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| 2. |
- Wort, Michael A. A.
(författare)
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Distance education and the training of primary school teachers in Tanzania
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Tanzania has been using distance education to train its teachers for twenty years. Thefirst programme, which began in 1976 and ended in 1984, was highly innovative inits approach. It provided both professional and up-grading studies within the primaryschools to try and meet the demand for universal primary education. The secondmajor programme used more conventional correspondence studies to up-date itsprimary school teachers and still continues today.The study explores why, and how, distance education has developed in Tanzaniaand why it has vigorously pursued this method as a major tool in training its primaryschool teachers. Historical, cultural socio-economic and political contexts werehelpful in understanding the motivations, origins and developments of the two majorprogrammes beginning in 1979. The empirical material in the study covers twomajor distance teacher education programmes for primary school teachers inTanzania. The first programme, the Distance School based Teacher Trainingprogramme from 1976-1984 was critically re-analysed using former evaluationstudies. The second programme, 1984 to date was evaluated using a frame-process-outcome' model and is also presented.A new framework for the provision of distance education was developed usingthe important interactive elements of the educational process - teacher, learner(s) andcontent. The framework focuses upon the intended learning and incorporatededucation and adult education theories. Ten framework categories were developedfor reappraisal and analyse of the Tanzanian distance teacher education programmes.Finally suggestions were made, using the framework model for a new approach todistance education and teacher training.The outcomes suggests the need for a more decentralised authority and a greaterdifferentiation of tasks in administration, the setting up of school cluster and learnergroups and the provision of more responsive support systems. Framework categoriessuggested a move towards interdependency in their working, within a distributivemodel of distance education.
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| 3. |
- Adlers, Mikael
(författare)
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Topics in Sparse Least Squares Problems
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses topics in sparse least squares computation. A stable method for solving the least squares problem, min ||Ax-b||2 is based on the QR factorization.Here we have addressed the difficulty for storing the orthogonal matrix Q. Using traditional methods, the number of nonzero elements in Q makes it in many cases not feasible to store. Using the multifrontal technique when computing the QR factorization,Q may be stored and used more efficiently. A new user friendly Matlab implementation is developed.When a row in A is dense the factor R from the QR factorization may be completely dense. Therefore problems with dense rows must be treated by special techniques. The usual way to handle dense rows is to partition the problem into one sparse and one dense subproblem. The drawback with this approach is that the sparse subproblem may be more ill-conditioned than the original problem or even not have a unique solution. Another method, useful for problems with few dense rows, is based on matrix stretching, where the dense rows are split into several less dense rows linked then together with new artificial variables. We give and analyze the conditioning of the matrix obtained by this method and show that no ill-conditioned subproblem arise.In many least squares problems upper and lower bounds on the variables have to be satisfied at the solution. This type of problem arises, for example, in reconstruction problems in geodesy and tomography. Here methods based on direct factorization methods for sparse matrix computation are explored. Two completely different approaches for solving the problem are discussed and compared, i.e. active set methods and primal-dual interior-point methods based on Mehrotra's predictor-corrector path following method. An active set block method suitable for sparse problems is developed and a convergence proof is presented. The choice of barrier parameter, multiple corrections and finite termination for the interior-point method are discussed. Numerical comparison is given of the active set method, the interior-point method, together with an trust region method based on the interior-reflective Newton implemented in the optimization toolbox for MATLAB. The numerical tests show that the block active set method is faster and gives better accuracy for both nondegenerate and degenerate problems.
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| 4. |
- Alayon Glazunov, Andres
(författare)
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On the Antenna-Channel Interactions: A Spherical Vector Wave Expansion Approach
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main focus of this thesis is the analysis of the interactions between antennas and channels where electromagnetic fields play a central role. Our goal has been to devise a general framework to enable a clear separation of the properties of the propagation channel from the influence of the antennas at the same time as it provides a common ground for a joint characterization of their properties. For this we have taken help of two tools: 1) a solution to Maxwell's equations, i.e., a spherical vector wave (svw) multi-modal expansion of the electromagnetic field and 2) the scattering matrix representation of an antenna that provides a full description of all its properties as a transmitting, receiving or scattering device. These tools offer a natural characterization of the polarizational, directional, and spatial properties of multiple-input multiple-output (MIMO) antenna systems. In this thesis we first show that under some assumptions the propagation channel and the antenna are equivalent. The equivalence is in the sense that the impact of the channel cross-polarization ratio (XPR) and the antenna effective cross-polarization discrimination (XPD) on the mean effective gain (MEG) of an antenna are symmetrical. We also find bounds on the MEG in a wireless channel. Then we provide closed form expressions for the covariance of the field multi-modes as a function of the Power Angle Spectrum (PAS) and the channel XPR. A new interpretation of the MEG of antennas in terms of field multi-modes is also provided where the maximum MEG is obtained by conjugate mode matching between the antennas and the channel. We also show the (intuitive) result that the optimum decorrelation of the antenna signals is obtained by the excitation of orthogonal spherical vector wave modes. The cross-correlation coefficient between signals at two antenna branches (ports) in the presence of spatially selective interference and additive white gaussian noise is also investigated showing that spatial interference can also be readily modeled in terms of the svw mode expansion. We further devise a correlation model for co- and cross-polarized field components and introduce the concept of mode-to-mode channel mapping, the M-matrix, between the receive and transmit antenna modes. The M-matrix maps the modes excited by the transmitting antenna to the modes exciting the receive antennas and vice versa. The covariance statistics of this M-matrix are expressed as a function of the double-directional power-angular spectrum (PAS) of co- and cross-polarized components of the electromagnetic field. We finally derive physical limitations on the interactions of antennas exciting TM or TE modes (but not both) and wireless propagation channels. Rather than maximizing antenna gain in a single direction we obtain physical limitations on the antenna gain pattern, which is directly translated to more condensed parameters, i.e. the instantaneous effective gain Gi and the mean effective gain Ge if instantaneous realizations or correlation statistics of the expansion coefficients of the electromagnetic field are known, respectively. The obtained limitations are on the maximum of Gi/Q and Ge/Q, which establish a trade-off between link gain and the antenna quality factor Q.
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| 5. |
- Belfort, Michael A
(författare)
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The cerebral circulation in preeclampsia : abnormalities in autoregulation and perfusion
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: Eclampsia continues to be a major cause of maternal death. Abnormal cerebral blood flow and autoregulation may play an important role in the causation. Doppler ultrasound now allows assessment of the pathophysiology of preeclampsia, and the mechanisms of action of drugs used to treat it. Objectives: The objectives of this thesis were to: (1) define normal ranges for middle cerebral artery velocity, resistance indices, and perfusion pressure in pregnancy, (2) validate a non- invasive method for the measurement of cerebral perfusion pressure (CPP), (3) evaluate cerebral arterial resistance in the middle cerebral artery (MCA) distribution in preeclampsia, (4) contrast CPP in mild and severe preeclampsia, (5) research the hemodynamics of headache in preeclampsia, and (6) compare the effects of magnesium sulfate (MgSO4) and nimodipine on CPP in preeclampsia. Materials and Methods: Normal pregnant and preeclamptic patients were recruited. Vital signs, epidural pressure, and the velocities in cerebral and orbital arteries were measured. Indices of resistance and cerebral perfusion pressure (CPP) were calculated for both groups and compared. Preeclamptic women were studied before and after they had been randomly assigned to receive MgSO4, or nimodipine. Appropriate parametric and non-parametric tests were used in the analysis of the data. A two-tailed p<0.05 denoted statistical significance. Major Findings and Conclusions: 1. Normal pregnancy is associated with a decrease in systolic and mean velocity, no change in the diastolic velocity, a decrease in resistance indices, and an increase in MCA CPP. 2. CPP may be reliably measured in the MCA using a simple Doppler and non-invasive blood pressure technique. 3. Preeclampsia preferentially effects the MCA and disturbs autoregulation in this artery. 4. More than 50% of women with preeclampsia have a normal CPP. In mild preeclampsia, the CPP may be low or high, but in severe preeclampsia, if abnormal, CPP is always high. 5. Preeclamptics with headache more likely to have abnormal CPP than those without, and when headache is present it is more commonly associated with high CPP than low. 6. Nimodipine increases CPP, while MgSO4, causes a decrease in CPP, within 3 0 minutes after administration. Significance: Normal ranges for velocity, resistance and CPP have been defined for pregnancy. A new technique for measuring MCA CPP in pregnant women has been validated and may prove useful in research in this condition. The potential for overperfusion of the brain due to MCA autoregulation abnormalities should now be considered when treating preeclamptics. The use of CPP measurements may help in the management of women at high risk for seizure. Efforts should perhaps be directed at determining the CPP in selected women to help tailor therapy. Since headache is associated with abnormally high CPP, efforts to lower CPP should be considered when headache develops in a preeclamptic woman. Drugs that increase CPP are probably best avoided in patients with preeclampsia (especially those with headache) because of their potential for worsening hypertensive encephalopathy. They should be reserved for use in known cases of low CPP.
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| 6. |
- Broomé, Sara, 1989-
(författare)
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Atlantic Water in the Nordic Seas : A satellite altimetry perspective on ocean circulation
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Atlantic Water in the Nordic Seas contributes to the mild climate of Northern Europe and is the main oceanic source of heat for the Arctic. The northward bound transport of the warm and saline Atlantic Water is mediated by a topographically constrained cyclonic boundary current along the Norwegian continental slope. The analysis within this thesis is based on satellite observations of dynamic Sea Surface Heights (SSH) from 1993 to the recent present, combined with both hydrographic observations and modelling. It provides some new perspectives and results, as well as corroborates the essential role of bottom topography for the circulation in the Nordic Seas.In the first part of the thesis, the topographic constraint is used in the analysis by examining the satellite-derived SSH along topographic contours. We find stationary along-contour anomalies that indicate deviations from strict topographic steering. However, we show that these deviations are dynamically consistent with, and can be explained by, potential vorticity conservation in an adiabatic steady-state model for flow over a topographic slope. The analysis along topographic contours is further developed to study northward-propagating, low-frequency ocean temperature signals. These signals have an expression in the SSH and their propagation speed is remarkably slow compared to the current speed. We propose a conceptual model of shear dispersion effects, in which the effective advection speed of a tracer is determined not only by the rapid current core, but by a mean velocity taken over the cross-flow extent of Atlantic Water. The model predicts a reduced effective tracer advection velocity, comparable to the one observed.The close connection between anomalies in SSH and heat content is further used to study decadal variability in the Nordic Seas. There is a shift in decadal trends in the mid-2000s, from a period of strong increase in SSH and heat content to a more stagnant period. We find this variability to be forced remotely, rather than by local air-sea heat fluxes. By developing a conceptual model of ocean heat convergence, we are able to explain the broad features of the decadal changes with the temperature variability of the inflowing Atlantic Water from the subpolar North Atlantic.In the final part of the thesis, satellite-derived surface geostrophic velocity fields are used as input to a Lagrangian trajectory model. Based on this, we study the fractionation of the Atlantic Water in the Nordic Seas between the two straits towards the Arctic Ocean: the Barents Sea Opening and the Fram Strait. This Lagrangian approach also provides insights on the origin of the water that reach the straits. We find that it is the frontal current branch, rather than the slope current, that contributes to the variability of the Barents Sea Opening inflow of warm Atlantic Water, and thus potentially to the climate of the Barents Sea and its sea ice cover.
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| 7. |
- Collinson, Mark A, 1964-
(författare)
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Striving against adversity. : the dynamics of migration, health and poverty in rural South Africa
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Background: The study is based in post-apartheid South Africa and looks at the health and well being of households in the rural northeast. Temporary migration remains important in South Africa because it functions as a mainstay for income and even survival of rural communities. The economic base of rural South Africans is surprisingly low because there is high inequity at a national level, within and between racial groups. There has now been a democratic system in place for 15 years and there is no longer restriction of mobility, but there remain high levels of poverty in rural areas and rising mortality rates. Migration patterns did not change after apartheid in the manner expected. We need to examine consequences of migration and learn how to offset negative impacts with targeted policies. Aims: To determine a relevant typology of migration in a typical rural sending community, namely the Agincourt sub-district of Mpumalanga, South Africa, and relate it to the urban transition at a national level – Paper (I) . To evaluate the dynamics of socio-economic status in this rural community and examine the relationship with migration – Paper (II). To explore, using longitudinal methods, the impact of migration on key dimensions of health, including adult and child mortality, and sexual partnerships, over a period of an emerging HIV/AIDS epidemic – Papers (III), (IV) and (V). Methods: The health and socio-demographic surveillance system (HDSS) is a large open cohort where the migration dynamics are monitored as they unfold. They are recorded as temporary or permanent migration. Settled refugees are captured using nationality on entry into the HDSS. Longitudinal methods, namely a household panel and two discrete time event history analyses, are used to examine consequences of migration. Results: Migration features prominently and different types have different age and sex profiles. Temporary migration impacts the most on socio-economic status (SES) and health, but permanent migration and the settlement of former refugees are also important. Remittances from migrants make a significant difference to SES. For the poorest households the key factors improving SES are government grants and female temporary migration, while for less poor it is male temporary migration and local employment. Migration has been associated with HIV. Migrants that return more frequently may be less exposed to outside partners and therefore less implicated in the HIV epidemic. There are links between migration and mortality including a higher risk of dying for returnee migrants compared to permanent residents. A mother’s migration can impact on child survival after accounting for other factors. There remains a higher mortality risk for children of Mozambican former refugee parents. Interpretation: Migration changes the risks and resources for health with positive and negative implications. Measures such as improved transportation and roads should be seen as a positive, not a negative intervention, even though it will create more migration. Health services need to adapt to a reality of high levels of circular migration ranging from budget allocation to referral systems. Data should be enhanced at a national level by accounting for temporary migration in national censuses and surveys. At individual level we can offset negative consequences by treating migrants as persons striving against adversity, instead of unwelcome visitors in our better-off communities.
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| 8. |
- Gamstedt, Heléne, 1964-
(författare)
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Ionic Liquid Electrolytes for Photoelectrochemical Solar Cells
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Potential electrolytes for dye-sensitized photoelectrochemical solar cells have been synthesized and their applicability has been investigated. Different experimental techniques were used in order to characterize the synthesized electrolytes, such as elemental analysis, electrospray ionisation/mass spectrometry, cyclic voltammetry, dynamic viscosity measurements, as well as impedance, Raman and NMR spectroscopy. Some crystal structures were characterized by using single crystal X-ray diffraction. In order to verify the eligibility of the ionic compounds as electrolytes for photoelectrochemical solar cells, photocurrent density/photovoltage and incident photon-to-current conversion efficiency measurements were performed, using different kinds of light sources as solar simulators. In electron kinetic studies, the electron transport times in the solar cells were investigated by using intensitymodulated photocurrent and photovoltage spectroscopy. The accumulated charge present in the semiconductor was studied in photocurrent transient measurements. The ionic liquids were successfully used as solar cell electrolytes, especially those originating from the diethyl and dibutyl-alkylsulphonium iodides. The highest overall conversion efficiency of almost 4 % was achieved by a dye-sensitized, nanocrystalline solar cell using (Bu2MeS)I:I2 (100:1) as electrolyte (Air Mass 1.5 spectrum at 100 W m-2), quite compatible with the standard efficiencies provided by organic solvent-containing cells. Several solar cells with iodine-doped metal-iodidebased electrolytes reached stable efficiencies over 2 %. The (Bu2MeS)I:I2-containing cells showed better long-term stabilities than the organic solvent-based cells, and provided the fastest electron transports as well as the highest charge accumulation. Several polypyridyl-ruthenium complexes were tested as solar cell sensitizers. No general improvements could be observed according to the addition of amphiphilic co-adsorbents to the dyes or nanopartices of titanium dioxide to the electrolytes. For ionic liquid-containing solar cells, a saturation phenomena in the short-circuit current densities emerged at increased light intensities, probably due to inherent material transport limitation within the systems. Some iodoargentates and -cuprates were structurally characterized, consisting of monomeric or polymeric entities with anionic networks or layers. A system of metal iodide crownether complexes were employed and tested as electrolytes in photoelectrochemical solar cells, though with poorer results. Also, the crystal structure of a copper-iodide-(12-crown-4) complex has been characterized
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| 9. |
- Gilmore, Michael C., 1995-
(författare)
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Studies on cell wall recycling and modification in Gram-negative bacteria
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The bacterial cell wall is made from peptidoglycan (PG), a heteropolymer which forms a bag-like exoskeleton that envelopes the cell. PG is constantly remodelled during growth and division, and in response to environmental stimuli. Decades of study of this process have focused largely on a select few model organisms, leaving its diversity poorly understood. In this thesis, I present studies on different aspects of PG recycling and modification in several Gram-negative models, with a particular focus on the plant pathogen Agrobacterium tumefaciens, a model of the Hyphomicrobiales group of the Alphaproteobacteria which includes several species of medical and environmental interest. It is shown that A. tumefaciens encodes a novel PG transporter, which is vital for cell wall integrity and resistance to β- lactam antibiotics, and widely conserved in the Hyphomicrobiales and Rhodobacterales orders. Growth defects caused by the loss of the transporter are suppressed by mutations in a novel glycopolymer, which is hypothesized to play a role in sequestering metal ions and thereby lowering periplasmic oxidative stress. Next, in collaboration, it is shown that PG recycling in the best studied model, Escherichia coli, is more complicated than previously thought. Rather than depending mostly on the MFS-family transporter AmpG, E. coli uses an ABC transporter, MppA-OppBCDF or AmpG depending on the growth phase and conditions. Finally, two studies on modification of PG by deacetylation are presented. First, A. tumefaciens is shown to encode a novel anhydroMurNAc deacetylase, which specifically deacetylates the PG chain termini. Then, it is shown that the causative agent of Legionnaires’ disease, Legionella pneumophila, depends on deacetylation of its PG during infection for defence against host lysozyme and correct polar placement of its type IV secretion system.
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| 10. |
- Grishin, Michael A., 1973-
(författare)
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Electronic materials : growth and characterisation
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis the InSb(111), InAs(111) and GaSb(001) surfaces have been studied by means of time- and angle-resolved photoemission spectroscopy based upon the femtosecond laser system. The pump-and-probe technique allows to analyse both electron states in the valence band and normally unpopulated electron states above the valence band, which can be occupied by transiently excited carriers at the optically pumped surface. The life time of excited carriers is analysed by controlling over the time delay between pump and probe pulses. Experimental studies of the InSb(111) surface and comparison with a previously studied InSb(110) surface show electron excitations in the bulk region with a minor surface contribution. Time-resolved experiments of carrier dynamics at the polar InAs(111)A and InAs(111)B surfaces show about the same life time of excited carriers, while no populated states above the valence band maximum have been found at the InAs(111)A due to the charge removal. Surface intergap electron states have been found at the GaSb(001) surface located at ~250 meV above the valence band maximum. Angle-resolved experiments showed a strong confinement of this state at the centre of the surface Brillouin zone. A new two dimensional angle-resolved multi-anode analyser for the femtosecond laser photoemission setup has been constructed. The analyser can resolve a cone opening angle of ~1º at a drift distance of ~0.5 m with an energy resolution of ~125 meV. A continuous series of binary system SrTiO3–PbZr0.52Ti0.48O3 has been grown by pulsed laser deposition (PLD) on sapphire substrate with crystalline quality control by x-ray diffraction (XRD). The maximum tunability has been tailored to room temperature, where STO�PZT (71/29) composition shows superior performance. A PbZr0.52Ti0.48O3 thin film pressure sensor has been fabricated by PLD and characterised by XRD and electrical measurements. The piezoelectric constant was found to be ~20 % higher compared to the bulk ceramics. A ferroelectric thin film electro-optical cell Na0.5K0.5NbO3/La0.5Sr0.5CoO3 (NKN/LSCO) on sapphire has been fabricated by PLD. Refractive indices and electro-optical coefficient of the cell were characterised by prism coupling refractometry. The tunability of the PLD fabricated 2 μm slot NKN thin film interdigital capacitor has been found ~23 % at 40 V bias voltage and frequency 1 MHz.
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