《自然》（20181101出版）一周论文导读

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《自然》（20181101出版）一周论文导读

2018 年 11 月 1 日 科学网

Nature, Volume 563 Issue 7729, 1 November 2018

《自然》2018年11月1日第7729期563卷

天文学Astronomy

The merger that led to the formation of the Milky Way’s inner stellar halo and thick disk

碰撞导致了银河系内部的恒星晕和厚银盘的形成

▲ 作者：Amina Helmi、CarineBabusiaux、Helmer H.Koppelman、DavideMassari、JovanVeljanoski、Anthony G. A.Brown

▲ 链接：

https://www.nature.com/articles/s41586-018-0625-x

▲ 摘要：

银河系由许多结构组成：核球、旋臂、银盘和银晕。通过观察各个恒星的年龄、化学特性、分布和运动，人们有可能确定它们是如何组合起来的。

该研究分析了最新发布的来自盖亚太空望远镜以及阿帕奇天文台星系演化实验的数据，发现大约100亿年前，银河系与一个矮星系碰撞，导致银河系银晕内充满了恒星，并且使银盘增厚。

该矮星系的质量约为当时银河系质量的1/4。银河系与这样大小的星系碰撞，会加热预先已存在的银盘，从而形成如今所存在的较厚的银盘。

研究人员将这个撞击星系命名为“盖亚—恩克拉多斯”。

▲ Abstract

The assembly of our Galaxy can be reconstructed using the motions and chemistry of individual stars. Chemo-dynamical studies of the stellar halo near the Sun have indicated the presence of multiple components, such as streams and clumps, as well as correlations between the stars’ chemical abundances and orbital parameters. Recently, analyses of two large stellar surveys revealed the presence of a well populated elemental abundance sequence, two distinct sequences in the colour–magnitude diagram and a prominent, slightly retrograde kinematic structure in the halo near the Sun, which may trace an important accretion event experienced by the Galaxy. However, the link between these observations and their implications for Galactic history is not well understood. Here we report an analysis of the kinematics, chemistry, age and spatial distribution of stars that are mainly linked to two major Galactic components: the thick disk and the stellar halo. We demonstrate that the inner halo is dominated by debris from an object that at infall was slightly more massive than the Small Magellanic Cloud, and which we refer to as Gaia–Enceladus. The stars that originate in Gaia–Enceladus cover nearly the full sky, and their motions reveal the presence of streams and slightly retrograde and elongated trajectories. With an estimated mass ratio of four to one, the merger of the Milky Way with Gaia–Enceladus must have led to the dynamical heating of the precursor of the Galactic thick disk, thus contributing to the formation of this component approximately ten billion years ago. These findings are in line with the results of galaxy formation simulations, which predict that the inner stellar halo should be dominated by debris from only a few massive progenitors.

物理学Physics

Measurement-based quantum control of mechanical motion

基于测量的机械运动量子控制

▲ 作者：MassimilianoRossi、David Mason、Junxin Chen、YeghisheTsaturyan、AlbertSchliesser

▲ 链接：

https://www.nature.com/articles/s41586-018-0643-8

▲ 摘要：

利用对量子系统动力学的观察来控制量子系统十分复杂，原因是测量过程的反作用，即由于系统与测量仪器的耦合而引起的不可避免的量子干扰。

一种有效的测量方法是使每次干扰所获得的信息量最大化。然后，实时反馈可以抵消测量的反作用，并控制量子态的演化。

在这里，研究人员演示了基于测量的毫米大小膜谐振器运动的量子控制。

一个光学机械传感器能在其一小部分的毫秒级相干时间中解析谐振器的零点运动，整体测量效率接近统一。而一个电子反馈回路将这个位置记录转换成一个力，使谐振器模式冷却到它的量子基态。

▲ Abstract

Controlling a quantum system by using observations of its dynamics is complicated by the backaction of the measurement process—that is, the unavoidable quantum disturbance caused by coupling the system to a measurement apparatus. An efficient measurement is one that maximizes the amount of information gained per disturbance incurred. Real-time feedback can then be used to cancel the backaction of the measurement and to control the evolution of the quantum state. Such measurement-based quantum control has been demonstrated in the clean settings of cavity and circuit quantum electrodynamics, but its application to motional degrees of freedom has remained elusive. Here we demonstrate measurement-based quantum control of the motion of a millimetre-sized membrane resonator. An optomechanical transducer resolves the zero-point motion of the resonator in a fraction of its millisecond-scale coherence time, with an overall measurement efficiency close to unity. An electronic feedback loop converts this position record to a force that cools the resonator mode to its quantum ground state (residual thermal occupation of about 0.29). This occupation is nine decibels below the quantum-backaction limit of sideband cooling and six orders of magnitude below the equilibrium occupation of the thermal environment. We thus realize a long-standing goal in the field, adding position and momentum to the degrees of freedom that are amenable to measurement-based quantum control, with potential applications in quantum information processing and gravitational-wave detectors.

人工智能 AI

The Moral Machine experiment

机器道德实验

▲ 作者：Edmond Awad、Sohan Dsouza、Richard Kim、JonathanSchulz、JosephHenrich、Azim Shariff、Jean-FrançoisBonnefon、Iyad Rahwan

▲ 链接：

https://www.nature.com/articles/s41586-018-0637-6

▲ 摘要：

随着人工智能的迅速发展，人们开始关注机器将如何做出道德决策，同时，如何量化社会对引导机器行为的伦理原则的预期也是一个重大挑战。

研究人员搭建了一个名为道德机器的大型在线调查平台，统计全球公民的道德偏好。调查内容为无人驾驶汽车应如何在无法避免的事故中决定拯救哪一方。

研究结果结合了全球参与者贡献的4000万个决策，或为制定社会普遍接受的人工智能道德标准提供了借鉴信息。研究识别出了许多共同的道德偏好，同时还有不同文化之间的道德偏好差异。

结果显示，放手让汽车进行道德抉择之前需要进行全球性对话，将人们的偏好告知那些道德算法设计公司以及执行监管的政策制定者。

▲ Abstract

With the rapid development of artificial intelligence have come concerns about how machines will make moral decisions, and the major challenge of quantifying societal expectations about the ethical principles that should guide machine behaviour. To address this challenge, we deployed the Moral Machine, an online experimental platform designed to explore the moral dilemmas faced by autonomous vehicles. This platform gathered 40 million decisions in ten languages from millions of people in 233 countries and territories. Here we describe the results of this experiment. First, we summarize global moral preferences. Second, we document individual variations in preferences, based on respondents’ demographics. Third, we report cross-cultural ethical variation, and uncover three major clusters of countries. Fourth, we show that these differences correlate with modern institutions and deep cultural traits. We discuss how these preferences can contribute to developing global, socially acceptable principles for machine ethics. All data used in this article are publicly available.

医学Medicine

Targeted neurotechnology restores walking in humans with spinal cord injury

靶向神经技术帮助脊髓损伤患者恢复行走

▲ 作者：Fabien B.Wagner、Jean-BaptisteMignardot、GrégoireCourtine，et al

▲ 链接：

https://www.nature.com/articles/s41586-018-0649-2

▲ 摘要：

脊髓损伤会扰乱神经系统内的通讯，导致基本神经功能丧失和瘫痪。

此次，研究人员对3名患有慢性脊髓损伤和下肢局部或完全瘫痪的男性患者施用了定向硬膜外电刺激（EES）。他们采用运动神经元激活图和模拟模型鉴定了针对不同肌肉群的最佳刺激模式。

结果显示，在开始治疗后的几天内，患者逐渐从在跑步机上踏步到借助支撑在地面上行走，而且能够调整抬脚高度和步长。最终，参与者可以在跑步机上行走长达一个小时。

复健后，这3名患者可以独立行走（依靠局部支撑或步行器），并且在没有EES的情况下恢复了腿部自主运动。

▲ Abstract

Spinal cord injury leads to severe locomotor deficits or even complete leg paralysis. Here we introduce targeted spinal cord stimulation neurotechnologies that enabled voluntary control of walking in individuals who had sustained a spinal cord injury more than four years ago and presented with permanent motor deficits or complete paralysis despite extensive rehabilitation. Using an implanted pulse generator with real-time triggering capabilities, we delivered trains of spatially selective stimulation to the lumbosacral spinal cord with timing that coincided with the intended movement. Within one week, this spatiotemporal stimulation had re-established adaptive control of paralysed muscles during overground walking. Locomotor performance improved during rehabilitation. After a few months, participants regained voluntary control over previously paralysed muscles without stimulation and could walk or cycle in ecological settings during spatiotemporal stimulation. These results establish a technological framework for improving neurological recovery and supporting the activities of daily living after spinal cord injury.

生物学Biology

Shared and distinct transcriptomic cell types across neocortical areas

新皮层中的共享和独特转录组细胞类型

▲ 作者：BosiljkaTasic、Zizhen Yao、Hongkui Zeng，et al

▲ 链接：

https://www.nature.com/articles/s41586-018-0654-5

▲ 摘要：

新大脑皮层包含许多细胞类型，它们被划分为不同的层和功能区域。

为了研究小鼠新大脑皮层细胞类型的多样性，研究人员分析了来自小鼠新大脑皮层远端两个区域的23822个细胞：初级视觉皮层和前外侧运动皮层。

研究组通过单细胞RNA测序确定了133种转录组细胞类型。几乎所有类型的包含GABA的神经元均在这两个区域共享，而大多数类型的谷氨酸神经元被发现仅存在于这两个区域中的一个。

该研究建立了来自成年小鼠皮层不同功能区的皮质细胞类型的转录组和投射分类学。

▲ Abstract

The neocortex contains a multitude of cell types that are segregated into layers and functionally distinct areas. To investigate the diversity of cell types across the mouse neocortex, here we analysed 23,822 cells from two areas at distant poles of the mouse neocortex: the primary visual cortex and the anterior lateral motor cortex. We define 133 transcriptomic cell types by deep, single-cell RNA sequencing. Nearly all types of GABA (γ-aminobutyric acid)-containing neurons are shared across both areas, whereas most types of glutamatergic neurons were found in one of the two areas. By combining single-cell RNA sequencing and retrograde labelling, we match transcriptomic types of glutamatergic neurons to their long-range projection specificity. Our study establishes a combined transcriptomic and projectional taxonomy of cortical cell types from functionally distinct areas of the adult mouse cortex.

Distinct descending motor cortex pathways and their roles in movement

不同下行运动皮质通路及其在运动中的作用

▲ 作者：Michael N.Economo、SaradaViswanathan、Erhan Bas、Karel Svoboda，et al

▲ 链接：

https://www.nature.com/articles/s41586-018-0642-9

▲ 摘要：

运动皮层在运动开始前几秒钟就已经预知了运动。这种预备活动已经在多层皮层中观察到，包括在第5层的下行锥体束神经元中。

一个关键问题是，这些预备活动是如何在不引起运动的情况下保持，并最终转换为一个命令以触发适当的运动。

在这里，使用单细胞转录谱和轴突重建，研究人员确定了两种类型的锥体束神经元。这两种类型都投射到基底神经节和脑干的几个靶点上，并且这两种运动皮层输出神经元在运动控制中有不同的作用。

▲ Abstract

Activity in the motor cortex predicts movements, seconds before they are initiated. This preparatory activity has been observed across cortical layers, including in descending pyramidal tract neurons in layer 5. A key question is how preparatory activity is maintained without causing movement, and is ultimately converted to a motor command to trigger appropriate movements. Here, using single-cell transcriptional profiling and axonal reconstructions, we identify two types of pyramidal tract neuron. Both types project to several targets in the basal ganglia and brainstem. One type projects to thalamic regions that connect back to motor cortex; populations of these neurons produced early preparatory activity that persisted until the movement was initiated. The second type projects to motor centres in the medulla and mainly produced late preparatory activity and motor commands. These results indicate that two types of motor cortex output neurons have specialized roles in motor control.

地球科学Geoscience

Quantification of ocean heat uptake from changes in atmospheric O₂ and CO₂ composition

大气中的氧气和二氧化碳组成变化对海洋热量吸收的量化研究

▲ 作者：L. Resplandy、Y. Eddebbar、M. K. Brooks、R. Wang、L. Bopp、A. Oschlies，et al

▲ 链接：

https://www.nature.com/articles/s41586-018-0651-8

▲ 摘要：

海洋是气候系统热惯性的主要来源。

近几十年来，利用水文温度测量和Argo浮子计划的数据，科学家对海洋热量吸收进行了量化。然而，这些估计都使用了不完美的海洋数据集。

此次，研究人员通过测量大气中的氧气和二氧化碳进行了独立估算。结果表明，1991年至2016年之间，海洋每年获得了1.33±0.20×10²²焦耳热量。

研究人员还发现，海洋变暖效应可以从人为排放和二氧化碳下沉的直接影响中分离出来。

该研究结果依赖于自1991年以来的高精度氧含量测量，表明海洋变暖是以前估计的最高水平。

▲ Abstract

The ocean is the main source of thermal inertia in the climate system. During recent decades, ocean heat uptake has been quantified by using hydrographic temperature measurements and data from the Argo float program, which expanded its coverage after 2007. However, these estimates all use the same imperfect ocean dataset and share additional uncertainties resulting from sparse coverage, especially before 2007. Here we provide an independent estimate by using measurements of atmospheric oxygen (O₂) and carbon dioxide (CO₂)—levels of which increase as the ocean warms and releases gases—as a whole-ocean thermometer. We show that the ocean gained1.33±0.20×10²²joules of heat per year between 1991 and 2016, equivalent to a planetary energy imbalance of 0.83 ±0.11 watts per square metre of Earth’s surface. We also find that the ocean-warming effect that led to the outgassing of O₂ and CO₂ can be isolated from the direct effects of anthropogenic emissions and CO₂ sinks. Our result—which relies on high-precision O₂ measurements dating back to 1991—suggests that ocean warming is at the high end of previous estimates, with implications for policy-relevant measurements of the Earth response to climate change, such as climate sensitivity to greenhouse gases and the thermal component of sea-level rise.