RESUMO
Information on base flow for river habit maintenance (BFRH) and its thresholds is necessary for water resource utilization and protection. BFRH and its thresholds have significant spatial differences; however, it is still unclear how to identify and assess these characteristics. In this study, a technical framework was proposed to clarify the specific procedures and methods for regionalization of BFRH and its thresholds in large-scale areas. The framework includes four parts: construction of controlling factor system, sub-region division, identification of dominant factors, and determination of the thresholds in sub-regions. The framework was then applied to China to analyzed the regionalized characteristics of BFRH and its thresholds from a national perspective. The results illustrate the following: (1) the country is divided into nine sub-regions, and the controlling factors and their action paths to BFRH vary greatly. The elements of climate, vegetation, soil, topography and morphology are satisfactory in explaining the variance of BFRH and its thresholds, as R2 of the partial least squares structural equation modeling is between 0.503 and 0.848. (2) The value of BFRH/MAF (i.e. the proportion of BFRH to mean annual natural flow) differs greatly among sub-regions. The mean value is the largest in the Northwest Region, reaching 20 %, while it is only 1.7 % in the Northeast Cold Region. (3) The dynamic and static thresholds are obtained by using the precipitation and other indices as the explanatory variables in the sub-regions. In general, the more abundant the water resources, the higher may be the threshold. Moreover, attention should be paid to the positive and negative effects of vegetation restoration on this threshold. The case study proves that the framework can guide the determination of BFRH, especially for ungagged rivers. Importantly, the framework is flexible and highly adaptable in different regions.
RESUMO
An unanesthetized cat model of acute focal cerebral ischemia has been establishes by the technique of transorbital snare ligature for middle cerebral artery (MCA) occlusion, The model was used to investigate patterns of changes of regional cerebral blood flow (rCBF) for up to 16 hours following MCA occlusion by the hydrogen clearance technique and to explore the correlation among microregional blood flow changes, neurological deficit, and pathological changes including size of infarct and severity of brain edema. The animals were divided into 2 groups according to size of infarct that was identified by 2% triphenyl tetrazolium chloride solution stain. The results were as follows : 1) Infarct larger than 10% of coronal section surface of the ipsilateral cerebral hemisphere was found in 18 cats( Group A), and smaller infarct was found in the remaining 7 cats (Group B). Between these 2 groups, there was a statistically significant difference in the average rCBF value of ipsilateral MCA territory during 16 hours of ischemia (Group A:6.5ml/100g/min, Group B:32.6ml/100g/min) (P<0.01). 2) Increasing grade of contralateral paralysis correlated well with decreasing rCBF in MCA territory of occlusion side and all animals showing complete paralysis belonged to Group A with their average rCBF from ipsilateral MCA territory below 10.0ml/100g/min. 3) Increasing grade of cerebral hemispheric swelling was directly proportional to increasing grade of paralysis and there was also a significant difference in hemispheric swelling between Group A and B, Correlation between grades of infarct size and severity of paralysis was not evident. 4) There patterns of charges of rCBF were observed :In 15 cats of Pattern I, MCA occlusion caused persistent severe ischemia, measuring less than 16-17ml/100g/min(average rCBF:6.28ml/100g/min), to produce large infarct, pronounced paralysis, and severe histological damage(Group A). 5) In 7 cats of Pattern I, persistent mild to moderate ischemia, maintaining more than 23-24ml/100g/min(average rCBF:32.6ml/100g/min), was noted in association with much smaller infarct and milder hemiparesis(Group B). 6) In the remaining 3 cats of Pattern I, MCA occlusion caused immediate severe ischemia followed by early postischemic hyperemia and death during 8 to 14 hours after MCA occlusion owing to marked brain swelling and transtentorial herniation (Group A). 7) During the initial stage of ischemia, significant decrease in rCBF of the contralateral hemisphere was observed in both groups, however, in Group A, rCBF gradually increased to preocclusion level. Only Group B presented further decrease in rCBF suggesting the presence of interhemispheric diaschisis. Thus Group B appeared to take advantage of diaschisis during the late phase of infarct development as well as substantial collateral flow from the surrounding posterior cerebral and anterior cerebral artery territories.