Critical behavior of a cellular automaton highway traffic model

We derive the critical behavior of a CA traffic flow model using an order parameter breaking the symmetry of the jam-free phase. Random braking appears to be the symmetry-breaking field conjugate to the order parameter. For $v_{\max}=2$, we determine the values of the critical exponents $\beta$, $\gamma$ and $\delta$ using an order-3 cluster approximation and computer simulations. These critical exponents satisfy a scaling relation, which can be derived assuming that the order parameter is a generalized homogeneous function of $|\rho-\rho_c|$ and p in the vicinity of the phase transition point.Comment: 6 pages, 12 figure

Vibrations and diverging length scales near the unjamming transition

We numerically study the vibrations of jammed packings of particles interacting with finite-range, repulsive potentials at zero temperature. As the packing fraction $\phi$ is lowered towards the onset of unjamming at $\phi_{c}$, the density of vibrational states approaches a non-zero value in the limit of zero frequency. For $\phi>\phi_{c}$, there is a crossover frequency, $\omega^{*}$ below which the density of states drops towards zero. This crossover frequency obeys power-law scaling with $\phi-\phi_{c}$. Characteristic length scales, determined from the dominant wavevector contributing to the eigenmode at $\omega^{*}$, diverge as power-laws at the unjamming transition.Comment: Submitted to PRL, 4 pages + 7 .eps figure

Microanalysis of serotonin by high pressure liquid chromatography with electrochemical detection

L'analyse de la sérotonine (5-HT) par chromatographie liquide haute pression avec un détecteur électrochimique a été adaptée pour quantifier des quantités inférieures au picogramme. Nous démontrons que le potentiel d'oxydation de la sérotonine est étroitement lié au pH de la solution tampon utilisée comme phase éluente. Le comportement électrochimique de la 5-HT dans un tampon acétate à pH 4,00 ou dans un tampon phosphate à pH 6,80 permet une quantification de cette molécule jusqu'à des quantités de l'ordre de 10 (puissance -18) g. La quantité de courant d'oxydation est proportionnelle à la quantité de sérotonine analysée. La réponse électrochimique de la 5-HT est différente pour les très faibles quantités dosées dans la gamme des attogrammes et pour celles des picogrammes. Deux courbes sont enregistrées en fonction de la réponse électrochimique de la 5-HT : l'une pour des dosages dans la gamme des 10 (puissance -18) g et l'autre pour des dosages dans la gamme des picogrammes et au-delà. Dans la gamme de concentrations qui encadre le point de jonction des 2 courbes de calibration, le dosage de la 5-HT n'est pas fiable. La méthode a été appliquée pour doser la 5-HT sur des coupes à congélation de moelle épinière de rats. Cette méthode qui utilise une extraction organique en une étape pourrait ouvrir de nouvelles perspectives pour la quantification de la 5-HT dans des localisations précises du système nerveux central sans avoir recours à l'utilisation de molécules radiomarquées. (Résumé d'auteur

Metastable States in Two-Lane Traffic Flow Models With Slow-To-Start Rule

Using computer simulations, we show that metastable states still occur in two-lane traffic models with slow to start rules. However, these metastable states no longer exist in systems where aggressive drivers (\textit{which do not look back before changing lanes}) are present. Indeed, the presence of only one aggressive driver in the circuit, triggers the breakdown of the high flow states. In these systems, the steady state is unique and its relaxation dynamics should depend on the lane changing probability $p_{ch}$ and the number of aggressive drivers present in the circuit. It is found also that the relaxation time $\tau$ diverges as the form of a power-law : $\tau\propto p_{ch}^{-\beta}, \beta=1$.Comment: 7 pages, 6 figure

5-State Rotation-Symmetric Number-Conserving Cellular Automata are not Strongly Universal

We study two-dimensional rotation-symmetric number-conserving cellular automata working on the von Neumann neighborhood (RNCA). It is known that such automata with 4 states or less are trivial, so we investigate the possible rules with 5 states. We give a full characterization of these automata and show that they cannot be strongly Turing universal. However, we give example of constructions that allow to embed some boolean circuit elements in a 5-states RNCA

Coarse-Grained Modeling of Genetic Circuits as a Function of the Inherent Time Scales

From a coarse-grained perspective the motif of a self-activating species, activating a second species which acts as its own repressor, is widely found in biological systems, in particular in genetic systems with inherent oscillatory behavior. Here we consider a specific realization of this motif as a genetic circuit, in which genes are described as directly producing proteins, leaving out the intermediate step of mRNA production. We focus on the effect that inherent time scales on the underlying fine-grained scale can have on the bifurcation patterns on a coarser scale in time. Time scales are set by the binding and unbinding rates of the transcription factors to the promoter regions of the genes. Depending on the ratio of these rates to the decay times of the proteins, the appropriate averaging procedure for obtaining a coarse-grained description changes and leads to sets of deterministic equations, which differ in their bifurcation structure. In particular the desired intermediate range of regular limit cycles fades away when the binding rates of genes are of the same order or less than the decay time of at least one of the proteins. Our analysis illustrates that the common topology of the widely found motif alone does not necessarily imply universal features in the dynamics.Comment: 29 pages, 16 figure

A Survey on Design and Implementation of Protected Searchable Data in the Cloud

While cloud computing has exploded in popularity in recent years thanks to the potential efficiency and cost savings of outsourcing the storage and management of data and applications, a number of vulnerabilities that led to multiple attacks have deterred many potential users. As a result, experts in the field argued that new mechanisms are needed in order to create trusted and secure cloud services. Such mechanisms would eradicate the suspicion of users towards cloud computing by providing the necessary security guarantees. Searchable Encryption is among the most promising solutions - one that has the potential to help offer truly secure and privacy-preserving cloud services. We start this paper by surveying the most important searchable encryption schemes and their relevance to cloud computing. In light of this analysis we demonstrate the inefficiencies of the existing schemes and expand our analysis by discussing certain confidentiality and privacy issues. Further, we examine how to integrate such a scheme with a popular cloud platform. Finally, we have chosen - based on the findings of our analysis - an existing scheme and implemented it to review its practical maturity for deployment in real systems. The survey of the field, together with the analysis and with the extensive experimental results provides a comprehensive review of the theoretical and practical aspects of searchable encryption