材料随机场是什么原因(条件随机场是什么)

编译 | 李言

Nature, Volume 597 Issue 7874, 2 September 2021

《自然》2021年9月2日，第597卷，7874期

物理学Physics

Emergent hydrodynamics in a strongly interacting dipolar spin ensemble

强相互作用偶极自旋系综中的流体动力学

▲ 作者：C. Zu, F. Machado, B. Ye, S. Choi, B. Kobrin, T. Mittiga, S. Hsieh, P. Bhattacharyya, M. Markham, D. Twitchen, A. Jarmola, D. Budker, C. R. Laumann, J. E. Moore & N. Y. Yao

▲ 链接：

https://www.nature.com/articles/s41586-021-03763-1

▲ 摘要

传统观点认为宏观经典现象是由微观量子定律自然产生的。然而，在这两者间建立直接的联系仍然是一个长期挑战。尤其是，很难从一般的微观量子哈密顿量预测系统的突现“经典”性质（例如扩散性、粘性和压缩性）。

在此，我们引入了一个混合固态自旋平台，其中无序的偶极量子哈密顿量导致了纳米尺度上非常规自旋扩散的出现。在此，我们引入了一个混合固态自旋平台，其中无序的偶极量子哈密顿量导致了纳米尺度上非常规自旋扩散的出现。特别是位置无序和随机场的结合，导致了非高斯的符合菲克定律的扩散动力学。

最后，通过结合静态场和驱动场来调整自旋哈密顿量中的基本参数，我们证明了对出射自旋扩散系数的直接控制。我们的工作使研究多体量子自旋系统中的流体动力学成为可能。

▲ Abstract

Conventional wisdom holds that macroscopic classical phenomena naturally emerge from microscopic quantum laws. However, despite this mantra, building direct connections between these two descriptions has remained an enduring scientific challenge. In particular, it is difficult to quantitatively predict the emergent ‘classical’ properties of a system (for example, diffusivity, viscosity and compressibility) from a generic microscopic quantum Hamiltonian. Here we introduce a hybrid solid-state spin platform, where the underlying disordered, dipolar quantum Hamiltonian gives rise to the emergence of unconventional spin diffusion at nanometre length scales. In particular, the combination of positional disorder and on-site random fields leads to diffusive dynamics that are Fickian yet non-Gaussian. Finally, by tuning the underlying parameters within the spin Hamiltonian via a combination of static and driven fields, we demonstrate direct control over the emergent spin diffusion coefficient. Our work enables the investigation of hydrodynamics in many-body quantum spin systems.

材料科学Materials Science

Scalable production of high-performing woven lithium-ion fibre batteries

高性能纤维锂离子电池的规模化构建

▲ 作者：Jiqing He, Chenhao Lu, Haibo Jiang, Fei Han, Xiang Shi, Jingxia Wu, Liyuan Wang, Taiqiang Chen, Jiajia Wang, Ye Zhang, Han Yang, Guoqi Zhang, Xuemei Sun, Bingjie Wang, Peining Chen, Yonggang Wang, Yongyao Xia & Huisheng Peng

▲ 链接：

https://www.nature.com/articles/s41586-021-03772-0

▲ 摘要

纤维锂离子电池作为一种灵活的电源解决方案很有吸引力，因为它们可以编织在纺织品上，为未来的可穿戴电子产品提供方便的供电方式。然而，它们的长度很难超过几厘米，而更长的纤维被认为具有更高的内阻，从而损害了电化学性能。

在此，我们的研究表明，这种纤维的内阻与纤维长度有一个双曲余切函数关系，随着长度的增加，它的内阻首先减少，然后趋于平稳。系统研究证实，这一发现适用于不同的纤维电池。通过优化的可扩展工业流程，我们能够生产数米高性能纤维锂离子电池。我们大规模生产的纤维电池的能量密度为每公斤85.69瓦时（典型值8小于每公斤1瓦时），这是基于氧化钴锂/石墨全电池的总重量，包括包装。

纤维弯曲10万次后，仍可保持80%以上的容量。我们展示了工业剑杆织机将纤维锂离子电池编织到安全且可清洗的纺织品中，可以给手机无线充电，或为集成了纤维传感器和纺织品显示器的衣物供电。

▲ Abstract

Fibre lithium-ion batteries are attractive as flexible power solutions because they can be woven into textiles, offering a convenient way to power future wearable electronics. However, they are difficult to produce in lengths of more than a few centimetres, and longer fibres were thought to have higher internal resistances that compromised electrochemical performance. Here we show that the internal resistance of such fibres has a hyperbolic cotangent function relationship with fibre length, where it first decreases before levelling off as length increases. Systematic studies confirm that this unexpected result is true for different fibre batteries. We are able to produce metres of high-performing fibre lithium-ion batteries through an optimized scalable industrial process. Our mass-produced fibre batteries have an energy density of 85.69 watt hour per kilogram (typical values8 are less than 1 watt hour per kilogram), based on the total weight of a lithium cobalt oxide/graphite full battery, including packaging. Its capacity retention reaches 90.5% after 500 charge–discharge cycles and 93% at 1C rate (compared with 0.1C rate capacity), which is comparable to commercial batteries such as pouch cells. Over 80 per cent capacity can be maintained after bending the fibre for 100,000 cycles. We show that fibre lithium-ion batteries woven into safe and washable textiles by industrial rapier loom can wirelessly charge a cell phone or power a health management jacket integrated with fibre sensors and a textile display.

化学Chemistry

Cleaving arene rings for acyclic alkenylnitrile synthesis

芳环开环裂解制备烯基腈

▲ 作者：Xu Qiu, Yueqian Sang, Hao Wu, Xiao-Song Xue, Zixi Yan, Yachong Wang, Zengrui Cheng, Xiaoyang Wang, Hui Tan, Song Song, Guisheng Zhang, Xiaohui Zhang, K. N. Houk & Ning Jiao

▲ 链接：

https://www.nature.com/articles/s41586-021-03801-y

▲ 摘要

合成化学是围绕碳碳键的形成而形成的。然而，选择性碳-碳键断裂方法的发展是一大挑战。这些方法在合成、煤液化、石油裂解、聚合物降解和生物质转化等方面具有广阔的应用前景。

在此，我们报告一个铜催化芳环的选择性碳碳键断裂开环策略。多种简单易得的芳烃衍生物（如苯胺、芳基硼酸、芳基叠氮化物、芳基卤化物等）通过选择性碳碳键裂解芳烃环转化成烯基腈。

该化学反应被应用于多环芳烃的改性和工业上重要的六亚甲基二胺和己二酸衍生物的制备。一些复杂分子和稠环化合物后期修饰的例子进一步支持了这种方法的潜在广泛应用。

▲ Abstract

Synthetic chemistry is built around the formation of carbon–carbon bonds. However, the development of methods for selective carbon–carbon bond cleavage is a largely unmet challenge. Such methods will have promising applications in synthesis, coal liquefaction, petroleum cracking, polymer degradation and biomass conversion. Here we report a copper-catalysed selective arene-ring-opening reaction strategy. Our aerobic oxidative copper catalyst converts anilines, arylboronic acids, aryl azides, aryl halides, aryl triflates, aryl trimethylsiloxanes, aryl hydroxamic acids and aryl diazonium salts into alkenyl nitriles through selective carbon–carbon bond cleavage of arene rings. This chemistry was applied to the modification of polycyclic aromatics and the preparation of industrially important hexamethylenediamine and adipic acid derivatives. Several examples of the late-stage modification of complex molecules and fused ring compounds further support the potential broad utility of this methodology.

Enantioselective synthesis of ammonium cations

铵离子的对映选择性合成

▲ 作者：Mark P. Walsh, Joseph M. Phelps, Marc E. Lennon, Dmitry S. Yufit & Matthew O. Kitching

▲ 链接：

https://www.nature.com/articles/s41586-021-03735-5

▲ 摘要

在这里，我们表明，通过超分子识别过程很容易控制铵离子的手性。通过将1,1 ' -联-2-萘酚支架介导的对映选择性铵离子识别与允许氮中心外消旋化的条件相结合，可以获得高收率和高选择性的手性铵离子。

机理研究表明，通过溶液和固相识别的结合，热力学驱动的加合结晶过程造成了观察到的选择性。不同于基于动态和动力学分辨率的过程，这是在动力学控制下，这允许增加选择性随时间的自我校正过程。

氮立体中心的重要性可以通过立体选择性超分子识别来揭示，这是自然存在的假对映体金鸡纳生物碱不可能的。随着对铵离子对映体形式的实际应用，这个以前被忽视的中心现在可以进行探索。

▲ Abstract

Here we show that control of the chirality of ammonium cations is easily achieved through a supramolecular recognition process. By combining enantioselective ammonium recognition mediated by 1,1′-bi-2-naphthol scaffolds with conditions that allow the nitrogen stereocentre to racemize, chiral ammonium cations can be produced in excellent yields and selectivities. Mechanistic investigations demonstrate that, through a combination of solution and solid-phase recognition, a thermodynamically driven adductive crystallization process is responsible for the observed selectivity. Distinct from processes based on dynamic and kinetic resolution, which are under kinetic control, this allows for increased selectivity over time by a self-corrective process. The importance of nitrogen stereocentres can be revealed through a stereoselective supramolecular recognition, which is not possible with naturally occurring pseudoenantiomeric Cinchona alkaloids. With practical access to the enantiomeric forms of ammonium cations, this previously ignored stereocentre is now available to be explored.

天体物理Astrophysics

Measuring the density structure of an accretion hot spot

测量吸积热点的密度结构

▲ 作者：C. C. Espaillat, C. E. Robinson, M. M. Romanova, T. Thanathibodee, J. Wendeborn, N. Calvet, M. Reynolds & J. Muzerolle

▲ 链接：

https://www.nature.com/articles/s41586-021-03751-5

▲ 摘要

磁层吸积模型预测，原行星盘的物质通过漏斗流吸积到恒星上，漏斗流遵循恒星磁场线和恒星表面的激波，留下密度梯度的热点。此前的工作提供了热点密度变化的观测证据，但这些观测结果对径向密度分布不敏感。

人们曾尝试用x射线观测来测量这种分布；然而，x射线辐射只跟踪到热点以及日冕辐射的一小部分。在此，我们报告了吸积恒星GM Aurigae的周期性紫外线和光学光曲线，它们的峰值之间有大约一天的时间间隔。这种周期性的产生是因为紫外线和光发射源随着恒星的旋转而进出。

这种时间差表明了恒星表面紫外线和光学亮度的空间分布的不同。在磁层吸积模型的框架内，这一发现表明在恒星表面的热点中存在径向密度梯度，因为不同密度的热点区域有不同的温度，因此发出不同波长的辐射。

▲ Abstract

Magnetospheric accretion models predict that matter from protoplanetary disks accretes onto stars via funnel flows, which follow stellar magnetic field lines and shock on the stellar surfaces, leaving hot spots with density gradients. Previous work has provided observational evidence of varying density in hot spots, but these observations were not sensitive to the radial density distribution. Attempts have been made to measure this distribution using X-ray observations; however, X-ray emission traces only a fraction of the hot spot and also coronal emission. Here we report periodic ultraviolet and optical light curves of the accreting star GM Aurigae, which have a time lag of about one day between their peaks. The periodicity arises because the source of the ultraviolet and optical emission moves into and out of view as it rotates along with the star. The time lag indicates a difference in the spatial distribution of ultraviolet and optical brightness over the stellar surface. Within the framework of a magnetospheric accretion model, this finding indicates the presence of a radial density gradient in a hot spot on the stellar surface, because regions of the hot spot with different densities have different temperatures and therefore emit radiation at different wavelengths.

地球科学Geoscience

The contribution of insects to global forest deadwood decomposition

昆虫对全球森林枯枝分解的贡献

▲ 作者：Sebastian Seibold, Werner Rammer, Torsten Hothorn, Rupert Seidl, Michael D. Ulyshen, Janina Lorz, Marc W. Cadotte, David B. Lindenmayer, Yagya P. Adhikari, Roxana Aragón et al.

▲ 链接：

https://www.nature.com/articles/s41586-021-03740-8

▲ 摘要

在此，我们提出了一个横跨55个站点、6大洲的木材分解实地试验。我们发现枯枝的分解速率随着温度的增加而增加，并且在高降水水平下有最强的温度效应。沉淀对分解速率的影响在低温下是负的，在高温下是正的。

作为净效应（包括昆虫的直接消耗和与微生物相互作用的间接效应），昆虫加速了热带森林的分解（每年平均损失3.9%）。在温带和寒带森林，我们发现了微弱的积极和消极影响，质量损失的中位数分别为每年0.9%和−0.1%。

此外，我们将实验推导出的分解函数应用到由经验和遥感数据合成的枯木碳全球地图上，获得了全球每年从枯木中释放的10.9±3.2千兆碳的估计，其中93%来自热带森林。在全球范围内，昆虫的净效应可能占枯木碳通量的29%，这表明昆虫在枯木分解和碳循环中具有重要的功能。

▲ Abstract

Here we present a field experiment of wood decomposition across 55 forest sites and 6 continents. We find that the deadwood decomposition rates increase with temperature, and the strongest temperature effect is found at high precipitation levels. Precipitation affects the decomposition rates negatively at low temperatures and positively at high temperatures. As a net effect—including the direct consumption by insects and indirect effects through interactions with microorganisms—insects accelerate the decomposition in tropical forests (3.9% median mass loss per year). In temperate and boreal forests, we find weak positive and negative effects with a median mass loss of 0.9 per cent and −0.1 per cent per year, respectively. Furthermore, we apply the experimentally derived decomposition function to a global map of deadwood carbon synthesized from empirical and remote-sensing data, obtaining an estimate of 10.9 ± 3.2 petagram of carbon per year released from deadwood globally, with 93 per cent originating from tropical forests. Globally, the net effect of insects may account for 29 per cent of the carbon flux from deadwood, which suggests a functional importance of insects in the decomposition of deadwood and the carbon cycle.