Convex Hull of Arithmetic Automata

Arithmetic automata recognize infinite words of digits denoting decompositions of real and integer vectors. These automata are known expressive and efficient enough to represent the whole set of solutions of complex linear constraints combining both integral and real variables. In this paper, the closed convex hull of arithmetic automata is proved rational polyhedral. Moreover an algorithm computing the linear constraints defining these convex set is provided. Such an algorithm is useful for effectively extracting geometrical properties of the whole set of solutions of complex constraints symbolically represented by arithmetic automata

Effect of Roadside Vegetation Cutting on Moose Browsing

Moose (Alces americanus ) vehicle collisions (MVCs) are an issue throughout the distribution of moose. Many mitigation strategies have been tested and implemented to reduce the number of MVCs, but there have been few empirical analyses of the effectiveness of roadside vegetation cutting. The goal of this study was to determine if roadside vegetation cutting attracted moose into roadside areas to browse on the vegetation regrowth. We hypothesized that moose would be attracted to roadside areas with cut vegetation. Consequently, we predicted that there would be higher levels of browsing in cut areas compared to uncut areas. To determine if moose were browsing more in cut or uncut areas, we measured the number of plants browsed by moose in paired treatment (cut on or after 2008) and control (not cut since at least 2008) sites, along with a suite of potential environmental covariates. Using a model selection approach, we fit generalized linear mixed-effects models to determine the most parsimonious set of environmental variables to explain variation in the proportion of moose browse among sites. In contrast to our hypothesis, our results show that the proportion of moose browse in the uncut control areas was significantly higher than in the cut treatment areas. The results of this study suggest that recently cut roadside areas (7 years or less based on our work) may create a less attractive foraging habitat for moose. The majority of the variance in the proportion of moose browse among sites was explained by treatment type and nested plot number within site identification (34.16%), with additional variance explained by traffic region (5.00%) and moose density (4.35%). Based on our study, we recommend that vegetation cutting be continued in roadside areas in Newfoundland as recently cut areas may be less attractive browsing sites for moose

La gouvernance locale du microcrédit professionnel entre jeux de proximités et lock in effect

National audienc

Les associations d'aide à la personne face à la règle de concurrence.Enjeux de légitimité territoriale et renouvellement des proximités

1National audienc

Nouvelle régulation concurrentielle et nouveaux jeux de proximités. Les associations d’aide à la personne à la reconquête de leur légitimité territoriale

The French home care services, organized around non-for-profit organizations, have been changed by the introduction of a new competitive regulation in 2005. Previously, these organizations were agreeing to share territories. They were benefiting from a strong territorial legitimacy, thus constituting territorial monopolies. These monopolies were based on both geographical and organized proximities, linked to the geographical constraints of such an activity and to the historical ties developed with local actors. Face to competition, their territorial legitimacy is today at stake. This article shows that non-for-profit organizations seek to establish their legitimacy by developing new proximity arrangements according to the departmental different policies and to the competitive intensity resulting from these policies. So the organized proximity is crucial in this process. It can be based on one hand on non-rivalry and non-intrusion agreements. On the other hand it can rely on rules aiming at the absorption of the weakest non-for-profit organizations

La stratégie des associations d'aide à la personne face à la nouvelle réglementation : coalitions stratégiques et re-territorialisation des activités

Date du colloque : 2009/06International audienc

Efficient Algorithms for Asymptotic Bounds on Termination Time in VASS

Vector Addition Systems with States (VASS) provide a well-known and fundamental model for the analysis of concurrent processes, parameterized systems, and are also used as abstract models of programs in resource bound analysis. In this paper we study the problem of obtaining asymptotic bounds on the termination time of a given VASS. In particular, we focus on the practically important case of obtaining polynomial bounds on termination time. Our main contributions are as follows: First, we present a polynomial-time algorithm for deciding whether a given VASS has a linear asymptotic complexity. We also show that if the complexity of a VASS is not linear, it is at least quadratic. Second, we classify VASS according to quantitative properties of their cycles. We show that certain singularities in these properties are the key reason for non-polynomial asymptotic complexity of VASS. In absence of singularities, we show that the asymptotic complexity is always polynomial and of the form $\Theta(n^k)$, for some integer $k\leq d$, where $d$ is the dimension of the VASS. We present a polynomial-time algorithm computing the optimal $k$. For general VASS, the same algorithm, which is based on a complete technique for the construction of ranking functions in VASS, produces a valid lower bound, i.e., a $k$ such that the termination complexity is $\Omega(n^k)$. Our results are based on new insights into the geometry of VASS dynamics, which hold the potential for further applicability to VASS analysis.Comment: arXiv admin note: text overlap with arXiv:1708.0925

The Social Biology of Quorum Sensing in a Naturalistic Host Pathogen System.

SummaryMany microorganisms cooperate by secreting products that are commonly available to neighboring cells. These “public goods” include autoinduced, quorum-sensing (QS) molecules and the virulence factors activated by these signals [1–4]. Public goods cooperation is exploitable by cheaters, cells that avoid the costs of production but gain an advantage by freeloading on the products of others [5–8]. QS signals and responses can be cooperative under artificial laboratory conditions [1–4, 9], but it remains unclear whether QS is cooperative in nature: little is known about the frequency of cheaters in natural populations [10, 11], and cheaters may do poorly because of the importance of QS in major transcriptional networks [12–14]. Here, we investigate the cooperative nature of QS in a natural system: the Gram-positive insect pathogen Bacillus thuringiensis and the larvae of the diamondback moth, Plutella xylostella. Although we find evidence of cooperation, QS null mutants are not effective cheats in vivo and cannot outcompete wild-type strains. We show that spatial structure limits mutant fitness and that well-separated microcolonies occur in vivo because of the strong population bottlenecks occurring during natural infection. We argue that spatial structure and low densities are the norm in early-stage infections, and this can explain why QS cheaters are rare in B. thuringiensis and its relatives [10]. These results contrast with earlier experiments describing the high fitness of Gram-negative QS cheaters and suggest that QS suppression (“quorum quenching”) can be clinically effective without having negative impacts on the evolution of virulence

Three-dimensional imaging and detection efficiency performance of orthogonal coplanar CZT strip detectors

We report on recent three-dimensional imaging performance and detection efficiency measurements obtained with 5 mm thick prototype CdZnTe detectors fabricated with orthogonal coplanar anode strips. In previous work, we have shown that detectors fabricated using this design achieve both very good energy resolution and sub-millimeter spatial resolution with fewer electronic channels than are required for pixel detectors. As electron-only devices, like pixel detectors, coplanar anode strip detectors can be fabricated in the thickness required to be effective imagers for photons with energies in excess of 500 keV. Unlike conventional double-sided strip detectors, the coplanar anode strip detectors require segmented contacts and signal processing electronics on only one surface. The signals can be processed to measure the total energy deposit and the photon interaction location in three dimensions. The measurements reported here provide a quantitative assessment of the detection capabilities of orthogonal coplanar anode strip detectors