The formation of shear and density layers in stably stratified trubulent flows: linear processes

The initial evolution of the momentum and buoyancy fluxes in a freely decaying, stably stratified homogeneous turbulent flow with r.m.s. velocity u′0 and integral lengthscale l0 is calculated using a weakly inhomogeneous and unsteady form of the rapid distortion theory (RDT) in order to study the growth of small temporal and spatial perturbations in the large-scale mean stratification N(z, t) and mean velocity profile u(z, t) (here N is the local Brunt–Väisälä frequency and u is the local velocity of the horizontal mean flow) when the ratio of buoyancy forces to inertial forces is large, i.e. Nl0/u′0[dbl greater-than sign]1. The lengthscale L of the perturbations in the mean profiles of stratification and shear is assumed to be large compared to l0 and the presence of a uniform background mean shear can be taken into account in the model provided that the inertial shear forces are still weaker than the buoyancy forces, i.e. when the Richardson number Ri = (N/[partial partial differential]zu)2[dbl greater-than sign]1 at each height. When a mean shear perturbation is introduced initially with no uniform background mean shear and uniform stratification, the analysis shows that the perturbations in the mean flow profile grow on a timescale of order N-1. When the mean density profile is perturbed initially in the absence of a background mean shear, layers with significant density gradient fluctuations grow on a timescale of order N−10 (where N0 is the order of magnitude of the initial Brunt–Väisälä frequency) without any associated mean velocity gradients in the layers. These results are in good agreement with the direct numerical simulations performed by Galmiche et al. (2002) and are consistent with the earlier physically based conjectures made by Phillips (1972) and Posmentier (1977). The model also shows that when there is a background mean shear in combination with perturbations in the mean stratification, negative shear stresses develop which cause the mean velocity gradient to grow in the density layers. The linear analysis for short times indicates that the scale on which the mean perturbations grow fastest is of order u′0/N0, which is consistent with the experiments of Park et al. (1994). We conclude that linear mechanisms are widely involved in the formation of shear and density layers in stratified flows as is observed in some laboratory experiments and geophysical flows, but note that the layers are also significantly influenced by nonlinear and dissipative processes at large times

Maldonne et rédemption. Le concept d’anarchisme littéraire dans l’histoire culturelle de l’Empire (austro-hongrois) – l’exemple tchèque

International audienceFor most of us, modern Czech literature began with Jaroslav Hašek’s The Good Soldier Svejk, a pillar of Central Europe’s literary anarchism. This article seeks to dispel such a perception by revealing the prolific yet tense interplay between anarchism of the political and literary varieties that took place from the 1890s to the 1920s. (The concept of literary anarchism came to be as a result of the close dependency of esthetical thinking on political discourse.) To that end, this article dwells on relevant analogies from other literary genres, and questions the radical nature of the modernity brought upon by these anarchists. Despite the initial misleading notion, this concept can prove quite useful to qualify certain literary values and practices: the ambitious transposition of socio-political ideals to the field of aesthetics, or a more general acknowledgement of another dependency, that of the artistic quest on a thirst for tradition and a spiritual absolute, at least going back to the romantic apophasis.Pour le grand public, la littérature tchèque moderne a commencé avec Les aventures du brave soldat Chweïk de Jaroslav Hašek, oeuvre cardinale de l’anarchisme littéraire d’Europe centrale. Cette contribution a pour but de revenir sur cette idée reçue en dessinant les rapports à la fois féconds mais tendus tissés entre anarchisme politique et littéraire, des années 1890 aux années 1920 environ (la naissance du concept d’anarchisme littéraire reflète la dépendance étroitement ancillaire de la réflexion esthétique au discours politicien), en proposant un élargissement du concept d’anarchisme littéraire vers les oeuvres expressionnistes (Kafka, Klíma, Váchal, Deml), en explorant les analogies repérables dans les littératures voisines, et en mettant en cause la radicalité de la modernité développée par ces anarchistes. En dépit de cette maldonne conceptuelle initiale, ce concept peut se révéler d’une grande utilité pour qualifier certaines valeurs et pratiques littéraires : l’ambition de transposer dans le champ esthétique un idéal sociopolitique, mais plus généralement, la reconnaissance d’une autre dépendance, celle du programme artistique à une soif d’absolu spirituel et à une tradition, remontant au moins à l’apophase romantique

Program development in constructive type theory

AbstractWe present the program development concept in a logical framework including constructive type theory and then show how to use such theories to derive programs from proofs of formal specifications. We are interested in two important facts that are the mechanization of the proof construction and the possibility to express in the theory significant concepts for programming (like inductively defined types and general recursion). We give here a survey on some results and problems appearing in logical frameworks devoted to the programming with proofs approach

Labelled Tableaux for Linear Time Bunched Implication Logic

In this paper, we define the logic of Linear Temporal Bunched Implications (LTBI), a temporal extension of the Bunched Implications logic BI that deals with resource evolution over time, by combining the BI separation connectives and the LTL temporal connectives. We first present the syntax and semantics of LTBI and illustrate its expressiveness with a significant example. Then we introduce a tableau calculus with labels and constraints, called TLTBI, and prove its soundness w.r.t. the Kripke-style semantics of LTBI. Finally we discuss and analyze the issues that make the completeness of the calculus not trivial in the general case of unbounded timelines and explain how to solve the issues in the more restricted case of bounded timelines

Semi-subsistence and sustainability: aquaculture in Tabasco, Mexico

This thesis explores the physical and the socio-economic conditions for aquaculture in Tabasco, Mexico, seeking to find how aquaculture can best be supported to reduce poverty. On-farm physical, technical and social surveys were carried out in four municipalities, covering different physiographic regions. The surveys establish that the environmental conditions are frequently good for aquaculture. Despite efforts to bring farmers into more intensive commercial systems, aquaculture has developed mainly to improve subsistence, as one component of semi-subsistence farms. In order to evaluate these semi- subsistence systems, the thesis explores current debates on 'sustainability' and on 'subsistence'. As no single approach to sustainability per se seems appropriate to apply to these systems, new indicators and methods need to be developed which are appropriate to evaluate systems poor in cash generation but rich in social assets. Subsistence aquaculture is arguably more sustainable than commercial, monocultural aquaculture in environmental and social terms. It has become part of the economic diversity of the communities, increases food security, reduces the use of fossil fuels, promotes the careful management and recycling of wastes and the careful stewardship of natural resources, can help in the protection and enhancement of biological diversity and yields a feeling of self- empowerment. From the surveys, socio-economic and cultural realities are more important than physical conditions in determining the present state of aquaculture in Tabasco. The existence of some successful farmers' micro-businesses shows that once farmers receive continuous technical assistance, subsidies and access to markets, bringing them into commercial aquaculture is possible. Such help however, is rarely provided at present by the local extension institutions, which face internal problems resulting from inadequate budgets. This thesis argues that, in these circumstances, semi-subsistence aquaculture is a good option for the poor as many semi-subsistence systems are highly valued and have the potential to become more efficient and productive if locally based research is conducted with an understanding of farmers' cultures and motivations

Sequent calculi and decidability for intuitionistic hybrid logic

AbstractIn this paper we study the proof theory of the first constructive version of hybrid logic called Intuitionistic Hybrid Logic (IHL) in order to prove its decidability. In this perspective we propose a sequent-style natural deduction system and then the first sequent calculus for this logic. We prove its main properties like soundness, completeness and also the cut-elimination property. Finally we provide, from our calculus, the first decision procedure for IHL and then prove its decidability

1918: konec konfliktu, válka afektů

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Effect of cytostatic drug presence on extracellular polymeric substances formation in municipal wastewater treated by membrane bioreactor

The effect of the cyclophosphamide and its mean metabolites on extracellular polymeric substances (EPS) formation was investigated. Two lab-scale membrane bioreactors were followed in parallel (one with the cytostatic drugs, the second without). Chromatographic and spectroscopic studies (UV–Vis spectroscopy and IR spectroscopy) showed that the presence of CPs induced an increase in EPS concentration in the biological sludge, especially of soluble substances, mainly polysaccharides and proteins. Size exclusion chromatography analysis revealed that in the presence of CPs, macromolecular EPS were formed (polysaccharides corresponding to about 6 KDa and proteins to about 18 KDa). The formation of EPS seemed to be a protection mechanism. More important membrane fouling in reactor with CPs seemed to be related to the retention of an increased amount of soluble substances

Fère-en-Tardenois – Château de Fère

Suite au dépôt par l’hôtel-restaurant « Château de Fère » à Fère-en-Tardenois d’une demande anticipée de prescription préalable à une extension de ses locaux, un diagnostic a été prescrit. Une tranchée de sondage a été réalisée dans la basse-cour du château devant le corps de logis. Cette construction qui date des années 1530 a été érigée au cours d’une campagne plus vaste de réaménagement du château dont l’origine remonte au xiiie s. Deux épais niveaux de remblais ont été mis en évidence sou..