Recent mathematical developments in the Skyrme model

In this review we present a pedagogical introduction to recent, more mathematical developments in the Skyrme model. Our aim is to render these advances accessible to mainstream nuclear and particle physicists. We start with the static sector and elaborate on geometrical aspects of the definition of the model. Then we review the instanton method which yields an analytical approximation to the minimum energy configuration in any sector of fixed baryon number, as well as an approximation to the surfaces which join together all the low energy critical points. We present some explicit results for B=2. We then describe the work done on the multibaryon minima using rational maps, on the topology of the configuration space and the possible implications of Morse theory. Next we turn to recent work on the dynamics of Skyrmions. We focus exclusively on the low energy interaction, specifically the gradient flow method put forward by Manton. We illustrate the method with some expository toy models. We end this review with a presentation of our own work on the semi-classical quantization of nucleon states and low energy nucleon-nucleon scattering.Comment: 129 pages, about 30 figures, original manuscript of published Physics Report

Mechanisms Gating the Flow of Information in the Cortex: What They Might Look Like and What Their Uses may be

The notion of gating as a mechanism capable of controlling the flow of information from one set of neurons to another, has been studied in many regions of the central nervous system. In the nucleus accumbens, where evidence is especially clear, gating seems to rely on the action of bistable neurons, i.e., of neurons that oscillate between a quiescent “down” state and a firing “up” state, and that act as AND-gates relative to their entries. Independently from these observations, a growing body of evidence now indicates that bistable neurons are also quite abundant in the cortex, although their exact functions in the dynamics of the brain remain to be determined. Here, we propose that at least some of these bistable cortical neurons are part of circuits devoted to gating information flow within the cortex. We also suggest that currently available structural, electrophysiological, and imaging data support the existence of at least three different types of gating architectures. The first architecture involves gating directly by the cortex itself. The second architecture features circuits spanning the cortex and the thalamus. The third architecture extends itself through the cortex, the basal ganglia, and the thalamus. These propositions highlight the variety of mechanisms that could regulate the passage of action potentials between cortical neurons sets. They also suggest that gating mechanisms require larger-scale neural circuitry to control the state of the gates themselves, in order to fit in the overall wiring of the brain and complement its dynamics

Baby Skyrmion Strings

We provide analytical and numerical evidence of the existence of classically stable, string-like configurations in a 2+1 dimensional analog of the Skyrme model. The model contains a conserved topological charge usually called the baryon number. Our strings are non-topological solitons which have a constant baryon number per unit length. The energy per length containing one baryon is, however, less than the energy of an isolated baryon (radially symmetric ``baby Skyrmion") in a region of the parameter space, which suggests a degree of stability for our configurations. In a limiting case, our configuration saturates a Bogomolnyi-type bound and is degenerate in energy per baryon with the baby Skyrmion. In another limiting case, the energies are still degenerate but do not saturate the corresponding Bogomolnyi-type bound. Nonetheless, we expect the string to be stable here. Both limiting cases are solvable analytically.Comment: Latex, (revtex), with one figure in a separate postscript file, 12 page

Scattering of Skyrmions

In this paper, we present a detailed study of Skyrmion-Skyrmion scattering for two B=1 Skyrmions in the attractive channel where we observe two different scattering regimes. For large separation, the scattering can be approximated as interacting dipoles. We give a qualitative estimate when this approximation breaks down. For small separations we observe an additional short-range repulsion which is qualitatively similar to monopole scattering. We also observe the interesting effect of "rotation without rotating" whereby two Skyrmions, whose orientations remain constant while well-separated, change their orientation after scattering. We can explain this effect by following preimages through the scattering process, thereby measuring which part of an in-coming Skyrmion forms part of an out-going Skyrmion. This leads to a new way of visualising Skyrmions. Furthermore, we consider spinning Skyrmions and find interesting trajectories

Swimming training increases the G4 acetylcholinesterase content of both fast ankle extensors and flexors

AbstractThe effect of endurance swimming training on AChE molecular forms was examined in 2 groups of functionally antagonist rat muscles, including ankle extensors and flexors, This exercise regimen, which entails predominant dynamic activity (i.e., involving extensive shortening) of both groups or muscles, resulted in marked selective G4 increases in all fast muscles. The G4 elevation exhibited by the ankle flexors was in sharp contrast to the G4 reduction reported in these same muscles following running training, during which their action is predominantly tonic. The results strengthen the conclusion that predominantly dynamic activity increases the G4 content of mature innervated fast muscles

Scraping of reeds by Brazilian oboist — a study of the adjustments in the oboe reeds under the action of external climatic agents

A presente pesquisa visa observar e identificar os ajustes propostos por oboístas brasileiros em palhetas de oboé preparadas para a performance e que sofrem alterações devido a ação da umidade do ar, temperatura do ambiente e altitude relativa ao nível do mar. Também, investigou-se possíveis tendências nas preferências de sonoridade e flexibilidade dos oboístas entrevistados, procurando compreender se existe algum fator que ligue tais tendências com os tipos de ajustes propostos. Com a finalidade de direcionar a pesquisa a um foco de interesse comum aos entrevistados, resumiu-se as diferentes escolas de raspado em duas, Escola Alemã e Escola Americana, tendo em vista que estas escolas exercem grande influência nos mais diversos estilos de raspagem. Um fenômeno notório brasileiro também foi investigado, que é a convivência pacífica das diferentes escolas dentro das orquestras. Como parte dos procedimentos metodológicos, foi realizado um breve levantamento bibliográfico de autores discorrendo sobre raspagens de palhetas de oboé, com a finalidade de compreender o que se considera uma palheta pronta para performance e o que a caracteriza. Utilizou-se também a ferramenta de pesquisas on-line “survey mokey” para uma investigação com oboístas brasileiros, mediante a observação das tendências de sonoridade, flexibilidade e ajustes da palheta. Após a análise dos dados, houve uma listagem graduada de ajustes classificada pelos oboístas brasileiros dentro de suas escolas de raspagem. Concluiu-se haver características muito semelhantes nas preferências de sonoridade, flexibilidade e ajustes, apontando uma provável causa que aproxima as diferentes escolas de oboé em território nacional.The present research aims to observe and identify the adjustments proposed by Brazilian oboists on oboe reeds prepared for the performance and which suffer changes due to the action of air humidity, temperature and altitude relative to sea level. Possible tendencies in the preferences of sonority and flexibility of the oboists interviewed were also investigated, trying to understand if there was any factor connecting such tendencies with the types of adjustments proposed. In order to direct the research to a focus of common interest to the interviews, we summarized the different schools of scraping in two: German School andAmerican School, considering that these schools exert great influence in the most diverse styles of scraping. A notorious Brazilian phenomenon was also investigated, which is the peaceful coexistence of the differentschools within the orchestras. As part of the methodological procedures, a brief bibliographic survey of authors discussing oboe scraping was carried out, in order to understand what is considered a ready prepared reed for a performance and what characterizes it. The online survey tool “survey mokey” was also used for an investigation with Brazilian oboists, observing the tendencies of sonority, flexibility and adjustments of the reed. After analyzing the data, there was a graduated list of adjustments classified by the Brazilian oboists within their scraping schools. It was concluded that there are very similar characteristics in the preferences of sonority, flexibility and adjustments, pointing to a probable cause that approaches the different schools of oboe in national territory

The mobilization of local commitment to urban development programs in Latin America

Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCHBibliography: leaves 87-93.by John Gisiger.M.C.P

Solitons in a Baby-Skyrme model with invariance under area preserving diffeomorphisms

We study the properties of soliton solutions in an analog of the Skyrme model in 2+1 dimensions whose Lagrangian contains the Skyrme term and the mass term, but no usual kinetic term. The model admits a symmetry under area preserving diffeomorphisms. We solve the dynamical equations of motion analytically for the case of spinning isolated baryon type solitons. We take fully into account the induced deformation of the spinning Skyrmions and the consequent modification of its moment of inertia to give an analytical example of related numerical behaviour found by Piette et al.. We solve the equations of motion also for the case of an infinite, open string, and a closed annular string. In each case, the solitons are of finite extent, so called "compactons", being exactly the vacuum outside a compact region. We end with indications on the scattering of baby-Skyrmions, as well as some considerations as the properties of solitons on a curved space.Comment: 30 pages, 5 figures, revtex, major modifications, conclusions modifie