571 research outputs found
Simple generalizations of Anti-de Sitter space-time
We consider new cosmological solutions which generalize the cosmological
patch of the Anti-de Sitter (AdS) space-time, allowing for fluids with
equations of state such that . We use them to derive the associated
full manifolds. We find that these solutions can all be embedded in flat
five-dimensional space-time with signature, revealing deformed
hyperboloids. The topology and causal-structure of these spaces is therefore
unchanged, and closed time-like curves are identified, before a covering space
is considered. However the structure of Killing vector fields is entirely
different and so we may expect a different structure of Killing horizons in
these solutions.Comment: 6 Pages, 5 Figures, Corrections and additions made for publication in
Journal of Classical and Quantum Gravit
The 100 most eminent psychologists of the 20th century.
A rank-ordered list was constructed that reports the first 99 of the 100 most eminent psychologists of the 20th century. Eminence was measured by scores on 3 quantitative variables and 3 qualitative variables. The quantitative variables were journal citation frequency, introductory psychology textbook citation frequency, and survey response frequency. The qualitative variables were National Academy of Sciences membership, election as American Psychological Association (APA) president or receipt of the APA Distinguished Scientific Contributions Award, and surname used as an eponym. The qualitative variables were quantified and combined with the other 3 quantitative variables to produce a composite score that was then used to construct a rank-ordered list of the most eminent psychologists of the 20th century. The discipline of psychology underwent a remarkable transformation during the 20th cen-tury, a transformation that included a shift away from the European-influenced philosophical psychology of the late 19th century to th
The helical phase of chiral nematic liquid crystals as the Bianchi VII(0) group manifold
We show that the optical structure of the helical phase of a chiral nematic
is naturally associated with the Bianchi VII(0) group manifold, of which we
give a full account. The Joets-Ribotta metric governing propagation of the
extraordinary rays is invariant under the simply transitive action of the
universal cover of the three dimensional Euclidean group of two dimensions.
Thus extraordinary light rays are geodesics of a left-invariant metric on this
Bianchi type VII(0) group. We are able to solve by separation of variables both
the wave equation and the Hamilton-Jacobi equation for this metric. The former
reduces to Mathieu's equation and the later to the quadrantal pendulum
equation. We discuss Maxwell's equations for uniaxial optical materials where
the configuration is invariant under a group action and develop a formalism to
take advantage of these symmetries. The material is not assumed to be impedance
matched, thus going beyond the usual scope of transformation optics. We show
that for a chiral nematic in its helical phase Maxwell's equations reduce to a
generalised Mathieu equation. Our results may also be relevant to helical
phases of some magnetic materials and to light propagation in certain
cosmological models.Comment: 15 pages, 1 figure; Version 2 updated and expanded, to appear in
Phys. Rev.
A Minimal Realization Technique for the Dynamical Structure Function of a Class of LTI Systems
The dynamical structure function of a linear time invariant (LTI) system reveals causal dependencies among manifest variables without specifying any particular relationships among the unmeasured states of the system. As such, it is a useful representation for complex networks where a coarse description of global system structure is desired without detailing the intricacies of a full state realization. In this paper, we consider the problem of finding a minimal state realization for a given dynamical structure function. Interestingly, some dynamical structure functions require uncontrollable modes in their state realizations to deliver the desired input-output behavior while respecting a specified system structure. As a result, the minimal order necessary to realize a particular dynamical structure function may be greater than that necessary to realize its associated transfer function. Although finding a minimal realization for a given dynamical structure function is difficult in general, we present a straightforward procedure here that works for a simplified class of systems
A Minimal Realization Technique for the Dynamical Structure Function of a Class of LTI Systems
The dynamical structure function of a linear time invariant (LTI) system reveals causal dependencies among manifest variables without specifying any particular relationships among the unmeasured states of the system. As such, it is a useful representation for complex networks where a coarse description of global system structure is desired without detailing the intricacies of a full state realization. In this paper, we consider the problem of finding a minimal state realization for a given dynamical structure function. Interestingly, some dynamical structure functions require uncontrollable modes in their state realizations to deliver the desired input-output behavior while respecting a specified system structure. As a result, the minimal order necessary to realize a particular dynamical structure function may be greater than that necessary to realize its associated transfer function. Although finding a minimal realization for a given dynamical structure function is difficult in general, we present a straightforward procedure here that works for a simplified class of systems
Zebrafish models in neuropsychopharmacology and CNS drug discovery
Despite the high prevalence of neuropsychiatric disorders, their aetiology and molecular mechanisms remain poorly understood. The zebrafish (Danio rerio) is increasingly utilized as a powerful animal model in neuropharmacology research and in vivo drug screening. Collectively, this makes zebrafish a useful tool for drug discovery and the identification of disordered molecular pathways. Here, we discuss zebrafish models of selected human neuropsychiatric disorders and drug-induced phenotypes. As well as covering a broad range of brain disorders (from anxiety and psychoses to neurodegeneration), we also summarize recent developments in zebrafish genetics and small molecule screening, which markedly enhance the disease modelling and the discovery of novel drug targets. © 2017 The British Pharmacological SocietyThe study was coordinated through the International Zebrafish Neuroscience Research Consortium (ZNRC), and this collaboration was funded by St. Petersburg State University, Ural Federal University and Guangdong Ocean University. A.V.K. is the Chair of ZNRC, and his research is supported by the Russian Foundation for Basic Research (RFBR) grant 16-04-00851
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The Digital Road to Scientific Knowledge Diffusion; A Faster, Better Way to Scientific Progress?
With the United States federal government spending billions annually for research and development, ways to increase the productivity of that research can have a significant return on investment. The process by which science knowledge is spread is called diffusion. It is therefore important to better understand and measure the benefits of this diffusion of knowledge. In particular, it is important to understand whether advances in Internet searching can speed up the diffusion of scientific knowledge and accelerate scientific progress despite the fact that the vast majority of scientific information resources continue to be held in deep web databases that many search engines cannot fully access. To address the complexity of the search issue, the term global discovery is used for the act of searching across heterogeneous environments and distant communities. This article discusses these issues and describes research being conducted by the Office of Scientific and Technical Information (OSTI)
A Deformation of Sasakian Structure in the Presence of Torsion and Supergravity Solutions
We discuss a deformation of Sasakian structure in the presence of totally
skew-symmetric torsion by introducing odd dimensional manifolds whose metric
cones are K\"ahler with torsion. It is shown that such a geometry inherits
similar properties to those of Sasakian geometry. As an example of them, we
present an explicit expression of local metrics and see how Sasakian structure
is deformed by the presence of torsion. We also demonstrate that our example of
the metrics admits the existence of hidden symmetries described by non-trivial
odd-rank generalized closed conformal Killing-Yano tensors. Furthermore, using
these metrics as an {\it ansatz}, we construct exact solutions in five
dimensional minimal (un-)gauged supergravity and eleven dimensional
supergravity. Finally, we discuss the global structures of the solutions and
obtain regular metrics on compact manifolds in five dimensions, which give
natural generalizations of Sasaki--Einstein manifolds and
. We also discuss regular metrics on non-compact manifolds in eleven
dimensions.Comment: 38 pages, 1 table, v2: version to appear in Class. Quant. Gra
Social preferences, accountability, and wage bargaining
We assess the extent of preferences for employment in a collective wage bargaining situation with heterogeneous workers. We vary the size of the union and introduce a treatment mechanism transforming the voting game into an individual allocation task. Our results show that highly productive workers do not take employment of low productive workers into account when making wage proposals, regardless of whether insiders determine the wage or all workers. The level of pro-social preferences is small in the voting game, while it increases as the game is transformed into an individual allocation task. We interpret this as an accountability effect
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