《科学》（20190830出版）一周论文导读

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《科学》（20190830出版）一周论文导读

2019 年 8 月 31 日 科学网

翻译 | 宗华

Science, 30 AUGUST 2019, VOL 365, ISSUE 6456

《科学》2019年8月30日，第365卷，第6456期

物理学Physics

Dynamical charge density fluctuations pervading the phase diagram of a Cu-based high-Tc superconductor

铜基高临界温度超导体的相图中充满动态电荷密度波动

▲ 作者：R. Arpaia, S. Caprara, R. Fumagalli, et al

▲ 链接：

https://science.sciencemag.org/content/365/6456/906

▲ 摘要：

在所有的高临界温度（T_c）超导铜酸盐中，电荷密度都发生了调制。

尽管它们始终在相图的低掺杂区和相对较低的温度下被发现，但它们在多大程度上影响了这些系统的不寻常性质仍不清楚。

利用共振光散射,我们仔细确定了电荷密度调制在若干掺杂水平的YBa₂Cu₃O_7–δ 和 Nd_1+xBa_2–xCu₃O_7–δ 中的温度依赖性。

除了已知的准临界电荷密度波，我们还分离出近程动态电荷密度波动。

它们能维持到远高于赝隙温度T^*的温度，以几毫伏的能量为特征，并在相图中占据很大的区域。

▲ Abstract

Charge density modulations have been observed in all families of high–critical temperature (T_c) superconducting cuprates. Although they are consistently found in the underdoped region of the phase diagram and at relatively low temperatures, it is still unclear to what extent they influence the unusual properties of these systems. Using resonant x-ray scattering, we carefully determined the temperature dependence of charge density modulations in YBa₂Cu₃O_7–δ and Nd_1+xBa_2–xCu₃O_7–δ for several doping levels. We isolated short-range dynamical charge density fluctuations in addition to the previously known quasi-critical charge density waves. They persist up to well above the pseudo gap temperature T^*, are characterized by energies of a few milli–electron volts, and pervade a large area of the phase diagram.

Skyrmion lattice with a giant topological Hall effect in a frustrated triangular-lattice magnet

阻挫三角形晶格磁体中具有巨大拓扑霍尔效应的斯格明子晶格

▲ 作者：Takashi Kurumaji, Taro Nakajima, Max Hirschberger, et al

▲ 链接：

https://science.sciencemag.org/content/365/6456/914

▲ 摘要：

几何阻挫磁体可以承载复杂的自旋结构，导致非常规的电磁响应。磁阻挫也可能促进拓扑上的非平凡自旋态，比如磁斯格明子。

然而，在实验上，斯格明子在非中心对称晶格结构或界面对称断裂的异质结构中被观察到。

这里，我们报告了在阻挫的中心对称三角形晶格磁体Gd₂PdSi₃中出现的布洛赫型斯格明子态。

我们观察到一个巨大的拓扑霍尔响应，表明一个场诱导的斯格明子相位。这通过观察到的由共振X射线散射探测的平面内自旋调制得到进一步证实。

我们的结果可能促成在磁阻挫中心对称材料中涌现电动力学的进一步发现。

▲ Abstract

Geometrically frustrated magnets can host complex spin textures, leading to unconventional electromagnetic responses. Magnetic frustration may also promote topologically nontrivial spin states such as magnetic skyrmions. Experimentally, however, skyrmions have largely been observed in noncentro symmetric lattice structures or interfacial symmetry-breaking heterostructures. Here, we report the emergence of a Bloch-type skyrmion state in the frustrated centrosymmetric triangular-lattice magnet Gd₂PdSi₃. We observed a giant topological Hall response, indicating a field-induced skyrmion phase, which is further corroborated by the observation of in-plane spin modulation probed by resonant x-ray scattering. Our results may lead to further discoveries of emergent electrodynamicsin magnetically frustrated centrosymmetric materials.

地球科学Geoscience

Archaeological assessment reveals Earth's early transformation through land use

考古评估通过土地利用揭示地球早期变化

▲ 作者：Lucas Stephens, Dorian Fuller, Nicole Boivin, et al

▲ 链接：

https://science.sciencemag.org/content/365/6456/897

▲ 摘要：

随着农业的出现，人类对土地的环境改造加速，但这些早期变化的范围、轨迹和影响尚不清楚。

一项全球土地利用的经验评估显示，从距今1万年到公元1850年的这段时间里，地球在3000年前主要由采猎者、农民和牧民改变，大大早于地球科学家通常采用的土地利用重建日期。

250多名考古学家贡献的综合知识突出了考古学专业知识和数据质量方面的差距。这种差距在公元前2000年达到顶峰，而且出现在传统研究和较为富裕的地区。

全球土地利用历史的考古重建揭示了地球变迁的深层根源，并对人类世范式提出了挑战，即大规模的人为全球环境变化大多是最近才出现的现象。

▲ Abstract

Environmentally transformative human use of land accelerated with the emergence of agriculture, but the extent, trajectory, and implications of these early changes are not well understood. An empirical global assessment of land use from 10,000 years before the present (yr B.P.) to 1850 CE reveals a planet largely transformed by hunter-gatherers, farmers, and pastoralists by 3000 years ago, considerably earlier than the dates in the land-use reconstructions commonly used by Earth scientists. Synthesis of knowledge contributed by more than 250 archaeologists highlighted gaps in archaeological expertise and data quality, which peaked for 2000 yr B.P. and intraditionally studied and wealthier regions. Archaeological reconstruction of global land-use history illuminates the deep roots of Earth's transformation and challenges the emerging Anthropocene paradigm that large-scale anthropogenic global environmental change is mostly a recent phenomenon.

Deep magma ocean formation set the oxidation state of Earth's mantle

深部岩浆海洋的形成决定了地幔的氧化状态

▲ 作者：Katherine Armstrong*, Daniel J. Frost†, Catherine A. McCammon, et al

▲ 链接：

https://science.sciencemag.org/content/365/6456/903

▲ 摘要：

地球大气的组成取决于地幔的氧化还原状态，而在地核形成后的某个阶段，地幔的氧化还原程度更高。

通过高压实验，我们发现深岩浆海洋中的Fe²⁺与高压下的Fe³⁺金属铁不成比例。这种金属铁与地核的分离提高了上地幔的氧化状态，改变了形成大气的脱气挥发物的化学性质，使其变成更多的氧化物质。

此外，岩浆海洋氧化还原状态的梯度使得大气中溶解的二氧化碳在深处以钻石的形式沉淀下来。

这解释了地球富含碳的内部，并表明在吸积过程中氧化还原的进化是决定陆地大气组成的一个重要变量。

▲ Abstract

The composition of Earth's atmosphere depends on the redox state of the mantle, which became more oxidizing at somestage after Earth's core started to form. Through high-pressure experiments, we found that Fe²⁺ in a deep magma ocean would disproportionate to Fe³⁺ plus metallic iron at high pressures. The separation of this metallic iron tothe core raised the oxidation state of the upper mantle, changing the chemistry of degassing volatiles that formed the atmosphere to more oxidized species. Additionally, the resulting gradient in redox state of the magma ocean allowed dissolved CO₂ from the atmosphere to precipitate as diamond at depth. This explains Earth's carbon-rich interior and suggests that redoxevolution during accretion was an important variable in determining the composition of the terrestrial atmosphere.

Solar System chaos and the Paleocene–Eocene boundary age constrained by geology and astronomy

太阳系混沌与古新世—始新世边界年龄受地质学和天文学制约

▲ 作者：Richard E. Zeebe, Lucas J. Lourens

▲ 链接：

https://science.sciencemag.org/content/365/6456/926

▲ 摘要：

天文计算揭示了太阳系的动力学演化，包括它的混沌性，并代表了循环地层学和天文年代学的主干。

到目前为止，一个绝对的、完全校准的天文时间尺度一直被限制在距今5000万年（MA）内，因为在此之前的轨道计算不一致。

在此，我们呈现了地质数据和一种新的天文学解决办法（ZB18a），并证实在58 ~ 53Ma之间有异常的一致性。

我们提供了一个新的高达58 Ma的绝对天文年代学和一个新的古新世—始新世边界年龄（56.01±0.05 Ma）。

▲ Abstract

Astronomical calculations reveal the Solar System's dynamical evolution, including its chaoticity, and represent the backbone of cyclostratigraphy and astrochronology. An absolute, fully calibrated astronomical time scale has hitherto been hampered beyond ~50 million years before the present (Ma) because orbital calculations disagree before that age. Here, we present geologic data and a new astronomical solution (ZB18a) showing exceptional agreement from ~58 to 53 Ma. We provide a new absolute as trochronology up to 58 Ma and a new Paleocene–Eocene boundary age (56.01 ± 0.05 Ma).

人工智能

Artificial Intelligence

Superhuman AI for multiplayer poker

针对多人扑克的超级人工智能

▲ 作者：Noam Brown, Tuomas Sandholm

▲ 链接：

https://science.sciencemag.org/content/365/6456/885

▲ 摘要：

近年来，人工智能（AI）取得了巨大进步。而游戏常常成为衡量进步的挑战性问题、基准和里程碑。

几十年来，扑克一直充当了这种具有挑战性的问题。过去在这类基准测试中取得的成功，包括扑克，仅限于两人参与的游戏。

然而，传统上玩扑克的人不止两人。多人游戏呈现了一些超越两人游戏的基本附加问题，而多人扑克是一个公认的AI里程碑。

在这篇文章中，我们介绍了Pluribus。这是一个在6人无限制德州扑克比赛中比顶级人类专业选手更强大的人工智能。6人德州扑克是人类玩的最流行的扑克形式。

▲ Abstract

In recent years there have been great strides in artificial intelligence (AI), with games often serving as challenge problems, benchmarks, and milestones for progress. Poker has served for decades as such a challenge problem. Past successes in such benchmarks, including poker, have been limited to two-player games. However, poker in particular is traditionally played with more than two players. Multiplayer games present fundamental additional issues beyond those in two-player games, and multiplayer poker is a recognized AI milestone. In this paper we present Pluri bus, an AI that we show is stronger than top human professionals in six-player no-limit Texas hold'em poker, the most popular form of poker played by humans.