| 1. |
- Zhang, Qi, 1995-
(författare)
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Ion escape from Mars
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When the solar wind reaches the Mars obstacle, mass loading by planetary ions slows down the solar wind and raises the bow shock. The Martian atmosphere is undergoing the a scavenging by the solar wind without the protection of a global magnetic field. Atmospheric escape is an important process for the evolution of the Martian climate. For present Mars, the dominant escape of atmospheric neutrals is through four channels: Jeans escape, photochemical reactions, sputtering and electron impact ionization. Ions above the exobase get accelerated by the solar wind electric field and can escape.We here apply a new method for estimating heavy ion (O+, O+2, and CO+2) escape rates at Mars, which combines a hybrid model and observations. We use observed upstream solar wind parameters as input for a hybrid plasma model, where the total ion upflux at the exobase is a free parameter. We then vary this ion upflux to find the best fit to the observed bow shock location. This method gives us a self-consistent description of the Mars-solar wind interaction, which can be used to study other properties of the solar wind interaction besides escape.
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| 2. |
- Nilsson, Maria, 1957-
(författare)
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Promoting health in adolescents : preventing the use of tobacco
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There is a robust evidence base for the negative health effects from smoking. Smoking is linked to severe morbidity and to mortality, and kills up to half of its regular users. Tobacco use and production also bring other negative consequences such as economic loss for countries, poverty for individuals, child labour, deforestation and other environmental problems in tobacco growing countries. A combination of comprehensive interventions at different levels is needed to curb the tobacco epidemic. Tobacco control strategies at national levels in the western world often include components of information/education, taxation, legislative measures and influencing public opinion. Two approaches have dominated at the meso and micro levels: cessation support for tobacco users and prevention activities to support young people refraining from tobacco use. Smoking uptake is a complex process that includes factors at the societal level as well as social and individual characteristics. At national level, taxation and legislation can contribute to a societal norm opposing tobacco and creating a context for primary prevention aimed at tobacco free youth. There is no magic bullet in primary prevention. At the meso and micro levels, a continued development of knowledge on the underlying mechanisms and primary prevention methods is essential to prevent young people from starting to use tobacco. The overall aim of this thesis was to gain knowledge about factors that influence young people’s use of tobacco and of preventive mechanisms. The specific aims included to study the relation between Tobacco Free Duo, an intervention program targeting youth in Västerbotten County, and tobacco use prevalence. A specific interest was to explore the role adults can play in supporting young people to refrain from tobacco use. The thesis is based on four studies with three separate sets of data, two were quantitative and one was qualitative. The studies were conducted among adolescents (aged 13-15 yr) in Västerbotten County and on national level in Sweden (aged 13, 15 and 17 yr). Tobacco Free Duo is a school-based community intervention that started in 1993. An essential component of the intervention was to involve adults in supporting adolescents to stay tobacco free. Results showed decreased smoking in adolescents among both boys and girls in the intervention area during the study period of seven years. There was no change in a national reference group during the same time period. A bonus effect was a decrease in adult tobacco use in the intervention area. One out of four adults who supported a young person taking part in the intervention stopped using tobacco. In a qualitative assessment of young smokers, starting to smoke was described as a means of gaining control of their feelings and their situation during early adolescence. They expected adults to intervene against their smoking and claimed that close relations with caring adults could be a reason for smoking less or trying to quit smoking. In a quantitative study that used three decades of national data, over time adolescents became more positive toward parental action on children’s smoking. The adolescents strongly supported the idea of parental action, regardless of whether or not they themselves smoked. Adolescents preferred that actions from parents were dissuading their children from smoking, not smoking themselves, and not allowing their children to smoke at home. These results suggest that the Tobacco Free Duo program contributed to a reduction in adolescent smoking among both boys and girls. Using a multi-faceted intervention that includes an adolescent-adult partnership can decrease adolescent smoking uptake. Engaging adults as partners in tobacco prevention interventions that target adolescents has an important tobacco reducing bonus effect in the adults. The intervention has proven sustainable within communities. A growing majority of adolescents support parental interventions to help them refrain from tobacco. The findings dismiss the notion that adolescents ignore or even disdain parental practices concerning tobacco. A common and consequent norm against tobacco from both schools and parents using a supportive attitude can prevent tobacco use in young people.
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| 3. |
- Olsson, Hans
(författare)
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Stage T1 Urinary Bladder Carcinoma : Investigation of A Population-Based Cohort
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Approximately 2 300 new cases of urinary bladder carcinoma (UBC) are diagnosed every year in Sweden. This type of cancer is characterized as a long-standing disease with a high risk of recurrence and progression from an indolent to a more aggressive course. UBC occurs in a non-muscle-invasive form (stages Ta and T1), which is treated mainly with local resection and BCG instillation, and a muscle-invasive form (stage ≥ T2), for which the treatment of choice is irradiation or cystectomy.The aim of the research underlying this thesis was to explore the factors involved in tumor development and progression, and to find prognostic markers for recurrence and progression in patients with primary stage T1 urothelial carcinoma of the bladder (UCB).Tumor tissue in archived paraffin blocks from patients diagnosed with that type of malignancy was used in the four studies that were conducted. This was a population-based project, because all of the patients had been reported to the cancer center in the Southeast Healthcare Region in Sweden from 1992 to 2001. The follow-up time was comparable long in the cases included and was intended to be at least 10 years.The hospital records were reviewed to gather information on clinical characteristics of the tumors, such as size and multiplicity, as well as treatment modalities, recurrence and/or progression, and eventual death from UBC. The original tumor slides were re-evaluated. These two initial activities yielded a study population comprising 211 well-characterized patients with primary T1 UCB. Some of the originally selected patients were excluded due to missing paraffin blocks or poor quality of the tumor material, the latter being particularly important in the genetic analyses conducted in the fourth study.Ordinary light microscopy was performed to evaluate specific tumor characteristics, such as lymphovascular tumor infiltration, and for T1 sub-staging. Immunohistochemistry was carried out to, among other things, analyze cell cycle regulators. Furthermore, pyrosequencing, single-strand conformation analysis (SSCA), and Sanger sequencing were conducted in the fourth study to assess mutations in the p53 gene and murine double minute 2 SNP309 promoter polymorphism. Statistical analyses to estimate the risk of tumor recurrence and progression were carried out in all four investigations.Conclusions: This population-based cohort of patients with well-characterized T1 tumors of the urinary bladder showed high rates of recurrence (80%) and progression (39%), and the aggressiveness is underlined by the fact that 32% died from the disease. Lymphovascular tumor infiltration and abnormal immunohistochemical staining for p16 were found to be associated with tumor progression, and in the future analysis of these parameters might be used in treatment decisions regarding T1 bladder tumors. No other clinical or pathological variable or cell cycle regulator was associated with progression, and none of the genetic analyses conducted in the current studies were helpful in predicting outcome or explaining the mechanisms of tumor development.
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| 4. |
- Eklund, Michael, 1988-, et al.
(författare)
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Effect of spironolactone on vascular stiffness in hemodialysis patients : a randomized crossover trial
- 2022
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Ingår i: Upsala Journal of Medical Sciences. - : Upsala Medical Society. - 0300-9734 .- 2000-1967. ; 127:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: The role of spironolactone treatment in hemodialysis patients is debated, but a survival benefit is suggested. Mineralocorticoids and chronic kidney disease have been linked to cardiovascular fibrosis. Therefore, we hypothesized that spironolactone would affect vascular stiffness, cardiac systolic, and diastolic function in hemodialysis patients.Methods: This was a randomized crossover study in hemodialysis patients supplemented with an echocardiographic case series. All outcomes reported here were secondary in the trial and were assessed without blinding. Block randomization and allocation determined treatment order. Participants received 50 mg spironolactone daily for 12 weeks and untreated observation for another 12 weeks. Pulse wave velocity (PWV) was measured before and after treatment and observation. Doppler-echocardiography was conducted before and after treatment. Systemic arterial compliance indexed to body surface area (SACi), left ventricular ejection fraction (LVEF), the peak early diastolic mitral inflow velocity (E), the peak late diastolic mitral inflow velocity (A), and the peak early diastolic myocardial lengthening velocity (E') were measured. E/A and E/E' were then calculated. Statistical analyses were conducted per protocol. A generalized linear mixed model with random participant effects was used for PWV. The Wilcoxon signed-rank test was used for echocardiographic variables.Results: Thirty participants were recruited, 18 completed follow-up, and 17 were included in PWV-analyses. Spironolactone treatment showed a tendency toward an increase in PWV of 1.34 (95% confidence interval: -0.11 to 2.78) m/s, which was not statistically significant (P = 0.07). There were no significant changes in any of the other variables (LVEF, E/A, E/E', or SACi).Conclusions: We found no evidence supporting an effect of 12-week administration of spironolactone 50 mg daily on vascular stiffness, cardiac systolic, or diastolic function in hemodialysis patients.
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| 5. |
- Eklund, Michael, 1988-, et al.
(författare)
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Effects of spironolactone on extrasystoles and heart rate variability in haemodialysis patients : a randomised crossover trial
- 2021
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Ingår i: Upsala Journal of Medical Sciences. - : Uppsala Läkareförening, Uppsala Medical Society. - 0300-9734 .- 2000-1967. ; 126:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Spironolactone treatment reduces mortality in haemodialysis (HD) patients. The objective of this study was to evaluate if spironolactone affects cardiac electric activity in this population.Methods: Participants were randomised to start with spironolactone 50 mg daily or observation (12 weeks) with subsequent washout (6 weeks) and crossover to the other intervention (12 weeks). Long-term electrocardiograms were recorded and assessed with blinding to treatment. The primary outcome was premature ventricular complexes (PVC), and secondary outcomes were atrial premature contractions (APC) and heart rate variability (HRV).Results: . HRV time-domain variables increased during treatment, the standard deviation of all beat-to-beat intervals by 18 (95% CI: 3.3 to 32) milliseconds (ms) and the standard deviation of the averages of beat-to-beat intervals in all 5-min segments of the entire recording by 16 (95% CI: 1.5 to 30) ms. There were no significant differences in other variables.Conclusion: Spironolactone treatment increases PVCs in HD, indicating a possible proarrhythmic effect. However, improved cardiac autonomic function, as indicated by an increased HRV, may contribute to the survival benefit from spironolactone treatment in HD patients.
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| 6. |
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| 7. |
- Thiagarajan, Kannan, 1981-
(författare)
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Monte Carlo simulation of electron transport in semiconducting zigzag carbon nanotubes
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Since the advent of nanoscale material based electronic devices, there has been a considerable interest in exploring carbon nanotubes from fundamental science and technological perspectives. In carbon nanotubes, the atoms form a cylindrical structure with a diameter of the order 1nm. The length of the nanotubes can extend up to several hundred micrometers. Carbon nanotubes exhibit a variety of intriguing electronic properties such as semiconducting and metallic behaviour, due to the quantum confinement of the electrons in the circumferential direction. Much of the study dedicated to describe the behaviour of carbon nanotube-based devices assumes for simplicity the nanotube to be a ballistic material. However, in reality the phonon scattering mechanism exists also in nanotubes, of course, and can generally not be neglected, except in very short nanotubes. In this work, we focus attention on exploring the steady-state electron transport properties of semiconducting single-walled carbon nanotubes, including both phonon scattering and defect (vacancy) scattering, using the semi-classical bulk single electron Monte Carlo method. The electron energy dispersion relations are obtained by applying the zone folding technique to the dispersion relations of graphene, which are calculated using the tight-binding description. The vibrational modes in the carbon nanotubes are studied using a fourth nearest-neighbour force constant model. Both the electron-phonon and the electron-defect interactions are formulated within the tight-binding framework, and their corresponding scattering rates are computed and analyzed. In particular, the dependence of the phonon scattering rate and the defect scattering rate on the diameter of the nanotube, on temperature and on electron energy is studied. It is shown that the differences observed in the scattering rate between different nanotubes mainly stem from the differences in their band structure. A bulk single electron Monte Carlo simulator was developed to study the electron transport in semiconducting zigzag carbon nanotubes. As a first step, we included only electron-phonon scattering, neglecting all other possible scattering mechanisms. With this scattering mechanism, the steady-state drift velocity and the mobility for the nanotubes (8,0), (10,0), (11,0), (13,0) and (25,0) were calculated as functions of the electric-field strength and lattice temperature, and the results are presented and analysed here. The dependence of the mobility on the lattice temperature can be clearly seen at low electric-field strengths. At such electric-field strengths, the scattering is almost entirely due to acoustic phonons, whereas at high electric-field strengths optical phonon emission processes dominate. It is shown that the saturation of the steady-state drift velocity at high electric-field strengths is due to the emission of high-energy optical phonons. The results indicate the presence of Negative differential resistance for some of the nanotubes considered in this work. The discrepancy found in the literature concerning the physical reason for the appearance of negative differential resistance is clarified, and a new explanation is proposed. It is also observed that the backward scattering is dominant over the forward scattering at high electric-field strengths. We then included also defect scattering, actually electron-vacancy scattering, for the nanotubes (10,0) and (13,0). The steady-state drift velocities for these nanotubes are calculated as functions of the density of vacancies, electric-field strength and the lattice temperature, using three different vacancy concentrations. The results indicate the presence of Negative differential resistance at very low concentration of defects, and how this feature may depend on the concentration of defects. The dependence of the steady-state drift velocity on the concentration of defect and the lattice temperature is discussed. The electron distribution functions for different temperatures and electric field strengths are also calculated and investigated for all the semiconducting nanotubes considered here. In particular, a steep barrier found in the electron distribution function is attributed to the emission of high energy optical phonons.
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