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Search Results: 1 - 10 of 107296 matches for " W. Zheng "
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Evidence of a Two-Component Jet in the Afterglow of GRB 070419A
W. Zheng,J. Deng
Physics , 2009, DOI: 10.1007/s11433-010-0022-4
Abstract: A two-component jet model is proposed to explain the unusual afterglow of GRB 070419A. Regarding the optical light curve, a wide "jet" with an opening angle of > 30-40 degrees is assumed to produce the late shallow decay, while the three early power-law segments must be caused by a narrow jet with an opening angle of about 2-4 degrees. Additional energy injections to both components are required. Late X-ray emission may come from either the wide jet or the narrow one. If the latter is correct, the jets may run into an ISM environment and the temporal index of the late energy injection q may be about 0.65.
Zero Temperature Series Expansions for the Kondo Lattice Model
W. Zheng,J. Oitmaa
Physics , 2002, DOI: 10.1103/PhysRevB.67.214406
Abstract: We present new results for the Kondo lattice model of strongly correlated electrons, in 1-, 2-, and 3-dimensions, obtained from high-order linked-cluster series expansions. Results are given for varies ground state properties at half-filling, and for spin and charge excitations. The existence and nature of the predicted quantum phase transition are explored.
Finite temperature strong-coupling expansions for the Kondo lattice model
J. Oitmaa,W. Zheng
Physics , 2002, DOI: 10.1103/PhysRevB.67.214407
Abstract: Strong-coupling expansions, to order $(t/J)^8$, are derived for the Kondo lattice model of strongly correlated electrons, in 1-, 2- and 3- dimensions at arbitrary temperature. Results are presented for the specific heat, and spin and charge susceptibilities.
Stripe Dynamics, Global Phase Ordering and Quantum Criticality in High Tc Superconductors
W. J. Zheng
Physics , 2000, DOI: 10.1103/PhysRevB.62.4042
Abstract: By modeling the stripe phase in cuprates as spin gapped stripes coupled to the RVB liquid of preformed electron pairs, I derive the low energy effective theory of the RVB phase variable. It is found that the effect of stripe dynamics (including both longitudinal and transverse modes) leads to incipient temporal phase stiffness in the RVB liquid, which tunes a quantum phase transition toward a superconducting ground state with global phase order. Physical consequences of this quantum criticality are discussed.
Luther-Emery Stripes, RVB Spin Liquid Background and High Tc Superconductivity
W. J. Zheng
Physics , 2000, DOI: 10.1103/PhysRevLett.83.3534
Abstract: The stripe phase in high Tc cuprates is modeled as a single stripe coupled to the RVB spin liquid background by the single particle hopping process. In normal state, the strong pairing correlation inherent in RVB state is thus transfered into the Luttinger stripe and drives it toward spin-gap formation described by Luther-Emery Model. The establishment of global phase coherence in superconducting state contributes to a more relevant coupling to Luther-Emery Stripe and leads to gap opening in both spin and charge sectors. Physical consequences of the present picture are discussed, and emphasis is put on the unification of different energy scales relevant to cuprates, and good agreement is found with the available experimental results, especially in ARPES.
Ferrimagnetism and compensation points in a decorated 3D Ising models
J. Oitmaa,W. Zheng
Physics , 2003, DOI: 10.1016/S0378-4371(03)00522-3
Abstract: We give a precise numerical solution for decorated Ising models on the simple cubic lattice which show ferromagnetism, compensation points, and reentrant behaviour. The models, consisting of $S={1\over 2}$ spins on a simple cubic lattice, and decorating S=1 or $S=3/2$ spins on the bonds, can be mapped exactly onto the normal spin-1/2 Ising model, whose properties are well known.
Integration of the Gene Ontology into an object-oriented architecture
Daniel Shegogue, W Jim Zheng
BMC Bioinformatics , 2005, DOI: 10.1186/1471-2105-6-113
Abstract: Using object-oriented models we have captured the static and dynamic events that occur during a representative GO process, "transforming growth factor-beta (TGF-beta) receptor complex assembly" (GO:0007181).We demonstrate that the utility of GO terms can be enhanced by object-oriented technology, and that the GO terms can be integrated into an object-oriented model by serving as a basis for the generation of object functions and attributes.Complexity combined with an imprecise terminology has hindered the understanding of biology. A formal and structured vocabulary is now being developed to address this imprecise biology terminology. This vocabulary or Gene Ontology (GO) is being developed by the Gene Ontology Consortium (GOC) [1] to standardize the descriptions of gene products. Ontologies define the basic terms and relations comprising the vocabulary of a topic area, as well as the rules for combining terms and relations to define extensions to the vocabulary [2]. Despite these efforts, the mechanism of representing these terms lacks a unifying architecture that can be applied to the annotation of a gene product. However, computer science has developed a well-defined process and methodology for the development of software models. Adapting this process and methodology can orchestrate the assembly of biological models with integrated gene ontologies. In doing so, a standardized terminology and object-oriented model is created that can facilitate communication between biologists and computer scientists.The Gene Ontology project is a collaborative effort that addresses the need for a controlled vocabulary that provides a consistent description of gene products in different databases [1]. The GO collaborators are developing three structured, controlled vocabularies that describe gene products, which have been classified into molecular function, biological process, and cellular component domains. GO terms are organized in structures called directed acyclic graphs (DAGs)
Limits to the fraction of high-energy photon emitting gamma-ray bursts
Carl W. Akerlof,WeiKang Zheng
Physics , 2012, DOI: 10.1088/0004-637X/764/2/190
Abstract: After almost 4 years of operation, the two instruments onboard the Fermi Gamma-ray Space Telescope have shown that the number of gamma-ray bursts with high energy photon emission above 100 MeV cannot exceed roughly 9% of the total number of all such events, at least at the present detection limits. In a recent paper (Zheng et al. 2012c), we found that GRBs with photons detected in the Large Area Telescope (LAT) have a surprisingly broad distribution with respect to the photon number above background. Extrapolation of our empirical fit to numbers of photons below our quoted detection limit suggests that the overall rate of such events could be determined by standard image co-adding techniques. In this case, we have taken advantage of the excellent angular resolution of the Swift mission to provide accurate reference points for 79 GRB events which have eluded any previous correlations with high energy photons. We find a small but significant signal. Guided by the power law fit obtained previously for the number distribution of GRBs, the data suggests that only a small fraction of GRBs are sources of high energy photons.
Two-Hole and Four-Hole Bound States in a t-J Ladder at half-filling
W. Zheng,C. J. Hamer
Physics , 2002, DOI: 10.1103/PhysRevB.66.085112
Abstract: The two-hole excitation spectrum of the t-J ladder at half-filling is studied using linked-cluster series expansion methods. A rich spectrum of bound states emerges, particularly at small $t/J$. Their dispersion relations and coherence lengths are computed, along with the threshold behaviour as the bound states merge into the continuum. A class of 4-hole bound states is also studied, leading to the conclusion that phase separation occurs for $t/J \lesssim 0.5$, in agreement with other studies.
A Characterization of Subspaces and Quotients of Reflexive Banach Spaces with Unconditional Bases
W. B. Johnson,Bentuo Zheng
Mathematics , 2007,
Abstract: We prove that the dual or any quotient of a separable reflexive Banach space with the unconditional tree property has the unconditional tree property. Then we prove that a separable reflexive Banach space with the unconditional tree property embeds into a reflexive Banach space with an unconditional basis. This solves several long standing open problems. In particular, it yields that a quotient of a reflexive Banach space with an unconditional finite dimensional decomposition embeds into a reflexive Banach space with an unconditional basis.
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