Test analysis of detection of damage to a complicated spatial model structure

A two-stage damage detection approach is proposed and experimentally demonstrated on a complicated spatial model structure with a limited number of measurements. In the experiment,five known damage patterns,including 3 brace damage cases and 2 joint damage cases,were simulated by removing braces and weakening beam鈥揷olumn connections in the structure. The limited acceleration response data generated by hammer impact were used for system identification,and modal parameters were extracted by using the eigensystem realization algorithm. In the first stage,the possible damaged locations are determined by using the damage index and the characteristics of the analytical model itself,and the extent of damage for those substructures identified at stage I is estimated in the second stage by using a second-order eigen-sensitivity approximation method. The main contribution of this paper is to test the two-stage method by using the real dynamic data of a complicated spatial model structure with limited sensors. The analysis results indicate that the two-stage approach is ableto detect the location of both damage cases,only the severity of brace damage cases can be assessed,and the reasonable analytical model is critical for successful damage detection.

Sheep grazing causes shift in sex ratio and cohort structure of Brandt’s vole:Implication of their adaptation to food shortage

Livestock grazing has been demonstrated to affect the population abundance of small rodents in grasslands,but the causative mechanism of grazing on demographic parameters,particularly the age structure and sex ratio,is rarely investigated.In this study,we examined the effects of sheep grazing on the cohort structure and sex ratio of Brandt’s vole(Lasiopodomys brandtii)in Inner Mongolia of China by using large manipulative experimental enclosures during 2010-2013.Our results indicated that sheep grazing significantly decreased the proportion of the spring-born cohort,but increased the proportion of the summer-born cohort.Grazing increased the proportion of males in both spring and summer cohorts.In addition,we found a negative relation between population density and the proportion of the overwinter cohort.Our results suggest that a shift in the cohort structure and the sex ratio may be an important strategy for small rodents to adapt to changes in food resources resulting from livestock grazing.

Post-fire regeneration dynamics in whitebark pine(Pinus albicaulis) forests in Wind River and Absaroka Mountains,Wyoming, USA

Whitebark pine （Pinus albicaulis） populations are in decline across the species＇ range due to historic wildfire exclusion, mountain pine beetle （Dendroctonus ponderosae, MPB） outbreaks, and an invasive fungal pathogen causing the disease white pine blister rust （Cronartium ribicola, WPBR）. Despite reliance on stand- replacing fires, information on whitebark pine regeneration occurrence is limited and the trajectory of future forests is largely unknown in some areas of the range. Regeneration densities were assessed in burned and adjacent non-burned areas at six high elevation locations in northwest Wyoming where stand-replacing fires occurred 8-32 years before thesurveys. In these locations at the eastern extent of the species range, we assessed what site factors were associ- ated with regeneration success. Whitebark pine regen- eration density was greater and seedlings were older in non-burned compared to burned areas. Within burns, north aspects had more regeneration than south aspects. Potential seed source densities and other species＇ regeneration were positively related to whitebark p^ne regeneration densities in burned areas. South facing slopes or grass covered areas may have either delayed or no regeneration of whitebark pine without the help of artificial planting.

Impact of Demographic Structure on Paddy and Forestland Management

In order to understand the impact of demographic structure on paddy and forestland managementafter the convening of the Third Plenary Session of the 11th CPC (Communist Party of China) CentralCommittee and the implementation of the Household Responsibility System (the government divided upland among peasants for cultivating and the peasants sell a set part of their produced goods to thegovernment at stipulated prices by contract in the countryside of China), 147 households in 6 villages,belonging to Xiangtan County and Zhuzhou County in Hunan Province, were selected as research samples,and interview, questionnaire survey and second hand data analyzing were used as the methods. The resultsshowed: Persons with different ages had different ideas, and young peasants would like to work in townsor cities for more income, so they used and depended on land less; In terms of sex, the male was still themain user of land, and therefore the ability, idea and activity of male played an important role in landmanagement; Generally, the labors with better educational background grasped more knowledge andtechnologies, and they had more opportunity to get jobs and had better working condition and moreincome in town or cities, so they depended on and used land less.