Zhang Jun. / "August 2000." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (p. 109-144). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Digitized by Kansas Correctional Industries

Huang Ji Ping. / "1st June, 2003." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (p. 125-134). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

A pressure cell apparatus has been designed, constructed and commissioned to measure the dielectric strength of liquid helium as a function of pressure for various temperatures in He I and He II. Breakdown experiments between a set of stainless steel parallel plate Rogowski profile electrodes with a separation of 1.27 mm have been made for temperatures ranging between 1.7 K to 4.2 K and applied pressures of SVP to ~ 2.2 bar. All pressure data taken above and below the λ-point exhibit similar features. At low pressure, near the SVP, breakdown voltage rapidly increases with applied pressure. This behaviour is linear for all temperatures and has an average gradient of 0.176 ± 0.0096 kVtorr-1. This regime changes at a pressure dependant kink point. Above this point a more gradual increase in breakdown voltage with pressure is observed. Data for all temperatures normalised to 50 kV and 1200 torr have an average gradient of 0.01693 ± 0.00092 kVtorr-1 with an average intercept of 29.69 ± 0.88 kV. A linear relationship is observed between the normalised kink pressure and the density of the helium (-34.4 ± 1.4 kg m-3torr-1 and intercept of 5130 ± 200 kg m-3). The normalised kink pressure as a function of SVP produces a linear relationship with a gradient consistent with unity (0.97 ± 0.04 torr2 with an intercept of 88 ± 13 torr). High voltage breakdown initiating at the cathode triple junction (CTJ) has been investigated in He I, He II and LN2 under SVP. Breakdown tests were made between parallel plate Rogowski profile electrodes with an Al2O3 ceramic spacer between them. Chips, cracks and tracks across the ceramic have been observed. LN2 breakdown tests cause catastrophic damage. Calculations of the E-fields in any gap between the ceramic and electrode show E-field enhancements of up to a factor of ~ 4.5. The end of a ceramic sample was sputtered with Gold in an attempted to prevent any E-field in the gap. This work has been carried out within the UK CryoEDM Collaboration and was aimed at understanding better the parameters which will ultimately limit the E-field in the Ramsey Cell of the main experiment.

Wong Chiu Tai, Andrew = 粒子懸浮液的自結合和場引發結合 / 黃昭泰. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references (leaves 70-73). / Text in English; abstracts in English and Chinese. / Wong Chiu Tai, Andrew = Li zi xuan fu ye de zi jie he he chang yin fa jie he / Huang Zhaotai. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Self assembly --- p.1 / Chapter 1.1.1 --- What is self assembly? --- p.1 / Chapter 1.1.2 --- Recent works --- p.1 / Chapter 1.2 --- Field induced assembly --- p.2 / Chapter 1.2.1 --- What is field induced assembly? --- p.2 / Chapter 1.2.2 --- Recent works --- p.3 / Chapter 1.3 --- Objective of the thesis --- p.4 / Chapter 2 --- Self Assembly of Binary Colloidal Alloys --- p.6 / Chapter 2.1 --- Interaction between colloidal suspensions --- p.7 / Chapter 2.1.1 --- Van der Waals interaction energy between two spheres --- p.7 / Chapter 2.1.2 --- Screened Coulomb Repulsion --- p.9 / Chapter 2.1.3 --- Derjaguin-Landau-Verwey-Overbeek potential --- p.12 / Chapter 2.1.4 --- DNA-mediated Colloidal Interaction --- p.13 / Chapter 2.2 --- 2D Molecular Dynamics Simulation --- p.14 / Chapter 2.2.1 --- One type of particles with attractive force --- p.16 / Chapter 2.2.2 --- Two type of particles --- p.18 / Chapter 2.2.3 --- Results --- p.19 / Chapter 2.2.4 --- Conclusion --- p.23 / Chapter 2.3 --- 3D Molecular Dynamics Simulation --- p.25 / Chapter 2.3.1 --- One type of particles with attractive force --- p.26 / Chapter 2.3.2 --- Two type of particles --- p.27 / Chapter 2.3.3 --- Results --- p.28 / Chapter 2.3.4 --- Conclusion --- p.32 / Chapter 3 --- Electrorheological Rotors --- p.34 / Chapter 3.1 --- Formalism --- p.35 / Chapter 3.2 --- MD Simulations and Results --- p.38 / Chapter 3.3 --- Discussion and conclusion --- p.39 / Chapter 4 --- Electrorheological Suspensions in Rotating Fields --- p.42 / Chapter 4.1 --- Long-range rotating field simulation --- p.43 / Chapter 4.1.1 --- Simulation method --- p.43 / Chapter 4.1.2 --- Result --- p.46 / Chapter 4.2 --- Uniform Rotating Shear Flow --- p.49 / Chapter 4.3 --- Discussion and conclusion --- p.50 / Chapter 5 --- Comparison between many body and multiple image effect --- p.53 / Chapter 5.1 --- Multiple image method --- p.54 / Chapter 5.2 --- Anisotropic many-body-MID model --- p.56 / Chapter 5.3 --- Computer simulation in the many-body-DID model --- p.59 / Chapter 5.4 --- Discussion and conclusion --- p.60 / Chapter 6 --- Conclusion --- p.68 / Bibliography --- p.70 / Chapter A --- Derivation of multiple image expression --- p.74 / Chapter A.1 --- Image of a point dipole on a sphere --- p.74 / Chapter A.2 --- Multiple images of induced dipole --- p.74 / Chapter B --- Derivation of anisotropic Maxwell-Garnett Approximation --- p.80 / Chapter B.1 --- Isotropic Maxwell-Garnett Approximation --- p.80 / Chapter B.2 --- Anisotropic Maxwell-Garnett Approximation --- p.82

Many microorganisms have the ability to propel themselves through their fluid environments by periodically actuating their body. The biological fluid environments surrounding these microswimmers are typically complex fluids containing many high-molecular weight protein molecules, which give the fluid non-Newtonian rheological properties. In this thesis, we investigate the effect that one such rheological property, viscoelasticity, has on microswimming. We consider a classical model of a microswimmer, the so-called Taylor's waving sheet and generalise it to arbitrary shapes. We employ the Oldroyd-B model to study its swimming analytically and numerically. We attempt to develop a mechanistic understanding of the swimmer's behaviour in viscoelastic fluids. It has recently been suggested that continuum models of complex biological fluids might not be appropriate for studying the swimming of flagellated microorganisms as the size of biological macromolecules is comparable to the typical width of a microorganism's flagellum. A part of this thesis is devoted to exploring this scenario. We propose an alternative method for modelling complex fluids using a two-fluid depletion region model and we have developed a numerical solver to find the swimming speed and rate of work for the generalised Taylor's waving sheet model swimmer using this alternate depletion region model. This thesis is organised as follows. In the first chapter, we outline a physical mechanism for the slowing down of Taylor's sheet in an Oldroyd-B fluid as the Deborah number increases. We demonstrate how a microswimmer can be designed to avoid this. In the second chapter, we investigate swimming in an Oldroyd-B fluid near a solid boundary and show that, at large amplitudes and low polymer concentrations, the swimming speed of Taylor's sheet increases with De. In the third chapter, we show how the Oldroyd-B model can be adapted using depletion regions. In the final chapter, we investigate optimal swimming in a Newtonian fluid. We show that while the organism's energetics are important, the kinematics of planar-wave microswimmers do not optimise the hydrodynamic 'efficiency' typically used for mathematical optimisation in the literature.

In this thesis we focus on a novel experimental exploration of fluid-driven fractures in a brittle hydrogel matrix. Fluid-driven fracturing is a procedure by which a fracture is initiated and propagates due to pressure applied by a fluid introduced inside the fracture. We describe how to construct the experimental setup utilised in this research, including how to synthesise polyacrylamide hydrogels to study the processes linked with fluid-driven fracturing. These transparent, linearly elastic and brittle gels permit fracturing at low pressures and speeds allowing accurate measurements to be obtained. The broad range of modulus and fracture energy values attainable from this medium allow the exploration of particular regimes of importance. Fracturing within these hydrogels also creates beautiful spiral patterns on the plastically deformed surfaces. We analyse these patterns and discuss their formation, while also commenting on their fractal-like nature. Initially, we study single fractures that are driven by an incompressible Newtonian fluid, injected at a constant rate into an elastic matrix. The injected fluid creates a radial fracture that propagates along a plane. We investigate this type of fracture theoretically and then verify the scaling predictions experimentally. We examine the rate of radial crack growth, fracture aperture, shape of the crack tip and internal fluid flow field. We exhibit the existence of two distinct fracturing regimes, and the transition between these, in which propagation is either dominated by viscous flow within the fracture or the material toughness. Particle image velocimetry measurements also strikingly show that the flow in the fracture can alter from an expected radial symmetry to circulation cells, dependent on the regime of propagation. We then expand our research to the problem of two coplanar fluid-driven radial fractures. This was chosen to focus on the physical mechanisms that are key to fracture network formation, related to many geophysical and industrial practices. Initially, the two fractures propagate independently of each other. At a critical separation they begin to interact, with non-uniform growth occurring along the fracture edges due to the evolving stress state in the gel matrix. When the radial extents of the fractures become sufficiently large, they coalesce and form a bridge between them. Following initial contact, a large increase in flow is seen into the newly created bridge and most of the growth is localised along this, perpendicular to the line connecting the injection sources. From experimental measurements, we observe a universal dynamic behaviour for the growth of this bridge. We model this universal behaviour theoretically and construct scalings related to the growth after coalescence, which again identifies both a viscous and toughness regime. The toughness regime is verified experimentally for the bridge growth and the universal shape of the thickness profile along the bridge. The coalesced fractures then transition into a single fracture at late times. Finally, we discuss a number of other interesting scenarios that may occur such as, non-coalescing fractures, asymmetric coalescence and ridge formation.

Ho, Yuk Kwan = 粒子鏈的布朗運動 : 相互關係時間之探討 / 何煜坤. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (p. 82-84). / Abstracts in English and Chinese. / Ho, Yuk Kwan = Li zi lian de Bulang yun dong : xiang hu guan xi shi jian zhi tan tao / He Yukun. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Historical background --- p.1 / Chapter 1.2 --- Motivation --- p.4 / Chapter 2 --- Modelling of the system of the particle chain --- p.6 / Chapter 2.1 --- Interactions between the particles --- p.7 / Chapter 2.2 --- Assumptions of the Brownian force --- p.10 / Chapter 3 --- Time evolution of the probability distribution --- p.14 / Chapter 3.1 --- Diffusion under a uniform external force field --- p.14 / Chapter 3.2 --- Multi-dimensional Fokker-Planck equation --- p.18 / Chapter 3.3 --- Fundamental solution to the Fokker-Planck equation --- p.21 / Chapter 3.3.1 --- Fulfillment of the Fokker-Planck equation by the stochas- tic process described by the Langevin equation --- p.21 / Chapter 3.3.2 --- Gaussian process of the stochastic process in the system --- p.24 / Chapter 3.4 --- Relaxation of the fluctuations and the variances of the system --- p.27 / Chapter 3.4.1 --- Dependence of system parameters - study of a two-body system --- p.27 / Chapter 3.4.2 --- Dependence of system size --- p.33 / Chapter 4 --- Time evolution of the correlation function --- p.36 / Chapter 4.1 --- Method of Rice - harmonic analysis --- p.38 / Chapter 4.1.1 --- Natural mode expansion of the correlation functions --- p.41 / Chapter 4.1.2 --- Satisfaction of the equipartition principle --- p.44 / Chapter 4.2 --- Relaxation of the correlation functions --- p.45 / Chapter 4.2.1 --- Dependence of system parameters - study of a two body system --- p.46 / Chapter 4.2.2 --- Dependence of system size --- p.50 / Chapter 4.3 --- Connection with relaxation modes of fluctuations and variances --- p.53 / Chapter 5 --- Coloured Brownian force --- p.58 / Chapter 5.1 --- Fluctuation-dissipation theorem --- p.59 / Chapter 5.2 --- The system of a large particle with a particle chain --- p.64 / Chapter 5.2.1 --- Equivalent heat bath with which the large particleis interacting --- p.67 / Chapter 5.2.2 --- Retarded friction from its underlying physical origin --- p.71 / Chapter 5.2.3 --- Effective random force of the heat bath and its underly- ing physical origin --- p.73 / Chapter 5.2.4 --- Displacement correlation function for the large particle interacting with the heat bath --- p.77 / Chapter 6 --- Conclusion --- p.81 / Bibliography --- p.82 / Chapter A --- Magnetic force between two magnetic dipoles --- p.85 / Chapter B --- Hydrodynamic interaction --- p.88 / Chapter B.l --- Faxen´ةs Law --- p.90 / Chapter B.2 --- Method of reflection --- p.92 / Chapter B.3 --- Interactions between three translating identical spheres --- p.94 / Chapter C --- Proof of the cross-correlation theorem and Wiener-Kintchine theorem --- p.97 / Chapter D --- Proof of the relation between θ(t) and β(t) in Eq. 5.42 --- p.99 / Chapter E --- Proof of the zero-value of k in Eq. 5.60 --- p.101

We study the dynamics of an elastic fiber in a viscoelastic fluid driven by a four-roll mill. The viscoelasticity is modeled by the FENE-P model and the coupling between the fiber and the fluid is resolved by the immersed boundary method. Numerically, we follow Peskin's formally second order method to solve the fiber-fluid equations and square root method to solve the viscoelasticity equations. We examine the effect of Weissenberg number (Wi) and fiber rigidity on fiber motion and the evolution of polymer stress. We also investigate the ability of the fiber to escape closed streamlines in Newtonian fluids and viscoelastic fluids. We find that large polymer stresses occur near the ends of the fiber when it is compressed. In addition, we find that viscoelasticity hinders a fiber's ability to traverse multiple cells in the domain. / 1 / Qiang Yang

Thesis (M.S.)--University of Nevada, Reno, 2005. / "August 2005." Includes bibliographical references (leaves 102-114). Online version available on the World Wide Web.