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41.
Human influenza A (subtype H3N2) is characterized genetically by the limited standing diversity of its hemagglutinin and antigenically by clusters that emerge and replace each other within 2 to 8 years. By introducing an epidemiological model that allows for differences between the genetic and antigenic properties of the virus's hemagglutinin, we show that these patterns can arise from cluster-specific immunity alone. Central to the formulation is a genotype-to-phenotype mapping, based on neutral networks, with antigenic phenotypes, not genotypes, determining the degree of strain cross-immunity. The model parsimoniously explains well-known, as well as previously unremarked, features of interpandemic influenza dynamics and evolution. It captures the observed boom-and-bust pattern of viral evolution, with periods of antigenic stasis during which genetic diversity grows, and with episodic contraction of this diversity during cluster transitions. 相似文献
42.
Katia Gil Vega Mario González Chavira Octavio Martínez de la Vega June Simpson George Vandemark 《Euphytica》2001,121(3):335-341
By federal law in Mexico, A. tequilana Weber var. Azul is the only variety of agave permitted for the production of any tequila. Our objective was to assay levels
of genetic variation in field populations of A. tequilana var. Azul using randomly amplified polymorphic DNA (RAPD) markers. Ten plants were collected from each of four different
fields, with two fields being located in each of two principal regions of Mexico for the cultivation of A. tequilana var. Azul. The two regions are separated geographically by approximately 100km. Genetic relationships between A. tequilana var. Azul and two other varieties of A. tequilana Weber, ‘Chato’ and ‘Siguin’, were also investigated using RAPDs. Among the three varieties, 19 decamer primers produced 130
markers, of which 20 (15.4%) were polymorphic betweenA. tequilana var. Chato and A. tequilana var. Siguin. The results of RAPD analysis suggest that A. tequilana var. Siguin is more closely related to A. tequilana var. Azul than is A. tequilana var. Chato. Among the 40 field selections of A. tequilana var. Azul, only 1 of124 RAPD products (0.8%) was polymorphic and 39 of 40 plants were completely isogenic. This is one of
the lowest levels of polymorphism detected to date for the analysis of a crop species, and is proposed to be the result of
the promotion of a single conserved genotype over many years due to an exclusive reliance on vegetative propagation for the
production of new planting materials. The significance of these results is discussed in relation to breeding programs focused
on the improvement of A. tequilana var. Azul.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
43.
Pezet R Perret C Jean-Denis JB Tabacchi R Gindro K Viret O 《Journal of agricultural and food chemistry》2003,51(18):5488-5492
Delta-viniferin is a resveratrol dehydrodimer, an isomer of epsilon-viniferin. This compound has been reported as a molecule produced in vitro by the oxidative dimerization of resveratrol by plant peroxidases or fungal laccases. It was also recently identified in wines and in grape cell cultures. We have now identified this dimer by NMR, high-performance liquid chromatography-diode array detection (HPLC-DAD), and HPLC-mass spectrometry (MS) in grapevine leaves infected by Plasmopara viticola (downy mildew) or UV-C irradiated. Its concentration was higher than that of epsilon-viniferin and constitutes one of the most important phytoalexins derived from resveratrol. 相似文献
44.
This paper shows the effects of several variables, which co-cause the Urban Heat Island effect on temperature distribution and outdoor thermal comfort (by using the Predicted Mean Vote, PMV) on dense urban environments. The study was conducted by means of a three-dimensional microclimate model, ENVI-met 3.1, which forecasts the microclimatic changes within urban environments. The effects of building density (% of built area) and canyon effect (building height) on potential temperature, mean radiant temperature, and Predicted Mean Vote distribution are quantified. The influence of several types of green areas (vegetation on the ground and on roofs) on temperature mitigation and on comfort improvements is investigated for different atmospheric conditions and latitudes in a Mediterranean climate. The research quantifies the effects of the variables investigated on temperature distributions and in determining outdoor comfort conditions. Vegetation on the ground and on roofs mitigates summer temperatures, decreases the indoor cooling load demand, and improves outdoor comfort. The results of the study demonstrate that density and height of buildings in a city area influence potential temperature, mean radiant temperature, and Predicted Mean Vote distribution; for most of the cases examined higher density causes higher temperatures and with taller buildings vegetation has higher cooling effects. Considering the cooling effect of vegetation, a difference can be noticed depending on the amount of green areas and vegetation type. The results of this study show also that vegetation is more effective with higher temperatures and lower relative humidity values in mitigating potential temperatures, mean radiant temperatures, and PMV and in decreasing the cooling load demand. 相似文献
45.
Robson Andr�� Armindo Tarlei Arriel Botrel Tiago Capello Garzella 《Irrigation Science》2011,29(3):233-240
Due to the rapid depletion of water resources, water must be used more efficiently in agriculture to maintain current levels
of yield in irrigated areas. The efficiency of irrigation systems can be increased by adjusting the amount of water applied
to specific conditions of soil and crop, which may vary in a field. Taking into account spatial and temporal variability,
it is evident that an equipment capable of providing different irrigation levels is necessary to meet the water requirement
of the soil. This work aims to develop and evaluate a flow rate sprinkler to be used in center pivots or linear moving irrigation
systems, with potential for utilization in irrigation scheduling. A prototype was developed by duplicating its calibrations,
and discharge coefficient adjustment was carried out in the laboratory. To predict the flow rate, a successful model that
represented the operation of the flow rate sprinkler was established. The calibration of the flow rate sprinkler prototype
showed satisfactory statistical and technical results. Automation of the prototype was achieved by driving a step motor using
communication from the parallel port of a microcomputer, which was controlled by a software developed for this purpose. The
results were satisfactory and technically feasible. 相似文献
46.
47.
Aditya Kesarcodi‐Watson Philippe Miner Jean‐Louis Nicolas Katia Asmani Rene Robert 《Aquaculture Research》2016,47(4):1221-1230
During a series of experiments, bacteriological elements in scallop larval rearing were investigated: larvae susceptibility to pathogens as a function of their age, and the use of probiotic bacteria during larviculture. Younger larvae (d5 PF) were highly more susceptible to pathogenic‐challenge than their older siblings, which were challenged at an older age (d15 PF). A challenge with 104 CFU mL?1 of V. pectenicida killed 100% of d5 PF larvae 7 days following challenge, yet killed only 9% of d15 PF larvae 9 days following challenge. Use of the probiotics Phaeobacter gallaeciensis, Alteromonas macleodii 0444 and Neptunomonas sp. 0536, provided for larger larvae, a high yield of competent larvae and, perhaps more importantly, protection against pathogen‐challenge similar to levels achieved from antibiotic use. When challenged with V. pectenicida, d29 survivals were 20.3%, 85.1% and 75.0% respectively for control (no probiotic), antibiotic treated, and ‘probiotic mix’ administered larvae. Use of potential probiotic Pseudoalteromonas sp. D41 appeared to hinder scallop larvae. Future use of probiotics in scallop larval rearing would benefit from combined use of P. gallaeciensis, A. macleodii 0444 and Neptunomonas sp. 0536. 相似文献
48.
49.
50.
Blondeau C Chbab N Beaumont C Courvoisier K Osterrieder N Vautherot JF Denesvre C 《Veterinary research》2007,38(3):419-433