By depositing insulating layers on oxide superconducting films, the films generally deteriorate. When an insulating multilayer of CeO2(50 )SrTiO3(200 ) was grown on 800--thick EuBa2Cu3O 7-δ (EBCO) films with Tce's (Tc endpoint) above 90 K, the films exhibited Tce's of about 40 K. Recovery of the deteriorated films was carried out by two treatment methods. A pure oxygen treatment, where the deteriorated films were annealed at a temperature (Tsa) of 550C and an oxygen pressure (PO2) of 100 kPa for 60 min, and then naturally cooled, restored the films with Tce's of about 60 K. An activated oxygen plasma (AOP) treatment, where the deteriorated films were exposed to oxygen plasma at a Tsa=550C for 40 min and subsequently oxygen gas was introduced into the chamber up to 2 kPa and then naturally cooled, restored the films with Tce's of about 84 K. The AOP-treated film was recovered with a cooling rate of less than 6.8C/min, and exhibited Tce of 90 K. The AOP-treated film took in oxygen more effectively than the pure oxygen-treated film with the cooling process at less than PO2=100 kPa.

Femtosecond optical pulses were irradiated into a YBa2Cu3O7-δ strip-line of 400 µm in width in order to investigate the relationship between the laser beam power profile and the distribution of the optically generated magnetic fluxes. To homogenize the current distribution in the strip-line, a half of the strip-line was patterned into the ordered array structure of holes of 2 µm in diameter at an interval of 4 µm, and several experimental conditions were examined by changing the focal size of the pulsed laser beam at the sample surface. As a result, it was found out that the generated optical magnetic fluxes strongly depend on the power profile of the femtosecond optical pulses, and showed a possibility for the application to a laser beam profiler and the other optical devices.

We have designed a torque magnetometer using a 60-kG split-type superconducting magnet. A balance torque compensates the torque acting on a sample in the magnetic field. The feedback circuit for a sample direction consists of an optical position sensor, a moving coil, and a PID controller. We measured the coil current to know a sample torque. The whole torque machinery is directly rotated by a stepping motor of angular resolution 0.0036. An advantage of the torque apparatus is a wide dynamic range up to 1000 dyncm. The sample temperature can be controlled between 4 K and 300 K.

In the magnetic stimulation of the peripheral nerve fiber with the figure-of-eight coil, the nerve fiber beneath the figure-of-eight coil is considered to be stimulated with the lowest intensity when it is parallel to the junction of the figure-of-eight coil. However, some experimental studies with the magnetic peripheral stimulation showed that the large compound muscle action potential is elicited with the figure-of-eight coil oriented in the other directions. In the present study, we try to explain the cause of such a discrepancy with the analysis of the model of the magnetic nerve stimulation, and confirm the validity of the result obtained from the model analysis by the experimental study of the magnetic peripheral nerve stimulation. We show that the threshold for the nerve excitation become lowest not only when the junction of the figure-of-eight coil is parallel to the nerve fiber but also when that is perpendicular to the nerve fiber.

In this paper, we propose a method to reconstruct current distributions in the human brain from neuromagnetic measurements. The proposed method is based on the weighted lead-field synthetic (WLFS) filtering technique with the weighting factors calculated from the results of previous source space scanning. In this method, in addition to the depth normalization technique, weighting factors of the WLFS are determined by the cost values previously calculated based on the multiple signal classification (MUSIC) scan. We performed computer simulations of this method under noisy measurement conditions and compared the results to those obtained with the conventional WLFS method. The results of the simulations indicate that the proposed method is effective for the reconstruction of the current distributions in the human brain using magnetoencephalographic (MEG) measurements, even if the signal-to-noise ratio of the measured data is relatively low. We applied the proposed method to the magnetoencephalographic data obtained during a mental image processing task that included object recognition and mental rotation operations. The results suggest that the proposed method can extract the neural activity in the extrastriate visual region and the parietal region. These results are in agreement with the results of previous positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies.

The purpose of our study is to estimate the imaging of ischemic myocardial muscles in rats. The magnetocardiograms (MCG) of rats were measured by a 12-channel high resolution gradiometer, which consisted of 5 mm diameter pick-up coils with a 7.5 mm distance between each coil. MCGs of seven male rats were measured in a magnetically shielded room pre and post coronary artery occlusion. The source imaging was estimated by minimum norm estimation (MNE). Changes of the current source imaging pre- and post coronary artery occlusion were clarified. As a result, in the ST segment, the current distribution significantly increased at the ischemic area. In the T wave, the direction of the current distribution clearly shifted to the left thorax. We proved that the increased area of the current distribution in the ST segment was related to the ischemic area of the ventricular muscles.

The VHF broadband radio interferometry operated from 25 MHz to 250 MHz has been developed for observing lightning discharge progression. The lightning images are derived by sensing the electromagnetic-waves which are radiated during the discharges. The perpendicular baseline geometry provides the angular locations (azimuth and elevation) of lightning radiation sources. The lightning observations have been conducted in the Hokuriku District in 1999. The station consisted of three broadband antennas and an electric field antenna as well as a GPS receiver. The system was able to reconstruct lightning discharge channels in two-spatial dimensions and in time sequence. As one of the observation results, an upward negative cloud-to-ground lightning flash will be presented.

Functional magnetic resonance imaging (fMRI) allows to display functional activities of certain brain areas. In combination with a three dimensional anatomical dataset, acquired with a standard magnetic resonance (MR) scanner, it can be used to identify eloquent brain areas, resulting in so-called functional neuronavigation, supporting the neurosurgeon while planning and performing the operation. But during the operation brain shift leads to an increasing inaccuracy of the navigation system. Intraoperative MR imaging is used to update the neuronavigation system with a new anatomical dataset. To preserve the advantages of functional neuronavigation, it is necessary to save the functional information. Since fMRI cannot be repeated intraoperatively with the unconscious patient easily we tried to solve this problem by means of image processing and pattern recognition algorithms. In this paper we present an automatic approach for transfering preoperative markers into an intraoperative 3-D dataset. In the first step the brains are segmented in both image sets which are then registered and aligned. Next, corresponding points are determined. These points are then used to determine the position of the markers by estimating the local influence of brain shift.

Turbo coding is widely known as one of effective error control coding techniques in various digital communication systems since this coding method has proposed by C. Berrou, etc in 1993. In digital magnetic recording, it has been cleared that the error correcting capability of turbo coding is superior to most of conventional recording codes as a matter of course. But, the performance of a partial response maximum-likelihood (PRML) system combined with any recording code is degraded by many undesirable factors or effects. To improve the performance of the PRML system in high areal density recording, it is useful to adopt a higher order PRML system or high rate code in a general case. In this paper, the rate 32/34 turbo code combined with an enhanced extended class-4 partial response (E2PR4) is proposed. We call this trellis coded partial response (TCPR) system the rate 32/34 turbo-coded E2PR4 (32/34 TC-E2PR4). Our proposed TCPR system can be expected to get large coding gain and improve the performance of PRML system. As a result, the proposed coding system provides a good performance compared with the conventional systems. In especial, our system can achieve a BER of 10-5 with SNR of approximately 1.5 dB less than the conventional 8/9 maximum transition run (MTR) coded E2PR4ML system at a normalized linear density of 3.

A multi-grid finite-difference time-domain (FDTD) method was applied for numerical dosimetry analysis in the human head for 5 GHz band portable terminals. By applying fine FDTD grids to the volumes in the human head where the highest electromagnetic (EM) absorption occurs and coarse grids to the remaining volumes of the head, the spatial peak specific absorption rate (SAR) assessment was achieved with a less computation memory and time. The accuracy of applying the multi-grid FDTD method to the spatial peak SAR assessment was checked in comparison with the results obtained from the usual uniform-grid method, and then the spatial peak SARs for three typical situations of a person using a 5.2 GHz band portable terminal were calculated in conjunction with an anatomically based human head model.

This paper describes an electromagnetically coupled microstrip divider that provides high output port isolation and DC cutting. The device consists of a parasitic resonator placed above microstrip patch resonators, achieving tight coupling for both input and output ports. FDTD simulation and measurements reveal that the device has a high isolation between output ports. Equal and unequal 2-way and 3-way power dividers are presented in this paper.

An efficient numerical source model is proposed to calculate the induced current densities in the human body from low-frequency inhomogeneous magnetic fields emitted by electronic devices. Due to the complex geometrical structure of electronic devices (e.g. household appliances, power tools), an efficient equivalent source model based on magnetic elementary dipoles is used instead of the real device or the approximated source model (current loop). Subsequently, the validity of the method proposed is confirmed.

The boundary integral equation (BIE) on interior walls with surface impedance conditions is implemented to the iterative physical optics method and how to treat the singularities involved in the BIE of an impedance cavity is described. Singular integrals over a rectangular region can be represented by simple elementary functions.

Employing reactive sputtering using an electron-cyclotron-resonance microwave plasma without oxidation process, high coercivity ferrite thin-films with perpendicular magnetic anisotropy were successfully prepared without NiO underlayer at low substrate temperature. The ferrite thin-film deposited on glass substrate had smooth surface and were composed of small grains. Perpendicular recording was performed on the ferrite thin-film hard disk. The ferrite thin-films with high coercivity could be prepared on flexible film substrates (Polyimide and PET).

Magnetoplumbite type Ba ferrite (BaM) disks were prepared on Pt and Pt-Ta underlayers using facing targets sputtering apparatus. Pt underlayers are more effective than ZnO underlayers to promote c-axis orientation of BaM layers, especially for extremely thin BaM films. Pt-Ta underlayer was used to decrease the grain size of BaM layers. BaM/Pt-Ta disks revealed larger S/N ratio than BaM/Pt disks because of their larger signal output and lower media noise level. BaM disks with 50 nm thick BaM layers revealed lower noise level and larger S/N ratio than that with 100 nm thick BaM layers due to smaller grain size.

Dual FDTS/DF detector is an advanced version of FDTS/DF detector that gives significant performance improvement over FDTS/DF scheme on linear channels, and moreover, in contrast to other dual-detector schemes, it is suitable for various d-constraint coded channels. As recording density increases, channel nonlinearities such as non-linear transition shift (NLTS) and partial erasure (PE) degrade the performance of detectors. In this paper, we use nonlinear channel models to study the BER performance of dual FDTS/DF detector and compare the performances with those of other detectors through bit-by-bit simulations. Simulation results show that the dual FDTS/DF detector is superior in performance compared to FDTS/DF and MDFE detectors even on nonlinear channels, and it gives comparable BER performance with M2DFE (adv.) on nonlinear channels. Results also indicate that the detectors on the d=1 coded channels are more robust to channel nonlinearities compared to those of other detectors (such as PRML family detectors) on the d=0 coded channels.

Microstructures of CoCr-alloy thin film media were investigated by cross-sectional transmission electron microscopy focussing on the initial growth region of the magnetic layer grown on nonmagnetic underlayers. An introduction of nonmagnetic hcp-CoCrRu layer between an hcp-CoCrPt recording layer and an hcp- or a bcc-underlayer improved the crystallographic quality of the initial growth region. Sharp compositional distributions of alloying elements at the interfaces of a CoCrPt/CoCrRu/CrTi perpendicular medium and a CoCrPt/CoCrRu/CrTi longitudinal medium were respectively confirmed by electron energy loss spectroscopy employing a finely focussed electron beam. Coercivity and squareness of the thin film media increased by realizing good hetero-epitaxy between the nonmagnetic and the magnetic hcp-layers.

Magnetic tunnel junctions (MTJ), i.e., structures consisting of two ferromagnetic layers (FM1 and FM2), separated by a very thin insulator barrier (I), have recently attracted attention for their large tunneling magnetoresistance (TMR) which appears when the magnetization of the ferromagnets of FM1 and FM2 changes their relative orientation from parallel to antiparallel in an applied magnetic field. Using an ultrahigh vacuum magnetron sputtering system, a variety of MTJ structures have been explored. Double Hc magnetic tunnel junction, NiFe/Al2O3/Co and FeCo/Al2O3/Co, were fabricated directly using placement of successive contact mask. The tunnel barrier was prepared by in situ plasma oxidation of thin Al layers sputter deposited. For NiFe/Al2O3/Co junctions, the maximum TMR value reaches 5.0% at room temperature, the switching field can be less than 10 Oe and the relative step width is about 30 Oe. The junction resistance changes from hundreds of ohms to hundreds of kilo-ohms and TMR values decrease monotonously with the increase of applied junction voltage bias. For FeCo/Al2O3/Co junctions, TMR values exceeding 7% were obtained at room temperature. It is surprising that an inverse TMR of 4% was observed in FeCo/Al2O3/Co. The physics governing the spin polarization of tunneling electrons remains unclear. Structures, NiFe/FeMn/NiFe/Al2O3/NiFe, in which one of the FM layers is exchange biased with an antiferromagnetic FeMn layer, were also prepared by patterning using optical lithography techniques. Thus, the junctions exhibit two well-defined magnetic states in which the FM layers are either parallel or antiparallel to one another. TMR values of 16% at room temperature were obtained. The switching field is less than 10 Oe and step width is larger than 30 Oe.

This paper presents a fast inversion method for electromagnetic imaging of cylindrical dielectric objects with the optimal regularization parameter used in the Levenberg-Marquardt method. A novel procedure for choosing the optimal regularization parameter is proposed. The method of moments with pulse-basis functions and point matching is applied to discretize the equations for the scattered electric field and the total electric field inside the object. Then the inverse scattering problem is reduced to solving the matrix equation for the unknown expansion coefficients of a contrast function, which is represented as a function of the relative permittivity of the object. The matrix equation may be solved in the least-squares sense with the Levenberg-Marquardt method. Thus the contrast function can be reconstructed by the minimization of a functional, which is expressed as the sum of a standard error term on the scattered electric field and an additional regularization term. While a regularization parameter is usually chosen according to the generalized cross-validation (GCV) method, the optimal one is now determined by minimizing the absolute value of the radius of curvature of the GCV function. This scheme is quite different from the GCV method. Numerical results are presented for a circular cylinder and a stratified circular cylinder consisting of two concentric homogeneous layers. The convergence behaviors of the proposed method and the GCV method are compared with each other. It is confirmed from the numerical results that the proposed method provides successful reconstructions with the property of much faster convergence than the conventional GCV method.

Particulate media composed of very small particles were studied to determine high-density recording performance and thermal stability. Studied media included metal particulate media with mean particle length of 71, 102 and 148 nm, and Ba ferrite particulate media with mean diameter of 22, 28 and 50 nm. Using a loss-term simulation program, taking into account gap-loss, spacing-loss and particle length loss, the recording capability (D20 of 265 kFRPI for MP and 290 kFRPI for Ba ferrite media) was estimated. Thermal stability was evaluated from magnetization time decay measurements. It was found that MP media with large Ku values and 71 nm particles were satisfactorily stable, and the particle volume is still large enough in respect of thermal stability. However, 22-nm Ba ferrite media were less stable, primarily because of small Ku values and particle volume. It was also clarified that positive inter-particle interaction accelerates magnetization time decay, in the presence of a large reverse field.