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991.
Yair Shapira Moshe Israeli Avram Sidi Uzi Zrahia 《Numerical Methods for Partial Differential Equations》1999,15(5):535-543
Spectral element schemes for the solution of elliptic boundary value problems are considered. Preconditioning methods based on finite difference and finite element schemes are implemented. Numerical experiments show that inverting the preconditioner by a single multigrid iteration is most efficient and that the finite difference preconditioner is superior to the finite element one for both definite and indefinite problems. A multigrid preconditioner is also derived from the finite difference preconditioner and is found suitable for the CGS acceleration method. It is pointed out that, for the finite difference and finite element preconditioners, CGS does not always converge to the accurate algebraic solution. © 1999 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 15: 535–543, 1999 相似文献
992.
closo-Undecaborates were synthesized by the deprotonation of B11H13(SMe2) with LitBu in thp or K[BHEt3] in thf, [Li(thp)3]2[B11H11] and K2[B11H11] being obtained in 83 and 93% yield, respectively. K2[B11H11] can be transformed into A2[B11H11] with the corresponding ammonium chlorides in aqueous solution (A = [NMe3Ph], [NBzlEt3], [N(PPh3)2]). The crystal structure analysis of [Li(thp)3]2[B11H11] (space group P21/c) reveals a rather distorted octadecahedron for the [B11H11]2– anion, whereas the corresponding octadecahedron in [NBzlEt3]2[B11H11] (space group P212121) exhibits a structure close to C2v symmetry, expected for the free anion. The protonation of [B11H11]2– at low temperature gives [B11H12]–, whose structure could be elucidated by NMR methods; it is formed, apparently, by the opening of the B1–B4 edge of [B11H11]2– in the course of its known degenerate skeletal rearrangement, followed by the protonation of the B2–B4 edge. The reaction of [B11H12]– with a second molecule of the acid HX (X = CF3COO) gives nido-[B11H13X]–. The addition of BH3 to [B11H11]2– yields closo-[B12H12]2– under loss of H2. Two [B11H11]2– units are fused by the aid of FeCl3, with the known anion [B22H22]2– as the product, whose 11B-NMR signals could completely be assigned on the basis of Cs symmetry. The compound [NBzlEt3][N(PPh3)2][B22H22] crystallizes in the space group Pna21. 相似文献
993.
994.
995.
铝粉是一种含能高的材料,它被广泛地添加到含能材料中。利用3台单色谱仪和OMA谱仪等多种谱仪技术,研究了铝粉在几种不同环境下的快速反应微观特性。研究表明:铝粉冲击波点火的临界条件和铝粉的物理状态相关。微米铝粉点火的临界温度为2 100 K,它接近Al2O3的熔化温度。它表明,在空气中容易氧化的微米铝粉点火,必须使铝粉表面的氧化层熔化。在气相反应中,微米铝粉和氧的反应是主要的;和水的反应是次要的。减小微米铝粉的颗粒尺寸,可以明显提高快速反应温度。 含铝复合燃料中的液体燃料反应后的铝粉才能参与反应;铝粉添加至气相反应介质后将明显提高反应温度。 相似文献
996.
综合使用光谱技术对作物养分进行实时、有效诊断,有助于作物的精准管理、保障产量和减少环境污染,提高肥料利用率,并且为定量估测作物生化组分状况提供了一种新的途径.光谱指数是进行作物叶片叶绿素实时估测的重要指标,然而由于受到环境条件及内在生化成分的影响,估测结果不尽满意.为了进一步提高光谱指数在估测作物叶片叶绿素含量时的抗干... 相似文献
997.
Zsanett Bodor Zoltan Kovacs Csilla Benedek Gza Hitka Hermann Behling 《Molecules (Basel, Switzerland)》2021,26(23)
The objective of the study was to check the authenticity of Hungarian honey using physicochemical analysis, near infrared spectroscopy, and melissopalynology. In the study, 87 samples from different botanical origins such as acacia, bastard indigo, rape, sunflower, linden, honeydew, milkweed, and sweet chestnut were collected. The samples were analyzed by physicochemical methods (pH, electrical conductivity, and moisture), melissopalynology (300 pollen grains counted), and near infrared spectroscopy (NIRS:740–1700 nm). During the evaluation of the data PCA-LDA models were built for the classification of different botanical and geographical origins, using the methods separately, and in combination (low-level data fusion). PC number optimization and external validation were applied for all the models. Botanical origin classification models were >90% and >55% accurate in the case of the pollen and NIR methods. Improved results were obtained with the combination of the physicochemical, melissopalynology, and NIRS techniques, which provided >99% and >81% accuracy for botanical and geographical origin classification models, respectively. The combination of these methods could be a promising tool for origin identification of honey. 相似文献
998.
Jing Jin Yi-Qing Lv Wei-Zhong He Da Li Ying Ye Zai-Fa Shu Jing-Na Shao Jia-Hao Zhou Ding-Mi Chen Qing-Sheng Li Jian-Hui Ye 《Molecules (Basel, Switzerland)》2021,26(23)
Both UV and blue light have been reported to regulate the biosynthesis of flavonoids in tea plants; however, the respective contributions of the corresponding regions of sunlight are unclear. Additionally, different tea cultivars may respond differently to altered light conditions. We investigated the responses of different cultivars (‘Longjing 43’, ‘Zhongming 192’, ‘Wanghai 1’, ‘Jingning 1’ and ‘Zhonghuang 2’) to the shade treatments (black and colored nets) regarding the biosynthesis of flavonoids. For all cultivars, flavonol glycosides showed higher sensitivity to light conditions compared with catechins. The levels of total flavonol glycosides in the young shoots of different tea cultivars decreased with the shade percentages of polyethylene nets increasing from 70% to 95%. Myricetin glycosides and quercetin glycosides were more sensitive to light conditions than kaempferol glycosides. The principal component analysis (PCA) result indicated that shade treatment greatly impacted the profiles of flavonoids in different tea samples based on the cultivar characteristics. UV is the crucial region of sunlight enhancing flavonol glycoside biosynthesis in tea shoots, which is also slight impacted by light quality according to the results of the weighted correlation network analysis (WGCNA). This study clarified the contributions of different wavelength regions of sunlight in a field experiment, providing a potential direction for slightly bitter and astringent tea cultivar breeding and instructive guidance for practical field production of premium teas based on light regimes. 相似文献
999.
采用B3LYP/6-311++g(3df,3pd)方法和基组对氟利昂物质CFC-11 (CFCl_3)分子进行了一系列的理论研究.包括了该分子的基态结构、电偶极矩、总能量、最高占据分子轨道能级E_H和最低未占据分子轨道能级E_L、能隙、红外与拉曼光谱性质、C-F键解离,并探讨电场对该分子的影响.结果表明:基态结构优化后的理论计算值和实验值的最大误差低于2%,C-F键受电场强度的增大而被拉长,能隙E_g随E_H和E_L的变化出现先增大后减小;电场影响着CFC-11分子的红外与拉曼光谱吸收强度,红外与拉曼光谱随着电场变化出现红移或蓝移现象.电场可作为一种辅助手段对其重叠或准重叠谱线进行分离.势阱深度随反向电场逐渐增大而减小,直至消失,使得C-F键的束缚能力逐渐减弱.本文有望为实现CFC-11分子最终发生解离而降解提供一种可行有效的调控手段. 相似文献
1000.
在激光驱动的惯性约束聚变装置中,常采用多种束匀滑手段对焦斑的时空特性进行调控.光传输链路中涉及的光学元件众多、传输变换复杂,往往导致光传输模型复杂,且在运用衍射光学方法分析焦斑形态和特征时面临大量的数据处理和计算,致使出现计算量大、计算效率低等问题,亟需寻求快速而简便的新方法来描述焦斑的统计特征.本文利用光场特性的统计表征方法对靶面光场进行表征,采用圆型复数高斯随机变量直接描述靶面光场的统计特征,并基于典型焦斑评价参数对衍射光学方法和统计表征方法得到的远场焦斑进行了对比和分析.结果表明,采用衍射光学方法和统计表征方法获得的焦斑的瞬时特征基本一致,其时间积分的远场焦斑有所不同,但仍可进一步采用相关系数来表征其远场焦斑的时间变化特征. 相似文献