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《天然》论文导读:2019年1月3日

 

 
 
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
 
 
 
▲ 择要:
 
晶体质料根据其电子布局的差别可以分别为金属和绝缘体两大类。拓扑金属具有特别的能带布局,它包罗一些能带布局的奇点。
 
 
 
在绝大少数金属质料中,如许的Weyl点都市阔别费米面,但是要是如许的点恰恰坐落在费米面上,就会给出一类十分特别的电子布局:拓扑半金属——其费米面减少为费米点,能隙为0,且具有线性色散。
 
 
 
但集成到功效设置装备摆设中必要逾越质料的拓扑掩护特性并在高速下利用拓扑的本领。
 
 
 
本文使用绝对论电子衍射的晶体丈量结果证明,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,从而构成拓扑上差别的亚稳态相。
 
 
 
这项事情证明白超快利用固体拓扑特性的大概性,以及开辟以太赫兹频率事情的拓扑开关的大概性。
 
 
 
▲ 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
 
 
 
▲ 择要:
 
自上世纪80年月初以来,大少数电子产物都依赖于利用互补的金属氧化物半导体(CMOS)晶体管。
 
 
 
但是,CMOS事情原理,包罗由绝缘栅控制的可开关半导体电导,在很大水平上连结稳定,纵然晶体管被减少到10纳米。而在当今数据期间,数据爆炸带来了对更高效盘算机的需求。
 
 
 
文章中,研讨者展现了一种制造新型逻辑器件和存储器件的要领。相比于传统 CMOS 集成的微处置惩罚器,新微处置惩罚器能效可以失掉明显加强。
 
 
 
结果表现,与CMOS技能相比,新设置装备摆设具有更高的转换能量、较低的开关电压和加强的逻辑密度。
 
 
 
▲ 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.
 
 
 
 
情况Enviroment
 
 
 
 
Greenland melt drives continuous export of methane from the ice-sheet bed
 
格陵兰岛消融推进了冰盖甲烷的连续输入
 
▲ 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
 
 
 
▲ 择要:
 
在环球甲烷预算中,冰盖现在被纰漏了。只管有人提出,冰盖中蕴藏着少量甲烷,要是这些气体在冰层疾速衰退时期开释,大概会招致大气甲烷浓度上升,但现在还没有关于冰盖甲烷脚印的数据。
 
 
 
在这里,研讨职员发明,格陵兰冰盖的冰川下集水区的有用排水体系敏捷地将冰川下孕育发生的甲烷驱动到冰川边沿。
 
 
 
他们陈诉了在消融季候,甲烷—过饱和水(CH4(aq))连续从冰盖中的一连输入。
 
 
 
结果评释,冰盖笼罩着遍及的、生物活性强的产甲烷湿地,冰川下水文学对付控制来自冰盖的甲烷通量至关紧张,此类情况要素曩昔被低估了,应该在地球的甲烷预算中加以思量。
 
 
 
▲ 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
 
地球吸积历程中捕获到的星云气体生存在深地幔氖中
 
▲ 作者:Curtis D. Williams、Sujoy Mukhopadhyay 
 
▲ 链接:
 
https://www.nature.com/articles/s41586-018-0771-1
 
 
 
▲ 择要:
 
行星外部捕捉星云气体的证据将对行星构成模子形成紧张的限定。这些束缚包罗吸积工夫标准、热演化、挥发性身分和行星氧化复原态。
 
 
 
现在,在地球外部存在这种气体的证据仍旧存在争议。与其他生命必需的化学元素差别,氖(Ne)是惰性的,意味着它不会随化学和生物历程产生变革。
 
 
 
在本文中,同位素丈量深地幔展现20Ne/22Ne比率高达13.03±0.04。这些比值显着高于太阳—风辐照物质和CI球粒陨石的比值,这必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
 
辨认与连续痛苦悲伤相干的应对举动所需的途径
 
▲ 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
 
 
 
▲ 择要:
 
植物和人类对损伤安慰有两种反响。第一种包罗防备或限定损伤的反射性防备反响,比方一小我私家的手在打仗热的物体时敏捷缩回。
 
 
 
当第一行反响不克不及制止毁伤时,孕育发生的痛苦悲伤会引发第二种应对反响——好比舔受伤部位以缓解痛苦悲伤。
 
 
 
这是两种差别的退化反响,但迷信家不停无法表明这种征象的分子劈头和信号传导途径。
 
 
 
本研讨确定了深条理连续痛疼面前的神经信号通路,这种连续性痛苦悲伤在受伤后立即产生。
 
 
 
同时还展现了促使反射性戒断以制止损伤,以及随后的痛苦悲伤应对反响,存在差别的信号传导途径。这是初次分析这些反响是怎样在大脑以外的中央孕育发生的。
 
 
 
▲ 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构成的卵白复合物
 
▲ 作者:WilsonWong、RickHuang、SebastienMenant、ZhihengYu、AlanF. Cowman, et al 
 
▲ 链接:
 
https://www.nature.com/articles/s41586-018-0779-6
 
 
 
▲ 择要:
 
疟疾每年招致环球约50万人殒命,此中恶性疟原虫是罕见的一种疟原虫,招致了很多疟疾殒命病例。它在入侵人体细胞时,依赖一种卵白复合物进入细胞外部。
 
 
 
本文中,研讨职员使用高温冷冻电子显微镜技能,初次刻画出恶性疟原虫体内由Rh5、CyPRA和Ripr三种卵白质构成的卵白复合物的三维布局图。
 
 
 
疟原虫依赖这种卵白复合物与人体血液中红细胞外部的受体创建接洽,从而进入红细胞外部并招致疾病。
 
 
 
展现这种卵白复合物的三维布局,有助深化明白疟原虫入侵细胞机制,并找出阻断其熏染的要领,在此底子上有大概开辟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结果
 
▲ 作者:Jeffrey J. Ishizuka、Robert T. Manguso、W. Nicholas Haining, etal 
 
▲ 链接:
 
https://www.nature.com/articles/s41586-018-0768-9
 
 
 
▲ 择要:
 
大少数癌症患者要么对免疫查抄点停滞没有相应,要么对其孕育发生耐药性,这每每是由于得到性渐变减弱了抗原出现。
 
 
 
在这里,研讨职员展现了肿瘤细胞中RNA编辑酶ADAR1功效的丧失,使肿瘤对免疫医治具有敏理性,并降服了对查抄点停滞的抵挡。
 
 
 
在ADAR1缺失的环境下,滋扰素诱导的RNA的A-to-I编辑淘汰,招致PKR和MDA5检测双链RNA配体;这辨别招致生长克制和肿瘤炎症。该结果有助于开辟针对免疫疗法生效的一样平常计谋。
 
 
 
▲ 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.
 
 
 
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