Soil fertility and forest structure influence tree carbon stocks.However,it remains unclear how tree mycorrhizal types affect these relationships.This study addressed the question of how aboveground and belowground tr...Soil fertility and forest structure influence tree carbon stocks.However,it remains unclear how tree mycorrhizal types affect these relationships.This study addressed the question of how aboveground and belowground tree carbon stocks in soils with different mycorrhizal types are affected by soil fertility and forest structure.Tree demographic data were used from a 21.12-ha study area collected over a ten-year period(2009-2019),covering 43species of woody plants and more than 50,000 individuals.Relationships between tree carbon stock,soil fertility and forest structure(stand density,diameter variation,species diversity and spatial distribution)were examined,as well as whether these relationships differed between arbuscular mycorrhiza and ectomycorrhizal mycorrhiza groups in a typical temperate conifer and broad-leaved mixed forest.We found that total tree carbon stock was positively impacted by variations in stand density and tree diameter but negatively influenced by soil fertility,tree species diversity and uniform angle index.Soil fertility promoted carbon stock of trees associated with arbuscular mycorrhiza(AM)but inhibited the carbon stock of trees with ectomycorrhizal mycorrhiza fungi(EcM).Carbon stock of AM trees was mainly influenced by soil fertility,while carbon stock of EcM trees was influenced by stand density.Our findings show that mycorrhizae types mediate the impact of stand structure and soil fertility on tree carbon stocks and provides new evidence on how forest tree carbon stocks may be enhanced based on the types of mycorrhizal associations.Tree species with different mycorrhizal types can be managed in different ways.展开更多
Sacred forests play a valuable role in the conservation of local biodiversity and provide numerous ecosystem services in Cameroon. The aim of this study was to estimate floristic diversity, stand structures and carbon...Sacred forests play a valuable role in the conservation of local biodiversity and provide numerous ecosystem services in Cameroon. The aim of this study was to estimate floristic diversity, stand structures and carbon stocks in the sacred forests of Bandrefam and Batoufam (western Cameroon). The floristic inventory and the stand structures were carried out in 25 m × 25 m plots for individuals with diameters greater than 10 cm;5 m × 5 m for individuals with diameters less than 10 cm. Carbon stocks were estimated using the non-destructive method and allometric equations. The floristic inventory identified 65 species divided into 57 genera and 30 families in the Bandrefam sacred forest and 45 species divided into 42 genera and 27 families in the Batoufam sacred forest. In the Bandrefam, the most important families are Phyllanthaceae (53.98%), Moraceae (21.69%), Lamiaceae (20.15%). At Batoufam, the most important families are Phyllanthaceae (39.73%), Fabaceae (28.47%), Araliaceae (23.77%). Malacantha alnifolia (55.14%), Vitex grandifolia (18.43%), Bosqueia angolensis (15.06%) were the most important species in Bandrefam. Otherwise, Malacantha alnifolia (28%), Polyscias fulva (22.73%), Psychotria sp. (21.28%) were the most important in Batoufam. The Bandrefam sacred forest has the highest tree density (2669 stems/ha). Total carbon stock is 484.88 ± 2.28 tC/ha at Batoufam and 313.95 ± 0.93 tC/ha at Bandrefam. The economic value varies between 5858.04 ± 27.62 USD/ha in Batoufam sacred forest and 3788.51 ± 11.26 USD/ha in Bandrefam sacred forest. The number of individuals and small-diameter trees has little influence on the carbon stocks in the trees. Medium-diameter trees store the most carbon, and very large-diameter trees, which are very poorly represented, store less carbon. In another way, wood density and the basal areas influence the carbon storage of the trees.展开更多
In this paper,it is first briefly described the basic situation and current policies of state owned enterprise reform in China.Then the major issues in the reform process are identified,the possible solutions in term...In this paper,it is first briefly described the basic situation and current policies of state owned enterprise reform in China.Then the major issues in the reform process are identified,the possible solutions in terms of reengineering stock equity structure and state share circulation are discussed,and finally some suggestions are made for the further state owned enterprise reform.Basing on the theory on the modern corporation system,relevant experiences of market economy nations and the practice of Chinese enterprise system reform.The approaches to determine the proportion of state share in the future corporations are proposed.Since the public ownership is not ideologically appropriate,the establishment of social security fund and mutual fund investment companies are suggested as new and acceptable pattern of public ownership.It is believed that these companies will be the major institutional shareholders in the future corporations.Their stock equity structure would mainly consist of institutional shareholders,which will be both consistent with international norms of modern corporations and with socialist public ownership with Chinese characteristics.展开更多
Oxygen and carbon isotope ratios（δ^（18）O and δ^（13）C） in otoliths were used to identify the stock structure of small yellow croaker,Larimichthys polyactis.Otoliths were collected from fish at five locations ac...Oxygen and carbon isotope ratios（δ^（18）O and δ^（13）C） in otoliths were used to identify the stock structure of small yellow croaker,Larimichthys polyactis.Otoliths were collected from fish at five locations across the Yellow Sea and the Bohai Sea representing most of their distributional range and fisheries areas.The significant differences in the isotopic signatures showed that the five locations could be chemically distinguished and clearly separated,indicating stock subdivision.Correlation of δ^（18）O and δ^（13）C values suggested that population of L.polyactis could be divided into the Bohai Sea group,the southern Yellow Sea group and the central Yellow Sea group.Discriminant analysis of δ^（18）O and δ^（13）C values demonstrated a high significant difference with 85.7% classification accuracy.The spatial separation of L.polyactis indicated a complex stock structure across the Yellow Sea and the Bohai Sea.These results indicate that optimal fisheries management may require a comprehensive consideration on the current spatial arrangements.This study has provided further evidence that measurement of the stable isotopes ratios in otolith can be a valuable tool in the delineation of fishery management units.展开更多
We investigate a stage-structured delayed predator-prey model with impulsive stocking on prey and continuous harvesting on predator. According to the fact of biological resource management, we improve the assumption o...We investigate a stage-structured delayed predator-prey model with impulsive stocking on prey and continuous harvesting on predator. According to the fact of biological resource management, we improve the assumption of a predator-prey model with stage structure for predator population that each individual predator has the same ability to capture prey. It is assumed that the immature and mature individuals of the predator population are divided by a fixed age, and immature predator population does not have the ability to attach prey. Sufficient conditions are obtained, which guarantee the global attractivity of predator-extinction periodic solution and the permanence of the system. Our results show that the behavior of impulsive stocking on prey plays an important role for the permanence of the system, and provide tactical basis for the biological resource management. Numerical analysis is presented to illuminate the dynamics of the system.展开更多
The present study examines the impact of short-term public opinion sentiment on the secondary market,with a focus on the potential for such sentiment to cause dramatic stock price fluctuations and increase investment ...The present study examines the impact of short-term public opinion sentiment on the secondary market,with a focus on the potential for such sentiment to cause dramatic stock price fluctuations and increase investment risk.The quantification of investment sentiment indicators and the persistent analysis of their impact has been a complex and significant area of research.In this paper,a structured multi-head attention stock index prediction method based adaptive public opinion sentiment vector is proposed.The proposedmethod utilizes an innovative approach to transform numerous investor comments on social platforms over time into public opinion sentiment vectors expressing complex sentiments.It then analyzes the continuous impact of these vectors on the market through the use of aggregating techniques and public opinion data via a structured multi-head attention mechanism.The experimental results demonstrate that the public opinion sentiment vector can provide more comprehensive feedback on market sentiment than traditional sentiment polarity analysis.Furthermore,the multi-head attention mechanism is shown to improve prediction accuracy through attention convergence on each type of input information separately.Themean absolute percentage error(MAPE)of the proposedmethod is 0.463%,a reduction of 0.294% compared to the benchmark attention algorithm.Additionally,the market backtesting results indicate that the return was 24.560%,an improvement of 8.202% compared to the benchmark algorithm.These results suggest that themarket trading strategy based on thismethod has the potential to improve trading profits.展开更多
Capital structure is regarded as the combination of debt and equity firms used to finance operations and investments.The choice of capital structure significantly impacts a company’s cost of capital,profitability,and...Capital structure is regarded as the combination of debt and equity firms used to finance operations and investments.The choice of capital structure significantly impacts a company’s cost of capital,profitability,and risk profile.Among a series of factors that affect capital structure,this paper focuses on stock returns and market timing.In this review,an array of papers is analyzed to summarize what current research claims regarding the influence of stock returns and market timing on capital structure.This paper centers on the stock return and market timing theories and also discusses other theories like the trade-off theory,the pecking order theory,and the signaling theory.展开更多
Various population structures or spatial heterogeneities in population distribution have been an important source of model misspecification and have had an impact on estimation performance in fisheries stock assessmen...Various population structures or spatial heterogeneities in population distribution have been an important source of model misspecification and have had an impact on estimation performance in fisheries stock assessment.In this study,we simulated the Indian Ocean albacore spatial heterogeneity in age-structure using Stock Synthesis according to the stage-dependent migration rate and region-dependent fishing mortality rate and generated the stock assessment data.Based on these data,we investigated the performances of different spatial configurations,selectivity curves and selections of CPUE(catch per unit effort)indices of the assessment models which were used to account for spatial heterogeneity.The results showed:(1)although the spatially explicit configurations,which exactly matched the operating model,provided unbiased and accurate estimates of relative spawning biomass,relative fishing mortality rate and maximum sustainable yield in all simulation scenarios,their performance may be very poor if there were mismatches between them and the operating model due to gaps in knowledge and data;(2)for spatially explicit assessment configuration,the correct boundary was required,but for non-spatially explicit assessment configuration,it seemed more important for analysts to partition the area to properly reflect the transition in field data and to effectively account for the impacts of ignoring the spatial structure by using the additional spatially referenced parameters;(3)although the areas-as-fleets methods and flexible time-varying selectivity curves could be used as better alternative approaches to account for spatial structure,these configurations could not completely eliminate the impacts of model misspecification and the quality of estimates of different quantities from the same assessment model may be inconsistent or the performance of the same assessment configuration may fluctuate significantly between simulation scenarios;(4)although the worst estimates could generally be avoided by using multiple CPUE indices,there were no best solutions to select or regenerate the CPUE indices to account for the impacts of the ignored spatial structure to obviously improve the quality of stock assessment.Compared with the results of assessment model configurations which are used to account for the spatial structure by different modelers,the performances of the configurations are always casespecific except for spatially explicit configurations which exactly match the operating model.In this sense,our study will not only provide some insights into the current Indian Ocean albacore stock assessment but also enrich existing knowledge regarding the performance of assessment configurations to account for spatial structure.展开更多
Primary forests are spatially diverse terrestrial ecosystems with unique characteristics,being naturally regenerative and heterogeneous,which supports the stability of their carbon storage through the accumulation of ...Primary forests are spatially diverse terrestrial ecosystems with unique characteristics,being naturally regenerative and heterogeneous,which supports the stability of their carbon storage through the accumulation of live and dead biomass.Yet,little is known about the interactions between biomass stocks,tree genus diversity and structure across a temperate montane primary forest.Here,we investigated the relationship between tree structure(variability in basal area and tree size),genus-level diversity(abundance,tree diversity)and biomass stocks in temperate primary mountain forests across Central and Eastern Europe.We used inventory data from726 permanent sample plots from mixed beech and spruce across the Carpathian Mountains.We used nonlinear regression to analyse the spatial variability in forest biomass,structure,and genus-level diversity and how they interact with plot-level tree age,disturbances,temperature and altitude.We found that the combined effects of genus and structural indices were important for addressing the variability in biomass across different spatial scales.Local processes in disturbance regimes and uneven tree age support forest hete rogeneity and the accumulation of live and dead biomass through the natural regeneration,growth and decay of the forest ecosystem.Structural complexities in basal area index,supporte d by genus-level abundance,positively influence total biomass stocks,which was modulated by tree age and disturbances.Spruce forests showed higher tree density and basal area than mixed beech forests,though mixed beech still contributes significantly to biomass across landscapes.Forest heterogeneity was strongly influenced by complexities in forest composition(tree genus diversity,structure).We addressed the importance of primary forests as stable carbon stores,achieved through structure and diversity.Safeguarding such ecosystems is critical for ensuring the stability of the primary forest,carbon store and biodiversity into the future.展开更多
Using sector-specific growth accounting method, this paper investigates the growth effect of inter-industry allocation of capital and labor in China. This paper has found that existing investment data are classified a...Using sector-specific growth accounting method, this paper investigates the growth effect of inter-industry allocation of capital and labor in China. This paper has found that existing investment data are classified according to investment entities rather than user entities and directly using such data for the measurement of capital inventory of various sectors will seriously overestimate the capital inventory of tertiary industry and lead to distorted conclusions of "structural burden" of capital allocation and its serious violation of the principle of efficiency. By excluding real estate sector, this paper has found that after the 1990 s, inter-industry capital allocation had been generally consistent with the principle of efficiency and the effect of capital allocation structure is not significant. Our estimates also found that the growth effect arising from the inter-industry allocation of labor since reform and opening up averages 0.63 percentage points, which is significantly positively correlated with residual economic growth rate and residual TFP and demonstrates a decade-long "reform cycle." According to the comparative study on the effect of labor allocation structure of 37 other countries and regions, by 2017, the effect of China's labor allocation structure will continue to remain in a relatively high stage; between 2017 and 2023, structural effect will significantly diminish and deceleration pressure will rise swiftly; after 2030, the effect of labor allocation structure will linger in a low level stage, when economy is likely to enter into a stage of low growth rate. These findings will help us better assess future economic growth tendencies.展开更多
Polynyas and their adjacent seasonal ice zones(SIZs)represent the most productive regions in the Southern Ocean,supporting unique food webs that are highly sensitive to climate change.Understanding the dynamics of phy...Polynyas and their adjacent seasonal ice zones(SIZs)represent the most productive regions in the Southern Ocean,supporting unique food webs that are highly sensitive to climate change.Understanding the dynamics of phytoplankton and the carbon pool in these areas is crucial for assessing the role of the Southern Ocean in global carbon cycling.During the late stage of an algal bloom,seawater samples at 14 stations were collected in the Amundsen Sea Polynya(ASP)and adjacent SIZ.Using nutrients,phytoplankton pigments,organic carbon(OC),remote sensing data,and physicochemical measurements,as well as CHEMTAX model simulations,we investigated the response of the phytoplankton crops,taxonomic composition,and OC pool to environmental factors.Our analyses revealed that hydrodynamic regimes of the polynya,adjacent SIZs and open sea were regulated by the regionally varying intrusion of Circumpolar Deep Water,photosynthetically active radiation and sea ice melt water.The ASP exhibited the highest seasonal nutrient utilization rates[ΔN=(1059±386)mmol/m^(2),ΔP=(50±17)mmol/m^(2) andΔSi=(956±904)mmol/m^(2)],while the open sea had lower rates.The integrated chlorophyll a(Chl a)concentration at depths of 0–200 m ranged from 20.4 mg/m^(2) to 1420.0 mg/m^(2) and peaked in the polynya.In the study area,Haptophytes Phaeocystis antarctica was the dominant functional group(34%±27%),and diatoms acted as a secondary contributor(23%±14%).The major functional group and particulate OC(POC)contributor varied from diatoms(36%±12%)in the open sea to haptophytes(48%±31%)in the polynya waters.Strong light conditions and microelement limitations promoted the dominance of P.antarctica(low Fe forms)dominance in the ASP.The strong correlations between the POC and Chl a depth-integrated concentration suggest that the POC was primarily derived from phytoplankton,while dissolved OC(DOC)was influenced by consumer activity and water mass transport.In addition,the transport of OC in the upper 200 m of the water column within the ASP was quantified,revealing the predominantly westward fluxes for both DOC[9.0 mg/(m^(2)·s)]and POC[7.2 mg/(m^(2)·s)].The latitudinal transport exhibited the northward transport of DOC[8.1 mg/(m^(2)·s)]and southward transport of POC[4.3 mg/(m^(2)·s)]movement.These findings have significant implications for enhancing our understanding of how hydrodynamics influence OC cycling in polynya regions.展开更多
The otolith morphology of two croaker species(C ollichthys lucidus and C ollichthys niveatus) from three areas(Liaodong Bay, LD; Huanghe(Yellow) River estuary, HRE; Jiaozhou Bay, JZ) along the northern Chinese coast w...The otolith morphology of two croaker species(C ollichthys lucidus and C ollichthys niveatus) from three areas(Liaodong Bay, LD; Huanghe(Yellow) River estuary, HRE; Jiaozhou Bay, JZ) along the northern Chinese coast were investigated for species identifi cation and stock discrimination. The otolith contour shape described by elliptic Fourier coefficients(EFC) were analysed using principal components analysis(PCA) and stepwise canonical discriminant analysis(CDA) to identify species and stocks. The two species were well dif ferentiated, with an overall classifi cation success rate of 97.8%. And variations in the otolith shapes were significant enough to discriminate among the three geographical samples of C. lucidus(67.7%) or C. niveatus(65.2%). Relatively high mis-assignment occurred between the geographically adjacent LD and HRE samples, which implied that individual mixing may exist between the two samples. This study yielded information complementary to that derived from genetic studies and provided information for assessing the stock structure of C. lucidus and C. niveatus in the Bohai Sea and the Yellow Sea.展开更多
The effect of COVID-19 on stock market performance has important implications for both financial theory and practice.This paper examines the relationship between COVID-19 and the instability of both stock return predi...The effect of COVID-19 on stock market performance has important implications for both financial theory and practice.This paper examines the relationship between COVID-19 and the instability of both stock return predictability and price volatility in the U.S over the period January 1st,2019 to June 30th,2020 by using the methodologies of Bai and Perron(Econometrica 66:47–78,1998.https://doi.org/10.2307/2998540;J Appl Econo 18:1–22,2003.https://doi.org/10.1002/jae.659),Elliot and Muller(Optimal testing general breaking processes in linear time series models.University of California at San Diego Economic Working Paper,2004),and Xu(J Econ 173:126–142,2013.https://doi.org/10.1016/j.jecon om.2012.11.001).The results highlight a single break in return predictability and price volatility of both S&P 500 and DJIA.The timing of the break is consistent with the COVID-19 outbreak,or more specifically the stock sellingoffs by the U.S.senate committee members before COVID-19 crashed the market.Furthermore,return predictability and price volatility significantly increased following the derived break.The findings suggest that the pandemic crisis was associated with market inefficiency,creating profitable opportunities for traders and speculators.Furthermore,it also induced income and wealth inequality between market participants with plenty of liquidity at hand and those short of funds.展开更多
Numerous approaches have been developed to quantify forest structure modules.A variety has measured each as part of stand attributes.This study was carried out in managed mixed stands in northern Iran.The objective wa...Numerous approaches have been developed to quantify forest structure modules.A variety has measured each as part of stand attributes.This study was carried out in managed mixed stands in northern Iran.The objective was to quantify stand structure and its variation before and after tree marking through the Gini index and structural triangle method.A full sampling inventory was taken in 2004 and 2014 at the beginning and end of a period,before and after tree marking operations in five stands.The results indicate that the Gini index was 39.5,62.2,43.0,82.0 and 74.0%forⅠ,Ⅱ,Ⅲ,ⅣandⅤstands respectively.Furthermore,approximate structural diameters were determined as a large category forⅠ,Ⅱ,ⅢandⅤstands while standⅡhad an intermediate-large class pre-tree marking to an intermediate-small class post-tree marking.The paired t-test results were not significant for tree numbers and growing stock changes for all species,and for beech,hornbeam,and velvet maple before and after tree harvesting in the whole stand.Therefore,the Gini index and the structural triangle method can be used for natural stand modeling,structural diversity designation,and for management practices in nature-oriented forestry strategies.展开更多
基金supported by the Science and Technology Project of the Department of Transportation of Heilongjiang Province(HJK2023B024-3)the National Key R&D Program of China(2023YFF1304001-01)。
文摘Soil fertility and forest structure influence tree carbon stocks.However,it remains unclear how tree mycorrhizal types affect these relationships.This study addressed the question of how aboveground and belowground tree carbon stocks in soils with different mycorrhizal types are affected by soil fertility and forest structure.Tree demographic data were used from a 21.12-ha study area collected over a ten-year period(2009-2019),covering 43species of woody plants and more than 50,000 individuals.Relationships between tree carbon stock,soil fertility and forest structure(stand density,diameter variation,species diversity and spatial distribution)were examined,as well as whether these relationships differed between arbuscular mycorrhiza and ectomycorrhizal mycorrhiza groups in a typical temperate conifer and broad-leaved mixed forest.We found that total tree carbon stock was positively impacted by variations in stand density and tree diameter but negatively influenced by soil fertility,tree species diversity and uniform angle index.Soil fertility promoted carbon stock of trees associated with arbuscular mycorrhiza(AM)but inhibited the carbon stock of trees with ectomycorrhizal mycorrhiza fungi(EcM).Carbon stock of AM trees was mainly influenced by soil fertility,while carbon stock of EcM trees was influenced by stand density.Our findings show that mycorrhizae types mediate the impact of stand structure and soil fertility on tree carbon stocks and provides new evidence on how forest tree carbon stocks may be enhanced based on the types of mycorrhizal associations.Tree species with different mycorrhizal types can be managed in different ways.
文摘Sacred forests play a valuable role in the conservation of local biodiversity and provide numerous ecosystem services in Cameroon. The aim of this study was to estimate floristic diversity, stand structures and carbon stocks in the sacred forests of Bandrefam and Batoufam (western Cameroon). The floristic inventory and the stand structures were carried out in 25 m × 25 m plots for individuals with diameters greater than 10 cm;5 m × 5 m for individuals with diameters less than 10 cm. Carbon stocks were estimated using the non-destructive method and allometric equations. The floristic inventory identified 65 species divided into 57 genera and 30 families in the Bandrefam sacred forest and 45 species divided into 42 genera and 27 families in the Batoufam sacred forest. In the Bandrefam, the most important families are Phyllanthaceae (53.98%), Moraceae (21.69%), Lamiaceae (20.15%). At Batoufam, the most important families are Phyllanthaceae (39.73%), Fabaceae (28.47%), Araliaceae (23.77%). Malacantha alnifolia (55.14%), Vitex grandifolia (18.43%), Bosqueia angolensis (15.06%) were the most important species in Bandrefam. Otherwise, Malacantha alnifolia (28%), Polyscias fulva (22.73%), Psychotria sp. (21.28%) were the most important in Batoufam. The Bandrefam sacred forest has the highest tree density (2669 stems/ha). Total carbon stock is 484.88 ± 2.28 tC/ha at Batoufam and 313.95 ± 0.93 tC/ha at Bandrefam. The economic value varies between 5858.04 ± 27.62 USD/ha in Batoufam sacred forest and 3788.51 ± 11.26 USD/ha in Bandrefam sacred forest. The number of individuals and small-diameter trees has little influence on the carbon stocks in the trees. Medium-diameter trees store the most carbon, and very large-diameter trees, which are very poorly represented, store less carbon. In another way, wood density and the basal areas influence the carbon storage of the trees.
基金Supported by National Natural Science Foundation of China(No.79770 0 63)
文摘In this paper,it is first briefly described the basic situation and current policies of state owned enterprise reform in China.Then the major issues in the reform process are identified,the possible solutions in terms of reengineering stock equity structure and state share circulation are discussed,and finally some suggestions are made for the further state owned enterprise reform.Basing on the theory on the modern corporation system,relevant experiences of market economy nations and the practice of Chinese enterprise system reform.The approaches to determine the proportion of state share in the future corporations are proposed.Since the public ownership is not ideologically appropriate,the establishment of social security fund and mutual fund investment companies are suggested as new and acceptable pattern of public ownership.It is believed that these companies will be the major institutional shareholders in the future corporations.Their stock equity structure would mainly consist of institutional shareholders,which will be both consistent with international norms of modern corporations and with socialist public ownership with Chinese characteristics.
基金The National Basic Research Program(973 Program)of China under contract Nos 2015CB453300 and 2010CB428900
文摘Oxygen and carbon isotope ratios（δ^（18）O and δ^（13）C） in otoliths were used to identify the stock structure of small yellow croaker,Larimichthys polyactis.Otoliths were collected from fish at five locations across the Yellow Sea and the Bohai Sea representing most of their distributional range and fisheries areas.The significant differences in the isotopic signatures showed that the five locations could be chemically distinguished and clearly separated,indicating stock subdivision.Correlation of δ^（18）O and δ^（13）C values suggested that population of L.polyactis could be divided into the Bohai Sea group,the southern Yellow Sea group and the central Yellow Sea group.Discriminant analysis of δ^（18）O and δ^（13）C values demonstrated a high significant difference with 85.7% classification accuracy.The spatial separation of L.polyactis indicated a complex stock structure across the Yellow Sea and the Bohai Sea.These results indicate that optimal fisheries management may require a comprehensive consideration on the current spatial arrangements.This study has provided further evidence that measurement of the stable isotopes ratios in otolith can be a valuable tool in the delineation of fishery management units.
基金the National Natural Science Foundation of China(No.10771179)the Emphasis Subject of Guizhou Province of China
文摘We investigate a stage-structured delayed predator-prey model with impulsive stocking on prey and continuous harvesting on predator. According to the fact of biological resource management, we improve the assumption of a predator-prey model with stage structure for predator population that each individual predator has the same ability to capture prey. It is assumed that the immature and mature individuals of the predator population are divided by a fixed age, and immature predator population does not have the ability to attach prey. Sufficient conditions are obtained, which guarantee the global attractivity of predator-extinction periodic solution and the permanence of the system. Our results show that the behavior of impulsive stocking on prey plays an important role for the permanence of the system, and provide tactical basis for the biological resource management. Numerical analysis is presented to illuminate the dynamics of the system.
基金funded by the Major Humanities and Social Sciences Research Projects in Zhejiang higher education institutions,grant number 2023QN082,awarded to Cheng ZhaoThe National Natural Science Foundation of China also provided funding,grant number 61902349,awarded to Cheng Zhao.
文摘The present study examines the impact of short-term public opinion sentiment on the secondary market,with a focus on the potential for such sentiment to cause dramatic stock price fluctuations and increase investment risk.The quantification of investment sentiment indicators and the persistent analysis of their impact has been a complex and significant area of research.In this paper,a structured multi-head attention stock index prediction method based adaptive public opinion sentiment vector is proposed.The proposedmethod utilizes an innovative approach to transform numerous investor comments on social platforms over time into public opinion sentiment vectors expressing complex sentiments.It then analyzes the continuous impact of these vectors on the market through the use of aggregating techniques and public opinion data via a structured multi-head attention mechanism.The experimental results demonstrate that the public opinion sentiment vector can provide more comprehensive feedback on market sentiment than traditional sentiment polarity analysis.Furthermore,the multi-head attention mechanism is shown to improve prediction accuracy through attention convergence on each type of input information separately.Themean absolute percentage error(MAPE)of the proposedmethod is 0.463%,a reduction of 0.294% compared to the benchmark attention algorithm.Additionally,the market backtesting results indicate that the return was 24.560%,an improvement of 8.202% compared to the benchmark algorithm.These results suggest that themarket trading strategy based on thismethod has the potential to improve trading profits.
文摘Capital structure is regarded as the combination of debt and equity firms used to finance operations and investments.The choice of capital structure significantly impacts a company’s cost of capital,profitability,and risk profile.Among a series of factors that affect capital structure,this paper focuses on stock returns and market timing.In this review,an array of papers is analyzed to summarize what current research claims regarding the influence of stock returns and market timing on capital structure.This paper centers on the stock return and market timing theories and also discusses other theories like the trade-off theory,the pecking order theory,and the signaling theory.
基金The National Key Research and Development Program of China under contract No.2016YFC1400903the NSFC Zhejiang Joint Fund for the Integration of Industrialization and Informatization under contract No.U1609202
文摘Various population structures or spatial heterogeneities in population distribution have been an important source of model misspecification and have had an impact on estimation performance in fisheries stock assessment.In this study,we simulated the Indian Ocean albacore spatial heterogeneity in age-structure using Stock Synthesis according to the stage-dependent migration rate and region-dependent fishing mortality rate and generated the stock assessment data.Based on these data,we investigated the performances of different spatial configurations,selectivity curves and selections of CPUE(catch per unit effort)indices of the assessment models which were used to account for spatial heterogeneity.The results showed:(1)although the spatially explicit configurations,which exactly matched the operating model,provided unbiased and accurate estimates of relative spawning biomass,relative fishing mortality rate and maximum sustainable yield in all simulation scenarios,their performance may be very poor if there were mismatches between them and the operating model due to gaps in knowledge and data;(2)for spatially explicit assessment configuration,the correct boundary was required,but for non-spatially explicit assessment configuration,it seemed more important for analysts to partition the area to properly reflect the transition in field data and to effectively account for the impacts of ignoring the spatial structure by using the additional spatially referenced parameters;(3)although the areas-as-fleets methods and flexible time-varying selectivity curves could be used as better alternative approaches to account for spatial structure,these configurations could not completely eliminate the impacts of model misspecification and the quality of estimates of different quantities from the same assessment model may be inconsistent or the performance of the same assessment configuration may fluctuate significantly between simulation scenarios;(4)although the worst estimates could generally be avoided by using multiple CPUE indices,there were no best solutions to select or regenerate the CPUE indices to account for the impacts of the ignored spatial structure to obviously improve the quality of stock assessment.Compared with the results of assessment model configurations which are used to account for the spatial structure by different modelers,the performances of the configurations are always casespecific except for spatially explicit configurations which exactly match the operating model.In this sense,our study will not only provide some insights into the current Indian Ocean albacore stock assessment but also enrich existing knowledge regarding the performance of assessment configurations to account for spatial structure.
基金funded by the Czech University of Life Sciences Prague(Internal Grant Agency:A_03_22-43110/1312/3101)the Czech Science(GACR 21-27454S)。
文摘Primary forests are spatially diverse terrestrial ecosystems with unique characteristics,being naturally regenerative and heterogeneous,which supports the stability of their carbon storage through the accumulation of live and dead biomass.Yet,little is known about the interactions between biomass stocks,tree genus diversity and structure across a temperate montane primary forest.Here,we investigated the relationship between tree structure(variability in basal area and tree size),genus-level diversity(abundance,tree diversity)and biomass stocks in temperate primary mountain forests across Central and Eastern Europe.We used inventory data from726 permanent sample plots from mixed beech and spruce across the Carpathian Mountains.We used nonlinear regression to analyse the spatial variability in forest biomass,structure,and genus-level diversity and how they interact with plot-level tree age,disturbances,temperature and altitude.We found that the combined effects of genus and structural indices were important for addressing the variability in biomass across different spatial scales.Local processes in disturbance regimes and uneven tree age support forest hete rogeneity and the accumulation of live and dead biomass through the natural regeneration,growth and decay of the forest ecosystem.Structural complexities in basal area index,supporte d by genus-level abundance,positively influence total biomass stocks,which was modulated by tree age and disturbances.Spruce forests showed higher tree density and basal area than mixed beech forests,though mixed beech still contributes significantly to biomass across landscapes.Forest heterogeneity was strongly influenced by complexities in forest composition(tree genus diversity,structure).We addressed the importance of primary forests as stable carbon stores,achieved through structure and diversity.Safeguarding such ecosystems is critical for ensuring the stability of the primary forest,carbon store and biodiversity into the future.
基金Major public tendering project of the National Social Sciences Fund--Study on Accelerating Economic Restructuring and Promoting Coordinated Economic Development(Grant No.12&ZD084)Project of the National Social Sciences Fund--Study on the Pattern,Evolutionary Mechanism and Sustainable Development of China's Urbanization(Grant No.12AJL009)
文摘Using sector-specific growth accounting method, this paper investigates the growth effect of inter-industry allocation of capital and labor in China. This paper has found that existing investment data are classified according to investment entities rather than user entities and directly using such data for the measurement of capital inventory of various sectors will seriously overestimate the capital inventory of tertiary industry and lead to distorted conclusions of "structural burden" of capital allocation and its serious violation of the principle of efficiency. By excluding real estate sector, this paper has found that after the 1990 s, inter-industry capital allocation had been generally consistent with the principle of efficiency and the effect of capital allocation structure is not significant. Our estimates also found that the growth effect arising from the inter-industry allocation of labor since reform and opening up averages 0.63 percentage points, which is significantly positively correlated with residual economic growth rate and residual TFP and demonstrates a decade-long "reform cycle." According to the comparative study on the effect of labor allocation structure of 37 other countries and regions, by 2017, the effect of China's labor allocation structure will continue to remain in a relatively high stage; between 2017 and 2023, structural effect will significantly diminish and deceleration pressure will rise swiftly; after 2030, the effect of labor allocation structure will linger in a low level stage, when economy is likely to enter into a stage of low growth rate. These findings will help us better assess future economic growth tendencies.
基金The National Polar Special Program under contract Nos IRASCC 01-01-02 and IRASCC 02-02the National Natural Science Foundation of China under contract Nos 41976228,42276255,41976227,42176227,and 42076243+1 种基金the International Cooperation Key Project of the Ministry of Science and Technology under contract No.2022YFE0136500the Scientific Research Fund of the Second Institute of Oceanography,Ministry of Natural Resources,under contract Nos JG2011,JG2211,JG2013,and JG1805.
文摘Polynyas and their adjacent seasonal ice zones(SIZs)represent the most productive regions in the Southern Ocean,supporting unique food webs that are highly sensitive to climate change.Understanding the dynamics of phytoplankton and the carbon pool in these areas is crucial for assessing the role of the Southern Ocean in global carbon cycling.During the late stage of an algal bloom,seawater samples at 14 stations were collected in the Amundsen Sea Polynya(ASP)and adjacent SIZ.Using nutrients,phytoplankton pigments,organic carbon(OC),remote sensing data,and physicochemical measurements,as well as CHEMTAX model simulations,we investigated the response of the phytoplankton crops,taxonomic composition,and OC pool to environmental factors.Our analyses revealed that hydrodynamic regimes of the polynya,adjacent SIZs and open sea were regulated by the regionally varying intrusion of Circumpolar Deep Water,photosynthetically active radiation and sea ice melt water.The ASP exhibited the highest seasonal nutrient utilization rates[ΔN=(1059±386)mmol/m^(2),ΔP=(50±17)mmol/m^(2) andΔSi=(956±904)mmol/m^(2)],while the open sea had lower rates.The integrated chlorophyll a(Chl a)concentration at depths of 0–200 m ranged from 20.4 mg/m^(2) to 1420.0 mg/m^(2) and peaked in the polynya.In the study area,Haptophytes Phaeocystis antarctica was the dominant functional group(34%±27%),and diatoms acted as a secondary contributor(23%±14%).The major functional group and particulate OC(POC)contributor varied from diatoms(36%±12%)in the open sea to haptophytes(48%±31%)in the polynya waters.Strong light conditions and microelement limitations promoted the dominance of P.antarctica(low Fe forms)dominance in the ASP.The strong correlations between the POC and Chl a depth-integrated concentration suggest that the POC was primarily derived from phytoplankton,while dissolved OC(DOC)was influenced by consumer activity and water mass transport.In addition,the transport of OC in the upper 200 m of the water column within the ASP was quantified,revealing the predominantly westward fluxes for both DOC[9.0 mg/(m^(2)·s)]and POC[7.2 mg/(m^(2)·s)].The latitudinal transport exhibited the northward transport of DOC[8.1 mg/(m^(2)·s)]and southward transport of POC[4.3 mg/(m^(2)·s)]movement.These findings have significant implications for enhancing our understanding of how hydrodynamics influence OC cycling in polynya regions.
基金Supported by the National Key Basic Research Program of China(973 Program)(No.2015CB453302)the NSFC-Shandong Joint Fund for Marine Science Research Centre(No.U1606404)the Aoshan Science and Technology Innovation Project(No.2015ASKJ02-04)
文摘The otolith morphology of two croaker species(C ollichthys lucidus and C ollichthys niveatus) from three areas(Liaodong Bay, LD; Huanghe(Yellow) River estuary, HRE; Jiaozhou Bay, JZ) along the northern Chinese coast were investigated for species identifi cation and stock discrimination. The otolith contour shape described by elliptic Fourier coefficients(EFC) were analysed using principal components analysis(PCA) and stepwise canonical discriminant analysis(CDA) to identify species and stocks. The two species were well dif ferentiated, with an overall classifi cation success rate of 97.8%. And variations in the otolith shapes were significant enough to discriminate among the three geographical samples of C. lucidus(67.7%) or C. niveatus(65.2%). Relatively high mis-assignment occurred between the geographically adjacent LD and HRE samples, which implied that individual mixing may exist between the two samples. This study yielded information complementary to that derived from genetic studies and provided information for assessing the stock structure of C. lucidus and C. niveatus in the Bohai Sea and the Yellow Sea.
基金This research was supported by the Social Science Foundation of Jiangxi Province(Grant No:20YJ09)the National Social Science Foundation of China(Grant No:17ZDA037).
文摘The effect of COVID-19 on stock market performance has important implications for both financial theory and practice.This paper examines the relationship between COVID-19 and the instability of both stock return predictability and price volatility in the U.S over the period January 1st,2019 to June 30th,2020 by using the methodologies of Bai and Perron(Econometrica 66:47–78,1998.https://doi.org/10.2307/2998540;J Appl Econo 18:1–22,2003.https://doi.org/10.1002/jae.659),Elliot and Muller(Optimal testing general breaking processes in linear time series models.University of California at San Diego Economic Working Paper,2004),and Xu(J Econ 173:126–142,2013.https://doi.org/10.1016/j.jecon om.2012.11.001).The results highlight a single break in return predictability and price volatility of both S&P 500 and DJIA.The timing of the break is consistent with the COVID-19 outbreak,or more specifically the stock sellingoffs by the U.S.senate committee members before COVID-19 crashed the market.Furthermore,return predictability and price volatility significantly increased following the derived break.The findings suggest that the pandemic crisis was associated with market inefficiency,creating profitable opportunities for traders and speculators.Furthermore,it also induced income and wealth inequality between market participants with plenty of liquidity at hand and those short of funds.
基金conducted by support of research credit(No:89034)from the University of Tehran
文摘Numerous approaches have been developed to quantify forest structure modules.A variety has measured each as part of stand attributes.This study was carried out in managed mixed stands in northern Iran.The objective was to quantify stand structure and its variation before and after tree marking through the Gini index and structural triangle method.A full sampling inventory was taken in 2004 and 2014 at the beginning and end of a period,before and after tree marking operations in five stands.The results indicate that the Gini index was 39.5,62.2,43.0,82.0 and 74.0%forⅠ,Ⅱ,Ⅲ,ⅣandⅤstands respectively.Furthermore,approximate structural diameters were determined as a large category forⅠ,Ⅱ,ⅢandⅤstands while standⅡhad an intermediate-large class pre-tree marking to an intermediate-small class post-tree marking.The paired t-test results were not significant for tree numbers and growing stock changes for all species,and for beech,hornbeam,and velvet maple before and after tree harvesting in the whole stand.Therefore,the Gini index and the structural triangle method can be used for natural stand modeling,structural diversity designation,and for management practices in nature-oriented forestry strategies.
