Blandford-Znajek process as a gamma ray burst central engine

We investigate the possibility that gamma-ray bursts are powered by a central engine consisting of a black hole with an external magnetic field supported by a surrounding disk or torus. The rotational energy of the black hole can be extracted electromagnetically as a Poynting flux, a mechanism proposed by Blandford and Znajek(1977). Recently observed magnetars indicate that some compact objects have very high magnetic fields, up to $10^{15}$ G, which is required to extract the energy within the duration of a GRB, i.e., in 1000 s or less. We demonstrate also that the Poynting flux need not be substantially dominated by the disk.Comment: 7 pages, no figure, paspconf.sty, to appear in Proceedings " Gamma Ray Bursts: The First Three Minutes", Gr\"aft{\aa}vallen, Sweden, Feb. 6 - 11, 199

Geodesic Motions in 2+1 Dimensional Charged Black Holes

We study the geodesic motions of a test particle around 2+1 dimensional charged black holes. We obtain a class of exact geodesic motions for the massless test particle when the ratio of its energy and angular momentum is given by square root of cosmological constant. The other geodesic motions for both massless and massive test particles are analyzed by use of numerical method.Comment: 13page

Consequences of the partial restoration of chiral symmetry in AdS/QCD

Chiral symmetry is an essential concept in understanding QCD at low energy. We treat the chiral condensate, which measures the spontaneous breaking of chiral symmetry, as a free parameter to investigate the effect of partially restored chiral symmetry on the physical quantities in the frame work of an AdS/QCD model. We observe an interesting scaling behavior among the nucleon mass, pion decay constant and chiral condensate. We propose a phenomenological way to introduce the temperature dependence of a physical quantity in the AdS/QCD model with the thermal AdS metric.Comment: 11 pages, 6 figure

Self-Assembled Charged Hydrogels Control the Alignment of Filamentous Actin

We demonstrate a novel route to control attachment of filamentous actin (F-actin) on hydrogel films. By incorporating an amine-terminated silane, the hydrogel surface charge and surface topography are varied. With increasing silane content, F-actin reorients from perpendicular to parallel to the hydrogel surface, ceases to wobble, and forms mainly elongated or cyclic structures. F-Actin coverage reaches a maximum at 2.5 vol% silane and declines at higher silane content. This biphasic behavior is explained by the simultaneous increase in surface charge and the self-assembly of a micron scale pattern of positively charged islands. Our approach provides guidelines for constructing nanoscale tracks to guide motor proteins underlying nano-engineered devices such as molecular shuttles

Euler number of Instanton Moduli space and Seiberg-Witten invariants

We show that a partition function of topological twisted N=4 Yang-Mills theory is given by Seiberg-Witten invariants on a Riemannian four manifolds under the condition that the sum of Euler number and signature of the four manifolds vanish. The partition function is the sum of Euler number of instanton moduli space when it is possible to apply the vanishing theorem. And we get a relation of Euler number labeled by the instanton number $k$ with Seiberg-Witten invariants, too. All calculation in this paper is done without assuming duality.Comment: LaTeX, 34 page

Effective Action for Membrane Dynamics in DLCQ MM theory on a Two-torus

The effective action for the membrane dynamics on the background geometry of the $N$-sector DLCQ $M$ theory compactified on a two-torus is computed via supergravity. We compare it to the effective action obtained from the matrix theory, i.e., the (2+1)-dimensional supersymmetric Yang-Mills (SYM) theory, including the one-loop perturbative and full non-perturbative instanton effects. Consistent with the DLCQ prescription of $M$ theory {\em a la} Susskind, we find the precise agreement for the finite $N$-sector (off-conformal regime), as well as for the large $N$ limit (conformal regime), providing us with a concrete example of the correspondence between the matrix theory and the DLCQ $M$ theory. Non-perturbative instanton effects in the SYM theory conspire to yield the eleven-dimensionally covariant effective action.Comment: 11 pages, latex, no figure

Ethical issues related to brain organoid research

This review provides a snapshot of the current ethical issues related to research with human brain organoids. The issues fall into the following main themes: research oversight; human biomaterials procurement and donor consent; translational delivery; animal research; and organoid consciousness and moral status. Each of these areas poses challenges for researchers, bioethicists, regulators, research institutions, and tissue banks. However, progress can be made if these parties build on past experiences with stem cell research, ethics, and policy, but adapted accordingly to new aspects of brain organoid research

Giant Gravitons in type IIA PP-wave Background

We examine giant gravitons with a worldvolume magnetic flux $q$ in type IIA pp-wave background and find that they can move away from the origin along $x^4$ direction in target space satisfying $Rx^4=-q$. This nontrivial relation can be regarded as a complementary relation of the giant graviton on IIA pp-wave and is shown to be connected to the spacetime uncertainty principle. The giant graviton is also investigated in a system of N D0-branes as a fuzzy sphere solution. It is observed that $x^4$ enters into the fuzzy algebra as a deformation parameter. Such a background dependent Myers effect guarantees that we again get the crucial relation of our giant graviton. In the paper, we also find a BIon configuration on the giant graviton in this background.Comment: 10 pages, no figure, content added, typo corrected, reference adde