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排序方式: 共有1308条查询结果,搜索用时 15 毫秒
141.
4‐Cyanoresorcinol‐Based Bent‐Core Mesogens with Azobenzene Wings: Emergence of Sterically Stabilized Polar Order in Liquid Crystalline Phases
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Mohammed Alaasar Marko Prehm Kathrin May Alexey Eremin Carsten Tschierske 《Advanced functional materials》2014,24(12):1703-1717
A new series of azobenzene containing bent‐core molecules incorporating 4‐cyanoresorcinol as the central core unit exhibiting cybotactic nematic, rectangular, columnar, and different types of tilted smectic (SmC) phases are synthesized. The mesophase behavior and phase structures are characterized in bulk and freely suspended films using a variety of experimental techniques. Depending on the chain length and temperature a series of different mesophases is observed in these compounds, ranging from cybotactic nematic via paraelectric SmC phases, polarization randomized SmCsPR phases to ferroelectric and antiferroelectric SmC phases, associated with increasing size and correlation length of the polar domains. Spontaneous formation of chiral domains is observed in the paraelectric SmC and the SmCsPR phases and discussed in relation with superstructural chirality, bend elastic constants, and surface effects. 相似文献
142.
Alexander Foertig Juliane Kniepert Markus Gluecker Thomas Brenner Vladimir Dyakonov Dieter Neher Carsten Deibel 《Advanced functional materials》2014,24(9):1306-1311
A combination of transient photovoltage (TPV), voltage dependent charge extraction (CE), and time delayed collection field (TDCF) measurements is applied to poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b']dithiophene‐2,6‐diyl] [3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl] thieno[3,4‐b]thiophenediyl]] (PTB7):[6,6]‐phenyl‐C71‐butyric acid (PC71BM) bulk heterojunction solar cells to analyze the limitations of photovoltaic performance. Devices are processed from pure chlorobenzene (CB) solution and a subset is optimized with 1,8‐diiodooctane (DIO) as co‐solvent. The dramatic changes in device performance are discussed with respect to the dominating loss processes. While in the devices processed from CB solution severe geminate and nongeminate recombination is observed, the use of DIO facilitates efficient polaron pair dissociation and minimizes geminate recombination. Thus, from the determined charge carrier decay rate under open circuit conditions and the voltage dependent charge carrier densities n(V), the nongeminate loss current Jloss of the samples with DIO alone enables the reconstruction of the current/voltage (j/V) characteristics across the whole operational voltage range. Geminate and nongeminate losses are considered to describe the j/V response of cells prepared without additive, but lead to a clearly overestimated device performance. The deviation between measured and reconstructed j/V characteristics is attributed to trapped charges in isolated domains of pure fullerene phases. 相似文献
143.
This study aimed at characterising 606 crossbred pigs of three commercially available breed types in terms of their carcass and meat quality. Breed G and H were German Large White (LW) × German Landrace (LR) sows sired with Pietrain (PI) boars, i.e. PI × (LW × LR). Breed S was 25% Duroc (DU), i.e. PI × (DU × LR). Most of the parameters were affected by breed and/or date of slaughter. The meat of crossbred pigs with 25% Duroc proportion appeared most favourable because of higher intramuscular fat content, lower drip loss and higher sensory liking scores. Conductivity is closely related to drip loss while the data suggests that the relationship is dependent on breed and carcass weight. The application of conductivity and lean meat yield thresholds to select carcasses with uniform and superior meat quality effectively decreased drip loss and increased intramuscular fat content as well as sensory liking scores. The variation of meat quality traits remains high, though. 相似文献
144.
145.
Ultrasonic investigations of high-Tc superconductors have been quite successful in determining the magnetic field and temperature dependence of the interaction between magnetic vortices and defect structures in the superconducting state. Recent advances in ultrasonic techniques, allowing the separation of effects due to coupling of the vortex ensemble to modulations of the superconducting current density from those due to pinning, show evidence of reentrant softening of the vortex ensemble as precursor to reentrant melting. It is demonstrated how a related experimental setup can be used to study the magnetic field-induced torque acting on a sample. Torque experiments on highly anisotropic superconductors yield valuable information about the anisotropy of the reduced mass of charge-carriers and the penetration depth. Important advantages of the approach described here over conventional torque experiments are: (a) high sensitivity to small changes in torque even at high ‘bias’-torque; and (b) constant angle between applied magnetic field and sample during the whole experiment, a property that is most important when investigating highly anisotropic superconducting samples in the presence of a magnetic field. Experimental results on a test system show the principle of operation, and investigations of a high-Tc superconducting sample are presented. 相似文献
146.
147.
SL Anliker MS McClure TC Britton EA Stephan SR Maple GG Cooke 《Canadian Metallurgical Quarterly》1994,83(5):716-719
The anti-tumor agent gemcitabine hydrochloride, a beta-difluoronucleoside, is remarkably stable in the solid state. In 0.1 N HCI solution at 40 degrees C, deamination of gemcitabine occurs, yielding its uridine analogue. Approximately 86% of the initial gemcitabine remains after 4 weeks under these conditions. Cleavage of the N-glycosidic bond of gemcitabine or conversion to its alpha-anomer in 0.1 N HCI solution is not observed over a 4-week period. However, this work has shown that gemcitabine hydrochloride anomerizes in 0.1 N NaOH at 40 degrees C. Approximately 72% of the initial gemcitabine remains after 4 weeks under the basic conditions used. Uridine hydrolysis products are also formed under these conditions. The anormerization reaction, which is unusual under basic conditions, has been confirmed by characterization of the chromatographically isolated alpha-anomer by NMR and mass spectrometry. A mechanism involving an acyclic intermediate is proposed. 相似文献
148.
In the paper, the development of final energy consumption in Lithuania, on the basis of realistic economic scenarios, is investigated. The main parameters influencing the energy consumption are the gross national product (GNP) and the wholesale price of energy. Owing to the uncertainties in former socialist economies, these parameters are described as ‘fuzzy sets.’ The theory of fuzzy sets is used to study the influences that the prices of preceding periods have on the actual final energy consumption, with a quasidynamic model. In so far as this mechanism cannot be ascertained for Lithuania, experiences with other former centrally planned economies, which have already turned into a kind of market economy, are applied to give realistic projections for the transitory period. The underlying scenarios for the GNP and price developments are taken from official Lithuanian projections. The results of the fuzzy quasidynamic model are compared with the official final energy demand projections, to provide policy advice for a proper restructuring of the energy system. 相似文献
149.
The selective oxidation of hydrocarbons is an important value-enhancing chemical transformation in particular with respect to fine chemicals and pharmaceuticals production. Enzymatic oxidations operate under mild reaction conditions and produce little if any waste. However, its industrial use is still limited mainly due to their high cost and the low space time yields. In the present work, chloroperoxiase from Calariomyces fumago immobilized on the mesoporous molecular sieve SBA-15 was applied for the oxidation of indole to 2-oxoindole using hydrogen peroxide or tert.-butyl hydroperoxide as oxidants. The performance of the immobilized enzyme was found to be superior to native chloroperoxidase with respect to maximum conversion and pH range applicable. However, immobilized CPO is still sensitive to high concentrations of hydrogen peroxide. The use of tert.-buty hydroperoxide is found to avoid this problem, but the reaction rate is significantly reduced. 相似文献
150.