《自然》（20190124出版）一周论文导读

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《自然》（20190124出版）一周论文导读

2019 年 1 月 25 日 科学网

翻译 | 宗华

Nature, 24 January 2019, Volume 565 Issue 7740

《自然》2019年1月24日第7740期565卷

地质学Geology

Southward propagation of Nazca subduction along the Andes

安第斯山脉沿线纳斯卡俯冲的向南扩展

▲ 作者：Yi-Wei Chen, Jonny Wu & John Suppe

▲ 链接：

https://www.nature.com/articles/s41586-018-0860-1

▲ 摘要：

安第斯山脉边缘是长期持续俯冲的板块构造模式。但自中生代晚期（过去1亿年左右）以来其地质情况一直未处于稳定状态。

这里，利用层析数据，我们重现了俯冲纳斯卡板块的板块构造几何学。这使得我们重建中生代以来的安第斯板块构造。

我们的模型显示，现在的纳斯卡俯冲阶段开始于白垩纪晚期（约8000万年前）的安第斯山脉北部（南纬5°），然后向南扩展，在新生代早期（约5500万年前）抵达安第斯山脉南部（南纬40°）。

▲ Abstract

The Andean margin is the plate-tectonic paradigm for long-lived, continuous subduction, yet its geology since the late Mesozoic era (the past 100 million years or so) has been far from steady state. Here, using tomographic data, we recreate the plate-tectonic geometry of the subducted Nazca slab, which enables us to reconstruct Andean plate tectonics since the late Mesozoic. Our model suggests that the current phase of Nazca subduction began at the northern Andes (5° S) during the late Cretaceous period (around 80 million years ago) and propagated southwards, reaching the southern Andes (40° S) by the early Cenozoic era (around 55 million year ago).

天文学Astronomy

A recurrent nova super-remnant in the Andromeda galaxy

仙女座星系中反复出现的新星超高密度残骸

▲ 作者：M. J. Darnley, R. Hounsell, T. J. O’Brien, M. Henze, P. Rodríguez-Gil, et al

▲ 链接：

https://www.nature.com/articles/s41586-018-0825-4

▲ 摘要：

白矮星上面的氢吸积引发了经典的新星爆发。

同时，接近白矮星（1.4个太阳质量）质量上限，来自伴星的氢快速吸积（每年约为太阳质量的10⁻⁷）带来了时间跨度为几年到几十年的频繁爆发。这种双星系统被称为再发新星。

这里，我们报告称，重复出现最频繁的新星——仙女座星系中每年都会爆发的M31N 2008-12a，的确由此类超高密度残骸环绕。据估测，其大小至少有134×90秒差距。

▲ Abstract

The accretion of hydrogen onto a white dwarf star ignites a classical nova eruption. Close to the upper mass limit of a white dwarf (1.4 solar masses), rapid accretion of hydrogen (about 10−7 solar masses per year) from a stellar companion leads to frequent eruptions on timescales of years to decades. Such binary systems are known as recurrent novae. Here we report that the most frequently recurring nova, M31N 2008-12a in the Andromeda galaxy (Messier 31 or NGC 224), which erupts annually, is indeed surrounded by such a super-remnant with a projected size of at least 134 by 90 parsecs.

物理学Physics

Unveiling the double-well energy landscape in a ferroelectric layer

揭示铁电层中双阱能量图景

▲ 作者：Michael Hoffmann, Franz P. G. Fengler, Melanie Herzig, et al

▲ 链接：

https://www.nature.com/articles/s41586-018-0854-z

▲ 摘要：

近1个世纪前被发现的铁电材料的性质带来了广泛的应用，比如数字信息存储、热电能量转换和神经形态计算。

最近，研究证实，铁电体可拥有负电容，从而可能使传统电子产品的能量效率超越基本限制。

这里，我们报告了铁电体Hf_0.5Zr_0.5O₂薄层中内在双阱能量图景的电学测量结果。

为做到这一点，我们将铁电体融合进带有第二介电层的异质结构电容器，以防止转换期间极化电荷的立即屏蔽。这些结果表明，负电容源自双阱图景中的能量障碍。

▲ Abstract

The properties of ferroelectric materials, which were discovered almost a century ago, have led to a huge range of applications, such as digital information storage, pyroelectric energy conversion and neuromorphic computing. Recently, it was shown that ferroelectrics can have negative capacitance6, which could improve the energy efficiency of conventional electronics beyond fundamental limits. Here we report electrical measurements of the intrinsic double-well energy landscape in a thin layer of ferroelectric Hf_0.5Zr_0.5O₂. To achieve this, we integrated the ferroelectric into a heterostructure capacitor with a second dielectric layer to prevent immediate screening of polarization charges during switching. These results show that negative capacitance has its origin in the energy barrier in a double-well landscape.

Spatially resolved steady-state negative capacitance

空间分辨率的稳定态负电容

▲ 作者：Ajay K. Yadav, Kayla X. Nguyen, Zijian Hong, et al

▲ 链接：

https://www.nature.com/articles/s41586-018-0855-y

▲ 摘要：

负电容是一种新发现的铁电材料状态。其通过利用一个通常无法接近的热力学空间区域，有希望应用于电子产品。

这里，我们展示了对铁电—介电异质结构中稳定态负电容的直接测量结果。

我们利用电子显微镜并辅以SrTiO₃/PbTiO₃超晶格中相场和基于第一原理方法的模拟结果，在原子分辨率水平上直接确定了铁电材料中负电容状态被稳定下来的局部区域。

▲ Abstract

Negative capacitance is a newly discovered state of ferroelectric materials that holds promise for electronics applications by exploiting a region of thermodynamic space that is normally not accessible. Here we demonstrate a direct measurement of steady-state negative capacitance in a ferroelectric–dielectric heterostructure. We use electron microscopy complemented by phase-field and first-principles-based simulations in SrTiO₃/PbTiO₃superlattices to directly determine, with atomic resolution, the local regions in the ferroelectric material where a state of negative capacitance is stabilized.

生态学Ecology

Large influence of soil moisture on long-term terrestrial carbon uptake

土壤湿度对长期陆地碳吸收的重要影响

▲ 作者：Julia K. Green, Sonia I. Seneviratne, Alexis M. Berg, et al

▲ 链接：

https://www.nature.com/articles/s41586-018-0848-x

▲ 摘要：

尽管陆地生物圈吸收了约25%的人类排放二氧化碳，但陆地碳吸收速率仍存在高度的不确定性，并且导致气候预测的不确定性。

这里，我们利用一系列试验中来自4个地球系统模型的数据输出，分析了陆地净生物群生产力对土壤湿度变化的响应，并且发现土壤湿度变化和趋势在整个21世纪诱发大量二氧化碳通量。

作为光合作用和净生态系统交换对土壤水分可利用度的响应以及温度上升和陆气相互作用引发的蒸气压差的结果，次季节和年际间土壤湿度变化产生了二氧化碳。

▲ Abstract

Although the terrestrial biosphere absorbs about 25 per cent of anthropogenic carbon dioxide (CO₂) emissions, the rate of land carbon uptake remains highly uncertain, leading to uncertainties in climate projections. Here we use the data output from four Earth system models from a series of experiments to analyse the responses of terrestrial net biome productivity to soil-moisture changes, and find that soil-moisture variability and trends induce large CO₂fluxes throughout the twenty-first century. Subseasonal and interannual soil-moisture variability generate CO₂as a result of the nonlinear response of photosynthesis and net ecosystem exchange to soil-water availability and of the increased temperature and vapour pressure deficit caused by land–atmosphere interactions.

光学Optics

Computational periscopy with an ordinary digital camera

带有普通数码相机的计算潜望镜

▲ 作者：Charles Saunders, John Murray-Bruce & Vivek K Goyal

▲ 链接：

https://www.nature.com/articles/s41586-018-0868-6

▲ 摘要：

计算从不同方向抵达的光线数量使扩散反射面得以在潜望镜中扮演镜子角色，即在障碍附近进行非视距成像。

由于潜望镜技术迄今依赖于同飞行时间成正比的光传播距离，因此它大多数利用昂贵且专业化的超快光学系统进行。

这里，我们引入一种二维计算潜望镜技术。其仅要求普通数码相机捕捉的单幅照片。

我们的技术复原了不透明物体的位置以及物体背后的景象，而无须得到控制或者随时间变化的照明。此时，物体和景象均在相机的视线之外。

▲ Abstract

Computing the amounts of light arriving from different directions enables a diffusely reflecting surface to play the part of a mirror in a periscope—that is, perform non-line-of-sight imaging around an obstruction. Because computational periscopy has so far depended on light-travel distances being proportional to the times of flight, it has mostly been performed with expensive, specialized ultrafast optical systems. Here we introduce a two-dimensional computational periscopy technique that requires only a single photograph captured with an ordinary digital camera. Our technique recovers the position of an opaque object and the scene behind (but not completely obscured by) the object, when both the object and scene are outside the line of sight of the camera, without requiring controlled or time-varying illumination.

生物学Biology

High levels of auxin signalling define the stem-cell organizer of the vascular cambium

高浓度生长素信号定义维管形成层的干细胞“组织者”

▲ 作者：Ondřej Smetana, Riikka Mäkilä, Munan Lyu, Ali Amiryousefi, et al

▲ 链接：

https://www.nature.com/articles/s41586-018-0837-0

▲ 摘要：

作为一种木质组织，木材源自维管形成层的细胞扩散。木质部和韧皮部分别在形成层里面和外面产生。

植物的形态发生通常由“组织者”细胞协调。这种细胞指挥相邻干细胞经历编程细胞的分裂和分化。

维管形成层干细胞的位置以及“组织者”概念能否应用于形成层目前仍然未知。

这里，利用对拟南芥的谱系追踪和分子遗传学研究，我们证实，拥有木质部身份的细胞指挥邻近维管形成层细胞分裂并且作为干细胞发挥作用。因此，这些木质部身份的细胞构成了“组织者”。

▲ Abstract

Wood, a type of xylem tissue, originates from cell proliferation of the vascular cambium. Xylem is produced inside, and phloem outside, of the cambium. Morphogenesis in plants is typically coordinated by organizer cells that direct the adjacent stem cells to undergo programmed cell division and differentiation. The location of the vascular cambium stem cells and whether the organizer concept applies to the cambium are currently unknown. Here, using lineage-tracing and molecular genetic studies in the roots of Arabidopsis thaliana, we show that cells with a xylem identity direct adjacent vascular cambial cells to divide and function as stem cells. Thus, these xylem-identity cells constitute an organizer.

Molecular control of macroscopic forces drives formation of the vertebrate hindgut

宏观力量的分子控制驱动脊椎动物后肠形成

▲ 作者：Nandan L. Nerurkar, ChangHee Lee, L. Mahadevan & Clifford J. Tabin

▲ 链接：

https://www.nature.com/articles/s41586-018-0865-9

▲ 摘要：

胚胎肠道管是一种可发育成呼吸道和肠胃道的圆柱结构。这里，我们研究了鸡胚中肠道管形态形成早期背后宏观力量的分子控制。

我们发现，后肠由通过固定尾部肠门（CIP）的集体细胞运动形成，而非由CIP本身的运动形成。

同时，结合体内成像、生物物理学分析以及利用分子和胚胎学方法的数学建模，我们辨别出驱动形成后肠的内胚层中细胞运动的收缩力梯度。

这种力梯度反过来是为了响应成纤维细胞生长因子信号的形态生长梯度而建立的。

▲ Abstract

The embryonic gut tube is a cylindrical structure from which the respiratory and gastrointestinal tracts develop. Here we investigate the molecular control of macroscopic forces underlying early morphogenesis of the gut tube in the chick embryo. We find that the hindgut is formed by collective cell movements through a stationary caudal intestinal portal (CIP), rather than by movement of the CIP itself. Further, combining in vivo imaging, biophysics and mathematical modelling with molecular and embryological approaches, we identify a contractile force gradient that drives cell movements in the hindgut-forming endoderm. The force gradient, in turn, is established in response to a morphogenic gradient of fibroblast growth factor signalling.