Superradiant Emission from Coherent Excitons in van Der Waals Heterostructures

Recent advancements in isolation and stacking of layered van der Waals materials have created an unprecedented paradigm for demonstrating varieties of 2D quantum materials. Rationally designed van der Waals heterostructures composed of monolayer transition-metal dichalcogenides (TMDs) and few-layer hBN show several unique optoelectronic features driven by correlations. However, entangled superradiant excitonic species in such systems have not been observed before. In this report, it is demonstrated that strong suppression of phonon population at low temperature results in a formation of a coherent excitonic-dipoles ensemble in the heterostructure, and the collective oscillation of those dipoles stimulates a robust phase synchronized ultra-narrow band superradiant emission even at extremely low pumping intensity. Such emitters are in high demand for a multitude of applications, including fundamental research on many-body correlations and other state-of-the-art technologies. This timely demonstration paves the way for further exploration of ultralow-threshold quantum-emitting devices with unmatched design freedom and spectral tunability.     

Hierarchical Coherent Phonons in a Superatomic Semiconductor

The coupling of phonons to electrons and other phonons plays a defining role in material properties, such as charge and energy transport, light emission, and superconductivity. In atomic solids, phonons are delocalized over the 3D lattice, in contrast to molecular solids where localized vibrations dominate. Here, a hierarchical semiconductor that expands the phonon space by combining localized 0D modes with delocalized 2D and 3D modes is described. This material consists of superatomic building blocks (Re₆Se₈) covalently linked into 2D sheets that are stacked into a layered van der Waals lattice. Using transient reflectance spectroscopy, three types of coherent phonons are identified: localized 0D breathing modes of isolated superatom, 2D synchronized twisting of superatoms in layers, and 3D acoustic interlayer deformation. These phonons are coupled to the electronic degrees of freedom to varying extents. The presence of local phonon modes in an extended crystal opens the door to controlling material properties from hierarchical phonon engineering.     

Sounds Stimulation on In Vitro HL1 Cells: A Pilot Study and a Theoretical Physical Model

Mechanical vibrations seem to affect the behaviour of different cell types and the functions of different organs. Pressure waves, including acoustic waves (sounds), could affect cytoskeletal molecules via coherent changes in their spatial organization and mechano-transduction signalling. We analyzed the sounds spectra and their fractal features. Cardiac muscle HL1 cells were exposed to different sounds, were stained for cytoskeletal markers (phalloidin, beta-actin, alpha-tubulin, alpha-actinin-1), and studied with multifractal analysis (using FracLac for ImageJ). A single cell was live-imaged and its dynamic contractility changes in response to each different sound were analysed (using Musclemotion for ImageJ). Different sound stimuli seem to influence the contractility and the spatial organization of HL1 cells, resulting in a different localization and fluorescence emission of cytoskeletal proteins. Since the cellular behaviour seems to correlate with the fractal structure of the sound used, we speculate that it can influence the cells by virtue of the different sound waves’ geometric properties that we have photographed and filmed. A theoretical physical model is proposed to explain our results, based on the coherent molecular dynamics. We stress the role of the systemic view in the understanding of the biological activity.     

复频电导技术在隧洞超前探水中的应用

围岩富水带是隧道超前预报最关注的问题，目前，多使用电磁方法来预报围岩的含水性，但受到场地条件限制，面临掌子面条件、金属机具干扰、三维波场定位等诸多困难，特别是掌子面前方100 m范围内围岩的含水性预报，在国内外都是一个新的高难课题。在研究了岩体电导率与电容率复频特性的基础上，结合巴基斯坦NJ-TBM引水隧洞工程，开发了复频电导探水(CFC)技术。该技术基于电磁波反射与相干原理，选用100 kHz～10 MHz频率范围，采用电偶极子发射与阵列接收方式和偏移成像技术，突破了隧道内场地条件的限制。依据1/4相干波长确定含水体的位置，相干能量确定含水量的大小。在巴基斯坦NJ-TBM隧洞超前探水的应用，证明了该方法的可行性与有效性。      

混凝土高温试验及高温后抗压残余强度研究

介绍混凝土高温试验过程和试验现象。对高温后混凝土的抗压强度进行了力学性能测试，得到高温后混凝土试块的抗压残余强度。综合4种高温后混凝土抗压残余强度公式，通过曲线图形与本试验结果进行对照比较，找出一致性较优公式。     

厚膜干涉的研究

对普通单色光源照射下厚膜不产生干涉现象的原因作了多方面分析，并从实验和理论两方面给出了能产生干涉现象的膜厚的量值。     

相干态光场的位相涨落

根据Pegg-Barnett位相理论,推导出相干态光场的位相概率分布函数,计算出位相涨落,并利用MATHEMATICA对相干态光场的位相函数和位相涨落进行了数值模拟,画出了示意图.结果表明位相函数同时受e指数函数和幂指数函数的制约,从均匀分布到泊松分布到均匀分布,直至呈现零分布;在位相变化的一个周期内,相干态位相分布曲线出现涨落,涨落同时受参考位相和相干系数的影响,随着n值的增加,曲线趋向于高斯分布.     

色噪声背景下基于声矢量阵列孔径扩展的相干目标波达方向估计

在目标波达方向(DOA)估计中,更大的阵列孔径往往能够获得更高估计分辨率和估计精度.然而,在色噪声背景或相干目标情况下,子空间类DOA估计算法性能急剧下降.针对这个问题,采用2个分置且相互垂直的均匀线性矢量阵列,通过阵列之间的协方差矩阵前向/后向平滑进行解相干预处理,并消除有色噪声的干扰;然后利用传播因子方法(PM)得...     

应用于高精度 ADC 频谱测试的改进加窗技术

在进行模数据转换器(ADC)频谱测试时,通常需要满足相干采样条件。但这一要求的实现较为困难,测试时如果不满足就会发生频谱泄漏现象。为了抑制泄漏,目前最常用的方法是使用加窗技术。但该方法的使用要求较为严格,无法胜任目前高精度ADC的测试,且需要使用者十分熟悉窗函数原理。通过对频谱泄漏和加窗技术进行详尽的理论推导,提出了一种选定合适窗函数类型以及扩展系数(span)的方法,使测试者不需要过多的先验知识。通过所提方法,在窗函数的第一旁瓣高于噪声基底时,仍然能完成高精度ADC的测试工作,扩大了常见窗函数的应用范围。使得常见窗函数如汉宁窗等,也能应用于18位的高精度ADC测试工作。仿真结果显示所提算法在任意非相干程度下仍可得到准确的测试结果,各项参数的最大误差均小于1 dB。同时,使用了一款商用18位ADC实验结果验证了所提算法的可行性。     

A Study of Total Transient Energy During the Fault Period

The total transient energy accumulated during the fault period is an important factor affecting power system dynamics. In this paper, we present a study of the total transient energy. First, we analyze the characteristics of energy interchange during the fault period. Then, an expression is developed based on characteristics analysis to estimate the total transient energy. Such an expression allows us to study how a fault, in terms of its magnitude, clearing time, and location, affects the total transient energy. Especially, the distribution factors of the total transient energy are defined based upon the expression to analyze the impact of fault location. It is found that for a fault with the given magnitude and clearing time, the total amount of total transient energy mainly depends on the difference in the distribution factors. Furthermore, it is found that the distribution factors can be applied to the identification of potential critical fault locations, the identification of coherent generators, and the identification of critical generators. The analysis results and their applications are demonstrated in the IEEE 9-bus system and the IEEE 39-bus system.