In situ Raman study on single- and double-walled carbon nanotubes as a function of lithium insertion

We investigated the electrochemical lithium ion (Li(+)) insertion/desertion behavior on highly pure and bundled single- and double-walled carbon nanotubes (SWNTs and DWNTs) using an in situ Raman technique. In general, two storage sites could host Li(+) in SWNT and DWNT bundles when varying an external potential: a) the outer surface sites, and b) the interstitial spaces within the bundles. The most sensitive changes in the tangential mode (TM) of the Raman spectra upon doping with Li(+) can be divided into two regions. The first region was found from 2.8 to 1.0 V (the coverage of Li(+) on the outer surface of a bundled nanotube) and was characterized by the loss of resonant conditions via partial charge transfer, where the G(+) line of the SWNT and the TM of the outer tube of DWNTs experienced a highly depressed intensity, but remained almost constant in frequency. The appearance of a Breit-Wigner-Fano (BWF) profile provided strong evidence of metallic inner tubes within DWNTs. The second region was observed when the applied potentials ranged from 0.9 to 0 V and was characterized by Li(+) diffusion into the interstitial sites of the bundled nanotube material. This phenomenon invoked a large downshift of the G(-) band in SWNTs, and a small downshift of the TM of the inner tube of DWNTs caused by expansion of the C--C bonds due to the charge transferred to the nanotubes, and the disappearance of the BWF profile through the screening effect of the interstitial Li(+) layers.     

Preparation of poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester Langmuir-Blodgett bulk hetero junctions on indium tin oxide

Mono-layers of aggregated Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) molecules were obtained by using solutions of P3HT, PCBM and P3HT-PCBM mixture without stabilizers such as stearates in chloroform at an air-water interface. 1 to 10 cycle-lifted LB films of P3HT and PCBM were successfully transferred to cleaned bare indium-tin-oxide coated glass substrate by vertical lifting method excluding the first 1 to 2 cycle layer. The dependence of P3HT and PCBM film thickness on the transfer cycles has been explained by the molecular sizes, where four edge-on P3HT molecular and six PCBM molecular stacking which result in thickness was taken into account. Work functions of deposited LB-layers were consistent with those of the ordinary casted films. P3HT and PCBM LB-layers showed optical activity in both infra-red (IR) and visible absorption regions of the spectrum. P-polarized IR absorption owing to C=C and C=O stretching vibrations observed in LB-layered films clearly indicate the enhancement of the orientation of these bonds perpendicular to the substrate surface in contrast to the spin-coated one. Visible optical absorption intensity was increased well in proportion with the lift cycle-numbers of both P3HT and PCBM LB films. The photovoltaic characteristics have been observed in the devices fabricated with P3HT (5 cycles-layer)/PCBM (5 cycles-layer) LB hetero structure as an active layer of the solar cells. The surface pressure of LB compression for the mixture of P3HT and PCBM, that is, bulk hetero mixtures, has also been well built up to 30 mN/m.     

Widening of harvesting layer and area of P3HT/PCBM bulk-heterojunction photovoltaic cells

We have fabricated P3HT/PCBM based bulk-heterojunction photovoltaic cells with P3HT layer as the hole transport layer and PCBM layer as the electron transport layer between electrode and blended P3HT/PCBM layer in order to widen the photon harvesting layer. Current density has increased by about 1 mA/cm² by the insertion of P3HT layer and the resulting conversion efficiency has been improved by about 20%. We have also fabricated a centimeter-scale active area with an efficiency of ∼1%.     

Thermal conductivity degradation analyses of LWR MOX fuel by the quasi-two phase material model

The temperature measurements of mixed oxide (MOX) and UO₂ fuels during irradiation suggested that the thermal conductivity degradation rate of the MOX fuel with burnup should be slower than that of the UO₂ fuel. In order to explain the difference of the degradation rates, the quasi-two phase material model is proposed to assess the thermal conductivity degradation of the MIMAS MOX fuel, which takes into account the Pu agglomerate distributions in the MOX fuel matrix as fabricated. As a result, the quasi-two phase model calculation shows the gradual increase of the difference with burnup and may expect more than 10% higher thermal conductivity values around 75 GWd/t. While these results are not fully suitable for thermal conductivity degradation models implemented by some industrial fuel manufacturers, they are consistent with the results from the irradiation tests and indicate that the inhomogeneity of Pu content in the MOX fuel can be one of the major reasons for the moderation of the thermal conductivity degradation of the MOX fuel.     

Simultaneous determination of ozone and carbonyls using trans-1,2-bis(4-pyridyl)ethylene as an ozone scrubber for 2,4-dinitrophenylhydrazine-impregnated silica cartridge

A new method for the simultaneous determination of ozone and carbonyls in air using a two-bed cartridge system has been developed. Each bed consists of reagent-impregnated silica particles. The first contains trans-1,2-bis-(4-pyridyl) ethylene (BPE) while the second contains 2,4-dinitrophenylhydrazine (DNPH). Air samples are drawn through the cartridge first through the BPE and then through the DNPH. Ozone in the air sample is trapped in the first bed by the BPE-coated silica particles and produce pyridine-4-aldehyde. Airborne carbonyls pass unimpeded thorough the BPE and are trapped in the second bed by the DNPH-coated silica particles. They produce carbonyl 2,4-DNPhydrazones. DNPH and carbonyl 2,4-DNPhydrazones are not influenced by ozone because of effective trapping by the BPE. Extraction is performed in the direction reverse to air sampling. When solvent is eluted through the BEP/DNPH cartridge, excess DNPH is washed into the BPE bed where it reacted with pyridine-4-aldehyde and forms the corresponding hydrazone derivative. All of the hydrazones derived from airborne carbonyls and pyridine-4-aldehyde (derived from ozone) are completely separated and measured using high-performance liquid chromatography. An Ascentis RP-Amide column is used, and the mobile phase is 40% aqueous acetonitrile containing 2 mmol/L ammonium acetate. The use of a BPE/DNPH cartridge has made possible the simultaneous determination of ozone and carbonyls. A separate ozone scrubber is not necessary with the BPE/DNPH cartridge because the BPE portion of the sampler serves this function.     

Domain observation and molecular orientation of chiral dipalmitoylphosphatidylcholine monolayer by Brewster angle microscopy and Maxwell displacement current

To understand the relationship between molecular chirality and electrical properties of monolayers, Maxwell displacement current (MDC) behaviors and domain shapes of chiral DPPC monolayers composed of dextro- (d-) and levo- (l-) rotatory molecules at the air-water interface are investigated during monolayer compression using MDC measurement and the Brewster angle microscopy (BAM) system. The experimental results show that for DPPC monolayers of the two pure enantiomers, the π-A isotherms and the MDC behaviors are similar to each other, while the domain patterns of them are mirror shapes of different sizes. This reveals that MDC behaviors due to molecular spontaneous polarization have no relation to chirality but domain shapes closely depend on the molecular chirality. Moreover, the observed domain shapes verify the domain shape theory which was recently developed by Iwamoto et al. [M. Iwamoto, Z.C. Ou-Yang, Phy. Rev. Letts, 93 (2004) 206101].     

Reduction of force interference and performance improvement of a consequent-pole bearingless motor

A bearingless motor combines the functions of both magnetic suspension and torque generation together in a single motor. A consequent-pole type of bearingless motor has already been proposed. In contrast to conventional bearingless motors, it is free from the trade-off between suspension force and torque. In addition, stable suspension can be achieved without detecting the rotational angle. However, a part of the X-axis current generates undesirable force in the Y-axis. This force interference influences the performances of bearingless motors; thus, the interference should be eliminated. In this paper, the authors propose an optimal winding design of the consequent-pole bearingless motor to minimize the suspension force interference. Here, the suspension forces in the radial direction are numerically calculated using the magneto-motive force distribution of the bearingless motor, and are compared with the analytical results of finite element method. To verify the theory, static and dynamic performance tests were carried out. It was found that the improved winding configuration significantly reduced the suspension force interference by 90% compared with the previous winding configuration. It was also found that the radial shaft vibration and the power consumption were considerably decreased, by approximately 16% and 44%, respectively.     

Consideration on the Relationship Between Dielectric Breakdown Voltage and Water Content in Fatty Acid Esters

Mineral oil is commonly used as an electrical insulating oil in transformers because of its relatively high electrical insulating ability and fluidity. Considering the depletion of resources and environmental problems, however, fatty acid esters synthesized from natural plant oils are attracting attention as an environmentally friendly insulating oil. In addition, fatty acid esters such as methyl octanoate, methyl dodecanoate, 2-ethylhexyl octanoate, and 2-ethylhexyl dodecanoate have high fluidity, and also show excellent moisture tolerance against dielectric breakdown compared to mineral oil. In the present study, to clarify the reason for the superior moisture tolerance of fatty acid esters, the status of dissolved water in esters is investigated with IR spectroscopic measurements and density functional theory (DFT) calculations. It is revealed that water molecules in fatty acid esters are trapped by the ester moiety of fatty acid esters. As a result, fatty acid esters have a higher moisture tolerance against dielectric breakdown than mineral oil.