| 1. |
- Dreifaldt, Mats, 1959-
(författare)
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Conduits in coronary artery bypass grafting surgery : Saphenous vein, radial and internal thoracic arteries
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A novel technique for saphenous vein (SV) graft harvesting, the No-touch technique (NT), has been developed at the Dept. of Cardiovascular surgery, Örebro University hospital. With NT the SV is harvested with a pedicle of surrounding tissue. This avoids graft spasm and eliminates the need for distension. The surrounding tissue acts as a structural support and is a rich source of vaso-dilating agents. A randomized controlled trial (RCT) has shown a significantly higher patency rate for NT SV grafts compared to SV grafts harvested with conventional technique (CT). This thesis evaluates some of the properties of the surrounding tissue and compares patency rates between NT SV and radial artery (RA) grafts and patency rates for internal thoracic artery (ITA) grafts harvested with and without surrounding tissue. Paper I investigated vasa vasorum (VV) in SV grafts and showed that the NT preserves an intact VV whereas CT does not. This could be one of the mechanisms underlying the improved patency for NT SV grafts. Paper II evaluated VV and associated nitric oxide (NO) in SV and arterial grafts. SV grafts showed a higher number and larger VV, which correlated with NO production, compared to arterial grafts. NT SV grafts showed higher activity for e-NOS compared to CT SV grafts. Paper III is a RCT comparing patency rates between NT SV and RA grafts, three years after surgery, showing a significantly higher patency rate for NT SV grafts. Paper IV is a RCT comparing patency rates for ITA graft harvested with and without surrounding tissue and did not show any difference between graft preparations. In conclusion, the NT for SV graft harvesting preserves an intact vasa vasorum and associated NO production. NT SV grafts show a higher patency rate than RA grafts. Harvesting of ITA with or without surrounding tissue does not affect patency rate.
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| 2. |
- Hamdan, Mohammed, 1978-
(författare)
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Effects of temperature and terrestrial carbon on primary production in lake ecosystems
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Climate warming is predicted to affect northern lake food webs in two ways: (1)directly via changes in water temperature and ice conditions, and (2) indirectlyvia changes in catchment characteristics and processes that influence input ofallochthonous coloured dissolved organic matter (cDOM) and nutrients. Input ofcDOM increases carbon dioxide (CO2) availability, causes brownification andreduced light conditions, and may increase nutrient availability especially forpelagic primary producers. Increased water temperature and light penetrationand longer ice-free periods affect metabolic rates. These changes are expected toinfluence gross primary production (GPP) and growth of higher trophic levels.However, majority of studies focus on pelagic processes and net effects at wholelake scale is not well understood. Consequently, the lack of knowledge of whatfactors control benthic GPP makes predictions of net effects of climate change onwhole-ecosystem GPP spurious. The aim of this thesis was to experimentally testeffects of warming and increased input of allochthonous cDOM on habitatspecific and whole-ecosystem GPP in lakes. First, by manipulating the CO2concentrations in large scale pond ecosystems, we showed that increased CO2stimulated whole-ecosystem GPP. In a separate incubation study with naturallake sediments in a boreal lake, we tested the role of CO2 as a limiting factor forbenthic GPP under different light levels. The results showed that CO2 supplystimulated benthic GPP at high but not at low light availability, suggesting thatbenthic GPP can be CO2-limited. In the same experimental pond ecosystems, thecombined effect of increased allochthonous cDOM and warming (+3.5°C) on GPPwas studied. The results showed that cDOM input decreases whole-ecosystemGPP, mainly as a result of decreased benthic GPP due to light limitation not fullycounteracted by an increase in pelagic GPP under ambient conditions. Warmingon the other caused a hump shaped increase in whole-ecosystem GPP withincreasing cDOM input mainly due to a positive response in pelagic GPP due torelaxed nutrient limitation. Finally, by manipulating the fish consumer biomassin the same experimental pond ecosystems we showed that whole-ecosystem GPPcan be controlled by top-down effects under warm (+ 3.0°C) but not ambienttemperature conditions. The decline in whole-ecosystem GPP was mainlyattributed to a warming-stimulated consumer-driven trophic cascade in thepelagic habitat and top-down control by zooplankton on phytoplankton growth,while no corresponding cascade was evident in the benthic habitat.Taken together, the results suggest that climate change impacts, as increasinginputs of cDOM, warming and changes in food webs, have different effects onhabitat specific GPP and alone or in combination have impacts on whole-lakeGPP. This thesis offers important insights to better understand the factors thatcontrol lake GPP and to predict future lake ecosystem responses to environmentalchange.
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| 3. |
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| 4. |
- Karlsson, Hyunjoo Kim
(författare)
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Dynamics of macroeconomic and financial variables in different time horizons
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation consists of an introductory chapter and four papers dealing with financial issues of open economies, which can be in two broad categorizations: 1) exchange rate movements and 2) stock market interdependence. The first paper covers how the exchange rate changes affect the prices of internationally traded goods. With the variables (the price of exports in exporters’ currency and the exchange rate, both of which are in logarithmic form) being cointegrated, a model with both long- and short-run characteristics (the Error Correction Model, ECM) is formulated.The second paper relates to the standard macroeconomic models of exchange rate determination. This paper investigates the relationship between the exchange rate and the domestic-foreign interest rate differential.A relevant issue associated with the relationship between export prices and exchange rates for different industries is found in the third paper. The responsiveness of firms’ profitability to changes in exchange rates (i.e. exchange rate exposure) is tested using a factor model.After the three papers noted above, the dissertation moves on to the final paper which explores the relationship between national stock markets (i.e. interdependence). The causal linkages of the U.S. stock market to each of six eastern Asian national stock markets (China, Hong Kong, Japan, Singapore, South Korea and Taiwan) as well as the causal linkages among those Asian equity markets are tested in a vector autoregression (VAR) model using wavelet-decomposed data.
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| 5. |
- Karlsson, Håkan K R
(författare)
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Insulin signaling and glucose transport in insulin resistant human skeletal muscle
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Insulin resistance in skeletal muscle is a hallmark feature of Type 2 diabetes mellitus. The overall aim of this thesis was to investigate downstream intermediates in the insulin signaling pathway in an attempt to characterize the molecular mechanism of skeletal muscle insulin resistance in Type 2 diabetes. Skeletal muscle biopsies were obtained from healthy and Type 2 diabetic subjects before and after an in vivo hyperinsulinemic infusion. Insulin infusion increased the phosphorylation of several proteins reacting with a phospho-Akt substrate antibody. We focused on AS160, as this Akt substrate has been linked to glucose transport. A phosphorylated protein of 160 kDa was identified as AS160 using an AS160-specific antibody. Insulin-stimulated AS160 phosphorylation was reduced in Type 2 diabetic patients, whereas AS160 protein expression was similar between Type 2 diabetic and control subjects. Impaired AS160 phosphorylation was related to a reduction in Akt Thr308-phosphorylation. To investigate whether pharmaceutical treatment improves glucose uptake due to enhanced insulin signaling in skeletal muscle, biopsies were obtained during a euglycemic hyperinsulinemic clamp from newly diagnosed Type 2 diabetic subjects before and after 26 weeks of metformin, rosiglitazone or placebo treatment. Insulin-mediated whole body and leg muscle glucose uptake was enhanced 36% and 32%, respectively, after rosiglitazone, but not after metformin or placebo treatment. Insulin-stimulated IRS-1 Tyr-phosphorylation, IRS-1 associated PI 3-kinse activity, Akt Ser473-phosphorylation, and AS160 phosphorylation were assessed. Gene expression of several targets involved in lipid and glucose metabolism was also determined. Insulin signaling parameters and gene expression were unaltered after metformin or rosiglitazone treatment, despite the improvement in glucose uptake. Since an altered metabolic milieu may secondarily cause insulin resistance in Type 2 diabetic subjects, we studied a cohort of healthy glucose tolerant first-degree relatives of Type 2 diabetic patients to determine whether early metabolic and molecular defects contribute to insulin resistance in skeletal muscle. Skeletal muscle from first-degree relatives and control subjects were incubated in vitro in the absence or presence of increasing concentrations of insulin. Glucose transport, AS160 phosphorylation, and GLUT4 expression were assessed. Insulin-stimulated glucose transport rate at a maximal insulin concentration tended to be reduced in skeletal muscle from first-degree relatives. Insulin increased AS160 phosphorylation in a dose-dependent manner, with no difference between first-degree relatives and control subjects. A tight correlation was observed between insulin action on AS160 and glucose transport in control subjects, whereas a weak correlation was observed in first-degree relatives. Tanis, a recently described putative receptor for serum amyloid A, has been implicated in inflammatory responses. We determined mRNA expression of the human homologue of Tanis, SelS/AD-015 in skeletal muscle and adipose tissue biopsies obtained from Type 2 diabetic patients and healthy subjects. Expression of Tanis/SelS mRNA in skeletal muscle and adipose tissue biopsies was similar between Type 2 diabetic and control subjects. Adipose tissue Tanis/SelS mRNA expression was unchanged after insulin infusion in control subjects, whereas Tanis/SelS mRNA increased following insulin stimulation in Type 2 diabetic subjects. Skeletal muscle and adipose tissue Tanis/SelS mRNA expression were positively correlated with plasma serum amyloid A. In summary, defects in insulin action on AS160 may impair GLUT4 trafficking in Type 2 diabetes. Further, insulin-sensitizing effects of rosiglitazone are independent of enhanced insulin signaling of the IRS-1/PI 3-kinase/Akt/AS160 pathway in Type 2 diabetes, suggesting that improvements might be achieved at distal events at the level of GLUT4 translocation. In addition, healthy first-degree relatives of Type 2 diabetic subjects have a tendency of impaired glucose transport at a super-physiological insulin concentration, despite a normal insulin action on AS160, implicating early insulin signaling defects are likely to be a consequence of an altered metabolic milieu. Moreover, the positive correlation of Tanis/SelS mRNA expression and serum amyloid A suggests a potential interaction between immune system responses and Tanis/SelS expression in muscle and adipose tissue. In conclusion, future strategies designed to treat insulin resistance in human skeletal muscle may target multiple sites along insulin signaling and GLUT4 pathways depending on the progression of the disease.
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| 6. |
- Karlsson, Mikael, 1970-
(författare)
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Micro-Optical Elements in Gallium Arsenide and Diamond: Fabrication and Applications
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis mainly treats the fabrication and applications of micro-optical elements in the semiconductor materials gallium arsenide (GaAs) and diamond.The recent trend in high-capacity data transfer using light as the information carrier creates new demands on the optoelectronic systems, such as small size, low cost and the integration of many components. Micro-optical components are key elements for building compact optoelectronic systems and are well suited for integration with other devices. Another area where micro-optical elements can play an important role is the use of lasers in medicine, industrial machining, metrology, etc. In most cases, the laser beam characteristic is not directly suited for the application and external optics is needed to focus, shape or split the laser beam.In the first part of this thesis, the fabrication of continuous-relief diffractive optical elements, such as diffractive lenses and blazed gratings, in GaAs is examined. The manufacturing technology uses electron-beam lithography followed by plasma etching in an inductively coupled plasma etching system. In the next step, these diffractive elements were monolithically integrated with vertical-cavity surface-emitting lasers.In the second part of this thesis a novel topic is examined, diamond micro-optics. Diamond is a unique material in many aspects, it is the hardest material mankind knows, it has an extremely wide optical transmission window, and it possesses the highest thermal conductivity of all solids. Until today, due to difficulties in machining diamond, the realization of diamond optics has been limited. By using the same technology we earlier developed for the fabrication of GaAs optics we demonstrate for the first time continuous-relief structures in diamond of optical quality. Several diamond micro-optical structures are presented; sub-wavelength gratings for reduction of unwanted Fresnel reflections, diffractive fan-out elements used to split a CO2-laser beam and refractive microlens arrays.The accuracy of the fabrication process by plasma etching was evaluated by optical and topographical measurements, in all cases the optical components were of very high quality.
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| 7. |
- Karlsson, Mikael R., 1964
(författare)
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Skolförändring, reformer och professionella villkor - en etnografisk studie
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This is a dissertation primarily built on ethnographic methodology. It examines how teachers and principals react to and handle change. The overall aim of the study is to investigate how general and specific changes have influenced the organization of power and relationships in the institutional practice of secondary schools, and how teachers and principals react to and reason about the consequences of these changes. Specifically, the dissertation addresses four sub-questions: How do teachers driving a local change process handle criticism and resistance from their colleagues? How does the implementation of a career reform affect the school's administrative logic and teachers' influence over the institutional practice? How does the implementation of a reform aimed at rewarding particularly skilled teachers affect the school's administrative logic and teachers' professional identity? How do larger societal changes in the welfare sector over the past three decades manifest in value changes in local school practices? The findings connect the reactions that arise and the strategies formulated at the micro-level to the transformation of Swedish welfare society in general and the education system in particular over the past three decades.
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| 8. |
- Karlsson, Peter R., 1963
(författare)
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Direct Extraction of MOS Transistor Current Model Parameters
- 1994
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a study of MOS transistor model parameter extraction. The objective of this study was to develop an efficient, accurate, robust extraction strategy which determines physically reasonable parameter values. The direct parameter extraction approach was chosen to meet these requirements. The basic idea in this approach is to determine the parameters from a small number of data points using analytical expressions. Ideally, only one data point is needed for each parameter. The parameters are determined sequentially in the region of operation where they have their most significant influence on the model characteristics. All interactions between parameters are taken into account during a subsequent iterative improvement procedure. Direct extraction algorithms for two popular and commonly used SPICE MOS transistor models, level 3 (MOS3) and level 4 (BSIM), are proposed. For the MOS3 and the BSIM models, all current parameters are extracted from 15 and 25 data points, respectively. Even if only a small number of data points are used, good agreement between measured and simulated device characteristics is obtained for both models. The influence of measurement noise on the data points taken in the linear region was studied using sensitivity analysis. The model accuracy was investigated through repeated extraction in the linear region using different combinations of data points. These two studies resulted in a recommendation for the selection of data points. A method of extracting the series resistance and series resistance independent model parameters for MOS3 is presented. During the experimental verification of this method different external resistors were connected to the transistors. When extracting transistor parameters according to the model, which did not include the series resistance explicitly, the values of three of the parameters were found to depend strongly on the connected external resistors. These were the mobility reduction factor due to the transverse electric field, the maximum drift velocity, and the saturation field factor. These results are in good agreement with results obtained from extractions using synthetic data as input to the extraction algorithm. From the simulations it was also found that the static feedback factor depends weakly on the series resistance but this was never confirmed experimentally. When the series resistance was included in the model, constant parameter values were obtained which were independent of the connected external resistors. A novel linear region four-point technique was developed for extraction of the threshold voltage, the gain, and the first and second order mobility reduction factors due to the transverse electric field for the BSIM2 transistor model developed for submicron transistors. This method shows that direct extraction is not limited by the transistor model. Instead, the strategy adopted in this study is applicable for a number of different models. This study also emphasises the similarity between direct extraction and least square fitting of the parameters and shows that least square fitting is a natural extension of direct extraction: similar analytical techniques are used to determine the parameters in both cases. An extraction algorithm based on least square fitting techniques which can be used for extracting the linear region parameters as well as the effective geometries is suggested. This algorithm together with algorithms for the saturation and subthreshold regions comprise a complete extraction scheme based on least square fitting techniques for the BSIM transistor model. Finally, a novel interpretation of the channel width dependence of the mobility reduction factor due to the transverse electric field is proposed. The electrical broadening of the channel is shown to have a similar influence on the drain current as the mobility reduction factor. A method for separating these two effects is presented.
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