Forced oscillations,optimal forcing and resonance of thermal convection under small,time-varying forcing

This study proposes a method to obtain forced oscillation induced by arbitrary small time-varying forcing on a stable thermal convection field, and a framework for finding universal and inherent resonance modes on the field, independent of the ways of forced vibration, indicators of resonance and other information. It is based on an eigenvalue analysis of a Hermitian matrix relating to the frequency response function, and the typical forced oscillation at a resonance is given by the response to the optimal forcing as the eigenvector corresponding to the largest eigenvalue of the matrix. The method also provides indicators to quantify the efficiency in realizing a given resonance mode by a specific forced vibration. We can find thereby that heat-flux vibration not on the bottom wall but on the left-hand sidewall is preferred for realizing the internal gravity wave resonance.     

Reinvestigation of Thermoelectric Properties of n- and p-Type Ba8−d Au x Si46−x−y Clathrate

We have synthesized n- and p-type clathrates Ba_8?d Au _x Si_46?x?y with various Au contents (4.6 < x < 6.0) by arc-melting, annealing at 1173 K, and spark plasma sintering at 1073 K. The Au compositions found by wavelength-dispersive x-ray spectrometry for the synthesized samples were slightly lower than the nominal compositions. Ba_7.8Au_4.6Si_41.4 and Ba_7.7Au_4.9Si_41.1 samples showed n- and p-type conduction, respectively. According to the electron count (Ba²⁺)₈Au(^3?)_5.33Si_40.67, the clathrate composition with x = 5.33 is expected to be an intrinsic semiconductor. Our experimental results show that increase of the Au composition causes a transition from n-type to p-type conduction between x = 4.6 and 4.9. We have also calculated the band structures of the Ba₈Au _x Si_46?x clathrate including a vacancy by ab initio calculation based on density functional theory with structure optimization. It was found that the vacancy behaves like an electron acceptor and the numbers of vacancies at 24k sites for the synthesized Ba₈Au _x Si_46?x?y clathrates can be estimated as ～0.4 in a unit cell.     

Radiation exposure to general public after permanent brachytherapy for prostate cancer

Permanent prostate brachytherapy patients are generally told to limit their time around children and pregnant women. However, there is little data available to validate the instruction. For the skin effective dose rate, ion chamber survey meter model 451B-DE-SI was used. The meter was scanned at the point of 4.5, 20, 50 and 100 cm from the skin surface in each plane. Life time exposure was calculated from the average anterior data. At the point of 4.5 cm from the anterior skin surface, the lifetime equivalent dose was 46.5 mSv, at 20 cm it was 13.2 mSv, at 50 cm it was 3.5 mSv and at 100 cm it was 0.9 mSv. The risk from the prostate brachytherapy patients to general public is quite low. Only the case of close and long-time contact with the pregnant and the infant should be paid attention to.     

Extended Transmission Reach Using Optical Filtering of Frequency-Modulated Widely Tunable SSG-DBR Laser

We propose a novel transmitter consisting of a frequency-modulated widely tunable super-structure-grating distributed Bragg reflector (SSG-DBR) laser and an optical filter. The SSG-DBR laser acts as a frequency modulating light source with a constant output power by modulating the reverse bias voltage in the phase control (PC) region. By optically filtering the output light from the frequency-modulated laser, we have demonstrated 60- and 180-km transmissions for 20- and 10-Gb/s nonreturn-to-zero (NRZ) signals, respectively. The power penalty was 2.2 dB after the 180-km transmission of a 10-Gb/s NRZ signal as determined by bit-error-rate measurements. Furthermore, an extended transmission reach was achieved with a wide tuning range without controlling the bias and modulating voltages in the PC region.     

Highly reliable spot-size converter integrated laser diodes over a wide temperature range for access network systems

In this paper, we present highly reliable high-temperature spot-size converter integrated laser diodes (LDs) fabricated using a full-wafer process with dry etching and MOVPE. The lasers lase at 150°C and operate stably for 10,000 h at 85°C and 10 mW. The median lifetime is estimated to be over 10⁵ h. We also demonstrate a novel screening test procedure for a bar configuration of LDs, which can greatly reduce optical module cost.     

Proposal of earthing resistance measurement method without auxiliary electrodes

This paper proposes an earthing resistance measurement method for a simple earthing electrode without two auxiliary electrodes. The proposed method can measure the earthing resistance by evaluating loop impedance of an earth return circuit composed of an earth electrode of the under test and a lead wire, a return wire, and the earth soil. The return wire is placed on the soil surface without any terminations. The earthing resistance of the electrode of the under test can be given by the earth return circuit impedance at a resonant frequency design between 100 kHz and 1 MHz. The measurement conditions for the proposed method are determined by numerical calculations. Earthing resistance deviations between the proposed method and the existing method are ?13% to +22% for earthing resistance values with 50, 100, or 300Ω. It is found that the proposed method can be used to evaluate an earthing resistance around 100Ω for a simple earthing electrode. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 16–26, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20196     

Thermoelectric Properties of Ga-Doped Ba8Al x Si46−x Clathrate

Single-crystalline Ba₈Al _x Ga _y Si_46?x?y clathrates were synthesized by the arc melting method and Czochralski method without subsequent treatment, and their thermoelectric properties were compared with those of Ba₈Al _x Ga _y Si_46?x?y and Ba₈Al _x Si_46?x clathrates with almost the same carrier concentration as estimated from the similar Seebeck coefficient and the Zintl concept. The resistivity of Ba_7.8Al_5.3Ga_7.4Si_33.3 was lower than that of Ba_7.9Al_12.6Si_33.4. The specific electrical resistance of Ba_7.9Al_12.6Si_33.4 and Ba_7.8Al_5.3Ga_7.4Si_33.3 was 0.573 mΩ cm and 0.282 mΩ cm at 750 K, respectively. The band structure of Ba₈Al₈Ga₈Si₃₀ and Ba₈Al₁₆Si₃₀ was estimated by first-principle calculations using density functional theory with the local density approximation. Based on these calculations, it was found that the shape of the bottom of the conduction band for Ba₈Al _x Si_46?x clathrate changed slightly on Ga doping and the radius of curvature of the bottom of the conduction band for Ba₈Al₈Ga₈Si₃₀ clathrate was lower than that for Ba₈Al₁₆Si₃₀ clathrate. These results indicate that the mobility was enhanced by Ga doping of Ba₈Al _x Si_46?x clathrate. We also synthesized single-crystalline Ga-doped Ba₈Al _x Si_46?x clathrate. The electrical resistivity decreased dramatically due to the single-crystallization because of reduced electron scattering on grain boundaries. These results suggest that Ga doping and single-crystallization are effective for improvement of the thermoelectric properties of Ba₈Al _x Si_46?x clathrate.     

Laser diodes integrated with butt-jointed spotsize converterfabricated on 2-in wafer

Laser diodes integrated with spotsize converters by butt-joint technology combined with selective area metal organic vapor phase epitaxial (MOVPE) growth have been successfully fabricated. Satisfactory uniformity, reproducibility (>99%) and tolerance for low threshold current, a narrow emitted beam, and low optical coupling loss to fiber (<-2.4 dB) are obtained by using 2-in full wafer fabrication technology in the experimental fabrication. To investigate the tolerance in fabrication, the characteristic dependence on the variation of the wet etching time just before the butt-joint MOVPE growth and also on the mesa stripe width are investigated. A wide tolerance for these fabrication parameters is confirmed. The results indicate that the butt-joint technology is a useful and reliable process for realizing spotsize converters of the present type and also suggest that the technology is widely applicable to various photonic integrated circuits     

Anion-exchange properties of nickel–aluminum layered double hydroxide prepared by liquid phase deposition

The optimum coordination structure of Ni–fluoro complexes for the preparation of Ni–Al LDH by LPD process and the diverse anion-exchange properties of as-deposited Ni–Al on α-alumina powder were quantitatively evaluated for the industrial application of new positive material for alkali secondary batteries. The [NiF_6−x−y(NH₃)_x(OH⁻)_y]ⁿ⁺ was more suitable than [NiF₆]⁴⁻ as the precursor of the deposition of Ni–Al LDH in the LPD reaction, and the improved LPD reaction achieved the synthesis of high purity and high crystallinity Ni–Al LDH. All anion-exchanged Ni–Al LDHs for OH⁻–, Cl⁻–, SO₄²⁻–, and CH₃COO⁻–forms kept the high crystallinity and showed the enlargement of interlayer distances. The tilting angle of the intercalated CH₃COO⁻ anions was about 15°. Anion-exchange capacity remained constant at a minimum of 0.8 meq g⁻¹ in pH >10, increased as pH decreased, and reached a maximum of 8 meq g⁻¹ at pH 2. Anion-exchange of OH⁻–form of Ni–Al LDH was accelerated by the neutralization of hydroxide ions in interlayers, in addition, the anion-exchange capacity and the crystallinity of Ni–Al LDH could be controlled by the amount of doped aluminum ions.