262 research outputs found
Theory of Boundary Effects in Invasion Percolation
We study the boundary effects in invasion percolation with and without
trapping. We find that the presence of boundaries introduces a new set of
surface critical exponents, as in the case of standard percolation. Numerical
simulations show a fractal dimension, for the region of the percolating cluster
near the boundary, remarkably different from the bulk one. We find a
logarithmic cross-over from surface to bulk fractal properties, as one would
expect from the finite-size theory of critical systems. The distribution of the
quenched variables on the growing interface near the boundary self-organises
into an asymptotic shape characterized by a discontinuity at a value ,
which coincides with the bulk critical threshold. The exponent of
the boundary avalanche distribution for IP without trapping is
; this value is very near to the bulk one. Then we
conclude that only the geometrical properties (fractal dimension) of the model
are affected by the presence of a boundary, while other statistical and
dynamical properties are unchanged. Furthermore, we are able to present a
theoretical computation of the relevant critical exponents near the boundary.
This analysis combines two recently introduced theoretical tools, the Fixed
Scale Transformation (FST) and the Run Time Statistics (RTS), which are
particularly suited for the study of irreversible self-organised growth models
with quenched disorder. Our theoretical results are in rather good agreement
with numerical data.Comment: 11 pages, 13 figures, revte
Dynamics of Fractures in Quenched Disordered Media
We introduce a model for fractures in quenched disordered media. This model
has a deterministic extremal dynamics, driven by the energy function of a
network of springs (Born Hamiltonian). The breakdown is the result of the
cooperation between the external field and the quenched disorder. This model
can be considered as describing the low temperature limit for crack propagation
in solids. To describe the memory effects in this dynamics, and then to study
the resistance properties of the system we realized some numerical simulations
of the model. The model exhibits interesting geometric and dynamical
properties, with a strong reduction of the fractal dimension of the clusters
and of their backbone, with respect to the case in which thermal fluctuations
dominate. This result can be explained by a recently introduced theoretical
tool as a screening enhancement due to memory effects induced by the quenched
disorder.Comment: 7 pages, 9 Postscript figures, uses revtex psfig.sty, to be published
on Phys. Rev.
Phase separation in systems with absorbing states
We study the problem of phase separation in systems with a positive definite
order parameter, and in particular, in systems with absorbing states. Owing to
the presence of a single minimum in the free energy driving the relaxation
kinetics, there are some basic properties differing from standard phase
separation. We study analytically and numerically this class of systems; in
particular we determine the phase diagram, the growth laws in one and two
dimensions and the presence of scale invariance. Some applications are also
discussed.Comment: Submitted to Europhysics Let
Trapping tetracycline-loaded nanoparticles into polycaprolactone fiber networks for periodontal regeneration therapy
The controlled delivery of antibiotics, anti-inflammatory agents, or chemotherapeutic agents to
the periodontal site is a recognized strategy to improve the efficiency of regenerative processes of
hard tissues. A novel approach based on the trapping of tetracycline hydrochloride–loaded particles
in polycaprolactone nanofibers was used to guide the regeneration processes of periodontal
tissue at the gum interface. Chitosan nanoparticles loaded with different levels of tetracycline
hydrochloride (up to 5% wt) were prepared by solution nebulization induced by electrical forces
(i.e. electrospraying). The fine tuning of process parameters allows to obtain nanoparticles with
tailored sizes ranging from 0.485 ± 0.147 μm to 0.639 ± 0.154 μm. The tetracycline hydrochloride
release profile had a predominant burst effect for the first 70% of release followed by a relatively
slow release over 24 h, which is promising for oral drug delivery. We also demonstrated that
trapping tetracycline hydrochloride–loaded particles with submicrometer diameters into a
polycaprolactone fiber network contributed to slowing the release of tetracycline hydrochloride
from the nanoparticles, thus providing a more prolonged release in the periodontal pocket during
clinical therapy. Preliminary studies on human mesenchymal stem cells confirm the viability of
cells up to 5 days after culture, and thereby, validate the use of nanoparticle-/nanofiber-integrated
systems in periodontal therapie
Dermanyssus gallinae in layer farms in Kosovo: a high risk for salmonella prevalence
Background
The poultry red mite (PRM), Dermanyssus gallinae (D.g.) is a serious ectoparasitic pest of poultry and potential pathogen vector. The prevalence of D. g. and the prevalence of Salmonella spp. within mites on infested laying poultry farms were investigated in Kosovo.
Findings
In total, 14 populated layer farms located in the Southern Kosovo were assessed for D. g. presence. Another two farms in this region were investigated 6 months after depopulation. Investigated flocks were all maintained in cages, a common housing system in Kosovo. A total of eight farms were found to be infested with D. g. (50%) at varying levels, including the two depopulated farms. The detection of Salmonella spp. from D. g. was carried out using PCR. Out of the eight layer farms infested with D. g., Salmonella spp. was present in mites on three farms (37.5%).
Conclusions
This study confirms the high prevalence of D. g. in layer flocks in Kosovo and demonstrates the link between this mite and the presence of Salmonella spp. on infested farms
Non-perturbative renormalization of the KPZ growth dynamics
We introduce a non-perturbative renormalization approach which identifies
stable fixed points in any dimension for the Kardar-Parisi-Zhang dynamics of
rough surfaces. The usual limitations of real space methods to deal with
anisotropic (self-affine) scaling are overcome with an indirect functional
renormalization. The roughness exponent is computed for dimensions
to 8 and it results to be in very good agreement with the available
simulations. No evidence is found for an upper critical dimension. We discuss
how the present approach can be extended to other self-affine problems.Comment: 4 pages, 2 figures. To appear in Phys. Rev. Let
Discretized Diffusion Processes
We study the properties of the ``Rigid Laplacian'' operator, that is we
consider solutions of the Laplacian equation in the presence of fixed
truncation errors. The dynamics of convergence to the correct analytical
solution displays the presence of a metastable set of numerical solutions,
whose presence can be related to granularity. We provide some scaling analysis
in order to determine the value of the exponents characterizing the process. We
believe that this prototype model is also suitable to provide an explanation of
the widespread presence of power-law in social and economic system where
information and decision diffuse, with errors and delay from agent to agent.Comment: 4 pages 5 figure, to be published in PR
Genomic characterization of a novel group A lamb rotavirus isolated in Zaragoza, Spain
An ovine rotavirus (OVR) strain, 762, was isolated from a 30-day-old lamb affected with severe gastroenteritis, in Zaragoza, Spain, and the VP4, VP7, VP6, NSP4, and NSP5/NSP6 genes were subsequently characterized molecularly. Strain OVR762 was classified as a P[14] rotavirus, as the VP4 and VP8* trypsin-cleavage product of the VP4 protein revealed the highest amino acid (aa) identity (94% and 97%, respectively) with that of the P11[14] human rotavirus (HRV) strain PA169, isolated in Italy. Analysis of the VP7 gene product revealed that OVR762 possessed G8 serotype specificity, a type common in ruminants, with the highest degree of aa identity(95–98%) shared with serotype G8 HRV, bovine rotavirus, and guanaco (Lama guanicoe) rotavirus strains. Moreover, strain OVR762 displayed a bovine-like NSP4 (genotype E2) and NSP5/NSP6 (genotype H3), and a VP6 genotype I2, as well as a long electropherotype pattern. This is the first report of a lamb rotavirus with P[14] and G8 specificities, providing additional evidence for the wide genetic and antigenic diversity of group A rotaviruses
Two-dimensional Granular Gas of Inelastic Spheres with Multiplicative Driving
We study a two-dimensional granular gas of inelastic spheres subject to
multiplicative driving proportional to a power of the
local particle velocity . The steady state properties of the model
are examined for different values of , and compared with the
homogeneous case . A driving linearly proportional to
seems to reproduce some experimental observations which could not be reproduced
by a homogeneous driving. Furthermore, we obtain that the system can be
homogenized even for strong dissipation, if a driving inversely proportional toComment: 4 pages, 5 figures (accepted as Phys. Rev. Lett.
Enhancing proteotoxic stress in leiomyosarcoma cells triggers mitochondrial dysfunctions, cell death, and antitumor activity in vivo
Leiomyosarcomas are rare and aggressive tumors characterized by a complex karyotype. Surgical resection with or without radiotherapy and chemotherapy is the standard curative treatment. Unfortunately, a high percentage of leiomyosarcomas recurs and metastasizes. In these cases, doxorubicin and ifosfamide represent the standard treatment but with low response rates. Here, we evaluated the induction of proteotoxic stress as a possible strategy to kill leiomyosarcoma cells in a therapeutic perspective. We show that aggressive leiomyosarcomas coexist with high levels of proteotoxic stress. As a consequence, we hypothesized that leiomyosarcoma cells are vulnerable to further increases of proteotoxic stress. The small compound 2c is a strong inducer of proteotoxic stress. In leiomyosarcoma cells, it triggers cell death coupled to a profound reorganization of the mitochondrial network. By using stimulated emission depletion microscopy, we have unveiled the existence of DIABLO/SMAC clusters that are modulated by 2c. Finally, we have engineered a new version of 2c linked to polyethylene glycol though a short peptide, named 2cPP. This new prodrug is specifically activated by proteases present in the tumor microenvironment. 2cPP shows a strong antitumor activity in vivo against leiomyosarcomas and no toxicity against normal cells
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