Optically pumped wavelength-tunable lasing from a GaN beam cavity with an integrated Joule heater pivoted on Si

Dynamically tunable laser sources are highly promising for realizing visionary concepts of integrated photonic circuits and other applications. In this paper, a Ga N-based laser with an integrated PN junction heater on Si is fabricated.The photoluminescence properties of the Ga N beam cavity are controlled by temperature, and the Joule heater provides electrically driven regulation of temperature. These two features of the cavity make it possible to realize convenient tuning of the lasing properties. The multi-functional Ga N beam cavity achieves optically pumped lasing with a single mode near 362.4 nm with a high Q-factor of 1394. The temperature of this device increases by 0–5℃ under the Joule heating effect. Then, electrical control of the lasing mode is demonstrated. The lasing resonant peak shows a continuous redshift of about 0.5 nm and the device also exhibits dynamic switching of its lasing mode. The lasing modulation can be ascribed to temperature-induced reduction of the bandgap. Our work may be of benefit for external optical modulation in future chip-based optoelectronic devices.

Aeolian transport over a developing transverse dune

The spatial and temporal changes in aeolian transport over a dune are fundamental factors that control the morphology of the dune. In the present study, we obtained direct field observations of aeolian transport over a developing transverse dune at the Shapotou Aeolian Experiment Site in the southeastern part of China＇s Tengger Desert. The transport rate versus wind speed relationship relationships over flat surfaces and over dunes that are s complicated over a developing dune compared with the n equilibrium with the wind. We obtained trend lines for transport rate over the transverse dune versus distance. The transport rate generally increased from the toe to the crest above the stoss slope, but the difference in transport rate between the crest and the toe was smaller than those that have been proposed for taller dunes. The crest/toe ratio for transport rates therefore seems to depend greatly on dune height. Flux density profiles for different points above the dune at different wind speeds were well described by the exponential decay law, as has been proposed for saltation flux density profiles. Coefficients in the flux density profile function can be defined in terms of the transport rate and wind speed. However, the dependence of relative decay rate with height and average saltation height on wind speed was weaker than that observed in a wind tunnel and above a fiat surface. The preliminary results obtained in this study require more evidence from field observations to fully describe aeolian transport above developing dunes.

Land use and land cover change and its driving forces in Maqu County, China in the past 25 years

Maqu County is located in the northeast Qinghai-Tibetan Plateau, and it is the main watershed for the Yellow River. The ecosystem there is extremely vulnerable and sensitive to climate change and human activities, which have caused significant deterioration of the eco-environment in this region. In order to restore the ecological environment, a government project to restore the grazing areas to grassland was implemented in Maqu County in early 2004. This study evaluates the effects of that restoration project on land use and land cover change （LUCC）, and explores the driving forces of LUCC in Maqu County. In the study we used Landsat images obtained in 1989, 2004, 2009, and 2014 to establish databases of land use and land cover. Then we derived LUCC information by overlaying these layers using GIS software. Finally, we analyzed the main forces responsible for LUCC. The results showed that forests, high-coverage grasslands, and marshes experienced the most significant decreases during 1989–2004, by 882.8 ha, 35,250.4 ha, and 2,753.4 ha, respectively. However, moderate- and low-coverage grasslands and sand lands showed the opposite trend, increasing by 12,529.7 ha, 25,491.0 ha, and 577.5 ha, respectively. LUCC in 2004–2009 showed that ecological degradation slowed compared with 1989？2004. During 2009–2014, high- and moderate-coverage grasslands increased obviously, but low-coverage grasslands, marshes, unused lands, sand lands, and water areas showed the opposite trend. These results suggested that the degradation of the eco-environment was obvious before 2009, showing a decrease in the forests, grasslands, and water areas, and an increase in unused lands. The ecological degradation was reversed after 2009, as was mainly evidenced by increases in high- and mod-erate-coverage grasslands, and the shrinkage rate of marshes decreased obviously. These results showed that the project of restoring grazing lands to grassland had a positive effect on the LUCC. Other major factors that influence the LUCC include increasing temperature, variation in the seasonal frozen soil environment, seasonal overgrazing, and pest and rodent damage.

一种具有类牙釉质多级结构的高强高韧羟基磷灰石基纤维

牙釉质是人体最硬的组织,力学性能优异.牙釉质内部的纳米线-微米簇-有序阵列的多级结构是其具有优异力学性能的关键.通过模仿牙釉质的微结构有望实现人造材料力学性能的突破,但是多级次模仿天然牙釉质的微结构仍是巨大的挑战.本文中,我们制备了由长程有序晶体/非晶羟基磷灰石(HAP)纳米线组成的HAP微米簇,并通过剪切诱导组装将其纺成类牙釉质高性能宏观纤维.该纤维具有高度有序的纳米线-微米簇结构,并且HAP纳米线、HAP微米簇和聚合物基体之间的强界面连接使得该纤维在受力时具有一种多级的能量耗散途径.因此该类牙釉质纤维兼具高强度(196.3 MPa)和高韧性(46.3 MJ m^(-3)),其断裂韧性超过了先前报道的HAP基复合纤维的最大值.这种多级类牙釉质设计策略为高强度和高韧性纤维的开发提供了新的思路,在潜在的工程和生物修复领域具有广阔的应用前景.

Concentration sensing system with monolithic InGaN/GaN photonic chips

Using an identical monolithic InGaN/GaN light emitting diode (LED) array as the sensing module and a well-designed data processing module, we demonstrate a small-size concentration sensing prototype. Overlap between the emission and the response spectra of the InGaN/GaN LED makes each pair of LEDs in the arrayed chip form a sensing channel. The changes in liquid concentration can be transformed into variation of photocurrent. The system's sensing properties are further optimized by varying the position, number of receivers, and packaging reflectors. With methyl orange as a tracer agent, the sensing system's resolution is 0.286 μmol/L with a linear measurement region below 40 μmol/L.

Distinct immune escape and microenvironment between RG-like and pri-OPC-like glioma revealed by single-cell RNA-seq analysis

The association of neurogenesis and gliogenesis with glioma remains unclear.By conducting single-cell RNA-seq analyses on 26 gliomas,we reported their classification into primitive oligodendrocyte precursor cell(pri-OPC)-like and radial glia(RG)-like tumors and validated it in a public cohort and TCGA glioma.The RG-like tumors exhibited wild-type isocitrate dehydrogenase and tended to carry EGFR mutations,and the pri-OPC-like ones were prone to carrying TP53 mutations.Tumor subclones only in pri-OPC-like tumors showed substantially down-regulated MHC-I genes,suggesting their distinct immune evasion programs.Furthermore,the two subgroups appeared to extensively modulate glioma-infiltrating lymphocytes in distinct manners.Some specific genes not expressed in normal immune cells were found in glioma-infiltrating lymphocytes.For example,glial/glioma stem cell markers OLIG1/PTPRZ1 and B cell-specific receptors IGLC2/IGKC were expressed in pri-OPC-like and RG-like glioma-infiltrating lymphocytes,respectively.Their expression was positively correlated with those of immune checkpoint genes(e.g.,LGALS33)and poor survivals as validated by the increased expression of LGALS3 upon IGKC overexpression in Jurkat cells.This finding indicated a potential inhibitory role in tumor-infiltrating lymphocytes and could provide a new way of cancer immune evasion.

Ionic liquid-trimetallic electrocatalytic system for C–O bond cleavage in lignin model compounds and lignin under ambient conditions

Electrocatalytic depolymerization of lignin into value-added chemicals offers a promising technique to make biorefining sustainable.Herein,we report a robust trimetallic PdNiBi electrocatalyst for reductive C–O bond cleavage of different lignin model dimers and oxidized lignin under mild conditions.The reduction reaction proceeds with complete substrate conversion and excellent yields toward monomers of phenols(80%–99%)and acetophenones(75%–96%)in the presence of an ionic liquid electrolyte with operational stability.Systematic experimental investigations together with density functional theory(DFT)calculations reveal that the outstanding performance of the catalyst results from the synergistic effect of the metal elements,which facilitates the easier formation of a key Cαradical intermediate and the facile desorption of the as-formed products at the electrode.The results open up new opportunities for lignin valorization through the green electrocatalytic approach.

Synergistic graphene/aluminum surface plasmon coupling for zinc oxide lasing improvement

Collective oscillations of free electrons generate plasmons on the surface of a material. A whispering-gallery microcavity effectively confines the light field on its surface based on the total reflection from its internal wall. When these two kinds of electromagnetic waves meet each other, the stimulated emissions from an individual ZnO microrod were enhanced more than 50-fold and the threshold was reduced after the whispering-gallery microcavity was coated with a monolayer of graphene and A1 nanoparticles. The improvement of the lasing performance was attributed to the synergistic energy coupling of the graphene/A1 surface plasmons with ZnO excitons. The lasing characteristics and the coupling mechanism were investigated systematically.

Memristive switching in two-dimensional BiSe crystals

In spite of the explosive rise of research on memristive switching,more improvements in tunability,versatility,and hetero-integration are required through the discovery and application of novel materials.Herein,we report resistance switching in nano-thick two-dimensional(2D)crystals of bismuth selenium(BiSe).The BiSe devices exhibit nonvolatile bipolar resistance switching,volatile switching,and electrical bistable behavior in different conditions.The different memristive behavior of BiSe devices may be related to the concentration of Bi ions in this Bi-rich structure,which directly affects the capability of filaments forming.Furthermore,the external mechanical strain is applied in modulation of multi-layer BiSe devices.The memristive BiSe devices show a large on/off ratio of~10^(4)and retention time of~104 s.The discovery of memristive switching behavior in multi-layer BiSe is attributed to the forming of Bi filaments.The resistance switching behavior in multi-layer BiSe demonstrates the potential application in the flexible memories and functional integrated devices.

氧化锌微腔激光的模式调控

振荡模式的调控与单模激光的实现是微腔激光器走向实际应用所需解决的关键问题.本文从微腔模式的基本理论出发,按不同的调控机理梳理了ZnO微腔激光在模式调控方面的主要进展.首先,阐述了分布布拉格反射(DBR)或分布反馈(DFB)结构、腔体尺寸控制、游标效应等传统静态调控方式在ZnO微腔激光模式调控中的结构设计与研究进展;进一步讨论了通过压电、电光等物理效应调制折射率来实现ZnO微腔激光模式的动态调控;最后,综述了表面等离激元效应在实现纳米激光调控方面的最新进展,并系统分析了相关调控手段在ZnO微腔激光模式调控中的优点及存在问题.这些模式调控的方法不仅适用于ZnO紫外激光,同时也为其他材料、其他波段的微腔激光提供了参考.

Controlled fabrication, lasing behavior and excitonic recombination dynamics in single crystal CH3NH3PbBr3 perovskite cuboids

As a direct bandgap semiconductor, organic-inorganic lead halide perovskite (MAPbX3, MA = CH3NH3, X =Cl, Br, I) have been considered as promising materials for laser due to their excellent optoelectronic properties. The perovskite materials with ID and 2D shapes were widely prepared and studied for Fabry-Perot mode and whispering-gallery-mode (WGM) microcavities, but cuboid-shape is rarely reported. In this work, we successfully fabricated single crystal cuboid-shaped MAPbBr3 perovskite w让h different morphologies, named microcuboid-MAPbBr3 (M-MAPbBr3) and multi-step-MAPbBr3 (MSMAPbBr3), via solvothermal method. Furthermore, the as-prepared *crystals excitonic recombination lifetime under different pumping energy density was studied by time-resolved photoiuminescence (TRPL). Based on controllable morphology and remarkable lasing properties, these cuboid shaped single crystal perovskite could be a promising candidate for small laser, and other optoelectronic devices.

Plasmon enhancement for Vernier coupled single-mode lasing from ZnO/Pt hybrid microcavities

It is essential to develop a single mode operation and improve the performance of lasing in order to ensure practical applicability of microlasers and nanolasers. In this paper, two hexagonal microteeth with varied nanoscaled air-gaps of a ZnO microcomb are used to construct coupled whispering-gallery cavities. This is done to achieve a stable single mode lasing based on Vernier effect without requiring any complicated or sophisticated manipulation to achieve positioning with nanoscale precision. Optical gain and the corresponding ultraviolet lasing performance were improved greatly through coupling with localized surface plasmons of Pt nanoparticles. The ZnO/Pt hybrid microcavities achieved a seven-fold enhancement of intensity of single mode lasing with higher side- mode suppression ratio and lower threshold. The mechanism that led to this enhancement has been described in detail.

Plasmon-enhanced ZnO whispering-gallery mode lasing

Collaborative enhancements from surface plasmons （SPs） and whispering-gallery modes （WGMs） can induce intense near-field effects with high spatial localization around the surface of a semiconducting material. One can construct a highly efficient hybrid microcavity using semiconducting materials through resonant coupling between SPs and WGMs. Hexagonal ZnO micro-/nanostructures, which have been employed as natural WGM microcavities for ultraviolet （UV） lasing, can be used as ideal platforms to construct such hybrid microcavities. Here, we comprehensively review the recent efforts for improving lasing performance by resonant coupling between SPs and WGMs. Traditional SPs originating from various metals as well as novel SPs originating from atomic layers such as graphene are considered. Moreover, we discuss the mechanism of light-matter interactions beyond the improvements in lasing performance.

Clinical applications of neurolinguistics in neurosurgery

The protection of language function is one of the major challenges of brain surgery.Over the past century,neurosurgeons have attempted to seek the optimal strategy for the preoperative and intraoperative identification of language-related brain regions.Neurosurgeons have investigated the neural mechanism of language,developed neurolinguistics theory,and provided unique evidence to further understand the neural basis of language functions by using intraoperative cortical and subcortical electrical stimulation.With the emergence of modern neuroscience techniques and dramatic advances in language models over the last 25 years,novel language mapping methods have been applied in the neurosurgical practice to help neurosurgeons protect the brain and reduce morbidity.The rapid advancements in brain-computer interface have provided the perfect platform for the combination of neurosurgery and neurolinguistics.In this review,the history of neurolinguistics models,advancements in modern technology,role of neurosurgery in language mapping,and modern language mapping methods(including noninvasive neuroimaging techniques and invasive cortical electroencephalogram)are presented.

基于COSI-Corr技术的龙羊峡库区1987—2019年风沙输移特征及潜在入库量估算

风沙活动威胁着龙羊峡水库的安全运营,查清沙害来源和入库量对于防治水患和沙害具有重要意义。基于1987、1995、2003、2013、2019年的Landsat卫星影像,利用COSI-Corr技术监测了龙羊峡库区不同时空的沙丘移动特征,并重新评估库区近32 a的潜在风沙入库量。结果显示:(1)1987-2019年龙羊峡库区沙丘平均移动速率为5.81 m·a^(-1),呈先加速(1987-2003年)后减速(2003-2013年)再加速(2013-2019年)趋势;沙丘移动方向在132.81°-165.82°范围内,与该区主风向一致。(2)近32 a向龙羊峡水库输送的潜在风沙量可达7.82×10^(7) m^(3)(1.20×10^(8) t)。上风向塔拉滩潜在输送量为7.38×10^(7) m^(3)(1.14×10^(8) t),下风向木格滩仅贡献了0.44×10^(7) m^(3)(0.68×10^(7) t)。(3)库区内风沙输移受风况、气候、植被等多种因素的影响,在未来全球变暖条件下,青藏高原的风沙活动将会持续发展,风沙入库量的长期累计效应将对水库安全构成严重威胁,必须引起足够重视。

A novel simple traumatic brain injury mouse model

Background:Traumatic brain injury,one of the leading causes of death in adults under 40 years of age in the world,is frequently caused by mechanical shock,resulting in diffuse neuronal damage and long-term cognitive dysfunction.Many existing TBI animal models revival with expensive equipment or special room are needed or the processes of operations are complex and not easy to be widely used.Therefore,a simpler TBI model needs to be designed.Methods:Our TBI model is an innovation of the modeling method through air guns shutting rubber bullets.A core facet is the application of our designed rubber bullet impact device.It could focus the hitting power to the fixed site of the brain,thus triggering a mild closed head injury.Moreover,the degree of damage can be adjusted by the times of shots.Results:Our model induced blood-brain barrier leakage and diffused neuronal damage.Besides,it led to an increased level of Tau phosphorylation and resulted in cognitive dysfunction within several weeks post-injury.Conclusion:Our TBI model is not only simple and time-saving but also can simulate mild brain injuries in clinical.It is suitable for exploring pathobiological mechanisms as well as a screening of potential therapies for TBI.