6,653 research outputs found
Black Hole with Quantum Potential
In this work, we investigate black hole (BH) physics in the context of
quantum corrections. These quantum corrections were introduced recently by
replacing classical geodesics with quantal (Bohmian) trajectories and hence
form a quantum Raychaudhuri equation (QRE). From the QRE, we derive a modified
Schwarzschild metric, and use that metric to investigate BH singularity and
thermodynamics. We find that these quantum corrections change the picture of
Hawking radiation greatly when the size of BH approaches the Planck scale. They
prevent the BH from total evaporation, predicting the existence of a quantum BH
remnant, which may introduce a possible resolution for the catastrophic
behavior of Hawking radiation as the BH mass approaches zero. Those corrections
also turn the spacelike singularity of the black hole to be timelike, and hence
this may ameliorate the information loss problem.Comment: 16 pages, 6 figures; Accepted in Nucl.Phys.
A Proposal for Testing Gravity's Rainbow
Various approaches to quantum gravity such as string theory, loop quantum
gravity and Horava-Lifshitz gravity predict modifications of the
energy-momentum dispersion relation. Magueijo and Smolin incorporated the
modified dispersion relation (MDR) with the general theory of relativity to
yield a theory of gravity's rainbow. In this paper, we investigate the
Schwarzschild metric in the context of gravity's rainbow. We investigate
rainbow functions from three known modified dispersion relations that were
introduced by Amelino-Camelia, et el. in [arXiv:hep-th/9605211,
arXiv:0806.0339v2, arXiv:astro-ph/9712103] and by Magueijo-Smolin in
[arXiv:hep-th/0112090]. We study the effect of the rainbow functions on the
deflection of light, photon time delay, gravitational red-shift, and the weak
equivalence principle. We compare our results with experiments to obtain upper
bounds on the parameters of the rainbow functions.Comment: 6 pages, no figures, to appear in Europhysics Letter
rDLB: A Novel Approach for Robust Dynamic Load Balancing of Scientific Applications with Parallel Independent Tasks
Scientific applications often contain large and computationally intensive
parallel loops. Dynamic loop self scheduling (DLS) is used to achieve a
balanced load execution of such applications on high performance computing
(HPC) systems. Large HPC systems are vulnerable to processors or node failures
and perturbations in the availability of resources. Most self-scheduling
approaches do not consider fault-tolerant scheduling or depend on failure or
perturbation detection and react by rescheduling failed tasks. In this work, a
robust dynamic load balancing (rDLB) approach is proposed for the robust self
scheduling of independent tasks. The proposed approach is proactive and does
not depend on failure or perturbation detection. The theoretical analysis of
the proposed approach shows that it is linearly scalable and its cost decrease
quadratically by increasing the system size. rDLB is integrated into an MPI DLS
library to evaluate its performance experimentally with two computationally
intensive scientific applications. Results show that rDLB enables the tolerance
of up to (P minus one) processor failures, where P is the number of processors
executing an application. In the presence of perturbations, rDLB boosted the
robustness of DLS techniques up to 30 times and decreased application execution
time up to 7 times compared to their counterparts without rDLB
Efficient Generation of Parallel Spin-images Using Dynamic Loop Scheduling
High performance computing (HPC) systems underwent a significant increase in
their processing capabilities. Modern HPC systems combine large numbers of
homogeneous and heterogeneous computing resources. Scalability is, therefore,
an essential aspect of scientific applications to efficiently exploit the
massive parallelism of modern HPC systems. This work introduces an efficient
version of the parallel spin-image algorithm (PSIA), called EPSIA. The PSIA is
a parallel version of the spin-image algorithm (SIA). The (P)SIA is used in
various domains, such as 3D object recognition, categorization, and 3D face
recognition. EPSIA refers to the extended version of the PSIA that integrates
various well-known dynamic loop scheduling (DLS) techniques. The present work:
(1) Proposes EPSIA, a novel flexible version of PSIA; (2) Showcases the
benefits of applying DLS techniques for optimizing the performance of the PSIA;
(3) Assesses the performance of the proposed EPSIA by conducting several
scalability experiments. The performance results are promising and show that
using well-known DLS techniques, the performance of the EPSIA outperforms the
performance of the PSIA by a factor of 1.2 and 2 for homogeneous and
heterogeneous computing resources, respectively
Performance Reproduction and Prediction of Selected Dynamic Loop Scheduling Experiments
Scientific applications are complex, large, and often exhibit irregular and
stochastic behavior. The use of efficient loop scheduling techniques in
computationally-intensive applications is crucial for improving their
performance on high-performance computing (HPC) platforms. A number of dynamic
loop scheduling (DLS) techniques have been proposed between the late 1980s and
early 2000s, and efficiently used in scientific applications. In most cases,
the computing systems on which they have been tested and validated are no
longer available. This work is concerned with the minimization of the sources
of uncertainty in the implementation of DLS techniques to avoid unnecessary
influences on the performance of scientific applications. Therefore, it is
important to ensure that the DLS techniques employed in scientific applications
today adhere to their original design goals and specifications. The goal of
this work is to attain and increase the trust in the implementation of DLS
techniques in present studies. To achieve this goal, the performance of a
selection of scheduling experiments from the 1992 original work that introduced
factoring is reproduced and predicted via both, simulative and native
experimentation. The experiments show that the simulation reproduces the
performance achieved on the past computing platform and accurately predicts the
performance achieved on the present computing platform. The performance
reproduction and prediction confirm that the present implementation of the DLS
techniques considered both, in simulation and natively, adheres to their
original description. The results confirm the hypothesis that reproducing
experiments of identical scheduling scenarios on past and modern hardware leads
to an entirely different behavior from expected
Remnants of Black Rings from Gravity's Rainbow
In this paper, we investigate a spinning black ring and a charged black ring
in the context of gravity's rainbow. By incorporating rainbow functions
proposed by Amelino-Camelia, et al. in [arXiv:hep-th/9605211,
arXiv:0806.0339v2] in the metric of the black rings, a considerable
modification happens to their thermodynamical properties. We calculate
corrections to the temperature, entropy and heat capacity of the black rings.
These calculations demonstrate that the behavior of Hawking radiation changes
considerably near the Planck scale in gravity's rainbow, where it is shown that
black rings do not evaporate completely and a remnant is left as the black
rings evaporate down to Planck scale.Comment: 14 pages, 6 figure
Remnant for all Black Objects due to Gravity's Rainbow
We argue that a remnant is formed for all black objects in gravity's rainbow.
This will be based on the observation that a remnant depends critically on the
structure of the rainbow functions, and this dependence is a model independent
phenomena. We thus propose general relations for the modified temperature and
entropy of all black objects in gravity's rainbow. We explicitly check this to
be the case for Kerr, Kerr-Newman-dS, charged-AdS, and higher dimensional
Kerr-AdS black holes. We also try to argue that a remnant should form for black
Saturn in gravity's rainbow. This work extends our previous results on remnants
of Schwarzschild black holes [ arXiv:1402.5320] and black rings
[arXiv:1409.5745].Comment: 21 pages, 13 figures, Accepted in Nucl.Phys.
Community Knowledge, Perceptions, and Practices Associated with Urogenital Schistosomiasis among School-Aged Children in Zanzibar, United Republic of Tanzania
Background: On the Zanzibar islands, United Republic of Tanzania, elimination of urogenital schistosomiasis is strived for in the coming years. This qualitative study aimed to better understand community knowledge, perceptions, and practices associated with schistosomiasis among school-aged children on Unguja and Pemba islands, in order to inform the development of behavior change interventions contributing to eliminate urogenital schistosomiasis.
Methodology: In 2011, we conducted 35 children’s discussion groups, 41 in-depth interviews with parents and teachers, and 5 focus group discussions with community members in Zanzibar. Using a modified-grounded theory approach, we transcribed and coded the narrative data followed by thematic analysis of the emergent themes.
Principal Findings: Urogenital schistosomiasis is a common experience among children in Zanzibar and typically considered a boys’ disease. Children engage in multiple high-risk behaviors for acquiring schistosomiasis because of poor knowledge on disease transmission, lack of understanding on severity of disease-associated consequences, and lack of alternative options for water related activities of daily living and recreational play. Local primary school teachers had little to no training about the disease and no teaching tools or materials for students.
Conclusions/Significance: Conducting activities in open natural freshwater contaminated by S. haematobium larvae compromises the health of school-aged children in Zanzibar. The perception of urogenital schistosomiasis as a minor illness rather than a serious threat to a child’s well-being contributes to the spread of disease. Understanding community perceptions of disease along with the barriers and facilitators to risk reduction behaviors among children can inform health promotion activities, campaigns, and programs for the prevention, control, and elimination of urogenital schistosomiasis in Zanzibar
The equity of admissions to the university hospital of Brasilia
Background: Brazil has a highly stratified population with large socioeconomic disparities, as evidenced by marked differentiation in health status and access to health services by the population. In addition, the fact that the universal national health care system and a liberalised private care model exist side by side leads to increasingly inequitable health outcomes. Aims: This study aims to appraise the equity of access to the University Hospital in Brasilia, Brazil, in 2013. Methods: This study was a quantitative analysis of hospital admissions data. The sample included all patients admitted over a six-month period in 2013. Patient data was crossed with socioeconomic data (income and private health insurance status). Frequency tabulations and chi-square calculations were used to describe the patient mix, observe trends and appraise equity of admissions. Results: Analysis of the data showed that the number of patients from each neighbourhood relative to the neighbourhood population was equitable. However, when assessed on the basis of insurance status (i.e., deducting the population covered by private health insurance), a high level of inequity was detected (chi-square 71.828, df 3, p<0,0001) whereby patients from wealthier neighbourhoods were over represented compared to those from poorer neighbourhoods. Conclusion: This study has shown that access to the University Hospital in Brasilia is not equitable when individual access to private health care is accounted for. The results show that dual access to both public and private health care is likely to be common, increasing some of the population’s access to health care while decreasing access for others, and therefore contributing to inequity of access to health care services
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