《科学》（20181123出版）一周论文导读

Science, 23 NOVEMBER 2018, VOL 362, ISSUE 6417

《科学》2018年11月23日第6417期362卷

拓扑物理学Topological Physics

Gate-induced superconductivity in a monolayer topological insulator

单层拓扑绝缘体中栅诱导的超导性

▲ 作者：Ebrahim Sajadi, Tauno Palomaki, Zaiyao Fei, Wenjin Zhao, et al

▲ 链接：

http://science.sciencemag.org/content/362/6417/922

▲ 摘要：

近期研究发现，当层状半金属二碲化钨（WTe₂）变薄成为一个单层时，会变成可在螺旋状边缘通道传导电流的二维拓扑绝缘体（2D TI）。

我们发现，内在的超导性可在这种单层2D TI中被诱导出来，方法是在低于1开尔文的温度下轻度掺杂静电。这一2D TI—超导体的转变可通过施加小的栅电压驱动。

这一发现为将超导性和非平庸拓扑性质结合起来的栅控设备提供了可能性，并且或为基于拓扑保护的量子信息方案提供了基石。

▲ Abstract

The layered semimetal tungsten ditelluride (WTe₂) has recently been found to be a two-dimensional topological insulator (2D TI) when thinned down to a single monolayer, with conducting helical edge channels. We found that intrinsic superconductivity can be induced in this monolayer 2D TI by mild electrostatic doping at temperatures below 1 kelvin. The 2D TI–superconductor transition can be driven by applying a small gate voltage. This discovery offers possibilities for gate-controlled devices combining superconductivity and nontrivial topological properties, and could provide a basis for quantum information schemes based on topological protection.

Electrically tunable low-density superconductivity in a monolayer topological insulator

单层拓扑绝缘体中电调谐低密度超导性

▲ 作者：Valla Fatemi, Sanfeng Wu, Yuan Cao, Landry Bretheau, et al

▲ 链接：

http://science.sciencemag.org/content/362/6417/926

▲ 摘要：

在拓扑非平庸的绝缘体中开启超导性或提供了一个寻找非阿贝尔拓扑状态的路径。不过，超导体—绝缘体转换的现有展示仅涉及拓扑平庸系统。

这里，我们报告了超导电性的可逆、原位静电开关转换。这是在最新建立的量子自旋霍尔绝缘体单层二碲化钨（WTe₂）中实现的。

该单层被制成范德瓦尔斯场效应晶体管，其基态可被持续地通过调节栅从拓扑绝缘变为超导状态，临界温度Tc达到1开尔文。

我们的结果证实单层WTe₂可作为将超导和物质拓扑相结合起来的工程纳米设备的材料平台。

▲ Abstract

Turning on superconductivity in a topologically nontrivial insulator may provide a route to search for non-Abelian topological states. However, existing demonstrations of superconductor-insulator switches have involved only topologically trivial systems. Here we report reversible, in situ electrostatic on-off switching of superconductivity in the recently established quantum spin Hall insulator monolayer tungsten ditelluride (WTe₂). Fabricated into a van der Waals field-effect transistor, the monolayer’s ground state can be continuously gate-tuned from the topological insulating to the superconducting state, with critical temperatures Tc up to ~1 kelvin. Our results establish monolayer WTe₂ as a material platform for engineering nanodevices that combine superconducting and topological phases of matter.

化学Chemistry

Neutral mass spectrometry of virus capsids above 100 megadaltons with nanomechanical resonators

利用纳米机械振子对超过1亿道尔顿的病毒衣壳进行中性质谱分析

▲ 作者：Sergio Dominguez-Medina, Shawn Fostner, Martial Defoort, Marc Sansa, et al

▲ 链接：

http://science.sciencemag.org/content/362/6417/918

▲ 摘要：

利用传统质谱分析法测量质量在100万~十亿道尔顿范围的粒子极具挑战性。

尽管这一质量范围对于纳米机械振子来说似乎是最优的，但纳米机械质谱仪通常遇到样本损失过高、分析时间延长或者分辨率不够等问题。

我们报告了一种将溶液分析物的气化（实现了高效转移且不依赖于电磁场便能聚焦）和利用纳米机械振子阵列测量单个粒子质量结合起来的系统架构。

该系统以较高的探测效率确定了质量超过3000万道尔顿的聚苯乙烯纳米粒子的质量分布，并且对空的或被DNA填充的T5噬菌体衣壳有效开展了分子质量测量。

这些噬菌体衣壳的质量达到1.05亿道尔顿，而研究人员利用的样本小于1皮摩尔，设备的分辨率则超过100。

▲ Abstract

Measurement of the mass of particles in the mega- to gigadalton range is challenging with conventional mass spectrometry. Although this mass range appears optimal for nanomechanical resonators, nanomechanical mass spectrometers often suffer from prohibitive sample loss, extended analysis time, or inadequate resolution. We report on a system architecture combining nebulization of the analytes from solution, their efficient transfer and focusing without relying on electromagnetic fields, and the mass measurements of individual particles using nanomechanical resonator arrays. This system determined the mass distribution of ~30-megadalton polystyrene nanoparticles with high detection efficiency and effectively performed molecular mass measurements of empty or DNA-filled bacteriophage T5 capsids with masses up to 105 megadaltons using less than 1picomole of sample and with an instrument resolution above 100.

人类学Anthropology

Plio-Pleistocene decline of Africanmegaherbivores: No evidence for ancient hominin impacts

非洲大型食物动物在上新世的衰退：没有针对古人类影响的证据

▲ 作者：J. Tyler Faith, John Rowan, Andrew Du, Paul L. Koch

▲ 链接：

http://science.sciencemag.org/content/362/6417/938

▲ 摘要：

一直有人提出，前现代古人类的影响驱动了灭绝并且塑造了非洲极其多样的大型哺乳动物群落的进化历史。但这一假设尚未得到严格测试。

我们分析了时间跨度为700万年（包括完整的古人类进化历史）的非洲东部食草动物群落，以测试这样一种假设：拥有工具的食肉古人类自上而下的影响在智人出现前导致了大型食草动物的灭绝。

我们记录了从460万年前开始的大型食草动物的稳定、长期衰退。这远早于能对大型哺乳动物群落施加自上而下控制的古人类物种的出现，并且早于古人类同大型食草动物猎物互动的证据。

碳4草原的扩张或许解释了大型食草动物多样性的丧失。

▲ Abstract

It has long been proposed that pre-modern hominin impacts drove extinctions and shaped the evolutionary history of Africa’s exceptionally diverse large mammal communities, but this hypothesis has yet to be rigorously tested. We analyzed eastern African herbivore communities spanning the past 7 million years—encompassing the entirety of hominin evolutionary history—to test the hypothesis that top-down impacts of tool-bearing, meat-eating hominins contributed to the demise of megaherbivores prior to the emergence of Homosapiens. We document a steady, long-term decline of megaherbivores beginning~4.6 million years ago, long before the appearance of hominin species capable of exerting top-down control of large mammal communities and predating evidence for hominin interactions with megaherbivore prey. Expansion of C4 grasslands can account for the loss of megaherbivore diversity.

动物学zoology

Social network plasticity decreases disease transmission in a eusocial insect

社交网络可塑性减少社会性昆虫的疾病传播

▲ 作者：Nathalie Stroeymeyt, Anna V. Grasse, Alessandro Crespi, et al

▲ 链接：

http://science.sciencemag.org/content/362/6417/941

▲ 摘要：

动物社交网络由多重选择压力形成，包括在限制疾病传播的同时确保高效沟通和运转的需求。

在面临病原体时，群居动物可能通过改变社交网络进一步减少疾病流行风险。不过，目前尚未有针对这种病原体触发反应的证据。

我们通过将自动跟踪、控制病原体暴露、疾病传播量化和短暂显示模拟结合，在黑蚁中实验验证了这一假设。

病原体暴露同时诱发了暴露蚂蚁及其同伴的行为变化。这些变化通过加强群落社交网络的抑制疾病传播的关键属性，帮助控制了疾病。

▲ Abstract

Animal social networks are shaped by multiple selection pressures, including the need to ensure efficient communication and functioning while simultaneously limiting disease transmission. Social animals could potentially further reduce epidemic risk by altering their social networks in the presence of pathogens, yet there is currently no evidence for such pathogen-triggered responses. We tested this hypothesis experimentally in the ant Lasius niger using a combination of automated tracking, controlled pathogen exposure, transmission quantification, and temporally explicit simulations. Pathogen exposure induced behavioral changes in both exposed ants and their nestmates, which helped contain the disease by reinforcing key transmission-inhibitory properties of the colony’s contact network.

生理学Physiology

Egocentric coding of external items in the lateral entorhinal cortex

横向内嗅皮层中外部物体的自我中心编码

▲ 作者：Cheng Wang, Xiaojing Chen, Heekyung Lee, Sachin S. Deshmukh, et al

▲ 链接：

http://science.sciencemag.org/content/362/6417/945

▲ 摘要：

情节记忆——对过去事件的有意识回忆——通常以第一人称（以自我为中心）的视角进行。海马体在情节记忆和空间认知中扮演了重要角色。

尽管人们对海马体空间编码的非自我中心性质有了很好的了解，但关于海马体是否接收关于外部物体的以自我为中心的信息仍知之甚少。

我们在小鼠中记录了来自横向内嗅皮层（LEC）和内侧内嗅皮层（MEC）的单个神经元的活动。

LEC和MEC是海马的两个主要信息输入源。很多LEC神经元表现出对外部物体以自我为中心的呈现方式的调整，而MEC细胞倾向于代表非自我中心的呈现。

这表明LEC和MEC神经表征的参考框架存在基本分离。

▲ Abstract

Episodic memory, the conscious recollection of past events, is typically experienced from a first-person (egocentric) perspective. The hippocampus plays an essential role in episodic memory and spatial cognition. Although the allocentric nature of hippocampal spatial coding is well understood, little is known about whether the hippocampus receives egocentric information about external items. We recorded in rats the activity of single neurons from the lateral entorhinal cortex (LEC) and medial entorhinal cortex (MEC), the two major inputs to the hippocampus. Many LEC neurons showed tuning for ego centric bearing of external items, whereas MEC cells tended to represent allocentric bearing. These results demonstrate a fundamental dissociation between the reference frames of LEC and MEC neural representations.

Molecular to organismal chirality is induced by the conserved myosin 1D

保守的肌凝蛋白1D诱导分子到有机体水平上的手性

▲ 作者：G. Lebreton, C. Géminard, F. Lapraz, S. Pyrpassopoulos, et al

▲ 链接：

http://science.sciencemag.org/content/362/6417/949

▲ 摘要：

来自初始对称态的非对称性的出现在自然界中是一种普遍的过渡。活的生物体在分子、细胞、组织和有机体水平上表现出非对称性。

不过，多级非对称性是否以及如何存在关联仍不明确。

在这项研究中，我们证实，果蝇肌凝蛋白1D（Myo1D）和肌凝蛋白1C（Myo1C）足以产生细胞、单个器官甚至整个身体的重新定向扭转。

定向性位于肌凝蛋白的马达结构域名，并且在Myo1D和Myo1C之间是可交换的。

▲ Abstract

The emergence of asymmetry from an initially symmetrical state is a universal transition in nature. Living organisms show asymmetries at the molecular, cellular, tissular, and organismal level. However, whether and how multilevel asymmetries are related remains unclear. In this study, we show that Drosophila myosin 1D(Myo1D) and myosin 1C (Myo1C) are sufficient to generate de novo directional twisting of cells, single organs, or the whole body in opposite directions. Directionality lies in the myosins’ motor domain and is swappable between Myo1D and Myo1C.

 

材料学Materials Science

Multicomponent intermetallic nanoparticles and superb mechanical behaviors of complex alloys

复杂合金的多组分金属金纳米粒子和优异机械行为

▲ 作者：T. Yang, Y. L. Zhao, Y. Tong, Z. B. Jiao, J. Wei, J. X. Cai, et al

▲ 链接：

http://science.sciencemag.org/content/362/6417/933

▲ 摘要：

基于单一主元素的合金设计在性能增强方面已逼近极限。强度大幅增至吉帕斯卡水平通常导致材料延性降低和过早损坏。

这里，我们报告了一种打破这一平衡的策略，即在复杂合金系统中可控地引入高密度延性多组分金属间纳米颗粒（MCINPs）。

和传统方法下的金属间诱导催化不同，这种由MCINP增强的合金展示出1.5吉帕斯卡的超过强度，同时室温下处于拉伸状态时延性高达50%。

▲ Abstract

Alloy design based on single–principal-element systems has approached its limit for performance enhancements. A substantial increase in strength up to gigapascal levels typically causes the premature failure of materials with reduced ductility. Here, we report a strategy to break this trade-off by controllably introducing high-density ductile multicomponent intermetallic nanoparticles (MCINPs) in complex alloy systems. Distinct from the intermetallic-induced embrittlement under conventional wisdom, such MCINP-strengthened alloys exhibit superior strengths of 1.5 gigapascals and ductility as high as 50% in tension at ambient temperature.

（宗华）

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