Palladium-catalyzed cross-coupling of acetates of Baylis-Hillman adducts and potassium organotrifluoroborates

[reaction: see text] The cross-coupling of potassium organotrifluoroborates and acetates of Baylis-Hillman adducts proceeds readily in moderate to excellent yield in the presence of Pd(OAc)(2). The reaction tolerates hindered trifluoroborate salts, and the process is stereoselective.     

Oscillatory behavior of the second-order nonlinear neutral difference equations

In this paper, we consider the oscillation of the second-order neutral difference equation $$\Delta ^2 \left( {x_n - px_{n - \tau } } \right) + q_n f\left( {x_{n - \sigma _n } } \right) = 0$$ as well as the oscillatory behavior of the corresponding ordinary difference equation $$\Delta ^2 z_n + q_n f\left( {R\left( {n,\lambda } \right)z_n } \right) = 0$$ .     

High-field 127I NMR of solid sheelite structures: periodates revisited

We report new solid-state ¹²⁷I NMR results for sheelite periodates, MIO₄ (M = Na⁺ , K⁺ , Rb⁺ , and NH⁺ ₄), and for pseudo-scheelite CsIO₄ and HIO₄. The observed ¹²⁷I quadrupole coupling constants were between 1.0 and 43.0 MHz in agreement with previous NQR data. In contrast to an early ¹²⁷I NMR study (S. L. Segel and H. M. Vyas, 1980, J. Chem. Phys.72, 1406), we found that the ¹²⁷I chemical shift anisotropy is negligibly small in sheelite periodates. A small but definite ¹²⁷I chemical shift tensor was observed for pseudo-scheelite CsIO₄.     

Laser-diode-pumped Cr(4)+, Nd(3)+:YAG with self-Q-switched laser output of 1.4 W

By use of a laser diode as a pump source, a self-Q-switched laser from a Cr, Nd:YAG crystal is demonstrated. The output Q-switched traces are very stable, the threshold pump power is 3.5 W, the pulse duration is 50 ns, and the slope efficiency is as high as 20%. In addition, the pulse width remains constant while the pulse repetition rate varies with pump power.     

Interferometric method of suppressing the pattern effect in a semiconductor optical amplifier

A new idea of using change in index of refraction to suppress gain variation in a saturated semiconductor optical amplifier (SOA) is presented. This kind of gain compensation has the advantage of high speed because it involves two phenomena that always accompany each other. This compensation can be achieved with a nonsymmetrical Mach-Zehnder interferometer structure. Calculated results show that with this structure the input and output power of the SOA can be extended to nearly 10 dB from the former small-signal limit when less than 1-dB gain variation is permitted. Numerical simulations with an advanced dynamic model of the SOA agree with the calculated results.     

自动波竞争神经网络及其在单源最短路问题中的应用

将竞争机理引入网络的自动波产生与传播过程中，提出自动波竞争神经网络(ACNN)模型，并成功地应用于求解单源最短路问题，给出了基于ACNN的最短路求解算法. 与其他神经网络最短路算法相比，基于ACNN的最短路算法具有网络所需的神经元数目少、神经元及网络的结构简单、易于软硬件的实现、以及全并行方式计算等特点，可用于求解非对称赋权图的最短路径树问题，且其计算时间(迭代次数)仅正比于最短路径上的跃点数，与赋权图的复杂度、路径总长、边长的精度、通路总数等因素无关. 计算机仿真结果表明该算法的有效性和快速求解能力. 关键词： 单源最短路问题 自动波竞争神经网络 脉冲耦合神经网络     

圆锥面PVDF聚焦换能器的非线性声场理论及实验研究

圆锥面聚焦换能器可在超声成像中获得较好径向分辨率的同时提高探测深度.利用高斯声源函数叠加法来近似表示圆锥面聚焦声源的分布函数，结合近轴近似的KZK方程，得到了圆锥面聚焦换能器在损耗媒质中产生的基波、二次谐波声场的解析解.在实验上制作了PVDF圆锥面聚焦换能器，测量了圆锥面聚焦换能器的基波及二次谐波声场，实验结果和理论计算相符.     

光学读出微梁阵列红外成像及性能分析

在构建的光学读出微梁阵列(焦平面阵列FPA)非制冷红外成像系统中，实现了无硅基底FPA置于空气中对人体的热成像. 通过FPA在不同真空度环境条件下的成像结果进行比较，分析了热导和系统噪声值随气压变化的关系，以及对系统成像性能的影响，并对气体分子热运动自由程大于空气传热层特征尺度时的气体热传导模型进行了修正分析和实验验证. 实验结果表明：FPA置于空气中时，气体分子撞击微梁引起的微梁反光板无序振动产生的光学读出噪声成为系统噪声的主要来源. 当真空度小于1Pa时，总热导和光学读出噪声值的变化都趋于平缓；当真空度小于10^-2Pa时，空气热导的影响可忽略，总热导降低到微梁感热像素的辐射极限，光学读出噪声也降低到一极小值. 实验结果与理论分析相符合. 关键词： 非制冷红外成像 光学读出 双材料微梁阵列 热导