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Performance of the fiber optic networks with different physical topologies such as point-to-point, bus, ring and star, with respect to requirements as bit rates, topology structure, bit. error rate (BER) and optical component characteristics including optical amplifiers, filters, sources and detectors, are analyzed and simulated. For this purpose, maximum number of supportable nodes and throughput, crosstalk due to optical amplifiers and optical filters, reliability, physical limitations and fiber induced limitations such as dispersion and nonlinear effects (self phase modulation) are considered as performance evaluation criteria of different topologies. Dispersion and nonlinearities are simulated with split-step Fourier method, sometimes referred to as beam-propagation method. The fiber length can be estimated by this method, with respect to above effects and maximum tolerable power penalties. Parameters such as maximum number of supportable nodes and crosstalk are evaluated using amount of degradation in BER of receiver, BER is calculated using Gaussian approximation. Reliability of networks is modeled on the bypassing of the failed station as recovery mechanism in ring and bus networks and reliable assumption for central node in star network. By the way physical limitations in each topology, regarding its structure, are derived as an economical criterion. Results indicate that no topology can be preferred to others, however imposed limitations and requirements determine the optimum topology. Neglecting economical aspects, star topology is preferred from different points of view such as reliability, crosstalk and maximum number of supportable nodes. Results of above simulations can be used in calculating power penalties of different factors such as dispersion, crosstalk and nonlinearities. This penalties perform important role in estimating power budget of networks.

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Knowledge of the aerodynamic properties of agricultural materials is needed in equip-ment design for operations such as pneumatic conveying in loading/unloading operations of corn silage into/from silos. While considerable information is available on seed grains, little is known about the aerodynamic behavior of corn (Zea mays L.) silage. In this re-search, the weighed mean terminal velocity of a sample representative of the entire bulk mass was determined using Wolf and Tatepo’s method. The terminal velocity of various particle types (leaf, stalk and corncob pieces) of chopped forage corn plants, which were kept in silo for six months, at different moisture contents (40-50, 50-60 and 60-70% w.b.) was also studied. The terminal velocity was determined by measuring the air velocity re-quired to suspend a particle in a vertical air stream using a wind tunnel. A 3 3 factorial treatment arrangement with 30 replications in a completely randomized design was used to study the effect of moisture content and particle type on the terminal velocity. The mass mean terminal velocities of the corn silage at 40-50, 50-60 and 60-70% moisture con-tents were 7.1, 7.3 and 7.8 m/s, respectively. The results showed that only the effect of par-ticle type on the terminal velocity of corn silage was significant. The mean values of the terminal velocity of corn leaf, stalk and cob pieces were 3.8, 6.8 and 8.8 m/s, respectively. For each particle type at a given moisture content, the terminal velocity was best de-scribed by means of the equation of velocity squared in terms of weight.

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The research was conducted in order to determine the bending stress, Young’s modulus, shearing stress, and shearing energy of safflower stalk as a function of moisture content and stalk region. The bending forces were measured at different moisture contents and the bending stress and the Young’s modulus were calculated from these data. For measuring the shear forces, the stalk specimens were severed by using a computer aided cutting apparatus. The shear energy was calculated by using the area under the shear force versus displacement curve. The experiments were conducted at four moisture contents (8.61, 16.37, 25.26, and 37.16% wb) and at three stalk regions (bottom, middle, and top). Based on the results obtained, the bending stress decreased as the moisture content increased. The value of the bending stress obtained at the lowest moisture content was approximately 2 times higher than that of the highest moisture content. Bending stress values also decreased from top to the bottom of stalks. The average bending stress value varied from 21.98 to 59.19 MPa. The Young’s modulus in bending also decreased as the moisture content and diameter of stalks increased. The average Young's modulus varied between 0.86 and 3.33 GPa. The shear stress and the shear energy increased with increasing moisture content. Values of the shear stress and energy also increased from top to the bottom of stalks due to the structural heterogeneity. The maximum shear stress and shear energy were found to be 11.04 MPa and 938.33 mJ, respectively, both occurring at the bottom region with the moisture content of 37.16%.