科学（20220318出版）一周论文导读

　　编译 | 冯维维
　　Science , 18 MAR 2022,VOLUME 375 ISSUE 6586
　　《科学》 2022年3月18日，第375卷，6586期
　　物理学 Physics
　　Frequency-dependent polarization of repeating fast radio bursts—implications for their origin
　　极化重复快速无线电脉冲
　　作者：YI FENG, DI LI, YUAN-PEI YANG, ONGKUN ZHANG, WEIWEI ZHU, BING ZHANG, LEI ZHANG
　　链接：
　　https://www.science.org/doi/10.1126/science.abl7759
　　摘要
　　快速射电暴（FRBs）是一种强烈的、毫秒级的、来自未知来源的河外射电发射。大多数快速射电暴只出现一次，但其他快速射电暴以不规则的间隔重复出现，因此可被跟踪。
　　作者测量了5个重复FRB的偏振。他们发现每个源在高频率下是极化的，但在阈值频率以下就会去极化，阈值频率在不同源之间是不同的。
　　作者发现，在无线电波散射出复杂的前景结构（如超新星遗迹）之前，所有重复的FRB在源处都是100%极化的。这些结果限制了重复FRB发射机理的理论。
　　Abstract
　　Fast radio bursts (FRBs) are intense, millisecond flashes of radio emission from extragalactic sources of unknown origin. Most FRBs are seen only once, but others repeat at irregular intervals and thereforre can be followed. Feng et al. measured the polarization of five repeating FRBs (see the Perspective by Caleb). They found that each source is polarized at high frequencies but becomes depolarized below a threshold frequency that varies between sources. The authors found that all repeating FRBs are 100% polarized at the source, before the radio waves scatter off complex foreground structures such as supernova remnants. These results constrain theories of the repeating FRB emission mechanism.
　　Reactions between layer-resolved molecules mediated by dipolar spin exchange
　　偶极自旋交换介导的层分辨分子之间的反应
　　作者：WILLIAM G. TOBIAS, KYLE MATSUDA, JUN-RU LI, CALDER MILLER, JUN YE, etc.
　　链接：
　　https://www.science.org/doi/10.1126/science.abn8525
　　摘要
　　由于长程各向异性和可调谐偶极相互作用，被困在二维层中的超冷极性分子预计会表现出其他平台无法提供的复杂量子现象。使用精密电场控制，作者演示了局限于光学晶格中二维平面的超低温钾铷分子的层分辨生成和成像。
　　他们还研究了自旋交换和化学反应，这些反应高度依赖于分子温度和由电场梯度引入的层间失稳。这项工作证明了超冷分子在光学晶格中的高度控制，并为探索降维量子气体系统中出现的现象迈出了有前途的一步。
　　Abstract
　　Ultracold polar molecules trapped in two-dimensional layers are predicted to exhibit complex quantum phenomena not available with other platforms because of long-range anisotropic and tunable dipolar interactions. Using precision electric field control, Tobias et al. demonstrated layer-resolved creation and imaging of ultracold potassium–rubidium molecules confined to two-dimensional planes in an optical lattice. They also studied spin exchange and chemical reactions, which are shown to be highly dependent on the molecule temperature and interlayer detunings introduced by an electric field gradient. This work demonstrates high control of ultracold molecules in an optical lattice and is a promising step toward exploring emerging phenomena in quantum gas systems with reduced dimensionality.
　　Spectroscopy signatures of electron correlations in a trilayer graphene/hBN moiré superlattice
　　三层石墨烯超晶格中电子关联的光谱特征
　　作者：JIXIANG YANG, GUORUI CHEN, TIANYI HAN, QIHANG ZHANG, YA-HUI ZHANG, LILI JIANG , LONG JU, etc.
　　链接：
　　https://www.science.org/doi/10.1126/science.abg3036
　　摘要
　　石墨烯层在特定结构上相互叠加，会对材料的电子性能产生深远的影响。光谱方法可以用来研究能带结构，但添加顶层来控制载流子密度和改善样品性质使这种测量变得棘手。
　　作者克服了这些挑战，并利用红外光谱技术，将双门控三层石墨烯堆叠在所谓的ABC结构中，并封装在六方氮化硼中。
　　研究人员绘制出了由叠加和电子关联产生的能带结构特征，并测量了有望描述这种材料的多体模型的参数。该方法可推广到其他相关超晶格的研究。
　　Abstract
　　Stacking graphene layers on top of each other in particular configurations can have a profound effect on the electronic properties of the resulting material. Spectroscopic methods can be used to study the band structure, but the addition of top layers to control the carrier density and improve sample properties makes such measurements tricky. Yang et al. overcame these challenges and used infrared spectroscopy in dual-gated trilayer graphene stacked in the so-called ABC configuration and encapsulated in hexagonal boron nitride. The researchers mapped out the band structure features created by the stacking and electron correlations and measured the parameters of the many-body model expected to describe this material. The method may be extended to study other related superlattices.
　　Tracking the sliding of grain boundaries at the atomic scale
　　在原子尺度上追踪晶界的滑动
　　作者：LIHUA WANG, YIN ZHANG, ZHI ZENG, HAO ZHOU, JIAN HE, XPAN LIU, MINGWEI CHEN, XIAODONG HAN
　　链接：
　　https://www.science.org/doi/10.1126/science.abm2612
　　摘要
　　金属在变形过程中晶界的行为是很重要的，它可以决定宏观行为。作者使用畸变校正的原位电子显微镜观察了应变过程中的铂晶界，详细描述它们是如何进化的。他们观察到晶界滑动，这是一个众所周知和预期的机制。
　　然而，作者也观察到一个意想不到的机制，涉及到晶界晶格平面的移除。他们的观察表明了使用高分辨率显微镜来理解晶界在变形过程中的作用的重要性。
　　Abstract
　　The behavior of grain boundaries in metals during deformation is important because it can dictate the macroscopic behavior. Lihua et al. used aberration-corrected in situ electron microscopy observation of platinum grain boundaries during straining to detail how they evolve. The authors observed grain boundary sliding, which is a well-known and expected mechanism. However, the authors also observed a unexpected mechanism that involves the removal of lattice planes at the grain boundaries. Their observations show the importance of using very-high-resolution microscopy to understand the role of grain boundaries during deformation.
　　化学 Chemistry
　　Recovery of particulate methane monooxygenase structure and activity in a lipid bilayer
　　脂质双分子层中甲烷单加氧酶结构和活性的恢复
　　作者：CHRISTOPHER W. KOO, FRANK J. TUCCI, YUAN HE AND AMY C. ROSENZWEIG
　　链接：
　　https://www.science.org/doi/10.1126/science.abm3282
　　摘要
　　颗粒物甲烷单加氧酶（pMMO）是需氧嗜甲烷细菌代谢甲烷的关键酶。作者在脂质纳米盘中重组了天然产生的pMMO，发现双分子层环境的恢复也恢复了酶的活性。一系列低温电子显微镜结构揭示了该酶之前缺失的区域，包括协调三聚体复合体内部孔附近金属离子的保守残基，这在以前的结构中尚未观察到。
　　脂类在稳定结构的各个部分中起着重要的作用，这些样品的活性恢复与新观察到的金属结合位点参与甲烷氧化是一致的。
　　Abstract
　　Particulate methane monooxygenase (pMMO) is a key enzyme for the metabolism of methane by aerobic, methanotropic bacteria.Koo et al. reconstituted natively produced pMMO in lipid nanodisks and found that restoration of the bilayer environment also restored activity of the enzyme. A series of cryo–electron microscopy structures revealed previously missing regions of the enzyme, including conserved residues that coordinate a metal ion near the inner pore of the trimeric complex in a site not seen in previous structures. Lipids play an important role in stabilizing various parts of the structure, and the recovery of activity in these samples is consistent with the newly observed metal-binding site being involved in methane oxidation.
　　生态 Ecology
　　Wildfire smoke destroys stratospheric ozone
　　野火烟雾破坏平流层臭氧
　　作者：PETER BERNATH, CHRIS BOONE AND JEFF CROUSE
　　链接：
　　https://www.science.org/doi/10.1126/science.abm5611
　　摘要
　　大型野火可以产生上升的大气羽流，其强度如此之大，可将烟和其他燃烧产物喷射到平流层。
　　作者指出，2019-2020年澳大利亚黑色夏季火灾进入平流层的化合物导致了平流层气体成分的极端扰动，有可能破坏臭氧。随着气候变化导致严重的野火变得更加频繁，它们对全球臭氧预算的影响将会增加。
　　Abstract
　　Large wildfires can produce ascending atmospheric plumes of such great intensity that they inject smoke and other combustion products into the stratosphere. Bernath et al. show that compounds transported into the stratosphere by the Black Summer Australian fires in 2019–2020 caused extreme perturbations in stratospheric gas composition that have the potential to destroy ozone. As climate change causes severe wildfires to become more frequent, their effects on the global ozone budget will grow.