The Experts below are selected from a list of 251148 Experts worldwide ranked by ideXlab platform
Abhay Ashtekar - One of the best experts on this subject based on the ideXlab platform.
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loop quantum cosmology a Status Report
Classical and Quantum Gravity, 2011Co-Authors: Abhay Ashtekar, Parampreet SinghAbstract:Loop quantum cosmology (LQC) is the result of applying principles of loop quantum gravity (LQG) to cosmological settings. The distinguishing feature of LQC is the prominent role played by the quantum geometry effects of LQG. In particular, quantum geometry creates a brand new repulsive force which is totally negligible at low spacetime curvature but rises very rapidly in the Planck regime, overwhelming the classical gravitational attraction. In cosmological models, while Einstein's equations hold to an excellent degree of approximation at low curvature, they undergo major modifications in the Planck regime: for matter satisfying the usual energy conditions, any time a curvature invariant grows to the Planck scale, quantum geometry effects dilute it, thereby resolving singularities of general relativity. Quantum geometry corrections become more sophisticated as the models become richer. In particular, in anisotropic models, there are significant changes in the dynamics of shear potentials which tame their singular behavior in striking contrast to older results on anisotropies in bouncing models. Once singularities are resolved, the conceptual paradigm of cosmology changes and one has to revisit many of the standard issues—e.g. the 'horizon problem'—from a new perspective. Such conceptual issues as well as potential observational consequences of the new Planck scale physics are being explored, especially within the inflationary paradigm. These considerations have given rise to a burst of activity in LQC in recent years, with contributions from quantum gravity experts, mathematical physicists and cosmologists. The goal of this review is to provide an overview of the current state of the art in LQC for three sets of audiences: young researchers interested in entering this area; the quantum gravity community in general and cosmologists who wish to apply LQC to probe modifications in the standard paradigm of the early universe. In this review, effort has been made to streamline the material so that each of these communities can read only the sections they are most interested in, without loss of continuity.
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loop quantum cosmology a Status Report
arXiv: General Relativity and Quantum Cosmology, 2011Co-Authors: Abhay Ashtekar, Parampreet SinghAbstract:The goal of this article is to provide an overview of the current state of the art in loop quantum cosmology for three sets of audiences: young researchers interested in entering this area; the quantum gravity community in general; and, cosmologists who wish to apply loop quantum cosmology to probe modifications in the standard paradigm of the early universe. An effort has been made to streamline the material so that, as described at the end of section I, each of these communities can read only the sections they are most interested in, without a loss of continuity.
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background independent quantum gravity a Status Report
Classical and Quantum Gravity, 2004Co-Authors: Abhay Ashtekar, Jerzy LewandowskiAbstract:The goal of this review is to present an introduction to loop quantum gravity—a background-independent, non-perturbative approach to the problem of unification of general relativity and quantum physics, based on a quantum theory of geometry. Our presentation is pedagogical. Thus, in addition to providing a bird's eye view of the present Status of the subject, the review should also serve as a vehicle to enter the field and explore it in detail. To aid non-experts, very little is assumed beyond elements of general relativity, gauge theories and quantum field theory. While the review is essentially self-contained, the emphasis is on communicating the underlying ideas and the significance of results rather than on presenting systematic derivations and detailed proofs. (These can be found in the listed references.) The subject can be approached in different ways. We have chosen one which is deeply rooted in well-established physics and also has sufficient mathematical precision to ensure that there are no hidden infinities. In order to keep the review to a reasonable size, and to avoid overwhelming non-experts, we have had to leave out several interesting topics, results and viewpoints; this is meant to be an introduction to the subject rather than an exhaustive review of it.
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background independent quantum gravity a Status Report
arXiv: General Relativity and Quantum Cosmology, 2004Co-Authors: Abhay Ashtekar, Jerzy LewandowskiAbstract:The goal of this article is to present an introduction to loop quantum gravity -a background independent, non-perturbative approach to the problem of unification of general relativity and quantum physics, based on a quantum theory of geometry. Our presentation is pedagogical. Thus, in addition to providing a bird's eye view of the present Status of the subject, the article should also serve as a vehicle to enter the field and explore it in detail. To aid non-experts, very little is assumed beyond elements of general relativity, gauge theories and quantum field theory. While the article is essentially self-contained, the emphasis is on communicating the underlying ideas and the significance of results rather than on presenting systematic derivations and detailed proofs. (These can be found in the listed references.) The subject can be approached in different ways. We have chosen one which is deeply rooted in well established physics and also has sufficient mathematical precision to ensure that there are no hidden infinities. In order to keep the article to a reasonable size, and to avoid overwhelming non-experts, we have had to leave out several interesting topics, results and viewpoints; this is meant to be an introduction to the subject rather than an exhaustive review of it.
Parampreet Singh - One of the best experts on this subject based on the ideXlab platform.
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loop quantum cosmology a Status Report
Classical and Quantum Gravity, 2011Co-Authors: Abhay Ashtekar, Parampreet SinghAbstract:Loop quantum cosmology (LQC) is the result of applying principles of loop quantum gravity (LQG) to cosmological settings. The distinguishing feature of LQC is the prominent role played by the quantum geometry effects of LQG. In particular, quantum geometry creates a brand new repulsive force which is totally negligible at low spacetime curvature but rises very rapidly in the Planck regime, overwhelming the classical gravitational attraction. In cosmological models, while Einstein's equations hold to an excellent degree of approximation at low curvature, they undergo major modifications in the Planck regime: for matter satisfying the usual energy conditions, any time a curvature invariant grows to the Planck scale, quantum geometry effects dilute it, thereby resolving singularities of general relativity. Quantum geometry corrections become more sophisticated as the models become richer. In particular, in anisotropic models, there are significant changes in the dynamics of shear potentials which tame their singular behavior in striking contrast to older results on anisotropies in bouncing models. Once singularities are resolved, the conceptual paradigm of cosmology changes and one has to revisit many of the standard issues—e.g. the 'horizon problem'—from a new perspective. Such conceptual issues as well as potential observational consequences of the new Planck scale physics are being explored, especially within the inflationary paradigm. These considerations have given rise to a burst of activity in LQC in recent years, with contributions from quantum gravity experts, mathematical physicists and cosmologists. The goal of this review is to provide an overview of the current state of the art in LQC for three sets of audiences: young researchers interested in entering this area; the quantum gravity community in general and cosmologists who wish to apply LQC to probe modifications in the standard paradigm of the early universe. In this review, effort has been made to streamline the material so that each of these communities can read only the sections they are most interested in, without loss of continuity.
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loop quantum cosmology a Status Report
arXiv: General Relativity and Quantum Cosmology, 2011Co-Authors: Abhay Ashtekar, Parampreet SinghAbstract:The goal of this article is to provide an overview of the current state of the art in loop quantum cosmology for three sets of audiences: young researchers interested in entering this area; the quantum gravity community in general; and, cosmologists who wish to apply loop quantum cosmology to probe modifications in the standard paradigm of the early universe. An effort has been made to streamline the material so that, as described at the end of section I, each of these communities can read only the sections they are most interested in, without a loss of continuity.
Jerzy Lewandowski - One of the best experts on this subject based on the ideXlab platform.
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background independent quantum gravity a Status Report
Classical and Quantum Gravity, 2004Co-Authors: Abhay Ashtekar, Jerzy LewandowskiAbstract:The goal of this review is to present an introduction to loop quantum gravity—a background-independent, non-perturbative approach to the problem of unification of general relativity and quantum physics, based on a quantum theory of geometry. Our presentation is pedagogical. Thus, in addition to providing a bird's eye view of the present Status of the subject, the review should also serve as a vehicle to enter the field and explore it in detail. To aid non-experts, very little is assumed beyond elements of general relativity, gauge theories and quantum field theory. While the review is essentially self-contained, the emphasis is on communicating the underlying ideas and the significance of results rather than on presenting systematic derivations and detailed proofs. (These can be found in the listed references.) The subject can be approached in different ways. We have chosen one which is deeply rooted in well-established physics and also has sufficient mathematical precision to ensure that there are no hidden infinities. In order to keep the review to a reasonable size, and to avoid overwhelming non-experts, we have had to leave out several interesting topics, results and viewpoints; this is meant to be an introduction to the subject rather than an exhaustive review of it.
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background independent quantum gravity a Status Report
arXiv: General Relativity and Quantum Cosmology, 2004Co-Authors: Abhay Ashtekar, Jerzy LewandowskiAbstract:The goal of this article is to present an introduction to loop quantum gravity -a background independent, non-perturbative approach to the problem of unification of general relativity and quantum physics, based on a quantum theory of geometry. Our presentation is pedagogical. Thus, in addition to providing a bird's eye view of the present Status of the subject, the article should also serve as a vehicle to enter the field and explore it in detail. To aid non-experts, very little is assumed beyond elements of general relativity, gauge theories and quantum field theory. While the article is essentially self-contained, the emphasis is on communicating the underlying ideas and the significance of results rather than on presenting systematic derivations and detailed proofs. (These can be found in the listed references.) The subject can be approached in different ways. We have chosen one which is deeply rooted in well established physics and also has sufficient mathematical precision to ensure that there are no hidden infinities. In order to keep the article to a reasonable size, and to avoid overwhelming non-experts, we have had to leave out several interesting topics, results and viewpoints; this is meant to be an introduction to the subject rather than an exhaustive review of it.
Tamitza Toroyan - One of the best experts on this subject based on the ideXlab platform.
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global Status Report on road safety
Injury Prevention, 2009Co-Authors: Tamitza ToroyanAbstract:The World Health Organization has just released the Global Status Report on road safety —the first broad assessment that describes the road safety situation in 178 countries, using data drawn from a standardised survey. The results provide a benchmark that countries can use to assess their road safety position relative to other countries, while at the international level these findings can be considered as a “baseline”, against which regional and global level progress can be measured. The questionnaire used for this survey was developed in consultation with an expert committee of road safety researchers and practitioners. Data collection was carried out using a self-administered questionnaire, the content of which was based on the recommendations of the World Report on road traffic injury prevention , developed by WHO, the World Bank and many other partners in 2004. The methodology used involved the identification of a National Data Coordinator in each country who identified up to seven other national road safety experts from multiple sectors who could complete the questionnaire. A consensus meeting was then held involving all …
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global Status Report on road safety time for action
2009Co-Authors: Tamitza ToroyanAbstract:This Report evaluates the Status of highway safety in 178 countries around the world. Some of the findings include the following: (1) Over 90% of the highway traffic accident fatalities in the world occur in low-income and middle-income countries, where 48% of the registered vehicles in the world are located. (2) Almost half of highway deaths are cyclists, pedestrians, or riders of motorized two-wheelers. (3) Many countries have inadequate traffic laws and law enforcement. They often do not have laws addressing drinking drivers, helmet use, seat belt use, child restraint use, or speeding. (4) Traffic accidents are underReported, and accident data quality is poor.
Carl Kesselman - One of the best experts on this subject based on the ideXlab platform.
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the globus project a Status Report
Future Generation Computer Systems, 1999Co-Authors: Ian Foster, Carl KesselmanAbstract:Abstract The Globus project is a multi-institutional research effort that seeks to enable the construction of computational grids providing pervasive, dependable, and consistent access to high-performance computational resources, despite geographical distribution of both resources and users. Computational grid technology is being viewed as a critical element of future high-performance computing environments that will enable entirely new classes of computation-oriented applications, much as the World Wide Web fostered the development of new classes of information-oriented applications. In this paper, we Report on the Status of the Globus project as of early 1998. We describe the progress that has been achieved to date in the development of the Globus toolkit, a set of core services for constructing grid tools and applications. We also discuss the Globus Ubiquitous Supercomputing Testbed Organization (GUSTO) that we have constructed to enable large-scale evaluation of Globus technologies, and we review early experiences with the development of large-scale grid applications on the GUSTO testbed.
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the globus project a Status Report
Proceedings Seventh Heterogeneous Computing Workshop (HCW'98), 1998Co-Authors: Ian Foster, Carl KesselmanAbstract:The Globus project is a multi-institutional research effort that seeks to enable the construction of computational grids providing pervasive, dependable, and consistent access to high-performance computational resources, despite geographical distribution of both resources and users. Computational grid technology is being viewed as a critical element of future high-performance computing environments that will enable entirely new classes of computation-oriented applications, much as the World Wide Web fostered the development of new classes of information-oriented applications. The authors Report on the Status of the Globus project as of early 1998. They describe the progress that has been achieved to date in the development of the Globus toolkit, a set of core services for constructing grid tools and applications. They also discuss the Globus Ubiquitous Supercomputing Testbed (GUSTO) that they have constructed to enable large-scale evaluation of Globus technologies, and they review early experiences with the development of large-scale grid applications on the GUSTO testbed.
