16,449 research outputs found
Three Applications of Instanton Numbers
We use instanton numbers to: (i) stratify moduli of vector bundles, (ii)
calculate relative homology of moduli spaces and (iii) distinguish curve
singularities.Comment: To appear in Communications in Mathematical Physic
Oddballs and a Low Odderon Intercept
We report an odderon Regge trajectory emerging from a field theoretical
Coulomb gauge QCD model for the odd signature JPC (P=C= -1) glueball states
(oddballs). The trajectory intercept is clearly smaller than the pomeron and
even the omega trajectory's intercept which provides an explanation for the
nonobservation of the odderon in high energy scattering data. To further
support this result we compare to glueball lattice data and also perform
calculations with an alternative model based upon an exact Hamiltonian
diagonalization for three constituent gluons.Comment: 4 pages, 2 figures, 1 tabl
A tensor instability in the Eddington inspired Born-Infeld Theory of Gravity
In this paper we consider an extension to Eddington's proposal for the
gravitational action. We study tensor perturbations of a homogeneous and
isotropic space-time in the Eddington regime, where modifications to Einstein
gravity are strong. We find that the tensor mode is linearly unstable deep in
the Eddington regime and discuss its cosmological implications.Comment: 5 pages, approved by Phys. Rev. D, additional references and minor
modification
Nonuniversal intensity correlations in 2D Anderson localizing random medium
Complex dielectric media often appear opaque because light traveling through
them is scattered multiple times. Although the light scattering is a random
process, different paths through the medium can be correlated encoding
information about the medium. Here, we present spectroscopic measurements of
nonuniversal intensity correlations that emerge when embedding quantum emitters
inside a disordered photonic crystal that is found to Anderson-localize light.
The emitters probe in-situ the microscopic details of the medium, and imprint
such near-field properties onto the far-field correlations. Our findings
provide new ways of enhancing light-matter interaction for quantum
electrodynamics and energy harvesting, and may find applications in
subwavelength diffuse-wave spectroscopy for biophotonics
Identificação molecular de fungos isolados de lesões necróticas de mancha branca do milho.
Edição dos resumos do 44º Congresso Brasileiro de Fitopatologia, 2011, Bento Gonçalves. Resumo 1378
Real-time evolution of a large-scale relativistic jet
Context. Astrophysical jets are ubiquitous in the Universe on all scales, but
their large-scale dynamics and evolution in time are hard to observe since they
usually develop at a very slow pace.
Aims. We aim to obtain the first observational proof of the expected
large-scale evolution and interaction with the environment in an astrophysical
jet. Only jets from microquasars offer a chance to witness the real-time,
full-jet evolution within a human lifetime, since they combine a 'short', few
parsec length with relativistic velocities.
Methods. The methodology of this work is based on a systematic recalibraton
of interferometric radio observations of microquasars available in public
archives. In particular, radio observations of the microquasar GRS 1758-258
over less than two decades have provided the most striking results.
Results. Significant morphological variations in the extended jet structure
of GRS 1758-258 are reported here that were previously missed. Its northern
radio lobe underwent a major morphological variation that rendered the hotspot
undetectable in 2001 and reappeared again in the following years. The reported
changes confirm the Galactic nature of the source. We tentatively interpret
them in terms of the growth of instabilities in the jet flow. There is also
evidence of surrounding cocoon. These results can provide a testbed for models
accounting for the evolution of jets and their interaction with the
environment.Comment: 5 pages, 3 figures, 2 tables. Accepted for publication in Astronomy
and Astrophysics Letter
The link between regularity and strong-pi-regularity
It is shown that if all powers of a ring element are regular, then will be strongly-pi-regular exactly when a suitable word in the powers of and their inner inverses is a unit.Research with financial support provided by the Research Centre of Mathematics of the University of Minho (CMAT) through the FCT Pluriannual Funding Program
A compositional semantics for Repairable Fault Trees with general distributions
Fault Tree Analysis (FTA) is a prominent technique in industrial and
scientific risk assessment. Repairable Fault Trees (RFT) enhance the classical
Fault Tree (FT) model by introducing the possibility to describe complex
dependent repairs of system components. Usual frameworks for analyzing FTs such
as BDD, SBDD, and Markov chains fail to assess the desired properties over RFT
complex models, either because these become too large, or due to cyclic
behaviour introduced by dependent repairs. Simulation is another way to carry
out this kind of analysis. In this paper we review the RFT model with Repair
Boxes as introduced by Daniele Codetta-Raiteri. We present compositional
semantics for this model in terms of Input/Output Stochastic Automata, which
allows for the modelling of events occurring according to general continuous
distribution. Moreover, we prove that the semantics generates (weakly)
deterministic models, hence suitable for discrete event simulation, and
prominently for Rare Event Simulation using the FIG tool
A Physical Limit to the Magnetic Fields of T Tauri Stars
Recent estimates of magnetic field strengths in T Tauri stars yield values
--. In this paper, I present an upper limit to the
photospheric values of by computing the equipartition values for different
surface gravities and effective temperatures. The values of derived from
the observations exceed this limit, and I examine the possible causes for this
discrepancy
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