6,983 research outputs found
BPS Saturated Amplitudes and Non-perturbative String Theory
The study of the special F^4 and R^4 in the effective action for the Spin(32)/Z_2 and type II strings shed some light on D-brane calculus and on instanton contributions counting. The D-instanton case is discussed separately
Utilizing Astroinformatics to Maximize the Science Return of the Next Generation Virgo Cluster Survey
The Next Generation Virgo Cluster Survey is a 104 square degree survey of the
Virgo Cluster, carried out using the MegaPrime camera of the
Canada-France-Hawaii telescope, from semesters 2009A-2012A. The survey will
provide coverage of this nearby dense environment in the universe to
unprecedented depth, providing profound insights into galaxy formation and
evolution, including definitive measurements of the properties of galaxies in a
dense environment in the local universe, such as the luminosity function. The
limiting magnitude of the survey is g_AB = 25.7 (10 sigma point source), and
the 2 sigma surface brightness limit is g_AB ~ 29 mag arcsec^-2. The data
volume of the survey (approximately 50 terabytes of images), while large by
contemporary astronomical standards, is not intractable. This renders the
survey amenable to the methods of astroinformatics. The enormous dynamic range
of objects, from the giant elliptical galaxy M87 at M(B) = -21.6, to the
faintest dwarf ellipticals at M(B) ~ -6, combined with photometry in 5 broad
bands (u* g' r' i' z'), and unprecedented depth revealing many previously
unseen structures, creates new challenges in object detection and
classification. We present results from ongoing work on the survey, including
photometric redshifts, Virgo cluster membership, and the implementation of fast
data mining algorithms on the infrastructure of the Canadian Astronomy Data
Centre, as part of the Canadian Advanced Network for Astronomical Research
(CANFAR).Comment: 8 pages, 2 figures. Accepted for the Joint Workshop and Summer
School: Astrostatistics and Data Mining in Large Astronomical Databases, La
Palma, May 30th - June 3rd 2011. A higher resolution version is available at
http://sites.google.com/site/nickballastronomer/publication
Exceptional biodiversity of the cryptofaunal decapods in the Chagos Archipelago, central Indian Ocean
The Chagos Archipelago is geographically remote and isolated from most direct anthropogenic pressures. Here, we quantify the abundance and diversity of decapod crustaceans inhabiting dead coral colonies, representing a standardised microhabitat, across the Archipelago. Using morphological and molecular techniques we recorded 1868 decapods from 164 nominal species within 54 dead coral colonies, but total species estimates (Chao1 estimator) calculate at least 217 species. Galatheids were the most dominant taxa, though alpheids and hippolytids were also very abundant. 32% of species were rare, and 46% of species were found at only one atoll. This prevalence of rarer species has been reported in other cryptofauna studies, suggesting these assemblages maybe comprised of low-abundance species. This study provides the first estimate of diversity for reef cryptofauna in Chagos, which will serve as a useful baseline for global comparisons of coral reef biodiversity
The group structure of non-Abelian NS-NS transformations
We study the transformations of the worldvolume fields of a system of
multiple coinciding D-branes under gauge transformations of the supergravity
Kalb-Ramond field. We find that the pure gauge part of these NS-NS
transformations can be written as a U(N) symmetry of the underlying Yang-Mills
group, but that in general the full NS-NS variations get mixed up non-trivially
with the U(N). We compute the commutation relations and the Jacobi identities
of the bigger group formed by the NS-NS and U(N) transformations.Comment: Latex, 11 pages. v2: Typos corrected; version to appear in JHEP
caos cad as an adaptive open platform service for high performance reconfigurable systems
The increasing demand for computing power in fields such as genomics, image processing and machine learning is pushing towards hardware specialization and heterogeneous systems in order to keep up with the required performance level at sustainable power consumption. Among the available solutions, Field Programmable Gate Arrays (FPGAs), thanks to their advancements, currently represent a very promising candidate, offering a compelling trade-off between efficiency and flexibility. Despite the potential benefits of reconfigurable hardware, one of the main limiting factor to the widespread adoption of FPGAs is complexity in programmability, as well as the effort required to port software solutions to efficient hardware-software implementations. In this chapter, we present CAD as an Adaptive Open-platform Service (CAOS), a platform to guide the application developer in the implementation of efficient hardware-software solutions for high performance reconfigurable systems. The platform assists the designer from the high-level analysis of the code, towards the optimization and implementation of the functionalities to be accelerated on the reconfigurable nodes. Finally, CAOS is designed to facilitate the integration of external contributions and to foster research on Computer Aided Design (CAD) tools for accelerating software applications on FPGA-based systems
Mapping 6D N = 1 supergravities to F-theory
We develop a systematic framework for realizing general anomaly-free chiral
6D supergravity theories in F-theory. We focus on 6D (1, 0) models with one
tensor multiplet whose gauge group is a product of simple factors (modulo a
finite abelian group) with matter in arbitrary representations. Such theories
can be decomposed into blocks associated with the simple factors in the gauge
group; each block depends only on the group factor and the matter charged under
it. All 6D chiral supergravity models can be constructed by gluing such blocks
together in accordance with constraints from anomalies. Associating a geometric
structure to each block gives a dictionary for translating a supergravity model
into a set of topological data for an F-theory construction. We construct the
dictionary of F-theory divisors explicitly for some simple gauge group factors
and associated matter representations. Using these building blocks we analyze a
variety of models. We identify some 6D supergravity models which do not map to
integral F-theory divisors, possibly indicating quantum inconsistency of these
6D theories.Comment: 37 pages, no figures; v2: references added, minor typos corrected;
v3: minor corrections to DOF counting in section
Estimation of Dietary Iron Bioavailability from Food Iron Intake and Iron Status
Currently there are no satisfactory methods for estimating dietary iron absorption (bioavailability) at a population level, but this is essential for deriving dietary reference values using the factorial approach. The aim of this work was to develop a novel approach for estimating dietary iron absorption using a population sample from a sub-section of the UK National Diet and Nutrition Survey (NDNS). Data were analyzed in 873 subjects from the 2000–2001 adult cohort of the NDNS, for whom both dietary intake data and hematological measures (hemoglobin and serum ferritin (SF) concentrations) were available. There were 495 men aged 19–64 y (mean age 42.7±12.1 y) and 378 pre-menopausal women (mean age 35.7±8.2 y). Individual dietary iron requirements were estimated using the Institute of Medicine calculations. A full probability approach was then applied to estimate the prevalence of dietary intakes that were insufficient to meet the needs of the men and women separately, based on their estimated daily iron intake and a series of absorption values ranging from 1–40%. The prevalence of SF concentrations below selected cut-off values (indicating that absorption was not high enough to maintain iron stores) was derived from individual SF concentrations. An estimate of dietary iron absorption required to maintain specified SF values was then calculated by matching the observed prevalence of insufficiency with the prevalence predicted for the series of absorption estimates. Mean daily dietary iron intakes were 13.5 mg for men and 9.8 mg for women. Mean calculated dietary absorption was 8% in men (50th percentile for SF 85 µg/L) and 17% in women (50th percentile for SF 38 µg/L). At a ferritin level of 45 µg/L estimated absorption was similar in men (14%) and women (13%). This new method can be used to calculate dietary iron absorption at a population level using data describing total iron intake and SF concentration
Biological measurement beyond the quantum limit
Quantum noise places a fundamental limit on the per photon sensitivity
attainable in optical measurements. This limit is of particular importance in
biological measurements, where the optical power must be constrained to avoid
damage to the specimen. By using non-classically correlated light, we
demonstrated that the quantum limit can be surpassed in biological
measurements. Quantum enhanced microrheology was performed within yeast cells
by tracking naturally occurring lipid granules with sensitivity 2.4 dB beyond
the quantum noise limit. The viscoelastic properties of the cytoplasm could
thereby be determined with a 64% improved measurement rate. This demonstration
paves the way to apply quantum resources broadly in a biological context
Charge Lattices and Consistency of 6D Supergravity
We extend the known consistency conditions on the low-energy theory of
six-dimensional N = 1 supergravity. We review some facts about the theory of
two-form gauge fields and conclude that the charge lattice Gamma for such a
theory has to be self-dual. The Green-Schwarz anomaly cancellation conditions
in the supergravity theory determine a sublattice of Gamma. The condition that
this sublattice can be extended to a self-dual lattice Gamma leads to a strong
constraint on theories that otherwise appear to be self-consistent.Comment: 15 pages. v2: minor changes; references, additional example added;
v3: minor corrections and clarifications added, JHEP versio
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