160 research outputs found
Conformal and Nonconformal Symmetries in 2d Dilaton gravity
We study finite-dimensional extra symmetries of generic 2D dilaton gravity
models. Using a non-linear sigma model formulation we show that the unique
theories admitting an extra (conformal) symmetry are the models with an
exponential potential (), which include the CGHS
model as a particular though limiting () case. These models give rise
to black hole solutions with a mass-dependent temperature. The underlying extra
symmetry can be maintained in a natural way in the one-loop effective action,
thus implying the exact solubility of the semiclassical theory including
back-reaction. Moreover, we also introduce three different classes of
(non-conformal) transformations which are extra symmetries for generic 2D
dilaton gravity models. Special linear combinations of these transformations
turn out to be the (conformal) symmetries of the CGHS and models. We show that one of the non-conformal extra symmetries
can be converted into a conformal one by means of adequate field redefinitions
involving the metric and the derivatives of the dilaton. Finally, by expressing
the Polyakov-Liouville effective action in terms of an invariant metric, we are
able to provide semiclassical models which are also invariant. This generalizes
the solvable semiclassical model of Bose, Parker and Peleg (BPP) for a generic
2D dilaton gravity model.Comment: Latex, no figures. Revised version published i
Symmetries and solvable models for evaporating 2D black holes
We study the evaporation process of a 2D black hole in thermal equilibrium
when the ingoing radiation is switched off suddenly. We also introduce global
symmetries of generic 2D dilaton gravity models which generalize the extra
symmetry of the CGHS model.Comment: 4 pages, Latex. Talk given at the Second Conference on Quantum
Gravity and Constrained Dynamics. To appear in Proc. Supp. Nucl. Phys.
Weyl Invariance and Black Hole Evaporation
We consider the semiclassical dynamics of CGHS black holes with a
Weyl-invariant effective action for conformal matter. The trace anomaly of
Polyakov effective action is converted into the Virasoro anomaly thus leading
to the same flux of Hawking radiation. The covariance of semiclassical
equations can be restored through a non-local redefinition of the
metric-dilaton fields. The resulting theory turns out to be equivalent to the
RST model. This provides a mechanism to solve semiclassical equations of 2D
dilaton gravity coupled to conformal matter for classically soluble models.Comment: LaTeX, needs amssymb, 8 pages. One reference adde
Production of entanglement in Raman three-level systems using feedback
We examine the theoretical limits of the generation of entanglement in a
damped coupled ion-cavity system using jump-based feedback. Using Raman
transitions to produce entanglement between ground states reduces the necessary
feedback bandwidth, but does not improve the overall effect of the spontaneous
emission on the final entanglement. We find that the fidelity of the resulting
entanglement will be limited by the asymmetries produced by vibrations in the
trap, but that the concurrence remains above 0.88 for realistic ion trap sizes.Comment: 8 pages, 8 figure
Electron/pion separation with an Emulsion Cloud Chamber by using a Neural Network
We have studied the performance of a new algorithm for electron/pion
separation in an Emulsion Cloud Chamber (ECC) made of lead and nuclear emulsion
films. The software for separation consists of two parts: a shower
reconstruction algorithm and a Neural Network that assigns to each
reconstructed shower the probability to be an electron or a pion. The
performance has been studied for the ECC of the OPERA experiment [1].
The separation algorithm has been optimized by using a detailed Monte
Carlo simulation of the ECC and tested on real data taken at CERN (pion beams)
and at DESY (electron beams). The algorithm allows to achieve a 90% electron
identification efficiency with a pion misidentification smaller than 1% for
energies higher than 2 GeV
Scientific and regulatory evaluation of mechanistic in silico drug and disease models in drug development: building model credibility
The value of in silico methods in drug development and evaluation has been demonstrated repeatedly and convincingly. While their benefits are now unanimously recognized, international standards for their evaluation, accepted by all stakeholders involved, are still to be established.
In this white paper, we propose a risk-informed evaluation framework for mechanistic model credibility evaluation. To properly frame the proposed verification and validation activities, concepts such as context of use, regulatory impact and risk-based analysis are discussed. To ensure common understanding between all stakeholders, an overview is provided of relevant in silico terminology used throughout this paper.
To illustrate the feasibility of the proposed approach, we have applied it to three real case examples in the context of drug development, using a credibility matrix currently being tested as a quick-start tool by regulators. Altogether, this white paper provides a practical approach to model evaluation, applicable in both scientific and regulatory evaluation contexts
Descriptors of Posidonia oceanica meadows: Use and application
The conservation of the coastal marine environment requires the possession of information that enables the global quality of the environment to be evaluated reliably and relatively quickly. The use of biological indicators is often an appropriate method. Seagrasses in general, and Posidonia oceanica meadows in particular, are considered to be appropriate for biomonitoring because of their wide distribution, reasonable size, sedentary habit, easy collection and abundance and sensitivity to modifications of littoral zone. Reasoned management, on the scale of the whole Mediterranean basin, requires standardized methods of study, to be applied by both researchers and administrators, enabling comparable results to be obtained. This paper synthesises the existing methods applied to monitor P. oceanica meadows, identifies the most suitable techniques and suggests future research directions. From the results of a questionnaire, distributed to all the identified laboratories working on this topic, a list of the most commonly used descriptors was drawn up, together with the related research techniques (e.g. standardization, interest and limits, valuation of the results). It seems that the techniques used to study meadows are rather similar, but rarely identical, even though the various teams often refer to previously published works. This paper shows the interest of a practical guide that describes, in a standardized way, the most useful techniques enabling P. oceanica meadows to be used as an environmental descriptor. Indeed, it constitutes the first stage in the process. (c) 2005 Elsevier Ltd. All rights reserved.Peer reviewe
Need for speed: Examining protein behavior during cryoEM grid preparation at different timescales
A host of new technologies are under development to improve the quality and reproducibility of cryoelectron microscopy (cryoEM) grid preparation. Here we have systematically investigated the preparation of three macromolecular complexes using three different vitrification devices (Vitrobot, chameleon, and a time-resolved cryoEM device) on various timescales, including grids made within 6 ms (the fastest reported to date), to interrogate particle behavior at the air-water interface for different timepoints. Results demonstrate that different macromolecular complexes can respond to the thin-film environment formed during cryoEM sample preparation in highly variable ways, shedding light on why cryoEM sample preparation can be difficult to optimize. We demonstrate that reducing time between sample application and vitrification is just one tool to improve cryoEM grid quality, but that it is unlikely to be a generic “silver bullet” for improving the quality of every cryoEM sample preparation
Search for black holes and other new phenomena in high-multiplicity final states in proton-proton collisions at root s=13 TeV
Peer reviewe
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Track A Basic Science
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138319/1/jia218438.pd
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