科学（20210521出版）一周论文导读

　　编译 冯维维
　　Science , 21 May 2021, Volume 372 Issue 6544
　　《科学》 2021年5月21日，第372卷，6544期
　　物理学 Physics
　　Electron ptychography achieves atomic-resolution limits set by lattice vibrations
　　电子叠层成像实现晶格振动规定的原子分辨率极限
　　作者：Zhen Chen, Yi Jiang, Yu-Tsun Shao, David A. Muller, etc.
　　链接：
　　https://science.sciencemag.org/content/372/6544/826
　　摘要
　　限制电子显微镜图像分辨率和解释的两个主要问题是透镜像差和多次散射。
　　作者利用叠层成像——一种使用相干散射和多个重叠照明点从远场衍射模式重建图像的技术，克服了这些问题。这种方法的分辨率不是受光学的限制，而是受样品散射强度的限制，所以它可以更好地用于较厚的样品。
　　作者获得了比PrScO3样品中原子的热振动更好的最终横向分辨率，表明在理论上可以识别单个掺杂原子。
　　Abstract
　　Two major problems that limit the resolution and interpretation of electron microscopy images are lens aberrations and multiple scattering. Chen et al. overcame these issues with ptychography, a technique that uses coherent scattering and multiple overlapping illumination spots to reconstruct an image from far-field diffraction patterns. This method works at a resolution that is limited, not by optics, but rather by the scattering strength of the sample, so it can work better with thicker samples. The authors achieved ultimate lateral resolution better than the thermal vibration of atoms in a PrScO3 sample and showed that it is theoretically possible to identify single dopant atoms.
　　Observation of superfluidity in a strongly correlated two-dimensional Fermi gas
　　二维费米气体中的超流体现象
　　作者：Lennart Sobirey, Niclas Luick, Markus Bohlen, Hauke Biss, Henning Moritz, VThomas Lompe
　　链接：
　　https://science.sciencemag.org/content/372/6544/844
　　摘要
　　理解紧密相关的二维系统如何在高温下产生非常规超导性是凝聚态物理中尚未解决的主要问题之一。
　　超冷的二维费米气体作为干净和可控的模型系统出现，用于研究强相关性和降维的相互作用，但这些系统中超流体的直接证据一直缺失。
　　作者通过在系统中移动一个周期势，并观察到在临界速度VC以下没有耗散，来证明在超冷二维费米气体中的超流体性。
　　他们将VC 作为相互作用强度的函数进行了测量，并在玻色子超流和费米超流的交叉域中找到一个极大值。作者表示，该测量使系统地研究降维对费米超流的影响成为可能。
　　Abstract
　　Understanding how strongly correlated two-dimensional (2D) systems can give rise to unconventional superconductivity with high critical temperatures is one of the major unsolved problems in condensed matter physics. Ultracold 2D Fermi gases have emerged as clean and controllable model systems to study the interplay of strong correlations and reduced dimensionality, but direct evidence of superfluidity in these systems has been missing. We demonstrate superfluidity in an ultracold 2D Fermi gas by moving a periodic potential through the system and observing no dissipation below a critical velocity vc. We measure vc as a function of interaction strength and find a maximum in the crossover regime between bosonic and fermionic superfluidity. Our measurements enable systematic studies of the influence of reduced dimensionality on fermionic superfluidity.
　　化学 Chemistry
　　Reversible ketone hydrogenation and dehydrogenation for aqueous organic redox flow batteries
　　有机水相氧化还原流电池酮可逆氢化和脱氢
　　作者：Ruozhu Feng, Xin Zhang, Vijayakumar Murugesan, Aaron Hollas, Ying Chen, Yuyan Shao, Eric Walter, Nadeesha P. N. Wellala, Litao Yan, Kevin M. Rosso, Wei Wang
　　链接：
　　https://science.sciencemag.org/content/372/6544/836
　　摘要
　　在液流电池中，阴极液和阳极液被存储在单独的槽中，泵被用于将液体循环到由薄膜隔开的电极堆中。这种电池是大规模电网存储应用的理想选择；然而，合适的氧化还原分子目前仍然有限。
　　作者利用＂分子工程＂对廉价的前体（9-芴酮）进行修饰，作为有机氧化还原流电池的基础。他们在一个氧化还原流电池中测试了一系列不同的分子，其中的反应涉及可逆的酮在水电解质中氢化和脱氢。这些反应具有双电子氧化还原和在空气、高温（50 ）下操作等优点，更适合于实际应用。
　　Abstract
　　In a flow battery, catholyte and anolyte are stored in separate tanks, and pumps are used to circulate the fluids into a stack with electrodes separated by a thin membrane. Such batteries are ideal for large-scale grid storage applications; however, suitable redox molecules are currently limited. Feng et al. used ＂molecular engineering＂ to modify an inexpensive precursor (9-fluorenone) as the basis for an organic-based redox flow battery. The authors tested a series of variant molecules in a redox flow battery in which the reactions involve reversible ketone hydrogenation and dehydrogenation in an aqueous electrolyte. These reactions have advantageous features, including two-electron redox and operation in air and at elevated temperatures (50 C), that are more suitable for real-world applications.
　　Biphenylene network: A nonbenzenoid carbon allotrope
　　联苯网络:一种非苯类碳同素异形体
　　作者：Qitang Fan, Linghao Yan, Matthias W. Tripp, Ondrej Krejcí, Stavrina Dimosthenous, Stefan R. Kachel, Mengyi Chen, Adam S. Foster, Ulrich Koert, Peter Liljeroth, J. Michael Gottfried
　　链接：
　　https://science.sciencemag.org/content/372/6544/852
　　摘要
　　虽然石墨烯形成了二维的碳片，但其他排列的碳环也可以组装成平面的薄片。
　　作者在金表面上合成了一种由 sp2 杂化碳原子组成的四元、六元和八元环的联苯碳片。吸附的卤代三苯分子经过两步互聚脱氢氟化聚合，通过碳-碳键形成四元环和八元环。
　　扫描隧道光谱显示，该碳同素异形体是金属的，而不是电介质。作者期望这种互聚体HF-zip方法能够补充其他非苯类碳同素异形体的合成工具箱。
　　Abstract
　　Although graphene forms two-dimensional carbon sheets, other arrangements of carbon rings could also assemble as flat sheers. Fan et al. synthesized an ultraflat biphenylene carbon sheet consisting of  sp2 -hybridized carbon atoms forming four-, six-, and eight-membered rings on a gold surface. An adsorbed halogenated terphenyl molecule undergoes a two-step interpolymer dehydrofluorination polymerization that creates the four- and eight-membered rings through carbon–carbon bond formation. Scanning tunneling spectroscopy revealed that this carbon allotrope is metallic. They expect the interpolymer HF-zipping method to complement the toolbox for the synthesis of other nonbenzenoid carbon allotropes.
　　气候与生态 Climate &Ecology
　　Global acceleration in rates of vegetation change over the past 18,000 years
　　过去18000年，全球植被变化加速
　　作者：Ondrej Mottl, Suzette G. A. Flantua, Kuber P. Bhatta1, John W. Williams, etc.
　　链接：
　　https://science.sciencemag.org/content/372/6544/860
　　摘要
　　在过去的18000年里，全球植被首先因伴随最后一次冰川消失的气候变化而发生变化，此后因为人类压力的增加而发生变化；然而，对全球植被变化率的幅度和模式了解甚少。
　　通过对1181个花粉化石序列的汇编和新开发的统计方法，作者发现，从4.6万年前到2.9万年前，全球范围内的植被组成变化速度在加速，这在过去1.8万年里的全球范围内都是前所未有的。
　　全新世晚期的变化速率等于或超过了所有大陆的除冰速率，这表明人类对陆地生态系统的影响规模甚至超过了气候驱动的最后一次除冰。作者表示，从上个世纪的生态数据中可以看出，生物多样性变化的加速始于数千年前。
　　Abstract
　　Global vegetation over the past 18,000 years has been transformed first by the climate changes that accompanied the last deglaciation and again by increasing human pressures; however, the magnitude and patterns of rates of vegetation change are poorly understood globally. Using a compilation of 1181 fossil pollen sequences and newly developed statistical methods, we detect a worldwide acceleration in the rates of vegetation compositional change beginning between 4.6 and 2.9 thousand years ago that is globally unprecedented over the past 18,000 years in both magnitude and extent. Late Holocene rates of change equal or exceed the deglacial rates for all continents, which suggests that the scale of human effects on terrestrial ecosystems exceeds even the climate-driven transformations of the last deglaciation. The acceleration of biopersity change demonstrated in ecological datasets from the past century began millennia ago.
　　Balancing conservation priorities for nature and for people in Europe
　　欧洲保护自然的优先事项
　　作者：Louise M. J. O’Connor, Laura J. Pollock, Julien Renaud, Willem Verhagen, Peter H. Verburg, Sandra Lavorel, Luigi Maiorano, Wilfried Thuiller
　　链接：
　　https://science.sciencemag.org/content/372/6544/856
　　摘要
　　保护科学家一致认为，应该扩大保护区以保护生物多样性和生态系统服务，但往往很难确定保护区的优先级。
　　考虑到推动整个欧洲保护的因素，作者的分析囊括了，以（>800）脊椎动物物种的分布为代表的物种的价值；以自然旅游等活动为代表的景观的文化价值；以及碳汇和防洪等生态系统服务的价值。
　　虽然这三个主要特征在景观中往往不一致，但作者发现，在空间保护规划中关注生物多样性是获取一系列自然价值的最有效手段。
　　Abstract
　　There is consensus among conservation scientists that protected areas should be expanded to safeguard biopersity and ecosystem services, but it is often difficult to prioritize areas for protection. Considering factors that motivate conservation across Europe, an analysis by O＂Connor et al. includes the value of species, represented by distribution of >800 vertebrate species; the cultural value of landscapes, represented by activities such as nature tourism; and the value of ecosystem services such as carbon sequestration and flood protection. Although these three main features often do not coincide in the landscape, the authors found that a focus on biopersity in spatial conservation planning is the most effective means of capturing a range of nature＂s values.