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3D Edge Diffraction Coefficients in the Azimuth and Emergence Domain
摘要： The conventional equation for 3D edge diffractions in the Cartesian coordinate system lacks angle information for studying the energy patterns in 3D seismic pre-stack data. Here, a new calculation method is presented for determining 3D edge diffraction coefficients in a spherical coordinate system that can formulate the coefficients according to the azimuth and emergence angles. In order to avoid the singularity phenomenon, a Haar wavelet operator matrix is used for this new method. Analysis of the edge diffraction coefficients variations with azimuth in the common shot domain, common receiver domain, and common midpoint domain reveals that the variation curves of the coefficients can be used to identify the trend of a fault. The phenomenon of polarity reversal of the edge diffraction coefficients is observed in the different domains, and the coefficients in the common shot domain are more sensitive than in other domains.
关键词： azimuth,faults,diffraction
更新于2025-09-04 15:30:14
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[IEEE 2018 15th European Radar Conference (EuRAD) - Madrid, Spain (2018.9.26-2018.9.28)] 2018 15th European Radar Conference (EuRAD) - Radar Cross Section and Near Field of an Engine Digital Mock-up under UHF and S Band Radar Illumination
摘要： RF stealth is an important feature of advanced fighters, and the engine represents a large scattering source. In this paper we present a digital mock-up of a fighter jet engine, and simulate its radar cross section (RCS) in UHF and S band with multi-level fast multipole method (MLFMM), and plot its near fields inside the engine. We found the boresight S-band RCS can be as high as 20 dBsm, and the near field plots indicate radar wave can transmit through the engine even at 400 MHz.
关键词： reflection,jet engine,diffraction,radar cross section,scattering center
更新于2025-09-04 15:30:14
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Reference Module in Materials Science and Materials Engineering || Photoelectron Diffraction
摘要： Surface structural information can be derived from a great variety of methods, but most quantitative data are based on elastic scattering of X-rays, electrons, or ions by the near-surface atoms. While the best-known methods based on electron (and X-ray) scattering are conventional diffraction methods, reliant on long-range order, the technique of photoelectron diffraction is a local scattering technique that thus provides local structural information not dependent on long-range periodicity. In this short article the physical principles of photoelectron diffraction are described, highlighting at least two fundamentally distinct versions of the technique. The main areas of utilization of the method are illustrated.
关键词： local scattering technique,long-range order,surface structural information,photoelectron diffraction,X-rays,electrons,elastic scattering,ions
更新于2025-09-04 15:30:14
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Structural and optical properties of (Cu6PS5Br)1-(Cu7PS6) mixed crystals
摘要： The structure and optical properties of Bridgman-grown (Cu6PS5Br)1-x(Cu7PS6)x mixed crystals are reported. X-ray diffraction data reveal a face-centred cubic lattice (Fm-34 space group) for Cu6PS5Br-rich crystals (0<x<0.4) and a primitive cubic lattice (P213 space group) for Cu7PS6-rich (0.4<x<1) crystals. These structural data correlate with the Raman spectra where, besides the common features typical for the argyrodite-type Cu6PS5Br and Cu7PS6 crystals, weaker bands characteristic only for the end-point compounds are observed in the corresponding compositional intervals. Based on the spectral position of the short-wavelength edge of diffuse reflection spectra, the compositional dependence of the energy gap is studied exhibiting a nonlinear behaviour.
关键词： Inorganic materials,crystal growth,diffuse reflection,Raman scattering,X-ray diffraction,crystal structure
更新于2025-09-04 15:30:14
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Local Strain and Crystalline Defects in GaN/AlGaN/GaN(0001) Heterostructures Induced by Compositionally Graded AlGaN Buried Layers
摘要： Plastic strain relaxation in epitaxial layers is one of the crucial factors that limit the performance of III-nitride-based heterostructures. In this work, we report on strain relaxation and crystalline defects in heterostructures consisting of compositionally graded AlGaN epitaxial layers tensile-strained between a GaN-buffer and a GaN-cap. We demonstrate the effects of Al concentration and the shape of the concentration-depth profile in the buried graded layers on the accumulated elastic strain energy and how this influences the critical thickness for crack generation or fracture. It is shown that this fracture leads to the formation of partially relaxed regions with their degree of strain relaxation directly related to the density of cracks. Nevertheless, even though the in-plane coherency between the AlGaN layer and the GaN-buffer is broken, the in-plane coherency within the AlGaN layer is preserved for all regions. Furthermore, the tensile strain released in the buried graded AlGaN layers is consistent with compressive strain induced in the GaN-cap layers. Finally, the localized stress and the densities of threading dislocations are correlated with the features of the resulting fractured heterostructures. These results are important towards the control of complex plastic strain relaxation and further facilitate the growth of high quality compositionally graded AlGaN-based devices.
关键词： X-ray diffraction,cracks,graded layers,epitaxy,strain relaxation,AlGaN
更新于2025-09-04 15:30:14
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Growth and surface structural study of tin oxide films on Ag(001)
摘要： Tin oxide was prepared by reactive deposition of Sn in an O2 atmosphere at both room temperature (RT) and high temperature (HT) at 573 K as well from one monolayer to ten monolayer film coverages. The grown films were studied at RT by a combination of x-ray photoemission spectroscopy (XPS), low energy electron diffraction (LEED) and ultraviolet photoemission spectroscopy (UPS). At RT, the coexistence of both SnO and SnO2 was confirmed by XPS and valence band data with more SnO being formed at higher coverage. However, only one oxidised phase of tin oxide mainly due to SnO2 was formed at HT for most of the coverage. Presence of SnO was also confirmed only at the highest coverage studied here for HT. A multidomain LEED pattern having square (1 × 1) domains at 30° to each other was reported for low coverage of tin oxide at RT, which with an increase in coverage, gives rise to diffused background confirming no ordered tin oxide was formed. The similar multi-domain structure was also noticed for HT growth from lower coverage up to 5 monolayer equivalent (MLE) coverage which then transformed into hexagonal multidomain LEED pattern for higher coverage confirming the presence of clear oxide phase, unlike the RT growth case.
关键词： Thin films,Low energy electron diffraction,Photoemission spectroscopy
更新于2025-09-04 15:30:14
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MBE Growth and Optical Properties of Isotopically Purified ZnSe Heterostructures
摘要： Wide-gap II/VI heterostructures (HS) and quantum wells (QW) composed of ZnSe, CdSe, MgSe and their ternary and quaternary compounds are attractive candidates for modern quantum optical devices such as single photon sources and optically controlled spin qubits in the visible spectral range. In contrast to similar III/V semiconductor based devices, generally, most of the II/VI compounds allow for isotope purification towards zero nuclear spin species in the semiconductor environment. Using the same molecular beam epitaxy (MBE) system for natural and isotopically purified materials opposes the challenge to achieve superior isotope purity for example of Zn and Se species on the background of operation of the other effusion cells filled with natural isotopes. Here we report on the crystallographic and optical properties of ZnMgSe/ZnSe heterostructures and quantum wells grown by using 64Zn and 80Se isotopes and Mg with natural isotope distribution. We present a detailed quantitative secondary ion mass spectrometry (SIMS) analysis, which confirms that an extremely high grade of isotope purification of the ZnSe can be maintained although naturally and enriched Zn and Se elements are used in the same MBE system. This pioneering growth study forms a solid base to generate a spin vacuum ZnSe host crystal that is particularly suited for future studies on the dynamics of localized spins in II/VI heterostructures on a strongly extended coherence time scale.
关键词： Heterostructures,Molecular beam epitaxy,Optical properties,Crystal structure,X-ray diffraction,Isotope purification,Elementary analysis
更新于2025-09-04 15:30:14
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Computer Tool for Simulating Frequency Modulated -Continuous Wave Radar Systems in Urban Traffic Scenes
摘要： In this work, a computer tool for the simulation of the responses of Frequency Modulated-Continuous Wave radar systems in Urban Traffic Scenes is presented. The radar echoes including frequency shifts due to distance and object speeds are computed using a new hybrid technique that combines Method of Moments, Physical Optics and Geometrical Theory of Diffraction. Arbitrarily time-shaped radar sequences can be set for obtaining output parameters like Doppler Spectrum, beat signals in frequency and time domains, distances and speeds of echoes, etc. The technique is efficient and accurate for solving the electrically large and multiscale problem that appears in the simulation of these systems in urban complex scenarios. Representative results are presented.
关键词： method of moments,FM-CW radar,hybrid methods,physical optics,geometrical theory of diffraction,anticolision,propagation,antenna,radar
更新于2025-09-04 15:30:14
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films
摘要： Noncollinear magnetism can play an important role in multiferroic materials but is relatively understudied in oxide heterostructures compared to their bulk counterparts. Using variable temperature magnetometry and neutron diffraction, we demonstrate the presence of helical magnetic ordering in CaMn7O12 and Ca1?xSrxMn7O12 (for x up to 0.51) thin ?lms. Consistent with bulk Ca1?xSrxMn7O12, the net magnetization increases with Sr doping. Neutron diffraction con?rms that the helical magnetic structure remains incommensurate at all values of x, while the fundamental magnetic wavevector increases upon Sr substitution. This result demonstrates a chemical-based approach for tuning helical magnetism in quadruple perovskite ?lms and enables future studies of strain and interfacial effects on helimagnetism in oxide heterostructures.
关键词： helical magnetism,oxide heterostructures,magnetometry,Sr-doped CaMn7O12,neutron diffraction
更新于2025-09-04 15:30:14
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Methods for <i>operando</i> coherent X-ray diffraction of battery materials at the Advanced Photon Source
摘要： Bragg coherent X-ray diffraction imaging has become valuable for visualization of the structural, morphological and strain evolution of crystals in operando electrode materials. As the electrode material particles (either in a single-crystal form or an aggregation form of single crystals) are evenly dispersed and randomly oriented in the electrode laminate, the submicrometer-sized coherent X-ray beam can be used to probe the local properties of electrode material crystals using two approaches. Coherent multi-crystal diffraction provides collective structural information of phase transitions in tens of crystals simultaneously as well as the individual behavior from single crystals, which are oriented at the Bragg condition in the X-ray illumination volume. Bragg coherent diffractive imaging enables one to monitor the evolution of the morphology and strain in individual crystals. This work explores and highlights the Bragg coherent X-ray diffraction measurements of battery electrode materials in operando conditions at the 34-ID-C beamline at the Advanced Photon Source. The experiment is demonstrated with NaNi1/3Fe1/3Mn1/3O2, a sodium-ion cathode material loaded in a half cell. The paper will discuss, in detail, the beamline setup, sample mounting and handling, alignment strategies and the data acquisition protocols.
关键词： experimental protocols,in operando characterization of battery materials,Bragg coherent diffractive imaging,coherent multi-crystal diffraction
更新于2025-09-04 15:30:14