115,830 research outputs found
Extended Uniform Ginzburg-Landau Theory for Novel Multiband Superconductors
The recently discovered multiband superconductors have created a new class of
novel superconductors. In these materials multiple superconducting gaps arise
due to the formation of Cooper pairs on different sheets of the Fermi surfaces.
An important feature of these superconductors is the interband couplings, which
not only change the individual gap properties, but also create new collective
modes. Here we investigate the effect of the interband couplings in the
Ginzburg-Landau theory. We produce a general expansion () and show that this expansion has unexpected behaviour for . This point emphasises the weaker validity of the GL theory for lower
temperatures and gives credence to the existence of hidden criticality near the
critical temperature of the uncoupled subdominant band.Comment: 10 pages, 4 figure
Leveraging HTC for UK eScience with very large Condor pools: demand for transforming untapped power into results
We provide an insight into the demand from the UK eScience community for very large HighThroughput Computing resources and provide an example of such a resource in current productionuse: the 930-node eMinerals Condor pool at UCL. We demonstrate the significant benefits thisresource has provided to UK eScientists via quickly and easily realising results throughout a rangeof problem areas. We demonstrate the value added by the pool to UCL I.S infrastructure andprovide a case for the expansion of very large Condor resources within the UK eScience Gridinfrastructure. We provide examples of the technical and administrative difficulties faced whenscaling up to institutional Condor pools, and propose the introduction of a UK Condor/HTCworking group to co-ordinate the mid to long term UK eScience Condor development, deploymentand support requirements, starting with the inaugural UK Condor Week in October 2004
Novel superconductivity: from bulk to nano systems
We begin with an introduction of superconductivity by giving a brief history of the phenomenon. The phenomenological Ginzburg–Landau theory and the microscopic theory of Bardeen, Cooper and Schrieffer are outlined. In view of recently available multi-band superconductors, relevant theories of both types are discussed. Unlike the traditional GL theory an extended GL theory is developed relevant to temperatures below the critical temperature. Superconductivity in a nanosystem is the highlight of the remaining part of the paper. Theories and experiments are discussed to give an interested reader an updated account and overview of what is new in this active area of research
Operational alternatives for LANDSAT in California
Data integration is defined and examined as the means of promoting data sharing among the various governmental and private geobased information systems in California. Elements of vertical integration considered included technical factors (such as resolution and classification) and institutional factors (such as organizational control, and legal and political barriers). Attempts are made to fit the theoretical elements of vertical integration into a meaningful structure for looking at the problem from a statewide focus. Both manual (mapped) and machine readable data systems are included. Special attention is given to LANDSAT imagery because of its strong potential for integrated use and its primary in the California Integrated Remote Sensing System program
The Brown dwarf Atmosphere Monitoring (BAM) Project I: The largest near-IR monitoring survey of L- & T-dwarfs
Using SofI on the 3.5m New Technology Telescope, we have conducted an
extensive near-infrared monitoring survey of an unbiased sample of 69 brown
dwarfs spanning the L0 and T8 spectral range, with at least one example of each
spectral type. Each target was observed for a 2-4 hour period in the Js-band,
and the median photometric precision of the data is ~0.7%. A total of 14 brown
dwarfs were identified as variables with min-to-max amplitudes ranging from
1.7% to 10.8% over the observed duration. All variables satisfy a statistical
significance threshold with a p-value <5% based on comparison with the median
reference star light curve. Approximately half of the variables show sinusoidal
amplitude variations similar to 2M2139, and the remainder shows short timescale
evolving light curves similar to SIMP0136. The L/T transition has been
suggested to be a region of a higher degree of variability if patchy clouds are
present and this survey was designed to test the patchy cloud model with
photometric monitoring of both the L/T transition and non-transition brown
dwarfs. Considering the targets identified as variable with the same
statistical threshold, the measured variability frequency of 13^{+10}_{-4}% for
the L7 -- T4 transition region is indistinguishable from that of the earlier
spectral types (32^{+11}_{-8}%), the later spectral types (13^{+10}_{-4}%), or
the combination of all non-transition region brown dwarfs (21^{+7}_{-5}%). The
variables are not concentrated at the transition, in a specific colour, or with
binaries. We note that of the systems previously monitored for variability only
~60% maintained the state of variability (variable or constant), with the
remaining switching states. The 14 variables include nine newly identified
variables that will provide important systems for follow-up multi-wavelength
monitoring to further investigate brown dwarf atmosphere physics.Comment: Accepted for publication in the Astronomy & Astrophysics. 15 pages,
13 figure
The effect of stirring on the heterogeneous nucleation of water and of clathrates of tetrahydrofuran/water mixtures
The statistics of liquid-to-crystal nucleation are measured for both water
and for clathrate-forming mixtures of tetrahydrofuran (THF) and water using an
automatic lag time apparatus (ALTA). We measure the nucleation temperature
using this apparatus in which a single sample is repeatedly cooled, nucleated
and thawed. The effect of stirring on nucleation has been evaluated numerically
and is discussed. We find that stirring of the solution makes no difference to
the nucleation temperature of a given solution in a given tube.Comment: 4 pages, 4 figure
Aerosol activation and cloud processing in the global aerosol-climate model ECHAM5-HAM
A parameterization for cloud processing is presented that calculates activation of aerosol particles to cloud drops, cloud drop size, and pH-dependent aqueous phase sulfur chemistry. The parameterization is implemented in the global aerosol-climate model ECHAM5-HAM. The cloud processing parameterization uses updraft speed, temperature, and aerosol size and chemical parameters simulated by ECHAM5-HAM to estimate the maximum supersaturation at the cloud base, and subsequently the cloud drop number concentration (CDNC) due to activation. In-cloud sulfate production occurs through oxidation of dissolved SO2 by ozone and hydrogen peroxide. The model simulates realistic distributions for annually averaged CDNC although it is underestimated especially in remote marine regions. On average, CDNC is dominated by cloud droplets growing on particles from the accumulation mode, with smaller contributions from the Aitken and coarse modes. The simulations indicate that in-cloud sulfate production is a potentially important source of accumulation mode sized cloud condensation nuclei, due to chemical growth of activated Aitken particles and to enhanced coalescence of processed particles. The strength of this source depends on the distribution of produced sulfate over the activated modes. This distribution is affected by uncertainties in many parameters that play a direct role in particle activation, such as the updraft velocity, the aerosol chemical composition and the organic solubility, and the simulated CDNC is found to be relatively sensitive to these uncertainties
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