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roaming文件夾是干嘛的 roaming文件夾( 二 )

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通過(guò)無(wú)監(jiān)督機(jī)器學(xué)習(xí)加速雙核鈀催化劑識(shí)別
▲ 作者：JULIAN A. HUEFFEL, THERESA SPERGER, IGNACIO FUNES-ARDOIZ, JAS S. WARD, KARI RISSANEN AND FRANZISKA SCHOENEBECK
▲ 鏈接：
https://www.science.org/doi/10.1126/science.abj0999
▲ 摘要
機(jī)器學(xué)習(xí)在加速同質(zhì)催化的發(fā)展方面具有巨大潛力 ， 但頻繁地需要大量的實(shí)驗(yàn)數(shù)據(jù)可能成為瓶頸 。作者報(bào)告了一個(gè)無(wú)監(jiān)督機(jī)器學(xué)習(xí)工作流 ， 只使用了5個(gè)實(shí)驗(yàn)數(shù)據(jù)點(diǎn) 。它利用了廣義參數(shù)數(shù)據(jù)庫(kù) ， 并輔以在硅數(shù)據(jù)采集和聚類(lèi)中針對(duì)特定問(wèn)題的數(shù)據(jù)庫(kù) 。
他們展示了該策略在鈀（Pd）催化劑形態(tài)形成的挑戰(zhàn)性問(wèn)題上的力量 ， 目前缺乏一個(gè)機(jī)械原理 。從348個(gè)配體的總空間中 ， 該算法預(yù)測(cè)并通過(guò)實(shí)驗(yàn)驗(yàn)證了一些膦配體（包括以前從未合成的配體) ， 它們?cè)诟Ｒ?jiàn)的Pd（0）和Pd（II）物種上產(chǎn)生雙核Pd（I）配合物 。
▲ Abstract
Although machine learning bears enormous potential to accelerate developments in homogeneous catalysis, the frequent need for extensive experimental data can be a bottleneck for implementation. Here, we report an unsupervised machine learning workflow that uses only five experimental data points. It makes use of generalized parameter databases that are complemented with problem-specific in silico data acquisition and clustering. We showcase the power of this strategy for the challenging problem of speciation of palladium (Pd) catalysts, for which a mechanistic rationale is currently lacking. From a total space of 348 ligands, the algorithm predicted, and we experimentally verified, a number of phosphine ligands (including previously never synthesized ones) that give dinuclear Pd(I) complexes over the more common Pd(0) and Pd(II) species.
Orbiting resonances in formaldehyde reveal coupling of roaming, radical, and molecular channels
甲醛軌道共振揭示漫游、自由基和分子通道的耦合
▲ 作者：CASEY D. FOLEY, CHANGJIAN XIE, HUA GUO, AND ARTHUR G. SUITS
▲ 鏈接：
https://www.science.org/doi/10.1126/science.abk0634
▲ 摘要
漫游化學(xué)反應(yīng)機(jī)制是指受電分子對(duì)自由基的接近解離 ， 在較長(zhǎng)距離重新定向后發(fā)生分子內(nèi)反應(yīng) 。令人驚訝的是 ， 盡管漫游事件具有量子性質(zhì) ， 但到目前為止還沒(méi)有觀察到清晰的漫游量子特征 。
作者在漫游閾值附近發(fā)現(xiàn)了甲醛光解離的量子動(dòng)力學(xué)證據(jù) 。這歸因于與H+HCO（Ka = 1）相關(guān)的共振 ， 它對(duì)CO的旋轉(zhuǎn)和平動(dòng)能量分布有深刻的影響 ， 并導(dǎo)致漫游分?jǐn)?shù)在10厘米- 1的能量范圍內(nèi)變化了2倍 。
漫游路徑用于調(diào)節(jié)和報(bào)道受激分子衰變成產(chǎn)物時(shí)復(fù)雜的振動(dòng)動(dòng)力學(xué)和三種解離路徑之間的耦合 。
▲ Abstract
The roaming chemical reaction mechanism involves near-dissociation of an energized molecule to radicals that leads instead to intramolecular reaction after reorientation at long range. Surprisingly, no clear quantum signatures of roaming have been observed to date, despite the quantum nature of the roaming event. We found evidence of quantum dynamics in the photodissociation of formaldehyde near the roaming threshold. This is ascribed to resonances associated to H+HCO(Ka = 1) that have a profound impact on the CO rotational and translational energy distributions and cause the roaming fraction to vary by a factor of 2 over an energy range of 10 cm–1. The roaming pathway serves both to modulate and report on the complex vibrational dynamics and coupling among the three dissociation pathways in the excited molecule as it decays to products.
地質(zhì)和生物Geology & biology
Global response of fire activity to late Quaternary grazer extinctions
野火對(duì)晚第四紀(jì)食草動(dòng)物滅絕的全球響應(yīng)
▲ 作者：ALLISON T. KARP, X J. TYLER FAITH, JENNIFER R. MARLONAND A. CARLA STAVER

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