作者:李言 来源:科学网微信公众号 发布时间:2023/9/2 20:34:55


编译 | 李言

Nature, 31 August 2023, Volume 620 Issue 7976




A binary pulsar in a 53-minute orbit


▲ 作者:Z. Pan, J. G. Lu, P. Jiang et al.

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在此,我们报告对双毫秒脉冲星PSR J1953+1844 (M71E)的射电观测,它的轨道周期为53.3分钟,伴星质量约为0.07 M⊙。它是一个微弱的x射线源,距离球状星团M71的中心2.5弧分。

▲ Abstract:

Spider pulsars are neutron stars that have a companion star in a close orbit. The companion star sheds material to the neutron star, spinning it up to millisecond rotation periods, while the orbit shortens to hours. Here we report radio observations of the binary millisecond pulsar PSR J1953+1844 (M71E) that show it to have an orbital period of 53.3 minutes and a companion with a mass of around 0.07 M⊙. It is a faint X-ray source and located 2.5 arcminutes from the centre of the globular cluster M71.


First observation of 28O


▲ 作者:Y. Kondo, N. L. Achouri et al.

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▲ Abstract:

Here we report on the first observation of 28O and 27O through their decay into 24O and four and three neutrons, respectively. The 28O nucleus is of particular interest as, with the Z=8 and N=20 magic numbers, it is expected in the standard shell-model picture of nuclear structure to be one of a relatively small number of so-called ‘doubly magic’ nuclei. Both 27O and 28O were found to exist as narrow, low-lying resonances and their decay energies are compared here to the results of sophisticated theoretical modelling, including a large-scale shell-model calculation and a newly developed statistical approach. In both cases, the underlying nuclear interactions were derived from effective field theories of quantum chromodynamics. Finally, it is shown that the cross-section for the production of 28O from a 29F beam is consistent with it not exhibiting a closed N=20 shell structure.


Frustration- and doping-induced magnetism in a Fermi–Hubbard simulator


▲ 作者:Muqing Xu, Lev Haldar Kendrick et al.

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在半填充之外,三角形极限显示了在空穴掺杂侧反铁磁相关增强,而在粒子掺杂超过20%时,铁磁关联反转提示了动力学磁性在阻挫系统中的作用。这项工作为探索三角形晶格中可能的手性有序相或超导相铺平了道路,并实现了可能是描述铜材料超导性所必需的t-t '方形晶格哈伯德模型

▲ Abstract:

Here we investigate the local spin order of a Hubbard model with controllable frustration and doping, using ultracold fermions in anisotropic optical lattices continuously tunable from a square to a triangular geometry. At half-filling and strong interactions U/t≈9, we observe at the single-site level how frustration reduces the range of magnetic correlations and drives a transition from a collinear Néel antiferromagnet to a short-range correlated 120° spiral phase. Away from half-filling, the triangular limit shows enhanced antiferromagnetic correlations on the hole-doped side and a reversal to ferromagnetic correlations at particle dopings above 20%, hinting at the role of kinetic magnetism in frustrated systems. This work paves the way towards exploring possible chiral ordered or superconducting phases in triangular lattices and realizing t–t′ square lattice Hubbard models that may be essential to describe superconductivity in cuprate materials.

人工智能Artificial Intelligence

Champion-level drone racing using deep reinforcement learning


▲ 作者:Elia Kaufmann, Leonard Bauersfeld et al.

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Here we introduce Swift, an autonomous system that can race physical vehicles at the level of the human world champions. The system combines deep reinforcement learning (RL) in simulation with data collected in the physical world. Swift competed against three human champions, including the world champions of two international leagues, in real-world head-to-head races. Swift won several races against each of the human champions and demonstrated the fastest recorded race time. This work represents a milestone for mobile robotics and machine intelligence, which may inspire the deployment of hybrid learning-based solutions in other physical systems.

环境科学Environmental Science

Agricultural pesticide land budget and river discharge to oceans


▲ 作者:Federico Maggi, Fiona H. M. Tang & Francesco N. Tubiello

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通过排水,河流以每年每公里-10至100公斤以上的速率吸收0.73克农药。与土壤中的情况相反,进入河流的农药中只有1.1%沿着溪流降解,在超过13000公里长度的河流中超过安全水平(浓度大于1 μg  l-1),每年有0.71克农药流入海洋。除草剂是土地(72%)和河流入海(62%)中的主要农药残留。

▲ Abstract:

Here, we develop a process-based model accounting for the hydrology and biogeochemistry of the 92 most used agricultural pesticide active substances to assess their pathways through the principal catchments of the world and draw a near-present picture of the global land and river budgets, including discharge to oceans. Of the 0.94 Tg net annual pesticide input in 2015 used in this study, 82% is biologically degraded, 10% remains as residue in soil and 7.2% leaches below the root zone. Rivers receive 0.73 Gg of pesticides from their drainage at a rate of 10 to more than 100 kg yr-1km-1. By contrast to their fate in soil, only 1.1% of pesticides entering rivers are degraded along streams, exceeding safety levels (concentrations >1 μg l-1) in more than 13,000 km of river length, with 0.71 Gg of pesticide active ingredients released to oceans every year. Herbicides represent the prevalent pesticide residue on both land (72%) and river outlets (62%).


Reef-building corals farm and feed on their photosynthetic symbionts


▲ 作者:Jörg Wiedenmann, Cecilia D’Angelo et al.

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Here we show, through a series of long-term experiments, that the uptake of dissolved inorganic nitrogen and phosphorus by the symbionts alone is sufficient to sustain rapid coral growth. Next, considering the nitrogen and phosphorus budgets of host and symbionts, we identify that these nutrients are gathered through symbiont ‘farming’ and are translocated to the host by digestion of excess symbiont cells. Finally, we use a large-scale natural experiment in which seabirds fertilize some reefs but not others, to show that the efficient utilization of dissolved inorganic nutrients by symbiotic corals established in our laboratory experiments has the potential to enhance coral growth in the wild at the ecosystem level.

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