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101.
Attention is focused on biological systems which are describable in terms of ordinary differential equations subject to human control inputs. The concept of an isochronal system is introduced in order to include systems for which the differential equations are valid only over regularly reoccurring time intervals.It is assumed that the control inputs are to be chosen so that an integral cost function of the state of the system, the control used, current time, and the time interval of the control program is minimized. Problems associated with minimizing this cost function over an infinitely long time interval is then considered. Difficulties inherent with minimizing a cost integral on an infinite time interval are shown to be avoided by minimizing an average of the cost function over an unknown but periodic time interval. Under proper circumstance, the optimal control program for the average cost function is either identical to or a good approximation to the optimal control program for the original cost function over an infinitely long time interval.Necessary conditions are obtained for minimizing an average cost function over an unspecified time interval subject to the system equations. For a given problem the necessary conditions will yield but a single system trajectory in the state space. For management purposes this trajectory may be thought of as a target to which the system should be driven and maintained.A number of examples illustrate the use of the necessary conditions to obtain control targets. Certain problems associated with the stability of the target solutions are illustrated with the examples. 相似文献
102.
Resource Depletion and Sustainability in Small Open Economies 总被引:1,自引:0,他引:1
Jeffrey R. Vincent Theodore Panayotou John M. Hartwick 《Journal of Environmental Economics and Management》1997,33(3):274-286
Exogenous price changes affect the amount that a small country exporting natural resource commodities must invest to sustain its consumption level. The necessary amount is given by the difference between Hotelling rent and the discounted sum of future terms-of-trade effects (capital gains). The latter term is found to be large relative to the former in the case of petroleum depletion in Indonesia. This suggests that resource-rich countries will need to invest more than previously expected to sustain their consumption levels, if natural resource prices continue their long-term historical decline. 相似文献
103.
Summary. This study reports on the impact of insecticidal resistance on the diel periodicity of the calling behaviour and pheromone
production of different-aged virgin females of the obliquebanded leafroller (OBL), Choristoneura rosaceana. While both resistant (R) and susceptible (S) females initiated calling on the first night following emergence, the periodicity
of the calling behaviour, as determined by the mean onset time of calling (MOTC) and the mean time spent calling (MTSC) over
the first six nights of calling, differed between the two strains. R females started calling significantly later in the night.
However, as the MOTC of R females advanced with age but did not do so in S individuals, the difference between strains was
more pronounced in younger than older females. Furthermore, R females spent less time calling than S individuals. However,
the MTSC increased as a function of age in both R and S females, so the difference between strains remained fairly constant
for each night of calling. The major component of OBL sex pheromone, the Z11-14: Ac, determined at peak calling activity,
significantly declined with female age. Overall, pheromone production was lower in R females than in S females, with the difference
being more pronounced in younger than in older individuals. Thus, resistant females may have a lower mating success. The mating
success of both R and S strain males did not vary with the number of previous matings acquired. With regard to males, although
there was a significant decline in spermatophore size with successive matings, there was no significant difference between
strains. However, R males are smaller and may be disadvantaged through female choice and/or may respond differently to pheromone
source compared with S individuals. If the reproductive success of both sexes is affected, this may have a profound influence
on the dynamics of insecticidal resistance in the presence or absence of selection in OBL populations.
Received 4 July 2001; accepted 19 October 2001. 相似文献
104.
Katharine D. Wenstrom Roger A. Williamson William W. Hoover Stanley S. Grant 《黑龙江环境通报》1989,9(7):527-532
The prenatal diagnosis of achondrogenesis in association with cystic hygroma is described. Ultrasound findings of severe short-limbed dwarfism, decreased vertebral ossification, and normal ossification of the calvarium were all consistent with achondrogenesis type II. Although the unusual finding of associated cystic hygroma raised the suspicion of a concurrent chromosome abnormality, the karyotype of both fetal lymphocytes and fetal fibroblasts was normal. Autopsy confirmed dilated lymphatic channels in the basal endothelial layer of the skin, cystic hygroma, and coarctation of the aorta. Although previously unreported, we suggest that the features of this case of achondrogenesis indicate an association with lymphatic stasis and jugular lymphatic obstruction sequence in this syndrome. 相似文献
105.
Amy M. Kahler Theresa L. Cromeans Maureen G. Metcalfe Charles D. Humphrey Vincent R. Hill 《Food and environmental virology》2016,8(2):148-155
It is generally accepted that viral particles in source water are likely to be found as aggregates attached to other particles. For this reason, it is important to investigate the disinfection efficacy of chlorine on aggregated viruses. A method to produce adenovirus particle aggregation was developed for this study. Negative stain electron microscopy was used to measure aggregation before and after addition of virus particles to surface water at different pH and specific conductance levels. The impact of aggregation on the efficacy of chlorine disinfection was also examined. Disinfection experiments with human adenovirus 2 (HAdV2) in source water were conducted using 0.2 mg/L free chlorine at 5 °C. Aggregation of HAdV2 in source water (≥3 aggregated particles) remained higher at higher specific conductance and pH levels. However, aggregation was highly variable, with the percentage of particles present in aggregates ranging from 43 to 71 %. Upon addition into source water, the aggregation percentage dropped dramatically. On average, chlorination CT values (chlorine concentration in mg/L × time in min) for 3-log10 inactivation of aggregated HAdV2 were up to three times higher than those for dispersed HAdV2, indicating that aggregation reduced the disinfection rate. This information can be used by water utilities and regulators to guide decision making regarding disinfection of viruses in water. 相似文献
106.
A.J. Khan Jianjun Li Vincent A. Dutkiewicz Liaquat Husain 《Atmospheric environment (Oxford, England : 1994)》2010,44(19):2364-2371
The effect of elemental carbon (EC) on global as well as regional climate forcing is potentially very important. However, the EC data for northeastern U.S. is sparse. Daily EC concentrations, [EC], and [SO4] were measured in the northeastern U.S. at a regionally representative rural site, Whiteface Mountain (WFM; 44.366°N, 73.903°W, 1.5 km amsl, above mean sea level), New York (NY), for 1997. The air mass origin was determined using 6-h backward in time air trajectories obtained from the Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HYSPLIT 4). [EC] and [SO4] were highly variable and influenced by synoptic–scale meteorology (rainy vs dry periods). The maximum daily [EC] and [SO4] were 364 ± 55 and 28,800 ± 3000 ng m?3, respectively. [EC] and [SO4] also showed seasonal variations at WFM. Occurrences of high daily [EC] were mainly in spring months, while peak daily [SO4] concentrations occurred in summer months. This behavior of aerosols is due to the fact that the sources of EC and SO4 are not the same and also due to the enhanced photochemical activity during summer months that increased the production of SO4 from SO2. High [EC] and [SO4] values were associated with westerly air flow from the industrialized Midwestern U.S. Sector analysis using HYSPLIT 4 air trajectories showed that regions lying between the southwest and northwest of the WFM contributed 81% and 83% of the [EC] and [SO4], respectively. The monthly net direct radiative forcing for shortwave (SW) due to EC and SO4 aerosols at the top of the atmosphere (TOA) varied from ?0.05 to ?0.50 W m?2, with an annual average of ?0.20 ± 0.15 W m?2 that gives a net cooling effect. Average net radiative forcing at WFM for clear sky is lower than the global average radiative forcing reported by IPCC (Foster and Ramaswamy, 2007). 相似文献
107.
Anne-Catherine Bénard Vincent Darcos Christian Drakides Claude Casellas Jean Coudane Michel Vert 《Journal of Polymers and the Environment》2011,19(1):40-48
Water-soluble synthetic polymers are extensively used in cosmetics, detergents and paints. Many end up in wastewater and,
later on, in wastewater-treatment plants. In order to gain an insight into their fate in such plants, fluorescence and radioactivity
labelings were compared using a lab-scale reactor designed to mimic industrial conditions. Two fermentation media were considered,
namely a mixture of E402 and E204 micro-organisms and an activated sludge collected from a water-treatment plant located in
the south of France. A sample of low molar mass commercial poly(acrylic acid) (PAA) was labeled by radioactivity with tritium
and by coupling the 6-aminofluorescein fluorescent dye. Labeled PAA-containing sludges were allowed to ferment. To monitor
the fate of the polymers, aliquots of the fermented mixtures were withdrawn at selected times and centrifuged. Liquid and
solid phases were analyzed by scintigraphy or UV spectrometry, depending of the labeling techniques. Both techniques led to
similar distributions, c.a. 75% in the supernatant and 25% in the solid phase. Distributions remained constant during the
biological tests. There was no degradation of the commercial PAA after aqueous size exclusion chromatography (SEC), in agreement
with literature. These features showed that fluorescence-labeling can be used instead of the complex and expensive radiolabeling.
The validated fluorescence-based method was then applied to a linear poly(acrylic acid) synthesized by ATRP and labeled with
6-aminofluorescein. There was no significant difference between the commercial and the linear poly(acrylic acid)s. In contrast,
a linear PAA with 5% of tert-butyl ester repeating units was predominantly found in the solid phase although adsorption or absorption by micro-organisms
could not be demonstrated. The method based on fluorescence labeling should be applicable to other water soluble polymers
provided that the dye remains attached to the polymer as it was the case for the studied poly(acrylic acid)s. 相似文献
108.
Vincent A. Formica Malcolm E. Augat Mollie E. Barnard R. Eileen Butterfield Corlett W. Wood Edmund D. Brodie III 《Behavioral ecology and sociobiology》2010,64(7):1199-1208
Social network analysis has become a vital tool for studying patterns of individual interactions that influence a variety
of processes in behavior, ecology, and evolution. Taxa in which interactions are indirect or whose social behaviors are difficult
to observe directly are being excluded from this rapidly expanding field. Here, we introduce a method that uses a probabilistic
and spatially implicit technique for delineating social interactions. Kernel density estimators (KDE) are nonparametric techniques
that are often used in home range analyses and allow researchers studying social networks to generate interaction matrices
based on shared space use. We explored the use of KDE analysis and the effects of altering KDE input parameters on social
network metrics using data from a natural population of the spatially persistent forked fungus beetle, Bolitotherus cornutus. 相似文献
109.
C D Vincent A J Lawlor E Tipping 《Environmental pollution (Barking, Essex : 1987)》2001,114(1):93-100
Measurements were made of the contents of Al, Mn, Fe, Cu, Zn, Cd and Pb in Scapania undulata in three streams (D2, D5, D11) in the English Lake District. The stream waters had average pH values of 5.35 (D2), 5.81 (D5) and 7.26 (D11), the main differences in other major chemical components being in Mg, Al, Ca and alkalinity. There was generally more metal accumulation in the older parts of the plants, but this was not significant in all cases. Extents of accumulation varied with stream pH and dissolved metal concentration. For Al, accumulation was greatest in streams D2 and D5. Mn accumulated most in D5 and Fe was without preference. Cu, Zn and Cd accumulated mostly in the plants in stream D11 and Pb accumulated more in D5 and D11. In terms of enrichment factors (amount of metal in the plants divided by stream water concentration) the sequence was Zn < Cd < Cu < Mn < Pb < Al < Fe. Laboratory experiments supported the findings of the field data, providing evidence that uptake increases with pH at constant total metal concentration. The results are interpreted qualitatively in terms of the chemical speciation of the metals in the stream water and competition between metal ions and protons at the plant-water interface. It is suggested that Al, Cu, Zn, Cd and Pb behave according to chemical complexation, whereas redox processes and/or colloidal interactions may be significant for Mn and Fe. 相似文献
110.
Controls on coarse wood decay in temperate tree species: birth of the LOGLIFE experiment 总被引:1,自引:0,他引:1
Cornelissen JH Sass-Klaassen U Poorter L van Geffen K van Logtestijn RS van Hal J Goudzwaard L Sterck FJ Klaassen RK Freschet GT van der Wal A Eshuis H Zuo J de Boer W Lamers T Weemstra M Cretin V Martin R Ouden Jd Berg MP Aerts R Mohren GM Hefting MM 《Ambio》2012,41(Z3):231-245
Dead wood provides a huge terrestrial carbon stock and a habitat to wide-ranging organisms during its decay. Our brief review highlights that, in order to understand environmental change impacts on these functions, we need to quantify the contributions of different interacting biotic and abiotic drivers to wood decomposition. LOGLIFE is a new long-term 'common-garden' experiment to disentangle the effects of species' wood traits and site-related environmental drivers on wood decomposition dynamics and its associated diversity of microbial and invertebrate communities. This experiment is firmly rooted in pioneering experiments under the directorship of Terry Callaghan at Abisko Research Station, Sweden. LOGLIFE features two contrasting forest sites in the Netherlands, each hosting a similar set of coarse logs and branches of 10 tree species. LOGLIFE welcomes other researchers to test further questions concerning coarse wood decay that will also help to optimise forest management in view of carbon sequestration and biodiversity conservation. 相似文献