Paulino Ribeiro Villas Boas - Profile on Academia.edu (original) (raw)
Papers by Paulino Ribeiro Villas Boas
Applications of Laser-Induced Breakdown Spectroscopy for Soil Characterization, Part II: Review of Elemental Analysis and Soil Classification
European Journal of Soil Science
Applications of Laser-Induced Breakdown Spectroscopy for Soil Analysis, Part I: Review of Fundamentals and Chemical and Physical Properties
European Journal of Soil Science
One-point calibration of Saha-Boltzmann plot to improve accuracy and precision of quantitative analysis using laser-induced breakdown spectroscopy
Spectrochimica Acta Part B: Atomic Spectroscopy
Evaluation of carbon content and humification index of soils under the application of by-products from sugarcane processing
Microchemical Journal
Several natural or human made complex systems can be represented by complex networks-a theory whi... more Several natural or human made complex systems can be represented by complex networks-a theory which integrates the study of graphs with statistical mechanics. This kind of representation, however, can be biased by the way in which the data is obtained. In general, the data used to represent such systems is not always accurate, as in the case of the World Wide Web (WWW). Therefore, even if the sampled networks are large, their properties are directly affected by the way in which they were obtained and may not correspond to those of their respective original networks. For instance, the most used sampling methodology for capturing routers of the Internet, if performed on random networks, tends to obtain scale-free networks as results. On the other hand, sampled scale-free networks are not guaranteed to have this property. Because of these and other problems which may occur during the network sampling, it is very important to evaluate the variation of the network properties with respect to noise (in order to know which of them have less variation, being therefore more suitable for the characterization of networks with sampling problems) and the effect of sampling in the characterization, classification, and analysis of complex networks. In this work, we investigated the effect of three types of perturbations (noise), namely, edge addition, removal, and rewiring on the respectively estimated complex network properties, and the most suitable properties to characterize sampled networks were identified. Furthermore, two novel structures in complex networks were defined, namely, border trees and chains of vertices, which are possibly related to sampling. The occurrence of these structures in poorly-sampled networks was found to be high, implying a relation with partially sampled networks. In order to investigate such a hypothesis, the presence of chains of vertices was investigated in networks which were gradually sampled by random walks.
Phosphorous quantification in fertilizers using laser induced breakdown spectroscopy (LIBS): a methodology of analysis to correct physical matrix effects
Anal. Methods, 2015
P analysis in fertilizers using LIBS.
Journal of the Brazilian Chemical Society, 2015
Laser-induced fluorescence spectroscopy (LIFS) has shown advantages for analyses of whole soil, p... more Laser-induced fluorescence spectroscopy (LIFS) has shown advantages for analyses of whole soil, providing results about chemical structure of soil organic matter (SOM) without the need for a chemical fractionating process; thus, allowing direct analysis of soils. Moreover, another advantage is the potential for the development of portable systems, which could be usable in field analyses. The aim of this paper is to evaluate the performance of a portable LIFS system to assess the humification degree (HD) of SOM. A good correlation (R > 0.8) was obtained for results (HD) achieved using the proposed portable system and a conventional fluorescence spectrometric method for humic acid. In addition, the results obtained using the portable LIFS system statistically agreed with the ones achieved using a benchtop LIFS system already described in the literature for such application (R = 0.953). Thus, the portable LIFS system constitutes an affordable option for the in situ characterization of SOM.
Desenvolvimento De Novo Método Para Quantificação De Potássio Em Fertilizantes Usando a Técnica Libs
Carbon Quantification in Forest Soils Using Low Resolution Laser-Induced Breakdown Spectroscopy
Modeling Highway Networks with Path-Geographical Transformations
Studies in Computational Intelligence, 2009
A model of highway networks is proposed which is based on the generalization of the concept of ge... more A model of highway networks is proposed which is based on the generalization of the concept of geographical networks to incorporate several of the intermediate towns found between two main localities. This model is validated with respect to the US highway ...
Physics Letters A, 2009
This letter addresses the problem of modeling the highway systems of different countries by using... more This letter addresses the problem of modeling the highway systems of different countries by using complex networks formalism. More specifically, we compare two traditional geographical models with a modified geometrical network model where paths, rather than edges, are incorporated at each step between the origin and destination nodes. Optimal configurations of parameters are obtained for each model and used in the comparison. The highway networks of Brazil, the US and England are considered and shown to be properly modeled by the modified geographical model. The Brazilian highway network yielded small deviations that are potentially accountable by specific developing and sociogeographic features of that country.
Physical Review E, 2008
Great part of the interest in complex networks has been motivated by the presence of structured, ... more Great part of the interest in complex networks has been motivated by the presence of structured, frequently non-uniform, connectivity. Because diverse connectivity patterns tend to result in distinct network dynamics, and also because they provide the means to identify and classify several types of complex networks, it becomes important to obtain meaningful measurements of the local network topology. In addition to traditional features such as the node degree, clustering coefficient and shortest path, motifs have been introduced in the literature in order to provide complementary description of the networks connectivity. The current work proposes a new type of motifs, namely chains of nodes, namely sequences of connected nodes with degree two. These chains have been subdivided into cords, tails, rings and handles, depending on the type of their extremities (e.g. open or connected). A theoretical analysis of the density of such motifs in random and scale free networks is described, and an algorithm for identifying those motifs in general networks is presented. The potential of considering chains for network characterization has been illustrated with respect to five categories of real-world networks including 16 cases. Several interesting findings were obtained, including the fact that several chains were observed in the real-world networks, especially the WWW, books, and power-grid. The possibility of chains resulting from incompletely sampled networks is also investigated.
Journal of Statistical Mechanics: Theory and Experiment, 2010
Journal of Physics A: Mathematical and Theoretical, 2008
The comprehensive characterization of the structure of complex networks is essential to understan... more The comprehensive characterization of the structure of complex networks is essential to understand the dynamical processes which guide their evolution. The discovery of the scale-free distribution and the small world property of real networks were fundamental to stimulate more realistic models and to understand some dynamical processes such as network growth. However, properties related to the network borders (nodes with degree equal to one), one of its most fragile parts, remain little investigated and understood. The border nodes may be involved in the evolution of structures such as geographical networks. Here we analyze complex networks by looking for border trees, which are defined as the subgraphs without cycles connected to the remainder of the network (containing cycles) and terminating into border nodes. In addition to describing an algorithm for identification of such tree subgraphs, we also consider a series of their measurements, including their number of vertices, number of leaves, and depth. We investigate the properties of border trees for several theoretical models as well as real-world networks.
Advances in Physics, 2011
The success of new scientific areas can be assessed by their potential for contributing to new th... more The success of new scientific areas can be assessed by their potential for contributing to new theoretical approaches and in applications to real-world problems. Complex networks have fared extremely well in both of these aspects, with their sound theoretical basis developed over the years and with a variety of applications. In this survey, we analyze the applications of complex networks to real-world problems and data, with emphasis in representation, analysis and modeling, after an introduction to the main concepts and models. A diversity of phenomena are surveyed, which may be classified into no less than 22 areas, providing a clear indication of the impact of the field of complex networks.
Arxiv preprint arXiv:0706.3225, Jun 21, 2007
Abstract: The models of the Internet reported in the literature are mainly aimed at reproducing t... more Abstract: The models of the Internet reported in the literature are mainly aimed at reproducing the scale-free structure, the high clustering coefficient and the small world effects found in the real Internet, while other important properties (eg related to centrality and hierarchical measurements) are not considered. For a better characterization and modeling of such network, a larger number of topological properties must be considered. In this work, we present a sound multivariate statistical approach, including feature spaces and ...
Advances in Physics, 2007
Each complex network (or class of networks) presents specific topological features which characte... more Each complex network (or class of networks) presents specific topological features which characterize its connectivity and highly influence the dynamics of processes executed on the network. The analysis, discrimination, and synthesis of complex networks therefore rely on the use of measurements capable of expressing the most relevant topological features. This article presents a survey of such measurements. It includes general considerations about complex network characterization, a brief review of the principal models, and the ...
Advances in Physics, 2007
Each complex network (or class of networks) presents specific topological features which characte... more Each complex network (or class of networks) presents specific topological features which characterize its connectivity and highly influence the dynamics of processes executed on the network. The analysis, discrimination, and synthesis of complex networks therefore rely on the use of measurements capable of expressing the most relevant topological features. This article presents a survey of such measurements. It includes general considerations about complex network characterization, a brief review of the principal models, and the ...
Identification of citrus varieties using laser-induced fluorescence spectroscopy (LIFS)
Computers and Electronics in Agriculture, 2013
Talanta, Jan 15, 2012
Huanglongbing (HLB) and citrus variegated chlorosis (CVC) are serious threats to citrus productio... more Huanglongbing (HLB) and citrus variegated chlorosis (CVC) are serious threats to citrus production and have caused considerable economic losses worldwide, especially in Brazil, which is one of the biggest citrus producers in the world. Neither disease has a cure nor an efficient means of control. They are also generally confused with each other in the field since they share similar initial symptoms, e.g., yellowing blotchy leaves. The most efficient tool for detecting these diseases is by polymerase chain reaction (PCR). However, PCR is expensive, is not high throughput, and is subject to cross reaction and contamination. In this report, a diagnostic method is proposed for detecting HLB and CVC diseases in leaves of sweet orange trees using attenuated total reflectance Fourier transform infrared spectroscopy and the induced classifier via partial least-squares regression. Four different leaf types were considered: healthy, CVC-symptomatic, HLB-symptomatic, and HLB-asymptomatic. The ...
Applications of Laser-Induced Breakdown Spectroscopy for Soil Characterization, Part II: Review of Elemental Analysis and Soil Classification
European Journal of Soil Science
Applications of Laser-Induced Breakdown Spectroscopy for Soil Analysis, Part I: Review of Fundamentals and Chemical and Physical Properties
European Journal of Soil Science
One-point calibration of Saha-Boltzmann plot to improve accuracy and precision of quantitative analysis using laser-induced breakdown spectroscopy
Spectrochimica Acta Part B: Atomic Spectroscopy
Evaluation of carbon content and humification index of soils under the application of by-products from sugarcane processing
Microchemical Journal
Several natural or human made complex systems can be represented by complex networks-a theory whi... more Several natural or human made complex systems can be represented by complex networks-a theory which integrates the study of graphs with statistical mechanics. This kind of representation, however, can be biased by the way in which the data is obtained. In general, the data used to represent such systems is not always accurate, as in the case of the World Wide Web (WWW). Therefore, even if the sampled networks are large, their properties are directly affected by the way in which they were obtained and may not correspond to those of their respective original networks. For instance, the most used sampling methodology for capturing routers of the Internet, if performed on random networks, tends to obtain scale-free networks as results. On the other hand, sampled scale-free networks are not guaranteed to have this property. Because of these and other problems which may occur during the network sampling, it is very important to evaluate the variation of the network properties with respect to noise (in order to know which of them have less variation, being therefore more suitable for the characterization of networks with sampling problems) and the effect of sampling in the characterization, classification, and analysis of complex networks. In this work, we investigated the effect of three types of perturbations (noise), namely, edge addition, removal, and rewiring on the respectively estimated complex network properties, and the most suitable properties to characterize sampled networks were identified. Furthermore, two novel structures in complex networks were defined, namely, border trees and chains of vertices, which are possibly related to sampling. The occurrence of these structures in poorly-sampled networks was found to be high, implying a relation with partially sampled networks. In order to investigate such a hypothesis, the presence of chains of vertices was investigated in networks which were gradually sampled by random walks.
Phosphorous quantification in fertilizers using laser induced breakdown spectroscopy (LIBS): a methodology of analysis to correct physical matrix effects
Anal. Methods, 2015
P analysis in fertilizers using LIBS.
Journal of the Brazilian Chemical Society, 2015
Laser-induced fluorescence spectroscopy (LIFS) has shown advantages for analyses of whole soil, p... more Laser-induced fluorescence spectroscopy (LIFS) has shown advantages for analyses of whole soil, providing results about chemical structure of soil organic matter (SOM) without the need for a chemical fractionating process; thus, allowing direct analysis of soils. Moreover, another advantage is the potential for the development of portable systems, which could be usable in field analyses. The aim of this paper is to evaluate the performance of a portable LIFS system to assess the humification degree (HD) of SOM. A good correlation (R > 0.8) was obtained for results (HD) achieved using the proposed portable system and a conventional fluorescence spectrometric method for humic acid. In addition, the results obtained using the portable LIFS system statistically agreed with the ones achieved using a benchtop LIFS system already described in the literature for such application (R = 0.953). Thus, the portable LIFS system constitutes an affordable option for the in situ characterization of SOM.
Desenvolvimento De Novo Método Para Quantificação De Potássio Em Fertilizantes Usando a Técnica Libs
Carbon Quantification in Forest Soils Using Low Resolution Laser-Induced Breakdown Spectroscopy
Modeling Highway Networks with Path-Geographical Transformations
Studies in Computational Intelligence, 2009
A model of highway networks is proposed which is based on the generalization of the concept of ge... more A model of highway networks is proposed which is based on the generalization of the concept of geographical networks to incorporate several of the intermediate towns found between two main localities. This model is validated with respect to the US highway ...
Physics Letters A, 2009
This letter addresses the problem of modeling the highway systems of different countries by using... more This letter addresses the problem of modeling the highway systems of different countries by using complex networks formalism. More specifically, we compare two traditional geographical models with a modified geometrical network model where paths, rather than edges, are incorporated at each step between the origin and destination nodes. Optimal configurations of parameters are obtained for each model and used in the comparison. The highway networks of Brazil, the US and England are considered and shown to be properly modeled by the modified geographical model. The Brazilian highway network yielded small deviations that are potentially accountable by specific developing and sociogeographic features of that country.
Physical Review E, 2008
Great part of the interest in complex networks has been motivated by the presence of structured, ... more Great part of the interest in complex networks has been motivated by the presence of structured, frequently non-uniform, connectivity. Because diverse connectivity patterns tend to result in distinct network dynamics, and also because they provide the means to identify and classify several types of complex networks, it becomes important to obtain meaningful measurements of the local network topology. In addition to traditional features such as the node degree, clustering coefficient and shortest path, motifs have been introduced in the literature in order to provide complementary description of the networks connectivity. The current work proposes a new type of motifs, namely chains of nodes, namely sequences of connected nodes with degree two. These chains have been subdivided into cords, tails, rings and handles, depending on the type of their extremities (e.g. open or connected). A theoretical analysis of the density of such motifs in random and scale free networks is described, and an algorithm for identifying those motifs in general networks is presented. The potential of considering chains for network characterization has been illustrated with respect to five categories of real-world networks including 16 cases. Several interesting findings were obtained, including the fact that several chains were observed in the real-world networks, especially the WWW, books, and power-grid. The possibility of chains resulting from incompletely sampled networks is also investigated.
Journal of Statistical Mechanics: Theory and Experiment, 2010
Journal of Physics A: Mathematical and Theoretical, 2008
The comprehensive characterization of the structure of complex networks is essential to understan... more The comprehensive characterization of the structure of complex networks is essential to understand the dynamical processes which guide their evolution. The discovery of the scale-free distribution and the small world property of real networks were fundamental to stimulate more realistic models and to understand some dynamical processes such as network growth. However, properties related to the network borders (nodes with degree equal to one), one of its most fragile parts, remain little investigated and understood. The border nodes may be involved in the evolution of structures such as geographical networks. Here we analyze complex networks by looking for border trees, which are defined as the subgraphs without cycles connected to the remainder of the network (containing cycles) and terminating into border nodes. In addition to describing an algorithm for identification of such tree subgraphs, we also consider a series of their measurements, including their number of vertices, number of leaves, and depth. We investigate the properties of border trees for several theoretical models as well as real-world networks.
Advances in Physics, 2011
The success of new scientific areas can be assessed by their potential for contributing to new th... more The success of new scientific areas can be assessed by their potential for contributing to new theoretical approaches and in applications to real-world problems. Complex networks have fared extremely well in both of these aspects, with their sound theoretical basis developed over the years and with a variety of applications. In this survey, we analyze the applications of complex networks to real-world problems and data, with emphasis in representation, analysis and modeling, after an introduction to the main concepts and models. A diversity of phenomena are surveyed, which may be classified into no less than 22 areas, providing a clear indication of the impact of the field of complex networks.
Arxiv preprint arXiv:0706.3225, Jun 21, 2007
Abstract: The models of the Internet reported in the literature are mainly aimed at reproducing t... more Abstract: The models of the Internet reported in the literature are mainly aimed at reproducing the scale-free structure, the high clustering coefficient and the small world effects found in the real Internet, while other important properties (eg related to centrality and hierarchical measurements) are not considered. For a better characterization and modeling of such network, a larger number of topological properties must be considered. In this work, we present a sound multivariate statistical approach, including feature spaces and ...
Advances in Physics, 2007
Each complex network (or class of networks) presents specific topological features which characte... more Each complex network (or class of networks) presents specific topological features which characterize its connectivity and highly influence the dynamics of processes executed on the network. The analysis, discrimination, and synthesis of complex networks therefore rely on the use of measurements capable of expressing the most relevant topological features. This article presents a survey of such measurements. It includes general considerations about complex network characterization, a brief review of the principal models, and the ...
Advances in Physics, 2007
Each complex network (or class of networks) presents specific topological features which characte... more Each complex network (or class of networks) presents specific topological features which characterize its connectivity and highly influence the dynamics of processes executed on the network. The analysis, discrimination, and synthesis of complex networks therefore rely on the use of measurements capable of expressing the most relevant topological features. This article presents a survey of such measurements. It includes general considerations about complex network characterization, a brief review of the principal models, and the ...
Identification of citrus varieties using laser-induced fluorescence spectroscopy (LIFS)
Computers and Electronics in Agriculture, 2013
Talanta, Jan 15, 2012
Huanglongbing (HLB) and citrus variegated chlorosis (CVC) are serious threats to citrus productio... more Huanglongbing (HLB) and citrus variegated chlorosis (CVC) are serious threats to citrus production and have caused considerable economic losses worldwide, especially in Brazil, which is one of the biggest citrus producers in the world. Neither disease has a cure nor an efficient means of control. They are also generally confused with each other in the field since they share similar initial symptoms, e.g., yellowing blotchy leaves. The most efficient tool for detecting these diseases is by polymerase chain reaction (PCR). However, PCR is expensive, is not high throughput, and is subject to cross reaction and contamination. In this report, a diagnostic method is proposed for detecting HLB and CVC diseases in leaves of sweet orange trees using attenuated total reflectance Fourier transform infrared spectroscopy and the induced classifier via partial least-squares regression. Four different leaf types were considered: healthy, CVC-symptomatic, HLB-symptomatic, and HLB-asymptomatic. The ...