voir fichier pdf

Voir PDF

De nouveaux radio-isotopes pour la médecine nucléaire peuvent être produits par des accélérateurs de particules. C'est l'un des buts d'Arronax, un cyclotron de hautes énergies - 70 MeV - et hautes intensités - 2*350 µA - installé à Nantes. Une liste d'émetteurs b- - 47Sc, 67Cu - b+ - 44Sc, 64Cu, 82Sr/82Rb, 68Ge/68Ga - et a - 211At - à étudier en priorité a été établie. Parmi ceux là, le 47Sc et le 67Cu présentent un intérêt en thérapie ciblée. L'optimisation de leurs productions nécessite la bonne connaissance de leurs sections efficaces, mais aussi de celles de tous les contaminants créés. Nous avons lancé sur Arronax un programme de mesures de sections efficaces utilisant la technique des Stacked-foils. Elle consiste en l'irradiation simultanée d'un groupe de feuilles - cibles, moniteurs et dégradeurs - et la mesure par spectro-gamma de la production d'isotopes. Les moniteurs permettent un contrôle des pertes de faisceau tandis que les dégradeurs en diminuent l'énergie. Nous avons étudié les réactions natTi(p,X)47Sc et 68Zn(p,2p)67Cu. Les cibles étant respectivement des feuilles de natTi - achetées chez Goodfellow - ou des électrodépositions sur Ag de 68Zn enrichi. Nous les réalisons nous même ainsi que la séparation chimique des isotopes de Cuivre et de Gallium indispensable avant de procéder au comptage gamma. Les sections efficaces de plus de 40 réactions ont ainsi été obtenues sur l'intervalle de 18 MeV à 70 MeV. Une comparaison avec le code Talys est systématiquement faite, et plusieurs paramètres des modèles théoriques étudiés. Nous montrons qu'il est impossible de reproduire avec exactitude toutes les sections efficaces à partir d'un seul jeu de ces paramètres.

I denna studie undersöks huruvida den ökade alkoholkonsumtionen utgör ett problem för att uppnå Nollvisionen. Genom att använda experimentet med lördagsöppna Systembolag estimeras effekterna av en ökning i alkoholkonsumtion på trafikolyckor. Försöket med de lördagsöppna Systembolagsbutikerna i sex län ledde till en ökad alkoholkonsumtion med 3,7 procent. En Difference-in-Difference metod används för att jämföra effekterna av denna ökning på trafikolyckor i de sex försökslän med utvecklingen i en kontrollgrupp. Resultaten visar att konsumtionsökningen har ökat det totala antalet trafikolyckor i försökslänen med 8,5±2,6 procent i jämförelse med kontrollgruppen. Effekterna visar sig även skilja sig åt mellan olika olycksutfall; större effekter uppvisades för de svårare olycksutfallskategorierna. Den starkaste effekten uppvisades för kategorin svårt skadade som ökade med hela 26,4±5,6 procent. Resultaten tyder alltså på att den ökade alkoholkonsumtionen utgör ett problem för att uppnå Nollvisionen.

Peat mosses (Sphagnum) are widely distributed and are a major component of mire vegetation and peat throughout the boreal and temperate regions. Most boreal Sphagnum species regularly produce sporophytes, but the ecological role of the spore has been questioned. This study shows that the spores can form a spore bank and have the ability to germinate and contribute to moss establishment whenever suitable conditions occur. The results suggest that spore production is important for explaining the wide distribution and omnipresence of Sphagnum in nutrient-poor wetlands. The results further imply that initial recruitment from spores predominates in Sphagnum after disturbance or formation of suitable habitats. A series of experiments showed that addition of phosphorus-containing substrates, such as fresh plant litter or moose dung, resulted in spore establishment on bare, moist peat. A field experiment indicated establishment rates of about 1% of sown, germinable spores on peat with added substrates. Plant litter on moist soil, without a closed cover of bryophytes, is an important safe site for the establishment of Sphagnum spores. The results fit the observed pattern of colonisation by Sphagnum beneath Eriophorum vaginatum tussocks in mires severely disturbed by peat extraction. Successful long-distance dispersal was indicated by the occurrence of several regionally new or rare Sphagnum species in disturbed mires. Spore number per sporophyte ranged among Sphagnum species from 18 500 to 240 000, with a trade-off between spore number and spore size. Annual spore production was estimated at 15 million spores per square metre on two investigated mires. Sporophyte production showed a large interannual variation. Sporophyte production was positively related to the amount of precipitation the preceding summer. This was probably because a high water level promoted gametangium formation. Spore dispersal occurred in July and August. The earlier timing of spore dispersal in the more drought-sensitive, hollow-inhabiting sphagna should reduce the risk of sporophytes drying out prematurely during summer droughts. Spores kept refrigerated up to 13 years retained high germinability. A field experiment showed that Sphagnum can form a persistent spore bank, with a potential longevity of several decades.

This thesis represents an attempt to reveal and explain the mysterious excitation sources which cause global wave induced vibrations of ships. The wave induced vibrations of the hull girder are referred to as springing when they are associated with a resonance phenomenon, and whipping when they are caused by a transient impact loading. Both phenomena excite the governing vertical 2-node mode and possibly higher order modes, and consequently increase the fatigue and extreme loading of the hull girder. These effects are currently disregarded in conventional ship design. The thesis focuses on the additional fatigue damage on large blunt ships. The study was initiated by conducting an extensive literature study and by organizing an international workshop. The literature indicated that wave induced vibrations should be expected on any ship type, but full scale documentation (and model tests) was mainly related to blunt ships. While the theoretical investigation of whipping mostly focused on slender vessels with pronounced bow flare, full scale measurements indicated that whipping could be just as important for blunt as for slender ships. Moreover, all estimates dealing with the fatigue damage due to wave induced vibration based on full scale measurements before the year of 2000 were nonconservative due to crude simplifications. The literature on the actual importance of the additional fatigue contribution is therefore scarce. The workshop was devoted to the wave induced vibrations measured onboard a 300m iron ore carrier. Full scale measurements in ballast condition were compared with numerical predictions from four state-of-the-art hydroelastic programs. The predicted response was unreliable, and the programs in general underestimated the vibration level. The excitation source was either inaccurately described or lacking. The prediction of sea state parameters and high frequency tail behavior of the wave spectra based on wave radars without proper setting and calibration was also questioned. The measurements showed that vibrations in ballast condition were larger than in the cargo condition, the vibration was more correlated with wind speed than wave height, head seas caused higher vibration levels than following seas, the vibration level towards beam seas decayed only slightly, and the damping ratio was apparently linear and about 0.5%. The additional vibration damage constituted 44% of the total measured fatigue loading in deck amidships in the North Atlantic iron ore trade, with prevailing head seas encountered in ballast condition. Four hypotheses, which may contribute to explain the high vibration levels, were formulated. They include the effect of the steady wave field and the interaction with the unsteady wave field, amplification of short incident waves due to bow reflection, bow impacts including the exit phase and sum frequency excitation due to the bow reflection. The first three features were included in a simplified program to get an idea of the relative importance. The estimates indicated that the stem flare whipping was insignificant in ballast condition, but contributed in cargo condition. The whipping was found to be sensitive to speed. Simplified theory was employed to predict the speed reduction, which was about 5kn in 5m significant wave height. The estimated speed reduction was in fair agreement with full scale measurements of the iron ore carrier. Extensive model tests of a large 4-segmented model of an iron ore carrier were carried out. Two loading conditions with three bow shapes were considered in regular and irregular waves at different speeds. By increasing the forward trim, the increased stem flare whipping was again confirmed to be of less importance than the reduced bottom forces in ballast condition. The bow reflection, causing sum frequency excitation, was confirmed to be important both in ballast and cargo condition. It was less sensitive to speed than linear springing. The second order transfer function amplitude displayed a bichromatic sum frequency springing (at resonance), which was almost constant independent of the frequency difference. The nondimensional monochromatic sum frequency springing response was even higher. The sum frequency pressure was mainly confined to the bow area. Surprisingly, for the sharp triangular bow with vertical stem designed to remove the sum frequency effect, the effect was still pronounced, although smaller. The reflection of incident waves did still occur. In irregular head sea states in ballast condition whipping occurred often due to bottom bilge (flare) impacts, starting with the first vibration cycle in hogging. This was also observed in cargo condition, and evident in full scale. This confirmed that the exit phase, which was often inaccurately represented or lacking in numerical codes, was rather important. Flat bottom slamming was observed at realistic speeds, but the vibratory response was not significantly increased. Stern slamming did not give any significant vibration at realistic forward speeds. The fatigue assessment showed that the relative importance of the vibration damage was reduced for increasing peak period, and secondly that it increased for increasing wave heights due to nonlinearities. All three bows displayed a similar behavior. For the sharp bow, the additional fatigue damage was reduced significantly in steep and moderate to small sea states, but the long term vibration damage was less affected. The effect of the bulb appeared to be small. The contribution of the vibration damage was reduced significantly with speed. For a representative North Atlantic iron ore trade with head sea in ballast and following sea in cargo condition the vibration damage reduced from 51% at full speed to 19% at realistic speeds. This was less than measured in full scale, but the damping ratio of 1-3.5% in model tests was too high, and the wave damage in following seas in cargo condition was represented by head sea states (to high wave damage due to too high encounter frequency). Furthermore, the contribution from vibration damage was observed to increase in less harsh environment from 19% in the North Atlantic to 26% in similarWorld Wide trade. This may also be representative for the effect of routing. The dominating wave and vibration damage came from sea states with a significant wave height of 5m. This was in agreement with full scale results. In ballast condition, the nonlinear sum frequency springing appeared to be more important than the linear springing, and the total springing seemed to be of equivalent importance as the whipping process, which was mainly caused by bottom bilge (flare) impacts. All three effects should be incorporated in numerical tools. In full scale, the vibration response reached an apparently constant level as a function of wave height in both ballast and cargo condition in head seas. This behaviour could be explained by the speed reduction in higher sea states. The vibration level in cargo condition was 60-70% of the level in ballast condition. Although common knowledge implies that larger ships may experience higher springing levels due to a lower eigenfrequency, a slightly smaller ore carrier displayed a higher contribution from the vibration damage (57%) in the same trade, explained by about 1m smaller draft. Moreover, the strengthening of the larger ship resulted in a 10% increase of the 2-node eigenfrequency. The subsequent measurements confirmed that an increased hull girder stiffness was not an effective means to reduce the relative importance of the vibration damage. The relative importance of the excitation sources causing wave induced vibration may differ considerably for a slender compared to a blunt vessel. Therefore, full scale measurements on a 300m container vessel were briefly evaluated. The damping ratio was almost twice as high as for several blunt ships, possibly due to significant contribution from the container stacks. The reduced relative importance of the vibration damage with increasing wave height for the iron ore carrier in full scale was opposite to the trend obtained for the container vessel. Less speed reduction in higher sea states was confirmed, and the whipping process was apparently relatively more important for the container vessel. Both for the blunt and slender ship of roughly 300m length, the total fatigue damage due to vibration was of similar importance as the conventional wave frequency damage. The contribution to fatigue damage from wave induced vibrations should be accounted for, for ships operating in harsh environment with limited effect of routing, especially when they are optimized with respect to minium steel weight. The four hypotheses were all relevant in relation to wave induced vibrations on blunt ships. Further numerical investigation should focus on the sum frequency springing caused by bow reflection and the whipping impacts at the bow quarter. The wave amplification, steady wave elevation and the exit phase must be properly incorporated. When it comes to design by testing, an optimized model size must be selected (wall interaction versus short wave quality). The speed must be selected in combination with sea state. The wave quality must be monitored, and a realistic damping ratio should be confirmed prior to testing. For the purpose of investigating sum frequency excitation, a large restrained bow model tested in higher waves may be utilized to reduce uncertainties in the small measured pressures.

Never before has the interest for charity been greater. At this writing, U.S. charities have collected nearly one billion U.S. dollars (!) only in the aid for the disaster victims in Haiti.But can you get people to give even more? Are there yet unexplored market in which charitable organizations still have growth potential? Traditional economic theory which is based in individuals' rational behavior and self-utility maximization has a hard time to explain the phenomenon of charitable donations. But relatively new research can possibly connect the theory and the phenomenon through the theorem of warm-glow in why people actually donate money anonymously and indirectly to people they never met or will ever know who made the donation. This thesis will examine whether or not a small change in the environment could influence individuals to donate more money and / or more frequently. The study was conducted as a field experiment at an ICA store deposit station where people are faced with the choice to donate their deposit to the Swedish Red Cross instead of getting a voucher for themselves. The obtained results shows a statistically significant difference between the donation of the pledge of over 13 percentage more in the presence of a visual stimulus, more specifically a picture of a poor boy drinking clean water from a tap. That results in a doubling in nominal amounts of donations for the charity. Moreover, I find that people who already before the experiment are sympathetic to donating the pledge do so to a greater extent than people who were not. Neither sex nor age seemed to affect the results in any way.

Speciation is the process describing the formation of new species and is at the heart of evolutionary biology. According to the biological species concept only reproductively isolated forms are regarded good species. This thesis aims at identifying evolutionary processes that cause population divergence and, ultimately, speciation. Natural and sexual selection are two major candidates driving changes in traits that could render populations reproductively incompatible. In recent years, biologists have recognized that most animal species are polygamous. Therefore, sexual selection does not end at mating but continues to include interactions between individuals after mating has occurred but before zygote formation. Male-male sperm competition and cryptic female choice are two main forms of postmating sexual selection shaping reproductive traits like behaviour. The studies presented in this thesis focus on laboratory experiments attempting to identify the role of postmating sexual selection in causing reproductive divergence across populations in beetles. The majority of studies were performed using a Bruchid beetle, Callosobruchus maculatus, a common, worldwide pest on stored leguminose seeds. I used two major methodological approaches. One approach seeks to identify the traces left by past selection among extant conspecific populations, by assessing the pattern of female reproductive responses to mating with males of decreasing relatedness. Second, I used a selection experiment to disentangle the joint effect of natural and sexual selection acting simultaneously on diverging replicated selection lines. In general, these experiments revealed that postmating sexual selection can be a powerful engine of incipient divergence between allopatric populations. Changes in traits underlying variables such as female reproductive output, female mating rate or male success in sperm competition evolved rapidly and could in some cases effectively reduce gene flow between conspecific populations. While postmating sexual selection per se can drive divergence, I found that interactions with natural selection can limit divergence in reproductive characters. Sexual selection tended to reinforce natural selection under strong directional selection. In contrast, sexual selection inflicted a reproductive load on populations under weak natural selection. Thus, the joint effects of natural and sexual selection on allopatric populations are non-trivial and should be considered in greater detail in future studies of early divergence.

In 1999, the Swedish Parliament decided to launch an experiment to test the idea of replacing, at the compulsory educational level, the national time schedule with localized control of schedules. This was in keeping with strategies of deregulation, decentralisation and increased local autonomy that had dominated Swedish education policy, particularly since the 1990s. The aim of the thesis is to describe and analyse the initiation, decision, implementation and consequences of this experiment The analytical framework combines several different approaches and theories from the literature on public policy and policy analysis. The framework encompasses four dimensions, which cover the experiment’s origins, local application in the classroom setting and consequences. On the empirical level, findings are based on interviews with 32 municipal school directors, and head teachers, teachers and pupils in three schools participating in the experiment, as well as written sources from schools, municipalities, and the national level. The thesis shows that the policy problem the experiment was intended to resolve was represented in an inconsistent manner: On the one hand, the experiment was perceived as a driving force for change; on the other hand, it was seen as legitimising a change that had already taken place. Furthermore, the experiment was formulated in vague terms, which accorded far-reaching discretionary space to the schools. The program’s causal theory expressed by the policy makers was complex, containing a multifaceted chain of presumptions on a range of activities and processes through which the experiment ultimately would lead to improved opportunities for pupils to reach the educational objectives. Empirically, this prediction proved to be invalid as student achievement did not increase. The degree of implementation at the local level varied according to the comprehension, capability and willingness of those involved to carry out the experiment. The courses of action taken by the schools frequently could have been undertaken within the existing legislative framework, as they mostly concerned new ways of working and organising staff and pupils. An assessment of the objectives attained showed that, even if elements of developmental work corresponding to the direction stated in the policy documents were observed, the experiment did not emerge as the primary explanatory factor for this result Thus, the net impact of the experiment can be questioned. If judged against the criterion of adaptiveness, the results are more successful than if the experiment is assessed according to goal-attainment and the validity of the program theory. The experiment was found to integrate, alter and accommodate itself readily to local needs. The thesis illustrates the complexity of formulating and implementing policy in a decentralised context and points to important aspects in the historical background of the programme, which often tend to be overlooked when policy is analysed and discussed. At the same time, the study sheds light on the significant role played by street-level implementation actors in the educational context.

This thesis includes both experimental and theoretical investigations, presented in a series of eight papers. The experimental part ranges from the construction procedures of an apparatus for Bose-Einstein condensates, to full scale experiments using three different set-ups for ultracold atoms in optical lattices. As one of the main themes of the thesis, an experimental apparatus for production of Bose-Einstein Condensates is under construction. A magneto-optically trapped sample, hosting more than 200 million 87Rb atoms, have successfully been loaded into a magnetic trap with high transfer rate. The lifetime of the sample in the magnetic trap is in the range of 9 s, and the atoms have been shown to respond to evaporative cooling. The experiment is ready for optimization of the magnetic trap loading, and evaporative cooling parameters, which are the final steps for reaching Bose-Einstein condensation. The set-up is designed to host experiments including variable geometry optical lattices, and includes the possibility to align laser beams with high angular precision for this purpose. The breakdown of Bloch waves in a Bose-Einstein condensate is studied, attributed to the effect of energetic and dynamical instability. This experimental study is performed using a Bose-Einstein condensate in a moving one-dimensional optical lattice at LENS, Florence Italy. The optical lattice parameters, and the thermal distribution of the atomic sample required to trigger the instabilities, are detected, and compared with a theoretical model developed in parallel with the experiments. In close connection with these one-dimensional lattice studies, an experimental survey to characterize regimes of superradiant Rayleigh scattering and Bragg scattering is presented. Tunneling properties of repulsively bound atom pairs in double well potentials are characterized in an experiment at Johannes Gutenberg University, Mainz Germany. A three-dimensional optical lattice, producing an array of double wells with tunable properties is let to interact with a Bose-Einstein condensate. Pairs of ultracold atoms are produced on one side in the double wells, and their tunneling behavior, dependent on potential barrier and repulsion properties, is studied. A theoretical study of the crossover between one- and two-dimensional systems has been performed. The simulations were made for a two-dimensional array of atoms, where the behavior for different tunneling probabilities and atom-atom repulsion strengths was studied. Scaling relations for systems of variable sizes have been examined in detail, and numerical values for the involved variables have been found.