Jitter and Decision-level Noise Separation in A/D Converters

Gaussian aperture jitter leads to a reduced SNR of A/D converters. Also other noise sources, faults and nonlinearities affect the digital output signal. A measurement setup for a new off-chip diagnosis method, which systematically separates the jitter-induced errors from the errors caused by these other factors, is described. Deterministic errors are removed via a subtracting technique. High-level ADC simulations and measurements have been carried out to determine relations between the size of the jitter or decision-level noise and the remaining random errors. By carrying out two tests at two different input frequencies and using the simulation results, errors induced by decision-level noise can be remove

Management options for restoring estuarine dynamics and implications for ecosystems: a quantitative approach for the Southwest Delta in the Netherlands

The Delta Works, a series of dams and barriers constructed in the 1960's–1980's changed the estuarine landscape of the Rhine-Meuse-Scheldt delta (SW Netherlands) into more stagnant and disengaged freshwater, brackish water or saltwater lakes. The remaining tidal systems were adapted by building a storm surge barrier in the Oosterschelde and dike reinforcement works along the Westerschelde. The Delta Works brought protection against flooding, but at the same time resulted in environmental and socio-economic problems, such as degradation of ecological quality and ecosystem functioning, disruption of fish migration routes, water and sediment quality problems.In this study we explore in an integrated, quantitative way the consequences of a number of management options for the Southwest Delta and their implications for the occurrence and distribution of aquatic and estuarine habitats, considering the mutual coherence between the water basins. Five scenarios were evaluated using a 1D hydraulic, water quality and primary production numerical model and GIS habitat mapping. Scenarios vary from small-scale interventions, such as changes in day-to-day management of hydraulic infrastructures or creation of small inlets in dams, feasible in the short term, to restoration of an open delta by removing dams and barriers, as a long term potential. We evaluate the outcomes in relation to the restoration of estuarine dynamics, as this is in policy plans proposed as a generic solution for the current ecological and environmental problems. Net water flow rates show more complex patterns when connectivity between water basins is increased and when sluice management is less strict. Estuarine transition zones and fish migration routes are partly restored, but only fully develop when basins are in open connection with each other. Area of intertidal habitats, tidal flats and tidal marshes, increases in each scenario, ranging between 7 and 83%, 1–56%, and 8–100% respectively, depending on scenario. Large scale infrastructural adaptations are needed to restore estuarine dynamics at large scale.The use of a 1D numerical model allowed to quantify the effect of different management measures for all water basins simultaneously, but also has its limitations. The model does not resolve more complex processes such as vertical mixing and morphodynamic changes. This requires expert judgment and more detailed 3D modelling

Sustainable scenarios for the Southwest Delta based on Building with Nature strategies

The concept of Building with Nature can be applied on a range of spatial and temporal scales: from improving the ecological value of a stretch of dyke to influencing an entire delta, and from anticipating to unwanted side effects of hard structures on the scale of years, to a multidecadal approach to dynamically reinforce the entire Dutch coast. The question therefore arose: would it be possible to design scenarios for the long-term future of the ZW Delta which make use of Building with Nature techniques on a large scale and what would this learn for possible pathways to a sustainable future

Retrieval of 3D polygonal objects based on multiresolution signatures

In this paper we present a method for retrieving 3D polygonal objects by using two sets of multiresolution signatures. Both sets are based on the progressive elimination of object's details by iterative processing of the 3D meshes. The first set, with five parameters, is based on mesh smoothing. This mainly affects an object's surface. The second set, with three parameters, is based on difference volumes after successive mesh erosions and dilations. Characteristic feature vectors are constructed by combining the features at three mesh resolutions of each object. In addition to being invariant to mesh resolution, the feature vectors are invariant to translation, rotation and size of the objects. The method was tested on a set of 40 complex objects with mesh resolutions different from those used in constructing the feature vectors. By using all eight features, the average ranking rate obtained was 1.075: 37 objects were ranked first and only 3 objects were ranked second. Additional tests were carried out to determine the significance of individual features and all combinations. The same ranking rate of 1.075 can be obtained by using some combinations of only three features. © 2011 Springer-Verlag

Sedimentstrategie voor de ZW Delta: een verkenning van kansen

In deze studie worden de ontwikkelingen in de sedimenthuishouding als uitgangspunt beschouwd voor duurzame inrichting van de ZW Delta. Centraal staan de kansen van een sedimentstrategie: het gericht beïnvloeden van de sedimenthuishouding, met het oog op het bereiken van een of meer (beleids)doelen

Wall shear stress as measured in vivo: consequences for the design of the arterial system

Based upon theory, wall shear stress (WSS), an important determinant of endothelial function and gene expression, has been assumed to be constant along the arterial tree and the same in a particular artery across species. In vivo measurements of WSS, however, have shown that these assumptions are far from valid. In this survey we will discuss the assessment of WSS in the arterial system in vivo and present the results obtained in large arteries and arterioles. In vivo WSS can be estimated from wall shear rate, as derived from non-invasively recorded velocity profiles, and whole blood viscosity in large arteries and plasma viscosity in arterioles, avoiding theoretical assumptions. In large arteries velocity profiles can be recorded by means of a specially designed ultrasound system and in arterioles via optical techniques using fluorescent flow velocity tracers. It is shown that in humans mean WSS is substantially higher in the carotid artery (1.1–1.3 Pa) than in the brachial (0.4–0.5 Pa) and femoral (0.3–0.5 Pa) arteries. Also in animals mean WSS varies substantially along the arterial tree. Mean WSS in arterioles varies between about 1.0 and 5.0 Pa in the various studies and is dependent on the site of measurement in these vessels. Across species mean WSS in a particular artery decreases linearly with body mass, e.g., in the infra-renal aorta from 8.8 Pa in mice to 0.5 Pa in humans. The observation that mean WSS is far from constant along the arterial tree implies that Murray’s cube law on flow-diameter relations cannot be applied to the whole arterial system. Because blood flow velocity is not constant along the arterial tree either, a square law also does not hold. The exponent in the power law likely varies along the arterial system, probably from 2 in large arteries near the heart to 3 in arterioles. The in vivo findings also imply that in in vitro studies no average shear stress value can be taken to study effects on endothelial cells derived from different vascular areas or from the same artery in different species. The cells have to be studied under the shear stress conditions they are exposed to in real life

Effect of tube diameter and capillary number on platelet margination and near-wall dynamics

The effect of tube diameter $D$ and capillary number $Ca$ on platelet margination in blood flow at $\approx 37\%$ tube haematocrit is investigated. The system is modelled as three-dimensional suspension of deformable red blood cells and nearly rigid platelets using a combination of the lattice-Boltzmann, immersed boundary and finite element methods. Results show that margination is facilitated by a non-diffusive radial platelet transport. This effect is important near the edge of the cell-free layer, but it is only observed for $Ca > 0.2$, when red blood cells are tank-treading rather than tumbling. It is also shown that platelet trapping in the cell-free layer is reversible for $Ca \leq 0.2$. Only for the smallest investigated tube ($D = 10 \mu\text{m}$) margination is essentially independent of $Ca$. Once platelets have reached the cell-free layer, they tend to slide rather than tumble. The tumbling rate is essentially independent of $Ca$ but increases with $D$. Tumbling is suppressed by the strong confinement due to the relatively small cell-free layer thickness at $\approx 37\%$ tube haematocrit.Comment: 16 pages, 10 figure

Determinants of Leukocyte Margination in Rectangular Microchannels

Microfabrication of polydimethylsiloxane (PDMS) devices has provided a new set of tools for studying fluid dynamics of blood at the scale of real microvessels. However, we are only starting to understand the power and limitations of this technology. To determine the applicability of PDMS microchannels for blood flow analysis, we studied white blood cell (WBC) margination in channels of various geometries and blood compositions. We found that WBCs prefer to marginate downstream of sudden expansions, and that red blood cell (RBC) aggregation facilitates the process. In contrast to tubes, WBC margination was restricted to the sidewalls in our low aspect ratio, pseudo-2D rectangular channels and consequently, margination efficiencies of more than 95% were achieved in a variety of channel geometries. In these pseudo-2D channels blood rheology and cell integrity were preserved over a range of flow rates, with the upper range limited by the shear in the vertical direction. We conclude that, with certain limitations, rectangular PDMS microfluidic channels are useful tools for quantitative studies of blood rheology