Federal University of Lavras

Lavras, Brazil
Time filter
Source Type

Alexandre S.S.,Federal University of Minas Gerais | Lucio A.D.,Federal University of Lavras | Neto A.H.C.,National University of Singapore | Nunes R.W.,Federal University of Minas Gerais
Nano Letters | Year: 2012

Ab initio calculations indicate that while the electronic states introduced by tilt grain boundaries in graphene are only partially confined to the defect core, a translational grain boundary introduces states near the Fermi level that are very strongly confined to the core of the defect, and display a ferromagnetic instability. The translational boundary lies along a graphene zigzag direction and its magnetic state is akin to that which has been theoretically predicted to occur on zigzag edges of graphene ribbons. Unlike ribbon edges, the translational grain boundary is fully immersed within the bulk of graphene, hence its magnetic state is protected from the contamination and reconstruction effects that have hampered experimental detection of the magnetic ribbon states. Moreover, our calculations suggest that charge transfer between grain boundaries and the bulk in graphene is short ranged, with charge redistribution confined to ∼5 Å from the geometric center of the 1D defects. © 2012 American Chemical Society.

Fire is frequently used as a land management tool for cattle ranching and annual crops in the Amazon. However, these maintenance fires often escape into surrounding forests, with potentially severe impacts for forest biodiversity. We examined the effect of experimental fires on leaf-litter arthropod abundance in a seasonally-dry forest in the Brazilian Amazon. The study plots (50 ha each) included a thrice-burned forest and an unburned control forest. Pitfall-trap samples were collected at 160 randomly selected points in both plots, with sampling stratified across four intra-annual replicates across the dry and wet seasons, corresponding to 6, 8, 10 and 12 months after the most recent fire. Arthropods were identified to the level of order (separating Formicidae). In order to better understand the processes that determine arthropod abundance in thrice-burned forests, we measured canopy openness, understory density and litter depth. All arthropod taxa were significantly affected by fire and season. In addition, the interactions between burn treatment and season were highly significant for all taxa but Isoptera. The burned plot was characterized by a more open canopy, lower understory density and shallower litter depth. Hierarchical partitioning revealed that canopy openness was the most important factor explaining arthropod order abundances in the thrice-burned plot, whereas all three environmental variables were significant in the unburned control plot. These results reveal the marked impact of recurrent wildfires and seasonality on litter arthropods in this transitional forest, and demonstrate the overwhelming importance of canopy-openness in driving post-fire arthropod abundance.

Mushroom cultivation is rapidly expanding in Brazil because Brazilians have discovered the medicinal and culinary value of mushrooms and their economic situation has improved. However, the horticultural technology for cultivating mushrooms under Brazilian conditions is lacking. For many years, the mushroom cultivation technology used in Brazil was adapted from developed countries whose materials and climate were different from those of Brazil. In order to exploit the Brazilian potential for mushroom cultivation it is essential to develop cultivation technology for family owned and operated rustic farms as well as for modern large scale industrial operations. Mushroom species cultivated in Brazil are discussed and some approaches for future research are suggested.

Ferreira D.F.,Federal University of Lavras
Ciencia e Agrotecnologia | Year: 2011

Sisvar is a statistical analysis system, first released in 1996 although its development began in 1994. The first version was done in the programming language Pascal and compiled with Borland Turbo Pascal 3. Sisvar was developed to achieve some specific goals. The first objective was to obtain software that could be used directly on the statistical experimental course of the Department of Exact Science at the Federal University of Lavras. The second objective was to initiate the development of a genuinely Brazilian free software program that met the demands and peculiarities of research conducted in the country. The third goal was to present statistical analysis software for the Brazilian scientific community that would allow research results to be analyzed efficiently and reliably. All of the initial goals were achieved. Sisvar gained acceptance by the scientific community because it provides reliable, accurate, precise, simple and robust results, and allows users a greater degree of interactivity.

do Val A.D.,Federal University of Lavras
Genetics and molecular research : GMR | Year: 2012

Olive trees have been grown since the beginning of civilization, and the consumption of olives and olive products is increasing worldwide, due to their health benefits and organoleptic qualities. To meet the growing market for olives, commercial cultivation of this species is expanding from traditional areas to new regions. Although the Brazilian olive industry has just begun to be established, breeding programs are already developing cultivars that are more adapted to local conditions. We used 12 microsatellite markers to evaluate 60 olive accessions, including several cultivars that were developed in Brazil. The analyses identified 72 distinct alleles; the largest number of alleles per locus were at the markers GAPU 101 and GAPU 71B, which contained 10 and 9 alleles, respectively. The largest allelic diversity and polymorphic information contents were also found at the GAPU 101 and GAPU 71B markers, with values of 0.8399/0.8203 and 0.8117/0.7863, respectively. Additionally, the 12 microsatellite markers generated a cumulative identity probability of 1.51 x 10(-10), indicating a high level of accuracy of accession identification. The set of markers that we used allowed the identification of 52 of the 60 olive genotypes, in addition to the recognition of several varietal synonyms. The components of a two-dimensional principal coordinate analysis explained 48.6% of the total genetic variation. The results obtained from the microsatellite markers showed a substantial degree of genetic diversity in the olive tree accessions used in Brazil.

Freitas M.R.,Federal University of Lavras
Bulletin of environmental contamination and toxicology | Year: 2014

Soil sorption, described as logK OC (the logarithm of the soil/water partition coefficient normalized to organic carbon), was modeled using the augmented multivariate image analysis applied to quantitative structure-property relationship method for a series of 11 carboxylic acid herbicides. The statistical model was found to be highly predictive and reliable to estimate logK OC of other persistent organic pollutants in the soil, which are analogues of the carboxylic acids used in the QSPR model. The QSPR model derived from images corresponding to the chemical structures of the 11 herbicides is superior to the uniparameter model based on the octanol/water partition coefficient (logP) and, in addition, a pattern recognition model was built using principal component analysis. This model allowed clustering and separating compounds with low/moderate soil sorption from those with moderate/high soil sorption (compounds with the aryloxy function) using the second principal component.

Freitas M.P.,Federal University of Lavras
Organic and Biomolecular Chemistry | Year: 2013

The anomeric effect has been assigned as being due to hyperconjugation, electrostatic/steric interactions or exchange effects; thus, there is no general consensus about its actual origin. The classical hyperconjugation model, usually investigated using natural bond orbital (NBO) analysis, has been arbitrarily refuted because it would not explain some cases of the preferred equatorial anomer over the axial one in polar solution. In this study, hyperconjugation was shown to be dependent on the medium and NBO analysis explains quite well the estimated amounts of axial and equatorial 2-substituted tetrahydropyrans (substituents = F, OH, NH2 and CN) both in the gas phase and aqueous solution. Overall, there is no reason to abandon the hyperconjugation model as it plays a dominating role of the anomeric effect in some systems, while NBO analysis reproduces the energetic profiles on the basis of both hyperconjugative and Lewis-type contributions. © 2013 The Royal Society of Chemistry.

Edible oils and fats are one of the foods most frequently counterfeited in many countries. Therefore, monitoring the authenticity and overall quality of these products is ultimately required. Chemometric analyses, such as Partial Least Square (PLS), Linear Discriminant Analysis (LDA), Soft Independent Modeling of Class Analogy (SIMCA), and others, applied to vibrational spectroscopic data have enabled the development of methods useful to assess quality aspects (authenticity, adulteration, free fatty acids and trans content, iodine, peroxide and saponification values, and others) of edible fats and oils. The methods are potential analytical tools for industries and inspection agencies for characterization of samples during the development, processing, quality control and inspection of oils and fats. In this original review, applications of near, mid and Raman infrared spectroscopy combined with multivariate analysis to authenticate, detect adulteration and determine intrinsic quality parameters in edible fats and oils are discussed. © 2013 Elsevier Ltd.

Sisvar is a statistical analysis system with a large usage by the scientific community to produce statistical analyses and to produce scientific results and conclusions. The large use of the statistical procedures of Sisvar by the scientific community is due to it being accurate, precise, simple and robust. With many options of analysis, Sisvar has a not so largely used analysis that is the multiple comparison procedures using bootstrap approaches. This paper aims to review this subject and to show some advantages of using Sisvar to perform such analysis to compare treatments means. Tests like Dunnett, Tukey, Student-Newman-Keuls and Scott-Knott are performed alternatively by bootstrap methods and show greater power and better controls of experimentwise type I error rates under non-normal, asymmetric, platykurtic or leptokurtic distributions.

Barcelos Q.L.,Federal University of Lavras
Genetics and molecular research : GMR | Year: 2011

The causal agent of common bean anthracnose, Colletotrichum lindemuthianum, has considerable genetic and pathogenic variability, which makes the development of resistant cultivars difficult. We examined variability within and between Brazilian pathotypes of C. lindemuthianum through the identification of vegetative compatibility groups (VCGs) and by RAPD analysis. Two hundred and ninety-five nit mutants were obtained from 47 isolates of various pathotypes of the fungus collected from different regions, host cultivars and years. In complementation tests, 45 VCGs were identified. Eighteen RAPD primers were employed in the molecular analyses, producing 111 polymorphic bands. Estimates of genetic similarities, determined from the Sorence-Dice coefficient, ranged from 0.42 to 0.97; the dendrogram obtained by cluster analysis revealed 18 groups of isolates. RAPD and VCG markers presented high genotypic diversity. The number of significant associations (P=0.05) between RAPD, VCG and pathogenicity markers ranged from 0 (VCG) to 80% (pathogenicity). The test of multilocus association (rd) for RAPD markers was significantly different from zero (P<0.001), suggesting linkage disequilibrium. However, the results for VCG markers show the presence of recombination mechanisms. In conclusion, RAPD markers and VCGs were useful for detecting genetic variability among isolates of C. lindemuthianum. We found considerable diversity among isolates from the same geographic origin within a short interval; this suggests rapid evolution. There is a need for further studies to elucidate the population structure of this pathogen in agro-ecosystems.

Loading Federal University of Lavras collaborators
Loading Federal University of Lavras collaborators