Relations between zero-inflated variables in trials with horticultural crops

Certain characteristics of some vegetable crops allow multiple harvests during the production cycle; however, to our knowledge, no study has described the behavior of fruit production with progression of the production cycle in vegetable crops with multiple harvests that present data overdispersion. We aimed to characterize the data overdispersion of zero-inflated variables and identify the behavior of these variables during the production cycle of several vegetable crops with multiple harvests. Data from 11 uniformity trials were used without applying treatments; these comprise the database from the Experimental Plants Group at the Federal University of Santa Maria, Brazil. The trials were conducted using four horticultural species grown during different cultivation seasons, cultivation environments, and experimental structures. Although at each harvest, a larger number of basic units with harvest fruit was observed than units without harvest fruit, the basic unit percentage without fruit was high, generating an overdispersion within each individual harvest. The variability within each harvest was high and increased with the evolution of the production cycle of Capsicum annuum, Solanum lycopersicum var. cerasiforme, Phaseolus vulgaris, and Cucurbita pepo species. However, the correlation coefficient between the mean weight and number of harvest fruits tended to remain constant during the crop production cycle. These behaviors show that harvest management should be done individually, at each harvest, such that data overdispersion is reduced.

Synthesis of waterborne polyurethane-urea dispersions with chain extension step in homogeneous and heterogeneous media

Hypothesis: The possibility of tailoring the final properties of environmentally friendly waterborne polyurethane and polyurethane-urea dispersions and the films they produce makes them attractive for a wide range of applications. Both the reagents content and the synthesis route contribute to the observed final properties. Experiments: A series of polyurethane-urea and polyurethane aqueous dispersions were synthesized using 1,2-ethanediamine and/or 1,4-butanediol as chain extenders. The diamine content was varied from 0 to 4.5 wt%. Its addition was carried out either by the classical heterogeneous reaction medium (after phase inversion step), or else by the alternative homogeneous medium (prior to dispersion formation). Dispersions as well as films prepared from dispersions have been later extensively characterized. Findings: 1,2-Ethanediamine addition in heterogeneous medium leads to dispersions with high particle sizes and broad distributions whereas in homogeneous medium, lower particle sizes and narrow distributions were observed, thus leading to higher uniformity and cohesiveness among particles during film formation. Thereby, stress transfer is favored adding the diamine in a homogeneous medium; and thus the obtained films presented quite higher stress and modulus values. Furthermore, the higher uniformity of films tends to hinder water molecules transport through the film, resulting, in general, in a lower water absorption capacity.