Time-dependent cosmological constant in the Jackiw-Teitelboim cosmology

We study the obtainment of a time-dependent cosmological constant at D=2 in a model based on the Jackiw-Teitelboim cosmology. We show that the cosmological term goes to zero asymptotically and can induce a nonsingular behavior at the origin.Comment: 4 pages, Revtex4, twocolum

On the trace anomaly and the energy-momentum conservation of quantum fields at D=2 in classical curved backgrounds

We study the conformal symmetry and the energy-momentum conservation of scalar field interacting with a curved background at D=2. We avoid to incorporate the metric determinant into the measure of the scalar field to explain the conformal anomaly and the consequent energy-momentum conservation. Contrarily, we split the scalar field in two other fields, in such a way that just one of them can be quantized. We show that the same usual geometric quantities of the anomaly are obtained, which are accompanied by terms containing the new field of the theory.Comment: 5 pages, no figure

Hipparcos distances of Ophiuchus and Lupus cloud complexes

We combine extinction maps from the Two Micron All Sky Survey (2MASS) with Hipparcos and Tycho parallaxes to obtain reliable and high-precision estimates of the distance to the Ophiuchus and Lupus dark complexes. Our analysis, based on a rigorous maximum-likelihood approach, shows that the rho-Ophiuchi cloud is located at (119 +/- 6) pc and the Lupus complex is located at (155 +/- 8) pc; in addition, we are able to put constraints on the thickness of the clouds and on their orientation on the sky (both these effects are not included in the error estimate quoted above). For Ophiuchus, we find some evidence that the streamers are closer to us than the core. The method applied in this paper is currently limited to nearby molecular clouds, but it will find many natural applications in the GAIA-era, when it will be possible to pin down the distance and three-dimensional structure of virtually every molecular cloud in the Galaxy.Comment: A&A in press - Corrected typo (Lupus distance) in the electronic abstrac

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&

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&

Discontinuous operation promotes efficient continuous anaerobic treatment of effluents with high lipid content

A mixture of skim milk and sodium oleate was fed to an upflow sludge bed reactor operated in cycles. Each cycle had a feeding phase under continuous operation and a reaction phase in batch. Five cycles were performed with organic loading rates applied during feeding phases varying between 4.4 and 8 kg COD.mˉ³.dˉ¹ and a constant hydraulic retention time of 1.6 days. In the first two cycles, 70% of the methane-COD was produced in the reaction batch phase, whereas from the third to the fifth cycles, biogas production in the reaction phase was less than 3% of total production. Overall methane yields increased steadily, from 0.67 to 0.91 kg COD-CH4.kg COD removedˉ¹. LCFA accumulated into the sludge in the first two cycles, being palmitate and stearate the dominant intermediates quantified. In the subsequent cycles no LCFA were detected in the solid or liquid phases. The specific methanogenic activity in the presence of acetate and H2/CO2 increased significantly along the operation, particularly between time zero and the end of the third cycle. These results show that a discontinuous operation promoted the development of an active anaerobic community able to efficiently convert a continuous organic load of 8.2 kg COD.mˉ³.dˉ¹, from which 50% was oleate.European Commission - LIFE03 ENV/P/000501.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/CTA/46328/2002

Fed-batch anaerobic degradation of long chain fatty acids

Efficient mineralization of effluents with high lipid content is possible in anaerobic digesters when a sequential operation mode is applied, favoring the adsorption of LCFA onto the sludge and then allowing the adsorbed substrate to be biodegraded1-3. The study of adsorption along time can help to optimize the process. Five batch assays were conducted in 160mL vials inoculated with flocculent biomass and fed with sodium oleate (1g CQO/gVSS). Feeding was applied during 10min (0.8ml/min), after which (t=0) a vial was immediately sacrificed and analyzed for soluble COD, VSS and biomass-associated LCFA. After 0.5, 1, 24 and 1000 hours of incubation at 37±1°C, 150rpm, one vial was sacrificed and analyzed for the parameters stated before. Two additional vials prepared and fed in a similar way and two blank controls (without substrate) were incubated in the same conditions to follow cumulative methane production. At the end of the feeding period, soluble COD removal efficiency was 73%, corresponding exclusively to LCFA accumulation onto the sludge. During the first 24 hours, methane or VFA production were negligible probably due to residual substrate degradation. Palmitic acid accounted for 46 to 54% of the biomass-associated LCFA and oleic acid for 31 to 40%. After 1000 hours of incubation soluble COD removal was 86% and palmitic acid accounted for 100% of the biomass-associated LCFA (45mg COD-LCFA/g VSS)

LCFA accumulation and biodegradation during anaerobic discontinuous treatment of an oleate-rich wastewater

The dynamics of medium and long-chain fatty acids (LCFA) accumulation and biodegradation was studied during the anaerobic treatment of an oleate-rich wastewater. This treatment was made in an upflow sludge bed reactor operated in cycles during 213 days. Five cycles were performed, each one with a feeding phase in continuous and a reaction phase in batch. Saturated and unsaturated fatty acids from C6 to C18 were extracted and analyzed by gas chromatography on biomass samples collected at different key moments of the reactor operation. These biomass samples were also incubated in batch assays and methane production from the accumulated substrate was followed. LCFA accumulated onto the sludge during the first two cycles, reaching a maximum value of 1.7 gCOD-LCFA.gVSˉ¹. Palmitate and stearate were the dominant intermediates quantified, approximately in equal quantities. On the subsequent cycles only residual amounts of LCFA were detected. Methane production on batch assays was higher than expected from the LCFA accumulated, suggesting that other substrates could also be entrapped with the sludge. The results show that during the first two cycles a specialized microbial consortium developed, able to treat oleate-rich wastewaters.European Commission - LIFE03 ENV/P/000501.Fundação para a Ciência e a Tecnologia (FCT) - POCTI/CTA/46328/2002