Photorefractive Four-Wave Mixing Switches Utilizing Pockels Effect -Longitudinal and Lateral Switches-

We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO₃, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO³ crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent.     

Facilitated sulfate transfer across the nitrobenzene-water interface as mediated by hydrogen-bonding ionophores.

Facilitated SO4(2-) transfers by hydrogen bond-forming ionophores are investigated across the nitrobenzene (NB)-water interface by using polarography with a dropping electrolyte electrode. Bis-thiourea 1, alpha,alpha'-bis(N'-p-nitrophenylthioureylene)-m-xylene, is found to significantly facilitate the transfer of the highly hydrophilic SO4(2-) whereas its counterpart, N-(p-nitrophenyl)-N'-propylthiourea (ionophore 2), cannot. In contrast to the predominant formation of a 1:1 complex with SO4(2-) in the bulk NB phase, the SO4(2-) transfer assisted by 1 is indeed based on the formation of a 1:2 complex between SO4(2-) and ionophore, even under the condition of [SO4(2-)]aq > [1]org. Such an exclusive formation of the 1:2 (SO4(2-) to ionophore) complex at the NB-water interface is not observed with structurally similar bis-thiourea 3, alpha,alpha'-bis(N'-phenylthioureylene)-m-xylene, where p-nitrophenyl moietes of bis-thiourea 1 are simply replaced by phenyl groups. The facilitated transfer of SO4(2-) with bis-thiourea 1 is further compared to that of HPO4(2-) and H2PO4- across the NB-water interface, which was previously shown to be assisted by 1 through the formation of the 1:1 and 2:1 (anion to ionophore) complexes, respectively. On the basis of these examinations, unique binding behaviors of hydrogen bond-forming ionophores at the NB-water interface are discussed, with a view towards development of ionophore-based anion-selective chemical sensors.     

Applying a Mode Selector to Improve the Pulse-Compression Performance of Asymmetric-Coupled-Waveguide-Based Dispersion Compensators

An InGaAsP slab-type asymmetric-coupled-waveguide-based dispersion compensator with a mode selector has been designed and fabricated. The mode selector is necessary to select either a symmetric [with a positive group-velocity dispersion (GVD)] or antisymmetric (with a negative GVD) supermode. These supermodes exist simultaneously in the dispersion-compensation region of the device. Pulse-compression experiments were used to test the dispersion compensator, evaluating the function of the mode selector. A theoretical study of the experimental results shows that the mode selector obtains a very strong selectivity (nearly 100%) for the antisymmetric supermode.     

Hetergeneous-nucleation synthesis of monodisperse ε-cobalt nanoparticles using palladium seeds

Monodisperse bimetallic Pd–Co nanoparticles were prepared via a thermal decomposition of cobalt carbonyl using palladium seeds at the Pd/Co molar ratios 0.5%, 1%, and 5%. The heterogeneously nucleated nanoparticles without any size-selective precipitation are sufficiently uniform to self-assemble into ordered arrays. The as-synthesized nanoparticles are each a single crystal with a complex cubic structure called ε-Co. The presence of Pd seeds seems to improve the stability of Co nanoparticles against oxidation based on the results from time-dependent magnetization measurement.     

Electronic effect on the regioselectivity in the ring opening of para-substituted phenyloxiranes by acetylides

The electronic effect on the regioselectivity in the alkynylation of phenyloxiranes was investigated using three kinds of metal acetylides. BF₃ mediated lithium acetylide provided either the α- or β-alkynylated products by controlling the effect of the para-substituents of the phenyloxiranes. LiClO₄ mediated lithium acetylide and titanium acetylide, on the other hand, afforded predominantly the β- and α-products, respectively.     

In Situ Processing of Nano Crystalline Oxide Particles/Polymer Hybrid

Nano sized crystalline particles/polymer hybrids were synthesized form designed metal-organic precursors. The newly developed method is composed of the synthesis of organic matrix by polymerization and the in situ nucleation and growth of crystalline oxide particles in the organic matrix below 100°C. The design of metal-organic precursor modified with polymerizable ligand and the selection of reaction conditions does influence the size and crystallinity of ceramic particles in organic matrix. The nano-sized magnetic particle/polymer hybrid exhibits the interesting feature of superparamagnetism and quantum size effect. The crystalline particles of BaTiO₃/, PbTiO₃/, and KNbO₃/polymer hybrids behave to be dielectric and show the typical electro-rheological behavior.     

Effects of Si−Al composition on the fluorescence spectra of 1-naphthol during the sol-gel-xerogel transitions

A systematic study has been carried out on the characteristic changes in the fluorescence spectra of 1-naphthol doped in the sol-gel-xerogel transition systems comprised of tetraethyl orthosilicate and diisobutoxyaluminium triethylsilicate catalyzed by a small amount of HCl, NH₄OH, as well as under uncatalyzed conditions. In the systems containing large amounts of silicon, the fluorescence of 1-naphthol shifts to the red (a predominant emission from the ¹L_a state) during the first stage of the reaction. This red shift indicates an increase in the polarity of the matrix surrounding 1-naphthol. In the second stage of the reaction, the spectrum shifts to the blue (a predominant emission from the ¹L_b state), reflecting an increase in the micro-viscosity around 1-naphthol. In the systems containing relatively large amounts of aluminum, however, the spectrum just after mixing shows a larger red shift than that originating from the ¹L₂ emission. This large red-shifted fluorescence reflects the formation of a complex between 1-naphthol and the −O−Al−O−Si−O-network. The spectrum then shifted to the blue. The spectral behaviours observed indicate that there is a large and dynamic molecular-level change in the physicochemical properties of the matrix surrounding the 1-naphthol molecules during the sol-gel-xerogel transitions of the systems while the gelation phenomenon reflects macroscopic inflexibility although it is completely different from the restriction of movement at the molecular level.     

Diastereoselective synthesis of the 19-epi-C18-C25 segment of (−)-lasonolide A and an unusual inversion at C19

Diastereoselective construction of the 19-epi-C₁₈-C₂₅ segment of (−)-lasonolide A was achieved using a 5-exo-trigonal mode of radical cyclization for the creation of the contiguous quaternary and tertiary stereogenic centers at C₂₂ and C₂₃ as the key reaction step. During the dehydration stage, it was found that an unusual inversion of configuration took place.     

A large thermal hysteresis loop produced by a charge-transfer phase transition in a rubidium manganese hexacyanoferrate

In a rubidium manganese hexacyanoferrate, RbMn[Fe(CN)(6)], the magnetic susceptibility (chi(M)) decreased at 225 K (=T(1/2)decreasing) and abruptly increased at 300 K (=T(1/2)increasing) in the cooling and warming processes, respectively. X-ray photoelectron spectroscopy and infrared spectroscopy indicated that the high-temperature (HT) and low-temperature (LT) phases were composed of Mn(II)-NC-Fe(III) and Mn(III)-NC-Fe(II), respectively. A structural change from cubic (F43m, a = 10.533 A) to tetragonal (I4m2, a = b = 7.090 A, c = 10.520 A) accompanied the phase transition, and, on the basis of these results, the HT and LT phases were assigned to Mn(II)(t(2g)(3)e(g)(2), (6)A(1g); S = (5)/(2))-NC-Fe(III) (t(2g)(5), (2)T(2g); S = (1)/(2)) and Mn(III)(e(g)(2)b(2g)(1)a(1g)(1), (5)B(1g); S = 2)-NC-Fe(II) (b(2g)(2)e(g)(4), (1)A(1g); S = 0), respectively. This phenomenon is caused by a metal-to-metal charge transfer from Mn(II) to Fe(III) and a Jahn-Teller distortion of the produced Mn(III) ion. The reaction mechanism is discussed, considering the entropy difference between the HT and LT phases.     

Polymerization of acrylamide initiated with pinacol–ceric ion redox system

Polymerization of acrylamide initiated with a pinacol–ceric ion redox system was investigated. The polymer obtained was found to contain one cerium atom in a polymer molecule. It was considered that the cerium atom was introduced into the polymer molecule by the termination reaction as there is no cerium atom in the initiating radical in the present system. A similar termination reaction was attained by ferric ion but not by cerous ion. The metal ion was considered to terminate the polymerization to form a stable polymer. Some considerations on the structure of the reaction product relating to the polymerization mechanism were discussed.