270 research outputs found
Typical orbits of quadratic polynomials with a neutral fixed point: Brjuno type
We describe the topological behavior of typical orbits of complex quadratic
polynomials P_alpha(z)=e^{2\pi i alpha} z+z^2, with alpha of high return type.
Here we prove that for such Brjuno values of alpha the closure of the critical
orbit, which is the measure theoretic attractor of the map, has zero area. Then
combining with Part I of this work, we show that the limit set of the orbit of
a typical point in the Julia set is equal to the closure of the critical orbit.Comment: 38 pages, 5 figures; fixed the issues with processing the figure
Holomorphic potentials for graded D-branes
We discuss gauge-fixing, propagators and effective potentials for topological
A-brane composites in Calabi-Yau compactifications. This allows for the
construction of a holomorphic potential describing the low-energy dynamics of
such systems, which generalizes the superpotentials known from the ungraded
case. Upon using results of homotopy algebra, we show that the string field and
low energy descriptions of the moduli space agree, and that the deformations of
such backgrounds are described by a certain extended version of `off-shell
Massey products' associated with flat graded superbundles. As examples, we
consider a class of graded D-brane pairs of unit relative grade. Upon computing
the holomorphic potential, we study their moduli space of composites. In
particular, we give a general proof that such pairs can form acyclic
condensates, and, for a particular case, show that another branch of their
moduli space describes condensation of a two-form.Comment: 47 pages, 7 figure
On the Efficiency of All-Pay Mechanisms
We study the inefficiency of mixed equilibria, expressed as the price of
anarchy, of all-pay auctions in three different environments: combinatorial,
multi-unit and single-item auctions. First, we consider item-bidding
combinatorial auctions where m all-pay auctions run in parallel, one for each
good. For fractionally subadditive valuations, we strengthen the upper bound
from 2 [Syrgkanis and Tardos STOC'13] to 1.82 by proving some structural
properties that characterize the mixed Nash equilibria of the game. Next, we
design an all-pay mechanism with a randomized allocation rule for the multi-
unit auction. We show that, for bidders with submodular valuations, the
mechanism admits a unique, 75% efficient, pure Nash equilibrium. The efficiency
of this mechanism outperforms all the known bounds on the price of anarchy of
mechanisms used for multi-unit auctions. Finally, we analyze single-item
all-pay auctions motivated by their connection to contests and show tight
bounds on the price of anarchy of social welfare, revenue and maximum bid.Comment: 26 pages, 2 figures, European Symposium on Algorithms(ESA) 201
Matrix Models and D-branes in Twistor String Theory
We construct two matrix models from twistor string theory: one by dimensional
reduction onto a rational curve and another one by introducing noncommutative
coordinates on the fibres of the supertwistor space P^(3|4)->CP^1. We comment
on the interpretation of our matrix models in terms of topological D-branes and
relate them to a recently proposed string field theory. By extending one of the
models, we can carry over all the ingredients of the super ADHM construction to
a D-brane configuration in the supertwistor space P^(3|4). Eventually, we
present the analogue picture for the (super) Nahm construction.Comment: 1+37 pages, reference added, JHEP style, published versio
Comments on D-brane Interactions in PP-wave Backgrounds
We calculate the interaction potential between widely separated D-branes in
PP-wave backgrounds in string theory as well as in low-energy supergravity.
Timelike and spacelike orientations are qualitatively different but in both
cases the effective brane tensions and RR charges take the same values as in
Minkowski space in accordance with the expectations from the sigma model
perturbation theory.Comment: Latex, 22 pages. Typos corrected and a reference added, final versio
Effect of a gap opening on the conductance of graphene superlattices
The electronic transmission and conductance of a gapped graphene superlattice
were calculated by means of the transfer-matrix method. The system that we
study consists of a sequence of electron-doped graphene as wells and hole-doped
graphene as barriers. We show that the transmission probability approaches
unity at some critical value of the gap. We also find that there is a domain
around the critical gap value for which the conductance of the system attains
its maximum value.Comment: 14 pages, 5 figures. To appear in Solid State Communication
Super D-branes from BRST Symmetry
Recently a new formalism has been developed for the covariant quantization of
superstrings. We study properties of Dp-branes and p-branes in this new
framework, focusing on two different topics: effective actions and boundary
states for Dp-branes. We present a derivation of the Wess-Zumino terms for
super (D)p-branes using BRST symmetry. To achieve this we derive the BRST
symmetry for superbranes, starting from the approach with/without pure spinors,
and completely characterize the WZ terms as elements of the BRST cohomology. We
also develope the boundary state description of Dp-branes by analyzing the
boundary conditions for open strings in the completely covariant (i.e., without
pure spinors) BRST formulation.Comment: 31 pp; journal version, expended discussion of D-brane pure spinor
constraints in Section 2.
Birth defects associated with paternal firefighting in the National Birth Defects Prevention Study
Background: Few studies have evaluated birth defects among children of firefighters. We investigated associations between birth defects and paternal work as a firefighter compared to work in non-firefighting and police officer occupations. Methods: We analyzed 1997–2011 data from the multi-site case-control National Birth Defects Prevention Study. Cases included fetuses or infants with major structural birth defects and controls included a random sample of live-born infants without major birth defects. Mothers of infants self-reported information about parents' occupations held during pregnancy. We investigated associations between paternal firefighting and birth defect groups using logistic regression to estimate odds ratios (ORs) and 95% confidence intervals (CIs). Referent groups included families reporting fathers working non-firefighting and police officer jobs. Results: Occupational groups included 227 firefighters, 36,285 non-firefighters, and 433 police officers. Twenty-nine birth defects were analyzed. In adjusted analyses, fathers of children with total anomalous pulmonary venous return (TAPVR; OR = 3.1; 95% CI = 1.1–8.7), cleft palate (OR = 1.8; 95% CI = 1.0–3.3), cleft lip (OR = 2.2; 95% CI = 1.2–4.2), and transverse limb deficiency (OR = 2.2; 95% CI = 1.1–4.7) were more likely than fathers of controls to be firefighters, versus non-firefighters. In police-referent analyses, fathers of children with cleft palate were 2.4 times more likely to be firefighters than fathers of controls (95% CI = 1.1–5.4). Conclusions: Paternal firefighting may be associated with an elevated risk of birth defects in offspring. Additional studies are warranted to replicate these findings. Further research may contribute to a greater understanding of the reproductive health of firefighters and their families for guiding workplace practices
Use of single photon emission computed tomography and magnetic resonance to evaluate central nervous system involvement in patients with juvenile systemic lupus erythematosus
- …