Visual motion perception.

The primate visual motion system performs numerous functions essential for survival in a dynamic visual world. Prominent among these functions is the ability to recover and represent the trajectories of objects in a form that facilitates behavioral responses to those movements. The first step toward this goal, which consists of detecting the displacement of retinal image features, has been studied for many years in both psychophysical and neurobiological experiments. Evidence indicates that achievement of this step is computationally straightforward and occurs at the earliest cortical stage. The second step involves the selective integration of retinal motion signals according to the object of origin. Realization of this step is computationally demanding, as the solution is formally underconstrained. It must rely--by definition--upon utilization of retinal cues that are indicative of the spatial relationships within and between objects in the visual scene. Psychophysical experiments have documented this dependence and suggested mechanisms by which it may be achieved. Neurophysiological experiments have provided evidence for a neural substrate that may underlie this selective motion signal integration. Together they paint a coherent portrait of the means by which retinal image motion gives rise to our perceptual experience of moving objects.

O garantidor e a novação recuperacional

O objetivo da presente dissertação é analisar os efeitos gerados aos garantidores dos devedores em recuperação judicial, quando aprovado e homologado o Plano de Recuperação Judicial destes, diante do fenômeno da novação previsto no art. 59 da Lei nº 11.101/05. Essa análise será feita a partir de um estudo geral do instituto da novação no direito civil, bem como da disciplina legal das garantias pessoais, principalmente o aval e a fiança. Com base nesta visão cível, serão comparadas as duas posições hoje existentes sobre a matéria no âmbito comercial, tanto na doutrina como na jurisprudência nacionais, com o estudo dos argumentos utilizados por aqueles que defendem a manutenção incólume da obrigação dos terceiros garantidores, independentemente da novação, com a possibilidade dos credores prosseguirem normalmente com sua cobrança, bem como por aqueles que acreditam deva ser extinta a obrigação dos garantidores com a novação. Será apontada uma interpretação alternativa, construída pelo autor, de, em um primeiro momento, ocorrer a extinção da obrigação dos garantidores, enquanto estiver sendo adimplido o Plano de Recuperação pelo devedor principal, e retorno as obrigações originais caso descumprida a proposta aprovada pelos credores. Além dos efeitos decorrentes da lei, será analisada a eficácia da cláusula comumente inserida em Planos de Recuperação, de extinção da obrigação dos garantidores com a concessão da recuperação judicial. Ao final, diante do entendimento apresentado pelo autor sobre os efeitos legais da novação para o garantidor e da eficácia da mencionada cláusula, será proposta uma alteração legislativa, nos moldes do direito argentino, para possibilitar que o terceiro garantidor apresente uma proposta de pagamento conjunta com a devedora principal, encerrando-se a divergência interpretativa hoje existente.

A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups

Context. Nearby late-type stars are excellent targets for seeking young objects in stellar associations and moving groups. The origin of these structures is still misunderstood, and lists of moving group members often change with time and also from author to author. Most members of these groups have been identified by means of kinematic criteria, leading to an important contamination of previous lists by old field stars. Aims. We attempt to identify unambiguous moving group members among a sample of nearby-late type stars by studying their kinematics, lithium abundance, chromospheric activity, and other age-related properties. Methods. High-resolution echelle spectra (R ~ 57 000) of a sample of nearby late-type stars are used to derive accurate radial velocities that are combined with the precise Hipparcos parallaxes and proper motions to compute galactic-spatial velocity components. Stars are classified as possible members of the classical moving groups according to their kinematics. The spectra are also used to study several age-related properties for young late-type stars, i.e., the equivalent width of the lithium Li i 6707.8 Å line or the R'_HK index. Additional information like X-ray fluxes from the ROSAT All-Sky Survey or the presence of debris discs is also taken into account. The different age estimators are compared and the moving group membership of the kinematically selected candidates are discussed. Results. From a total list of 405 nearby stars, 102 have been classified as moving group candidates according to their kinematics. i.e., only ~25.2% of the sample. The number reduces when age estimates are considered, and only 26 moving group candidates (25.5% of the 102 candidates) have ages in agreement with the star having the same age as an MG member.

Emission-line galaxy surveys with GTC: The Hα Universe

Emission line galaxies are the most easily detected and studied objects in the high redshift Universe. They are being used to trace the evolution of critical observables of the Universe such as Star Formation Rate densities, starburst properties and abundances. Most of the research is being done using [OII]3727 and UV lines, but Hα is still one the best tracers for Star Formation Rate and physical properties of current star-forming galaxies. As a complementary contribution to studies of galaxy evolution, our team has focused into a long-term project to study the population of Hα-selected star-forming galaxies of the Universe at different redshifts. In 1995 we first determined the local Hα luminosity function, and from it the Star Formation Rate density (SFRd) of the local Universe. We then, using narrow-band imaging in the optical, extended this measurement to z ≃ 0.24 and z ≃ 0.4. Working in the near-infrared, GTC will be a very powerful tool to study the evolution of the Hα emission-line galaxy populations at different redshifts. We will both quantify the SFRd evolution and characterize the star-forming galaxy populations by directly comparing the same observables at all redshifts up to z ≃ 2.5.