Fabrication of freestanding m-plane GaN wafer by using the HVPE technique on an aluminum carbide buffer layer on an m-plane sapphire substrate

A freestanding m-plane GaN wafer is fabricated by using the hydride vapor-phase epitaxy (HVPE) technique on an aluminum carbide buffer layer on an m-plane sapphire substrate. X-ray pole-figure measurements show a clear m-plane orientation of the GaN surface. The full-width at half-maximum (FWHM) of GaN (1 1¯ 0 0) X-ray rocking curve (XRC) with the scattering vector along the [1 1 2¯ 0] direction is approximately 800 arcsec; this indicates good crystallinity. On the other hand, the FWHM for the case in which the scattering vector is oriented along the [0 0 0 1] direction is broad; this suggests the influence of structural defects along this direction. In fact, basal plane stacking faults (BSF) with a density of approximately 3×10⁵ cm⁻¹ is observed by transmission electron microscopy (TEM). The preparation of a 45-mm-diameter m-plane GaN wafer due to spontaneous separation of the GaN layer from the sapphire substrate is demonstrated.     

Two distinct pathways for essential metabolic precursors for isoprenoid biosynthesis

Isoprenoids are a diverse group of molecules found in all organisms, where they perform such important biological functions as hormone signaling (e.g., steroids) in mammals, antioxidation (e.g., carotenoids) in plants, electron transport (e.g., ubiquinone), and cell wall biosynthesis intermediates in bacteria. All isoprenoids are synthesized by the consecutive condensation of the five-carbon monomer isopentenyl diphosphate (IPP) to its isomer, dimethylallyl diphosphate (DMAPP). The biosynthetic pathway for the formation of IPP from acetyl-CoA (i.e., the mevalonate pathway) had been established mainly in mice and the budding yeast Saccharomyces cerevisiae. Curiously, most prokaryotic microorganisms lack homologs of the genes in the mevalonate pathway, even though IPP and DMAPP are essential for isoprenoid biosynthesis in bacteria. This observation provided an impetus to search for an alternative pathway to synthesize IPP and DMAPP, ultimately leading to the discovery of the mevalonate-independent 2-C-methyl-D-erythritol 4-phosphate pathway. This review article focuses on our significant contributions to a comprehensive understanding of the biosynthesis of IPP and DMAPP.     

Precise measurement of positronium hyperfine splitting using the Zeeman effect

Positronium is an ideal system for the research of the quantum electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of positronium, Δ_HFS, gives a good test of the bound state calculations and probes new physics beyond the Standard Model. A new method of QED calculations has revealed the discrepancy by 15 ppm (3.9σ) of Δ_HFS between the QED prediction and the experimental average. There would be possibility of new physics or common systematic uncertainties in the previous all experiments. We describe a new experiment to reduce possible systematic uncertainties and will provide an independent check of the discrepancy. We are now taking data and the current result of Δ_HFS?=?203.395 1 ±0.002 4 (stat., 12 ppm) ±0.001 9 (sys., 9.5 ppm) GHz has been obtained so far. A measurement with a precision of O(ppm) is expected within a year.     

Simultaneous determination of sodium dodecyl sulphate and sodium linear-dodecylbenzenesulphonate with 1-stearyl-4-(4-aminonaphthylazo)-pyridinium bromide by spectrophotometry

A rapid and sensitive spectrophotometric method for the simultaneous determination of sodium dodecyl sulphate (SDS) and sodium linear-dodecylbenzenesulphonate (DBS) with 1-stearyl-4-(4-aminonaphthylazo)-pyridinium bromide (SAPB) is described using the difference at the maximum absorption wavelength of the SDS- and the DBS-ion associate. SDS and DBS have been determined independently by measuring their respective absorbances at the maximum absorption wavelength. The apparent molar absorptivities of the SDS- and the DBS-ion associate are 8.0×10⁴ l mol^–1 cm^–1 at 445 nm and 4.5×10⁴ l mol^–1 cm^–1 at 424 nm, respectively. The calibration graph for SDS is linear in the range from 0.1 to 1.0×10^–6 mol/l in the presence of 1.2×10^–6 mol/l DBS and for DBS from 0.8 to 2.0×10^–6 mol/l in the presence of 8.0×10^–7 mol/l SDS. The relative standard deviation (n=15) for 8.0×10^–7 mol/l SDS is 3.4% and for 1.6×10^–6 mol/l DBS 2.1%. The proposed method has been applied to the simulatenous determination of SDS and DBS in river water samples.     

Triphenylstibine oxide–phosphorus(V) sulfide as a novel condensation catalyst system: application to the synthesis of dipeptides

Triphenylstibine oxide (Ph₃SbO) and phosphorus(V) sulfide (P₄S₁₀) synergistically catalyzed the aminolysis of N-protected amino-acids with amino-acid esters in benzene. Ph₃SbO accelerated both the initial conversion of carboxylic moieties into the corresponding thiocarboxylic moieties by P₄S₁₀ and the subsequent aminolysis of the resulting thiocarboxylic acids. Thus, dipeptides such as Z–A–A′–OEt (where Z = PhCH₂OC(O)– and A,A′ = Ala,Gly; Gly,Gly; Leu,Gly; Phe,Gly; Phe,Leu;Ser,Gly; Val,Gly, respectively) were conveniently prepared even at 35°C.     

T-matrix analysis of electromagnetic wave differaction from a Fourier grating

This paper is described for T-matrix analysis of the electromagnetic wave diffraction from a Fourier grating that the boundary value problem is treated by applying the extended boundary condition. The rigorous form of the expression of matrix elements is presented in the term of Bessel functions of the first kind. The error of power conservation versus the truncated number has been examined for mode number. Diffraction efficiencies versus groove depth and wavelength for a second or third harmonic wave of Fourier grating have been discussed. Numerical results are in good agreement with those obtained from other method and experimental values. Reasonable numerical results are presented for a groove depth per period of the Fourier grating less than 0.25.     

Performance test of a shell-and-plate type evaporator for OTEC

The performance test of a shell-and-plate type evaporator (total surface area 21.95 m², length 1450 mm, width 235 mm, 100 plates) for ocean thermal energy conversion (OTEC) plants is reported. Freon 22 (R22) and ammonia (NH₃) were used as the working fluid. Empirical correlations are proposed for predicting the boiling heat transfer and the heat transfer coefficients on the water side. The water-side pressure drop is about 2.9 × 10⁴ N/m² when the warm water velocity is 0.7 m/s. The water-side friction factor is obtained.     

Preparation of copper-indium sulfide thin films by single-source OMCVD: Mass-spectral investigation of decomposition path of the organometallic sources

In order to prepare high-quality CuInS₂ thin films vapor phase decomposition patterns of three copper-indium binuclear complexes, and as candidates for source materials were investigated using EI MS. The complex 1c showed series of intensive peaks due to the fragmentation of M⁺. For 1a, only a fragmentation pattern starting from BuIn(S₂CNBu₂)₂ was detectable. This should suggest that 1a decomposed into BuIn(S₂CNBu₂)₂ and copper sulfide before vaporization. In addition an ambiguous feature could be observed for 1b, viz. two fragmentation paths. Consequently, we judge that 1c is a suitable source complex to prepare CuInS₂ thin films via a single-source OMCVD process. Thus chalcopyrite CuIns₂ thin films were successfully prepared via single-source OMCVD using 1c as a source complex, with T_substrate400°C, T_source80°C, base pressure 0.7 Torr and carrier (nitrogen) flow rate 0.8 L min^?1. Fragmentation of two copper dithiocarbmates, Cu(S₂CNBu₂)₂ and Cu[S₂CN(i-Pr)₂]₂, and two butylindium thiolates, Bu₂InS(i-Pr) and BuIn[S(i-Pr)]₂, as components of 1 is additionally discussed.     

Effects of a vanadate-support on the reactivity of theBis(Methallyl)Rhodium Complex [{(η3-C4H7)2Rh}2(V4O12)]2−. A comparison with the acetylacetonato complex

The methallyl moieties of [{(³-C₄H₇)₂Rh}₂(V₄O₁₂)]^2– couple to yield 2,5-dimethyl-1,5-hexadiene in a selective manner by the action of P(OEt),₃, while the reaction of [( ³-C₄H₇)₂ Rh(acac)] with P(OEt)₃ produces a mixture of organic compounds. The result shows that the vanadate support has a significant influence on the reactivity of organometallic complexes.     

Microscopic structures of adsorbed cationic porphyrins on clay surfaces: molecular alignment in artificial light-harvesting systems

The intercalation behavior of cationic porphyrin derivatives within the interlayer spaces of nano-layered clay minerals has been investigated. The porphyrins were successfully intercalated by the newly adopted method of repeated freeze-thaw cycles. The absorption spectra of the porphyrins were compared in the solution phase, adsorbed onto the exfoliated clay nano-sheets, intercalated within the interlayer spaces of clay sheets dispersed in water and intercalated in dry films. Substantial red shifts of the λ_max values in the absorption spectra of the porphyrins were observed on the exfoliated clay sheets, and further red shifts were induced within the interlayer space. The dry films of the intercalated samples exhibited the largest red shifts. X-ray diffraction studies revealed that the clearance space between the layers in these intercalated hybrid compounds is only large enough for the porphyrins to be rigidly packed parallel to the clay layer. For the exfoliated clay nano-sheets, theoretical calculations were carried out on the correlation between the dihedral angle of the meso-substituted pyridiniumyl plane vs. the porphyrin ring and the λ_max of the porphyrin Soret band. An extrapolation of the experimental λ_max value to the correlation curve, afforded the dihedral angle to be 61.6°. The microscopic structure of the adsorbed state of the cationic porphyrins on the exfoliated clay nano-sheets was, thus, proposed to involve an orientation parallel to the clay surface, with a distance of 0.15 nm from the surface, which implies the expulsion of the solvent water molecules.