Composition mechanisms for retrenchment

Retrenchment is a flexible model evolution formalism that arose as a reaction to the limitations imposed by refinement, and for which the proof obligations feature additional predicates for accommodating design data. Composition mechanisms for retrenchment are studied. Vertical, horizontal, dataflow, parallel and fusion compositions are described. Of particular note are the means by which the additional predicates compose. It is argued that all of the compositions introduced are associative, and that they are mutually coherent. Composition of retrenchment with refinement, so important for the smooth interworking of the two techniques, is discussed. Decomposition, allowing finer grained retrenchments to be extracted from a single large grained retrenchment, is also investigated

Charge stripes due to electron correlations in the two-dimensional spinless Falicov-Kimball model

We calculate the restricted phase diagram for the Falicov-Kimball model on a two-dimensional square lattice. We consider the limit where the conduction electron density is equal to the localized electron density, which is the limit related to the S_z=0 states of the Hubbard model. After considering over 20,000 different candidate phases (with a unit cell of 16 sites or less) and their thermodynamic mixtures, we find only about 100 stable phases in the ground-state phase diagram. We analyze these phases to describe where stripe phases occur and relate these discoveries to the physics behind stripe formation in the Hubbard model.Comment: (34 pages, 9 figures, submitted to Journal of Statistical Physics to celebrate Elliott Lieb's 70th birthday

Retrenching the Purse: Finite Exception Logs, and Validating the Small

The Mondex Electronic Purse is an outstanding example of industrial scale formal refinement, and was the first verification to achieve ITSEC level E6 certification. A formal abstract model and a formal concrete model were developed, and a formal refinement was hand-proved between them. Nevertheless, certain requirements issues were set beyond the scope of the formal development, or handled in an unnatural manner. The retrenchment Tower Pattern is used to address one such issue in detail: the finiteness of the purse log (which records unsuccessful transactions). A retrenchment is constructed from the lowest level model of the purse system to a model in which logs are finite, and is then lifted to create two refinement developments of the purse, working at different levels of detail, and connected via retrenchments, forming the tower. The tower development is appropriately validated, vindicating the design used

Dynamic aspects of retrenchments through temporal logic

Refinement is used as a way to verify an implementation with respect to a specification. States of related systems are linked through a so called gluing invariant which remains always true during the synchronous execution of both systems. Refinement is a sufficient condition for this property. Retrenchment is a generalization of refinement which relax the constraints between both systems. This paper proposes a temporal logic counterpart for some specific forms of retrenchment

Protein-protein interaction encoded as an exposure of hydrophobic residues on the surface

According to the fuzzy oil drop model, information required for complexation of an external polypeptide chain should be encoded as a local exposure of hydrophobicity on the protein surface. Of course, this is not the sole mechanism by which protein complexes may emerge; however, exposed hydrophobicity appears to play an important part in the complexation process. A local excess of hydrophobicity – especially if occurring on the surface – creates an environment which favors interaction with other polypeptide chains; particularly those, which also expose a hydrophobic interface

Stochastic effects on biodiversity in cyclic coevolutionary dynamics

Finite-size fluctuations arising in the dynamics of competing populations may have dramatic influence on their fate. As an example, in this article, we investigate a model of three species which dominate each other in a cyclic manner. Although the deterministic approach predicts (neutrally) stable coexistence of all species, for any finite population size, the intrinsic stochasticity unavoidably causes the eventual extinction of two of them.Comment: 5 pages, 2 figures. Proceedings paper of the workshop "Stochastic models in biological sciences" (May 29 - June 2, 2006 in Warsaw) for the Banach Center Publication

Cultural barriers in the moulding of prosocial attitudes among participants in economic life in Poland

Celem artykułu jest wskazanie na elementy szeroko pojętej kultury, które stanowić mogą różnego rodzaju utrudnienia i bariery w skutecznym kształtowaniu postaw prospołecznych wśród uczestników życia gospodarczego w Polsce. Autor wychodzi z założenia, że satysfakcjonujące kształcenie odpowiednich postaw obywatelskich – zarówno obecnych, jak i przyszłych studentów, kadr pracowniczych i menedżerskich, a nawet konsumentów i klientów – nie może być oderwane od kontekstu kulturowego. Innymi słowy, jeśli podejmowane działania edukacyjne przynieść mają pożądany rezultat, nie mogą abstrahować od dominujących w danym społeczeństwie wartości, norm, postaw czy wzorów zachowań. Należy przy tym zdawać sobie sprawę, że dokonywanie zmian w sferze kultury jest dość ograniczone i zawsze rozciągnięte w czasie. Artykuł podejmuje próbę wskazania na najbardziej charakterystyczne cechy polskiej mentalności, ugruntowane zwłaszcza w ostatnich dekadach, które stanowią uciążliwą spuściznę komunizmu. To wówczas wykształciły się antyspołeczne postawy egoizmu, prywaty, wyuczonej bierności, braku motywacji i inicjatywy. Autor referatu podkreśla, że zarówno jako społeczeństwo, jak i poszczególni jego członkowie nie do końca potrafiliśmy zerwać z tą spuścizną. Wydaje się zatem, że współczesne działania edukacyjne nie przyniosą w pełni zadowalających efektów póki nie pozbędziemy się tego zbędnego balastu.The aim of the article is to point to those elements of broadly understood culture that may constitute various obstacles and barriers to the effective development of prosocial attitudes among participants of Polish economic life. The author assumes that the satisfactory education of appropriate civic attitudes – among present and future students, staff and managers, and even consumers and customers – cannot be detached from the cultural context. In other words, if the educational activities are to produce the desired result, they cannot abstain from the v alues, norms, attitudes or behavioural patterns prevailing in a given society. It is important to realise that changes in the sphere of culture are quite limited, and always stretched out in time. The paper attempts to point to the most characteristic features of Polish mentality, grounded in particular in the last decades, that constitute a burdensome legacy of communism. It was then that the antisocial attitudes of selfishness, self-interest, learned passivity, and a lack of motivation or initiative emerged. The author of the paper emphasises that both as a society and its individual members, we have been unable to break free of this legacy. It seems therefore that modern educational activities will not produce satisfactory results until we get rid of this redundant ballast