366 research outputs found
Anaerobic digestion and gasification coupling for wastewater sludge treatment and recovery
ABSTRACT Sewage sludge management is an energy intensive process. Anaerobic digestion contributes to energy efficiency improvement but is limited by the biological process. A review has been conducted prior to experimentation in order to evaluate the mass and energy balances on anaerobic digestion followed by gasification of digested sludge. The purpose was to improve energy recovery and reuse. Calculations were based on design parameters and tests that are conducted with the anaerobic digester of a local wastewater treatment plant and a small commercial gasification system. Results showed a very significant potential of energy recovery. More than 90% of the energy content from sludge was extracted. Also, about the same amount of energy would be transferred to the gasifier (biogas) as thermal energy to the digester. This extraction resulted in the same use of biogas as the reference scenario but final product was a totally dry biochar which represented a fraction of the initial mass. Phosphorus was concentrated and significantly preserved. This analysis suggests that anaerobic digestion followed by dehydration, drying and gasification could be a promising and viable option for energy and nutrient recovery from municipal sludge in replacement of conventional paths
Anaerobic digestion and gasification coupling for wastewater sludge treatment and recovery
ABSTRACT Sewage sludge management is an energy intensive process. Anaerobic digestion contributes to energy efficiency improvement but is limited by the biological process. A review has been conducted in order to evaluate the mass and energy balances on anaerobic digestion followed by gasification of digested sludge in order to improve energy recovery. Calculations are based on design parameters and tests that are conducted with the anaerobic digester of a local wastewater treatment plant and a small commercial gasification system. Results show a very important potential of energy recovery. More than 95% of the energy content from sludge was extracted. This extraction resulted in a 5% reduction of biogas but final product was a totally dry biochar. Final product was then a fraction of the initial mass. This analysis suggests that anaerobic digestion followed by dewatering, drying and gasification could be a promising and viable option for energy and nutrient recovery from municipal sludge in replacement of conventional paths
Studies of Acute Intestinal Obstruction. I. Different Types of Obstruction Produced under Local Anesthesia
11 p. Reprinted from: Archives of Internal Medicine, Vol. 34, No. 1, July 1924
A Mass Bound for Spherically Symmetric Black Hole Spacetimes
Requiring that the matter fields are subject to the dominant energy
condition, we establish the lower bound for the
total mass of a static, spherically symmetric black hole spacetime. ( and denote the area and the surface gravity of the horizon,
respectively.) Together with the fact that the Komar integral provides a simple
relation between and the strong energy condition,
this enables us to prove that the Schwarzschild metric represents the only
static, spherically symmetric black hole solution of a selfgravitating matter
model satisfying the dominant, but violating the strong energy condition for
the timelike Killing field at every point, that is, .
Applying this result to scalar fields, we recover the fact that the only black
hole configuration of the spherically symmetric Einstein-Higgs model with
arbitrary non-negative potential is the Schwarzschild spacetime with constant
Higgs field. In the presence of electromagnetic fields, we also derive a
stronger bound for the total mass, involving the electromagnetic potentials and
charges. Again, this estimate provides a simple tool to prove a ``no-hair''
theorem for matter fields violating the strong energy condition.Comment: 16 pages, LATEX, no figure
Cytochrome oxidase subunit VI of Trypanosoma brucei is imported without a cleaved presequence and is developmentally regulated at both RNA and protein levels
Mitochondrial respiration in the African trypanosome undergoes dramatic developmental stage regulation. This requires co-ordinated control of components encoded by both the nuclear genome and the kinetoplast, the unusual mitochondrial genome of these parasites. As a model for understanding the co-ordination of these genomes, we have examined the regulation and mitochondrial import of a nuclear-encoded component of the cytochrome oxidase complex, cytochrome oxidase subunit VI (COXVI). By generating transgenic trypanosomes expressing intact or mutant forms of this protein, we demonstrate that COXVI is not imported using a conventional cleaved presequence and show that sequences at the N-terminus of the protein are necessary for correct mitochondrial sorting. Analyses of endogenous and transgenic COXVI mRNA and protein expression in parasites undergoing developmental stage differentiation demonstrates a temporal order of control involving regulation in the abundance of, first, mRNA and then protein. This represents the first dissection of the regulation and import of a nuclear-encoded protein into the cytochrome oxidase complex in these organisms, which were among the earliest eukaryotes to possess a mitochondrion
An Explanation for the Observed Weak Size Evolution of Disk Galaxies
Surveys of distant galaxies with the Hubble Space Telescope and from the
ground have shown that there is only mild evolution in the relationship between
radial size and stellar mass for galactic disks from z~1 to the present day.
Using a sample of nearby disk-dominated galaxies from the Sloan Digital Sky
Survey (SDSS), and high redshift data from the GEMS (Galaxy Evolution from
Morphology and SEDs) survey, we investigate whether this result is consistent
with theoretical expectations within the hierarchical paradigm of structure
formation. The relationship between virial radius and mass for dark matter
halos in the LCDM model evolves by about a factor of two over this interval.
However, N-body simulations have shown that halos of a given mass have less
centrally concentrated mass profiles at high redshift. When we compute the
expected disk size-stellar mass distribution, accounting for this evolution in
the internal structure of dark matter halos and the adiabatic contraction of
the dark matter by the self-gravity of the collapsing baryons, we find that the
predicted evolution in the mean size at fixed stellar mass since z~1 is about
15-20 percent, in good agreement with the observational constraints from GEMS.
At redshift z~2, the model predicts that disks at fixed stellar mass were on
average only 60% as large as they are today. Similarly, we predict that the
rotation velocity at a given stellar mass (essentially the zero-point of the
Tully-Fisher relation) is only about 10 percent larger at z~1 (20 percent at
z~2) than at the present day.Comment: 13 pages, 6 figures, accepted for publication in ApJ. Revised in
response to referee's comments to improve clariry. Results are unchange
GEMS: The Size Evolution of Disk Galaxies
We combine HST imaging from the GEMS survey with photometric redshifts from
COMBO-17 to explore the evolution of disk-dominated galaxies since z<1.1. The
sample is comprised of all GEMS galaxies with Sersic indices n<2.5, derived
from fits to the galaxy images. We account fully for selection effects through
careful analysis of image simulations; we are limited by the depth of the
redshift and HST data to the study of galaxies with absolute magnitudes
M(V)10. We find strong evolution in
the magnitude-size scaling relation for galaxies with M(V)<-20, corresponding
to a brightening of 1 mag per sqarcsec in rest-frame V-band by z=1. Yet, disks
at a given absolute magnitude are bluer and have lower stellar mass-to-light
ratios at z=1 than at the present day. As a result, our findings indicate weak
or no evolution in the relation between stellar mass and effective disk size
for galaxies with log(M)>10 over the same time interval. This is strongly
inconsistent with the most naive theoretical expectation, in which disk size
scales in proportion to the halo virial radius, which would predict that disks
are a factor of two denser at fixed mass at z=1. The lack of evolution in the
stellar mass-size relation is consistent with an ``inside-out'' growth of
galaxy disks on average (galaxies increasing in size as they grow more
massive), although we cannot rule out more complex evolutionary scenarios.Comment: 22 pages, 16 figures, submitted to Ap
- âŠ