristic velocity. Uncertainties are quantified by ensemble simulation of noise on the phase signals carried through to the observations of the spaced-receiver linear system. These covariances are then propagated through to uncertainties on drifts through linearization about the estimated values of the state. Five receivers of SAGA, the Scintillation Auroral Global Positioning System (GPS) Array, provide 100 Hz power and phase data for each channel at L1 frequency. The array is sited in the auroral zone at Poker Flat Research Range, Alaska. A case study of a single scintillating satellite observed by the array is used to demonstrate the spaced-receiver and uncertainty estimation process. A second case study estimates drifts as measured by multiple scintillating channels. These scintillations are correlated with auroral activity, based on all-sky camera images. Measurements and uncertainty estimates made over a 30 min period are compared to a collocated incoherent scatter radar and show good agreement in horizontal drift speed and direction during periods of scintillation for which the characteristic velocity is less than the drift velocity.

Capturing Callisto

NASA Technical Reports Server (NTRS)

2007-01-01

The New Horizons Long Range Reconnaissance Imager (LORRI) captured these two images of Jupiter's outermost large moon, Callisto, as the spacecraft flew past Jupiter in late February. New Horizons' closest approach distance to Jupiter was 2.3 million kilometers (1.4 million miles), not far outside Callisto's orbit, which has a radius of 1.9 million kilometers (1.2 million miles). However, Callisto happened to be on the opposite side of Jupiter during the spacecraft's pass through the Jupiter system, so these images, taken from 4.7 million kilometers (3.0 million miles) and 4.2 million kilometers (2.6 million miles) away, are the closest of Callisto that New Horizons obtained.

Callisto's ancient, crater-scarred surface makes it very different from its three more active sibling satellites, Io, Europa and Ganymede. Callisto, 4,800 kilometers (3000 miles) in diameter, displays no large-scale geological features other than impact craters, and every bright spot in these images is a crater. The largest impact feature on Callisto, the huge basin Valhalla, is visible as a bright patch at the 10 o'clock position. The craters are bright because they have excavated material relatively rich in water ice from beneath the dark, dusty material that coats most of the surface.

The two images show essentially the same side of Callisto -- the side that faces Jupiter -- under different illumination conditions. The images accompanied scans of Callisto's infrared spectrum with New Horizons' Linear Etalon Imaging Spectral Array (LEISA). The New Horizons science team designed these scans to study how the infrared spectrum of Callisto's water ice changes as lighting and viewing conditions change, and as the ice cools through Callisto's late afternoon. The infrared spectrum of water ice depends slightly on its temperature, and a goal of New Horizons when it reaches the Pluto system (in 2015) is to use the water ice features in the spectrum of Pluto's moon Charon, and perhaps on Pluto itself, to measure surface temperature. Callisto provided an ideal opportunity to test this technique on a much better-known body.

The left image, taken at 05:03 Universal Time on February 27, 2007, is centered at 5 degrees south, 5 degrees west, and has a solar phase angle of 46 degrees. The right image was taken at 03:25 Universal Time on February 28, 2007. It is centered at 4 degrees south, 356 degrees west, and has a solar phase angle of 76 degrees.

Detection of a ULVZ at the base of the mantle beneath the northwest Pacific

NASA Astrophysics Data System (ADS)

Xu, Yan; Koper, Keith D.

2009-09-01

We used the Yellowknife seismic array (YKA) to measure the slowness of 1,371 P and P diff waves from earthquakes occurring in the circum-Pacific region. The corresponding anomalies in P-velocity show a sharp reduction of up to 6% across a patch of the lowermost mantle beneath the Northwest Pacific with lateral dimensions of several hundred kilometers. The location of this ultra low velocity zone (ULVZ) correlates with a long-wavelength compositional boundary revealed by probabilistic mantle tomography. We interpret the ULVZ as partial melt created by paleo-slab material that is being swept laterally from northwestern Pacific subduction zones towards the large, chemically distinct province beneath the south-central Pacific.

The UV Survey Mission Concept, CETUS

NASA Astrophysics Data System (ADS)

Heap, Sara; and the CETUS Team

2018-01-01

In March 2017, NASA selected CETUS for study of a Probe-class mission concept. W. Danchi is the CETUS PI, and S. Heap is the Science PI. CETUS is primarily a UV survey telescope to complement survey telescopes of the 2020’s including E-ROSITA, Subaru Hyper Suprime Cam and Prime-Focus Spectrograph, WFIRST, and the Square Kilometer Array. CETUS comprises a 1.5-m wide-field telescope and three science instruments: a wide-field (1045” on a side) far-UV and near-UV camera; a similarly wide-field near-UV multi-object spectrograph utilizing a next-generation micro-shutter array; and a single-object spectrograph with options of spectral region (far-UV or near-UV) and spectral resolving power (2,000 or 40,000). The survey instruments will operate simultaneously thereby producing wide-field images in the near-UV and far-UV and a spectrogram containing near-UV spectra of up to 100 sources free of spectral overlap and astronomical background. ln concert with other survey telescopes, CETUS will focus on understanding galaxy evolution at cosmic noon (z~1-2).

Route-Specific Passage and Survival of Steelhead Kelts at The Dalles and Bonneville Dams, 2012 - Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rayamajhi, Bishes; Ploskey, Gene R.; Woodley, Christa M.

2013-07-31

This study was mainly focused on evaluating the route-specific passage and migration success of steelhead kelts passing downstream through The Dalles Dam (TDA) and Bonneville Dam (BON) at Columbia River (CR) river kilometers 309 and 234 respectively. Oregon Department of Fish and Wildlife (ODFW) personnel collected, tagged and released out-migrating steelhead kelts in the tributaries of the Deschutes River, 15 Mile Creek and Hood River between April 14 and June 4, 2012. A PIT tag was injected into each kelt’s dorsal sinus whereas a Juvenile Salmon Acoustic Telemetry System (JSATS) acoustic micro-transmitter was attached to an external FLoy T-bar tagmore » and inserted into the dorsal back musculature using a Floy tagging gun. JSATS cabled arrays were deployed at TDA and BON and autonomous node arrays were deployed near Celilo, Oregon (CR325); the BON forebay (CR236); the BON tailrace (CR233); near Knapp, Washington (CR156); and near Kalama, Washington (CR113) to monitor the kelts movement while passing through the dams and above mentioned river cross-sections.« less

Water Masers and Accretion Disks in Galactic Nuclei

NASA Astrophysics Data System (ADS)

Greenhill, L. J.

2005-12-01

There are over 50 sources of H2O maser emission in type-2 active galactic nuclei, a large fraction discovered in the last two years. Interferometer maps of water masers are presently the only means by which structures ⪉ 1 pc from massive black holes can be mapped directly, which is particularly important for type-2 systems because edge-on orientation and obscuration complicate study by other means. Investigations of several sources have demonstrated convincingly that the maser emission traces warped accretion disks 0.1 to 1 pc from central engines of order 106-108 M⊙. The same may be true for almost half the known (but unmapped) sources, based on spectral characteristics consistent with emission from edge-on accretion disks. Mapping these sources is a high priority. Study of most recently discovered masers requires long baseline arrays that include 100-m class apertures and would benefit from aggregate bit rates on the order of 1 gigabit per second. The Square Kilometer Array should provide an order of magnitude boost in mapping sensitivity, but outrigger antennas will be needed to achieve necesssary angular resolutions, as may be space-borne antennas.

Beaming Structures of Jupiter's Decametric Radiation from LWA1, NDA, and URAN2 Simultaneous Observations

NASA Astrophysics Data System (ADS)

Imai, M.; Lecacheux, A.; Higgins, C. A.; Clarke, T.; Panchenko, M.; Brazhenko, A. I.; Frantsuzenko, A. V.; Konovalenko, A. A.; Imai, K.

2015-12-01

From December 2014 to March 2015, Jupiter's decametric (DAM) radio observations were carried out by using simultaneously three powerful low-frequency radio telescopes: Long Wavelength Array One (LWA1), Socorro, USA; Nançay Decameter Array (NDA), Nançay, France; and URAN2 telescope, Poltava, Ukraine. Baselines are 10000, 8600, and 2400 kilometers for LWA1-URAN2, NDA-LWA1, and URAN2-NDA, respectively. One Io-B and two Io-A emissions were simultaneously observed. Using cross-correlation analysis of obtained spectrograms, it was found that, as a function of lag time in a pair of two stations, Io-B (mainly S-bursts) and Io-A (L-bursts) show different kinds of cross-correlation coefficients, with sharp and broad peaks, respectively. By measuring lag times between LWA1-URAN2, NDA-LWA1, and URAN2-NDA pairs, it can be tested if either flashlight- or beacon-like beaming is emanated from Jupiter. Measurements of beaming width are also analyzed. Most probable beaming scenarios for Io-B and -A events are suggested.

Air temperature, wind speed, and wind direction in the National Petroleum Reserve—Alaska and the Arctic National Wildlife Refuge, 1998–2011

USGS Publications Warehouse

Urban, Frank E.; Clow, Gary D.

2013-01-01

This report provides air temperature, wind speed, and wind direction data collected on Federal lands in Arctic Alaska over the period August 1998 to July 2011 by the U.S. Department of the Interior's climate monitoring array, part of the Global Terrestrial Network for Permafrost. In addition to presenting data, this report also describes monitoring, data collection, and quality control methodology. This array of 16 monitoring stations spans 68.5°N to 70.5°N and 142.5°W to 161°W, an area of roughly 150,000 square kilometers. Climate summaries are presented along with provisional quality-controlled data. Data collection is ongoing and includes several additional climate variables to be released in subsequent reports, including ground temperature and soil moisture, snow depth, rainfall, up- and downwelling shortwave radiation, and atmospheric pressure. These data were collected by the U.S. Geological Survey in close collaboration with the Bureau of Land Management and the U.S. Fish and Wildlife Service.

Status report of the end-to-end ASKAP software system: towards early science operations

NASA Astrophysics Data System (ADS)

Guzman, Juan Carlos; Chapman, Jessica; Marquarding, Malte; Whiting, Matthew

2016-08-01

The Australian SKA Pathfinder (ASKAP) is a novel centimetre radio synthesis telescope currently in the commissioning phase and located in the midwest region of Western Australia. It comprises of 36 x 12 m diameter reflector antennas each equipped with state-of-the-art and award winning Phased Array Feeds (PAF) technology. The PAFs provide a wide, 30 square degree field-of-view by forming up to 36 separate dual-polarisation beams at once. This results in a high data rate: 70 TB of correlated visibilities in an 8-hour observation, requiring custom-written, high-performance software running in dedicated High Performance Computing (HPC) facilities. The first six antennas equipped with first-generation PAF technology (Mark I), named the Boolardy Engineering Test Array (BETA) have been in use since 2014 as a platform to test PAF calibration and imaging techniques, and along the way it has been producing some great science results. Commissioning of the ASKAP Array Release 1, that is the first six antennas with second-generation PAFs (Mark II) is currently under way. An integral part of the instrument is the Central Processor platform hosted at the Pawsey Supercomputing Centre in Perth, which executes custom-written software pipelines, designed specifically to meet the ASKAP imaging requirements of wide field of view and high dynamic range. There are three key hardware components of the Central Processor: The ingest nodes (16 x node cluster), the fast temporary storage (1 PB Lustre file system) and the processing supercomputer (200 TFlop system). This High-Performance Computing (HPC) platform is managed and supported by the Pawsey support team. Due to the limited amount of data generated by BETA and the first ASKAP Array Release, the Central Processor platform has been running in a more "traditional" or user-interactive mode. But this is about to change: integration and verification of the online ingest pipeline starts in early 2016, which is required to support the full 300 MHz bandwidth for Array Release 1; followed by the deployment of the real-time data processing components. In addition to the Central Processor, the first production release of the CSIRO ASKAP Science Data Archive (CASDA) has also been deployed in one of the Pawsey Supercomputing Centre facilities and it is integrated to the end-to-end ASKAP data flow system. This paper describes the current status of the "end-to-end" data flow software system from preparing observations to data acquisition, processing and archiving; and the challenges of integrating an HPC facility as a key part of the instrument. It also shares some lessons learned since the start of integration activities and the challenges ahead in preparation for the start of the Early Science program.

Vision 2010: Pharmacy Executive Leadership Skills and Associated Competencies in the Department of Defense

DTIC Science & Technology

2002-01-01

management , drug therapy management , pharmacy benefit management , and leadership . During the Delphis second phase, respondents provided...of the top 15 rated SKA items came from the drug therapy management , leadership , and formulary management domains. Results indicate that the issues... management and technology, financial resources, formulary management , drug therapy management , pharmacy benefit management , and leadership . During

Astronomy in Mozambique

NASA Astrophysics Data System (ADS)

Ribeiro, Valério A. R. M.; Paulo, Cláudio M.

2015-03-01

We present the state of Astronomy in Mozambique and how it has evolved since 2009 following the International Year of Astronomy. Activities have been lead by staff at University Eduardo Mondlane and several outreach activities have also flourished. In 2010 the University introduced its first astronomy module, Introduction to Astronomy and Astrophysics, for the second year students in the Department of Physics. The course has now produced the first students who will be graduating in late 2012 with some astronomy content. Some of these students will now be looking for further studies and those who have been keen in astronomy have been recommended to pursue this as a career. At the university level we have also discussed on the possibility to introduce a whole astronomy course by 2016 which falls well within the HCD that the university is now investing in. With the announcement that the SKA will be split between South Africa with its partner countries (including Mozambique), and Australia we have been working closely with the Ministry of Science and Technology to make astronomy a priority on its agenda. In this respect, an old telecommunications antenna is being converted by the South Africa SKA Project Office, and donated to Mozambique for educational purposes. It will be situated in Maluana, Mozambique.

The protection of parsley seedlings (Petroselinum sativum Hoffm. ssp. microcarpum) against damping-off.

PubMed

Nawrocki, J

2006-01-01

The experiment was carried out in the years 2003 and 2004 on parsley cultivar: 'Berlinska', 'Cukrowa', 'Vistula' and 'Kinga'. Mycological analysis of parsley seeds showed, that the most common inhabitans were fungi from genus Alternaria (mainly A. alternata and A. radicina) and Fusarium, especially F. avenaceum and F. oxysporum. The two-year study on the effectiveness of 5 substances--biopreparate Biochikol 020 PC (polymer of chitosol) and Biosept 33 SL (extract of grape-fruit); and fungicides: Amistar 250 SC (BAS azoxystrobin), Dithane M-45 80WP (mancozeb) and Zaprawa Funaben T (carbendazim+thiram) used against parsley damping-off was conducted in glasshouse and field conditions. Seeds of parsley were treated one of tested substances before sowing. The results of glasshouse experiments showed, that the best efficacy exibited Amistar and Zaprawa Funaben T for seedlings cultivar 'Berlińska' and 'Cukrowa' and Biochikol for 'Kinga'. During field experiments Zaprawa Funaben T showed the best efficacy for seedlings 'Berlińska' and 'Vistula'. Preparate Amistar was the best seed dressing for parsley cultivar 'Cukrowa' and 'Kinga'. During glasshouse experiments in control the highest number of decaying seedlings had cultivar 'Berlinska', in field experiments 'Kinga'.

Ambient and Cryogenic, Decade Bandwidth, Low Noise Receiving System for Radio Astronomy Using Sinuous Antenna

NASA Astrophysics Data System (ADS)

Gawande, Rohit Sudhir

Traditionally, radio astronomy receivers have been limited to bandwidths less than an octave, and as a result multiple feeds and receivers are necessary to observe over a wide bandwidth. Next generation of instruments for radio astronomy will benefit greatly from reflector antenna feeds that demonstrate very wide instantaneous bandwidth, and exhibit low noise behavior. There is an increasing interest in wideband systems from both the cost and science point of view. A wideband feed will allow simultaneous observations or sweeps over a decade or more bandwidth. Instantaneous wide bandwidth is necessary for detection of short duration pulses. Future telescopes like square kilometer array (SKA), consisting of 2000 to 3000 coherently connected antennas and covering a frequency range of 70 MHz to 30 GHz, will need decade bandwidth single pixel feeds (SPFs) along with integrated LNAs to achieve the scientific objectives in a cost effective way. This dissertation focuses on the design and measurement of a novel decade bandwidth sinuous-type, dual linear polarized, fixed phase center, low loss feed with an integrated LNA. A decade bandwidth, low noise amplifier is specially designed for noise match to the higher terminal impedance encountered by this antenna yielding an improved sensitivity over what is possible with conventional 50 O amplifiers. The self-complementary, frequency independent nature of the planar sinuous geometry results in a nearly constant beam pattern and fixed phase center over more than a 10:1 operating frequency range. In order to eliminate the back-lobe response over such a wide frequency range, we have projected the sinuous pattern onto a cone, and a ground plane is placed directly behind the cone's apex. This inverted, conical geometry assures wide bandwidth operation by locating each sinuous resonator a quarter wavelength above the ground plane. The presence of a ground plane near a self complementary antenna destroys the self complementary nature of the composite structure resulting in frequency dependent impedance variations. We demonstrate, using simulations and measurements, how the return loss can be improved by modifying the sinuous geometry. The feed-LNA combination is characterized for important properties such as return loss, system noise, far field beam patterns including cross-polarization over a wide frequency range. The system is developed as a feed for a parabolic reflector. The overall system performance is calculated in terms of the A/Tsys ratio. A cryogenic version would have a direct impact on specialized observing applications requiring large instantaneous bandwidths with high sensitivity. A novel cryogenic implementation of this system is demonstrated using a Stirling cycle, one-stage refrigerator. The cryocooler offers advantages like low cost, light weight, small size, low power consumption, and does not require routine maintenance. The higher antenna input impedance and a balanced feeding method for the sinuous antenna offers a unique set of challenges when developing a cryogenic system.

The Early Development of Indian Radio Astronomy: A Personal Perspective

NASA Astrophysics Data System (ADS)

Swarup, Govind

In this chapter I recall my initiation into the field of radio astronomy during 1953-1955 at CSIRO, Australia; the transfer of thirty-two 6-feet (1.8-m) diameter parabolic dishes from Potts Hill, Sydney, to India in 1958; and their erection at Kalyan, near Bombay (Mumbai), in 1963-1965. The Kalyan Radio Telescope was the first modern radio telescope built in India. This led to the establishment of a very active radio astronomy group at the Tata Institute of Fundamental Research, which subsequently built two world-class radio telescopes during the last 50 years and also contributed to the development of an indigenous microwave antenna industry in India. The Ooty Radio Telescope, built during 1965-1970, has an ingenious design which takes advantage of India's location near the Earth's Equator. The long axis of this 530-m × 30-m parabolic cylinder was made parallel to the Equator, by placing it on a hill with the same slope as the geographic latitude ( 11°), thus allowing it to track celestial sources continuously for 9.5 h every day. By utilizing lunar occultations, the telescope was able to measure the angular sizes of a large number of faint radio galaxies and quasars with arc-second resolution for the first time. Subsequently, during the 1990s, the group set up the Giant Metrewave Radio Telescope (GMRT) near Pune in western India, in order to investigate certain astrophysical phenomena which are best studied at decimetre and metre wavelengths. The GMRT is an array of 30 fully steerable 45-m diameter parabolic dishes, which operates at several frequencies below 1.43 GHz. These efforts have also contributed to the international proposal to construct the Square Kilometre Array (SKA). This chapter is a revised version of Swarup (Journal of Astronomical History and Heritage, 9: 21-33, 2006).

Tunka-Rex: Status, Plans, and Recent Results

NASA Astrophysics Data System (ADS)

Schröder, F. G.; Bezyazeekov, P. A.; Budnev, N. M.; Fedorov, O.; Gress, O. A.; Haungs, A.; Hiller, R.; Huege, T.; Kazarina, Y.; Kleifges, M.; Korosteleva, E. E.; Kostunin, D.; Krömer, O.; Kungel, V.; Kuzmichev, L. A.; Lubsandorzhiev, N.; Mirgazov, R. R.; Monkhoev, R.; Osipova, E. A.; Pakhorukov, A.; Pankov, L.; Prosin, V. V.; Rubtsov, G. I.; Wischnewski, R.; Zagorodnikov, A.

2017-03-01

Tunka-Rex, the Tunka Radio extension at the TAIGA facility (Tunka Advanced Instrument for cosmic ray physics and Gamma Astronomy) in Siberia, has recently been expanded to a total number of 63 SALLA antennas, most of them distributed on an area of one square kilometer. In the first years of operation, Tunka-Rex was solely triggered by the co-located air-Cherenkov array Tunka-133. The correlation of the measurements by both detectors has provided direct experimental proof that radio arrays can measure the position of the shower maximum. The precision achieved so far is 40 g/cm2, and several methodical improvements are under study. Moreover, the cross-comparison of Tunka-Rex and Tunka-133 shows that the energy reconstruction of Tunka-Rex is precise to 15 %, with a total accuracy of 20 % including the absolute energy scale. By using exactly the same calibration source for Tunka-Rex and LOPES, the energy scale of their host experiments, Tunka-133 and KASCADE-Grande, respectively, can be compared even more accurately with a remaining uncertainty of about 10 %. The main goal of Tunka-Rex for the next years is a study of the cosmic-ray mass composition in the energy range above 100 PeV: For this purpose, Tunka-Rex now is triggered also during daytime by the particle detector array Tunka-Grande featuring surface and underground scintillators for electron and muon detection.

Characterizing seismic noise in the 2-20 Hz band at a gravitational wave observatory

NASA Astrophysics Data System (ADS)

Coward, D.; Turner, J.; Blair, D.; Galybin, K.

2005-04-01

We present a study of seismic noise, using an array of seismic sensors, at the Australian International Gravitational Observatory. We show that despite excellent attenuation of 2-20 Hz seismic waves from the soil properties of the site, which is confirmed by a specific experiment, there are important technical issues associated with local sources of vibration originating from within the laboratory buildings. In particular, we identify vibrations from air-filtration equipment propagating throughout the site. We find significant building resonances in the 2-13 Hz band and identify seismic noise originating from regional mine blasts hundreds of kilometers distant. All these noise sources increase the performance requirements on vibration isolation in the 2-20 Hz frequency band.

Sound from apollo rockets in space.

PubMed

Cotten, D; Donn, W L

1971-02-12

Low-frequency sound has been recorded on at least two occasions in Bermuda with the passage of Apollo rocket vehicles 188 kilometers aloft. The signals, which are reminiscent of N-waves from sonic booms, are (i) horizontally coherent; (ii) have extremely high (supersonic) trace velocities across the tripartite arrays; (iii) have nearly identical appearance and frequencies; (iv) have essentially identical arrival times after rocket launch; and (v) are the only coherent signals recorded over many hours. These observations seem to establish that the recorded sound comes from the rockets at high elevation. Despite this high elevation, the values of surface pressure appear to be explainable on the basis of a combination of a kinetic theory approach to shock formation in rarefied atmospheres with established gas-dynamics shock theory.

Water Ice on Pluto

NASA Image and Video Library

2015-10-08

Regions with exposed water ice are highlighted in blue in this composite image from New Horizons' Ralph instrument, combining visible imagery from the Multispectral Visible Imaging Camera (MVIC) with infrared spectroscopy from the Linear Etalon Imaging Spectral Array (LEISA). The strongest signatures of water ice occur along Virgil Fossa, just west of Elliot crater on the left side of the inset image, and also in Viking Terra near the top of the frame. A major outcrop also occurs in Baré Montes towards the right of the image, along with numerous much smaller outcrops, mostly associated with impact craters and valleys between mountains. The scene is approximately 280 miles (450 kilometers) across. Note that all surface feature names are informal. http://ppj2:8080/catalog/PIA19963

Genetic and Molecular Analysis of the Mechanisms by Which TSC Regulates Neuronal Differentiation

DTIC Science & Technology

2007-02-01

Baskin , D. G., Porte, D. Jr, Guest, K. and Dorsa, D. M. (1983) Regional concentrations of insulin in the rat brain. Endocrinol- ogy 112, 898–903. 5 van...895–906. 18 Boulton, T. G., Nye, S. H., Robbins , D. J., Ip, N. Y. Radziejew- ska, E., Morgenbesser S. D., DePinho, R. A., Panayotatos, N., Cobb, M. H

Iceland: Eyjafjallajökull Volcano

Atmospheric Science Data Center

2013-04-17

... plume height map, which is retrieved at 1.1 kilometer (0.68 mile) horizontal resolution, and with vertical accuracy of about half a ... the plume reaches altitudes exceeding 8 kilometers (26,247 feet), descending to about 6 kilometers (19,685 feet) about 250 kilometers (155 ...

Evaluation of Water Resources in Bolivia, South America

DTIC Science & Technology

1991-01-01

sub-basins: Madre de Dios 31,000 square kilometers Beni 183,000 square kilometers Mamore 216,000 square kilometers Itenez/Cuapore 294,000 square...infrastructure; cumbersome institutional bureaucracies and a viable and growing black market production and retail sector ( de Soto 1989); and the human and...See Figure 3 oi, page 34): The Amazon Basin 724,000 square kilometers The De La Plata Basin 229,500 square kilometers The Altiplano Basin 145,081

An Integrated Circuit for Radio Astronomy Correlators Supporting Large Arrays of Antennas

NASA Technical Reports Server (NTRS)

D'Addario, Larry R.; Wang, Douglas

2016-01-01

Radio telescopes that employ arrays of many antennas are in operation, and ever larger ones are being designed and proposed. Signals from the antennas are combined by cross-correlation. While the cost of most components of the telescope is proportional to the number of antennas N, the cost and power consumption of cross-correlationare proportional to N2 and dominate at sufficiently large N. Here we report the design of an integrated circuit (IC) that performs digital cross-correlations for arbitrarily many antennas in a power-efficient way. It uses an intrinsically low-power architecture in which the movement of data between devices is minimized. In a large system, each IC performs correlations for all pairs of antennas but for a portion of the telescope's bandwidth (the so-called "FX" structure). In our design, the correlations are performed in an array of 4096 complex multiply-accumulate (CMAC) units. This is sufficient to perform all correlations in parallel for 64 signals (N=32 antennas with 2 opposite-polarization signals per antenna). When N is larger, the input data are buffered in an on-chipmemory and the CMACs are re-used as many times as needed to compute all correlations. The design has been synthesized and simulated so as to obtain accurate estimates of the IC's size and power consumption. It isintended for fabrication in a 32 nm silicon-on-insulator process, where it will require less than 12mm2 of silicon area and achieve an energy efficiency of 1.76 to 3.3 pJ per CMAC operation, depending on the number of antennas. Operation has been analyzed in detail up to N = 4096. The system-level energy efficiency, including board-levelI/O, power supplies, and controls, is expected to be 5 to 7 pJ per CMAC operation. Existing correlators for the JVLA (N = 32) and ALMA (N = 64) telescopes achieve about 5000 pJ and 1000 pJ respectively usingapplication-specific ICs in older technologies. To our knowledge, the largest-N existing correlator is LEDA atN = 256; it uses GPUs built in 28 nm technology and achieves about 1000 pJ. Correlators being designed for the SKA telescopes (N = 128 and N = 512) using FPGAs in 16nm technology are predicted to achieve about 100 pJ.

Giant sand waves at the mouth of San Francisco Bay

USGS Publications Warehouse

Barnard, P.L.; Hanes, D.M.; Rubin, D.M.; Kvitek, R.G.

2006-01-01

A field of giant sand waves, among the largest in the world, recently was mapped in high resolution for the first time during a multibeam survey in 2004 and 2005 through the strait of the Golden Gate at the mouth of San Francisco Bay in California (Figure la). This massive bed form field covers an area of approximately four square kilometers in water depths ranging from 30 to 106 meters, featuring more than 40 distinct sand waves with crests aligned approximately perpendicular to the dominant tidally generated cross-shore currents, with wavelengths and heights that measure up to 220 meters and 10 meters, respectively. Sand wave crests can be traced continuously for up to two kilometers across the mouth of this energetic tidal inlet, where depth-averaged tidal currents through the strait below the Golden Gate Bridge exceed 2.5 meters per second during peak ebb flows. Repeated surveys demonstrated that the sand waves are active and dynamic features that move in response to tidally generated currents. The complex temporal and spatial variations in wave and tidal current interactions in this region result in an astoundingly diverse array of bed form morphologies, scales, and orientations. Bed forms of approximately half the scale of those reported in this article previously were mapped inside San Francisco Bay during a multibeam survey in 1997 [Chin et al., 1997].

Investigating cosmic rays and air shower physics with IceCube/IceTop

NASA Astrophysics Data System (ADS)

Dembinski, Hans

2017-06-01

IceCube is a cubic-kilometer detector in the deep ice at South Pole. Its square-kilometer surface array, IceTop, is located at 2800 m altitude. IceTop is large and dense enough to cover the cosmic-ray energy spectrum from PeV to EeV energies with a remarkably small systematic uncertainty, thanks to being close to the shower maximum. The experiment offers new insights into hadronic physics of air showers by observing three components: the electromagnetic signal at the surface, GeV muons in the periphery of the showers, and TeV muons in the deep ice. The cosmic-ray flux is measured with the surface signal. The mass composition is extracted from the energy loss of TeV muons observed in the deep ice in coincidence with signals at the surface. The muon lateral distribution is obtained from GeV muons identified in surface signals in the periphery of the shower. The energy spectrum of the most energetic TeV muons is also under study, as well as special events with laterally separated TeV muon tracks which originate from high-pT TeV muons. A combination of all these measurements opens the possibility to perform powerful new tests of hadronic interaction models used to simulate air showers. The latest results will be reviewed from this perspective.

Expansion of industrial logging in Central Africa.

PubMed

Laporte, Nadine T; Stabach, Jared A; Grosch, Robert; Lin, Tiffany S; Goetz, Scott J

2007-06-08

Industrial logging has become the most extensive land use in Central Africa, with more than 600,000 square kilometers (30%) of forest currently under concession. With use of a time series of satellite imagery for the period from 1976 to 2003, we measured 51,916 kilometers of new logging roads. The density of roads across the forested region was 0.03 kilometer per square kilometer, but areas of Gabon and Equatorial Guinea had values over 0.09 kilometer per square kilometer. A new frontier of logging expansion was identified within the Democratic Republic of Congo, which contains 63% of the remaining forest of the region. Tree felling and skid trails increased disturbance in selectively logged areas.

Macroscopic Relationships among Latent Heating, Precipitation, Organized Convection and the Environment

NASA Technical Reports Server (NTRS)

Moncrieff, Mitchell W.; Liu, Changhai

2002-01-01

Three-dimensional Cloud Resolving Model (CRM) simulations were conducted to examine the squall line observed on 26 January, 1999 from the Tropical Rainfall Measuring Mission Large Scale Biosphere Atmosphere Experiment in Amazonia (TRMM-LBA) field campaign. The computational domain was 600 kilometers x 180 kilometers x 20 kilometers with a horizontal resolution of 1 kilometer and a vertical resolution of 200 meters. The CRM was initialized from the Abracos Hill and Rebio soundings. Convection was initiated by a surface-based and NW-SE oriented cold pool over a region 60 kilometers in the y-direction and 30 kilometers wide in the x-direction. The cold pool temperature perturbation is a maximum of -6K at the surface, decreasing linearly to zero at 3 kilometers. The simulated convection is in the form of a NW-SE band that moves toward the southwest at a speed of 8 meters per second, and is generally comparable to radar observations.

Photographer : JPL Range : 225,000 kilometers (140,625 miles) This image of the Jovian moon Europa

NASA Technical Reports Server (NTRS)

1979-01-01

Photographer : JPL Range : 225,000 kilometers (140,625 miles) This image of the Jovian moon Europa was taken by Voyager 2 along the evening terminator, which best shows the surface topography of complex narrow ridges, seen as curved bright streaks, 5 to 10 kilometers wide, and typically 100 kilometers in length. The area shown is about 600 by 800 kilometers, and the smallest features visible are about 4 kilometers in size. Also visable are dark bands, more diffused in character, 20 to 40 kilometers wide and hundreds to thousands of kilometers in length. A few features are suggestive of impact craters but are rare, indication that the surface thought to be dominantly ice is still active, perhaps warmed by tidal heating like Io. The larger icy satellites, Callisto and Ganymede, are evidently colder with much more rigid crusts and ancient impact craters. The complex intersection of dark markings and bright ridges suggest that the surface has been fractured and material from beneath has welled up to fill the cracks.

Building from within: identifying leadership competencies for future navy nurse executives.

PubMed

Palarca, Christine; Johnson, Scott; Mangelsdorff, A David; Finstuen, Kenn

2008-01-01

The purpose of this research is to forecast the relevant competencies and important skills, knowledge, and abilities (SKAs) for Navy nurse executives in the next 5 to 10 years. Using 2 iterations, Wave I and Wave II, of the Delphi technique, 6 competency domains emerged: business management, executive leadership, professional development, global awareness and interoperability, communications, and personnel management. For Wave I, 38 (19%) of 200 nurses identified what they considered to be the 5 most relevant competencies and skills, knowledge, and abilities. Reviewed by an expert panel, the results were used to develop the Wave II questionnaire to determine SKA importance ratings. Using the same respondent pool, 93 (47%) of the 200 nurses rated 100 SKA items. The top 3 rated SKAs were as follows: "Maintains the utmost integrity: has the trust of all members inside and outside of the organization," "Communication skills: ability to communicate in all forms," and "Ability to lead and mentor junior personnel." The Cronbach coefficient alpha was used to assess internal consistency. All results were above the recommended and acceptable level of .70. The results will provide the foundation for a leadership education continuum enabling the critical link among educational offerings, role-based experiences, timely mentoring, and specific career milestones.

Epigenetic modification of miR-141 regulates SKA2 by an endogenous ‘sponge’ HOTAIR in glioma

PubMed Central

Wang, Chao; Zong, Gang; Wang, Hong-Liang; Zhao, Bing

2016-01-01

Aberrant expression of miR-141 has recently implicated in the occurrence and development of various types of malignant tumors. However whether the involvement of miR-141 in the pathogenesis of glioma remains unknown. Here, we showed that miR-141 was markedly downregulated in glioma tissues and cell lines compared with normal brain tissues, and its expression correlated with the pathological grading. Enforced expression of miR-141 in glioma cells significantly inhibited cell proliferation, migration and invasion, whereas knockdown of miR-141 exerted opposite effect. Mechanistic investigations revealed that HOTAIR might act as an endogenous ‘sponge’ of miR-141, thereby regulating the derepression of SKA2. Further, we explored the molecular mechanism by which miR-141 expression was regulated, and found that the miR-141 promoter was hypermethylated and that promoter methylation of miR-141 was mediated by DNMT1 in glioma cells. Finally, both overexpression of miR-141 and knockdown of HOTAIR in a mouse model of human glioma resulted in significant reduction of tumor growth in vivo. Collectively, these results suggest that epigenetic modification of miR-141 and the interaction of ceRNA regulatory network will provide a new approach for therapeutics against glioma. PMID:27121316

Recorded earthquake responses from the integrated seismic monitoring network of the Atwood Building, Anchorage, Alaska

USGS Publications Warehouse

Celebi, M.

2006-01-01

An integrated seismic monitoring system with a total of 53 channels of accelerometers is now operating in and at the nearby free-field site of the 20-story steel-framed Atwood Building in highly seismic Anchorage, Alaska. The building has a single-story basement and a reinforced concrete foundation without piles. The monitoring system comprises a 32-channel structural array and a 21-channel site array. Accelerometers are deployed on 10 levels of the building to assess translational, torsional, and rocking motions, interstory drift (displacement) between selected pairs of adjacent floors, and average drift between floors. The site array, located approximately a city block from the building, comprises seven triaxial accelerometers, one at the surface and six in boreholes ranging in depths from 15 to 200 feet (???5-60 meters). The arrays have already recorded low-amplitude shaking responses of the building and the site caused by numerous earthquakes at distances ranging from tens to a couple of hundred kilometers. Data from an earthquake that occurred 186 km away traces the propagation of waves from the deepest borehole to the roof of the building in approximately 0.5 seconds. Fundamental structural frequencies [0.58 Hz (NS) and 0.47 Hz (EW)], low damping percentages (2-4%), mode coupling, and beating effects are identified. The fundamental site frequency at approximately 1.5 Hz is close to the second modal frequencies (1.83 Hz NS and 1.43 EW) of the building, which may cause resonance of the building. Additional earthquakes prove repeatability of these characteristics; however, stronger shaking may alter these conclusions. ?? 2006, Earthquake Engineering Research Institute.

Microsat and Lunar-Based Imaging of Radio Bursts

NASA Technical Reports Server (NTRS)

MacDowall, R. J.; Gopalswamy, N.; Kaiser, M. L.; Demaio, L. D.; Bale, S. D.; Kasper, J. C.; Lazarus, A. J.; Howard, R. E.; Jones, D. L.; Reiner, M. J.;

All-Particle Cosmic Ray Energy Spectrum Measured with 26 Icetop Stations

NASA Technical Reports Server (NTRS)

Abbasi, R.; Abdou, Y.; Abu-Zayyad, T.; Ackermann, M.; Adams, J.; Aguilar, J. A.; Ahlers, M.; Altmann, D.; Andeen, K.; Auffenberg, J.;

Ancient Biomolecules from Deep Ice Cores Reveal a Forested Southern Greenland

PubMed Central

Willerslev, Eske; Cappellini, Enrico; Boomsma, Wouter; Nielsen, Rasmus; Hebsgaard, Martin B.; Brand, Tina B.; Hofreiter, Michael; Bunce, Michael; Poinar, Hendrik N.; Dahl-Jensen, Dorthe; Johnsen, Sigfus; Steffensen, Jørgen Peder; Bennike, Ole; Schwenninger, Jean-Luc; Nathan, Roger; Armitage, Simon; de Hoog, Cees-Jan; Alfimov, Vasily; Christl, Marcus; Beer, Juerg; Muscheler, Raimund; Barker, Joel; Sharp, Martin; Penkman, Kirsty E.H.; Haile, James; Taberlet, Pierre; Gilbert, M. Thomas P.; Casoli, Antonella; Campani, Elisa; Collins, Matthew J.

2009-01-01

One of the major difficulties in paleontology is the acquisition of fossil data from the 10% of Earth’s terrestrial surface that is covered by thick glaciers and ice sheets. Here we reveal that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores and allow reconstructions of past flora and fauna. We show that high altitude southern Greenland, currently lying below more than two kilometers of ice, was once inhabited by a diverse array of conifer trees and insects that may date back more than 450 thousand years. The results provide the first direct evidence in support of a forested southern Greenland and suggest that many deep ice cores may contain genetic records of paleoenvironments in their basal sections. PMID:17615355

Cosmic ray spectrum, composition, and anisotropy measured with IceCube

NASA Astrophysics Data System (ADS)

Tamburro, Alessio

2014-04-01

Analysis of cosmic ray surface data collected with the IceTop array of Cherenkov detectors at the South Pole provides an accurate measurement of the cosmic ray spectrum and its features in the "knee" region up to energies of about 1 EeV. IceTop is part of the IceCube Observatory that includes a deep-ice cubic kilometer detector that registers signals of penetrating muons and other particles. Surface and in-ice signals detected in coincidence provide clear insights into the nuclear composition of cosmic rays. IceCube already measured an increase of the average primary mass as a function of energy. We present preliminary results on both IceTop-only and coincident events analysis. Furthermore, we review the recent measurement of the cosmic ray anisotropy with IceCube.

Tilt precursors before earthquakes on the San Andreas fault, California

USGS Publications Warehouse

Johnston, M.J.S.; Mortensen, C.E.

1974-01-01

An array of 14 biaxial shallow-borehole tiltmeters (at 10-7 radian sensitivity) has been installed along 85 kilometers of the San Andreas fault during the past year. Earthquake-related changes in tilt have been simultaneously observed on up to four independent instruments. At earthquake distances greater than 10 earthquake source dimensions, there are few clear indications of tilt change. For the four instruments with the longest records (>10 months), 26 earthquakes have occurred since July 1973 with at least one instrument closer than 10 source dimensions and 8 earthquakes with more than one instrument within that distance. Precursors in tilt direction have been observed before more than 10 earthquakes or groups of earthquakes, and no similar effect has yet been seen without the occurrence of an earthquake.

Small-scale structure and 21cm fluctuations by primordial black holes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gong, Jinn-Ouk; Kitajima, Naoya, E-mail: jinn-ouk.gong@apctp.org, E-mail: kitajima.naoya@f.mbox.nagoya-u.ac.jp

We discuss early structure formation of small scales sourced by primordial black holes (PBHs) which constitute a small part of present cold dark matter component. We calculate the mass function and power spectrum of haloes originated from the Poisson fluctuations of PBH number and show that the number of small haloes is significantly modified in the presence of PBHs even if their fraction accounts for only 10{sup −4}–10{sup −3} of total dark matter abundance. We then compute the subsequent 21cm signature from those haloes. We find that PBHs can provide major contributions at high redshifts within the detectability of futuremore » experiments such as Square Kilometer Array, and provide a forecast constraint on the PBH fraction.« less

Peering through Jupiter’s clouds with radio spectral imaging

NASA Astrophysics Data System (ADS)

de Pater, Imke; Sault, R. J.; Butler, Bryan; DeBoer, David; Wong, Michael H.

2016-06-01

Radio wavelengths can probe altitudes in Jupiter’s atmosphere below its visible cloud layers. We used the Very Large Array to map this unexplored region down to ~8 bar, ~100 kilometers below the visible clouds. Our maps reveal a dynamically active planet at pressures less than 2 to 3 bar. A radio-hot belt exists, consisting of relatively transparent regions (a low ammonia concentration, NH3 being the dominant source of opacity) probing depths to over ~8 bar; these regions probably coincide with 5-micrometer hot spots. Just to the south we distinguish an equatorial wave, bringing up ammonia gas from Jupiter’s deep atmosphere. This wave has been theorized to produce the 5-micrometer hot spots; we observed the predicted radio counterpart of such hot spots.

Multistatic GNSS Receiver Array for Passive Air Surveillance

NASA Astrophysics Data System (ADS)

Wachtl, Stefan; Koch, Volker; Westphal, Robert; Schmidt, Lorenz-Peter

2016-03-01

The performance of a passive air surveillance sensor based on Global Navigation Satellite Systems (GNSS) is mainly limited by the receiver noise efficiency, the achievable signal processing gain and the radar cross section (RCS) of an airplane. For surveillance applications large detection ranges as well as a high probability of detection are crucial parameters. Due to the very low GNSS signal powers received on the earth's surface, high radar cross sections are mandatory to achieve detection ranges for airplanes at some kilometers distance. This paper will discuss a multistatic transmitter and receiver arrangement, which is indispensable to get a reasonable detection rate with respect to a hemispheric field of view. The strong performance dependency of such a sensor on the number of transmitters and receivers will be shown by means of some exemplary simulation results.

ARC-1979-A79-7093

NASA Image and Video Library

1979-07-09

Range : 225,000 kilometers (140,625 miles) This image of the Jovian moon Europa was taken by Voyager 2 along the evening terminator, which best shows the surface topography of complex narrow ridges, seen as curved bright streaks, 5 to 10 kilometers wide, and typically 100 kilometers in length. The area shown is about 600 by 800 kilometers, and the smallest features visible are about 4 kilometers in size. Also visable are dark bands, more diffused in character, 20 to 40 kilometers wide and hundreds to thousands of kilometers in length. A few features are suggestive of impact craters but are rare, indication that the surface thought to be dominantly ice is still active, perhaps warmed by tidal heating like Io. The larger icy satellites, Callisto and Ganymede, are evidently colder with much more rigid crusts and ancient impact craters. The complex intersection of dark markings and bright ridges suggest that the surface has been fractured and material from beneath has welled up to fill the cracks.

Multi-disciplinary contributions of HartRAO to global geodesy and geodynamics

NASA Astrophysics Data System (ADS)

Combrinck, Ludwig

2015-04-01

The Hartebeesthoek Radio Astronomy Observatory (South Africa) supports global initiatives in both geodesy and geodynamics through an active programme of science platform provision in Africa, the Atlantic Ocean, Indian Ocean and Antarctica. Our involvement ranges from the installation of tide gauges, Global Navigation Satellite Systems stations, seismometers and accelerometers on remote islands to the installation of radar reflectors in Antarctica which enable accurate, geo-referenced maps of the Antarctic coast line to be made. Currently we also participate in the African VLBI Network (AVN), with the aim to densify not only astronomical observatories in Africa, but to improve the geometry and distribution of advanced geodetic and geophysical equipment to facilitate development of research platforms in Africa, which can be used for geodynamics and related sciences, supporting international projects such as the WEGENER initiative. We present our multi-disciplinary activities during the last decade and sketch the way forward. Participation of Africa in the global arena of astronomy, geodesy, geodynamics and related fields will receive a major boost during the next decade. This is partially due to the development of a component of the Square Kilometre Array (SKA) in Africa but also due to the Global Geodetic Observing System (GGOS) project and the international objectives of higher geodetic accuracies and more stable reference frames. Consequent spinoffs into many disciplines relying on global reference frames and sub-cm positional accuracies stand to benefit and Africa can play a major role in improving both science and network geometries.

A Tour of Big Data, Open Source Data Management Technologies from the Apache Software Foundation

NASA Astrophysics Data System (ADS)

Mattmann, C. A.

2012-12-01

The Apache Software Foundation, a non-profit foundation charged with dissemination of open source software for the public good, provides a suite of data management technologies for distributed archiving, data ingestion, data dissemination, processing, triage and a host of other functionalities that are becoming critical in the Big Data regime. Apache is the world's largest open source software organization, boasting over 3000 developers from around the world all contributing to some of the most pervasive technologies in use today, from the HTTPD web server that powers a majority of Internet web sites to the Hadoop technology that is now projected at over a $1B dollar industry. Apache data management technologies are emerging as de facto off-the-shelf components for searching, distributing, processing and archiving key science data sets both geophysical, space and planetary based, all the way to biomedicine. In this talk, I will give a virtual tour of the Apache Software Foundation, its meritocracy and governance structure, and also its key big data technologies that organizations can take advantage of today and use to save cost, schedule, and resources in implementing their Big Data needs. I'll illustrate the Apache technologies in the context of several national priority projects, including the U.S. National Climate Assessment (NCA), and in the International Square Kilometre Array (SKA) project that are stretching the boundaries of volume, velocity, complexity, and other key Big Data dimensions.

Tracking marine mammals and ships with small and large-aperture hydrophone arrays

NASA Astrophysics Data System (ADS)

Gassmann, Martin

Techniques for passive acoustic tracking in all three spatial dimensions of marine mammals and ships were developed for long-term acoustic datasets recorded continuously over months using custom-designed arrays of underwater microphones (hydrophones) with spacing ranging from meters to kilometers. From the three-dimensional tracks, the acoustical properties of toothed whales and ships, such as sound intensity and directionality, were estimated as they are needed for the passive acoustic abundance estimation of toothed whales and for a quantitative description of the contribution of ships to the underwater soundscape. In addition, the tracks of the toothed whales reveal their underwater movements and demonstrate the potential of the developed tracking techniques to investigate their natural behavior and responses to sound generated by human activity, such as from ships or military SONAR. To track the periodically emitted echolocation sounds of toothed whales in an acoustically refractive environment in the upper ocean, a propagation-model based technique was developed for a hydrophone array consisting of one vertical and two L-shaped subarrays deployed from the floating instrument platform R/P FLIP. The technique is illustrated by tracking a group of five shallow-diving killer whales showing coordinated behavior. The challenge of tracking the highly directional echolocation sounds of deep-diving (< 1 km) toothed whales, in particular Cuvier's beaked whales, was addressed by embedding volumetric small-aperture (≈ 1 m element spacing) arrays into a large-aperture (≈ 1 km element spacing) seafloor array to reduce the minimum number of required receivers from five to two. The capabilities of this technique are illustrated by tracking several groups of up to three individuals over time periods from 10 min to 33 min within an area of 20 km2 in the Southern California Bight. To track and measure the underwater radiated sound of ships, a frequency domain beamformer was implemented for a volumetric hydrophone array (< 2 m element spacing) that was coupled to an autonomous acoustic seafloor recorder. This allows for the tracking and measurement of underwater radiated sound from ships of opportunity with a single instrument deployment and without depending on track information from the automatic information system (AIS).

Now You See Me ...

NASA Image and Video Library

2006-05-18

Enceladus briefly passes behind the crescent of Rhea in these images, which are part of a "mutual event" sequence taken by Cassini. These sequences help scientists refine our understanding of the orbits of Saturn's moons. The images were taken one minute apart as smaller Enceladus (505 kilometers, or 314 miles across) darted behind Rhea (1,528 kilometers, or 949 miles across) as seen from the Cassini spacecraft's point of view. The images were taken in visible light with the Cassini spacecraft narrow-angle camera on April 14, 2006, at a distance of approximately 3.4 million kilometers (2.1 million miles) from Rhea and 4.1 million kilometers (2.5 million miles) from Enceladus. The image scale is 20 kilometers (13 miles) per pixel on Rhea and 24 kilometers (15 miles) per pixel on Enceladus. http://photojournal.jpl.nasa.gov/catalog/PIA08180

Lunar Shape via the Apollo Laser Altimeter.

PubMed

Sjogren, W L; Wollenhaupt, W R

1973-01-19

Data from the Apollo 15 and Apollo 16 laser altimeters reveal the first accurate elevation differences between distant features on both sides of the moon. The large far-side depression observed in the Apollo 15 data is not present in the Apollo 16 data. When the laser results are compared with elevations on maps from the Aeronautical Chart and Information Center, differences of 2 kilometers over a few hundred kilometers are detected in the Mare Nubium and Mare Tranquillitatis regions. The Apollo 16 data alone would put a 2-kilometer bulge toward the earth; however, the combined data are best fit by a sphere of radius 1737.7 kilometers. The offset of the center of gravity from the optical center is about 2 kilometers toward the earth and 1 kilometer eastward. The polar direction parameters are not well determined.

Triple Crescents

NASA Image and Video Library

2015-06-22

A single crescent moon is a familiar sight in Earth's sky, but with Saturn's many moons, you can see three or even more. The three moons shown here -- Titan (3,200 miles or 5,150 kilometers across), Mimas (246 miles or 396 kilometers across), and Rhea (949 miles or 1,527 kilometers across) -- show marked contrasts. Titan, the largest moon in this image, appears fuzzy because we only see its cloud layers. And because Titan's atmosphere refracts light around the moon, its crescent "wraps" just a little further around the moon than it would on an airless body. Rhea (upper left) appears rough because its icy surface is heavily cratered. And a close inspection of Mimas (center bottom), though difficult to see at this scale, shows surface irregularities due to its own violent history. This view looks toward the anti-Saturn hemisphere of Titan. North on Titan is to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 25, 2015. The view was obtained at a distance of approximately 2.7 million miles (4.3 million kilometers) from Titan. Image scale at Titan is 16 miles (26 kilometers) per pixel. Mimas was 1.9 million miles (3.0 million kilometers) away with an image scale of 11 miles (18 kilometers) per pixel. Rhea was 1.6 million miles (2.6 million kilometers) away with an image scale of 9.8 miles (15.7 kilometer) per pixel. http://photojournal.jpl.nasa.gov/catalog/pia18322

Study of Ground Response Curve (GRC) Based on a Damage Model / Badanie Krzywej Odpowiedzi Gruntu (Grc) W Oparciu O Model Pękania Skał

NASA Astrophysics Data System (ADS)

Molladavoodi, H.

2013-09-01

Analysis of stresses and displacements around underground openings is necessary in a wide variety of civil, petroleum and mining engineering problems. In addition, an excavation damaged zone (EDZ) is generally formed around underground openings as a result of high stress magnitudes even in the absence of blasting effects. The rock materials surrounding the underground excavations typically demonstrate nonlinear and irreversible mechanical response in particular under high in situ stress states. The dominant cause of irreversible deformations in brittle rocks is damage process. One of the most widely used methods in tunnel design is the convergence-confinement method (CCM) for its practical application. The elastic-plastic models are usually used in the convergence-confinement method as a constitutive model for rock behavior. The plastic models used to simulate the rock behavior, do not consider the important issues such as stiffness degradation and softening. Therefore, the use of damage constitutive models in the convergence-confinement method is essential in the design process of rock structures. In this paper, the basic concepts of continuum damage mechanics are outlined. Then a numerical stepwise procedure for a circular tunnel under hydrostatic stress field, with consideration of a damage model for rock mass has been implemented. The ground response curve and radius of excavation damage zone were calculated based on an isotropic damage model. The convergence-confinement method based on damage model can consider the effects of post-peak rock behavior on the ground response curve and excavation damage zone. The analysis of results show the important effect of brittleness parameter on the tunnel wall convergence, ground response curve and excavation damage radius. Analiza naprężeń i przemieszczeń powstałych wokół otworu podziemnego wymagana jest przy szerokiej gamie projektów z zakresu budownictwa lądowego, inżynierii górniczej oraz naftowej. Ponadto, wokół otworu podziemnego powstaje strefa naruszona działalnością górniczą wskutek oddziaływania wysokich naprężeń, nawet w przypadku gdy nie są prowadzone prace strzałowe. Reakcja materiału skalnego znajdującego się w otoczeniu wyrobisk podziemnych jest zazwyczaj procesem nieliniowym i nieodwracalnym, zwłaszcza w stanach wysokich naprężeń in situ. Główną przyczyną nieodwracalnych odkształceń skał kruchych jest pękanie. Jedną z najczęściej stosowanych metod w projektowaniu tuneli (wyrobisk podziemnych) jest metoda konwergencji i zamknięcia, popularna ze względu na zakres zastosowań. Metoda ta zazwyczaj wykorzystuje modele sprężysto- plastyczne, jako konstytutywne modele zachowania skał. Modele plastyczne wykorzystywane dotychczas do symulacji zachowania skał nie uwzględniają pewnych kluczowych aspektów, takich jak obniżenie sztywności czy rozmiękczanie. Dlatego też zastosowanie konstytutywnych modeli w metodzie konwergencji i zamknięcia jest sprawą kluczową przy projektach obejmujących struktury skalne. W pracy tej omówiono podstawowe założenia modelu continuum uszkodzeń i spękań. Zaimplementowano wielostopniową procedurę do badania tunelu o przekroju kolistym znajdującego się pod polem naprężeń hydrostatycznych, przy wykorzystaniu modelu pękania górotworu. Krzywą odpowiedzi gruntu oraz promień strefy naruszonej wybieraniem obliczono przy wykorzystaniu izotropowego modelu uszkodzeń. Metoda konwergencji i zamykania oparta na tym modelu uwzględnia zachowanie skał po wystąpieniu szczytowych naprężeń i powstaniu strefy naruszonej wybieraniem. Analiza wyników wykazała znaczny wpływ parametrów związanych z kruchością na konwergencję ścian wyrobiska, kształt krzywej odpowiedzi gruntu oraz promień strefy naruszonej wybieraniem.

First Data from Mars Climate Sounder

NASA Technical Reports Server (NTRS)

2006-01-01

The Mars Climate Sounder, an instrument on NASA's Mars Reconnaissance Orbiter designed to monitor daily changes in the global atmosphere of Mars, made its first observations of Mars on March 24, 2006.

These tests were conducted to demonstrate that the instrument could, if needed, support the mission's aerobraking maneuvers (dips into the atmosphere to change the shape of the orbit) by providing hemisphere-scale coverage of atmospheric activity. The instrument scanned nine arrays of detectors four times across the entire disc of the planet, including the north pole, from an altitude of about 45,000 kilometers (28,000 miles). This is about 150 times farther away than the spacecraft will be during its main science phase. At this great range, the planet appears only 40 pixels wide, as suggested by the pixilation of the images. However, this is sufficient to identify regional dust storms in the lower atmosphere. Regional dust storms could perturb atmospheric densities at the higher altitudes (about 100 kilometers or 60 miles) where the orbiter will conduct more than 500 aerobraking passes during the next six months. Such storms are rare in the current season on Mars, early northern spring, and no large storms are present as the orbiter prepares for the start of aerobraking.

Each of the Mars Climate Sounder's arrays looks in a different wavelength band, and three of the resulting images are shown here. The view on the left is from data collected in a broad spectral band (wavelengths of 0.3 microns to 3 microns) for reflected sunlight. The view in the center is from data collected in the 12-micron thermal-infrared band. This band was chosen to sense infrared radiation from the surface when the atmosphere is clear and from dust clouds when it is not. The view on the right is from data collected at 15 microns, a longer-wavelength band still in the thermal-infrared part of the spectrum. At this wavelength, carbon dioxide, the main ingredient in Mars' atmosphere, hides the surface emission, and the thermal-infrared radiation comes only from the atmosphere.

The visible-and-near-infrared image (left) is bright where surface ice and atmospheric hazes reflect sunlight back to space. The view is of the northern half of Mars, with the north polar cap visible as the bright semicircle at upper left. The night half of the planet (lower left) is dark. The 'terminator' boundary between the day side and night side of the planet cuts from lower left to upper right, through the polar area. During the science phase of the mission, after the spacecraft has shrunk its orbit to a nearly circular loop approximately 300 kilometers (186 miles) above the surface, these visible-and-near-infrared readings by the Mars Climate Sounder will track how the amount of solar energy reflected from Mars varies from place-to-place and season-to-season, particularly in the polar regions where absorbed sunlight vaporizes the seasonal carbon-dioxide ice.

The 12-micron image (center) indicates that heat is being emitted from both the day side and the night side of the planet. The polar cap is dark in this image because it is cold (minus 190 degrees Fahrenheit) and emits less heat than surrounding areas. During the science phase of the mission, the thermal-infrared readings at this wavelength by Mars Climate Sounder will be used to track dust and clouds in the atmosphere. In the current season on Mars, the atmosphere is relatively clear except for an equatorial belt of thin water-ice clouds present in the visible-and-near-infrared image, and so the 12-micron image is dominated by the infrared radiation from the surface on the relatively hot dayside (upper right).

The 15-micron image (right) indicates the temperatures of the atmosphere at an altitude of about 25 kilometers (15 miles), where there is not much temperature difference even between the night side and the day side of the planet. The polar atmosphere is colder, so it appears darker.

Once deployed in a low-altitude, nearly circular orbit next fall, the Mars Climate Sounder will systematically alternate views of the surface with views of the atmosphere above the limb (horizon) of the planet from the surface to an altitude of 80 kilometers (50 miles), with a vertical resolution of 5 kilometers (3 miles). In this way it will monitor atmospheric and surface changes through a full annual cycle to characterize the present climate of Mars.

The Mars Climate Sounder was provided by NASA's Jet Propulsion Laboratory, Pasadena, Calif., which also manages the Mars Reconnaissance Orbiter mission for the NASA Science Mission Directorate.

Distant Moons

NASA Image and Video Library

2016-08-15

Saturn's moons Tethys and Hyperion appear to be near neighbors in this Cassini view, even though they are actually 930,000 miles (1.5 million kilometers) apart here. Tethys is the larger body on the left. These two icy moons of Saturn are very different worlds. To learn more about Hyperion (170 miles or 270 kilometers across). This view looks toward the trailing side of Tethys. North on Tethys is up and rotated 1 degree to the left. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Aug. 15, 2015. The view was acquired at a distance of approximately 750,000 miles (1.2 million kilometers) from Tethys. Image scale is 4.4 miles (7.0 kilometers) per pixel. The distance to Hyperion was 1.7 million miles (2.7 million kilometers) with an image scale of 10 mile (16 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA20493

Lightning discharges produced by wind turbines

NASA Astrophysics Data System (ADS)

Montanyà, Joan; van der Velde, Oscar; Williams, Earle R.

2014-02-01

New observations with a 3-D Lightning Mapping Array and high-speed video are presented and discussed. The first set of observations shows that under certain thunderstorm conditions, wind turbine blades can produce electric discharges at regular intervals of 3 s in relation to its rotation, over periods of time that range from a few minutes up to hours. This periodic effect has not been observed in static towers indicating that the effect of rotation is playing a critical role. The repeated discharges can occur tens of kilometers away from electrically active thunderstorm areas and may or may not precede a fully developed upward lightning discharge from the turbine. Similar to rockets used for triggering lightning, the fast movement of the blade tip plays an important role on the initiation of the discharge. The movement of the rotor blades allows the tip to "runaway" from the generated corona charge. The second observation is an uncommon upward/downward flash triggered by a wind turbine. In that flash, a negative upward leader was initiated from a wind turbine without preceding lightning activity. The flash produced a negative cloud-to-ground stroke several kilometers from the initiation point. The third observation corresponds to a high-speed video record showing simultaneous upward positive leaders from a group of wind turbines triggered by a preceding intracloud flash. The fact that multiple leaders develop simultaneously indicates a poor shielding effect among them. All these observations provide some special features on the initiation of lightning by nonstatic and complex tall structures.

Teleseismic studies indicate existence of deep magma chamber below Yellowstone National Park

USGS Publications Warehouse

Iyer, H.M.

1974-01-01

The secrets of Yellowstone National Park's spectacular geysers and other hot water and steam phenomena are being explored by the U.S Geological Survey with the aid of distant earthquakes (teleseisms). For some time geologists have known that the remarkable array of steam and hot water displays, for which the park is internationally famous, is associated with intense volcanic activity that occurred in the reigon during the last 2 million years. The most recent volcanic eruption took place about 600,000 years ago creating a large caldera, or crater, 75 kilometers long and 50 kilometers wide. This caldera occupies most of the central part of the present-day park. geologists knew from studies of the surface geology that the volcanic activity which creates the present caldera was caused the present caldera was caused by a large body of magma, a mixture composed of molten rock, hot liquids, and gases, that had forced its way from the deep interior of the Earth into the upper mantle and crust below the Yellowstone area. The dimensions and depth below the surface of this magma body were largely unknown, however, because there was no way to "see" deep below the surface. A tool was needed that would enable earth scientists to look into the curst and upper mantle of the Earth. Such a tool became availabe with the installation by the Geological Survey of a network of seismograph stations in the park. 

Seismo-acoustic analysis of the near quarry blasts using Plostina small aperture array

NASA Astrophysics Data System (ADS)

Ghica, Daniela; Stancu, Iulian; Ionescu, Constantin

2013-04-01

Seismic and acoustic signals are important to recognize different type of industrial blasting sources in order to discriminate between them and natural earthquakes. We have analyzed the seismic events listed in the Romanian catalogue (Romplus) for the time interval between 2011 and 2012, and occurred in the Dobrogea region, in order to determine detection seismo-acoustic signals of quarry blasts by Plostina array stations. Dobrogea is known as a seismic region characterized by crustal earthquakes with low magnitudes; at the same time, over 40 quarry mines are located in the area, being sources of blasts recorded both with the seismic and infrasound sensors of the Romanian Seismic Network. Plostina seismo-acoustic array, deployed in the central part of Romania, consists of 7 seismic sites (3C broad-band instruments and accelerometers) collocated with 7 infrasound instruments. The array is particularly used for the seismic monitoring of the local and regional events, as well as for the detection of infrasonic signals produced by various sources. Considering the characteristics of the infrasound sensors (frequency range, dynamic, sensibility), the array proved its efficiency in observing the signals produced by explosions, mine explosion and quarry blasts. The quarry mines included for this study cover distances of two hundreds of kilometers from the station and routinely generate explosions that are detected as seismic and infrasonic signals with Plostina array. The combined seismo-acoustic analysis uses two types of detectors for signal identification: one, applied for the seismic signal identification, is based on array processing techniques (beamforming and frequency-wave number analysis), while the other one, which is used for infrasound detection and characterization, is the automatic detector DFX-PMCC (Progressive Multi-Channel Correlation Method). Infrasonic waves generated by quarry blasts have frequencies ranging from 0.05 Hz up to at least 6 Hz and amplitudes below 5 Pa. Seismic data analysis shows that the frequency range of the signals are above 2 Hz. Surface explosions such as quarry blasts are useful sources for checking detection and location efficiency, when seismic measurements are added. The process is crucial for discrimination purposes and for establishing of a set of ground-truth infrasound events. Ground truth information plays a key role in the interpretation of infrasound signals, by including near-field observations from industrial blasts.

VizieR Online Data Catalog: GRB list (1990-2014) (Ruggeri+, 2016)

NASA Astrophysics Data System (ADS)

Ruggeri, A. C.; Capozziello, S.

2017-08-01

To investigate the potentialities of the SKA related to the GRB detections in radio band, we need a good instrumental probability, so that we present here a useful repository of all GRBs taken by several catalogues. The thesis is available at: http://www.fedoa.unina.it/10538/1/RuggeriAlanCosimo_27.pdf The paper is available at: http://adsabs.harvard.edu/abs/2016Ap%26SS.361..279R (1 data file).

Constraining warm dark matter with 21 cm line fluctuations due to minihalos

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sekiguchi, Toyokazu; Tashiro, Hiroyuki, E-mail: toyokazu.sekiguchi@helsinki.fi, E-mail: hiroyuki.tashiro@nagoya-u.jp

2014-08-01

Warm dark matter (WDM) with mass m{sub WDM} = O(1) keV has long been discussed as a promising solution for discrepancies between cosmic structures observed at small scales and predications of the concordance CDM model. Though several cosmological observations such as the Lyman-alpha forest have already begun to constrain the range of m{sub WDM}, WDM is yet to be fully excluded as a solution for these so-called small-scale problems. In this paper, we study 21 cm line fluctuations from minihalos in a WDM model and evaluate constraints on m{sub WDM} for future cosmological 21 cm surveys, such as SKA andmore » FFTT. We show that, since WDM with mass m{sub WDM}∼>10 keV decreases the abundance of minihalos by suppressing the matter power spectrum on small scales via free-streaming, such WDM can significantly affect the resultant 21 cm line fluctuations from minihalos. We find that if the 21 cm signal from minihalos can be observed above z≥5, SKA and FFTT can give lower bounds m{sub WDM}∼>24 keV and 31 keV, respectively, which are tighter than the current constraint. These future 21 cm surveys might be able to rule out a WDM model as a solution of small-scale problems.« less

Deep in shadows, deep in time: the oldest mesophotic coral ecosystems from the Devonian of the Holy Cross Mountains (Poland)

NASA Astrophysics Data System (ADS)

Zapalski, Mikołaj K.; Wrzołek, Tomasz; Skompski, Stanisław; Berkowski, Błażej

2017-09-01

Recent mesophotic coral ecosystems (MCE) occur at depths between 30 and 150 m and are characterized by dominance of platy corals. Such morphology is an effect of specific adaptation to efficient light harvesting. Here, we describe and analyze platy coral assemblages from two Middle Devonian localities in the Holy Cross Mountains (Poland) that during this time were located on the southern shelf of Laurussia at tropical latitudes. The Eifelian argillaceous sediments of Skały are dominated by platy and encrusting tabulate corals ( Roseoporella, Platyaxum and Alveolites). Coeval faunas from the shallow-water parts of the Holy Cross Mountains basin display bulbous and branching morphology, thus indicating a Paleozoic coral zonation similar to that known in the Recent. Hence, the Skały site seems to be the oldest known MCE (ca. 390 Ma). A Givetian biostrome from Laskowa Quarry is a second example dominated by platy corals, with abundant branching forms; this site can be recognized as another Devonian MCE. Frondescent Platyaxum, common at both sites, had a growth habit similar to that of Recent Leptoseris, Mycedium or Pavona. Platy morphology is photoadaptive and may evidence photosymbiosis in tabulate ( Alveolites, Roseoporella, Platyaxum) and rugose corals ( Phillipsastrea). Furthermore, it may serve as a tool for recognition of the lower euphotic zone in the fossil record.

Zróżnicowanie warunków topoklimatycznych w wyższych partiach Bieszczadów Zachodnich w wybranych dniach czerwca 2002 roku

NASA Astrophysics Data System (ADS)

Wereski, Sylwester

2008-01-01

In this paper the author presented characteristics of topoclimatic conditions in the higher parts of the Bieszczady Mountains in selected days of June 2002. The data used for this study come from three measurement points. Two of them were located at mountain tops: Połonina Wetlińska and Tarnica and the third measurement point was located in a mountain valley at Wołosate village. The range of measurements was: air temperature, relative humidity, wind direction and speed and cloudiness. The measurements at Połonina Wetlińska and Tarnica were made every hour from 6 till 18 UTC and every three hours from 18 till 6 UTC, whereas at Wołosate village the measurements were made three times a day: at 6, 12 and 18 UTC. During the day the air temperature was lower at the mountain tops than in the mountain valley. On the night of the 26th June inversion of temperature was recorded in the mountain valley. Wind direction was consistent with the direction of air masses at mountain tops and with the orientation of valley axis in Wołosate village. On the 28th June the wind reached the speed of twenty meters per second. It was connected with foehn effect which occurred that day.

Near-surface velocities and attenuation at two boreholes near Anza, California, from logging data

USGS Publications Warehouse

Fletcher, Joe B.; Fumal, T.; Hsi-Ping, Liu; Carroll, L.C.

1990-01-01

To investigate near-surface site effects in granite rock, we drilled 300-m deep boreholes at two sites which are collocated with stations from the digital array at Anza, California. Significant motion perpendicular to the polarizations of the first shear-wave arrival was recorded within a few meters of the surface. Apparently, the rock structure is sufficiently complicated that body waves are being converted (SH to SV at oblique incidence) very close to the surface. The presence of these elliptical particle motions within a mere few m of the pure shear-wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not, by itself, a good method for detecting shear-wave splitting within the upper few tens of kilometers of the earth's crust. -from Authors

KSC-97PC1079

NASA Image and Video Library

1997-07-22

Applied Physics Laboratory Engineer Cliff Willey (kneeling) and Engineering Assistant Jim Hutcheson from Johns Hopkins University install solar array panels on the Advanced Composition Explorer (ACE) in KSC’s Spacecraft Assembly and Encapsulation Facility-II. Scheduled for launch on a Delta II rocket from Cape Canaveral Air Station on Aug. 25, ACE will study low-energy particles of solar origin and high-energy galactic particles for a better understanding of the formation and evolution of the solar system as well as the astrophysical processes involved. The ACE observatory will be placed into an orbit almost a million miles (1.5 million kilometers) away from the Earth, about 1/100 the distance from the Earth to the Sun. The collecting power of instrumentation aboard ACE is at least 100 times more sensitive than anything previously flown to collect similar data by NASA

Intersecting Channels near Olympica Fossae

NASA Image and Video Library

2016-09-21

This complicated area contains various types of channels, pits and fractures. We can determine the relative ages of the pits and channels based on which features cross-cut others. Older channels appear smooth-edged and shallow. Younger channels and pits are deeper and more sharp-edged, as well as less sinuous than the shallower channels. What caused this array of various channels and intersecting pits? This region is covered in vast lava flows. The collapse pits here may be collapsed lava tubes or where overlying rock "drained" into voids created by extensional faulting. The older smoother channel that seems to source from this region may have carried an outflow of groundwater. It continues on for over 100 kilometers (62 miles). The orientation and shapes of these features make an interesting geological puzzle. http://photojournal.jpl.nasa.gov/catalog/PIA21066

Modular telerobot control system for accident response

NASA Astrophysics Data System (ADS)

Anderson, Richard J. M.; Shirey, David L.

1999-08-01

The Accident Response Mobile Manipulator System (ARMMS) is a teleoperated emergency response vehicle that deploys two hydraulic manipulators, five cameras, and an array of sensors to the scene of an incident. It is operated from a remote base station that can be situated up to four kilometers away from the site. Recently, a modular telerobot control architecture called SMART was applied to ARMMS to improve the precision, safety, and operability of the manipulators on board. Using SMART, a prototype manipulator control system was developed in a couple of days, and an integrated working system was demonstrated within a couple of months. New capabilities such as camera-frame teleoperation, autonomous tool changeout and dual manipulator control have been incorporated. The final system incorporates twenty-two separate modules and implements seven different behavior modes. This paper describes the integration of SMART into the ARMMS system.

TeV electron measurement with CREST experiment

NASA Astrophysics Data System (ADS)

Park, Nahee; Anderson, T.; Bower, C.; Coutu, S.; Gennaro, J.; Geske, M.; Muller, D.; Musser, J.; Nutter, S.

CREST, the Cosmic Ray Electron Synchrotron Telescope is a balloon-borne experiment de-signed to measure the spectrum of multi-TeV electrons by the detection of the x-ray synchrotron photons generated in the magnetic field of the Earth. Electrons in the TeV range are expected to reflect the properties of local sources because fluxes from remote locations are suppressed by radiative losses during propagation. Since CREST needs to intersect only a portion of the kilometers-long trail of photons generated by the high-energy electron, the method yields a larger effective area than the physical size of the detector, boosting detection areas. The in-strument is composed of an array of 1024 BaF2 crystals and a set of scintillating veto counters. A long duration balloon flight in Antarctica is currently planned for the 2010-11 season.

Structure of the atmosphere of Venus up to 110 kilometers: Preliminary results from the four Pioneer Venus entry probes

USGS Publications Warehouse

Seiff, A.; Kirk, D.B.; Sommer, S.C.; Young, R.E.; Blanchard, R.C.; Juergens, D.W.; Lepetich, J.E.; Intrieri, P.F.; Findlay, J.T.; Derr, J.S.

1979-01-01

The four Pioneer Venus entry probes transmitted data of good quality on the structure of the atmosphere below the clouds. Contrast of the structure below an altitude of 50 kilometers at four widely separated locations was found to be no more than a few degrees Kelvin, with slightly warmer temperatures at 30?? south latitude than at 5?? or 60?? north. The atmosphere was stably stratified above 15 or 20 kilometers, indicating that the near-adiabatic state is maintained by the general circulation. The profiles move from near-adiabatic toward radiative equilibrium at altitudes above 40 kilometers. There appears to be a region of vertical convection above the dense cloud deck, which lies at 47.5 to 49 kilometers and at temperature levels near 360 K. The atmosphere is nearly isothermal around 100 kilometers (175 to 180 K) and appears to exhibit a sizable temperature wave between 60 and 70 kilometers. This is where the 4-day wind is believed to occur. The temperature wave may be related to some of the wavelike phenomena seen in Mariner 10 ultraviolet photographs. Copyright ?? 1979 AAAS.

First evidence of the Ellesmerian metamorphism on Svalbard

NASA Astrophysics Data System (ADS)

Kośmińska, Karolina; Majka, Jarosław; Manecki, Maciej; Schneider, David A.

2016-04-01

The Ellesmerian fold-and-thrust belt is exposed in the High Arctic from Ellesmere Island in the east, through North Greenland, to Svalbard in the west (e.g. Piepjohn et al., 2015). It developed during Late Devonian - Early Carboniferous, and overprinted older (mainly Caledonian) structures. It is thought that this fold-and-thrust belt was formed due to collision of the Pearya Terrane and Svalbard with the Franklinian Basin of Laurentia. Traditionally, the Ellesmerian fold-and-thrust belt comprises a passive continental margin affected by foreland deformation processes, but the exact larger scale tectonic context of this belt is disputable. It is partly because the Eocene Eurekan deformation superimposed significantly the Ellesmerian structures, thus making the reconstruction of the pre-Eurekan history very difficult. Here we present for the first time evidence for Ellesmerian metamorphism within the crystalline basement of Svalbard. These rocks are exposed in the Pinkie unit on Prins Karls Forland (W-Svalbard), which exhibits tectonic contacts with the overlying sequences. The Pinkie unit is mainly composed of strongly deformed lithologies such as laminated quartzites, siliciclastic rocks and garnet-bearing mica schists. Detrital zircon dating yielded ages as young as Neoproterozoic (0.95-1.05 Ga), thus the Pinkie unit is considered to be Neoproterozoic (Kośmińska et al., 2015a). The M1 assemblages and D1 structures are affected by D2 mylonitization (cf. Faehnrich et al., 2016, this meeting). Petrological characterization and Th-U-total Pb chemical monazite dating have been performed on the Pinkie metapelites. These rocks exhibit an apparent inverted Barrovian metamorphic sequence, within which three metamorphic zones have been distinguished: garnet+staurolite+muscovite+biotite, garnet+staurolite+kyanite+muscovite+biotite, garnet+kyanite+muscovite+biotite. The P-T estimates using the QuiG barometry coupled with thermodynamic modelling revealed that the metapelites were formed under amphibolite facies conditions at c. 7-9 kbar and 550-650 °C (Kośmińska et al., 2015b). Monazite dating was performed on samples from these three metamorphic zones. The chemical zonation of monazite allows the identification of several monazite populations, which likely developed during different stages of Barrovian metamorphism. The geochronology demonstrate protracted monazite growth from the early prograde stage at c. 370 Ma to the peak conditions at c. 355 Ma. Thus it is evident that the Ellesmerian event was not limited to the relatively cold deformation as previously thought. The amphibolite facies metamorphism of c. 370-355 Ma that was documented in our study sheds new light on understanding of the character of this tectonothermal event. This project is financed by NCN research project No 2013/11/N/ST10/00357 and partially funded by AGH research grant no 11.11.140.319. References: Faehnrich et al., 2016. A tectonic window into the crystalline basement of Prins Karls Forland, Spitsbergen. EGU General Assembly 2016. Kośmińska et al., 2015b. Metamorphic evolution of the Pinkie unit metapelites from Svalbard (High Arctic): P-T-t study including Quartz-in-garnet barometry (QuiG). GSA 2015: Annual Meeting, Baltimore. Kośmińska et al., 2015a. Detrital zircon U-Pb geochronology of metasediments from southwestern Svalbard's Caledonian Province. EGU General Assembly 2015. Piepjohn et al., 2015. Tectonic map of the Ellesmerian and Eurekan deformation belts on Svalbard, North Greenland, and the Queen Elizabeth Islands (Canadian Arctic). Arktos, DOI 10.1007/s41063-015-0015-7.

Prospection for Copper Mineralization with Contribution of Remote Sensing, Geochemical and Mineralographical Data in Abhar 1:100,000 Sheet, NW Iran / Poszukiwania ZASOBÓW Rud Miedzi Z Zastosowaniem Zdalnych Technik WYKORZYSTUJĄCYCH Dane Geochemiczne i Mineralogiczne W POKŁADZIE Geologicznym Abhar 1:100,000 W PÓŁNOCNO-ZACHODNIM Iranie

NASA Astrophysics Data System (ADS)

Nouri, Reza; Jafari, Mohammadreza; Arian, Mehran; Feizi, Faranak; Afzal, Peyman

2013-12-01

Abhar 1:100,000 sheet is located within the Cenozoic Tarom volcano-plutonic belt, NW Iran. The present study is based on the integration of remote sensing techniques on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), geochemical data analysis consisting of stream sediment and lithogeochemical samples, within geological field observations and mineralographical studies to identify Cu prospect. On ASTER data; using a number of selected methods including band ratio, Least Square Fit (LS-Fit) and Minimum Noise Fraction (MNF) distinguished alternation zones. These methods revealed that three types of alterations: argillic, phyllic, and iron oxide zones occurring at the NE and SE of Abhar sheet, while the propylitic and silica zones are developed in NW and SW of the studied area. Lineaments were identified by aid of false color composite, high pass filters and hill-shade DEM techniques that two NW-SE and NE-SW major trends were determined. Geochemical anomalies were separated by number-size (N-S) method. Interpretation of N-S log-log plots of Cu in the area may be a result of the three steps of enrichment, i.e., mineralization and later dispersions. Field checks and Mineralgraphical studies also confirm the existence of suitable copper mineralization. Pokład geologiczny Abhar 1:100,100 zlokalizowany jest w obrębie kenozoicznego pasa skał magmowych pochodzenia wulkanicznego Tarom w północno-zachodnim Iranie. W pracy przedstawiono połączenie zastosowań metod zdalnych wykorzystujących technologię ASTER (Advanced Spaceborne Thermal Emission and Refelection Radiometer), analizę danych geochemicznych zebranych na podstawie osadów dennych ze strumieni oraz próbek skał w obrębie pola obserwacji a także danych mineralogicznych w celu rozpoznania skupisk rud miedzi. Na podstawie danych uzyskanych przy użyciu technologiiASTER i poddanych obróbce przy użyciu różnorodnych technik: badanie układu pasm, dopasowanie metodę najmniejszych kwadratów oraz minimalny współczynnik szumów, rozróżniono strefy przeobrażeń skał. Metody te pozwoliły na wykrycie trzech typów skał przeobrażonych: gliniaste, łupki ilasto-mikowe oraz strefy występowania tlenków żelaza występujące na północno-wschodnich (NE) i południowo- -zachodnich (NW) krańcach pasa Abhar. W części północno-zachodnie (NW) i południowo-zachodniej (SW) badanego obszaru stwierdzono występowanie stref propilitu i krzemianów. Lineacje wykryto przy pomocy metody badania zakresu barw, filtrów wysoko-przepustowych, techniki określania wysokości, na tej podstawie określono dwa główne trendy: NW-SE oraz NE-SW. Anomalie geologiczne wydzielono za pomocą metody N-S (liczba-wymiar). Interpretacja wykresów N-S wykonanych w skali logarytmicznej wykazała, że zaobserwowany układ może być wynikiem trzech etapów wzbogacania: mineralizacji i późniejszego rozproszenia. Badania terenowe oraz analizy mineralograficzne potwierdzają obecność odpowiednio zmineralizowanej miedzi.

Summary of Migration and Survival Data from Radio-Tagged Juvenile Coho Salmon in the Trinity River, Northern California, 2008

USGS Publications Warehouse

Beeman, John W.; Hansel, Hal; Juhnke, Steve; Stutzer, Greg

2009-01-01

The survival of hatchery-origin juvenile coho salmon from the Trinity River Hatchery was estimated as they migrated seaward through the Trinity and Klamath Rivers. The purpose of the study was to collect data for comparison to a similar study in the Klamath River and provide data to the Trinity River Restoration Program. A total of 200 fish fitted with radio transmitters were released into the Trinity River near the hatchery (river kilometer 252 from the mouth of the Klamath River) biweekly from March 19 to May 28, 2008. Fish from the earliest release groups took longer to pass the first detection site 10 kilometers downstream of the hatchery than fish from the later release groups, but travel times between subsequent sites were often similar among the release groups. The travel times of individuals through the 239 kilometer study area ranged from 15.5 to 84.6 days with a median of 43.3 days. The data and models did not support differences in survival among release groups, but did support differences among river reaches. The probability of survival in the first 53 kilometers was lower than in the reaches farther downstream, which is similar to trends in juvenile coho salmon in the Klamath River. The lowest estimated survival in this study was in the first 10 kilometers from release in the Trinity River (0.676 SE 0.036) and the highest estimated survival was in the final 20 kilometer reach in the Klamath River (0.987 SE 0.013). Estimated survivals of radio-tagged juvenile coho salmon from release to Klamath River kilometer 33 were 0.639 per 100 kilometers for Trinity River fish and 0.721 per 100 kilometers for Klamath River fish.

Looking Up to the Giant

NASA Image and Video Library

2015-08-03

Thanks to the illumination angle, Mimas (right) and Dione (left) appear to be staring up at a giant Saturn looming in the background. Although certainly large enough to be noticeable, moons like Mimas (246 miles or 396 kilometers across) and Dione (698 miles or 1123 kilometers across) are tiny compared to Saturn (75,400 miles or 120,700 kilometers across). Even the enormous moon Titan (3,200 miles or 5,150 kilometers across) is dwarfed by the giant planet. This view looks toward the unilluminated side of the rings from about one degree of the ring plane. The image was taken with the Cassini spacecraft wide-angle camera on May 27, 2015 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 728 nanometers. The view was obtained at a distance of approximately 634,000 miles (one million kilometers) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 85 degrees. Image scale is 38 miles (61 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18331

Moon Patrol

NASA Image and Video Library

2007-12-24

This colorful view, taken from edge-on with the ringplane, contains four of Saturn's attendant moons. Tethys (1,071 kilometers, 665 miles across) is seen against the black sky to the left of the gas giant's limb. Brilliant Enceladus (505 kilometers, 314 miles across) sits against the planet near right. Irregular Hyperion (280 kilometers, 174 miles across) is at the bottom of the image, near left. Much smaller Epimetheus (116 kilometers, 72 miles across) is a speck below the rings directly between Tethys and Enceladus. Epimetheus casts an equally tiny shadow onto the blue northern hemisphere, just above the thin shadow of the F ring. Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were acquired with the Cassini spacecraft wide-angle camera on July 24, 2007 at a distance of approximately 2 million kilometers (1.2 million miles) from Saturn. Image scale is 116 kilometers (72 miles) per pixel on Saturn. http://photojournal.jpl.nasa.gov/catalog/PIA08394

Titan Accent Mark

NASA Image and Video Library

2015-10-05

A coincidence of viewing angle makes Pandora appear to be hovering over Titan, almost like an accent mark. Little Pandora is much closer to Cassini than hazy Titan in this view. (Titan is nearly three times farther away.) Even so, Titan (3,200 miles or 5,150 kilometers across) dwarfs Pandora (50 miles or 81 kilometers across). This gives us some sense of the diversity in sizes, and shapes, of Saturn's many moons. North on Titan is up and rotated 19 degrees to the right. The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on July 4, 2015. The view was acquired at a distance of approximately 1.2 million miles (1.9 million kilometers) from Titan. Image scale is 7 miles (12 kilometers) per pixel on Titan. Pandora is at a distance of 436,000 miles (698,000 kilometers) away from the spacecraft. The scale on Pandora is about 3 miles (4 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18338

Localization of short-range acoustic and seismic wideband sources: Algorithms and experiments

NASA Astrophysics Data System (ADS)

Stafsudd, J. Z.; Asgari, S.; Hudson, R.; Yao, K.; Taciroglu, E.

2008-04-01

We consider the determination of the location (source localization) of a disturbance source which emits acoustic and/or seismic signals. We devise an enhanced approximate maximum-likelihood (AML) algorithm to process data collected at acoustic sensors (microphones) belonging to an array of, non-collocated but otherwise identical, sensors. The approximate maximum-likelihood algorithm exploits the time-delay-of-arrival of acoustic signals at different sensors, and yields the source location. For processing the seismic signals, we investigate two distinct algorithms, both of which process data collected at a single measurement station comprising a triaxial accelerometer, to determine direction-of-arrival. The direction-of-arrivals determined at each sensor station are then combined using a weighted least-squares approach for source localization. The first of the direction-of-arrival estimation algorithms is based on the spectral decomposition of the covariance matrix, while the second is based on surface wave analysis. Both of the seismic source localization algorithms have their roots in seismology; and covariance matrix analysis had been successfully employed in applications where the source and the sensors (array) are typically separated by planetary distances (i.e., hundreds to thousands of kilometers). Here, we focus on very-short distances (e.g., less than one hundred meters) instead, with an outlook to applications in multi-modal surveillance, including target detection, tracking, and zone intrusion. We demonstrate the utility of the aforementioned algorithms through a series of open-field tests wherein we successfully localize wideband acoustic and/or seismic sources. We also investigate a basic strategy for fusion of results yielded by acoustic and seismic arrays.

Camera Development for the Cherenkov Telescope Array

NASA Astrophysics Data System (ADS)

Moncada, Roberto Jose

2017-01-01

With the Cherenkov Telescope Array (CTA), the very-high-energy gamma-ray universe, between 30 GeV and 300 TeV, will be probed at an unprecedented resolution, allowing deeper studies of known gamma-ray emitters and the possible discovery of new ones. This exciting project could also confirm the particle nature of dark matter by looking for the gamma rays produced by self-annihilating weakly interacting massive particles (WIMPs). The telescopes will use the imaging atmospheric Cherenkov technique (IACT) to record Cherenkov photons that are produced by the gamma-ray induced extensive air shower. One telescope design features dual-mirror Schwarzschild-Couder (SC) optics that allows the light to be finely focused on the high-resolution silicon photomultipliers of the camera modules starting from a 9.5-meter primary mirror. Each camera module will consist of a focal plane module and front-end electronics, and will have four TeV Array Readout with GSa/s Sampling and Event Trigger (TARGET) chips, giving them 64 parallel input channels. The TARGET chip has a self-trigger functionality for readout that can be used in higher logic across camera modules as well as across individual telescopes, which will each have 177 camera modules. There will be two sites, one in the northern and the other in the southern hemisphere, for full sky coverage, each spanning at least one square kilometer. A prototype SC telescope is currently under construction at the Fred Lawrence Whipple Observatory in Arizona. This work was supported by the National Science Foundation's REU program through NSF award AST-1560016.

High-Energy Particle Showers Observed at Ground Level in Coincidence with Downward Lightning Leaders at the Telescope Array Observatory

NASA Astrophysics Data System (ADS)

Belz, John; Abbasi, Rasha; Le Von, Ryan; Krehbiel, Paul; Remington, Jackson; Rison, William

Terrestrial Gamma Ray Flashes (TGFs) detected by satellite observations have been shown to be generated by upward propagating negative leaders at altitudes of about 10 to 12 km above Mean Sea Level (MSL), and have durations ranging between a few hundred microseconds and a few milliseconds. The Telescope Array Cosmic Ray observatory, designed to observe air showers induced by ultra high energy cosmic rays, includes a surface scintillator detector (SD) covering approximately 700 square kilometers on a 1.2 km grid. Following the observation of anomalous SD triggers correlated with local lightning activity, a Lightning Mapping Array (LMA) and slow electric field antenna were installed at the TA site in order to characterize the lightning associated with these anomalous triggers. In this talk, we present evidence that the anomalous triggers are produced during the initial breakdown phase of fast, downward propagating, negative leaders above the detectors which produced the triggers. The durations of the high energy radiation are a few hundred microseconds, similar to satellite observations of TGFs. The triggers were produced within a few hundred microseconds of the initiation of the leaders, when the leaders were at an altitude of about 3 to 4 km MSL. The TA scintillation detectors are not optimized for gamma ray detection, however we present the results of simulations demonstrating that the fluxes observed are consistent with this picture. We conclude that the anomalous triggers observed by TA are clearly due to high energy radiation produced by the fast downward propagating negative leaders, and are probably downward-directed TGFs.

Calibration of LOFAR data on the cloud

NASA Astrophysics Data System (ADS)

Sabater, J.; Sánchez-Expósito, S.; Best, P.; Garrido, J.; Verdes-Montenegro, L.; Lezzi, D.

2017-04-01

New scientific instruments are starting to generate an unprecedented amount of data. The Low Frequency Array (LOFAR), one of the Square Kilometre Array (SKA) pathfinders, is already producing data on a petabyte scale. The calibration of these data presents a huge challenge for final users: (a) extensive storage and computing resources are required; (b) the installation and maintenance of the software required for the processing is not trivial; and (c) the requirements of calibration pipelines, which are experimental and under development, are quickly evolving. After encountering some limitations in classical infrastructures like dedicated clusters, we investigated the viability of cloud infrastructures as a solution. We found that the installation and operation of LOFAR data calibration pipelines is not only possible, but can also be efficient in cloud infrastructures. The main advantages were: (1) the ease of software installation and maintenance, and the availability of standard APIs and tools, widely used in the industry; this reduces the requirement for significant manual intervention, which can have a highly negative impact in some infrastructures; (2) the flexibility to adapt the infrastructure to the needs of the problem, especially as those demands change over time; (3) the on-demand consumption of (shared) resources. We found that a critical factor (also in other infrastructures) is the availability of scratch storage areas of an appropriate size. We found no significant impediments associated with the speed of data transfer, the use of virtualization, the use of external block storage, or the memory available (provided a minimum threshold is reached). Finally, we considered the cost-effectiveness of a commercial cloud like Amazon Web Services. While a cloud solution is more expensive than the operation of a large, fully-utilized cluster completely dedicated to LOFAR data reduction, we found that its costs are competitive if the number of datasets to be analysed is not high, or if the costs of maintaining a system capable of calibrating LOFAR data become high. Coupled with the advantages discussed above, this suggests that a cloud infrastructure may be favourable for many users.

East Part of Sapas Mons with Flooded Crater

NASA Technical Reports Server (NTRS)

1991-01-01

This Magellan image centered near 9.6 degrees north latitude, 189.5 degrees east longitude of an area 140 kilometers (87 miles) by 110 kilometers (68 miles) covers part of the eastern flank of the volcano Sapas Mons on the western edge of Atla Regio. The bright lobate features along the southern and the western part of the image, oriented in northeast to southwest directions, are lava flows that are rough at the 12.6 centimeter wavelength of the radar. These flows range in width from 5 kilometers to 25 kilometers (3 to 16 miles) with lengths of 50 kilometers to 100 kilometers (31 to 62 miles), extending off the area shown here. Additional radar-dark (smooth) flows are also present. The radar-bright linear structures in the northwest part of the image are interpreted to be faults and fractures possibly associated with the emplacement of magma in the subsurface. Located near the center of the image is a 20 kilometer (12 mile) diameter impact crater. This crater is superimposed on a northeast/southwest trending fracture while the southern part of the crater's ejecta blanket is covered by a 6 kilometer (4 mile) wide radar-bright lava flow. These relations indicate that the crater post dates an episode of fracturing and is older than the lava flows covering its southern edge. This is one of only a few places on Venus in which an impact crater is seen to be covered by volcanic deposits.

Wide Field Radio Transient Surveys

NASA Astrophysics Data System (ADS)

Bower, Geoffrey

2011-04-01

The time domain of the radio wavelength sky has been only sparsely explored. Nevertheless, serendipitous discovery and results from limited surveys indicate that there is much to be found on timescales from nanoseconds to years and at wavelengths from meters to millimeters. These observations have revealed unexpected phenomena such as rotating radio transients and coherent pulses from brown dwarfs. Additionally, archival studies have revealed an unknown class of radio transients without radio, optical, or high-energy hosts. The new generation of centimeter-wave radio telescopes such as the Allen Telescope Array (ATA) will exploit wide fields of view and flexible digital signal processing to systematically explore radio transient parameter space, as well as lay the scientific and technical foundation for the Square Kilometer Array. Known unknowns that will be the target of future transient surveys include orphan gamma-ray burst afterglows, radio supernovae, tidally-disrupted stars, flare stars, and magnetars. While probing the variable sky, these surveys will also provide unprecedented information on the static radio sky. I will present results from three large ATA surveys (the Fly's Eye survey, the ATA Twenty CM Survey (ATATS), and the Pi GHz Survey (PiGSS)) and several small ATA transient searches. Finally, I will discuss the landscape and opportunities for future instruments at centimeter wavelengths.

RADIO TRANSIENTS FROM ACCRETION-INDUCED COLLAPSE OF WHITE DWARFS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moriya, Takashi J., E-mail: takashi.moriya@nao.ac.jp

2016-10-20

We investigate observational properties of accretion-induced collapse (AIC) of white dwarfs (WDs) in radio frequencies. If AIC is triggered by accretion from a companion star, a dense circumstellar medium can be formed around the progenitor system. Then, the ejecta from AIC collide with the dense circumstellar medium, creating a strong shock. The strong shock can produce synchrotron emission that can be observed in radio frequencies. Even if AIC occurs as a result of WD mergers, we argue that AIC may cause fast radio bursts (FRBs) if a certain condition is satisfied. If AIC forms neutron stars (NSs) that are somore » massive that rotation is required to support themselves (i.e., supramassive NSs), the supramassive NSs may immediately lose their rotational energy by the r-mode instability and collapse to black holes. If the collapsing supramassive NSs are strongly magnetized, they may emit FRBs, as previously proposed. The AIC radio transients from single-degenerate systems may be detected in future radio transient surveys like the Very Large Array Sky Survey or the Square Kilometer Array transient survey. Because AIC has been proposed as a source of gravitational waves (GWs), GWs from AIC may be accompanied by radio-bright transients that can be used to confirm the AIC origin of observed GWs.« less

In situ calibration of atmospheric-infrasound sensors including the effects of wind-noise-reduction pipe systems.

PubMed

Gabrielson, Thomas B

2011-09-01

A worldwide network of more than 40 infrasound monitoring stations has been established as part of the effort to ensure compliance with the Comprehensive Nuclear Test Ban Treaty. Each station has four to eight individual infrasound elements in a kilometer-scale array for detection and bearing determination of acoustic events. The frequency range of interest covers a three-decade range-roughly from 0.01 to 10 Hz. A typical infrasound array element consists of a receiving transducer connected to a multiple-inlet pipe network to average spatially over the short-wavelength turbulence-associated "wind noise." Although the frequency response of the transducer itself may be known, the wind-noise reduction system modifies that response. In order to understand the system's impact on detection and identification of acoustical events, the overall frequency response must be determined. This paper describes a technique for measuring the absolute magnitude and phase of the frequency response of an infrasound element including the wind-noise-reduction piping by comparison calibration using ambient noise and a reference-microphone system. Measured coherence between the reference and the infrasound element and the consistency between the magnitude and the phase provide quality checks on the process. © 2011 Acoustical Society of America

Jupiter's Moons: Family Portrait

NASA Technical Reports Server (NTRS)

2007-01-01

This montage shows the best views of Jupiter's four large and diverse 'Galilean' satellites as seen by the Long Range Reconnaissance Imager (LORRI) on the New Horizons spacecraft during its flyby of Jupiter in late February 2007. The four moons are, from left to right: Io, Europa, Ganymede and Callisto. The images have been scaled to represent the true relative sizes of the four moons and are arranged in their order from Jupiter.

Io, 3,640 kilometers (2,260 miles) in diameter, was imaged at 03:50 Universal Time on February 28 from a range of 2.7 million kilometers (1.7 million miles). The original image scale was 13 kilometers per pixel, and the image is centered at Io coordinates 6 degrees south, 22 degrees west. Io is notable for its active volcanism, which New Horizons has studied extensively.

Europa, 3,120 kilometers (1,938 miles) in diameter, was imaged at 01:28 Universal Time on February 28 from a range of 3 million kilometers (1.8 million miles). The original image scale was 15 kilometers per pixel, and the image is centered at Europa coordinates 6 degrees south, 347 degrees west. Europa's smooth, icy surface likely conceals an ocean of liquid water. New Horizons obtained data on Europa's surface composition and imaged subtle surface features, and analysis of these data may provide new information about the ocean and the icy shell that covers it.

New Horizons spied Ganymede, 5,262 kilometers (3,268 miles) in diameter, at 10:01 Universal Time on February 27 from 3.5 million kilometers (2.2 million miles) away. The original scale was 17 kilometers per pixel, and the image is centered at Ganymede coordinates 6 degrees south, 38 degrees west. Ganymede, the largest moon in the solar system, has a dirty ice surface cut by fractures and peppered by impact craters. New Horizons' infrared observations may provide insight into the composition of the moon's surface and interior.

Callisto, 4,820 kilometers (2,995 miles) in diameter, was imaged at 03:50 Universal Time on February 28 from a range of 4.2 million kilometers (2.6 million miles). The original image scale was 21 kilometers per pixel, and the image is centered at Callisto coordinates 4 degrees south, 356 degrees west. Scientists are using the infrared spectra New Horizons gathered of Callisto's ancient, cratered surface to calibrate spectral analysis techniques that will help them to understand the surfaces of Pluto and its moon Charon when New Horizons passes them in 2015.

Reionization Models Classifier using 21cm Map Deep Learning

NASA Astrophysics Data System (ADS)

Hassan, Sultan; Liu, Adrian; Kohn, Saul; Aguirre, James E.; La Plante, Paul; Lidz, Adam

2018-05-01

Next-generation 21cm observations will enable imaging of reionization on very large scales. These images will contain more astrophysical and cosmological information than the power spectrum, and hence providing an alternative way to constrain the contribution of different reionizing sources populations to cosmic reionization. Using Convolutional Neural Networks, we present a simple network architecture that is sufficient to discriminate between Galaxy-dominated versus AGN-dominated models, even in the presence of simulated noise from different experiments such as the HERA and SKA.

Vector Antenna and Maximum Likelihood Imaging for Radio Astronomy

DTIC Science & Technology

2016-03-05

Maximum Likelihood Imaging for Radio Astronomy Mary Knapp1, Frank Robey2, Ryan Volz3, Frank Lind3, Alan Fenn2, Alex Morris2, Mark Silver2, Sarah Klein2...haystack.mit.edu Abstract1— Radio astronomy using frequencies less than ~100 MHz provides a window into non-thermal processes in objects ranging from planets...observational astronomy . Ground-based observatories including LOFAR [1], LWA [2], [3], MWA [4], and the proposed SKA-Low [5], [6] are improving access to

Calculation of (n,α) reaction cross sections by using some Skyrme force parameters for Potassium (41K) target nuclei

NASA Astrophysics Data System (ADS)

Tel, Eyyup; Sahan, Muhittin; Alkanli, Hasancan; Sahan, Halide; Yigit, Mustafa

2017-09-01

In this study, the (n,α) nuclear reaction cross section was calculated for 41K target nuclei for neutron and proton density parameters using SKa, SKb, SLy5, and SLy6 Skyrme force. Theoretical cross section for the (n,α) nuclear reaction was obtained using a formula constituted by Tel et al. (2008). Results are compared with experimental data from EXFOR. The calculated results from formula was found in a close agreement with experimental data.

Radar observations of asteroid 216 Kleopatra

NASA Technical Reports Server (NTRS)

Ostro, S.; Hudson, R.; Nolan, M.; Margot, J.; Scheeres, D.; Campbell, D.; Magri, C.; Giorgini, J.; Yeomans, D.

2000-01-01

Radar observations of the main-belt, M-class asteroid 216 Kleopatra reveal a dumbbell-shaped object with overall dimensions of 217 kilometers by 94 kilometers by 81 kilometers (+/-25%). The asteroid's surface properties are consistent with a regolith having a metallic composition and a porosity comparable to that of Lunar soil.

Indian Wells Valley FORGE Aeromagnetic Data

DOE Data Explorer

Doug Blankenship

1994-11-01

Aeromagnetic data was collected over the Indian Wells Valley, CA in November 1994. It consisted of 9,033 line-kilometers covering ~4,150 square kilometers, flown at a 250 meter drape with principal line spacing of 0.54 kilometers and 10% cross-lines. The principal orientation is N65E.

iss031e146306

NASA Image and Video Library

2012-06-27

ISS031-E-146306 (27 June 2012) --- An Expedition 31 crew member aboard the International Space Station, flying approximately 240 miles (386 kilometers) above Earth, captured this view of the Fontenelle fire on June 27, 2012. The fire, burning in Wyoming 18 miles (29 kilometers) west of Big Piney, was discovered on June 24. [Editor?s update --- By the morning of June 28, the fire had burned 25,000 acres (101 square kilometers). By July 6, the area burned had more than doubled to 57,324 acres (232 square kilometers), and the fire was 25 percent contained].

High altitude gust acceleration environment as experienced by a supersonic airplane

NASA Technical Reports Server (NTRS)

Ehernberger, L. J.; Love, B. J.

1975-01-01

High altitude turbulence experienced at supersonic speeds is described in terms of gust accelerations measured on the YF-12A airplane. The data were obtained during 90 flights at altitudes above 12.2 kilometers (40,000 feet). Subjective turbulence intensity ratings were obtained from air crew members. The air crew often rated given gust accelerations as being more intense during high altitude supersonic flight than during low altitude subsonic flight. The portion of flight distance in turbulence ranged from 6 percent to 8 percent at altitudes between 12.2 kilometers and 16.8 kilometers (40,000 feet and 55,000 feet) to less than 1 percent at altitudes above 18.3 kilometers (60,000 feet). The amount of turbulence varied with season, increasing by a factor of 3 or more from summer to winter. Given values of gust acceleration were less frequent, on the basis of distance traveled, for supersonic flight of the YF-12A airplane at altitudes above 12.2 kilometers (40,000 feet) than for subsonic flight of a jet passenger airplane at altitudes below 12.2 kilometers (40,000 feet). The median thickness of high altitude turbulence patches was less than 400 meters (1300 feet); the median length was less than 16 kilometers (10 miles). The distribution of the patch dimensions tended to be log normal.

Astronomy Landscape in Africa

NASA Astrophysics Data System (ADS)

Nemaungani, Takalani

2015-01-01

The vision for astronomy in Africa is embedded in the African Space Policy of the African Union in early 2014. The vision is about positioning Africa as an emerging hub for astronomy sciences and facilities. Africa recognized the need to take advantage of its natural resource, the geographical advantage of the clear southern skies and pristine sites for astronomy. The Pan African University (PAU) initiative also presents an opportunity as a post-graduate training and research network of university nodes in five regions of Africa and supported by the African Union. The Southern African node based in South Africa concentrates on space sciences which also includes astronomy. The PAU aims to provide the opportunity for advanced graduate training and postgraduate research to high-performing African students. Objectives also include promoting mobility of students and teachers and harmonizing programs and degrees.A number of astronomy initiatives have burgeoned in the Southern African region and these include the Southern Africa Largest Optical Telescope (SALT), HESS (High Energy Stereoscopic System), the SKA (Square Kilometre Array) and the AVN (African Very Long Baseline Interferometer Network). There is a growing appetite for astronomy sciences in Africa. In East Africa, the astronomy community is well organized and is growing - the East African Astronomical society (EAAS) held its successful fourth annual conference since 2010 on 30 June to 04 July 2014 at the University of Rwanda. Centred around the 'Role of Astronomy in Socio-Economic Transformation,' this conference aimed at strengthening capacity building in Astronomy, Astrophysics and Space Science in general, while providing a forum for astronomers from the region to train young and upcoming scientists.

Astronomy for teachers: A South African Perspective

NASA Astrophysics Data System (ADS)

de Witt, Aletha; West, Marion; Leeuw, Lerothodi; Gouws, Eldrie

2015-08-01

South Africa has nominated Astronomy as a “flagship science” and aims to be an international Astronomy hub through projects such as the Square Kilometre Array (SKA) and the South African Large Telescope (SALT). These projects open up career opportunities in maths, science and engineering and therefore offers a very real door for learners to enter into careers in science and technology through Astronomy. However, the Trends in International Mathematics and Science Survey (TIMSS), the Global Competitiveness Report (GCR) and Annual National Assessment (ANA) have highlighted that South Africa’s Science and Mathematics education is in a critical condition and that South African learners score amongst the worst in the world in both these subjects. In South Africa Astronomy is generally regarded as the worst taught and most avoided Natural Science knowledge strand, and most teachers that specialised in Natural Sciences, never covered Astronomy in their training.In order to address these issues a collaborative project between the University of South Africa (UNISA) and the Hartebeesthoek Radio Astronomy Observatory (HartRAO) was initiated, which aims to assist teachers to gain more knowledge and skills so that they can teach Astronomy with confidence. By collaborating we aim to ensure that the level of astronomy development will be raised in both South Africa and the rest of Africa.With the focus on Teaching and Learning, the research was conducted within a quantitative paradigm and 600 structured questionnaires were administered to Natural Science teachers in Public primary schools in Gauteng, South Africa. This paper reports the findings of this research and makes recommendations on how to assist teachers to teach Astronomy with confidence.

Collaboration and Development of Radio Astronomy in Australasia and South-Pacific Region: New Zealand Perspectives

NASA Astrophysics Data System (ADS)

Gulyaev, S.; Natusch, T.

2006-08-01

Radio telescopes in the Asia-Pacific region form a natural network for VLBI observations, similar to the very successful networks in North America (Network Users Group) and Europe (European VLBI Network). New Zealand's VLBI facility, which we are developing since 2005, has the potential to strengthen the Asian-Pacific VLBI network and its role in astronomy, geodesy and geoscience. It will positively influence regional and international activities in geoscience and geodesy that advance New Zealand's national interests. A self-contained radio astronomy system for VLBI, including a 1.658 GHz (centre frequency), 16 MHz bandwidth RF system (feed and downconversion system locked to a Rubidium maser and GPS clock), an 8-bit sampler/digitisation system, and a disk-based recording system built around a commodity PC was developed in New Zealand Centre for Radiophysics and Space Research. This was designed as a portable system for use on various radio telescopes. A number of Trans-Tasman tests has been conducted in 2005-2006 between the CRSR system installed on a 6 metre dish located in Auckland and the Australia Telescope Compact Array in Narrabri, Australia. This work has been successful, with fringes located from the recorded data and high resolution image of the quasar PKS1921-231 obtained. Experiments were recently conducted with Japan; new tests are planned with Korea and Fiji. Plans have been made to build a new 16.5 m antenna in New Zealand's North Island and to upgrade an 11 m dish in the South Island. A possible future of New Zealand's participation in the SKA is being discussed.

47 CFR 22.589 - One-way or two-way application requirements.

Code of Federal Regulations, 2012 CFR

2012-10-01

... transmitter located within 108 kilometers (67 miles) of the proposed transmitter in directions in which the distance to the interfering contour is 76.4 kilometers (47.5 miles) or less, and within 178 kilometers (111 miles) of the proposed transmitter in directions in which the distance to the interfering contour...

47 CFR 22.589 - One-way or two-way application requirements.

Code of Federal Regulations, 2013 CFR

2013-10-01

... transmitter located within 108 kilometers (67 miles) of the proposed transmitter in directions in which the distance to the interfering contour is 76.4 kilometers (47.5 miles) or less, and within 178 kilometers (111 miles) of the proposed transmitter in directions in which the distance to the interfering contour...

47 CFR 22.589 - One-way or two-way application requirements.

Code of Federal Regulations, 2014 CFR

2014-10-01

... transmitter located within 108 kilometers (67 miles) of the proposed transmitter in directions in which the distance to the interfering contour is 76.4 kilometers (47.5 miles) or less, and within 178 kilometers (111 miles) of the proposed transmitter in directions in which the distance to the interfering contour...

47 CFR 22.589 - One-way or two-way application requirements.

Code of Federal Regulations, 2011 CFR

2011-10-01

... transmitter located within 108 kilometers (67 miles) of the proposed transmitter in directions in which the distance to the interfering contour is 76.4 kilometers (47.5 miles) or less, and within 178 kilometers (111 miles) of the proposed transmitter in directions in which the distance to the interfering contour...

47 CFR 22.589 - One-way or two-way application requirements.

Code of Federal Regulations, 2010 CFR

2010-10-01

... transmitter located within 108 kilometers (67 miles) of the proposed transmitter in directions in which the distance to the interfering contour is 76.4 kilometers (47.5 miles) or less, and within 178 kilometers (111 miles) of the proposed transmitter in directions in which the distance to the interfering contour...

47 CFR 22.1013 - Effective radiated power limitations.

Code of Federal Regulations, 2012 CFR

2012-10-01

... not exceed 100 Watts. The ERP of mobile transmitters, when located within 32 kilometers (20 miles) of the 4.8 kilometer (3 mile) limit, must not exceed 25 Watts. The ERP of airborne mobile stations must.... The ERP of offshore stations located within 128.8 kilometers (80 miles) of the main transmitter...

47 CFR 22.1013 - Effective radiated power limitations.

Code of Federal Regulations, 2013 CFR

2013-10-01

... not exceed 100 Watts. The ERP of mobile transmitters, when located within 32 kilometers (20 miles) of the 4.8 kilometer (3 mile) limit, must not exceed 25 Watts. The ERP of airborne mobile stations must.... The ERP of offshore stations located within 128.8 kilometers (80 miles) of the main transmitter...

40 CFR 86.410-90 - Emission standards for 1990 and later model year motorcycles.

Code of Federal Regulations, 2010 CFR

2010-07-01

... petroleum gas-fueled motorcycles): (i) Hydrocarbons. 5.0 grams per vehicle kilometer. (ii) Carbon monoxide. 12 grams per vehicle kilometer. (2) Exhaust emissions from 1990 and later model year methanol-fueled motorcycles shall not exceed: (i) Total hydrocarbon equivalent. 5.0 grams per vehicle kilometer. (ii) Carbon...

40 CFR 86.410-90 - Emission standards for 1990 and later model year motorcycles.

Code of Federal Regulations, 2013 CFR

2013-07-01

... petroleum gas-fueled motorcycles): (i) Hydrocarbons. 5.0 grams per vehicle kilometer. (ii) Carbon monoxide. 12 grams per vehicle kilometer. (2) Exhaust emissions from 1990 and later model year methanol-fueled motorcycles shall not exceed: (i) Total hydrocarbon equivalent. 5.0 grams per vehicle kilometer. (ii) Carbon...

40 CFR 86.410-90 - Emission standards for 1990 and later model year motorcycles.

Code of Federal Regulations, 2012 CFR

2012-07-01

... petroleum gas-fueled motorcycles): (i) Hydrocarbons. 5.0 grams per vehicle kilometer. (ii) Carbon monoxide. 12 grams per vehicle kilometer. (2) Exhaust emissions from 1990 and later model year methanol-fueled motorcycles shall not exceed: (i) Total hydrocarbon equivalent. 5.0 grams per vehicle kilometer. (ii) Carbon...

40 CFR 86.410-90 - Emission standards for 1990 and later model year motorcycles.

Code of Federal Regulations, 2014 CFR

2014-07-01

... petroleum gas-fueled motorcycles): (i) Hydrocarbons. 5.0 grams per vehicle kilometer. (ii) Carbon monoxide. 12 grams per vehicle kilometer. (2) Exhaust emissions from 1990 and later model year methanol-fueled motorcycles shall not exceed: (i) Total hydrocarbon equivalent. 5.0 grams per vehicle kilometer. (ii) Carbon...

40 CFR 86.410-90 - Emission standards for 1990 and later model year motorcycles.

Code of Federal Regulations, 2011 CFR

2011-07-01

... petroleum gas-fueled motorcycles): (i) Hydrocarbons. 5.0 grams per vehicle kilometer. (ii) Carbon monoxide. 12 grams per vehicle kilometer. (2) Exhaust emissions from 1990 and later model year methanol-fueled motorcycles shall not exceed: (i) Total hydrocarbon equivalent. 5.0 grams per vehicle kilometer. (ii) Carbon...

Fire and Ice

NASA Image and Video Library

2013-12-23

Saturn's largest and second largest moons, Titan and Rhea, appear to be stacked on top of each other in this true-color scene from NASA's Cassini spacecraft. The north polar hood can be seen on Titan (3,200 miles or 5,150 kilometers across) appearing as a detached layer at the top of the moon on the top right. See PIA08137 to learn more about Titan's atmosphere and the north polar hood. This view looks toward the Saturn-facing side of Rhea (949 miles or 1528 kilometers across). North on Rhea is up and rotated 35 degrees to the right. Images taken using red, green and blue spectral filters were combined to create this natural-color view. The images were acquired with the Cassini spacecraft narrow-angle camera on June 16, 2011, at a distance of approximately 1.1 million miles (1.8 million kilometers) from Rhea and 1.5 million miles (2.5 million kilometers) from Titan. Image scale is 7 miles (11 kilometers) per pixel on Rhea and 9 miles (15 kilometers) on Titan. http://photojournal.jpl.nasa.gov/catalog/PIA17174

Venus - Ovda Regio

NASA Technical Reports Server (NTRS)

1991-01-01

This Magellan image shows part of the northern boundary of Ovda Regio, one of the large highlands ringing the equator of Venus. The scene consists largely of low-relief, rounded linear ridges. These ridges, 8-15 kilometers (5-9 miles) in width and 30-60 kilometers (20-40 miles) long, lie mostly along a 100-200 kilometer (60-120 mile) wide slope where the elevation drops 3 kilometers (2 miles) from Ovda Regio to the surrounding plains. Some of the ridges have been cut at right angles by extension fractures. Dark material, either lava or windblown dirt, fills the region between the ridges. The curvilinear, banded nature of these ridges suggests that crustal shortening, roughly oriented north-south, is largely responsible for their formation. Such crustal shortening was unexpected by Magellan scientists, who believed that Ovda Region, a likely site of hot upwelling from the interior of Venus, should be dominated by volcanism and crustal extension. This image, centered approximately at 1 degree north, 81 degrees east, measures 300 kilometers (190 miles) by 225 kilometers (140 miles) and was acquired by Magellan in November 1990.

Worlds Apart

NASA Image and Video Library

2015-10-12

Although Mimas and Pandora, shown here, both orbit Saturn, they are very different moons. Pandora, "small" by moon standards (50 miles or 81 kilometers across) is elongated and irregular in shape. Mimas (246 miles or 396 kilometers across), a "medium-sized" moon, formed into a sphere due to self-gravity imposed by its higher mass. The shapes of moons can teach us much about their history. For example, one explanation for Pandora's elongated shape and low density is that it may have formed by gathering ring particles onto a dense core. This view looks toward the unilluminated side of the rings from 0.26 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 26, 2015. The view was obtained at a distance of approximately 485,000 miles (781,000 kilometers) from Pandora. Image scale is 3 miles (5 kilometers) per pixel. Mimas is 904,000 miles (1.4 million kilometers) from the spacecraft in this image. The scale on Mimas is 5.4 miles (8.4 kilometers) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA18339

Seismicity Increase in North China After the 2008 Mw7.9 Wenchuan Earthquake.

NASA Astrophysics Data System (ADS)

Goldhagen, G.; Li, C.; Peng, Z.; Wu, J.; Zhao, L.

2016-12-01

A large mainshock is capable of setting off an increase in seismicity in areas thousands of kilometers away. This phenomenon, known as remote triggering, is more likely to occur along active fault lines, aftershock zones, or regions with anthropogenic activities (e.g., mining, reservoirs, and fluid injections). By studying these susceptible areas, we can gain a better understanding of subsurface stress conditions, and long-range earthquake interactions. In this study we conduct a systematic search for remotely triggered seismicity in North China along two linear dense arrays (net code 1A and Z8) deployed by Chinese Academy of Sciences (CAS) following the 2008 Mw7.9 Wenchuan earthquake. A 5 Hz high pass filter is applied to the broadband seismogram recorded at the 1A array, which is more than 2,000 km away from the mainshock, in order to manually pick local events with double peaks. These local events have higher frequencies than earthquakes in the aftershock zone of the Wenchuan earthquake. An STA/LTA method is then employed as a way to automatically detect microseismicity in a section of the array that showed preliminary evidence of remote triggering. We find a clear increase of small earthquakes, right after the surface waves of the Wenchuan mainshock. These events, were recorded at stations close to the north section of the Tanlu fault and aftershock zones of the 1975, Ms7.3 Haicheng earthquake. This result suggests that remote triggering is more likely near active fault zones or other specific regions, as previous studies have proposed. Future work includes applying a waveform matching method to both arrays and automatically detecting micro-earthquakes missed on the catalog, and using them to better confirm the existence (or lack of) remote triggering following the Wenchuan mainshock. Our finding helps to better classify conditions that lead to the occurrence of remotely triggered earthquakes at intraplate regions.

A high performance cost-effective digital complex correlator for an X-band polarimetry survey.

PubMed

Bergano, Miguel; Rocha, Armando; Cupido, Luís; Barbosa, Domingos; Villela, Thyrso; Boas, José Vilas; Rocha, Graça; Smoot, George F

2016-01-01

The detailed knowledge of the Milky Way radio emission is important to characterize galactic foregrounds masking extragalactic and cosmological signals. The update of the global sky models describing radio emissions over a very large spectral band requires high sensitivity experiments capable of observing large sky areas with long integration times. Here, we present the design of a new 10 GHz (X-band) polarimeter digital back-end to map the polarization components of the galactic synchrotron radiation field of the Northern Hemisphere sky. The design follows the digital processing trends in radio astronomy and implements a large bandwidth (1 GHz) digital complex cross-correlator to extract the Stokes parameters of the incoming synchrotron radiation field. The hardware constraints cover the implemented VLSI hardware description language code and the preliminary results. The implementation is based on the simultaneous digitized acquisition of the Cartesian components of the two linear receiver polarization channels. The design strategy involves a double data rate acquisition of the ADC interleaved parallel bus, and field programmable gate array device programming at the register transfer mode. The digital core of the back-end is capable of processing 32 Gbps and is built around an Altera field programmable gate array clocked at 250 MHz, 1 GSps analog to digital converters and a clock generator. The control of the field programmable gate array internal signal delays and a convenient use of its phase locked loops provide the timing requirements to achieve the target bandwidths and sensitivity. This solution is convenient for radio astronomy experiments requiring large bandwidth, high functionality, high volume availability and low cost. Of particular interest, this correlator was developed for the Galactic Emission Mapping project and is suitable for large sky area polarization continuum surveys. The solutions may also be adapted to be used at signal processing subsystem levels for large projects like the square kilometer array testbeds.

Long-baseline optical intensity interferometry. Laboratory demonstration of diffraction-limited imaging

NASA Astrophysics Data System (ADS)

Dravins, Dainis; Lagadec, Tiphaine; Nuñez, Paul D.

2015-08-01

Context. A long-held vision has been to realize diffraction-limited optical aperture synthesis over kilometer baselines. This will enable imaging of stellar surfaces and their environments, and reveal interacting gas flows in binary systems. An opportunity is now opening up with the large telescope arrays primarily erected for measuring Cherenkov light in air induced by gamma rays. With suitable software, such telescopes could be electronically connected and also used for intensity interferometry. Second-order spatial coherence of light is obtained by cross correlating intensity fluctuations measured in different pairs of telescopes. With no optical links between them, the error budget is set by the electronic time resolution of a few nanoseconds. Corresponding light-travel distances are approximately one meter, making the method practically immune to atmospheric turbulence or optical imperfections, permitting both very long baselines and observing at short optical wavelengths. Aims: Previous theoretical modeling has shown that full images should be possible to retrieve from observations with such telescope arrays. This project aims at verifying diffraction-limited imaging experimentally with groups of detached and independent optical telescopes. Methods: In a large optics laboratory, artificial stars (single and double, round and elliptic) were observed by an array of small telescopes. Using high-speed photon-counting solid-state detectors and real-time electronics, intensity fluctuations were cross-correlated over up to 180 baselines between pairs of telescopes, producing coherence maps across the interferometric Fourier-transform plane. Results: These interferometric measurements were used to extract parameters about the simulated stars, and to reconstruct their two-dimensional images. As far as we are aware, these are the first diffraction-limited images obtained from an optical array only linked by electronic software, with no optical connections between the telescopes. Conclusions: These experiments serve to verify the concepts for long-baseline aperture synthesis in the optical, somewhat analogous to radio interferometry.

A Near-Infrared and Thermal Imager for Mapping Titan's Surface Features

NASA Technical Reports Server (NTRS)

Aslam, S.; Hewagma, T.; Jennings, D. E.; Nixon, C.

2012-01-01

Approximately 10% of the solar insolation reaches the surface of Titan through atmospheric spectral windows. We will discuss a filter based imaging system for a future Titan orbiter that will exploit these windows mapping surface features, cloud regions, polar storms. In the near-infrared (NIR), two filters (1.28 micrometer and 1.6 micrometer), strategically positioned between CH1 absorption bands, and InSb linear array pixels will explore the solar reflected radiation. We propose to map the mid, infrared (MIR) region with two filters: 9.76 micrometer and 5.88-to-6.06 micrometers with MCT linear arrays. The first will map MIR thermal emission variations due to surface albedo differences in the atmospheric window between gas phase CH3D and C2H4 opacity sources. The latter spans the crossover spectral region where observed radiation transitions from being dominated by thermal emission to solar reflected light component. The passively cooled linear arrays will be incorporated into the focal plane of a light-weight thin film stretched membrane 10 cm telescope. A rad-hard ASIC together with an FPGA will be used for detector pixel readout and detector linear array selection depending on if the field-of-view (FOV) is looking at the day- or night-side of Titan. The instantaneous FOV corresponds to 3.1, 15.6, and 31.2 mrad for the 1, 5, and 10 micrometer channels, respectively. For a 1500 km orbit, a 5 micrometer channel pixel represents a spatial resolution of 91 m, with a FOV that spans 23 kilometers, and Titan is mapped in a push-broom manner as determined by the orbital path. The system mass and power requirements are estimated to be 6 kg and 5 W, respectively. The package is proposed for a polar orbiter with a lifetime matching two Saturn seasons.

Variation of the shower lateral spread with air temperature at the ground

NASA Astrophysics Data System (ADS)

Wilczyńska, B.; Engel, R.; Homola, P.; Keilhauer, B.; Klages, H.; Pękala, J.; Wilczyński, H.

The vertical profile of air density at a given site varies considerably with time. Well understood seasonal differences are present, but sizeable effects on shorter time scales, like day to night or day to day variations, are also observed. In consequence, the Moliere radius changes, influencing the lateral distribution of particles in the air showers and therefore may influence the shower detection in surface detector arrays. In air shower reconstruction, usually seasonal average profiles of the atmosphere are used, because local daily measurements of the profile are rarely available. Therefore, the daily fluctuations of the atmosphere are not accounted for. This simplification increases the inaccuracies of shower reconstruction. We show that a universal correlation exists between the ground temperature and the shape of the atmospheric profile, up to altitudes of several kilometers, hence providing a method to reduce inaccuracies in shower reconstruction due to weather variation.

KSC-97PC1080

NASA Image and Video Library

1997-07-22

Applied Physics Laboratory engineers and technicians from Johns Hopkins University install solar array panels on the Advanced Composition Explorer (ACE) in KSC’s Spacecraft Assembly and Encapsulation Facility-II. The panel on which they are working is identical to the panel (one of four) seen in the foreground on the ACE spacecraft. Scheduled for launch on a Delta II rocket from Cape Canaveral Air Station on Aug. 25, ACE will study low-energy particles of solar origin and high-energy galactic particles for a better understanding of the formation and evolution of the solar system as well as the astrophysical processes involved. The ACE observatory will be placed into an orbit almost a million miles (1.5 million kilometers) away from the Earth, about 1/100 the distance from the Earth to the Sun. The collecting power of instrumentation aboard ACE is at least 100 times more sensitive than anything previously flown to collect similar data by NASA

Backprojection of volcanic tremor

USGS Publications Warehouse

Haney, Matthew M.

2014-01-01

Backprojection has become a powerful tool for imaging the rupture process of global earthquakes. We demonstrate the ability of backprojection to illuminate and track volcanic sources as well. We apply the method to the seismic network from Okmok Volcano, Alaska, at the time of an escalation in tremor during the 2008 eruption. Although we are able to focus the wavefield close to the location of the active cone, the network array response lacks sufficient resolution to reveal kilometer-scale changes in tremor location. By deconvolving the response in successive backprojection images, we enhance resolution and find that the tremor source moved toward an intracaldera lake prior to its escalation. The increased tremor therefore resulted from magma-water interaction, in agreement with the overall phreatomagmatic character of the eruption. Imaging of eruption tremor shows that time reversal methods, such as backprojection, can provide new insights into the temporal evolution of volcanic sources.

Constraining the CMB optical depth through the dispersion measure of cosmological radio transients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fialkov, A.; Loeb, A., E-mail: anastasia.fialkov@cfa.harvard.edu, E-mail: aloeb@cfa.harvard.edu

2016-05-01

The dispersion measure of extragalactic radio transients can be used to measure the column density of free electrons in the intergalactic medium. The same electrons also scatter the Cosmic Microwave Background (CMB) photons, affecting precision measurements of cosmological parameters. We explore the connection between the dispersion measure of radio transients existing during the Epoch of Reionization (EoR) and the total optical depth for the CMB showing that the existence of such transients would provide a new sensitive probe of the CMB optical depth. As an example, we consider the population of FRBs. Assuming they exist during the EoR, we showmore » that: (i) such sources can probe the reionization history by measuring the optical depth to sub-percent accuracy, and (ii) they can be detected with high significance by an instrument such as the Square Kilometer Array.« less

STS-55 Earth observation shows a sunset over South America

NASA Technical Reports Server (NTRS)

1993-01-01

STS-55 Earth observation taken aboard Columbia, Orbiter Vehicle (OV) 102, shows a spectacular sunset view over South America and the cleanest atmosphere since before the volcanic eruptions of 1991, according to NASA scientists studying the STS-55 photography. A dark cloud layer is evident at an altitude of 7 to 9 kilometers. Five kilometers higher, a pink layer of sulfuric acid droplets and ammonium sulfate particles begins at the tropopause and extends upward into the stratosphere to 19 kilometers. Above that, blue scattering by the atmosphere diminishes until, at an altitude of 60 kilometers, the blackness of space is predominant.

Communications system using a mirror kept in outer space by electromagnetic radiation pressure

DOEpatents

Csonka, Paul L.

1981-01-01

A method and system are described for transmitting electromagnetic radiation by using a communications mirror located between about 100 kilometers and about 200 kilometers above ground. The communications mirror is kept aloft above the atmosphere by the pressure of the electromagnetic radiation which it reflects, and which is beamed at the communications mirror by a suitably constructed transmitting antenna on the ground. The communications mirror will reflect communications, such as radio, radar, or television waves up to about 1,100 kilometers away when the communications mirror is located at a height of about 100 kilometers.

On farm intervention studies on reduction of boar taint prevalence: Feeding strategies, presence of gilts and time in lairage.

PubMed

Heyrman, E; Millet, S; Tuyttens, F A M; Ampe, B; Janssens, S; Buys, N; Wauters, J; Vanhaecke, L; Aluwé, M

2018-05-09

One of the challenges in the production of entire male pigs is the occurrence of boar taint. We separately tested the effect of 3 management strategies to reduce boar taint on respectively 2, 3, and 6 Flemish pig farms: 1) adapted feeding strategies, 2) presence of gilts in the compartment, and 3) varying lairage duration at the slaughterhouse. A commercialized feed concept resulted in a significant reduction of olfactory boar taint prevalence when fed for 2 weeks (T2W) compared to control (T-CON) (P = 0.030). For T2W and when fed for 3 weeks (T3W), androstenone (AND) (P = 0.002 for T2W, P = 0.029 for T3W) and skatole (SKA) (P < 0.001 for T2W and T3W) were significantly reduced compared to T-CON. Olfactory boar taint prevalence was significantly reduced when feeding 5% dried chicory roots (FI5%) (P = 0.032), but not for 3% dried chicory roots (FI3%) (P = 0.958). SKA concentration was significantly lower when feeding FI5% (P < 0.001) and when feeding FI3% (P = 0.034). Rearing entire male pigs separately from gilts and increasing lairage duration from <1 h to >3 h did not significantly affect boar taint. Copyright © 2018 Elsevier Ltd. All rights reserved.

Experimental Setup for the Laboratory Investigation of Micrometeoroid Ablation Using a Dust Accelerator

NASA Technical Reports Server (NTRS)

Thomas, Evan; Simolka, Jonas; DeLuca, Michael; Horanyi, Mihaly; Janches, Diego; Marshall, Robert A.; Munsat, Tobin; Plane, John M. C.; Sternovsky, Zoltan

2017-01-01

A facility has been developed to simulate the ablation of micrometeoroids in laboratory conditions. An electrostatic dust accelerator is used to generate iron particles with velocities of 10-70 kilometers. The particles are then introduced into a chamber pressurized with a target gas, where the pressure is adjustable between 0.01 and 0.5 Torr, and the particle partially or completely ablates over a short distance. An array of biased electrodes above and below the ablation path is used to collect the generated ions/electrons with a spatial resolution of 2.6 centimeters along the ablating particles path, thus allowing the study of the spatiotemporal evolution of the process. For completely ablated particles, the total collected charge directly yields the ionization coefficient of a given dust material-target gas combination. The first results of this facility measured the ionization coefficient of iron atoms with N2, air, CO2, and He target gases for impact velocities greater than 20 kilometers per second, and are reported by Thomas et al. The ablation chamber is also equipped with four optical ports that allow for the detection of the light emitted by the ablating particle. A multichannel photomultiplier tube system is used to observe the ablation process with a spatial and temporal resolution of 0.64 centimeters and 90 nanoseconds. The preliminary results indicate that it is possible to calculate the velocity of the ablating particle from the optical observations, and in conjunction with the spatially resolved charge measurements allow for experimental validation of ablation models in future studies.

Flyby Comet Imaged By Radar

NASA Image and Video Library

2016-03-24

Radar data of comet P/2016 BA14 taken over three days (March 21-23, 2016), when the comet was between 2.5 million miles and 2.2 million miles (4.1 million kilometers and 3.6 million kilometers) from Earth. Radar images from the flyby indicated that the comet is about 3,000 feet (1 kilometer) in diameter.

Distribution of virulence factors and association with emm polymorphism or isolation site among beta-hemolytic group G Streptococcus dysgalactiae subspecies equisimilis.

PubMed

Lo, Hsueh-Hsia; Cheng, Wei-Shan

2015-01-01

Distribution of virulence factors and association with emm polymorphism or isolation site among beta-hemolytic group G Streptococcus dysgalactiae subspecies equisimilis. Streptococcus dysgalactiae subspecies equisimilis (SDSE), the dominant human pathogenic species among group G streptococci, is the causative agent of several invasive and non-invasive diseases worldwide. However, limited information is available about the distribution of virulence factors among SDSE isolates, or their association with emm types and the isolation sites. In this study, 246 beta-hemolytic group G SDSE isolates collected in central Taiwan between February 2007 and August 2011 were under investigation. Of these, 66 isolates were obtained from normally sterile sites and 180 from non-sterile sites. emm typing revealed 32 types, with the most prevalent one being stG10.0 (39.8%), followed by stG245.0 (15.4%), stG840.0 (12.2%), stG6.1 (7.7%), and stG652.0 (4.1%). The virulence genes lmb (encoding laminin-binding protein), gapC (glyceraldehyde 3-phosphate dehydrogenase), sagA (streptolysin S), and hylB (hyaluronidase) existed in all isolates. Also, 99.2% of the isolates possessed slo (streptolysin O) and scpA (C5a peptidase) genes. In addition, 72.8%, 14.6%, 9.4%, and 2.4% of the isolates possessed the genes ska (streptokinase), cbp (putative collagen-binding protein, SDEG_1781), fbp (putative fibronectin-binding protein, SDEG_0161), and sicG (streptococcal inhibitor of complement), respectively. The only superantigen gene detected was spegg (streptococcus pyrogenic exotoxin G(dys) ), which was possessed by 74.4% of the isolates; these isolates correlated with non-sterile sites. Positive correlations were observed between the following emm types and virulence genes: stG10.0 and stG840.0 with spegg, stG6.1 and stG652.0 with ska, and stG840.0 with cbp. On the other hand, negative correlations were observed between the following: stG245.0, stG6.1, and stG652.0 types with spegg, stG10.0 with ska, and stG10.0, stG245.0, and stG6.1 types with cbp. The prevalence of emm types of SDSE in central Taiwan was investigated for the first time. Moreover, the distribution of virulence factors among beta-hemolytic group G SDSE isolates, as well as their association with emm types or isolation sites were also examined. © 2014 APMIS. Published by John Wiley & Sons Ltd.

Kilometer-Scale Topographic Roughness of Mercury: Correlation with Geologic Features and Units

NASA Technical Reports Server (NTRS)

Kreslavsky, Mikhail A.; Head, James W.; Neumann, Gregory A.; Zuber, Maria T.; Smith, David E.

2014-01-01

We present maps of the topographic roughness of the northern circumpolar area of Mercury at kilometer scales. The maps are derived from range profiles obtained by the Mercury Laser Altimeter (MLA) instrument onboard the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission. As measures of roughness, we used the interquartile range of profile curvature at three baselines: 0.7 kilometers, 2.8 kilometers, and 11 kilometers. The maps provide a synoptic overview of variations of typical topographic textures. They show a dichotomy between the smooth northern plains and rougher, more heavily cratered terrains. Analysis of the scale dependence of roughness indicates that the regolith on Mercury is thicker than on the Moon by approximately a factor of three. Roughness contrasts within northern volcanic plains of Mercury indicate a younger unit inside Goethe basin and inside another unnamed stealth basin. These new data permit interplanetary comparisons of topographic roughness.

Dot Against the Dark

NASA Image and Video Library

2014-09-02

As if trying to get our attention, Mimas is positioned against the shadow of Saturn's rings, bright on dark. As we near summer in Saturn's northern hemisphere, the rings cast ever larger shadows on the planet. With a reflectivity of about 96 percent, Mimas (246 miles, or 396 kilometers across) appears bright against the less-reflective Saturn. This view looks toward the sunlit side of the rings from about 10 degrees above the ringplane. The image was taken with the Cassini spacecraft wide-angle camera on July 13, 2014 using a spectral filter which preferentially admits wavelengths of near-infrared light centered at 752 nanometers. The view was acquired at a distance of approximately 1.1 million miles (1.8 million kilometers) from Saturn and approximately 1 million miles (1.6 million kilometers) from Mimas. Image scale is 67 miles (108 kilometers) per pixel at Saturn and 60 miles (97 kilometers) per pixel at Mimas. http://photojournal.jpl.nasa.gov/catalog/PIA18282

Determining Home Range and Preferred Habitat of Feral Horses on the Nevada National Security Site Using Geographic Information Systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Burns, Ashley V.

2014-05-30

Feral horses (Equus caballus) are free-roaming descendants of domesticated horses and legally protected by the Wild and Free-Roaming Horses and Burros Act of 1971, which mandates how feral horses and burros should be managed and protected on federal lands. Using a geographic information system to determine the home range and suitable habitat of feral horses on the federally managed Nevada National Security Site can enable wildlife biologists in making best management practice recommendations. Home range was estimated at 88.1 square kilometers. Site suitability was calculated for elevation, forage, slope, water presence and horse observations. These variables were combined in successivemore » iterations into one polygon. Suitability rankings established that 85 square kilometers are most suitable habitat, with 2,052 square kilometers of good habitat 1,252 square kilometers of fair habitat and 122 square kilometers of least suitable habitat.« less

Venus - Landslide in Navka Region

NASA Technical Reports Server (NTRS)

1992-01-01

The Magellan spacecraft has observed remnant landslide deposits apparently resulting from the collapse of volcanic structures. This Magellan radar image is centered about 25.4 degrees south latitude and 308 degrees east longitude in the southwestern Navka Region of Venus. The image shows a 17.4 kilometer (10.8 mile) diameter volcanic dome on the plains. The dome is approximately 1.86 kilometers (1.2 mile) in height and it has a slope of about 23 degrees. The northwest and northeast flanks of the dome have collapsed to form landslides that have deposited debris on the plains. The image shows an area 110 kilometers (68 miles) across and 100 kilometers (62 miles) in length.

Mountainous Ecosystem Sensor Array (MESA): a mesh sensor network for climate change research in remote mountainous environments

NASA Astrophysics Data System (ADS)

Robinson, P. W.; Neal, D.; Frome, D.; Kavanagh, K.; Davis, A.; Gessler, P. E.; Hess, H.; Holden, Z. A.; Link, T. E.; Newingham, B. A.; Smith, A. M.

2013-12-01

Developing sensor networks robust enough to perform unattended in the world's remote regions is critical since these regions serve as important benchmarks that lack anthropogenic influence. Paradoxically, the factors that make these remote, natural sites challenging for sensor networking are often what make them indispensable for climate change research. The MESA (Mountainous Ecosystem Sensor Array) project has faced these challenges and developed a wireless mesh sensor network across a 660 m topoclimatic gradient in a wilderness area in central Idaho. This sensor array uses advances in sensing, networking, and power supply technologies to provide near real-time synchronized data covering a suite of biophysical parameters used in ecosystem process models. The 76 sensors in the network monitor atmospheric carbon dioxide concentration, humidity, air and soil temperature, soil water content, precipitation, incoming and outgoing shortwave and longwave radiation, snow depth, wind speed and direction, and leaf wetness at synchronized time intervals ranging from two minutes to two hours and spatial scales from a few meters to two kilometers. We present our novel methods of placing sensors and network nodes above, below, and throughout the forest canopy without using meteorological towers. In addition, we explain our decision to use different forms of power (wind and solar) and the equipment we use to control and integrate power harvesting. Further, we describe our use of the network to sense and quantify its own power use. Using examples of environmental data from the project, we discuss how these data may be used to increase our understanding of the effects of climate change on ecosystem processes in mountainous environments. MESA sensor locations across a 700 m topoclimatic gradient at the University of Idaho Taylor Wilderness Research Station.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Resmi, Lekshmi; Zhang, Bing, E-mail: l.resmi@iist.ac.in

Reverse shock (RS) emission from gamma-ray bursts is an important tool in investigating the nature of the ejecta from the central engine. If the magnetization of the ejecta is not high enough to suppress the RS, a strong RS emission component, usually peaking in the optical/IR band early on, would provide an important contribution to early afterglow light curve. In the radio band, synchrotron self-absorption may suppress early RS emission and also delay the RS peak time. In this paper, we calculate the self-absorbed RS emission in the radio band under different dynamical conditions. In particular, we stress that themore » RS radio emission is subject to self-absorption in both RSs and forward shocks (FSs). We calculate the ratio between the RS to FS flux at the RS peak time for different frequencies, which is a measure of the detectability of the RS emission component. We then constrain the range of physical parameters for a detectable RS, in particular the role of magnetization. We notice that unlike optical RS emission which is enhanced by moderate magnetization, moderately magnetized ejecta do not necessarily produce a brighter radio RS due to the self-absorption effect. For typical parameters, the RS emission component would not be detectable below 1 GHz unless the medium density is very low (e.g., n < 10{sup −3} cm{sup −3} for the interstellar medium and A {sub *} < 5 × 10{sup −4} for wind). These predictions can be tested using the afterglow observations from current and upcoming radio facilities such as the Karl G. Jansky Very Large Array, the Low-Frequency Array, the Five Hundred Meter Aperture Spherical Telescope, and the Square Kilometer Array.« less

Summary of Research, Academic Departments, 1983-1984.

DTIC Science & Technology

1984-10-01

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Signing of ESO-Poland Accession Agreement

NASA Astrophysics Data System (ADS)

2014-12-01

An agreement was signed by Professor Lena Kolarska-Bobińska, the Polish Minister of Science and Higher Education, and the ESO Director General Tim de Zeeuw in Warsaw on 28 October 2014 that will lead to the country joining ESO. The signing of the agreement followed its unanimous approval by the ESO Council during an extraordinary meeting on 8 October 2014. Poland will be welcomed as a new Member State, following subsequent ratification of the accession agreement by the Polish Parliament. Tim de Zeeuw’s speech at this ceremony is reproduced below.

South-Central Tibetan Seismicity from HiCLIMB Seismic Array Data

NASA Astrophysics Data System (ADS)

Carpenter, S.; Nabelek, J.; Braunmiller, J.

2010-12-01

The HiCLIMB broadband passive seismic experiment (2002-2005) operated 233 sites along a 800-km long north-south array extending from the Himalayan foreland into the Central Tibetan Plateau and a flanking 350x350 km lateral array in southern Tibet and eastern Nepal. We use data from the experiment’s second phase (June 2004 to August 2005), when stations operated in Tibet, to locate earthquakes in south-central Tibet, a region with no permanent seismic network where little is known about its seismicity. We used the Antelope software for automatic detection and arrival time picking, event-arrival association and event location. Requiring a low detection and event association threshold initially resulted in ~110,000 declared events. The large database size rendered manual inspection unfeasible and we developed automated post-processing modules to weed out spurious detections and erroneous phase and event associations, which stemmed, e.g., from multiple coincident earthquakes within the array or misplaced seismicity from the great 2004 Sumatra earthquake. The resulting database contains ~32,000 events within 5° distance from the closest station. We consider ~7,600 events defined by more than 30 P and S arrivals well located and discuss them here. Seismicity in the subset correlates well with mapped faults and structures seen on satellite imagery attesting to high location quality. This is confirmed by non-systematic, kilometer-scale differences between automatic and manual locations for selected events. Seismicity in south-central Tibet is intense north of the Yarlung-Tsangpo Suture. Almost 90% of events occurred in the Lhasa Terrane mainly along north-south trending rifts. Vigorous activity (>4,800 events) accompanied two M>6 earthquakes in the Payang Basin (84°E), ~100 km west of the linear array. The Tangra-Yum Co (86.5°E) and Pumqu-Xianza (88°E) rifts were very active (~1,000 events) without dominant main shocks indicating swarm like-behavior possibly related to shallow magmatic or geothermal activity. Seismicity in the Qiangtang Terrane accounts for less than 10% of activity; seismicity is distributed and, except for the Yibuk-Caka Rift (87°E), difficult to associate with known structures. Lower seismicity may be apparent and simply reflect a larger distance to the array. Fewer than 5% of events occurred south of the Yarlong Tsangpo Suture in the Tethyan Himalaya, the only region where in addition to shallow seismicity a significant number of deep (mantle) events was located. Hypocenter depth, particularly for shallow events, is usually not well constrained due to array geometry and large distances to closest sites. The nature of deep events inside the array, though, is resolved.

The Jagged Shores of Pluto Highlands

NASA Image and Video Library

2016-06-09

This enhanced color view from NASA's New Horizons spacecraft zooms in on the southeastern portion of Pluto's great ice plains, where at lower right the plains border rugged, dark highlands informally named Krun Macula. Krun Macula -- Krun is the lord of the underworld in the Mandaean religion, and a macula is a dark feature on a planetary surface -- is believed to get its dark red color from tholins, complex molecules found across Pluto. Krun Macula rises 1.5 miles (2.5 kilometers) above the surrounding plain -- informally named Sputnik Planum -- and is scarred by clusters of connected, roughly circular pits that typically reach between 5 and 8 miles (8 and 13 kilometers) across, and up to 1.5 miles (2.5 kilometers) deep. At the boundary with Sputnik Planum, these pits form deep valleys reaching more than 25 miles (40 kilometers) long, 12.5 miles (20 kilometers) wide and almost 2 miles (3 kilometers) deep (almost twice as deep as the Grand Canyon in Arizona), and have floors covered with nitrogen ice. New Horizons scientists think these pits may have formed through surface collapse, although what may have prompted such a collapse is a mystery. This scene was created using three separate observations made by New Horizons in July 2015. The right half of the image is composed of 260 feet- (80 meter-) per-pixel data from the Long Range Reconnaissance Imager (LORRI), obtained at 9,850 miles (15,850 kilometers) from Pluto, about 23 minutes before New Horizons' closest approach. The left half is composed of 410 feet- (125 meter-) per-pixel LORRI data, obtained about six minutes earlier, with New Horizons 15,470 miles (24,900 kilometers) from Pluto. These data respectively represent portions of the highest- and second-highest-resolution observations obtained by New Horizons in the Pluto system. The entire scene was then colorized using 2230 feet- (680 meter-) per-pixel data from New Horizons' Ralph/Multispectral Visual Imaging Camera (MVIC), obtained at 21,100 miles (33,900 kilometers) from Pluto, about 45 minutes before closest approach. http://photojournal.jpl.nasa.gov/catalog/PIA20732

The Jagged Shores of Pluto Highlands

NASA Image and Video Library

2016-06-09

This enhanced color view from NASA's New Horizons spacecraft zooms in on the southeastern portion of Pluto's great ice plains, where at lower right the plains border rugged, dark highlands informally named Krun Macula. Krun Macula -- Krun is the lord of the underworld in the Mandaean religion, and a macula is a dark feature on a planetary surface -- is believed to get its dark red color from tholins, complex molecules found across Pluto. Krun Macula rises 1.5 miles (2.5 kilometers) above the surrounding plain -- informally named Sputnik Planum -- and is scarred by clusters of connected, roughly circular pits that typically reach between 5 and 8 miles (8 and 13 kilometers) across, and up to 1.5 miles (2.5 kilometers) deep. At the boundary with Sputnik Planum, these pits form deep valleys reaching more than 25 miles (40 kilometers) long, 12.5 miles (20 kilometers) wide and almost 2 miles (3 kilometers) deep (almost twice as deep as the Grand Canyon in Arizona), and have floors covered with nitrogen ice. New Horizons scientists think these pits may have formed through surface collapse, although what may have prompted such a collapse is a mystery. This scene was created using three separate observations made by New Horizons in July 2015. The right half of the image is composed of 260 feet- (80 meter-) per-pixel data from the Long Range Reconnaissance Imager (LORRI), obtained at 9,850 miles (15,850 kilometers) from Pluto, about 23 minutes before New Horizons' closest approach. The left half is composed of 410 feet- (125 meter-) per-pixel LORRI data, obtained about six minutes earlier, with New Horizons 15,470 miles (24,900 kilometers) from Pluto. These data respectively represent portions of the highest- and second-highest-resolution observations obtained by New Horizons in the Pluto system. The entire scene was then colorized using 2230 feet- (680 meter-) per-pixel data from New Horizons' Ralph/Multispectral Visual Imaging Camera (MVIC), obtained at 21,100 miles (33,900 kilometers) from Pluto, about 45 minutes before closest approach. http://photojournal.jpl.nasa.gov/catalog/PIA20733

Steep-dip seismic imaging of the shallow San Andreas Fault near Parkfield

USGS Publications Warehouse

Hole, J.A.; Catchings, R.D.; St. Clair, K.C.; Rymer, M.J.; Okaya, D.A.; Carney, B.J.

2001-01-01

Seismic reflection and refraction images illuminate the San Andreas Fault to a depth of 1 kilometer. The prestack depth-migrated reflection image contains near-vertical reflections aligned with the active fault trace. The fault is vertical in the upper 0.5 kilometer, then dips about 70° to the southwest to at least 1 kilometer subsurface. This dip reconciles the difference between the computed locations of earthquakes and the surface fault trace. The seismic velocity cross section shows strong lateral variations. Relatively low velocity (10 to 30%), high electrical conductivity, and low density indicate a 1-kilometer-wide vertical wedge of porous sediment or fractured rock immediately southwest of the active fault trace.

Ancient Multiring Basins on the Moon Revealed by Clementine Laser Altimetry

NASA Astrophysics Data System (ADS)

Spudis, Paul D.; Reisse, Robert A.; Gillis, Jeffrey J.

1994-12-01

Analysis of laser altimetry data from Clementine has confirmed and extended our knowledge of nearly obliterated multiring basins on the moon. These basins were formed during the early bombardment phase of lunar history, have been filled to varying degrees by mare lavas and regional ejecta blankets, and have been degraded by the superposition of large impact craters. The Mendel-Rydberg Basin, a degraded three-ring feature over 600 kilometers in diameter on the lunar western limb, is about 6 kilometers deep from rim to floor, only slightly less deep than the nearby younger and much better preserved Orientale Basin (8 kilometers deep). The South Pole-Aitken Basin, the oldest discernible impact feature on the moon, is revealed as a basin 2500 kilometers in diameter with an average depth of more than 13 kilometers, rim crest to floor. This feature is the largest, deepest impact crater yet discovered in the solar system. Several additional depressions seen in the data may represent previously unmapped ancient impact basins.

The association between graduated driver licensing laws and travel behaviors among adolescents: an analysis of US National Household Travel Surveys.

PubMed

Zhu, Motao; Cummings, Peter; Zhao, Songzhu; Rice, Thomas

2016-07-27

Young novice drivers have crash rates higher than any other age group. To address this problem, graduated driver licensing (GDL) laws have been implemented in the United States to require an extended learner permit phase, and create night time driving or passenger restrictions for adolescent drivers. GDL allows adolescents to gain experience driving under low-risk conditions with the aim of reducing crashes. The restricted driving might increase riding with parents or on buses, which might be safer, or walking or biking, which might be more dangerous. We examined whether GDL increases non-driver travels, and whether it reduces total travels combining drivers and non-drivers. We used data from the US National Household Travel Survey for the years 1995-1996, 2001-2002, and 2008-2009 to estimate the adjusted ratio for the number of trips and trip kilometers made by persons exposed to a GDL law, compared with those not exposed. Adolescents aged 16 years had fewer trips and kilometers as drivers when exposed to a GDL law: ratio 0.84 (95 % confidence interval (CI) 0.71, 1.00) for trips; 0.79 (0.63, 0.98) for kilometers. For adolescents aged 17 years, the trip ratio was 0.94 (0.83, 1.07) and the kilometers ratio 0.80 (0.63, 1.03). There was little association between GDL laws and trips or kilometers traveled by other methods: ratio 1.03 for trips and 1.00 for kilometers for age 16 years, 0.94 for trips and 1.07 for kilometers for age 17. If these associations are causal, GDL laws reduced driving kilometers by about 20 % for 16 and 17 year olds, and reduced the number of driving trips by 16 % among 16 year olds. GDL laws showed little relationship with trips by other methods.

UAV and SfM in Detailed Geomorphological Mapping of Granite Tors: An Example of Starościńskie Skały (Sudetes, SW Poland)

NASA Astrophysics Data System (ADS)

Kasprzak, Marek; Jancewicz, Kacper; Michniewicz, Aleksandra

2017-11-01

The paper presents an example of using photographs taken by unmanned aerial vehicles (UAV) and processed using the structure from motion (SfM) procedure in a geomorphological study of rock relief. Subject to analysis is a small rock city in the West Sudetes (SW Poland), known as Starościńskie Skały and developed in coarse granite bedrock. The aims of this paper were, first, to compare UAV/SfM-derived data with the cartographical image based on the traditional geomorphological field-mapping methods and the digital elevation model derived from airborne laser scanning (ALS). Second, to test if the proposed combination of UAV and SfM methods may be helpful in recognizing the detailed structure of granite tors. As a result of conducted UAV flights and digital image post-processing in AgiSoft software, it was possible to obtain datasets (dense point cloud, texture model, orthophotomap, bare-ground-type digital terrain model—DTM) which allowed to visualize in detail the surface of the study area. In consequence, it was possible to distinguish even the very small forms of rock surface microrelief: joints, aplite veins, rills and karren, weathering pits, etc., otherwise difficult to map and measure. The study includes also valorization of particular datasets concerning microtopography and allows to discuss indisputable advantages of using the UAV/SfM-based DTM in geomorphic studies of tors and rock cities, even those located within forest as in the presented case study.

Linear and non-linear Modified Gravity forecasts with future surveys

NASA Astrophysics Data System (ADS)

Casas, Santiago; Kunz, Martin; Martinelli, Matteo; Pettorino, Valeria

2017-12-01

Modified Gravity theories generally affect the Poisson equation and the gravitational slip in an observable way, that can be parameterized by two generic functions (η and μ) of time and space. We bin their time dependence in redshift and present forecasts on each bin for future surveys like Euclid. We consider both Galaxy Clustering and Weak Lensing surveys, showing the impact of the non-linear regime, with two different semi-analytical approximations. In addition to these future observables, we use a prior covariance matrix derived from the Planck observations of the Cosmic Microwave Background. In this work we neglect the information from the cross correlation of these observables, and treat them as independent. Our results show that η and μ in different redshift bins are significantly correlated, but including non-linear scales reduces or even eliminates the correlation, breaking the degeneracy between Modified Gravity parameters and the overall amplitude of the matter power spectrum. We further apply a Zero-phase Component Analysis and identify which combinations of the Modified Gravity parameter amplitudes, in different redshift bins, are best constrained by future surveys. We extend the analysis to two particular parameterizations of μ and η and consider, in addition to Euclid, also SKA1, SKA2, DESI: we find in this case that future surveys will be able to constrain the current values of η and μ at the 2-5% level when using only linear scales (wavevector k < 0 . 15 h/Mpc), depending on the specific time parameterization; sensitivity improves to about 1% when non-linearities are included.

21SSD: a public data base of simulated 21-cm signals from the epoch of reionization

NASA Astrophysics Data System (ADS)

Semelin, B.; Eames, E.; Bolgar, F.; Caillat, M.

2017-12-01

The 21-cm signal from the epoch of reionization (EoR) is expected to be detected in the next few years, either with existing instruments or by the upcoming SKA and HERA projects. In this context, there is a pressing need for publicly available high-quality templates covering a wide range of possible signals. These are needed both for end-to-end simulations of the up-coming instruments and to develop signal analysis methods. We present such a set of templates, publicly available, for download at 21ssd.obspm.fr. The data base contains 21-cm brightness temperature lightcones at high and low resolution, and several derived statistical quantities for 45 models spanning our choice of 3D parameter space. These data are the result of fully coupled radiative hydrodynamic high-resolution (10243) simulations performed with the LICORICE code. Both X-ray and Lyman line transfer are performed to account for heating and Wouthuysen-Field coupling fluctuations. We also present a first exploitation of the data using the power spectrum and the pixel distribution function (PDF) computed from lightcone data. We analyse how these two quantities behave when varying the model parameters while taking into account the thermal noise expected of a typical SKA survey. Finally, we show that the noiseless power spectrum and PDF have different - and somewhat complementary - abilities to distinguish between different models. This preliminary result will have to be expanded to the case including thermal noise. This type of results opens the door to formulating an optimal sampling of the parameter space, dependent on the chosen diagnostics.

Bubble size statistics during reionization from 21-cm tomography

NASA Astrophysics Data System (ADS)

Giri, Sambit K.; Mellema, Garrelt; Dixon, Keri L.; Iliev, Ilian T.

2018-01-01

The upcoming SKA1-Low radio interferometer will be sensitive enough to produce tomographic imaging data of the redshifted 21-cm signal from the Epoch of Reionization. Due to the non-Gaussian distribution of the signal, a power spectrum analysis alone will not provide a complete description of its properties. Here, we consider an additional metric which could be derived from tomographic imaging data, namely the bubble size distribution of ionized regions. We study three methods that have previously been used to characterize bubble size distributions in simulation data for the hydrogen ionization fraction - the spherical-average (SPA), mean-free-path (MFP) and friends-of-friends (FOF) methods - and apply them to simulated 21-cm data cubes. Our simulated data cubes have the (sensitivity-dictated) resolution expected for the SKA1-Low reionization experiment and we study the impact of both the light-cone (LC) and redshift space distortion (RSD) effects. To identify ionized regions in the 21-cm data we introduce a new, self-adjusting thresholding approach based on the K-Means algorithm. We find that the fraction of ionized cells identified in this way consistently falls below the mean volume-averaged ionized fraction. From a comparison of the three bubble size methods, we conclude that all three methods are useful, but that the MFP method performs best in terms of tracking the progress of reionization and separating different reionization scenarios. The LC effect is found to affect data spanning more than about 10 MHz in frequency (Δz ∼ 0.5). We find that RSDs only marginally affect the bubble size distributions.

Radio weak lensing shear measurement in the visibility domain - II. Source extraction

NASA Astrophysics Data System (ADS)

Rivi, M.; Miller, L.

2018-05-01

This paper extends the method introduced in Rivi et al. (2016b) to measure galaxy ellipticities in the visibility domain for radio weak lensing surveys. In that paper, we focused on the development and testing of the method for the simple case of individual galaxies located at the phase centre, and proposed to extend it to the realistic case of many sources in the field of view by isolating visibilities of each source with a faceting technique. In this second paper, we present a detailed algorithm for source extraction in the visibility domain and show its effectiveness as a function of the source number density by running simulations of SKA1-MID observations in the band 950-1150 MHz and comparing original and measured values of galaxies' ellipticities. Shear measurements from a realistic population of 104 galaxies randomly located in a field of view of 1 \\deg ^2 (i.e. the source density expected for the current radio weak lensing survey proposal with SKA1) are also performed. At SNR ≥ 10, the multiplicative bias is only a factor 1.5 worse than what found when analysing individual sources, and is still comparable to the bias values reported for similar measurement methods at optical wavelengths. The additive bias is unchanged from the case of individual sources, but it is significantly larger than typically found in optical surveys. This bias depends on the shape of the uv coverage and we suggest that a uv-plane weighting scheme to produce a more isotropic shape could reduce and control additive bias.

Dawn Survey Orbit Image 36

NASA Image and Video Library

2015-07-29

This image, taken by NASA's Dawn spacecraft, shows Dantu crater on dwarf planet Ceres from an altitude of 2,700 miles (4,400 kilometers). The image, with a resolution of 1,400 feet (410 meters) per pixel, was taken on June 24, 2015. Dantu, at bottom center, is about 75 miles (120 kilometers) across and 3 miles (5 kilometers) deep, has small patches of bright material sprinkled around it. http://photojournal.jpl.nasa.gov/catalog/PIA19609

Radar observations of asteroid 216 kleopatra

PubMed

Ostro; Hudson; Nolan; Margot; Scheeres; Campbell; Magri; Giorgini; Yeomans

2000-05-05

Radar observations of the main-belt, M-class asteroid 216 Kleopatra reveal a dumbbell-shaped object with overall dimensions of 217 kilometers by 94 kilometers by 81 kilometers (+/-25%). The asteroid's surface properties are consistent with a regolith having a metallic composition and a porosity comparable to that of lunar soil. Kleopatra's shape is probably the outcome of an exotic sequence of collisional events, and much of its interior may have an unconsolidated rubble-pile structure.

Translations on USSR Military Affairs, Number 1278

DTIC Science & Technology

1977-05-19

plans for conducting them. Here special responsibility rests on the staff, as the command body. Precisely clear planning based upon a pro - found...swimming 100 meters freestyle , cross-country race of 3 kilo- meters or skiing 10 kilometers (for age group I), 1-kilometer cross-country race or...Classification), swimming 100 meters freestyle , 3-kilometer cross-country race, figure driving of vehicle Categories 290 3’UO 3^0 3^0 1+00 270 300

Venus - Impact Crater in Eastern Navka Region

NASA Technical Reports Server (NTRS)

1991-01-01

This Magellan image, which is 50 kilometers (31 miles) in width and 80 kilometers (50 miles) in length, is centered at 11.9 degrees latitude, 352 degrees longitude in the eastern Navka Region of Venus. The crater, which is approximately 8 kilometers (5 miles) in diameter, displays a butterfly symmetry pattern. The ejecta pattern most likely results from an oblique impact, where the impactor came from the south and ejected material to the north.

Mimas Looks On

NASA Image and Video Library

2004-09-07

Lonely Mimas swings around Saturn, seeming to gaze down at the planet's splendid rings. The outermost, narrow F ring is visible here and exhibits some clumpy structure near the bottom of the frame. The shadow of Saturn's southern hemisphere stretches almost entirely across the rings. Mimas is 398 kilometers (247 miles) wide. The image was taken with the Cassini spacecraft narrow angle camera on August 15, 2004, at a distance of 8.8 million kilometers (5.5 million miles) from Saturn, through a filter sensitive to visible red light. The image scale is 53 kilometers (33 miles) per pixel. Contrast was slightly enhanced to aid visibility.almost entirely across the rings. Mimas is 398 kilometers (247 miles) wide. http://photojournal.jpl.nasa.gov/catalog/PIA06471

Global positioning system measurements for crustal deformation: Precision and accuracy

USGS Publications Warehouse

Prescott, W.H.; Davis, J.L.; Svarc, J.L.

1989-01-01

Analysis of 27 repeated observations of Global Positioning System (GPS) position-difference vectors, up to 11 kilometers in length, indicates that the standard deviation of the measurements is 4 millimeters for the north component, 6 millimeters for the east component, and 10 to 20 millimeters for the vertical component. The uncertainty grows slowly with increasing vector length. At 225 kilometers, the standard deviation of the measurement is 6, 11, and 40 millimeters for the north, east, and up components, respectively. Measurements with GPS and Geodolite, an electromagnetic distance-measuring system, over distances of 10 to 40 kilometers agree within 0.2 part per million. Measurements with GPS and very long baseline interferometry of the 225-kilometer vector agree within 0.05 part per million.

Venus - Volcanic features in Atla Region

NASA Technical Reports Server (NTRS)

1991-01-01

This Magellan image from the Atla region of Venus shows several types of volcanic features and superimposed surface fractures. The area in the image is approximately 350 kilometers (217 miles) across, centered at 9 degrees south latitude, 199 degrees east longitude. Lava flows emanating from circular pits or linear fissures form flower-shaped patterns in several areas. A collapse depression approximately 20 kilometers by 10 kilometers (12 by 6 miles) near the center of the image is drained by a lava channel approximately 40 kilometers (25 miles) long. Numerous surface fractures and graben (linear valleys) criss-cross the volcanic deposits in north to northeast trends. The fractures are not buried by the lavas, indicating that the tectonic activity post-dates most of the volcanic activity.

Larval retention and connectivity among populations of corals and reef fishes: history, advances and challenges

NASA Astrophysics Data System (ADS)

Jones, G. P.; Almany, G. R.; Russ, G. R.; Sale, P. F.; Steneck, R. S.; van Oppen, M. J. H.; Willis, B. L.

2009-06-01

The extent of larval dispersal on coral reefs has important implications for the persistence of coral reef metapopulations, their resilience and recovery from an increasing array of threats, and the success of protective measures. This article highlights a recent dramatic increase in research effort and a growing diversity of approaches to the study of larval retention within (self-recruitment) and dispersal among (connectivity) isolated coral reef populations. Historically, researchers were motivated by alternative hypotheses concerning the processes limiting populations and structuring coral reef assemblages, whereas the recent impetus has come largely from the need to incorporate dispersal information into the design of no-take marine protected area (MPA) networks. Although the majority of studies continue to rely on population genetic approaches to make inferences about dispersal, a wide range of techniques are now being employed, from small-scale larval tagging and paternity analyses, to large-scale biophysical circulation models. Multiple approaches are increasingly being applied to cross-validate and provide more realistic estimates of larval dispersal. The vast majority of empirical studies have focused on corals and fishes, where evidence for both extremely local scale patterns of self-recruitment and ecologically significant connectivity among reefs at scales of tens of kilometers (and in some cases hundreds of kilometers) is accumulating. Levels of larval retention and the spatial extent of connectivity in both corals and fishes appear to be largely independent of larval duration or reef size, but may be strongly influenced by geographic setting. It is argued that high levels of both self-recruitment and larval import can contribute to the resilience of reef populations and MPA networks, but these benefits will erode in degrading reef environments.

Local Group dSph radio survey with ATCA (III): constraints on particle dark matter

NASA Astrophysics Data System (ADS)

Regis, Marco; Colafrancesco, Sergio; Profumo, Stefano; de Blok, W. J. G.; Massardi, Marcella; Richter, Laura

2014-10-01

We performed a deep search for radio synchrotron emissions induced by weakly interacting massive particles (WIMPs) annihilation or decay in six dwarf spheroidal (dSph) galaxies of the Local Group. Observations were conducted with the Australia Telescope Compact Array (ATCA) at 16 cm wavelength, with an rms sensitivity better than 0.05 mJy/beam in each field. In this work, we first discuss the uncertainties associated with the modeling of the expected signal, such as the shape of the dark matter (DM) profile and the dSph magnetic properties. We then investigate the possibility that point-sources detected in the proximity of the dSph optical center might be due to the emission from a DM cuspy profile. No evidence for an extended emission over a size of few arcmin (which is the DM halo size) has been detected. We present the associated bounds on the WIMP parameter space for different annihilation/decay final states and for different astrophysical assumptions. If the confinement of electrons and positrons in the dSph is such that the majority of their power is radiated within the dSph region, we obtain constraints on the WIMP annihilation rate which are well below the thermal value for masses up to few TeV. On the other hand, for conservative assumptions on the dSph magnetic properties, the bounds can be dramatically relaxed. We show however that, within the next 10 years and regardless of the astrophysical assumptions, it will be possible to progressively close in on the full parameter space of WIMPs by searching for radio signals in dSphs with SKA and its precursors.

SKA weak lensing - III. Added value of multiwavelength synergies for the mitigation of systematics

NASA Astrophysics Data System (ADS)

Camera, Stefano; Harrison, Ian; Bonaldi, Anna; Brown, Michael L.

2017-02-01

In this third paper of a series on radio weak lensing for cosmology with the Square Kilometre Array, we scrutinize synergies between cosmic shear measurements in the radio and optical/near-infrared (IR) bands for mitigating systematic effects. We focus on three main classes of systematics: (I) experimental systematic errors in the observed shear; (II) signal contamination by intrinsic alignments and (III) systematic effects due to an incorrect modelling of non-linear scales. First, we show that a comprehensive, multiwavelength analysis provides a self-calibration method for experimental systematic effects, only implying <50 per cent increment on the errors on cosmological parameters. We also illustrate how the cross-correlation between radio and optical/near-IR surveys alone is able to remove residual systematics with variance as large as 10-5, I.e. the same order of magnitude of the cosmological signal. This also opens the possibility of using such a cross-correlation as a means to detect unknown experimental systematics. Secondly, we demonstrate that, thanks to polarization information, radio weak lensing surveys will be able to mitigate contamination by intrinsic alignments, in a way similar but fully complementary to available self-calibration methods based on position-shear correlations. Lastly, we illustrate how radio weak lensing experiments, reaching higher redshifts than those accessible to optical surveys, will probe dark energy and the growth of cosmic structures in regimes less contaminated by non-linearities in the matter perturbations. For instance, the higher redshift bins of radio catalogues peak at z ≃ 0.8-1, whereas their optical/near-IR counterparts are limited to z ≲ 0.5-0.7. This translates into having a cosmological signal 2-5 times less contaminated by non-linear perturbations.

HI observations of Sextans A and B with the SKA pathfinder KAT-7

NASA Astrophysics Data System (ADS)

Namumba, B.; Carignan, C.; Passmoor, S.

2018-04-01

HI observations of the Local Group dwarf irregular galaxies Sextans A and B, obtained with the Karoo Array Telescope (KAT-7) are presented. The KAT-7 wide field of view and excellent surface brightness sensitivity allows us to verify the true HI extent of the galaxies. We derive HI extends of 30' and 20' and total HI fluxes of 181 ± 2.0 Jy.km.s-1 and 105 ± 1.4 Jy.km.s-1 for Sextans A and B respectively. This result shows clearly the overestimate of the HI extent and total flux of 54' and 264 Jy.km.s-1 reported for Sextans A using the Effelsberg observations. Tilted ring models allow us to derive the rotation curves (RCs) of Sextans A and B out to 550″ (˜ 3.5 kpc) and 650″ (˜ 4 kpc) respectively. The RCs of the two galaxies are seen to decline in the outer parts. The dark matter distribution in Sextans A is better described by the pseudo-isothermal halo model when a M/L ratio of 0.2 is used. For Sextans B, the mass model fits are not as good but again an isothermal sphere with a M/L of 0.2 represents best the data. Using the MOdified Newtonian Dynamics (MOND), better fits are obtained when the constant a0 is allowed to vary. The critical densities for gravitational instabilities are calculated using the Toomre-Q and cloud-growth based on shear criterion. We find that in regions of star formation, the cloud growth criterion based on shear explains better the star formation in both Sextans A and B.

Post-Newtonian evolution of massive black hole triplets in galactic nuclei - III. A robust lower limit to the nHz stochastic background of gravitational waves

NASA Astrophysics Data System (ADS)

Bonetti, Matteo; Sesana, Alberto; Barausse, Enrico; Haardt, Francesco

2018-06-01

Inspiraling massive black hole binaries (MBHBs) forming in the aftermath of galaxy mergers are expected to be the loudest gravitational-wave (GW) sources relevant for pulsar-timing arrays (PTAs) at nHz frequencies. The incoherent overlap of signals from a cosmic population of MBHBs gives rise to a stochastic GW background (GWB) with characteristic strain around hc ˜ 10-15 at a reference frequency of 1 yr-1, although uncertainties around this value are large. Current PTAs are piercing into the GW amplitude range predicted by MBHB-population models, but no detection has been reported so far. To assess the future success prospects of PTA experiments, it is therefore important to estimate the minimum GWB level consistent with our current understanding of the formation and evolution of galaxies and massive black holes (MBHs). To this purpose, we couple a semi-analytic model of galaxy evolution and an extensive study of the statistical outcome of triple MBH interactions. We show that even in the most pessimistic scenario where all MBHBs stall before entering the GW-dominated regime, triple interactions resulting from subsequent galaxy mergers inevitably drive a considerable fraction of the MBHB population to coalescence. At frequencies relevant for PTA, the resulting GWB is only a factor of 2-3 suppressed compared to a fiducial model where binaries are allowed to merge over Gyr time-scales . Coupled with current estimates of the expected GWB amplitude range, our findings suggest that the minimum GWB from cosmic MBHBs is unlikely to be lower than hc ˜ 10-16 (at f = 1 yr-1), well within the expected sensitivity of projected PTAs based on future observations with FAST, MeerKAT, and SKA.

Constraining the contribution of active galactic nuclei to reionization

NASA Astrophysics Data System (ADS)

Hassan, Sultan; Davé, Romeel; Mitra, Sourav; Finlator, Kristian; Ciardi, Benedetta; Santos, Mario G.

2018-01-01

Recent results have suggested that active galactic nuclei (AGN) could provide enough photons to reionize the Universe. We assess the viability of this scenario using a semi-numerical framework for modelling reionization, to which we add a quasar contribution by constructing a Quasar Halo Occupancy Distribution (QHOD) based on Giallongo et al. observations. Assuming a constant QHOD, we find that an AGN-only model cannot simultaneously match observations of the optical depth τe, neutral fraction and ionizing emissivity. Such a model predicts τe too low by ∼2σ relative to Planck constraints, and reionizes the Universe at z ≲ 5. Arbitrarily increasing the AGN emissivity to match these results yields a strong mismatch with the observed ionizing emissivity at z ∼ 5. If we instead assume a redshift-independent AGN luminosity function yielding an emissivity evolution like that assumed in Madau & Haardt model, then we can match τe albeit with late reionization; however, such evolution is inconsistent with observations at z ∼ 4-6 and poorly motivated physically. These results arise because AGN are more biased towards massive haloes than typical reionizing galaxies, resulting in stronger clustering and later formation times. AGN-dominated models produce larger ionizing bubbles that are reflected in ∼×2 more 21 cm power on all scales. A model with equal part galaxies and AGN contribution is still (barely) consistent with observations, but could be distinguished using next-generation 21 cm experiments such as Hydrogen Epoch of Reionization Array and SKA-low. We conclude that, even with recent claims of more faint AGN than previously thought, AGN are highly unlikely to dominate the ionizing photon budget for reionization.

H I observations of Sextans A and B with the SKA pathfinder KAT-7

NASA Astrophysics Data System (ADS)

Namumba, B.; Carignan, C.; Passmoor, S.

2018-07-01

H I observations of the Local Group dwarf irregular galaxies Sextans A and B, obtained with the Karoo Array Telescope (KAT-7) are presented. The KAT-7 wide field of view and excellent surface brightness sensitivity allows us to verify the true H I extent of the galaxies. We derive H I extends of 30 and 20 arcmin and total H I fluxes of 181 ± 2.0 and 105 ± 1.4 Jy km s-1 for Sextans A and B, respectively. This result shows clearly the overestimate of the H I extent and total flux of 54 arcmin and 264 Jy km s-1 reported for Sextans A using the Effelsberg observations. Tilted ring models allow us to derive the rotation curves (RCs) of Sextans A and B out to 550 arcsec (˜3.5 kpc) and 650 arcsec (˜4 kpc), respectively. The RCs of the two galaxies are seen to decline in the outer parts. The dark matter distribution in Sextans A is better described by the pseudo-isothermal halo model when an M/L ratio of 0.2 is used. For Sextans B, the mass model fits are not as good but again an isothermal sphere with an M/L of 0.2 represents best the data. Using the MOdified Newtonian Dynamics, better fits are obtained when the constant a0 is allowed to vary. The critical densities for gravitational instabilities are calculated using the Toomre-Q and cloud-growth based on shear criterion. We find that in regions of star formation, the cloud growth criterion based on shear explains better the star formation in both Sextans A and B.

Sedimentary Rocks Associated with the Coal Seams of the Saddle Beds from the Chwałowice Trough - West Part of Upper Silesian Coal Basin / Skały Osadowe Towarzyszące Pokładom Węgla Warstw Siodłowych Niecki Chwałowickiej - Zachodnia Część Górnośląskiego Zagłębia Węglowego

NASA Astrophysics Data System (ADS)

Stanienda, Katarzyna

2015-03-01

The results of investigation of the associated rocks with the Saddle Beds Coals Seams from Chwałowice Trough were presented in this article. The results of researches show that sandstones and mudstones dominate in the investigating profile. Claystones are situated mainly in ceilings and floors of coal seams. Grains of sandstones include mainly quartz, feldspars, micas and also quartzite's and gneiss's fragments. It is also possible to observe small grains of heavy minerals. Some of sandstones present bad compactness and are destroyed during transportation. This feature is connected with presence of little quantity of cement, especially in medium grained sandstones, which include more matrix than typical cement. The cement is built mainly of clay minerals, kaolinite and illite, carbonates and chalcedony but X-ray diffraction confirmed also the presence of halite in the cement of investigated sandstones. Mudstones and claystones are composed mainly of clay minerals. It's also possible to find quartz and micas there. Higher amounts of quartz and micas are possible to find rather in mudstones. The associated rocks with the Saddle Beds Coal Seams from Chwałowice Trough include also organic matter. W artykule przedstawiono wyniki badań skał towarzyszących pokładom węgla warstw siodłowych Niecki Chwałowickiej. Wyniki badań wskazują, że w badanym profilu dominują piaskowce oraz mułowce. Iłowce natomiast występują głównie w stropach i spągach pokładów węgla. Okruchy piaskowców to głównie ziarna kwarcu, skaleni, mik oraz fragmenty kwarcytów i gnejsów. Można tu również zaobserwować drobne okruchy minerałów ciężkich. Niektóre piaskowce charakteryzują się obniżoną zwięzłością i podczas transportu ulegają rozpadowi. Cecha ta związana jest z niewielką ilością spoiwa, szczególnie w piaskowcach średnioziarnistych, w których matrix przeważa nad typowym cementem. Spoiwo zbudowane jest głównie z minerałów ilastych, takich jak kaolinit i illit, węglanów i chalcedonu, chociaż wyniki dyfraktometrii rentgenowskiej potwierdziły występowanie w spoiwie badanych piaskowców również halitu. Na podstawie składu mineralnego piaskowców, dokonano ich klasyfikacji, stosując podziały skał okruchowych Krynina (1948) i Pettijohn'a-Potter'a-Siever'a (1973). Według klasyfikacji Krynina badane piaskowce reprezentują szarogłazy (szarowaki). W klasyfikacji Pettijohn'a, próbki 6, 8 i 13 reprezentują arenity lityczne, natomiast próbki 3 i 10- waki. Mułowce i iłowce zbudowane SA głównie z minerałów ilastych. Można w nich również spotkać ziarna kwarcu oraz miki. Wyższy udział kwarcu i mik jest jednak charakterystyczny dla mułowców. Skały towarzyszące pokładom węgla warstw siodłowych Niecki Chwałowickiej zawierają również domieszki substancji organicznej.

47 CFR 90.545 - TV/DTV interference protection criteria.

Code of Federal Regulations, 2012 CFR

2012-10-01

... 40 dB at the hypothetical Grade B contour (64 dBµV/m) (88.5 kilometers or 55.0 miles) of the TV station or 17 dB at the equivalent Grade B contour (41 dBµV/m) (88.5 kilometers or 55.0 miles) of the DTV... contour (64 dBµV/m) (88.5 kilometers or 55.0 miles) of the TV station or −23 dB at the equivalent Grade B...

Saturn Methane Image

NASA Image and Video Library

2004-03-05

NASA's Cassini narrow angle camera took this image of Saturn on Feb. 16, 2004, from a distance of 66.1 million kilometers (41.1 million miles) in a special filter which reveals clouds and haze high in the atmosphere. The image scale is 397 kilometers (247 miles) per pixel. The MT2 spectral filter samples a near-infrared region of the electromagnetic spectrum where methane gas absorbs light at a wavelength of 727 nanometers. In the image, methane gas is uniformly mixed with hydrogen, the main gas in Saturn's atmosphere. Dark locales are places of strong methane absorption, relatively free of high clouds; the bright areas are places with high, thick clouds which shield the methane below. Image details reveal a high, thick equatorial cloud and a relatively deep or thin haze encircling the pole, as well as several distinct latitude bands with different cloud height attributes. It also shows a high atmospheric disturbance, just south of the equator, which has persisted throughout the 1990s in images returned by NASA's Hubble Space Telescope. Four of Saturn's moons are visible (clockwise from above right): Enceladus (499 kilometers, or 310 miles across); Mimas (396 kilometers, or 245 miles across); Tethys (1,060 kilometers, or 659 miles across); and Rhea (1,528 kilometers, or 949 miles across). The imaging team enhanced the brightness of Mimas and Enceladus by a factor of three. http://photojournal.jpl.nasa.gov/catalog/PIA05381

Juno Observes Jupiter, Io and Europa

NASA Image and Video Library

2017-10-06

This color-enhanced image of Jupiter and two of its largest moons -- Io and Europa -- was captured by NASA's Juno spacecraft as it performed its eighth flyby of the gas giant planet. The image was taken on Sept. 1, 2017 at 3:14 p.m. PDT (6:14 p.m. EDT). At the time the image was taken, the spacecraft was about 17,098 miles (27,516 kilometers) from the tops of the clouds of the planet at a latitude of minus 49.372 degrees. Closer to the planet, the Galilean moon of Io can be seen at an altitude of 298,880 miles (481,000 kilometers) and at a spatial scale of 201 miles (324 kilometers) per pixel. In the distance (to the left), another one of Jupiter's Galilean moons, Europa, is visible at an altitude of 453,601 miles (730,000 kilometers) and at a spatial scale of 305 miles (492 kilometers) per pixel. Citizen scientist Roman Tkachenko processed this image using data from the JunoCam imager. https://photojournal.jpl.nasa.gov/catalog/PIA21968

The ionosphere of Europa from Galileo radio occultations

NASA Technical Reports Server (NTRS)

Kliore, A. J.; Hinson, D. P.; Flasar, F. M.; Nagy, A. F.; Cravens, T. E.

1997-01-01

The Galileo spacecraft performed six radio occultation observations of Jupiter's Galilean satellite Europa during its tour of the jovian system. In five of the six instances, these occultations revealed the presence of a tenuous ionosphere on Europa, with an average maximum electron density of nearly 10(4) per cubic centimeter near the surface and a plasma scale height of about 240 +/- 40 kilometers from the surface to 300 kilometers and of 440 +/- 60 kilometers above 300 kilometers. Such an ionosphere could be produced by solar photoionization and jovian magnetospheric particle impact in an atmosphere having a surface density of about 10(8) electrons per cubic centimeter. If this atmosphere is composed primarily of O2, then the principal ion is O2+ and the neutral atmosphere temperature implied by the 240-kilometer scale height is about 600 kelvin. If it is composed of H2O, the principal ion is H3O+ and the neutral temperature is about 340 kelvin. In either case, these temperatures are much higher than those observed on Europa's surface, and an external heating source from the jovian magnetosphere is required.

Biomass energy inventory and mapping system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kasile, J.D.

1993-12-31

A four-stage biomass energy inventory and mapping system was conducted for the entire State of Ohio. The product is a set of maps and an inventory of the State of Ohio. The set of amps and an inventory of the State`s energy biomass resource are to a one kilometer grid square basis on the Universal Transverse Mercator (UTM) system. Each square kilometer is identified and mapped showing total British Thermal Unit (BTU) energy availability. Land cover percentages and BTU values are provided for each of nine biomass strata types for each one kilometer grid square. LANDSAT satellite data was usedmore » as the primary stratifier. The second stage sampling was the photointerpretation of randomly selected one kilometer grid squares that exactly corresponded to the LANDSAT one kilometer grid square classification orientation. Field sampling comprised the third stage of the energy biomass inventory system and was combined with the fourth stage sample of laboratory biomass energy analysis using a Bomb calorimeter and was then used to assign BTU values to the photointerpretation and to adjust the LANDSAT classification. The sampling error for the whole system was 3.91%.« less

Barren area evapotranspiration estimates generated from energy budget measurements in the Gila River valley of Arizona

USGS Publications Warehouse

Leppanen, O.E.

1980-01-01

Estimates of evapotranspiration for 479 successive days were created by using energy budget measurements. The measurement point was on the 2-kilometer wide flood plain of the Gila River in east-central Arizona, about 18 kilometers above Coolidge Dam. The flood plain had been cleared of all tall vegetation for distances of about 20 kilometers upstream and 5 kilometers downstream from the measurement site. Chaining, raking, and burning had been used to clear the area immediately surrounding the measurement site about 6 months before measurements began. Ground cover was sparse volunteer Bermudagrass and scattered seepwillow for a distance of at least 1 kilometer in all directions from the measurement point . The water table was deep , so most of the evaporated water came from rainfall, but some came from soil moisture deeper than 2 meters. The March to March water loss (evapotranspiration less rain) was about 47 millimeters, evapotranspiration demand was 377 millimeters. Daily rates varied from very small amounts of condensation to almost 5 millimeters of evapotranspiration. (USGS)

The ionosphere of Europa from Galileo radio occultations.

PubMed

Kliore, A J; Hinson, D P; Flasar, F M; Nagy, A F; Cravens, T E

1997-07-18

The Galileo spacecraft performed six radio occultation observations of Jupiter's Galilean satellite Europa during its tour of the jovian system. In five of the six instances, these occultations revealed the presence of a tenuous ionosphere on Europa, with an average maximum electron density of nearly 10(4) per cubic centimeter near the surface and a plasma scale height of about 240 +/- 40 kilometers from the surface to 300 kilometers and of 440 +/- 60 kilometers above 300 kilometers. Such an ionosphere could be produced by solar photoionization and jovian magnetospheric particle impact in an atmosphere having a surface density of about 10(8) electrons per cubic centimeter. If this atmosphere is composed primarily of O2, then the principal ion is O2+ and the neutral atmosphere temperature implied by the 240-kilometer scale height is about 600 kelvin. If it is composed of H2O, the principal ion is H3O+ and the neutral temperature is about 340 kelvin. In either case, these temperatures are much higher than those observed on Europa's surface, and an external heating source from the jovian magnetosphere is required.

Magellan 3D perspective of Venus surface in western Eistla Regio

NASA Technical Reports Server (NTRS)

1991-01-01

Magellan synthetic aperture radar data was used to create this three- dimensional (3D) perspective view of Venus' western Eistla Regio. This viewpoint is located at 1,310 kilometers (812 miles) southwest of Gula Mons at an elevation of 0.178 kilometers (0.48 miles). The view is of the northeast with Gula Mons appearing on the horizon. Gula Mons, a 3 kilometer (1.86 mile) high volcano, is located at approximately 22 degrees north latitude, 359 degrees east longitude. The impact crater Cunitz, named for the astronomer and mathematician Maria Cunitz, is visible in the center of the image. The crater is 48.5 kilometers (30 miles) in diameter and is 215 kilometers (133 miles) from the viewer's position. Magellan synthetic aperture radar data is combined with radar altimetry to develop a 3D map of the surface. Rays cast in a computer intersect the surface to create a 3D view. Simulated color and a digital elevation map developed by the United States (U.S.) Geological Survey is used to enhanc

Multi-mode phase speed measurements with array-based analysis: Application to the North American continent

NASA Astrophysics Data System (ADS)

Matsuzawa, H.; Yoshizawa, K.

2017-12-01

Recent high-density broad-band seismic networks allow us to construct improved 3-D upper mantle models with unprecedented horizontal resolution using surface waves. Such dispersion measurements have been primarily based on the analysis of fundamental mode. Higher-mode information can be of help in enhancing vertical resolution of 3-D models, but their dispersion analysis is intrinsically difficult, since wave-packets of several modes are overlapped each other in an observed seismogram. In this study, we measure phase dispersion of multi-mode surface waves with an array-based analysis. Our method is modeled on a one-dimensional frequency-wavenumber method originally developed by Nolet (1975, GRL), which can be applied to a set of broadband seismic records observed in a linear array along a great circle path. Through this analysis, we can obtain a spectrogram in c-T (phase speed - period) domain, which is characterized by mode-branch dispersion curves and relative spectral powers for each mode. Synthetic experiments indicate that we can separate the modal contribution using a long linear array with typical array length of about 2000 to 4000 km. The method is applied to a large data set from USArray using nearly 400 seismic events in 2007 - 2014 with Mw 6.5 or greater. Our phase-speed maps for the fundamental-mode Love and Rayleigh waves and the first higher-mode Rayleigh waves match well with the earlier models. The phase speed maps reflect typical large-scale features of regional seismic structure in North America, but smaller-scale variations are less constrained in our model, since our measured phase speeds represent path-average features over a long path (about a few thousands kilometers). Our multi-mode dispersion measurements can also be used for the extraction of mode-branch waveforms for the first a few modes. This can be done by applying a narrow filter around the dispersion curves of a target mode in c-T spectrogram. The mode-branch waveforms can then be reconstructed based on a linear Radon transform (e.g., Luo et al., 2015, GJI). Synthetic experiments suggest that we can successfully retrieve the mode-branch waveforms for several mode branches, which can be used in the secondary analysis for constraining local-scale heterogeneity with enhanced depth resolution.

Astrophysical targets of the Fresnel diffractive imager

NASA Astrophysics Data System (ADS)

Koechlin, L.; Deba, P.; Raksasataya, T.

2017-11-01

The Fresnel Diffractive imager is an innovative concept of distributed space telescope, for high resolution (milli arc-seconds) spectro-imaging in the IR, visible and UV domains. This paper presents its optical principle and the science that can be done on potential astrophysical targets. The novelty lies in the primary optics: a binary Fresnel array, akin to a binary Fresnel zone plate. The main interest of this approach is the relaxed manufacturing and positioning constraints. While having the resolution and imaging capabilities of lens or mirrors of equivalent size, no optical material is involved in the focusing process: just vacuum. A Fresnel array consists of millions void subapertures punched into a large and thin opaque membrane, that focus light by diffraction into a compact and highly contrasted image. The positioning law of the aperture edges drives the image quality and contrast. This optical concept allows larger and lighter apertures than solid state optics, aiming to high angular resolution and high dynamic range imaging, in particular for UV applications. Diffraction focusing implies very long focal distances, up to dozens of kilometers, which requires at least a two-vessel formation flying in space. The first spacecraft, "the Fresnel Array spacecraft", holds the large punched foil: the Fresnel Array. The second, the "Receiver spacecraft" holds the field optics and focal instrumentation. A chromatism correction feature enables moderately large (20%) relative wavebands, and fields of a few to a dozen arc seconds. This Fresnel imager is adapted to high contrast stellar environments: dust disks, close companions and (we hope) exoplanets. Specific to the particular grid-like pattern of the primary focusing zone plate, is the very high dynamic range achieved in the images, in the case of compact objects. Large stellar photospheres may also be mapped with Fresnel arrays of a few meters opertaing in the UV. Larger and more complex fields can be imaged with a lesser dynamic range: galactic or extragalactic, or at the opposite distance scale: small solar system bodies. This paper will briefly address the optical principle, and in more detail the astrophysical missions and targets proposed for a 4-meter class demonstrator: - Exoplanet imaging, Exoplanet spectroscopic analysis in the visible and UV, - Stellar environments, young stellar systems, disks, - Galactic clouds, astrochemistry, - IR observation of the galactic center, - Small objects of our solar system.

Airborne lidar measurements of the soufriere eruption of 17 april 1979.

PubMed

Fuller, W H; Sokol, S; Hunt, W H

1982-06-04

At the time of the Soufriere, St. Vincent, volcanic eruption of 17 April 1979, a NASA P-3 aircraft with an uplooking lidar (light detection and ranging) system onboard was airborne 130 kilometers east of the island. Lidar measurements of the fresh volcanic ash were made approximately 2 hours after the eruption, 120 kilometers to the northeast and east. On the evening of 18 April, the airborne lidar, on a southerly flight track, detected significant amounts of stratospheric material in layers at 16, 17, 18, and 19.5 kilometers. These data, and measurements to the north on 19 April, indicate that the volcanic plume penetrated the stratosphere to an altitude of about 20 kilometers and moved south during the first 48 hours after the eruption.

Airborne lidar measurements of the Soufriere eruption of 17 April 1979

NASA Technical Reports Server (NTRS)

Fuller, W. H., Jr.; Sokol, S.; Hunt, W. H.

1982-01-01

At the time of the Soufriere, St. Vincent, volcanic eruption of April 17, 1979, a NASA P-3 aircraft with an uplooking lidar (light detection and ranging) system onboard was airborne 130 kilometers east of the island. Lidar measurements of the fresh volcanic ash were made approximately 2 hours after the eruption, 120 kilometers to the northeast and east. On the evening of April 18, the airborne lidar, on a southerly flight track, detected significant amounts of stratospheric material in layers at 16, 17, 18, and 19.5 kilometers. These data, and measurements to the north on April 19, indicate that the volcanic plume penetrated the stratosphere to an altitude of about 20 kilometers and moved south during the first 48 hours after the eruption.

Data Management challenges in Astronomy and Astroparticle Physics

NASA Astrophysics Data System (ADS)

Lamanna, Giovanni

2015-12-01

Astronomy and Astroparticle Physics domains are experiencing a deluge of data with the next generation of facilities prioritised in the European Strategy Forum on Research Infrastructures (ESFRI), such as SKA, CTA, KM3Net and with other world-class projects, namely LSST, EUCLID, EGO, etc. The new ASTERICS-H2020 project brings together the concerned scientific communities in Europe to work together to find common solutions to their Big Data challenges, their interoperability, and their data access. The presentation will highlight these new challenges and the work being undertaken also in cooperation with e-infrastructures in Europe.

[Chromosome variability in the tissue culture of rare Gentiana species].

PubMed

Tvardovs'ka, M O; Strashniuk, N M; Mel'nyk, V M; Adonin, V I; Kunakh, V A

2008-01-01

Cytogenetic analysis of plants and tissue culture of Gentiana lutea, G. punctata, G. acaulis has been carried out. Culturing in vitro was found to result in the changes of chromosome number in the calluses of the species involved. Species specificity for variation of the cultured cell genomes was shown. Contribution of the original plant genotypes to the cytogenetic structure of the tissue culture was established. Gentiana callus tissues (except for in vitro culture of G. punctata, derived from plant of Breskul'ska population) were found to exhibit modal class with the cells of diploid and nearly diploid chromosome sets.

Radio Astronomy at the Centre for High Performance Computing in South Africa

NASA Astrophysics Data System (ADS)

Catherine Cress; UWC Simulation Team

2014-04-01

I will present results on galaxy evolution and cosmology which we obtained using the supercomputing facilities at the CHPC. These include cosmological-scale N-body simulations modelling neutral hydrogen as well as the study of the clustering of radio galaxies to probe the relationship between dark and luminous matter in the universe. I will also discuss the various roles that the CHPC is playing in Astronomy in SA, including the provision of HPC for a variety of Astronomical applications, the provision of storage for radio data, our educational programs and our participation in planning for the SKA.

The Cosmic Evolution Through UV Spectroscopy (CETUS) Probe Mission Concept

NASA Astrophysics Data System (ADS)

Danchi, William; Heap, Sara; Woodruff, Robert; Hull, Anthony; Kendrick, Stephen E.; Purves, Lloyd; McCandliss, Stephan; Kelly Dodson, Greg Mehle, James Burge, Martin Valente, Michael Rhee, Walter Smith, Michael Choi, Eric Stoneking

2018-01-01

CETUS is a mission concept for an all-UV telescope with 3 scientific instruments: a wide-field camera, a wide-field multi-object spectrograph, and a point-source high-resolution and medium resolution spectrograph. It is primarily intended to work with other survey telescopes in the 2020’s (e.g. E-ROSITA (X-ray), LSST, Subaru, WFIRST (optical-near-IR), SKA (radio) to solve major, outstanding problems in astrophysics. In this poster presentation, we give an overview of CETUS key science goals and a progress report on the CETUS mission and instrument design.

A Study of the Nearfield of an Excited Spherical Shell.

DTIC Science & Technology

1980-03-17

8217 tte exact wave harmonic series and the approximate Geometrical Theory of Diffraction (GTD) were used to predict the acoustic near field of an elastic...rr) )1/3 n 4 n14 XV e i+ (424 (ka) (2h (ka) nn an1 % Tte SkaI/ rA’ (k)2 nn in Ap ndi B]. =Q (ikc)~ (4.25)h(1 (a n Tn whee i adeayftore fo acosi prpaa3o...Approach to Scattering from Elastic Spherical Shells," NUC TP425, September 1974, Naval Undersea Center, San Diego, California. 36. Pathak, P. H. and

The origin of a coarse lithic breccia in the 34 ka caldera-forming Sounkyo eruption, Taisetsu volcano group, central Hokkaido, Japan

NASA Astrophysics Data System (ADS)

Yasuda, Y.; Suzuki-Kamata, K.

2018-05-01

The 34 ka Sounkyo eruption produced 7.6 km3 of tephra ( 5 km3 DRE) as fallout, ignimbrite, and lithic breccia units, forming a small, 2-km-diameter summit caldera in the Taisetsu volcano group, Japan. The Sounkyo eruption products are made up of five eruptive units (SK-A to -E) in proximal regions, corresponding to the distal deposits, a 1- to 2-m-thick pumice fallout and the Px-type ignimbrite up to 220 m thick. The eruption began with a fallout phase, producing unstable low eruption columns during the earlier phase to form a <7-m-thick succession of well-stratified fallouts (SK-A1 and the lower part of the distal fallout). The eruption column reached up to 25 km high (subplinian to plinian) and became more stable at the late of the phase, producing a < 60-m-thick, pumice-dominated fallout (SK-A2 and the upper part of the distal fallout). The second phase, the climax of the Sounkyo eruption, produced a widespread, valley-filling ignimbrite in both proximal and distal regions (SK-B and the Px-type ignimbrite). At the end of the climactic phase, the waning of the eruption led to extensive failure of the walls of the shallow conduit, generating a dense, lithic-rich, low-mobile pyroclastic density current (PDC) to form a >27-m-thick, unstratified and ungraded, coarse lithic breccia (SK-C). The failure in turn choked the conduit, and then the eruption stopped. After a short eruptive hiatus, the eruption resumed with a short-lived fall phase, establishing an eruption column up to 16 km high and producing a <6-m-thick scoria fallout (SK-D). Finally, the eruption ended with the generation of PDCs by eruption column collapse to form a 5- to 15-m-thick ignimbrite in the proximal area (SK-E). Volume relationships between the caldera, ejected magma, and ejected lithic fragments suggest that the caldera was not essentially formed by caldera collapse but, instead, by vent widening as a consequence of explosive erosion and failure of the shallow conduit. The dominance of shallow-origin volcanic rocks in the lithic fraction throughout the Sounkyo eruption products implies the development of a flaring funnel-shaped vent. Hence, the occurrence of lithic breccias within small caldera-forming eruption products does not necessarily reflect either the existence or the timing of caldera collapse, as commonly assumed in literature. Lithic breccias commonly overlie climactic ignimbrite/fallout deposits in small caldera-forming eruptions, and an alternative explanation is that this reflects the collapse of the shallow conduit after an eruption climax, whose walls had been highly fractured and had become unstable owing to progressive erosion.

Dawn HAMO Image 67

NASA Image and Video Library

2015-12-01

The tall, cone-shaped mountain Ahuna Mons is seen in this image taken by NASA's Dawn spacecraft. Ahuna Mons, named for the traditional post-harvest festival of the Sumi tribe of Nagaland in India, is about 4 miles (6 kilometers) tall and 12 miles (20 kilometers) in diameter. Dawn took this image on Oct. 14, 2015, from an altitude of 915 miles (1,470 kilometers). It has a resolution of 450 feet (140 meters) per pixel. http://photojournal.jpl.nasa.gov/catalog/PIA20130

Dawn HAMO Image 53

NASA Image and Video Library

2015-11-05

This image, taken by NASA's Dawn spacecraft, shows the surface of dwarf planet Ceres from an altitude of 915 miles (1,470 kilometers) around mid-latitudes. The image was taken on Sept. 28, 2015, and has a resolution of 450 feet (140 meters) per pixel. The unusual mountain Ahuna Mons is featured in this image, named for the traditional post-harvest festival of the Sumi tribe of Nagaland, India. It is 4 miles (6 kilometers) tall and 12 miles (20 kilometers) in diameter. http://photojournal.jpl.nasa.gov/catalog/PIA19995

Deformation studies on soufriere, st. Vincent, between 1977 and 1981.

PubMed

Fiske, R S; Shepherd, J B

1982-06-04

Dry-tilt measurements at two stations indicate that Soufriere Volcano gradually inflated at least 10 microradians prior to the initial explosions of April 1979 and then rapidly deflated more than 20 microradians after the activity got under way. The tilt measured at the station 6.5 kilometers from the summit was about twice that measured at a distance of 2.5 kilometers. This finding suggests the existence of a magma chamber at a depth of more than 10 kilometers.

Chaos Region

NASA Image and Video Library

2015-09-10

In the center of this 300-mile (470-kilometer) wide image of Pluto from NASA's New Horizons spacecraft is a large region of jumbled, broken terrain on the northwestern edge of the vast, icy plain informally called Sputnik Planum, to the right. The smallest visible features are 0.5 miles (0.8 kilometers) in size. This image was taken as New Horizons flew past Pluto on July 14, 2015, from a distance of 50,000 miles (80,000 kilometers). http://photojournal.jpl.nasa.gov/catalog/PIA19934

Venus - Impact Crater in Eastern Navka Region

NASA Image and Video Library

1996-11-20

This Magellan image, which is 50 kilometers (31 miles) in width and 80 kilometers (50 miles) in length, is centered at 11.9 degrees latitude, 352 degrees longitude in the eastern Navka Region of Venus. The crater, which is approximately 8 kilometers (5 miles) in diameter, displays a butterfly symmetry pattern. The ejecta pattern most likely results from an oblique impact, where the impactor came from the south and ejected material to the north. http://photojournal.jpl.nasa.gov/catalog/PIA00474

Site Testing at the Mexican National Astronomical Observatory in San Pedro Martir

NASA Astrophysics Data System (ADS)

Costero, R.; Echevarria, J.; Tapia, M.

1996-05-01

Measurements on the local seeing have been carried out during two and a half yea rs (March 29, 1992 to October 7, 1994), over a total of 378 nights. The Site Tes ting Telescope (STT) from the Steward Observatory yields a median seeing of 0.61 arcsec and a first quartile of 0.50 arcsec. Additional measurements with the Carnegie Monitor (CM), many of them done simultaneously with the STT, yield almost identical results. The Micro--Thermal Array (MTA), also from Steward Observatory, show that the seeing size decreases about 0.1 arcsec at 15 meters above the ground. The seeing does not show any dependence on wind velocity or direction, at least for wind velocities smaller than 40 kilometers per hour. We will present the details of these results. The participation of several persons in this project is here acknowledge, especially that of R. Cromwell and N. Wolf, from Steward Observatory, and S.E. Persson and D.M. Carr, from The Observatories of the Carnegie Institution of Washington.

Check-Up of Planet Earth at the Turn of the Millennium: Contribution of EOS-Terra to a New Phase in Earth Sciences

NASA Technical Reports Server (NTRS)

Kaufman, Yoram

1999-01-01

Langley's remarkable solar and lunar spectra collected from Mt. Whitney inspired Arrhenius to develop the first quantitative climate model in 1896. In 1999, NASA's Earth Observing AM Satellite (EOS-Terra) will repeat Langley's experiment, but for the entire planet, thus pioneering a wide array of calibrated spectral observations from space of the Earth System. Conceived in response to real environmental problems, EOS-Terra, in conjunction with other international satellite efforts, will fill a major gap in current efforts by providing quantitative global data sets with a resolution of few kilometers on the physical, chemical and biological elements of the earth system. Thus, like Langley's data, EOS-Terra can revolutionize climate research by inspiring a new generation of climate system models and enable us to assess the human impact on the environment. In the talk I shall review the historical developments that brought to the Terra mission, its objectives and example of application to biomass burning.

Neutrino astronomy at the South Pole: Latest results from the IceCube neutrino observatory and its future development

NASA Astrophysics Data System (ADS)

Toscano, S.; IceCube Collaboration

2017-12-01

The IceCube Neutrino Observatory is a cubic-kilometer neutrino telescope located at the geographic South Pole. Buried deep under the Antarctic ice sheet, an array of 5160 Digital Optical Modules (DOMs) is used to capture the Cherenkov light emitted by relativistic particles generated from neutrino interactions. The main goal of IceCube is the detection of astrophysical neutrinos. In 2013 the IceCube neutrino telescope discovered a high-energy diffuse flux of neutrino events with energy ranging from tens of TeV up to few PeV of cosmic origin. Meanwhile, different analyses confirm the discovery and search for possible correlations with astrophysical sources. However, the source of these neutrinos remains a mystery, since no counterparts have been identified yet. In this contribution we give an overview of the detection principles of IceCube, the most recent results, and the plans for a next-generation neutrino detector, dubbed IceCube-Gen2.

Crest: A Balloon-borne Instrument to Measure Cosmic-ray Electrons above TeV Energies

NASA Astrophysics Data System (ADS)

Nutter, S.; Anderson, T.; Coutu, S.; Geske, M.; Bower, C.; Musser, J.; Muller, D.; Park, N.; Wakely, S.; Schubnell, M.; Tarle, G.; Yagi, A.

2009-05-01

The flux of high-energy (>1 TeV) electrons provides information about the spatial distribution and abundance of nearby cosmic ray sources. CREST, a balloon-borne array of 1024 BaF2 crystals viewed by PMTs, will measure the spectrum of multi-TeV electrons through detection of the x-ray synchrotron photons generated as the electrons traverse the Earth's magnetic field. This method naturally discriminates against the proton and gamma ray backgrounds, and achieves very large detector apertures, since the instrument need only intersect a portion of the kilometers-long line of photons and not the electron itself. Thus CREST's acceptance is several times its geometric area up to energies of 50 TeV, ˜10 times higher in energy than ground based techniques can reach. This measurement will overlap the recent HESS results and extend to higher energies. CREST is scheduled to fly in a long duration circumpolar orbit over Antarctica in 2010. An overview of the detector design and status will be presented.

ARC-1988-AC88-0595

NASA Image and Video Library

1988-10-07

Artist: Rick Guidice SIRTF Artwork update - cutaway Space Infrared Telescope Facility's will orbit at 900 kilometers aboard a platform-type spacecraft, providing power, pointing, and communications to Earth. The telescope and its infrared instruments, will reside within a cylindrical cryogen tank. The hollow walls of the tank will contain the superfluid helium that cools the telescope to its operating temperature, a few degrees above absolute zero. SIRTF will carry three versatile instruments to analyze the radiation it collects, the Multiband Imaging Photometer, the Infrared Array Camera, and the Infrared Spectrograph. SIRTF long lifetime - 5 years or more - will permit astronomers of all disciplines to use the facililty to carry out a wide variety of astrophysical programs. It will provide ongoing coverage of variable objects, such as quasars, as well as the capability to study rare and transient events such as comets and supernovae. SIRTF's long lifetime will also allow it to distinguish nearby objects by detecting their gradual motions relative to the more distant background stars.

AUTONOMOUS GAUSSIAN DECOMPOSITION

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lindner, Robert R.; Vera-Ciro, Carlos; Murray, Claire E.

2015-04-15

We present a new algorithm, named Autonomous Gaussian Decomposition (AGD), for automatically decomposing spectra into Gaussian components. AGD uses derivative spectroscopy and machine learning to provide optimized guesses for the number of Gaussian components in the data, and also their locations, widths, and amplitudes. We test AGD and find that it produces results comparable to human-derived solutions on 21 cm absorption spectra from the 21 cm SPectral line Observations of Neutral Gas with the EVLA (21-SPONGE) survey. We use AGD with Monte Carlo methods to derive the H i line completeness as a function of peak optical depth and velocitymore » width for the 21-SPONGE data, and also show that the results of AGD are stable against varying observational noise intensity. The autonomy and computational efficiency of the method over traditional manual Gaussian fits allow for truly unbiased comparisons between observations and simulations, and for the ability to scale up and interpret the very large data volumes from the upcoming Square Kilometer Array and pathfinder telescopes.« less

MUSIC for localization of thunderstorm cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mosher, J.C.; Lewis, P.S.; Rynne, T.M.

1993-12-31

Lightning represents an event detectable optically, electrically, and acoustically, and several systems are already in place to monitor such activity. Unfortunately, such detection of lightning can occur too late, since operations need to be protected in advance of the first lightning strike. Additionally, the bolt itself can traverse several kilometers before striking the ground, leaving a large region of uncertainty as to the center of the storm and its possible strike regions. NASA Kennedy Space Center has in place an array of electric field mills that monitor the (effectively) DC electric field. Prior to the first lightning strike, the surfacemore » electric fields rise as the storm generator within a thundercloud begins charging. Extending methods we developed for an analogous source localization problem in mangnetoencephalography, we present Cramer-Rao lower bounds and MUSIC scans for fitting a point-charge source model to the electric field mill data. Such techniques can allow for the identification and localization of charge centers in cloud structures.« less

Upper crustal structure of the Hawaiian Swell from seafloor compliance measurements

NASA Astrophysics Data System (ADS)

Doran, A. K.; Laske, G.

2017-12-01

We present new constraints on elastic properties of the marine sediments and crust surrounding the Hawaiian Islands derived from seafloor compliance measurements. We analyze long-period seismic and pressure data collected during the Plume-Lithosphere Undersea Mantle Experiment [Laske et al, 2009], a deployment consisting of nearly 70 broadband ocean-bottom seismometers with an array aperture of over 1000 kilometers. Our results are supported by previous reflection & refraction studies and by direct sampling of the crust from regional drilling logs. We demonstrate the importance of simultaneously modeling density, compressional velocity, and shear velocity, the former two of which are often ignored during compliance investigations. We find variable sediment thickness and composition across the Hawaiian Swell, with the thickest sediments located within the Hawaiian Moat. Improved resolution of near-surface structure of the Hawaiian Swell is crucially important to improve tomographic images of the underlying lithosphere and asthenosphere and to address outstanding questions regarding the size, source, and location of the hypothesized mantle plume.

Seismic scatterers in the mid-lower mantle beneath Tonga-Fiji

NASA Astrophysics Data System (ADS)

Kaneshima, Satoshi

2018-01-01

We analyze deep and intermediate-depth earthquakes at the Tonga-Fiji region in order to reveal the distribution of scattering objects in the mid-lower mantle. By array processing waveform data recorded at regional seismograph stations in the US, Alaska, and Japan, we investigate S-to-P scattering waves in the P coda, which arise from kilometer-scale chemically distinct objects in the mid-lower mantle beneath Tonga-Fiji. With ten scatterers previously reported by the author included, twenty-three mid-lower mantle scatterers have been detected below 900 km depth, while scatterers deeper than 1900 km have not been identified. Strong mid-lower mantle S-to-P scattering most frequently occurs at the scatterers located within a depth range between 1400 km and 1600 km. The number of scatterers decreases below 1600 km depth, and the deeper objects tend to be weaker. The scatterer distribution may reflect diminishing elastic anomalies of basaltic rocks with depth relative to the surrounding mantle rocks, which mineral physics has predicted to occur. The predominant occurrence of strong S-to-P scattering waves within a narrow depth range may reflect significant reduction of rigidity due to the ferro-elastic transformation of stishovite in basaltic rocks. Very large signals associated with mid-mantle scatterers are observed only for a small portion of the entire earthquake-array pairs. Such infrequent observations of large scattering signals, combined with quite large event-to-event differences in the scattering intensity for each scatterer, suggest both that the strong arrivals approximately represent ray theoretical S-to-P converted waves at objects with a plane geometry. The plane portions of the strong scatterers may often dip steeply, with the size exceeding 100 km. For a few strong scatterers, the range of receivers showing clear scattered waves varies substantially from earthquake-array pair to pair. Some of the scatterers are also observed at different arrays that have significantly different directions of incident waves to the scatterers. Furthermore, weak but coherent P-to-P scattered waves as well as S-to-P waves are observed for a few of the scatterers. These observations indicate that the locally plane scatterers also possess substantial topography.

Large eddy simulation study of the kinetic energy entrainment by energetic turbulent flow structures in large wind farms

NASA Astrophysics Data System (ADS)

VerHulst, Claire; Meneveau, Charles

2014-02-01

In this study, we address the question of how kinetic energy is entrained into large wind turbine arrays and, in particular, how large-scale flow structures contribute to such entrainment. Previous research has shown this entrainment to be an important limiting factor in the performance of very large arrays where the flow becomes fully developed and there is a balance between the forcing of the atmospheric boundary layer and the resistance of the wind turbines. Given the high Reynolds numbers and domain sizes on the order of kilometers, we rely on wall-modeled large eddy simulation (LES) to simulate turbulent flow within the wind farm. Three-dimensional proper orthogonal decomposition (POD) analysis is then used to identify the most energetic flow structures present in the LES data. We quantify the contribution of each POD mode to the kinetic energy entrainment and its dependence on the layout of the wind turbine array. The primary large-scale structures are found to be streamwise, counter-rotating vortices located above the height of the wind turbines. While the flow is periodic, the geometry is not invariant to all horizontal translations due to the presence of the wind turbines and thus POD modes need not be Fourier modes. Differences of the obtained modes with Fourier modes are documented. Some of the modes are responsible for a large fraction of the kinetic energy flux to the wind turbine region. Surprisingly, more flow structures (POD modes) are needed to capture at least 40% of the turbulent kinetic energy, for which the POD analysis is optimal, than are needed to capture at least 40% of the kinetic energy flux to the turbines. For comparison, we consider the cases of aligned and staggered wind turbine arrays in a neutral atmospheric boundary layer as well as a reference case without wind turbines. While the general characteristics of the flow structures are robust, the net kinetic energy entrainment to the turbines depends on the presence and relative arrangement of the wind turbines in the domain.

Mystery #6 Answer

Atmospheric Science Data Center

2013-04-22

... title:  MISR Mystery Image Quiz #6: Brazil's Duck Lagoon     View Larger Image ... Imaging SpectroRadiometer (MISR) image of Brazil's Duck Lagoon covers an area of about 298 kilometers x 358 kilometers, and was ...

Earth Observations taken by Expedition 34 crewmember

NASA Image and Video Library

2013-02-21

ISS034-E-056100 (21 Feb. 2013) --- One of the most recognizable natural features on Earth, when viewing from space, is the Manicouagan Crater, one of the oldest known impact craters on Earth. Photographed by one of the Expedition 34 crew members onboard the International Space Station, the crater is located primarily in Manicouagan Regional County Municipality in the Côte-Nord region of Québec, Canada, about 300 kilometers (190 miles) north of the city of Baie-Comeau. Manicouagan is one of the oldest large astroblemes still visible on the surface. The crater is a multiple-ring structure about 100 kilometers (60 miles) across, with its 70 kilometer (40 mile) diameter inner ring its most prominent feature; it contains a 70 kilometer (40 mile) diameter annular lake, the Manicouagan Reservoir, surrounding an inner island plateau.

Venus - Large Impact Crater in the Eistla Region

NASA Image and Video Library

1996-09-26

This image from NASA Magellan spacecraft shows the central Eistla Region of the equatorial highlands of Venus. It is centered at 15 degrees north latitude and 5 degrees east longitude. The image is 76.8 kilometers (48 miles) wide. The crater is slightly irregular in platform and approximately 6 kilometers (4 miles) in diameter. The walls appear terraced. Five or six lobes of radar-bright ejecta radiate up to 13.2 kilometers (8 miles) from the crater rim. These lobes are up to 3.5 kilometers (2 miles) in width and form a "starfish" pattern against the underlying radar-dark plains. The asymmetric pattern of the ejecta suggests the angle of impact was oblique. The alignment of two of the ejecta lobes along fractures in the underlying plains is apparently coincidental. http://photojournal.jpl.nasa.gov/catalog/PIA00466

Comparison of SPHC Hydrocode Results with Penetration Equations and Results of Other Codes

NASA Technical Reports Server (NTRS)

Evans, Steven W.; Stallworth, Roderick; Stellingwerf, Robert F.

2004-01-01

The SPHC hydrodynamic code was used to simulate impacts of spherical aluminum projectiles on a single-wall aluminum plate and on a generic Whipple shield. Simulations were carried out in two and three dimensions. Projectile speeds ranged from 2 kilometers per second to 10 kilometers per second for the single-wall runs, and from 3 kilometers per second to 40 kilometers per second for the Whipple shield runs. Spallation limit results of the single-wall simulations are compared with predictions from five standard penetration equations, and are shown to fall comfortably within the envelope of these analytical relations. Ballistic limit results of the Whipple shield simulations are compared with results from the AUTODYN-2D and PAM-SHOCK-3D codes presented in a paper at the Hypervelocity Impact Symposium 2000 and the Christiansen formulation of 2003.

Upper atmosphere and ionosphere of Mars.

PubMed

Donahue, T M

1966-05-06

It is argued that the single-layer ionosphere at 125 kilometers discovered in the Mariner IV occultation experiment is an Fl region coinciding with the ultraviolet photoionization peak. The CO(2) density there must be of the order of 10(11) molecules per cubic centimeter. Such a density is consistent with the properties of the lower atmosphere by Mariner IV anid the temperature model of Chamberlain and McElroy if the atmosphere is mainly CO(2) below 70 kilometers. The absence of an F2 region can be explained even if the density ratio of O to CO(2) is 100 at 230 kilometers on the basis of the rapid conversion of O(+) to O(2) by CO(2). Thus a model with an exospheric temperature of 400 degrees K, a modest degree of CO(2) dissociation, and diffusive separation above 70 kilometers is possible.

Venus - 3D Perspective View of Sapas Mons

NASA Technical Reports Server (NTRS)

1992-01-01

Sapas Mons is displayed in the center of this computer-generated three-dimensional perspective view of the surface of Venus. The viewpoint is located 527 kilometers (327 miles) northwest of Sapas Mons at an elevation of 4 kilometers (2.5 miles) above the terrain. Lava flows extend for hundreds of kilometers across the fractured plains shown in the foreground to the base of Sapas Mons. The view is to the southeast with Sapas Mons appearing at the center with Maat Mons located in the background on the horizon. Sapas Mons, a volcano 400 kilometers (248 miles) across and 1.5 kilometers (0.9 mile) high is located at approximately 8 degrees north latitude, 188 degrees east longitude, on the western edge of Atla Regio. Its peak sits at an elevation of 4.5 kilometers (2.8 miles) above the planet's mean elevation. Sapas Mons is named for a Phoenician goddess. The vertical scale in this perspective has been exaggerated 10 times. Rays cast in a computer intersect the surface to create a three-dimensional perspective view. Simulated color and a digital elevation map developed by the U.S. Geological Survey are used to enhance small-scale structure. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image was produced by the Solar System Visualization project and the Magellan Science team at the JPL Multimission Image Processing Laboratory and is a single frame from a video released at the April 22, 1992 news conference.

Earth Observations taken by STS-122 Crewmember

NASA Image and Video Library

2008-02-10

S122-E-007690 (10 Feb. 2008) --- An almost nadir view of the John F. Kennedy Space Center (KSC) was provided by one of STS-122 crewmembers with a digital camera. KSC is the NASA space vehicle launch facility and launch control center (spaceport) on Merritt Island, Brevard County, Florida. The site is near Cape Canaveral, between Miami and Jacksonville. It is 34 miles (55 kilometers) long and around 6 miles (10 kilometers) wide, covering 219 square miles (567 square kilometers). Because much of KSC is a restricted area and only 9 percent of the land is developed, the site also serves as an important wildlife sanctuary; Mosquito Lagoon, Indian River, Merritt Island Wildlife Refuge and Canaveral National Seashore are also features of this area. Pictured just below center is Launch Complex 39, with the roadway leading to the giant Vehicle Assembly Building (VAB), 3 miles (5 kilometers) to the west (above) of the two launch pads. Located 5 miles (8 kilometers) south is the KSC industrial area, where many of the Center's support facilities and the administrative Headquarters Building are located. The Shuttle Landing Facility can be seen northwest of the VAB, in frame center.

Passage through the Ring Plane

NASA Image and Video Library

2004-06-03

The path that lies ahead for the Cassini-Huygens mission is indicated in this image which illustrates where the spacecraft will be just 27 days from now, when it arrives at Saturn and crosses the ring plane 33 minutes before performing its critical orbital insertion maneuver. The X indicates the point where Cassini will pierce the ring plane on June 30, 2004, going from south to north of the ring plane, 33 minutes before the main engine fires to begin orbital insertion. The indicated point is between the narrow F-ring on the left and Saturn's tenuous G-ring which is too faint to be seen in this exposure. The image was taken on May 11, 2004 when the spacecraft was 26.3 million kilometers (16.3 million miles) from Saturn. Image scale is 158 kilometers (98 miles) per pixel. Moons visible in this image: Janus (181 kilometers or 113 miles across), one of the co-orbital moons; Pandora (84 kilometers or 52 miles across), one of the F ring shepherding moons; and Enceladus (499 kilometers or 310 miles across), a moon which may be heated from within and thus have a liquid sub-surface ocean. http://photojournal.jpl.nasa.gov/catalog/PIA06061