985 resultados para mixed groups
Resumo:
Mixed methods research is becoming increasingly important in several scientific areas. The analysis of prevalence rates is a new line of research that has emerged in mixed methods research, and this methodological approach has only been applied carefully in a handful of journals. The purpose of this article was to analyse the prevalence of mixed methods research in interdisciplinary educational journals. Moreover, the main characteristics of the mixed methods articles identified were examined. This study used a mixed methods approach to analyse these aspects. Specifically, a partially mixed sequential equal status multiple-case study design was applied with a development mixed methods purpose. Three educational journals in different disciplines were reviewed from 2005 to 2010 (Academy of Management Learning and Education, Educational Psychology Review, Journal of the Learning Sciences). The findings show differences among the journals in the prevalence rates and characteristics of the mixed methods studies
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Eight compounds comprising four groups of polyketides, the xanthone fusarindin, the mixed peptide alkaloid-polyketide GKK1032, the anthraquinones crisophanol, citreoveridin and janthinone, and the azaphylones dihydrocitrinone, citrinin and citrinin H-1, were identified in Penicillium species isolated as endophytic fungi from Melia azedarach and Murraya paniculata. The antibacterial activity of the azaphylones was tested and showed that citrinin H-1 is more active than citrinin.
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Introduction. This study presents the results of the implementation process of portfolio in the course of four consecutive years. The plan includes three phases (initiation, development and consolidation). The sample is 480 students studying the first year of nursing at the University of Girona. The objective is to evaluate the effectiveness of the instrument and achieve its construction in a self-regulated process. Subjects and methods. The proposed methodology is based on the sequential triangulation between methods. The study of the same empirical unit it’s used two investigation strategies, quantitative and qualitative. Study 1: quantitative, descriptive, longitudinal and prospective. The statistical analysis of paired data for continuous variables that follow a normaldistribution is made with t Student-Fisher test. The correlation between two numerical variables is used the Pearson correlation index. Study 2: qualitative, uses the discussion groups and topics. For textual data analysis is used Atlas.ti. Results. The final score for students who prepare the portfolio is higher (7.78) than the score who do not prepare (7) (p ≤ 0.001). A significant correlation exists between the portfolio score and final score (p ≤ 0.001). The trend study showsa greater sensitivity of the instrument assessment. Conclusion. The final design of the portfolio is characterized by mixed, flexible and encourages the student reflection and empowers the reflection on the continuum of learning
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Genetic diversity is one of the levels of biodiversity that the World Conservation Union (IUCN) has recognized as being important to preserve. This is because genetic diversity is fundamental to the future evolution and to the adaptive flexibility of a species to respond to the inherently dynamic nature of the natural world. Therefore, the key to maintaining biodiversity and healthy ecosystems is to identify, monitor and maintain locally-adapted populations, along with their unique gene pools, upon which future adaptation depends. Thus, conservation genetics deals with the genetic factors that affect extinction risk and the genetic management regimes required to minimize the risk. The conservation of exploited species, such as salmonid fishes, is particularly challenging due to the conflicts between different interest groups. In this thesis, I conduct a series of conservation genetic studies on primarily Finnish populations of two salmonid fish species (European grayling, Thymallus thymallus, and lake-run brown trout, Salmo trutta) which are popular recreational game fishes in Finland. The general aim of these studies was to apply and develop population genetic approaches to assist conservation and sustainable harvest of these populations. The approaches applied included: i) the characterization of population genetic structure at national and local scales; ii) the identification of management units and the prioritization of populations for conservation based on evolutionary forces shaping indigenous gene pools; iii) the detection of population declines and the testing of the assumptions underlying these tests; and iv) the evaluation of the contribution of natural populations to a mixed stock fishery. Based on microsatellite analyses, clear genetic structuring of exploited Finnish grayling and brown trout populations was detected at both national and local scales. Finnish grayling were clustered into three genetically distinct groups, corresponding to northern, Baltic and south-eastern geographic areas of Finland. The genetic differentiation among and within population groups of grayling ranged from moderate to high levels. Such strong genetic structuring combined with low genetic diversity strongly indicates that genetic drift plays a major role in the evolution of grayling populations. Further analyses of European grayling covering the majority of the species’ distribution range indicated a strong global footprint of population decline. Using a coalescent approach the beginning of population reduction was dated back to 1 000-10 000 years ago (ca. 200-2 000 generations). Forward simulations demonstrated that the bottleneck footprints measured using the M ratio can persist within small populations much longer than previously anticipated in the face of low levels of gene flow. In contrast to the M ratio, two alternative methods for genetic bottleneck detection identified recent bottlenecks in six grayling populations that warrant future monitoring. Consistent with the predominant role of random genetic drift, the effective population size (Ne) estimates of all grayling populations were very low with the majority of Ne estimates below 50. Taken together, highly structured local populations, limited gene flow and the small Ne of grayling populations indicates that grayling populations are vulnerable to overexploitation and, hence, monitoring and careful management using the precautionary principles is required not only in Finland but throughout Europe. Population genetic analyses of lake-run brown trout populations in the Inari basin (northernmost Finland) revealed hierarchical population structure where individual populations were clustered into three population groups largely corresponding to different geographic regions of the basin. Similar to my earlier work with European grayling, the genetic differentiation among and within population groups of lake-run brown trout was relatively high. Such strong differentiation indicated that the power to determine the relative contribution of populations in mixed fisheries should be relatively high. Consistent with these expectations, high accuracy and precision in mixed stock analysis (MSA) simulations were observed. Application of MSA to indigenous fish caught in the Inari basin identified altogether twelve populations that contributed significantly to mixed stock fisheries with the Ivalojoki river system being the major contributor (70%) to the total catch. When the contribution of wild trout populations to the fisheries was evaluated regionally, geographically nearby populations were the main contributors to the local catches. MSA also revealed a clear separation between the lower and upper reaches of Ivalojoki river system – in contrast to lower reaches of the Ivalojoki river that contributed considerably to the catch, populations from the upper reaches of the Ivalojoki river system (>140 km from the river mouth) did not contribute significantly to the fishery. This could be related to the available habitat size but also associated with a resident type life history and increased cost of migration. The studies in my thesis highlight the importance of dense sampling and wide population coverage at the scale being studied and also demonstrate the importance of critical evaluation of the underlying assumptions of the population genetic models and methods used. These results have important implications for conservation and sustainable fisheries management of Finnish populations of European grayling and brown trout in the Inari basin.
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Understanding the factors controlling fine root respiration (FRR) at different temporal scales will help to improve our knowledge about the spatial and temporal variability of soil respiration (SR) and to improve future predictions of CO2 effluxes to the atmosphere. Here we present a comparative study of how FRR respond to variability in soil temperature and moisture in two widely spread species, Scots pines (Pinus sylvestris L.) and Holm-oaks (HO; Quercus ilex L.). Those two species show contrasting water use strategies during the extreme summer-drought conditions that characterize the Mediterranean climate. The study was carried out on a mixed Mediterranean forest where Scots pines affected by drought induced die-back are slowly being replaced by the more drought resistant HO. FRR was measured in spring and early fall 2013 in excised roots freshly removed from the soil and collected under HO and under Scots pines at three different health stages: dead (D), defoliated (DP) and non-defoliated (NDP). Variations in soil temperature, soil water content and daily mean assimilation per tree were also recorded to evaluate FRR sensibility to abiotic and biotic environmental variations. Our results show that values of FRR were substantially lower under HO (1.26 ± 0.16 microgram CO2 /groot·min) than under living pines (1.89 ± 0.19 microgram CO2 /groot·min) which disagrees with the similar rates of soil respiration previously observed under both canopies and suggest that FRR contribution to total SR varies under different tree species. The similarity of FRR rates under HO and DP furthermore confirms other previous studies suggesting a recent Holm-oak root colonization of the gaps under dead trees. A linear mixed effect model approach indicated that seasonal variations in FRR were best explained by soil temperature (p<0.05) while soil moisture was not exerting any direct control over FRR, despite the low soil moisture values during the summer sampling. Plant assimilation rates were positively related to FRR explaining part of the observed variability (p<0.01). However the positive relations of FRR with plant assimilation occurred mainly during spring, when both soil moisture and plant assimilation rates were higher. Our results finally suggest that plants might be able to maintain relatively high rates of FRR during the sub-optimal abiotic and biotic summer conditions probably thanks to their capacity to re-mobilize carbon reserves and their capacity to passively move water from moister layers to upper layers with lower water potentials (where the FR were collected) by hydraulic lift.
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The catalytic performance of Mg,Al-mixed oxides (MO20, MO25 and MO33) derived from hydrotalcites was evaluated in the Knoevenagel reaction between benzaldehyde and phenylsulfonylacetonitrile at 373 and 383 K. The best results were obtained for the sample MO20 that presented the highest basic sites density and external area and the smallest crystallite sizes. The relative amount of basic sites with weak to intermediate strength also played an important role on catalytic performance. By increasing the catalyst content from 1 to 5 wt.% at 383 K, a complete conversion of the reactants is attained, producing α-phenylsulfonylcinnamonitrile with a selectivity of 100%.
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This review first discusses the limitations of many of the supports and stationary phases used in reversed phase high performance liquid chromatography and then describes those, developed more recently, that present better stabilities and more versatile selectivities. Emphases will be given to stationary phases that use higher purity silicas, hybrid silicas, monolithic silicas, metallic oxides and mixed oxides as supports and those that have embedded polar groups or contain phenyl or fluoro groups as the stationary phase as well as the phases used for mixed mode or hydrophilic interaction separations. These modern stationary phases facilitate the analysis of complex mixtures.
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Mixed micellization and surface properties of cationic and nonionic surfactants dimethyl decyl-, tetradecyl- and hexadecyl phosphineoxide mixtures are studied using conductivity and surface tension measurements. The models of Rubingh, Rosen, and Clint, are used to obtain the interaction parameter, minimum area per molecule, mixed micelle composition, free energies of mixing and activity coefficients. The micellar mole fractions were always higher than ideal values indicating high contributions of cationics in mixed micelles. Activity coefficients were less than unity indicating synergism in micelles. The negative free energies of mixing showed the stability of the surfactants in the mixed micelles.
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Synthetic antioxidants are an alternative to prevent or retard the degradation of biofuels made from vegetable oils. In this study, it was evaluated the oxidative stability of B100 soybean oil biodiesel, in the presence of tercbutylhydroquinone (TBHQ). The results showed that the induction period, that precedes the seeding process, was delayed in the presence of the antioxidant. Moreover, the obtained results suggest that the B100 biodiesel containing TBHQ can present a storage time at 25 ºC, three times longer than the estimated time for the pure B100.
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The porous mixed oxide SiO2/TiO2/Sb2O5 obtained by the sol-gel processing method presented a good ion exchange property and a high exchange capacity towards the Li+, Na+ and K+ ions. In the H+/M+ ion exchange process, the H+ / Na+ could be described as presenting an ideal character. The ion exchange equilibria of Li+ and K+ were quantitatively described with the help of the model of fixed tetradentate centers. The results of simulation evidence that for the H+ / Li+ exchange the usual situation takes place: the affinity of the material to the Li+ ions is decreased with increasing the degree of ion exchange. On the contrary, for K+ the effects of positive cooperativity, that facilitate the H+ / K+ exchange, were revealed.
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A direct potentiometric titration method was applied to commercial and soil humic acids in order to determine their carboxyl and phenol group concentrations and apparent and intrinsic pK. In that context, acid-base properties of humic acids are interpreted by selective blocking of carboxylic and phenolic groups by esterification and acetylation. Differences in underivatized and derivatized HA's acid-base properties are ascribed to carboxyl and phenol groups influence on total humic acidity. Potentiometric data were treated with the modified Henderson-Hasselbalch equation. Infra red results, the acidic group contents and the average values of apparent and intrinsic pK for underivatized and derivatized HAs confirmed the selectivity of esterification derivatization method. After blocking of the functional groups, the values of acidic group contents decreased, while the value of apparent pK increased after derivatization. Phenol groups cannot be specifically identified by the acetylation method, due to low selectivity of the acetylation method.