Symmetron Cosmology

The symmetron is a scalar field associated with the dark sector whose coupling to matter depends on the ambient matter density. The symmetron is decoupled and screened in regions of high density, thereby satisfying local constraints from tests of gravity, but couples with gravitational strength in regions of low density, such as the cosmos. In this paper we derive the cosmological expansion history in the presence of a symmetron field, tracking the evolution through the inflationary, radiation- and matter-dominated epochs, using a combination of analytical approximations and numerical integration. For a broad range of initial conditions at the onset of inflation, the scalar field reaches its symmetry-breaking vacuum by the present epoch, as assumed in the local analysis of spherically-symmetric solutions and tests of gravity. For the simplest form of the potential, the energy scale is too small for the symmetron to act as dark energy, hence we must add a cosmological constant to drive late-time cosmic acceleration. We briefly discuss a class of generalized, non-renormalizable potentials that can have a greater impact on the late-time cosmology, though cosmic acceleration requires a delicate tuning of parameters in this case.Comment: 42 page

RPNet: an End-to-End Network for Relative Camera Pose Estimation

This paper addresses the task of relative camera pose estimation from raw image pixels, by means of deep neural networks. The proposed RPNet network takes pairs of images as input and directly infers the relative poses, without the need of camera intrinsic/extrinsic. While state-of-the-art systems based on SIFT + RANSAC, are able to recover the translation vector only up to scale, RPNet is trained to produce the full translation vector, in an end-to-end way. Experimental results on the Cambridge Landmark dataset show very promising results regarding the recovery of the full translation vector. They also show that RPNet produces more accurate and more stable results than traditional approaches, especially for hard images (repetitive textures, textureless images, etc). To the best of our knowledge, RPNet is the first attempt to recover full translation vectors in relative pose estimation

Magnetic structure and phase diagram of TmB4

Magnetic structure of single crystalline TmB4 has been studied by magnetization, magnetoresistivity and specific heat measurements. A complex phase diagram with different antiferromagnetic (AF) phases was observed below TN1 = 11.7 K. Besides the plateau at half-saturated magnetization (1/2 MS), also plateaus at 1/9, 1/8 and 1/7 of MS were observed as function of applied magnetic field B//c. From additional neutron scattering experiments on TmB4, we suppose that those plateaus arise from a stripe structure which appears to be coherent domain boundaries between AF ordered blocks of 7 or 9 lattice constants. The received results suggest that the frustration among the Tm3+ magnetic ions, which maps to a geometrically frustrated Shastry-Sutherland lattice lead to strong competition between AF and ferromagnetic (FM) order. Thus, stripe structures in intermediate field appear to be the best way to minimize the magnetostatic energy against other magnetic interactions between the Tm ions combined with very strong Ising anisotropy.Comment: 4 pages, 4 figures, conference contribution - CSMAG 0

Los Eucaliptos en las tierras altas de Angola, su papel social durante el conflicto armado y en el desarrollo de las comunidades rurales y urbanas

Las tierras altas de Angola han tenido un complicado desarrollo histórico desde que fueron colonizadas a inicios del siglo XX. Este proceso histórico también ha afectado a los bosques naturales y las plantaciones de eucaliptos que se crearon durante los años 60 y 70. El uso de estas plantaciones, inicialmente planificadas como suministro de combustible y materias primas para la industria colonial, se vio truncado con la independencia y los posteriores avatares políticomilitares. En la nueva situación de inseguridad en el medio rural, se convirtieron en la principal fuente de combustible para la creciente población urbana que huía del campo. Actualmente, los polígonos forestales sobrevivientes pueden ser utilizados en la rehabilitación de esta zona del país. El objetivo de este trabajo de investigación es conocer el proceso histórico de uso y gestión de estas plantaciones su papel social en este proceso y la situación en la que se encuentran actualmente._________________________________The Angolan highlands were involved in a complicated historical process since the beginning of colonization in the early 1900´s. The process also affected the natural forest and eucalyptus plantations that were implanted in the sixties and seventies. Its primary planning uses were for fuel wood and timber supply to the colonial industries. The forest uses changed with the independence and the later war conflicts. The insecurity in the rural areas caused a strong rural peasant migration to the more secure cities. Forest plantation close to cities became the main fuel wood supply for the growing urban population. Currently, some forest plantations remain in the less accessible areas and can be use for the rehabilitation of the region. The main objective of the research was to increase the knowledge concern the eucalyptus forests uses and management during the historical process, its social importance during the war time and the state of the forests in present days

Influence of the Stimulation Current on the Differences between Cell and Tissue Electrophysiological Simulations

This study compares stimulation waveforms for single-cell simulations. The alternatives include monophasic and biphasic current pulses, and a new waveform that resembles the transmembrane current responsible for conduction in tissue. Results indicate that the new stimulation produces the lowest mismatch between action potential markers simulated in cell and in tissue. In comparison with the monophasic stimulation, the new stimulation reduced cell-fiber differences by 99% for triangulation, by 95% for maximum transmembrane voltage, and by 76% for the maximum voltage slope. In conclusion, the new stimulation waveform could help to improve the trustworthiness of single-cell simulations in studies involving tissue-derived markers

Early queen infection shapes developmental dynamics and induces long-term disease protection in incipient ant colonies

Infections early in life can have enduring effects on an organism's development and immunity. In this study, we show that this equally applies to developing ‘superorganisms’––incipient social insect colonies. When we exposed newly mated Lasius niger ant queens to a low pathogen dose, their colonies grew more slowly than controls before winter, but reached similar sizes afterwards. Independent of exposure, queen hibernation survival improved when the ratio of pupae to workers was small. Queens that reared fewer pupae before worker emergence exhibited lower pathogen levels, indicating that high brood rearing efforts interfere with the ability of the queen's immune system to suppress pathogen proliferation. Early-life queen pathogen exposure also improved the immunocompetence of her worker offspring, as demonstrated by challenging the workers to the same pathogen a year later. Transgenerational transfer of the queen's pathogen experience to her workforce can hence durably reduce the disease susceptibility of the whole superorganism