视频显著性目标检测旨在利用计算机自动识别提取视频序列中具有显著性特征的区域或目标.随着大数据时代的到来,视频内部包含的空时信息愈发复杂,实现高效准确的检测成为当下研究的难点.因此,提出基于帧间差分和深度语义特征的视频显著性目标检测算法.首先,利用改进后的帧间差分算法计算相邻视频帧在RGB这3个颜色通道上的差分值,加权求和后提取视频流在时间上的运动特征,计算时间显著性线索;其次,基于深度卷积神经网络提取每一帧视频的深度空间特征,计算空间显著性线索;最后,运用GOP算法从语义层次提取每一帧视频的建议目标候选对象,并结合时间显著性线索和空间显著性线索评估每个目标候选对象,得出每个候选对象为显著性目标的置信度得分,根据置信度得分将这些目标候选对象进行加权融合,得到最后的视频显著性目标检测结果.在公开数据集上的测试结果表明,所提算法实时性好,检测精度高,整体性能优于目前的主流算法.

显著性目标检测旨在提取图像场景中最显著的目标成分.常规的显著性目标检测算法主要对单一的图像进行处理,得到的检测结果往往不够准确,存在检测错误的情况.为解决上述问题,提出基于协同特征的显著性目标检测算法,通过利用图像组之间的协同性来实现对显著目标的准确检测.通过在已公开的数据集进行实验表明,所提算法在检测效果上优于目前的主流算法,具有较强的鲁棒性.

随着宽带电子侦察接收机的广泛使用,同时进入接收机的信号越来越多,输出的数据量越来越大,传统的雷达辐射源识别方法很难适应分析处理的实时性和准确性要求.为解决这一问题,提出基于空时编码的雷达脉冲辐射源识别算法.通过设计一种空时编码算法来对雷达辐射源全脉冲数据中的载频、脉宽及重频等参数进行编码和特征提取,形成包含全脉冲数据时空信息的特征序列.这些特征序列既保留了雷达全脉冲数据的主要信息,又实现了对雷达全脉冲数据的简化,为利用深度学习和大数据处理技术实现对雷达辐射源快速精准识别奠定基础.利用长短时记忆网络(Long Short-Term Memory,LSTM)深度神经网络模型,结合提取的空时特征序列,通过大数据学习训练,实现了对7型雷达辐射源的精确识别.在数据集上的对比实验表明,提出的识别方法在处理识别精度和普适性上优于目前的主流算法,具有较强的鲁棒性.

显著性目标分割旨在提取图像场景中最显著的目标成分.在以往算法中,人们往往基于图像自身的显著要素如对比度、边界背景性等设计低层次人工特征或者深度语义特征进行显著性目标的分割,忽略了人类自身的视觉注意特征.为解决这一问题,提出眼动预测和多层次邻域感知的显著目标检测算法.首先,根据GBVS原理预测人眼感兴趣区域,并基于该感兴趣区域生成目标种子;其次,对图像进行超像素分割,联合颜色、纹理、视觉注意等多维度特征计算超像素之间的相似性权重;再次,基于目标种子和节点权重,在多个分割尺度下采用元胞模型对显著性种子进行传播,使得初始目标种子能够扩散至整个显著目标;最后,基于sigmoid强化和多尺度融合生成最终显著目标分割图,较好地解决了复杂场景下显著目标的检测问题.在公开数据集上的实验结果表明,所提算法在检测精度和适用性上优于目前的主流算法.

Taking polycarbosilane and antimony-modified polysilane for precursors and drawing lessons from the transformation process of high temperature graphitization of spare free carbon in SiC materials,the polymer-derived SiC nanocomposites were prepared by employing hot-press sintering,precursor infiltrating-cracking methods and annealing.The phases and microstructures were characterized and analyzed by using SEM, TEM,XRD and Raman test methods.The thermoelectric parameters of samples,such as thermal conductivity,electrical conductivity and Seebeck coefficient,were studied.Results show that the dense SiC nanocomposites acquired are n-type thermoelectric materials.The thermal conductivity is suppressed at the range of 4~8W/(m·K)due to the function of nano-graphite.At the annealing temperature of 1600°C,the thermal conductivity reduces while both the electrical conductivity and the Seebeck coefficient increase,and ZT value of SiC nanocomposites derived from precursor reaches to 0.0028(650°C),which is higher than that of SiC/C composites or nanocomposites ever reported.

连续SiC纤维是一种具有高抗拉强度、耐高温、抗氧化及与陶瓷基体良好相容性的新型陶瓷纤维，在航天、航空、兵器、船舶和核工业等高技术领域具有广泛的应用前景。

A liquid polycarbosilane with vinyl groups was synthesized via Grignard coupling reaction and the subsequent reduction reaction by the core dilution/slow addition technique, with 1,1,3,3-tetrachloro-1,3-disilabutane as the core molecules and chloromethyltrichlorosilane, vinyl-magnesium chloride as the monomers. The as-synthesized VHPCS and its ceramic product were investigated by means of FT-W, NMR, GPC, TG XRD and SEM. Results show that VHPCS possesses a hyperbranched structure and could convert to non-porous ceramic product after pyrolysis. The ceramic yield of cross-linked VHPCS at 1000 degrees C in N-2 atmosphere is 85.9wt%, and beta-SiC crystallite appeares in the ceramic product at 1200 degrees C.

As a polymer precursor of SiC ceramics,liquid hyperbranched polycarbosilane has drawn a great attention for its excellent fluidity,self-cross-linking,high ceramic yield and near-stoichiometric pyrolysis product.According to the characteristics of liquid hyperbranched polycarbosilane,the preparation methods are reviewed,including the ring-opening polymerization,Grignard coupling method,Wurtz coupling method and hydrosilysition reaction.In addition,the research progress of its application in silicon carbide based ceramic composites,silicon carbide fiber and silicon carbide membrane is summarized.Finally,the prospect of further research,large-scale synthesis and modification of liquid hyperbranched polycarbosilane,is also addressed.

In this paper,the interphase types and the effects of interphase on the material properties of conti-nuous fiber reinforced ceramic matrix composites (CFRCMCs) are analyzed,and the research development of the PyC,BN,refractory oxide and mutli-layer interphase are reviewed.Finally,the development trends of interphase in SiCf/SiC composites are prospected.

Si-Zr-C-O fibers were obtained from polyzirconocarbosilane (PZCS), which was synthesized by the reaction of polysilacarbosilane (PSCS) and Zr(AcAc)(4). The high-temperature resistance and oxidation resistance performance of Si-Zr-C-O fibers were examined by measurements of X-ray diffraction (XRD), scanning electron microscope (SEM), auger electron spectroscopy (AES) and element analysis. The surface of Si-Zr-C-O fibers is smooth, and do not exhibit obvious disfigurements. The average diameter of the fibers is 11 mu m, the average tensile strength is 2.5 GPa. Si-Zr-C-O fibers have good high-temperature-resistant performance. Processing at 1450 and 1600 C, the tensile strength retention rate is 72% and 36% respectively. The chemical formula of Si-Zr-C-O fibers is SiC(0.99)HxO(0.1)Zr(y) after processing at 1800 degrees C, the oxygen content of the fibers decreases obviously. Si-Zr-C-O fibers also have good oxidation-resistance properties. After processing for 20 h at 1000 degrees C in the air, the tensile strength retention rate is 71.2%, after processing for 100 h, the tensile strength retention rate is 50%.

A polyferrocarbosilane(PFCS) was synthesized from polydimethylsilane(PDMS) and ferrocene.Nano-Fe3Si/SiC composite ceramic absorbent can be obtained by pyrolyzing PFCS.It was systematically studied that e-lectromagnetic parameter of absorbents was affected by some factors,for example,ferrocene,sintering temperature and holding time and so on.The results show ε'、ε″ and εr increase greatly by adding more ferrocene,raising sintering tem-perature and prolonging holding time.

The pyrolysis of polyborosilazane(PBSZ) synthesized via co-condensadition approach using methyldichlorosilane(MeHSiCl2),boron trichloride(BCl3) and hexamethydisilazane(HMDZ) was studied via TGA,IR spectrum and 29Si NMR spectrum.The results indicated that the pyrolysis of PBSZ involved four steps:(1) below 240℃,no apparent weight loss or weight gain;(2) from 240~400℃,the weight loss was about 30% from the evaporation of low molecular weight products and transamination;(3) from 400~600℃,weight loss reduced,dehydrocoupling reaction between Si—H and N—H might occur;(4) from 600~1000℃,only a little weight loss,the formation of inorganic nearly completed.

In this paper, the disadvantages of calculating the absorbing properties of single layer radar absorbing materials containing capacitive FSSs using equivalent circuit method were analyzed, and the absorbing properties were studied by finite element method. The calculated results indicate that the band-widths will be broadened while the capacitive FSSs are close to the conducting plate and the absorbing properties at low frequency can be improved when the capacitive FSSs are on the surfaces of the RAMs, which are in agreement with experimental results. So, the capacitive FSSs can improve the absorbing properties of the single layer RAMs significantly, and have better application future in the RAMs.

Polyborosilazane(PBSZ),a novel precursor of SiBNC ceramic,was synthesized via polycondensation approach with a yield of about 90%(mass fraction) from dichloromethylsilane(MeHSiCl2),boron trichloride(BCl3) and hexamethydisilazane((CH3)3SiNHSi(CH3)3). Precursors with different softening points can be obtained by altering the dosage of MeHSiCl2. Rheological study shows that PBSZ melt is a typical shear thinning fluid. The shear rate,the flow index,the apparent viscosity and the viscous flow activation energy are 10~110 s-1,0.83~0.90,440~2 460 Pa·s,and 142 kJ/mol,respectively. The as-synthesized polyborosilazane shows a good melt-spinning processability and continuous fibers with diameter 20 μm and length1 600 m can easily be obtained.

In order to prepare high-performance Si-Zr-C-O fibers,polyzirconocarbosilane(PZCS)was synthesized by the reaction of zirconium acetylacetonate(Zr(AcAc)_4)(AcAc:aletylacetanate)with polysilacarbosilane(PSCS)at normal pressure.Si-Zr-C-O fibers were obtained by melting spinning of PZCS,air curing and pyrolysis at 1200℃.The composition and structure of Si-Zr-C-O fibers was examined by X-ray diffraction,nuclear magnetic resonance,scanning electron microscope,auger electron spectroscopy and ele- ment analysis.The results show that the empirical formula of Si-Zr-C-O fibers is SiC_(1.24)H_xO_(0.56)Zr_(0.0129),and the tensile strength and diameter of the fibers are 2.5 GPa and 11μm,respectively.The results of SEM indicate that the surface of Si-Zr-C-O fibers is smooth, and there are no obvious disfigurements.The Si-Zr-C-O fibers are non-crystal fibers,which contain much free C and O with the form of multiplicity phase SiC_xO_y.The multiplicity phase of Zr bonding O exists in it.

A polyferrocarbosilane(PFCS) was synthesized from polydimethylsilane(PDMS) and ferrocene.The ordered-porous Fe-containing SiC ceramic with BET specific surface area of 703.46 m2/g was prepared.The preparing process included the formation of silica template,PFCS precursor infiltration into the template,curing of the precursor,pyrolysis of the cured preceramic polymer and etching of the silica template.The ceramic showed some magnetic properties.

To prepare preceramic polymers in the SiBNC system,different synthetic routes of preceramic polymers and single source precursors for SiBN,SiBC and SiBNC ceramics known to date were compiled and critically reviewed.The synthetic routes of the preceramic polymers were classified into two groups: co-condensation of different molecular species and polycondensation of single source precursors.The latter one was paid more attention these days since the single source precursors exhibit structural features that are desired to be present in the final ceramics.Current situations of the preceramic polymers in the SiBNC system at home and abroad,as well as their prospects,were also discussed in this paper.

Manufacturing of ceramic materials from preceramic polymers bas recently obtained particular interest.Tailoring of molec- ular structure and composition of the appropriate starting compounds,low fabrication temperatures and versatile plastic shaping technologies favor the polymer route for the fabrication of ceramics.In tbis paper,nano-ferrum particle,average 30 nm in di- ameter,was dispersed into polycarbosilane(PCS)homogeneously by ultra-sonic method,then porous Si-C-Fe ceramic was obtained by precursor pyrolysis.The microstructure of the ceramic was observed by SEM and the form of nano-ferrum particle in ceramic was studied by X-ray diffraction analysis.The electromagnetic properties of tbe porous ceramic were characterized and the effects of nano-ferrum particle content on the electromagnetic properties were studied.

As an excellent reinforcement material of high property structural radar absorbing composites,SiC fibers exhibit very important military values. But the electromagnetic properties of common SiC fibers fabricated with precursor polymer route should be modified if we want to use them as reinforcement material with good radar absorbing function. The modification means of the electromagnetic properties of SiC fibers were explained detailedly in the essay,and their advantage and disadvantage were compared. Then the shortcomings of the modification research of electromagnetic properties of SiC fibers at home were analyzed

介绍了红外低发射率材料研究的理论基础,从组成的角度分析了低发射率涂料的研究进展,并对影响低发射率性能的各种因素进行了讨论分析.