Skipped dienes are of great importance but remain challenging to synthesize because of the presence of a sp hybrid carbon between the two alkenes.Herein,we have developed the first nickel-catalyzed regio-,(E)-stereo-a...Skipped dienes are of great importance but remain challenging to synthesize because of the presence of a sp hybrid carbon between the two alkenes.Herein,we have developed the first nickel-catalyzed regio-,(E)-stereo-and linear-selective ring-opening/cross-coupling reaction of vinylaziridines with organoboronic acids under mild conditions to construct various skipped aminodienes.The reaction exhibits wide functional-group compatibility,and could be adapted for the introduction of skipped aminodiene functionality into bioactive molecules.展开更多
In February 2014, the Beijing-Tianjin-Hebei(BTH) area experienced a weeklong episode of heavy haze pollution. Cities such as Beijing(BJ) and Shijiazhuang(SJZ) issued heavy pollution alerts for the first time and took ...In February 2014, the Beijing-Tianjin-Hebei(BTH) area experienced a weeklong episode of heavy haze pollution. Cities such as Beijing(BJ) and Shijiazhuang(SJZ) issued heavy pollution alerts for the first time and took emergency control measures. This study employed the Nested Air Quality Prediction Modeling System(NAQPMS) to simulate and analyze the three-dimensional structure of the source contributions of PM2.5 in the BTH area during this pollution episode and quantitatively assessed the effects of the emergency control measures. The results showed that during the polluted period(February 19–26), surface PM2.5 mainly originated from local sources(48%–72%). In the entire BTH area, southern Hebei(SHB) represented the largest internal contribution(33%), while the main external contributions came from Shandong(SD)(10%) and Henan(HN)(4%). Vertically, the local contribution was constrained below the near-ground layer, and rapidly decreased with altitude. The regional transport path from SHB and Shanxi(SX) to BJ appeared at 0.5–1.5 and 1.5–2.5 km, with contributions of 32%–42% and 13%–27%, respectively. The non-local source regions for the BTH area were SD below 1 km and mainly SX and HN above 1 km. Compared to the non-polluted period(February 27–28), the contribution from regional transport increased during the polluted period, indicating the key role of regional transport in the pollution formation. The emergency control measures had a relatively large effect on NOx and SO2 concentrations, but a limited effect on PM2.5. The stronger regional transport during the polluted period may have weakened the effects of the local emergency control measures. These results indicated that a coordinated emission control should be implemented not only over the BTH area but also over its surrounding provinces(e.g. SD, HN).展开更多
This paper introduces a non-classical nonlinear acoustic theory for microcrack detection in materials,comparing contact nonlinearity with material nonlinearity.The paper's main work concentrates on the experimenta...This paper introduces a non-classical nonlinear acoustic theory for microcrack detection in materials,comparing contact nonlinearity with material nonlinearity.The paper's main work concentrates on the experimental and numerical verification of the effectivity of contact nonlinear acoustic detection by using the contact nonlinear parameter fl',which can be represented by the ratio of the second-harmonic amplitude to the square of the firstharmonic amplitude.Both experiments and numerical tests are performed.The results show that fl'is sensitive to the initiation of microcracks and varies with the development of the microcracks.The numerical test illustrates the decline offl'when microcracks penetrate each other.展开更多
基金the funding support of this work by the National Natural Science Foundation of China(Nos.21831005 and 21991112)National Key R&D Program of China(No.2018YFE0126800).
文摘Skipped dienes are of great importance but remain challenging to synthesize because of the presence of a sp hybrid carbon between the two alkenes.Herein,we have developed the first nickel-catalyzed regio-,(E)-stereo-and linear-selective ring-opening/cross-coupling reaction of vinylaziridines with organoboronic acids under mild conditions to construct various skipped aminodienes.The reaction exhibits wide functional-group compatibility,and could be adapted for the introduction of skipped aminodiene functionality into bioactive molecules.
基金supported by the CAS Strategic Priority Research Program(XDB05030200,XDB05030101)the National Natural Science Foundation of China(41405119,41275138)+2 种基金the National Key Technology R&D Program(2014BAC21B02,2014BAC06B03)the Environmental Public Welfare Research Project(201309071,201509014)the National Basic Research Program of China(2014CB447900)
文摘In February 2014, the Beijing-Tianjin-Hebei(BTH) area experienced a weeklong episode of heavy haze pollution. Cities such as Beijing(BJ) and Shijiazhuang(SJZ) issued heavy pollution alerts for the first time and took emergency control measures. This study employed the Nested Air Quality Prediction Modeling System(NAQPMS) to simulate and analyze the three-dimensional structure of the source contributions of PM2.5 in the BTH area during this pollution episode and quantitatively assessed the effects of the emergency control measures. The results showed that during the polluted period(February 19–26), surface PM2.5 mainly originated from local sources(48%–72%). In the entire BTH area, southern Hebei(SHB) represented the largest internal contribution(33%), while the main external contributions came from Shandong(SD)(10%) and Henan(HN)(4%). Vertically, the local contribution was constrained below the near-ground layer, and rapidly decreased with altitude. The regional transport path from SHB and Shanxi(SX) to BJ appeared at 0.5–1.5 and 1.5–2.5 km, with contributions of 32%–42% and 13%–27%, respectively. The non-local source regions for the BTH area were SD below 1 km and mainly SX and HN above 1 km. Compared to the non-polluted period(February 27–28), the contribution from regional transport increased during the polluted period, indicating the key role of regional transport in the pollution formation. The emergency control measures had a relatively large effect on NOx and SO2 concentrations, but a limited effect on PM2.5. The stronger regional transport during the polluted period may have weakened the effects of the local emergency control measures. These results indicated that a coordinated emission control should be implemented not only over the BTH area but also over its surrounding provinces(e.g. SD, HN).
文摘This paper introduces a non-classical nonlinear acoustic theory for microcrack detection in materials,comparing contact nonlinearity with material nonlinearity.The paper's main work concentrates on the experimental and numerical verification of the effectivity of contact nonlinear acoustic detection by using the contact nonlinear parameter fl',which can be represented by the ratio of the second-harmonic amplitude to the square of the firstharmonic amplitude.Both experiments and numerical tests are performed.The results show that fl'is sensitive to the initiation of microcracks and varies with the development of the microcracks.The numerical test illustrates the decline offl'when microcracks penetrate each other.