Interaction between a screw dislocation and an elliptical hole with two asymmetrical cracks in a one-dimensional hexagonal quasicrystal with piezoelectric effect

The interaction between a screw dislocation and an elliptical hole with two asymmetrical cracks in a one-dimensional(1 D) hexagonal quasicrystal with piezoelectric effect is considered. A general formula of the generalized stress field, the field intensity factor, and the image force is derived, and the special cases are discussed. Several numerical examples are given to show the effects of the material properties and the dislocation position on the field intensity factors and the image forces.

Vector tracking loops in GNSS receivers for dynamic weak signals

Vehicle positioning with the global navigation satellite system （GNSS） in urban environments faces two problems which are attenuation and dynamic. For traditional GNSS receivers hardly able to track dynamic weak signals, the coupling between all visible satellite signals is ignored in the absence of navigation state feedback, and thermal noise error and dynamic stress threshold are contradictory due to non-coherent discriminators. The vector delay/frequency locked loop （VDFLL） with navigation state feedback and the joint vector tracking loop （JVTL） with coherent discriminator which is a synchronization parameter tracking loop based on maximum likelihood estimation （MLE） are proposed to improve the tracking sensitivity of GNSS receiver in dynamic weak signal environments. A joint vector position tracking loop （JVPTL） directly tracking user position and velocity is proposed to further improve tracking sensitivity. The coherent navigation parameter discriminator of JVPTL, being able to ease the contradiction between thermal noise error and dynamic stress threshold, is based on MLE according to the navigation parameter based linear model of received baseband signals. Simulation results show that JVPTL, which combines the advantages of both VDFLL and JVTL, performs better than both VDFLL and JVTL in dynamic weak signal environments.

A GNSS Anti-Spoofing Technique Based on the Spatial Distribution Characteristic of the Residual Vectors

Anti-spoofing is becoming a crucial technique for applications with high navigation accuracy and reliability requirements.Anti-spoofing technique based on Receiver Autonomous Integrity Monitoring(RAIM)is a good choice for most Global Navigation Satellite System(GNSS)receivers because it does not require any change to the hardware of the receiver.However,the conventional RAIM method can only detect and mitigate a single spoofing signal.Some improved RAIM methods can deal with more spoofing signals,but the computational complexity increases dramatically when the number of satellites in view increase or need additional information.This paper proposes a new RAIM method,called the SRV-RAIM method,which has a very low computation complexity regardless of the number of satellites in view and can deal with any number of spoofing signals.The key to the new method is the spatial distribution characteristic of the Satellites'Residual Vectors(SRV).In replay or generative spoofing scenarios,the pseudorange measurements of spoofing signals are consistent,the residual vectors of real satellites and those of spoofing satellites have good separation characteristics in spatial distribution.Based on this characteristic,the SRV-RAIM method is proposed,and the simulation results show that the method can separate the real signals and the spoofing signals with an average probability of 86.55%in the case of 12 visible satellites,regardless of the number of spoofing signals.Compared to the conventional traversal-RAIM method,the performance is only reduced by 3.59%,but the computational cost is reduced by 98.3%,so most of the GNSS receivers can run the SRV-RAIM algorithm in time.

细菌培养及核酸检测在儿童百日咳诊断中的临床应用

目的分析经细菌培养及实时荧光聚合酶链反应(RT-PCR)检测确诊的百日咳病例临床特征,探讨2种实验方法在百日咳诊断中的临床应用价值。方法收集河北省儿童医院于2019年4月至2020年1月送检的165例百日咳疑似患儿的双侧鼻咽拭子标本和临床信息,对其鼻咽拭子进行百日咳鲍特菌培养及RT-PCR检测,采用χ^(2)检验对以上2种检测方法确诊的百日咳病例进行统计学分析。结果以临床诊断为标准,细菌培养和RT-PCR诊断百日咳的敏感度分别为61.70%(58/94)和86.17%(81/94),特异度分别为92.96%(66/71)和71.83%(51/71)。RT-PCR在各个年龄段、季节和不同咳嗽病程患儿中的检出率均高于细菌培养。分别经细菌培养和RT-PCR检测确诊的百日咳患儿其年龄、季节和咳嗽病程分布基本相似,均以≤3月龄最多,夏秋季呈现高发趋势,患儿咳嗽病程大多位于15~21 d。不同年龄段之间的培养阳性率差异有统计学意义(χ^(2)=11.929,P=0.036):>3岁患儿的细菌培养阳性率最高,为51.85%(14/27),其次为≤3月龄48.72%(19/39),>6~12月龄患儿阳性率最低15.00%(3/20)。不同咳嗽病程患儿间的培养阳性率也具有统计学意义(χ^(2)=9.841,P=0.020):咳嗽病程位于15~21 d的患儿细菌培养阳性率最高,达到了49.23%(32/65),8~14 d次之为43.59%(17/39),咳嗽病程≤7 d的患儿培养阳性率最低,为22.86%(8/35)。结论细菌培养与RT-PCR检测百日咳相比,其敏感度较低、特异度较高。这2种检测方法各具优势和局限性,各级医疗机构应对不同的实验室检测方法进行综合分析,二者结合,方能有效地提高诊断价值及诊断水平。

Anchor Self-Localization Algorithm Based on UWB Ranging and Inertial Measurements

Localization systems utilizing Ultra-WideBand(UWB) have been widely used in dense urban and indoor environments. A moving UWB tag can be located by ranging to fixed UWB anchors whose positions are surveyed in advance. However, manually surveying the anchors is typically a dull and time-consuming process and prone to artificial errors. In this paper, we present an accurate and easy-to-use method for UWB anchor self-localization,using the UWB ranging measurements and readings from a low-cost Inertial Measurement Unit(IMU). The locations of the anchors are automatically estimated by freely moving the tag in the environment. The method is inspired by the Simultaneous Localization And Mapping(SLAM) technique used by the robotics community. A tightly-coupled Error-State Kalman Filter(ESKF) is utilized to fuse UWB and inertial measurements, producing UWB anchor position estimates and six Degrees of Freedom(6 DoF) tag pose estimates. Simulated experiments demonstrate that our proposed method enables accurate self-localization for UWB anchors and smooth tracking of the tag.

A Robust Graph Optimization Realization of Tightly Coupled GNSS/INS Integrated Navigation System for Urban Vehicles

This paper describes a robust integrated positioning method to provide ground vehicles in urban environments with accurate and reliable localization results. The localization problem is formulated as a maximum a posteriori probability estimation and solved using graph optimization instead of Bayesian filter. Graph optimization exploits the inherent sparsity of the observation process to satisfy the real-time requirement and only updates the incremental portion of the variables with each new incoming measurement. Unlike the Extended Kalman Filter （EKF） in a typical tightly coupled Global Navigation Satellite System/Inertial Navigation System （GNSS/INS） integrated system, optimization iterates the solution for the entire trajectory. Thus, previous INS measurements may provide redundant motion constraints for satellite fault detection. With the help of data redundancy, we add a new variable that presents reliability of GNSS measurement to the original state vector for adjusting the weight of corresponding pseudorange residual and exclude faulty measurements. The proposed method is demonstrated on datasets with artificial noise, simulating a moving vehicle equipped with GNSS receiver and inertial measurement unit. Compared with the solutions obtained by the EKF with innovation filtering, the new reliability factor can indicate the satellite faults effectively and provide successful positioning despite contaminated observations.

Effects of Power Inversion Spatial Only Adaptive Array on GNSS Receiver Measurements

The Spatial Only Processing Power Inversion(SOP-PI) algorithm is frequently used in Global Navigation Satellite System(GNSS) adaptive array receivers for interference mitigation because of its simplicity of implementation. This study investigates the effects of SOP-PI on receiver measurements for high-precision applications. Mathematical deductions show that if an array with a centro-symmetrical geometry is used, ideally,SOP-PI is naturally bias-free; however, this no longer stands when non-ideal factors, including array perturbations and finite-sample effect, are added. Simulations are performed herein to investigate how exactly the array perturbations affect the carrier phase biases, while diagonal loading and forward-backward averaging are proposed to counter the finite-sample effect. In conclusion, whether SOP-PI with a centro-symmetrical array geometry will satisfy the high precision demands mainly depends on the array perturbation degree of the element amplitude and the phase center.

Space and Frequency Diversity Characterization of Mobile GNSS Receivers in Multipath Fading Channels

Diversity reception of multipath Global Navigation Satellte System(GNSS)signals offers a new insight into carrier phase-based high-precision positioning.The focus of this paper is to demonstrate the fading independence between space and frequency diversity GNSS signals.In harsh urban environments,multipath components arrive to the mobile receiver antenna with different phases and Doppler shifts,therefore giving rise to the discontinuity of code and Doppler observations and large tracking errors.In this paper,an empirical model of fading GNSS signals is constructed,including power fluctuations and spread metrics.Based on this model,real BeiDou Navigation Satellite System(BDS)signals from two GNSS dual-frequency antennas are characterized,at both information and signal level.The block processing algorithm is utilized for signal investigation.Results show that:(1)a high proportion of asynchronous loss-of-lock(around 16%)is experienced by observations of diversity signals;and(2)power fluctuations of fading signals are uncorrelated in frequency separated branches unconditionally,yet for space diversity signals the independency exists in dynamic fading channels only.The results above corroborate the significant potential gain of diversity reception,and could be further implemented in researches of diversity combined GNSS parameter estimation in dense fading conditions.

Efficient Signal Separation Method Based on Antenna Arrays for GNSS Meaconing

As an effective deceptive interference technique for military navigation signals, meaconing can be divided into two main types: those that replay directly and those that replay after signal separation. The latter can add different delays to each satellite signal and mislead the victim receiver with respect to any designated position,thus has better controllability and concealment capability. A previous study showed there to be two main spatial processing techniques for separating military signals, whereby either multiple large-caliber antennas or antenna arrays are used to form multiple beams that align with all visible satellites. To ensure sufficient spatial resolution,the main lobe width of the antenna or beam must be sufficiently narrow, which requires the use of a large antenna aperture or a large number of array elements. In this paper, we propose a convenient and effective signal separation method, which is based on an antenna array with fewer elements. While the beam of the array is pointing to a specified satellite, the other satellite signals are regarded as interference and their power is suppressed to a level below the receiver's sensitivity. With this method, the number of array elements depends only on the number of visible satellites, thus greatly reducing the hardware cost and required processing capacity.

pH-Switched fluorescent pseudorotaxane assembly of cucurbit[7]uril with bispyridinium ethylene derivatives

The host-guest properties of cucurbit[7]uril （0_[7]） and bispyridinium ethylene derivatives have been studied by 1H NMR spectroscopy, UV-vis absorption spectra, and fluorescence emission analysis. The proton shifts associated with the guest encapsulated by the host suggested that the Q[7]-based [2] pseudorotaxane behaves like a fast molecular shuttle along the bispyridinium ethylene axle of the guest upon protonation and deprotonation of the terminal carboxylates. In particular, the distinct fluorescent response signals indicated that the bispyridinium component for the pseudorotaxane system, but also ~uest comDlexation. ethylene moiety not only behaves as the axle acts as an optical reporting unit during the host-