1,186 research outputs found
Theoretical evidence for a dense fluid precursor to crystallization
We present classical density functional theory calculations of the free
energy landscape for fluids below their triple point as a function of density
and crystallinity. We find that for both a model globular protein and for a
simple atomic fluid modeled with a Lennard-Jones interaction, it is
free-energetically easier to crystallize by passing through a metastable dense
fluid in accord with the Ostwald rule of stages but in contrast to the
alternative of ordering and densifying at once as assumed in the classical
picture of crystallization.Comment: 4 pages, 3 figure
Mechanism for the stabilization of protein clusters above the solubility curve
Pan, Vekilov and Lubchenko[\textit{J. Phys. Chem. B}, 2010, \textbf{114},
7620] have proposed that dense stable protein clusters appearing in weak
protein solutions above the solubility curve are composed of protein oligomers.
The hypothesis is that a weak solution of oligomer species is unstable with
respect to condensation causing the formation of dense, oligomer-rich droplets
which are stabilized against growth by the monomer-oligomer reaction. Here, we
show that such a combination of processes can be understood using a simple
capillary model yielding analytic expressions for the cluster properties which
can be used to interpret experimental data. We also construct a microscopic
Dynamic Density Functional Theory model and show that it is consistent with the
predictions of the capillary model. The viability of the mechanism is thus
confirmed and it is shown how the radius of the stable clusters is related to
physically interesting quantities such as the monomer-oligomer rate constants
Reactive dynamics on fractal sets: anomalous fluctuations and memory effects
We study the effect of fractal initial conditions in closed reactive systems
in the cases of both mobile and immobile reactants. For the reaction , in the absence of diffusion, the mean number of particles is shown to
decay exponentially to a steady state which depends on the details of the
initial conditions. The nature of this dependence is demonstrated both
analytically and numerically. In contrast, when diffusion is incorporated, it
is shown that the mean number of particles decays asymptotically as
, the memory of the initial conditions being now carried by the
dynamical power law exponent. The latter is fully determined by the fractal
dimension of the initial conditions.Comment: 7 pages, 2 figures, uses epl.cl
The effect of the range of interaction on the phase diagram of a globular protein
Thermodynamic perturbation theory is applied to the model of globular
proteins studied by ten Wolde and Frenkel (Science 277, pg. 1976) using
computer simulation. It is found that the reported phase diagrams are
accurately reproduced. The calculations show how the phase diagram can be tuned
as a function of the lengthscale of the potential.Comment: 20 pages, 5 figure
Radiation reaction and quantum damped harmonic oscillator
By taking a Klein-Gordon field as the environment of an harmonic oscillator
and using a new method for dealing with quantum dissipative systems (minimal
coupling method), the quantum dynamics and radiation reaction for a quantum
damped harmonic oscillator investigated. Applying perturbation method, some
transition probabilities indicating the way energy flows between oscillator,
reservoir and quantum vacuum, obtainedComment: 12 pages. Accepted for publication in Mod. Phys. Lett.
Stochastic resonance in periodic potentials: realization in a dissipative optical lattice
We have observed the phenomenon of stochastic resonance on the Brillouin
propagation modes of a dissipative optical lattice. Such a mode has been
excited by applying a moving potential modulation with phase velocity equal to
the velocity of the mode. Its amplitude has been characterized by the
center-of-mass (CM) velocity of the atomic cloud. At Brillouin resonance, we
studied the CM-velocity as a function of the optical pumping rate at a given
depth of the potential wells. We have observed a resonant dependence of the CM
velocity on the optical pumping rate, corresponding to the noise strength. This
corresponds to the experimental observation of stochastic resonance in a
periodic potential in the low-damping regime
Ratio control in a cascade model of cell differentiation
We propose a kind of reaction-diffusion equations for cell differentiation,
which exhibits the Turing instability. If the diffusivity of some variables is
set to be infinity, we get coupled competitive reaction-diffusion equations
with a global feedback term. The size ratio of each cell type is controlled by
a system parameter in the model. Finally, we extend the model to a cascade
model of cell differentiation. A hierarchical spatial structure appears as a
result of the cell differentiation. The size ratio of each cell type is also
controlled by the system parameter.Comment: 13 pages, 7 figure
Chapman-Enskog expansion about nonequilibrium states: the sheared granular fluid
The Chapman-Enskog method of solution of kinetic equations, such as the
Boltzmann equation, is based on an expansion in gradients of the deviations fo
the hydrodynamic fields from a uniform reference state (e.g., local
equilibrium). This paper presents an extension of the method so as to allow for
expansions about \emph{arbitrary}, far-from equilibrium reference states. The
primary result is a set of hydrodynamic equations for studying variations from
the arbitrary reference state which, unlike the usual Navier-Stokes
hydrodynamics, does not restrict the reference state in any way. The method is
illustrated by application to a sheared granular gas which cannot be studied
using the usual Navier-Stokes hydrodynamics.Comment: 23 pages, no figures. Submited to PRE Replaced to correct misc.
errors Replaced to correct misc. errors, make notation more consistant,
extend discussio
Catalytic Activity of Myoglobin Immobilized on Zirconium Phosphonates.
The adsorption and catalytic activity of myoglobin (Mb) on zirconium phosphonates (R-zirconium
benzenephosphonate (R-ZrBP), R-zirconium carboxyethanephosphonate (R-ZrCEP), and a novel layered
zirconium fluoride aminooctyl-N,N-bis(methylphosphonate) (ZrC8)) were investigated. The maximum
adsorption was reached after 16 h of contact and was greater on hydrophobic supports such as R-ZrBP
and ZrC8 compared to hydrophilic supports such as R-ZrCEP. The equilibrium adsorption isotherms fitted
the Langmuir equation, suggesting the presence of a monolayer of protein molecules on the support surfaces.
The catalytic activities of free Mb and of the obtained biocomposites were studied in terms of the oxidation
of two aromatic substrates, o-phenylenediamine and 2-methoxyphenol (guaiacol), by hydrogen peroxide.
The oxidation catalyzed by immobilized myoglobin followed the Michaelis-Menten kinetics, similar to
oxidation by free Mb. The kinetic parameters, kcat and KM, were significantly affected by the adsorption
process. Mb/R-ZrCEP was the most efficient biocatalyst obtained, probably because of the hydrophilic
nature of the support. The effect of immobilization on the stability of Mb toward inactivation by hydrogen
peroxide was also investigated, and an increased resistance was found. The biocomposites obtained can
be stored at 4 °C for months without a significant loss of catalytic activity
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