参量阵水下通讯

一、引 言 随着海洋开发和水下潜艇航行的需要,水下信息的传送已成为日益重要的问题.对于潜艇水下通讯、深海水下摄象及水下电视的长距离无线传输,声波是一种有效的传输工具。通常的线性声学水下声通讯系统存在着指向性与传送距离的矛盾。为了减少多径干扰,必须提高发射器的指向性,亦即提高工作频率,从而就要牺牲作用距离。     

随机单调减算子的随机不动点定理

利用锥理论和非对称迭代法,讨论了随机单调减算子的随机不动点的存在唯一性,同时给出了迭代序列收敛于解的误差估计,改进和推广了某些已知结果.     

利用群速度匹配的级联二阶非线性实现超短激光脉冲压缩

提出了一种采用倾斜脉冲的级联二阶非线性来实现超短激光脉冲压缩的方法. 对基于单块BBO晶体中基频光与倍频光群速度匹配的级联二阶非线性的脉冲压缩方案进行了理论分析. 对比研究了群速度匹配与失配情况下利用级联二阶非线性进行脉冲压缩的效果, 并模拟分析了基频光与倍频光的位相失配量、非线性晶体长度、 基频光初始峰值光强和初始脉宽等因素对脉冲压缩效果的影响. 结果表明, 基频光与倍频光的群速度匹配将会大幅度改善压缩脉冲的时间波形和频谱分布. 通过对位相失配量、晶体长度、初始光强等参数的优化和选取可获得较理想的压缩效果. 采用倾斜脉冲的级联二阶非线性的脉宽压缩方法, 针对中心波长800 nm、脉宽100 fs, 峰值光强为50 GW/cm²的基频光脉冲, 采用25 mm厚BBO晶体, 当基频光与倍频光位相失配量Δk=60 mm^-1(对应失谐角1.98°), 晶体外部脉冲前沿倾斜角γ₀=74°时, 计算获得了质量较好的20 fs剩余基频光, 并同时产生了14 fs的倍频光. 关键词： 倾斜波 级联二阶非线性 群速度失配 脉冲压缩     

Synthesis,Crystal Structure and Anti-breast Cancer Activity of ((3S,5R)-5-((1H-1,2,4-triazol-1-yl)methyl)-5-(2,4-difluorophenyl)tetrahydrofuran-3-yl)methyl 4-Methylbenzenesulfonate

The new heterocycle compound ((3S,5R)-5-((1H-1,2,4-triazol-1-yl)methyl)-5-(2,4-difluorophenyl)tetrahydrofuran-3-yl)methyl 4-methylbenzenesulfonate (1), designed using((3R,5S)-5-(2,4-difluorophenyl)-5-iodotetrahydrofuran-3-yl)methyl isobutyrate(2) as the start material, was successfully obtained via multiple synthesis route and finally characterized by IR, ~1H NMR, and single-crystal X-ray crystallography. In addition, the in vitro anticancer activities of the newly synthesized complex 1 have been emulated against three human breast cancer cell lines BT474, MCF7 and MB.     

云南腾冲土官寨离子吸附型稀土矿床地球化学特征

运用岩石地球化学方法,对云南腾冲土官寨矿区离子吸附型稀土矿床的地球化学特征进行研究。结果显示:风化层较基岩明显富集Al_2O_3, Fe_2O_3, FeO等,贫化CaO, Na_2O, MgO, K_2O等元素,绝大多数微量及稀土元素均有不同程度的富集;垂向上从上到下稀土含量总体呈现"低-高-低"的抛物线形态, Ce元素与其他元素之间发生了明显的分异现象,个别样品中表土层稀土含量较高且含矿层较厚可能是由于风化历史时期的构造沉降作用造成的;由半风化层到全风化层, REE元素均为迁入,其中∑LREE迁入程度较∑HREE高,与不同稀土元素的水解能力和黏土矿物吸附选择性有关,而由全风化层到表土层, REE元素则发生了不同程度的降低。     

水溶性葛根素衍生物的合成

以葛根素为起始原料,分别经亲核取代反应和羟甲基化反应得到水溶性4′-羟乙基葛根素和3′,5′-二羟甲基葛根素,对首次得到的3′,5′-二羟甲基葛根素,用正交实验对的合成条件进行了优化,当n(葛根素)∶n(甲醛)∶n(氢氧化钠)=1∶2∶4,反应温度为60℃,反应时间为4.0 h,产率为69.0%。目标化合物的结构经IR、~1H NMR、~(13)C NMR和元素分析方法进行表征。经测试4′-羟乙基葛根素和3′,5′-二羟甲基葛根素水溶性分别是葛根素的5倍和10倍。     

利用空间位阻和氢溢流协同作用促进5-羟甲基糠醛选择性加氢制备5-甲基糠醛

化学工业生产中，用氢气为还原剂，通过选择性加氢可以制备多种重要化学品。5-羟甲基糠醛是重要的生物质基平台化合物，而5-甲基糠醛是用途广泛的化学品。由5-羟甲基糠醛加氢得到5-甲基糠醛是一条非常理想的路径，但是选择性活化C-OH非常困难。本文设计并制备了Pt@PVP/Nb₂O₅(PVP: 聚乙烯吡咯烷酮)催化剂，该催化体系巧妙地结合了位阻效应、氢溢流和催化剂界面的电子效应，系统研究了该催化剂对5-羟甲基糠醛选择性加氢制备5-甲基糠醛催化性能，在最优条件下，5-甲基糠醛的选择性可达92%。利用密度泛函理论计算研究了5-羟甲基糠醛选择性加氢制备5-甲基糠醛反应路径。     

恒星对增长螺旋引力扰动的非线性响应及其对增长模式的致稳作用*

本文计算了在增长的螺旋扰动引力场中恒星响应的非线性效应.结果表明,这一非线性效应会导致Q值的增加,从而降低增长率.对于振幅很小,增长率也较小的螺旋形模式,Q值增加较慢;对于振幅较大或增民率较大的模式,Q值也增加较快,从而有效地抑正振幅的增长.这一调节机制是使得由线性理论所得出的增长模式最终达到准稳状态的原因之一。     

On the sensitive dynamical system and the transition from the apparently deterministic process to the completely random process

The detailed analysis of the dynamical process of coin tossing is made. Through calculations, it is illustrated how and why the result is extremely sensitive to the initial conditions. It is also shown that, as the initial height of the mass center of the coin increases, the final configuration, i.e. head or tail, becomes more and more sensitive to the initial parameters (the initial velocity angular velocity, and the initial orientation), the coefficient of the air drag, and the energy absorption factor of the surface on which the coin bounces. If we keep the head upward initially but allow a small range for the change of some other initial parameters, the frequency that the final configuration is head, would be 1 if the initial height h of the mass center is sufficiently small, and would be clo to 1/2 if h is sufficiently large. An interesting question is how this frequency changes continuously from 1 to 1/2 as h increases. Detailed calculations show that such a transition is very similar to the transition from laminar to turbulent flows. A basic difference between the transition stage and the completely random stage is indicated: In the completely random stage, the deterministic process of the individual case is extremely sensitive to the initial conditions and the dynamical parameters, out the statistical properties of the ensemble are insensitive to the small changes of the initial conditions and the dynamical parameters. On the contrary, in the transition stage, both the deterministic process of the individual case and the statistical properties of the ensemble are sensitive to the initial conditions and the dynamical parameters. The mechanism for this feature of the transition stage is the existence of the long-train structure in the parameter space. The illuminations of this analysis on some other random phenomena are discussed.