《自然》(20240523出版)一周论文导读
编译 | 未玖
Nature, 23 May 2024, VOL 629, ISSUE 8013
《自然》2024年5月23日,第629卷,8013期
天文学Astronomy
The solar dynamo begins near the surface
太阳发电机效应始于太阳表面附近
▲ 作者:Geoffrey M. Vasil, Daniel Lecoanet, Kyle Augustson, Keaton J. Burns, Jeffrey S. Oishi, Benjamin P. Brown, et al.
▲ 链接:
https://www.nature.com/articles/s41586-024-07315-1
▲ 摘要:
太阳磁发电机效应周期具有独特模式:太阳黑子出现的传播区域位于纬度30°附近,每11年在赤道附近消失。此外,被称为扭转振荡的纵向流动与太阳黑子迁移密切相关,毫无疑问具有共同原因。
与暗示这些现象深层起源的理论相反,日震学将低纬度扭转振荡精确定位于太阳外层的5~10%,即近太阳表面剪切层。在该区域内,向内增加的差动旋转与极向磁场耦合,强烈暗示了磁旋转不稳定性,这在吸积盘理论中很突出,在实验室中亦可观测。总之,这两个事实引出了一个普遍的问题:太阳发电机效应是否源于近太阳表面的不稳定性。
研究组报告了强有力的肯定证据,与关注更深差旋层的传统模型形成鲜明对比。简单的分析估计表明,近太阳表面磁旋转不稳定性更好地解释了扭转振荡的时空尺度和推断的太阳内部磁场振幅。
最先进的数值模拟证实了这些估计,并重现了半球磁流螺旋度定律。发电机效应产生于一个被充分理解的近太阳表面现象,这有助于对影响地球电磁基础设施的全磁周期和空间天气进行准确预测。
▲ Abstract:
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating region of sunspot emergence appears around 30° latitude and vanishes near the equator every 11?years. Moreover, longitudinal flows called torsional oscillations closely shadow sunspot migration, undoubtedly sharing a common cause. Contrary to theories suggesting deep origins of these phenomena, helioseismology pinpoints low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface shear layer. Within this zone, inwardly increasing differential rotation coupled with a poloidal magnetic field strongly implicates the magneto-rotational instability, prominent in accretion-disk theory and observed in laboratory experiments. Together, these two facts prompt the general question: whether the solar dynamo is possibly a near-surface instability. Here we report strong affirmative evidence in stark contrast to traditional models focusing on the deeper tachocline. Simple analytic estimates show that the near-surface magneto-rotational instability better explains the spatiotemporal scales of the torsional oscillations and inferred subsurface magnetic field amplitudes. State-of-the-art numerical simulations corroborate these estimates and reproduce hemispherical magnetic current helicity laws. The dynamo resulting from a well-understood near-surface phenomenon improves prospects for accurate predictions of full magnetic cycles and space weather, affecting the electromagnetic infrastructure of Earth.
物理学Physics
Lithium tantalate photonic integrated circuits for volume manufacturing
可量产的钽酸锂光子集成电路
▲ 作者:Chengli Wang, Zihan Li, Johann Riemensberger, Grigory Lihachev, Mikhail Churaev, Wil Kao, et al.
▲ 链接:
https://www.nature.com/articles/s41586-024-07369-1
▲ 摘要:
基于铌酸锂(LiNbO3)的电-光光子集成电路(PICs)已被证明具有高Pockels系数材料的巨大能力。这实现了互补金属-氧化物-半导体电压水平下工作的线性和高速调制器可用于数据中心通信、高性能计算和AI光子加速器等应用。
然而,这种技术的工业应用受到单片晶圆高成本和有限晶圆尺寸的阻碍。高成本是由于在微电子领域的巨大投资推动了绝缘体上硅(SOI)光子学的采用,而在其他领域缺乏现有的高容量应用。
研究组报道了由钽酸锂(LiTaO3)制成的低损耗PIC,LiTaO3已在商业上用于5G射频滤波器,因此可以低成本进行可扩展的制造,并且LiTaO3具有与LiNbO3相似甚至在某些情况下更优的性能。结果表明,使用基于深紫外(DUV)步进的制造工艺,LiTaO3可被蚀刻以创建低损耗(5.6 dB m-1)PIC。