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Search Results: 1 - 10 of 283400 matches for " Terence C. W. Poon "
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Identification and Characterization of Tropomyosin 3 Associated with Granulin-Epithelin Precursor in Human Hepatocellular Carcinoma
Ching Yan Lam, Chi Wai Yip, Terence C. W. Poon, Christine K. C. Cheng, Eddy W. Y. Ng, Nicholas C. L. Wong, Phyllis F. Y. Cheung, Paul B. S. Lai, Irene O. L. Ng, Sheung Tat Fan, Siu Tim Cheung
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0040324
Abstract: Background and Aim Granulin-epithelin precursor (GEP) has previously been reported to control cancer growth, invasion, chemo-resistance, and served as novel therapeutic target for cancer treatment. However, the nature and characteristics of GEP interacting partner remain unclear. The present study aims to identify and characterize the novel predominant interacting partner of GEP using co-immunoprecipitation and mass spectrometry. Methods and Results Specific anti-GEP monoclonal antibody was used to capture GEP and its interacting partner from the protein extract of the liver cancer cells Hep3B. The precipitated proteins were analyzed by SDS-PAGE, followed by mass spectrometry and the protein identity was demonstrated to be tropomyosin 3 (TPM3). The interaction has been validated in additional cell models using anti-TPM3 antibody and immunoblot to confirm GEP as the interacting partner. GEP and TPM3 expressions were then examined by real-time quantitative RT-PCR in clinical samples, and their transcript levels were significantly correlated. Elevated TPM3 levels were observed in liver cancer compared with the adjacent non-tumorous liver, and patients with elevated TPM3 levels were shown to have poor recurrence-free survival. Protein expression of GEP and TPM3 was observed only in the cytoplasm of liver cancer cells by immunohistochemical staining. Conclusions TPM3 is an interacting partner of GEP and may play an important role in hepatocarcinogenesis.
From Clarkia to Escherichia and Janus: the physics of natural and synthetic active colloids
W C K Poon
Quantitative Biology , 2013,
Abstract: An active colloid is a suspension of particles that transduce free energy from their environment and use the energy to engage in intrinsically non-equilibrium activities such as growth, replication and self-propelled motility. An obvious example of active colloids is a suspension of bacteria such as Escherichia coli, their physical dimensions being almost invariably in the colloidal range. Synthetic self-propelled particles have also become available recently, such as two-faced, or Janus, particles propelled by differential chemical reactions on their surfaces driving a self-phoretic motion. In these lectures, I give a pedagogical introduction to the physics of single-particle and collective properties of active colloids, focussing on self propulsion. I will compare and contrast phenomena in suspensions of `swimmers' with the behaviour of suspensions of passive particles, where only Brownian motion (discovered by Robert Brown in granules from the pollen of the wild flower {\it Clarkia pulchella}) is relevant. I will pay particular attention to issues that pertain to performing experiments using these active particle suspensions, such as how to characterise the suspension's swimming speed distribution, and include an appendix to guide physicists wanting to start culturing motile bacteria.
Ionic effects in self-propelled Pt-coated Janus swimmers
A. T. Brown,W. C. K Poon
Physics , 2013,
Abstract: Colloidal particles partially coated with platinum and dispersed in H2O2 solution are often used as model self-propelled colloids. Most current data suggest that neutral self-diffusiophoresis propels these particles. However, several studies have shown strong ionic effects in this and related systems, such as a reduction of propulsion speed by salt. We investigate these ionic effects in Pt-coated polystyrene colloids, and find here that the direction of propulsion can be reversed by addition of an ionic surfactant, and that although adding pH neutral salts reduces the propulsion speed, adding the strong base NaOH has little effect. We use these data, as well as measured reaction rates, to argue against propulsion by either neutral or ionic self-diffusiophoresis, and suggest instead that the particle's propulsion mechanism may in fact bear close resemblance to that operative in bimetallic swimmers.
Diffusive Evolution of Stable and Metastable Phases II: Theory of Non-Equilibrium Behaviour in Colloid-Polymer Mixtures
R. M. L. Evans,W. C. K. Poon
Physics , 1997, DOI: 10.1103/PhysRevE.56.5748
Abstract: By analytically solving some simple models of phase-ordering kinetics, we suggest a mechanism for the onset of non-equilibrium behaviour in colloid-polymer mixtures. These mixtures can function as models of atomic systems; their physics therefore impinges on many areas of thermodynamics and phase-ordering. An exact solution is found for the motion of a single, planar interface separating a growing phase of uniform high density from a supersaturated low density phase, whose diffusive depletion drives the interfacial motion. In addition, an approximate solution is found for the one-dimensional evolution of two interfaces, separated by a slab of a metastable phase at intermediate density. The theory predicts a critical supersaturation of the low-density phase, above which the two interfaces become unbound and the metastable phase grows ad infinitum. The growth of the stable phase is suppressed in this regime.
A cluster mode-coupling approach to weak gelation in attractive colloids
K. Kroy,M. E. Cates,W. C. K. Poon
Physics , 2003, DOI: 10.1103/PhysRevLett.92.148302
Abstract: Mode-coupling theory (MCT) predicts arrest of colloids in terms of their volume fraction, and the range and depth of the interparticle attraction. We discuss how effective values of these parameters evolve under cluster aggregation. We argue that weak gelation in colloids can be idealized as a two-stage ergodicity breaking: first at short scales (approximated by the bare MCT) and then at larger scales (governed by MCT applied to clusters). The competition between arrest and phase separation is considered in relation to recent experiments. We predict a long-lived `semi-ergodic' phase of mobile clusters, showing logarithmic relaxation close to the gel line.
A unified description of the rheology of hard-particle suspensions
B. M. Guy,M. Hermes,W. C. K. Poon
Physics , 2015, DOI: 10.1103/PhysRevLett.115.088304
Abstract: The rheology of suspensions of Brownian, or colloidal, particles (diameter $d \lesssim 1$ $\mu$m) differs markedly from that of larger grains ($d \gtrsim 50$ $\mu$m). Each of these two regimes has been separately studied, but the flow of suspensions with intermediate particle sizes (1 $\mu\textrm{m} \lesssim d \lesssim 50$ $\mu$m), which occur ubiquitously in applications, remains poorly understood. By measuring the rheology of suspensions of hard spheres with a wide range of sizes, we show experimentally that shear thickening drives the transition from colloidal to granular flow across the intermediate size regime. This insight makes possible a unified description of the (non-inertial) rheology of hard spheres over the full size spectrum. Moreover, we are able to test a new theory of friction-induced shear thickening, showing that our data can be well fitted using expressions derived from it.
Polydispersity Effects in Colloid-Polymer Mixtures
S. M. Liddle,T. Narayanan,W. C. K. Poon
Physics , 2010, DOI: 10.1088/0953-8984/23/19/194116
Abstract: We study phase separation and transient gelation in a mixture consisting of polydisperse colloids and non-adsorbing polymers, where the ratio of the average size of the polymer to that of the colloid is approximately 0.063. Unlike what has been reported previously for mixtures with somewhat lower colloid polydispersity, the addition of polymers does not expand the fluid-solid coexistence region. Instead, we find a region of fluid-solid coexistence which has an approximately constant width but an unexpected re-entrant shape. We detect the presence of a metastable gas-liquid binodal, which gives rise to two-stepped crystallization kinetics that can be rationalized as the effect of fractionation. Finally, we find that the separation into multiple coexisting solid phases at high colloid volume fractions predicted by equilibrium statistical mechanics is kinetically suppressed before the system reaches dynamical arrest.
Protein crystallization in confined geometries
S. Tanaka,S. U. Egelhaaf,W. C. K. Poon
Quantitative Biology , 2003,
Abstract: We studied the crystallization of a globular protein, lysozyme, in the cubic phase of the lipid monoolein. The solubility of lysozyme in salt solution decreased by a factor of $\sim 4$ when confined in cubic phase. Calculations and Monte Carlo simulations show that this can be explained by the {\it confinement} of lysozyme molecules to the narrow water cells in the cubic phase.
Hard Spheres: Crystallization and Glass Formation
P. N. Pusey,E. Zaccarelli,C. Valeriani,E. Sanz,W. C. K. Poon,M. E. Cates
Physics , 2009, DOI: 10.1098/rsta.2009.0181
Abstract: Motivated by old experiments on colloidal suspensions, we report molecular dynamics simulations of assemblies of hard spheres, addressing crystallization and glass formation. The simulations cover wide ranges of polydispersity s (standard deviation of the particle size distribution divided by its mean) and particle concentration. No crystallization is observed for s > 0.07. For 0.02 < s < 0.07, we find that increasing the polydispersity at a given concentration slows down crystal nucleation. The main effect here is that polydispersity reduces the supersaturation since it tends to stabilise the fluid but to destabilise the crystal. At a given polydispersity (< 0.07) we find three regimes of nucleation: standard nucleation and growth at concentrations in and slightly above the coexistence region; "spinodal nucleation", where the free energy barrier to nucleation appears to be negligible, at intermediate concentrations; and, at the highest concentrations, a new mechanism, still to be fully understood, which only requires small re-arrangement of the particle positions. The cross-over between the second and third regimes occurs at a concentration, around 58% by volume, where the colloid experiments show a marked change in the nature of the crystals formed and the particle dynamics indicate an "ideal" glass transition.
Nonequilibrium phase transition in the sedimentation of reproducing particles
C. Barrett-Freeman,M. R. Evans,D. Marenduzzo,W. C. K. Poon
Physics , 2008, DOI: 10.1103/PhysRevLett.101.100602
Abstract: We study numerically and analytically the dynamics of a sedimenting suspension of active, reproducing particles, such as growing bacteria in a gravitational field. In steady state we find a non-equilibrium phase transition between a `sedimentation' regime, analogous to the sedimentation equilibrium of passive colloids, and a `uniform' regime, in which the particle density is constant in all but the top and bottom of the sample. We discuss the importance of fluctuations in particle density in locating the phase transition point, and report the kinetics of sedimentation at early times.
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