To investigate the effect of void defects on the shock response of hexanitrohexaazaisowurtzitane(CL-20)co-crystals,shock responses of CL-20 co-crystals with energetic materials ligands trinitrotoluene(TNT),1,3-dinitro...To investigate the effect of void defects on the shock response of hexanitrohexaazaisowurtzitane(CL-20)co-crystals,shock responses of CL-20 co-crystals with energetic materials ligands trinitrotoluene(TNT),1,3-dinitrobenzene(DNB),solvents ligands dimethyl carbonate(DMC) and gamma-butyrolactone(GBL)with void were simulated,using molecular dynamics method and reactive force field.It is found that the CL-20 co-crystals with void defects will form hot spots when impacted,significantly affecting the decomposition of molecules around the void.The degree of molecular fragmentation is relatively low under the reflection velocity of 2 km/s,and the main reactions are the formation of dimer and the shedding of nitro groups.The existence of voids reduces the safety of CL-20 co-crystals,which induced the sensitivity of energetic co-crystals CL-20/TNT and CL-20/DNB to increase more significantly.Detonation has occurred under the reflection velocity of 4 km/s,energetic co-crystals are easier to polymerize than solvent co-crystals,and are not obviously affected by voids.The results show that the energy of the wave decreases after sweeping over the void,which reduces the chemical reaction frequency downstream of the void and affects the detonation performance,especially the solvent co-crystals.展开更多
The interfacial structure has an important effect on the mechanical properties and safety of the energetic material.In this work,a mesostructure model reflecting the real internal structure of PBX is established throu...The interfacial structure has an important effect on the mechanical properties and safety of the energetic material.In this work,a mesostructure model reflecting the real internal structure of PBX is established through image digital modeling and vectorization processing technology.The microscopic molecular structure model of PBX is constructed by molecular dynamics,and the interface bonding energy is calculated and transferred to the mesostructure model.Numerical simulations are used to study the influence of the interface roughness on the dynamic compression and impact ignition response of PBX,and to regulate and optimize the mechanical properties and safety of the explosive to obtain the optimal design of the surface roughness of the explosive crystal.The results show that the critical hot spot density of PBX ignition under impact loading is 0.68 mm^(-2).The improvement of crystal surface roughness can improve the mechanical properties of materials,but at the same time it can improve the impact ignition sensitivity and reduce the safety of materials.The optimal friction coefficient range for the crystal surface that satisfies both the mechanical properties and safety of PBX is 0.06-0.12.This work can provide a reference basis for the formulation design and production processing of energetic materials.展开更多
For this study of long-term spatial patterns and trends of active fires in southern hemispheric Africa and on Madagascar from 2001 to 2020,active fire data from the MODIS FIRMS global fire data products were analyzed....For this study of long-term spatial patterns and trends of active fires in southern hemispheric Africa and on Madagascar from 2001 to 2020,active fire data from the MODIS FIRMS global fire data products were analyzed.The annual center of fire concentration tended to migrate toward the preserved rainforests and nature conservation areas in the Congo Basin and the mountain forests on the northeastern coast of Madagascar.Fire frequency varied seasonally at both study areas.We used geo statistical analysis techniques,such as measures of dispersion and emerging hot spot analysis,to reveal long-term trends in spatial patterns of fire events.In southern hemispheric Africa,the observed active fires tended to drift northward toward the Zambia-DRC border in the Congo basin.This northward migration progressed toward humid rainforests,which were better suited to sustaining repeated fire events.On Madagascar,the observed active fires tended to migrate toward the east coast in protected mountain forests.The spatial patterns of long-term trends showed a concentration of fires in the tropical regions of southern hemispheric Africa.Moreover,smaller clusters of new hot spots were located over eastern South Africa,overlapping with undifferentiated woodlands.On Madagascar,both hot and cold spots were identified and were separated by the highland region in the center of the island.Most of the eastern island was characterized by cold spots that received less precipitation than did the rest of the island.The presence of increasing hots spots in the densely vegetated areas highlights the urgent need for fire prevention and management in this region.展开更多
Fragmental size and distribution of explosive particles play a more important role in the formation of hot-spot than original particles size under drop weight impact.Because the particles breakage and the hot-spots ig...Fragmental size and distribution of explosive particles play a more important role in the formation of hot-spot than original particles size under drop weight impact.Because the particles breakage and the hot-spots ignition will form in a sequence between fragments and between the fragments and the drop weight surface under the impact.In this paper,the size and distribution of the cyclotetramethylenete tranitramine(HMX)fragments were analyzed by the Laser Particle Size Analyzer Malvern MS2000.The post-analysis results of fragments showed that size distribution of fragments was strongly dependent on drop height.An empirical formula is established to describe the relationship between the average size and drop height.The volume-based probability distribution of explosive fragments was also studied by experiments and theoretical calculations.展开更多
The preparation of surface-enhanced fluorescence(SEF) substrates is often influenced by experimental strategies and factors such as the morphology and size of the nanostructures. In this study, using the natural reed ...The preparation of surface-enhanced fluorescence(SEF) substrates is often influenced by experimental strategies and factors such as the morphology and size of the nanostructures. In this study, using the natural reed leaves(RLs) without any special pretreatment as the substrate, metal silver is modified by magnetron sputtering technology to prepare a stable and efficient SEF system. The abundant “hedgehog-like” protrusions on the RL substrate surface can generate high-density“hot spots”, thus enhancement factor(EF) is enhanced up to 3345 times. The stability and reproducibility are verified in many measurements. The contribution of the intervention of silver nanostructure to the radiation attenuation process of fluorescent molecules is analyzed with the aid of Jablonski diagrams. Three-dimensional(3D) finite difference time domain(FDTD) simulates the spatial electric field and “hot spots” distribution of the substrate. The “hedgehog-like” protrusion structure generates multiple “hot spots”, which produce an excellent local surface plasmon resonance(LSPR) effect and provide higher fluorescence signal. Finally, RL/Ag-35 substrate is used to detect crystal violet(CV), and the detection limit is as low as 10^(-13) M. This “hedgehog-like” SEF substrate provides a new strategy for the trace detection of CV, which has a good practical application value.展开更多
BACKGROUND: Less attention is directed toward gaining a better understanding of the burden and prevention of injuries, in low and middle income countries(LMICs). We report the establishment of a trauma registry at the...BACKGROUND: Less attention is directed toward gaining a better understanding of the burden and prevention of injuries, in low and middle income countries(LMICs). We report the establishment of a trauma registry at the Adult Emergency and Trauma Centre(AETC) at Queen Elizabeth Central Hospital(QECH) in Blantyre, Malawi and identify high risk geographic areas. METHODS: We devised a paper based two-page trauma registry form. Ten data clerks and all AETC clinicians were trained to complete demographic and clinical details respectively. Descriptive data, regression and hotspot analyses were done using STATA 15 statistical package and ArcGIS(16) software respectively.RESULTS: There were 3,747 patients from May 2013 to May 2015. The most common mechanisms of injury were assault(38.2%), and road traffi c injuries(31.6%). The majority had soft tissue injury(53.1%), while 23.8% had no diagnosis indicated. Fractures(OR 19.94 [15.34–25.93]), head injury and internal organ injury(OR 29.5 [16.29–53.4]), and use of ambulance(OR 1.57 [1.06–2.33]) were found to be predictive of increased odds of being admitted to hospital while assault(OR 0.69 [0.52–0.91]) was found to be associated with less odds of being admitted to hospital. Hot spot analysis showed that at 99% confidence interval, Ndirande, Mbayani and Limbe were the top hot spots for injury occurrence. CONCLUSION: We have described the process of establishing an integrated and potentially sustainable trauma registry. Signifi cant data were captured to provide details on the epidemiology of trauma and insight on how care could be improved at AETC and surrounding health facilities. This approach may be relevant in similar poor resource settings.展开更多
Air traffic is a typical complex system, in which movements of traffic components （pilots, controllers, equipment, and environment）, especially airport arrival and departure traffic, form complicated spatial and tem...Air traffic is a typical complex system, in which movements of traffic components （pilots, controllers, equipment, and environment）, especially airport arrival and departure traffic, form complicated spatial and temporal dynamics. The fluctuations of airport arrival and departure traffic are studied from the point of view of networks as the special correlation between different airports. Our collected flow volume data on the time-dependent activity of US airport arrival and departure traffic indicate that the coupling between the average flux and the fluctuation of an individual airport obeys a certain scaling law with a wide variety of scaling exponents between 1/2 and 1. These scaling phenomena can explain the interaction between the airport internal dynamics （e.g. queuing at airports, a ground delay program and following flying traffic） and a change in the external （network-wide） traffic demand （e.g. an increase in traffic during peak hours every day）, allowing us to further understand the mechanisms governing the collective behaviour of the transportation system. We separate internal dynamics from external fluctuations using a scaling law which is helpful for us to systematically determine the origin of fluctuations in airport arrival and departure traffic, uncovering the collective dynamics. Hot spot features are observed in airport traffic data as the dynamical inhomogeneity in the fluxes of individual airports. The intrinsic characteristics of airport arrival and departure traffic under severe weather is discussed as well.展开更多
A dispersion model is developed to provide a generic tool for configuring plasmonic resonance spectral characteristics.The customized design of the resonance curve aiming at specific detection requirements can be achi...A dispersion model is developed to provide a generic tool for configuring plasmonic resonance spectral characteristics.The customized design of the resonance curve aiming at specific detection requirements can be achieved.According to the model,a probe-type nano-modified fiber optic configurable plasmonic resonance(NMF-CPR)sensor with tip hot spot enhancement is demonstrated for the measurement of the refractive index in the range of 1.3332-1.3432 corresponding to the low-concentration biomarker solution.The new-type sensing structure avoids excessive broadening and redshift of the resonance dip,which provides more possibilities for the surface modification of other functional nanomaterials.The tip hot spots in nanogaps between the Au layer and Au nanostars(AuNSs),the tip electric field enhancement of AuNSs,and the high carrier mobility of the WSe_(2)layer synergistically and significantly enhance the sensitivity of the sensor.Ex-perimental results show that the sensitivity and the figure of merit of the tip hot spot enhanced fiber NMF-CPR sensor can achieve up to 2995.70 nm/RIU and 25.04 RIU^(−1),respectively,which are 1.68 times and 1.29 times higher than those of the conventional fiber plasmonic resonance sensor.The results achieve good agreements with numerical simulations,demonstrate a better level compared to similar reported studies,and verify the correctness of the dispersion model.The detection resolution of the sensor reaches up to 2.00×10^(−5)RIU,which is obviously higher than that of the conventional side-polished fiber plasmonic resonance sensor.This indicates a high detection accuracy of the sensor.The dense Au layer effectively prevents the intermediate nanomaterials from shedding and chemical degradation,which enables the sensor with high stability.Furthermore,the terminal reflective sensing structure can be used as a practical probe and can allow a more convenient operation.展开更多
The bow structure of FPSO moored by the single mooring system is rather complicated. There are many potential hot spots in connection parts of structures between the mooring support frame and the forecastle. Mooring f...The bow structure of FPSO moored by the single mooring system is rather complicated. There are many potential hot spots in connection parts of structures between the mooring support frame and the forecastle. Mooring forces, which are induced by wave excitation and transferred by the YOKE and the mooring support frame, may cause fatigue damage to the bow structure. Different from direct wave-in duced-forces, the mooring force consists of wave frequency force (WF) and 2nd dr aft low frequency force (LF) [3] , which are represented by two sets of short-term distribution respectively. Based on two sets of short-term distribution of moor ing forces obtained by the model test, the fatigue damage of the bow structure of FPSO is analyzed, with emphasis on two points. One is the procedure and position selection for fatigue check, and the other is the application of new formulae for the calculation of accumulative fatigue damage caused by two sets of short-term distribution of hot spot stress range. From the results distingui shed features of fatigue damage to the FPSO’s bow structure can be observed.展开更多
基金supported by the National Natural Science Foundation of China (22275018)the Project of State Key Laboratory of Explosion Science and Technology (Beijing Institute of Technology)(Grant No.QNKT20-04)。
文摘To investigate the effect of void defects on the shock response of hexanitrohexaazaisowurtzitane(CL-20)co-crystals,shock responses of CL-20 co-crystals with energetic materials ligands trinitrotoluene(TNT),1,3-dinitrobenzene(DNB),solvents ligands dimethyl carbonate(DMC) and gamma-butyrolactone(GBL)with void were simulated,using molecular dynamics method and reactive force field.It is found that the CL-20 co-crystals with void defects will form hot spots when impacted,significantly affecting the decomposition of molecules around the void.The degree of molecular fragmentation is relatively low under the reflection velocity of 2 km/s,and the main reactions are the formation of dimer and the shedding of nitro groups.The existence of voids reduces the safety of CL-20 co-crystals,which induced the sensitivity of energetic co-crystals CL-20/TNT and CL-20/DNB to increase more significantly.Detonation has occurred under the reflection velocity of 4 km/s,energetic co-crystals are easier to polymerize than solvent co-crystals,and are not obviously affected by voids.The results show that the energy of the wave decreases after sweeping over the void,which reduces the chemical reaction frequency downstream of the void and affects the detonation performance,especially the solvent co-crystals.
基金National Natural Science Foundation of China(Grant No.U22B20131)General Program of National Nature Science Foundation of China(Grant No.12202060)for supporting this project。
文摘The interfacial structure has an important effect on the mechanical properties and safety of the energetic material.In this work,a mesostructure model reflecting the real internal structure of PBX is established through image digital modeling and vectorization processing technology.The microscopic molecular structure model of PBX is constructed by molecular dynamics,and the interface bonding energy is calculated and transferred to the mesostructure model.Numerical simulations are used to study the influence of the interface roughness on the dynamic compression and impact ignition response of PBX,and to regulate and optimize the mechanical properties and safety of the explosive to obtain the optimal design of the surface roughness of the explosive crystal.The results show that the critical hot spot density of PBX ignition under impact loading is 0.68 mm^(-2).The improvement of crystal surface roughness can improve the mechanical properties of materials,but at the same time it can improve the impact ignition sensitivity and reduce the safety of materials.The optimal friction coefficient range for the crystal surface that satisfies both the mechanical properties and safety of PBX is 0.06-0.12.This work can provide a reference basis for the formulation design and production processing of energetic materials.
文摘For this study of long-term spatial patterns and trends of active fires in southern hemispheric Africa and on Madagascar from 2001 to 2020,active fire data from the MODIS FIRMS global fire data products were analyzed.The annual center of fire concentration tended to migrate toward the preserved rainforests and nature conservation areas in the Congo Basin and the mountain forests on the northeastern coast of Madagascar.Fire frequency varied seasonally at both study areas.We used geo statistical analysis techniques,such as measures of dispersion and emerging hot spot analysis,to reveal long-term trends in spatial patterns of fire events.In southern hemispheric Africa,the observed active fires tended to drift northward toward the Zambia-DRC border in the Congo basin.This northward migration progressed toward humid rainforests,which were better suited to sustaining repeated fire events.On Madagascar,the observed active fires tended to migrate toward the east coast in protected mountain forests.The spatial patterns of long-term trends showed a concentration of fires in the tropical regions of southern hemispheric Africa.Moreover,smaller clusters of new hot spots were located over eastern South Africa,overlapping with undifferentiated woodlands.On Madagascar,both hot and cold spots were identified and were separated by the highland region in the center of the island.Most of the eastern island was characterized by cold spots that received less precipitation than did the rest of the island.The presence of increasing hots spots in the densely vegetated areas highlights the urgent need for fire prevention and management in this region.
基金Science Challenging Program(TZ2016001)the National Natural Science Foundation of China(11572045,11472051)Innovative Group of Material and Structure Impact Dynamics(11521062)。
文摘Fragmental size and distribution of explosive particles play a more important role in the formation of hot-spot than original particles size under drop weight impact.Because the particles breakage and the hot-spots ignition will form in a sequence between fragments and between the fragments and the drop weight surface under the impact.In this paper,the size and distribution of the cyclotetramethylenete tranitramine(HMX)fragments were analyzed by the Laser Particle Size Analyzer Malvern MS2000.The post-analysis results of fragments showed that size distribution of fragments was strongly dependent on drop height.An empirical formula is established to describe the relationship between the average size and drop height.The volume-based probability distribution of explosive fragments was also studied by experiments and theoretical calculations.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11674275, 21872119, 22072127, and 12104392)the Science and Technology Project of Hebei Education Department, China (Grant No. ZD2019069 and QN2021142))。
文摘The preparation of surface-enhanced fluorescence(SEF) substrates is often influenced by experimental strategies and factors such as the morphology and size of the nanostructures. In this study, using the natural reed leaves(RLs) without any special pretreatment as the substrate, metal silver is modified by magnetron sputtering technology to prepare a stable and efficient SEF system. The abundant “hedgehog-like” protrusions on the RL substrate surface can generate high-density“hot spots”, thus enhancement factor(EF) is enhanced up to 3345 times. The stability and reproducibility are verified in many measurements. The contribution of the intervention of silver nanostructure to the radiation attenuation process of fluorescent molecules is analyzed with the aid of Jablonski diagrams. Three-dimensional(3D) finite difference time domain(FDTD) simulates the spatial electric field and “hot spots” distribution of the substrate. The “hedgehog-like” protrusion structure generates multiple “hot spots”, which produce an excellent local surface plasmon resonance(LSPR) effect and provide higher fluorescence signal. Finally, RL/Ag-35 substrate is used to detect crystal violet(CV), and the detection limit is as low as 10^(-13) M. This “hedgehog-like” SEF substrate provides a new strategy for the trace detection of CV, which has a good practical application value.
基金The trauma registry project was supported financially by the Health Partnership Scheme funded by the Tropical Health and Education Trust(THET)funded by the UK Department for International Development(DFID)
文摘BACKGROUND: Less attention is directed toward gaining a better understanding of the burden and prevention of injuries, in low and middle income countries(LMICs). We report the establishment of a trauma registry at the Adult Emergency and Trauma Centre(AETC) at Queen Elizabeth Central Hospital(QECH) in Blantyre, Malawi and identify high risk geographic areas. METHODS: We devised a paper based two-page trauma registry form. Ten data clerks and all AETC clinicians were trained to complete demographic and clinical details respectively. Descriptive data, regression and hotspot analyses were done using STATA 15 statistical package and ArcGIS(16) software respectively.RESULTS: There were 3,747 patients from May 2013 to May 2015. The most common mechanisms of injury were assault(38.2%), and road traffi c injuries(31.6%). The majority had soft tissue injury(53.1%), while 23.8% had no diagnosis indicated. Fractures(OR 19.94 [15.34–25.93]), head injury and internal organ injury(OR 29.5 [16.29–53.4]), and use of ambulance(OR 1.57 [1.06–2.33]) were found to be predictive of increased odds of being admitted to hospital while assault(OR 0.69 [0.52–0.91]) was found to be associated with less odds of being admitted to hospital. Hot spot analysis showed that at 99% confidence interval, Ndirande, Mbayani and Limbe were the top hot spots for injury occurrence. CONCLUSION: We have described the process of establishing an integrated and potentially sustainable trauma registry. Signifi cant data were captured to provide details on the epidemiology of trauma and insight on how care could be improved at AETC and surrounding health facilities. This approach may be relevant in similar poor resource settings.
基金Project supported by the National Natural Science Foundation of China (Grant No. 61039001)
文摘Air traffic is a typical complex system, in which movements of traffic components （pilots, controllers, equipment, and environment）, especially airport arrival and departure traffic, form complicated spatial and temporal dynamics. The fluctuations of airport arrival and departure traffic are studied from the point of view of networks as the special correlation between different airports. Our collected flow volume data on the time-dependent activity of US airport arrival and departure traffic indicate that the coupling between the average flux and the fluctuation of an individual airport obeys a certain scaling law with a wide variety of scaling exponents between 1/2 and 1. These scaling phenomena can explain the interaction between the airport internal dynamics （e.g. queuing at airports, a ground delay program and following flying traffic） and a change in the external （network-wide） traffic demand （e.g. an increase in traffic during peak hours every day）, allowing us to further understand the mechanisms governing the collective behaviour of the transportation system. We separate internal dynamics from external fluctuations using a scaling law which is helpful for us to systematically determine the origin of fluctuations in airport arrival and departure traffic, uncovering the collective dynamics. Hot spot features are observed in airport traffic data as the dynamical inhomogeneity in the fluxes of individual airports. The intrinsic characteristics of airport arrival and departure traffic under severe weather is discussed as well.
基金financial supports from in part by National Natural Science Foundation of China under Grants 61922061, 61775161 and 61735011in part by the Tianjin Science Fund for Distinguished Young Scholars under Grant 19JCJQJC61400
文摘A dispersion model is developed to provide a generic tool for configuring plasmonic resonance spectral characteristics.The customized design of the resonance curve aiming at specific detection requirements can be achieved.According to the model,a probe-type nano-modified fiber optic configurable plasmonic resonance(NMF-CPR)sensor with tip hot spot enhancement is demonstrated for the measurement of the refractive index in the range of 1.3332-1.3432 corresponding to the low-concentration biomarker solution.The new-type sensing structure avoids excessive broadening and redshift of the resonance dip,which provides more possibilities for the surface modification of other functional nanomaterials.The tip hot spots in nanogaps between the Au layer and Au nanostars(AuNSs),the tip electric field enhancement of AuNSs,and the high carrier mobility of the WSe_(2)layer synergistically and significantly enhance the sensitivity of the sensor.Ex-perimental results show that the sensitivity and the figure of merit of the tip hot spot enhanced fiber NMF-CPR sensor can achieve up to 2995.70 nm/RIU and 25.04 RIU^(−1),respectively,which are 1.68 times and 1.29 times higher than those of the conventional fiber plasmonic resonance sensor.The results achieve good agreements with numerical simulations,demonstrate a better level compared to similar reported studies,and verify the correctness of the dispersion model.The detection resolution of the sensor reaches up to 2.00×10^(−5)RIU,which is obviously higher than that of the conventional side-polished fiber plasmonic resonance sensor.This indicates a high detection accuracy of the sensor.The dense Au layer effectively prevents the intermediate nanomaterials from shedding and chemical degradation,which enables the sensor with high stability.Furthermore,the terminal reflective sensing structure can be used as a practical probe and can allow a more convenient operation.
文摘The bow structure of FPSO moored by the single mooring system is rather complicated. There are many potential hot spots in connection parts of structures between the mooring support frame and the forecastle. Mooring forces, which are induced by wave excitation and transferred by the YOKE and the mooring support frame, may cause fatigue damage to the bow structure. Different from direct wave-in duced-forces, the mooring force consists of wave frequency force (WF) and 2nd dr aft low frequency force (LF) [3] , which are represented by two sets of short-term distribution respectively. Based on two sets of short-term distribution of moor ing forces obtained by the model test, the fatigue damage of the bow structure of FPSO is analyzed, with emphasis on two points. One is the procedure and position selection for fatigue check, and the other is the application of new formulae for the calculation of accumulative fatigue damage caused by two sets of short-term distribution of hot spot stress range. From the results distingui shed features of fatigue damage to the FPSO’s bow structure can be observed.
