Neumann Boundary Conditions from D1-Brane Description at the Presence of Electric Field

We study the fluctuations of D1$\bot$D3 branes from D1-Brane description in the presence of world volume electric field. The fluctuations are found to obey Neumann boundary conditions separating the system into two regions depending on electric field $E$.Comment: 10 pages, v2: some equations are corrected and some points have been clarifie

Subsectors, Dynkin Diagrams and New Generalised Geometries

We examine how generalised geometries can be associated with a labelled Dynkin diagram built around a gravity line. We present a series of new generalised geometries based on the groups $\mathit{Spin}(d,d)\times\mathbb{R}^+$ for which the generalised tangent space transforms in a spinor representation of the group. In low dimensions these all appear in subsectors of maximal supergravity theories. The case $d=8$ provides a geometry for eight-dimensional backgrounds of M theory with only seven-form flux, which have not been included in any previous geometric construction. This geometry is also one of a series of "half-exceptional" geometries, which "geometrise" a six-form gauge field. In the appendix, we consider examples of other algebras appearing in gravitational theories and give a method to derive the Dynkin labels for the "section condition" in general. We argue that generalised geometry can describe restrictions and subsectors of many gravitational theories.Comment: 42 pages, v2: minor improvements and changes, published versio

Virtual Evidence: A Constructive Semantics for Classical Logics

This article presents a computational semantics for classical logic using constructive type theory. Such semantics seems impossible because classical logic allows the Law of Excluded Middle (LEM), not accepted in constructive logic since it does not have computational meaning. However, the apparently oracular powers expressed in the LEM, that for any proposition P either it or its negation, not P, is true can also be explained in terms of constructive evidence that does not refer to "oracles for truth." Types with virtual evidence and the constructive impossibility of negative evidence provide sufficient semantic grounds for classical truth and have a simple computational meaning. This idea is formalized using refinement types, a concept of constructive type theory used since 1984 and explained here. A new axiom creating virtual evidence fully retains the constructive meaning of the logical operators in classical contexts. Key Words: classical logic, constructive logic, intuitionistic logic, propositions-as-types, constructive type theory, refinement types, double negation translation, computational content, virtual evidenc

Praca socjalna i terapia rodziny: interdyscyplinarne korzenie interwencji w rodzinie

Social work practice takes place between persons in families and other social institutions, such as schools, health systems, welfare systems or courts. Drawing from multi-disciplinary theoretical sources, the article brings together social work and family therapy to develop a contemporary model of social work practice with families. There are five generic principles of family systemic practice: 1) persons are inherently relational; 2) families have resilient strengths; 3) family life cycles proceed systemically generating relational tasks for family members; 4) repetitive family interaction generates relational structures; 5) cultures, as perceived by family members, are themselves in dynamic motion, necessitating a transcultural understanding of family interaction.Praktyka pracy socjalnej odbywa się pomiędzy członkami rodzin a innymi instytucjami społecznymi, takimi jak: szkoły, systemy opieki zdrowotnej, systemy opieki społecznej i sądy. Czerpiąc z multidyscyplinarnych źródeł teoretycznych, artykuł łączy pracę socjalną i terapię rodzinną w celu opracowania współczesnego modelu praktyki pracy socjalnej z rodzinami. Istnieje pięć ogólnych zasad systemowej praktyki rodzinnej: 1) osoby są z natury relacyjne; 2) rodziny mają siły rodzące sprężystość psychiczną; 3) cykle życia rodzinnego postępują systemowo, generując relacyjne zadania dla członków rodziny; 4) powtarzające się interakcje rodzinne generują struktury relacyjne; 5) kultury, postrzegane przez członków rodziny, znajdują się w stanie dynamicznego ruchu, co wymaga transkulturowego zrozumienia interakcji rodziny

Exotic Scalar States in the AdS/CFT Correspondence

We investigate a family of solutions of Type IIb supergravity which asymptotically approach AdS_5 X S^5 but contain a non-constant dilaton and volume scalar for the five-sphere. These solutions preserve an SO(1,3) X SO(6) symmetry. We discuss the solution in the context of the AdS/CFT correspondence, and we find that as well as running coupling from the nontrivial dilaton, the corresponding field theory has no supersymmetry and displays confinement at least for a certain range of parameters.Comment: 18 pages. 3 figures. Revised discussion section, added references. Final version to appear in JHE

Stationary solutions for metapopulation Moran models with mutation and selection

We construct an individual-based metapopulation model of population genetics featuring migration, mutation, selection and genetic drift. In the case of a single `island', the model reduces to the Moran model. Using the diffusion approximation and timescale separation arguments, an effective one-variable description of the model is developed. The effective description bears similarities to the well-mixed Moran model with effective parameters which depend on the network structure and island sizes, and is amenable to analysis. Predictions from the reduced theory match the results from stochastic simulations across a range of parameters. The nature of the fast-variable elimination technique we adopt is further studied by applying it to a linear system, where it provides a precise description of the slow-dynamics in the limit of large timescale separation.Comment: 16 pages, 8 figure