3,221 research outputs found
Chaos in the Gauge/Gravity Correspondence
We study the motion of a string in the background of the Schwarzschild black
hole in AdS_5 by applying the standard arsenal of dynamical systems. Our
description of the phase space includes: the power spectrum, the largest
Lyapunov exponent, Poincare sections and basins of attractions. We find
convincing evidence that the motion is chaotic. We discuss the implications of
some of the quantities associated with chaotic systems for aspects of the
gauge/gravity correspondence. In particular, we suggest some potential
relevance for the information loss paradox.Comment: 29 pages, 11 figure
Pulsar spins from an instability in the accretion shock of supernovae
Rotation-powered radio pulsars are born with inferred initial rotation
periods of order 300 ms (some as short as 20 ms) in core-collapse supernovae.
In the traditional picture, this fast rotation is the result of conservation of
angular momentum during the collapse of a rotating stellar core. This leads to
the inevitable conclusion that pulsar spin is directly correlated with the
rotation of the progenitor star. So far, however, stellar theory has not been
able to explain the distribution of pulsar spins, suggesting that the birth
rotation is either too slow or too fast. Here we report a robust instability of
the stalled accretion shock in core-collapse supernovae that is able to
generate a strong rotational flow in the vicinity of the accreting
proto-neutron star. Sufficient angular momentum is deposited on the
proto-neutron star to generate a final spin period consistent with
observations, even beginning with spherically symmetrical initial conditions.
This provides a new mechanism for the generation of neutron star spin and
weakens, if not breaks, the assumed correlation between the rotational periods
of supernova progenitor cores and pulsar spin.Comment: To be published in Natur
General relativistic null-cone evolutions with a high-order scheme
We present a high-order scheme for solving the full non-linear Einstein
equations on characteristic null hypersurfaces using the framework established
by Bondi and Sachs. This formalism allows asymptotically flat spaces to be
represented on a finite, compactified grid, and is thus ideal for far-field
studies of gravitational radiation. We have designed an algorithm based on
4th-order radial integration and finite differencing, and a spectral
representation of angular components. The scheme can offer significantly more
accuracy with relatively low computational cost compared to previous methods as
a result of the higher-order discretization. Based on a newly implemented code,
we show that the new numerical scheme remains stable and is convergent at the
expected order of accuracy.Comment: 24 pages, 3 figure
Creation of Laryngeal Grafts from Primary Human Cells and Decellularized Laryngeal Scaffolds
Current reconstruction methods of the laryngotracheal segment fail to replace the complex functions of the human larynx. Bioengineering approaches to reconstruction have been limited by the complex tissue compartmentation of the larynx. We attempted to overcome this limitation by bio-engineering laryngeal grafts from decellularized canine laryngeal scaffolds recellularized with human primary cells under one uniform culture medium condition. First, we generated laryngeal scaffolds with preserved glycosaminoglycan content and biomechanical properties by detergent perfusion-decellularization over nine days. We proofed biocompatibility by absence of a CD3 lymphocyte response to subcutaneously implanted scaffolds in immune-competent rats. We then developed a uniform culture medium that strengthened the endothelial barrier over 5 days after an initial growth phase. Simultaneously, this culture medium supported airway epithelial cell and skeletal myoblast growth while maintaining their full differentiation and maturation potential. We then applied the uniform culture medium composition to whole laryngeal scaffolds seeded with endothelial cells from both carotid arteries and external jugular veins and generated re-endothelialized arterial and venous vascular beds. Under the same culture medium condition, we bio-engineered epithelial monolayers onto laryngeal mucosa and repopulated intrinsic laryngeal muscle. We were then able to demonstrate early muscle formation in heterotopic transplantations in immuno-deficient mice. The model supported the formation of three humanized laryngeal tissue compartments under one uniform culture condition, possibly a key factor in developing, complex, multicellular, ready-to-transplant tissue grafts
Historical changes in the phenology of British Odonata are related to climate
Responses of biota to climate change take a number of forms including distributional shifts, behavioural changes and life history changes. This study examined an extensive set of biological records to investigate changes in the timing of life history transitions (specifically emergence) in British Odonata between 1960 and 2004. The results show that there has been a significant, consistent advance in phenology in the taxon as a whole over the period of warming that is mediated by life history traits. British odonates significantly advanced the leading edge (first quartile date) of the flight period by a mean of 1.51 ±0.060 (SEM, n=17) days per decade or 3.08±1.16 (SEM, n=17) days per degree rise in temperature when phylogeny is controlled for. This study represents the first review of changes in odonate phenology in relation to climate change. The results suggest that the damped temperature oscillations experienced by aquatic organisms compared with terrestrial organisms are sufficient to evoke phenological responses similar to those of purely terrestrial taxa
Fast synthesis of platinum nanopetals and nanospheres for highly-sensitive non-enzymatic detection of glucose and selective sensing of ions
Novel methods to obtain Pt nanostructured electrodes have raised particular interest due to their high performance in electrochemistry. Several nanostructuration methods proposed in the literature use costly and bulky equipment or are time-consuming due to the numerous steps they involve. Here, Pt nanostructures were produced for the first time by one-step template-free electrodeposition on Pt bare electrodes. The change in size and shape of the nanostructures is proven to be dependent on the deposition parameters and on the ratio between sulphuric acid and chloride-complexes (i.e., hexachloroplatinate or tetrachloroplatinate). To further improve the electrochemical properties of electrodes, depositions of Pt nanostructures on previously synthesised Pt nanostructures are also performed. The electroactive surface areas exhibit a two order of magnitude improvement when Pt nanostructures with the smallest size are used. All the biosensors based on Pt nanostructures and immobilised glucose oxidase display higher sensitivity as compared to bare Pt electrodes. Pt nanostructures retained an excellent electrocatalytic activity towards the direct oxidation of glucose. Finally, the nanodeposits were proven to be an excellent solid contact for ion measurements, significantly improving the time-stability of the potential. The use of these new nanostructured coatings in electrochemical sensors opens new perspectives for multipanel monitoring of human metabolism
Dimension reduction for systems with slow relaxation
We develop reduced, stochastic models for high dimensional, dissipative
dynamical systems that relax very slowly to equilibrium and can encode long
term memory. We present a variety of empirical and first principles approaches
for model reduction, and build a mathematical framework for analyzing the
reduced models. We introduce the notions of universal and asymptotic filters to
characterize `optimal' model reductions for sloppy linear models. We illustrate
our methods by applying them to the practically important problem of modeling
evaporation in oil spills.Comment: 48 Pages, 13 figures. Paper dedicated to the memory of Leo Kadanof
Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre
Recent measurements of stellar orbits provide compelling evidence that the
compact radio source Sagittarius A* at the Galactic Centre is a
3.6-million-solar-mass black hole. Sgr A* is remarkably faint in all wavebands
other than the radio region, however, which challenges current theories of
matter accretion and radiation surrounding black holes. The black hole's
rotation rate is not known, and therefore neither is the structure of
space-time around it.Here we report high-resolution infrared observations of
Sgr A* that reveal 'quiescent' emission and several flares. The infrared
emission originates from within a few milliarcseconds of the black hole, and
traces very energetic electrons or moderately hot gas within the innermost
accretion region. Two flares exhibit a 17-minute quasi-periodic variability. If
the periodicity arises from relativistic modulation of orbiting gas, the
emission must come from just outside the event horizon, and the black hole must
be rotating at about half of the maximum possible rate.Comment: 5 pages, 3 figures to appear in the Oct 30 issue of Natur
Genetic linkage analysis in the age of whole-genome sequencing
For many years, linkage analysis was the primary tool used for the genetic mapping of Mendelian and complex traits with familial aggregation. Linkage analysis was largely supplanted by the wide adoption of genome-wide association studies (GWASs). However, with the recent increased use of whole-genome sequencing (WGS), linkage analysis is again emerging as an important and powerful analysis method for the identification of genes involved in disease aetiology, often in conjunction with WGS filtering approaches. Here, we review the principles of linkage analysis and provide practical guidelines for carrying out linkage studies using WGS data
Expression of Drug Targets in Patients Treated with Sorafenib, Carboplatin and Paclitaxel
Introduction: Sorafenib, a multitarget kinase inhibitor, targets members of the mitogen-activated protein kinase (MAPK) pathway and VEGFR kinases. Here we assessed the association between expression of sorafenib targets and biomarkers of taxane sensitivity and response to therapy in pre-treatment tumors from patients enrolled in ECOG 2603, a phase III comparing sorafenib, carboplatin and paclitaxel (SCP) to carboplatin, paclitaxel and placebo (CP). Methods: Using a method of automated quantitative analysis (AQUA) of in situ protein expression, we quantified expression of VEGF-R2, VEGF-R1, VEGF-R3, FGF-R1, PDGF-Rβ, c-Kit, B-Raf, C-Raf, MEK1, ERK1/2, STMN1, MAP2, EB1 and Bcl-2 in pretreatment specimens from 263 patients. Results: An association was found between high FGF-R1 and VEGF-R1 and increased progression-free survival (PFS) and overall survival (OS) in our combined cohort (SCP and CP arms). Expression of FGF-R1 and VEGF-R1 was higher in patients who responded to therapy ((CR+PR) vs. (SD+PD+ un-evaluable)). Conclusions: In light of the absence of treatment effect associated with sorafenib, the association found between FGF-R1 and VEGF-R1 expression and OS, PFS and response might reflect a predictive biomarker signature for carboplatin/paclitaxel-based therapy. Seeing that carboplatin and pacitaxel are now widely used for this disease, corroboration in another cohort might enable us to improve the therapeutic ratio of this regimen. © 2013 Jilaveanu et al
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