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排序方式: 共有1249条查询结果,搜索用时 15 毫秒
991.
This paper is devoted to the motion planning problem for control-affine systems by using trigonometric polynomials as control functions. The class of systems under consideration satisfies the controllability rank condition with the Lie brackets up to the second order. The approach proposed here allows to reduce a point-to-point control problem to solving a system of algebraic equations. The local solvability of that system is proved, and formulas for the parameters of control functions are presented. Our local and global control design schemes are illustrated by several examples. 相似文献
992.
Metal‐coordinated epoxy polymers with suppressed combustibility. Preparation technology,thermal degradation,and combustibility test of new epoxy‐amine polymers containing the curing agent with chelated copper(II) carbonate
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The diethylenetriamine chelate complex of copper(II) carbonate—DETA‐CuCO3 (a fire retardant hardener of epoxy resins)—and the CuCO3‐containing epoxy‐amine polymers—DGEBA/DETA‐CuCO3(6), DGEBA/DETA‐CuCO3(12), DGEBA/DETA‐CuCO3(40), and DGEBA/DETA‐CuCO3(80) with suppressed combustibility—have been obtained in the DETA‐DGEBA‐CuCO3 system (DETA and DGEBA are diethylenetriamine and bisphenol A diglycidyl ether, respectively). The DETA‐CuCO3 chelate complex was characterized by X‐ray powder diffraction, infrared spectra, and thermal analysis. The thermal gravimetric analysis results have revealed that thermal destruction of DETA‐CuCO3 was finished at 400°С, and the maximal temperature of the combustion gases amounted to 520°С. The thermal behavior and combustibility of the CuCO3‐containing epoxy‐amine polymers were studied using thermal analysis and “Ceramic tube” (CT) method. Thermal gravimetric analysis confirms that incorporation of the DETA‐CuCO3 into DGEBA appreciably heightens the thermal stability and antiflammability of the CuCO3‐containing epoxy‐amine polymers. Results of CT measurement reveal that maximal temperature of the combustion gases under burning of the DGEBA/DETA‐CuCO3(12) sample in comparison with unmodified epoxy‐amine polymer (DGEBA/DETA) is lowered on 219°С and the loss of weight is decreased on 20.5 wt%. According to ASTM 635‐14, ASTM D2863‐13, and ASTM D1929‐16, the flame propagation rate, limiting oxygen index, and temperatures of ignition and self‐ignition have been measured for the elaborated polymer samples. 相似文献
993.
Leandro González Rodríguez Roberto Campana Prada Margarita Sanchez-Molina Tonatiuh Alejandro Rodríguez Victoria 《International Journal of Hydrogen Energy》2021,46(33):17550-17561
The electrochemical performance of membrane electrode assemblies (MEAs) with ultra-low platinum load (0.02 mgPt cm?2) and different compositions of Nafion/C in the catalytic layer have been investigated. The electrodes were fabricated depositing the catalytic ink, prepared with commercial catalyst (HiSPEC 2000), onto the gas diffusion layers by wet powder spraying. The MEAs were electrochemically tested using current-voltage curves and electrochemical impedance spectroscopy measurements. The experiments were carried out at 70 °C in H2/O2 and H2/air as reactant gases at 1 and 2 bar pressure and 100% of relative humidity. For all MEAs tested, power density increases when the gasses pressure is increased from 1 to 2 bar. On the other hand, power density also increased when oxygen is used instead of air as oxidant gas in cathode. The lower power density (34 mW cm?2) and power per Pt loading (0.86 kW gPt?1) corresponds to the MEA prepared without Nafion in anode and cathode catalytic layers working with hydrogen and air at 1 bar pressure as reactants gas. The MEA with 30% wt Nafion/C reached the highest power density (422 mW cm?2) and power per Pt loading (10.60 kW gPt?1) using hydrogen and oxygen at 2 bar pressure. Finally, electrode surface microstructure and cross sections of MEAs were analyzed by Scanning Electron Microscopy (SEM). Examination of the electrodes, revealed that the most uniform ionomer network surface corresponds to the electrode with 40 wt% Nafion/C, and MEA ionomer-free catalytic layer shows delamination, it leads to low electrochemical performance. 相似文献
994.
995.
Léa Mélin Shuay Abdullayev Ahmed Fnaiche Dr. Victoria Vu Narjara González Suárez Hong Zeng Dr. Magdalena M. Szewczyk Dr. Fengling Li Dr. Guillermo Senisterra Dr. Abdellah Allali-Hassani Irene Chau Dr. Aiping Dong Dr. Simon Woo Prof. Borhane Annabi Dr. Levon Halabelian Prof. Steven R. LaPlante Prof. Masoud Vedadi Dr. Dalia Barsyte-Lovejoy Dr. Vijayaratnam Santhakumar Prof. Alexandre Gagnon 《ChemMedChem》2021,16(19):2982-3002
996.
Alice Pierre Anne Mayeur Clmentine Marie Victoria Cluzet Jonathan Chauvin Nelly Frydman Michael Grynberg Joelle Cohen-Tannoudji Cline J. Guigon Stphanie Chauvin 《International journal of molecular sciences》2021,22(9)
Estrogen receptor beta (ERβ) plays a critical role in granulosa cell (GC) functions. The existence of four human ERβ splice isoforms in the ovary suggests their differential implication in 17β-estradiol (E2) actions on GC apoptosis causing follicular atresia. In this study, we investigated whether E2 can regulate ERβ isoforms expression to fine tune its apoptotic activities in human GC. For this purpose, we measured by RT-qPCR the expression of ERβ isoforms in primary culture of human granulosa cells (hGCs) collected from patients undergoing in vitro fertilization, before and after E2 exposure. Besides, we assessed the potential role of ERβ isoforms on cell growth and apoptosis after their overexpression in a human GC line (HGrC1 cells). We confirmed that ERβ1, ERβ2, ERβ4, and ERβ5 isoform mRNAs were predominant over that of ERα in hGCs, and found that E2 selectively regulates mRNA levels of ERβ4 and ERβ5 isoforms in these cells. In addition, we demonstrated that overexpression of ERβ1 and ERβ4 in HGrC1 cells increased cell apoptosis by 225% while ERβ5 or ERβ2 had no effect. Altogether, our study revealed that E2 may influence GC fate by specifically regulating the relative abundance of ERβ isoforms mRNA to modulate the balance between pro-apoptotic and non-apoptotic ERβ isoforms. 相似文献
997.
Montoya-Bautista Claudia Victoria Acevedo-Peña Próspero Zanella Rodolfo Ramírez-Zamora Rosa-María 《Topics in Catalysis》2021,64(1-2):131-141
Topics in Catalysis - With the goal of providing an economically viable method for reducing water pollution and health impact by the mezcal industry wastes, photocatalytic degradation of toxic... 相似文献
998.
Ilya ZADIRIEV Elena KRALKINA Vladimir SAMOILOV Victoria ELCHANINOVA Valentina GORINA Ilya IVANENKO Konstantin VAVILIN Alexander NIKONOV 《等离子体科学和技术》2021,23(12):125504-160
In this work we carried out an experimental investigation into enhancement of the sorption capacity of carbon fabric using plasma treatment methods.Carbon fabric is based on viscose fiber and is hydrophobic by nature.Enhancement of the fabric sorption capacity is required for its application in medicine.For this purpose,two plasma treatment methods were considered,i.e.atmospheric nonequilibrium radiofrequency(RF)discharge and a vacuum RF plasma source with an external magnetic field.Samples treated by atmospheric discharge demonstrated aging effects during the first week after treatment.The sorption capacity of samples treated by the RF plasma source was stable over the same period and reached values as high as 0.95.Parameters of the beam created by the vacuum RF plasma source were analyzed and dependences of the fabric sorption capacity and specific surface area on plasma treatment time were investigated.We found that sorption capacity reached its maximum value after 30 min of treatment and did not change significantly if processing was continued,while the specific surface area reached its maximum after 3 min of treatment and quickly decreased after that.It was found that the micropore structure of the fabric remained almost the same during plasma treatment.The volume of mesopores in a unit of the fabric mass(specific volume)doubled during the first 5 min of treatment and returned to initial values after 30 min of treatment.The sorption capacity continued to increase even when the specific surface area decreased after reaching its peak value.This indicates the important role of surface functional groups formed on carbon fibers during plasma treatment.This is consistent with the results of x-ray photoelectron spectroscopy analysis showing changes in surface oxidation during plasma treatment. 相似文献
999.
1000.
Victoria Bernardo Judith Martin‐de Leon Miguel Angel Rodriguez‐Perez 《Polymer International》2019,68(6):1204-1214
This work presents a new strategy for obtaining nanocellular materials with high anisotropy ratios by means of the addition of needle‐like nanoparticles. Nanocellular polymers are of great interest due to their outstanding properties, whereas anisotropic structures allow the realization of improved thermal and mechanical properties in certain directions. Nanocomposites based on poly(methyl methacrylate) (PMMA) with nanometric sepiolites are generated by extrusion. From the extruded filaments, cellular materials are produced using a two‐step gas dissolution foaming method. The effect of adding various types and contents of sepiolites is investigated. As a result of the extrusion process, the needle‐like sepiolites are aligned in the machine direction in the solid nanocomposites. Regarding the cellular materials, the addition of sepiolites allows one to obtain anisotropic nanocellular polymers with cell sizes of 150 to 420 nm and cell nucleation densities of 1013–1014 nuclei cm?3 and presenting anisotropy ratios ranging from 1.38 to 2.15, the extrusion direction being the direction of the anisotropy. To explain the appearance of anisotropy, a mechanism based on cell coalescence is proposed and discussed. In addition, it is shown that it is possible to control the anisotropy ratio of the PMMA/sepiolite nanocellular polymers by changing the amount of well‐dispersed sepiolites in the solid nanocomposites. © 2019 Society of Chemical Industry 相似文献