Phase-locked single-mode terahertz quantum cascade lasers array

We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback(DFB)grating,resulting in nearly five times amplification of the single-mode power.Due to the optimum length of Talbot cavity depends on wavelength,the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry-Perot(F-P)cavities.The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array,enabling phase-locked operation of ridges.We set the spacing between adjacent elements to be 220μm,much larger than the free-space wavelength,ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution.This scheme provides a new approach for enhancing the single-mode power of THz QCLs.

Research Advances on Cyclohexane Catalytic Cracking

This article elaborates on the research achievements of domestic and foreign researchers in exploring the conversion pathways and reaction mechanisms of cyclohexane catalytic cracking in recent years.It analyzes the effects of different catalysts and process conditions on the conversion laws of cyclohexane,summarizes the conversion pathways of cyclohexane,and discusses the chemical mechanisms of several main reactions of cyclohexane in catalytic cracking,such as cracking,isomerization,hydrogen transfer,dehydrogenation,and alkylation;Several advanced characterization methods and common research methods were listed,and prospects for future development in this field were proposed based on existing research.

Disaster Risk Reduction,Climate Change Adaptation and Their Linkages with Sustainable Development over the Past 30 Years:AReview

The severe damage and impacts caused by extreme events in a changing climate will not only make the sustainable development goals difficult to achieve,but also erode the hard-won development gains of the past.This article reviews the major impacts and challenges of disaster and climate change risks on sustainable development,and summarizes the courses and linkages of disaster risk reduction(DRR),climate change adaptation(CCA),and sustainable development over the past 30 years.Our findings show that the conceptual development of DRR actions has gone through three general phases:disaster management in the 1990s,risk management in the 2000s,and resilient management and development in the 2010s.Gradually,CCA has been widely implemented to overcome the adverse effects of climate change.A framework is proposed for tackling climate change and disaster risks in the context of resilient,sustainable development,indicating that CCA is not a subset of DRR while they have similarities and differences in their scope and emphasis.It is crucial to transform governance mechanisms at different levels,so as to integrate CCA and DRR to reduce disaster and climate change risks,and achieve safe growth and a resilient future in the era of the Anthropocene.

基于网络大数据和水文-水动力模型的沿海城市洪水风险与适应

气候变化、海平面上升、地面沉降和快速城市化很可能将加剧沿海城市洪水风险.如何定量刻画洪水风险未来变化趋势并进行有效适应是亟待解决的前沿科学问题.为此,我们提出了一套多学科的综合方法:(1)基于网络大数据和机器学习对承灾体分布与暴露价值进行精细尺度建模;(2)基于水文-水动力模型对未来极端风暴洪水进行淹没情景模拟;(3)针对不同情景进行经济损失风险分析和适应措施的成本效益评估.以上海为例,将上述方法应用于综合评估极端风暴洪水情景下的住宅建筑风险、未来演化(2050年)和适应措施的成本效益.结果表明,海平面上升和地面沉降将显著加剧上海的洪水风险,RCP4.5、RCP8.5和RCP8.5 High-end三种典型浓度情景下住宅建筑的年期望损失在2050年达7.0亿元~9.0亿元,是当前结果的1.6~2.0倍.实施干适应措施和湿适应措施可分别将年期望损失减少76%~79%和88%~90%;并且两种措施均具有可观的成本效益,净现值分别达28.4亿元~55.3亿元和58.5亿元~99.4亿元,效益/成本比分别为1.9~2.4和7.9~9.8.上述研究可为科学理解和有效适应上海未来洪水风险提供依据,该综合分析方法也可应用于其他沿海城市的洪水风险和适应策略研究.

Continuous-wave single-mode quantum cascade laser at 5.1 THz based on graded sampled grating design

We report on the terahertz(THz)quantum cascade lasers in continuous-wave(CW)operation with an emitting frequency above 5 THz.Excellent performance with a smaller leakage current and higher population inversion efficiency is obtained by one-well bridged bound-to-continuum hybrid quantum design at 5 THz.By designing and fabricating a graded metallic sampled distributed feedback grating in the waveguide,the first single-mode THz quantum cascade laser at 5.13 THz in CW operation mode is achieved.The maximum single-mode optical power of~48 mW is achieved at 15 K with a side-mode suppression ratio above 24 dB.This will draw great interest in the spectroscopy applications above the 5 THz range for THz quantum cascade lasers.