作者:冯维维 来源:科学网微信公众号 发布时间:2024/4/20 21:01:46


编译 | 冯维维

Nature,  Volume 628 Issue 8008, 18 April 2024




Methane emission from a cool brown dwarf


▲ 作者:Jacqueline K. Faherty, Ben Burningham, Jonathan Gagné, Genaro Suárez, Johanna M. Vos, Sherelyn Alejandro Merchan, Caroline V. Morley, Melanie Rowland, Brianna Lacy, Rocio Kiman, Dan Caselden, J. Davy Kirkpatrick, Aaron Meisner, Adam C. Schneider, Marc Jason Kuchner, Daniella Carolina Bardalez Gagliuffi, Charles Beichman, Peter Eisenhardt, Christopher R. Gelino, Ehsan Gharib-Nezhad, Eileen Gonzales, Federico Marocco, Austin James Rothermich & Niall Whiteford

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▲ 摘要:

在太阳系之外,极光是从对孤立的褐矮星的无线电观测中推断出来的。在太阳系中,巨大的行星在电磁波谱上有极光发射的特征,包括H3+和甲烷的红外发射。科学家尝试在无线电中寻找具有极光特征的孤立的褐矮星,以寻找相应的红外特征,但只报道了无效探测。CWISEP j193518.59 - 154620.3.(简称W1935)是一颗孤立的褐矮星,温度约为482 K。

研究者报告了詹姆斯·韦布太空望远镜观测到W1935在3.326 μm波段强烈的甲烷排放。大气模拟得出的结论表示,以1-10毫巴为中心的大约300 K的逆温重复了这一特征。这代表了没有主星辐射的类木星大气的大气温度反演。


▲ Abstract:

Beyond our Solar System, aurorae have been inferred from radio observations of isolated brown dwarfs. Within our Solar System, giant planets have auroral emission with signatures across the electromagnetic spectrum including infrared emission of H3+ and methane. Isolated brown dwarfs with auroral signatures in the radio have been searched for corresponding infrared features, but only null detections have been reported. CWISEP J193518.59-154620.3. (W1935 for short) is an isolated brown dwarf with a temperature of approximately 482?K. Here we report James Webb Space Telescope observations of strong methane emission from W1935 at 3.326?μm. Atmospheric modelling leads us to conclude that a temperature inversion of approximately 300?K centred at 1–10?mbar replicates the feature. This represents an atmospheric temperature inversion for a Jupiter-like atmosphere without irradiation from a host star. A plausible explanation for the strong inversion is heating by auroral processes, although other internal and external dynamical processes cannot be ruled out. The best-fitting model rules out the contribution of H3+ emission, which is prominent in Solar System gas giants. However, this is consistent with rapid destruction of H3+ at the higher pressure where the W1935 emission originates.

A hybrid topological quantum state in an elemental solid


▲ 作者:Md Shafayat Hossain, Frank Schindler, Rajibul Islam, Zahir Muhammad, Yu-Xiao Jiang, Zi-Jia Cheng, Qi Zhang, Tao Hou, Hongyu Chen, Maksim Litskevich, Brian Casas, Jia-Xin Yin, Tyler A. Cochran, Mohammad Yahyavi, Xian P. Yang, Luis Balicas, Guoqing Chang, Weisheng Zhao, Titus Neupert & M. Zahid Hasan

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▲ Abstract:

Topology and interactions are foundational concepts in the modern understanding of quantum matter. Their nexus yields three important research directions: (1) the competition between distinct interactions, as in several intertwined phases, (2) the interplay between interactions and topology that drives the phenomena in twisted layered materials and topological magnets, and (3) the coalescence of several topological orders to generate distinct novel phases. The first two examples have grown into major areas of research, although the last example remains mostly unexplored, mainly because of the lack of a material platform for experimental studies. Here, using tunnelling microscopy, photoemission spectroscopy and a theoretical analysis, we unveil a ‘hybrid’ topological phase of matter in the simple elemental-solid arsenic. Through a unique bulk-surface-edge correspondence, we uncover that arsenic features a conjoined strong and higher-order topology that stabilizes a hybrid topological phase. Although momentum-space spectroscopy measurements show signs of topological surface states, real-space microscopy measurements unravel a unique geometry of topologically induced step-edge conduction channels revealed on various natural nanostructures on the surface. Using theoretical models, we show that the existence of gapless step-edge states in arsenic relies on the simultaneous presence of both a non-trivial strong Z2 invariant and a non-trivial higher-order topological invariant, which provide experimental evidence for hybrid topology. Our study highlights pathways for exploring the interplay of different band topologies and harnessing the associated topological conduction channels in engineered quantum or nano-devices.

Phononic switching of magnetization by the ultrafast Barnett effect


▲ 作者:C. S. Davies, F. G. N. Fennema, A. Tsukamoto, I. Razdolski, A. V. Kimel & A. Kirilyuk

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▲ Abstract:

The historic Barnett effect describes how an inertial body with otherwise zero net magnetic moment acquires spontaneous magnetization when mechanically spinning. Breakthrough experiments have recently shown that an ultrashort laser pulse destroys the magnetization of an ordered ferromagnet within hundreds of femtoseconds, with the spins losing angular momentum to circularly polarized optical phonons as part of the ultrafast Einstein–de Haas effect. However, the prospect of using such high-frequency vibrations of the lattice to reciprocally switch magnetization in a nearby magnetic medium has not yet been experimentally explored. Here we show that the spontaneous magnetization gained temporarily by means of the ultrafast Barnett effect, through the resonant excitation of circularly polarized optical phonons in a paramagnetic substrate, can be used to permanently reverse the magnetic state of a heterostructure mounted atop the said substrate. With the handedness of the phonons steering the direction of magnetic switching, the ultrafast Barnett effect offers a selective and potentially universal method for exercising ultrafast non-local control over magnetic order.

气候和生态Climate & Ecology

The economic commitment of climate change


▲ 作者:Maximilian Kotz, Anders Levermann & Leonie Wenz

▲ 链接:https://www.nature.com/articles/s41586-024-07219-0

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▲ Abstract:

Global projections of macroeconomic climate-change damages typically consider impacts from average annual and national temperatures over long time horizons. Here we use recent empirical findings from more than 1,600 regions worldwide over the past 40?years to project sub-national damages from temperature and precipitation, including daily variability and extremes. Using an empirical approach that provides a robust lower bound on the persistence of impacts on economic growth, we find that the world economy is committed to an income reduction of 19% within the next 26?years independent of future emission choices (relative to a baseline without climate impacts, likely range of 11–29% accounting for physical climate and empirical uncertainty). These damages already outweigh the mitigation costs required to limit global warming to 2?°C by sixfold over this near-term time frame and thereafter diverge strongly dependent on emission choices. Committed damages arise predominantly through changes in average temperature, but accounting for further climatic components raises estimates by approximately 50% and leads to stronger regional heterogeneity. Committed losses are projected for all regions except those at very high latitudes, at which reductions in temperature variability bring benefits. The largest losses are committed at lower latitudes in regions with lower cumulative historical emissions and lower present-day income.

FSC-certified forest management benefits large mammals compared to non-FSC


▲ 作者:Joeri A. Zwerts, E. H. M. Sterck, Pita A. Verweij, Fiona Maisels, Jaap van der Waarde, Emma A. M. Geelen, Georges Belmond Tchoumba, Hermann Frankie Donfouet Zebaze & Marijke van Kuijk

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▲ Abstract:

More than a quarter of the world’s tropical forests are exploited for timber. Logging impacts biodiversity in these ecosystems, primarily through the creation of forest roads that facilitate hunting for wildlife over extensive areas. Forest management certification schemes such as the Forest Stewardship Council (FSC) are expected to mitigate impacts on biodiversity, but so far very little is known about the effectiveness of FSC certification because of research design challenges, predominantly limited sample sizes. Here we provide this evidence by using 1.3?million camera-trap photos of 55 mammal species in 14 logging concessions in western equatorial Africa. We observed higher mammal encounter rates in FSC-certified than in non-FSC logging concessions. The effect was most pronounced for species weighing more than 10?kg and for species of high conservation priority such as the critically endangered forest elephant and western lowland gorilla. Across the whole mammal community, non-FSC concessions contained proportionally more rodents and other small species than did FSC-certified concessions. The first priority for species protection should be to maintain unlogged forests with effective law enforcement, but for logged forests our findings provide convincing data that FSC-certified forest management is less damaging to the mammal community than is non-FSC forest management. This study provides strong evidence that FSC-certified forest management or equivalently stringent requirements and controlling mechanisms should become the norm for timber extraction to avoid half-empty forests dominated by rodents and other small species.


Jurassic shuotheriids show earliest dental diversification of mammaliaforms


▲ 作者:Fangyuan Mao, Zhiyu Li, Zhili Wang, Chi Zhang, Thomas Rich, Patricia Vickers-Rich & Jin Meng

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▲ Abstract:

Shuotheriids are Jurassic mammaliaforms that possess pseudotribosphenic teeth in which a pseudotalonid is anterior to the trigonid in the lower molar, contrasting with the tribosphenic pattern of therian mammals (placentals, marsupials and kin) in which the talonid is posterior to the trigonid. The origin of the pseudotribosphenic teeth remains unclear, obscuring our perception of shuotheriid affinities and the early evolution of mammaliaforms. Here we report a new Jurassic shuotheriid represented by two skeletal specimens. Their complete pseudotribosphenic dentitions allow reidentification of dental structures using serial homology and the tooth occlusal relationship. Contrary to the conventional view, our findings show that dental structures of shuotheriids can be homologized to those of docodontans and partly support homologous statements for some dental structures between docodontans and other mammaliaforms. The phylogenetic analysis based on new evidence removes shuotheriids from the tribosphenic ausktribosphenids (including monotremes) and clusters them with docodontans to form a new clade, Docodontiformes, that is characterized by pseudotribosphenic features. In the phylogeny, docodontiforms and ‘holotherians’ (Kuehneotherium, monotremes and therians)13 evolve independently from a Morganucodon-like ancestor with triconodont molars by labio-lingual widening their posterior teeth for more efficient food processing. The pseudotribosphenic pattern passed a cusp semitriangulation stage9, whereas the tribosphenic pattern and its precursor went through a stage of cusp triangulation. The two different processes resulted in complex tooth structures and occlusal patterns that elucidate the earliest diversification of mammaliaforms.

Fossils document evolutionary changes of jaw joint to mammalian middle ear


▲ 作者:Fangyuan Mao, Chi Zhang, Jicheng Ren, Tao Wang, Guofu Wang, Fakui Zhang, Thomas Rich, Patricia Vickers-Rich & Jin Meng

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研究者报告了两种侏罗纪哺乳动物的下颌中耳:一种新的morganucodondon 样种和一种Shuotheriid水生动物。Morganucodonan样种显示出许多以前未知的后牙状骨形态,并显示出其关节-方关节丧失承重功能的特征。Shuotheriid的中耳接近哺乳动物的状态,因为它的特征只适合于听觉功能,尽管后牙骨仍然附着在牙上。


▲ Abstract:

The dual jaw joint of Morganucodon consists of the dentary–squamosal joint laterally and the articular–quadrate one medially. The articular–quadrate joint and its associated post-dentary bones constitute the precursor of the mammalian middle ear. Fossils documenting the transition from such a precursor to the mammalian middle ear are poor, resulting in inconsistent interpretations of this hallmark apparatus in the earliest stage of mammaliaform evolution. Here we report mandibular middle ears from two Jurassic mammaliaforms: a new morganucodontan-like species and a pseudotribosphenic shuotheriid species. The morganucodontan-like species shows many previously unknown post-dentary bone morphologies and exhibits features that suggest a loss of load-bearing function in its articular–quadrate joint. The middle ear of the shuotheriid approaches the mammalian condition in that it has features that are suitable for an exclusively auditory function, although the post-dentary bones are still attached to the dentary. With size reduction of the jaw-joint bones, the quadrate shifts medially at different degrees in relation to the articular in the two mammaliaforms. These changes provide evidence of a gradual loss of load-bearing function in the articular–quadrate jaw joint—a prerequisite for the detachment of the post-dentary bones from the dentary and the eventual breakdown of the Meckel’s cartilage during the evolution of mammaliaforms.

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