Home About us Contact
|
Home About us Contact | ||
|
|
||
Different Length Scales (different + length_scale)
Selected AbstractsThermodynamic consistent modelling of defects and microstructures in ferroelectricsGAMM - MITTEILUNGEN, Issue 2 2008Ralf Müller Abstract The paper describes the main phenomena associated with fatigue in ferroelectricmaterials due to defects and microstructural effects. An analysis the modelling on different length scales is presented. Starting from a thermodynamic analysis of the macroscopic material behavior other microscopic aspects are addressed. The introduction of an orientation distribution function allows for a computationally efficient extension of a single crystal model to realistic 3D structures. Additionally, the thermodynamic treatment of defects and domain wall motion is discussed to provide a better understanding of various micro-mechanisms. It is explained by the concept of configurational/driving forces, how defects influence each other and how the mobility of domain walls is reduced in the presence of defects. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Influence of Structural Principles on the Mechanics of a Biological Fiber-Based Composite Material with Hierarchical Organization: The Exoskeleton of the Lobster Homarus americanusADVANCED MATERIALS, Issue 4 2009Helge-Otto Fabritius Abstract The cuticle of the lobster Homarus americanus is a nanocomposite, such as most structural biological materials. It consists of a matrix of chitin-protein fibers associated with various amounts of crystalline and amorphous calcium carbonate in the rigid parts of the body, and is organized hierarchically at all length scales. One prominent design principle found in the hierarchical structure of such biological fibrous composite materials is the twisted plywood structure. In the lobster cuticle, it is formed by superimposing and gradually rotating planes of parallel aligned chitin-protein fibers. To adjust the mechanical properties to the requirements on the macroscopic level, the spatial arrangement and the grade of mineralization of the fibers can be modified. A second design principle of lobster cuticle is its honeycomb-like structure, generated by the well-developed pore canal system, whose twisted ribbon-shaped canals penetrate the cuticle perpendicular to its surface. Due to the hierarchical structure, the mechanical properties of the lobster cuticle have to be investigated at different length scales, which is essential for the understanding of the structure,mechanical function relations of mineralized tissues (e.g., potentially also bone and teeth). In order to investigate the influence of the structural principles on the mechanical properties on the macroscopic scale miniaturized tensile, compression, and shear tests were carried out to obtain integral mechanical data. Characterization of the microstructure included scanning electron microscopy (SEM) combined with energy dispersive X-ray (EDX) measurements. [source] A feature-preserving volumetric technique to merge surface triangulationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 2 2002Juan R. Cebral Abstract Several extensions and improvements to surface merging procedures based on the extraction of iso-surfaces from a distance map defined on an adaptive background grid are presented. The main objective is to extend the application of these algorithms to surfaces with sharp edges and corners. In order to deal with objects of different length scales, the initial background grids are created using a Delaunay triangulation method and local voxelizations. A point enrichment technique that introduces points into the background grid along detected surface features such as ridges is used to ensure that these features are preserved in the final merged surface. The surface merging methodology is extended to include other Boolean operations between surface triangulations. The iso-surface extraction algorithms are modified to obtain the correct iso-surface for multi-component objects. The procedures are demonstrated with various examples, ranging from simple geometrical entities to complex engineering applications. The present algorithms allow realistic modelling of a large number of complex engineering geometries using overlapping components defined discretely, i.e. via surface triangulations. This capability is very useful for grid generation starting from data originated in measurements or images. Copyright © 2002 John Wiley & Sons, Ltd. [source] Investigation of bone and cartilage by synchrotron scanning-SAXS and -WAXD with micrometer spatial resolutionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000Biological materials such as bone or wood are hierarchically structured to optimize mechanical and other properties. Several methods and experimental techniques are usually needed to study these materials on different length scales. We developed a device for small angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD), optimized for position resolved investigations of bone sections using synchrotron radiation. Thin samples can be scanned with 20 µm steps, acquiring two-dimensional SAXS or WAXD patterns at every point. The system was tested by performing one-dimensional scans across bone cartilage interfaces, revealing information about size, shape and orientation of nanometer sized mineral particles as well as about crystal type and texture of these particles. [source] Radiation damage in protein crystals examined under various conditions by different methodsJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2009Elspeth F. Garman Investigation of radiation damage in protein crystals has progressed in several directions over the past couple of years. There have been improvements in the basic procedures such as calibration of the incident X-ray intensity and calculation of the dose likely to be deposited in a crystal of known size and composition with this intensity. There has been increased emphasis on using additional techniques such as optical, Raman or X-ray spectroscopy to complement X-ray diffraction. Apparent discrepancies between the results of different techniques can be explained by the fact that they are sensitive to different length scales or to changes in the electronic state rather than to movement of atoms. Investigations have been carried out at room temperature as well as cryo-temperatures and, in both cases, with the introduction of potential scavenger molecules. These and other studies are leading to an overall description of the changes which can occur when a protein crystal is irradiated with X-rays at both cryo- and room temperatures. Results from crystallographic and spectroscopic radiation-damage experiments can be reconciled with other studies in the field of radiation physics and chemistry. [source] Synthesis of Biomorphous Nickel Oxide from a Pinewood Template and Investigation on a Hierarchical Porous StructureJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2 2006Zhaoting Liu The hydrothermal synthesis of biomorphous nickel oxide (NiO) with pine template and nickel nitrate precursor is reported here. The morphology, porosity and connectivity of porous products in different length scales were characterized by field emission scanning electron microscopy, X-ray diffraction and nitrogen adsorption measurements. Their porous structures were found to be hierarchical from 1 up to 25 ,m (in micrometer scale) and from 2 nm to 60 nm (in nanometer scale). Furthermore, depending on the heat-treatment temperatures, the porosity of the pine-templated NiO can be designed. [source] Dissipative Particle Dynamics Simulations of Polymer Brushes: Comparison with Molecular Dynamics SimulationsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 9 2006Sandeep Pal Abstract Summary: The structure of polymer brushes is investigated by dissipative particle dynamics (DPD) simulations that include explicit solvent particles. With an appropriate choice of the DPD interaction parameters , we obtain good agreement with previous molecular dynamics (MD) results where the good solvent behavior has been modeled by an effective Lennard,Jones potential. The present results confirm that DPD simulation techniques can be applied for large length scale simulations of polymer brushes. A relation between the different length scales and is established. Polymer brush at a solid,liquid interface. [source] Relationship between Floc Short Range Structure and Sediment Compaction,PARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5 2003Mandalena Hermawan Abstract This paper studies the short and long-range structure of silica aggregates using the small angle light scattering technique. Silica particles were made to aggregate by the addition of MgCl2, with and without continuous shear. Two different short-range structures were observed for different aggregation conditions. The small angle light scattering reveals two different floc structures at different length scales, a very compact floc at short length scale and a loose floc at large length scale. The sediments of these flocs were studied by allowing them to settle under gravity and consolidate at different centrifugal forces. The results show that the floc short-range structure is important in governing the compaction behaviour of sediment. [source] Structural order on different length scales in amorphous silicon investigated by Raman spectroscopyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2010S. Muthmann Abstract Parameters for the structural short (SRO) and medium range order (MRO) of hydrogenated amorphous silicon (a-Si:H) films on the edge of the microcrystalline silicon (µc-Si:H) phase transition were studied with Raman spectroscopy. The observed samples were deposited using radio frequency plasma enhanced chemical vapor deposition. The studied films were grown with various constant and non-constant silane concentrations (SCs). A substrate dependent correlation of SC to the intensity ratio (IMRO) of the transversal acoustical (TA) and the transversal optical (TO) phonon bands was found. A strong correlation between width and position of the (TO) phonon band was observed. These two easily accessible parameters show an increase of SRO when IMRO decreases. [source] Analyzing characteristic length scales in biofilm structuresBIOTECHNOLOGY & BIOENGINEERING, Issue 2 2009K. Milferstedt Abstract The quantification of biofilm structure based on image analysis requires a statistical measure like representative elemental areas (REA) to determine the necessary size of biofilm area to be imaged. In this study, REAs for biofilm structure were calculated for the descriptors Gray level and Correlation (COR) derived from a spatial gray level dependence matrix analysis (SGLDM). An important difference between these two descriptors is their response to structural features at different spatial scales. Gray level is a scale-independent descriptor, whereas COR is scale-dependent. For scale-independent descriptors, the size of the individual images is not relevant when determining REAs. This is in contrast to scale-dependent descriptors for which REAs can only be determined when the area of each image covers the range of structural variability of the biofilm. We used COR to analyze scale dependence of structural heterogeneity at different length scales. A characteristic length of 400 µm in biofilm images provides structural information relevant for mass transport phenomena in biofilms. Overall REAs for gray level and COR were on average 3.4 mm2. The scale-dependent descriptor COR could not in all cases accurately be determined from combining individual image analysis results,even when the combined area resulted in the REA. Microscope and camera specifications define the upper and lower limit of detectable characteristic length that can be extracted from images and should therefore be considered in the experimental design when choosing an imaging technique. Biotechnol. Bioeng. 2009;102: 368,379. © 2008 Wiley Periodicals, Inc. [source] | |||||||||||||