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色氨酸操纵子调控机制详析
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作者 冯慧 李红民 《中国生物化学与分子生物学报》 CAS CSCD 北大核心 2020年第1期6-13,共8页
色氨酸操纵子是最早被研究的细菌合成代谢调控、基因表达调控的模型之一。其中阻遏蛋白对转录起始的抑制作用、色氨酸作为辅阻遏物的作用以及通过定点突变揭示的弱化作用的分子机制已基本被阐明。此外,色氨酸操纵子RNA结合弱化蛋白、Nus... 色氨酸操纵子是最早被研究的细菌合成代谢调控、基因表达调控的模型之一。其中阻遏蛋白对转录起始的抑制作用、色氨酸作为辅阻遏物的作用以及通过定点突变揭示的弱化作用的分子机制已基本被阐明。此外,色氨酸操纵子RNA结合弱化蛋白、NusA、Nus G、Trp Y等调节蛋白对细菌色氨酸操纵子弱化作用的调节机制也在近年来得到进一步揭示。特别是在枯草芽孢杆菌中,色氨酸操纵子主要依赖于转录衰减机制调控,包括由色氨酸激活的色氨酸操纵子RNA结合弱化蛋白与新生转录产物结合形成内部终止子,导致5’非翻译区(5’UTR)转录终止。Nus A、Nus G通过刺激RNA聚合酶在5’UTR的U107和U144位点暂停,释放出RNA聚合酶,最终造成转录终止。不同的是,在U144位点NusA参与的转录弱化机制依赖其发夹结构,且NusA与RNA聚合酶作用促进了RNA结合弱化蛋白与新生转录产物的结合,使转录终止。而NusG是通过与非模板DNA链中的一段富含T碱基序列和RNA聚合酶同时互作,阻止了RNA聚合酶向下游移动,从而引起RNA聚合酶高效停滞。但在细菌操纵子中,绝大多数调节因子参与的弱化机制最终依赖于ρ因子,从而导致多达一半的转录终止事件发生。近年来,随着学科的发展,越来越多关于色氨酸操纵子调节机制新概念被挖掘报道,这也使人类对色氨酸操纵子的表达调控机制的认知愈加详尽。 展开更多
关键词 色氨酸操纵子 弱化作用 色氨酸操纵子RNA结合弱化蛋白 NUSA NUSG
Attenuation coefficients of gamma and X-rays passing through six materials 预览
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作者 Xue-Dou Su Gao-Long Zhang +8 位作者 Shou-Ping Xu Wei-Wei Qu Lin Song Yu-Hua Huang Ben Wang Yi-Feng Wang Ze-Tao Zhang Wu-Fu Xu Ming-Li Wang 《核技术:英文版》 SCIE CAS CSCD 2020年第1期26-31,共6页
The aim of this study was to determine the attenuation of gamma and X-rays with different energies caused by passage through different materials.To this end,different materials with a range of atomic numbers were chos... The aim of this study was to determine the attenuation of gamma and X-rays with different energies caused by passage through different materials.To this end,different materials with a range of atomic numbers were chosen to measure gamma and X-ray attenuation coefficients and to explore the mechanisms of interaction of gamma and X-rays with matter of various kinds.It is shown that the attenuation coefficients first decrease and then increase with increase in the radiation(photon)energy.The attenuation of gamma and X-rays passing through materials with high atomic number is greater than that in materials with low atomic number.The attenuation minimum is related to the atomic number of the irradiated materials.The larger the atomic number is,the lower the energy corresponding to attenuation minimum is.Photoelectric and Compton effects are the main processes when gamma rays pass through individual materials with high and low atomic numbers,respectively.Therefore,for radiotherapy and radiation protection,different methods should be considered and selected for the use of gamma and X-rays of different energies for use in different materials. 展开更多
关键词 Attenuation coefficient Interaction mechanisms Gamma rays High-energy X-rays Therapy and protection
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公路交通引起的地下深层土体振动实测及其衰减分析 预览
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作者 谢永健 李宁 徐宏文 《城市道桥与防洪》 2020年第1期133-136,M0016,共5页
为了研究公路交通荷载引起的振动随深度的衰减规律,分别对深度为5.5 m.19.5 m、34.5 m.39.5 m的孔中测点以及孔口附近地面测点进行了位移振动同步测试,并在时域和频域上分别对有车工况和无车工况下的实测数据进行了分析。结果表明:随着... 为了研究公路交通荷载引起的振动随深度的衰减规律,分别对深度为5.5 m.19.5 m、34.5 m.39.5 m的孔中测点以及孔口附近地面测点进行了位移振动同步测试,并在时域和频域上分别对有车工况和无车工况下的实测数据进行了分析。结果表明:随着深度的增加,交通振动中的高频部分会迅速衰减.低频部分则衰减缓慢,铅垂方向位移衰减因子相比水平方向衰减因子衰减得更快;有车工况下,铅垂方向位移幅值在深度39.5 m处仅为地面的15%.振动衰减已很明显。 展开更多
关键词 公路交通振动 土体振动 衰减
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有效测量套管井泄漏Lamb波衰减的实验研究 预览
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作者 李疾翎 陶爱华 +2 位作者 刘临政 程林波 王明辉 《应用声学》 CSCD 北大核心 2020年第1期142-148,共7页
低密度水泥在油气井中的广泛应用使得常规的声阻抗类测井方法难以准确、有效地评价固井质量,而声波倾斜入射在套管中激发的弯曲型Lamb波对水泥的性质及胶结情况具有很高的分辨能力,能够很好地解决低密度水泥的固井质量评价问题。弯曲型L... 低密度水泥在油气井中的广泛应用使得常规的声阻抗类测井方法难以准确、有效地评价固井质量,而声波倾斜入射在套管中激发的弯曲型Lamb波对水泥的性质及胶结情况具有很高的分辨能力,能够很好地解决低密度水泥的固井质量评价问题。弯曲型Lamb波对套管后介质声学信息的响应反映在声波衰减中,因此该文通过实验研究了激发弯曲型Lamb波的有效方式,分析了声波入射和接收角度对Lamb波衰减的影响。实验结果表明,入射和接收角度在一定范围内变化时,虽然激发出的Lamb波模式均为弯曲型Lamb波,但在同一套管模型下测量的声波衰减值会有差异,选择激发弯曲型Lamb波的最有效方式,计算得到的Lamb波衰减对套管后介质的灵敏度才会最高。 展开更多
关键词 弯曲型Lamb波 衰减 频散
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Wave Attenuation Performance and the Influencing Factors of A LowerArc-Plate Breakwater 预览
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作者 LI Xue-yan WANG Qing +6 位作者 YOU Zai-jin GUO Wei-jun ZHANG Jun-bin ZHAN Chao ZHANG Zhi-chen WANG Li-xue LI Qin 《中国海洋工程:英文版》 SCIE EI CSCD 2020年第1期89-98,共10页
Comprehensive experimental and numerical studies have been undertaken to investigate wave energy dissipation performance and main influencing factors of a lower arc-plate breakwater. The numerical model, which conside... Comprehensive experimental and numerical studies have been undertaken to investigate wave energy dissipation performance and main influencing factors of a lower arc-plate breakwater. The numerical model, which considers nonlinear interactions between waves and the arc-plate breakwater, has been constructed by using the velocity wave- generating method, the volume of fluid (VOF) method and the finite volume method. The results show that the relative width, relative height and relative submergence of the breakwater are three main influencing factors and have significant influence on wave energy dissipation of the lower arc-plate open breakwater. The transmission coefficient is found to decrease with the increasing relative width, and the minimum transmission coefficient is 0.15 when the relative width is 0.45. The reflection coefficient is found to vary slightly with the relative width, and the maximum reflection coefficient is 0.53 when the relative width is 0.45. The transmission and reflection coefficients are shown to increase with the relative wave height for approximately 85% of the experimental tests when the relative width is 0.19 0.45. The transmission coefficients at relative submergences of 0.04, 0.02 and 0 are clearly shown to be greater than those at relative submergences of 0.02 and 0.04, while the reflection coefficient exhibits the opposite relationship. After the wave interacts with the lower arc-plate breakwater, the wave energy is mainly converted into transmission, reflection and dissipation energies. The wave attenuation performance is clearly weakened for waves with greater heights and longer periods. 展开更多
关键词 arc-plate breakwater wave attenuation performance influencing factors VOF method
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广播电视微波传输阻挡探析 预览
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作者 周萍 童衍材 《广播与电视技术》 2020年第1期90-93,共4页
本文通过对微波传输阻挡过程实际情况和相关数据的分析,得出微波传输通道阻挡-衰减量变化关系曲线,并用实际案例通过具体测量、计算和分析进行验证,为微波传输工程技术人员对微波传输受建筑物的阻情况提供一种分析方法,从而对微波传输... 本文通过对微波传输阻挡过程实际情况和相关数据的分析,得出微波传输通道阻挡-衰减量变化关系曲线,并用实际案例通过具体测量、计算和分析进行验证,为微波传输工程技术人员对微波传输受建筑物的阻情况提供一种分析方法,从而对微波传输受阻挡的情况有个清晰的了解。 展开更多
关键词 传输断面 阻挡 衰减 限高 海拔
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Study on gamma-ray attenuation characteristics of some amino acids for 133Ba,137Cs,and 60Co sources 预览
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作者 Reza Bagheri Ali Yousefi Seyed Pezhman Shirmardi 《核技术:英文版》 SCIE CAS CSCD 2020年第2期67-81,共15页
Amino acids are the building blocks of proteins,which are the most abundant macromolecules in living cells.From the standpoint of the photon interaction cross sections of amino acids,the mass attenuation coefficients,... Amino acids are the building blocks of proteins,which are the most abundant macromolecules in living cells.From the standpoint of the photon interaction cross sections of amino acids,the mass attenuation coefficients,half and tenth value layers,mean free path,effective atomic and electronic cross sections,effective atomic number,and effective electron density of fifteen essential amino acids have been determined for 133Ba,137Cs,and 60Co gamma-ray sources.The MCNP-4C code and the XCOM program have been used to calculate these parameters.The results have been compared to the available experimental and theoretical data.The theoretical results agreed with the experimental data,with RD values of ≤±7%.In the energy region of 81-1332.5 keV,it was found that the μm,σa,and revalues of the amino acids decreased as the photon energy increased,and the increasing density of amino acids had no steady effect on these quantities.Additionally,results demonstrated that the HVL,TVL,and MFP values increased with the increase in photon energy.The μm,σa,and Zeff values of aspartic acid were the highest among those of all amino acids,and they were the lowest for isoleucine.The Zeff value of each sample containing H,C,N,and O atoms was nearly constant in the studied energy region.The Neffvalues of the studied amino acids varied in the range of 3.14×10^23-3.44×10^23 electron/g.Furthermore,the Neffvalues were approximately independent of the amino acid type in this energy region. 展开更多
关键词 Amino acids Mass attenuation coefficient Effective electron density and atomic number MCNP-4C XCOM
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Ultrasound-based techniques for the diagnosis of liver steatosis 预览
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作者 Giovanna Ferraioli Livia Beatriz Soares Monteiro 《世界胃肠病学杂志:英文版》 SCIE CAS 2019年第40期6053-6062,共10页
Non-alcoholic fatty liver disease(NAFLD)is the leading cause of diffuse liver disease.An accurate estimate of the fat in the liver is important in the diagnostic work-up of patients with NAFLD because the degree of li... Non-alcoholic fatty liver disease(NAFLD)is the leading cause of diffuse liver disease.An accurate estimate of the fat in the liver is important in the diagnostic work-up of patients with NAFLD because the degree of liver steatosis is linked to the metabolic syndrome and the cardiovascular risk.Ultrasound(US)B-mode imaging allows to subjectively estimate the fatty infiltration in the liver;however,it has a low performance for the detection of mild steatosis.Quantitative US is based on the analysis of the radiofrequency echoes detected by an US system,and it allows to calculate a backscatter coefficient or an attenuation coefficient or the sound speed.The estimation of the backscatter coefficient is rather cumbersome and requires the use of a phantom for addressing all sources of variability.Controlled attenuation parameter(CAP)available on the FibroScan®system(Echosens,France)measures the attenuation of the US beam.CAP is accurate in grading fatty infiltration-even though there is an overlap between consecutive grade of liver steatosis-and the values are not influenced by liver fibrosis.Several US manufacturers are developing or have already developed software for quantifying the attenuation of the US beam.Preliminary results show that proprietary technologies implemented in US systems seem more accurate than CAP for grading liver steatosis.Another available method for quantifying liver steatosis is based on the computation of the sound speed and the initial results appear promising. 展开更多
关键词 Non-alcoholic fatty liver disease Chronic liver disease ULTRASOUND Controlled attenuation parameter Quantitative ultrasound Attenuation imaging
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磨料水射流对脆性材料的冲蚀研究 预览 被引量:1
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作者 王志敏 武美萍 魏晶晶 《工程设计学报》 CSCD 北大核心 2019年第1期79-86,共8页
磨料水射流技术作为一种特种加工技术,具有无刀具接触、无热影响区和加工范围广等优势,在众多领域得到应用。为了探究磨料水射流对脆性材料的冲蚀效果,构建和设计了磨料水射流外流场冲蚀仿真模型与磨料水射流冲蚀实验。以30mm×50m... 磨料水射流技术作为一种特种加工技术,具有无刀具接触、无热影响区和加工范围广等优势,在众多领域得到应用。为了探究磨料水射流对脆性材料的冲蚀效果,构建和设计了磨料水射流外流场冲蚀仿真模型与磨料水射流冲蚀实验。以30mm×50mm的喷嘴外流场域为计算域,建立磨料水射流冲蚀仿真模型,并分析射流冲蚀过程中压力分布、水与磨料的速度分布及它们在射流中心线上的衰减规律。通过对氧化铝陶瓷材料的冲蚀实验,分析工艺参数对冲蚀孔径的影响,并结合仿真结果对比分析了射流束宽度与冲蚀孔径的关系。结果表明:水的速度随着喷嘴距离的增大而减小且分布范围变宽,射流宽度呈线性增大,磨料速度随喷嘴距离的增大而减小且分布范围基本不变;射流中心线上水的速度与磨料速度呈三段式衰减,水的第1段速度衰减段长度比磨料的长,但水的第2段速度衰减段长度比磨料的短;射流束能量的有效利用部分逐渐减小,但在15~25mm的靶距范围内其有效利用部分较稳定,为40%;冲蚀孔径随喷嘴距离增大呈线性增大。研究结果为磨料水射流切割、铣削及抛光加工的参数选择提供实验依据,同时为磨料水射流加工过程仿真提供参考。 展开更多
关键词 磨料水射流 冲蚀性能 速度分布 衰减 冲蚀孔径
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无砟轨道地基泥岩膨胀变形及水分迁移速率衰减规律 预览
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作者 王炳忠 王起才 +3 位作者 张戎令 王天双 张唐瑜 李航辉 《水利水运工程学报》 CSCD 北大核心 2019年第2期41-47,共7页
高铁无砟轨道对膨胀变形值要求极为严格,地基膨胀泥岩浸水引起的胀缩变形将对行车安全性和舒适性产生影响。为研究泥岩随浸水位置水平距离和深度增加时膨胀速率及水分迁移速率的衰减规律,以兰新铁路第二双线某处典型膨胀泥岩为研究对象... 高铁无砟轨道对膨胀变形值要求极为严格,地基膨胀泥岩浸水引起的胀缩变形将对行车安全性和舒适性产生影响。为研究泥岩随浸水位置水平距离和深度增加时膨胀速率及水分迁移速率的衰减规律,以兰新铁路第二双线某处典型膨胀泥岩为研究对象,通过顶部和侧面两种浸水方式进行三组重塑泥岩膨胀变形试验。试验结果表明:距离浸水管水平长度不同,膨胀时程曲线变化规律不同。距离浸水管水平长度越远,膨胀速率越慢,水分迁移速率亦越小;侧面浸水时沿深度方向首先引起底部土体膨胀。通过对试验数据进一步分析,提出用初期平均渗透系数分析水分迁移速率衰减规律,经计算可知,水分迁移速率随与浸水管水平距离和垂直距离的增大均呈衰减趋势。研究结果可为地基泥岩上拱病害治理及预警提供理论支撑。 展开更多
关键词 无砟轨道 膨胀速率 水分迁移速率 距离 衰减
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影响光纤高低温附加损耗的因素探究 预览 被引量:1
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作者 彭楚宇 熊涛 《现代信息科技》 2019年第3期35-37,共3页
为了保证光纤在低温或高温下的正常工作,需确保光纤在不同温度环境下的附加衰减维持在较低的水平。本文通过光纤的高低温循环实验,探究影响光纤环境温度性能的因素,实验结果表明,提高涂料的流动性、提高光纤涂覆层的固化度、降低涂层内... 为了保证光纤在低温或高温下的正常工作,需确保光纤在不同温度环境下的附加衰减维持在较低的水平。本文通过光纤的高低温循环实验,探究影响光纤环境温度性能的因素,实验结果表明,提高涂料的流动性、提高光纤涂覆层的固化度、降低涂层内部缺陷、使用与拉丝工艺相匹配的涂料可以降低低温环境下光纤的附加损耗。本文的研究为改善光纤在恶劣环境中的使用条件提供了理论依据。 展开更多
关键词 光纤 高低温循环 微弯 衰减 附加损耗
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Attenuation of coda waves in the SW of High-Atlas area, Morocco
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作者 Roumaissae Azguet Ghizlane Bouskri +2 位作者 Youssef Timoulali Mimoun Harnafi Younes EL.Fellah 《大地测量与地球动力学:英文版》 2019年第4期297-306,共10页
We investigate attenuation scattering and loss properties in Souss basin(SW of High-Atlas) as a transition zone between the High and Anti Atlas ranges. This district consists in a thinned crustal patch with shallow se... We investigate attenuation scattering and loss properties in Souss basin(SW of High-Atlas) as a transition zone between the High and Anti Atlas ranges. This district consists in a thinned crustal patch with shallow seismicity and loose sedimentary trenches that perform an important contribution to augment seismic attenuation. So far, no coda waves approach in our knowledge have been used to draw satisfying outputs about the attenuation properties in the region. Therefore, this update suggests to correlate the lateral changes of seismic attenuation to different characteristics and asperities i.e. seismic activity,crustal age and thickness, heat flow, and ground deformation rate. To do so, we analysed coda waves derived from waveform data of more than 23 local earthquakes from seven broadband seismometers recorded during 2010 e2012 period. As a starter, we utilized the backscattering model which defines theseismic attenuation as inversely proportional to quality factor by the equation A ?1=. QQcestimates c were deducted at various central frequency bands 1.5, 3.0, 6.0, 9.0, 12.0 and 18.0 Hz according to different lapses times. The estimated average frequency dependence quality factor gives relation Qc? 120 f1;01,while the average Qcvalues vary from 149 at 1.5 Hz to 1895 at 18 Hz central frequencies. We observed an intimate dependence between quality factor and frequency ranges, which reflects the complexity of geological/geophysical pattern in the Souss basin and the presence of a variety of heterogeneities within the underlying crust. 展开更多
关键词 ATTENUATION CODA WAVES Quality factor Frequency Souss BASIN Morocco
未雨绸缪:变革前非正式信息对员工变革抵制意愿的影响 预览
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作者 杜旌 崔雨萌 《心理学报》 CSSCI CSCD 北大核心 2019年第2期248-258,共11页
组织变革前总会有小道消息等非正式信息传播,这些信息是员工提前了解变革的重要来源。研究探索变革前非正式信息对员工变革前抵制意愿的影响,以及员工变革抵制意愿随时间推移的变化。基于255位样本数据的结构方程模型及多层次线性增长... 组织变革前总会有小道消息等非正式信息传播,这些信息是员工提前了解变革的重要来源。研究探索变革前非正式信息对员工变革前抵制意愿的影响,以及员工变革抵制意愿随时间推移的变化。基于255位样本数据的结构方程模型及多层次线性增长模型分析表明:(1)变革前非正式信息的消极性及不完整性,显著负向影响员工变革认知,进而使员工变革抵制意愿上升;(2)随着时间推移,员工变革抵制意愿显著衰减,即从变革前到变革发生时抵制意愿显著降低。研究揭示了变革前非正式信息对员工有“热身准备”的作用,能够帮助员工提前适应,从而更好地应对变革。研究结果有助于变革的顺利实施。 展开更多
关键词 变革前非正式信息 变革认知 变革抵制意愿 衰减
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爆炸冲击波在不同断面竖井中的传播规律研究
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作者 刘涛 王海亮 +1 位作者 王有权 刘鹏 《煤矿安全》 CAS 北大核心 2019年第3期212-216,共5页
为探明爆炸冲击波在竖井内的传播规律,利用ANSYS/LS-DYNA动力分析软件,对4.8kg乳化炸药在竖井内的爆炸过程进行数值模拟,分析了冲击波在长宽比相同、断面大小不同的3个竖井内轴向与径向的传播规律。结果表明:在竖井轴向,爆心距大于6 m后... 为探明爆炸冲击波在竖井内的传播规律,利用ANSYS/LS-DYNA动力分析软件,对4.8kg乳化炸药在竖井内的爆炸过程进行数值模拟,分析了冲击波在长宽比相同、断面大小不同的3个竖井内轴向与径向的传播规律。结果表明:在竖井轴向,爆心距大于6 m后,不同断面的竖井衰减速度不同,小、中、大竖井每2 m平均衰减率分别为25.02%、26.29%、32.32%;在竖井径向,冲击波由球面波转别为平面波的速度随着断面的增大而加快。 展开更多
关键词 爆炸 竖井 冲击波 超压 ALE算法 衰减
A New Time-Aware Collaborative Filtering Intelligent Recommendation System 预览
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作者 Weijin Jiang Jiahui Chen +4 位作者 Yirong Jiang Yuhui Xu Yang Wang Lina Tan Guo Liang 《计算机、材料和连续体(英文)》 2019年第8期849-859,共11页
Aiming at the problem that the traditional collaborative filtering recommendation algorithm does not fully consider the influence of correlation between projects on recommendation accuracy,this paper introduces projec... Aiming at the problem that the traditional collaborative filtering recommendation algorithm does not fully consider the influence of correlation between projects on recommendation accuracy,this paper introduces project attribute fuzzy matrix,measures the project relevance through fuzzy clustering method,and classifies all project attributes.Then,the weight of the project relevance is introduced in the user similarity calculation,so that the nearest neighbor search is more accurate.In the prediction scoring section,considering the change of user interest with time,it is proposed to use the time weighting function to improve the influence of the time effect of the evaluation,so that the newer evaluation information in the system has a relatively large weight.The experimental results show that the improved algorithm improves the recommendation accuracy and improves the recommendation quality. 展开更多
关键词 Fuzzy clustering time weight attenuation function Collaborative filtering method recommendation algorithm
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The Secret of Fear Memory Attenuation: Facing Fears
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作者 Yan-Chen Guo Tifei Yuan Ben-Yu Guo 《神经科学通报:英文版》 SCIE CAS CSCD 2019年第4期775-777,共3页
Exposure therapy, an effective treatment for fear disorders, requires memory retrieval of previous horror experiences in controllable environment. However, it remains unknown whether previous fear memories have been u... Exposure therapy, an effective treatment for fear disorders, requires memory retrieval of previous horror experiences in controllable environment. However, it remains unknown whether previous fear memories have been updated [1] or inhibited [2] during the formation of new memories, as well as the underlying neural mechanisms involved (eg. the type of cells engaged in this process). 展开更多
关键词 SECRET FEAR MEMORY ATTENUATION FACING FEARS
Lg-Q model and its implication on high-frequency ground motion for earthquakes in the Sichuan and Yunnan region 预览
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作者 Zhi Wei Li Zhao 《地球与行星物理:英文版》 CSCD 2019年第6期526-536,共11页
Low-rise buildings are susceptible to high-frequency ground motion.The high-frequency ground motions at regional distances are mainly controlled by crustal Lg waves whose amplitudes are typically much larger than thos... Low-rise buildings are susceptible to high-frequency ground motion.The high-frequency ground motions at regional distances are mainly controlled by crustal Lg waves whose amplitudes are typically much larger than those of body waves.In this study,we develop a Lg-wave Q model for the Sichuan and Yunnan region in the frequency band of 0.3–2.0 Hz using regional seismic records of 1166 earthquakes recorded at 152 stations.Comparison between the observed pattern of ground motion from real earthquake and model prediction demonstrates the robustness and effectiveness of our Lg-Q model.Then,assuming that the Lg-wave Q structure is the main factor affecting the propagation of the high-frequency ground motions,we calculate the spatial distributions of high-frequency ground motions from scenario earthquakes at different locations in the region using the average Lg-wave attenuation model over the frequency band of 0.3–2.0 Hz.We also use the Lg-Q model to estimate the distribution of cumulative energy of high-frequency ground motions based on the historical seismicity of the Sichuan and Yunnan region.Results show that the Lg-Q model can be used effectively in estimating the spatial distribution of high-frequency seismic energies and thus can contribute to the assessment of seismic hazard to low-rise buildings. 展开更多
关键词 Lg-wave attenuation MODEL HIGH-FREQUENCY ground MOTIONS seismic hazards LOW-RISE buildings
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Seismic attenuation in the lower mantle beneath Northeast China constrained from short-period reflected core phases at short epicentral distances 预览
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作者 BaoLong Zhang SiDao Ni YuLin Chen 《地球与行星物理:英文版》 CSCD 2019年第6期537-546,共10页
The thermal structure of the lower mantle plays a key role in understanding the dynamic processes of the Earth's evolution and mantle convection.Because intrinsic attenuation in the lower mantle is highly sensitiv... The thermal structure of the lower mantle plays a key role in understanding the dynamic processes of the Earth's evolution and mantle convection.Because intrinsic attenuation in the lower mantle is highly sensitive to temperature,determining of the attenuation of the lower mantle could help us determine its thermal state.We attempted to constrain the attenuation of the lower mantle by measuring the amplitude ratios of p to ScP on the vertical component and s to ScS on the tangential component at short epicentral distances for seismic wave data from deep earthquakes in Northeast China.We calculated the theoretical amplitude ratios of p to ScP and s to ScS by using ray theory and the axial-symmetric spectral element method AxiSEM,as well as by considering the effects of radiation patterns,geometrical spreading,and ScP reflection coefficients.By comparing the observed amplitude ratios with the synthetic results,we constrained the quality factors as Qα≈3,000 and Qβ≈1,300 in the lower mantle beneath Northeast China,which are much larger than those in the preliminary reference Earth model(PREM)model of Qα~800 and Qβ~312.We propose that the lower mantle beneath Northeast China is relatively colder than the average mantle,resulting in weaker intrinsic attenuation and higher velocity.We estimated the temperature of the lower mantle beneath Northeast China as approximately 300–700 K colder than the global average value. 展开更多
关键词 seismic attenuation lower MANTLE NORTHEAST China reflected CORE PHASES thermal state
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电磁辐射信号在金属矿岩中的传播 预览
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作者 万国香 王其胜 +1 位作者 李夕兵 蔡十华 《中国钨业》 2019年第3期7-11,共5页
基于压电效应,研究理想平面纵波和衰减平面纵波两种情况下岩石产生的电磁信号在金属矿中的传播。根据金属矿岩中波矢量的改变,得到了两种纵波条件下金属矿岩中电场的表达式。通过对表达式的计算,结果表明:电场随着电导率、传播距离和初... 基于压电效应,研究理想平面纵波和衰减平面纵波两种情况下岩石产生的电磁信号在金属矿中的传播。根据金属矿岩中波矢量的改变,得到了两种纵波条件下金属矿岩中电场的表达式。通过对表达式的计算,结果表明:电场随着电导率、传播距离和初始损伤增大而不断减小。在电导率为10^-8S/m量级时,电导率对电场的衰减作用并不明显,当电导率增加到10^-4S/m量级时,电导率对电场的衰减逐渐增强。当电导率到达10^-2S/m时,电导率对电场的衰减作用十分显著。当电导率低于10^-3量级时,电导率对电场的衰减作用相比于初始损伤显得“弱”一些。当电导率增大到近10^-2S/m时,电导率对电场的衰减作用越来越“强”。 展开更多
关键词 衰减 纵波 电磁信号 电导率
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不同绿化配置对交通噪声的衰减效果比较 预览
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作者 聂蕾 《安徽化工》 CAS 2019年第4期96-99,103共5页
为了研究不同绿化配置对交通噪声的衰减效应,在昆明市主干道东三环的绿化带以及周边城市森林设置20 m宽林带10个,测试不同类型林带对交通噪声的降噪值,并分析了季节和距离对各林带降噪效果的影响。研究表明:①昆明市东三环马路上的噪声... 为了研究不同绿化配置对交通噪声的衰减效应,在昆明市主干道东三环的绿化带以及周边城市森林设置20 m宽林带10个,测试不同类型林带对交通噪声的降噪值,并分析了季节和距离对各林带降噪效果的影响。研究表明:①昆明市东三环马路上的噪声值超过国家4类标准,而各个不同类型的绿化林带的噪声值均达到国家4类标准以内;②20 m宽林带的降噪值随距离声源距离的变化而差异明显;③由叶片更宽且表面被毛、枝叶繁茂、分枝点低的乔灌木树种隔行栽植所组成的20m宽且靠近道路的乔灌草复层结构绿化带可以更好地消减交通噪音;④香樟和石楠的降噪声最大,均达到4.9 dB,而圆柏、华山松和云南松的降噪声稍微低一点;灌木和草本植物没有乔木的降噪效果好,因此选择生长良好,枝繁叶茂的植物,冠幅大且枝叶浓密对声波的反射和吸收效果好,能起到较好的降噪效果;⑤不同绿化配置对噪声的降噪作用不相同,其中乔灌草这种绿化配置对噪声的降噪效果最为明显;⑥雨季的噪声值比旱季的噪声值低,因为降雨量对植物的降噪效果有影响。 展开更多
关键词 交通噪声 林带 衰减效应 降噪值
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