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L. Reverberi - One of the best experts on this subject based on the ideXlab platform.
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Spherically symmetric solutions in FðRÞ gravity and gravitational repulsion
2014Co-Authors: E. V. Arbuzova, Alexander D. Dolgov, L. ReverberiAbstract:Spherically symmetric solutions in FðRÞ theories in Astronomical Systems with rising energy density are studied. The range of parameters is established for which the flat space–time approximation for the background metric is valid. For the solutions in which the curvature scalar oscillates with large amplitude and high frequency, found in our previous papers, it is shown that the analysis of the Jeans instability is strongly modified. It is discovered that for large Astronomical objects modified gravity can be repulsive, so such objects would shrink forming relatively thin shells instead of quasi uniform bodies. 2013 Published by Elsevier B.V.
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Spherically symmetric solutions in F(R) gravity and gravitational repulsion
Astroparticle Physics, 2014Co-Authors: E. V. Arbuzova, Alexander D. Dolgov, L. ReverberiAbstract:Abstract Spherically symmetric solutions in F ( R ) theories in Astronomical Systems with rising energy density are studied. The range of parameters is established for which the flat space–time approximation for the background metric is valid. For the solutions in which the curvature scalar oscillates with large amplitude and high frequency, found in our previous papers, it is shown that the analysis of the Jeans instability is strongly modified. It is discovered that for large Astronomical objects modified gravity can be repulsive, so such objects would shrink forming relatively thin shells instead of quasi uniform bodies.
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Particle production in f(R) gravity during structure formation
Physical Review D, 2013Co-Authors: E. V. Arbuzova, Alexander D. Dolgov, L. ReverberiAbstract:We study particle production in infrared-modified gravitational theories in the contemporary universe. It is shown that in Astronomical Systems with rising mass density, the curvature scalar may oscillate with very high frequency. These oscillations lead to efficient particle production and in an interesting range of model parameters could be a source of energetic cosmic rays. This effect either excludes some models of modified gravity or suggests a new mechanism of cosmic ray production.
E. V. Arbuzova - One of the best experts on this subject based on the ideXlab platform.
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Spherically symmetric solutions in FðRÞ gravity and gravitational repulsion
2014Co-Authors: E. V. Arbuzova, Alexander D. Dolgov, L. ReverberiAbstract:Spherically symmetric solutions in FðRÞ theories in Astronomical Systems with rising energy density are studied. The range of parameters is established for which the flat space–time approximation for the background metric is valid. For the solutions in which the curvature scalar oscillates with large amplitude and high frequency, found in our previous papers, it is shown that the analysis of the Jeans instability is strongly modified. It is discovered that for large Astronomical objects modified gravity can be repulsive, so such objects would shrink forming relatively thin shells instead of quasi uniform bodies. 2013 Published by Elsevier B.V.
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Spherically symmetric solutions in F(R) gravity and gravitational repulsion
Astroparticle Physics, 2014Co-Authors: E. V. Arbuzova, Alexander D. Dolgov, L. ReverberiAbstract:Abstract Spherically symmetric solutions in F ( R ) theories in Astronomical Systems with rising energy density are studied. The range of parameters is established for which the flat space–time approximation for the background metric is valid. For the solutions in which the curvature scalar oscillates with large amplitude and high frequency, found in our previous papers, it is shown that the analysis of the Jeans instability is strongly modified. It is discovered that for large Astronomical objects modified gravity can be repulsive, so such objects would shrink forming relatively thin shells instead of quasi uniform bodies.
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Particle production in f(R) gravity during structure formation
Physical Review D, 2013Co-Authors: E. V. Arbuzova, Alexander D. Dolgov, L. ReverberiAbstract:We study particle production in infrared-modified gravitational theories in the contemporary universe. It is shown that in Astronomical Systems with rising mass density, the curvature scalar may oscillate with very high frequency. These oscillations lead to efficient particle production and in an interesting range of model parameters could be a source of energetic cosmic rays. This effect either excludes some models of modified gravity or suggests a new mechanism of cosmic ray production.
Christopher Cullen - One of the best experts on this subject based on the ideXlab platform.
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Hanli 19 November 2018
2018Co-Authors: Christopher CullenAbstract:This is an Excel spreadsheet workbook, made with Excel for Mac 2011, with additional VBA functions created by myself. It may function on other Systems, but I can make no guarantee of this. The workbook is designed to automate the operation of an ancient Chinese Astronomical system, the Han li 漢曆 'Han Astronomical system' which was created c. 85 CE by Bian Xin 遍訢 and Li Fan 李梵, for use in producing the imperial luni-solar calendar. This text of this system is fully translated and explicated in Cullen, Christopher (2017). The Foundations of Celestial Reckoning: Three Ancient Chinese Astronomical Systems. London, Routledge, pages 138-234. The principles underlying a workbook of this kind are discussed in Cullen, Christopher (2005). "Translating Ancient Chinese Astronomical Systems with Excel: How not to stew the strawberries?" Journal for the History of Astronomy xxxvi: 336-338. To operate the system, go to the worksheet 'Front page' and type the year of interest in the cell indicated near the top left of the sheet, cell D1. This is the only cell in the workbook that you can modify: all others are locked. Years CE may be entered as plain numbers; years BCE should be entered preceded by a minus sign. Press 'Enter,' and the workbook will recalculate automatically. Basic calendrical data are shown on 'Front page'; the main calculation engines for these are the worksheet 'Main Sequence' and 'Month Table'. The sheet 'Planets Conjunctions' shows how the dates of conjunctions of all five planets with the sun are calculated, and other sheets show their daily positions. The worksheet is too complicated for a full explanation here: much of its function will become evident on exploration in the light of the explanations given in Cullen (2017) cited above. This is a work in progress; although the core functions of the system are reliable, some parts of the worksheet are of an experimental or provisional nature.
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Oxford Scholarship Online - Li in everyday life: dates and calendars
Oxford Scholarship Online, 2018Co-Authors: Christopher CullenAbstract:In the preceding chapter we noted the importance of the role of specialists in Astronomical Systems, li曆, as part of the machinery of the Chinese imperial state, and sketched the kind of mathematical and Astronomical structures that they used in their work, as well as reviewing the historical sources through which modern historians can study that work. In this chapter we examine more closely the structures and forms of li as they were presented to the subjects of the empire, and at the ways in which the mass of the population made use of the data that li put before them.
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Oxford Scholarship Online - The Astronomical empire
Oxford Scholarship Online, 2018Co-Authors: Christopher CullenAbstract:This chapter begins by sketching the historical and cultural foundations of the role played by astronomy in the self-presentation of the early imperial Chinese state, principally through its claim to have the right to structure the time of its subjects by issuing a luni-solar calendar. This claim was presented as fulfilling a need on the part of the population; we discuss how far this claim was an accurate perception of the power relations involved. There follows a preliminary account of the main components of such a calendar, and of how they formed an integrated whole. Finally there is an introductory review of the main written sources on li曆‘[Astronomical] Systems’ on which much of this book will be based.
Daniel A. Schwartz - One of the best experts on this subject based on the ideXlab platform.
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Chandra enables study of x-ray jets.
Proceedings of the National Academy of Sciences of the United States of America, 2010Co-Authors: Daniel A. SchwartzAbstract:The exquisite angular resolution of the Chandra x-ray telescope has enabled the detection and study of resolved x-ray jets in a wide variety of Astronomical Systems. Chandra has detected extended jets in our galaxy from protostars, symbiotic binaries, neutron star pulsars, black hole binaries, extragalactic jets in radio sources, and quasars. The x-ray data play an essential role in deducing the emission mechanism of the jets, in revealing the interaction of jets with the intergalactic or intracluster media, and in studying the energy generation budget of black holes.
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An X-ray view of radio sources
EAS Publications Series, 2005Co-Authors: Daniel A. SchwartzAbstract:We review recent examples where the synergy between radio and X-ray observations has led to substantial progress in understanding Astronomical Systems. The sub-arcsecond imaging capabilities of the Chandra X-ray observatory provides a 100-fold improvement for com- paring X-ray and radio structures. We specifically discuss examples which provide insight into the outflow of material and energy from pul- sars and supernovae, the centers of clusters of galaxies, and the nuclei of quasars.
Alexander D. Dolgov - One of the best experts on this subject based on the ideXlab platform.
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Spherically symmetric solutions in FðRÞ gravity and gravitational repulsion
2014Co-Authors: E. V. Arbuzova, Alexander D. Dolgov, L. ReverberiAbstract:Spherically symmetric solutions in FðRÞ theories in Astronomical Systems with rising energy density are studied. The range of parameters is established for which the flat space–time approximation for the background metric is valid. For the solutions in which the curvature scalar oscillates with large amplitude and high frequency, found in our previous papers, it is shown that the analysis of the Jeans instability is strongly modified. It is discovered that for large Astronomical objects modified gravity can be repulsive, so such objects would shrink forming relatively thin shells instead of quasi uniform bodies. 2013 Published by Elsevier B.V.
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Spherically symmetric solutions in F(R) gravity and gravitational repulsion
Astroparticle Physics, 2014Co-Authors: E. V. Arbuzova, Alexander D. Dolgov, L. ReverberiAbstract:Abstract Spherically symmetric solutions in F ( R ) theories in Astronomical Systems with rising energy density are studied. The range of parameters is established for which the flat space–time approximation for the background metric is valid. For the solutions in which the curvature scalar oscillates with large amplitude and high frequency, found in our previous papers, it is shown that the analysis of the Jeans instability is strongly modified. It is discovered that for large Astronomical objects modified gravity can be repulsive, so such objects would shrink forming relatively thin shells instead of quasi uniform bodies.
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Particle production in f(R) gravity during structure formation
Physical Review D, 2013Co-Authors: E. V. Arbuzova, Alexander D. Dolgov, L. ReverberiAbstract:We study particle production in infrared-modified gravitational theories in the contemporary universe. It is shown that in Astronomical Systems with rising mass density, the curvature scalar may oscillate with very high frequency. These oscillations lead to efficient particle production and in an interesting range of model parameters could be a source of energetic cosmic rays. This effect either excludes some models of modified gravity or suggests a new mechanism of cosmic ray production.
