| 1. |
- Abdu, Yassir Ahmed Mohamed, 1966-
(författare)
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Mössbauer Spectroscopy of Meteoritic and Synthetic Fe-Ni Alloys
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis reports on the results of investigating Fe-containing minerals in meteorites, with focus on Fe-Ni minerals and their magnetic properties, along with some synthetic Fe-Ni analogues. The New Halfa meteorite, which fell in Sudan 1994, has been studied using Mössbauer spectroscopy, X-ray diffraction, and electron microprobe analysis techniques, and classified as an ordinary L-type chondrite of petrologic type 4. Mössbauer spectra of taenite-enriched samples from the metal particles of the New Halfa (L4) and Al Kidirate (H6) meteorites identify the following γ (fcc) Fe-Ni phases: the ferromagnetic atomically ordered taenite (tetrataenite) with ~ 50 at % Ni, the ferromagnetic disordered taenite with ~ 50 at % Ni, the low-Ni (~ 25 at %) paramagnetic taenite (antitaenite). The presence of the superstructure of tetrataenite is confirmed by synchrotron X-ray diffraction.Fe-rich γ (fcc) Fe-Ni alloys with compositions Fe79Ni21, Fe76Ni24, and Fe73Ni27, which serve as synthetic analogues of antitaenite, are prepared by mechanical alloying and subsequent annealing at 650 °C. The Mössbauer results indicate that these alloys are inhomogeneous and contain a high moment (HM) ferromagnetic Ni-rich phase (> 30 at % Ni) and a low moment (LM) paramagnetic Fe-rich phase, which orders antiferromagnetically at low temperature. The coexistence of these phases is attributed to phase segregation occurring on short range, probably nanometer scale, consistent with the Fe-Ni phase diagram below 400 °C where there is a miscibility gap associated with a spinodal decomposition in alloys with < 50 at % Ni.The combined high field Mössbauer spectroscopy and SQUID magnetometry results on these alloys at room temperature indicate large induced local magnetic moments in the paramagnetic part of the sample, which increases with increasing the Ni content. The results, when compared with the high field Mössbauer results on antitaenite from the metal particle of Al Kidirate and New Halfa meteorites may be used to estimate the Ni content of antitaenite in meteorites.High pressure 57Fe Mössbauer spectroscopy measurements up to ~ 41 GPa have been carried out at room temperature using the diamond anvil cell (DAC) technique in order to investigate the magnetic properties of γ (fcc) 57Fe53Ni47 alloy. The results indicate a pressure induced Invar effect at ~ 7 GPa and a non-magnetic or paramagnetic state above 20 GPa, demonstrating the volume dependence of the magnetic moment of γ (fcc) Fe-Ni alloys.
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| 2. |
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| 3. |
- Abrahamsson, Malin L. A.
(författare)
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Electron Transfer in Ruthenium-Manganese Complexes for Artificial Photosynthesis : Studies in Solution and on Electrode Surfaces
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In today’s society there is an increasing need for energy, an increase which for the most part is supplied by the use of fossil fuels. Fossil fuel resources are limited and their use has harmful effects on the environment, therefore the development of technologies that produce clean energy sources is very appealing. Natural photosynthesis is capable of converting solar energy into chemical energy through a series of efficient energy and electron transfer reactions with water as the only electron source. Thus, constructing an artificial system that uses the same principles to convert sunlight into electricity or storable fuels like hydrogen is one of the major forces driving artificial photosynthesis research.This thesis describes supramolecular complexes with the intention of mimicking the electron transfer reactions of the donor side in Photosystem II, where a manganese cluster together with a tyrosine catalyses the oxidation of water. All complexes are based on Ru(II)-trisbipyridine as a photosensitizer that is covalently linked to electron donors like tyrosine or manganese. Photochemical reactions are studied with time-resolved transient absorption and emission measurements. Electrochemical techniques are used to study the electrochemical behavior, and different photoelectrochemical techniques are used to investigate the complexes adsorbed onto titanium dioxide surfaces. In all complexes, intramolecular electron transfer occurs from the linked donor to photo-oxidized Ru(III). It is also observed that coordinated Mn(II) quenches the excited state of Ru(II), a reaction that is found to be distance dependent. However, by modifying one of the complexes, its excited state properties can be tuned in a way that decreases the quenching and keeps the electron transfer properties. The obtained results are of significance for the development of multinuclear Ru-Mn complexes that are capable of multi-electron transfer.
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| 4. |
- Abramson, Jeff
(författare)
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Structural studies on the integral membrane protein, ubiquinol oxidase from Escherichia coli
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heme-copper oxidases are redox-driven proton pumps that couple the reduction of molecular oxygen to water with the vectorial translocation of protons across the membrane. The proton gradient generated by heme-copper oxidases and the other members of the aerobic respiratory chain is ultimately used to drive the synthesis of ATP. There are two main branches of the heme-copper oxidases that are characterized by the electron donating substrate; the cytochrome c oxidases, which use cytochrome c as the electron donor, and the ubiquinol oxidases, which use a lipid-soluble molecule, ubiquinol, as their electron donor. These enzymes share important structural and functional features. This thesis presents the procedures that have led to the first crystal structure of a ubiquinol oxidase, cytochrome bo, oxidase from Escherichia coli, at a resolution of 3.5 Å. The overall structure of the enzyme is similar to those of cytochrome c oxidases; however the membrane spanning region of subunit I contains a cluster of polar residues exposed to the interior of the lipid bilayer. No such structural feature is present in cytochrome c oxidases. Mutagenesis studies on residues in this region strongly suggest that this area forms a ubiquinone binding site. A comparison of this region with known ubiquinone binding sites shows remarkable similarities. In light of these findings specific roles for these polar residues is proposed in electron and proton transfer in ubiquinol oxidase. A fusion protein of cytochrome bo3-Protein Z was generated in an attempt to increase the hydrophilic surface of the protein, thus extending protein-protein contacts within the crystal lattice structure. Such an approach can be used to facilitate crystallization.
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| 5. |
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| 6. |
- Acharya, Parag, 1972-
(författare)
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Studies on the Non-covalent Interactions (Stereoelectronics, Stacking and Hydrogen Bonding) in the Self-assembly of DNA and RNA
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is based on ten publications (Papers I-X). The phosphodiester backbone makes DNA or RNA to behave as polyelectrolyte, the pentose sugar gives the flexibility, and the aglycones promote the self-assembly or the ligand-binding process. The hydrogen bonding, stacking, stereoelectronics and hydration are few of the important non-covalent forces dictating the self-assembly of DNA/RNA. The pH-dependent thermodynamics clearly show (Papers I and II) that a change of the electronic character of aglycone modulates the conformation of the sugar moiety by the tunable interplay of stereoelectronic anomeric and gauche effects, which are further transmitted to steer the sugar-phosphate backbone conformation in a cooperative manner. 3'-anthraniloyl adenosine (a mimic of 3'-teminal CCAOH of the aminoacyl-tRNAPhe) binds to EF-Tu*GTP in preference over 2'-anthraniloyl adenosine, thereby showing (Paper III) that the 2’-endo sugar conformation is a more suitable mimic of the transition state geometry than the 3’-endo conformation in discriminating between correctly and incorrectly charged aminoacyl-tRNAPhe by EF-Tu during protein synthesis. The presence of 2'-OH in RNA distinguishes it from DNA both functionally as well as structurally. This work (Paper IV) provides straightforward NMR evidence to show that the 2'-OH is intramolecularly hydrogen bonded with the vicinal 3'-oxygen, and the exposure of the 3'-phosphate of the ribonucleotides to the bulk water determines the availability of the bound water around the vicinal 2'-OH, which then can play various functional role through inter- or intramolecular interactions. The pH-dependent 1H NMR study with nicotinamide derivatives demonstrates (Paper V) that the cascade of intramolecular cation (pyridinium)-π(phenyl)-CH(methyl) interaction in edge-to-face geometry is responsible for perturbing the pKa of the pyridine-nitrogen as well as for the modulation of the aromatic character of the neighboring phenyl moiety, which is also supported by the T1 relaxation studies and ab initio calculations. It has been found (Papers VI-IX) that the variable intramolecular electrostatic interaction between electronically coupled nearest neighbor nucleobases (steered by their respective microenvironments) can modulate their respective pseudoaromatic characters. The net result of this pseudoaromatic cross-modulation is the creation of a unique set of aglycones in an oligo or polynucleotide, whose physico-chemical properties are completely dependent upon the propensity and geometry of the nearest neighbor interactions (extended genetic code). The propagation of the interplay of these electrostatic interactions across the hexameric ssDNA chain is considerably less favoured (effectively up to the fourth nucleobase) compared to that of the isosequential ssRNA (up to the sixth nucleobase). The dissection of the relative strength of basepairing and stacking in a duplex shows that stability of DNA-DNA duplex weakens over the corresponding RNA-RNA duplexes with the increasing content of A-T/U base pairs, while the strength of stacking of A-T rich DNA-DNA duplex increases in comparison with A-U rich sequence in RNA-RNA duplexes (Paper X).
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| 7. |
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| 8. |
- Adawi, Tom W., 1970-
(författare)
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From Branes to Brains : On M-theory and Understanding Thermodynamics
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is concerned with research in both physics and physics education, and is divided into two parts.Part IString theory has been the leading candidate over the past few years for a theory that unifies all the fundamental forces of nature. The fundamental objects are one-dimensional strings whose vibrational modes should correspond to the usual elementary particles. However, the recent discovery of the profound role played by extended solitonic objects in string theory, referred to as p-branes, has questioned the foundational position of the string itself. A key ingredient in these developments is the notion of duality, a symmetry which provides a handle on non-perturbative physics. As a result, all five string theories, as well as eleven-dimensional supergravity, are but special limits of a conjectural theory, referred to as M-theory. In this part of the thesis, various aspects of p-branes with relevance for M-theory are investigated. Special emphasis is given to the interpretation of p-branes as solitons. Furthermore, some of the features of the superembedding approach to describe p-brane dynamics are examined.Part IIThere is now a consensus among educational researchers that it is essential to gain a better understanding of how people understand key concepts in physics in order to improve teaching and learning in physics. This part of the thesis reports on a phenomenographic study investigating the qualitatively different ways in which lay adults, taking an introductory overview course in physics, understand the concepts of heat and temperature. Implications for teaching the topics in higher education forms an essential component of the analysis. This is followed by a theoretical component that draws on the empirical analysis as a contribution to the development of the notion of context in phenomenographic research.
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| 9. |
- Adsten, Monika, 1972-
(författare)
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Solar Thermal Collectors at High Latitudes : Design and performance of non-tracking concentrators
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Solar thermal collectors at high latitudes have been studied, with emphasis on concentrating collectors. A novel design of concentrating collector, the Maximum Reflector Collector (MaReCo), especially designed for high latitudes, has been investigated optically and thermally. The MaReCo is an asymmetrical compound parabolic concentrator with a bi-facial absorber. The collector can be adapted to various installation conditions, for example stand-alone, roof- or wall mounted. MaReCo prototypes have been built and outdoor-tested. The evaluation showed that all types work as expected and that the highest annually delivered energy output, 340 kWh/m2, is found for the roof MaReCo. A study of the heat-losses from the stand-alone MaReCo lead to the conclusion that teflon transparent insulation should be placed around the absorber, which decreases the U-value by about 30%. A method was developed to theoretically study the projected radiation distribution incident on the MaReCo bi-facial absorber. The study showed that the geometry of the collectors could be improved by slight changes in the acceptance intervals. It also indicated that the MaReCo design concept could be used also at mid-European latitudes if the geometry is changed. A novel method was used to perform outdoor measurements of the distribution of concentrated light on the absorber and then to calculate the annually collected zero-loss energy, Ea,corr, together with the annual optical efficiency factor. A study using this method indicated that the absorber should be mounted along the 20º optical axis instead of along the 65º optical axis, which leads to an increase of about 20% in Ea,corr. The same absorber mounting is suggested from heat loss measurements. The Ea,corr at 20º absorber mounting angle can be increased by 5% if the absorber fin thickness is changed from 0.5 to 1 mm and by 13% if two 71.5 mm wide fins are used instead of one that is 143 mm wide. If the Ea,corr for the standard stand-alone MaReCo with 143 mm wide absorber mounted at 65º is compared to that of a collector with a 71.5 mm wide absorber mounted at 20º, the theoretical increase is 38%.
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| 10. |
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| 11. |
- Ahlsén, Göran
(författare)
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Structure-activity and resistance studies of HIV-1 protease inhibitors
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present investigation was undertaken in order to identify inhibitors of HIV-1 protease that would be efficient in vivo and against HIV-1 protease carrying mutations known to confer resistance to inhibitors in clinical use. A second interest was to understand details of inhibitory mechanisms and to gain understanding of the molecular details of resistance.Linear inhibitors of transition-state type showed to have a resistance pattern similar to protease inhibitors in clinical use, whereas cyclic inhibitors of sulfonamide were somewhat different in their inhibitory profiles. It was found that mutation L90M in some situations could lessen the decrease in overall efficiency suffered by the enzyme when aquiring other mutations. Also presented are results from the characterization of double mutation I84V/L90M, formerly not investigated. Testing of triple and quadruple mutant confirmed the additive features of some mutations. In an attempt to find new leads for inhibitor development, extracts from bee propolis, a natural product, was investigated, and it was found that one extract inhibited wild-type enzyme with an I50-value of 0.2 μg/mL. Even more interesting is the result that propolis extract also inhibited all the investigated mutant enzymes.
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| 12. |
- Akyuz, Mose, 1972-
(författare)
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Positive streamer discharges in air and along insulating surfaces: experiment and simulation
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The power quality of modern society relies on the electrical properties of the dielectric insulators used in the power industry. Much research work has been conducted with an aim to understand and predict the insulating behaviour of such materials under different kinds of atmospheric conditions, but still there are many unsolved problems. In particular, there is a lack of knowledge concerning the electrohydrodynamic and electrophysical processes at the insulator surface and the surrounding medium. No detailed knowledge exists at present of the processes governing the development of electrical discharges along the surface of insulators.With an aim to enhance the knowledge in this field in general and on the electrical performance of outdoor insulators in particular a detailed study of the positive streamer discharges in air and along dielectric surfaces was conducted. The study was also extended to gain more knowledge on the water drop initiated electrical discharges in air and the attachment of natural lightning flashes to a Franklin conductor.In the first phase, the study was focused on positive streamer discharges propagating in air. The spatial distribution of the charge of a branched streamer discharge was obtained and the charge contained in a single streamer branch was quantified. In the second phase measurements and simulations of streamer discharges propagating along insulating surfaces were conducted with an aim to understand how the insulating surfaces interact with streamer discharges. In addition to quantifying the parameters of streamer discharges propagating along insulating surfaces, the results of these studies made it possible to separate and quantify the effects of the dielectric constant and the surface properties on the streamer discharges. In the third phase a comprehensive computer algorithm was developed to simulate 3-dimensional propagation of positive streamer discharges in air and along dielectric surfaces taking into account the branching effect. The conditions necessary for the initiation of streamer discharges were applied to obtain the minimum strength of the background electric field required to initiate electrical discharges in the presence of water drops. In particular the study provided an explanation of how lightning flashes are initiated in thunderclouds in background electric fields as low as 200 kV/m. Finally, the study was extended to understand the performance of lightning conductors paying special attention to the influence of conductor radius and the streamer inception criterion.
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| 13. |
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| 14. |
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| 15. |
- Alexander, James N.
(författare)
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Novel detection schemes and high resolution separations in microcolumn liquid separations
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Three micro detectors were developed and studied using micro-liquidchromatography (micro-LC). An evaporative light scattering detector (ELSD) nebulizer was developed for use with flow rates ranging from 0.5 to 10 µL/min. The parameters that affect analyte response were investigated and the most influential were capillary tip position and nebulization gas flow rate. One unique advantage of thismicro detector is that it can be operated at ambient conditions which allows for the analysis of semi-volatile compounds.A radio activity monitor (RAM) flow cell was developed for use at 3 µL/min and was designed for coupling to mass spectrometry (MS). The parameters that affect analyte response and band broadening were studied. Reducing the solid scintillant particle size to 9 µm and efficiently packing the solid cells allowed for direct coupling to MS without compromising the chromatographic separation.A nano-electrospray ionization (BSI) source for MS was developed and coupled to nano-LC and capillary electrophoresis (CE). This source incorporated a 50 µm i.d. stainless steel tip that was coupled to the separation capillary. At flow rates of 100 nL/min a stable electrospray was achieved.A multi-use separations system was developed for isocratic and gradient elution micro-LC, capillary electrochromatography (CEC), and pressure CEC (PEC). The details of the system and studies on peak area and retention time repeatability are reported. Comparisons are made between nano-LC and CEC. On average, column efficiency is 57% greater for CEC compared to nano-LC using the same nanocolumn.
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| 16. |
- Alfredsson, Maria
(författare)
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Polar molecules in crystalline and surface environments : From first principles
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- With the knowledge of the composition and structure of a chemical system, be it a molecule, a two-dimensional surface or a three-dimensional crystal, it is now possible to predict the specific properties of the compound under consideration via computational studies. Molecular and periodic Hartree-Fock and DFT calculations have been used as a tool to study polar molecules and how their properties respond to the molecular environment in a crystal or on an ionic surface. The investigation covers a range of molecules (HF, HC1, HCN, H2O, OH-, OH., N2, CO and LiF) with different net charges, dipole moments and polarisibility, and a range of crystals and crystalline surfaces: hydrogen-bonded, ionic and ferroelectric.The step-wise build up of the molecular properties (geometries, energies, dipole moments, vibrational frequencies etc.) has been investigated. It was found that sorne molecular properties converge quickly towards the crystal value, others more slowly. Molecules adsorbed on a solid surface were studied as a function of adsorptionenergy, substrate and surface coverage. For the ionic surfaces studied here it was found that the properties of the chemi- and physisorbed molecules are as sensitive to the surface coverage as to the adsorption of the ad-molecule to the surface. The vibrational frequency shift of the ad-molecule has been given special attention.Finally the spontaneous polarisation in two ferroelectric crystals was calculated within the Berry-phase approach.
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| 17. |
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| 18. |
- Alsmark, Cecilia
(författare)
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Comparative Genomics of Obligate and Facultative Intracellular Parasites
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The α-proteobacteria Rickettsia prowazekii and Bartonella henselae are the causative agents of epidemic typhus and cat scratch disease respectively. Whereas R. prowazekii is an obligate intracellular parasite, B. henselae can live and proliferate both outside and inside the eukaryotic host cell. Besides the obvious medical interest to identify the complete gene set of two human pathogens, their genome sequences are also important for the study of evolutionary processes. Both R. prowazekii and B. henselae have small genomes, but their last common ancestor of these two bacteria was most likely a free-living organism with a substantially larger genome.The aim of this thesis is to compare the complete genomes of R. prowazekii and B. henselae and to decipher the evolutionary processes leading to the adaptation to an intracellular lifestyle. The working hypothesis was that the facultative intracellular B. henselae is an intermediate between a free living bacteria and the obligate R. prowazekii, which is corroborated. B. henselae has a broader biosynthetic repertoire than R. prowazekii, including the presence of genes for glycolysis and de novo biosynthesis of purines and pyrimidines. However, both bacteria have reduced gene sets for biosynthesis of amino acids and cofactors compared to free-living bacteria.Comparisons of gene order in bacteria reveal that several operons are well conserved between distantly related species. The genome sequences of R. prowazekii and B. henselae show that many of the operons that are usually conserved, are broken and rearranged in these species. One of the mechanisms of reductive evolution include intra-chromosomal recombination between repeated loci. This process expels one of the repeats and cause rearrangements in the gene order of the flanking regions. While the R. prowazekii genome almost completely lack repeated sequences, the B. henselae genome is rich in repeats. These repeats are, however, most often located within regions associated with pathogenicity islands. The higher number of scrambled operons, and the lower number of repeats, in R. prowazekii compared to B. henselae imply that the reductive process has gone further in the former species.
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| 19. |
- Alström, Per
(författare)
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Species Limits and Systematics in Some Passerine Birds
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I use morphological, vocal, molecular, behavioural, ecological and distributional data to re-evaluate the systematics of three passerine bird groups, the Mirafraassamica complex (bush-larks), the genus Seicercus ("spectacled-warblers"; with emphasis on the the S. burkii complex) and the genus Motacilla (wagtails). Two new species are described: Seicercus soror and Motacilla samveasnae. I propose that the polytypic species M. assamica should be treated as four separate species: M. assamica, M. affinis, M. microptera and M. marionae (it is also remarked that the proper name of the latter is M. erythrocephala). That is primarily supported by vocalisations and mitochondrial DNA. The latter data set also suggests that M. assamica sensu lato is paraphyletic, since M. erythroptera, which is always treated as a separate species, is nested within the M. assamica complex. I propose that the polytypic species S. burkii comprises six sibling species. Some of these are found to breed sympatrically, although mainly or entirely segregated altitudinally. Mitochondrial DNA suggests that the S. burkii complex is non-monophyletic, and also that the divergence of the different taxa is much older than indicated by morphological and vocal data. According to the molecular phylogeny, both the genera Seicercus and its assumed sister genus Phylloscopus are paraphyletic. That is corroborated by independent data. The phylogenetic study of the genus Motacilla reveals incongruence between mitochondrial DNA, nuclear DNA and non-molecular data. I conclude that the nuclear gene tree reflects the organismal phylogeny more faithfully than the mitochondrial gene tree. The latter is likely to have been affected by introgressive hybridisation, possibly also stochastic lineage sorting. The most remarkable result that is strongly supported by both mitochondrial and nuclear DNA is that M. flava is non-monophyletic.
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| 20. |
- Amiri, Haleh, 1966-
(författare)
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Patterns and Processes of Molecular Evolution in Rickettsia
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Species of the genus Rickettsia are obligate intracellular parasites of the a-proteobacterial subdivision. It has been suggested that obligate intracellular bacteria have evolved from free-living bacteria with much larger genome sizes. Transitions to intracellular growth habitats are normally associated with radical genomic alterations, particularly genome rearrangements and gene losses.This thesis presents a comparative study of evolutionary processes such as gene rearrangements, deletions and duplications in a variety of Rickettsia species. The results show that early intrachromosomal recombination events mediated by duplicated genes and short repeats have resulted in deletions as well as rearrangements. For example, an exceptional organization of the elongation factor genes was found in all species examined, suggesting that this rearrangement event occurred at the early stage of the evolution of Rickettsia. Likewise, it was found that a repetitive element, the so-called Rickettsia Palindromic Element (RPE) flourished prior to species divergence in Rickettsia. Finally, a phylogenetic analysis shows that the duplication events that gave rise to the five genes encoding ATP/ADP transporters occurred long before the divergence of the two major groups of Rickettsia. Taken together, this suggests that Rickettsia have been intracellular parasites for an extensive period of time.A detailed analysis of the patterns of nucleotide changes in genes and intergenic regions among the different species provides evidence for a gradual accumulation of short deletions. This suggests that different distributions of genes and repeated sequences in modern Rickettsia species reflect species-specific differences in rates of deterioration rather than variation in rates of intra-genomic sequence proliferation.
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| 21. |
- Amirkhani, Ardeshir, 1965-
(författare)
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Development of Techniques and Methods for the Quantitative Analysis of Endogenous Substances by Microcolumn Liquid Chromatography Coupled to Mass Spectrometry
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Liquid chromatography-mass spectrometry (LC-MS) is a powerful technique for the analysis of endogenous compounds. The introduction of electrospray ionization (ESI) as an interface between LC and MS has contributed strongly to a trend towards miniaturization of LC, due to the possibility to perform ESI at low flow rates. In this thesis, several aspects regarding the design of miniaturized LC systems and electrospray emitters were investigated. In addition miniaturized LC-ESI-MS have been used for the qualitative and quantitative analysis of endogenous polar compounds, peptides and protein digests.The performance of miniaturized LC-MS was compared using different electrospray emitter configurations. The results indicated that the efficiency of the LC system is rather independent of the configuration of the emitter.The lifetime of gold-coated fused silica electrospray emitters based on vapor deposited adhesion layers of titanium were investigated. The long lifetime of the emitter facilitates the use in LC-MS experiments, exemplified LC-MS by analysis of neuropeptides.The ESI voltage is shown to interfere with liquid chromatographic separations performed in packed porous graphitic carbon capillary column. This interference is ascribed to the presence of an electric field over the conductive column in absence of a ground point between the column and the ESI emitter.The solid supported enhanced microdialysis for analysis of neuropeptides were compared with conventional microdialysis. The difference between the two methodologies were evaluated by LC-MS analysis of the microdialysates. The solid supported method gave in general higher relative recoveries.Finally, a method of standard addition was developed to determine total level of tryptophan and two of its metabolites in human plasma by capillary LC-ESI tandem mass spectrometry. The method was applied in a clinical study of multiple scleroses patients treated with cytokines (IFN Beta 1a, 1b). The results show that the intervention effects the tryptophan metabolism.
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| 22. |
- Andersson, Anna-Carin, 1970-
(författare)
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Postglacial Population History of the Common Shrew (Sorex araneus) in Fennoscandia : Molekylära studier av återkolonisation, könsbundet genflöde och kromosomrasbildning.
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The common shrew, Sorex araneus, has one of the most variable karyotypes among mammals, displaying numerous chromosomes races throughout its distribution, which can be categorized into different karyotypic groups. The objective of this thesis was to examine the postglacial population history of Fennoscandian common shrews using autosomal microsatellites, mitochondrial DNA (mtDNA) and a Y chromosome specific microsatellite (L8Y).Autosomal microsatellites and mtDNA revealed weak genetic structure over a hybrid zone between the karyotypically divergent Northern and Western karyotypic groups. However, the genetic structure displayed by the Y chromosome microsatellite was orders of magnitude higher. Hence, considerable chromosomal differences between the groups do not prevent female gene flow, while male gene flow is reduced (cf. Haldane's rule). Further, the results suggest that the Haldane effect may be caused by the chromosomal differences between the karyotypic groups.No mtDNA differentiation was observed either between chromosome races or between the Northern and Western karyotypic groups in Fennoscandia. The combined pattern of karyotypic and mtDNA variation of Fennoscandian common shrews, suggest bi-directional postglacial recolonisation from a single refugium in Europe. The variation of the Y-linked microsatellite supported this conclusion. In contrast, significant mtDNA structure, discordant with the karyotypic variation, revealed that common shrews in southern Finland belong to a different lineage than remaining Fennoscandian regions, implying postglacial recolonisation from a different source.MtDNA variation of the chromosome races in Sweden supports the hypothesis that three races of the Western karyotypic group have been formed through whole arm reciprocal translocations (WARTs), as suggested by their mutual karyotypic variation. The variation of the molecular markers supports the theory of rapid karyotypic evolution in the common shrew.
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| 23. |
- Andersson, Anna S.
(författare)
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Lithium iron phosphates as cathode materials in lithium batteries
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Iron-based oxides are perhaps the only realistic cathode materials for electric and electric-hybrid vehicle applications. Two types of lithium iron phosphate, LiFePO4 andR-Li3Fe2(PO4)3, have been investigated for use within the lithium/lithium-ion polymer batteryconcept. The main techniques exploited have been: electrochemical cycling; X-ray andneutron diffraction - to study structural changes of the host material during lithiuminsertion/extraction; Mössbauer spectroscopy - to probe changes in the local structure of theFe atoms.Lithium extraction/insertion for LiFePO4, (olivine-type structure) has been followed by acombination of in situ X-ray diffraction and in situ Mössbauer spectroscopy. QuantitativeRietveld analysis of diffraction data has given good agreement with electrochemical andMössbauer spectroscopy data: ca. 20% of the LiFePO4 phase remains after charging. Possiblemechanisms to describe the capacity loss are proposed. High-temperature cycling (at 40oC and60oC) has shown the specific capacity to be markedly enhanced at higher temperatures.In situ Mössbauer spectroscopy has also been used to study the insertion of lithium into R-Li3Fe2(PO4)3. The two non-equivalent Fe3+ ions cannot be distinguished, whereas two typesof Fe2+ site appear on lithium insertion. Lithium appears to enter a site closer to one of theFe atoms. Elevated-temperature cycling shows the temperature dependence of R-Li3Fe2(PO4)3to be less marked than for the LiFePO4 system.The magnetic properties of R-Li3Fe2(PO4)3 have been investigated for the first time: a para- to antiferromagnetic transition is seen at 28 ~ K. Neutron powder diffraction shows that the Fe magnetic dipoles lie close to the ab-plane and are ferromagnetically aligned within an Fesheet perpendicular to the c-axis, but are antiferromagnetically coupled to adjacent sheets.
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| 24. |
- Andersson, Anna
(författare)
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Surface Phenomena in Li-Ion Batteries
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The formation of surface films on electrodes in contact with non-aqueous electrolytes in lithium-ion batteries has a vital impact on battery performance. A basic understanding of such films is essential to the development of next-generation power sources. The surface chemistry, morphology and thermal stability of two typical anode and cathode materials, graphite and LiNi0.8Co0.2O2, have here been evaluated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction, scanning electron microscopy and differential scanning calorimetry, and placed in relation to the electrochemical performance of the electrodes. Chemical and morphological information on electrochemically formed graphite surface films has been obtained accurately by combining XPS measurements with Ar+ ion etching. An improved picture of the spatial organisation, including thickness determination of the surface film and characterisation of individual component species, has been established by a novel sputtering calibration procedure. The stability of the surface films has been shown to depend strongly on temperature and choice of lithium salt. Decomposition products from elevated-temperature storage in different electrolyte systems were identified and coupled to effects such as capacity loss and increase in electrode resistance. Different decomposition mechanisms are proposed for surface films formed in electrolytes containing LiBF4, LiPF6, LiN(SO2CF3)2 and LiCF3SO3 salts.Surface film formation due to electrolyte decomposition has been confirmed on LiNi0.8Co0.2O2 positive electrodes. An overall surface-layer increase with temperature has been identified and provides an explanation for the impedance increase the material experiences on elevated-temperature storage. Surface phenomena are clearly major factors to consider in selecting materials for practical Li-ion batteries.
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| 25. |
- Andersson, C. Evalena, 1973-
(författare)
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Structure-Function Studies of Enzymes from Ribose Metabolism
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the pentose phosphate pathway, carbohydrates such as glucose and ribose are degraded with production of reductive power and energy. Another important function is to produce essential pentoses, such as ribose 5-phosphate, which later can be used in biosynthesis of nucleic acids and cofactors. This thesis presents structural and functional studies on three enzymes involved in ribose metabolism in Escherichia coli. Ribokinase is an enzyme that phosphorylates ribose in the presence of ATP and magnesium, as the first step of exogenous ribose metabolism. Two important aspects of ribokinase function, not previously known, have been elucidated. Ribokinase was shown to be activated by monovalent cations, specifically potassium. Structural analysis of the monovalent ion binding site indicates that the ion has a structural rather than catalytic role; a mode of activation involving a conformational change has been suggested. Product inhibition studies suggest that ATP is the first substrate to bind the enzyme. Independent Kd measurements with the ATP analogue AMP-PCP support this. The results presented here will have implications for several enzymes in the protein family to which ribokinase belongs, in particular the medically interesting enzyme adenosine kinase. Ribose 5-phosphate isomerases convert ribose 5-phosphate into ribulose 5-phosphate or vice versa. Structural studies on the two genetically distinct isomerases in E. coli have shown them to be fundamentally different in many aspects, including active site architecture. However, a kinetic study has demonstrated both enzymes to be efficient in terms of catalysis. Sequence searches of completed genomes show ribose 5-phosphate isomerase B to be the sole isomerase in many bacteria, although ribose 5-phosphate isomerase A is a nearly universal enzyme. All genomes contain at least one of the two enzymes. These results confirm that both enzymes must be independently capable of supporting ribose metabolism, a fact that had not previously been established.
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| 26. |
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| 27. |
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| 28. |
- Andersson, Gunnar, 1972-
(författare)
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Differentiation and Pathogenicity within the Saprolegniaceae : Studies on Physiology and Gene Expression Patterns in Saprolegnia parasitica and Aphanomyces astaci
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Saprolegnia parasitica and Aphanomyces astaci are parasitic water moulds belonging to the Oomycetes. Despite their importance as parasites they are very little studied at the molecular level and the work described in this thesis was aimed at increasing the molecular knowledge of these organisms by cloning and characterising genes of potential importance for reproduction and pathogenicity.Stage-specific transcripts from Saprolegnia parasitica were isolated by differential display RT-PCR. One of the markers, puf1 encodes a putative mRNA binding protein which may be involved in post-transcriptional regulation of gene expression. S. parasitica puf1 is expressed exclusively in spore cysts that have not been determined for germination or repeated zoospore emergence indicating that the cyst stage has two phases, of about equal duration, which are physiologically and transcriptionally distinct. A similar expression pattern is observed in Aphanomyces spp. with different regulation of spore development and in the transcript is detected in both primary and secondary cysts.A putative chitinase AaChi1, was cloned from the crayfish plague fungus, Aphanomyces astaci. Analysis of chitinase activity and AaChi1 expression showed that chitinase in A. astaci is constitutively expressed in growing and sporulating mycelia, but absent in zoospores, a pattern which reflects the infectious life cycle of A. astaci. This expression pattern is conserved between the four known genotypes of A. astaci, in contrast to saprophytic and fish-pathogenic Aphanomyces spp. Genetic and physiological analysis were conducted on five strains of Aphanomyces, isolated from suspected outbreaks of crayfish plague in Spain and Italy. The strains are not virulent against freshwater crayfish, and RAPD PCR and ITS sequence analysis show that they are unrelated to the crayfish plague fungus, A. astaci.
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| 29. |
- Andersson, Gabriella
(författare)
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Hydrogen in ultrathin vanadium layers
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The influence of elastic boundary conditions on the thermodynamics of hydrogen in vanadium were investigated using resistometry, x-ray diffraction and nuclear reaction analysis. To provide varying lattice strain states Mo/V (110) and Fe/V (001) superlattices with thickness L of individual layers in the range 3-16 monolayers (ML) were used. In addition the thickness ratio LFe/LV in the latter samples was varied. The results were compared with earlier work on Mo/V (001) superlattices.In the Mo/V (110) superlattices the H-H interaction was found to be repulsive in contrast to the (001) oriented samples and bulk V. This was also the case for Fe/V (001). For the thickness ratios LFe/LV = 3/10 and 3/16 it was found that the hydrogen-depleted interface region in V was populated at lower average concentration than in the symmetric samples (LFeLV = 1). This was related to the decreased Fe thickness.For Fe(3ML)/V(12-15 ML) samples the effects of hydrogenation on the magnetic exchange coupling between the Fe layers were investigated using neutron reflectometry. For 12 and 14 ML of V the coupling was switched continuously from antiferromagnetic (AFM) to ferromagnetic (FM) upon introduction of small amounts of hydrogen, whereas the initially FM-coupled 15-ML sampleexhibited an antiferromagnetic "resonance" at H/V ≈ 0.02. This was found to be due to changes in the vanadium Fermi surface. An intermediate state of noncollinear coupling was also observed in the 14-ML sample.
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| 30. |
- Andersson, Hans Ola
(författare)
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Structure-aided design of antiviral drugs : Application of the method on HIV-1 protease and SIV reverse transcriptase
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many efforts have been made to control the AIDS epidemic. Extensive studies have been done on the biology, biochemistry, and structural biology of HIV in the search for antiviral drugs. The viral-encoded enzymes reverse transcriptase and protease have been main targets for drug design.Our study on the HIV-1 protease involves the X-ray structure determination of ten complexes with C-terminally duplicated linear inhibitors and two complexes with C2-symmetric cyclic inhibitors. The structural study of the HIV-1 protease/linear inhibitors revealed several interesting properties of the protease, such as the flexibility of S2/S2' subsites, and the presence of coupled and symmetry restricted adaptation of the inhibitor binding subsites. We also found that the inhibitors adopted specific asymmetric conformation of their central parts, where only one of the gemdiol-hydroxyls is pointing toward the catalytic aspartates. The study of the C2-symmetric cyclic inhibitors showed that despite our efforts to promote a symmetric binding of the sulfamide compound, it seems prone to bind non-symmetrically. Our research has resulted in several highly competent inhibitor compounds.The work on sooty mangabey SIV reverse transcriptase (SIVsm RT) involves the expression,purification, characterization and studies of inhibition. A simple and efficient large-scalepreparation method was developed for SIVsm RT, in which processing of the p65/p65homodimer to the p65/p51 heterodimer was done with HIV-1 protease. The catalyticproperties of SIVsm RT were characterized. The sensitivity toward non-nucleoside inhibitorsNNI's) of SIVsm RT was distinct from HIV-1. By screening an inhibitor-library, two leadcompounds, MSK-046 and MSK-076 (IC50-values of ~10 µ), belonging to the PETT-serieswere identified.
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| 31. |
- Andersson, Joakim, 1971-
(författare)
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Microengineered CVD Diamond Surfaces : Tribology and Applications
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recent developments in thin film synthesis of diamond have facilitated a host of new technical applications. These are motivated by the many attractive properties of diamond, for example high hardness, chemical inertness, transparency and heat conductivity. Unfortunately, these properties also make it difficult to fashion complex geometries. Other problems are the severely limited choice of suitable substrate materials and large surface roughness. To reduce these complications, a technology denoted replication and bodybuilding has been developed. The basic principle is to grow the diamond film onto a mold and then build a mechanical support on top of the diamond film. Then the mold is removed. Thereby, a diamond surface with the desired 3D geometry and the same surface roughness as the mold is created.Three potential applications for devices built using the replication and bodybuilding concept have been explored. Grinding tools for hard materials have proved superior to conventional technology in rate of removal as well as in resulting surface finish. Diamond surfaces have also been crafted into ultra-durable dies for injection molding of hard particle reinforced polymers. Initial testing of an abrasive diamond device, intended to make CMP processes more economical and easier to control has successfully been carried out.Diamond and diamond-like carbon is well-known for being “low-friction materials”, but are here demonstrated to actually be “high-friction materials” with the ability to disguise themselves in certain environments, most notably with the aid of water molecules. The mechanisms involved in these variations have been investigated. Using NEXAFS it is shown that high friction sliding is accompanied by changes in the material structure. These changes are induced by surface roughness as well as by strong adhesive forces.Highly hydrogenated carbon coatings, on the other hand, affording super-low friction coefficients (<0.01) under certain circumstances, will suffer an increase in friction in the presence of water.
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| 32. |
- Andersson, Jan O.
(författare)
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Molecular evolutionary studies of genome degradation in bacteria
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The genus Rickettsia belongs to the α-proteobacteria and consists of obligate intracellular bacteria, which often are pathogenic for humans. All Rickettsia have small genomes, highly adapted to an intracellular lifestyle. However, the ancestors of Rickettsia were most likely free-living organisms with substantially larger genomes, This thesis is a study of the reductive evolutionary processes by which Rickettsia has adapted to a life inside eukaryotic cells. The Rickettsia prowazekii genome sequence confirmed the close phylogenetic relationship between the genus Rickettsia and the mitochondria. In addition, 12 putative pseudogenes and an unusually large fraction of non-coding DNA (24%) were identified. Analysis of the metK genomic region in different Rickettsia species identified metK as a pseudogene in all but two lineages. The pattern of mutations indicated that the pseudogenes are no longer under purfying selection, and that metK was inactivated several times independently in different lineages. Similar patterns were found in many other Rickettsia pseudogenes, revealing an ongoing genome degradation process in the Rickettsia.Analysis of neutrally evolving pseudogenes showed that deletions dominate over insertions, and that there is a mutational bias towards A+T nucleotides, in the Rickettsia genomes. In agreement, the long intergenic regions in the R. prowazekii genome have a decreased G+C content. Several of these regions showed sequence homology to genes in orthologous positions in other Rickettsia genomes, which indicated that the long intergenic regions represent old genes that are disappearing from the genome.The ancestor of the two major Rickettsia groups may have encoded 200-300 additional genes compared to R. prowazekii. Differential loss of mostly genus specific genes during the evolution resulted in the present-day Rickettsia genomes. Currently, Rickettsia inactivates genes at a higher than they are eliminated from the genome by fixation of deletions.
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| 33. |
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| 34. |
- Andersson, Ki, 1975-
(författare)
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Aspects of locomotor evolution in the Carnivora (Mammalia)
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the shape of the distal humerus trochlea is analysed using landmark-based morphometrics and multivariate methods, with the aim of exploring locomotor evolution in carnivorans. Elbow joint morphology is used together with body size and craniodental morphology to characterize past and present carnivorans. Evolutionary implications are studied at the ordinal, familial, and species levels, testing specific hypotheses about scaling, morphological constraints, evolutionary trajectories, and potential for social pack-hunting behaviour. The circumference of the distal humerus trochlea is found to be highly correlated with body mass, and appears to scale similarly throughout the order Carnivora. A general predictive model for carnivoran bodymass is presented (a=0.601; b= 2.552; r2=0.952, SEE=0.136, p<0001, n=92), which removes the need for the investigator to actively choose between the diverging estimates that different predictors and their equations often produce. At the elbow joint, manual manipulation and locomotion appear to be conflicting functions, thus suggesting mutually exclusive lifestyles involving either forelimb grappling or pursuit. At large body sizes, carnivorans are distributed over a strongly dichotomised pattern (grappling or locomotion), a pattern coinciding with the postulated threshold in predator-prey size ratio at 21.5-25 kg. This pattern is compared to that of two carnivoran faunas from the Tertiary. In the Oligocene (33.7-23.8 Myr BP), the overall pattern is remarkably similar to that observed for extant Carnivora. In the Miocene (23.8-11.2 Myr BP) carnivores show a similarly dichotomised pattern as the Oligocene and Recent, although the whole pattern is shifted towards larger body sizes. This difference is suggested to be a reflection of the extraordinary species richness of browsing ungulates in the early Miocene of North America. Such an increase in prey spectrum would create a unique situation, in which large carnivores need not commit to a cursorial habitus in order to fill their nutritional requirements. Finally, the elbow joints and craniodental morphology (14 measurements) of fossil canids were examined with the aim of assessing the potential for pack-hunting in fossil canids. It is clear that small and large members of the Recent Caninae share similar craniodental morphologies. However, this pattern is not present in Borophaginae and Hesperocyoninae. In the latter, large representatives are characterized by being short-faced, with reduced anterior premolars and enlarged posterior premolars, thus approaching a “pantherine-like” craniodental configuration. These traits are interpreted as an adaptation for killing prey with canine bites. It is similarly determined that, unlike recent Caninae, all analyzed species of borophagines and hesperocyonines have retained the ability to supinate their forearms. It is therefore likely that manual manipulation was part of their hunting behaviour, thus removing an essential part of the argument for social pack-hunting in these forms, as the benefits of such a strategy become less obvious.
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| 35. |
- Andersson, Mauritz
(författare)
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Quantum Dynamics of Molecular Systems and Guided Matter Waves
- 2001
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quantum dynamics is the study of time-dependent phenomena in fundamental processes of atomic and molecular systems. This thesis focuses on systems where nature reveals its quantum aspect; e.g. in vibrational resonance structures, in wave packet revivals and in matter wave interferometry. Grid based numerical methods for solving the time-dependent Schrödinger equation are implemented for simulating time resolved molecular vibrations and to compute photo-electron spectra, without the necessity of diagonalizing a large matrix to find eigenvalues and eigenvectors.Pump-probe femtosecond laser spectroscopy on the sodium potassium molecule, showing a vibrational period of 450 fs, is theoretically simulated. We find agreement with experiment by inclusion of the finite length laser pulse and finite temperature effects.Complicated resonance structures observed experimentally in photo-electron spectra of hydrogen- and deuterium chloride is analyzed by a numerical computation of the spectra. The dramatic difference in the two spectra arises from non-adiabatic interactions, i.e. the interplay between nuclear and electron dynamics. We suggest new potential curves for the 32Σ+ and 42Σ+ states in HCI+.It is possible to guide slow atoms along magnetic potentials like light is guided in optical fibers. Quantum mechanics dictates that matter can show wave properties. A proposal for a multi mode matter wave interferometer on an atom chip is studied by solving the time-dependent Schrödinger equation in two dimensions. The results verifies a possible route for an experimental realization.An improved representation for wave functions using a discrete set of coherent states is presented. We develop a practical method for computing the expansion coefficients in this non-orthogonal set. It is built on the concept of frames, and introduces an iterative method for computing a representation of the identity operator. The phase-space localization property of the coherent states gives adaptability and better sampling efficiency.
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| 36. |
- Andersson, Måns S.
(författare)
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Physiological trade-offs in reproduction and condition dependence of a secondary sexual trait
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines parental condition, how it is traded off against reproduction and how it is displayed in a secondary sexual trait. The studies were performed on nest-box breeding collared flycatchers Ficedula albicollis on the island of Gotland, in the Baltic Sea. Early breeding and high fitness were found to be associated with high levels of glycosylated haemoglobin possibly governed by migratory exertion and infectious disease. In order to test if immune function is expressed in secondary sexual traits and how it is traded off against reproductive effort a series of experiments were performed, in which birds were challenged with an antigen, via a vaccine containing neutralised paramyxovirus. The forehead patch of the male collared flycatcher serves as a badge of status and is under sexual selection. Good condition, as reflected in strong immune response and low levels of blood parasites was found to be associated with bigger patch size. Patch size was also found to vary in size within the same breeding season in a pattern predictable from immune response data. Immune response, in itself, was found to be costly in terms of reduced survival, confirming that trade-offs involving suppression of immune response may increase fitness. Mating effort was found to be traded off against immune function and moult. Experimental brood size manipulations revealed a trade-off females between number of offspring and immune function. Thus I suggest a set of parameters useful for condition estimation. I also show that immune response is costly and, second, that pathogen resistance probably plays an important role in the shaping of secondary sexual traits and life-history decisions.
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| 37. |
- Andersson, Mikael
(författare)
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Tuning electron transfer reactions by selective excitation in porphyrin-acceptor assemblies
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns electron transfer reactions from different excited states in porphyrins, and the effect of changing the energy of the link connecting the donor and acceptor. Photoinduced electron transfer, and subsequent processes were studied using ultrashort laser pulses and nanosecond laser flash photolysis.Excitation of Zn(II)-porphyrins in the Soret band lead to population of the higher lying S2 state. The lifetime and transient absorption spectrum was measured for the S2 state. When an electron acceptor was attached to the Zn(II)-porphyrin, either as an ion pair, or covalently bound through an amide link, electron transfer was found to compete with S2 to S1 relaxation. In the ion pair, electron transfer was faster than 200 fs, with a lifetime of the charge separated state of 1.3 ps. Further, in the covalently linked dyad, the Zn(II) porphyrin triplet state was repopulated from a charge transfer state.In [2]-rotaxanes, the Zn(II) porphyrin donor (ZnP) and Au(III) porphyrin acceptor (AuP+) are not connected by a direct covalent link. Selective excitation of either the ZnP or the AuP+ resulted in rapid electron transfer from the ZnP to the AuP+. The bis-phenanthroline link connecting the. different porphyrins was changed by coordination of Cu(I) or Ag(I). Electron transfer from the 1ZnP singlet was unaffected by coordination of either Ag(I) or Cu(I), while electron transfer to the 3AuP+ triplet was in the Ag(I) link found to occur by an enhanced superexchange, and by a sequential mechanism in the Cu(I) coordinated link.
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| 38. |
- Andersson, Per
(författare)
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Theoretical Investigations of Selected Heavy Elements and Metal-hydrogen Systems by Means of Electronic Structure Calculations
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Using ab initio electronic structure calculations based on density functional theory the crystal, electronic and magnetic structures of selected materials have been investigated. The materials which are the subjects of these investigations can be divided into two groups. Parts of the investigations have concerned actinides and rare earths, heavy elements with an f-shell electronic configuration. Here the effects of delocalization on EuCo2P2 have been studied as well as the effect of including relativistic interactions when calculating the properties of thorium. For EuCo2P2 it was found that at a low pressure the valence state of Eu changes from divalent to trivalent with associated effects on the crystal structure and magnetic state.The other group of materials investigated are the metal-hydrogen and metal- lithium systems. Both of these have an important technological application in the form of batteries. Here the emphasis of the investigations has been the fundamental understanding of the mechanism of hydrogenation, and a novel theory explaining the driving force behind hydrogenation is suggested. Vanadium hydride, VHx, has been examined in detail and the reason for the anomalous non-isotropic expansion is explained. A scheme to make vanadium magnetic is also proposed. Finally a method based on electron-hole coupled Green's functions has been used to facilitate the comparison between calculated electronic structures and X-ray absorption spectra. In connection to this a novel theory of charge transfer in the X-ray absorption process applied to transition metal oxides and lithium intercalated transition metal oxides is presented.
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| 39. |
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| 40. |
- Andersson, Staffan
(författare)
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Photoelectron spectroscopic studies of deposited metal clusters and model catalyst systems
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metal clusters are small metal aggregates between atomic and metal systems. Their physical and chemical properties have been observed to change with size. Their surface fraction is large which makes them of particular interest for catalysis. Most presently used catalyst systems consist of small metal particles on porous oxide supports. By replacing these particles with selected clusters it may be possible to produce better catalysts. To do this, fundamental knowledge of clusters is important and this can be gained by applying surface science techniques, such as photoelectron and X-ray absorption spectroscopy.Practical catalytic systems are difficult to study with surface science techniques because of their rather complex nature. Therefore model systems have been developed to enable detailed studies of clusters. The results presented apply to one such model system, metal particles on a thin alumina film grown through oxidation of a NiAl(110) surface. The structure of this film and the interaction between it and deposited particles is discussed.The electronic structure of deposited metal clusters change with size, approaching a bulk-like character as the size increases. This has been observed both for the valence band of Pd particles and the core levels of Pd and Rh particles. It is also found that the Rh particles deposited on the thin alumina film undergo a transition from electronically-isolated to metallic anchored character in the size range of 1000-3000 atoms.The chemical reactivity of clusters is known to change with particle size. This has been observed for CO interaction with both Pd and Rh clusters. Of special interest is the observation that the heat-induced CO dissociation ability of Rh particles is strongly size-dependent, exhibiting a maximum for particles with around 1000 atoms. In this case the important factor for the catalyst is not to exhibit as much surface as possible, but to exhibitthe right type of surface. This is an example of how knowledge about the size-dependent properties of clusters can be important for the application of catalyst systems. The development of a size-selected cluster source and results from it is presented.
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| 41. |
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| 42. |
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| 43. |
- Ankarberg, Emma, 1973-
(författare)
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Neurotoxic Effects of Nicotine During Neonatal Brain Development : Critical Period and Adult Susceptibility
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examined neurotoxic effects of nicotine exposure during a defined critical period of neonatal brain development in mice.In our environment there are numerous hazardous contaminants that an individual can be exposed to during its entire lifetime. In many mammalian species the neonatal period is characterised by a rapid development of the brain. The present studies have identified a defined critical period during the neonatal brain development in mice, where exposure to low doses of nicotine causes permanent disturbances in the cholinergic nicotinic receptors and altered behaviour response to nicotine at adult age. This adult reaction to nicotine, a hypoactive response, was the opposite of that observed in control animals and animals exposed to nicotine before or after this period. Animals showing a hypoactive response to nicotine lacked nicotinic low affinity binding sites in the cerebral cortex. Furthermore, neonatal exposure to nicotine affected learning and memory in adult animals, an effect that was time-dependent. This thesis also showed that neonatal exposure to nicotine increased adult susceptibility to a repeated exposure of nicotine, manifested as an even more pronounced effect in spontaneous behaviour after challenging doses of nicotine. In these animals the nicotinic receptors in the cerebral cortex, assayed by a-bungarotoxin, was decreased. Neonatal exposure to nicotine was also shown to increase adult susceptibility to the organophosphate paraoxon, a known cholinergic agent, and to the brominated flame retardant 2,2´,4,4´,5-pentabromodiphenyl ether, a novel environmental agent, at adult age. This was seen at doses that did not affect behaviour in control animals, and was manifested as deranged spontaneous behaviour and reduced habituation, aberrations that also worsened with age. The results indicate that differences in adult susceptibility to environmental pollutants are not necessarily an inherited condition. Rather they may well be acquired by low dose exposure to toxic agents during early life.
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| 44. |
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| 45. |
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| 46. |
- Aranyos, Viviane
(författare)
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Dyes and their adsorption onto nanocrystalline TiO2 electrodes : Synthesis, characterisation and applications
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The syntheses of two type of dyes (phthalocyanine and ruthenium tris-bipyridyl) are presented here. Their characterisation involves the use of cyclic voltammetry, NMR- and UV-visible spectroscopy. Once adsorbed on nanocrystalline TiO2 electrodes, their electrochemical, spectroelectrochemical and photoelectrochemical properties were investigated.In the first part, the syntheses of aryl-substituted phthalocyanines are described. The key intermediate, an aryl-substituted phthalonitrile, was prepared by a Pd(0)-catalysed Stille-coupling. The physical properties of tetra-(2,5-dirnetoxyphenyl)phthalocyanine (1a), tetraphenylphthalocyanine (1b) are discussed, An interesting display behaviour was characterised by spectroelectrochemistry in the case of 1b. Considering the system, unexpectedly high efficiencies of the resulting solar cells are observed for both dyes.The second part deals with two types of ruthenium tris-bipyridyl complexes. Syntheses of three carboxylated heteroleptic ruthenium complexes [Ru(bpy)2(bpy-R)](PF6)2 (bpy-R, R= (COOLi)n, n= 1, 2, 4) were synthesised for a study of the influence of the number of carboxylic groups on solar cell efficiencies. A lateral electron transfer mechanism for the dyes adsorbed on TiO2, is observed. Homoleptic and heteroleptic ruthenium complexes possessing the polymerisable groups vinyl, methoxyphenyl or thiophene were prepared for an investigation of the substituent effect on the dye-monolayer in the solar cell, both by electrochemistry and absorption spectroscopy. The methoxyphenyl-substituted complexes showed good polymerisation behaviour both at negative and at positive potentials. They also showed good resistance towards water when adsorbed onto TiO2 electrodes.
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| 47. |
- Articus, Kristina, 1971-
(författare)
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Phylogenetic Studies in Usnea (Parmeliaceae) and Allied Genera
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the phylogeny of the lichen genus Usnea (Parmeliaceae, Ascomycetes). The relationships and the morphological variation among Usnea species has been studied, as well as the relationship of Usnea to allied genera. Two species, U. florida and U. subfloridana, which earlier were regarded to form two separate species have been synonymized. In an analysis based on sequence data these two taxa formed a monophyletic group of intermixed specimens. Usnea florida and U. subfloridana have earlier been regarded to form a species pair, but the species pairs concept cannot be applied in this case. The morphological characters traditionally used for species recognition of a number of European Usnea species have been analyzed regarding their reliability. The evolution and distribution of the morphological characters was studied in relation to a phylogeny based on sequence data. Most characters proved to be homoplastic in relation to the phylogeny. Few characters were consistent in a clade, and the same character could be inconsistent in another clade. Therefore a combination of several characters is recommended for species recognition. The relationship of Neuropogon to Usnea was investigated based on sequence data. Neuropogon showed to be closely related to Usnea subg. Usnea. The subgenera Eumitria and Dolichousnea formed the sister group to the clade comprising subg. Usnea and Neuropogon. Usnea is paraphyletic in this investigation. Eumitria is treated as a genus and the subgenus Dolichousnea is elevated to generic rank. The position of Usnea, Neuropogon, Eumitria, and Dolichousnea in the family Parmeliaceae was investigated based on a phylogeny obtained by sequence data. Protousnea probably forms the sister group to the clade of Usnea, Neuropogon, Eumitria, and Dolichousnea. Several monophyletic groups in the family Parmeliaceae were identified.
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| 48. |
- Arvola, Marie
(författare)
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Immunological aspects of maternal-foetal interactions in mice
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Mammalian pregnancy is an immunological paradox. The foetus, which expresses both paternal and maternal cell-surface molecules, has to be protected from rejection by the maternal immune system. At the same time, the mother has to have an efficient immune defence and must provide her offspring with antibodies.The first part of this thesis investigates some of the mechanisms involved in the foetal avoidance of maternal rejection reactions. Placental absence of MHC class II expression, as well as a bias for Th2-cytokines at the maternal-foetal interface are suggested to be important for foetal survival. The results showed that placental MHC class II expression cannot be induced in vivo. Transfections of trophoblast cells with MHC class II genes, however, resulted in detectable MHC class II cell-surface expression, indicating that a post-transcriptional block does not exist in these cells.By using IL-4- and IL-10-double deficient mice, it was shown that neither maternal nor foetal expression of these cytokines were crucial for completion of allogeneic pregnancy.In the second part of the thesis, the effect of transmission of immunoglobulin G (IgG) from the mother to the offspring was studied. It was observed that viable maternal Ig-secreting cells occasionally infiltrated the B cell-deficient offspring and remained functional for long periods. In this study "green fluorescent mice" were used as a tool. Furthermore, neonatal ingestion of wild type milk increased the survival of adoptively transferred B-lineage cells in B cell-deficient mice, suggesting that suckling of IgG-containing milk could be used to facilitate B cell-reconstitution in B cell-deficient mice. Finally, results from studies on normal mice showed that absence of maternal IgG-transmission during their neonatal development resulted in elevated serum-IgG production, as well as enhanced immune reactions upon immunisations in adult life. This showed that maternal IgG can have long-term immunoregulatory effects in the offspring.
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| 49. |
- Asp, Elina
(författare)
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Drift-Type Waves in Rotating Tokamak Plasma
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The concept of energy production through the fusion of two light nuclei has been studied since the 1950’s. One of the major problems that fusion scientists have encountered is the confinement of the hot ionised gas, i.e. the plasma, in which the fusion process takes place. The most common way to contain the plasma is by using at magnetic field configuration, in which the plasma takes a doughnut-like shape. Experimental devices of this kind are referred to as tokamaks. For the fusion process to proceed at an adequate rate, the temperature of the plasma must exceed 100,000,000C. Such a high temperature forces the plasma out of thermodynamical equilibrium which plasma tries to regain by exciting a number of turbulent processes. After successfully quenching the lager scale magnetohydrodynamic turbulence that may instantly disrupt the plasma, a smaller scale turbulence revealed itself. As this smaller scale turbulence behaved contrary to the common theory at the time, it was referred to as anomalous. This kind of turbulence does not directly threaten existents of the plasma, but it allows for a leakage of heat and particles which inhibits the fusion reactions. It is thus essential to understand the origin of anomalous turbulence, the transport it generates and most importantly, how to reduce it. Today it is believed that anomalous transport is due to drift-type waves driven by temperature and density inhomogeneities and the theoretical treatment of these waves is the topic of this thesis.The first part of the thesis contains a rigorous analytical two-fluid treatment of drift waves driven solely by density inhomogeneities. Effects of the toroidal magnetic field configuration, the Landau resonance, a peaked diamagnetic frequency and a sheared rotation of the plasma have been taken into account. These effects either stabilise or destabilise the drift waves and to determine the net result on the drift waves requires careful analysis. To this end, dispersion relations have been obtained in various limits to determine when to expect the different effects to be dominant. The main result of this part is that with a large enough rotational shear, the drift waves will be quenched.In the second part we focus on temperature effects and thus treat reactive drift waves, specifically ion temperature gradient and trapped electron modes. In fusion plasmas the α-particles, created as a by-product of the fusion process, transfer the better part of their energy to the electrons and hence the electron temperature is expected to exceed the ion temperature. In most experiments until today, the ion temperature is greater than the electron temperature and this have been proven to improve the plasma confinement. To predict the performance of future fusion plasmas, where the fusion process is ongoing, a comprehensive study of hot-electron plasmas and external heating effects have been carried out. Especially the stiffness (heat flux vs. inverse temperature length scale) of the plasma has been examined. This work was performed by simulations done with the JETTO code utilising the Weiland model. The outcome of these simulations shows that the plasma response to strong heating is very stiff and that the plasma energy confinement time seems to vary little in the hot-electron mode.
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