Showing papers by "University of Electro-Communications published in 2005"

Micromagnetic understanding of current-driven domain wall motion in patterned nanowires

Abstract: In order to explain recent experiments reporting a motion of magnetic domain walls (DW) in nanowires carrying a current, we propose a modification of the spin transfer torque term in the Landau-Lifchitz-Gilbert equation. We show that it explains, with reasonable parameters, the measured DW velocities as well as the variation of DW propagation field under current. We also introduce coercivity by considering rough wires. This leads to a finite DW propagation field and finite threshold current for DW propagation, hence we conclude that threshold currents are extrinsic. Some possible models that support this new term are discussed.

Spontaneous emission of a cesium atom near a nanofiber: Efficient coupling of light to guided modes

Abstract: We study the spontaneous emission of a cesium atom in the vicinity of a subwavelength-diameter fiber. We show that the confinement of the guided modes and the degeneracy of the excited and ground states substantially affect the spontaneous emission process. We demonstrate that different magnetic sublevels have different decay rates. When the fiber radius is about $200\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, a significant fraction (up to 28%) of spontaneous emission by the atom can be channeled into guided modes. Our results may find applications for developing nanoprobes for atoms and efficient couplers for subwavelength-diameter fibers.

Minority carrier diffusion length in GaN: Dislocation density and doping concentration dependence

Abstract: We investigated the minority carrier diffusion length in p- and n-GaN by performing electron-beam-induced current measurements of GaN p–n junction diodes. Minority electron diffusion length in p-GaN strongly depended on the Mg doping concentration for relatively low dislocation density below 108cm−2. It increased from 220to950nm with decreasing Mg doping concentration from 3×1019to4×1018cm−3. For relatively high dislocation density above 109cm−2, it was less than 300nm and independent of the Mg doping concentration. On the other hand, the minority hole diffusion length in n-GaN was shorter than 250nm and less affected by the dislocation density and Si doping concentration. We discuss the doping-concentration and dislocation-density dependence of minority carrier diffusion length.

Holographic manipulation of nanoparticle distribution morphology in nanoparticle-dispersed photopolymers

Abstract: We report on experimental verification of mass transfer of nanoparticles during holographic recording in nanoparticle-dispersed photopolymers. Through direct observations of the microscopic structure of recorded holograms as well as optical measurements of the phase shift between the light interference pattern and a recorded hologram we find that holographic exposure causes nanoparticles to be redistributed from bright to dark regions, leading to periodic assembly of nanoparticles and thereby to formation of high-contrast holograms.

Nanofiber-mediated radiative transfer between two distant atoms

Abstract: We study spontaneous emission from a pair of two-level atoms near a nanofiber. We demonstrate a substantial radiative exchange between distant atoms mediated by the guided modes of the nanofiber. The exchange is shown to lead to increased and decreased lifetimes of the subradiant and superradiant states, respectively. Our analysis is based on the full quantization of both the radiation and guided modes of the fiber in the framework of the Heisenberg-Langevin theory and the master equation formalism.

Electronic and magnetic properties of BNC ribbons

Abstract: Both electronic and magnetic properties have been studied for hexagonally bonded honeycomb ribbons consisting of B, N, and C atoms, with zigzag edges terminated by H atoms. We have used first-principles total-energy electronic-structure calculations within the local spin-density functional theory. The energy gap of BN ribbons is dominated by the edge states and it decreases monotonically with increasing ribbon width. For metallic BNC ribbons with different zigzag edges, C and BN or NB, the ground state becomes ferrimagnetic; this originates from the coexistence of the border state and the edge state.

Syntheses and structures of hypervalent pentacoordinate carbon and boron compounds bearing an anthracene skeleton--elucidation of hypervalent interaction based on X-ray analysis and DFT calculation.

Abstract: Pentacoordinate and tetracoordinate carbon and boron compounds (27, 38, 50-52, 56-61) bearing an anthracene skeleton with two oxygen or nitrogen atoms at the 1,8-positions were synthesized by the use of four newly synthesized tridentate ligand precursors. Several carbon and boron compounds were characterized by X-ray crystallographic analysis, showing that compounds 27, 56-59 bearing an oxygen-donating anthracene skeleton had a trigonal bipyramidal (TBP) pentacoordinate structure with relatively long apical distances (ca. 2.38-2.46 A). Despite the relatively long apical distances, DFT calculation of carbon species 27 and boron species 56 and experimental accurate X-ray electron density distribution analysis of 56 supported the existence of the apical hypervalent bond even though the nature of the hypervalent interaction between the central carbon (or boron) and the donating oxygen atom was relatively weak and ionic. On the other hand, X-ray analysis of compounds 50-52 bearing a nitrogen-donating anthracene skeleton showed unsymmetrical tetracoordinate carbon or boron atom with coordination by only one of the two nitrogen-donating groups. It is interesting to note that, with an oxygen-donating skeleton, the compound 61 having two chlorine atoms on the central boron atom showed a tetracoordinate structure, although the corresponding compound 60 with two fluorine atoms showed a pentacoordinate structure. The B-O distances (av 2.29 A) in 60 were relatively short in comparison with those (av 2.44 A) in 59 having two methoxy groups on the central boron atom, indicating that the B-O interaction became stronger due to the electron-withdrawing nature of the fluorine atoms.

Trajectory Tracking Control of Snake Robots Based on Dynamic Model

Abstract: In this paper, we derive a dynamic model and a trajectory tracking control law for snake robots, which have passive wheels and active joints, based on the dynamic model. For a trajectory tracking control of snake robots, it is one of the important problem to avoid the singular configuration like a straight line. Using input-ouput linearization for the head position of snake robots based on dynamic model, we can control the head position by PD feedback, but the robot will converge to the singular configuration. In order to solve this problem, we propose a control law that controls shape controllable points for avoiding the singular configuration. Using the proposed control law, the robot can accomplish trajectory tracking of the head position without converging to the singular configuration. Simulation results show the effectiveness of the proposed control law.

Energy-based control of axially translating beams: varying tension, varying speed, and disturbance adaptation

Abstract: In this brief, the investigational results for a robust adaptive vibration control of a translating tensioned beam with a varying traveling speed are presented. The dynamics of beam and actuator is modeled via the extended Hamilton's principle, in which the tension applied to the beam is given as a nonlinear spatiotemporally varying function. The moving beam is divided into two parts, a controlled span and an uncontrolled span, by a hydraulic touch-roll actuator that is located in the middle section of the beam. The transverse vibration of the controlled span is suppressed by the touch-roll actuator, whereas the vibration of the uncontrolled span is treated as a disturbance, and the magnitude of unknown disturbance is estimated. In a proper mathematical manner, the Lyapunov method is employed to design robust adaptive boundary control laws for ensuring the vibration reduction of the nonlinear time-varying system, and also to ensure the stability of the closed-loop system. The effectiveness of the proposed controller is demonstrated via numerical simulations.

Three‐dimensional ionospheric tomography using observation data of GPS ground receivers and ionosonde by neural network

Abstract: [1] In this paper we present a new method based on a Residual Minimization Training Neural Network (RMTNN) to reconstruct the three-dimensional electron density distribution of the local ionosphere with high spatial resolution (about 50 km × 50 km in east/west and 30 km in altitude) using GPS and ionosonde observation data. In this method we reconstruct an approximate three-dimensional electron density distribution as a computer tomographic image by making use of the excellent capability of a multilayer neural network to approximate an arbitrary function. For this application the network training is carried out by minimizing the squared residuals of an integral equation. We combine several additional techniques with the new method, i.e., input space discretization, use of ionosonde observation data to improve the vertical resolution, automatic estimation of the biases of the satellite and the ground receivers by using the parameter estimation method, and estimation of plasmasphere contributions to the total electron content on the basis of an assumption of diffusive equilibrium with constant scale height. Numerical experiments for the actual positions of the GPS satellites and the ground receivers are used to validate the reliability of the method. We also applied the method to the analysis of real observation data and compared the results with ionosonde observations which were not used for the network training.

Depth profile of diffuse reflectance near-infrared spectroscopy for measurement of water content in skin.

Abstract: Background/purpose: The penetration depth of light in diffuse reflectance near-infrared spectroscopy for measuring water content in skin is assessed both from theoretical and experimental points of view. Methods: The Monte Carlo simulation was implemented to investigate the dependencies of the light penetration depth on a source–detector distance. To compare with the simulation results, an in vivo experiment for water contents of skin was performed introducing two different optical fiber probes. Results: It is found that the minimum separation between a source and detector fibers influences largely the measurement depth. The larger separation leads to a deeper measurement depth at a particular wavelength. The measurement depth is also influenced fairly by the absorption coefficient of the tissue. The larger absorption coefficient results in a shallower measurement depth. Conclusion: The correlations between the water contents measured by the optical and capacitance techniques were discussed. The dependencies of the light penetration depth on the source-detector geometry and wavelength are presented.

Chemical Reactivity of Sc3N@C80 and La2@C80

Abstract: Sc3N@C80 has a lower thermal reactivity than La2@C80, although Sc3N@C80 has the same carbon cage (Ih) and oxidation state (C806-) as La2@C80. This result is attributed to the difference in the energy level and distribution of LUMO between Sc3N@C80 and La2@C80.

Ultra-fine grain development in an AZ31 magnesium alloy during multi-directional forging under decreasing temperature conditions

Abstract: Grain refinement of a magnesium alloy, AZ31, was studied in multi-directional forging (MDF) with decreasing temperature from 623 to 423 K. The MDF was carried out up to cumulative strains of around 5 with changing the loading direction during decreasing temperature from pass to pass. The structural changes are characterized by the development of many mutually crossing kink bands accompanied by MDF at low strains, followed by full development of very fine grains at high strains. The dynamic changes in grain size evolved can be expressed by two different power law functions of flow stress for the regions of flow stress above or below around 100 MPa. The MDF under decreasing temperature condition can accelerate the uniform development of much finer grains and the improvement in plastic workability, leading to the minimal grain size of 0.36 μm at a final processing temperature of 423 K. The mechanism of grain refinement is discussed in detail.

Digitally Signed Document Sanitizing Scheme with Disclosure Condition Control

Abstract: A digital signature does not allow any alteration of the document to which it is attached. Appropriate alteration of some signed documents, however, should be allowed because there are security requirements other than that for the integrity of the document. In the disclosure of official information, for example, sensitive information such as personal information or national secrets is masked when an official document is sanitized so that its nonsensitive information can be disclosed when it is demanded by a citizen. If this disclosure is done digitally by using the current digital signature schemes, the citizen cannot verify the disclosed information correctly because the information has been altered to prevent the leakage of sensitive information. That is, with current digital signature schemes, the confidentiality of official information is incompatible with the integrity of that information. This is called the digital document sanitizing problem, and some solutions such as digital document sanitizing schemes and content extraction signatures have been proposed. In this paper, we point out that the conventional digital signature schemes are vulnerable to additional sanitizing attack and show how this vulnerability can be eliminated by using a new digitally signed document sanitizing scheme with disclosure condition control.

Lu2O3:Yb3+ ceramics – a novel gain material for high-power solid-state lasers

Abstract: We have developed Yb3+:Lu2O3 ceramics with nanocrystalline technology and a vacuum sintering method. A laser diode end-pumped efficient Yb3+:Lu2O3 ceramic laser was demonstrated. A 0.7 W cw output power was obtained with the slope efficiency of ≈36% at 1035 nm wavelength, and 0.95 W with the slope efficiency of ≈53% at 1079 nm. We classify the Lu2O3:Yb3+ ceramics as gain medium for high-power solid-state lasers (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Microhardness and fracture toughness of Y2O3-and Y3Al5O12-based nanocrystalline laser ceramics

Abstract: The microhardness and fracture toughness of laser nanocrystalline ceramics based on the cubic oxides Y2O3 and Y3Al5O12 are determined experimentally. It is shown by comparative measurements that the fracture toughness and microhardness of Y2O3 ceramics exceed the corresponding parameters of Y2O3 single crystals by factors of 2.5 and 1.3, respectively. The fine morphology of grains and grain boundaries in fractures is investigated. It is ascertained that changes in the mechanical properties of the nanocrystalline ceramics under study are related to both the sizes and structure of grains and the structure of grain boundaries. It is suggested that twinning processes determine the mechanisms of formation of nanocrystalline ceramics.

Analysis of warranty claim data: a literature review

Abstract: Purpose – To provide a brief survey of the literature directed towards the analysis of warranty claim data.Design/methodology/approach – For convenience, this survey of the analysis of warranty claims data is somewhat arbitrarily be classified by topics as follows: age‐based claims analysis, aggregated warranty claims analysis, marginal counts of claims analysis, warranty claims analysis by using covariates, estimation of lifetime distribution using supplementary data, two‐dimensional warranty, warranty costs analysis, sales lag and reporting lag analysis, and forecasts of warranty claims.Findings – Emphasis is placed on a discussion of different kinds of warranty claims data selected from reviews and on a comparison of the statistical models and methods used to analyze such data.Research limitations/implications – Since the literature on product warranty data is vast, more work on this problem is needed.Practical implications – This review points out why warranty claims data is important and gives a surv...

Positional control of encapsulated atoms inside a fullerene cage by exohedral addition.

Abstract: The exohedrally functionalized derivative of endohedral metallofullerene, Ce2@C80(Mes2SiCH2SiMes2), was successfully synthesized and fully characterized. X-ray crystallographic and NMR spectroscopic analyses reveal that the free random motion of two metal atoms in Ce2@C80 is controlled inside the cage by exohedral chemical functionalization.

Image region entropy: a measure of "visualness" of web images associated with one concept

Abstract: We propose a new method to measure "visualness" of concepts, that is, what extent concepts have visual characteristics. To know which concept has visually discriminative power is important for image annotation, especially automatic image annotation by image recognition system, since not all concepts are related to visual contents. Our method performs probabilistic region selection for images which are labeled as concept "X" or "non-X", and computes an entropy measure which represents "visualness" of concepts. In the experiments, we collected about forty thousand images from the World-Wide Web using the Google Image Search for 150 concepts. We examined which concepts are suitable for annotation of image contents.

Experimental investigation of local properties and statistics of optical vortices in random wave fields.

Abstract: We present the first direct experimental evidence of the local properties of optical vortices in a random laser speckle field. We have observed the Berry anisotropy ellipse describing the anisotropic squeezing of phase lines close to vortex cores and quantitatively verified the Dennis angular momentum rule for its phase. Some statistics associated with vortices, such as density, anisotropy ellipse eccentricity, and its relation to zero crossings of real and imaginary parts of the random field, are also investigated by experiments.

Overwhelming O+ contribution to the plasma sheet energy density during the October 2003 superstorm: Geotail/EPIC and IMAGE/LENA observations

Abstract: [1] We studied dynamics of O+ ions during the superstorm that occurred on 29–31 October 2003, using energetic (9–210 keV/e) ion flux data obtained by the energetic particle and ion composition (EPIC) instrument on board the Geotail satellite and neutral atom data in the energy range of 10 eV to a few keV acquired by the low-energy neutral atom (LENA) imager on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite. Since the low-energy neutral atoms are created from the outflowing ionospheric ions by the charge exchange process, we could examine variations of ionospheric ion outflow with the IMAGE/LENA data. In the near-Earth plasma sheet of XGSM ∼ −6 RE to −8.5 RE, we found that the H+ energy density showed no distinctive differences between the superstorm and quiet intervals (1–10 keV cm−3), while the O+ energy density increased from 0.05–3 keV cm−3 during the quiet intervals to ∼100 keV cm−3 during the superstorm. The O+/H+ energy density ratio reached 10–20 near the storm maximum, which is the largest ratio in the near-Earth plasma sheet ever observed by Geotail, indicating more than 90% of O+ in the total energy density. We argued that such extreme increase of the O+/H+ energy density ratio during the October 2003 superstorm was due to mass-dependent acceleration of ions by storm-time substorms as well as an additional supply of O+ ions from the ionosphere to the plasma sheet. We compared the ion composition between the ring current and the near-Earth plasma sheet reported by previous studies and found that they are rather similar. On the basis of the similarity, we estimated that the ring current had the O+/H+ energy density ratio as large as 10–20 for the October 2003 superstorm.

Anomalous effect in Schumann resonance phenomena observed in Japan, possibly associated with the Chi-chi earthquake in Taiwan

Abstract: . The Schumann resonance phenomenon has been monitored at Nakatsugawa (near Nagoya) in Japan since the beginning of 1999, and due to the occurance of a severe earthquake (so-called Chi-chi earthquake) on 21 September 1999 in Taiwan we have examined our Schumann resonance data at Nakatsugawa during the entire year of 1999. We have found a very anomalous effect in the Schumann resonance, possibly associated with two large land earthquakes (one is the Chi-chi earthquake and another one on 2 November 1999 (Chia-yi earthquake) with a magnitude again greater than 6.0). Conspicuous effects are observed for the larger Chi-chi earthquake, so that we summarize the characteristics for this event. The anomaly is characterized mainly by the unusual increase in amplitude of the fourth Schumann resonance mode and a significant frequency shift of its peak frequency (~1.0Hz) from the conventional value on the By magnetic field component which is sensitive to the waves propagating in the NS meridian plane. Anomalous Schumann resonance signals appeared from about one week to a few days before the main shock. Secondly, the goniometric estimation of the arrival angle of the anomalous signal is found to coincide with the Taiwan azimuth (the unresolved dual direction indicates toward South America). Also, the pulsed signals, such as the Q-bursts, were simultaneously observed with the "carrier" frequency around the peak frequency of the fourth Schumann resonance mode. The anomaly for the second event for the Chia-yi earthquake on 2 November had much in common. But, most likely due to a small magnitude, the anomaly appears one day before and lasts until one day after the main shock, with the enhancement at the fourth Schumann resonance mode being smaller in amplitude than the case of the Chi-chi earthquake. Yet, the other characteristics, including the goniometric direction finding result, frequency shift, etc., are nearly the same. Although the emphasis of the present study is made on experimental aspects, a possible generation mechanism for this anomaly is discussed in terms of the ELF radio wave scattered by a conducting disturbance, which is likely to take place in the middle atmosphere over Taiwan. Model computations show that the South American thunderstorms (Amazon basin) play the leading role in maintaining radio signals, leading to the anomaly in the Schumann resonance.

A hybrid multi-agent system architecture for enterprise integration using computer networks

Abstract: The manufacturing industries are now experiencing fierce pressure of competition from every corner on this planet. In addition, the advancement in computer networks and information technologies has been gradually reshaping the manufacturing companies by shifting from the industrial age to the information era. Due to these elevated competitiveness and advanced computer technology, a number of new manufacturing and management strategies (e.g., CE or CIM) have emerged for the innovation of manufacturing enterprises. Although they have different definitions and scopes, there are several common issues: inter-enterprise functions integration; inter-enterprise resources integration; and collaboration. This paper proposes a new multi-agent system (MAS) architecture to support the inter-enterprise functions/resources integration and collaboration over the networked environment, including the hybrid agent architecture and hybrid network architecture. In contrast to the existing agent architectures, the proposed agent architecture enables agents to exhibit the hybrid (continuous and discrete) behavior and interactions. In addition, our network architecture is more suitable for building the large-scale distributed manufacturing systems that are prone to dynamic random changes of their environment. Based on the proposed MAS architecture, a collaborative product development environment is implemented as a starting point, and a multidisciplinary team-oriented design problem is illustrated to provide the vision of the proposed MAS architecture.

Generation of Laguerre-Gaussian modes in Nd:YAG laser using diffractive optical pumping

Abstract: A beam of pulsed laser radiation at the wavelength λ = 0.532 μm was diffracted at a circular diaphragm to produce a hollow-shape intensity distribution in the near field. This light distribution was used to pump an Nd:YAG laser, resulting in the formation of an inversion profile with a minimum at the laser resonator axis and enabling the suppression of the fundamental mode. Under this condition, the oscillation at λ = 1.064 μm of Laguerre-Gaussian modes (LG0m) with low and high values of the azimuthal index m was produced in the gain-switching regime. By changing the geometry of the resonator, the size of its waist parameter was changed, enabling the selection of the mode with an index m that best overlaps with the inversion profile. Oscillation of LG0m modes with indices ranging from m=1 to more than m=200 was obtained. LG0m modes with m ≤ 50 were produced using the dependence of the waist parameter on the length of the resonator near the boundary of its stability region. A LG0m mode of the highest order, m ≈ 240 was obtained by building a miniature laser resonator and using a pair of diaphragms in order to form a sharper ring-shape pumping distribution. Applications of diffractive optical pumping and ``hollow'' LG0m laser beams are discussed.

Robust boundary control of an axially moving string by using a PR transfer function

Abstract: In this note, a scheme for the vibration suppression of a translating string using a positive real (PR) transfer function is investigated. The transverse vibration of the string is controlled by hydraulic touch-rolls located at the right end of the string. The mathematical model of the system, which consists of a hyperbolic partial differential equation (PDE) describing the dynamics of the moving string and an ordinary differential equation (ODE) for the actuator dynamics, is derived by using Hamilton's principle for translating continua. The transfer function of the proposed boundary controller is a nonproper but PR function. The asymptotic stability of the closed-loop system in the presence of output disturbance is proved.

Probabilistic web image gathering

Abstract: We propose a new method for automated large scale gathering of Web images relevant to specified concepts. Our main goal is to build a knowledge base associated with as many concepts as possible for large scale object recognition studies. A second goal is supporting the building of more accurate text-based indexes for Web images. In our method, good quality candidate sets of images for each keyword are gathered as a function of analysis of the surrounding HTML text. The gathered images are then segmented into regions, and a model for the probability distribution of regions for the concept is computed using an iterative algorithm based on the previous work on statistical image annotation. The learned model is then applied to identify which images are visually relevant to the concept implied by the keyword. Implicitly, which regions or the images are relevant is also determined. Our experiments reveal that the new method performs much better than Google Image Search and a simple method based on more standard content based image retrieval methods.