Fundamental characteristics of five-level double converters with adjustable dc voltages for induction motor drives

In this paper, two kinds of control strategies for a three-phase five-level double converter are described on the assumption that the converter is applied to an induction motor drive system. The purposes of the proposed control strategies are to correct voltage imbalance of the DC-bus capacitors, to keep the input power factor at near unity, and to achieve an adjustable-speed drive. Characteristics of the converter operated by each of the two control strategies are examined and the validity is verified by experiments using a 3.7-kW induction motor.     

Luminescent passive-oxidized silicon quantum dots as biological staining labels and their cytotoxicity effects at high concentration

Semiconductor quantum dots (QDs) hold some advantages over conventional organic fluorescent dyes. Due to these advantages, they are becoming increasingly popular in the field of bioimaging. However, recent work suggests that cadmium based QDs affect cellular activity. As a substitute for cadmium based QDs, we have developed photoluminescent stable silicon quantum dots (Si-QDs) with a passive-oxidation technique. Si-QDs (size: 6.5 ± 1.5?nm) emit green light, and they have been used as biological labels for living cell imaging. In order to determine the minimum concentration for cytotoxicity, we investigated the response of HeLa cells. We have shown that the toxicity of Si-QDs was not observed at 112?μg?ml(-1) and that Si-QDs were less toxic than CdSe-QDs at high concentration in mitochondrial assays and with lactate dehydrogenase (LDH) assays. Especially under UV exposure, Si-QDs were more than ten times safer than CdSe-QDs. We suggest that one mechanism for the cytotoxicity is that Si-QDs can generate oxygen radicals and these radicals are associated with membrane damages. This work has demonstrated the suitability of Si-QDs for bioimaging in lower concentration, and their cytotoxicity and one toxicity mechanism at high concentration.     

地震引起的边坡灾害风险评估

 2005年日本福冈县7级地震引起大量边坡破坏。震中附近的志贺岛的环岛公路由于其上方边坡崩塌导致交通中断达1.5 a之久。其原因是崩塌边坡上方出现了较大的沉降裂缝,有可能受将来的暴雨或地震的触发再次导致边坡崩塌。根据钻孔资料及实验室实验结果,对该边坡未来可能发生的崩塌规模产生3种意见：小规模表层崩塌(A)、中规模中层崩塌(B)及大规模深层崩塌(C)。而边坡修复费用则根据所想定的可能崩塌规模从几千万日元到几十亿日元不等。为了合理决定对策规模,对3种可能的崩塌规模分别进行风险评估。结果表明,大规模深层崩塌(C)由于发生概率较小使得其风险远远小于小规模表层崩塌(A)和中规模中层崩塌(B),因而在修复中可以不予考虑。另外,虽然小规模表层崩塌(A)和中规模中层崩塌(B)的风险相当,但考虑到对策效果(加固后的风险减少与投入的加固资金费用之比),认为以小规模表层崩塌为对象制定修复计划较为合理,但在部分区域可考虑有关针对中规模中层崩塌的对策。本提案被相关部门所采用。     

Effective Work Function Reduction of Practical Electrodes Using an Organometallic Dimer

The control of the cathode work function (WF) is essential to enable efficient electron injection and extraction at organic semiconductor/cathode interfaces in organic electronic devices. In this paper, ultraviolet photoelectron spectroscopy is used to confirm that depositing an ultrathin layer of the moderately air‐stable pentamethylrhodocene dimer onto various conducting electrodes, by either vacuum deposition or drop casting from solution, substantially reduces their WF to less than 3.6 eV, with 2.7 eV being the lowest attainable value. Detailed measurements of the Rh core levels with X‐ray photoelectron spectroscopy reveal that the electron transfer from the molecule to the respective substrates is responsible for the appreciable WF reduction. Notably, even after air exposure, the WF of the donor‐covered electrodes remains below those of typically used clean cathode metals, such as Al and Ag, rendering the approach appealing for practical applications. The WF reduction, together with the observed air stability of the covered electrodes, demonstrates the ability of the pentamethylrhodocene dimer to reduce the WF for a wide range of electrodes used in all‐organic or organic–inorganic hybrid devices.     

Correlation between energy level alignment and device performance in planar heterojunction organic photovoltaics

Information on the interfacial electronic structure in organic photovoltaics (OPVs) is essential for fully understanding features of device operation such as the photocurrent generation and relative energy band offsets at the donor/acceptor interface, which directly affect the open circuit voltage (V_oc). Kelvin probe (KP) measurements fully reveal the energy level alignment in a prototype OPV with a copper phthalocyanine (CuPc)/fullerene (C₆₀) planar heterojunction. Energy level pinning at the CuPc/C₆₀ junction fixes the energy band offsets of C₆₀. A downward energy shift of about 0.9 eV appears at the C₆₀/bathocuproine junction, which may act as a hole-blocking barrier. A combination of KP and current density–voltage measurements indicates that photocurrent generation depends strongly on the magnitude of the upward energy shift at the CuPc/C₆₀ junction. The dependence of V_oc on the substrate work function is also discussed in terms of the energy level alignment at indium tin oxide/CuPc/C₆₀ junctions.     

Electronic structure and surface morphology of [6,6]-phenyl-C71-butyric acid methyl ester films

We investigate the electronic structure of [6,6]-phenyl-C₇₁-butyric acid methyl ester (PC₇₀BM) films by ultraviolet photoelectron and inverse photoemission spectroscopy. We discuss the electronic structure of PC₇₀BM in comparison with C₇₀ and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₀BM). The molecular orbitals around the energy gap of PC₇₀BM are broadly distributed due to the low symmetry of the molecular structure. Consequently, the energy gap of PC₇₀BM is smaller than that of C₇₀ and PC₆₀BM. The film deposition method affects the polarization energy between the PC₇₀BM molecules, and thus affects the electronic structure of the films.     

Boiling Heat Transfer and Pressure Drop of a Refrigerant R32 Flowing in a Small Horizontal Tube

In this study, experiments were performed to examine characteristics of flow boiling heat transfer and pressure drop of a low global warming potential refrigerant R32 flowing in a horizontal copper circular tube with 1.0 mm inside diameter for the development of a high-performance heat exchanger using small-diameter tubes or minichannels for air conditioning systems. Axially local heat transfer coefficients were measured in the range of mass fluxes from 30 to 400 kg/(m²·s), qualities from 0.05 to 1.0, and heat fluxes from 2 to 24 kW/m² at the saturation temperature of 10°C. Pressure drops were also measured in the rage of mass fluxes from 30 to 400 kg/(m²·s) and qualities from 0.05 to 0.9 at the saturation temperature of 10°C under adiabatic condition. In addition, two-phase flow patterns were observed through a sight glass fixed at the tube exit with a digital camera. The characteristics of boiling heat transfer and pressure drop were clarified based on the measurements and the comparison with data of R410A obtained previously. Also, measured heat transfer coefficients were compared with two existing correlations.