In response to the demand for short-range detection of anti-smoke environment interference by laser fuzes,this study proposes a smoke environment simulation of non-uniform continuous point source diffusion and investi...In response to the demand for short-range detection of anti-smoke environment interference by laser fuzes,this study proposes a smoke environment simulation of non-uniform continuous point source diffusion and investigates an experimental laboratory smoke environment using an ammonium chloride smoke agent.The particle size distribution,composition,and mass flow distribution of the smoke were studied.Based on a discrete phase model and a kεturbulence model,a numerical simulation was developed to model the smoke generation and diffusion processes of the smoke agent in a confined space.The temporal and spatial distribution characteristics of the smoke mass concentration,velocity,and temperature in the space after smoke generation were analyzed,and the motion law governing the smoke diffusion throughout the entire space was summarized.Combined with the experimental verification of the smoke environment laboratory,the results showed that the smoke plume changed from fan-shaped to umbrella-shaped during smoke generation,and then continued to spread around.Meanwhile,the mass concentration of smoke in the space decreased from the middle outward;the changes in temperature and velocity were small and stable.In the diffusion stage(after 900 s),the mass concentration of smoke above 0.8 m was relatively uniform across an area of smoke that was 12 m thick.The concentration decreased over time,following a consistent decreasing trend,and the attenuation was negligible in a very short time.Therefore,this system was suitable for conducting experimental research on laser fuzes in a smoke environment.Owing to the stability of the equipment and facilities,the setup could reproduce the same experimental smoke environment by artificially controlling the smoke emission of the smoke agent.Overall,this work provides a theoretical reference for subsequent research efforts regarding the construction of uniform smoke environments and evaluating laser transmission characteristics in smoky environments.展开更多
为准确掌握广东省森林干扰与森林恢复的动态特征,文章基于谷歌地球引擎(Google Earth Engine,GEE)云平台构建Landsat长时序年度无云地表反射率影像集,采用LandTrendr(Landsat-based detection of Trends in Distur-bance and Recovery)...为准确掌握广东省森林干扰与森林恢复的动态特征,文章基于谷歌地球引擎(Google Earth Engine,GEE)云平台构建Landsat长时序年度无云地表反射率影像集,采用LandTrendr(Landsat-based detection of Trends in Distur-bance and Recovery)算法提取广东省1990—2020年森林干扰与森林恢复的时空分布特征,并分析其演变的驱动因素,比较不同森林类型的干扰与恢复特征。结果表明:(1)1990—2020年,广东省的森林干扰总面积约为1.35×10^(4)km^(2),集中分布在广东省西部、东部和中部小范围地区,干扰面积最大的3个城市分别为韶关、梅州、清远市;森林恢复总面积约为1.91×10^(4)km^(2),集中分布在广东省北部和西部地区,恢复面积最大的3个城市分别为韶关、清远、肇庆市。(2)广东省森林干扰与森林恢复均集中发生在海拔小于等于600 m的地区,高海拔地区的森林面积较为稳定;广东省森林干扰集中发生在坡度小于等于25°的地区,森林恢复集中发生在坡度小于等于35°的地区。(3)广东省森林干扰在1996年后发生较为频繁,其中2011年的森林干扰面积最大;森林恢复主要集中在2001—2016年,其中2012年的森林恢复面积最大。(4)广东省的森林干扰与森林恢复主要受雨雪冰冻灾害、台风、病虫害等自然因素以及森林火灾、城市化、采伐、林业政策等人为因素的综合影响,其中雨雪冰冻灾害对广东省北部地区的常绿针叶林的影响较大,但该类型的森林恢复也较快。展开更多
During the Late Miocene,numerous medium to large-sized herbivores,that resemble the living Ovibos in skeletal morphology,dispersed throughout the Holarctic realm and comprised eleven genera:Lantiantragus,Shaanxispira,...During the Late Miocene,numerous medium to large-sized herbivores,that resemble the living Ovibos in skeletal morphology,dispersed throughout the Holarctic realm and comprised eleven genera:Lantiantragus,Shaanxispira,Tsaidamotherium,Criotherium,Mesembriacerus,Hezhengia,Urmiatherium,Parurmiatherium,Plesiaddax,Sinotragus,and Prosinotragus.These genera are primarily found in eastern Asia,in which nine genera are found in northern China,as well as in countries in eastern Europe and western Asia.They are distinguished by unique characteristics,including a perpendicular braincase,specialized horn cores,and a robust basioccipital.Previous studies have often classified these‘ovibovin’bovids as part of the conventional subfamily/tribe Ovibovinae/Ovibovini,along with extant Ovibos.Nevertheless,an increasing number of studies do not support the monophyly of the subfamily/tribe Ovibovinae/Ovibovini,nor is a close relationship likely between these Late Miocene‘ovibovin’bovids and extant Ovibos.Among the eleven genera of‘ovibovin’bovids,Plesiaddax,Hezhengia,and Urmiatherium are often considered to have a very close relationship and conventionally form the tribe Urmiatheriini.However,previous phylogenetic analyses do not support the monophyly of Urmiatheriini.This paper presents a summary of the transmutation of the terms Ovibovidae/Ovibovinae/Ovibovini/Ovibovina,the temporal and spatial distribution of the Late Miocene‘ovibovin’bovids in Eurasia,the principal characteristics of these taxa,and the previous phylogenetic analyses.展开更多
蒸散发是水文循环和地表能量平衡的关键组成部分,对于水资源的有效管理、干旱情况的监测以及农业生产的优化均有着不可或缺的作用。选取红碱淖流域为研究区,基于Landsat8遥感数据,结合地表能量平衡系统(surface energy balance system,S...蒸散发是水文循环和地表能量平衡的关键组成部分,对于水资源的有效管理、干旱情况的监测以及农业生产的优化均有着不可或缺的作用。选取红碱淖流域为研究区,基于Landsat8遥感数据,结合地表能量平衡系统(surface energy balance system,SEBS)模型,估算了流域内2019年的6个日期的日蒸散发量,并对其进行了验证。通过对蒸散发的时空变化趋势和影响因素进行分析,获得结果表明:通过SEBS模型估算的日实际蒸散发量与通过Penman-Monteith(P-M)公式估算的潜在蒸散发量,以及气象站蒸发皿实际观测的蒸散发量的拟合优度R^(2)分别为0.84(P<0.01)、0.602(P<0.05),验证了SEBS模型在红碱淖流域的蒸散发量估算中具有较高的准确性和可靠性。红碱淖流域日蒸散发量呈现出明显的季节差异,夏季最高,春季次之,秋季再次,而冬季最低。流域东部红碱淖水体和流域西部查干淖尔及其周边区域的蒸散发量相对较高。流域中部蒸散发量相对较低。不同的土地利用类型中,水体的蒸散发量最高,其次是林地、耕地、建设用地、草地,最低的是未利用地。气象因素中,气温、气压和日照时数是主要影响因素,分别与蒸散发量呈显著正相关(r=0.847,P<0.05)、负相关(r=-0.840,P<0.05)和正相关(r=0.801,P<0.05),而相对湿度和风速与蒸散发量相关性较弱。展开更多
基金the Central University Special Funding for Basic Scientific Research(Grant No.30918012201)the Foundation of JWKJW Field(Grant 2020-JCJQ-JJ-392)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX20_0315).
文摘In response to the demand for short-range detection of anti-smoke environment interference by laser fuzes,this study proposes a smoke environment simulation of non-uniform continuous point source diffusion and investigates an experimental laboratory smoke environment using an ammonium chloride smoke agent.The particle size distribution,composition,and mass flow distribution of the smoke were studied.Based on a discrete phase model and a kεturbulence model,a numerical simulation was developed to model the smoke generation and diffusion processes of the smoke agent in a confined space.The temporal and spatial distribution characteristics of the smoke mass concentration,velocity,and temperature in the space after smoke generation were analyzed,and the motion law governing the smoke diffusion throughout the entire space was summarized.Combined with the experimental verification of the smoke environment laboratory,the results showed that the smoke plume changed from fan-shaped to umbrella-shaped during smoke generation,and then continued to spread around.Meanwhile,the mass concentration of smoke in the space decreased from the middle outward;the changes in temperature and velocity were small and stable.In the diffusion stage(after 900 s),the mass concentration of smoke above 0.8 m was relatively uniform across an area of smoke that was 12 m thick.The concentration decreased over time,following a consistent decreasing trend,and the attenuation was negligible in a very short time.Therefore,this system was suitable for conducting experimental research on laser fuzes in a smoke environment.Owing to the stability of the equipment and facilities,the setup could reproduce the same experimental smoke environment by artificially controlling the smoke emission of the smoke agent.Overall,this work provides a theoretical reference for subsequent research efforts regarding the construction of uniform smoke environments and evaluating laser transmission characteristics in smoky environments.
文摘为准确掌握广东省森林干扰与森林恢复的动态特征,文章基于谷歌地球引擎(Google Earth Engine,GEE)云平台构建Landsat长时序年度无云地表反射率影像集,采用LandTrendr(Landsat-based detection of Trends in Distur-bance and Recovery)算法提取广东省1990—2020年森林干扰与森林恢复的时空分布特征,并分析其演变的驱动因素,比较不同森林类型的干扰与恢复特征。结果表明:(1)1990—2020年,广东省的森林干扰总面积约为1.35×10^(4)km^(2),集中分布在广东省西部、东部和中部小范围地区,干扰面积最大的3个城市分别为韶关、梅州、清远市;森林恢复总面积约为1.91×10^(4)km^(2),集中分布在广东省北部和西部地区,恢复面积最大的3个城市分别为韶关、清远、肇庆市。(2)广东省森林干扰与森林恢复均集中发生在海拔小于等于600 m的地区,高海拔地区的森林面积较为稳定;广东省森林干扰集中发生在坡度小于等于25°的地区,森林恢复集中发生在坡度小于等于35°的地区。(3)广东省森林干扰在1996年后发生较为频繁,其中2011年的森林干扰面积最大;森林恢复主要集中在2001—2016年,其中2012年的森林恢复面积最大。(4)广东省的森林干扰与森林恢复主要受雨雪冰冻灾害、台风、病虫害等自然因素以及森林火灾、城市化、采伐、林业政策等人为因素的综合影响,其中雨雪冰冻灾害对广东省北部地区的常绿针叶林的影响较大,但该类型的森林恢复也较快。
文摘During the Late Miocene,numerous medium to large-sized herbivores,that resemble the living Ovibos in skeletal morphology,dispersed throughout the Holarctic realm and comprised eleven genera:Lantiantragus,Shaanxispira,Tsaidamotherium,Criotherium,Mesembriacerus,Hezhengia,Urmiatherium,Parurmiatherium,Plesiaddax,Sinotragus,and Prosinotragus.These genera are primarily found in eastern Asia,in which nine genera are found in northern China,as well as in countries in eastern Europe and western Asia.They are distinguished by unique characteristics,including a perpendicular braincase,specialized horn cores,and a robust basioccipital.Previous studies have often classified these‘ovibovin’bovids as part of the conventional subfamily/tribe Ovibovinae/Ovibovini,along with extant Ovibos.Nevertheless,an increasing number of studies do not support the monophyly of the subfamily/tribe Ovibovinae/Ovibovini,nor is a close relationship likely between these Late Miocene‘ovibovin’bovids and extant Ovibos.Among the eleven genera of‘ovibovin’bovids,Plesiaddax,Hezhengia,and Urmiatherium are often considered to have a very close relationship and conventionally form the tribe Urmiatheriini.However,previous phylogenetic analyses do not support the monophyly of Urmiatheriini.This paper presents a summary of the transmutation of the terms Ovibovidae/Ovibovinae/Ovibovini/Ovibovina,the temporal and spatial distribution of the Late Miocene‘ovibovin’bovids in Eurasia,the principal characteristics of these taxa,and the previous phylogenetic analyses.
文摘蒸散发是水文循环和地表能量平衡的关键组成部分,对于水资源的有效管理、干旱情况的监测以及农业生产的优化均有着不可或缺的作用。选取红碱淖流域为研究区,基于Landsat8遥感数据,结合地表能量平衡系统(surface energy balance system,SEBS)模型,估算了流域内2019年的6个日期的日蒸散发量,并对其进行了验证。通过对蒸散发的时空变化趋势和影响因素进行分析,获得结果表明:通过SEBS模型估算的日实际蒸散发量与通过Penman-Monteith(P-M)公式估算的潜在蒸散发量,以及气象站蒸发皿实际观测的蒸散发量的拟合优度R^(2)分别为0.84(P<0.01)、0.602(P<0.05),验证了SEBS模型在红碱淖流域的蒸散发量估算中具有较高的准确性和可靠性。红碱淖流域日蒸散发量呈现出明显的季节差异,夏季最高,春季次之,秋季再次,而冬季最低。流域东部红碱淖水体和流域西部查干淖尔及其周边区域的蒸散发量相对较高。流域中部蒸散发量相对较低。不同的土地利用类型中,水体的蒸散发量最高,其次是林地、耕地、建设用地、草地,最低的是未利用地。气象因素中,气温、气压和日照时数是主要影响因素,分别与蒸散发量呈显著正相关(r=0.847,P<0.05)、负相关(r=-0.840,P<0.05)和正相关(r=0.801,P<0.05),而相对湿度和风速与蒸散发量相关性较弱。
