A Neural Circuit for Coordinating Reaching with Grasping: Autocompensating Variable Initial Apertures, Perturbations to Target Size, and Perturbations to Target Orientation

A neural network model is presented, that extends principles of the VITE (vector integration to end-point) model [1, 2, 3, 4] of primate reaching to the more complex case of reach-grasp coordination. The main new planning problem addressed by the model is how to simulate human data on temporal coordination between reaching and grasping, while at the same time remaining stable and compensating for altered initial apertures and perturbations of object size and object location/ orientation. Simulations of the model replicate key features of four different experimental protocols with a single set of parameters. The proposed circuit computes reaching to grasp trajectories in real-time, by continuously updating vector positioning commands, and with no precomputation of total or component movement times. The model consists of three generator channels: transport, which generates a reaching trajectory; aperture, which controls distance between thumb and index finger; and orientation, which controls hand orientation vis-a-vis target's orientation.CONACYT of Mexico; Defense Advanced Research Projects Agency and Office of Naval Research (N00014-95-1-0409

HERMANOS EN EL CAMINO, UNA LUCHA DESDE LA SOCIEDAD CIVIL

se realizó un análisis teórico sobre el papel de la sociedad civil en los Estados modernos, tomando como base los postulados teóricos de Andrew Cohen y Jean Lee Arato, para quienes el papel de la sociedad civil es fundamental en la consolidación de los Estados democráticos, ya que con la creación de conciencia social se genera un mayor grado de participación y por ende todos quienes componen el Estado trabajan en la consolidación del mismo. De igual modo se consideran las bases teóricas que establecen que una sociedad civil consolidada trabaja para la mejora del desarrollo social, tomando en cuenta los postulados teóricos de Habermas, pasando por Gramsci, Hegel, David Held, Jeffrey Alexander, entre otros, los cuales nos permiten reforzar la propuesta teórica de Arato y Cohen. Con el propósito de consolidar el presente trabajo de investigación es necesario considerar a todos los actores que intervienen en la atención del fenómeno migratorio, sin dejar de lado al principal actor estudiado que es la sociedad civil organizada

Spin polarization control by electric field gradients

We show that the propagation of spin polarized carriers may be dramatically affected by {\em inhomogeneous} electric fields. Surprisingly, the spin diffusion length is found to strongly depend on the sign and magnitude of electric field \emph{gradients}, in addition to the previously reported dependence on the sign and magnitude of the electric field [Yu & Flatt\'e, Phys. Rev. B {\bf 66}, 201202(R) 2002; {\em ibid.} {\bf 66}, 235302 (2002)]. This indicates that purely electrical effects may play a crucial role in spin polarized injection, transport and detection in semiconductor spintronics. A generalized drift-diffusion equation that describes our findings is derived and verified by numerical calculations using the Boltzmann transport equation.Comment: 7 pages, 4 figures; updated and extended version, added figure, updated reference lis

Magnon spin Hall magnetoresistance of a gapped quantum paramagnet

Motivated by recent experimental work, we consider spin transport between a normal metal and a gapped quantum paramagnet. We model the latter as the magnonic Mott-insulating phase of an easy-plane ferromagnetic insulator. We evaluate the spin current mediated by the interface exchange coupling between the ferromagnet and the adjacent normal metal. For the strongly interacting magnons that we consider, this spin current gives rise to a spin Hall magnetoresistance that strongly depends on the magnitude of the magnetic field, rather than its direction. This Letter may motivate electrical detection of the phases of quantum magnets and the incorporation of such materials into spintronic devices.Comment: 5 pages, 5 figure

Zeeman splitting of shallow donors in GaN

The Zeeman splitting of the donor spectra in cubic- and hexagonal-GaN are studied using an effective mass theory approach. Soft-core pseudopotentials were used to describe the chemical shift of the different substitutional dopants. The donor ground states calculated range from 29.5 to 33.7 meV, with typically 1 meV higher binding in the hexagonal phase. Carbon is found to produce the largest donor binding energy. The ionization levels and excited states are in excellent agreement with Hall and optical measurements, and suggest the presence of residual C in recent experiments.Comment: REVTEX file - 2 figure

Esclarecimiento de algunos puntos dudosos en la vida de Fray Bernardo Boil

Sus misiones diplomáticas en Francia antes de su viaje a América. Las reclamaciones de Fernando el Católico contra los corsarios Casenove-Coullo

A Neural Circuit for Coordinating Reaching with Grasping: Autocompensating Variable Initial Apertures, Perturbations to Target Size, and Perturbations to Target Orientation

A neural network model is presented, that extends principles of the VITE (vector integration to end-point) model [1, 2, 3, 4] of primate reaching to the more complex case of reach-grasp coordination. The main new planning problem addressed by the model is how to simulate human data on temporal coordination between reaching and grasping, while at the same time remaining stable and compensating for altered initial apertures and perturbations of object size and object location/ orientation. Simulations of the model replicate key features of four different experimental protocols with a single set of parameters. The proposed circuit computes reaching to grasp trajectories in real-time, by continuously updating vector positioning commands, and with no precomputation of total or component movement times. The model consists of three generator channels: transport, which generates a reaching trajectory; aperture, which controls distance between thumb and index finger; and orientation, which controls hand orientation vis-a-vis target's orientation.CONACYT of Mexico; Defense Advanced Research Projects Agency and Office of Naval Research (N00014-95-1-0409