On stick-slip homoclinic chaos and bifurcations in a mechanical system with dry friction

In this paper we consider a self-excited mechanical system by dry friction in order to study the bifurcational behavior of the arisen vibrations. The oscillating system consists of a mass block-belt-system which is self-excited by static and Coulomb friction. We analyze the system behavior numerically through bifurcation diagrams, phase portraits, frequency spectra and Poincare maps, which show the existence of nonhomoclinic and homoclinic chaos and a route to homoclinic chaos. The homoclinic chaos is also analyzed analytically via the Melnikov prediction method. The system dynamic is characterized by the existence of two potential wells in the phase plane which exhibit rich bifurcational and chaotic behavior.

A comment on a nonideal centrifugal vibrator machine behavior with soft and hard springs

This paper concerns a type of rotating machine (centrifugal vibrator), which is supported on a nonlinear spring. This is a nonideal kind of mechanical system. The goal of the present work is to show the striking differences between the cases where we take into account soft and hard spring types. For soft spring, we prove the existence of homoclinic chaos. By using the Melnikov's Method, we show the existence of an interval with the following property: if a certain parameter belongs to this interval, then we have chaotic behavior; otherwise, this does not happen. Furthermore, if we use an appropriate damping coefficient, the chaotic behavior can be avoided. For hard spring, we prove the existence of Hopf's Bifurcation, by using reduction to Center Manifolds and the Bezout Theorem (a classical result about algebraic plane curves).

THE EFFECT of WEAK DISSIPATION IN TWO-DIMENSIONAL MAPPING

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

On a Nonideal (MRD) Damper-Electro-mechanical Absorber Dynamics

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

CRITICAL EXPONENTS and SCALING PROPERTIES FOR THE CHAOTIC DYNAMICS of A PARTICLE IN A TIME-DEPENDENT POTENTIAL BARRIER

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

On chaotic behavior of a fixed offshore structure

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efeitos de probióticos sobre a digestibilidade, escore fecal e características hematológicas em cães

Avaliaram-se os efeitos da suplementação de dois tipos de probióticos para cães filhotes, que receberam dois tipos de dieta - de alta e de baixa qualidade -, sobre a digestibilidade dos nutrientes, escore fecal e parâmetros sanguíneos. Foram utilizados 18 animais, distribuídos em três tratamentos. No tratamento 1, controle, os cães receberam somente a ração; no tratamento 2, ração com probiótico 1 (Bifidobacterium) e, no tratamento 3, ração com probiótico 2 (Lactobacillus). O experimento foi dividido em duas fases. Verificaram-se que os valores médios do coeficiente de metabolizabilidade da energia bruta (CMEB) na fase 1, caracterizada pela troca da dieta Super Premium para a dieta Standard, apresentaram resultados significativos (P<0,05), sendo os melhores resultados obtidos nos animais que receberam o probiótico 2. Não houve diferenças significativas (P>0,05) para o escore fecal e para as análises hematológicas.

TOXIC EFFECTS OF WATER EUTROPHICATION ON PANCREATIC, HEPATIC AND OSTEOGENIC TISSUES OF RATS

Pollution, industrial solvents, concentrations of metals and other environmental agents are widely related to biochemicals values which are used in disease diagnosis of environmental toxicity. A rat bioassay validated for the identification of toxic effects of eutrophication revealed increased serum activities of amylase, alanine transaminase (BLT) and alkaline phosphatase (ALP) in rats that received algae, filtered water and nickel or cadmium from drinking water. Serum Cu-Zn superoxide dismutase activity decreased from its basal level of 40.8 +/- 2.3 to 26.4 U/mg protein, at 7 days of algae and at 48 hr of nickel and cadmium water ingestion. The observation that lipoperoxide concentration was not altered in rats treated with filtered water, while amylase, ALT and ALP were increased in these rats and in those treated with nickel or cadmium, indicated that pancreatic, hepatic and osteogenic lesions by eutrophication were not related to superoxide radicals, and might be due to a novel toxic environmental agent found in filtered and non-filtered algae water.

Atividade microbiana em solos, influenciada por resíduos de algodão e torta de mamona

Microbial activity constitutes a good indicator of soil quality, and is influenced by the addition of carbon in the system serving as a substrate for microorganisms that increase their activity and release of CO2, comprising the edaphic respiration of the soil. The objective of this study was to evaluate the microbial activity in different soil types with the addition of cake press of castor bean and cotton textile residue. The study was conducted in a greenhouse at the headquarters of Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA) Cotton in randomized block design in 4 x 3 factorial arrangement with four replications. At predetermined intervals of 4 days, the containers were opened and the solution of NaOH titrated with HCl 2N in the presence of acid/base indicator phenolphthalein. After reading, the same amount of NaOH was added and the containers were closed again. The difference between the amounts of acid needed to neutralize the sodium hydroxide in a control container and the treatments was equivalent to the amount of carbon dioxide produced by soil microorganisms. It was found that the residues influenced the microbial activity in different soil types, especially in the initial determinations, presenting themselves as good sources for mineralization and nutrient supply, the castor bean proportionating higher cumulative release of CO2 by microorganisms.

Proteinuria predicts relapse in adolescent and adult minimal change disease

OBJECTIVE: This study sought to outline the clinical and laboratory characteristics of minimal change disease in adolescents and adults and establish the clinical and laboratory characteristics of relapsing and non-relapsing patients.METHODS: We retrospectively evaluated patients with confirmed diagnoses of minimal change disease by renal biopsy from 1979 to 2009; the patients were aged >13 years and had minimum 1-year follow-ups.RESULTS: Sixty-three patients with a median age (at diagnosis) of 34 (23-49) years were studied, including 23 males and 40 females. At diagnosis, eight (12.7%) patients presented with microscopic hematuria, 17 (27%) with hypertension and 17 (27%) with acute kidney injury. After the initial treatment, 55 (87.3%) patients showed complete remission, six (9.5%) showed partial remission and two (3.1%) were nonresponders. Disease relapse was observed in 34 (54%) patients who were initial responders (n = 61). In a comparison between the relapsing patients (n = 34) and the non-relapsing patients (n = 27), only proteinuria at diagnosis showed any significant difference (8.8 (7.1-12.0) vs. 6.0 (3.6-7.3) g/day, respectively, p = 0.001). Proteinuria greater than 7 g/day at the initial screening was associated with relapsing disease.CONCLUSIONS: In conclusion, minimal change disease in adults may sometimes present concurrently with hematuria, hypertension, and acute kidney injury. The relapsing pattern in our patients was associated with basal proteinuria over 7 g/day.

Comparative phylogeography of Trypanosoma cruzi TCIIc: New hosts, association with terrestrial ecotopes, and spatial clustering

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Antimicrobial activity of coffee-based solutions and their effects on Streptococcus mutans adherence

The aim of this study was to evaluate the antimicrobial activity of different coffee solutions and their effects on the adherence of Streptococcus mutans to glass surface. Coffee solutions were prepared with three commercial products (Pilao, Mellita and Café do Ponto) by two different methods (simple and boiled) (n=15). A control group was also included in the study. For antimicrobial activity testing, tubes containing coffee solution and culture medium were inoculated with a suspension of S. mutans ATCC 35688 and incubated for 1 min 1h, 2h and 4h. Serial dilutions and plating on BHI agar were performed. S, mutans adherence to glass in presence of different coffee solutions was also tested. The number of adhered bacteria (CFU/mL) was determined by plating method. The results were statistically analyzed by ANOVA and Turkey's test. The tested coffee solutions did not reduce the number of colony forming units of S. mutans in relation to the control at all evaluation periods. All the solutions reduced significantly the adherence of S. mutans to the glass surface in relation to control. The tested coffee solutions did not present any antimicrobial effect on Streptococcus mutans, however, all the coffee solutions reduced significantly the adherence of S mutans to the glass surface.

Degenerate hope bifurcations in Chua's system

In this paper we study the local codimension one, two and three Hopf bifurcations which occur in the classical Chua's differential equations with cubic nonlinearity. A detailed analytical description of the regions in the parameter space for which multiple small periodic solutions bifurcate from the equilibria of the system is obtained. As a consequence, a complete answer for the challenge proposed in [Moiola & Chua, 1999] is provided. © 2009 World Scientific Publishing Company.

Some remarks on bifurcation analysis of a nonlinear vibrating system excited by a shape memory alloy material (SMA)

In this paper, the dynamical response of a coupled oscillator is investigated, taking in consideration the nonlinear behavior of a SMA spring coupling the two oscillators. Due to the nonlinear coupling terms, the system exhibits both regular and chaotic motions. The Poincaré sections for different sets of coupling parameters are verified. © 2011 World Scientific Publishing Company.