1,650 research outputs found
Synthetic wastewaters treatment by electrocoagulation to remove silver nanoparticles produced by different routes
International audienceNanoscience is a field that has stood out in recent years. The accurate long-term health and environmental risks associated with these emerging materials are unknown. Therefore, this work investigated how to eliminate silver nanoparticles (AgNPs) from synthetic effluents by electrocoagulation (EC) due to the widespread use of this type of nanoparticle (NP) in industry and its potential inhibition power over microorganisms responsible for biological treatment in effluent treatment plants. Synthesized AgNPs were studied via four different routes by chemical reduction in aqueous solutions to simulate the chemical variations of a hypothetical industrial effluent, and efficiency conditions of the EC treatment were determined. All routes used silver nitrate as the source of silver ions, and two synthesis routes were studied with sodium citrate as a stabilizer. In route I, sodium citrate functioned simultaneously as the reducing agent and stabilizing agent, whereas route II used sodium borohydride as a reducing agent. Route III used d-glucose as the reducing agent and sodium pyrophosphate as the stabilizer; route IV used sodium pyrophosphate as the stabilizing agent and sodium borohydride as the reducing agent. The efficiency of the EC process of the different synthesized solutions was studied. For route I, after 85 min of treatment, a significant decrease in the plasmon resonance peak of the sample was observed, which reflects the efficiency in the mass reduction of AgNPs in the solution by 98.6%. In route II, after 12 min of EC, the absorbance results reached the detection limit of the measurement instrument, which indicates a minimum reduction of 99.9% of AgNPs in the solution. During the 4 min of treatment in route III, the absorbance intensities again reached the detection limit, which indicates a minimum reduction of 99.8%. In route IV, after 10 min of treatment, a minimum AgNP reduction of 99.9% was observed. Based on these results, it was possible to verify that the solutions containing citrate considerably increased the necessary times required to eliminate AgNPs from the synthesized effluent, whereas solutions free of this reagent showed better results on floc formation and, therefore, are best for the treatment. The elimination of AgNPs from effluents by EC proved effective for the studied routes
A screening mechanism for extra W and Z gauge bosons
We generalize a previous construction of a fermiophobic model to the case of
more than one extra and gauge bosons. We focus in particular on the
existence of screening configurations and their implication on the gauge boson
mass spectrum. One of these configurations allows for the existence of a set of
relatively light new gauge bosons, without violation of the quite restrictive
bounds coming from the parameter. The links with Bess and
degenerate Bess models are also discussed. Also the signal given here by this
more traditional gauge extension of the SM could help to disentangle it from
the towers of Kaluza-Klein states over and gauge bosons in extra
dimensions.Comment: 23 pages, 1 figure, extended discussion on precision tests. To appear
in International Journal of Modern Physics
Lensing of the CMB: Non Gaussian aspects
We study the generation of CMB anisotropies by gravitational lensing on small
angular scales. We show these fluctuations are not Gaussian. We prove that the
power spectrum of the tail of the CMB anisotropies on small angular scales
directly gives the power spectrum of the deflection angle. We show that the
generated power on small scales is correlated with the large scale gradient.
The cross correlation between large scale gradient and small scale power can be
used to test the hypothesis that the extra power is indeed generated by
lensing. We compute the three and four point function of the temperature in the
small angle limit. We relate the non-Gaussian aspects presented in this paper
as well as those in our previous studies of the lensing effects on large scales
to the three and four point functions. We interpret the statistics proposed in
terms of different configurations of the four point function and show how they
relate to the statistic that maximizes the S/N.Comment: Changes to match accepted version in PRD, 20 pages 10 figures. Better
resolution images of the figures can be found at
http://www.sns.ias.edu/~matiasz/RESEARCH/cmblensing.htm
Direct Signature of Evolving Gravitational Potential from Cosmic Microwave Background
We show that time dependent gravitational potential can be directly detected
from the cosmic microwave background (CMB) anisotropies. The signature can be
measured by cross-correlating the CMB with the projected density field
reconstructed from the weak lensing distortions of the CMB itself. The
cross-correlation gives a signal whenever there is a time dependent
gravitational potential. This method traces dark matter directly and has a well
defined redshift distribution of the window projecting over the density
perturbations, thereby avoiding the problems plaguing other proposed
cross-correlations. We show that both MAP and Planck will be able to probe this
effect for observationally relevant curvature and cosmological constant models,
which will provide additional constraints on the cosmological parameters.Comment: 4 pages, 2 figures. Submitted to PR
Fast, multi-band photon detectors based on quantum well devices for beam-monitoring in new generation light sources
In order to monitor the photon-beam position for both diagnostics and calibration purposes, we have investigated the possibility to use InGaAs/InAlAs
Quantum Well (QW) devices as position-sensitive photon detectors for Free-Electron Laser (FEL) or Synchrotron Radiation (SR).
Owing to their direct, low-energy band gap and high electron mobility, such QW devices may be used also at Room Temperature (RT) as fast multi-band sensors for photons ranging from visible light to hard X-rays. Moreover, internal charge-amplification mechanism can be applied for very low signal levels, while the high carrier mobility allows the design of very fast photon detectors with sub-nanosecond response times. Segmented QW sensors have been preliminary tested with 100-fs-wide 400 nm laser pulses and X-ray SR. The reported results indicate that these devices respond with 100 ps rise-times to such ultra-fast laser pulses. Besides, linear scan on the back-pixelated device has shown that these detectors are sensitive to the position of each ultrashort beam bunch
Reconstructing Projected Matter Density from Cosmic Microwave Background
Gravitational lensing distorts the cosmic microwave background (CMB)
anisotropies and imprints a characteristic pattern onto it. The distortions
depend on the projected matter density between today and redshift . In this paper we develop a method for a direct reconstruction of the
projected matter density from the CMB anisotropies. This reconstruction is
obtained by averaging over quadratic combinations of the derivatives of CMB
field. We test the method using simulations and show that it can successfully
recover projected density profile of a cluster of galaxies if there are
measurable anisotropies on scales smaller than the characteristic cluster size.
In the absence of sufficient small scale power the reconstructed maps have low
signal to noise on individual structures, but can give a positive detection of
the power spectrum or when cross correlated with other maps of large scale
structure. We develop an analytic method to reconstruct the power spectrum
including the effects of noise and beam smoothing. Tests with Monte Carlo
simulations show that we can recover the input power spectrum both on large and
small scales, provided that we use maps with sufficiently low noise and high
angular resolution.Comment: 21 pages, 9 figures, submitted to PR
A SUSY SU(5) Grand Unified Model of Tri-Bimaximal Mixing from A4
We discuss a grand unified model based on SUSY SU(5) in extra dimensions and
on the flavour group A4xU(1) which, besides reproducing tri-bimaximal mixing
for neutrinos with the accuracy required by the data, also leads to a natural
description of the observed pattern of quark masses and mixings.Comment: 19 page
Cepheid variables in the LMC cluster NGC 1866. I. New BVRI CCD photometry
We report BV(RI)c CCD photometric data for a group of seven Cepheid variables
in the young, rich cluster NGC 1866 in the Large Magellanic Cloud. The
photometry was obtained as part of a program to determine accurate distances to
these Cepheids by means of the infrared surface brightness technique, and to
improve the LMC Cepheid database for constructing Cepheid PL and PLC relations.
Using the new data together with data from the literature, we have determined
improved periods for all variables. For five fundamental mode pulsators, the
light curves are now of excellent quality and will lead to accurate distance
and radius determinations once complete infrared light curves and radial
velocity curves for these variables become available.Comment: To appear in ApJ Supp., AASTeX, 24 pages, 8 tables, 8 figure
CMB polarization as a direct test of Inflation
We study the auto-correlation function of CMB polarization anisotropies and
their cross correlation with temperature fluctuations as probe of the causal
structure of the universe. Because polarization is generated at the last
scattering surface, models in which fluctuations are causally produced on
sub-horizon scales cannot generate correlations on scales larger then . Inflationary models, on the other hand, predict a peak in the correlation
functions at these scales: its detection would be definitive evidence in favor
of a period of inflation. This signal could be detected with the next
generation of satellites.Comment: 4 pages, 1 figure. Minor changes to match the Phys. Rev. Lett.
versio
Efeito do congelamento na qualidade fisiológica de sementes de Lírio-da-Caatinga [Zephyranthes sylvatica (Mart.) Baker].
Número especial. Resumos do XVIII Congresso Brasileiro de Sementes, Florianópolis, set. 2013
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