1,811 research outputs found
Physical and chemical signatures of a developing anticyclonic eddy in the Leeuwin Current, eastern Indian Ocean
A multidisciplinary cruise aboard the R/V Southern Surveyor was conducted in May 2006 to sample a developing anticyclonic eddy of the Leeuwin Current off Western Australia. The eddy formed from a meander of the Leeuwin Current in mid-April 2006 and remained attached to the current until mid-August. In this study, a combination of satellite data (altimeter, sea surface temperature, and chlorophyll a) and shipboard measurements (acoustic Doppler current profiler and conductivity-temperature-depth) were used to characterize the physical and chemical signatures of the eddy. The temperature-salinity properties of the mixed layer waters within the anticyclonic eddy and on the shelf were both connected to that of the Leeuwin Current, indicating the water mass in the eddy is mainly derived from the Leeuwin Current and the modified Leeuwin Current water on the shelf. Above the salinity maximum near the eddy center, there was a regionally significant concentration of nitrate (>0.9 μmol L-1), and the maximum (2 μmol L-1) was at 150 in depth, below the photic zone. Nitrification within the eddy and/or local upwelling due to the forming eddy could be responsible for this high concentration of nitrate near the eddy center which potentially makes the eddy a relatively productive feature in the Leeuwin Current
Model design for scalable 2-D model-based video coding
3D face synthesis has been extensively used in many applications over the last decade. Although many methods have been reported, automatic 3D face synthesis from a single video frame still remains unsolved. An automatic 3D face synthesis algorithm is proposed, which resolves a number of existing bottlenecks
Science with the EXTraS Project: Exploring the X-ray Transient and variable Sky
The EXTraS project (Exploring the X-ray Transient and variable Sky) will
characterise the temporal behaviour of the largest ever sample of objects in
the soft X-ray range (0.1-12 keV) with a complex, systematic and consistent
analysis of all data collected by the European Photon Imaging Camera (EPIC)
instrument onboard the ESA XMM-Newton X-ray observatory since its launch. We
will search for, and characterize variability (both periodic and aperiodic) in
hundreds of thousands of sources spanning more than nine orders of magnitude in
time scale and six orders of magnitude in flux. We will also search for fast
transients, missed by standard image analysis. Our analysis will be completed
by multiwavelength characterization of new discoveries and phenomenological
classification of variable sources. All results and products will be made
available to the community in a public archive, serving as a reference for a
broad range of astrophysical investigations.Comment: 4 pages, 1 figure. Refereed Proceeding of "The Universe of Digital
Sky Surveys" conference held at the INAF - Observatory of Capodimonte,
Naples, on 25th-28th November 2014, to be published in the Astrophysics and
Space Science Proceedings, edited by Longo, Napolitano, Marconi, Paolillo,
Iodic
Stepwise Projection: Toward Brane Setups for Generic Orbifold Singularities
The construction of brane setups for the exceptional series E6,E7,E8 of SU(2)
orbifolds remains an ever-haunting conundrum. Motivated by techniques in some
works by Muto on non-Abelian SU(3) orbifolds, we here provide an algorithmic
outlook, a method which we call stepwise projection, that may shed some light
on this puzzle. We exemplify this method, consisting of transformation rules
for obtaining complex quivers and brane setups from more elementary ones, to
the cases of the D-series and E6 finite subgroups of SU(2). Furthermore, we
demonstrate the generality of the stepwise procedure by appealing to Frobenius'
theory of Induced Representations. Our algorithm suggests the existence of
generalisations of the orientifold plane in string theory.Comment: 22 pages, 3 figure
Holographic dual of the Standard Model on the throat
We apply recent techniques to construct geometries, based on local Calabi-Yau
manifolds, leading to warped throats with 3-form fluxes in string theory, with
interesting structure at their bottom. We provide their holographic dual
description in terms of RG flows for gauge theories with almost conformal
duality cascades and infrared confinement. We describe a model of a throat with
D-branes at its bottom, realizing a 3-family Standard Model like chiral sector.
We provide the explicit holographic dual gauge theory RG flow, and describe the
appearance of the SM degrees of freedom after confinement. As a second
application, we describe throats within throats, namely warped throats with
discontinuous warp factor in different regions of the radial coordinate, and
discuss possible model building applications.Comment: 46 pages, 21 figures, reference adde
Fast finite difference solvers for singular solutions of the elliptic Monge-Amp\`ere equation
The elliptic Monge-Ampere equation is a fully nonlinear Partial Differential
Equation which originated in geometric surface theory, and has been applied in
dynamic meteorology, elasticity, geometric optics, image processing and image
registration. Solutions can be singular, in which case standard numerical
approaches fail. In this article we build a finite difference solver for the
Monge-Ampere equation, which converges even for singular solutions. Regularity
results are used to select a priori between a stable, provably convergent
monotone discretization and an accurate finite difference discretization in
different regions of the computational domain. This allows singular solutions
to be computed using a stable method, and regular solutions to be computed more
accurately. The resulting nonlinear equations are then solved by Newton's
method. Computational results in two and three dimensions validate the claims
of accuracy and solution speed. A computational example is presented which
demonstrates the necessity of the use of the monotone scheme near
singularities.Comment: 23 pages, 4 figures, 4 tables; added arxiv links to references, added
coment
Constraints on ultracompact minihalos from extragalactic {\gamma}-ray background
It has been proposed that ultracompact minihalos (UCMHs) might be formed in
earlier epoch. If dark matter consists of Weakly Interacting Massive Particles
(WIMPs), UCMHs can be treated as the {\gamma}-ray sources due to dark matter
annihilation within them. In this paper, we investigate the contributions of
UCMHs formed during three phase transi- tions (i.e., electroweak symmetry
breaking, QCD confinement and e+ e- annihilation) to the extragalactic
{\gamma}-ray background. Moreover, we use the Fermi-LAT observation data of the
extragalactic {\gamma}-ray background to get the constraints on the current
abundance of UCMHs produced during these phase transitions. We also compare
these results with those obtained from Cosmic Microwave Background (CMB)
observations and find that the constraints from the Fermi-LAT are more
stringent than those from CMBComment: 13 pages, 4 figures, 1 tabl
Chesapeake Bay Nitrogen Fluxes Derived From a Land-Estuarine Ocean Biogeochemical Modeling System: Model Description, Evaluation, and Nitrogen Bonds
The Chesapeake Bay plays an important role in transforming riverine nutrients before they are exported to the adjacent continental shelf. Although the mean nitrogen budget of the Chesapeake Bay has been previously estimated from observations, uncertainties associated with interannually varying hydrological conditions remain. In this study, a land-estuarine-ocean biogeochemical modeling system is developed to quantify Chesapeake riverine nitrogen inputs, within-estuary nitrogen transformation processes and the ultimate export of nitrogen to the coastal ocean. Model skill was evaluated using extensive in situ and satellite-derived data, and a simulation using environmental conditions for 2001-2005 was conducted to quantify the Chesapeake Bay nitrogen budget. The 5 year simulation was characterized by large riverine inputs of nitrogen (154 x 109 g N yr-1) split roughly 60: 40 between inorganic: organic components. Much of this was denitrified (34 x 109 g N yr-1) and buried (46 x 109 g N yr-1) within the estuarine system. A positive net annual ecosystem production for the bay further contributed to a large advective export of organic nitrogen to the shelf (91 x 109 g N yr-1) and negligible inorganic nitrogen export. Interannual variability was strong, particularly for the riverine nitrogen fluxes. In years with higher than average riverine nitrogen inputs, most of this excess nitrogen (50-60%) was exported from the bay as organic nitrogen, with the remaining split between burial, denitrification, and inorganic export to the coastal ocean. In comparison to previous simulations using generic shelf biogeochemical model formulations inside the estuary, the estuarine biogeochemical model described here produced more realistic and significantly greater exports of organic nitrogen and lower exports of inorganic nitrogen to the shelf
G(2) quivers
We present, in explicit matrix representation and a modernity befitting the community, the classification of the finite discrete subgroups of G2 and compute the McKay quivers arising therefrom. Of physical interest are the classes of Script N = 1 gauge theories descending from M-theory and of mathematical interest are possible steps toward a systematic study of crepant resolutions to smooth G2 manifolds as well as generalised McKay Correspondences. This writing is a companion monograph to hep-th/9811183 and hep-th/9905212, wherein the analogues for Calabi-Yau three- and four-folds were considered
From Sasaki-Einstein spaces to quivers via BPS geodesics: Lpqr
The AdS/CFT correspondence between Sasaki-Einstein spaces and quiver gauge
theories is studied from the perspective of massless BPS geodesics. The
recently constructed toric Lpqr geometries are considered: we determine the
dual superconformal quivers and the spectrum of BPS mesons. The conformal
anomaly is compared with the volumes of the manifolds. The U(1)^2_F x U(1)_R
global symmetry quantum numbers of the mesonic operators are successfully
matched with the conserved momenta of the geodesics, providing a test of
AdS/CFT duality. The correspondence between BPS mesons and geodesics allows to
find new precise relations between the two sides of the duality. In particular
the parameters that characterize the geometry are mapped directly to the
parameters used for a-maximization in the field theory. The analysis simplifies
for the special case of the Lpqq models, which are shown to correspond to the
known "generalized conifolds". These geometries can break conformal invariance
through toric deformations of the complex structure.Comment: 30 pages, 8 figures, LaTeX. v2: One more figure. References added,
typos correcte
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