Remanufacturing end-of-life products requires setting up an economically and environmentally viable reverse logistics channel for supplying reusable used modules to the production chain. This paper introduces a framework to allow generating and assessing different reverse logistics channel structures. The framework is then applied to a product remanufacturing case. We analyze the current reverse logistics channel structure and propose alternative structures with less environmental impact and higher economic benefits. 相似文献
Pesticide volatilization to the atmosphere may be a major pathway of dissipation closely linked with environmental, physico-chemical and technical factors. Understanding the volatilization process requires systems that make it possible to control some of these factors. Wind tunnels meet to these criteria. The volatilization flux is determined from a mass balance, using the difference in atmospheric pesticide concentration between the entrance and the exit of the tunnel and the airflow rate. An experiment was carried out in June 2000 to study the repeatability of this technique. Volatilization of trifluralin was measured in three wind tunnels for 8 days with a sampling period varying between 3 h and 2 days. Pesticide concentration was determined by trapping by XAD-2 resin in a two-stage cartridge, solvent extraction and analysis by gas chromatography. Cumulated losses through volatilization reached 30% of the measured application dose after 8 days, with a variability of less than 20% between the three tunnels. Approximately 20% remained in the topsoil (0–2 cm), with a variability of 14% between the three tunnels. The decrease in the volatilization flux over time is coherent with the expected theoretical evolution for a volatile pesticide such as trifluralin and with previous experimental works. 相似文献
Regulatory agencies are interested in a fecal indicator bacterium with a host range limited to humans because human fecal contamination represents the greatest hazard to humans, yet is a relatively easy nonpoint source to remedy. Watersheds with human fecal contamination could be given first priority for cleanup. A fecal indicator bacterium with a host range limited to humans and a few other warm-blooded animal species would also simplify microbial source tracking because only a few animal species would be required for any host origin database. The literature suggests that the fecal indicator bacterium Enterococcus faecalis has a limited host range. On this basis, we selected this bacterium for study. Of 583 fecal streptococcal isolates obtained on Enterococcosel agar from Canada goose, cattle, deer, dog, human, chicken, and swine, 392 were considered presumptive enterococci and were subsequently speciated with the API 20 Strep system. Of these isolates, 22 were Ent. durans (5.6%), 61 were Ent. faecalis (15.6%), 98 were Ent. faecium (25.0%), 86 were Ent. gallinarum (21.9%), and 125 were unidentified (31.9%). The host range of the Ent. faecalis isolates was limited to dogs, humans, and chickens. Media were developed to isolate and identify Ent. faecalis quickly from fecal samples and this scheme eliminated Ent. faecalis isolates from dogs. When the remaining Ent. faecalis isolates were ribotyped, it was possible to differentiate clearly among the isolates from human and chicken. It may be that combining the potentially limited host range of Ent. faecalis with ribotyping is useful for prioritizing watersheds with fecal contamination. 相似文献
Summary. In the rabbit, lactating females emit a volatile
compound in milk, the mammary pheromone (MP), that
triggers rooting for the nipple and its grasping in pups.
Previous studies have shown that the MP seems to act selectively,
in terms both of intensity and quality. Here, we aimed
to add new evidence to these properties of the MP. Newborn
rabbits (n=825) were submitted to an oral activation test
allowing to measure their searching/grasping responses
towards different stimuli. In Experiment 1 we assessed
whether pups respond to the MP in an intensity-dependent
manner. In Experiment 2 we assessed the activity of 20
volatiles previously identified in rabbit milk, other than the
MP, which were never systematically tested for intensitydependence.
The assays showed that a) neonatal responses
are released by the MP only for a limited range of concentrations;
b) the 20 other odorants from milk are inactive at
any concentration. Thus, the MP appears to be the single
volatile from rabbit milk that releases searching/grasping
behaviour in pups. 相似文献
In ants, nest relocations are frequent but nevertheless perilous, especially for the reproductive caste. During emigrations, queens are exposed to predation and face the risk of becoming lost. Therefore the optimal strategy should be to move the queen(s) swiftly to a better location, while maintaining maximum worker protection at all times in the new and old nests. The timing of that event is a crucial strategic issue for the colony and may depend on queen number. In monogynous colonies, the queen is vital for colony survival, whereas in polygynous colonies a queen is less essential, if not dispensable. We tested the null hypothesis that queen movement occurs at random within the sequence of emigration events in both monogynous and polygynous colonies of the ponerine ant Pachycondyla obscuricornis. Our study, based on 16 monogynous and 16 polygynous colony emigrations, demonstrates for the first time that regardless of the number of queens per colony, the emigration serial number of a queen occurs in the middle of all emigration events and adult ant emigration events, but not during brood transport events. It therefore appears that the number of workers in both nests plays an essential role in the timing of queen movement. Our results correspond to a robust colony-level strategy since queen emigration is related neither to colony size nor to queen number. Such an optimal strategy is characteristic of ant societies working as highly integrated units and represents a new instance of group-level adaptive behaviors in social insect colonies. 相似文献
Analytical solutions are widely used as screening tools for estimating the potential for contaminant transport in groundwater, or for interpreting tracer tests or groundwater quality data. A solution for three-dimensional solute migration from a plane-source source that is frequently used in practice is the approximate solution of Domenico [J. Hydrol. 91 (1987) 49-58]. A more rigorous solution to the same problem was provided by Sagar [ASCE, J. Hydraul. Div. 108, no. HY1 (1982) 47-62]. A comprehensive and unambiguous comparison between these two solutions is provided using dimensionless analysis. The solutions are first cast in terms of dimensionless parameters and then used to provide type curves covering a wide range of dimensionless parameter values. Results show that while discrepancies between the two solutions are relatively negligible along the plume centreline (for flow regimes dominated by advection and mechanical dispersion), large concentration differences can be observed as lateral distance from the centreline increases, especially in the presence of solute decay. 相似文献
Miniaturized queens, microgynes, are regarded as an alternative reproductive strategy sparsely present through the ant world.
The described roles of miniaturized queens include alternative short-distance dispersal morphs, an adaptation to polygyny
and inquiline parasites. Some of these inquiline parasite microgynes have been described as a separate species from their
host. In the poneromorph group, miniaturized queens are only reported in two Mexican populations of two Ectatomminae: Ectatomma tuberculatum, in which small queens represent an inquiline species (Ectatomma parasiticum) and Ectatomma ruidum. E. ruidum presents apparently facultative polygyny with microgynes. We used mitochondrial DNA markers and newly developed microsatellite
loci to investigate the status as well as the role of microgynes in E. ruidum. We confirmed that microgynes and macrogynes are from the same species. This species is almost exclusively monogynous and
monoandrous, supernumerary dealate queens of both types being actually daughters of the mother queen. An apparently polygynous
nest was more often headed by a macrogyne than a microgyne. We didn't find any inbreeding or isolation by distance in the
studied population, indicating that new gynes are inseminated by unrelated males and can establish a new nest far from their
natal nest. However, re-adoption of daughter queens seems to be the rule and rate of microgyny appears to be linked to nest
density and environmental factors. 相似文献
Net primary production (NPP), the difference between CO2 fixed by photosynthesis and CO2 lost to autotrophic respiration, is one of the most important components of the carbon cycle. Our goal was to develop a simple regression model to estimate global NPP using climate and land cover data. Approximately 5600 global data points with observed mean annual NPP, land cover class, precipitation, and temperature were compiled. Precipitation was better correlated with NPP than temperature, and it explained much more of the variability in mean annual NPP for grass- or shrub-dominated systems (r2 = 0.68) than for tree-dominated systems (r2 = 0.39). For a given precipitation level, tree-dominated systems had significantly higher NPP (approximately 100-150 g C m(-2) yr(-1)) than non-tree-dominated systems. Consequently, previous empirical models developed to predict NPP based on precipitation and temperature (e.g., the Miami model) tended to overestimate NPP for non-tree-dominated systems. Our new model developed at the National Center for Ecological Analysis and Synthesis (the NCEAS model) predicts NPP for tree-dominated systems based on precipitation and temperature; but for non-tree-dominated systems NPP is solely a function of precipitation because including a temperature function increased model error for these systems. Lower NPP in non-tree-dominated systems is likely related to decreased water and nutrient use efficiency and higher nutrient loss rates from more frequent fire disturbances. Late 20th century aboveground and total NPP for global potential native vegetation using the NCEAS model are estimated to be approximately 28 Pg and approximately 46 Pg C/yr, respectively. The NCEAS model estimated an approximately 13% increase in global total NPP for potential vegetation from 1901 to 2000 based on changing precipitation and temperature patterns. 相似文献
Health risks associated with inhalation of fine particulate matter of 2.5 µm in diameter or smaller depend on their atmospheric levels and physicochemical properties. The relationships between chemical compositions and genotoxic activities of particles emitted by mineral industries, traffic and urban sources during summer and winter in the region of Provence-Alpes-Côte d'Azur (France) were investigated.
The fine particles were separated in respect to water-soluble (13 minerals and metals) and organic-extractable (16 polycyclic aromatic hydrocarbons) components that were quantified. The chromosome damaging properties of the hydrophilic and lipophilic extracts were assessed using the centromeric micronucleus assay on a human lung fibroblast cell line.
The composition of the fine particulate matter was variable and depended upon the sources and seasons. Both the hydrophilic and lipophilic extracts induced chromosome damage: (1) in hydrophilic extracts, Ca and Zn affected chromosome losses induction; (2) acenapthylene affected chromosome damage (breakages and losses) induction and naphthalene affected chromosome damage and losses induction in lipophilic extracts without metabolic activation; and (3) benzo[a]pyrene affected chromosome losses induction in lipophilic extracts with metabolic activation. Fine particulate matter arising from coal-fired power station, road traffic, and other urban sources were the most efficient to induce chromosome breakage. 相似文献