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Crack buckling in soft gels under compression

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Acta Mechanica Sinica 2012年第4期28卷 1098-1105页

作者： Rong Long Chung-yuen Hui Department of Biological and Environmental Engineering Cornell University Ithaca 14853 New York USA Field of Theoretical and Applied Mechanics Cornell University Ithaca 14850 New York USA

Recent interest in designing soft gels with high fracture toughness has called for simple and robust methods to test fracture behavior. The conventional method of applying tension to a gel sample suffers from a difficulty of sample gripping. In this paper, we study a possible fracture mechanism of soft gels under uni-axial compression. We show that the surfaces of a pre-existing crack, oriented parallel to the loading axis, can buckle at a critical compressive stress. This buckling instability can open the crack surfaces and cre- ate highly concentrated stress fields near the crack tip, which can lead to crack growth. We show that the onset of crack buckling can be deduced by a dimensional argument com- bined with an analysis to determine the critical compression needed to induce surface instabilities of an elastic half space. The critical compression for buckling was verified for a neo- Hookean material model using finite element simulations.

关键词： Fracture mechanics. Soft gels. Buckling. Crack Compression

Regional Stress Fields under Tibet from 3D Global Flow Simulation

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Journal of Earth Science 2011年第2期22卷 155-159页

作者：张斯奇 David A yuen 张怀石耀霖 Laboratory of Computational Geodynamics Graduate University of Chinese Academy of Sciences Earth System Sciences Computational Center The University of QueenslandSt LuciaQLD 4072Australia Department of Geology and Geophysics and Minnesota Supercomputing Institute University of MinnesotaMinneapolisMN 55415USA

Tibetan area is the most active continental collision zone on earth. Several major earthquakes occurred around the boundaries of Tibetan plateau and caused massive damages and casualties. The dynamics of this area is not well understood due to the complex structure of Tibet and its surrounding area. In this study, a 3D global flow simulation with only viscous rheology is applied to studying the stress distribution in this area, and the interaction between Tibet and its surrounding areas is investigated. Finally, the possibility of combining regional modeling with global models is also discussed.

关键词： Tibet global flow stress simulation.

Probabilistic characterization of cyclic shear modulus reduction for normally to moderately over-consolidated clays

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Earthquake Engineering and Engineering Vibration 2016年第3期15卷 495-508页

作者： Iok-Tong Ng Ka-Veng yuen Ngai-Kuan Lao Dept.of Civil and Environmental Engineering Faculty of Science and Technology University of Macao

Evaluation of the cyclic shear modulus of soils is a crucial but challenging task for many geotechnical earthquake engineering and soil dynamic issues. Improper determination of this property unnecessarily drives up design and maintenance costs or even leads to the construction of unsafe structures. Due to the complexities involved in the direct measurement, empirical curves for estimating the cyclic shear modulus have been commonly adopted in practice for simplicity and economical considerations. However, a systematic and robust approach for formulating a reliable model and empirical curve for cyclic shear modulus prediction for clayey soils is still lacking. In this study, the Bayesian model class selection approach is utilized to identify the most significant soil parameters affecting the normalized cyclic shear modulus and a reliable predictive model for normally to moderately over-consolidated clays is proposed. Results show that the predictability and reliability of the proposed model out performs the well-known empirical models. Finally, a new design chart is established for practical usage.

关键词： Bayesian analysis cyclic shear modulus empirical model geotechnical earthquake engineering normally tomoderately over-consolidated clays

Valuation of CDS counterparty risk under a reduced-form model with regime-switching shot noise default intensities

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Frontiers of Mathematics in China 2017年第5期12卷 1085-1112页

作者： Yinghui DONG Kam Chuen yuen Guojing WANG Department of Mathematics and Physics Suzhou University of Science and TechnologySuzhou 215009 China Department of Statistics and Actuarial Science University of Hong Kong Hong KongChina Department of Mathematics and Center for Financial Engineering Soochow UniversitySuzhou 215006 China

We study the counterparty risk for a credit default swap （CDS） in a regime-switching market driven by an underlying continuous-time Markov chain. We model the default dependence via some correlated Cox processes with regime-switching shot noise intensities containing common shock. Under the proposed model, the general bilateral counterparty risk pricing formula for CDS contracts with the possibility of joint defaults is presented. Based on some expressions for the conditional Laplace transform of the integrated intensity processes, semi-analytical solution for the bilateral credit valuation adjustment （CVA） is derived. When the model parameters satisfy some conditions, explicit formula for the bilateral CVA at time 0 is also given.

关键词： Credit default swap (CDS) bilateral credit valuation adjustment,Markov chain common shock regime-switching shot noise process

Joint timing and frequency synchronization in coherent optical OFDM systems

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Frontiers of Optoelectronics 2019年第1期12卷 4-14页

作者： Xinwei DU Pooi-yuen KAM Changyuan YU Department of Electrical and Computer Engineering National University of SingaporeSingapore 117583Singapore National University of Singapore(Suzhou)Research Institute Suzhou 21512China Department of Electrical and Information Engineering The Hong Kong Polytechnic UniversityHung HomKowloonHong KongChina

In this paper,we review our joint timing and frequency synchronization algorithms in coherent optical orthogonal frequency division multiplexing(CO-OFDM)*** first present a timing estimation method by designing the pattern of the training symbol,whose timing metric has a sharp and clear peak,to ensure accurate timing offset(TO)estimation *** we provide both data-aided(DA)and blind(BL)approaches to estimate the carrier frequency offset(CFO).For the DA algorithm,we utilize the same training symbol structure as the timing estimation does,while for the BL algorithm,we utilize the zero-subcarrier power(ZSP)to achieve full-range CFO *** that our joint timing and frequency synchronization approaches require only one OFDM symbol,which ensure not only the data transmission efficiency,but also the TO and CFO estimation performance.A modified BL ZSP algorithm is proposed to further improve the CFO estimation performance by taking the power average over a series of OFDM *** effectiveness of the TO estimation algorithm,and both the DA and BL CFO estimation algorithms are verified and demonstrated in both simulations and experiments.

关键词： timing offset (TO) carrier frequency offset (CFO) coherent optical orthogonal frequency division multiplexing (CO-OFDM) zero-subcarrier power (ZSP)

Rock brittleness indices and their applications to different fields of rock engineering:A review

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Journal of Rock Mechanics and Geotechnical Engineering 2021年第1期13卷 221-247页

作者： Fanzhen Meng Louis Ngai yuen Wong Hui Zhou College of Science Qingdao University of TechnologyQingdao266033China Department of Earth Sciences The University of Hong KongPokfulamHong KongChina State Key Laboratory of Geomechanics and Geotechnical Engineering Institute of Rock and Soil MechanicsChinese Academy of SciencesWuhan430071China

Brittleness is an important parameter controlling the mechanical behavior and failure characteristics of rocks under loading and unloading conditions,such as fracability,cutability,drillability and rockburst *** such,it is of high practical value to correctly evaluate rock ***,the definition and measurement method of rock brittleness have been very diverse and not yet been *** this paper,the definitions of rock brittleness are firstly reviewed,and several representative definitions of rock brittleness are identified and briefly *** development and role of rock brittleness in different fields of rock engineering are also *** brittleness indices publicly available in rock mechanics literature are compiled,and the measurement method,applicability and limitations of some indices are *** results show that(1)the large number of brittleness indices and brittleness definitions is attributed to the different foci on the rock behavior when it breaks;(2)indices developed in one field usually are not directly applicable to other fields;and(3)the term“brittleness”is sometimes misused,and many empirically-obtained brittleness indices,which lack theoretical basis,fail to truly reflect rock *** the basis of this review,three measurement methods are identified,i.e.(1)elastic deformation before fracture,(2)shape of post-peak stressestrain curves,and(3)methods based on fracture mechanics theory,which have the potential to be further refined and unified to become the standard measurement methods of rock *** is highly beneficial for the rock mechanics community to develop a robust definition of rock *** study will undoubtedly provide a comprehensive timely reference for selecting an appropriate brittleness index for their applications,and will also pave the way for the development of a standard definition and measurement method of rock brittleness in the long term.

关键词： Rock brittleness Practical applicability Hydraulic fracturing Rockburst proneness Crack propagation Fragmentation efficiency

Uniform Asymptotics for Finite-time Ruin Probability in a Dependent Risk Model with General Stochastic Investment Return Process

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Acta Mathematicae Applicatae Sinica 2021年第4期37卷 847-857页

作者： Yang YANG Kam Chuen yuen Jun-feng LIU School of Statistics and Data Science Nanjing Audit UniversityNanjing211815China Department of Statistics and Actuarial Science The University of Hong KongPokfulam RoadHong KongChina

In this paper,we consider a non-standard renewal risk model with dependent claim sizes,where an insurance company is allowed to invest his/her wealth in financial assets,leading to some stochastic investment log-returns described as a general adapted càdlàg *** the assumptions that the claim sizes are heavy-tailed and the stochastic log-return process on investments is bounded from below almost surely,we derive some asymptotic formulas for the finite-time ruin probability holding uniformly in any finite time horizon.

关键词： finite-time ruin probability stochastic log-return process on investments upper tail asymptotic independence dominated variation uniformity

Tips and tricks for getting more out of your delayed primary repair of ruptured flexor pollicis longus tendon

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Plastic and Aesthetic Research 2017年第8期4卷 135-136页

作者： Charles yuen yung Loh Alethea Tan Makarand Tare St Andrew's Centre for Plastic and Reconstructive Surgery Broomfield HospitalChelmsford CM17ETUK

Sir, Primary tendon repairs are often difficult in patients with delayed presentation. Tendons are contracted and shortened with extensive scarring occurring along the path of the tendon. Pulleys and the wound bed can be filled with granulation tissue which obstructs the passage of the tendon. Many of such patients would then be treated with a two stage tendon reconstruction, which involves the insertion of a silicone rod for pseudosheath formation[1] before tendon grafting at a second stage. This however, would set the patient back for roughly six months, especially involving multiple visits to physiotherapy and being off work. We would like to describe several tips and tricks in our armamentarium and illustrate these using a case we recently encountered [Figure 1].

关键词： Primary Presentation Armamentarium

Progressive drain withdrawal without suture removal: a technical note

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Plastic and Aesthetic Research 2014年第1期1卷 41-42页

作者： Zaher Jandali Charles yuen yung Loh Athanassopoulos Thanassi Department of Plastic Aesthetic and Reconstructive surgeryAsklepios Klinik WandsbekHamburgGermany Ninewells Hospital Dundee ScotlandUK

Sir,Drains are traditionally used in a variety of surgical procedures;[1,2]although there is limited evidence of their usefulness.[3]Drains are classified based on various characteristics:as open or closed systems,as active versus passive,as prophylactic versus therapeutic;or by composition(***,silicone,or rubber).[2,4]Closed vacuum drains apply negative suction(60-80 kPa)in a sealed environment.[5]Drains are often secured using a single suture or adhesive tape to prevent inadvertent *** from drains include pain,hemorrhage,drain entrapment,and retrograde bacterial migration that can result in postoperative infections.[1,2]

关键词： drain passive sealed