Electrokinetic Manipulation of Particles and Cells in Microfluidic Devices

With the recent advancement in micro-fabrication technology, lab-on-a-chip devices have been developed in order to perform biological analysis through cell manipulation. Microchannels used in these lab-on-a-chip devices have been demonstrated to accurately perform many different cell manipulation techniques such as focusing, separation, trapping, and lysis. Although there are many methods available for these techniques, electrokinetics has been rapidly gaining popularity due to the simplicity of application and removal of the need for in channel micro-structures. This thesis studies the use of electrokinetic flow and accompanying phenomena in various structured microchannels to perform focusing, separation, trapping, and lysis of cells. Three related projects were conducted in series. First, a parametric study of the focusing of yeast cells using negative dielectrophoresis in a serpentine microchannel was studied. Focusing cells into a single stream is usually a necessary step prior to counting and separating them in microfluidic devices such as flow cytometers and cell sorters. This work demonstrated a sheathless electrokinetic focusing of yeast cells in a planar serpentine microchannel using DC-biased AC electric fields. The concurrent pumping and focusing of yeast cells arose from the DC electrokinetic transport and the turn-induced AC/DC dielectrophoretic motion, respectively. The effects of electric field (including AC to DC field ratio, and AC field frequency) and concentration (including buffer concentration and cell concentration) on the cell focusing performance were studied experimentally and numerically. A continuous electrokinetic filtration of E. coli cells from yeast cells was also demonstrated via their differential electrokinetic focusing in the serpentine microchannel. Next, negative and positive dielectrophoretic focusing were also studied in their application to particle separation in a serpentine microchannel. This work first demonstrated negative and positive dielectrophoretic focusing of by changing only the electric conductivity of the suspending fluid. Due to the channel turn-induced dielectrophoretic force, particles were focused to either the centerline or the sidewalls of the channel when their electric conductivity was lower (i.e., negative DEP) or higher (i.e., positive DEP) than that of the fluid. These distinctive dielectrophoretic focusing phenomena in the serpentine microchannel were then combined to implement a continuous separation between particles of different sizes and electric conductivities. Such separation eliminates the fabrication of in-channel microelectrodes or micro-insulators that are typically required in DEP-based separation techniques. Lastly, red blood cells were used to study cell lysis and trapping in a microchannel constriction. Cell Lysis is an important step in the analysis of intracellular contents. Electrical lysis of red blood cells was demonstrated in a hurdle microchannel using a low continuous DC-biased AC electric field amplified by channel geometry. Trapping of cells was also demonstrated using this DC-biased AC electric field, and the transition between trapping and lysis of red blood cells in this microchannel was demonstrated by simply adjusting the applied DC voltage. Further, these phenomena were used in conjunction to demonstrate the separation of Leukemia cells from red blood cells

A Feasibility Study On The Implementation Of Satellite-To-Satellite Tracking Around A Small Near-Earth Object

Near-earth objects (NEOs) are asteroids and comets that have a perihelion distance of less than 1.3 astronomical units (AU). There are currently more than 10,000 known NEOs. The majority of these objects are less than 1 km in diameter. Despite the number of NEOs, little is known about most of them. Characterizing these objects is a crucial component in developing a thorough understanding of solar system evolution, human exploration, exploitation of asteroid resources, and threat mitigation. Of particular interest is characterizing the internal structure of NEOs. While ground-based methods exist for characterizing the internal structure of NEOs, the information that can be gleaned from such studies is limited and often accompanied by large uncertainty. An alternative is to use in situ studies to examine an NEO\u27s shape and gravity field, which can be used to assess its internal structure. This thesis investigates the use of satellite-to-satellite tracking (SST) to map the gravity field of a small NEO on the order of 500 m or less. An analysis of the mission requirements of two previously flown SST missions, GRACE and GRAIL, is conducted. Additionally, a simulation is developed to investigate the dynamics of SST in the vicinity of a small NEO. This simulation is then used to simulate range and range-rate data in the strongly perturbed environment of the small NEO. These data are used in conjunction with the analysis of the GRACE and GRAIL missions to establish a range of orbital parameters that can be used to execute a SST mission around a small NEO. Preliminary mission requirements for data collection and orbital correction maneuvers are also established. Additionally, the data are used to determine whether or not proven technology can be used to resolve the expected range and range-rate measurements. It is determined that the orbit semi-major axis for each spacecraft should be approximately 100% to 200% of the NEO\u27s mean diameter and the two spacecraft should be in circular, near polar orbits. This configuration will produce trajectories, which exhibit reasonable stability over a period of roughly 24 hours. Corrective maneuvers will therefore be required with a frequency of approximately once per day. Due to the potentially rapid changes caused by the highly perturbed environment, it is likely that these maneuvers will need to be made autonomously. During the period between corrective maneuvers SST data collection will be possible. The expected range and range-rate measurements will be on the order of ±10-5 m and ±10-5 m/s respectively and can be resolved using proven technology

The electrification of hail

Reynolds, Brook and Gourley (1957) derived a value of 5 % 10(^-4) e.s.u. for the charge separated per crystal collision when a simulated hailstone rotated in o cloud consisting of ice crystals together with supercooled water droplets of some 5 μ size. From this estimate they concluded that .the electrification of thunderclouds could be explained in terms of the electrification of hail by impacting ice crystals. Latham and Mason (1961 B) performed similar experiments in the absence of water droplets and obtained in estimate which was 5, orders of magnitude less than Reynolds' value. They also measured the electrification of an iced probe by supercooled water droplets shattering on it and derived a value of 4 x 10(^-6) e.s.u. for the mean charge separated per droplet diameter range 40 ≡100. They concluded from these experiments that the charge separated by ice crystal impacts was not sufficient to explain thunderstorm electrification. They proposed instead that the droplet shattering mechanism offered a satisfactory explanation of the magnitude of the charge separated in thunderclouds. It was the purpose of this thesis to investigate the results of these two authorities and in particular to seek an explanation for the large discrepancy between their results on ice crystal impactions m this laboratory similar experiments to Reynolds , Brook and Gourley were performed, and it was concluded that the results could be, explained qualitatively In terms of the temperature gradient theory, but quantitatively the charge separated was larger than predicted by the theory. Experiments similar to those of latham and Mason on crystals impacts were performed. The quantity of charge separated per crystal collision and how it defended on the sign and magnitude of the measured temperature difference between the iced probe and the crystals, the presence of impurities in the probe, and the impact velocity of the ice crystals was determined. An estimate of 2.5 X 10(^-7) e.s.u. was obtained for an impact velocity of 20 m sec(^-1) and measured temperature difference of 10 C. This was 50 times greater than the value found by Latham and Mason but it was shown that the two values could be reconciled. It was shown that they could also be reconciled with the previous value of 5 x 10(^-6) e.s.u. It was further observed that the charge separated per crystal collision increased markedly as the impact velocity increased. Apparatus was built which enabled stable streams of uniformly sized uncharged water droplets in the radius range 50 - 150µ to be produced. Smaller droplets down to 30µ radius were produced in unstable streams. Droplets were made to encounter a rotating iced robe connected to an electrometer. It was found that appreciable quantities of charge wore separated only for the larger droplets. If the droplets were above about 0 C they charged the probe positively and if they were supercooled they charged it negatively. The quantity of negative charge separated decreased as the decree of supercooling increased. The maximum mean charge separated for a 150 µ radius droplet was l0(^-5) e.s.u. and for a 90µ radius droplet was 4 X 10(^-7) e.s.u. It was concluded that the charge was separated by the droplets splashing. Droplets which were in the process of freezing were allowed to encounter the probe. The droplets always charged the probe negatively and mean charges of up to 2 x l0(^-4) e.s.u. per 150 µ radius droplet were separated. The charge separated appeared to be proportional to the cube of the droplet radius. Although the results were not directly comparable with the results of Latham and Mason, it was considered that a Similar charge separation mechanism was operative, and that it could be explained more readily by the Workman - Reynolds effect than by the temperature gradient theory

Rethinking Foster Care: Why Our Current Approach to Child Welfare Has Failed

Over the past decade, the child welfare system has expanded, with vast public and private resources being spent on the system. Despite this investment, there is scant evidence suggesting a meaningful return on investment. This Article argues that without a change in the values held by the system, increased funding will not address the public health problems of child abuse and neglect

Rethinking Foster Care: Why Our Current Approach to Child Welfare has Failed

Over the past decade, the child welfare system has expanded, with vast public and private resources being spent on the system. Despite this investment, there is scant evidence suggesting a meaningful return on investment. This Article argues that without a change in the values held by the system, increased funding will not address the public health problems of child abuse and neglect

Empty nose syndrome—What do we know?

Empty nose syndrome is a complication of nasal surgery wherein patients develop a persistent, debilitating sense of nasal obstruction and dyspnea despite clear nasal cavities. It is characterized by a discrepancy between prominent subjective symptoms and near total lack of objective findings, making it difficult to diagnose. The pathophysiology of empty nose syndrome is a complex mix of aerodynamic, physiologic, and neurological changes leading to altered airflow and diminished sensory function. Evolving treatment options consist of medical symptom control or surgical reconstruction

A Quiet Revolution: How Judicial Discipline Essentially Eliminated Foster Care and Nearly Went Unnoticed.

This Article argues that juvenile court judges can safely reduce the number of children entering foster care by faithfully and rigorously applying the law. Judges often fail to perform this core functon when a state child welfare agency separates a child from their family. Judges must perform their role as impartial gatekeeper despite the temptation to be omnipotent moral busybodies

Charles W. Bolen Faculty Recital Series: Christopher Hollingsworth, Tenor; Gretchen Church, Piano; March 29, 2010

Kemp Recital HallMarch 29, 2010Monday Evening7:00 p.m