A bouncing ball model with two nonlinearities: a prototype for Fermi acceleration

Some dynamical properties of a bouncing ball model under the presence of an external force modeled by two nonlinear terms are studied. The description of the model is made by use of a two dimensional nonlinear measure preserving map on the variables velocity of the particle and time. We show that raising the straight of a control parameter which controls one of the nonlinearities, the positive Lyapunov exponent decreases in the average and suffers abrupt changes. We also show that for a specific range of control parameters, the model exhibits the phenomenon of Fermi acceleration. The explanation of both behaviours is given in terms of the shape of the external force and due to a discontinuity of the moving wall's velocity.Comment: A complete list of my papers can be found in: http://www.rc.unesp.br/igce/demac/denis

The influence of loading on the heat of transformation in shape memory alloys

Standard caloric measurements on Shape Memory Alloys (SMAs) are usually carried out with the specimen in a state free of stress, by means of standard calorimeters. However, in its every application, the material is subjected to some load, being therefore necessary to investigate the influence of loading on the caloric behavior of SMAs, in order to take this into account when modeling their thermodynamic behavior. The present work investigates the influence of loading on the heat of transformation in SMAs. Experimental measurements were carried out on Ni Ti samples and a mathematical description of the observed behavior was developed. The theoretical results are in agreement with the experimental ones

Risks and benefits of colonoscopy in patients aged 80 and older: a prospective study

OBJECTIVE: this study aims to compare colonoscopy results in patients aged 50-79 and those aged 80 and older. PATIENTS AND METHODS: a total of 533 diagnostic colonoscopies performed from August 2011 to January 2012 were evaluated in a prospective study analyzing age, ASA classification, comorbidities, endoscopic findings, time to reach the cecum, number of complete examinations, difficulties and complications. Chi-square test was used to compare categorical data whereas Student's t test to compare means. A p value < 0.05 was considered significant. RESULTS: 479 patients were in Group A - age 50 to 79, whereas 54 were in Group B, 80 versus older. The following results are shown for Group A and B, respectively: age 63 &#177; 8 versus 84 &#177; 4 years. ASA 1 difficult examination: 58 (21 %) versus 12 (27%) p > 0.05, ASA > 2 difficult examination: 41 (20%) versus 6 (60%) p < 0,05. Comorbidities 255 (53%) versus 36 (66%) p > 0.05. Complete colonoscopy in 450 (94%) versus 45 (83%), p < 0.01. Difficulties in 99 (20%) versus 32 (40%), p < 0.01. Complications in 1 (0.2%) versus 3 (5%) p < 0.01. Diverticulitis/ sequelae in 3 (0.6%) versus 3 (5%) p < 0.01. CRC in 42 (8.7%) and 10 (18.5%), p < 0.05. Adenoma in 130 (27 %) versus 15 (27%), p > 0.05 Time to reach the cecum was 39 &#177; 10 minutes for difficult procedures and 13 &#177; 9 for the easy ones. CONCLUSION: age 80 and older is associated with more adverse events during colonoscopy

Comparative study of vibration measuring techniques applied to Aluminum beams with localized damage

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáWhen a structural damage changes the characteristics of stiffness and mass of a mechanical system, the dynamic behavior of this beam will also change. Only a few studies about the correlation between damage and the effect caused in dynamic behavior can be found. Based on this, this study will analyze the behavior of the natural frequencies and damping ratios of four aluminum beams, with and without damages. This work aims to determine the error between the two methods of data acquisition and the effects of the damage inflicted on the shape modes, natural frequencies and damping ratios for each beam. To achieve the purposes, initially, a numerical FEM simulation will be performed, followed by experimental impact tests, aiming to obtain the estimated natural frequencies and damping ratios. After this, damages will be made on these beams and the impact tests will be repeated for each beam. The FEM analysis will be performed using Ansys. For the impact tests, two data acquirement methods will be used during the impact testing, the first, using accelerometers to obtain the vibration response, the second using a Brüel & Kjær’s sound level meter. The obtained data will be compared and will be possible to determinate the error between the natural frequencies measured using both methods. The results obtained will be used to correlates the dynamic behavior with the damages inflicted on the beams. This paper allowed analyzing the usage viability of the sound level meter to measure the output of a vibrating system, considering certain limitations. In addition, the damage effects on the natural frequencies of the beams.Quando um dano altera as características de massa e rigidez de um sistema (uma viga, por exemplo), seu comportamento dinâmico também é afetado. O estudo dos efeitos do dano infligido no comportamento modal é relativamente recente, tendo poucos estudos correlacionando o dano com seus efeitos em vigas. Baseado nisso, este estudo visa analisar o comportamento e variação do valor das frequências naturais e dos fatores de amortecimento de quatro vigas de alumínio com e sem danos. Este trabalho tem por objetivo determinar: o erro entre as medições efetuadas utilizando ambos os métodos de obtenção da resposta de vibração das vigas e os efeitos dos danos causados no comportamento modal do sistema analisado (modos de vibração, frequências naturais e fatores de amortecimento). Para tal, incialmente, uma simulação numérica utilizando elementos finitos será efetuada, seguida por testes de impacto, com o objetivo de obter as frequências naturais e os fatores de amortecimento para cada caso. A simulação numérica será efetuada utilizando o software Ansys e os testes de impacto utilizarão dois métodos de aquisição da resposta do sistema: utilizando acelerômetros e um medidor de pressão sonora. Os dados obtidos serão comparados e será possível determinar o erro entre os métodos de medição utilizados. Os resultados obtidos também serão utilizados para analisar os efeitos dos danos no comportamento dinâmico das vigas utilizadas. A elaboração deste trabalho possibilitou averiguar a viabilidade do uso de um medidor de pressão sonora para medição de vibrações, dentro de seus limites de utilização e suas limitações. Também foi possível analisar os efeitos dos danos nos valores de frequências naturais das vigas analisadas