745 research outputs found
Equation of state for the MCFL phase and its implications for compact star models
Using the solutions of the gap equations of the magnetic-color-flavor-locked
(MCFL) phase of paired quark matter in a magnetic field, and taking into
consideration the separation between the longitudinal and transverse pressures
due to the field-induced breaking of the spatial rotational symmetry, the
equation of state (EoS) of the MCFL phase is self-consistently determined. This
result is then used to investigate the possibility of absolute stability, which
turns out to require a field-dependent bag constant to hold. That is, only if
the bag constant varies with the magnetic field, there exists a window in the
magnetic field vs. bag constant plane for absolute stability of strange matter.
Implications for stellar models of magnetized (self-bound) strange stars and
hybrid (MCFL core) stars are calculated and discussed.Comment: 11 pp. 11 figure
Modeling cancer metabolism on a genome scale
Cancer cells have fundamentally altered cellular metabolism that is associated with their tumorigenicity and malignancy. In addition to the widely studied Warburg effect, several new key metabolic alterations in cancer have been established over the last decade, leading to the recognition that altered tumor metabolism is one of the hallmarks of cancer. Deciphering the full scope and functional implications of the dysregulated metabolism in cancer requires both the advancement of a variety of omics measurements and the advancement of computational approaches for the analysis and contextualization of the accumulated data. Encouragingly, while the metabolic network is highly interconnected and complex, it is at the same time probably the best characterized cellular network. Following, this review discusses the challenges that genome‐scale modeling of cancer metabolism has been facing. We survey several recent studies demonstrating the first strides that have been done, testifying to the value of this approach in portraying a network‐level view of the cancer metabolism and in identifying novel drug targets and biomarkers. Finally, we outline a few new steps that may further advance this field
Immuno-virological and toxicity outcomes of HIV-infected patients after 48 months of ART in Phnom Penh, Cambodia
Mexico AIDS Conference 200
Tautomeric mutation: A quantum spin modelling
A quantum spin model representing tautomeric mutation is proposed for any DNA
molecule. Based on this model, the quantum mechanical calculations for
mutational rate and complementarity restoring repair rate in the replication
processes are carried out. A possible application to a real biological system
is discussed.Comment: 7 pages (no figures
Shear-free radiating collapse and conformal flatness
Here we study some general properties of spherical shear-free collapse. Its
general solution when imposing conformal flatness is reobtained [1,2] and
matched to the outgoing Vaidya spacetime. We propose a simple model satisfying
these conditions and study its physical consequences. Special attention
deserve, the role played by relaxational processes and the conspicuous link
betweeen dissipation and density inhomogeneity.Comment: 13 pages Latex. Some misprints in eqs.(17), (30) and (35) have been
correcte
Managing Dynamic User Communities in a Grid of Autonomous Resources
One of the fundamental concepts in Grid computing is the creation of Virtual
Organizations (VO's): a set of resource consumers and providers that join
forces to solve a common problem. Typical examples of Virtual Organizations
include collaborations formed around the Large Hadron Collider (LHC)
experiments. To date, Grid computing has been applied on a relatively small
scale, linking dozens of users to a dozen resources, and management of these
VO's was a largely manual operation. With the advance of large collaboration,
linking more than 10000 users with a 1000 sites in 150 counties, a
comprehensive, automated management system is required. It should be simple
enough not to deter users, while at the same time ensuring local site autonomy.
The VO Management Service (VOMS), developed by the EU DataGrid and DataTAG
projects[1, 2], is a secured system for managing authorization for users and
resources in virtual organizations. It extends the existing Grid Security
Infrastructure[3] architecture with embedded VO affiliation assertions that can
be independently verified by all VO members and resource providers. Within the
EU DataGrid project, Grid services for job submission, file- and database
access are being equipped with fine- grained authorization systems that take VO
membership into account. These also give resource owners the ability to ensure
site security and enforce local access policies. This paper will describe the
EU DataGrid security architecture, the VO membership service and the local site
enforcement mechanisms Local Centre Authorization Service (LCAS), Local
Credential Mapping Service(LCMAPS) and the Java Trust and Authorization
Manager.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics
(CHEP03), La Jolla, Ca, USA, March 2003, 7 pages, LaTeX, 5 eps figures. PSN
TUBT00
The Einstein static universe with torsion and the sign problem of the cosmological constant
In the field equations of Einstein-Cartan theory with cosmological constant a
static spherically symmetric perfect fluid with spin density satisfying the
Weyssenhoff restriction is considered. This serves as a rough model of space
filled with (fermionic) dark matter. From this the Einstein static universe
with constant torsion is constructed, generalising the Einstein Cosmos to
Einstein-Cartan theory.
The interplay between torsion and the cosmological constant is discussed. A
possible way out of the cosmological constant's sign problem is suggested.Comment: 8 pages, LaTeX; minor layout changes, typos corrected, one new
equation, new reference [5], completed reference [13], two references adde
Mission to planet Earth : the first two billion years
Solar radiation and geological processes over the first few million years of Earth’s history, followed soon thereafter by the origin of life, steered our planet towards an evolutionary trajectory of long-lived habitability that ultimately enabled the emergence of complex life. We review the most important conditions and feedbacks over the first 2 billion years of this trajectory, which perhaps represent the best analogue for other habitable worlds in the galaxy. Crucial aspects included: (1) the redox state and volatile content of Earth’s building blocks, which determined the longevity of the magma ocean and its ability to degas H2O and other greenhouse gases, in particular CO2, allowing the condensation of a water ocean; (2) the chemical properties of the resulting degassed mantle, including oxygen fugacity, which would have not only affected its physical properties and thus its ability to recycle volatiles and nutrients via plate tectonics, but also contributed to the timescale of atmospheric oxygenation; (3) the emergence of life, in particular the origin of autotrophy, biological N2 fixation, and oxygenic photosynthesis, which accelerated sluggish abiotic processes of transferring some volatiles back into the lithosphere; (4) strong stellar UV radiation on the early Earth, which may have eroded significant amounts of atmospheric volatiles, depending on atmospheric CO2/N2 ratios and thus impacted the redox state of the mantle as well as the timing of life’s origin; and (5) evidence of strong photochemical effects on Earth’s sulfur cycle, preserved in the form of mass-independent sulfur isotope fractionation, and potentially linked to fractionation in organic carbon isotopes. The early Earth presents itself as an exoplanet analogue that can be explored through the existing rock record, allowing us to identify atmospheric signatures diagnostic of biological metabolisms that may be detectable on other inhabited planets with next-generation telescopes. We conclude that investigating the development of habitable conditions on terrestrial planets, an inherently complex problem, requires multi-disciplinary collaboration and creative solutions.Publisher PDFPeer reviewe
Supertube domain-walls and elimination of closed time-like curves in string theory
We show that some novel physics of supertubes removes closed time-like curves
from many supersymmetric spaces which naively suffer from this problem. The
main claim is that supertubes naturally form domain-walls, so while analytical
continuation of the metric would lead to closed time-like curves, across the
domain-wall the metric is non-differentiable, and the closed time-like curves
are eliminated. In the examples we study the metric inside the domain-wall is
always of the G\"odel type, while outside the shell it looks like a localized
rotating object, often a rotating black hole. Thus this mechanism prevents the
appearance of closed time-like curves behind the horizons of certain rotating
black holes.Comment: 22 pages, JHEP3 class. V2: Some corrections and clariffications,
references added. V3: more corrections to formulas, results unchanged. V4:
minor typos, as published in PR
Holographic Protection of Chronology in Universes of the Godel Type
We analyze the structure of supersymmetric Godel-like cosmological solutions
of string theory. Just as the original four-dimensional Godel universe, these
solutions represent rotating, topologically trivial cosmologies with a
homogeneous metric and closed timelike curves. First we focus on
"phenomenological" aspects of holography, and identify the preferred
holographic screens associated with inertial comoving observers in Godel
universes. We find that holography can serve as a chronology protection agency:
The closed timelike curves are either hidden behind the holographic screen, or
broken by it into causal pieces. In fact, holography in Godel universes has
many features in common with de Sitter space, suggesting that Godel universes
could represent a supersymmetric laboratory for addressing the conceptual
puzzles of de Sitter holography. Then we initiate the investigation of
"microscopic" aspects of holography of Godel universes in string theory. We
show that Godel universes are T-dual to pp-waves, and use this fact to generate
new Godel-like solutions of string and M-theory by T-dualizing known
supersymmetric pp-wave solutions.Comment: 35 pages, 5 figures. v2: typos corrected, references adde
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