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英国资助330万英镑开发下一代核技术 快报文章
气候变化快报,2022年第18期
作者:  迪里努尔,刘燕飞
Microsoft Word(16Kb)  |  收藏  |  浏览/下载:734/0  |  提交时间:2022/09/20
Nuclear Technology  Advanced Modular Reactor  HTGR  
Detection of metastable electronic states by Penning trap mass spectrometry 期刊论文
NATURE, 2020, 581 (7806) : 42-+
作者:  Rauch, Jennifer N.;  Luna, Gabriel;  Guzman, Elmer;  Audouard, Morgane;  Challis, Collin;  Sibih, Youssef E.;  Leshuk, Carolina;  Hernandez, Israel;  Wegmann, Susanne;  Hyman, Bradley T.;  Gradinaru, Viviana;  Kampmann, Martin;  Kosik, Kenneth S.
收藏  |  浏览/下载:30/0  |  提交时间:2020/07/03

State-of-the-art optical clocks(1) achieve precisions of 10(-18) or better using ensembles of atoms in optical lattices(2,3) or individual ions in radio-frequency traps(4,5). Promising candidates for use in atomic clocks are highly charged ions(6) (HCIs) and nuclear transitions(7), which are largely insensitive to external perturbations and reach wavelengths beyond the optical range(8) that are accessible to frequency combs(9). However, insufficiently accurate atomic structure calculations hinder the identification of suitable transitions in HCIs. Here we report the observation of a long-lived metastable electronic state in an HCI by measuring the mass difference between the ground and excited states in rhenium, providing a non-destructive, direct determination of an electronic excitation energy. The result is in agreement with advanced calculations. We use the high-precision Penning trap mass spectrometer PENTATRAP to measure the cyclotron frequency ratio of the ground state to the metastable state of the ion with a precision of 10(-11)-an improvement by a factor of ten compared with previous measurements(10,11). With a lifetime of about 130 days, the potential soft-X-ray frequency reference at 4.96 x 10(16) hertz (corresponding to a transition energy of 202 electronvolts) has a linewidth of only 5 x 10(-8) hertz and one of the highest electronic quality factors (10(24)) measured experimentally so far. The low uncertainty of our method will enable searches for further soft-X-ray clock transitions(8,12) in HCIs, which are required for precision studies of fundamental physics(6).


Penning trap mass spectrometry is used to measure the electronic transition energy from a long-lived metastable state to the ground state in highly charged rhenium ions with a precision of 10(-11).


  
Late-stage oxidative C(sp(3))-H methylation 期刊论文
NATURE, 2020, 580 (7805) : 621-+
作者:  Fessler, Evelyn;  Eckl, Eva-Maria;  Schmitt, Sabine;  Mancilla, Igor Alves;  Meyer-Bender, Matthias F.;  Hanf, Monika;  Philippou-Massier, Julia;  Krebs, Stefan;  Zischka, Hans;  Jae, Lucas T.
收藏  |  浏览/下载:72/0  |  提交时间:2020/07/03

Frequently referred to as the '  magic methyl effect'  , the installation of methyl groups-especially adjacent (alpha) to heteroatoms-has been shown to dramatically increase the potency of biologically active molecules(1-3). However, existing methylation methods show limited scope and have not been demonstrated in complex settings(1). Here we report a regioselective and chemoselective oxidative C(sp(3))-H methylation method that is compatible with late-stage functionalization of drug scaffolds and natural products. This combines a highly site-selective and chemoselective C-H hydroxylation with a mild, functional-group-tolerant methylation. Using a small-molecule manganese catalyst, Mn(CF3PDP), at low loading (at a substrate/catalyst ratio of 200) affords targeted C-H hydroxylation on heterocyclic cores, while preserving electron-neutral and electron-rich aryls. Fluorine- or Lewis-acid-assisted formation of reactive iminium or oxonium intermediates enables the use of a mildly nucleophilic organoaluminium methylating reagent that preserves other electrophilic functionalities on the substrate. We show this late-stage C(sp(3))-H methylation on 41 substrates housing 16 different medicinally important cores that include electron-rich aryls, heterocycles, carbonyls and amines. Eighteen pharmacologically relevant molecules with competing sites-including drugs (for example, tedizolid) and natural products-are methylated site-selectively at the most electron rich, least sterically hindered position. We demonstrate the syntheses of two magic methyl substrates-an inverse agonist for the nuclear receptor RORc and an antagonist of the sphingosine-1-phosphate receptor-1-via late-stage methylation from the drug or its advanced precursor. We also show a remote methylation of the B-ring carbocycle of an abiraterone analogue. The ability to methylate such complex molecules at late stages will reduce synthetic effort and thereby expedite broader exploration of the magic methyl effect in pursuit of new small-molecule therapeutics and chemical probes.


A manganese-catalysed oxidative C(sp(3))-H methylation method allows a methyl group to be selectively installed into medicinally important heterocycles, providing a way to improve pharmaceuticals and better understand the '  magic methyl effect'  .


  
The case for a tortoise approach to US nuclear research and development 期刊论文
ENERGY POLICY, 2019, 135
作者:  Ford, Michael J.;  Schrag, Daniel P.
收藏  |  浏览/下载:21/0  |  提交时间:2020/02/17
Advanced nuclear  Nuclear energy research and development  Technology transition  Grid decarbonization  
Expert assessments of the state of US advanced fission innovation 期刊论文
ENERGY POLICY, 2017, 108
作者:  Ford, Michael J.;  Abdulla, Ahmed;  Morgan, M. Granger;  Victor, David G.
收藏  |  浏览/下载:17/0  |  提交时间:2019/04/09
Advanced nuclear  Advanced fission research  Energy transition  
A retrospective analysis of funding and focus in US advanced fission innovation 期刊论文
ENVIRONMENTAL RESEARCH LETTERS, 2017, 12 (8)
作者:  Abdulla, A.;  Ford, M. J.;  Morgan, M. G.;  Victor, D. G.
收藏  |  浏览/下载:11/0  |  提交时间:2019/04/09
nuclear power  advanced reactors  energy innovation  federal research and development  
Laboratory Directed Research and Development Annual Report for 2011 科技报告
来源:US Department of Energy (DOE). 出版年: 2012
作者:  Hughes, Pamela J.
收藏  |  浏览/下载:9/0  |  提交时间:2019/04/05
advanced sensors and instrumentation  biological sciences  chemistry  earth and space sciences  energy supply and use  engineering and manufacturing processes  materials science and technology  mathematics and computing sciences  nuclear science and engin  
Laboratory Directed Research and Development Annual Report for 2009 科技报告
来源:US Department of Energy (DOE). 出版年: 2010
作者:  Hughes, Pamela J.
收藏  |  浏览/下载:9/0  |  提交时间:2019/04/05
advanced sensors and instrumentation  biological sciences  chemistry  earth and space sciences  energy supply and use  engineering and manufacturing processes  materials science and technology  mathematics and computing sciences  nuclear science and engin