Preparation of nano-sized YAG:Eu3+ particles by a microwave-assisted polyol process and their luminescence properties

Phases of yttrium-aluminum binary oxide have been selectively prepared by selecting a polyol solvent in a microwave-assisted polyol process. Using 1,4-butanediol as a polyol solvent, nano-sized particles of a pure phase of YAG have been prepared. Furthermore, Eu³⁺-doped YAG has been synthesized by applying this method. We have demonstrated that 8 at% Eu³⁺-doped YAG (replacement of Y³⁺) gave the strongest emission when the content of Eu³⁺ was varied.     

Preparation and porous control of amorphous carbons by co-defluorination of perfluorooctane and octafluorotoluene in vapor phases at 423 K

Two types of perfluorocarbon compounds, aliphatic perfluorooctane and aromatic octafluorotoluene, were co-defluorinated using sodium metal, and amorphous carbons were deposited from the vapor phase at very low temperature, 423 K. The products showed morphologies composed of fibrous, platelet, and spherical forms, which were dependent on the mixing ratio of the two. The BET surface areas also correlated well with the ratio of the starting mixtures, indicating that the surface area could be adjusted by changing the mixing ratio of these two compounds. However, when the carbonaceous product was further annealed in situ at 573 or 673 K, the porosities also modified. First the porosity decreased at 573 K, then increased greatly at 673 K, where radical interaction to shrink the pores and crystal growth of template fluoride occurred at 573 K and 673 K, respectively.     

Photoluminescence dynamics of coupled quantum dots

We have investigated effects of the strain-compensating spacer layer on photoluminescence (PL) properties of excitons in the multilayered self-assembled quantum dots (SAQDs). The PL decay time of excitons in the sample with a thin spacer layer is longer than that with a thick spacer layer. This is attributed to the lowering of the oscillator strengths owing to reduction of the overlap integral between the electrons and holes envelope functions because of spatially extended electron envelope functions in the growth direction. In addition, the PL intensity of the transverse-magnetic mode in the sample with the thinner spacer layer has been found to be enhanced in the polarized PL measurement from the cleaved edge surface of the samples. These results indicate the possibility of QDs connecting along the growth direction via penetration of the electron envelope function.     

Iron‐catalyzed radical polymerization of acrylamides in the presence of Lewis acid for simultaneous control of molecular weight and tacticity

This work is directed to the stereospecific living radical polymerization of acrylamides such as N,N‐dimethylacrylamide and N‐isopropylacrylamide with an iron complex and a Lewis acid. DMAM was polymerized with [FeCp(CO)₂]₂ in conjunction with an alkyl iodide [(CH₃)₂C(CO₂Et)I] as an initiator in the presence of Y(OTf)₃ in toluene/methanol (1/1) at 60 °C to be converted almost quantitatively to the polymers with controlled molecular weights and high isotacticity (m > 80%), wherein the Fe‐complex generates radical species from a covalent C? I bond of the dormant species and the Lewis acid controls the stereochemistry of the polymerization via coordination with the amide groups of the polymer terminal and the monomer. A series of Lewis acids were also used for the iron(I)‐catalyzed DMAM polymerization, and Yb(OTf)₃ and Yb(NTf₂)₃ proved effective in giving isotactic polymers without deteriorating the molecular weight control similar to Y(OTf)₃. Furthermore, a slight enhancement of isospecificity was observed for the iron‐catalyzed system in comparison with the α,α‐Azobisisobutyronitrile‐initiated, when coupled with Y(OTf)₃. Stereoblock polymerization of DMAM via a one‐pot reaction was also achieved by just adding the Y(OTf)₃ methanol solution in the course of the polymerization to give atactic‐b‐isotactic poly(DMAM). A similar but slightly lower control in the molecular weight and tacticity was achieved in the polymerization of NIPAM with [FeCp(CO)₂]₂/Y(OTf)₃. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2086–2098, 2006     

The minimum weight triangulation problem with few inner points

We look at the computational complexity of 2-dimensional geometric optimization problems on a finite point set with respect to the number of inner points (that is, points in the interior of the convex hull). As a case study, we consider the minimum weight triangulation problem. Finding a minimum weight triangulation for a set of n points in the plane is not known to be NP-hard nor solvable in polynomial time, but when the points are in convex position, the problem can be solved in O(n³) time by dynamic programming. We extend the dynamic programming approach to the general problem and describe an exact algorithm which runs in O(6^kn⁵logn) time where n is the total number of input points and k is the number of inner points. If k is taken as a parameter, this is a fixed-parameter algorithm. It also shows that the problem can be solved in polynomial time if k=O(logn). In fact, the algorithm works not only for convex polygons, but also for simple polygons with k inner points.     

Synthesis of 11Z‐9‐demethyl‐9‐((3‐indolyl)methyl)retinal

A convenient synthesis of 11Z‐9‐demethyl‐9‐((3‐indolyl)methyl)retinal, which has an amino acid residue of tryptophan at the 9 position in retinal, is described using a tricarbonyliron complex.     

The reaction γ +d → π+ + π− +p + n between 570 and 850 MeV andΔ ++ Δ − production

The reaction γ+d → π⁺+π^? +p + n has been measured in a kinematically complete way at incident photon energies from 570 to 850 MeV in steps of 40 MeV. From detailed comparison of measured data with results of event simulations, it is concluded that three different mechanisms, the quasi-free, double-delta and phase space productions, contribute to the reaction. Each of the cross sections corresponding to these mechanisms is determined separately.