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Östermalm, Sweden

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.

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.

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.

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.

Zaralis K.,Swedish University of Agricultural Sciences | Norgaard P.,Copenhagen University | Helander C.,Swedish University of Agricultural Sciences | Murphy M.,SE | And 2 more authors.
Livestock Science | Year: 2014

Whole-crop maize silage as forage in diets of finishing cattle can promote high intakes and thus, enhances animal performance. In the present study we evaluated the effect of whole-crop maize maturity at harvest and the proportion of maize-silage in diets of finishing bulls, on feed intake and performance. An indoor experiment with 64 dairy bulls was replicated over two consecutive rearing periods, under the same experimental design. Two groups of 4 light and two groups of 4 heavy bulls were randomly allocated into one of the 4 dietary treatments, which formed a 2×2 factorial arrangement of treatments, involving two maturity stages of maize at harvest (i.e. dough stage or dent stage) and two maize silage proportions (i.e. 100% maize silage or 50% maize and 50% grass silage). The diets were offered ad libitum as total mixed rations (TMRs) with inclusion of concentrates (i.e. rolled barley; dried distillers' grain plus soluble; cold-pressed rapeseed cake) in a 40% proportion on DM basis. All animals were slaughtered at a target body weight of 630 kg. Bulls fed on diets containing maize silage as sole forage achieved higher live-weight gain (P<0.01) compared to their counterparts. This is likely due to the higher ME (P<0.01) and CP (P<0.001) intakes they achieved. Interestingly, the dough stage compared to dent stage maturity of maize at harvest tended to increase live-weight gain (P=0.06). © 2014 Elsevier B.V. All rights reserved.

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