Theoretical modeling of ionospheric electrodynamics including induction effects

This thesis deals with theoretical modeling of the electrodynamics of auroral ionospheres. In the five research articles forming the main part of the thesis we have concentrated on two main themes: Development of new data-analysis techniques and study of inductive phenomena in the ionospheric electrodynamics. The introductory part of the thesis provides a background for these new results and places them in the wider context of ionospheric research. In this thesis we have developed a new tool (called 1D SECS) for analysing ground based magnetic measurements from a 1-dimensional magnetometer chain (usually aligned in the North-South direction) and a new method for obtaining ionospheric electric field from combined ground based magnetic measurements and estimated ionospheric electric conductance. Both these methods are based on earlier work, but contain important new features: 1D SECS respects the spherical geometry of large scale ionospheric electrojet systems and due to an innovative way of implementing boundary conditions the new method for obtaining electric fields can be applied also at local scale studies. These new calculation methods have been tested using both simulated and real data. The tests indicate that the new methods are more reliable than the previous techniques. Inductive phenomena are intimately related to temporal changes in electric currents. As the large scale ionospheric current systems change relatively slowly, in time scales of several minutes or hours, inductive effects are usually assumed to be negligible. However, during the past ten years, it has been realised that induction can play an important part in some ionospheric phenomena. In this thesis we have studied the role of inductive electric fields and currents in ionospheric electrodynamics. We have formulated the induction problem so that only ionospheric electric parameters are used in the calculations. This is in contrast to previous studies, which require knowledge of the magnetospheric-ionosphere coupling. We have applied our technique to several realistic models of typical auroral phenomena. The results indicate that inductive electric fields and currents are locally important during the most dynamical phenomena (like the westward travelling surge, WTS). In these situations induction may locally contribute up to 20-30% of the total ionospheric electric field and currents. Inductive phenomena do also change the field-aligned currents flowing between the ionosphere and magnetosphere, thus modifying the coupling between the two regions.

Fertility in Namibia : Changes in fertility levels in North-Central Namibia 1960-2001, including an assessment of the impact of HIV

The aim of this study was to estimate the development of fertility in North-Central Namibia, former Ovamboland, from 1960 to 2001. Special attention was given to the onset of fertility decline and to the impact of the HIV epidemic on fertility. An additional aim was to introduce parish registers as a source of data for fertility research in Africa. Data used consisted of parish registers from Evangelical Lutheran congregations, the 1991 and 2001 Population and Housing Censuses, the 1992 and 2000 Namibia Demographic and Health Surveys, and the HIV sentinel surveillances of 1992-2004. Both period and cohort fertility were analysed. The P/F ratio method was used when analysing census data. The impact of HIV infection on fertility was estimated indirectly by comparing the fertility histories of women who died at an age of less than 50 years with the fertility of other women. The impact of the HIV epidemic on fertility was assessed both among infected women and in the general population. Fertility in the study population began to decline in 1980. The decline was rapid during the 1980s, levelled off in the early 1990s at the end of war of independence and then continued to decline until the end of the study period. According to parish registers, total fertility was 6.4 in the 1960s and 6.5 in the 1970s, and declined to 5.1 in the 1980s and 4.2 in the 1990s. Adjustment of these total fertility rates to correspond to levels of fertility based on data from the 1991 and 2001 censuses resulted in total fertility declining from 7.6 in 1960-79 to 6.0 in 1980-89, and to 4.9 in 1990-99. The decline was associated with increased age at first marriage, declining marital fertility and increasing premarital fertility. Fertility among adolescents increased, whereas the fertility of women in all other age groups declined. During the 1980s, the war of independence contributed to declining fertility through spousal separation and delayed marriages. Contraception has been employed in the study region since the 1980s, but in the early 1990s, use of contraceptives was still so limited that fertility was higher in North-Central Namibia than in other regions of the country. In the 1990s, fertility decline was largely a result of the increased prevalence of contraception. HIV prevalence among pregnant women increased from 4% in 1992 to 25% in 2001. In 2001, total fertility among HIV-infected women (3.7) was lower than that among other women (4.8), resulting in total fertility of 4.4 among the general population in 2001. The HIV epidemic explained more than a quarter of the decline in total fertility at population level during most of the 1990s. The HIV epidemic also reduced the number of children born by reducing the number of potential mothers. In the future, HIV will have an extensive influence on both the size and age structure of the Namibian population. Although HIV influences demographic development through both fertility and mortality, the effect through changes in fertility will be smaller than the effect through mortality. In the study region, as in some other regions of southern Africa, a new type of demographic transition is under way, one in which population growth stagnates or even reverses because of the combined effects of declining fertility and increasing mortality, both of which are consequences of the HIV pandemic.

Diffusion of Be, Co and Mn impurities in compound semiconductors and glassy carbon studied by the modified radiotracer technique

The main method of modifying properties of semiconductors is to introduce small amount of impurities inside the material. This is used to control magnetic and optical properties of materials and to realize p- and n-type semiconductors out of intrinsic material in order to manufacture fundamental components such as diodes. As diffusion can be described as random mixing of material due to thermal movement of atoms, it is essential to know the diffusion behavior of the impurities in order to manufacture working components. In modified radiotracer technique diffusion is studied using radioactive isotopes of elements as tracers. The technique is called modified as atoms are deployed inside the material by ion beam implantation. With ion implantation, a distinct distribution of impurities can be deployed inside the sample surface with good con- trol over the amount of implanted atoms. As electromagnetic radiation and other nuclear decay products emitted by radioactive materials can be easily detected, only very low amount of impurities can be used. This makes it possible to study diffusion in pure materials without essentially modifying the initial properties by doping. In this thesis a modified radiotracer technique is used to study the diffusion of beryllium in GaN, ZnO, SiGe and glassy carbon. GaN, ZnO and SiGe are of great interest to the semiconductor industry and beryllium as a small and possibly rapid dopant hasn t been studied previously using the technique. Glassy carbon has been added to demonstrate the feasibility of the technique. In addition, the diffusion of magnetic impurities, Mn and Co, has been studied in GaAs and ZnO (respectively) with spintronic applications in mind.

On the Benefits and Problems of the Object-Oriented Paradigm including a Finnish Study

Several researchers are of the opinion that there are many benefits in using the object-oriented paradigm in information systems development. If the object-oriented paradigm is used, the development of information systems may, for example, be faster and more efficient. On the other hand, there are also several problems with the paradigm. For example, it is often considered complex, it is often difficult to make use of the reuse concept and it is still immature in some areas. Although there are several interesting features in the object-oriented paradigm, there is still little comprehensive knowledge of the benefits and problems associated with it. The objective of the following study was to investigate and to gain more understanding of the benefits and problems of the object-oriented paradigm. A review of previous studies was made and twelve benefits and twelve problems were established. These benefits and problems were then analysed, studied and discussed. Further a survey and some case studies were made in order to get some knowledge on what benefits and problems with the object-oriented paradigm Finnish software companies had experienced. One hundred and four companies answered the survey that was sent to all Finnish software companies with five or more employees. The case studies were made with six large Finnish software companies. The major finding was that Finnish software companies were exceptionally positive towards the object-oriented information systems development and had experienced very few of the proposed problems. Finally two models for further research were developed. The first model presents connections between benefits and the second between problems.