612 research outputs found
Two-dimensional structures in the quintic Ginzburg-Landau equation
By using ZEUS cluster at Embry-Riddle Aeronautical University we perform
extensive numerical simulations based on a two-dimensional Fourier spectral
method Fourier spatial discretization and an explicit scheme for time
differencing) to find the range of existence of the spatiotemporal solitons of
the two-dimensional complex Ginzburg-Landau equation with cubic and quintic
nonlinearities. We start from the parameters used by Akhmediev {\it et. al.}
and slowly vary them one by one to determine the regimes where solitons exist
as stable/unstable structures. We present eight classes of dissipative solitons
from which six are known (stationary, pulsating, vortex spinning, filament,
exploding, creeping) and two are novel (creeping-vortex propellers and spinning
"bean-shaped" solitons). By running lengthy simulations for the different
parameters of the equation, we find ranges of existence of stable structures
(stationary, pulsating, circular vortex spinning, organized exploding), and
unstable structures (elliptic vortex spinning that leads to filament,
disorganized exploding, creeping). Moreover, by varying even the two initial
conditions together with vorticity, we find a richer behavior in the form of
creeping-vortex propellers, and spinning "bean-shaped" solitons. Each class
differentiates from the other by distinctive features of their energy
evolution, shape of initial conditions, as well as domain of existence of
parameters.Comment: 19 pages, 19 figures, 8 tables, updated text and reference
From Feynman Proof of Maxwell Equations to Noncommutative Quantum Mechanics
In 1990, Dyson published a proof due to Feynman of the Maxwell equations
assuming only the commutation relations between position and velocity. With
this minimal assumption, Feynman never supposed the existence of Hamiltonian or
Lagrangian formalism. In the present communication, we review the study of a
relativistic particle using ``Feynman brackets.'' We show that Poincar\'e's
magnetic angular momentum and Dirac magnetic monopole are the consequences of
the structure of the Lorentz Lie algebra defined by the Feynman's brackets.
Then, we extend these ideas to the dual momentum space by considering
noncommutative quantum mechanics. In this context, we show that the
noncommutativity of the coordinates is responsible for a new effect called the
spin Hall effect. We also show its relation with the Berry phase notion. As a
practical application, we found an unusual spin-orbit contribution of a
nonrelativistic particle that could be experimentally tested. Another practical
application is the Berry phase effect on the propagation of light in
inhomogeneous media.Comment: Presented at the 3rd Feynman Festival (Collage Park, Maryland,
U.S.A., August 2006
Interrupt Timed Automata: verification and expressiveness
We introduce the class of Interrupt Timed Automata (ITA), a subclass of
hybrid automata well suited to the description of timed multi-task systems with
interruptions in a single processor environment. While the reachability problem
is undecidable for hybrid automata we show that it is decidable for ITA. More
precisely we prove that the untimed language of an ITA is regular, by building
a finite automaton as a generalized class graph. We then establish that the
reachability problem for ITA is in NEXPTIME and in PTIME when the number of
clocks is fixed. To prove the first result, we define a subclass ITA- of ITA,
and show that (1) any ITA can be reduced to a language-equivalent automaton in
ITA- and (2) the reachability problem in this subclass is in NEXPTIME (without
any class graph). In the next step, we investigate the verification of real
time properties over ITA. We prove that model checking SCL, a fragment of a
timed linear time logic, is undecidable. On the other hand, we give model
checking procedures for two fragments of timed branching time logic. We also
compare the expressive power of classical timed automata and ITA and prove that
the corresponding families of accepted languages are incomparable. The result
also holds for languages accepted by controlled real-time automata (CRTA), that
extend timed automata. We finally combine ITA with CRTA, in a model which
encompasses both classes and show that the reachability problem is still
decidable. Additionally we show that the languages of ITA are neither closed
under complementation nor under intersection
Monopole and Berry Phase in Momentum Space in Noncommutative Quantum Mechanics
To build genuine generators of the rotations group in noncommutative quantum
mechanics, we show that it is necessary to extend the noncommutative parameter
to a field operator, which one proves to be only momentum dependent.
We find consequently that this field must be obligatorily a dual Dirac monopole
in momentum space. Recent experiments in the context of the anomalous Hall
effect provide for a monopole in the crystal momentum space. We suggest a
connection between the noncommutative field and the Berry curvature in momentum
space which is at the origine of the anomalous Hall effect.Comment: 4 page
Intrauterine crowding impairs formation and growth of secondary myofibers in pigs
There are indications that intrauterine crowding may cause intrauterine growth retardation with the possibility of an impaired myofiber hyperplasia. The aim of the study was to confirm this by generating large differences in uterine space using sows that were unilaterally hysterectomized-ovariectomized (HO; crowded) or unilaterally oviduct ligated (OL; non-crowded). In the study, seven HO and seven OL Swiss Large White third parity sows were used. At farrowing, litter size and litter birth weight were determined. Subsequently, within each litter two male and two female progenies each with the respectively lowest (L) and highest (H) birth weight were sacrificed. Internal organs and brain were weighed, and longissimus (LM) and semitendinosus muscle (SM) samples were collected. Histological analyses were performed in both muscles using mATPase staining after preincubation at pH 4.3 and 10.2. Myosin heavy chain (MyHC) polymorphism was determined in the LM by means of SDS-PAGE. The number of piglets born alive was similar in both sow groups, but litter size expressed per uterine horn was lower (P < 0.05) in OL than HO sows. Consequently, OL progeny were markedly heavier (P < 0.01). Regardless of gender, the organs, the brain and the SM were heavier (P < 0.001) in OL and H compared with HO and L offspring, respectively. Compared with HO pigs, the SM of OL offspring tended (P < 0.1) to have more myofibers, which were of larger (P < 0.05) size. However, myofiber density appeared to be lower (P < 0.1) in the SM of OL than HO pigs. The impact of birth weight on myofiber characteristics was limited to the lower (P < 0.05) myofiber density in the SM and the larger (P < 0.01) myofiber size in the light portion of the SM of H than L offspring, whereas myofiber hyperplasia did not differ between birth weight categories. The SM, but not the LM, of male offspring had a greater (P < 0.05) myofiber density. This did not affect total SM myofiber number. The relative abundance of fetal and type I MyHC in the LM was lower (P < 0.05) and that of type II MyHC was greater (P < 0.001) in OL than HO pigs. The current data suggest that regardless of birth weight and gender, in the LM and SM of individuals born from a crowded environment, not only hyperplasia but also hypertrophy of myofibers is impaired and their maturity seems delaye
Novel phages of Pseudomonas syringae unveil numerous potential auxiliary metabolic genes.
Relatively few phages that infect plant pathogens have been isolated and investigated. The Pseudomonas syringae species complex is present in various environments, including plants. It can cause major crop diseases, such as bacterial canker on apricot trees. This study presents a collection of 25 unique phage genomes that infect P. syringae. These phages were isolated from apricot orchards with bacterial canker symptoms after enrichment with 21 strains of P. syringae. This collection comprises mostly virulent phages, with only three being temperate. They belong to 14 genera, 11 of which are newly discovered, and 18 new species, revealing great genetic diversity within this collection. Novel DNA packaging systems have been identified bioinformatically in one of the new phage species, but experimental confirmation is required to define the precise mechanism. Additionally, many phage genomes contain numerous potential auxiliary metabolic genes with diversified putative functions. At least three phages encode genes involved in bacterial tellurite resistance, a toxic metalloid. This suggests that viruses could play a role in bacterial stress tolerance. This research emphasizes the significance of continuing the search for new phages in the agricultural ecosystem to unravel novel ecological diversity and new gene functions. This work contributes to the foundation for future fundamental and applied research on phages infecting phytopathogenic bacteria
Last passage percolation and traveling fronts
We consider a system of N particles with a stochastic dynamics introduced by
Brunet and Derrida. The particles can be interpreted as last passage times in
directed percolation on {1,...,N} of mean-field type. The particles remain
grouped and move like a traveling wave, subject to discretization and driven by
a random noise. As N increases, we obtain estimates for the speed of the front
and its profile, for different laws of the driving noise. The Gumbel
distribution plays a central role for the particle jumps, and we show that the
scaling limit is a L\'evy process in this case. The case of bounded jumps
yields a completely different behavior
Special K\"ahler-Ricci potentials on compact K\"ahler manifolds
A special K\"ahler-Ricci potential on a K\"ahler manifold is any nonconstant
function such that is a Killing vector field
and, at every point with , all nonzero tangent vectors orthogonal
to and are eigenvectors of both and
the Ricci tensor. For instance, this is always the case if is a
nonconstant function on a K\"ahler manifold of complex
dimension and the metric , defined wherever , is Einstein. (When such exists, may be called {\it
almost-everywhere conformally Einstein}.) We provide a complete classification
of compact K\"ahler manifolds with special K\"ahler-Ricci potentials and use it
to prove a structure theorem for compact K\"ahler manifolds of any complex
dimension which are almost-everywhere conformally Einstein.Comment: 45 pages, AMSTeX, submitted to Journal f\"ur die reine und angewandte
Mathemati
Quantitative information flow, with a view
We put forward a general model intended for assessment of system security against passive eavesdroppers, both quantitatively ( how much information is leaked) and qualitatively ( what properties are leaked). To this purpose, we extend information hiding systems ( ihs ), a model where the secret-observable relation is represented as a noisy channel, with views : basically, partitions of the state-space. Given a view W and n independent observations of the system, one is interested in the probability that a Bayesian adversary wrongly predicts the class of W the underlying secret belongs to. We offer results that allow one to easily characterise the behaviour of this error probability as a function of the number of observations, in terms of the channel matrices defining the ihs and the view W . In particular, we provide expressions for the limit value as n → ∞, show by tight bounds that convergence is exponential, and also characterise the rate of convergence to predefined error thresholds. We then show a few instances of statistical attacks that can be assessed by a direct application of our model: attacks against modular exponentiation that exploit timing leaks, against anonymity in mix-nets and against privacy in sparse datasets
Bounded Determinization of Timed Automata with Silent Transitions
Deterministic timed automata are strictly less expressive than their
non-deterministic counterparts, which are again less expressive than those with
silent transitions. As a consequence, timed automata are in general
non-determinizable. This is unfortunate since deterministic automata play a
major role in model-based testing, observability and implementability. However,
by bounding the length of the traces in the automaton, effective
determinization becomes possible. We propose a novel procedure for bounded
determinization of timed automata. The procedure unfolds the automata to
bounded trees, removes all silent transitions and determinizes via disjunction
of guards. The proposed algorithms are optimized to the bounded setting and
thus are more efficient and can handle a larger class of timed automata than
the general algorithms. The approach is implemented in a prototype tool and
evaluated on several examples. To our best knowledge, this is the first
implementation of this type of procedure for timed automata.Comment: 25 page
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