Pair Density Waves in coupled doped two-leg Ladders

Motivated by Resonant X-ray scattering experiments in cuprate ladder materials showing charge order modulation of period $\lambda=3$ and 5 at specific hole densities, we investigate models involving the electronic t-J ladders and bosonic chains coupled via screened Coulomb repulsion. Extensive density matrix renormalization group calculations applied to the ladders/chains supplemented by a self-consistent mean-field treatment of the inter-ladder/chain coupling provide quantitative estimates of the charge order for $\lambda=3,4$ and 5. As previously proposed, such patterns correspond to the emergence of pair density waves which stem from the strong electronic correlations. We comment on the existence of a $\lambda=4$ modulation not seen so far in experiment.Comment: 4 pages, 4 figure

Formal Verification of Real-time Systems with Preemptive Scheduling

International audienceIn this paper, we propose a method for the verification of timed properties for real-time systems featuring a preemptive scheduling policy: the system, modeled as a scheduling time Petri net, is first translated into a linear hybrid automaton to which it is time-bisimilar. Timed properties can then be verified using HyTech. The efficiency of this approach leans on two major points: first, the translation features a minimization of the number of variables (clocks) of the resulting automaton, which is a critical parameter for the efficiency of the ensuing verification. Second, the translation is performed by an over-approximating algorithm, which is based on Difference Bound Matrix and therefore efficient, that nonetheless produces a time-bisimilar automaton despite the over-approximation. The proposed modeling and verification method are generic enough to account for many scheduling policies. In this paper, we specifically show how to deal with Fixed Priority and Earliest Deadline First policies, with the possibility of using Round-Robin for tasks with the same priority. We have implemented the method and give some experimental results illustrating its efficiency

Énergie et climat : défis et innovations

Access to energy is a key factor in the economic development of countries. We will first examine the evolution of different ways to access to energy and their correlations with world population and countries’ GDP. We will see that the objectives of reducing carbon dioxide emissions which require a profound transformation of our access to energy will be very difficult to achieve. We will also see that the thermal improvement of buildings, and in particular the renovation of existing housing, is one of the possible objective

Énergie et climat : défis et innovations

Access to energy is a key factor in the economic development of countries. We will first examine the evolution of different ways to access to energy and their correlations with world population and countries’ GDP. We will see that the objectives of reducing carbon dioxide emissions which require a profound transformation of our access to energy will be very difficult to achieve. We will also see that the thermal improvement of buildings, and in particular the renovation of existing housing, is one of the possible objective

Dense Integer-Complete Synthesis for Bounded Parametric Timed Automata

Ensuring the correctness of critical real-time systems, involving concurrent behaviors and timing requirements, is crucial. Timed automata extend finite-state automata with clocks, compared in guards and invariants with integer constants. Parametric timed automata (PTAs) extend timed automata with timing parameters. Parameter synthesis aims at computing dense sets of valuations for the timing parameters, guaranteeing a good behavior. However, in most cases, the emptiness problem for reachability (i.e., whether the emptiness of the parameter valuations set for which some location is reachable) is undecidable for PTAs and, as a consequence, synthesis procedures do not terminate in general, even for bounded parameters. In this paper, we introduce a parametric extrapolation, that allows us to derive an underapproximation in the form of linear constraints containing not only all the integer points ensuring reachability, but also all the (non-necessarily integer) convex combinations of these integer points, for general PTAs with a bounded parameter domain. We also propose two further algorithms synthesizing parameter valuations guaranteeing unavoidability, and preservation of the untimed behavior w.r.t. a reference parameter valuation, respectively. Our algorithms terminate and can output constraints arbitrarily close to the complete result. We demonstrate their applicability and efficiency using the tool Rom\'eo on two classical benchmarks.Comment: This is an extended version of the paper by the same authors published in the proceedings of the 9th International Workshop on Reachability Problems (RP 2015

Coverability Synthesis in Parametric Petri Nets

We study Parametric Petri Nets (PPNs), i.e., Petri nets for which some arc weights can be parameters. In that setting, we address a problem of parameter synthesis, which consists in computing the exact set of values for the parameters such that a given marking is coverable in the instantiated net. Since the emptiness of that solution set is already undecidable for general PPNs, we address a special case where parameters are used only as input weights (preT-PPNs), and consequently for which the solution set is downward-closed. To this end, we invoke a result for the representation of upward closed set from Valk and Jantzen. To use this procedure, we show we need to decide universal coverability, that is decide if some marking is coverable for every possible values of the parameters. We therefore provide a proof of its EXPSPACE-completeness, thus settling the previously open problem of its decidability. We also propose an adaptation of this reasoning to the case of parameters used only as output weights (postT-PPNs). In this case, the condition to use this procedure can be reduced to the decidability of the existential coverability, that is decide if there exists values of the parameters making a given marking coverable. This problem is known decidable but we provide here a cleaner proof, providing its EXPSPACE-completeness, by reduction to Omega Petri Nets

Evolution and diversity of the Microviridae viral family through a collection of 81 new complete genomes assembled from virome reads.

International audienceRecent studies suggest that members of the Microviridae (a family of ssDNA bacteriophages) might play an important role in a broad spectrum of environments, as they were found in great number among the viral fraction from seawater and human gut samples. 24 completely sequenced Microviridae have been described so far, divided into three distinct groups named Microvirus, Gokushovirinae and Alpavirinae, this last group being only composed of prophages. In this study, we present the analysis of 81 new complete Microviridae genomes, assembled from viral metagenomes originating from various ecosystems. The phylogenetic analysis of the core genes highlights the existence of four groups, confirming the three sub-families described so far and exhibiting a new group, named Pichovirinae. The genomic organizations of these viruses are strikingly coherent with their phylogeny, the Pichovirinae being the only group of this family with a different organization of the three core genes. Analysis of the structure of the major capsid protein reveals the presence of mushroom-like insertions conserved within all the groups except for the microviruses. In addition, a peptidase gene was found in 10 Microviridae and its analysis indicates a horizontal gene transfer that occurred several times between these viruses and their bacterial hosts. This is the first report of such gene transfer in Microviridae. Finally, searches against viral metagenomes revealed the presence of highly similar sequences in a variety of biomes indicating that Microviridae probably have both an important role in these ecosystems and an ancient origin

Assessment of viral community functional potential from viral metagenomes may be hampered by contamination with cellular sequences.

International audienceAlthough the importance of viruses in natural ecosystems is widely acknowledged, the functional potential of viral communities is yet to be determined. Viral genomes are traditionally believed to carry only those genes that are directly pertinent to the viral life cycle, though this view was challenged by the discovery of metabolism genes in several phage genomes. Metagenomic approaches extended these analyses to a community scale, and several studies concluded that microbial and viral communities encompass similar functional potentials. However, these conclusions could originate from the presence of cellular DNA within viral metagenomes. We developed a computational method to estimate the proportion and origin of cellular sequences in a set of 67 published viromes. A quarter of the datasets were found to contain a substantial amount of sequences originating from cellular genomes. When considering only viromes with no cellular DNA detected, the functional potential of viral and microbial communities was found to be fundamentally different-a conclusion more consistent with the actual picture drawn from known viruses. Yet a significant number of cellular metabolism genes was still retrieved in these viromes, suggesting that the presence of auxiliary genes involved in various metabolic pathways within viral genomes is a general trend in the virosphere

Comparison of Different Semantics for Time Petri Nets

International audienceIn this paper we study the model of Time Petri Nets (TPNs) where a time interval is associated with the firing of a transition, but we extend it by considering general intervals rather than closed ones. A key feature of timed models is the memory policy, i.e. which timing informations are kept when a transition is fired. The original model selects an \emphintermediate semantics where the transitions disabled after consuming the tokens, as well as the firing transition, are reinitialised. However this semantics is not appropriate for some applications. So we consider here two alternative semantics: the \emphatomic and the \emphpersistent atomic ones. First we present relevant patterns of discrete event systems which show the interest of these semantics. Then we compare the expressiveness of the three semantics w.r.t. the weak time bisimilarity establishing inclusion results in the general case. Furthermore we show that some inclusions are strict with unrestricted intervals even when nets are bounded. Then we focus on bounded TPNs with upper-closed intervals and we prove that the semantics are equivalent. Finally taking into account both the practical and the theoretical issues, we conclude that persistent atomic semantics should be preferred