Ultramicroscopy最新文献

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State-of-the-art electron beams for compact tools of ultrafast science.
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2025-01-01 Epub Date: 2024-11-26 DOI: 10.1016/j.ultramic.2024.114080
Peter Salén, Anatoliy Opanasenko, Giovanni Perosa, Vitaliy Goryashko
{"title":"State-of-the-art electron beams for compact tools of ultrafast science.","authors":"Peter Salén, Anatoliy Opanasenko, Giovanni Perosa, Vitaliy Goryashko","doi":"10.1016/j.ultramic.2024.114080","DOIUrl":"10.1016/j.ultramic.2024.114080","url":null,"abstract":"<p><p>We review state-of-the-art electron beams for single-shot megaelectronvolt ultrafast electron diffraction (MeV-UED) and compact light sources. Our primary focus is on sub-100 femtosecond electron bunches in the 2-30 MeV energy range. We demonstrate that our new and recent simulation results permit significantly improved bunch parameters for these applications.</p>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"268 ","pages":"114080"},"PeriodicalIF":2.1,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142772741","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Enhancing subsurface imaging in ultrasonic atomic force microscopy with optimized contact force.
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2024-12-08 DOI: 10.1016/j.ultramic.2024.114094
Mingyu Duan, Chengjian Wu, Jinyan Tang, Yuyang Wang, Shiquan Liu, Bing-Feng Ju, Yuan-Liu Chen
{"title":"Enhancing subsurface imaging in ultrasonic atomic force microscopy with optimized contact force.","authors":"Mingyu Duan, Chengjian Wu, Jinyan Tang, Yuyang Wang, Shiquan Liu, Bing-Feng Ju, Yuan-Liu Chen","doi":"10.1016/j.ultramic.2024.114094","DOIUrl":"https://doi.org/10.1016/j.ultramic.2024.114094","url":null,"abstract":"<p><p>Ultrasonic atomic force microscopy (UAFM) is a powerful nondestructive subsurface imaging tool that is widely used to inspect material defects and analyze biological cells. The contrast in UAFM images, which is crucial for subsurface imaging quality, is directly influenced by the contact force between the probe and material. This contact force affects the subsurface contrast by influencing the propagation of the stress field from the vibrating probe into the material. Therefore, optimizing the contact force is essential for achieving superior subsurface contrast with better resolution and greater detectable depth. This paper proposes a model for determining the optimal contact force for high-contrast, high-resolution subsurface imaging. The model was designed to improve UAFM imaging across samples with a wide range of Young's moduli, from tens to hundreds of GPa. The use of this model resulted in significant improvements to imaging quality, with a detectable depth exceeding 337.7 nm and lateral resolution below 56.9 nm. Hence, this model demonstrates better results than experiments conducted under arbitrary contact forces. This study provides a pathway for optimizing subsurface imaging and delivering enhanced contrast, higher resolution, and greater detectable depth. Consequently, the results of this study contribute to the advancement of the capabilities of subsurface imaging techniques.</p>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"269 ","pages":"114094"},"PeriodicalIF":2.1,"publicationDate":"2024-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142824516","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Workflow automation of SEM acquisitions and feature tracking.
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2024-12-08 DOI: 10.1016/j.ultramic.2024.114093
Sabrina Clusiau, Nicolas Piché, Nicolas Brodusch, Mike Strauss, Raynald Gauvin
{"title":"Workflow automation of SEM acquisitions and feature tracking.","authors":"Sabrina Clusiau, Nicolas Piché, Nicolas Brodusch, Mike Strauss, Raynald Gauvin","doi":"10.1016/j.ultramic.2024.114093","DOIUrl":"https://doi.org/10.1016/j.ultramic.2024.114093","url":null,"abstract":"<p><p>Acquiring multiple high magnification, high resolution images with scanning electron microscopes (SEMs) for quantitative analysis is a time consuming and repetitive task for microscopists. We propose a workflow to automate SEM image acquisition and demonstrate its use in the context of nanoparticle (NP) analysis. Acquiring multiple images of this type of specimen is necessary to obtain a complete and proper characterization of the NP population and obtain statistically representative results. Indeed, a single high magnification image only scans a small area of sample, containing only few NPs. The proposed workflow is successfully applied to obtain size distributions from image montages at three different magnifications (20,000x, 60,000x and 200,000x) on the same area of the sample using a Python based script. The automated workflow consists of sequential repositioning of the electron beam, stitching of adjacent images, feature segmentation, and NP size computation. Results show that NPs are best characterized at higher magnifications, since lower magnifications are limited by their pixel size. Increased accuracy of feature characterization at high magnification highlights the importance of automation: many high-magnification acquisitions are required to cover a similar area of the sample at low magnification. Therefore, we also present feature tracking with smart beam positioning as an alternative to blind acquisition of very large image arrays. Feature tracking is achieved by integrating microscope tasks with image processing tasks, and only areas of interest will be imaged at high resolution, reducing total acquisition duration.</p>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"269 ","pages":"114093"},"PeriodicalIF":2.1,"publicationDate":"2024-12-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142819184","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Improved precision and accuracy of electron energy-loss spectroscopy quantification via fine structure fitting with constrained optimization.
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2024-12-05 DOI: 10.1016/j.ultramic.2024.114084
Daen Jannis, Wouter Van den Broek, Zezhong Zhang, Sandra Van Aert, Jo Verbeeck
{"title":"Improved precision and accuracy of electron energy-loss spectroscopy quantification via fine structure fitting with constrained optimization.","authors":"Daen Jannis, Wouter Van den Broek, Zezhong Zhang, Sandra Van Aert, Jo Verbeeck","doi":"10.1016/j.ultramic.2024.114084","DOIUrl":"https://doi.org/10.1016/j.ultramic.2024.114084","url":null,"abstract":"<p><p>By working out the Bethe sum rule, a boundary condition that takes the form of a linear equality is derived for the fine structure observed in ionization edges present in electron energy-loss spectra. This condition is subsequently used as a constraint in the estimation process of the elemental abundances, demonstrating starkly improved precision and accuracy and reduced sensitivity to the number of model parameters. Furthermore, the fine structure is reliably extracted from the spectra in an automated way, thus providing critical information on the sample's electronic properties that is hard or impossible to obtain otherwise. Since this approach allows dispensing with the need for user-provided input, a potential source of bias is prevented.</p>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"269 ","pages":"114084"},"PeriodicalIF":2.1,"publicationDate":"2024-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142814197","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Relativistic EELS scattering cross-sections for microanalysis based on Dirac solutions.
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2024-12-02 DOI: 10.1016/j.ultramic.2024.114083
Zezhong Zhang, Ivan Lobato, Hamish Brown, Dirk Lamoen, Daen Jannis, Johan Verbeeck, Sandra Van Aert, Peter D Nellist
{"title":"Relativistic EELS scattering cross-sections for microanalysis based on Dirac solutions.","authors":"Zezhong Zhang, Ivan Lobato, Hamish Brown, Dirk Lamoen, Daen Jannis, Johan Verbeeck, Sandra Van Aert, Peter D Nellist","doi":"10.1016/j.ultramic.2024.114083","DOIUrl":"https://doi.org/10.1016/j.ultramic.2024.114083","url":null,"abstract":"<p><p>The rich information of electron energy-loss spectroscopy (EELS) comes from the complex inelastic scattering process whereby fast electrons transfer energy and momentum to atoms, exciting bound electrons from their ground states to higher unoccupied states. To quantify EELS, the common practice is to compare the cross-sections integrated within an energy window or fit the observed spectrum with theoretical differential cross-sections calculated from a generalized oscillator strength (GOS) database with experimental parameters. The previous Hartree-Fock-based and DFT-based GOS are calculated from Schrödinger's solution of atomic orbitals, which does not include the full relativistic effects. Here, we attempt to go beyond the limitations of the Schrödinger solution in the GOS tabulation by including the full relativistic effects using the Dirac equation within the local density approximation, which is particularly important for core-shell electrons of heavy elements with strong spin-orbit coupling. This has been done for all elements in the periodic table (up to Z = 118) for all possible excitation edges using modern computing capabilities and parallelization algorithms. The relativistic effects of fast incoming electrons were included to calculate cross-sections that are specific to the acceleration voltage. We make these tabulated GOS available under an open-source license to the benefit of both academic users and to allow integration into commercial solutions.</p>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"269 ","pages":"114083"},"PeriodicalIF":2.1,"publicationDate":"2024-12-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142792288","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Aberration calculation of microlens array using differential algebraic method.
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2024-11-30 DOI: 10.1016/j.ultramic.2024.114085
Jintao Hu, Lei Yue, Yihao Ma, Fu Liu, Yongfeng Kang
{"title":"Aberration calculation of microlens array using differential algebraic method.","authors":"Jintao Hu, Lei Yue, Yihao Ma, Fu Liu, Yongfeng Kang","doi":"10.1016/j.ultramic.2024.114085","DOIUrl":"https://doi.org/10.1016/j.ultramic.2024.114085","url":null,"abstract":"<p><p>Microlens array (MLA), through which all the sub-beams are focused, is widely used in multi-electron-beam systems. In this work, based on the differential algebraic (DA) method, we propose an approach in calculating the high-order aberrations for both axial and off-axial microlenses, considering the multipole fields that are introduced by the neighborhood structures in MLA, as well as the rotationally symmetric field. To perform the DA calculation, the electric fields of the microlenses are analyzed by using the azimuthal Fourier analysis and the Fourier-Bessel series Expansion. The resulting field components, including both rotationally symmetric field and the multipole fields, are transferred into DA arguments and operated as per DA methodology. Then, by developing and employing the DA theory and algorithm, the primary and high-order aberrations are calculated and obtained simultaneously for both the axial and off-axial microlenses by tracing only one reference ray. Finally, we calculate, analyze and discuss the primary and high-order aberrations of two example MLAs, for both axial and off-axial microlenses. The effects of the dodecapole fields on the aberrations are also analyzed.</p>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"269 ","pages":"114085"},"PeriodicalIF":2.1,"publicationDate":"2024-11-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142792283","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Effect of the surrounding environment on electron beam irradiation damage of enhanced green fluorescent protein
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2024-11-25 DOI: 10.1016/j.ultramic.2024.114082
Haruyoshi Osakabe , Mihiro Suzuki , Toshiki Shimizu , Hiroki Minoda
{"title":"Effect of the surrounding environment on electron beam irradiation damage of enhanced green fluorescent protein","authors":"Haruyoshi Osakabe ,&nbsp;Mihiro Suzuki ,&nbsp;Toshiki Shimizu ,&nbsp;Hiroki Minoda","doi":"10.1016/j.ultramic.2024.114082","DOIUrl":"10.1016/j.ultramic.2024.114082","url":null,"abstract":"<div><div>Fluorescent proteins exhibit fluorescence and photoconversion, which are used to study biological phenomena. Among these, enhanced green fluorescent protein (EGFP) emits cathodoluminescence when irradiated with electron beams; this phenomenon has numerous applications in new research tools for biological phenomena. However, bleaching during electron irradiation is a major problem. Generally, the presence of water is important for biological samples, and structural observations are often performed under cryogenic conditions. One of the advantages of cryogenic conditions is the stabilization of the sample due to cooling. However, it is unclear which factor is more effective: the presence of water molecules or cryogenic preservation. To explore the stabilizing factors of the sample structure, we prepared four environments around the sample–dry at room temperature, wet at room temperature, dry at low temperature, and under cryogenic conditions–and investigated the electron beam irradiation damage by measuring the fluorescence emission spectra. Emission intensity from EGFP was attenuated, and the peak was red-shifted by electron beam irradiation; however, the intensity attenuation was fast under dry conditions at low temperature and slow under wet conditions at room temperature. These results imply that sample cooling has no significant effect on the stability of the EGFP chromophore and that the presence of water molecules is extremely important.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"268 ","pages":"Article 114082"},"PeriodicalIF":2.1,"publicationDate":"2024-11-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142746083","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Direct electron detection for EBSD of low symmetry & beam sensitive ceramics 用于低对称性和光束敏感陶瓷 EBSD 的直接电子探测
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2024-11-23 DOI: 10.1016/j.ultramic.2024.114079
Nicolò M. Della Ventura , Andrew R. Ericks , McLean P. Echlin , Kalani Moore , Tresa M. Pollock , Matthew R. Begley , Frank W. Zok , Marc De Graef , Daniel S. Gianola
{"title":"Direct electron detection for EBSD of low symmetry & beam sensitive ceramics","authors":"Nicolò M. Della Ventura ,&nbsp;Andrew R. Ericks ,&nbsp;McLean P. Echlin ,&nbsp;Kalani Moore ,&nbsp;Tresa M. Pollock ,&nbsp;Matthew R. Begley ,&nbsp;Frank W. Zok ,&nbsp;Marc De Graef ,&nbsp;Daniel S. Gianola","doi":"10.1016/j.ultramic.2024.114079","DOIUrl":"10.1016/j.ultramic.2024.114079","url":null,"abstract":"<div><div>Electron backscatter diffraction (EBSD) is a powerful tool for determining the orientations of near-surface grains in engineering materials. However, many ceramics present challenges for routine EBSD data collection and indexing due to small grain sizes, high crack densities, beam and charge sensitivities, low crystal symmetries, and pseudo-symmetric pattern variants. Micro-cracked monoclinic hafnia, tetragonal hafnon, and hafnia/hafnon composites exhibit all such features, and are used in the present work to show the efficacy of a novel workflow based on a direct detecting EBSD sensor and a state-of-the-art pattern indexing approach. At 5 and 10 keV primary beam energies (where beam-induced damage and surface charge accumulation are minimal), the direct electron detector produces superior diffraction patterns with 10x lower doses compared to a phosphor-coupled indirect detector. Further, pseudo-symmetric variant-related indexing errors from a Hough-based approach (which account for at least 4%-14% of map areas) are easily resolved by dictionary indexing. In short, the workflow unlocks fundamentally new opportunities to characterize materials historically unsuited for EBSD.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"268 ","pages":"Article 114079"},"PeriodicalIF":2.1,"publicationDate":"2024-11-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142721238","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Chinese knot inspired isotropic linear scanning method for improved imaging performance in AFM 受中国结启发的各向同性线性扫描方法可提高原子力显微镜的成像性能
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2024-11-18 DOI: 10.1016/j.ultramic.2024.114081
Xiaolong Jia , Haitao Wu , Qubo Jiang , Qilin Zeng , Wentao Zhang , Yanding Qin
{"title":"Chinese knot inspired isotropic linear scanning method for improved imaging performance in AFM","authors":"Xiaolong Jia ,&nbsp;Haitao Wu ,&nbsp;Qubo Jiang ,&nbsp;Qilin Zeng ,&nbsp;Wentao Zhang ,&nbsp;Yanding Qin","doi":"10.1016/j.ultramic.2024.114081","DOIUrl":"10.1016/j.ultramic.2024.114081","url":null,"abstract":"<div><div>Atomic force microscope (AFM) is an important nano-scale surface characterization and measurement method. Raster scanning method (RSM), widely used in AFMs, faces limitations on scanning speed and imaging accuracy. In this paper, an isotropic linear scanning method (ILSM) is proposed to improve the AFM imaging performance. Inspired by Chinese knot, ILSM is constructed by integrating two iterative triangular scanning trajectories in X and Y axes, similar to triangular Lissajous. Compared with the other scanning methods, ILSM features isotropic scanning trajectory across the scanning region. It is also easy to increase either the scanning speed or scanning resolution using ILSM. Subsequently, to address the hysteresis associated with the piezoelectric actuator, a new tracking algorithm is proposed by combining adaptive Kalman filtering and direct inverse modeling approach. Finally, AFM imaging experiments are conducted to validate the effectiveness of the proposed method. It can be found that the artifacts in RSM can be efficiently eliminated using the proposed method, thus improving the imaging quality.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"268 ","pages":"Article 114081"},"PeriodicalIF":2.1,"publicationDate":"2024-11-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142699969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
Toward quantitative thermoelectric characterization of (nano)materials by in-situ transmission electron microscopy 利用原位透射电子显微镜对(纳米)材料进行定量热电表征。
IF 2.1 3区 工程技术
Ultramicroscopy Pub Date : 2024-11-06 DOI: 10.1016/j.ultramic.2024.114071
Simon Hettler , Mohammad Furqan , Andrés Sotelo , Raul Arenal
{"title":"Toward quantitative thermoelectric characterization of (nano)materials by in-situ transmission electron microscopy","authors":"Simon Hettler ,&nbsp;Mohammad Furqan ,&nbsp;Andrés Sotelo ,&nbsp;Raul Arenal","doi":"10.1016/j.ultramic.2024.114071","DOIUrl":"10.1016/j.ultramic.2024.114071","url":null,"abstract":"<div><div>We explore the possibility to perform an <em>in-situ</em> transmission electron microscopy (TEM) thermoelectric characterization of materials. A differential heating element on a custom <em>in-situ</em> TEM microchip allows to generate a temperature gradient across the studied materials, which are simultaneously measured electrically. A thermovoltage was induced in all studied devices, whose sign corresponds to the sign of the Seebeck coefficient of the tested materials. The results indicate that <em>in-situ</em> thermoelectric TEM studies can help to profoundly understand fundamental aspects of thermoelectricity, which is exemplary demonstrated by tracking the thermovoltage during <em>in-situ</em> crystallization of an amorphous Ge thin film. We propose an improved <em>in-situ</em> TEM microchip design, which should facilitate a full quantitative measurement of the induced temperature gradient, the electrical and thermal conductivities, as well as the Seebeck coefficient. The benefit of the <em>in-situ</em> approach is the possibility to directly correlate the thermoelectric properties with the structure and chemical composition of the entire studied device down to the atomic level, including grain boundaries, dopants or crystal defects, and to trace its dynamic evolution upon heating or during the application of electrical currents.</div></div>","PeriodicalId":23439,"journal":{"name":"Ultramicroscopy","volume":"268 ","pages":"Article 114071"},"PeriodicalIF":2.1,"publicationDate":"2024-11-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142629442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
引用次数: 0
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