《自然》（20190214出版）一周論文導讀

知識 02-18

翻譯 | 宗華

Nature, 14 February 2019, Volume 566 Issue 7743

《自然》2019年2月14日第7743期566卷

《自然》（20190214出版）一周論文導讀

打開今日頭條，查看更多圖片

天文學Astronomy

Observations of fast radio bursts at frequencies down to 400 megahertz

對頻率低至400兆赫的快速射電暴的觀測

作者：CHIME/FRB協作組

鏈接：

https://www.nature.com/articles/s41586-018-0867-7

摘要：

快速射電暴（FRBs）是高度彌散且持續時間在毫秒級的射電閃光。它可能來自遠離銀河系的地方。

這一現象在接近1.4千兆赫的射電頻率上被發現，並且迄今為止只在高達8千兆赫的情形下被觀測到一次。儘管研究人員在低頻率下進行了大量搜索，但尚未在700兆赫以下發現過FRBs。

我們在加拿大氫強度測繪實驗（CHIME）中利用CHIME/FRB設備，在低至400兆赫的射電頻率下對13次FRBs進行了探測。

它們是在望遠鏡試運行階段被探測到的，此時望遠鏡的敏感度和視場尚未完成達到設計規格。多次事件中的輻射被發現低至400兆赫，這是該望遠鏡敏感範圍內的最低射電頻率。

Abstract

Fast radio bursts (FRBs) are highly dispersed millisecond-duration radio flashes probably arriving from far outside the Milky Way. This phenomenon was discovered at radio frequencies near 1.4 gigahertz and so far has been observed in one case at as high as 8 gigahertz, but not at below 700 megahertz in spite of substantial searches at low frequencies. Here we report detections of 13 FRBs at radio frequencies as low as 400 megahertz, on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using the CHIME/FRB instrument. They were detected during a telescope pre-commissioning phase, when the sensitivity and field of view were not yet at design specifications. Emission in multiple events is seen down to 400 megahertz, the lowest radio frequency to which the telescope is sensitive.

A second source of repeating fast radio bursts

重複快速射電暴的另一個來源

作者：The CHIME/FRB協作組

鏈接：

https://www.nature.com/articles/s41586-018-0864-x

摘要：

重複快速射電暴（FRB）來源——FRB 121102的發現，排除了涉及這個源頭的災難性事件的模型。

迄今為止，儘管有很多最新發現和後續研究，但尚未有其他重複FRB被探測到。這表明，「重複者」可能在FRB群體中非常罕見。

這裡，我們報告了對來自FRB 180814.J0422+73的6次重複射電暴的探測結果。FRB 180814.J0422+73是加拿大氫強度測繪實驗（CHIME）FRB項目在2018年7月和8月試運行階段探測到的13次FRBs之一。

這些重複射電暴的來源一致，即來自天空中的單一位置。同時，它們的色散量也相同，約為每立方厘米189秒差距。

Abstract

The discovery of a repeating fast radio burst (FRB) source, FRB 121102, eliminated models involving cataclysmic events for this source. No other repeating FRB has hitherto been detected despite many recent discoveries and follow-ups, suggesting that repeaters may be rare in the FRB population. Here we report the detection of six repeat bursts from FRB 180814.J0422+73, one of the 13 FRBs detected6 by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB project7 during its pre-commissioning phase in July and August 2018. These repeat bursts are consistent with its origin from a single position on the sky, with the same dispersion measure, about 189 parsecs per cubic centimetre.

物理學Physics

Near-field photonic cooling through control of the chemical potential of photons

通過控制光子化學勢的近場光子冷卻

作者：Linxiao Zhu, Anthony Fiorino, Dakotah Thompson, et al

鏈接：

https://www.nature.com/articles/s41586-019-0918-8

摘要：

物質的光子冷卻使接觸未被探索過的物質狀態比如玻色愛因斯坦凝聚體，以及尋找固體製冷的新方法成為可能。

這些光子冷卻方法的關鍵是利用來自激光的低熵相干輻射。這使得冷卻過程在熱力學上是切實可行的。

我們利用定製製造的納米級量熱裝置和光電二極體，實驗演示了沒有激光情形下的光子冷卻。

我們證實，當它們位於彼此的近場中時，即量熱裝置的平面表面和反向偏置的光電二極體之間的真空間隙大小被縮小至十幾納米時，由於光子在施加的反向偏壓下化學勢的變化，量熱裝置的固態冷卻可通過光子隧道效應和來自發光二極體的光子發射抑制相結合而得以實現。其中，光子隧道效應增強了光子在納米尺度孔隙間的傳送。

Abstract

Photonic cooling of matter has enabled both access to unexplored states of matter, such as Bose–Einstein condensates, and novel approaches to solid-state refrigeration. Critical to these photonic cooling approaches is the use of low-entropy coherent radiation from lasers, which makes the cooling process thermodynamically feasible. Here we report an experimental demonstration of photonic cooling without laser light using a custom-fabricated nanocalorimetric device and a photodiode. We show that when they are in each other』s near-field—that is, when the size of the vacuum gap between the planar surfaces of the calorimetric device and a reverse-biased photodiode is reduced to tens of nanometres—solid-state cooling of the calorimetric device can be accomplished via a combination of photon tunnelling, which enhances the transport of photons across nanoscale gaps, and suppression of photon emission from the photodiode due to a change in the chemical potential of the photons under an applied reverse bias.

Mapping orbital changes upon electron transfer with tunnelling microscopy on insulators

利用隧道顯微術描繪絕緣體電子轉移的軌道變化

作者：Laerte L. Patera, Fabian Queck, Philipp Scheuerer & Jascha Repp

鏈接：

https://www.nature.com/articles/s41586-019-0910-3

摘要：

電子轉移在包括光合作用、燃燒和腐蝕在內的很多化學反應中起到了關鍵作用。

不過，儘管氧化還原狀態轉換改變了所涉及的分子電子結構，但在單分子水平描繪這些變化具有挑戰性。

這裡，我們證實，當使控制導電原子力顯微鏡尖端和基板之間的電子隧道效應的電壓脈衝和顯微鏡尖端的振蕩同步時,我們能在非導電性基板上開展隧道效應試驗並因此將孤立分子的軌道結構描述為其氧化還原狀態的函數。

Abstract

Electron transfer plays a crucial part in many chemical reactions, including photosynthesis, combustion and corrosion. But even though redox-state transitions change the electronic structure of the molecules involved, mapping these changes at the single-molecule level is challenging. Here we show that when synchronizing voltage pulses that steer electron tunnelling between a conductive atomic force microscope tip and a substrate with the oscillation of the tip, we can perform tunnelling experiments on non-conductive substrates and thereby map the orbital structure of isolated molecules as a function of their redox state.

生物學Biology

Interleukin-22 protects intestinal stem cells against genotoxic stress

白介素-22保護腸幹細胞對抗基因毒性壓力

作者：Konrad Gronke, Pedro P. Hernández, Jakob Zimmermann, et al

鏈接：

https://www.nature.com/articles/s41586-019-0899-7

摘要：

環境遺傳毒性因素對將宿主生物體同環境分開的屏障表面的上皮細胞的基因組完整性帶來了挑戰。

上皮幹細胞的基因組完整性由進化上保守的分子響應通路——DNA損傷應答（DDR）來維持。

這裡，我們證實，3型先天淋巴細胞（ILC3）和γδ T細胞產生的細胞因子白介素-22（IL-22)是DDR機制在腸上皮幹細胞中的重要調控者。

利用使結腸上皮幹細胞中的IL-22受體分散激活成為可能的新小鼠模型，我們證實，IL-22是DNA損傷後DDR有效啟動所必需的。

Abstract

Environmental genotoxic factors pose a challenge to the genomic integrity of epithelial cells at barrier surfaces that separate host organisms from the environment. Genome integrity in epithelial stem cells is maintained by an evolutionarily conserved cellular response pathway, the DNA damage response (DDR). Here we show that the cytokine interleukin-22 (IL-22), produced by group 3 innate lymphoid cells (ILC3) and γδ T cells, is an important regulator of the DDR machinery in intestinal epithelial stem cells. Using a new mouse model that enables sporadic inactivation of the IL-22 receptor in colon epithelial stem cells, we demonstrate that IL-22 is required for effective initiation of the DDR following DNA damage.

Discrete attractor dynamics underlies persistent activity in the frontal cortex

離散吸引子動力學是額皮質持續行為的基礎

作者：Hidehiko K. Inagaki, Lorenzo Fontolan, Sandro Romani & Karel Svoboda

鏈接：

https://www.nature.com/articles/s41586-019-0919-7

摘要：

短期記憶將在時間上分開的事件聯繫起來，比如過去的感覺和未來的行動。這種記憶同包括選擇性持續行為在內、可維持在幾秒鐘內的緩慢神經動力學存在關聯。

在一項要求短期記憶的延遲響應任務中，小鼠前外側運動皮質（ALM）的神經元表現出指示未來行動的持續行為。為確定這一持續行為背後的原理，我們將細胞內和細胞外電生理學同光發生擾動和網路建模相結合。

我們證實，在延遲期，ALM神經元的活動朝對特定運動指令作出響應的離散終點移動。我們的結果證實，離散的吸引子動力學是同動作計劃相關的短期記憶的基礎。

Abstract

Short-term memories link events separated in time, such as past sensation and future actions. Short-term memories are correlated with slow neural dynamics, including selective persistent activity, which can be maintained over seconds. In a delayed response task that requires short-term memory, neurons in the mouse anterior lateral motor cortex (ALM) show persistent activity that instructs future actions. To determine the principles that underlie this persistent activity, here we combined intracellular and extracellular electrophysiology with optogenetic perturbations and network modelling. We show that during the delay epoch, the activity of ALM neurons moved towards discrete end points that correspond to specific movement directions. Our results show that discrete attractor dynamics underlie short-term memory related to motor planning.

《自然》（20190214出版）一周論文導讀