4,862 research outputs found
Effect of pine bark and compost on the biological denitrification process of non-hazardous landfill leachate: Focus on the microbiology
In an attempt to optimize the cost-efficiency of landfill leachate treatment by biological denitrification process, our study focused on finding low-cost alternatives to traditional expensive chemicals such as composted garden refuse and pine bark, which are both available in large amount in South African landfill sites. The overall objective was to assess the behaviour of the bacterial community in relation to each substrate while treating high strength landfill leachates. Denitrification processes in fixed bed reactors were simulated at laboratory scale using anaerobic batch tests with immature compost and pine bark. High strength leachate was simulated using a solution of water and nitrate at a concentration of 500 mg lâ1. Results suggest that pine bark released large amounts of phenolic compounds and hydroxylated benzene rings, which both can delay the acclimatization time and inhibit the biological denitrification (only 30% efficiency). Furthermore, presence of potential pathogens like Enterobacter and Pantoea agglomerans prevents the applicability of the pine bark in full-scale operations. On the other hand, lightly composted garden refuse (CGR) offered an adequate substrate for the formation of a biofilm necessary to complete the denitrification process (total nitrate removal observed within 7 days). CGR further contributed to a rapid establishment of an active consortium of denitrifiers including Acinetobacter, Rhizobium, Thermomonas, Rheinheimera, Phaeospirillum and Flavobacterium. Clearly the original composition, nature, carbon to nitrogen ratio (C/N) and degree of maturity and stability of the substrates play a key role in the denitrification process, impacting directly on the development of the bacterial population and, therefore, on the long-term removal efficiency
Experimental investigations and numerical modelling of in-situ reactive caps for PAH contaminated marine sediments
The present study compared numerical modelling and experimental investigations to evaluate the effectiveness of in-situ reactive capping for marine sediments contaminated by polycyclic aromatic hydrocarbons (PAHs). As a case study, sediment samples from Mar Piccolo (Italy) were analyzed and experiments were undertaken using batch columns. Two types of capping amendments were tested: AquaGateÂź + 5 % of powdered activated carbon (AG PAC) and Organoclay Reactive Core Mat (OC RCM). The column tests were carried out for 20 days, obtaining a short-term PAH distribution for three cases analysed, which compared the application of the two caps with no intervention. In parallel, in order to evaluate the intervention long term efficacy, an ad-hoc multilayered model predicting PAH concentrations into the sediments and the overlying water column was developed and validated with the experimental results. Both capping systems considerably reduced PAH concentrations in the overlying water, with the highest performance seen in AG PAC for benzo[a]pyrene (99 %) and anthracene (72 %); results also confirmed in the model predictions. In addition, the numerical simulations indicated a good efficiency of both caps over time, obtaining PAH values below the threshold limit in the long term. Although further experiments need to be developed accounting for multiple contamination competitiveness
The variable finesse locking technique
Virgo is a power recycled Michelson interferometer, with 3 km long Fabry-Perot cavities in the arms. The locking of the interferometer has been obtained with an original lock acquisition technique. The main idea is to lock the instrument away from its working point. Lock is obtained by misaligning the power recycling mirror and detuning the Michelson from the dark fringe. In this way, a good fraction of light escapes through the antisymmetric port and the power build-up inside the recycling cavity is extremely low. The benefit is that all the degrees of freedom are controlled when they are almost decoupled, and the linewidth of the recycling cavity is large. The interferometer is then adiabatically brought on to the dark fringe. This technique is referred to as variable finesse, since the recycling cavity is considered as a variable finesse Fabry-Perot. This technique has been widely tested and allows us to reach the dark fringe in few minutes, in an essentially deterministic way
A Cross-correlation method to search for gravitational wave bursts with AURIGA and Virgo
We present a method to search for transient GWs using a network of detectors
with different spectral and directional sensitivities: the interferometer Virgo
and the bar detector AURIGA. The data analysis method is based on the
measurements of the correlated energy in the network by means of a weighted
cross-correlation. To limit the computational load, this coherent analysis step
is performed around time-frequency coincident triggers selected by an excess
power event trigger generator tuned at low thresholds. The final selection of
GW candidates is performed by a combined cut on the correlated energy and on
the significance as measured by the event trigger generator. The method has
been tested on one day of data of AURIGA and Virgo during September 2005. The
outcomes are compared to the results of a stand-alone time-frequency
coincidence search. We discuss the advantages and the limits of this approach,
in view of a possible future joint search between AURIGA and one
interferometric detector.Comment: 11 pages, 6 figures, submitted to CQG special issue for Amaldi 7
Proceeding
Spin-wave scattering at low temperatures in manganite films
The temperature and magnetic field dependence of the resistivity
has been measured for LaSrMnO (y=0 and 0.128)
films grown on (100) SrTiO substrates. The low-temperature in the
ferromagnetic metallic region follows well with being the residual resistivity. We attribute the second and third term to
small-polaron and spin-wave scattering, respectively. Our analysis based on
these scattering mechanisms also gives the observed difference between the
metal-insulator transition temperatures of the films studied. Transport
measurements in applied magnetic field further indicate that spin-wave
scattering is a key transport mechanism at low temperatures.Comment: 5 pages, 4 figures. to appear in Phys. Rev.
Mother-offspring recognition via contact calls in cattle, Bos taurus.
Individual recognition in gregarious species is fundamental in order to avoid misdirected parental investment. In ungulates, two very different parental care strategies have been identified: âhiderâ offspring usually lie concealed in vegetation whereas offspring of âfollowerâ species remain with their mothers while they forage. These two strategies have been suggested to impact on mother-offspring vocal recognition, with unidirectional recognition of the mother by offspring occurring in hiders and bidirectional recognition in followers. In domestic cattle, Bos taurus, a facultative hider species, vocal communication and recognition have not been studied in detail under free-ranging conditions, where cows and calves can graze freely and where hiding behaviour can occur. We hypothesized that, as a hider species, cattle under these circumstances would display unidirectional vocal recognition. To test this hypothesis, we conducted playback experiments using mother-offspring contact calls. We found that cows were more likely to respond, by moving their ears and/or looking, turning or walking towards the loudspeaker, to calls of their own calves than to calls from other calves. Similarly, calves responded more rapidly, and were more likely to move their ears and/or look, turn or walk towards the loudspeaker, and to call back and/or meet their mothers, in response to calls from their own mothers than to calls from other females. Contrary to our predictions, our results suggest that mother-offspring vocal individual recognition is bidirectional in cattle. Additionally, mothers of younger calves tended to respond more strongly to playbacks than mothers of older calves. Therefore, mother responses to calf vocalizations are at least partially influenced by calf age
Reconstruction of the gravitational wave signal during the Virgo science runs and independent validation with a photon calibrator
The Virgo detector is a kilometer-scale interferometer for gravitational wave
detection located near Pisa (Italy). About 13 months of data were accumulated
during four science runs (VSR1, VSR2, VSR3 and VSR4) between May 2007 and
September 2011, with increasing sensitivity.
In this paper, the method used to reconstruct, in the range 10 Hz-10 kHz, the
gravitational wave strain time series from the detector signals is
described. The standard consistency checks of the reconstruction are discussed
and used to estimate the systematic uncertainties of the signal as a
function of frequency. Finally, an independent setup, the photon calibrator, is
described and used to validate the reconstructed signal and the
associated uncertainties.
The uncertainties of the time series are estimated to be 8% in
amplitude. The uncertainty of the phase of is 50 mrad at 10 Hz with a
frequency dependence following a delay of 8 s at high frequency. A bias
lower than and depending on the sky direction of the GW is
also present.Comment: 35 pages, 16 figures. Accepted by CQ
Virgo calibration and reconstruction of the gravitational wave strain during VSR1
Virgo is a kilometer-length interferometer for gravitational waves detection
located near Pisa. Its first science run, VSR1, occured from May to October
2007. The aims of the calibration are to measure the detector sensitivity and
to reconstruct the time series of the gravitational wave strain h(t). The
absolute length calibration is based on an original non-linear reconstruction
of the differential arm length variations in free swinging Michelson
configurations. It uses the laser wavelength as length standard. This method is
used to calibrate the frequency dependent response of the Virgo mirror
actuators and derive the detector in-loop response and sensitivity within ~5%.
The principle of the strain reconstruction is highlighted and the h(t)
systematic errors are estimated. A photon calibrator is used to check the sign
of h(t). The reconstructed h(t) during VSR1 is valid from 10 Hz up to 10 kHz
with systematic errors estimated to 6% in amplitude. The phase error is
estimated to be 70 mrad below 1.9 kHz and 6 micro-seconds above.Comment: 8 pages, 8 figures, proceedings of Amaldi 8 conference, to be
published in Journal of Physics Conference Series (JPCS). Second release:
correct typo
Calibration and sensitivity of the Virgo detector during its second science run
The Virgo detector is a kilometer-length interferometer for gravitational
wave detection located near Pisa (Italy). During its second science run (VSR2)
in 2009, six months of data were accumulated with a sensitivity close to its
design. In this paper, the methods used to determine the parameters for
sensitivity estimation and gravitational wave reconstruction are described. The
main quantities to be calibrated are the frequency response of the mirror
actuation and the sensing of the output power. Focus is also put on their
absolute timing. The monitoring of the calibration data as well as the
parameter estimation with independent techniques are discussed to provide an
estimation of the calibration uncertainties. Finally, the estimation of the
Virgo sensitivity in the frequency-domain is described and typical
sensitivities measured during VSR2 are shown.Comment: 30 pages, 23 figures, 1 table. Published in Classical and Quantum
Gravity (CQG), Corrigendum include
Midgap edge states and pairing symmetry of quasi-one-dimensional organic superconductors
The singlet s-, d- and triplet p-wave pairing symmetries in
quasi-one-dimensional organic superconductors can be experimentally
discriminated by probing the Andreev bound states at the sample edges. These
states have the energy in the middle of the superconducting gap and manifest
themselves as a zero-bias peak in tunneling conductance into the corresponding
edge. Their existence is related to the sign change of the pairing potential
around the Fermi surface. We present an exact self-consistent solution of the
edge problem showing the presence of the midgap states for p_x-wave
superconductivity. The spins of the edge state respond paramagnetically to a
magnetic field parallel to the vector d that characterizes triplet pairing.Comment: 6 pages, 4 figures. V.2: New section on spin response is added and
references are updated. V.3: Final version accepted to PRB. Typos are
corrected and important note is added in proof
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