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In this dissertation the linearized dynamics and stability of a two-craft Coulomb tether formation are investigated. With a Coulomb tether the relative distance between two satellites is controlled using electrostatic Coulomb forces. A charge feedback law is introduced to stabilize the relative distance between the satellites to a constant value. Compared to previous Coulomb thrusting research, this is the first feedback control law that stabilizes a particular formation shape. The two craft are connected by an electrostatic virtual tether that essentially acts as a long, slender near-rigid body. Inter-spacecraft Coulomb forces cannot influence the inertial angular momentum of this formation. However, the differential gravitational attraction can be exploited to stabilize the attitude of this Coulomb tether formation about an orbit nadir direction. Stabilizing the separation distance will also stabilize the in-plane rotation angle, while the out-of-plane rotational motion remains unaffected. The other two relative equilibriums of the charged 2-craft problem are along the orbit-normal and the along-track direction. Unlike the charged 2-craft formation scenario aligned along the orbit radial direction, a feedback control law using inter-spacecraft electrostatic Coulomb forces and the differential gravitational accelerations is not sufficient to stabilize the Coulomb tether length and the formation attitude. Therefore, hybrid feedback control laws are presented which combine conventional thrusters and Coulomb forces. The Coulomb force feedback requires measurements of separation distance error and error rate, while the thruster feedback is in terms of Euler angles and their rates. This hybrid feedback control is designed to asymptotically stabilize the satellite formation shape and attitude while avoiding plume impingement issues. The relative distance between the two satellites can be increased or decreased using electrostatic Coulomb forces. The linear dynamics and stability analysis of such reconfiguration are studied for all the three equilibrium. The Coulomb tether expansion and contraction rates affect the stability of the structure and limits on these rates are discussed using the linearized time-varying dynamical models. These limits allow the reference length time histories to be designed while ensuring linear stability of the virtual structure. Throughout this dissertation the Coulomb tether is modeled as a massless, elastic component and, a point charge model is used to describe the charged craft. / Ph. D.

<p>The fatty acid linoleic acid has been identified as a potential mediator of atherosclerotic plaque development. Treatment of monocytes with linoleic acid leads to an increase in monocyte adhesion to endothelial cells under flow conditions; however, the mechanisms through which linoleic acid affect monocyte adhesion remain unclear. Using a combination of micropipette aspiration techniques and fluorescent microscopy, I tested the hypothesis that linoleic acid increases membrane tether formation between monocytes and endothelial cells. </p><p>Treatment of U937 monocytes with free linoleic acid or albumin-bound linoleic acid reduced the cortical tension of the monocytes. The effects of albumin-bound linoleic acid on the membrane were governed by the exchange of linoleic acid from albumin to the membrane and by the removal of fatty acids from the membrane by fatty acid binding sites on albumin. </p><p>The frequency of tether formation between U937 monocytes and TNF-α stimulated HUVECs increased following treatment with free linoleic acid or albumin-bound linoleic acid. The increase in tether frequency was not due to an increase in monocyte deformability or adhesion receptor expression. Tether extraction occurred primarily through E-selectin. Treatment with free linoleic acid increased the localization of E-selectin to clathrin-coated pits suggesting an increase in the formation of nanoclusters of E-selectin on HUVECs. The increase in tether frequency was blocked by the U73122 phospholipase C inhibitor indicating that linoleic acid increased monocyte adhesion through a phospholipase C mediated mechanism.</p><p>Treatment with free linoleic acid did not affect the threshold force for tether extraction or the effective viscosity of tethers extracted from HUVECs, but it decreased the threshold force for tether extraction from U937 monocytes and increased the effective tether viscosity. Treatment with U73122 blocked the reduction in the threshold force indicating that linoleic acid affected the regulation of the membrane adhesion energy through the hydrolysis of PIP2 by phospholipase C.</p><p>The results of the study indicated that linoleic acid promoted membrane tether formation by increasing E-selectin bond formation and reducing the adhesion energy between the U937 plasma membrane and the actin cytoskeleton through the hydrolysis of PIP2 by phospholipase C.</p> / Dissertation

In the last decade, there has been a surge of interest from the chemistry community in developing synthetic catalysts that emulate the remarkable rate accelerations observed for enzymatic reactions. One approach utilized by enzymes involves preorganization of substrate(s) using a favourable binding event to orient the substrate(s) in a reactive arrangement. Although the “induced intramolecularity” is entropically unfavourable, it is facilitated by the enzymes and utilized to accelerate the subsequent chemical transformation. Chemists have often used a conceptually related stepwise approach in which temporary tethers are assembled to induce a temporary intramolecularity. This preorganization often enables difficult intermolecular reactions, and typically leads to increased regio-, chemo-, and stereoselectivity in chemical reactions. Seeking to develop a catalytic approach, we focused our efforts in developing a mild, carbonyl-catalyzed hydration protocol for - and -amino nitriles to give the corresponding - and -amino amide and acid. This work highlights the value of employing induced intramolecularity in accessing structurally important chemical motifs that otherwise require harsh reaction conditions. Additionally, this thesis presents the background material, design process, optimization and scope of this reactivity.

Sculpting membranes into dynamic, curved shapes is central to intracellular cargo trafficking and other cellular functions. However, generation of membrane curvature during trafficking involves lipids and membrane-associated proteins; current mechanisms focus on creating rigid cages, curved scaffolds, or membrane surface area changes by proteins. This dissertation provides an alternative mechanistic example for the control of membrane deformations, involving modulation of membrane material properties. Sar1, a GTPase of the COPII family, regulates vesicle trafficking from the endoplasmic reticulum. We find that Sar1p lowers the rigidity of the lipid bilayer membrane to which it binds. We examine the behavior of Saccharomyces cerevisiae Sar1 (Sar1p) and Homo sapiens paralogs of Sar1 (Sar1A and Sar1B). Like Sar1p, human Sar1s lower membrane rigidity. Unlike Sar1p, the rigidity is not a monotonically decreasing function of concentration. At high concentrations, we find increased bending rigidity and decreased protein mobility. These features imply a model in which human Sar1 clustering governs membrane mechanical properties. Membrane rigidity measurements remain rare, however, and show a large variance, a situation that can be addressed by improving techniques and comparing disparate techniques applied to the same systems. I introduce applying selective plane illumination microscopy (SPIM) to image thermal fluctuations of giant vesicles. SPIM's optical sectioning enables high-speed fluorescence imaging of freely suspended vesicles and quantification of edge localization precision, yielding robust fluctuation spectra and rigidity estimates. For lipid-only membranes and membranes bound by the intracellular trafficking protein Sar1p, we show rigidity values from giant unilamellar vesicle fluctuations in close agreement with those derived from our independent assay based on membrane tether pulling. We also show that a model of homogeneous quasi-spherical vesicles poorly fits fluctuation spectra of vesicles bound by Sar1A at high concentrations, suggesting that SPIM-based analysis can offer insights into spatially inhomogeneous properties. I conclude by discussing our current work on amphipathic alpha helices, their ability to reduce membrane rigidity, and our hopes to create artificial helical structures capable of mimicking trafficking systems. Supplemental videos represent membrane disintegration with Sar1p and fluctuations of membrane only and Sar1p incubated vesicles. This dissertation contains previously published co-authored material.

In the last decade, there has been a surge of interest from the chemistry community in developing synthetic catalysts that emulate the remarkable rate accelerations observed for enzymatic reactions. One approach utilized by enzymes involves preorganization of substrate(s) using a favourable binding event to orient the substrate(s) in a reactive arrangement. Although the “induced intramolecularity” is entropically unfavourable, it is facilitated by the enzymes and utilized to accelerate the subsequent chemical transformation. Chemists have often used a conceptually related stepwise approach in which temporary tethers are assembled to induce a temporary intramolecularity. This preorganization often enables difficult intermolecular reactions, and typically leads to increased regio-, chemo-, and stereoselectivity in chemical reactions. Seeking to develop a catalytic approach, we focused our efforts in developing a mild, carbonyl-catalyzed hydration protocol for - and -amino nitriles to give the corresponding - and -amino amide and acid. This work highlights the value of employing induced intramolecularity in accessing structurally important chemical motifs that otherwise require harsh reaction conditions. Additionally, this thesis presents the background material, design process, optimization and scope of this reactivity.

Electrodynamic tethers have a wide range of proposed applications in the fields of satellite propulsion and space plasma research. The fundamental purpose of this dissertation is to improve the understanding of the behavior of an electrodynamic tether (EDT) system in Earth's ionosphere. An electrodynamic tether system consists of two satellites connected by a long tether that generates current to produce either power or thrust via the system's electromagnetic interaction with the space environment. Previous electrodynamic tether investigations decouple the interaction between the tether and the constantly changing plasma environment. The limiting factor inhibiting the development of a full system model that has an accurate characterization of the tether/plasma interaction is that the understanding of that interaction is not well developed over a wide range of system parameters. The EDT system model developed in this study uses a high fidelity dynamics model that includes a tether current described by an analytical current collection model whose plasma parameters are determine by the International Reference Ionosphere. It is first shown that new instabilities are induced in the system dynamics under a basic analytical current model versus a constant current model. A 2-D3$v$ Particle-in-Cell (PIC) code has been developed to study the plasma dynamics near a positively charged EDT system end-body and their impact on the current collected. Simulations are run over a range of system parameters that occur throughout a LEO orbit. The azimuthal current structures observed during the TSS-1R mission are found to enhance the current collected by the satellite when the magnetic field is slightly off of perpendicular to the orbital velocity. When the in-plane component of the magnetic field becomes large, the electrons are not able to easily cross the field lines causing plasma lobes form above and below the satellite. The lobes limit the current arriving to the satellite and also cause an enhanced wake to develop. A high satellite bias causes a stable bow-shock structure to form in the ram region of the satellite, which limits the number of electrons entering the sheath region and thus limiting the current collected. Electron-neutral collisions are found to destabilize the bow-shock structure and remove its current limiting effects. Additionally, as the magnetization of the plasma is increased, the current becomes limited by the charged particle's inability to cross magnetic field lines. Analytical curve fits based on the simulation results are presented that characterize the dependence of the average current collected on the local magnetic field orientations, space plasma magnetization and satellite potential. The results from the PIC simulations characterizing the magnetic field's influence on the tether's current are incorporated into the system dynamics model to study the behavior of the EDT system over a range of inclinations. The magnetic field is found to limit the diurnal variations in the current collected by the system throughout its orbit. As the inclination of the system's orbit is increased, the impact of the magnetic field becomes more pronounced as its orientation sweeps through a larger range of angles. The impact of the magnetic field on the collected current is, therefore, found to limit the ability of an EDT system to boost the system's orbit as the orbit's inclination is increased. In summary, new system dynamics have been observed due to the previously unobserved behavior of the current over a range of end-body configurations. / Ph. D.

When working under water at great depths, or in tough environments, remotely controlled underwater vehicles, so called ROV:s, are a good tool too use. With the help of these robots it is possible to work for longer periods of time and at larger depths then with ordinary divers. Ocean Robotics is a company from Linköping, Sweden, that has over 40 years of experience with ROV:s. They produce several different models for different kind of jobs. The purpose of this project was to develop a concept of a device that keeps the tension constant on the tether that connects the ROV with the operator. The tension needs to be constant when the tether is being rolled in on and out from the winch. The work was executed on behalf of Ocean Robotics and a prerequisite was that it should be possible to integrate the device with the winch system they have today. The work have followed Ulrich and Eppingers method for product development and together with requirements from the contractor several concepts was generated. The concepts were validated in a decision matrix and the concepts with the highest score was modeled in the CAD-program CREO Parametrics. The concepts got further developed and was compared against each other once again. Which generated the final concept. Furthermore a couple of friction tests were executed to find appropriate materials for the construction. The final concept will be mounted on the winch and connected to Ocean Robotics self reversing screw. To measure the tension on the tether a load cell is used and the tether is fed by a rubberized wheel that is driven by an electric motor. To adjust the force around the tether a trapezoidal thread is driven by another electric motor, which adjust the pinch wheels height. The tether goes as a tangent between the two wheels that has a profile that insures that the force goes around the tether.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / The National Aeronautics and Space Administration’s (NASA) Marshall Space Flight Center (MSFC) in Huntsville, Alabama will launch the Propulsive Small Expendable Deployer System (ProSEDS) space experiment in late 2000. ProSEDS will demonstrate the use of an electrodynamic tether propulsion system and will utilize a conducting wire tether to generate limited spacecraft power. This paper will provide an overview of the ProSEDS mission and will discuss the design, and test of the spacecraft telemetry system. The ProSEDS telemetry subsystem employs a combination of Commercial Off-The-Shelf (COTS) hardware and launch vehicle telemetry system components to minimize costs as well as power consumption. Several measures were used to aid the conservation of spacecraft power resources. First, the transmitter was modified to limit input power consumption to less that 20 watts while providing approximately two watts Radio Frequency (RF) output power. Secondly, the ProSEDS on board Global Positioning System (GPS) receiver is being used to control input power to the transmitter in order to limit the telemetry operations to occasions when the spacecraft is in proximity to preprogrammed ground station locations.

The dynamics of a tether cable for a flying wind generator, employed to generate electricity by utilising the high velocity jet-stream winds in the troposphere, is analysed. A non-linear mathematical model for the study of the dynamics of the cable is described by a partial differential equation, which is solved analytically without damping. For unsteady and damped states, ordinary differential equations are obtained by adopting a discrete analysis approach, which are solved numerically with the aid of MATLAB software. Solutions are found for a range of lumped masses to represent the cable and each solution is verified against a previous case. Likewise, the result for the three masses is checked against the cable using a single lumped mass. The analysis is extended to seven discrete masses. This research highlights the dynamic behaviour of the cable subjected to wind gusts on the rotors and it also represents an appreciable input to the flying wind generator concept. The dynamic behaviour of the cable is critical for a flying electric generator. / Master of Engineering (Hons)