Morphology and crystal-plane effects of Zr-doped CeO2 nanocrystals on the epoxidation of styrene with tert-butylhydroperoxide as the oxidant

The morphology effect of Zr-doped CeOwas studied in terms of their activities in the selective oxidation of styrene to styrene oxide using tert-butyl hydroperoxide as the oxidant. In the present work, Zrdoped CeOnanorods exhibited the highest catalytic performance（yield of styrene oxide and TOF value）followed by nanoparticles and nanocubes. For the Zr-doped CeOnanorods, the apparent activation energy is 56.3 k J/mol, which is much lower than the values of catalysts supported on nanoparticles and nanocubes（73.3 and 93.4 k J/mol）. The high resolution transmission electron microscopy results indicated that（100） and（110） crystal planes are predominantly exposed for Zr-doped CeOnanorods while（100）and（111） for nanocubes,（111） for nanoparticles. The remarkably increased catalytic activity of the Zrdoped CeOnanorods is mainly attributed to the higher percentage of Cespecies and more oxygen vacancies, which are associated with their exposed（100） and（110） crystal planes. Furthermore, recycling studies proved that the heterogeneous Zr-doped CeOnanorods did not lose its initial high catalytic activity after five successive recycles.

混合水溶液中金属元素的偏最小二乘法激光诱导击穿光谱

为提高激光诱导击穿光谱技术(LIBS)对水中重金属元素含量的检测精确度,将LIBS技术分别与单变量定标(SVCC)和偏最小二乘法(PLS)分析方法相结合,对Cr、Mn、Ca混合水溶液中的金属元素进行了定量分析。利用PLS-LIBS技术研究了样品中共存元素对分析元素的影响,研究结果表明分析元素的检测精确度受共存元素的影响较大,将共存元素与分析元素的分析线强度同时作为PLS模型的输入变量,得到的分析元素浓度总预测相对误差明显减小。利用SVCC-LIBS方法检测Cr、Mn、Ca元素的浓度总预测相对误差分别为14.3%、8.46%、6.35%,而利用PLS-LIBS方法各相对误差分别改善至2.30%、0.74%、0.03%,其中Mn元素的浓度预测相关曲线线性度R 2由SVCC-LIBS方法的0.985改善至0.999,表明PLS-LIBS技术能有效提高混合水溶液中微量金属元素的检测精确度。

金属特性对激光诱导击穿光谱最佳实验参数的影响

采用波长为532 nm的单脉冲激光诱导两种金属样品铜和锌,产生等离子光谱,固定激光能量40 mJ、门宽100 ns、光谱仪入射狭缝0.1 mm、ICCD增益100等参数,研究金属样品物理化学特性对会聚透镜焦点到样品表面距离、ICCD采集延迟等最优化实验参数的影响.实验中分别选取铜样品Cu(I)521.82 nm和锌样品Zn(I)481.053 nm谱线作为LIBS信号,实验测定的透镜焦点在距样品表面不同距离处的LIBS信号强度,结果表明铜和锌样品的聚焦透镜焦点分别在样品表面内距表面的距离为5 mm和5.5 mm时得到光谱信号强度最大;铜和锌的ICCD探测延时分别为1300 ns和1100 ns时等离子体光谱信号的信噪比最大并具有可观测的强度,依据铜和锌样品物理化学特性的差异对实验结果进行了合理的分析与讨论,为后续研究金属样品LIBS技术的基底效应、纳米结构增强激光诱导击穿光谱机理提供数据参考.

UAV target tracking algorithm based on task allocation consensus

In order to adapt to the changes in the states of moving targets and meet the requirements of quality of service in communication among unmanned aerial vehicles (UAVs), the UAVs formation needs to dynamically adjust tracking tasks and tracking paths, when they carry out a mission of tracking multiple moving targets. A multi-targets tracking algorithm based on task allocation consensus is proposed for UAVs to track multiple moving targets under the distributed control architecture in the limited communication range. This algorithm creates a distributed dynamic task allocation model using intermittent asynchronous communication principle to realize the sharing of observation information gathered by each UAV with fewer communications. In addition, this algorithm also makes it possible that multi-UAVs can plan tracking paths for multiple moving targets. We implement the algorithm on the formation with three UAVs to track three moving targets through simulation. Simulation results show the effectiveness of the proposed algorithm. © 2016 Beijing Institute of Aerospace Information.

A review on direct synthesis of dimethoxymethane

Polyoxymethylene dimethyl ethers are recognized as the prospective diesel additive to decrease the pollutant emission from the light-duty vehicles,which can be polymerize form the monomer of dimethoxymethane(DMM).The industrial synthesis of DMM is mainly involved two-step process:methanol is oxidized to form the formaldehyde in fixed bed reactor and then reacted with the generated formaldehyde through acetalization in continuous stirred-tank reactor.Due to huge energy consumption,this typical synthesis route of DMM needs to be upgraded and more green routes should be determined.In this review,four state-of-the-art one-step direct synthetic routes,including two upgrading routes(methanol direct oxidation and direct dehydrogenation)and two green routes(methanol diethyl ether direct oxidation and carbon oxides direct hydrogenation),have been summarized and compared.Combination with the reaction mechanism and catalytic performance on the different catalysts,the challenges and opportu nities for every synthetic route are proposed.The relationships between catalyst structu re and property in different synthesis strategy are also investigated and then the suggestions of the design of catalyst are given about future research directions that efforts should be made in.Hopefully,this review can bridge the gap between newly developed catalysts and synthesis technology to realize their commercial applications in the near future.

Proportion integral-type active disturbance rejection generalized predictive control for distillation process based on grey wolf optimization parameter tuning

The high-purity distillation column system is strongly nonlinear and coupled,which makes it difficult to control.Active disturbance rejection control(ADRC)has been widely used in distillation systems,but it has limitations in controlling distillation systems with large time delays since ADRC employs ESO and feedback control law to estimate the total disturbance of the system without considering the large time delays.This paper designs a proportion integral-type active disturbance rejection generalized predictive control(PI-ADRGPC)algorithm to control the distillation column system with large time delay.It replaces the PD controller in ADRC with a proportion integral-type generalized predictive control(PI-GPC),thereby improving the performance of control systems with large time delays.Since the proposed controller has many parameters and is difficult to tune,this paper proposes to use the grey wolf optimization(GWO)to tune these parameters,whose structure can also be used by other intelligent optimization algorithms.The performance of GWO tuned PI-ADRGPC is compared with the control performance of GWO tuned ADRC method,multi-verse optimizer(MVO)tuned PI-ADRGPC and MVO tuned ADRC.The simulation results show that the proposed strategy can track reference well and has a good disturbance rejection performance.

Facile oxalic acid-assisted construction of laminated porous N-deficient graphitic carbon nitride: Highly efficient visible-light-driven hydrogen evolution photocatalyst

The laminated porous N-deficient g-C3N4(CN–H)is successfully synthesized by a facile two-step hydrothermal calcination method using oxalic acid-assisted melamine as the precursor.Compared with pristine g-C3N4(224μmol g-1h-1),the CN–H shows superior photocatalytic hydrogen production activity(up to 728μmol g-1h-1),which is three times higher than the unmodified counterpart.To draw out the multifaceted influences of oxalic acid modification on the visible-light-induced photocatalytic activity,various techniques are utilized to investigate the formation mechanism,structural characteristics and photoelectrical properties of CN–H.The results indicate that the addition of a trace amount of oxalic acid to the precursor melamine results in a g-C3N4 structure possessing the advantage of both nitrogen defects and laminated porosity.These properties can enlarge specific surface areas of g-C3N4,enhance an efficient separating of photogenerated electron-hole pairs and extend the range of spectral response,all contributing to the enhancement of the visible-light-induced photocatalytic activity.

Confocal photoluminescence characterization of silicon-vacancy color centers in 4H-SiC fabricated by a femtosecond laser

Silicon-vacancy(VSi)centers in silicon carbide(SiC)are expected to serve as solid qubits,which can be used in quantum computing and sensing.As a new controllable color center fabrication method,femtosecond(fs)laserwriting has been gradually applied in the preparation of VSi in SiC.In this study,4H-SiCwas directlywritten by an fs laser and characterized at 293 K by atomic force microscopy,confocal photoluminescence(PL),and Raman spectroscopy.PL signals of VSi were found and analyzed using 785 nm laser excitation by means of depth profiling and two-dimensional mapping.The influence of machining parameters on the VSi formation was analyzed,and the three-dimensional distribution of VSi defects in the fs laser writing of 4H-SiC was established.

An X-Ray Burst Associated with FRB 200428 from a Magnetar-asteroid Impact

Fast radio bursts(FRBs)are extragalactic radio transients with millisecond duration and brightness temperature.An FRB-associated X-ray burst(XRB)was recently found to arise from the Galactic magnetar SGR J1935+2154.Following the model of Dai,in which an FRB may originate from a magnetar encountering an asteroid,we focus on explaining the spectrum of the XRB associated with FRB 200428 from SGR J1935+2154.Collisions between asteroidal fragments and the magnetar surface produce a fireball,which further expands relativistically.Due to the velocity difference among some shells in the fireball,internal shocks would form far away from the magnetar,and further emit X-ray emission.We propose that the FRB-associated XRB can be produced by synchrotron emission from the internal shocks,and then constrain the physical parameters by the observed XRB spectrum.

Self-Awakened Particle Swarm Optimization BN Structure Learning Algorithm Based on Search Space Constraint

To obtain the optimal Bayesian network(BN)structure,researchers often use the hybrid learning algorithm that combines the constraint-based(CB)method and the score-and-search(SS)method.This hybrid method has the problemthat the search efficiency could be improved due to the ample search space.The search process quickly falls into the local optimal solution,unable to obtain the global optimal.Based on this,the Particle SwarmOptimization(PSO)algorithm based on the search space constraint process is proposed.In the first stage,the method uses dynamic adjustment factors to constrain the structure search space and enrich the diversity of the initial particles.In the second stage,the update mechanism is redefined,so that each step of the update process is consistent with the current structure which forms a one-to-one correspondence.At the same time,the“self-awakened”mechanism is added to prevent precocious particles frombeing part of the best.After the fitness value of the particle converges prematurely,the activation operation makes the particles jump out of the local optimal values to prevent the algorithmfromconverging too quickly into the local optimum.Finally,the standard network dataset was compared with other algorithms.The experimental results showed that the algorithmcould find the optimal solution at a small number of iterations and a more accurate network structure to verify the algorithm’s effectiveness.

A new insight into aggregation structure of organic solids and its relationship to room-temperature phosphorescence effect

In order to improve the performance of organic luminescent materials,lots of studies have been carried out at the molecular level.However,these materials are mostly applied as solids or aggregates in practical applications,in which the relationship between aggregation structure and luminescent property should be paid more attention.Here,we obtained five phenothiazine 5,5-dioxide(O-PTZ)derivatives with distinct molecular conformations by rational design of chemical structures,and systematically studied their room-temperature phosphorescence(RTP)effect in solid state.It was found that O-PTZ dimers with quasi-equatorial(eq)conformation tended to show strongerπ-πinteraction than quasi-axial(ax)conformers in crystal state,which was more conducive to the generation of RTP.Based on this result,a multi-level structural model of organic solids was proposed to draw the relationship between aggregation structure and RTP effect,just like the research for the structureproperty relationship of proteins.Using this structural model as the guide,boosted RTP efficiency from 1%to 20%was successfully achieved in the corresponding host-guest doping system,showing its wide applicability.

Efficient photo-induced RTP materials based on phenothiazine and polycyclic aromatic hydrocarbons:Tunable emission color and thermal stimulus response

The development of photo-responsive room temperature phosphorescence(RTP)materials has attracted more and more attention for their broad application pro-spects.Until now,it is still difficult to obtain the related ma-terials with both high efficiency and long lifetime.And the lacking of emission in blue and red regions also largely re-stricts their further applications.In this work,we reported a new strategy to maintain both high efficiency and long lifetime in RTP luminogens through the integration of phenothiazine to facilitate n-π*transition and polycyclic aromatic hydro-carbons(PAHs)dominated byπ-π*transition.When they were doped into polymer matrix,full color photo-induced RTP materials were obtained for the changedπ-conjugation of PAHs.Among them,PTri@PVP showed the best RTP per-formance with phosphorescence efficiency of 20.73%and lifetime up to 819 ms.Specifically,after turning off the ul-traviolet-visible(UV)irradiation upon this system,time-de-pendent phosphorescence afterglow from green to blue was exhibited,which was found to originate from two distinct molecular conformations and could be further regulated by thermal stimulus.Accordingly,multiple anti-counterfeiting applications,including screen printing,multi-color patterns and multi-dimensional information encryption,were suc-cessfully demonstrated.

三级医院临床医师循证医学认知及服务需求分析

目的通过调查了解三级医院临床医师对循证医学的认知及服务需求情况,为循证医学的发展及其在临床实践中的进一步推广提供科学依据和参考。方法以河南省12家三级医院,898名临床医师为研究对象,采用统一自填式问卷调查其对循证医学的认知及服务需求情况。结果本研究共发放并回收问卷916份,其中有效问卷898份,有效回收率98.03%。被调查的研究对象男女性别比为0.96∶1,平均年龄36.4(25.0~59.0)岁。对循证医学重要性的总体认可度高达90.98%,对循证医学相关知识的需求率为93.43%。三级医院临床医师对循证医学相关知识需求度较高的依次是循证医学专业资源库(91.20%),文献检索的技巧(90.09%),如何发表高质量的循证医学论文(89.42%),循证医学证据的评价(86.41%)及循证医学的实施步骤(82.52%);期望获取循证医学相关知识的方式方面,总体需求率从高到低依次为微信公众号(92.09%),讲座培训(89.42%),学术会议(84.63%),同事交流(84.41%),课程研修(82.74%),专著期刊(80.85%)以及网站宣传(78.40%)。此外,不同年龄、不同工作年限、不同学历、不同科室间的临床医师对循证医学重要性的认识和需求差异有统计学意义。结论三级医院临床医师对循证医学重要性认识度较高,对循证医学相关知识的需求也较大,应根据临床医生的不同需求,有针对性及侧重点地制定措施、进行培训、促进实践。

金属基质激光诱导击穿光谱最佳离焦量的基质效应研究

在激光诱导击穿光谱(LIBS)技术中,离焦量的选取对LIBS的探测灵敏度具有重要影响。LIBS光谱强度最大时对应的最佳离焦量具有基质效应,不同物理特性的金属基质样品具有不同的最佳离焦量。通过实验测定了12个物理性质有明显差异的高纯金属样品的最佳离焦量,初步推测了最佳离焦量与金属基质元素物理特性参数之间的关联,所得结论支持前期LIBS击穿阈值的研究结果。本文研究结果表明金属基质元素的力学、光学、电学和热学特性对最佳离焦量有影响,尤其是基质金属元素的热导率和比热容对最佳离焦量影响很大,且都与最佳离焦量正向关联。本文依据基质元素物理特性参数的本质对最佳离焦量的基质效应机理进行了合理分析,分析结果对进一步理解LIBS技术中的基质效应机理和修正基质效应提供了基础支撑。

Structure Engineered g-C3N4 Nano-Sheets by Switching the Pyrolysis Gas Atmosphere for Enhanced Photo-Catalytic Degradation

We developed a new one step approach to synthesize g-C3N4 nano-sheets by direct thermal pyrolysis process of urea in NH3 atmosphere. For the first time, the influence of the preparation gas atmosphere on the composition, crystalline and polymerization degree, and the activity of the g-C3N4 synthesized from thermal condensation of urea was investigated. Impressively, the g-C3N4 nano-sheets obtained under NH3 gas atmosphere exhibited much superi- or photo-catalytic activities to the prepared g-C3N4 in air or N2, and the rate of the g-C3N4-NH3 was about 5 times higher than that on g-C3N4-N2 sample. The detailed characterization analysis revealed that NH3 thermal pyrolysis atmosphere contributed to the polymerization degree and the formation of the layer with a more regular structure due to the efficiently extending of the conjugated π-conjugative system, which was favorable to the transfer of the photo-induced charge carriers. Furthermore, we studied in depth the structure-performance relationship in the sys- tem, and it was found that the synergistic effect of the larger surface area, the adjusted band energy structure and the well crystallization may be conductive to the higher separation of the electron-hole pair, thus leading to the won- derful performance for the g-C3N4-NH3. Notably, the method has the merits of low cost, scalable production and environmental friendliness.

Direct demonstration of triplet excimer in purely organic room temperature phosphorescence through rational molecular design

Organic luminogens with room temperature phosphorescence(RTP)have been paid great attention and developed rapidly for their wide application values.Until now,the internal mechanism and source of phosphorescence are still obscure,especially for the relationship between molecular dimer and RTP emission.Hence,we designed and synthesized eight phenothiazine 5,5-dioxide derivatives to directly reveal how the monomer and dimer in packing affect the RTP behavior.Dimers with strongπ-πstacking(θ<20.66°;d<3.86A)lead to pure triplet excimer emission,while those with weakπ-πstacking(27.02°<θ<40.64°;3.84A<d<4.41A)contribute to dual RTP emissions of both monomer and triplet excimer.The valuable information of this work would promote the further development of this research field,as well as others in aggregate.

Global Existence,Asymptotic Behavior and Uniform Attractors for Non-autonomous Thermoelastic Systems

In this paper, we first establish the global existence and asymptotic behavior of solutions by using the semigroup method and multiplicative techniques, then further prove the existence of a uniform attractor for a non-autonomous thermoelastic system by using the method of uniform contractive functions. The main advantage of this method is that we need only to verify compactness condition with the same type of energy estimates as that for establishing absorbing sets. Moreover, we also investigate an alternative result of solutions to the semilinear thermoelastic systems by virtue of the semigroup method.

Induced Abortion and the Risk of Tubal Infertility

Objective To explore the association between induced abortion and tubal infertility in Chengdu, China.Methods A 1 ： 2 case-control study was designed. Infertile women with bilateral tubal occlusion in the case group compared with two control groups： infertile control group with bilateral tubal patency and pregnant control group with currently pregnancy. Data were collected using questionnaires through face-to-face interviews, covering the subjects＇ demographic details and histories of gynecology and obstetrics. Adjusted odds ratio was calculated as a measure of the association using stepwise multiple logistic regression analysis.Results Induced abortion was not found to be associated with tubal infertility in the analysis including either the infertile controls or the pregnant controls, but other risk factors were found, such as history of acute pelvic inflammatory disease （PID）, lower abdominal surgeries, dysmenorrhea and pregnancy.Conclusion It is contended that facing an increasing trend of infertile cases with tubal occlusion in China, it is emphasized that special attention should paid to the long term impact of reproductive tract infection, especially, asymptomatic ones, rather than induced abortion.

A reduced order model for coupled mode cascade flutter analysis

A Reduced Order Model(ROM)based analysis method for turbomachinery cascade coupled mode flutter is presented in this paper.The unsteady aerodynamic model is established by a system identification technique combined with a set of Aerodynamic Influence Coefficients(AIC).Subsequently,the aerodynamic model is encoded into the state space and then coupled with the structural dynamic equations,resulting in a ROM of the cascade aeroelasticity.The cascade flutter can be determined by solving the eigenvalues of the ROM.Bending-torsional coupled mode flutter analysis for the Standard Configuration Eleven(SC11)cascade is used to validate the proposed method.

胎盘生长因子水平联合唐氏筛查结果预测子痫前期的价值

目的探讨孕早中期胎盘生长因子(placental growth factor,PLGF)联合甲胎蛋白(alpha-fetoprotein,AFP)、β-hCG及游离雌三醇(unconjugated estriol,uE3)水平预测子痫前期(pre-eclampsia,PE)的价值。方法分析2018年5月—2020年3月郑州大学附属郑州中心医院妇产科行常规产检并分娩的367例孕妇,据随访结果分为PE组、对照组,采用ELISA法检测PLGF、AFP、β-hCG、uE3水平。分析各血清指标与部分产科结局相关性,应用受试者工作曲线(ROC曲线)及约登指数评判预测PE的价值,并确定相应界值。结果PE组PLGF、AFP及uE3水平均低于对照组,差异有统计学意义(P<0.05);两组β-hCG水平差异无统计学意义(P>0.05)。PLGF、AFP及uE3水平分别与新生儿出生体重及分娩孕周均呈正相关(P<0.05)。PLGF、AFP及uE3联合因子为检验变量时约登指数最大为0.622,特异度91.23%,敏感度68.92%。结论无论是PLGF、AFP、uE3各单项指标还是联合预测因子,对子痫前期发病均有预测价值,但联合预测因子的预测价值要优于任一单项血清指标。