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High-order phase-field model with the local and second-order max-entropy approximants
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作者 Fatemeh AMIRI 《结构与土木工程前沿:英文版》 EI CSCD 2019年第2期406-416,共11页
We approximate the fracture surface energy functional based on phase-field method with smooth local maximum entropy (LME) and second-order maximum entropy (SME) approximants. The higher-order continuity of the meshfre... We approximate the fracture surface energy functional based on phase-field method with smooth local maximum entropy (LME) and second-order maximum entropy (SME) approximants. The higher-order continuity of the meshfree methods such as LME and SME approximants allows to directly solve the fourth-order phase-field equations without splitting the fourth?ordcr differential equation into two second-order differential equations. We will first show that the crack surface functional can be captured more accurately in the fourth-order model with smooth approximants such as LME, SME and B-spline. Furthermore, smaller length scale parameter is needed for the fourth-order model to approximate the energy functional. We also study SME approximants and drive the formulations. The proposed meshfree fourth-order phase-field formulation show more stable results tor SME compared to LME meshfree methods. 展开更多
关键词 SECOND-ORDER MAXIMUM ENTROPY LOCAL MAXIMUM ENTROPY second-and fourth-order PHASE-FIELD models B-spline
Establishment of Numerical Wave Flume Based on the Second-Order Wave-Maker Theory 预览
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作者 ZHANG Hao-chen LIU Shu-xue +1 位作者 LI Jin-xuan WANG Lei 《中国海洋工程:英文版》 SCIE EI CSCD 2019年第2期160-171,共12页
With growing computational power, the first-order wave-maker theory has become well established and is widely used for numerical wave flumes. However, existing numerical models based on the first-order wave-maker theo... With growing computational power, the first-order wave-maker theory has become well established and is widely used for numerical wave flumes. However, existing numerical models based on the first-order wave-maker theory lose accuracy as nonlinear effects become prominent. Because spurious harmonic waves and primary waves have different propagation velocities, waves simulated by using the first-order wave-maker theory have an unstable wave profile. In this paper, a numerical wave flume with a piston-type wave-maker based on the second-order wave-maker theory has been established. Dynamic mesh technique was developed. The boundary treatment for irregular wave simulation was specially dealt with. Comparisons of the free-surface elevations using the first-order and second-order wave-maker theory prove that second-order wave-maker theory can generate stable wave profiles in both the spatial and time domains. Harmonic analysis and spectral analysis were used to prove the superiority of the second-order wave-maker theory from other two aspects. To simulate irregular waves, the numerical flume was improved to solve the problem of the water depth variation due to low-frequency motion of the wave board. In summary, the new numerical flume using the second-order wave-maker theory can guarantee the accuracy of waves by adding an extra motion of the wave board. The boundary treatment method can provide a reference for the improvement of nonlinear numerical flume. 展开更多
关键词 SECOND-ORDER WAVE generation nonlinear WAVE SPURIOUS HARMONIC WAVE numerical FLUME
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DFT Studies on Second-order Nonlinear Optical Response of Ir(C∧N)2(pic)Complexes
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作者 WANG Huiying SHEN Zhaobin +2 位作者 YE Jinting WANG Hongqiang QIU Yongqing 《高等学校化学研究:英文版》 SCIE CAS CSCD 2019年第2期333-339,共7页
Density flmctional theory(DFT)was employed to calculate the geometrical structures,UV-Vis absorption spectra and second-order nonlinear optical(NLO)properties of a family of iridium(Ⅲ)complexes,which possess of diffe... Density flmctional theory(DFT)was employed to calculate the geometrical structures,UV-Vis absorption spectra and second-order nonlinear optical(NLO)properties of a family of iridium(Ⅲ)complexes,which possess of different cyclometallated ligands(C∧N)and ancillary ligands[pyridme-2-carboxylate(pic)].It was found that the mo-dification of the LUMO energy levels was achieved by changing pic ligands and the energy gaps between the HOMO and LUMO were notably increased or decreased.In addition,the degree of conjugation was significantly changed with the substituent groups varied,which led to that the first hyperpolarizabilityβcould be effectively modulated.Through the analysis of time-dependent DFT(TD-DFT)results,we predicted that these studied complexes withπ→π^*charge transfer was beneficial to the large second-order NLO properties.Therefore,we hope that these studied iridium(III)complexes can be considered as versatile second-order NLO materials. 展开更多
关键词 Density FUNCTIONAL theory Iridium(III)complex SECOND-ORDER nonlinear optical(NLO)property
An R(x)-orthonormal theory for the vibration performance of a non-smooth symmetric composite beam with complex interface 预览
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作者 Chein-Shan Liu Bo-Tong Li 《力学学报:英文版》 SCIE EI CAS CSCD 2019年第1期228-241,I0007共15页
A composite beam is symmetric if both the material property and support are symmetric with respect to the middle point. In order to study the free vibration performance of the symmetric composite beams with different ... A composite beam is symmetric if both the material property and support are symmetric with respect to the middle point. In order to study the free vibration performance of the symmetric composite beams with different complex nonsmooth/discontinuous interfaces, we develop an R(x)-orthonormal theory, where R(x) is an integrable flexural rigidity function. The R(x)-orthonormal bases in the linear space of boundary functions are constructed, of which the second-order derivatives of the boundary functions are asked to be orthonormal with respect to the weight function R(x). When the vibration modes of the symmetric composite beam are expressed in terms of the R(x)-orthonormal bases we can derive an eigenvalue problem endowed with a special structure of the coefficient matrix A :=[aij ],aij= 0 if i + j is odd. Based on the special structure we can prove two new theorems, which indicate that the characteristic equation of A can be decomposed into the product of the characteristic equations of two sub-matrices with dimensions half lower. Hence, we can sequentially solve the natural frequencies in closed-form owing to the specialty of A. We use this powerful new theory to analyze the free vibration performance and the vibration modes of symmetric composite beams with three different interfaces. 展开更多
关键词 SYMMETRIC composite beams R(x)-orthogonality of second-order derivatives of boundary functions R(x)-orthonormal THEORY Non-smooth/discontinuous interface Sequentially closed-from natural frequencies
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Interval optimal power flow applied to distribution networks under uncertainty of loads and renewable resources 预览
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作者 Pengwei CHEN Xiangning XIAO Xuhui WANG 《现代电力系统与清洁能源学报(英文)》 CSCD 2019年第1期139-150,共12页
Optimal power flow(OPF) has been used for energy dispatching in active distribution networks.To satisfy constraints fully and achieve strict operational bounds under the uncertainties from loads and sources, this pape... Optimal power flow(OPF) has been used for energy dispatching in active distribution networks.To satisfy constraints fully and achieve strict operational bounds under the uncertainties from loads and sources, this paper derives an interval optimal power flow(I-OPF)method employing affine arithmetic and interval Taylor expansion.An enhanced I-OPF method based on successive linear approximation and second-order cone programming is developed to improve solution accuracy.The proposed methods are benchmarked against Monte Carlo simulation(MCS) and stochastic OPF.Tests on a modified IEEE 33-bus system and a real 113-bus distribution network validate the effectiveness and applicability of the proposed methods. 展开更多
关键词 Active distribution network Optimal power flow INTERVAL UNCERTAINTY AFFINE ARITHMETIC SECOND-ORDER cone programming
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On the thixotropic effect of turbulence 预览
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作者 Yu-Ning Huang 《力学快报:英文版》 CAS CSCD 2019年第2期113-119,共7页
As a follow-up research of the work on the natural viscosity of turbulence of Huang et al.[Journal of Turbulence (2003)], here we investigate the thixotropic effect of a turbulent Newtonian fluid on the basis of the e... As a follow-up research of the work on the natural viscosity of turbulence of Huang et al.[Journal of Turbulence (2003)], here we investigate the thixotropic effect of a turbulent Newtonian fluid on the basis of the ensemble-averaged Navier–Stokes equation. In view of the natural viscosity, we show that in homogeneous isotropic turbulence the turbulent Newtonian fluid behaves like a thixotropic fluid, exhibiting the thixotropic effect with its natural viscosity decreasing with time. 展开更多
关键词 SECOND-ORDER CLOSURE Natural viscosity of TURBULENCE Launder Reece and Rodi model Homogeneous ISOTROPIC TURBULENCE THIXOTROPY
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Existence of periodic solutions for second-order Hamiltonian systems with asymptotically linear conditions
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作者 Xingfan CHEN Fei GUO Peng LIU 《中国数学前沿:英文版》 SCIE CSCD 2018年第6期1313-1323,共11页
We consider a class of asymptotically linear nonautonomous second- order Hamiltonian systems.Using the Saddle Point Theorem,we obtain the existence result,which extends some previously known results.
关键词 EXISTENCE periodic solution SECOND-ORDER HAMILTONIAN systems SADDLE Point THEOREM
具有非单调项的二阶微分方程的振动准则 预览
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作者 李沙 韩蓄 李巧銮 《上海师范大学学报:自然科学版》 2018年第3期315-325,共11页
主要利用降阶法,得到具有非单调项的二阶微分方程振动的充分条件.首先根据降阶法及相关的不等式知识,将带有非单调项的二阶微分方程转变为一阶微分方程.之后运用具有非单调项的一阶微分方程已知的相关结果,得到了二阶微分方程的振... 主要利用降阶法,得到具有非单调项的二阶微分方程振动的充分条件.首先根据降阶法及相关的不等式知识,将带有非单调项的二阶微分方程转变为一阶微分方程.之后运用具有非单调项的一阶微分方程已知的相关结果,得到了二阶微分方程的振动准则,改进了以往的二阶微分方程解的振动结果.最后通过例题说明所得结论的可应用性. 展开更多
关键词 振动 二阶 时滞型方程 超前型方程 非单调
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Modeling and nonlinear analysis of 14 bit 100MS/s pipelined ADC 预览
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作者 Zheng Hao Fan Xiangning 《高技术通讯:英文版》 CAS 2018年第1期36-45,共10页
In this paper, detailed models of 14-bit 100MS/s pipelined analog-to-digital converter (ADC)are presented. In order to help design of ADC system, blocks for pipelined ADC and disturbancesources are carefully analyze... In this paper, detailed models of 14-bit 100MS/s pipelined analog-to-digital converter (ADC)are presented. In order to help design of ADC system, blocks for pipelined ADC and disturbancesources are carefully analyzed. Critical parameters, such as capacitor mismatch, clock jitter are pro-posed and simulated. The pipelined ADC system is divided into five parts, clock generator, sampleand hold (S/H) circuit, multiplying digital-to-analog converters (MDAC), backend, and digitalcorrection. These blocks introduce several interferences, which attenuate performance of pipelinedADC severely. Modeling and simulations of these disturbance sources are presented particularly. Anew nlodel of S/H is introduced. Results derived from simulations can supervise design and optimi-zation of the ADC system. 展开更多
关键词 capacitor MISMATCH OFFSET CLOCK JITTER flip-around sample and hold (S/H) SECOND-ORDER response
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Nonlinear Time-Domain Theory for the Simulation of Moored Floating Body Motion 预览
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作者 Bin Teng Peiwen Cong Ying Gou 《船舶与海洋工程学报:英文版》 CSCD 2018年第3期341-352,共12页
Nonlinear wave loads can induce low-frequency and high-frequency resonance motions of a moored platform in deep water. For the analysis of the nonlinear response of an offshore platform under the action of irregular w... Nonlinear wave loads can induce low-frequency and high-frequency resonance motions of a moored platform in deep water. For the analysis of the nonlinear response of an offshore platform under the action of irregular waves, the most widely used method in practice is the Cummins method, in which the second-order exciting forces in the time domain are computed by a two-term Volterra series model based on incident waves, first-order body motion response, and quadratic transfer functions(QTFs). QTFs are bichromatic waves acting on a body and are computed in the frequency domain in advance. For moving bodies, QTFs are related to the first-order body response, which is to be determined in the simulation process of body motion response but is unknown in the computation procedure of QTFs. In solving this problem, Teng and Cong(2017) proposed a method to divide the QTFs into different components,which are unrelated to the body response. With the application of the new QTF components, a modified Cummins method can be developed for the simulation of the nonlinear response of a moored floating platform. This paper presents a review of the theory. 展开更多
关键词 SECOND-ORDER DIFFRACTION theory QTF components TIME-DOMAIN SIMULATION CUMMINS method Response of FLOATING bodies
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Unified optimal power flow model for AC/DC grids integrated with natural gas systems considering gas-supply uncertainties 预览
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作者 Jiale FAN Xiaoyang TONG Junbo ZHAO 《现代电力系统与清洁能源学报(英文)》 2018年第6期1193-1203,共11页
A unified optimal power flow(OPF) model for AC/DC grids integrated with natural gas systems is proposed for the real-time scheduling of power systems.Herein, the primary physical couplings underlying this coordinated ... A unified optimal power flow(OPF) model for AC/DC grids integrated with natural gas systems is proposed for the real-time scheduling of power systems.Herein, the primary physical couplings underlying this coordinated system are modeled and investigated. In addition, the uncertainties of gas loads are considered when studying the role of gas supply for gas-fired units in power system operations. The nonlinear gas system constraints are converted to the second-order cone forms that allow for the use of the Benders decomposition techniques and the interior-point method to obtain the optimal solution. The numerical results of the modified IEEE 118-bus test system that integrates the Belgium 20-node natural gas system demonstrate the effectiveness of the proposed model. The effects of gas demand uncertainties on the optimal schedule of thermal generators are investigated as well. 展开更多
关键词 AC/DC optimal power flow(OPF) Natural gas system Benders decomposition SECOND-ORDER CONE programming
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Effects of Second-Order Sum-and Difference-Frequency Wave Forces on the Motion Response of a Tension-Leg Platform Considering the Set-down Motion 预览
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作者 WANG Bin TANG Yougang CAI Runbo 《中国海洋大学学报:英文版》 SCIE CAS CSCD 2018年第2期311-319,共9页
This paper presents a study on the motion response of a tension-leg platform(TLP)under first-and second-order wave forces,including the mean-drift force,difference and sum-frequency forces.The second-order wave force ... This paper presents a study on the motion response of a tension-leg platform(TLP)under first-and second-order wave forces,including the mean-drift force,difference and sum-frequency forces.The second-order wave force is calculated using the full-field quadratic transfer function(QTF).The coupled effect of the horizontal motions,such as surge,sway and yaw motions,and the set-down motion are taken into consideration by the nonlinear restoring matrix.The time-domain analysis with 50-yr random sea state is performed.A comparison of the results of different case studies is made to assess the influence of second-order wave force on the motions of the platform.The analysis shows that the second-order wave force has a major impact on motions of the TLP.The second-order difference-frequency wave force has an obvious influence on the low-frequency motions of surge and sway,and also will induce a large set-down motion which is an important part of heave motion.Besides,the second-order sum-frequency force will induce a set of high-frequency motions of roll and pitch.However,little influence of second-order wave force is found on the yaw motion. 展开更多
关键词 tension-leg platform random WAVE SECOND-ORDER WAVE force quadratic transfer function sum-frequency differencefrequency set-down MOTION
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一类二阶中立随机偏微分方程的吸引集和拟不变集 预览
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作者 范英飞 章囯鹏 +1 位作者 江欣囯 马剑 《数学物理学报:A辑》 CSCD 北大核心 2018年第6期1135-1143,共9页
研究了一类二阶中立随机偏微分方程.运用随机分析与不等式技巧,获得了这类方程存在吸引集和拟不变集的充分条件,推广了一些已有的相关结果.
关键词 吸引 拟不变 二阶 随机 偏微分
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Terminal sliding mode control based on super-twisting algorithm 预览
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作者 Zhanshan Zhao Hongru Gu +1 位作者 Jing Zhang Gang Ding 《系统工程与电子技术:英文版》 SCIE EI CSCD 2017年第1期145-150,共6页
An improved non-singular terminal sliding mode control based on the super-twisting algorithm is proposed for a class of second-order uncertain nonlinear systems. This method can effectively avoid the singularity probl... An improved non-singular terminal sliding mode control based on the super-twisting algorithm is proposed for a class of second-order uncertain nonlinear systems. This method can effectively avoid the singularity problem and obviously reduce the chattering phenomenon. The stability of the proposed procedure is proven to be finite-time convergence using the Lyapunov theory against uncertain unmodeled dynamic and external disturbances.An example is given to show the proposed improved non-singular terminal sliding mode control (SMC) law effectively. 展开更多
关键词 SLIDING mode control (SMC) super-twisting FINITE-TIME CONVERGENCE SECOND-ORDER nonlinear system
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一类带有阻尼项的二阶中立型微分方程振动性准则 预览
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作者 韩红梅 崔小萌 《曲阜师范大学学报:自然科学版》 CAS 2017年第1期19-25,50共8页
该文研究了二阶中立型微分方程的振动性准则,推广了已有文献中的许多振动结果,最后给出一个例子说明结果的有效性.
关键词 振动准则 二阶 中立型微分方程 阻尼
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Effects of Second-Order Difference-Frequency Wave Forces on Floating Wind Turbine Under Survival Condition 预览
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作者 Jiawen Li Yichen Jiang +2 位作者 Yougang Tang Xiaoqi Qu Jiawei Zhai 《天津大学学报:英文版》 EI CAS 2017年第2期130-137,共8页
In this paper, the effects of second-order difference-frequency wave forces on the global motion of an offshore wind turbine system with a large displacement under the survival condition are studied. In this case, the... In this paper, the effects of second-order difference-frequency wave forces on the global motion of an offshore wind turbine system with a large displacement under the survival condition are studied. In this case, the hydrodynamic force is the main force because the blades are feathered to reduce the lifting force. The first-order hydrodynamic forces are calculated by WADAM, while the second-order wave forces are calculated by a customized MATLAB module. Then the hydrodynamic coefficients are transferred to the wind turbine analytical code FAST. Through the comparisons of dynamic responses between the first- and second-order numerical models, it is found that the second-order wave forces significantly influence the motion of floating wind turbine under the survival condition. Moreover, neglecting the second-order force significantly underestimates the tension forces in the mooring lines. 展开更多
关键词 OFFSHORE WIND TURBINE SECOND-ORDER wave force Coupled dynamic analysis SURVIVAL condition FAST
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二阶益贫式增长的绝对与相对同步测定方法构建
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作者 周华 韦丽霞 赵轩 《管理评论》 CSSCI 北大核心 2017年第2期3-12,共10页
本文首先尝试构建一个二阶益贫式增长的绝对与相对同步测定函数;所谓二阶益贫式增长,是指相较整个穷人群体、更关注“穷人中的穷人”的增长,而同步测定通过将绝对益贫与相对益贫相结合,恰好能够弥补二者各自的缺陷。其次,本文对该... 本文首先尝试构建一个二阶益贫式增长的绝对与相对同步测定函数;所谓二阶益贫式增长,是指相较整个穷人群体、更关注“穷人中的穷人”的增长,而同步测定通过将绝对益贫与相对益贫相结合,恰好能够弥补二者各自的缺陷。其次,本文对该函数所具备的优良属性进行证明。最后,运用所构建的函数对中国及其各省市的益贫式增长进行测定,并将测定结果与相对益贫式增长的结果进行比较。研究发现,中国及各省市的农村与城镇地区在大部分年份均未实现二阶同步益贫,且实现同步益贫的会被测定为实现相对益贫,反之则不成立;与相对测定函数相比。同步测定函数不仅更加严格,也更能反映益贫情况的波动。 展开更多
关键词 益贫式增长 二阶 绝对益贫 相对益贫
所有解非振动的二阶非线性泛函动力方程 预览
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作者 梁诗媚 《广东技术师范学院学报》 2016年第5期23-26,共4页
本文研究了二阶非线性时标动力方程(a(t)x^Δ(t))^Δ+f(t,x(q(t)))=r_0(t),t∈T的非振动性,并得到它的全体解非振动的两个充分性判别准则.发展了文[7]的方法,所得结果具有更广泛的适应性,见最后例题.
关键词 时标 二阶 泛函微分方程 非振动解
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带混合型非线性项的二阶中立型时标动力方程的振动准则 预览
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作者 黄先勇 杨启贵 曹俊飞 《工程数学学报》 CSCD 北大核心 2016年第4期402-418,共17页
中立型时标动力方程的振动性在理论上和应用中有着重要的意义.本文研究了一类二阶带混合型非线性项的中立型时标动力方程的振动性.首先,我们定义了中立项系数函数π(t).当π(t0)=∞时,利用广义李卡提变换技巧和均值技巧,建立了二... 中立型时标动力方程的振动性在理论上和应用中有着重要的意义.本文研究了一类二阶带混合型非线性项的中立型时标动力方程的振动性.首先,我们定义了中立项系数函数π(t).当π(t0)=∞时,利用广义李卡提变换技巧和均值技巧,建立了二阶中立型动力方程振动的一些新的判据.其次,当π(t0)<∞时,通过加强假设条件及应用某些不等式和一些分析技巧,我们也得到了该方程振动的几个判据.我们的工作推广并改进了相关文献关于二阶中立型动力方程振动的结果.最后,作为应用给出两个实例说明所获定理的重要性. 展开更多
关键词 振动 中立型动力方程 二阶 时标
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二阶变系数非齐次线性微分方程的周期解 预览
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作者 韩卫卫 《新乡学院学报》 2016年第6期7-9,共3页
在假设已知二阶变系数非齐次线性微分方程的两个变系数关系的前提下,利用降阶法导出了几类二阶变系数非齐次线性微分方程的周期解。
关键词 变系数 周期解 二阶 非齐次线性微分方程
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