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Search Results: 1 - 10 of 238 matches for " Descriptors "
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Genetic Divergence in Mango and Obtaining Minimum Efficient Descriptors  [PDF]
Sandra da Costa Preisigke, Adryellison Lemes de Campos, Nadsley Seraglio Souza, Leonarda Grillo Neves, Marco Antonio Aparecido Barelli, Petterson Baptista da Luz, Kelly Lana Araújo, Severino de Paiva Sobrinho
American Journal of Plant Sciences (AJPS) , 2013, DOI: 10.4236/ajps.2013.412287
Abstract:

Mangifera indica (mango) is a typically tropical fruit with considerable economic value. Brazil features a wide variety of cultivars of this fruit, most of which are known under several different names. Indeed, the nomenclature of mango varieties is still quite confusing. Up to now there has been no well-defined scientific principle to differentiate them. The objective of the present work is to compare the different clustering methods in assessing genetic divergence among mango accessions, as well as identify the minimum efficient descriptors for that crop. A total of 20 mango accessions in Cáceres, Mato Grosso state, Brazil were evaluated. When building dissimilarity matrices, the descriptors were divided according to the following groups: leaf, flower/inflorescence, fruit, seed and growth habit/ripening period. With these divisions, combinations were performed among the groups of descriptors. The similarity index was used to obtain the dissimilarity matrices. Later, the accessions were clustered using the methods of Tocher, Ward and UPGMA. The study observed that it was possible to reduce the number of descriptors from 64 to 35, and that the clustering methods were compatible with the study of the genetic diversity of mango.

Proposed Extension to the Natta Projection Notation System for Enabling an Indication of Relative Stereochemistry and the Stereochemical State  [PDF]
Karel D. Klika
International Journal of Organic Chemistry (IJOC) , 2011, DOI: 10.4236/ijoc.2011.14031
Abstract: A system of structure depiction, as an extension of the wedge and hashed wedge bonds (Natta projection), and text notation is herein suggested that embodies more explicit information—or reduced over-statement as circumstances warrant—on the stereochemical nature of the system at hand, in particular, for those cases where only the relative stereochemistry of a compound is known.
Extracting and smoothing contours in mammograms using Fourier descriptors  [PDF]
Cyrille K. Feudjio, Alain Tiedeu, Marie-Laure Noubeg, Mihaela Gordan, Aurel Vlaicu, Samuel Domngang
Journal of Biomedical Science and Engineering (JBiSE) , 2014, DOI: 10.4236/jbise.2014.73017
Abstract:

Contour is an important pattern descriptor in image processing and particularly in region description, registration and length estimation. In many applications where contour is used, a good segmentation and an efficient smoothing method are needed. In X-ray images, such as mammograms, where object edge is not clearly discernible, estimating the object’s contour may yield substantial shift along the boundary due to noise or segmentation drawbacks. An appropriate smoothing is therefore required to reduce these effects. In this paper, an approach based on local adaptive threshold segmentation to extract contour and a new smoothing approach founded on Fourier descriptors are introduced. The experimental results of extraction obtained from a set of mammograms and compared with the breast regions delineated by radiologists yielded a percent overlap area of 98.7% ± 0.9% with false positive and negative rates of 0.36 ± 0.74 and 0.93 ± 0.44 respectively. The proposed method was tested on a set of images and improved the accuracy, leading to an average error of less than one pixel.

MDF - A New QSPR/QSAR Molecular Descriptors Family
Lorentz J?NTSCHI
Leonardo Journal of Sciences , 2004,
Abstract: MotivationIn the present are many QSAR/QSPR models, based on varied considerations, from mathematical through topological and geometrical to 3D molecular geometry approaches.IdeaThe idea is to create a unitary approach, based on a minimal set of well-known truths, capable to generate an efficient model of property behavior depending on molecular structure.MethodFirst step in order to reach the proposed goal is to create a huge family of molecular descriptors starting from molecular structure as a graph, considering the bonds and bond types, atom types and a most probable 3D geometry of the molecule. More, using this family of molecular descriptors, a preliminary selection is done in simple linear regression with the measured property. The resulted set of valid descriptors serves for multivariate regressions in order to reach the best QSAR/QSPR model.Results The comparisons of the obtained results with other models shows that the proposed model of Molecular Descriptors Family is superior to most of the all other models.AdvantagesThe model is dependent only of the microscopic molecular structure and it can be applies at any macroscopic molecular property.For a given molecular structure or set of structures, is necessary only one calculation of the descriptors, and can be applies to more than one measured property without changes. In other words, the MDF of a molecular structure is a molecular invariant.DisadvantagesBecause the set of molecular descriptors are huge (787968 computed values), the processing time of the model finding is time consuming.ConclusionConsidering the obtained results, advantages and disadvantages and also the trend of computing performances, the MDF method promise a great expansion of using.
Theoretical Study by Density Functional Theory Method (DFT) of Stability, Tautomerism, Reactivity and Prediction of Acidity of Quinolein-4-One Derivatives  [PDF]
Affoué Lucie Bédé, Amon Benjamine Assoma, Kicho Denis Yapo, Mamadou Guy-Richard Koné, Soleymane Koné, Mawa Koné, Boka Robert N’Guessan, El-Hadji Sawaliho Bamba
Computational Chemistry (CC) , 2018, DOI: 10.4236/cc.2018.63005
Abstract:
A theoretical study of the reactivity of quinoline-4-one derivatives is undertaken in order to understand the involved mechanisms. The calculations were carried out in gas phase and in N, N-Dimethylformamide (DMF) solution. The Density Functional Theory (DFT) with B3LYP functional associated to 6-311G (d) and 6-311+G (d) bases is used to perform these calculations. The results of the thermodynamic parameters showed that there is an equilibrium relation between the different tautomers. This equilibrium can be used to explain the failure to obtain tetrahydroquinoline from 5,8-dimethoxy-quinolin-4-one. Reactivity analysis from Frontier Molecular Orbitals theory and Fukui function calculations revealed that ketone forms are less reactive than enol ones. The methoxyl substituent decreases the acidity of the nitrogen and oxygen atoms of quinolin-4-one while the bromine increases the acidity of the same sites. These results foresee that nitrogen deprotonation in the case of the brominated compound is easier than in the case of methoxylated ones.
QSAR studies on urea and thiourea derivatives: Relationship between descriptors log P, p, MR and MV and antibacterial acvtivity in Staphylococcus aureus, Klebsiella pneumoniae and Escherichia coli
Figueroa,V.L; Díaz,C.F; Ceballos,R.G.; López,R.M; Maldonado,V. G; Camacho,L. A;
The Journal of Argentine Chemical Society , 2008,
Abstract: in this work the structural requirements of both urea and thiourea derivatives were evaluated for optimal antibacterial activity on staphylococcus aureus, klebsiella pneumoniae and escherichia coli, using several organic compounds (vi-x) as chemical tools. in order to delineate the structural chemical requirements of studied compounds, the descriptors log p, p mr and mv were calculated. the results showed that bacterial growth of the studied microorganisms, in presence of iv and vi compounds was inhibited at low concentrations in comparison with i-iii, v and vii-x. other results indicate that log p increase in ii-v, viii compounds and decrease in the vi-x substances in comparison with i thiourea-derivative. in addition, other data indicate that the p values are lower in the ii-x substances in comparison with i compound. other data showed an increase in both mr and mv values in the i-v and viii compounds and a decrease in the vi, vii, ix and x substances. in conclusion, the results found indicate that substituents involved in the chemical structure of both urea and thiourea derivatives increase the lipophilicity and changes in the functional groups decrease the log p. therefore, this phenomenon can affect the antibacterial activity on staphylococcus aureus, klebsiella pneumoniae and escherichia coli. in addition the results indicate that steric impediment, the molecular mechanism, conformational preferences and internal rotation of different compounds could affect the antibacterial effect of studied compounds.
Diversidade genética entre acessos de espécies cultivadas de pimentas
Monteiro, Eliane Rodrigues;Bastos, Ethyenne Moraes;Lopes, ?ngela Celis de Almeida;Gomes, Regina Lucia Ferreira;Nunes, Jose Airton Rodrigues;
Ciência Rural , 2010, DOI: 10.1590/S0103-84782010005000015
Abstract: the knowledge of the genetic diversity among the accessions in germplasm banks it is important for the conservation of genetic resources and the use in breeding programs. this study aimed to evaluate the genetic divergence of 23 accessions of the genus capsicum, and was based in seven quantitative and nineteen qualitative multicategorical descriptors and using multivariate techniques. the analyses of variance revealed significant difference (p<0.05) among the accessions of peppers for all quantitative descriptors. the coefficient variation ranged from 8,97% (lf) to 30,91% (nfa). the tocher optimization method detected eight clusters for quantitative descriptors and also in as well as qualitative multicategoric descriptors. the upgma method detected three clusters for quantitative descriptors and four clusters within qualitative multicategoricdescriptors. there is genetic diversity inter and intraspecific in germplasm bank of capsicum coming from the federal university of piauí, and these results indicate that there are not duplicated accessions.
Classifica??o de germoplasma de Dioscorea sp. através da análise das componentes principais
Melo Filho, Péricles de Albuquerque;Santos, Roseane Cavalcanti dos;Santos, Rivaldo Chagas Mafra José Weilinghton dos;Anuncia??o Filho, Clodoaldo José da;
Ciência Rural , 2000, DOI: 10.1590/S0103-84782000000400010
Abstract: interspecific classification m dioscorea germplasm was made aiming to characterize them by morphological descriptors and classify by principal component analysis. eleven accesses belonging to universidade federal rural de pernambuco brasil (ufrpe germplasm collection) were studied. fourteen descriptors were chosen for each access: leaf color and shape, petiole pigment, stem color and shape, presence and color of membranes, presence of good, presence of aerial tubers, tuber shape, presence of roots m lhe tuber, pigment in lhe tuber and leaf length and width. it was observed that leaf length and width provided high contribution on lhe access discriminations. the accumulated variance to the 1st and 2nd principal components were 89% of the whole variation. six groups were made up representing dioscorea accesses.
Novas características para diferencia??o de cultivares de soja pela análise discriminante
Nogueira, Ana Paula Oliveira;Sediyama, Tuneo;Cruz, Cosme Dami?o;Reis, Múcio Silva;Pereira, Derval Gomes;Jangarelli, Marcelo;
Ciência Rural , 2008, DOI: 10.1590/S0103-84782008005000025
Abstract: cultivar differentiation is carried out by the least margin of specific descriptors in each species. nowadays, approximately 38 descriptors, including the obligatory and additional ones, are used to differentiate soybean cultivars. since these descriptors are still not enough, it is necessary to increase the number of descriptors used, which should be previously identified and evaluated. the objectives of this study were to identify and evaluate new traits for the differentiation of soybean cultivars. the experiments were conducted in a greenhouse at the plant science department of the federal university of vi?osa at four different times (two during summer and two during winter). the treatments consisted of 11 soybean cultivars arranged in a complete randomized design with five replicates. each experimental unit consisted of one pot with two plants. the following characteristics were evaluated: hypocotyl length (ch), epicotyl length (ce), petiole length of the unifoliate leaf (cpfu), base shape coefficient of the unifoliate leaf (cfb), base width coefficient of the unifoliate leaf (clb), petiole length of the first trifoliate leaf (cpft) and rachis length of terminal leaflet in the first trifoliate leaf (crft). anderson's discriminant analysis was performed, and statistical analyses were carried out using the genetics and statistics software 'programa genes'. significant differences were found for all characteristics in the four sowing times. discriminant analysis allowed the differentiation of the soybean cultivars. it was concluded that the characteristics are useful as additional descriptors of soybean cultivars.
Caracteriza??o agromorfológica do maracujazeiro (Passiflora spp.)
Crochemore, Maria Lúcia;Molinari, Hugo Bruno;Stenzel, Neusa Maria Colauto;
Revista Brasileira de Fruticultura , 2003, DOI: 10.1590/S0100-29452003000100004
Abstract: the germoplasm evaluated is composed by 55 accessions of p. edulis, p. alata, p. coccinea, p. caerulea, p. foetida, p. giberti, p. macrocarpa, p. macrocarpa x p. alata, p. serrato digitata and p. suberosa; and one passiflora sp. accession. on isolated plants field cultivated under trellising system, 22 morphological descriptors were studied. the phylogenetic relationships evaluated by the principal component analysis and genetic distances showed a wide genetic diversity among the species studied. monomorphics characters were showed by some species. important variability is observed within p. alata and p. edulis and small divergences are found between accessions of the flavicarpa form.
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