共查询到20条相似文献,搜索用时 31 毫秒
1.
Valeriy Titarenko Sofya Titarenko Philip J. Withers Francesco De Carlo Xianghui Xiao 《Journal of synchrotron radiation》2010,17(5):689-699
The first processing step in synchrotron‐based micro‐tomography is the normalization of the projection images against the background, also referred to as a white field. Owing to time‐dependent variations in illumination and defects in detection sensitivity, the white field is different from the projection background. In this case standard normalization methods introduce ring and wave artefacts into the resulting three‐dimensional reconstruction. In this paper the authors propose a new adaptive technique accounting for these variations and allowing one to obtain cleaner normalized data and to suppress ring and wave artefacts. The background is modelled by the product of two time‐dependent terms representing the illumination and detection stages. These terms are written as unknown functions, one scaled and shifted along a fixed direction (describing the illumination term) and one translated by an unknown two‐dimensional vector (describing the detection term). The proposed method is applied to two sets (a stem Salix variegata and a zebrafish Danio rerio) acquired at the parallel beam of the micro‐tomography station 2‐BM at the Advanced Photon Source showing significant reductions in both ring and wave artefacts. In principle the method could be used to correct for time‐dependent phenomena that affect other tomographic imaging geometries such as cone beam laboratory X‐ray computed tomography. 相似文献
2.
The flow patterns and wall stresses in a two‐dimensional louvered moving granular filter bed of quartz sand were investigated. The flow pattern histories of granular solids in the filter bed were recorded using a digital camcorder and a pressure gauge for simultaneously measuring the normal stresses as well as shear stresses of the granular solids. The static wall stress distributions produced by the granular solids were measured, and agreed with a theoretical prediction formed using the differential slice and Runge‐Kutta (order four) methods. The variations in the dynamic wall stresses with time in a moving granular filter bed were obtained and the effect of the louver angle upon the flow patterns and wall stresses was also investigated. Employing the results obtained by stress measurements and image processing, the wall pressure pulsation phenomena in a moving granular filter bed may be further understood. The results reported here provide fundamental information for the design of moving granular filter beds to act as high‐temperature flue gas cleanup filters. 相似文献
3.
Daisy Tysmans Philippe Claeys Luc Deriemaeker Dominique Maes Robert Finsy Marc Van Molle 《Particle & Particle Systems Characterization》2006,23(5):381-387
The application of Automated Dynamic Image Analysis (ADIA) for measuring the size and shape of sedimentary grains is presented. This technique determines the size and shape of a large number of particles (typically 5,000 to 50,000 or greater) in the size range between 10 to 1,500 μm. ADIA measurements are carried out using a RapidVue particle analyzer. The size and shape of particles are obtained by analyzing digital images. Each image is composed of shapes representing two‐dimensional projections of particles. The analysis yields the area and perimeter of each particle cross‐section, which are transformed into size‐independent shape values. The analysis of such a large number of particles results in a very small statistical variation of the results, ca. 0.3% for 50,000 particles. Since operator selection of images does not enter the measurement procedure, the risk of bias caused by subjective sample selection is eliminated. The combination of ADIA with a two‐dimensional Kolmogorov‐Smirnov test, allows the identification of similarities and differences between sedimentary grains. 相似文献
4.
Sofya Titarenko Valeriy Titarenko Albrecht Kyrieleis Philip J. Withers Francesco De Carlo 《Journal of synchrotron radiation》2011,18(3):427-435
There are many objects for which the attenuation varies significantly as they are rotated during computerized X‐ray tomography, for example plate samples. This can lead to significant ring artefacts in the subsequent tomographic reconstructions. In this paper a new method is presented that can successfully suppress such ring artefacts and is applicable to both parallel and cone‐beam geometries. Rapid correction is achieved via an analytical formula which involves only a matrix‐vector multiplication, for which the matrix is known and depends on a regularization parameter. The efficacy of the method is demonstrated for a paleontological sample (calcified shark cartilage) and a carbon–carbon composite/Ti–SiC metal matrix composite test sample. 相似文献
5.
L. Bertrand M.‐A. Languille S. X. Cohen L. Robinet C. Gervais S. Leroy D. Bernard E. Le Pennec W. Josse J. Doucet S. Schöder 《Journal of synchrotron radiation》2011,18(5):765-772
IPANEMA, a research platform devoted to ancient and historical materials (archaeology, cultural heritage, palaeontology and past environments), is currently being set up at the synchrotron facility SOLEIL (Saint‐Aubin, France; SOLEIL opened to users in January 2008). The new platform is open to French, European and international users. The activities of the platform are centred on two main fields: increased support to synchrotron projects on ancient materials and methodological research. The IPANEMA team currently occupies temporary premises at SOLEIL, but the platform comprises construction of a new building that will comply with conservation and environmental standards and of a hard X‐ray imaging beamline today in its conceptual design phase, named PUMA. Since 2008, the team has supported synchrotron works at SOLEIL and at European synchrotron facilities on a range of topics including pigment degradation in paintings, composition of musical instrument varnishes, and provenancing of medieval archaeological ferrous artefacts. Once the platform is fully operational, user support will primarily take place within medium‐term research projects for `hosted' scientists, PhDs and post‐docs. IPANEMA methodological research is focused on advanced two‐dimensional/three‐dimensional imaging and spectroscopy and statistical image analysis, both optimized for ancient materials. 相似文献
6.
3D‐printed photo‐spectroelectrochemical devices for in situ and in operando X‐ray absorption spectroscopy investigation 下载免费PDF全文
Elisabetta Achilli Alessandro Minguzzi Alberto Visibile Cristina Locatelli Alberto Vertova Alberto Naldoni Sandra Rondinini Ferdinando Auricchio Stefania Marconi Martina Fracchia Paolo Ghigna 《Journal of synchrotron radiation》2016,23(2):622-628
7.
Tomáš Faragó Petr Mikulík Alexey Ershov Matthias Vogelgesang Daniel Hänschke Tilo Baumbach 《Journal of synchrotron radiation》2017,24(6):1283-1295
An open‐source framework for conducting a broad range of virtual X‐ray imaging experiments, syris, is presented. The simulated wavefield created by a source propagates through an arbitrary number of objects until it reaches a detector. The objects in the light path and the source are time‐dependent, which enables simulations of dynamic experiments, e.g. four‐dimensional time‐resolved tomography and laminography. The high‐level interface of syris is written in Python and its modularity makes the framework very flexible. The computationally demanding parts behind this interface are implemented in OpenCL, which enables fast calculations on modern graphics processing units. The combination of flexibility and speed opens new possibilities for studying novel imaging methods and systematic search of optimal combinations of measurement conditions and data processing parameters. This can help to increase the success rates and efficiency of valuable synchrotron beam time. To demonstrate the capabilities of the framework, various experiments have been simulated and compared with real data. To show the use case of measurement and data processing parameter optimization based on simulation, a virtual counterpart of a high‐speed radiography experiment was created and the simulated data were used to select a suitable motion estimation algorithm; one of its parameters was optimized in order to achieve the best motion estimation accuracy when applied on the real data. syris was also used to simulate tomographic data sets under various imaging conditions which impact the tomographic reconstruction accuracy, and it is shown how the accuracy may guide the selection of imaging conditions for particular use cases. 相似文献
8.
Jie Zhang Gang Li Qiru Yi Yu Chen Zhenhua Gao Xiaoming Jiang 《Journal of synchrotron radiation》2015,22(1):130-135
Synchrotron radiation computed laminography (SR‐CL) has been in use in three‐dimensional non‐destructive imaging of flat objects for several years. A new set‐up is proposed based on the traditional SR‐CL method but with the detector inclined at the same angle as the sample inclination to collect projections. The results of computer simulations and real‐sample experiments demonstrate that reconstructions acquired using an inclined detector are of better quality compared with those acquired using ordinary detecting methods, especially for the situation of few projections and small difference of attenuation ratio of the sample. This method could be applied to obtain high‐quality images of weak‐contrast samples with short measurement time and mild radiation damage. 相似文献
9.
搜索二维运动轨迹的方法研究 总被引:1,自引:1,他引:0
进行多目标轨迹测量数据处理的过程中,需要在平面内搜索出每一目标的二维轨迹投影。本文提出了进行这种搜索的一套系统方法,详细地论述了方法的原理及编程思想,并给出计算机仿真结果。 相似文献
10.
Patrik Vagovič Dušan Korytár Petr Mikulík Angelica Cecilia Claudio Ferrari Yang Yang Daniel Hänschke Elias Hamann Daniele Pelliccia Tamzin A. Lafford Michael Fiederle Tilo Baumbach 《Journal of synchrotron radiation》2011,18(5):753-760
In this work an X‐ray imaging system based on a recently developed in‐line two‐dimensional Bragg magnifier composed of two monolithic V‐shaped crystals made of dislocation‐free germanium is presented. The channel‐cut crystals were used in one‐dimensional and in two‐dimensional (crossed) configurations in imaging applications and allowed measurement of phase‐contrast radiograms both in the edge‐enhanced and in the holographic regimes. The measurement of the phase gradient in two orthogonal directions is demonstrated. The effective pixel size attained was 0.17 µm in the one‐dimensional configuration and 0.5 µm in the two‐dimensional setting, offering a twofold improvement in spatial resolution over devices based on silicon. These results show the potential for applying Bragg magnifiers to imaging soft matter at high resolution with reduced dose owing to the higher efficiency of Ge compared with Si. 相似文献
11.
We report an incipient exploration of the Lense‐Thirring precession effect in a rotating acoustic analogue black hole spacetime. An exact formula is deduced for the precession frequency of a gyroscope due to inertial frame dragging, close to the ergosphere of a ‘Draining Bathtub’ acoustic spacetime which has been studied extensively for acoustic Hawking radiation of phonons and also for ‘superresonance’. The formula is verified by embedding the two dimensional spatial (acoustic) geometry into a three dimensional one where the similarity with standard Lense‐Thirring precession results within a strong gravity framework is well known. Prospects of experimental detection of this new ‘fixed‐metric’ effect in acoustic geometries, are briefly discussed. 相似文献
12.
13.
Quadratic nonlinear photonic crystals are materials in which the second order susceptibility χ(2) is spatially modulated while the linear susceptibility remains constant. These structures are significantly different than the more common photonic crystals, in which the linear susceptibility is modulated. Nonlinear processes in nonlinear photonic crystals are governed by the phase matching requirements, which are determined by the reciprocal lattice of these crystals. Therefore, the modulation of the nonlinear susceptibility enables to engineer the spatial and spectral response in various three‐wave mixing processes. It enables to support the efficient generation of new optical frequencies at multiple directions. We analyze three wave mixing processes in nonlinear photonic crystals in which the modulation is either periodic, quasi‐periodic, radially symmetric or even random. We discuss both one‐dimensional and two‐dimensional modulations. In addition to harmonic generations, we outline several new possibilities for all‐optical control of the spatial and polarization properties of optical beams in specially designed nonlinear photonic crystals. 相似文献
14.
Akihisa Takeuchi Yasuko Terada Yoshio Suzuki Kentaro Uesugi Sadao Aoki 《Journal of synchrotron radiation》2009,16(5):616-621
A confocal full‐field X‐ray microscope has been developed for use as a novel three‐dimensional X‐ray imaging method. The system consists of an X‐ray illuminating `sheet‐beam' whose beam shape is micrified only in one dimension, and an X‐ray full‐field microscope whose optical axis is normal to the illuminating sheet beam. An arbitral cross‐sectional region of the object is irradiated by the sheet‐beam, and secondary X‐ray emission such as fluorescent X‐rays from this region is imaged simultaneously using the full‐field microscope. This system enables a virtual sliced image of a specimen to be obtained as a two‐dimensional magnified image, and three‐dimensional observation is available only by a linear translation of the object along the optical axis of the full‐field microscope. A feasibility test has been carried out at beamline 37XU of SPring‐8. Observation of the three‐dimensional distribution of metallic inclusions in an artificial diamond was performed. 相似文献
15.
Ditter M Stork H Schuster B Fujara F 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,209(1):47-52
A new spectrometer design combining stray-field micro-imaging with mechanical field-cycling Nuclear Magnetic Resonance (FC-NMR), allowing for one dimensional spatial resolution in the order of 10 μm is described. The field-cycle is implemented by moving the probe in the stray-field of a superconducting gradient magnet. In this way a field range between 10 mT and 6.3 T is covered. The maximum transfer time is less than 5 s. Further, methods to correct for some of the imaging artefacts found in previous studies are implemented. The main objective of this design is a depth- and field-dependent investigation of the defect structure caused by heavy-ion irradiation of ionic crystals. 相似文献
16.
E. X. Miqueles J. Rinkel F. O'Dowd J. S. V. Bermúdez 《Journal of synchrotron radiation》2014,21(6):1333-1346
A fast algorithm for ring artefact reduction in high‐resolution micro‐tomography with synchrotron radiation is presented. The new method is a generalization of the one proposed by Titarenko and collaborators, with a complete sinogram restoration prior to reconstruction with classical algorithms. The generalized algorithm can be performed in linear time and is easy to implement. Compared with the original approach, with an explicit solution, this approach is fast through the use of the conjugate gradient method. Also, low/high‐resolution sinograms can be restored using higher/lower‐order derivatives of the projections. Using different order for the derivative is an advantage over the classical Titarenko's approach. Several numerical results using the proposed method are provided, supporting our claims. 相似文献
17.
Akihisa Takeuchi Kentaro Uesugi Yoshio Suzuki Seiichi Itabashi Masatoshi Oda 《Journal of synchrotron radiation》2017,24(3):586-594
Fresnel zone plates with apodized apertures [apodization FZPs (A‐FZPs)] have been developed to realise Gaussian beam optics in the hard X‐ray region. The designed zone depth of A‐FZPs gradually decreases from the center to peripheral regions. Such a zone structure forms a Gaussian‐like smooth‐shouldered aperture function which optically behaves as an apodization filter and produces a Gaussian‐like focusing spot profile. Optical properties of two types of A‐FZP, i.e. a circular type and a one‐dimensional type, have been evaluated by using a microbeam knife‐edge scan test, and have been carefully compared with those of normal FZP optics. Advantages of using A‐FZPs are introduced. 相似文献
18.
Numerical modeling is increasingly becoming an indispensable tool for investigations in many fields of physics. Such modeling is especially useful in today's big science projects as a tool that can provide predictions and design parameters. The reliability of simulation results is thus essential. Code‐to‐code comparisons can help increase our confidence in simulation results, especially when other verification methods – such as comparison to theoretical models or experimental results – are limited or unavailable. In this paper, we describe a code‐to‐code comparison exercise wherein we compare one‐dimensional vacuum arc discharge simulation results from two independent particle‐in‐cell (PIC) codes. As part of our case study, we define a vacuum arc discharge test problem that can be used by other research groups for further comparison. Early disagreement between the two sets of our results motivated us to re‐examine the underlying methods in our codes. After remedying discrepancies, we observe good agreement in vacuum arc discharge time‐to‐breakdown, as well as in the time evolution of particle and current densities. This exercise demonstrates the usefulness of code‐to‐code comparisons and provides an example case study for the benefit of other research groups who may wish to carry out similar code‐to‐code comparisons (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
Transmission of an X‐ray beam through a two‐dimensional photonic crystal and the Talbot effect 下载免费PDF全文
V. G. Kohn 《Journal of synchrotron radiation》2018,25(2):425-431
Results of computer simulations of the transmission of an X‐ray beam through a two‐dimensional photonic crystal as well as the propagation of an X‐ray beam in free space behind the photonic crystal are reported. The photonic crystal consists of a square lattice of silicon cylinders of diameter 0.5 µm. The amount of matter in the path of the X‐ray beam rapidly decreases at the sides of the cylinder projections. Therefore the transmission is localized near the boundaries, and appears like a channeling effect. The iterative method of computer simulations is applied. This method is similar to the multi‐slice method that is widely used in electron microscopy. It allows a solution to be obtained with acceptable accuracy. A peculiarity in the intensity distribution inside the Talbot period zT in free space was found when the intensity is approximately equal to the initial value at a distance 0.46zT, and it is shifted by half a period at distance 0.5zT. The reason for this effect is the existence of a periodic phase of the wavefunction of radiation inside the intensity peaks. Simulations with zero phase do not show this effect. Symmetry rules for the Talbot effect are discussed. 相似文献
20.
Edward Witten 《Journal of Geometry and Physics》1992,9(4):303-368
Two dimensional quantum Yang-Mills theory is reexamined using a non-abelian version of the Duistermaat-Heckman integration formula to carry out the functional integral. This makes it possible to explain properties of the theory that are inaccessible to standard methods and to obtain general expressions for intersection pairings on moduli spaces of flat connections on a two dimensional surface. The latter expressions agree, for gauge group SU (2), with formulas obtained recently by several methods. 相似文献