Marasmioid and gymnopoid fungi of the Republic of Korea. 2. Marasmius sect. Globulares.

Seven species of Marasmius sect. Globulares with smooth pileipellis cells (sect. Globulares s. Singer) have been collected in the Republic of Korea (South Korea) to date, viz. M. aurantioferrugineus, M. brunneospermus, M. maximus, M. nivicola, M. purpureostriatus, M. wynneae and M. fusicystidiosus. Descriptions of their macro- and microscopic features with a discussion of similar taxa are given. Their taxonomic position was confirmed using DNA data. Marasmius fusicystidiosus is described as a new species. A key to aid in their identification is also provided.

Synthesis of thermally stable mesoporous cerium oxide with nanocrystalline frameworks using mesoporous silica templates.

Highly ordered mesoporous cerium oxides, composed of nanocrystalline pore walls and exhibiting high thermal stability even at 973 K, were synthesized using mesoporous silica templates with hexagonal p6mm and cubic Ia3d symmetries.

Ordered nanoporous arrays of carbon supporting high dispersions of platinum nanoparticles.

Nanostructured carbon materials are potentially of great technological interest for the development of electronic, catalytic and hydrogen-storage systems. Here we describe a general strategy for the synthesis of highly ordered, rigid arrays of nanoporous carbon having uniform but tunable diameters (typically 6 nanometres inside and 9 nanometres outside). These structures are formed by using ordered mesoporous silicas as templates, the removal of which leaves a partially ordered graphitic framework. The resulting material supports a high dispersion of platinum nanoparticles, exceeding that of other common microporous carbon materials (such as carbon black, charcoal and activated carbon fibres). The platinum cluster diameter can be controlled to below 3 nanometres, and the high dispersion of these metal clusters gives rise to promising electrocatalytic activity for oxygen reduction, which could prove to be practically relevant for fuel-cell technologies. These nanomaterials can also be prepared in the form of free-standing films by using ordered silica films as the templates.

Synthesis of ordered and disordered silicas with uniform pores on the border between micropore and mesopore regions using short double-chain surfactants.

Silica molecular sieves with uniform pores on the borderline between micropore (diameter <2 nm) and mesopore (from 2 to 50 nm) ranges were synthesized by a novel method using judiciously chosen mixtures of short double-chain alkylammonium surfactants. These silicas were characterized using X-ray diffraction (XRD), thermogravimetry, and nitrogen and argon adsorption. The calcined materials exhibited either 2-dimensional (2-D) hexagonal or disordered structures with XRD interplanar spacing from 2.51 to 2.93 nm, including the value of as small as 2.69 nm for highly ordered 2-D hexagonal silica. The dependence of the pore size and surfactant content on the surfactant chain length provided strong evidence for supramolecular templating being operative in the formation of small-pore silicas, even for the surfactant chain length of six carbon atoms. Both hexagonally ordered and disordered calcined samples were shown to exhibit narrow pore size distributions with maxima in the range from 1.96 to 2.61 nm (reliably evaluated on the basis of the unit-cell dimension and pore volume for 2-D hexagonal materials, and calculated using a properly calibrated procedure), tailored by the surfactant chain length. The samples exhibited primary pore volumes from 0.28 to 0.54 cm(3) g(-1) and specific surface areas from 730 to 930 m(2) g(-1). Because of their small yet uniform pore size and large specific surface area, the silicas reported herein promise to be useful in applications in adsorption and catalysis. Adsorption studies of these materials provided a unique new insight into the pore-filling mechanism for small-pore materials. Moreover, the approach proposed herein is expected to facilitate the synthesis of not only small-pore silicas but also materials with other framework compositions, thus largely contributing to bridging the gap in attainable pore sizes between micropore and mesopore ranges.

An HREM study of channel structures in mesoporous silica SBA-15 and platinum wires produced in the channels.

The hyperbolic geometry of the pores in SBA-15 are drawn into a three-dimensional structure by small lateral pores, distributed in a random way, as shown in the picture, which interconnect the main channels. This construction was established by forming a "negative" of the structure with platinum precipitated in the channel and dissolving the SBA-15 material.

Direct imaging of the pores and cages of three-dimensional mesoporous materials.

Mesostructured composite materials, with features ranging from 20 to 500 A in size, are obtained by the kinetically controlled competitive assembly of organic and inorganic species into nanostructured domains. Short-range order is limited, and long-range order is determined by weak forces such as van der Waals or hydrogen-bonding. Three-dimensional mesoporous materials obtained by removing the organic phase are of particular interest for applications such as catalysis and chemical sensing or separation, for which structural features such as cavity shape, connectivity and ordered bimodal porosity are critical. But atomic-scale structural characterization by the usual diffraction techniques is challenging for these partially ordered materials because of the difficulty in obtaining large (> 10 microm) single crystals, and because large repeat spacings cause diffraction intensities to fall off rapidly with scattering angle so that only limited small-angle data are available. Here we present a general approach for the direct determination of three-dimensional mesoporous structures by electron microscopy. The structure solutions are obtained uniquely without pre-assumed models or parametrization. We report high-resolution details of cage and pore structures of periodically ordered mesoporous materials, which reveal a highly ordered dual micro- and mesoscale pore structure.

Temperature and pressure dependence of viscosity of quantum liquid He according to significant structure theory.

Both solid-like and gas-like flow structures are considered in the calculation of viscosity of liquid (4)He using the significant structure theory of liquids. The predominance of quantum mechanical zero-point motion over that arising from thermal excitation is taken into account for the solid-like motion of molecules. The viscosity of liquid (4)He under its own vapor pressure calculated over its whole temperature range is in reasonably good agreement with experimental data. The pressure dependence of viscosity also was obtained. The calculation does not yield good results at high densities where the free jumping of molecules into the nearest neighboring vacancies through the kinetic zero-point motion is no longer plausible.

Significant structure theory applied to liquid He.

The large kinetic zero-point motion of (4)He molecules has been properly taken into account in the significant structure theory of liquids in order to describe the liquidity of liquid (4)He. The Debye and the Bose-Einstein partition functions are used for the solid-like molecules of the normal fluid component and for the whole gas-like molecules, respectively. The solid-like molecules of the superfluid component are considered as ground state molecules without having positional degeneracies. The Bragg-Williams approximation of an order/disorder phase transition has been applied to the lambda transition of liquid (4)He. Thermodynamic and surface properties of liquid (4)He have been calculated up to the critical point. The results are satisfactory when compared with the observed values.