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Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[general, instrumentation, optics] (syn.: resolution) {use: imaging} The ability to distinguish two neighboring points, the resolving power between these two points based on the angular resolution of the instrument (eye, microscope). This concept was independently described by both the German physicist Ernst Karl Abbe (1840–1905), while working for Carl Zeiss (1816–1888) in 1878, and the English physicist John William Strut, the 3rd Baron Rayleigh (1842–1919). When two objects are projecting their images through the same aperture, each object will generate its own diffraction pattern: Airy disk. The Airy disk of object 1: image A will overlap with the Airy disk of object 2: image B. Under the condition that the first maximum from the center of image A is adjacent to the first maximum of image B, and not overlapping, the two images can be separated or resolved. The resolution is a direct function of the wavelength λ of the electromagnetic radiation used for imaging. The Rayleigh criterion for a circular aperture (e.g., lens) will require corrections for the separation between the edges, and results in the fact that the angle ω that can separate two objects in respect to the aperture of the viewing device (pupil, lens, and aperture, as in a camera obscura) needs to satisfy the following angular definition that defines the two points that can be resolved: ω=λ/nsin(ω)≡1.22λ/D, in air at 550 nm for human eye, where D is the diameter of the opening or the diameter of the aperture and ω is the half-angle of the cone of rays emitted from the opening and nsin(ω)=NA is the numerical aperture (NA). A bird of prey has a very high resolution due to the fact that the eye only has a relatively small angle of vision resulting from a densely packed retinal rods configuration and a large pupil diameter, approximately ω = 0.18 arcmin compared to the fovea of the human eye with both cones and rods: ω = 0.30 arcmin. In addition, some birds of prey have a double foveae that allows for simultaneous high-resolution (this is in particular called the convexiclivate fovea) and low-resolution vision (seerefraction;also seeRayleigh criterion) (see Figure A.2).
The HighNESS Project at the European Spallation Source: Current Status and Future Perspectives
Published in Nuclear Science and Engineering, 2023
V. Santoro, K. H. Andersen, P. Bentley, M. Bernasconi, M. Bertelsen, Y. Beßler, A. Bianchi, T. Brys, D. Campi, A. Chambon, V. Czamler, D. D. Di Julio, E. Dian, K. Dunne, M. J. Ferreira, P. Fierlinger, U. Friman-Gayer, B. T. Folsom, A. Gaye, G. Gorini, C. Happe, M. Holl, Y. Kamyshkov, T. Kittelmann, E. B. Klinkby, R. Kolevatov, S. I. Laporte, B. Lauritzen, J. I. Marquez Damian, B. Meirose, F. Mezei, D. Milstead, G. Muhrer, V. Neshvizhevsky, B. Rataj, N. Rizzi, L. Rosta, S. Samothrakitis, H. Schober, J. R. Selknaes, S. Silverstein, M. Strobl, M. Strothmann, A. Takibayev, R. Wagner, P. Willendrup, S. Xu, S. C. Yiu, L. Zanini, O. Zimmer
The moderator setup consists of three interchangeable vessels filled with a 10-mm-thick layer of ND powder, MgH2 powder and an identical empty vessel for background subtraction, respectively, that will be placed around a hydrogen cold moderator (Fig. 19). The cold moderator is fed by the thermal neutron field diffused by a beryllium cylinder located in the line of sight of beam channel 4 (see also Fig. 22 in Sec. VI). The moderated neutrons of the moderator/reflector assembly are led into a 600-mm-long beam guide surrounded by a 5-mm-thick ND powder layer. The spectra of the reflector/moderator/guide assembly are measured by a pinhole (“camera obscura”) ToF two-dimensional detector setup (see Fig. 18). All structures of the setup that are placed in the neutron beam are manufactured of aluminum to minimize neutron absorption and activation. The H2 supply lines are led into the cryostat system outside the bunker where the LH2 liquefaction takes place and a defined LH2 ortho/para ratio can be generated.
Monte Carlo simulations of deformation behaviour of unbound granular materials based on a real aggregate library
Published in International Journal of Pavement Engineering, 2023
Jue Li, Junhui Zhang, Xinrui Yang, Anshun Zhang, Miao Yu
Morphological characteristics of aggregates, such as angularity, shapes and texture, play important roles on the deformation behaviour of UGMs (Cook et al. 2017). In general, the more cubic and angular the shape of the coarse aggregate is, the better the interlocking between the aggregates in a certain gradation will be (Byun et al. 2020). Therefore, the current research practices have focused on the evaluation of angles and shapes, and these characteristics are important in the improvement of strength and fatigue properties of UGMs (Venkatesh et al. 2020, Wang et al. 2019). In addition, complex surface textures also contribute to the slip resistance of aggregates. However, since it is difficult to be measured accurately in submicroscopic category, the friction coefficient is often used to represent the effect of complex texture on mechanical properties (Li et al. 2016). Researchers have introduced advanced techniques such as digital image processing technology and laser scanning into the characteristic analysis of aggregate morphology (Wang et al. 2021, Wang et al. 2021). With the development of measuring technology, a number of quantitative evaluation indexes have been proposed in the current studies (Wang et al. 2022). For example, Mahmoud et al. (2010) developed the Aggregate Morphology Measurement System (AIMS) and compared the stability of three-dimensional measurements of coarse aggregates using X-ray CT tomography. Based on their work, Rezaei and Masad (2013) proposed an improved AIMS II system that uses a closed camera obscura to eliminate the effect of ambient light, to get a more accurate aggregate texture. Zhang et al. (2012) investigated the properties of coarse aggregates in terms of shape, size, angularity and surface texture, and proposed an angularity-texture index to consider the joint effect of coarse aggregate angularity and surface texture based on two-dimensional aggregate images. Gong et al. (2017) obtained digital images of aggregates by laser scanning, and used MATLAB algorithms to process the key outputs as characteristic values of the surface texture of the coarse aggregates. These indexes based on aggregate images have a great potential in the future, since they can present the statistical characteristics of aggregate mixtures (Wang et al. 2022). However, the acquisition of digital images is still expensive and time-consuming, and these indexes usually need a large number of samples to obtain statistically significant results (Pouranian et al. 2020). The influence of different morphological indexes on the mechanical behaviour of UGMs has rarely been investigated, and a heterogeneous modelling approach for UGMs considering real aggregate characteristics is still a challenge (Jin et al. 2020).