A theoretical study of the signal enhancement mechanism of coaxial DP-LIBS

In the field of dual-pulse laser-induced breakdown spectroscopy(DP-LIBS)research,the pursuit of methods for determining pulse intervals and other parameters quickly and conveniently in order to achieve optimal spectral signal enhancement is paramount.To aid researchers in identification of optimal signal enhancement conditions and more accurate interpretation of the underlying signal enhancement mechanisms,theoretical simulations of the spatiotemporal processes of coaxial DP-LIBS-induced plasma have been established in this work.Using a model based on laser ablation and two-dimensional axisymmetric fluid dynamics,plasma evolutions during aluminum–magnesium alloy laser ablation under single-pulse and coaxial dualpulse excitations have been simulated.The influences of factors,such as delay time,laser fluence,plasma temperature,and particle number density,on the DP-LIBS spectral signals are investigated.Under pulse intervals ranging from 50 to 1500 ns,the time evolutions of spectral line intensity,dual-pulse emission enhancement relative to the single-pulse results,laser irradiance,spatial distribution of plasma temperature and species number density,as well as laser irradiance shielded by plasma have been obtained.The study indicates that the main reason behind the radiation signal enhancement in coaxial DP-LIBS-induced plasma is attributed to the increased species number density and plasma temperature caused by the second laser,and it is inferred that the shielding effect of the plasma mainly occurs in the boundary layer of the stagnation point flow over the target surface.This research provides a theoretical basis for experimental research,parameter optimization,and signal enhancement tracing in DP-LIBS.

Development of miniaturized SAF-LIBS with high repetition rate acousto-optic gating for quantitative analysis

The self-absorption effect in laser-induced breakdown spectroscopy(LIBS)reduces the accuracy of quantitative measurement results.The self-absorption-free LIBS(SAF-LIBS)has been proved to directly capture the optically thin plasma spectra by setting an appropriate exposure time.In this work,a novel SAF-LIBS technique with high repetition rate acousto-optic gating is developed,in which an acousto-optic modulator is used as the shutter to diffract the optically thin fluorescence,and a high repetition rate laser is used to produce quasi-continuous plasmas to enhance the integral spectral intensity,so that the CCD spectrometer can replace an intensified CCD(ICCD)and echelle spectrometer in SAF-LIBS.Experimental results show that the average absolute prediction error of aluminum is reduced to 0.18%,which is equivalent to that of traditional SAF-LIBS.This technique not only effectively shields continuous background radiation and broadened spectral lines in optically thick plasma,but also has advantages of miniaturization,low cost,convenience and reliability.

亚硝酸盐对鱼类生长的影响

亚硝酸盐是铵氧化成硝酸盐过程的一个中间产物,水体中亚硝酸盐的存在将会对淡水鱼类的生长产生严重的威胁。本文对水体中亚硝酸盐的来源、吸收机制、生理影响、毒性及解毒机制等方面进行了阐述,以便人们对亚硝酸盐对鱼类生长的影响有一个深刻的了解。

水体中亚硝酸盐的来源与去除

亚硝酸盐是自然界中氮循环的一个中间产物,广泛存在于水体中,其生物毒性越来越受到人们的关注。本文阐述了水体中亚硝酸盐的来源、影响因素以及去除技术,并指出了解决水体中亚硝酸盐的现实意义。

Elemental and proximate analysis of coal by x-ray fluorescence assisted laser-induced breakdown spectroscopy

Although laser-induced breakdown spectroscopy(LIBS),as a fast on-line analysis technology,has great potential and competitiveness in the analysis of chemical composition and proximate analysis results of coal in thermal power plants,the measurement repeatability of LIBS needs to be further improved due to the difficulty in controlling the stability of the generated plasmas at present.In this paper,we propose a novel x-ray fluorescence(XRF) assisted LIBS method for high repeatability analysis of coal quality,which not only inherits the ability of LIBS to directly analyze organic elements such as C and H in coal,but also uses XRF to make up for the lack of stability of LIBS in determining other inorganic ash-forming elements.With the combination of elemental lines in LIBS and XRF spectra,the principal component analysis and the partial least squares are used to establish the prediction model and perform multi-elemental and proximate analysis of coal.Quantitative analysis results show that the relative standard deviation(RSD) of C is 0.15%,the RSDs of other elements are less than 4%,and the standard deviations of calorific value,ash content,sulfur content and volatile matter are 0.11 MJ kg,0.17%,0.79% and 0.41%respectively,indicating that the method has good repeatability in determination of coal quality.This work is helpful to accelerate the development of LIBS in the field of rapid measurement of coal entering the power plant and on-line monitoring of coal entering the furnace.

An Improved Modal Strain Energy Method for Damage Detection in Offshore Platform Structures

The development of robust damage detection methods for offshore structures is crucial to prevent catastrophes caused by structural failures. In this research, we developed an Improved Modal Strain Energy （IMSE） method for detecting damage in offshore platform structures based on a traditional modal strain energy method （the Stubbs index method）. The most significant difference from the Stubbs index method was the application of modal frequencies. The goal was to improve the robustness of the traditional method. To demonstrate the effectiveness and practicality of the proposed IMSE method, both numerical and experimental studies were conducted for different damage scenarios using a jacket platform structure. The results demonstrated the effectiveness of the IMSE method in damage location when only limited, spatially incomplete, and noise-polluted modal data is available. Comparative studies showed that the IMSE index outperformed the Stubbs index and exhibited stronger robustness, confirming the superiority of the proposed approach.

Measurement and analysis of species distribution in laser-induced ablation plasma of an aluminum–magnesium alloy

We proposed a theoretical spatio-temporal imaging method,which was based on the thermal model of laser ablation and the two-dimensional axisymmetric multi-species hydrodynamics model.By using the intensity formula,the integral intensity of spectral lines could be calculated and the corresponding images of intensity distribution could be drawn.Through further image processing such as normalization,determination of minimum intensity,combination and color filtering,a relatively clear species distribution image in the plasma could be obtained.Using the above method,we simulated the plasma ablated from Al-Mg alloy by different laser energies under 1 atm argon,and obtained the theoretical spatio-temporal distributions of Mg I,Mg II,Al I,Al II and Ar I species,which are almost consistent with the experimental results by differential imaging.Compared with the experimental decay time constants,the consistency is higher at low laser energy,indicating that our theoretical model is more suitable for the plasma dominated by laser-supported combustion wave.

Numerical simulation of laser-induced plasma in background gas considering multiple interaction processes

Laser-induced plasma is often produced in the presence of background gas,which causes some new physical processes.In this work,a two-dimensional axisymmetric radiation fluid dynamics model is used to numerically simulate the expansion process of plasma under different pressures and gases,in which the multiple interaction processes of diffusion,viscosity and heat conduction between the laser ablated target vapor and the background gas are further considered,and the spatio-temporal evolutions of plasma parameters(species number density,expansion velocity,size and electron temperature)as well as the emission spectra are obtained.The consistency between the actual and simulated spectra of aluminum plasma in 1 atm argon verifies the correctness of the model and the numerical simulation,thus providing a refinement analysis method for the basic research of plasma expansion in gases and the application of laser-induced breakdown spectroscopy.

A New Fiber Detection Method for LAMOST Based on the Front-illuminated Method

The double revolving fiber positioning technology is one of the key technologies for the success of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST).The accuracy of fiber positioning will directly affect the observation efficiency of LAMOST.To achieve higher fiber positioning accuracy,the original open-loop controlled fiber positioning system urgently needs to be upgraded into a closed-loop control system.The fiber detection is the most important part of the closed-loop controlled fiber positioning system.The back-illuminated detection method is usually used to detect the fiber position by directly detecting the light spot generated at the fiber end in the multi-fiber spectral surveys.In this paper,we introduce a new method to measure the fiber position based on the image of the front-illuminated LAMOST focal plane.The front-illuminated image does not require lighting devices inside the spectrograph,and it could reduce the instability and light pollution in the spectrograph end.Our method measures the fiber position by fitting the profile of the fiber pinhole with a 2D Gaussian function.A series of tests show that the relative position measurement precision of the front-illuminated method is about 012,and the method could have the same accuracy as the back-illuminated method once the system bias is calibrated by a simple radial correction function.The required fiber positioning accuracy of LAMOST is 04,and the new method satisfies the requirement of LAMOST fiber detection accuracy and could be used in the closed-loop fiber control system.

Alterative application of five anticonvulsants according to the half life for the treatment of status epilepticus in children with severe viral encephalitis

BACKGROUND： Traditional subhibernation therapy may easily cause complications, such as respiratory depression and hyportension because of application of chlorpromazine hydrochloride and promethazine in a large dosage. OBJECTIVE： To observe therapeutic effect of modified subhibernation therapy （alterative application of five anticonvulsants according to the half life） on status epilepticus in children with severe viral encephalitis （VE）. DESIGN： Contrast observation. SETTING： Department of Pediatrics, the First Hospital of Jilin University. PARTICIPANTS： The participants in present study were 96 patients with severe viral encephalitis including 52 boys and 44 girls who received treatment in the Department of Pediatrics, the First Hospital of Jilin University from February 2000 to March 2006. All children met the diagnostic criteria of Zhufutong Practice Pediatrics （the seventh edition）. Two weeks ago, they ever got upper respiratory infection or enteronitis and so on before the onset, spirit abnormal, behavior disorder, limbs act disorder, vomit, headache, convulsion, nervous system masculine signs such as limbs act disord, autonomic nerve damage manifestation, brain nerve palsy, dysreflexia, meningeal irritation sign, cerebrospinal fluid and electroencephalography （EEG） abnormity. All parents provided the confirmed consent. The patients were randomly divided into control group （n =40） and experimental group （n =56）. METHODS： Patients in the control group received anticonvulsion, ice compress and routine treatment. The convulsion was treated with five drugs： 0.5 mg/kg wintermin and phenergan, respectively, 100 g/L chlorpromazine hydrochloride （0.5 mL/kg）, 5 mg/kg luminal, 0.3 mg/kg ansiolin. When convulsion attacked, those five drugs were given alternatively; however, those were not given if the convulsion did not attack. Children in the experimental group were treated with improved subhibernation therapy based on routine treatment. The dosages of anticonvulsants were as the same as those in the control group. Based on the half life, every drug was alternated every 4-6 hours. In addition, anticonvulsants administrated for 2 successive days whether tic attacked or not. Then the hypnotic was removed gradually. MAIN OUTCOME MEASURES： Therapeutic efficacy, time of disappeared clinical symptoms and physical sign, and security of administration. RESULTS： All the 96 patients were involved in the final analysis. ① Total effective rate and reliability： Total effective rate was higher in the treatment groups than the control group （χ2=5.871 7, P 〈 0.05）. All patients did not have respiratory depression and side effects. ② Time of disappeared clinical symptoms and physical sign： Recovery time of convulsion, fever, headache and vomit was shorter in the treatment group than that in the control group, and there was significant difference （t =17.612 1-34.330 7, P 〈 0.05）; in addition, symptoms of status epilepticus were relieved obviously. Meanwhile, recovery time of paralysis, coma and anepia was shorter in the treatment group than that in the control group, and there was significant difference （t =10.660 8-24.700 8, P 〈 0.05）. CONCLUSION： Therapeutic effect of improved subhibernation therapy on status epilepticus induced by severe viral encephalitis is positively and safer.

Spatio-temporal Change Characteristics of Summer Mean Temperature in Northeast China during 1974-2004 Based on Geostatistics

[ Objective] The research aimed to study the spatio-temporal change characteristics of summer mean temperature in northeast China during 1974 -2004 based on geostatistics. [ Method ] By combining climate tendency rate with geostatistics, the spatio-temporal change characteris- tics of summer mean temperature in northeast China during 1974 -2004 were discussed. [ Result] Summer mean temperature distribution in north- east China for many years showed a trend of decreasing from south and west to north and east. Summer mean temperature in northeast China overall showed rise trend, and the biggest temperature rise magnitude was in Liaoning Province. Summer average temperature in 1994 was significantly higher than that in other years, and climate was abnormal. The rise speed of summer mean temperature in northeast China showed a trend of decreasing from southeast Jilin Province to other areas. [ Conclusion ] The research contributed to recognize spatio-temporal structure and change characteristics of the temperature in northeast China.

Fully Developed Turbulence of Power⁃Law Fluids in Circular Pipe Based on Large Eddy Simulation

In this study,Large eddy simulation(LES)of the fully developed turbulence of power⁃law fluids in a circular pipe was performed using the dynamic subgrid⁃scale model.Under a specific Reynolds number,the flow information of three fluids with a range of power⁃law indexes was obtained.The trends of the mean axial velocity and the normalized apparent viscosity were analyzed.Simulation results show that shearing⁃thinning fluid displayed more noticeable non⁃Newtonian characteristics than shear⁃thickening fluid.The predicted friction factors were approximately equal to the Dodge and Metzner correlation and Gomes correlation.The peak values of root mean squares(RMS)and Reynolds stress increased as the power⁃law index increased.The turbulence statistics(skewness and flatness)from the wall to the pipe center were calculated.From the calculated results,the velocity fluctuation near the wall had strong intermittent and asymmetry.As demonstrated by the contours of the normalized instantaneous axial velocity and viscosity,the turbulence was more developed as the power⁃law index increased.It is concluded that the LES is feasible to predict the turbulence of pipe flow under higher Reynolds numbers.

Polymer-encapsulated metal complex catalysts:An emerging and efficient platform for electrochemical CO_(2) reduction

Over the past decade,electrocatalytic reduction of CO_(2)has gained substantial attention.However,hardly any of the previous reviews have focused on the systematic discussion of polymer-molecular catalyst composites as an emerging system for the electrochemical transformation of CO_(2)to value-added products.In this review,we first give a brief overview of the general features of solid-state and molecular catalysts,and then advance the discussion to polymer-catalyst composite systems,with particular emphasis on polymer-encapsulated molecular catalysts,where the coordination environment surrounding molecular catalysts can be modified via polymer encapsulation to promote the overall performance of CO_(2)electrocatalysis.The elucidation of the possible reaction mechanisms of this emerging electrocat-alytic system along with proposed optimization strategies is also summarized and discussed based on recently published reports,followed by the challenges and prospects of their industrial applications at the end of this review.From this review,we hope the audience can gain a comprehensive understanding of the electrocatalytic mechanism of the coordinating polymers and valuable insights into engineering the microenvironment surrounding the metal complexes for potential future research directions.

PdPb bimetallic nanowires as electrocatalysts for enhanced ethanol electrooxidation

Less-expensive but efficient electrocatalysts are essential to accelerate the commercialization of fuel cells.Herein,ultrathin PdPb nanowires(PdPb NWs)with a diameter of around 3.5 nm were prepared by using a one-step hydrothermal method.The introduction of Pb in Pd-based bimetallic nanostructures produced high differences in the morphology from Pd nanoparticles(NPs)to various PdPb NWs.All the as-prepared PdPb NWs exhibited better electrocatalytic activity and durability than Pd NPs due to the synergistic effect.Especially,Pd65Pb35 possessed the highest current density of about 3460 mA mgPd^−1 for the ethanol electrooxidation which was around 6.3 times higher than commercial Pd/C.The high-performance of Pd65Pb35 is attributed to the defect-rich and stable nanowire structure with optimized surface atomic arrangement,as evidenced by high resolution transmission electron microscopy measurements and long-time treatment in an acidic media.The differences in the morphologies and electrocatalytic activities of PdPb NWs with varied Pb contents have also been discussed and analyzed.

Structural basis of interaction between the hepatitis C virus p7 channel and its blocker hexamethylene amiloride

Dear Editor, Hepatitis C virus （HCV） infection, which causes hepatitis C and can chronically lead to serious and life-threatening dis- eases including liver cirrhosis and hepatocellular carcinoma （Lauer and Walker, 2001）, is a rising global health problem. More than 170 million people are infected by HCV worldwide and 3-4 million people are infected each year. No effective vaccines are available to prevent HCV infection. Moreover, HCV is a fast mutating RNA virus with seven distinct genotypes and many subtypes within each genotype. The high degree of genetic diversity can lead to further viral resistance to the current therapies within individual patients （Li et al., 2012）. Hence, there remains a strong desire in the medical community to explore new therapeutic opportunities.

Integrative analysis of transcriptome and metabolome reveals the effect of DNA methylation of chalcone isomerase gene in promoter region on Lithocarpus polystachyus Rehd flavonoids

Metabolite biosynthesis is regulated by gene expression,which is altered by DNA methylation in the promoter region.Chalcone isomerase(CHI)gene encodes a key enzyme in the Lithocarpus polystachyus Rehd flavonoid pathway,and the expression of L.polystachyus CHI(LpCHI)is closely related to the synthesis of flavonoid metabolites.In this study,we analyzed the DNA methylation site of the LpCHI promoter and its effect on gene expression and metabolite accumulation.The proportions of three types of LpCHI promoter DNA methylation are 7.5%,68.75%,18.75%,determined by bisulfite sequencing.Transcriptome sequencing shows that LpCHI is strongly up-regulated in LpCHI promoter methylation Type A but down-regulated in LpCHI promoter methylation Type B and Type C.The expression of LpCHI shows no significant difference between Type B and Type C.Moreover,nine kinds of differentially expressed transcription factors(DETFs)bind to seven CpG-sites of the LpCHI promoter region to regulate LpCHI expression.The results of metabolomics show that differentially accumulated flavonoids are higher in LpCHI promoter methylation Type A than in LpCHI promoter methylation Type B and Type C.Additionally,a positive correlation was found between the LpCHI expression and flavonoids accumulation.These results show that the effect of CpG site-specificity on gene transcription is great than that of overall promoter DNA methylation on gene transcription.The mechanisms of flavonoid genes regulating metabolite accumulation are further revealed.