1,032 research outputs found
Purification of a lectin from Eugenia uniflora L. seeds and its potential antibacterial activity
Aims: The aim of this work was to analyse the antimicrobial properties of a purified lectin from Eugenia uniflora L. seeds.
Methods and Results: The E. uniflora lectin (EuniSL) was isolated from the seed extract and purified by ion-exchange chromatography in DEAE-Sephadex with a purification factor of 11·68. The purified lectin showed a single band on denaturing electrophoresis, with a molecular mass of 67 kDa. EuniSL agglutinated rabbit and human erythrocytes with a higher specificity for rabbit erythrocytes. The haemagglutination was not inhibited by the tested carbohydrates but glycoproteins exerted a strong inhibitory action. The lectin proved to be thermo resistant with the highest stability at pH 6·5 and divalent ions did not affect its activity. EuniSL demonstrated a remarkable nonselective antibacterial activity. EuniSL strongly inhibited the growth of Staphylococcus aureus, Pseudomonas aeruginosa and Klebsiella sp. with a minimum inhibitory concentration (MIC) of 1·5 μg ml−1, and moderately inhibited the growth of Bacillus subtilis, Streptococcus sp. and Escherichia coli with a MIC of 16·5 μg ml−1.
Conclusions: EuniSL was found to be effective against bacteria.
Significance and Impact of the Study: The strong antibacterial activity of the studied lectin indicates a high potential for clinical microbiology and therapeutic applications.VALNATURA of ALFA Programme; Conselho Nacional de
Desenvolvimento CientÃfico e Tecnológico-CNPq
Fluctuating Elastic Rings: Statics and Dynamics
We study the effects of thermal fluctuations on elastic rings. Analytical
expressions are derived for correlation functions of Euler angles, mean square
distance between points on the ring contour, radius of gyration, and
probability distribution of writhe fluctuations. Since fluctuation amplitudes
diverge in the limit of vanishing twist rigidity, twist elasticity is essential
for the description of fluctuating rings. We find a crossover from a small
scale regime in which the filament behaves as a straight rod, to a large scale
regime in which spontaneous curvature is important and twist rigidity affects
the spatial configurations of the ring. The fluctuation-dissipation relation
between correlation functions of Euler angles and response functions, is used
to study the deformation of the ring by external forces. The effects of inertia
and dissipation on the relaxation of temporal correlations of writhe
fluctuations, are analyzed using Langevin dynamics.Comment: 43 pages, 9 Figure
D-Brane Chemistry
We study several different kinds of bound states built from D-branes and
orientifolds. These states are to atoms what branonium - the bound state of a
brane and its anti-brane - is to positronium, inasmuch as they typically
involve a light brane bound to a much heavier object with conserved charges
which forbid the system's decay. We find the fully relativistic motion of a
probe Dp'-brane in the presence of source Dp-branes is integrable by
quadratures. Keplerian conic sections are obtained for special choices for p
and p' and the systems are shown to be equivalent to nonrelativistic systems.
Their quantum behaviour is also equivalent to the corresponding
non-relativistic limit. In particular the p=6, p'=0 case is equivalent to a
non-relativistic dyon in a magnetic monopole background, with the trajectories
in the surface of a cone. We also show that the motion of the probe branes
about D6-branes in IIA theory is equivalent to the motion of the corresponding
probes in the uplift to M-theory in 11 dimensions, for which there are no
D6-branes but their fields are replaced by a particular Taub-NUT geometry. We
further discuss the interactions of D-branes and orientifold planes having the
same dimension. this system behaves at large distances as a brane-brane system
but at shorter distances it does not have the tachyon instability.Comment: ref. added and typos correcte
Entropy Crisis, Ideal Glass Transition and Polymer Melting: Exact Solution on a Husimi Cactus
We introduce an extension of the lattice model of melting of semiflexible
polymers originally proposed by Flory. Along with a bending penalty, present in
the original model and involving three sites of the lattice, we introduce an
interaction energy that corresponds to the presence of a pair of parallel bonds
and a second interaction energy associated with the presence of a hairpin turn.
Both these new terms represent four-site interactions. The model is solved
exactly on a Husimi cactus, which approximates a square lattice. We study the
phase diagram of the system as a function of the energies. For a proper choice
of the interaction energies, the model exhibits a first-order melting
transition between a liquid and a crystalline phase. The continuation of the
liquid phase below this temperature gives rise to a supercooled liquid, which
turns continuously into a new low-temperature phase, called metastable liquid.
This liquid-liquid transition seems to have some features that are
characteristic of the critical transition predicted by the mode-coupling
theory.Comment: To be published in Physical Review E, 68 (2) (2003
Quantum induced w = -1 crossing of the quintessence and phantom models
Considering the single scalar field models of dark energy, i.e. the
quintessence and phantom models, it is shown that the quantum effects can cause
the system crosses the w = -1 line. This phenomenon does not occur in classical
level. The quantum effects are described via the account of conformal anomaly.Comment: LaTex, 7 pages, the version to be appeared in JCAP (2009
Blackbody Radiation and the Scaling Symmetry of Relativistic Classical Electron Theory with Classical Electromagnetic Zero-Point Radiation
It is pointed out that relativistic classical electron theory with classical
electromagnetic zero-point radiation has a scaling symmetry which is suitable
for understanding the equilibrium behavior of classical thermal radiation at a
spectrum other than the Rayleigh-Jeans spectrum. In relativistic classical
electron theory, the masses of the particles are the only scale-giving
parameters associated with mechanics while the action-angle variables are scale
invariant. The theory thus separates the interaction of the action variables of
matter and radiation from the scale-giving parameters. Classical zero-point
radiation is invariant under scattering by the charged particles of
relativistic classical electron theory. The basic ideas of the matter
-radiation interaction are illustrated in a simple relativistic classical
electromagnetic example.Comment: 18 page
On The Stability of Non-Supersymmetric Attractors in String Theory
We study non-supersymmetric attractors obtained in Type IIA compactifications
on Calabi Yau manifolds. Determining if an attractor is stable or unstable
requires an algebraically complicated analysis in general. We show using group
theoretic techniques that this analysis can be considerably simplified and can
be reduced to solving a simple example like the STU model. For attractors with
D0-D4 brane charges, determining stability requires expanding the effective
potential to quartic order in the massless fields. We obtain the full set of
these terms. For attractors with D0-D6 brane charges, we find that there is a
moduli space of solutions and the resulting attractors are stable. Our analysis
is restricted to the two derivative action.Comment: 20 pages, Late
The Void Abundance with Non-Gaussian Primordial Perturbations
We use a Press-Schechter-like calculation to study how the abundance of voids
changes in models with non-Gaussian initial conditions. While a positive
skewness increases the cluster abundance, a negative skewness does the same for
the void abundance. We determine the dependence of the void abundance on the
non-Gaussianity parameter fnl for the local-model bispectrum-which approximates
the bispectrum in some multi-field inflation models-and for the equilateral
bispectrum, which approximates the bispectrum in e.g. string-inspired DBI
models of inflation. We show that the void abundance in large-scale-structure
surveys currently being considered should probe values as small as fnl < 10 and
fnl^eq < 30, over distance scales ~10 Mpc.Comment: Submitted to JCA
The theory of canonical perturbations applied to attitude dynamics and to the Earth rotation. Osculating and nonosculating Andoyer variables
The Hamiltonian theory of Earth rotation, known as the Kinoshita-Souchay
theory, operates with nonosculating Andoyer elements. This situation parallels
a similar phenomenon that often happens (but seldom gets noticed) in orbital
dynamics, when the standard Lagrange-type or Delaunay-type planetary equations
unexpectedly render nonosculating orbital elements. In orbital mechanics,
osculation loss happens when a velocity-dependent perturbation is plugged into
the standard planetary equations. In attitude mechanics, osculation is lost
when an angular-velocity-dependent disturbance is plugged in the standard
dynamical equations for the Andoyer elements. We encounter exactly this
situation in the theory of Earth rotation, because this theory contains an
angular-velocity-dependent perturbation (the switch from an inertial frame to
that associated with the precessing ecliptic of date).
While the osculation loss does not influence the predictions for the figure
axis of the planet, it considerably alters the predictions for the
instantaneous spin-axis' orientation. We explore this issue in great detail
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