Showing papers by "University of Electro-Communications published in 1996"

Chemical nature of the light emitter of the aequorea green fluorescent protein

Abstract: The jellyfish Aequorea victoria possesses in the margin of its umbrella a green fluorescent protein (GFP, 27 kDa) that serves as the ultimate light emitter in the bioluminescence reaction of the animal. The protein is made up of 238 amino acid residues in a single polypeptide chain and produces a greenish fluorescence (lambda max = 508 nm) when irradiated with long ultraviolet light. The fluorescence is due to the presence of a chromophore consisting of an imidazolone ring, formed by a post-translational modification of the tripeptide -Ser65-Tyr66-Gly67-. GFP has been used extensively as a reporter protein for monitoring gene expression in eukaryotic and prokaryotic cells, but relatively little is known about the chemical mechanism by which fluorescence is produced. To obtain a better understanding of this problem, we studied a peptide fragment of GFP bearing the chromophore and a synthetic model compound of the chromophore. The results indicate that the GFP chromophore consists of an imidazolone ring structure and that the light emitter is the singlet excited state of the phenolate anion of the chromophore. Further, the light emission is highly dependent on the microenvironment around the chromophore and that inhibition of isomerization of the exo-methylene double bond of the chromophore accounts for its efficient light emission.

Results of ultra-low-frequency magnetic field measurements during the Guam Earthquake of 8 August 1993

Abstract: We report the results of measurements of ultra-low-frequency magnetic noise during a large earthquake (Ms=7.1) at Guam of 8 August, 1993 (depth ∼60 km). The ULF observing system is located in the Guam Island, about 65 km from the epicenter. Several distinct features of this analysis are summarized. (1) We have proposed rather sophisticated statistical analyses (monthly mean, standard deviation) in order to estimate the wave intensity and polarization (i.e. ratio Z/H). (2) A comparison between the ULF wave activity and ΣKp, is useful in distinguishing between the space geomagnetic pulsations and non-space emissions. (3) Then, the use of the ratio (Z/H) is found to be of essential importance in discrimating the emissions presumably of seismic origin from space plasma waves. (4) The statistical analysis of the temporal evolution of this ratio, has yielded that it shows a broad maximum only about one month before the earthquake, and this suggests that the emissions during this period are very likely to be magnetic precursors. (5) The temporal variation of Z component is similar to that for the Loma Prieta earthquake such that it shows a broad maximum ten days ∼ two weeks before the earthquake and another increase a few days before the earthquake. (6) The emissions presumably associated with the earthquake are of noise-like nature, and their main frequency is 0.02 ∼ 0.05 Hz (with maximum intensity ∼0.1 nT).

Tunneling conductance of connected carbon nanotubes

Abstract: A three-dimensional structure of two carbon nanotubes (CN) joined by a connecting region containing a pentagon and heptagon pair is given by the use of a projection method. The connecting joint is uniquely determined for the given two chiral vectors of CN by a vector which defines a three-dimensional dihedral angle. The tunneling conductance is calculated for a metal-metal CN junction and a metal-semiconducting CN junction. The calculated results clearly show that these junctions work as the smallest semiconductor devices.

Effects of antenna directivity and polarization on indoor multipath propagation characteristics at 60 GHz

Abstract: In millimeter-wave indoor communications systems, the radiation patterns and polarizations of the antennas at base stations and remote terminals have a significant influence on channel characteristics. The work reported in this paper investigated the effects of the radiation patterns of the antennas at remote terminals on multipath propagation characteristics. These effects were investigated by indoor propagation measurements at 60 GHz conducted in a modern office room and by ray-tracing simulations based on geometrical optics. Multipath channel characteristics are compared in terms of impulse responses and their root-mean-square (rms) delay spreads for an omnidirectional antenna and for three directive antennas with different beam widths. From the results of measurements and ray-tracing simulations, the use of a directive antenna at the remote terminal is demonstrated to be an effective method of reducing the effects of multipath propagation. Further reduction in the multipath effects is found to be achieved by the use of circular polarization instead of linear polarization with the directive antennas.

Text Segmentation Based on Similarity between Words

Abstract: This paper proposes a new indicator of text structure, called the lexical cohesion profile (LCP), which locates segment boundaries in a text. A text segment is a coherent scene; the words in a segment are linked together via lexical cohesion relations. LCP records mutual similarity of words in a sequence of text. The similarity of words, which represents their cohesiveness, is computed using a semantic network. Comparison with the text segments marked by a number of subjects shows that LCP closely correlates with the human judgments. LCP may provide valuable information for resolving anaphora and ellipsis.

Similarity between Words Computed by Spreading Activation on an English Dictionary

Abstract: This paper proposes a method for measuring semantic similarity between words as a new tool for text analysis. The similarity is measured on a semantic network constructed systematically from a subset of the English dictionary, LDOCE (Longman Dictionary of Contemporary English). Spreading activation on the network can directly compute the similarity between any two words in the Longman Defining Vocabulary, and indirectly the similarity of all the other words in LDOCE. The similarity represents the strength of lexical cohesion or semantic relation, and also provides valuable information about similarity and coherence of texts.

A new versatile electron-beam ion trap

Abstract: We have constructed an electron-beam ion trap (EBIT) to facilitate the creation and study of highly charged ions. After a brief introduction to EBITs in general, we describe the design of the new device, highlighting its unique features. Some preliminary results are presented which demonstrate the devices capability to produce and study highly charged ions.

Many-electron ground states in anisotropic parabolic quantum dots.

Abstract: The many-electron ground states in anisotropic parabolic quantum dots with the cylindrical symmetry are investigated by means of an unrestricted Hartree-Fock method. The calculated ground state of a large quantum dot is completely spin polarized up to 12 electrons, while the spin configuration of a small quantum dot obeys the Hund rule. The chemical potential and the differential capacitance of quantum dots are calculated as well. The capacitance shows the characteristic oscillation with an electron number caused by the shell structures of single-electron energy levels which are determined self-consistently with the spin configuration of the many-electron ground state. On the differential capacitance, the effect of the vertical extent of a dot is also studied. It becomes larger as the lateral extent of a quantum dot decreases, maintaining the same ratio to the vertical extent. Further, the effect in a small dot becomes especially enhanced at the special number of electrons, N=2,5,10,17,..., due to the shell structure. The excited states, which have different quantum numbers from the ground state, are also studied. \textcopyright{} 1996 The American Physical Society.

Anomalies in the Sub-ionospheric VLF Signals for the 1995 Hyogo-ken Nanbu Earthquake.

Abstract: The sub-ionospheric VLF Omega signal transmitted from Tsushima, Japan (geographic coordinates: 34°37'N, 129°27'E) is continuously received at Inubo (35°42'N, 140°52'E). The signal's propagation characteristics (especially phase) exhibited abnormal behavior (especially around the sunrise and sunset local times) a few days before the main shock of the 1995 Hyogo-ken Nanbu earthquake. We found from the computer simulation of VLF signal propagation that the observed effect can be explained by a decrease of about 0.7 km of VLF reflection height at the atmosphere-ionosphere boundary.

Calculation of Demagnetizing Field Distribution Based on Fast Fourier Transform of Convolution

Abstract: It is confirmed that the calculation of the demagnetizing field in micromagnetic simulations can be accelerated significantly by using the discrete convolution theorem and the fast Fourier transform (FFT). When the magnetization distribution is periodic, application of the theorem to the demagnetizing field calculation is straightforward. Unlike the previously reported FFT method which is based on the continuous Fourier transform of the demagnetizing field, the method can also be used in the case of non-periodic magnetization structures. It is also confirmed that the result obtained using the new FFT method coincides with that of the conventional direct method, as expected. The principle of calculation and the results of one- and two-dimensional calculations which show the validity and effectiveness of the developed method are presented.

Fade statistics in Nakagami fading environments

Abstract: The Nakagami fading model is becoming more prevalent in performance analysis and other studies related to mobile radio communications. Fade statistics is studied for the Nakagami fading model. Closed form expressions are given for the rate of occurrence of fades, as well as the average time duration of fades and interfades. Approximations for these quantities are also deduced for some diversity reception schemes.

Simultaneous Determination of Ruthenium, Palladium, Iridium, and Platinum at Ultratrace Levels by Isotope Dilution Inductively Coupled Plasma Mass Spectrometry in Geological Samples

Abstract: Inductively coupled plasma mass spectrometry employing isotope dilution quantification (ID-ICPMS) has been applied to determine trace levels of Ru, Pd, Ir, and Pt in geological materials. Accuracy, precision, and reproducibility are better than those obtained by other ICPMS calibration methods. For this purpose, it is important to achieve isotopic equilibrium by use of a microwave oven. Due to the trace concentration of these elements in geological samples, a method for separation of these elements from the matrix has been developed, taking advantage of formation of strong anionic complexes of Pd, Pt, Ru, and Ir in a hydrochloric acid medium. Since doubly charged complexes, MCl62-, are strongly sorbed by the anion exchange resin, whereas triply charged complexes, MCl63-, are weakly bound, various oxidizing agents were examined in this study to convert the lower oxidation states of these elements to their higher oxidation states. Systematic studies on retention and elution of these elements were carried ou...

A 718-kb DNA Sequence of the Escherichia coli K-12 Genome Corresponding to the 12.7–28.0 min Region on the Linkage Map

Abstract: The 718,122 base pair sequence of the Escherichia coli K-12 genome corresponding to the region from 12.7 to 28.0 minutes on the genetic map is described. This region contains at least 681 potential open reading frames, of which 277 (41%) have been previously identified, 147 (22%) are homologous to other known genes, 139 (20%) are identical or similar to the hypothetical genes registered in databases, and the remaining 118 (17%) do not show a significant similarity to any other gene. In this region, we assigned a cluster of cit genes encoding multienzyme citrate lyase, two clusters of fimbrial genes and a set of lysogenic phage genes encoding integrase, excisionase and repressor in the e14 genetic element. In addition, a new valine tRNA gene, designated valZ, and a family of long directly repeated sequences, LDR-A, -B and -C, were found.

Brillouin scattering study in the GaN epitaxial layer

Abstract: We have investigated the elastic properties of a GaN epitaxial layer on a sapphire substrate by Brillouin scattering in the backward and 90° scattering geometries. A sample of high optical quality grown by the two-flow MOCVD method with a complex structure of In 0.05 Ga 0.95 N(0.05 μm)/GaN(2 μm)/sapphire was used. The weak spectra were not simple due to the boundaries and the InGaN thin film. The elastic constants of GaN were estimated and compared with those obtained from X-ray diffraction.

The influence of location of electrode on muscle fiber conduction velocity and EMG power spectrum during voluntary isometric contraction measured with surface array electrodes.

Abstract: A surface array electrode was used to investigate muscle fiber conduction velocity (MFCV) and EMG power spectrum during voluntary isometric contraction of m. biceps brachii. The mean power frequency (MPF) and the total power (TP) at various locations of the muscle were obtained from the power spectrum. MFCVs at various locations of the muscle were measured directly using the averaging method. The values of MPF, TP and MFCV were identified with respect to the electrode locations on the m. biceps brachii. MPF was shown as high near the end-plate and low near the tendon of the muscle during contraction of 40% of isometric maximum voluntary contraction (MVC). TP showed low value near the end-plate and the tendon of the muscle fiber and different values at different location setting electrode during voluntary isometric contraction. TP at each location on the muscle surface increased when the contraction levels increased in the contractions range of 20 to 60% MVC. MFCVs showed a high value near the end-plate and the tendon of the muscle during the contraction of 40% MVC. These results indicated that MPF, TP and MFCV at different locations on the muscle were different along the length of the muscle fiber.

CO2 reforming and partial oxidation of methane

Abstract: CO2 reforming and partial oxidation of CH4 were investigated on different supported noble metal and Ni catalysts. A detailed thermodynamic analysis was performed for both reactions. The observed reaction behaviour can be predicted by thermodynamics. Product selectivity is catalyst independent, the role of the catalyst is to bring the reactants to approach equilibrium. The partial oxidation is a two-stage process, total oxidation of CH4 is followed by CO2 and H2O reforming of the remaining CH4. A staged addition of O2 to the reactor is tested and recommended. TPSR show that the catalyst surface for CO2 reforming was highly covered with carbonaceous species of four different types; two were identified as reactive intermediates.

Self-Induced Vibration of a Water Drop Placed on an Oscillating Plate

Abstract: Vibration of a water drop placed on a vertically oscillating plate was observed, and the amplitudes and frequencies of the plate were measured with which the drop showed large amplitude vibrations. A special cloth was used so that the drop did not wet the plate. The results are compared with a simple theoretical prediction based on the Mathieu equation. The experimental data are shown to lie within the unstable growing region derived from the theory.

Crystallographic heterodyne phase detection for highly sensitive lattice-distortion measurements

Abstract: Noting the structural similarity between a distorted lattice in a crystal and a spatially phase-modulated fringe pattern in optical metrology, we propose a crystallographic lattice heterodyne technique. The technique detects lattice distortions as spatial phase modulations, where the phase change by 2π corresponds to the displacement of atoms or lattice points by a distance equal to the lattice constant. By virtue of heterodyne detection, the technique has the potential for determining the lattice distortions to several hundredths of the lattice constant.

Degradation of moving‐image quality in PDPs: Dynamic false contours

Abstract: When moving images are displayed on matrix displays which reproduce gray levels utilizing pulse-number/width-modulation techniques, degradation of the gray levels and colors are often observed. The degradation originates from a temporal non-uniformity of the light-emission pattern, which is transformed into a spatial non-uniformity of the light emission due to an after-image effect of the eyes, which follow the image motion. The degradation becomes appreciable when the product of the speed of the viewing point on a screen and the light-emission period of a pixel is greater than the pixel pitch. The degree of degradation is also affected by the pixel arrangement; disturbances for the stripe arrangement are worse than those for the triangle arrangement. The temporal uniformity is degraded when the major light-emitting blocks of the pulse-number/width-modulation change. The uniformity can be improved by dividing the blocks of the major bits. It was analytically verified that the perceived luminance of periodic light emission is proportional to the emission duty factor (which coincides with Talbot-Plateau's law) and also to the integral of f(t)dt from zero to infinity, independent of decay shape, f(t), of the after-image.

Fuzzy modeling and control of chaotic systems

Abstract: In this paper we explore the interaction between fuzzy control systems and chaos. First we show that fuzzy modeling techniques can be used to model chaotic dynamical systems. Then we apply some of the newly developed fuzzy control design techniques to the control of chaotic systems. The design procedure is conceptually simple, natural and computationally efficient. Therefore the proposed fuzzy methodology represents a systematic and effective framework for modeling and control of chaotic systems. The method is illustrated by application to Chua's circuits.

On the construction of maximal prefix-synchronized codes

Abstract: We present a systematic procedure for mapping data sequences into codewords of a prefix-synchronized code (PS-code), as well as for performing the inverse mapping. A PS-code, proposed by Gilbert (1960), belongs to a subclass of comma-free codes and is useful to recover word synchronization when errors have occurred in the stream of codewords. A PS-code is defined as a set of codewords with the property that each codeword has a known sequence as a prefix, followed by a coded data sequence in which this prefix is not allowed to occur. The largest PS-code among all PS-codes of the same code length is called a maximal prefix-synchronized code (MPS-code). We develop an encoding and decoding algorithm for Gilbert's MPS-code with a prefix of the form 11...10 and extend the algorithm to the class PS-codes of which the prefix is self-uncorrelated. The computational complexity of the entire mapping process is proportional to the length of the codewords.

Logical reversibility in quantum measurement: General theory and specific examples

Abstract: A measurement process is logically reversible if the premeasurement density operator of the measured system is uniquely determined from the postmeasurement density operator and the outcome of the measurement. This paper analyzes the necessary and sufficient condition for a measurement process to be logically reversible and discusses specific examples on quantum-nondemolition measurements, quantum counting, and measurement of spin systems. It is shown that for any sharp measurement we can construct a logically reversible measurement that continuously approaches the sharp measurement with a decrease in the measurement error. A general condition for a measurement process to be reversed by another with a nonzero probability of success is given, and the implications of such physical reversibility are discussed. \textcopyright{} 1996 The American Physical Society.