Synthesis of phosphodiester-containing bacterial cell wall components : teichoic acids, capsular polysaccharides and phosphatidyl glycerol analogues

This thesis describes the synthesis of various teichoic acid (TA)-fragments, capsular polysaccharide (CPS)-mimics and a toolbox of glycerol phosphate probes. Most of these molecules feature one or more phosphodiester functions, the introduction of which has been accomplished with phosphoramidite chemistry. The versatility of glycerol- and carbohydrate building blocks provided with a 2-cyanoethyl-protected phosphoramidite is illustrated by their application both in solution and in automated solid phase syntheses of TA and CPS oligomers as well as probes. The CPS-mimics are based on a polysaccharide present in the capsule of the gram negative bacterium Neisseria meningitidis, the pathogen that is the major cause of bacterial meningitis. The TA-fragments described in this thesis correspond to lipoteichoic acids (LTA) and wall teichoic acids (WTA) from Enterococcus faecalis and Enterococcus faecium, two commensal Gram-positive bacteria inhabiting the gastrointestinal tract. In both these bacterial families multi-drug-resistant strains have evolved and they are responsible for the majority of hospital-acquired infections. Enterococcal LTA generally consists of sn-glycerol-1-phosphate repeating units that can be decorated with carbohydrate- or D-alanyl appendages on the 2-OH of the glycerol moieties. The biosynthetic machinery of WTA is more complicated and can result in completely different structures

A case for incorporating standby generators into the South African electricity system

This paper examines how existing standby generators may benefit the South African electricity system. Eskom, the national electricity utility, supplies 92% of South Africa’s electricity needs at a price to consumers that is the lowest in the world, making it virtually impossible for alternative generation to compete. Installed electricity generation capacity is 38 154MW with a reserve margin of 8-10%. Eskom would prefer a margin closer to 15% but demand growth for the next year will reduce the margin further, to 3.75%. One response has been to introduce a demand management programme The country has begun to suffer more frequent outages, particularly during winter when demand is highest. One aspect of the management programme is to shift the two daily peaks to the ‘valleys’. Eskom estimates a possible 3 000MW capacity available from standby generators. The research should deliver a more accurate figure, as well as the location of these generators, particularly with respect to network constraints. Also considered are issues of synchronisation with the grid, emissions, noise and other environmental impacts associated with the operation of distributed generation, as well as the contractual conditions under which such an arrangement may be possible

Success has many fathers, failure remains an orphan

Was the sharp upturn of life expectancy in the Netherlands partly due to increased health care funding for the elderly? I argue that there is nothing unusual to the increasing life expectancy since the beginning of the twenty-first century, and that there is no observable relationship with changed health care funding whatsoever. What was highly unusual was the rather dramatic lagging of Dutch life expectancy between 1980 and 2000. The reasons of this failure remain clouded in mystery

Application of hydropedological insights in hydrological modelling of the Stevenson-Hamilton Research Supersite, Kruger National Park, South Africa

Soil information is increasingly sought after for hydrological modelling, as the importance of soil in the hydrological cycle is understood better. In this paper the output of a digital soil mapping exercise was used as the soil input into a distributed hydrological model (ACRU) for a test site within the Stevenson-Hamilton Research Supersite, Kruger National Park (South Africa). The aim was to determine the effect of parameterising a hydrological model with increased levels of soil information, at different scales. To accommodate this aim, ACRU was run in 3 different modes, each with increasing levels of input, on 3 catchments, including a 1st, 2nd and 3rd order catchment. The outputs evaluated included both streamflow and soil water content at selected soil profiles. Simulation accuracy increased with higher levels of soil input, as well as with increasing catchment size. The improved accuracy with increased soil input underscores the value of detailed soil information in modelling, while the improved results with increased catchment size show that the optimal scale for including soil information has not yet been reached.Keywords: ACRU; digital soil mapping; hillslope hydrology; hydropedology; Kruger National Par

Spin transport in graphene nanostructures

Graphene is an interesting material for spintronics, showing long spin relaxation lengths even at room temperature. For future spintronic devices it is important to understand the behavior of the spins and the limitations for spin transport in structures where the dimensions are smaller than the spin relaxation length. However, the study of spin injection and transport in graphene nanostructures is highly unexplored. Here we study the spin injection and relaxation in nanostructured graphene with dimensions smaller than the spin relaxation length. For graphene nanoislands, where the edge length to area ratio is much higher than for standard devices, we show that enhanced spin-flip processes at the edges do not seem to play a major role in the spin relaxation. On the other hand, contact induced spin relaxation has a much more dramatic effect for these low dimensional structures. By studying the nonlocal spin transport through a graphene quantum dot we observe that the obtained values for spin relaxation are dominated by the connecting graphene islands and not by the quantum dot itself. Using a simple model we argue that future nonlocal Hanle precession measurements can obtain a more significant value for the spin relaxation time for the quantum dot by using high spin polarization contacts in combination with low tunneling rates

Yang-Yang thermodynamics on an atom chip

We investigate the behavior of a weakly interacting nearly one-dimensional (1D) trapped Bose gas at finite temperature. We perform in situ measurements of spatial density profiles and show that they are very well described by a model based on exact solutions obtained using the Yang-Yang thermodynamic formalism, in a regime where other, approximate theoretical approaches fail. We use Bose-gas focusing [Shvarchuck etal., Phys. Rev. Lett. 89, 270404 (2002)] to probe the axial momentum distribution of the gas, and find good agreement with the in situ results.Comment: extended introduction and conclusions, and minor changes throughout; accepted for publication in Phys. Rev. Let

The relation between sleep quality, sleep quantity, and gastrointestinal problems among colorectal cancer survivors:Result from the PROFILES registry

PURPOSE: Common residual symptoms among survivors of colorectal cancer (CRC) are sleep difficulties and gastrointestinal symptoms. Among patients with various gastrointestinal (inflammatory) diseases, sleep quality has been related to gastrointestinal symptoms. For CRC survivors, this relation is unclear; therefore, we examined the association between sleep quality and quantity with gastrointestinal symptoms among CRC survivors. METHODS: CRC survivors registered in the Netherlands Cancer Registry—Southern Region diagnosed between 2000 and 2009 received a survey on sleep quality and quantity (Pittsburgh Sleep Quality Index) and gastrointestinal symptoms (European Organisation for Research and Treatment of Cancer, Quality of Life Questionnaire-Colorectal 38, EORTC QLQ-CR38) in 2014 (≥ 4 years after diagnosis). Secondary cross-sectional data analyses related sleep quality and quantity separately with gastrointestinal symptoms by means of logistic regression analyses. RESULTS: In total, 1233 CRC survivors were included, of which 15% reported poor sleep quality. The least often reported gastrointestinal symptom was pain in the buttocks (15.1%) and most often reported was bloating (29.2%). CRC survivors with poor sleep quality were more likely to report gastrointestinal symptoms (p’s < 0.01). Survivors who slept < 6 h were more likely to report symptoms of bloating or flatulence, whereas survivors who slept 6–7 h reported more problems with indigestion. CONCLUSIONS: Worse sleep quality and short sleep duration were associated with higher occurrence of gastrointestinal symptoms. IMPLICATIONS FOR CANCER SURVIVORS: Understanding the interplay between sleep quality and gastrointestinal symptoms and underlying mechanisms adds to better aftercare and perhaps reduction of residual gastrointestinal symptoms in CRC survivors by improving sleep quality

Spin transport in high quality suspended graphene devices

We measure spin transport in high mobility suspended graphene (\mu ~ 10^5 cm^2/Vs), obtaining a (spin) diffusion coefficient of 0.1 m^2/s and giving a lower bound on the spin relaxation time (\tau_s ~ 150 ps) and spin relaxation length (\lambda_s=4.7 \mu m) for intrinsic graphene. We develop a theoretical model considering the different graphene regions of our devices that explains our experimental data.Comment: 22 pages, 6 figures; Nano Letters, Article ASAP (2012) (http://pubs.acs.org/doi/abs/10.1021/nl301050a