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​《自然》(20210429出版)一周论文导读

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发表于 2021-5-2 09:48:02 | 显示全部楼层 |阅读模式

编译 | 李言

Nature, 29 April 2021, Volume 592 Issue 7856

《自然》2021年4月29日,第592卷,7856期

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天文学Astronomy

X-ray quasi-periodic eruptions from two previously quiescent galaxies

两个之前静止的星系的X射线准周期性爆发

▲ 作者:R. Arcodia, A. Merloni, K. Nandra, J. Buchner, M. Salvato, et al.

▲ 链接:

https://www.nature.com/articles/s41586-021-03394-6

▲ 摘要

准周期性爆发(QPEs)是每隔几小时发生一次的x射线辐射的高振幅爆发,通常起源于星系核的中心特大质量黑洞附近。在此,我们报告了对另外两个星系的QPEs的观测,这是通过对X射线天空的一半进行系统的盲搜获得的。

这些星系的光谱没有显示出黑洞活动的特征,这表明活跃星系核的一个典型的预先存在的吸积流并不需要触发这些事件。事实上,这里报告的QPEs的周期、振幅和剖面与当前的模型不一致,这些模型在吸积盘中引发了辐射压力驱动的不稳定性。

相反,QPEs可能是由一个轨道上的致密物体驱动的。此外,它们的观测性质要求次级天体的质量要比主体的质量小得多,未来的X射线观测可能会限制由于轨道演化而导致的周期变化。

▲ Abstract

Quasi-periodic eruptions (QPEs) are very-high-amplitude bursts of X-ray radiation recurring every few hours and originating near the central supermassive black holes of galactic nuclei. Here we report observations of QPEs in two further galaxies, obtained with a blind and systematic search of half of the X-ray sky. The optical spectra of these galaxies show no signature of black hole activity, indicating that a pre-existing accretion flow that is typical of active galactic nuclei is not required to trigger these events. Indeed, the periods, amplitudes and profiles of the QPEs reported here are inconsistent with current models that invoke radiation-pressure-driven instabilities in the accretion disk. Instead, QPEs might be driven by an orbiting compact object. Furthermore, their observed properties require the mass of the secondary object to be much smaller than that of the main body, and future X-ray observations may constrain possible changes in their period owing to orbital evolution.


化学Chemistry


Transition from an atomic to a molecular Bose–Einstein condensate

从原子到分子的玻色-爱因斯坦凝聚物的跃迁

▲ 作者:Zhendong Zhang, Liangchao Chen, Kai-Xuan Yao & Cheng Chin

▲ 链接:

https://www.nature.com/articles/s41586-021-03443-0

▲ 摘要

分子量子气体(即超冷高密度分子气体)有许多潜在的应用方式,包括化学反应的量子控制、精密测量、量子模拟和量子信息处理。在此,我们报告在g波费希巴赫共振附近的原子凝聚物中,通过诱导对相互作用制备旋转分子的二维玻色-爱因斯坦凝聚物(BECs)。

陷阱的几何形状和分子的低温有助于减少非弹性损失,确保热平衡。从状态方程测量,我们确定分子散射长度为+ 220(±30)玻尔半径(95%置信区间)。我们还研究了强耦合条件下的解对动力学,发现在费什巴赫共振附近的动力学时间尺度符合统一极限。

▲ Abstract

Molecular quantum gases (that is, ultracold and dense molecular gases) have many potential applications, including quantum control of chemical reactions, precision measurements, quantum simulation and quantum information processing. Here we report the preparation of two-dimensional Bose–Einstein condensates (BECs) of spinning molecules by inducing pairing interactions in an atomic condensate near a g-wave Feshbach resonance. The trap geometry and the low temperature of the molecules help to reduce inelastic loss, ensuring thermal equilibrium. From the equation-of-state measurement, we determine the molecular scattering length to be + 220(±30) Bohr radii (95% confidence interval). We also investigate the unpairing dynamics in the strong coupling regime and find that near the Feshbach resonance the dynamical timescale is consistent with the unitarity limit.


Direct observation of chemical short-range order in a medium-entropy alloy

对中熵合金中化学短程顺序的直接观察

▲ 作者:Xuefei Chen, Qi Wang, Zhiying Cheng, Mingliu Zhu, Hao Zhou, Ping Jiang, et al.

▲ 链接:

https://www.nature.com/articles/s41586-021-03428-z

▲ 摘要

在此,我们发现使用适当的区域轴、微/纳米束衍射以及通过透射电子显微镜的原子分辨率成像和化学映射,可以明确地发现在面心立方VCoNi浓缩溶液中的CSRO。

我们的互补工具套件提供了关于CSRO的程度/程度、原子填充配置和化学物种对邻近晶格面/位的优先占用的具体信息。对最近原子壳层上的CSRO阶数参数和对相关性的建模表明,CSRO源自最近邻偏好,朝向不同的(V-Co和V-Ni)对,并避免了V-V对。

我们的发现为鉴定浓溶液合金中的CSRO提供了一种方法。我们还使用原子应变映射来展示由CSRO增强的位错相互作用,阐明这些CSRO对变形时塑性机制和力学性能的影响。

▲ Abstract

Here we discover that, using an appropriate zone axis, micro/nanobeam diffraction, together with atomic-resolution imaging and chemical mapping via transmission electron microscopy, can explicitly reveal CSRO in a face-centred-cubic VCoNi concentrated solution. Our complementary suite of tools provides concrete information about the degree/extent of CSRO, atomic packing configuration and preferential occupancy of neighbouring lattice planes/sites by chemical species. Modelling of the CSRO order parameters and pair correlations over the nearest atomic shells indicates that the CSRO originates from the nearest-neighbour preference towards unlike (V−Co and V−Ni) pairs and avoidance of V−V pairs. Our findings offer a way of identifying CSRO in concentrated solution alloys. We also use atomic strain mapping to demonstrate the dislocation interactions enhanced by the CSROs, clarifying the effects of these CSROs on plasticity mechanisms and mechanical properties upon deformation.


Direct assessment of the acidity of individual surface hydroxyls

直接评估单个表面羟基的酸度

▲ 作者:Margareta Wagner, Bernd Meyer, Martin Setvin, Michael Schmid & Ulrike Diebold

▲ 链接:

https://www.nature.com/articles/s41586-021-03432-3

▲ 摘要

矿物表面的酸度是通过半经验概念来估计的,如键序价和,并越来越多地采用第一性原理分子动力学模拟。目前,这种预测还无法通过实验测量得到验证,比如在整个表面上或者在某些情况下的单个晶体刻面的零电荷点。

在此,我们评估了In2O3(111)上单个羟基的酸性。In2O3(111)是一种具有四种不同表面氧原子的模型氧化物。我们用非接触原子力显微镜的尖端探测了它们的氢键强度,发现了与密度泛函理论计算的定量一致。

通过将结果与气相分子的质子亲合能联系起来,我们以原子的精度确定了In2O3不同表面位点的质子亲合能。

▲ Abstract

For mineral surfaces, the acidity is estimated by semi-empirical concepts, such as bond-order valence sums, and increasingly modelled with first-principles molecular dynamics simulations. At present, such predictions cannot be tested—experimental measures, such as the point of zero charge, integrate over the whole surface or, in some cases, individual crystal facets. Here we assess the acidity of individual hydroxyl groups on In2O3(111)—a model oxide with four different types of surface oxygen atom. We probe the strength of their hydrogen bonds with the tip of a non-contact atomic force microscope and find quantitative agreement with density functional theory calculations. By relating the results to known proton affinities of gas-phase molecules, we determine the proton affinity of the different surface sites of In2O3 with atomic precision.


地球科学Geoscience


Accelerated global glacier mass loss in the early twenty-first century

21世纪初全球冰川数量的加速流失

▲ 作者:Romain Hugonnet, Robert McNabb, Etienne Berthier, et al

▲ 链接:

https://www.nature.com/articles/s41586-021-03436-z

▲ 摘要

在此,我们揭示了冰川质量在21世纪早期加速流失的模式。我们的研究显示,2000-2019年期间,冰川每年损失267±160亿吨,相当于观测到的海平面上升的21±3%。

我们发现,质量损失的加速度为每年每10年48±160亿吨,这解释了观测到的6%至19%海平面上升的加速度。特别是,冰盖外围的冰川变薄的速度在过去20年里翻了一番。目前,与格陵兰岛或南极冰原分别相比,冰川的质量损失更大,速度相近或更快。

通过揭示许多地区的质量变化模式,我们发现冰川的对比波动与降水和温度的年代际变化一致。包括北大西洋异常的质量减少,美国西北部冰川的异常强烈减少,以及喀喇昆仑山脉异常增多的明显终结。

▲ Abstract

Here we reveal the accelerated, albeit contrasting, patterns of glacier mass loss during the early twenty-first century. We show that during 2000–2019, glaciers lost a mass of 267 ± 16 gigatonnes per year, equivalent to 21 ± 3 per cent of the observed sea-level rise. We identify a mass loss acceleration of 48 ± 16 gigatonnes per year per decade, explaining 6 to 19 per cent of the observed acceleration of sea-level rise. Particularly, thinning rates of glaciers outside ice sheet peripheries doubled over the past two decades. Glaciers currently lose more mass, and at similar or larger acceleration rates, than the Greenland or Antarctic ice sheets taken separately. By uncovering the patterns of mass change in many regions, we find contrasting glacier fluctuations that agree with the decadal variability in precipitation and temperature. These include a North Atlantic anomaly of decelerated mass loss, a strongly accelerated loss from northwestern American glaciers, and the apparent end of the Karakoram anomaly of mass gain.


Plume-driven recratonization of deep continental lithospheric mantle

地幔柱驱动岩石圈地幔的克拉通再生

▲ 作者:Jingao Liu, D. Graham Pearson, Lawrence Hongliang Wang, et al.

▲ 链接:

https://www.nature.com/articles/s41586-021-03395-5

▲ 摘要

克拉通的地幔根被认为是地球大陆长期稳定的特征,但也有证据表明它们在最近和更遥远的过去发生了分裂。在此,我们研究了加拿大北极克拉通岩石圈的地幔橄榄岩携带的地幔包体和地震学,其中包括12.7亿年前受麦肯齐地幔柱事件影响的地区。

我们论证了地幔柱上升流对奴隶克拉通北部约200公里厚克拉通岩石圈地幔的破坏和再活化的重要作用。通过数值模拟,我们展示了在两个厚克拉通地块之间的岩石圈变薄的区域中,麦肯齐地幔柱事件产生的新的熔融地幔残余体是如何被捕获的。

我们的结果确定在山根被破坏后,克拉通能够愈合并恢复到原来的厚度。

▲ Abstract

The mantle roots of cratons are renowned as being long-lived, stable features of Earth’s continents, but there is also evidence of their disruption in the recent and more distant past. Here we study kimberlite-borne mantle xenoliths and seismology across a transect of the cratonic lithosphere of Arctic Canada, which includes a region affected by the Mackenzie plume event 1.27 billion years ago. We demonstrate the important role of plume upwelling in the destruction and recratonization of roughly 200-kilometre-thick cratonic lithospheric mantle in the northern portion of the Slave craton. Using numerical modelling, we show how new, buoyant melt residues produced by the Mackenzie plume event are captured in a region of thinned lithosphere between two thick cratonic blocks. Our results identify a process by which cratons heal and return to their original lithospheric thickness after substantial disruption of their roots.


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