Mechanical Fault Diagnosis Based on Band-phase-randomized Surrogate Data and Multifractal

The vibration signals of machinery with various faults often show clear nonlinear characteristics.Currently,fractal dimension analysis as the common useful method for nonlinear signal analysis,is a kind of single fractal form,which only reflects the overall irregularity of signals,but cannot describe its local scaling properties.For comprehensive revealing of internal properties,a combinatorial method based on band-phase-randomized（BPR） surrogate data and multifractal is introduced.BPR surrogate data method is effective to eliminate nonlinearity in specified frequency band for a fault signal,which can be utilized to detect nonlinear degree in whole fault signal by nonlinear titration method,and the overall nonlinear distribution of fault signal is displayed in nonlinear characteristic curve that can be used to analyze the fault signal qualitatively.Then multifractal theory as a quantitative analysis method is used to describe geometrical characteristics and local scaling properties,and asymmetry coefficient of multifractal spectrum and multifractal entropy for fault signals are extracted as new criterions to diagnose machinery faults.Several typical faults include rotor misalignment,transversal crack,and static-dynamic rubbing fault are analyzed,and the results indicate that those faults can be distinguished by the proposed method effectively,which provides a qualitative and quantitative analysis way in the field of machinery fault diagnosis.

Comparison of the Observation Capability of an X-band Phased-array Radar with an X-band Doppler Radar and S-band Operational Radar

An X-band phased-array meteorological radar （XPAR） was developed in China and will be installed in an airplane to observe precipitation systems for research purposes.In order to examine the observational capability of the XPAR and to test the operating mode and calibration before installation in the airplane,a mobile X-band Doppler radar （XDR） and XPAR were installed at the same site to observe convective precipitation events.Nearby S-band operational radar （SA） data were also collected to examine the reflectivity bias of XPAR.An algorithm for quantitative analysis of reflectivity and velocity differences and radar sensitivity of XPAR is presented.The reflectivity and velocity biases of XPAR are examined with SA and XDR.Reflectivity sensitivities,the horizontal and vertical structures of reflectivity by the three radars are compared and analyzed.The results indicated that while the XPRA with different operating modes can capture the main characteristic of 3D structures of precipitation,and the averaged reflectivity differences between XPAR and XDR,and XDR and SA,were 0.4 dB and 6.6 dB on 13 July and-4.5 dB and 5.1 dB on 2 August 2012,respectively.The minimum observed reflectivities at a range of 50 km for XPAR,XDR and SA were about 15.4 dBZ,13.5 dBZ and-3.5 dBZ,respectively.The bias of velocity between XPAR and XDR was negligible.This study provides a possible method for the quantitative comparison of the XPAR data,as well as the sensitivity of reflectivity,calibration,gain and bias introduced by pulse compression.

Deformation, Phase Transformation and Recrystallization in the Shear Bands Induced by High-Strain Rate Loading in Titanium and Its Alloys

α-titanium and its alloys with a dual-phase structure （α＋β） were deformed dynamically under strain rate of about 10^4 s^-1. The formation and microstructural evolution of the localized shear bands were characterized by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. The results reveal that both the strain and strain rate should be considered simultaneously as the mechanical conditions for shear band formation, and twinning is an important mode of deformation. Both experimental and calculation show that the materials within the bands underwent a superhigh strain rate （9×10^5 S^-1） deformation, which is two magnitudes of that of average strain rate required for shear band formation; the dislocations in the bands can be constricted and developed into cell structures; the phase transformation from α to α2 within the bands was observed, and the transformation products （α2） had a certain crystallographic orientation relationship with their parent; the equiaxed grains with an average size of 10 μm in diameter observed within the bands are proposed to be the results of recrystallization.

PHASE CORRECTION AND BAND-PASS FILTERS IN CT IMAGING

This paper reports the use of the fast Fourier transform (FFT) in the direct Fourier transform method (DFM) in Computerized Tomography (CT) reconstruction. Phase corrections are needed in the CT reconstruction. In order to eliminate the image distortion from the basic DFM, Padding and band-pass filters are used in the improved DFM. Finally, some reconstructions from simulated projections and several experimental results are given.

Discrimination of Motor Imagery Patterns by Electroencephalogram Phase Synchronization Combined With Frequency Band Energy

Central nerve signal evoked by thoughts can be directly used to control a robot or prosthetic devices without the involvement of the peripheral nerve and muscles.This is a new strategy of human-computer interaction.A method of electroencephalogram(EEG) phase synchronization combined with band energy was proposed to construct a feature vector for pattern recognition of brain-computer interaction based on EEG induced by motor imagery in this paper,rhythm and beta rhythm were first extracted from EEG by band pass filter and then the frequency band energy was calculated by the sliding time window;the instantaneous phase values were obtained using Hilbert transform and then the phase synchronization feature was calculated by the phase locking value(PLV) and the best time interval for extracting the phase synchronization feature was searched by the distribution of the PLV value in the time domain.Finally,discrimination of motor imagery patterns was performed by the support vector machine(SVM).The results showed that the phase synchronization feature more effective in4s-7s and the correct classification rate was 91.4%.Compared with the results achieved by a single EEG feature related to motor imagery,the correct classification rate was improved by 3.5 and4.3 percentage points by combining phase synchronization with band energy.These indicate that the proposed method is effective and it is expected that the study provides a way to improve the performance of the online real-time brain-computer interaction control system based on EEG related to motor imagery.

Cognitive anti-jamming receiver under phase noise in high frequency bands

This paper investigates the jamming sensing performance of the simultaneous transmit and receive based cognitive anti-jamming(SCAJ) receiver impaired by phase noise in local oscillators(LO) over fading channels. Firstly, energy detection(ED)based on the jamming to noise ratio(JNR) of the high frequency bands SCAJ receiver with phase noise under different channels is analyzed. Then, the probabilities of jamming detection and false alarm in closed-form for the SCAJ receiver are derived. Finally,the modified Bayesian Cramer-Rao bound(BCRB) of jamming sensing for the SCAJ receiver is presented. Simulation results show that the performance degradation of the SCAJ system due to phase noise is more severe than that due to the channel fading in the circumstances where the signal bandwidth(BW) is kept a constant. Moreover, the signal BW has an effect on the phase noise in LO, and the jamming detection probability of the wideband SCAJ receiver with lower phase noise outperforms that of the narrowband receiver using the same center frequency. Furthermore,an accurate phase noise estimation and compensation scheme can improve the jamming detection capability of the SCAJ receiver in high frequency bands and approach to the upper bound.

Evaluation of Energy Band Gap, Thermal Conductivity, Phase Transition Temperature and Elastic Response of PS/CdS Semiconducting Optical Nanocomposite

Thick film of Polystyrene (PS)/CdS semiconducting optical nanocomposite has been synthesized by dispersing nanofiller particles of CdS in PS matrix. The nanostructure of the CdS particles has been ascertained through X-ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Small angle x-ray scattering analysis has been performed in order to ascertain nanocomposite character of the PS/CdS sample. Scanning Electron Microscopy (SEM) analyses of these samples have been carried out to establish the surface morphology. Optical Absorption Spectroscopy is used to measure the energy band gap of PS/CdS nanocomposite by using Tauc relation whereas Transient Plane Source Technique is used for the determination of thermal conductivity of the prepared samples. The phase transition temperature and elastic response of the prepared samples have been ascertained through Dynamic Mechanical Analyzer (DMA). This study reveals that the thermal conductivity, Young’s modulus and the toughness of the material are greatly influenced by the existence of interfacial energetic interaction between dispersed CdS nanofiller particles and matrix of PS.

Phase field modeling of the ring-banded spherulites of crystalline polymers: The role of thermal diffusion

The ring-banded spherulite is a special morphology of polymer crystals and has attracted considerable attention over recent decades. In this study, a new phase field model with polymer characteristics is established to investigate the emergence and formation mechanism of the ring-banded spherulites of crystalline polymers. The model consists of a nonconserved phase field representing the phase transition and a temperature field describing the diffusion of the released latent heat. The corresponding model parameters can be obtained from experimentally accessible material parameters.Two-dimensional calculations are carried out for the ring-banded spherulitic growth of polyethylene film under a series of crystallization temperatures. The results of these calculations demonstrate that the formation of ring-banded spherulites can be triggered by the self-generated thermal field. Moreover, some temperature-dependent characteristics of the ring-banded spherulites observed in experiments are reproduced by simulations, which may help to study the effects of crystallization temperature on the ring-banded structures.

Prediction of shear bands in sand based on granular flow model and two-phase equilibrium

In contrast to the traditional interpretation of shear bands in sand as a bifurcation problem in continuum mechanics,shear bands in sand are considered as high-strain phase(plastic phase) of sand and the materials outside the bands are still in low-strain phase(elastic phase),namely,the two phases of sand can coexist under certain condition.As a one-dimensional example,the results show that,for materials with strain-softening behavior,the two-phase solution is a stable branch of solutions,but the method to find two-phase solutions is very different from the one for bifurcation analysis.The theory of multi-phase equilibrium and the slow plastic flow model are applied to predict the formation and patterns of shear bands in sand specimens,discontinuity of deformation gradient and stress across interfaces between shear bands and other regions is considered,the continuity of displacements and traction across interfaces is imposed,and the Maxwell relation is satisfied.The governing equations are deduced.The critical stress for the formation of a shear band,both the stresses and strains inside the band and outside the band,and the inclination angle of the band can all be predicted.The predicted results are consistent with experimental measurements.

A Novel Receiving Method for Baseband DSSS Signal based on Phase Domain Processing

In this paper, the phase characteristic disturbance model for baseband direct sequence spread spectrum (DSSS) signal in additive white Gaussian noise (AWGN) environment is established, and the probability density function (PDF) of phase characteristic disturbance is obtained. Then a novel receiver model for baseband DSSS signal based on maximum likelihood (ML) criterion is proposed. The simulation results show that, comparing with correlation scheme, the performance of the proposed method for baseband DSSS signal is 1dB worse in AWGN environment. However, if there is narrow interference in the AWGN environment, the proposed method will show better performance up to 2.5dB, and it has good adaptive resistance to narrowband interference located in different frequency points. This method could be used as an alterative communication scheme for military circumstance when existing strong narrowband interference of various frequencies.

磁性形状记忆合金Mn_2NiGa band Jahn-Teller效应的第一性原理研究

运用第一性原理的方法,研究了磁性形状记忆合金Mn_2NiGa在马氏体相变中晶格结构、磁结构、Mn原子d电子结构的变化.研究表明,伴随Mn_2NiGa马氏体相变的发生,形成了一个由两根长键及四根短键组成的拉长八面体结构,即产生了沿z轴拉长的Jahn-Teller畸变;在相变时,位于八面体中心的Mn原子的磁矩发生显著的变化,而作为配体的Ni、Ga原子的磁矩变化很微小;Jahn-Teller畸变的发生,是由于晶体的畸变使配住场产生变化,导致Mn原子d电子态密度重新分布,从而使e_g和t_(2g)能级分裂所致.

Effect of Pressure on Cesium Iodide Band Gap

The evolution of cesium iodide band gap as a function of pressure is studied in the range from 0 to 60 GPa. Within this range, two structural phase transitions occurred, and the band gap was affected by the compression pressure and structural rearrangement. The band gap estimation under pressure, as obtained by the density functional theory methods, successfully reproduced the experimental trend of the optical gap and electrical resistivity, namely, a general decreasing tendency, an early maximum, and a discontinuous peak around 40 GPa.

A phase-field model for simulating various spherulite morphologies of semi-crystalline polymers

A modified phase-field model is proposed for simulating the isothermal crystallization of polymer melts. The model consists of a second-order phase-field equation and a heat conduction equation. It obtains its model parameters from the real material parameters and is easy to use with tolerable computational cost. Due to the use of a new free energy functional form, the model can reproduce various single crystal morphologies of polymer melts under quiescent conditions, including dendritic, lamellar branching, ring-banded, breakup of ring-banded, faceted hexagonal, and spherulitic structures. Simulation results of isotactic polystyrene crystals demonstrate that the present phase-field model has the ability to give qualitative predictions of polymer crystallization under isothermal and quiescent conditions.

HIGH-ACCURACY BAND TO BAND REGISTRATION METHOD FOR MULTI-SPECTRAL IMAGES OF HJ-1A/B

Band-to-band registration accuracy is an important parameter of multispectral data. A novel band-to-band registration approach with high precision is proposed for the multi-spectral images of HJ-1A/B. Firstly, the main causes resulted in misregistration are analyzed, and a high-order polynomial model is proposed. Secondly, a phase fringe filtering technique is employed to Phase Correlation Method based on Singular Value Decomposition (SVD-PCM) for reducing the noise in phase difference matrix. Then, experiments are carried out to build nonlinear registration models, and images of green band and red band are aligned to blue band with an accuracy of 0.1 pixels, while near infrared band with an accuracy of 0.2 pixels.

Phase transition,structural and thermodynamic properties of Mg_2 Si polymorphs

The plane-wave pseudo-potential method within the framework of first principles is used to investigate the structural and elastic properties of Mg2Si in its intermediate pressure （Pnma） and high pressure phases （P63/mrnc）. The lattice constants, the band structures. The bulk moduli of the Mg2Si polymorphs are presented and discussed. The phase transition from anti-cotunnite to Ni2In-type Mg2Si is successfully reproduced using a vibrational Debye-like model. The phase boundary can be described as P = 24.02994 ＋ 3.93 × 10^-3T -- 4.66816 × 10^-5T2 -- 2.2501 × 10^-9T3＋ 2.33786 × 10^-11T4. To complete the fundamental characteristics of these polymorphs we have analysed thermodynamic properties, such as thermal expansion and heat capacity, in a pressure range of 1-40 GPa and a temperature range of 0-1300 K. The obtained results tend to support the available experimental data and other theoretical results. Therefore, the present results indicate that the combination of first principles and a vibrational Debye-like model is an efficient scheme to simulate the high temperature behaviours of Mg2Si.

FREQUENCY OPTIMIZATION APPROACH FOR DESIGNING M-BAND BIORTHOGONAL SYMMETRIC WAVELETS

In this paper,a new method is presented for designing M-band biorthogonal symmetric wavelets.The design problem of biorthogonal linear-phase scaling filters and wavelet filters as a quadratic programming problem with the linear constraints is formulated.The closed-form solution is given and a design example is presented.

Energy Band-gap Calculation of d-Ta_2O_5 Using sX-LDA and B3LYP Methods

The energy band-gap and related factors of tantalum pentoxide with hexagonal phase were investigated using hybrid functional B3LYP and sX-LDA methods. The results showed that both sX-LDA and B3LYP techniques reveal the indirect semiconductor nature of δ-Ta2O5, whereas the obtained value of energy band-gap is much higher than previous theoretical reports but closer to the experimental data. The optical band- gap of δ-Ta2O5 is expected to originate from the O 2p→Ta 5d transition which may benefit from the d-s-p hybridization.

水利测雨雷达的应用优势与挑战

监测近地面2 km以下“云中雨”的测雨雷达,是水利行业以流域为单元建设雨水情监测预报“第一道防线”的重要内容,也是实现洪水防御关口前移、防线外推的重要举措。总结了水利测雨雷达的发展历程和技术特点,评估了河北大清河流域和湖南捞刀河、浏阳河流域试点应用中测雨雷达对强降水监测的精度,阐述了水利测雨雷达在雨水情监测预警方面的技术优势,并对进一步发展水利测雨雷达监测系统提出了建议。

A Subthreshold Low-Voltage Low-Phase-Noise CMOS LC-VCO with Resistive Biasing

This paper presents a low-phase-noise LC voltage-controlled oscillator (LC-VCO) with top resistive biasing in subthreshold region. The subthreshold LC-VCO has low-power and low-phase-noise due to its high transconductance efficiency and low gate bias condition. The top resistive biasing has more benefit with the feature of phase noise than MOS current source since it can support the low-noise characteristics and large output swing. The LC-VCO designed in 130-nm CMOS process with 0.7-V supply voltage achieves phase noise of -116 dBc/Hz at 200 kHz offset with tuning range of 398 MHz to 408 MHz covering medical implant communication service (MICS) band.

Electronic properties and topological phases of ThXY(X= Pb, Au, Pt and Y= Sb, Bi, Sn) compounds

The electronic properties and topological phases of ThXY （X = Pb, Au, Pt, Pd and Y = Sb, Bi, Sn） compounds in the presence of spin-orbit coupling, using density functional theory are investigated. The ThPtSn compound is stable in the ferromagnetic phase and the other ThXY compounds are stable in nonmagnetic phases. Band structures of these compounds in topological phases （insulator or metal） and normal phases within generalized gradient approximation （GGA） and Engel- Vosko generalized gradient approximation （GGA_EV） are compared. The ThPtSn, ThPtBi, ThPtSb, ThPdBi, and ThAuBi compounds have topological phases and the other ThXY compounds have normal phases. Band inversion strengths and topological phases of these compounds at different pressure are studied. It is seen that the band inversion strengths of these compounds are sensitive to pressure and for each compound a second-order polynomial fitted on the band inversion strengths-pressure curves.