编译｜冯维维
Science, 30 August 2024, Volume 385, Issue 6712
In situ observations of large-amplitude Alfvén waves heating and accelerating the solar wind
大振幅阿尔芬波加热和加速太阳风的现场观测
▲ 作者：YEIMY J. RIVERA, SAMUEL T. BADMAN, MICHAEL L. STEVENS, JAYE L. VERNIERO, JULIA E. STAWARZ, CHEN SHI, JIM M. RAINES, KRISTOFF W. PAULSON, CHRISTOPHER J. OWEN, AND STUART D. BALE
▲链接：
https://www.science.org/doi/10.1126/science.adk6953
▲摘要：
离开日冕后，太阳风继续加速和冷却，但比预期的自由膨胀的绝热气体要慢得多。阿尔芬波是传输能量的行星际磁场的扰动。研究者使用帕克太阳探测器和太阳轨道飞行器的现场测量来调查太阳风流，因为它穿过内部日球层。
观测结果显示，日冕外缘和金星轨道附近的等离子体正在升温和加速，同时还存在着振幅较大的阿尔芬波。研究者计算出，阿尔芬波所产生的阻尼和机械功足以为内日球层中快速太阳风的加热和加速提供动力。
▲ Abstract：
After leaving the Sun’s corona, the solar wind continues to accelerate and cools, but more slowly than expected for a freely expanding adiabatic gas. Alfvén waves are perturbations of the interplanetary magnetic field that transport energy. We use in situ measurements from the Parker Solar Probe and Solar Orbiter spacecraft to investigate a stream of solar wind as it traverses the inner heliosphere. The observations show heating and acceleration of the plasma between the outer edge of the corona and near the orbit of Venus, along with the presence of large-amplitude Alfvén waves. We calculate that the damping and mechanical work performed by the Alfvén waves are sufficient to power the heating and acceleration of the fast solar wind in the inner heliosphere.
Grain boundaries are Brownian ratchets
晶界是布朗棘轮
▲ 作者：CAIHAO QIU, MAIK PUNKE, YUAN TIAN, YING HAN, SIQI WANG, YISHI SU, MARCO SALVALAGLIO, XIAOQING PAN, DAVID J. SROLOVITZ , AND JIAN HAN
▲链接：
https://www.science.org/doi/10.1126/science.adp1516
▲摘要：
多晶材料的晶粒尺寸是制约其性能的重要组成部分。与之前的假设相反，研究者通过建模表明，在非定向驱动力的作用下，晶界（GBs）可以向一个方向移动。然而，并不是所有的晶界类型都是这样，主要是那些几何上不对称的晶界。这一观察结果有助于更好地理解一些晶粒粗化行为，也可能是工程微观结构和改善材料性能的另一种工具。
研究者证明晶界表现为布朗棘轮，在振荡驱动力或循环热退火下表现出方向依赖的迁移和单向运动。他们在几乎所有非对称GB中观察到这些现象，但在对称GB中没有。这一观察建立在分子动力学和相场晶体模拟的基础上，模拟了广泛的GB类型以及双晶和多晶微观结构中的驱动力。
研究者通过现场实验观察证实了这些模拟结果，并用马尔可夫链模型分析了这些结果，并探讨了GB棘轮行为对材料加工和微观结构定制的影响。
▲ Abstract：
The grain size of a polycrystalline material is one important part of the microstructure that constrains the properties. In contrast to previous assumptions, Qiu et al. have shown through modeling that grain boundaries (GBs) can move in one direction in response to a nondirectional driving force. However, not all grain boundary types do so, mostly just the ones that are geometrically nonsymmetric. This observation helps us better understand some grain-coarsening behavior and may also be another tool for engineering microstructures and improving the material properties.
We demonstrate that grain boundariesbehave as Brownian ratchets, exhibiting direction-dependent mobilities and unidirectional motion under oscillatory driving forces or cyclic thermal annealing. We observed these phenomena for nearly all nonsymmetric GBs but not for symmetric ones. Our observations build on molecular dynamics and phase-field crystal simulations for a wide range of GB types and driving forces in both bicrystal and polycrystalline microstructures. We corroborate these simulation results through in situ experimental observations. We analyze these results with a Markov chain model and explore the implications of GB ratchet behavior for materials processing and microstructure tailoring.
地质与地理Geology & Geography
The marine biodiversity impact of the Late Miocene Mediterranean salinity crisis
晚中新世地中海盐度危机对海洋生物多样性的影响
▲ 作者：KonSTANTINA AGIADI, NIKLAS HOHMANN, ELSA GLIOZZI, DANAE THIVAIOU, FRANCESCA R. BOSELLINI, MARCO TAVIANI, GIOVANNI BIANUCCI, ALBERTO COLLARETA, LAURENT LONDEIX, AND DANIEL GARCíA-CASTELLANOS
▲链接：
https://www.science.org/doi/10.1126/science.adp3703
▲摘要：
在整个地质历史中，在高度受限的海洋盆地中形成了大量的盐堆积或“盐巨人”，但它们对生物多样性的影响只得到零星的研究。500万到600万年前中新世晚期，地中海与大西洋的分离导致地中海几乎完全干涸，只剩下几个类似于今天死海的高盐湖泊。
在597至533万年前的墨西尼亚盐危机（MSC）期间，地中海的“盐巨人”是由于其通往大西洋的门户受到限制而形成的。研究者根据地中海化石记录的汇编量化了与MSC相关的生物多样性变化。结果表明，2006年MSC前的86种特有物种在危机中幸存下来，地中海目前向东递减的丰富度梯度是MSC后形成的。
▲ Abstract：
Massive salt accumulations, or salt giants, have formed in highly restricted marine basins throughout geological history, but their impact on biodiversity has been only patchily studied. The disconnection of the Mediterranean Sea from the Atlantic in the late Miocene 5 to 6 million years ago led to the sea’s nearly complete desiccation, leaving only a few hypersaline lakes similar to the present-day Dead Sea. The salt giant in the Mediterranean Sea formed as a result of the restriction of its gateway to the Atlantic during the Messinian Salinity Crisis (MSC) 5.97 to 5.33 million years ago. Here, we quantify the biodiversity changes associated with the MSC based on a compilation of the Mediterranean fossil record. We conclude that 86 endemic species of the 2006 pre-MSC marine species survived the crisis, and that the present eastward-decreasing richness gradient in the Mediterranean was established after the MSC.
Dryland self-expansion enabled by land–atmosphere feedbacks
陆地—大气反馈使旱地自我扩张
▲ 作者：AKASH KOPPA, JESSICA KEUNE, DOMINIK L. SCHUMACHER, KATERINA MICHAELIDES, MICHAEL SINGER, SonIA I. SENEVIRATNE, AND DIEGO G. MIRALLES
▲链接：
https://www.science.org/doi/10.1126/science.adn6833
▲摘要：
旱地扩张造成广泛的水资源短缺和生物多样性丧失。虽然全球变暖对干旱的影响是公认的，但现有旱地在其自身扩张中的作用却相对未知。旱地，即大气需水量大大超过降水的地区，占据了地球陆地表面的近一半。它们将如何应对气候变暖？
作者研究表明，流经旱地的温暖干燥空气有助于顺风旱地的扩张，并可能导致这些地区的干旱化。他们发现，从1981年到2018年，在干旱地区观测到的干旱增加中，有40%以上是由于自我扩张。研究结果证实，干旱地区迫切需要采取减缓气候变化措施，以减缓其自身的扩张。
▲ Abstract：
Dryland expansion causes widespread water scarcity and biodiversity loss. Although the drying influence of global warming is well established, the role of existing drylands in their own expansion is relatively unknown. Drylands, regions in which atmospheric water demand considerably exceeds precipitation, occupy nearly half of Earth’s land surface. How will they respond to our warming climate? Koppa et al. show that the warm, dry air flowing over drylands contributes to downwind dryland expansion and can cause the aridification of those areas. They found that more than 40% of the observed increase in aridity over regions that became drylands from 1981 to 2018 was due to self-expansion. The results corroborate the urgent need for climate change mitigation measures in drylands to decelerate their own expansion.
化学Chemistry
Stereodivergent access to non-natural α-amino acids via enantio- and Z/E-selective catalysis
获得非天然α-氨基酸的立体发散途径
▲ 作者：PANPAN LI, EN ZHENG, GUANLIN LI, YICONG LUO, XIAOHONG HUO, SHENGMING MA , AND WANBIN ZHANG
▲链接：
https://www.science.org/doi/10.1126/science.ado4936
▲摘要：
在化学合成中，对碳碳双键两端基团的配置进行适应性控制是一个挑战。在E构型中，最大的基团对角相对，而在Z构型中，它们在同一侧。研究者将铜和钯催化剂配对，根据配体的选择，在非天然氨基酸中传递E-或z-构型双键。
该反应在季碳立体中心也具有高度的对映选择性。通过钯/铜共催化的三组分组装，通过简单地调整钯和铜催化剂的手性配体，容易获得芳基碘化物、烯和醛胺酯。
▲ Abstract：
Adaptable control over the disposition of groups at each end of a carbon-carbon double bond remains a challenge in chemical synthesis. In the E configuration, the largest groups are diagonally opposed, whereas in the Z configuration, they’re on the same side. Li et al. paired up copper and palladium catalysts to deliver either E- or Z-configured double bonds in unnatural amino acids, depending on the ligand choice. The reaction is also highly enantioselective at the quaternary alpha carbon stereocenter. This success is achieved through a palladium/copper–cocatalyzed three-component assembly of readily available aryl iodides, allenes, and aldimine esters by simply tuning the chiral ligands of the palladium and copper catalysts.
生命科学Life Science
Morphine-responsive neurons that regulate mechanical antinociception
调节机械抗痛觉的吗啡反应神经元
▲ 作者：MICHAEL P. FATT, MING-DONG ZHANG, JUSSI KUPARI, MüGE ALTINK?K, YUNTING YANG, YIZHOU HU, PER SVENNINGSSON, AND PATRIK ERNFORS
▲链接：
https://www.science.org/doi/10.1126/science.ado6593
▲摘要：
几十年来，人们已经知道，脑干中一个被称为吻侧腹内侧髓质的区域对阿片类药物诱导的镇痛很重要，但这一现象背后的神经基质仍然难以捉摸。通过应用小鼠遗传学和用工程病毒操纵神经元活动，研究者发现，位于该大脑区域的单一类型的兴奋性神经元赋予吗啡抗痛觉性。
这些神经元投射到脊髓——在那里，通过单突触连接，它们激活一种确定的抑制性脊髓神经元类型，在上升疼痛通路中控制疼痛信号。研究发现，对延髓吻侧腹内侧兴奋性神经元或脊髓抑制性神经元的抑制可消除全身注射吗啡的所有镇痛作用。
▲ Abstract：