Livres sur le sujet « Fluctuation de densité »

The Bose–Einstein condensation and appearance of superfluidity and superconductivity are introduced from basic phenomena. A systematic theory based on the asymmetric expansion of chapter 11 is shown to correct the T-matrix from unphysical multiple-scattering events. The resulting generalised Soven scheme provides the Beliaev equations for Boson’s and the Nambu–Gorkov equations for fermions without the usage of anomalous and non-conserving propagators. This systematic theory allows calculating the fluctuations above and below the critical parameters. Gap equations and Bogoliubov–DeGennes equations are derived from this theory. Interacting Bose systems with finite temperatures are discussed with successively better approximations ranging from Bogoliubov and Popov up to corrected T-matrices. For superconductivity, the asymmetric theory leading to the corrected T-matrix allows for establishing the stability of the condensate and decides correctly about the pair-breaking mechanisms in contrast to conventional approaches. The relation between the correlated density from nonlocal kinetic theory and the density of Cooper pairs is shown.

The technique of small angle solution scattering has been revolutionized in the last two decades. Exponential increases in computing power, parallel algorithm development, and the development of synchrotron, free-electron X-ray sources, and neutron sources, have combined to allow new classes of studies for biological specimens. These include time-resolved experiments in which functional motions of proteins are monitored on a picosecond timescale, and the first steps towards determining actual electron density fluctuations within particles. In addition, more traditional experiments involving the determination of size and shape, and contrast matching that isolate substructures such as nucleic acid, have become much more straightforward to carry out, and simultaneously require much less material. These new capabilities have sparked an upsurge of interest in solution scattering on the part of investigators in related disciplines. Thus, this book seeks to guide structural biologists to understand the basics of small angle solution scattering in both the X-ray and neutron case, to appreciate its strengths, and to be cognizant of its limitations. It is also directed at those who have a general interest in its potential. The book focuses on three areas: theory, practical aspects and applications, and the potential of developing areas. It is an introduction and guide to the field but not a comprehensive treatment of all the potential applications.

Os contextos pandémico e pós-pandémico vêm impondo às cidades outras dinâmicas, outros sons, outros ecos, outros percursos, outros visitantes humanos e não humanos. Durante o confinamento, o encerramento de espaços teatrais e expositivos – bem como, durante o desconfinamento, as limitações para a sua utilização - têm tido consequências penosas nas programações artísticas e efeitos dramáticos nos quotidianos dos seus agentes (artistas, técnicos, programadores, curadores, etc.). Ao mesmo tempo, a desaceleração da vida da cidade (do trânsito, do ritmo nas ruas, do frenesim produtivo e de consumo, etc.) veio contribuir beneficamente para uma diminuição das emissões de CO2. Neste quadro, a cidade - mais concretamente as suas zonas públicas a céu aberto – surgem mais nitidamente como espaços de circulação e de interferência (ou de suspensão de interferência) entre pessoas. O que aprendemos com a experiência de confinamento e desconfinamento? Em primeiro lugar, que a cidade tem uma densidade flutuante, na medida em que as concentrações populacionais se esvaem quando nos encerramos em casa. Em segundo lugar, que o encontro com o outro (uma das prerrogativas da cidade) pode acontecer em outras escalas que não apenas a dimensão cultural. Em terceiro lugar, que o medo pode ser um sentimento público capaz de fazer implodir as próprias cidades, se não for transformado numa força para a vida. Como é que, neste processo, os artistas se organizam e se constituem como agentes na cidade? Como é que a cidade passou a ser representada? Que cidade é aquela que desejamos? Este congresso surge assim da necessidade de intensificar o diálogo entre a cidade e a arte, em particular as artes performativas. Este encontro efoi o culminar de dois anos de investigação consistente e consolidada no âmbito do projecto TEPe (Technologically Expanded Performance). Ao longo destes dois anos, desenvolvemos atividades com a comunidade com o intuito de promover um diálogo intercultural e transdisciplinar, e proporcionar o encontro com vivências urbanas variadas. Através das diferentes propostas de percursos pela cidade, mapeámos acontecimentos, hoje invisíveis, mas ainda assim presentes: desde “memórias soterradas” a “caminhadas sensoriais”, passando por registos íntimos de confinamento. O encontro visou partilhar as experiências realizadas com a contribuição de duas equipas: a portuguesa, em Lisboa, e a brasileira, em Fortaleza. Para além de apresentarmos as conclusões das pesquisas realizadas, lançamos esta chamada para apresentações, especialmente destinada a artistas e estudiosos de performance art, historiadores das cidades, antropólogos, urbanistas, geógrafos, estudiosos da escuta e do som e a todxs aquelxs a quem interessa pensar (e projectar) a vida na cidade. -------------------------------------------------------------------------------------------------------------- The pandemic and post-pandemic contexts have imposed on cities other dynamics, other sounds, other echoes, other routes, other human and non-human visitors. During the lockdown, the closure of theatrical and exhibition spaces - as well as, during lockdown unlocking, the limitations for their use - have had painful consequences in artistic programming and dramatic effects in the daily lives of its agents (artists, technicians, programmers, curators, etc.). At the same time, the slowing down of city life (traffic, the pace of the streets, the frenzy of production and consumption, etc.) has made a beneficial contribution to a reduction in CO2 emissions. In this context, the city - and more specifically its open-air public areas - emerge more clearly as spaces for circulation and interference (or suspension of interference) between people. What have we learned from the experience of national lockdown and unlocking? Firstly, that the city has a fluctuating density, insofar as population concentrations fade when we shut ourselves indoors. Secondly, the encounter with the other (one of the prerogatives of the city) can take place on other scales than the cultural dimension alone. Thirdly, fear can be a public sentiment capable of imploding cities themselves if it is not transformed into a force for life. How, in this process, are artists organised and constituted as agents in the city? How did the city come to be represented? What kind of city do we want? This congress thus arises from the need to intensify the dialogue between the city and art, particularly the performing arts. This international meeting is the culmination of two years of consistent and consolidated research within the TEPe (Technologically Expanded Performance) project. Throughout these two years, we have developed activities with the community to promote intercultural and transdisciplinary dialogue and provide an encounter with varied urban experiences. Through the different proposals of walks through the city, we have mapped events, today invisible, but still present: from "buried memories" to "sensorial walks", passing through intimate records of confinement. The meeting aims to share the experiences carried out with the contribution of two teams: the Portuguese, in Lisbon, and the Brazilian, in Fortaleza. Besides presenting the conclusions of the researches carried out, we launch this call for presentations, especially addressed to artists and scholars of performance art, historians of cities, anthropologists, urban planners, geographers, scholars of listening and sound and to all those who are interested in thinking (and projecting) life in the city.