Primordial magnetic field and spectral distortion of cosmic background radiation

The role played by a primordial magnetic field during the pre-recombination epoch is analysed through the cyclotron radiation (due to the free electrons) it might produce in the primordial plasma. We discuss the constraint implied by the measurement or lack thereof COBE on this primordial field.Comment: to appear in International Journal of Mod. Phy

Non-equilibrium h-2 formation in the early universe: energy exchanges, rate coefficients, and spectral distortions

Energy exchange processes play a crucial role in the early universe, affecting the thermal balance and the dynamical evolution of the primordial gas. In the present work we focus on the consequences of a non-thermal distribution of the level populations of H2: first, we determine the excitation temperatures of vibrational transitions and the non-equilibrium heat transfer; second, we compare the modifications to chemical reaction rate coefficients with respect to the values obtained assuming local thermodynamic equilibrium; and third, we compute the spectral distortions to the cosmic background radiation generated by the formation of H2 in vibrationally excited levels. We conclude that non-equilibrium processes cannot be ignored in cosmological simulations of the evolution of baryons, although their observational signatures remain below current limits of detection. New fits to the equilibrium and non-equilibrium heat transfer functions are provided

Limits on decaying dark energy density models from the CMB temperature-redshift relation

The nature of the dark energy is still a mystery and several models have been proposed to explain it. Here we consider a phenomenological model for dark energy decay into photons and particles as proposed by Lima (J. Lima, Phys. Rev. D 54, 2571 (1996)). He studied the thermodynamic aspects of decaying dark energy models in particular in the case of a continuous photon creation and/or disruption. Following his approach, we derive a temperature redshift relation for the CMB which depends on the effective equation of state $w_{eff}$ and on the "adiabatic index" $\gamma$. Comparing our relation with the data on the CMB temperature as a function of the redshift obtained from Sunyaev-Zel'dovich observations and at higher redshift from quasar absorption line spectra, we find $w_{eff}=-0.97 \pm 0.034$, adopting for the adiabatic index $\gamma=4/3$, in good agreement with current estimates and still compatible with $w_{eff}=-1$, implying that the dark energy content being constant in time.Comment: 8 pages, 1 figur

Constraining decaying dark energy density models with the CMB temperature-redshift relation

We discuss the thermodynamic and dynamical properties of a variable dark energy model with density scaling as $\rho_x \propto (1+z)^{m}$, z being the redshift. These models lead to the creation/disruption of matter and radiation, which affect the cosmic evolution of both matter and radiation components in the Universe. In particular, we have studied the temperature-redshift relation of radiation, which has been constrained using a recent collection of cosmic microwave background (CMB) temperature measurements up to $z \sim 3$. We find that, within the uncertainties, the model is indistinguishable from a cosmological constant which does not exchange any particles with other components. Future observations, in particular measurements of CMB temperature at large redshift, will allow to give firmer bounds on the effective equation of state parameter $w_{eff}$ for such types of dark energy models.Comment: 9 pages, 1 figure, to appear in the Proceedings of the 3rd Italian-Pakistani Workshop on Relativistic Astrophysics, Lecce 20-22 June 2011, published in Journal of Physics: Conference Series (JPCS

Resilience of small-scale societies: a view from drylands.

To gain insights on long-term social-ecological resilience, we examined adaptive responses of small-scale societies to dryland-related hazards in different regions and chronological periods, spanning from the mid-Holocene to the present. Based on evidence from Africa (Sahara and Sahel), Asia (south margin of the Thar desert), and Europe (South Spain), we discuss key traits and coping practices of small-scale societies that are potentially relevant for building resilience. The selected case studies illustrate four main coping mechanisms: mobility and migration, storage, commoning, and collective action driven by religious beliefs. Ultimately, the study of resilience in the context of drylands emphasizes the importance of adaptive traits and practices that are distinctive of small-scale societies: a strong social-ecological coupling, a solid body of traditional ecological knowledge, and a high degree of internal cohesion and self-organization.SP2016http://www.ecologyandsociety.org/vol21/iss2/art53

Reference normal values and design of a vision screening for 4 to 5 years old preschoolers

A vision screening program for preschool children of 4-5 years old was designed and analyzed. Information of the prevalence of ocular conditions among preschool children was obtained. The vision health of a group of 127 children was evaluated by a comprehensive examination in their own school. If a child failed one or more screening tests, he was referred to the ophthalmologist. Of the children screened in this study, 61% passed distance visual acuity and retinoscopy tests, 17% were referred to the ophthalmologist and 22% will be annually monitoring. Values of monocular/binocular acuity worse than 0.5/0.6 are too poor for 4 years old children, whereas these limits increase up to 0.6/0.8 for 5 years old children. In conclusion, the prevalence of undetected vision problems in preschool children has been clearly demonstrated. Vision screening programs in schools are highly recommended. Nevertheless, coordination among professionals conducting screening, school personnel and parents are needed to reach high levels of success. The results of this study validate an easy and fast battery of tests. The vision screening has been highly reliable because reference normal values have been defined by analyzing statistically the results of these tests. Se diseñó y analizó un screening visual en preescolares de 4-5 años de edad. Se obtuvo información de la prevalencia de las condiciones oculares entre estos preescolares. Se evaluó la salud visual de un grupo de 127 niños con un examen completo en su propia escuela. Si el niño fallaba uno o más test era referido al oftalmólogo. De los niños revisados en el estudio, el 61% superó los test de agudeza visual y retinoscopía, al 17% se le refirió al oftalmólogo y el 22% será controlado anualmente. Valores de agudeza monocular/binocular peores de 0.5/0.6 son demasiado bajos para niños de 4 años de edad, mientras que estos límites se incrementan a 0.6/0.8 para niños de 5 años. En conclusión, la prevalencia de problemas de visión sin detectar en niños preescolares ha sido claramente demostrada. Sin embargo, es necesaria la coordinación entre profesionales que realicen el screening, personal del colegio y padres para alcanzar niveles altos de éxito. Los resultados de este estudio validan una batería rápida de test. El screening visual ha sido altamente fiable porque los valores normales de referencia han sido definidos analizando estadísticamente los resultados de estos tests

Low-Mass Star Formation, Triggered by Supernova in Primordial Clouds

The evolution of a gas shell, swept by the supernova remnant of a massive first generation star, is studied with H_2 and HD chemistry taken into account. When a first-generation star explodes as a supernova, H_2 and HD molecules are formed in the swept gas shell and effectively cool the gas shell to temperatures of 32 K - 154 K. If the supernova remnant can sweep to gather the ambient gas, the gas shell comes to be dominated by its self-gravity, and hence, is expected to fragment. Our result shows that for a reasonable range of temperatures (200 K - 1000 K) of interstellar gas, the formation of second-generation stars can be triggered by a single supernova or hypernova.Comment: 38pages, 10 figures, The Astrophysical Journal, accepted 8 Dec. 200