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Evolving role of magnetic resonance techniques in primary sclerosing cholangitis 预览
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作者 Emmanuel A Selvaraj Emma L Culver +3 位作者 Helen Bungay Adam Bailey Roger W Chapman Michael Pavlides 《世界胃肠病学杂志:英文版》 SCIE CAS 2019年第6期644-658,共15页
Development of non-invasive methods to risk-stratify patients and predict clinical endpoints have been identified as one of the key research priorities in primary sclerosing cholangitis(PSC).In addition to serum and h... Development of non-invasive methods to risk-stratify patients and predict clinical endpoints have been identified as one of the key research priorities in primary sclerosing cholangitis(PSC).In addition to serum and histological biomarkers,there has been much recent interest in developing imaging biomarkers that can predict disease course and clinical outcomes in PSC.Magnetic resonance imaging/magnetic resonance cholangiopancreatography(MRI/MRCP)continue to play a central role in the diagnosis and follow-up of PSC patients.Magnetic resonance(MR)techniques have undergone significant advancement over the last three decades both in MR data acquisition and interpretation.The progression from a qualitative to quantitative approach in MR acquisition techniques and data interpretation,offers the opportunity for the development of objective and reproducible imaging biomarkers that can potentially be incorporated as an additional endpoint in clinical trials.This review article will discuss how the role of MR techniques have evolved over the last three decades from emerging as an alternative diagnostic tool to endoscopic retrograde cholangiopancreatography,to being instrumental in the ongoing search for imaging biomarker of disease stage,progression and prognosis in PSC. 展开更多
关键词 Primary SCLEROSING CHOLANGITIS MAGNETIC RESONANCE IMAGING MAGNETIC RESONANCE CHOLANGIOPANCREATOGRAPHY MAGNETIC RESONANCE elastography Diffusion MAGNETIC RESONANCE IMAGING Endoscopic retrograde CHOLANGIOPANCREATOGRAPHY
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Evaluation of tumor response to antiangiogenic therapy in patients with recurrent gliomas using contrast-enhanced perfusion-weighted magnetic resonance imaging techniques: A meta-analysis 预览
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作者 Akanganyira Kasenene Aju Baidya +1 位作者 Salman Shams Hai-Bo Xu 《世界荟萃分析杂志》 2019年第2期51-65,共15页
BACKGROUND It is of vital importance to find radiologic biomarkers that can accurately predict treatment response. Usually, the initiation of antiangiogenic therapy causes a rapid decrease in the contrast enhancing tu... BACKGROUND It is of vital importance to find radiologic biomarkers that can accurately predict treatment response. Usually, the initiation of antiangiogenic therapy causes a rapid decrease in the contrast enhancing tumor. However, the treatment response is observed only in a fraction of patients due to the partial radiological response secondary to stabilization of abnormal vessels which does not essentially indicate a true antitumor effect. Perfusion-weighted magnetic resonance imaging (PWMRI) techniques have shown implicitness as a strong imaging biomarker for gliomas since they give hemodynamic information of blood vessels. Hence, there is a rapid expansion of PW-MRI related studies and clinical applications. AIM To determine the diagnostic performance of PW-MRI techniques including:(A) dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI);and (B) dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) for evaluating response to antiangiogenic therapy in patients with recurrent gliomas. METHODS Databases such as PubMed (MEDLINE included), EMBASE, and Google Scholar were searched for relevant original articles. The included studies were assessed for methodological quality with the Quality Assessment of Diagnostic Accuracy Studies 2 tool. Medical imaging follow-up or histopathological analysis was used as the reference standard. The data were extracted by two reviewers independently, and then the sensitivity, specificity, summary receiver operating characteristic curve, area under the curve (AUC), and heterogeneity were calculated using Meta-Disc 1.4 software.RESULTS This study analyzed a total of six articles. The overall sensitivity for DCE-MRI and DSC-MRI was 0.69 [95% confidence interval (CI): 0.53-0.82], and the specificity was 0.99 (95%CI: 0.93-1) by a random effects model (DerSimonianee- Laird model). The likelihood ratio (LR)+, LR-, and diagnostic odds ratio (DOR) were 12.84 (4.54-36.28), 0.35 (0.22-0.53), and 24.44 (7.19-83.06), respectively. The AUC (± SE) was 0.9921 (± 0.0120), 展开更多
关键词 Glioma Perfusion-weighted MAGNETIC RESONANCE IMAGING DYNAMIC contrastenhanced MAGNETIC RESONANCE IMAGING DYNAMIC susceptibility contrast MAGNETIC RESONANCE IMAGING Anti-vascular endothelial growth factor ANTIANGIOGENIC Metaanalysis
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固有频率与共振频率影响因素及实验研究 预览
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作者 张枫茁 顾吉林 +2 位作者 李欣阳 杨青 王震 《大学物理实验》 2019年第2期37-41,共5页
从实验室常见的实验仪器烧杯入手,先测量烧杯的固有频率,然后在测得的固有频率附近寻找烧杯的共振频率,并研究了相关参量对烧杯系统共振频率的影响。实验结论表明:系统的共振频率与烧杯口径、烧杯所加液体质量以及烧杯中所盛放液体的表... 从实验室常见的实验仪器烧杯入手,先测量烧杯的固有频率,然后在测得的固有频率附近寻找烧杯的共振频率,并研究了相关参量对烧杯系统共振频率的影响。实验结论表明:系统的共振频率与烧杯口径、烧杯所加液体质量以及烧杯中所盛放液体的表面张力有关。当烧杯中所加液体体积一定时,烧杯系统的共振频率与烧杯的口径成反比;当烧杯口径一定时,烧杯系统的共振频率与所加液体质量成反比;在使用相同口径的烧杯,并加入相同质量的甘油和水时,烧杯中所盛放液体的表面张力越大,共振频率越大。 展开更多
关键词 共振 固有频率 烧杯系统 共振频率 实验
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Imaging plaque inflammation in asymptomatic cocaine addicted individuals with simultaneous positron emission tomography/magnetic resonance imaging 预览
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作者 Keren Bachi Venkatesh Mani +4 位作者 Audrey E Kaufman Nadia Alie Rita Z Goldstein Zahi A Fayad Nelly Alia-Klein 《世界放射学杂志:英文版(电子版)》 2019年第5期62-73,共12页
BACKGROUND Chronic cocaine use is associated with stroke, coronary artery disease and myocardial infarction, resulting in severe impairments or sudden mortality. In the absence of clear cardiovascular symptoms, indivi... BACKGROUND Chronic cocaine use is associated with stroke, coronary artery disease and myocardial infarction, resulting in severe impairments or sudden mortality. In the absence of clear cardiovascular symptoms, individuals with cocaine use disorder (iCUD) seeking addiction treatment receive mostly psychotherapy and psychiatric pharmacotherapy, with no attention to vascular disease (i.e., atherosclerosis). Little is known about the pre-clinical signs of cardiovascular risk in iCUD and early signs of vascular disease are undetected in this underserved population. AIM To assess inflammation, plaque burden and plaque composition in iCUD aiming to detect markers of atherosclerosis and vascular disease. METHODS The bilateral carotid arteries were imaged with positron emission tomography/magnetic resonance imaging (PET/MRI) in iCUD asymptomatic for cardiovascular disease, healthy controls, and individuals with cardiovascular risk. PET with 18F-fluorodeoxyglucose (18F-FDG) evaluated vascular inflammation and 3-D dark-blood MRI assessed plaque burden including wall area and thickness. Drug use and severity of addiction were assessed with standardized instruments. RESULTS The majority of iCUD and controls had carotid FDG-PET signal greater than 1.6 but lower than 3, indicating the presence of mild to moderate inflammation. However, the MRI measure of wall structure was thicker in iCUD as compared to the controls and cardiovascular risk group, indicating greater carotid plaque burden. iCUD had larger wall area as compared to the healthy controls but not as compared to the cardiovascular risk group, indicating structural wall similarities between the non-control study groups. In iCUD, wall area correlated with greater cocaine withdrawal and craving. CONCLUSION These preliminary results show markers of carotid artery disease burden in cardiovascular disease-asymptomatic iCUD. Broader trials are warranted to develop protocols for early detection of cardiovascular risk and preventive intervention in iCUD. 展开更多
关键词 3-D dark-blood magnetic resonance imaging 18F-fluorodeoxyglucose POSITRON emission TOMOGRAPHY SIMULTANEOUS POSITRON emission TOMOGRAPHY Magnetic resonance Substance use disorder COCAINE addiction Atherosclerosis PLAQUE burden Vascular INFLAMMATION
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Analysis of in-plane 1:1:1 internal resonance of a double cable-stayed shallow arch model with cables’ external excitations 预览
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作者 Yunyue CONG Houjun KANG Tieding GUO 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第7期977-1000,共24页
The nonlinear dynamic behaviors of a double cable-stayed shallow arch model are investigated under the one-to-one-to-one internal resonance among the lowest modes of cables and the shallow arch and external primary re... The nonlinear dynamic behaviors of a double cable-stayed shallow arch model are investigated under the one-to-one-to-one internal resonance among the lowest modes of cables and the shallow arch and external primary resonance of cables. The in-plane governing equations of the system are obtained when the harmonic excitation is applied to cables. The excitation mechanism due to the angle-variation of cable tension during motion is newly introduced. Galerkin’s method and the multi-scale method are used to obtain ordinary differential equations (ODEs) of the system and their modulation equations, respectively. Frequency- and force-response curves are used to explore dynamic behaviors of the system when harmonic excitations are symmetrically and asymmetrically applied to cables. More importantly, comparisons of frequency-response curves of the system obtained by two types of trial functions, namely, a common sine function and an exact piecewise function, of the shallow arch in Galerkin’s integration are conducted. The analysis shows that the two results have a slight difference;however, they both have sufficient accuracy to solve the proposed dynamic system. 展开更多
关键词 nonlinear dynamics CABLE-STAYED system internal RESONANCE primary RESONANCE MULTI-SCALE method
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Dynamical modeling and non-planar coupled behavior of inclined CFRP cables under simultaneous internal and external resonances 预览
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作者 Houjun KANG Tieding GUO +2 位作者 Weidong ZHU Junyi SU Bingyu ZHAO 《应用数学和力学:英文版》 SCIE EI CSCD 2019年第5期649-678,共30页
A dynamic model for an inclined carbon fiber reinforced polymer (CFRP) cable is established, and the linear and nonlinear dynamic behaviors are investigated in detail. The partial differential equations for both the i... A dynamic model for an inclined carbon fiber reinforced polymer (CFRP) cable is established, and the linear and nonlinear dynamic behaviors are investigated in detail. The partial differential equations for both the in-plane and out-of-plane dynamics of the inclined CFRP cable are obtained by Hamilton’s principle. The linear eigenvalues are explored theoretically. Then, the ordinary differential equations for analyzing the dynamic behaviors are obtained by the Galerkin integral and dimensionless treatments. The steady-state solutions of the nonlinear equations are obtained by the multiple scale method (MSM) and the Newton-Raphson method. The frequency- and force-response curves are used to investigate the dynamic behaviors of the inclined CFRP cable under simultaneous internal (between the lowest in-plane and out-of-plane modes) and external resonances, i.e., the primary resonances induced by the excitations of the in-plane mode, the out-of-plane mode, and both the in-plane mode and the out-of-plane mode, respectively. The effects of the key parameters, e.g., Young’s modulus, the excitation amplitude, and the frequency on the dynamic behaviors, are discussed in detail. Some interesting phenomena and results are observed and concluded. 展开更多
关键词 inclined carbon fiber reinforced polymer (CFRP) cable BIFURCATION nonlinear dynamics INTERNAL RESONANCE EXTERNAL RESONANCE
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Instability inspection of parametric vibrating rectangular Mindlin plates lying on Winkler foundations under periodic loading of moving masses 预览
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作者 E.Torkan M.Pirmoradian M.Hashemian 《力学学报:英文版》 SCIE EI CAS CSCD 2019年第1期242-263,I0007共23页
Parametric resonance is one of the most important issues in the study of dynamical behavior of structures. In this paper, dynamic instability of a moderately thick rectangular plate on an elastic foundation is investi... Parametric resonance is one of the most important issues in the study of dynamical behavior of structures. In this paper, dynamic instability of a moderately thick rectangular plate on an elastic foundation is investigated in the case of parametric and external resonances due to periodic passage of moving masses. The governing coupled partial differential equations (PDEs) of the system, with consideration of the first-order shear deformation theory (FSDT) or Mindlin plate theory, are presented and they are reduced to a set of ordinary differential equations (ODEs) with time-dependent coefficients using the Galerkin procedure. All inertial components of the moving masses are adopted in the dynamical formulation. Instability survey is carried out for three different loading trajectories considerably interested in many practical applications of the issue, i.e. rectilinear, diagonal and orbiting trajectories. In order to analyze the resonance conditions, the incremental harmonic balance (IHB) method is introduced to calculate instability boundaries, as well as external resonance curves in parameters plane. A comprehensive study is done to assess effects of thickness ratio and foundation stiffness on the resonance conditions. It is found that an increase in the plate's thickness ratio leads to a reduction in values of critical parameters. Moreover, it is observed that in creasing the foundation stiffness moves the in stability regions and resona nee curves to higher frequencies of the moving masses and also leads to further stability of the parametrically excited system at lower frequencies. Time response simulations done via Runge-Kutta method confirmed the results predicted by IHB method. 展开更多
关键词 Mass-plate interaction MINDLIN plate PARAMETRIC RESONANCE External RESONANCE INCREMENTAL HARMONIC balanee method
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Enhanced organic solar cell performance: Multiple surface plasmon resonance and incorporation of silver nanodisks into a grating‐structure electrode 预览
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作者 Thitirat Putnin Chutiparn Lertvachirapaiboon +5 位作者 Ryousuke Ishikawa Kazunari Shinbo Keizo Kato Sanong Ekgasit Kontad Ounnunkad Akira Baba 《光电进展(英文)》 2019年第7期7-20,共14页
In this study, plasmonic nanostructures were examined to enhance the light harvesting of organic thin-film solar cells (OSCs) by multiple surface plasmon resonance (SPR) phenomena originating from the grating-coupled ... In this study, plasmonic nanostructures were examined to enhance the light harvesting of organic thin-film solar cells (OSCs) by multiple surface plasmon resonance (SPR) phenomena originating from the grating-coupled configuration with a Blu-ray Disc recordable (BD-R)-imprinted aluminum (Al) grating structure and the incorporation of a series of silver nanodisks (Ag NDs). The devices with such a configuration maximize the light utilization inside OSCs via light absorption, light scattering, and trapping via multiple surface plasmon resonances. Different types and sizes of metallic nanoparticles (NPs), i.e., gold nanoparticles (Au NPs), Ag nanospheres (Ag NSs), and Ag NDs, were used, which were blended separately in a PEDOT:PSS hole transport layer (HTL). The device structure comprised of grating- imprinted-Al/P3HT:PCBM/Ag ND:PEDOT:PSS/ITO. Results obtained from the J–V curves revealed that the power conversion efficiency (PCE) of grating-structured Al/P3HT:PCBM/PEDOT:PSS/ITO is 3.16%;this value is ~6% higher than that of a flat substrate. On the other hand, devices with flat Al and incorporated Au NPs, Ag NSs, or Ag NDs in the HTL exhibited PCEs ranging from 3.15% to 3.37%. Furthermore, OSCs with an Al grating substrate were developed by the incorporation of the Ag ND series into the PEDOT:PSS layer. Compared with that of a reference device, the PCEs of the devices increased to 3.32%–3.59%(11%–20% improvement), indicating that the light absorption enhancement at the active layer corresponds to the grating-coupled surface plasmon resonance and localized surface plasmon resonance excitations with strong near-field distributions penetrating into the active layer leading to higher efficiencies and subsequent better current generation. 展开更多
关键词 grating-coupled SURFACE PLASMON RESONANCE LOCALIZED SURFACE PLASMON RESONANCE Ag NANODISKS organic solar cells imprinted GRATING
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Accuracy of multi-echo Dixon sequence in quantification of hepatic steatosis in Chinese children and adolescents 预览
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作者 Yu-Zhen Zhao Yun-Gen Gan +7 位作者 Jian-Li Zhou Jia-Qi Liu Wei-Guo Cao Shu-Mei Cheng Da-Ming Bai Meng-Zhu Wang Fang-Qin Gao Shao-Ming Zhou 《世界胃肠病学杂志:英文版》 SCIE CAS 2019年第12期1513-1523,共11页
BACKGROUND Nonalcoholic fatty liver disease (NAFLD) is currently the outstanding cause of chronic liver disease in children and adolescents, especially in overweight and obese groups. Liver biopsy is the reference sta... BACKGROUND Nonalcoholic fatty liver disease (NAFLD) is currently the outstanding cause of chronic liver disease in children and adolescents, especially in overweight and obese groups. Liver biopsy is the reference standard to diagnose NAFLD but invasive, thus it is not the best choice in clinical diagnosis and follow-up. Magnetic resonance (MR) is widely used in clinical trials to noninvasively quantify liver fat content in adults and children in foreign countries. While currently, it is rarely used in Chinese children and adolescents. We postulated that quantifying hepatic steatosis by MR could be extended to children and adolescents in China. AIM To investigate the accuracy of MR imaging (MRI) in quantifying liver fat with MR spectroscopy (MRS) as a reference. A secondary goal was to assess the prevalence of NAFLD in overweight and obese Chinese children and adolescents. METHODS There were 86 children and adolescents enrolled in this study, including 65 overweight and obese children and 21 healthy children. The participants underwent MRI and MRS. MRI and MRS were performed using multi-echo Dixon and HISTO sequences, respectively, to calculate hepatic proton density fat fraction (PDFF). Hepatic steatosis was diagnosed using MRS-PDFF>5% as the threshold. Spearman’s analysis was used to evaluate the correlation between MRI and MRS. The agreement between these two methods was assessed by Bland- Altman analysis. RESULTS The MRI-PDFF in the MRS region of interest and the entire liver was 9.9%±10.3% with a range of 0.3%-39.9%, and 10.6%±9.4% with a range of 1.9%-38.9%, respectively. The MRS-PDFF was 9.1%±10.0%, with a range of 0.5%-37.8%. The incidence of hepatic steatosis detected by MRS-PDFF was 46.5%(40/86) of all participants, all of whom belonged to the overweight and obese group. Spearman’s analysis indicated an excellent correlation between multi-echo Dixon and MRS (r>0.9, P<0.01). Bland-Altman analysis also demonstrated a good agreement between these two methods. CONCLUSION Multi-echo Dixon shows an exc 展开更多
关键词 NONALCOHOLIC FATTY liver disease MAGNETIC RESONANCE imaging MAGNETIC RESONANCE spectroscopy Children and adolescents Hepatic STEATOSIS
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塔式起重机风振响应分析 预览
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作者 王玲娟 陈建永 《科技视界》 2019年第10期55-57,共3页
以某公司生产的TC7040型塔式起重机为研究对象,在大型有限元软件ABAQUS中建立金属结构模型,对其进行模态分析,得出塔机的前8阶固有频率和振型;在模态分析的基础上,分析了塔机在前10级风工况下的谐响应曲线,得出共振频率和节点位移,在无... 以某公司生产的TC7040型塔式起重机为研究对象,在大型有限元软件ABAQUS中建立金属结构模型,对其进行模态分析,得出塔机的前8阶固有频率和振型;在模态分析的基础上,分析了塔机在前10级风工况下的谐响应曲线,得出共振频率和节点位移,在无风状态下,塔机的第2、 4阶固有频率易引起结构共振,塔机起重臂端点在风速小于6级时,挠度变化较小,从6级开始急剧增大,分析结果可为起重机安全使用和合理设计提供科学的指导。为研究塔机在风荷载作用下的振动响应。 展开更多
关键词 塔机 模态分析 谐响应分析 风荷载 共振
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Standardized Xin-Ke-Shu Tablets Improves the Disturbances of Lipid, Energy, and Amino Acid Metabolism in a Rabbit Model of Atherosclerosis
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作者 Yong Yang Jing-Bo Peng +3 位作者 Meng Yu Hong-Mei Jia Hong-Wu Zhang Zhong-Mei Zou 《世界中医药杂志:英文版》 2019年第2期71-80,共10页
Objective:Xin-Ke-Shu(XKS),a patent drug,used to treat coronary artery diseases in China for many years.Previous research indicates that XKS has similar therapeutic effect as atorvastatin(AS)against atherosclerotic in ... Objective:Xin-Ke-Shu(XKS),a patent drug,used to treat coronary artery diseases in China for many years.Previous research indicates that XKS has similar therapeutic effect as atorvastatin(AS)against atherosclerotic in rabbits.However,biochemical assays demonstrate that XKS could have a different therapeutic mechanism from AS.The aim of this study is to explore the mechanism of XKS therapeutic effect,especially those different from AS.Materials and Methods:~1H nuclear magnetic resonance-based metabonomics were applied to profile the low-molecular-weight polar metabolites in the plasma of rabbits fed a high cholesterol diet.Results:Seven of the eleven pathological biomarkers related to atherosclerosis in rabbits were mediated by XKS treatment,namely low-density lipoprotein/very-low-density lipoprotein LDL/VLDL),lactate,citrate,phosphatidylcholine,glutamine,creatinine,and methionine,as well as two characteristic metabolites of pyruvate and α-glucose.These metabolites involved lipid,energy,and amino acid metabolism,and all could be considered XKS treatment targets.However,AS only affected the metabolic disorders associated with LDL/VLDL and phosphatidylcholine,which is mainly target lipid metabolism.Conclusions:This study indicates that the anti-atherosclerosis effects of AS mainly involve reducing blood–lipid levels,but those of XKS involve a multitargeted activity. 展开更多
关键词 1^H nuclear magnetic resonance ATHEROSCLEROSIS plasma METABONOMICS polar small molecules METABOLITES Xin-Ke-Shu
Alteration of functional connectivity in patients with Alzheimer’s disease revealed by resting-state functional magnetic resonance imaging 预览
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作者 Jie Zhao Yu-Hang Du +2 位作者 Xue-Tong Ding Xue-Hu Wang Guo-Zun Men 《中国神经再生研究:英文版》 SCIE CAS CSCD 2020年第2期285-292,共8页
The main symptom of patients with Alzheimer’s disease is cognitive dysfunction. Alzheimer’s disease is mainly diagnosed based on changes in brain structure. Functional connectivity reflects the synchrony of function... The main symptom of patients with Alzheimer’s disease is cognitive dysfunction. Alzheimer’s disease is mainly diagnosed based on changes in brain structure. Functional connectivity reflects the synchrony of functional activities between non-adjacent brain regions, and changes in functional connectivity appear earlier than those in brain structure. In this study, we detected resting-state functional connectivity changes in patients with Alzheimer’s disease to provide reference evidence for disease prediction. Functional magnetic resonance imaging data from patients with Alzheimer’s disease were used to show whether particular white and gray matter areas had certain functional connectivity patterns and if these patterns changed with disease severity. In nine white and corresponding gray matter regions, correlations of normal cognition, early mild cognitive impairment, and late mild cognitive impairment with blood oxygen level-dependent signal time series were detected. Average correlation coefficient analysis indicated functional connectivity patterns between white and gray matter in the resting state of patients with Alzheimer’s disease. Functional connectivity pattern variation correlated with disease severity, with some regions having relatively strong or weak correlations. We found that the correlation coefficients of five regions were 0.3–0.5 in patients with normal cognition and 0–0.2 in those developing Alzheimer’s disease. Moreover, in the other four regions, the range increased to 0.45–0.7 with increasing cognitive impairment. In some white and gray matter areas, there were specific connectivity patterns. Changes in regional white and gray matter connectivity patterns may be used to predict Alzheimer’s disease;however, detailed information on specific connectivity patterns is needed. All study data were obtained from the Alzheimer’s Disease Neuroimaging Initiative Library of the Image and Data Archive Database. 展开更多
关键词 Alzheimer's disease blood oxygen level-dependent signal correlation coefficient FUNCTIONAL connectivity pattern FUNCTIONAL magnetic resonance imaging gray MATTER RESTING state white MATTER
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Texture Feature Extraction from Thyroid MR Imaging Using High-Order Derived Mean CLBP
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作者 Zhe Liu Cheng-Jian Qiu +3 位作者 Yu-Qing Song Xiao-Hong Liu Juan Wang Victor S.Sheng 《计算机科学技术学报:英文版》 SCIE EI CSCD 2019年第1期35-46,共12页
In the field of medical imaging,the traditional local binary pattern (LBP)and its improved algorithms are often sensitive to noise.Traditional LBPs are solely based on the signal information from local differences,and... In the field of medical imaging,the traditional local binary pattern (LBP)and its improved algorithms are often sensitive to noise.Traditional LBPs are solely based on the signal information from local differences,and the binary quantization method oversimplifies the local texture features while disregarding the imaging information from the concaveconvex regions between the high-order pixels and the neighboring sampling points.Therefore,we propose an improved Derived Mean Complete Local Binary Pattern (DM_CLBP) algorithm based on high-order derivatives.In the DM_CLBP method,the grey value of a single pixel is replaced by the mean grey value of the rectangular area block,and the difference between pixel values in the area is obtained using the second-order differentiation method.Based on the calculation concept of the complete local binary pattern (CLBP)algorithm,the cascade signs and magnitudes of the two components are encoded and recombined in DM_CLBP using a uniform pattern.The results from the experiments showed that the proposed DM_CLBP descriptors achieved a classification accuracy of 94.4%.Compared with LBP and other improved algorithms,the DM_CLBP algorithm presented in this study can effectively differentiate between lesion areas and normal areas in thyroid MR,(magnetic resonance)images and shows the improved accuracy of area classification. 展开更多
关键词 THYROID magnetic resonance imaging (MRI) LOCAL BINARY PATTERN texture feature complete LOCAL BINARY PATTERN (CLBP)
基于有限元法对异步电动机电磁噪声分析与优化 预览
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作者 王长江 黄鹏程 李德金 《防爆电机》 2019年第3期22-25,共4页
电磁噪声是电机噪声的一个重要组成部分。使用有限元方法,从作用于定子内表面的电磁力波和定子结构的动态特性两个方面对一款三相异步电动机空载工况的电磁噪声进行研究。计算了电机在空载工况下电磁力波的波次、频率和幅值,得到了可与... 电磁噪声是电机噪声的一个重要组成部分。使用有限元方法,从作用于定子内表面的电磁力波和定子结构的动态特性两个方面对一款三相异步电动机空载工况的电磁噪声进行研究。计算了电机在空载工况下电磁力波的波次、频率和幅值,得到了可与电磁力共振的定子模态频率和噪声频谱,并对电磁噪声优化进行了分析。 展开更多
关键词 力波 共振 有限元法
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等离子清洗用谐振电源混合调制技术研究 预览
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作者 薛家祥 丁度焓 《中国测试》 CAS 北大核心 2019年第3期121-126,共6页
针对现有等离子体放电电源及其控制系统低效率和高成本的缺点,该文以串联谐振型高频高压电源为研究对象,对不同的控制模式进行研究,提出基于PWM-PFM混合调制的功率跟踪控制策略。同时,对感性和容性两种控制模式进行对比,根据IGBT的关断... 针对现有等离子体放电电源及其控制系统低效率和高成本的缺点,该文以串联谐振型高频高压电源为研究对象,对不同的控制模式进行研究,提出基于PWM-PFM混合调制的功率跟踪控制策略。同时,对感性和容性两种控制模式进行对比,根据IGBT的关断特点和工作频率,提出高功率欠谐振和低功率过谐振的工作模式,解决等离子清洗用电源在高频率下功率因数低、开关损耗大的问题。实验结果表明:混合调制策略能够有效降低IGBT的损耗,使整机效率提高0.65%~5.51%;在相同工况下,将设备的调功范围从600~950 W提升到550~1 000 W,使得等离子清洗机的清洗对象更为丰富,更容易推广。 展开更多
关键词 电源控制系统 等离子清洗 混合调制 谐振
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某后驱SUV车型匀速共振问题研究 预览
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作者 夏立峰 韩超 +3 位作者 李杰 李永放 冷鸿彬 陈志洋 《汽车实用技术》 2019年第2期63-65,共3页
针对某后驱SUV车型在匀速工况出现车内共振异常问题,利用能量平均分析方法和模态分析方法找出了共振问题的原因是后桥与传动轴的第三级传动系统所引起的。文章采用提高刚度的方法来改变第三级传动系统的固有频率,以达到避频减振的目的... 针对某后驱SUV车型在匀速工况出现车内共振异常问题,利用能量平均分析方法和模态分析方法找出了共振问题的原因是后桥与传动轴的第三级传动系统所引起的。文章采用提高刚度的方法来改变第三级传动系统的固有频率,以达到避频减振的目的。再使用Lms.testlab软件对结构优化后的整车进行测试,验证改进方法的有效性。 展开更多
关键词 共振 能量平均 模态分析 传动系统
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CNG公交车高压供气管路共振隐患防控技术 预览
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作者 王意东 何太碧 +1 位作者 张新岩 王艳 《天然气工业》 EI CAS CSCD 北大核心 2019年第5期123-128,共6页
为了消减压缩天然气(CNG)公交车高压管路的共振隐患,提高管路的安全性和可靠性,根据CNG公交车高压供气管路实际布局及约束特点构建仿真分析模型,进行了管路约束位置模态分析,然后基于平均驱动自由度理论,运用层次分析法对管路模态结果... 为了消减压缩天然气(CNG)公交车高压管路的共振隐患,提高管路的安全性和可靠性,根据CNG公交车高压供气管路实际布局及约束特点构建仿真分析模型,进行了管路约束位置模态分析,然后基于平均驱动自由度理论,运用层次分析法对管路模态结果做出了评价,得出了针对管路约束位置的优化方案,并对比研究了优化前后的管路振动属性及动力特性。研究结果表明:①优化后的高压供气管路第1、2、3阶次的固有频率与发动机各工况转速激励频率不接近,管路发生共振的可能性极小;②管路其余阶次的固有频率都不在发动机各工况转速激励频率范围内,完全避免了管路共振;③优化后各约束位置的振动传递力有了明显减小。结论认为,该管路约束位置布局优化方案对控制CNG公交车高压供气管路振动特性、提高管路安全性和可靠性等都具有指导意义和实践价值。 展开更多
关键词 CNG 公交车 高压供气管路 模态分析 有限元分析 层次分析法 约束位置 共振 优化
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中低速磁浮列车-桥梁系统竖向耦合振动理论分析与试验验证
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作者 王党雄 李小珍 梁林 《土木工程学报》 EI CSCD 北大核心 2019年第8期81-90,共10页
为探讨中低速磁浮列车-桥梁系统竖向动力相互作用特性,文章将中低速磁浮列车进行两种方式的简化,考虑PID主动悬浮控制系统,基于模态叠加法,建立2种类型的中低速磁浮列车-桥梁系统竖向耦合振动分析模型。随后基于长沙中低速磁浮运营线桥... 为探讨中低速磁浮列车-桥梁系统竖向动力相互作用特性,文章将中低速磁浮列车进行两种方式的简化,考虑PID主动悬浮控制系统,基于模态叠加法,建立2种类型的中低速磁浮列车-桥梁系统竖向耦合振动分析模型。随后基于长沙中低速磁浮运营线桥梁动载试验,对建立的2种仿真模型进行对比与验证。基于仿真模型2,以不同梁高的桥A、桥B、桥C为研究对象,对中低速磁浮列车-桥梁系统耦合振动特性进行分析。研究表明:将磁浮列车简化为均布荷载的方式能较为准确的模拟实际状况;桥梁刚度的减小会导致作用于车辆和桥梁上的电磁悬浮力增大,使得车体和桥梁的动力响应变大;磁浮列车低速运行时悬浮力频谱分布较离散,而正常速度运行时较集中;中低速磁浮列车-桥梁系统竖向存在着由电磁悬浮力自身频率引起的共振现象,该共振频率较低。 展开更多
关键词 中低速磁浮列车 桥梁 模型验证 竖向动力相互作用 共振
某型半转速核能汽轮发电机测振支架共振故障处理 预览
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作者 杨璋 舒相挺 蒋彦龙 《大电机技术》 2019年第4期16-20,共5页
研究某型半转速核能汽轮发电机测振支架共振时的振动信号特征并提出有效治理措施。建立测振支架的单自由度有阻尼系统运动方程,分析支架系统在谐和激励或脉冲激励作用下共振时的位移与速度响应关系o研究发现轴振幅值与瓦振幅值的比例系... 研究某型半转速核能汽轮发电机测振支架共振时的振动信号特征并提出有效治理措施。建立测振支架的单自由度有阻尼系统运动方程,分析支架系统在谐和激励或脉冲激励作用下共振时的位移与速度响应关系o研究发现轴振幅值与瓦振幅值的比例系数变化情况可以辨别测振支架是否存在谐和激励导致的共振;测振支架受脉冲激励共振时,瓦振的响应比轴振更敏感,且固有频率越低放大系数越高。应通过规范支架紧固力矩、改变质量分布等措施将支架固有频率提高到转速频率的5~6倍以上及优化振动高的自动打闸逻辑等处理支架共振故障。 展开更多
关键词 半转速汽轮发电机 测振支架 共振 力矩 阻尼比 振动
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船用增压器系统模态分析及优化 预览
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作者 尹晓青 柳海涛 +2 位作者 邰强娟 王继勇 陈经伟 《内燃机与动力装置》 2019年第4期85-88,共4页
为提升船用增压器系统的可靠性,以零部件的固有模态属性为基础,利用Abaqus软件对现有某6缸中速柴油机的增压器及相关零部件模型进行仿真模态分析,并通过试验对仿真结果进行校验。结果表明:基于仿真的模态分析满足精度要求,增压器系统一... 为提升船用增压器系统的可靠性,以零部件的固有模态属性为基础,利用Abaqus软件对现有某6缸中速柴油机的增压器及相关零部件模型进行仿真模态分析,并通过试验对仿真结果进行校验。结果表明:基于仿真的模态分析满足精度要求,增压器系统一阶模态频率为67.36 Hz,低于设计要求的90 Hz,且转速为1150~1300 r/min时,共振倾向明显。根据仿真模态分析结果提出相应的优化解决方案,通过优化增压器支架结构形式,增加整个增压器及相关零部件的支撑刚度。试验结果表明:增压器系统的一阶模态频率提高到90.8 Hz,避免增压器系统在发动机运行区间内发生共振,提升了柴油机整机的运行可靠性,优化方案满足设计要求。 展开更多
关键词 仿真模态 试验模态 船用柴油机 增压器 零部件 刚度 共振
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