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.

Cluster growth in far-from-equilibrium particle models with diffusion, detachment, reattachment and deposition

Monolayer cluster growth in far-from-equilibrium systems is investigated by applying simulation and analytic techniques to minimal hard core particle (exclusion) models. The first model (I), for post-deposition coarsening dynamics, contains mechanisms of diffusion, attachment, and slow activated detachment (at rate epsilon<<1) of particles on a line. Simulation shows three successive regimes of cluster growth: fast attachment of isolated particles; detachment allowing further (epsilon t)^(1/3) coarsening of average cluster size; and t^(-1/2) approach to a saturation size going like epsilon^(-1/2). Model II generalizes the first one in having an additional mechanism of particle deposition into cluster gaps, suppressed for the smallest gaps. This model exhibits early rapid filling, leading to slowing deposition due to the increasing scarcity of deposition sites, and then continued power law (epsilon t)^(1/2) cluster size coarsening through the redistribution allowed by slow detachment. The basic (epsilon t)^(1/3) domain growth laws and epsilon^(-1/2) saturation in model I are explained by a simple scaling picture. A second, fuller approach is presented which employs a mapping of cluster configurations to a column picture and an approximate factorization of the cluster configuration probability within the resulting master equation. This allows quantitative results for the saturation of model I in excellent agreement with the simulation results. For model II, it provides a one-variable scaling function solution for the coarsening probability distribution, and in particular quantitative agreement with the cluster length scaling and its amplitude.Comment: Accepted in Phys. Rev. E; 9 pages with figure

Modeling one-dimensional island growth with mass-dependent detachment rates

We study one-dimensional models of particle diffusion and attachment/detachment from islands where the detachment rates gamma(m) of particles at the cluster edges increase with cluster mass m. They are expected to mimic the effects of lattice mismatch with the substrate and/or long-range repulsive interactions that work against the formation of long islands. Short-range attraction is represented by an overall factor epsilon<<1 in the detachment rates relatively to isolated particle hopping rates [epsilon ~ exp(-E/T), with binding energy E and temperature T]. We consider various gamma(m), from rapidly increasing forms such as gamma(m) ~ m to slowly increasing ones, such as gamma(m) ~ [m/(m+1)]^b. A mapping onto a column problem shows that these systems are zero-range processes, whose steady states properties are exactly calculated under the assumption of independent column heights in the Master equation. Simulation provides island size distributions which confirm analytic reductions and are useful whenever the analytical tools cannot provide results in closed form. The shape of island size distributions can be changed from monomodal to monotonically decreasing by tuning the temperature or changing the particle density rho. Small values of the scaling variable X=epsilon^{-1}rho/(1-rho) favour the monotonically decreasing ones. However, for large X, rapidly increasing gamma(m) lead to distributions with peaks very close to and rapidly decreasing tails, while slowly increasing gamma(m) provide peaks close to /2$ and fat right tails.Comment: 16 pages, 6 figure

Internet gaming disorder, aggression and psychological distress in young adults

Introduction: Internet gaming has become a topic of interest since it has positive but also negative effects. Objectives: To explore the relationship between internet gaming, aggression and psychological distress in young adults. Methods: 229 Portuguese subjects (55.5% females), with a mean age of 21.13 years old (SD = 2.075, range: 18-29) filled in the Internet Gaming Disorder Scale-Short Form, the Buss-Perry Aggression Questionnaire, and the Depression, Anxiety and Stress Scales-21. Results: The total score of internet gaming was of 15.90 (SD=6.32), 79.9% (n=183) of the sample used to play videogames and 24.5% (n=56) spent more than ten hours playing a week. Internet gaming was correlated with physical aggression (r=.23**), anger (r=.31**) and hostility (r=.35**); and with depression (r=.36**), anxiety (r=.28**), and stress (r=.31**). A Mann Whitney U test revealed significant differences in internet gaming disorder levels of males (Md=130.75, n=102) and females (Md=102.35, n=127), U=4871.000 z=-3.232, p=.001, r=4.49. Conclusions: Internet gaming disorder is associated with aggression and psychological distress, and males presented higher internet gaming disorder levels. Future studies are needed to explore the bidirectional relationships between gaming disorder, aggression and psychological distress.info:eu-repo/semantics/publishedVersio

Porous bioactive composites from marine origin based in chitosan and hydroxylapatite particles

An optimal carrier for bone tissue engineering should be both a controlled release system and a scaffold. In the former role, the carrier must prevent rapid factor clearance and ideally meter out the growth factor in a predictable manner, allowing therapeutic doses to stimulate target cells for the appropriate duration. In the latter role, the material should act as a permissive environment into which bone cells would be attracted to migrate and begin the process of depositing bone matrix. Therefore the direct incorporation of growth factor in porous scaffolds should be a desirable goal. The inclusion of a bioactive ceramic on the scaffold design will confer to the systems a bone bonding behaviour that will guide bone formation. This work reports the development of composite chitosan/HA (from algal origin) porous structures produced by means of freeze-drying processing routes that can be further loaded with a biologically active agent. The developed bioactive 3D structures (completely from marine origin) have potential application as tissue engineering scaffolds and drug delivery systems due to their morphological and bioactive properties.(undefined

A discussion on the development of wind engineering for the design of mining related structures

Mining related structures are often of a form which is outside of the guidance of published standards and guidelines due to the difficulty in assessing the aerodynamic shape factor. The historical drive to better understand the nature of wind loading on structures coincided with the failure of significant industrial revolution era structures, and now the general state of the art is well advanced. In an era of complex non-linear analysis, we still lack a detailed understanding of the wind loads for mining related structures. There is now the ability to digitally prototype a structure in CAD, analyse and optimise in CFD, then validate via wind tunnel testing a 3D printed hard-copy of the digital design. This paper examines the relevant history of the development of wind engineering for industrial structures and looks to the near future where risk and cost can be reduced in design using combinations of existing 3D technologies

Bilayered chitosan-based scaffolds for osteochondral tissue engineering : influence of hydroxyapatite on in vitro cytotoxicity and dynamic bioactivity studies in a specific double-chamber bioreactor

Osteochondral tissue engineering presents a current research challenge due to the necessity of combining both bone and cartilage tissue engineering principles. In the present study, bilayered chitosan-based scaffolds are developed based on the optimization of both polymeric and composite scaffolds. A particle aggregation methodology is proposed in order to achieve an improved integrative bone–cartilage interface needed for this application, since any discontinuity is likely to cause long-term device failure. Cytotoxicity was evaluated by the MTS assay with the L929 fibroblast cell line for different conditions. Surprisingly, in composite scaffolds using unsintered hydroxyapatite, cytotoxicity was observed in vitro. This work reports the investigation that was conducted to overcome and explain this behaviour. It is suggest that the uptake of divalent cations may induce the cytotoxic behaviour. Sintered hydroxyapatite was consequently used and showed no cytotoxicity when compared to the controls. Microcomputed tomography (micro-CT) was carried out to accurately quantify porosity, interconnectivity, ceramic content, particle and pore sizes. The results showed that the developed scaffolds are highly interconnected and present the ideal pore size range to be morphometrically suitable for the proposed applications. Dynamical mechanical analysis (DMA) demonstrated that the scaffolds are mechanically stable in the wet state even under dynamic compression. The obtained elastic modulus was, respectively, 4.21 ± 1.04, 7.98 ± 1.77 and 6.26 ± 1.04 MPa at 1 Hz frequency for polymeric, composite and bilayered scaffolds. Bioactivity studies using both a simulated body fluid (SBF) and a simulated synovial fluid (SSF) were conducted in order to assure that the polymeric component for chondrogenic part would not mineralize, as confirmed by scanning electron microscopy (SEM), inductively coupled plasma-optical emission spectroscopy (ICP) and energy-dispersive spectroscopy (EDS) for different immersion periods. The assays were carried out also under dynamic conditions using, for this purpose, a specifically designed double-chamber bioreactor, aiming at a future osteochondral application. It was concluded that chitosan-based bilayered scaffolds produced by particle aggregation overcome any risk of delamination of both polymeric and composite parts designed, respectively, for chondrogenic and osteogenic components that are mechanically stable. Moreover, the proposed bilayered scaffolds could serve as alternative, biocompatible and safe biodegradable scaffolds for osteochondral tissue engineering applications

Optimization of chitosan-based composite and bi-layered scaffolds produced by particles aggregation for osteochondral tissue engineering: Influence of hydroxylapatite

[Excerpt] Osteochondral tissue engineering presents a challenge to the present research due to requirements’ combination of both bone and cartilage tissue engineering. In the present study, bilayered chitosan scaffolds are proposed based in the optimization of polymeric and composite scaffolds. µ-CT was carried out for accurate morphometric characterization quantifying porosity, interconnectivity, ceramic content, particles and pores size. The results showed that the developed scaffolds are highly interconnected and present ideal pore size range, being morphometrically adequate for the proposed applications. [...]info:eu-repo/semantics/publishedVersio

Development of novel carrageenan scaffolds for tissue engineering using rapid prototyping

[Excerpt] In the Tissue Engineering (TE) field, great attention has been given devoted to the use of rapid prototyping (RP). The combined use of Computer Assisted Design (CAD) with advanced RP techniques enables the design and fabrication in a reproducible way of patient adapted scaffolds featuring complex 3D architectures. In this context, Carrageenan is a natural polymer that exhibits a very high biomedical potential. Carrageenan is a sulphated hydrocolloid capable of forming hydrogels with very different behaviours and properties depending on the experimental conditions. [...]info:eu-repo/semantics/publishedVersio