Numerous mechanisms contribute to peripheral nerve injuries such as chemical intoxication, compression, stretching and avulsion, which usually result in severe damage to the sensory and motor functions. The current approaches for evaluating nerve regeneration include expression analysis of molecular markers, histological analysis, behavior testing and electrophysiological studies. The aim of this study is to compare the diagnostic efficacy using the recently developed magnetic stimulation approach with that of conventional electrical stimulation method in different models of peripheral neuropathy and to compare in terms of latency and amplitude of the evoked response by electrical and magnetic stimulation. Adult male Sprague Dawley rats (250-300 g, n = 24) were divided into three groups: (1) control group, (2) sciatic nerve ligation group and (3) acrylamide intoxication group. The electrophysiological studies were carried out 3 days before ligation and every 7 days after ligation for 4 weeks. The measurements included amplitude and onset latency of maximal compound nerve action potential (CMAP) in branches of sciatic nerve (nerves to the gastrocnemius, tibialis anterior), motor nerve conduction velocity, H-reflex, F-wave, amplitude and onset latency of motor evoked potential by lumbosacral motor root magnetic stimulation, and denervation by electromyography (gastrocnemius, tibialis anterior). The results from studies using magnetic and electrical stimulation showed prominent reduction of CMAP amplitude in rats of sciatic nerve ligation and acrylamide intoxication group. The CMAP amplitude measured by magnetic stimulation was 76~85% of that by electrical stimulation. By either magnetic stimulation or electrical stimulation, there was no significant difference in the mean onset latency of CMAP between control and neuropathy groups. Volume conduction accounts for the interference of waveform and error is inevitable. Because of the short distance of hind limb of the rat, the nerve conduction velocity (NCV), H-reflex and F-wave could not be determined using magnetic stimulation. In contrast, electrophysiological analysis by electrical stimulation revealed slowed NCV, prolonged or absent H-reflex and F-wave in animals of neuropathy groups. Electromyography showed prominent denervation potentials over the sampling muscles in both models. In conclusion, magnetic stimulation of lumbosacral motor root is non-invasive and convenient. However, further improvement and establishment of basic parameters are required to facilitate a reliable tool in evaluation of peripheral nerve injury.

In recent years, there has been increasing interest in the advancement of microrobotic systems in micro-engineering, micro-fabrication, biological research and biomedical applications. Untethered magnetic-based microrobotic systems are one of the most widely developing groups of microrobotic systems that have been extensively explored for biological and biomedical micro-manipulations. These systems show promise in resolving problems related to on-board power supply limitations as well as mechanical contact sealing and lubrication. In this thesis, a high precision magnetic untethered microrobotic system is demonstrated for micro-handling tasks. A key aspect of the proposed platform concerns the integration of magnetic levitation technology and bilateral macro-micro teleoperation for human intervention to avoid imperceptible failures in poorly observed micro-domain environments. The developed platform has three basic subsystems: a magnetic untethered microrobotic system (MUMS), a haptic device, and a scaled bilateral teleoperation system. The MUMS produces and regulates a magnetic field for non-contact propelling of a microrobot. In order to achieve a controlled motion of the magnetically levitated microrobot, a mathematical force model of the magnetic propulsion mechanism is developed and used to design various control systems. In the workspace of 30 ?? 32 ?? 32 mm ³, both PID and LQG\LTR controllers perform similarly the position accuracy of 10 ?? m in a vertical direction and 2 ?? m in a horizontal motion. The MUMS is equipped with an eddy-current damper to enhance its inherent damping factor in the microrobot's horizontal motions. This paper deals with the modeling and analysis of an eddy-current damper that is formed by a conductive plate placed below the levitated microrobot to overcome inherent dynamical vibrations and improve motion precision. The modeling of eddy-current distribution in the conductive plate is investigated by solving the diffusion equation for vector magnetic potential, and an analytical expression for the horizontal damping force is presented and experimentally validated. It is demonstrated that eddy-current damping is a crucial technique for increasing the damping coefficient in a non-contact way and for improving levitation performance. The damping can be widely used in applications of magnetic actuation systems in micro-manipulation and micro-fabrication. To determine the position of the microrobot in a workspace, the MUMS uses high-accuracy laser sensors. However, laser positioning techniques can only be used in highly transparent environments. A novel technique based on real-time magnetic flux measurement has been proposed for the position estimation of the microrobot in case of laser beam blockage, whereby a combination of Hall-effect sensors is employed to find the microrobot's position in free motion by using the produced magnetic flux. In free motion, the microrobot tends to move toward the horizontally zero magnetic field gradient, B_max location. As another key feature of the magnetic flux measurement, it was realized that the applied force from the environment to the microrobot can be estimated as linearly proportional to the distance of the microrobot from the B_max location. The developed micro-domain force estimation method is verified experimentally with an accuracy of 1.27 ?? N. A bilateral macro-micro teleoperation technique is employed in the MUMS for the telepresence of a human operator in the task environment. A gain-switching position-position teleoperation scheme is employed and a human operator controls the motion of the microrobot via a master manipulator for dexterous micro-manipulation tasks. The operator can sense a strong force during micro-domain tasks if the microrobot encounters a stiff environment, and the effect of hard contact is fed back to the operator's hand. The position-position method works for both free motion and hard contact. However, to enhance the feeling of a micro-domain environment in the human operator, the scaled force must be transferred to a human, thereby realizing a direct-force-reflection bilateral teleoperation. Additionally, a human-assisted virtual reality interface is developed to improve a human operator's skills in using the haptic-enabled platform, before carrying out an actual dexterous task.

Thesis (MEng) -- University of South Australia, 1994

No description available.

Thesis (M. Eng.)--Victoria University (Melbourne, Vic.), 2007.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

No description available.

This thesis examines optimum designs for broad-band helix to be used in electron spin resonance.

Thesis (MSc (Chemistry and Biochemistry))--University of Limpopo, 2009. / Magnetic nanoparticles have been proposed for use as biomedical purposes to a large extent for several years. In recent years, nanotechnology has developed to a stage that makes it possible to produce, characterize and specifically tailor the functional properties of nanoparticles for clinical applications. This has led to various opportunities such as improving the quality of magnetic resonance imaging, hyperthemic treatment for malignant cells, site-specific drug delivery and the manipulation of cell membranes. To this end a variety of iron oxide particles have been synthesized. A common failure in targeted systems is due to the opsonization of the particles on entry into the bloodstreams, rendering the particles recognizable by the body’s major defense system, the reticulo-endothelial system. The co-precipitation method: nanoparticles comprised of gold shell and magnetite/maghemite inclusion were synthesized by overgrowing the gold shell onto the magnetic seeds using sodium citrates as a reducing agent. Oxidized magnetites (Fe3O4) fabricated by co-precipitation of Fe2+ and Fe3+ in strong alkaline solution were used as magnetic cores. These magnetic nanoparticles were characterized by X-ray diffraction (XRD), Transmission Electron Microscope (TEM), ultraviolet-visible (UV-vis) spectroscopy and Vibrating Sample Magnetometer (VSM). Results from x-ray diffraction show that the gold-iron oxide nanoparticles have a face-centered cubic shape, a=8.39 Å and a special group Fd3-m=227 with the dominant crystal planes of {311}. The gold-coated magnetic nanoparticles exhibited a surface plasmon resonance peak at 520 nm. The nanoparticles are well dispersed in distilled water. The particle size of the magnetite nanoparticles was about 0.5 μm (500 nm) confirmed by transmission electron microscope image. The saturation magnetization of the as-synthesized iron oxide nanopowders was 38 emu/g and the blocking temperatures for magnetization 1, magnetization 2, magnetization 3, and magnetization 4 are 150, 143, 138, and 135 K, respectively. The reverse micelle (Micro emulsion) method: a unique reverse micelle method has been developed to prepare gold-coated iron (Fe@Au) nanoparticles. X-ray diffraction, iv ultraviolet/visible, transmission electron microscope, and magnetic measurements are utilized to characterize the nanocomposites. X-ray diffraction only gives Face-Centered Cubic (FCC) patterns of gold for the obtained nanoparticles and indicated that gold exists as a metal. The absorption band of the iron@gold colloid shifts to a longer wavelength and broadens relative to that of the pure gold colloid. Transmission electron microscope results show that the average size of the iron@gold nanoparticles is about 2 μm (2000 nm) and indicated that the nanocomposite was single-nanosized and has a sharp size distribution. These nanoparticles are self-assembled into chains on micron scale under a 0.5T magnetic field. Magnetic measurements show that the particles are super paramagnetic with a blocking temperature (TB) of 42 K. At 300 K (above blocking temperature), no coercivity (Hc) and remanence (Mr) is observed in the magnetization curve, while at 2 K (below TB), coercivity and remanence are observed to be 728 Oe and 4.12 emu/g, respectively.

No description available.