基于ARIMA和支撑矢量机组合预测的惯性器件故障预报

文中提出一种基于ARIMA和支撑矢量机进行组合预测的方法,该方法综合运用ARIMA良好的线性拟合能力和支撑矢量机强大的非线性映射功能,将两种预测模型有机地组合在一起,综合各自优点,以期有效改善模型的拟合能力,获得最优预测效果.文中将该方法应用于某飞行器惯性器件的故障预报当中并进行了仿真实验.结果表明,这种方法相对于单项模型的预测具有更高的精度,对于复杂时间序列的分析和预测有很好的应用价值,在故障预报中具有广泛的应用前景.     

Amorphous diffusion bonding of steel pipe and its impact toughness

An iron-based amorphous foil (FeNiCrSiB) was used as an interlayer for the amorphous diffusion bonding of low carbon steel pipes under argon flux. The microstructure and mechanical properties of the joint were analyzed using an electron probe micro-analyzer (EPMA), tensile test, bending test and impact test. The results show that the joint microstructure resembles that of the base metal and no precipitates form at the joint. Melting point depressants (B, Si) diffuse far away from the joint and the base metal element is homogenous across the joint. The joint impact toughness is greater than the base metal toughness and the mechanical properties of the joint are similar around the pipe.     

Preparation and photochromism of nanocomposite thin film based on polyoxometalate and polyethyleneglycol

A photochromic nanocomposite based on Keggin structure phosphomolybdic acid (PMoA) well dispersed in polyethyleneglycol (PEG) was fabricated. TEM image showed that PMoA nanoparticles with narrow size distribution were finely dispersed in polymer matrix. FT-IR results showed that the Keggin geometry of polyoxometalates was still preserved inside the composites and strong coulombic interaction was built between PMoA and polymer matrix. Under UV irradiation, the film was reduced photochemically to yield a blue species, which was in accordance with a charge-transfer mechanism.     

一种基于判决反馈的OFDM系统载波频率跟踪算法

研究了多径信道下OFDM系统的一种新的载波频率跟踪算法，这种算法以判决反馈和接收端的时域信号重构为基础。推导了估计结果的精确解，比较了使用原估计结果和新的估计结果进行频偏补偿时系统跟踪性能的不同。通过对算法的仔细分析，发现除了通常的加性噪声外，信道估计误差、子载波数目和子载波的调制方式也影响频偏的估计结果和跟踪范围，而且子载波的数目和调制方式是决定性的因素。这种频率跟踪方法的优点是即使在很低的信噪比下仍然能获得高的跟踪精度，且实现相对简单。     

Optimal diagonal precoder for multiantenna communication systems

In this paper, we examine a multiantenna single-user wireless communication system fitted with a QR-based successive cancellation receiver (QR receiver). Initially, our consideration is confined to uncoded binary phase shift keying (BPSK) signals transmitted through independent and identically distributed (IID) Rayleigh fading channels and to the design of an optimum precoder for the transmitter. For minimum feeding back of the channel state information (CSI) to the transmitter from the receiver, we stipulate the precoder to be in the form of a power loading square diagonal matrix. We proceed to develop the theory for the design of this diagonal matrix based on the minimization of the lower bound of the average bit error rate (BER) of transmission. The design obtained provides substantially lower error rates than most of other existing schemes under the same environment. The corresponding gain in signal-to-noise ratio (SNR) can be several decibels. To further improve the performance, we extend the design to include an optimal detection order of the received bits using an iterative approach. This iterative process proves to have fast convergence and results in a design providing significant SNR gain. We also propose a subchannel dropping scheme for cases in which SNR is low, and when the minimum BER precoder is equipped with this scheme, its average performance can be substantially superior to the Vertical Bell Laboratories Layered Space-Time (V-BLAST) detection. We extend our design of the optimum precoder to quadrature amplitude modulation (QAM) modulation scheme and similar performance gain has been observed.     

用于实时数据传输的滑动帧方法及其实现

根据某雷达系统对测量信号的快速传输要求,提出采用滑动帧的处理方法并在FPGA中实现,克服了传统帧处理难以满足快速传输要求的不足。阐述了滑动帧结构的构造思想,详述了滑动帧结构的特点及具体功能模块的实现。根据实际应用需求构造了滑动帧结构处理器,试验和应用结果表明设计可行有效,能充分满足实时数据传输的要求。     

Phase transition of LCP fluids confined in nanochannels through MD simulation

Manipulation of molecular orientation alignment in MCTLCPs (main-chain thermotropic liquid crystalline polymers) by pure shear at nano scale has been investigated for the first time using molecular dynamics (MD) simulation. Results indicate that high planar shear induces long-range uniform orientation ordering (liquid crystalline phase) of initially randomly orientated molecules of MCTLCP fluid confined in a nanochannel, which is confirmed by analyzing the orientation order parameter and the snapshots of MCTLCP liquid in a nanochannel under different shear rates. Insights into the origin of the phase transition phenomena are given at molecular level through investigating the thermodynamic density distribution of MCTLCP molecules in the nanochannel, suggesting that the energy shift due to a radical jump of system density affects both the magnitude and the orientation of the molecular ordering. Simulation results also show that there is a critical shear rate for transforming isotropic phase into liquid crystalline phase. The critical shear rate is dependent on the temperature of the MCTLCP system. Findings in this paper may present useful information for processing TLCP molecules at nano scale and the understanding of nanoflow.     

湖南省水库与城市水资源供求评价

对湖南省29个城市及靠近这些城市的67座大中型水库,采用模糊数学多级多因子综合评价方法,按水库人均供水量、水质类别、水库向城市可供水率等8个评价指标及其隶属度,评价得到2020年湖南省水库向城市可供水资源的程度.分析结果表明:至2020年,近城水库供水资源完全满足城市需水量的有7个城市,基本满足需水的城市有10座,说明在当前与将来城市供水资源紧缺的形势下,开发现有水库水资源,向城市供水意义重大.