Tsallis Information Measure, Multiresolution Analysis, and Nonlinear Dynamics

Projet PROMATHWe undertake the study of signals originated in time-dependent nonlinear systems by recourse to a wavelet based multiresolution analysis, as adapted to a non-extensive (Tsallis) scenario. Diverse applications are discussed that illustrate the fact that a Tsallis environment seems to provide one with more detailed information than the conventional Shannon one

Species-Specific Diversity of a Fixed Motor Pattern: The Electric Organ Discharge of Gymnotus

Understanding fixed motor pattern diversity across related species provides a window for exploring the evolution of their underlying neural mechanisms. The electric organ discharges of weakly electric fishes offer several advantages as paradigmatic models for investigating how a neural decision is transformed into a spatiotemporal pattern of action. Here, we compared the far fields, the near fields and the electromotive force patterns generated by three species of the pulse generating New World gymnotiform genus Gymnotus. We found a common pattern in electromotive force, with the far field and near field diversity determined by variations in amplitude, duration, and the degree of synchronization of the different components of the electric organ discharges. While the rostral regions of the three species generate similar profiles of electromotive force and local fields, most of the species-specific differences are generated in the main body and tail regions of the fish. This causes that the waveform of the field is highly site dependant in all the studied species. These findings support a hypothesis of the relative separation of the electrolocation and communication carriers. The presence of early head negative waves in the rostral region, a species-dependent early positive wave at the caudal region, and the different relationship between the late negative peak and the main positive peak suggest three points of lability in the evolution of the electrogenic system: a) the variously timed neuronal inputs to different groups of electrocytes; b) the appearance of both rostrally and caudally innervated electrocytes, and c) changes in the responsiveness of the electrocyte membrane

A conceptual view of internationalization strategies under dual institutional pressures for legitimacy and conformity

Internacionalizar as operações requer que as empresas multinacionais (EMNs) desenvolvam estratégias capazes de lidar, simultaneamente, com as pressões institucionais externas, para a legitimidade, e as pressões institucionais internas, para a conformidade. Neste artigo conceitual e baseado na literatura de teoria institucional em negócios internacionais, desenvolve-se um conjunto de proposições teóricas sobre quais as estratégias de entrada nos mercados externos seguidas pelas EMNs face aos ambientes institucionais. Com foco predominante no ambiente institucional externo e nas diferenças de desenvolvimento institucional, também aborda a relevância de considerar o ambiente interno. As estratégias de entrada tendem a ser baseadas em modos de baixo envolvimento e em parcerias, como joint ventures, para entrar em países institucionalmente imaturos ou institucionalmente mais distantes. As aquisições e as parcerias podem ser usadas se as pressões institucionais forem menores. Conclui-se com uma discussão geral e o apontamento de questões para pesquisas futuras.info:eu-repo/semantics/publishedVersio

Voltage-gated potassium conductances in Gymnotus electrocytesAB

Electrocytes are muscle-derived cells that generate the electric organ discharge (EOD) in most gymnotiform fish. We used an in vitro preparation to determine if the complex EOD of Gymnotus carapo was related to the membrane properties of electrocytes. We discovered that in addition to the three Na+-mediated conductances described in a recent paper [Sierra F, Comas V, Buño W, Macadar O (2005) Sodium-dependent plateau potentials in electrocytes of the electric fish Gymnotus carapo. J Comp Physiol A 191:1-11] there were four K+-dependent conductances. Membrane depolarization activated a delayed rectifier (IK) and an A-type (IA) current. IA displayed fast voltage-dependent activation-inactivation kinetics, was blocked by 4-aminopyridine (1 mM) and played a major role in action potential (AP) repolarization. Its voltage dependence and kinetics shape the brief AP that typifies Gymnotus electrocytes. The IK activated by depolarization contributed less to AP repolarization. Membrane hyperpolarization uncovered two inward rectifiers (IR1 and IR2) with voltage dependence and kinetics that correspond to the complex >hyperpolarizing responses> (HRs) described under current-clamp. IR1 shows >instantaneous> activation, is blocked by Ba2+ and Cs+ and displays a voltage and time dependent inactivation that matches the hyperpolarizing phase of the HR. The activation of IR2 is slower and at more negative potentials than IR1 and is resistant to Ba2+ and Cs+. This current fits the depolarizing phase of the HR. The EOD waveform of Gymnotus carapo is more complex than that of other gymnotiform fish species, the complexity originates in the voltage responses generated through the interactions of three Na+ and four K+ voltage- and time-dependent conductances although the innervation pattern also contributes [Trujillo-Cenóz O, Echagüe JA (1989) Waveform generation of the electric organ discharge in Gymnotus carapo. I. Morphology and innervation of the electric organ. J Comp Physiol A 165:343-351]. © 2006 IBRO.Peer Reviewe