11.2 W/mm power density AlGaN/GaN high electron-mobility transistors on a GaN substrate

In this letter,high power density AlGaN/GaN high electron-mobility transistors(HEMTs)on a freestanding GaN substrate are reported.An asymmetricΓ-shaped 500-nm gate with a field plate of 650 nm is introduced to improve microwave power performance.The breakdown voltage(BV)is increased to more than 200 V for the fabricated device with gate-to-source and gate-to-drain distances of 1.08 and 2.92μm.A record continuous-wave power density of 11.2 W/mm@10 GHz is realized with a drain bias of 70 V.The maximum oscillation frequency(f_(max))and unity current gain cut-off frequency(f_(t))of the AlGaN/GaN HEMTs exceed 30 and 20 GHz,respectively.The results demonstrate the potential of AlGaN/GaN HEMTs on freestanding GaN substrates for microwave power applications.

基于蝶翅三级微纳米结构的定制光子工程辐射制冷纺织品

People could potentially mitigate heat discomfort when outdoors by combining passive radiative cooling(PRC)strategies with personal thermal management techniques.However,most current PRC materials lack wearing comfort and durability.In this study,a microarray technique is applied to fabricate the tailoring photonic-engineered textiles with intriguing PRC capability and appealing wearability.The developed radiative cooling textiles(RCTs)demonstrate appropriate air-moisture permeability,structural stability,and extended spectroscopic response with high sunlight reflectivity(91.7%)and robust heat emissivity(95.8%)through the atmospheric transparent spectral window(ATSW).In a hot outdoor cooling test,a skin simulator covered by the RCTs displays a temperature drop of approximately 4.4℃at noon compared with cotton textiles.The evolution of our mimetic structures may provide new insights into the generation of wearable,thermal-wet comfortable,and robust textiles for exploring PRC techniques in personal thermal management applications.

Research on high-performance English translation based on topic model

Retelling extraction is an important branch of Natural Language Processing(NLP),and high-quality retelling resources are very helpful to improve the performance of machine translation.However,traditional methods based on the bilingual parallel corpus often ignore the document background in the process of retelling acquisition and application.In order to solve this problem,we introduce topic model information into the translation mode and propose a topic-based statistical machine translation method to improve the translation performance.In this method,Probabilistic Latent Semantic Analysis(PLSA)is used to obtains the co-occurrence relationship between words and documents by the hybrid matrix decomposition.Then we design a decoder to simplify the decoding process.Experiments show that the proposed method can effectively improve the accuracy of translation.

Distribution pattern of Caragana species under the influence of climate gradient in the Inner Mongolia region, China

There is a strong climate gradient in the Inner Mongolia region, China, with solar radiation and air temperature increasing but precipitation decreasing gradually from the northeast to the southwest. Sixteen Cara- gana species exist in the Inner Mongolia region. These Caragana species exhibit a distribution pattern across moisture zones and form a geographical replacement series. In order to examine the mechanisms responsible for Caragana species distribution pattern, we selected 12 Caragana species that exhibit a distinct distribution pattern across multiple moisture zones in the Inner Mongolia region, and determined the relationships between the leaf ecological and physiological traits of these Caragana species and the aridity index and solar radiation. Along with the climatic drought gradient and the solar radiation intensification from the northeast to the southwest, leaf eco- logical characteristics of Caragana species changed drastically, i.e. the leaf shape gradually turned from flat into tegular or tubbish; the leaf hair became denser, longer and lighter in color; the leaf area, leaf biomass and specific leaf area （SLA） decreased significantly; the leaf thickness and the ratio of leaf thickness to leaf area increased sig- nificantly; and the leaf chlorophyll content decreased significantly. As the climatic drought stress increased, osmotic potentials of the main osmotic adjustment substances and the cytoplasmic ion concentration of Caragana species increased significantly. Meanwhile, the total and free water contents and water potential of leaves decreased sig- nificantly; the ratio of bound to free water increased significantly; the stomatal conductance and transpiration rate reduced significantly; and the water use efficiency （WUE） increased significantly. In addition, with the intensification of climatic drought stress, peroxidase （POD） and superoxide dismutase （SOD） activities in leaves increased significantly. As a result, the malondialdehyde （MDA） content increased while the oxygen free radical content decreased. Our results showed that most of the leaf ecological and physiological traits of the 12 Caragana species varied in accordance with the climatic drought gradient in the Inner Mongolia region, which reflected the adaptation of the Caragana species to the local climate conditions. With relatively more active metabolism and faster growth, the Caragana species in the northeast had strong competitive abilities; on the other hand, with stronger resistance to climatic drought stress, the Caragana species in the southwest could survive in harsh environments. Based on our results, we con- cluded that both the environmental gradients and the adaptive responses of Caragana species to their environments played important roles in the formation of the Caragana species distribution pattern across the Inner Mongolia region.

Effect of Lamb Age and in vitro Culture System of Oocytes on JIVET Technology

[Objectives] This study was conducted to investigate the effects of lamb age and in vitro culture system of oocytes on the results of juvenile in vitro embryo transfer( JIVET). [Methods]Ten Dorper × small-tailed Han lambs aged 5 to 10 weeks were induced to superovulate via i. p. injection of pregnant mare's serum gonadotropin( PMSG). The oocytes were matured in basal maturation solution or modified maturation solution,which was prepared by adding 200 μmol/L cysteine to the basal maturation solution. Then,the oocytes were fertilized in fertilization medium I containing 2% estrus sheep serum( ESS) or fertilization medium II containing 3 mg/ml bull serum albumin( BSA). Finally,the number of oocytes,oocyte maturation rate and cleavage rate of the lambs of different ages were determined. [Results]The average number of oocytes recovered per lamb was( 111. 00 ± 16. 97),( 139. 50 ± 28. 99),( 108. 50 ± 17. 68) and( 42. 00 ± 11. 31) for5-,7-,8-and 10-week-old Dorper × small-tailed Han lambs,respectively. The number of oocytes obtained from 5-,7-and 8-week-old lambs was significantly higher than that from 10-week-old lambs( P < 0. 05),but there was no significant difference among 5-,7-and 8-week-old lambs( P > 0. 05). The maturation rate of oocytes cultured in modified maturation solution was 3. 64% higher than that in basal maturation solution. The cleavage rate of oocytes in fertilization medium I was very significantly higher than that in fertilization medium II( P < 0. 01). [Conclusions] The results of JIVET can be improved by harvesting oocytes from lambs aged 5-8 weeks,adding a certain amount of cysteine into oocyte maturation solution,and a certain amount of ESS into fertilization medium.

JIVET Research on Texel Sheep

The present study was conducted to explore ways of JIVET research on Texel sheep,and to provide technical support for the improvement of the JIVET technology system for research on Texel sheep.Superovulation was conducted on 4-8-week old Texel sheep,and in-vivo ovum collection,in-vitro oocyte maturation and fertilization,and fertilized-embryo culture and transplantation were adopted to perform JIVET research on Texel sheep.The results showed that 296 available oocytes were obtained at an average of 74 oocytes per sheep;205 fertilized eggs were obtained at the 2-4 cell stage at an average of 51.25 eggs per sheep and a cleavage rate of 69.26%;and 66 of the fertilized eggs were transplanted to 11 receptor sheep.Six sheep were conceived at a conception rate of 54.55%,and 11 lambs were born.These results indicated that the present test could be used as a method for the study of JIVET technique on Texel sheep.

Astroglial glutamate-glutamine cycle is involved in the modulation of inflammatory nociception in rats

Our previous behavioral studies have indicated that the astroglial glutamate-giutamine cycle is involved in the process of formalin-induced spinal cord central sensitization, but there was little morphological evidence. In this study, double-labeling immunofluorescence techniques showed that after rats were intrathecally injected with PBS and plantarly injected with formalin, glial fibrillary acidic protein （GFAP） and glutamine synthesase （GS） expression were increased and GFAP/GS coexpression was changed to include layers III and IV. After intrathecal injection of methionine sulfoximine, a GS specific inhibitor, the formalin-induced change in expression and coexpression of GFAP and GS in spinal cord dorsal horns was inhibited. The morphology, distribution and quantity of astrocytes recovered to normal levels. An intrathecal glutamine injection reversed the inhibitory effect of methionine sulfoximine. Astrocytes showed significant activation and distribution extended to layers V and VI. The present study provides morphological evidence that the astroglial glutamateglutamine cycle is involved in the process of formalin-induced spinal cord central sensitization.

Effects of β-mercaptoethanol Concentrations on Developmental Ability of Oocytes in 6-week-old Dorper Sheep

This study was conducted to investigate the effects of different concentrations ofβ-mercaptoethanol on the development ability of oocytes in Dorper sheep at the age of 6 weeks.In this study,6 Dorper sheep of 6 weeks old were chosen to induce oocyte collection in vivo by gonadotropin,and A and B grade cumulus oocyte complexes were obtained(COCs)with different concentrations of(0,50,70 and 100μmol/L)ofβ-mercaptoethanol in the mature liquid.The cleavage rate and blastocyst rate were counted after matured oocytes and capacitated sperm were co-incubated and fertilized eggs were cultivated.The results showed that compared with the cleavage rate(59.13%)and the blastocyst rate(12.17%)of the control group,the cleavage rates(60.87%,63.48%and 65.22%)and blastocyst rates(14.78%,17.39%and 21.74%)of the test groups I,II and III were higher(P>0.05),and the order was test group III>test group II>test group I>control group.The cleavage rate and blastocyst rate of the 100μmol/Lβ-mercaptoethanol group increased by 6.09 percentage points and 9.57 percentage points,respectively.It indicated that the addition of a certain amount ofβ-mercaptoethanol in the mature liquid could improve the developmental ability of oocytes and the quality of fertilized eggs of the 6-week-old Doper sheep.When theβ-mercaptoethanol concentration was within 100μmol/L,the cleavage rate and the blastocyst rate of oocytes were on the rise.The optimal concentration ofβ-mercaptoethanol in the mature liquid still needs further study.

Study on In-vitro Production Technology of Embryos from Young Dorper Sheep

This study was conducted to investigate the in-vitro production technology of embryos from young Dorper sheep, so as to provide technical support for the utilization of ovarian follicles in young Dorper sheep. Tests were conducted from the induction of Dorper sheep of 4 to 8 weeks old using follicle stimulating hormone(FSH) and pregnant horse serum(PMSG), collection of oocytes, in-vitro oocyte maturation-fertilization-zygote cultivation and 2-4-cell-stage fertilized ovum transfer. The results showed that 585 oocytes were collected from eight Dorper sheep at the age of 4 and 8 weeks, with an average of 73.13 oocytes/sheep. 346 of the 2-4-cell-stage fertilized eggs were obtained, whose cleavage rate was 59.15%. 77 in-vitro fertilized eggs at 2-4-cell stage were transplanted into 17 recipient sheep, seven of which were pregnant and gave birth to 13 "test-tube sheep" with a conception rate of 41.18%. It is indicated that the hormone induction technique, in-vitro oocyte maturation-fertilization-zygote cultivation technique and 2-4-cell-stage fertilized ovum transfer technique used in this study can serve as effective techniques for the in-vitro production of embryos from Dorper sheep of 4-8 weeks old.

High-stability _(4)H-SiC avalanche photodiodes for UV detection at high temperatures

In this work,high-stability _[4]H-SiC avalanche photodiodes[APDs]for ultraviolet[UV]detection at high temperatures are fabricated and investigated.With the temperature increasing from room temperature to 150℃,a very small temperature coefficient of 7.4 m V/℃is achieved for the avalanche breakdown voltage of devices.For the first time,the stability of 4H-SiC APDs is verified based on an accelerated aging test with harsh stress conditions.Three different stress conditions are selected with the temperatures and reverse currents of 175℃/100μA,200℃/100μA,and 200℃/500μA,respectively.The results show that our 4H-SiC APD exhibits robust high-temperature performance and can even endure more than120 hours at the harsh aging condition of 200℃/500μA,which indicates that 4H-SiC APDs are very stable and reliable for applications at high temperatures.

发行DC/EP会降低商业银行的存款供给吗?——基于货币竞争的视角

中央银行数字货币的发行会降低商业银行的存款供给,影响金融体系的货币创造能力与宏观经济稳定性吗?本文构建多种货币竞争共存的环境,依托货币的交易媒介属性对中国人民银行设计的中央银行数字货币(DC/EP)进行理论建模。研究结论表明,交易网络化和可控匿名的特征使DC/EP在交易费用和交易安全性上与传统支付工具存在明显差异。独特的交易支付特性深刻影响了DC/EP的相对竞争力,部分社会公众能从DC/EP交易中获益更多,从而促使他们改变交易决策,最终潜在降低银行存款市场的实际供给水平、抑制商业银行的盈利能力。本文建议商业银行和中央银行应具体评估发行DC/EP对其存款供给的潜在影响,适度降低商户的转账支付费用,关注DC/EP发行的相关配套措施,以提高存款货币的竞争力,稳定商业银行的存贷款业务。

Theoretical and simulation research of hydrodynamic instabilities in inertial-confinement fusion implosions

Inertial fusion energy （IFE） has been considered a promising, nearly inexhaustible source of sustainable carbon-free power for the world＇s energy future. It has long been recognized that the control of hydrodynamic instabilities is of critical importance for ignition and high-gain in the inertial-confinement fusion （ICF） hot-spot ignition scheme. In this mini-review, we summarize the progress of theoretical and simulation research of hydrodynamic instabilities in the ICF central hot-spot implosion in our group over the past decade. In order to obtain sufficient understanding of the growth of hydrodynamic instabilities in ICF, we first decompose the problem into different stages according to the implosion physics processes. The decomposed essential physics pro- cesses that are associated with ICF implosions, such as Rayleigh-Taylor instability （RTI）, Richtmyer-Meshkov instability （RMI）, Kelvin-Helmholtz instability （KHI）, convergent geometry effects, as well as perturbation feed-through are reviewed. Analyti- cal models in planar, cylindrical, and spherical geometries have been established to study different physical aspects, including density-gradient, interface-coupling, geometry, and convergent effects. The influence of ablation in the presence of preheating on the RTI has been extensively studied by numerical simulations. The KHI considering the ablation effect has been discussed in detail for the first time. A series of single-mode ablative RTI experiments has been performed on the Shenguang-II laser facility. The theoretical and simulation research provides us the physical insights of linear and weakly nonlinear growths, and nonlinear evolutions of the hydrodynamic instabilities in ICF implosions, which has directly supported the research of ICF ignition target design. The ICF hot-spot ignition implosion design that uses several controlling features, based on our current understanding of hydrodynamic instabilities, to address shell implosion stability, has been briefly described, several of which are novel.

Large-area 4H-SiC avalanche photodiodes with high gain and low dark current for visible-blind ultraviolet detection

In this Letter, we report large-area（600 μm diameter） 4H-SiC avalanche photodiodes（APDs） with high gain and low dark current for visible-blind ultraviolet detection. Based on the separate absorption and multiplication structure, 4H-SiC APDs passivated with SiNxinstead of SiO2 are demonstrated for the first time, to the best of our knowledge. Benefitting from the SiNx passivation, the surface leakage current is effectively suppressed. At room temperature, high multiplication gain of 6.5 × 10^5 and low dark current density of 0.88 μA∕cm^2 at the gain of 1000 are achieved for our devices, which are comparable to the previously reported small-area Si C APDs.

Circularly polarized luminescence based on cholesterol-tetraphenylethylene-perylene liquid crystal

Perylene derivative with circularly polarized luminescence(CPL) at aggregated state was seldom reported due to the strong ACQ(aggregation-caused quench) effect at aggregation. In this work, a novel cholesterol-tetraphenylethylene-perylene derivative(TPE-P) was designed and synthesized in moderate yield. It exhibited liquid crystalline behavior with orderly hexagonal columnar mesophase and good fluorescence emission at long wavelength(600-700 nm) not only in solution but also at aggregated states based on the AIE(aggregation-induced emission)-FRET(fluorescence resonance energy transfer) effect between tetraphenylethylene unit and perylene moiety. Moreover, the circular dichroism(CD) and CPL studies suggested the effective chiral transfer from cholesterol unit to tetraphenylethylene unit and perylene skeleton due to the spiral liquid crystalline self-assembly. The CD and CPL signals showed the order of THF < THF-hexane < solid film < meosphase, indicating that the higher spiral orderly degree resulted in the stronger chiral transfer. The largest |glum| value for mesophase excited at 320 nm was as high as 1.5×10^(−2) based on the combining effect of AIE-FRET and chiral transfer. This research not only reported a novel CPL perylene derivative at aggregated state, but also confirmed that the combination of AIE-FRET effect and chiral transfer of liquid crytalline phase was an effective method to construct normal dye with excellent CPL property in aggregated state.

Competition and abiotic stress affect the size of mangroves near their geographic range limit

Studies of competition in mangroves are mostly limited to seedlings and artificial settings like forestry projects.We conducted the first experimental study of intraspecific competition among adult mangroves in a natural mangrove forest to examine how important competition is in determining tree size compared with abiotic conditions.We conducted a study near Port Aransas,TX,USA,which is near the geographical limit of mangroves and dominated by monospecific stands of‘scrub’form black mangroves,Avicennia germinans.We thinned 10 plots to create a gradient of mangrove cover,and quantified the effects of mangrove cover on the growth of tagged mangroves from 2013 to 2019,and the mangrove canopy height in 2019.The relative growth rate of tagged mangroves declined as mangrove cover increased,and plants in the plot with 100%mangrove cover did not grow,indicating that they had attained their maximum size.In plots with reduced mangrove cover,plant height increased sharply,with plants in the plot with 11%mangrove cover growing~52%taller over 6 years.Canopy height was~30%taller in the plot fringe than in the interior,and canopy height in both fringe and interior declined as mangrove cover increased.Measures of leaf chlorophyll concentration and light interception suggested that plants were primarily limited by nitrogen.Our results showed that scrub mangroves compete strongly despite being limited by abiotic conditions,and that the importance of competition was greater in magnitude than that of abiotic differences between the fringe and interior.