Impact of the Kuroshio intrusion on the nutrient inventory in the upper northern South China Sea: insights from an isopycnal mixing model

Based on four cruises covering a seasonal cycle in 2009-2011, we examined the impact of the Kuroshio intrusion, featured by extremely oligotrophic waters, on the nutrient inventory in the central northern South China Sea (NSCS). The nutrient inventory in the upper 100m of the water column in the study area ranged from similar to 200 to similar to 290 mmol m(-2) for N+N (nitrate plus nitrite), from similar to 13 to similar to 24 mmol m(-2) for soluble reactive phosphate and from similar to 210 to similar to 430 mmol m(-2) for silicic acid. The nutrient inventory showed a clear seasonal pattern with the highest value appearing in summer, while the N+N inventory in spring and winter had a reduction of similar to 13 and similar to 30 %, respectively, relative to that in summer. To quantify the extent of the Kuroshio intrusion, an isopycnal mixing model was adopted to derive the proportional contribution of water masses from the SCS proper and the Kuroshio along individual isopycnal surfaces. The derived mixing ratio along the isopycnal plane was then employed to predict the genuine gradients of nutrients under the assumption of no biogeochemical alteration. These predicted nutrient concentrations, denoted as N-m, are solely determined by water mass mixing. Results showed that the nutrient inventory in the upper 100m of the NSCS was overall negatively correlated to the Kuroshio water fraction, suggesting that the Kuroshio intrusion significantly influenced the nutrient distribution in the SCS and its seasonal variation. The difference between the observed nutrient concentrations and their corresponding Nm allowed us to further quantify the nutrient removal/addition associated with the biogeochemical processes on top of the water mass mixing. We revealed that the nutrients in the upper 100m of the water column had a net consumption in both winter and spring but a net addition in fall.Based on four cruises covering a seasonal cycle in 2009-2011, we examined the impact of the Kuroshio intrusion, featured by extremely oligotrophic waters, on the nutrient inventory in the central northern South China Sea (NSCS). The nutrient inventory in the upper 100m of the water column in the study area ranged from similar to 200 to similar to 290 mmol m(-2) for N+N (nitrate plus nitrite), from similar to 13 to similar to 24 mmol m(-2) for soluble reactive phosphate and from similar to 210 to similar to 430 mmol m(-2) for silicic acid. The nutrient inventory showed a clear seasonal pattern with the highest value appearing in summer, while the N+N inventory in spring and winter had a reduction of similar to 13 and similar to 30 %, respectively, relative to that in summer. To quantify the extent of the Kuroshio intrusion, an isopycnal mixing model was adopted to derive the proportional contribution of water masses from the SCS proper and the Kuroshio along individual isopycnal surfaces. The derived mixing ratio along the isopycnal plane was then employed to predict the genuine gradients of nutrients under the assumption of no biogeochemical alteration. These predicted nutrient concentrations, denoted as N-m, are solely determined by water mass mixing. Results showed that the nutrient inventory in the upper 100m of the NSCS was overall negatively correlated to the Kuroshio water fraction, suggesting that the Kuroshio intrusion significantly influenced the nutrient distribution in the SCS and its seasonal variation. The difference between the observed nutrient concentrations and their corresponding Nm allowed us to further quantify the nutrient removal/addition associated with the biogeochemical processes on top of the water mass mixing. We revealed that the nutrients in the upper 100m of the water column had a net consumption in both winter and spring but a net addition in fall

In-Plane Deformation Mechanics for Highly Stretchable Electronics

Scissoring in thick bars suppresses buckling behavior in serpentine traces that have thicknesses greater than their widths, as detailed in a systematic set of analytical and experimental studies. Scissoring in thick copper traces enables elastic stretchability as large as approximate to 350%, corresponding to a sixfold improvement over previously reported values for thin geometries (approximate to 60%).</p

Pan-cancer analysis of whole genomes

Cancer is driven by genetic change, and the advent of massively parallel sequencing has enabled systematic documentation of this variation at the whole-genome scale(1-3). Here we report the integrative analysis of 2,658 whole-cancer genomes and their matching normal tissues across 38 tumour types from the Pan-Cancer Analysis of Whole Genomes (PCAWG) Consortium of the International Cancer Genome Consortium (ICGC) and The Cancer Genome Atlas (TCGA). We describe the generation of the PCAWG resource, facilitated by international data sharing using compute clouds. On average, cancer genomes contained 4-5 driver mutations when combining coding and non-coding genomic elements; however, in around 5% of cases no drivers were identified, suggesting that cancer driver discovery is not yet complete. Chromothripsis, in which many clustered structural variants arise in a single catastrophic event, is frequently an early event in tumour evolution; in acral melanoma, for example, these events precede most somatic point mutations and affect several cancer-associated genes simultaneously. Cancers with abnormal telomere maintenance often originate from tissues with low replicative activity and show several mechanisms of preventing telomere attrition to critical levels. Common and rare germline variants affect patterns of somatic mutation, including point mutations, structural variants and somatic retrotransposition. A collection of papers from the PCAWG Consortium describes non-coding mutations that drive cancer beyond those in the TERT promoter(4); identifies new signatures of mutational processes that cause base substitutions, small insertions and deletions and structural variation(5,6); analyses timings and patterns of tumour evolution(7); describes the diverse transcriptional consequences of somatic mutation on splicing, expression levels, fusion genes and promoter activity(8,9); and evaluates a range of more-specialized features of cancer genomes(8,10-18).Peer reviewe

Modelling plastic deformation of metals using irreversible thermodynamics

The main objective of this thesis is to provide an irreversible thermodynamics framework to describe and predict the work hardening and stress-strain phenomena occurring in single grained and polycrystalline metals. Models to quantitatively describe these are presented. Especial emphasis is placed on the understanding of the evolution of dislocations. The models are applied to pure metals and single phase alloys with FCC or BCC structures over a wide range of temperatures, strain rates and grain sizes.Aerospace Engineerin

Wake and wind farm aerodynamics of vertical axis wind turbines

The development of offshore wind energy, especially the steps towards deep water and/or higher density wind farms, revives the prospects of vertical axis wind turbines (VAWTs). Because VAWTs may reduce the cost of floating structures, there is a potential to lower energy costs. However, VAWTs are often assumed to be less efficient and less reliable due to a lack of understanding of their complex aerodynamics. This research is motivated by the fact that the performance of isolated turbines is no longer the most important factor, but rather performance at the wind farm level. The objective is to comprehend the possible performance of VAWTs in a wind farm. This dissertation advances the knowledge of wind farm aerodynamics of VAWTs mainly in four aspects: a) It demonstrates the relationship between the rotor loading and wake deflection/deformation, indicating directions for simplified modelling of VAWT wake control; b) It identifies vital characteristics of a VAWT wake, confirming the positive effects of wake deflection on wake recovery and interaction; c) It presents high fidelity experimental data on the wakes and wake interactions of VAWTs placed upwind and downwind, and validates some cutting-edge models with the data; d) it demonstrates the potential of increased power performance of VAWT arrays by controlling the VAWT flow fields. In pursuit of these advances, the dissertation identifies and tackles a series of research topics. The first is on the simplified wake models. The state-of-the-art VAWT wake models are mostly transposed from that for HAWTs, based on the planar actuator disc model. However, the effects of the actuator discs’ shape, specifically the aspect ratio of rectangular ones (corresponding to VAWTs with various height-to-width ratios), on the wake recovery are not considered. We propose the effective mixing diameter D∗ to normalise the shape effects on the wake velocity recovery based on momentum conservation. D∗ is validated through particle image velocimetry (PIV) experiments and Reynolds averaged Navier-Stokes (RANS) simulations, and it outperforms the existing scaling lengths in the literature. The dissertation further questions the validity of planar actuators as surrogates of VAWTs. It compares the three-dimensional wakes of an actuator disc and a lab-scale VAWT using robotic volumetric PIV. The comparison reveals substantial differences in the vortex systems, pointing out the limitations of planar actuators in reproducing VAWT wakes, especially when the wakes are deflected. The results indicate that surrogates for VAWTs should be three-dimensional, coinciding with the swept areas of blades. Based on the three-dimensional actuator cylinder model and a simplified formulation of the vorticity transport equation, we demonstrate the underlying physics of the generation of the streamwise vortex system, highlighting the effect of different load distributions on the wake convection and mixing. We propose four idealised force distributions resulting in different vortex systems and wake topologies; The proposed model is validated qualitatively with stereoscopic PIV measurements on a lab-scale VAWT. We quantify the faster wake recovery consequent from the wake deflection using the experimental data. Furthermore, the wake interaction of two VAWTs placed upwind and downwind is investigated experimentally via PIV and load measurements. The upwind VAWT with positively pitched blades deflects the wake significantly, improving the inflow condition of the downwind VAWT, and thus increasing the overall extraction of the streamwise momentum. With the high-quality experimental data, we validate the state-of-the-art analytical wake models and simulations for VAWTs and identify their validity ranges. Two analytical wake models (the Jensen model and the Bastankhah-Porte-Agel model), five wake superposition models (four algebraic models and one momentum-conservation based model) and an unsteady Reynolds averaged Navier-Stokes (URANS) simulation with VAWTs represented by the actuator line model are compared in both isolated and interaction scenarios. Based on the validated URANS simulation, we explore the wake deflection effects on the enhancement of wind power extraction for two up-scaled VAWTs placed in tandem. The blades of these large H-type VAWTs operate in a high Reynolds number (chordbased, Rec ≈ 1×107), which ensures a high stall angle; The tip speed ratio is set to a relatively high value (4.5) to avoid severe dynamic stalls. And thus, the simulated VAWTs are optimised for engineering operations and perform better than the lab-scale model introduced earlier. Combinations where each turbine operates in three different fixed pitch angles (-10◦, 0◦, 10◦) resulting in different wake deflections are compared. With wake deflections, the overall power coefficient is increased by up to 45%for a tested configuration, which also depends on the inter-turbine distances. Most interestingly, when the turbine blades are pitched in the same direction, the vorticity system in the wake is enhanced and thus yields a flying formation effect for a VAWT array. Furthermore, wakes of three inline VAWTs are scrutinised, focusing on the wake interactions, floor effects and momentum recovery. For all the cases the three VAWTs’ blades are pitched in the same direction following the so-called flying formation scheme. The vertical flux of momentum is notably enhanced by the VAWT array with positive blade pitches even with the floor present, which is vital to the overall increment of power extraction in a wind farm operating in the atmospheric boundary layer. The overall power extraction is increased by 35% compared to the array with zero blade pitches; More importantly, the downwind VAWTs increase their performances by 113%-154%. The latter indicates the tremendous potential of large wind farms consisting of VAWTs employing blade pitching.Wind Energ

Comparative Study of Flood Risk Management and Land Use in the Deltas of Rhine River, Yellow River and Mississippi River

The Rhine River in the Netherlands, the Yellow River in China and the Mississippi River in the U.S. are three great rivers in the world. Each of them is performing a significant role in the country. The delta area for each river, in particular, is served as the centre in importance and commonly the most developed region in the whole river basin. These three deltas are not excepted. All of them are the economic and cultural centre either in the district or in the whole country and all have a big harbour. However, because of the special location, near the sea and the river passing through, the delta area is always threatened both by river flood and the storm surge or hurricane. As a result, flood risk management is the main task for the local people and the government. The objective of our study is focused on the flood risk management and land use in these three deltas, and a comparison is made on several aspects: physical, socio-economical, technical, organizational and institutional, legal and policy. First we would put forward the main problems on flood risk management existing in each region, then make an analysis for each problem, after that come up with possible solutions, at last a comparison between three deltas is discussed and recommendation is followed. The whole report is composed by five parts, part A, B and C are separated for each delta. It includes the problems, analysis of the problems and possible solutions; part D and E are comparisons and recommendation respectively. The problems existing in each delta are similar in some extent or in a certain scope. The common problems are high flood from the river, storm surge (hurricane) from sea, land subsidence and land loss, coastal erosion, sea level rise, etc. In each delta area, there are common or special reasons for different problems and traditional or peculiar measures are carried out in problem addressing. These measures are very valuable for each other, and could be learned from their experience and lessons.Civil Engineering and Geoscience

Effect of freeze-thaw cycles on shear resistance of reinforced concrete beams strengthened with UHPFRC

Ultra-high performance fiber-reinforced concrete (UHPFRC) has emerged as one of the promising materials for strengthening of concrete structures. For the strengthening application of UHPFRC, one of the primary concerns is to evaluate the degradation of bond behavior and structural re-sponse of strengthened elements under harsh environmental conditions. Therefore, an experi-mental program has been carried out to investigate the interfacial behavior between UHPFRC and normal concrete, as well as the shear performance of UHPFRC-concrete hybrid beams subjected to combined freeze-thaw cycles and mechanical load. In this study, two groups of shear-deficient reinforced concrete beams were first strengthened by UHPFRC precast panels using epoxy resin. Then, the specimens subjected to 0 and 30 freeze-thaw cycles were loaded to failure under three-point bending. The results indicate that the utilization of epoxy resin is an effective bonding tech-nique to ensure the integral performance of the composite beams and the shear capacity is greatly enhanced with the application of UHPFRC. In addition, it is observed that the effect of applied freeze-thaw regime on the UHPFRC-concrete interfacial bond strength and shear resistance of unstrengthened and strengthened beams is negligible.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Concrete Structure

On the wake deflection of vertical axis wind turbines by pitched blades

Wake losses are a critical consideration in wind farm design. The ability to steer and deform wakes can result in increased wind farm power density and reduced energy costs and can be used to optimize wind farm designs. This study investigates the wake deflection of a vertical axis wind turbine (VAWT) experimentally, emphasizing the effect of different load distributions on the wake convection and mixing. A trailing vortex system responsible for the wake topology is hypothesized based on a simplified vorticity equation that describes the relationship between load distribution and its vortex generation; the proposed vorticity system and the resulting wake topology are experimentally validated in the wind tunnel via stereoscopic particle image velocimetry measurements of the flow field at several wake cross-sections. Variations in load distribution are accomplished by a set of fixed blade pitches. The experimental results not only validate the predicted vorticity system but also highlight the critical role of the streamwise vorticity component in the deflection and deformation of the wake, thus affecting the momentum and energy recoveries. The evaluation of the various loading cases demonstrates the significant effect of the wake deflection on the wind power available to a downwind turbine, even when the distance between the two turbines is only three diameters.Flow Physics and TechnologyWind EnergyAerodynamic

Graph transformation based simulation model generation

The graph transformation based method presented in this paper can automatically generate simulation models assuming that the models are intended for a certain domain. The method differs from other methods in that: the data used for model generation does not contain specifications of the model structures to be generated; the generated simulation models have structures that are dynamically constructed during the model generation process. Existing data typically has quality issues and does not contain all types of information, particularly in terms of model structure, that are required for modelling. To solve the problem, transformation rules are designed to infer the required model selection and structure information from the data. The rules are specified on meta-models of the original data structure, of intermediate structures and of the simulation model. Graph patterns, pattern composites and graph pattern matching algorithms are used to define and identify potential model components. Model composite structures are represented by hypergraphs according to which simulation models are generated using model components as building blocks. The method has been applied practically in the domain of light-rail transport.Policy AnalysisSystem Engineerin