Construction of a non-standard quantum field theory through a generalized Heisenberg algebra

We construct a Heisenberg-like algebra for the one dimensional quantum free Klein-Gordon equation defined on the interval of the real line of length $L$. Using the realization of the ladder operators of this type Heisenberg algebra in terms of physical operators we build a 3+1 dimensional free quantum field theory based on this algebra. We introduce fields written in terms of the ladder operators of this type Heisenberg algebra and a free quantum Hamiltonian in terms of these fields. The mass spectrum of the physical excitations of this quantum field theory are given by $\sqrt{n^2 \pi^2/L^2+m_q^2}$, where $n= 1,2,...$ denotes the level of the particle with mass $m_q$ in an infinite square-well potential of width $L$.Comment: Latex, 16 page

Inter-relação da estrutura muscular e textura da carne.

Organização do sistema miofibrilar; Atividade enzimática durante a maturação da carne; Influência do tipo de fibra muscular na maturação; Gordura subcutânea e intramuscular; tecido conjuntivo; Quantidades e tipos de colágenos, ligações cruzadas do colágeno; Métodos para avaliação da textura.bitstream/item/110554/1/INTER-RELACAO-DA-ESTRUTURA.pd

Criação geográfica contemporânea

Esta reflexão de carácter exploratório pretende, como o próprio nome indica, ser um estudo preliminar das questões que se colocam com maior acuidade na contemporaneidade, no âmbito do ensino-aprendizagem da composição coreográfica. Partindo da (in)definição que caracteriza a Dança Contemporânea e os seus métodos e processos de criação, na qual é possível reconhecer como fundamental o desenvolvimento de percursos essencialmente singulares, pretendemos refletir sobre a necessidade de contribuir para o desenvolvimento das capacidades criativas dos intérpretes-criadores contemporâneos em contextos de formação. Esta é uma problemática que a nossa intervenção pedagógica e interesse profissional de forma plena justificam. Debruçamonos sobre a singularidade de dois projetos no âmbito da Criação Coreográfica Contemporânea Portuguesa, refletindo sobre aspetos da relação entre coreógrafo - intérprete - pesquisa - materialização do movimento. Pretendemos sublinhar a importância que reconhecemos do ensino-aprendizagem da composição coreográfica e a necessidade de o repensar na proximidade com as práticas artísticas atuais, procurando fazer emergir questões sobre a problemática aqui abordada

Negative modes and the thermodynamics of Reissner-Nordstr\"om black holes

We analyse the problem of negative modes of the Euclidean section of the Reissner-Nordstr\"om black hole in four dimensions. We find analytically that a negative mode disappears when the specific heat at constant charge becomes positive. The sector of perturbations analysed here is included in the canonical partition function of the magnetically charged black hole. The result obeys the usual rule that the partition function is only well-defined when there is local thermodynamical equilibrium. We point out the difficulty in quantising Einstein-Maxwell theory, where the so-called conformal factor problem is considerably more intricate. Our method, inspired by hep-th/0608001, allows us to decouple the divergent gauge volume and treat the metric perturbations sector in a gauge-invariant way.Comment: 24 pages, 1 figure; v2 minor changes to fit published versio

Classical diffusion in double-delta-kicked particles

We investigate the classical chaotic diffusion of atoms subjected to {\em pairs} of closely spaced pulses (`kicks) from standing waves of light (the $2\delta$-KP). Recent experimental studies with cold atoms implied an underlying classical diffusion of type very different from the well-known paradigm of Hamiltonian chaos, the Standard Map. The kicks in each pair are separated by a small time interval $\epsilon \ll 1$, which together with the kick strength $K$, characterizes the transport. Phase space for the $2\delta$-KP is partitioned into momentum `cells' partially separated by momentum-trapping regions where diffusion is slow. We present here an analytical derivation of the classical diffusion for a $2\delta$-KP including all important correlations which were used to analyze the experimental data. We find a new asymptotic ($t \to \infty$) regime of `hindered' diffusion: while for the Standard Map the diffusion rate, for $K \gg 1$, $D \sim K^2/2[1- J_2(K)..]$ oscillates about the uncorrelated, rate $D_0 =K^2/2$, we find analytically, that the $2\delta$-KP can equal, but never diffuses faster than, a random walk rate. We argue this is due to the destruction of the important classical `accelerator modes' of the Standard Map. We analyze the experimental regime $0.1\lesssim K\epsilon \lesssim 1$, where quantum localisation lengths $L \sim \hbar^{-0.75}$ are affected by fractal cell boundaries. We find an approximate asymptotic diffusion rate $D\propto K^3\epsilon$, in correspondence to a $D\propto K^3$ regime in the Standard Map associated with 'golden-ratio' cantori.Comment: 14 pages, 10 figures, error in equation in appendix correcte