Ni-catalyzed [3+2+2] cycloaddition of ethyl cyclopropylideneacetate and 1,3-diynes. Application to the three-component cycloaddition

The Ni-catalyzed [3+2+2] cocyclization between ethyl cyclopropylideneacetate (1) and 1,3-diynes afforded cycloheptadiene derivatives. The three-component reaction of 1, 1,3-diynes, and alkynes proceeded with good yield and high selectivity. Scope of the substrates was studied, and the origin of chemo- and regioselectivity of the reaction is discussed.     

Irreversible temperature‐responsive formation of high‐strength hydrogel from an enantiomeric mixture of starburst triblock copolymers consisting of 8‐arm PEG and PLLA or PDLA

Starburst triblock copolymers consisting of 8‐arm poly(ethylene glycol) (8‐arm PEG) and biodegradable poly(L ‐lactide) (PLLA) or its enantiomer poly(D ‐lactide) (PDLA), 8‐arm PEG‐b‐PLLA‐b‐PEG ( Stri‐L ), and 8‐arm PEG‐b‐PDLA‐b‐PEG ( Stri‐D ) were synthesized. An aqueous solution of a 1:1 mixture ( Stri‐Mix ) of Stri‐L and Stri‐D assumed a sol state at room temperature, but instantaneously formed a physically crosslinked hydrogel in response to increasing temperature. The resulting hydrogel exhibited a high‐storage modulus (9.8 kPa) at 37 °C. Interestingly, once formed at the transition temperature, the hydrogel was stable even after cooling below the transition temperature. The hydrogel formation process was irreversible because of the formation of stable stereocomplexes. In aqueous solution, gradual hydrolytic erosion was observed because of degradation of the hydrogel. The combination of rapid temperature‐triggered irreversible hydrogel formation, high‐mechanical strength, and degradation behavior render this polymer mixture system suitable for use in injectable biomedical materials, for example, as a drug delivery system for bioactive reagents or a biodegradable scaffold for tissue engineering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6317–6332, 2008     

When does the subadditivity theorem for multiplier ideals hold?

Demailly, Ein and Lazarsfeld proved the subadditivity theorem for multiplier ideals on nonsingular varieties, which states the multiplier ideal of the product of ideals is contained in the product of the individual multiplier ideals. We prove that, in the two-dimensional case, the subadditivity theorem holds on log terminal singularities. However, in the higher dimensional case, we have several counterexamples. We consider the subadditivity theorem for monomial ideals on toric rings and construct a counterexample on a three-dimensional toric ring.

     

Compact directed acyclic word graphs for a sliding window

Suffix trees are a well-known and widely-studied data structure highly useful for string matching. The suffix tree of a string w can be constructed in O(n) time and space, where n denotes the length of w. Larsson achieved an efficient algorithm to maintain suffix trees for a sliding window. It contributes to prediction by partial matching (PPM) style statistical data compression scheme. Compact directed acyclic word graphs (CDAWGs) are a more space-economical data structure for indexing strings. In this paper we propose a linear-time algorithm to maintain CDAWGs for a sliding window.     

Reproduction of distance matrices and original time series from recurrence plots and their applications

We propose a method to reproduce distance matrices and original time series from recurrence plots. The procedure is to (i)convert a recurrence plot to a weighted graph and (ii)calculate a distance between each pair of nodes on this weighted graph. We demonstrate this method by reproducing the topological shape of original time series. We also propose two applications. The first application is to obtain the maximal Lyapunov exponent from a recurrence plot without reproducing the shapes of original time series. The second application is to reconstruct a common deterministic driving force from observations of forced systems. Thus, the method opens new fields in data analysis.     

Effect of Particle Size on Electro-Optic Properties of Liquid Crystal Devices Doped with γ-Cyclodextrin Stabilized Barium Titanate Nanoparticles

Barium titanate stabilized by γ-cyclodextrin nanoparticles were prepared by using a microwave reactor equipped with ultrasonic nozzle mixing at 240°C in a tetraethylene glycol solution of barium ethoxide and titanium ethoxide in the presence of γ-cyclodextrin. Particles in γ-cyclodextrin-stabilized BaTiO₃ nanoparticles had an average diameter of 2.1 nm and mainly distributed within the range of about 1 to 4 nm. The γ-cyclodextrin-stabilized BaTiO₃ nanoparticles were mixed with 4-cyano-4′-pentylbiphenyl at room temperature resulting in a liquid crystal sol of 4-cyano-4′-pentylbiphenyl. The response time of liquid crystal devices in the presence of γ-cyclodextrin-stabilized BaTiO₃ nanoparticles was faster than that in the absence.     

Branched/Crosslinked Sulfonated Polyimide Membranes for Polymer Electrolyte Fuel Cells

Summary: Branched/crosslinked sulfonated polyimide membranes incorporating superior mechanical properties, high proton conductivity, and excellent fuel cell performance were successfully developed. The resulting polymer electrolytes displayed conductivity values of about 0.2 S · cm⁻¹ at 120 °C and 100% relative humidity. In a single H₂/O₂ fuel cell system at 90 °C, they exhibited reasonably high fuel cell performances comparable to that of Nafion 112.

The structure of the branched/crosslinked sulfonated polyimide membranes studied here.     

Controlled assembly of silica microspheres in spherically confined polymer particles by using self-organized precipitation (SORP) method

Assembly of submicron-sized microspheres has received much attention due to its high potential for wide variety of applications. We have developed a preparation method of polymer particles by simple mixing of a poor solvent into the polymer solution followed by evaporation of a good solvent. By using this technique, silica nanoparticles and polymer composite particles were prepared. Preparation of three-dimensional assemblies of silica particles in polymer particles and composite Janus particles are shown.