Asymmetric vortex shedding flow past an inclined flat plate at high incidence

This paper reports an experimental investigation of the vortex shedding wake behind a long flat plate inclined at a small angle of attack to a main flow stream. Detailed velocity fields are obtained with particle-image velocimetry (PIV) at successive phases in a vortex shedding cycle at three angles of attack, α=20°, 25° and 30°, at a Reynolds number Re≈5,300. Coherent patterns and dynamics of the vortices in the wake are revealed by the phase-averaged PIV vectors and derived turbulent properties. A vortex street pattern comprising a train of leading edge vortices alternating with a train of trailing edge vortices is found in the wake. The trailing edge vortex is shed directly from the sharp trailing edge while there are evidences that the formation and shedding of the leading edge vortex involve a more complicated mechanism. The leading edge vortex seems to be shed into the wake from an axial location near the trailing edge. After shedding, the vortices are convected downstream in the wake with a convection speed roughly equal to 0.8 the free-stream velocity. On reaching the same axial location, the trailing edge vortex, as compared to the leading edge vortex, is found to possess a higher peak vorticity level at its centre and induce more intense fluid circulation and Reynolds stresses production around it. It is found that the results at the three angles of attack can be collapsed into similar trends by using the projected plate width as the characteristic length of the flow. © 2004 Elsevier SAS. All rights reserved.postprin

香港的選擇性墮胎: 合法與否?

There is legal uncertainty as to whether selective foeticide is authorised under section 47A of the Offences Against the Person Ordinance (1967). Medical and legal issues surrounding a case of selective foeticide in a triplet pregnancy are reported.published_or_final_versio

Wind flow in the recessed cavities of a tall building

Fulltext in: http://www.iawe.org/Proceedings/7APCWE/M3D_3.pdfTechnical Session: M3-D Computational Wind Engineering (2), no.3In a congested city like Hong Kong, residential tall buildings are often built with an irregular plan form and with a number of apartments arranged as wing sections extending from a central core. To provide views and sufficient ventilation to the apartments, deeply recessed cavities are placed between adjacent building wings. This paper reports a CFD study of the wind-induced flow inside a recessed cavity of a tall building with an objective to assess the adequacy of ventilation inside the cavity. The dimensions of the cavity are varied systematically to investigate the flow exchange between the cavity and the outside at different heights. It is found that the flow inside the cavity is not a simple cross flow or a stagnation flow. Flow exchange takes place in different directions along the building heights.link_to_subscribed_fulltex

Wind-induced loading and dynamic responses of a row of tall buildings under strong interference

This paper studies wind-induced interference effects on a row of five square-plan tall buildings arranged in close proximity. Mean and fluctuating wind loads are measured on each building member and wind-induced dynamic responses of the building are estimated with the high-frequency force-balance technique. The modifications of building responses from interference over a practical range of reduced velocities are represented by an envelope interference factor. Wind tunnel experiments and response analysis are carried out under all possible angles of wind incidence, at four different building separation distances, and for two arrangement patterns of buildings in the row, that is the parallel and diamond patterns. It is found that building interference leads to amplified dynamic responses in many cases but reduction in responses also occurs at some wind incidence. For a building row of the parallel pattern, five distinct wind incidence sectors of different levels and mechanisms of interference effect can be identified. The largest values of envelope interference factors can reach 2.4 for the torsional responses. When the row of tall buildings is arranged in the diamond pattern, increase in wind excitation occurs at many wind angles due to a "wind catchment" effect. The interference factors have larger peak values, reaching 2.1 in the sway directions and above 4 in torsion. However, all large amplifications of building responses do not occur in the situations of peak resonant dynamic responses of the single isolated building. Thus, the design values of peak dynamic responses of a tall building are not significantly magnified when placed in a row. © 2011 Elsevier Ltd.postprin

Computation of dynamic wind-induced interferencein a row of tall buildings

The article can be viewed at: http://wgy091.ust.hk:8080/document/HKWE1papers.pdfSection B: Numerical simulation and theoretical analysisLarge-eddy simulation is applied to compute the dynamic wind loads on three tall buildings arranged closely in a row. The computed values and spectra of along-wind and across-wind forces on the buildings reproduces reasonably the dynamic interference effects observed in the wind tunnel, despites the use of a simple model of turbulence characteristics of the incident wind flow.published_or_final_versio

The effects of stent porosity on the endovascular treatment of intracranial aneurysms located near a bifurcation

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Vibrio cholerae O139 synonym Bengal in Hong Kong [12]

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Computational fluid dynamics study of bifurcation aneurysms treated with pipeline embolization device: side branch diameter study

An intracranial aneurysm, abnormal swelling of the cerebral artery, may lead to undesirable rates of mortality and morbidity upon rupture. Endovascular treatment involves the deployment of a flow-diverting stent that covers the aneurysm orifice, thereby reducing the blood flow into the aneurysm and mitigating the risk of rupture. In this study, computational fluid dynamics analysis is performed on a bifurcation model to investigate the change in hemodynamics with various side branch diameters. The condition after the deployment of a pipeline embolization device is also simulated. Hemodynamic factors such as flow velocity, pressure, and wall shear stress are studied. Aneurysms with a larger side branch vessel might have greater risk after treatment in terms of hemodynamics. Although a stent could lead to flow reduction entering the aneurysm, it would drastically alter the flow rate inside the side branch vessel. This may result in side-branch hypoperfusion subsequent to stenting. In addition, two patient-specific bifurcation aneurysms are tested, and the results show good agreement with the idealized models. Furthermore, the peripheral resistance of downstream vessels is investigated by varying the outlet pressure conditions. This quantitative analysis can assist in treatment planning and therapeutic decision-making.published_or_final_versio

Carotid blowout syndrome: EC-IC bypass and endovascular management of ruptured radiation-related pseudoaneurym in nasopharyngeal cancer patients

Parallel Session: Free Paper Session VB - Oral Presentation (Epilepsy & General)PURPOSE: With prolonged survival in nasopharyngeal cancer patients treated with radiation therapy, delayed vascular complication such as carotid blowout due to ruptured pseudoaneurysm has emerged as an not infrequent and often fatal clinical emergency. Management of carotid blowout syndrome in these patients is challenging and controversial, including endovascular flow-diverting stents, coiling, balloon occlusion, and EC-IC bypass; alone or in combination. We review our experience of treating carotid blowout syndrome and discuss on different management strateg...postprin

Alterations in Gastric Microbiota After H. Pylori Eradication and in Different Histological Stages of Gastric Carcinogenesis

The role of bacteria other than Helicobacter pylori (HP) in the stomach remains elusive. We characterized the gastric microbiota in individuals with different histological stages of gastric carcinogenesis and after receiving HP eradication therapy. Endoscopic gastric biopsies were obtained from subjects with HP gastritis, gastric intestinal metaplasia (IM), gastric cancer (GC) and HP negative controls. Gastric microbiota was characterized by Illumina MiSeq platform targeting the 16 S rDNA. Apart from dominant H. pylori, we observed other Proteobacteria including Haemophilus, Serratia, Neisseria and Stenotrophomonas as the major components of the human gastric microbiota. Although samples were largely converged according to the relative abundance of HP, a clear separation of GC and other samples was recovered. Whilst there was a strong inverse association between HP relative abundance and bacterial diversity, this association was weak in GC samples which tended to have lower bacterial diversity compared with other samples with similar HP levels. Eradication of HP resulted in an increase in bacterial diversity and restoration of the relative abundance of other bacteria to levels similar to individuals without HP. In conclusion, HP colonization results in alterations of gastric microbiota and reduction in bacterial diversity, which could be restored by antibiotic treatment.published_or_final_versio