In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-...In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced.Compared to the previous as-cast microstructure,the grain size was reduced from more than 1 mm to around 4μm within 3 s by a single process cycle.The compressive yield strength was increased by 350%while the ultimate compressive strength by 53%.According to the established material flow behaviors by“tracer material”,the plastic material was transported by shear deformation.From the base material to the rod,the material experienced three stages,i.e.deformation by the tool,upward flow with additional tilt,followed by upward transportation.The microstructural evolution was revealed by“stop-action”technique.The microstructural development at regions adjacent to the rod is mainly controlled by twinning,dynamic recrystallization(DRX)as well as particle stimulated nucleation,while that within the rod is related to DRX combined with grain growth.展开更多
Since 2015, community forests have been promoted in Togo as an alternative to protect areas from degradation and as a means of contributing to forest landscape restoration. The study focuses on the Nakpadjouak Communi...Since 2015, community forests have been promoted in Togo as an alternative to protect areas from degradation and as a means of contributing to forest landscape restoration. The study focuses on the Nakpadjouak Community Forest (NCF) in Tami (Togo, West Africa) which contributes to community forests sustainable management. It aims in (i) mapping forest ecosystems and analysing their dynamic and (ii) characterizing the floristic diversity of the NCF. The ecosystems were mapped and their dynamic was evaluated based on Google Earth images of 2014 and 2020. Floristic and forestry inventories were carried out using the transect technique in a sample of 20 plots of 50 m × 20 m. The NCF was made up mainly by wooded/shrub savannahs (95.37%) and croplands/fallow (4.63%) in 2014. These two land use types undergone changes over the 6 years prior to 2020. By 2020, the NCF had 3 land use types: wooded/shrub savannahs (77.59%), open forest/wooded savannahs (22.23%), and croplands/fallows (0.18%). A total of 89 plant species belonging to 70 genera and 28 families were recorded within the NCF. The dominant species are: Heteropogon contortus (L.) P.Beauv. and Combretum collinum Fresen. followed by Pteleopsissuberosa Engl. & Diels, Annona senegalensis Pers. The most common species are: Lannea acida A.Rich. s.l., A. senegalensis, Vitellaria paradoxa C.F.Gaertner subsp. paradoxa, C. collinum and Acacia dudgeonii Craib ex Holland. Due to its small area of just 40 hectares and its diverse plant life, this community forest of Savannahs Region is a significant biodiversity hotspot and warrants conservation efforts.展开更多
Magnesium and its alloys have such advantages with lightweight, high specific strength, good damping, high castability and machinability,which make them an attractive choice for applications where weight reduction is ...Magnesium and its alloys have such advantages with lightweight, high specific strength, good damping, high castability and machinability,which make them an attractive choice for applications where weight reduction is important, such as in the aerospace and automotive industries.However, their practical applications are still limited because of their poor corrosion resistance, low high temperature strength and ambient formability. Based on such their property shortcomings, recently degradable magnesium alloys were developed for broadening their potential applications. Considering the degradable Mg alloys for medical applications were well reviewed, the present review put an emphasis on such degradable magnesium alloys for structural and functional applications, especially the applications in the environmental and energy fields. Their applications as fracture ball in fossil energy, sacrificial anode, washing ball, and as battery anodes, transient electronics, were summarized. The roles of alloying elements in magnesium and the design concept of such degradable magnesium alloys were discussed. The existing challenges for extending their future applications are explored.展开更多
The present work reports the creep behavior and microstructural evolution of the sand-cast Mg-14Gd-0.4Zr alloy(wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 ℃ were ...The present work reports the creep behavior and microstructural evolution of the sand-cast Mg-14Gd-0.4Zr alloy(wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 ℃ were performed under various applied stresses(i.e., 60, 80 and100 MPa). Among them, the sand-cast Mg-14Gd-0.4Zr samples examined under 250 ℃/80 MPa for 39 and 95 h, respectively, were chosen to systemically analyze their creep mechanisms using high-angle annular dark field-scanning transmission electron microscopy(HAADF-STEM).The obtained results showed that the enhancement of creep resistance can be mainly attributed to the coherent β' and β'_F phases with an alternate distribution, effectively impeding the basal dislocations movement. However, with the creep time increasing, the fine β'+β'_F precipitate chains coarsened and transformed to semi-coherent β_1 phase and even to large incoherent β phase(surrounded by precipitate-free areas) in grain interiors. The precipitate-free zones(PFZs) at grain boundaries(GBs) were formed, and they could expand during creep deformation. Apart from the main cross-slip of basal and prismatic dislocations, type dislocations were activated and tended to distribute near the GBs. The aforementioned phenomena induced the stress concentrations, consequently leading to the increment of the creep strain.展开更多
Background:Species-specific genotypic features,local neighbourhood interactions and resource supply strongly influence the tree stature and growth rate.In mixed-species forests,diversity-mediated biomass allocation ha...Background:Species-specific genotypic features,local neighbourhood interactions and resource supply strongly influence the tree stature and growth rate.In mixed-species forests,diversity-mediated biomass allocation has been suggested to be a fundamental mechanism underlying the positive biodiversity-productivity relationships.Empirical evidence,however,is rare about the impact of local neighbourhood diversity on tree characteristics analysed at a very high level of detail.To address this issue we analysed these effects on the individual-tree crown architecture and tree productivity in a mature mixed forest in northern Germany.Methods:Our analysis considers multiple target tree species across a local neighbourhood species richness gradient ranging from 1 to 4.We applied terrestrial laser scanning to quantify a large number of individual mature trees(N=920)at very high accuracy.We evaluated two different neighbour inclusion approaches by analysing both a fixed radius selection procedure and a selection based on overlapping crowns.Results and conclusions:We show that local neighbourhood species diversity significantly increases crown dimension and wood volume of target trees.Moreover,we found a size-dependency of diversity effects on tree productivity(basal area and wood volume increment)with positive effects for large-sized trees(diameter at breast height(DBH)>40 cm)and negative effects for small-sized(DBH<40 cm)trees.In our analysis,the neighbour inclusion approach has a significant impact on the outcome.For scientific studies and the validation of growth models we recommend a neighbour selection by overlapping crowns,because this seems to be the relevant scale at which local neighbourhood interactions occur.Because local neighbourhood diversity promotes individual-tree productivity in mature European mixed-species forests,we conclude that a small-scale species mixture should be considered in management plans.展开更多
To have a better understand on the change of microstructure via kinetics, the diffusion behavior of Mg alloys is of special interest to researchers. Meanwhile, diffusion coefficients of Mg based alloys can explain and...To have a better understand on the change of microstructure via kinetics, the diffusion behavior of Mg alloys is of special interest to researchers. Meanwhile, diffusion coefficients of Mg based alloys can explain and represent their diffusion behavior well. The evolution of experimental and calculated methods for detecting and extracting diffusion coefficients was discussed briefly. The reasonable diffusion data, especially self-diffusion coefficients, impurity diffusion coefficients and inter-diffusion coefficients of Mg alloys, were reviewed in detail serving to design the Mg alloys with higher accuracy. Then the practical applications of diffusion coefficients of Mg alloys were summarized,including diffusional mobility establishing, precipitation simulation and mechanical properties prediction.展开更多
Scientists in Egypt are particularly interested in the sustainable management of water and land resources. Global climate change will have a dramatic impact on the Egyptian water and land resources as well as its coas...Scientists in Egypt are particularly interested in the sustainable management of water and land resources. Global climate change will have a dramatic impact on the Egyptian water and land resources as well as its coastline and agriculture. Egypt is likely to become one of the most vulnerable countries in the world in the next several decades. Many climate scenarios predict that climate change will severely affect rainfall in the Nile basin and the flow of the Nile River in general and the High Aswan Dam Reservoir (HADR) in particular. Global warming and the higher temperatures will lead to higher evaporation rates, which, in turn, will result in less water availability at the HADR. Egypt’s Ministry of Water Resources and Irrigation predicts that the evaporation losses will, compared to the mean annual evaporation rates for the last 30 years, be approximately 3% to 10% higher by the year 2100. Since the construction of the High Aswan Dam fifty years ago, high sediment loads are a tremendous problem. 6.6 Billion Cubic Meter (km3) of sediments were deposited in the HADR during this period. The sediment has raised the lakebed level as well as the water level and caused a larger surface area. These developments have decreased the storage capacity of HADR and have increased the evaporation rate. The presented paper investigates the impact of lowering the lakebed by removing sediments from the HADR with a distinct emphasis on evaporation losses. A digital elevation model for the HADR was developed to describe the hydrological characteristics and to assess the consequences of removing sediment deposits. The results show that the removal of sediments will reduce evaporation losses by about 1.1 km3 projected for 2100, which represents 6.5% of the total projected evaporation losses.展开更多
The Lower Saxonian Elbe Valley Biosphere Reserve is part of the UNESCO Biosphere Reserve “Elbe River Landscape”, and used mainly for agriculture. One of tasks of the Biosphere Reserve Administration is to develop su...The Lower Saxonian Elbe Valley Biosphere Reserve is part of the UNESCO Biosphere Reserve “Elbe River Landscape”, and used mainly for agriculture. One of tasks of the Biosphere Reserve Administration is to develop sustainable forms of land use which requires comprehensive updated land cover maps. Land use maps are hard to produce because of surveying costs and time. Nevertheless, these large areas need to be monitored. TerraSAR-X images are used to establish agricultural land use maps. In this study, two areas are selected within the Elbe Biosphere Reserve situated around the oxbows Wehninger Werder and Walmsburger Werder. Multi temporal classification methods were used to identify the different crops using maximum likelihood classifier for the years 2010 and 2011. The crop classifications were used to evaluate the effect of the number of images, the necessity of polarizations, and the consequences of some missing images within the crop calendar. These classifications were analyzed to estimate producer accuracy and Kappa index for each crop besides the overall accuracy for each agricultural land use map. The study shows that using dual polarization imagery enhances producer accuracies for many crops over the single polarization imagery, and demonstrates the importance of using frequent images during the cultivation period.展开更多
Egypt is considered as an extremely arid country with annual rainfall under 200 mm within coastal zones. High Aswan Dam Reservoir (HADR) experiences high evaporation losses of 15 BCM/year on average. Meanwhile, the wa...Egypt is considered as an extremely arid country with annual rainfall under 200 mm within coastal zones. High Aswan Dam Reservoir (HADR) experiences high evaporation losses of 15 BCM/year on average. Meanwhile, the water demand is increasing due to rapid population growth. Hence, measurements must be taken to decrease its evaporation losses. This can be achieved through controlling evaporation losses from the shallow lagoons, locally known as khors. The first step in the control process is to model the lake morphology using topographic data. Topographic maps are available for the time span before the construction of the High Aswan DAM (HAD), but they have not been updated. Hence, this study utilized satellite imagery since 1984 to develop a digital elevation model (DEM) that simulated the lake surface area. Correlated water levels were gained from the assembled hydrological database of HADR. This paper reports on the different alternatives for reducing the evaporation losses of two large khors, Kalabsha and El-Alaky, and two small khors, Korosko and Sara. It shows that the developed DEM allows estimation of the different hydrological features of HADR and its khors and recommends some measures to eliminate these khors to save up to 3 BCM by 2100 according to global climate model scenarios.展开更多
This paper proposes the solution of tasks set required for autonomous robotic group behavior optimization during the mission on a distributed area in a cluttered hazardous terrain.The navigation scheme uses the benefi...This paper proposes the solution of tasks set required for autonomous robotic group behavior optimization during the mission on a distributed area in a cluttered hazardous terrain.The navigation scheme uses the benefits of the original real-time technical vision system(TVS)based on a dynamic triangulation principle.The method uses TVS output data with fuzzy logic rules processing for resolution stabilization.Based on previous researches,the dynamic communication network model is modified to implement the propagation of information with a feedback method for more stable data exchange inside the robotic group.According to the comparative analysis of approximation methods,in this paper authors are proposing to use two-steps post-processing path planning aiming to get a smooth and energy-saving trajectory.The article provides a wide range of studies and computational experiment results for different scenarios for evaluation of common cloud point influence on robotic motion planning.展开更多
Dry afromontane forests are among the most poorly managed and endangered ecosystems.Therefore,we assessed the composition,diversity,and conservation status of woody plant species of the Debre Libanos church forests an...Dry afromontane forests are among the most poorly managed and endangered ecosystems.Therefore,we assessed the composition,diversity,and conservation status of woody plant species of the Debre Libanos church forests and surrounding forest lands in Oromiya Regional National State,central Ethiopia in 62 nested circular sample plots spaced 200 m apart along two transect lines.Large circular plots 314 m^(2)were used to sample trees with DBH of at least 10 cm,and subplots of 28.26 m^(2)were laid in each main plot were used to assess saplings and shrubs;a small subplot of 3.14 m2 was used to assess seedlings.In total,70 woody plant species belonging to 62 genera and 43 families were recorded.Of these,59,28 and 32 were in the church,government and private forest types,respectively.The most dominant families were Fabaceae and Verbenaceae,each represented by five species.In the forests considered,trees accounted for 61%,and shrubs with diameter at breast height(DBH)of 1-10 cm accounted for ca.33%.Among growth forms of woody species,shrubs and seedlings,followed by trees constituted much of the density of woody species in all the three ownership types of forests.The church forest had the most species(59)and highest Shannon(3.12)and Simpson(0.92)species diversity indices,and the government and private forests had a nearly similar total number of species and Shannon and Simpson species diversity indices.Most of the species with higher importance value indices(IVI)were indigenous in origin within the church forest(Juniperus procera=82),government forest(J.procera=66)and private forest(Acacia abyssinica=84).The composition,diversity,and population structure of woody species in the church forest were significantly higher than in the other forest lands.However,interventions of the government and private sectors to conserve forest systems in the areas,particularly the government-owned forest and specific species such as Olea europaea need active enrichment plantings due to their limited natural regeneration.Without improved management interventions,livelihood income diversification and ecosystem services obtained from the forest will not be sustainable.展开更多
Floods are one of the major hazards worldwide. They are the source of huge risks in rural and urban areas, resulting in severe impacts on the civil society, industry and the economy. The Elbe River has suffered from m...Floods are one of the major hazards worldwide. They are the source of huge risks in rural and urban areas, resulting in severe impacts on the civil society, industry and the economy. The Elbe River has suffered from many severe floods during recent decades. In this study, the zones flooded during 2011 were analyzed using TerraSAR-X images and a digital elevation model for the area in order to identify possible ways to mitigate flood hazards in the future, regarding sustainable land-use. Two study areas are investigated, around the Walmsburg oxbow and the Wehningen oxbow. These are located between Elbe-Kilometer (505-520) and (533-543), respectively, within the Lower Saxonian Elbe River Biosphere Reserve. Those areas are characterized by several types of land use, with agricultural land use being predominant. The study investigated the possibility of using a Decision-Tree object-based classifier for determining the major land uses and the extent of the inundation areas. The inundation areas identify for 2011 submerged some agricultural fields that must be added to existing flood risk maps, and future cultivation activities there prevented to avoid the possible economic losses. Furthermore, part of the residential area is located within the high flood zone, and must be included in risk maps to avoid the possible human and economic losses, to achieve sustainable land use for the areas studied.展开更多
This work explores ceramic additive manufacturing in combination with liquid metal infiltration for the production of degradable interpenetrating phase magnesium/hydroxyapatite(Mg/HA) composites. Material extrusion ad...This work explores ceramic additive manufacturing in combination with liquid metal infiltration for the production of degradable interpenetrating phase magnesium/hydroxyapatite(Mg/HA) composites. Material extrusion additive manufacturing was used to produce stoichiometric,and calcium deficient HA preforms with a well-controlled open pore network, allowing the customization of the topological relationship of the composite. Pure Mg and two different Mg alloys were used to infiltrate the preforms by means of an advanced liquid infiltration method inspired by spark plasma sintering, using a novel die design to avoid the structural collapse of the preform. Complete infiltration was achieved in 8 min, including the time for the Mg melting. The short processing time enabled to restrict the decomposition of HA due to the reducing capacity of liquid Mg. The pure Mg-base composites showed compressive yield strength above pure Mg in cast state. Mg alloy-based composites did not show higher strength than the bare alloys due to grain coarsening, but showed similar mechanical properties than other Mg/HA composites that have significantly higher fraction of metallic phase. The composites showed faster degradation rate under simulated body conditions than the bare metallic component due to the formation of galvanic pairs at microstructural level. Mg dissolved preferentially over HA leaving behind a scaffold after a prolonged degradation period. In turn, the fast production of soluble degradation products caused cell metabolic changes after 24 h of culture with not-diluted material extracts. The topological optimization and reduction of the degradation rate are the topics for future research.展开更多
Constrained Friction Processing(CFP)is a novel solid-state processing technique suitable for lightweight materials,such Mg-and Al-alloys.The technique enables grain size refinement to fine or even ultrafine scale.In t...Constrained Friction Processing(CFP)is a novel solid-state processing technique suitable for lightweight materials,such Mg-and Al-alloys.The technique enables grain size refinement to fine or even ultrafine scale.In this study,the effect of CFP on the microstructural refinement of AM50 rods is investigated in terms of particle size and morphology of the eutectic and secondary phases originally present in the base material,in particular the eutecticβ-Mg_(17)Al_(12)and Al-Mn phases.For that purpose,as-cast and solution heat-treated base material and processed samples were analyzed.The Al_(8)Mn_(5) intermetallic phase was identified as the main secondary phase present in all samples before and after the processing.A notorious refinement of these particles was observed,starting from particles with an average equivalent length of a few micrometers to around 560 nm after the processing.The refinement of the secondary phase refinement is attributed to a mechanism analogous to the attrition comminution,where the combination of temperature increase and shearing of the material enables the continuous breaking of the brittle intermetallic particles into smaller pieces.As for the eutectic phase,the results indicate the presence of the partially divorcedβ-Mg_(17)Al_(12)particles exclusively in the as-cast base material,indicating that no further phase transformations regarding the eutectic phase,such as dynamic precipitation,occurred after the CFP.In the case of the processed as-cast material analyzed after the CFP,the thermal energy generated during the processing led to temperature values above the solvus limit of the eutectic phase,which associated with the mechanical breakage of the particles,enabled the complete dissolution of this phase.Therefore,CFP was successfully demonstrated to promote an extensive microstructure refinement in multiple aspects,in terms of grain sizes of theα-Mg phase and presence and morphology of the Al-Mn and eutecticβ-Mg_(17)Al_(12).展开更多
Aims Plant diversity has been linked to both increasing and decreasing levels of arthropod herbivore damage in different plant communities.So far,these links have mainly been studied in grasslands or in artificial tre...Aims Plant diversity has been linked to both increasing and decreasing levels of arthropod herbivore damage in different plant communities.So far,these links have mainly been studied in grasslands or in artificial tree plantations with low species richness.Furthermore,most studies provide results from newly established experimental plant communities where trophic links are not fully established or from stands of tree saplings that have not yet developed a canopy.Here,we test how tree diversity in a species-rich subtropical forest in China with fully developed tree canopy affects levels of herbivore damage caused by different arthropod feeding guilds.Methods We established 27 plots of 30×30 m area.The plots were selected randomly but with the constraint that they had to span a large range of tree diversity as required for comparative studies in contrast to sample surveys.We recorded herbivore damage caused by arthropod feeding guilds(leaf chewers,leaf skeletonizers and sap feeders)on canopy leaves of all major tree species.Important Findings Levels of herbivore damage increased with tree species richness and tree phylogenetic diversity.These effects were most pronounced for damage caused by leaf chewers.Although the two diversity measures were highly correlated,we additionally found a significant interaction between them,whereby species richness increased herbivory mostly at low levels of phylogenetic diversity.Tree species with the lowest proportion of canopy leaf biomass in a plot tended to suffer the highest levels of herbivore damage,which is in contrast to expectations based on the resource concentration hypothesis.Our results are in agreement with expectations of the dietary mixing hypothesis where generalist herbivores with a broad spectrum of food plants benefit from increased resource diversity in tree species-rich forest patches.展开更多
Traditional farming landscapes have evolved as tightly coupled socioecological systems that support high biodiversity.However,land-use change severely threatens the high biodiversity of these landscapes.Navigating nat...Traditional farming landscapes have evolved as tightly coupled socioecological systems that support high biodiversity.However,land-use change severely threatens the high biodiversity of these landscapes.Navigating nature conservation in such landscapes requires a thorough understanding of the key drivers underpinning biodiversity.Through empirical research on mammals,birds,butterflies,and plants in a traditional cultural landscape in Romania,we revealed seven hypothesized drivers facilitating biodiversity conservation.Similar proportions of three main land-use types support the landscape species pool,most likely through habitat connectivity and frequent spillover between land-use types.Landscape complementation and supplementation provide additional habitat for species outside their core habitats.Gradients of woody vegetation cover and gradients in land-cover heterogeneity provide mosaic landscapes with wide ranges of resources.Traditional land-use practices underpin landscape heterogeneity,traditional land-use elements such as wood pastures,and human-carnivore coexistence.Top-down predator control may limit herbivore populations.Lastly,cultural ties between humans and nature have a central influence on people’s values and sustainable use of natural resources.Conservation approaches should aim to maintain or restore these socioecological drivers by targeting the heterogeneous character of the forest-farmland mosaic at large scales through"broad and shallow"conservation measures.These large-scale measures should be complemented with"deep and narrow"conservation measures addressing specific land-use types,threats,or species.In both cases,conservation measures should integrate the entire socioecological system,by recognizing and strengthening important links between people and the environment.展开更多
基金the China Scholarship Council for the award of fellowship and funding(No.202006230137)。
文摘In order to obtain Mg alloys with fine microstructures and high mechanical performances,a novel friction-based processing method,name as“constrained friction processing(CFP)”,was investigated.Via CFP,defect-free Mg-Zn-Ca rods with greatly refined grains and high mechanical properties were produced.Compared to the previous as-cast microstructure,the grain size was reduced from more than 1 mm to around 4μm within 3 s by a single process cycle.The compressive yield strength was increased by 350%while the ultimate compressive strength by 53%.According to the established material flow behaviors by“tracer material”,the plastic material was transported by shear deformation.From the base material to the rod,the material experienced three stages,i.e.deformation by the tool,upward flow with additional tilt,followed by upward transportation.The microstructural evolution was revealed by“stop-action”technique.The microstructural development at regions adjacent to the rod is mainly controlled by twinning,dynamic recrystallization(DRX)as well as particle stimulated nucleation,while that within the rod is related to DRX combined with grain growth.
文摘Since 2015, community forests have been promoted in Togo as an alternative to protect areas from degradation and as a means of contributing to forest landscape restoration. The study focuses on the Nakpadjouak Community Forest (NCF) in Tami (Togo, West Africa) which contributes to community forests sustainable management. It aims in (i) mapping forest ecosystems and analysing their dynamic and (ii) characterizing the floristic diversity of the NCF. The ecosystems were mapped and their dynamic was evaluated based on Google Earth images of 2014 and 2020. Floristic and forestry inventories were carried out using the transect technique in a sample of 20 plots of 50 m × 20 m. The NCF was made up mainly by wooded/shrub savannahs (95.37%) and croplands/fallow (4.63%) in 2014. These two land use types undergone changes over the 6 years prior to 2020. By 2020, the NCF had 3 land use types: wooded/shrub savannahs (77.59%), open forest/wooded savannahs (22.23%), and croplands/fallows (0.18%). A total of 89 plant species belonging to 70 genera and 28 families were recorded within the NCF. The dominant species are: Heteropogon contortus (L.) P.Beauv. and Combretum collinum Fresen. followed by Pteleopsissuberosa Engl. & Diels, Annona senegalensis Pers. The most common species are: Lannea acida A.Rich. s.l., A. senegalensis, Vitellaria paradoxa C.F.Gaertner subsp. paradoxa, C. collinum and Acacia dudgeonii Craib ex Holland. Due to its small area of just 40 hectares and its diverse plant life, this community forest of Savannahs Region is a significant biodiversity hotspot and warrants conservation efforts.
文摘Magnesium and its alloys have such advantages with lightweight, high specific strength, good damping, high castability and machinability,which make them an attractive choice for applications where weight reduction is important, such as in the aerospace and automotive industries.However, their practical applications are still limited because of their poor corrosion resistance, low high temperature strength and ambient formability. Based on such their property shortcomings, recently degradable magnesium alloys were developed for broadening their potential applications. Considering the degradable Mg alloys for medical applications were well reviewed, the present review put an emphasis on such degradable magnesium alloys for structural and functional applications, especially the applications in the environmental and energy fields. Their applications as fracture ball in fossil energy, sacrificial anode, washing ball, and as battery anodes, transient electronics, were summarized. The roles of alloying elements in magnesium and the design concept of such degradable magnesium alloys were discussed. The existing challenges for extending their future applications are explored.
基金the Shanghai Sailing Program (23YF1417100)National Natural Science Foundation of China (U2037601)China Scholarship Council (Grant No: 202006890008) for the financial support。
文摘The present work reports the creep behavior and microstructural evolution of the sand-cast Mg-14Gd-0.4Zr alloy(wt.%) prepared by the differential pressure casting machine. Their compressive creep tests at 250 ℃ were performed under various applied stresses(i.e., 60, 80 and100 MPa). Among them, the sand-cast Mg-14Gd-0.4Zr samples examined under 250 ℃/80 MPa for 39 and 95 h, respectively, were chosen to systemically analyze their creep mechanisms using high-angle annular dark field-scanning transmission electron microscopy(HAADF-STEM).The obtained results showed that the enhancement of creep resistance can be mainly attributed to the coherent β' and β'_F phases with an alternate distribution, effectively impeding the basal dislocations movement. However, with the creep time increasing, the fine β'+β'_F precipitate chains coarsened and transformed to semi-coherent β_1 phase and even to large incoherent β phase(surrounded by precipitate-free areas) in grain interiors. The precipitate-free zones(PFZs) at grain boundaries(GBs) were formed, and they could expand during creep deformation. Apart from the main cross-slip of basal and prismatic dislocations, type dislocations were activated and tended to distribute near the GBs. The aforementioned phenomena induced the stress concentrations, consequently leading to the increment of the creep strain.
基金LG was funded by the German Research Foundation(DFG 320926971)through the project“Analysis of diversity effects on above-groundproductivity in forests:advancing the mechanistic understanding of spatiotemporal dynamics in canopy space filling using mobile laser scanning”。
文摘Background:Species-specific genotypic features,local neighbourhood interactions and resource supply strongly influence the tree stature and growth rate.In mixed-species forests,diversity-mediated biomass allocation has been suggested to be a fundamental mechanism underlying the positive biodiversity-productivity relationships.Empirical evidence,however,is rare about the impact of local neighbourhood diversity on tree characteristics analysed at a very high level of detail.To address this issue we analysed these effects on the individual-tree crown architecture and tree productivity in a mature mixed forest in northern Germany.Methods:Our analysis considers multiple target tree species across a local neighbourhood species richness gradient ranging from 1 to 4.We applied terrestrial laser scanning to quantify a large number of individual mature trees(N=920)at very high accuracy.We evaluated two different neighbour inclusion approaches by analysing both a fixed radius selection procedure and a selection based on overlapping crowns.Results and conclusions:We show that local neighbourhood species diversity significantly increases crown dimension and wood volume of target trees.Moreover,we found a size-dependency of diversity effects on tree productivity(basal area and wood volume increment)with positive effects for large-sized trees(diameter at breast height(DBH)>40 cm)and negative effects for small-sized(DBH<40 cm)trees.In our analysis,the neighbour inclusion approach has a significant impact on the outcome.For scientific studies and the validation of growth models we recommend a neighbour selection by overlapping crowns,because this seems to be the relevant scale at which local neighbourhood interactions occur.Because local neighbourhood diversity promotes individual-tree productivity in mature European mixed-species forests,we conclude that a small-scale species mixture should be considered in management plans.
基金financially supported by the China Scholarship Council (Grant No: 202006890008), ChinaScience and Technology Committee of Shanghai (19010500400)+1 种基金the “111” project (D16002)the Independent Research Project of State Key Laboratory of Mechanical Transmissions (Grant No. SKLMT-ZZKT-2021M11)。
文摘To have a better understand on the change of microstructure via kinetics, the diffusion behavior of Mg alloys is of special interest to researchers. Meanwhile, diffusion coefficients of Mg based alloys can explain and represent their diffusion behavior well. The evolution of experimental and calculated methods for detecting and extracting diffusion coefficients was discussed briefly. The reasonable diffusion data, especially self-diffusion coefficients, impurity diffusion coefficients and inter-diffusion coefficients of Mg alloys, were reviewed in detail serving to design the Mg alloys with higher accuracy. Then the practical applications of diffusion coefficients of Mg alloys were summarized,including diffusional mobility establishing, precipitation simulation and mechanical properties prediction.
文摘Scientists in Egypt are particularly interested in the sustainable management of water and land resources. Global climate change will have a dramatic impact on the Egyptian water and land resources as well as its coastline and agriculture. Egypt is likely to become one of the most vulnerable countries in the world in the next several decades. Many climate scenarios predict that climate change will severely affect rainfall in the Nile basin and the flow of the Nile River in general and the High Aswan Dam Reservoir (HADR) in particular. Global warming and the higher temperatures will lead to higher evaporation rates, which, in turn, will result in less water availability at the HADR. Egypt’s Ministry of Water Resources and Irrigation predicts that the evaporation losses will, compared to the mean annual evaporation rates for the last 30 years, be approximately 3% to 10% higher by the year 2100. Since the construction of the High Aswan Dam fifty years ago, high sediment loads are a tremendous problem. 6.6 Billion Cubic Meter (km3) of sediments were deposited in the HADR during this period. The sediment has raised the lakebed level as well as the water level and caused a larger surface area. These developments have decreased the storage capacity of HADR and have increased the evaporation rate. The presented paper investigates the impact of lowering the lakebed by removing sediments from the HADR with a distinct emphasis on evaporation losses. A digital elevation model for the HADR was developed to describe the hydrological characteristics and to assess the consequences of removing sediment deposits. The results show that the removal of sediments will reduce evaporation losses by about 1.1 km3 projected for 2100, which represents 6.5% of the total projected evaporation losses.
文摘The Lower Saxonian Elbe Valley Biosphere Reserve is part of the UNESCO Biosphere Reserve “Elbe River Landscape”, and used mainly for agriculture. One of tasks of the Biosphere Reserve Administration is to develop sustainable forms of land use which requires comprehensive updated land cover maps. Land use maps are hard to produce because of surveying costs and time. Nevertheless, these large areas need to be monitored. TerraSAR-X images are used to establish agricultural land use maps. In this study, two areas are selected within the Elbe Biosphere Reserve situated around the oxbows Wehninger Werder and Walmsburger Werder. Multi temporal classification methods were used to identify the different crops using maximum likelihood classifier for the years 2010 and 2011. The crop classifications were used to evaluate the effect of the number of images, the necessity of polarizations, and the consequences of some missing images within the crop calendar. These classifications were analyzed to estimate producer accuracy and Kappa index for each crop besides the overall accuracy for each agricultural land use map. The study shows that using dual polarization imagery enhances producer accuracies for many crops over the single polarization imagery, and demonstrates the importance of using frequent images during the cultivation period.
文摘Egypt is considered as an extremely arid country with annual rainfall under 200 mm within coastal zones. High Aswan Dam Reservoir (HADR) experiences high evaporation losses of 15 BCM/year on average. Meanwhile, the water demand is increasing due to rapid population growth. Hence, measurements must be taken to decrease its evaporation losses. This can be achieved through controlling evaporation losses from the shallow lagoons, locally known as khors. The first step in the control process is to model the lake morphology using topographic data. Topographic maps are available for the time span before the construction of the High Aswan DAM (HAD), but they have not been updated. Hence, this study utilized satellite imagery since 1984 to develop a digital elevation model (DEM) that simulated the lake surface area. Correlated water levels were gained from the assembled hydrological database of HADR. This paper reports on the different alternatives for reducing the evaporation losses of two large khors, Kalabsha and El-Alaky, and two small khors, Korosko and Sara. It shows that the developed DEM allows estimation of the different hydrological features of HADR and its khors and recommends some measures to eliminate these khors to save up to 3 BCM by 2100 according to global climate model scenarios.
文摘This paper proposes the solution of tasks set required for autonomous robotic group behavior optimization during the mission on a distributed area in a cluttered hazardous terrain.The navigation scheme uses the benefits of the original real-time technical vision system(TVS)based on a dynamic triangulation principle.The method uses TVS output data with fuzzy logic rules processing for resolution stabilization.Based on previous researches,the dynamic communication network model is modified to implement the propagation of information with a feedback method for more stable data exchange inside the robotic group.According to the comparative analysis of approximation methods,in this paper authors are proposing to use two-steps post-processing path planning aiming to get a smooth and energy-saving trajectory.The article provides a wide range of studies and computational experiment results for different scenarios for evaluation of common cloud point influence on robotic motion planning.
基金supported financially by the Fundamental Research Funds of Environment and Coffee Forest Forum。
文摘Dry afromontane forests are among the most poorly managed and endangered ecosystems.Therefore,we assessed the composition,diversity,and conservation status of woody plant species of the Debre Libanos church forests and surrounding forest lands in Oromiya Regional National State,central Ethiopia in 62 nested circular sample plots spaced 200 m apart along two transect lines.Large circular plots 314 m^(2)were used to sample trees with DBH of at least 10 cm,and subplots of 28.26 m^(2)were laid in each main plot were used to assess saplings and shrubs;a small subplot of 3.14 m2 was used to assess seedlings.In total,70 woody plant species belonging to 62 genera and 43 families were recorded.Of these,59,28 and 32 were in the church,government and private forest types,respectively.The most dominant families were Fabaceae and Verbenaceae,each represented by five species.In the forests considered,trees accounted for 61%,and shrubs with diameter at breast height(DBH)of 1-10 cm accounted for ca.33%.Among growth forms of woody species,shrubs and seedlings,followed by trees constituted much of the density of woody species in all the three ownership types of forests.The church forest had the most species(59)and highest Shannon(3.12)and Simpson(0.92)species diversity indices,and the government and private forests had a nearly similar total number of species and Shannon and Simpson species diversity indices.Most of the species with higher importance value indices(IVI)were indigenous in origin within the church forest(Juniperus procera=82),government forest(J.procera=66)and private forest(Acacia abyssinica=84).The composition,diversity,and population structure of woody species in the church forest were significantly higher than in the other forest lands.However,interventions of the government and private sectors to conserve forest systems in the areas,particularly the government-owned forest and specific species such as Olea europaea need active enrichment plantings due to their limited natural regeneration.Without improved management interventions,livelihood income diversification and ecosystem services obtained from the forest will not be sustainable.
文摘Floods are one of the major hazards worldwide. They are the source of huge risks in rural and urban areas, resulting in severe impacts on the civil society, industry and the economy. The Elbe River has suffered from many severe floods during recent decades. In this study, the zones flooded during 2011 were analyzed using TerraSAR-X images and a digital elevation model for the area in order to identify possible ways to mitigate flood hazards in the future, regarding sustainable land-use. Two study areas are investigated, around the Walmsburg oxbow and the Wehningen oxbow. These are located between Elbe-Kilometer (505-520) and (533-543), respectively, within the Lower Saxonian Elbe River Biosphere Reserve. Those areas are characterized by several types of land use, with agricultural land use being predominant. The study investigated the possibility of using a Decision-Tree object-based classifier for determining the major land uses and the extent of the inundation areas. The inundation areas identify for 2011 submerged some agricultural fields that must be added to existing flood risk maps, and future cultivation activities there prevented to avoid the possible economic losses. Furthermore, part of the residential area is located within the high flood zone, and must be included in risk maps to avoid the possible human and economic losses, to achieve sustainable land use for the areas studied.
基金supported by the Czech Science Foundation (grant 19-22662S)Czech Nano Lab project LM2018110 funded by MEYS CR is gratefully acknowledged for the support of the measurements at CEITEC Nano Research Infrastructure+2 种基金MCL acknowledges to Brno Ph.D. Talent scholarship and to the Brno University of Technology Internal Project: CEITEC VUT-J-19-5915SDT acknowledges to CONACYTSNI and SIP-IPN (SAPPI 20220438)LV acknowledges to project no. NU20-08-00150 (MH, Czechia)。
文摘This work explores ceramic additive manufacturing in combination with liquid metal infiltration for the production of degradable interpenetrating phase magnesium/hydroxyapatite(Mg/HA) composites. Material extrusion additive manufacturing was used to produce stoichiometric,and calcium deficient HA preforms with a well-controlled open pore network, allowing the customization of the topological relationship of the composite. Pure Mg and two different Mg alloys were used to infiltrate the preforms by means of an advanced liquid infiltration method inspired by spark plasma sintering, using a novel die design to avoid the structural collapse of the preform. Complete infiltration was achieved in 8 min, including the time for the Mg melting. The short processing time enabled to restrict the decomposition of HA due to the reducing capacity of liquid Mg. The pure Mg-base composites showed compressive yield strength above pure Mg in cast state. Mg alloy-based composites did not show higher strength than the bare alloys due to grain coarsening, but showed similar mechanical properties than other Mg/HA composites that have significantly higher fraction of metallic phase. The composites showed faster degradation rate under simulated body conditions than the bare metallic component due to the formation of galvanic pairs at microstructural level. Mg dissolved preferentially over HA leaving behind a scaffold after a prolonged degradation period. In turn, the fast production of soluble degradation products caused cell metabolic changes after 24 h of culture with not-diluted material extracts. The topological optimization and reduction of the degradation rate are the topics for future research.
文摘Constrained Friction Processing(CFP)is a novel solid-state processing technique suitable for lightweight materials,such Mg-and Al-alloys.The technique enables grain size refinement to fine or even ultrafine scale.In this study,the effect of CFP on the microstructural refinement of AM50 rods is investigated in terms of particle size and morphology of the eutectic and secondary phases originally present in the base material,in particular the eutecticβ-Mg_(17)Al_(12)and Al-Mn phases.For that purpose,as-cast and solution heat-treated base material and processed samples were analyzed.The Al_(8)Mn_(5) intermetallic phase was identified as the main secondary phase present in all samples before and after the processing.A notorious refinement of these particles was observed,starting from particles with an average equivalent length of a few micrometers to around 560 nm after the processing.The refinement of the secondary phase refinement is attributed to a mechanism analogous to the attrition comminution,where the combination of temperature increase and shearing of the material enables the continuous breaking of the brittle intermetallic particles into smaller pieces.As for the eutectic phase,the results indicate the presence of the partially divorcedβ-Mg_(17)Al_(12)particles exclusively in the as-cast base material,indicating that no further phase transformations regarding the eutectic phase,such as dynamic precipitation,occurred after the CFP.In the case of the processed as-cast material analyzed after the CFP,the thermal energy generated during the processing led to temperature values above the solvus limit of the eutectic phase,which associated with the mechanical breakage of the particles,enabled the complete dissolution of this phase.Therefore,CFP was successfully demonstrated to promote an extensive microstructure refinement in multiple aspects,in terms of grain sizes of theα-Mg phase and presence and morphology of the Al-Mn and eutecticβ-Mg_(17)Al_(12).
基金supported by the Natural Science Foundation of China(32171634)Open Grant for Key Laboratory of Sustainable Forest Ecosystem Management(Northeast Forestry University)+1 种基金Ministry of Education(KFJJ2021ZD02)Starting Research Fund from Hangzhou Normal University(2018QDL005).
基金the European project BACCARA funded by the European Commission’s Seventh Framework Program(FP7/2007-2013 under Grant Agreement No.226299)for financial supportthe administration of the Gutianshan National Nature Reserve and to the members of the BEF-China consortium for logistic and intellectual support+1 种基金the National Science Foundation of China(NSFC 30710103907 and 30930005)the German Research Foundation(DFG FOR 891)that granted and permitted the establishment of the experiment.
文摘Aims Plant diversity has been linked to both increasing and decreasing levels of arthropod herbivore damage in different plant communities.So far,these links have mainly been studied in grasslands or in artificial tree plantations with low species richness.Furthermore,most studies provide results from newly established experimental plant communities where trophic links are not fully established or from stands of tree saplings that have not yet developed a canopy.Here,we test how tree diversity in a species-rich subtropical forest in China with fully developed tree canopy affects levels of herbivore damage caused by different arthropod feeding guilds.Methods We established 27 plots of 30×30 m area.The plots were selected randomly but with the constraint that they had to span a large range of tree diversity as required for comparative studies in contrast to sample surveys.We recorded herbivore damage caused by arthropod feeding guilds(leaf chewers,leaf skeletonizers and sap feeders)on canopy leaves of all major tree species.Important Findings Levels of herbivore damage increased with tree species richness and tree phylogenetic diversity.These effects were most pronounced for damage caused by leaf chewers.Although the two diversity measures were highly correlated,we additionally found a significant interaction between them,whereby species richness increased herbivory mostly at low levels of phylogenetic diversity.Tree species with the lowest proportion of canopy leaf biomass in a plot tended to suffer the highest levels of herbivore damage,which is in contrast to expectations based on the resource concentration hypothesis.Our results are in agreement with expectations of the dietary mixing hypothesis where generalist herbivores with a broad spectrum of food plants benefit from increased resource diversity in tree species-rich forest patches.
文摘Traditional farming landscapes have evolved as tightly coupled socioecological systems that support high biodiversity.However,land-use change severely threatens the high biodiversity of these landscapes.Navigating nature conservation in such landscapes requires a thorough understanding of the key drivers underpinning biodiversity.Through empirical research on mammals,birds,butterflies,and plants in a traditional cultural landscape in Romania,we revealed seven hypothesized drivers facilitating biodiversity conservation.Similar proportions of three main land-use types support the landscape species pool,most likely through habitat connectivity and frequent spillover between land-use types.Landscape complementation and supplementation provide additional habitat for species outside their core habitats.Gradients of woody vegetation cover and gradients in land-cover heterogeneity provide mosaic landscapes with wide ranges of resources.Traditional land-use practices underpin landscape heterogeneity,traditional land-use elements such as wood pastures,and human-carnivore coexistence.Top-down predator control may limit herbivore populations.Lastly,cultural ties between humans and nature have a central influence on people’s values and sustainable use of natural resources.Conservation approaches should aim to maintain or restore these socioecological drivers by targeting the heterogeneous character of the forest-farmland mosaic at large scales through"broad and shallow"conservation measures.These large-scale measures should be complemented with"deep and narrow"conservation measures addressing specific land-use types,threats,or species.In both cases,conservation measures should integrate the entire socioecological system,by recognizing and strengthening important links between people and the environment.