GaSe/ZnS异质结的结构和界面性质的第一性原理研究

本文设计了一种GaSe/ZnS范德瓦耳斯异质结构(vdWH),并用第一性原理计算系统地分析了该异质结构的几何、电子、输运性质。通过结合能、声子谱、从头算分子动力学(AIMD)模拟验证了所构建GaSe/ZnS范德瓦耳斯异质结构的稳定性。详细计算了GaSe/ZnS vdWH界面性质中的平面平均电子密度差和平均静电势。结果表明,GaSe/ZnS vdWH是一种直接带隙为2.19 eV,载流子迁移率较高的异质结构。其中,沿x方向的电子迁移率可达1394.63 cm^(2)·V^(-1)·s^(-1),而沿y方向的电子迁移率可达1913.18 cm^(2)·V^(-1)·s^(-1),性能优异,有望应用于电子纳米器件。

Self-absorption effects of laser-induced breakdown spectroscopy under different gases and gas pressures

The self-absorption effect is one of the main factors affecting the quantitative analysis accuracy of laser-induced breakdown spectroscopy.In this paper,the self-absorption effects of laserinduced 7050 Al alloy plasma under different pressures in air,Ar,and N2have been studied.Compared with air and N2,Ar significantly enhances the spectral signal.Furthermore,the spectral self-absorption coefficient is calculated to quantify the degree of self-absorption,and the influences of gas species and gas pressure on self-absorption are analyzed.In addition,it is found that the spectral intensity fluctuates with the change of pressure of three gases.It can also be seen that the fluctuation of spectral intensity with pressure is eliminated after correcting,which indicates that the self-absorption leads to the fluctuation of spectral intensity under different pressures.The analysis shows that the evolution of optical thin spectral lines with pressure in different gases is mainly determined by the gas properties and the competition between plasma confinement and Rayleigh–Taylor instability.

Climate Responses to Direct Radiative Forcing of Anthropogenic Aerosols,Tropospheric Ozone,and Long-Lived Greenhouse Gases in Eastern China over 1951–2000

A unified chemistry-aerosol-climate model is applied in this work to compare climate responses to changing concentrations of long-lived greenhouse gases （GHGs, CO2, CH4, N2O）, tropospheric O3, and aerosols during the years 1951-2000. Concentrations of sulfate, nitrate, primary organic carbon （POA）, secondary organic carbon （SOA）, black carbon （BC） aerosols, and tropospheric 03 for the years 1950 and 2000 are obtained a priori by coupled chemistry-aerosol-GCM simulations, and then monthly concentrations are interpolated linearly between 1951 and 2000. The annual concentrations of GHGs are taken from the IPCC Third Assessment Report. BC aerosol is internally mixed with other aerosols. Model results indicate that the sinmlated climate change over 1951-2000 is sensitive to anthropogenic changes in atmospheric components. The predicted year 2000 global mean surface air temperature can differ by 0.8℃ with different forcings. Relative to the climate simulation without changes in GHGs, O3, and aerosols, anthropogenic forcings of SO4^2-, BC, BC＋SO4^2-, BC＋SO4^2- ＋POA, BC＋SO4^2- ＋POA＋SOA＋NO3^-, O3, and GHGs are predicted to change the surface air temperature averaged over 1971-2000 in eastern China, respectively, by -0.40℃, ＋0.62℃, ＋0.18℃, ＋0.15℃, -0.78℃, ＋0.43℃, and ＋0.85℃, and to change the precipitation, respectively, by -0.21, ＋0.07, -0.03, ＋0.02, -0.24, -0.08, and ＋0.10 mm d^-1. The authors conclude that all major aerosols are as important as GHGs in influencing climate change in eastern China, and tropospheric O3 also needs to be included in studies of regional climate change in China.

Selective catalytic methanation of CO in hydrogen-rich gases over Ni/ZrO_2 catalyst

Ni/ZrO2 catalysts were prepared by the incipient-wetness impregnation method and were investigated in activity and selectivity for the selective catalytic methanation of CO in hydrogen-rich gases with more than 20 vol% CO2. The result showed that Ni loadings significantly influenced the performance of Ni/ZrO2 catalyst. The 1.6 wt% Ni loading catalyst exhibited the highest catalytic activity among all the catalysts in the selective methanation of CO in hydrogen-rich gas. The outlet concentration of CO was less than 20 ppm with the hydrogen consumption below 7%, at a gas-hourly-space velocity as high as 10000 h-1 and a temperature range of 260 °C to 280 °C. The X-ray diffraction （XRD） and temperature programmed reduction （TPR） measurements showed that NiO was dispersed thoroughly on the surface of ZrO2 support if Ni loading was under 1.6 wt%. When Ni loading was increased to 3 wt% or above, the free bulk NiO species began to assemble, which was not favorable to increase the selectivity of the catalyst.

Effect of CO_2 on explosion limits of flammable gases in goafs

In order to reduce the number of accidents due to explosions of flammable gases in the goaf of coalmines,the conditions for explosion of flammable gases and their explosion limits,affected to a considerable extent by CO2,are explored.With the use of our experimental equipment suitable for the study of explosion of polybasic explosive gas mixtures,we investigated the effect of CH4/H2=10/1 and CH4/C2H4=10/1 gases mixed with CO2 on their explosion limits.The results indicate that after adding CO2,the explosion limit of the CH4/H2(or C2H4) =10/1 gas mixtures decreased markedly with increasing amounts of CO2.When the amount of CO2 exceeded 25%,the CH4/C2H4=10/1 flammable gas mixture did not lead to explosions.Similar results were obtained when the amount of CO2 exceeded 23% in the CH4/H2=10/1 flammable gas mixture.We also compared the explosion limits and the explosion suppression effect of N2 or CO2 on the explosion limits of the CH4+CO and CH4+C2H4 dual explosive gas mixtures.Along with the increases in the amounts of CO2 or N2,the area of the explosion limits of gas mixtures decreased.Under the same conditions,the explosion suppression effect of CO2 was greater than that of N2.CO2 has clearly the better suppression effect on the explosion of flammable gases in goafs.

All-silica zeolites screening for capture of toxic gases from molecular simulation

The exhaust gases, including SO_2,NH_3, H_2S, NO_2, NO, and CO, are principal air pollutants due to their severe harms to the ecological environment.Zeolites have been considered as good absorbent candidates to capture the six exhaust gases.In this work, we performed grand canonical ensemble Monte Carlo(GCMC) simulations to examine the capability of 95 kinds of all-silica zeolites in the removal of the six toxic gases, and to predict the adsorption isotherms of the six gases on all the zeolites.The simulation results showed that, H_2S, NO, NO_2, CO and NH_3 are well-captured by zeolite structures with accessible surface area of 1600–1800 m^2·g^(-1) and pore diameter of 0.6–0.7 nm, such as AFY and PAU, while SO_2 is well-adsorbed by zeolites containing larger accessible surface area(1700–2700 m^2·g^(-1)) and pore diameter(0.7–1.4 nm) at room temperature and an atmospheric pressure.However, at saturated adsorption, zeolites RWY, IRR, JSR, TSC, and ITT are found to exhibit better abilities to capture these gases.Our study provides useful computational insights in choosing and designing zeolite structures with high performance to remove toxic gases for air purification, thereby facilitating the development and application of exhaust gas-processing technology in green industry.

A quantitative comparison and analysis on the assessment indicators of greenhouse gases emission

Anthropogenic greenhouse gases （GHG） emission and related global warming issues have been the focus of international communities for some time. The international communities have reached a consensus to reduce anthropogenic GHG emissions and restrain global warming. The quantitative assessment of anthropogenic GHG emissions is the scientific basis to find out the status of global GHG emission, identify the commitments of each country, and arrange the international efforts of GHG emission reduction. Currently the main assessment indicators for GHG emission include national indicator, per capita indicator, per GDP indicator, and international trade indicator etc. The introduction to the above indi- cators is put forward and their merits and demerits are analyzed. Based on the GHG emission data from the World Resource Institute （WRI）, the US Energy Information Administration （EIA）, and the Carbon Dioxide Information Analysis Center （CDIAC）, the results of each indictor are calculated for the world, for the eight G8 industrialized countries （USA, UK, Canada, Japan, Germany, France, Italy and Russia）, and the five major developing countries including China, Brazil, India, South Africa and Mexico. The paper points out that all these indicators have some limitations. The Indicator of Industrialized Accumulative Emission per Capita （IAEC） is put forward as the equitable indicator to evaluate the industrialized historical accumulative emission per capita of every country. IAEC indicator can reflect the economic achievement of GHG emission enjoyed by the current generations in every country and their commitments. The analysis of IAEC indicates that the historical accumulative emission per capita in indus- trialized countries such as UK and USA were typically higher than those of the world average and the developing countries. Emission indicator per capita per GDP, consumptive emission indicator and survival emission indicator are also put forward and discussed in the paper.

A Review of Research on Human Activity Induced Climate ChangeⅠ. Greenhouse Gases and Aerosols

Extensive research on the sources and sinks of greenhouse gases, carbon cycle modeling, and the characterization of atmospheric aerosols has been carried out in China during the last 10 years or so. This paper presents the major achievements in the fields of emissions of greenhouse gases from agricultural lands, carbon cycle modeling, the characterization of Asian mineral dust, source identification of the precursors of the tropospheric ozone, and observations of the concentrations of atmospheric organic compounds. Special, more detailed Information on the emissions of methane from rice fields and the physical and chemical characteristics of mineral aerosols are presented.

Kinetic Modeling the Formation of Low-mature Gases and Analysis of the Possibility to Be Accumulated

At present, shallow gases have received much attention due to low cost in exploration and production. Low-mature gases, as one significant origin to shallow gas, turns to be an important research topic. The present understanding of low-mature gases is confined within some geological cases, and few laboratory studies have been reported. Therefore, the potential and characters of low- mature gases are not clear up to now. Here, two premature samples （one coal and the other shale） were pyrolyzed in a gold confined system. The gaseous components including hydrocarbon gases and non-hydrocarbon gases were analyzed. Based on kinetic modeling, the formation of low-mature gases was modeled. The results showed that during low mature stage, about 178 mL/gTOC gas was generated from the shale and 100 mL/gTOC from the coal. Two third to three fourth of the generated gases are non-hydrocarbon gases such as H2S and CO2. The total yields of C1-5 for the two samples are almost the same, 30-40 mL/gTOC, but individual gaseous hydrocarbon is different. The shale has much lower C1 but higher C2-5, whereas the coal has higher C1 but lower C2-5. Hydrocarbon gases formed during low-mature stage are very wet. The stable carbon isotope ratios of methane range from -40‰ to -50‰ （PDB）, in good consistence with empiric criterion for low-mature gases summed up by the previous researchers. The generation characters suggest that the low-mature gases could be accumulated to form an economic gas reservoir, but most of them occur only as associated gases.

Computer simulation of the air flow distribution in goaf regarding the use of inert gases and chemical agents

This paper presents the use of a computer method of the ventilation process simulation for the analysis of the flow distribution of air and gases in the area of wall mining work and the adjacent goaf.In workings and goaf,the complex issue of the formation of a gaseous atmosphere under variable ventilation conditions and an existing fire hazard level,with the possibility of feeding goaf with an additional carbon dioxide flux as the inertizing agent is considered.Some examples of the simulation of feeding goaf with carbon dioxide illustrating the different patterns of the distribution of the goaf atmosphere gases concentration,said distribution patterns being gas supply place dependent,have been presented.In addition,the impact of the additional sealing of goaf on the distribution level of the concentration of gases,the said sealing made from the wall side with chemical agents has also been considered.The capabilities of the VentGoaf computer simulation program,being the basis for our calculations,enable consideration of the use of the inert gases supplied to the goaf depending on: the location of the gas feeding the pipe outlet,tightness of the fire field,fire centre location,and spatial situation of the mined wall.It has been found that fire prevention elements,such as chemical sealing agents,are of great impact on the effectiveness of fire prevention.

A UNIFIED VISCOSITY MODEL FOR HYDROCARBON GASES AND LIQUIDS BASED ON TRANSPoSED PATEL-TEJA EQUATION OF STATE

A unified model for predicting high-pressure viscosities of both hydrocarbon gases and liquids was developed,which is based on the similarity between P-V-T and T-μ-P plots and Patel-Teja equation of state.The characteristic feature of this new model is its capability of describing the continuous variation of fluid viscosity throughciritical region.The pure component parameters are generalized into functions of reduced temperature,reducedpressure,acentric factor and molecular weight.The overall average absolute deviation of predicted viscositiesof 20 pure hydrocarbon fluids(a total of 1941 data points)is 8.7%.

Effects of Active Gases on Droplet Transfer and Weld Morphology in Pulsed-Current NG-GMAW of Mild Steel

The current research of narrow-gap gas metal arc welding(NG-GMAW)primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect.However,the high cost and operation difficulty of the methods limit the industrial application.In this study,small amount of active gases CO_(2) and O_(2) were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding(NG-GMAW)of mild steel.Their effects on droplet transfer and arc behavior were investigated.A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology.When the proportion of CO_(2),being added into the pure argon shielding gas,changes from 5%to 25%,the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer,while it remains the pulsed spray streaming transfer when 2%to 10%O_(2) is added.Both CO2 and O_(2) are favorable to stabilizing arc and welding process.O_(2) is even more effective than CO_(2).However,O_(2) is more likely to cause slags on the weld surface,while CO_(2) can improve the weld appearance in some sense.The weld surface concavity in NG-GMAW is greatly influenced by the addition of active gas,but the weld width and weld penetration almost keep constant.This study proposes a new method which is beneficial to improving the weld bead formation and welding process stability.

The Emission Reduction Potential of Non-CO_2 Greenhouse Gases in China and Its Policy Implications

Using the improved Energy-Environmental Version of the GTAP Model (GTAP-E) and the sixth version of emission database of non-CO2 greenhouse gases, we simulate the emission reduction potential of non-CO2 greenhouse gases in China and its policy implications. The results show that at present, China is a country with the greatest emission of non-CO2 greenhouse gases in the world, and the emission will account for about 20% of the world's total emission in 2020. The proportion of emission of non-CO2 greenhouse gases from the agricultural sector reaches 73%. In the next 10 years, the emission of non-CO2 gases from cattle and sheep, industry and service industry will experience the highest growth rate; the growth rate of emission from service industry will be higher than that of emission from industry, and the emission from service industry will exceed that from industry after 2010. China can implement emission reduction policy of non-CO2 greenhouse gases to ease the international pressure of CO2 emission reduction. Although the high carbon tax collected can reduce considerable non-CO2 emission, there is little difference in policy efficiency between high carbon tax and low carbon tax. So, in the implementation of emission reduction carbon tax policy of non-CO2 gases, it is necessary to control the carbon tax at a low level.

Experimental Realization of Degenerate Fermi Gases of 87Sr Atoms with 10 or Two Spin Components

We report the experimental realization of quantum degenerate Fermi gases of87Sr atoms under controlled 10-and dual-nuclear-spin configurations.Based on laser cooling and evaporative cooling,we achieve an ultracold Fermi gas of 105 atoms equally distributed over 10 spin states,with a temperature of T/TF = 0.21.We further prepare a dual-spin gas by optically pumping atoms to the mF = 9/2 and mF = 7/2 states and observe a slightly lower T/TF than that for a 10-spin gas under the same trapping condition,showing efficient evaporative cooling under a decreasing number N of spin states(N≥2)despite the increasing importance of Pauli exclusion.Given that rethermalization becomes less efficient with N approaching unity,we evaporatively cool an almost polarized gas to 130 nK.The simple and efficient preparation of ultracold Fermi gases of 87Sr with tunable spin configurations provides a first step towards engineering topological quantum systems.

A Computational Study of Radio Frequency Atmospheric Pressure Discharge in Nitrogen and Oxygen Mixture Gases

The characteristics of radio frequency atmospheric pressure discharge in nitrogen and oxygen mixture gases are investigated by using a one-dimensional fluid model.The model consists of equations of particle continuity,Poisson's equation,and the electron energy equation.The effect of the concentrations of O_(2) in N_(2) on the discharge characteristics is analyzed.The results show that when the concentration of O_(2) in N_(2) is less than 12%,as the amount of O_(2) grows,the electron density and the N4+ion density decrease;the main negative particles are electrons.When the concentration of O_(2) in N_(2) is greater than 12%,the electron density and the N_(4)^(+) ion density increase with the increasing admixture of oxygen;the main negative particle is the O^(-) ion.Moreover,the O^(-) ion density,the O_(2)^(+) ion density,the electron temperature and the mixture gases electronegativity increase with growth of O_(2) in the range from 4%to 20%and with density of O_(2) in N_(2).

Exploring Greenhouse Gases Water and Climate Changes:Scientific Opportunities for the Climate and Atmospheric Composition Exploring Satellites Mission

The Essential Climate Variables(ECVs),such as the atmospheric thermodynamic state variables and greenhouse gases,play an important role in the atmosphere physical processes and global climate change.Given the need of improvements in existing ground-based and satellite observations to successfully deliver atmosphere and climate benchmark data and reduce data ambiguity,the Climate and Atmospheric Composition Exploring Satellites mission(CACES)was proposed and selected as a candidate mission of the Strategic Priority Research Program of Chinese Academy Science(SPRPCAS).This paper presents an overview of the key scientific questions and responses of EC Vs in relation to global change;the principles,algorithms,and payloads of microwave occultation using centimeter and millimeter wave signals between low Earth orbit satellites(LEO-LEO microwave occultation,LMO)as well as of the LEO-LEO infrared-laser occultation(LIO);the CACES mission with its scientific objectives,mission concept,spacecraft and instrumentation.

Explosion limits for combustible gases

Combustible gases in coal mines are composed of methane,hydrogen,some multi-carbon alkane gases and other gases.Based on a numerical calculation,the explosion limits of combustible gases were studied,showing that these limits are related to the concentrations of different components in the mixture.With an increase of C4H10 and C6H14,the Lower ExplosionLimit(LEL) and Upper Explosion-Limit(UEL) of a combustible gas mixture will decrease clearly.For every 0.1% increase in C4H10 and C6H14,the LEL decreases by about 0.19% and the UEL by about 0.3%.The results also prove that,by increasing the amount of H2,the UEL of a combustible gas mixture will increase considerably.If the level of H2 increases by 0.1%,the UEL will increase by about 0.3%.However,H2 has only a small effect on the LEL of the combustible gas mixture.Our study provides a theoretical foundation for judging the explosion risk of an explosive gas mixture in mines.

A study of emissions and marker gases from smouldering combustion in Larix gmelinii plantations of the Daxing'an Mountains

Underground fires are characterized by smouldering combustion with a slow rate of spread rate and without flames.Although smouldering combustion releases large amounts of gaseous pollutants,it is difficult to discover by today's forest fire monitoring technologies.Carbon monoxide(CO),nitrogen oxides(NO_(x))and sulfur dioxide(SO_(2))were identified as high concentration marker gases of smouldering combustion-easily-be monitored.According to a two-way ANOVA,combustion time had a significant impact on CO and NO_(x) emissions;smoldering-depth also had a significant impact on NO_(x) emissions but not on CO emissions.Gas emission equations were established by multiple linear regression,C_(co)=156.989-16.626 t and C_(NOx)=3.637-0.252 t-0.039 h.

Isotopic compositional Characteristics of Terrigenous Natural Gases in China

The C and H isotopic compositions of the methane in more than 160 gas samples from 10 basins in China are presented in this paper.The natural gases are classified as four types: biogenic gas ,bio-thermocatalytic transitional gas, gas associated with condensate oil ,and coal-type gas. The isotopic compositions of these gases closely related to the depositional basins, the types of organic matter,the stages of thermal evolution and the genetic characteristics of different gas reservoirs.Studies of the C and H isotopic compositions of terrigenous natural gases will provide valua-ble information on the prospecting and development of natural gases of different genetic types.

Topological phase transitions driven by next-nearest-neighbor hopping in noncentrosymmetric cold Fermi gases

We investigate the topological phase marked by the Thouless–Kohmoto–Nightingale–Nijs（TKNN） number and the phase transitions driven by the next nearest neighbor（NNN） hopping in noncentrosymmetric cold Fermi gases, both spinsinglet pairing and spin-triplet pairing are considered. There exists a critical t＇c for the NNN hopping, at which the quantum phase transition occurs, and the system changes from an Abelian（non-Abelian） phase to a non-Abelian（Abelian） one. By numerically diagonalizing the Hamiltonian in the real space, the energy spectra with edge states for different topological phases and the Majorana zero modes are discussed. Although the spin-triplet pairing does not contribute to the gap closing and the phase diagram, it induces gapless states in the presence of a magnetic field, and the TKNN number in this region is still zero.