As a result of global competition, international companies that manufacture photocopiers, printers or car navigation systems have to purchase low-cost electronic components such as semiconductors and hard disk drives by outsourcing production. However, it is often difficult for these companies to evaluate the quality of their suppliers through interviews and technical documentations. This article proposes new measures for supplier assessment and a systematic approach to select suppliers that have in-depth knowledge of component reliability and technology. The measures for selection not only include the physical quality of components but also information disclosures provided by suppliers, which consist of failure analysis, reliability data and details of the design-manufacturing process. The proposed measures are applied to real data of photocopier manufacturing enterprises. Experiments conducted show that a systematic assessment will enable selecting appropriate suppliers with a lower failure rate. 相似文献
Urbanization generally reduces wildlife populations. Individual species responses, however, are often highly variable, and such variability can be explained by differences in species ecological traits. To examine this hypothesis, we focused on two co-occurring land snails, Ezohelix gainesi and Euhadra brandtii sapporo; the former is ground-dwelling and the latter is arboreal. We first estimated their population densities at nine sites distributed along an urbanization gradient: three were located in continuous natural forests, three at the edge of natural forests, and the rest in small isolated forests in urban areas. As a result, the ground-dwelling E. gainesi occurred at highest density in urban forests, followed by forest edges and continuous forests. By contrast, the arboreal E. b. sapporo occurred at highest density in continuous forests, but declined in forest edges and urban forests. We then conducted manipulative field experiments to quantify changes in predation pressure on these species. Ground-tethered E. gainesi and E. b. sapporo were repeatedly predated upon by forest-living mammals in continuous forests, but their survival rates increased in forest edges and urban forests. By contrast, canopy-tethered E. b. sapporo maintained high survival rates in all three forest types. The results indicate that a lack of mammalian predators enables ground-dwelling species to occur at high densities in urban forests, whereas the arboreal species was not affected by this predator relaxation effect. The combination of species-specific behavioural traits and changes in predator communities across an urbanization gradient has important effects on the biodiversity of urban ecosystems.
Urban Ecosystems - The original version of the article unfortunately contained mistakes in the legends of Fig. 3. The legends (1) Blue square: Euhadra brandtii sapporo, ground is changed... 相似文献
Summary
Luehdorfia butterflies lay eggs in clusters. Clones of their host plants (Asiasarum andHeterotropa) are distributed pacthily among the understory of deciduous forests. Groups ofLuehdorfia larvae often exhaust the clones and may wander over the forest floor seeking new clones. The highest mortality observed is
during this wandering period. To elucidate whyLuehdorfia butterflies lay eggs in clusters, a simulation experiment was made for hypothetical populations which lay eggs in clusters
or singly. Field data on larval mortality, consumption, density of host clones and leaf weight forLuehdorfia japonica were incorporated into the model. The predictions of the simulation were: (1) When the egg density is low, the single egg
type could leave many more pupae than the egg clustering type, but when the egg density is high, the former might leave smaller
number of pupae than the latter; and (2) There are optimal sizes of egg clusters for different egg densities and the optimal
size becomes larger as the egg density increased.
This work was supported in part by Grant-in-Aid No. 439017 and No. 56480039 from the Ministry of Education, Science and Culture,
Japan. 相似文献
Genetic hazards associated with the stocking of fish juveniles produced in hatcheries were studied with simple mathematical
models. Domestication is the process of acquiring a genetic characteristics that are advantageous in a hatchery environment
but that are disadvantageous in a natural environment due to the selection pressure in the hatchery differing from that in
the natural environment. Conditions for the propagation of mutants enhancing domestication were obtained for a variety of
stocking strategies specified by parameters related to hatchery productivity and kind of brood stock used. By using this,
the possibility of reducing the risk of domestication was studied. As a means of reducing the risk, selective use of wild-born
individuals for brood stock was considered. The effectiveness of this was analyzed for both the cases where all brood stock
is collected from the wild, and the male brood stock is collected from the wild and the female brood stock is born and reared
in a hatchery. We also estimate how much hatchery release can be increased without increasing the risk by employing these
means. It is concluded that the use of only male brood stock from the wild is not very effective in reducing the risk of domestication.
Further, it is concluded that selective use of the wild-born individuals of both sexes for brood stock is highly desirable
if the contribution of released individuals to the natural reproduction is high. In other words, substantial increase of hatchery
release may be possible while keeping risk at a level comparable to that under moderate hatchery release, if it is accompanied
by the selective use of wild-born individuals for brood stock. 相似文献
This paper proposes a realistic queueing model of automated guided vehicle (agv) systems in just-in-time production systems. The model takes into consideration return paths, Erlang distributed service times, and pull-type dispatching rule, assuming finite buffer capacities. Since it has no product-form solution and natural decomposability due to complex nontree fork-cum-join architecture and dynamic dispatching rules, we propose a machine-based decomposition algorithm for the performance evaluation of the model. Each decomposed module consists of the processing machine and its dispatching station. Three flow probabilities, derived from flow conservation analysis, relate the modules, which are updated iteratively until the parameters converge. The numerical results from a real-life Agv system application show that the algorithm is reasonably accurate. 相似文献