用垂直阵和单水听器测量水下目标辐射噪声的误差分析及其修正方法

文章给出了水声波导模型下垂直阵和单水听器测量水下目标辐射噪声的误差和修正方法,以便使两种测量结果一致和统一。在设定典型水声波导的参数后,用波数积分方法计算出声源到垂直阵各阵元的信道传输函数,再推导出垂直嵌套阵聚焦波束的信道传输函数,从而得到单水听器和垂直嵌套阵的测量误差。数值计算表明在70 m海深条件下,不同深度单水听器测量单频信号频谱级起伏达15 dB以上,总声级测量误差的均值为3 dB,而垂直嵌套阵测量单频信号频谱级起伏仅4 dB,总声级测量误差的均值趋于0 dB。海上实验测量单频信号声源级的结果与数值计算的起伏一致,海试中垂直阵获得较高的空间增益。结论是在浅海条件下垂直阵的测量精度高于单水听器的测量精度,用单水听器测量的目标总声级需要修正时可以修正,而用单水听器测量的单频信号声源级则难以修正。     

饱和放大情形下光纤参量放大器的增益和带宽特性研究

利用龙格库塔法数值求解非线性耦合方程,研究了单抽运光纤参量放大器在增益饱和区的增益谱特性.通过比较考虑抽运光损耗与忽略抽运光损耗增益谱的差别,分析了抽运光损耗对增益谱的影响.此外,给出了在饱和放大区,信号光的增益谱与光纤长度、输入信号光功率、抽运光波长与零色散波长偏离之间的关系.发现在饱和放大区,增益的整体水平有所下降,增益谱的可用带宽相对于小信号放大有所减少,增益谱在可用带宽范围内出现了旁瓣.这些结果将对工作在饱和放大区的单抽运光参量放大器的设计提供有益的帮助.     

AlGaN/GaN抛物量子点的尺寸相关三阶非线性极化率研究

在有效质量近似框架下,通过求解AlxGa1－xN/GaN自组织圆柱形量子点的薛定谔方程,计算了量子点中导带电子在两个正交方向：Z‖和Z⊥方向上产生的三阶非线性极化率.计算中,电子的运动受到自组织量子点的抛物型束缚势和内建压电场的影响.计算表明,量子点的三阶非线性极化率的数量级达到了10－14m2/V2.进一步在Z‖和Z⊥方向上,考察了三阶非线性极化率与两个方向上的抛物束缚势的频率ωp、ωz,量子点的高度L,半径R,Al的含量x之间的关系.     

用蒙特卡罗方法模拟直接转换X射线探测器的响应特性

采用Monte Carlo方法模拟了HgI₂、非晶Se和CdTe几种直接X射线转换探测器在医用X射线范围(10—100keV)的透过谱、背向散射谱、吸收效率和光电灵敏度. 对X射线和HgI₂的作用过程模拟采用了EGSnrc Monte Carlo代码系统, 对信号电荷的产生考虑了电荷产生的高斯噪声和材料深陷阱作用造成的部分电荷收集影响. 结果表明, 载流子平均自由程(Schubweg)在相对于探测材料厚度较小时, 陷阱作用能很大地影响探测灵敏度. HgI₂的灵敏度是非晶Se的5倍以上, CdTe的灵敏度是非晶Se的10倍以上, 采用高Z序数材料可以大大提高探测灵敏度.     

电容器特性组合演示仪

第一，课本原有的充放电电路如图1所示，如用这个电路演示充放电过程，没有任何可以观察到的实验现象，因此难以令学生信服，何时充电、放电也无法得知．     

Banach空间中微分方程解的存在与唯一性

在一般Banach空间中,作者讨论了微分方程的初值问题u=f(t,u),u(0)=x0.在比文[6]中弱Carathodory条件更弱的情况下,不仅放宽了[6]中的一个重要不等式条件,还去掉了另一与之相关的不等式限制,仍获得了初值问题解的存在与唯一性及解的迭代逼近.对周期边值问题也获得了类似结果.     

Analysis of lignans in Schisandra chinensis and rat plasma by high‐performance liquid chromatography diode‐array detection,time‐of‐flight mass spectrometry and quadrupole ion trap mass spectrometry

High‐performance liquid chromatography/diode‐array detection (HPLC/DAD), time‐of‐flight mass spectrometry (HPLC/TOFMS) and quadrupole ion trap mass spectrometry (HPLC/QIT‐MS) were used for separation, identification and structural analysis of lignans in Schisandra chinensis and rat plasma after oral administration of the herbal extract. Six lignans in Schisandra chinensis extract were identified unambiguously by comparing the retention time, their characteristic ultraviolet (UV) absorption and accurate mass measurement. A formula database of known lignans in Schisandra chinensis was established, against which the other 15 lignans were identified effectively based on the accurate extract masses and formulae acquired by HPLC/TOFMS. In order to distinguish the isomers, multi‐stage mass spectrometry (ion trap mass spectrometry, MSⁿ) was also used. The fragmentation behavior of the lignans in the ion trap mass spectrometer was studied by the six lignan standards, and their fragmentation rules in MSⁿ spectra were summarized. These deduced fragmentation rules of lignans were successfully implemented in distinguishing the three groups of isomers in Schisandra chinensis by HPLC/QIT‐MS. By using the three different analytical techniques, 21 lignans in Schisandra chinensis were identified within 30 min. After oral administration of the extract, 11 lignans in rat plasma were detected and identified by comparing their retention time, characteristic UV absorption and accurate mass measurement of peaks in HPLC/TOFMS chromatograms of the herbal extract. Finally, HPLC/TOFMS fingerprints of Schisandra chinensis in vitro and rat plasma in vivo were established. It is concluded that a rapid and effective method based on three analytical techniques for identification of chemical components was established, which is useful for rapid identification of multiple components in Schisandra chinensis in vitro and in vivo. In addition, it can provide help for further pharmacology and action mechanism study of lignans in Schisandra chinensis. Copyright © 2009 John Wiley & Sons, Ltd.     

湿有效能量预报暴雨的动力分析

根据7个例子的对比分析表明:湿有效能量对预报暴雨具有较好的指示性,但在某些条件下湿有效能量在有无暴雨发生两者上并无明显差别。对暴雨和无暴雨个例的动力条件分析表明:(1)有暴雨时,在杭州地区为一个相对辐散区(300—900百帕),并伴有较强的上升运动,无暴雨时则为相对辐合区;(2)暴雨时高空有一支强的急流,暴雨区位于高空发散流场和急流中心的入口区右侧。(3)稳定度大小两者也有明显差异。分析结果对业务预报有一定参考价值。     

Synthesis and characterization of high molecular weight hexafluoroisopropylidene‐containing polybenzimidazole for high‐temperature polymer electrolyte membrane fuel cells

A high molecular weight, thermally and chemical stable hexafluoroisopropylidene containing polybenzimidazole (6F‐PBI) was synthesized from 3,3′‐diaminobenzidine (TAB) and 2,2‐bis(4‐carboxyphenyl) hexafluoropropane (6F‐diacid) using polyphosphoric acid (PPA) as both the polycondensation agent and the polymerization solvent. Investigation of polymerization conditions to achieve high molecular weight polymers was explored via stepwise temperature control, monomer concentration in PPA, and final polymerization temperature. The polymer characterization included inherent viscosity (I.V.) measurement and GPC as a determination of polymer molecular weight, thermal and chemical stability assessment via thermo gravimetric analysis and Fenton test, respectively. The resulting high molecular weight polymer showed excellent thermal and chemical stability. Phosphoric acid doped 6F‐PBI membranes were prepared using the PPA process. The physiochemical properties of phosphoric acid doped membranes were characterized by measuring the phosphoric acid doping level, mechanical properties, and proton conductivity. These membranes showed higher phosphoric acid doping levels and higher proton conductivities than the membranes prepared by the conventional membrane fabrication processes. These membranes had sufficient mechanical properties to be easily fabricated into membrane electrode assemblies (MEA) and the prepared MEAs were tested in single cell fuel cells under various conditions, with a focus on the high temperature performance and fuel impurity tolerance. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4064–4073, 2009     

Photoelectrochemical determination of Hg(II) via dual signal amplification involving SPR enhancement and a folding-based DNA probe

The authors describe a highly sensitive and selective photoelectrochemical (PEC) assay for mercury(II) ions. It is based on a dual signal amplification strategy. The first enhancement results from the surface plasmon resonance (SPR) of Au@Ag nanoparticles (NPs) absorbed on MoS₂ nanosheets. Here, the injection of hot electrons of Au@Ag NPs into MoS₂ nanosheets produces a strong photocurrent, while background signals are strongly reduced. The second enhancement results from the use of a thymine rich ct-DNA aptamer attached to the Au@Ag-MoS₂ nanohybrid. The DNA specifically binds Hg(II) ions to form thymine-Hg(II)-thymine (T-Hg-T) complexes. This leads to the formation of a hairpin-shaped dsDNA structure. The use of a CdSe quantum dot label at the terminal end of the ct-DNA further facilitates electron–hole separation. The photocurrent of the detector is measured as a function of Hg(II) concentration at a bias voltage of 0.1 V and under irradiation of 430 nm light. Due to the two-fold amplification strategy presented here, the linear range extends from 10 pmol·L^?1 to 100 nmol·L^?1, with a detection limit of 5 pmol·L^?1 (at S/N?=?3).

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Graphical Abstract The injection of hot electrons of Au@Ag into MoS₂ produces a strong photocurrent, and the formation of thymine-Hg(II)-thymine further facilitates electron–hole separation by CdSe. This dual signal amplification strategy is used to detect Hg(II) ions via a photoelectrochemical assay.