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A cooperação internacional Brasil-Canadá para pesquisa científica em Ciências Naturais, Matemática e Engenharia foi o tema da nossa mesa-redonda no IX Congresso Internacional da Associação Brasileira de Estudos Canadenses (ABECAN). Apresentamos o quadro atual da cooperação em pesquisa científica nessas áreas, na Universidade Federal da Bahia (UFBA) com o objetivo de desenvolver um programa institucional mais sistemático, com a ajuda da Assessoria para Relações Internacionais da UFBA, a fim de aumentar o intercâmbio tanto entre docentes, quanto entre alunos.Abstract: The international cooperation Brazil-Canada for Scientific Research in Natural Sciences, Mathematics and Engineering was the subject of our round table in IX International Congress of Associação Brasileira de Estudos Canadenses (ABECAN). We present the current scenario of scientific research collaboration on those areas at Federal University of Bahia (Universidade Federal da Bahia – UFBA) with the aim of developing a more systematic institutional program with the help of office for International Affairs of UFBA in order to increase both staff faculty and student exchange.

p.1-8 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2015-03-25T14:34:46Z No. of bitstreams: 1 V. S. T. Silva.pdf: 398364 bytes, checksum: d360b872b1eee32720f924403ca50495 (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2015-04-08T18:43:21Z (GMT) No. of bitstreams: 1 V. S. T. Silva.pdf: 398364 bytes, checksum: d360b872b1eee32720f924403ca50495 (MD5) Made available in DSpace on 2015-04-08T18:43:21Z (GMT). No. of bitstreams: 1 V. S. T. Silva.pdf: 398364 bytes, checksum: d360b872b1eee32720f924403ca50495 (MD5) Previous issue date: 2014 We consider an Ising model on the triangular Apollonian network (AN), with a thermalized distribution of vacant sites. The statistical problem is formulated in a grand canonical ensemble, in terms of the temperature T and a chemical potential μ associated with the concentration of active magnetic sites. We use a well-known transfer-matrix method, with a number of adaptations, to write recursion relations between successive generations of this hierarchical structure. We also investigate the analogous model on the diamond hierarchical lattice (DHL). From the numerical analysis of the recursion relations, we obtain various thermodynamic quantities. In the μ→∞ limit, we reproduce the results for the uniform models: in the AN, the system is magnetically ordered at all temperatures, while in the DHL there is a ferromagnetic-paramagnetic transition at a finite value of T. Magnetic ordering, however, is shown to disappear for sufficiently large negative values of the chemical potential.

Texto completo: acesso restrito. p.1-8 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2015-03-25T15:11:32Z No. of bitstreams: 1 C. P. de Castro.pdf: 556153 bytes, checksum: c564ea425534d329ec978f2a353e61a0 (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2015-04-08T18:39:42Z (GMT) No. of bitstreams: 1 C. P. de Castro.pdf: 556153 bytes, checksum: c564ea425534d329ec978f2a353e61a0 (MD5) Made available in DSpace on 2015-04-08T18:39:42Z (GMT). No. of bitstreams: 1 C. P. de Castro.pdf: 556153 bytes, checksum: c564ea425534d329ec978f2a353e61a0 (MD5) Previous issue date: 2014 This work considers the behavior of the height distributions of the equipotential lines in a region confined by two interfaces: a cathode with an irregular interface and a distant flat anode. Both boundaries, which are maintained at distinct and constant potential values, are assumed to be conductors. The morphology of the cathode interface results from the deposit of 2 × 104 monolayers that are produced using a single competitive growth model based on the rules of the Restricted Solid on Solid and Ballistic Deposition models, both of which belong to the Kadar–Parisi–Zhang (KPZ) universality class. At each time step, these rules are selected with probability p and q = 1 − p. For several irregular profiles that depend on p, a family of equipotential lines is evaluated. The lines are characterized by the skewness and kurtosis of the height distribution. The results indicate that the skewness of the equipotential line increases when they approach the flat anode and this increase has a non-trivial convergence to a delta distribution that characterizes the equipotential line in a uniform electric field. The morphology of the equipotential lines is discussed; the discussion emphasizes their features for different ranges of p that correspond to positive, null and negative values of the coefficient of the non-linear term in the KPZ equation.

p. 1-9 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2014-04-22T15:59:35Z No. of bitstreams: 1 10.1103PhysRevE.88.042122.pdf: 358066 bytes, checksum: d9a397972fbdbf85b551dab7dc4c3b0e (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2014-09-09T14:23:38Z (GMT) No. of bitstreams: 1 10.1103PhysRevE.88.042122.pdf: 358066 bytes, checksum: d9a397972fbdbf85b551dab7dc4c3b0e (MD5) Made available in DSpace on 2014-09-09T14:23:38Z (GMT). No. of bitstreams: 1 10.1103PhysRevE.88.042122.pdf: 358066 bytes, checksum: d9a397972fbdbf85b551dab7dc4c3b0e (MD5) Previous issue date: 2013 This work analyzes a percolation model on the diamond hierarchical lattice (DHL), where the percolation transition is retarded by the inclusion of a probability of erasing specific connected structures. It has been inspired by the recent interest on the existence of other universality classes of percolation models. The exact scale invariance and renormalization properties of DHL leads to recurrence maps, from which analytical expressions for the critical exponents and precise numerical results in the limit of very large lattices can be derived. The critical exponents ν and β of the investigated model vary continuously as the erasing probability changes. An adequate choice of the erasing probability leads to the result ν=∞, like in some phase transitions involving vortex formation. The percolation transition is continuous, with β>0, but β can be as small as desired. The modified percolation model turns out to be equivalent to the Q→1 limit of a Potts model with specific long range interactions on the same lattice.

Texto completo: acesso restrito. p. 1-9 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2014-05-15T14:17:45Z No. of bitstreams: 1 0953-8984_25_28_285106.pdf: 1243512 bytes, checksum: 6df6c734ce1536978c6b4f16757c2e81 (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2014-09-08T21:03:19Z (GMT) No. of bitstreams: 1 0953-8984_25_28_285106.pdf: 1243512 bytes, checksum: 6df6c734ce1536978c6b4f16757c2e81 (MD5) Made available in DSpace on 2014-09-08T21:03:19Z (GMT). No. of bitstreams: 1 0953-8984_25_28_285106.pdf: 1243512 bytes, checksum: 6df6c734ce1536978c6b4f16757c2e81 (MD5) Previous issue date: 2013 In this work, we present systematic theoretical evidence of a relationship between the point local roughness exponent (PLRE) (which quantifies the heterogeneity of an irregular surface) and the cold field emission properties (indicated by the local current density and the macroscopic current density) of real polyaniline (PANI) surfaces, considered nowadays as very good candidates in the design of field emission devices. The latter are obtained from atomic force microscopy data. The electric field and potential are calculated in a region bounded by the rough PANI surface and a distant plane, both boundaries held at distinct potential values. We numerically solve Laplace's equation subject to appropriate Dirichlet's condition. Our results show that local roughness reveals the presence of specific sharp emitting spots with a smooth geometry, which are the main ones responsible (but not the only) for the emission efficiency of such surfaces for larger deposition times. Moreover, we have found, with a proper choice of a scale interval encompassing the experimentally measurable average grain length, a highly structured dependence of local current density on PLRE, considering different ticks of PANI surfaces.

Texto completo. Acesso restrito. p. 815–828 Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-07-08T12:50:01Z No. of bitstreams: 1 333333333333.pdf: 367669 bytes, checksum: 1db9139e1173944e84894dee89d7428a (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Material de Física on 2013-08-16T19:14:54Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-19T16:52:56Z No. of bitstreams: 1 333333333333.pdf: 367669 bytes, checksum: 1db9139e1173944e84894dee89d7428a (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Unidade fora da demanda on 2013-08-23T22:07:40Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-26T12:32:19Z No. of bitstreams: 1 333333333333.pdf: 367669 bytes, checksum: 1db9139e1173944e84894dee89d7428a (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-10-09T19:44:18Z (GMT) No. of bitstreams: 1 333333333333.pdf: 367669 bytes, checksum: 1db9139e1173944e84894dee89d7428a (MD5) Made available in DSpace on 2013-10-09T19:44:18Z (GMT). No. of bitstreams: 1 333333333333.pdf: 367669 bytes, checksum: 1db9139e1173944e84894dee89d7428a (MD5) Previous issue date: 2013 A model consisting of a system of five ordinary differential equations to simulate the interactions between normal cells, cancer cells, endothelial cells, chemotherapy agent and anti-angiogenic agent in tumour growth is developed. By a partial analysis of the cancerfree subspace, it is shown how the anti-angiogenic agent may help the chemotherapy agent in controlling the cancer. This is illustrated by numerical examples and bifurcation diagrams Salvador

Texto completo: acesso restrito. p. 1-13 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-12-01T11:40:39Z No. of bitstreams: 1 A. M. C. Souza.pdf: 473397 bytes, checksum: d8dede07d2f9deec1ba7ea69d9acb6b1 (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2014-12-02T19:33:31Z (GMT) No. of bitstreams: 1 A. M. C. Souza.pdf: 473397 bytes, checksum: d8dede07d2f9deec1ba7ea69d9acb6b1 (MD5) Made available in DSpace on 2014-12-02T19:33:31Z (GMT). No. of bitstreams: 1 A. M. C. Souza.pdf: 473397 bytes, checksum: d8dede07d2f9deec1ba7ea69d9acb6b1 (MD5) Previous issue date: 2013 This work discusses the discrete time quantum walk (DTQW) on the first five generations of the Apollonian network. This structure is constructed in a geometric recurrent way and is characterized by, among other features, a scale-free distribution of node degrees. The DTQW formalism requires a node-dependent coin operator that, for each node, has as many different output states as that node degree, so that each local coin operator is expressed by the Fourier operator. The DTQW time evolution matrix has a larger rank than that of the network adjacency matrix or the matrix representation of the continuous time quantum walk (CTQW). Results for the time evolution, return time to specific nodes and asymptotic probability of site occupancy are obtained. Such DTQW-specific features are discussed and compared to those obtained for the classical random walk and CTQW on the same lattice.

Texto completo. Acesso restrito. p. 2195–2201 Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-06-13T20:36:48Z No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Material de Física on 2013-08-16T19:15:17Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-19T16:42:47Z No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Unidade fora da demanda on 2013-08-23T22:08:00Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-26T12:34:31Z No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-10-15T15:12:41Z (GMT) No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Made available in DSpace on 2013-10-15T15:12:42Z (GMT). No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Previous issue date: 2013 Detrended cross correlation analysis (DCCA) is used to identify and characterize correlated data obtained in drilled oil wells. The investigation is focused on different petro-physical measurements within the same well, and of the same measurement from two wells in the same oil field. The evaluation of cross correlation exponents indicates if scaling properties in two measurements are alike. The work considers also the values of cross correlated coefficients, which provide an assessment on the local correlation between measurements. The existence of several highly correlated events provides information on the continuity of geological structures, including partial and global dislocations of deposited layers. Salvador

p. 824-831 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2014-05-20T11:13:42Z No. of bitstreams: 1 1-s2.0-S0142061513002603-main.pdf: 1039783 bytes, checksum: e9957a6802c4aa424ab79cb3382f1dc0 (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2014-09-09T14:30:45Z (GMT) No. of bitstreams: 1 1-s2.0-S0142061513002603-main.pdf: 1039783 bytes, checksum: e9957a6802c4aa424ab79cb3382f1dc0 (MD5) Made available in DSpace on 2014-09-09T14:30:45Z (GMT). No. of bitstreams: 1 1-s2.0-S0142061513002603-main.pdf: 1039783 bytes, checksum: e9957a6802c4aa424ab79cb3382f1dc0 (MD5) Previous issue date: 2013 Recent experimental advances have measured individual coin components in discrete time quantum walks, which have not received the due attention in most theoretical studies on the theme. Here is presented a detailed investigation of the properties of M, the difference between square modulus of coin states of discrete quantum walks on a linear chain. Local expectation values are obtained in terms of real and imaginary parts of the Fourier transformed wave function. A simple expression is found for the average difference between coin states in terms of an angle θ gauging the coin operator and its initial state. These results are corroborated by numerical integration of dynamical equations in real space. The local dependence is characterized both by large and short period modulations. The richness of revealed patterns suggests that the amount of information stored and retrieved from quantum walks is significantly enhanced if M is taken into account.

Texto completo. Acesso restrito. p. 2195–2201 Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-06-13T20:36:48Z No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Material de Física on 2013-08-16T19:15:17Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-19T16:42:47Z No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Unidade fora da demanda on 2013-08-23T22:08:00Z (GMT) Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2013-08-26T12:34:31Z No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-10-15T15:12:41Z (GMT) No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Made available in DSpace on 2013-10-15T15:12:42Z (GMT). No. of bitstreams: 1 555555555555555.pdf: 1082351 bytes, checksum: 950d0d8d2c5da725f3fa4b880b734726 (MD5) Previous issue date: 2013 Detrended cross correlation analysis (DCCA) is used to identify and characterize correlated data obtained in drilled oil wells. The investigation is focused on different petro-physical measurements within the same well, and of the same measurement from two wells in the same oil field. The evaluation of cross correlation exponents indicates if scaling properties in two measurements are alike. The work considers also the values of cross correlated coefficients, which provide an assessment on the local correlation between measurements. The existence of several highly correlated events provides information on the continuity of geological structures, including partial and global dislocations of deposited layers. Salvador

p. 1-6 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-05-06T16:45:50Z No. of bitstreams: 1 T. A. de Assis.pdf: 866565 bytes, checksum: f93c72d8d7ee5ea813a1a64df7836372 (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2014-09-11T17:48:22Z (GMT) No. of bitstreams: 1 T. A. de Assis.pdf: 866565 bytes, checksum: f93c72d8d7ee5ea813a1a64df7836372 (MD5) Made available in DSpace on 2014-09-11T17:48:22Z (GMT). No. of bitstreams: 1 T. A. de Assis.pdf: 866565 bytes, checksum: f93c72d8d7ee5ea813a1a64df7836372 (MD5) Previous issue date: 2012 This work investigates the scaled height distribution, ρ(q), of irregular profiles that are grown based on two sets of local rules: those of the restricted solid on solid (RSOS) and ballistic deposition (BD) models. At each time step, these rules are respectively chosen with probability p and r=1−p. Large-scale Monte Carlo simulations indicate that the system behaves differently in three succeeding intervals of values of p: IB≈[0,0.75),IT≈(0.75,0.9), and IR≈(0.9,1.0]. In IB, the ballistic character prevails: the growth velocity υ∞ decreases with p in a linear way, and similar behavior is found for Γ∞(p), the amplitude of the t1/3-fluctuations, which is measured from the second-order height cumulant. The distribution of scaled height fluctuations follows the Gaussian orthogonal ensemble (GOE) Tracy-Widom (TW) distribution with resolution roughly close to 10−4. The skewness and kurtosis of the computed distribution coincide with those for TW distribution. Similar results are observed in the interval IR, with prevalent RSOS features. In this case, the skewness become negative. In the transition interval IT, the system goes smoothly from one regime to the other: the height distribution becomes apparently Gaussian, which motivates us to identify this phenomenon as a transition from Kardar-Parisi-Zhang (KPZ) behavior to Edwards-Wilkinson (EW) behavior back to KPZ behavior.

Texto completo: acesso restrito. p. 1-9 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-06-10T13:51:21Z No. of bitstreams: 1 B. B. M. Silva.pdf: 1414870 bytes, checksum: 4abf1341bbfe0b16cdcc798e0d7d606e (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2014-11-11T18:09:07Z (GMT) No. of bitstreams: 1 B. B. M. Silva.pdf: 1414870 bytes, checksum: 4abf1341bbfe0b16cdcc798e0d7d606e (MD5) Made available in DSpace on 2014-11-11T18:09:07Z (GMT). No. of bitstreams: 1 B. B. M. Silva.pdf: 1414870 bytes, checksum: 4abf1341bbfe0b16cdcc798e0d7d606e (MD5) Previous issue date: 2012 This work uses a complex network approach to analyze temporal sequences of electrophysiological signals of brain activity from freely behaving rats. A network node represents a neuron and a network link is included between a pair of nodes whenever their firing rates are correlated. The framework of time varying graph (TVG) is used to deal with a very large number (>30 000) of time dependent networks, which are set up by taking into account correlations between neuron firing rates in a moving time lag window of suitable width. Statistical distributions for the following network measures are obtained: size of the largest connected cluster, number of edges, average node degree, and average minimal path. We find that the number of networks with highly correlated activity in distinct brain areas has a fat-tailed distribution, irrespective of the behavioral state of the animal. This contrasts with short-tailed distributions for surrogates obtained by shuffling the original data, and reflects the fact that neurons in the neocortex and hippocampus often act in precise temporal coordination. Our results also suggest that functional neuronal networks at the millimeter scale undergo statistically nontrivial rearrangements over time, thus delimitating an empirical constraint for models of brain activity.

texto completo: acesso restrito. p.170–179 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-02-03T23:02:17Z No. of bitstreams: 1 Detecting switching points using asymmetric detrended fluctuation.pdf: 525716 bytes, checksum: 951dfafec2f6cdb2f2597959770170b6 (MD5) Made available in DSpace on 2012-02-03T23:02:17Z (GMT). No. of bitstreams: 1 Detecting switching points using asymmetric detrended fluctuation.pdf: 525716 bytes, checksum: 951dfafec2f6cdb2f2597959770170b6 (MD5) Previous issue date: 2012 This work uses the concept of Asymmetric Detrended Fluctuation Analysis (A-DFA) to investigate and characterize the occurrence of trend switching in financial series. A-DFA introduces two new roughness exponents, H+ and H−, which differ from the usual one H by separately taking into account contributions to the fluctuations according to whether the local trend is, respectively, upward or downward. The developed methodology requires the evaluation of local values of H(t), H+(t), and H−(t), by restricting the size of the largest window around the value t. We show that H+(t) and H−(t) behave differently in the neighborhoods of switching points (SPs) where trends change sign. Properly taken differences between shifted local values of H(t), H+(t), and H−(t) allow to identify and characterize SP’s. Tests with Weiertrasse functions, isolated peaks, and actual financial series are presented, supporting the validity of the proposed method.

Texto completo: acesso restrito. p. 1489–1496 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-08-25T13:08:06Z No. of bitstreams: 1 Miguel A. Rivera Castro.pdf: 508913 bytes, checksum: d180e26b7f49b28f48dd5f03ef5805b8 (MD5) Approved for entry into archive by Patricia Barroso (pbarroso@ufba.br) on 2014-08-26T18:57:48Z (GMT) No. of bitstreams: 1 Miguel A. Rivera Castro.pdf: 508913 bytes, checksum: d180e26b7f49b28f48dd5f03ef5805b8 (MD5) Made available in DSpace on 2014-08-26T18:57:48Z (GMT). No. of bitstreams: 1 Miguel A. Rivera Castro.pdf: 508913 bytes, checksum: d180e26b7f49b28f48dd5f03ef5805b8 (MD5) Previous issue date: 2012 The presence of sequences of top and bottom (TB) events in financial series is investigated for the purpose of characterizing such switching points. They clearly mark a change in the trend of rising or falling prices of assets to the opposite tendency, are of crucial importance for the players’ decision and also for the market stability. Previous attempts to characterize switching points have been based on the behavior of the volatility and on the definition of microtrends. The approach used herein is based on the smoothing of the original data with a Gaussian kernel. The events are identified by the magnitude of the difference of the extreme prices, by the time lag between the corresponding events (waiting time), and by the time interval between events with a minimal magnitude (return time). Results from the analysis of the inter day Dow Jones Industrial Average index (DJIA) from 1928 to 2011 are discussed. qq-Gaussian functions with power law tails are found to provide a very accurate description of a class of measures obtained from the series statistics.

texto completo: acesso restrito. p. 132–141 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-02-03T19:01:12Z No. of bitstreams: 1 A model of partial differential equations for HIV propagation.pdf: 774672 bytes, checksum: 88c7db9285e53ccb8a9023bf22a97f39 (MD5) Made available in DSpace on 2012-02-03T19:01:12Z (GMT). No. of bitstreams: 1 A model of partial differential equations for HIV propagation.pdf: 774672 bytes, checksum: 88c7db9285e53ccb8a9023bf22a97f39 (MD5) Previous issue date: 2012 A system of partial differential equations is used to model the dissemination of the Human Immunodeficiency Virus (HIV) in CD4+T cells within lymph nodes. Besides diffusion terms, the model also includes a time-delay dependence to describe the time lag required by the immunologic system to provide defenses to new virus strains. The resulting dynamics strongly depends on the properties of the invariant sets of the model, consisting of three fixed points related to the time independent and spatial homogeneous tissue configurations in healthy and infected states. A region in the parameter space is considered, for which the time dependence of the space averaged model variables follows the clinical pattern reported for infected patients: a short scale primary infection, followed by a long latency period of almost complete recovery and third phase characterized by damped oscillations around a value with large HIV counting. Depending on the value of the diffusion coefficient, the latency time increases with respect to that one obtained for the space homogeneous version of the model. It is found that same initial conditions lead to quite different spatial patterns, which depend strongly on the latency interval.

Texto completo: acesso restrito. p. 1-5 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-04-15T13:36:52Z No. of bitstreams: 1 R. F. S. Andrade.pdf: 1575474 bytes, checksum: d71f8b6f2fcfc31227707a6493094a8d (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2014-11-11T18:00:49Z (GMT) No. of bitstreams: 1 R. F. S. Andrade.pdf: 1575474 bytes, checksum: d71f8b6f2fcfc31227707a6493094a8d (MD5) Made available in DSpace on 2014-11-11T18:00:49Z (GMT). No. of bitstreams: 1 R. F. S. Andrade.pdf: 1575474 bytes, checksum: d71f8b6f2fcfc31227707a6493094a8d (MD5) Previous issue date: 2011 The capacity to resist perturbations from the environment is crucial to the survival of all organisms. We quantitatively analyze the susceptibility of protein interaction networks of numerous organisms to random and targeted failures. We find for all organisms studied that random rewiring improves protein network robustness, so that actual networks are more fragile than rewired surrogates. This unexpected fragility contrasts with the behavior of networks such as the Internet, whose robustness decreases with random rewiring. We trace this surprising effect to the modular structure of protein networks.

p. 13 Submitted by JURANDI DE SOUZA SILVA (jssufba@hotmail.com) on 2012-02-14T13:12:25Z No. of bitstreams: 1 journal.pcbi.1001131.pdf: 618605 bytes, checksum: 54da2471f0b1aa746472042e6e3679b6 (MD5) Made available in DSpace on 2012-02-14T13:12:25Z (GMT). No. of bitstreams: 1 journal.pcbi.1001131.pdf: 618605 bytes, checksum: 54da2471f0b1aa746472042e6e3679b6 (MD5) Previous issue date: 2011 This paper proposes a new method to identify communities in generally weighted complex networks and apply it to phylogenetic analysis. In this case, weights correspond to the similarity indexes among protein sequences, which can be used for network construction so that the network structure can be analyzed to recover phylogenetically useful information from its properties. The analyses discussed here are mainly based on the modular character of protein similarity networks, explored through the Newman-Girvan algorithm, with the help of the neighborhood matrix Mˆ . The most relevant networks are found when the network topology changes abruptly revealing distinct modules related to the sets of organisms to which the proteins belong. Sound biological information can be retrieved by the computational routines used in the network approach, without using biological assumptions other than those incorporated by BLAST. Usually, all the main bacterial phyla and, in some cases, also some bacterial classes corresponded totally (100%) or to a great extent (.70%) to the modules. We checked for internal consistency in the obtained results, and we scored close to 84% of matches for community pertinence when comparisons between the results were performed. To illustrate how to use the network-based method, we employed data for enzymes involved in the chitin metabolic pathway that are present in more than 100 organisms from an original data set containing 1,695 organisms, downloaded from GenBank on May 19, 2007. A preliminary comparison between the outcomes of the network-based method and the results of methods based on Bayesian, distance, likelihood, and parsimony criteria suggests that the former is as reliable as these commonly used methods. We conclude that the network-based method can be used as a powerful tool for retrieving modularity information from weighted networks, which is useful for phylogenetic analysis.

Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-08-05T12:48:00Z No. of bitstreams: 1 PhysRevE.82.031108.pdf: 121284 bytes, checksum: fabef59b6315eb9b812c220bff109023 (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-10-15T15:23:53Z (GMT) No. of bitstreams: 1 PhysRevE.82.031108.pdf: 121284 bytes, checksum: fabef59b6315eb9b812c220bff109023 (MD5) Made available in DSpace on 2013-10-15T15:23:53Z (GMT). No. of bitstreams: 1 PhysRevE.82.031108.pdf: 121284 bytes, checksum: fabef59b6315eb9b812c220bff109023 (MD5) Previous issue date: 2010 A dynamical programming approach is used to deal with the problem of controlling the directed abelian Dhar-Ramaswamy model on two-dimensional square lattice. Two strategies are considered to obtain explicit results to this task. First, the optimal solution of the problem is characterized by the solution of the Bellman equation obtained by numerical algorithms. Second, the solution is used as a benchmark to value how far from the optimum other heuristics that can be applied to larger systems are. This approach is the first attempt on the direction of schemes for controlling self-organized criticality that are based on optimization principles that consider explicitly a tradeoff between the size of the avalanches and the cost of intervention.

p. 114512-(1-7) Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-06-17T14:32:11Z No. of bitstreams: 1 Thiago de Assis.pdf: 482374 bytes, checksum: 3b5378eeb4a24e4de6783ad77dd036f5 (MD5) Rejected by Alda Lima da Silva(sivalda@ufba.br), reason: Material de Física on 2013-08-16T19:14:35Z (GMT) Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-08-27T11:09:49Z No. of bitstreams: 1 Thiago de Assis.pdf: 482374 bytes, checksum: 3b5378eeb4a24e4de6783ad77dd036f5 (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2013-11-14T20:01:36Z (GMT) No. of bitstreams: 1 Thiago de Assis.pdf: 482374 bytes, checksum: 3b5378eeb4a24e4de6783ad77dd036f5 (MD5) Made available in DSpace on 2013-11-14T20:01:36Z (GMT). No. of bitstreams: 1 Thiago de Assis.pdf: 482374 bytes, checksum: 3b5378eeb4a24e4de6783ad77dd036f5 (MD5) Previous issue date: 2010 The effect of geometrical irregularities in the work function and emitting properties of metallic surfaces at low potentials is studied. For this purpose, we propose a simplified model consisting of rectangular fractures and a classical formalism for the work function determination. The dependence of the work function with the fractures size is determined by using the electrostatic image potential method. The emission current density properties when an external electric field is applied are also analyzed.

p. 1-5 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-09-10T15:40:45Z No. of bitstreams: 1 PhysRevB.81.014204.pdf: 127331 bytes, checksum: 91c015061a806c6c3ab0ecee608b11e0 (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-09-16T16:31:44Z (GMT) No. of bitstreams: 1 PhysRevB.81.014204.pdf: 127331 bytes, checksum: 91c015061a806c6c3ab0ecee608b11e0 (MD5) Made available in DSpace on 2013-09-16T16:31:44Z (GMT). No. of bitstreams: 1 PhysRevB.81.014204.pdf: 127331 bytes, checksum: 91c015061a806c6c3ab0ecee608b11e0 (MD5) Previous issue date: 2010 A next-neighbor Ising model with disordered but long range correlated coupling constants is investigated. The model is built on a hierarchical lattice and the correlation strength depends on a tuning parameter α. The results are obtained within a transfer-matrix framework, which allows for the evaluation of the properties of individual samples. Collective behavior is computed by averaging over a large number of independent realizations. The dependence of the thermodynamic and magnetic functions with respect to the temperature is investigated for each value of α. Phase diagrams in the (α,T) plane are constructed for two distinct versions of the model, indicating the existence of regions of paramagnetic and ordered phases. Critical values αc, below which the system always assumes the paramagnetic phase, are found for both versions.

Acesso restrito: Texto completo. p. 59-66. Submitted by JURANDI DE SOUZA SILVA (jssufba@hotmail.com) on 2012-05-04T11:12:01Z No. of bitstreams: 1 __ac.els-cdn.com_S030326...16faa388efd8f4cd8751f9d6e7992.pdf: 662548 bytes, checksum: 6507d76ce9fdd8584861e9f7e948345b (MD5) Made available in DSpace on 2012-05-04T11:12:01Z (GMT). No. of bitstreams: 1 __ac.els-cdn.com_S030326...16faa388efd8f4cd8751f9d6e7992.pdf: 662548 bytes, checksum: 6507d76ce9fdd8584861e9f7e948345b (MD5) Previous issue date: 2010 Chitin is a structural endogenous carbohydrate, which is a major component of fungal cell walls and arthropod exoskeletons. A renewable resource and the second most abundant polysaccharide in nature after cellulose, chitin is currently used for waste water clearing, cosmetics, medical, and veterinary applications. This work comprises data mining of protein sequences related to the chitin metabolic pathway of completely sequenced genomes of extant organisms pertaining to the three life domains, followed by meta-analysis using traditional sequence similarity comparison and complex network approaches. Complex networks involving proteins of the chitin metabolic pathway in extant organisms were constructed based on protein sequence similarity. Several usual network indices were estimated in order to obtain information on the topology of these networks, including those related to higher order neighborhood properties. Due to the assumed evolutionary character of the system, we also discuss issues related to modularity properties, with the concept of edge betweenness playing a particularly important role in our analysis. Complex network approach correctly identifies clusters of organisms that belong to phylogenetic groups without any a priori knowledge about the biological features of the investigated protein sequences. We envisage the prospect of using such a complex network approach as a high-throughput phylogenetic method.

Texto completo: acesso restrito. p. 5750-5755 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-09-04T12:49:04Z No. of bitstreams: 1 PNAS-2010-Galvão-5750-5.pdf: 1691733 bytes, checksum: 7c44e87f181c5d7302d142ee4539ef03 (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2013-11-26T13:13:55Z (GMT) No. of bitstreams: 1 PNAS-2010-Galvão-5750-5.pdf: 1691733 bytes, checksum: 7c44e87f181c5d7302d142ee4539ef03 (MD5) Made available in DSpace on 2013-11-26T13:13:55Z (GMT). No. of bitstreams: 1 PNAS-2010-Galvão-5750-5.pdf: 1691733 bytes, checksum: 7c44e87f181c5d7302d142ee4539ef03 (MD5) Previous issue date: 2010 Cell differentiation in multicellular organisms is a complex process whose mechanism can be understood by a reductionist approach, in which the individual processes that control the generation of different cell types are identified. Alternatively, a large-scale approach in search of different organizational features of the growth stages promises to reveal its modular global structure with the goal of discovering previously unknown relations between cell types. Here, we sort and analyze a large set of scattered data to construct the network of human cell differentiation (NHCD) based on cell types (nodes) and differentiation steps (links) from the fertilized egg to a developed human. We discover a dynamical law of critical branching that reveals a self-similar regularity in the modular organization of the network, and allows us to observe the network at different scales. The emerging picture clearly identifies clusters of cell types following a hierarchical organization, ranging from sub-modules to super-modules of specialized tissues and organs on varying scales. This discovery will allow one to treat the development of a particular cell function in the context of the complex network of human development as a whole. Our results point to an integrated large-scale view of the network of cell types systematically revealing ties between previously unrelated domains in organ functions.

Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-07-23T11:30:09Z No. of bitstreams: 1 PhysRevE.82.046109.pdf: 282129 bytes, checksum: e96625a1992615b758189c704d266818 (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-08-19T13:45:43Z (GMT) No. of bitstreams: 1 PhysRevE.82.046109.pdf: 282129 bytes, checksum: e96625a1992615b758189c704d266818 (MD5) Made available in DSpace on 2013-08-19T13:45:43Z (GMT). No. of bitstreams: 1 PhysRevE.82.046109.pdf: 282129 bytes, checksum: e96625a1992615b758189c704d266818 (MD5) Previous issue date: 2010 The q-state Potts model is studied on the Apollonian network with Monte Carlo simulations and the transfer matrix method. The spontaneous magnetization, correlation length, entropy, and specific heat are analyzed as a function of temperature for different number of states, q. Different scaling functions in temperature and q are proposed. A quantitative agreement is found between results from both methods. No critical behavior is observed in the thermodynamic limit for any number of states.

Acesso restrito: Texto completo. p. 147-156. Submitted by JURANDI DE SOUZA SILVA (jssufba@hotmail.com) on 2012-04-26T11:32:35Z No. of bitstreams: 1 __www.springerlink.com_c...t776l7t876409286_fulltext.pdf: 395064 bytes, checksum: aa7f9f3e8c63feca3523a7eeee415fdb (MD5) Made available in DSpace on 2012-04-26T11:32:35Z (GMT). No. of bitstreams: 1 __www.springerlink.com_c...t776l7t876409286_fulltext.pdf: 395064 bytes, checksum: aa7f9f3e8c63feca3523a7eeee415fdb (MD5) Previous issue date: 2010 The minority game (MG) is used as a source of information to design complex networks where the nodes represent the playing agents. Differently from classical MG consisting of independent agents, the current model rules that connections between nodes are dynamically inserted or removed from the network according to the most recent game outputs. This way, preferential attachment based on the concept of social distance is controlled by the agents wealth. The time evolution of the network topology,quantitatively measured by usual parameters, is characterized by a transient phase followed by a steady state, where the network properties remain constant. Changes in the local landscapes around individual nodes depend on the parameters used to control network links. If agents are allowed to access the strategies of their network neighbors, a feedback effect on the network structure and game outputs is observed. Such effect, known as herding behavior, considerably changes the dependence of volatility σ on memory size: it is shown that the absolute value of σ as well as the corresponding value of memory size depend both on the network topology and on the way along which the agents make their playing decisions in each game round.

Acesso restrito: Texto completo. p. 291-296. Submitted by JURANDI DE SOUZA SILVA (jssufba@hotmail.com) on 2012-04-18T18:23:01Z No. of bitstreams: 1 __www.springerlink.com_c...4lw0782575784400_fulltext.pdf: 219739 bytes, checksum: 7722b8ff41934873a0c2a9f2f37919f5 (MD5) Made available in DSpace on 2012-04-18T18:23:01Z (GMT). No. of bitstreams: 1 __www.springerlink.com_c...4lw0782575784400_fulltext.pdf: 219739 bytes, checksum: 7722b8ff41934873a0c2a9f2f37919f5 (MD5) Previous issue date: 2010 A control scheme to reduce the size of avalanches of the Bak-Tang-Wiesenfeld model on complex networks is proposed. Three network types are considered: those proposed by Erd˝os-Renyi, Goh-Kahng-Kim, and a real network representing the main connections of the electrical power grid of the western United States. The control scheme is based on the idea of triggering avalanches in the highest degree nodes that are near to become critical. We show that this strategy works in the sense that the dissipation of mass occurs most locally avoiding larger avalanches. We also compare this strategy with a random strategy where the nodes are chosen randomly. Although the random control has some ability to reduce the probability of large avalanches, its performance is much worse than the one based on the choice of the highest degree nodes. Finally, we argue that the ability of the proposed control scheme is related to its ability to reduce the concentration of mass on the network. 1 Introduction

p.417-422 Submitted by Texeira Ana (atanateixeira@gmail.com) on 2012-09-28T18:59:17Z No. of bitstreams: 1 Carvalho Neto.pdf: 1070386 bytes, checksum: c89e1c859ab71906df0181a3d88e7c73 (MD5) Made available in DSpace on 2012-09-28T18:59:17Z (GMT). No. of bitstreams: 1 Carvalho Neto.pdf: 1070386 bytes, checksum: c89e1c859ab71906df0181a3d88e7c73 (MD5) Previous issue date: 2009-08 A numerically efficient transfer matrix approach is used to investigate the validity of the Tsallis scaling hypothesis in the long-range Ising spin chain with competitive interactions. In this model, the interaction between two spins i and j placed r lattice steps apart is Ji, j = (-1)ζ(i,j)J0/rα, where ζ(i, j) is either 0 or 1. This procedure has succeeded to show the validity of the scaling hypothesis for the well investigated ferromagnetic version of the model, i.e., ζ(i, j)= 0,∀i, j, ∀α > 0. Results are reported for some models of a set, which is defined by requiring ζ(i, j) to be a periodic sequence of 0's and 1's. As expected from symmetry arguments, we find that the hypothesis is not valid when ζ(i, j)= 1,∀i, j and α < 1. however, it is verified, with high degree of numerical accuracy, when α < 1, for sequences in which the occurrence of ζ(i, j)= 0 is more frequent than that of ζ(i, j)= 1. São Paulo

p. 1-4 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-10-15T17:12:02Z No. of bitstreams: 1 PhysRevE.79.037101-1.pdf: 133869 bytes, checksum: 8836226516f57d46645a819afd666af2 (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2013-10-30T17:47:19Z (GMT) No. of bitstreams: 1 PhysRevE.79.037101-1.pdf: 133869 bytes, checksum: 8836226516f57d46645a819afd666af2 (MD5) Made available in DSpace on 2013-10-30T17:47:19Z (GMT). No. of bitstreams: 1 PhysRevE.79.037101-1.pdf: 133869 bytes, checksum: 8836226516f57d46645a819afd666af2 (MD5) Previous issue date: 2009 This work investigates the scaling properties of fluctuations in the flux of individual agents with respect to their average flux in an interbank network. The analyzed data provide information on daily values of fiasset, the credit provided by bank i in the interbank network, and filiab, the credit received by bank i from the other banks of the network. The investigation focuses on the scaling properties of the fluctuations in the raw data fiasset, filiab, and fR,iext(t)=fiasset−filiab, as well as on similar properties internal and external fluctuations fiint and fiext, which are derived according to a recently proposed methodology [ M. Argollo de Menezes and A. L. Barabasi Phys. Rev. Lett. 93 068701 (2004)]. Finally, a “rolling sampling” approach is introduced in order to deal with the nonstationarity of the fluxes. The results suggest that exponents are time varying, hinting that the considered interbank network is changing with time.

p. 1-6 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-09-30T12:23:00Z No. of bitstreams: 1 0295-5075_87_5_58004.pdf: 524288 bytes, checksum: 6f1b82631b64634c4b9a7bf0dc0c9dad (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2013-11-19T20:34:43Z (GMT) No. of bitstreams: 1 0295-5075_87_5_58004.pdf: 524288 bytes, checksum: 6f1b82631b64634c4b9a7bf0dc0c9dad (MD5) Made available in DSpace on 2013-11-19T20:34:43Z (GMT). No. of bitstreams: 1 0295-5075_87_5_58004.pdf: 524288 bytes, checksum: 6f1b82631b64634c4b9a7bf0dc0c9dad (MD5) Previous issue date: 2009 This letter addresses the issue of learning shortest paths in complex networks, which is of utmost importance in real-life navigation. The approach has been partially motivated by recent progress in characterizing navigation problems in networks, having as extreme situations the completely ignorant (random) walker and the rich directed walker, which can pay for information that will guide to the target node along the shortest path. A learning framework based on a first-visit Monte Carlo algorithm is implemented, together with four independent measures that characterize the learning process. The methodology is applied to a number of network classes, as well as to networks constructed from actual data. The results indicate that the navigation difficulty and learning velocity are strongly related to the network topology.

Texto completo: acesso restrito. p.272–277 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-10-01T13:09:54Z No. of bitstreams: 1 1-s2.0-S1476945X0900052X-main.pdf: 354082 bytes, checksum: 0ffe2897da95481d70aae35ae01b3408 (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-10-15T15:19:02Z (GMT) No. of bitstreams: 1 1-s2.0-S1476945X0900052X-main.pdf: 354082 bytes, checksum: 0ffe2897da95481d70aae35ae01b3408 (MD5) Made available in DSpace on 2013-10-15T15:19:02Z (GMT). No. of bitstreams: 1 1-s2.0-S1476945X0900052X-main.pdf: 354082 bytes, checksum: 0ffe2897da95481d70aae35ae01b3408 (MD5) Previous issue date: 2009 This work shows that graph theory provides a framework to quantify the behavior of the time-correlation function among precipitation records within a given region. The method amounts to consider each station, where one data series was recorded, as a vertex in the graph. An edge, characterized by its geodesic distance d, is inserted between any pair of nodes, for which the Pearson correlation coefficient R, calculated from the corresponding series, is larger than a threshold value Rth. Then, the dependence between N(ɛ), the total number of Pearson-correlated pairs of stations with geodesic distance d ≤ ɛ, is evaluated as a function of ɛ. Results are presented for a set of spatially distributed pluviometric stations in Northeast Brazil. The reliability of the proposed procedure is tested in a two-fold way: First, values of N(ɛ) are evaluated for graphs built up by sets of regular and random distributions of nodes within the actual region where the data is collected. Next, an investigation of the influence of the choice for Rth on the results is performed. The results lead to the identification of a power law N(ɛ) ∼ ɛα for all time periods and regions that have been investigated, suggesting the presence of a robust non-metric fractal behavior. The value of α is found to depend both on seasonal and intrinsic features of the region rainfall distribution, but rather weakly on the value of Rth. The comparison of the results shows that, in contrast with the values obtained from Hurst exponent analysis, the values of α are related to the uniformity of Pearson correlation within the considered region, not with persistence of the signal.

p. 1-7 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-10-15T17:19:59Z No. of bitstreams: 1 PhysRevE.79.036105.pdf: 233641 bytes, checksum: d25fa0cf18d70ce670c0a7a26f076bb0 (MD5) Approved for entry into archive by Alda Lima da Silva(sivalda@ufba.br) on 2013-10-15T18:25:14Z (GMT) No. of bitstreams: 1 PhysRevE.79.036105.pdf: 233641 bytes, checksum: d25fa0cf18d70ce670c0a7a26f076bb0 (MD5) Made available in DSpace on 2013-10-15T18:25:14Z (GMT). No. of bitstreams: 1 PhysRevE.79.036105.pdf: 233641 bytes, checksum: d25fa0cf18d70ce670c0a7a26f076bb0 (MD5) Previous issue date: 2009 This work considers an Ising model on the Apollonian network, where the exchange constant Ji,j∼1/(kikj)μ between two neighboring spins (i,j) is a function of the degree k of both spins. Using the exact geometrical construction rule for the network, the thermodynamical and magnetic properties are evaluated by iterating a system of discrete maps that allows for very precise results in the thermodynamic limit. The results can be compared to the predictions of a general framework for spin models on scale-free networks, where the node distribution P(k)∼k−γ, with node-dependent interacting constants. We observe that, by increasing μ, the critical behavior of the model changes from a phase transition at T=∞ for a uniform system (μ=0) to a T=0 phase transition when μ=1: in the thermodynamic limit, the system shows no true critical behavior at a finite temperature for the whole μ≥0 interval. The magnetization and magnetic susceptibility are found to present noncritical scaling properties.

p. 1-9 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-10-02T12:00:40Z No. of bitstreams: 1 PhysRevE.80.016102.pdf: 620636 bytes, checksum: 757087643116445634e02dada0cfd145 (MD5) Approved for entry into archive by Rodrigo Meirelles(rodrigomei@ufba.br) on 2013-10-15T15:17:50Z (GMT) No. of bitstreams: 1 PhysRevE.80.016102.pdf: 620636 bytes, checksum: 757087643116445634e02dada0cfd145 (MD5) Made available in DSpace on 2013-10-15T15:17:50Z (GMT). No. of bitstreams: 1 PhysRevE.80.016102.pdf: 620636 bytes, checksum: 757087643116445634e02dada0cfd145 (MD5) Previous issue date: 2009 A periodically forced two-dimensional cellular automata model is used to reproduce and analyze the complex spatiotemporal patterns observed in the transmission of vector infectious diseases. The system, which comprises three population levels, is introduced to describe complex features of the dynamics of the vector-transmitted dengue epidemics, known to be very sensitive to seasonal variables. The three coupled levels represent the human, the adult, and immature vector populations. The dynamics includes external seasonality forcing, human and mosquito mobility, and vector control effects. The model parameters, even if bounded to well-defined intervals obtained from reported data, can be selected to reproduce specific epidemic outbursts. In the current study, explicit results are obtained by comparison with actual data retrieved from the time series of dengue epidemics in two cities in Brazil. The results show fluctuations that are not captured by mean-field models. It also reveals the qualitative behavior of the spatiotemporal patterns of the epidemics. In the extreme situation of the absence of external periodic drive, the model predicts a completely distinct long-time evolution. The model is robust in the sense that it is able to reproduce the time series of dengue epidemics of different cities, provided that the forcing term takes into account the local rainfall modulation. Finally, an analysis is provided of the effect of the dependence between epidemics threshold and vector control actions, both in the presence and absence of human mobility factor.

An investigation on the properties of electronic states of a tight-binding Hamiltonian on the Apollonian network is presented. This structure, which is defined based on the Apollonian packing problem, has been explored both as a complex network and as a substrate on the top of which physical models can be defined. The Schrödinger equation of the model, which includes only nearest-neighbor interactions, is written in a matrix formulation. In the uniform case, the resulting Hamiltonian is proportional to the adjacency matrix of the Apollonian network. The characterization of the electronic eigenstates is based on the properties of the spectrum, which is characterized by a very large degeneracy. The 2π/3 rotation symmetry of the network and large number of equivalent sites are reflected in all eigenstates, which are classified according to their parity. Extended and localized states are identified by evaluating the participation rate. Results for other two nonuniform models on the Apollonian network are also presented. In one case, interaction is considered to be dependent of the node degree, while in the other one random on-site energies are considered.

p. 1-7 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-12-09T17:06:16Z No. of bitstreams: 1 PhysRevE.77.041410.pdf: 207074 bytes, checksum: b74c95ed6e85d03d033b58e30bb979a4 (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2014-02-21T18:49:04Z (GMT) No. of bitstreams: 1 PhysRevE.77.041410.pdf: 207074 bytes, checksum: b74c95ed6e85d03d033b58e30bb979a4 (MD5) Made available in DSpace on 2014-02-21T18:49:04Z (GMT). No. of bitstreams: 1 PhysRevE.77.041410.pdf: 207074 bytes, checksum: b74c95ed6e85d03d033b58e30bb979a4 (MD5) Previous issue date: 2008 When the invasion percolation model is applied as a simplified model for the displacement of a viscous fluid by a less viscous one, the distribution of displaced mass follows two distinct universality classes, depending on the criteria used to stop the displacement. Here we study the distribution of mass for this process, in the case where four extraction wells are placed around a single injection well in the middle of a square lattice. Our analysis considers the limit where the pressure of the extraction well Pe is zero; in other words, an extraction well is capped as soon as less viscous fluid reaches that extraction well. Our results show that, as expected, the probability of stopping the production with small amounts of displaced mass is greatly reduced. We also investigate whether or not creating extra extraction wells is an efficient strategy. We show that the probability of increasing the amount of displaced fluid by adding an extra extraction well depends on the total recovered mass obtained before adding this well. The results presented here could be relevant to determine efficient strategies in oil exploration.

P. 2304.1-2304.10. Submitted by JURANDI DE SOUZA SILVA (jssufba@hotmail.com) on 2011-10-24T13:05:20Z No. of bitstreams: 1 a05v30n2.pdf: 431858 bytes, checksum: e266af03b2de5a0e04ce6a2c3c6d8332 (MD5) Made available in DSpace on 2011-10-24T13:05:20Z (GMT). No. of bitstreams: 1 a05v30n2.pdf: 431858 bytes, checksum: e266af03b2de5a0e04ce6a2c3c6d8332 (MD5) Previous issue date: 2008 Descobertas recentes revelam que modelos matemáticos euclidianos, de há muito estabelecidos e que procuram reproduzir a geometria da natureza, às vezes se apresentam incompletos e, em determinadas situações, inadequados. Especificamente, muitas das formas encontradas na natureza não são círculos, triângulos, esferas, icosaedros ou retângulos. Enfim, não são simples curvas, superfícies ou sólidos, conforme definidos na geometria clássica de Euclides (300 a.C), cujos teoremas possuem lugar de destaque nos textos de geometria. Neste trabalho apresenta-se uma breve e elementar, mas que busca ser consistente, discussão sobre algumas definições e aplicações relacionadas à geometria fractal, em particular fractais ideais. Caracterizaremos alguns fractais auto-similares que, por sua importância histórica ou riqueza de características, constituem exemplos ilustrativos "clássicos" de propriedades de fractais, propriedades estas que muitas vezes aparecem dispersas numa literatura mais especializada. Mostra-se, por construção, que suas medidas de comprimento, área e volume, nas dimensões euclidianas usuais, dão margem a resultados contraditórios. Estes podem ser explicados pelo fato de que tais objetos só podem ser adequadamente mensurados em espaços de dimensão fracionária. São Paulo

p. 247-256 Submitted by JURANDI DE SOUZA SILVA (jssufba@hotmail.com) on 2012-07-18T15:20:23Z No. of bitstreams: 1 __www.springerlink.com_c...m08tk08r56501v6n_fulltext.pdf: 481637 bytes, checksum: d870ac096ad1b250f8c10bd60dc62cc4 (MD5) Made available in DSpace on 2012-07-18T15:20:23Z (GMT). No. of bitstreams: 1 __www.springerlink.com_c...m08tk08r56501v6n_fulltext.pdf: 481637 bytes, checksum: d870ac096ad1b250f8c10bd60dc62cc4 (MD5) Previous issue date: 2008 A concept of higher order neighborhood in complex networks, introduced previously [Phys. Rev. E 73, 046101 (2006)], is systematically explored to investigate larger scale structures in complex networks. The basic idea is to consider each higher order neighborhood as a network in itself, represented by a corresponding adjacency matrix, and to settle a plenty of new parameters in order to obtain a best characterization of the whole network. Usual network indices are then used to evaluate the properties of each neighborhood. The identification of high order neighborhoods is also regarded as intermediary step towards the evaluation of global network properties, like the diameter, average shortest path between node, and network fractal dimension. Results for a large number of typical networks are presented and discussed.

Acesso restrito: Texto completo. p. 5265-5269 Submitted by JURANDI DE SOUZA SILVA (jssufba@hotmail.com) on 2012-06-06T17:41:17Z No. of bitstreams: 1 __ac.els-cdn.com_S037596...c471b0794ad18aed68a88bbcb307e.pdf: 449087 bytes, checksum: c63d3a64b2c3c2513076b5daf3b4ef2b (MD5) Made available in DSpace on 2012-06-06T17:41:17Z (GMT). No. of bitstreams: 1 __ac.els-cdn.com_S037596...c471b0794ad18aed68a88bbcb307e.pdf: 449087 bytes, checksum: c63d3a64b2c3c2513076b5daf3b4ef2b (MD5) Previous issue date: 2008 A previously introduced concept of higher order neighborhoods in complex networks, [R.F.S. Andrade,J.G.V. Miranda, T.P. Lobão, Phys. Rev. E 73 (2006) 046101] is used to define a distance between networks with the same number of nodes. With such measure, expressed in terms of the matrix elements of the neighborhood matrices of each network, it is possible to compare, in a quantitative way, how far apart in the space of neighborhood matrices two networks are. The distance between these matrices depends on both the network topologies and the adopted node numberings. While the numbering of one network is fixed, a Monte Carlo algorithm is used to find the best numbering of the other network, in the sense that it minimizes the distance between the matrices. The minimal value found for the distance reflects differences in the neighborhood structures of the two networks that arise only from distinct topologies. This procedure ends up by providing a projection of the first network on the pattern of the second one. Examples are worked out allowing for a quantitative comparison for distances among distinct networks, as well as among distinct realizations of random networks.

p. 1-7 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2013-11-20T10:35:16Z No. of bitstreams: 1 PhysRevB.78.235427-1.pdf: 449941 bytes, checksum: eb89ba43bdd191400c31c0e08b749b03 (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2013-11-26T12:48:05Z (GMT) No. of bitstreams: 1 PhysRevB.78.235427-1.pdf: 449941 bytes, checksum: eb89ba43bdd191400c31c0e08b749b03 (MD5) Made available in DSpace on 2013-11-26T12:48:05Z (GMT). No. of bitstreams: 1 PhysRevB.78.235427-1.pdf: 449941 bytes, checksum: eb89ba43bdd191400c31c0e08b749b03 (MD5) Previous issue date: 2008 The density of emission current by a rough surface with fractal structure is analyzed. A possible experimental setup is modeled by an irregular emitting surface, iteratively generated by a fractional Brownian motion (FBM) algorithm with roughness (or Hurst) exponent H=0.3 and a far away plane representing the anode. The boundaries are held at a fixed potential difference and the Laplace’s equation, with lateral periodic conditions, was numerically solved. The solution for the potential leads to the evaluation of the local field and, subsequently, the current density evaluated by using the Fowler-Nordheim’s approach. The results hint at a strong local dependence of the electric field with small variations in the roughness of the irregular boundary. The value of the turn-on electric field is found to be ∼8×106 V/cm. Finally, Fowler-plot curves make possible to discuss the connection between the field amplification factor and geometric properties of the emitter surfaces.

p. 1-8 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2014-01-21T11:44:22Z No. of bitstreams: 1 PhysRevE.76.026111.pdf: 207822 bytes, checksum: d7dadf30179dd9f5f66e3035f18d42ac (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2014-02-13T18:09:18Z (GMT) No. of bitstreams: 1 PhysRevE.76.026111.pdf: 207822 bytes, checksum: d7dadf30179dd9f5f66e3035f18d42ac (MD5) Made available in DSpace on 2014-02-13T18:09:18Z (GMT). No. of bitstreams: 1 PhysRevE.76.026111.pdf: 207822 bytes, checksum: d7dadf30179dd9f5f66e3035f18d42ac (MD5) Previous issue date: 2007 We investigate a set of directed sandpile models on the Apollonian network, which are inspired by the work of Dhar and Ramaswamy [Phys. Rev. Lett. 63, 1659 (1989)] on Euclidian lattices. They are characterized by a single parameter q, which restricts the number of neighbors receiving grains from a toppling node. Due to the geometry of the network, two- and three-point correlation functions are amenable to exact treatment, leading to analytical results for avalanche distributions in the limit of an infinite system for q=1,2. The exact recurrence expressions for the correlation functions are numerically iterated to obtain results for finite-size systems when larger values of q are considered. Finally, a detailed description of the local flux properties is provided by a multifractal scaling analysis.

Texto completo: acesso restrito. p. 1-12 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2014-01-07T16:05:52Z No. of bitstreams: 1 0953-8984_19_47_476215.pdf: 522156 bytes, checksum: 8995f338508be865b17d7a05489ee9f5 (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2014-09-09T15:49:18Z (GMT) No. of bitstreams: 1 0953-8984_19_47_476215.pdf: 522156 bytes, checksum: 8995f338508be865b17d7a05489ee9f5 (MD5) Made available in DSpace on 2014-09-09T15:49:18Z (GMT). No. of bitstreams: 1 0953-8984_19_47_476215.pdf: 522156 bytes, checksum: 8995f338508be865b17d7a05489ee9f5 (MD5) Previous issue date: 2007 In this study, the behavior of the electric field and its potential are investigated in a region bounded by a rough fractal surface and a distant plane. Both boundaries, maintained at distinct potential values, are assumed to be conductors and, as such, the electric potential is obtained by numerically solving Laplace's equation subject to the appropriate Dirichlet's condition. The rough boundaries, generated by the ballistic deposition and fractal Brownian motion methods, are characterized by the values of the surface roughness W and the local fractal dimension df = 3−α, where α is the usual roughness exponent. The equipotential surfaces, obtained from Laplace's equation, are characterized by these same parameters. Results presented show how df depends on the potential value, on the method used to generate the boundary and on W. The behavior of the electric field with respect to the equipotential surface is also considered. Its average intensity was found to increase as a function of the average distance from the equipotential to the fractal boundary; however, its intensity reaches a maximum before decreasing towards an asymptotic constant value, an effect that increases as the value of W increases.

Texto completo: acesso restrito. p. 469-474 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2014-01-21T14:01:37Z No. of bitstreams: 1 art%3A10.1140%2Fepjb%2Fe2007-00248-6.pdf: 264784 bytes, checksum: ced1f313e82f529acec8ed77b3522394 (MD5) Approved for entry into archive by Alda Lima da Silva (sivalda@ufba.br) on 2014-02-13T18:32:12Z (GMT) No. of bitstreams: 1 art%3A10.1140%2Fepjb%2Fe2007-00248-6.pdf: 264784 bytes, checksum: ced1f313e82f529acec8ed77b3522394 (MD5) Made available in DSpace on 2014-02-13T18:32:12Z (GMT). No. of bitstreams: 1 art%3A10.1140%2Fepjb%2Fe2007-00248-6.pdf: 264784 bytes, checksum: ced1f313e82f529acec8ed77b3522394 (MD5) Previous issue date: 2007 The objective of this study is to design a procedure to characterize chaotic dynamical systems, in which they are mapped onto a complex network. The nodes represent the regions of space visited by the system, while the edges represent the transitions between these regions. Parameters developed to quantify the properties of complex networks, including those related to higher order neighbourhoods, are used in the analysis. The methodology is tested on the logistic map, focusing on the onset of chaos and chaotic regimes. The corresponding networks were found to have distinct features that are associated with the particular type of dynamics that generated them.