RBOE is a new type of DNAN-based high-energy melt-cast mixed explosive,whose safety under thermal stimulation is significantly affected by heating conditions and venting area of the warhead.Based on the thermal decomp...RBOE is a new type of DNAN-based high-energy melt-cast mixed explosive,whose safety under thermal stimulation is significantly affected by heating conditions and venting area of the warhead.Based on the thermal decomposition reaction characteristics and combustion characteristics of each component of RBOE explosive,the cook-off calculation models of RBOE warhead before and after ignition were established.In addition,closed and vented warheads were designed,as well as fast and slow cook-off test devices.The cook-off characteristics and thermal safety venting area of RBOE warhead were extensively studied.The results showed that the closed RBOE warhead underwent deflagration reaction under both slow and fast cook-off conditions.The calculation result of the shell wall temperature before slow cookoff ignition response of the warhead was 454.06 K,with an error of+1.75%compared to the test result of462.15 K,and the temperature rise rate calculated was in good agreement with the test.The calculated ignition time of RBOE warhead under fast cook-off was 161 s,with an error of+8.8%compared to the test result of 148 s,which verified the accuracy of cook-off model of RBOE warhead before ignition.According to the cook-off calculation model of the warhead after ignition and cook-off test of the vented warhead,it was determined that the thermal safety venting area was 1124.61 mm^(2)for fast cook-off and 530.66 mm~2 for slow cook-off,effectively preventing the reaction of warhead above combustion.Therefore,this study provides a scientific basis for the thermal safety design and evaluation of insensitive warheads.展开更多
PCrNi3MoV steel is a medium-carbon,low-alloy quenched and tempered steel that finds its applications in military gun barrels due to the high wear resistance and ablation resistance.To study the penetration and failure...PCrNi3MoV steel is a medium-carbon,low-alloy quenched and tempered steel that finds its applications in military gun barrels due to the high wear resistance and ablation resistance.To study the penetration and failure modes of PCrNi3MoV plates impacted by tungsten spheres,tungsten spheres of various diameters(5 mm,8 mm,and 10 mm)were used to impact PCrNi3MoV steel plates with thicknesses of 6 mm,9 mm,and 14 mm.The penetration performance of the spheres was analyzed for different velocities,and the ultimate penetration velocity of the plate was obtained.It was found that the primary failure modes of the PCrNi3MoV plate were compression pitting failure and shear failure.Using the dimensional analysis method,a relationship between the bulge height of the steel plate and the fragment velocity,an equation for the ultimate penetration velocity,and a relationship between the target penetration energy and the fragment velocity were obtained.Then,a projectile-target action index was proposed to describe the process of tungsten spheres with different velocities impacting target plates.The results suggested that under the same thickness of the target plate,a larger-diameter fragment required more kinetic energy to obtain the same ultimate penetration effect as a smaller-diameter fragment.The equations obtained through dimensional analysis predicted values that agreed well with experimental values,indicating that these equations can be applied to engineering applications.展开更多
Climatic factors impact vegetation. Our study was to examine and analyze the climate variability and relationship to vegetation in Garamba National Park of the Democratic Republic of the Congo over the past 30 years (...Climatic factors impact vegetation. Our study was to examine and analyze the climate variability and relationship to vegetation in Garamba National Park of the Democratic Republic of the Congo over the past 30 years (1990 to 2020), then to relate the climatic variables. Mann Kendall’s non parametric test, ANOVA, and p-value tests are used to analyze existing trends and relationships between vegetation cover, climatic factors, land surface temperature (LST) and normalized difference in temperature Vegetation index (NDVI), Enhanced vegetation index (EVI) in Garamba national park which is of particular importance for the network of protected areas of the Democratic republic of Congo because its position at the northern limit of the savanna-forest mosaics gives it a unique biodiversity. The southern part of the park is dominated by grassy shrub savannas. The results showed that: 1) In Garamba, the monthly correlation coefficient of Kendall and Pearsan between temperature and precipitation are negative respectively 0.763 and <span style="white-space:nowrap;">−0.876 (p-value < 0.00001). 2) Annually during the three decades in Garamba, the correlation between precipitation and NDVI is significant 0.416 (Kendall) and 0.496 (Pearsan);the same between precipitation and EVI 0.291 (Kendall) and 0.496 (Pearsan) while LST and precipitation are negatively correlated (p-value < 0.00001).展开更多
The aim of our study is to highlight the spatial structure of the trees and to determine its influence on the natural regeneration of the Kalikuku dense forest, with a view of its optimal conservation and enhancement....The aim of our study is to highlight the spatial structure of the trees and to determine its influence on the natural regeneration of the Kalikuku dense forest, with a view of its optimal conservation and enhancement. Data collection was done by measuring diameter at breast height along 10 plots of 0.5 ha in size. In analyzing these data, the Dajoz test was used to determine the horizontal spatial distribution pattern of the two most abundant tree species in the forest (Piptadeniastrum africanum and Ocotea usambarensis). The χ<sup>2</sup> test was used to compare the frequency distribution of diameter classes for the two species tested. To estimate the difference between the number of seedlings in aggregate versus non-aggregate areas, the Wilcoxon signed-rank test was used. In addition, the equability index was used to test the preponderance of proportions between diameter classes. Finally, the natural regeneration index was evaluated.展开更多
Improving conditions to maintain soil fertility levels by avoiding deforestation would require an assessment of the contribution of forests to soil regeneration in complex and unpredictable farming systems involving a...Improving conditions to maintain soil fertility levels by avoiding deforestation would require an assessment of the contribution of forests to soil regeneration in complex and unpredictable farming systems involving alternating slash-and-burn farming. Results on forest cover over the period 1990-2018 indicate a net annual deforestation rate of 2.12% ± 0.07% and 0.12% annual degradation. The rate of deforestation is estimated mainly in relation to dense forests. Deforestation is the degradation that seems relatively important for DR Congo with relative population densities or the demand for agricultural land is greater which will lead to several consequences such as climate change, soil erosion, biodiversity loss, CO<sub>2</sub> emissions, and natural disasters.展开更多
Lamto Reserve area is a savannah landscape threatened by periodic drought, and anthropogenic activities leading to natural ecological imbalance. The ecological support services of the landscape had been significantly ...Lamto Reserve area is a savannah landscape threatened by periodic drought, and anthropogenic activities leading to natural ecological imbalance. The ecological support services of the landscape had been significantly impacted by the grassland ecosystem. The Breaks for Additive Season and Trend Algorithms have been implemented in R to analyze the land cover/land use dynamic in relation to the climatic driver of Lamto forest from 2000 to 2020. We examine the vegetation state breaks using vegetation phenological patterns, and several time series including the Normalized Difference Vegetation Index and the Enhanced Vegetation Index, were studied utilizing Breaks for Additive Season and Trend. The findings indicate that the phenological changes in the vegetation in 2020 resulted from an increased temperature from (27.7°C) to (32.17°C), and a decrease in precipitation (71.75 millimeters). The analysis of variance ANOVA of the non-parametric Mann-Kendall test reveals a strong correlation between Precipitation/Evapotranspiration Grass (p mperature/Evapotranspiration Grass (p < 0.311), and Temperature/Normalized Difference Vegetation Index (p in vegetation detected by the Breaks for Additive Season and Trend Algorithms were caused by temperature extremes and reduced rainfall.展开更多
The Ulan Buh Desert is one of the eight deserts in China that provides wind erosion prevention service(i.e.,the ecosystem;vegetation,production,and construction activities that promote sand fixation).It is significant...The Ulan Buh Desert is one of the eight deserts in China that provides wind erosion prevention service(i.e.,the ecosystem;vegetation,production,and construction activities that promote sand fixation).It is significant for the construction of the national ecological barrier,and the protection of the ecological security in the Yellow River and North China.In this study,we selected two representative years(2008 and 2018)and quantified wind erosion prevention service from the Ulan Buh Desert using the RWEQ model.Meanwhile,the HYSPLIT model was used to simulate the spatial flow process from the service supply area to the beneficiary area and to determine its scope.The specific dust reduction amount in the beneficiary area was then calculated.The energy and the time-space relation of wind erosion prevention service in the areas that receive benefits from Ulan Buh Desert were compared before and after implementing environmental restoration measures.The results showed that:(1)the total amount of wind erosion prevention in the Ulan Buh Desert in 2018 was 2.12×10^(10)kg,which was 5.17 times higher than that in 2008;(2)in 2018,the distribution density of the flow path of wind erosion prevention service was lower than that in 2008,and the flow paths in each year were concentrated in the beneficiary areas with the path distribution frequency of less than 10%;(3)the total dust reduction in the downwind area of the Ulan Buh Desert in 2018 was higher than that in 2008,totaling 15.54 million tons.Inner Mongolia Autonomous Region and Shanxi Province had the most significant amount of dust reduction.展开更多
This study aims to identify the drivers of environmental degradation due to the dependency of surrounding residents on three protected areas in Togo, Africa (Oti-Keran, Togodo, and Abdoulaye national parks (abbr. OTA ...This study aims to identify the drivers of environmental degradation due to the dependency of surrounding residents on three protected areas in Togo, Africa (Oti-Keran, Togodo, and Abdoulaye national parks (abbr. OTA national parks)). Surveys of villagers conducted in and around the OTA national parks added to data downloaded from Indexmundi data portal. National-level trend analysis results indicated: 1) the number of terrestrial protected areas showed an upward trend, while savannah and forest cover showed alarming decrease trends. 2) At the local level, supplying socio-economic needs in the three selected protected areas directly resulted in biodiversity degradation through animal grazing, hunting and farming. 3) Over 70% of the respondent’s livelihoods consisted of farming and related dependencies on the protected areas for timber and non-timber forest products and income despite the protected status hold by these classified areas. 4) The OTA national parks have been experiencing an increase of anthropogenic pressure such as uncontrolled tree logging and hunting, which seriously impacts animal and vegetation biodiversity. 5) Policymakers should invest more resources in implementing an integrated management system based not only on a holistic vision of the PA that includes participatory management but also accounts for multi-dimensional principles to enable anthropogenic activities in and around the protected areas to satisfy sustainable development requirements.展开更多
基金National Natural Science Foundation of china(Grant No.12402468)。
文摘RBOE is a new type of DNAN-based high-energy melt-cast mixed explosive,whose safety under thermal stimulation is significantly affected by heating conditions and venting area of the warhead.Based on the thermal decomposition reaction characteristics and combustion characteristics of each component of RBOE explosive,the cook-off calculation models of RBOE warhead before and after ignition were established.In addition,closed and vented warheads were designed,as well as fast and slow cook-off test devices.The cook-off characteristics and thermal safety venting area of RBOE warhead were extensively studied.The results showed that the closed RBOE warhead underwent deflagration reaction under both slow and fast cook-off conditions.The calculation result of the shell wall temperature before slow cookoff ignition response of the warhead was 454.06 K,with an error of+1.75%compared to the test result of462.15 K,and the temperature rise rate calculated was in good agreement with the test.The calculated ignition time of RBOE warhead under fast cook-off was 161 s,with an error of+8.8%compared to the test result of 148 s,which verified the accuracy of cook-off model of RBOE warhead before ignition.According to the cook-off calculation model of the warhead after ignition and cook-off test of the vented warhead,it was determined that the thermal safety venting area was 1124.61 mm^(2)for fast cook-off and 530.66 mm~2 for slow cook-off,effectively preventing the reaction of warhead above combustion.Therefore,this study provides a scientific basis for the thermal safety design and evaluation of insensitive warheads.
文摘PCrNi3MoV steel is a medium-carbon,low-alloy quenched and tempered steel that finds its applications in military gun barrels due to the high wear resistance and ablation resistance.To study the penetration and failure modes of PCrNi3MoV plates impacted by tungsten spheres,tungsten spheres of various diameters(5 mm,8 mm,and 10 mm)were used to impact PCrNi3MoV steel plates with thicknesses of 6 mm,9 mm,and 14 mm.The penetration performance of the spheres was analyzed for different velocities,and the ultimate penetration velocity of the plate was obtained.It was found that the primary failure modes of the PCrNi3MoV plate were compression pitting failure and shear failure.Using the dimensional analysis method,a relationship between the bulge height of the steel plate and the fragment velocity,an equation for the ultimate penetration velocity,and a relationship between the target penetration energy and the fragment velocity were obtained.Then,a projectile-target action index was proposed to describe the process of tungsten spheres with different velocities impacting target plates.The results suggested that under the same thickness of the target plate,a larger-diameter fragment required more kinetic energy to obtain the same ultimate penetration effect as a smaller-diameter fragment.The equations obtained through dimensional analysis predicted values that agreed well with experimental values,indicating that these equations can be applied to engineering applications.
文摘Climatic factors impact vegetation. Our study was to examine and analyze the climate variability and relationship to vegetation in Garamba National Park of the Democratic Republic of the Congo over the past 30 years (1990 to 2020), then to relate the climatic variables. Mann Kendall’s non parametric test, ANOVA, and p-value tests are used to analyze existing trends and relationships between vegetation cover, climatic factors, land surface temperature (LST) and normalized difference in temperature Vegetation index (NDVI), Enhanced vegetation index (EVI) in Garamba national park which is of particular importance for the network of protected areas of the Democratic republic of Congo because its position at the northern limit of the savanna-forest mosaics gives it a unique biodiversity. The southern part of the park is dominated by grassy shrub savannas. The results showed that: 1) In Garamba, the monthly correlation coefficient of Kendall and Pearsan between temperature and precipitation are negative respectively 0.763 and <span style="white-space:nowrap;">−0.876 (p-value < 0.00001). 2) Annually during the three decades in Garamba, the correlation between precipitation and NDVI is significant 0.416 (Kendall) and 0.496 (Pearsan);the same between precipitation and EVI 0.291 (Kendall) and 0.496 (Pearsan) while LST and precipitation are negatively correlated (p-value < 0.00001).
文摘The aim of our study is to highlight the spatial structure of the trees and to determine its influence on the natural regeneration of the Kalikuku dense forest, with a view of its optimal conservation and enhancement. Data collection was done by measuring diameter at breast height along 10 plots of 0.5 ha in size. In analyzing these data, the Dajoz test was used to determine the horizontal spatial distribution pattern of the two most abundant tree species in the forest (Piptadeniastrum africanum and Ocotea usambarensis). The χ<sup>2</sup> test was used to compare the frequency distribution of diameter classes for the two species tested. To estimate the difference between the number of seedlings in aggregate versus non-aggregate areas, the Wilcoxon signed-rank test was used. In addition, the equability index was used to test the preponderance of proportions between diameter classes. Finally, the natural regeneration index was evaluated.
文摘Improving conditions to maintain soil fertility levels by avoiding deforestation would require an assessment of the contribution of forests to soil regeneration in complex and unpredictable farming systems involving alternating slash-and-burn farming. Results on forest cover over the period 1990-2018 indicate a net annual deforestation rate of 2.12% ± 0.07% and 0.12% annual degradation. The rate of deforestation is estimated mainly in relation to dense forests. Deforestation is the degradation that seems relatively important for DR Congo with relative population densities or the demand for agricultural land is greater which will lead to several consequences such as climate change, soil erosion, biodiversity loss, CO<sub>2</sub> emissions, and natural disasters.
文摘Lamto Reserve area is a savannah landscape threatened by periodic drought, and anthropogenic activities leading to natural ecological imbalance. The ecological support services of the landscape had been significantly impacted by the grassland ecosystem. The Breaks for Additive Season and Trend Algorithms have been implemented in R to analyze the land cover/land use dynamic in relation to the climatic driver of Lamto forest from 2000 to 2020. We examine the vegetation state breaks using vegetation phenological patterns, and several time series including the Normalized Difference Vegetation Index and the Enhanced Vegetation Index, were studied utilizing Breaks for Additive Season and Trend. The findings indicate that the phenological changes in the vegetation in 2020 resulted from an increased temperature from (27.7°C) to (32.17°C), and a decrease in precipitation (71.75 millimeters). The analysis of variance ANOVA of the non-parametric Mann-Kendall test reveals a strong correlation between Precipitation/Evapotranspiration Grass (p mperature/Evapotranspiration Grass (p < 0.311), and Temperature/Normalized Difference Vegetation Index (p in vegetation detected by the Breaks for Additive Season and Trend Algorithms were caused by temperature extremes and reduced rainfall.
基金This research was funded by the National Key Research and De-velopment Program(Grant No.2019YFC0507600/2019YFC0507601)the National Natural Science Foundation of China(Grant No.41671080).
文摘The Ulan Buh Desert is one of the eight deserts in China that provides wind erosion prevention service(i.e.,the ecosystem;vegetation,production,and construction activities that promote sand fixation).It is significant for the construction of the national ecological barrier,and the protection of the ecological security in the Yellow River and North China.In this study,we selected two representative years(2008 and 2018)and quantified wind erosion prevention service from the Ulan Buh Desert using the RWEQ model.Meanwhile,the HYSPLIT model was used to simulate the spatial flow process from the service supply area to the beneficiary area and to determine its scope.The specific dust reduction amount in the beneficiary area was then calculated.The energy and the time-space relation of wind erosion prevention service in the areas that receive benefits from Ulan Buh Desert were compared before and after implementing environmental restoration measures.The results showed that:(1)the total amount of wind erosion prevention in the Ulan Buh Desert in 2018 was 2.12×10^(10)kg,which was 5.17 times higher than that in 2008;(2)in 2018,the distribution density of the flow path of wind erosion prevention service was lower than that in 2008,and the flow paths in each year were concentrated in the beneficiary areas with the path distribution frequency of less than 10%;(3)the total dust reduction in the downwind area of the Ulan Buh Desert in 2018 was higher than that in 2008,totaling 15.54 million tons.Inner Mongolia Autonomous Region and Shanxi Province had the most significant amount of dust reduction.
文摘This study aims to identify the drivers of environmental degradation due to the dependency of surrounding residents on three protected areas in Togo, Africa (Oti-Keran, Togodo, and Abdoulaye national parks (abbr. OTA national parks)). Surveys of villagers conducted in and around the OTA national parks added to data downloaded from Indexmundi data portal. National-level trend analysis results indicated: 1) the number of terrestrial protected areas showed an upward trend, while savannah and forest cover showed alarming decrease trends. 2) At the local level, supplying socio-economic needs in the three selected protected areas directly resulted in biodiversity degradation through animal grazing, hunting and farming. 3) Over 70% of the respondent’s livelihoods consisted of farming and related dependencies on the protected areas for timber and non-timber forest products and income despite the protected status hold by these classified areas. 4) The OTA national parks have been experiencing an increase of anthropogenic pressure such as uncontrolled tree logging and hunting, which seriously impacts animal and vegetation biodiversity. 5) Policymakers should invest more resources in implementing an integrated management system based not only on a holistic vision of the PA that includes participatory management but also accounts for multi-dimensional principles to enable anthropogenic activities in and around the protected areas to satisfy sustainable development requirements.
