NRD leaky-wave antenna for narrow beams in 94GHz

Theoretical analyses and numerical results of NRD leaky-wave antenna are presented. The results show that the characteristics of frequency scanning and very narrow beam can be implemented by NRD leaky-wave antenna. At the freguency of 94GHz, the half-power beamwidth of 0.14° of the antenna canbe obtained when the length of the antenna is 1.5m. From 90 to 98GHz, frequency scanning is about ±7° relating to the beam angle at 94GHz. The theoretical results are compared with the experimental data.     

200KV重离子加速器及其应用

本文介绍一台采用双潘宁型多电荷重离子源的200kV重离子加速器,简述它在GaP光探测器的研制、聚合物材料和金属材料的离子注入改性等方面的研究与应用。     

SPOC：结合高校教学的融合创新

从2008年开始,MOOCs经历了一个四年沉淀,两年爆发的发展历程.与以往的网络教育相比,名校名师效应、易学易用性的优势作用于教育资源绝对稀缺、网络环境大幅改善的环境,迅速点燃了人们强烈的学习动机,形成爆发式增长.在基于教学需求的探索过程当中,与传统教育方式的“融合创新”开始兴起,其中有一种非常值得关注的模式就是由Armando Fox教授提出的SPOC模式,哈佛、MIT、加州伯克利都在进行SPOC教学试验.在中国,清华大学出版社率先打造出SPOC平台,推出《大学物理》等课程,配套了完整的教学资源,开启了SPOC模式在中国的应用.     

Systematically investigating the polarization gradient cooling in an optical molasses of ultracold cesium atoms

We systematically investigate the polarization gradient cooling （PGC） process in an optical molasses of ultracold cesium atoms. The SR mode for changing the cooling laser, which means that the cooling laser frequency is stepped to the setting value while its intensity is ramped, is found to be the best for the PGC, compared with other modes studied. We verify that the heating effect of the cold atoms, which appears when the cooling laser intensity is lower than the saturation intensity, arises from insufficient polarization gradient cooling. Finally, an exponential decay function with a statistical explanation is introduced to explain the dependence of the cold atom temperature on the PGC interaction time.     

Ocean internal waves interpreted as oscillation travelling waves in consideration of ocean dissipation

Most studies of the synthetic aperture radar remote sensing of ocean internal waves are based on the solitary wave solutions of the Korteweg-de Vries （KdV） equation, and the dissipative term in the KdV equation is not taken into account. However, the dissipative term is very important, both in the synthetic aperture radar images and in ocean models. In this paper, the traveling-wave structure to characterize the ocean internal wave phenomenon is modeled, the results of numerical experiments are advanced, and a theoretical hypothesis of the traveling wave to retrieve the ocean internal wave parameters in the synthetic aperture radar images is introduced.     

音频信号压缩技术的物理基础

信号压缩是数字电路中的一个基本概念，就其物理本质而言，这里的“压”指的是增加单位面积上的信号储存的密度；“缩”指的是在不影响感知效果的条件下减小信号中不必要的成分．人们对于“压”的理解通常比较深刻，下面以音频信号为例，主要从“缩”的角度出发谈谈音频信号压缩技术的物理基础．     

Warm-white light-emitting diodes integrated with colloidal quantum dots for high luminous efficacy and color rendering

Warm-white LEDs (WLEDs) with high spectral quality and efficiency are required for lighting applications, but current experimental performances are limited. We report on nanocrystal quantum dot (NQD) hybridized WLEDs with high performance that exhibit a high luminous efficacy of optical radiation exceeding 350lm/W(opt) and a high color rendering index close to 90 at a low correlated color temperature <3000K. These spectrally engineered WLEDs are obtained using a combination of CdSe/ZnS core/shell NQD nanophosphors integrated on blue InGaN/GaN LEDs.     

Large transport critical currents of powder-in-tube Sr0.6K0.4Fe2As2/Ag superconducting wires and tapes

We report the achievement of transport critical currents in Sr_0.6K_0.4Fe₂As₂ wires and tapes with a T_c = 34 K. The wires and tapes were fabricated through an in situ powder-in-tube process. Silver was used as a chemical addition as well as a sheath material. All the wire and tape samples have shown the ability to transport superconducting current. Critical current density J_c was enhanced upon silver addition, and at 4.2 K, a largest J_c of ～1200 A/cm² (I_c = 9 A) was achieved for 20% silver added tapes, which is the highest in iron-based wires and tapes so far. The J_c is almost field independent between 1 T and 10 T, exhibiting a strong vortex pinning. Such a high transport critical current density is attributed to the weak reaction between the silver sheath and the superconducting core, as well as an improved connectivity between grains. We also identify a weak-link behavior from the apparent drop of J_c at low fields and a hysteretic phenomenon. Finally, we found that compared to Fe, Ta and Nb tubes, Ag was the best sheath material for the fabrication of high-performance 122 type pnictide wires and tapes.