Rapid and controlled deswelling of porous poly(N‐isopropylacrylamide) hydrogels prepared by the templating of interpenetrated nanoporous silica particles

Free radical polymerization of N‐isopropylacrylamide (NIPAAm) and crosslinker solutions, which were fulfilled in silica particles with an interpenetrated and nanometer‐sized porous structure (a diameter of 3 mm and mean pore sizes of 15, 30, and 50 nm), fabricated hybrids of organic hydrogels and inorganic silica. Differential scanning calorimetric analyses of the hybrids revealed that silica components affected the thermoresponsive properties of polyNIPAAm hydrogels. Porous polyNIPAAm hydrogels were prepared by the subsequent acid treatment of the hybrids to remove silica. Transmission Fourier transformed infrared spectra indicated the selective extraction of silica. Scanning electron microscopic observation of the hydrogels confirmed the porous structure. The deswelling rate of porous hydrogels was 7 times larger than that of conventional hydrogels and increased with increasing the pore size of silica used. However, the swelling was not affected by the pore formation. The thermoresponsiveness of porous polyNIPAAm hydrogels could be regulated by the pore size. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3542–3547, 2002     

Highly practical and general synthesis of monodisperse linear pi-conjugated oligoenynes and oligoenediynes with either trans- or cis-olefin configuration

Efficient and practical synthesis of a variety of 1-iodo-4-(trimethylsilyl)but-1-en-3-yne derivatives 1 and 2 with trans- and cis-olefin configuration was described. Their repeated use as building blocks allowed the facile synthesis of trans- and cis-oligoenynes, respectively. Development of a highly practical method for preparing monodisperse trans- and cis-oligoenediynes having the effective conjugation length was also accomplished by using 5 and 4, which can be readily prepared from 1 and 2, respectively.     

A simulation study to evaluate the statistical noise and spatial resolution in image reconstruction of emission computed tomography--with respect to the optimization of the filter function in the convolution integral

Filtered backprojection method has been commonly used to reconstruct images in the field of the computed tomography (CT). However, in the emission CT such as positron and single photon CT, poor counting static which are caused by limited dosage to patients, limited counting rate capacity and limited efficiency of the imaging device, produce a statistical noise in the reconstructed image. The magnitude of the statistical noise and the spatial resolution were evaluated for various shapes of the filter used in the convolution integrals of the filtered back-projection procedure. The statistical noise was proportional to the inverse of the root of the total number of counts for any filters. The high-frequency-cut characteristic of the filter reduced the statistical noise, but increased the spatial resolution in the images. It was possible to optimize the shape of the filter for given total number of counts and required statistical noise and spatial resolution.     

Asymmetric Synthesis of Axially Chiral Anilides by Enantiotopic Lithiation of Tricarbonyl(N-methyl-N-acyl-2,6-dimethylanilide)chromium Complex

Axially chiral N-methylanilides were synthesized by enantioselective lithiation of prochiral tricarbonyl(N-methyl-N-pivaloyl-2,6-dimethylaniline)chromium (1) with the lithium amide of the 4-methylpiperazinylethylamine derivative 13 followed by electrophilic quenching up to 97% ee in good yields. The resulting axially chiral chromium-complexd anilides 2 were oxidized under air to give the axially chiral anilides 14 in enantiomerically active form without axial bond rotation at room temperature.     

Formation and oxidation mechanisms of Pd-Zn nanoparticles on a ZnO supported Pd catalyst studied by in situ time-resolved QXAFS and DXAFS

Formation and oxidation processes of PdZn nanoparticles on ZnO were successfully observed by means of in situ time-resolved X-ray absorption fine structure spectroscopy (XAFS), and the analysis of data on near-edge (XANES) and extended (EXAFS) structures revealed detailed changes in Pd during both processes. PdZn nanoparticles were formed on ZnO through a two-step scheme under a hydrogen atmosphere. The first process was the formation of metallic Pd nanoparticles, which was quickly finished within 1 s. The second process was the formation of PdZn nanoparticles, which took several tens of minutes. Oxidation of the PdZn nanoparticles also consisted of two processes. Zn atoms were oxidized prior to Pd atoms and the metallic Pd nanoparticles surrounded by ZnO were formed afterwards. Oxidation of the metallic Pd nanoparticles was scarce and very slow. According to the results of kinetic analyses, the metallic Pd surrounded by ZnO was a stable species under the oxidative atmosphere.     

Universal correlations, pseudo‐gaps and condensation mechanisms in high‐Tc superconductors

We combine universal correlations between T_c and n_s/m^* (superconducting carrier density/effective mass) found by μSR with the pseudo gap behavior found in the underdoped region by various techniques to develop a picture for explaining doping dependence of high‐T_c superconductivity in terms of a crossover from Bose–Einstein to BCS condensation. μSR results in overdoped and Zn‐substituted systems suggest that behavior on the high‐density side is more complicated than expected in a simple BCS model. This revised version was published online in August 2006 with corrections to the Cover Date.     

Positive muon spin depolarization in quenched aluminium dilute alloys

Aluminum dilute alloys (Al-0.047 at% Mg, Al-0.052 at% Cu and Al-0.051 at% Si) were quenched from 600 and 450C. The positive muon behavior in the quenched alloys has been studied. Three peaks (Peak I, II and III) are found. Peak I is due to the trapping and detrapping of positive muons at single impurity atoms. The muon spin depolarization rate at the trap in Peak I was found to be 0.36sec^–1. Peak II is connected to impurity clusters. Peak III is the trapping of muons at quenched-in vacancies. The depolarization rate at the trapping site was found to be 0.2sec^–1. The activation energy of the trapping rate was found to be 25 meV. As the quenched-in vacancies annealed out, the trapping rates decreased to near zero.     

Quadruple-layered perovskite (CuCl)Ca2NaNb4O13

We will present the synthesis, structure and magnetic properties of a new quadruple-layered perovskite (CuCl)Ca₂NaNb₄O₁₃. Through a topotactic ion-exchange reaction with CuCl₂, the precursor RbCa₂NaNb₄O₁₃ presumably having an incoherent octahederal tliting changes into (CuCl)Ca₂NaNb₄O₁₃ with a 2a_p×2a_p×2c_p superstructure (tetragonal; a=7.73232(5) Å, c=39.2156(4) Å). The well-defined superstructure for the ion-exchanged product should be stabilized by the inserted CuCl₄O₂ octahedral layers that firmly connect with neighboring perovskite layers. Magnetic studies show the absence of long-range magnetic ordering down to 2 K despite strong in-plane interactions. Aleksandrov′s group theory and Rietveld refinement of synchrotron X-ray diffraction data suggest the structure to be of I4/mmm space group with in-phase tilting along the a and b axes, a two-tilt system (++0).