A review of salt marsh dynamics

Salt marshes have been the subject of extensive research over many years. As well as gaining the interest of biologists, physical processes within the marsh have been measured in some detail since at least the 1920s. There have been various attempts to develop a fuller understanding of the inter‐relationship between physical and biological processes within salt marshes. Advances often go in step changes. Over the last 10–20 years, there has been such a change with the ability to capture and manipulate spatial data in sufficient detail to be able to resolve not only surface topography but also variations in vegetation and a number of relevant physical properties. This review paper seeks to highlight the advances in the understanding of salt marsh dynamics and our ability to investigate the relationships between physical and biological properties. Some consideration is also given to the areas that would benefit from new or further research.     

Passive samplers provide a better prediction of PAH bioaccumulation in earthworms and plant roots than exhaustive, mild solvent, and cyclodextrin extractions

A number of extraction methods have been developed to assess polycyclic aromatic hydrocarbon (PAH) bioavailability in soils. As these methods are rarely tested in a comparative manner, against different test organisms, and using field-contaminated soils, it is unclear which method gives the most accurate measure of the actual soil ecosystem exposure. In this study, PAH bioavailability was assessed in ten field-contaminated soils by using exhaustive acetone/hexane extractions, mild solvent (butanol) extractions, cyclodextrin extractions, and two passive sampling methods; solid phase micro extraction (SPME) and polyoxymethylene solid phase extraction (POM-SPE). Results were compared to actual PAH bioaccumulation in earthworms (Eisenia fetida) and rye grass (Lolium multiflorum) roots. Exhaustive, mild solvent and cyclodextrin extractions consistently overpredicted biotic concentrations by a factor of 10-10?000 and therefore seem inappropriate for predicting PAH bioaccumulation in field contaminated soils. In contrast, passive samplers generally predicted PAH concentrations in earthworms within a factor of 10, although correlations between predicted and measured concentrations were considerably scattered. The same applied to the plant data, where passive samplers also tended to underpredict root concentrations. These results indicate the potential of passive samplers to predict PAH bioaccumulation, yet call for comparative studies between passive samplers and further research on plant bioavailability.     

Covid-19 pandemic and the unprecedented mobilisation of scholarly efforts prompted by a health crisis: Scientometric comparisons across SARS,MERS and 2019-nCoV literature

Scientometrics - During the current century, each major coronavirus outbreak has triggered a quick and immediate surge of academic publications on its respective topic. The spike in research...     

Maintaining range trees in secondary memory

Summary When storing and maintaining a data structure in secondary memory it is important to partition it into parts such that each query and update passes through a small number of parts. In this way the number of disk accesses and the amount of data transport required can be kept low. In Part I of this paper a number of partition schemes were given for partitioning range trees. In this paper we study lower bounds for partitions. In this way we prove that many of the partitions given in Part I are optimal.Supported by the Netherlands Organization for Scientific Research (NWO)     

Lead time anticipation in Supply Chain Operations Planning

Linear programming (LP) models for Supply Chain Operations Planning are widely used in Advanced Planning Systems. The solution to the LP model is a proposal for order releases to the various production units (PU) in the supply network. There is a non-linear relationship between the work-in-process in the PU and the lead time that is difficult to capture in the LP model formulation. We propose a two-step lead time anticipation (LTA) procedure where the LP model is first solved irrespective of the available production capacity and is subsequently updated with aggregate order release targets. The order release targets are generated by a local smoothing algorithm that accounts for the evolution of the stochastic workload in the PU. A solution that is both feasible with respect to the planned lead time and meets the material requirements may not exist. By means of discrete event simulation, we compare a conservative strategy where the production quantities are reduced to an optimistic strategy where the planned lead time constraint is allowed to be violated.     

Spatially oversampled TDC with digital resolution enhancement

A digital resolution enhancement technique for time-to-digital converters (TDC) is proposed. This involves a simultaneous multi-channel measurement of a time interval with low complexity TDC of varying low resolutions. The coarse outputs of each converter are digitally post-processed to obtain an output whose precision is much better than that of the individual converters. Three post-processing algorithms are proposed and their limitations in presence of converter non-idealities are analyzed. A prototype system with 8 channels is implemented in 90 nm CMOS. 40MS/s output of each channel is algorithmically combined to obtain over 2.2–3X measured improvement in the resolution in 4/6/8 channel modes, validating the system principle. The chip occupies 0.3 mm² and draws up to a maximum of 4 mA from a 1.2 V supply.     

斯芬克司住宅，赫依曾，荷兰

5座斯芬克司住宅的每一栋各容纳了14间为了充分利用地段和阳光而组织起来的公寓。建筑的体量在背向水面的方向被斜切，从而使得从湖岸和公寓所能看到的湖景不被阻隔。当人在从楼里往上走时，公寓的数目逐层递减。结果产生了一种斯芬克司式的轮廓，面向太阳的屋顶退台置于这个神话中的怪兽的脊背上。每个建筑体量的雨篷设计是不同的，从而使其独特的头部产生一种韵律感——从连接新开拓地和现有大陆的stichtse桥上看去的一条激动人心的天际线。     

Living in highly dynamic polluted river floodplains, do contaminants contribute to population and community effects?

The aim of this paper was to collect evidence for the effects of contaminants on biota in a highly dynamic river Rhine floodplain. To this purpose we reviewed the results of circa 10 studies performed in this floodplain. The floodplain was contaminated with elevated levels of cadmium, copper, PAHs, and PCBs and high levels of zinc which were at some sites above legislative values. The results showed that the present contaminants were accumulated by the floodplain inhabiting organisms, but meanwhile population and community effects were ambiguous. Only for the mayfly Ephoron virgo clear effects were detected at the level of the single floodplain. The absence of clear population and community effects is puzzling since at lower contaminant concentrations adverse effects were detected in other environments. Factors that may mask toxic effects include flooding and food quality and quantity. We conclude that given the site specific conditions, being an open, eutrophic system with a highly dynamic flooding pattern, assessment of the contribution of toxicants to observed population density or biomass and community composition requires 1] an increase in number of replicates; 2] a larger scale of investigation and 3] comparison to stable systems with comparable contamination levels.