Interactive topology optimization on hand-held devices

This paper presents an interactive topology optimization application designed for hand-held devices running iOS or Android. The TopOpt app solves the 2D minimum compliance problem with interactive control of load and support positions as well as volume fraction. Thus, it is possible to change the problem settings on the fly and watch the design evolve to a new optimum in real time. The use of an interactive app makes it extremely simple to learn and understand the influence of load-directions, support conditions and volume fraction. The topology optimization kernel is written in C# and the graphical user interface is developed using the game engine Unity3D. The underlying code is inspired by the publicly available 88 and 99 line Matlab codes for topology optimization but does not utilize any low-level linear algebra routines such as BLAS or LAPACK. The TopOpt App can be downloaded on iOS devices from the Apple App Store, at Google Play for the Android platform, and a web-version can be run from www.topopt.dtu.dk.     

Variational Segmentation of Image Sequences Using Region-Based Active Contours and Deformable Shape Priors

In this paper we address the problem of segmentation in image sequences using region-based active contours and level set methods. We propose a novel method for variational segmentation of image sequences containing nonrigid, moving objects. The method is based on the classical Chan-Vese model augmented with a novel frame-to-frame interaction term, which allow us to update the segmentation result from one image frame to the next using the previous segmentation result as a shape prior. The interaction term is constructed to be pose-invariant and to allow moderate deformations in shape. It is expected to handle the appearance of occlusions which otherwise can make segmentation fail. The performance of the model is illustrated with experiments on synthetic and real image sequences.     

A Multicast-Enabled Delivery Framework for QoE Assurance of Over-The-Top Services in Multimedia Access Networks

Over-The-Top (OTT) video services are becoming more and more important in today’s broadband access networks. While original OTT services only offered short duration medium quality videos, more recently, premium content such as high definition full feature movies and live video are offered as well. For operators, who see the potential in providing Quality of Experience (QoE) assurance for an increased revenue, this introduces important new network management challenges. Traditional network management paradigms are often not suited for ensuring QoE guarantees as the provider does not have any control on the content’s origin. In this article, we focus on the management of an OTT-based video service. We present a loosely coupled architecture that can be seamlessly integrated into an existing OTT-based video delivery architecture. The framework has the goal of resolving the network bottleneck that might occur from high peaks in the requests for OTT video services. The proposed approach groups the existing Hypertext Transfer Protocol (HTTP) based video connections to be multicasted over an access network’s bottleneck and then splits them again to reconstruct the original HTTP connections. A prototype of this architecture is presented, which includes the caching of videos and incorporates retransmission schemes to ensure robust transmission. Furthermore, an autonomic algorithm is presented that allows to intelligently select which OTT videos need to be multicasted by making a remote assessment of the cache state to predict the future availability of content. The approach was evaluated through both simulation and large scale emulation and shows a significant gain in scalability of the prototype compared to a traditional video delivery architecture.     

Carbon nanotube electron sources and applications

In this review we give an overview of the present status of research on carbon nanotube (CNT) field emitters and their applications. Several different construction principles of field-emission devices with CNTs are summarized. The emission mechanism is introduced and a detailed overview is given of the measured emission properties and related topics of CNT electron sources. We give also several examples of field-emission devices with CNT electron emitters that are presently being investigated in the academic world as well as in industry. Carbon nanotube electron sources clearly have interesting properties, such as low voltage operation, good stability, long lifetime and high brightness. The most promising applications are the field-emission display and high-resolution electron-beam instruments. But several hurdles remain, such as the manufacture of an electron source or an array of electron sources with exactly the desired properties in a reproducible manner.     

Initial stages of recrystallization in aluminum of commercial purity

In commercial aluminum with a purity of 99.4 pct, the formation and growth of recrystallization nuclei were studied by techniques such asin-situ annealing in a high voltage electron microscope, transmission electron microscopy and light microscopy. Sample parameters were the initial grain size (370 and 19 microns) and the degree of deformation (50 and 90 pct reduction in thickness by cold-rolling). It was found that the initial grain boundaries and high angle boundaries within the original grains are preferential sites for recrystallization nuclei, and that the effect of such sites is enhanced by the FeAl₃ particles present in the commercial aluminum as impurities. The nucleation temperatures determined by high voltage electron microscopy and transmission electron microscopy decrease markedly when the initial grain size is decreased both after 50 and 90 pct cold rolling; a less pronounced temperature decrease is obtained by increasing the degree of deformation. The size of the recrystallization nuclei, the recrystallization temperature and the recrystallized grain size are reported for the four sample states, and finally the structural and kinetic observations are discussed.     

Selective Conversion of Ethane to Ethene via Oxidative Dehydrogenation Over Ca-doped ThO2 Using CO2 as Oxidant

Ca-doped ThO₂, synthesized by solution combustion method was tested for dehydrogenation of ethane with CO₂. Doping ThO₂ with Ca resulted in the creation of oxide ion vacancies and an increased conversion of ethane compared to pure ThO₂. On Th_0.75Ca_0.25O₂ selectivity to ethene was 97 at 46% ethane conversion at 725 °C. Well-known reference catalysts like 5%Cr/TS-1 or OMS-2 showed significantly lower selectivity, but the former was more active under the same conditions.     

Crosslinking of polybenzimidazole membranes by divinylsulfone post‐treatment for high‐temperature proton exchange membrane fuel cell applications

Phosphoric acid‐doped polybenzimidazole (PBI) has been suggested as a promising electrolyte for proton exchange membrane fuel cells operating at temperatures up to 200 °C. This paper describes the development of a crosslinking procedure for PBI membranes by post‐treatment with divinylsulfone. The crosslinking chemistry was studied and optimized on a low‐molecular‐weight model system and the results were used to optimize the crosslinking conditions of PBI membranes. The crosslinked membranes were characterized with respect to chemical and physiochemical properties, showing improved mechanical strength and oxidative stability compared with their linear analogues. Fuel cell tests were further conducted in order to demonstrate the feasibility of the crosslinked membranes. Copyright © 2011 Society of Chemical Industry     

Absorbable polymer stent technologies for vascular regeneration

Stents are structural implants with widespread clinical use in vascular intervention to re‐open stenotic vessels for the treatment of coronary artery disease and peripheral arterial occlusive disease. Apart from their mechanical function, current drug‐eluting stents (DES) utilize local drug delivery from a drug‐incorporated permanent polymer coating to prevent in‐stent restenosis. This delayed closure of the stented vessel is considered one of the major limitations of conventional bare metal stents (BMS). The long‐term safety of DES, however, is still under debate, with reported cases of delayed healing, late thrombosis and hypersensitivity demanding further evolution in this field. A promising approach to circumvent the limitations of first generation DES is the application of degradable polymer coatings in second generation DES, and fully absorbable polymer stents. From a materials and engineering perspective, this paper provides a mini‐review of current clinically relevant DES technology and recent advancements in the development of stents from degradable polymeric materials as an alternative to permanent BMS and DES. This review, includes work on degradable stents and coatings based on blends of polylactic acid and the microbially‐produced poly(4‐hydroxybutyrate). Copyright © 2009 Society of Chemical Industry