Nonlinear Dynamics

This volume covers a diverse collection of topics dealing with some of the fundamental concepts and applications embodied in the study of nonlinear dynamics. Each of the 15 chapters contained in this compendium generally fit into one of five topical areas: physics applications, nonlinear oscillators, electrical and mechanical systems, biological and behavioral applications or random processes. The authors of these chapters have contributed a stimulating cross section of new results, which provide a fertile spectrum of ideas that will inspire both seasoned researches and students

Force-Sensing-Based Multi-Platform Robotic Assistance for Vitreoretinal Surgery

Vitreoretinal surgery aims to treat disorders of the retina, vitreous body, and macula, such as retinal detachment, diabetic retinopathy, macular hole, epiretinal membrane and retinal vein occlusion. Challenged by several technical and human limitations, vitreoretinal practice currently ranks amongst the most demanding fields in ophthalmic surgery. Of vitreoretinal procedures, membrane peeling is the most common to be performed, over 0.5 million times annually, and among the most prone to complications. It requires an extremely delicate tissue manipulation by various micron scale maneuvers near the retina despite the physiological hand tremor of the operator. In addition, to avoid injuries, the applied forces on the retina need to be kept at a very fine level, which is often well below the tactile sensory threshold of the surgeon. Retinal vein cannulation is another demanding procedure where therapeutic agents are injected into occluded retinal veins. The feasibility of this treatment is limited due to challenges in identifying the moment of venous puncture, achieving cannulation and maintaining it throughout the drug delivery period. Recent advancements in medical robotics have significant potential to address most of the challenges in vitreoretinal practice, and therefore to prevent traumas, lessen complications, minimize intra-operative surgeon effort, maximize surgeon comfort, and promote patient safety. This dissertation presents the development of novel force-sensing tools that can easily be used on various robotic platforms, and robot control methods to produce integrated assistive surgical systems that work in partnership with surgeons against the current limitations in vitreoretinal surgery, specifically focusing on membrane peeling and vein cannulation procedures. Integrating high sensitivity force sensing into the ophthalmic instruments enables precise quantitative monitoring of applied forces. Auditory feedback based upon the measured forces can inform (and warn) the surgeon quickly during the surgery and help prevent injury due to excessive forces. Using these tools on a robotic platform can attenuate hand tremor of the surgeon, which effectively promotes tool manipulation accuracy. In addition, based upon certain force signatures, the robotic system can precisely identify critical instants, such as the venous puncture in retinal vein cannulation, and actively guide the tool towards clinical targets, compensate any involuntary motion of the surgeon, or generate additional motion that will make the surgical task easier. The experimental results using two distinct robotic platforms, the Steady-Hand Eye Robot and Micron, in combination with the force-sensing ophthalmic instruments, show significant performance improvement in artificial dry phantoms and ex vivo biological tissues

COMMERCIALIZATION OF A SMALL, LIGHTWEIGHT, LOW-COST SEISMIC BOREHOLE RECEIVER

Herein, conceptualization of a recently patented seismic borehole receiver and its components is developed for commercialization. The device is significantly cheaper, lighter, and smaller than existing technologies on the market. Additionally, it has the potential to achieve better seismic readings than its competitors via patented sensor-to-borehole coupling mechanism. It is the hope that the commercialization of this device will not only provide a more affordable alternative to engineers and geophysicists in the existing market, but the significant cost difference may open new seismic measurement opportunities in the developing world. Its compact size and light weight will increase mobility, allowing investigators to conduct surveys where previously deemed infeasible. Many impoverished states in regions of high seismicity lack the seismic data this and other such devices can provide. This data has been crucial to infrastructure advancements and public safety in seismic hazard areas of the developed world, yet the technology used to ascertain it is inaccessible in the developing world due to cost and availability. This thesis will outline the potential impact of the device, review governing seismic wave behavior and the current state of the seismic measurement field, as well as outline the components, development, and future development of the instrument

Aeronautical Engineering: A special bibliography with indexes, supplement 62

This bibliography lists 306 reports, articles, and other documents introduced into the NASA scientific and technical information system in September 1975

DEVELOPMENT OF A LINE-FIELD MAGNETO-MOTIVE OPTICAL COHERENCE TOMOGRAPHY SYSTEM

The mechanism by which certain species of animals are able to detect the Earth’s magnetic field has remained a mystery for as long as we have known that they exhibit geomagnetic navigation. Certain species of bacteria are known to contain single chains of magnetite crystals, each with a diameter of ~50 nm, that are used to orient the bacteria. Searching for similar magnetoreceptors in larger animals requires a high-speed, high-resolution imaging system with the ability to detect single magnetic nanoparticles. Optical coherence tomography (OCT) is a biomedical imaging modality that produces 2D, cross-sectional images of optically turbid media with a resolution on the order of 1-10 µm. Magneto-motive OCT (MMOCT) is a functional form of OCT that can detect the sub-resolution displacement of magnetic nano- or micro-particles embedded in weakly diamagnetic, optically scattering, elastic media (such as human and animal tissues) subject to a sinusoidally-varying magnetic gradient force. This dissertation describes the design and implementation of an MMOCT system composed of a novel combination of a line-field configuration with a supercontinuum light source and a faster MMOCT imaging scheme. The combination of the line illumination with a high-speed 2D camera and the low-noise, high-power supercontinuum light source produces the best combination of axial resolution, optical SNR, and imaging speed of any line-field-OCT (LFOCT) system to date. The performance of the LF-OCT system combined with the faster magnet modulation scheme results in a LF-MMOCT system with a volumetric imaging speed comparable to that of the highest speed MMOCT system to date. High volumetric imaging speed is essential for the problem of endogenous magnetite detection, as is high magnetic sensitivity. The LF-MMOCT system is optimized to produce the best possible magnetic SNR at kilohertz framerates. We then demonstrate the detection of single magnetic point particles, measure the vibration amplitude produced by an external magnetic gradient force on each point particle, and compare that vibration amplitude to a theoretical value. The ability to image a single magnetic point particle with a high-resolution, high-sensitivity, and high-speed LF-MMOCT system provides a key proof of concept that this system may be used for endogenous magnetite detection.Doctor of Philosoph

The breakup of intravascular microbubbles and its impact on the endothelium

Encapsulated microbubbles (MBs) serve as endovascular agents in a wide range of medical ultrasound applications. The oscillatory response of these agents to ultrasonic excitation is determined by MB size, gas content, viscoelastic shell properties and geometrical constraints. The viscoelastic parameters of the MB capsule vary during an oscillation cycle and change irreversibly upon shell rupture. The latter results in marked stress changes on the endothelium of capillary blood vessels due to altered MB dynamics. Mechanical effects on microvessels are crucial for safety and efficacy in applications such as focused ultrasound-mediated blood-brain barrier (BBB) opening. Since direct in vivo quantification of vascular stresses is currently not achievable, computational modelling has established itself as an alternative. We have developed a novel computational framework combining fluid-structure coupling and interface tracking to model the nonlinear dynamics of an encapsulated MB in constrained environments. This framework is used to investigate the mechanical stresses at the endothelium resulting from MB shell rupture in three microvessel setups of increasing levels of geometric detail. All configurations predict substantial elevation of up to 150 % for peak wall shear stress upon MB breakup, whereas global peak transmural pressure levels remain unaltered. The presence of red blood cells causes confinement of pressure and shear gradients to the proximity of the MB, and the introduction of endothelial texture creates local modulations of shear stress levels. With regard to safety assessments, the mechanical impact of MB breakup is shown to be more important than taking into account individual red blood cells and endothelial texture. The latter two may prove to be relevant to the actual, complex process of BBB opening induced by MB oscillations