Nature , 6 December 2018, Volume 564 Issue 7734
《自然》 2018年12月6日 第7734期564卷
环境 Enviroment
Industrial and agricultural ammonia point sources exposed
揭秘工业和农业的氨排放源
作者：Martin VanDamme、Lieven Clarisse、Simon Whitburn、Juliette Hadji-Lazaro、Daniel Hurtmans、Cathy Clerbaux、Pierre-François Coheur
链接：
https://www.nature.com/articles/s41586-018-0747-1
摘要：
大气中的氨能影响空气质量、人体健康和预期寿命。
环境中过量的氨也会导致生态系统的酸化和富营养化以及气候变化。
自然界中的氨以人为排放为主，主要来源于农业、家庭和工业活动。
然而，在不同的空间尺度上，氨排放总额和具体来源仍然不确定。
在这里，研究人员利用一幅高分辨率的大气氨排放地图，对世界上的氨排放热点进行了识别、分类和量化。
他们报告了248个直径小于50公里的热点，这些热点几乎都与农业和工业点源有关，只有一个热点可以追溯到自然源。
Abstract
Through its important role in the formation of particulate matter, atmospheric ammonia affects air quality and has implications for human health and life expectancy. Excess ammonia in the environment also contributes to the acidification and eutrophication of ecosystems and to climate change. Anthropogenic emissions dominate natural ones and mostly originate from agricultural, domestic and industrial activities. However, the total ammonia budget and the attribution of emissions to specific sources remain highly uncertain across different spatial scales. Here we identify, categorize and quantify the world’s ammonia emission hotspots using a high-resolution map of atmospheric ammonia obtained from almost a decade of daily IASI satellite observations. We report 248 hotspots with diameters smaller than 50 kilometres, which we associate with either a single point source or a cluster of agricultural and industrial point sources—with the exception of one hotspot, which can betraced back to a natural source. The state-of-the-art EDGAR emission inventory mostly agrees with satellite-derived emission fluxes within a factor of three for larger regions. However, it does not adequately represent the majority of point sources that we identified and underestimates the emissions of two-thirds of them by at least one order of magnitude. Industrial emitters in particular are often found to be displaced or missing. Our results suggest that it is necessary to completely revisit the emission inventories of anthropogenic ammonia sources and to account for the rapid evolution of such sources over time. This will lead to better health and environmental impact assessments of atmospheric ammonia and the implementation of suitable nitrogen management strategies.
Nonlinearrise in Greenland runoff in response to post-industrial Arctic warming
北极变暖让格陵兰岛径流非线性上升
作者：Luke D.Trusel、Sarah B. Das、Matthew B.Osman、Matthew J.Evans、Ben E. Smith、XavierFettweis、Joseph R.McConnell、Brice P. Y.Noël、Michiel R.van den Broeke
链接：
https://www.nature.com/articles/s41586-018-0752-4
摘要：
格陵兰冰盖是现代海平面上升的主要贡献因素。但是，目前的融化速度是否异常仍未可知，因为观测记录的追溯时长不够，而且过往研究没有分析整个冰盖。
本论文分析了西格陵兰岛冰芯的融化层，据此编制了一个跨越逾350年的记录。
研究人员将这些融化层与现代格陵兰岛更大范围的融化过程关联起来。通过这种关系，他们将格陵兰冰盖融化记录推至1650年。
报告还称近年来格陵兰冰盖的融化和径流速度加快，超出了过去的变化范围。格陵兰冰盖的融化速度相较于气温升高呈非线性上升。
因此，虽然过去的小型变暖事件可能对冰盖融化鲜有或没有影响，但在未来气候进一步变暖的情况下，可能会产生更大规模的融化事件。
Abstract
The Greenland ice sheet (GrIS) is a growing contributor to global sea-level rise, with recent ice mass loss dominated by surface meltwater runoff. Satellite observations reveal positive trends in GrIS surface melt extent, but melt variability, intensity and runoff remain uncertain before the satellite era. Here we present the first continuous, multi-century and observationally constrained record of GrIS surface melt intensity and runoff, revealing that the magnitude of recent GrIS melting is exceptional over at least the last 350years. We develop this record through stratigraphic analysis of central west Greenland ice cores, and demonstrate that measurements of refrozen melt layers in percolation zone ice cores can be used to quantifiably, and reproducibly, reconstruct past melt rates. We show significant (P < 0.01) and spatially extensive correlations between these ice-core-derived melt records and modelled melt rates and satellite-derived melt duration4across Greenland more broadly, enabling the reconstruction of past ice-sheet-scale surface melt intensity and runoff. We find that the initiation of increases inGrIS melting closely follow the onset of industrial-era Arctic warming in the mid-1800s, but that the magnitude of GrIS melting has only recently emerged beyond the range of natural variability. Owing to a nonlinear response of surface melting to increasing summer air temperatures, continued atmospheric warming will lead to rapid increases in GrIS runoff and sea-level contributions.
物理学 Physics
Atomic clock performance enabling geodesy below the centimetre level
原子钟能更精确测量时空扭曲
作者：W. F. McGrew、X. Zhang、R. J. Fasano、T. H. Yoon、A. D. Ludlow，et al
链接：
https://www.nature.com/articles/s41586-018-0738-2
摘要：
时间的流逝并非绝对，而是取决于给定的参照标准。
因此，时钟测量很容易受到相对速度、加速度和重力势的影响。为了对引力场中不同位置的钟进行比对，就需要一个共同的参照面。
地球上的参照面为大地水准面，大地水准面是与全球平均海水面重合的等势面，目前由全球卫星定位系统和一个计入重力的大地水准面模型的高程测量确定。
两者当前均有几厘米的不确定度，而使用原子钟可以降低这种不确定度。
研究人员根据3个基准表征了两个镱原子光晶格钟，结果显示，以钟频为单位，系统不确定度为1.4×10-18，测量不稳定度为3.2×10-19，并能通过反复本地频率比对，达到不同钟频差为10-19量级的再现性。
如此高的精确度可以确保大地水准面测定的不确定度小于1厘米，超过现有技术。
Abstract
The passage of time is tracked by counting oscillations of a frequency reference, such as Earth’s revolutions or swings of a pendulum. By referencing atomic transitions, frequency (and thus time) can be measured more precisely than any other physical quantity, with the current generation of optical atomic clocks reporting fractional performance below the 10−17level. However, the theory of relativity prescribes that the passage of time is not absolute, but is affected by an observer’s reference frame. Consequently, clock measurements exhibit sensitivity to relative velocity, acceleration and gravity potential. Here we demonstrate local optical clock measurements that surpass the current ability to account for the gravitational distortion of space-time across the surface of Earth. In two independent ytterbium optical lattice clocks, we demonstrate unprecedented values of three fundamental benchmarks of clock performance. In units of the clock frequency,we report systematic uncertainty of 1.4 × 10−18, measurement instability of 3.2 × 10−19and reproducibility characterized by ten blinded frequency comparisons, yielding a frequency difference of[−7 ± (5)stat ± (8)sys] × 10−19, where ‘stat’ and ‘sys’ indicate statistical and systematic uncertainty, respectively. Although sensitivity to differences in gravity potential could degrade the performance of the clocks as terrestrial standards of time, this same sensitivity can be used as a very sensitive probe of geopotential. Near the surface of Earth, clock comparisons at the 1 × 10−18level provide a resolution of one centimetre along the direction of gravity, so the performance of these clocks should enable geodesy beyond the state-of-the-art level. These optical clocks could further be used to explore geophysical phenomena, detect gravitational waves, test general relativity and search for dark matter.
An experiment to search for dark-matter interactions using sodium iodide detectors
用碘化钠探测器寻找暗物质相互作用的实验
作者：The COSINE-100Collaboration
链接：
https://www.nature.com/articles/s41586-018-0739-1
摘要：
对星系和原始辐射的观察表明，宇宙大部分是由不发光的暗物质构成的。
几种新的基本粒子被认为是暗物质的候选者，例如弱相互作用大质量粒子。这些粒子有望与地球上合适的探测材料中的原子核相互作用。
然而，尽管经过许多研究人员的共同努力，仍然没有发现这种暗物质相互作用的明确信号。但DAMA合作提出核相互作用事件速率的年调制具有统计学意义。
为了确定碘化钠中是否存在超出预期背景的过量事件的证据，COSINE-100实验使用碘化钠作为目标介质，对DAMA的声明进行模型独立测试。
初始结果显示，在前59.5天数据中，我们没有观察到超过预期背景的信号类事件。
该实验将继续收集数据两年以上，以确保能够进行相关模型独立测试。
Abstract
Observations of galaxies and primordial radiation suggest that the Universe is made mostly of non-luminous dark matter. Several new types of fundamental particle have been proposed as candidates for dark matter, such as weakly interacting massive particles (WIMPs). These particles would be expected to interact with nuclei in suitable detector materials on Earth, for example, causing them to recoil. However, no definitive signal from such dark-matter interactions has been detected despite concerted efforts by many collaborations. One exception is the much-debated claim by the DAMA collaboration of a statistically significant(more than nine standard deviations) annual modulation in the rate of nuclear interaction events. Annual modulation is expected because of the variation inEarth’s velocity relative to the Galaxy’s dark-matter halo that arises fromEarth’s orbital motion around the Sun. DAMA observed a modulation in the rate of interaction events in their detector with a period and phase consistent with that expected for WIMPs. Several groups have been working to develop experiments with the aim of reproducing DAMA’s results using the same target medium (sodium iodide).
To determine whether there is evidence for an excess of events above the expected background in sodium iodide and to look for evidence of an annual modulation, the COSINE-100 experiment uses sodium iodide as the target medium to carry outa model-independent test of DAMA’s claim. Here we report results from the initial operation of the COSINE-100 experiment related to the first task. We observe no excess of signal-like events above the expected background in the first 59.5 days of data from COSINE-100. Assuming the so-called standarddark-matter halo model, this result rules out WIMP–nucleon interactions as the cause of the annual modulation observed by the DAMA collaboration. The exclusion limit on the WIMP–sodium interaction cross-section is 1.14 × 10− 40cm2for10-GeVc − 2WIMPs at a 90% confidence level. The COSINE-100experiment will continue to collect data for two more years, enabling a model-independent test of the annual modulation observed by the DAMAcollaboration.
Transformation between meron and skyrmion topological spin textures in a chiral magnet
手性磁铁中半子与斯基米子拓扑自旋结构的转换
作者：X. Z. Yu、W. Koshibae、Y. Tokunaga、K. Shibata、Y. Taguchi、N. Nagaosa、Y. Tokura
链接：
https://www.nature.com/articles/s41586-018-0745-3
摘要：
具有四边形或六边形结构的晶格在受到外界刺激时往往会发生结构转变。
人们猜测，拓扑自旋结构的晶格形式也会出现类似的行为，但尚未得到实验验证。
本论文报道了手性晶格磁铁Co8Zn9Mn3自旋结构的实空间观测。
这些观测结果表明，在室温磁场的作用下，由螺旋态的半子和反半子组成的二维方形晶格出现，并在磁场的作用下转变为六边形的斯格明子晶格。
研究结果显示了拓扑自旋结构及其晶格形式的丰富性，并将带动电磁特性的进一步研究。
Abstract
Crystal lattices with tetragonal or hexagonal structure often exhibit structural transitions in response to external stimuli. Similar behaviour is anticipated for the lattice forms of topological spin textures, such as lattices composed of merons and antimerons or skyrmions and antiskyrmions (types of vortex related to the distribution of electron spins in a magnetic field), but has yet to be verified experimentally. Here we report real-space observations of spin textures in a thin plate of the chiral-lattice magnet Co8Zn9Mn3, which exhibits in-plane magnetic anisotropy. The observations demonstrate the emergence of a two-dimensional square lattice of merons and antimerons from ahelical state, and its transformation into a hexagonal lattice of skyrmions in the presence of a magnetic field at room temperature. Sequential observations with decreasing temperature reveal that the topologically protected skyrmions remain robust to changes in temperature, whereas the square lattice of meronsand antimerons relaxes to non-topological in-plane spin helices, highlighting the different topological stabilities of merons, antimerons and skyrmions. Our results demonstrate the rich variety of topological spin textures and their lattice forms, and should stimulate further investigation of emergentelectro magnetic properties.
生物学 Biology
Amphioxusfunctional genomics and the origins of vertebrate gene regulation
文昌鱼功能基因组学与脊椎动物基因调控的起源
作者：Ferdin and Marlétaz、Panos N.Firbas、Manuel Irimia，et al
链接：
https://www.nature.com/articles/s41586-018-0734-6
摘要：
脊椎动物已经非常详细地阐述了脊索动物的基本身体结构，并通过两次全基因组复制形成了高度独特的基因组。
在此，我们对地中海文昌鱼的基因组进行测序，并对DNA甲基化、染色质可及性、组蛋白修饰以及跨多个发育阶段和成体组织的转录组进行表征，以研究脊索动物基因组调控的进化。
通过比较，确定了文昌鱼和脊椎动物之间差异甲基化增强子进化的中间阶段，以及基因表达和顺式调控逻辑的高度保守。
我们还发现在脊椎动物中，超过80%的广泛表达的基因家族中有来自全基因组复制的多个同源基因。
这些基因限制了其祖先的表达，并经历了专业化而不是亚功能化发展。
Abstract
Vertebrates have greatly elaborated the basic chordate body plan and evolved highly distinctive genomes that have been sculpted by two whole-genome duplications. Here we sequence the genome of the Mediterranean amphioxus (Branchiostomalanceolatum) and characterize DNA methylation, chromatin accessibility, histone modifications and transcriptomes across multiple developmental stages and adult tissues to investigate the evolution of the regulation of the chordate genome.Compa risons with vertebrates identify an intermediate stage in the evolution of differentially methylated enhancers, and a high conservation of gene expression and its cis-regulatory logic between amphioxus and vertebrates that occurs maximally at an earlier mid-embryonic phylotypic period. We analyse regulatory evolution after whole-genome duplications, and find that—in vertebrates—over80% of broadly expressed gene families with multiple paralogues derived from whole-genome duplications have members that restricted their ancestral expression, and underwent specialization rather than subfunctionalization. Counter-intuitively, paralogues that restricted their expression increased the complexity of their regulatory landscapes. These data pave the way for a better understanding of the regulatory principles that underlie key vertebrate innovations.
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