物理学Physics

 

 

 

An ultrafast symmetry switch in a Weyl semimetal

 

Weyl半金属的超快对称性开关

 

▲ 作者：Edbert J. Sie、Clara M. Nyby、C. D. Pemmaraju、Su Ji Park、Xijie Wang、Aaron M. Lindenberg， et al 

 

▲ 链接：

 

https://www.nature.com/articles/s41586-018-0809-4

 

 

 

▲ 摘要：

 

晶体材料按照其电子结构的不同可以划分为金属和绝缘体两大类。拓扑金属具有特殊的能带结构，它包含一些能带结构的奇点。

 

 

 

在绝大多数金属材料中，这样的Weyl点都会远离费米面，但是如果这样的点恰好坐落在费米面上，就会给出一类非常特殊的电子结构：拓扑半金属——其费米面缩小为费米点，能隙为0，且具有线性色散。

 

 

 

但集成到功能设备中需要超越材料的拓扑保护特性并在高速下操纵拓扑的能力。

 

 

 

本文利用相对论电子衍射的晶体测量结果证明，太赫兹光脉冲可以在Weyl半金属WTe2中诱发太赫兹频层间剪切应变，且应变幅较大，从而形成拓扑上不同的亚稳态相。

 

 

 

这项工作证明了超快操纵固体拓扑特性的可能性，以及开发以太赫兹频率工作的拓扑开关的可能性。

 

 

 

▲ Abstract

 

Topological quantum materials exhibit fascinating properties, with important applications for dissipationless electronics and fault-tolerant quantum computers. Manipulating the topological invariants in these materials would allow the development of topological switching applications analogous to switching of transistors. Lattice strain provides the most natural means of tuning these topological invariants because it directly modifies the electron–ion interactions and potentially alters the underlying crystalline symmetry on which the topological properties depend. However, conventional means of applying strain through heteroepitaxial lattice mismatch and dislocations are not extendable to controllable time-varying protocols, which are required in transistors. Integration into a functional device requires the ability to go beyond the robust, topologically protected properties of materials and to manipulate the topology at high speeds. Here we use crystallographic measurements by relativistic electron diffraction to demonstrate that terahertz light pulses can be used to induce terahertz-frequency interlayer shear strain with large strain amplitude in the Weyl semimetal WTe2, leading to a topologically distinct metastable phase. Separate nonlinear optical measurements indicate that this transition isassociated with a symmetry change to a centrosymmetric, topologically trivialphase. We further show that such shear strain provides an ultrafast, energy-efficient way of inducing robust, well separated Weyl points or of annihilating all Weyl points of opposite chirality. This work demonstrates possibilities for ultrafast manipulation of the topological properties of solids and for the development of a topological switch operating at terahertz frequencies.

 

 

 

Scalable energy-efficient magnetoelectric spin–orbit logic

 

高扩展、高效能磁电自旋逻辑电路

 

▲ 作者：SasikanthManipatruni、Dmitri E.Nikonov、Chia-ChingLin、Tanay A.Gosavi，et al

 

▲ 链接：

 

https://www.nature.com/articles/s41586-018-0770-2

 

 

 

▲ 摘要：

 

自上世纪80年代初以来，大多数电子产品都依赖于使用互补的金属氧化物半导体（CMOS）晶体管。

 

 

 

然而，CMOS工作原理，包括由绝缘栅控制的可开关半导体电导，在很大程度上保持不变，即使晶体管被缩小到10纳米。而在当今数据时代，数据爆炸带来了对更高效计算机的需求。

 

 

 

文章中，研究者展示了一种制作新型逻辑器件和存储器件的方法。相比于传统 CMOS 集成的微处理器，新微处理器能效可以得到显著增强。

 

 

 

结果显示，与CMOS技术相比，新设备具有更高的转换能量、较低的开关电压和增强的逻辑密度。

 

 

 

▲ Abstract

 

Since the early 1980s, most electronics have relied on the use of complementary metal–oxide–semiconductor (CMOS) transistors. However, the principles of CMOS operation, involving a switchable semiconductor conductance controlled by aninsulating gate, have remained largely unchanged, even as transistors are miniaturized to sizes of 10 nanometres. We investigated what dimensionally scalable logic technology beyond CMOS could provide improvements in efficiency and performance for von Neumann architectures and enable growth in emerging computing such as artifical intelligence. Such a computing technology needs to allow progressive miniaturization, reduce switching energy, improve device interconnection and provide a complete logic and memory family. Here we propose a scalable spintronic logic device that operates via spin–orbit transduction (the coupling of an electron’s angular momentum with its linear momentum) combined with magnetoelectric switching. The device uses advanced quantum materials, especially correlated oxides and topological states of matter, for collective switching and detection. We describe progress in magnetoelectric switching and spin–orbit detection of state, and show that in comparison with CMOS technology our devicehas superior switching energy (by a factor of 10 to 30), lower switching voltage (by a factor of 5) and enhanced logic density (by a factor of 5). Inaddition, its non-volatility enables ultralow standby power, which is critical to modern computing. The properties of our device indicate that the proposed technology could enable the development of multi-generational computing.

 

 

 

环境Enviroment

 

 

 

Greenland melt drives continuous export of methane from the ice-sheet bed

 

格陵兰岛融化推动了冰盖甲烷的持续输出

 

▲ 作者：Guillaume Lamarche-Gagnon、Barbara Sherwood Lollar、Sandra Arndt, Peer Fietzek、Alexander D. Beaton,et al

 

▲ 链接：

 

https://www.nature.com/articles/s41586-018-0800-0

 

 

 

▲ 摘要：

 

在全球甲烷预算中，冰盖目前被忽略了。尽管有人提出，冰盖中蕴藏着大量甲烷，如果这些气体在冰层快速消退期间释放，可能会导致大气甲烷浓度上升，但目前还没有关于冰盖甲烷足迹的数据。

 

 

 

在这里，研究人员发现，格陵兰冰盖的冰川下集水区的有效排水系统迅速地将冰川下产生的甲烷驱动到冰川边缘。

 

 

 

他们报告了在融化季节，甲烷—过饱和水（CH4(aq)）持续从冰盖中的连续输出。

 

 

 

结果表明，冰盖覆盖着广泛的、生物活性强的产甲烷湿地，冰川下水文学对于控制来自冰盖的甲烷通量至关重要，此类环境因素以前被低估了，应该在地球的甲烷预算中加以考虑。

 

 

 

▲ Abstract

 

Ice sheets are currently ignored in global methane budgets. Although ice sheets have been proposed to contain large reserves of methane that may contribute to a rise in atmospheric methane concentration if released during periods of rapid iceretreat, no data exist on the current methane footprint of ice sheets. Here we find that subglacially produced methane is rapidly driven to the ice margin by the efficient drainage system of a subglacial catchment of the Greenland ice sheet. We report the continuous export of methane-supersaturated waters (CH4(aq)) from the ice-sheet bed during the melt season. Pulses of high CH4(aq) concentration coincide with supraglacially forced subglacial flushing events, confirming a subglacial source and highlighting the influence of melt on methane export. Sustained methane fluxes over the melt season are indicative of subglacial methane reserves that exceed methane export, with an estimated 6.3 tonnes (discharge-weighted mean; range from 2.4 to 11 tonnes) of CH4(aq) transported laterally from the ice-sheet bed. Stable-isotope analyses reveal a microbial origin for methane, probably from a mixture of inorganic and ancient organic carbon buried beneath the ice. We show that subglacial hydrology is crucial for controlling methane fluxes from the ice sheet, with efficient drainage limiting the extent of methane oxidation to about 17 per cent of methane exported. Atmospheric evasion is the main methane sink once run off reaches the ice margin, with estimated diffusive fluxes (4.4 to 28 millimoles of CH4 per square metre per day) rivalling that of major world rivers. Overall, our results indicate that ice sheets overlie extensive, biologically active methanogenic wetlands and that high rates of methane export to the atmospherecan occur via efficient subglacial drainage pathways. Our findings suggest that such environments have been previously underappreciated and should be consideredin Earth’s methane budget.

 

 

 

Capture of nebular gases during Earth’s accretion is preserved in deep-mantle neon

 

地球吸积过程中捕捉到的星云气体保存在深地幔氖中

 

▲ 作者：Curtis D. Williams、Sujoy Mukhopadhyay 

 

▲ 链接：

 

https://www.nature.com/articles/s41586-018-0771-1

 

 

 

▲ 摘要：

 

行星内部捕获星云气体的证据将对行星形成模型造成重要的限制。这些约束包括吸积时间尺度、热演化、挥发性成分和行星氧化还原态。

 

 

 

目前，在地球内部存在这种气体的证据仍然存在争议。与其他生命必须的化学元素不同，氖（Ne）是惰性的，意味着它不会随化学和生物过程发生变化。

 

 

 

在本文中，同位素测量深地幔揭示20Ne/22Ne比率高达13.03±0.04。这些比值明显高于太阳—风辐照物质和CI球粒陨石的比值，这需要在地幔深处存在星云氖。

 

 

 

▲ Abstract

 

Evidence for the capture of nebular gases by planetary interiors would place important constraints on models of planet formation. These constraints include accretion timescales, thermal evolution, volatile compositions and planetary redox states. Retention of nebular gases by planetary interiors also constrains the dynamics of outgassing and volatile loss associated with the assembly and ensuing evolution of terrestrial planets. But evidence for such gases in Earth’s interior remains controversia. The ratio of the two primordial neon isotopes, 20Ne/22Ne, is significantly different for the three potential sources of Earth’s volatiles: nebular gas, solar-wind-irradiated material and CI chondrites. Therefore, the 20Ne/22Ne ratio is a powerful tool for assessingthe source of volatiles in Earth’s interior. Here we present neon is otope measurements from deep mantle plumes that reveal 20Ne/22Ne ratios of up to 13.03 ± 0.04 (2 standard deviations). These ratiosare demonstrably higher than those for solar-wind-irradiated material and CI chondrites, requiring the presence of nebular neon in the deep mantle. Furthermore, we determine a 20Ne/22Ne ratio for the primordial plume mantle of 13.23 ± 0.22 (2 standard deviations), which is indistinguishable from the nebular ratio, providing robust evidence for a reservoir of nebular gas preserved in the deep mantle today. The acquisition of nebular gases requires planetary embryos to grow to sufficiently large mass before the dissipation of the protoplanetary disk. Our observations also indicate distinct 20Ne/22Ne ratios between deep mantle plumes and mid-ocean-ridge basalts, which is best explained by addition of a chondritic component to the shallower mantle during the main phase of Earth’s accretion and by subsequent recycling of seawater-derived neon in platetectonic processes.

 

 

 

生物学Biology

 

 

 

Identifying the pathways required for coping behaviours associated with sustained pain

 

识别与持续疼痛相关的应对行为所需的途径

 

▲ 作者：Tianwen Huang、Shing-Hong Lin、Nathalie M. Malewicz、Qiufu Ma , et al

 

▲ 链接：

 

https://www.nature.com/articles/s41586-018-0793-8

 

 

 

▲ 摘要：

 

动物和人类对伤害刺激有两种反应。第一种包括防止或限制伤害的反射性防御反应，例如一个人的手在接触热的物体时迅速缩回。

 

 

 

当第一行反应不能阻止损伤时，产生的疼痛会引发第二种应对反应——比如舔受伤部位以缓解疼痛。

 

 

 

这是两种不同的进化反应，但科学家一直无法解释这种现象的分子起源和信号传导路径。

 

 

 

本研究确定了深层次持续痛疼背后的神经信号通路，这种持续性疼痛在受伤后立刻发生。

 

 

 

同时还揭示了促使反射性戒断以避免伤害，以及随后的疼痛应对反应，存在不同的信号传导路径。这是首次阐明这些反应是如何在大脑以外的地方产生的。

 

 

 

▲ Abstract

 

Animals and humans display two types of response to noxious stimuli. The first includes reflexive defensive responses that prevent or limit injury; a well-known example of these responses is the quick withdrawal of one’s hand upon touching a hot object. When the first-line response fails to prevent tissue damage (for example, a finger is burnt), the resulting pain invokes a second-line coping response—such as licking the injured area to soothe suffering. However, the underlying neural circuits that drive these two strings of behaviour remain poorly understood. Here we show in mice that spinal neurons marked by coexpression of TAC1Cre and LBX1Flpo drive coping responses associated with pain. Ablation of these spinal neurons led to the loss of both persistent licking and conditioned aversion evoked by stimuli (including skin pinching and burn injury) that—in humans—produce sustained pain, without affecting any of the reflexive defensive reactions that we tested. This selective in difference to sustained pain resembles the phenotype seen in humans with lesions of medial thalamic nuclei. Consistently, spinal TAC1-lineage neuronsare connected to medial thalamic nuclei by direct projections and via indirect routes through the superior lateral parabrachial nuclei. Furthermore, the anatomical and functional segregation observed at the spinal level also applies to primary sensory neurons. For example, in response to noxious mechanical stimuli, MRGPRD- and TRPV1-positive nociceptors are required to elicit reflexive and coping responses, respectively. Our study therefore reveals a fundamental subdivision within the cutaneous somatosensory system, and challenges the validity of using reflexive defensive responses to measure sustained pain.

 

 

 

Structure of Plasmodium falciparum Rh5–CyRPA–Ripr invasion complex

 

恶性疟原虫体内由 Rh5–CyRPA–Ripr组成的蛋白复合物

 

▲ 作者：WilsonWong、RickHuang、SebastienMenant、ZhihengYu、AlanF. Cowman, et al 

 

▲ 链接：

 

https://www.nature.com/articles/s41586-018-0779-6

 

 

 

▲ 摘要：

 

疟疾每年导致全球约50万人死亡，其中恶性疟原虫是常见的一种疟原虫，导致了许多疟疾死亡病例。它在入侵人体细胞时，依靠一种蛋白复合物进入细胞内部。

 

 

 

本文中，研究人员利用低温冷冻电子显微镜技术，首次描绘出恶性疟原虫体内由Rh5、CyPRA和Ripr三种蛋白质组成的蛋白复合物的三维结构图。

 

 

 

疟原虫依靠这种蛋白复合物与人体血液中红细胞内部的受体建立联系，从而进入红细胞内部并导致疾病。

 

 

 

揭示这种蛋白复合物的三维结构，有助深入理解疟原虫入侵细胞机制，并找出阻断其感染的方法，在此基础上有可能开发出针对恶性疟原虫的疫苗。

 

 

 

▲ Abstract

 

Plasmodium falciparum causes the severe form of malaria that has high levels of mortality in humans. Blood-stage merozoites of P. falciparum invade erythrocytes, and this requires interactions between multiple ligands from the parasite and receptors in hosts. These interactions include the binding of the Rh5–CyRPA–Ripr complex with the erythrocyte receptor basigin1, which is an essential step for entry into human erythrocytes. Here we show thatthe Rh5–CyRPA–Ripr complex binds the erythrocyte cell line JK-1 significantlybetter than does Rh5 alone, and that this binding occurs through the insertion of Rh5 and Ripr into host membranes as a complex with high molecular weight. We report a cryo-electron microscopy structure of the Rh5–CyRPA–Ripr complex at subnanometre resolution, which reveals the organization of this essential invasion complex and the mode of interactions between members of the complex, and shows that CyRPA is a critical mediator of complex assembly. Our structure identifies blades 4–6 of the β-propeller of CyRPA as contact sites for Rh5 and Ripr. The limited contacts between Rh5–CyRPA and CyRPA–Ripr are consistent with the dissociation of Rh5 and Ripr from CyRPA for membrane insertion. A comparision of the crystal structure of Rh5–basigin with the cryo-electron microscopy structure of Rh5–CyRPA–Ripr suggests that Rh5 and Ripr are positioned parallel to the erythrocyte membrane before membrane insertion. This provides information on the function of this complex, and thereby provides insights into invasion by P.falciparum.

 

 

 

Loss of ADAR1 in tumours overcomesresistance to immune checkpoint blockade

 

肿瘤中的ADAR1缺失能影响免疫疗法效果

 

▲ 作者：Jeffrey J. Ishizuka、Robert T. Manguso、W. Nicholas Haining, etal 

 

▲ 链接：

 

https://www.nature.com/articles/s41586-018-0768-9

 

 

 

▲ 摘要：

 

大多数癌症患者要么对免疫检查点阻滞没有响应，要么对其产生耐药性，这往往是因为获得性突变削弱了抗原呈现。

 

 

 

在这里，研究人员展示了肿瘤细胞中RNA编辑酶ADAR1功能的丧失，使肿瘤对免疫治疗具有敏感性，并克服了对检查点阻滞的抵抗。

 

 

 

在ADAR1缺失的情况下，干扰素诱导的RNA的A-to-I编辑减少，导致PKR和MDA5检测双链RNA配体；这分别导致生长抑制和肿瘤炎症。该成果有助于开发针对免疫疗法失效的一般策略。

 

 

 

▲ Abstract

 

Most patients with cancer either do not respond to immune checkpoint blockade or develop resistance to it, often because of acquired mutations that impair antigen presentation. Here we show that loss of function of the RNA-editing enzyme ADAR1 in tumour cells profoundly sensitizes tumours to immunotherapy and overcomes resistance to checkpoint blockade. In the absence of ADAR1, A-to-I editing of interferon-inducible RNA species is reduced, leading to double-stranded RNA ligand sensing by PKR and MDA5; this results in growth inhibition and tumour inflammation, respectively. Loss of ADAR1 overcomes resistance to PD-1 checkpoint blockade caused by inactivation of antigen presentation by tumour cells. Thus, effective anti-tumour immunity is constrained by inhibitory checkpoints such as ADAR1 that limit the sensing of innate ligands. The induction of sufficient inflammation in tumours that are sensitized to interferon can bypass the therapeutic requirement for CD8+ T cell recognition of cancer cells and may provide a general strategy to overcome immunotherapy resistance.

 

 

 

（唐一尘）