Mechanical Behavior of the Lamellar Structure in Semi-Crystalline Polymers

We have employed molecular dynamics simulations to study the behavior of virtual polymeric materials under an applied uniaxial tensile load. Through computer simulations, one can obtain experimentally inaccessible information about phenomena taking place at the molecular and microscopic levels. Not only can the global material response be monitored and characterized along time, but the response of macromolecular chains can be followed independently if desired. The computer-generated materials were created by emulating the step-wise polymerization, resulting in self-avoiding chains in 3D with controlled degree of orientation along a certain axis. These materials represent a simplified model of the lamellar structure of semi-crystalline polymers,being comprised of an amorphous region surrounded by two crystalline lamellar regions. For the simulations, a series of materials were created, varying i) the lamella thickness, ii) the amorphous region thickness, iii) the preferential chain orientation, and iv) the degree of packing of the amorphous region. Simulation results indicate that the lamella thickness has the strongest influence on the mechanical properties of the lamella-amorphous structure, which is in agreement with experimental data. The other morphological parameters also affect the mechanical response, but to a smaller degree. This research follows previous simulation work on the crack formation and propagation phenomena, deformation mechanisms at the nanoscale, and the influence of the loading conditions on the material response. Computer simulations can improve the fundamental understanding about the phenomena responsible for the behavior of polymeric materials, and will eventually lead to the design of knowledge-based materials with improved properties.

Factores determinantes do nível de divulgação sobre instrumentos derivados de acordo com as recomendações do Basel Committee on Banking Supervision e da Organisation of Securities Commissions - evidência empírica no sector bancário português

Este estudo analisa o nível de divulgação sobre instrumentos derivados e seus factores determinantes nas entidades bancárias portuguesas. Para o efeito, foi utilizado um índice de divulgação, baseado nas recomendações emitidas pelo Basel Committee on Banking Supervision e pela Organisation of Securities Commissions, e analisados os Relatórios & Contas anuais, individuais, relativos a 2009. Conclui-se que o número de empresas que apresenta informação sobre a utilização de instrumentos derivados é bastante elevado, mas o valor médio de divulgação apresentado é bastante reduzido. Identificam-se, como factores determinantes do nível de divulgação, o tamanho da empresa, a qualidade do auditor externo e o facto de a empresa ter procedido a um aumento de capital durante o exercício económico em análise.

Grau de cumprimento com as recomendações do Basel Committee on Banking Supervision e da Organisation of Securities Commissions, sobre divulgação de informação relacionada com instrumentos derivados - evidência empírica no sector bancário português

This study analyzes the level of disclosure on derivatives, in accordance with the recommendations issued by the Basel Committee on Banking Supervision and the Organization of Securities Commission, by Portuguese banks. We have analyzed individual annual reports related to 2009, using a disclosure index based on those recommendations. We concluded that the number of companies that provides information about derivative instruments is quite high, but the average value of disclosure is very low. The information disclosed more frequently is that related to general aspects, followed by information related to accounting and valuation methods.

Estudo do grau de cumprimento com as recomendações do Basel Committee on Banking Supervision e da Organisation of Securities Commissions, sobre divulgação de informação relacionada com instrumentos derivados, pelas entidades portuguesas pertencentes ao sector bancário

Este estudo analisa o nível de divulgação sobre instrumentos derivados, de acordo com as recomendações emitidas pelo Basel Committee on Banking Supervision e pela Organisation of Securities Commissions, pelas entidades bancárias portuguesas. Para o efeito, foi utilizado um índice de divulgação e analisados os Relatórios & Contas anuais, individuais, relativos a 2009. Conclui-se que o número de empresas que apresenta informação sobre a utilização de instrumentos derivados é bastante elevado, mas o valor médio de divulgação apresentado é bastante reduzido. A informação mais divulgada é a relativa a informações gerais, seguida da informação relacionada com contabilidade e métodos de avaliação.

Semi-automatic 3D Segmentation Of Costal Cartilage In CT Data From Pectus Excavatum Patients

One of the current frontiers in the clinical management of Pectus Excavatum (PE) patients is the prediction of the surgical outcome prior to the intervention. This can be done through computerized simulation of the Nuss procedure, which requires an anatomically correct representation of the costal cartilage. To this end, we take advantage of the costal cartilage tubular structure to detect it through multi-scale vesselness filtering. This information is then used in an interactive 2D initialization procedure which uses anatomical maximum intensity projections of 3D vesselness feature images to efficiently initialize the 3D segmentation process. We identify the cartilage tissue centerlines in these projected 2D images using a livewire approach. We finally refine the 3D cartilage surface through region-based sparse field level-sets. We have tested the proposed algorithm in 6 noncontrast CT datasets from PE patients. A good segmentation performance was found against reference manual contouring, with an average Dice coefficient of 0.75±0.04 and an average mean surface distance of 1.69±0.30mm. The proposed method requires roughly 1 minute for the interactive initialization step, which can positively contribute to an extended use of this tool in clinical practice, since current manual delineation of the costal cartilage can take up to an hour.