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Search Results: 1 - 10 of 12869 matches for " Anderson Ho Cheung SHUM "
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Editorial: Soft  [PDF]
Anderson Ho Cheung SHUM
Soft (Soft) , 2013, DOI: 10.4236/soft.2013.22002
Abstract: Editorial: Soft
Beating the jetting regime
Alban Sauret,Ho Cheung Shum
Physics , 2013, DOI: 10.1515/ijnsns-2011-0183
Abstract: We study numerically the dynamics of jets and drops in a microcapillary co-flow device. The co-flow stream encounters different flow regimes, including dripping, jetting. Using a level-set/finite element axysimmetric numerical simulation, we study the dynamics of breakup of a jet subject to flow rate perturbations. A scaling law for the width of the unperturbed jet is presented and compared to existing experimental results as well as numerical measurements. Then, we show that the introduction of a sinusoidal perturbation of the inner fluid flow rate can facilitate breakup of the fluid in regimes where a jet is usually observed. Moreover, the flow rate perturbation leads to a good control over the size and the frequency of the resulting droplets. Using theoretical modelling, we provide a criterion to determine the optimal frequency to break up the jet. We also derive scaling laws to determine the volume of inner fluid encapsulated in the emulsion droplets as a function of the frequency and to estimate the distance for the jet to break up as a function of the amplitude of perturbation. These scaling laws are in good agreement with results of numerical simulations. Our work suggests a novel approach and offers guiding principles to break up liquid jets in cases where dripping is difficult to achieve.
Forced generation of simple and double emulsions in all-aqueous system
Alban Sauret,Ho Cheung Shum
Physics , 2012, DOI: 10.1063/1.3702434
Abstract: We report an easy-to-implement method that allows the direct generation of water-in-water (w/w) single emulsions. The method relies on direct perturbation of the pressure that drives the flow of the dispersed phase of the emulsions. The resultant inner jet is induced to break up into droplets due to the growth of the perturbation through Rayleigh-Plateau instability [L. Rayleigh, Proc. R. Soc. London 29, 71-97 (1879)]; this leads to the formation of monodisperse droplets. By implementing this method on a modified microfluidic device, we directly generate water-in-water-in-water (w/w/w) double emulsions with good control over the size and the number of encapsulated droplets. Our approach suggests a new route to apply droplet-based microfluidics to completely water-based systems.
Fluctuation-induced dynamics of multiphase liquid jets with ultra-low interfacial tension
Alban Sauret,Constantinos Spandagos,Ho Cheung Shum
Physics , 2013, DOI: 10.1039/c2lc40524e
Abstract: Control of fluid dynamics at the micrometer scale is essential to emulsion science and materials design, which is ubiquitous in everyday life and is frequently encountered in industrial applications. Most studies on multiphase flow focus on oil-water systems with substantial interfacial tension. Advances in microfluidics have enabled the study of multiphase flow with more complex dynamics. Here, we show that the evolution of the interface in a jet surrounded by a co-flowing continuous phase with an ultra-low interfacial tension presents new opportunities to the control of flow morphologies. The introduction of a harmonic perturbation to the dispersed phase leads to the formation of interfaces with unique shapes. The periodic structures can be tuned by controlling the fluid flow rates and the input perturbation; this demonstrates the importance of the inertial effects in flow control at ultra-low interfacial tension. Our work provides new insights into microfluidic flows at ultra-low interfacial tension and their potential applications.
Controlled Buckling and Crumpling of Nanoparticle-Coated Droplets
Sujit S. Datta,Ho Cheung Shum,David A. Weitz
Physics , 2010, DOI: 10.1021/la103874z
Abstract: We introduce a new experimental approach to study the structural transitions of large numbers of nanoparticle-coated droplets as their volume is reduced. We use an emulsion system where the dispersed phase is slightly soluble in the continuous phase. By adding a fixed amount of unsaturated continuous phase, the volume of the droplets can be controllably reduced, causing them to buckle or crumple, thereby becoming nonspherical. The resultant morphologies depend both on the extent of volume reduction and the average droplet size. The buckling and crumpling behavior implies that the droplet surfaces are solid.
Corrugated interfaces in multiphase core-annular flow
Ho Cheung Shum,Alban Sauret,Alberto Fernandez-nieves,Howard A. Stone,David A. Weitz
Physics , 2012, DOI: 10.1063/1.3480561
Abstract: Microfluidic devices can be used to produce highly controlled and monodisperse double or multiple emulsions. The presence of inner drops inside a jet of the middle phase introduces deformations in the jet, which leads to breakup into monodisperse double emulsions. However, the ability to generate double emulsions can be compromised when the interfacial tension between the middle and outer phases is low, leading to flow with high capillary and Weber numbers. In this case, the interface between the fluids is initially deformed by the inner drops but the jet does not break into drops. Instead, the jet becomes highly corrugated, which prevents formation of controlled double emulsions. We show using numerical calculations that the corrugations are caused by the inner drops perturbing the interface and the perturbations are then advected by the flow into complex shapes.
After the Treatment Phase of Colorectal Cancer Care: Survivorship and Follow-Up  [PDF]
Maria Y. Ho, Winson Y. Cheung
Journal of Cancer Therapy (JCT) , 2012, DOI: 10.4236/jct.2012.326125
Abstract: The number of long-term colorectal cancer (CRC) survivors has increased substantially over the past three decades due to both ongoing advances in early detection and improvements in cancer therapies. Adult survivors of CRC experience chronic health conditions due to normal issues associated with aging, which is further compounded by the long-term adverse effects of having had cancer and anti-cancer therapies. In addition, they are at a higher risk for CRC recurrences, new primary cancers, and other co-morbidities. This article will provide an overview of the clinical care of adult survivors of CRC. Epidemiologic data will be presented followed by a discussion of the approach to the care of long-term adult survivors of CRC, including surveillance of recurrences and new primary cancers, interventions to manage both physical and psychological consequences of cancer and its treatments, and strategies to address concerns related to unemployment and disability. Finally, we will explore the challenges of healthcare delivery, especially with respect to the coordination of follow-up between cancer specialists and primary care physicians, so as to ensure that all of the survivor’s health needs are met promptly and appropriately.
Asymmetric-detection time-stretch optical microscopy (ATOM) for ultrafast high-contrast cellular imaging in flow
Terence T. W. Wong,Andy K. S. Lau,Kenneth K. Y. Ho,Matthew Y. H. Tang,Joseph D. F. Robles,Xiaoming Wei,Antony C. S. Chan,Anson H. L. Tang,Edmund Y. Lam,Kenneth K. Y. Wong,Godfrey C. F. Chan,Ho Cheung Shum,Kevin K. Tsia
Physics , 2013,
Abstract: Accelerating imaging speed in optical microscopy is often realized at the expense of image contrast, image resolution, and detection sensitivity- a common predicament for advancing high-speed and high-throughput cellular imaging. We here demonstrate a new imaging approach, called asymmetric-detection time-stretch optical microscopy (ATOM), which can deliver ultrafast label-free high-contrast flow imaging with well delineated cellular morphological resolution and in-line optical image amplification to overcome the compromised imaging sensitivity at high speed. We show that ATOM can separately reveal the enhanced phase-gradient and absorption contrast in microfluidic live-cell imaging at a flow speed as high as ~10 m/s, corresponding to an imaging throughput of ~100,000 cells/sec. ATOM could thus be the enabling platform to meet the pressing need for intercalating optical microscopy in cellular assay, e.g. imaging flow cytometry- permitting high-throughput access to the morphological information of the individual cells simultaneously with a multitude of parameters obtained in the standard assay.
Information Flow in One-Dimensional Vehicular Ad Hoc Networks
Chi Wan Sung,Kenneth W. Shum,Wing Ho Yuen
Mathematics , 2010,
Abstract: We consider content distribution in vehicular ad hoc networks. We assume that a file is encoded using fountain code, and the encoded message is cached at infostations. Vehicles are allowed to download data packets from infostations, which are placed along a highway. In addition, two vehicles can exchange packets with each other when they are in proximity. As long as a vehicle has received enough packets from infostations or from other vehicles, the original file can be recovered. In this work, we show that system throughput increases linearly with number of users, meaning that the system exhibits linear scalability. Furthermore, we analyze the effect of mobility on system throughput by considering both discrete and continuous velocity distributions for the vehicles. In both cases, system throughput is shown to decrease when the average speed of all vehicles increases. In other words, higher overall mobility reduces system throughput.
Generation of Innovative and Sparse Encoding Vectors for Broadcast Systems with Feedback
Ho Yuet Kwan,Kenneth W. Shum,Chi Wan Sung
Mathematics , 2011,
Abstract: In the application of linear network coding to wireless broadcasting with feedback, we prove that the problem of determining the existence of an innovative encoding vector is NP-complete when the finite field size is two. When the finite field size is larger than or equal to the number of users, it is shown that we can always find an encoding vector which is both innovative and sparse. The sparsity can be utilized in speeding up the decoding process. An efficient algorithm to generate innovative and sparse encoding vectors is developed. Simulations show that the delay performance of our scheme with binary finite field outperforms a number of existing schemes in terms of average and worst-case delay.
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