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Predicting the motion of superparamagnetic iron oxide nanoparticles (SPION) in biological systems is one of the most relevant parameters for the biomedical application of SPION. Recently, magnetic nanoparticles such as SPION have been utilized as the MR image contrast agent, targeted drug delivery, magnetic separation, biosensor, etc. Because the size of SPION is in the nanometer scale, it is difficult to test their dynamics under an external magnetic field experimentally. Moreover, when the SPION moves in a viscous fluid such as blood, the situation can be more complicated. To overcome these difficulties, we proposed a fast-solving technique combined with the finite-element method for analyzing the dynamic characteristics of SPION in a viscous fluid under an external magnetic field. Using this numerical modeling, the effective system dimension, external magnetic field, particle size, and trajectory of SPION can be estimated. To verify the proposed method, three magnetic systems with permanent magnet and micro capillary were tested. Index Terms--Superparamagnetic iron oxide nanoparticles (SPION), targeted drug delivery, trajectory, viscous fluid.

The depth of penetration of periodic-field magnetoquasistatic sensors depends on two factors: the skin depth into the material under test and the spatial wavelength of the imposed periodic magnetic field. In applications where high depth of penetration is desirable, the second factor may result in the need for sensors with impractically large dimensions. We describe a way to overcome this problem by generating a field whose effective spatial wavelength is on the order of the sensor length. The magnetic field is shaped by a distributed primary winding that consists of multiple winding segments, with the total current amplitude in each segment following a sinusoidal envelope function. The effective spatial wavelength of the imposed magnetic field may be changed dynamically by changing the excitation current pattern in the primary windings. From a modeling perspective, an advantage of this kind of magnetic field excitation is that the drive current distribution is known from the beginning, since the width of the individual windings is small compared to the wavelength and may be approximated as being infinitely narrow. This greatly simplifies numerical computation, since it makes it possible to apply fast discrete Fourier transform methods directly. We discuss first sensors with Cartesian geometry. We then discuss cylindrical geometry sensors whose models use fast Hankel transforms. Index Terms--Eddy current, fast Fourier transform WFT), Hankel transform, magnetometer, shaped field.

This paper presents a finite element method used to evaluate the induced current density in a realistic model of the human head exposed to a time varying magnetic field. The tissue electric properties were varied to ascertain their influence on the induced currents. Current density magnitude and vector plots were generated throughout the tissue layers to determine the effects of tissue boundaries on the field. The current density magnitude correlated to the conductivity of the tissue in all the cases tested except where the tissue permittivity was raised to a level to allow for displacement currents. In this case, the permittivity of the tissue was the dominant factor. Current density components normal to the tissue interface were shown to exist in all solutions within the cortex contrary to the predictions of present models that rely on symmetrical geometries. Additionally, modifications in the cortical geometry were shown to perturb the field so that the site of activation could be altered in diseased patient populations. Finally, by varying the tissue permittivity values and the source frequency, we tested the effects of alpha dispersion theories on transcranial magnetic stimulation. Index Terms--Biomagnetism, field computation, finite element model, transcranial magnetic stimulation.

Measurements of magnetic-field-induced torque in applied uniform rotating magnetic' fields are presented and compared to theoretical analyses for water- and oil-based ferrofluids. These experiments measure the viscous torque on the inner wall of a stationary hollow polycarbonate spindle that is completely .filled with ferrofluid and attached to a viscometer functioning, as a torque meter. The spindle remains stationary and is centered inside a three-phase AC 2-pole motor stator winding, creating uniform time-varying rotating magnetic fields. The viscous torque is measured as a function of magnetic' field amplitude, frequency, and direction of rotation. These measurements demonstrate that ferrofluid flow and torque are present even in the absence of free surfaces and agree with a recently derived analysis of the torque during spin-up flow of ferrofluids.

The Kerr electro-optic field mapping technique has been used to study space charge effects in HV pulsed propylene carbonate ([C.sub.4][H.sub.6][O.sub.3]) using stainless steel parallel-plane, aluminum blade-plane, and aluminum point-plane electrodes. Measurements presented here were taken using a circular polariscope with aligned polarizers at room temperature (T ~ 20 to 27[degrees]C). Average peak space charge free electric field strengths were [E.sub.O] ~ 52 kV/cm for the parallel-plane electrodes, [E.sub.O] ~ 210 kV/cm at the blade electrode tip and [E.sub.O] ~ 240 kV/cm at the point electrode tip. The measurement times ranged from 10 [micro]s to 1 ms. For the parallel-plane electrodes, the light intensity pictures were analyzed along a line between electrodes in the center of the electrode gap and for the blade-plane and point-plane electrodes the light intensity pictures were analyzed both from the tip of the blade and point, to the plane, and along the plane surface. From the light intensity distribution for the parallel-plane and blade-plane electrodes, the electric field and space charge density were calculated as a function of position and time. The calculated space charge distributions show both positive and negative charge injections from the electrodes as well as bulk charge dissociation and recombination. The light intensity was recorded on Polaroid film for the parallel-plane, blade-plane and point-plane electrode measurements and also with a CCD camera for the point-plane electrodes. A CCD camera was used for the point-plane electrodes to resolve more accurately the gray-scale light intensity distribution because of the short optical path length. All the HV Kerr electro-optic measurements showed significant space charge effects in propylene carbonate because the light intensity distributions differed significantly from the calculated Kerr effect patterns from numerical solutions to Laplace's equation under space-charge free conditions.

Concrete guideways for proposed MAGLEV vehicles may be reinforced with electrically conducting and magnetizable steel rebars. Transient magnetic fields due to passing MAGLEV vehicles will then induce transient currents in the rebars leading to power dissipation and temperature rise as well as Lorentz and magnetization forces on the rebars. In order to evaluate if this heating and force on the rebars affects concrete life and performance, analysis is presented for an infinitely long conducting and magnetizable cylinder in imposed uniform axial or transverse magnetic fields. Exact and approximate solutions are presented for sinusoidal steady state and step transient magnetic fields inside and outside the cylinder, the induced current density, the vector potential for transverse magnetic fields, the time average dissipated power in the sinusoidal steady state, and the total energy dissipated for step transients. Forces are approximately calculated for imposed magnetic fields with a weak spatial gradient. The analysis is applied to representative rebar materials. Index Terms - Eddy currents, MAGLEV, magnetic fields, magnetic forces, rebars.

Electric field distributions measured using the Kerr effect cause a phase shift between light components polarized parallel and perpendicular to the electric field, proportional to the magnitude squared of the electric field components in the plane perpendicular to light propagation integrated over the light path length. One wishes to recover the electric field distribution from measurements of light phase shifts. For axisymmetric geometries where the electric field depends only on the radial coordinate and whose direction is constant along the light path, as is the case along a planar electrode, the total phase shift for light propagating at a constant distance from the center of symmetry and the electric field distribution are related by an Abel transform pair, a special case of Radon transforms typically used in image reconstructions with medical tomography and holography. The more general Radon transform relates the optical phase shift to non-axisymmetric electric field distributions but is restricted to cases where the applied electric field is perpendicular to the plane of light propagation. If the applied electric field direction changes along the light path, it becomes necessary to account for the change in direction of the light components parallel and perpendicular to the applied electric field and the light polarization equations are generalized.

Streamer branching in liquid dielectrics is driven by stochastic and deterministic factors. The presence of stochastic causes of streamer branching such as inhomogeneities inherited from noisy initial states, impurities, or charge carrier density fluctuations is inevitable in any dielectric. A fully three-dimensional streamer model presented in this paper indicates that deterministic origins of branching are intrinsic attributes of streamers, which in some cases make the branching inevitable depending on shape and velocity of the volume charge at the streamer frontier. Specifically, any given inhomogeneous perturbation can result in streamer branching if the volume charge layer at the original streamer head is relatively thin and slow enough. Furthermore, discrete nature of electrons at the leading edge of an ionization front always guarantees the existence of a non-zero inhomogeneous perturbation ahead of the streamer head propagating even in perfectly homogeneous dielectric. Based on the modeling results for streamers propagating in a liquid dielectric, a gauge on the streamer head geometry is introduced that determines whether the branching occurs under particular inhomogeneous circumstances. Estimated number, diameter, and velocity of the born branches agree qualitatively with experimental images of the streamer branching. [ABSTRACT FROM AUTHOR]

Generalized analysis is presented extending recent work of the charging of a perfectly conducting sphere from a single charge carrier to two charge carriers of opposite polarity, with different values of volume charge density and mobility and including an ohmic lossy dielectric region surrounding a perfectly conducting sphere. Specific special cases treated are: (1) unipolar positive or negative charging and discharging and (2) bipolar charging and discharging; both cases treating zero and nonzero conductivity of the dielectric region surrounding a sphere. It is found that there exists a theoretical limit to the amount of charge, either positive or negative, that can accumulate on a perfectly conducting sphere for a specific applied electric field magnitude, permittivity of the surrounding medium, and sphere size. However, in practice this saturation charge limit is not reached and the sphere is charged to a lower value due to the nonzero conductivity of the surrounding medium and the existence of both positive and negative mobile carriers. Moreover, it is the respective effective conductivities of these positive and negative carriers, as well as the conductivity of the surrounding medium, which strongly influences the sphere's lowered saturation charge limit, charge polarity, charging rate, and discharging rate. [ABSTRACT FROM AUTHOR]

Transformer oil-based nanofluids with conductive nanoparticle suspensions defy conventional wisdom as past experimental work showed that such nanofluids have substantially higher positive voltage breakdown levels with slower positive streamer velocities than that of pure transformer oil. This paradoxical superior electrical breakdown performance compared to that of pure oil is due to the electron charging of the nanoparticles to convert fast electrons from field ionization to slow negatively charged nanoparticle charge carriers with effective mobility reduction by a factor of about 1×105. The charging dynamics of a nanoparticle in transformer oil with both infinite and finite conductivities shows that this electron trapping is the cause of the decrease in positive streamer velocity, resulting in higher electrical breakdown strength. Analysis derives the electric field in the vicinity of the nanoparticles, electron trajectories on electric field lines that charge nanoparticles, and expressions for the charging characteristics of the nanoparticles as a function of time and dielectric permittivity and conductivity of nanoparticles and the surrounding transformer oil. This charged nanoparticle model is used with a comprehensive electrodynamic analysis for the charge generation, recombination, and transport of positive and negative ions, electrons, and charged nanoparticles between a positive high voltage sharp needle electrode and a large spherical ground electrode. Case studies show that transformer oil molecular ionization without nanoparticles cause an electric field and space charge wave to propagate between electrodes, generating heat that can cause transformer oil to vaporize, creating the positive streamer. With nanoparticles as electron scavengers, the speed of the streamer is reduced, offering improved high voltage equipment performance and reliability. [ABSTRACT FROM AUTHOR]

Mechanical deformation in incompressible linear and nonlinear magnetic materials is evaluated using various conventional electromagnetic volume and surface force density methods. A magnetic systems is tested to compare the mechanical deformation in linear and nonlinear magnetic materials.

Superparamagnetic iron oxide nanoparticles(SPIONs) with a diameter of 11nm were prepared by controlled coprecipitation and coated with oleic acid to prevent agglomeration and flocculation in the solvent. The rates of heat loss and energy absorption were obtained by nonlinear fitting of the experimental data.

A study was conducted to demonstrate accurate calculation of surface tension at interfaces of magnetic fluids with nonmagnetic fluids from peak spacing measurements at incipience of perpendicular field instability. This perpendicular field instability technique for determining surface tension is especially valuable for two superposed liquids since accurate tensiometer measurements for two fluids are difficult.

A study is conducted to report the successful preparation of monodispersed Fe-Pt nanoparticles by a polyol process of platinum acetylacetonate and thermal decomposition of iron pentacarbonyl. The cytoxicity of unmodified Fe-Pt nanoparticles was performed in brain endothelial cells, which showed no significant toxicity in Fe-Pt nanoparticles on bEnd3 cells during a 24 h period.

Magnetic fluid spin velocity shear stress, and magnetoviscosity are calculated for a planar-Couette magnetic fluid flow by applying uniform dc magnetic field transverse to the duct axis and by using Shliomis' first magnetization relaxation equation. The conditions for multivalued effective magnetoviscosity and spin velocity are described in the analysis.