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71.
Janina Lulek Maurycy Opielewicz Katarzyna Szyrwińska Bart?omiej Milanowski 《Analytica chimica acta》2005,540(1):25-31
The database of the relative retention times (RRTs) of polychlorinated biphenyls (PCBs) reported in literature was used to calculate the retention indices (RIs) of all 209 PCB congeners on temperature programmed capillary column Rtx-5. Calculation of retention indices was based on reference series of seven congeners (PCB IUPAC Nos. 18, 52, 101, 143, 185, 203 and 206) that exhibit linear relative retention time behaviour as a function of chlorine number. The calculated indices were compared to those determined in our laboratory as well as to those obtained by other authors. The proposed indices system was applied for identification individual congeners in mixture of Aroclors 1242:1254:1260, using only reference series of PCBs. 相似文献
72.
以去离子水与乙二醇的混合液(体积分数分别为36.5%,48.7%,59.0%及71.2%,以下简称混合液)作为同轴传输线的绝缘介质,进行了μs级高电压负充电条件下的正电极击穿实验,研究了混合液的击穿电压、击穿时间、相对介电常数及电阻率与体积分数的关系。实验结果表明:在充电电压为20kV时,71.2%的混合液比36.5%的混合液的平均击穿电压提高25.1%,平均击穿时间延长10.49%,而相对介电常数减小868%。同时,随着充电时间的缩短,混合液的击穿电压提高。 相似文献
73.
《Journal of polymer science. Part A, Polymer chemistry》2018,56(17):1978-1988
New donor–π–acceptor (D–π–A) type conjugated copolymers, poly[(4,8‐bis((2‐hexyldecyl)oxy)benzo[1,2‐b:4,5‐b′]dithiophene)‐alt‐(2,5‐bis(4‐octylthiophen‐2‐yl)thiazolo[5,4‐d]thiazole)] (PBDT‐tTz), and poly[(4,8‐bis((2‐hexyldecyl)oxy)benzo[1,2‐b:4,5‐b′]dithiophene)‐alt‐(2,5‐bis(6‐octylthieno[3,2‐b]thiophen‐2‐yl)thiazolo[5,4‐d]thiazole)] (PBDT‐ttTz) were synthesized and characterized with the aim of investigating their potential applicability to organic photovoltaic active materials. While copolymer PBDT‐tTz showed a zigzagged non‐linear structure by thiophene π‐bridges, PBDT‐ttTz had a linear molecular structure with thieno[3,2‐b]thiophene π‐bridges. The optical, electrochemical, morphological, and photovoltaic properties of PBDT‐tTz and PBDT‐ttTz were systematically investigated. Furthermore, bulk heterojunction photovoltaic devices were fabricated by using the synthesized polymers as p‐type donors and [6,6]‐phenyl‐C71‐butyric acid methyl ester as an n‐type acceptor. PBDT‐ttTz showed a high power conversion efficiency (PCE) of 5.21% as a result of the extended conjugation arising from the thienothiophene π‐bridges and enhanced molecular ordering in the film state, while PBDT‐tTz showed a relatively lower PCE of 2.92% under AM 1.5 G illumination (100 mW/cm2). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1978–1988 相似文献
74.
Improved estimation of duality gap in binary quadratic programming using a weighted distance measure
We present in this paper an improved estimation of duality gap between binary quadratic program and its Lagrangian dual. More specifically, we obtain this improved estimation using a weighted distance measure between the binary set and certain affine subspace. We show that the optimal weights can be computed by solving a semidefinite programming problem. We further establish a necessary and sufficient condition under which the weighted distance measure gives a strictly tighter estimation of the duality gap than the existing estimations. 相似文献
75.
P. Lakshmi Praveen 《Liquid crystals》2013,40(6):872-882
The substituent- and solvent-induced shifts in UV-visible absorption bands of naphthyl-ester nematic liquid crystals, viz., 4-octylphenyl-6-octyloxy-2-naphthoate (NAPHE1) and 6-octyloxy-2-naphthylyl-4-octyloxybenzoate (NAPHE2), have been investigated using the DFT, CNDO/S and INDO/S methods. A correlation has been made between molecular charge distribution and phase stability based on Mulliken, Loewdin, AM1, PM3, MNDO, CNDO/S and INDO/S methods. The observed π→π* and n→π* electronic transitions have been reported. The substituent- and solvent-induced shifts in absorption bands, transition energies and energy gaps have been discussed. The photosensitivity of the molecules has been analysed based on these shifts. It has been observed that the substituent has a dominant role on both absorption maxima and energy band gap, whereas the solvent has a dominant role only on absorption maxima, and no effect has been observed on the energy gap. These shifts may provide beneficial consequences in determining the end use of compounds. 相似文献
76.
77.
Naturally fractured reservoirs contain about 25–30% of the world supply of oil. In these reservoirs, fractures are the dominant flow path. Therefore, a good understanding of transfer parameters such as relative permeability as well as flow regimes occurring in a fracture plays an important role in developing and improving oil production from such complex systems. However, in contrast with gas–liquid flow in a single fracture, the flow of heavy oil and water has received less attention. In this research, a Hele-Shaw apparatus was built to study the flow of water in presence of heavy oil and display different flow patterns under different flow rates and analyze the effect of fracture orientations on relative permeability curves as well as flow regimes. The phase flow rates versus phase saturation results were converted to experimental relative permeability curves. The results of the experiments demonstrate that, depending on fracture and flow orientation, there could be a significant interference between the phases flowing through the fracture. The results also reveal that both phases can flow in both continuous and discontinuous forms. The relative permeability curves show that the oil–water relative permeability not only depends on fluid saturations and flow patterns but also fracture orientation. 相似文献
78.
Ling Wang Xiao-Tong Wang Jia-Huan Zhong Dr. Kang Xiao Dr. Ting Ouyang Prof. Zhao-Qing Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(18):5796-5802
The high charge–discharge voltage gap is one of the main bottlenecks of zinc–air batteries (ZABs) because of the kinetically sluggish oxygen reduction/evolution reactions (ORR/OER) on the oxygen electrode side. Thus, an efficient bifunctional catalyst for ORR and OER is highly desired. Herein, honeycomb-like MnCo2O4.5 spheres were used as an efficient bifunctional electrocatalyst. It was demonstrated that both ORR and OER catalytic activity are promoted by MnIV-induced oxygen vacancy defects and multiple active sites. Importantly, the multivalent ions present in the material and its defect structure endow stable pseudocapacitance within the inactive region of ORR and OER; as a result, a low charge–discharge voltage gap (0.43 V at 10 mA cm−2) was achieved when it was employed in a flexible hybrid Zn-based battery. This mechanism provides unprecedented and valuable insights for the development of next-generation metal–air batteries. 相似文献
79.
Young‐gi kim Emilie M. Galand Barry C. Thompson John walker Stephen A. Fossey Tracy D. Mccarley 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(7):665-674
Isoregic conjugated polymers composed of thiophene and dialkoxybenzene units were designed to harvest incident light in the mid‐visible energy range (band gap of 2.1 eV). Poly(1,4‐bis(2‐thienyl)‐2,5‐diheptoxybenzene) (PBTB(OC7H15)2) and poly(1,4‐bis(2‐thienyl)‐2,5‐didodecyloxybenzene) (PBTB(OC12H25)2) have shown significant photovoltaic performance as an electron donor when used in tandem with the electron acceptor [6, 6]‐phenyl C61‐butyric acid methyl ester (PCBM) in bulk hetero‐junction photovoltaic devices. Photovoltaic devices incorporating PBTB(OC7H15)2 and PCBM have shown AM1.5 efficiencies of ~0.6% with a short circuit current density of 2.5 mA/cm2, an open circuit voltage of 0.74 V, and a fill factor of 0.32. Incident Photon‐to‐Current Efficiency (IPCE) of the device was found to be ca. 16% at 410 nm. In order to examine the relationship between the molecular structure of the polymers and their electronic energy levels, and to correlate this with photovoltaic performance, optoelectronic and electrochemical results are discussed in relation to the I‐V characteristics of the devices. Additionally, a computer‐aided simulation is used to gain further insight into the effect of polymer structure on the energetic relationships in the bulk heterojunction devices. 相似文献
80.
Zhaojie Gu Lijun Deng Hao Luo Xia Guo Haohao Li Zhencai Cao Xunshan Liu Xinwei Li Hongyan Huang Yingzi Tan Yong Pei Songting Tan 《Journal of polymer science. Part A, Polymer chemistry》2012,50(18):3848-3858
A series of novel low band gap polymers containing conjugated side chains with 4,7‐dithien‐5‐yl‐2,1,3‐benzodiathiazole and different electron‐withdrawing end groups of aldehyde ( PT‐DTBTCHO ), 2‐ethylhexyl cyanoacetate ( PT‐DTBTCN ), 1,3‐diethyl‐2‐thiobarbituric acid ( PT‐DTBTDT ), and electron‐donating end group of 2‐methylthiophene ( PT‐DTBTMT ) have been designed and synthesized. All polymers exhibit good solubility in common organic solvents, film‐forming ability, and thermal stability. These conjugated polymers show the broad ultraviolet‐visible absorption and the narrow optical band gaps in the range of 1.65–1.90 eV. Through changing the end group of conjugated side chains, the photophysical properties and energy levels of the polymers were tuned effectively. Bulk heterojunction solar cells based on the blend of these polymers and (6,6)‐phenyl‐C61‐butyric acid methyl ester (PC61BM) reached the best power conversion efficiency (PCE) of 2.72%. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献