In this paper,we consider the price of catastrophe options with credit risk in a regime-switching model.We assume that the macroeconomic states are described by a continuous-time Markov chain with a finite state space...In this paper,we consider the price of catastrophe options with credit risk in a regime-switching model.We assume that the macroeconomic states are described by a continuous-time Markov chain with a finite state space.By using the measure change technique,we derive the price expressions of catastrophe put options.Moreover,we conduct some numerical analysis to demonstrate how the parameters of the model affect the price of the catastrophe put option.展开更多
In this paper,we study the dynamics of a Susceptible-Exposed-Infectious-Recovered(SEIR)nancial risk contagion model with time delay.Using stability theory and Hopf bifurcation theory,equilibria stability and Hopf bifu...In this paper,we study the dynamics of a Susceptible-Exposed-Infectious-Recovered(SEIR)nancial risk contagion model with time delay.Using stability theory and Hopf bifurcation theory,equilibria stability and Hopf bifurcation are analyzed in detail.Based on the epidemic model,we improve it by taking prior prevention and self-rescue into consideration,conclude pre-ventive intensity and self-rescue capabilities e ect the number of infections.At the same time,the analytical conditions for Hopf bifurcation are obtained,and the relevant results are veri ed by numerical simulations.展开更多
Nasopharyngeal carcinoma(NPC)has been a focus of medical research for more than 100 years,with significant interest emerging over the last 58 years following the identification of the link between the disease and Epst...Nasopharyngeal carcinoma(NPC)has been a focus of medical research for more than 100 years,with significant interest emerging over the last 58 years following the identification of the link between the disease and Epstein-Barr virus(EBV)infection.NPC possesses several distinctive characteristics among human cancers,notably its well-documented global epidemiology,which reveals localized high-incidence regions primarily in Southeast Asia,particularly in the Southern provinces of China near the Pearl river,as well as in Greenland and North Africa.Epidemiological data indicate a marked male predominance,early disease onset,and a nearly 100%prevalence of latent EBV infection in the tumors.Due to lack of consistent pattern of cancer-related mutations in NPC genomes and excessive DNA-methylation in the tumor cells,NPC can be considered"an epigenetic cancer".Despite extensive researches,convincing biological explanations for these unique characteristics remain elusive.Recently,suggestive evidence has been published that specific local variants of EBV may represent major high risk factors.In spite of tumor and virus specific immunity,it has not been possible to use this for improved treatment.Ongoing studies on the role of the local microflora and tumor microenvironment are essential for a comprehensive understanding of host-EBV-tumor interactions.Ultimately,this knowledge aims to enhance diagnosis,disease fractionation,treatment strategies,and potentially prevention of NPC.展开更多
According to news reports on severe earthquakes since 2008,a total of 51 cases with magnitudes of 6.0 or above were analyzed,and 14 frequently occurring secondary disasters were identified.A disaster chain model was d...According to news reports on severe earthquakes since 2008,a total of 51 cases with magnitudes of 6.0 or above were analyzed,and 14 frequently occurring secondary disasters were identified.A disaster chain model was developed using principles from complex network theory.The vulnerability and risk level of each edge in this model were calculated,and high-risk edges and disaster chains were identified.The analysis reveals that the edge“floods→building collapses”has the highest vulnerability.Implementing measures to mitigate this edge is crucial for delaying the spread of secondary disasters.The highest risk is associated with the edge“building collapses→casualties,”and increased risks are also identified for chains such as“earthquake→building collapses→casualties,”“earthquake→landslides and debris flows→dammed lakes,”and“dammed lakes→floods→building collapses.”Following an earthquake,the prompt implementation of measures is crucial to effectively disrupt these chains and minimize the damage from secondary disasters.展开更多
A general prediction model for seven heavy metals was established using the heavy metal contents of 207soil samples measured by a portable X-ray fluorescence spectrometer(XRF)and six environmental factors as model cor...A general prediction model for seven heavy metals was established using the heavy metal contents of 207soil samples measured by a portable X-ray fluorescence spectrometer(XRF)and six environmental factors as model correction coefficients.The eXtreme Gradient Boosting(XGBoost)model was used to fit the relationship between the content of heavy metals and environment characteristics to evaluate the soil ecological risk of the smelting site.The results demonstrated that the generalized prediction model developed for Pb,Cd,and As was highly accurate with fitted coefficients(R^(2))values of 0.911,0.950,and 0.835,respectively.Topsoil presented the highest ecological risk,and there existed high potential ecological risk at some positions with different depths due to high mobility of Cd.Generally,the application of machine learning significantly increased the accuracy of pXRF measurements,and identified key environmental factors.The adapted potential ecological risk assessment emphasized the need to focus on Pb,Cd,and As in future site remediation efforts.展开更多
A model of continuous-time insider trading in which a risk-neutral in-sider possesses two imperfect correlated signals of a risky asset is studied.By conditional expectation theory and filtering theory,we first establ...A model of continuous-time insider trading in which a risk-neutral in-sider possesses two imperfect correlated signals of a risky asset is studied.By conditional expectation theory and filtering theory,we first establish three lemmas:normal corre-lation,equivalent pricing and equivalent profit,which can guarantee to turn our model into a model with insider knowing full information.Then we investigate the impact of the two correlated signals on the market equilibrium consisting of optimal insider trading strategy and semi-strong pricing rule.It shows that in the equilibrium,(1)the market depth is constant over time;(2)if the two noisy signals are not linerly correlated,then all private information of the insider is incorporated into prices in the end while the whole information on the asset value can not incorporated into prices in the end;(3)if the two noisy signals are linear correlated such that the insider can infer the whole information of the asset value,then our model turns into a model with insider knowing full information;(4)if the two noisy signals are the same then the total ex ant profit of the insider is increasing with the noise decreasing,while down to O as the noise going up to infinity;(5)if the two noisy signals are not linear correlated then with one noisy signal fixed,the total ex ante profit of the insider is single-peaked with a unique minimum with respect to the other noisy signal value,and furthermore as the noisy value going to O it gets its maximum,the profit in the case that the real value is observed.展开更多
Between March and May 2005, bird communities in four sample plots at Baita Airport were studied using strips methods in Hohhot, Inner Mongolia. A total of 59 species belonging to 10 orders and 26 families were recorde...Between March and May 2005, bird communities in four sample plots at Baita Airport were studied using strips methods in Hohhot, Inner Mongolia. A total of 59 species belonging to 10 orders and 26 families were recorded. Based on the principles of avian community ecology, the community parameters were discussed, including the comparative importance value, distribution coefficient, density and probability of interactive encounter. By analyzing these indices, combined with their flight behaviors at the airport and its neighbourhood, we identified bird species that have the potential to threaten flight security at Baita Airport; The results showed that the 23 bird species including magpie and red falcon are the most hazard to flight security and the eight bird species including sparrow Hawk and Greenfinch are the hazard. Furthermore, we assessed the bird species' different hazard grades to flight security.展开更多
Modified potential ecological risk index (MRI) was proposed based on the potential ecological risk index (RI) and risk assessment code (RAC) by modifying an index. The modified index was relevant to the chemical...Modified potential ecological risk index (MRI) was proposed based on the potential ecological risk index (RI) and risk assessment code (RAC) by modifying an index. The modified index was relevant to the chemical speciation of heavy metals. Xiawan Port, a typical region contaminated by industrial production, was selected as a case study area. The total concentrations and chemical speciation of heavy metals in sediments of Xiawan Port were analyzed. The experimental data indicate that Xiawan Port is seriously polluted by heavy metals, especially by Cd. The risks of heavy metals are evaluated by RI, RAC and MRI, respectively. The resluts of MRI show that the risks of heavy metals are in the decreasing order of Cd〉Pb〉Cu〉Zn. Comparison of results by different methods reveals that MRI integrates the characters of RI and RAC. MRI is recognized to be useful for risk managemnt of heavy metals in sediments.展开更多
Study was carried out to analyze the distribution and migration patterns,soil-to-plant transfer and potential health risks of chromium in soil-vegetable system in areas near a ferro-alloy manufactory in Hunan province...Study was carried out to analyze the distribution and migration patterns,soil-to-plant transfer and potential health risks of chromium in soil-vegetable system in areas near a ferro-alloy manufactory in Hunan province.The results show that soils near sewer outlet,sewer channel and in control area are averaged 2 239.5,995.33 and 104.9 mg/kg,respectively.The total Cr has a relative accumulation in soil depth of 200-400 mm near the sewer outlet,mainly enriches in the surface layer(0-200 mm) near the sewer channel and decreases gradually in unpolluted soils.The differential concentration level of enrichment between layers is little.The results also indicate that the three vegetables of celery,lettuce and Chinese cabbage are able to convert the potentially toxic Cr(Ⅵ) species into the non-toxic Cr(Ⅲ) species,and the chromium contents in the edible parts of the vegetables are averaged 11.95 mg/kg.The transfer factors of the three vegetables follow the order:Chinese cabbage lettuce celery.The estimated total daily intake of chromium substantially exceeds the dietary allowable value,which may pose health risks to local population.展开更多
In order to evaluate the reliability of long-lifetime products with degradation data, a new proportional hazard degradation model is proposed. By the similarity between time-degradation data and stress-accelerated lif...In order to evaluate the reliability of long-lifetime products with degradation data, a new proportional hazard degradation model is proposed. By the similarity between time-degradation data and stress-accelerated lifetime, and the failure rate function of degradation data which is assumed to be proportional to the time covariate, the reliability assessment based on a proportional hazard degradation model is realized. The least squares method is used to estimate the model's parameters. Based on the failure rate of the degradation data and the proportion function of the known time, the failure rate and the reliability function under the given time and the predetermined failure threshold can be extrapolated. A long life GaAs laser is selected as a case study and its reliability is evaluated. The results show that the proposed method can accurately describe the degradation process and it is effective for the reliability assessment of long lifetime products.展开更多
A Bayes discriminant analysis method to identify the risky of complicated goaf in mines was presented. Nine factors influencing the stability of goaf risky, including uniaxial compressive strength of rock, elastic mod...A Bayes discriminant analysis method to identify the risky of complicated goaf in mines was presented. Nine factors influencing the stability of goaf risky, including uniaxial compressive strength of rock, elastic modulus of rock, rock quality designation (RQD), area ratio of pillar, ratio of width to height of pillar, depth of ore body, volume of goaf, dip of ore body and area of goal, were selected as discriminant indexes in the stability analysis of goal. The actual data of 40 goals were used as training samples to establish a discriminant analysis model to identify the stability of goaf. The results show that this discriminant analysis model has high precision and misdiscriminant ratio is 0.025 in re-substitution process. The instability identification of a metal mine was distinguished by using this model and the identification result is identical with that of practical situation.展开更多
Pinus radiata was introduced to the summer rainfall environments of Sichuan Province, China in the 1990s as a part of an afforestation pmgram for soil and water conservation in the arid and semi-arid river valley area...Pinus radiata was introduced to the summer rainfall environments of Sichuan Province, China in the 1990s as a part of an afforestation pmgram for soil and water conservation in the arid and semi-arid river valley area of Aba Prefecture. Within this region a total area of 26 000 ha have been identified through climate matching as suitable and a further 63 000 ha potentially suitable for environmental plantings of P. radiata. The plantations are being established in widely separated small patches on steep and degraded slopes along the dry river valley The newly introduced P. radiata are exposed to two kinds of forest health risks: they may be attacked by (a) indigenous pathogens and pests against which they may not possess any resistance or (b) by inadvertently introduced foreign pests or pathogens. This paper presents a survey of the potential damaging pests and a preliminary assessment of forest health risks facing the P. radiata plantations over a much longer timeframe than the initial phase of introduction and early plantation establishment. An empirical appmach was adopted to evaluate forest health risks by a combination of literature review, examination of historical records of pest and disease outbreaks in the surrounding conifemus forests, field surveys and inspections, specimen collection and identification, and most importantly, expert analysis of the likelihood of attack by specific pests and pathogens and the subsequent impact of such attacks. The assessment identified some specific forest health risks to the long-term success of P. radiata introduction in this area. These risks are closely associated with the indigenous pests and pathogens of the two native pine species, P. tabulaeformis and P. armondii since these pests and pathogens are considered more likely to establish on P. radiata over time. Exotic pests and pathogens are of a quarantine concern at present. Based on the results of assessment, recommendations are pmvided to improve forest vigour and to reduce the forest health risks posed by indigenous as well as exotic pests and pathogens to the introduced P. radiata. Ways to increase the ability to manage the forest health risks once a particular pest infestation and disease eventuates are also recommended. Although detrimental to the survival and growth of the introduced P. radiata, the impact of identified forest health risks are not considered to be fatal to the long term success ofP. radiata in this area.展开更多
Literature lacked in providing a comprehensive research on heavy metal detection in aquatic, biological and sedimentary states of rivers. The present study was imparted with all these three components of the river. He...Literature lacked in providing a comprehensive research on heavy metal detection in aquatic, biological and sedimentary states of rivers. The present study was imparted with all these three components of the river. Heavy metal toxicity or pollution index was used as a tool for ecological risk assessment by considering the single state studies conducted by many researchers. An intensive ecological risk assessment model was constructed and heavy metals were indicated as a serious threat to the environment. The model was applied to determining five toxic heavy metals in three states of the Songhua River. According to the ecological risk index, heavy metal pollution in three phases was categorized as aquatic〉biological〉sedimentary, while the overall descending order of heavy metal ecological risk index was as Cd〉Hg〉As〉Pb〉Cr. Cd and Hg were selected as the priority pollutants of Songhua River.展开更多
基金supported by the Jiangsu University Philosophy and Social Science Research Project(Grant No.2019SJA1326).
文摘In this paper,we consider the price of catastrophe options with credit risk in a regime-switching model.We assume that the macroeconomic states are described by a continuous-time Markov chain with a finite state space.By using the measure change technique,we derive the price expressions of catastrophe put options.Moreover,we conduct some numerical analysis to demonstrate how the parameters of the model affect the price of the catastrophe put option.
基金Supported by National Natural Science Foundation of China(12272062).
文摘In this paper,we study the dynamics of a Susceptible-Exposed-Infectious-Recovered(SEIR)nancial risk contagion model with time delay.Using stability theory and Hopf bifurcation theory,equilibria stability and Hopf bifurcation are analyzed in detail.Based on the epidemic model,we improve it by taking prior prevention and self-rescue into consideration,conclude pre-ventive intensity and self-rescue capabilities e ect the number of infections.At the same time,the analytical conditions for Hopf bifurcation are obtained,and the relevant results are veri ed by numerical simulations.
文摘Nasopharyngeal carcinoma(NPC)has been a focus of medical research for more than 100 years,with significant interest emerging over the last 58 years following the identification of the link between the disease and Epstein-Barr virus(EBV)infection.NPC possesses several distinctive characteristics among human cancers,notably its well-documented global epidemiology,which reveals localized high-incidence regions primarily in Southeast Asia,particularly in the Southern provinces of China near the Pearl river,as well as in Greenland and North Africa.Epidemiological data indicate a marked male predominance,early disease onset,and a nearly 100%prevalence of latent EBV infection in the tumors.Due to lack of consistent pattern of cancer-related mutations in NPC genomes and excessive DNA-methylation in the tumor cells,NPC can be considered"an epigenetic cancer".Despite extensive researches,convincing biological explanations for these unique characteristics remain elusive.Recently,suggestive evidence has been published that specific local variants of EBV may represent major high risk factors.In spite of tumor and virus specific immunity,it has not been possible to use this for improved treatment.Ongoing studies on the role of the local microflora and tumor microenvironment are essential for a comprehensive understanding of host-EBV-tumor interactions.Ultimately,this knowledge aims to enhance diagnosis,disease fractionation,treatment strategies,and potentially prevention of NPC.
基金National Key Research and Development Program of China(No.2022YFC3803000).
文摘According to news reports on severe earthquakes since 2008,a total of 51 cases with magnitudes of 6.0 or above were analyzed,and 14 frequently occurring secondary disasters were identified.A disaster chain model was developed using principles from complex network theory.The vulnerability and risk level of each edge in this model were calculated,and high-risk edges and disaster chains were identified.The analysis reveals that the edge“floods→building collapses”has the highest vulnerability.Implementing measures to mitigate this edge is crucial for delaying the spread of secondary disasters.The highest risk is associated with the edge“building collapses→casualties,”and increased risks are also identified for chains such as“earthquake→building collapses→casualties,”“earthquake→landslides and debris flows→dammed lakes,”and“dammed lakes→floods→building collapses.”Following an earthquake,the prompt implementation of measures is crucial to effectively disrupt these chains and minimize the damage from secondary disasters.
基金financially supported from the National Key Research and Development Program of China(No.2019YFC1803601)the Fundamental Research Funds for the Central Universities of Central South University,China(No.2023ZZTS0801)+1 种基金the Postgraduate Innovative Project of Central South University,China(No.2023XQLH068)the Postgraduate Scientific Research Innovation Project of Hunan Province,China(No.QL20230054)。
文摘A general prediction model for seven heavy metals was established using the heavy metal contents of 207soil samples measured by a portable X-ray fluorescence spectrometer(XRF)and six environmental factors as model correction coefficients.The eXtreme Gradient Boosting(XGBoost)model was used to fit the relationship between the content of heavy metals and environment characteristics to evaluate the soil ecological risk of the smelting site.The results demonstrated that the generalized prediction model developed for Pb,Cd,and As was highly accurate with fitted coefficients(R^(2))values of 0.911,0.950,and 0.835,respectively.Topsoil presented the highest ecological risk,and there existed high potential ecological risk at some positions with different depths due to high mobility of Cd.Generally,the application of machine learning significantly increased the accuracy of pXRF measurements,and identified key environmental factors.The adapted potential ecological risk assessment emphasized the need to focus on Pb,Cd,and As in future site remediation efforts.
文摘A model of continuous-time insider trading in which a risk-neutral in-sider possesses two imperfect correlated signals of a risky asset is studied.By conditional expectation theory and filtering theory,we first establish three lemmas:normal corre-lation,equivalent pricing and equivalent profit,which can guarantee to turn our model into a model with insider knowing full information.Then we investigate the impact of the two correlated signals on the market equilibrium consisting of optimal insider trading strategy and semi-strong pricing rule.It shows that in the equilibrium,(1)the market depth is constant over time;(2)if the two noisy signals are not linerly correlated,then all private information of the insider is incorporated into prices in the end while the whole information on the asset value can not incorporated into prices in the end;(3)if the two noisy signals are linear correlated such that the insider can infer the whole information of the asset value,then our model turns into a model with insider knowing full information;(4)if the two noisy signals are the same then the total ex ant profit of the insider is increasing with the noise decreasing,while down to O as the noise going up to infinity;(5)if the two noisy signals are not linear correlated then with one noisy signal fixed,the total ex ante profit of the insider is single-peaked with a unique minimum with respect to the other noisy signal value,and furthermore as the noisy value going to O it gets its maximum,the profit in the case that the real value is observed.
文摘Between March and May 2005, bird communities in four sample plots at Baita Airport were studied using strips methods in Hohhot, Inner Mongolia. A total of 59 species belonging to 10 orders and 26 families were recorded. Based on the principles of avian community ecology, the community parameters were discussed, including the comparative importance value, distribution coefficient, density and probability of interactive encounter. By analyzing these indices, combined with their flight behaviors at the airport and its neighbourhood, we identified bird species that have the potential to threaten flight security at Baita Airport; The results showed that the 23 bird species including magpie and red falcon are the most hazard to flight security and the eight bird species including sparrow Hawk and Greenfinch are the hazard. Furthermore, we assessed the bird species' different hazard grades to flight security.
基金Projects (51039001, 50978087, 51009063, 50808071) supported by the National Natural Science Foundation of ChinaProject (SX2010-026) supported by State Council Three Gorges Project Construction Committee Executive Office,China+2 种基金Project (2009ZX07212-001) supported by Ministry of Environmental Protection of ChinaProject (BYHGLC-2010-02) supported by Guangzhou Water Authority,ChinaProject (CX2010B157) supported by Hunan Provincial Innovation Foundation for Postgraduate,China
文摘Modified potential ecological risk index (MRI) was proposed based on the potential ecological risk index (RI) and risk assessment code (RAC) by modifying an index. The modified index was relevant to the chemical speciation of heavy metals. Xiawan Port, a typical region contaminated by industrial production, was selected as a case study area. The total concentrations and chemical speciation of heavy metals in sediments of Xiawan Port were analyzed. The experimental data indicate that Xiawan Port is seriously polluted by heavy metals, especially by Cd. The risks of heavy metals are evaluated by RI, RAC and MRI, respectively. The resluts of MRI show that the risks of heavy metals are in the decreasing order of Cd〉Pb〉Cu〉Zn. Comparison of results by different methods reveals that MRI integrates the characters of RI and RAC. MRI is recognized to be useful for risk managemnt of heavy metals in sediments.
基金Project (2009ZX07212-001-01) supported by the Key Project of National Natural Science Foundation for Water Pollution Control and RemediationProject (50925417) supported by the National Funds for Distinguished Young Scientists+1 种基金Project (50830301) supported by the National Natural Science Foundation of ChinaProject (51074191) supported by the National Natural Science Foundation of China
文摘Study was carried out to analyze the distribution and migration patterns,soil-to-plant transfer and potential health risks of chromium in soil-vegetable system in areas near a ferro-alloy manufactory in Hunan province.The results show that soils near sewer outlet,sewer channel and in control area are averaged 2 239.5,995.33 and 104.9 mg/kg,respectively.The total Cr has a relative accumulation in soil depth of 200-400 mm near the sewer outlet,mainly enriches in the surface layer(0-200 mm) near the sewer channel and decreases gradually in unpolluted soils.The differential concentration level of enrichment between layers is little.The results also indicate that the three vegetables of celery,lettuce and Chinese cabbage are able to convert the potentially toxic Cr(Ⅵ) species into the non-toxic Cr(Ⅲ) species,and the chromium contents in the edible parts of the vegetables are averaged 11.95 mg/kg.The transfer factors of the three vegetables follow the order:Chinese cabbage lettuce celery.The estimated total daily intake of chromium substantially exceeds the dietary allowable value,which may pose health risks to local population.
基金The National Natural Science Foundation of China (No.50405021)
文摘In order to evaluate the reliability of long-lifetime products with degradation data, a new proportional hazard degradation model is proposed. By the similarity between time-degradation data and stress-accelerated lifetime, and the failure rate function of degradation data which is assumed to be proportional to the time covariate, the reliability assessment based on a proportional hazard degradation model is realized. The least squares method is used to estimate the model's parameters. Based on the failure rate of the degradation data and the proportion function of the known time, the failure rate and the reliability function under the given time and the predetermined failure threshold can be extrapolated. A long life GaAs laser is selected as a case study and its reliability is evaluated. The results show that the proposed method can accurately describe the degradation process and it is effective for the reliability assessment of long lifetime products.
基金Project (2010CB732004) supported by the National Basic Research Program of China
文摘A Bayes discriminant analysis method to identify the risky of complicated goaf in mines was presented. Nine factors influencing the stability of goaf risky, including uniaxial compressive strength of rock, elastic modulus of rock, rock quality designation (RQD), area ratio of pillar, ratio of width to height of pillar, depth of ore body, volume of goaf, dip of ore body and area of goal, were selected as discriminant indexes in the stability analysis of goal. The actual data of 40 goals were used as training samples to establish a discriminant analysis model to identify the stability of goaf. The results show that this discriminant analysis model has high precision and misdiscriminant ratio is 0.025 in re-substitution process. The instability identification of a metal mine was distinguished by using this model and the identification result is identical with that of practical situation.
文摘Pinus radiata was introduced to the summer rainfall environments of Sichuan Province, China in the 1990s as a part of an afforestation pmgram for soil and water conservation in the arid and semi-arid river valley area of Aba Prefecture. Within this region a total area of 26 000 ha have been identified through climate matching as suitable and a further 63 000 ha potentially suitable for environmental plantings of P. radiata. The plantations are being established in widely separated small patches on steep and degraded slopes along the dry river valley The newly introduced P. radiata are exposed to two kinds of forest health risks: they may be attacked by (a) indigenous pathogens and pests against which they may not possess any resistance or (b) by inadvertently introduced foreign pests or pathogens. This paper presents a survey of the potential damaging pests and a preliminary assessment of forest health risks facing the P. radiata plantations over a much longer timeframe than the initial phase of introduction and early plantation establishment. An empirical appmach was adopted to evaluate forest health risks by a combination of literature review, examination of historical records of pest and disease outbreaks in the surrounding conifemus forests, field surveys and inspections, specimen collection and identification, and most importantly, expert analysis of the likelihood of attack by specific pests and pathogens and the subsequent impact of such attacks. The assessment identified some specific forest health risks to the long-term success of P. radiata introduction in this area. These risks are closely associated with the indigenous pests and pathogens of the two native pine species, P. tabulaeformis and P. armondii since these pests and pathogens are considered more likely to establish on P. radiata over time. Exotic pests and pathogens are of a quarantine concern at present. Based on the results of assessment, recommendations are pmvided to improve forest vigour and to reduce the forest health risks posed by indigenous as well as exotic pests and pathogens to the introduced P. radiata. Ways to increase the ability to manage the forest health risks once a particular pest infestation and disease eventuates are also recommended. Although detrimental to the survival and growth of the introduced P. radiata, the impact of identified forest health risks are not considered to be fatal to the long term success ofP. radiata in this area.
基金Project(2010467038)supported by the Special Fund for Environmental Research in the Public Interest,China
文摘Literature lacked in providing a comprehensive research on heavy metal detection in aquatic, biological and sedimentary states of rivers. The present study was imparted with all these three components of the river. Heavy metal toxicity or pollution index was used as a tool for ecological risk assessment by considering the single state studies conducted by many researchers. An intensive ecological risk assessment model was constructed and heavy metals were indicated as a serious threat to the environment. The model was applied to determining five toxic heavy metals in three states of the Songhua River. According to the ecological risk index, heavy metal pollution in three phases was categorized as aquatic〉biological〉sedimentary, while the overall descending order of heavy metal ecological risk index was as Cd〉Hg〉As〉Pb〉Cr. Cd and Hg were selected as the priority pollutants of Songhua River.