Magnetic particles with active functional groups offer numerous advantages for use in μ-TAS (Micro Total Analytical Systems). The functional site allows chemical binding of the particle with the target species in the fluid sample. Selection of the functional group establishes the target molecule and vice versa under assumptions of highly specific biding. The particles hence act as mobile reaction substrates with high surface to volume ratios owing to their small size. The concept of action at a distance allows their use as agents for separation in microchannels based on relatively simple design. It is possible to manipulate magnetic particles and bound target species using an externally applied magnetic field. Hence, the particles can be effectively separated from the flow of a carrier fluid. Magnetic fields create dipolar interactions causing the particles to form interesting structures and aggregates. Depending upon the applied field, the microstructure evolution of the aggregate is interesting in its own right, e.g. related to improvements in material properties and bottom-up self assembly. The shape of the aggregates can be determined a priori if the interaction between the particles is well characterized. The dominant competing forces that influence magnetic particle dynamics in a flow are magnetic and viscous. There are a number of physical parameters such as viscosity, magnetic susceptibility, fluid velocity, etc. which are varied to study their individual effects. Initially dilute suspensions are studied experimentally and numerically using a particle based dynamics approach. Once established, a force model for particle interaction is investigated for concentrated suspensions. A Lagrangian particle tracking algorithm that returns positions of the particles is used for this work that focuses on studying the dynamics of these particles. A mathematical model is proposed and investigated for functionalization between magnetic and non-magnetic particles. Having characterized the collection of magnetic particles, the effect of relative concentrations is investigated on the collection of the non-magnetic species. / Ph. D.

No description available.

International Telemetering Conference Proceedings / October 30-November 02, 1989 / Town & Country Hotel & Convention Center, San Diego, California / Multiple channel magnetic tape recording is often used for signal analysis of intelligence and telemetry data. To insure accuracy of the reproduced data, these systems require frequent calibration and alignment. As the number of tracks on these systems has increased, this task has become more time-consuming. Even with a well-trained technician, this task can take several hours at a minimum. To alleviate this problem, we developed a system for performing this calibration automatically. The implementation utilizes a Fast-Fourier-Transform technique to analyze the output of a pre-recorded signal on tape. The desired response, most frequently defined by IRIG Standards, is stored in a look-up table in the machine. The actual response is compared to that desired, and, under micro-processor control, adjustment made in the signal channel until an acceptable response is achieved. A unique photo-resistor technique is used in the signal path to control such parameters as gain and phase. A description of the hardware system will be given, as well as a description of the algorithms utilized for implementation.

International Telemetering Conference Proceedings / October 30-November 02, 1989 / Town & Country Hotel & Convention Center, San Diego, California / Multiple channel magnetic tape recording is often used for signal analysis of intelligence and telemetry data. To insure accuracy of the reproduced data, these systems require frequent calibration and alignment. As the number of tracks on these systems has increased, this task has become more time-consuming. Even with a well-trained technician, this task can take several hours at a minimum. To alleviate this problem, we developed a system for performing this calibration automatically. The implementation utilizes a Fast-Fourier-Transform technique to analyze the output of a pre-recorded signal on tape. The desired response, most frequently defined by IRIG Standards, is stored in a look-up table in the machine. The actual response is compared to that desired, and, under micro-processor control, adjustment made in the signal channel until an acceptable response is achieved. A unique photo-resistor technique is used in the signal path to control such parameters as gain and phase. A description of the hardware system will be given, as well as a description of the algorithms utilized for implementation.

The investigation covers two possible areas of application of magnetic fluids, one involving the production of torque by means of rotating magnetic fields and the other the use Of magnetic fluids in the separation of non-magnetic ores on a density basis. The' emphasis-was upon the use of cheap, primitive ferrofluids Le'. non-collOidal suspension of relatively large particles. a Moskowitz and Rosensweig were the first to report electromechanical energy conversion with a rotating magnetic field. Their theory is not confirmed by their experimental results, howevert nor the fact that the fluid can rotate in the opposite direction to the field. This phenomenon has been investigated experimentally for a range of field intensities, wave velocities, particle sizes, volume loading and fluid viscosities. The torque per unit volume has been found to be related linearly to the volume loading but-nonlinearly to the frequency of the supply, field intensity and viscosity. For the primitive ferrofluids the results clearly indicate a combination of saliency and hysteresis torques. No satisfactory explanation for the reverse motion of the fluid has been produced and attempts to quantify the energy transfer have not been successful. Due to the inherently low permeability of the fluid, the torque per unit volume is much smaller than for conventional a. c. machines. Primitive magnetic fluids have also been shown to have potential in the separation of ores according to their densities. The novelty of this work is that the particles, which flocculate in the presence of stationary fields, are kept in suspension by agitation caused by a rotating wave. This agitation also serves to reduce the effective viscosity which at high volume loading can be high at zero field conditions. An effective specific gravity of about 12 has been obtained. The experimental results confirm the theory that the magnetic force in the linear condition is proportional to the magnetic energy - density gradient (in space) but with saturation the force is proportional to the field gradient and independent of body shape. A practical system seems to be feasible.

Solutions of the magnetohydrodynamic (MHD) equations are very important for modelling laboratory, space and astrophysical plasmas, for example the solar and stellar coronae, as well as for modelling many of the dynamic processes that occur in these different plasma environments such as the fundamental process of magnetic reconnection. Our previous understanding of the behavior of plasmas and their associated dynamic processes has been developed through two-dimensional (2D) models. However, a more realistic model should be three-dimensional (3D), but finding 3D solutions of the MHD equations is, in general, a formidable task. Only very few analytical solutions are known and even calculating solutions with numerical methods is usually far from easy. In this thesis, 3D solutions which model magnetic reconnection and rigidly rotating magnetized coronae are presented. For magnetic reconnection, a 3D stationary MHD model is used. However, the complexity of the problem meant that so far no generic analytic solutions for reconnection in 3D exist and most work consists of numerical simulations. This has so far hampered progress in our understanding of magnetic reconnection. The model used here allows for analytic solutions at least up to a certain order of approximation and therefore gives some better insight in the significant differences between 2D and 3D reconnection. Three-dimensional numerical solutions are also obtained for this model. Rigidly rotating magnetized coronae, on the other hand, are modeled using a set of magnetohydrostatic (MHS) equations. A general theoretical framework for calculating 3D MHS solutions outside massive rigidly rotating central bodies is presented. Under certain assumptions, the MHS equations are reduced to a single linear partial differential equation referred to as the fundamental equation of the theory. As a first step, an illustrative case of a massive rigidly rotating magnetized cylinder is considered, which somehow allows for analytic solutions in a certain domain of validity. In general, the fundamental equation of the theory can only be solved numerically and hence numerical example solutions are presented. The theory is then extended to include a more realistic case of massive rigidly rotating spherical bodies. The resulting fundamental equation of the theory in this case is too complicated to allow for analytic solutions and hence only numerical solutions are obtained using similar numerical methods to the ones used in the cylindrical case.

published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

This study uses a range of magnetic parameters, eg. Susceptibility (X), Saturation Isothermal Remanence (SIRM), Anhysteretic Remanence (ARM), interparametric ratios (ARM/X, SIRM/X, SIRM/ARM) and coercivity of remanence data (IRM-n/SIRM, (BO)CR), coupled with various dating methods (eg. moss increment counting and radiometric dating) to estimate the magnetic deposition onto some Scandinavian peat bogs. The sites available included 4 from southern Finland, 5 from northern Finland, 2 from northern Norway and 1 from southern Denmark. In addition to the magnetic techniques, a range of chemical determinations (iron, copper, zinc, lead, nickel and, where available, manganese) have been made, or are utilised, for all the peat cores. The reproducibility of the primary magnetic deposition record at Kaurastensuo, southern Finland has been examined. The rise in magnetic particulate concentrations, termed the magnetic 'take-off', was consistently dated to about 1931 for 7 of the 8 cores used, regardless of hummock-hollow micro topography. The persistence of magnetic minerals over timescales of 101-103 years has been examined by means of long core profiles from 4 southern Finnish bogs. The mineral magnetic and heavy metal profiles (iron, copper, zinc, lead and nickel) were in reasonable accord with the development of the individual bogs above different mineral soils. The development of peat profiles is dated from between 8000-9000 years BP using 14C dates spanning both the ombrotrophic and minerotrophic phases. The availability of moss increment counts for the northern Scandinavian sites and 210Pb determinations for Draved Moss, southern Denmark and Mo-I-Rana, northern Norway, has allowed estimates of variation in the magnetic deposition to be made. The northern Scandinavian sites all show increasing deposition from 1900, although maximum surface deposition varies from site to site, between 1.24-22.6 10-6Am2yr-1. The magnetic deposition at Draved Moss was estimated to be 21.6 10-6Am2yr-1 at a subsurface maximum dated to between 1967-1978. The increase in lead deposition at Draved Moss is in reasonable agreement with that of published lead deposition profiles from the same site, using earlier attempts at 210Pb determinations. At Mo-I-Rana, northern Norway the maximum magnetic deposition value is estimated to be 8.65 10-6Am'yr-1 for the surface slice, spanning the last 21 years. Any spatial variation in deposition within the Scandinavian sites appears to be partly masked by site-specific features, for example the close proximity of industrial sources at 2 of the Finnish sites and the iron and steel works at Mo-I-Rana. Magnetic deposition at the latter site is in good agreement with the history of iron and steel production within the region since the turn of the century.

Brain operates on a network level. Magnetic resonance imaging (MRI) provides structural and functional images noninvasively with large field of view and at high spatial resolution and thus assumes an extremely valuable role in studying brain networks. The objectives of this doctoral work were to develop and apply novel MRI methods on human and rodent brains, for in vivo and global assessments of functional brain networks at resting and task-evoked states. Firstly, the feasibility of passband balanced steady-state free precession (bSSFP) imaging for distortion-free and high-resolution resting-state fMRI (rsfMRI) was investigated. Resting-state networks (RSNs) derived from bSSFP images were shown spatially and spectrally comparable to those derived from conventional gradient-echo echo-planar imaging (GE-EPI) with considerable intra- and inter-subject reproducibility. High-resolution bSSFP corresponded well to the anatomical images, with RSNs exquisitely co-localized to gray matter. Furthermore, RSNs at areas of severe susceptibility were proved accessible including human anterior prefrontal cortex and rat piriform cortex. These findings demonstrated for the first time that passband bSSFP approach can be a promising alternative to GE-EPI for rsfMRI. It offers distortion-free and high-resolution RSNs and is potentially suited for high field studies. Secondly, to examine the macrovascular contributions to the spatial and spectral prosperities of resting-state networks, spin-echo echo-planar imaging (SE-EPI) with moderate diffusion weighting (DW) was proposed for rsfMRI. SE and DW suppressed the extravascular and intravascular contributions from macrovessels respectively. Significantly lower functional connectivity strength was observed in the posterior cingulate cortex of the default mode network derived from DW SE-EPI data comparing to that derived from SE-EPI, suggesting a confounding role played by the intravascular component from large veins, whereas no significant spectral difference was detected. Therefore, the DW SEEPI approach for rsfMRI may assist in better identifying and interpreting largescale brain networks with future improvement in temporal resolution by acceleration techniques and in sensitivity at higher field. Thirdly, rsfMRI was performed to evaluate the intrinsic functional networks in the corresponding anatomical visual brain connections traced by Mn-enhanced MRI (MEMRI). Strengths of resting-state functional connectivity appeared to couple with structural connectivity in MEMRI, demonstrating the sensitivity of these structural and functional connectivity MRI techniques for assessing the neuroarchitecture, neurophysiology and structural-functional relationships in the visual brain in vivo. Fourthly, the hypothesis that a regional activation identified via general linear model analysis of fMRI data reflects the summation of multiple distinct networks that carry different functional purposes was tested. Overlapping frontoparietal networks engaged in a simple single-digit multiplication task were found and their functional roles were evaluated through independent components analysis and contributive source analysis. Future studies incorporating different arithmetic tasks and resting state will shed more light upon how brain accomplishes arithmetic and more complex tasks in general. Lastly, benefiting from higher SNR, better spatial and temporal resolution at higher field, exploratory fMRI studies were conducted on rats at 7 T for in vivo assessments of 1) the effect of dark-rearing on postnatal visual development, 2) sound amplitude modulations and 3) sound frequency modulation sweep direction selectivity in auditory system. ( / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

No description available.