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Search Results: 1 - 10 of 44195 matches for " Yumei Wu "
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Thermodynamics and classification of cosmological models in the Horava-Lifshitz theory of gravity
Anzhong Wang,Yumei Wu
Physics , 2009, DOI: 10.1088/1475-7516/2009/07/012
Abstract: We study thermodynamics of cosmological models in the Horava-Lifshitz theory of gravity, and systematically investigate the evolution of the universe filled with a perfect fluid that has the equation of state $p=w\rho$, where $p$ and $\rho$ denote, respectively, the pressure and energy density of the fluid, and $w$ is an arbitrary real constant. Depending on specific values of the free parameters involved in the models, we classify all of them into various cases. In each case the main properties of the evolution are studied in detail, including the periods of deceleration and/or acceleration, and the existence of big bang, big crunch, and big rip singularities. We pay particular attention on models that may give rise to a bouncing universe.
Kink Stability of Isothermal Spherical Self-Similar Flow Revisited
Anzhong Wang,Yumei Wu
Physics , 2005, DOI: 10.1007/s10714-006-0343-9
Abstract: The problem of kink stability of isothermal spherical self-similar flow in newtonian gravity is revisited. Using distribution theory we first develop a general formula of perturbations, linear or non-linear, which consists of three sets of differential equations, one in each side of the sonic line and the other along it. By solving the equations along the sonic line we find explicitly the spectrum, $k$, of the perturbations, whereby we obtain the stability criterion for the self-similar solutions. When the solutions are smoothly across the sonic line, our results reduce to those of Ori and Piran. To show such obtained perturbations can be matched to the ones in the regions outside the sonic line, we study the linear perturbations in the external region of the sonic line (the ones in the internal region are identically zero), by taking the solutions obtained along the line as the boundary conditions. After properly imposing other boundary conditions at spatial infinity, we are able to show that linear perturbations, satisfying all the boundary conditions, exist and do not impose any additional conditions on $k$. As a result, the complete treatment of perturbations in the whole spacetime does not alter the spectrum obtained by considering the perturbations only along the sonic line.
Generalized Vaidya Solutions
Anzhong Wang,Yumei Wu
Physics , 1998, DOI: 10.1023/A:1018819521971
Abstract: A large family of solutions, representing, in general, spherically symmetric Type II fluid, is presented, which includes most of the known solutions to the Einstein field equations, such as, the monopole-de Sitter-charged Vaidya ones.
Kink Stability of Self-Similar Solutions of Scalar Field in 2+1 Gravity
Anzhong Wang,Yumei Wu
Physics , 2005, DOI: 10.1007/s10714-007-0413-7
Abstract: The kink stability of self-similar solutions of a massless scalar field with circular symmetry in 2+1 gravity is studied, and found that such solutions are unstable against the kink perturbations along the sonic line (self-similar horizon). However, when perturbations outside the sonic line are considered, and taking the ones along the sonic line as their boundary conditions, we find that non-trivial perturbations do not exist. In other words, the consideration of perturbations outside the sonic line limits the unstable mode of the perturbations found along the sonic line. As a result, the critical solution for the scalar collapse remains critical even after the kink perturbations are taken into account.
Cosmology in nonrelativistic general covariant theory of gravity
Anzhong Wang,Yumei Wu
Physics , 2010, DOI: 10.1103/PhysRevD.83.044031
Abstract: Horava and Melby-Thompson recently proposed a new version of the Horava-Lifshitz theory of gravity, in which the spin-0 graviton is eliminated by introducing a Newtonian pre-potential $\phi$ and a local U(1) gauge field $A$. In this paper, we first derive the corresponding Hamiltonian, super-momentum constraints, the dynamical equations, and the equations for $\phi$ and $A$, in the presence of matter fields. Then, we apply the theory to cosmology, and obtain the modified Friedmann equation and the conservation law of energy, in addition to the equations for $\phi$ and $A$. When the spatial curvature is different from zero, terms behaving like dark radiation and stiff-fluid exist, from which, among other possibilities, bouncing universe can be constructed. We also study linear perturbations of the FRW universe with any given spatial curvature $k$, and derive the most general formulas for scalar perturbations. The vector and tensor perturbations are the same as those recently given by one of the present authors [A. Wang, Phys. Rev. D{\bf 82}, 124063 (2010)] in the setup of Sotiriou, Visser and Weinfurtner. Applying these formulas to the Minkowski background, we have shown explicitly that the scalar and vector perturbations of the metric indeed vanish, and the only remaining modes are the massless spin-2 gravitons.
Self-Similar Collapse of Scalar Field with Plane Symmetry
Anzhong Wang,Yumei Wu,Zhong Chao Wu
Physics , 2004, DOI: 10.1023/B:GERG.0000018289.60173.c5
Abstract: Plane symmetric self-similar solutions to Einstein's four-dimensional theory of gravity are studied and all such solutions are given analytically in closed form. The local and global properties of these solutions are investigated and it is shown that some of the solutions can be interpreted as representing gravitational collapse of the scalar field. During the collapse, trapped surfaces are never developed. As a result, no black hole is formed. Although the collapse always ends with spacetime singularities, it is found that these singularities are spacelike and not naked.
Amphiphysin I and regulation of synaptic vesicle endocytosis
Acta Medica Okayama , 2009,
Abstract: Amphiphysin I, known as a major dynamin-binding partner localized on the collars of nascent vesicles, plays a key role in clathrin-mediated endocytosis (CME) of synaptic vesicles. Amphiphysin I mediates the invagination and fission steps of synaptic vesicles by sensing or facilitating membrane curvature and stimulating the GTPase activity of dynamin. Amphiphysin I may form a homodimer by itself or a heterodimer with amphiphysin II in vivo. Both amphiphysin I and II function as multilinker proteins in the clathrin-coated complex. Under normal physiological conditions, the functions of amphiphysin I and some other endocytic proteins are known to be regulated by phosphorylation and dephosphorylation. During hyperexcited conditions, the most recent data showed that amphiphysin I is truncated by the ca2-dependent protease calpain. Overexpression of the truncated form of amphi-physin I inhibited transferrin uptake and synaptic vesicle endocytosis (SVE). This suggests that amphi-physin I may be an important regulator for SVE when massive amounts of Ca2 flow into presynaptic terminals, a phenomenon observed in neurodegenerative disorders such as ischemia/anoxia, epilepsy, stroke, trauma and Alzheimer's disease. This review describes current knowledge regarding the general properties and functions of amphiphysin I as well as the functional regulations such as phosphorylation and proteolysis in nerve terminals.
Collapse of a Scalar Field in 2+1 Gravity
Eric W. Hirschmann,Anzhong Wang,Yumei Wu
Physics , 2002, DOI: 10.1088/0264-9381/21/7/006
Abstract: We consider the problem of critical gravitational collapse of a scalar field in 2+1 dimensions with spherical (circular) symmetry. After surveying all the analytic, continuously self-similar solutions and considering their global structure, we examine their perturbations with the intent of understanding which are the critical solutions with a single unstable mode. The critical solution which we find is the one which agrees most closely with that found in numerical evolutions. However, the critical exponent which we find does not seem to agree with the numerical result.
p150 ADAR1 isoform involved in maintenance of HeLa cell proliferation
Haifang Wang, Zheng Hou, Yumei Wu, Xue Ma, Xiaoxing Luo
BMC Cancer , 2006, DOI: 10.1186/1471-2407-6-282
Abstract: A conditional site-specific, ribozyme-based gene knock-down strategy was utilized to study the function of full-length isoform of ADAR1 (p150 protein) in HeLa cell. Double-stable HeLa cell lines were developed by transfecting HeLa Tet-On cells with a pTRE-derived plasmid that can express a hammerhead ribozyme against mRNA of p150 ADAR1 isoform under induction condition. Semi-quantitative RT-PCR and Western blotting were performed to measure the expression of p150 in selected cell clones. Cell proliferation was evaluated by means of MTT assay and growth curve analysis. Cellular morphological changes were observed under light microscope. Flow Cytometry was used for cell cycle analysis. Growth rate of cell transplants in BALB/c nude mice was also investigated.Both HeLa cell proliferation in vitro and the growth rate of transplanted HeLa cell-derived tumors in nude mice in vivo were significantly inhibited due to reduced expression of ADAR1 p150. Additionally, cell cycle analysis showed that cell progression from G1 phase to S phase was retarded in the ADAR1 p150 suppressed cells.Our results suggest that normal expression and functioning of p150 ADAR1 is essential for the maintenance of proper cell growth. The mechanisms underlying ADAR1's action might include both editing of currently unknown double-stranded RNAs and interacting with other cellular dsRNA-related processes.Adenosine (A) to inosine (I) conversion catalyzed by adenosine deaminases acting on RNA (ADAR) is an evolutionally conserved process, occurring in organisms from unicellular protozoa to humans [1,2]. Through site-specific modification of pre-mRNAs, this process provides an important post-transcriptional mechanism for expanding the functional diversities of RNA and protein products, such as those that encode the glutamate receptors and serotonin receptors [3,4]. In contrast, nonspecific editing is more frequent and has been considered mainly implicated in host defense mechanisms [5].Due to the use of d
Nan Wu,Rongli Zhang,Yumei Wang,Xin Xu
Acta Crystallographica Section E , 2011, DOI: 10.1107/s1600536811038736
Abstract: In the title compound, C22H19NO, the pyridine ring and the adjacent naphthalene ring system are nearly coplanar, making a dihedral angle of 3.3 (1)°, while the pyridine and benzene rings are perpendicular to each other, with a dihedral angle of 89.9 (1)°. The crystal packing is stabilized by intermolecular O—H...N hydrogen bonds and C—H...π interactions.
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