abdollah eslami majd

The hemispherical resonator gyro (HRG) is a type of precision inertial sensor that has the advantages of direct angle measurement and unlimited dynamic range. The overall accuracy of the HRG is due to the quality of its resonator shell, and improving the performance of resonators requires a proper understanding of the processes of energy damping in each resonance cycle, which has a significant impact on sensor performance. In this paper, in order to investigate the losses in the hemisphere shell resonator, first, the equations governing the shell are studied, and three-dimensional modeling is performed in COMSOL software. By performing mechanical simulations, the resonance modes and the natural frequency of the shell are investigated, and finally, the second and third resonance modes are selected as the optimal operating mode of the gyroscope. Also, by performing thermal simulations, the dominant energy damping processes, such as thermo-elastic damping and anchor loss were analyzed and simulated, and the effect of shell material on damping was investigated. Then the quality factor of the resonator was evaluated based on its geometry and material. In this way, according to the scope of work of the gyroscope, this process can be used to design the specifications of the shell to achieve a resonator with the desired quality factor.

In this paper, a quasi-optical millimeter wave imaging antenna at central frequency of 94 GHz in W-band is designed. The designed imaging system requires resolution less than 30 mm at distance of 5 meters to recognize metal objects. This passive system consists of a combination of a dielectric lens (primary optics) to focus the radiation and a pyramidal horn (secondary optics) with open metal walls to properly direct and couple the focal radiation to the detector. The general parameters of this system are calculated using the geometrical optics method. Then the combination of Gaussian beam method and ABCD ray transfer matrix is used to analyze the lens antenna to find the location and size of the feeding horn. The powerful optical design software ZEMAX was used to design the lens and to verify the design results based on ray tracing. The designed dielectric lens is made of High Density Polyethylene (HDPE) with a diameter of 650 mm. Then, an optimized pyramidal horn with gain of 18.9 dB at center frequency of 94 GHz is designed. The simulation of the horn and investigation of its results performed using the FEKO and CST commercial softwares. The simulation results of the pyramid horn antenna indicate that its combination with dielectric lens is appropriate and the hybrid method (geometrical optics, Gaussian beam and ABCD matrix) to design the quasi-optical system, including the lens and the horn antenna for imaging with considered requirements, is accurate, simple and efficient.

Electrospray is a branch of the scientific area of electrohydrodynamics which is based on electrical charging of liquids. The electrospray governing equations are a combination of hydrodynamic and electrostatic equations to which the addition of liquid breakup process escalates their complexity. This research work aims at developing a numerical solver to simulate the electrospray process in an emitter-disc configuration using Heptane as a working liquid under various electrical potentials. The simulation results in comparison with CFD and experimental data show good agreements both quantitatively and qualitatively. The results clearly have captured the formation of liquid flow profiles at the emitter exit demonstrating various electrospray modes. These modes initiate a microdripping mode at the lowest voltage, i.e. 3.5kV, prompting consecutively to spindle and pulsating cone-jet modes and ending in a stable cone-jet mode at the highest charging voltage, i.e. 6.5kV. In addition, it is also observed that the liquid cone and the vortex shaped within it would shrink as an increase in the electric potential is imposed. Although the increase in electric potential results in rise of the maximum magnitudes of electric field and velocity, the electric charge accumulation at all electric potential values occurs on the outer surface of the liquid flow implying its electrical conductivity.

Background and Cereals are the most important components of a healthy diet. Rice is one of the most common consumed grains in the world and a staple food of people in everyday meals. This study aimed at introducing a novel analytical approach in investigation of harmful metals and necessary elements in some types of Iranian rice by using Laser Induced Breakdown Spectroscopy (LIBS) method. Six types of consumed rice produced in different parts of the country have been collected from the market in 2013. All types of rice have been analyzed for seven times using LIBSCAN100 system and then spectra recorded have been analyzed by Plasus Specieline software. In this study، necessary elements and harmful metals have been analyzed in all samples. The average concentrations of zinc، phosphorus، iron، potassium، calcium، fluorine، chromium (III)، and magnesium were 93. 660mg/kg، 87. 666mg/kg، 348mg/kg، 379. 166mg/kg، 343. 66 mg/kg، 22mg/kg، 24. 848mg/kg 1071. 833mg/kg، respectively. This average content for harmful metals were 6. 095mg/kg for lead، 0. 773mg/kg for mercury، 0. 963mg/kg for nickel، 2. 391mg/kg for chromium (VI)، and 0. 940mg/kg for arsenic. No samples were found with cadmium. The results indicate that، the concentration of magnesium was higher in necessary elements and that Isfahan Lenjan rice contained higher content of necessary elements. Chromium (VI) was the most common harmful metal among all samples. Furthermore، the local Tarom rice was found to be the safest in all samples. Laser Induced Breakdown Spectroscopy technique could be used as a fast، nondestructive، multi elemental analyzer that does not need initial preparation.