220 research outputs found
Constraints on Flows in Horava-Lifshitz Gravity by Classical Solutions
We find exact static stringy solutions of Horava-Lifshitz gravity with the
projectability condition but imposing the detailed balance condition near the
UV fixed point, and propose a method on constraining the possible pattern of
flows in Horava-Lifshitz gravity by using the obtained classical solutions. In
the obtained vacuum solutions, the parameters related to the speed of the
graviton and the coefficients of quartic spatial derivative terms lead to
intriguing effects: the change of graviton speed yields a surplus angle and the
quartic derivatives make the square of effective electric charge negative. The
result of a few tests based on the geometries of a cone, an excess cone, a
black string, and a charged (black) string seems suggestive. For example, the
flow of constant graviton speed and variable Newton's coupling can be favored
in the vicinity of IR fixed point, but the conclusion is indistinct and far
from definite yet. Together with the numerous classical solutions, static or
time-dependent, which have already been found, the accumulated data from
various future tests will give some hints in constraining the flow patterns
more deterministic.Comment: 27 pages, 3 figures, version to appear in PR
Surplus Solid Angle as an Imprint of Horava-Lifshitz Gravity
We consider the electrostatic field of a point charge coupled to
Horava-Lifshitz gravity and find an exact solution describing the space with a
surplus (or deficit) solid angle. Although, theoretically in general
relativity, a surplus angle is hardly to be obtained in the presence of
ordinary matter with positive energy distribution, it seems natural in
Horava-Lifshitz gravity. We present the sudden disappearance and reappearance
of a star image as an astrophysical effect of a surplus angle. We also consider
matter configurations of all possible power law behaviors coupled to
Horava-Lifshitz gravity and obtain a series of exact solutions.Comment: 23 pages, 1 figure; minor changes, published versio
Block Matching-Based Background Generation and Non-Rigid Shape Tracking for Video Surveillance
Cosmic D- and DF-strings from D3Dbar3: Black Strings and BPS Limit
We study D- and DF-strings in a D3 system by using
Dirac-Born-Infeld type action. In the presence of an electric flux from the
transverse direction, we discuss gravitating thick D-string solutions of a
spatial manifold, , in which straight D-strings
stretched along the R direction are attached to the south and north
poles of the two-sphere. There is a horizon along its equator, which means the
structure of black strings is formed. We also discuss the BPS limit for thin
parallel D- and DF-strings in both flat and curved spacetime. We obtain the BPS
sum rule for an arbitrarily-separated multi-string configuration with a
Gaussian type tachyon potential. At the site of each thin BPS D(F)-string, the
pressure takes a finite value. We find that there exists a maximum deficit
angle in the conical geometry induced by thin BPS D- and DF-strings.Comment: 24 pages, 5 figure
Multi-BPS D-vortices
We investigate the BPS configuration of the multi D-vortices produced from
the D22 system. Based on the DBI-type action with a
Gaussian-type runaway potential for a complex tachyon field, the BPS limit is
achieved when the tachyon profile is thin. The solution states
randomly-distributed static D-vortices with zero interaction. With the
obtained BPS configuration, we derive the relativistic Lagrangian which
describes the dynamics of free massive D-vortices. We also discuss the
90 and 180 scattering of two identical D-vortices, and
present its implications on the reconnection in the dynamics of cosmic
superstrings.Comment: 11 pages, 4 figures. To appear in the proceedings of APCTP Winter
School on Black Hole Astrophysics 2008, Daejeon and Pohang, Korea, 24-29
January, 2008. Submitted to J. Korean Phys. So
Chinese-Style Of Reward-Based Crowd-Funding: Financial Approaches Or Marketing Tools?
Crowd-funding is an emerging industry in China. However, Chinese crowd-funding market has some different characteristics to its US-based or Europe-based predecessors. Some of Chinese founders regard reward-based crowd-funding as a funding approach, while others highlight its marketing functions. Thus, which play more important role at present? This paper investigates the reason for the special performance of reward-based crowd-funding in China from multiple perspectives. The results indicate that the special institutional environments of China---lack of perfect social credit systems and legal systems, not granting legal definition and status for crowd-funding, leads to an inevitable result that Chinese founders make heavy use of the marketing functions of crowd-funding but make light use of the funding function at the present stage. With the perfecting of the institutional and legal environment, many small-and-medium-enterprises and individual entrepreneurs are expected to pay more attention on the funding function of crowd-funding than today
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