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Material Structure (material + structure)
Selected AbstractsQuestioning Cognitivism and Constructivism in IR Theory: Reflections on the Material Structure of IdeasPOLITICS, Issue 2 2001Andreas Bieler In recent years, it has been highlighted in international relations theory that mainstream approaches neglect the role of ideas in relation to the formation of interests and international co-operation. This article critically discusses the renewed emphasis on ideas. ,Cognitive' and ,constructivist' approaches are outlined as the two main strands in the debate and a neo-Gramscian position within it is sketched. Importantly, a neo-Gramscian position is able to conceptualise the material structure of ideas, thereby overcoming the separation between ideas and material structure from the very beginning. [source] Integration of CdSe quantum dots with GaN optoelectronic materialsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005J. G. Pagan Abstract Material structures on the nanoscale can enable enhancement of optoelectronic device performance. For example, in the InGaN active layers of MOCVD grown blue light emitting diodes, indium segregation plays a critical role in the interplay between blue luminescent channels and non-radiative recombination centers such as crystal defects. Unfortunately, high efficiency luminescence of InGaN does not extend into the "deep green" spectral region, around the wavelength of peak human eye response. We are investigating whether commercially available luminescent nanostructures such as CdSe quantum dots can be incorporated into III-nitride devices to extend their high-efficiency performance into the "deep green". Surfactant stabilized CdSe particles in liquid dispersions are drop-cast onto HVPE grown GaN. Physical properties of resultant CdSe surface structures are examined. Luminescence is reported before and after subsequent growth of GaN. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Exploiting the Kubas Interaction in the Design of Hydrogen Storage MaterialsADVANCED MATERIALS, Issue 18 2009Tuan K. A. Hoang Abstract Hydrogen adsorption and storage using solid-state materials is an area of much current research interest, and one of the major stumbling blocks in realizing the hydrogen economy. However, no material yet researched comes close to reaching the DOE 2015 targets of 9,wt% and 80,kg,m,3 at this time. To increase the physisorption capacities of these materials, the heats of adsorption must be increased to ,20,kJ,mol,1. This can be accomplished by optimizing the material structure, creating more active species on the surface, or improving the interaction of the surface with hydrogen. The main focus of this progress report are recent advances in physisorption materials exhibiting higher heats of adsorption and better hydrogen adsorption at room temperature based on exploiting the Kubas model for hydrogen binding: (,2 -H2),metal interaction. Both computational approaches and synthetic achievements will be discussed. Materials exploiting the Kubas interaction represent a median on the continuum between metal hydrides and physisorption materials, and are becoming increasingly important as researchers learn more about their applications to hydrogen storage problems. [source] NEXAFS multiple scattering calculations of KO2JOURNAL OF SYNCHROTRON RADIATION, Issue 2 2001M. Pedio Since many years the oxidation of alkali metals has being attracted much interest due to the catalytic properties of metal promoters and the simple electronic structure of alkali atoms. The alkali-oxides phase diagram indicates that the interaction of oxygen with alkali metals can lead to the formation of different atomic O2- ions and molecular O2 - and O22- ions. Potassium superoxide has been prepared in situ and high resolution O k-edge absorption NEXAFS spectra have been measured at the VUV beam-line at ELETTRA facility. The experimental data have been analyzed by multiple scattering approach deriving many geometrical and electronic details. In particular, we have found that the growth material structure is of the KO2 type with an O-O distance of about 1.35Å and that the transition involving single , molecular empty state of the superoxide O2 - anion has a fine structure. Multiple Scattering self consistent calculation indicates that the bond between oxygen anion and K atom is totally ionic and that the fine structure is essentially due to solid state effects. [source] Generalized pair approximation in the description of the ac conductivity of a dense disordered array of quantum dotsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2006I. P. Zvyagin Abstract The frequency dependence of the hopping conductivity of dense arrays of semiconductor quantum dots of size substantially exceeding the edge-to-edge separation between the neighboring quantum dots is considered. It is shown that at low frequencies in a wide frequency range the conductivity obeys a fractional power law and its magnitude depends on the structural characteristics of the material. The possibility of the deviations from universality related to the material structure is discussed. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Questioning Cognitivism and Constructivism in IR Theory: Reflections on the Material Structure of IdeasPOLITICS, Issue 2 2001Andreas Bieler In recent years, it has been highlighted in international relations theory that mainstream approaches neglect the role of ideas in relation to the formation of interests and international co-operation. This article critically discusses the renewed emphasis on ideas. ,Cognitive' and ,constructivist' approaches are outlined as the two main strands in the debate and a neo-Gramscian position within it is sketched. Importantly, a neo-Gramscian position is able to conceptualise the material structure of ideas, thereby overcoming the separation between ideas and material structure from the very beginning. [source] Optical properties of highly transparent polypropylene cast films: Influence of material structure, additives, and processing conditionsPOLYMER ENGINEERING & SCIENCE, Issue 4 2006Katharina Resch Polypropylene homopolymers and ethylene/propylene-random-copolymers formulated with and without anti-blocking additives were extruded to cast films with an industrial scale extruder equipped with a soft box, a specific air knife that expels a higher volume of air at lower velocity. The films were analyzed as to their optical properties haze and clarity. A comprehensive topographical characterization was performed using atomic force microscopy (AFM) and confocal microscopy. To obtain morphological information on a nanometer scale AFM phase imaging, micro-thermal analysis and small angle X-ray scattering (SAXS) were done. A significant effect of additives and processing conditions on the film topography and the optical properties was revealed. The films without anti-blocking and antacid aids showed the best optical properties and lowest vertical roughness fluctuations. In contrast, the addition of anti-blocking and antacid aids reduced the optical properties associated with an increase in surface roughness. While for films without anti-blocking aids an enhanced soft box condition resulted in lower vertical fluctuations of roughness and better optical properties, the behavior was in reverse for films with anti-blocking aid. By means of SAXS crystalline lamellae with a thickness of about 2.5 nm were detected. High-resolution phase imaging AFM yielded thicker crystal lamellae on the film surface. POLYM. ENG. SCI., 46:520,531, 2006. © 2006 Society of Plastics Engineers. [source] Synchrotron-Based Micro-CT and Refraction-Enhanced Micro-CT for Non-Destructive Materials Characterisation,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Bernd R. Müller Abstract X-ray computed tomography is an important tool for non-destructively evaluating the 3-D microstructure of modern materials. To resolve material structures in the micrometer range and below, high brilliance synchrotron radiation has to be used. The Federal Institute for Materials Research and Testing (BAM) has built up an imaging setup for micro-tomography and -radiography (BAMline) at the Berliner storage ring for synchrotron radiation (BESSY). In computed tomography, the contrast at interfaces within heterogeneous materials can be strongly amplified by effects related to X-ray refraction. Such effects are especially useful for materials of low absorption or mixed phases showing similar X-ray absorption properties that produce low contrast. The technique is based on ultra-small-angle scattering by microstructural elements causing phase-related effects, such as refraction and total reflection. The extraordinary contrast of inner surfaces is far beyond absorption effects. Crack orientation and fibre/matrix debonding in plastics, polymers, ceramics and metal-matrix-composites after cyclic loading and hydro-thermal aging can be visualized. In most cases, the investigated inner surface and interface structures correlate to mechanical properties. The technique is an alternative to other attempts on raising the spatial resolution of CT machines. [source] Structure and Properties of PHA/Clay Nano-Biocomposites Prepared by Melt IntercalationMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2008Perrine Bordes Abstract PHA-based nano-biocomposites have been prepared by melt intercalation. Two main PHAs, poly(hydroxybutyrate) and poly(hydroxybutyrate -co- hydroxyvalerate) have been studied. Structural characterizations were conducted by advanced techniques like SAXS and TEM. A recent method has determined the degree of clay intercalation and dispersion using solid-state NMR. Well intercalated small tactoids (3,10 layers) homogeneously dispersed into the polymer are obtained when good PHA,clay affinity exists, i.e., with organo-modified MMT. In the case of non-modified MMT, microcomposites are evidenced. Crystallization, mechanical, and thermal properties have been correlated to the materials structures. [source] | |||||||||||||||||||