Modeling an emissions peak in China around 2030: Synergies or trade-offs between economy, energy and climate security

China has achieved a political consensus around the need to transform the path of economic growth toward one that lowers carbon intensity and ultimately leads to reductions in carbon emissions, but there remain different views on pathways that could achieve such a transformation. The essential question is whether radical or incremental reforms are required in the coming decades. This study explores relevant pathways in China beyond 2020, particularly modeling the major target choices of carbon emission peaking in China around 2030 as China-US Joint Announcement by an integrated assessment model for climate change IAMC based on carbon factor theory. Here scenarios DGS-2020, LGS2025, LBS-2030 and DBS-2040 derived from the historical pathways of developed countries are developed to access the comprehensive impacts on the economy, energy and climate security for the greener development in China. The findings suggest that the period of 2025--2030 is the window of opportunity to achieve a peak in carbon emissions at a level below 12 Gt CO2 and 8.5 t per capita by reasonable trade-offs from economy growth, annually -0.2% in average and cumulatively -3% deviation to BAU in 2030. The oil and natural gas import dependence will exceed 70% and 45% respectively while the non-fossil energy and electricity share will rise to above 20% and 45%. Meantime, the electrification level in end use sectors will increase substantially and the electricity energy ratio approaching 50%, the labor and capital productivity should be double in improvements and the carbon intensity drop by 65% by 2030 compared to the 2005 level, and the cumulative emission reductions are estimated to be more than 20 Gt CO2 in 2015-2030.

An analysis of China's CO_2 emission peaking target and pathways

China has set the goal for its CO2 emissions to peak around 2030, which is not only a strategic decision coordinating domestic sustainable development and global climate change mitigation but also an overarching target and a key point of action for China＇s resource conservation, environmental protection, shift in economic development patterns, and CO2 emission reduction to avoid climate change. The development stage where China maps out the CO2 emission peak target is earlier than that of the developed countries. It is a necessity that the non-fossil energy supplies be able to meet all the increased energy demand for achieving CO2 emission peaking. Given that China＇s potential GDP annual increasing rate will be more than 4%, and China＇s total energy demand will continue to increase by approximately 1.0%--1.5% annually around 2030, new and renewable energies will need to increase by 6%-8% annually to meet the desired CO2 emission peak. The share of new and renewable energies in China＇s total primary energy supply will be approximately 20% by 2030. At that time, the energy consumption elasticity will decrease to around 0.3, and the annual decrease in the rate of CO2 intensity will also be higher than 4% to ensure the sustained growth of GDE To achieve the CO2 emission peaking target and substantially promote the low-carbon deve!opment transformation, China needs to actively promote an energy production and consumption revolution, the innovation of advanced energy technologies, the reform of the energy regulatory system and pricing mechanism, and especially the construction of a national carbon emission cap and trade system.

The economic impact of emission peaking control policies and China's sustainable development

To achieve the goals of national sustainable development, the peaking control of CO2 emissions is pivotal, as well as other pollutants. In this paper, we build a Chinese inter-regional CGE model and simulate 13 policies and their combinations. By analyzing the energy consumptions, coal consumptions, relating emissions and their impacts on GDP, we found that with the structure adjustment policy, the proportion of coal in primary fossil fuels in 2030 will decrease from 53% to 48% and CO2 emissions will decrease by 11.3%-22.8% compared to the baseline scenario. With the energy intensity reduction policy, CO2 emissions will decrease by 33.3% in 2030 and 47.8% in 2050 than baseline scenario. Other pollutants will also be controlled as synergetic effects. In this study we also find that although the earlier the peaking time the better for emission amounts control, the economic costs can not be ignored. The GDP will decrease by 2.96%-8.23% under different scenarios. Therefore, integrated policy solutions are needed for realizing the peaks package and more targeted measures are required to achieve the peaks of other pollutants earlier.

Estimate of China's energy carbon emissions peak and analysis on electric power carbon emissions

China＇s energy carbon emissions are projected to peak in 2030 with approximately 110% of its 2020 level under the following conditions： 1） China＇s gross primary energy consumption is 5 Gtce in 2020 and 6 Gtce in 2030; 2） coal＇s share of the energy consumption is 61% in 2020 and 55% in 2030; 3） non-fossil energy＇s share increases from 15% in 2020 to 20% in 2030; 4） through 2030, China＇s GDP grows at an average annual rate of 6%; 5） the annual energy consumption elasticity coefficient is 0.30 in average; and 6） the annual growth rate of energy consumption steadily reduces to within 1%. China＇s electricity generating capacity would be 1,990 GW, with 8,600 TW h of power generation output in 2020. Of that output 66% would be from coal, 5% from gas, and 29% from non-fossil energy. By 2030, electricity generating capacity would reach 3,170 GW with 11,900 TW h of power generation output. Of that output, 56% would be from coal, 6% from gas, and 37% from non-fossil energy. From 2020 to 2030, CO2 emissions from electric power would relatively fall by 0.2 Gt due to lower coal consumption, and rela- tively fall by nearly 0.3 Gt with the installation of more coal-fired cogeneration units. During 2020--2030, the portion of carbon emissions from electric power in China＇s energy consumption is projected to increase by 3.4 percentage points. Although the carbon emissions from electric power would keep increasing to 118% of the 2020 level in 2030, the electric power industry would continue to play a decisive role in achieving the goal of increase in non-fossil energy use. This study proposes countermeasures and recommendations to control carbon emissions peak, including energy system optimization, green-coal-fired electricity generation, and demand side management.

Analysis of CO_2 emissions peak:China's objective and strategy

Establishing positive and urgent targets for CO_2 reduction and emission peak,and promoting energy conservation and energy structure adjustment are among the strategies to address global climate change and CO_2 emissions reduction.They are also means to break through the constraints of domestic resources and environment,and internal needs,to achieve sustainable development.Generally speaking,a country's CO_2 emission peak appears after achieving urbanization and industrialization.By then,connotative economic growth will appear,GDP will grow slowly,energy consumption elasticity will decrease,and energy consumption growth will slow down-dependent mainly on new and renewable energies.Fossil fuel consumption will not increase further.When CO_2 emission reaches its peak,the annual reduction rate of CO_2 intensity of GDP is greater than GDP annual growth rate;and the annual reduction rate of CO_2 intensity of energy use is greater than the annual growth rate of energy consumption.Therefore,three important approaches to promotion of CO_2 emission peak can be concluded:maintaining reasonable control of GDP growth,strengthening energy conservation to significantly reduce the GDP energy intensity,and optimizing the energy mix to reduce the CO_2 intensity of energy use.By around 2030,China will basically have completed its rapid development phase of industrialization and urbanization.Connotative economic growth will appear with the acceleration of industrial structure adjustment The target of GDP energy intensity will still be to maintain an average annual reduction of 3%or higher.The proportion of non-fossil fuels will reach 20-25%,and the aim will be to maintain an average annual growth rate of 6-8%.The total annual energy demand growth of 1.5%will be satisfied by the newly increased supply of non-fossil fuels.The annual decline in CO_2 intensity of GDP will reach 4.5%or higher,which is compatible with an average annual GDP growth rate of approximately 4.5%in order to reach CO_2 emission peak.This corresponds to the level of China's potential economic growth.Achieving CO_2 emission peak will not impose a rigid constraint on economic development,but rather promote economic development and accelerate the transformation of green,low-carbon development.The CO_2 emission peak can be controlled with a cap of 11 billion tons,which means that CO_2 emission will increase by less than 50%compared with 2010.The per capita emission peak will be controlled at a level of less than 8 tons,which is lower than the 9.5 tons in the EU and Japan and much lower than the 20 tons in the US,future economic and social development faces many uncertainties in achieving the CO_2 emission peak discussed above.It depends on current and future strategies and policies,as well as the pace and strength of economic transformation,innovation,and new energy technologies.If the economic transformation pattern fails to meet expectations,the time required to reach CO_2emission peak would be delayed and the peak level would be higher than expected.Therefore,we need to coordinate thoughts and ideas and deploy these in advance;to highlight the strategic position of low-carbon development and its priorities;to enact mid-to long-term energy development strategies;and to establish and improve a system of laws,regulations,and policies as well as an implementation mechanism for green,low-carbon development Oriented by positive and urgent CO_2 reduction and peak targets,the government would form a reversed mechanism to promote economic transformation and embark on the path of green,low-carbon development as soon as possible.

An Empirical Study on China＇s Energy Supply-and-Demand Model Considering Carbon Emission Peak Constraints in 2030

China＇s energy supply-and-demand model and two related carbon emission scenarios, including a planned peak scenario and an advanced peak scenario, are designed taking into consideration China＇s economic development, technological progress, policies, resources, environmental capacity, and other factors. The analysis of the defined scenarios provides the following conclusions： Primary energy and power demand will continue to grow leading up to 2030, and the growth rate of power demand will be much higher than that of primary energy demand. Moreover, low carbonization will be a basic feature of energy supply-and-demand structural changes, and non-fossil energy will replace oil as the second largest energy source. Finally, energy- related carbon emissions could peak in 2025 through the application of more efficient energy consumption patterns and more low-carbon energy supply modes. The push toward decarbonization of the power industry is essential for reducing the peak value of carbon emissions.

A review of research on China's carbon emission peak and its forcing mechanism

In order to make further steps in dealing with climate change, China proposed to peak carbon dioxide emissions by about 2030 and to make best efforts for the peaking early. The carbon emission peak target(CEPT) must result in a forcing mechanism on China's economic transition. This paper, by following the logical order from "research on carbon emission history" to "carbon emission trend prediction," from "research on paths of realizing peak" to "peak restraint research," provides a general review of current status and development trend of researches on China's carbon emission and its peak value. Furthermore,this paper also reviews the basic theories and specific cases of the forcing mechanism.Based on the existing achievements and development trends in this field, the following research directions that can be further expanded are put forward. First, from the perspective of long-term strategy of sustainable development, we should analyze and construct the forcing mechanism of CEPT in a reverse thinking way. Second, economic transition paths under the forcing mechanism should be systematically studied. Third, by constructing a large-scale policy evaluation model, the emission reduction performance and economic impact of a series of policy measures adopted during the transition process should be quantitatively evaluated.

Estimate of Peaks of Carbon Emissions and Pricing of Carbon Emission Permit in China

With the aid of Matlab software, the peaks of China＇s carbon emissions and their appearing time in three situations were simulated, and the shallow price of carbon emission permit and its effects on China＇s economic growth were analyzed. The results show that it is most effective and feasible to reduce energy consumption per GDP by 25%, and the peak of China＇s carbon emissions will appear in 2017. As a result, energy conser- vation and emission reduction is realized, and China＇s international talk power about carbon emission will improved. However, the shallow price and permit rate of carbon emission permit calculated in the situation are the lowest, and the adverse impact of the initial price of carbon emissions on China＇s economic growth is the largest. Therefore, consideration should be given to both the promotion of pricing and trading of carbon emission permit to reduction of carbon emissions and their adverse effects on GDP in China.

Research on Carbon Reduction Strategy of China’s Industrial Chain with the Goal of Carbon Emission Peak and Carbon Neutrality

In order to achieve the development goals of emission peak in 2030 and carbon neutrality in 2060,carbon reduction measures should be implemented in the whole industrial chain.Based on the existing research,the basic logic of carbon reduction in the industrial chain is analyzed,and then the specific strategies for carbon reduction in the industrial chain are proposed,including:reducing the use of fossil energy and vigorously developing the new energy industry;reducing carbon through energy conservation,industrial upgrading,development of circular economy,and application of carbon capture technology;reducing carbon through low-carbon transformation of logistics industry,innovation of trading methods,and promotion of low-carbon green consumption.The external guarantee system for carbon reduction includes the introduction of relevant policies,laws and regulations,and the use of carbon emission trading mechanism.

Recycling Carbon Resources from Waste PET to Reduce Carbon Dioxide Emission:Carbonization Technology Review and Perspective

Greenhouse gas emissions from waste plastics have caused global warming all over the world,which has been a central threat to the ecological environment for humans,flora and fauna.Among waste plastics,waste polyethylene terephthalate(PET)is attractive due to its excellent stability and degradation-resistant.Therefore,merging China’s carbon peak and carbon neutrality goals would be beneficial.In this review,we summarize the current state-of-the-art of carbon emission decrease from a multi-scale perspective technologically.We suggest that the carbon peak for waste PET can be achieved by employing the closed-loop supply chain,including recycling,biomass utilization,carbon capture and utilization.Waste PET can be a valuable and renewable resource in the whole life cycle.Undoubtedly,all kinds of PET plastics can be ultimately converted into CO_(2),which can also be feedstock for various kinds of chemical products,including ethyl alcohol,formic acid,soda ash,PU,starch and so on.As a result,the closed-loop supply chain can help the PET plastics industry drastically reduce its carbon footprint.

Progress, challenge and significance of building a carbon industry system in the context of carbon neutrality strategy

Carbon dioxide storage and utilization has become an inevitable trend and choice for sustainable development under the background of global climate change and carbon neutrality.Carbon industry which is dominated by CO_(2) capture,utilization and storage/CO_(2) capture and storage(CCUS/CCS)is becoming a new strategic industry under the goal of carbon neutrality.The sustainable development of carbon industry needs to learn from the experiences of global oil and gas industry development.There are three types of“carbon”in the earth system.Black carbon is the CO_(2) that has not been sequestered or used and remains in the atmosphere for a long time;grey carbon is the CO_(2) that has been fixed or permanently sequestered in the geological body,and blue carbon is the CO_(2) that could be converted into products for human use through biological,physical,chemical and other ways.The carbon industry system covers carbon generation,carbon capture,carbon transportation,carbon utilization,carbon sequestration,carbon products,carbon finance,and other businesses.It is a revolutionary industrial field to completely eliminate“black carbon”.The development of carbon industry technical system takes carbon emission reduction,zero carbon,negative carbon and carbon economy as the connotation,and the construction of a low-cost and energy-efficient carbon industry system based on CCUS/CCS are strategic measures to achieve the goal of carbon neutrality and clean energy utilization globally.This will promote the“four 80%s”transformation of China's energy supply,namely,to 2060,the percentage of zero-carbon new energy in the energy consumption will be over 80%and the CO_(2) emission will be decreased by 80%to ensure the carbon emission reduction of total 80×10^(8) t from the percentage of carbon-based fossil energy in the energy consumption of over 80%,and the percentage of CO_(2) emission from energy of over 80%in 2021.The carbon industry in China is facing three challenges,large CO_(2) emissions,high percentage of coal in energy consumption,and poor innovative system.Three strategic measures are proposed accordingly,including:(1)unswervingly develop carbon industrial system and ensure the achievement of carbon neutrality as scheduled by 2060;(2)vigorously develop new energy sources and promote a revolutionary transformation of China’s energy production and consumption structure;(3)accelerate the establishment of scientific and technological innovation system of the whole CO_(2) industry.It is of great significance for continuously optimization of ecological environment and construction of green earth and ecological earth to develop the carbon industry system,utilize clean energy,and achieve the strategic goal of global carbon neutrality.

Decarbonization options of the iron and steelmaking industry based on a three-dimensional analysis

Decarbonization is a critical issue for peaking CO_(2) emissions of energy-intensive industries,such as the iron and steel industry.The decarbonization options of China’s ironmaking and steelmaking sector were discussed based on a systematic three-dimensional low-carbon analysis from the aspects of resource utilization(Y),energy utilization(Q),and energy cleanliness which is evaluated by a process general emission factor(PGEF)on all the related processes,including the current blast furnace(BF)-basic oxygen furnace(BOF)integrated process and the specific sub-processes,as well as the electric arc furnace(EAF)process,typical direct reduction(DR)process,and smelting reduction(SR)process.The study indicates that the three-dimensional aspects,particularly the energy structure,should be comprehensively considered to quantitatively evaluate the decarbonization road map based on novel technologies or processes.Promoting scrap utilization(improvement of Y)and the substitution of carbon-based energy(improvement of PGEF)in particular is critical.In terms of process scale,promoting the development of the scrap-based EAF or DR-EAF process is highly encouraged because of their lower PGEF.The three-dimensional method is expected to extend to other processes or industries,such as the cement production and thermal electricity generation industries.

China's INDC and non-fossil energy development

Global climate change promotes the energy system reform. Achieving a high proportion of renewable energy becomes the major countries＇ energy strategy. As proposed in its Intended Nationally Determined Contributions （INDC）, China intends to raise the proportion of non-fossil energy in primary energy consumption to about 20% by 2030. That ambitious goal means the non-fossil energy supplies by 2030 will be 7-8 times that of 2005, and the annual increase rate is more than 8% within the 25 years. Besides, the capacity of wind power, solar power, hy- dropower and nuclear power reaches 400 GW, 350 GW, 450 GW, and 150 GW respectively, and China＇s non-fossil power capacity is even greater than the U.S.＇s total power capacity. In addition, the scale of natural gas increases. Consequently, by 2030, the proportion of coal falls from the current 70% to below 50%, and the CO2 intensity of energy consumption decreases by 20% compared with the level of 2005, which play important roles in significantly reducing the CO2 intensity of GDE Since China has confirmed to achieve the CO2 emissions peak around 2030, at that time, the newly added energy demand will be satisfied by non-fossil energy, and the consumption of fossil fuel will stop growing. By 2030, non-fossil energy accounts for 20%, and the large scale and sound momentum of new and renewable energy industry will support the growth of total energy demand, which plays a key role in CO2 emissions peaking and beginning to decline, and lays the foundation for establishing a new energy system dominated by new and renewable energy in the second half of the 21 st century as well as finally achieving the CO2 zero-emission.

Analysis of Dynamic Tensile Process of Fiber Reinforced Concrete by Acoustic Emission Technique

The fiber reinforced concrete has good dynamic mechanical properties. But corresponding research lacks the dynamic damage characteristics of the polypropylene fiber（fiber of low elastic modulus） and steel fiber（fiber of high elastic modulus） reinforced concrete under medium strain rate（10-6 s-1-10-4 s-1）. In order to study the effect of strain rate on the damage characteristics of fiber reinforced concrete during the full curve damage process, the real time dynamic acoustic emission（AE） technique was applied to monitor the damage process of fiber reinforced concrete at three strain rates. The AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency at three strain rates were analyzed. With the accumulation of damage, the AE wavelet energy spectrum in ca8 frequency band increased first and then decreased, and the average AE peak frequency increased gradually. With the increase of strain rate, the AE wavelet energy spectrum in ca8 frequency band and average AE peak frequency decreased gradually. The polypropylene fiber content has more obvious effect on the Dynamic increase factor（DIF） of the peak stress than the steel fiber content. The theoretical basis was provided for the monitoring of dynamic damage of fiber reinforced concrete based on the AE technique.

Pathway and policy analysis to China's deep decarbonization

The Paris Agreement marks the beginning of a new era in the global response to climate change, which further clarifies the long-term goal and underlines the urgency addressing climate change. For China,promoting the decoupling between economic growth and carbon emissions as soon as possible is not only the core task of achieving the medium-and long-term goals and strategies to address climate change, but also the inevitable requirement for ensuring the sustainable development of economy and society. Based on the analysis of the historical trends of the economy and social development, as well as society, energy consumption, and key end-use sectors in China, this paper studies the deep carbon emission reduction potential of carbon emission of in energy, industry, building, and transportation and other sectors with "bottom-up" modeling analysis and proposes a medium-and long-term deep decarbonization pathway based on key technologies' mitigation potentials for China. It is found that under deep decarbonization pathway, China will successfully realize the goals set in China's Intended Nationally Determined Contributions of achieving carbon emissions peak around 2030 and lowering carbon dioxide emissions per unit of gross domestic product(GDP) by 60-65% from the 2005 level.From 2030 onward, the development of nonfossil energy will further accelerates, and the share of nonfossil energies in primary energy will amounts to about 44% by 2050. Combined with the acceleration of low-carbon transformation in end-use sectors including industry, building, and transportation, the carbon dioxide emissions in 2050 will fall to the level before 2005, and the carbon dioxide emissions per unit of GDP will decreases by more than 90% from the 2005 level. To ensure the realization of the deep decarbonization pathway, this paper puts forward policy recommendations from four perspectives, including intensifying the total carbon dioxide emissions cap and strengthening the related institutional systems and regulations, improving the incentive policies for industrial lowcarbon development, enhancing the role of the market mechanism, and advocating low-carbon life and consumption patterns.

Research on China’s technology lists for addressing climate change

The compilation of technology lists addressing climate change has a guiding effect on promoting technological research and development,demonstration,and popularization.It is also crucial for China to strengthen ecological civilization construction,achieve the carbon emission peak and carbon neutrality target,and enhance global climate governance capabilities.This study first proposes the existing classification outline of the technology promotion lists,technology demand lists,and future technology lists.Then,different methodologies are integrated on the basis of the existing outline of four technology lists:China’s existing technological promotion list for addressing climate change,China’s demand list for climate change mitigation technology,China’s key technology list for addressing climate change,and China’s future technology list for addressing climate change.What’s more,core technologies are analyzed in the aspects of technology maturity,carbon reduction cost,carbon reduction potential,economic benefits,social influence,uncertainty,etc.The results show that:key industries and sectors in China already have relatively mature mitigation/adaptation technologies to support the achievement of climate change targets.The multi-sectoral system of promoting climate friendly technologies has been established,which has played an active role in tackling climate change.Currently,climate technology needs are concentrated in the traditional technology and equipment upgrading,renewable energy technology,and management decision-making support technology.The key technologies are concentrated in 3 major areas and 12 technological directions that urgently need a breakthrough.For carbon emmission peak and nentrality,carbon depth reduction and zero carbon emissions and geoengineering technology(CDR and SRM)have played an important role in forming the structure of global emissions and achieving carbon neutrality in the future.Thus,the uncertainty assessment for the comprehensive technology cost effectiveness,technology integration direction,technical maturity,ethics and ecological impacts is supportive to the national technology strategy.Finally,the presented study proposes several policy implications for medium-and long-term technology deployment,improving technology conversion rate,promoting the research and development of core technologies,and forming a technology list collaborative update and release mechanism.

The role of new energy in carbon neutral

Carbon dioxide is an important medium of the global carbon cycle,and has the dual properties of realizing the conversion of organic matter in the ecosystem and causing the greenhouse effect.The fixed or available carbon dioxide in the atmosphere is defined as"gray carbon",while the carbon dioxide that cannot be fixed or used and remains in the atmosphere is called"black carbon".Carbon neutral is the consensus of human development,but its implementation still faces many challenges in politics,resources,technology,market,and energy structure,etc.It is proposed that carbon replacement,carbon emission reduction,carbon sequestration,and carbon cycle are the four main approaches to achieve carbon neutral,among which carbon replacement is the backbone.New energy has become the leading role of the third energy conversion and will dominate carbon neutral in the future.Nowadays,solar energy,wind energy,hydropower,nuclear energy and hydrogen energy are the main forces of new energy,helping the power sector to achieve low carbon emissions."Green hydrogen"is the reserve force of new energy,helping further reduce carbon emissions in industrial and transportation fields.Artificial carbon conversion technology is a bridge connecting new energy and fossil energy,effectively reducing the carbon emissions of fossil energy.It is predicted that the peak value of China’s carbon dioxide emissions will reach 110×10^(8) t in 2030.The study predicts that China’s carbon emissions will drop to 22×10^(8) t,33×10^(8) t and 44×10^(8) t,respectively,in 2060 according to three scenarios of high,medium,and low levels.To realize carbon neutral in China,seven implementation suggestions have been put forward to build a new"three small and one large"energy structure in China and promote the realization of China’s energy independence strategy.

Auction mechanism design of the Chinese national carbon market for carbon neutralization

The carbon market auction mechanism is an important policy tool for carbon pricing and a key mechanism that supports carbon emission neutralization,especially for China.A few systematic studies exist on China’s carbon market auction mechanism.This article focuses on the five auction mechanisms in Chinese pilot emission trading schemes(ETS),reviews the structures and bidding situation of the five-pilot auction mechanism,extracts the similarities,and analyzes their different features,such as auction mode,bidding scale,participants,pricing mode,auction frequency,and so on.This study conducts an in-depth analysis of the carbon allowance auction mechanism in the Guangdong pilot ETS of China,including its development and the evolution of the key elements,its operational effects,and related disputes.Finally,this study puts forward the trend forecast and suggestions for the Chinese allowance auction mechanism,such as the time window of launching national allowance auctions,the most likely auction mode,carbon pricing,and bidding revenue management.Carbon pricing by auction is the most powerful policy tool for addressing carbon emissions reduction and implementing the Glasgow Climate Pact.

Security in gas discharge while unsealing a closed stope

Given the problem of harmful gas discharge in unsealing coal mining faces, we numerically simulated the process of change of gas flows and movements, We have pointed out that, at the moment of unsealing a closed stope, the gas discharge is naturally divided into two parts, i.e., the discharge of gas in the working face and that in the goaf, because of the difference in the spatial medium. The absolute volume of gas discharged has a tendency to decrease from its initial peak value to a final stable value. The rate of decrease and the time needed to reach a stable discharge are related to the scale of the mining stope. The discharge of gas from the working face is closely related to the amount of air distributed in the air return way. The most important thing in unsealing a stope is to have the initial peak volume of gas discharged well under control. A commonly used method in solving this problem is at first to use a small amount of air and then increasing it gradually. Our study shows that, by extracting gas from the upper corner, we can use a large volume of air at first in order to shorten considerably the discharge time and improve efficiency, thereby making mining, activitv safer.

Numerical study of strained InGaAs quantum well lasers emitting at 2.33 μm using the eight-band model

We investigate the band structure of a compressively strained In（Ga）As/In0.53Ga0.47As quantum well （QW） on an InP substrate using the eight-band k.p theory. Aiming at the emission wavelength around 2.33 μm, we discuss the influences of temperature, strain and well width on the band structure and on the emission wavelength of the QW. The wavelength increases with the increase of temperature, strain and well width. Furthermore, we design an InAs /In0.53Ga0.47As QW with a well width of 4.1 nm emitting at 2.33 μm by optimizing the strain and the well width.