naturewater期刊

naturewater期刊

naturewater学术期刊非常好！

学术期刊《自然-水》（Nature Water）在线发表在的一篇研究论文报告称，全球尚未开发的水能经济潜力（可获利的水力资源）为5.27万亿度每年。其中三分之二分布在喜马拉雅地区。亚洲和非洲拥有上述总量的85%。

《自然》（20210408出版）一周论文导读

编译 | 李言

Nature , 8 April 2021, Volume 592 Issue 7853

《自然》 2021年4月8日，第592卷，7853期

天文学 Astronomy

Five carbon- and nitrogen-bearing species in a hot giant planet’s atmosphere

在炎热巨型行星大气层中的五种含碳和氮的物质

作者：Paolo Giacobbe, Matteo Brogi, Siddharth Gandhi, Patricio E. Cubillos, et al.

链接：

摘要

先前对热木星的观测表明，它们在其主星前面经过时大气层中经常存在水蒸气和一氧化碳；这已经通过在通常的化学平衡假设下根据太阳的比例组成进行了研究。

氰化氢和这两种分子都在HD 209458b的大气中被发现。HD 209458b是一个被充分研究过的热木星（平衡温度在1500 k左右），曾经检测出氨，但随后被否认。

在此，我们报告HD 209458b的观察结果，显示存在水、一氧化碳、氰化氢、甲烷、氨和乙炔，每个分子5.3到9.9个标准偏差。辐射和化学平衡的大气模型表明，探测到的物质具有富碳化学成分，碳氧比接近或大于1，高于太阳的值（0.55）。

根据现有的关于大气化学与行星形成和迁移情景的模型，这可能表明HD 209458b在远离目前位置的地方形成，随后向内迁移。

Abstract

Previous observations of hot Jupiters as they transit in front of their host stars have revealed the frequent presence of water vapour and carbon monoxide in their atmospheres; this has been studied in terms of scaled solar composition under the usual assumption of chemical equilibrium. Both molecules as well as hydrogen cyanide were found in the atmosphere of HD 209458b, a well studied hot Jupiter (with equilibrium temperature around 1,500 kelvin), whereas ammonia was tentatively detected there and subsequently refuted. Here we report observations of HD 209458b that indicate the presence of water ( H2 O), carbon monoxide (CO), hydrogen cyanide (HCN), methane (C H4 ), ammonia (N H3 ) and acetylene ( C2H2 ), with statistical significance of 5.3 to 9.9 standard deviations per molecule. Atmospheric models in radiative and chemical equilibrium that account for the detected species indicate a carbon-rich chemistry with a carbon-to-oxygen ratio close to or greater than 1, higher than the solar value (0.55). According to existing models relating the atmospheric chemistry to planet formation and migration scenarios, this would suggest that HD 209458b formed far from its present location and subsequently migrated inwards.

考古学 Archaeology

Innovative Homo sapiens behaviours 105,000 years ago in a wetter Kalahari

发生在105000年前卡拉哈里盆地中的人类创新行为

作者：Jayne Wilkins, Benjamin J. Schoville, Robyn Pickering, Luke Gliganic, et al.

链接：

摘要

非洲的考古记录为智人复杂的符号和技术行为的出现提供了最早的证据。然而，保存完好、年代学较强的晚更新世地层遗址在南非内陆非常罕见，因此海岸假说仍未得到验证。

在此，我们展示了与大约10.5万年前南部非洲沿海地区的人类发明相似的早期人类发明，他们大约在同一时期生活在600多公里外的内陆地区。我们报告了有意收集非实用物体（方解石晶体）和鸵鸟蛋壳的证据。

这些证据来自对于卡拉哈里盆地南部的一个层状岩石矿床的挖掘现场，我们通过光释光测年技术确定其距今约10.5万年。残存凝灰岩矿床的铀钍定年法表明，这里偶尔会有大量淡水流动；这些岩层中最古老的可以追溯到11至10万年之间，与考古发现相一致。

我们的结果表明，南部非洲内陆人类的创新行为并不落后于靠近海岸的人群，而且这些创新行为可能是在潮湿的大草原环境中发展起来的。

Abstract

The archaeological record of Africa provides the earliest evidence for the emergence of the complex symbolic and technological behaviours that characterize Homo sapiens. However, stratified Late Pleistocene sites with good preservation and robust chronologies are rare in the interior of southern Africa, and the coastal hypothesis therefore remains untested. Here we show that early human innovations that are similar to those dated to around 105 thousand years ago (ka) in coastal southern Africa existed at around the same time among humans who lived over 600 km inland. We report evidence for the intentional collection of non-utilitarian objects (calcite crystals) and ostrich eggshell from excavations of a stratified rockshelter deposit in the southern Kalahari Basin, which we date by optically stimulated luminescence to around 105 ka. Uranium–thorium dating of relict tufa deposits indicates sporadic periods of substantial volumes of fresh, flowing water; the oldest of these episodes is dated to between 110 and 100 ka and is coeval with the archaeological deposit. Our results suggest that behavioural innovations among humans in the interior of southern Africa did not lag behind those of populations near the coast, and that these innovations may have developed within a wet savannah environment.

材料科学 Material Science

Entropic evidence for a Pomeranchuk effect in magic-angle graphene

魔角石墨烯中波梅兰丘克效应的熵证据

作者：Asaf Rozen, Jeong Min Park, Uri Zondiner, Yuan Cao, Daniel Rodan-Legrain, et al.

链接：

摘要

20世纪50年代，波梅兰丘克预测，液态氦-3加热后可能会凝固，这与我们的直觉相反。这种效应是由于固相中原子在空间局部的高过量核自旋熵引起的。在此，我们发现在魔角扭曲双层石墨烯中也发生了类似的效应。

使用局部和全局电子熵测量，我们发现，在每摩尔单胞填充近一个电子时，电子熵显著增加到约每单胞1 k B。这个巨大的过量熵被指向其磁源的平面内磁场淬灭。可压缩性随电子密度的变化而急剧下降，伴随着费米能级的重置回到狄拉克点附近，标志着两相之间的清晰边界。

我们将这种跃变映射为电子密度，温度和磁场的函数。这揭示了一个相图，与波梅兰丘克一样，温度和磁场驱动了从低熵电子液体到具有几乎自由磁矩的高熵相关态转变。

相关态的特征是表面上相互矛盾性质的不寻常组合，一些与流动的电子有关——例如缺乏热力学间隙、金属性和狄拉克式的可压缩性——另一些与局部矩有关，例如大的熵及其在磁场下的消失。

Abstract

In the 1950s, Pomeranchuk predicted that, counterintuitively, liquid 3He may solidify on heating. This effect arises owing to high excess nuclear spin entropy in the solid phase, where the atoms are spatially localized. Here we find that an analogous effect occurs in magic-angle twisted bilayer graphene. Using both local and global electronic entropy measurements, we show that near a filling of one electron per moiré unit cell, there is a marked increase in the electronic entropy to about 1 k B per unit cell ( k B is the Boltzmann constant). This large excess entropy is quenched by an in-plane magnetic field, pointing to its magnetic origin. A sharp drop in the compressibility as a function of the electron density, associated with a reset of the Fermi level back to the vicinity of the Dirac point, marks a clear boundary between two phases. We map this jump as a function of electron density, temperature and magnetic field. This reveals a phase diagram that is consistent with a Pomeranchuk-like temperature- and field-driven transition from a low-entropy electronic liquid to a high-entropy correlated state with nearly free magnetic moments. The correlated state features an unusual combination of seemingly contradictory properties, some associated with itinerant electrons—such as the absence of a thermodynamic gap, metallicity and a Dirac-like compressibility—and others associated with localized moments, such as a large entropy and its disappearance under a magnetic field.

Isospin Pomeranchuk effect in twisted bilayer graphene

扭曲双层石墨烯的同位旋波梅兰丘克效应

作者：Yu Saito, Fangyuan Yang, Jingyuan Ge, Xiaoxue Liu, Takashi Taniguchi, Kenji Watanabe, et al.

链接：

摘要

在此，我们展示了一种机制来描述魔角扭曲双层石墨烯中自旋和波谷同位旋的有限温度动力学。

值得注意的是，在超晶格填充因子 1附近，高温时电阻率出现峰值，而在低温极限时则没有出现相应的相。倾斜磁场的磁输运和面内磁矩的热力学测量表明，电阻率峰值与系统发展为有限同位旋极化的有限场磁相变有关。这些数据提示了一种波梅兰丘克型机制。

在这种机制中，相对于同位旋未极化的费米液相，铁磁相中的无序同位旋矩的熵在更高的温度下使相稳定。

Abstract

Here we show that a similar mechanism describes the finite-temperature dynamics of spin and valley isospins in magic-angle twisted bilayer graphene. Notably, a resistivity peak appears at high temperatures near a superlattice filling factor of 1, despite no signs of a commensurate correlated phase appearing in the low-temperature limit. Tilted-field magnetotransport and thermodynamic measurements of the in-plane magnetic moment show that the resistivity peak is connected to a finite-field magnetic phase transition at which the system develops finite isospin polarization. These data are suggestive of a Pomeranchuk-type mechanism, in which the entropy of disordered isospin moments in the ferromagnetic phase stabilizes the phase relative to an isospin-unpolarized Fermi liquid phase at higher temperatures.

Diversity-oriented synthesis of polymer membranes with ion solvation cages

基于离子溶剂化聚合物膜的多样性取向合成

作者：Miranda J. Baran, Mark E. Carrington, Swagat Sahu, Artem Baskin, Junhua Song, et al.

链接：

摘要

在此，我们描述了一种面向多样性的微孔聚合物膜合成策略，以识别具有FVEs的候选材料，作为锂离子的溶剂笼。

这一策略包括通过曼尼希反应使双联邻苯二酚单体多样化，从而在FVEs中引入锂离子协调功能，加强拓扑聚合使FVEs进入不同的孔结构，以及多种多样的孔几何和介电性能的聚合物反应。

具有离子溶剂化笼的候选膜比控制膜具有更高的离子电导率和更高的阳离子转移数，其中FVEs具有特异性，表明可以克服常规的膜渗透性边界和离子转移的选择性。

Abstract

Here we describe a persity-oriented synthetic strategy for microporous polymer membranes to identify candidates featuring FVEs that serve as solvation cages for lithium ions (Li+). This strategy includes persification of bis(catechol) monomers by Mannich reactions to introduce Li+-coordinating functionality within FVEs, topology-enforcing polymerizations for networking FVEs into different pore architectures, and several on-polymer reactions for persifying pore geometries and dielectric properties. The most promising candidate membranes featuring ion solvation cages exhibited both higher ionic conductivity and higher cation transference number than control membranes, in which FVEs were aspecific, indicating that conventional bounds for membrane permeability and selectivity for ion transport can be overcome.

地球科学 Geoscience

A 200-million-year delay in permanent atmospheric oxygenation

延迟了2亿年的永久大气氧化

作者：Simon W. Poulton, Andrey Bekker, Vivien M. Cumming, Aubrey L. Zerkle, Donald E. Canfield & David T. Johnston

链接：

摘要

早期大气氧化发生在以多次全球冰期为标志的长期极端气候不稳定时期，氧浓度最初上升到目前大气水平的 10- 5 以上的时间则推定为24.3亿年前。然而，随后大气氧含量的波动一直持续到大约23.2亿年前，这代表了大气中不可逆氧化的估计时间。

在此，我们通过南非德兰士瓦尔超群的海洋沉积物，对古代早期最后两次冰期的大气和局部海洋氧化还原条件进行了高分辨率重建。利用多重硫同位素和铁-硫-碳系统，我们证明了大约23.2亿年前之后大气氧水平的持续振荡，这与海洋氧化还原化学和气候的主要扰动有关。

因此，在大约2亿年的时间里，氧气水平在目前大气水平的 10- 5 的阈值上下波动。永久的大氧化事件比目前估计的晚了大约1亿年。

Abstract

Early atmospheric oxygenation occurred over a protracted period of extreme climatic instability marked by multiple global glaciations, with the initial rise of oxygen concentration to above 10- 5 of the present atmospheric level constrained to about 2.43 billion years ago. Subsequent fluctuations in atmospheric oxygen levels have, however, been reported to have occurred until about 2.32 billion years ago, which represents the estimated timing of irreversible oxygenation of the atmosphere. Here we report a high-resolution reconstruction of atmospheric and local oceanic redox conditions across the final two glaciations of the early Palaeoproterozoic era, as documented by marine sediments from the Transvaal Supergroup, South Africa. Using multiple sulfur isotope and iron–sulfur–carbon systematics, we demonstrate continued oscillations in atmospheric oxygen levels after about 2.32 billion years ago that are linked to major perturbations in ocean redox chemistry and climate. Oxygen levels thus fluctuated across the threshold of 10- 5 of the present atmospheric level for about 200 million years, with permanent atmospheric oxygenation finally arriving with the Lomagundi carbon isotope excursion at about 2.22 billion years ago, some 100 million years later than currently estimated.

为什么老美不推崇Water Research？为什么EST更受欢迎

Water Research的出版社在欧洲，而EST是美国化学学会的杂志，这可能是EST在美国比较火的原因之一。
Water Research注重水污染方面的研究，在水处理领域当之无愧地排在第一位；EST关注的是大的环境领域（水气固等多方面），在环境领域的影响力也有目共睹。
Water Research和EST的影响力在传统环境领域稳坐头两把交椅，至于影响因子更高的EES，ACB等杂志在该领域的认可度其实并没这么高，当然如果能发到nature子刊，PNAS级别就另当别论。

《自然》（20210527出版）一周论文导读

编译 | 未玖

Nature , 27 May 2021, VOL 593, ISSUE 7860

《自然》 2021年5月27日，第593卷，7860期

天文学 Astronomy

Evidence of hydrogen helium immiscibility at Jupiter-interior conditions

木星内部条件下氢-氦不混溶的证据

作者：S. Brygoo, P. Loubeyre, M. Millot, J. R. Rygg, P. M. Celliers, J. H. Eggert, et al.

链接：

摘要

温致密氢 氦（H-He）混合物的相行为影响了人们对木星和土星及其内部结构演化的理解。然而，尽管H-He相具有重要意义，但在相关的行星条件下，它的相行为仍然很难约束，因为通过计算来确定它极具挑战性，且极端温度和压力也难以通过实验达到。

研究组报道了通过激光驱动的冲击压缩已在钻石砧电池中预压缩的H2 He样品，可以达到适当的温度和压力。这使研究组能够探测木星内部条件下H-He混合物的性质，揭示了沿雨贡纽曲线的一个不混溶区域。

样品反射率的明显不连续变化表明，在10200 K时，该区域结束于150吉帕以上；在4700 K时，93吉帕以上的反射率发生了更细微的变化。考虑到木星的压力-温度分布，这些近原太阳混合物的实验不混溶约束表明H-He相分离影响了木星内部的很大一部分，研究组估计该部分大约占木星半径的15%。

这一发现为木星模型提供了微物理支持，该模型利用分层内部来解释朱诺号和伽利略号航天器的观测。

Abstract

The phase behaviour of warm dense hydrogen helium (H He) mixtures affects our understanding of the evolution of Jupiter and Saturn and their interior structures. But despite its importance, H He phase behaviour under relevant planetary conditions remains poorly constrained because it is challenging to determine computationally and because the extremes of temperature and pressure are difficult to reach experimentally. Here we report that appropriate temperatures and pressures can be reached through laser-driven shock compression of H2 He samples that have been pre-compressed in diamond-anvil cells. This allows us to probe the properties of H He mixtures under Jovian interior conditions, revealing a region of immiscibility along the Hugoniot. A clear discontinuous change in sample reflectivity indicates that this region ends above 150 gigapascals at 10,200 kelvin and that a more subtle reflectivity change occurs above 93 gigapascals at 4,700 kelvin. Considering pressure–temperature profiles for Jupiter, these experimental immiscibility constraints for a near-protosolar mixture suggest that H He phase separation affects a large fraction—we estimate about 15 per cent of the radius—of Jupiter’s interior. This finding provides microphysical support for Jupiter models that invoke a layered interior to explain Juno and Galileo spacecraft observations.

材料科学 Materials Science

Long-range nontopological edge currents in charge-neutral graphene

电荷中性石墨烯中的长程非拓扑边缘电流

作者：A. Aharon-Steinberg, A. Marguerite, D. J. Perello, K. Bagani, T. Holder, Y. Myasoedov, et al.

链接：

摘要

范德华异质结构显示出许多独特的电子性质。单层、双层和薄层石墨烯、过渡金属二卤化物和莫尔超晶格已被发现显示出明显的非局域效应。

然而，这些效应的起源却引起了激烈的争论。尤其是石墨烯，在电荷中性时表现出巨大的非局域性，这一惊人行为吸引了各种不同的解释。

利用尖端超导量子干涉装置（SQUID-on-tip）进行纳米尺度的热成像和扫描门成像，研究组证明了石墨烯边缘常见的电荷积累会导致巨大的非局域性，产生了支持长程电流的狭窄导电通道。

出乎意料的是，虽然边缘电导对零磁场中的电流流动影响不大，但在中等磁场下，它会导致边缘和体输运之间的场诱导解耦。由此产生的巨大非局域性在电荷中性和远离电荷时产生了对边缘无序敏感的奇异流型，在这种流型中电荷可以对抗全局电场流动。

所观察到的一维边缘输运是通用和非拓扑的，有望支持许多电子系统中的非局域输运，为深入研究众多争论提供了线索，并将它们与系统边缘的远程引导电子态联系起来。

Abstract

Van der Waals heterostructures display numerous unique electronic properties. Monolayer, bilayer and few-layer graphene, transition-metal dichalcogenides and moiré superlattices have been found to display pronounced nonlocal effects. However, the origin of these effects is hotly debated. Graphene, in particular, exhibits giant nonlocality at charge neutrality, a striking behaviour that has attracted competing explanations. Using a superconducting quantum interference device on a tip (SQUID-on-tip) for nanoscale thermal and scanning gate imaging, here we demonstrate that the commonly occurring charge accumulation at graphene edges leads to giant nonlocality, producing narrow conductive channels that support long-range currents. Unexpectedly, although the edge conductance has little effect on the current flow in zero magnetic field, it leads to field-induced decoupling between edge and bulk transport at moderate fields. The resulting giant nonlocality at charge neutrality and away from it produces exotic flow patterns that are sensitive to edge disorder, in which charges can flow against the global electric field. The observed one-dimensional edge transport is generic and nontopological and is expected to support nonlocal transport in many electronic systems, offering insight into the numerous controversies and linking them to long-range guided electronic states at system edges.

Perovskite-type superlattices from lead halide perovskite nanocubes

卤化铅钙钛矿纳米立方体的钙钛矿型超晶格

作者：Ihor Cherniukh, Gabriele Rainò, Thilo Stöferle, Max Burian, Alex Travesset, Denys Naumenko, et al.

链接：

摘要

铯-铅卤化物钙钛矿型纳米晶体是长程有序超晶格很有前途的构建基块，因其明亮三重态激子的高振荡强度、缓慢失相（高达80皮秒的相干时间）和最小发射线不均匀展宽。到目前为止，人们从这些纳米晶体中仅设计出来单组分超晶格与简单立方堆积。

研究组提出了钙钛矿型（ABO3）二元和三元纳米晶超晶格，通过立体稳定、高发光的立方CsPbBr3纳米晶（占据B和/或O晶格位）、球形Fe3O4或NaGdF4纳米晶（A位）和截角立方PbS纳米晶（B位）的形状定向共组装而成。

这些ABO3超晶格，以及研究组展示的二元NaCl和AlB2超晶格结构，均表明了CsPbBr3纳米立方体的高度取向有序性。它们还表现出超荧光——一种集体发射，导致超快辐射衰减（22皮秒）的光子爆发，可用于定制超亮（量子）光源。

研究组的工作为进一步 探索 复杂有序、功能有用的钙钛矿介观结构奠定了基础。

Abstract

Caesium lead halide perovskite nanocrystals are promising building blocks for long-range-ordered superlattices, owing to the high oscillator strength of bright triplet excitons, slow dephasing (coherence times of up to 80 picoseconds) and minimal inhomogeneous broadening of emission lines. So far, only single-component superlattices with simple cubic packing have been devised from these nanocrystals. Here we present perovskite-type (ABO3) binary and ternary nanocrystal superlattices, created via the shape-directed co-assembly of steric-stabilized, highly luminescent cubic CsPbBr3 nanocrystals (which occupy the B and/or O lattice sites), spherical Fe3O4 or NaGdF4 nanocrystals (A sites) and truncated-cuboid PbS nanocrystals (B sites). These ABO3 superlattices, as well as the binary NaCl and AlB2 superlattice structures that we demonstrate, exhibit a high degree of orientational ordering of the CsPbBr3 nanocubes. They also exhibit superfluorescence—a collective emission that results in a burst of photons with ultrafast radiative decay (22 picoseconds) that could be tailored for use in ultrabright (quantum) light sources. Our work paves the way for further exploration of complex, ordered and functionally useful perovskite mesostructures.

地球科学 Earth Science

A 10 per cent increase in global land evapotranspiration from 2003 to 2019

2003-2019年，全球陆地蒸散量增加10%

作者：Madeleine Pascolini-Campbell, John T. Reager, Hrishikesh A. Chandanpurkar & Matthew Rodell

链接：

摘要

准确量化全球陆地蒸散量对于理解全球水循环的变异性是必要的，在气候变化下，这种变异性预计将加剧。目前的全球蒸散量产品来源很多，包括模型、遥感和现场观测。

然而，现有的方法包含广泛不确定性；例如，与模型结构相关，或将观测值提升到全球水平。因此，全球蒸散量的变异性和趋势仍不清楚。

研究组表明，2003至2019年，全球陆地蒸散量增加了10 2%，陆地降水越来越多地被划分为蒸散量，而非径流。

该结果基于全球陆地蒸散量的独立水平衡集合时间序列和相应的不确定性分布，使用的数据来自重力恢复及气候实验（GRACE）和GRACE后续（GRACE-FO）卫星。

全球陆地蒸散量的变异性与厄尔尼诺-南方涛动正相关。然而，这种趋势的主要驱动力是不断升高的地表温度。

研究组的发现为全球陆地蒸散量提供了一个观测约束，且与全球蒸散量在气候变暖下增加的假设相一致。

Abstract

Accurate quantification of global land evapotranspiration is necessary for understanding variability in the global water cycle, which is expected to intensify under climate change. Current global evapotranspiration products are derived from a variety of sources, including models, remote sensing and in situ observations. However, existing approaches contain extensive uncertainties; for example, relating to model structure or the upscaling of observations to a global level. As a result, variability and trends in global evapotranspiration remain unclear. Here we show that global land evapotranspiration increased by 10 2 per cent between 2003 and 2019, and that land precipitation is increasingly partitioned into evapotranspiration rather than runoff. Our results are based on an independent water-balance ensemble time series of global land evapotranspiration and the corresponding uncertainty distribution, using data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE-Follow On (GRACE-FO) satellites. Variability in global land evapotranspiration is positively correlated with El Niño–Southern Oscillation. The main driver of the trend, however, is increasing land temperature. Our findings provide an observational constraint on global land evapotranspiration, and are consistent with the hypothesis that global evapotranspiration should increase in a warming climate.

Overriding water table control on managed peatland greenhouse gas emissions

地下水位控制泥炭地温室气体排放

作者：C. D. Evans, M. Peacock, A. J. Baird, R. R. E. Artz, A. Burden, N. Callaghan, et al.

链接：

摘要

全球泥炭地储存的碳比大气中自然存在的还要多。然而，许多泥炭地受到基于排水的农业、种植开发和火灾的压力，仅相当于排水泥炭地排放的所有人为温室气体的3%左右。通过保护未排水的泥炭地和使排水系统再湿润，人们正加强努力来遏制此类排放。

研究组报道了来自16个地点的 CO2 涡流协方差数据和来自英国和爱尔兰41个地点的 CH4 静态室测量数据，并将这些数据与所有主要泥炭地生物群落公布的数据相结合。

结果表明，年平均有效地下水位（ WTDe ；即通气泥炭层的平均深度）超过了所有其他与温室气体排放相关的生态系统和管理控制。

研究组估计， WTDe 每减少10 cm， CO2 和 CH4 排放（100年全球变暖潜势）的净变暖效应每年每公顷至少减少3吨 CO2 ，直到 WTDe 小于30 cm。进一步提高水位将继续产生净冷却效应，直到 WTDe 位于地表10 cm以内。

研究结果表明，农业泥炭地的温室气体排放可以大大减少，而不必停止其生产性使用。例如，将所有排干的农业泥炭地中的 WTDe 减半，可减少的排放量相当于全球人为排放的1%以上。

Abstract

Global peatlands store more carbon than is naturally present in the atmosphere. However, many peatlands are under pressure from drainage-based agriculture, plantation development and fire, with the equivalent of around 3 per cent of all anthropogenic greenhouse gases emitted from drained peatland. Efforts to curb such emissions are intensifying through the conservation of undrained peatlands and re-wetting of drained systems. Here we report eddy covariance data for carbon dioxide from 16 locations and static chamber measurements for methane from 41 locations in the UK and Ireland. We combine these with published data from sites across all major peatland biomes. We find that the mean annual effective water table depth ( WTDe ; that is, the average depth of the aerated peat layer) overrides all other ecosystem- and management-related controls on greenhouse gas fluxes. We estimate that every 10 centimetres of reduction in WTDe could reduce the net warming impact of CO2 and CH4 emissions (100-year global warming potentials) by the equivalent of at least 3 tonnes of CO2 per hectare per year, until WTDe is less than 30 centimetres. Raising water levels further would continue to have a net cooling effect until WTDe is within 10 centimetres of the surface. Our results suggest that greenhouse gas emissions from peatlands drained for agriculture could be greatly reduced without necessarily halting their productive use. Halving WTDe in all drained agricultural peatlands, for example, could reduce emissions by the equivalent of over 1 per cent of global anthropogenic emissions.

社会 学 Sociology

The universal visitation law of human mobility

人群流动的普遍访问规律

作者：Markus Schläpfer, Lei Dong, Kevin O’Keeffe, Paolo Santi, Michael Szell, Hadrien Salat, et al.

链接：

摘要

人的流动性影响着城市的许多方面，从城市的空间结构到城市对流行病的反应。它最终也是 社会 互动、创新和生产力的关键。

研究组揭示了一个简单而稳健的标度律，它基于全球不同城市的人口大规模流动数据，来捕捉人口流动的时空谱。根据这一规律，任何地点的游客人数都会随着其访问频率和旅行距离乘积的平方反比而减少。

研究组进一步证明流向不同地点的时空流产生了显著的空间集群，其区域分布遵循齐夫定律。最后，研究组建立了一个基于 探索 和优先返回的个体流动模型，为所发现的标度律和新兴的空间结构提供了一个机制解释。

该研究结果证实了人文地理学中长期存在的猜想，并允许对人群重复流动进行预测，这为在城市规划、交通工程和减少流行病方面的应用提供了基础。

Abstract

Human mobility impacts many aspects of a city, from its spatial structure to its response to an epidemic. It is also ultimately key to social interactions, innovation and productivity. However, our quantitative understanding of the aggregate movements of inpiduals remains incomplete. Existing models—such as the gravity law or the radiation model—concentrate on the purely spatial dependence of mobility flows and do not capture the varying frequencies of recurrent visits to the same locations. Here we reveal a simple and robust scaling law that captures the temporal and spatial spectrum of population movement on the basis of large-scale mobility data from perse cities around the globe. According to this law, the number of visitors to any location decreases as the inverse square of the product of their visiting frequency and travel distance. We further show that the spatio-temporal flows to different locations give rise to prominent spatial clusters with an area distribution that follows Zipf’s law. Finally, we build an inpidual mobility model based on exploration and preferential return to provide a mechanistic explanation for the discovered scaling law and the emerging spatial structure. Our findings corroborate long-standing conjectures in human geography and allow for predictions of recurrent flows, providing a basis for applications in urban planning, traffic engineering and the mitigation of epidemic diseases.

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