Non-meanfield deterministic limits in chemical reaction kinetics far from equilibrium

A general mechanism is proposed by which small intrinsic fluctuations in a system far from equilibrium can result in nearly deterministic dynamical behaviors which are markedly distinct from those realized in the meanfield limit. The mechanism is demonstrated for the kinetic Monte-Carlo version of the Schnakenberg reaction where we identified a scaling limit in which the global deterministic bifurcation picture is fundamentally altered by fluctuations. Numerical simulations of the model are found to be in quantitative agreement with theoretical predictions.Comment: 4 pages, 4 figures (submitted to Phys. Rev. Lett.

Mesh update techniques for free-surface flow solvers using spectral element method

This paper presents a novel mesh-update technique for unsteady free-surface Newtonian flows using spectral element method and relying on the arbitrary Lagrangian--Eulerian kinematic description for moving the grid. Selected results showing compatibility of this mesh-update technique with spectral element method are given

When Madagascar produced natural rubber: a brief, forgotten yet informative history.

From 1891 to 1914, Madagascar, like other western African countries, was a production zone for forest rubber destined for export to Europe when Asian plantations where not yet sufficiently developed . Numerous species endemic to the forests of the three major Malagasy ecosystems were exploited, often with a view to maximising short term productivity without any consideration for the sustainable management of the resource. This episode represents one of the first cases of industrial exploitation of Madagascar's biological resources. Although Madagascar occupies a modest position on the world rubber market at that time, the exploitation of rubber bore major consequences for the island's forestry resources and, moreover, influenced the vision and discourse of scientists and politicians concerning their management. It was one of the factors triggering awareness of the value of Madagascar's biodiversity and the threat to which it might be exposed through poorly-controlled human activity. As a result, highly repressive and forcible legislation was introduced aimed at containing the activity practiced by local populations considered to be mostly to blame. But from the early days of French colonial rule, naturalists judged the outcomes of political decisions too weak to offer any guarantee of an effective defence. They responded by adopting an intentionally alarmist and catastrophist discourse with the object of provoking a reaction from the politicians, considered too lax. This discourse, in fact, took an about-turn from 1942-45 when the war effort led to a revitalisation of the Malagasy rubber sector as Asian production was mainly out of reach. A second consequence came in 1927 with the creation of a network of protected areas managed by naturalists, making Madagascar at that time, a pioneer in Africa. There was a simultaneous flurry of activity to promote the domestication of Malagasy rubber species, combined with the introduction of new species with high potential (Hevea brasiliensis, Castilloa elastica). However, with the emergence of far more profitable Asian rubber, all attempts at cultivation in Madagascar were abandoned when exploitation ceased to be profitable, and thus the Malagasy forests were redeemed. This episode demonstrates how it was in fact economic reality, by condemning an unprofitable sector, that was the real vehicle by which the survival of Malagasy rubber species was secured, and not the naturalists' discourse, nor the creation of protected zones, nor the promulgation of repressive legislations. This case study is of more than purely historical interest, in that it still has currency where, for example, the exploitation of Prunus africana is concerned

Kinetics of CheY phosphorylation by small molecule phosphodonors

AbstractThe chemotaxis response regulator CheY can acquire phosphoryl groups either from its associated autophosphorylating protein kinase, CheA, or from small phosphodonor molecules such as acetyl phosphate. We report a stopped-flow kinetic analysis of CheY phosphorylation by acetyl phosphate. The results show that CheY has a very low affinity for this phosphodonor (Ks≫0.1 M), consistent with the conclusion that, whereas CheY provides catalytic functions for the phosphotransfer reaction, the CheA kinase may act simply to increase the effective phosphodonor concentration at the CheY active site

Structural pathway of regulated substrate transfer and threading through an Hsp100 disaggregase

Refolding aggregated proteins is essential in combating cellular proteotoxic stress. Together with Hsp70, Hsp100 chaperones, including Escherichia coli ClpB, form a powerful disaggregation machine that threads aggregated polypeptides through the central pore of tandem adenosine triphosphatase (ATPase) rings. To visualize protein disaggregation, we determined cryo–electron microscopy structures of inactive and substrate-bound ClpB in the presence of adenosine 5′-O-(3-thiotriphosphate), revealing closed AAA+ rings with a pronounced seam. In the substrate-free state, a marked gradient of resolution, likely corresponding to mobility, spans across the AAA+ rings with a dynamic hotspot at the seam. On the seam side, the coiled-coil regulatory domains are locked in a horizontal, inactive orientation. On the opposite side, the regulatory domains are accessible for Hsp70 binding, substrate targeting, and activation. In the presence of the model substrate casein, the polypeptide threads through the entire pore channel and increased nucleotide occupancy correlates with higher ATPase activity. Substrate-induced domain displacements indicate a pathway of regulated substrate transfer from Hsp70 to the ClpB pore, inside which a spiral of loops contacts the substrate. The seam pore loops undergo marked displacements, along with ordering of the regulatory domains. These asymmetric movements suggest a mechanism for ATPase activation and substrate threading during disaggregation

A Method for Compiling and Executing Expressive Assertions

Programming with assertions constitutes an effective tool to detect and correct programming errors. The ability of executing formal specifications is essential in order to test automatically a program with respect to its assertions. However, formal specifications may describe recursive models which are difficult to identify so current assertion checkers limit, in a considerable way, the expressivity of the assertion language. In this paper, we are interested in showing how transformational synthesis can help to execute “expressive” assertions of the form ∀x(r(x) ⇔ QyR(x, y)) where x is a set of variables to be instantiated at execution time, Q is an existential or universal quantifier and R a quantifier free formula in the language of a particular first-order theory A we call assertion context. The class of assertion contexts is interesting because it presents a balance between expressiveness for writing assertions and existence of effective methods for executing them by means of synthesized (definite) logic programs

On Distributive Subalgebras of Qualitative Spatial and Temporal Calculi

Qualitative calculi play a central role in representing and reasoning about qualitative spatial and temporal knowledge. This paper studies distributive subalgebras of qualitative calculi, which are subalgebras in which (weak) composition distributives over nonempty intersections. It has been proven for RCC5 and RCC8 that path consistent constraint network over a distributive subalgebra is always minimal and globally consistent (in the sense of strong $n$-consistency) in a qualitative sense. The well-known subclass of convex interval relations provides one such an example of distributive subalgebras. This paper first gives a characterisation of distributive subalgebras, which states that the intersection of a set of $n\geq 3$ relations in the subalgebra is nonempty if and only if the intersection of every two of these relations is nonempty. We further compute and generate all maximal distributive subalgebras for Point Algebra, Interval Algebra, RCC5 and RCC8, Cardinal Relation Algebra, and Rectangle Algebra. Lastly, we establish two nice properties which will play an important role in efficient reasoning with constraint networks involving a large number of variables.Comment: Adding proof of Theorem 2 to appendi

Fluxys tracé Weelde - Oud-Turnhout (gem. Ravels en Oud-Turnhout)

Dit rapport werd ingediend bij het agentschap samen met een aantal afzonderlijke digitale bijlagen. Een aantal van deze bijlagen zijn niet inbegrepen in dit pdf document en zijn niet online beschikbaar. Sommige bijlagen (grondplannen, fotos, spoorbeschrijvingen, enz.) kunnen van belang zijn voor een betere lezing en interpretatie van dit rapport. Indien u deze bijlagen wenst te raadplegen kan u daarvoor contact opnemen met: [email protected]

Low-Temperature Mobility of Surface Electrons and Ripplon-Phonon Interaction in Liquid Helium

The low-temperature dc mobility of the two-dimensional electron system localized above the surface of superfluid helium is determined by the slowest stage of the longitudinal momentum transfer to the bulk liquid, namely, by the interaction of surface and volume excitations of liquid helium, which rapidly decreases with temperature. Thus, the temperature dependence of the low-frequency mobility is \mu_{dc} = 8.4x10^{-11}n_e T^{-20/3} cm^4 K^{20/3}/(V s), where n_e is the surface electron density. The relation T^{20/3}E_\perp^{-3} << 2x10^{-7} between the pressing electric field (in kV/cm) and temperature (in K) and the value \omega < 10^8 T^5 K^{-5}s^{-1} of the driving-field frequency have been obtained, at which the above effect can be observed. In particular, E_\perp = 1 kV/cm corresponds to T < 70 mK and \omega/2\pi < 30 Hz.Comment: 4 pages, 1 figur

Progress report and first operation of the GANIL injector

http://accelconf.web.cern.ch/AccelConf/c81/papers/abp-07.pdfInternational audienc