On the collapse in fourth order gravities

The gravitational collapse in fourth order theories of gravity defined by an arbitrary action of the scalar curvature shows significant deviations with General Relativity. The presence of a new scalar mode produces a higher initial contraction that favors the reduction of the collapsing time. However, depending on the particular model, there are fundamental differences when the modifications to the General Relativity collapse leave the linear regime. These analyses can be used to exclude an important region of the parameter space associated with alternative gravitational models.Comment: 4 pages, 2 figures, Contribution to the Proceedings of Spanish Relativity Meeting ERE2011, Madrid 201

Opposite polarity field with convective downflow and its relation to magnetic spines in a sunspot penumbra

We discuss NICOLE inversions of Fe I 630.15 nm and 630.25 nm Stokes spectra from a sunspot penumbra recorded with the CRISP imaging spectropolarimeter on the Swedish 1-m Solar Telescope at a spatial resolution close to 0.15". We report on narrow radially extended lanes of opposite polarity field, located at the boundaries between areas of relatively horizontal magnetic field (the intra-spines) and much more vertical field (the spines). These lanes harbor convective downflows of about 1 km/s. The locations of these downflows close to the spines agree with predictions from the convective gap model (the "gappy penumbra") proposed six years ago, and more recent 3D MHD simulations. We also confirm the existence of strong convective flows throughout the entire penumbra, showing the expected correlation between temperature and vertical velocity, and having vertical RMS velocities of about 1.2 km/s.Comment: Accepted for publication in A&A (06-March-2013). Minor corrections made in this version

A Simple Kinetic Model Describes the Processivity of Myosin-V

Myosin-V is a motor protein responsible for organelle and vesicle transport in cells. Recent single-molecule experiments have shown that it is an efficient processive motor that walks along actin filaments taking steps of mean size close to 36 nm. A theoretical study of myosin-V motility is presented following an approach used successfully to analyze the dynamics of conventional kinesin but also taking some account of step-size variations. Much of the present experimental data for myosin-V can be well described by a two-state chemical kinetic model with three load-dependent rates. In addition, the analysis predicts the variation of the mean velocity and of the randomness -- a quantitative measure of the stochastic deviations from uniform, constant-speed motion -- with ATP concentration under both resisting and assisting loads, and indicates a {\it sub}step of size $d_{0} \simeq$ 13-14 nm (from the ATP-binding site) that appears to accord with independent observations.Comment: 20 pages, 7 figures, to be published in Biophys. J. in 200

Comment on `Strong Vortex Liquid Correlation' from Multiterminal Measurements on Untwinned YBa2_2Cu3_3O7−δ_{7-\delta} Single Crystals'

A.Rydh and \"O.Rapp [Phys. Rev. Lett. {\bf 86}, 1873 (2001).] claim that the vortex liquid in untwinned YBa$_2$Cu$_3$O$_{7-\delta}$ crystals is correlated above the melting transition, in striking contrast to previous work [D.L\'opez {\it et al.}, Phys. Rev. Lett. {\bf 76}, 4034 (1996).]. In this Comment we present new measurements using the same experimental technique on twinned and untwinned YBa$_2$Cu$_3$O$_{7-\delta}$ crystals with similar overall characteristics as those reported by Rydh and Rapp . The comparison of the vortex correlation response in both cases indicates that the central conclusion of their work is not correct. Our results reconfirm the work by L\'opez {\it et al.} and points on the origin of the misinterpretation in the work of Rydh and Rapp.Comment: comment on A.Rydh and \"O.Rapp, Phys. Rev. Lett. {\bf 86}, 1873 (2001). accepted in Phys. Rev. Let

Generation of two-photon states with arbitrary degree of entanglement via nonlinear crystal superlattices

We demonstrate a general method of engineering the joint quantum state of photon pairs produced in spontaneous parametric downconversion (PDC). The method makes use of a superlattice structure of nonlinear and linear materials, in conjunction with a broadband pump, to manipulate the group delays of the signal and idler photons relative to the pump pulse, and realizes a joint spectral amplitude with arbitrary degree of entanglement for the generated pairs. This method of group delay engineering has the potential of synthesizing a broad range of states including factorizable states crucial for quantum networking and states optimized for Hong-Ou-Mandel interferometry. Experimental results for the latter case are presented, illustrating the principles of this approach.Comment: 4 pages, 4 figures, accepted Phys. Rev. Let

Gimnasia rítmica deportiva, ¿una práctica excluida o excluyente?

Contiene: 1-Gimnasia Rítmica Deportiva, su concepción y su lógica; 2- Esbozo de reseña histórica en el mundo y en Argentina; 3-Su lenguaje a partir de su reglamentación y código de puntuación; 4- Su práctica a partir de la lógica gímnica; 5- El cuerpo desde la mirada del alto rendimiento; 6-La construcción de cierta feminidadPanel: "Discursos y Practicas Corporales"Departamento de Educación Físic