25 research outputs found

    Enhanced predictor–corrector Mars entry guidance approach with atmospheric uncertainties

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    Due to the long-range data communication and complex Mars environment, the Mars lander needs to promote the ability to autonomously adapt uncertain situations ensuring high precision landing in future Mars missions. Based on the analysis of multiple disturbances, this study demonstrates an enhanced predictor–corrector guidance method to deal with the effect of atmospheric uncertainties during the entry phase of the Mars landing. In the proposed method, the predictor–corrector guidance algorithm is designed to autonomously drive the Mars lander to the parachute deployment. Meanwhile, the disturbance observer is designed to onboard estimate the effect of fiercely varying atmospheric uncertainties resulting from rapidly height decreasing. Then, with the estimation of atmospheric uncertainties compensated in the feed-forward channel, the composite guidance method is put forward such that both anti-disturbance and autonomous performance of the Mars lander guidance system are improved. Convergence of the proposed composite method is analysed. Simulations for a Mars lander entry guidance system demonstrates that the proposed method outperforms the baseline method in consideration of the atmospheric uncertainties

    Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenyl­ethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

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    The straightforward synthesis of 3,5-di­(triphenyl­ethylenyl) BODIPYs <b>1</b>–<b>3</b> from the condensation of 2-(triphenyl­ethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of <b>1</b> resulted in a “1,2-migratory shift” of one triphenyl­ethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry

    Unusual Intramolecular Hydrogen Transfer in 3,5-Di(triphenyl­ethylenyl) BODIPY Synthesis and 1,2-Migratory Shift in Subsequent Scholl Type Reaction

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    The straightforward synthesis of 3,5-di­(triphenyl­ethylenyl) BODIPYs <b>1</b>–<b>3</b> from the condensation of 2-(triphenyl­ethylenyl) pyrrole with aryl aldehydes are surprisingly found to produce side products that are hydrogenated at one of the two triphenylethylene substituents. It was also observed that the subsequent Scholl type reaction of <b>1</b> resulted in a “1,2-migratory shift” of one triphenyl­ethylene substituent in addition to a ring closing reaction. Preliminary investigations, including DFT calculations and isolation of intermediates, were conducted to study these unusual observations on BODIPY chemistry

    How to Fabricate a Surface-Grafted Polythiophene on H‑Si(100)2×1 Surface via Self-Assembling and in Situ Surface Polymerization: A Theoretical Guide

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    Based on density functional theory calculations, we have studied the self-assembled growth of thiophene substituted alkenes, [H<sub>2</sub>CCH-(CH<sub>2</sub>)<sub><i>n</i></sub>-thiophene] on hydrogen-terminated H-Si(100)­2×1 and H-Ge(100)­2×1 surfaces into aligned one-dimensional (1D) molecular arrays which are chemically bonded to the surfaces via the alkane chain. The thiophene rings at the top end of the molecular arrays are situated side by side and can undergo an in situ polymerization reaction into polythiophene once radicals are introduced to the thiophene rings, thereby forming polyalkylthiophene-Si/Ge(100)­2×1 surface-grafted polymers. Like most of conductive polymers, these surface single polymer chains exhibit semiconducting character and can be made conductive either by p-doping or by applying an external electric field. More importantly, both surface-grafted polymers and substrates retain their electrical properties, and the polythiophene chains are the sole conductive channels in the structures. Our findings put forth a new way to fabricate conductive polymeric molecular wires on traditional semiconducting substrates, and could find potential application in nanoelectronic devices

    Sulfonic Acid- and Lithium Sulfonate-Grafted Poly(Vinylidene Fluoride) Electrospun Mats As Ionic Liquid Host for Electrochromic Device and Lithium-Ion Battery

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    Electrospun polymer nanofibrous mats loaded with ionic liquids (ILs) are promising nonvolatile electrolytes with high ionic conductivity. The large cations of ILs are, however, difficult to diffuse into solid electrodes, making them unappealing for application in some electrochemical devices. To address this issue, a new strategy is used to introduce proton conduction into an IL-based electrolyte. Poly­(vinylidene fluoride<b>-</b>co<b>-</b>hexafluoropropylene) (P­(VDF-HFP)) copolymer is functionalized with sulfonic acid through covalent attachment of taurine. The sulfonic acid-grafted P­(VDF-HFP) electrospun mats consist of interconnected nanofibers, leading to remarkable improvement in dimensional stability of the mats. IL-based polymer electrolytes are prepared by immersing the modified mats in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM<sup>+</sup>BF<sub>4</sub><sup>–</sup>). It is found that the SO<sub>3</sub><sup>–</sup> groups can have Lewis acid–base interactions with the cations (BMIM<sup>+</sup>) of IL to promote the dissociation of ILs, and provide additional proton conduction, resulting in significantly improved ionic conductivity. Using this novel electrolyte, polyaniline-based electrochromic devices show higher transmittance contrast and faster switching behavior. Furthermore, the sulfonic acid-grafted P­(VDF-HFP) electrospun mats can also be lithiated, giving additional lithium ion conduction for the IL-based electrolyte, with which Li/LiCoO<sub>2</sub> batteries display enhanced C-rate performance

    Sheet-Like Lignin Particles as Multifunctional Fillers in Polypropylene

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    Lignin is an attractive renewable reinforcing agent for polyolefins and also a promising low-cost antioxidant for polymers. It, however, exhibits poor compatibility with nonpolar polymers. In this work, alkali lignin was freeze-dried to achieve sheet-like morphology and then incorporated into polypropylene (PP) by melt compounding. Owing to the significantly increased interfacial area and improved dispersion, with the addition of only 2 wt % freeze-dried lignin, the PP/lignin composites show much enhanced tensile mechanical properties, including a moderately improved Young’s modulus and almost doubled elongation at break compared with those of neat PP. The enhancements brought by the sheet-like lignin are far more impressive than those achieved with the same amount of as-received lignin. The composites with the freeze-dried lignin also have rough fractured surfaces with fiber pull-out near the interface, revealing a significant toughening effect of the lignin, which can be attributed to the crazing near the interface, and enhanced relaxation in PP-lignin interphase as evidenced by the reduced <i>T</i><sub>g</sub>. Furthermore, the large interfacial area also drastically improves the antioxidant effect of lignin, greatly slowing the UV-induced and thermo-oxidative degradation of PP. After 2 weeks of intense UV exposure, neat PP becomes very brittle with its yield strain reduced to about 37% of its original value, whereas the yield strain of the composite with 2 wt % sheet-like lignin is almost unchanged, demonstrating the excellent free-radical scavenger effect of the lignin

    Cyclization of Tetraaryl-Substituted Benzoquinones and Hydroquinones through the Scholl Reaction

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    2,3,5,6-Tetrakis­(5′-dodecylthiophen-2-yl)-benzoquinones and 2,3,5,6-tetrakis­(5′-dodecylthiophen-2′-yl)-hydroquinones were prepared via the Stille or Suzuki cross-coupling reactions, followed by oxidation by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in the case that aryl groups are dodecylthiophenyl. 2,3,5,6-Tetrakis­(5′-dodecylthiophen-2′-yl)­benzoquinone and 2,3,5,6-tetrakis­(5′-dodecylthiophen-2′-yl)-1,4-bis­(dodecyloxy)­benzene underwent the Scholl reaction to give their corresponding predictable cyclization products anthra­[2,1-<i>b</i>:3,4-<i>b</i>′:6,5-<i>b</i>″:7,8-<i>b</i>‴]­tetrathiophene-7,14-dione (<b>3</b>) and anthra­[1,2-<i>b</i>:4,3-<i>b</i>′:5,6-<i>b</i>″:8,7-<i>b</i>‴]­tetrathiophene (<b>5</b>), respectively. Cyclization of 2,3,4,5-tetra­(<i>p</i>-<i>tert</i>-butyl-phenyl) benzoquinones through the Scholl reaction, however, gave rise to a mixture of two cyclization products including an unusual major product, benzo­[4′,5′]­furo­[3′,2′:3,4]­triphenyleno­[1,2-<i>b</i>]­benzofuran (<b>9</b>), with 84% yield and a minor product, 2,3-diphenyltriphenylene-1,4-diol (<b>10</b>), with 11% yield. In contrast, cyclization of 2,3,4,5-tetrakis­(<i>p</i>-dodecyloxyphenyl)­benzoquinone only afforded 2,3-diphenyltriphenylene-1,4-diol (<b>8</b>) with 34% yield. The optical and electrochemistry properties of these fused aromatics were studied. Light emitting diode devices using compound <b>9</b> as the fluorescent dopant were fabricated. A maximum external quantum efficiency of 3.23% was achieved for a 4,4′-bis­(carbazole)­biphenyl/<b>9</b> based device, revealing the potential for such fused aromatics as dopant to be a blue LED component, subject to the functionalization on these novel π-structures as well as further device optimization

    Cyclization of Tetraaryl-Substituted Benzoquinones and Hydroquinones through the Scholl Reaction

    No full text
    2,3,5,6-Tetrakis­(5′-dodecylthiophen-2-yl)-benzoquinones and 2,3,5,6-tetrakis­(5′-dodecylthiophen-2′-yl)-hydroquinones were prepared via the Stille or Suzuki cross-coupling reactions, followed by oxidation by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in the case that aryl groups are dodecylthiophenyl. 2,3,5,6-Tetrakis­(5′-dodecylthiophen-2′-yl)­benzoquinone and 2,3,5,6-tetrakis­(5′-dodecylthiophen-2′-yl)-1,4-bis­(dodecyloxy)­benzene underwent the Scholl reaction to give their corresponding predictable cyclization products anthra­[2,1-<i>b</i>:3,4-<i>b</i>′:6,5-<i>b</i>″:7,8-<i>b</i>‴]­tetrathiophene-7,14-dione (<b>3</b>) and anthra­[1,2-<i>b</i>:4,3-<i>b</i>′:5,6-<i>b</i>″:8,7-<i>b</i>‴]­tetrathiophene (<b>5</b>), respectively. Cyclization of 2,3,4,5-tetra­(<i>p</i>-<i>tert</i>-butyl-phenyl) benzoquinones through the Scholl reaction, however, gave rise to a mixture of two cyclization products including an unusual major product, benzo­[4′,5′]­furo­[3′,2′:3,4]­triphenyleno­[1,2-<i>b</i>]­benzofuran (<b>9</b>), with 84% yield and a minor product, 2,3-diphenyltriphenylene-1,4-diol (<b>10</b>), with 11% yield. In contrast, cyclization of 2,3,4,5-tetrakis­(<i>p</i>-dodecyloxyphenyl)­benzoquinone only afforded 2,3-diphenyltriphenylene-1,4-diol (<b>8</b>) with 34% yield. The optical and electrochemistry properties of these fused aromatics were studied. Light emitting diode devices using compound <b>9</b> as the fluorescent dopant were fabricated. A maximum external quantum efficiency of 3.23% was achieved for a 4,4′-bis­(carbazole)­biphenyl/<b>9</b> based device, revealing the potential for such fused aromatics as dopant to be a blue LED component, subject to the functionalization on these novel π-structures as well as further device optimization

    MiR-1178 Promotes the Proliferation, G1/S Transition, Migration and Invasion of Pancreatic Cancer Cells by Targeting CHIP

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    <div><p>CHIP, a co-chaperone protein that interacts with Hsc/Hsp70, has been shown to be under-expressed in pancreatic cancer cells and has demonstrated a potential tumor suppressor property. Nevertheless, the underlying mechanisms of CHIP regulation in pancreatic cancer cells remain unknown. In this study, we found that miR-1178 decreased the translation of the CHIP protein by targeting the 3′-UTR region. We observed that over-expression of miR-1178 facilitated the proliferation, G1/S transition, migration and invasion of pancreatic cancer cells. Conversely, the inhibition of miR-1178 expression significantly suppressed these phenotypes. Furthermore, CHIP over-expression abrogated miR-1178-induced cell proliferation and invasion. Our data suggest that miR-1178 acts as an oncomiR in pancreatic cancer cells by inhibiting CHIP expression.</p></div
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