5,389 research outputs found
Fluctuating brane in a dilatonic bulk
We consider a cosmological brane moving in a static five-dimensional bulk
spacetime endowed with a scalar field whose potential is exponential. After
studying various cosmological behaviours for the homogeneous background, we
investigate the fluctuations of the brane that leave spacetime unaffected. A
single mode embodies these fluctuations and obeys a wave equation which we
study for bouncing and ever-expanding branes.Comment: 17 pages, 7 figures, revte
(Non)-singular brane-world cosmology induced by quantum effects in d5 dilatonic gravity
5d dilatonic gravity (bosonic sector of gauged supergravity) with non-trivial
bulk potential and with surface terms (boundary cosmological constant and trace
anomaly induced effective action for brane quantum matter) is considered. For
constant bulk potential and maximally SUSY Yang-Mills theory (CFT living on the
brane) the inflationary brane-world is constructed. The bulk is singular
asymptotically AdS space with non-constant dilaton and dilatonic de Sitter or
hyperbolic brane is induced by quantum matter effects. At the same time,
dilaton on the brane is determined dynamically. This all is natural realization
of warped compactification in AdS/CFT correspondence. For fine-tuned toy
example of non-constant bulk potential we found the non-singular dilatonic
brane-world where bulk again represents asymptotically AdS space and de Sitter
brane (inflationary phase of observable Universe) is induced exclusively by
quantum effects. The radius of the brane and dilaton are determined
dynamically. The analytically solvable example of exponential bulk potential
leading to singular asymptotically AdS dilatonic bulk space with de Sitter (or
hyperbolic) brane is also presented.In all cases under discussion the gravity
on the brane is trapped via Randall-Sundrum scenario. It is shown that
qualitatively the same types of brane-worlds occur when quantum brane matter is
described by dilaton coupled spinors.Comment: LaTeX file 28 pages and two eps files, few misprints are correcte
Specialized dynamical properties of promiscuous residues revealed by simulated conformational ensembles
The ability to interact with different partners is one of the most important features in proteins. Proteins that bind a large number of partners (hubs) have been often associated with intrinsic disorder. However, many examples exist of hubs with an ordered structure, and evidence of a general mechanism promoting promiscuity in ordered proteins is still elusive. An intriguing hypothesis is that promiscuous binding sites have specific dynamical properties, distinct from the rest of the interface and pre-existing in the protein isolated state. Here, we present the first comprehensive study of the intrinsic dynamics of promiscuous residues in a large protein data set. Different computational methods, from coarse-grained elastic models to geometry-based sampling methods and to full-atom Molecular Dynamics simulations, were used to generate conformational ensembles for the isolated proteins. The flexibility and dynamic correlations of interface residues with a different degree of binding promiscuity were calculated and compared considering side chain and backbone motions, the latter both on a local and on a global scale. The study revealed that (a) promiscuous residues tend to be more flexible than nonpromiscuous ones, (b) this additional flexibility has a higher degree of organization, and (c) evolutionary conservation and binding promiscuity have opposite effects on intrinsic dynamics. Findings on simulated ensembles were also validated on ensembles of experimental structures extracted from the Protein Data Bank (PDB). Additionally, the low occurrence of single nucleotide polymorphisms observed for promiscuous residues indicated a tendency to preserve binding diversity at these positions. A case study on two ubiquitin-like proteins exemplifies how binding promiscuity in evolutionary related proteins can be modulated by the fine-tuning of the interface dynamics. The interplay between promiscuity and flexibility highlighted here can inspire new directions in protein-protein interaction prediction and design methods. © 2013 American Chemical Society
Social sciences research in neglected tropical diseases 2: A bibliographic analysis
The official published version of the article can be found at the link below.Background
There are strong arguments for social science and interdisciplinary research in the neglected tropical diseases. These diseases represent a rich and dynamic interplay between vector, host, and pathogen which occurs within social, physical and biological contexts. The overwhelming sense, however, is that neglected tropical diseases research is a biomedical endeavour largely excluding the social sciences. The purpose of this review is to provide a baseline for discussing the quantum and nature of the science that is being conducted, and the extent to which the social sciences are a part of that.
Methods
A bibliographic analysis was conducted of neglected tropical diseases related research papers published over the past 10 years in biomedical and social sciences. The analysis had textual and bibliometric facets, and focussed on chikungunya, dengue, visceral leishmaniasis, and onchocerciasis.
Results
There is substantial variation in the number of publications associated with each disease. The proportion of the research that is social science based appears remarkably consistent (<4%). A textual analysis, however, reveals a degree of misclassification by the abstracting service where a surprising proportion of the "social sciences" research was pure clinical research. Much of the social sciences research also tends to be "hand maiden" research focused on the implementation of biomedical solutions.
Conclusion
There is little evidence that scientists pay any attention to the complex social, cultural, biological, and environmental dynamic involved in human pathogenesis. There is little investigator driven social science and a poor presence of interdisciplinary science. The research needs more sophisticated funders and priority setters who are not beguiled by uncritical biomedical promises
The problematic backreaction of SUSY-breaking branes
In this paper we investigate the localisation of SUSY-breaking branes which,
in the smeared approximation, support specific non-BPS vacua. We show, for a
wide class of boundary conditions, that there is no flux vacuum when the branes
are described by a genuine delta-function. Even more, we find that the smeared
solution is the unique solution with a regular brane profile. Our setup
consists of a non-BPS AdS_7 solution in massive IIA supergravity with smeared
anti-D6-branes and fluxes T-dual to ISD fluxes in IIB supergravity.Comment: 27 pages, Latex2e, 5 figure
The material soul: Strategies for naturalising the soul in an early modern epicurean context
We usually portray the early modern period as one characterised by the âbirth of subjectivityâ with Luther and Descartes as two alternate representatives of this radical break with the past, each ushering in the new era in which âIâ am the locus of judgements about the world. A sub-narrative called âthe mind-body problemâ recounts how Cartesian dualism, responding to the new promise of a mechanistic science of nature, âsplit offâ the world of the soul/mind/self from the world of extended, physical substanceâa split which has preoccupied the philosophy of mind up until the present day. We would like to call attention to a different constellation of textsâneither a robust âtraditionâ nor an isolated âepisodeâ, somewhere in betweenâwhich have in common their indebtedness to, and promotion of an embodied, Epicurean approach to the soul. These texts follow the evocative hint given in Lucretiusâ De rerum natura that âthe soul is to the body as scent is to incenseâ (in an anonymous early modern French version). They neither assert the autonomy of the soul, nor the dualism of body and soul, nor again a sheer physicalism in which âintentionalâ properties are reduced to the basic properties of matter. Rather, to borrow the title of one of these treatises (LâĂme MatĂ©rielle), they seek to articulate the concept of a material soul. We reconstruct the intellectual development of a corporeal, mortal and ultimately material soul, in between medicine, natural philosophy and metaphysics, including discussions of Malebranche and Willis, but focusing primarily on texts including the 1675 Discours anatomiques by the Epicurean physician Guillaume Lamy; the anonymous manuscript from circa 1725 entitled LâĂme MatĂ©rielle, which is essentially a compendium of texts from the later seventeenth century (Malebranche, Bayle) along with excerpts from Lucretius; and materialist writings such Julien Offray de La Mettrieâs LâHomme-Machine (1748), in order to articulate this concept of a âmaterial soulâ with its implications for notions of embodiment, materialism and selfhood
Integration and disruption effects of shape and texture in haptic search
In a search task, where one has to search for the presence of a target among distractors, the target is sometimes easily found, whereas in other searches it is much harder to find. The performance in a search task is influenced by the identity of the target, the identity of the distractors and the differences between the two. In this study, these factors were manipulated by varying the target and distractors in shape (cube or sphere) and roughness (rough or smooth) in a haptic search task. Participants had to grasp a bundle of items and determine as fast as possible whether a predefined target was present or not. It was found that roughness and edges were relatively salient features and the search for the presence of these features was faster than for their absence. If the task was easy, the addition of these features could also disrupt performance, even if they were irrelevant for the search task. Another important finding was that the search for a target that differed in two properties from the distractors was faster than a task with only a single property difference, although this was only found if the two target properties were non-salient. This means that shape and texture can be effectively integrated. Finally, it was found that edges are more beneficial to a search task than disrupting, whereas for roughness this was the other way round
Cosmological Perturbations in Brane-World Theories: Formalism
We develop a gauge-invariant formalism to describe metric perturbations in
five-dimensional brane-world theories. In particular, this formalism applies to
models originating from heterotic M-theory. We introduce a generalized
longitudinal gauge for scalar perturbations. As an application, we discuss some
aspects of the evolution of fluctuations on the brane. Moreover, we show how
the five-dimensional formalism can be matched to the known four-dimensional one
in the limit where an effective four-dimensional description is appropriate.Comment: 16 pages, no figure, matches version to appear in PR
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