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841.
Geraldo Da Silva e Souza Ricardo Coelho De Faria Tito Belchior S. Moreira 《Journal of the American Water Resources Association》2007,43(5):1237-1244
Abstract: This paper assesses cost efficiencies of Brazilian public and private companies of water supply. To measure the efficiency, we used a stochastic frontier model derived from the translog family – a specification similar to a Cobb‐Douglas including a quadratic term in log output. The model parameters are estimated by maximum likelihood using Brazilian data for the year 2002. Statistical inference leads to the conclusion that there is no evidence that private firms and public firms are significantly different in terms of efficiency measurements. 相似文献
842.
843.
844.
W.T. De Groot 《Ecological modelling》1983,18(2):99-119
The way in which simultaneously limiting nutrients are supposed to act upon the algal growth rate is an important aspect of aquatic ecosystem modelling and research. Three different relations between the multiple nutrient limitation and two single nutrient limitations are developed from different biochemical models: a “multiplicative” relation, used in most dynamic ecosystem models, a new “sequential” relation and a “threshold” relation, sensu Liebig. The characteristics and practical consequences of these relations are investigated. By means of three experiments, derived from the literature, it is shown that the multiplicative relation yields the statistically significant worst growth rate predictions. 相似文献
845.
van Put P Debauche A De Lellis C Adam V 《Journal of environmental radioactivity》2004,72(1-2):177-186
Following the recognition of their usefulness by the authorities and the scientific community, automatic water monitoring networks were developed again to be able to measure seawater. For that purpose, they had to be fully autonomous, with low power consumption (solar panel power supply), wireless communicating (satellite, GSM, radio) and very sensitive (a few Bq/m3). 相似文献
846.
Ibrahim Hafeezur Rehman Abhishek Kar Rob Raven Dilip Singh Jitendra Tiwari Rakesh Jha Pramod Kumar Sinha Asim Mirza 《Environmental Science & Policy》2010,13(4):303-311
In most developing countries, at the household level, traditional burning of biomass or use of inefficient technologies for domestic applications like lighting is common, triggering concerns related to fuel or technology switching. The paper focuses on opportunities to promote cleaner energy options through development of value chains delivering improved energy efficiency and access in developing countries. We discuss the example of Uttam Urja, a field project involving the dissemination of photovoltaic lighting technologies in rural areas of India. We focus on the challenges of introducing radical innovations into the residential energy sector in developing countries. For the purpose of this paper the Uttam Urja project is conceptualized as an ‘experiment’ and analysed using the Strategic Niche Management (SNM) framework. The paper emphasizes that to effect socio-technical transitions to clean energy options on the ground, it is desirable to focus on technology customization and innovative financing to cater to the needs and concerns of end users. 相似文献
847.
848.
To understand the consequences of the invasion of the nonnative rainbow trout Oncorhynchus mykiss on the native marble trout Salmo marmoratus, we compared two distinct headwater sectors where marble trout occur in allopatry (MTa) or sympatry (MTs) with rainbow trout
(RTs) in the Idrijca River (Slovenia). Using data from field surveys from 2002 to 2009, with biannual (June and September)
sampling and tagging from June 2004 onwards, we analyzed body growth and survival probabilities of marble trout in each stream
sector. Density of age-0 in September over the study period was greater for MTs than MTa and very similar between MTs and
RTs, while density of trout ≥age-1 was similar for MTa and MTs and greater than density of RTs. Monthly apparent survival
probabilities were slightly higher in MTa than in MTs, while RTs showed a lower survival than MTs. Mean weight of marble and
rainbow trout aged 0+ in September was negatively related to cohort density for both marble and rainbow trout, but the relationship
was not significantly different between MTs and MTa. No clear depression of body growth of sympatric marble trout between
sampling intervals was observed. Despite a later emergence, mean weight of RTs cohorts at age 0+ in September was significantly
higher than weight of both MTs and MTa. The establishment of a self-sustaining population of rainbow trout does not have a
significant impact on body growth and survival probabilities of sympatric marble trout. The numerical dominance of rainbow
trout in streams at lower altitudes seem to suggest that while the low summer flow pattern of Slovenian streams is favorable
for rainbow trout invasion, the adaptation of marble trout to headwater environments may limit the invasion success of rainbow
trout in headwaters. 相似文献
849.
van Ginneken V Ballieux B Antonissen E van der Linden R Gluvers A van den Thillart G 《Die Naturwissenschaften》2007,94(2):128-133
In birds and mammals, the thyroid gland secretes the iodothyronine hormones of which tetraiodothyronine (T4) is less active
than triiodothyronine (T3). The action of T3 and T4 is calorigenic and is involved in the control of metabolic rate. Across
all vertebrates, thyroid hormones also play a major role in differentiation, development and growth. Although the fish thyroidal
system has been researched extensively, its role in thermogenesis is unclear. In this study, we measured overall heat production
to an accuracy of 0.1 mW by direct calorimetry in a free-moving European eel (Anguilla anguilla L.) with different thyroid status. Hyperthyroidism was induced by injection of T3 and T4, and hypothyroidism was induced
with phenylthiourea. The results show for the first time at the organismal level, using direct calorimetry, that neither overall
heat production nor overall oxygen consumption in eels is affected by hyperthyroidism. Therefore, we conclude that the thermogenic
metabolism-stimulating effect of thyroid hormones (TH) is not present with a cold-blooded fish species like the European eel.
This supports the concept that TH does not stimulate thermogenesis in poikilothermic species. 相似文献
850.
A river ecosystem in East Java, Indonesia, fed by a volcanic lake with high concentrations of dissolved metals and a low pH, was found to support only few macroinvertebrates. To unravel the causes of toxicity and to determine the level of dilution necessary to obtain non-toxic water, a bioassay was conducted with the fairy shrimp Thamnocephalus platyurus. A partial toxicity identification evaluation (TIE) approach was used with EDTA as a chelating agent to relate toxicity to pH and metal concentrations. Three water samples were tested, with pHs ranging from 0.72 to 4.5, and diluted with water from a neutral river to different degrees. The dilution factor necessary to achieve no more than 50% mortality in the Thamnotox test (Ldf(50)) varied from >300 at the most acidic site, to 7 for water of pH 2.6 and 1.5 for water of pH 4.5. Toxicity was best explained from both low pH and high concentrations of metals, especially Al and Fe. The key role of Al and Fe in the toxicity was confirmed by relating concentrations of the different compounds in the river water to toxicity data from the literature. EDTA addition did not significantly influence Ldf(50) or the lethal pH 50% (LpH(50)), suggesting a large effect, besides cationic components and pH, of anions (F, SO(4) and Cl). 相似文献