| 1. |
- Akkerman, V., et al.
(författare)
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Analysis of flame acceleration induced by wall friction in open tubes
- 2010
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Ingår i: Physics of Fluids. - : AIP Publishing. - 1070-6631 .- 1089-7666. ; 22:5, s. 1-14
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Tidskriftsartikel (refereegranskat)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. |
- Andersson, Mats, 1957, et al.
(författare)
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Explicit representation of membership of polynomial ideals
- 2011
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Ingår i: Mathematische Annalen. - : Springer Science and Business Media LLC. - 0025-5831 .- 1432-1807. ; 349:2, s. 345-365
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Tidskriftsartikel (refereegranskat)abstract
- We introduce a new division formula on projective space which provides explicit solutions to various polynomial division problems with sharp degree estimates. We consider simple examples as the classical Macaulay theorem as well as a quite recent result by Hickel, related to the effective Nullstellensatz. We also obtain a related result that generalizes Max Noether's classical AF + BG theorem.
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| 3. |
- Berge, John, 1979, et al.
(författare)
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Design considerations for tunable bulk acoustic wave resonators based on paraelectric phase BaxSr1-xTiO3 thin films
- 2010
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Ingår i: 19th International Symposium on the Applications of Ferroelectrics.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 4. |
- Berge, John, 1979, et al.
(författare)
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The effect of Bragg reflectors on the electromechanical performance of parallel-plate ferroelectric capacitors
- 2010
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Ingår i: 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-
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Konferensbidrag (refereegranskat)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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| 5. |
- Berge, John, et al.
(författare)
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Tunable bulk acoustic wave resonators based on Ba0.25Sr0.75TiO3 thin films and a HfO2/SiO2 Bragg reflector
- 2011
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - 0885-3010 .- 1525-8955. ; 58:12, s. 2768-2771
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Tidskriftsartikel (refereegranskat)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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| 6. |
- Berge, Maria, 1979
(författare)
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Group work and physics – characteristics, learning possibilities and patterns of interaction
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 7. |
- Cohen, David, et al.
(författare)
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Geometric finite difference schemes for the generalized hyperelastic-rod wave equation
- 2011
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Ingår i: Journal of Computational and Applied Mathematics. - : Elsevier BV. - 0377-0427 .- 1879-1778. ; 235:8, s. 1925-1940
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Tidskriftsartikel (refereegranskat)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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| 8. |
- Cohen, David, et al.
(författare)
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Linear energy-preserving integrators for Poisson systems
- 2011
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Ingår i: BIT Numerical Mathematics. - : Springer Science and Business Media LLC. - 0006-3835 .- 1572-9125. ; 51:1, s. 91-101
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Cronie, Ottmar, 1979, et al.
(författare)
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Some edge correction methods for marked spatio-temporal point process models
- 2011
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Ingår i: Computational Statistics & Data Analysis. - : Elsevier BV. - 0167-9473 .- 1872-7352. ; 55:7, s. 2209-2220
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Tidskriftsartikel (refereegranskat)abstract
- Three edge correction methods for (marked) spatio-temporal point processes are proposed. They are all based on the idea of placing an approximated expected behaviour of the process at hand (simulated realisations) outside the study region which interacts with the data during the estimation. These methods are applied to the so-called growth-interaction model. The specific choices of growth function and interaction function made are purely motivated by the forestry applications considered. The parameters of the growth and interaction functions, i.e. the parameters related to the development of the marks, are estimated using the least-squares approach together with the proposed edge corrections. Finally, the edge corrected estimation methods are applied to a data set of Swedish Scots pine.
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| 10. |
- Cuklev, Filip, 1981, et al.
(författare)
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Diclofenac in fish : blood plasma levels similar to human therapeutic levels affect global hepatic gene expression
- 2011
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Ingår i: Environmental Toxicology and Chemistry. - New York : Pergamon. - 0730-7268 .- 1552-8618. ; 30:9, s. 2126-2134
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Tidskriftsartikel (refereegranskat)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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