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An unsupervised learning approach to study synchroneity of past events in the South China Sea

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Frontiers of Earth Science 2019年第3期13卷 628-640页

作者： Kevin C. Tse Hon-Chim Chiu Man-yin Tsang yiliang Li Edmund y. lam Department of Earth Sciences The University of Hong KongPokfulamHong KongChina Department of Geography and Centre for Geo-computation Studies Hong Kong Baptist UniversityKowloon TongHong KongChina Department of Earth Sciences University of TorontoCanada Department of Electrical and Electronic Engineering The University of Hong KongPokfulamHong KongChina

Unsupervised machine learning methods were applied on multivariate geophysical and geochemical datasets of ocean floor sediment cores collected from the South China Sea. The well-preserved and continuous core samples comprising high resolution Cenozoic sediment records enable scientists to carry out paleoenvironment studies in detail. Bayesian age-depth chronological models constructed from biostratigraphic control points for the drilling sites are applied on cluster boundaries generated from two popular unsupervised learning methods: K-means and random forest. The unsupervised learning methods experimented have produced compact and unambiguous clusters from the datasets, indicating that previously unknown data patterns can be revealed when all variables from the datasets are taken into account simultaneously. A study of synchroneity of past events represented by the cluster boundaries across geographically separated ocean drilling sites is achieved through converting the fixed depths of cluster boundaries into chronological ranges represented by Gaussian density plots which are then compared with known past events in the region. A Gaussian density peak at around 7.2 Ma has been identified from results of all three sites and it is suggested to coincide with the initiation of the East Asian monsoon. Contrary to traditional statistical approach, a priori assumptions are not required for unsupervised learning, and the clustering results serve as a novel data-driven proxy for study.ng the complex and dynamic processes of the paleoenvironment surrounding the ocean sediment. This work serves as a pioneering approach to extract valuable information of regional events and opens up a systematic and objective way to study the vast global ocean sediment datasets.

关键词： machine learning ocean sediments unsupervised classification

Unsupervised learning on scientific ocean drilling datasets from the South China Sea

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Frontiers of Earth Science 2019年第1期13卷 180-190页

作者： Kevin C.TSE Hon-Chim CHIU Man-yin TSAng yiliang LI Edmund y.lam Department of Earth Sciences The University of Hong KongPokfulamHong KongChina Department of Geography and Centre for Geo-computation Studies Hong Kong Baptist UniversityKowloon TongHong KongChina Department of Earth Sciences University of TorontoTorontoON M5S 2M8Canada Department of Electrical and Electronic Engineering The University of Hong KongPokfulamHong KongChina

Unsupervised learning methods were applied to explore data patterns in multivariate geophysical datasets collected from ocean floor sediment core samples coming from scientific ocean drilling in the South China *** to studies on similar datasets,but using supervised learning methods which are designed to make predictions based on sample training data,unsupervised learning methods require no a priori information and focus only on the input *** this study,popular unsupervised learning methods including K-means,self-organizing maps,hierarchical clustering and random forest were coupled with different distance metrics to form exploratory data *** resulting data clusters were externally validated with lithologic units and geologic time scales assigned to the datasets by conventional methods. Compact and connected data clusters displayed vary.ng degrees of correspondence with existing classification by lithologic units and geologic time scales.K-means and self-organizing maps were observed to perform better with lithologic units while random forest corresponded best with geologic time *** study sets a pioneering example of how unsupervised machine learning methods can be used as an automatic processing tool for the increasingly high volume of scientific ocean drilling data.

关键词： machine learning unsupervised learning ODP IODP clustering

Rotating electroosmotic flow of an Eyring fluid

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Acta Mechanica Sinica 2017年第2期33卷 295-315页

作者： Cheng Qi Chiu-On ng Department of Mechanical Engineering The University of Hong Kong Hong Kong China

A perturbation analysis is presented in this paper for the electroosmotic (EO) flow of an Eyring fluid through a wide rectangular microchannel that rotates about an axis perpendicular to its own. Mildly shear-thinning rheology is assumed such that at the leading order the problem reduces to that of Newtonian EO flow in a rotating channel, while the shear thinning effect shows up in a higher-order problem. Using the relaxation time as the small ordering parameter, analytical solutions are deduced for the leading- as well as first-order problems in terms of the dimensionless Debye and rotation parameters. The velocity profiles of the Ekman-electric double layer (EDL) layer, which is the boundary layer that arises when the Ekman layer and the EDL are comparably thin, are also deduced for an Eyring fluid. It is shown that the present perturbation model can yield results that are close to the exact solutions even when the ordering parameter is as large as order unity. By this order of the relaxation time parameter, the enhancing effect on the rotating EO flow due to shear-thinning Eyring rheology can be significant.

关键词： Electroosmotic flow Eyring fluid Rotating channel

Remodeling of astrocyte secretome in amyotrophic lateral sclerosis:uncovering novel targets to combat astrocyte-mediated toxicity

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Translational Neurodegeneration 2022年第1期11卷 84-97页

作者： Winanto ng Shi-yan ng Institute of Molecular and Cell Biology A*STAR Research EntitiesSingapore 138673Singapore

Amyotrophic lateral sclerosis(ALS)is an adult-onset paralytic disease characterized by progressive degeneration of upper and lower motor neurons in the motor cortex,brainstem and spinal *** neuron degeneration is typically caused by a combination of intrinsic neuronal(cell autonomous)defects as well as extrinsic(non-cell autonomous)factors such as astrocyte-mediated *** are highly plastic cells that react to their microenvironment to mediate relevant *** neurodegeneration,astrocytes often turn reactive and in turn secrete a slew of factors to exert pro-inflammatory and neurotoxic *** efforts have been carried out to characterize the diseased astrocyte secretome over the years,revealing that pro-inflammatory chemokines,cytokines and microRNAs are the main players in mediating neuronal *** metabolomic technologies mature,these studies begin to shed light on neurotoxic metabolites such as secreted *** this focused review,we will discuss changes in the astrocyte secretome during *** particular,we will discuss the components of the reactive astrocyte secretome that contribute to neuronal death in ALS.

关键词： Motor neuron disease Astrocyte Astrocyte-mediated toxicity Secretome

On the time development of dispersion in electroosmotic flow througha rectangular channel

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Acta Mechanica Sinica 2012年第3期28卷 631-643页

作者： Suvadip Paul Chiu-On ng Department of Mechanical Engineering The University of Hong Kong

This is an analytical study on the time develop- ment of hydrodynamic dispersion of an inert species in elec- troosmotic flow through a rectangular channel. The objec- tive is to determine how the channel side walls may affect the dispersion coefficient at different instants of time. To this end, the generalized dispersion model, which is valid for short and long times, is employed in the present study. An- alytical expressions are derived for the convection and dis- persion coefficients as functions of time, the aspect ratio of the channel, and the Debye-Htickel parameter representing the thickness of the electric double layer. For transport in a channel of large aspect ratio, the dispersion may undergo several stages of transience. The initial, fast time develop- ment is controlled by molecular diffusion across the narrow channel height, while the later, slower time development is governed by diffusion across the wider channel breadth. For a sufficiently large aspect ratio, there can be an interlude between these two periods during which the coefficient is nearly steady, signify.ng the resemblance of the transport to that in a parallel-plate channel. Given a sufficiently long time, the dispersion coefficient will reach a fully-developed steady value that may be several times higher than that with- out the side wall effects. The time scales for these periods of transience are identified in this paper.

关键词： Taylor dispersion. Electroosmotic flow. Gener-alized dispersion model

Complete characterization of ultrashort optical pulses with a phase-shifting wedged reversal shearing interferometer

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Light(Science & Applications) 2018年第1期7卷 755-765页

作者： Billy lam Chunlei Guo The Institute of Optics University of RochesterRochesterNY 14627USA Changchun Institute of Optics Fine Mechanics and PhysicsChinese Academy of Sciences130033 ChangchunChina

The ability of an interferometer to characterize the spatial information of a light beam is often limited by the temporal profile of the beam,with femtosecond pulse characterization being particularly *** this study,we developed a simple,stable,controllable shearing and vectorial phase-shifting wedged reversal shearing interferometer that is able to characterize all types of coherent and partially coherent light *** proposed interferometer consists of only a single beam splitter cube with one wedged entrance face and is insensitive to environmental vibration due to its common path configuration.A near zero-path length difference of the proposed interferometer ensures its operation for ultrashort pulses,providing,for the first time,a simple and stable interferometric tool to fully characterize sub-100 fs laser *** common beam characterization can be carried out with the interferometer,such as the amplitude,phase,polarization,wavelength,and pulse ***,this technique is sensitive to the wavefront tilt and can be used for precise beam ***,this interferometer can be an essential tool for beam characterization,optical imaging,and the testing required for a wide range of applications,including astronomy,biomedicine,ophthalmology,optical testing and imaging systems,and adaptive optics.

关键词： interferometer ultrashort shearing

Dynamic response and optimization of an inclined steel rock shed by the graded energy dissipating method

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Journal of Mountain Science 2019年第1期16卷 138-152页

作者： WU y.ng HE Si-ming LI Xin-po Wang Dong-po Key Laboratory of Mountain Hazards and Earth Surface Process Chinese Academy of Sciences Institute of Mountain Hazards and Environment Chinese Academy of Sciences State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Chengdu University of Technology

Blocking rockfalls directly by reinforced concrete(RC) flat sheds with thick sand cushions is an outdated method. Such conventional sheds typically accumulate rock heavily, and become progressively damaged and are difficult to repair, and are very costly. To address these problems, we propose a new structure called a Graded Dissipating Inclined Steel Rock(GDISR) shed that utilizes the graded energy dissipation method. Here, we study the dynamic response of the GDISR shed with model test and numerical simulation, and give its optimization design combining with a practical engineering case. Our results show that the optimized modular E-block and corrugated steel tube can deform to sufficiently absorb the energy of different impact intensities. This efficiently and economically provides GDISR sheds with two security lines. Compared with conventional RC sheds, GDISR sheds with optimal incline have a more efficient anti-impact function, are faster and easier to repair, and are much simpler and cheaper to build.

关键词： Dynamic response Optimization design Graded dissipating inclined steel rock shed

Jetting-based bioprinting:process,dispense physics,and applications

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Bio-Design and Manufacturing 2024年第5期7卷 771-799页

作者： Wei Long ng Viktor Shkolnikov Singapore Centre for 3D Printing(SC3DP) School of Mechanical and Aerospace EngineeringNanyang Technological University(NTU)Singapore 639798Singapore HP Inc. Palo AltoCA 94304USA

Jetting-based bioprinting facilitates contactless drop-on-demand deposition of subnanoliter droplets at well-defined positions to control the spatial arrangement of cells,growth factors,drugs,and biomaterials in a highly automated layer-by-layer fabrication *** to its immense versatility,jetting-based bioprinting has been used for various applications,including tissue engineering and regenerative medicine,wound healing,and drug development.A lack of in-depth understanding exists in the processes that occur during jetting-based *** review paper will comprehensively discuss the physical considerations for bioinks and printing conditions used in jetting-based *** first present an overview of different jetting-based bioprinting techniques such as inkjet bioprinting,laser-induced forward transfer bioprinting,electrohydrodynamic jet bioprinting,acoustic bioprinting and microvalve ***,we provide an in-depth discussion of various considerations for bioink formulation relating to cell deposition,print chamber design,droplet formation and droplet ***,we highlight recent accomplishments in jetting-based *** present the advantages and challenges of each method,discuss considerations relating to cell viability and protein stability,and conclude by providing insights into future directions of jetting-based bioprinting.

关键词： 3D bioprinting Biofabrication Jetting-based Dispense physics Machine learning

potential Hydrodynamic Performance Enhancement of Hydrokinetic Turbine with Hydrophobic Coatings

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China Ocean Engineering 2021年第6期35卷 924-932页

作者： CHEN Long ng Kai-Wern School of Hydraulic and Environmental Engineering Changsha University of Science and TechnologyChangsha 410114China Department of Civil Engineering Faculty of EngineeringUniversity of MalayaKuala Lumpur 50603Malaysia Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province Changsha University of Science and TechnologyChangsha 410114China

Hydrokinetic energy is a promising technology to harness predictable renewable energy from free-flowing water,tides and ocean *** studies have been conducted by researchers and engineers to find out ways to enhance the performance of the hydrokinetic *** current paper reports the experimental study of using hydrophobic coating as an alternative way to improve the performance of hydrokinetic turbine.A hydrophobic coating can lower the friction drag of a surface that is in contact with *** hydrokinetic turbine blade,reduction in friction drag may allow a blade section to have a better lift/drag ratio and have its efficiency *** this study,a formula to predict the pattern of drag reduction over a hydrophobic surface has been *** hydrophobic coatings were applied on NACA 63418 hydrofoils and their performances were *** was found that NACA 63418 hydrofoil with the hydrophobic coatings had its drag reduced by an average of 3%−4.0%.When the coatings were applied on a 350 mm diameter three-bladed turbine,the maximum increment of rotational speed of the turbine was found to be 2.5%.The performance of the two coatings against marine fouling was also *** weight of plate with and without the coatings increased by 10%and 100%,respectively.

关键词： hydrophobic coating hydrokinetic energy marine fouling