2,306 research outputs found
Dispersionless limit of the noncommutative potential KP hierarchy and solutions of the pseudodual chiral model in 2+1 dimensions
The usual dispersionless limit of the KP hierarchy does not work in the case
where the dependent variable has values in a noncommutative (e.g. matrix)
algebra. Passing over to the potential KP hierarchy, there is a corresponding
scaling limit in the noncommutative case, which turns out to be the hierarchy
of a `pseudodual chiral model' in 2+1 dimensions (`pseudodual' to a hierarchy
extending Ward's (modified) integrable chiral model). Applying the scaling
procedure to a method generating exact solutions of a matrix (potential) KP
hierarchy from solutions of a matrix linear heat hierarchy, leads to a
corresponding method that generates exact solutions of the matrix
dispersionless potential KP hierarchy, i.e. the pseudodual chiral model
hierarchy. We use this result to construct classes of exact solutions of the
su(m) pseudodual chiral model in 2+1 dimensions, including various multiple
lump configurations.Comment: 37 pages, 10 figures, 2nd version: some extensions (Fig 3, Appendix
A, additional references), 3rd version: some minor changes, additional
reference
Applying a User-centred Approach to Interactive Visualization Design
Analysing users in their context of work and finding out how and why they use different information resources is essential to provide interactive visualisation systems that match their goals and needs. Designers should actively involve the intended users throughout the whole process. This chapter presents a user-centered approach for the design of interactive visualisation systems. We describe three phases of the iterative visualisation design process: the early envisioning phase, the global specification hase, and the detailed specification phase. The whole design cycle is repeated until some criterion of success is reached. We discuss different techniques for the analysis of users, their tasks and domain. Subsequently, the design of prototypes and evaluation methods in visualisation practice are presented. Finally, we discuss the practical challenges in design and evaluation of collaborative visualisation environments. Our own case studies and those of others are used throughout the whole chapter to illustrate various approaches
Why Global Inequality Matters: Derivative Global Egalitarianism
This article integrates empirical and normative discussions about why global economic inequalities matter in critically examining an approach known as derivative global egalitarianism (DGE). DGE is a burgeoning perspective that opposes excessive global economic inequality not based on the intrinsic value of equality but inequality\u27s negative repercussions on other values. The article aims to advance the research agenda by identifying and critically evaluating four primary varieties of DGE arguments from related but distinct literatures, which span a number of disciplines, including economics, international relations, and political philosophy. Overall, DGE offers a number of persuasive arguments as to why current levels of global inequality are of concern, but aspects of DGE beg further philosophical and empirical examination. By situating DGE within the wider theoretical and empirical contexts, this article provides resources for its critical assessment and theoretical development
Boundary Conditions on Internal Three-Body Wave Functions
For a three-body system, a quantum wave function with definite
and quantum numbers may be expressed in terms of an internal wave
function which is a function of three internal coordinates. This
article provides necessary and sufficient constraints on to
ensure that the external wave function is analytic. These
constraints effectively amount to boundary conditions on and its
derivatives at the boundary of the internal space. Such conditions find
similarities in the (planar) two-body problem where the wave function (to
lowest order) has the form at the origin. We expect the boundary
conditions to prove useful for constructing singularity free three-body basis
sets for the case of nonvanishing angular momentum.Comment: 41 pages, submitted to Phys. Rev.
Primary non Hodgkin's lymphoma of the lacrimal sac
<p>Abstract</p> <p>Background</p> <p>Primary Non Hodgkin's Lymphoma (NHL) of the lacrimal sac is rare.</p> <p>Methods</p> <p>The clinical features of a 78 year old female who presented with epiphora and swelling of the left lacrimal sac are described.</p> <p>Results</p> <p>Computerised tomography showed a mass involving the left lacrimal sac. Histopathological examination revealed a diffuse large B cell NHL. Immunohistological examination demonstrated B cell origin. Chemotherapy could not be administered due to co morbid conditions. The patient was treated with radiotherapy to a dose of 45 Gy in 25 fractions. Patient is disease free and on follow up after 36 months.</p> <p>Conclusion</p> <p>Primary radiotherapy is a treatment option with curative potential for localized NHL of the lacrimal sac and may be considered in patients who cannot tolerate appropriate chemotherapy.</p
Reassessment of the Lineage Fusion Hypothesis for the Origin of Double Membrane Bacteria
In 2009, James Lake introduced a new hypothesis in which reticulate phylogeny reconstruction is used to elucidate the origin of Gram-negative bacteria (Nature 460: 967–971). The presented data supported the Gram-negative bacteria originating from an ancient endosymbiosis between the Actinobacteria and Clostridia. His conclusion was based on a presence-absence analysis of protein families that divided all prokaryotes into five groups: Actinobacteria, Double Membrane bacteria (DM), Clostridia, Archaea and Bacilli. Of these five groups, the DM are by far the largest and most diverse group compared to the other groupings. While the fusion hypothesis for the origin of double membrane bacteria is enticing, we show that the signal supporting an ancient symbiosis is lost when the DM group is broken down into smaller subgroups. We conclude that the signal detected in James Lake's analysis in part results from a systematic artifact due to group size and diversity combined with low levels of horizontal gene transfer.Exobiology Program (U.S.) (Grant NNX08AQ10G)Assembling the Tree of Life (Program) (Grant DEB 0830024
Role-play for medical students learning about communication: Guidelines for maximising benefits
BACKGROUND: Role-play is widely used as an educational method for learning about communication in medical education. Although educational theory provides a sound rationale for using this form of simulation, there is little published evidence for its effectiveness. Students' prior experiences of role-play may influence the way in which they engage in this method. This paper explores students' experiences with the aim of producing guidelines for maximising the benefits of role-play within this learning context. METHODS: First-year undergraduate medical students participated in a role-play session as part of their communication programme. Before and after the session, students completed questionnaires. In the pre-session questionnaire, students were asked about their experiences of role-play and asked to identify helpful and unhelpful elements. Immediately after the session, students answered similar questions in relation to the role-play activity they had just completed. Descriptive statistics were used to analyse quantitative data and qualitative data was thematically analysed. RESULTS: 284 students completed evaluation forms. Although 63 (22.2%) had prior unhelpful experiences, most students (n = 274; 96.5%) found this experience helpful. Summary findings were that students reported the key aspects of helpful role-play were opportunities for observation, rehearsal and discussion, realistic roles and alignment of roles with other aspects of the curriculum. Unhelpful aspects were those that evoked strong negative emotional responses and factors that contributed to a lack of realism. CONCLUSION: Role-play was valued by students in the acquisition of communication skills even though some had prior unhelpful experiences. Guidelines for effective role-play include adequate preparation, alignment of roles and tasks with level of practice, structured feedback guidelines and acknowledgment of the importance of social interactions for learning
Holographic Vitrification
We establish the existence of stable and metastable stationary black hole
bound states at finite temperature and chemical potentials in global and planar
four-dimensional asymptotically anti-de Sitter space. We determine a number of
features of their holographic duals and argue they represent structural
glasses. We map out their thermodynamic landscape in the probe approximation,
and show their relaxation dynamics exhibits logarithmic aging, with aging rates
determined by the distribution of barriers.Comment: 100 pages, 25 figure
Baryonic Popcorn
In the large N limit cold dense nuclear matter must be in a lattice phase.
This applies also to holographic models of hadron physics. In a class of such
models, like the generalized Sakai-Sugimoto model, baryons take the form of
instantons of the effective flavor gauge theory that resides on probe flavor
branes. In this paper we study the phase structure of baryonic crystals by
analyzing discrete periodic configurations of such instantons. We find that
instanton configurations exhibit a series of "popcorn" transitions upon
increasing the density. Through these transitions normal (3D) lattices expand
into the transverse dimension, eventually becoming a higher dimensional (4D)
multi-layer lattice at large densities.
We consider 3D lattices of zero size instantons as well as 1D periodic chains
of finite size instantons, which serve as toy models of the full holographic
systems. In particular, for the finite-size case we determine solutions of the
corresponding ADHM equations for both a straight chain and for a 2D zigzag
configuration where instantons pop up into the holographic dimension. At low
density the system takes the form of an "abelian anti-ferromagnetic" straight
periodic chain. Above a critical density there is a second order phase
transition into a zigzag structure. An even higher density yields a rich phase
space characterized by the formation of multi-layer zigzag structures. The
finite size of the lattices in the transverse dimension is a signal of an
emerging Fermi sea of quarks. We thus propose that the popcorn transitions
indicate the onset of the "quarkyonic" phase of the cold dense nuclear matter.Comment: v3, 80 pages, 18 figures, footnotes 5 and 7 added, version to appear
in the JHE
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