The reduction of the critical current in Nb3Sn cables under transverse loads

The degradation of the critical current of impregnated Rutherford type Nb3Sn cables was investigated as a function of the applied transverse load and magnetic field. The cable is made of modified jelly-roll-type strand material and has a keystone angle of 1.0°. The voltage-current characteristics were determined for the magnetic field ranging from 2 to 11 T and transverse pressure up to 250 MPa on the cable surface. It was found that the 48-strand cable, made of strands with six elements in the matrix, showed a larger critical current degradation than the 26-strand cable with 36 elements per strand. The global degradation of the 48-strand cable was 63% at 150 MPa, and 40% at 150 MPa for the 26-strand cable. Microanalysis of the cross-section before and after compression is presented, showing significant permanent damage to the superconducting strands

Authentieke contexten in wiskundemethoden in het vmbo

Centrale vraag Zijn de bestaande wiskundemethoden die gebruikt worden in de beroepsgerichte leerwegen van het vmbo bruikbaar in verband met authentiek leren en wat is daarvoor eventueel nog extra nodig. Belangrijkste conclusies De bestaande wiskundemethoden bevatten enkele authentieke leertaken, maar over het algemeen bevatten de opdrachten weinig kenmerken passend bij authentiek leren. Wel bevatten de boeken diverse aangrijpingspunten om, dicht bij de methode, meer authentieke leertaken te ontwikkelen. In deze publicatie worden aanbevelingen gedaan en enkele mogelijkheden daartoe beschreven. Dit is een Ico-Isor rapport

Theoretical and physical modelling of the thermal performance of water wall systems

Water wall is an excellent passive solar strategy which can maintain thermal comfort in buildings while reducing energy consumption. Existing water wall studies are mainly based on simple heat balance models, in which convective heat transfer coefficients are assumed constant and radiation exchange is commonly neglected. Further, the application of the CFD approach to water wall research is very rare. These research gaps are addressed in this study through the development of a comprehensive transient heat balance model and unsteady CFD modelling. The thesis covers three major topics. Firstly, the turbulent natural convection with and without radiation transfer in two-dimensional and three-dimensional air-filled differentially heated cavities is numerically investigated using various RANS (Reynolds Averaged Navier-Stokes) turbulence models and the Discrete Ordinates radiation model. It is found that the shear-stress transport k-ω model has the best overall performance in terms of capturing the main features of the flow and predicting the time-averaged quantities. Secondly, a comprehensive conjugate conduction-convection-radiation model for transient analysis of a semi-transparent water wall system is developed. It is found that reducing the transmissivity of the Perspex or glass walls is the most effective, practical and economical way to improve the thermal performance of the semi-transparent water wall system. Finally, the thermal performance of an opaque water wall system is numerically investigated and compared against a conventional concrete wall system for the typical climate conditions in Sydney, Australia. The results indicate that less supplementary energy is required in winter than that in summer to maintain a comfortable interior temperature. Further, the water wall system performs significantly better than the concrete wall system of the same thickness in the winter climate of Sydney, whereas both systems have a similar performance in summer

Climate reconstruction in the High Arctic: development and validation of a new tree-ring-like climate proxy

Rozema, J. [Promotor

Revised calibration of the mbt-cbt paleotemperature proxy based on branched tetraether membrane lipids in surface soils

The MBT-CBT proxy for the reconstruction of paleotemperatures and past soil pH is based on the distribution of branched glycerol dialkyl glycerol tetraether (brGDGT) membrane lipids. The Methylation of Branched Tetraether (MBT) and the Cyclisation of Branched Tetraether (CBT) indices were developed to quantify these distributions, and significant empirical relations between these indices and annual mean air temperature (MAT) and/or soil pH were found in a large data set of soils. In this study, we extended this soil dataset to 278 globally distributed surface soils. Of these soils, 26% contains all nine brGDGTs, while in 63% of the soils the seven most common brGDGTs were detected, and the latter were selected for calibration purposes. This resulted in new transfer functions for the reconstruction of pH based on the CBT index: pH = 7.90-1.97 x CBT (r(2) = 0.70; RMSE = 0.8; n = 176), as well as for MAT based on the CBT index and methylation index based on the seven most abundant GDGTs (defined as MBT'): MAT = 0.81-5.67 x CBT + 31.0 x MBT' (r(2) = 0.59; RMSE = 5.0 degrees C; n = 176). The new transfer function for MAT has a substantially lower correlation coefficient than the original equation (r(2) = 0.77). To investigate possible improvement of the correlation, we used our extended global surface soil dataset to statistically derive the indices that best describe the relations of brGDGT composition with MAT and soil pH. These new indices, however, resulted in only a relatively minor increase in correlation coefficients, while they cannot be explained straightforwardly by physiological mechanisms. The large scatter in the calibration cannot be fully explained by local factors or by seasonality, but MAT for soils from arid regions are generally substantially (up to 20 degrees C) underestimated, suggesting that absolute brGDGT-based temperature records for these areas should be interpreted with caution.<br>The applicability of the new MBT'-CBT calibration function was tested using previously published MBT-CBT-derived paleotemperature records covering the last deglaciation in Central Africa and East Asia, the Eocene-Oligocene boundary and the Paleocene-Eocene thermal maximum. The results show that trends remain similar in all records, but that absolute temperature estimates and the amplitude of temperature changes are lower for most records, and generally in better agreement with independent proxy data

Provenance of tetraether membrane lipids in a large temperate lake (Loch Lomond, UK): implications for glycerol dialkyl glycerol tetraether (GDGT)-based palaeothermometry

The application of glycerol dialkyl glycerol tetraether (GDGT)-based palaeoenvironmental proxies, such as the branched vs. isoprenoidal tetratether (BIT) index, TEX86 and the MBT–CBT palaeothermometer, has lately been expanded to lacustrine sediments. Given recent research identifying the production of branched, bacterial GDGTs (brGDGTs) within lakes, it is necessary to ascertain the effect of this lacustrine production on GDGT-based proxies. This study profiles a temperate, monomictic lake (Loch Lomond, UK), analysing labile intact polar GDGT lipids (IPLs) and resilient core GDGT lipids (CLs) in catchment soils, small tributary rivers, lake water and lake sediments

Constraints on the sources of branched tetraether membrane lipids in distal marine sediments

Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are membrane lipids produced by soil bacteria and occur in near coastal marine sediments as a result of soil organic matter input. Their abundance relative to marine-derived crenarchaeol, quantified in the BIT index, generally decreases offshore. However, in distal marine sediments, low relative amounts of brGDGTs can often still be observed. Sedimentary in situ production as well as dust input have been suggested as potential, though as yet not well constrained, sources. In this study brGDGT distributions in dust were examined and compared with those in distal marine sediments. Dust was sampled along the equatorial West African coast and brGDGTs were detected in most of the samples, albeit in low abundance. Their degree of methylation and cyclisation, expressed in the MBT' (methylation index of branched tetraethers) and DC (degree of cyclisation) indices, respectively, were comparable with those for African soils, their presumed source. Comparison of DC index values for brGDGTS in global soils, Congo deep-sea river fan sediments and dust with those of distal marine sediments clearly showed, however, that distal marine sediments had significantly higher values. This distinctive distribution is suggestive of sedimentary in situ production as a source of brGDGTs in marine sediments, rather than dust input. The presence of in situ produced brGDGTs in marine sediments means that caution should be exercised when applying the MBT'–CBT palaeothermometer to sediments with low BIT index values, i.e. < 0.1, based on our dataset