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Within-Cluster Variability Exponent for Identifying Coherent Structures in Dynamical Systems

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Communications in Computational Physics 2023年第3期33卷 824-848页

作者： wai Ming Chau Shingyu leung Department of Mathematics The Hong Kong University of Science and TechnologyClear Water BayHong Kong

We propose a clustering-based approach for identifying coherent flow structuresin continuous dynamical systems. We first treat a particle trajectory over a finitetime interval as a high-dimensional data point and then cluster these data from differentinitial locations into groups. The method then uses the normalized standarddeviation or mean absolute deviation to quantify the deformation. Unlike the usualfinite-time Lyapunov exponent (FTLE), the proposed algorithm considers the completetraveling history of the particles. We also suggest two extensions of the method. To improvethe computational efficiency, we develop an adaptive approach that constructsdifferent subsamples of the whole particle trajectory based on a finite time interval. Tostart the computation in parallel to the flow trajectory data collection, we also developan on-the-fly approach to improve the solution as we continue to provide more measurementsfor the algorithm. The method can efficiently compute the WCVE over adifferent time interval by modifying the available data points.

关键词： Dynamical system visualization finite time Lyapunov exponent numerical methods for differential equations k-means clustering

Application of Big Data analysis in gastrointestinal research

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World Journal of Gastroenterology 2019年第24期25卷 2990-3008页

作者： Ka-Shing Cheung wai K leung wai-Kay Seto Department of Medicine The University of Hong KongQueen Mary HospitalHong KongChina Department of Medicine The University of Hong Kong- Shenzhen HospitalShenzhen 518053Guangdong ProvinceChina

Big Data,which are characterized by certain unique traits like volume,velocity and value,have revolutionized the research of multiple fields including *** Data in health care are defined as large datasets that are collected routinely or automatically,and stored *** the rapidly expanding volume of health data collection,it is envisioned that the Big Data approach can improve not only individual health,but also the performance of health care *** application of Big Data analysis in the field of gastroenterology and hepatology research has also opened new research *** it retains most of the advantages and avoids some of the disadvantages of traditional observational studies(case-control and prospective cohort studies),it allows for phenomapping of disease heterogeneity,enhancement of drug safety,as well as development of precision medicine,prediction models and personalized *** randomized controlled trials,it reflects the real-world situation and studies patients who are often under-represented in randomized controlled ***,residual and/or unmeasured confounding remains a major concern,which requires meticulous study design and various statistical adjustment *** potential drawbacks include data validity,missing data,incomplete data capture due to the unavailability of diagnosis codes for certain clinical situations,and individual *** continuous technological advances,some of the current limitations with Big Data may be further *** review will illustrate the use of Big Data research on gastrointestinal and liver diseases using recently published examples.

关键词： Healthcare dataset Epidemiology Gastric cancer Inflammatory bowel disease Colorectal cancer Hepatocellular carcinoma Gastrointestinal bleeding

Gastrointestinal bleeding in patients on novel oral anticoagulants:Risk,prevention and management

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World Journal of Gastroenterology 2017年第11期23卷 1954-1963页

作者： Ka-Shing Cheung wai K leung Department of Medicine The University of Hong KongQueen Mary HospitalHong KongChina

Novel oral anticoagulants(NOACs), which include direct thrombin inhibitor(dabigatran) and direct factor Xa inhibitors(rivaroxaban, apixaban and edoxaban), are gaining popularity in the prevention of embolic stroke in non-valvular atrial fibrillation as well as in the prevention and treatment of venous thromboembolism. However, similar to traditional anticoagulants, NOACs have the side effects of bleeding, including gastrointestinal bleeding(GIB). Results from both randomized clinical trials and observations studies suggest that high-dose dabigatran(150 mg b.i.d), rivaroxaban and high-dose edoxaban(60 mg daily) are associated with a higher risk of GIB compared with warfarin. Other risk factors of NOAC-related GIB include concomitant use of ulcerogenic agents, older age, renal impairment, Helicobacter pylori infection and a past history of GIB. Prevention of NOAC-related GIB includes proper patient selection, using a lower dose of certain NOACs and in patients with renal impairment, correction of modifiable risk factors, and prescription of gastroprotective agents. Overt GIB can be managed by withholding NOACs followed by delayed endoscopic treatment. In severe bleeding, additional measures include administration of activated charcoal, use of specific reversal agents such as idarucizumab for dabigatran and andexanent alfa for factor Xa inhibitors, and urgent endoscopic management.

关键词： Warfarin Endoscopy Apixaban Edoxaban Gastrointestinal bleeding Dabigatran Rivaroxaban Novel anticoagulants

Is artificial intelligence the final answer to missed polyps in colonoscopy?

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World Journal of Gastroenterology 2020年第35期26卷 5248-5255页

作者： Thomas K L Lui wai K leung Department of Medicine Queen Mary HospitalUniversity of Hong KongHong KongChina

Lesions missed by colonoscopy are one of the main reasons for post-colonoscopy colorectal cancer,which is usually associated with a worse *** the adenoma miss rate could be as high as 26%,it has been noted that endoscopists with higher adenoma detection rates are usually associated with lower adenoma miss *** intelligence(AI),particularly the deep learning model,is a promising innovation in *** studies have shown that AI is not only accurate in colorectal polyp detection but can also reduce the miss ***,the application of AI in real-time detection has been hindered by heterogeneity of the AI models and study design as well as a lack of long-term ***,we discussed the principle of various AI models and systematically reviewed the current data on the use of AI on colorectal polyp detection and miss *** limitations and future prospects of AI on colorectal polyp detection are also discussed.

关键词： Artificial intelligence Adenoma Colonoscopy Colorectal cancer Polyps

Magnetic activity of the spotted dwarf AP149 in the α Persei open cluster

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Research in Astronomy and Astrophysics 2010年第3期10卷 253-265页

作者： Xiang-Song Fang Sheng-Hong Gu Sze-leung Cheung Ho-keung Hui Chi-Tai Kwok Kam-Cheung leung National Astronomical Observatories / Yunnan Observatory Chinese Academy of Sciences Kunming 650011 China Graduate University of Chinese Academy of Sciences Beijing 100049 China Ho Koon Nature Education cum Astronomical Centre Sik Sik Yuen Hong Kong China Hong Kong Astronomical Society Hong Kong China

The simultaneous photometric and spectroscopic observations of the spotted G dwarf AP149 in the young open cluster α Persei are analyzed here. We reconstruct the observed light curves with a two-starspot model by means of a light curve modeling technique, and find that the active regions shift oppositely along longitude on a time scale of one day. Combining with the observational data obtained by other groups, we discuss the evolution of spotted regions in the photosphere, and find that its starspots evolve not only on a short time scale but also on a long time scale. The pure chromospheric emissions for Ca IIHK and Hβ lines are derived by using the spectral subtraction technique. The variation of Ca IIHK lines＇ excess emission is spatially correlated to the starspot regions. There is no clear rotational modulation for the Hβ line＇s excess emission, probably due to the contamination of prominence emission.

关键词： stars: activity -- stars: late-type -- stars: spots -- stars: individual AP149

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Risk of gastric cancer development after eradication of Helicobacter pylori

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World Journal of Gastrointestinal Oncology 2018年第5期10卷 115-123页

作者： Ka-Shing cheung wai K leung Department of Medicine The University of Hong Kong Queen Mary Hospital

Helicobacter pylori(H. pylori) infection is the most important risk factor for gastric cancer(gc) development through the correa's gastric carcinogenesis cascade. However, H. pylori eradication alone does not eliminate gc, as pre-neoplastic lesions(atrophic gastritis, intestinal metaplasia and dysplasia) may have already developed in some patients. It is therefore necessary to identify patients at high-risk for gastric cancer after H. pylori eradication to streamline the management plan. If the patients have not undergone endoscopy with histologic assessment, the identification of certain clinical risk factors and non-invasive testing(serum pepsinogen) can predict the risk of atrophic gastritis. For those with suspected atrophic gastritis, further risk stratification by endoscopy with histologic assessment according to validated histologic staging systems would be advisable. Patients with higher stages may require long-term endoscopic surveillance. Apart from secondary prevention to reduce deaths by diagnosing gc at an early stage, identifying medications that could potentially modify the gc risk would be desirable. The potential roles of a number of medications have been suggested by various studies, including proton pump inhibitors(PPIs), aspirin, statins and metformin. However, there are currently no randomized clinical trials to address the impact of these medications on gc risk after H. pylori eradication. In addition, most of these studies failed to adjust for the effect of concurrent medications on gc risk. Recently, large population-based retrospective cohort studies have shown that PPIs were associated with an increased gc risk after H. pylori eradication, while aspirin was associated with a lower risk. The roles of other agents in reducing gc risk after H. pylori eradication remain to be determined.

关键词： Gastric adenocarcinoma Stomach cancer Helicobacter pylori Chemoprevention Intestinal metaplasia

Risk of stroke after acute myocardial infarction among Chinese

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Chinese Medical Journal 2001年第2期114卷 98-99页

作者： Ping-WingNG wai-KwongCHAN Patrick Kwok-leung K WAN Department of Medicine and Geriatrics United Christian Hospital Hong Kong China

Following an acute myocardial infarction (AMI), patients have an increased risk of stroke. Estimates of risk are mainly derived from AMI treatment trials or secondary prevention studies. The reported incidence of stroke in Caucasians in the early phase after AMI ranged from 0.5% to 2.5%.1-3 Similar assessment of risk in the Chinese population is lacking. As thrombolytic therapy becomes standard treatment for AMI, there is concern that there may be an increase in haemorrhagic stroke complicating AMI treatment, especially since haemorrhagic stroke is more common in Asian populations.

关键词： TERM

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Urocortin and cardiovascular protection

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Acta Pharmacologica Sinica 2004年第3期25卷 3-11页

作者： Chi-wai LAU,Yau-chi CHAN,Suk-ying TSANG,Franky leung CHAN The Chinese University of Hong Kong Hong Kong China Department of Anatomy The Chinese University of Hong Kong Hong Kong China Department of Anatomy The Chinese University of Hong Kong Hong Kong China Department of Anatomy The Chinese University of Hong Kong Hong Kong China Department of Anatomy

Urocortin and other hypothalamus corticotropin-releasing factor (CRF) polypeptides play biologically diverse roles in the stress, cardiovascular and inflammatory responses by acting on central and peripheral CRF receptors. Urocortin shows a significantly high sequence homology to CRF, and the concurrent expression of type-2 CRF (CRF2) receptors with urocortin in the heart suggests that urocortin may play a physiological role in the cardiac function. Urocortin is thought to be the endogenous agonist producing the cardiovascular actions previously attributed to CRF. This review highlights the current novel findings on the molecular and cellular mechanisms by which urocortin may exert its cardiovascular protective action.

关键词： urocortin corticotropin-releasing hormone vascular smooth muscle heart vasodilaion second messenger system protein kinases

Rapid testing methods for food contaminants and toxicants

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Journal of Integrative Agriculture 2015年第11期14卷 2243-2264页

作者： Jiachi Chiou Arthur Ho Hon leung Hang wai Lee Wing-tak Wong Department of Applied Biology and Chemical Technology Food Safety and Technology Research CenterThe Hong Kong Polytechnic University Shenzhen Key Laboratory for Food Biological Safety Control Food Safety and Technology Research CentreThe Hong Kong Polytechnic University Shenzhen Research Institute

Food safety is one of the major concerns in every country regardless of the economic and social development. The frequent occurrence of food scandals in the world has led the Chinese government to implement several strategies to fortify the food supply system to a high food safety standard. This relies heavily on laboratory testing services but conventional methods for detection of food contaminants and toxicants are limited by sophisticated sample preparation procedures, long analysis time, large instruments and professional personnel to meet the increasing demands. In this review, we have incorporated most of the current and potential rapid detection methods for many notorious food contaminants and toxicants including microbial agents, toxic ions, pesticides, veterinary drugs and preservatives, as well as detection of genetically modified food genes and adulterated edible oil. Development of rapid, accurate, easy-to-use and affordable testing methods could urge food handlers and the public to actively screen for food contaminants and toxicants instead of passively relying on monitoring by the government examination facility. This review also provides several recommendations including how to encourage the public to engage in the food safety management system and provide optimal education and financial assistance that may improve the current Chinese food safety control system.

关键词： rapid testing food contaminants and toxins microbial agents pesticides veterinary drugs preservatives formaldehyde nitrite nitrate test strips

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