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Final Number (final + number)

Distribution by Scientific Domains

Life Sciences	80%

Selected Abstracts

Methyl methacrylate emulsion polymerization at low monomer concentration: Kinetic modeling of nucleation, particle size distribution, and rate of polymerization

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2001
Jorge Herrera-Ordóñez
Abstract The results of a mathematical model developed in the authors' previous work are discussed and compared against final number (N) and size distribution of particles (PSD) and the rate of polymerization (RP) experimental data of methyl methacrylate (MMA) emulsion polymerization above the critical micelle concentration (cmc) of the surfactant. On the basis of the model results, the hypothesis that the observed bimodal PSD can be ascribed to secondary nucleation as proposed in the literature is questionable. It is discussed that this PSD can also be caused by differences in the growing rate of different-size particles as predicted for styrene emulsion polymerization. Because of the small particle size obtained at low initial monomer concentration, the high rate of free-radical desorption reduces the accumulation of these species; therefore, the autoacceleration effect is less pronounced for the conditions under study compared with the usual behavior of the RP during MMA emulsion polymerization above cmc. Similarities and differences between model predictions and experimental data are discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2547,2556, 2001 [source]

How does the meristem of sunflower capitulum cope with tissue expansion and floret initiation?

NEW PHYTOLOGIST, Issue 4 2006
A quantitative analysis
Summary ,,The coordination between floret initiation and tissue expansion has been studied and quantified in the apical meristem of sunflower (Helianthus annuus) plants grown under different light availability. ,,A method was developed to quantify tissue expansion in the meristem during floret initiation from measurements of meristem area, number of florets and primordium size. ,,Initially, floret initiation and tissue expansion occurred simultaneously at the meristem surface. The duration of this phase remained unchanged across environments, whereas the rate of tissue expansion varied greatly. Floret initiation rate depended on meristem initial size and tissue-expansion rate. Thereafter, floret initiation continued without tissue expansion in the meristem, resulting in a rapid decrease of meristem area. ,,A set of equations was proposed to predict floret initiation rate and floret number as a function of the rates of tissue expansion in the meristem before and during floret initiation. This formalism demonstrated the role of tissue expansion in determining the final number of florets, and provided a framework to analyse the response of floret initiation to genotype and environment. [source]

Analysis of nodulation kinetics in Frankia,Discaria trinervis symbiosis reveals different factors involved in the nodulation process

PHYSIOLOGIA PLANTARUM, Issue 4 2008
Luciano Andrés Gabbarini
The induction of root nodule development in actinorhizal symbiosis would depend on the concentration of factors produced by the bacteria and the plant. A detailed analysis of nodulation description parameters revealed different factors related to the nodulation process. The initial time for nodulation (t0), the initial nodulation rate (v0) and the total time of nodule development (tNOD) were defined and consequently quantified in different experimental conditions: co-inoculation of Discaria trinervis with increasing concentrations of different non-infective bacteria together with the full compatible infective Frankia strain (the indicator strain) used at a limiting concentration or by changing plant factor(s) concentration. All the above nodulation parameters were modified by changing doses of full compatibility infective strain Frankia BCU110501; v0 appears to be an expression of symbiotic recognition between partners as only fully symbiotic indicator Frankia BCU110501 was able to change it; t0 seems not to reflect symbiotic recognition because it can also be modified by non-infective Frankia but suggest the existence of a basic level of plant microbe recognition. The initial time for nodulation t0, reflecting the time required for the early interactions toward nodulation, is an inverse measure of the ability to establish early interactions toward nodulation. The increase in plant factors concentration also reduces t0 values, suggesting that a plant factor is involved and favors very early interactions. Increases in plant factors concentration also modify the final number of nodules per plant and the nodule cluster profile along the taproot as an expression of the autoregulation phenomenon. Meanwhile, Frankia inoculums' concentration, either infective or not, modified tNOD in an opposite way plant factors did. In conclusion, the analysis of nodulation kinetics appears to be an appropriate tool to investigate factors involved in the symbiotic interaction leading to the formation of nitrogen-fixing nodules. [source]

Key phenological events in globe artichoke (Cynara cardunculus var.scolymus) development

ANNALS OF APPLIED BIOLOGY, Issue 3 2009
A. Virdis
Abstract A priority for the field vegetable grower is to be able to schedule a regular supply of product throughout the growing season. This requires a predictive framework, based on the identification of key developmental events of the crop, and an understanding of how genotypic and environmental factors interact to determine plant development. Four globe artichoke (Cynara cardunculus var. scolymus) cultivars, representing the existing phenological range, were grown in a field experiment, and a range of environmental conditions was imposed by varying both the timing of the first irrigation (which determines the initiation of regrowth) and by repeating the experiment across two locations and 2 years. The timing of the appearance of the main stem capitulum was sensitive to both the growing environment and the cultivar. These differences persisted till flowering and were correlated with final leaf number. As the plant developed, the phyllochron decreased, resulting in three values of phyllochron, each of which was responsive to genotype, and hardly to environment. The timing of the first change in phyllochron was associated with the final leaf number and the appearance of the capitulum. For all the cultivars, the rate of development fell and the final leaf number increased as the length of the photoperiod increased. The later flowering cultivars shared a similar vernalisation requirement, but ,Spinoso sardo' did not require a cold period to flower. Leaf length reached a peak before the beginning of stem elongation, and maximum leaf length was correlated with final leaf number. The sensitiveness of the phyllochron to the genotype, and of the number of leaves and the timing of the appearance of the capitulum to both genotype and environment makes them suitable as variables in developmental models. The importance of the final number of leaves is not only because of its phenological significance, but also because of its effect on the ability of the canopy to intercept radiation. [source]

Carcinogenicity test in B6C3F1 mice after parental and prenatal exposure to 50 Hz magnetic fields

BIOELECTROMAGNETICS, Issue 3 2002
Yoshihisa Otaka
Abstract Some epidemiological studies suggest association of childhood cancer with occupational exposure of the parents to magnetic fields. To test this relationship, 50 each of C57BL/6J female and C3H/HeJ male mice were exposed for 2 and 9 weeks, respectively, to 50 Hz sham (group A), 0.5 (group B), and 5 mT (group C) sinusoidal alternating magnetic fields. They were mated under the exposure for up to 2 weeks, and the exposure was continued until parturition. All the B6C3F1 offspring, without adjusting numbers of animals, were clinically observed without exposure to magnetic field for a nominal 78 weeks from 6,8 weeks of age after weaning and then euthanized for pathological examination according to a routine carcinogenicity test. 540 pups entered the test, and the survival rate was 96.7%. No F1 mouse died of tumoral diseases before a male in A group died of stomach cancer at 43 weeks of age. The first animal death in the exposed groups due to tumor occurred at 71 weeks of age. Eighteen animals died before necropsy at 84,86 weeks of age. No significant difference was detected in the final number of survivors and incidence of tumors between groups A and B, or A and C. Concerning reproduction total implants in group B were less than in group A and the difference was on the borderline of significance (P,=,.05). This difference was not reproduced in a later duplicate experiment. Bioelectromagnetics 23:206,213, 2002. © 2002 Wiley-Liss, Inc. [source]