Materials Literature
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We investigate the energy landscape of two dimensional network models for covalent glasses by means of the lid algorithm. For three different particle densities and for a range of network sizes, we exhaustively analyse many configuration space regions enclosing deep-lying energy minima. We extract the local densities…
Amphiphilic block copolymers containing a poly(styrene) tail and a charged helical poly(isocyanide) headgroup derived from isocyano-L-alanine-L-alanine and isocyano-L-alanine-L-histidine were prepared. Analogous to low-molecular mass surfactants, these block copolymers self-assembled in aqueous systems to form micelle…
The tunability and dielectric losses of ferroelectric (Ba,Sr)TiO3 film varactors were measured under DC voltage at microwave frequencies (~20 GHz). A new microwave two-pole tunable waveguide filter containing four ferroelectric (Ba,Sr)TiO3 film varactors was designed and tested. The frequency tuning of the filter resu…
The arrangement of the crystalline cellulose microfibrils in native flax fibers was studied by means of position-resolved microbeam X-ray small-angle scattering (μSAXS) at the ESRF. The nearly perfect alignment of the microfibrils parallel to the fiber axis could for the first time be determined directly on a single f…
New experimental evidence on the formation of spatio-temporal concentration patterns as imaged by photoemission electron microscopy (PEEM) supports our earlier kinetic model for subsurface oxygen formation in the CO oxidation reaction on Pt(110). Extensive experimental data on oxygen island growth and conversion is us…
A reinvestigation is reported of a prototype literature arene hydrogenation system, one previously believed to involve a [(C 8 H 17 ) 3 NCH 3 ] + [RhCl 4 ] - ion-pair catalyst. The methodology employed to uncover the true catalyst, and to deal with the classic and difficult mechanistic problem of “is it homogeneous or…
Various mechanisms to explain negative thermal expansion in oxides are presented. Our search for compounds having this unusual property has focused on the mechanism based on transverse thermal motion of oxygen in M−O−M linkages. Such a mechanism can give strong negative thermal expansion over broad temperature ranges.…
A series of zirconia powder samples with different crystallographic phases and surface areas, either prepared at the laboratory or obtained commercially, have been studied in relation to the interaction of CO 2 with their surfaces. Three complementary techniques such as infrared spectroscopy, adsorption microcalorimet…
Six polylactides, polymerized with Salen−Al−OCH 3 initiator and having optical purities between 43% and 100%, were analyzed by differential scanning calorimetry, X-ray diffraction, and optical microscopy, following various crystallization conditions. It was found that each of those polylactides can crystallize, even t…
An ab initio study on three hypothetical nitrogen−oxygen clusters is presented. The investigated systems are N 2 O 3, N 4 O 6, and N 8 O 12 with highly symmetric geometries, D 3 h, T d, and O h symmetry, respectively. Calculations were performed at SCF and MP2 level (MP2, for the two smallest clusters only). Several b…
ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTLinear Ferrocenylene−Siloxyl−Diacetylene Polymers and Their Conversion to Ceramics with High Thermal and Oxidative StabilitiesEric J. Houser and Teddy M. KellerView Author Information Materials Chemistry Branch, CODE 6127, Chemistry…
Traditionally it was thought that the unidirectional strength in the fiber direction of fiber dominated composites was not influenced by the matrix material. As long as the fiber was not affected then the strength would remain. However this thesis will challange that belief. The unidirectional strength in the fiber di…
ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTDetermination of Order−Order and Order−Disorder Transition Temperatures of SIS Block Copolymers by Differential Scanning Calorimetry and RheologyJin Kon Kim, Hee Hyun Lee, Qi-Jiang Gu, Taihyun Chang, and Yoon Hee JeongView Author In…
The universal form for the average scattering intensity from systems undergoing order-disorder transitions is found by numerical integration of the Langevin dynamics. The result is nearly identical for simulations involving two different forms of the local contribution to the free energy, supporting the idea that the…
Precise microwave measurements of sample conductivity, dielectric, and magnetic properties are routinely performed with cavity perturbation measurements. These methods require the accurate determination of quality factor and resonant frequency of microwave resonators. Seven different methods to determine the resonant…
We present an ab initio exploration of the phenomena which will become important for freestanding structures of silicon as they are realized on the nanoscale. We find that not only surface but also edge effects are important considerations in structures of dimensions on the order of 3 nm. Specifically, for long nanosc…
Multiresolution analyses based upon interpolets, interpolating scaling functions introduced by Deslauriers and Dubuc, are particularly well-suited to physical applications because they allow exact recovery of the multiresolution representation of a function from its sample values on a finite set of points in space. We…
The lattice instability related to ferroelectric phase transitions of and its family has been studied by Raman scattering in the temperature range between 293 K and 958 K. The lowest optical mode of of at room temperature shows remarkable temperature variation towards . Its mode frequency decreases markedly and the da…
An x-ray photoelectron spectroscopy system with a laser-plasma x-ray source is shown to have energy resolution high enough to observe chemical shifts of Si 2p electrons in SiO2, Si3N4, and pure Si. A boron nitride (BN) plasma x-ray source is produced by irradiation of 100 mJ Q-switched YAG laser pulses. A single line…
A detailed investigation of with a very small radius of the A-site cations reveals the occurrence of a charge-ordering transition in the paramagnetic state, at a relatively high temperature of 260 K. The orthorhombic lattice distortion, as measured by the dimensionless index D , is large over the entire 300-100 K rang…