MICROFLUIDIC PARTICLE AND CELL MANIPULATION USING RESERVOIR-BASED DIELECTROPHORESIS

Controlled manipulation of synthetic particles and biological cells from a complex mixture is important to a wide range of applications in biology, environmental monitoring, and pharmaceutical industry. In the past two decades microfluidics has evolved to be a very useful tool for particle and cell manipulations in miniaturized devices. A variety of force fields have been demonstrated to control particle and cell motions in microfluidic devices, among which electrokinetic techniques are most often used. However, to date, studies of electrokinetic transport phenomena have been primarily confined within the area of microchannels. Very few works have addressed the electrokinetic particle motion at the reservoir-microchannel junction which acts as the interface between the macro (i.e., reservoir) and the micro (i.e., microchannel) worlds in real microfluidic devices. This Dissertation is dedicated to the study of electrokinetic transport and manipulation of particles and cells at the reservoir-microchannel junction of a microfluidic device using a combined experimental, theoretical, and numerical analysis. First, we performed a fundamental study of particles undergoing electrokinetic motion at the reservoir-microchannel junction. The effects of AC electric field, DC electric field, and particle size on the electrokinetic motion of particles passing through the junction were studied. A two-dimensional numerical model using COMSOL 3.5a was developed to investigate and understand the particle motion through the junction. It was found that particles can be continuously focused and even trapped at the reservoir-microchannel junction due to the effect of reservoir-based dielectrophoresis (rDEP). The electrokinetic particle focusing increases with the increase in AC electric field and particle size but decreases with the increase in DC electric field. It was also found that larger particles can be trapped at lower electric fields compared to smaller counterparts. Next, we utilized rDEP to continuously separate particles with different sizes at the reservoir-microchannel junction. The separation process utilized the inherent electric field gradients formed at the junction due to the size difference between the reservoir and the microchannel. It was observed, that the separation efficiency was reduced by inter-particle interactions when particles with small size differences were separated. The effect of enhanced electrokinetic flow on the separation efficiency was investigated experimentally and was observed to have a favorable effect. We also utilized rDEP approach to separate particles based on surface charge. Same sized particles with difference in surface charge were separated inside the microfluidic reservoir. The streaming particles interacted with the trapped particles and reduced the separation efficiency. The influences from the undesired particle trapping have been found through experiments to decrease with a reduced AC field frequency. Then, we demonstrated a continuous microfluidic separation of live yeast cells from dead cells using rDEP. Because the membrane of a cell gets distorted when it loses its viability, a higher exchange of ions results from such viability loss. The increased membrane conductivity of dead cells leads to a different Claussius-Mossoti factor from that of live cells, which enables their selective trapping and continuous separation based on cell viability. A two-shell numerical model was developed to account for the varying conductivities of different cell layers, the results of which agree reasonably with the experimental observations. We also used rDEP to implement a continuous concentration and separation of particles/cells in a stacked microfluidics device. This device has multiple layers and multiple microchannels on each layer so that the throughput can be significantly increased as compared to a single channel/single layer device. Finally, we compared the two-dimensional and three-dimensional particle focusing and trapping at the reservoir-microchannel junction using rDEP. We observed that the inherent electric field gradients in both the horizontal and vertical planes of the junction can be utilized if the reservoir is created right at the reservoir-microchannel junction. Three-dimensional rDEP utilizes the additional electric field gradient in the depth wise direction and thus can produce three-dimensional focusing. The electric field required to trap particles is also considerably lower in three-dimensional rDEP as compared to the two-dimensional rDEP, which thus considerably reduces the non-desired effects of Joule heating. A three-dimensional numerical model which accounted for the entire microfluidic device was also developed to predict particle trajectories

Reservoir-Based Dielectrophoresis (rDEP) for concentration and separation of cells/particles.

Dielectrophoresis (DEP) is the translation of a particle either along (i.e., positive dielectrophoresis) or against (i.e., negative dielectrophoresis) an electric field gradient if the particle is more or less polarizable than the suspending medium. The polarizability of a particle is dependent on its electrical and mechanical properties. This makes DEP a versatile tool for particle and cell handling, especially in microdevices due to its favorable scaling. Traditional DEP is realized through patterning pair(s) of microelectrodes onto the surface of a micro channel. Recently DEP has also been implemented by the use of channel geometry, which can be the variation in channel cross-section or the curvature of the channel itself. Both methods, however, rely on in-channel electrical or mechanical parts to create electric field gradients, which complicate device fabrication and causes fouling trouble due to electrochemical reactions and electrothermal flow effects etc. Reservoir-based dielectrophoresis (rDEP) is a newly developed microfluidic method that exploits negative dielectrophoresis induced at the reservoir-microchannel junction to manipulate particles inside a reservoir. As the rDEP focusing, concentration and separation of particles all take place inside a reservoir; the entire microchannel can be spared for pre- and post-analysis. This makes the rDEP method perfectly positioned for lab-on-a-chip applications

Portfolio Turnover Activity and Mutual Fund Performance

We propose a new measure of portfolio activity, the Modified Turnover, which represents the portion of the portfolio that the manager changes from one quarter to the next. Compared with the traditional turnover, our Modified Turnover measure relies on portfolio holdings and takes into account the effects of offsetting trades and fund flows on portfolio turnover. We find evidence that high Modified Turnover predicts lower performance. The comparison between the highest and lowest quintiles sorted based on Modified Turnover reveals a difference of -2.41% in the annual risk-adjusted return. Furthermore, high Modified Turnover predicts lower net flows. We also find that Modified Turnover relates positively to other activeness measures while volatility, flows, size, number of stocks, and the expense ratio are significant determinants of Modified Turnover. Overall, our results suggest that frequent churning of a portfolio is value-destroying for investors and signals a manager’s lack of skill

The Role of Mutual Funds in Corporate Social Responsibility

This paper examines the role of mutual funds in corporate social responsibility (CSR). Using a fund-level, holdings-based CSR score, we find that CSR-friendly mutual funds improve firms’ CSR standings. This effect is more pronounced for firms with higher mutual fund ownership and stronger corporate governance. We further show that while CSR-friendly mutual funds have influence on almost all CSR categories, they focus on increasing CSR strengths rather than reducing CSR concerns. We also discover that CSR-friendly funds are more likely to vote in favor of CSR proposals, and that firms owned by CSR-friendly funds are more likely to link their CEO compensation to CSR outcomes. These results suggest that actively managed mutual funds, which were previously thought to be indifferent (or even detrimental) to social and ethical issues, play a significant role in corporate social outcomes of the firms they invest in

To Group or Not to Group? Evidence from Mutual Funds

The literature has conflicting reports regarding the impact of group decision making on performance. We first observe that in mutual fund studies this results from large discrepancies in reported managerial structures between CRSP and Morningstar databases reaching on average 20% per year. Then we show that with more superior Morningstar data team-managed funds exhibit higher risk-adjusted returns than single-managed funds. The performance spread is present across all fund categories, except aggressive funds, and is robust to the inclusion of fund- and manager-level controls. Across various managerial structures, the largest team-induced gains are reached among funds managed by three individuals. Furthermore, teams significantly improve fund performance when funds are located in financial centers, reflecting larger networking potential and/or better skills of people who reside in larger cities. This improvement is achieved in teams more homogeneous in age and education. In spite of higher returns however, team-managed funds are not riskier than single-managed funds in terms of market exposure or idiosyncratic volatility. Finally, team-managed funds trade less aggressively and are able to generate extra inflows for their funds. Thus, collective decision making is beneficial, but its scale depends on team size and diversity as well as its geographic location

To Group or Not to Group? Evidence from Mutual Funds

The literature has conflicting reports regarding the impact of group decision making on performance. We first observe that in mutual fund studies this results from large discrepancies in reported managerial structures between CRSP and Morningstar databases reaching on average 20% per year. Then we show that with more superior Morningstar data team-managed funds exhibit higher risk-adjusted returns than single-managed funds. The performance spread is present across all fund categories, except aggressive funds, and is robust to the inclusion of fund- and manager-level controls. Across various managerial structures, the largest team-induced gains are reached among funds managed by three individuals. Furthermore, teams significantly improve fund performance when funds are located in financial centers, reflecting larger networking potential and/or better skills of people who reside in larger cities. This improvement is achieved in teams more homogeneous in age and education. In spite of higher returns however, team-managed funds are not riskier than single-managed funds in terms of market exposure or idiosyncratic volatility. Finally, team-managed funds trade less aggressively and are able to generate extra inflows for their funds. Thus, collective decision making is beneficial, but its scale depends on team size and diversity as well as its geographic location

Functional outcome of patients undergoing lumbar discectomy

Background: Sciatica resulting from a lumbar intervertebral disc herniation is the most common cause of radicular leg pain in adult working population. It can be treated with both conservative and operative methods. In our study, surgical treatment of lumbar disc prolapse has been done by open discectomy. We wish to assess the outcome of surgery in patients with lumbar disc prolapse undergoing lumbar discectomy.Methods: 40 patients were included in this study and were followed up for up to 1 year postoperatively. We assessed the outcome of each patient with ODI and VAS post-operatively and on follow-up at 3 weeks, 6 months and 1 year. Subjective evaluation of the patient’s satisfaction at the final follow-up was also done.Results: We found that males had higher incidence of PIVD with an average duration of symptoms before surgery about 8.62 months. Left side was most involved and level l4-l5 was most involved level. The mean ODI and VAS score pre-operatively were 26.85±4.20 and 7.73±0.88 respectively, which changed to 4.48±5.15 and 1.70±1.57, respectively at 1 year post-operative follow-up. These were statistically highly significant. Most of the patients (34) gave a subjective evaluation as excellent at 1 year follow-up.Conclusions: Our study established that open discectomy has a satisfactory functional outcome and leads to a significant improvement in the patients’ quality of life

Text-based Image Segmentation Methodology

AbstractIn computer vision, segmentation is the process of partitioning a digital image into multiple segments (sets of pixels). Image segmentation is thus inevitable. Segmentation used for text-based images aim in retrieval of specific information from the entire image. This information can be a line or a word or even a character. This paper proposes various methodologies to segment a text based image at various levels of segmentation. This material serves as a guide and update for readers working on the text based segmentation area of Computer Vision. First, the need for segmentation is justified in the context of text based information retrieval. Then, the various factors affecting the segmentation process are discussed. Followed by the levels of text segmentation are explored. Finally, the available techniques with their superiorities and weaknesses are reviewed, along with directions for quick referral are suggested. Special attention is given to the handwriting recognition since this area requires more advanced techniques for efficient information extraction and to reach the ultimate goal of machine simulation of human reading

Assessment of outcome of distal radius inta-articular fractures using wrist-spanning mini-fixator in distraction

Background: The distal radius fractures are complex injuries. There are many treatment options for these fractures. The benefits of external fixation with mini fixator have been seen in many studies. In our study, the distal radius fracture belonging to type B and C of AO classification were treated with wrist spaning mini extrernal fixator with/without additional k wires. We wish to analyse the functional outcome and to determine any complications of this procedure.Methods: 20 patients were included in this study and were followed up for up to 6 months postoperatively. We assessed pain using VAS score at 6 weeks follow-up and the outcome of each patient was assessed using Mayo wrist score post-operatively on follow-up at 3 months and 6 months.Results: Predominance towards males and left upper limb was observed in our study. At the end of six months, the range of motion as assessed according to the criteria given by Mayo wrist score, excellent results (MWS>=90) were seen in 4 patients (20%), good results (MWS 80-89) were seen in 12 patients (60%),and fair (MWS 70-79) in 4 patient (20%). At the end of result, significant reduction in terms of pain, wellbeing, personal life, social life, lifting, travelling and sleeping was seen.Conclusions: Predominance towards males and left upper limb was observed in our study. At the end of six months, the range of motion as assessed according to the criteria given by Mayo Wrist Score, excellent results (MWS>=90) were seen in 4 patients (20%), good results (MWS 80-89) were seen in 12 patients (60%),and fair (MWS 70-79) in 4 patient (20%). At the end of result, significant reduction in terms of pain, wellbeing, personal life, social life, lifting, travelling and sleeping was seen.