16,623 research outputs found
Non-universal coarsening and universal distributions in far-from equilibrium systems
Anomalous coarsening in far-from equilibrium one-dimensional systems is
investigated by simulation and analytic techniques. The minimal hard core
particle (exclusion) models contain mechanisms of aggregated particle
diffusion, with rates epsilon<<1, particle deposition into cluster gaps, but
suppressed for the smallest gaps, and breakup of clusters which are adjacent to
large gaps. Cluster breakup rates vary with the cluster length x as kx^alpha.
The domain growth law x ~ (epsilon t)^z, with z=1/(2+alpha) for alpha>0, is
explained by a scaling picture, as well as the scaling of the density of double
vacancies (at which deposition and cluster breakup are allowed) as 1/[t(epsilon
t)^z]. Numerical simulations for several values of alpha and epsilon confirm
these results. An approximate factorization of the cluster configuration
probability is performed within the master equation resulting from the mapping
to a column picture. The equation for a one-variable scaling function explains
the above results. The probability distributions of cluster lengths scale as
P(x)= 1/(epsilon t)^z g(y), with y=x/(epsilon t)^z. However, those
distributions show a universal tail with the form g(y) ~ exp(-y^{3/2}), which
disagrees with the prediction of the independent cluster approximation. This
result is explained by the connection of the vacancy dynamics with the problem
of particle trapping in an infinite sea of traps and is confirmed by
simulation.Comment: 30 pages (10 figures included), to appear in Phys. Rev.
Viscoelastic monitoring of starch-based biomaterials in simulated physiological conditions
Dynamic mechanical analysis (DMA) was used to investigate the solid-state rheological behaviour in a starch-based thermoplastic aimed to be used in different biomedical applications. The tested samples were processed by different injection moulding procedures. The dry samples were immersed in a simulated physiological solution and the relevant viscoelastic parameters were monitored against time. The decrease
of stiffness due to swelling can be followed in real time, being less pronounced for the composite sample with hydroxyapatite (HA). The temperature control of the liquid bath was found to be very good. Frequency scans were also performed in wet conditions in samples previously immersed during different times, indicating that DMA is a suitable method to control in-vitro the changes on the viscoelastic properties of biomaterials during degradation
Finite-size effects in roughness distribution scaling
We study numerically finite-size corrections in scaling relations for
roughness distributions of various interface growth models. The most common
relation, which considers the average roughness . This illustrates how
finite-size corrections can be obtained from roughness distributions scaling.
However, we discard the usual interpretation that the intrinsic width is a
consequence of high surface steps by analyzing data of restricted
solid-on-solid models with various maximal height differences between
neighboring columns. We also observe that large finite-size corrections in the
roughness distributions are usually accompanied by huge corrections in height
distributions and average local slopes, as well as in estimates of scaling
exponents. The molecular-beam epitaxy model of Das Sarma and Tamborenea in 1+1
dimensions is a case example in which none of the proposed scaling relations
works properly, while the other measured quantities do not converge to the
expected asymptotic values. Thus, although roughness distributions are clearly
better than other quantities to determine the universality class of a growing
system, it is not the final solution for this task.Comment: 25 pages, including 9 figures and 1 tabl
Some trends on how one can learn from and mimic nature in order to design better biomaterials
Chemistry and applications of phosphorylated chitin and chitosan
Chitin and chitosan are natural based non-toxic,
biodegradable and biocompatible polymers and have been used in
biomedical areas in the form of sutures, wound healing materials and
artificial skin, and for the sustained release of drugs as well as in various
industrial applications. However, practical use of these polymers has
been mainly confined to the unmodified forms. Recently, there has been
a growing interest in chemical modification of chitin and chitosan to
improve their solubility and widen their applications. Among them,
phosphorylated chitin and chitosan have attracted considerable interest
because of their various advantages: anti-inflammatory property, ability
to form metal complexes, blood compatibility and formation of anionic
polyelectrolyte hydrogels. The purpose of this review is to take a closer
look of different synthetic methods of phosphorylated chitin and chitosan
and their potential applications in environmental, food, fuel cell, and
biomedical fields. Based on current research and existing products,
some new and futuristic approaches in this context area are discussed.R. Jayakumar acknowledges the Portuguese Foundation for Science and Technology for providing him a Post-Doc scholarship (SFRH/BPD/14670/2003). This work was partially supported by FCT Foundation for Science and Technology, through funds from the POCTI and/or FEDER program. This work was partially supported by the European Union funded STREP Project HIPPOCRATES (NMP3-CT-2003-505758)
Synthesis and characterization of N-methylenephenyl phosphonic chitosan
Chitosan is a natural based polymer obtained by alkaline deacetylation of chitin, exhibiting excellent properties such as nonâtoxicity, biocompatibility and biodegradability. NâMethylenephenyl phosphonic chitosan (NMPPC) is synthesized from chitosan by reacting with phenyl phosphonic acid using formaldehyde. The NMPPC was characterized by FTIR, 31PâNMR, Xâray diffraction, scanning electron microscopy, thermogravimeteric analysis and solubility studies. A significant decrease of molecular weight was observed in the NMPPC. The TGA studies suggested that NMPPC has less thermal stability than chitosan. The Xâray diffraction analysis showed that NMPPC was amorphous in nature. The solubility property of the polymer was improved after the incorporation of a phenyl phosphonic grou
Broad Iron Emission from Gravitationally Lensed Quasars Observed by Chandra
Recent work has demonstrated the potential of gravitationally lensed quasars
to extend measurements of black hole spin out to high-redshift with the current
generation of X-ray observatories. Here we present an analysis of a large
sample of 27 lensed quasars in the redshift range 1.0<z<4.5 observed with
Chandra, utilizing over 1.6 Ms of total observing time, focusing on the
rest-frame iron K emission from these sources. Although the X-ray
signal-to-noise (S/N) currently available does not permit the detection of iron
emission from the inner accretion disk in individual cases in our sample, we
find significant structure in the stacked residuals. In addition to the narrow
core, seen almost ubiquitously in local AGN, we find evidence for an additional
underlying broad component from the inner accretion disk, with a clear red wing
to the emission profile. Based on simulations, we find the detection of this
broader component to be significant at greater than the 3-sigma level. This
implies that iron emission from the inner disk is relatively common in the
population of lensed quasars, and in turn further demonstrates that, with
additional observations, this population represents an opportunity to
significantly extend the sample of AGN spin measurements out to high-redshift.Comment: 5 pages, 2 figures, accepted for publication in Ap
Study of the fosfosal controlled permeation through glutaraldehyde crosslinked chitosan membranes
Advanced material forum III : proceedings of the III International Materials Symposium, Aveiro, 2005Fosfosal, a phosphate derivative of salicylic acid, which presents both analgesic and antiinflammatory
properties, was used as a model drug to study the potential of recently developed
chitosan membranes (with different crosslinking degrees) to be used as drug release rate-controlling
membranes. The fosfosal permeation across these membranes was studied using an in-house built
developed diffusion cell with online automatic monitoring. Experiments were performed using
phosphate buffer saline (PBS) solution at 37ÂșC. Different flow properties of the detection set up
were determined in order to estimate the errors introduced by the automatic online monitoring
system. For increasing crosslinking degrees the permeability initially decreased, and then increased,
likely as a consequence of the crosslinking influence on a variety of properties like crystallinity and
hydrophilicity that have opposite influence on permeability. In summary, it was possible to control
the drug release profile by means of changing the degree of crosslinking of chitosan membranes and
to follow the respective release kinetics by means of using the developed diffusion cell(undefined
Surface properties of extracts from cork black condensate
The insulation corkboard production generates black condensate
(BC), a paste-like solid waste. It is hydrophobic and
has the potential to be used as protective coating. To evaluate
this potential, coatings were prepared from BC extracts and
their surface behavior was evaluated by contact angle (CA)
measurements. The CA dynamics were recorded as a function
of time; advancing CAs were also registered; the
approaches were applied according to Fowkes, Owens-
Wendt-Rabel-Kaelble (OWRK), and Van Oss to determine
the surface energy (SE) for each coating. Depending on the
liquid probe, three phenomena were observed: water evaporation,
diiodomethane diffusion into the coating, and rearrangement
of the chemical groups on the coating surface,
when glycerol was dropped onto the surface. Based on the
results from the CA dynamics, the applicability of the coatings
against hydrophobic environments was limited owing to
its affinity to apolar compounds. The results show that the
coating prepared by the toluene BC extract was the best coating.
The key data were: water CA of 99.38, total SE (between
37.4 mN m-1 and 40.1 mN m-1), SE polar component
(0.1 mN m-1), and the acidic and basic characters were negligible.
It can be concluded that the BC extracts have potential
for coatings.R.P. acknowledges a post-doc research grant BPD/39333/2007 from the Portuguese Foundation for Science and Technology (FCT). We gratefully acknowledge Amorim Isolamentos S.A. for the supply of black condensate
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