In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommend...In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.展开更多
Meroplankton play a crucial role in both benthic and pelagic ecosystems.Existing quantitative research on estimating the quantities of meroplankton groups is both underrepresented and inaccurate.To investigate and eva...Meroplankton play a crucial role in both benthic and pelagic ecosystems.Existing quantitative research on estimating the quantities of meroplankton groups is both underrepresented and inaccurate.To investigate and evaluate the influence of varying mesh sizes(505 and 160μm)on the sampling efficiency of meroplankton,we conducted an examination using two commonly used plankton nets during the spring season in the Southern Yellow Sea(SYS).Our study revealed a total of 12 meroplankton groups,with 9 groups identified in the 505-μm mesh nets and 11 groups in the 160-μm mesh nets.The results demonstrated the superior collection efficiency of the 160-μm net compared to the 505-μm net across the majority of meroplankton groups.Furthermore,we focused on exploring the abundance,distribution patterns,and realized niches of meroplankton collected by the two mesh size nets,and observed that the distribution of meroplankton closely resembled the distribution of possible benthic adults in the SYS.Correlation analysis of the six dominant groups collected in the 160-μm mesh nets revealed that seawater temperature and salinity emerged as the key environmental factors driving variations in meroplankton abundance within the SYS.This study also found that a smaller mesh size net does not necessarily capture meroplankton more comprehensively.A comprehensive understanding of the ecological characteristics of meroplankton requires the combination of two types of nets for research.Our research significantly advances our understanding of the quantification,abundance,and distribution of meroplankton,serving as a valuable contribution to the broader landscape of detailed quantitative meroplankton studies.展开更多
Numerical method is popular in analysing the blast wave propagation and interaction with structures.However,because of the extremely short duration of blast wave and energy trans-mission between different grids,the nu...Numerical method is popular in analysing the blast wave propagation and interaction with structures.However,because of the extremely short duration of blast wave and energy trans-mission between different grids,the numerical results are sensitive to the finite element mesh size.Previous numerical simulations show that a mesh size acceptable to one blast scenario might not be proper for another case,even though the difference between the two scenarios is very small,indicating a simple numerical mesh size convergence test might not be enough to guarantee accu-rate numerical results.Therefore,both coarse mesh and fine mesh were used in different blast scenarios to investigate the mesh size effect on numerical results of blast wave propagation and interaction with structures.Based on the numerical results and their comparison with field test re-sults and the design charts in TM5-1300,a numerical modification method was proposed to correct the influence of the mesh size on the simulated results.It can be easily used to improve the accu-racy of the numerical results of blast wave propagation and blast loads on structures.展开更多
Zooplankton samples were collected using 505, 160 and 77 μm mesh nets around a power plant during four seasons in 2011. We measured total length of zooplankton and divided zooplankton into seven size classes in order...Zooplankton samples were collected using 505, 160 and 77 μm mesh nets around a power plant during four seasons in 2011. We measured total length of zooplankton and divided zooplankton into seven size classes in order to explore how zooplankton community size-structure might be altered by thermal discharge from power plant. The total length of zooplankton varied from 93.7 to 40 074.7 μm. The spatial distribution of mesozooplankton(200-2 000 μm) populations were rarely affected by thermal discharge, while macro-(2 000-10 000 μm)and megalo-zooplankton(>10 000 μm) had an obvious tendency to migrate away from the outfall of power plant.Thus, zooplankton community tended to become smaller and biodiversity reduced close to power plant.Moreover, we compared the zooplankton communities in three different mesh size nets. Species richness,abundance, evenness index and Shannon-Wiener diversity index of the 505 μm mesh size were significantly lower than those recorded from the 160 and 77 μm mesh size. Average zooplankton abundance was highest in the 77 μm mesh net((27 690.0±1 633.7) ind./m^3), followed by 160 μm mesh net((9 531.1±1 079.5) ind./m^3), and lowest in 505 μm mesh net((494.4±104.7) ind./m^3). The ANOSIM and SIMPER tests confirmed that these differences were mainly due to small zooplankton and early developmental stages of zooplankton. It is the first time to use the 77 μm mesh net to sample zooplankton in such an environment. The 77 μm mesh net had the overwhelming abundance of the copepod genus Oithona, as an order of magnitude greater than recorded for 160 μm mesh net and 100% loss through the 505 μm mesh net. These results indicate that the use of a small or even multiple sampling net is necessary to accurately quantify entire zooplankton community around coastal power plant.展开更多
Sphere packing is an attractive way to generate high quality mesh. Several algorithms have been proposed in this topic, however these algorithms are not sufficiently fast for large scale problems. The paper presents a...Sphere packing is an attractive way to generate high quality mesh. Several algorithms have been proposed in this topic, however these algorithms are not sufficiently fast for large scale problems. The paper presents an efficient sphere packing algorithm which is much faster and appears to be the most practical among all sphere packing methods presented so far for mesh generation. The algorithm packs spheres inside a domain using advancing front method. High efficiency has resulted from a concept of 4R measure, which localizes all the computations involved in the whole sphere packing process.展开更多
Arthropod assemblages and decomposition rates were compared in the litter of pure and mixed Quercus(Quercus petraea L.)and Fagus(Fagus orientalis L.)stands.Litter was sampled on a monthly basis for 1 year and stored i...Arthropod assemblages and decomposition rates were compared in the litter of pure and mixed Quercus(Quercus petraea L.)and Fagus(Fagus orientalis L.)stands.Litter was sampled on a monthly basis for 1 year and stored in litterbags of different mesh sizes.The experimental objective was to test the effect of mesh size on litter decomposition,decomposition rates of litter,and diversity of the invertebrate fauna between the two types of stands.Decomposition rates were measured by filling three fiber litterbags of different mesh sizes with pure Quercus litter(3 g)left in the pure Quercus stand,and litterbags with Fagus litter(3 g)were left in the pure Fagus stand.Mixed litter samples were prepared by mixing of equal amounts of each litter in the same litterbag and leaving them in the mixed stand.The residual mass of litter from the pure Quercus stand was significantly lower in fine-and coarse-mesh bags than in the medium-mesh bags in pure the Fagus stand.Carbon and nitrogen levels in the pure Quercus litter were significantly different among the mesh sizes at the end of the incubation period.Macroarthropods from 27 taxa were collected from pitfall traps every month.Their relative numbers differed significantly between the pure and mixed-stand litter samples.Litter-dwelling Isotomidae(Collembola)and Mesostigmata(Acarina),and soil-dwelling Mesostigmata were the most numerous in the mixed stand.It is significant that the abundance of macroarthropods contributed to the mass loss of litter in both the medium and coarse mesh sizes in the mixed stand,but did not significantly affect the mass of litter in the pure stands.In the mixed stand,there was a negative correlation between litter mass loss and total number of microarthropods in all mesh sizes.Mixed-stand litter decomposed more slowly than pure-stand litter.展开更多
Soil fauna decompose litter, whereas land use changes may significantly alter the composition and structure of soil fauna assemblages. However, little is known of the effects of land-use on the contribution of soil fa...Soil fauna decompose litter, whereas land use changes may significantly alter the composition and structure of soil fauna assemblages. However, little is known of the effects of land-use on the contribution of soil fauna to litter decomposition. We studied the impacts of soil fauna on the decomposition of litter from poplar trees under three different land uses （i.e. poplar-crop integrated system, poplar plantation, and cropland）, from December 2013 to December 2014, in a coastal area of Northern Jiangsu Province. We collected litter samples in litterbags with three mesh sizes （5, 1 and 0. 01 mm, respectively） to quantify the contribution of various soil fauna to the decomposition of poplar leaf litter. Litter decomposition rates differed significantly by land use and were highest in the cropland, intermediate in the poplar-crop integrated system, and lowest in the poplar plantation. Soil fauna in the poplar-crop integrated system was characterized by the highest numbers of taxa and individuals, and highest Margalef＇s diversity, which suggested that agro-forestry ecosystems may support a greater quantity, distribution, and biodiversity of soil fauna than can single-species agriculture or plantation forestry. The individuals and groups of soil fauna in the macro-mesh litterbags were higher than in the meso-mesh litterbags underthe same land use types. The average contribution rate of meso- and micro-fauna to litter decomposition was 18.46%, which was higher than the contribution rate of macro-fauna （3.31%）. The percentage of remaining litter mass was inversely related to the density of the soil fauna （P 〈 0.05） in poplar plantations; however, was unrelated in the poplar-crop integrated system and cropland. This may have been the result of anthropogenic interference in poplar-crop integrated systems and croplands. Our study suggested that when land-use change alters vegetation types, it can affect species composition and the structure of soil fauna assemblages, which, in turn, affects litter decomposition.展开更多
Pampus argenteus and Pampus chinensis form the high-value demersal Pomfret fishery of Bangladesh.But,due to a monotonic decline in catches over the last five years,it is essential to explore the current stock status c...Pampus argenteus and Pampus chinensis form the high-value demersal Pomfret fishery of Bangladesh.But,due to a monotonic decline in catches over the last five years,it is essential to explore the current stock status concerning the removal rate to ensure the sustainability of this fishery.Therefore,given the reliability and minimal data requirements,this study employed an extended Bayesian State-Space Surplus Production Model,JABBA(Just Another Bayesian Biomass Assessment),to assess the stock rigorously.The results revealed that the stock biomass of the Pomfret fishery in the final year of the time series is significantly lower than BMSY,the biomass required to produce MSY.Consequently,this study recommends a yearly catch limit(TAC)of 10,000 metric tons to prevent further depletion of the stock biomass.Furthermore,to avoid growth overfishing by allowing all immature fishes to reproduce at least once before being caught,this study also calculated the optimum length(Lopt)for catch for both species at which biologically maximum yield and revenue can be obtained.The estimated Lopt is 25 cm for P.argenteus and 30 cm for P.chinensis,and not to capture fishes with lengths lower than these limits,this study further calculated the minimum mesh size limits for gill and set bag nets is 7.5 cm.Though the mesh size regulation was estimated using length-based reference points derived from an empirical equation,this regulation can be used as an associate reference point when TAC is applied to assure the sustainability of this fishery.展开更多
In south-eastern Australia,the same baited,round traps(comprising 50–57-mm mesh netting)are used to target giant mud,Scylla serrata and blue swimmer crabs,Portunus armatus in spatially separated fisheries.Both fisher...In south-eastern Australia,the same baited,round traps(comprising 50–57-mm mesh netting)are used to target giant mud,Scylla serrata and blue swimmer crabs,Portunus armatus in spatially separated fisheries.Both fisheries are characterised by the common,problematic discarding of undersized portunids(<85 and 65 mm carapace length;CL for S.serrata and P.armatus)and fish(yellowfin bream,Acanthopagrus australis).This poor selectivity was addressed here in two experiments assessing the utility of(1)traps partially or completely covered in larger mesh(91 mm to match the minimum legal size of the smaller P.armatus),and then(2)any cumulative benefits of fitting species-specific escape gaps.In experiment 1,there were no differences among catches of legal-sized portunids associated with either partial,or complete trap coverage with larger mesh.Irrespective of mesh coverage,both designs of 91-mm traps also retained significantly fewer(by up to 42%)undersized P.armatus and A.australis.In experiment 2,replicate traps completely covered in 91-mm mesh were tested against conventional traps comprising 56-mm mesh,and traps with the same mesh sizes,but also three escape gaps configured for either S.serrata(46×120 mm)or P.armatus(36×120 mm)(i.e.four treatments in total).All modified traps maintained catches of legal-sized S.serrata,and only the 91-mm traps with escape gaps caught fewer legal-sized P.armatus.Fewer undersized S.serrata,P.armatus and A.australis(mean catches reduced by up to 49%)were retained in all larger-meshed than small-meshed traps,and in all of those traps with escape gaps(by up to 95%)than without.While there were no significant cumulative benefits of escape gaps in largermeshed traps(measured by a statistical interaction),there was a trend of fewer unwanted catches overall.These data support configuring portunid traps with mesh sizes matching the morphology of the smallest legal-sized target species.But,simply retroactively fitting escape gaps in existing,smaller-meshed traps will also realize positive selectivity benefits.展开更多
In this paper,a scaling law relating the mesh size to the Reynolds number was proposed to ensure consistent results for large eddy simulation(LES)as the Reynolds number was varied.The grid size scaling law was develop...In this paper,a scaling law relating the mesh size to the Reynolds number was proposed to ensure consistent results for large eddy simulation(LES)as the Reynolds number was varied.The grid size scaling law was developed by analyzing the lengthscale of the turbulent motion by using DNS data from the literature.The wall-resolving LES was then applied to a plane channel flow to validate the scaling law.The scaling law was tested at different Reynolds numbers(Ret=395,590 and 1000),and showed good results compared to direct numerical simulation(DNS)in terms of mean flow and various turbulent statistics.The velocity spectra analysis shows the evidence of the Kolmogorov–5/3 inertial subrange and verifies that the current LES can resolve the bulk of the turbulent kinetic energy by satisfying the grid scaling law.Meanwhile,the near-wall turbulent flow structures can also be well captured.Reasonably accurate predictions can thus be obtained for flows at even higher Reynolds numbers with significantly lower computational costs compared to DNS by applying the mesh scaling law.展开更多
An experimental and numerical investigation on the aeroengine blade/case containment analysis is presented. Blade out containment capability analysis is an essential step in the new aeroengine design, but containment ...An experimental and numerical investigation on the aeroengine blade/case containment analysis is presented. Blade out containment capability analysis is an essential step in the new aeroengine design, but containment tests are time-consuming and incur significant costs; thus, developing a short-period and low-cost numerical method is warranted. Using explicit nonlinear dynamic finite element analysis software, the present study numerically investigated the high-speed impact process for simulated blade containment tests which were carried out on high-speed spin testing facility. A number of simulations were conducted using finite element models with different mesh sizes and different values of both the contact penalty factor and the friction coefficient. Detailed comparisons between the experimental and numerical results reveal that the mesh size and the friction coefficient have a considerable impact on the results produced. It is shown that a finer mesh will predict lower containment capability of the case, which is closer to the test data. A larger value of the friction coefficient also predicts lower containment capability. However, the contact penalty factor has little effect on the simulation results if it is large enough to avoid false penetration.展开更多
In the 1980s,China’s offshore marine fishery resources declined,thus fishing gear selectivity gradually became a focus of scientific fishery research.Studies of fishing gear selectivity mainly focus on five kinds of ...In the 1980s,China’s offshore marine fishery resources declined,thus fishing gear selectivity gradually became a focus of scientific fishery research.Studies of fishing gear selectivity mainly focus on five kinds of fishing gear:trawls,shrimp beam trawls,stow nets,gillnets,and pots.Cover net method is the main method used in the comparative study of codend selectivity of both trawls and stow nets.These results showed that(1)Bottom trawls,targeting Larimichthys polyactis(the Little yellow croaker)and Trichiurus haumela(the Hairtail),should have a minimum mesh size of the codend no less than 60 mm in the Yellow and East China Seas.While the codend should use a square mesh with a minimum mesh size of 40 mm due to the variety of targeted species in the South China Sea.(2)Pair pelagic trawls,targeting pelagic species such as Engraulis japonicus(the Japanese anchovy),Pampus argenteus(the Silvery pomfret),Scomberomorus niphonius(the Spanish mackerel),as well as bottom species such as L.polyactis and T.haumela,should have a minimum mesh size of the codend no less than 56 mm in the Yellow Sea.(3)Shrimp beam trawls should use shrimp/fish separator devices(e.g.,separator panels,vertical separator panels,and sorting grids)to improve intra-species selectivity and reduce by-catch of non-target fish.(4)Canvas stow nets,targeting L.polyactis and T.haumela,should have a minimum mesh size of the codend no less than 55 mm.(5)Gillnets,the minimum mesh size should be determined for catching traditional economic species,but also the optimal mesh size for newly developed species.Such as,gillnets with mesh size of 35-38.71 mm targeting Harpodon nehereus(the Bombay duck),55 mm targeting L.polyactis and Nemipterus virgatus(the Golden threadfin bream),72 mm targeting Dentex tumifrons(the yellow sea breams)or Scomberomorus commersoni with body length of 280 mm,100 mm targeting P.argenteus,104 mm or 146 mm targeting 2-3 year or 6-7 year S.niphonius,120 mm targeting S.commersoni with body length of 380 mm,and 144 mm targeting Pampus chinensis(the Chinese pomfret).(6)Pots,the steel-framed round pots targeting Portunus trituberculatus(the swimming crab)should have a 33 mm height of escape vent or an 8 cm diameter escape hole,and the steel-framed round pots or accordion-shaped trap targeting Charybdis japonica(the Asian paddle crabs)should have a 30 mm height of escape vent installed on the side of pots.These results of fishing gear selectivity from the scientific basis for the implementation of fishing gear access systems,especially for identifying the minimum mesh size of fishing gear.In the future,the Fisheries Research Institute of China should conduct long-term investigations of selectivity in trans areas.Developing fishing gear access systems that are in line with a sustainable development is of great significance for the conservation and restoration of offshore fishery resources in China.展开更多
Hydrogels are cross-linked polymeric networks swollen in water,physiological aqueous solutions or biological fluids.They are synthesized by a wide range of polymerization methods that allow for the introduction of lin...Hydrogels are cross-linked polymeric networks swollen in water,physiological aqueous solutions or biological fluids.They are synthesized by a wide range of polymerization methods that allow for the introduction of linear and branched units with specific molecular characteristics.In addition,they can be tuned to exhibit desirable chemical characteristics including hydrophilicity or hydrophobicity.The synthesized hydrogels can be anionic,cationic,or amphiphilic and can contain multifunctional crosslinks,junctions or tie points.Beyond these characteristics,hydrogels exhibit compatibility with biological systems,and can be synthesized to render systems that swell or collapse in response to external stimuli.This versatility and compatibility have led to better understanding of how the hydrogel’s molecular architecture will affect their physicochemical,mechanical and biological properties.We present a critical summary of the main methods to synthesize hydrogels,which define their architecture,and advanced structural characteristics for macromolecular/biological applications.展开更多
基金the funding supports of the National Key Research and Development Plan,China(Grant No.2022YFC3801800)National Natural Science Foundation of China(Grant Nos.52038010 and 52078368)。
文摘In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.
基金Supported by the Laoshan Laboratory(Nos.LSKJ 202203700,LSKJ 202203704,LSKJ 202204005)the National Natural Science Foundation of China(NSFC)(Nos.42076166,42130411)the NSFC Ship Time Sharing Project(No.42149901)。
文摘Meroplankton play a crucial role in both benthic and pelagic ecosystems.Existing quantitative research on estimating the quantities of meroplankton groups is both underrepresented and inaccurate.To investigate and evaluate the influence of varying mesh sizes(505 and 160μm)on the sampling efficiency of meroplankton,we conducted an examination using two commonly used plankton nets during the spring season in the Southern Yellow Sea(SYS).Our study revealed a total of 12 meroplankton groups,with 9 groups identified in the 505-μm mesh nets and 11 groups in the 160-μm mesh nets.The results demonstrated the superior collection efficiency of the 160-μm net compared to the 505-μm net across the majority of meroplankton groups.Furthermore,we focused on exploring the abundance,distribution patterns,and realized niches of meroplankton collected by the two mesh size nets,and observed that the distribution of meroplankton closely resembled the distribution of possible benthic adults in the SYS.Correlation analysis of the six dominant groups collected in the 160-μm mesh nets revealed that seawater temperature and salinity emerged as the key environmental factors driving variations in meroplankton abundance within the SYS.This study also found that a smaller mesh size net does not necessarily capture meroplankton more comprehensively.A comprehensive understanding of the ecological characteristics of meroplankton requires the combination of two types of nets for research.Our research significantly advances our understanding of the quantification,abundance,and distribution of meroplankton,serving as a valuable contribution to the broader landscape of detailed quantitative meroplankton studies.
基金Supported by National Natural Science Foundation of China (No.50638030, 50528808)the National Key Technologies R&D Program of China (No.2006BAJ13B02)the Australian Research Council (No.DP0774061).
文摘Numerical method is popular in analysing the blast wave propagation and interaction with structures.However,because of the extremely short duration of blast wave and energy trans-mission between different grids,the numerical results are sensitive to the finite element mesh size.Previous numerical simulations show that a mesh size acceptable to one blast scenario might not be proper for another case,even though the difference between the two scenarios is very small,indicating a simple numerical mesh size convergence test might not be enough to guarantee accu-rate numerical results.Therefore,both coarse mesh and fine mesh were used in different blast scenarios to investigate the mesh size effect on numerical results of blast wave propagation and interaction with structures.Based on the numerical results and their comparison with field test re-sults and the design charts in TM5-1300,a numerical modification method was proposed to correct the influence of the mesh size on the simulated results.It can be easily used to improve the accu-racy of the numerical results of blast wave propagation and blast loads on structures.
基金The National Key Research and Development Program of China under contract No.2018YFD0900702the K.C.Wong Magna Fund in Ningbo University(SS)。
文摘Zooplankton samples were collected using 505, 160 and 77 μm mesh nets around a power plant during four seasons in 2011. We measured total length of zooplankton and divided zooplankton into seven size classes in order to explore how zooplankton community size-structure might be altered by thermal discharge from power plant. The total length of zooplankton varied from 93.7 to 40 074.7 μm. The spatial distribution of mesozooplankton(200-2 000 μm) populations were rarely affected by thermal discharge, while macro-(2 000-10 000 μm)and megalo-zooplankton(>10 000 μm) had an obvious tendency to migrate away from the outfall of power plant.Thus, zooplankton community tended to become smaller and biodiversity reduced close to power plant.Moreover, we compared the zooplankton communities in three different mesh size nets. Species richness,abundance, evenness index and Shannon-Wiener diversity index of the 505 μm mesh size were significantly lower than those recorded from the 160 and 77 μm mesh size. Average zooplankton abundance was highest in the 77 μm mesh net((27 690.0±1 633.7) ind./m^3), followed by 160 μm mesh net((9 531.1±1 079.5) ind./m^3), and lowest in 505 μm mesh net((494.4±104.7) ind./m^3). The ANOSIM and SIMPER tests confirmed that these differences were mainly due to small zooplankton and early developmental stages of zooplankton. It is the first time to use the 77 μm mesh net to sample zooplankton in such an environment. The 77 μm mesh net had the overwhelming abundance of the copepod genus Oithona, as an order of magnitude greater than recorded for 160 μm mesh net and 100% loss through the 505 μm mesh net. These results indicate that the use of a small or even multiple sampling net is necessary to accurately quantify entire zooplankton community around coastal power plant.
基金the National Natural Science Foundation of China (10602002 and 10772005)
文摘Sphere packing is an attractive way to generate high quality mesh. Several algorithms have been proposed in this topic, however these algorithms are not sufficiently fast for large scale problems. The paper presents an efficient sphere packing algorithm which is much faster and appears to be the most practical among all sphere packing methods presented so far for mesh generation. The algorithm packs spheres inside a domain using advancing front method. High efficiency has resulted from a concept of 4R measure, which localizes all the computations involved in the whole sphere packing process.
基金supported by the Scientific Research Projects Coordination Unit of Istanbul University,Project number3122
文摘Arthropod assemblages and decomposition rates were compared in the litter of pure and mixed Quercus(Quercus petraea L.)and Fagus(Fagus orientalis L.)stands.Litter was sampled on a monthly basis for 1 year and stored in litterbags of different mesh sizes.The experimental objective was to test the effect of mesh size on litter decomposition,decomposition rates of litter,and diversity of the invertebrate fauna between the two types of stands.Decomposition rates were measured by filling three fiber litterbags of different mesh sizes with pure Quercus litter(3 g)left in the pure Quercus stand,and litterbags with Fagus litter(3 g)were left in the pure Fagus stand.Mixed litter samples were prepared by mixing of equal amounts of each litter in the same litterbag and leaving them in the mixed stand.The residual mass of litter from the pure Quercus stand was significantly lower in fine-and coarse-mesh bags than in the medium-mesh bags in pure the Fagus stand.Carbon and nitrogen levels in the pure Quercus litter were significantly different among the mesh sizes at the end of the incubation period.Macroarthropods from 27 taxa were collected from pitfall traps every month.Their relative numbers differed significantly between the pure and mixed-stand litter samples.Litter-dwelling Isotomidae(Collembola)and Mesostigmata(Acarina),and soil-dwelling Mesostigmata were the most numerous in the mixed stand.It is significant that the abundance of macroarthropods contributed to the mass loss of litter in both the medium and coarse mesh sizes in the mixed stand,but did not significantly affect the mass of litter in the pure stands.In the mixed stand,there was a negative correlation between litter mass loss and total number of microarthropods in all mesh sizes.Mixed-stand litter decomposed more slowly than pure-stand litter.
基金supported by the National Basic Research Program of China(973 Program,2012CB416904)partially supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘Soil fauna decompose litter, whereas land use changes may significantly alter the composition and structure of soil fauna assemblages. However, little is known of the effects of land-use on the contribution of soil fauna to litter decomposition. We studied the impacts of soil fauna on the decomposition of litter from poplar trees under three different land uses （i.e. poplar-crop integrated system, poplar plantation, and cropland）, from December 2013 to December 2014, in a coastal area of Northern Jiangsu Province. We collected litter samples in litterbags with three mesh sizes （5, 1 and 0. 01 mm, respectively） to quantify the contribution of various soil fauna to the decomposition of poplar leaf litter. Litter decomposition rates differed significantly by land use and were highest in the cropland, intermediate in the poplar-crop integrated system, and lowest in the poplar plantation. Soil fauna in the poplar-crop integrated system was characterized by the highest numbers of taxa and individuals, and highest Margalef＇s diversity, which suggested that agro-forestry ecosystems may support a greater quantity, distribution, and biodiversity of soil fauna than can single-species agriculture or plantation forestry. The individuals and groups of soil fauna in the macro-mesh litterbags were higher than in the meso-mesh litterbags underthe same land use types. The average contribution rate of meso- and micro-fauna to litter decomposition was 18.46%, which was higher than the contribution rate of macro-fauna （3.31%）. The percentage of remaining litter mass was inversely related to the density of the soil fauna （P 〈 0.05） in poplar plantations; however, was unrelated in the poplar-crop integrated system and cropland. This may have been the result of anthropogenic interference in poplar-crop integrated systems and croplands. Our study suggested that when land-use change alters vegetation types, it can affect species composition and the structure of soil fauna assemblages, which, in turn, affects litter decomposition.
文摘Pampus argenteus and Pampus chinensis form the high-value demersal Pomfret fishery of Bangladesh.But,due to a monotonic decline in catches over the last five years,it is essential to explore the current stock status concerning the removal rate to ensure the sustainability of this fishery.Therefore,given the reliability and minimal data requirements,this study employed an extended Bayesian State-Space Surplus Production Model,JABBA(Just Another Bayesian Biomass Assessment),to assess the stock rigorously.The results revealed that the stock biomass of the Pomfret fishery in the final year of the time series is significantly lower than BMSY,the biomass required to produce MSY.Consequently,this study recommends a yearly catch limit(TAC)of 10,000 metric tons to prevent further depletion of the stock biomass.Furthermore,to avoid growth overfishing by allowing all immature fishes to reproduce at least once before being caught,this study also calculated the optimum length(Lopt)for catch for both species at which biologically maximum yield and revenue can be obtained.The estimated Lopt is 25 cm for P.argenteus and 30 cm for P.chinensis,and not to capture fishes with lengths lower than these limits,this study further calculated the minimum mesh size limits for gill and set bag nets is 7.5 cm.Though the mesh size regulation was estimated using length-based reference points derived from an empirical equation,this regulation can be used as an associate reference point when TAC is applied to assure the sustainability of this fishery.
基金This study was funded by Hunter Local Land Services and the NSW Department of Primary Industries,and would not have been possible without the assistance of Wallis Lake commercial fishers,and especially,Malcolm,Adrian and Danny.
文摘In south-eastern Australia,the same baited,round traps(comprising 50–57-mm mesh netting)are used to target giant mud,Scylla serrata and blue swimmer crabs,Portunus armatus in spatially separated fisheries.Both fisheries are characterised by the common,problematic discarding of undersized portunids(<85 and 65 mm carapace length;CL for S.serrata and P.armatus)and fish(yellowfin bream,Acanthopagrus australis).This poor selectivity was addressed here in two experiments assessing the utility of(1)traps partially or completely covered in larger mesh(91 mm to match the minimum legal size of the smaller P.armatus),and then(2)any cumulative benefits of fitting species-specific escape gaps.In experiment 1,there were no differences among catches of legal-sized portunids associated with either partial,or complete trap coverage with larger mesh.Irrespective of mesh coverage,both designs of 91-mm traps also retained significantly fewer(by up to 42%)undersized P.armatus and A.australis.In experiment 2,replicate traps completely covered in 91-mm mesh were tested against conventional traps comprising 56-mm mesh,and traps with the same mesh sizes,but also three escape gaps configured for either S.serrata(46×120 mm)or P.armatus(36×120 mm)(i.e.four treatments in total).All modified traps maintained catches of legal-sized S.serrata,and only the 91-mm traps with escape gaps caught fewer legal-sized P.armatus.Fewer undersized S.serrata,P.armatus and A.australis(mean catches reduced by up to 49%)were retained in all larger-meshed than small-meshed traps,and in all of those traps with escape gaps(by up to 95%)than without.While there were no significant cumulative benefits of escape gaps in largermeshed traps(measured by a statistical interaction),there was a trend of fewer unwanted catches overall.These data support configuring portunid traps with mesh sizes matching the morphology of the smallest legal-sized target species.But,simply retroactively fitting escape gaps in existing,smaller-meshed traps will also realize positive selectivity benefits.
文摘In this paper,a scaling law relating the mesh size to the Reynolds number was proposed to ensure consistent results for large eddy simulation(LES)as the Reynolds number was varied.The grid size scaling law was developed by analyzing the lengthscale of the turbulent motion by using DNS data from the literature.The wall-resolving LES was then applied to a plane channel flow to validate the scaling law.The scaling law was tested at different Reynolds numbers(Ret=395,590 and 1000),and showed good results compared to direct numerical simulation(DNS)in terms of mean flow and various turbulent statistics.The velocity spectra analysis shows the evidence of the Kolmogorov–5/3 inertial subrange and verifies that the current LES can resolve the bulk of the turbulent kinetic energy by satisfying the grid scaling law.Meanwhile,the near-wall turbulent flow structures can also be well captured.Reasonably accurate predictions can thus be obtained for flows at even higher Reynolds numbers with significantly lower computational costs compared to DNS by applying the mesh scaling law.
基金supported by the Zhejiang Provincial Natural Science Foundation of China (No. Y1090245)the Chinese Aviation Propulsion Technology Development Program (No. APTD-11)
文摘An experimental and numerical investigation on the aeroengine blade/case containment analysis is presented. Blade out containment capability analysis is an essential step in the new aeroengine design, but containment tests are time-consuming and incur significant costs; thus, developing a short-period and low-cost numerical method is warranted. Using explicit nonlinear dynamic finite element analysis software, the present study numerically investigated the high-speed impact process for simulated blade containment tests which were carried out on high-speed spin testing facility. A number of simulations were conducted using finite element models with different mesh sizes and different values of both the contact penalty factor and the friction coefficient. Detailed comparisons between the experimental and numerical results reveal that the mesh size and the friction coefficient have a considerable impact on the results produced. It is shown that a finer mesh will predict lower containment capability of the case, which is closer to the test data. A larger value of the friction coefficient also predicts lower containment capability. However, the contact penalty factor has little effect on the simulation results if it is large enough to avoid false penetration.
基金This study was financially supported by the National Natural Science Foundation of China(Grand No.31902426)the Shanghai Sailing Program(19YF1419800)the Special project for the exploitation and utilization of Antarctic biological resources of the Ministry of Agriculture and Rural Affairs.
文摘In the 1980s,China’s offshore marine fishery resources declined,thus fishing gear selectivity gradually became a focus of scientific fishery research.Studies of fishing gear selectivity mainly focus on five kinds of fishing gear:trawls,shrimp beam trawls,stow nets,gillnets,and pots.Cover net method is the main method used in the comparative study of codend selectivity of both trawls and stow nets.These results showed that(1)Bottom trawls,targeting Larimichthys polyactis(the Little yellow croaker)and Trichiurus haumela(the Hairtail),should have a minimum mesh size of the codend no less than 60 mm in the Yellow and East China Seas.While the codend should use a square mesh with a minimum mesh size of 40 mm due to the variety of targeted species in the South China Sea.(2)Pair pelagic trawls,targeting pelagic species such as Engraulis japonicus(the Japanese anchovy),Pampus argenteus(the Silvery pomfret),Scomberomorus niphonius(the Spanish mackerel),as well as bottom species such as L.polyactis and T.haumela,should have a minimum mesh size of the codend no less than 56 mm in the Yellow Sea.(3)Shrimp beam trawls should use shrimp/fish separator devices(e.g.,separator panels,vertical separator panels,and sorting grids)to improve intra-species selectivity and reduce by-catch of non-target fish.(4)Canvas stow nets,targeting L.polyactis and T.haumela,should have a minimum mesh size of the codend no less than 55 mm.(5)Gillnets,the minimum mesh size should be determined for catching traditional economic species,but also the optimal mesh size for newly developed species.Such as,gillnets with mesh size of 35-38.71 mm targeting Harpodon nehereus(the Bombay duck),55 mm targeting L.polyactis and Nemipterus virgatus(the Golden threadfin bream),72 mm targeting Dentex tumifrons(the yellow sea breams)or Scomberomorus commersoni with body length of 280 mm,100 mm targeting P.argenteus,104 mm or 146 mm targeting 2-3 year or 6-7 year S.niphonius,120 mm targeting S.commersoni with body length of 380 mm,and 144 mm targeting Pampus chinensis(the Chinese pomfret).(6)Pots,the steel-framed round pots targeting Portunus trituberculatus(the swimming crab)should have a 33 mm height of escape vent or an 8 cm diameter escape hole,and the steel-framed round pots or accordion-shaped trap targeting Charybdis japonica(the Asian paddle crabs)should have a 30 mm height of escape vent installed on the side of pots.These results of fishing gear selectivity from the scientific basis for the implementation of fishing gear access systems,especially for identifying the minimum mesh size of fishing gear.In the future,the Fisheries Research Institute of China should conduct long-term investigations of selectivity in trans areas.Developing fishing gear access systems that are in line with a sustainable development is of great significance for the conservation and restoration of offshore fishery resources in China.
文摘Hydrogels are cross-linked polymeric networks swollen in water,physiological aqueous solutions or biological fluids.They are synthesized by a wide range of polymerization methods that allow for the introduction of linear and branched units with specific molecular characteristics.In addition,they can be tuned to exhibit desirable chemical characteristics including hydrophilicity or hydrophobicity.The synthesized hydrogels can be anionic,cationic,or amphiphilic and can contain multifunctional crosslinks,junctions or tie points.Beyond these characteristics,hydrogels exhibit compatibility with biological systems,and can be synthesized to render systems that swell or collapse in response to external stimuli.This versatility and compatibility have led to better understanding of how the hydrogel’s molecular architecture will affect their physicochemical,mechanical and biological properties.We present a critical summary of the main methods to synthesize hydrogels,which define their architecture,and advanced structural characteristics for macromolecular/biological applications.
