Growth functions with upper horizontal asymptote do not have a maximum point, but we frequently question from which point growth can be considered practically constant, that is, from which point the curve is sufficiently close to its asymptote, so that the difference can be considered non-significant. Several methods have been employed for this purpose, such as one that verifies the significance of the difference between the curve and its asymptote using a t-test, and that of Portz et al. (2000), who used segmented regression. In the present work, we used logistic growth function, which has horizontal asymptote and one inflection point, and applied a new method consisting in the mathematical determination of a point in the curve from which the growth acceleration asymptotically tends to zero. This method showed the advantage to have biological meaning besides leading to a point quite close to those obtained using the beforementioned methods. Key words: nonlinear regression, logistic model, critical point of growth Determinação de um ponto suficientemente próximo à assíntota em funções de crescimento não lineares RESUMO: Em funções de crescimento que apresentam uma assíntota horizontal superior à curva, frequentemente surge a questão sobre quando se pode considerar o crescimento como praticamente constante, isto é, quando a curva está suficientemente próxima à sua assíntota, de modo que se possa declarar a diferença como sendo não-significativa. Vários métodos têm sido empregados, entre eles o que verifica através do teste t a significância da diferença entre a curva e sua assíntota. O uso de regressão segmentada, como em Portz et al., também tem esse objetivo, isto é, a determinação de um ponto de início de crescimento praticamente constante. Utilizou-se a função logística de crescimento, a qual possui assíntota horizontal e ponto de inflexão, e aplicou-se um novo método, que consiste na determinação matemática de um ponto da curva a partir do qual a aceleração do crescimento tende assintoticamente a zero. Este método, além de ter um significado biológico, conduz a um ponto bastante próximo aos obtidos pelos métodos anteriormente citados. Palavras-chave: regressão não linear, modelo logístico, ponto crítico de crescimento
It is often necessary to process large plant samples for light microscopy studies, but due to structural characteristics of plant tissues, especially intercellular spaces, large vacuoles, and phenolic substances, results are often unsatisfactory. When large samples are embedded in glycol methacrylate (GMA), their core may not polymerize, remaining soft and moist and making it difficult to cut microtome sections. This situation has been erroneously interpreted as the result of poor infiltration, when the soft core of these samples is actually the result of incomplete polymerization. While GMA is in fact present inside samples, unsatisfactory polymerization results from rapid external polymerization that does not allow sufficient hardener to reach the sample core, while the relatively large volume of GMA inside the tissue block also dilutes the hardener. In this chapter we propose a new method for processing large plant specimens that avoids these problems by: (1) slowing the polymerization process through cooling in order to permit the penetration of hardener into the sample core and (2) increasing the hardener:GMA ratio to aid polymerization of the sample core.
The objective of this research was to study the effect of osmotic potential and salinity on the germination of seeds of Senna occidentalis, with and without a change of solutions. The percentage and rates of germination decreased according to decrease of potential, being more drastic when the substitutions of solutions were not made. The largest reductions were observed with the PEG solutions, with and without substitutions.
O objetivo da pesquisa foi estudar o efeito de potenciais osmóticos e salinidade na germinação de sementes de Senna occidentalis, com e sem troca da solução. A porcentagem e a velocidade de germinação diminuíram com o decréscimo do potencial, sendo mais drástica quando as soluções não foram trocadas. As maiores reduções foram observadas nas soluções com PEG, com e sem troca da solução
A cultura do inhame (Dioscorea ssp.) está presente em várias partes do mundo, mas a grande maioria das espécies cultivadas procede originalmente das zonas tropicais da Ásia e do Oeste da África. O inhame é uma planta monocotiledônea, herbácea, trepadeira, de clima tropical e subtropical. Seus tubérculos são ricos em carboidratos e vitaminas do complexo B, além de encerrar teores das vitaminas A e C [9].No Brasil, a Paraíba é o Estado de maior produção (17.800 t) numa área de 4.300 hectares (ha), com produtividade média de 4,2 t/ha. O Estado de São Paulo apresenta baixa expressão na produção nacional dessa cultura (317,4 ha com 2.600 t), porém apresenta a maior produtividade média (9,0 t/ha) [11]. EFEITOS DE PARÂMETROS DE EXTRUSÃO NAS PROPRIEDADES FÍSICAS SUMMARY EFFECT OF EXTRUSION PARAMETERS IN THE PHYSICAL PROPERTIES OF EXPANDED YAM SNACKS. Effect of extrusionparameters was studied on the expansion index, specific volume, water absorption index (WAI) and water solubility index (WSI) of expanded yam snacks. The central composite design was used to study the parameters effect. It was verified three levels of temperature in the barrel (100, 115 and 130ºC), three levels of screw speed (163, 204 and 245 rpm) and three levels of flour moisture (12, 15 and 18%). The results showed that expansion properties (expansion index and specific volume) depend on flour moisture and extrusion temperature. The WSI was dependant of three parameters. Higher levels of temperature and screw speed increase the water solubility index (WSI). The studied parameters did not influence the water absorption index (WAI).
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