There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications

Covalent organic frameworks (COFs) have been designed and successfully synthesized by condensation reactions of phenyl diboronic acid {C6H4[B(OH)2]2} and hexahydroxytriphenylene [C18H6(OH)6]. Powder x-ray diffraction studies of the highly crystalline products (C3H2BO)6.(C9H12)1 (COF-1) and C9H4BO2 (COF-5) revealed expanded porous graphitic layers that are either staggered (COF-1, P6(3)/mmc) or eclipsed (COF-5, P6/mmm). Their crystal structures are entirely held by strong bonds between B, C, and O atoms to form rigid porous architectures with pore sizes ranging from 7 to 27 angstroms. COF-1 and COF-5 exhibit high thermal stability (to temperatures up to 500 degrees to 600 degrees C), permanent porosity, and high surface areas (711 and 1590 square meters per gram, respectively).

Porous, Crystalline, Covalent Organic Frameworks

A critical review of adsorption methods that are currently used in the characterization of ordered organic−inorganic nanocomposite materials is presented, and the adsorption methodology that is potentially useful for this characterization, but has not yet been applied, is discussed. The ordered organic−inorganic nanocomposites include surface-functionalized ordered mesoporous materials (OMMs) with siliceous frameworks (synthesized either via postsynthesis surface modification or via direct co-condensation method), periodic mesoporous organosilicas, and surfactant-containing OMMs. This review covers the methods for determination of the specific surface area and pore volume. The available methods for mesopore size analysis are critically compared and evaluated, with special emphasis on the recent developments related to the application of advanced computational methods for studying adsorption in porous media and to the direct modeling of adsorption using highly ordered surface-functionalized OMMs as model a...

Gas adsorption characterization of ordered organic-inorganic nanocomposite materials

Three silicon oxycarbide glasses (SiCO) with increasing C content were obtained through pyrolysis in inert atmosphere at 1000 °C of sol−gel derived siloxane networks containing Si−CH3 and Si−H bonds. The glasses were further annealed at 1200, 1400, and 1500 °C to follow their evolution at high temperature. Quantitative information concerning the structure of glasses before and after annealing at high temperature was collected with a wide range of techniques (some of them used for the first time in this field) with the aim of probing the following:  (i) the short-range order and chemical composition (29Si and 1H MAS NMR, RDF derived from X-ray and neutron scattering, inelastic neutron scattering, FT-IR, and elemental analysis), and (ii) the long-range order (X-ray and neutron diffraction) and microstructural features (HR-TEM combined with electron diffraction, Raman, porosity, and surface area measurements). This extensive collection of data, carried out on the same set of specimens, provided detailed and ...

Systematic Structural Characterization of the High-Temperature Behavior of Nearly Stoichiometric Silicon Oxycarbide Glasses

Selective protein adsorption property and characterization of nano-crystalline zinc-containing hydroxyapatite

Dimethyldiethoxysilane/tetraethoxysilane copolymers: precursors for the silicon-carbon-oxygen system

The aim of this work was to study the pyrolytic conversion of a novel commercial polysilazane, poly(ureamethylvinyl)silazane (PUMVS; Ceraset™, Allied Signal Composites Inc., USA), into silicon-based ceramics. The precursor was thermally cross-linked and pyrolyzed between 200 and 1700 °C under argon or nitrogen atmosphere and the products were investigated by spectroscopic techniques (FTIR and Raman spectroscopy, solid-state NMR), elemental analysis and simultaneous thermal analysis coupled with mass spectrometry. Upon heating under argon, the starting liquid precursor transformed into an infusible solid polymer at T > 250 °C with a conversion yield of >95 wt%. The cross-linking solidification occurred predominantly through hydrosilylation or addition reaction involving vinyl groups. Subsequent pyrolysis of the cross-linked products around 1000 °C in argon yielded amorphous silicon carbonitride ceramics with a composition of SiN0.82C0.86. The overall ceramic yield (with respect to the starting PUMVS) was around 70 wt%, which was found to be independent of the initial cross-linking step. Solid-state NMR (29Si and 13C) revealed that the amorphous silicon carbonitrides contain predominately CSiN3 units. There is evidence for the formation of free amorphous carbon between 700 and 800 °C. Graphitic phases were detected by X-ray diffraction in the samples heated to T > 1000 °C at high heating rates. Upon annealing at T > 1500 °C, the excess carbon reacted completely with the silicon (carbo)nitride to form SiC and nitrogen. The final ceramics contained a large amount of crystalline SiC (∼90 wt%), and were free of excess carbon or silicon. Therefore, PUMVS is an ideal precursor for the formation of high-quality SiC-based ceramics. Copyright © 2001 John Wiley & Sons, Ltd.

Thermal cross-linking and pyrolytic conversion of poly(ureamethylvinyl)silazanes to silicon-based ceramics

Surfactant templated silica mesophases belong to the class of self-assembled materials that exhibit long range ordered two-dimensional (2D) hexagonal, three-dimensional (3D) hexagonal, or 3D cubic mesostructures when the composition of the initial deposited solution and its aging time have been optimized. Thin films of such mesophases with a thickness typically less than 300 nm are now routinely obtained by dip coating. In this study a reference solution was used with a chemical composition leading to the formation of thin films with a 3D hexagonal (P63/mmc) mesostructure by dip coating. Thick films (about 10 μm thick) were alternatively prepared by a evaporation-controlled self-assembly (ECSA) process and studied with grazing incidence small-angle X-ray scattering (GISAXS). In the ECSA process, the mesostructure was developed under slower evaporation conditions than for dip-coated films by finely tuning the ethanol/H2O evaporation rate of the reference solution horizontally deposited on a silicon wafer. ...

Florence Babonneau

Papers

Systematic Structural Characterization of the High-Temperature Behavior of Nearly Stoichiometric Silicon Oxycarbide Glasses

Selective protein adsorption property and characterization of nano-crystalline zinc-containing hydroxyapatite

Dimethyldiethoxysilane/tetraethoxysilane copolymers: precursors for the silicon-carbon-oxygen system

Thermal cross-linking and pyrolytic conversion of poly(ureamethylvinyl)silazanes to silicon-based ceramics

Evaporation-Controlled Self-Assembly of Silica Surfactant Mesophases