检索结果-内蒙古大学图书馆

Passive-mode treadmill test effectively reveals neuromuscular modification of a lower limb muscle: sEMG-based study from experiments on ISS

引用

ACTA ASTRONAUTICA 2022年 199卷 471-479页

作者： Meigal, Alexander Ivanov, Danil Senatorova, Natalia Monakhova, Uliana Fomina, Elena Petrozavodsk State Univ Lenin St 33 Petrozavodsk Russia RAS Keldysh Inst Appl Math Miusskaya Sq 4 Moscow Russia RAS Inst Biomed Problems State Sci Ctr Russian Federat Khoroshevskoe Sh 76 A Moscow Russia

The study was aimed at exploring informative value of nonlinear parameters of surface electromyogram (sEMG) to characterization of neuromuscular activity in respect with duration of space flight (SF) and stepping mode. The working hypothesis held that sEMG entropy, correlation dimension (CD), and Lyapunov???s exponent, which characterize signals in terms of regularity and predictability, may inform on motor units (MUs) synchronization or content of MUs of different types in muscle activity. In addition, median frequency (MDF), mean amplitude, and kurtosis of the probability distribution of sEMG were computed. sEMG samples were collected from the soleus of 6 cosmonauts on board of the International Space Station during 5 modes of stepping on the passive -mode treadmill in the MO-3 test, and 5 study points -before and after SF on ground (preSF, postSF) and for 3 periods of time in SF (1???80, 81???120, 120???170 days of SF). Altogether, 15 individual sEMG sample sets were successfully obtained. It was found that 1) the sEMG parameters pooled for all subjects by the stepping mode, except for MDF and kurtosis, did modify in the direction of higher regularity of the signal with growing speed of stepping, 2) the conditions of SF exerted effect on MDF, Lyapunov???s exponent, entropy, and kurtosis of the probability distribution of sEMG, which probably indicated on greater involvement of the faster type motor units in muscle activity. In conclusion, nonlinear sEMG parameters look promising for characterizing the neuromus-cular activity of skeletal muscles under SF conditions. Nonetheless, a small number of sample sets combined with different study points in different cosmonauts allow considering these facts as promising, but not yet definitely established.

关键词： Surface electromyogram Motor unit nonlinear parameters Space flight Soleus muscle

来源：评论

学校读者我要写书评

暂无评论

Estimation of second-, third- and fourth-order nonlinearity parameters for specific fluorocarbon drug-delivering nanosystems

引用

PHYSICS AND CHEMISTRY OF LIQUIDS 2011年第3期49卷 309-317页

作者： Jayalatha, K. Arockia Amoros, J. Ravi, S. Natl Coll Dept Phys Tiruchirappalli 620001 Tamil Nadu India Univ Cantabria Dept Fis Aplicada E-39005 Santander Spain Cauvery Coll Dept Phys Tiruchirappalli 620001 Tamil Nadu India

The nonlinear B/A, C/A and D/A are new parameters in ultrasound fluorocarbon nanosystem characterisation. In this article, all the three parameters are estimated for specific fluorocarbons, such as perfluorohexane (C6F14), perfluoroheptanes (C7F16), perfluoro-1-butyl tetrahydrofuran (C8F16O), perfluoro octanes (C8F18), perfluorodecalin (C10F18), perfluorodichloro octane (C8F16Cl2) and perfluorooctyl bromide (C8F17Br) through their experimental ultrasonic velocity for different temperatures. The fluorocarbons under study are powerful drug-delivering agents. Since these parameters have not been so far calculated for such systems, it becomes more important to evaluate them. The range of all the three parameters of our results is highly encouraging. The values resemble the most of biological systems. It is interesting to note that the classical model also suits very well in nanoscales too.

关键词： nonlinear parameters perfluorocarbons nanoparticles

来源：评论

学校读者我要写书评

暂无评论

Shimmy vibration analysis of unmanned aircraft coupled with landing gears

引用

JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY 2024年第1期38卷 137-147页

作者： Sivakumar, S. Subramanian, L. R. Ganapathy Giridharan, V. SRM Inst Sci & Technol Fac Engn & Technol Dept Aerosp Engn Kattankulathur 603203 Tamil Nadu India

The stability of aircraft during taxiing is an important issue in the development of landing gear and airworthiness certification. Incidents and abnormal problems consistently arise due to landing gear shimmy. The integration of a model involving tricycle landing gear and aircraft structure is a major advancement in addressing shimmy oscillations. A formulated nonlinear mathematical modeling approach integrates airframe motions with landing gear modes, which provides deep insights into their coupling effect. It effectively determines the critical speed region and types of shimmy oscillations that can occur. An increase in landing gear shimmy intensifies lateral forces on landing gear components, which affects the yaw motion of the aircraft. The optimization of aircraft mass, the critical value of torsional damping, and their influence on directional stability are investigated. This work is useful in the conceptual design of landing gears and in avoiding the potential risks associated with shimmy oscillations to extend the lifespan of landing gears.

关键词： nonlinear parameters Shimmy critical speed Landing gear response Aircraft body motion Coupling

来源：评论

学校读者我要写书评

暂无评论

Hessian Matrix Estimation in Hybrid Systems Based on an Embedded FFNN

引用

IEEE TRANSACTIONS ON NEURAL NETWORKS 2010年第10期21卷 1533-1542页

作者： Baek, Seung-Mook Park, Jung-Wook Yonsei Univ Sch Elect & Elect Engn Seoul 120749 South Korea

This paper describes the Hessian matrix estimation of nonsmooth nonlinear parameters by the identifier based on a feedforward neural network (FFNN) embedded in a hybrid system, which is modeled by the differential-algebraic-impulsive-switched (DAIS) structure. After identifying full dynamics of the hybrid system, the FFNN is used to estimate second-order derivatives of an objective function with respect to the nonlinear parameters from the gradient information, which are trajectory sensitivities. Then, the estimated Hessian matrix is applied to the optimal tuning of a saturation limiter used in a practical engineering system.

关键词： Feedforward neural network (FFNN) Hessian matrix estimation hybrid system nonlinear parameters optimal tuning power system stabilizer (PSS) saturation limiter

来源：评论

学校读者我要写书评

暂无评论

Recasted models-based hierarchical extended stochastic gradient method for MIMO nonlinear systems

引用

IET CONTROL THEORY AND APPLICATIONS 2017年第4期11卷 476-485页

作者： Wang, Dongqing Mao, Li Ding, Feng Qingdao Univ Coll Automat Engn Qingdao 266071 Peoples R China Qingdao Univ Sci & Technol Coll Automat & Elect Engn Qingdao 266061 Peoples R China Jiangnan Univ Sch Internet Things Engn Wuxi 214122 Peoples R China

For the identification of a class of nonlinear multi-input multi-output (MIMO) Hammerstein systems with different types of coefficients: a matrix coefficient and scalar coefficients, it is difficult to parameterise such Hammerstein systems into an identification model to which the standard identification method can be easily applied to implement parameter estimation. By the matrix transformation and the over-parametrisation idea, this study transforms an MIMO Hammerstein system with different types of coefficients into an over-parametrisation regression identification model, and points out the aroused large computation problem. To overcome the large computational load of the over-parametrisation method, by the matrix transformation and the hierarchical identification principle, this study recasts the MIMO Hammerstein system into two models, each of which is expressed as a regression form in the parameters of the nonlinear part or in the parameters of the linear part. Then a hierarchical extended stochastic gradient algorithm is presented to alternatively estimate the parameters of the nonlinear part and the parameters of the linear part. The simulation results indicate that the proposed algorithm can effectively identify the nonlinear MIMO Hammerstein system.

关键词： MIMO systems nonlinear control systems hierarchical systems stochastic processes gradient methods matrix algebra parameter estimation regression analysis linear systems recasted model-based hierarchical extended stochastic gradient method nonlinear implement Hammerstein systems nonlinear multiinput multioutput Hammerstein systems matrix coefficient scalar coefficients identification model parameter estimation matrix transformation over-parametrisation regression identification model computational load hierarchical identification principle nonlinear parameters linear parameters nonlinear MIMO Hammerstein system

来源：评论

学校读者我要写书评

暂无评论

Comparison of sensitivity in nonlinear ultrasonic detection based on Lamb wave phase velocity matching mode

引用

NONDESTRUCTIVE TESTING AND EVALUATION 2023年第2期38卷 297-312页

作者： Zhao, Gaozheng Jiang, Mingshun Luo, Yuxiang Li, Wei Sui, Qingmei Shandong Univ Sch Control Sci & Engn Jinan Peoples R China China Acad Space Technol Shandong Inst Space Elect Technol Yantai Peoples R China

In nonlinear ultrasonic damage detection, the appropriate Lamb wave mode to accurately characterise the nonlinearity attributed to the material damage should be selected important. However, an effective mode is more difficult to select practically as impacted by the dispersion and multi-mode characteristic of the Lamb wave. In this study, based on the dispersion curve of Lamb waves, the modes meeting the second harmonics and third harmonics phase velocity matching were given, and the nonlinear cumulative effects exerted by different modes on fatigue cracks were compared. In addition, an investigation was conducted on the amplitude change of the second and third harmonics signal of the identical fatigue damage. The results show that the harmonic amplitude decreases with the increase of the fatigue crack length. The third harmonics under the two modes are more sensitive to fatigue damage than the second harmonics. Moreover, the amplitude of the third harmonic excited by S1 mode exceeds that of the other mode. As the fatigue crack length increases, the relative second- and third-order nonlinear coefficients generated by S1 mode have approximately the same trend, first increasing and then decreasing. The results reveal that the third harmonic under S1 mode could more effectively characterise fatigue damage.

关键词： Lamb wave nonlinear parameters second harmonics third harmonics

来源：评论

学校读者我要写书评

暂无评论

Comparison of entropy-based regularity estimators: Application to the fetal heart rate signal for the identification of fetal distress

引用

IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING 2006年第1期53卷 119-125页

作者： Ferrario, M Signorini, MG Magenes, G Cerutti, S Univ Milan Politecn Milan Dipartimento Bioingn I-20133 Milan Italy Univ Pavia Dipartimento Informat & Sistemist I-27100 Pavia Italy

This paper considers the multiscale entropy (MSE) approach for estimating the regularity of time series at different scales. Sample entropy (SampEn) and approximate entropy (ApEn) are evaluated in MSE analysis on simulated data to enhance the main features of both estimators. We applied the approximate entropy and the sample entropy estimators to fetal heart rate signals on both single and multiple scales for an early identification of fetal sufferance antepartum. Our results show that the ApEn index significantly distinguishes suffering from normal fetuses between the 30th and the 35th week of gestation. Furthermore, our data shows that the MSE entropy values are reliable indicators of the fetal distress associated with the presence of a pathological condition at birth.

关键词： cardiotocography fetal heart rate fetal pathologies nonlinear parameters spectral analysis

来源：评论

学校读者我要写书评

暂无评论

Microchip laser Q-switched with GaInNAs/GaAs SESAM emitting 204 ps pulses at 1342 nm

引用

ELECTRONICS LETTERS 2015年第11期51卷 850-U38页

作者： Nikkinen, J. Korpijarvi, V. -M. Leino, I. Harkonen, A. Guina, M. Tampere Univ Technol Optoelect Res Ctr FI-33720 Tampere Finland

A 1342 nm Nd:YVO4 microchip laser is reported, Q-switched with a dilute nitride GaInNAs/GaAs saturable absorber mirror. The laser produced optical pulses as short as 204 ps with 2.3 MHz repetition rate and 24 mW average output power. In comparison to conventional InP-based saturable absorber mirrors, the advantage of the proposed approach is the availability of excellent Bragg mirror materials that enable high reflectivity and more flexibility in designing the non-linear parameters owing to the use of lattice matched GaInNAs/GaAs quantum wells.

关键词： III-V semiconductors Q-switching gallium arsenide high-speed optical techniques indium compounds microchip lasers mirrors neodymium optical saturable absorption reflectivity yttrium compounds Bragg mirror materials GaInNAs-GaAs Q-switched microchip laser SESAM YVO4:Nd flexibility frequency 2.3 MHz lattice matched quantum wells nonlinear parameters optical pulses power 24 mW reflectivity repetition rate saturable absorber mirror time 204 ps wavelength 1342 nm

来源：评论

学校读者我要写书评

暂无评论

MESFET LARGE-SIGNAL MODEL BASED ON SMALL-SIGNAL MEASUREMENTS FOR TIME-DOMAIN CAD

引用

ELECTRONICS LETTERS 1988年第15期24卷 973-974页

作者： OUSLIMANI, A VERNET, G HENAUX, JC CROZAT, P ADDE, R Univ. de Paris-Sud Orsay

A large-signal model using a full transistor characterisation is developed for time-domain CAD of circuits. It uses 2-D look-up tables to describe the FETs nonlinear parameters which are a function of two internal vol... 详细信息

关键词： 2D lookup tables MESFET NEC3SK Schottky gate field effect transistors circuit CAD computer aided design equivalent circuits full transistor characterisation large-signal model nonlinear parameters semiconductor device models small-signal measurements step response table lookup time-domain CAD time-domain synthesis

来源：评论

学校读者我要写书评

暂无评论

Characterization of sandwich beams with debonding by linear and nonlinear vibration method

引用

COMPOSITE STRUCTURES 2015年 120卷 200-207页

作者： Idriss, M. El Mahi, A. El Guerjouma, R. Univ Maine Acoust Lab LAUM CNRS UMR 6613 F-72085 Le Mans 9 France

The nonlinear vibration method is used to characterize the behavior of sandwich beams with debonding. The technique focuses on the response of the material's resonance modes as a function of the driving amplitude by sweeping the frequency at various drive levels. Sandwich material used in this study is constructed with glass fibre laminates as skins and with PVC closed-cell foams as core. For an undamaged specimen, the resonance frequency does not change with increased excitation amplitude. For a damaged specimen, the resonance frequency decreases and the inverse quality factor (loss factor) increases proportional with the increasing excitation amplitude. The nonlinear parameters corresponding to the elastic modulus and damping were determined for each frequency mode and each debonding length. The results showed that nonlinear parameters were much more sensitive to damage than linear parameters. (C) 2014 Elsevier Ltd. All rights reserved.

关键词： Composite sandwich Debonding Frequency Loss factor Loss quality factor nonlinear parameters

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

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

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

时间限定

文献类型

馆藏选择

核心期刊

语言

文献类型

帮助

文字说明：

检索规则说明：

检索范例：

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：