Mechanical, electrical and electro-mechanical properties of thermoplastic elastomer styrene–butadiene–styrene/multiwall carbon nanotubes composites

Composites of styrene–butadiene–styrene (SBS) block copolymer with multiwall carbon nanotubes were processed by solution casting to investigate the influence of filler content, the different ratios of styrene/butadiene in the copolymer and the architecture of the SBS matrix on the electrical, mechanical and electro-mechanical properties of the composites. It was found that filler content and elastomer matrix architecture influence the percolation threshold and consequently the overall composite electrical conductivity. The mechanical properties are mainly affected by the styrene and filler content. Hopping between nearest fillers is proposed as the main mechanism for the composite conduction. The variation of the electrical resistivity is linear with the deformation. This fact, together with the gauge factor values in the range of 2–18, results in appropriate composites to be used as (large) deformation sensors.

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.

Voxel-based registration of simulated and real patient CBCT data for accurate dental implant pose estimation

The success of dental implant-supported prosthesis is directly linked to the accuracy obtained during implant’s pose estimation (position and orientation). Although traditional impression techniques and recent digital acquisition methods are acceptably accurate, a simultaneously fast, accurate and operator-independent methodology is still lacking. Hereto, an image-based framework is proposed to estimate the patient-specific implant’s pose using cone-beam computed tomography (CBCT) and prior knowledge of implanted model. The pose estimation is accomplished in a threestep approach: (1) a region-of-interest is extracted from the CBCT data using 2 operator-defined points at the implant’s main axis; (2) a simulated CBCT volume of the known implanted model is generated through Feldkamp-Davis-Kress reconstruction and coarsely aligned to the defined axis; and (3) a voxel-based rigid registration is performed to optimally align both patient and simulated CBCT data, extracting the implant’s pose from the optimal transformation. Three experiments were performed to evaluate the framework: (1) an in silico study using 48 implants distributed through 12 tridimensional synthetic mandibular models; (2) an in vitro study using an artificial mandible with 2 dental implants acquired with an i-CAT system; and (3) two clinical case studies. The results shown positional errors of 67±34μm and 108μm, and angular misfits of 0.15±0.08º and 1.4º, for experiment 1 and 2, respectively. Moreover, in experiment 3, visual assessment of clinical data results shown a coherent alignment of the reference implant. Overall, a novel image-based framework for implants’ pose estimation from CBCT data was proposed, showing accurate results in agreement with dental prosthesis modelling requirements.

Fast left ventricle tracking in CMR images using localized anatomical affine optical flow

In daily cardiology practice, assessment of left ventricular (LV) global function using non-invasive imaging remains central for the diagnosis and follow-up of patients with cardiovascular diseases. Despite the different methodologies currently accessible for LV segmentation in cardiac magnetic resonance (CMR) images, a fast and complete LV delineation is still limitedly available for routine use. In this study, a localized anatomically constrained affine optical flow method is proposed for fast and automatic LV tracking throughout the full cardiac cycle in short-axis CMR images. Starting from an automatically delineated LV in the end-diastolic frame, the endocardial and epicardial boundaries are propagated by estimating the motion between adjacent cardiac phases using optical flow. In order to reduce the computational burden, the motion is only estimated in an anatomical region of interest around the tracked boundaries and subsequently integrated into a local affine motion model. Such localized estimation enables to capture complex motion patterns, while still being spatially consistent. The method was validated on 45 CMR datasets taken from the 2009 MICCAI LV segmentation challenge. The proposed approach proved to be robust and efficient, with an average distance error of 2.1 mm and a correlation with reference ejection fraction of 0.98 (1.9 ± 4.5%). Moreover, it showed to be fast, taking 5 seconds for the tracking of a full 4D dataset (30 ms per image). Overall, a novel fast, robust and accurate LV tracking methodology was proposed, enabling accurate assessment of relevant global function cardiac indices, such as volumes and ejection fraction.

O papel do comprador no processo de compras em instituições públicas de ciência e tecnologia em saúde (C&T/S)

Este artigo aborda o papel do comprador público nas aquisições de bens e serviços para as instituições públicas de ciência e tecnologia em saúde (C&T/S), tendo como referência o CPqAM/Fiocruz. O estudo contempla características e causas que potencializam os contextos da gestão das compras institucionais, os aspectos da administração pública brasileira, a função administrativa de compra, o papel do comprador público no processo, o seu perfil, o seu comportamento ético, bem como a possibilidade de redução de custos na aquisição de materiais para a pesquisa científica.

Redes de C&T em institutos públicos de pesquisa brasileiros: o caso do Instituto Agronômico do Paraná (Iapar)

Este artigo demonstra como foram e como são executados projetos em rede de C & T no Instituto Agronômico do Paraná (Iapar). Em relação aos procedimentos metodológicos, a pesquisa é qualitativa, descritiva e seccional, com perspectiva longitudinal, e foi desenvolvida por meio de um estudo de caso. Os dois projetos selecionados foram os que mais trouxeram visibilidade ao instituto, de acordo com informações extraídas de entrevistas com as várias pessoas que dirigiram o Iapar desde a sua fundação. Os dados da pesquisa foram coletados de forma primária (por meio de entrevistas semiestruturadas com dirigentes e pesquisadores envolvidos nos projetos) e secundária (pesquisa documental). A compreensão do fenômeno apoiou-se fundamentalmente na interpretação das falas dos sujeitos de pesquisa. A análise dos dois projetos executados em rede de C & T em épocas distintas pelo Iapar revelou que seu significado mudou ao longo do tempo. As primeiras redes foram formadas para o cumprimento do papel social do Iapar no Paraná. Mais recentemente, os projetos conduzidos em rede pelo instituto têm o objetivo prioritário de captação de recursos e obtenção de legitimidade ante o Estado e a sociedade.

Expedições coloniais de coleta e a busca por oportunidades no sertão amazônico, c. 1750-1800

O artigo analisa a participação dos indígenas nas atividades de coleta das drogas do sertão, durante a vigência do Diretório dos Índios. Ele sugere uma explicação para os casos de participação voluntária naquelas expedições: nelas os indígenas encontravam espaço para ação independente, fomentavam a expansão de redes sociais e configuravam perspectivas econômicas.

"Em trajes brasileiros": justiça e constituição na América ibérica (c. 1750-1850)

Situando-se na intersecção entre constitucionalismo e independências, o artigo tem como objetivo discutir a dinâmica institucional da justiça na formação do Império do Brasil como parte de uma compartilhada tradição jurídica em todo o mundo ibero-americano, centrando-se no ciclo de mudanças ocorrido entre meados dos séculos XVIII e XIX. Para tanto, o recorte está nas garantias de justiça que, existentes na cultura do ius commune, seriam centrais aos novos estados independentes na América por meio da estatização de elementos que previam o funcionamento de uma antiga chave: a de que a "boa administração da justiça" dependia do "bom juiz", e do seu reto comportamento, e não das leis e de sua devida aplicação. A partir da prevalência de uma justiça de juízes, conclui-se que, sem códigos, no sentido moderno, foi impossível se implantar um regime de justiça de leis.