一种简单高效的前沿检测时间估计算法及其应用

在基于时间的无线定位系统中，时间估计算法的精度和复杂度是衡量系统性能的关键因素。在直接相关检测的基础上提出一种新的前沿检测算法，通过设定检测门限对相关峰的前沿进行检测得到时间估计。经过仿真分析验证，此算法有效地提高了定位精度和一致性，并对多径误差具有一定的抑制作用。     

双基地米波MIMO 雷达低空目标俯仰维DOD和DOA联合估计方法

对于双基地米波多输入多输出(MIMO)雷达低空目标俯仰维测向场景,受多径效应影响,发射接收导向矢量因存在耦合现象而与噪声子空间失去正交性,导致以多重信号分类(MUSIC)为主的子空间类算法在该场景下不可用,而基于空间平滑预处理的子空间类算法由于阵列孔径损失存在角度估计精度不高的问题。为解决上述难题,建立了双基地米波MIMO 雷达单目标和非相干多目标镜面反射信号模型,在信号模型数学变换和分析的基础上发现了一种仍旧与噪声子空间正交的导向矢量矩阵,然后利用新的导向矢量矩阵结合广义MUSIC和最大似然算法提出了双基地米波MIMO 雷达低空目标俯仰维波离方向和波达方向联合估计方法,最后通过仿真验证了所提方法的有效性和俯仰维测向性能的优越性。     

基于过程控制的分离式多通道超声探伤方案

通过对制约超声探伤在过程控制应用中的因素分析，提出了分离式多通道探伤方案，采用RS-485通信方式实现各通道与主机联系；单通道采用闸门，连续A/D和单点A/D等技术，有效地减少采样时间和噪声影响，提高了探伤的准确性，保证了系统的可靠性；实践结果证明该方案的有效性和可行性。     

Capacity fading of LiCr0.1Mn1.9O4/MPCF cells at elevated temperature

Capacity fading of LiCr_0.1Mn_1.9O₄ /MPCF (mesophase pitch-based carbon fiber) cells was investigated at elevated temperature (55 °C). The cells showed very fast capacity fading, keeping only 60% of capacity retention at the 100th cycle at 55 °C. The cycled electrodes and the electrolyte were analyzed using electrochemical test, inductively coupled plasma, and X-ray diffraction. Results of the analyses indicated that LiCr_0.1Mn_1.9O₄ exhibited good effects on restraint of Mn dissolution and stabilization of structure at 55 °C. The cycled LiCr_0.1Mn_1.9O₄ electrode and the cycled MPCF electrode presented good electrochemical performance again with fresh electrolyte. Therefore, it was proposed that the cycling fading of LiCr_0.1Mn_1.9O₄/MPCF cells was mainly caused by decomposition of electrolyte upon LiCr_0.1Mn_1.9O₄ electrode during cycling. It was found that the decomposition of electrolyte led to the formation of a surface layer comprised of Li₂CO₃, Li _x PF _y , CH₃OCO₂Li or (CH₂OCO₂Li)₂, polymeric ether etc. The formation of this film consumed active lithium ions, leading to fast capacity fading of LiCr_0.1Mn_1.9O₄/MPCF cell at elevated temperature.     

Red luminescence from potassium feldspar for dating applications: a study of some properties relevant for dating

Aspects of the red thermoluminescence (RTL) and IR (833±5 nm) stimulated red (λ_emission=600–750 nm) luminescence (orange-red IRSL) of potassium feldspar from different origins are described. Anomalous fading of RTL (300–500°C) from a selection of potassium feldspar samples was tested. High temperature RTL (300–450°C) exhibits less anomalous fading in comparison to UV luminescence, for the samples under study. The result supports the contention of Zink and Visocekas (1997) that the red TL emission from feldspar does not fade. It was found that RTL is bleachable due to IR exposure, and the relationship between RTL lost and orange-red IRSL produced is linear. It is shown that around one third of the trapped charge responsible for the orange-red IRSL signal gives rise to an RTL signal, indicating that some traps and luminescence centres are shared for RTL and orange-red IRSL.

Specific characteristics of orange-red IRSL from feldspar were identified. It was found that the orange-red IRSL decay curve is bleachable by IR and daylight and can be described by the sum of three exponential components. Orange-red IRSL fading was tested. Short-term storage tests (up to 2 weeks) showed no fading. Longer-term (ca. months) storage of orange-red IRSL do in fact indicate fading, though at levels considerably lower than for the UV emission. The contradictory result is possibly due to the detection wavelength. As such, it is highly likely that the long-term fading experiment is strongly influenced by the feldspar emission centred at ca. 570 nm, which exhibits anomalous fading, while the short-term fading experiment is more greatly influenced by the far red emission centred at ca. 710 nm that in comparison to UV emission shows no or less fading.     

高锰酸根褪色光度法测定食盐中的微量碘离子

在稀硫酸介质中，碘离子能快速、定量地还原高锰酸根，在加入碘离子前后，高锰酸钾溶液在波长525nm处的吸光度发生显著变化，且吸光度之差ΔA与加入的碘离子的浓度成正比，确定了最佳反应条件，建立了高锰酸根褪色光度法测定食盐中微量碘离子的新方法。方法的线性范围为0-20μg／mL，线性回归方程为ΔA=0．0165c 0．0041，相关系数r=0．9987，检出限为0．17μg／mL。用于食盐中微量碘离子的测定，加标回收率为91．0％～95．0％．相对标准偏差为0．35％～0．75％。     

Variation of constants formula and almost periodic solutions for some partial functional differential equations with infinite delay

In this work, we give a variation of constants formula for partial functional differential equations with infinite delay. We assume that the linear part is not necessarily densely defined and its resolvent operator satisfies the Hille-Yosida condition. We establish a reduction of the problem to a finite-dimensional space which allows us to prove the existence of almost periodic solutions.     

基于小波滤波及载噪比估计的GPS接收机多径抑制

为了抑制城市环境GPS(global positioning system)导航应用中由复杂信号反射引起的多径效应,提出了一种基于假设检验小波阈值滤波处理并联合载噪比估计的GPS接收机多径抑制方法.这种方法作用于GPS导航接收机的码和载波跟踪环路,通过估计由多径引起的跟踪误差,补偿伪距估计量,进而消除多径效应引起的定位误差.仿真实验结果表明,对于城市环境典型导航应用的多径场景,所提出的方法显著改善用户定位精度,能够将定位误差从标准接收机处理下的15.95 m降至1.75 m,而计算量无明显增加.     

天波超视距雷达多径信道均衡方法

具有大范围、远距离、隐身和超低空目标探测等特点的天波超视距雷达已成为目前雷达领域研究的重点技术之一.针对天波超视距雷达工作中多径效应对雷达回波信号的污染问题,提出了一种抑制多径污染的信道均衡方法.首先利用已知的训练序列对多径信道进行估计,然后利用具有一定结构的滤波器实现信道的均衡,最终达到了抑制多径信道对雷达回波信号影响的目的.仿真实验证明,该方法可以有效地对多径效应引起雷达回波信号的污染进行抑制,进而提高雷达对目标的检测能力.     

Memory effects during the flow of thixotropic fluids in pipes

Summary The paper presents the phenomenon of thioxotropy from the point of view of the theory of fluids with fading memory. In the first part of the paper the mechanism of thixotropy was discussed in order to justify the application of the concept of structural parameter (this parameter occurs in the previously presented rheological model of thixotropic materials). In the second part of the paper an equation was derived, which enables the prediction of the mean value of the friction factor during the flow of a thixotropic fluid in a pipe. According to the obtained equation the friction factor is a function of three dimensionless numbers: the generalized Reynolds number, a modified Deborah number and a new dimensionless number which may be called a structural number. The preliminary experimental results confirmed the applicability of the obtained equation.

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Zusammenfassung Die Veröffentlichung behandelt das Phänomen der Thixotropie vom Standpunkt der Theorie der Flüssigkeiten mit schwindendem Gedächtnis. Im ersten Teil wird der Mechanismus der Thixotropie untersucht und die Einführung eines sog. Strukturparameters begründet (dieser Parameter kommt bereits in dem früher behandelten rheologischen Modell eines thixotropen Körpers vor). Im zweiten Teil wird dann eine Formel abgeleitet, welche die Voraussage des mittleren Wertes des Widerstandskoeffizienten bei der Strömung einer thixotropen Flüssigkeit durch ein Rohr ermöglicht. Dieser Formel gemäß ist der Widerstandskoeffizient eine Funktion von drei dimensionslosen Zahlen: einer verallgemeinerten Reynolds-Zahl, einer modifizierten Deborah-Zahl und einer neuen dimensionslosen Zahl, die als Struktur-Kennzahl bezeichnet werden kann. Die vorläufigen Versuchsergebnisse bestätigen die Brauchbarkeit der abgeleiteten Formel.

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a rheological parameter in eq. [1], s^–1 - A rheological parameter in eq. [1]; function defined in eq. [15] - b rheological parameter in eq. [1] - B constant in eq. [15] - c rheological parameter in eq. [4] - c function defined in eq. [4] - C function defined in eq. [48] (see also eq. [43]) - D pipe diameter,m - K ₁,K₂ coefficients of proportionality in eq. [6] - k rheological parameter in eq. [12], Nsⁿ/m² - k ^* rheological parameter in eq. [1], Ns^m/m² - L pipe length, m - m rheological parameter in eq. [1] - n rheological parameter in eq. [12] - N number of particles in unit volume - p pressure, Pa - p ₀ pressure at the pipe entrance, Pa - r radial coordinate, m - R pipe radius, m - s rheological parameter in eq. [1] - t time, s - u _z axial local velocity in the pipe, m/s - v mean linear velocity in the pipe, m/s - z axial coordinate, m - rheological parameter in eq. [5], = 1 s - shear rate, s^–1 - nominal shear rate defined by eq. [39], s^–1 - structural parameter - substantial derivative of structural parameter, s^–1 - _e equilibrium structural parameter in eqs. [2] and [5] - _en nominal structural parameter - ₀ initial value of structural parameter - function of natural time - mean value of natural time, s - shear stress, Pa - ₀ shear stress field atZ = 0 (at pipe entrance) - _y0 equilibrium yield stress, Pa - shear stress field atz - fluid density, kg/m³ - v number of bonds in an average aggregate - mean value of the friction factor - De modified Deborah number defined by eq. [46] - Re generalized Reynolds number defined by eq. [45] - Se structural number defined by eq. [41a] With 4 figures and 1 table