Dry tree semi is a fast developing technology and becomes more and more appealing to the operators as a solution for producing deepwater reserves. Utilizing a dry tree semi means spending less cost on well mainte-nanc...Dry tree semi is a fast developing technology and becomes more and more appealing to the operators as a solution for producing deepwater reserves. Utilizing a dry tree semi means spending less cost on well mainte-nance and interventions,while the production platform can be integrated and commissioned at quayside. This paper presents a comprehensive overview of various technologies for dry tree semi,such as E-semi,T-semi,paired-column semi and long stroke tensioners. Each dry tree semi concept is briefed in terms of global performance,top tension riser (TTR) tensioner system,quayside integration and feasibility to environment.展开更多
Background: Climate-induced challenge remains a growing concern in the dry tropics, threatening carbon sink potential of tropical dry forests. Hence, understanding their responses to the changing climate is of high pr...Background: Climate-induced challenge remains a growing concern in the dry tropics, threatening carbon sink potential of tropical dry forests. Hence, understanding their responses to the changing climate is of high priority to facilitate sustainable management of the remnant dry forests. In this study, we examined the long-term climate-growth relations of main tree species in the remnant dry Afromontane forests in northern Ethiopia. The aim of this study was to assess the dendrochronological potential of selected dry Afromontane tree species and to study the influence of climatic variables (temperature and rainfall) on radial growth. It was hypothesized that there are potential tree species with discernible annual growth rings owing to the uni-modality of rainfall in the region. Ring width measurements were based on increment core samples and stem discs collected from a total of 106 trees belonging to three tree species (Juniperus procera, Olea europaea p. cuspidate and Podocarpus falcatus). Thesubsp. collected samples were prepared, crossdated, and analyzed using standard dendrochronological methods. The formation of annual growth rings of the study species was verified based on successful crossdatability and by correlating tree-ring widths with rainfall. Results: The results showed that all the sampled tree species form distinct growth boundaries though differences in the distinctiveness were observed among the species. Positive and significant correlations were found between the tree-ring widths and rainfall, implying that rainfall plays a vital role in determining tree growth in the region. The study confirmed the formation of annual growth rings through successful crossdating, thus highlighted the potential applicability of dendroclimatic studies in the region. Conclusions: Overall, the results proved the strong linkage between tree-ring chronologies and climate variability in the study region, which further strengthens the potential of dendrochronological studies developing in Ethiopia, and also has great implications for further paleo-climatic reconstructions and in the restoration of degraded lands. Further knowledge on the growth characteristics of tree species from the region is required to improve the network of tree-ring data and quality of the chronology so as to successfully reconstruct historic environmental changes.展开更多
Based on 120 stem discs collected during3 months of fieldwork along a 12 km route,the history of fires in the Wari Maro Forest（09 1000 N–02 1000E） over the past century in savanna woodland and dry forest was recons...Based on 120 stem discs collected during3 months of fieldwork along a 12 km route,the history of fires in the Wari Maro Forest（09 1000 N–02 1000E） over the past century in savanna woodland and dry forest was reconstituted.Three major ecological areas are characterized：one highly burnt zone located between two relative less burnt areas.By analyzing tree rings,246 fire scars were identified.The scars were caused by 51 fire years,occurring at a mean interval of 2.23 years.From 1890 to1965,only 6 years with fires were recorded from sampled trees.Since 1966,no year has passed without fire.The fire frequency point scale reached 14 years.This was the case of Burkea africana,which has been identified as a species tolerant to fire and could be planted to create a natural firewall.In contrast,Anogeissus leiocarpa is highly sensitive to fire,and in a dry forest ecosystem that burns seasonally,it requires a special conservation plan.Two new concepts are described：the rebarking of trees after fire and Mean Kilometer Fire Interval.The first concept was tested with Daniellia oliveri（Rolfe） Hutch ＆ Dalz trees,and the second concept was used to evaluate spatial fire distribution.We demonstrate that savanna woodland and dry forest were subject to a degradation process caused by destructive fires related to vegetation cover clearance and illegal logging.展开更多
为研究谐波成分对电-热工作环境下干式阀侧套管内部绝缘用环氧树脂材料的绝缘特性影响,采用多阶谐波叠加负极性直流偏置电压模拟干式阀侧套管运行波形,在80~120℃的温度范围内研究了不同谐波成分对环氧树脂绝缘劣化特性的影响。研究结...为研究谐波成分对电-热工作环境下干式阀侧套管内部绝缘用环氧树脂材料的绝缘特性影响,采用多阶谐波叠加负极性直流偏置电压模拟干式阀侧套管运行波形,在80~120℃的温度范围内研究了不同谐波成分对环氧树脂绝缘劣化特性的影响。研究结果表明,谐波与高温均对环氧树脂的绝缘劣化起到促进作用,在电-热工作环境下多阶谐波成分的引入环氧树脂劣化的引发电压降低了40.0%,试样的绝缘失效时间降低了64.8%,同时谐波成分导致绝缘劣化面积扩大,基于场驱动电树枝生长模型(field-driven tree growth,FDTG)的分析,高阶谐波成分的引入使电树生长速率系数增高了190.9%,电树生长临界场强降低到17.88 kV/mm,最后通过仿真计算说明多谐波情况下材料介质损耗发热加剧,针对长时工作设备需进一步关注局部过热问题。展开更多
Partial Rootzone Drying (PRD) is an irrigation technique which offers a means of modifying the growth and development of crops through relatively simple changes to the method of water delivery. The technique causes th...Partial Rootzone Drying (PRD) is an irrigation technique which offers a means of modifying the growth and development of crops through relatively simple changes to the method of water delivery. The technique causes the stimulation of physiological responses which are normally associated with water stress and this results in a significant reduction in water use through the production of chemical signals in drying roots. Partial drying of one half of the roots of plants grown with two root systems is rapidly translated into a reduction in transpiration and assimilation of all the crop leaves. The aim of this research is to examine and simulate the novel irrigation method (PRD), which would stimulate the endogenous stress response mechanisms of Conocarpus erectus trees in the pilot area of the Arabian Gulf University in Bahrain and wheat and maize crops in the Mashtul Pilot Area (MPA), Egypt using Saltmed model so that vigor is reduced and the efficiency of water use is enhanced. This is to be achieved by the manipulation of the hydration status of parts of a crop’s roots that could be used to control vegetative vigor without detrimental effects on canopy water relations. The PRD technique is researched for wheat as a winter crop and maize as a summer crop in Egypt. The technique causes the stimulation of physiological responses which are normally associated with water stress and this results in a significant reduction in water use through the production of chemical signals in drying roots. The results confirmed an increase in irrigation water use efficiency using PRD comparing with conventional flood irrigation. The research highly recommends applying the PRD method in the Gulf Cooperation Council (GCC) countries and in new reclaimed areas in Egypt to save water and improve crop quality.展开更多
We carried out this research at Abu-Gaddaf Natural Forest Reserve (ANFR) which is located east of Blue Nile River, in Blue Nile State, Sudan. It aims at exploring tree composition assessing their diversity indices, an...We carried out this research at Abu-Gaddaf Natural Forest Reserve (ANFR) which is located east of Blue Nile River, in Blue Nile State, Sudan. It aims at exploring tree composition assessing their diversity indices, and ecological importance values. For survey of types and estimation of density of tree species in the forest, we randomly distributed 97 circular sample plots (0.1 hectare (ha)). In each sample plot we identified all trees to the species level, recorded their frequencies and computed species diversity and importance value indices (IVI). A total of 13 tree species, which belong to 12 genera and nine families, were identified in the tree layer of the forest. Mean tree density in ANFR was 116 trees/ha, composed mainly of Boswellia papyrifera (Del.) Hochst. (48), followed by Combretum hartmannianu (19) and Lannea fruticosa (18). Fabaceae was the most common family followed by Combretaceae and Malvaceae. B. papyrifera Delile Hochst was the most abundant while Acacia seyal was the least abundant species. Species richness (R = 1.71), evenness (E = 0.69), dominance (0.24) indices and Simpson’s Index of Diversity (D' = 0.76) suggest a moderate diversity, moderate numbers of individuals in each species and a moderate community stability. The research provides empirical results on diversity and ecological importance value of species, signifies the urging need to safeguard threatened species and to prioritize them for conservation, as well as the need to promote management of abundant species to provide multiple forest ecosystem services.展开更多
文摘Dry tree semi is a fast developing technology and becomes more and more appealing to the operators as a solution for producing deepwater reserves. Utilizing a dry tree semi means spending less cost on well mainte-nance and interventions,while the production platform can be integrated and commissioned at quayside. This paper presents a comprehensive overview of various technologies for dry tree semi,such as E-semi,T-semi,paired-column semi and long stroke tensioners. Each dry tree semi concept is briefed in terms of global performance,top tension riser (TTR) tensioner system,quayside integration and feasibility to environment.
基金financial supports for this study were obtained from the Pan African University(PAU)African Union(AU)Addis Ababa,Ethiopia as part of its PhD scholarship scheme
文摘Background: Climate-induced challenge remains a growing concern in the dry tropics, threatening carbon sink potential of tropical dry forests. Hence, understanding their responses to the changing climate is of high priority to facilitate sustainable management of the remnant dry forests. In this study, we examined the long-term climate-growth relations of main tree species in the remnant dry Afromontane forests in northern Ethiopia. The aim of this study was to assess the dendrochronological potential of selected dry Afromontane tree species and to study the influence of climatic variables (temperature and rainfall) on radial growth. It was hypothesized that there are potential tree species with discernible annual growth rings owing to the uni-modality of rainfall in the region. Ring width measurements were based on increment core samples and stem discs collected from a total of 106 trees belonging to three tree species (Juniperus procera, Olea europaea p. cuspidate and Podocarpus falcatus). Thesubsp. collected samples were prepared, crossdated, and analyzed using standard dendrochronological methods. The formation of annual growth rings of the study species was verified based on successful crossdatability and by correlating tree-ring widths with rainfall. Results: The results showed that all the sampled tree species form distinct growth boundaries though differences in the distinctiveness were observed among the species. Positive and significant correlations were found between the tree-ring widths and rainfall, implying that rainfall plays a vital role in determining tree growth in the region. The study confirmed the formation of annual growth rings through successful crossdating, thus highlighted the potential applicability of dendroclimatic studies in the region. Conclusions: Overall, the results proved the strong linkage between tree-ring chronologies and climate variability in the study region, which further strengthens the potential of dendrochronological studies developing in Ethiopia, and also has great implications for further paleo-climatic reconstructions and in the restoration of degraded lands. Further knowledge on the growth characteristics of tree species from the region is required to improve the network of tree-ring data and quality of the chronology so as to successfully reconstruct historic environmental changes.
基金funded by Deutscher Akademisher Austausch Dienst(DAAD)Biodiversity Monitoring Transect Analysis(BIOTA)project
文摘Based on 120 stem discs collected during3 months of fieldwork along a 12 km route,the history of fires in the Wari Maro Forest（09 1000 N–02 1000E） over the past century in savanna woodland and dry forest was reconstituted.Three major ecological areas are characterized：one highly burnt zone located between two relative less burnt areas.By analyzing tree rings,246 fire scars were identified.The scars were caused by 51 fire years,occurring at a mean interval of 2.23 years.From 1890 to1965,only 6 years with fires were recorded from sampled trees.Since 1966,no year has passed without fire.The fire frequency point scale reached 14 years.This was the case of Burkea africana,which has been identified as a species tolerant to fire and could be planted to create a natural firewall.In contrast,Anogeissus leiocarpa is highly sensitive to fire,and in a dry forest ecosystem that burns seasonally,it requires a special conservation plan.Two new concepts are described：the rebarking of trees after fire and Mean Kilometer Fire Interval.The first concept was tested with Daniellia oliveri（Rolfe） Hutch ＆ Dalz trees,and the second concept was used to evaluate spatial fire distribution.We demonstrate that savanna woodland and dry forest were subject to a degradation process caused by destructive fires related to vegetation cover clearance and illegal logging.
文摘为研究谐波成分对电-热工作环境下干式阀侧套管内部绝缘用环氧树脂材料的绝缘特性影响,采用多阶谐波叠加负极性直流偏置电压模拟干式阀侧套管运行波形,在80~120℃的温度范围内研究了不同谐波成分对环氧树脂绝缘劣化特性的影响。研究结果表明,谐波与高温均对环氧树脂的绝缘劣化起到促进作用,在电-热工作环境下多阶谐波成分的引入环氧树脂劣化的引发电压降低了40.0%,试样的绝缘失效时间降低了64.8%,同时谐波成分导致绝缘劣化面积扩大,基于场驱动电树枝生长模型(field-driven tree growth,FDTG)的分析,高阶谐波成分的引入使电树生长速率系数增高了190.9%,电树生长临界场强降低到17.88 kV/mm,最后通过仿真计算说明多谐波情况下材料介质损耗发热加剧,针对长时工作设备需进一步关注局部过热问题。
文摘Partial Rootzone Drying (PRD) is an irrigation technique which offers a means of modifying the growth and development of crops through relatively simple changes to the method of water delivery. The technique causes the stimulation of physiological responses which are normally associated with water stress and this results in a significant reduction in water use through the production of chemical signals in drying roots. Partial drying of one half of the roots of plants grown with two root systems is rapidly translated into a reduction in transpiration and assimilation of all the crop leaves. The aim of this research is to examine and simulate the novel irrigation method (PRD), which would stimulate the endogenous stress response mechanisms of Conocarpus erectus trees in the pilot area of the Arabian Gulf University in Bahrain and wheat and maize crops in the Mashtul Pilot Area (MPA), Egypt using Saltmed model so that vigor is reduced and the efficiency of water use is enhanced. This is to be achieved by the manipulation of the hydration status of parts of a crop’s roots that could be used to control vegetative vigor without detrimental effects on canopy water relations. The PRD technique is researched for wheat as a winter crop and maize as a summer crop in Egypt. The technique causes the stimulation of physiological responses which are normally associated with water stress and this results in a significant reduction in water use through the production of chemical signals in drying roots. The results confirmed an increase in irrigation water use efficiency using PRD comparing with conventional flood irrigation. The research highly recommends applying the PRD method in the Gulf Cooperation Council (GCC) countries and in new reclaimed areas in Egypt to save water and improve crop quality.
文摘We carried out this research at Abu-Gaddaf Natural Forest Reserve (ANFR) which is located east of Blue Nile River, in Blue Nile State, Sudan. It aims at exploring tree composition assessing their diversity indices, and ecological importance values. For survey of types and estimation of density of tree species in the forest, we randomly distributed 97 circular sample plots (0.1 hectare (ha)). In each sample plot we identified all trees to the species level, recorded their frequencies and computed species diversity and importance value indices (IVI). A total of 13 tree species, which belong to 12 genera and nine families, were identified in the tree layer of the forest. Mean tree density in ANFR was 116 trees/ha, composed mainly of Boswellia papyrifera (Del.) Hochst. (48), followed by Combretum hartmannianu (19) and Lannea fruticosa (18). Fabaceae was the most common family followed by Combretaceae and Malvaceae. B. papyrifera Delile Hochst was the most abundant while Acacia seyal was the least abundant species. Species richness (R = 1.71), evenness (E = 0.69), dominance (0.24) indices and Simpson’s Index of Diversity (D' = 0.76) suggest a moderate diversity, moderate numbers of individuals in each species and a moderate community stability. The research provides empirical results on diversity and ecological importance value of species, signifies the urging need to safeguard threatened species and to prioritize them for conservation, as well as the need to promote management of abundant species to provide multiple forest ecosystem services.
