Browsing by Subject "Relativity"
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Item Einstein, Relativity and Myths(2012-10-18) Martinez, Alberto A.Item Exploring the bizarrerie : research on selective physical processes in gamma-ray bursts(2010-08) Shen, Rongfeng; Kumar, Pawan; Wheeler, J. Craig; Robinson, Edward L.; Bromm, Volker; Zhang, Bing; Hoeflich, Peter; Milosavljevic, MilosGamma-ray bursts (GRBs) are the mysterious, short and intense flashes of gamma-rays in the space, and are believed to originate from the rare, explosively devastating, stellar events that happens at cosmological distances. Enormous progress has been made from four decades of GRB research endeavor but the ultimate understanding of their origins has yet to arrive. Recently revealed features in their early afterglows broadened the opportunity space for exploration. We have carried out extensive studies on various physical processes in GRBs. We showed that the distribution of electrons' energy spectral index in GRBs and other relativistic sources is inconsistent with the prediction from the first-order Fermi theory of the shock particle acceleration. We investigated the photon scattering processes within the relativistic outflow that produces the GRB and calculated the resultant emission flux from it. We showed the scattering of the GRB prompt photons by the circum-burst dust, although an attractive possibility, can not explain the puzzling plateau component in the GRB afterglow light curve. We made meaningful constraint on the GRB prompt emission radius, R [greater-than or equal to] 10¹⁴, by studying the synchrotron self absorption for a small sample of bursts with good data. We showed that a late jet, which is thought to be producing the late X-ray flares in GRB afterglows, will produce detectable emissions from its interactions with other components in the explosive event of GRB, and identification of these emissions could verify the existence of the late jet and further prove the massive star origin of long-duration GRBs.Item Magnetofluid dynamics in curved spacetime : theory and application(2016-05) Bhattacharjee, Chinmoy; Hazeltine, R. D. (Richard D.); Mahajan, Swadesh M.; Berk, Herbert; Bohm, Arno; Yoshida, ZenshoA grand unified field tensor [Greek capital letter Mu] [Greek small letter mu] [Greek small letter nu] is constructed from Maxwell's field tensor and appropriately modified flow field, both nonminimally coupled to gravity, to analyze the dynamics of hot charged fluids in curved background space-time. With suitable 3+1 decomposition, this new formalism of hot fluid is then applied to investigate vorticity generation and a class of states known as the Beltrami-Bernoulli (BB) equilibria in the accretion disk around Schwarzschild and Kerr black holes. Of the two principle sources of vorticity i.e. baroclinic and relativistic, the relativistic drive peaks near innermost (isco) circular orbit for both black holes, whereas baroclinic drive dominates at larger distances. For General Relativity as well as modified gravity, the Kerr geometry leads to a ``stronger" vorticity generation than its Schwarzschild counterpart. On the other hand, modelling the disk plasma as a Hall MHD system, it has been shown that velocity/magnetic decay rate gets altered due to space time curvature, for example the velocity profile in BB states deviate substantially from the predicted geodesic velocity profiles. Moreover, these equilibrium states have their origin in the two helicity invariants which conspire to introduce a new oscillatory length scale into the system that is strongly influenced by relativistic and thermal effects. Consequences of this formalism are also discussed in several astrophysical settings.Item Relativism and the critique of reason(1995-12) Westacott, Emrys; Not availableItem Theory and application of extremely precise frequency standards on low Earth orbit to the determination of geopotential time-variability(2022-12-02) Giuliani, Simone; Tapley, Byron D.; Ries, John C; Matzner, Richard A; Bettadpur, Srinivas V; Russell, Ryan PEarth’s gravity plays a major role in molding our world. Monitoring the geopotential and its time variability reveals the mass redistribution occurring across our planet, thus informing us on matters like climate change and availability of water resources. The gravity features we are most interested in are characterized by spatial and temporal scales that can only be accessed via a mission in space. Among the most important gravity missions are GRACE/GRACE-FO and GOCE, which sense gravity through the derivatives of the Earth’s gravity field. We propose to apply chronometric geodesy, whose task is to measure gravity with clocks, in space through frequency comparison between orbiting clocks by means of the Doppler-canceling technique. The novelty of this approach consists in estimating Earth’s gravity via measurements of the geopotential itself, rather than its derivatives. The behavior of clocks in a gravitational field is governed by Einstein’s general relativity, which provides the best available description of gravitation. On the other hand, the frequency stability of clocks is now reaching 10¹⁹, becoming precise enough for geodesy applications. After describing the proposed gravity mission architecture, we provide a mathematical derivation of the Doppler-canceled frequency shift measurement. Then, we outline the estimation method and its numerical implementation, followed by a presentation of results. Our findings indicate the measurement can retrieve the geopotential coefficients with an accuracy potentially better than currently available gravity models employing clocks with a frequency stability of 10¹⁹. This result represents a proof of concept for the measurement, with gravity field solutions obtained from a mission simulation being shown here for the first time. However, once we introduce the orbit error, the kinematical approach utilized to solve the estimation problem presents severe limitations. The remedy is to adopt a dynamical approach, which would let us directly address the orbit error and other issues, e.g., frequency drift in clocks. In the conclusions, we discuss how to improve on our analysis and the necessary steps to follow in preparation for a future gravity mission, whose realization will be possible only when clock technology reaches the required performance (high frequency stability in a short integration time)