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
The severe drought that Australia has endured over the past few years has impacted adversely on the environment and is the major cause of the reduction of water levels in the Coorong and Lower Lakes. The over-allocati...The severe drought that Australia has endured over the past few years has impacted adversely on the environment and is the major cause of the reduction of water levels in the Coorong and Lower Lakes. The over-allocation and over-use of water in the MDB （Murray-Darling Basin） has caused the system to endure the longest period ever of reduced freshwater inflows and levels. The environmental state of Coorong and Lower Lakes is an issue that requires immediate action by governments and the surrounding community. This article will explore current data regarding the social and planning implications of the degradation of the Coorong and Lower Lakes. It primarily focuses on the social impacts that will occur if the Coorong and Lower Lakes area is significantly environmentally degraded. Drawing on Beck＇s risk theory, this paper analyses the adaptive capacity of settlements in the Coorong and Lower Lakes area and how they respond to the stresses and risks caused by environmental degradation. Economic and environmental implications will also be explored to provide an understanding of the interdependencies, This article provides a foundation and theoretical structure for further investigative research to be undertaken.展开更多
The Grain-for-Green Policy aims to convert cropland to grassland and forest across western China, and evaluating ecological risk is essential to its implementation. Because few recent studies have focused on eco-risk ...The Grain-for-Green Policy aims to convert cropland to grassland and forest across western China, and evaluating ecological risk is essential to its implementation. Because few recent studies have focused on eco-risk changes of land use in the areas affected by significant policies, this paper took Zhengning County in Gansu Province as our focal area, and studied spatial-temporal changes in ecological risk before and after policy implementation. Based on indices of landscape fragmentation and ecosystem service value, an ecological risk assessment method using ArcGIS and Fragstats was done. The regional gravity center model and land spatial distribution model were also used to enrich the quantitative description of divisional eco-risk and its spatial-temporal variation in the county. Results showed that the implementation of the policy has contributed to an overall reduction in ecological risk in Zhengning County, with a divisional degree order reduction following the pattern： eastern Zhengning 〉 western Zhengning 〉 central Zhengning. The gravity center for eco-risk shifted 4288 m southwest from 1995 to 2010 due to landscape fragmentation. The study implies that greater attention should be paid to forest and grassland restoration in eastern Zhengning, cropland protection in central Zhengning, and soil and water conservation in western Zhengning.展开更多
The entire land of Southern Iran faces problems arising out of various types of land degradation of which vegetation degradation forms one of the major types. The Qareh Aghaj basin（1 265 000 ha）,which covers the upp...The entire land of Southern Iran faces problems arising out of various types of land degradation of which vegetation degradation forms one of the major types. The Qareh Aghaj basin（1 265 000 ha）,which covers the upper reaches of Mond River,has been chosen for a test risk assessment of this type. The different kinds of data for indicators of vegetation degradation were gathered from the records and published reports of the governmental offices of Iran. A new model has been developed for assessing the risk of vegetation degradation. Taking into consideration nine indicators of vegetation degradation the model identifies areas with ＂Potential Risk＂（risky zones） and areas of ＂Actual Risk＂ as well as projects the probability of the worse degradation in future. The preparation of risk maps based on the GIS analysis of these indicators will be helpful for prioritizing the areas to initiate remedial measures. By fixing the thresholds of severity classes of the nine indicators a hazard map for each indicator was first prepared in GIS. The risk classes were defined on the basis of risk scores arrived at by assigning the appropriate attributes to the indicators and the risk map was prepared by overlaying nine hazard maps in the GIS. Areas under actual risk have been found to be widespread（78%） in the basin and when the risk map classified into subclasses of potential risk with different probability levels the model projects a statistical picture of the risk of vegetation degradation.展开更多
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.
文摘The severe drought that Australia has endured over the past few years has impacted adversely on the environment and is the major cause of the reduction of water levels in the Coorong and Lower Lakes. The over-allocation and over-use of water in the MDB （Murray-Darling Basin） has caused the system to endure the longest period ever of reduced freshwater inflows and levels. The environmental state of Coorong and Lower Lakes is an issue that requires immediate action by governments and the surrounding community. This article will explore current data regarding the social and planning implications of the degradation of the Coorong and Lower Lakes. It primarily focuses on the social impacts that will occur if the Coorong and Lower Lakes area is significantly environmentally degraded. Drawing on Beck＇s risk theory, this paper analyses the adaptive capacity of settlements in the Coorong and Lower Lakes area and how they respond to the stresses and risks caused by environmental degradation. Economic and environmental implications will also be explored to provide an understanding of the interdependencies, This article provides a foundation and theoretical structure for further investigative research to be undertaken.
基金National Natural Science Foundation of China (No. 40971282)
文摘The Grain-for-Green Policy aims to convert cropland to grassland and forest across western China, and evaluating ecological risk is essential to its implementation. Because few recent studies have focused on eco-risk changes of land use in the areas affected by significant policies, this paper took Zhengning County in Gansu Province as our focal area, and studied spatial-temporal changes in ecological risk before and after policy implementation. Based on indices of landscape fragmentation and ecosystem service value, an ecological risk assessment method using ArcGIS and Fragstats was done. The regional gravity center model and land spatial distribution model were also used to enrich the quantitative description of divisional eco-risk and its spatial-temporal variation in the county. Results showed that the implementation of the policy has contributed to an overall reduction in ecological risk in Zhengning County, with a divisional degree order reduction following the pattern： eastern Zhengning 〉 western Zhengning 〉 central Zhengning. The gravity center for eco-risk shifted 4288 m southwest from 1995 to 2010 due to landscape fragmentation. The study implies that greater attention should be paid to forest and grassland restoration in eastern Zhengning, cropland protection in central Zhengning, and soil and water conservation in western Zhengning.
文摘The entire land of Southern Iran faces problems arising out of various types of land degradation of which vegetation degradation forms one of the major types. The Qareh Aghaj basin（1 265 000 ha）,which covers the upper reaches of Mond River,has been chosen for a test risk assessment of this type. The different kinds of data for indicators of vegetation degradation were gathered from the records and published reports of the governmental offices of Iran. A new model has been developed for assessing the risk of vegetation degradation. Taking into consideration nine indicators of vegetation degradation the model identifies areas with ＂Potential Risk＂（risky zones） and areas of ＂Actual Risk＂ as well as projects the probability of the worse degradation in future. The preparation of risk maps based on the GIS analysis of these indicators will be helpful for prioritizing the areas to initiate remedial measures. By fixing the thresholds of severity classes of the nine indicators a hazard map for each indicator was first prepared in GIS. The risk classes were defined on the basis of risk scores arrived at by assigning the appropriate attributes to the indicators and the risk map was prepared by overlaying nine hazard maps in the GIS. Areas under actual risk have been found to be widespread（78%） in the basin and when the risk map classified into subclasses of potential risk with different probability levels the model projects a statistical picture of the risk of vegetation degradation.
