《自然》（20181101出版）一周論文導讀

Nature, Volume 563 Issue 7729, 1 November 2018

《自然》2018年11月1日第7729期563卷

天文學Astronomy

Themerger that led to the formation of the Milky Way』s inner stellar halo and thick disk

碰撞導致了銀河系內部的恆星暈和厚銀盤的形成

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

鏈接：

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

摘要：

銀河系由許多結構組成：核球、旋臂、銀盤和銀暈。通過觀察各個恆星的年齡、化學特性、分布和運動，人們有可能確定它們是如何組合起來的。

該研究分析了最新發布的來自蓋亞太空望遠鏡以及阿帕奇天文台星系演化實驗的數據，發現大約100億年前，銀河系與一個矮星系碰撞，導致銀河系銀暈內充滿了恆星，並且使銀盤增厚。

該矮星系的質量約為當時銀河系質量的1/4。銀河系與這樣大小的星系碰撞，會加熱預先已存在的銀盤，從而形成如今所存在的較厚的銀盤。

研究人員將這個撞擊星系命名為「蓋亞—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.

物理學Physics

Measurement-based quantum control of mechanical motion

基於測量的機械運動量子控制

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

鏈接：

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

摘要：

利用對量子系統動力學的觀察來控制量子系統十分複雜，原因是測量過程的反作用，即由於系統與測量儀器的耦合而引起的不可避免的量子干擾。

一種有效的測量方法是使每次干擾所獲得的信息量最大化。然後，實時反饋可以抵消測量的反作用，並控制量子態的演化。

在這裡，研究人員演示了基於測量的毫米大小膜諧振器運動的量子控制。

一個光學機械感測器能在其一小部分的毫秒級相干時間中解析諧振器的零點運動，整體測量效率接近統一。而一個電子反饋迴路將這個位置記錄轉換成一個力，使諧振器模式冷卻到它的量子基態。

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.

人工智慧AI

The Moral Machine experiment

機器道德實驗

作者：Edmond Awad、Sohan Dsouza、Richard Kim、JonathanSchulz、JosephHenrich、Azim Shariff、Jean-Fran?oisBonnefon、Iyad Rahwan

鏈接：

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

摘要：

隨著人工智慧的迅速發展，人們開始關注機器將如何做出道德決策，同時，如何量化社會對引導機器行為的倫理原則的預期也是一個重大挑戰。

研究人員搭建了一個名為道德機器的大型在線調查平台，統計全球公民的道德偏好。調查內容為無人駕駛汽車應如何在無法避免的事故中決定拯救哪一方。

研究結果結合了全球參與者貢獻的4000萬個決策，或為制定社會普遍接受的人工智慧道德標準提供了借鑒信息。研究識別出了許多共同的道德偏好，同時還有不同文化之間的道德偏好差異。

結果顯示，放手讓汽車進行道德抉擇之前需要進行全球性對話，將人們的偏好告知那些道德演算法設計公司以及執行監管的政策制定者。

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.

醫學Medicine

Targeted neurotechnology restores walking in humans with spinal cord injury

靶向神經技術幫助脊髓損傷患者恢復行走

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

鏈接：

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

摘要：

脊髓損傷會擾亂神經系統內的通訊，導致基本神經功能喪失和癱瘓。

此次，研究人員對3名患有慢性脊髓損傷和下肢局部或完全癱瘓的男性患者施用了定向硬膜外電刺激（EES）。他們採用運動神經元激活圖和模擬模型鑒定了針對不同肌肉群的最佳刺激模式。

結果顯示，在開始治療後的幾天內，患者逐漸從在跑步機上踏步到藉助支撐在地面上行走，而且能夠調整抬腳高度和步長。最終，參與者可以在跑步機上行走長達一個小時。

復健後，這3名患者可以獨立行走（依靠局部支撐或步行器），並且在沒有EES的情況下恢復了腿部自主運動。

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.

生物學Biology

Shared anddistinct transcriptomic cell types across neocortical areas

新皮層中的共享和獨特轉錄組細胞類型

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

鏈接：

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

摘要：

新大腦皮層包含許多細胞類型，它們被劃分為不同的層和功能區域。

為了研究小鼠新大腦皮層細胞類型的多樣性，研究人員分析了來自小鼠新大腦皮層遠端兩個區域的23822個細胞：初級視覺皮層和前外側運動皮層。

研究組通過單細胞RNA測序確定了133種轉錄組細胞類型。幾乎所有類型的包含GABA的神經元均在這兩個區域共享，而大多數類型的谷氨酸神經元被發現僅存在於這兩個區域中的一個。

該研究建立了來自成年小鼠皮層不同功能區的皮質細胞類型的轉錄組和投射分類學。

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 inmovement

不同下行運動皮質通路及其在運動中的作用

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

鏈接：

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

摘要：

運動皮層在運動開始前幾秒鐘就已經預知了運動。這種預備活動已經在多層皮層中觀察到，包括在第5層的下行錐體束神經元中。

一個關鍵問題是，這些預備活動是如何在不引起運動的情況下保持，並最終轉換為一個命令以觸發適當的運動。

在這裡，使用單細胞轉錄譜和軸突重建，研究人員確定了兩種類型的錐體束神經元。這兩種類型都投射到基底神經節和腦幹的幾個靶點上，並且這兩種運動皮層輸出神經元在運動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.

地球科學Geoscience

Quantification of ocean heat uptake from changes in atmosphericO₂and CO₂composition

大氣中的氧氣和二氧化碳組成變化對海洋熱量吸收的量化研究

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

鏈接：

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

摘要：

海洋是氣候系統熱慣性的主要來源。

近幾十年來，利用水文溫度測量和Argo浮子計劃的數據，科學家對海洋熱量吸收進行了量化。然而，這些估計都使用了不完美的海洋數據集。

此次，研究人員通過測量大氣中的氧氣和二氧化碳進行了獨立估算。結果表明，1991年至2016年之間，海洋每年獲得了1.33±0.20×10²²焦耳熱量。

研究人員還發現，海洋變暖效應可以從人為排放和二氧化碳下沉的直接影響中分離出來。

該研究結果依賴於自1991年以來的高精度氧含量測量，表明海洋變暖是以前估計的最高水平。

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 O₂and CO₂can be isolated from the direct effects of anthropogenic emissions and CO₂sinks. Our result—which relies on high-precision O₂measurements 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.

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