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1.
  • Akkerman, V., et al. (creator_code:aut_t)
  • Analysis of flame acceleration induced by wall friction in open tubes
  • 2010
  • record:In_t: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 22:5, s. 1-14
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • Spontaneous flame acceleration leading to explosion triggering in open tubes/channels due to wall friction was analytically and computationally studied. It was first demonstrated that the acceleration is affected when the thermal expansion across the flame exceeds a critical value depending on the combustion configuration. For the axisymmetric flame propagation in cylindrical tubes with both ends open, a theory of the initial (exponential) stage of flame acceleration in the quasi-isobaric limit was developed and substantiated by extensive numerical simulation of the hydrodynamics and combustion with an Arrhenius reaction. The dynamics of the flame shape, velocity, and acceleration rate, as well as the velocity profile ahead and behind the flame, have been determined. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3425646]
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2.
  • Berge, John, 1979, et al. (creator_code:aut_t)
  • Design considerations for tunable bulk acoustic wave resonators based on paraelectric phase BaxSr1-xTiO3 thin films
  • 2010
  • record:In_t: 19th International Symposium on the Applications of Ferroelectrics.
  • swepub:Mat_conferencepaper_t (swepub:level_scientificother_t)abstract
    • Paraelectric phase BaxSr1-xTiO3 (BSTO) is due to the pronounced field induced piezoelectric effect a promising candidate to realize hysteresis-free tunable thin film bulk acoustic wave resonators (TFBARs) at GHz frequencies. Compared to the conventional fixed-frequency TFBAR technology, mainly based on piezoelectric AlN films, the design of tunable BSTO based resonators require additional considerations due to the demanding conditions necessary for the growth of the BSTO active layer (high temperature, O2 ambient). In this work a number of problems and possible solutions are presented for the specific case of solidly mounted resonators based on an acoustic Bragg reflector structure. Simulation results for a proposed tunable resonator based on a BSTO film and a SiO2/HfO2 reflector stack co-optimized for both longitudinal and shear waves are presented and compared to simulations and existing experimental data from other structures.
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3.
  • Berge, John, 1979, et al. (creator_code:aut_t)
  • The effect of Bragg reflectors on the electromechanical performance of parallel-plate ferroelectric capacitors
  • 2010
  • record:In_t: IOP Conference Series: Materials Science and Engineering - Fundamentals and Technology of Multifunctional Oxide Thin Films (Symposium G, EMRS 2009 Spring Meeting) 8–12 June 2009, Strasbourg, France. - 1757-8981. ; 8:1, s. 012011-
  • swepub:Mat_conferencepaper_t (swepub:level_refereed_t)abstract
    • Parallel-plate capacitors based on ferroelectric thin films are considered as high density capacitors and varactors. Due to the small thickness of the ferroelectric films, typically less than 1.0 mu m, high electric fields are generated even at relatively low voltages inducing piezoelectric effect associated with electrostriction. This induced piezoelectric effect has negative impact on ferroelectric capacitors since it causes extra loss (electroacoustic transformation of microwave energy). In this work the use of Bragg reflectors between the substrate and ferroelectric film is proposed as a possible way of suppression of the enhanced losses associated with the piezoelectric activity of the ferroelectric film.
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4.
  • Berge, John, et al. (creator_code:aut_t)
  • Tunable bulk acoustic wave resonators based on Ba0.25Sr0.75TiO3 thin films and a HfO2/SiO2 Bragg reflector
  • 2011
  • record:In_t: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010 .- 1525-8955. ; 58:12, s. 2768-2771
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • A switchable and tunable bulk acoustic wave resonator based on a paraelectric phase Ba0.25Sr0.75TiO3 thin film and an all-dielectric HfO2/SiO2 Bragg reflector is presented. The achieved tuning range (3.8%) and effective electromechanical coupling coefficient (7.1%) are the highest reported for solidly mounted tunable bulk acoustic wave resonators. The non-conductive Bragg reflector stack provides excellent integration possibilities.
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5.
  • Berge, Maria, 1979 (creator_code:aut_t)
  • Group work and physics – characteristics, learning possibilities and patterns of interaction
  • 2011
  • swepub:Mat_doctoralthesis_t (swepub:level_scientificother_t)abstract
    • This thesis explores group work in physics at university level. The guiding research interest is what happens in the students’ interactions during such (instructional) activities, focusing both on the physics content and group dynamics. The four collated papers are based on empirical data consisting of video and audio-recordings of seven groups of students solving physics problems concerning force and friction in Newtonian mechanics. The students belonged to the Engineering Physics and Bioengineering programmes at Chalmers University of Technology.In line with the guiding research interest, different facets of group work data were analysed using a multi-theoretic perspective at three levels with focus on the content, the context and the components. The three distinct approaches were based on different theoretical frameworks: phenomenography combined with variation theory, positioning theory, and conversation analysis. The results presented in this thesis relate to pedagogical characteristics of the learning situation, learning possibilities and patterns of interaction and all the analytical approaches contribute to all the aspects of the results. The purpose of this design was to achieve a deeper understanding of a complex empirical situation by offering several accounts that are analytically and theoretically differently grounded. The theoretical frameworks have been interpreted, and sometimesadapted, in order to offer analytical strength in reflecting essential facets of the empirical data with respect to the research interest. Each level of analysis uncovered new dimensions of the learning situation, potentially enabling a synthesis of different understandings of group work. This synthesis will inform and support instructional advice for the learning of physics.The results show that learning physics in small groups is a complex and nonlinear process where the students’ learning possibilities differ and have many levels. These learning possibilities take place simultaneously in group sessions and are interconnected, for example, developing through discussion the way of experiencing physics concepts, becoming and being part of a physics or an engineering community and interactively producing answers, as well as communicative and representational tools for learning.
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6.
  • Cohen, David, et al. (creator_code:aut_t)
  • Geometric finite difference schemes for the generalized hyperelastic-rod wave equation
  • 2011
  • record:In_t: Journal of Computational and Applied Mathematics. - : Elsevier BV. - 0377-0427 .- 1879-1778. ; 235:8, s. 1925-1940
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • Geometric integrators are presented for a class of nonlinear dispersive equations which includes the Camassa-Holm equation, the BBM equation and the hyperelastic-rod wave equation. One group of schemes is designed to preserve a global property of the equations: the conservation of energy; while the other one preserves a more local feature of the equations: the multi-symplecticity. (C) 2010 Elsevier B.V. All rights reserved.
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7.
  • Cohen, David, et al. (creator_code:aut_t)
  • Linear energy-preserving integrators for Poisson systems
  • 2011
  • record:In_t: BIT Numerical Mathematics. - : Springer Science and Business Media LLC. - 0006-3835 .- 1572-9125. ; 51:1, s. 91-101
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • For Hamiltonian systems with non-canonical structure matrix a new class of numerical integrators is proposed. The methods exactly preserve energy, are invariant with respect to linear transformations, and have arbitrarily high order. Those of optimal order also preserve quadratic Casimir functions. The discussion of the order is based on an interpretation as partitioned Runge-Kutta method with infinitely many stages.
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8.
  • Cuklev, Filip, 1981, et al. (creator_code:aut_t)
  • Diclofenac in fish : blood plasma levels similar to human therapeutic levels affect global hepatic gene expression
  • 2011
  • record:In_t: Environmental Toxicology and Chemistry. - New York : Pergamon. - 0730-7268 .- 1552-8618. ; 30:9, s. 2126-2134
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • Diclofenac is a non-steroidal anti-inflammatory drug frequently found in the aquatic environment. Previous studies have reported histological changes in the liver, kidney and gills of fish at concentrations similar to those measured in treated sewage effluents (approximately 1 µg/L). Analyses or predictions of blood plasma levels in fish allow a direct comparison with human therapeutic plasma levels, and may therefore be used to indicate a risk for pharmacological effects in fish. To relate internal exposure to a pharmacological interaction we investigated global hepatic gene expression together with bioconcentration in blood plasma and liver of rainbow trout (Oncorhynchus mykiss) exposed to waterborne diclofenac. At the highest exposure concentration (81.5 µg/L) the fish plasma concentration reached approximately 88% of the human therapeutic levels (C(max) ) after two weeks. Using an oligonucleotide microarray followed by quantitative PCR we found extensive effects on hepatic gene expression at this concentration, and some genes were found to be regulated down to the lowest concentration tested (1.6 µg/L) corresponding to approximately 1.5% of the human C(max) . Thus, at concentrations detected in European surface waters, diclofenac can affect the expression of multiple genes in exposed fish. Functional analysis of differentially expressed genes revealed effects on biological processes such as inflammation and immune response, in agreement with the mode of action of diclofenac in mammals. In contrast to some previously reported results, the bioconcentration factor was found to be stable (4.02 ± 0.75 for blood plasma and 2.54 ± 0.36 for liver) regardless of the water concentration. Environ. Toxicol. Chem. © 2011 SETAC.
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9.
  • Jonsson, Bertil, et al. (creator_code:aut_t)
  • Development of Whiplash associated Disorders for adult and child occupants in cars launched since the 1980s in different impact directions
  • 2011
  • record:In_t: 2011 IRCOBI Conference Proceedings - International Research Council on the Biomechanics of Injury (;Krakow;14 -16 September 2011). - : International Research Council on the Biomechanics of Injury. ; , s. 62-72, s. 62-72
  • swepub:Mat_conferencepaper_t (swepub:level_scientificother_t)abstract
    • Studies have shown that crashworthiness of cars addressing fatal and serious injuries has generally improved over time. However, the development regarding injuries leading to medical impairment has not been shown to the same extent. The objective was to investigate the development of Whiplash associated Disorders (WAD) leading to long-term consequences for adult front seat occupants and for children 0-12 years of age in cars introduced at different year intervals and in different impact directions separated for gender. Long-term consequences were defined as occupants with WAD symptoms at least one month and those resulting in medical impairment. The developments were studied for cars divided into intervals according to year of introduction and for frontal, side and rear-end impacts. All adult occupants (35 611) and 76% of all children (973) reporting WAD between 1998 and 2008 were selected. Approximately 2% of the children reporting initial symptoms sustained medical impairment. The corresponding figure for adult occupants was approximately 10%. Between the introduction years 1980-84 and 2000-04 the proportions of adult occupants with medical impairment dropped by approximately 70% (both males and females) in frontal and rear-end crashes, while the reduction in lateral impacts appears to be somewhat lower. For children there is a tendency that the proportion of WAD increases in newer models in frontal collisions. The result indicates that protecting children facing forward deserves more attention from the automotive industry and governmental bodies.
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10.
  • Kassman, Håkan, 1962, et al. (creator_code:aut_t)
  • Measures to reduce chlorine in deposits: Application in a large-scale circulating fluidised bed boiler firing biomass
  • 2011
  • record:In_t: Fuel. - Amsterdam : Elsevier BV. - 0016-2361 .- 1873-7153. ; 90:4, s. 1325-1334
  • swepub:Mat_article_t (swepub:level_refereed_t)abstract
    • Combustion of biomass with a high content of alkali (mainly potassium, K) and chlorine (Cl) can result in operational problems including deposit formation and superheater corrosion. Among the measures applied to decrease such problems are co-combustion and the use of additives. The positive effects of these measures are to a large extent either sulphation of the alkali chlorides (KCl) to less corrosive alkali sulphates or capture of alkali from KCl during release of HCl. A test campaign was carried out in a large-scale circulating fluidised boiler fired with biomass where the measures applied were sulphation by ammonium sulphate and co-combustion with peat. Their performance was evaluated by means of several advanced measurement tools including: IACM (on-line measurements of gaseous KCl); a low-pressure impactor (size distribution and chemical composition of extracted fly ash particles) and deposit measurements (chemical composition in collected deposits). The overall performance was better for ammonium sulphate, which significantly lowered KCl in the flue gas. Meanwhile no chlorine was found in the deposits. Only a minor reduction of gaseous KCl was obtained during co-combustion with peat although the chlorine content in the deposits was greatly reduced. These findings were supported by the results from the impactor measurements. (C) 2010 Elsevier Ltd. All rights reserved.
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