Thermoelectric properties of Bi and Cu co-doped Ca3Co2O6single crystals

Single crystals of Bi and Cu-doped Ca₃Co₂O₆were synthesized in a molten K₂CO₃flux. Using an obtained single crystal of (Ca_0.985(5)Bi_0.015(5))₃(Co_0.990(3)Cu_0.010(3))₂O₆elongated to the c-axis direction of the crystal structure, the electric resistivity (ρ) and Seebeck coefficient (S) were measured from room temperature to over 1000 K in air. The single crystal showed p-type semiconducting behavior with ρ values of 1.8 Ω cm at 303 K and 0.017 Ω cm at 1000 K. The S values were +254 μ VK^{− 1} at 325 K, +360 μ VK^{− 1} at 420 K, and +214 μ VK^{− 1} at 1000 K. The power factor (S ² ρ ^{− 1}) increased with an increase of temperature and attained 2.70 × 10^{− 4} Wm^{− 1}K^{− 2} at 1000 K.     

Nyquist stability criterion of intrinsic zeros for continuous-time pure imaginary zeros

This note treats a stability condition of the zeros of sampled systems corresponding to continuous-time pure imaginary zeros with multiplicity one for systems with the relative degree one. It is shown that the Nyquist plot can be used to check the stability condition.     

Wavelength dependence of repetitive-pulse laser-induced damage threshold in beta-BaB2O4

The dependence on wavelength of repetitive-pulse (10 Hz, 8-10 ns) laser-induced damage on beta barium metaborate (BBO) has been investigated. The thresholds of dielectric breakdown in bulk crystal have been found to be 0.3 GW/cm(2) at 266 nm, 0.9 GW/cm(2) at 355 nm, 2.3 GW/cm(2) at 532 nm, and 4.5 GW/cm(2) at 1064 nm. Results indicate two-photon absorption at 266 and 355 nm, which helps to produce an avalanche effect that causes breakdown at each of the four wavelengths tested. Neither the BBO refractive indices nor the absorption spectrum change until breakdown occurs.     

A new artificial life body: biologically inspired dynamic bipedal humanoid robots

Recently, a biologically inspired, bipedal, dynamic, humanoid robot was developed at the Artificial Life and Robotics Laboratory of Oita University. This bipedal humanoid robot is able to walk dynamically and to go up and down stairs. The central pattern generator developed produces various types of walking pattern. This robot has a pair of small CMOS color CCD cameras, a speaker, and a microphone in the head part, and will have a GPS, a portable telephone, and other sensors in the body part, so that the integration of locomotion and behavior to achieve specific demonstrations will be realized. This project develops dynamic mobility and the ability for autonomous recognition and navigation using the biological central nervous system, the brain system, and the real-time control system. Also, the design principles that demonstrate the dynamic interaction between neural and mechanical controls will be clarified. In Phase I, the platform of a small, bipedal, humanoid robot is used to develop autonomous locomotion and autonomous sensing and navigation. In Phase II of the project, an iteration on the platform design for human-size, bipedal, humanoid robots will be performed for operational testing. The development of bipedal humanoid robots that capture biological systems with unique principles and practices could dramatically increase their performance in tasks for national security needs.This work was presented in part at the 8th International Symposium on Artificial Life and Robotics, Oita, Japan, January 24–26, 2003     

Parameter’s setting of the ant colony algorithm applied in preventive maintenance optimization

Meta-heuristic applications have evolved a lot nowadays and have been used in many domains. However, their parameter setting stills, till now, a serious problem which influences their efficiency and their attitude. Under the title of preventive maintenance optimization, the Ant Colony (AC) is used as a search technique for the best intervention dates to preventively maintain a series-parallel system. The AC proves once again its efficiency (Samrout, M., Yalaoui, F., Chatelet, E., & Chebbo, N. (2005). Reliability Engineering & System Safety, 89, 346–354), but the parameter setting’s issue persists as a critical issue which needs more analysis. This paper offers a detailed study about the influence of the parameters on the AC operation. An experimental plan design is done. Obtained results are coherent with the convergence conditions of the ant colony algorithms. Based on those latter, improvements are done to the original ant colony algorithm and interesting results are obtained.     

Pressure- and Field-induced Non-Fermi-liquid Behaviors in a Heavy-Fermion Antiferromagnet Ce7Ni3

We review recent investigations of the heavy-fermion antiferromagnet Ce₇Ni₃ with a geometrically frustrated structure under hydrostatic pressures and magnetic fields. Below T _N1=1.9 K, an incommensurate spin-density-wave (SDW) develops, and another antiferromagnetic transition occurs at T _N2 = 0.7 K. At a rather low critical pressure (P _c ), P _c = 0.39 GPa, both T _N1 and T _N2 vanish, and the specific heat divided by temperature (C/T) exhibits –lnT dependence (i.e., non-Fermi liquid behavior). At P = 0.43 GPa > P _c , a T-independent behavior of C/T, i.e., Fermi-liquid behavior, recovers below 0.2 K. However, the magnetic susceptibility continues to increase down to 0.09 K at 0.43 GPa, which is not consistent with a conventional Fermi-liquid theory. On the other hand, upon applying magnetic fields B along the hexagonal c axis, T _N1 decreases and vanishes at 0.3 T. Magnetoresistance, specific-heat, and magnetization measurements reveal that a field-induced magnetic (FIM) phase appears in a B–T region for B _{∥ c} > 0.7 T and T < 0.5 K. Neutron diffraction experiments indicate that the magnetic unit cell in the c plane for the FIM phase is treble that of the chemical unit cell. Moreover, the intensity of the magnetic reflection remains even in the region between the FIM phase and SDW phase. This observation indicates the presence of large spin fluctuations in the c-plane associated with the magnetic frustration, which should be responsible for the non-Fermi-liquid behavior of Ce₇Ni₃.     

Feature extraction by supervised independent component analysis based on category information

Independent component analysis (ICA) is a technique of transforming observation signals into their unknown independent components; hence, ICA has often been applied to blind signal separation problems. In this application, it is expected that the obtained independent components extract essential information of independent signal sources from input data in an unsupervised fashion. Based on such characteristics, ICA is currently utilized as a feature extraction method for images and sounds for recognition purposes. However, since ICA is an unsupervised learning, the obtained independent components are not always useful in recognition. To overcome this problem, we propose a supervised approach to ICA using category information. The proposed method is implemented in a conventional three‐layered neural network, but its objective function to be minimized is defined not only for the output layer but also for the hidden layer. The objective function consists of the following two terms: one evaluates the kurtosis of hidden unit outputs and the other evaluates the error between output signals and their teacher signals. The experiments are performed using several standard datasets to evaluate performance of the proposed algorithm. It is confirmed that a higher recognition accuracy is attained by the proposed method as compared with a conventional ICA algorithm. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(2): 25–32, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20522     

Approximate method of estimating seismic performance of high‐rise buildings with oil‐dampers

When subjected to long‐period ground motions, many existing high‐rise buildings constructed on plains with soft, deep sediment layers experience severe lateral deflection, caused by the resonance between the long‐period natural frequency of the building and the long‐period ground motions, even if they are far from the epicenter. This was the case for a number of buildings in Tokyo, Nagoya, and Osaka affected by the ground motions produced by the 2011 off the Pacific coast of Tohoku earthquake in Japan. Oil‐dampers are commonly used to improve the seismic performance of existing high‐rise buildings subjected to long‐period ground motion. This paper proposes a simple but accurate analytical method of predicting the seismic performance of high‐rise buildings retrofitted with oil‐dampers installed inside and/or outside of the frames. The method extends the authors' previous one‐dimensional theory to a more general method that is applicable to buildings with internal and external oil‐dampers installed in an arbitrary story. The accuracy of the proposed method is demonstrated through numerical calculations using a model of a high‐rise building with and without internal and external oil‐dampers. The proposed method is effective in the preliminary stages of improving the seismic performance of high‐rise buildings.     

Carbon doping and etching in GaxIn1−xAsyP1−y on GaAs substrates using CBr4 by metalorganic chemical vapor deposition

Carbon doping and etching by CBr₄ were studied for Ga_xIn_1−xAs_yP_1−y (0≤y≤1) on GaAs grown by metalorganic chemical vapor deposition. It was found that the hole concentration drastically decreases with decreasing y when the flow rate of CBr₄ is constant. When y is under 0.5, the conduction type of GaInAsP changes ton-type. In the region of 0<y<0.6, the surface morphology was degraded and the carrier compensation became higher than could be estimated from the C concentration. This seems to be due to the micro defects because this range of composition is within the unstable region which is theoretically predicted. The etching effect by CBr₄ was observed during the growth. The rate of etching for InAsP component is about three times larger than that for the GaAsP component. The thermodynamic analysis suggests that the etching is due to the increase of the partial pressure of GaBr and InBr.