19,235 research outputs found
Global aspects of accelerating and rotating black hole space-times
The complete family of exact solutions representing accelerating and rotating
black holes with possible electromagnetic charges and a NUT parameter is known
in terms of a modified Plebanski-Demianski metric. This demonstrates the
singularity and horizon structure of the sources but not that the complete
space-time describes two causally separated black holes. To demonstrate this
property, the metric is first cast in the Weyl-Lewis-Papapetrou form. After
extending this up to the acceleration horizon, it is then transformed to the
boost-rotation-symmetric form in which the global properties of the solution
are manifest. The physical interpretation of these solutions is thus clarified.Comment: 15 pages, 1 figure. To appear in Class. Quantum Gra
The C-metric as a colliding plane wave space-time
It is explicitly shown that part of the C-metric space-time inside the black
hole horizon may be interpreted as the interaction region of two colliding
plane waves with aligned linear polarization, provided the rotational
coordinate is replaced by a linear one. This is a one-parameter generalization
of the degenerate Ferrari-Ibanez solution in which the focussing singularity is
a Cauchy horizon rather than a curvature singularity.Comment: 6 pages. To appear in Classical and Quantum Gravit
Image charge effects in single-molecule junctions: Breaking of symmetries and negative differential resistance in a benzene transistor
Both experiments and theoretical studies have demonstrated that the
interaction between the current carrying electrons and the induced polarization
charge in single-molecule junctions leads to a strong renormalization of
molecular charging energies. However, the effect on electronic excitations and
molecular symmetries remain unclear. Using a theoretical framework developed
for semiconductor nanostructure based single-electron transistors (SETs), we
demonstrate that the image charge interaction breaks the molecular symmetries
in a benzene based single-molecule transistor operating in the Coulomb blockade
regime. This results in the appearance of a so-called blocking state, which
gives rise to negative differential resistance (NDR). We show that the
appearance of NDR and its magnitude in the symmetry-broken benzene SET depends
in a complicated way on the interplay between the many-body matrix elements,
the lead tunnel coupling asymmetry, and the bias polarity. In particular, the
current reducing property of the blocking state causing the NDR, is shown to
vanish under strongly asymmetric tunnel couplings, when the molecule is coupled
stronger to the drain electrode. The calculated IV characteristic may serve as
an indicator for image charge broken molecular symmetries in experimental
situations.Comment: Accepted version (Phys. Rev. B), 16 pages, 8 figure
Radiation generated by accelerating and rotating charged black holes in (anti-)de Sitter space
Asymptotic behaviour of gravitational and electromagnetic fields of exact
type D solutions from the large Plebanski-Demianski family of black hole
spacetimes is analyzed. The amplitude and directional structure of radiation is
evaluated in cases when the cosmological constant is non-vanishing, so that the
conformal infinities have either de Sitter-like or anti-de Sitter-like
character. In particular, explicit relations between the parameters that
characterize the sources (that is their mass, electric and magnetic charges,
NUT parameter, rotational parameter, and acceleration) and properties of the
radiation generated by them are presented. The results further elucidate the
physical interpretation of these solutions and may help to understand radiative
characteristics of more general spacetimes than those that are asymptotically
flat.Comment: 24 pages, 18 figures. To appear in Classical and Quantum Gravit
Interpreting the C-metric
The basic properties of the C-metric are well known. It describes a pair of
causally separated black holes which accelerate in opposite directions under
the action of forces represented by conical singularities. However, these
properties can be demonstrated much more transparently by making use of
recently developed coordinate systems for which the metric functions have a
simple factor structure. These enable us to obtain explicit
Kruskal-Szekeres-type extensions through the horizons and construct
two-dimensional conformal Penrose diagrams. We then combine these into a
three-dimensional picture which illustrates the global causal structure of the
space-time outside the black hole horizons. Using both the weak field limit and
some invariant quantities, we give a direct physical interpretation of the
parameters which appear in the new form of the metric. For completeness,
relations to other familiar coordinate systems are also discussed.Comment: 22 pages, 14 figures (low-resolution figures; for the version with
high-resolution figures see http://utf.mff.cuni.cz/~krtous/papers/ or
http://www-staff.lboro.ac.uk/~majbg/
Quantum probe and design for a chemical compass with magnetic nanostructures
Magnetic fields as weak as Earth's may affect the outcome of certain
photochemical reactions that go through a radical pair intermediate. When the
reaction environment is anisotropic, this phenomenon can form the basis of a
chemical compass and has been proposed as a mechanism for animal
magnetoreception. Here, we demonstrate how to optimize the design of a chemical
compass with a much better directional sensitivity simply by a gradient field,
e.g. from a magnetic nanostructure. We propose an experimental test of these
predictions, and suggest design principles for a hybrid metallic-organic
chemical compass. In addition to the practical interest in designing a
biomimetic weak magnetic field sensor, our result shows that gradient fields
can server as powerful tools to probe spin correlations in radical pair
reactions.Comment: 8 pages, 6 figures, comments are welcom
Gambling in Great Britain:a response to Rogers
A recent issue of Practice: Social Work in Action featured a paper by Rogers that examined whether the issue of problem gambling was a suitable case for social work. Rogers’ overview was (in various places) out of date, highly selective, contradictory, presented unsupported claims and somewhat misleading. Rogers’ paper is to be commended for putting the issue of problem gambling on the social work agenda. However, social workers need up-to-date information and contextually situated information if they are to make informed decisions in helping problem gamblers
Economic evaluation of a nursing-led intermediate care unit
Objectives: The aim of this paper is to examine the costs of introducing a nursing-led ward program together with examining the impact this may have on patients' outcomes. Methods; The study had a sample size of 177 patients with a mean age of 77, and randomized to either a treatment group (care on a nursing-led ward, n = 97) or a control group (standard care usually on a consultant-led acute ward, n = 80). Resource use data including length of stay, tests and investigations performed, and multidisciplinary involvement in care were collected. Results: There were no significant differences in outcome between the two groups. The inpatient costs for the treatment group were significantly higher, due to the longer length of stay in this group. However, the postdischarge costs were significantly lower for the treatment group. Conclusions: The provision of nursing-led intermediate care units has been proposed as a solution to inappropriate use of acute medical wards by patients who require additional nursing rather than medical care. Whether the treatment group is ultimately cost-additive is dependent on how long reductions in postdischarge resource use are maintained
An exploration of social and economic outcome and associated health-related quality of life after critical illness in general intensive care unit survivors: a 12-month follow-up study.
INTRODUCTION: The socio-economic impact of critical illnesses on patients and their families in Europe has yet to be determined. The aim of this exploratory study was to estimate changes in family circumstances, social and economic stability, care requirements and access to health services for patients during their first 12 months after ICU discharge. METHODS: Multi-center questionnaire-based study of survivors of critical illness at 6 and 12 months after ICU discharge. RESULTS: Data for 293 consenting patients who spent greater than 48 hours in one of 22 UK ICUs were obtained at 6 and 12 months post-ICU discharge. There was little evidence of a change in accommodation or relationship status between pre-admission and 12 months following discharge from an ICU. A negative impact on family income was reported by 33% of all patients at 6 months and 28% at 12 months. There was nearly a 50% reduction in the number of patients who reported employment as their sole source of income at 12 months (19% to 11%) compared with pre-admission. One quarter of patients reported themselves in need of care assistance at 6 months and 22% at 12 months. The majority of care was provided by family members (80% and 78%, respectively), for half of whom there was a negative impact on employment. Amongst all patients receiving care, 26% reported requiring greater than 50 hours a week. Following discharge, 79% of patients reported attending their primary care physician and 44% had seen a community nurse. Mobility problems nearly doubled between pre-admission and 6 months (32% to 64%). Furthermore, 73% reported moderate or severe pain at 12 months and 44% remained significantly anxious or depressed. CONCLUSIONS: Survivors of critical illness in the UK face a negative impact on employment and commonly have a care requirement after discharge from hospital. This has a corresponding negative impact on family income. The majority of the care required is provided by family members. This effect was apparent by 6 months and had not materially improved by 12 months. This exploratory study has identified the potential for a significant socio-economic burden following critical illness
Combining Thesaurus Knowledge and Probabilistic Topic Models
In this paper we present the approach of introducing thesaurus knowledge into
probabilistic topic models. The main idea of the approach is based on the
assumption that the frequencies of semantically related words and phrases,
which are met in the same texts, should be enhanced: this action leads to their
larger contribution into topics found in these texts. We have conducted
experiments with several thesauri and found that for improving topic models, it
is useful to utilize domain-specific knowledge. If a general thesaurus, such as
WordNet, is used, the thesaurus-based improvement of topic models can be
achieved with excluding hyponymy relations in combined topic models.Comment: Accepted to AIST-2017 conference (http://aistconf.ru/). The final
publication will be available at link.springer.co
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