基于多模态平稳序列建模的雷达高分辨距离像有限样本目标识别方法

为了解决雷达高分辨距离像识别系统对训练样本需求量过大的问题,提出了一种有限样本条件下的目标识别新方法。分析了距离像频谱幅度的统计特性,从其广义平稳性和多模态分布特性出发,定义一种线性混合高斯状态空间模型对其统计建模,利用期望最大化算法进行了模型参数估计。实验结果表明:即使在很少的训练样本条件下,该方法仍能获得较高的正确识别率和良好的拒判性能。     

Effects of nanoparticle doping on the phase transitional behaviour of ferroelectric liquid crystal Langmuir–Blodgett composite films

Langmuir–Blodgett films of ferroelectric liquid crystals (FLCs) doped with a low concentration of functionalized Al: ZnO (AZO) nanoparticles were prepared and characterized. Pressure–area isotherms show that the nanoparticles as well as FLC composite systems have the capability to form stable monolayers at the air–water interface. The molecular interaction between nanoparticles and FLC molecules increased during barrier compression, which resulted in increased surface pressure. We observed various phases in isotherms with increasing concentration of nanoparticles in the FLC matrix. An X-ray diffraction profile at a low angle confirmed that FLCs retain their layer structure at a low concentration doping of AZO nanoparticles in the FLC matrix. Atomic force microscopy images indicate that low wt% composites are uniformly deposited without disturbing the translation behaviour of SmC* liquid crystals.     

Measurement of electro-optical parameters of a high contrast FLC film

We have fabricated a ferroelectric liquid crystal (FLC) film by using a novel ferroelectric mixture. The various ferroelectric parameters such as response time, spontaneous polarization and contrast ratio of the FLC film have been measured. Experimental results show that the FLC film exhibits high contrast ratios and fast optical response. The FLC film has a possibility of the use in display applications because of the performance characteristics.     

基于STAMP的航空管制空中危险目标识别方法研究

为了保证航空管制中航空器的完整性,提高航空器的使用寿命,并且可以最大限度的保障航空乘客和其他航空人员的人身安全,需要对航空管制空中危险目标进行识别。但采用当前目标识别方法对空中危险目标识别时,识别系统对空中危险目标无法稳定识别,存在空中危险目标识别精度低的问题。为此,提出一种基于STAMP的航空管制空中危险目标识别方法。该方法先利用STAMP模型对航空管制空中危险目标识别系统各组成部分进行任务分配,然后采用Harris法对空中危险目标进行特征选择和提取,依据Mean-Shift法的Bhattacharyya系数,描述候选空中危险目标和空中目标的危险概率分布相似度,随着Bhattacharyya系数的不断增加,候选空中危险目标和空中危险目标的相似度越大,使危险目标跟踪系统朝着空中目标危险密度增大的位置移动,在最优位置收敛,从而实现空中危险目标跟踪,最后利用D-S理论对跟踪结果进行识别,通过引入空中目标危险性基本概率赋值函数获得空中目标危险基本概率,采用Dempster组合规则对空中目标危险证据进行合成,依据空中危险目标证据融合结果完成对航空管制空中危险目标的识别。实验仿真证明,所提方法增强了航空管制空中危险目标识别的效果,提高了航空管制空中危险目标识别的精度。     

Evaluation of structural and adhesive properties of nylon 6 and PTFE alignment films by means of atomic force microscopy

Atomic force microscopy (AFM) has become a powerful technique for submicron investigation of surface properties. In this work we use the capability of this technique to investigate dielectric films used to align ferroelectric liquid crystals (FLC). In fact, the final performance of a surface stabilized FLC (SSFLC) flat panel display strongly depends on the alignment layer properties and quality. This work focuses on a comparison of two alignment films: the more conventional polyamide, nylon 6, and polytetrafluoroethilene (PTFE, commercially known as Teflon), only recently used as a new aligning material. A micromorphological characterization of the sample surfaces has been carried out in order to correlate structure with alignment properties of both polymer films. The results show varying roughness and periodicity wavelengths for the two alignment layers. These different properties can be related to different anchoring forces between aligning surfaces and FLC molecules and therefore to a different electrooptical response of SSFLC cells. In addition to the topographic characterization, AFM non-conventional measurements have been performed on alignment layers deposited on different transparent conductive oxides, such as indium tin oxide (ITO) and SnO₂, used to make electrodes in SSFLC displays. These measurements provide local information on the adhesive properties of the studied alignment materials as a function of substrate coating. These observations indicate less adhesion of PTFE with respect to nylon 6. Received: 16 April 2000 / Accepted: 16 April 2000 / Published online: 13 September 2000     

Static and dynamic electro-optic properties of a SmC* phase in surface stabilized geometry and dispersed in the polymer matrix

Comparative electro-optical measurements have been made on a ferroelectric liquid crystal (FLC) in surface stabilized geometry and confined to an ellipsoidal cavity within a polymer matrix. The static and dynamic electro-optical characteristics were measured for both systems and show qualitatively similar behaviours. A fast switching and important bistability were observed and characterized as a function of the applied electric field strength. The switching time between the two stable states of the surface stabilized cell was found to be longer than that found for the composite films. We argue that the faster switching dynamic of the FLC in cavities is due to the enhance of the rotational mobility of the molecules, probably (and partly) because of the soft anchoring character of the molecules at the cavity walls. Using a collective switching model in the high field regime, which assume a linear coupling between the spontaneous polarization and the local cavity electric field, we give an estimate of the rotational viscosity of the FLC molecules in the droplets.Received: 5 October 2003, Published online: 5 February 2004PACS: 61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems - 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions - 77.80.Fm Switching phenomena     

Ignition delay time measurements and modeling for gasoline at very high pressures

Ignition delay times (IDT) for high-octane-number gasolines and gasoline surrogates were measured at very high pressures behind reflected shock waves. Fuels tested include gasoline, gasoline with oxygenates, and two surrogate fuels, one dominated by iso-octane and one by toluene. RON/MON for the fuels varied from 101/94 to 106.5/91.5. Measurements were conducted in synthetic air at pressures from 30 to 250 atm, for temperatures from 700 to 1100 K, and equivalence ratios near 0.85. Results were compared with a recent gasoline mechanism of Mehl et al. (2017). IDT measurements of the iso-octane-dominated surrogate were very well reproduced by the model over the entire pressure and temperature range. IDT measurements for the toluene-dominated surrogate were also reproduced by the model to a lesser extent. By contrast, IDT measurements for the neat gasoline and gasoline with oxygenates, show excellent agreement with the trends of the Mehl et al. model only below 900 K. Above 900 K, the model returned IDT values for the two gasolines that were approximately 1.6× the measured values. Finally, we observed that IDT measurements for the toluene-dominated surrogate fuel and the two gasolines, near 70 atm and below 900 K, appeared to be shortened, possibly by non-homogeneous ignition or non-ideal gas processes. This dataset provides a critically needed set of IDT targets to test and refine boosted gasoline models at high pressures.     

Aircraft recognition based on improved iterative threshold selection and skeleton Zernike moment

Using the visible optics images to identify targets is an important part in the development of remote sensing technology. In this paper, a new aircraft recognition method based on the improved iterative threshold selection and the skeleton Zernike moment is presented. The method segment aircraft targets under complex background using iterative threshold selection with between-class distance and scatter, and calculate the skeleton Zernike moment for the aircraft target recognition using template matching method. The experimental results show that the new method can effectively achieve the target segmentation under complex backgrounds, and provide a satisfactory performance both in recognition rate and recognition speed.     

Modelling and characterization of ferroelectric liquid crystal displays

Modelling of liquid crystal displays is useful to predict their optical properties and dynamic behaviour. An integrated modelling system for ferroelectric liquid crystal displays has been developed. The system employs data from real FLC materials, polarizers, glasses, backlights, and colour filters, aiming to describe actual devices accurately. Optical transmission dependence on light wavelength and angle of incidence is obtained as a function of the liquid crystal director profile. This profile is in turn derived from energy minimization of bulk and glass surface conditioning contributions.The above static model has been extended to study sample switching in multiplexed displays. Usual slot times in actual displays are quite close to time response of FLC materials, hence no energy-minimized configurations are obtained upon switching. A dynamic model has been formulated to derive the director profile evolution with time, according to the employed driving scheme, and the rotational viscosity of the material.Predicted dynamic and optical results have been compared to experimental measurements on FLC test cells. It has been found that the behaviour of FLC cells depends on a large number of physical and optical parameters. Some of them may be obtained from FLC data sheets, and manufacturing conditions. Other parameters related to director profiles in relaxed states may be experimentally obtained by sample characterization through optical transmission measurements. A few little known parameters (e.g. specific elastic constants) remain; fortunately their influence on cell dynamics is low.     

Electro-optic and dielectric behavior of a FLC material having doped with a non-mesogenic polar molecules

Liquid crystal mixtures of non-mesogenic polar molecule with a commercial ferroelectric liquid crystal (FLC) mixture were prepared. Two mixtures were prepared by mixing 0.5% (w/w) and 1% (w/w) of polar molecules with commercial FLC mixture. Comprehensive studies of dielectric and electro-optic properties of the commercial FLC mixture and the polar molecules doped FLC mixtures have been made as a function of temperatures. Our studies reveal a higher tilt angle in lower concentration (0.5%) mixture but in case of 1% mixture tilt angle is decreased in comparison to 0.5% mixture. The spontaneous polarization of the commercial FLC mixture and other two mixtures is almost equal in magnitude at all temperatures. At the lower temperature region of SmC¹ phase, Goldstone mode (GM) dielectric strength of the commercial FLC mixture and low concentration (0.5%) mixture is found almost equal but it is slightly higher in case of high concentration (1%) mixture. With the increase of temperature GM dielectric strength of both the doped mixtures rapidly converges at different temperatures which are much lower than the temperature of transition (T_C) from SmC¹ – SmA phase. The results have been discussed.     

Long duration light emission from femtosecond laser–target interactions

Time resolved emission from the interaction of ultra-short (∼200 fs) laser pulses with aluminum and copper targets was investigated. Measurements show that emission from the laser produced plasma in air is significantly more intense than in near vacuum conditions and that the emission in air can extend for periods exceeding 100 ns. Modeling the laser–target–air coupling shows that the laser–target interaction can lead to blast wave shock waves being launched in the ambient air and that the emission from the shocked air dominates over emission from the target surface. The long term emission measurements in air are in agreement with the modeling results.     

Implications on the origin of cosmic rays in light of 10 TV spectral softenings

Precise measurements of the energy spectra of cosmic rays(CRs)show various kinds of features deviating from single power-laws,which give very interesting and important implications on their origin and propagation.Previous measurements from a few balloon and space experiments indicate the existence of spectral softenings around 10 TV for protons(and probably also for Helium nuclei).Very recently,the DArk Matter Particle Explorer(DAMPE)measurement about the proton spectrum clearly reveals such a softening with a high significance.Here we study the implications of these new measurements,as well as the groundbased indirect measurements,on the origin of CRs.We find that a single component of CRs fails to fit the spectral softening and the air shower experiment data simultaneously.In the framework of multiple components,we discuss two possible scenarios,the multiple source population scenario and the background plus nearby source scenario.Both scenarios give reasonable fits to the wide-band data from TeV to 100 PeV energies.Considering the anisotropy observations,the nearby source model is favored.     

基于形状特征的水声图像小目标识别方法

为了抑制背景噪声,提高目标识别准确率,该文提出一种基于形状特征的水声图像小目标识别方法.对含有目标的水声图像进行非局部均值去噪处理后,使用OTSU算法自适应选取阈值对去噪图像进行二值化分割,结合形态学处理获得分割后的目标区域;提取目标区域的矩形度、圆形度、几何不变矩等各项形状参数,将目标的特征向量输入随机森林分类器实现...     

基于光谱探测与图像识别的反伪装目标系统研究

为了在野外环境中快速有效地识别敌方伪装的机动目标,设计了基于光谱探测与视频图像目标识别方法联用的目标识别系统。采用视频图像识别技术获取被测区域的二维影像,再通过光谱探测技术识别目标,最终将目标重建在图像相应位置上从而实现目标识别的可视化。理论推导得到了系统可识别目标的函数关系式,根据该函数关系进行了目标识别的量化实验。实验采用汽车模拟被测机动目标,在不同距离上分别以平坦荒地、灌木丛和废弃建筑物为背景,对明显目标、涂覆迷彩色的目标以及遮挡伪装物的目标分别进行光谱探测。实验结果显示,测试背景对光谱探测效果有一定影响,背景的连续性有利于目标识别;伪装方式以伪装物遮挡最难识别,且随着目标与系统的距离增大而信噪比随之降低。综上所述,采用光谱探测技术克服了传统图像目标识别无法识别伪装目标的缺点,可以实现对伪装目标的有效识别。     

Fourier-transform, integrated-optic spatial heterodyne spectrometer on a silica-based planar waveguide with 1 GHz resolution

Spatial heterodyne spectrometers (SHS) can achieve high resolution with excellent optical throughput. We demonstrate a planar waveguide SHS incorporating 64 asymmetric Mach-Zehnder interferometers and show measurements that verify 1 GHz resolution across a 64 GHz measurement range.     

开放光程TDLAS系统对北京城区NH3浓度的连续检测

氨气是大气酸性成分的主要中和剂,是影响区域空气质量、大气能见度以及酸性沉降的重要因素。研制了基于开放光程近红外可调谐半导体激光吸收光谱(Tunable diode laser absorption spectroscopy,TDLAS)技术的大气NH3浓度连续监测系统,并对北京城区大气NH3浓度进行了两个星期的连续检测。检测结果表明,北京城区大气具有较高的NH3浓度,且具有明显的日变化周期特征,基本特点是白天浓度低,夜晚浓度高且变化相对平缓。相关性研究表明,非农业排放源,特别是城市交通的机动车尾气排放是北京城区大气NH3的主要来源。     

Suppression of relaxation modes in dye dispersed SmC* phase

We report the results of dielectric and electro-optical properties of ferroelectric liquid crystal (FLC), Felix 17/100, exhibiting chiral smectic C phase and dye dispersed FLCs. The polarization measurement on pristine and dye dispersed FLC mixture shows decrease in the value of polarization, indicating the distribution of dye dipole in a direction opposite to the orientation of FLC molecule. The rotational viscosity also decreases accordingly as shown by the measurement of response time. Dielectric measurement shows existence of two relaxation modes both in pure FLC and dye dispersed FLC. The relaxation strength of Goldstone mode decreases with the dispersion of dye and the relaxation frequency of this mode shifts towards the high-frequency side. The second relaxation mode arises due to the formation of domains at the surface interface. The dispersion of dye into FLC suppresses the domains.     

A model based technique for recognizing targets by using millimeter wave radar signatures

A technique for recognizing real targets by millimeter wave (MMW) radar at 35 GHz and 94 GHz is presented. The recognition is performed by a model based technique in which real targets are represented by their high range resolution (HRR) profiles in hierarchical fashion.The unknown signal is classified by a model matching method and a coarse-fine searching technique. The advantages of this model based method are in low storage capacity, fast processing time and high recognition performance. Moreover this technique is very easily modifiable to incorporate multi sensor processing.We will present the results of the several experiments that we have conducted.     

基于6LoWPAN的智慧校园空调监控系统设计

针对总线制空调监控系统存在布线施工成本高、联网结构复杂、维护难度大等问题,设计了一种基于6LoWPAN的智慧校园空调监控系统。首先给出了系统的整体功能及网络架构;然后,给出了传感器节点、系统核心模块及网关节点的硬件设计;接下来对6LoWPAN协议及简化进行了描述,给出了系统嵌入式软件的设计;最后给出了相关的空调控制策略。测试和实验结果表明,该空调监控系统具有结构简洁,扩展性高,实时在线响应,有效解决了校园空调物联网的信息互联问题,利用云平台智能管理达到节能减排目标。     

Spatial light modulators using ferroelectric liquid crystal

Basic structures and functions of optically addressed spatial light modulators (SLMs) are discussed in the context of system applications. The most important functions imposed on spatial light modulators are those of image acceptance and transducers. SLMs using ferroelectric liquid crystal (FLC) satisfy essential requirements for high levels of resolution, sensitivity and response speed. We specifically surveyed the current performance of bipolar-operational spatial light modulators (BSLMs) that sufficiently exploit the bistability of FLC to output reversibly positive and negative images and to store them. The high performance of BSLMs makes them useful for many optical applications including image processing and real-time holography.