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871.
In recent years, a variety of effective chaos-based image cryptosystems have been proposed. One of the architectures of this kind of cryptosystems is composed of multiple rounds of substitution and diffusion. As the confusion and diffusion effects are solely contributed by the substitution and the diffusion stages, respectively, the required overall rounds of operations in achieving a certain level of security is found more than necessary. In this Letter, we suggest to introduce a certain diffusion effect in the substitution stage by simple sequential add-and-shift operations. Although this leads to a longer processing time in a single round, the overall encryption time is reduced as fewer rounds are required. Simulation results show that at a similar performance level, the proposed cryptosystem needs less than one-third the encryption time of an existing fast cryptosystem. The effective acceleration of chaos-based image cryptosystems is thus achieved. 相似文献
872.
Increasing rewriting speed of optical rewritable e-paper by selecting proper liquid crystals
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Effect of interaction between liquid crystal (LC) and photoalignment material on speed of optical rewriting process is investigated. The theoretical analysis shows that smaller frank elastic constant K22 of liquid crystal corresponds to larger twist angle, which gives rise to larger rewriting speed. Six different LC cells with the same boundary conditions (one substrate is covered with rubbed polyimide (PI) and other with photo sensitive rewritable sulfuric dye 1(SD1)) are tested experimentally under the same illumination intensity (450 nm, 80 mW/cm2). The results demonstrate that with suitable liquid crystal, LC optical rewriting speed for e-paper application can be obviously improved. For two well known LC materials E7 (K22 is larger) and 5CB (K22 is smaller), they require 11 s and 6 s corresponding to change alignment direction for generating image information. 相似文献
873.
Qidong Tai Xuyun Guo Guanqi Tang Peng You Tsz‐Wai Ng Dong Shen Jiupeng Cao Chun‐Ki Liu Naixiang Wang Ye Zhu Chun‐Sing Lee Feng Yan 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(3):816-820
Tin‐based perovskites with excellent optoelectronic properties and suitable band gaps are promising candidates for the preparation of efficient lead‐free perovskite solar cells (PSCs). However, it is challenging to prepare highly stable and efficient tin‐based PSCs because Sn2+ in perovskites can be easily oxidized to Sn4+ upon air exposure. Here we report the fabrication of air‐stable FASnI3 solar cells by introducing hydroxybenzene sulfonic acid or its salt as an antioxidant additive into the perovskite precursor solution along with excess SnCl2. The interaction between the sulfonate group and the Sn2+ ion enables the in situ encapsulation of the perovskite grains with a SnCl2–additive complex layer, which results in greatly enhanced oxidation stability of the perovskite film. The corresponding PSCs are able to maintain 80 % of the efficiency over 500 h upon air exposure without encapsulation, which is over ten times longer than the best result reported previously. Our results suggest a possible strategy for the future design of efficient and stable tin‐based PSCs. 相似文献
874.
Jia‐Xiong Chen Wen‐Wen Tao Wen‐Cheng Chen Ya‐Fang Xiao Kai Wang Chen Cao Jia Yu Shengliang Li Feng‐Xia Geng Chihaya Adachi Chun‐Sing Lee Xiao‐Hong Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14802-14807
Developing red thermally activated delayed fluorescence (TADF) emitters, attainable for both high‐efficient red organic light‐emitting diodes (OLEDs) and non‐doped deep red/near‐infrared (NIR) OLEDs, is challenging. Now, two red emitters, BPPZ‐PXZ and mDPBPZ‐PXZ, with twisted donor–acceptor structures were designed and synthesized to study molecular design strategies of high‐efficiency red TADF emitters. BPPZ‐PXZ employs the strictest molecular restrictions to suppress energy loss and realizes red emission with a photoluminescence quantum yield (ΦPL) of 100±0.8 % and external quantum efficiency (EQE) of 25.2 % in a doped OLED. Its non‐doped OLED has an EQE of 2.5 % owing to unavoidable intermolecular π–π interactions. mDPBPZ‐PXZ releases two pyridine substituents from its fused acceptor moiety. Although mDPBPZ‐PXZ realizes a lower EQE of 21.7 % in the doped OLED, its non‐doped device shows a superior EQE of 5.2 % with a deep red/NIR emission at peak of 680 nm. 相似文献
875.
Liu Beibei He Wei Lu Hao Wang Kun Huang Mingming Kwok Ryan Tsz Kin Lam Jacky Wing Yip Gao Longcheng Yang Jiping Tang Benzhong 《中国科学:化学(英文版)》2019,62(6):732-738
Aniline oligomers have been widely used in many fields due to their excellent physicochemical properties. Owing to strong intermolecular interactions, their emission is always weakened or quenched when they are in high concentration or aggregated state, which greatly limits their fluorescent applications. Inspired by the concept of aggregation-induced emission(AIE), herein we introduced large steric groups onto the aniline oligomer to prevent the formation of packing structure. In particular, diphenyl vinyl group was bonded with oligomeric tetraaniline by a facile synthetic procedure with high yield. The obtained aniline oligomer derivative exhibited typical AIE features, which was also confirmed by density functional theoretical calculation. More importantly, this AIE oligomer was able to detect Fe~(3+) ions selectively and quantitatively. The fluorescence intensity decreased linearly along with the increment of Fe~(3+) concentration. Moreover, we demonstrated that this AIE oligomer could stain live bacteria, such as E. coli and S. aureus efficiently. All these results suggest that such a readily accessible and multifunctional tetraaniline derivative provides a new platform for the construction of fluorescent materials. 相似文献
876.
Chan PY Kwok WM Lam SK Chiu P Phillips DL 《Journal of the American Chemical Society》2005,127(23):8246-8247
Time-resolved resonance Raman spectroscopy was used to directly observe the reaction of the 2-fluorenylnitrenium ion with guanosine to produce a C8 intermediate species. Comparison of the Raman spectra with results of density functional theory calculations indicates the C8 intermediate forms two C=N conjugated bonds in ring 1 of the guanosine moiety. 相似文献
877.
Mi B Dong Y Li Z Lam JW Häussler M Sung HH Kwok HS Dong Y Williams ID Liu Y Luo Y Shuai Z Zhu D Tang BZ 《Chemical communications (Cambridge, England)》2005,(28):3583-3585
Appending carbazolyl groups to a hexaphenylsilole core yielded thermally and morphologically stable carbazolylsiloles; the silole carrying two carbazolyl peripheral groups showed photovoltaic activity. 相似文献
878.
879.
Leung KM Chan CY Chong YM Yao Y Ma KL Bello I Zhang WJ Lee ST 《The journal of physical chemistry. B》2005,109(34):16272-16277
The growth of cubic boron nitride (cBN) films on bare silicon and amorphous tetrahedral carbon (ta-C) layers prepared on silicon substrates was studied. The cBN films were prepared by radio frequency magnetron sputter deposition at approximately 870 degrees C. The original ta-C interlayers were graphitized and restructured under high temperature and possibly under ion bombardment during BN deposition. The majority of graphitic basal planes were nearly perpendicular to the surface of silicon substrates. The BN films grown on these restructured carbon layers were deposited with higher content of cubic phase and did not show delamination signs. Turbostratic BN (tBN) basal planes extended carbon basal planes and their edges served as cBN nucleation sites. The cBN films grown on textured ta-C interlayers were insensitive to the ambient environment. The residual sp(3)-bonded carbon phase confined in the interlayers probably acts as a diffusion barrier preventing the oxidation of dangling bonds near BN interface and thus precludes weakening the interface as a result of volume expansion. The carbon interlayers also improve the crystallinity of the oriented tBN because they are continuation of carbon graphitic basal planes so that the volume fraction of nitrogen-void (N-void) defects in the sp(2)-bonded BN intermediate layers is reduced. The strong sp(3)-bonded carbon matrix could thereto withstand large compressive stress and facilitates deposition of thicker cBN films. 相似文献
880.
We studied wetting phenomena on heterogeneous surfaces by a mean-field free-energy lattice Boltzmann method recently proposed [Phys. Rev. E 69 (2004) 32,602]. Our results suggest that the Cassie equation in macroscopic contact angle measurements is in general not valid. It was found that the Cassie equation is valid only when the patch size is on the same order of the liquid-vapor interfacial thickness. We also demonstrated that contact angle manifests itself from local surface properties near the contact point and does not result from the specific solid-liquid interactions across the contact area. 相似文献