30,700 research outputs found
Molecular correlations and solvation in simple fluids
We study the molecular correlations in a lattice model of a solution of a
low-solubility solute, with emphasis on how the thermodynamics is reflected in
the correlation functions. The model is treated in Bethe-Guggenheim
approximation, which is exact on a Bethe lattice (Cayley tree). The solution
properties are obtained in the limit of infinite dilution of the solute. With
, , and the three pair correlation functions
as functions of the separation (subscripts 1 and 2 referring to solvent and
solute, respectively), we find for lattice steps that
. This illustrates a general
theorem that holds in the asymptotic limit of infinite . The three
correlation functions share a common exponential decay length (correlation
length), but when the solubility of the solute is low the amplitude of the
decay of is much greater than that of , which in turn is
much greater than that of . As a consequence the amplitude of the
decay of is enormously greater than that of . The
effective solute-solute attraction then remains discernible at distances at
which the solvent molecules are essentially no longer correlated, as found in
similar circumstances in an earlier model. The second osmotic virial
coefficient is large and negative, as expected. We find that the
solvent-mediated part of the potential of mean force between solutes,
evaluated at contact, , is related in this model to the Gibbs free energy
of solvation at fixed pressure, , by , where is the coordination number of the lattice, the
pressure, and the volume of the cell associated with each lattice site. A
large, positive associated with the low solubility is thus
reflected in a strong attraction (large negative at contact), which is the
major contributor to the second osmotic virial coefficient. In this model, the
low solubility (large positive ) is due partly to an unfavorable
enthalpy of solvation and partly to an unfavorable solvation entropy, unlike in
the hydrophobic effect, where the enthalpy of solvation itself favors high
solubility, but is overweighed by the unfavorable solvation entropy.Comment: 9 pages, 2 figure
Critical interfaces and duality in the Ashkin Teller model
We report on the numerical measures on different spin interfaces and FK
cluster boundaries in the Askhin-Teller (AT) model. For a general point on the
AT critical line, we find that the fractal dimension of a generic spin cluster
interface can take one of four different possible values. In particular we
found spin interfaces whose fractal dimension is d_f=3/2 all along the critical
line. Further, the fractal dimension of the boundaries of FK clusters were
found to satisfy all along the AT critical line a duality relation with the
fractal dimension of their outer boundaries. This result provides a clear
numerical evidence that such duality, which is well known in the case of the
O(n) model, exists in a extended CFT.Comment: 5 pages, 4 figure
On the Design of Fault-Tolerant Logical Topologies in Wavelength-RoutedNetworks supporting Packet Datagrams
Basic properties of nonsmooth Hormander's vector fields and Poincare's inequality
We consider a family of vector fields defined in some bounded domain of R^p,
and we assume that they satisfy Hormander's rank condition of some step r, and
that their coefficients have r-1 continuous derivatives. We extend to this
nonsmooth context some results which are well-known for smooth Hormander's
vector fields, namely: some basic properties of the distance induced by the
vector fields, the doubling condition, Chow's connectivity theorem, and, under
the stronger assumption that the coefficients belong to C^{r-1,1}, Poincare's
inequality. By known results, these facts also imply a Sobolev embedding. All
these tools allow to draw some consequences about second order differential
operators modeled on these nonsmooth Hormander's vector fields.Comment: 60 pages, LaTeX; Section 6 added and Section 7 (6 in the previous
version) changed. Some references adde
In vitro ion chelating, antioxidative mechanism of extracts from fruits and barks of tetrapleura tetraptera and their protective effects against fenton mediated toxicity of metal ions on liver homogenates
The aim of the present study was to investigate the antioxidant activity and protective potential of T. tetraptera extracts against ion toxicity. The antioxidant activity of the extracts was investigated spectrophotometrically against several radicals (1,1-diphenyl-2-picrylhydrazyl (DPPH•), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS•), hydroxyl radical (HO•), and nitric oxide (NO•)), followed by the ferric reducing power, total phenols, flavonoid, and flavonol contents. The effects of the extracts on catalase (CAT), superoxide dismutase (SOD), and peroxidase activities were also determined using the standard methods as well as the polyphenol profile using HPLC. The results showed that the hydroethanolic extract of T. tetraptera (CFH) has the lowest ICvalue with the DPPH, ABTS, OH, and NO radicals. The same extract also exhibited the significantly higher level of total phenols (37.24 ± 2.00 CAE/g dried extract); flavonoids (11.36 ± 1.88 QE/g dried extract); and flavonols contents (3.95 ± 0.39 QE/g dried extract). The HPLC profile of T. tetraptera revealed that eugenol (958.81 ± 00 mg/g DW), quercetin (353.78 ± 00 mg/g DW), and rutin (210.54 ± 00 mg/g DW) were higher in the fruit than the bark extracts. In conclusion, extracts from T. tetraptera may act as a protector against oxidative mediated ion toxicity. © 2015 Bruno Moukette Moukette et al
Translocating the blood-brain barrier using electrostatics
Copyright © 2012 Ribeiro,Domingues,
Freire,Santos and Castanho. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.Mammalian cell membranes regulate homeostasis, protein activity, and cell signaling. The charge at the membrane surface has been correlated with these key events. Although mammalian cells are known to be slightly anionic, quantitative information on the membrane charge and the importance of electrostatic interactions in pharmacokinetics and pharmacodynamics remain elusive. Recently, we reported for the first time that brain endothelial cells (EC) are more negatively charged than human umbilical cord cells, using zeta-potential measurements by dynamic light scattering. Here, we hypothesize that anionicity is a key feature of the blood-brain barrier (BBB) and contributes to select which compounds cross into the brain. For the sake of comparison, we also studied the membrane surface charge of blood components—red blood cells (RBC), platelets, and peripheral blood mononuclear cells (PBMC).To further quantitatively correlate the negative zeta-potential values with membrane charge density, model membranes with different percentages of anionic lipids were also evaluated. From all the cells tested, brain cell membranes are the most anionic and those having their lipids mostly exposed, which explains why lipophilic cationic compounds are more prone to cross the blood-brain barrier.Fundação para a Ciência e Tecnologia — Ministério da Educação e Ciência (FCT-MEC, Portugal) is acknowledged for funding (including fellowships SFRH/BD/42158/2007 to Marta M.B. Ribeiro, SFRH/BD/41750/2007 to Marco M. Domingues and SFRH/BD/70423/2010 to João M. Freire) and project PTDC/QUI-BIQ/119509/2010. Marie Curie Industry-Academia Partnerships and Pathways (European Commission) is also acknowledged for funding (FP7-PEOPLE-2007-3-1-IAPP, Project 230654)
Evolution of the disc atmosphere in the X-ray binary MXB 1659-298, during its 2015-2017 outburst
We report on the evolution of the X-ray emission of the accreting neutron
star (NS) low mass X-ray binary (LMXB), MXB 1659-298, during its most recent
outburst in 2015-2017. We detected 60 absorption lines during the soft state
(of which 21 at more than 3 ), that disappeared in the hard state
(e.g., the Fe xxv and Fe xxvi lines). The absorbing plasma is at rest, likely
part of the accretion disc atmosphere. The bulk of the absorption features can
be reproduced by a high column density () of highly
ionised () plasma. Its disappearance during the
hard state is likely the consequence of a thermal photo-ionisation instability.
MXB 1659-298's continuum emission can be described by the sum of an absorbed
disk black body and its Comptonised emission, plus a black body component. The
observed spectral evolution with state is in line with that typically observed
in atoll and stellar mass black hole LMXB. The presence of a relativistic Fe
K disk-line is required during the soft state. We also tentatively
detect the Fe xxii doublet, whose ratio suggests an electron density of the
absorber of , hence, the absorber is likely located at
from the illuminating source, well inside the Compton and
outer disc radii. MXB 1659-298 is the third well monitored atoll LMXB
showcasing intense Fe xxv and Fe xxvi absorption during the soft state that
disappears during the hard state.Comment: MNRAS in pres
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