Fibers in the NGC1333 proto-cluster

Are the initial conditions for clustered star formation the same as for non-clustered star formation? To investigate the initial gas properties in young proto-clusters we carried out a comprehensive and high-sensitivity study of the internal structure, density, temperature, and kinematics of the dense gas content of the NGC1333 region in Perseus, one of the nearest and best studied embedded clusters. The analysis of the gas velocities in the Position-Position-Velocity space reveals an intricate underlying gas organization both in space and velocity. We identified a total of 14 velocity-coherent, (tran-)sonic structures within NGC1333, with similar physical and kinematic properties than those quiescent, star-forming (aka fertile) fibers previously identified in low-mass star-forming clouds. These fibers are arranged in a complex spatial network, build-up the observed total column density, and contain the dense cores and protostars in this cloud. Our results demonstrate that the presence of fibers is not restricted to low-mass clouds but can be extended to regions of increasing mass and complexity. We propose that the observational dichotomy between clustered and non-clustered star-forming regions might be naturally explained by the distinct spatial density of fertile fibers in these environments.Comment: 25 pages, 17 figures; Accepted for publication in A&

Intensification of continuous bio-hydrogen production from C5/C6 sugars

Chemoheterotrophic (”dark”) fermentation at extreme thermophilic (70oC) conditions presents a promising route of biological hydrogen production. To achieve satisfactory hydrogen production rate, immobilized-cell systems such as EGSB could be an alternative to carrier-free (suspended-cell) systems. However, a major drawback in the immobilized system is the long period that takes to develop the active hydrogen producing granules. Therefore, ready constructed anaerobic granules containing active and fast growing hydrogen producers is a prerequisite for fast and efficient hydrogen production. This work aimed to develop an efficient EGSB reactor system containing engineered granules for high rate extreme thermophilic biohydrogen production from carbohydrate feedstocks. Heat treated methanogenic granules (HTG) and engineered heat treated methanogenic granules (EHTG) were individually inoculated in each reactor operated at 70±1ºC, pH 5.5 and fed with a mixture of glucose and arabinose (1:1) at a final concentration of 5 g COD.L-1. HTG were obtained by treatment of the granules at 121oC for 45 min heat treatment, to completely inhibit methanogenic activity. EHTG were obtained by surface attachment immobilized-cell technique with an H2-producing mixed culture enriched from digested household solid waste, using HTG as carriers. Scaning electron microscope (SEM) analysis showed microorganisms attached to surface of granules in both reactor systems. A greatly improved hydrogen production rate amounting up to 2500 mL H2 L-1d-1 in steady state was demonstrated by EHTG in EGSB system. In comparison, almost no hydrogen production was recorded by HTG, only occasional hydrogen production peaks in the range 800-1500 mL H2 L-1d-1 without real steady state were observed. EGSB reactor system with EHTG as microbial carriers, appears to be the most preferred a promising process for highly efficient dark fermentative hydrogen production from sugar containing feedstocks under extreme thermophilic conditions

Dynamics and Constraints of the Massive Gravitons Dark Matter Flat Cosmologies

We discuss the dynamics of the universe within the framework of Massive Graviton Dark Matter scenario (MGCDM) in which gravitons are geometrically treated as massive particles. In this modified gravity theory, the main effect of the gravitons is to alter the density evolution of the cold dark matter component in such a way that the Universe evolves to an accelerating expanding regime, as presently observed. Tight constraints on the main cosmological parameters of the MGCDM model are derived by performing a joint likelihood analysis involving the recent supernovae type Ia data, the Cosmic Microwave Background (CMB) shift parameter and the Baryonic Acoustic Oscillations (BAOs) as traced by the Sloan Digital Sky Survey (SDSS) red luminous galaxies. The linear evolution of small density fluctuations is also analysed in detail. It is found that the growth factor of the MGCDM model is slightly different ($\sim1-4$) from the one provided by the conventional flat $\Lambda$CDM cosmology. The growth rate of clustering predicted by MGCDM and $\Lambda$CDM models are confronted to the observations and the corresponding best fit values of the growth index ($\gamma$) are also determined. By using the expectations of realistic future X-ray and Sunyaev-Zeldovich cluster surveys we derive the dark-matter halo mass function and the corresponding redshift distribution of cluster-size halos for the MGCDM model. Finally, we also show that the Hubble flow differences between the MGCDM and the $\Lambda$CDM models provide a halo redshift distribution departing significantly from the ones predicted by other DE models. These results suggest that the MGCDM model can observationally be distinguished from $\Lambda$CDM and also from a large number of dark energy models recently proposed in the literature.Comment: Accepted for publication in Physical Review D (12 pages, 4 figures

Gravitational collapse of the OMC-1 region

We have investigated the global dynamical state of the Integral Shaped Filament in the Orion A cloud using new N$_2$H$^+$ (1-0) large-scale, IRAM30m observations. Our analysis of its internal gas dynamics reveals the presence of accelerated motions towards the Orion Nebula Cluster, showing a characteristic blue-shifted profile centred at the position of the OMC-1 South region. The properties of these observed gas motions (profile, extension, and magnitude) are consistent with the expected accelerations for the gravitational collapse of the OMC-1 region and explain both the physical and kinematic structure of this cloud.Comment: 5 pages, 2 figures; Accepted by A&