Vacuum polarization by electric fields is a well established fact. Assuming that anti-matter has negative gravitational properties, the fluctating electric dipoles from the quantum vacuum may also have gravitational dipolar properties. A model is developed that describes how electric fields could gravitationally polarize the vacuum causing gravitational screening or anti-screening effects. This leads to a violation of the Weak Equivalence Principle or a general mass change most notabily for elementary particles, such as the electron or positron, below but close to measured boundaries. Also a gravitational vacuum torque is predicted to act on a charged capacitor perpendicular to a gravitational field. The predictions could be verified by future laboratory experiments that could contribute on our understanding of the gravitational properties of anti-matter.

We use the shear catalogue from the CFHT Stripe-82 Survey to measure the subhalo masses of satellite galaxies in redMaPPer clusters. Assuming a Chabrier initial mass function and a truncated NFW model for the subhalo mass distribution, we find that the subhalo mass to galaxy stellar mass ratio increases as a function of projected halo-centric radius r(p), from M-sub/M-star = 4.43(-2.23)(+6.63) at r(p) is an element of [0.1, 0.3] h(-1) Mpc toM(sub)/M-star = 75.40(-19.09)(+19.73) at r(p) is an element of [0.6, 0.9] h(-1) Mpc. We also investigate the dependence of subhalo masses on stellar mass by splitting satellite galaxies into two stellar mass bins: 10 < log (M-star/h(-1) M-circle dot) < 10.5 and 11 < log (M-star/h(-1) M-circle dot) < 12. The best-fitting subhalomass of the more massive satellite galaxy bin is larger than that of the lessmassive satellites: log(M-sub/h(-1) M-circle dot) = 11.14(-0.73)(+0.66) (M-sub/M-star = 19.5(-17.9)(+19.8)) versus log(M-sub/h(-1) M-circle dot) = 12.38(-0.16)(+0.16) (M-sub/M-star = 21.1(-7.7)(+7.4)).

Thesis (MSc (Physics))--University of Stellenbosch, 2009. / In this thesis a general relativistic formalism for neutrino-induced weak production of strange particles is presented. In our formalism it is shown that the differential cross section is constructed as a contraction between a leptonic tensor and a hadronic tensor. The electroweak theory of Glashow, Salam and Weinberg is used to calculate the leptonic tensor exactly. The hadronic current is determined from the newly derived general form of the weak hadronic current which is expressed in terms of eighteen invariant amplitudes that parametrize the hadron vertex. The Born diagram is used to approximate the unknown hadronic vertex and the numerical calculation is made by evaluating the tree diagrams in terms of standard weak form factors and the strong coupling constants in the framework of the Cabibbo theory and SU(3) symmetry. The investigation is made for charged current reactions in terms of the angular distribution of the differential cross section with respect to the outgoing kaon angle and the results are discussed.

The topological insulator Bi2Te3 has been grown on Si(111)-(7 × 7) surface by molecular beam epitaxy. Reflection high energy electron diffraction, in situ scanning tunnelling microscopy, x-ray photoelectron spectroscopy and ex situ x-ray diffraction studies have been performed to analyze the quality of the growth. These analyses suggest a very good layer-by-layer epitaxial growth of Bi2Te3 on the atomically at Si surface. The magnetoresistance of the samples has been studied with magnetic field perpendicular and parallel to the sample surface, up to 9 T, over a temperature range of 2 K to 20 K. A sharp dip at low fields (0 T - 1 T) and near-linear behavior for high fields (> 4 T) have been observed in the perpendicular field magnetoresistance. The low field dip is due to weak antilocalization that agrees well with the simplified Hikami-Larkin-Nagaoka model. It has been demonstrated that both the low field dip and the high field near-linear behavior can be explained by the original Hikami-Larkin-Nagaoka formula alone in a system with strong spin-orbit coupling. From the fitting of the perpendicular field magnetoresistance the phase coherence length, the mean free path and the spin-orbit relaxation time have been estimated. The phase coherence length shows power law dependence with temperature indicating two dimensional nature of the transport. The power law also suggests electron electron interaction as the prominent dephasing mechanism. The out-of-plane spin-orbit relaxation time is determined to be small and the in-plane spin-orbit relaxation time is found to be comparable to the momentum relaxation time. The estimation of these charge and spin transport parameters is useful for topological insulator based magneto electric device applications. It also has been shown that the strong spin-orbit coupling suppresses the Zeeman contribution in perpendicular field magnetoresistance. The logarithmic divergence of perpendicular field magnetoresistance with temperature for low temperature range (2 K - 20 K) at high fields shows the presence of Coulomb interaction in the spin singlet channel. For magnetoresistance with the field parallel to the sample surface, the observed magnetoresistance has parabolic dependence for small fields (0 T - 0.6 T) and logarithmic dependence for large fields (> 3 T), which is due to the Zeeman effect. It is found that the data are inconsistent with only the Maekawa and Fukuyama theory of non interacting electrons with Zeeman contributions to the transport, but are consistent with theory if one also takes into account the electron electron interaction and the Zeeman splitting term in the electron electron interaction theory of Lee and Ramakrishnan. The Zeeman g-factor and the strength of Coulomb scattering due to electron electron interaction have been estimated from fitting of the parallel field magnetoresistance. The magnetoresistance also shows anisotropy with respect to the field directions. The angle dependent anisotropic magnetoresistance can be fitted well by the original HLN theory alone. The anisotropy can have potential application in anisotropic magnetic sensors. / text

<p>Denna uppsats syftar till att testa The Weak Government Hypothesis. Hypotesen är att en fragmenterad regering ackumulerar större skulder än ickefragmenterade regeringar och att graden av fragmentering påverkar storleken på skulden. Hypotesen testas med paneldata över 283 svenska kommuner under perioden 1996-2004. Resultaten från den empiriska studien ger inte något enhälligt stöd åt hypotesen. Studien finner dock visst stöd för att en lokal koalitionsregering bestående av flera jämnstora partier tenderar att ha en positiv effekt på de långfristiga skuldnivåerna under valår. Lokala koalitionsregeringar med partier från olika ideologiska block, så kallade regnbågskoalitioner, tenderar också att ha en generell positiv effekt på de långfristiga skulderna. Resultaten är dock ingalunda robusta. En studie över en längre tidsperiod är önskvärd för att några konkreta slutsatser kring validiteten i hypotesen ska kunna dras.</p>

We investigate the uses of gravitational lensing for analysing the dark matter haloes around galaxies, comparing galaxies within groups and clusters to those in the field. We consider two cases: when only photometric redshift data is available, and when spectroscopic redshift data is available for a sufficiently large sample of galaxies. For the case of data with photometric redshifts, we analyse the CFHTLenS dataset. This dataset is derived from the CFHTLS-Wide survey, and encompasses 154 deg^2 of high-quality shape data. Using the photometric redshifts to estimate local density, we divide the sample of lens galaxies with stellar masses in the range 10^9 Msun to 10^10.5 Msun into those likely to lie in high-density environments (HDE) and those likely to lie in low-density environments (LDE). Through comparison with galaxy catalogues extracted from the Millennium Simulation, we show that the sample of HDE galaxies should primarily (~61%) consist of satellite galaxies in groups, while the sample of LDE galaxies should consist of mostly (~87%) non-satellite (field and central) galaxies. Comparing the lensing signals around samples of HDE and LDE galaxies matched in stellar mass, we show that the subhaloes of HDE galaxies are less massive than those around LDE galaxies by a factor 0.65+/-0.12, significant at the 2.9 sigma level. A natural explanation is that the haloes of satellite galaxies are stripped through tidal effects in the group environment. Our results are consistent with a typical tidal truncation radius of ~40 kpc. For the case of data with spectroscopic redshifts, we analyse the GAMA-I and the ongoing GAMA-II surveys. We demonstrate the possibility of detecting tidal stripping of dark matter subhaloes within galaxy groups using weak gravitational lensing. We have run ray-tracing simulations on galaxy catalogues from the Millennium Simulation to generate mock shape catalogues. The ray-tracing catalogues assume a halo model for galaxies and groups, using various models with different distributions of mass between galaxy and group haloes to simulate different stages of group evolution. Using these mock catalogues, we forecast the lensing signals that will be detected around galaxy groups and satellite galaxies, as well as test two different methods for isolating the satellites' lensing signals. A key challenge is to determine the accuracy to which group centres can be identified. We show that with current and ongoing surveys, it will possible to detect stripping in groups of mass 10^12 Msun to 10^15 Msun.

The ability of yeasts to grow and adapt under extreme environmental conditions including within the presence of weak organic acid preservatives has led to substantial economic losses through manufactured food and beverage spoilage. The food industry has employed the use of various weak organic acids such as sorbic, benzoic and acetic acid as preservatives to help prevent spoilage by yeasts and moulds. The mechanisms by which S. cerevisiae is able to adapt to these weak organic acids have been extensively studied. A lesser studied weak organic acid preservative is citric acid. The aim of this study was to gain further information on the mechanisms of citric acid adaptation and through this identify potential targets for new preservation strategies. Current knowledge indicates the involvement of the HOG pathway in citric acid adaptation. A citric acid sensitivity screen from a previous study also isolated a SR protein kinase Sky1p, involved in polyamine metabolism, which has been connected with other crucial cellular processes including modulation of ion homeostasis and osmotic shock. In this study we have undertaken a systematic screen for genes that confer increased sensitivity to citric acid paying particular attention to those involved in polyamine metabolism and those known to encode proteins which have evidence of interactions with Sky1p. Many of the deletion strains tested exhibited hypersensitivity to citric acid including Δsky1. Protein-protein interaction maps for Sky1p highlighted an interesting secondary interacting protein Nmd5p, an importin crucial for the nuclear localization of Hog1p. This information suggested there may be the possibility of linkage between Sky1p and Hog1p and their roles in citric acid tolerance, perhaps through Nmd5p. This provided an incentive to perform a range of experiments to test this theory. Proteomic and phosphoproteomic analyses were carried out to study protein expression and phosphorylation changes in response to citric acid stress. Comparative proteomic analyses for Δsky1, Δhog1 and BY4741a with and without citric acid identified four instances of analogous protein expression responses in both Δsky1 and Δhog1, suggesting functional overlap upon exposure to citric acid. Epistasis studies of Δhog1Δsky1 suggested that the two protein kinases do not function on the same pathway. However, overexpression analyses did suggest some functional interaction between Hog1p and Sky1p in mediating citric acid resistance since overexpression of Sky1p in Δhog1 resulted in partial rescue of growth. Further supporting evidence for some functional interaction or linkage was provided by Hog1p phosphorylation and localisation studies. Δsky1 exhibited dual phosphorylation of Hog1p in the absence of citric acid stress; implying that loss of SKY1 results in dual phosphorylation of Hog1p by either prompting phosphorylation or perhaps by interfering with dephosphorylation of Hog1p. Localisation studies of Hog1p proved that like osmotic stress, citric acid stress results in nuclear translocation of Hog1p and deletion of SKY1 seemed to interfere with this localisation to some extent. In light of the results attained in this study we believe we have evidence to propose a novel role for Sky1p in mediating resistance to citric acid and that there is also substantial evidence to suggest that Sky1p shares some functional redundancy and perhaps functional linkage with Hog1p in citric acid adaptation.

Writing concurrent programs with shared memory is often not trivial. Correctly synchronising the threads and handling the non-determinism of executions require a good understanding of the interleaving semantics. Yet, interleavings are not sufficient to model correctly the executions of modern, multicore processors. These executions follow rules that are weaker than those observed by the interleavings, often leading to reorderings in the sequence of updates and readings from memory; the executions are subject to a weaker memory consistency. Reorderings can produce executions that would not be observable with interleavings, and these possible executions also depend on the architecture that the processors implement. It is therefore necessary to locate and understand these reorderings in the context of a program running, or to prevent them in an automated way. In this dissertation, we aim to automate the reasoning behind weak memory consistency and perform transformations over the code so that developers need not to consider all the specifics of the processors when writing concurrent programs. We claim that we can do automatic static analysis for axiomatically-defined weak memory models. The method that we designed also allows re-use of automated verification tools like model checkers or abstract interpreters that were not designed for weak memory consistency, by modification of the input programs. We define an abstraction in detail that allows us to reason statically about weak memory models over programs. We locate the parts of the code where the semantics could be affected by the weak memory consistency. We then provide a method to explicitly reveal the resulting reorderings so that usual verification techniques can handle the program semantics under a weaker memory consistency. We finally provide a technique that synthesises synchronisations so that the program would behave as if only interleavings were allowed. We finally test these approaches on artificial and real software. We justify our choice of an axiomatic model with the scalability of the approach and the runtime performance of the programs modified by our method.

The foreign policy decisions of small, weak states often go overlooked in the international system. Most understandings of small states emphasize their limited foreign policy choices under the influence of larger, global powers. Yet, there are numerous examples of small states selecting their own foreign policies unencumbered by the international system. This study seeks out those examples and argues that weak states often have the freedom to form their own policies and positions uninfluenced by global powers. To explain the foreign policy decision-making process of small, weak states and explore the relationship between small and large powers, this paper asks when and how do small, weak client states choose to not comply with the demands of large patron states in patron-client relationships? The use of the patron-client framework is a valuable tool for analyzing the foreign policy selection process of small and large states interacting in dyadic relationships. To answer the question, the study examines three separate cases involving patron-client relationships. In each case, the United States serves as the patron state while El Salvador, Pakistan, and Thailand represent the separate client states. The case studies examine moments of client-driven noncompliance to reveal how small states form foreign policy decisions. Ultimately, small states not only wield significant control of their own foreign policy decisions, choosing not to comply with the demands of a stronger patron state, but they also form policy based off diverse considerations—including domestic factors, self-interest, and capacity to comply. Findings suggest that clients in international patron-client relationship have more influence over stronger states than current theories would suggest.

This thesis concerns several advances in electroanalytical chemistry which are separated into four parts: the electrochemical investigation of diffusional behaviour, the mechanistic and kinetic study of electrochemistry with room temperature ionic liquids (RTILs), the study of weakly-supported electrochemistry and a comparison of the Butler-Volmer and Marcus-Hush kinetic theories of electron transfer. A study of the diffusional behaviour of electroactive species is essential for further studies, especially in the case when electrochemistry is complicated through ion-pairing interactions between the electroactive species and other electrolytes. In Part II of this thesis, the possibility of the ferricenium ion-paired with perchlorate and hexauorophosphate in acetonitrile was discussed firstly employing chronoamperometric technique. Afterwards, the hexaammineruthenium III/II couple supported by chloride, nitrate and sulfate respectively was studied by a similar method. In order to avoid unwanted ion-pairing effects, room temperature ionic liquids can be applied as solvent, which provide high conductivity by their own ionic nature so that experiments can be conducted without adding additional supporting ions. Because of RTILs have distinctive properties, for example, high viscosity, high conductivity and ionic nature, electrochemistry could be greatly changed compared to those in conventional solvents. Part III of this thesis gives a detailed description of this topic. First, a study of the reduction of 1,4-benzonquinone in 1-ethyl-3-methylimidazolium bis(triuoromethanesulfonyl)imide is presented to show the new mechanistic insight into comproportionation in a electrochemical process. Second, a discussion of the oxidation of hydroquinone in the same RTIL is introduced to suggest a possible ECE scheme which was never reported before. The interest of weakly supported electrochemistry is also well-established, which not only provides another alternative strategy to avert ion-pairings but also offers more physical insights into electrochemical processes. Quantitative methods analysing voltammetries without an excess amount of supporting electrolyte are developed by introducing a migration term into the mass transport equation. In Part IV, new mechanistic insights into the reduction of 2-nitrobromobenzene and the dimerisation of 2,6-diphenylpyrylium in acetonitrile were provide by using weakly-supported cyclic voltammetry. Also, pulse techniques was also adopted to investigate the reduction of cobaltocenium and cobalt(III) sepulchrate, giving an alternative way for electrochemical analysis. A major application of electroanalytical chemistry is investigating electrochemical kinetics. Two kinetic models mostly concerned by electrochemists are Butler-Volmer and Marcus-Hush formalisms. The classic phenomenological model, Butler-Volmer formalism successfully describes most common electron transfer kinetics but shows little reference with nature of the involved species, solution and electrode material, while a more physically insightful theory, the Marcus-Hush formalism, takes species natural properties, for instance, a change of distances or geometry in the solvation or coordination shells of the redox, into account although it requires more complex formulations. Comparative studies of these two theories are presented in Part V in order to improve our understanding of the electron transfer kinetics under different circumstances. First, comparison of cyclic voltammograms of the reduction of europium(III) and 2-methyl-2-nitropropane at mercury microhemispherical electrodes was carried out. Second, square wave and differential pulse voltammetric techniques were also employed to further discriminate the two kinetic models. These studies all find that the symetric Marcus-Hush theory assuming the reactants and products have identical force constant dose not satisfactorily agree with the experimental results. Hence, the introduction of asymmetric Marcus-Hush theory was presented considering different oxidative and reductive reorganization energies, which gives reasonable agreement with experiments and makes this theory more insightful.