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Search Results: 1 - 10 of 54685 matches for " Jiang Z "
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Accurate GLONASS Time Transfer for the Generation of the Coordinated Universal Time
Z. Jiang,W. Lewandowski
International Journal of Navigation and Observation , 2012, DOI: 10.1155/2012/353961
Abstract: The spatial techniques currently used in accurate time transfer are based on GPS, TWSTFT, and GLONASS. The International Bureau of Weights and Measures (BIPM) is mandated for the generation of Coordinated Universal Time (UTC) which is published monthly in the BIPM Circular T. In 2009, the international Consultative Committee for Time and Frequency (CCTF) recommended the use of multitechniques in time transfer to ensure precision, accuracy, and robustness in UTC. To complement the existing GPS and TWSTFT time links, in November 2009 the first two GLONASS time links were introduced into the UTC worldwide time link network. By November 2011, 6 GLONASS time links are used in the UTC computation. In the frame of the application in the UTC computation, we establish the technical features of GLONASS time transfer: the short- and long-term stabilities, the calibration process, and in particular the impact of the multiple GLONASS frequency biases. We then outline various considerations for future developments, including the uses of P-codes and carrier-phase information. 1. Introduction GLONASS (from GLObal NAvigation Satellite System, GLN for short) is a radio-based satellite navigation system operated by the Russian Space Forces with the aim of providing real-time, all-weather, three-dimensional positioning, velocity measuring, and timing with a worldwide coverage. The completely deployed GLN constellation is composed of 24 satellites in three orbital planes of which the ascending nodes are 120° apart. Eight satellites are equally distributed in each plane. The first satellite was launched on 12 October 1982, and the constellation was completed in 1995, although until recent years it has not always been well maintained. With respect to present and future techniques for accurate time transfers, GLN is comparable to other global navigation satellite systems (GNSSs): the United States’ Global Positioning System (GPS), the upcoming Chinese Compass navigation system, and the Galileo positioning system of the European Union. To guarantee the accuracy and robustness of UTC generation, a multitechnique strategy for UTC time transfer is indispensable. Over the last two decades much effort has been devoted to introducing GLN in UTC. However, earlier GLN studies [1–9] remained at an experimental stage because there were only a few operationalGLN timing receivers, the GLN constellation was incomplete, and there were unsolved technical issues; among them the major difficulty was of the multiple GLN frequency biases. The situation has greatly improved in recent years. As of
Mid-Holocene ocean and vegetation feedbacks over East Asia
Z. Tian,D. Jiang
Climate of the Past Discussions , 2013, DOI: 10.5194/cpd-9-75-2013
Abstract: Mid-Holocene ocean and vegetation feedbacks over East Asia were investigated by a set of numerical experiments performed with the latest version 4 of the Community Climate System Model (CCSM4). Most of the annual and seasonal surface air temperature and precipitation changes during the mid-Holocene relative to the pre-industrial period were found to result from a direct response of the atmosphere to insolation forcing, while dynamic ocean and vegetation could modulate regional climate over East Asia to a certain extent. Because of its thermal inertia, the dynamic ocean induced an additional warming (cooling) of 0.5 K in boreal winter, 0.0003 K in boreal summer, and 1.0 K in boreal autumn (0.6 K in boreal spring) averaged across China during the mid-Holocene, and hence counteracted (amplified) the direct response except in summer, collectively leading to a weak annual warming of 0.2 K at the national scale. The contribution of dynamic vegetation to mid-Holocene temperature change was small overall. It gave rise to an additional annual cooling of 0.2 K, 0.1 K in winter, 0.2 K in summer, and 0.4 K in autumn, but a warming of 0.1 K in spring regionally averaged over China. On the other hand, ocean feedback led to a small enhancement of precipitation by 0.04 mm day 1 in winter and 0.05 mm day 1 in autumn, but induced a reduction of precipitation by 0.14 mm day 1 for the annual mean, 0.29 mm day 1 in spring, and 0.34 mm day 1 in summer at the national scale, which tended to weaken East Asian summer monsoon rainfall. The influence of dynamic vegetation on precipitation was comparatively small, with a regionally averaged precipitation change of –0.002 mm day 1 on the annual scale, –0.03 mm day 1 in winter and spring, –0.01 mm day 1 in summer, and 0.06 mm day 1 in autumn over the country. Taken together, ocean feedback narrowed the model–data mismatch in annual and winter temperatures over China during the mid-Holocene, while dynamic vegetation feedback contributed little to temperature and precipitation changes over East Asia.
Is the temperature as a Lorentz scalar?
W. Z. Jiang
Physics , 2003,
Abstract: For the free Fermion gas at thermodynamic equilibrium, the temperature which represents the averaged kinetic energy is demonstrated to have the proper property which is invariant under the Lorentz boost, using the conceptions of the relativistic quantum field theory and statistical physics. The thermodynamic interaction is described by the coupling of particles with the vacuum of a scalar pseudo boson which features a self-interaction. The various measurement of the apparent temperature of a moving body is also investigated.
Roles of isoscalar hyperons in probing the density dependence of the nuclear symmetry energy
W. Z. Jiang
Physics , 2006, DOI: 10.1016/j.physletb.2006.09.020
Abstract: The role of the isoscalar hyperon Lambda in probing the density dependence of the nuclear symmetry energy is studied in multi-Lambda hypernuclei, hyperon-rich matter and neutron stars in relativistic models. Relationships between the properties of three types of objects and the neutron thickness in 208Pb are established with respect to the isoscalar-isovector coupling that modifies the density dependence of the symmetry energy. The exotic isotopes far from the neutron drip line can be stabilized by filling in considerable Lambda hyperons. The difference of the binding energy of multi-Lambda hypernuclei from different models is attributed to different symmetry energies. The isovector potential together with the neutron thickness in multi-Lambda hypernuclei investigated is very sensitive to the isoscalar-isovector coupling. The large sensitivity of the Lambda hyperon fraction to the isoscalar-isovector coupling occurs at about 2-3 rho_0 in beta equilibrated hyperon-rich matter. In neutron stars with hyperonization, an on-off effect with respect to the isoscalar-isovector coupling exists for the neutron star radius.
Thermal conductance of Andreev interferometers
Z. Jiang,V. Chandrasekhar
Physics , 2005, DOI: 10.1103/PhysRevLett.94.147002
Abstract: We calculate the thermal conductance $G^T$ of diffusive Andreev interferometers, which are hybrid loops with one superconducting arm and one normal-metal arm. The presence of the superconductor suppresses $G^T$; however, unlike a conventional superconductor, $G^T/G^T_N$ does not vanish as the temperature $T\to0$, but saturates at a finite value that depends on the resistance of the normal-superconducting interfaces, and their distance from the path of the temperature gradient. The reduction of $G^T$ is determined primarily by the suppression of the density of states in the proximity-coupled normal metal along the path of the temperature gradient. $G^T$ is also a strongly nonlinear function of the thermal current, as found in recent experiments.
Quantitative measurements of the thermal resistance of Andreev interferometers
Z. Jiang,V. Chandrasekhar
Physics , 2005, DOI: 10.1103/PhysRevB.72.020502
Abstract: Using a local thermometry technique, we have been able to quantitatively measure the thermal resistance $R^T$ of diffusive Andreev interferometers. We find that $R^T$ is strongly enhanced from its normal state value at low temperatures, and behaves non-linearly as a function of the thermal current through the sample. We also find that the $R^T$ oscillates as a function of magnetic flux with a fundamental period corresponding to one flux quantum $\Phi_0=h/2e$, demonstrating the phase coherent nature of thermal transport in these devices. The magnitude of $R^T$ is larger than predicted by recent numerical simulations.
Study of Oxygen Diffusion and Clustering in Silicon using an Empirical Interatomic Potential
Z. Jiang,R. A. Brown
Physics , 1995,
Abstract: The diffusion path and diffusivity of oxygen in crystalline silicon are computed using an empirical interatomic potential which was recently developed for modelling the interactions between oxygen and silicon atoms. The diffusion path is determined by constrained energy minimization, and the diffusivity is computed using jump rate theory. The calculated diffusivity is in excellent agreement with experiemental data. The same interatomic potntial also is used to study the formation of small clusters of oxygen atoms in silicon. The structures of these clusters are found by NPT molecular dynamics simulations, and their free energies are calculated by thermodynamic integration. These free energies are used to predict the temperature dependence of the equilibrium partitioning of oxygen into clusters of different sizes. The calculations show that, for given total oxygen concentration, most oxygen atoms are in clusters at temperature below 1300K, and that the average cluster size increases with decreasing temperature. These results are in qualitative agreement with effects of thermal annealing on oxygen precipitation in silicon crystals.
On perpetual American put valuation and first-passage in a regime-switching model with jumps
Z. Jiang,M. R. Pistorius
Mathematics , 2008,
Abstract: In this paper we consider the problem of pricing a perpetual American put option in an exponential regime-switching L\'{e}vy model. For the case of the (dense) class of phase-type jumps and finitely many regimes we derive an explicit expression for the value function. The solution of the corresponding first passage problem under a state-dependent level rests on a path transformation and a new matrix Wiener-Hopf factorization result for this class of processes.
Sensitivity of deexcitation energies of superdeformed secondary minima to the density dependence of symmetry energy with the relativistic mean-field theory
W. Z. Jiang,Z. Z. Ren,Z. Q. Sheng,Z. Y. Zhu
Physics , 2010, DOI: 10.1140/epja/i2010-10962-6
Abstract: The relationship between deexcitation energies of superdeformed secondary minima relative to ground states and the density dependence of the symmetry energy is investigated for heavy nuclei using the relativistic mean field (RMF) model. It is shown that the deexcitation energies of superdeformed secondary minima are sensitive to differences in the symmetry energy that are mimicked by the isoscalar-isovector coupling included in the model. With deliberate investigations on a few Hg isotopes that have data of deexcitation energies, we find that the description for the deexcitation energies can be improved due to the softening of the symmetry energy. Further, we have investigated deexcitation energies of odd-odd heavy nuclei that are nearly independent of pairing correlations, and have discussed the possible extraction of the constraint on the density dependence of the symmetry energy with the measurement of deexcitation energies of these nuclei.
Accelerating Face Recognition for Large Data Applications in Visual Internet of Things
Zhuoxuan Jiang,Yaping Lin,Stan Z. Li
Information Technology Journal , 2013,
Abstract: This study described a face recognition system for large scale data applications in the framework of Visual Internet of Things (VIoT). The main issue here was the speed in large face matching. In order to solve this problem, this study proposed a general method that could accelerate the computation in several magnitudes based on classical k-means clustering while approximately maintaining the original face recognition rate. Experimental results showed that it can speed up existing face recognition systems about 3 times.
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