Concentrations of Polychlorinated dibenzo-p-dioxins and dibenzofurans（PCDD/Fs） and polychlorinated biphenyls（PCBs） in soil samples from Tibetan Plateau were determined. The average concentration of total 2,3,7,8-P...Concentrations of Polychlorinated dibenzo-p-dioxins and dibenzofurans（PCDD/Fs） and polychlorinated biphenyls（PCBs） in soil samples from Tibetan Plateau were determined. The average concentration of total 2,3,7,8-PCDD/Fs was（2.30 ± 1.02） pg/g, and World Health Organization Toxicity Equivalency（WHO-TEQ） average concentration was（0.013 ± 0.010）pg WHO-TEQ/g. The average concentration of ∑PCBs（7 indicator PCB and 12 dioxin like-PCB congeners） was（16.2 ± 9.25） pg/g, and WHO-TEQ average concentration was 0.043 ±0.049 pg WHO-TEQ/g. Comparing to previous studies in similar environmental conditions,PCDD/Fs and PCBs in this study showed a relatively lower concentration. The altitude dependences of PCDD/Fs and PCBs were also studied. Total organic carbon（TOC） normalized concentrations presented a quadratic relation with the altitudes, and an inflection could be found on the parabola of the total concentrations and some congeners of high concentration.The concentrations decreased with altitudes below about 4500 m above sea level（a.s.l.）, while they increased with altitudes above it. These phenomena indicate that cold condensation of PCDD/Fs and PCBs would happen above 4500 m a.s.l, on the Tibetan Plateau.展开更多
An unmet challenge in radical relay difunctionalization of alkenes is the incorporation of two discrete transient radicals in a regiocontrolled manner under transition-metal-free conditions.Current protocols typically...An unmet challenge in radical relay difunctionalization of alkenes is the incorporation of two discrete transient radicals in a regiocontrolled manner under transition-metal-free conditions.Current protocols typically rely on persistent radicals or organometallic surrogates to trap radical adducts,thereby suppressing the undesired reactions but limiting the diversity.The direct use of two transient radicals remains synthetically elusive.We present a visible-light photoredox catalyzed alkene dialkylation strategy via a kinetically guided conjugative radical–radical coupling.This transition-metal-free approach enables two direct C(sp^(3))–C(sp^(3))bond formations across the C=C double bond using alkyl and allyl or benzyl radicals.Mechanistic investigations reveal the radical nature of the process.The success of this approach hinges on kinetically controlled radical addition to alkene substrates and the steric protection of the resulting radical adducts.This mild and functional-group-tolerant reaction exhibits broad substrate scope and tolerates structurally complex substrates,highlighting its potential for late-stage functionalization.展开更多
A superconducting magnet prototype for Accelerator Driven Sub-critical System Injection- I had been designed and fabricated, and tested in a new made vertical Dewar in November 2012. Batch magnet production was proces...A superconducting magnet prototype for Accelerator Driven Sub-critical System Injection- I had been designed and fabricated, and tested in a new made vertical Dewar in November 2012. Batch magnet production was processed after some major revision from the magnet prototype, they include： removing off the perm-alloy shield, extending the iron yoke, using thin superconducting wire, etc. The first one of the batch magnets was tested in the vertical Dewar at the Harbin Institute of Technologyin in September 2013. A field measurement was carried out at the same time by the measurement platform that was seated on the top of the vertical Dewar, the measurement results met the design requirements. This paper will present the field measurement system design, measurement results and discussion on the residual field from the persistent current effect.展开更多
基金supported by the National Basic Research Program (973) of China (No. 2011CB201500)the Environmental Public Welfare Projects (No. 201209019)+1 种基金the National High Technology Research and Development Program (863) of China (No. 2012AA062803)the National Natural Science Foundation of China (No. 21477150, 21321004)
文摘Concentrations of Polychlorinated dibenzo-p-dioxins and dibenzofurans（PCDD/Fs） and polychlorinated biphenyls（PCBs） in soil samples from Tibetan Plateau were determined. The average concentration of total 2,3,7,8-PCDD/Fs was（2.30 ± 1.02） pg/g, and World Health Organization Toxicity Equivalency（WHO-TEQ） average concentration was（0.013 ± 0.010）pg WHO-TEQ/g. The average concentration of ∑PCBs（7 indicator PCB and 12 dioxin like-PCB congeners） was（16.2 ± 9.25） pg/g, and WHO-TEQ average concentration was 0.043 ±0.049 pg WHO-TEQ/g. Comparing to previous studies in similar environmental conditions,PCDD/Fs and PCBs in this study showed a relatively lower concentration. The altitude dependences of PCDD/Fs and PCBs were also studied. Total organic carbon（TOC） normalized concentrations presented a quadratic relation with the altitudes, and an inflection could be found on the parabola of the total concentrations and some congeners of high concentration.The concentrations decreased with altitudes below about 4500 m above sea level（a.s.l.）, while they increased with altitudes above it. These phenomena indicate that cold condensation of PCDD/Fs and PCBs would happen above 4500 m a.s.l, on the Tibetan Plateau.
基金support of the National Natural Science Foundation of China(grant no.22271151)the Natural Science Foundation of Jiangsu Province(grant no.BK20211534)the US National Science Foundation(grant no.CHE-2154593)。
文摘An unmet challenge in radical relay difunctionalization of alkenes is the incorporation of two discrete transient radicals in a regiocontrolled manner under transition-metal-free conditions.Current protocols typically rely on persistent radicals or organometallic surrogates to trap radical adducts,thereby suppressing the undesired reactions but limiting the diversity.The direct use of two transient radicals remains synthetically elusive.We present a visible-light photoredox catalyzed alkene dialkylation strategy via a kinetically guided conjugative radical–radical coupling.This transition-metal-free approach enables two direct C(sp^(3))–C(sp^(3))bond formations across the C=C double bond using alkyl and allyl or benzyl radicals.Mechanistic investigations reveal the radical nature of the process.The success of this approach hinges on kinetically controlled radical addition to alkene substrates and the steric protection of the resulting radical adducts.This mild and functional-group-tolerant reaction exhibits broad substrate scope and tolerates structurally complex substrates,highlighting its potential for late-stage functionalization.
文摘A superconducting magnet prototype for Accelerator Driven Sub-critical System Injection- I had been designed and fabricated, and tested in a new made vertical Dewar in November 2012. Batch magnet production was processed after some major revision from the magnet prototype, they include： removing off the perm-alloy shield, extending the iron yoke, using thin superconducting wire, etc. The first one of the batch magnets was tested in the vertical Dewar at the Harbin Institute of Technologyin in September 2013. A field measurement was carried out at the same time by the measurement platform that was seated on the top of the vertical Dewar, the measurement results met the design requirements. This paper will present the field measurement system design, measurement results and discussion on the residual field from the persistent current effect.
