No hair for spherical black holes: charged and nonminimally coupled scalar field with self--interaction

We prove three theorems in general relativity which rule out classical scalar hair of static, spherically symmetric, possibly electrically charged black holes. We first generalize Bekenstein's no--hair theorem for a multiplet of minimally coupled real scalar fields with not necessarily quadratic action to the case of a charged black hole. We then use a conformal map of the geometry to convert the problem of a charged (or neutral) black hole with hair in the form of a neutral self--interacting scalar field nonminimally coupled to gravity to the preceding problem, thus establishing a no--hair theorem for the cases with nonminimal coupling parameter $\xi<0$ or $\xi\geq {1\over 2}$. The proof also makes use of a causality requirement on the field configuration. Finally, from the required behavior of the fields at the horizon and infinity we exclude hair of a charged black hole in the form of a charged self--interacting scalar field nonminimally coupled to gravity for any $\xi$.Comment: 30 pages, RevTeX. Sec.IV corrected, simplified and shortened. Corrections to Sec.IIA between Eqs. 2.7 and Eq.2.1. First two paragraphs of Sec. VC new. To appear Phys. Rev. D, Oct. 15, 199

Non-stoichiometry in monoclinic zirconia and amorphous zirconia

A combination of materials modelling techniques and targeted experimental investigations have identified the manner in which non-stoichiometry is accommodated within both crystalline and amorphous ZrO2. Not only is excess oxygen possible in both crystalline and amorphous ZrO2, but it is found that there is a high propensity for significant deviations – especially in the amorphous system – forming ZrO2+x. This has clear implications to the behavior and degradation of ZrO2 as a thermal barrier coating in aerospace and energy components, but also as the boundary oxide protecting zirconium alloys in aggressive environments, including within a water cooled nuclear power reactor. The behavior was highlighted through a combination of both Raman spectroscopy and associated atomic scale predictions coupled with thermodynamic analysis of the system. As excess oxygen cannot readily oxidize Zr4+ ions beyond this charge state, the additional oxygen is accommodated instead as a peroxide ion – O22-. This peroxide specie has a distinct covalent bond not expected in the stoichiometric ionic ZrO2 system that is readily observable using Raman spectroscopy. Now that excess oxygen accommodation in ZrO2 has been highlighted, an understanding of how various dopant or alloying elements can impact its behavior can be targeted to improve component reliability. The presence of amorphous phases at grain boundaries is also discussed in terms of potential super-highways for oxygen transport through the oxide system

Motif Discovery through Predictive Modeling of Gene Regulation

We present MEDUSA, an integrative method for learning motif models of transcription factor binding sites by incorporating promoter sequence and gene expression data. We use a modern large-margin machine learning approach, based on boosting, to enable feature selection from the high-dimensional search space of candidate binding sequences while avoiding overfitting. At each iteration of the algorithm, MEDUSA builds a motif model whose presence in the promoter region of a gene, coupled with activity of a regulator in an experiment, is predictive of differential expression. In this way, we learn motifs that are functional and predictive of regulatory response rather than motifs that are simply overrepresented in promoter sequences. Moreover, MEDUSA produces a model of the transcriptional control logic that can predict the expression of any gene in the organism, given the sequence of the promoter region of the target gene and the expression state of a set of known or putative transcription factors and signaling molecules. Each motif model is either a $k$-length sequence, a dimer, or a PSSM that is built by agglomerative probabilistic clustering of sequences with similar boosting loss. By applying MEDUSA to a set of environmental stress response expression data in yeast, we learn motifs whose ability to predict differential expression of target genes outperforms motifs from the TRANSFAC dataset and from a previously published candidate set of PSSMs. We also show that MEDUSA retrieves many experimentally confirmed binding sites associated with environmental stress response from the literature.Comment: RECOMB 200

AdS/CFT for Four-Point Amplitudes involving Gravitino Exchange

In this paper we compute the tree-level four-point scattering amplitude of two dilatini and two axion-dilaton fields in type IIB supergravity in AdS5 x S5. A special feature of this process is that there is an "exotic" channel in which there are no singleparticle poles. Another novelty is that this process involves the exchange of a bulk gravitino. The amplitude is interpreted in terms of N = 4 supersymmetric Yang-Mills theory at large 't Hooft coupling. Properties of the Operator Product Expansion are used to analyze the various contributions from single- and double-trace operators in the weak and strongly coupled regimes, and to determine the anomalous dimensions of semi-short operators. The analysis is particularly clear in the exotic channel, given the absence of BPS states.Comment: 32 pages, 1 figure. Published Version. Minor change

On the Ricci dark energy model

We study the Ricci dark energy model (RDE) which was introduced as an alternative to the holographic dark energy model. We point out that an accelerating phase of the RDE is that of a constant dark energy model. This implies that the RDE may not be a new model of explaining the present accelerating universe.Comment: 8 page

Chern-Simons Vortices in Supergravity

We study supersymmetric vortex solutions in three-dimensional abelian gauged supergravity. First, we construct the general U(1)-gauged D=3, N=2 supergravity whose scalar sector is an arbitrary Kahler manifold with U(1) isometry. This construction clarifies the connection between local supersymmetry and the specific forms of some scalar potentials previously found in the literature -- in particular, it provides the locally supersymmetric embedding of the abelian Chern-Simons Higgs model. We show that the Killing spinor equations admit rotationally symmetric vortex solutions with asymptotically conical geometry which preserve half of the supersymmetry.Comment: 26 pages, LaTeX2

Holographic Coulomb branch vevs

We compute holographically the vevs of all chiral primary operators for supergravity solutions corresponding to the Coulomb branch of N=4 SYM and find exact agreement with the corresponding field theory computation. Using the dictionary between 10d geometries and field theory developed to extract these vevs, we propose a gravity dual of a half supersymmetric deformation of N=4 SYM by certain irrelevant operators.Comment: 16 pages, v2 corrections in appendi

Oxidation of UC: an in-situ high temperature environmental scanning electron microscopy study

Uranium carbide (UC) has the potential to be used as fuel in Generation IV nuclear reactors thanks to its higher metal atom density and better thermal conductivity when compared to the most commonly used fuel: uranium dioxide (UO2) [1]. Although UC offers improved properties during operation, it needs to be converted into an oxide form after usage as it is reactive and potentially pyrophoric [2] in oxidising environments. Previous oxidation studies on UC, performed over a range of oxygen atmospheres and temperatures, suggest different mechanisms lead to the formation of either a protective or a pulverised non-protective oxide layer [3]. New experimental observations of the oxidation and self-ignition of UC were reported in our previous work [4] involving a combination of state-of-the-art techniques: high temperature environmental scanning electron microscopy (HT-ESEM), high-resolution transmission electron microscopy (HRTEM) combined with an image analysis technique (ImageJ). In situ HT-ESEM oxidation of sintered UC fragments from 723 to 848 K in 10 to 100 Pa oxygen atmosphere revealed the morphological changes to the oxide during the transformations between UC to UO2 and UO2 to U3O8. Oxidation at 723 K in a low O2 atmosphere (≤ 25 Pa O2) produced a compact UO2+x oxide layer, confirmed by post mortem HRTEM analysis. The oxide formed after an induction period and it was accompanied by an exponential followed by logarithmic sample area expansion and crack propagation. Furthermore, samples oxidised at 50 Pa O2 at 723 K and at 773-848 K in an oxygen atmosphere of 10 to 100 Pa O2 showed “explosive” oxidation (see Figure 1). Sample expansion and crack propagation are well described by an exponential law until the “explosion” occurred causing a transformation to a popcorn-like morphology which is typical for oxidation from UO2 to U3O8. HRTEM analysis on the sample powder showed the oxide to be formed of a mixture of U3O7/U3O8 with U3O8 showing preferential growth in the [001] direction. The explosive nature of the oxide is triggered by ignition of UC, which set off this reaction throughout the entire sample with a propagation speed of 150-500 ± 50 µm/s, which shows similarities to a self-propagating high-temperature synthesis reaction. Please click Additional Files below to see the full abstract