Interactive Kalman Filtering for Differential and Gaussian Frequency Shift Keying Modulation with Application in Bluetooth

Some applications are constrained only to implement low cost receivers. In this case, designers are required to use less complex and non-expensive modulation techniques. Differential Quadrature Phase Shift Keying (DQPSK) and Gaussian Frequency Shift Keying (GFSK) can be non-coherently demodulated with simple algorithms. However, these types of demodulation are not robust and suffer from poor performance. This paper proposes a new method to enhance the performance of DQPSK and GFSK using Interactive Kalman Filtering (IKF) technique, in which a one Unscented Kalman Filter (UKF) and two Kalman Filters (KF) are coupled to optimize the demodulated signals. This method consists of simple but very effective algorithms without adding complexity to the demodulators comparing to other very complex methods. UKF is used in this method due to its superiority in approximating and estimating nonlinear systems and its ability to handle non-Gaussian noise environments. The proposed method has been validated by creating a MATLAB/SIMULINK Bluetooth system model, in which the IKF is integrated into the receiver, which implement both DQPSK and GFSK, and run simulation in Gaussian and Non-Gaussian noise environments. Results have shown the effectiveness of this method in optimizing the received signals, and that the UKF outperforms the Extended Kalman Filter (EKF).

A discussion of the bi-directional ranking of occurrence-frequency based non-interactive literature method for knowledge discovery

Based on the analysis of the existing ranking terminology or subject relevancy of documents methods through an intermediary collection as a catalyst(designated as Group B collection) for the purpose of of non-interactive literature-based discovery, this article proposes a bi-directional document occurrence frequency based ranking method according to the 'concurrence theory' and the degree and extent of the subject relevancy. This method explores and further refines the ranking method that is based on the occurrence frequency of the usage of certain terminologies and documents and injects a new insightful perspective of the concurrence of appropriate terminologies/documents in the 'low occurrence frequency component' of three non-interactive document collections. A preliminary experiment was conducted to analyze and to test the significance and viability of our newly designed operational method.

Improved frequency modeling and solution for parallel liquid-filled pipes considering both fluid-structure interaction and structural coupling

The dynamic characteristics of a single liquid-filled pipe have been broadly studied in the previous literature.The parallel liquid-filled pipe(PLFP)system is also widely used in engineering,and its structure is more complex than that of a single pipe.However,there are few reports about the dynamic characteristics of the PLFPs.Therefore,this paper proposes improved frequency modeling and solution for the PLFPs,involving the logical alignment principle and coupled matrix processing.The established model incorporates both the fluid-structure interaction(FSI)and the structural coupling of the PLFPs.The validity of the established model is verified by modal experiments.The effects of some unique parameters on the dynamic characteristics of the PLFPs are discussed.This work provides a feasible method for solving the FSI of multiple pipes in parallel and potential theoretical guidance for the dynamic analysis of the PLFPs in engineering.

Smartphone-based bridge frequency identification using vehicle contact-point response

Bridge frequency(BF)identification using the vehicle scanning method has attracted considerable attention during the last two decades.However,most previous studies have adopted unrealistic vehicle models,thus finding limited practical applications.This study proposes a smartphone-based BF identification method that uses the contact-point acceleration response of a four degree-of-freedom vehicle model.The said response can be inferred from the vehicle body response measured by a smartphone.For realizing practical applications,this method is incorporated into a self-developed smartphone app to obtain data smoothly and identify BFs in a timely manner.Numerical and experimental investigations are performed to verify the effectiveness of the proposed method.In particular,the robustness of this method is investigated numerically against various factors,including the vehicle speed,bridge span,road roughness,and bridge type.Furthermore,laboratory calibration tests are performed to investigate the accuracy of the smartphone gyroscope in measuring the angular velocity,where anomalous data are detected and eliminated.Laboratory experiment results for a simply supported bridge indicate that the proposed method can be used to identify the first two BFs with acceptable accuracy.

The Structure of Low Frequency Phenomena in the Tropics and Its Interaction with the Extratropics

The structure of planetary scale low freonency phenomena in the tropics is studied, and an attempt is made to determine its influence and interactions with phenomena at higher latitudes.In the tropics, it is found that the majority of the variance in the zonal wind structure is made up in wave numbers I and 2. During warm events in the Pacific Ocean, when the Southern Oscillation Index is negative, almost all of the variance resides in the gravest mode which undergoes a 40° eastward phase shift. Meanwhile, the second logitudinal mode almost disappears. On the other hand, the meridional wind field possesses maximum amplitude at higher wave numbers. However, near the equator,the amplitude is small with extreme values occurring in the subtropics. The difference in scale and the location of cxtrcma of the meridional and zonal wind components indicate that the tropical atmosphere is responding to two different driving mechanisms.Correlation analyses between variations of the zonal wind at reference points along the equator with variations of component elsewhere show that there are strong logitudinal connections. The strongest correlations between the tropics and higher latitudes exist in the region of the equatorial westerlies. In fact, stronger correlations occur between variations in U anywhere along the equator and the middle latitudes to the north and south of the equatorial westerlies than to the latitudes immediately to the north and south of the reference points. We interpret this 'remote' correlation pattern as indicating a two-stage teleconnection process which emphasizes the importance of the equatorial tropical westerlies of the Pacific Ocean as a 'corridor' of communication between the low and high latitudes. The regionality of the correlations confirms, to some extent, recent theoretical development regarding trapped equatorial modes. Finally, time lagged correlations from plus and minus six months between variations of U and OLR indicate that the interactions between the extratropics and low latitudes possess an organized sequence. The extratropical influence appears to propagate into the tropics followed by an eastward propagation along the equator. Finally, a propagation from the tropics to the extratropics in the upper troposphere occurs in the eastern Pacific Ocean. The time-lagged correlation sequence does not appear to be symmetric about the equator.

Changes in the natural frequency of a ferromagnetic rod in a magnetic field due to magnetoelastic interaction

Based on the magnetoelastic generalized variational principle and Hamilton＇s principle, a dynamic theoretical model characterizing the magnetoelastic interaction of a soft ferromagnetic medium in an applied magnetic field is developed in this paper. From the variational manipulation of magnetic scale potential and elastic displacement, all the fundamental equations for the magnetic field and mechanical deformation, as well as the magnetic body force and magnetic traction for describing magnetoelastic interaction are derived. The theoretical model is applied to a ferromagnetic rod vibrating in an applied magnetic field using a perturbation technique and the Galerkin method. The results show that the magnetic field will change the natural frequencies of the ferromagnetic rod by causing a decrease with the bending motion along the applied magnetic field where the magnetoelastic buckling will take place, and by causing an increase when the bending motion of the rod is perpendicular to the field. The prediction by the mode presented in this paper qualitatively agrees with the natural frequency changes of the ferromagnetic rod observed in the experiment.

Test particle simulations of resonant interactions between energetic electrons and discrete, multi-frequency artificial whistler waves in the plasmasphere

Modulated high frequency （HF） heating of the ionosphere provides a feasible means of artificially generating ex- tremely low frequency （ELF）/very low frequency （VLF） whistler waves, which can leak into the inner magnetosphere and contribute to resonant interactions with high energy electrons. Combining the ray tracing method and test particle simulations, we evaluate the effects of energetic electron resonant scattering driven by the discrete, multi-frequency arti- ficially generated ELF/VLF waves. The simulation results indicate a stochastic behavior of electrons and a linear profile of pitch angle and kinetic energy variations averaged over all test electrons. These features are similar to those associated with single-frequency waves. The computed local diffusion coefficients show that, although the momentum diffusion of relativistic electrons due to artificial ELF/VLF whistlers with a nominal amplitude of ~ 1 pT is minor, the pitch angle scattering can be notably efficient at low pitch angles near the loss cone, which supports the feasibility of artificial triggering of multi-frequency ELF/VLF whistler waves for the removal of high energy electrons from the magnetosphere. We also investigate the dependences of diffusion coefficients on the frequency interval （△f） of the discrete, multi-frequency waves. We find that there is a threshold value of Af for which the net diffusion coefficient of multi-frequency whistlers is inversely proportional to △f （proportional to the frequency components Nw） when △f is below the threshold value but it remains unchanged with increasing Af when △f is larger than the threshold value. This is explained as being due to the fact that the resonant scattering effect of broadband waves is the sum of the effects of each frequency in the ＇effective frequency band＇. Our results suggest that the modulation frequency of HF heating of the ionosphere can be appropriately selected with reasonable frequency intervals so that better performance of controlled precipitation of high energy electrons in the plasmasphere by artificial ELF/VLF whistler waves can be achieved.

RELATIONSHIPS BETWEEN DIFFERENT TROPICAL CONVECTIVE ACTIVITIES AND LOW FREQUENCY WAVE－MEAN FLOW INTERACTIONS

Based on ECMWF objective analysis data, and with use of Batterworth bandpass-filtered skill and diagnostic analysis method, the interaction characteristics of low frequency wave and mean flow in midlatitudes during the winter years of 1983 / 1984 and 1986 / 1987 have been studied in this paper. The main results point out the important role of the tropical convective activity on the above mentioned interaction process.

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.

A study of inner-outer interactions in turbulent channel flows by interactive POD

The amplitude and frequency modulation of near-wall flow structures by the large-scale motions in outer regions is studied in turbulent channel flows. The proper orthogonal decomposition(POD) method is applied to investigate the interactions between the near-wall motions and the large-scale flow modes of the outer regions based on two datasets from direct numerical simulation of turbulent channel flows at Reynolds numbers of 550–10 0 0. The fluctuations in the fields u+, v+, w+ and Reynolds shear stress-(uv)+ are studied to understand the mechanism of amplitude and frequency modulation of the nearwall structures by the outer large-scale motions. The amplitude modulation coefficient of the Reynolds shear stress is larger than that of the velocity components. The frequency modulation effect has an opposite influence in the spanwise direction compared to the streamwise direction. The streamwise characteristic frequency increases with increasing large-scale velocity. However, the spanwise characteristic frequency exhibits a decreasing trend with increasing large-scale velocity in the near-wall region.

Does communication increase investors’trading frequency?Evidence from a Chinese social trading platform

This study examines the impact of communication on investors’trading frequency based on a unique dataset drawn from a Chinese social trading platform.We find robust evidence that real-account portfolio owners on the platform trade more frequently under the influence of the comments posted by their leaders(the owners of portfolios they have followed).Moreover,portfolio owners are more sensitive to the quantity than to the tone of leaders’comments.Finally,both trading frequency and leaders’comments negatively impact portfolio owners’future performance.Our find-ings support the notion that social interaction promotes active investment strategies.

Spin wave resonance frequency in bilayer ferromagnetic films with the biquadratic exchange interaction

The dependences of spin wave resonance(SWR)frequency on the surface anisotropy field,interface exchange coupling,symmetry,biquadratic exchange(BQE)interaction,film thickness,and the external magnetic field in bilayer ferromagnetic films are theoretically analyzed by employing the linear spin wave approximation and Green’s function method.A remarkable increase of SWR frequency,except for energetically lower two modes,can be obtained in our model that takes the BQE interaction into account.Again,the effect of the external magnetic field on SWR frequency can be increased by increasing the biquadratic to interlayer exchange ratio.It has been identified that the BQE interaction is of utmost importance in improving the SWR frequency of the bilayer ferromagnetic films.In addition,for bilayer ferromagnetic films,the frequency gap between the energetically highest mode and lowest mode is found to increase by increasing the biquadratic to interlayer exchange ratio and film thickness and destroying the symmetry of the system.These results can be used to improve the understanding of magnetic properties in bilayer ferromagnetic films and thus may have prominent implications for future magnetic devices.

软黏土中含桩地下结构地震响应离心试验模拟

针对大空间含桩地下结构(如地下车行系统)在地震作用下的动力响应特性以及场地震陷、结构上浮等危害展开离心振动台试验。试验采用饱和软黏土作为地基土,设计了自由场、整体浅埋地下结构以及等效单元浅埋地下结构3种试验情况,利用层状剪切箱消除边界反射效应,在50g的离心加速度下开展水平地震试验。试验结果表明,不同结构在地震过程中会产生自振在特定的频率区段放大响应,在整体质量、静态浮力及转动惯量等效的前提下,整体结构相对单元结构形式能够降低地震作用下结构的自振效应,且整体结构具有更好地震后抗浮性能。

基于流固耦合的卡车油箱振动特性研究

卡车油箱在使用过程中,存在因振动产生本体及焊缝开裂的问题。针对某400 L卡车柴油油箱,基于流固耦合理论,运用ANSYS软件分析油箱的振动特性。锤击法模态试验和仿真模态分析结果,仿真与试验测得的结构模态参数数据误差最大为13%,仿真的准确性得到验证。油箱结构自由状态下计算得到的前6阶固有频率略大于油箱安装状态下的固有频率,油箱固有频率会随着液体含量的增加而降低。油箱的固有频率在液体量从0到100 L以及300到400 L这两阶段变化明显。油箱充液比低于1/2时,油箱结构的各阶固有频率均高于危险区域的频率,不会产生共振。充液量大于3/4时固有频率接近于30 Hz的标准规定值,存在共振风险。油箱设计时,应优化油箱的结构,使其在充满液量时也能避开30 Hz标准值,更为安全。

非单频声场中耦合双泡振动特性研究

利用Keller-Miksis方程,计算了初始半径分别为2、5μm的耦合气泡在非单频声场中气泡半径、次Bjerknes力的变化规律.计算结果表明,非单频驱动声场中耦合双泡的半径、次Bjerknes力与驱动声压幅值、声压幅值之比、驱动频率有关.当声压幅值比、驱动频率一定时,驱动声压越大,最大膨胀半径越大、次Bjerknes力越大;驱动声压、驱动频率一定时,声压幅值比越大,最大膨胀半径越大、次Bjerknes力越大;当驱动声压的振幅、声压幅值比一定时,驱动频率越大,最大膨胀半径越小、次Bjerknes力越小.

社区尺度斜入射波场下场地-建筑群耦合作用模拟方法

场地-城市相互作用(site-city interaction,SCI)效应会显著改变场地地震波场分布及建筑反应,基于SCI效应理论计算研究方法的发展现状,发挥谱元(spectral element,SE)法可快速高效求解三维地震波场传播和多自由度(multi-degree of freedom,MDOF)模型计算量小且可同时模拟大量建筑的优势,同时,结合频率波数域(frequency wave number analysis,FK)方法,以等效地震荷载的方式施加地震波场,建立了FK-SE-MDOF耦合方法,实现了SE-MDOF耦合模型中多种波型(P波、SV波和SH波)的斜入射输入,解决了当前三维SCI效应研究方法中未能同时考虑建筑非线性、频谱特性、地震波波型及入射角度影响的问题。首先对方法原理进行了介绍;然后,通过与振动台试验的对比,验证了方法的正确性;进而,采用该方法建立理想场地-城市建筑群相互作用耦合模型,主要探讨了入射角度和地震波波型对SCI效应的影响,得到了一些有益结论。该方法较为真实地反映SCI效应影响的同时,可反映建筑基础轮廓对地震波场的影响,适用于需考虑建筑轮廓信息的社区尺度SCI效应研究,可为城市规划、抗震设计、风险评估以及震后救援等工作提供定量指导。

离子液体[Bmim][BF_(4)]与氧化苯乙烯分子间相互作用及催化机理的和频振动光谱研究

离子液体作为多用途的反应介质和催化剂,在绿色化学和可持续化学领域引起了广泛的关注.本文采用和频产生振动光谱技术,深入研究了1-丁基-3-甲基咪唑四氟硼酸盐([Bmim][BF_(4)])与苯乙烯氧化物(SO)在空气/液体界面上的相互作用:在1000~3700cm^(-1)的光谱范围内,仅观察到了体系中碳氢键的振动模式.值得注意的是,研究发现苯乙烯氧化物的环氧环的取向是朝向体相的,而阳离子的咪唑环上的三个碳氢基则平行于界面表面,因此,在该体系中并未观察到阳离子与苯乙烯氧化物之间的相互作用.然而,在C-H键的振动谱中,发现CH(SO)和CH_(3)(阳离子)的振动光谱峰发生蓝移,这证明了阴离子BF4与环氧环上的CH_(2)基团之间存在相互作用,这种相互作用证实了离子液体首先催化苯乙烯氧化物并随后与CO_(2)反应的反应机制.本研究为反应界面的分子间相互作用和分子取向提供了重要的见解.

高压隔膜泵单向阀流固耦合建模与振动特性研究

针对单向阀开启过程中强迫振动产生的根源和流激振动问题,构建了开度为5%、15%、30%、50%、75%和100%的流固耦合仿真模型,对不同开度情况下的流体与固体场特性以及流体施加于阀芯上的流激振力进行数值分析,得到了流场压力云图、速度矢量云图和流激振力脉动峰值频率以及阀芯在各开度下的模态振型和固有频率。结果表明:单向阀开启过程中,阀芯两侧存在较大的压差,变形区域主要集中于胶垫,阀腔内高速流体与低速流体接触时出现剪切形成涡流,流动涡流周期性变化产生的流激振力导致阀芯被迫振动,阀芯上的流激振力脉动峰值频率分布范围逐渐增加且波动更大。

荷载作用下砂土边坡-管道相互作用试验研究

随着我国西气东输、南水北调等重大工程的快速推进,埋地管道不可避免地会穿越高陡山区,并受到区域地形地貌的影响,而关于边坡-管道相互作用机制的认识还相对滞后,相关研究亟需加强。基于分布式光纤应变传感(distributed strain sensing,简称DSS)、粒子图像测速(particle image velocimetry,简称PIV)技术,开展加载工况下砂土边坡-管道相互作用的室内模型试验,探究了临坡地基极限承载力的影响因素,并研究了不同坡角下边坡土体变形破坏机制及埋地管道的结构响应特征。研究结果表明:(1)临坡地基经历了弹性压密、局部剪切和整体破坏3个阶段,并呈现不对称楔形破坏模式;(2)临坡地基极限承载力随着坡角的增大呈减小趋势,同一坡角下埋地管道的存在会降低临坡地基极限承载力;(3)管道对边坡滑裂面形成路径的影响程度随着坡角的增大而变大;(4)在荷载作用下埋地管道横截面环向应变呈“椭圆化”分布,据此提出了管周界面土抗力的简化计算模型与椭圆度计算式。相关结论对边坡-管道系统的变形控制与结构设计有一定的参考和借鉴意义。