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- Ravn, Hans, 1958-
(författare)
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Popliteal Artery Aneurysm : Epidemiology, Surgical Management and Outcome
- 2007
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Even if popliteal artery aneurysm (PAA) is the most common peripheral aneurysm, no single surgeon or institution has enough patients to study this disease with appropriate scientific methods, and no population-based investigation exists. PAA epidemiology, treatment, management, and outcome were studied in a population-based study of 571 patients (717 legs) primarily operated on for PAAs and 100 episodes of preoperative thrombolysis in Sweden between 1987 and 2002. Patients were identified in the Swedish Vascular Registry and case-records were reviewed. Information on amputation and survival was obtained for all patients, and 190 patients were re-examined with ultrasound, after mean 7.2 years (range 2-18)Median age was 71 years; 5.8% were women. Patients with unilateral PAA had AAA in 28%, increasing to 38% when PAAs were bilateral. Crude survival was 91.4% at one and 70% at five years, significantly lower than among age and sex matched controls. The cumulative incidence for operation of PAA in Sweden was estimated to 8.3/million person year. One-year amputation-rate was 8.8 %, increasing to 11% after follow-up (7.2 years). Independent risk factors for amputation within one year were poor run-off, age, emergency procedure, and prosthetic graft. Run-off was improved by preoperative thrombolysis among 87% of legs, when acute ischemia. After surgical repair with a medial approach the risk of late expansion of the aneurysm was 33%, with a posterior approach 8% , p=0.014. Among 190 re-examined patients, 108 (57%) had at least one additional aneurysm at index-operation, increasing to 131 (68%) at re-examination, the total number of aneurysms increasing by 42% (from 244 to 346).Conclusions: Multiple aneurysms are common among patients operated on for PAA. Preoperative thrombolysis improves run-off and decreases the amputation-rate in PAAs with acute ischemia. Vein grafts do better than prosthetic grafts, especially when a long bypass is needed. Posterior approach, when possible, reduces the risk of late expansion. A complete examination of the aorto-iliac and femoro-popliteal arteries is warranted at the time of surgery. All patients should be kept under life-long surveillance in order to detect and treat newly developed aneurysms timely. Normal arterial segments should be re-examined after three years.
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| 2. |
- Ribca, Iuliana, 1993-
(författare)
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Lignin-Based Thermosets with Tunable Mechanical and Morphological Properties : A Study of Structure-Property Relationships
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nowadays, there is an urgent need to decrease our dependence on fossilresources and shift towards the use of renewable resources for advancingsustainable development. Utilizing renewable and bio-based raw materials,such as lignocellulosic biomass, for designing new materials is a promisingapproach to promote this objective. The main components of lignocellulosicbiomass are cellulose, hemicellulose, and lignin. Lignin is the most abundantaromatic biopolymer in nature and it is produced on a large scale fromchemical pulping processes as technical lignin. Lignin has the potential as asustainable and renewable alternative to fossil-based aromatics in variousapplications, e.g. thermosetting resins.Technical lignin has a complex and heterogeneous structure, with arelatively low chemical reactivity. It is characterized by a high dispersity, thepresence of various functional groups that are unevenly distributed along thelignin chains, and various interunit linkages between the monoaromatics. Toovercome the challenges associated with lignin heterogeneity, technicallignin can be fractionated and/or chemically modified.In this work, LignoBoost Kraft lignin was used as a starting material toproduce lignin-based thiol-ene thermosets. Firstly, lignin was fractionatedusing two approaches: 1) sequential solvent fractionation, and 2) microwaveassistedextraction. These fractionation approaches enabled access to ligninfractions with unique and tunable properties. Subsequently, lignin waschemically modified, in particular through allylation. Two allylation reagentswere used: allyl chloride and diallyl carbonate. The use of allyl chlorideenables a selective allylation of the phenolic OH groups, leaving the aliphaticand carboxylic acid OH groups unmodified. On the other hand, diallylcarbonate can react with all the aforementioned OH groups, leading to ahigher degree of allylation. Subsequently, allylated lignin was thermallycross-linked with various polyfunctional thiols, leading to thiol-enethermosets. The structure-property relationships of the thermosets wereinvestigated by varying several parameters, including the lignin source,fractionation approach, chemical modification, and thiol cross-linker. Byadjusting these parameters, various thermosets with tunable mechanical andmorphological properties were produced. Understanding the structurepropertyrelationships of these bio-based materials is crucial for identifyingpotential applications.
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| 3. |
- Strömgren, Tobias, 1978-
(författare)
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Model predictions of turbulent gas-particle shear flows
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A turbulent two-phase flow model using kinetic theory of granularflows for the particle phase is developed and implmented in afinite element code. The model can be used for engineeringapplications. However, in this thesis it is used to investigateturbulent gas-particle flows through numerical simulations. The feedback from the particles on the turbulence and the meanflow of the gas in a vertical channel flow is studied. In particular,the influence of the particle response time, particle volumefraction and particle diameter on the preferential concentration ofthe particles near the walls, caused by the turbophoretic effect isexplored. The study shows that when particle feedback is includedthe accumulation of particles near the walls decreases. It is also foundthat even at low volume fractions particles can have a significant impacton the turbulence and the mean flow of the gas. The effect of particles on a developing turbulent vertical upward pipeflow is also studied. The development length is found to substantiallyincrease compared to an unladen flow. To understand what governs thedevelopment length a simple estimation was derived, showing that itincreases with decreasing particle diameters in accordance with themodel simulations. A model for the fluctuating particle velocity in turbulentgas-particle flow is derived using a set of stochastic differentialequations taking into account particle-particle collisions. Themodel shows that the particle fluctuating velocity increases whenparticle-particle collisions become more important and that increasingparticle response times reduces the fluctuating velocity. The modelcan also be used for an expansion of the deterministic model for theparticle kinetic energy.
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