4,167 research outputs found
Scalar meson spectroscopy: achievements and traps
Interactions in three coupled channels: pi-pi, K-anti K and sigma-sigma have
been investigated in a wide two-pion effective mass region from the pi-pi
threshold up to 1600 MeV. Analytical structure of amplitudes in all channels
has been studied. It was shown that its knowledge is necessary to understand
spectrum of scalar mesons and their nature.Comment: 6 pages, Invited talk at YITP Workshop on Possible Existence of the
sigma meson and it Implications to Hadron Physics (sigma-meson 2000), Kyoto,
Japan, 12-14 Jun 200
Elliptic solutions of isentropic ideal compressible fluid flow in (3 + 1) dimensions
A modified version of the conditional symmetry method, together with the classical method, is used to obtain new classes of elliptic solutions of the isentropic ideal compressible fluid flow in (3+1) dimensions. We focus on those types of solutions which are expressed in terms of the Weierstrass P-functions of Riemann invariants. These solutions are of special interest since we show that they remain bounded even when these invariants admit the gradient catastrophe. We describe in detail a procedure for constructing such classes of solutions. Finally, we present several examples of an application of our approach which includes bumps, kinks and multi-wave solutions
Multi-criteria scheduling of pipeline workflows
Mapping workflow applications onto parallel platforms is a challenging
problem, even for simple application patterns such as pipeline graphs. Several
antagonist criteria should be optimized, such as throughput and latency (or a
combination). In this paper, we study the complexity of the bi-criteria mapping
problem for pipeline graphs on communication homogeneous platforms. In
particular, we assess the complexity of the well-known chains-to-chains problem
for different-speed processors, which turns out to be NP-hard. We provide
several efficient polynomial bi-criteria heuristics, and their relative
performance is evaluated through extensive simulations
Reclaiming the energy of a schedule: models and algorithms
We consider a task graph to be executed on a set of processors. We assume
that the mapping is given, say by an ordered list of tasks to execute on each
processor, and we aim at optimizing the energy consumption while enforcing a
prescribed bound on the execution time. While it is not possible to change the
allocation of a task, it is possible to change its speed. Rather than using a
local approach such as backfilling, we consider the problem as a whole and
study the impact of several speed variation models on its complexity. For
continuous speeds, we give a closed-form formula for trees and series-parallel
graphs, and we cast the problem into a geometric programming problem for
general directed acyclic graphs. We show that the classical dynamic voltage and
frequency scaling (DVFS) model with discrete modes leads to a NP-complete
problem, even if the modes are regularly distributed (an important particular
case in practice, which we analyze as the incremental model). On the contrary,
the VDD-hopping model leads to a polynomial solution. Finally, we provide an
approximation algorithm for the incremental model, which we extend for the
general DVFS model.Comment: A two-page extended abstract of this work appeared as a short
presentation in SPAA'2011, while the long version has been accepted for
publication in "Concurrency and Computation: Practice and Experience
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How does the franchisor’s choice of different control mechanisms affect franchisees’ and employee-managers’ satisfaction?
Satisfaction of franchisees and employee-managers affects the overall performance of a franchise system. We argue that different actors in the same franchise system need to be treated in different ways. The franchisor’s choice of control mechanisms affects the satisfaction of franchisees and employee-managers differently. Drawing on data from the largest German franchise system, we show that the effectiveness of different control mechanisms depends on actor type and experience. Outcome control leads to higher satisfaction among franchisees and employee-managers, while behavior control enhances employee-managers’ satisfaction. Thereby, outcome control leads to higher satisfaction among more experienced franchisees, while behavior control enhances both highly and lowly experienced employee-managers’ satisfaction. Our results suggest that franchisors face a dilemma: On the one hand, behavior control is associated with high costs and has no impact on franchisees’ satisfaction at all. On the other hand, it might still be necessary to prevent franchisees from behaving opportunistically
Co-Scheduling Algorithms for High-Throughput Workload Execution
This paper investigates co-scheduling algorithms for processing a set of
parallel applications. Instead of executing each application one by one, using
a maximum degree of parallelism for each of them, we aim at scheduling several
applications concurrently. We partition the original application set into a
series of packs, which are executed one by one. A pack comprises several
applications, each of them with an assigned number of processors, with the
constraint that the total number of processors assigned within a pack does not
exceed the maximum number of available processors. The objective is to
determine a partition into packs, and an assignment of processors to
applications, that minimize the sum of the execution times of the packs. We
thoroughly study the complexity of this optimization problem, and propose
several heuristics that exhibit very good performance on a variety of
workloads, whose application execution times model profiles of parallel
scientific codes. We show that co-scheduling leads to to faster workload
completion time and to faster response times on average (hence increasing
system throughput and saving energy), for significant benefits over traditional
scheduling from both the user and system perspectives
Mesurer la résilience des ménages ruraux sénégalais : Une approche en termes de trajectoires et seuils de moyens d’existence
Full Text / Article completSince the 1970s, the consequences of climatic shocks have affected people in Senegalese rural areas. However, these populations aren’t passive when facing a major event and often try to resist. This is why we question the resilience of rural households. This paper aims to develop a theoretical and methodological approach of this concept. It mobilizes the sustainable livelihoods framework with livelihoods trajectories and livelihoods thresholds. The empirical part of this study focuses on two case studies in Senegalese rural areas (Niayes region and Groundnut Basin). Finally, we develop an household’s typology with three components: resilience, resistance and destitution. The results show the interest of a located resilience approach.Comment mesurer la résilience de ménages ruraux ? L’article aborde ce sujet complexe au travers de deux études de cas menées auprès de populations paysannes au Sénégal (bassin arachidier et zone des Niayes). Celles-ci sont marquées, depuis les années 1970, par une situation incertaine résultant principalement des aléas climatiques. Un constat qui amène un questionnement sur la possibilité d’une résilience locale. En mobilisant une approche sustainable livelihoods, la résilience est approchée par l’analyse des trajectoires des ménages, délimitées par des seuils de moyens d’existence. Nous en proposons une méthodologie d’élaboration et d’observation. La démarche d’enquête cible les chocs ayant eu un impact majeur dans la zone, pour conserver une temporalité longue dans l’étude des trajectoires. Pour terminer, une typologie de trajectoires de moyens d’existence sera présentée. Elle distingue les ménages résilients, des résistants et déchéants. Ceci nous permet de conclure sur la nécessité d’une approche d’une résilience située
The effects of bar-spiral coupling on stellar kinematics in the Galaxy
We investigate models of the Milky Way disc taking into account
simultaneously the bar and a two-armed quasi-static spiral pattern. Away from
major resonance overlaps, the mean stellar radial motions in the plane are
essentially a linear superposition of the isolated effects of the bar and
spirals. Thus, provided the bar is strong enough, even in the presence of
spiral arms, these mean radial motions are predominantly affected by the
Galactic bar for large scale velocity fluctuations. This is evident when
comparing the peculiar line-of-sight velocity power spectrum of our coupled
models with bar-only models. However, we show how forthcoming spectroscopic
surveys could disentangle bar-only non-axisymmetric models of the Galaxy from
models in which spiral arms have a significant amplitude. We also point out
that overlaps of low-order resonances are sufficient to enhance stellar
churning within the disc, even when the spirals amplitude is kept constant.
Nevertheless, for churning to be truly non-local, stronger or (more likely)
transient amplitudes would be needed: otherwise the disc is actually mostly
unaffected by churning in the present models. Finally, regarding vertical
breathing modes, the combined effect of the bar and spirals on vertical motions
is a clear non-linear superposition of the isolated effects of both components,
significantly superseding the linear superposition of modes produced by each
perturber separately, thereby providing an additional effect to consider when
analysing the observed breathing mode of the Galactic disc in the extended
Solar neighbourhood.Comment: 13 pages, 12 figures. MNRAS. Accepted for publication. v2 is the
published versio
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