Feasibility of Laser Bathymetry for Hydrographic Surveys on the Baltic Sea

Airborne laser bathymetry (ALB) is considered to be a new technology for hydrographic purposes in shallow waters. However, previous tests have shown greater problems especially regarding point density and the detection of obstructions. Before introducing this technology as a regular means of surveying, it is necessary to identify its possibilities and limitations, especially in the shallow waters of the Baltic Sea. New tests have been carried out in several of the Baltic Sea’s coastal states. The first results demonstrate that the accuracy of the surveys is not a major issue for using ALB in modelling the sea floor. However, point density remains a limit in deeper waters, where small obstructions cannot to be detected.Se considera que la Batimetría Láser Aerotransportada (ALB) es una nueva tecnología para fines hidrográficos en aguas poco profundas. Sin embargo, las pruebas anteriores han mostrado mayores problemas especialmente en lo que respecta a la densidad de los puntos y a la detección de obstrucciones. Antes de incorporar esta tecnología como un medio regular para efectuar levantamientos, es necesario identificar sus posibilidades y limitaciones, especialmente en las aguas poco profundas del Mar Báltico. Se han llevado a cabo nuevas pruebas en varios de los estados costeros del Mar Báltico. Los primeros resultados demuestran que la exactitud de los levantamientos no es un tema fundamental para utilizar la ALB en la modelización del fondo marino. Sin embargo, la densidad de los puntos sigue siendo un factor limitante en aguas más profundas, donde no pueden detectarse las pequeñas obstrucciones.La bathymétrie laser aéroportée (ALB) est considérée comme une nouvelle technologie répondant aux besoins de l’hydrographie en eaux peu profondes. Toutefois, des tests précédents ont mis en évidence des problèmes plus importants, notamment en ce qui concerne la densité des points et la détection des obstructions. Avant l’introduction de cette technologie en tant que moyen courant d’exécution des levés, il est nécessaire d’identifier ses possibilités et ses limites, notamment dans les eaux peu profondes de la mer Baltique. De nouveaux essais ont été effectués dans plusieurs Etats côtiers de la mer Baltique. Les premiers résultats ont montré que la précision des levés n’est pas un problème majeur pour l’utilisation de la bathymétrie ALB dans la modélisation du fond de la mer. Néanmoins, la densité des points reste toujours une limite en eaux plus profondes, là où les petites obstructions ne peuvent pas être détectées

On the number of types in sparse graphs

We prove that for every class of graphs $\mathcal{C}$ which is nowhere dense, as defined by Nesetril and Ossona de Mendez, and for every first order formula $\phi(\bar x,\bar y)$, whenever one draws a graph $G\in \mathcal{C}$ and a subset of its nodes $A$, the number of subsets of $A^{|\bar y|}$ which are of the form $\{\bar v\in A^{|\bar y|}\, \colon\, G\models\phi(\bar u,\bar v)\}$ for some valuation $\bar u$ of $\bar x$ in $G$ is bounded by $\mathcal{O}(|A|^{|\bar x|+\epsilon})$, for every $\epsilon>0$. This provides optimal bounds on the VC-density of first-order definable set systems in nowhere dense graph classes. We also give two new proofs of upper bounds on quantities in nowhere dense classes which are relevant for their logical treatment. Firstly, we provide a new proof of the fact that nowhere dense classes are uniformly quasi-wide, implying explicit, polynomial upper bounds on the functions relating the two notions. Secondly, we give a new combinatorial proof of the result of Adler and Adler stating that every nowhere dense class of graphs is stable. In contrast to the previous proofs of the above results, our proofs are completely finitistic and constructive, and yield explicit and computable upper bounds on quantities related to uniform quasi-wideness (margins) and stability (ladder indices)

Fluid mechanical performance of ureteral stents: The role of side hole and lumen size

Abstract Ureteral stents are indispensable devices in urological practice to maintain and reinstate the drainage of urine in the upper urinary tract. Most ureteral stents feature openings in the stent wall, referred to as side holes (SHs), which are designed to facilitate urine flux in and out of the stent lumen. However, systematic discussions on the role of SH and stent lumen size in regulating flux and shear stress levels are still lacking. In this study, we leveraged both experimental and numerical methods, using microscopic‐Particle Image Velocimetry and Computational Fluid Dynamic models, respectively, to explore the influence of varying SH and lumen diameters. Our results showed that by reducing the SH diameter from 1.1 to 0.4mm the median wall shear stress levels of the SHs near the ureteropelvic junction and ureterovesical junction increased by over 150%, even though the flux magnitudes through these SH decreased by about 40%. All other SHs were associated with low flux and low shear stress levels. Reducing the stent lumen diameter significantly impeded the luminal flow and the flux through SHs. By means of zero‐dimensional models and scaling relations, we summarized previous findings on the subject and argued that the design of stent inlet/outlet is key in regulating the flow characteristics described above. Finally, we offered some clinically relevant input in terms of choosing the right stent for the right patient