| 1. |
- Andersson, Anders, et al.
(författare)
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Acoustic Transmission in Ducts of Various Shapes with an Impedance Condition
- 2008
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Ingår i: International Conference on Numerical Analysis and Applied Mathematics 2008. - Melville : AIP, Melville, USA. - 9780735405769 ; , s. 33-36
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Konferensbidrag (refereegranskat)abstract
- Propagation of acoustic waves in a two-dimensional duct with an impedance condition at the boundary, is studied. The duct is assumed to have two ends at infinity being asymptotically straight, but otherwise to be arbitrarily shaped.The so called Building Block Method allows us to synthesize propagation properties for ducts with complicated geometries from results for simpler ducts. Conformal mappings can be used to transform these simple ducts to straight ducts with constant cross-sections.By using recently developed techniques for numerical conformal mappings, it is possible to construct a transformation between an infinite strip and an arbitrarily shaped duct with smooth or piecewise smooth boundary, keeping both smoothness and the well controlled boundary direction towards infinity that the above mentioned method requires.To accomplish a stable formulation of the problem, we express it in terms of scattering operators. The resulting differential equation is solved using wave splitting and invariant embedding techniques. We expand the involved functions in Fourier series, and hence, it is possible to give the operators a matrix representation. Numerical results are produced using truncated matrices.
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| 2. |
- Andersson, Anders, 1957-, et al.
(författare)
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Electro-Magnetic Scattering in Variously Shaped Waveguides with an Impedance Condition
- 2009
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Ingår i: AIP Conference Proceedings: Third Conference on Mathematical Modeling of Wave Phenomena. - Melville, New York : American Institute of Physics. - 9780735406438 ; , s. 36-45
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Konferensbidrag (refereegranskat)abstract
- Electro-magnetic scattering is studied in a waveguide with varying shape and crosssection. Furthermore, an impedance or admittance condition is applied to two of the waveguide walls. Under the condition that variations in geometry or impedance take place in only one plane at the time, the problem can be solved as a two-dimensional wave-scattering problems. By using newly developed numerical conformal mapping techniques, the problem is transformedinto a wave-scattering problem in a straight two-dimensional channel. A numerically stable formulation is reached in terms of transmission and reflection operators. Numerical results are given for a slowly varying waveguide with a bend and for one more complex geometry.
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| 3. |
- Andersson, Anders, 1957-
(författare)
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Numerical Conformal mappings for regions Bounded by Smooth Curves
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Inom många tillämpningar används konforma avbildningar för att transformera tvådimensionella områden till områden med enklare utseende. Ett exempel på ett sådant område är en kanal av varierande tjocklek begränsad av en kontinuerligt deriverbar kurva. I de tillämpningar som har motiverat detta arbete, är det viktigt att dessa egenskaper bevaras i det område en approximativ konform avbildning producerar, men det är också viktigt att begränsningskurvans riktning kan kontrolleras, särkilt i kanalens båda ändar. Denna avhandling behandlar tre olika metoder för att numeriskt konstruera konforma avbildningar mellan ett enkelt standardområde, företrädesvis det övre halvplanet eller enhetscirkeln, och ett område begränsat av en kontinuerligt deriverbar kurva, där begränsningskurvans riktning kan kontrolleras, exakt eller approximativt. Den första metoden är en utveckling av en idé, först beskriven av Peter Henrici, där en modifierad Schwarz-Christoffel-avbildning avbildar det övre halvplanet konformt på en polygon med rundade hörn. Med utgångspunkt i denna idé skapas en algoritm för att konstruera avbildningar på godtyckliga områden med släta randkurvor. Den andra metoden bygger också den på Schwarz-Christoffel-avbildningen, och utnyttjar det faktum att om enhetscirkeln eller halvplanet avbildas på en polygon kommer ett område Q i det inre av dessa, som till exempel en cirkel med centrum i origo och radie mindre än 1, eller ett område i övre halvplanet begränsat av två strålar, att avbildas på ett område R i det inre av polygonen begränsat av en slät kurva. Vi utvecklar en metod för att hitta ett polygonalt område P, utanför det Omega som man önskar att skapa en avbildning för, sådant att den Schwarz-Christoffel-avbildning som avbildar enhetscirkeln eller halvplanet på P, avbildar Q på Omega. I båda dessa fall används tangentpolygoner för att numeriskt bestämma den önskade avbildningen. Slutligen beskrivs en metod där en av Don Marshalls så kallade zipper-algoritmer används för att skapa en avbildning mellan det övre halvplanet och en godtycklig kanal, begränsad av släta kurvor, som i båda ändar går mot oändligheten som räta parallella linjer.
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| 4. |
- Andersson, Anders, 1957-
(författare)
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Numerical Conformal Mappings for Waveguides
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Acoustic or electro-magnetic scattering in a waveguide with varying direction and cross-section can be re-formulated as a two-dimensional scattering problem, provided that the variations take place in only one dimension at a time. By using the so-called Building Block Method, it is possible to construct the scattering properties of a combination of scatterers when the properties of each scatterer are known. Hence, variations in the waveguide geometry or in the boundary conditions can be treated one at a time. Using the Building Block Method, the problem takes the form of the Helmholtz equation for stationary waves in a waveguide of infinite length and with smoothly varying geometry and boundary conditions. A conformal mapping is used to transform the problem into a corresponding problem in a straight horizontal waveguide, and by expanding the field in Fourier trigonometric series, the problem can be reformulated as an infinite-dimensional ordinary differential equation. From this, numerically solvable differential equations for the reflection and transmission operators are derived. To be applicable in the Building Block Method, the numerical conformal mapping must be constructed such that the direction of the boundary curve can be controlled. At the channel ends ,it is an indispensable requirement, that the two boundary curves are (at least) asymptotically parallel and straight. Furthermore, to achieve bounded operators in the differential equations, the boundary curves must satisfy different regularity conditions, depending on the boundary conditions. In this work, several methods to accomplish such conformal mappings are presented. The Schwarz–Christoffel mapping, which is a natural starting point and for which also efficient numerical software exists, can be modified in different ways in order to achieve polygons with rounded corners. We present algorithms by which the parameters in the mappings can be determined after such modifications. We show also how the unmodified Schwarz–Christoffel mapping can be used for regions with a smooth boundary. This is done by constructing an appropriate outer polygon to the considered region.Finally, we introduce one method that is not Schwarz–Christoffel-related, by showing how one of the so-called zipper algorithms can be used for waveguides. Keywords: waveguides, building block method, numerical conformalmappings, Schwarz–Christoffel mapping, rounded corners method, approximate curve factors, outer polygon method, boundary curvature, zipper method, geodesic algorithm, acoustic wave scattering, electro-magnetic wave scattering
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| 5. |
- Andersson, Maria, 1976, et al.
(författare)
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Mild renal ischemia-reperfusion reduces charge and size selectivity of the glomerular barrier
- 2007
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Ingår i: American Journal of Physiology Renal Physiology. - : American Physiological Society. - 0363-6127 .- 1931-857X .- 1522-1466. ; 292:6
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Tidskriftsartikel (refereegranskat)abstract
- Despite recent discoveries of molecules in podocytes, the mechanisms behind most conditions of proteinuria are still poorly understood. To understand more about this delicate barrier, we studied the functional and morphological effects of mild (15 min) renal ischemia-reperfusion injury (IRI). Renal function was studied in rats in vivo, followed by a more detailed analysis of the glomerular barrier in cooled (8 degrees C) isolated perfused kidneys (cIPK). Renal blood flow was quickly restored, whereas the glomerular filtration rate remained halved 30 min after IRI. Tubular cell activity was intact as judged from the unaffected Cr-EDTA U/P concentration ratio. In vivo, the fractional clearance (theta) for albumin increased 16 times. In rats subjected to cIPK starting 30 min after in vivo IRI, theta(albumin) was 15 times and theta(Ficoll_36angstroms) 1.8 times higher than in control cIPKs. According to the heterogeneous charged fiber model, IRI reduced the fiber charge density to 38% of control (P < 0.01, n = 7). Morphometric analysis with electron microscopy did not reveal any changes in the podocytes or the glomerular basement membrane (GBM) after IRI, suggesting more subtle changes of the GBM and/or the endothelial glycocalyx. We conclude that mild renal IRI induces formation of reactive oxygen species, massive proteinuria, and loss of charged fibers with no apparent change in morphology. These novel findings stress the importance of other components of the barrier, such as proteoglycans produced by the glomerular cells, and provide a tentative explanation for the mechanisms behind proteinuria in glomerulonephritis, for example.
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| 6. |
- Asekritova, Irina, et al.
(författare)
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Diffractive Index Determination by Tikhonov Regularization on Forced String Vibration Data
- 2009
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Ingår i: Mathematical modelling of wave phenomena. - Melville, New York : American Institute of Physics. ; , s. 224-232, s. 224-232
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Konferensbidrag (refereegranskat)abstract
- Wave analysis is efficient for investigating the interior of objects. Examples are ultra sound examination of humans and radar using elastic and electromagnetic waves. A common procedure is inverse scattering where both transmitters and receivers are located outside the object or on its boundary. A variant is when both transmitters and receivers are located on the scattering object. The canonical model is a finite inhomogeneous string driven by a harmonic point force. The inverse problem for the determination of the diffractive index of the string is studied. This study is a first step to the problem for the determination of the mechanical strength of wooden logs. An inverse scattering theory is formulated incorporating two regularizing strategies. The results of simulations using this theory show that the suggested method works quite well and that the regularization methods based on the couple of spaces (L2; H1 ) could be very useful in such problems.
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| 7. |
- Berglund, Mats, 1970-
(författare)
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Massans röst : Upplopp och gatubråk i Stockholm 1719–1848
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis examines riots and street violence in Stockholm between 1719 and 1848. By studying open conflicts, the thesis explores changes in societal power structures which otherwise are hidden. The study shows how these levels of power and conflict structures interacted with one another and thereby contributed to the social development during the period; from a patriarchal society of privilege to a society based on a democratic view of the world. The thesis focuses on three collective actors; the people, the authorities and the press.The investigation of the people in the crowds shows that the military element, as well as the lower strata of labourers and servants, was significant in the early events. However, in later phases, middle class groupings such as burghers and civil servants, dominated the masses. These changes in the social composition of the crowds are tightly connected to a similar change in the aims of the riots; from local issues to national policy matters.Tactics of the authorities in their encounter with street disturbances also changed during the period, from passive observation by the police in the 18th century to an active military confrontational approach in the 19th century. The legal base was however strong throughout the period. The parties attached great importance to court proceedings, and knowledge of the legal system was surprisingly good among the common people.During the second half of the period, the press became firmly established. At the turn of the century 1800, there were two short glimpses of free press in connection to the political turbulence in 1792 and 1809. But it was mainly from the 1830's that the newspaper editors became significant actors in the riots. The popular demands for international news and politics gradually grew stronger during the period. A bottom-up perspective thus shows that popular political involvement in a significant way helped to pave the way for the coming breakthrough of democracy.
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| 8. |
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| 9. |
- Biro, Thomas, et al.
(författare)
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Substrate Integrated Waveguide
- 2008
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Ingår i: Proceedings of RVK08/MMWP08, Växjö June 9-13, 2008. - : Växjö universitet. ; , s. 284-286
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A substrate integrated waveguide, SIW, is a waveguide that is integrated directly on a subtrate. These structeres has recently been developed for different applications. The simplest SIW design is a rectangular waveguide in a subtrate formed by metallization of the upper and lower surfaces of the substrate and by placing vertical metal vias periodically along two parallel lines. Different types of SIW are analyzed and simulated in this contribution. In particular wave propagation along an SIW is analyzed.
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| 10. |
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