Effects of mistuning on dynamic behavior of nonlinear cyclic systems with lump masses and cubic nonlinearity

Mistuning in cyclic symmetric systems increases severely the forced response of system and splits the modes. This paper concerns with nonlinear behavior of mistuned cyclic systems. A nonlinear, mistuned model based on the method of multiple scales is proposed and formulated in which nonlinearity and mistuning parameter is assumed to be in of low order. Next, two mistuned systems were considered and solved by the multiple scale technique. Numerical results demonstrate that mistuning can lead to repeating and scattering of jump phenomena during the excitation frequency whereas in tuned cyclic system it occurs simultaneously (synchronously).Peer ReviewedPostprint (published version

MicroRNA-129-1 acts as tumour suppressor and induces cell cycle arrest of GBM cancer cells through targeting IGF2BP3 and MAPK1

Background MicroRNA-129-1 (miR-129-1) seems to behave as a tumour suppressor since its decreased expression is associated with different tumours such as glioblastoma multiforme (GBM). GBM is the most common form of brain tumours originating from glial cells. The impact of miR-129-1 downregulation on GBM pathogenesis has yet to be elucidated. Methods MiR-129-1 was overexpressed in GBM cells, and its effect on proliferation was investigated by cell cycle assay. MiR-129-1 predicted targets (CDK6, IGF1, HDAC2, IGF2BP3 and MAPK1) were also evaluated by western blot and luciferase assay. Results Restoration of miR-129-1 reduced cell proliferation and induced G1 accumulation, significantly. Several functional assays confirmed IGF2BP3, MAPK1 and CDK6 as targets of miR-129-1. Despite the fact that IGF1 expression can be suppressed by miR-129-1, through 30-untranslated region complementary sequence, we could not find any association between IGF1 expression and GBM. MiR-129-1 expression inversely correlates with CDK6, IGF2BP3 and MAPK1 in primary clinical samples. Conclusion This is the first study to propose miR129-1 as a negative regulator of IGF2BP3 and MAPK1 and also a cell cycle arrest inducer in GBM cells. Our data suggests miR-129-1 as a potential tumour suppressor and presents a rationale for the use of miR-129-1 as a novel strategy to improve treatment response in GBM

Sensitivity analysis on dynamic responses of geometrically imperfect base excited cantilevered beams

The non-linear non-planar dynamic responses of a near-square cantilevered geometrically imperfect (i.e., slightly curved) beam under harmonic primary resonant base excitation with a one-to-one internal resonance is investigated. By assuming two different geometric imperfection shapes, the sensitivity of the perfect beam model predicted limit-cycles to small geometric imperfections is analyzed by continuing them versus the imperfection parameter incorporating the imperfect beam model. This was carried out by assuming that the corresponding frequency detuning parameter associated with each limit-cycle is fixed. Also, other possible branches of dynamic solutions for the corresponding fixed detuning parameter within the interval of the imperfection amplitude are determined and the importance of accounting for the small geometric imperfections is discussed

Sexual dysfunctions in patients with diabetes: a study from Iran

Abstract Background Diabetes mellitus is a chronic disease that causes short and long-term complications. This study aimed to investigate the prevalence of sexual dysfunctions (SD) among diabetic patients in Iran and to examine whether glycemic control has a role in SD. Methods A consecutive sample of diabetic women and men who were registered in the Isfahan Endocrine and Metabolism Center, Iran were studied. Sexual dysfunction was evaluated using the Female Sexual Function Index (FSFI) in women and the International Index of Erectile Function (IIEF) in men. In addition the level of glycosylated hemoglobin was assessed to classify the diabetes status in patients. Results In all 200 patients (100 male and 100 female) were entered into the study. The mean age of patients was 48.6 (SD = 7.3) years and most had type 2 diabetes (91.0%). The results showed that sexual dysfunctions were widespread in both gender and 165 (82.5%) patients reported that experienced at least one sexual dysfunction. There were significant associations between sexual dysfunctions and gender and type of diabetes (P = 0.04). Women and patients with type 1 diabetes had higher rates of SD. No major differences were found between SD and age, diabetes status, duration of diabetes and hypertension. In addition, glycemic control did not show a significant association with SD in both genders. Conclusion The findings of this study showed that SD prevalence was high in diabetic patients of both genders and the glycemic control did not correlate with the frequency of SD in the study population. It is recommended that SD should be addressed more precisely in health care practice in Iran.</p

Effective reduction of stiffness at peak frequency in hydraulic engine mounts by using magneto-rheological fluids

Hydraulic engine mounts are generally used in aerospace and automotive applications for the purpose of cabin noise and vibration reduction. By careful selection of hydraulic mount design parameters, at a certain frequency, namely the notch frequency, the dynamic stiffness will be smaller than the static stiffness and cabin vibration and noise reduction is provided at that frequency. Literature review indicates that in all previous designs of hydraulic engine mounts the dynamic stiffness increases after the notch frequency. This phenomenon undesirable because of the increase in the force transmitted to the cabin. This paper proposes a new hydraulic engine mount that uses two working fluids. The new design has two notch frequencies and two peak frequencies. In this study, effective reduction of the peak frequencies has been demonstrated by using a controllable fluid as one of the working fluids and a non-controllable fluid as the second working fluid. As a result, one can obtain a hydraulic engine mount design with only one notch frequency but having no peak frequency. The new hydraulic engine mount design and its mathematical model are presented in detail and some discussions on the simulation results are provided

Bearings coefficients effects on chaotic and bifurcation behavior of flexible rotor systems subjected to rub-impact

This study investigates the influence of end-support conditions on the chaotic and bifurcation behavior of a rotating flexible shaft-disk system. The system is modeled as a continuous shaft with a rigid disk in its mid span whilst supported by multi-coefficients bearings. Both Coriolis and centrifugal effects due to shaft flexibility are included. The partial differential equations of motion are extracted using the Rayleigh beam theory and the assumed mode method is used to discretize them in order to be solved numerically. The analytical tools used in this work include time series, phase plane portrait, power spectrum, Poincaré map, bifurcation diagrams, and Lyapunov exponents. The main objective of the present study is to investigate the effects of end-supports stiffness and damping coefficients on the chaotic vibration behavior of a rotating system. Periodic, sub-harmonic, quasi-periodic, and chaotic states have been observed for each case. As demonstrated, inclusion of the bearing effects can primarily change the speed ratios at which rub-impact occurs. The principal and cross-coupling stiffness and damping coefficients have quite different effects in the chaotic behavior of the system

A micromechanics-informed phase field model for brittle fracture accounting for the unilateral constraint

We propose a new direction-dependent model for the unilateral constraint involved in the phase field approach to fracture and also in the continuous damage mechanics models. The construction of this phase field model is informed by micromechanical modeling through the homogenization theory, where the representative volume element (RVE) has a planar crack in the center. The proposed model is made closely match the response of the RVE, including the frictionless self-contact condition. This homogenization approach allows to identify a direction-dependent phase field model with the tension-compression split obtained from cracked microstructures. One important feature of the proposed model is that unlike most other models, the material degradation is consistently determined without artificial assumptions or ad hoc parameters with no physical interpretation, thus, a more realistic modeling is resulted. With standard tests such as uniaxial loadings, three-point bending, simple shear, and through-crack tests, the proposed model predicts reasonable crack paths. Moreover, with the RVE response as a benchmark, the proposed model gives rise to an accurate stress-strain curve under shear loads, more accurate than most existing models

Numerical prediction of developing flow in gas pipelines

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.In this paper the numerical modeling of the dynamic behavior of compressible gas flow is investigated in pipelines. The numerical simulation is performed by solving the coupled conservation form of the governing equations for twodimensional, laminar, viscous, supersonic flow in developing region under different thermal boundary conditions. The numerical procedure is a finite-volume based finite-element method applied on unstructured grids. The convection terms are discretized by well-defined Roe Method and diffusion terms by a Galerkin finite element formulation. The temporal terms are evaluated based on an explicit fourth order Runge-Kutta scheme. The results indicate that heating the gas flow leads to an increase in pressure loss. In the other words, cooling the gas flow leads to decrease the pressure drop or power consumption of booster pressure station. Furthermore, change in the gas viscosity has considerable effects on the flow quantities such as pressure loss and friction factor

Orthogonal decomposition of anisotropic constitutive models for the phase field approach to fracture

We propose a decomposition of constitutive relations into crack-driving and persistent portions, specifically designed for materials with anisotropic/orthotropic behavior in the phase field approach to fracture to account for the tension-compression asymmetry. This decomposition follows a variational framework, satisfying the orthogonality condition for anisotropic materials. This implies that the present model can be applied to arbitrary anisotropic elastic behavior in a three-dimensional setting. On this basis, we generalize two existing models for tension-compression asymmetry in isotropic materials, namely the volumetric-deviatoric model and the no-tension model, towards materials with anisotropic nature. Two benchmark problems, single notched tensile shear tests, are used to study the performance of the present model. The results can retain the anisotropic constitutive behavior and the tension-compression asymmetry in the crack response, and are qualitatively in accordance with the expected behavior for orthotropic materials. Furthermore, to study the direction of maximum energy dissipation, we modify the surface integral based energy release computation, $G_\theta$, to account only for the crack-driving energy. The computed energies with our proposed modifications predict the fracture propagation direction correctly compared with the standard G-theta method