870 research outputs found

    Evolution in the Clustering of Galaxies for Z < 1

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    Measuring the evolution in the clustering of galaxies over a large redshift range is a challenging problem. For a two-dimensional galaxy catalog, however, we can measure the galaxy-galaxy angular correlation function which provides information on the density distribution of galaxies. By utilizing photometric redshifts, we can measure the angular correlation function in redshift shells (Brunner 1997, Connolly et al. 1998) which minimizes the galaxy projection effect, and allows for a measurement of the evolution in the correlation strength with redshift. In this proceedings, we present some preliminary results which extend our previous work using more accurate photometric redshifts, and also incorporate absolute magnitudes, so that we can measure the evolution of clustering with either redshift or intrinsic luminosity.Comment: 6 pages, 6 figures requires paspconf.sty. To be published in "Photometric Redshifts and High Redshift Galaxies", eds. R. Weymann, L. Storrie-Lombardi, M. Sawicki & R. Brunner, (San Francisco: ASP Conference Series

    The National Virtual Observatory

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    As a scientific discipline, Astronomy is rather unique. We only have one laboratory, the Universe, and we cannot, of course, change the initial conditions and study the resulting effects. On top of this, acquiring Astronomical data has historically been a very labor-intensive effort. As a result, data has traditionally been preserved for posterity. With recent technological advances, however, the rate at which we acquire new data has grown exponentially, which has generated a Data Tsunami, whose wave train threatens to overwhelm the field. In this conference proceedings, we present and define the concept of virtual observatories, which we feel is the only logical answer to this dilemma.Comment: 5 pages, uses newpasp.sty (included), to appear in "Extragalactic Gas at Low Redshfit", ASP Conf. Series, J. S. Mulchaey and J. T. Stocke (eds.

    Massive Datasets in Astronomy

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    Astronomy has a long history of acquiring, systematizing, and interpreting large quantities of data. Starting from the earliest sky atlases through the first major photographic sky surveys of the 20th century, this tradition is continuing today, and at an ever increasing rate. Like many other fields, astronomy has become a very data-rich science, driven by the advances in telescope, detector, and computer technology. Numerous large digital sky surveys and archives already exist, with information content measured in multiple Terabytes, and even larger, multi-Petabyte data sets are on the horizon. Systematic observations of the sky, over a range of wavelengths, are becoming the primary source of astronomical data. Numerical simulations are also producing comparable volumes of information. Data mining promises to both make the scientific utilization of these data sets more effective and more complete, and to open completely new avenues of astronomical research. Technological problems range from the issues of database design and federation, to data mining and advanced visualization, leading to a new toolkit for astronomical research. This is similar to challenges encountered in other data-intensive fields today. These advances are now being organized through a concept of the Virtual Observatories, federations of data archives and services representing a new information infrastructure for astronomy of the 21st century. In this article, we provide an overview of some of the major datasets in astronomy, discuss different techniques used for archiving data, and conclude with a discussion of the future of massive datasets in astronomy.Comment: 46 Pages, 21 Figures, Invited Review for the Handbook of Massive Datasets, editors J. Abello, P. Pardalos, and M. Resende. Due to space limitations this version has low resolution figures. For full resolution review see http://www.astro.caltech.edu/~rb/publications/hmds.ps.g

    Dietary garlic and hip osteoarthritis: evidence of a protective effect and putative mechanism of action

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    Background Patterns of food intake and prevalent osteoarthritis of the hand, hip, and knee were studied using the twin design to limit the effect of confounding factors. Compounds found in associated food groups were further studied in vitro. Methods Cross-sectional study conducted in a large population-based volunteer cohort of twins. Food intake was evaluated using the Food Frequency Questionnaire; OA was determined using plain radiographs. Analyses were adjusted for age, BMI and physical activity. Subsequent in vitro studies examined the effects of allium-derived compounds on the expression of matrix-degrading proteases in SW1353 chondrosarcoma cells. Results Data were available, depending on phenotype, for 654-1082 of 1086 female twins (median age 58.9 years; range 46-77). Trends in dietary analysis revealed a specific pattern of dietary intake, that high in fruit and vegetables, showed an inverse association with hip OA (p = 0.022). Consumption of 'non-citrus fruit' (p = 0.015) and 'alliums' (p = 0.029) had the strongest protective effect. Alliums contain diallyl disulphide which was shown to abrogate cytokine-induced matrix metalloproteinase expression. Conclusions Studies of diet are notorious for their confounding by lifestyle effects. While taking account of BMI, the data show an independent effect of a diet high in fruit and vegetables, suggesting it to be protective against radiographic hip OA. Furthermore, diallyl disulphide, a compound found in garlic and other alliums, represses the expression of matrix-degrading proteases in chondrocyte-like cells, providing a potential mechanism of action

    Tropical Pacific observing system

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    This paper reviews the design of the Tropical Pacific Observing System (TPOS) and its governance and takes a forward look at prospective change. The initial findings of the TPOS 2020 Project embrace new strategic approaches and technologies in a user-driven design and the variable focus of the Framework for Ocean Observing. User requirements arise from climate prediction and research, climate change and the climate record, and coupled modeling and data assimilation more generally. Requirements include focus on the upper ocean and air-sea interactions, sampling of diurnal variations, finer spatial scales and emerging demands related to biogeochemistry and ecosystems. One aim is to sample a diversity of climatic regimes in addition to the equatorial zone. The status and outlook for meeting the requirements of the design are discussed. This is accomplished through integrated and complementary capabilities of networks, including satellites, moorings, profiling floats and autonomous vehicles. Emerging technologies and methods are also discussed. The outlook highlights a few new foci of the design: biogeochemistry and ecosystems, low-latitude western boundary currents and the eastern Pacific. Low latitude western boundary currents are conduits of tropical-subtropical interactions, supplying waters of mid to high latitude origin to the western equatorial Pacific and into the Indonesian Throughflow. They are an essential part of the recharge/discharge of equatorial warm water volume at interannual timescales and play crucial roles in climate variability on regional and global scales. The tropical eastern Pacific, where extreme El Niño events develop, requires tailored approaches owing to the complex of processes at work there involving coastal upwelling, and equatorial cold tongue dynamics, the oxygen minimum zone and the seasonal double Intertropical Convergence Zone. A pilot program building on existing networks is envisaged, complemented by a process study of the East Pacific ITCZ/warm pool/cold tongue/stratus coupled system. The sustainability of TPOS depends on effective and strong collaborative partnerships and governance arrangements. Revisiting regional mechanisms and engaging new partners in the context of a planned and systematic design will ensure a multi-purpose, multi-faceted integrated approach that is sustainable and responsive to changing needs

    Ultrafast optical control of entanglement between two quantum dot spins

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    The interaction between two quantum bits enables entanglement, the two-particle correlations that are at the heart of quantum information science. In semiconductor quantum dots much work has focused on demonstrating single spin qubit control using optical techniques. However, optical control of entanglement of two spin qubits remains a major challenge for scaling from a single qubit to a full-fledged quantum information platform. Here, we combine advances in vertically-stacked quantum dots with ultrafast laser techniques to achieve optical control of the entangled state of two electron spins. Each electron is in a separate InAs quantum dot, and the spins interact through tunneling, where the tunneling rate determines how rapidly entangling operations can be performed. The two-qubit gate speeds achieved here are over an order of magnitude faster than in other systems. These results demonstrate the viability and advantages of optically controlled quantum dot spins for multi-qubit systems.Comment: 24 pages, 5 figure

    The DEEP Groth Strip Survey. I. The Sample

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    The Deep Extragalactic Exploratory Probe (DEEP) is a multi-phase research program dedicated to the study of the formation and evolution of galaxies and of large scale structure in the distant Universe. This paper describes the first five-year phase, denoted DEEP1. A series of ten DEEP1 papers will discuss a range of scientific topics (e.g., the study of photometric and spectral properties of a general distant galaxy survey, the evolution observed in galaxy populations of varied morphologies). The observational basis for these studies is the Groth Survey Strip field, a 127 square arcminute region which has been observed with the Hubble Space Telescope in both broad I-band and V-band optical filters and with the Low Resolution Imaging Spectrograph on the Keck Telescopes. Catalogs of photometric and structural parameters have been constructed for 11,547 galaxies and stars at magnitudes brighter than 29, and spectroscopy has been conducted for a magnitude-color weighted subsample of 818 objects. We evaluate three independent techniques for constructing an imaging catalog for the field from the HST data, and discuss the depth and sampling of the resultant catalogs. The selection of the spectroscopic subsample is discussed, and we describe the multifaceted approach taken to prioritizing objects of interest for a variety of scientific subprograms. A series of Monte Carlo simulations then demonstrates that the spectroscopic subsample can be adequately modeled as a simple function of magnitude and color cuts in the imaging catalog.Comment: ApJS accepted, 15 pages, 12 figures. Version with higher-quality figures available at http://astronomy.nmsu.edu/nicol
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