Enhancement of third-order optical nonlinearities in 3-dimensional films of dielectric shell capped Au composite nanoparticles

The composite nanoparticles of Au-core capped by CdS shells of different thickness were prepared and assembled into densely packed 3-dimensional films by the layer-by-layer self-assembly (LBL) technique. These films exhibited the 3-dimensional structure of densely packed Au@CdS composite nanoparticles and the shell thickness was tunable by changing the concentration of Cd2+-thiourea complexes. These multilayer films exhibited enhanced third-order optical nonlinear responses and ultrafast response times (several picoseconds). The third-order nonlinear optical susceptibility of the film with the CdS shell thickness of 4.4 nm was estimated to be 1.48 x 10(-9) esu and the value decreases with the increase of the CdS shell thickness. The enhancement of the optical nonlinearity was explained based on the calculation according to the electrostatic approximation by the solution of Laplace's equation under the boundary conditions appropriate to the model of core-shell nanoparticles, and mainly attributed to localized electric field effects in the CdS shell region. Additionally, the nonlinearity was optimized by determination of the values of the dielectric constant and thickness of the different shell.     

Magnetic domain wall motion by current injection in CoPt nanowires consisting of notches

Magnetic domain wall behaviors in CoPt nanowires consisting of multiple pairs of notches were investigated by experimental measurements as well as by micromagnetic modeling. The nanowires were fabricated by ion-beam sputter deposition and e-beam lithography where one to three triangular shaped notches were installed at an interval of 1 μm. Based on the evaluated I–V characteristics, we observed that differential resistance curves showed two peaks with a local minimum at around zero current; the domain wall was trapped between the current ranges within these two peaks. As the number of notch was increased, the resistance of the nanowire became larger.     

Single-cell Trapping Using Microwell Arrays Fabricated from Self-assembled Particle Monolayers

This paper proposes a self-assembly fabrication method of microwells and investigates the effect of surface treatment for the cell trapping. The target cell is unicellular cyanobacterium Synechocystis sp. strain PCC 6803, which has been widely investigated as a model organism for photosynthesis. The self-assembly monolayer of polystyrene particles (3.0 μm diameter) etched by reactive-ion etching was used as a template of polydimethylsiloxane molds. The well diameter in the mold could be controlled by the etching time. The cell-trapping efficiency was discussed with the viewpoint of hydrophilically treatment and poly-L-lysine treatment on the well arrays.     

Adsorptivity of silica-supported monoamide resins to U(IV) in nitric acid media

For the selective extraction of radionuclides from nitrate media, the extraction properties of organopolyphosphine polyoxides were examined in the form of impregnated adsorbents. It was found that the extraction property of 1,1,3,5,5-pentaphenyl-1,3,5-triphosphapentane trioxide (PPTPT) for U(VI) is quite unusual with very high values of the distribution ratio in nitric acid solutions of both low and high concentration ranges, which is not observed for other types of extractants. From the extraction properties for other metal ions, this type of extracant may be promising for the selective extraction of U(VI) from HNO₃ of very low and high concentrations.     

Adsorptivity of polyvinylpolypyrrolidone for selective separation of U(VI) from nitric acid media

Adsorptivity of polyvinylpolypyrrolidone (PVPP), a candidate resin with selectivity to U(VI) in HNO₃ media, to various metal ions was examined. It was found that PVPP has a strong adsorptivity to U(VI) in wide concentration range of HNO₃. The Scatchard plot analysis revealed that the adsorption of U(VI) by PVPP occurs at plural binding sites. The infrared spectroscopic analysis suggested that the strong binding site is due to the coordination of the carbonyl oxygen atom and the nitrogen atom in the pyrrolidone ring to UO₂ ²⁺. It was also found that fission product ions except Re(VII) as the simulant of Tc(VII) and Pd(II) are not adsorbed onto PVPP. The adsorptivities to Tc(VII) and Pd(II) species are weak, indicating that U(VI) can be separated from other metal ions by PVPP.     

Confinement limit of a Dirac particle in two and three dimensions

Consider a particle that is in a stationary state described by the Dirac equation with a finite-range potential. In two and three dimensions the particle can be confined to an arbitrarily small spatial region. This is in contrast to the one-dimensional case in which the confinement region cannot be much narrower than the Compton wavelength.     

The dependence of catalytic activities of secondary functional beta-cyclodextrins on cavity structures.

Secondary imidazole-appended beta-cyclodextrin 5 with a nondistorted cavity synthesized from a novel intermediate 3-amino-3-deoxy-beta-cyclodextrin exhibits much greater catalytic activity in the ester hydrolysis than its isomer 6 with a distorted cavity, indicating that the catalytic activities of secondary functional cyclodextrins are dependent on cavity structures.     

Synthesis of novel antitumor agent 1-methoxy-5,10- dioxo-5,10-dihydro-1H-benzo[g]isochromene carboxylic acid (3-dimethylylaminopropyl)amide with a dual role Pd(II) catalyst

A convenient and simple method for the synthesis of 1-methoxy-5,10-dioxo-5,10-dihydro-1H-benzo[g]isochromene-3-carboxylic acid (3-(dimethylamino)propyl)amide 4c was developed. The key step involves the easy formation of 1,3-disubstituted cyclic alkenyl ether, an important framework of isochromene natural products, with a dual role Pd(II) catalyst.     

Pd(II) acts simultaneously as a Lewis acid and as a transition-metal catalyst: synthesis of cyclic alkenyl ethers from acetylenic aldehydes

The reaction of carbon-tethered acetylenic aldehydes with alcohols in the presence of a catalytic amount of Pd(OAc)2 in 1,4-dioxane at room temperature gave the 5- or 6-membered acetal products in high yields. The 13C NMR studies suggested that a Pd(II) catalyst exhibited dual roles in the present reaction; the attack of ROH to aldehyde is catalyzed by Lewis acidic Pd(OAc)2, and the nucleophilic oxygen of the resulting hemiacetal reacts with alkyne complexed by Pd(II), giving the alkenyl ethers.     

Sol-Gel Synthesis of Ge Nanocrystals-Doped Glass and Its Photoluminescence

Ge nanocrystal-embedded SiO₂ glasses were prepared by a sol-gel process. The glasses synthesized through the hydrolysis of Si(OC₂H₅)₄ and GeCl₄ were heated in H₂ gas atmosphere at 500 to 800°C, in which Ge⁴⁺ ions were reduced to precipitate nanosized Ge crystals with the size smaller than 10 nm diameter. Glasses doped with Ge nanocrystals of diameter of ≈5 nm showed the optical absorption edge at ≈2.8 eV and a broad photoluminescence exhibiting the peak at around 2.2 eV. Large Ge crystals precipitated by heating above 800°C showed no photoluminescence.