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961.
The general sum-connectivity index of a graph G is defined as χ
α
(G) = ∑edges (d
u
+ d
v
)
α
, where d
u
denotes the degree of vertex u in G and α is a real number. In this report, we determine the minimum and the second minimum values of the general sum-connectivity
indices of n-vertex unicyclic graphs for non-zero α ≥ −1, and characterize the corresponding extremal graphs. 相似文献
962.
L. Shen H.W. Du H. Ding J. Tang Z.Q. Ma 《Materials Science in Semiconductor Processing》2010,13(5-6):339-343
The discrepancy of rectifying characteristics in n-ZnO:Al/p-Si heterojunctions from diode to diode was demonstrated by region dependent dark I–V characteristics, where the junction is laterally cut to sequentially decrease the area. Further investigation shows that the junction (2.1×2.1 cm2) with the barrier height Φ=0.693 eV consists of one part (2.1×1.4 cm2) with Φ=0.695 eV and the other part (2.1×0.7 cm2) with Φ=0.686 eV. It is found that reverse currents saturate with different values of 3.6×10?3, 2.5×10?3 and 1.58×10?3 A for the light I–V curves of the three junctions with the same areas. To explain this peculiarity, the probable reason is discussed in terms of carrier transportation through the spatially fluctuating barrier. 相似文献
963.
Jiankang He Yanan Du José L. Villa‐Uribe Changmo Hwang Dichen Li Ali Khademhosseini 《Advanced functional materials》2010,20(1):131-137
Many biological processes are regulated by gradients of bioactive chemicals. Thus, the generation of materials with embedded chemical gradients may be beneficial for understanding biological phenomena and generating tissue‐mimetic constructs. Here a simple and versatile method to rapidly generate materials containing centimeter‐long gradients of chemical properties in a microfluidic channel is described. The formation of a chemical gradient is initiated by a passive‐pump‐induced forward flow and further developed during an evaporation‐induced backward flow. The gradient is spatially controlled by the backward flow time and the hydrogel material containing the gradient is synthesized via photopolymerization. Gradients of a cell‐adhesion ligand, Arg‐Gly‐Asp‐Ser (RGDS), are incorporated in poly(ethylene glycol)‐diacrylate (PEG‐DA) hydrogels to test the response of endothelial cells. The cells attach and spread along the hydrogel material in a manner consistent with the RGDS‐gradient profile. A hydrogel containing a PEG‐DA concentration gradient and constant RGDS concentration is also shown. The morphology of cells cultured on such hydrogel changes from round in the lower PEG‐DA concentration regions to well‐spread in the higher PEG‐DA concentration regions. This approach is expected to be a valuable tool to investigate the cell–material interactions in a simple and high‐throughput manner and to design graded biomimetic materials for tissue engineering applications. 相似文献
964.
Guang-jin Wang Yun-zhi Gao Zhen-bo Wang Chun-yu Du Ge-ping Yin 《Electrochemistry communications》2010,12(8):1070-1073
Here, we report the development of a new membrane electrode assembly (MEA) structure for passive direct borohydride fuel cells (DBFCs). The anode of this type of MEA includes upper and lower parts for the electro-oxidation of borohydride and hydrogen, respectively. In comparison to conventional MEAs, the maximum power of this MEA is increased by 28.1%, and the anode polarization is decreased due to the current contribution of hydrogen electro-oxidation. The hydrogen generated from borohydride hydrolysis can be oxidized inside the cell, and the fuel coulombic efficiency reaches 100%. Therefore, high fuel utilization and cell safety can be obtained by employing this novel MEA in DBFCs. 相似文献
965.
Hongmei Zhang Weiqiang Zhou Yukou Du Ping Yang Chuanyi Wang 《Electrochemistry communications》2010,12(7):882-885
A facile, one-step and template-free electrodeposition method has been developed for the first time to prepare porous Pt nanoflowers. The flowerlike architectures were confirmed by SEM, and further structurally characterized by XRD and electrochemical analyses. Compared to conventional nanosized Pt catalysts, as-prepared Pt nanoflowers exhibit remarkably higher catalytic activity and stronger poisoning-tolerance for the methanol electro-oxidation, and thus they are anticipated to find interesting applications in many important fields such as energy and catalysis. 相似文献
966.
Dr. Sylvain Antoniotti Prof. Dr. Vincent Dalla Dr. Elisabet Duñach 《Angewandte Chemie (International ed. in English)》2010,49(43):7860-7888
The continuously increasing need for novel and selective methods in organic synthesis to aid drug discovery and to address environmental concerns is a constant source of stimulation to develop novel and more efficient reaction systems. This has often resulted in a focus on transition metals, ligands, and additives, with much less attention paid to the counterion(s) of the metal cation. Recently, metal salts with one or more triflimidate counterion(s) have appeared as a unique class of catalysts that display outstanding σ‐ and π‐Lewis acid character. The highly delocalized nature of the triflimidate counterion, combined with its high steric hindrance results in virtually no nucleophilic behavior and an extremely high positive charge density on the metal cation, thus enhancing its Lewis acid character. Consequently, these metal triflimidates often outperform their metal halide or triflate analogues. This Review describes general methods for the preparation of metal triflimidate salts and their use as catalysts. 相似文献
967.
968.
Wei Zhang Yongzhai Du Zhili Feng Jun Xu 《International Journal for Ion Mobility Spectrometry》2010,13(2):65-71
Membrane-extraction Ion Mobility Spectrometry (ME-IMS) is a feasible technique for the continuous monitoring of chlorinated hydrocarbons in water. This work studies theoretically the time-dependent characteristics of sampling and detection of trichloroethylene (TCE). The sampling is configured so that aqueous contaminants permeate through a hollow polydimethylsiloxane (PDMS) membrane and are carried away by a transport gas flowing through the membrane tube into IMS analyzer. The theoretical study is based on a two-dimensional transient fluid flow and mass transport model. The model describes the TCE mixing in the water, permeation through the membrane layer, and convective diffusion in the air flow inside membrane tube. The effect of various transport gas flow rates on temporal profiles of IMS signal intensity is investigated. The results show that fast time response and high transport yield can be achieved for ME-IMS by controlling the flow rate in the extraction membrane tube. These modeled time-response profiles are important for determining duty cycles of field-deployable sensors for monitoring chlorinated hydrocarbons in water. 相似文献
969.
Dušan Berek 《Journal of separation science》2010,33(3):315-335
Size exclusion chromatography, SEC is one of the most popular methods for the separation of different kinds of macromolecules. This critical review gives concise information about macromolecules and their behavior in solution, basic understanding about principles, instrumentation, and application possibilities of SEC, and more in detail discusses drawbacks and pitfalls of the method with the emphasis on synthetic polymers. Selected practical advices are included to help enhance the quality of SEC results. 相似文献
970.
Hongyuan Yan Jingjing Du Xiguo Zhang Gengliang Yang Kyung Ho Row Yunkai Lv 《Journal of separation science》2010,33(12):1829-1835
A simple and rapid ultrasound‐assisted dispersive liquid–liquid microextraction method coupled with GC‐flame ionization detection was developed for simultaneous determination of nine pyrethroids in domestic wastewater samples. An ultrasound‐assisted process was applied to accelerate the formation of the fine cloudy solution using small volume of disperser solvent, which markedly increased the extraction efficiency and reduced the equilibrium time. Various parameters affecting the extraction efficiency were investigated, including the type and volume of extraction solvent and disperser solvent, extraction and ultrasonic time. Good linearity was obtained for all analytes in the range of 0.8–100 μg/L with the correlation coefficient (r2)≥0.998. The recoveries at three spiking levels ranged from 75.3 to 101.2% with the RSD less than 8.7% (n=5). Under the optimum condition, the enrichment factors for the nine pyrethroids ranged from 728‐ to 1725‐fold. This method offered a good alternative for routine analysis due to its simplicity and reliability. 相似文献