Modeling of autoresonant control of a parametrically excited screen machine

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Modelling of nonlinear dynamic response of a screen machine described by the nonlinear coupled differential equations and excited by the system of autoresonant control is presented. The displacement signal of the screen is fed to the screen excitation directly by means of positive feedback. Negative feedback is used to fix the level of screen amplitude response within the expected range. The screen is anticipated to vibrate with a parametric resonance and the excitation, stabilization and control response of the system are studied in the stable mode. Autoresonant control is thoroughly investigated and output tracking is reported. The control developed provides the possibility of self-tuning and self-adaptation mechanisms that allow the screen machine to maintain a parametric resonant mode of oscillation under a wide range of uncertainty of mass and viscosit

3D printing of PEEK-based medical devices

open access articlePolyether-ether-ketone (PEEK) is an excellent thermoplastic alternative to metallic biomaterials which is used for loadbearing applications due to its high strength and stiffness, and biocompatibility with no cytotoxic effects. However, a potential clinical concern is that PEEK alone is not bioactive enough, and thus has limited fixation to bone. To overcome this problem, bioactive materials and/or porosity are incorporated into PEEK medical devices. The latest developments in these two strategies are presented. in this paper. Bioactive PEEK/hydroxyapatite (HA) prepared by integration of 3D printing and compression molding is presented in this paper. In addition, nozzle and build plate temperatures for 3D printing of porous PEEK were optimized using genetic algorithm (GA) to achieve the highest mechanical strength for load bearing applications such as spinal fusion cages

THE EFFECTS OF INDUSTRY STRUCTURE ON PRICE: A CASE IN THE BEEF INDUSTRY

This study estimates the influence of concentration and other structural variables on the price of slaughter cattle. Cross-sectional data were used to estimate a single equation model which included, in addition to traditional factor demand variables, packer concentration and a measure of market power exerted by feedlots. Results suggest that packer concentration has had a significant and increasing negative impact on fed cattle prices during the years of analysis, 1972 and 1977.Industrial Organization, Livestock Production/Industries,

Grazing Effects on Some Soil Characteristics in Lar Rangelands

Heavy grazing pressures jeopardise the sustainability of the ecosystem by reducing soil fertility (Dormaar et al., 1998). Different results have been reported of grazing intensities on soil chemical properties, which stem from climate, soil, vegetation, management and kind of animal (Dormaar et al., 1998; Javadi, 2003; Sanadgool, 2002)

Numerical predictions of U-notched sample failure based on a discrete energy argument

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link.Kodsi (2016) proposed a criterion for isotropic, linear elastic media in a brittle state applicable to both sharp and blunt notches. Fracture toughness and material strength are the only parameters required to operate the criterion. This paper provides a formulation of the criterion speci c to blunt notches and further examines the capability of the criterion for samples weakened by U-notches. Predictions are compared to signi cant experimental results from U-notched samples that were subject to mixed-mode fracture. Good agreement is demonstrated, justifying and substantiating the theory

Akbari–Ganji Method for Solving Equations of Euler–Bernoulli Beam with Quintic Nonlinearity

open access articleIn many real word applications, beam has nonlinear transversely vibrations. Solving nonlinear beam systems is complicated because of the high dependency of the system variables and boundary conditions. It is important to have an accurate parametric analysis for understanding the nonlinear vibration characteristics. This paper presents an approximate solution of a nonlinear transversely vibrating beam with odd and even nonlinear terms using the Akbari–Ganji Method (AGM). This method is an effective approach to solve nonlinear differential equations. AGM is already used in the heat transfer science for solving differential equations, and in this research for the first time, it is applied to find the approximate solution of a nonlinear transversely vibrating beam. The advantage of creating new boundary conditions in this method in additional to predefined boundary conditions is checked for the proposed nonlinear case. To illustrate the applicability and accuracy of the AGM, the governing equation of transversely vibrating nonlinear beams is treated with different initial conditions. Since simply supported and clamped-clamped structures can be encountered in many engineering applications, these two boundary conditions are considered. The periodic response curves and the natural frequency are obtained by AGM and contrasted with the energy balance method (EBM) and the numerical solution. The results show that the present method has excellent agreements in contrast with numerical and EBM calculations. In most cases, AGM is applied straightforwardly to obtain the nonlinear frequency– amplitude relationship for dynamic behaviour of vibrating beams. The natural frequencies tested for various values of amplitude are clearly stated the AGM is an applicable method for the proposed nonlinear system. It is demonstrated that this technique saves computational time without compromising the accuracy of the solution. This approach can be easily extended to other nonlinear systems and is therefore widely applicable in engineering and other sciences

The incidence of prostate cancer in Iran: Results of a population-based cancer registry

Background: Little is known about the epidemiology of prostate cancer in Iranian men. We carried out an active prostate cancer surveillance program in five provinces of Iran. Methods: Data used in this study were obtained from population-based cancer registries between 1996 and 2000. Results: The age-standardized incidence rate of prostate carcinoma in the five provinces was 5.1 per 100,000 person-years. No significant difference was seen in the age-standardized incidence rate of prostate cancer within the provinces studied. The mean±SD age of patients with prostate cancer was 67±13.5 years. Conclusion: The incidence of prostate cancer in Iran is very low as compared to the Western countries. This can partly be explained by lack of nationwide screening program, younger age structure and quality of cancer registration system in Iran

A visual guide for lower limb prothetic alignment

A novel method to provide an objective visual guide during lower limb prosthetic alignment is proposed. A customized ambulatory device was built to collect kinematic and temporal gait data from 3 subjects walking in four different experiment setups. Multiple gait events within a gait cycle and stride time were derived as feature variables and were pre-processed using Principle Component Analysis (PCA). Distinctive clusters due to different walking setups were noticed in a PCA plot in two dimensions. Dispersion of each clusters and distances amongst each other explains the walking variability and differences under different setups

A Stabilized Cut Streamline Diffusion Finite Element Method for Convection-Diffusion Problems on Surfaces

We develop a stabilized cut finite element method for the stationary convection diffusion problem on a surface embedded in R d . The cut finite element method is based on using an embedding of the surface into a three dimensional mesh consisting of tetrahedra and then using the restriction of the standard piecewise linear continuous elements to a piecewise linear approximation of the surface. The stabilization consists of a standard streamline diffusion stabilization term on the discrete surface and a so called normal gradient stabilization term on the full tetrahedral elements in the active mesh. We prove optimal order a priori error estimates in the standard norm associated with the streamline diffusion method and bounds for the condition number of the resulting stiffness matrix. The condition number is of optimal order for a specific choice of method parameters. Numerical examples supporting our theoretical results are also included

High temperature optical absorption investigation into the electronic transitions in sol–gel derived C12A7 thin films

Optical absorption into 6 mm thick sol–gel derived films, annealed at 1300 °C of 12CaO·7Al2O3 calcium aluminate binary compound on MgO〈100〉 single crystal substrates was studied at temperatures ranging from room temperature to 300 °C. Experimental data were analysed in both Tauc and Urbach regions. The optical band gap decreased from 4.088 eV at 25 °C to 4.051 eV at 300 °C, while Urbach energy increased from 0.191 eV at 25 °C to 0.257 eV at 300 °C. The relationship between the optical band gap and the Urbach energy at different temperatures showed an almost linear relationship from which the theoretical values of 4.156 and 0.065 eV were evaluated for the band gap energy and Urbach energy of a 12CaO·7Al2O3 crystal with zero structural disorder at 0 K