Richard A. Williams

A packing algorithm for particles of arbitrary shapes

Particle packing is a subject of both academic and industrial importance, and a number of packing algorithms have been proposed and widely used. However, most of these packing algorithms can only deal with spheres and a few regular shapes. If applied to arbitrarily shaped particles, they would have difficulties in at least one of three aspects. First, arbitrary shapes are notoriously difficult to model mathematically. Secondly, efficient algorithms for collision and overlap detection of arbitrary shapes are difficult to derive and more difficult to implement. Thirdly, the packing program would be very computationally expensive for routine and practical use. This paper describes a new, digital approach to particle packing, which can avoid many of the difficulties suffered by conventional methods. The key innovation is digitisation of both particle shapes and the packing space. Thus, a particle is now just a coherent collection of pixels or voxels, regardless of its shape, moving on a square lattice, onto which the packing space is mapped. Using the digital approach, it is easy to pack particles of any shapes and sizes into a container of any geometry, generally requiring no more than an ordinary PC. Although, as yet, the packing algorithm does not involve physical forces explicitly, it can simulate some physical phenomena such as size segregation. The ability to pack particles in their real shapes, rather than approximated as spheres, opens up many new industrial and academic opportunities, some of which are discussed. Examples of packing density predictions of particles subject to various effects, including vibration and rotation, are given.

Discovery and Evaluation of BMS-708163, a Potent, Selective and Orally Bioavailable γ-Secretase Inhibitor

During the course of our research efforts to develop a potent and selective γ-secretase inhibitor for the treatment of Alzheimers disease, we investigated a series of carboxamide-substituted sulfonamides. Optimization based on potency, Notch/amyloid-β precursor protein selectivity, and brain efficacy after oral dosing led to the discovery of 4 (BMS-708163). Compound 4 is a potent inhibitor of γ-secretase (Aβ40 IC50 = 0.30 nM), demonstrating a 193-fold selectivity against Notch. Oral administration of 4 significantly reduced Aβ40 levels for sustained periods in brain, plasma, and cerebrospinal fluid in rats and dogs.

A high-performance EIT system

This paper presents the development of a new electrical impedance tomography system for online measurement of two-phase flows with axial velocities up to 10 ms/sup -1/. The system is designed in a modular fashion and can consist of several data acquisition modules and computing modules. The data acquisition module includes a voltage controlled current source with a direct-current-restoration circuit, an equal-width pulse synthesizer unit and a synchronized digital demodulation unit. A new concept of current switching scheme is developed to enhance the ac coupling speed. The computing module includes a digital signal processor (TMS320C6202/6713) with memory, multichannel buffered serial ports and an IEEE1394 communication interface. Several DSP modules can be pipelined for a series of tasks ranging from measurement control to image reconstruction to flow velocity implementation. The performances have been tested and some trial results are reported. A data acquisition speed of 1164 dual-frames (2.383 million data points) per second has been achieved with a root mean square error less than 0.6% at 80 kHz in static test application. An application in the measurement of vertical oil-in-water pipe flow is reported.

Understanding the Hydrocyclone Separator Through Computational Fluid Dynamics

The hydrocyclone provides an efficient means for solids separation from suspension, de-watering or purification, but there is little detailed understanding of the swirl flow and separation mechanism prevailing within the device. We report on the application of transient three-dimensional computational fluid dynamics incorporating a second-order accurate pressure-strain Reynolds-stress turbulence model. This has led to new understanding of the mechanism that leads to air-core development. Simulations of a water-core development and associated flow and pressure fields are reported. From this, air-core development is demonstrated to be transport-driven as opposed to pressure-driven, for which experimental validation has been acquired. In addition, examination of three-dimensional particle tracking challenges some of the common conceptions of the particle-separation mechanism. A highly asymmetric helical structure of alternating radial velocity, throughout the hydrocyclone, results in stochastic turbulent transport of particles between the wall and core flows to occur principally in regions of favourable radial velocity.

Responsive core-shell latex particles as colloidosome microcapsule membranes.

Responsive core-shell latex particles are used to prepare colloidosome microcapsules using thermal annealing and internal cross linking of the shell, allowing the production of the microcapsules at high concentrations. The core-shell particles are composed of a polystyrene core and a shell of poly[2-(dimethylamino)ethyl methacrylate]-b-poly[methyl methacrylate] (PDMA-b-PMMA) chains adsorbed onto the core surface, providing steric stabilization. The PDMA component of the adsorbed polymer shell confers thermally responsive and pH-responsive characteristics to the latex particle, and it also provides glass transitions at temperatures lower than those of the core and reactive amine groups. These features facilitate the formation of stable Pickering emulsion droplets and the immobilization of the latex particle monolayer on these droplets to form colloidosome microcapsules. The immobilization is achieved through thermal annealing or cross linking of the shell under mild conditions feasible for large-scale economic production. We demonstrate here that it is possible to anneal the particle monolayer on the emulsion drop surface at 75-86 °C by using the lower glass-transition temperature of the shell compared to that of the polystyrene cores (∼108 °C). The colloidosome microcapsules that are formed have a rigid membrane basically composed of a densely packed monolayer of particles. Chemical cross linking has also been successfully achieved by confining a cross linker within the disperse droplet. This approach leads to the formation of single-layered stimulus-responsive soft colloidosome membranes and provides the advantage of working at very high emulsion concentrations because interdroplet cross linking is thus avoided. The porosity and mechanical strength of the microcapsules are also discussed here in terms of the observed structure of the latex particle monolayers forming the capsule membrane.

Design and application of a multi-modal process tomography system

This paper presents a design and application study of an integrated multi-modal system designed to support a range of common modalities: electrical resistance, electrical capacitance and ultrasonic tomography. Such a system is designed for use with complex processes that exhibit behaviour changes over time and space, and thus demand equally diverse sensing modalities. A multi-modal process tomography system able to exploit multiple sensor modes must permit the integration of their data, probably centred upon a composite process model. The paper presents an overview of this approach followed by an overview of the systems engineering and integrated design constraints. These include a range of hardware oriented challenges: the complexity and specificity of the front-end electronics for each modality; the need for front-end data pre-processing and packing; the need to integrate the data to facilitate data fusion; and finally the features to enable successful fusion and interpretation. A range of software aspects are also reviewed: the need to support differing front-end sensors for each modality in a generic fashion; the need to communicate with front-end data pre-processing and packing systems; the need to integrate the data to allow data fusion; and finally to enable successful interpretation. The review of the system concepts is illustrated with an application to the study of a complex multi-component process.

Tomographic imaging of particulate systems

The review illustrates selected applications of tomographic analysis applied to dry and wet particulate systems. The examples show the use of the method to gain information at different levels of inspection, such as the detailed structure of individual particles, structured particulate assemblies, and on the concentration and velocity of solids in a moving mixture. The utilization of the unique spatial information derived from tomography for the purpose of model validation, and, in some cases, for the monitoring and control of processes is discussed. Emerging applications show that utilization of tomographic methods can facilitate the creation of new and sophisticated models for particulate systems.

Measurement and analysis of flows in a gas-liquid column reactor

Abstract Bubble columns are widely used across a range of industries. A number of flow regimes can arise but their identification in practice is very challenging. An electrical capacitance tomography (ECT) sensor has been applied to investigate the potential of ECT for bubble-column visualization and control. Different methods of flow regime analysis are reported including a repeatable and robust analytical procedure that has been designed to quantify heterogeneity.

Markov chain Monte Carlo techniques and spatial–temporal modelling for medical EIT

Many imaging problems such as imaging with electrical impedance tomography (EIT) can be shown to be inverse problems: that is either there is no unique solution or the solution does not depend continuously on the data. As a consequence solution of inverse problems based on measured data alone is unstable, particularly if the mapping between the solution distribution and the measurements is also nonlinear as in EIT. To deliver a practical stable solution, it is necessary to make considerable use of prior information or regularization techniques. The role of a Bayesian approach is therefore of fundamental importance, especially when coupled with Markov chain Monte Carlo (MCMC) sampling to provide information about solution behaviour. Spatial smoothing is a commonly used approach to regularization. In the human thorax EIT example considered here nonlinearity increases the difficulty of imaging, using only boundary data, leading to reconstructions which are often rather too smooth. In particular, in medical imaging the resistivity distribution usually contains substantial jumps at the boundaries of different anatomical regions. With spatial smoothing these boundaries can be masked by blurring. This paper focuses on the medical application of EIT to monitor lung and cardiac function and uses explicit geometric information regarding anatomical structure and incorporates temporal correlation. Some simple properties are assumed known, or at least reliably estimated from separate studies, whereas others are estimated from the voltage measurements. This structural formulation will also allow direct estimation of clinically important quantities, such as ejection fraction and residual capacity, along with assessment of precision.

The hydrodynamics of a hydrocyclone based on a three-dimensional multi-continuum model

Abstract The concept and principles of applying a multi-continuum model for calculating a hydrocyclone performance is presented. In this model the carrying liquid is described as one continuum, and each particle fraction, with its characteristic size is described as a separate continuum. Particle–particle and particle–fluid interactions derived from a lubrication theory and a collision theory are discussed. A set of governing partial differential equations consisting of mass and momentum conservation equations together with constitutive expressions is discussed. These equations were discretized by applying an unstructured grid consisting of tetrahedral elements. A numerical solver based on a finite element method combined with a segregated approach is described. The numerical approach is subject to ongoing research.