Hypertension is a widespread condition which may cause cardiovascular events when left untreated. If high blood pressure (BP) is noticed at all, it is mostly only sub-optimally controlled making nutritional interventions a cost-effective and safe preventive measure and an alternative to medical treatment. Previous studies have shown that increased fibre consumption reduces BP which was particularly effective in hypertensive subjects. Fibres are indigestible and hence are available for fermentation by the colonic microbiota which produces the short chain fatty acids (SCFAs) acetate, propionate and butyrate. Intriguingly, recent studies carried out in mice showed that SCFAs can reduce BP. Therefore, we hypothesised that gut microbiota-derived SCFAs can (1) reduce BP in middle-aged male volunteers and (2) influence the protein expression of BP regulatory systems in a cellular model. As the development of a cellular angiotensin II-induced hypertension model was unsuccessful, the effects of SCFAs on a molecular level were assessed in unstimulated human aortic endothelial cells (HAECs). The expression of proteins involved in the BP regulating renin angiotensin system (RAS) was assessed by western blotting. Additionally, a human supplementation trial is being carried out looking at the acute consumption of a low (0.16 g) and high (2.35 g) propionate dose on BP and other cardiovascular markers in middle-aged male volunteers. In vitro work showed that SCFAs did not affect RAS expression in HAECs. However, acute propionate supplementation influenced BP and its regulation. Preliminary data show, that while a high propionate dose led to increases in plasma propionate by on average 4 µM and acetate levels with concurrent increases in BP, arterial stiffness and plasma renin concentration, a low propionate dose resulted in plasma propionate increases of about 0.5 µM with simultaneous reductions in systolic BP. Taken together, these results suggest that SCFAs play a regulatory role in the homoeostasis of BP.

No description available.

Bismuth is among the most studied of all elements, but its behaviour under pressure exhibits myriad unexpected puzzles even after many decades of research. Bismuth narrowly avoids being an insulator: a Peierls-type distortion almost completely gaps the electronic energy bands, producing a rhombohedral metal with a tiny overlap of conduction and valence bands. The resulting solitary free electron per 100,000 atoms can travel large distances in high-purity crystals, leading to a host of unusual properties. We show that the rhombohedral structure can be tuned with pressure, driving the carrier concentration to nearly zero. We compare our measurements to recent experimental advances implying the formation of novel electronic order driven by the pairing of low-density electrons and holes, and show evidence for a previously unseen phase at very low temperatures in the semiconducting state. We also present a method for calculating the carrier density and resistivity as a function of pressure, based on phenomenological band parameters and a simple charge-balance argument, and demonstrate that this approach can quite well describe most - but not all - of the observed behaviour of the resistivity. At higher pressures, bismuth undergoes a transition into a quasiperiodic host-guest structure. Here, two distinct crystal lattices coexist and interpenetrate, but the lattice parameters are incommensurate. This crystal thus lacks a single unit cell - an unexpected complexity for a simple element. The discovery of such unusual structures in elements is a new phenomenon and their physical properties are rather unexplored. We present experimental measurements of the resistivity and magnetic susceptibility in the incommensurate host-guest state. We argue that the experimental data (in particular, the shape of the normal-state electrical resistivity, and the high value of the low-temperature upper critical field) may be evidence for strong electron-phonon coupling. This strong coupling is consistent with theoretical predictions which suggest the presence of a low-energy phonon mode arising due to the vanishing energy cost of moving guest atoms through the host lattice.

The vapour pressures of some inorganic sulphates at high temperatures were determined by the combined use of the Knudsen effusion, transpiration, and matrix isolation methods. After a detailed comparison with the results of other investigators, it is concluded that the principal vapour species in the case of K2SO4, Rb2SO4, and Cs2SO4 are the undecomposed sulphate molecules themselves, and in the case of Li2SO4 the decomposition products, Li, SO2, and O2. The sodium salt also decomposes to some extent into Na, SO2, and O2, but it is deduced that the vapour concentration of the species Na2O4 is probably greater than was formerly supposed. The decomposition of alkaline earth sulphates is also discussed, especially in the light of the dependence of the Knudsen effusion results upon the size of the orifice used. On the basis of the vapour constitutions deduced, thermodynamic functions for the important species present are tabulated up to 1400 K or above. Reference is also made to the function of sodium sulphate in the glass-making industry and to the possible mechanism of its corrosive action on furnace walls.

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M.Ing. / Vehicles used in military, agricultural, forestry, or construction applications often encounter different road surfaces during a single journey. In order to optimise the mobility of these vehicles, different tyre pressures are required for different types of terrain (sand, mud, cross country, tar road, etc.). An in-motion tyre pressure control system will enable the vehicle's operator to change the tyre pressures without leaving the vehicle. Such a system will not only allow optimum surface contact between the tyres and the terrain - thus improving vehicletraction, but it can also increase the lifespan of the tyres and reduce fuel consumption. The key design criteria for such a system are: quick reaction times, an effective operator interface, and reliability. In case of system failure, the operator must be able to override the control, and the tyres should be inflated to a pre-set default pressure. When the fault had been corrected, the system can be restarted from within the cabin, to inflate or deflate the tyres as required. The focus of this thesis is on the design criteria of a tyre pressure control system, receiving inputs from the driver and from onboard vehicle sensors; and then adjusting individual tyre pressures if necessary, while the vehicle is on the move. Based on the inputs to the control system, the optimum setting for the tyre pressure is determined from a look-up table stored in memory of an onboard computer. This table contains the pressure-speed and pressure-axle load relationship. A unique relation is programmed into the microprocessor for each different vehicle. To install a tyre pressure control system on a vehicle, a computer program is used to control the following hardware which are necessary to inflate or deflate tyres: An air compressor and storage tank. Pneumatic valve. Rotating seal. Pressure and speed sensing elements. Electronic control unit. An experimental set-up was built, from various components or sub-systems, which were integrated systematically until the system was working as a unit. The functionality of the system was tested, and although the results obtained do not yet justify the commercial manufacturing of such systems, it is trusted that this research has contributed towards the increased emphasis that is placed upon vehicle safety and comfort systems.

M.Tech.