In recent years, the contactless and non-invasive magnetic stimulation is used to diagnose the function of nerve in the clinical application. It is, however, difficult to predict distributions of eddy currents in an inhomogeneous medium like as the human brain. In order to investigate the characteristics of eddy currents in the cranium, the distributions of eddy current in the simple cranium model which is filled with the saline solution was measured by the probe made of a flexible mini-coaxial cable. Moreover, the estimation of the stimulated point in the nerve was performed by using the nerve-muscle model of a bull frog's sciatic nerve. As a result, the distribution of eddy current depends on the structure of boundary of the skull or narrow space. From the results of the nerve-muscle model in the internal acoustic meatus by the magnetic stimulation, it is showed that the nerve is easy to be stimulated at where the change of eddy current density is very large or the nerve is bent in the finite medium.
Magnetic nerve stimulation has been widely used in neurophysiological research and clinical diagnosis. We have developed localized magnetic stimulation of the brain and peripheral nerve by means of a figure-of-eight coil. In this paper, we have developed repetitive magnetic stimulation with pulse trains. We have obtained the long latency motor evoked responses in human subjects by means of a single pulsed magnetic stimulation. We have also obtained the effects of repetitive magnetic stimulation in long latency motor evoked responses. Effects of repititive stimulation of median nerves on long latency motor evoked responses are also discussed. The time duration between a nerve signal's initiation and motor activity varies with the “Functional Path” chosen by the nerve signals.
Apparent movement is the experience of motion that occurs when at least two spatially separated stimuli are delivered sequentially under appropriate temporal conditions. In the present study, we measured and analyzed visual evoked electric and magnetic fields to localize the electric brain sources associated with the perception of apparent movement. Evoked magnetic fields associated with the perception of visual apparent movement were measured with a multi channel dc SQUID. The sources of visual apparent movement were estimated at at least three current dipoles. Two dipoles were located in the bilateral middle temporal area, and the third dipole was estimated in the occipital visual area.
We studied the fibrinolytic process in static magnetic fields. Fibrinolytic processes in magnetic fields were investigated by the fibrin plate method. We observed that levels of fibrin degradation products which were released from the fibrin plates with magnetic fields at 7.84T-7.74T were higher than those without magnetic fields by 15% on the average. Especially, gradient magnetic fields (B=7.14T-5.72T, dB/dz=50T/m-60T/m) enhanced fibrinolysis more than 190% of the control samples. In contrast, we obtained no effect of a homogeneous magnetic field at 7.84T on the dissolution of a fibrin clot in a micro tube. To clarify the effect of a homogeneous magnetic field on enzymatic activity of plasmin, we investigated the plasmin activity in a magnetic field at 7.84T by using a synthetic substrate for plasmin. We obtained the result that initial reaction rate of plasmin was not affected by a magnetic field at 7.84T. However, absorbance of the reaction mixture at 405nm decreased when plasmin was incubated with synthetic substrates in magnetic fields of 4T-7.84T for 60min. We also studied the effect of magnetic fields of up to 8T on the stability of plasmin. Thermal stability of plasmin decreased in magnetic fields of up to 8T when plasmin was thermally destabilized at 34°C for 48-80hours. There is a possibility that magnetic fields of 7T-8T affect the conformational change in the process of degradation of enzymes, and increase the rate of destabilization of enzymes.
This paper presents a visual specification environment EVE and its underlying executable specification language P-Eunice. Their primary application field is control systems for, e.g., plants. P-Eunice supports component-based building of specifications. Either logical aspects or physical aspects, or both, can be described formally for each component in P-Eunice. Connection between components is validated in regards to both logical and physical aspects at the time of connection. In conventional approaches to specifications of control systems, physical aspects of entities (e.g., pipes, valves, motors, etc.) that appear in specifications have rarely been taken into consideration. EVE allows non-professional users to build specifications interactively and intuitively by user-friendly graphical, point-and-click interface. Professional users are also provided full access to the underlying P-Eunice language.
A new 19 channel SQUID magnetometer system has been developed for research use in order to measure the neuromagnetic fields originating from cortices of human brain. This is the total hardware system consisting of 19 SQUID sensors with detecting coils, readout electronics, a liquid helium dewar, a gantry, and an electro-magnetically shielded room. The detecting coils cover an area of 15 cm radius circle. The dewar is newly designed for low consumption of liquid He, and we used fine stainless steel leads for low thermal conduction between the sensors and room temperature electronics. The system could work for a week with one time supply of liquid He. The noise characteristics, including both time and frequency domain, of all channels were measured. The power spectrums of the noise field are under 10fT/_??_Hz at 30-100Hz and under 18fT/_??_Hz at 1-30Hz. Some other peaks such as 27, 30, 50, and 60Hz are observed at several channels, suggesting power line noise and vibrations of sensors. An alpha rhythm occurring from a subject's head was recorded with the amplitude of about 1 pTpp. From these results, the system has a sufficient ability to measure magnetic fields from human brain.
Electromagnetic devices such as superconducting magnets, magnetically levitated vehicles and magnetic resonance imaging(MRI) create strong magnetic fields within their immediate vicinity. This has generated some concerns over the effects that these fields may have on the outside environment and in particular on living organisms. 50/60Hz magnetic fields are of special concern because living organisms are exposed to them on a continuing basis. We investigate the influence of a strong 60Hz AC magnetic field of 1.2T on organisms. The high AC magnetic field is generated by using a multilayer eddy-current type AC magnetic generator developed in our laboratory. In this paper, in vitro experiments were performed with biochemical reactions, enzyme and restriction endonuclese activities. As a result, the magnetic field inhibited catalase activity slightly only in biochemical reactions. Other reactions such as β-galactosidase activity and restriction endonuclese activity were not influenced at all. The results suggest that high 60Hz AC magnetic fields may influence biological functions in some organisms.
In the study of clarifying the biological effects caused by ELF (Extremely Low Frequency) magnetic fields, we have concentrated on induced currents because the induced current is considered an inner index of outer magnetic fields. By surveying the results of animal experiments, we consider that it is significant to clarify the difference of induced current distribution inside the living body, when exposed to various kinds of AC magnetic fields, for example, linearly and circularly polarized magnetic fields. For this purpose, the methods used to estimate induced current distribution which include measurement (probe method) and calculation (charge simulation method) were developed and applied to an inhomogeneous saline model which simulates the living body. These methods were verified by comparing them with the conventional calculation method and it is feasible for these method to be used in estimating induced current distribution by several kinds of magnetic fields.
Recently magnetic-field measurements of the brain have become a useful tool to study higher brain function. The purpose of this study is to propose source models on the brain during both memory and identification tasks. The components of magnetic fields perpendicular to the surface of the head were measured by using a whole cortex type of dc SQUID with a third-derivative gradiometer. We observed the extremely slow components of MEG activities during both the memory and identification tasks. We estimated the sources using two current dipoles, and compared the two cases.
The purpose of this study is to propose a model in which both magnetoencephalogram (MEG) and electroencephalogram (EEG) activities evoked by color imagination are treated simultaneously. The components of magnetic fields perpendicular to the surface of a head were measured by using a dc SQUID with a first-derivative gradiometer. We observed that both MEG and EEG activities were effected by color imagination. The power spectrum of MEG evoked by color imagination showed a single sharp peak at 11Hz. In contrast, the power spectrum of EEG showed two peaks at 9 Hz and 11 Hz. The EEG topography showed that the spectrum component at 11Hz dominated in the occipital region. We proposed a two-dipole model of color imagination using the 14 points of EEG activities. The dipoles were estimated in the visual cortex.
In the source localization of brain activity by MEG (Magnetoencephalogram), spherical model using single dipole is usually used. Since the human head is not spherical, volume current also contributes to the MEG. There is a possibility of improving the accuracy of the source localization in consideration of volume current. We investigated the effects of volume current on MEG by experiment and computer simulation. A single layer hemispherical phantom was used as the model of the human head. A vector magnetometer was used in the measurement of MEG. The magnetic field by volume current was calculated by the boundary element method. The calculated MEG agreed with the measured MEG. It is shown that MEG is greatly influenced in the inhomogeneous part, bottom part of hemisphere by volume current. We simulated how volume current effects on MEG depending on the dipole position. The effect decreases as the dipole moves to the top of hemisphere.
Magnetoencephalograms (MEGs) recorded with a 37-channel SQUID magnetometer were used to detectregional changes in spontaneous cortical activity accompanying a short-term memory scan. Graphical identification (GI) and phonemical identification (PI) for the same probe were required when subjects scan memory in a Sternberg paradigm. Japanese kana-characters were used as the probe and target items in the experiment. For two subjects, reaction time (RT) increased linearly with memory set size (MSZ). The slope of the regression line relating RT to MSZ in the GI task was significantly larger (p<0.001) than the one in the PI task. The spontaneous cortical rhythms in the alpha (8-13Hz) band were found to be suppressed while subjects scanned memory for visually presented probe characters. The largest suppression in the alpha band was observed at the occipital region. The suppression time (ST) of the variance in the alpha band measured at the occipital region increased linearly with RT in the GI task, whereas the ST was invariable in the PI task.
Biomagnetic sources composed of a small number of significant current dipoles often play an important role in clinical applications. This paper describes how to reconstruct such sparse dipole distribution from externally measured biomagnetic fields. After a brief review of the original Selective Minimum-Norm (SMN) method, chance constraints are introduced. These constraints take into account the probability density function of the noise and represent how strictly we should obey the measurements. Thus, chance-constrained SMN method allows us to deal with noisy data with S/N ratios lower than 10dB; computer simulation gave desirably sparse solutions without any explicit source models.
To investigate the electrical activity in the human heart by the electrocardiogram (ECG) is one of the inverse source problems which are difficult to get a unique solution. This paper proposes an approach to identifying the electrical activity in the human heart by measuring both of the local magnetic and electric fields. As a result, it is revealed that our method makes it possible to show the distinguished different power distributions depending on the human hearts.
A few reports point to pulmonary exposure to GaAs dust as a potential occupational health hazard. In vivo pulmonary toxicity, immunotoxicity and effects on porphyrin metabolism have been demonstrated in animals exposed to GaAs. A rapid decrease in the magnetic field after magnetization of the thorax of animals intratracheally instilled with magnetic particles has been noted and designated as “relaxation”. In the first part of study, in vivo experiment, delayed relaxation was observed in rabbits exposed to GaAs. In the latter part of study, in vitro experiment, alveolar macrophages adhered to glass in wells were exposed to iron oxide with or without GaAs in culture medium. Rapid relaxation was observed in the sample of GaAs free medium, whereas relaxation for the specimen with GaAs was delayed. GaAs impaired relaxation dose-dependently. In vivo cellular magnetometry appears applicable to evaluate toxicity of chemical substance on phagocytic cells.
This study investigates whether the metamorphosis of a frog (Rana joponica) is influenced by static magnetic fields. Two groups of tadpoles are grown up and metamorphosed in static magnetic fields which are produced by ferrite magnets placed under the vessels. One group is exposed to upward magnetic fields, and the other is exposed to downward fields. The group exposed with upward magnetic fields shows that their growth and metamorphosis are inhibited significantly compared with the control group, whereas the group exposed with downward magnetic fields shows that their growth and metamorphosis are not influenced by the magnetic fields.
In this paper, we investigated the flux noise generated from a copper covering a niobium-titanium alloy wire. The flux noise from a twisted pair of wires wound with niobium-titanium alloy wire wrapped with copper (Nb-Ti/Cu) is both measured and calculated for various wire lengths. Flux noise is confirmed to be related to the wire length. The flux noise from a first-order gradiometer wound with Nb-Ti/Cu wire is also measured and calculated. And we also developed a new method for making the superconducting connection between the SQUID input coil and pick-up coil wound with superconducting wire. By driving the SQUID at the bias current below the critical current, a high flux-to-voltage transfer function and a low flux noise is achieved. This gradiometer has a radius of 7mm, a baseline of 50mm, and the length of the twisted pair of wires is 60mm. The flux resolution is 1.58μΦ0/Hz1/2 and the magnetic field resolution is 3.0 fT/Hz1/2.
We have demonstrated a gradiometer using a 20-dc SQUID array for biomagentic measurement. Because this SQUID array has a large voltage swing, it can be directly connected to room temperature amplifier without imped-ance matching circuit such as transformer, resonator or additional positive feedback. The voltage swing of the array has been 1.7 mV and the maximum voltage to flux transfer function has been 9.5 mV/Φo. The flux noise of the series SQUID array has been 0.56μ Φo/√ Hz in a flux locked mode, and the field sensitivity of the gradiometer which has an planner type pickup coil of 10 mm square has been 2.9 fT/√ Hz at 1kHz.
In this paper, 3-D magnetic field analysis of magnetically shielded room (MSR) for biomagnetic measurements is carried out by using the finite element method taking into account eddy currents to investigate magnetic shielding effect. First, the method of analysis is verified by comparing results computed with those measured in a hexagonal type of MSR which is actually installed. The spatial distribution of magnetic field in MSR which is computed by the 3-D analysis is fairly in agreement with those measured qualitatively. Second, the 3-D magnetic field analysis of a brick type of MSR is carried out to discuss the relationship between the magnetic field distribution and eddy currents in detail, and the following results are obtained: (1) A gap between a door and wall which isolates them magnetically and electrically does not affect the magnetic field distribution at low frequency of less than about 1Hz, (2) At frequency of more than several ten Hz, the magnetic field distribution becomes non-uniform because of undesirable eddy currents due to the gap, especially when the magnetic noise is applied in the vertical direction, (3) A frame which electrically connects edges of isolated layers of shielding plates at a doorway causes the non-uniform magnetic field distribution, (4) The shielding effect should be accessed three-dimensionally, and (5) The 3-D magnetic field analysis taking into account eddy currents is fairly effective for the design of MSR.
Pose estimation of known quadratic surfaces from possibly noisy data is important in robotics, and there is room for generating improved algorithms which achieve global optinia, and if possible on line. Current algorithms frequently converge to local minima of the performance index and are unsuited for online applications because of the intensive computer effort required. Algebraic solutions are first proposed based on a two stage optimization involving least squares estimation, or better the method of instrumental variables, and 3×3 matrix diagonalizations. The resulting estimates are optimal in a reasonable sense and can be implemented on line. In the noise free, finite data case, or in the infinite data, white noise case the results give zero error, and small error for the case of finite data and small noise. The first stage of the procedure ignores a priori knowledge of the surface shape and estimates the quadratic coefficient matrix via least squares or the method of instrumental variables. The second stage exploits the priori shape information to estimate the pose of the object using diagonalization of 3×3 matrices.
A computational analysis of shortest-route methord is one of the most important problems in computational geometry. In this paper, an inference model which measures escapability from various types of 2-dimensional network-mazes by taking some searching rules of choosing routes into consideration is proposed, and the model aims to compare by the formularization of the escapability of the different types of mazes, and to find the most effective escape routes on the location. By applying this model to three different kinds of mazes, it is ascertained that this model is of use for the following purposes. 1. To measure the escapability from a maze. 2. To compare metricaliy escapabilities of various kinds of mazes. 3. To know the most escapable arrangement of goalpoints and the least escapable arrangement of goalpoints in a maze.
These days, it has been pointed that ultrasonic range finder is very useful for some purpose in robot navigation. The usages of ultrasonic range finders are, for example, recognition of the type of a crossing, detection the obstacle and avoidance of it and so on. This paper represents some features of an array type and a rotary type ultrasonic range finder for autonomous mobile robot. And by using these ultrasonic sensor systems, we describe a means of recognizing workspace, and avoiding obstacles among others in detail. We have made some experiments with 2 types ultrasonic range finder. Experimental results verify its effectiveness in a mobile robot navigation.
Petri nets have been developed by many researchers as a useful form for describing and analyzing the structure of discrete event systems. In applying Petri nets into practical systems, finding firing sequences for the reachability problem can be regarded as one of the most important issues. In general, the reachability problem has been approached with the reachability tree method or the incidence matrix method. These two different types of approaches have, however, their respective drawbacks, i.e. state space explosion in exhaustive enumeration processes, and the presence of spurious integer solutions for a net state equation. The purpose of this study is to develop a new method for finding firing sequences for the reachability problem of Petri nets. First, defining an extended incidence matrix equation, the proposed method is formulated as an optimization problem whose non-negative integer solution can provide sufficient information on the firing sequences of the transitions. Secondly, the optimization problem is solved through a well-established linear programming technique without the condition of integrity. Evaluating the reduced-costs of the respective variables, and examining whether each variable is active or inactive, we can systematically sort out of the irrelevant variables. In other words, before proceeding into a problem having combinatorial complexity, the proposed method attempts to make as much reduction as possible in the number of the variables on the basis of the algebraic properties of the incidence matrix equation. In our paper, we also discuss the usefulness of the proposed method by evaluating a simple computational example.
When the travelling salesman problem (TSP) is solved by the Hopfield Neural Network with analog output, it is difficult to determine two parameters of its energy function, that is, a penalty factor and a temperature. In this paper, by numerical experiments, we investigate the influence of both parameters upon the quality of _??_ solutions, and propose a method where the penalty factor is controlled so as to obtain a feasible solution and the temperature is optimized by the golden section search. Computational results for the TSPs with random 5_??_40 cities, the proposed method improves the quality of the solution by 48% on the average, compared with the conventional method.