Ultra-Broadband Infrared Metamaterial Absorber for Passive Radiative Cooling

Infrared metamaterial absorber(MMA) based on metal-insulator-metal(MIM) configuration with flexible design,perfect and selective absorption,has attracted much attention recently for passive radiative cooling applications.To cool objects passively,broadband infrared absorption(i.e.8-14 μm) is desirable to emit thermal energy through atmosphere window.We present a novel MMA composed of multilayer MIM resonators periodically arranged on a PbTe/MgF_2 bilayer substrate.Verified by the rigorous coup led-wave analysis method,the proposed MMA shows a relative bandwidth of about 45%(from 8.3 to 13.1 μm with the absorption intensity over 0.8).The broadband absorption performs stably over a wide incident angle range(below 50°) and predicts 12 K cooling below ambient temperature at nighttime.Compared with the previous passive radiative coolers,our design gets rid of the continuous metal substrate and provides an almost ideal transparency window(close to 100%)for millimeter waves over 1 mm.The structure is expected to have potential applications in thermal control of integrated devices,where millimeter wave signal compatibility is also required.     

H2S、HCN、PH3在FeO（100）表面吸附的密度泛函理论研究

基于密度泛函理论研究了H2S、HCN、PH3 在FeO(100)表面的吸附行为,其吸附位点主要考虑四个：Fe-top(铁顶位)、O-top(氧顶位)、Hollow(空位)、Bridge(桥位)。结果表明H2S吸附在O-top吸附位点的吸附能最小,为-1.02ev,即在该位点的吸附体系最稳定。当HCN吸附在FeO(100)表面时,各吸附位点的稳定顺序为Hollow>Fe-top>Bridge>O-top。PH3 的最稳定的吸附位点与H2S的一致,为O-top吸附位点,其吸附能为-1.11ev。当H2S吸附在O-top吸附位点时,H2S与FeO（100）表面的电荷转移量最多,说明该吸附构型最稳定,而HCN吸附在FeO(100)表面,在Hollow吸附位点的电荷转移量最多,也即该吸附位点属于最稳定吸附位点。PH3与FeO（100）表面之间的电荷转移量最多的吸附位点与H2S的相同。当H2S和PH3吸附在O-top吸附位点时,吸附后的态密度曲线整体向低能级移动,峰值降低,其吸附结构变得更加稳定。而HCN吸附在Hollow位点时,吸附后的HCN态密度曲线向能量更低的区域移动,吸附体系变得更稳定。     

GDP vs. LDP: A Survey from the Perspective of Information-Theoretic Channel

The existing work has conducted in-depth research and analysis on global differential privacy (GDP) and local differential privacy (LDP) based on information theory. However, the data privacy preserving community does not systematically review and analyze GDP and LDP based on the information-theoretic channel model. To this end, we systematically reviewed GDP and LDP from the perspective of the information-theoretic channel in this survey. First, we presented the privacy threat model under information-theoretic channel. Second, we described and compared the information-theoretic channel models of GDP and LDP. Third, we summarized and analyzed definitions, privacy-utility metrics, properties, and mechanisms of GDP and LDP under their channel models. Finally, we discussed the open problems of GDP and LDP based on different types of information-theoretic channel models according to the above systematic review. Our main contribution provides a systematic survey of channel models, definitions, privacy-utility metrics, properties, and mechanisms for GDP and LDP from the perspective of information-theoretic channel and surveys the differential privacy synthetic data generation application using generative adversarial network and federated learning, respectively. Our work is helpful for systematically understanding the privacy threat model, definitions, privacy-utility metrics, properties, and mechanisms of GDP and LDP from the perspective of information-theoretic channel and promotes in-depth research and analysis of GDP and LDP based on different types of information-theoretic channel models.     

半导体激光泵浦亚稳态氩气激光器实现激光振荡

采用基于体布拉格光栅的窄线宽半导体激光器作为泵浦源,以电容耦合式射频激励Ar, He混合气体放电等离子体为增益介质,在双程纵向泵浦的结构下实现了连续波模式的912 nm的激光输出。     

六角星形MoSe_2双层纳米片的制备及其光致发光性能

采用化学气相沉积法,以三氧化钼作为钼源,硒粉作为硒源,在H_2/Ar气氛下生长出硒化钼纳米片.扫描电镜、X射线衍射表征结果表明,MoSe_2产物呈六角星状,横向尺寸约10μm,具有很好的晶体质量和结构.拉曼光谱表征其结构,确定其为双层纳米片.研究表明,高温反应时间对双层纳米片的生长具有重要的影响.通过对双层纳米片的生长机理的探究,推测其经历了3个生长过程:在高温下,Mo源和Se源被气化成气态分子并发生硒化反应形成晶核;晶核呈三角形外延生长;当反应时间持续增加,在空间位阻效应的影响下,晶体以中心原子岛为核,外延耦合生长出第二层三角形,最终形成六角星状双层纳米片.光致发光光谱结果表明,六角星状MoSe_2双层纳米片在1.53 eV处具有直接带隙和1.78 eV处具有间接带隙,其较宽范围的激发光谱响应预测其在光电探测器件领域具有潜在的应用前景.     

化学战剂的SERS检测及应用前景研究

化学武器和技术的扩散使化学恐怖活动成为事关世界安全的突出问题之一.针对化学战剂的高毒性和快速致命特点,表面增强拉曼散射(SERS)光谱技术研究可以实现生化战剂的快速、高灵敏实时检测,有助于战时和突发恐怖袭击时对人员的及时救治和预防,为更好的防范化学武器威胁和恐怖袭击提供必要的技术保障.本文主要对SERS技术在化学战剂检...     

Morphology and elemental behaviour in the alteration layer of borosilicate glass in simulated groundwater

To understand the behaviour of nuclear waste glass in groundwater, borosilicate glasses were placed in simulated groundwater for more than 200 days. The composition of the simulated groundwater was similar to that of the groundwater in Beishan (a potential nuclear waste site). The pH value of groundwater was adjusted to 7.5, and the ratio of the surface area of glass to the volume of the solution (SA/V) was set to 10?m^?1. Solutions and bulk glasses were characterised to obtain the elemental behaviour and surface morphology of the glass/solution interface, which was named the alteration layer. The mean thicknesses of the alteration layer were 5.16?±?0.11?µm and 11.67?±?0.28?µm at 70°C and 90°C, respectively. A thicker alteration layer was attributed to the lower surface activation energy of the glass and a high ion exchange between K⁺ and Na⁺ in the interface between the glass surface and the solution. For the elemental behaviour, mobile species B and Na were depleted, while K and Ca from the solution were enriched in the alteration layer due to ion exchange. Network species Si decreased in the layer, leading to the corrosion of the backbone of the glass; however, species Al increased, which implied that some [SiO₄] units were partially replaced by [AlO₄] units. In this work, glass in groundwater suffered much more intense corrosion than that in de-ionised water.     

Frequency and intensity readouts of micro-wave electric field using Rydberg atoms with Doppler effects

A scheme of electric-field measurement of micro-waves is proposed in Rydberg atoms with Doppler effects. A cascade-type electromagnetically-induced-transparency (EIT) system is disturbed by a perturbative field coupling a metastable transition. The original dark state splits and two EIT window appear with a central absorption peak. When a micro-wave (MW) field couples the Rydberg transition, the central absorption peak is divided into two. The frequency splitting of two central peaks is proportional to the MW field intensity, which can be used to probe MW electric field strength. This frequency-readout method based on a double-dark state system increases the probe sensitivity nearly by a factor of 7, compared with that of the single-dark state case. At room temperature, Doppler effects can enhance the absorption spectrum, moreover, its peak value varies linearly with the MW field strength. This can also serve to measure MW electric field strength. Numerical results show that the latter intensity-readout method after Doppler averaging improves the probe sensitivity by a factor of 10 with respect to the case without Doppler effects.     

巡天光谱中拼接异常光谱的自动检测和异常分级方法

拼接异常是光谱在红蓝两端拼接区域表现出的光谱连续性差的一种现象。在LAMOST的光谱处理中,仪器的稳定性、观测条件以及获得的响应函数等问题都是造成拼接异常的原因。光谱拼接是否正常对于光谱发布等后续工作的质量有重要影响。提出一种拼接异常光谱的自动检测方法,有效地提高了工作效率。该研究可以为LAMOST数据提供一个自动的标记,来评价拼接质量,也可以为用户提供一个使用数据时的选择。该方法首先将待测光谱进行流量归一化、去除钠线等预处理,并将其分为红蓝两端;然后对红蓝两端分别进行拟合;最后对两条拟合曲线,选取一系列等波长间隔的点,计算在这些点处的流量差值,得到所有流量差值的均值,标准差,并且计算两条曲线积分面积的差值;基于上述统计量,提出了一个判断光谱是否异常及其异常程度的评价函数。大量的实验证明,该方法具有良好的拼接异常光谱检测效果。     

High-power 880-nm diode-directly-pumped passively mode-locked Nd:YVO₄ laser at 1342 nm with a semiconductor saturable absorber mirror

A high-power 880-nm diode-directly-pumped passively mode-locked 1342 nm Nd:YVO? laser was demonstrated with a semiconductor saturable absorber mirror (SESAM). The laser mode radii in the laser crystal and on the SESAM were optimized carefully using the ABCD matrix formalism. An average output power of 2.3 W was obtained with a repetition rate of 76 MHz and a pulse width of 29.2 ps under an absorbed pump power of 12.1 W, corresponding to an optical-optical efficiency of 19.0% and a slope efficiency of 23.9%, respectively.