Confluences play a major role in the dynamics of networks of natural and man-made open channels, and field measurements on river confluences reveal that discordance in bed elevation is common. ...Studies of schematized confluences with a step at the interface between the tributary and the main channel bed reveal that bed elevation discordance is an important additional control for the confluence hydrodynamics. This study aimed to improve understanding of the influence of bed elevation discordance on the flow patterns and head losses in a right-angled confluence of an open channel with rectangular cross-sections. A large eddy simulation (LES)-based numerical model was set up and validated with experiments by others. Four configurations with different bed discordance ratios were investigated. The results confirm that, with increasing bed elevation discordance, the tributary streamlines at the confluence interface deviate less from the geometrical confluence angle, the extent of the recirculation zone (RZ) gets smaller, the ratio of the water depth upstream to that downstream of the confluence decreases, and the water level depression reduces. The bed elevation discordance also leads to the development of a large-scale structure in the lee of the step. Despite the appearance of the large-scale structure, the reduced extent of the RZ and associated changes in flow deflection/contraction reduce total head losses experienced by the main channel with an increase of the bed discordance ratio. It turns out that bed elevation discordance converts the lateral momentum from the tributary to streamwise momentum in the main channel more efficiently.
The authors measured and computed the hydrodynamics and passive scalar dispersion in 90-degree open channel confluences over flat and degraded beds with a dominant upstream or tributary inflow. The ...present discussion essentially deals with the direction of rotation of the secondary currents, reported for the flat bed configuration with dominant tributary inflow. This rotation direction is indeed surprisingly opposite to the ones reported in the literature, both from calculations and measurements, even if present geometry slightly differs from literature geometries.
A study on the time development of local scour around a complex pier was developed using a small-scale model embedded in a sediment bed. A total of 15 laboratorial tests were performed at the ...Hydraulics Laboratory of the Faculty of Engineering of the University of Porto. The duration of each experiment was previously established to progressively characterize the scour cavity. After each experiment, the flume was gradually emptied to facilitate the application of close-range photogrammetry. The scour depth values resulting from the application of photogrammetry at the pile cap front agree well with the values obtained experimentally. The temporal development of the scour cavity is presented and discussed. Empirical formulas for the scour cavity time development and for the relation of scour depths to scour cavity volumes were obtained. The obtained three-dimensional models can also be used for calibration and validation of numerical models.
A presença de um obstáculo no seio de um escoamento propicia a ocorrência de fenómenos erosivos, cujos métodos de previsão são ainda demasiados empíricos, baseados em experiências executadas no ...ambiente controlado de um laboratório.Nesta dissertação, foi dado valor não só ao conhecimento que pode extrair-se de experiências laboratoriais, como de igual modo às vantagens que o avanço das novas tecnologias proporciona, através da modelação numérica.Numa primeira fase, foi simulado numericamente o escoamento em torno de um pilar circular (50 mm de diâmetro), num fundo plano, correspondendo ao início do processo erosivo. Com isto, obtiveram-se valores do campo de velocidades, pressões, tensões de arrastamento e força de arrasto no pilar, de modo a melhor caraterizar o fenómeno erosivo que ocorre devido à perturbação induzida pela presença do pilar. Neste processo, foram testados dois modelos de turbulência distintos: o LES e o SST k-ω, resultando assim num total de duas simulações numéricas que possibilitaram a comparação entre os dois modelos utilizados.Posteriormente, elaborou-se um ensaio laboratorial de um escoamento em torno do pilar, fundado num leito arenoso, de modo a poder caraterizar a geometria da cavidade de erosão que se forma em torno do dito obstáculo.Após a atividade experimental, efetuou-se a modelação numérica do escoamento com uma configuração correspondente à geometria de fundo correspondente à profundidade de equilíbrio medida em laboratório, onde foram empregues os modelos de turbulência acima mencionados. Esta simulação permitiu identificar as diferenças no escoamento entre a situação de início e final do processo. Pretendeu-se, assim, identificar os principais mecanismos que dão início ao processo erosivo junto de pilares.Com o intuito de alargar os objetivos iniciais da dissertação, foi realizada uma última simulação numérica do escoamento em torno de um pilar, também ele em fundo plano, com a diferença do diâmetro ser o dobro do utilizado anteriormente.O conjunto de simulações permitiu caraterizar numericamente os fenómenos descritos pela bibliografia e testar a eficiência dos modelos de turbulência utilizados, evidenciando, assim, parte do contributo que a área da modelação numérica pode oferecer ao estudo da erosão em pilares. Assim, foi demonstrado que o modelo LES conduz a melhores resultados comparativamente ao SST k-ω, apesar de exigir maior tempo de processamento. A dificuldade do softwareem simular o escoamento aumenta com a complexidade da geometria.
The therapeutic response to statins has a high interindividual variability with respect to reductions in plasma LDL-cholesterol (c-LDL) and increases in HDL cholesterol (c-HDL). Many studies suggest ...that there is a relationship between the rs20455 KIF6 gene variant (c.2155T> C, Trp719Arg) and a lower risk of cardiovascular disease in patients being treated with statins.
The aim of this study was to investigate whether or not the c.2155T> C KIF6 gene variant modulates the hypercholesteremic effects of treatment with simvastatin, atorvastatin, or rosuvastatin.
This was a prospective, observational and multicenter study. Three hundred and forty-four patients who had not undergone prior lipid-lowering treatment were recruited. Simvastatin, atorvastatin or rosuvastatin were administered. Lipid profiles and multiple clinical and biochemical variables were assessed before and after treatment.
The c.2155T> C variant of the KIF6 gene was shown to influence physiological responses to treatment with simvastatin and atorvastatin. Patients who were homozygous for the c.2155T> C variant (CC genotype, ArgArg) had a 7.0% smaller reduction of LDL cholesterol levels (p = 0.015) in response to hypolipidemic treatment compared to patients with the TT (TrpTrp) or CT (TrpArg) genotype. After pharmacological treatment with rosuvastatin, patients carrying the genetic variant had an increase in c-HDL that was 21.9% lower compared to patients who did not carry the variant (p = 0.008).
Being a carrier of the c.2155T> C variant of the KIF6 gene negatively impacts patient responses to simvastatin, atorvastatin or rosuvastatin in terms of lipid lowering effect. Increasing the intensity of hypolipidemic therapy may be advisable for patients who are positive for the c.2155T> C variant.
To evaluate the risk factors for lymph node metastasis (LNM) after a non-curative (NC) gastric endoscopic submucosal dissection (ESD) and to validate and eventually refine the eCura scoring system in ...the Western setting. Also, to assess the rate and risk factors for parietal residual disease.
Retrospective multicentre multinational study of prospectively collected registries from 19 Western centres. Patients who had been submitted to surgery or had at least one follow-up endoscopy were included. The eCura system was applied to assess its accuracy in the Western setting, and a modified version was created according to the results (W-eCura score). The discriminative capacities of the eCura and W-eCura scores to predict LNM were assessed and compared.
A total of 314 NC gastric ESDs were analysed (72% high-risk resection (HRR); 28% local-risk resection). Among HRR patients submitted to surgery, 25% had parietal disease and 15% had LNM in the surgical specimen. The risk of LNM was significantly different across the eCura groups (areas under the receiver operating characteristic curve (AUC-ROC) of 0.900 (95% CI 0.852 to 0.949)). The AUC-ROC of the W-eCura for LNM (0.916, 95% CI 0.870 to 0.961; p=0.012) was significantly higher compared with the original eCura. Positive vertical margin, lymphatic invasion and younger age were associated with a higher risk of parietal residual lesion in the surgical specimen.
The eCura scoring system may be applied in Western countries to stratify the risk of LNM after a gastric HRR. A new score is proposed that may further decrease the number of unnecessary surgeries.
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