针对散射激光的全向激光告警系统激光威胁源定位技术研究

针对目前散射激光告警中只能定位到散射激光光斑,而不能追溯到敌方来袭激光源的现状,构建了战场环境下包括敌方威胁激光源、照射于某平台上的散射激光光斑以及全向激光告警系统在内的空间三维几何模型,推导了平台上散射激光光斑轮廓解析表达式,以及轮廓上任意一点相对鱼眼镜头的物方半视场角表达式。将成像于探测器上的光斑进行鱼眼成像畸变校正并取光斑边缘点,计算得到三维几何模型诸参数。再将模型参数与传感器阵列信息相结合,可最终获取敌方威胁激光源相对系统的方位和距离信息。最后对以上方法进行了实验验证并对产生误差的原因进行了分析。     

种子注入环形腔人眼安全KTP参变振荡器的研究

利用电光调Q的Nd:YAG激光器抽运非临界相位匹配(θ=90°,φ=0°)环形腔KTP光学参变振荡器(OPO),实现了高能量人眼安全波段的1.57μm激光输出。理论与实验结果表明,减小谐振腔长度和注入种子源激光可以有效降低阈值,提高输出能量。当Nd:YAG激光器抽运能量为88mJ时,注入种子源功率由0mW增加到6mW,输出能量由8.8mJ增加到14mJ。当抽运能量为167.7mJ,注入种子源功率达到6mW时,最大输出能量达到46mJ,峰值功率7.44MW。     

Diffusion properties of cortical and pericortical tissue: regional variations, reliability and methodological issues

Characterizing the diffusion properties of cortical tissue is complicated by intersubject variability in the relative locations of gyri and sulci. Here we extend methods of measuring the average diffusion properties of gyral and sulcal structures after they have been aligned to a common template of cortical surface anatomy. Diffusion tensor image (DTI) data were gathered from 82 young subjects and co-registered with high-resolution T1 images that had been inflated and co-registered to a hemispherically unified spherical coordinate system based on FreeSurfer. We analyzed fractional anisotropy (FA), mean diffusivity (MD) and the novel quantity of cortical primary diffusion direction (cPDD) at five surfaces parallel to the white/gray junction, spanning approximately 5 mm from the pial surface into white matter. FA increased with increasing depth, whereas MD and cPDD were reduced. There were highly significant and reliable regional differences in FA, MD and cPDD as well as systematic differences between cortical lobes and between the two hemispheres. The influence of nearby cortical spinal fluid (CSF), local cortical curvature and thickness, and sulcal depth was also investigated. We found that FA correlated significantly with cortical curvature and sulcal depth, while MD was strongly influenced by nearby CSF. The measurement of FA, MD and cPDD near the cortical surface clarifies the organization of fiber projections to and from the cortex.     

Studies of the structural,electronic and dielectric properties of Ca1−xSrxTiO3

The lattice constants, band structure and dielectric properties of Ca_1−xSr_xTiO₃ (0<x<1) (CSTO) have been studies by using the first-principles implemented with the GGA-PBEsol method. The calculation results shows that the lattice constants of CSTO obeys the Vegard model while the energy gap of CSTO shows a decreasing trend with the changing molar fraction x. The real and imaginary parts of the dielectric function and the static dielectric constant of the CSTO, optical permittivity and the static refractive index, are given to support the potential applications of the compounds in the future.     

Novel methods for synthesizing halide-free alane without the formation of adducts

Many of the current synthesis methods for aluminum hydride (alane—AlH₃) involve reacting AlCl₃ and LiAlH₄ in solvents. The reaction requires the formation of an alane adduct such as AlH₃⋅[(C₂H₅)₂O] prior to obtaining crystallized stable α-AlH₃. This process requires several hours of pumping in a vacuum system to remove the ether and convert the alane etherate into stable α-alane. This crystallization process is both costly and hazardous because a large amount of highly flammable material (e.g. ether) is removed by vacuum pumps over several hours. Conversely, the work presented herein describes novel methods to synthesize adduct-free alane. It is demonstrated here that AlH₃ can form by mixing AlCl₃ and LiAlH₄ in the solid state and heating to 75^∘C; only α-AlH₃ was obtained. The α-AlH₃ product can be washed with minimal solvents leading to zero formation of alane adducts. In addition, the unwanted LiCl by-product is also removed during the solvent wash, resulting in halide-free α-alane. Although simply mixing and heating the reactants led to a 40% yield of alane, having the reactants compacted and mechanically pressed while heating increases the yield to 60% crystalline α-AlH₃.     

Electrical properties of ferroelectric-gate FETs with SrBi2Ta2O9 formed using MOCVD technique

Ferroelectric-gate?field-effect?transistors?(FeFETs) with a Pt/SrBi₂Ta₂O₉/Hf-Al-O/Si gate stack were fabricated using the metal-organic chemical vapor deposition (MOCVD) technique to prepare the SrBi₂Ta₂O₉ (SBT) ferroelectric layer. A?good threshold voltage (V _th) distribution was found for more than 90?n-channel FeFETs in one chip with a 170?nm SBT layer owing to the good film uniformity of the SBT layer deposited by MOCVD. The average memory window $(V_{\mathrm{w}}^{\mathrm{av}})$ and the standard deviations (σ _thl,σ _thr) of the left- and right-side branches of the drain-gate voltage curves of the FeFETs yielded a $V_{\mathrm{w}}^{\mathrm{av}}/(\sigma_{\mathrm{thl}} + \sigma_{\mathrm{thr}})$ value of 5.45, indicating that the FeFETs can be adapted for large-scale-integration. The electric field, the energy band profile in the gate stack, and the gate leakage current were also investigated at high gate voltages. We found that the effect of Fowler–Nordheim tunneling appeared under these conditions. Because of the tunneling injection and trapping of electrons into the gate insulators, the operation voltage ranges of the FeFETs were limited by this tunneling.     

Bandgap tuning in armchair MoS(2) nanoribbon

We report on the first-principles calculations of bandgap modulation in armchair MoS(2) nanoribbon (AMoS(2)NR) by transverse and perpendicular electric fields respectively. In the monolayer AMoS(2)NR case, it is shown that the bandgap can be significantly reduced and be closed by transverse field, whereas the bandgap modulation is absent under perpendicular field. The critical strength of transverse field for gap closure decreases as ribbon width increases. In the multilayer AMoS(2)NR case, in contrast, it is shown that the bandgap can be effectively reduced by both transverse and perpendicular fields. Nevertheless, it seems that the two fields exhibit different modulation effects on the gap. The critical strength of perpendicular field for gap closure decreases with increasing number of layers, while the critical strength of transverse field is almost independent of it.     

Insulator, semiclassical oscillations and quantum Hall liquids at low magnetic fields

Magneto-transport measurements are performed on two-dimensional GaAs electron systems to probe the quantum Hall (QH) effect at low magnetic fields. Oscillations following the Shubnikov-de Haas (SdH) formula are observed in the transition from the insulator to QH liquid when the observed almost temperature-independent Hall slope indicates insignificant interaction correction. Our study shows that the existence of SdH oscillations in such a transition can be understood based on the non-interacting model.     

NaK(61∑+)与H2碰撞传能中的H2的振转态分布

光学-光学双共振激发NaK至61Σ+高位电子态,研究了NaK(61Σ+)与H2的电子-振转能量转移.利用相干反斯托克斯拉曼散射(CARS)光谱技术检测H2的振转态分布.扫描CARS谱表明H2在(1,1),(2,1),(2,2),(2,3),(3,1),(3,2),(3,3)和(3,5)振转能级上有布居.对于(3,1),(3,2),(3,3)和(3,5)能级,扫描CARS谱峰值直接给出布居数之比.对于(1,1),(2,1),(2,2)和(2,3)能级,扫描CARS谱峰值给出二个可能的布居数之比,利用一个速率方程组,由时间分辨CARS轮廓可以得到真实的比值.用n1～n8分别表示H2的(3,1),(2,1),(1,1),(3,3),(2,3),(2,2),(3,2)和(3,5)能级上布居密度,得到n2/n1～n8/n1分别为0.51,0.97,0.45,0.18,0.10,0.26和0.31.利用Stern-Volmer公式,得到61Σ+态的总退布速率系数为(2.1±0.4)×10-10 cm3 s-1,由H2各振转能级布居数之比,得到61Σ+-(1,1),(2,1),(2,2),(2,3),(3,1),(3,2),(3,3)和(3,5)转移速率系数(10-11 cm3·S-1单位)分别为5.4±1.6,2.8±0.8,0.6±0.2,1.0±0.3,5.6±1.7,1.4±0.4,2.5±0.8和1.7±0.5.