Investigation of the wind load on heliostats in stow position

In recent years there has been an increasing effort to lower the capital costs of concentrating solar thermal (CST) power tower (PT) plants to make their levelised cost of electricity (LCOE) more competitive with base-load energy systems. The field of heliostats contributes the most to the capital cost of a PT plant, hence the costs of manufacturing and installation of heliostat components can be reduced by optimising their structural design to withstand the maximum wind loads during high-wind conditions in the stow position. Heliostats are moved from operational positions and aligned parallel to the ground in the stow position during periods of high wind speeds to minimise the effect of fluctuating pressures and unsteady forces that can lead to structural failure. While the effects of temporal variation of turbulence on heliostat design wind loads have been investigated for operational positions, further knowledge of the spatial distribution of turbulence in the frequency domain of the atmospheric boundary layer (ABL) and the dynamic wind loads in stow position needs to be developed. The purpose of this thesis is to develop an understanding of the turbulence effects in the ABL that can lead to maximum wind loads during gusty high-wind conditions. This is achieved by studying the dynamic effects of the wind arising from turbulence characteristics in the lowest 10 m of the ABL and their influence on the peak wind loads on stowed heliostats. With this knowledge, reduction of the design wind loads in the stow position can allow the optimisation of the size and cost of heliostats with respect to the turbulent flow approaching them. One of the principal factors in the design criteria for a heliostat field is the design wind speed at which the heliostats are moved from operating positions to the stow position. The sensitivity of both the capital cost of heliostats and the LCOE of a PT plant was investigated by developing a statistical model assuming quasi-steady wind loads and simplified cost-area proportionality exponents. A parametric study using wind speed and solar irradiation data showed that a significant reduction in the design wind speed at windy sites can be achieved with only a small reduction in the capacity factor, thus offering potential to reduce the cost of heliostats and the LCOE of a PT plant. Optimal heliostat sizes were found to decrease significantly with increasing stow design wind speed, such as from 50 m2 to 25 m2 when the design wind speed increases from 10 m/s to 20 m/s. Velocity measurements in the lowest 25 m of a low-roughness atmospheric surface layer (ASL) were analysed to further understand the relationships between turbulence characteristics and their effect on the velocity gust factor that is widely used in design wind codes to estimate the peak wind loads on physical structures. It was found that the peak wind speeds associated with low-frequency gusts were under-predicted by 5% at heights below 10 m in desert terrain. Hence, simplified gust factor methods and semi-empirical turbulence models can under-estimate the peak wind loads, which are proportional to the square of peak wind speed, by 10% at heights below 10 m in low-roughness terrains where heliostat fields are located. Subsequently, an experimental investigation was carried out to identify the effects of turbulence characteristics in the lower ABL on the peak wind loads on stowed heliostats. The temporal and spatial turbulence characteristics were characterised over a wide range of turbulence intensities and integral length scales ( ) in a simulated part-depth ABL using two geometries of spires and roughness elements. A range of square heliostat mirror chord lengths () was used to investigate the effect of the length-scale-to-chord-length ratio ( /) on the peak wind loads on an isolated heliostat in stow position and on a second downstream heliostat in a tandem configuration. It was found that both the peak lift coefficient and the peak hinge moment coefficient on the isolated heliostat increased linearly as / increased from 2.5 to 10 and at longitudinal turbulence intensities greater than 10%. In contrast, the peak lift forces and hinge moments on a second downstream heliostat were up to 30% lower than those on an isolated heliostat at / of 10. Peak energies of measured pressure spectra were an order of magnitude smaller on the downstream heliostat than the isolated heliostat and showed a shift to higher frequencies corresponding to smaller vortices. Peak wind loads on the downstream heliostat were observed to increase to 10% above those on an isolated heliostat as the spacing between the heliostat mirrors in tandem, defined by the gap ratio /, was lowered below 1. In contrast, peak wind loads on a downstream heliostat were up to 30% lower than an isolated heliostat at / of approximately 2 at intermediate field densities. When stowing the heliostat mirror at a range of elevation heights, it was found that both peak lift forces and hinge moments can be minimised at an elevation axis height equal to or less than half of the mirror chord length. Hence, optimisation of the mirror chord length and the elevation axis height of the stowed heliostat for the approaching turbulence can significantly reduce design wind loads for high-wind events in the atmospheric surface layer and the cost of manufacturing the heliostat components. The results of the research in the current thesis can be used to optimise the spacing between stowed heliostats at different field densities and the critical scaling parameters of the heliostat, based on known characteristics of the approaching turbulence in a given ABL. Peak wind loads on isolated heliostats in stow position are likely to be over-designed for in-field heliostats positioned in lowdensity regions of a field, thus offering the potential to manufacture in-field heliostats from lower strength, lighter and cheaper materials. Consequently, uniform designs for heliostats in the first two rows of a field need to consider the critical wind load that leads to failure modes to determine the pylon length and mirror chord length of the heliostat.Thesis (Ph.D.) -- University of Adelaide, School of Mechanical Engineering, 201

Radiation Tolerance of Fully-Depleted P-Channel CCDs Designed for the SNAP Satellite

Thick, fully depleted p-channel charge-coupled devices (CCDs) have been developed at the Lawrence Berkeley National Laboratory (LBNL). These CCDs have several advantages over conventional thin, n-channel CCDs, including enhanced quantum efficiency and reduced fringing at near-infrared wavelengths and improved radiation tolerance. Here we report results from the irradiation of CCDs with 12.5 and 55 MeV protons at the LBNL 88-Inch Cyclotron and with 0.1-1 MeV electrons at the LBNL Co60 source. These studies indicate that the LBNL CCDs perform well after irradiation, even in the parameters in which significant degradation is observed in other CCDs: charge transfer efficiency, dark current, and isolated hot pixels. Modeling the radiation exposure over a six-year mission lifetime with no annealing, we expect an increase in dark current of 20 e/pixel/hr, and a degradation of charge transfer efficiency in the parallel direction of 3e-6 and 1e-6 in the serial direction. The dark current is observed to improve with an annealing cycle, while the parallel CTE is relatively unaffected and the serial CTE is somewhat degraded. As expected, the radiation tolerance of the p-channel LBNL CCDs is significantly improved over the conventional n-channel CCDs that are currently employed in space-based telescopes such as the Hubble Space Telescope.Comment: 11 pages, 10 figures, submitted to IEEE Transaction

Genome-wide profiling in treatment-naive early rheumatoid arthritis reveals DNA methylome changes in T and B lymphocytes

AIM: Although aberrant DNA methylation has been described in rheumatoid arthritis (RA), no studies have interrogated this epigenetic modification in early disease. Following recent investigations of T- and B-lymphocytes in established disease, we now characterize in these cell populations genome-wide DNA methylation in treatment-naive patients with early RA. PATIENTS & METHODS: HumanMethylation450 BeadChips were used to examine genome-wide DNA methylation in lymphocyte populations from 23 early RA patients and 11 healthy individuals. RESULTS: Approximately 2000 CpGs in each cell type were differentially methylated in early RA. Clustering analysis identified a novel methylation signature in each cell type (150 sites in T-lymphocytes, 113 sites in B-lymphocytes) that clustered all patients separately from controls. A subset of sites differentially methylated in early RA displayed similar changes in established disease. CONCLUSION: Treatment-naive early RA patients display novel disease-specific DNA methylation aberrations, supporting a potential role for these changes in the development of RA

Epigenome-wide profiling identifies significant differences in DNA methylation between matched-pairs of T- and B-lymphocytes from healthy individuals

Multiple reports now describe changes to the DNA methylome in rheumatoid arthritis and in many cases have analyzed methylation in mixed cell populations from whole blood. However, these approaches may preclude the identification of cell type-specific methylation, which may subsequently bias identification of disease-specific changes. To address this possibility, we conducted genome-wide DNA methylation profiling using HumanMethylation450 BeadChips to identify differences within matched pairs of T-lymphocytes and B-lymphocytes isolated from the peripheral blood of 10 healthy females. Array data were processed and differential methylation identified using NIMBL software. Validation of array data was performed by bisulfite Pyrosequencing. Genome-wide DNA methylation was initially determined by analysis of LINE-1 sequences and was higher in B-lymphocytes than matched T-lymphocytes (69.8 vs. 65.2%, p ≤ 0.01). Pairwise analysis identified 679 CpGs, representing 250 genes, which were differentially methylated between T-lymphocytes and B-lymphocytes. The majority of sites (76.6%) were hypermethylated in B-lymphocytes. Pyrosequencing of selected candidates confirmed the array data in all cases. Hierarchical clustering revealed perfect segregation of samples into two distinct clusters based on cell type. Differentially methylated genes showed enrichment for biological functions/pathways associated with leukocytes and T-lymphocytes. Our work for the first time shows that T-lymphocytes and B-lymphocytes possess intrinsic differences in DNA methylation within a restricted set of functionally-related genes. These data provide a foundation for investigating DNA methylation in diseases in which these cell types play important and distinct roles

Quantitative genome-wide methylation analysis of high-grade non-muscle invasive bladder cancer

High-grade non-muscle invasive bladder cancer (HG-NMIBC) is a clinically unpredictable disease with greater risks of recurrence and progression relative to their low-intermediate-grade counterparts. The molecular events, including those affecting the epigenome, that characterise this disease entity in the context of tumour development, recurrence and progression, are incompletely understood. We therefore interrogated genome-wide DNA methylation using HumanMethylation450 BeadChip-arrays in 21 primary HG-NMIBC tumours relative to normal bladder controls. Using strict inclusion-exclusion criteria we identified 1,057 hypermethylated CpGs within gene promoter-associated CpG islands, representing 256 genes. Bisulphite Pyrosequencing validated the array data and examined 25 array-identified candidate genes in an independent cohort of 30 HG-NMIBC and 18 low-intermediate-grade NMIBC. These analyses revealed significantly higher methylation frequencies in high-grade tumours relative to low-intermediate-grade tumours for the ATP5G2, IRX1 and VAX2 genes (p<0.05), and similarly significant increases in mean levels of methylation in high-grade tumours for the ATP5G2, VAX2, INSRR, PRDM14, VSX1, TFAP2b, PRRX1, and HIST1H4F genes (p<0.05). Although inappropriate promoter methylation was not invariantly associated with reduced transcript expression, a significant association was apparent for the ARHGEF4, PON3, STAT5a, and VAX2 gene transcripts (p<0.05). Herein, we present the first genome-wide DNA methylation analysis in a unique HG-NMIBC cohort, showing extensive and discrete methylation changes relative to normal bladder and low-intermediate-grade tumours. The genes we identified hold significant potential as targets for novel therapeutic intervention either alone, or in combination, with more conventional therapeutic options in the treatment of this clinically unpredictable disease

Combined exome and whole-genome sequencing identifies mutations in ARMC4 as a cause of primary ciliary dyskinesia with defects in the outer dynein arm

Primary ciliary dyskinesia (PCD) is a rare, genetically heterogeneous ciliopathy disorder affecting cilia and sperm motility. A range of ultrastructural defects of the axoneme underlie the disease, which is characterised by chronic respiratory symptoms and obstructive lung disease, infertility and body axis laterality defects. We applied a next-generation sequencing approach to identify the gene responsible for this phenotype in two consanguineous families

Simultaneous high resolution meausurement of phonons and ionization created by particle interactions in a 60 g germanium crystal at 25 mK

We demonstrate simultaneous high energy resolution (rms≊800 eV) measurements of ionization and phonons created by particle interactions in a semiconductor crystal of macroscopic size (60 g germanium) at 25 mK. We present first studies of charge collection at biases below 1 V/cm, and find that, contrary to commonly held opinion, the full recoil energy of particle interactions is recovered as phonons when charge trapping is negligible. We also report an unanticipated correlation between charge collection and phonon energy at very low bias, and discuss this effect in terms of charge trapping

DNA methylation at diagnosis is associated with response to disease-modifying drugs in early rheumatoid arthritis

Aim: A proof-of-concept study to explore whether DNA methylation at first diagnosis is associated with response to disease-modifying antirheumatic drugs (DMARDs) in patients with early rheumatoid arthritis (RA). Patients & methods: DNA methylation was quantified in T-lymphocytes from 46 treatment-naive patients using HumanMethylation450 BeadChips. Treatment response was determined in 6 months using the European League Against Rheumatism (EULAR) response criteria. Results: Initial filtering identified 21 cytosine-phosphate-guanines (CpGs) that were differentially methylated between responders and nonresponders. After conservative adjustment for multiple testing, six sites remained statistically significant, of which four showed high sensitivity and/or specificity (?75%) for response to treatment. Moreover, methylation at two sites in combination was the strongest factor associated with response (80.0% sensitivity, 90.9% specificity, AUC 0.85). Conclusion: DNA methylation at diagnosis is associated with disease-modifying antirheumatic drug treatment response in early RA

Measurement of ionization and phonon production by nuclear recoils in a 60 g crystal of germanium at 25 mK

We report on the first measurement of the absolute phonon energy and the amount of ionization produced by the recoil of nuclei and electrons in a 60 g germanium cyrstal at a temperature of ≊25 mK. We find good agreement between our results and previous measurements of ionization yield from nuclear recoils in germanium. Our device achieves 10:1 discrimination between neutrons and photons in the few keV energy range, demonstrating the feasibility of this technique for large reductions of background in searches for direct interactions of weakly interacting massive particle dark matter