5,932 research outputs found
Data Mining the SDSS SkyServer Database
An earlier paper (Szalay et. al. "Designing and Mining MultiTerabyte
Astronomy Archives: The Sloan Digital Sky Survey," ACM SIGMOD 2000) described
the Sloan Digital Sky Survey's (SDSS) data management needs by defining twenty
database queries and twelve data visualization tasks that a good data
management system should support. We built a database and interfaces to support
both the query load and also a website for ad-hoc access. This paper reports on
the database design, describes the data loading pipeline, and reports on the
query implementation and performance. The queries typically translated to a
single SQL statement. Most queries run in less than 20 seconds, allowing
scientists to interactively explore the database. This paper is an in-depth
tour of those queries. Readers should first have studied the companion overview
paper Szalay et. al. "The SDSS SkyServer, Public Access to the Sloan Digital
Sky Server Data" ACM SIGMOND 2002.Comment: 40 pages, Original source is at
http://research.microsoft.com/~gray/Papers/MSR_TR_O2_01_20_queries.do
Matrix convex functions with applications to weighted centers for semidefinite programming
In this paper, we develop various calculus rules for general smooth matrix-valued functions and for the class of matrix convex (or concave) functions first introduced by Loewner and Kraus in 1930s. Then we use these calculus rules and the matrix convex function -log X to study a new notion of weighted convex centers for semidefinite programming (SDP) and show that, with this definition, some known properties of weighted centers for linear programming can be extended to SDP. We also show how the calculus rules for matrix convex functions can be used in the implementation of barrier methods for optimization problems involving nonlinear matrix functions
On the line shape of the electrically detected ferromagnetic resonance
This work reviews and examines two particular issues related with the new
technique of electrical detection of ferromagnetic resonance (FMR). This
powerful technique has been broadly applied for studying magnetization and spin
dynamics over the past few years. The first issue is the relation and
distinction between different mechanisms that give rise to a photovoltage via
FMR in composite magnetic structures, and the second is the proper analysis of
the FMR line shape, which remains the "Achilles heel" in interpreting
experimental results, especially for either studying the spin pumping effect or
quantifying the spin Hall angles via the electrically detected FMR.Comment: 14 pages, 9 figure
The factorization method for systems with a complex action -a test in Random Matrix Theory for finite density QCD-
Monte Carlo simulations of systems with a complex action are known to be
extremely difficult. A new approach to this problem based on a factorization
property of distribution functions of observables has been proposed recently.
The method can be applied to any system with a complex action, and it
eliminates the so-called overlap problem completely. We test the new approach
in a Random Matrix Theory for finite density QCD, where we are able to
reproduce the exact results for the quark number density. The achieved system
size is large enough to extract the thermodynamic limit. Our results provide a
clear understanding of how the expected first order phase transition is induced
by the imaginary part of the action.Comment: 27 pages, 25 figure
Site-selective measurement of coupled spin pairs in an organic semiconductor
From organic electronics to biological systems, understanding the role of intermolecular interactions between spin pairs is a key challenge. Here we show how such pairs can be selectively addressed with combined spin and optical sensitivity. We demonstrate this for bound pairs of spin-triplet excitations formed by singlet fission, with direct applicability across a wide range of synthetic and biological systems. We show that the site sensitivity of exchange coupling allows distinct triplet pairs to be resonantly addressed at different magnetic fields, tuning them between optically bright singlet (S=0) and dark triplet quintet (S=1,2) configurations: This induces narrow holes in a broad optical emission spectrum, uncovering exchange-specific luminescence. Using fields up to 60 T, we identify three distinct triplet-pair sites, with exchange couplings varying over an order of magnitude (0.3–5 meV), each with its own luminescence spectrum, coexisting in a single material. Our results reveal how site selectivity can be achieved for organic spin pairs in a broad range of systems
Investigating Master-Slave Architecture for Underwater Wireless Sensor Network.
A significant increase has been observed in the use of Underwater Wireless Sensor Networks (UWSNs) over the last few decades. However, there exist several associated challenges with UWSNs, mainly due to the nodes' mobility, increased propagation delay, limited bandwidth, packet duplication, void holes, and Doppler/multi-path effects. To address these challenges, we propose a protocol named "An Efficient Routing Protocol based on Master-Slave Architecture for Underwater Wireless Sensor Network (ERPMSA-UWSN)" that significantly contributes to optimizing energy consumption and data packet's long-term survival. We adopt an innovative approach based on the master-slave architecture, which results in limiting the forwarders of the data packet by restricting the transmission through master nodes only. In this protocol, we suppress nodes from data packet reception except the master nodes. We perform extensive simulation and demonstrate that our proposed protocol is delay-tolerant and energy-efficient. We achieve an improvement of 13% on energy tax and 4.8% on Packet Delivery Ratio (PDR), over the state-of-the-art protocol
On the universality of distribution of ranked cluster masses at critical percolation
The distribution of masses of clusters smaller than the infinite cluster is
evaluated at the percolation threshold. The clusters are ranked according to
their masses and the distribution of the scaled masses M for any
rank r shows a universal behaviour for different lattice sizes L (D is the
fractal dimension). For different ranks however, there is a universal
distribution function only in the large rank limit, i.e., (y and are defined in the text), where the
universal scaling function g is found to be Gaussian in nature.Comment: 4 pages, to appear in J. Phys.
Testing of quantum phase in matter wave optics
Various phase concepts may be treated as special cases of the maximum
likelihood estimation. For example the discrete Fourier estimation that
actually coincides with the operational phase of Noh, Fouge`res and Mandel is
obtained for continuous Gaussian signals with phase modulated mean.Since
signals in quantum theory are discrete, a prediction different from that given
by the Gaussian hypothesis should be obtained as the best fit assuming a
discrete Poissonian statistics of the signal. Although the Gaussian estimation
gives a satisfactory approximation for fitting the phase distribution of almost
any state the optimal phase estimation offers in certain cases a measurable
better performance. This has been demonstrated in neutron--optical experiment.Comment: 8 pages, 4 figure
Multisite prospective investigation of psychological outcomes following cataract surgery in Vietnam
Copyright © 2017 BMJ Global Health. All rights reserved. Background: Cataract surgery is a low-cost and effective intervention. There is increasing evidence to suggest that cataract surgery is associated with improvements in mobility, overall functioning and reductions in psychological distress. Within lowincome and middle-income countries, cataract surgery has also been documented to lead to reductions in psychological distress; however, differences in economic activity and engagement in paid and domestic work in these countries may moderate such reductions. We aimed to examine the psychological outcomes following cataract surgery among a diverse Vietnamese sample. Methods: We report findings from the VISIONARY study, a 12-month multisite prospective study of cataract surgery outcomes conducted in Vietnam (N=462). Generalised estimating equations (GEEs) were used to identify the variables which were associated with reduced psychological distress. Results: A high proportion of participants (56.6%) reported psychological distress before surgery and severity of psychological distress had decreased by 12 months following surgery (95% CI (4.13 to 4.95)). There were regional differences in the extent of improvement in psychological distress and change in paid and unpaid work. The extent of improvement in visual acuity, male gender, and increase in paid and unpaid work hours were significant predictors of reductions in psychological distress. Conclusions: Cataract surgery appears to result in the greatest reductions in psychological distress in communities where work engagement is highest. Funding: The VISIONARY study was funded by a grant provided by the Fred Hollows Foundation, Australia. During the course of this work, BME was in receipt of an Ian Potter Foundation Fellowship and a National Health and Medical Research Council (NHMRC) fellowship (1072148), SJ received an NHMRC Senior Research Fellowship, MLH was in receipt of a National Heart Foundation Future Leader Fellowship 100034
Review of biodegradable synthetic-based drilling fluid: progression, performance and future prospect
This paper provides a comprehensive review on ester based drilling fluid (EBDF). It is no secret that esters with biodegradability and bioaccumulation attributes are among the promising alternatives to synthetic base oil in drilling fluids. The findings from the literature explained the critical parameters for drilling fluid base which are i) kinematic viscosity, ii) pour point and iii) flash point iv) thermal stability and v) hydrolytic stability and vi) elastomer compatibility. In an ideal case, an EBDF requires base oil with low viscosity, low pour, high flash point, high thermal and hydrolytic stability and compatibility with existing elastomer. However in the real application, these requirements may not be the same as the bottom hole condition which is always subjected to high pressure and high temperature environment. At the moment, the performance of EBDF is considered outstanding for normal borehole depth and complexity. Nevertheless the constraints such as low temperature at the seabed while high temperature and high pressure at the bottom hole may be slightly different when dealing with an EBDF. This is due to its unique molecular structure of ester. Affected parameters include i) high kinematic viscosity, ii) hydrolytic degradation and iii) thermal stability. Failure in managing these parameters may lead to detrimental impacts on the drilling fluid performances and the fluid's stabilities. The application of low viscosity, high thermal and hydrolytic properties of esters and combination with unique carbon based nanomaterials into formulation might be able to close the gap of current EBDF performances
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