5,347 research outputs found
SU(2) WZW D-branes and quantized worldvolume U(1) flux on S^2
We discuss possible D-brane configurations on SU(2) group manifolds in the
sigma model approach. When we turn the boundary conditions of the spacetime
fields into the boundary gluing conditions of chiral currents, we find that for
all D-branes except the spherical D2-branes, the gluing matrices R^a_{b} depend
on the fields, so the chiral Kac-Moody symmetry is broken, but conformal
symmetry is maintained. Matching the spherical D2-branes derived from the sigma
model with those from the boundary state approach we obtain a U(1) field
strength that is consistent with flux quantization.Comment: 10 pages, Latex, several corrections (the previous version was not
approved by the first two authors
Steady-State Ab Initio Laser Theory for N-level Lasers
We show that Steady-state Ab initio Laser Theory (SALT) can be applied to
find the stationary multimode lasing properties of an N-level laser. This is
achieved by mapping the N-level rate equations to an effective two-level model
of the type solved by the SALT algorithm. This mapping yields excellent
agreement with more computationally demanding N-level time domain solutions for
the steady state
The Power of Poincar\'e: Elucidating the Hidden Symmetries in Focal Conic Domains
Focal conic domains are typically the "smoking gun" by which smectic liquid
crystalline phases are identified. The geometry of the equally-spaced smectic
layers is highly generic but, at the same time, difficult to work with. In this
Letter we develop an approach to the study of focal sets in smectics which
exploits a hidden Poincar\'e symmetry revealed only by viewing the smectic
layers as projections from one-higher dimension. We use this perspective to
shed light upon several classic focal conic textures, including the concentric
cyclides of Dupin, polygonal textures and tilt-grain boundaries.Comment: 4 pages, 3 included figure
Multispectral Bioluminescence Tomography: Methodology and Simulation
Bioluminescent imaging has proven to be a valuable tool for
monitoring physiological and pathological activities at cellular
and molecular levels in living small animals. Using biological
techniques, target cells can be tagged with reporters encoding
several kinds of luciferase enzymes, which generate characteristic
photons in a wide spectrum covering the infrared range. Part of
the diffused light can reach the body surface of the small animal,
be separated into several spectral bands using appropriate
filters, and collected by a sensitive CCD camera. Here we present
a bioluminescence tomography (BLT) method for a bioluminescent
source reconstruction from multispectral data measured on the
external surface, and demonstrate the advantages of multispectral
BLT in a numerical study using a heterogeneous mouse chest
phantom. The results show that the multispectral approach
significantly improves the accuracy and stability of the BLT
reconstruction even if the data are highly noisy
Vertical Integration and Competitive Balance in Professional Sports: Evidence from Minor League Baseball
Major League Baseball (MLB) teams regularly call up players from their Minor League Baseball (MiLB) affliates to fulfill roster needs. This paper utilizes a manually collected panel of player call-ups between 1946 and 2019 and studies their impact on competitive balance in the minor leagues. Our results indicate an overall positive relationship between call-ups and competitive balance in the MiLB, with the pro-competitive effect primarily driven by the AA leagues and not AAA leagues. We also find suggestive evidence of the effect being likely explained by the promotion of MiLB players to MLB, rather than the demotion of MLB players to MiLB. Our findings provide important policy implications regarding vertical relationships and human capital development in professional sports
Stock Market Reactions to Presidential Statements: Evidence from Company-Specific Tweets
When the President of the United States tweets, do investors respond? We analyze the impact of tweets from President Trump\u27s official Twitter accounts from November 9, 2016 to July 31, 2017 that include the name of a publicly traded company. We find that these tweets move company stock prices and increase trading volume, volatility and institutional investor attention, with a stronger impact before the presidential inauguration. The initial impact of the presidential tweets on stock prices appears to dissipate over the next few trading days. Overall, the results show that investors pay attention to presidential company-specific statements even when such statements have no lasting effect on shareholder value
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