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Peftitsis D.,KTH Royal Institute of Technology | Tolstoy G.,KTH Royal Institute of Technology | Antonopoulos A.,KTH Royal Institute of Technology | Rabkowski J.,KTH Royal Institute of Technology | And 5 more authors.
IEEE Transactions on Power Electronics | Year: 2012

This paper studies the possibility of building a modular multilevel converter (M2C) using silicon carbide (SiC) switches. The main focus is on a theoretical investigation of the conduction losses of such a converter and a comparison to a corresponding converter with silicon-insulated gate bipolar transistors. Both SiC BJTs and JFETs are considered and compared in order to choose the most suitable technology. One of the submodules of a down-scaled 3 kVA prototype M2C is replaced with a submodule with SiC JFETs without antiparallel diodes. It is shown that the diodeless operation is possible with the JFETs conducting in the negative direction, leaving the possibility to use the body diode during the switching transients. Experimental waveforms for the SiC submodule verify the feasibility during normal steady-state operation. The loss estimation shows that a 300 MW M2C for high-voltage direct current transmission would potentially have an efficiency of approximately 99.8 if equipped with future 3.3 kV 1.2 kA SiC JFETs. © 2011 IEEE.


Geterud E.G.,GlobalView Systems | Yang J.,SE | Ostling T.,Arkivator AB | Bergmark P.,Art and Technology
IEEE Transactions on Antennas and Propagation | Year: 2013

We present a new design of the hat-fed reflector antenna for satellite communications, where a low reflection coefficient, high gain, low sidelobes and low cross-polar level are required over a wide frequency band. The hat feed has been optimized by using the Genetic Algorithm through a commercial FDTD solver, QuickWave-V2D, together with an own developed optimization code. The Gaussian vertex plate has been applied at the center of the reflector in order to improve the reflection coefficient and reduce the far-out sidelobes. A parabolic reflector with a ring-shaped focus has been designed for obtaining nearly 100% phase efficiency. The antenna's reflection coefficient is below $-$17 dB and the radiation patterns satisfy the M-x standard co- and cross-polar sidelobe envelopes for satellite ground stations over a bandwidth of 30%. A low-cost monolayer radome has been designed for the antenna with satisfactory performance. The simulations have been verified by measurements; both of them are presented in the paper. © 1963-2012 IEEE.


Lobovkina T.,SE | Gozen I.,SE | Erkan Y.,SE | Olofsson J.,SE | And 2 more authors.
Soft Matter | Year: 2010

Local signaling, cell polarization, and protrusive growth are key steps in directed migration of biological cells guided by chemical gradients. Here we present a minimal system which captures several key features of cellular migration from signaling-to-motion. The model system consists of flat, negatively charged phospholipid vesicles, a negatively charged surface, and a local, and controllable point-source supply of calcium ions. In the presence of a Ca2+ gradient, the surface-adhered vesicles form protrusions in the direction of the gradient. We also observe membrane shape oscillations between expanded (flattened), and spherical states as a function of the Ca 2+-concentration. The observed phenomena can be of importance in explaining motile action in prebiotic, primitive, and biomimetic systems, as well as in development of novel soft-matter nano- and microscale mechanical devices. © 2011 The Royal Society of Chemistry.


Sandberg E.,SE | Abrahamsson M.,SE
International Journal of Logistics Research and Applications | Year: 2011

The purpose of this paper is to explore how sustainable competitive advantage is generated in two Swedish best practice companies that successfully exploit logistics as a source for competitive advantage. Using a theoretical framework based on the resource-based view of the firm, this research elaborates on the links between operational and dynamic logistics capabilities and sustainable competitive advantage. The findings conclude that a sustainable competitive advantage is based on a combination of efficient and effective logistics operations and well-functioning, adjusted, in-house-developed IT systems. This operational capability is in turn sustained through five dynamic capabilities: managerial knowledge and presence, cross-functional teamwork, control, learning and supply chain relationships. © 2011 Taylor & Francis.


The assessment of adsorbed surfactant mass by quartz crystal microbalance with dissipation (QCM-D) monitoring is often complicated due to large bulk responses, particularly for surfactants with high critical micelle concentration (CMC). We present in this work means to interpret QCM-D data that enables the response from the bulk contribution to be separated from the response originating from adsorbed mass. Adsorption of two surfactants, Triton X100 and C12AspNa 2 with low and high CMCs, respectively, at the gold-liquid interface surface has been evaluated. Two different approaches to quantify the bulk response are compared. The first approach involves the use of a nonadsorbing surface (silica), yielding a calibration curve for the concentration dependent bulk response. The second method is based on the fact that the overtone-dependent QCM-D response that originates from changes in the bulk differs from that induced by the adsorbed layer of the surfactants. Under the reasonable assumption that the bulk solution and the adsorbed surfactants can be treated as a Newtonian liquid and an acoustically rigid film, it is demonstrated that the bulk contribution can be quantified without control measurements involving inert surfaces. An excellent agreement between the two methods is reported. © 2010 American Chemical Society.


Gozen I.,SE | Billerit C.,SE | Dommersnes P.,SE | Dommersnes P.,University Paris Diderot | And 2 more authors.
Soft Matter | Year: 2011

Biological nanotubes, often referred to as tunneling nanotubes, fulfill important functions within the cell, e.g. by supplying cell components, conducting signals and transporting virus particles and bacteria. Many functions are still insufficiently understood, which has placed these nanostructures in the focus of recent investigation. We report here on our observations of transient tubulation in nanoparticle-containing, supported flat giant unilamellar vesicles (FGUVs). The encapsulation of nanoparticles in FGUVs in conjunction with low (1-4 mM) Ca 2+ in the ambient buffer solution resulted in transient tube formation. Tubes extended from the FGUV up to a length of several hundred micrometres and exhibited, on some occasions, vesicle encapsulation. The findings represent an interesting confirmation of several reported theoretical and practical models of tube formation in biological or biomimetic systems. © 2011 The Royal Society of Chemistry.


Ehliar A.,SE
7th FPGAworld Conference - Academic Proceedings 2010, FPGAworld 2010 | Year: 2010

This paper is intended as a guideline for people who are interested in manual instantiation of FPGA primitives as a way of improving the performance of an FPGA design. The focus of the paper is on designs where slice primitives like flip-fops and lookup tables are instantiated. Guidelines on how to develop a design with manual instantiation are presented together with a case study of a high performance bitserial two's complement divider where a majority of the area is manually instantiated. This divider is capable of reaching a maximum frequency of 345 MHz in the fastest Virtex- 4 while utilizing less than 150 LUTs thanks to the high amount of manual optimizations. An open source library containing modules intended to promote the structured development of modules with manually instantiated components is also presented. Copyright © 2010 ACM.


Bladh M.,SE
Energy Policy | Year: 2012

The development of total energy consumption is important in a world with limited resources. It is the result of two basic tendencies working in opposite directions: growth in number and in use (such as more cars and driving more) and improvements in energy efficiency (such as more fuel-efficient engines). Since the 1970s growth of energy consumption has slowed down in Sweden. This means that increasing supply has been counteracted by measures improving overall energy efficiency to a larger degree than before. How can long-term development in energy consumption be analysed? This paper proposes a focus on stocks of energy-converting artefacts as a tool for such analyses. In order to show the fruitfulness of this approach, historical data on cars, dwellings and lamps in Sweden are used.Results from the cases in this paper show considerable gains of efficiency in fuel consumption in private cars and heating efficiency in multi-dwelling houses. Demographic factors are important for the outcome. The approach seems to promise a way to analyse energy efficiency that captures both promoting and counteracting factors at both the micro and macro level. © 2012.


Kolb G.S.,University of Stockholm | Jerling L.,University of Stockholm | Essenberg C.,University of Stockholm | Palmborg C.,se | Hamback P.A.,University of Stockholm
Ecography | Year: 2012

Seabirds can strongly affect several major factors correlated with species diversity by concentrating marine nutrients on their nesting islands and by physically disturbing island vegetation. In this study, we investigated the effects of nesting cormorants on the abundance, species richness, and composition of plants and arthropods (Coleoptera, Heteroptera, Araneae, and Chironomidae) on islands in Stockholm archipelago, Sweden. Nesting cormorants negatively affected plant species richness and vegetation cover and that changed plant species composition. The effect of nesting cormorants on island arthropods varied between feeding groups and sampling methods. Most orders did not change in abundance or species richness but some, such as coleopterans and spiders changed in species composition. Herbivorous coleopterans were generally negatively affected by cormorants whereas fungivorous species and scavengers were generally positively affected. In structural equation modeling we found that the effect of cormorants was sometimes direct, such as on scavengers, but many effects on island consumers were mediated by changes in vegetation caused by cormorant presence. Overall, arthropod communities were highly dissimilar between cormorant and reference islands, and we therefore conclude that nesting cormorants not only affect the diversity of their nesting islands but also of the archipelago as a whole. The total diversity in the archipelago may increase through regional increased habitat heterogeneity and by adding species which are favored by seabirds (e.g. scavenging and fungivorous coleopterans). © 2012 The Authors. Ecography © 2012 Nordic Society Oikos.


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