This dissertation investigates the emulsification of aqueous liquid in immiscible organic liquid in various microfluidic environments, and addresses both experimental characterization and theoretical interpretation of the dynamics and design guidelines, as well as an application of microfluidic emulsification in fabrication of disk-like colloidal particle suspensions for studying its sedimentation behavior. In an attempt to understand the dynamics of drop formation in flow-focusing microfluidic channels, especially for an explanation of a transition from unique drop size to bimodal oscillating drop sizes as observed in the experiments, numerical simulation is developed to use the volume-of-fraction method to model the drop formation, and the simulation results help to interpret the transition in the theory of saddle-node transition in drop formation, as well as show the importance of selecting proper orifice length in flow-focusing microfluidic channel design. The electric technique for controlling of microfluidic emulsification is explored by a detailed study on low-frequency alternating-current electro-flow-focusing (EFF) emulsification in microfluidic channels. It is found that the droplet size variation is not a monotonic function of the electric field as in the case of direct-current EFF emulsification, which originates from the relaxation oscillation of the flow rate through the Taylor cone, and a power-law droplet size distribution was obtained at the voltage ramping-up stage. This emulsification process was modeled in analog to the charge accumulation and release in a resistor-capacitor electric circuit with an adjustable resistor, and the simulated data exhibit good agreement with the experiments. As an application of the microfluidic emulsification, a method of fabricating disk-like wax colloidal particle suspensions using electrospray is reported. Based on this technique, the first measurement of the hindrance function for sedimentation and creaming of disk-shaped colloids via the analytical centrifugation is reported. Disks align with the external flow right above the volume fraction of a few percent and this effect is extremely sensitive to the aspect ratio of disks. Due to this alignment effect, disk sedimentation/creaming demonstrate distinct trends in dilute and semi-dilute region.

Reliability modelling of RAID storage systems with its various components such as RAID controllers, enclosures, expanders, interconnects and disks is important from a storage system designer's point of view. A model that can express all the failure characteristics of the whole RAID storage system can be used to evaluate design choices, perform cost reliability trade-offs and conduct sensitivity analyses. We present a reliability model for RAID storage systems where we try to model all the components as accurately as possible. We use several state-space reduction techniques, such as aggregating all in-series components and hierarchical decomposition, to reduce the size of our model. To automate computation of reliability, we use the PRISM model checker as a CTMC solver where appropriate. Initially, we assume a simple 3-state disk reliability model with independent disk failures. Later, we assume a Weibull model for the disks; we also consider a correlated disk failure model to check correspondence with the field data available. For all other components in the system, we assume exponential failure distribution. To use the CTMC solver, we approximate the Weibull distribution for a disk using sum of exponentials and we first confirm that this model gives results that are in reasonably good agreement with those from the sequential Monte Carlo simulation methods for RAID disk subsystems. Next, our model for whole RAID storage systems (that includes, for example, disks, expanders, enclosures) uses Weibull distributions and, where appropriate, correlated failure modes for disks, and exponential distributions with independent failure modes for all other components. Since the CTMC solver cannot handle the size of the resulting models, we solve such models using hierarchical decomposition technique. We are able to model fairly large configurations with upto 600 disks using this model. We can use such reasonably complete models to conduct several "what-if" analyses for many RAID storage systems of interest. Our results show that, depending on the configuration, spanning a RAID group across enclosures may increase or decrease reliability. Another key finding from our model results is that redundancy mechanisms such as multipathing is beneficial only if a single failure of some other component does not cause data inaccessibility of a whole RAID group.

We perform spectral energy distribution fitting to the total integrated light, bulge and disk components of ≈ 650,000 spectroscopically selected galaxies from the sloan digital sky survey data release 7. Using 4-band photometry (u, g, r, i) we derive physical properties for these components with particular emphasis placed on the star formation rates (SFR) and stellar masses. Using the total integrated fits as an indicator of the goodness of fit, we show that reliable estimates of the SFR can be recovered using a specific SFR (sSFR) cut of log(sSFR /yr) ≥ −10.45. We construct a close pairs sample and match isolated controls based on stellar mass, z and local density for galaxies that pass the sSFR cut. We develop a method to cross correlate the pair galaxies’ star formation rate posterior probability distribution functions (SFR PDFs) with the control SFR PDFs as a function of the pair galaxies projected separation, rp. We show that the SFR of the close pair galaxies is enhanced relative to the control sample. The SFR enhancement is at a level of ≈ 0.25 dex above that of the control at the closest separations and declines to a plateau at ≈ 0.15 dex for separations of 30 < rp < 60 kpc/h. Between 60 < rp < 80 kpc/h there appears to be a slight increase in the enhancement to a level ≈ 0.25 dex above the control. It is suggested that we observe this increase, where other studies have failed to, based on the updated photometry provided by Simard et al. (2011). From our total pair sample we also select a subsample of galaxies that are classified as active galactic nuclei (AGN). We note that at close separations the pair AGN galaxies have enhanced SFRs relative to their matched controls. The SFR enhancement is largest at the smallest separations, reaching a level of ≈ 0.3 dex above the control. The SFR enhancement for the AGN pairs becomes consistent with their controls at projected separations of 20 < rp < 80 kpc/h. We construct a bulge and disk pair sample that are required to pass the sSFR cut and match control bulges and disks, respectively, that also pass the sSFR cut. We cross correlate the bulge and disk pairs with their respective controls. We measure significant SFR enhancement in the bulge component of the interacting pairs. The SFR enhancement is highest at small separations, ≈ 0.4 dex, and steadily declines to ≈ 0.1 dex before turning around beyond rp > 50 kpc/h to again reach a level ≈ 0.4 dex above the control bulges. The disk SFR enhancement is relatively flat beyond rp > 30 kpc/h to a level ≈ 0.1 dex above the control and largely consistent with the control at close separations. The bulge and disk results suggest that the majority of induced star formation during an interaction is occurring in the bulge component, but that there is still slight SFR enhancement in the disk. We suggest that the upturn in the total and bulge SFR enhancement could potentially be caused by a delay between the interaction of the galaxy pairs and the onset of induced star formation. / Graduate

Thesis (Ph. D.)--University of Hong Kong, 2008. / Also available in print.

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 5 uppsatser.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 4 uppsatser.

Thesis (M.Eng.). / Written for the Dept. of Biomedical Engineering. Title from title page of PDF (viewed 2008/07/29). Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2008. / Includes bibliographical references (leaves 151-192) Also available in print.

Zugl.: Duisburg, Essen, Univ., Diss., 2005

Thesis (M. Phil.)--University of Hong Kong, 2008. / Includes bibliographical references (leaves 151-192) Also available online.