891 research outputs found
Anaerobic Digester Bioaugmentation Influences Quasi Steady State Performance and Microbial Community
Nine anaerobic digesters, each seeded with biomass from a different source, were operated identically and their quasi steady state function was compared. Subsequently, digesters were bioaugmented with a methanogenic culture previously shown to increase specific methanogenic activity. Before bioaugmentation, different seed biomass resulted in different quasi steady state function, with digesters clustering into three groups distinguished by methane (CH4) production. Digesters with similar functional performance contained similar archaeal communities based on clustering of Illumina sequence data of the V4V5 region of the 16S rRNA gene. High CH4 production correlated with neutral pH and high Methanosarcina abundance, whereas low CH4production correlated to low pH as well as high Methanobacterium and DHVEG 6 family abundance. After bioaugmentation, CH4 production from the high CH4 producing digesters transiently increased by 11 ± 3% relative to non-bioaugmented controls (p \u3c 0.05, n = 3), whereas no functional changes were observed for medium and low CH4producing digesters that all had pH higher than 6.7. The CH4 production increase after bioaugmentation was correlated to increased relative abundance of Methanosaeta and Methaospirillum originating from the bioaugment culture. In conclusion, different anaerobic digester seed biomass can result in different quasi steady state CH4production, SCOD removal, pH and effluent VFA concentration in the timeframe studied. The bioaugmentation employed can result in a period of increased methane production. Future research should address extending the period of increased CH4 production by employing pH and VFA control concomitant with bioaugmentation, developing improved bioaugments, or employing a membrane bioreactor to retain the bioaugment
Reduction of Dilute Ising Spin Glasses
The recently proposed reduction method for diluted spin glasses is
investigated in depth. In particular, the Edwards-Anderson model with \pm J and
Gaussian bond disorder on hyper-cubic lattices in d=2, 3, and 4 is studied for
a range of bond dilutions. The results demonstrate the effectiveness of using
bond dilution to elucidate low-temperature properties of Ising spin glasses,
and provide a starting point to enhance the methods used in reduction. Based on
that, a greedy heuristic call ``Dominant Bond Reduction'' is introduced and
explored.Comment: 10 pages, revtex, final version, find related material at
http://www.physics.emory.edu/faculty/boettcher
Laue Lens Development for Hard X-rays (>60 keV)
Results of reflectivity measurements of mosaic crystal samples of Cu (111)
are reported. These tests were performed in the context of a feasibility study
of a hard X-ray focusing telescope for space astronomy with energy passband
from 60 to 600 keV. The technique envisaged is that of using mosaic crystals in
transmission configuration that diffract X-rays for Bragg diffraction (Laue
lens). The Laue lens assumed has a spherical shape with focal length . It is
made of flat mosaic crystal tiles suitably positioned in the lens. The samples
were grown and worked for this project at the Institute Laue-Langevin (ILL) in
Grenoble (France), while the reflectivity tests were performed at the X-ray
facility of the Physics Department of the University of Ferrara.Comment: 6 pages, 12 figures, accepted for publication in IEEE Transactions on
Nuclear Scienc
Energy backtransfer and infrared photoresponse in erbium-doped silicon p-n diodes
Temperature-dependent measurements of the photoluminescence (PL) intensity, PL lifetime, and
infrared photocurrent, were performed on an erbium-implanted silicon p - n junction in order to
investigate the energy transfer processes between the silicon electronic system and the Er 4 f energy
levels. The device features excellent light trapping properties due to a textured front surface and a
highly reflective rear surface. The PL intensity and PL lifetime measurements show weak
temperature quenching of the erbium intra-4 f transition at 1.535 mm for temperatures up to 150 K,
attributed to Auger energy transfer to free carriers. For higher temperatures, much stronger
quenching is observed, which is attributed to an energy backtransfer process, in which Er deexcites
by generation of a bound exciton at an Er-related trap. Dissociation of this exciton leads to the
generation of electron-hole pairs that can be collected as a photocurrent. In addition, nonradiative
recombination takes place at the trap. It is shown for the first time that all temperature-dependent
data for PL intensity, PL lifetime, and photocurrent can be described using a single model. By fitting
all temperature-dependent data simultaneously, we are able to extract the numerical values of the
parameters that determine the ~temperature-dependent! energy transfer rates in erbium-doped
silicon. While the external quantum efficiency of the photocurrent generation process is small
(1.831026) due to the small erbium absorption cross section and the low erbium concentration, the
conversion of Er excitations into free e - h pairs occurs with an efficiency of 70% at room
temperature
Exploring the Hard X-/soft gamma-ray Continuum Spectra with Laue Lenses
The history of X-ray astronomy has shown that any advancement in our
knowledge of the X-ray sky is strictly related to an increase in instrument
sensitivity. At energies above 60 keV, there are interesting prospects for
greatly improving the limiting sensitivity of the current generation of direct
viewing telescopes (with or without coded masks), offered by the use of Laue
lenses. We will discuss below the development status of a Hard X-Ray focusing
Telescope (HAXTEL) based on Laue lenses with a broad bandpass (from 60 to 600
keV) for the study of the X-ray continuum of celestial sources. We show two
examplesof multi-lens configurations with expected sensitivity orders of
magnitude better ( photons cm s keV
at 200 keV) than that achieved so far. With this unprecedented sensitivity,
very exciting astrophysical prospects are opened.Comment: 4 pages, 10 figures, to be published in the Proc. of the 39th ESLAB
Symosium, 19-21 April 200
Findings from the PP-SESAME experiment on board the Philae/ROSETTA lander on the surface of comet 67P
International audienceThe Permittivity Probe (PP-SESAME [1]) on-board the Philae Lander of the ROSETTA mission was designed to constrain the complex permittivity of the first 2 meters of the nucleus of comet 67P/Churyumov-Gerasimenko and to monitor its variations with time. Doing so, it is meant to provide unique insight into the composition (and activity if data could have been acquired longer) of the comet. In this paper, we present the analysis of the PP-SESAME measurements acquired during the first science sequence, on November 13, 2014, on the surface of the comet
Feasibility study of a Laue lens for hard X-rays for space astronomy
We report on the feasibility study of a Laue lens for hard X-rays (>60
keV)based on mosaic crystals, for astrophysical applications. In particular we
discuss the scientific motivations, its functioning principle, the procedure
followed to select the suitable crystal materials, the criteria adopted to
establish crystal dimensions and their distribution on the lens in order to
obtain the best lens focusing capabilities, and the criteria for optimizing the
lens effective area in a given passband. We also discuss the effects of
misalignments of the crystal tiles due to unavoidable mechanical errors in
assembling the lens. A software was developed to face all these topics and to
evaluate the expected lens performance.Comment: 10 pages, corrected Fig. 1b and Fig. 2, which are wrong in the
published version, corrected typo
The Huygens Atmospheric Structure Instrument (HASI): Expected Results at Titan and Performance Verification in Terrestrial Atmosphere
The Huygens ASI is a multi-sensor package resulting from an international cooperation, it has been designed to measure the physical quantities characterizing Titan's atmosphere during the Huygens probe mission. On 14th January, 2005, HASI will measure acceleration, pressure, temperature and electrical properties all along the Huygens probe descent on Titan in order to study Titan s atmospheric structure, dynamics and electric properties. Monitoring axial and normal accelerations and providing direct pressure and temperature measurements during the descent, HASI will mainly contribute to the Huygens probe entry and trajectory reconstruction. In order to simulate the Huygens probe descent and verify HASI sensors performance in terrestrial environment, stratospheric balloon flight experiment campaigns have been performed, in collaboration with the Italian Space Agency (ASI). The results of flight experiments have allowed to determine the atmospheric vertical profiles and to obtain a set of data for the analysis of probe trajectory and attitude reconstruction
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