CMB anisotropy: deviations from Gaussianity due to non-linear gravity

Non-linear evolution of cosmological energy density fluctuations triggers deviations from Gaussianity in the temperature distribution of the cosmic microwave background. A method to estimate these deviations is proposed. N-body simulations -- in a $\Lambda$CDM cosmology -- are used to simulate the strongly non-linear evolution of cosmological structures. It is proved that these simulations can be combined with the potential approximation to calculate the statistical moments of the CMB anisotropies produced by non-linear gravity. Some of these moments are computed and the resulting values are different from those corresponding to Gaussianity.Comment: 6 latex pages with mn.sty, 3 eps figures. Accepted in MNRA

Comportamiento biológico intraarticular de distintos aloinjertos tendinosos: estudio experimental

Se ha efectuado un estudio experimental comparativo, con valoración macro y microscópica, de la supervivencia, dentro de la articulación de la rodilla del conejo, de tendones flexores sobre extensores y dentro de estos, entre tendones conservados en fresco, congelados, liofilizados y fijados en solución de glutaraldehido al 0,2%. Los tendones se mantuvieron libres en la articulación receptora durante periodos distintos de tiempo. Entre los resultados destaca la pérdida de volumen, en el tiempo, de la masa tendinosa (18% de despariciones totales, con un 28% de pérdida final global). Los tendones fijados en glutaraldehido fueron los que presentaron menor pérdida de volumen. Los tendones implantados en fresco y los congelados presentaron una mayor tasa de infección. La mejor respuesta de supervivencia se detectó en los tendones conservados en glutaraldehido y los congelados. Así mismo, tenían más posibilidades de sobrevivir los flexores que los extensores. Desde el punto de vista histológico, los tendones conservados en fresco desencadenaron una mayor respuesta inflamatoria, con gran alteración estructural. Desde el punto de vista microscópico no se han hallado diferencias significativas entre flexores y extensores.Different groups of flexor and extensor tendons have been compared in their abitihty survive within the rabbit knee joint. Tendons were grouped and compared according four different storage procedures like freezing, lyophylization and fixation in 0,2% glutaraldehid. Some of them were used in fresh. All tendons have been kept inside the joint as free graft. All specimens lost weight along the study (18% of total loosing of specimen, and 28% of global loosing). Tendons fixed in disclosed less loosing of volume. Allograft infection was related to the method o glutaraildehid of storage, relationship being statistically significant (fresh tendons and frozen tendons were infected more easily). The best survival was found in both frozen and glutaraldehid fixed tendons. Flexor tendons show more chances of survival than extensors tendons. Histologically, fresh tendons disclosed the greatest inflammatory reaction. Opposite to the macroscopic findings, there were no significant differences between flexors and extensors tendons in the microscopical study

The Tully-Fisher relation of intermediate redshift field and cluster galaxies from Subaru spectroscopy

We have carried out spectroscopic observations in 4 cluster fields using Subaru's FOCAS multi-slit spectrograph and obtained spectra for 103 bright disk field and cluster galaxies at $0.06 \le z \le 1.20$. Seventy-seven of these show emission lines, and 33 provide reasonably-secure determinations of the galaxies' rotation velocity. The rotation velocities, luminosities, colours and emission-line properties of these galaxies are used to study the possible effects of the cluster environment on the star-formation history of the galaxies. Comparing the Tully-Fisher relations of cluster and field galaxies at similar reshifts we find no measurable difference in rest-frame $B$-band luminosity at a given rotation velocity (the formal difference is $0.18\pm0.33$mag). The colours of the cluster emission line galaxies are only marginally redder in rest-frame $B-V$ (by $0.06\pm0.04$mag) than the field galaxies in our sample. Taken at face value, these results seem to indicate that bright star-forming cluster spirals are similar to their field counterparts in their star-formation properties. However, we find that the fraction of disk galaxies with absorption-line spectra (i.e., with no current star formation) is larger in clusters than in the field by a factor of $\sim3$--5. This suggests that the cluster environment has the overall effect of switching off star formation in (at least) some spiral galaxies. To interpret these observational results, we carry out simulations of the possible effects of the cluster environment on the star-formation history of disk galaxies and thus their photometric and spectroscopic properties. Finally, we evaluate the evolution of the rest-frame absolute $B$-band magnitude per unit redshift at fixed rotation velocity.Comment: 21 pages, 13 figures, accepted for publication in MNRA

Efecto de la congelación en rodillas animales. Estudio biomecánico experimental

Se estudia el comportamiento mecánico de rodillas animales que han sido congeladas en 1 o varias ocasiones mediante la aplicación de cargas axiales hasta la fractura o test destructivos. Se analizan el tipo y localización de fracturas aparecidas mediante un estudio radiográfico.We study the mechanical behavior in animal knees who are fresh frozen in one or various times. Axial loading are applied until the final fracture ( destructive test). Also it evaluates the tipe and localization of the fractures with radiological study

The star formation activity in cosmic voids

Using a sample of cosmic voids identified in the Sloan Digital Sky Survey Data Release 7, we study the star formation activity of void galaxies. The properties of galaxies living in voids are compared with those of galaxies living in the void shells and with a control sample, representing the general galaxy population. Void galaxies appear to form stars more efficiently than shell galaxies and the control sample. This result cannot be interpreted as a consequence of the bias towards low masses in underdense regions, as void galaxy subsamples with the same mass distribution as the control sample also show statistically different specific star formation rates. This highlights the fact that galaxy evolution in voids is slower with respect to the evolution of the general population. Nevertheless, when only the star-forming galaxies are considered, we find that the star formation rate is insensitive to the environment, as the main sequence is remarkably constant in the three samples under consideration. This fact implies that environmental effects manifest themselves as fast quenching mechanisms, while leaving the non-quenched galaxies almost unaffected, as their star formation activity is largely regulated by the mass of their halo. We also analyse galaxy properties as a function of void-centric distance and find that the enhancement in the star formation activity with respect to the control sample is observable up to a radial distance 1.5Rvoid. This result can be used as a suitable definition of void shells. Finally, we find that larger voids show an enhanced star formation activity in the shells with respect to their smaller counterparts, which could be related to the different dynamical evolution experienced by voids of different size

Gravitational waves from galaxy encounters

We discuss the emission of gravitational radiation produced in encounters of dark matter galactic halos. To this aim we perform a number of numerical simulations of typical galaxy mergers, computing the associated gravitational radiation waveforms as well as the energy released in the processes. Our simulations yield dimensionless gravitational wave amplitudes of the order of $10^{-13}$ and gravitational wave frequencies of the order of $10^{-16}$ Hz, when the galaxies are located at a distance of 10 Mpc. These values are of the same order as those arising in the gravitational radiation originated by strong variations of the gravitational field in the early Universe, and therefore, such gravitational waves cannot be directly observed by ground-based detectors. We discuss the feasibility of an indirect detection by means of the B-mode polarization of the Cosmic Microwave Background (CMB) induced by such waves. Our results show that the gravitational waves from encounters of dark matter galactic halos leave much too small an imprint on the CMB polarization to be actually observed with ongoing and future missions.Comment: 9 pages with revtex style, 3 ps figures; to be published in Physical Review

Dynamical effects of the neutrino gravitational clustering at Planck angular scales

We study the CMB anisotropy induced by the non-linear perturbations in the massive neutrino density associated to the non-linear gravitational clustering proceses. Our results show that for the neutrino fraction in agreement with that indicated by the astroparticle and nuclear physics experiments and a cosmological accreting mass comparable with the mass of known clusters, the angular resolution and the sensitivity of the CMB anisotropy measurements from the Planck surveyor will allow the detection of the dynamical effects of the neutrino gravitational clustering.Comment: 40 pages and 12 figures, submitted to ApJ (14 March 2002

Microwave Background Anisotropies and Nonlinear Structures I. Improved Theoretical Models

A new method is proposed for modelling spherically symmetric inhomogeneities in the Universe. The inhomogeneities have finite size and are compensated, so they do not exert any measurable gravitational force beyond their boundary. The region exterior to the perturbation is represented by a Friedmann-Robertson-Walker (FRW) Universe, which we use to study the anisotropy in the cosmic microwave background (CMB) induced by the cluster. All calculations are performed in a single, global coordinate system, with nonlinear gravitational effects fully incorporated. An advantage of the gauge choices employed here is that the resultant equations are essentially Newtonian in form. Examination of the problem of specifying initial data shows that the new model presented here has many advantages over `Swiss cheese' and other models. Numerical implementation of the equations derived here is described in a subsequent paper.Comment: 10 pages, 4 figures; Monthly Notices of the Royal Astronomical Society (MNRAS), in pres