干涉条纹空间频率对数字叠栅移相干涉测量精度的影响

基于数字叠栅移相干涉原理,分析了CCD像元尺寸、随机噪声和量化误差对采样后干涉条纹和合成叠栅条纹对比度的影响,并就干涉条纹频率对叠栅移相干涉相位测量精度的影响进行了理论分析和仿真研究。结果表明,随着干涉条纹空间频率的增大,CCD的采样过程、随机噪声和量化噪声会影响叠栅条纹信号的对比度和信噪比,并通过相位解算过程直接影响数字叠栅移相干涉的相位测量精度。以相位测量精度为π/50(折合光程差精度为λ/100)作为判断标准,对应可探测干涉条纹的最大空间频率为0.45λ/pixel,为后续数字叠栅移相干涉测量范围的研究提供了定量理论依据。     

Total ionizing dose effects in elementary devices for 180-nm flash technologies

The response of single flash cell in a 180-nm flash technology to total ionizing dose (TID) is studied. The results indicate that the erased cell flips at a dose level of 100 krad(Si), whereas the programmed cell does not even at the dose level up to 1 Mrad(Si). This asymmetric phenomenon is attributed to the difference between the reference current of the comparator circuit and the intrinsic current of the flash cell. For the first time, we show that the irradiation-induced flash cell drain-current variation does not saturate at the intrinsic value, i.e. the drain current of a device with neutrally charged floating gate. After degrading to the intrinsic state, the read current of the erased cell gradually increases while the programmed cell continues to increase and then slightly drops back. Radiation tolerance comparison of single flash cell, I/O transistors and high-voltage (HV) transistors demonstrates that HV NMOS is most susceptible to ionizing radiation. The radiation tolerance of the circuit level is also evaluated from the elementary devices.     

便携式无源探测雷达研究

针对静默哨兵系统等隐身雷达的战场机动能力不足,提出了一种便携式无源侦察系统的设计方法.通过三点布站对目标测距定位,对信号作相关处理提高侦测距离,用时域遍历代替相控天线在空域遍历实现多目标功能.方法简洁、造价低廉,对构建国土和城市重点防御有一定参考价值.     

基于SVM的语音情感识别研究

随着计算机技术的发展,人们对和谐人机交互的要求不断提高,这就要求计算机能理解说话人的情感信息,即能进行语音情感识别。本文提出了一种基于支持向量机（SVM）的语音情感识别方法,主要对人类的6种基本情感：高兴、惊奇、愤怒、悲伤、恐惧、平静进行研究。首先对自建语音情感数据库的情感语句提取特征,然后运用序列前向选择（SFS）算...     

文件系统的快速启动机制研究

文章提供一种文件系统的快速启动方法,通过设计一种合理的文件系统一致性方案以减少文件系统的完整性检查,且只在合适的时机扫描磁盘以减少磁盘扫描开销有效缩短文件系统启动时间。     

Bisanthracene‐Based Donor–Acceptor‐type Light‐Emitting Dopants: Highly Efficient Deep‐Blue Emission in Organic Light‐Emitting Devices

Deep‐blue fluorescent compounds are particularly important in organic light‐emitting devices (OLEDs). A donor–accepotor (DA)‐type blue‐emitting compound, 1‐(10‐(4‐methoxyphenyl)anthracen‐9‐yl)‐4‐(10‐(4‐cyanophenyl)anthracen‐9‐yl)benzene ( BD3 ), is synthesized, and for comparison, a nonDA‐type compound, 1,4‐bis(10‐phenylanthracene‐9‐yl)benzene ( BD1 ) and a weak DA‐type compound, 1‐(10‐phenylanthracen‐9‐yl)‐4‐(10‐(4‐cyanophenyl)anthracen‐9‐yl)‐benzene ( BD2 ), are also synthesized. The twisted conformations of the two anthracene units in the compounds, confirmed by single crystal X‐ray analysis, effectively prevent π‐conjugation, and the compound shows deep‐blue photoluminescence (PL) with a high PL quantum efficiency, almost independent of the solvent polarity, resulting from the absence of an intramolecular charge transfer state. The DA‐type molecule BD3 in a non‐doped device exhibits a maximum external quantum efficiency (EQE) of 4.2% with a slight roll‐off, indicating good charge balance due to the DA‐type molecular design. In the doped device with 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl (CBP) host, the BD3 exhibits higher EQE than 10% with Commission International de L'Eclairge (CIE) coordinates of (0.15, 0.06) and a narrow full‐width at half‐maximum of 45 nm, which is close to the CIE of the high definition television standard blue.     

Ultrahigh Infrared Photoresponse from Core–Shell Single‐Domain‐VO2/V2O5 Heterostructure in Nanobeam

Infrared (IR) harvesting and detection in red and near‐IR (NIR) part of the solar spectrum have always been a long‐term research area of intense interest. However, limited choices of current photoactive materials have significantly hampered the realization of ultrahigh IR sensitivity under room temperature conditions. The trigger for this requires the exploration of new photo­active materials and the ability to fabricate new photoactive structural design. Herein, a new oxide‐catalogue photoconductive NIR detector with ultrahigh performance built by core/shell nanobeam heterostructures (CSNHs) with the inner single‐domain monoclinic VO₂ (M) core and outer V₂O₅ shell, which is the first example of photoconductive IR detector made from transition metal oxides (TMOs), is presented. Benefited from the well‐defined TMO hetero­junction interface, the ultrahigh responsivity (R_λ) of 2873.7 A W^‐1 and specific detectivity (D*) of 9.23 × 10¹² Jones are achieved at room temperature (at 990 nm; 0.2 mW cm^‐2), recording the best performance compared with those reported IR detectors based on heavy‐metal‐free materials, and even comparable/superior to those traditional ones made from materials including heavy metals. These findings pave a new way to design oxide heterostructures for intriguing applications in optoelectronic and energy harvesting nanodevices.     

Topological‐Structure Modulated Polymer Nanocomposites Exhibiting Highly Enhanced Dielectric Strength and Energy Density

Dielectric materials with high electric energy densities and low dielectric losses are of critical importance in a number of applications in modern electronic and electrical power systems. An organic–inorganic 0–3 nanocomposite, in which nanoparticles (0‐dimensional) are embedded in a 3‐dimensionally connected polymer matrix, has the potential to combine the high breakdown strength and low dielectric loss of the polymer with the high dielectric constant of the ceramic fillers, representing a promising approach to realize high energy densities. However, one significant drawback of the composites explored up to now is that the increased dielectric constant of the composites is at the expense of the breakdown strength, limiting the energy density and dielectric reliability. In this study, by expanding the traditional 0–3 nanocomposite approach to a multilayered structure which combines the complementary properties of the constituent layers, one can realize both greater dielectric displacement and a higher breakdown field than that of the polymer matrix. In a typical 3‐layer structure, for example, a central nanocomposite layer of higher breakdown strength is introduced to substantially improve the overall breakdown strength of the multilayer‐structured composite film, and the outer composite layers filled with large amount of high dielectric constant nanofillers can then be polarized up to higher electric fields, hence enhancing the electric displacement. As a result, the topological‐structure modulated nanocomposites, with an optimally tailored nanomorphology and composite structure, yield a discharged energy density of 10 J/cm³ with a dielectric breakdown strength of 450 kV mm^–1, much higher than those reported from all earlier studies of nanocomposites.     

Mesostructured Arrays of Nanometer‐spaced Gold Nanoparticles for Ultrahigh Number Density of SERS Hot Spots

A novel one‐trough synthesis via an air‐water interface is demonstrated to provide hexagonally packed arrays of densely spaced metallic nanoparticles (NPs). In the synthesis, a mesostructured polyoxometalate (POM)‐silicatropic template (PSS) is first self‐assembled at the air‐water interface; upon UV irradiation, anion exchange cycles enable the free‐floating PSS film to continuously uptake gold precursors from the solution subphase for diffusion‐controlled and POM‐site‐directed photoreduction inside the silica channels. NPs ≈ 2 nm can hence be homogeneously formed inside the silica‐surfactant channels until saturation. As revealed via X‐ray diffraction, small‐angle X‐ray scattering (SAXS), grazing incidence SAXS, and transmission electron microscopy, the Au NPs directed by the PSS template are arrayed into a 2D hexagonal lattice with inter‐channel spacing of 3.2 nm and a mean along‐channel NP spacing of 2.8 nm. This corresponds to an ultra‐high number density (≈10¹⁹ NPs cm^?3) of narrowly spaced Au NPs in the Au‐NP@PSS composite, leading to 3D densely deployed hot‐spots along and across the mesostructured POM‐silica channels for surface‐enhanced Raman scattering (SERS). Consequently, the Au‐NP@PSS composite exhibits prominent SERS with 4‐mercaptobenzoic acid (4‐MBA) adsorbed onto Au NPs. The best 4‐MBA detection limit is 5 nm , with corresponding SERS enhancement factors above 10⁸.     

Three‐Dimensional Branched Nanowire Heterostructures as Efficient Light‐Extraction Layer in Light‐Emitting Diodes

A facile method to fabricate three‐dimensional branched ZnO/MgO nanowire heterostructures and their application as the efficient light‐extraction layer in light‐emitting diodes are reported. The branched MgO nanowires are produced on the hydrothermally‐grown ZnO nanowires with a small tapering angle towards the tip (≈6°), by the oblique angle flux incidence of MgO. The structural evolution during the growth verifies the formation of the MgO nanoscale islands with strong (111) preferred orientation on very thin (5–7 nm) MgO (110) layer. The MgO nanobranches, then grown on the islands, are polycrystalline consisting of many grains oriented in specific directions of <200> and <220>, supported by the nucleation theory. The LEDs with the branched ZnO/MgO nanowire arrays show a remarkable enhancement in the light output power by 21% compared with that of LEDs with pristine ZnO nanowires. Theoretical calculations using a finite‐difference time‐domain method reveal that the nanostructure is very effective in breaking the wave‐guiding mode inside the ZnO nanowires, extracting more light especially in radial direction through the MgO nanobranches.