2,322 research outputs found
An introduction to Multitrace Formulations and Associated Domain Decomposition Solvers
Multitrace formulations (MTFs) are based on a decomposition of the problem
domain into subdomains, and thus domain decomposition solvers are of interest.
The fully rigorous mathematical MTF can however be daunting for the
non-specialist. We introduce in this paper MTFs on a simple model problem using
concepts familiar to researchers in domain decomposition. This allows us to get
a new understanding of MTFs and a natural block Jacobi iteration, for which we
determine optimal relaxation parameters. We then show how iterative multitrace
formulation solvers are related to a well known domain decomposition method
called optimal Schwarz method: a method which used Dirichlet to Neumann maps in
the transmission condition. We finally show that the insight gained from the
simple model problem leads to remarkable identities for Calderon projectors and
related operators, and the convergence results and optimal choice of the
relaxation parameter we obtained is independent of the geometry, the space
dimension of the problem{\color{black}, and the precise form of the spatial
elliptic operator, like for optimal Schwarz methods. We illustrate our analysis
with numerical experiments
Fiscal Regime Shifts in Portugal
We estimate changes in fiscal policy regimes in Portugal with a Markov Switching regression of fiscal policy rules for the period 1978-2007, using a new dataset of fiscal quarterly series. We find evidence of a deficit bias, while repeated reversals of taxes making the budget procyclical. Economic booms have typically been used to relax tax pressure, especially during elections. One-off measures have been preferred over structural ones to contain the deficit during economic crises. The EU fiscal rules prompted temporary consolidation, but did not permanently change the budgeting process.fiscal regimes, Markov Switching, Portugal.
Fiscal Regime Shifts in Portugal
We estimate changes in fiscal policy regimes in Portugal with a Markov Switching regression of fiscal policy rules for the period 1978-2007, using a new dataset of fiscal quarterly series. We find evidence of a deficit bias, while repeated reversals of taxes making the budget procyclical. Economic booms have typically been used to relax tax pressure, especially during elections. One-off measures have been preferred over structural ones to contain the deficit during economic crises. The EU fiscal rules prompted temporary consolidation, but did not permanently change the budgeting process.fiscal regimes, Markov Switching, Portugal.
QoE-centric management of advanced multimedia services
Over the last years, multimedia content has become more prominent than ever. Particularly, video streaming is responsible for more than a half of the total global bandwidth consumption on the Internet. As the original Internet was not designed to deliver such real-time, bandwidth-consuming applications, a serious challenge is posed on how to efficiently provide the best service to the users. This requires a shift in the classical approach used to deliver multimedia content, from a pure Quality of Service (QoS) to a full Quality of Experience (QoE) perspective. While QoS parameters are mainly related to low-level network aspects, the QoE reflects how the end-users perceive a particular multimedia service. As the relationship between QoS parameters and QoE is far from linear, a classical QoS-centric delivery is not able to fully optimize the quality as perceived by the users. This paper provides an overview of the main challenges this PhD aims to tackle in the field of end-to-end QoE optimization of video streaming services and, more precisely, of HTTP Adaptive Streaming (HAS) solutions, which are quickly becoming the de facto standard for video delivery over the Internet
The existence of a real pole-free solution of the fourth order analogue of the Painleve I equation
We establish the existence of a real solution y(x,T) with no poles on the
real line of the following fourth order analogue of the Painleve I equation,
x=Ty-({1/6}y^3+{1/24}(y_x^2+2yy_{xx})+{1/240}y_{xxxx}). This proves the
existence part of a conjecture posed by Dubrovin. We obtain our result by
proving the solvability of an associated Riemann-Hilbert problem through the
approach of a vanishing lemma. In addition, by applying the Deift/Zhou
steepest-descent method to this Riemann-Hilbert problem, we obtain the
asymptotics for y(x,T) as x\to\pm\infty.Comment: 27 pages, 5 figure
Progenitors of Supernovae Type Ia
Despite the significance of Type Ia supernovae (SNeIa) in many fields in
astrophysics, SNeIa lack a theoretical explanation. The standard scenarios
involve thermonuclear explosions of carbon/oxygen white dwarfs approaching the
Chandrasekhar mass; either by accretion from a companion or by a merger of two
white dwarfs. We investigate the contribution from both channels to the SNIa
rate with the binary population synthesis (BPS) code SeBa in order to constrain
binary processes such as the mass retention efficiency of WD accretion and
common envelope evolution. We determine the theoretical rates and delay time
distribution of SNIa progenitors and in particular study how assumptions affect
the predicted rates.Comment: 6 pages, 6 figures, appeared in proceedings for "The 18th European
White Dwarf Workshop
Proprioceptive changes impair balance control in individuals with chronic obstructive pulmonary disease
Copyright @ 2013 Janssens et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Introduction: Balance deficits are identified as important risk factors for falling in individuals with chronic obstructive pulmonary disease (COPD). However, the specific use of proprioception, which is of primary importance during balance control, has not been studied in individuals with COPD. The objective was to determine the specific proprioceptive control strategy during postural balance in individuals with COPD and healthy controls, and to assess whether this was related to inspiratory muscle weakness. Methods: Center of pressure displacement was determined in 20 individuals with COPD and 20 age/gender-matched controls during upright stance on an unstable support surface without vision. Ankle and back muscle vibration were applied to evaluate the relative contribution of different proprioceptive signals used in postural control. Results: Individuals with COPD showed an increased anterior-posterior body sway during upright stance (p=0.037). Compared to controls, individuals with COPD showed an increased posterior body sway during ankle muscle vibration (p=0.047), decreased anterior body sway during back muscle vibration (p=0.025), and increased posterior body sway during simultaneous ankle-muscle vibration (p=0.002). Individuals with COPD with the weakest inspiratory muscles showed the greatest reliance on ankle muscle input when compared to the stronger individuals with COPD (p=0.037). Conclusions: Individuals with COPD, especially those with inspiratory muscle weakness, increased their reliance on ankle muscle proprioceptive signals and decreased their reliance on back muscle proprioceptive signals during balance control, resulting in a decreased postural stability compared to healthy controls. These proprioceptive changes may be due to an impaired postural contribution of the inspiratory muscles to trunk stability. Further research is required to determine whether interventions such as proprioceptive training and inspiratory muscle training improve postural balance and reduce the fall risk in individuals with COPD.This work was supported by the Research Foundation – Flanders (FWO) grants 1.5.104.03, G.0674.09, G.0598.09N and G.0871.13N
Asymptotics for a special solution to the second member of the Painleve I hierarchy
We study the asymptotic behavior of a special smooth solution y(x,t) to the
second member of the Painleve I hierarchy. This solution arises in random
matrix theory and in the study of Hamiltonian perturbations of hyperbolic
equations. The asymptotic behavior of y(x,t) if x\to \pm\infty (for fixed t) is
known and relatively simple, but it turns out to be more subtle when x and t
tend to infinity simultaneously. We distinguish a region of algebraic
asymptotic behavior and a region of elliptic asymptotic behavior, and we obtain
rigorous asymptotics in both regions. We also discuss two critical transitional
asymptotic regimes.Comment: 19 page
Quality of high dimensional numerical “Space filling designs” for the sensitivity analysis of interference optical filters
AbstractIn the field of computer experiments, when the relations between the outputs and the inputs of the computer code are complex, the Space Filling Designs (SFD) are used to study the outputs all over the domain or to build metamodels. We introduce here the results of SFD quality obtained in high dimensional case by the methodology of Minimum Spanning Tree (MST). Then, different SFD are used for the sensitivity analysis of interference optical filters. The intrinsic quality of SFD is assessed by MST criterion and is proved to be in accordance with the results of the optical filter sensitivity analysis. This study can be considered as a first step to connect intrinsic quality and extrinsic quality of SFD designs
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