Últimos itens adicionados do Acervo: Universidade Federal de Ouro Preto

A Universidade Federal de Ouro Preto (UFOP) é uma universidade pública brasileira mantida pelo governo federal do Brasil. Foi criada em 21 de agosto de 1969 a partir da incorporação de duas centenárias instituições de ensino superior: a Escola de Farmácia fundada em 1839 e a Escola de Minas fundada em 1876, ambas localizadas em Ouro Preto, Minas Gerais.

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An?lise num?rica bidimensional da morfologia dendr?tica do n?quel e do ferro utilizando o m?todo de campo de fase.

Furtado, Henrique Silva; Bernardes, Am?rico Trist?o; Machado, Romuel Figueiredo; Silva, Carlos Ant?nio da
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Nesse trabalho, s?o apresentados os resultados de simula??es bidimensionais da forma??o de dendritas durante a solidifica??o do n?quel e do ferro puros, utilizando um modelo de campo de fase. A morfologia obtida mostrou-se qualitativamente semelhante ? forma dendr?tica, com bra?os prim?rios e secund?rios bem desenvolvidos. Al?m disso, as velocidades de crescimento em regime permanente, calculadas no presente trabalho, apresenta ram boa conformidade com os dados experimentais em uma grande faixa de super-resfriamentos. Foi observado que a espessura da interface apresenta um forte efeito sobre a morfologia e a velocidade de solidifica??o. Interfaces espessas reduzem o tempo computacional; entretanto podem gerar resultados inconsistentes. A espessura que apresentou os melhores resultados sem aumento acentuado do tempo de processamento foi 4x10-8 m. ______________________________________________________________________________________________________________________________________________________; ABSTRACT: Numerical results for the solidification morphologies of pure Nickel and Iron, obtained by a two dimensional Phase Field model, conformed qualitatively well with the dendritic form, clearly depicting developed primary and secondary branches. Additionally...

Numerical simulation of solute trapping phenomena using phase-field solidification model for dilute binary alloys

Furtado, Henrique Silva; Bernardes, Am?rico Trist?o; Machado, Romuel Figueiredo; Silva, Carlos Ant?nio da
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Numerical simulation of solute trapping phenomena using phase-field solidification model for dilute binary alloys Numerical simulation of solute trapping during solidification, using two phase-field model for dilute binary alloys developed by Kim et al. [Phys. Rev. E, 60, 7186 (1999)] and Ramirez et al. [Phys. Rev. E, 69, 05167 (2004)] is presented here. The simulations on dilute Cu-Ni alloy are in good agreement with one dimensional analytic solution of sharp interface model. Simulation conducted under small solidification velocity using solid liquid interface thickness (2?) of 8 nanometers reproduced the solute (Cu) equilibrium partition coefficient. The spurious numerical solute trapping in solid phase, due to the interface thickness was negligible. A parameter used in analytical solute trapping model was determined by isothermal phase-field simulation of Ni-Cu alloy. Its application to Si-As and Si-Bi alloys reproduced results that agree reasonably well with experimental data. A comparison between the three models of solute trapping (Aziz, Sobolev and Galenko [Phys. Rev. E, 76, 031606 (2007)]) was performed. It resulted in large differences in predicting the solidification velocity for partition-less solidification...

Matrices of science and technology interactions and patterns of structured growth: implications for development

Ruiz, Ricardo Machado; Bernardes, Am?rico Trist?o; Albuquerque, Eduardo da Motta e
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Scientific and other non-patent references (NPRs) in patents are important tools to analyze interactions between science and technology. This paper organizes a database with 514,894 USPTO patents granted globally in 1974, 1982, 1990, 1998 and 2006. There are 165,762 patents with at least one reference to science and engineering (S&E) literature, from a total of 1,375,503 references. Through a lexical analysis, 71.1% of this S&E literature is classified by S&E fields. These data serve as the basis for the elaboration of global and national 3-dimensional matrices (technological domains, S&E fields and number of references). Three indicators are proposed to analyze these matrices, allowing us to identify patterns of structured growth that differentiate developed and non-developed countries. This differentiation informs suggestions for public policies for development, emphasizing the need for an articulation between the industrial and technological dimension and scientific side. The intertwinement of these two dimensions is a key component of developmental policies for the twenty-first century.

Global analysis of the immune response

Ribeiro, Leonardo Costa; Dickman, Ronald; Bernardes, Am?rico Trist?o
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
The immune system may be seen as a complex system, characterized using tools developed in the study of such systems, for example, surface roughness and its associated Hurst exponent. We analyze densitometric (Panama blot) profiles of immune reactivity, to classify individuals into groups with similar roughness statistics. We focus on a population of individuals living in a region in which malaria endemic, as well as a control group from a disease-free region. Our analysis groups individuals according to the presence, or absence, of malaria symptoms and number of malaria manifestations. Applied to the Panama blot data, our method proves more effective at discriminating between groups than principal-components analysis or super-paramagnetic clustering. Our findings provide evidence that some phenomena observed in the immune system can be only understood from a global point of view. We observe similar tendencies between experimental immune profiles and those of artificial profiles, obtained from an immune network model. The statistical entropy of the experimental profiles is found to exhibit variations similar to those observed in the Hurst exponent.

Dynamic stability in random and scale-free B-lymphocyte networks

Ribeiro, Leonardo Costa; Dickman, Ronald; Bernardes, Am?rico Trist?o; Vaz, Nelson Monteiro
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
One of the most intriguing features of the immune system is regulation: a limited response when perturbed repeatedly. We propose a minimal network model for immune regulation in a lymphocyte network containing two types of elements: B lymphocytes and ligands that bind to their receptors. Effective interactions between B cells, mediated by other components of the immune system can be excitatory or inhibitory. In our model, B cell clones and ligand species are represented by nodes, and interactions by links. We expect that, as in many complex systems, the connectivity distribution is broad, motivating study of the model on a scale-free network; for comparison we study the same dynamics on a random graph. We characterize the dynamics of the model and its response to perturbations. Our model reproduces several key features of immune system dynamics: regulation saturation of response , and more rapid response upon repeated perturbation with the same agents. Our results suggest that a scale-free network of interactions contributes to the regulation and dynamics of the immune system.

National systems of innovation and technological differentiation: a multi-country model

Ribeiro, Leonardo Costa; Ruiz, Ricardo Machado; Albuquerque, Eduardo da Motta e; Bernardes, Am?rico Trist?o
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Science and technology have a fundamental role in the economic development. Although This statement is generally well accepted, the internal mechanisms which are responsible for these interactions are not clear. In the last decade, dealing with this problem, many models have been proposed. In this paper, we introduce a model that creates an artificial world economy that is a network of countries. Each country has its own national system of innovation and the interactions between countries are given by functions that connect the competitiveness of their prices and their technological capabilities. Starting from different conjurations, the artiffcial world economy self-organizes itself and creates a hierarchies of countries.

Scale-free fuse network and its robustness

Pinheiro, Carlos Felipe Saraiva; Bernardes, Am?rico Trist?o
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
The robustness and reliability of scale-free networks are tested as a fuse network. The idea is to examine the robustness of a scale-free network when links are irreversibly removed after failing. Due to inherent characteristics of the fuse network model, the sequence of links removal is deterministic and conditioned to fuse tolerance and connectivity of its ends. It is a different situation from classical robustness analysis of complex networks, when they are usually tested under random fails and deliberate attacks of nodes. The use of this system to study the fracture of elastic material brought some interesting results.

Survival-extinction phase transition in a bit-string population with mutation

Fehsenfeld, Kathia Mariane; Dickman, Ronald; Bernardes, Am?rico Trist?o
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
A bit string model for the evolution of a population of haploid organisms , subject to competition , reproduction with mutation and selection is studied , using mean field theory an d Monte Carlo simulation s . We show that, depending on environmental flexibility an d genetic variability, the model exhibits a phase transition between extinction and survival. T h e mean field theory describes the infinite size limit, while simulations are used to study quasistationary properties.

Cross-over, thresholds, and interactions between science and technology: lessons for less-developed countries

Bernardes, Am?rico Trist?o; Albuquerque, Eduardo da Motta e
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Presently, science is an important precondition for the economic development of less-developed countries. This paper discusses the specific roles that science has at initial stages of development, pointing to its contributions for the countries? absorptive capability. Furthermore, this paper specifies the role of science for initiating a positive interaction with technological development, since initial stages of development and during catching up processes. For less-developed countries, neither the linear model of technology nor an ?inverted linear model? would take place: a more interactive approach is necessary for development. Using statistics of patents (USPTO) and scientific papers (ISI) for 120 countries (1974, 1982, 1990, and 1998), this paper analyses some evidences on thresholds levels of scientific production to originate an interactive relationship between science and technology. These data also document that the value of this threshold seems to double from one period to another. Although this paper presents tentative results, some policy implications are discussed: scientific institutional building must be seen as a component of modern industrial policies.

Computer simulation of polydioxolane (PDXL) and poly(tetrahydrofuran) (PTHF): a comparative study of some poly(ethylene oxide) (PEO) properties

Ferreira, Beatriz Alves; Bernardes, Am?rico Trist?o; Almeida, Wagner Batista de
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Classical methods (molecular mechanics and molecular dynamics) and semiempirical calculations were applied to study structural and energetic properties of polydioxolane (PDXL) and poly(tetrahydrofuran) (PTHF). Then, these properties were compared with poly(ethylene oxide) (PEO) in order to investigate the possibility of using PDXL and PTHF as an alternative to PEO based systems. It was found that the behaviour of molecular simulation is similar for all of them, with the folded structure observed in equilibrium. It was noted that the main contribution to potential energy is due to electrostatic term. The O/C ratio and oxygen atom positions have a strong in?uence on charge distribution. Semiempirical calculations of free energy including enthalpic, entropic and zero point energy (ZPE) contributions showed that the folding process is favourable for PEO, PTHF and PDXL at 300 and 400 K.

Simulating inbreeding depression through the mutation accumulation theory

Sousa, Adriano de Oliveira; Oliveira, Suzana Maria Moss de; Bernardes, Am?rico Trist?o
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Using the Penna model for biological aging, which is based on the mutation accumulation theory, we show that the number of homozygous loci corresponding to deleterious mutations is higher in small populations than in large ones. This decrease of heterozygosity may drive small populations to extinction even when no drastic change of the environment occurs.

Monte Carlo simulation of inherited longevity

Oliveira, Paulo Murilo Castro de; Oliveira, Suzana Maria Moss de; Bernardes, Am?rico Trist?o; Stauffer, Dietrich
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Within the Penna model of biological ageing, we show that longevity is heritable, for both sexual and asexual reproduction.

Theoretical study of solvent and temperature effects on the behaviour of poly(ethylene oxide) (PEO)

Ferreira, Beatriz Alves; Santos, Helio Ferreira dos; Bernardes, Am?rico Trist?o; Silva, Glaura Goulart; Almeida, Wagner Batista de
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Molecular mechanics and molecular dynamics simulations were applied in order to study the behaviour of poly ethylene. oxide PEO in different temperatures and solvents. It was found that over the temperature range of 50?500 K the equilibrium structure of PEO is folded. Both kinetic and potential energies increase with temperature. The behaviour of PEO . in two different solvents ? CHCl ? s5 and H O ? s80 ? was found to be similar, with the folded structure observed 32 in equilibrium. The solvation energy calculated using the GBrSA model yielded essentially the same value in CHCl and H2O.

Computer simulation of the morphological characteristics of thermally sprayed coatings

Bernardes, Am?rico Trist?o; Ara?jo, Fernando Gabriel da Silva; Branco, Jos? Roberto Tavares
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
We present a computational model for the simulation of thermal spray deposition of powders on the surface of solid substrates kept at low temperatures. The method of simulation relates the deposition temperature, the particle size, and the mechanical properties of the powder and of the substrate in an attempt to predict the shape of the deposited particle after cooling. A porous structure is obtained and the dynamical evolution of its surface roughness is measured for different temperatures.

Immunization and aging: a learning process in the immune network

Bernardes, Am?rico Trist?o; Santos, Rita Maria Zorzenon dos
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Immunization and aging: a learning process in the immune network. The immune system can be thought as a complex network of different interacting elements. A cellular automaton , defined in shape- space, was recently shown t o exhibit self- regulation an d complex behavior an d is, therefore, a good candidate t o model the immune system . Using this model t o simulate a real immune system we find good agreement with recent experiments on mice. The model exhibits the experimentally ob served refractory behavior of the immune system under multiple antigen present at ion s as well as loss of it s plasticity caused by aging.

Siblings of centenarians live longer: a computer simulation

Oliveira, Paulo Murilo Castro de; Oliveira, Suzana Maria Moss de; Bernardes, Am?rico Trist?o; Stauffer, Dietrich
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português

Immune Network at the Edge of Chaos

Bernardes, Am?rico Trist?o; Santos, Rita Maria Zorzenon dos
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Some time ago Jerne proposed a new theory to explain the basis of the behaviour of the immune system. He suggested the existence of a functional connected network, based on pattern recognition of the idiotypes carried by the lymphocytes, which is responsible for the self regulation of the immune system. Only 04 19) of the lymphocytes available in the immune repertoire will participate in this functional network, while the rest of the lymphocytes will be free to respond to any foreign antigen. Each individual immune repertoire will be different depending on the lymphocytes that participate in the connected network. Using a very simple cellular automata model of the immune repertoire dynamics we show that, although the usual regimes "stable and chaotic# attained by this automata, are not interesting from the biological point of view, the transition region, at the edge of chaos, is very appropriate to describe such dynamics[ In this region we have obtained a functional connected network involving 09 19) of the lymphocytes available in the repertoire, as suggested by Jerne and others[ The model also reproduces the immune system signature, the ensemble of different lymphocytes that each individual expresses in his immune repertoire, which varies from one individual to another[ We show how the immune memory comes out as a consequence of the dynamics of the system[ From our results we confirm and present evidence that the chaotic regime corresponds to a sort of non- healthy state...

Mutation load and the extinction of large populations

Bernardes, Am?rico Trist?o
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
In the time evolution of finite populations, the accumulation of harmful mutations in further generations might lead to a temporal decay in the mean fitness of the whole population that, after sufficient time, would reduce population size and so lead to extinction. This joint action of mutation load and population reduction is called Mutational Meltdown and is usually considered only to occur in small asexual or very small sexual populations. However, the problem of extinction cannot be discussed in a proper way if one previously assumes the existence of an equilibrium state, as initially discussed in this paper. By performing simulations in a genetically inspired model for time-changing populations, we show that mutational meltdown also occurs in large asexual populations and that the mean time to extinction is a nonmonotonic function of the selection coefficient. The stochasticity of the extinction process is also discussed. The extinction of small sexual N ,-~ 700 populations is shown and our results confirm the assumption that the existence of recombination might be a powerful mechanism to avoid extinction.

Dynamics of interacting polymer chains and solvents

Pandey, R. B.; Bernardes, Am?rico Trist?o; Foo, G. M.; Stauffer, Dietrich
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
Conformation and dynamics of charged polymer chains in counter-ion solvent is studied by a Monte Carlo simulation in two and three dimensions. The nodes of the chains are positively charged while the solvent particles possess negative charge. The concentration of the polymer ( p ), and the empty sites ( pe ) is varied along with the temperature. Reptation, kink-jump, and a buckling governed by the interaction energy are considered in moving the chain segments. The variation of the root mean square (rms) displacement of the center of mass, and the relaxation of the radius of gyration of the chains with time are studied as a function of polymer concentration and temperature. The rms displacement of the polymer chains exhibits various power laws in different time regimes which depend on the concentration of the chains. Relaxation of the radius of gyration is enhanced on increasing the temperature; the relaxation time seems to decrease on reducing the chain length and increase on increasing the concentration. The motion of solvent particles show subdiffusive behavior which is sensitive to polymer concentration.

Efeito da rugosidade recortada polida no escoamento em modelo de passagem de min?rio

Silva Filho, Amilton Bernardinho da; Silva, Jos? Margarida da; Curi, Adilson
Fonte: Universidade Federal de Ouro Preto Publicador: Universidade Federal de Ouro Preto
Tipo: Artigo publicado em periodico
Português
O principal objetivo desse trabalho ? analisar o comportamento do fluxo de material fragmentado em passagens de min?rio com paredes rugosas. Nesse estudo, um modelo f?sico de passagem de min?rio em escala reduzida foi utilizado para observar o efeito da rugosidade sobre o fluxo. A inser??o de placas de madeira nas paredes internas do modelo foi realizada de modo a simular as rugosidades do tipo recortada polida. A escolha desse modelo de rugosidade, selecionado a partir dos padr?es adotados internacionalmente pela ISRM (Sociedade Internacional de Mec?nica de Rochas), foi devido ? sua grande similaridade com o padr?o de rugosidade encontrado em passagens de min?rio reais constru?das por explosivos. Os resultados dos ensaios realizados no modelo revelaram que as rugosidades do tipo recortada polida provocam uma queda significativa de vaz?o em rela??o aos ensaios realizados em paredes lisas. Tamb?m foi observada, para esse modelo de rugosidade, a ocorr?ncia de arcos mec?nicos, fluxo em funil e fluxo turbulento. ______________________________________________________________________________________________________________________________________________________