On the basis of the second order solution of two-dimensional random gravity waves in finite uniform depth,which is rederived by a perturbation expansion method,the analytical expression of the second order spectrum is...On the basis of the second order solution of two-dimensional random gravity waves in finite uniform depth,which is rederived by a perturbation expansion method,the analytical expression of the second order spectrum is strictly deduced, and for infinite depth, the correct form of the kernel function is given for each octant do main.In fact,the present study improves and corrects the generally accepted results obtained by Tick展开更多
A random periodic spectrum sensing scheme is proposed for cognitive radio networks. The sensing period, the transmission time for primary users and cognitive radios are extended to general forms as random variables. A...A random periodic spectrum sensing scheme is proposed for cognitive radio networks. The sensing period, the transmission time for primary users and cognitive radios are extended to general forms as random variables. A generalized Markov analytical model for sensing period optimization is presented, and the applications of the proposed analytical model by using examples involving primary user systems with both voice and data traffic are illustrated. The analysis and numerical results show that sensing period does affect the maximum rewards of the channel, and the analytical model is justified by its flexibility since it uses general forms of the sensing period, the transmission time for primary users and cognitive radios. Hence the model can be easily adapted for the analysis of many different applications.展开更多
Random Matrix Theory (RMT) is a valuable tool for describing the asymptotic behavior of multiple systems,especially for large matrices. In this paper,using asymptotic random matrix theory,a new cooperative Multiple-In...Random Matrix Theory (RMT) is a valuable tool for describing the asymptotic behavior of multiple systems,especially for large matrices. In this paper,using asymptotic random matrix theory,a new cooperative Multiple-Input Multiple-Output (MIMO) scheme for spectrum sensing is proposed,which shows how asymptotic free property of random matrices and the property of Wishart distribution can be used to assist spectrum sensing for Cognitive Radios (CRs). Simulations over Rayleigh fading and AWGN channels demonstrate the proposed scheme has better detection performance compared with the energy detection techniques even in the case of a small sample of observations.展开更多
鉴于恢复力曲面法(Restoring Force Surface,RFS)和随机森林(Random Forest,RF)模型在参数辨识领域的优越性,结合上述两种方法提出一种新的基于RFS-RF的局部非线性模型辨识方法。首先,针对局部非线性模型求解其动力响应。其次,根据获得...鉴于恢复力曲面法(Restoring Force Surface,RFS)和随机森林(Random Forest,RF)模型在参数辨识领域的优越性,结合上述两种方法提出一种新的基于RFS-RF的局部非线性模型辨识方法。首先,针对局部非线性模型求解其动力响应。其次,根据获得的动力响应计算恢复力曲面与边际谱,然后再通过边际谱求解非线性指标。再次,通过多次改变结构的刚度和阻尼参数生成若干组非线性指标并建立随机森林模型。然后,将新的非线性指标作为预测集输入已经建立的随机森林模型并判断系统的非线性类型和非线性函数形式。最后,采用最小二乘法对局部非线性系统的待求参数进行精确识别。通过一个四层剪切型框架结构模型对所提方法进行验证,研究结果表明:基于RFS-RF的多自由度局部非线性模型辨识方法能够准确识别结构系统的非线性类型、函数形式以及未知参数。展开更多
目的使用孟德尔随机化(MR)研究方法验证肠道微生物群(GM)与自闭症谱系障碍(ASD)的因果关系。方法GM数据来源于MiBioGen联盟进行的全基因组关联研究荟萃分析,包括18340例受试者;ASD汇总统计数据来自爱丁堡大学开放型全基因组关联研究项目...目的使用孟德尔随机化(MR)研究方法验证肠道微生物群(GM)与自闭症谱系障碍(ASD)的因果关系。方法GM数据来源于MiBioGen联盟进行的全基因组关联研究荟萃分析,包括18340例受试者;ASD汇总统计数据来自爱丁堡大学开放型全基因组关联研究项目(IEU Open GWAS)发布数据。采用逆方差加权法(IVW)、加权众数和加权中位数估计(WME)进行两样本孟德尔随机化研究;采用Cochran’s Q检验、MR-PRESSO和MR Egger截距检验进行敏感性分析,以评估结果的稳定性。结果Dorea(OR=0.783,95%CI:0.676~0.908)、瘤胃球菌(RuminococcaceaeUCG005)(OR=0.781,95%CI:0.693~0.880)、瘤胃球菌(RuminococcaceaeUCG014)(OR=0.863,95%CI:0.761~0.980)和Victivallis菌属(OR=0.917,95%CI:0.857~0.981)可能对ASD有保护作用,而巴恩斯氏菌(Barnesiella)(OR=1.182,95%CI:1.047~1.334)、副拟杆菌(Parabacteroides)(OR=1.213,95%CI:1.017~1.447)和苏黎世杆菌(Turicibacter)菌属(OR=1.129,95%CI:1.007~1.267)可能增加ASD的风险(P均<0.05)。结论GM和ASD之间具有因果关系,改善GM可能对预防和治疗ASD有一定的临床意义。展开更多
This paper presents the heave responses and the moonpool water motions of a truss Spar platform with semi-closed moonpool in random waves. A 2-DOF（degree of freedom） coupling dynamical equations of the platform heav...This paper presents the heave responses and the moonpool water motions of a truss Spar platform with semi-closed moonpool in random waves. A 2-DOF（degree of freedom） coupling dynamical equations of the platform heave and vertical motions of the moonpool water are derived. The linear wave theory is used to simulate the random waves. The response statistical values and the power spectrums are calculated to analyze the mutual influences between the platform heave and the moonpool water motions for different opening ratios of the moonpool. The effect of coupling parameters on the platform heave and the moonpool water motions are analyzed. The results show that motions of the moonpool water significantly affected the platform heave when the characteristic wave period is far away from the natural period of the platform heave, and different moonpool opening ratios lead to different heave amplitudes of the platform. In the actual design, an optimized moonpool opening ratio can be designed to reduce heave motions of the platform.展开更多
Numerical simulations of freak wave generation are studied in random oceanic sea states described by JONSWAP spectrum. The evolution of initial random wave trains is namerically carried out within the framework of the...Numerical simulations of freak wave generation are studied in random oceanic sea states described by JONSWAP spectrum. The evolution of initial random wave trains is namerically carried out within the framework of the modified fourorder nonlinear Schroedinger equation （mNLSE）, and some involved influence factors are also discussed. Results show that if the sideband instability is satisfied, a random wave train may evolve into a freak wave train, and simultaneously the setting of the Phillips paranleter and enhancement coefficient of JONSWAP spectrum and initial random phases is very important for the formation of freak waves. The way to increase the generation efficiency of freak waves thsough changing the involved parameters is also presented.展开更多
Volterra series is a powerful mathematical tool for nonlinear system analysis,and there is a wide range of nonlinear engineering systems and structures that can be represented by a Volterra series model.In the present...Volterra series is a powerful mathematical tool for nonlinear system analysis,and there is a wide range of nonlinear engineering systems and structures that can be represented by a Volterra series model.In the present study,the random vibration of nonlinear systems is investigated using Volterra series.Analytical expressions were derived for the calculation of the output power spectral density（PSD） and input-output cross-PSD for nonlinear systems subjected to Gaussian excitation.Based on these expressions,it was revealed that both the output PSD and the input-output crossPSD can be expressed as polynomial functions of the nonlinear characteristic parameters or the input intensity.Numerical studies were carried out to verify the theoretical analysis result and to demonstrate the effectiveness of the derived relationship.The results reached in this study are of significance to the analysis and design of the nonlinear engineering systems and structures which can be represented by a Volterra series model.展开更多
文摘On the basis of the second order solution of two-dimensional random gravity waves in finite uniform depth,which is rederived by a perturbation expansion method,the analytical expression of the second order spectrum is strictly deduced, and for infinite depth, the correct form of the kernel function is given for each octant do main.In fact,the present study improves and corrects the generally accepted results obtained by Tick
文摘A random periodic spectrum sensing scheme is proposed for cognitive radio networks. The sensing period, the transmission time for primary users and cognitive radios are extended to general forms as random variables. A generalized Markov analytical model for sensing period optimization is presented, and the applications of the proposed analytical model by using examples involving primary user systems with both voice and data traffic are illustrated. The analysis and numerical results show that sensing period does affect the maximum rewards of the channel, and the analytical model is justified by its flexibility since it uses general forms of the sensing period, the transmission time for primary users and cognitive radios. Hence the model can be easily adapted for the analysis of many different applications.
基金Supported by the National Natural Science Foundation of China (No.60972039)Natural Science Foundation of Jiangsu Province (No.BK2007729)Natural Science Funding of Jiangsu Province (No.06KJA51001)
文摘Random Matrix Theory (RMT) is a valuable tool for describing the asymptotic behavior of multiple systems,especially for large matrices. In this paper,using asymptotic random matrix theory,a new cooperative Multiple-Input Multiple-Output (MIMO) scheme for spectrum sensing is proposed,which shows how asymptotic free property of random matrices and the property of Wishart distribution can be used to assist spectrum sensing for Cognitive Radios (CRs). Simulations over Rayleigh fading and AWGN channels demonstrate the proposed scheme has better detection performance compared with the energy detection techniques even in the case of a small sample of observations.
文摘鉴于恢复力曲面法(Restoring Force Surface,RFS)和随机森林(Random Forest,RF)模型在参数辨识领域的优越性,结合上述两种方法提出一种新的基于RFS-RF的局部非线性模型辨识方法。首先,针对局部非线性模型求解其动力响应。其次,根据获得的动力响应计算恢复力曲面与边际谱,然后再通过边际谱求解非线性指标。再次,通过多次改变结构的刚度和阻尼参数生成若干组非线性指标并建立随机森林模型。然后,将新的非线性指标作为预测集输入已经建立的随机森林模型并判断系统的非线性类型和非线性函数形式。最后,采用最小二乘法对局部非线性系统的待求参数进行精确识别。通过一个四层剪切型框架结构模型对所提方法进行验证,研究结果表明:基于RFS-RF的多自由度局部非线性模型辨识方法能够准确识别结构系统的非线性类型、函数形式以及未知参数。
文摘目的使用孟德尔随机化(MR)研究方法验证肠道微生物群(GM)与自闭症谱系障碍(ASD)的因果关系。方法GM数据来源于MiBioGen联盟进行的全基因组关联研究荟萃分析,包括18340例受试者;ASD汇总统计数据来自爱丁堡大学开放型全基因组关联研究项目(IEU Open GWAS)发布数据。采用逆方差加权法(IVW)、加权众数和加权中位数估计(WME)进行两样本孟德尔随机化研究;采用Cochran’s Q检验、MR-PRESSO和MR Egger截距检验进行敏感性分析,以评估结果的稳定性。结果Dorea(OR=0.783,95%CI:0.676~0.908)、瘤胃球菌(RuminococcaceaeUCG005)(OR=0.781,95%CI:0.693~0.880)、瘤胃球菌(RuminococcaceaeUCG014)(OR=0.863,95%CI:0.761~0.980)和Victivallis菌属(OR=0.917,95%CI:0.857~0.981)可能对ASD有保护作用,而巴恩斯氏菌(Barnesiella)(OR=1.182,95%CI:1.047~1.334)、副拟杆菌(Parabacteroides)(OR=1.213,95%CI:1.017~1.447)和苏黎世杆菌(Turicibacter)菌属(OR=1.129,95%CI:1.007~1.267)可能增加ASD的风险(P均<0.05)。结论GM和ASD之间具有因果关系,改善GM可能对预防和治疗ASD有一定的临床意义。
基金financially supported by the National Natural Science Foundation of China(Grant No.51179125)the Innovation Foundation of Tianjin University(Grant No.1301)
文摘This paper presents the heave responses and the moonpool water motions of a truss Spar platform with semi-closed moonpool in random waves. A 2-DOF（degree of freedom） coupling dynamical equations of the platform heave and vertical motions of the moonpool water are derived. The linear wave theory is used to simulate the random waves. The response statistical values and the power spectrums are calculated to analyze the mutual influences between the platform heave and the moonpool water motions for different opening ratios of the moonpool. The effect of coupling parameters on the platform heave and the moonpool water motions are analyzed. The results show that motions of the moonpool water significantly affected the platform heave when the characteristic wave period is far away from the natural period of the platform heave, and different moonpool opening ratios lead to different heave amplitudes of the platform. In the actual design, an optimized moonpool opening ratio can be designed to reduce heave motions of the platform.
基金supported by the International Science and Technology Cooperation Program(Grant No.2007DFA60490)the National Natural Science Foundation of China(Grant No.50679078)the Innovation Foundation of Guangzhou Institute of Energy Conversion (Grant No.0807r51001)
文摘Numerical simulations of freak wave generation are studied in random oceanic sea states described by JONSWAP spectrum. The evolution of initial random wave trains is namerically carried out within the framework of the modified fourorder nonlinear Schroedinger equation （mNLSE）, and some involved influence factors are also discussed. Results show that if the sideband instability is satisfied, a random wave train may evolve into a freak wave train, and simultaneously the setting of the Phillips paranleter and enhancement coefficient of JONSWAP spectrum and initial random phases is very important for the formation of freak waves. The way to increase the generation efficiency of freak waves thsough changing the involved parameters is also presented.
基金supported by the National Science Fund for Distinguished Young Scholars (11125209)the National Natural Science Foundation of China (10902068,51121063 and 10702039)+1 种基金the Shanghai Pujiang Program (10PJ1406000)the Opening Project of State Key Laboratory of Mechanical System and Vibration (MSV201103)
文摘Volterra series is a powerful mathematical tool for nonlinear system analysis,and there is a wide range of nonlinear engineering systems and structures that can be represented by a Volterra series model.In the present study,the random vibration of nonlinear systems is investigated using Volterra series.Analytical expressions were derived for the calculation of the output power spectral density（PSD） and input-output cross-PSD for nonlinear systems subjected to Gaussian excitation.Based on these expressions,it was revealed that both the output PSD and the input-output crossPSD can be expressed as polynomial functions of the nonlinear characteristic parameters or the input intensity.Numerical studies were carried out to verify the theoretical analysis result and to demonstrate the effectiveness of the derived relationship.The results reached in this study are of significance to the analysis and design of the nonlinear engineering systems and structures which can be represented by a Volterra series model.
