Two-Phase Flow In Microchannels: Morphology And Interface Phenomena

The existence and morphology, as well as the dynamics of micro-scale gas-liquid interfaces is investigated numerically and experimentally. These studies can be used to assess liquid management issues in microsystems such as PEMFC gas flow channels, and are meant to open new research perspectives in two-phase flow, particularly in film deposition on non-wetting surfaces. For example the critical plug volume data can be used to deliver desired length plugs, or to determine the plug formation frequency. The dynamics of gas-liquid interfaces, of interest for applications involving small passages (e.g. heat exchangers, phase separators and filtration systems), was investigated using high-speed microscopy - a method that also proved useful for the study of film deposition processes. The existence limit for a liquid plug forming in a mixed wetting channel is determined by numerical simulations using Surface Evolver. The plug model simulate actual conditions in the gas flow channels of PEM fuel cells, the wetting of the gas diffusion layer (GDL) side of the channel being different from the wetting of the bipolar plate walls. The minimum plug volume, denoted as critical volume is computed for a series of GDL and bipolar plate wetting properties. Critical volume data is meant to assist in the water management of PEMFC, when corroborated with experimental data. The effect of cross section geometry is assessed by computing the critical volume in square and trapezoidal channels. Droplet simulations show that water can be passively removed from the GDL surface towards the bipolar plate if we take advantage on differing wetting properties between the two surfaces, to possibly avoid the gas transport blockage through the GDL. High speed microscopy was employed in two-phase and film deposition experiments with water in round and square capillary tubes. Periodic interface destabilization was observed and the existence of compression waves in the gas phase is discussed by taking into consideration a naturally occurring convergent-divergent nozzle formed by the flowing liquid phase. The effect of channel geometry and wetting properties was investigated through two-phase water-air flow in square and round microchannels, having three static contact angles of 20, 80 and 105 degrees. Four different flow regimes are observed for a fixed flow rate, this being thought to be caused by the wetting behavior of liquid flowing in the corners as well as the liquid film stability. Film deposition experiments in wetting and non-wetting round microchannels show that a thicker film is deposited for wetting conditions departing from the ideal 0 degrees contact angle. A film thickness dependence with the contact angle theta as well as the Capillary number, in the form h_R ~ Ca^(2/3)/ cos(theta) is inferred from scaling arguments, for contact angles smaller than 36 degrees. Non-wetting film deposition experiments reveal that a film significantly thicker than the wetting Bretherton film is deposited. A hydraulic jump occurs if critical conditions are met, as given by a proposed nondimensional parameter similar to the Froude number. Film thickness correlations are also found by matching the measured and the proposed velocity derived in the shock theory. The surface wetting as well as the presence of the shock cause morphological changes in the Taylor bubble flow

A randomized encoding of the pi-calculus with mixed choice

International audienceWe consider the problem of encoding the pi-calculus with mixed choice into the asynchronous pi-calculus via a uniform translation while preserving a reasonable semantics. Although it has been shown that this is not possible with an exact encoding, we suggest a randomized approach using a probabilistic extension of the asynchronous pi-calculus, and we show that our solution is correct with probability 1 under any proper adversary wrt a notion of testing semantics. This result establishes the basis for a distributed and symmetric implementation of mixed choice which, differently from previous proposals in literature, does not rely on assumptions on the relative speed of processes and it is robust to attacks of proper adversaries

A computational group theoretic symmetry reduction package for the SPIN model checker

Symmetry reduced model checking is hindered by two problems: how to identify state space symmetry when systems are not fully symmetric, and how to determine equivalence of states during search. We present TopSpin, a fully automatic symmetry reduction package for the Spin model checker. TopSpin uses the Gap computational algebra system to effectively detect state space symmetry from the associated Promela specification, and to choose an efficient symmetry reduction strategy by classifying automorphism groups as a disjoint/wreath product of subgroups. We present encouraging experimental results for a variety of Promela examples

Benefits of the Mediterranean Diet in the Prevention of Non-communicable Diseases as the Epidemic of the 21st century

Non-communicable diseases are known as the epidemic of the 21st century. In Romania, these are responsible for almost 91% of all the deaths. A balanced diet and regular physical activity (at least 30 minutes throughout the day) are the keys to a healthy and long living life. Mediterranean diet is shown to be the optimal diet for preventing non-communicable diseases and preserving good health. The concept of the Mediterranean diet is defined by the food pyramid, which is meant to provide an overall impression of healthy food choices, rather than to define recommended weights of certain foods or proportions of energy obtained from them. In Romania the concept of Mediterranean diet is unknown to most ordinary people. Even in medicine field there are few doctors who really know about this diet and its effects on patients’ health. Our purpose in writing this article was to draw a warning signal about the impact of Mediterranean diet on the health of people, in hope that through media, the importance of a healthy and active life in raising quality of life and decreasing morbidity and mortality can be fully understood.</span

Probabilistic Anonymity

The concept of anonymity comes into play in a wide range of situations, varying from voting and anonymous donations to postings on bulletin boards and sending mails. A formal definition of this concept has been given in literature in terms of nondeterminism. In this paper, we investigate a notion of anonymity based on probability theory, and we we discuss the relation with the nondeterministic one. We then formulate this definition in terms of observables for processes in the probabilistic $pi$-calculus, and propose a method to verify automatically the anonymity property. We illustrate the method by using the example of the dining cryptographers

Iamque opus exegi: the Ode III 30 of Horace in words of Ovid

Estudio de las huellas de Horacio Carm. III 30 en Ovidio Met. XV 871-879, especialmente en el léxico y la sintaxis.Study of Horace Carm. III 30 traces in Ovid Met. XV 871-879, specially in vocabulary and syntax.Este trabajo se ha realizado dentro del proyecto «Ars grammatica y ars musica», FFI2012-36647, financiado por la Dirección General de Investigación del M.E.C

Rebooting Ecumenism, the Theological Equivalent of the Climate Crisis: The Role of Urgency and Accountability on the Road to Ecclesial Interdependence

Peer reviewed: TruePublication status: PublishedThis article puts forward the argument for the acute and urgent need to move from ecclesial self-sufficiency to ecclesial interdependency in the ecumenical process. The difficulties in ecumenical cooperation mirror those in the climate crisis, as despite a global crisis of relevance for Christianity and for the ecumenical movement, individual Churches, much like individual states, fail to work together effectively as they negotiate their own internal challenges. Not dissimilar to the ecological climate breakdown, what we understand as the history-bound reality of the Church will not be safeguarded and will not be made relevant in a today’s globalised, pluralistic, interconnected, and dominantly secular, in many contexts, world, except by concerted action from all Churches.</jats:p