66 research outputs found
Thermodynamic properties and atomistic structure of the dry amorphous silica surface from a reactive force field model
Random lasing in a solution of reflective colloidal particles: the effect of interfaces and inter-particle correlations
The propagation of light across 2D and 3D slabs of reflective colloidal
particles in a fluid-like state has been investigated by simulation. The
colloids are represented as hard spheres with and without an attractive
square-well tail. Representative configurations of particles have been
generated by Monte Carlo. The path of rays entering the slab normal to its
planar surface has been determined by exact geometric scattering conditions,
assuming that particles are macroscopic spheres fully reflective at the surface
of their hard-core potential. The analysis of light paths provides the
transmission and reflection coefficients, the mean-free path, the average
length of transmitted and reflected paths, the distribution of scattering
events across the slab, and the angular spread of the outcoming rays as a
function of dimensionality and thermodynamic state. The results highlight the
presence of a sizeable population of very long paths, which play an important
role in random lasing from solutions of metal particles in an optically active
fluid. The output power spectrum resulting from the stimulated emission
amplification decays asymptotically as an inverse power law. The present study
goes beyond the standard approach based on a random walk confined between two
planar interfaces and parametrised in terms of the mean-free path and
scattering matrix. Here, instead, the mean free path, the correlation among
scattering events, and memory effects are not assumed a priori but emerge from
the underlying statistical mechanics model of interacting particles. Moreover,
the approach joins smoothly the ballistic regime of light propagation at low
density with the diffusive regime at high density of scattering centres. These
properties are exploited to investigate the effect of weak polydispersivity and
of large density fluctuations at the critical point of the model with the
attractive potential tail
Sviluppo di vettori virali per la terapia genica della β−Talassemia
Beta−thalassemia major is a severe congenital anemi for which there is presently no curative therapy other than allogeneic hematopoietic stem cell transplantation. This therapeutic option, however, applies only to the minority of thalassemia patients who have an HLA−matched bone marrow donor. Gene therapy by the delivery of a regulated globin gene to autologous hematopoietic stem cells is an attractive alternative approach as it is in principle applicable to all thalassemic subjects. Current vectors, althougheffective in correcting thalassemia in murine models still suffer some drawbacks in terms of safety and also in terms of low titer and expression. The aim of this study was to assemble globin vectors improved in both these aspects. Modifications of the globin cassette in the intron2 and in the LCR of the beta-‐globin gene can increase the expression of the globin gene without reducing the vector titer. We also examine the variegation in the expression among the different pools of transduce cells and we suppose that the presence of sequences with chromatin opening activity among the segments of b-‐globin IVS
Sviluppo di vettori virali per la terapia genica della β−Talassemia
Beta−thalassemia major is a severe congenital anemi for which there is presently no curative therapy other than allogeneic hematopoietic stem cell transplantation. This therapeutic option, however, applies only to the minority of thalassemia patients who have an HLA−matched bone marrow donor. Gene therapy by the delivery of a regulated globin gene to autologous hematopoietic stem cells is an attractive alternative approach as it is in principle applicable to all thalassemic subjects. Current vectors, althougheffective in correcting thalassemia in murine models still suffer some drawbacks in terms of safety and also in terms of low titer and expression. The aim of this study was to assemble globin vectors improved in both these aspects. Modifications of the globin cassette in the intron2 and in the LCR of the beta-‐globin gene can increase the expression of the globin gene without reducing the vector titer. We also examine the variegation in the expression among the different pools of transduce cells and we suppose that the presence of sequences with chromatin opening activity among the segments of b-‐globin IVS
Precursors of fluidisation in the creep response of a soft glass
Using extensive numerical simulations, we study the fluidisation process of
dense amorphous materials subjected to an external shear stress, using a
three-dimensional colloidal glass model. In order to disentangle possible
boundary effects from finite size effects in the process of fluidisation, we
implement a novel geometry-constrained protocol with periodic boundary
conditions. We show that this protocol is well controlled and that the longtime
fluidisation dynamics is, to a great extent, independent of the details of the
protocol parameters. Our protocol, therefore, provides an ideal tool to
investigate the bulk dynamics prior to yielding and to study finite size
effects regarding the fluidisation process. Our study reveals the existence of
precursors to fluidisation observed as a peak in the strain-rate fluctuations,
that allows for a robust definition of a fluidisation time. Although the
exponents in the power-law creep dynamics seem not to depend significantly on
the system size, we reveal strong finite size effects for the onset of
fluidisation
Communication: Non-monotonic supersaturation dependence of the nucleus size of crystals with anisotropically interacting molecules.
We study the nucleation of model two-dimensional crystals formed from anisotropically interacting molecules using kinetic Monte Carlo simulations and the forward flux sampling algorithm. The growth probability P(n) of a cluster of n molecules is measured while the supersaturation s and interaction anisotropy of the molecules are varied, in order to gain insight into the nucleation mechanism. It is found that with increasing degree of interaction anisotropy the nucleus size (defined as the cluster size at which P(n) = 0.5) can increase with increasing s, with sharp jumps at certain s values. Analysis of the cluster shape reveals that nucleation in the system studied is of a non-standard form, in that it embodies elements of both the classical nucleation theory and the density functional theory frameworks
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