Alternate islands of multiple isochronous chains in wave-particle interactions

We analyze the dynamics of a relativistic particle moving in a uniform magnetic field and perturbed by a standing electrostatic wave. We show that a pulsed wave produces an infinite number of perturbative terms with the same winding number, which may generate islands in the same region of phase space. As a consequence, the number of isochronous island chains varies as a function of the wave parameters. We observe that in all the resonances, the number of chains is related to the amplitude of the various resonant terms. We determine analytically the position of the periodic points and the number of island chains as a function of the wave number and wave period. Such information is very important when one is concerned with regular particle acceleration, since it is necessary to adjust the initial conditions of the particle to obtain the maximum acceleration.Comment: Submitte

Phase separation in asymmetrical fermion superfluids

Motivated by recent developments on cold atom traps and high density QCD we consider fermionic systems composed of two particle species with different densities. We argue that a mixed phase composed of normal and superfluid components is the energetically favored ground state. We suggest how this phase separation can be used as a probe of fermion superfluidity in atomic traps.Comment: 9 pages, LaTeX2e, version to appear in Phys.Rev.Let

First principle theory of correlated transport through nano-junctions

We report the inclusion of electron-electron correlation in the calculation of transport properties within an ab initio scheme. A key step is the reformulation of Landauer's approach in terms of an effective transmittance for the interacting electron system. We apply this framework to analyze the effect of short range interactions on Pt atomic wires and discuss the coherent and incoherent correction to the mean-field approach.Comment: 5 pages, 3 figure

Economics and social psychology on public goods: experiments and explorations

Economics and social psychology come from different traditions in social science, and in the past they seldom met. Their territories seemed to be well delimited. The former discipline’s mainstream focused on market mediated interactions, making sense of an asocial concept of action by referring it to “the ordinary business of life” (Marshall, 1920, I.II.1) where agent’s choices supposedly are independent from those of other parties in the transactions (Sugden, 2002); on the other hand, the second discipline descends from the more romantic view of man as a social being, and was stimulated by questions on why and how the immersion of individuals in the multitude, or the simple presence of others, appeared to transform behaviour. Lately, however, economics has started moving in a direction that reduces this gap. In a double but interrelated move, economics is adopting experimental methods familiar to those of social psychology, and is becoming more concerned with the relevance of rational choice in contexts where there is clear inter-individual dependence, raising questions to which social psychologists have already devoted considerable time and effort. As a part of this movement, social dilemmas, that is, “situations in which (a) individual group members can obtain higher outcomes (at least under some circumstances) if they pursue their individual interest while (b) the group obtains higher incomes if all group members further the group interest” (Dijk and Wilke, 1998: 110) have become the focus of shared interest of both economists and social psychologists. The motivation for the study of social dilemmas does not differ much in economics and social psychology and it arises out of two major types of challenges. The first (Fontaine, 2002) is related to the growing consciousness of the pervasiveness of market failures (combined with government failures) concerning issues of major social urgency like pollution and the use of scarce resources. The second, (Dawes, 1991) cropped up out of the finding that people both in real-life and experimental contexts fail to behave systematically in the way depicted by standard game theory, often opting for more benign strategies. Interest in social dilemmas is thus related, on the one hand, with the concern with problems that the market cannot solve, and, on the other, with understanding the reasons that may drive people to act in ways that are not in line with rational self-interest. For economics those questions are arcane questions 1 that were never ignored by the best minds in this discipline. Marshall’s sentence in epigraph is a clear instance of this concern. This essay does not intend to cover the whole scope of existing approaches to social dilemmas since it only deals with dilemma situations that somehow fit into the economist’s category of public good provision problems and with the experimental studies in economics and social psychology2. On the basis of an exploratory joint survey of experimental literature from both disciplines, it focuses on their differences in theoretical framing and their use of the experimental method. The following points will be argued: (a) Twenty five years of experimental research in both disciplines have produced an impressive accumulation of coherent results showing that in spite of the free-riding prediction, there is a tendency to voluntary contribution in “small” groups; (b) Notwithstanding the abundance of experimental studies, several interesting problems remain unexplored. In economics, the research focus has been on “are the game theoretical predictions corroborated by experimental evidence?”, whereas in social psychology it has been on “what may cause the voluntary disposition to contribute”. Questions pertaining to “what institutional contexts might hinder or foster voluntary contribution” still offer a vast domain of unexplored possibilities. (c) In spite of all efforts, the conceptual framework that may account for the contributive disposition in public good dilemma situations and help “discover how this latent social asset can be developed” remains rather sketchy

Dexamethasone-induced and estradiol-induced CREB activation and annexin 1 expression in CCRF-CEM lymphoblastic cells: evidence for the involvement of cAMP and p38 MAPK.

AIMS: Annexin 1 (ANXA1), a member of the annexin family of calcium-binding and phospholipid-binding proteins, is a key mediator of the anti-inflammatory actions of steroid hormones. We have previously demonstrated that, in the human lymphoblastic CCRF-CEM cell line, both the synthetic glucocorticoid hormone, dexamethasone (Dex), and the estrogen hormone, 17beta-estradiol (E2beta), induce the synthesis of ANXA1, by a mechanism independent of the activation of their nuclear receptors. Recently, it was reported that the gene coding for ANXA1 contains acAMP-responsive element (CRE). In this work, we investigated whether Dex and E2beta were able to induce the activation of CRE binding proteins (CREB) in the CCRF-CEM cells. Moreover, we studied the intracellular signalling pathways involved in CREB activation and ANXA1 synthesis in response to Dex and E2beta; namely, the role of cAMP and the p38 mitogen activated protein kinase (MAPK). RESULTS: The results show that Dex and E2beta were as effective as the cAMP analogue, dBcAMP, in inducing CREB activation. On the contrary, dBcAMP induced ANXA1 synthesis as effectively as these steroid hormones. Furthermore, the cAMP antagonist, Rp-8-Br-cAMPS, and the specific p38 MAPK inhibitor,SB203580, effectively prevented both Dex-induced, E2beta-induced and dBcAMP-induced CREB activation and ANXA1 synthesis. CONCLUSIONS: Taken together, our results suggest that,in CCRF-CEM cells, Dex-induced and E2beta-inducedANXA1 expression requires the activation of the transcription factor CREB, which in turn seems to be mediated by cAMP and the p38 MAPK. These findings also suggest that, besides the nuclear steroid hormone receptors, other transcription factors, namely CREB, may play important roles in mediating the anti-inflammatory actions of glucocorticoids and oestrogen hormone

Wave-particle interactions in a long traveling wave tube with upgraded helix

We investigate the interaction of electromagnetic waves and electron beams in a 4 meters long traveling wave tube (TWT). The device is specially designed to simulate beam-plasma experiments without appreciable noise. This TWT presents an upgraded slow wave structure (SWS) that results in more precise measurements and makes new experiments possible. We introduce a theoretical model describing wave propagation through the SWS and validated by the experimental dispersion relation, impedance, phase and group velocities. We analyze nonlinear effects arising from the beam-wave interaction, such as the modulation of the electron beam and the wave growth and saturation process. When the beam current is low, the wave growth coefficient and saturation amplitude follow the linear theory predictions. However, for high values of current, nonlinear space charge effects become important and these parameters deviate from the linear predictions, tending to a constant value. After saturation, we also observe trapping of the beam electrons, which alters the wave amplitude along the TWT.Comment: Submitted for publicatio

Interferência da iluminância nos parâmetros monocíclicos do patossistema Mycosphaerella musicola - Musa spp.

A bananicultura está distribuída em praticamente todo o mundo. A sigatoka-amarela é uma das doenças de maior importância de alguns países tropicais, e pode ter sua severidade aumentada em condições ambientais favoráveis (2, 3, 5)