Electronic properties of a single-walled carbon nanotube/150mer-porphyrin system measured by point-contact current imaging atomic force microscopy

The electronic properties of a single-walled carbon nanotube/150mer of porphyrin polymer wire system were investigated. Current-voltage (I-V) curves were measured simultaneously along with topographic observations using point-contact current imaging atomic force microscopy. Symmetric I-V curves were obtained at bare single-walled carbon nanotubes but characteristic asymmetrical rectifying behavior was found at the single-walled carbon nanotube/150mer-porphyrin junctions. This finding is of key importance for the development of new nanoscale molecular electronic devices.     

Improved quality data systems through the use of standard electronic data deliverables (EDDs) and environmental data assessment software.

One of the challenges facing professionals in the environmental arena today is the collection and assessment of large amounts of environmental analytical data. The assessment of the quality of that data is essential as multi-million dollar decisions for environmental site cleanups and/or long term monitoring efforts are made based on the analytical results. Also critical to environmental programs is the sharing and access of data across multiple data users. The ability to share data allows for better use of the limited resources available to clean up and monitor contaminated environmental sites. Standardization of electronic deliverables allows for collection of data from multiple data collectors into a single database for use by numerous data users and stakeholders on a project. This paper discusses the benefits of using a standard EDD deliverable format and use of environmental data assessment software tools to do project planning and data assessment throughout the duration of the environmental project.     

Performance characteristics of barometric-type open-cycle OTEC system

Open Cycle-Ocean Thermal Energy Conversion (OC-OTEC) system has a merit to use a heat exchanger of direct contact type without a heat transfer tube. Therefore, it is expected that the capital cost of OC-OTEC is reduced by use of this simply designed heat exchanger. However, non-condensable gas is released in the system, because in a direct contact evaporator, the steam driving a turbine is generated by surface sea water including air, and existing air causes a reduction of system performance. From the above point of view, we carried out an experimental study on the operating characteristics and the effect of structure of a heat exchanger and the existence of non-condensable gas on the performance of a direct contact heat exchanger in an experimental apparatus of barometric type OC-OTEC. As a result, the performance of the direct contact evaporator can be satisfied. However, we cannot get satisfactory results in a direct contact condenser. Therefore, we conducted further experiments through the improvement of the structure of the condenser and the control of the non-condensable gas. Finally, we concluded that the major factor affecting the system performance is the non-condensable gas, but its effect can be ignored when its concentration is below 8%. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res 25(4): 226–237, 1996     

1.55-μm buried-heterostructure VCSELs with InGaAsP/lnP-GaAs/AlAsDBRs on a GaAs substrate

We demonstrate 1.55-μm buried-heterostructure (BH) vertical-cavity surface-emitting lasers (VCSELs) on a GaAs substrate. Thin-film wafer-fusion technology enables InP-based BH VCSELs to be fabricated on GaAs/AlAs distributed Bragg reflectors. Detailed investigations of the device resistance are also described. As a result of introducing BH and obtaining low device resistance, the threshold current density under CW operation shows the independence of mesa size due to a strong index guide and small noneffective current. A 5-μm VCSEL exhibits a record threshold current of 380 μA at 20°C. This VCSEL also operates with single transverse mode up to the maximum optical output power     

High purity InxGa1−xSb single crystals with cutoff wavelength of 7–8 µm grown by melt epitaxy

For the first time, InGaSb single crystals with a cutoff wavelength of 7–8 μm were successfully grown on GaAs substrates by a new growth technique named melt epitaxy. The band gap of InGaSb layers obviously narrowed compared with those with the same compositions grown by ordinary methods and the longest cutoff wavelength reached 8.3 μm. High electron mobility of 8.05×10⁴ cm²/Vs and low carrier density of 1×10¹⁵ cm⁻³ at 77 K were obtained indicating high purity of InGaSb epilayers.     

Nitride-based laser diodes using thick n-AlGaN layers

We obtained 1 μm crack-free AlGaN layers up to an AlN molar fraction of 0.4 by growing directly on low-temperature-deposited buffer layers. The buffer layer is effective for growing AlGaN layers without the stress caused by the lattice mismatch. We also demonstrated nitride-based laser diodes with such a 1 μm crack-free n-AlGaN cladding layer/n-AlGaN contact layer/low-temperature-deposited buffer layer/sapphire structure, which showed a clear single spot in a far field pattern. The AlGaN-based structure can suppress optical leakage from the waveguide region to the underlying layer. The threshold current of the laser diode is about 230 mA, which is comparable to or better than that of our laser diodes with the conventional GaN-based structure.     

An 850-nm InAlGaAs strained quantum-well vertical-cavitysurface-emitting laser grown on GaAs (311)B substrate withhigh-polarization stability

The polarization stability of 850-nm InAlGaAs strained quantum-well (QW) vertical-cavity surface-emitting laser (VCSEL) grown on GaAs (311)B substrate was investigated by comparing it with that of GaAs unstrained QW VCSEL grown on GaAs (311)B substrate. Photoluminescence measurement showed that strained QWs grown on GaAs (311)B substrate had larger anisotropy in optical gain than unstrained QWs. The VCSEL with strained QWs showed an orthogonal polarization suppression ratio (OPSR) as high as 21 dB under CW operation. Time-dependent OPSR measurement indicated that the strained QW VCSEL had higher polarization stability than the unstrained QW VCSEL under zero-bias modulation     

Purification, characterization and gene analysis of exo-cellulase II (Ex-2) from the white rot basidiomycete Irpex lacteus

A new exo-type cellulase, named exo-cellulase II (Ex-2), was purified from the crude enzyme preparation of Irpex lacteus. Ex-2 was very similar to the previously characterized exo-cellulase I (Ex-1) with respect to enzymatic features such as optimal pH, temperature, heat stability, and catalytic activity. However, Ex-2 exhibited greater pH stability than Ex-1. The molecular mass and carbohydrate content of Ex-2 (56,000, 4.0%) were different from those of Ex-1 (53,000, 2.0%). A cellulase gene (named cel2) encoding both Ex-2 and Ex-1 was isolated from an I. lacteus genomic library. The cel2 gene was found to consist of 1569 bp with an open reading frame encoding 523 amino acids, interrupted by two introns. The deduced amino acid sequences revealed that cel2 ORF has a modular structure consisting of a catalytic domain and a fungal-type cellulose-binding domain (CBD) separated by a serine-rich linker region. The catalytic domain was homologous to those of fungal cellobiohydrolases belonging to family 7 of the glycosyl hydrolases. Northern blot analysis showed that expression of the cel2 gene was induced by various cellulosic substrates and repressed by glucose, fructose, and lactose.     

Analysis of an adjustable speed rotary condenser for power system stabilization

Over the last five to ten years, significant progress has been made in high‐power semiconductor devices and in their practical applications to power systems. This comes not only from sophisticated semiconductor technology but also from the demand for a higher degree of frequency and voltage stability, and for greater reliability in power systems. This paper deals with an adjustable speed rotary condenser capable of not only reactive power control but also active power control based on a flywheel effect of the rotor. The behavior of a power system consisting of the adjustable speed rotary condenser, a synchronous generator, and a transmission line is subjected to a set of nonlinear differential equations. The set of nonlinear equations can be linearized by limiting attention to small perturbations around a reference state, thus leading to the so‐called Heffron–Phillips model of the power system. The Heffron–Phillips model derived is effective in analyzing effects of the adjustable speed rotary condenser on power system stabilization. The validity of the analysis is confirmed by computer simulation based on EMTDC. Finally, it is discussed how well power system stabilization is achieved by the rotary condenser. As a result, the rotary condenser has the function of decoupling reactive power control from active power control, thus producing a good effect on power system stabilization which would not be achieved by a conventional inverter‐based static var compensator. © 2000 Scripta Technica, Electr Eng Jpn, 133(1): 31–42, 2000     

Frequency‐weighted model reduction via interpolation

We propose a numerical method of frequency‐weighted model reduction. The model to be reduced (an original model) is a stable SISO discrete‐time model described by high‐order state‐space equations. We design the reduced‐order model so that it can interpolate 1st‐ and 2nd‐order information of the original model at complex frequency points (interpolation points) in the unit circle. The characteristics of the reduced‐order model greatly depend on the choice of the interpolation points. The proposed model reduction method is a numerical one that chooses the interpolation points by searching in the unit circle to find the reduced‐order model such that L_∞‐norm of the reduction error is less than a prescribed value. This method has the following features that show that it is an effective numerical method of the frequency‐weighted model reduction. i) The reduced‐order model is guaranteed to be stable. ii) The procedure for finding the reduced‐order model is simple and requires a relatively small amount of computation. iii) The order of the reduced‐order model can be controlled by choosing the number of interpolation points. © 1998 Scripta Technica, Electr Eng Jpn, 126(2): 31–39, 1999