3,955 research outputs found
Initial pseudo-steady state & asymptotic KPZ universality in semiconductor on polymer deposition
The Kardar-Parisi-Zhang (KPZ) class is a paradigmatic example of universality
in nonequilibrium phenomena, but clear experimental evidences of asymptotic
2D-KPZ statistics are still very rare, and far less understanding stems from
its short-time behavior. We tackle such issues by analyzing surface
fluctuations of CdTe films deposited on polymeric substrates, based on a huge
spatio-temporal surface sampling acquired through atomic force microscopy. A
\textit{pseudo}-steady state (where average surface roughness and spatial
correlations stay constant in time) is observed at initial times, persisting up
to deposition of monolayers. This state results from a fine
balance between roughening and smoothening, as supported by a phenomenological
growth model. KPZ statistics arises at long times, thoroughly verified by
universal exponents, spatial covariance and several distributions. Recent
theoretical generalizations of the Family-Vicsek scaling and the emergence of
log-normal distributions during interface growth are experimentally confirmed.
These results confirm that high vacuum vapor deposition of CdTe constitutes a
genuine 2D-KPZ system, and expand our knowledge about possible
substrate-induced short-time behaviors.Comment: 13 pages, 8 figures, 2 table
The use of flocculating brewer's yeast for Cr(III) and Pb(II) removal from residual wastewaters
The use of inexpensive biosorbents to sequester
heavy metals from aqueous solutions, is one of the most
promising technologies being developed to remove these
toxic contaminants from wastewaters. Considering this
challenge, the viability of Cr(III) and Pb(II) removal from
aqueous solutions using a flocculating brewer's yeast residual
biomass from a Portuguese brewing industry was
studied. The influence of physicochemical factors such as
medium pH, biomass concentration and the presence of a
co-ion was characterised. Metal uptake kinetics and
equilibrium were also analysed, considering different incubation
temperatures. For both metals, uptake increased
with medium pH, being maximal at 5.0. Optimal biomass
concentration for the biosorption process was determined
to be 4.5 g dry weight/l. In chromium and lead mixture
solutions, competition for yeast binding sites was observed
between the two metals, this competition being pH dependent.
Yeast biomass showed higher selectivity and
uptake capacity to lead. Chromium uptake kinetic was
characterised as having a rapid initial step, followed by a
slower one. Langmuir model describes well chromium
uptake equilibrium. Lead uptake kinetics suggested the
presence of mechanisms other than biosorption, possibly
including its precipitation.Instituto de Biotecnologia e Química Fina (IBQF) - Junta Nacional de Investigação Cientifica e Tecnologica (J.N.I.C.T), project PEAM/SEL/516/95
Trivalent chromium removal using flocculating yeasts : effect of pre-treatments on removal efficiency
Praxis XXI; Fundação para a Ciência e a Tecnologia (FCT)
Relationship between top executive compensation and corporate governance: evidence from large Italian listed companies
The modernization of corporate governance aims the alignment of the interests of managers with those of companies, promoting a new discipline of internal controls and risk analysis with an enforcement of shareholder rights of information. This research investigates the impact of corporate governance variables –ownership, board of directors and remuneration committee– on executive compensation. A balanced sample of 52 Italian listed companies has been adopted to test the hypotheses, covering 55.98% and 47.13% of market capitalization in 2011 and 2015 respectively and including 669 board members. Theoretical models evidence a certain stability of compensation schemes for Italian managers over time. Findings suggest that there is a statistically significant positive effect of familiar ownership on the amount of compensation. Along with nature of ownership, the number of directors in the remuneration committee appointed by minorities assume a determinant role. With statistical significance, it affects negatively the compensation level, but, contrarily to best practices, it affects negatively the adoption of forms of incentive compensation.info:eu-repo/semantics/acceptedVersio
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
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
Field-theoretical renormalization group for a flat two-dimensional Fermi surface
We implement an explicit two-loop calculation of the coupling functions and
the self-energy of interacting fermions with a two-dimensional flat Fermi
surface in the framework of the field theoretical renormalization group (RG)
approach. Throughout the calculation both the Fermi surface and the Fermi
velocity are assumed to be fixed and unaffected by interactions. We show that
in two dimensions, in a weak coupling regime, there is no significant change in
the RG flow compared to the well-known one-loop results available in the
literature. However, if we extrapolate the flow to a moderate coupling regime
there are interesting new features associated with an anisotropic suppression
of the quasiparticle weight Z along the Fermi surface, and the vanishing of the
renormalized coupling functions for several choices of the external momenta.Comment: 16 pages and 22 figure
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
Convergence of simple adaptive Galerkin schemes based on h − h/2 error estimators
We discuss several adaptive mesh-refinement strategies based on (h − h/2)-error estimation. This class of adaptivemethods is particularly popular in practise since it is problem independent and requires virtually no implementational overhead. We prove that, under the saturation assumption, these adaptive algorithms are convergent. Our framework applies not only to finite element methods, but also yields a first convergence proof for adaptive boundary element schemes. For a finite element model problem, we extend the proposed adaptive scheme and prove convergence even if the saturation assumption fails to hold in general
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