Tadakuni Murai

Electrical Impedance Computed Tomography Based on a Finite Element Model

A simulation study of electrical impedance computed tomography is presented. This is an inverse problem. A field is discretized by the finite element method and an iterative approach derived from the sensitivity theorem is examined for leads taken on the field surface. It is shown that the conductivity distribution in the field can be estimated from the impedance data obtained for the body surface leads. Simulation suggests the availability and the limitation for impedance plethysmography application. The finite element model must be chosen properly to provide the unique solution.

Objective picture quality scale for video coding

To design the image communication system including human visual system systematically, the objective quality estimation method of the picture based on the model of the human vision is necessary. We develop the objective picture quality scale (PQSvideo) for video coding considering the relation between the physical distortion factors and the psychological picture estimation factors. The obtained cross correlation coefficient between the PQSvideo and the mean opinion score (MOS), becomes 0.978.

Quality evaluation model of coded stereoscopic color image

To consider the quality of service for stereoscopic image through the network, it is necessary to develop a quality evaluation method for coded stereoscopic image. We propose a quality evaluation model of the coded stereoscopic color image. This evaluation model considers not only the distortions of the edge region and smooth region but also the texture features of the left image. In addition, this model takes into account the disparity information between the left and right images. Instead of the disparity compensated coded image, we employ the JPEG coded image for the subjective assessment test. As the results, the evaluation model is useful for coded stereoscopic image.

Boundary element models of the vocal tract and radiation field and their response characteristics

Abstract Accurate vocal tract models become increasingly important for the investigation of speech analysis, synthesis and identification. The geometrical configuration of the vocal tract is determined by the position of the vocal tracts wall in association with the movement of the jaws and the mouth. One-dimensional models cannot provide the direct correspondence of the geometrical shape with its acoustical characteristic properly, taking the wall impedance and the end conditions into account. The vocal tract is a bent tube, and sound radiates to the outer space from the mouth opening. Here we demonstrate more realistic three-dimensional models of the vocal tract and the head made of boundary elements. The vocal tracts transmission responses and the sound field around the head are discussed separately, showing the capability of the boundary element models.

Passive Millimeter-Wave Microscopy

A new type of millimeter-wave imaging technique, passive millimeter-wave microscopy is proposed and demonstrated. Passive millimeter-wave imaging techniques when combined with scanning near-field microscopy enable direct observation of millimeter-wave signals thermally emitted from the viewed object with a spatial resolution below the diffraction limit. Details of our passive microscope system operating at Ka-band frequencies are explained. Millimeter-wave images obtained with the system are presented to demonstrate the feasibility of this new imaging technique.

Evaluation model considering static-temporal quality degradation and human memory for SSCQE video quality

To perform Quality of Service (QoS) control of video communication more efficiently, it is necessary to develop an objective quality evaluation method for coded video. Many proposed conventional methods to obtain video quality require the availability of both reference and processed video sequence. However, in case of re-encoding the coded video stream at the receiver side where reference video sequence is not present, it is impossible to do such a full-reference evaluation. Therefore, we have developed a video quality evaluation model by using reduced reference for evaluated value obtained by SSCQE method. In this approach, we use some features extracted from reference video. It is called reduced-reference method by VQEG. Transmitting these features with coded video, the proposed model can estimate the video quality, even in the absent of the full original video in the decoder side. The video quality rating obtained from the proposed model shows good agreement with subjective quality.

Region segmentation using K-mean clustering and genetic algorithms

One of the hard problems in image recognition and understanding is region segmentation. A traditional segmentation method such as clustering is not fully useful for any image, because of the initial values of clusters and the evaluation functions of segmented clusters affect the results of region segmentation. To solve this problem, we introduce the genetic algorithm (GA) for clustering. The experimental result shows the satiable results of region segmentation which have been achieved by applying GA.<<ETX>>

A millimeter-wave quasi-optical grid phase shifter using liquid crystal

A new type of millimeter-wave quasi-optical variable phase shifter which exploits the dielectric anisotropy of liquid crystal (LC) materials is presented. The device is operated in transmission mode and consists of inductive and capacitive metal grids, each patterned on a dielectric substrate, which are separated by a thin layer of LC. The grids together with the LC form a parallel resonant circuit. Prototype devices with a 25-µm-thick LC layer for use at a millimeter-wave frequency of 50GHz were designed and fabricated. Experiments performed at U-band frequencies show that a phase shift of 7.8° is obtained with a low insertion loss of ∼ 0.6dB at the resonant frequency by applying a control signal of 20V. Good time response for the device is demonstrated. It is suggested that the phase shift attainable with the device can be further enhanced by using LC materials with larger dielectric anisotropy and/or thinner dielectric substrates.

Quality evaluation method considering time transition of coded video quality

We propose the new quality evaluation method of coded video which is considering the time transition of video quality. The evaluated quality value is computed as the weighted mean of the frame quality by using the weighted function which is derived from the short-term characteristic of human memory. In this case, the time transition of video quality is obtained from the series of the frame quality of whole frame. The optimal weighted function for each coded video is found by using the Genetic Algorithm. The obtained video quality has a good agreement with MOS.

Thunderstorm tracking system using neural networks and measured electric fields from few field mills

The paper presents a novel system to asses quickly the direction of thunderstorm by using a few field mills on the ground. As opposed to traditional methods using expensive radar systems to detect thundercloud movement, the presented method simply uses the electric waveforms detected by the field mills and, by using a neural network of suitable complexity, can determine the thunderclouds direction with reasonable accuracy. The neural system is trained with data obtained from the simulation of thundercloud dynamics using parameters observed through experiments. Through extensive testing, it is found that the presented system can reasonably track the direction of the thunderstorm as it propagates while dynamically changing its parameters, and, thus, offers the possibility of creating a practical system. Two types of neural networks are developed and their efficiencies compared.