384 research outputs found
On Nonlocal Modified Gravity and Cosmology
Despite many nice properties and numerous achievements, general relativity is
not a complete theory. One of actual approaches towards more complete theory of
gravity is its nonlocal modification. We present here a brief review of
nonlocal gravity with its cosmological solutions. In particular, we pay special
attention to two nonlocal models and their nonsingular bounce solutions for the
cosmic scale factor.Comment: 11 pages, Published in Springer Proceedings in Mathematics &
Statistics 111 (2014) 251-26
Variations of Infinite Derivative Modified Gravity
We consider nonlocal modified Einstein gravity without matter, where nonlocal
term has the form . For this model, in this paper we give
the derivation of the equations of motion in detail. This is not an easy task
and presented derivation should be useful to a researcher who wants to
investigate nonlocal gravity. Also, we present the second variation of the
related Einstein-Hilbert modified action and basics of gravity perturbations.Comment: 22 page
On the Schwarzschild-de Sitter metric of nonlocal de Sitter gravity
Earlier constructed a simple nonlocal de Sitter gravity model has a
cosmological solution in a very good agreement with astronomical observations.
In this paper, we continue the investigation of the nonlocal de Sitter model of
gravity, focusing on finding an appropriate solution for the Schwarzschild-de
Sitter metric. We succeeded to solve the equations of motion in a certain
approximation. The obtained approximate solution is of particular interest for
examining the possible role of non-local de Sitter gravity in describing the
effects in galactic dynamics that are usually attributed to dark matter.Comment: 10 page
Theoretical determination of lifetimes of metastable states in Sc III and Y III
Lifetimes of the first two metastable states in Sc^{2+} and Y^{2+} are
determined using the relativistic coupled-cluster theory. There is a
considerable interest in studying the electron correlation effects in these
ions as though their electronic configurations are similar to the neutral
alkali atoms, their structures are very different from the latter. We have made
a comparative study of the correlation trends between the above doubly ionized
systems with their corresponding neutral and singly ionized iso-electronic
systems. The lifetimes of the excited states of these ions are very important
in the field of astrophysics, especially for the study of post-main sequence
evolution of the cool giant stars.Comment: 13 pages, 1 figure and 5 table
Perceived need of, and interest in, HIV pre-exposure prophylaxis amongst men who have sex with men attending three sexual health clinics in London, UK
HIV pre-exposure prophylaxis (PrEP) has proven efficacy in reducing the risk of HIV infection in men who have sex with men (MSM), but has not yet been commissioned in the UK. The aim of this study was to investigate perceived need and benefit (or experience of) PrEP among HIV-negative MSM attending sexual health clinics. HIV-negative MSM attending three sexual health centres in London, UK were opportunistically invited to complete a questionnaire. Data collected comprised demographic data and sexual and drug use behaviours as well as questions regarding perceptions of risk and need for PrEP. Logistic regression analysis was undertaken to identify variables predicting acceptability of, and intention to use, PrEP. In addition, data were gathered in respondents already taking PrEP. Eight hundred and thirty-nine questionnaires were analysed. The median age of respondents was 35 years (IQR 28–41, range 18–78), 650 (77%) were of white ethnicity and 649 (77%) had a university education. Four hundred and fifty-six (54%) reported at least one episode of condomless anal sex in the preceding three months, 437 (52%) reported recreational drug use in the preceding three months and 311 (37%) had been diagnosed with a sexually transmitted infection within the preceding six months. Four hundred and sixty-three (64%) of 726 strongly agreed with the statement ‘I think I would benefit from PrEP’. Multivariate logistic regression analysis demonstrated that having receptive anal intercourse (RAI) without condoms, having an awareness of the risk of unprotected RAI and having belief in the effectiveness of PrEP were independent predictors for someone thinking they would benefit from taking PrEP. Eight percent of respondents (59/724) had already taken or were currently taking PrEP. The results suggest that individuals at risk are likely to perceive themselves as benefiting from PrEP. The majority perceived their risk of acquiring HIV and benefit from PrEP accurately. Overall they appeared to have little concern over the use of PrEP and generally positive attitudes. Further investigation is warranted to understand why those at risk do not perceive benefit from PrEP
Detecting Carried Objects in Short Video Sequences
Abstract. We propose a new method for detecting objects such as bags carried by pedestrians depicted in short video sequences. In common with earlier work [1, 2] on the same problem, the method starts by averaging aligned foreground regions of a walking pedestrian to produce a rep-resentation of motion and shape (known as a temporal template) that has some immunity to noise in foreground segmentations and phase of the walking cycle. Our key novelty is for carried objects to be revealed by comparing the temporal templates against view-specific exemplars generated offline for unencumbered pedestrians. A likelihood map ob-tained from this match is combined in a Markov random field with a map of prior probabilities for carried objects and a spatial continuity as-sumption, from which we obtain a segmentation of carried objects using the MAP solution. We have re-implemented the earlier state of the art method [1] and demonstrate a substantial improvement in performance for the new method on the challenging PETS2006 dataset [3]. Although developed for a specific problem, the method could be applied to the de-tection of irregularities in appearance for other categories of object that move in a periodic fashion.
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