4,022 research outputs found
Teachers representations about students' misbehaviours in physical education related with subjects, class moments and their targets
FCT (Fundação para a Ciência e a Tecnologia), IDP (Instituto do Desporto de Portugal), AIESEP World Congres
Cr(III) removal and recovery from Saccharomyces cerevisiae
Heavy metal recovery from biosorbents is of major importance in the assessment of competitiveness of biosorption processes. Several
desorption agents (H2SO4, HNO3, HCl, CH3COOH and EDTA) were tested for the selection of the optimal elution conditions for Cr(III)
recovery from Saccharomyces cerevisiae cells.
Sorption time was optimised as it plays an important role in the sorption–desorption process, being shown that a 30 min sorption period is
the best option to ensure metal removal from solution and good recovery from biosorbent. The optimal contact time with desorption agents
was also studied, as long exposures to these ones may cause cell damage, affecting biosorbent metal uptake capacity in subsequent sorption
cycles.
Each eluant was analysed in terms of its desorption capacity and its effect on the biomass metal uptake capacity in multiple
sorption–desorption cycles. Considering the effectiveness of chromium desorption from loaded biomass, it was possible to conclude that
H2SO4 (pH≈1) was the most effective eluant tested, accomplishing the highest Cr(III) recovery from S. cerevisiae in three consecutive
sorption/desorption cycles.
Regarding the damage caused by acid treatment on S. cerevisiae cells, assessed by the reduction on metal uptake capacity after elution,
it was possible to observe that sulphuric acid was the most harmful eluant causing long term negative effects in metal uptake. By the time
the experiments were interrupted (nearly 26 h of continuous cycles) biomass uptake capacity was reduced to about 77% of the value reached
before acid treatment.Fundação para a Ciência e a Tecnologia (FCT) – PRAXIS XXI/BD/15945/98
Sorption of Cr(III) from aqueous solutions by spent brewery grain
Two types of spent brewery grains were tested for Cr(III) uptake from aqueous solutions: not treated
spent grains (NTSG), obtained by abundant washing of spent grain obtained from a Portuguese
brewing industry with distilled water, and treated spent grain (TSG), prepared by treating NTSG with
NaOH 0.5 M for four hours followed by washing with distilled water.
Both materials were mixed with chromium solutions (50 and 100 mg Cr(III)/L), varying medium pH
from 3 to 5. Maximum metal uptake occurred at pH 5. Langmuir isotherm model well describes
Cr(III) biosorption by NTSG and TSG. The maximum uptake capacity obtained was 17.84 mg
Cr(III)/g NTSG and 13.87 mg Cr(III)/g TSG. Considering that Langmuir constant, b, reflecting the
affinity between the sorbent and the sorbate is lower for NTSG (0.0749 L/mg) it is possible to
conclude that the alkalis treatment does not improve spent grain uptake capacity for Cr(III).Fundação para a Ciência e a Tecnologia (FCT) - PRAXIS XXI/BD/15945/98
Radiative decay Z_H-> \gamma A_H in the little Higgs model with T-parity
In the little Higgs model with T-parity (LHTM), the only tree-level
kinematically allowed two-body decay of the Z_H boson is Z_H-> A_H H and thus
one-loop induced two-body decays may have a significant rate. We study the
Z_H-> \gamma A_H decay, which is induced at the one-loop level by a fermion
triangle and is interesting as it depends on the mechanism of anomaly
cancellation of the model. All the relevant two- and three-body decays of the
Z_H gauge boson arising at the tree-level are also calculated. We consider a
small region of the parameter space where the scale of the symmetry breaking f
is still allowed to be as low as 500 GeV by electroweak precision data. We
first analyze the scenario of a Higgs boson with a mass of 120 GeV. We found
that the Z_H->\gamma A_H branching ratio can be of the order of a tree-level
three-body decay and may be at the reach of detection at the LHC for f close to
500 GeV, but it may be difficult to detect for f=1 TeV. There is also an
scenario where the Higgs boson has an intermediate mass such that the Z_H-> A_H
H decay is closed, the Z_H-> \gamma A_H gets considerably enhanced and the
chances of detection get a large boost.Comment: 19 pages, 9 figures, 2 table
Long-term variability of the optical spectra of NGC 4151: II. Evolution of the broad Ha and Hb emission-line profiles
Results of the long-term (11 years, from 1996 to 2006) H and H
line variations of the active galactic nucleus of NGC 4151 are presented. High
quality spectra (S/N>50 and R~8A) of H and H were investigated.
We analyzed line profile variations during monitoring period. Comparing the
line profiles of H and H, we studied different details (bumps,
absorption features) in the line profiles. The variations of the different
H and H line profile segments have been investigated. Also, we
analyzed the Balmer decrement for whole line and for line segments. We found
that the line profiles were strongly changing during the monitoring period,
showing blue and red asymmetries. This indicates a complex BLR geometry of NGC
4151 with, at least, three kinematically distinct regions: one that contributes
to the blue line wing, one to the line core and one to the red line wing. Such
variation can be caused by an accelerating outflow starting very close to the
black hole, where the red part may come from the region {closer to the black
hole than the blue part, which is coming} from the region having the highest
outflow velocities. Taking into account the fact that the BLR of NGC 4151 has a
complex geometry (probably affected by an outflow) and that a portion of the
broad line emission seems to have not a pure photoionization origin, one can
ask the question whether the study of the BLR by reverberation mapping may be
valid in the case of this galaxy.Comment: 24 pages, 18 figures, accepted for publications in A&
Cr (III) recovery from Saccharomyces cerevisiae by elution : a preliminary study
To recover adsorbed metals from biosorbents, in order to recycle metal and reuse biomass in
several adsorption/desorption cycles, elution conditions need to be optimized. The present work
aimed to study the following elution parameters: eluant type and concentration (H2SO4, HNO3,
HCl, CH3COOH and Na2CO3 0.1, 0.5 and 1.0 M, and EDTA 0.01, 0.05 and 0.1 M); biosorbent
contact time with Cr (III) solution (15 min, 2 and 24 h), and S/L ratio (4 and 8 g/L).
Experimental data show a decrease in Cr recovery efficiency with increasing sorption time,
probably due to metal bioaccumulation. Concerning the S/L ratio, it was possible to observe, in
most essays, that best recoveries were achieved using biosorbent concentration of 8 g/L.
Comparing the eluants tested according to their metal recovery efficiencies, it can be concluded
that Na2CO3 is not a good eluant (maximum recovery of 21 %). All the others showed
equivalent behaviours, being necessary more assays to determine eluant treatment effect in Cr
uptake capacity in subsequent sorption cycles.Fundação para a Ciência e a Tecnologia (FCT
Cokebildung und Entcoking während der Methanbildung und des Methanzerfalls auf Ni-Cu-Trägerkatalysatoren
The effect of the composition of silica supported Ni-Cu alloy
catalysts on the process of coking and decoking during methane
decomposition and during methanation was considered. The kinetics
of methanation was studied and compared to those of carbon
deposition and of strong adsorption of hydrogen. Initiation of the
formation of filamentous carbon formation on mono-metallic surfaces
may take place if the ratio of the partial pressures, pCO/pH2, is
larger than 2 (T 673 K). Once the process starts,
the chemical potential of the gas phase may be reduced to lower
values without interruption of filament growth. Besides, it was concluded
that the methanation reaction includes two steps: the dissociative
adsorption of CO and the hydrogenation of the adsorbed
species. It was possible to establish the mechanism through which
Cu affects the activity of Ni. The effect of the composition of the
alloy catalysts on the methane formation and on the simultaneous
carbon deposition indicates that those reactions belong to group I
and to group II, respectively, following Ponec's classification. It
was possible to find the optimal Cu concentration that maximises
methanation and minimises carbon deposition. The kinetics of
methane decomposition was also considered and is well described
by adapting a model developed by other authors for Fe catalysts
The XMM spectral catalog of SDSS optically selected Seyfert 2 galaxies
We present an X-ray spectroscopic study of optically selected (SDSS) Seyfert
2 (Sy2) galaxies. The goal is to study the obscuration of Sy2 galaxies beyond
the local universe, using good quality X-ray spectra in combination with high
S/N optical spectra for their robust classification. We analyzed all available
XMM-Newton archival observations of narrow emission line galaxies that meet the
above criteria in the redshift range 0.05<z<0.35. We initially selected narrow
line AGN using the SDSS optical spectra and the BPT classification diagram. We
further modeled and removed the stellar continuum, and we analyzed the residual
emission line spectrum to exclude any possible intermediate-type Seyferts. Our
final catalog comprises 31 Sy2 galaxies with median redshift z~0.1. X-ray
spectroscopy is performed using the available X-ray spectra from the 3XMM and
the XMMFITCAT catalogs. Implementing various indicators of obscuration, we find
seven (~23%) Compton-thick AGN. The X-ray spectroscopic Compton-thick
classification agrees with other commonly used diagnostics, such as the X-ray
to mid-IR luminosity ratio and the X-ray to [OIII] luminosity ratio. Most
importantly, we find four (~13%) unobscured Sy2 galaxies, at odds with the
simplest unification model. Their accretion rates are significantly lower than
the rest of our Sy2 sample, in agreement with previous studies that predict the
absence of the broad line region below a certain Eddington ratio threshold.Comment: 12 pages, 6 figures, accepted for publication in A&
Mechanisms of Cr(III) biosorption onto residual brewer's yeast
The knowledge and understanding of metal-biomass interactions is crucial to develop and maximize biosorption processes potential to the concentration, removal and recovery of heavy metals from
dilute solutions, as well as to define strategies to regenerate and reuse biosorbent in multiple cycles (Ahluwalia and Goyal, 2007; Volesky, 2001). It also turns possible biosorption optimization at a
molecular level, including biomass genetic modification to induce changes in morphologic and physiologic characteristics in order to increase metal uptake (Srinath et al., 2002; Volesky, 2001). To
reach that purpose, and considering that several mechanisms may contribute to the overall metal uptake depending on the metal and the biosorbent used, environmental factors, and the cell
metabolic activity (Dhankhar and Hooda, 2011), it is necessary to study in detail the interactions established in each biosorption system.
Heavy metal biosorption involves a combination of several passive accumulation processes, that may include: i) physical adsorption; ii) chemisorption, including ion exchange, coordination,
complexation and chelation; iii) and inorganic precipitation (Ahluwalia and Goyal, 2007; Wang and Chen, 2006). According to Gadd (2004), metal-microorganism interactions may be seen as natural
strategies to remove, recover or diminish metal toxicity in organic or inorganic forms. Different organisms exhibit different responses to the exposure to toxic ions, varying from transport through
cellular membrane, biosorption onto cell walls, entrapment in extracellular structures, precipitation, complexation and redox reactions
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