Dispersion of single-walled carbon nanotubes modified with poly-l-tyrosine in water

In this study, complexes composed of poly-l-tyrosine (pLT) and single-walled carbon nanotubes (SWCNTs) were produced and the dispersibility of the pLT/SWCNT complexes in water by measuring the ζ potential of the complexes and the turbidity of the solution were investigated. It is found that the absolute value of the ζ potential of the pLT/SWCNT complexes is as high as that of SWCNTs modified with double-stranded DNA (dsDNA) and that the complexes remain stably dispersed in the water at least for two weeks. Thermogravimetry analysis (TGA) and visualization of the surface structures of pLT/SWCNT complexes using an atomic force microscope (AFM) were also carried out.     

Exfoliated graphene sheets decorated with metal/metal oxide nanoparticles: Simple preparation from cation exchanged graphite oxide

We produced carbon hybrid materials of graphene sheets decorated with metal or metal oxide nanoparticles of gold, silver, copper, cobalt, or nickel from cation exchanged graphite oxide. Measurements using powder X-ray diffraction, transmission electron microscopy, and X-ray absorption spectra revealed that the Au and Ag in the materials (Au–Gr and Ag–Gr) existed on graphene sheets as metal nanoparticles, whereas Cu and Co in the materials (Cu–Gr and Co–Gr) existed as a metal oxide. Most Ni particles in Ni–Gr were metal, but the surfaces of large particles were partly oxidized, producing a core–shell structure. The Ag–Gr sample showed a catalytic activity for the oxygen reduction reaction in 1.0 M KOH aq. under an oxygen atmosphere. Ag–Gr is superior as a cathode in alkaline fuel cells, which should not be disturbed by the methanol cross-over problem from the anode. We established an effective approach to prepare a series of graphene-nanoparticle composite materials using heat treatment.     

Stability of Cu(In,Ga)Se2 solar cells and evaluation by C–V characteristics

To confirm the long-term reliability of Cu(In,Ga)Se₂, (CIGS) solar cells, we investigated the I–V and C–V characteristics during tests under irradiation or dark condition. Under irradiation, the test samples showed a little increase in efficiency (η) and open-circuit voltage (V_oc) which showed their electrical durability to light irradiation. But the diode factor (n) and series resistance (R_s) showed large changes in value. Also, the built-in voltage (V_b) and density gradient (dN_A/d_x) in the CIGS layer calculated from the C–V characteristics showed distinct changes during the test. After 4 SUN irradiation, two samples in the same fabrication-lot showed new light absorption in the lower-energy range than sun the energy gap of CIGS. We explain the change of C–V characteristics for the samples under strong irradiation with a new model named “Junction retrograde” which can treat defect generation by irradiation to reduce the acceptor density in graded p-n junction. This model for C–V analysis can be used to investigate the long-term reliability of CIGS solar cells under irradiation.     

Multi-bit Sigma-Delta TDC Architecture with Improved Linearity

This paper describes the architecture and principles of operation of sigma-delta ( ΣΔ) time-to-digital converters (TDC) for high-speed I/O interface circuit test applications. In particular, we describe multi-bit ΣΔ TDC architectures; they offer good accuracy with short testing time. However, mismatches among delay cells in delay lines degrade their linearity. Here we propose two methods to improve the overall TDC linearity: a data-weighted-average (DWA) algorithm, and a self-calibration method that measures delay values using a ring oscillator circuit. Our Matlab simulation results demonstrate the effectiveness of these approaches.     

SiC coating as hydrogen permeation reduction and oxidation resistance for nuclear fuel cladding

Silicon carbide (SiC) coating is one of the countermeasures for the prevention of oxidation and hydrogen embrittlement of fuel claddings because SiC has high resistance of oxidation and hydrogen permeation. Hydrogen permeation and oxidation experiments for the cladding materials with SiC coatings were conducted in unirradiated conditions. The sputtering method was employed to make SiC coatings. In the hydrogen permeation experiment, 316 type of stainless steel (SS316) was used as a base material of the coating. SS316 with SiC coatings showed hydrogen permeation reduction by one order of magnitude. In the oxidation experiments, Zircaloy 4 (Zry-4) and SS316 were used as base materials of the coatings. The weight gain of the Zry-4 specimens with a SiC coating decreased by about one-fifth compared to the uncoated ones at 750 °C and 1200°C. This phenomenon was observed for SS316 at 750 °C as well. The peel-off of the coating was observed in several experiments, and it is considered that the peel-off was caused by the difference of the thermal expansions between coatings and base materials. Thicker coatings showed better oxidation resistance, but thinner coatings showed more tolerance of peel-off.     

Tribological Performance of Halogen-Free Ionic Liquids as Lubricants of Hard Coatings and Ceramics

Ionic liquids are expected to be used as new high-performance lubricants because of their low volatility, high thermal stability, and high oxidation stability. It is well known that halogen-containing ionic liquids exhibit excellent lubricity for metals. However, there is a concern about the corrosiveness of ionic liquids caused by the formation of halides. The lubricity of halogen-free ionic liquids for metals is inferior to that of halogen-containing ionic liquids; however, they do not cause any remarkable corrosion effects. In this study, the lubricity of halogen-free ionic liquids—1-butyl-3-methylimidazolium tricyanomethanide ([BMIM] [TCC]) and 1-ethyl-3-methylimidazolium dicyanamide ([EMIM] [DCN])—for hard coatings and ceramics was evaluated using an SRV oscillating sliding tester. Ionic liquids exhibited excellent lubricity for sintered ceramics. It is supposed that the lubricity of ceramics depends on the chemical interaction between the surface and the ionic liquids. Ionic liquids exhibited different lubricating properties with each nitride coating. [EMIM] [DCN] exhibited a better wear reduction than [BMIM] [TCC] on CrN, and its friction coefficient was higher than that of [BMIM] [TCC]. DLC coatings with [EMIM] [DCN] exhibited better lubricity than with [BMIM] [TCC], and the combination of H-free DLC and [EMIM] [DCN] particularly showed excellent lubricity. XPS analysis showed that two kinds of nitrogen compounds were on the sliding surface of H-free DLC lubricated with [EMIM] [DCN].     

Enantioselective Reaction of Imines and Benzyl Nitriles Using Palladium Pincer Complexes with C2‐Symmetric Chiral Bis(imidazoline)s

Enantioselective reactions of a wide variety of benzyl nitriles with N‐tosylimines catalyzed by novel chiral 1,3‐bis(imidazolin‐2‐yl)benzene‐palladium(II) [Phebim‐Pd(II)] complexes have afforded the respective products in high yield with good enantioselectivity. A reaction mechanism is proposed based on X‐ray crystal structures of palladium complexes.     

Application of Continuously Frequency-Tunable 0.4 THz Gyrotron to Dynamic Nuclear Polarization for 600 MHz Solid-State NMR

In this paper we present results that demonstrate the utility of a continuously frequency-tunable 0.4 THz-gyrotron in a dynamic nuclear polarization (DNP)-enhanced solid-state NMR (SSNMR) spectroscopy at one of the highest magnetic fields, B ₀ = 14.1 T (600 MHz for ¹H Larmor frequency). Our gyrotron called FU CW VI generates sub-mm wave at a frequency near 0.4 THz with an output power of 4–25 W and a tunability over a range of more than 1 GHz by sweeping the magnetic field at the gyrotron cavity. We observed overall down shifting of the central frequency by up to ~1 GHz at high radiation duty factors and beam current, presumably due to the cavity thermal expansion by a heating, but the tunable range was not significantly changed. The frequency tunability facilitated the optimization of the DNP resonance condition without time-consuming field-sweep of the high-resolution NMR magnet, and enabled us to observe substantial enhancement of the SSNMR signal (ε _DNP = 12 at 90 K).     

Synthesis and photo-electrochemical properties of novel thienopyrazine and quinoxaline derivatives,and their dye-sensitized solar cell performance

Light absorption from visible to NIR region is required to increase the photocurrent and to enhance the photo-energy conversion efficiencies in dye-sensitized solar cells (DSSCs). We have now developed novel thienopyrazine dye TP1 which has absorption up to 700 nm. Quinoxaline dye QX2 with absorption at shorter wavelengths than TP1 has been synthesized for comparisons. The power conversion efficiencies of DSSCs with TP1 and QX2 showed 4.4% and 3.2%, respectively. The absorption edge in IPCE of TP1 reached 800 nm and the open circuit voltage (Voc) of QX2 was high (0.77 V). To improve the device performances, QX2 was used as a co-adsorbent dye with TP1. In the mixed sensitizer based DSSC, a high power conversion efficiency of 6.2% was achieved due to the effective light harvesting and steric effect of QX2.     

A ZCZ‐CDMA system with BFSK modulation

A quasi‐timing synchronous code division multiple access (CDMA) system called ZCZ‐CDMA, which uses a set of sequences with a zero‐correlation zone called ZCZ code as a spreading code, is useful for short‐range wireless communications because of its excellent properties such as co‐channel interference‐free performance, simplified hardware design, and low transmit power as well as fast frame synchronization capability. In this paper, a ZCZ‐CDMA system with binary frequency‐shift keying (BFSK) modulation called BFSK‐ZCZ‐CDMA is proposed. This system is characterized by using a pair of balanced ZCZ codes for spreading and transmitting the two spread components over the respective keying carrier frequencies. Its bit error rate performance, compared with those of existing BPSK‐ZCZ‐CDMA, ASK‐ZCZ‐CDMA, and CDMA systems using the other spreading codes, is evaluated in theory and simulation. The bit error rate performance of the three ZCZ‐CDMA systems over additive white Gaussian noise and Rayleigh fading channels are formulated. It is proved that BFSK‐ZCZ‐CDMA is much more robust in anti‐fading performance and low transmit power in such an environment that fading distributions on the keying frequencies are independent mutually. Fading versus frequency characteristics are also investigated. Copyright © 2012 John Wiley & Sons, Ltd.