141,227 research outputs found
The Cauchy problem for the Pavlov equation
Commutation of multidimensional vector fields leads to integrable nonlinear
dispersionless PDEs arising in various problems of mathematical physics and
intensively studied in the recent literature. This report is aiming to solve
the scattering and inverse scattering problem for integrable dispersionless
PDEs, recently introduced just at a formal level, concentrating on the
prototypical example of the Pavlov equation, and to justify an existence
theorem for global bounded solutions of the associated Cauchy problem with
small data.Comment: In the new version the analytical technique was essentially revised.
The previous version contained a wrong statement about the solvability of the
inverse problem for large data. This problem remains ope
Model checking probabilistic and stochastic extensions of the pi-calculus
We present an implementation of model checking for probabilistic and stochastic extensions of the pi-calculus, a process algebra which supports modelling of concurrency and mobility. Formal verification techniques for such extensions have clear applications in several domains, including mobile ad-hoc network protocols, probabilistic security protocols and biological pathways. Despite this, no implementation of automated verification exists. Building upon the pi-calculus model checker MMC, we first show an automated procedure for constructing the underlying semantic model of a probabilistic or stochastic pi-calculus process. This can then be verified using existing probabilistic model checkers such as PRISM. Secondly, we demonstrate how for processes of a specific structure a more efficient, compositional approach is applicable, which uses our extension of MMC on each parallel component of the system and then translates the results into a high-level modular description for the PRISM tool. The feasibility of our techniques is demonstrated through a number of case studies from the pi-calculus literature
Risk of acute myocardial infarction with nonselective non-steroidal anti-inflammatory drugs: a meta-analysis
The use of cyclo-oxygenase 2 selective nonsteroidal anti-inflammatory drugs (NSAIDs) is associated with increased risk of acute myocardial infarction (AMI). The association between the risks of AMI with nonselective NSAIDs is less clear. We reviewed the published evidence and assessed the risk of AMI with nonselective NSAIDs. We performed a meta-analysis of all studies containing data from population databases that compared the risk of AMI in NSAID users with that in non-users or remote NSAID users. The primary outcome was objectively confirmed AMI. Fourteen studies met predefined criteria for inclusion in the meta-analysis. Nonselective NSAIDs as a class was associated with increased AMI risk (relative AMI risk 1.19, 95% confidence interval [CI] 1.08 to 1.31). Similar findings were found with diclofenac (relative AMI risk 1.38, 95% CI 1.22–1.57) and ibuprofen (relative AMI risk 1.11, 95% CI 1.06 to 1.17). However, this effect was not observed with naproxen (relative AMI risk 0.99, 95% CI 0.88–1.11). In conclusion, based on current evidence, there is a general direction of effect, which suggests that at least some nonselective NSAIDs increase AMI risk. Analysis based on the limited data available for individual NSAIDs, including diclofenac and ibuprofen, supported this finding; however, this was not the case for naproxen. Nonselective NSAIDs are frequently prescribed, and so further investigation into the risk of AMI is warranted because the potential for harm can be substantial
Pion Form Factor in the Factorization Formalism
Based on the light-cone (LC) framework and the factorization formalism,
the transverse momentum effects and the different helicity components'
contributions to the pion form factor are recalculated. In
particular, the contribution to the pion form factor from the higher helicity
components (), which come from the spin-space Wigner
rotation, are analyzed in the soft and hard energy regions respectively. Our
results show that the right power behavior of the hard contribution from the
higher helicity components can only be obtained by fully keeping the
dependence in the hard amplitude, and that the dependence in LC wave
function affects the hard and soft contributions substantially. As an example,
we employ a model LC wave function to calculate the pion form factor and then
compare the numerical predictions with the experimental data. It is shown that
the soft contribution is less important at the intermediate energy region.Comment: 21 pages, 4 figure
Theory of point contact spectroscopy in electron-doped cuprates
In the hole-doped -wave cuprate superconductor, due to the
midgap surface state (MSS), a zero bias conductance peak (ZBCP) is widely
observed in [110] interface point contact spectroscopy (PCS). However, ZBCP of
this geometry is rarely observed in the electron-doped cuprates, even though
their pairing symmetry is still likely the -wave. We argue
that this is due to the coexistence of antiferromagnetic (AF) and the
superconducting (SC) orders. Generalizing the Blonder-Tinkham-Klapwijk (BTK)
formula to include an AF coupling, it is shown explicitly that the MSS is
destroyed by the AF order. The calculated PCS is in good agreement with the
experiments.Comment: 5 pages, 2 figures. Replaced with published versio
Two-dimensional Poisson Trees converge to the Brownian web
The Brownian web can be roughly described as a family of coalescing
one-dimensional Brownian motions starting at all times in and at all
points of . It was introduced by Arratia; a variant was then studied by
Toth and Werner; another variant was analyzed recently by Fontes, Isopi, Newman
and Ravishankar. The two-dimensional \emph{Poisson tree} is a family of
continuous time one-dimensional random walks with uniform jumps in a bounded
interval. The walks start at the space-time points of a homogeneous Poisson
process in and are in fact constructed as a function of the point
process. This tree was introduced by Ferrari, Landim and Thorisson. By
verifying criteria derived by Fontes, Isopi, Newman and Ravishankar, we show
that, when properly rescaled, and under the topology introduced by those
authors, Poisson trees converge weakly to the Brownian web.Comment: 22 pages, 1 figure. This version corrects an error in the previous
proof. The results are the sam
Advanced solutions for quality-oriented multimedia broadcasting
Multimedia content is increasingly being delivered via different types of networks to viewers in a variety of locations and contexts using a variety of devices. The ubiquitous nature of multimedia services comes at a cost, however. The successful delivery of multimedia services will require overcoming numerous technological challenges many of which have a direct effect on the quality of the multimedia experience. For example, due to dynamically changing requirements and networking conditions, the delivery of multimedia content has traditionally adopted a best effort approach. However, this approach has often led to the end-user perceived quality of multimedia-based services being negatively affected. Yet the quality of multimedia content is a vital issue for the continued acceptance and proliferation of these services. Indeed, end-users are becoming increasingly quality-aware in their expectations of multimedia experience and demand an ever-widening spectrum of rich multimedia-based services. As a consequence, there is a continuous and extensive research effort, by both industry and academia, to find solutions for improving the quality of multimedia content delivered to the users; as well, international standards bodies, such as the International Telecommunication Union (ITU), are renewing their effort on the standardization of multimedia technologies. There are very different directions in which research has attempted to find solutions in order to improve the quality of the rich media content delivered over various network types. It is in this context that this special issue on broadcast multimedia quality of the IEEE Transactions on Broadcasting illustrates some of these avenues and presents some of the most significant research results obtained by various teams of researchers from many countries. This special issue provides an example, albeit inevitably limited, of the richness and breath of the current research on multimedia broadcasting services. The research i- - ssues addressed in this special issue include, among others, factors that influence user perceived quality, encoding-related quality assessment and control, transmission and coverage-based solutions and objective quality measurements
- …