452 research outputs found
Numerical study of vortex system quantum melting
We report a numerical study of the vortex system in the two dimensional
II-type superconductors. We have proposed a phenomenological model that takes
into account quantum fluctuations of Abrikosov's vortices. The results of the
quantum Monte-Carlo simulations by the SSE algorithm show that the thermal
fluctuations are dominated by quantum fluctuations at low temperatures. In
particular, we demonstrate the possibility of the quantum melting transition
for vortex system in the temperature region where thermal melting transition is
improbable
Coupled-mode equations and gap solitons in a two-dimensional nonlinear elliptic problem with a separable periodic potential
We address a two-dimensional nonlinear elliptic problem with a
finite-amplitude periodic potential. For a class of separable symmetric
potentials, we study the bifurcation of the first band gap in the spectrum of
the linear Schr\"{o}dinger operator and the relevant coupled-mode equations to
describe this bifurcation. The coupled-mode equations are derived by the
rigorous analysis based on the Fourier--Bloch decomposition and the Implicit
Function Theorem in the space of bounded continuous functions vanishing at
infinity. Persistence of reversible localized solutions, called gap solitons,
beyond the coupled-mode equations is proved under a non-degeneracy assumption
on the kernel of the linearization operator. Various branches of reversible
localized solutions are classified numerically in the framework of the
coupled-mode equations and convergence of the approximation error is verified.
Error estimates on the time-dependent solutions of the Gross--Pitaevskii
equation and the coupled-mode equations are obtained for a finite-time
interval.Comment: 32 pages, 16 figure
Is manganese-doped diamond a ferromagnetic semiconductor?
We use density-functional theoretical methods to examine the recent
prediction, based on a mean-field solution of the Zener model, that diamond
doped by Mn (with spin S=5/2) would be a dilute magnetic semiconductor that
remains ferromagnetic well above room temperature. Our findings suggest this to
be unlikely, for four reasons: (1) substitutional Mn in diamond has a low-spin
S=1/2 ground state; (2) the substitutional site is energetically unfavorable
relative to the much larger "divacancy" site; 3) Mn in the divacancy site is an
acceptor, but with only hyperdeep levels, and hence the holes are likely to
remain localized; (4) the calculated Heisenberg couplings between Mn in nearby
divacancy sites are two orders of magnitude smaller than for substitutional Mn
in germanium.Comment: 5 pages, 5 figure
Two-electron self-energy contribution to the ground state energy of heliumlike ions
The two-electron self-energy contribution to the ground state energy of
heliumlike ions is calculated both for a point nucleus and an extended nucleus
in a wide interval of Z. All the two-electron contributions are compiled to
obtain most accurate values for the two-electron part of the ground state
energy of heliumlike ions in the range Z=20-100. The theoretical value of the
ground state energy of heliumlike uranium, based on currently available theory,
is evaluated to be -261382.9(8) eV, without higher order one-electron QED
corrections.Comment: 12 pages, 1 figure, LATE
Collective excitations of trapped Bose condensates in the energy and time domains
A time-dependent method for calculating the collective excitation frequencies
and densities of a trapped, inhomogeneous Bose-Einstein condensate with
circulation is presented. The results are compared with time-independent
solutions of the Bogoliubov-deGennes equations. The method is based on
time-dependent linear-response theory combined with spectral analysis of
moments of the excitation modes of interest. The technique is straightforward
to apply, is extremely efficient in our implementation with parallel FFT
methods, and produces highly accurate results. The method is suitable for
general trap geometries, condensate flows and condensates permeated with vortex
structures.Comment: 6 pages, 3 figures small typos fixe
Building and Improving Reference Genome Assemblies: This paper reviews the problems and algorithms of assembling a complete genome from millions of short DNA sequencing reads
A genome sequence assembly provides the foundation for studies of genotypic and phenotypic variation, genome structure, and evolution of the target organism. In the past four decades, there has been a surge of new sequencing technologies, and with these developments, computational scientists have developed new algorithms to improve genome assembly. Here we discuss the relationship between sequencing technology improvements and assembly algorithm development and how these are applied to extend and improve human and nonhuman genome assemblies. © 1963-2012 IEEE
Ability of the 4-D-Var analysis of the GOSAT BESD XCOâ retrievals to characterize atmospheric COâ at large and synoptic scales
This study presents results from the European Centre for Medium-Range Weather Forecasts (ECMWF) carbon dioxide (COâ) analysis system where the atmospheric COâ is controlled through the assimilation of column-averaged dry-air mole fractions of COâ (XCOâ) from the Greenhouse gases Observing Satellite (GOSAT). The analysis is compared to a free-run simulation (without assimilation of XCOâ), and they are both evaluated against XCOâ data from the Total Carbon Column Observing Network (TCCON). We show that the assimilation of the GOSAT XCOâ product from the Bremen Optimal Estimation Differential Optical Absorption Spectroscopy (BESD) algorithm during the year 2013 provides XCOâ fields with an improved mean absolute error of 0.6 parts per million (ppm) and an improved station-to-station bias deviation of 0.7⯠ppm compared to the free run (1.1 and 1.4 âŻppm, respectively) and an improved estimated precision of 1 âŻppm compared to the GOSAT BESD data (3.3⯠ppm). We also show that the analysis has skill for synoptic situations in the vicinity of frontal systems, where the GOSAT retrievals are sparse due to cloud contamination. We finally computed the 10-day forecast from each analysis at 00:00⯠UTC, and we demonstrate that the COâ forecast shows synoptic skill for the largest-scale weather patterns (of the order of 1000 âŻkm) even up to day 5 compared to its own analysis
Validation of TANSO-FTS/GOSAT XCO<sub>2</sub> and XCH<sub>4</sub> glint mode retrievals using TCCON data from near-ocean sites
The thermal And near infrared sensor for carbon observations Fourier transform spectrometer (TANSO-FTS) on board the Greenhouse Gases Observing Satellite (GOSAT) applies the normal nadir mode above the land (âland dataâ) and sun glint mode over the ocean (âocean dataâ) to provide global distributions of column-averaged dry-air mole fractions of CO2 and CH4, or XCO2 and XCH4. Several algorithms have been developed to obtain highly accurate greenhouse gas concentrations from TANSO-FTS/GOSAT spectra. So far, all the retrieval algorithms have been validated with the measurements from ground-based Fourier transform spectrometers from the Total Carbon Column Observing Network (TCCON), but limited to the land data. In this paper, the ocean data of the SRPR, SRFP (the proxy and full-physics versions 2.3.5 of SRON/KIT's RemoTeC algorithm), NIES (National Institute for Environmental Studies operational algorithm version 02.21) and ACOS (NASA's Atmospheric CO2 Observations from Space version 3.5) are compared with FTIR measurements from five TCCON sites and nearby GOSAT land data.For XCO2, both land and ocean data of NIES, SRFP and ACOS show good agreement with TCCON measurements. Averaged over all TCCON sites, the relative biases of ocean data and land data are â0.33 and â0.13âŻ% for NIES, 0.03 and 0.04âŻ% for SRFP, 0.06 and â0.03âŻ% for ACOS, respectively. The relative scatter ranges between 0.31 and 0.49âŻ%. For XCH4, the relative bias of ocean data is even less than that of the land data for the NIES (0.02 vs. â0.35âŻ%), SRFP (0.04 vs. 0.20âŻ%) and SRPR (â0.02 vs. 0.06âŻ%) algorithms. Compared to the results for XCO2, the XCH4 retrievals show larger relative scatter (0.65â0.81âŻ%)
Statistics of the gravitational force in various dimensions of space: from Gaussian to Levy laws
We discuss the distribution of the gravitational force created by a
Poissonian distribution of field sources (stars, galaxies,...) in different
dimensions of space d. In d=3, it is given by a Levy law called the Holtsmark
distribution. It presents an algebraic tail for large fluctuations due to the
contribution of the nearest neighbor. In d=2, it is given by a marginal
Gaussian distribution intermediate between Gaussian and Levy laws. In d=1, it
is exactly given by the Bernouilli distribution (for any particle number N)
which becomes Gaussian for N>>1. Therefore, the dimension d=2 is critical
regarding the statistics of the gravitational force. We generalize these
results for inhomogeneous systems with arbitrary power-law density profile and
arbitrary power-law force in a d-dimensional universe
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