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991.
Long-chain alkenones in Hotong Qagan Nur Lake sediments and its paleoclimatic implications 总被引:8,自引:0,他引:8
Sheng Guoying Cai Keqin Yang Xuexian Lu Jialan Jia Guodong Peng Ping’an Fu Jiamo 《科学通报(英文版)》1999,44(3):259-259
The long-chain alkenones present in the shallow sediment of Hotong Qagan Nur Lake in China are reported. According to the similarity of compositions and distributions of the alkenones determined commonly in the sediment section to those of marine sediment, it is reasonably referred that the alkenones might also originate from Prymnesiophyceae. In addition, the parameter U37k of alkenone is in positive correlation to δ18O values of authigenic calcium and magnesium minerals. This indicates that the parameter U37k of long-chain alkenone is also available to indicate paleoclimate of high-salinity alkaline lake. 相似文献
992.
An improved ray-optics theory and Mie theory for single scattering and the adding-dou-bling method for multiple scattering are used to study the relationship between the radiation in the wavelengths of 1.38, 3.979, 6.5, and 11.03 μm and the microphysics of cirrus clouds. It is shown that the strong 1.38 μm water vapor band in the near-IR region is superior to the other three IR channels used in current operational satellites and has potential possibility of remote sensing of microphysical and optical properties of cirrus clouds. 相似文献
993.
贵州蚋类调查研究初报(双翅目:蚋科) 总被引:3,自引:1,他引:2
报道自80年代以来,先后对贵州省26个县(市)不同生境的蚋类进行调查研究的结果,记录蚋科Simuliidae蚋属Simulium共38种,包括19个新种,其中含14个待发表新种,分别隶属于绳蚋亚属Gomphostilbia(5种)、门蚋亚属Momtisimulium(1种)、纺蚋亚属Nevermannia(7种)、真蚋亚属Eusimulium(2种)、维蚋亚属Wilhelmia(2种)和蚋亚属Simulium(21种)等6个亚属。制订了贵州省蚋类名录并进行了相关讨论。 相似文献
994.
对多媒体在过程控制中的应用进行了讨论 ,提出了一种分布式多媒体系统的体系结构——共享式白板结构 ,给出系统的设计要求和平台以及系统的实施过程 .共享式白板结构可被看作设计和实施多媒体协作系统的工具 .基于白板的多媒体系统可用来研究、确定、开发和测试一个基于多用户的人机接口以完成协作式的工作 相似文献
995.
Qi Xu Ziyu Chen Borong Zhu Yiming Li Manju B. Reddy Huilin Liu Guodong Dang Qi Jia Xiaojun Wu 《Molecules (Basel, Switzerland)》2021,26(21)
Cinnamon procyanidin oligomers (CPOs) are water-soluble components extracted from cinnamon. This study aims to explore the neuroprotection of B-type CPO (CPO-B) against 1-methyl-4-phenylpyridinium (MPP+)-mediated cytotoxicity and the molecular mechanisms underlying its protection. The results demonstrated that CPO-B showed protection by increasing cell viability, attenuating an intracellular level of reactive oxygen species, downregulating cleaved caspase-3 expression, and upregulating the Bcl-2/Bax ratio. Moreover, CPO-B completely blocked the dephosphorylation of extracellular, signal-regulated kinase 1 and 2 (Erk1/2) caused by MPP+. Treatment with an Erk1/2 inhibitor, SCH772984, significantly abolished the neuroprotection of CPO-B against MPP+. Taken together, we demonstrate that CPO-B from cinnamon bark provided protection against MPP+ in cultured SH-SY5Y cells, and the potential mechanisms may be attributed to its ability to modulate the dysregulation between pro-apoptotic and anti-apoptotic proteins through the Erk1/2 signaling pathway. Our findings suggest that the addition of cinnamon to food or supplements might benefit patients with PD. 相似文献
996.
The stable structures and vibrational spectra of protonated acetone molecule clusters with different sizes (CH3COCH3)nH +(n=1-7)are calculated at the 6-31G(d)level by means of density functional theory (B3LYP)quantum chemical calculations. The corresponding energies are analyzed at the level B3LYP/6-311+G(3df,2p)in order to obtain more accurate results. The proton affinity of neutral cyclic acetone molecule clusters increases with the increasing of cluster size. The calculated results show that the protonated acetone clusters have certain growth regularity with forming a solvation shell at the beginning and then new added acetone molecule attacking different active sites including the middle carbon atoms and the different methyl in solvation shell. The IR spectra of the protonated clusters are more complicate than that of neutral ones. The strongest peaks result from the movement of the proton between the two oxygen atoms in solvant shell apart from the case of n=1. Carbonyl stretching vibraional peaks split into the more and more and in general the corresponding intensities are weakened due to the protonation with the increasing of cluster size. 相似文献
997.
胀锚型锚栓锚固破坏及承载力研究 总被引:2,自引:1,他引:1
混凝土基材锥体受拉破坏是后锚固锚栓受拉的基本破坏形式,采用混凝土破坏准则和弹性力学方法,推导了胀锚型锚栓基于混凝土基材破坏的抗拔极限承载力简化计算公式.通过对不同混凝土强度的极限状态数值分析,发现基材锚固破坏锥面底部直径R与有效锚固深度he为近似比值关系。与试验的对比结果表明,简化计算方法精度满足工程需要,和多种试验测试结果相当吻合。 相似文献
998.
Xiaowei Zhan Mujie Yang Gang Xu Xuchun Liu Peixian Ye 《Macromolecular rapid communications》2001,22(5):358-362
A new series of poly(p‐diethynylbenzene) derivatives with trans structure and long‐conjugation side chains were synthesized. These polymers possess good solubility and thermal stability. The maximum absorptions and band gaps depend on the nature and number of the substituents. Third‐order nonlinear optical properties of these polymers were characterized with second‐order hyperpolarizability as large as ≈10–30 esu in the non‐resonant region. 相似文献
999.
1000.