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Search Results: 1 - 10 of 348993 matches for " X. R. Wang "
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A Control Strategy for Smoothing Active Power Fluctuation of Wind Farm with Flywheel Energy Storage System Based on Improved Wind Power Prediction Algorithm  [PDF]
J. C. Wang, X. R. Wang
Energy and Power Engineering (EPE) , 2013, DOI: 10.4236/epe.2013.54B075
Abstract: The fluctuation of active power output of wind farm has many negative impacts on large-scale wind power integration into power grid. In this paper, flywheel energy storage system (FESS) was connected to AC side of the doubly-fed induction generator (DFIG) wind farm to realize smooth control of wind power output. Based on improved wind power prediction algorithm and wind speed-power curve modeling, a new smooth control strategy with the FESS was proposed. The requirement of power system dispatch for wind power prediction and flywheel rotor speed limit were taken into consideration during the process. While smoothing the wind power fluctuation, FESS can track short-term planned output of wind farm. It was demonstrated by quantitative analysis of simulation results that the proposed control strategy can smooth the active power fluctuation of wind farm effectively and thereby improve power quality of the power grid.
A thermodynamic theory for thermal-gradient-driven domain wall motion
X. S. Wang,X. R. Wang
Physics , 2014, DOI: 10.1103/PhysRevB.90.014414
Abstract: Spin waves (or magnons) interact with magnetic domain walls (DWs) in a complicated way that a DW can propagate either along or against magnon flow. However, thermally activated magnons always drive a DW to the hotter region of a nanowire of magnetic insulators under a temperature gradient. We theoretically illustrate why it is surely so by showing that DW entropy is always larger than that of a domain as long as material parameters do not depend on spin textures. Equivalently, the total free energy of the wire can be lowered when the DW moves to the hotter region. The larger DW entropy is related to the increase of magnon density of states at low energy originated from the gapless magnon bound states.
Domain Walls as Spin Wave Waveguides
X. S. Wang,X. R. Wang
Physics , 2015,
Abstract: We numerically demonstrate that domain walls can be used as spin wave waveguides. We show that gapless spin waves bounded inside a domain wall can be guided by the domain wall. For Bloch walls, we further show that the bound spin waves can pass through Bloch lines and corners without reflection. This finding makes domain-wall-based spin wave devices possible.
Spin Wave Emission in Field-Driven Domain Wall Motion
X. S. Wang,X. R. Wang
Physics , 2014, DOI: 10.1103/PhysRevB.90.184415
Abstract: A domain wall (DW) in a nanowire can propagate under a longitudinal magnetic field by emitting spin waves (SWs). We numerically investigated the properties of SWs emitted by the DW motion, such as frequency and wavenumber, and their relation with the DW motion. For a wire with a low transverse anisotropy and in a field above a critical value, a DW emits SWs to both sides (bow and stern), while it oscillates and propagates at a low average speed. For a wire with a high transverse anisotropy and in a weak field, the DW emits mostly stern waves, while the DW distorts itself and DW center propagates forward like a drill at a relative high speed.
Light Emitting Diodes of Inverse Spin Valves
X. R. Wang
Physics Research International , 2008, DOI: 10.1155/2008/434936
Abstract: Light emitting diodes made out of inverse spin valves of a ferromagnetic half metal sandwiched between two nonmagnetic metals are proposed. Based on a giant spin-dependent chemical potential difference created under an external bias, the inverse spin valves are possible to emit light when electrons with the higher chemical potential flip their spins and become the electrons of the opposite spin with the lower chemical potential. The frequency of this type of light emitting diodes is tunable by the bias.
Giant dynamical Zeeman split in inverse spin valves
X. R. Wang
Physics , 2008,
Abstract: The inversion of a spin valve device is proposed. Opposite to a conventional spin valve of a non-magnetic spacer sandwiched between two ferromagnetic metals, an inverse spin valve is a ferromagnet sandwiched between two non-magnetic metals. It is predicted that, under a bias, the chemical potentials of spin-up and spin-down electrons in the metals split at metal-ferromagnet interfaces, a dynamical Zeeman effect. This split is of the order of an applied bias. Thus, there should be no problem of generating an $eV$ split that is not possible to be realized on the earth by the usual Zeeman effect.
Asymptotic results on the product of random probability matrices
X. R. Wang
Physics , 1997,
Abstract: I study the product of independent identically distributed $D\times D$ random probability matrices. Some exact asymptotic results are obtained. I find that both the left and the right products approach exponentially to a probability matrix(asymptotic matrix) in which any two rows are the same. A parameter $\lambda$ is introduced for the exponential coefficient which can be used to describe the convergent rate of the products. $\lambda$ depends on the distribution of individual random matrices. I find $\lambda = 3/2$ for D=2 when each element of individual random probability matrices is uniformly distributed in [0,1]. In this case, each element of the asymptotic matrix follows a parabolic distribution function. The distribution function of the asymptotic matrix elements can be numerically shown to be non-universal. Numerical tests are carried out for a set of random probability matrices with a particular distribution function. I find that $\lambda$ increases monotonically from $\simeq 1.5$ to $\simeq 3$ as D increases from 3 to 99, and the distribution of random elements in the asymptotic products can be described by a Gaussian function with its mean to be 1/D.
Noninvasive Blood Glucose Measurement Based on NIR Spectrums and Double ANN Analysis  [PDF]
D. X. Guo, Y. Z. Shang, R. Peng, S. S. Yong, X. A. Wang
Journal of Biosciences and Medicines (JBM) , 2015, DOI: 10.4236/jbm.2015.36007
Abstract:

This paper presents a new noninvasive blood glucose monitoring method based on four near infrared spectrums and double artificial neural network analysis. We choose four near infrared wavelengths, 820 nm, 875 nm, 945 nm, 1050 nm, as transmission spectrums, and capture four fingers transmission PPG signals simultaneously. The wavelet transform algorithm is used to remove baseline drift, smooth signals and extract eight eigenvalues of each PPG signal. The eigenvalues are the input parameters of double artificial neural network analysis model. Double artificial neural network regression combines the classification recognition algorithm with prediction algorithm to improve the accuracy of measurement. Experiments show that the root mean square error of the prediction is between 0.97 mg/dL - 6.69 mg/dL, the average of root mean square error is 3.80 mg/dL.

Negative Magnetoresistance in the Nearest-neighbor Hopping Conduction
X. R. Wang,X. C. Xie
Physics , 1997,
Abstract: We propose a size effect which leads to the negative magnetoresistance in granular metal-insulator materials in which the hopping between two nearest neighbor clusters is the main transport mechanism. We show that the hopping probability increases with magnetic field. This is originated from the level crossing in a few-electron cluster. Thus, the overlap of electronic states of two neighboring clusters increases, and the negative magnetoresistance is resulted.
A direct calculation of critical exponents of two-dimensional anisotropic Ising model
Gang Xiong,X. R. Wang
Physics , 2005, DOI: 10.1088/0253-6102/45/5/033
Abstract: Using an exact solution of the one-dimensional (1D) quantum transverse-field Ising model (TFIM), we calculate the critical exponents of the two-dimensional (2D) anisotropic classical Ising model (IM). We verify that the exponents are the same as those of isotropic classical IM. Our approach provides an alternative means of obtaining and verifying these well-known results.
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