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991.
1人工神经网络──自组织神经树模型人工神经网络(ANN)是八十年代中期迅速兴起的一门非线性科学.它力图模拟人脑的一些基本特性,如自适应性、自组织性、容错性等,已在模式识别、数据处理及自动化控制等领域得到了初步应用,取得了相当好的效果[1,2].1993年,Tao-Li等提出了自组织神经树网络.它是一个多层树状网络(见图1),每个输入节点与所有神经树的节点(神经元)通过权W相联系,实现对输入信号的非线性降维映射.映射中保持拓扑不变性,即把拓扑意义下相似的输入(即在高维空间中距离较近的输入向量)映射到相同子树的节… 相似文献
992.
993.
Masatoshi Taniguchi Ken-ichi SuzumuraKoji Nagai Tomihisa KawasakiTetsu Saito Jun TakasakiKen-ichi Suzuki Shigeo FujitaShin-ichi Tsukamoto 《Tetrahedron》2003,59(25):4533-4538
The isolation and structure elucidation of YM-254890, a novel Gq/11 inhibitor from Chromobacterium sp. QS3666, is described. The gross structure was determined by one- and two-dimensional NMR studies and mass spectrometry. YM-254890 is a cyclic depsipeptide containing uncommon amino acids; β-hydroxyleucine (two residues), N,O-dimethylthreonine and N-methyldehydroalanine. YM-254890 exists as a mixture of two conformers in a variety of NMR solvents, and the distinction between major and minor conformers appears to lie in the geometry of the amide bond between 3-phenyllactic acid and N-methyldehydroalanine. The absolute stereochemistery was elucidated by Marfey's analysis and chiral HPLC analysis of the acid hydrolysate of YM-254890. 相似文献
994.
ShiGuoSUN XiaoJunPENG MingWenFAN YongQianXU LeiSHI LiChengSU 《中国化学快报》2004,15(8):965-968
Two novel rhenium(I) 2, 2′-bipyridyl complexes, [(4,4′-di-COOEt-bipy) Re(CO)3 (NCCH3)PF6] and [(4,4′-di-COOEt-bipy) Re (CO)3 (NCS)], a model complex [(4,4′-di-COOEt-bipy) Re (CO)3 (pyridine)PF6], were synthesized. Their ground state electronic spectra and emission spectra were measured in acetonitrile. The MLCT absorption maximum of the complex exhibited a considerable red shift as the ligand changed from pyridine to CNCH3, or SCN. 相似文献
995.
996.
Yajing Yin Ping Wu Yafen Lü Pan Du Yanmao Shi Chenxin Cai 《Journal of Solid State Electrochemistry》2007,11(3):390-397
A single-walled carbon nanotube (SWNT)-modified electrode was fabricated and characterized by SEM and ac impedance techniques.
The direct electrochemistry of cytochrome c (Cyt c), which was adsorbed on the surface of the SWNT, was studied by cyclic voltammetry. The results from cyclic voltammetry and
infrared spectroscopy indicated that Cyt c remained in its original structure and did not undergo structural change after its immobilization on the SWNT. Further results
demonstrated that the SWNT had promotional effects on the direct electron transfer of Cyt c and also indicated that the immobilized Cyt c retained its electrocatalytic activity to the reduction of H2O2. This modified electrode might be used in development of new biosensors and the biofuel cells. 相似文献
997.
提供了三元乙丙橡胶(EPDM)交联的一种方法.以二甲苯为溶剂,溶液法制备马来酸酐(MAH)接枝EPDM,然后向溶液中加入适量碳酸钙(CaCO3),与已接枝的马来酸酐(MAH)反应.待反应完全后,滴加丙酮作为沉淀剂,沉淀物真空干燥,制得EPDM-g-MAH/CaCO3弹性体复合材料.溶解、溶胀及拉伸性能测试结果表明,复合材料样品已形成有效的交联,且材料的抗张强度、断裂伸长率和模量均得到较大幅度的提高,当CaCO3含量达到体系总重的20%时,复合材料呈现最佳力学性能.上述实验结果是因为碱性的CaCO3的Ca2+可以与接枝在EPDM上的MAH发生配合反应,进而成为EPDM的交联中心,形成有效交联,从而促进了EPDM机械性能的提高,ATR-FTIR和TGA的测试结果被用于证实上述观点. 相似文献
998.
Jun Liu Kelton A. Schleyer Tyrel L. Bryan Changjian Xie Gustavo Seabra Yongmei Xu Arjun Kafle Chao Cui Ying Wang Kunlun Yin Benjamin Fetrow Paul K. P. Henderson Peter Z. Fatland Jian Liu Chenglong Li Hua Guo Lina Cui 《Chemical science》2021,12(1):239
Heparanase (HPA) is a critical enzyme involved in the remodeling of the extracellular matrix (ECM), and its elevated expression has been linked with diseases such as various types of cancer and inflammation. The detection of heparanase enzymatic activity holds tremendous value in the study of the cellular microenvironment, and search of molecular therapeutics targeting heparanase, however, no structurally defined probes are available for the detection of heparanase activity. Here we present the development of the first ultrasensitive fluorogenic small-molecule probe for heparanase enzymatic activity via tuning the electronic effect of the substrate. The probe exhibits a 756-fold fluorescence turn-on response in the presence of human heparanase, allowing one-step detection of heparanase activity in real-time with a picomolar detection limit. The high sensitivity and robustness of the probe are exemplified in a high-throughput screening assay for heparanase inhibitors.Heparanase, a critical enzyme involved in the remodeling of the extracellular matrix, activates a disaccharide probe HADP to give a strong fluorescence signal. 相似文献
999.
An electrochemical biosensor for the specific detection of short DNA sequences from the E. coli pathogen is described. This hybridization device relies on the immobilization of a 25-mer oligonucleotide probe, from the E. coli lacZ gene, onto a screen-printed carbon electrode. Chronopotentiometric detection of the Co(bpy)3+3 indicator is used for monitoring the hybridization event. Numerous variables of the assay protocol, including those of the probe immobilization step, the hybridization event, and the indicator association/detection, are characterized and optimized. Hybridization times of 2- and 30-min are sufficient for detecting 300- and 50 ng/mL, respectively, of the E. coli DNA target. Applicability to analysis of untreated environmental water samples is illustrated. Such single-use electrochemical sensors hold great promise for decentralized environmental and food testing for the E. coli pathogen. 相似文献
1000.
Ab initio molecular orbital theory and density functional theory have been employed to study N14 cluster with low spin at the HF/6-31G*, B3LYP/6-31G*, B3PW91/6-31G*, BP86/6-31G*, and BHLYP/6-31G* levels of theory. Twelve isomers were studied, including one previously investigated cage molecule. The most stable isomer of N14 is a C
2h
-symmetric molecule that contains two separated five-membered nitrogen rings connected by a —N=N—N=N— bridge. The second, third, and fifth most stable isomers each have one five-membered nitrogen ring. The theoretical results suggest that the five-membered nitrogen ring gives rise to a particularly stable structural unit, and the more side chains that the five-membered nitrogen ring links with, the less stable the structure will become. 相似文献