28,790 research outputs found
Effect of Nitrate, Acetate and Hydrogen on Native Perchlorate-reducing Microbial Communities and Their Activity in Vadose Soil
The effect of nitrate, acetate, and hydrogen on native perchlorate-reducing bacteria (PRB) was examined by conducting microcosm tests using vadose soil collected from a perchlorate-contaminated site. The rate of perchlorate reduction was enhanced by hydrogen amendment and inhibited by acetate amendment, compared with unamendment. Nitrate was reduced before perchlorate in all amendments. In hydrogen-amended and unamended soils, nitrate delayed perchlorate reduction, suggesting that the PRB preferentially use nitrate as an electron acceptor. In contrast, nitrate eliminated the inhibitory effect of acetate amendment on perchlorate reduction and increased the rate and the extent, possibly because the preceding nitrate reduction/denitrification decreased the acetate concentration that was inhibitory to the native PRB. In hydrogen-amended and unamended soils, perchlorate reductase gene (pcrA) copies, representing PRB densities, increased with either perchlorate or nitrate reduction, suggesting that either perchlorate or nitrate stimulates the growth of the PRB. In contrast, in acetate-amended soil pcrA increased only when perchlorate was depleted: a large portion of the PRB may have not utilized nitrate in this amendment. Nitrate addition did not alter the distribution of the dominant pcrA clones in hydrogen-amended soil, likely because of the functional redundancy of PRB as nitrate-reducers/denitrifiers, whereas acetate selected different pcrA clones from those with hydrogen amendment
Analysis of the generation of photon pairs in periodically poled lithium niobate
The process of spontaneous parametric down-conversion (SPDC) in nonlinear
crystals makes it fairly easy to generate entangled photon states. It has been
known for some time that the conversion efficiency can be improved by employing
quasi-phase-matching in periodically poled crystals. Using two single-photon
detectors, we have analyzed the photon pairs generated by SPDC in a
periodically poled lithium niobate crystal pumped by a femtosecond laser.
Several parameters could be varied in our setup, allowing us to obtain data in
close agreement with both thermal and Poissonian photon-pair distributions.Comment: 4 pages, 4 figures, uses ws-procs10x7.cls; v2: Sign in equation (5)
correcte
Contrasting the beam interaction characteristics of selected lasers with a partially stabilised zirconia (PSZ) bio-ceramic
Differences in the beam interaction characteristics of a CO2 laser, a Nd:YAG laser, a high power diode laser (HPDL) and an excimer laser with a partially stabilised zirconia (PSZ) bio-ceramic have been studied. A derivative of Beer-Lambertâs law was applied and the laser beam absorption lengths of the four lasers were calculated as 33.55 x 10-3 cm for the CO2 laser, 18.22 x 10-3 cm for the Nd:YAG laser, 17.17 x 10-3 cm for the HPDL and 8.41 x 10-6 cm for the excimer laser. It was determined graphically that the fluence threshold values at which significant material removal was effected by the CO2 laser, the Nd:YAG laser, the HPDL and the excimer laser were 52 J/cm2, 97 J/cm2, 115 J/cm2 and 0.48 J/cm2 respectively. The thermal loading value for the CO2 laser, the Nd:YAG laser, the HPDL and the excimer laser were calculated as being 1.55 kJ/cm3, 5.32 kJ/cm3, 6.69 kJ/cm3 and 57.04 kJ/cm3 respectively
Spin Liquid State in an Organic Mott Insulator with Triangular Lattice
H NMR and static susceptibility measurements have been performed in an
organic Mott insulator with nearly isotropic triangular lattice,
-(BEDT-TTF)Cu(CN), which is a model system of
frustrated quantum spins. The static susceptibility is described by the spin
= 1/2 antiferromagnetic triangular-lattice Heisenberg model with the
exchange constant 250 K. Regardless of the large magnetic
interactions, the H NMR spectra show no indication of long-range magnetic
ordering down to 32 mK, which is four-orders of magnitude smaller than .
These results suggest that a quantum spin liquid state is realized in the close
proximity of the superconducting state appearing under pressure.Comment: 4 pages, 4 figure
Mesons in Nuclei: eta and omega mesons
Data on the photoproduction of omega mesons on nuclei have been re-analyzed
in search for in-medium modifications. The data were taken with the Crystal
Barrel(CB)/TAPS detector system at the ELSA accelerator facility in Bonn. The
extracted omega line shape was found to be sensitive to the background
subtraction. In experiments at the tagged photon facility of the Mainz MAMI
accelerator photoproduction of mesons from light nuclear targets (deuteron and
3He) has been studied. The experiments used the combined Crystal Ball/TAPS
setup in Mainz. Measurements of eta- and pi0-photoproduction off a liquid
3He-target have been used for the search for the formation of eta-mesic 3He.
The installation of the WASA detector at COSY opened a unique possibility to
search for the 4He-eta bound state with high statistics and high acceptance. We
are conducting a search via an exclusive measurement of the excitation function
for the dd -> 3He p pi- reaction.Comment: Proceedings of New Frontiers In QCD 2010: Exotic Hadron Systems And
Dense Matter 18 Jan - 19 Mar 2010, Kyoto, Japa
Modeling and evolving biochemical networks: insights into communication and computation from the biological domain
This paper is concerned with the modeling and evolving
of Cell Signaling Networks (CSNs) in silico. CSNs are
complex biochemical networks responsible for the coordination of cellular activities. We examine the possibility to computationally evolve and simulate Artificial Cell Signaling Networks (ACSNs) by means of Evolutionary Computation techniques. From a practical point of view, realizing and evolving ACSNs may provide novel computational paradigms for a variety of application areas. For example, understanding some inherent properties of CSNs such as crosstalk may be of interest: A potential benefit of engineering crosstalking systems is that it allows the modification of a specific process according to the state of other processes in the system. This is clearly necessary in order to achieve complex control tasks. This work may also contribute to the biological understanding of the origins and evolution of real CSNs. An introduction to CSNs is first
provided, in which we describe the potential applications
of modeling and evolving these biochemical networks in
silico. We then review the different classes of techniques to model CSNs, this is followed by a presentation of two alternative approaches employed to evolve CSNs within the
ESIGNET project. Results obtained with these methods
are summarized and discussed
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