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- Nilsson, Thorbjörn, 1960-
(författare)
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Den lokalpolitiska karriären : en socialpsykologisk studie av tjugo kommunalråd
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis studies the combination of an actor's course of life with a field-specific career. The career is seen runs through a social room assuming an objective shape. It also runs through a field characterized by the competition for positions and resources.The field is of a relatively stable character and is closely attached to the social room. Emphasis is laid on the municipal commissioner career and the local political field. Becoming a municipal commissioner is not a matter of a superficial change in the work situation, but of acquiring and embodying a field-specific manner and perspective.Municipal commissioners are confronted with a range of paradoxes. The paradoxes are manifested in a structure of expectation, which permeates the entire field, and which is directed towards the position of commissioner. The expectation structure of the field creates the conditions for the commissioner career as a whole and consequently defines its framework.Within this framework the overall patterns emerge as a funnel-like process during which the career tapers off successively. Commissioners develop attitudes and actions to deal with the expectations and with the paradoxes involved. These actions and attitudes evolve through a field-specific career.This dissertation focuses the sociopsychological mechanisms involved in the career. These mechanisms include the way social meaning is externalized, objectified and internalized. Social meaning guides the actors and their interaction. Meanings are fundamental to a given social order by forming an essential part of the field-specific attitude embodied by the actor. The adhesive glue of the career consists of social meanings, which form the basis of the sociopsychological profile of the career. The aim of the study is to explain social meanings in career development in the local political field.The social meanings show what guides the handling of paradoxes and the linking of the actor's life and career. The field-specific meanings also reflect the expectation structures that define the career and its phases. By explaining the social meanings of the career it also becomes apparent in what way the life an actor is phased with the field-specific career.
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| 2. |
- Persson, Anders, 1975
(författare)
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Diversity and Interference Aspects in the Downlink of Code Division Multiple Access Systems
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of six included papers and technical reports, plus an introduction. The topic studied is interference and diversity aspects in code division multiple access (CDMA) systems for mobile cellular communications. The focus in the papers is on the downlink - the communication link from the base station to the mobile terminal. A performance limiting factor in the downlink of single-carrier CDMA systems is multiple access interference due to lost orthogonality on the time-dispersive radio channel. On such channels, orthogonal frequency division multiplexing (OFDM) is a very powerful technique and, recently, several proposals of CDMA for OFDM systems have been made. Although some results for single-carrier systems are provided (paper A), it is to the area of OFDM-CDMA that the main contributions of this thesis are made (papers B-F). In the included papers, low-complexity single-user detectors are assumed. In agreement with existing results, it is concluded that direct-sequence spreading in OFDM systems is beneficial when the number of active users is low compared to the length of the spreading codes used, i.e., for low system loads. However, assuming a single-cell scenario and a channel code of a sufficiently large free distance, it is at high system loads concluded that coded orthogonal frequency division multiplexing access (OFDMA) outperforms all the considered direct-sequence schemes. This is most clearly the case in a near-far scenario - a situation that naturally will occur in the downlink due to the requirement for different transmit powers for different users. It is also concluded that coded OFDMA achieves essentially the same robustness against inter-cell interference as schemes that use direct-sequence spreading. If a low complexity detector is required, the results presented in this thesis indicate that coded OFDMA is a competitive candidate for the downlink of mobile cellular systems.
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| 3. |
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| 4. |
- Persson, Anders I., 1973
(författare)
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Opioids regulate proliferation of neural progenitors. A study on the effects of opioids on adult rat hippocampal progenitors in vitro and in vivo
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The opioid receptors were among the first pharmacologically described brain receptors. These opioid receptors have thereafter been shown to mediate effects on proliferation and differentiation in both the embryonal and adult central nervous system. The aim of this thesis was to investigate if cultured hippocampal progenitors from the adult rat brain expressed opioids and opioid receptors and to investigate a possible regulation by opioids on proliferation, differentiation and gene expression in these cultures. Furthermore, we wanted to extend the results and investigate if endogenous opioids regulated hippocampal proliferation in vivo by using opioid receptor antagonists in both non-running and voluntary running rats, a situation associated with increased levels of endogenous opioids. Hippocampal progenitors were found to release b-endorphin that bound to mu- (MOR) and delta- (DOR) but not kappa- (KOR) opioid receptors in vitro. Incubation with MOR or DOR antagonists reduced proliferation whereas stimulation with b-endorphin increased proliferation in these cultures, respectively. The opioid-induced proliferation involved both intracellular calcium and phosphatidylinositol 3-kinase that stimulated phosphorylation of mitogen-activated protein kinase (MAPK). Incubation with naloxone for ten days increased neurogenesis and reduced astrogliogenesis and oligodendrogenesis whereas stimulation with b-endorphin increased oligodendrogenesis but had no effect on astrogliogenesis. Using cDNA arrays, the levels of endogenous opioids were found to regulate gene expression for several cell cycle and oligodendrocyte-specific proteins. Stimulation with b-endorphin also increased Id1, but not Id3 mRNA levels. Down-regulation of Id1 protein using antisense oligonucleotides was suggested to antagonize the opioid-induced oligodendrogenesis.Using bromodeoxyuridine (BrdU), we observed a five-fold increase in hippocampal proliferation after nine days of wheel running in spontaneously hypertensive rats, a rat strain known to run voluntary. This increased BrdU labelling was reduced by peripheral administration of a preferential MOR, but not a DOR antagonist. In non-running rats, MOR and DOR antagonists increased hippocampal proliferation. In non-running, but not in running rats, the opioid receptor antagonists reduced adrenal gland weights and plasma levels of corticosterone. This stress hormone is known to reduce hippocampal neurogenesis. Running rats had three-fold higher levels of hippocampal Met-enkephalin-Arg-Phe levels compared to non-running rats, indicating increased opioid activity in hippocampus during running. These findings demonstrate that the levels of endogenous opioids, acting on MORs and DORs, regulate proliferation of adult rat hippocampal progenitors both in vitro and in vivo. Endogenous opioids were also shown to regulate differentiation and gene expression in cultures of hippocampal progenitors. Finally, we show that exercise robustly increases proliferation of hippocampal progenitors and that such an effect is partly mediated by endogenous opioids.
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| 5. |
- Persson, Anders
(författare)
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On Tool Failure in Die Casting
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Die casting is a very cost-efficient method of forming thin-walled and complex near net-shaped products with close geometric tolerances and good surface finish. A permanent die tool is used to make large quantities of identical products. The performance and tool life are limited by several mechanisms, e.g. thermal fatigue cracking, erosion, and corrosion. To develop new and more resistant tool materials for die casting detailed knowledge of the actual casting conditions and the tool failure mechanisms are essential. This thesis contributes to an increased knowledge of tool failure in die casting by investigating and simulating actual casting conditions and tool failure mechanisms.A method to record the temperature fluctuations in a cavity insert during actual brass die casting was developed, and details of the temperature conditions were obtained. Also, a test method based on cyclic induction heating and internal cooling of hollow cylindrical test rods was developed, where the surface strain during thermal cycling could be measured. This method reproduced the characteristic type of surface cracking observed on die casting tools, and proved to give information of the strains and stresses behind the fatigue failure.In actual die casting, the dominant tool failure mechanism is thermal fatigue cracking. The formation of the cracks is associated to accumulation of the local plastic strain that occurs during each casting cycle. Initial crack growth is facilitated by oxidation of the crack surfaces, and proceeded growth is facilitated by this oxidation in combination with crack filling of cast material, and by softening of the tool material. In addition, local enrichment of Pb at the crack front from the cast alloy melt was also observed to promote the crack growth in die casting of brass.In an investigation of thermal fatigue of two hot work tool steels, quenched and tempered to different conditions, it was found that low-cycle fatigue occurs, although the estimated tensile stress never exceed the initial yield strength of the steel. The reason is a gradual softening of the steel during the thermal cycling, and the presence of stress raising defects. The resistance against thermal cracking improves with initial tool steel hardness, because any initial ranking in hardness among the steels is unaffected by the thermal cycling.Another investigation on a selection of surface engineered tool steels, including common diffusion treatments, PVD coatings and combinations of these, showed that surface engineering generally reduce the resistance against thermal cracking as compared to untreated references, since the engineering processes influence negatively on the mechanical properties of the hot work tool steels.Finally, corrosion tests of CrN PVD-coated tool steels by exposing them to molten aluminium revealed the mechanisms of initiation and progress of liquid metal corrosion of this material combination, and that the corrosion resistance improves with the CrN coating thickness.
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