EMG oscillator model-based energy kernel method for characterizing muscle intrinsic property under isometric contraction

This paper presents a new method for estimating the isometric contraction force and the characterization of muscle’s intrinsic property.The method,called the energy kernel method,starts with converting the electromyography(EMG)signal into planar phase portraits,on which the elliptic distribution of the state points is named as the energy kernel,while that formed by the noise signal is called the noise kernel.Based on such stochastic features of the phase portraits,we approximate the EMG signal within a rectangular window as a harmonic oscillator(EMG oscillator).The study establishes the relationship between the energy of control signal(EMG)and that of output signal(force/power),and a characteristic energy is proposed to estimate the muscle force.On the other hand,the natural frequencies of the noise and the EMG signal can be attained with the energy kernel and noise kernel.In this way,the direct signal–noise recognition and separation can be accomplished.The results show that the representativeness of the characteristic energy toward the force is satisfactory,and the method is very robust since it combines the advantages of both RMS and MPF.Moreover,the natural frequency of the EMG oscillator is not governed by the MU firing rate of a specific muscle,indicating that this frequency correlates with the intrinsic property of muscle.The physical meanings of the model provide new insights into the understanding of EMG.     

A buffering method for quadruped robots based on active impedance control①

Compared with wheeled or tracked robots , legged robots exhibit advantages on agile locomotion and higher survival chance for deadly impacts .A buffering strategy is proposed for quadruped robots with non-extreme initial attitudes from the end of air-righting to the steady standing on the ground . This approach consists of landing phase , buffering phase and recovering phase .The variable stiff-ness control, proportional-derivative(PD) force control and foot trajectory planning are applied to the joints of quadruped robots until the end of the recovering phase .The PD parameters are tuned according to the desired performance of each phase .The above approach is verified on a virtual plat-form.     

CALPHAD modeling of molar volume

Databases concerning basic physical properties of materials, such as molar volume, density, thermal expansion coefficient, elastic constants, thermal conduc- tivity, etc., are essential parts of the underlying knowledge for materials design. While thermodynamic databases provide chemical driving forces and phase equilibrium data, physical property databases provide essential physical parameters, such as volume, lattice constant, lattice misfit, elastic energy, interfacial energy, etc., for phase transfor- mation and microstructure simulations. Combined with thermodynamic databases, physical property databases established on the basis of the calculation of phase diagram （CALPHAD） method can be used to calculate physical properties together with phase equilibria, phase fractions, phase compositions, and thermodynamic properties for multi-component and multi-phase material systems and for the constituent phases. In this paper, we will discuss in detail various volume models based on the CALPHAD method which are capable of describing experimental data in a wide range from cryogenic temperatures to melting points, from the atmospheric pressure to high pressures for pure substances as well as multi-component and multi- phase materials.     

Seismic design and analysis of nuclear power plant structures

The seismic design and analysis of nuclear power plant (NPP) begin with the seismic hazard assessment and design ground motion development for the site. The following steps are needed for the seismic hazard assessment and design ground motion development： a. the development of regional seismo-tectonic model with seismic source areas within 500 km radius centered to the site; b. the development of strong motion prediction equations; c. logic three development for taking into account uncertainties and seismic hazard quantification; d. the development of uniform hazard response spectra for ground motion at the site; e. simulation of acceleration time histories compatible with uniform hazard response spectra. The following phase two in seismic design of NPP structures is the analysis of structural response for the design ground motion. This second phase of the process consists of the following steps： a. development of structural models of the plant buildings; b. development of the soil model underneath the plant buildings for soil-structure interaction response analysis; c. determination of in-structure response spectra for the plant buildings for the equipment response analysis. In the third phase of the seismic design and analysis the equipment is analyzed on the basis of in-structure response spectra. For this purpose the structural models of the mechanical components and piping in the plant are set up. In large 3D-structural models used today the heaviest equipment of the primary coolant circuit is included in the structural model of the reactor building. In the fourth phase the electrical equipment and automation and control equipment are seismically qualified with the aid of the in-structure spectra developed in the phase two using large three-axial shaking tables. For this purpose the smoothed envelope spectra for calculated in-structure spectra are constructed and acceleration time is fitted to these smoothed envelope spectra.     

Atomic phase diagram

Based on the Thomas-Fermi-Dirac-Cheng model, atomic phase diagram or electron density versus atomic radius diagram describing the interaction properties of atoms of different kinds in equilibrium state is developed. Atomic phase diagram is established based on the two-atoms model. Besides atomic radius, electron density and continuity condition for electron density on interfaces between atoms, the lever law of atomic phase diagram involving other physical parameters is taken into account, such as the binding energy, for the sake of simplicity.     

The effect of laser surface texturing on the tribological performance of different Sialon ceramic phases

A tribological performance was carried out on different types of hot press Sialon ceramics regarding the phases, i.e., the α-Sialon phase, the β-Sialon phase, and the α/β-Sialon composite phase. The different phases of Sialon ceramics were analyzed by XRD patterns. For the tribological performance, the Sialon ceramics were laser textured and the starved lubrication method was applied with different dimple pitches under a load of 10 N at room temperature. The material having a dimple pitch of 200 mm shows the lowest coefficient of friction. The α/β-Sialon composite phase shows the least coefficient of friction i.e. 0.04 and 0.1 for the textured and polished(without being textured) samples, respectively. The Sialon ceramics show mild wear and therefore, the wear rate of the steel ball(mating partner) was taken into account for the wear analysis. The α-Sialon phase having a higher hardness shows the least wear in comparison to the α/β-Sialon composite phase and the β-Sialon phase.     

High-frequency characterization of an optical phase modulator with phase modulation-to-intensity modulation conversion in dispersive fibers

We propose a new method for characterizing optical phase modulators based on phase modulation-to-intensity modulation (PM-to-IM) conversion in dispersive fibers.The fiber dispersion spectrally alters the relative phasing of the phase-modulated signal and leads to the PM-to-IM conversion,which is extended to measure the modulation efficiency of optical phase modulators.In the demonstration,the frequency-dependent modulation index and half-wave voltage are experimentally measured for a commercial phase modulator.Compared with conventional methods,the proposed method works without the restriction of small-signal operations,and allows swept-frequency measurement with high resolution and accuracy by using a vector network analyzer.     

X-ray diffraction investigation of amorphous calcium phosphate and hydroxyapatite under ultra-high hydrostatic pressure

The changes in the crystal structures of synthetically prepared amorphous calcium phosphate (ACP) and hydroxyapatite (HAP) in water (1:1 mass ratio) were studied by synchrotron X-ray diffraction (XRD) under ultra-high hydrostatic pressures as high as 2.34 GPa for ACP and 4 GPa for HAP. At ambient pressure, the XRD patterns of the ACP and HAP samples in capillary tubes and their environmental scanning electron micrographs indicated amorphous and crystalline characteristics for ACP and HAP, respectively. At pressures greater than 0.25 GPa, an additional broad peak was observed in the XRD pattern of the ACP phase, indicating a partial phase transition from an amorphous phase to a new high-pressure amorphous phase. The peak areas and positions of the ACP phase, as obtained through fitting of the experimental data, indicated that the ACP exhibited increased pseudo-crystalline behavior at pressures greater than 0.96 GPa. Conversely, no structural changes were observed for the HAP phase up to the highest applied pressure of 4 GPa. For HAP, a unit-cell reduction during compression was evidenced by a reduction in both refined lattice parameters a and c. Both ACP and HAP reverted to their original structures when the pressure was fully released to ambient pressure.     

Atomic-scale computer simulation for early precipitation process of Ni75Al10V15 alloy

The kinetic model for a ternary system is introduced based on the microscopic diffusion form of the phase-field equations for a binary alloy. The equation is solved in the reciprocal space. This model is used to investigate the early precipitation process of Ni75-Al10V15 by simulating the atomic pictures of the two ordered phases and calculating the order parameters of γ′(Ni3Al) phase. Simulation results show that the γ′ ordered phases precipitate from the disordered matrix by a non-classical nucleation mechanism, and the nonstoichiometric γ′ ordered phase appears first and then transforms into the stoichiometric one. Clusters of V atoms appear at the γ′ phase boundaries followed by the formation of the nonstoichiometric θ ordered phase. The farther the location from γ′ phase boundary is, the lower the order degree of θ phase is. There exist two kinds of DO22 ordered domains: a horizontal one and a vertical one, related to their adjacent γ′ phase boundaries. The model could describe the atomic ordering and composition clustering simultaneously, and any a priori assumption about the new phase structure and precipitation mechanism etc. is unnecessary.     

Finite Element Simulation of Metal Quenching

The evolution of the phase transformation and the resulting internal stresses and strains in metallic parts during quenching were modeled numerically. The numerical simulation of the metal quenching process was based on the metallo-thermo-mechanical theory using the finite element method to couple the temperature, phase transformation, and stress-strain fields. The numerical models are presented for the heat treatment and kinetics of the phase transformation. The finite element models and the phase transition kinetics accurately predict the distribution of the microstructure volume fractions, the temperature, the distortion, and the stress-strain relation during quenching. The two examples used to validate the models are the quenching of a small gear and of a large turbine rotor. The simulation results for the martensite phase volume fraction, the stresses, and the distortion in the gear agree well with the experimental data. The models can be used to optimize the quenching conditions to ensure product quality.     

一类三次Hamilton系统的相图

用定性理论方法研究了一类三次Hamilton系统的相图,得出该类系统的相图共有10种,并且给出了这10种相图.     

一类二次系统的全局相图

本文用定性分析研究了一类二次系统的全局相图 ,得出了该类系统的全局相图只有 8种 ,并且给出了这 8种全局相图     

广义Boussinesq方程的光滑孤子解和各种周期行波解

本文利用平面动力系统分支理论和Jacobi椭圆函数法,研究了一类广义Boussinesq方程.在不同的参数条件下,绘出了各种分支相图,利用这些相图,讨论了各种行波解的存在性.通过相图中的各种轨道,获得了孤立波,扭子波和周期波的精确解.     

一类二次微分系统的相图

用微分方程定性分析方法研究了叶彦谦教授提到的一类二次微分系统的相图,得出该类系统的相图共有9种,并且给出了这9种相图。     

一类四次系统的相图

用微用方程定性分析方法和分支方法研究一类四次系统，参数空间被划分，系统的相图被分成8类，具体相图被给出，数值模拟进一步验证了理论结果的正确性．     

一类平面二次系统的相图

用定性理论知识研究了一类平面二次系统的相图，得出该类系统的相图共有11种，并且给出了这11种相图。     

一类二次系统全局分析

本文给出了一类平面二次系统的全局相图。     

数学软件及分支方法在一类向量场中的应用

 用数学软件Mathematica和动力系统分支方法对一类四次平面向量场的相图进行研究,参数半平面被9条分支曲线分成10个区域,在软件Mathematica下,每一个区域和每一条分支曲线上的相图被计算机画出.所有相图共分成18类,从而得到了该向量场相图的完整分类.     

有界的平面五次多项式系统

平面多项式系统在动力系统理论研究中起着极重要的作用，目前很多问题需探索。文中从定性角度对平面五次多项式系统在无穷远赤道上只有孤立奇点时的有界性问题进行了讨论，并给出其所有可能的在无穷远点附近的相图，同时补充Ａ．Ｃｉｍａ和Ｊ．Ｌｌｉｂｒｅ一文中所遗漏的一个相图。     

一类具有Z2—等变性质的五次平面哈密顿向量场的全局性质

利用定性分析的方法，研究一类具有Z2－等变性质的五次哈密顿系统，画出了其全局相图。