Search

This paper introduced a virtual roaming system which can be effectively used in studying ocean scenes based on 3ds max modeling tools and virtools development software. Establishing this system needs the following steps: building geometric model, making texture mapping, light treatment, importing model and designing interactive function. Taking jack-up offshore platform as an example, the system has three roaming modes including manual roaming with character, manual roaming without character and automatic roaming. Users can roam in this platform freely. The collision detection technology and the immersive technology were integrated into the system to improve the reality of it. The system also has a good visual effect and interactive function.

The primary goal of concurrent engineering is to minimize the time spend and to reduce quality problems encountered between a product's conception and customer use, thereby minimizing cost and maximizing product quality. Tolerance is an important index of product design and manufacture. Although they are small as compared with part dimensions, tolerances can propagate and accumulate in an assembly affecting the product assimilability. Moreover, tolerance is inevitable because manufacturing exactly equal parts is known to be impossible. This paper presents a brief review of statistical tolerance and clearance analysis for the assembly, and proposes a method of tolerance analysis by a leading commercial computer-aided tolerance (CAT) analysis system, VisVSA. This method can ensure assembly precision requirements, and design optimally tolerance distribution based on Monte Carlo simulation, take a example of brake assembly to detailed introduce the use of this method. The purpose of this article is expected to make the following contributions: (i) to help the designers to evaluate products for assimilability, (ii) to provide a new perspective to tolerance problems, and (iii) to provide a tolerance analysis tool, VisVSA, which can be incorporated into a CAD or solid modeling system.

For decades, arid desert ecosystems in northwest China, covering one-fourth the country’s land surface, have experienced a rapid decline in plant species diversity, productivity and soil carbon stock owing to degradation by overgrazing. In this study, plant community composition, diversity and productivity, as well as soil carbon (C) and nitrogen (N) stocks, were monitored over 26 years from 1981 to 2006 in a severely degraded Haloxylon ammodendron-dominated shrubland where livestock densities were reduced from 4–5 to 1–2 dry sheep equivalent ha-1. The objective was to assess long-term grazing effects on vegetation and soil C and N accumulation dynamics. Results showed that the reduction of grazing pressure significantly increased vegetation cover, plant diversity and productivity, resulting primarily from an increase in livestock-preferred species. Controlled grazing also led to marked increases in soil C and N stocks in the top 30 cm of soil. This increase was strongly associated with increased plant species richness, vegetation cover and biomass production. Averaged over 26 years, soil C and N accumulated at rates of 89.9 g C and 8.4 g N m-2 year-1, respectively, but rates of C and N accumulation varied greatly at different time periods. The greatest species regeneration occurred in the first 8 years, but the largest C and N accumulation took place during years 9–18, with a time-lag in response to changes in vegetation. Our results provide insights into the long-term recovery patterns of different ecosystem components from the influence of prolonged overgrazing disturbance that cannot be inferred from a short-term study. The findings are important for assessing the resilience of these livestock-disturbed desert ecosystems and developing a more effective strategy for the management of this important biome from a long-term perspective.

To understand the neutralized antibody level of the poliomyelitis among healthy people and provide scientific evidence for the immunization strategy since routine and intensified immunization with oral polio vaccine (OPV) in Fujian province.The poliomyelitis antibody level of healthy people were detected by neutralization test of the micro cells.The neutralizing antibody positive rates were 99.0%, 99.3%, 97.5% and GMTs were 1:79.1, 1:31.2, 1:24.7 for polio I, II, III respectively in 400 serum specimens from 1-59 years old. GMTs present a trend of decreasing as age's increasing.A protective barrier had been built against poliomyelitis in healthy people in Fujian province through routine and intensified immunization with OPV.