Symmetry breaking perturbations and strange attractors

The asymmetrically forced, damped Duffing oscillator is introduced as a prototype model for analyzing the homoclinic tangle of symmetric dissipative systems with \textit{symmetry breaking} disturbances. Even a slight fixed asymmetry in the perturbation may cause a substantial change in the asymptotic behavior of the system, e.g. transitions from two sided to one sided strange attractors as the other parameters are varied. Moreover, slight asymmetries may cause substantial asymmetries in the relative size of the basins of attraction of the unforced nearly symmetric attracting regions. These changes seems to be associated with homoclinic bifurcations. Numerical evidence indicates that \textit{strange attractors} appear near curves corresponding to specific secondary homoclinic bifurcations. These curves are found using analytical perturbational tools

Knowledge-Salvage Practices for Dormant R&D Projects

Most successful firms have an abundance of new and old knowledge in their research and development laboratories, and only a fraction is being put into use in new product development. This knowledge is left over from projects that have been killed at different development stages and may actually carry considerable value. In this article, we propose a knowledge bank as a possible solution to preserve and possibly grow this knowledge. It is a self-sustaining institute with minimal or no ongoing effort from the donor company, yet manages the knowledge in a way that protects proprietary interests and actively fosters communication and interchange among sponsoring companies wherever possible. The framework of this structure, as well as how it works, is described here. Specifically, a system dynamics modeling of the knowledge bank is developed, and a simulation study is conducted using VENSIM®. The results confirm the viability of creating such a system in a consortium of organizations

Admissible equilibria of non-neutral plasmas in a Malmberg-Penning trap

A "parallel current constraint" is derived, that in combination with the Poisson equation allows one to select admissible equilibria of non-neutral plasmas in a Malmberg-Penning trap in the presence of a nonuniform and nonaxisymmetric magnetic field. Asymmetry-induced currents (analogous to the Pfirsch-Schluter currents in Tokamaks) appearing in a non-neutral plasma even in the absence of magnetic drifts are explicitly computed in the case of a uniformly tilted magnetic field

Equilibrium of non-neutral plasmas in a Malmberg\u2013Penning trap with a weakly tilted magnetic field

The effect of small asymmetric magnetic perturbations on the equilibrium of a non-neutral plasma confined in a Malmberg-Penning trap is analyzed. A constraint, known in the theory of tandem mirrors as the condition of current closure, is derived for non-neutral plasmas. Together with Poisson's equation, this constraint provides a set of equations for determining self-consistent asymmetric equilibria of non-neutral plasmas in Malmberg-Penning traps. As an example of this approach, the non-neutral plasma equilibrium in the presence of a weak magnetic tilt is analyzed. Analytical and semianalytical solutions for the electric potential variations inside the trap are found in a paraxial limit for various radial density profiles of the plasma, including the case of global thermal equilibrium. The numerical procedure aimed to obtain self-consistent plasma equilibria for a magnetic field with a large asymmetry is also discussed. The newly developed method can be straightforwardly applied to determine plasma equilibria under the effect of the magnetic perturbations of higher multipolarity (such as, quadrupole or octupole fields)

Será a insuficiência renal uma contra-indicação relativa para as biópsias broncoscópicas?

Resumo: Em 1977, Cunningham e col. demonstraram que, nos doentes urémicos sujeitos a broncofibroscopia com biopsias, 45% tiveram hemorragias.Actualmente, não há trabalhos publicados que avaliem este risco.Os autores resolveram avaliar os processos de todas as broncofibroscopias realizadas entre 1997 e 2002 no Hospital de Bellvue, Nova Iorque, registando os resultados da ureia, da creatinina, do hemograma, do estudo da coagulação, do tipo de biópsias executadas da pré-medicação e das complicações.Os doentes eram incluídos nos trabalhos desde que tivessem a ureia superior ou igual a 30 mg/dl e/ou a creatinina superior ou igual a 2,0 mg/dl. Perante estes critérios foram incluídos no estudo 72 doentes.Vinte e cinco doentes dos 72(35 %) foram submetidos a biopsias. Sete dos 25 (28 %) foram hemodializados e 18 dos 25(72 %) não foram hemodializados. Todos os doentes hemodializados foram submetidos à broncofibroscopia 24 horas depois da hemodiálise e foram submetidos a uma perfusão de desmopressina pré-broncofibroscopia, e um doente com coagulopatia recebeu plaquetas e plasma fresco.Os doentes hemodializados submetidos a biópsias tinham valores de ureia que oscilavam entre 31-65 mg/ /dl e valores de creatinina que oscilavam entre 5,2-18,7 mg/dl, e o único doente deste grupo que fez punção aspirativa transbrônquica tinha uma ureia de 32 mg/dl e uma creatinina de 4,3 mg/dl.Em doze dos 18 doentes não submetidos a hemodiálise e submetidos a biópsias, os valores de ureia oscilavam entre 20-69 mg/dl e os valores de creatinina entre 0,9-2,5 mg/dl. Deste grupo, os quatro doentes que foram submetidos a punção aspirativa transbrônquica tinham valores de ureia entre 20-62 mg/dl e valores de creatinina entre 1,1-4,5 mg/dl. Os dois doentes sujeitos a biópsias e punção aspirativa transbrônquica tinham valores de ureia de 30 e 35 mg/dl e valores de de 1,4 e 1,5 mg/dl. Um dos 25 doentes não hemodializados teve uma complicação major, hemorragia maciça que obrigou a intervenção. Um outro deste mesmo grupo teve apenas uma hemorragia minor.Não houve complicações nos doentes hemodializados.Estes resultados sugerem que não há tantas complicações como seria de esperar nos doentes com insuficiência renal, como demonstrou Cullingam e col. em 1977. Mostram que não há complicações nos doentes hemodializados e sujeitos a uma perfusão de desmopressina antes de ser efectuada a broncofibroscopia.Estes dados obrigam à realização de novos estudos para avaliar de facto se as biópsias broncoscópicas são uma contra-indicação relativa na insuficiência renal. Palavras-chave: Broncofibroscopia, biópsias broncoscópicas, insuficiência renal, complicações hemorrágica

Free fermion antibunching in a degenerate atomic Fermi gas released from an optical lattice

Noise in a quantum system is fundamentally governed by the statistics and the many-body state of the underlying particles. Whereas for bosonic particles the correlated noise observed for e.g. photons or bosonic neutral atoms can still be explained within a classical field description with fluctuating phases, the anticorrelations in the detection of fermionic particles have no classical analogue. The observation of such fermionic antibunching is so far scarce and has been confined to electrons and neutrons. Here we report on the first direct observation of antibunching of neutral fermionic atoms. Through an analysis of the atomic shot noise in a set of standard absorption images, of a gas of fermionic 40K atoms released from an optical lattice, we find reduced correlations for distances related to the original spacing of the trapped atoms. The detection of such quantum statistical correlations has allowed us to characterise the ordering and temperature of the Fermi gas in the lattice. Moreover, our findings are an important step towards revealing fundamental fermionic many-body quantum phases in periodic potentials, which are at the focus of current research.Comment: (Nature, in press

Global Superdiffusion of Weak Chaos

A class of kicked rotors is introduced, exhibiting accelerator-mode islands (AIs) and {\em global} superdiffusion for {\em arbitrarily weak} chaos. The corresponding standard maps are shown to be exactly related to generalized web maps taken modulo an ``oblique cylinder''. Then, in a case that the web-map orbit structure is periodic in the phase plane, the AIs are essentially {\em normal} web islands folded back into the cylinder. As a consequence, chaotic orbits sticking around the AI boundary are accelerated {\em only} when they traverse tiny {\em ``acceleration spots''}. This leads to chaotic flights having a quasiregular {\em steplike} structure. The global weak-chaos superdiffusion is thus basically different in nature from the strong-chaos one in the usual standard and web maps.Comment: REVTEX, 4 Figures: fig1.jpg, fig2.ps, fig3.ps, fig4.p