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排序方式: 共有220条查询结果,搜索用时 93 毫秒
161.
M. Ziya Söğüt 《International Journal of Green Energy》2018,15(3):169-180
Design and modernization of the micro turbojet engine technology have an important problem related to fuel consumption in terms of economics and environmental. For this purpose, in this study, first, energy and exergy efficiencies of the Jet A-1 and seven different alternative fuels were examined. Then, Exergy—based sustainability indicators were evaluated via exergetic irreversibility seperately. For this purpose, operational data of SR-30 micro-turbojet engine was taken as reference. According to this, the exergy efficiencies of engine as fuel for blending of methanol and ethanol were fixed with 22.35% and 20.56%, respectively. At the end of the study, some evaluations about alternative fuels and sustainability were made. 相似文献
162.
Sonne C Rigét FF Beck Jensen JE Hyldstrup L Teilmann J Dietz R Kirkegaard M Andersen S Letcher RJ Jakobsen J 《Environment international》2008,34(6):811-820
There is a great need for understanding the impact from dietary OHCs (organohalogen compounds) on bone mineral composition - and thereby osteoporosis - in especially arctic wildlife such as polar bears (Ursus maritimus) as well as humans. For that purpose, we measured BMD (bone mineral density) by DXA scanning (g/cm(-2)) in 15 age and weight normalized sledge dog (Canis familiaris) bitches and their 26 pups divided into a control group (n=26) given 50-200 g/day clean pork (Suis scrofa) fat and a treated group (n=15) given 50-200 g/day OHC polluted minke whale (Balaenoptera acutorostrata) blubber as main lipid sources. The results showed that BMD increased significantly with age (linear regression: p<0.0001, r(2)=0.83, n=41) while no sex difference was found in the F-generation (two-way ANOVA: all p>0.3). No differences in BMD(femur) or BMD(vertebrae) between exposed and control individuals in the bitch generation were found (linear mixed effect model: both p>0.38). Likewise, no difference between exposed and control subadults and juveniles in the F-generation was found (two-way ANOVA: all p>0.33). Correlation analyses between BMD(femur), BMD(vertebrae) and groups of OHCs, respectively, did not show any statistically significant relationships nor a clear or decreasing trend (Pearson's: p: 0.07-0.78; r: -0.2-0.59; n: 10-18). As the groups were similar regarding genetics, age and sex are the only factors that can explain this observation. Either the pollutants did not have an impact on BMD using the present time frame and OHC concentrations (threshold levels not reached), or the difference in food composition (mainly vitamins and n3 fatty acids) conceal the potential OHC impact on BMD. Such information is important when evaluating the positive and negative health consequences from eating polluted marine species. 相似文献
163.
Thomas?HartmannEmail author H?kan?H?ggstr?m Claudine?Theuring Rainer?Lindigkeit Martine?Rahier 《Chemoecology》2003,13(3):123-127
Summary. The harvestman Mitopus morio (Phalangidae) is
a generalist predator. It is known to prey on larvae of the
chrysomelid leaf beetle Oreina cacaliae defended by plant
acquired pyrrolizidine alkaloids (PAs). Tracer feeding
experiments were performed to determine how harvestmen
tolerate protoxic PAs. Minced meat containing either
[14C]senecionine or [14C]senecionine N-oxide was fed to
M. morio and subsequently feces and bodies were analyzed.
Labeled alkaloid N-oxide remained stable and was eliminated
almost unaltered with the feces; only 10% was recovered
as tertiary PA. In contrast, approximately 80% of
labeled tertiary alkaloid (senecionine) ingested with the diet
was N-oxidized and eliminated; the remaining 20% consisted
of unchanged senecionine and a polar metabolite
of unknown structure. Harvestmen process their diet by
excreting digestive juice, indicated by bleaching of the meat
color. Analysis of the processed diet revealed some N-oxidation
of [14C]senecionine, suggesting the gut as the site of Noxidation.
Analysis of the bodies of harvestmen 80 hours
after the tracer feeding pulse revealed only trace amounts of
the polar metabolite. Neither senecionine nor its N-oxide
could be detected in the body extracts. The results are discussed
in relation to the strategies of PA adapted insects to
avoid accumulation of tertiary PAs in living tissues. 相似文献
164.
In order to study the influence of advective processes on the zooplankton distribution in a shallow sill-fjord, we examined the temporal variations (tidal and seasonal) of currents, density, abundance and composition of zooplankton in the Saguenay fjord, Québec, Canada, in August 1978 and October 1979. Our results demonstrate the existence of a regular exchange of water (every tidal cycle) between the St. Lawrence estuary and the two outer basins of the Saguenay fjord which is characterized by an important transport of mesoplankton from the estuary into the deep waters of the Saguenay during the rising tide and from the surface waters of the Saguenay to those of the estuary during falling tide. Variations of abundance and composition of zooplankton in the outer basin are therefore mainly controlled by advective processes. The plankton community of the downstream region of the fjord is strongly influenced by variations of abundance and composition taking place in the estuary, and the establishment and development of local populations of zooplankton are made difficult. In the upstream region of the fjord, the advective processes are less intense and endogeneous mesoplankton populations thrive under local temperature conditions. 相似文献
165.
Jean-François Therrien Steeve D. Côté Marco Festa-Bianchet Jean-Pierre Ouellet 《Behavioral ecology and sociobiology》2007,62(2):193-199
When resources are limited, life history theory predicts a trade-off between growth, reproduction and survival. In summer,
lactating females of temperate large herbivores such as the white-tailed deer (Odocoileus virginianus) normally have access to abundant forage but also face the high energetic needs of lactation and recovery from winter mass
loss. At high population density, however, females may face a trade-off between allocating resources for maintenance and for
reproduction. To simulate the effects of increased intra-specific competition at high density, we measured for 2 years how
an experimental food restriction of approximately 20% affected current reproduction and body mass changes of adult females
and their fawns during the fawning and lactation periods. Fawn survival decreased 35%, and fawn growth decreased 26% in the
food-restricted treatment. There was no effect of food restriction on female mass. Irrespective of treatment, however, lactating
females gained 30 g/day less than non-lactating females, and females that had weaned a fawn the previous year gained 20 g/day
less than females that had not. We conclude that when resources were scarce, females adopted a conservative strategy favouring
their own survival, mass recovery and future reproductive potential over their current reproduction, probably to maximise
their lifetime reproductive success. 相似文献
166.
T.?A.?R.?PriceEmail author Z.?Lewis D.?T.?Smith G.?D.?D.?Hurst N.?Wedell 《Behavioral ecology and sociobiology》2012,66(4):561-568
Selfish genetic elements (SGEs) that spread by manipulating spermatogenesis often have highly deleterious effects on males
that carry them. Females that mate with male carriers of SGEs can also suffer significant costs: they receive fewer and poorer-quality
sperm, their offspring will inherit the deleterious allele, and the sex ratio of their offspring will be biased towards the
more common sex. To counter these costs, females are therefore expected to prefer to mate with males that do not carry sex
ratio distorters or other deleterious selfish genetic elements. However, despite the potential costs, there are few examples
of female choice against males carrying SGEs. We searched for evidence of a female preference in fruit fly Drosophila pseudoobscura against males carrying a costly meiotic driving X-chromosome Sex Ratio (SR). In a series of five non-competitive mate preference experiments, we find no evidence that females prefer to mate with non-SR males. Our use of five separate experiments, involving more than 800 females, makes it unlikely that this lack of a difference
was due to low power or simple chance. We suggest that the lack of female choice against SGE-carrying males may be due to
strong selection on SGEs to be indistinguishable from alternative alleles. Furthermore, polyandry, either in direct response
to receiving an ejaculate from an SGE-carrying male or carried out indiscriminately when at risk of mating with carriers,
may be an alternative response by females to limit the exposure of their offspring to SGEs. 相似文献
167.
In simultaneous hermaphrodites, gender conflicts that arise from two potential mates sharing the same gender preference may
be solved through conditional reciprocity (or gamete trading). Conditional reciprocity had initially been considered widespread,
but recent studies suggest that its real occurrence may have been overestimated, possibly because most mating observations
have been performed on isolated pairs of individuals. Some resulting patterns (e.g., non-random alternation of sexual roles)
were indeed compatible with conditional reciprocity but could also have stemmed from the two partners independently executing
their own mating strategy and being experimentally enforced to do so with the same partner. Non-random alternation of gender
roles was recently documented in the simultaneously hermaphroditic freshwater snail Physa acuta. To distinguish between conditional and unconditional gender alternations, we observed copulations of individually marked
snails reared at three contrasted densities. We showed that density affected the overall frequency of copulations during the
first 2 days of the experiment with high-density boxes showing more copulations than low density boxes, but it did not affect
gender alternation patterns. A change in gender role was observed more often than expected by chance over two successive copulations
by the same individual, confirming previous studies. However, gender switches did not preferentially occur with the same partner.
We conclude that gender alternation is not due to conditional reciprocity in P. acuta. It may rather stem from each individual having a preference for gender alternation. We finally discuss the mechanisms and
the potential extent of this unconditional reciprocity. 相似文献
168.
Bruno David Stuart R. Stock Francesco De Carlo Vincent Hétérier Chantal De Ridder 《Marine Biology》2009,156(8):1559-1572
The echinoderm endoskeleton, located in the connective layer of the tegument, is organized into a three-dimensional mesh,
the stereom. Among echinoids, the cidaroids depart from this pattern, and the shaft of the spine lacks an epidermis. Thus,
the spines lack antifouling protection, allowing ectosymbionts such as bryozoans and foraminiferans to attach. This raises
a question about the adaptive role of the cortical layer of the stereom. This study examined the micro- and mesostructure
of the spines of 11 cidaroid species collected in the Weddell Sea and Drake Passage, and the nature of their ectosymbiont
attachments. Scanning electron microscopy was used to characterize the cortex surface and X-ray micro computed tomography
(μCT) to describe the symbiont attachments. Spine microstructure features provide a useful taxonomic character for distinguishing
among three species in the genus Ctenocidaris, and challenge a previous parasitic interpretation of cortical filaments on the spines of Rhynchocidaris triplopora. Ectosymbiont attachments were classified as Anchoring, Molding, Cementing, or Corroding. The study suggests that some microstructure
features may be protective, keeping the ectosymbionts away from the cortex and loosely attached at intervals along the shaft
of the spine, while other micro-structures facilitate attachment over considerable areas of the shaft.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
169.
ebnem Andreani-Aksoyolu Johannes Keller Carlos Ordez Michel Tinguely Martin Schultz Andr S.H. Prvt 《Ecological modelling》2009,217(3-4):209
In this study, we investigated the effect of numerous regulations enforced since 1985 to improve air quality on ozone in Europe with the focus on Switzerland, using the Comprehensive Air Quality Model with Extensions (CAMx) for a specific summer period. Several emission scenarios for the year 2010 were also considered. The model results suggest that the emission reductions of ozone precursors should have been effective to reduce ozone production between 1985 and 2000 in northern Switzerland. However, observations do not indicate any significant change in surface ozone levels since early 1990s, except in the region of Zurich where there is a small negative trend. On the other hand, the model predictions match very well the spatial variability of the trends but the calculated trends are around 0.5 ppb year−1 lower than those observed. This difference is similar to the background ozone increase as suggested by the long-term observations at the high Alpine station Jungfraujoch. These results support the hypothesis that the decrease in local ozone production due to emission reductions might have been partly or completely compensated by the simultaneous increase in the background ozone. In 2010, a strict application of the Gothenburg Protocol in Europe would lead to a decrease in peak ozone concentrations by about 5% in Switzerland under the meteorological conditions applied. Our calculations also indicated that emission controls only in Switzerland would not be very effective to improve the air quality in the future. The further development of the background ozone will in any case be very important for the tropospheric ozone levels. 相似文献
170.
The paper explores the objectives, strategies and barriers to cleaner production (CP) implementation in China. Successful demonstration projects in China have shown that CP is a strategy for reducing pollution and costs, increasing competitiveness and achieving an integrated balance between economic and environmental benefits. As such, it is an inevitable choice and important contribution to sustainable development. However, it has not progressed enough as a strategy for continuous improvement since its effects are limited to industrial sectors or regions. CP implementation can be assisted by further popularization, policy system improvement, perception and awareness raising and technology innovation. These dimensions are the key tasks and incentives for all levels of government, enterprises and social organizations in moving toward sustainability. 相似文献