411 research outputs found
Three-component carboacylation of alkenes via cooperative nickelaphotoredox catalysis
No full textVarious commercially available acyl chlorides, aldehydes, and alkanes were exploited for versatile three-component 1,2-carboacylations of alkenes to forge two vicinal C–C bonds through the cooperative action of nickel and sodium decatungstate catalysis. A wealth of ketones with high levels of structural complexity was rapidly obtained via direct functionalization of C(sp(2))/C(sp(3))–H bonds in a modular manner. Furthermore, a regioselective late-stage modification of natural products showcased the practical utility of the strategy, generally featuring high resource economy and ample substrate scope
Electrochemical Rearrangement for Remote Functionalizations of Unactivated Alkenes
No full textAn electrochemical strategy for the dual functionalizations of unactivated alkenes through an intramolecular migration process was realized in the absence of sacrificial chemical oxidants and noble-metal catalysts under mild reaction conditions. The electrochemistry enabled a (hetero)aryl migration while providing access to alkenyl/alkynyl-migration products. Thus, electricity was employed for the formation of functionalized fluoroalkyl radicals through activation of C−H/C−Br bonds from fluorinated esters. Thereby, we obtained a variety of di and mono-fluorinated alkyl products with good functional group tolerance as well as chemo, and regioselectivities. Likewise, defluorinative allylation of α-carbonyl alkyl bromides proved viable. The reaction mechanism was established by experiments and computations.European Research Council http://dx.doi.org/10.13039/501100000781Alexander von Humboldt-Stiftung http://dx.doi.org/10.13039/100005156China Scholarship Council http://dx.doi.org/10.13039/501100004543Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/50110000165
Photoelectrochemical nickel-catalyzed carboacylation/silanoylation of alkenes with unactivated C/Si–H bonds
No full textA photoelectrochemical approach for the carboacylation/silanoylation of alkenes with alkanes/hydrosilanes is described. The method offers a new perspective for chemists to rapidly obtain various ketones with high levels of structural complexity.Direct and selective installation of two different functional groups into the unsaturated bonds of alkenes constitutes a long-standing goal in organic synthesis. Herein, we first report a photoelectrochemical approach for the carboacylation/silanoylation of alkenes with unactivated alkanes/hydrosilanes
via
the LMCT process. A number of ketones with high complexity and diversity were rapidly obtained from commercially available materials in an economical and sustainable manner. Furthermore, this protocol can be scaled up to the gram-level. This paired electrocatalysis strategy features excellent regioselectivity, and ample substrate scope, is external-oxidant-free, and features a high resource economy. A series of mechanistic experiments were performed to determine the preferred pathway for the photoelectrochemical Ni(
i
)/Ni(
ii
)/Ni(
iii
) cycles in these transformations.A photoelectrochemical approach for the carboacylation/silanoylation of alkenes with alkanes/hydrosilanes is described. The method offers a new perspective for chemists to rapidly obtain various ketones with high levels of structural complexity.Direct and selective installation of two different functional groups into the unsaturated bonds of alkenes constitutes a long-standing goal in organic synthesis. Herein, we first report a photoelectrochemical approach for the carboacylation/silanoylation of alkenes with unactivated alkanes/hydrosilanes
via
the LMCT process. A number of ketones with high complexity and diversity were rapidly obtained from commercially available materials in an economical and sustainable manner. Furthermore, this protocol can be scaled up to the gram-level. This paired electrocatalysis strategy features excellent regioselectivity, and ample substrate scope, is external-oxidant-free, and features a high resource economy. A series of mechanistic experiments were performed to determine the preferred pathway for the photoelectrochemical Ni(
i
)/Ni(
ii
)/Ni(
iii
) cycles in these transformations.National Natural Science Foundation of China https://doi.org/10.13039/501100001809Deutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
Ruthenium(II)-Catalyzed Remote C–H Alkylation of Arenes Using Diverse N-Directing Groups through Aziridine Ring Opening
No full textsj-docx-1-eso-10.1177_23969873221151142 – Supplemental material for Sex differences in outcomes after endovascular treatment of patients with vertebrobasilar artery occlusion
No full textSupplemental material, sj-docx-1-eso-10.1177_23969873221151142 for Sex differences in outcomes after endovascular treatment of patients with vertebrobasilar artery occlusion by Pan Zhang, Hao Li, Jinjing Wang, Feng Zhang, Lulu Xiao, Yirong Fang, Dingyi Yan, Guoqiang Xu, Chaolai Liu, Zhixin Huang, Mengmeng Gu, Hanhong Zhang and Wen Sun in European Stroke Journal</p
HCl-mediated silylation of C\u2013H bonds in (hetero)arenes with trialkylsilanes
No full textOur study presents a practical, eco-friendly electron donor–acceptor (EDA) strategy that enables highly efficient C–H silylation of (hetero)arenes by using affordable and readily available HCl as the only additive under visible-light excitation.Direct C–H silylation of (hetero)arenes provides a straightforward route for synthesizing valuable organosilicon molecules. Contrasting with traditional methods that rely on costly photocatalysts, toxic metal reagents, excess strong oxidants, and high temperatures. Herein, our study presents a practical, eco-friendly electron donor–acceptor (EDA) strategy that enables highly efficient C–H silylation of (hetero)arenes by using affordable and readily available HCl as the only additive under visible-light excitation. Substrate classes previously challenging to activate are efficiently silylated with high yields and excellent regioselectivity. Furthermore, this protocol enables the direct silylation of active pharmaceutical ingredients. The resulting heteroarylsilane products undergo versatile transformations, enabling advanced synthetic strategies for heteroaromatic functionalization. This synthetic strategy shows great potential for industrial-scale applications, attributed to readily available raw materials, simple reaction conditions, air and water tolerance, broad substrate scope, and excellent scalability. Notably, this reaction system facilitates other versatile functionalizations of heteroarenes, including trifluoromethylation, acylation, and alkylation. More significantly, the quinoline salt derived from quinoline and hydrochloric acid serves as a novel photocatalyst, converting silanes or alkyl trifluoroborates into corresponding radicals for diverse chemical bond construction. In future studies, these results provide valuable insights for achieving new chemical transformations with quinoline hydrochloride, an EDA complex, as a photocatalyst or additive.Our study presents a practical, eco-friendly electron donor–acceptor (EDA) strategy that enables highly efficient C–H silylation of (hetero)arenes by using affordable and readily available HCl as the only additive under visible-light excitation.Direct C–H silylation of (hetero)arenes provides a straightforward route for synthesizing valuable organosilicon molecules. Contrasting with traditional methods that rely on costly photocatalysts, toxic metal reagents, excess strong oxidants, and high temperatures. Herein, our study presents a practical, eco-friendly electron donor–acceptor (EDA) strategy that enables highly efficient C–H silylation of (hetero)arenes by using affordable and readily available HCl as the only additive under visible-light excitation. Substrate classes previously challenging to activate are efficiently silylated with high yields and excellent regioselectivity. Furthermore, this protocol enables the direct silylation of active pharmaceutical ingredients. The resulting heteroarylsilane products undergo versatile transformations, enabling advanced synthetic strategies for heteroaromatic functionalization. This synthetic strategy shows great potential for industrial-scale applications, attributed to readily available raw materials, simple reaction conditions, air and water tolerance, broad substrate scope, and excellent scalability. Notably, this reaction system facilitates other versatile functionalizations of heteroarenes, including trifluoromethylation, acylation, and alkylation. More significantly, the quinoline salt derived from quinoline and hydrochloric acid serves as a novel photocatalyst, converting silanes or alkyl trifluoroborates into corresponding radicals for diverse chemical bond construction. In future studies, these results provide valuable insights for achieving new chemical transformations with quinoline hydrochloride, an EDA complex, as a photocatalyst or additive.National Natural Science Foundation of China https://doi.org/10.13039/501100001809Natural Science Foundation of Liaoning Province https://doi.org/10.13039/501100005047Natural Science Foundation of Zhejiang Province https://doi.org/10.13039/501100004731Zhejiang Normal University https://doi.org/10.13039/50110000470
Red emitting and highly stable carbon dots with dual response to pH values and ferric ions
No full textThe authors describe strongly red-emitting carbon dots (CDs) which were obtained via microwave synthesis using phenylenediamine as the carbon source. The structural and optical properties of the resultant CDs are studied in some detail. The CDs possess (a) longwave emission (peaking at 620 nm under 470 nm excitation), (b) a quantum yield of similar to 15%, (c) a size of typically 3.8 nm; and (d) good photostability. The CDs have a pH-dependet response that covers the pH 5 to 10 range, and their fluorescence is quenched by ferric ions. The CDs can detect ferric ions in aqueous samples in the 0 to 30 mu M concentration range with a lower detection limit of 15 nM. The CDs were also used to image pH values and ferric ions in E. coli bacteria
Advanced controller design for wind turbine systems
No full textIn the report, the theory, function, model of a wind turbine system are introduced.
The key point of the report is put on the design of the advanced control scheme for
the wind turbine system, by the use of which, the performance of the system can be
improved.
The serious result caused by the greenhouse effect makes a growing attention in the
whole world. The use of renewable energy for decreasing the usage of fossil fuel
becomes a significant issue. As one of the renewable energy, wind energy is
abundant, having a wide distribution, without producing greenhouse gas. The
conversion and the stability of the wind energy is an important issue for the
application of wind energy. To solve these problems, controllers, normally PI
controller, are used in the wind turbine.
The objective of this project is to build a model of wind turbine system and make
control scheme for the system for the improvement of the performance of the system
with the help of the computer and the software simulation.Master of Science (Power Engineering
Control of tidal turbine drive systems
No full textIn this report, the function, model and data of a tidal turbine drive system are summarized. The emphasis is placed on the methods which are used to design a controller to improve the performance of the tidal turbine drive system in the following aspect, the faster response time and less overshoot.
A growing attention to the greenhouse effect caused by converting the energy of fossil fuels has been paid in the whole world, which leads to the utilizing clean and renewable energy source to decrease the using of fossil fuels. There are various kinds of renewable energy, and tidal energy is one of them. Tidal energy is still a new form of renewable relatively, but the methods of harnessing the tidal energy are similar to wind energy. Generally the Horizontal Axis Wave Turbine(HAWT) is chosen to harness the tidal energy due to its better efficiency. To improve the performance of the system, a controller is installed in generally. PID controller is widely used in industrial control systems, because of its effectiveness, robust, insensitive and simple to be setup and maintained.
The objective of this project is to set up a model of tidal turbine drive system, design control scheme to improve the performance of tidal turbine drive system and evaluating the system performance by computer simulation.Bachelor of Engineerin
Using Generative Adversarial Networks to Break and Protect Text Captchas
Full text linkText-based CAPTCHAs remains a popular scheme for distinguishing between a legitimate human user and an automated program. This article presents a novel genetic text captcha solver based on the generative adversarial network. As a departure from prior text captcha solvers that require a labor-intensive and time-consuming process to construct, our scheme needs significantly fewer real captchas but yields better performance in solving captchas. Our approach works by first learning a synthesizer to automatically generate synthetic captchas to construct a base solver. It then improves and fine-tunes the base solver using a small number of labeled real captchas. As a result, our attack requires only a small set of manually labeled captchas, which reduces the cost of launching an attack on a captcha scheme. We evaluate our scheme by applying it to 33 captcha schemes, of which 11 are currently used by 32 of the top-50 popular websites. Experimental results demonstrate that our scheme significantly outperforms four prior captcha solvers and can solve captcha schemes where others fail. As a countermeasure, we propose to add imperceptible perturbations onto a captcha image. We demonstrate that our countermeasure can greatly reduce the success rate of the attack
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