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《科学》（20211126出版）一周论文导读2021-11-28 20:23·科学网编译｜冯维维Science, 26 NOVEMBER 2021, VOL 374, ISSUE 6571《科学》2021年11月26日第374卷6571期物理学PhysicsDirect visualization of magnetic domains and moiré magnetism in twisted 2D magnets在扭曲的二维磁体中磁畴和moiré磁性的直接可视化▲ 作者：TIANCHENG SONG, QI-CHAO SUN, ERIC ANDERSON, CHONG WANGJIMIN QIANTAKASHI TANIGUCHI, KENJI WATANABE, MICHAEL A. MCGUIR, RAINER ST?HR, XIAODONG XU▲ 链接：https://www.science.org/doi/10.1126/science.abj7478▲ 摘要石墨烯的单分子扭转层导致了许多不寻常的相关状态这种方法激发了研究人员尝试扭转二维磁铁但这种实验被证明是一个艰巨的挑战作者用小扭曲角的二维磁铁三碘化铬层制作了结构利用金刚石中的氮空位中心作为磁强计对扭曲单层结构和扭曲三层结构的磁畴进行了成像发现了扭曲三层薄膜的铁磁和反铁磁畴的周期性模式▲ AbstractTwisting monolayers of graphene with respect to each other has led to a number of unusual correlated states. This approach has inspired researchers to try their hand at twisting two-dimensional (2D) magnets, but such experiments have proven a difficult challenge. Song et al. made structures out of layers of the 2D magnet chromium triiodide with a small twist angle (see the Perspective by Lado). Using nitrogen vacancy centers in diamond as a magnetometer, the authors imaged the magnetic domains in both twisted monolayer and twisted trilayer structures. For twisted trilayers, a periodic pattern of ferromagnetic and antiferromagnetic domains was revealed.Floquet Hamiltonian engineering of an isolated many-body spin system孤立多体自旋系统的弗洛奎特哈密顿工程▲ 作者：SEBASTIAN GEIER, NITHIWADEE THAICHAROEN, CL?MENT HAINAUT, TITUS FRANZ, ANDRE SALZINGER, XANNIKA TEBBEN, DAVID GRIMSHANDL, GERHARD Z?RN, AND MATTHIAS WEIDEM?LLER▲ 链接：https://www.science.org/doi/10.1126/science.abd9547▲ 摘要控制相互作用是多体系统量子工程的关键要素利用时间周期驱动一个封闭量子系统的自然给定的多体哈密顿量可以转化为一个表现出极大不同动力学特性的有效目标哈密顿量作者在超冷的原子气体中用里德堡态代表的自旋系统来演示弗洛奎特工程通过应用一系列自旋操作他们改变了有效海森堡XYZ哈密顿量的对称性因此总自旋的松弛行为被极大地改变了观测到的动力学可以用半经典模拟来定性地捕捉设计广泛的哈密顿量为在单一的实验设置中实现非平衡动力学的量子模拟提供了巨大的机会▲ AbstractControlling interactions is the key element for the quantum engineering of many-body systems. Using time-periodic driving, a naturally given many-body Hamiltonian of a closed quantum system can be transformed into an effective target Hamiltonian that exhibits vastly different dynamics. We demonstrate such Floquet engineering with a system of spins represented by Rydberg states in an ultracold atomic gas. By applying a sequence of spin manipulations, we change the symmetry properties of the effective Heisenberg XYZ Hamiltonian. As a consequence, the relaxation behavior of the total spin is drastically modified. The observed dynamics can be qualitatively captured by a semiclassical simulation. Engineering a wide range of Hamiltonians opens vast opportunities for implementing quantum simulation of nonequilibrium dynamics in a single experimental setting.化学ChemistryAccelerated dinuclear palladium catalyst identification through unsupervised machine learning通过无监督机器学习加速双核钯催化剂识别▲ 作者：JULIAN A. HUEFFEL, THERESA SPERGER, IGNACIO FUNES-ARDOIZ, JAS S. WARD, KARI RISSANEN AND FRANZISKA SCHOENEBECK▲ 链接：https://www.science.org/doi/10.1126/science.abj0999▲ 摘要机器学习在加速同质催化的发展方面具有巨大潜力但频繁地需要大量的实验数据可能成为瓶颈作者报告了一个无监督机器学习工作流只使用了5个实验数据点它利用了广义参数数据库并辅以在硅数据采集和聚类中针对特定问题的数据库他们展示了该策略在钯（Pd）催化剂形态形成的挑战性问题上的力量目前缺乏一个机械原理从348个配体的总空间中该算法预测并通过实验验证了一些膦配体（包括以前从未合成的配体)它们在更常见的Pd（0）和Pd（II）物种上产生双核Pd（I）配合物▲ AbstractAlthough 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甲醛轨道共振揭示漫游、自由基和分子通道的耦合▲ 作者：CASEY D. FOLEY, CHANGJIAN XIE, HUA GUO, AND ARTHUR G. SUITS▲ 链接：https://www.science.org/doi/10.1126/science.abk0634▲ 摘要漫游化学反应机制是指受电分子对自由基的接近解离在较长距离重新定向后发生分子内反应令人惊讶的是尽管漫游事件具有量子性质但到目前为止还没有观察到清晰的漫游量子特征作者在漫游阈值附近发现了甲醛光解离的量子动力学证据这归因于与H+HCO（Ka = 1）相关的共振它对CO的旋转和平动能量分布有深刻的影响并导致漫游分数在10厘米- 1的能量范围内变化了2倍漫游路径用于调节和报道受激分子衰变成产物时复杂的振动动力学和三种解离路径之间的耦合▲ AbstractThe 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.地质和生物Geology & biologyGlobal response of fire activity to late Quaternary grazer extinctions野火对晚第四纪食草动物灭绝的全球响应▲ 作者：ALLISON T. KARP, X J. TYLER FAITH, JENNIFER R. MARLONAND A. CARLA STAVER▲ 链接：https://www.science.org/doi/10.1126/science.abj7478▲ 摘要众所周知草原食草动物通过消耗可能易燃的物质在限制野火方面发挥着作用作者提出的证据表明食草动物-火的相互作用在过去影响了全球范围内的火他们将晚第四纪大陆层面巨型草食动物灭绝的严重程度与草食生物群落沉积木炭数据计算出的古火活动变化进行了比较不同大陆的物种灭绝程度不同这种模式反映在火灾活动的变化上在大型食草动物灭绝最严重的地方（南美洲）和灭绝发生最少的地方（非洲）火灾频率增加最多大型食草动物在第四纪的消失极大地改变了全球的野火状况▲ AbstractGrassland herbivores are known to play a role in limiting wildfires by consuming potentially flammable material. Karp et al. present evidence that that herbivore-fire interactions affected fire on a global scale in the past. They compared the severity of late Quaternary continent-level megaherbivore extinctions with changes in paleofire activity calculated from sedimentary charcoal data from grassy biomes. The extent of extinctions varied between continents, and this pattern was reflected in the changes in fire activity. Fire frequency increased most where the megaherbivore extinctions were greatest (South America) and least where few extinctions occurred (Africa). This loss of large-bodied grazers in the Quaternary drastically altered global fire regimes.Adaptive evolution of flight in Morpho butterflies大闪蝶飞行的适应性进化▲ 作者：CAMILLE LE ROY, DARIO AMADORISAMUEL CHARBERETJAAP WINDTFLORIAN T. MUIJRES , VIOLAINE LLAURENS AND VINCENT DEBAT▲ 链接：https://www.science.org/doi/10.1126/science.abh2620▲ 摘要森林通常是拥挤和复杂的给在其中飞行的物种带来了无数和各种各样的挑战作者观察了亚马逊大闪蝶群体发现在形态和行为方面占据冠层的物种与占据林下植被的物种存在差异那些进化到占据冠层的物种由于翅膀形状和飞行行为的结合它们的滑翔能力有所提高这些特征的组合在不同的物种中是不同的甚至在这个单一的属中这表明没有一条路径导致了这片森林的殖民▲ AbstractForests are often crowded and complex, presenting numerous and varied challenges for species flying through them. Le Roy et al. looked at the Amazonian Morpho butterfly group and found differences in both morphological and behavioral perspectives across species that occupy the canopy relative the understory. Species that evolved to occupy the canopy have improved gliding abilities because of a combination of wing shape and flight behavior. The combination of these traits varied across species even within this single genus, which suggests that there was not one route that led to colonization of this part of the forest.
揽胜极光在动力方面就没有什么改动了，依然是2.0T的低高功率引擎，分别为200马力和249马力，并且全系标配9挡手自一体变速箱。原创2024-07-15 12:42·极目新闻