An efficient catalyst-free regio- and stereoselective ring-opening of epoxides with phenoxides using polyethylene glycol as the reaction medium

A catalyst-free regio- and stereoselective ring-opening of epoxides with phenoxides has been carried out efficiently using polyethylene glycol as the reaction medium to form the corresponding β-aryloxyalcohols in high yields at room temperature.     

Modification of poly(styrene-co-divinylbenzene) membrane by grafting of salicylic acid via a ketone bridge

Chelating solid phase extraction is a method particularly adapted to the recovery of metallic ions in polluted waters. The principle consists in the partitioning of the analyte between the solution and a solid sorbent grafted by a ligand. Aromatic organic crosslinked copolymers, which are commercially available, permit to consider numerous ways of linking the ligand to the sorbent. In this way, the grafting of salicylic acid (SA) via a ketone bridge on Amberlite^® XAD-4 resin has been previously achieved with success. Then the same grafting on Empore^™ SDB-XC membrane was also considered. The yield obtained is 33%. The determination of complexing capacities highlights the fact that about 20% of the grafted complexing sites could efficiently retain metallic ions. For the first time, a ligand has been covalently linked to Empore^™ SDB-XC membrane.     

Improvement of photoluminescence mechanism of CTA-treated Si-implanted SiO2 films by using RTA

In this paper, a shift in the photoluminescence (PL) peak from blue to near-infrared region was observed in the Si⁺-implanted 400-nm-thick SiO₂ films with the rapid thermal annealing (RTA) method only. As the Si⁺-fluence was 1×10¹⁶ ions/cm², a blue band was observed in the films after RTA at 1050 °C for 5 s in dry-N₂ atmosphere; then, the band shifted from blue to orange upon increasing the holding temperature of RTA to 1250 °C in the films after the isochronal RTA in dry N₂. Furthermore, while the fluence was increased to 3×110¹⁶ ions/cm² and the holding temperature was at the same range between 1050 and 1250 °C, the PL peak occurred between red and near-infrared regions. Although the RTA and conventional thermal annealing (CTA) methods produce a similar mechanism, the CTA method needs a much longer annealing-time and a higher Si⁺-implanted dose than the RTA method for producing the same shift and intensity of PL peak from the as-implanted sample. Therefore, the RTA method can produce the mechanism in the Si⁺-implanted sample with the PL energy between blue and near-infrared band in place of the CTA method.     

A one-pot direct regioselective iodination of Fischer-Borsche product using periodic acid in PEG-400

A metal-free and greener approach for the one-pot direct iodination and dehydrogenation of dihydrobenzo[a]carbazoles has been developed using periodic acid in polyethylene glycol-400 (PEG-400) under mild condition. This method has been proven to be tolerate to a broad range of functional groups, with good to excellent yields include metal-free inexpensive catalyst, easy work-up, benign reaction condition and high regioselectivity. The solvent has been successfully recycled up to 5 times without any loss of activity in an aqueous medium.     

Sub-critical crack growth in sodium germanate glasses

Sub-critical crack growth in binary sodium germanate glass was investigated over a wide range of the crack velocities, 10⁻⁷-10⁻² m s⁻¹, by using small-size specimens with double cleavage drilled compression configuration. For evaluating the intrinsic sub-critical crack growth, crack initiation and subsequent propagation of the crack were performed in heptane. With increasing Na₂O content in sodium germanate glass, sub-critical crack growth curve shifted toward higher stress intensity factors first up to 10 mol% Na₂O, but more addition of Na₂O caused the curve to shift to lower stress intensity factor regions. In other words, fracture toughness shows a maximum at the composition of 10Na₂O·90GeO₂, whose value is 1.07 MPa m^1/2. This compositional dependence of fracture toughness originates from the so-called germanate anomaly. On the other hand, the slope of sub-critical crack growth curve for the glass containing >10 mol% Na₂O was much shallower than that for soda-lime glass. These glasses are very fatigable even in inert condition. It is considered that this fatigue behavior can be caused by the microscopic structural variation, which is the presence of GeO₆ units in GeO₂ glass network, and that these units can be the fatigue crack path.     

The a-C:H/p-Si solar cell deposited by pulsed laser deposition

Hydrogenated amorphous carbon films (a-C:H) were deposited on p-type silicon as well as silica substrates by pulsed laser deposition technique using a mixture of graphite and camphor powders. The Fourier transform infrared spectroscopy measurement revealed the presence of hydrogen in the a-C:H films. The optical properties and structure of the a-C:H film were investigated by UV-visible and Raman scattering spectroscopy. The formation of a heterojunction between the a-C:H film and silicon substrate was confirmed by the current-voltage (I-V) measurement. Furthermore, the structure of a-C:H/p-Si showed photovoltaic characteristics with an open-circuit voltage (V_oc) of 0.4 V and short-circuit current density (J_sc) of about 15 mA/cm² under AM1.5 (100 mW/cm²) illumination. From the calculation, the energy conversion efficiency and fill factor were found to be 2.1% and 0.38, respectively. The carbon layer contributed to the energy conversion efficiency, which was proved by the measurement of quantum efficiency.     

二氧化锰纳米棒的固相合成与表征

上世纪90年代以来,纳米科技向化学电源领域渗透,科技工作者开始研发纳米级MnO2电极材料,主要包括MnO2纳米粉体的制备[1-8]和将其作为碱锰电池正极材料[1-3]、高能量密度锂电池正极材料以及超级电容器电极材料的性能研究[4-8].     

The convergence of three spline methods for scattered data interpolation and fitting

The convergences of three L₁ spline methods for scattered data interpolation and fitting using bivariate spline spaces are studied in this paper. That is, L₁ interpolatory splines, splines of least absolute deviation, and L₁ smoothing splines are shown to converge to the given data function under some conditions and hence, the surfaces from these three methods will resemble the given data values.     

New data on the p + N → [Σ0K+] + N reaction at E p= 70 GeV and the search for exotic baryons

New data for the diffractive reaction p+N→ [Σ⁰ K ⁺] +N at E _p= 70 GeV were obtained with partially upgraded SPHINX setup. The data are in a good agreement with the results of our previous study of this reaction. In the mass spectrum M(Σ⁰ K ⁺) a structure at the threshold region with a mass ∼1810 MeV and a distinct X(2000) peak with M= 1989 ± 6 MeV and γ= 91 ± 20 MeV are observed. Unusual features of the massive X(2000) state (narrow decay width, anomalously large branching ratio for the decay channel with strange particle emission) make it a serious candidate for cryptoexotic pentaquark baryon with hidden strangeness |qqqsˉs>. We also present new results on the narrow threshold structure X(1810) with M= 1807 ± 7 MeV and γ= 62 ± 19 MeV which is produced in the region of very small P ² _T < 0.01 GeV². The possibility of the Coulomb production mechanism for X(1810) is discussed. Received: 28 April 1999