A comparison of two nonlinear damping mechanisms in a vibration isolator

The vibration transmissibility characteristics of a single-degree-of- freedom (SDOF) passive vibration isolation system with different nonlinear dampers are investigated in this paper. In one configuration, the damper is assumed to be linear and viscous, and is connected to the mass so that it is perpendicular to the spring (horizontal damper). The vibration is in the direction of the spring. The second configuration is one in which the damper is in parallel with the spring but the damping force is proportional to the cube of the relative velocity across the damper (cubic damping). Both configurations are studied for small amplitudes of excitation, when some analysis can be conducted based on analytical expressions, and for large amplitudes of excitation, where the analysis is based on numerical simulations. It is found that the two nonlinear systems can outperform the linear system when force transmissibility is considered. However, for displacement transmissibility, the system with the horizontal damper exhibits some desirable properties, but the system with cubic damping does not. © 2012 Elsevier Ltd.

Electrocardiographic evaluation of the degree of sedation and the isolated use of methadone in healthy dogs

Objective: The present study aimed to investigate the influence of methadone on cardiorespiratory parameters, electrocardiogram and clinical sedation in dogs. Further possible side effects are reported.Study designProspective experimental cross-over study.DogsEight, 1-4-year-old, various breeds of dogs of both genders weighing 9-36kg.MethodsEach dog was treated three times: methadone 0.3mgkg(-1) (M0.3), 0.5mgkg(-1) (M0.5) and 1.0mgkg(-1) (M1.0) intramuscularly. Respiratory rate, heart rate and arterial blood pressure were recorded as well as electrocardiographic evaluation of lead II. Clinical sedation in each treatment received a score (0-3) after drug administration and at 30minute intervals until scores and measurements returned to baseline values.ResultsA significant decrease in heart rate was seen with each dose of methadone and bradycardia (HR<60bpm) was noted in a few dogs at each dose. A clinically significant arrhythmia occurred in one dog at 1mgkg(-1) that required reversal with butorphanol. There was no significant difference in SAP, MAP and DAP between treatments. Some side effects such as salivation, defecation, vocalization and panting, after administration of methadone were observed. There were no differences in mean values of heart rate, P-wave and QRS complex duration and QT interval between treatments.Conclusion and clinical relevanceMethadone administration was associated with panting and a decrease in heart rate at all doses tested in this study. The cardiac rhythm should be monitored carefully in dogs when methadone is administered on its own, especially at higher doses.

Degree of conversion of different composite resins photo-activated with light-emitting diode and argon ion laser

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

Characterization of grazing bifurcation in airfoils with control surface freeplay nonlinearity

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

Aeroelastic Analysis of a Typical Section Using of Shape memory wire actuator

Shape memory alloys (SMAs) provide a compact and effective actuation for a variety of mechanical systems. In this paper, a numerical simulation study of a three degree of-freedom airfoil, subjected to two-dimensional incompressible inviscid flow using a SMA is presented. SMA wire actuators are used to control the flap movement of a wing section. Through the thermo-mechanical constitutive equation of the SMA proposed by Brison, we simulate numerically the behavior of a double SMA wire actuator. Two SMA actuators are used: one to move the flap down and the other to move the flap up. Through the numerical results conducted in the present study, the behavior and characteristics of an SMA actuator with two SMA wires are shown the effectiveness of the SMA actuator. In conclusion, this paper shows the feasibility of using SMA wire actuators for flap movement, with success

Order-disorder degree of self-assembled clusters: Influence on photoluminescence emission and morphology of BaxSr1-xTiO3 nanocrystals

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

Notes on vibration control of a micro/macromanipulator mounted on a flexible structure

The objective of this study is to describe the design and the implementation of an experimental set-up used to study the dynamics, the experimental identification, and the active vibration control of a flexible structure mounted manipulator system. The system consists of a three-degree-of-freedom cylindrical manipulator system with a flexible link on its tip. A two-degree-of-freedom polar rigid manipulator is mounted on the flexible macromanipulator. The dynamic modelling and experimental modal analysis identification in the frequency domain are being applied to design active digital control strategies for the micro-manipulator system to damp the mechanical vibrations of the flexible structure on the tip of the macro-manipulator system.

On the dynamic behaviour of a mass supported by a parallel combination of a spring and an elastically connected damper

This paper presents a consistent and concise analysis of the free and forced vibration of a mass supported by a parallel combination of a spring and an elastically supported damper (a Zener model). The results are presented in a compact form and the physical behaviour of the system is emphasised. This system is very similar to the conventional single-degree-of freedom system (sdof)-(Voigt model), but the dynamics can be quite different depending on the system parameters. The usefulness of the additional spring in series with the damper is investigated, and optimum damping values for the system subject to different types of excitation are determined and compared.There are three roots to the characteristic equation for the Zener model; two are complex conjugates and the third is purely real. It is shown that it is not possible to achieve critical damping of the complex roots unless the additional stiffness is at least eight times that of the main spring. For a harmonically excited system, there are some possible advantages in using the additional spring when the transmitted force to the base is of interest, but when the displacement response of the system is of interest then the benefits are marginal. It is shown that the additional spring affords no advantages when the system is excited by white noise. (c) 2007 Elsevier Ltd. All rights reserved.

Force and displacement transmissibility of a nonlinear isolator with high-static-low-dynamic-stiffness

Engineers often face the challenge of reducing the level of vibrations experienced by a given payload or those transmitted to the support structure to which a vibrating source is attached. In order to increase the range over which vibrations are isolated, soft mounts are often used in practice. The drawback of this approach is the static displacement may be too large for reasons of available space for example. Ideally, a vibration isolator should have a high-static stiffness, to withstand static loads without too large a displacement, and at the same time, a low dynamic stiffness so that the natural frequency of the system is as low as possible which will result in an increased isolation region. These two effects are mutually exclusive in linear isolators but can be overcome if properly configured nonlinear isolators are used. This paper is concerned with the characterisation of such a nonlinear isolator comprising three springs, two of which are configured to reduce the dynamic stiffness of the isolator. The dynamic behaviour of the isolator supporting a lumped mass is investigated using force and displacement transmissibility, which are derived by modelling the dynamic system as a single-degree-of-freedom system. This results in the system dynamics being approximately described by the Duffing equation. For a linear isolator, the dynamics of the system are the same regardless if the source of the excitation is a harmonic force acting on the payload (force transmissibility) or a harmonic motion of the base (displacement transmissibility) on which the payload is mounted. In this paper these two expressions are compared for the nonlinear isolator and it is shown that they differ. A particular feature of the displacement transmissibility is that the response is unbounded at the nonlinear resonance frequency unless the damping in the isolator is greater than some threshold value, which is not the case for force transmissibility. An explanation for this is offered in the paper. (C) 2011 Elsevier Ltd. All rights reserved.

Glass transition and degree of conversion of a light-cured orthodontic composite

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

Continuous and gradual photo-activation methods: influence on degree of conversion and crosslink density of composite resins

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cytogenetic analysis of B chromosomes in one population of the fish Moenkhausia sanctaefilomenae (Steindachner, 1907) (Teleostei, Characiformes)

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

DNA Psi-condensation and reentrant decondensation: Effect of the PEG degree of polymerization

psi-Condensation of DNA fragments of about 4 kbp was induced by poly(ethylene glycol) (PEG), with degrees of polymerization ranging from 45 to 182, and univalent salt (NaCl). Using circular dichroism spectroscopy, we were able to accurately determine the critical amount of PEG needed to induce condensation, as a function of the NaCl concentration. A significant dependence on the PEG degree of polymerization was found. Phase boundaries determined for the multimolecular condensation were very similar to those observed previously for the monomolecular collapse, with two asymptotic regimes at low and high salt concentrations. We analyze our data using a theoretical model that properly takes into account both the polyelectrolyte nature of the DNA and the liquid crystallinity of the condensed phase. The model assumes that all PEG is excluded from the condensates and shows reentrant decondensation only at low salt. We also systematically study reentrant decondensation and find a very strong dependence on PEG molecular weight. At low PEG molecular weight, decondensation occurs at relatively low concentrations of PEG, and over a wide range of salt concentrations. This suggests that in the reentrant decondensation the flexible polymers used are not completely excluded from the condensed phase.

Infrared degrees of freedom of Yang-Mills theory in the Schrodinger representation

We set up a new calculational framework for the Yang-Mills vacuum transition amplitude in the Schrodinger representation. After integrating out hard-mode contributions perturbatively and performing a gauge-invariant gradient expansion of the ensuing soft-mode action, a manageable saddle-point expansion for the vacuum overlap can be formulated. In combination with the squeezed approximation to the vacuum wave functional this allows for an essentially analytical treatment of physical amplitudes. Moreover, it leads to the identification of dominant and gauge-invariant classes of gauge field orbits which play the role of gluonic infrared (IR) degrees of freedom. The latter emerge as a diverse set of saddle-point solutions and are represented by unitary matrix fields. We discuss their scale stability, the associated virial theorem and other general properties including topological quantum numbers and action bounds. We then find important saddle-point solutions (most of them solitons) explicitly and examine their physical impact. While some are related to tunneling solutions of the classical Yang-Mills equation, i.e. to instantons and merons, others appear to play unprecedented roles. A remarkable new class of IR degrees of freedom consists of Faddeev-Niemi type link and knot solutions, potentially related to glueballs.