Actively mode-locked strained-InGaAsP multiquantum-well lasersintegrated with electroabsorption modulators and distributed Braggreflectors

This paper describes picosecond pulse generation at 20 Gb/s by monolithic mode-locked lasers integrated with electroabsorption modulators and distributed Bragg reflectors. The electroabsorption modulator using strained-InGaAsP multiquantum wells acts as a pulse shortening gate when a sinusoidal voltage is driven at a large reverse bias voltage. To obtain transform-limited picosecond pulses, the required spectral bandwidth of the distributed Bragg reflector is estimated. Pulse generation around 4 ps with a time-bandwidth product of 0.5 has been performed at a repetition rate of 20 GHz. Driving conditions of the modulator, such as bias voltage and modulation frequency, are investigated. It is shown that an increase in the intensity noise is the main factor limiting performance     

Quantum discord for two-qubit systems in the Bloch channel: effects of longitudinal and transversal relaxation times

Quantum discord is studied for two-qubit systems with different settings under the influence of the Bloch channel which is characterized by the longitudinal and transversal relaxation times and the environmental temperature. The relaxation of the quantum discord strongly depends on the ratio of the two relaxation times and the environmental temperature. It is found that the ratio of the quantum discord to the total correlation becomes finite or zero asymptotically, depending on the ratio of the relaxation times and the system setting. Furthermore, the optimal setting for sharing the quantum discord is discussed for given environmental temperature and ratio of the relaxation times.     

A concentrator module of spherical Si solar cell

Spherical Si solar cell, which is made up of Si spheres with a diameter of approximately 1.0 mm, is expected to be a promising candidate for low consumption of Si feedstock and simple process technology. This paper describes the formation process and the structure of a concentrator module in detail. The concentrator lens was formed by casting with ultraviolet light hardening resin. The concentration ratio was 4.4 times and the pitch between the spheres was 2.0 mm. By this module design, it was possible to realize a consumption of the Si feedstock of about 3.0 g/W. Conversion efficiencies of 11.3% from single-sphere cell, 8.5% from a 23-spheres module and 5.2% from a 105-spheres module under AM1.5, 100 mW/cm² illumination were achieved.     

Temperature imaging of sub-millimeter-thick water using a near-infrared camera

This paper presents a method of imaging temperature distributions of sub-millimeter-thick water using a near-infrared camera and optical narrow-bandpass filter. The principle is based on the temperature dependence of the ν₁ + ν₃ absorption band of water. Temperature images are constructed by measuring the absorbance of water at the wavelength of 1412 nm through the filter for all pixels of the camera. From calibration measurements on 0.5-mm thick water at temperatures from 26.0 °C to 40.0 °C, the temperature coefficient was 6.3 × 10^?4 K^?1 and the standard deviation of absorbance was 1.9 × 10^?4. Thermal diffusion in 0.5-mm thick water caused by a thin heating wire was visualized with this method. The obtained images were verified against temperature distributions calculated by solving a two-dimensional thermal conduction model. This method would be useful for temperature measurement applications and control of aqueous solutions in microchips.     

Hydrogen production by combining two types of photosynthetic bacteria with different characteristics

The double-layer photobioreactor using two types of photosynthetic bacteria, Rhodobacter sphaeroides RV and its reduced-pigment mutant, MTP4, was developed for efficient hydrogen production. The two types of bacteria had different characteristics on light energy, hydrogen production rate and conversion efficiency. MTP4 produced hydrogen more efficiently under high light conditions and RV did so under low light conditions. Illuminated light toward the surface of a photobioreactor quasi-exponentially declines as it penetrates into the reactor. When two types of bacteria were placed using the developed reactor according to this light distribution, the hydrogen production rate reached 3.64 l/m²/h at a light intensity of 500 W/m² in 24 h and the conversion efficiency of light energy to hydrogen was 2.18%. These values were 33% higher than those of only using RV. The low light in the deep part of the reactor was utilized efficiently, resulting in a higher hydrogen production rate.     

Microstructure and mechanical properties of Pt-added and Pd-added Zr-20Nb alloys and their metal release in 1 mass% lactic acid solution

The effects of Pt and Pd addition to a Zr-20Nb alloy on its microstructure and mechanical property, as well as the elution of metals from the alloys in lactic acid solution, were investigated. The microstructure was characterized with an X-ray diffractometer (XRD), an optical microscope (OM), and a transmission electron microscope (TEM). The mechanical properties were evaluated by a tensile test. The β phase is dominantly observed in the Zr-20Nb as well as in the Pt-added and Pd-added Zr-20Nb alloys. Needle-like microstructures are observed in equiaxed grains in all alloys. Pd addition to the Zr-20Nb alloy suppresses ω phase formation more than Pt addition does. The 0.2% offset yield strength and the ultimate tensile strength of the Pt-added and Pd-added Zr-20Nb alloys increase with the Pt and Pd concentrations. XRD analysis revealed that the lattice parameter of β-Zr in the Pt-added and Pd-added Zr-20Nb alloys decreases with the Pt and Pd concentrations. Pt and Pd solute in β-Zr as a substitutional element and contribute to the increase in the strength by solid solution hardening. The addition of 2Pt and 2Pd to the Zr-20Nb alloy also improves metal elution from the alloys in lactic acid solution.     

Preliminary spectrum shifter design for intermediate energy nuclear data benchmark experiments with DT neutrons

Integral benchmark experiments with DT neutrons are not always sufficient for nuclear data benchmarking in the MeV region, below 10 MeV. A neutron spectrum shifter, which will be placed between a sample and a DT neutron source, is effective to moderate DT neutrons incident to the sample. In order to estimate effects of the spectrum shifter, the ratio of the contribution of 14 MeV neutrons in the leakage neutron and gamma-ray spectra was calculated with MCNP-4C for an experimental configuration at FNS of JAEA, Japan. The calculations were carried out for a Li₂TiO₃ sample with a Be, D₂O, or ⁷LiD spectrum shifter. It was found out that the Be shifter was superior to others and the Be shifter was effective to decrease the contribution of 14 MeV neutrons especially for secondary gamma-ray spectrum measurements.     

High-Performance Vector-Controlled AC Motor Drives: Applications and New Technologies

A high-performance ac motor control has been developed by employing the vector control concept. Its versatility has been proven through the six years of experience in applications to pinch roll drives of continuous casting plants, machine tool spindle drives, and other drive systems in industry. Equivalent torque characteristics are achieved with ac motors compared to dc motors without direct detection of the magnetic flux. The effect of rotor temperature on the torque characteristics has been compensated to a satisfactory level in actual industrial use by various means. Servo drives, both synchronous motor and induction motor types, have been introduced. The test results show that the performance of ac servo drives is equivalent or superior to that of the PWM-controlled dc servo drives. Furthermore, an example of the direct-drive servo is described, where an ultra-low speed high-torque motor and an ultra-high resolution position sensor play key roles. In addition, the possibility of a more sophisticated servo drive exploiting modern control theory is suggested.     

Large-aperture automatic focimeter for the measurement of optical power and other optical characteristics of ophthalmic lenses

We propose an optical apparatus enabling the measurement of spherical power, cylindrical power, and optical center coordinates of ophthalmic lenses. The main advantage of this new focimeter is to provide a full bidimensional mapping of the characteristics of ophthalmic glasses. This is made possible thanks to the use of a large-area and high-resolution position-sensitive detector. We describe the measurement principle and present some typical mappings, particularly for progressive lenses. We then discuss the advantages in terms of speed and versatility of such a focimeter for the measurement of complex lens mappings.