8,796 research outputs found
Wave optical simulations of x-ray nano-focusing optics
No full textSoftcover, 17x24Curved x-ray multilayer mirrors focus synchrotron beams down to tens of nano metres. A wave-optical theory describing propagation of two waves in an elliptically curved focusing multilayer mirror is developed in this thesis. Using numerical integration, the layer shapes can be optimised for reflectivity and aberrations. Within this framework, performance of both existing and currently upgraded synchrotron beamlines is simulated. Using a more theoretical model case, limits of the theory are studied. A significant part of this work is dedicated to partial spatial coherence, modelled using the method of stochastic superpositions. Coherence propagation and filtering by x-ray waveguides is shown analytically and numerically. This comprehensive model is put forward that shall help in development and testing of new algorithms for a variety of imaging techniques using coherent x-ray beams. Advanced simulations accounting for real structure effects are compared to experimental data obtained at the GINIX instrument at the coherence beamline P10 at PETRA III, DESY. This thesis presents results of a collaboration between the Georg-August-Universität Göttingen and the European Synchrotron Radiation Facility (ESRF) Grenoble
Partially coherent x-ray beam simulations: mirrors and more
No full textPenetration, micro-resolution, and scattering were the keywords of x-ray analyses in the 20th century. Over the last 15 years, a great class of coherent imaging techniques has emerged as new tools, allowing for low-dose imaging of biological specimen on the nanoscale. Apart from experimental and technical challenges, a better understanding of partially coherent beam propagation is the key for exploiting the new methods' full performance. We present a simulation framework to calculate the mutual intensity and the degree of spatial coherence of typical x-ray focusing and filtering devices used at 3rd generation synchrotron radiation sources. We propose the following modeling scheme: A set of independent point-sources yield independent basic fields, which are superposed in a stochastic manner; by taking the ensemble average, both partially coherent intensity and degree of coherence can be obtained from the mutual intensity. By including real structure effects, like height deviations of focusing mirrors, and vibration of optical components, advanced predictions of x-ray beams can be made. This knowledge is expected to improve reconstruction results from coherent imaging experiments. Coherence simulations of focusing mirrors are presented and validated with analytical results as well as with experimental tests. Coherence filtering by use of x-ray waveguides is shown numerically. We also present first simulations for partially coherent focusing by compound refractive lenses
JBendge: An Object-Oriented System for Solving, Estimating and Selecting Nonlinear Dynamic Models
No full textWe present an object-oriented software framework allowing to specify, solve, and estimate nonlinear dynamic general equilibrium (DSGE) models. The imple- mented solution methods for nding the unknown policy function are the standard linearization around the deterministic steady state, and a function iterator using a multivariate global Chebyshev polynomial approximation with the Smolyak op- erator to overcome the course of dimensionality. The operator is also useful for numerical integration and we use it for the integrals arising in rational expecta- tions and in nonlinear state space lters. The estimation step is done by a parallel Metropolis-Hastings (MH) algorithm, using a linear or nonlinear lter. Implemented are the Kalman, Extended Kalman, Particle, Smolyak Kalman, Smolyak Sum, and Smolyak Kalman Particle lters. The MH sampling step can be interactively moni- tored and controlled by sequence and statistics plots. The number of parallel threads can be adjusted to benet from multiprocessor environments. JBendge is based on the framework JStatCom, which provides a standardized ap- plication interface. All tasks are supported by an elaborate multi-threaded graphical user interface (GUI) with project management and data handling facilities.Dynamic Stochastic General Equilibrium (DSGE) Models, Bayesian Time Series Econometrics, Java, Software Development
Coherence Filtering of X-Ray Waveguides: Analytical and Numerical Approach
No full textWe model and describe the spatial coherence and mutual intensity of focused synchrotron radiation x-ray beams, based on ensemble averagesof stochastic superpositions. Within this framework, we present numerical calculations for typical synchrotron sources with focusing mirrors, and simulate the evolution of coherence inside x-ray waveguides used for filtering by analytical and numerical methods. Simulated focus fields are compared with an experimental setup, including figure errors and vibrations
Evidence based leadership
No full textAuthor Markus PodduikinMasterarbeit Johannes Kepler Universität Linz 2024Arbeit gesperr
Improving the search for monitoring tools using recommender technology
No full textAuthor Markus Eisl BSc.Masterarbeit Universität Linz 2023Arbeit gesperr
Improving the search for monitoring tools using recommender technology
No full textAuthor Markus Eisl BSc.Masterarbeit Universität Linz 2023Arbeit gesperr
Structure and Dynamics of Confined Liquids: Challenges and Perspectives for the X-ray Surface Forces Apparatus
No full textThe molecular-scale structure and dynamics of confined liquids has increasingly gained relevance for applications in nanotechnology. Thus, a detailed knowledge of the structure of confined liquids on molecular length scales is of great interest for fundamental and applied sciences. To study confined structures under dynamic conditions, we constructed an in situ X-ray surface forces apparatus (X-SFA). This novel device can create a precisely controlled slit-pore confinement down to dimensions on the 10 nm scale by using a cylinder-on-flat geometry for the first time. Complementary structural information can be obtained by simultaneous force measurements and X-ray scattering experiments. The in-plane structure of liquids parallel to the slit pore and density profiles perpendicular to the confining interfaces are studied by X-ray scattering and reflectivity. The normal load between the opposing interfaces can be modulated to study the structural dynamics of confined liquids. The confinement gap distance is tracked simultaneously with nanometer precision by analyzing optical interference fringes of equal chromatic order. Relaxation processes can be studied by driving the system out of equilibrium by shear stress or compression/decompression cycles of the slit pore. The capability of the new device is demonstrated on the liquid crystal 4'-octyl-4-cyano-biphenyl (8CB) in its smectic A (SmA) mesophase. Its molecular-scale structure and orientation confined in 100 nm to 1.7 mu m slit pores was studied under static and dynamic nonequilibrium conditions.The authors acknowledge the help of Thomas Buslaps (ESRF) at beamline ID31, Marie Ruat (ESRF) for support on the CdTe MAXIPIX detector, and Michael Kappl (MPI-P) for AFM measurements and thank Harald Reichert (ESRF), Milena Lippmann (PETRA III), and Hans-Jürgen Butt (MPI-P) for helpful discussions. J.M. and M.M. acknowledge the MAINZ Graduate School of Excellence, funded through the Excellence Initiative (DFG/GSC 266). M.V. was supported by an ERC Starting Grant (no. 677663), and H.L., by the China Scholarship Council.Mezger, M (reprint author), Max Planck Inst Polymer Res, Ackermannweg 10, D-55128 Mainz, Germany, Johannes Gutenberg Univ Mainz, Inst Phys, D-55128 Mainz, Germany.
Valtiner, M (reprint author), Vienna Inst Technol, Inst Appl Phys, Wiedner Hauptstr 8-10-E134, A-1040 Vienna, Austria, Max Planck Inst Eisenforsch GmbH, Max Planck Str 1, D-40237 Dusseldorf, Germa
Combined scanning small-angle X-ray scattering and holography probes multiple length scales in cell nuclei
No full textX‐rays are emerging as a complementary probe to visible‐light photons and electrons for imaging biological cells. By exploiting their small wavelength and high penetration depth, it is possible to image whole, intact cells and resolve subcellular structures at nanometer resolution. A variety of X‐ray methods for cell imaging have been devised for probing different properties of biological matter, opening up various opportunities for fully exploiting different views of the same sample. Here, a combined approach is employed to study cell nuclei of NIH‐3T3 fibroblasts. Scanning small‐angle X‐ray scattering is combined with X‐ray holography to quantify length scales, aggregation state, and projected electron and mass densities of the nuclear material. Only by joining all this information is it possible to spatially localize nucleoli, heterochromatin and euchromatin, and physically characterize them. It is thus shown that for complex biological systems, like the cell nucleus, combined imaging approaches are highly valuable.The combination of small‐angle X‐ray scattering and X‐ray holography enables us to visualize and characterize biological material in cell nuclei spanning multiple length scales. imag
Fusion of interventional ultrasound & X-ray
No full textOtto-von-Guericke-Universität Magdeburg, Fakultät für Elektrotechnik und Informationstechnik, Dissertation, 2016von Dipl.-Inf. Markus KaiserLiteraturverzeichnis: Seite 117-13
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