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373 results on '"Yao, Weijun"'

1. Electric Charging Effects on Insulating Surfaces in Cryogenic Liquids

Author

Korsch, Wolfgang, Broering, Mark, Timsina, Ashok, Leung, Kent K. H., Abney, Joshua, Budker, Dmitry, Filippone, Bradley W., He, Jiachen, Kandu, Suman, McCrea, Mark, Roy, Murchhana, Swank, Christopher, and Yao, Weijun

Subjects
Physics - Applied Physics, Condensed Matter - Soft Condensed Matter, Physics - Optics
Abstract

This paper presents a new technique to study the adsorption and desorption of ions and electrons on insulating surfaces in the presence of strong electric fields in cryoliquids. The experimental design consists of a compact cryostat coupled with a sensitive electro-optical Kerr device to monitor the stability of the electric fields. The behavior of nitrogen and helium ions on a poly(methyl methacrylate) (PMMA) surface was compared to a PMMA surface coated with a mixture of deuterated polystyrene and deuterated polybutadiene. Ion accumulation and removal on these surfaces were unambiguously observed. Within the precision of the data, both surfaces behave similarly for the physisorbed ions. The setup was also used to measure the (quasi-)static dielectric constant of PMMA at T = 70 K. The impact of the ion adsorption on the search for a neutron permanent electric dipole moment in a cryogenic environment, like the nEDM@SNS experiment, is discussed.

Published
2023

4. Phosphine-catalyzed enantioselective and diastereodivergent [3+2] cyclization for the construction of oxetane dispirooxindole skeletons.

Author

Han, Xiao, Hou, Jie, Zhang, Haiyan, Wang, Zhen, and Yao, Weijun

Subjects
DIASTEREOISOMERS, PHOSPHINE, SKELETON, CATALYSTS, CARBONATES
Abstract

We have developed a phosphine catalyzed asymmetric [3+2] cyclization of 3-oxetanone derived MBH carbonates with activated methyleneoxindole, to construct oxetane dispirooxindole skeletons. Diastereodivergent synthesis was realized via the control of the phosphine catalyst. The (−)-DIOP provides the syn diastereoisomers, while the spiro phosphine (R)-SITCP achieves the anti-epimers. [ABSTRACT FROM AUTHOR]

Published
2024
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6. Electric charging effects on insulating surfaces in cryogenic liquids

Author

Korsch, Wolfgang, primary, Broering, Mark, additional, Timsina, Ashok, additional, Leung, Kent K. H., additional, Abney, Joshua, additional, Budker, Dmitry, additional, Filippone, Bradley W., additional, He, Jiachen, additional, Kandu, Suman, additional, McCrea, Mark, additional, Roy, Murchhana, additional, Swank, Christopher, additional, and Yao, Weijun, additional

Published
2024
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9. gem-Difluoroalkylation of Cyclic Ethers Enabled by Cobalt-Catalyzed C(sp3)–H Oxidation under Mild Conditions

Author

Yang, Jingjie, Wang, Zhiming, Zhang, Yiheng, Wang, Yurong, Yao, Weijun, and Gao, Kai

Abstract

Fluorinated rings have emerged as privileged structural modules in the fields of drug discovery and materials research. The incorporation of fluorine atoms into aromatic rings or heterocycles can lead to significant improvements in the physicochemical and biological properties of small molecules, making them valuable components in the design of new drugs and functional materials. Herein, we presented a cobalt-catalyzed C–H oxidation/gem-difluorination cascade reaction of readily available cyclic ethers with difluoroenoxysilanes, affording a series of gem-difluorinated analogues with moderate to high yields. The obtained products as versatile fluoroalkyl building blocks were showcased through divergent-oriented transformations.

Published
2024
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10. The Asymmetric Synthesis of Polycyclic Tetrahydroxanthone via the Cascade Reaction of Alkene‐Substituted 1,3‐diketones and Alkenyloxindoles.

Author

Zhang, Rong, Wang, Wenhui, Zhang, Yonghui, Chen, Yushuang, Yao, Weijun, and Wang, Zhen

Subjects
POLYCYCLIC compounds, ORGANOCATALYSIS, CATALYSTS, ASYMMETRIC synthesis, IMINES, CATALYSIS
Abstract

Enantioselective access to polycyclic tetrahydroxanthone compounds was achieved through an organocatalyzed cascade reaction of alkene‐substituted 1,3‐diketones and alkenyloxindoles, using quinine‐derived squaramide as an efficient catalyst. It afforded a variety of optically active spirooxindole‐based tetrahydroxanthones with 18–94% yields, >19:1 dr, and 86–99% ee. [ABSTRACT FROM AUTHOR]

Published
2024
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14. Quantum computing with single electron bubbles in helium

Author

Yao, Weijun

Subjects
Condensed Matter - Other Condensed Matter, Quantum Physics
Abstract

An electron inside liquid helium forms a bubble of 17 \AA in radius. In an external magnetic field, the two-level system of a spin 1/2 electron is ideal for the implementation of a qubit for quantum computing. The electron spin is well isolated from other thermal reservoirs so that the qubit should have very long coherence time. By confining a chain of single electron bubbles in a linear RF quadrupole trap, a multi-bit quantum register can be implemented. All spins in the register can be initialized to the ground state either by establishing thermal equilibrium at a temperature around 0.1 K and at a magnetic field of 1 T or by sorting the bubbles to be loaded into the trap with magnetic separation. Schemes are designed to address individual spins and to do two-qubit CNOT operations between the neighboring spins. The final readout can be carried out through a measurement similar to the Stern-Gerlach experiment.

Published
2005

18. Phosphine-catalyzed Rauhut–Currier reaction of γ-alkyl allenoate and subsequent trapping using the Diels–Alder reaction.

Author

Zhang, Juan, Hao, Wei, Chen, Ying, Wang, Zhen, Yao, Jinzhong, and Yao, Weijun

Subjects
DIELS-Alder reaction, STEREOSPECIFICITY, SUCCINIMIDES, PHOSPHINE
Abstract

We have disclosed a Rauhut–Currier reaction of γ-alkyl-substituted allenoate, catalyzed by L -valine-derived amide phosphine, to form trisubstitued allenoate, which was trapped by maleimide or DMAD via the Diels–Alder reaction. Exo-bicyclic succinimide derivatives including three continuous stereocenters with an exo-carbon–carbon double bound were constructed in up to quantitative yields with high stereospecificity. [ABSTRACT FROM AUTHOR]

Published
2023
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32. DABCO-Catalyzed [3+2] Cycloaddition of Isatin-Derived Nitrones and Electron-Deficient Dienes via a 1,6-Addition Reaction.

Author

Luo, Zihao, Wang, Zhen, and Yao, Weijun

Subjects
RING formation (Chemistry), NITRONES, DIOLEFINS, ORGANIC bases, YLIDES
Abstract

Regio-, chemo-, and diastereoselective [3+2] dipolar cycloadditions of isatin-derived nitrone ylides with penta-2,4-dienenitriles have been developed. The reaction proceeds through the organic base DABCO catalyzed 1,6-addition to linear penta-2,4-dienenitriles, followed by the intramolecular cyclization. This procedure is capable of tolerating a relatively wide range of nitrone ylides under mild conditions, facilitating the preparation of various 1′-hydroxyspiro[indoline-3,2′-pyrrolidine] derivatives. [ABSTRACT FROM AUTHOR]

Published
2022
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35. Beamforming for phased arrays on vibrating apertures

Author

Yao, Weijun and Wang, Yuanxun Ethan

Subjects
Beamforming -- Methods, Phased array antennas -- Design and construction, Error analysis (Mathematics), Business, Computers, Electronics, Electronics and electrical industries
Abstract

A beamforming approach for phased arrays on vibrating apertures is proposed. The essence is to dynamically calibrate the antenna element position errors due to aperture vibrations. This is achieved by estimating element positions through the aid of a few near field reference sources attached to the antenna. The reference sources need to be mounted on rigid frames and be impervious to vibrations. The estimated position information is then substituted into the beamforming process to correct the distorted pattern of the antenna array. To validate the proposed concept, a 5.8 GHz eight-element array with artiticially displaced element positions is built to emulate the vibration effect. The proposed calibration approach gives, a close estimate of position errors with deviations under 4% of the free space wavelength. Based on the estimated information, an array pattern with desired features is constructed. Index Terms--Beamforming, calibration, phased arrays, phase error, vibrating apertures.

Published
2006

39. Relay Rhodium(I)/Acid Catalysis for Rapid Access to Benzo‐2H‐Pyrans and Benzofurans.

Author

Zhu, Huilong, Zhou, Qianqian, Liu, Na, Xing, Junhao, Yao, Weijun, and Dou, Xiaowei

Subjects
RHODIUM, CATALYSIS, PROPARGYL alcohol, BENZOFURAN synthesis, BENZOFURANS, CHEMOSELECTIVITY
Abstract

Relay rhodium(I)/Brønsted acid catalysis for tandem arylation−cyclization reaction was developed. Chemodivergent syntheses of benzo‐2H‐pyrans and benzofurans from propargyl alcohols and ortho‐hydroxylated arylboronic acids were achieved under this relay catalysis system. An ortho‐hydroxy effect on changing the chemoselectivity and reactivity was observed. [ABSTRACT FROM AUTHOR]

Published
2022
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44. Catalyst-controlled regioselectivity in phosphine catalysis: the synthesis of spirocyclic benzofuranones via regiodivergent [3 + 2] annulations of aurones and an allenoate† †Electronic supplementary information (ESI) available. CCDC 1517706 and 1517707. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc02176c Click here for additional data file. Click here for additional data file

Author

Ni, Huanzhen, Yu, Zhaoyuan, Yao, Weijun, Lan, Yu, Ullah, Nisar, and Lu, Yixin

Subjects
Chemistry
Abstract

Catalyst-controlled regiodivergent [3 + 2] annulations of aurones and allenoates have been developed., Catalyst-controlled regiodivergent [3 + 2] annulations of aurones and allenoates have been developed. When a dipeptide phosphine catalyst with an l-d- configuration was employed, α-selective [3 + 2] annulation products could be obtained with good regioselectivities and enantioselectivities. With the employment of l-l- dipeptide phosphines, γ-selective annulation products could be selectively obtained with excellent enantioselectivities. By simply tuning the catalyst configurations, a wide range of α-selective or γ-selective spirocyclic benzofuranones with either aryl or alkyl substitutions could be readily prepared. DFT calculations suggest that the conformation of the dipeptide phosphines influences the hydrogen bonding interactions or the distortion energy, resulting in delicate energy differentiation in the transition states, and accounting for the observed regioselectivity.

Published
2017

45. Chiral phosphine-mediated intramolecular [3 + 2] annulation: enhanced enantioselectivity by achiral Brønsted acid† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7sc00952f Click here for additional data file

Author

Yao, Weijun, Yu, Zhaoyuan, Wen, Shan, Ni, Huanzhen, Ullah, Nisar, Lan, Yu, and Lu, Yixin

Subjects
Chemistry
Abstract

Enantioselective intramolecular [3 + 2] annulation of chalcone–allenes catalyzed by amino acid-derived phosphines and achiral Brønsted acids has been developed., Enantioselective intramolecular [3 + 2] annulation of chalcones bearing an allene moiety has been successfully developed. The reaction was effectively promoted by amino acid-derived phosphines, in combination with achiral Brønsted acids. Dihydrocoumarin architectures were constructed in high yields and with excellent enantiomeric excesses. Theoretical studies via DFT calculations revealed that the hydrogen bonding network induced by achiral Brønsted acids/chiral phosphines could more efficiently distinguish between two enantioselective pathways, thus leading to enhanced enantioselectivity.

Published
2017

46. Transition‐Metal‐Free C(sp2)‐H Dithiocarbamation and Chromone Annulation Cascade for 3‐Dithiocarbamyl Chromone Synthesis.

Author

Zhang, Tao, Yao, Weijun, Wan, Jie‐Ping, and Liu, Yunyun

Subjects
*ANNULATION, *CHROMONES, *PYRIMIDINES, *SCISSION (Chemistry)
Abstract

The transition‐metal‐free synthesis of 3‐dithiocarbamyl chromones by reacting o‐hydroxyphenylenaminones with thiurams in the presence of KIO3 and TEMPO is reported. In addition, the 3‐dithiocarbamyl chromones synthesized herein have been successfully utilized as starting materials in the synthesis of 3‐dithiocarbamyl pyrimidines and 3‐(benzylthio)chromones via featured chromone ring opening and C−S bond cleavage, respectively. [ABSTRACT FROM AUTHOR]

Published
2021
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48. Potential environmental risks of nanopesticides: Application of Cu(OH)2 nanopesticides to soil mitigates the degradation of neonicotinoid thiacloprid

Author

Zhang, Xiaoxia, primary, Xu, Zhenlan, additional, Wu, Mansha, additional, Qian, Xiaoting, additional, Lin, Daohui, additional, Zhang, Hangjun, additional, Tang, Juan, additional, Zeng, Tao, additional, Yao, Weijun, additional, Filser, Juliane, additional, Li, Lingxiangyu, additional, and Sharma, Virender K., additional

Published
2019
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50. Analytical accuracy of hydrogen measurement using gas chromatography with thermal conductivity detection

Author

Yao Weijun

Subjects
Hydrogen, Thermal conductivity detector, Detector, Analytical chemistry, chemistry.chemical_element, Linearity, Filtration and Separation, Molecular sieve, Analytical Chemistry, Adsorption, Thermal conductivity, chemistry, Gas chromatography, Astrophysics::Galaxy Astrophysics
Abstract

Gas chromatography employing a thermal conductivity detector with a nitrogen carrier gas and a molecular sieve 5 A column is commonly used for the analysis of widely varying hydrogen concentrations. Flow variation of the column, caused by carrier gas adsorption, affects the peak shape and impacts the analytical accuracy. The mechanism and factors affecting the adsorption effect are explored, errors caused by the deviation from the linearity of the detector's response are considered, and practical advice is given for improving the analytical accuracy.

Published
2015

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