Visualisation of Avogadro’s Number

Con motivo de la redefinición de la constante de Avogadro, se presenta una breve historia y algunas reflexiones didácticas sobre su magnitud. Se revisan algunas analogías y se sugieren otras para ayudar a visualizar el alcance de su magnitud y se evalúa su utilidad. Estas analogías se enmarcan en el contexto docente de los cursos primero y segundo de las titulaciones en diversas disciplinas científicas y técnicas. Su efectividad se discute por primera vez sobre la base de un cuestionario realizado por los estudiantes correspondientes. Los resultados sugieren que los modelos más útiles, siguiendo la opinión de los estudiantes, son aquellos relacionados con ítems más sustanciales, por ejemplo, neuronas, individuos, planetas, por encima de analogías sobre construcciones geométricas. Podemos concluir, en contraste el pensamiento actual, que las descripciones visuales no siempre son las más ventajosas.On the occasion of the redefinition of the Avogadro constant, a brief history and some didactic reflections on its magnitude are presented. Some analogies are reviewed and others are suggested to help visualize the extent of its magnitude, and their usefulness is assessed. These analogies are set in the teaching context of the first and second courses of the degrees in several scientific and technic disciplines. Their effectiveness is discussed for the first time on the basis of a questionnaire filled by the corresponding students. The suggestions for educating and learning are that the most helpful models, following the opinion of the students, are those related to more substantial items, for example, neurons, individuals, planets, above analogies on geometric constructions. Challenging current thought, pictorial descriptions are not all the times so advantageousCiencias Experimentale

True prediction of lowest observed adverse effect levels

Summary A database of structurally heterogeneous chemical structures with their experimental values of Lowest Observed Adverse Effect Levels (LOAELs) was modeled using graph theoretical descriptors. Variable selection for multiple linear regression (MLR) and linear discriminant analysis (LDA) was accomplished by the Internal Test Set (ITS) method in order to achieve true predicted LOAEL values. The results obtained can be considered good if we take in count the structural diversity of the training set

Influence of the Temperature and the Genotype of the HSP90AA1 Gene over Sperm Chromatin Stability in Manchega Rams

The present study addresses the effect of heat stress on males' reproduction ability. For that, we have evaluated the sperm DNA fragmentation (DFI) by SCSA of ejaculates incubated at 37°C during 0, 24 and 48 hours after its collection, as a way to mimic the temperature circumstances to which spermatozoa will be subject to in the ewe uterus. The effects of temperature and temperature-humidity index (THI) from day 60 prior collection to the date of semen collection on DFI were examined. To better understand the causes determining the sensitivity of spermatozoa to heat, this study was conducted in 60 males with alternative genotypes for the SNP G/C−660 of the HSP90AA1 promoter, which encode for the Hsp90α protein. The Hsp90α protein predominates in the brain and testis, and its role in spermatogenesis has been described in several species. Ridge regression analyses showed that days 29 to 35 and 7 to 14 before sperm collection (bsc) were the most critical regarding the effect of heat stress over DFI values. Mixed model analyses revealed that DFI increases over a threshold of 30°C for maximum temperature and 22 for THI at days 29 to 35 and 7 to 14 bsc only in animals carrying the GG−660 genotype. The period 29–35 bsc coincide with the meiosis I process for which the effect of the Hsp90α has been described in mice. The period 7–14 bsc may correspond with later stages of the meiosis II and early stages of epididymal maturation in which the replacement of histones by protamines occurs. Because of GG−660 genotype has been associated to lower levels of HSP90AA1 expression, suboptimal amounts of HSP90AA1 mRNA in GG−660 animals under heat stress conditions make spermatozoa DNA more susceptible to be fragmented. Thus, selecting against the GG−660 genotype could decrease the DNA fragmentation and spermatozoa thermal susceptibility in the heat season, and its putative subsequent fertility gainsPublishe

Internal Test Sets Studies in a Group of Antimalarials

Topological indices have been applied to build QSAR models for a set of 20 an-timalarial cyclic peroxy cetals. In order to evaluate the reliability of the proposed linearmodels leave-n-out and Internal Test Sets (ITS) approaches have been considered. The pro-posed procedure resulted in a robust and consensued prediction equation and here it isshown why it is superior to the employed standard cross-validation algorithms involvingmultilinear regression models