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Image Simulation (image + simulation)
Selected AbstractsForced Detection Monte Carlo Algorithms for Accelerated Blood Vessel Image SimulationsJOURNAL OF BIOPHOTONICS, Issue 3 2009Ingemar Fredriksson Abstract Two forced detection (FD) variance reduction Monte Carlo algorithms for image simulations of tissue-embedded objects with matched refractive index are presented. The principle of the algorithms is to force a fraction of the photon weight to the detector at each and every scattering event. The fractional weight is given by the probability for the photon to reach the detector without further interactions. Two imaging setups are applied to a tissue model including blood vessels, where the FD algorithms produce identical results as traditional brute force simulations, while being accelerated with two orders of magnitude. Extending the methods to include refraction mismatches is discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Quantitative evaluation of the atomic structure of defects and composition fluctuations at the nanometer scale inside InGaN/GaN heterostructuresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 12 2004P. Ruterana Abstract Investigation is carried out by high-resolution electron microscopy on threading dislocations using data treatments with procedures that allow the extraction of the most likely atomic configurations. We also report In composition fluctuations inside InGaN/GaN quantum wells by coupling HRTEM, image simulation and Finite Element Modelling (FEM) of the thin foil relaxation. The results show that the indium content may be close to x = 1.0 in the clusters and this is much higher that was previously suggested by 2D FEM modelling. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Size and shape of In rich clusters and InGaN QWs at the nanometer scalePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005P. Ruterana Abstract Following the need to accurately understand the In composition fluctuations and their role on the optical properties of the GaN based heterostructures, an investigation of MOCVD InGaN/GaN quantum wells is carried out. To this end, quantitative High Resolution Transmission Electron Microscopy (HRTEM) is coupled with image simulation and Finite Element Method (FEM) for the thin foil relaxation modelling. The results show that the indium content can reach x = 1 in the clusters inside the core. In these MOCVD QWs, we attempt to connect the Quantum dot density, composition, and shape to the growth conditions, in order to help the engineering process of highly efficient devices. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Extended dynamical HAADF STEM image simulation using the Bloch-wave methodACTA CRYSTALLOGRAPHICA SECTION A, Issue 4 2006Takashi Yamazaki An extended method is proposed for the precise simulation of high-angle annular dark-field (HAADF) scanning transmission electron-microscope (STEM) images for materials containing elements with large atomic numbers and for thick specimens. The approach combines a previously reported method utilizing two kinds of optical potential [Watanabe, Yamazaki, Hashimoto & Shiojiri (2001). Phys. Rev. B, 64, 115432] with a representation of a crystal sliced into multiple layers. The validity of the method is demonstrated by simulated images for elements with the diamond structure (Si, Ge and ,-Sn) and for the perovskite BaTiO3. [source] Structural elucidation of the Bi2(n,+,2)MonO6(n,+,1) (n = 3, 4, 5 and 6) family of fluorite superstructures by transmission electron microscopyACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2009Ángel R. Landa-Cánovas The cationic framework structure of a whole new family of compounds with the general formula Bi2(n,+,2)MonO6(n,+,1) (n = 3, 4, 5 and 6) has been elucidated by transmission electron microscopy (TEM) methods. High-resolution transmission electron microscopy (HRTEM) has been used to postulate heavy-atom models based on the known structure of the n = 3 phase, Bi10Mo3O24. These models were tested by HRTEM image simulation, electron diffraction and powder X-ray diffraction simulation methods which agreed with the experimental results. The four known phases of this family correspond to n = 3, 4, 5 and 6 members and all show fluorite superstructures. They consist of a common ,-Bi2O3 fluorite-type framework, inside of which are distributed ribbons of {MoO4} tetrahedra which are infinite along b, one tetrahedron thick along c, and of variable widths of 3, 4, 5 or 6 {MoO4} tetrahedra along a depending on the family member (n value). These {MoO4} tetrahedra are isolated, i.e. without sharing any corner as in the [Bi12O14] columnar structural-type phase Bi[Bi12O14][MoO4]4[VO4]. The structure of all these family members can be described as crystallographic shear derivatives from Aurivillius-type phases such as Bi2MoO6, the n = , end member. All these compounds are good oxygen-ion conductors. [source] Forced Detection Monte Carlo Algorithms for Accelerated Blood Vessel Image SimulationsJOURNAL OF BIOPHOTONICS, Issue 3 2009Ingemar Fredriksson Abstract Two forced detection (FD) variance reduction Monte Carlo algorithms for image simulations of tissue-embedded objects with matched refractive index are presented. The principle of the algorithms is to force a fraction of the photon weight to the detector at each and every scattering event. The fractional weight is given by the probability for the photon to reach the detector without further interactions. Two imaging setups are applied to a tissue model including blood vessels, where the FD algorithms produce identical results as traditional brute force simulations, while being accelerated with two orders of magnitude. Extending the methods to include refraction mismatches is discussed. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanometric crystal defects in transmission electron microscopyMICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2006Robin Schäublin Abstract Transmission electron microscopy (TEM) is revisited in order to define methods for the identification of nanometric defects. Nanometric crystal defects play an important role as they influence, generally in a detrimental way, physical properties. For instance, radiation-induced damage in metals strongly degrades mechanical properties, rendering the material stronger but brittle. The difficulty in using TEM to identify the nature and size of such defects resides in their small size. TEM image simulations are deployed to explore limits and possible ways to improve on spatial resolution and contrast. The contrast of dislocation loops, cavities, and a stacking fault tetrahedra (SFT) are simulated in weak beam, interfering reflections (HRTEM), and scanned condensed electron probe (STEM) mode. Results indicate that STEM is a possible way to image small defects. In addition, a new objective aperture is proposed to improve resolution in diffraction contrast. It is investigated by simulations of the weak beam imaging of SFT and successfully applied in experimental observations. Microsc. Res. Tech. 69:305,316, 2006. © 2006 Wiley-Liss, Inc. [source] HRTEM of dislocation cores and thin-foil effects in metals and intermetallic compoundsMICROSCOPY RESEARCH AND TECHNIQUE, Issue 5 2006M.J. Mills Abstract Examples of the observation and analysis of dislocation cores and dislocation fine structure in metals and intermetallics using high resolution transmission electron microscopy are discussed. Specific examples include the 60° dislocations in aluminum, a,011, edge dislocations in NiAl, and screw dislocations in Ni3Al. The effect of the thin TEM foils on the structure and imaging of these dislocations is discussed in light of embedded atom method calculations for several configurations and coupled with image simulations. Some generalizations based on these calculations are discussed. These analyses enables determination of the spreading or decomposition of the edge component of the cores, both in and out of the glide plane, which can have significant implications for the modeling of macroscopic behavior. Microsc. Res. Tech. 69:317,329, 2006. © 2006 Wiley-Liss, Inc. [source] Gliding dislocations in Bi2Te3 materialsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2009N. Peranio Abstract In Bi2Te3, dislocations were found with an uniquely high mobility at room temperature. The gliding dislocations were analysed and their effect on the thermoelectric properties is discussed. The glide of dislocations was induced by heating with a focused electron beam at 120 keV, external stresses were not applied. The dislocations were bowed out in the glide direction and were only pinned at the surface of the samples. Stereomicroscopy combined with image simulations yielded basal plane dislocations with a density of 109 cm,2 and Burgers vectors of type ,110,. Video sequences showing the glide of single dislocations and groups of dislocations were recorded. Isolated dislocations showed a high mobility in ±,110, direction at a velocity of 10,100 nm s,1. Dislocation dipoles were pinned and did not glide. Dislocations equidistantly arranged within the same glide plane showed a collective movement. Dislocations piled up in different glide planes were fixed and acted as barriers for gliding dislocations. The motion of dislocations was attributed to residual shear stresses of about 10 MPa, and their glide directions depended on the sign of the Burgers vector. Attractive and repulsive forces of dislocations directly visualise the forces due to the elastic strain fields of other dislocations. The relevance of phonon scattering on dislocations in Bi2Te3, particularly due to their high mobility and density, was confirmed by two inspections: (i) Dislocations decrease the lattice thermal conductivity due to phonon scattering on the elastic strain field. The phonon mean free path was estimated to about 800 µm at 3 K and agreed with published data. (ii) The dislocation resonance theory of Granato and Lücke predicts an interaction between phonons and dislocations acting as oscillating strings. The attenuation of ultrasound was estimated and was compared with published data. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||