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Search Results: 1 - 10 of 378489 matches for " D. P. Jin "
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X-ray flashes from off-axis nonuniform jets
Z. P. Jin,D. M. Wei
Physics , 2003, DOI: 10.1088/1009-9271/4/5/473
Abstract: It is widely believed that outflows of gamma-ray bursts are jetted. Some people also suggest that the jets may have structures like $\epsilon(\theta)\propto\theta^{-k}$. We test the possibility of X-ray flashes coming from such jets in this paper. Both qualitative and quantitative analyses have shown that this model can reproduce most observational features for both X-ray flashes and gamma-ray bursts. Using common parameters of gamma-ray bursts, we have done both uniform and nonuniform jets' numerical calculations for their fluxes, spectra and peak energies. It seems that nonuniform jets are more appropriated to these observational properties than uniform ones. We also give a spectrum and flux fit to the most significant X-ray flash, XRF971019 by our model. We also have shown that in our model the observational ratio of gamma-ray bursts to X-ray flashes is about several.
GRB afterglow light curves from uniform and non-uniform jets
D. M. Wei,Z. P. Jin
Physics , 2002, DOI: 10.1051/0004-6361:20030007
Abstract: Here we calculate the GRB afterglow light curves from a relativistic jet as seen by observers at a wide range of viewing angles from the jet axis, and the jet is uniform or non-uniform. We find that, for uniform jet the afterglow light curves for different viewing angles are somewhat different: in general, there are two breaks in the light curve, corresponding to the time $\gamma\sim (\theta_j-\theta_v)^{-1}$ and $\gamma\sim (\theta_j+\theta_v)^{-1}$ respectively. However, for non-uniform jet, the things become more complicated. For the case $\theta_v=0$, we can obtain the analytical results, for $k<8/(p+4)$ there should be two breaks in the light curve correspond to $\gamma\sim\theta_c^{-1}$ and $\gamma\sim\theta_j^{-1}$ respectively, while for $k>8/(p+4)$ there should be only one break corresponds to $\gamma\sim\theta_c^{-1}$, and this provides a possible explanation for some rapidly fading afterglows whose light curves have no breaks since the time at which $\gamma\sim\theta_c^{-1}$ is much earlier than our first observation time. For the case $\theta_v\neq 0$, our numerical results show that, the afterglow light curves are strongly affected by the values of $\theta_v$, $\theta_c$ and $k$. If the values of $\theta_v/\theta_c$ and $k$ are larger, there will be a prominent flattening in the afterglow light curve, which is quite different from the uniform jet, and after the flattening a very sharp break will be occurred at the time $\gamma\sim (\theta_v + \theta_c)^{-1}.
Using photoemission spectroscopy to probe a strongly interacting Fermi gas
J. T. Stewart,J. P. Gaebler,D. S. Jin
Physics , 2008, DOI: 10.1038/nature07172
Abstract: Ultracold atom gases provide model systems in which many-body quantum physics phenomena can be studied. Recent experiments on Fermi gases have realized a phase transition to a Fermi superfluid state with strong interparticle interactions. This system is a realization of the BCS-BEC crossover connecting the physics of BCS superconductivity and that of Bose-Einstein condensation (BEC). While many aspects of this system have been investigated, it has not yet been possible to measure the single-particle excitation spectrum, which is a fundamental property directly predicted by many-body theories. Here we show that the single-particle spectral function of the strongly interacting Fermi gas at T ~ Tc is dramatically altered in a way that is consistent with a large pairing gap. We use photoemission spectroscopy to directly probe the elementary excitations and energy dispersion in the Fermi gas of atoms. In these photoemission experiments, an rf photon ejects an atom from our strongly interacting system via a spin-flip transition to a weakly interacting state. We measure the occupied single-particle density of states for an ultracold Fermi gas of 40-potassium atoms at the cusp of the BCS-BEC crossover and on the BEC side of the crossover, and compare these results to that for a nearly ideal Fermi gas. Our results probe the many-body physics in a way that could be compared to data for high-Tc superconductors. This new measurement technique for ultracold atom gases, like photoemission spectroscopy for electronic materials, directly probes low energy excitations and thus can reveal excitation gaps and/or pseudogaps. Furthermore, this technique can provide an analog to angle-resolved photoemission spectroscopy (ARPES) for probing anisotropic systems, such as atoms in optical lattice potentials.
Second Quantization of Cini Model for High Order Quantum Decoherence in Quantum Measurement
D. L. Zhou,G. R. Jin,C. P. Sun
Physics , 2001,
Abstract: By making the second quantization for the Cini Model of quantum measurement without wave function collapse [M. Cini, Nuovo Cimento, B73 27(1983)], the second order quantum decoherence (SOQD) is studied with a two mode boson system interacting with an idealized apparatus composed by two quantum oscillators. In the classical limit that the apparatus is prepared in a Fock state with a very large quantum number, or in a coherent state with average quantum numbers large enough, the SOQD phenomenon appears similar to the first order case of quantum decoherence.
Raman scattering as a probe of intermediate phases in glassy networks
P. Boolchand,Mingji Jin,D. I. Novita,S. Chakravarty
Physics , 2007, DOI: 10.1002/jrs.1707
Abstract: Bulk glass formation occurs over a very small part of phase space, and "good" glasses (which form even at low quench rates ~ 10K/sec) select an even smaller part of that accessible phase space. An axiomatic theory provides the physical basis of glass formation, and identifies these sweet spots of glass formation with existence of rigid but stress-free networks for which experimental evidence is rapidly emerging. Recently, theory and experiment have come together to show that these sweet spots of glass formation occur over a range of chemical compositions identified as Intermediate Phases. These ranges appear to be controlled by elements of local and medium range molecular structures that form isostatically rigid networks. Intermediate Phase glasses possess non-hysteretic glass transitions (Tgs) that do not age much. Raman scattering has played a pivotal role in elucidating molecular structure of glasses in general, and in identifying domains of Intermediate Phases. Experiments reveal these phases to possess sharp phase boundaries and to be characterized by an optical elasticity that varies with network mean coordination number, r, as power-law. In this review, we provide examples in chalcogenide and oxide glass systems where these phases along with optical elasticity power-laws have been established. Intermediate Phase glasses represent self-organized nanostructured functional materials optimized by nature.
Observation of Bulk Superconductivity in NaxCoO2.yH2O and NaxCoO2.yD2O Powder and Single Crystals
R. Jin,B. C. Sales,P. Khalifah,D. Mandrus
Physics , 2003, DOI: 10.1103/PhysRevLett.91.217001
Abstract: Poly- and single-crystalline Na$_x$CoO$_2$ has been successfully intercalated with H$_2$O and D$_2$O as confirmed by X-ray diffraction and thermogravimetric analysis. Resistivity, magnetic susceptibility, and specific heat measurements show bulk superconductivity with T$_c$ close to 5 K in both cases. The substitution of deuterium for hydrogen has an effect on T$_c$ of less than 0.2 K. Investigation of the resistivity anisotropy of Na$_x$CoO$_2\cdot$yH$_2$O single crystals shows: (a) almost zero resistivity below T$_c$, and (b) an abrupt upturn at $T^* \sim$ 52 K in both the $\it {ab}$ plane and the $\it {c}$ direction. The implications of our results on the possible superconducting mechanism will be discussed.
The X-ray afterglow of GRB 081109A: clue to the wind bubble structure
Z. P. Jin,D. Xu,S. Covino,P. D'Avanzo,A. Antonelli,Y. Z. Fan,D. M. Wei
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.15555.x
Abstract: We present the prompt BAT and afterglow XRT data of Swift-discovered GRB081109A up to ~ 5\times 10^5 sec after the trigger, and the early ground-based optical follow-ups. The temporal and spectral indices of the X-ray afterglow emission change remarkably. We interpret this as the GRB jet first traversing the freely expanding supersonic stellar wind of the progenitor with density varying as $\rho \propto r^{-2}$. Then after approximately 300 sec the jet traverses into a region of apparent constant density similar to that expected in the stalled-wind region of a stellar wind bubble or the interstellar medium (ISM). The optical afterglow data are generally consistent with such a scenario. Our best numerical model has a wind density parameter {$A_{*} \sim 0.02$, a density of the stalled wind $n\sim 0.12 {\rm cm}^{-3}$, and a transition radius $ \sim 4.5 \times 10^{17}$ cm}. Such a transition radius is smaller than that predicted by numerical simulations of the stellar wind bubbles and may be due to a rapidly evolving wind of the progenitor close to the time of its core-collapse.
Comparative study of atmospheric water vapor budget associated with precipitation in Central US and eastern Mediterranean
A. Zangvil, P. J. Lamb, D. H. Portis, F. Jin,S. Malka
Advances in Geosciences (ADGEO) , 2010,
Abstract: Water vapor budget (WVB) analysis is a powerful tool for studying processes leading to precipitation (P), since the linkages among atmospheric dynamics, water vapor fields, surface conditions, and P are constrained by the moisture continuity equation. This paper compares WVB calculations over the US Midwest (MW), the US Southern Great Plains (SGP), and the eastern Mediterranean Sea (EM) during their seasons of maximum P. Despite the inter-regional differences in time of year, size of region, and surface characteristics, the WVBs over these regions have common features. First, the change in precipitable water (dPW) is highly correlated with the moisture flux divergence (MFD) and not evaporation (E), implying that atmospheric humidity is affected more by the large-scale atmospheric circulation than land-atmosphere interactions. Second, P is positively correlated with moisture inflow (IF/A). However, a pronounced difference exists between the North American and the Mediterranean study regions with respect to the processes associated with increased P. For the MW and the SGP, increased P is associated with moisture flux convergence ( MFD) due to increased IF/A. In contrast, increased P over the EM is not associated with MFD, since both the outflow (OF/A) and IF/A increase at similar rates. Recycling ratio (R) estimates were calculated for each region using an equation previously developed. The moisture recycling methodology involves the externally advected versus locally evaporated contributions to P being expressed in terms of a "bulk" formulation in which IF/A and OF/A are defined at the boundaries of the study area. Due to its scale dependence, R cannot be directly compared among the different regions, and a normalization procedure was developed for this comparative study. Its results suggest the normalized R ranges between 12-25% for the study regions, with the value for the oceanic EM being somewhat larger than over the continental MW and SGP.
Phytoplankton distribution in the Western Arctic Ocean during a summer of exceptional ice retreat
P. Coupel,H. Y. Jin,D. Ruiz-Pino,J. F. Chen
Biogeosciences Discussions , 2011, DOI: 10.5194/bgd-8-6919-2011
Abstract: A drastic ice decline in the Arctic Ocean, triggered by global warming, could generate rapid changes in the upper ocean layers. The ice retreat is particularly intense over the Canadian Basin where large ice free areas were observed since 2007. The CHINARE 2008 expedition was conducted in the Western Arctic (WA) ocean during a year of exceptional ice retreat (August–September 2008). This study investigates whether a significant reorganization of the primary producers in terms of species, biomass and productivity has to be observed in the WA as a result of the intense ice melting. Both pigments (HPLC) and taxonomy (microscopy) acquired in 2008 allowed to determine the phytoplanktonic distribution from Bering Strait (65° N) to extreme high latitudes over the Alpha Ridge (86° N) encompassing the Chukchi shelf, the Chukchi Borderland and the Canadian Basin. Two different types of phytoplankton communities were observed. Over the ice-free Chukchi shelf, relatively high chl-a concentrations (1–5 mg m 3) dominated by 80 % of diatoms. In the Canadian Basin, surface waters are oligotrophic (<0.1 mg m 3) and algal assemblages were dominated by haptophytes and diatoms while higher biomasses (~0.4 mg m 3) related to a deep Subsurface Chlorophyll Maximum (SCM) are associated to small-sized (nano and pico) phytoplankton. The ice melting onset allows to point out three different zones over the open basin: (i) the ice free condition characterized by deep and unproductive phytoplankton communities dominated by nanoplankton, (ii) an extended (78°–83° N) Active Melting Zone (AMZ) where light penetration associated to the stratification start off and enough nutrient availability drives to the highest biomass and primary production due to both diatoms and large flagellates, (iii) heavy ice conditions found north to 83° N allowing light limitation and consequently low biomass and primary production associated to pico and nanoplankton. To explain the poverty (Canadian Basin) and the richness (Chukchi shelf) of the WA, we explore the role of the nutrient-rich Pacific Waters, the bathymetry and two characteristics linked to the intense ice retreat: the stratification and the Surface Freshwater Layer (SFL). The freshwater accumulation induced a strong stratification limiting the nutrient input from the subsurface Pacific waters. This results in a biomass impoverishment of the well-lit layer and compels the phytoplankton to grow in subsurface. The phytoplankton distribution in the Chukchi Borderland and north Canadian Basin, during the summer of exceptional ice retreat (2008), su
Verification of universal relations in a strongly interacting Fermi gas
J. T. Stewart,J. P. Gaebler,T. E. Drake,D. S. Jin
Physics , 2010, DOI: 10.1103/PhysRevLett.104.235301
Abstract: Many-body fermion systems are important in many branches of physics, including condensed matter, nuclear, and now cold atom physics. In many cases, the interactions between fermions can be approximated by a contact interaction. A recent theoretical advance in the study of these systems is the derivation of a number of exact universal relations that are predicted to be valid for all interaction strengths, temperatures, and spin compositions. These equations, referred to as the Tan relations, relate a microscopic quantity, namely, the amplitude of the high-momentum tail of the fermion momentum distribution, to the thermodynamics of the many-body system. In this work, we provide experimental verification of the Tan relations in a strongly interacting gas of fermionic atoms. Specifically, we measure the fermion momentum distribution using two different techniques, as well as the rf excitation spectrum and determine the effect of interactions on these microscopic probes. We then measure the potential energy and release energy of the trapped gas and test the predicted universal relations.
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