Analysis of exerted stresses of final drive in MF 285 tractor by Theoretical and Finite Element Method (FEM)

Gears is a rotating cylindrical wheel having tooth cut on it and which meshes with another toothed part to transmit the power or torque.. In this investigation, at first, bending stress and contact stress between sun gear and planet gear tooth were determined using of Lewis and Hertzian equations. Afterward, a 3D model of final drives gear was investigated via FEM method. According to the obtained results, maximum of bending stress and contact stress occurred in Gear 1 and low status of helping gear, according to the results that given in the table 3, maximum bending stress using of theoretical and FEM simulation methods were obtained 918.62 Mpa and 951.82 Mpa, respectively. Also, maximum contact stress in same status using of theoretical and FEM simulation methods were obtained 2952.71 Mpa and 2903.20 Mpa, respectively. The percentage difference between the theoretical and FEM bending stress results and contact stress results are of average 3.48% and 11%, respectively, which are still acceptable. As regards, some parameters are ignored in theoretical calculation such as: radial forces in Lewis equation and tangential forces in Hertzian equation, FEM simulation results are acceptable than theoretical results

Product Development Teams Formation:Effects of Organizational and Product Related Factors

While teams are an essential means for developing products in organizations, how to assemble product development teams remains largely unexplored. According to the social network research, teams might be arranged in either closely connected or sparse structures. Conceptualizing a product development project as collective problem solving endeavour, we develop a computational model of these projects in which a number of designers, who are arranged in teams with a particular structure, conduct search over an NK(C) performance landscape. Simulation of this model enables us to compare the design performance of teams with either closely connected or sparse structures. Our results indicate that how effectively organizations can integrate design solutions determines which of these two structures results in higher development performance. In addition, with our simulation model, design performance of strategies that employ both closely connected and sparse teams, is contrasted with that of those policies which solely use either of these structures. We find that, regardless of product development project integration capability, strategies that simultaneously utilize both closely connected and sparse teams are likely to achieve higher development performance than the other strategies that only use teams with one particular structure. We discuss the implications of our findings in managing product development project

On matching property for groups and field extensions

In this paper we prove a sufficient condition for the existence of matchings in arbitrary groups and its linear analogue, which lead to some generalizations of the existing results in the theory of matchings in groups and central extensions of division rings. We introduce the notion of relative matchings between arrays of elements in groups and use this notion to study the behavior of matchable sets under group homomorphisms. We also present infinite families of prime numbers p such that ℤ/pℤ does not have the acyclic matching property. Finally, we introduce the linear version of acyclic matching property and show that purely transcendental field extensions satisfy this property

Electron Diffraction

Electron microscopes are usually supplied with equipment for obtaining diffraction patterns and micrographs from the same area of a specimen and the best results are attained if the complete use is to be made of these combined facilities. Electron diffraction patterns are used to obtain quantitative data including phase identification, orientation relationship and crystal defects in materials, etc. At first, a general introduction including a geometrical and quantitative approach to electron diffraction from a crystalline specimen, the reciprocal lattice and electron diffraction in the electron microscope are presented. The scattering process by an individual atom as well as a crystal, the Bragg law, Laue conditions and structure factor are also discussed. Types of diffraction patterns such as ring pattern, spot pattern and Kikuchi pattern, and general and unique indexing diffraction patterns are explained. The procedure for indexing simple, complicated and imperfect patterns as well as Kikuchi lines and a combination of Kikuchi lines and spots is outlined. The known and unknown materials are identified by indexing patterns. Practical comparisons between various methods of analysing diffraction patterns are also described. The basic diffraction patterns and the fine structure in the patterns including specimen tilting experiments, orientation relationship determination, phase identification, twinning, second phases, crystallographic information, dislocation, preferred orientation and texture, extra spots and streaks are described in detail. Finally, electron diffraction patterns of new materials are investigated

Tehran Geotechnical Microzonation Project

Megacity of Tehran with a population of more than 8 million is located in a very active region, both in terms of tectonic and seismicity. Due to socio-economic and political importance of Tehran, in 1994 IIEES has initiated a comprehensive geotechnical hazard study in Tehran. The geotechnical microzonation part of the program was composed of two parts: site effect and liquefaction potential microzonation. Site effect microzonation was started for south of Tehran using one dimensional site response analysis and microtremor measurement. The results of these studies were compiled and presented in three microzonation maps for south of Tehran including: natural site period map, dynamic site period map and the PGA distribution map. Based on the preliminary result, comprehensive studies for south as well as for north of Tehran have been started. Liquefaction potential study of Tehran alluvium was started in 1995. Considering that the northern part of the Tehran is located on coarse grain clayey alluvium and deep water table the liquefaction study was concentrated in the south of Tehran. The liquefaction potential was evaluated and the microzonation maps were developed. A more detailed investigation is now underway to assess more accurately the liquefaction potential for the south of Tehran

Design and fabrication of a tractor powered leaves collector machine equipped with suction-blower system

Leaves scattered on the parks, passages, and other places have a detrimental effect on the beauty of the environment, and decrease photosynthesis, hence, the efficiency of plants.  Leaves are also used in the production of peat.  This makes using leaves collectors in parks, and organizations with a green space useful.  Due to the fact that leaves take up a high volume, their transportation is difficult.  Using the machine introduced in this paper which was equipped with a suction-blower system, increases efficiency, and at the same time decreases the costs of green space, and their workforce cost.  Focusing on overcoming the mentioned difficulties, this study was carried out in order to design and produce a tractor powered leaves collector equipped with suction-blower system.  Various designs were studied and based on their advantages and disadvantages, the best design was selected.  The initial modeling was carried out using the engineering software of SolidWorks.  After designing different parts of the machine, such as the chassis, transmission system, the tank, handling system, suction-blower system, they were analyzed.  Furthermore, the effects of pump suction duration, the length of suction pipe, and different intervals of PTO on the system's performance were studied.  The required power for various parts of the system was calculated.  The overall power consumption of the system was calculated to be 18,392 W which amounts to 25 hp.Keywords: leaves collector, blower system, suction system, design, power, tracto

The Effect of Exchange Rate Uncertainty on Import of Medical and Pharmaceutical Products in Iran

Background: The field of medicine and medical equipment are partially dependent on the exchange rate. The aim of this study was to investigate the effect of real exchange rate uncertainty on the import of medical and pharmaceutical products during 1971-2012. Methods: In this longitudinal study, the related data were collected from the World Bank, the Central Bank of the Islamic Republic of Iran and Iran customs office during 1971-2012. Generalized Autoregressive Conditional Heteroskedastic (GARCH) model was used for modelling the real exchange rate. In order to evaluate the impact of real exchange rate uncertainty on import of medical and pharmaceutical products, the exchange rate uncertainty index and other variables such as gross domestic product (GDP), oil revenues (OILR) and private sector health expenditure (PRI) were applied in the import model. Finally, VAR model was estimated using Eviews software version 6. Results: Estimation of medical and pharmaceutical products import model using Johansson test showed a significant negative coefficient for the exchange rate uncertainty variable. Error correction factor in this study was -0.039. Results show that in each period, 3.9 percent of the shocks in the short term can be adjusted to long-run equilibrium values. Conclusion: The exchange rate uncertainty had a significant negative impact on imports of medical and pharmaceutical products. This issue is very important for policy makers of the health field and health economists

Control surface freeplay effects investigation on airfoil's aero-elastic behavior in the sub-sonic regime

One of the main limitations of linearity assumptions in airfoil’s aero-elastic problems is the inability to predict the system behavior after starting the instability. In reality, nonlinearities may prevent the amplitudes from going to infinity. This paper presents a methodological approach for predicting airfoil aero-elastic behavior to investigate the control surface freeplay effects on the state responses and the flutter speed. For this purpose, the airfoil structural model is firstly developed while using the Lagrange’s method. The aerodynamic model is then generated by utilizing the Theodorsen approach for lift and moment calculation and Jones approximation with P-method for unstable aerodynamic modelling. After that, the aero-elastic model is developed by combination of structural and aerodynamic models and a numerical integration method is used to extract the time responses in the state space. The flutter analysis has been completed by utilizing the P-method for the system without freeplay and by the time response approach for the system with freeplay. The results that were obtained from simulations confirm the effectiveness of the proposed method to predict the aero-elastic behavior and stability condition of a two-dimensional airfoil as well as to estimate the flutter speed with reasonable accuracy and low computational effort. Moreover, a sensitivity analysis of freeplay degree on time response results has been done and the results are discussed in detail. It is also showed that the control surface freeplay decreases the flutter speed. The results of the paper are also validated against publicly available data