Observational Constraints on Silent Quartessence

We derive new constraints set by SNIa experiments (`gold' data sample of Riess et al.), X-ray galaxy cluster data (Allen et al. Chandra measurements of the X-ray gas mass fraction in 26 clusters), large scale structure (Sloan Digital Sky Survey spectrum) and cosmic microwave background (WMAP) on the quartessence Chaplygin model. We consider both adiabatic perturbations and intrinsic non-adiabatic perturbations such that the effective sound speed vanishes (Silent Chaplygin). We show that for the adiabatic case, only models with equation of state parameter $|\alpha |\lesssim 10^{-2}$ are allowed: this means that the allowed models are very close to \LambdaCDM. In the Silent case, however, the results are consistent with observations in a much broader range, -0.3<\alpha<0.7.Comment: 7 pages, 12 figures, to be submitted to JCA

Adequação de métodos para estimar a população de Elasmopalpus lignosellus em condições de laboratório.

Tres metodos (extracao de ovos, contagem direta de ovos e emergencia de lagartas recem-eclodidas para determinar o potencial de infestacao de Elasmopalpus lignosellus, Zeller 1848 foram testados em laboratorio. Para o metodo de extracao de ovos a amostra de solo foi tratada com hipoclorito de sodio a 1% sendo posteriormente lavada em peneiras de 10, 20 e 100 mesh. Os residuos retirados na peneira de 100 mesh foram tratados com uma solucao saturada de sulfato de magnesio e deixados decantar; o liquido sobrenadante contendo os ovos foi filtrado com um filtro de organdi, e os ovos foram contados com o auxilio de uma lupa binocular. No metodo de contagem direta de ovos no solo foi utilizada uma lupa binocular, e no metodo de emergencia de lagartas utilizaram-se folhas de milho para atrair lagartas recem-eclodidas e afetou-se a contagem destas. Os resultados indicaram que em condicoes de laboratorio o metodo de contagem direta de ovos e mais eficiente do que o metodo de extracao de ovos; nas outras comparacoes, os metodos nao foram estatisticamente diferentes. Utilizando o metodo de extracao de ovos observou-se que os ovos postos pela largado diretamente no solo nao sao removidos com a mesma eficiencia que os ovos misturados manualmente no solo

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

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

Caging dynamics in a granular fluid

We report an experimental investigation of the caging motion in a uniformly heated granular fluid, for a wide range of filling fractions, $\phi$. At low $\phi$ the classic diffusive behavior of a fluid is observed. However, as $\phi$ is increased, temporary cages develop and particles become increasingly trapped by their neighbors. We statistically analyze particle trajectories and observe a number of robust features typically associated with dense molecular liquids and colloids. Even though our monodisperse and quasi-2D system is known to not exhibit a glass transition, we still observe many of the precursors usually associated with glassy dynamics. We speculate that this is due to a process of structural arrest provided, in our case, by the presence of crystallization.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Let

Sodium silicate gel as a precursor for the in vitro nucleation and grow of a bone-like apatite coating in compact and porous polymeric structures

In the present work, a new methodology to produce bioactive coatings on the surface of starch-based biodegradable polymers or other polymeric biomaterials is proposed. A sodium silicate gel is employed as an alternative nucleating agent to the more typical bioactive glasses for inducing the formation of a calcium-phosphate (Ca-P) layer. The method has the advantage of being able to coat efficiently both compact materials and porous 3D architectures aimed at being used on tissue replacement applications and as tissue engineering scaffolds. By means of this treatment, it is possible to observe the formation of an apatite-like layer, only after 6 hours of simulated body fluid immersion. For the porous materials, this layer could also be observed inside the pores, clearly covering the cell walls. Furthermore, an increase of the surface hydrophilicity (higher amount of polar groups in the surface) might contribute to the formation of silanol groups that also act as apatite inductors. After 30 days of SBF immersion, the apatite-like films exhibit a partially amorphous nature and the Ca/P ratios became much closer to the value attributed to hydroxyapatite (1.67). The obtained results are very promising for the development of cancellous bone replacement materials and for pre-calcifying bone tissue engineering scaffolds