11,571 research outputs found
Contact angle of a hemispherical bubble: an analytical approach
We have calculated the equilibrium shape of the axially symmetric Plateau border along which a spherical bubble contacts a flat wall, by analytically integrating Laplace’s equation in the presence of gravity, in the limit of small Plateau border sizes. This method has the advantage that it provides closed-form expressions for the positions and orientations of the Plateau border surfaces. Results are in very good overall agreement with those obtained from a numerical solution procedure, and are consistent with
experimental data. In particular we find that the effect of gravity on Plateau border shape is relatively small for typical bubble sizes, leading to a widening of the Plateau border for sessile bubbles and to a narrowing for pendant bubbles. The contact angle of the bubble is found to depend even more weakly on gravity
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 QuÃmica 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)
Spikes in Cosmic Crystallography
If the universe is multiply connected and small the sky shows multiple images
of cosmic objects, correlated by the covering group of the 3-manifold used to
model it. These correlations were originally thought to manifest as spikes in
pair separation histograms (PSH) built from suitable catalogues. Using
probability theory we derive an expression for the expected pair separation
histogram (EPSH) in a rather general topological-geometrical-observational
setting. As a major consequence we show that the spikes of topological origin
in PSH's are due to translations, whereas other isometries manifest as tiny
deformations of the PSH corresponding to the simply connected case. This result
holds for all Robertson-Walker spacetimes and gives rise to two basic
corollaries: (i) that PSH's of Euclidean manifolds that have the same
translations in their covering groups exhibit identical spike spectra of
topological origin, making clear that even if the universe is flat the
topological spikes alone are not sufficient for determining its topology; and
(ii) that PSH's of hyperbolic 3-manifolds exhibit no spikes of topological
origin. These corollaries ensure that cosmic crystallography, as originally
formulated, is not a conclusive method for unveiling the shape of the universe.
We also present a method that reduces the statistical fluctuations in PSH's
built from simulated catalogues.Comment: 25 pages, LaTeX2e. References updated. To appear in Int. J. Mod.
Phys. D (2002) in the present for
Lignocellulose as raw material in fermentation processes
Lignocellulose in the form of forestry, agricultural, and agro-industrial wastes is accumulated in large quantities every
year. These materials are mainly composed of three groups of polymers, namely cellulose, hemicellulose, and lignin.
Cellulose and hemicellulose are sugar rich fractions of interest for use in fermentation processes, since microorganisms
may use the sugars for growth and production of value added compounds such as ethanol, food additives, organic acids,
enzymes, and others. Submerged and solid-state fermentation systems have been used to produce compounds of industrial
interest from lignocellulose, as an alternative for valorization of these wastes and also to solve environmental problems
caused by their disposal. When submerged fermentation systems are used, a previous stage of hydrolysis for separation of
the lignocellulose constituents is required. This work is an overview about the potential uses of lignocellulosic materials in
fermentation processes. Aspects related to submerged and solid-state fermentation systems will be described focusing on
the raw materials, hydrolysis processes, fermentation conditions, microorganisms, and products that can be obtained
Derivation of an Abelian effective model for instanton chains in 3D Yang-Mills theory
In this work, we derive a recently proposed Abelian model to describe the
interaction of correlated monopoles, center vortices, and dual fields in three
dimensional SU(2) Yang-Mills theory. Following recent polymer techniques,
special care is taken to obtain the end-to-end probability for a single
interacting center vortex, which constitutes a key ingredient to represent the
ensemble integration.Comment: 18 pages, LaTe
Betalains and phenolic compounds of leaves and stems of Alternanthera brasiliana and Alternanthera tenella
Betacyanins and phenolic compounds from acetonitrile:acidified water extracts of Alternanthera brasiliana and Alternanthera tenella were characterized and quantified using a high-performance liquid chromatography system coupled with diode array and electrospray mass spectrometry detection. Four betacyanins (amaranthine, isoamaranthine, betanin and isobetanin) were tentatively identified and quantified. Twenty eight phenolic compounds of four different families (hydroxybenzoic and hydroxycinnamic acids, flavones and flavonols) were separated and characterized on the basis of their accurate MS and MS/MS information out of which ten compounds were confirmed by authentic standards. These plant species could be considered as an especially rich source of natural bioactive compounds and potential food colorants. A. brasiliana showed the highest betacyanin and polyphenols content (89 μg/g and 35,243 μg/g, respectively). Among polyphenols, flavonols were the more abundant (kaempferol-glucoside, kaempferol-rutinoside and kaempferol-rhamnosyl-rhamnosyl-glycoside). Meanwhile, A. tenella showed a different polyphenols profile with flavones as major compounds (glucopyranosil-vitexin and vitexin). As a novelty, pentosyl-vitexin and pentosyl-isovitexin were detected for the first time in Alternanthera plants. Both A. brasiliana and A. tenella leaves showed high total polyphenol content and in vitro antioxidant activity (FRAP). These results provide an analytical base concerning the phenolic and betalains composition and the antioxidant properties of two members of the promising Alternanthera gender, for subsequent applications, such as functional food ingredients.Fil: Deladino, Lorena. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Centro de Investigación y Desarrollo en CriotecnologÃa de Alimentos. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en CriotecnologÃa de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en CriotecnologÃa de Alimentos; ArgentinaFil: Alvarez, I.. Consejo Superior de Investigaciones CientÃficas. Instituto de Ciencia y Tecnologia de Alimentos y Nutrición; EspañaFil: De Ancos, B.. Consejo Superior de Investigaciones CientÃficas. Instituto de Ciencia y Tecnologia de Alimentos y Nutrición; EspañaFil: Sánchez Moreno, C.. Consejo Superior de Investigaciones CientÃficas. Instituto de Ciencia y Tecnologia de Alimentos y Nutrición; EspañaFil: Molina GarcÃa, A. D.. Consejo Superior de Investigaciones CientÃficas. Instituto de Ciencia y Tecnologia de Alimentos y Nutrición; EspañaFil: Schneider Teixeira, Aline. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones CientÃficas. Centro de Investigación y Desarrollo en CriotecnologÃa de Alimentos. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Centro CientÃfico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en CriotecnologÃa de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en CriotecnologÃa de Alimentos; Argentina. Consejo Superior de Investigaciones CientÃficas. Instituto de Ciencia y Tecnologia de Alimentos y Nutrición; Españ
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
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