A complex networks approach for data clustering

This work proposes a method for data clustering based on complex networks theory. A data set is represented as a network by considering different metrics to establish the connection between each pair of objects. The clusters are obtained by taking into account five community detection algorithms. The network-based clustering approach is applied in two real-world databases and two sets of artificially generated data. The obtained results suggest that the exponential of the Minkowski distance is the most suitable metric to quantify the similarities between pairs of objects. In addition, the community identification method based on the greedy optimization provides the best cluster solution. We compare the network-based clustering approach with some traditional clustering algorithms and verify that it provides the lowest classification error rate. (C) 2012 Elsevier B.V. All rights reserved.

Inhomogeneous Fermi and quantum spin systems on lattices

We study the thermodynamic properties of a certain type of space-inhomogeneous Fermi and quantum spin systems on lattices. We are particularly interested in the case where the space scale of the inhomogeneities stays macroscopic, but very small as compared to the side-length of the box containing fermions or spins. The present study is however not restricted to "macroscopic inhomogeneities" and also includes the (periodic) microscopic and mesoscopic cases. We prove that - as in the homogeneous case - the pressure is, up to a minus sign, the conservative value of a two-person zero-sum game, named here thermodynamic game. Because of the absence of space symmetries in such inhomogeneous systems, it is not clear from the beginning what kind of object equilibrium states should be in the thermodynamic limit. However, we give rigorous statements on correlations functions for large boxes. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4763465]

A peculiar Maxwell's Demon observed in a time-dependent stadium-like billiard

The dynamics of a driven stadium-like billiard is considered using the formalism of discrete mappings. The model presents a resonant velocity that depends on the rotation number around fixed points and external boundary perturbation which plays an important separation rule in the model. We show that particles exhibiting Fermi acceleration (initial velocity is above the resonant one) are scaling invariant with respect to the initial velocity and external perturbation. However, initial velocities below the resonant one lead the particles to decelerate therefore unlimited energy growth is not observed. This phenomenon may be interpreted as a specific Maxwell's Demon which may separate fast and slow billiard particles. (C) 2012 Elsevier B.V. All rights reserved.

Fractal descriptors based on Fourier spectrum applied to texture analysis

This work proposes the development and study of a novel technique lot the generation of fractal descriptors used in texture analysis. The novel descriptors are obtained from a multiscale transform applied to the Fourier technique of fractal dimension calculus. The power spectrum of the Fourier transform of the image is plotted against the frequency in a log-log scale and a multiscale transform is applied to this curve. The obtained values are taken as the fractal descriptors of the image. The validation of the proposal is performed by the use of the descriptors for the classification of a dataset of texture images whose real classes are previously known. The classification precision is compared to other fractal descriptors known in the literature. The results confirm the efficiency of the proposed method. (C) 2012 Elsevier B.V. All rights reserved.

Feasibility of Intralaminar, Lateral Mass, or Pedicle Axis Vertebra Screws in Children Under 10 Years of Age: A Tomographic Study

BACKGROUND: There are several techniques for screw insertion in upper cervical spine surgery, and the use of the 3.5-mm screw is usually the standard. However, there is no consensus regarding the feasibility of using these screws in the pediatric population. OBJECTIVE: To determine the measurement of the lamina angle, lamina and pedicle length and thickness, and lateral mass length of the topographic axial view of the axis vertebra of 2- to 10-year-old children to guide the use of surgical screws. METHODS: Seventy-five computed tomography scans from 24- to 120-month-old patients were studied. Measurements were taken in an axial view of C2 and correlated with 2 age groups and both sexes. Statistical analysis was performed with the Student t test. RESULTS: In the 24- to 48-month age group, only 5.5% of the lamina and 8.3% of the pedicles had thicknesses < 3.5 mm. In the 49- to 120-month age group, there were no lamina thickness values < 3.5 mm, and 1.2% of pedicle thicknesses were < 3.5 mm. Both age groups had no lamina and pedicle lengths < 12 mm and no lateral mass lengths > 12 mm. CONCLUSION: In the majority of cases, the use of 3.5-mm lamina and pedicle screws in children is feasible. A base value of 45 degrees for the spinolaminar angle can be adopted as a reference for insertion of screws in the C2 lamina. This information can be particularly useful for decision making during preoperative planning for C1-C2 or craniocervical arthrodesis in children.

Extractive summarization using complex networks and syntactic dependency

The realization that statistical physics methods can be applied to analyze written texts represented as complex networks has led to several developments in natural language processing, including automatic summarization and evaluation of machine translation. Most importantly, so far only a few metrics of complex networks have been used and therefore there is ample opportunity to enhance the statistics-based methods as new measures of network topology and dynamics are created. In this paper, we employ for the first time the metrics betweenness, vulnerability and diversity to analyze written texts in Brazilian Portuguese. Using strategies based on diversity metrics, a better performance in automatic summarization is achieved in comparison to previous work employing complex networks. With an optimized method the Rouge score (an automatic evaluation method used in summarization) was 0.5089, which is the best value ever achieved for an extractive summarizer with statistical methods based on complex networks for Brazilian Portuguese. Furthermore, the diversity metric can detect keywords with high precision, which is why we believe it is suitable to produce good summaries. It is also shown that incorporating linguistic knowledge through a syntactic parser does enhance the performance of the automatic summarizers, as expected, but the increase in the Rouge score is only minor. These results reinforce the suitability of complex network methods for improving automatic summarizers in particular, and treating text in general. (C) 2011 Elsevier B.V. All rights reserved.

The influence of connectivity on the firing rate in a neuronal network with electrical and chemical synapses

We study the firing rate properties of a cellular automaton model for a neuronal network with chemical synapses. We propose a simple mechanism in which the nonlocal connections are included, through electrical and chemical synapses. In the latter case, we introduce a time delay which produces self-sustained activity. Nonlocal connections, or shortcuts, are randomly introduced according to a specified connection probability. There is a range of connection probabilities for which neuron firing occurs, as well as a critical probability for which the firing ceases in the absence of time delay. The critical probability for nonlocal shortcuts depends on the network size according to a power-law. We also compute the firing rate amplification factor by varying both the connection probability and the time delay for different network sizes. (C) 2011 Elsevier B.V. All rights reserved.

Quantitative histological analysis of the mandibular branch of the facial nerve in rats

PURPOSE: To establish a model to quantitative histological analysis of the mandibular branch of the facial nerve in rats. METHODS: Eleven Wistar rats had their right and left mandibular branches of the facial nerve surgically removed and were sacrificed afterwards. Quantitative histological analysis was performed with: a) partial number of axons; b) partial area of the transversal cut of the nerve (9000 mu m(2)); c) partial density. The averages of partial density were obtained. The statistical study was established by Wilcoxon test (p=0.05). RESULTS: In relation to density of axons, comparison between sides shows no statistically significant difference (p=0.248; p=0.533). Mean partial density of distal and proximal samples was, respectively, 0.18 +/- 0.02 and 0.19 +/- 0.02 axons/mu m(2). Comparison between proximal and distal samples shows no statistically significant difference (p=0.859; p=0.182). CONCLUSION: This study has successfully established a model to histological quantitative analysis of the mandibular branch of the facial nerve in rats.

RESULTS OF ULNAR NERVE NEUROTIZATION TO BICEPS BRACHII MUSCLE IN BRACHIAL PLEXUS INJURY

Objective: To evaluate the factors influencing the results of ulnar nerve neurotization at the motor branch of the brachii biceps muscle, aiming at the restoration of elbow flexion in patients with brachial plexus injury. Methods: 19 patients, with 18 men and 1 woman, mean age 28.7 years. Eight patients had injury to roots C5-C6 and 11, to roots C5-C6-C7. The average time interval between injury and surgery was 7.5 months. Four patients had cervical fractures associated with brachial plexus injury. The postoperative follow-up was 15.7 months. Results: Eight patients recovered elbow flexion strength MRC grade 4; two, MRC grade 3 and nine, MRC <3. There was no impairment of the previous ulnar nerve function. Conclusion: The surgical results of ulnar nerve neurotization at the motor branch of brachii biceps muscle are dependent on the interval between brachial plexus injury and surgical treatment, the presence of associated fractures of the cervical spine and occipital condyle, residual function of the C8-T1 roots after the injury and the involvement of the C7 root. Signs of reinnervation manifested up to 3 months after surgery showed better results in the long term. Level of Evidence: IV, Case Series.

Multi-q pattern analysis: A case study in image classification

This paper compares the effectiveness of the Tsallis entropy over the classic Boltzmann-Gibbs-Shannon entropy for general pattern recognition, and proposes a multi-q approach to improve pattern analysis using entropy. A series of experiments were carried out for the problem of classifying image patterns. Given a dataset of 40 pattern classes, the goal of our image case study is to assess how well the different entropies can be used to determine the class of a newly given image sample. Our experiments show that the Tsallis entropy using the proposed multi-q approach has great advantages over the Boltzmann-Gibbs-Shannon entropy for pattern classification, boosting image recognition rates by a factor of 3. We discuss the reasons behind this success, shedding light on the usefulness of the Tsallis entropy and the multi-q approach. (C) 2012 Elsevier B.V. All rights reserved.

Quantum spherical model with competing interactions

We analyse the phase diagram of a quantum mean spherical model in terms of the temperature T, a quantum parameter g, and the ratio p = -J(2)/J(1) where J(1) > 0 refers to ferromagnetic interactions between first-neighbour sites along the d directions of a hypercubic lattice, and J(2) < 0 is associated with competing anti ferromagnetic interactions between second neighbours along m <= d directions. We regain a number of known results for the classical version of this model, including the topology of the critical line in the g = 0 space, with a Lifshitz point at p = 1/4, for d > 2, and closed-form expressions for the decay of the pair correlations in one dimension. In the T = 0 phase diagram, there is a critical border, g(c) = g(c) (p) for d >= 2, with a singularity at the Lifshitz point if d < (m + 4)/2. We also establish upper and lower critical dimensions, and analyse the quantum critical behavior in the neighborhood of p = 1/4. 2012 (C) Elsevier B.V. All rights reserved.

Stochastic simulation of time-series models combined with geostatistics to predict water-table scenarios in a Guarani Aquifer System outcrop area, Brazil

Stochastic methods based on time-series modeling combined with geostatistics can be useful tools to describe the variability of water-table levels in time and space and to account for uncertainty. Monitoring water-level networks can give information about the dynamic of the aquifer domain in both dimensions. Time-series modeling is an elegant way to treat monitoring data without the complexity of physical mechanistic models. Time-series model predictions can be interpolated spatially, with the spatial differences in water-table dynamics determined by the spatial variation in the system properties and the temporal variation driven by the dynamics of the inputs into the system. An integration of stochastic methods is presented, based on time-series modeling and geostatistics as a framework to predict water levels for decision making in groundwater management and land-use planning. The methodology is applied in a case study in a Guarani Aquifer System (GAS) outcrop area located in the southeastern part of Brazil. Communication of results in a clear and understandable form, via simulated scenarios, is discussed as an alternative, when translating scientific knowledge into applications of stochastic hydrogeology in large aquifers with limited monitoring network coverage like the GAS.

Changes in the surface of four calcium silicate-containing endodontic materials and an epoxy resin-based sealer after a solubility test

Aim To compare the changes in the surface structure and elemental distribution, as well as the percentage of ion release, of four calcium silicate-containing endodontic materials with a well-established epoxy resin-based sealer, submitted to a solubility test. Methodology Solubility of AH Plus, iRoot SP, MTA Fillapex, Sealapex and MTA-Angelus (MTA-A) was tested according to ANSI/ADA Specification 57. The deionized water used in the solubility test was submitted to atomic absorption spectrophotometry to determine and quantify Ca2+, Na+, K+, Zn2+, Ni2+ and Pb2+ ions release. In addition, the outer and inner surfaces of nonsubmitted and submitted samples of each material to the solubility test were analysed by means of scanning electron microscopy and energy-dispersive spectroscopy (SEM/EDX). Statistical analysis was performed by using one-way anova and Tukeys post hoc tests (a = 0.05). Results Solubility results, in percentage, sorted in an increasing order were -1.24 +/- 0.19 (MTA-A), 0.28 +/- 0.08 (AH Plus), 5.65 +/- 0.80 (Sealapex), 14.89 +/- 0.73 (MTA Fillapex) and 20.64 +/- 1.42 (iRoot SP). AH Plus and MTA-A were statistically similar (P > 0.05), but different from the other materials (P < 0.05). High levels of Ca2+ ion release were observed in all groups except AH Plus sealer. MTA-A also had the highest release of Na2+ and K+ ions. Zn+2 ion release was observed only with AH Plus and Sealapex sealers. After the solubility test, all surfaces had morphological changes. The loss of matrix was evident and the filler particles were more distinguishable. EDX analysis displayed high levels of calcium and carbon at the surface of Sealapex, MTA Fillapex and iRoot SP. Conclusions AH Plus and MTA-A were in accordance with ANSI/ADAs requirements regarding solubility whilst iRoot SP, MTA Fillapex and Sealapex did not fulfil ANSI/ADAs protocols. High levels of Ca2+ ion release were observed in all materials except AH Plus. SEM/EDX analysis revealed that all samples had morphological changes in both outer and inner surfaces after the solubility test. High levels of calcium and carbon were also observed at the surface of all materials except AH Plus and MTA-A.

Using complex networks to quantify consistency in the use of words

In this paper we have quantified the consistency of word usage in written texts represented by complex networks, where words were taken as nodes, by measuring the degree of preservation of the node neighborhood. Words were considered highly consistent if the authors used them with the same neighborhood. When ranked according to the consistency of use, the words obeyed a log-normal distribution, in contrast to Zipf's law that applies to the frequency of use. Consistency correlated positively with the familiarity and frequency of use, and negatively with ambiguity and age of acquisition. An inspection of some highly consistent words confirmed that they are used in very limited semantic contexts. A comparison of consistency indices for eight authors indicated that these indices may be employed for author recognition. Indeed, as expected, authors of novels could be distinguished from those who wrote scientific texts. Our analysis demonstrated the suitability of the consistency indices, which can now be applied in other tasks, such as emotion recognition.

Cochlear implant in postlingual children: functional results 10 years after the surgery

The benefits of cochlear implants (CI) for communication skills are obtained over the years. There are but a few studies regarding the long-term outcomes in postlingual deaf children who grew up using the electronic device. Aim: To assess the functional results in a group of postlingual children, 10 years after using a CI. Methods: Ten postlingual deaf children, implanted before 18 years of age, participated in this study. We assessed: sentence recognition and speech intelligibility. We documented: device use and function and the patient's academic/occupational status. Study design: series. Results: The mean scores were 73% for sentence recognition in silence and 40% in noise. The average write-down intelligibility score was 92% and the average rating-scale intelligibility score was 4.15. There were no cases of device failure. Regarding educational/vocational status, three subjects graduated from the University. Five quit education after completing high school. Eight subjects had a professional activity. Conclusion: This study showed that cochlear implantation is a safe and reliable procedure. The postlingual profoundly hearing-impaired children after 10 years of CI use developed satisfactory levels regarding speech perception and intelligibility, and completed at least high school and were inserted in the labor market. Clinical Trials Registry: NCT01400178.