<p>We investigate the dielectrophoretic separation of microparticles. Two different models are formulated in two characteristic time scales. The first model mainly accounts for the orientation behavior and rotational motion of non-spheric microparticles. The concept of effective charge is suggested to calculate the finite size non-spheric particles. It is combined with the fluid particle dynamics method to calculate hydrodynamic as well as dielectrophoretic forces and torques. The translational motion and the particle-particle interaction are calculated also, but they take much longer time to be observed due to the different time scales of the rotational and translational motions By viewing the particle as spheres, the second model focus on the translational motion of spheres. The hydrodynamic force between particles and particle-particle electrostatic interactions are also taken into account. We check the relative magnitude ratio between these forces in order to determine the importance of these forces. To predict and guide the design of experimental dielectrophoretic separation, two numerical applications are carried out. The first calculation suggests optimum patterns to improve the trapping efficiency of<em> E.coli.</em> cells by applying superimposed AC electric fields. The second calculation finds out the mobility and separation rate of particles which differs in size and electric properties by a multi-step trapping-releasing strategy.</p>

Sequential Monte Carlo (SMC) and Markov chain Monte Carlo (MCMC) methods provide computational tools for systematic inference and learning in complex dynamical systems, such as nonlinear and non-Gaussian state-space models. This thesis builds upon several methodological advances within these classes of Monte Carlo methods.Particular emphasis is placed on the combination of SMC and MCMC in so called particle MCMC algorithms. These algorithms rely on SMC for generating samples from the often highly autocorrelated state-trajectory. A specific particle MCMC algorithm, referred to as particle Gibbs with ancestor sampling (PGAS), is suggested. By making use of backward sampling ideas, albeit implemented in a forward-only fashion, PGAS enjoys good mixing even when using seemingly few particles in the underlying SMC sampler. This results in a computationally competitive particle MCMC algorithm. As illustrated in this thesis, PGAS is a useful tool for both Bayesian and frequentistic parameter inference as well as for state smoothing. The PGAS sampler is successfully applied to the classical problem of Wiener system identification, and it is also used for inference in the challenging class of non-Markovian latent variable models.Many nonlinear models encountered in practice contain some tractable substructure. As a second problem considered in this thesis, we develop Monte Carlo methods capable of exploiting such substructures to obtain more accurate estimators than what is provided otherwise. For the filtering problem, this can be done by using the well known Rao-Blackwellized particle filter (RBPF). The RBPF is analysed in terms of asymptotic variance, resulting in an expression for the performance gain offered by Rao-Blackwellization. Furthermore, a Rao-Blackwellized particle smoother is derived, capable of addressing the smoothing problem in so called mixed linear/nonlinear state-space models. The idea of Rao-Blackwellization is also used to develop an online algorithm for Bayesian parameter inference in nonlinear state-space models with affine parameter dependencies. / CNDM / CADICS

Spray drying is a widely used unit operation for producing particulate products directly from a liquid feed. Important processes that occur inside the spray dryer are droplet formation, droplet drying and interactions between droplets and recycled fines. Various studies have looked at the first two processes, but the latter phenomenon has received less attention. Literature on droplet-particle interaction which aims at quantitatively describing agglomeration in spray drying is scarce and mainly qualitative. For product quality the formation of agglomerates is often desirable. This thesis models and investigates the collisions of individual particles with single droplets. The surface tack of drying droplets has been identified as an important variable for the formation of agglomerates. In this thesis a novel method for measuring tack from the liquid phase has been further improved. The improvements are a more accurate load measurement, an automated control of the tack probe and an improved layout of the sample holder and probe. The key feature of the device is its ability to measure tack of drying droplets, whereas other devices measure tack by wetting a powder. Using our method the tack of a commonly spray dried product, yeast extract, has been measured. From these experiments it was found that with decreasing average moisture content the surface tack increases to a maximum. Below a critical average moisture content the surface of the droplet is dry and the tack rapidly decreases upon further drying. Another important parameter in determining the degree of agglomeration is the degree of penetration. If the particle penetrates the droplet too deeply, the agglomerate structure becomes too dense. To predict the penetration depth, a non-dimensional model has been developed. It describes the penetration of a particle into a liquid droplet during a head-on collision. It is based on a force balance and incorporates surface tension force, viscous force and capillary pressure force. The important parameters determining the collision outcome are the contact angle, the size of the droplet relative to the particle, the Reynolds and Weber numbers. For each contact angle an equilibrium penetration position exists, at this point the surface tension force vector is perpendicular to the penetration direction. Five different penetrations regimes are identified. At low Reynolds numbers, viscous forces dominate and the particle asymptotically travels towards the equilibrium position. Reducing the viscous drag force by increasing the Reynolds number results in initially overshooting the equilibrium position, but the surface tension force pulls the particle back, to attain the equilibrium in an oscillating motion. At even higher Reynolds numbers the particle fully penetrates the droplet, and reaches the centre of the droplet for even higher values for the Reynolds number. The ejection regime is found at high Reynolds number and low Weber numbers and the liquid should be non-wetting. Using the regime maps one is able to identify in which region a spray dryer is operating. Although the full penetration regimes are useful for capturing fines, it should be avoided when agglomeration is desired. The ejection regime should be avoided as well. To validate the model, impact experiments were carried out by dropping glass spheres on the surface of different liquids. These validation experiments were the first attempt to experimentally validate the collision of a single particle with a liquid surface. Besides yeast extract, which has non-Newtonian rheological properties, silicone oils with constant viscosities of 100 mPa•s and 1 Pa•s have been tested. The penetration over time for different impact velocities was determined by analysing high speed camera recordings. The typical penetration times ranged from 0.2 s to 2 s. To obtain accurate location data was recorded at frame rates up to 38 000 frames per second. Glass spheres, with a size of 2 mm were used to allow the visual tracking. Modelling the impacts showed that the model consistently predicted faster penetration times than were observed experimentally. The relative difference increased with increasing viscosity. A parameter fitting exercise showed that better agreement could be obtained by using a higher viscosity and a higher contact angle in the model. With this knowledge the most likely factor influencing the model-experiment mismatch was identified as being the dynamics of wetting of the particle surface. It was also found that using the dynamic contact angle in the model would improve its results. The non-Newtonian characteristics of the yeast extract resulted in the particle rebound and the formation of an air cavity upon impact. The tack measurement technique and penetration model presented in this thesis will be useful tools for the design of spray dryers. Recommendations are made for further model improvement. The experimental validation is the first attempt to validate the presented model. Future improvements are recommended and suggestions are presented.

We investigate the dielectrophoretic separation of microparticles. Two different models are formulated in two characteristic time scales. The first model mainly accounts for the orientation behavior and rotational motion of non-spheric microparticles. The concept of effective charge is suggested to calculate the finite size non-spheric particles. It is combined with the fluid particle dynamics method to calculate hydrodynamic as well as dielectrophoretic forces and torques. The translational motion and the particle-particle interaction are calculated also, but they take much longer time to be observed due to the different time scales of the rotational and translational motions By viewing the particle as spheres, the second model focus on the translational motion of spheres. The hydrodynamic force between particles and particle-particle electrostatic interactions are also taken into account. We check the relative magnitude ratio between these forces in order to determine the importance of these forces. To predict and guide the design of experimental dielectrophoretic separation, two numerical applications are carried out. The first calculation suggests optimum patterns to improve the trapping efficiency of E.coli. cells by applying superimposed AC electric fields. The second calculation finds out the mobility and separation rate of particles which differs in size and electric properties by a multi-step trapping-releasing strategy. / QC 20101118

No description available.

<p dir="ltr">Particle tracking velocimetry, also known as PTV, is a technology to measure velocity and study the flow field in fluid by observing change in position of individual tracer particles over time. A laser sheet illuminates a thin layer of the sample, in which particles emit fluorescent light and are visible to the camera. Particles at different distances from the microscope lens focal plane are visible, because particle diameter is much smaller than the thickness of laser sheet in micro-scale. The defocused distance changes the shape of particle seen by the camera. Analyzing particle shapes and obtaining the defocused distance of particles completes the third dimension of PTV with the use of a single camera. One approach to obtain defocused distance from particle shape is by comparing particle shapes with calibration images of known defocused distance. The accuracy of PTV relies on the collection of proper calibration images. There are three methods involved in this work. The first approach is to use synthetic images generated by solving Lommel differential equations, which describe the intensity distribution of particles under the impact of defocusing aberration. It was later discovered that the point source assumption inherent in Lommel function causes inaccuracy in generated calibration images. The second approach captures particle images while manually shifting the microscope stage in the z-direction. This approach causes systematic error by ignoring the refractive index of the immersion medium. The third approach is to use a microscale reference ramp as calibration target. Results are experimentally compared with particle shapes obtained from pressure driven flow with known velocity profile.</p>

FIR filters occupy a central place many signal processing applications which either alter the shape, frequency or the sampling frequency of the signal. FIR filters are used because of their stability and possibility to have linear-phase but require a high filter order to achieve the same magnitude specifications as compared to IIR filters. Depending on the size of the required transition bandwidth the filter order can range from tens to hundreds to even thousands. Since the implementation of the filters in digital domain requires multipliers and adders, high filter orders translate to a large number of these arithmetic units for its implementation. Research towards reducing the complexity of FIR filters has been going on for decades and the techniques used can be roughly divided into two categories; reduction in the number of multipliers and simplification of the multiplier implementation.  One technique to reduce the number of multipliers is to use cascaded sub-filters with lower complexity to achieve the desired specification, known as FRM. One of the sub-filters is a upsampled model filter whose band edges are an integer multiple, termed as the period L, of the target filter's band edges. Other sub-filters may include complement and masking filters which filter different parts of the spectrum to achieve the desired response. From an implementation point-of-view, time-multiplexing is beneficial because generally the allowable maximum clock frequency supported by the current state-of-the-art semiconductor technology does not correspond to the application bound sample rate. A combination of these two techniques plays a significant role towards efficient implementation of FIR filters. Part of the work presented in this dissertation is architectures for time-multiplexed FRM filters that benefit from the inherent sparsity of the periodic model filters. These time-multiplexed FRM filters not only reduce the number of multipliers but lowers the memory usage. Although the FRM technique requires a higher number delay elements, it results in fewer memories and more energy efficient memory schemes when time-multiplexed. Different memory arrangements and memory access schemes have also been discussed and compared in terms of their efficiency when using both single and dual-port memories. An efficient pipelining scheme has been proposed which reduces the number of pipelining registers while achieving similar clock frequencies. The single optimal point where the number of multiplications is minimum for non-time-multiplexed FRM filters is shown to become a function of both the period, L and time-multiplexing factor, M. This means that the minimum number of multipliers does not always correspond to the minimum number of multiplications which also increases the flexibility of implementation. These filters are shown to achieve power reduction between 23% and 68% for the considered examples. To simplify the multiplier, alternate number systems like the LNS have been used to implement FIR filters, which reduces the multiplications to additions. FIR filters are realized by directly designing them using ILP in the LNS domain in the minimax sense using finite word length constraints. The branch and bound algorithm, a typical algorithm to implement ILP problems, is implemented based on LNS integers and several branching strategies are proposed and evaluated. The filter coefficients thus obtained are compared with the traditional finite word length coefficients obtained in the linear domain. It is shown that LNS FIR filters provide a better approximation  error compared to a standard FIR filter for a given coefficient word length. FIR filters also offer an opportunity in complexity reduction by implementing the multipliers using Booth or standard high-radix multiplication. Both of these multiplication schemes generate pre-computed multiples of the multiplicand which are then selected based on the encoded bits of the multiplier. In TDF FIR filters, one input data is multiplied with a number of coefficients and complexity can be reduced by sharing the pre-computation of the multiplies of the input data for all multiplications. Part of this work includes a systematic and unified approach to the design of such computation sharing multipliers and a comparison of the two forms of multiplication. It also gives closed form expressions for the cost of different parts of multiplication and gives an overview of various ways to implement the select unit with respect to the design of multiplexers. Particle filters are used to solve problems that require estimation of a system. Improved resampling schemes for reducing the latency of the resampling stage is proposed which uses a pre-fetch technique to reduce the latency between 50% to 95%  dependent on the number of pre-fetches. Generalized division-free architectures and compact memory structures are also proposed that map to different resampling algorithms and also help in reducing the complexity of the multinomial resampling algorithm and reduce the number of memories required by up to 50%.

A simplified description is given of the operation of a multiwire proportional chamber (MWPC) in the soft X-ray imaging application. Expressions are developed to allow the calculation of the distribution of induced charge on the cathodes of an MWPC. With extensions to permit direct comparison, the calculations are subjected to detailed experimental verification. A generalised, approximate formulation of the distribution with one independent parameter is described. The prediction of cathode system position response using the theoretical distributions is demonstrated. The available MWPC position readout methods are reviewed, and where possible their differential non-linearity is measured experimentally. A new position-sensitive cathode of good linearity and spatial resolution is presented. The effect of the wires of an MWPC on its imaging performance is briefly considered. An attempt is made to assess the contribution to MWPC spatial resolution of the range of the electrons produced initially by an X-ray absorption event in argon-methane mixtures. In conclusion, the important causes of MWPC imaging imperfection are noted and classified.

A first measurement of Electroweak W + 2 jets production at high dijet mass is performed using sqrt(s) = 7 TeV pp collision data from the Atlas experiment corresponding to 4.6 fb−1 of integrated luminosity. The background only hypothesis is excluded with a significance of 4.89-σ. A cross section of σ = 325 ± 6 (lumi) ±32 (stat) +63−70(syst) ±86 (theo) fb is extracted in the fiducial region.

This study on the hydrodynamics of fishing gear focuses on fish nets. A multi-scale concept has been introduced. By decomposing the fish net structure into 4 distinct scales of flow structure interaction (twine, node, mesh and substructure scales) the complexity is reduced with the potential to integrate new knowledge at each scale to form an overall picture of flow-gear interactions. Within the scope and time-frame of the project, experiments were carried out at the twine and mesh scales. Two sets of experiments were designed at twine scale. The first featured synchronous velocity and drag force measurements on various rigid cylinders consisting of circular cylinders and cylinders inspired by twisted twine. The second aimed to study the cylinder near-wakes in greater detail than previously using PIV. At mesh scale, experiments using rigid bi-plane grids were conducted with individual focus on investigating grid turbulence and flow-grid interactions respectively. The twisted cylinders did not affect mean drag, likely due to free-stream turbulence acting on the boundary layers and free shear layers possibly negating the effects of the twisted cylinder geometry. In the near-wake, the twisted cylinders deflected the free stream into the wake and secondary vortices were introduced, shed along the cylinder span, de-correlating the flow field and in one instance, destroying regular vortex shedding. At mesh scale, for low solidities, a limiting value for mesh length was found where the total drag was dominated by individual contribution of bars. The key to altering the turbulence properties of the flow was found to be alteration of the spectral energy in the largest turbulence scales. For turbulence generation, the spectral energy should be increased and for turbulence suppression, spectral energy should be decreased in the largest turbulence scales.