A simple two-dimensional phononic crystal hosting topologically protected edge states is proposed to emulate the quantum spin Hall effect in electronic systems, whose phononic topological phase can be reconfigured thr...A simple two-dimensional phononic crystal hosting topologically protected edge states is proposed to emulate the quantum spin Hall effect in electronic systems, whose phononic topological phase can be reconfigured through the rotation of scatters. In particular, the band inversion occurs between two pairs of high-order compound states, resulting in topological phase transition from trivial to nontrivial over a relatively broad high-frequency range. This is further evidenced by an effective Hamiltonian derived by the k·p perturbation theory. The phononic topology is related to a pseudo-timereversal symmetry constructed by the point group symmetry of two doubly degenerate eigenstates. Numerical simulations unambiguously demonstrate robust helical edge states whose pseudospin indices are locked to the propagation direction along the interface between topologically trivial and nontrivial phononic crystals. Our designed phononic systems provide potential applications in robust acoustic signal transport along any desired path over a high-frequency range.展开更多
This article compiles the actual knowledge of the biogenic volatile organic compound（BVOC） emissions estimated using model methods in the Pearl River Delta（PRD） region, one of the most developed regions in China. ...This article compiles the actual knowledge of the biogenic volatile organic compound（BVOC） emissions estimated using model methods in the Pearl River Delta（PRD） region, one of the most developed regions in China. The developed history of BVOC emission models is presented briefly and three typical emission models are introduced and compared. The results from local studies related to BVOC emissions have been summarized. Based on this analysis, it is recommended that local researchers conduct BVOC emission studies systematically, from the assessment of model inputs, to compiling regional emission inventories to quantifying the uncertainties and evaluating the model results. Beyond that,more basic researches should be conducted in the future to close the gaps in knowledge on BVOC emission mechanisms, to develop the emission models and to refine the inventory results. This paper can provide a perspective on these aspects in the broad field of research associated with BVOC emissions in the PRD region.展开更多
The low-temperature heat capacities are studied for antiperovskite compounds AX M_3（A = Al, Ga, Cu, Ag, Sn, X = C,N, M = Mn, Fe, Co）. A large peak in（C- γ T）/T^3 versus T is observed for each of a total of 18 com...The low-temperature heat capacities are studied for antiperovskite compounds AX M_3（A = Al, Ga, Cu, Ag, Sn, X = C,N, M = Mn, Fe, Co）. A large peak in（C- γ T）/T^3 versus T is observed for each of a total of 18 compounds investigated,indicating an existence of low-energy phonon mode unexpected by Debye T^3 law. Such a peak is insensitive to the external magnetic field up to 80 k Oe（1 Oe = 79.5775 A·m-1）. For compounds with smaller lattice constant, the peak shifts towards higher temperatures with a reduction of peak height. This abnormal peak in（C- γ T）/T^3 versus T of antiperovskite compound may result from the strongly dispersive acoustic branch due to the heavier A atoms and the optical-like mode from the dynamic rotation of X M_6 octahedron. Such a low-energy phonon mode may not contribute negatively to the normal thermal expansion in AX M_3 compounds, while it is usually concomitant with negative thermal expansion in open-structure material（e.g., ZrW_2O_8, Sc F_3）.展开更多
In recent years,major exploration breakthroughs and subsequent booming development of marine shale gas in both Upper Ordovician Wufeng and Lower Silurian Longmaxi Fms in the Sichuan Basin and its periphery highlight t...In recent years,major exploration breakthroughs and subsequent booming development of marine shale gas in both Upper Ordovician Wufeng and Lower Silurian Longmaxi Fms in the Sichuan Basin and its periphery highlight the strategic importance for the theoretical innovation and technological advances of gas in China.A number of key theories and technologies,such as continuous hydrocarbon accumulation and horizontal well volume fracturing,and so on,have contributed to the large-scale development of shale gas fields such as Shunan,Fuling,etc.,in Sichuan Basin.Based on China's geological conditions,industrial practices and current limitations in executing the full-scale development of shale gas,a new concept called“volume development(VD)”has been proposed.Under the framework of this theory,manmade volumetric fracture network systems are established through the combination of horizontal well drilling and transverse hydraulic fracturing through which gas flow become much more efficient due to the lateral flow superimposed by vertical fracture flow.VD has become a very efficient development model for shale gas because it can make gas in the volume affected by the man-made fracture network system become commercial reserves,and be produced more cost-effectively.VD includes five core technologies,i.e.comprehensive evaluation of“sweet areas”,optimization design of well patterns for volume development,optimization and trajectory design of horizontal well drilling in target window,massive fracturing technology for horizontal wellbores,design of production system and platform-based well factory-like management.The VD theory and technology provides important theoretical basis and technical support not only for the present three-dimensional development of shale gas in Changning,Fuling and other nearby blocks,but for the overall utilization of unconventional oil and gas resources such as continental,transitional shale gas.It is believed that VD will have broad application prospects in shale gas development.展开更多
This paper investigates the modal properties of semiconductor lasers operating in the strong-feedback regime. Analytical expressions are developed based on an iterative travelling-wave model, which enable a complete a...This paper investigates the modal properties of semiconductor lasers operating in the strong-feedback regime. Analytical expressions are developed based on an iterative travelling-wave model, which enable a complete and quantitative description of a compound cavity mode in its steady state. Additional information is provided about the physical inside into a compound laser system, such as a bifurcation diagram of the compound cavity modes for full variation range （from 0 to 1） of the external reflection coefficient and a more general shape for the diagram of photon density versus mode phase - this latter will reduce to the classical ＂ellipse＂ in the weak-feedback regime. It is shown that in the strong-feedback regime, a feedback laser is characterized by a small mode number and a high density of photons. This behavior confirms previous experimental observations, showing that beyond the coherence-collapse regime, the compound laser system could be re-stabilized, and that as a result power-enhanced low-noise stable laser operation with quasi-uniform pulsation is possible with external-mirror reflectivity close to 1. Moreover, it is also shown that for a compound system operating in the strong-feedback regime, an anti-reflection treatment of a laser can significantly reduce its current threshold, and that in the absence of this treatment excitation of a minimum-linewidth mode with higher output power would be possible inside such a system. Finally, it is shown that in the weak-feedback regime except for a phase shift the iterative travelling-wave model will reduce to the Lang-Kobayashi model in cases where the product of the feedback rate and the internal round-trip time is much less than unity （that would mean in situations of as-cleaved lasers）.展开更多
基金Project supported by the Young Scientists Fund of the Natural Science Foundation of Shandong Province,China(Grant No.ZR2016AQ09)Young Scientists Fund of the National Natural Science Foundation of China(Grant No.11704219).
文摘A simple two-dimensional phononic crystal hosting topologically protected edge states is proposed to emulate the quantum spin Hall effect in electronic systems, whose phononic topological phase can be reconfigured through the rotation of scatters. In particular, the band inversion occurs between two pairs of high-order compound states, resulting in topological phase transition from trivial to nontrivial over a relatively broad high-frequency range. This is further evidenced by an effective Hamiltonian derived by the k·p perturbation theory. The phononic topology is related to a pseudo-timereversal symmetry constructed by the point group symmetry of two doubly degenerate eigenstates. Numerical simulations unambiguously demonstrate robust helical edge states whose pseudospin indices are locked to the propagation direction along the interface between topologically trivial and nontrivial phononic crystals. Our designed phononic systems provide potential applications in robust acoustic signal transport along any desired path over a high-frequency range.
基金supported by the National Science Fund for Outstanding Young Scholars(No.41425020)the China Special Fund for Meteorological Research in the Public Interest(No.GYHY201406031)and the Key Projects in the National Science&Technology Pillar Program(No.2014BAC21B02)
文摘This article compiles the actual knowledge of the biogenic volatile organic compound（BVOC） emissions estimated using model methods in the Pearl River Delta（PRD） region, one of the most developed regions in China. The developed history of BVOC emission models is presented briefly and three typical emission models are introduced and compared. The results from local studies related to BVOC emissions have been summarized. Based on this analysis, it is recommended that local researchers conduct BVOC emission studies systematically, from the assessment of model inputs, to compiling regional emission inventories to quantifying the uncertainties and evaluating the model results. Beyond that,more basic researches should be conducted in the future to close the gaps in knowledge on BVOC emission mechanisms, to develop the emission models and to refine the inventory results. This paper can provide a perspective on these aspects in the broad field of research associated with BVOC emissions in the PRD region.
基金Project supported by the National Key Basic Research Program of China(Grant Nos.2011CBA00111)the National Natural Science Foundation of China(Grant Nos.51322105,U1632158,51301165,and 51301167)
文摘The low-temperature heat capacities are studied for antiperovskite compounds AX M_3（A = Al, Ga, Cu, Ag, Sn, X = C,N, M = Mn, Fe, Co）. A large peak in（C- γ T）/T^3 versus T is observed for each of a total of 18 compounds investigated,indicating an existence of low-energy phonon mode unexpected by Debye T^3 law. Such a peak is insensitive to the external magnetic field up to 80 k Oe（1 Oe = 79.5775 A·m-1）. For compounds with smaller lattice constant, the peak shifts towards higher temperatures with a reduction of peak height. This abnormal peak in（C- γ T）/T^3 versus T of antiperovskite compound may result from the strongly dispersive acoustic branch due to the heavier A atoms and the optical-like mode from the dynamic rotation of X M_6 octahedron. Such a low-energy phonon mode may not contribute negatively to the normal thermal expansion in AX M_3 compounds, while it is usually concomitant with negative thermal expansion in open-structure material（e.g., ZrW_2O_8, Sc F_3）.
基金supported by the National Science and Technology Major Project of the Ministry of Science and Technology of China“Shale Gas Reservoir Engineering and Gas Production Technology”(No.:2016ZX05037)“Shale Gas Formation and Enrichment Conditions in the Sichuan Basin and its Periphery and the Prospect Evaluation Technology and its Application”(No.:2017ZX05035).
文摘In recent years,major exploration breakthroughs and subsequent booming development of marine shale gas in both Upper Ordovician Wufeng and Lower Silurian Longmaxi Fms in the Sichuan Basin and its periphery highlight the strategic importance for the theoretical innovation and technological advances of gas in China.A number of key theories and technologies,such as continuous hydrocarbon accumulation and horizontal well volume fracturing,and so on,have contributed to the large-scale development of shale gas fields such as Shunan,Fuling,etc.,in Sichuan Basin.Based on China's geological conditions,industrial practices and current limitations in executing the full-scale development of shale gas,a new concept called“volume development(VD)”has been proposed.Under the framework of this theory,manmade volumetric fracture network systems are established through the combination of horizontal well drilling and transverse hydraulic fracturing through which gas flow become much more efficient due to the lateral flow superimposed by vertical fracture flow.VD has become a very efficient development model for shale gas because it can make gas in the volume affected by the man-made fracture network system become commercial reserves,and be produced more cost-effectively.VD includes five core technologies,i.e.comprehensive evaluation of“sweet areas”,optimization design of well patterns for volume development,optimization and trajectory design of horizontal well drilling in target window,massive fracturing technology for horizontal wellbores,design of production system and platform-based well factory-like management.The VD theory and technology provides important theoretical basis and technical support not only for the present three-dimensional development of shale gas in Changning,Fuling and other nearby blocks,but for the overall utilization of unconventional oil and gas resources such as continental,transitional shale gas.It is believed that VD will have broad application prospects in shale gas development.
文摘This paper investigates the modal properties of semiconductor lasers operating in the strong-feedback regime. Analytical expressions are developed based on an iterative travelling-wave model, which enable a complete and quantitative description of a compound cavity mode in its steady state. Additional information is provided about the physical inside into a compound laser system, such as a bifurcation diagram of the compound cavity modes for full variation range （from 0 to 1） of the external reflection coefficient and a more general shape for the diagram of photon density versus mode phase - this latter will reduce to the classical ＂ellipse＂ in the weak-feedback regime. It is shown that in the strong-feedback regime, a feedback laser is characterized by a small mode number and a high density of photons. This behavior confirms previous experimental observations, showing that beyond the coherence-collapse regime, the compound laser system could be re-stabilized, and that as a result power-enhanced low-noise stable laser operation with quasi-uniform pulsation is possible with external-mirror reflectivity close to 1. Moreover, it is also shown that for a compound system operating in the strong-feedback regime, an anti-reflection treatment of a laser can significantly reduce its current threshold, and that in the absence of this treatment excitation of a minimum-linewidth mode with higher output power would be possible inside such a system. Finally, it is shown that in the weak-feedback regime except for a phase shift the iterative travelling-wave model will reduce to the Lang-Kobayashi model in cases where the product of the feedback rate and the internal round-trip time is much less than unity （that would mean in situations of as-cleaved lasers）.
