检索结果-内蒙古大学图书馆

Structure determination from unindexed powder data from scratch by a global optimization approach using pattern comparison based on cross-correlation functions

引用

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS 2022年第2期78卷 195-213页

作者： Habermehl, Stefan Schlesinger, Carina Schmidt, Martin U. Goethe Univ Inst Inorgan & Analyt Chem Max Von Laue Str 7 D-60438 Frankfurt Germany

A method of ab initio crystal structure determination from powder diffraction data for organic and metal-organic compounds, which does not require prior indexing of the powder pattern, has been developed. Only a reasonable molecular geometry is required, needing knowledge of neither unit-cell parameters nor space group. The structures are solved from scratch by a global fit to the powder data using the new program FIDEL-GO ('FIt with DEviating Lattice parameters - Global Optimization'). FIDEL-GO uses a similarity measure based on cross-correlation functions, which allows the comparison of simulated and experimental powder data even if the unit-cell parameters deviate strongly. The optimization starts from large sets of random structures in various space groups. The unit-cell parameters, molecular position and orientation, and selected internal degrees of freedom are fitted simultaneously to the powder pattern. The optimization proceeds in an elaborate multi-step procedure with built-in clustering of duplicate structures and iterative adaptation of parameter ranges. The best structures are selected for an automatic Rietveld refinement. Finally, a user-controlled Rietveld refinement is performed. The procedure aims for the analysis of a wide range of 'problematic' powder patterns, in particular powders of low crystallinity. The method can also be used for the clustering and screening of a large number of possible structure candidates and other application scenarios. Examples are presented for structure determination from unindexed powder data of the previously unknown structures of the nanocrystalline phases of 4,11-difluoro-, 2,9-dichloro- and 2,9-dichloro-6,13-dihydro-quinacridone, which were solved from powder patterns with 14-20 peaks only, and of the coordination polymer dichloro-bis(pyridine-N)copper(II).

关键词： structure determination from powder diffraction data global optimization cross-correlation functions unindexed powder patterns fit with deviating unit-cell parameters

来源：评论

学校读者我要写书评

暂无评论

Comparison and evaluation of pair distribution functions, using a similarity measure based on cross-correlation functions

引用

JOURNAL OF APPLIED CRYSTALLOGRAPHY 2021年第2期54卷 612-623页

作者： Habermehl, Stefan Schlesinger, Carina Prill, Dragica Goethe Univ Inst Inorgan & Analyt Chem Max von Laue Str 7 D-60438 Frankfurt Germany

An approach for the comparison of pair distribution functions (PDFs) has been developed using a similarity measure based on cross-correlation functions. The PDF is very sensitive to changes in the local structure, i.e. small deviations in the structure can cause large signal shifts and significant discrepancies between the PDFs. Therefore, a comparison based on pointwise differences (e.g. R values and difference curves) may lead to the assumption that the investigated PDFs as well as the corresponding structural models are not in agreement at all, whereas a careful visual inspection of the investigated structural models and corresponding PDFs may reveal a relatively good match. To quantify the agreement of different PDFs for those cases an alternative approach is introduced: the similarity measure based on cross-correlation functions. In this paper, the power of this application of the similarity measure to the analysis of PDFs is highlighted. The similarity measure is compared with the classical R-wp values as representative of the comparison based on pointwise differences as well as with the Pearson product-moment correlation coefficient, using polymorph IV of barbituric acid as an example.

关键词： pair distribution functions similarity measures total scattering techniques cross-correlation functions R values

来源：评论

学校读者我要写书评

暂无评论

Ambient noise data selection based on the asymmetry of cross-correlation functions for near surface applications

引用

JOURNAL OF APPLIED GEOPHYSICS 2018年 159卷 803-813页

作者： Zhou, Changjiang Xi, Chaoqiang Pang, Jingyin Liu, Ya Zhejiang Univ Sch Earth Sci Subsurface Imaging & Sensing Lab 38 Zheda Rd Hangzhou 310012 Zhejiang Peoples R China China Univ Geosci Inst Geophys & Geomat Subsurface Imaging & Sensing Lab 388 Rumo Rd Wuhan 430074 Hubei Peoples R China

Passive surface wave methods utilizing traffic noise have been studied in recent years to estimate shear wave velocity in urban near-surface explorations. Suitable processing scheme is necessary for the emergence of coherent signal, and even to account for the azimuthal effects in acquired noise data. We propose a new ambient noise data selection technique based on the asymmetry of the cross-correlation functions to refine the quality of data processing in the complex city environment. The asymmetry coefficient is defined by the logarithmic energy ratio of the casual and acausal surface waves to measure the correlation asymmetry, and two kinds of symmetric functions are taken into account to establish the screening conditions. The underlying physics for the symmetries of the correlation functions are demonstrated to prove the feasibility of our algorithm. Two numerical tests suggest that the bidirectional inline sources are adequately highlighted, and the high velocity anomalies caused by the offline sources are eliminated by our method. Furthermore, the significances of the applications of time window and normalization are investigated to improve the reliability of the algorithm. We also apply the method to three-component field data acquired from the city pavement. The comparisons between the results of raw and selected data confirmed that the random noise and the artifacts can be effectively suppressed, and the dispersion energy trends emerge clearly and become more convergent toward the lower frequency. Finally, our method is concluded to be practical for urban bidirectional traffic noise. (C) 2018 Elsevier B.V. All rights reserved.

关键词： Data selection Azimuthal effects Passive surface wave cross-correlation functions

来源：评论

学校读者我要写书评

暂无评论

Synthesis of cross-correlation functions of Partial Responses and the Extended Kalman Filter Approach for Structural Damage Detection Under Ambient Excitations

引用

INTERNATIONAL JOURNAL OF STRUCTURAL STABILITY AND DYNAMICS 2018年第8期18卷

作者： Lei, Y. Xia, D. D. Chen, F. Deng, Y. M. Xiamen Univ Sch Architecture & Civil Engn Xiamen 361005 Peoples R China Xiamen Univ Technol Sch Civil & Architecture Engn Xiamen Peoples R China

It is still necessary to investigate the detection of structural damage under ambient excitations since the excitations are random and unmeasured while measurement noises are inevitable. In this paper, a method based on the synthesis of cross-correlation functions of partial structural responses and the extended Kalman filter (EKF) approach is proposed for the identification and damage detection of structures under ambient excitations, in which both independent stationary and non-stationary white noise excitations in the product models are discussed. First, the equations of cross-correlation functions of structural responses are established when the ambient excitations are independent stationary white noise processes. Then, the EKF approach is utilized to identify structural parameters and cross-correlation functions using partial measurements of structural acceleration responses. Structural damage is detected based on the degradations of the identified structural element stiffness parameters. Finally, the proposed method is extended to deal with independent non-stationary white noise excitations in the product models. The numerical simulation examples of the ASCE structural health monitoring benchmark building subject to ambient excitation, a moment resisting frame model under white noise excitation, and a cantilever beam model under multiple independent non-stationary excitations are used to validate the feasibility of the proposed method. It is shown that the method is not sensitive to measurement noises. Also, a lab experimental study of the identification of a multi-story shear structure is investigated to further illustrate the applicability of the proposed method.

关键词： Ambient excitation stationary/non-stationary excitation cross-correlation functions incomplete measurement measurement noise extended Kalman filter structural damage detection

来源：评论

学校读者我要写书评

暂无评论

Structure determination from powder data without prior indexing, using a similarity measure based on cross-correlation functions

引用

ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS 2014年第2期70卷 347-359页

作者： Habermehl, Stefan Moerschel, Philipp Eisenbrandt, Pierre Hammer, Sonja M. Schmidt, Martin U. Goethe Univ Frankfurt Inst Inorgan & Analyt Chem D-60438 Frankfurt Germany

A method to refine organic crystal structures from powder diffraction data with incorrect lattice parameters has been developed. The method is based on the similarity measure developed by de Gelder et al. [J. Comput. Chem. (2001), 22, 273-289], using the cross-and auto-correlation functions of a simulated and an experimental powder pattern. The lattice parameters, molecular position, molecular orientation and selected intramolecular degrees of freedom are optimized until the similarity measure reaches a maximum;subsequently, a Rietveld refinement is carried out. The program FIDEL (FIt with DEviating Lattice parameters) implements this method. The procedure is also suitable for unindexed powder data, powder diagrams of very low quality and powder diagrams of non-phase-pure samples. Various applications are shown, including structure determinations from powder data using crystal structure predictions by standard force-field methods. Other useful applications include the automatic structure determination from powder data starting from the crystal structures of isostructural compounds (e. g. a solvate, hydrate or chemical derivative), or from crystal data measured at a different temperature or pressure.

关键词： cross-correlation functions X-ray powder diffraction force-field methods

来源：评论

学校读者我要写书评

暂无评论

A Novel Approach to Tsunami Prediction Using Ambient Noise-Derived Green's functions

引用

GEOPHYSICAL RESEARCH LETTERS 2025年第5期52卷

作者： Ho, Kun-Chi Ko, Justin Yen-Ting Huang, Hsin-Hua Lee, Shiann-Jong Natl Taiwan Univ Inst Oceanog Taipei Taiwan Acad Sinica Inst Earth Sci Taipei Taiwan Natl Taiwan Univ Dept Geosci Taipei Taiwan

Conventional tsunami simulations rely on accurate bathymetric data, posing challenges in regions lacking such information. We introduce a novel approach using ambient noise interferometry to derive empirical Green's functions of infragravity waves from noise correlation functions (NCFs) extracted from a 10-year Deep-ocean Assessment and Reporting of Tsunamis data set in the Pacific Ocean. Our analysis reveals pronounced propagating behavior in NCFs, indicative of wave dispersion relationships. Long-period NCFs align with shallow-water wave dynamics, making them suitable for tsunami simulations. By eliminating the need for precise bathymetry, our method offers a practical solution for data-sparse regions. A case study of an Alaska tsunami demonstrates our NCFs effectively fit observed pressure data, outperforming conventional Cornell Multi-Grid Coupled Tsunami Model simulations. The fidelity of our results underscores the potential of ambient noise interferometry-derived NCFs to enhance tsunami predictions, even in complex environments. Our findings advance tsunami research and have significant implications for disaster preparedness and mitigation.

关键词： tsunami prediction ambient noise interferometry infragravity waves cross-correlation functions disaster preparedness

来源：评论

学校读者我要写书评

暂无评论

Fault detection by reflected surface waves based on ambient noise interferometry

引用

Earthquake Research Advances 2021年第4期1卷 22-27页

作者： Ning Gu Haijiang Zhang Nori Nakata Ji Gao School of Earth and Space Sciences University of Science and Technology of ChinaHefei230026AnhuiChina Mengcheng National Geophysical Observatory University of Science and Technology of ChinaHefei230026AnhuiChina Department of Earth Atmospheric and Planetary SciencesMassachusetts Institute of TechnologyCambridgeMA02139United States

Detecting subsurface fault structure is important for evaluating potential earthquake risks associated with active *** this study,we propose a new method to detect faults using reflected surface waves observed in ambient noise cross correlation *** noise tomography using direct surface waves obtained from ambient noise interferometry has been widely used to characterize active fault *** cases where a strong velocity contrast exists across the fault interface,fault-reflected surface waves are *** test this idea using a linear array deployed in the Suqian segment of Tanlu fault zone in Eastern *** fault-reflected surface waves can be clearly seen in the cross-correlation functions of the ambient noise data,and the spatial position of the fault on the surface is close to the stations where the reflected signals first *** reflected surface waves could also be used to infer the dip angle,fault zone thickness and the degree of velocity contrast across the fault by comparing synthetic and observed waveforms.

关键词： Fault detection Ambient noise cross-correlation functions Reflected surface wave Tanlu fault zone

来源：评论

学校读者我要写书评

暂无评论

Thermal noise performance analysis for dual binary phase-shift keying tracking of standard BOC signals

引用

IET RADAR SONAR AND NAVIGATION 2020年第7期14卷 1019-1028页

作者： Wang, Chuhan Cui, Xiaowei Zhu, Yonghui Lu, Mingquan Tsinghua Univ Dept Elect Engn Beijing Peoples R China Techtotop Microelect Technol Co Ltd Guangzhou Peoples R China Beijing Natl Res Ctr Informat Sci & Technol Beijing Peoples R China

Among the existing binary offset carrier (BOC) signal receiving technologies, the dual binary phase-shift keying tracking (DBT), originally designed for alternate BOC (AltBOC) modulated Galileo E5 signal and then extended to standard BOC signals, has its unique characteristics. It incorporates both single-band and dual-band processing schemes into a unified and simple structure to meet both requirements of improving ranging precision and anti-jamming. However, in this study, the authors propose that it is problematic to directly extend the DBT technique from the AltBOC signal to the standard BOC signal. The root cause of this problem lies in the fact that the cross-correlation functions between the received standard BOC signal and the local replicas in the upper and lower sidebands are not an ideal correlation triangle as the AltBOC case, but with some ripples. This leads to more complex behaviours when the DBT technique is applied to standard BOC signals. The rigorous theoretical analysis of this technique is given in respect of thermal noise performance in this study, which can be used not only to optimise the tracking loop parameters of DBT but also to compare the tracking performance of DBT and other tracking technologies.

关键词： satellite navigation phase shift keying thermal noise correlation methods signal processing received standard BOC signal DBT technique dual binary phase-shift keying tracking AltBOC signal thermal noise performance analysis binary offset carrier signal receiving technologies alternate BOC modulated Galileo E5 signal single-band processing scheme dual-band processing scheme cross-correlation functions

来源：评论

学校读者我要写书评

暂无评论

Identification of structural element mass and stiffness changes using partial acceleration responses of chain-like systems under ambient excitations

引用

JOURNAL OF SOUND AND VIBRATION 2020年 488卷 115678-115678页

作者： Lei, Ying Qiu, Hao Zhang, Fubo Xiamen Univ Sch Architecture & Civil Engn Xiamen 361005 Peoples R China

It is important to conduct structural damage detection using only output time histories of structures under ambient excitations. Recently, an approach has been proposed for structural damage detection under ambient excitations using the synthesis of cross-correlation functions of partial structural responses and the extended Kalman filter (EKF). However, structural mass is assumed known in this approach. Although some methodologies have been presented for detecting damage due to relative structural mass and stiffness changes in chain-like systems, measurements of structural responses including acceleration, velocity, and displacement at each degree of freedom are required. This greatly limits the application of these methodologies. In this paper, without structural mass information, an algorithm is proposed to identify structural element mass and stiffness changes using only partial acceleration responses of chain-like systems under ambient excitations. First, based on the equations for cross-correlation functions of structural responses under ambient stationary excitations modeled as independent stationary white noise processes, EKF is utilized for identifying the structural element stiffness-mass coupled coefficients using only partial acceleration responses. Then, these coefficients are decoupled by cluster analysis and the least squares estimation to obtain structural element stiffness and mass changes. Furthermore, the proposed algorithm is extended for identifying chain-like structural element mass and stiffness changes under non-stationary ambient excitations assumed as time modulating white noises. The performances of the proposed algorithm are numerically investigated using the Phase I The American Society of Civil Engineers structural health monitoring benchmark building under stationary or non-stationary ambient excitations, respectively. Moreover, the experimental data with structural element mass and stiffness changes conducted at the Los Alamos Nationa

关键词： Unknown mass Ambient excitation cross-correlation functions extended Kalman filter Stationary/non-stationary excitation Partial measurements Measurement noise

来源：评论

学校读者我要写书评

暂无评论

Thermoviscous fluid flow in nonisothermal layer: structures, scales, and correlations

引用

THERMOPHYSICS AND AEROMECHANICS 2020年第2期27卷 243-258页

作者： Kulikov, Yu. M. Son, E. E. RAS Joint Inst High Temp Moscow Russia

The paper studies turbulent mixing in thermoviscous fluid flow in a 3D cubic domain which is extended periodically in two directions (XandY). The flow turbulization develops under the impact of two-dimensional chaotic disturbances at mass average Reynolds number Re-1= 4704. The vortex field structure is discussed in terms of an isosurface ofQ-criterion and local enstrophy zeta(1). For the advanced stages of flow evolution, the study considers Eulerian correlation coefficients for velocity fluctuations (auto-correlation functions) and the cross-correlations of pressure and temperature. The Eulerian correlation coefficient is split for analysis of correlation characteristics in periodicity and wall-normal directions. The integral scale is evaluated depending on the distance to the walls. The flow analysis is performed in the terms of viscous scale. The mesh resolution is evaluated for the flow regions corresponding to the logarithmic boundary layer and the near-wall thermal layers.

关键词： thermoviscosity Q-criterion enstrophy velocity autocorrelation functions cross-correlation functions hairpin vortex Eulerian correlation coefficient correlation length integral scale friction velocity Reynolds scaling

来源：评论

学校读者我要写书评

暂无评论

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案：

请选择收藏分类：

通借通还

建议与咨询 留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

分类表

所选分类

限定检索结果

文献类型

馆藏范围

日期分布

学科分类号

主题

机构

作者

语言

请选择保存的检索档案： 新增检索档案 确定 取消

请选择收藏分类： 新增自定义分类 确定 取消

通借通还

建议与咨询留下您的常用邮箱和电话号码，以便我们向您反馈解决方案和替代方法

请选择保存的检索档案：

请选择收藏分类：