فهرست مطالب mohammadtaghi ahmadi

In this article, an electrochemical sensor in the form of a field effect transistor is designed and fabricated. This sensor is based on carbon nanoparticles grown between two metal electrodes. These nanoparticles have been synthesized by the electric arc discharge method in suitable environmental conditions and in different lengths from the decomposition of butane gas. Considering this set as a field effect transistor, its channel is always established and it is responsible for detecting the desired material. To check the correct functioning of the sensor, its sensitivity to different concentrations of saltwater was checked and the resistance diagram of the sensor as its electrical output was obtained in the presence of different concentrations of saltwater for different lengths of the channel. In this article, an electrochemical sensor in the form of a field effect transistor is designed and fabricated. This sensor is based on carbon nanoparticles grown between two metal electrodes. These nanoparticles have been synthesized by the electric arc discharge method in suitable environmental conditions and in different lengths from the decomposition of butane gas. Considering this set as a field effect transistor, its channel is always established and it is responsible for detecting the desired material. To check the correct functioning of the sensor, its sensitivity to different concentrations of saltwater was checked and the resistance diagram of the sensor as its electrical output was obtained in the presence of different concentrations of saltwater for different lengths of the channel.

In this research project a special shield made up of lead is designed and produced by our team, in which the production of this shield the next generation of x-ray producers which their accelerators and multipliers aren't together a new form is constructed, considering the fact that for increase in accuracy and lowering the costs the source of the ionized rays is located outside the accelerating compound, hence an unique lead interference is formed by which based on the foundation of the  machine it'll prevent from the leakage of x-rays. The design has been tested several times while taking all the precautions required and Geiger detector established there is no leakage of x-ray. This machine also reduces the risk factors such as forgetting and also difficulty in the utilization of protective equipment and it also helps the new users and will reduce costs meanwhile widening the usage of x-ray producers.

In the presented work an industrial and medical based radiography system is fabricated. To design a proper system first of all four sub domain of the whole system is considered namely known as control system, transformer driver, multiplier and hosing system. To control the entire system a Wi-Fi and remote controllable mechanism is considered also it is expected by this controlling system the operator can be in the safe distance from the x ray. On the other hand, to drive a transformer that feeds the multiplier a suitable driver is used based on the x ray tube performance and a chine of multiplier that generates enough voltage deference in the chosen tube is designed. Finally tube hosing that prevents x-ray from scattering in the lab environment is fabricated which is been presented in another paper.

Todays, the application of science and advanced technologies, the management of quality risks imposed on environmental resources, has particular importance. Considering the toxicity of wastewater agricultural, industrial, and domestic effluents on the environment, a thorough and separate study of the toxic wastewater treatment and contaminated water, in general, seems necessary to complete the non-destructive development process. In this regard, to recover compounds containing heavy metals and pollutants such as copper, in wastewater containing harmful fertilizers and pesticides, the production of nanofibers (polymer nanoparticles) in the form of electrospray (under four treatments of solute concentration, applied voltage, Injection Needle and Injection rate), using electrospinning machine and selected polymeric Polyacrylamide Methacrylate and Dimethylmethyl Formamide solvent with using the low-cost raw materials approach for the selected hazardous pollutants. The nanoparticle production technology was used in the form of wire blasting (under four concentrations of nanoparticle solution concentration, the diameter of carbon wires used, flow and arc force), also. Finally, by extracting the results in each phase, their analysis was carried out and the results showed that the combination of the polymer treatment with dimethylformamide solvent at 25 wt%, applied voltage kV. 30, the distance between the tip of the needle and the plate 15 cm and the feeding rate of 2 ml / h worked best. Thus, with the preparation of nanofibers and the use of relatively inexpensive laboratory materials, compared to the costly methods of water treatment, significant results were observed in the process of removal of toxic copper > 50% in all selected samples indicated a positive and high effect of the nanoparticles-nanofibers.

The present paper investigates and compares the crack propagation in concrete gravity dams using two models of linear fracture mechanics and plasticity damage concrete. The first model is based on linear concrete behavior using the extended finite element method without considering the effect of strain softening on the crack tip while the second model is based on the nonlinear concrete behavior and the strain softening in tension with damage parameter. According to two different algorithms and based on two models, several benchmark examples are reviewed and the results compared with those reported in the literature. Then, path of the crack growth in Koyna gravity dam due to a seismic excitation of Koyna earthquake in 1962 has been performed by considering the dam-reservoir interaction. The results show that due to low compressive stresses during analysis of concrete gravity dams, consideration of compressive nonlinear behavior has no effect on crack initiation and almost is the same for two models. However because of crack opening and closing with tapping the crack faces together in extended finite element model, the compressive stress will be more than the allowable stress of concrete. Crack initiation at downstream and upstream face occurred at angle of 90 and zero degrees respectively, which in both models, the numerical results are in agreement with the experimental model. The crack in the extended finite element model grows faster such that the crest block of dam in this model is separated from the dam body, earlier than the concrete plastic damage model. Also the values of dam crest displacement and hydrodynamic pressure in the reservoir in extended finite element model with linear elastic fracture mechanic are more than the other model, which can be attributed to the linear and nonlinear behavior of concrete in extended finite element and concrete plastic damage model respectively. In the extended finite element model, due to using linear fracture mechanic, the maximum principal stress in the cracked elements reaches the values greater than the maximum tensile strength, but in the concrete plastic damage model as soon as the stress reaches a tension limit value, elements are damaged and the stress is reduced. In both models, the crack located at the slope change area, propagates with the downward slope from downstream dam face and connects to the crack at upstream face which is growth horizontally. Because of laboratory sample dimension and boundary condition of dam-reservoir compared with actual manner, neither of two crack profiles covered the experimental model, accurately. But it is shown that the crack profiles in the extended finite element model are more consistent with experimental results. Finally, the results show that the crack profile are slightly different in the two models because of quasi brittle behavior of the dam concrete, which can be attributed to the small fracture process zone of the crack tip in comparison with the dimension of the concrete gravity dams such that by removing strain softness part, the error in the amount of additional computation can be neglected.

Investigation of physicochemical variations of physalis crop, as a species with various medicinal and nutritional properties, was performed under combined treatments of magnetism intensity (M) in four levels of zero, 0.2, 0.3 and 0.4 T and concentration of nano zinc fertilizer (N) in three levels 1, 1.5 and 2 g/l. The results showed that the effect of combined treatments on all biochemical properties (except carotenoid factor), as well as all morphological traits (with exception of fruit diameter) was significant at 1% and 5% levels. By analyzing the phytochemical factors, chlorophyll b factor was significantly improved by 5.3 times as compared to the control treatment, under treatments of 0.4 Tesla and 1.5 g/l. Also, among the morphological factors, a* factor showed the highest increment (2.7 times as compared to the control) under 1.5 g/l zinc fertilizer without magnetism intensity. In general, the balanced use of these treatments could be applied in economical production of this crop.

This study was carried out to investigate the effect of different levels of magnetic intensity (0, 0.2, 0.3 and 0.4 tesla) and different concentrations of nutrient solusion (0.25, 0.50, 0.75 and 1 unit of Hogland) on phytochemical and morphological changes of Physalis, as one of the high valuable species of medicinal plants. The results showed that the effect of the combined treatments on all phytochemical properties (with the except of antioxidant activity factor), as well as all morphological traits, was significant at 1% level. The maximum significant and positive effect on phytochemical factors improving chlorophyll b characteristic 15 times was obtained under 0.4 tesla magnetic intensity and 50% Hoagland concentration. Also, the most significant positive effect on morphological factors improving fruit weight by 2.5 times was obtained under 0.3 tesla magnetic intensity and 0.75 Hoagland concentration. In general, the application of magnetic water and nutrient solution concentration is suggested to be considered in Physalis production plannings.

Gravity dams are vital structures whose proper design and evaluation for stability are quite important. Effective issues on the stability of gravity dams are the uplift force and its distribution below the dam base. The uplift load pattern and distribution according to common codes are influenced by some factors such as head and tail water, assuming a segmented linear load distribution below the dam. In this research, to investigate the sensitivity of the load pattern to dam height, a number of gravity dams of Pine Flat type with different heights and their foundations are modeled. Coupled p-u finite element analysis is performed accounting for the seepage and stress field simultaneously. Dam body is considered to be completely impervious. The foundation rock is assumed as homogeneous and uniform, in terms of elasticity and permeability. The stresses generated in the dam interface for each case of the coupled hydro-mechanical analysis is compared against that of the conventional load pattern according to the USACE regulation for the same dam model. It was found that the error magnitude due to the conventional pattern has a direct relationship with the dam height. As the dam height increases, the amount of error of calculated stress increases. In particular, the error at the critical zones of the foundation such as at the dam heel, may raise even up to 40%. In the group of dams studied, the error increases even up to 12 times in respect to the expected error in the shorter dams. The deficiency could in some cases completely affect the safety of the dam. This research indicates the necessity of using more accurate methods of estimating uplift load under high gravity dams. Gravity dams are vital structures whose proper design and evaluation for stability are quite important. Effective issues on the stability of gravity dams are the uplift force and its distribution below the dam base. The uplift load pattern and distribution according to common codes are influenced by some factors such as head and tail water, assuming a segmented linear load distribution below the dam. In this research, to investigate the sensitivity of the load pattern to dam height, a number of gravity dams of Pine Flat type with different heights and their foundations are modeled. Coupled p-u finite element analysis is performed accounting for the seepage and stress field simultaneously. Dam body is considered to be completely impervious. The foundation rock is assumed as homogeneous and uniform, in terms of elasticity and permeability. The stresses generated in the dam interface for each case of the coupled hydro-mechanical analysis is compared against that of the conventional load pattern according to the USACE regulation for the same dam model. It was found that the error magnitude due to the conventional pattern has a direct relationship with the dam height. As the dam height increases, the amount of error of calculated stress increases. In particular, the error at the critical zones of the foundation such as at the dam heel, may raise even up to 40%. In the group of dams studied, the error increases even up to 12 times in respect to the expected error in the shorter dams. The deficiency could in some cases completely affect the safety of the dam. This research indicates the necessity of using more accurate methods of estimating uplift load under high gravity dams.

The Graphene based single electron transistor (SET) as a coulomb blockade device need to be explored .It is a unique device for high-speed operation in a nano scale regime. A single electron transfers via the coulomb barriers, but its movement may be prevented by coulomb blockade, so its effect is investigated in this research. The conditions of coulomb blockade and its controlling factors such as material, temperature, gate voltage and island length are investigated. At first, the coulomb blockade on fullerene SET as a nano transistor with new material is modeled and compared with experimental data of silicon SET. The comparison study indicates that the coulomb blockade range of fullerene SET is lower than the silicon one. On the other hand, the analysis demonstrates that, temperature and gate voltage play direct associations with zero current SET. In addition, island length and its material effect on coulomb blockade and desired current are achieved by decreasing the coulomb blockade range.

The importance of the seismic behavior of concrete gravity dams in their safety evaluation and stability is inevitable. Many factors affect the prediction of the behavior of concrete dams such as dam-foundation-reservoir interaction, dam and foundation cracking and also displacement due to fault movement that could causes nonlinear behavior. The aim of this study is nonlinear analysis of concrete gravity dams, including displacement caused by normal fault movement in the dam foundation. For this purpose, dam-foundation-reservoir system is modeled using Lagrangian method and analysis of system is done by finite element method. The coordinate smeared crack model based on the nonlinear fracture mechanics is used for crack modeling in the dam body and foundation. Using two separate method including split node technique and contact element, the fault movement are modeled and the position and angle of fault has been studied. To verify the results, dam crest displacement and crack profile in the body of a concrete gravity dam is presented as an example. The results show that low fault movement causes the cracks in the dam body and could be jeopardizes the stability and safety of concrete dam.

The FAO Penman - Monteith (F-P-M) method is now broadly accepted as the standard for estimating the reference evapotranspiration (ET0). The method is also now used for evaluating the temperature-based [Blaney-Criddle (B-C) and Hargreaves-Samani (H-S)] and radiation-based [Jensen-Haise (J-H) and Turc (Tc)] methods. The objective was to compare the ET0 estimated by the B-C، H-S، J-H، Tc methods with that estimated by the F-P-M method in a semiarid climate using the meteorological data recorded in Hashem-Abad Agro-Meteorological Station، Gorgan. The mean value of ET0 was 3. 13 mm. day-1 using the F-P-M method. At daily scale، Tc method showed the lowest RMSE (Root Mean Square Error)، 0. 98 mm. day-1. At monthly scale، in compare to the other methods، the RMSE values by Tc method were lower in April as well as from September to March، averaged 0. 06 mm. day-1 with the percentage error of 3%. During the summer season، July and August، however، B-C method suggested the lowest RMSE value than those of the others (RMSE 0. 32 mm. day-1 with the percentage error of 6%). The H-S method behaves the best for monthly estimation (RMSE 0. 42 mm. day-1، the percentage error of 7%) during May to June. The F-P-M method for estimating ET0 requires data often not recording in the meteorological stations; hence ET0 should be estimated using the proposed simpler methods in compare to the F-P-M. The adaptation of the methods to different climates should be essentially tested by the standard F-P-M method.

Elevated water tanks as one of the main lifeline elements are the structures of high importance. Since they are extremely vulnerable under lateral forces, their serviceability performance during and after strong earthquakes is a matter of concern. As such, in recent years, the seismic behavior of water tanks has been the focus of a significant amount of studies. According to the literature review, it has been realized that although many studies have been investigated the effects dynamic characteristics of structure, only a few studies have been conducted on the seismic behavior of the elevated water tanks. In The current study, three reinforced concrete elevated water tanks, with a capacity of 900 cubic meters and Height of 25, 32 and 39 meters have been utilized and subjected to an ensemble of earthquake records. The behavior of concrete material was assumed to be nonlinear. Seismic demand of the elevated water tanks for a wide range of structural characteristics has been assessed. The obtained result revealed that scattering of responses in the mean minus standard deviation and mean plus standard deviation are approximately 60 to 70 percents Moreover, simultaneous effects of mass increase and stiffness decrease of tank staging led to increase in the base shear, overturning moment, displacement and hydrodynamic pressure Equal to 10 to 20 %, 13 to 32 %, 10 to 15 % and 8 to 9 %, respectively.

Underwater explosion is a common phenomenon to be considered for marine and coastal structures. Although it is not wise to design such structures based on explosion loads, but having studied the explosion wave and its demotic effects, location and geometries of these structures can be improved. In this study after introducing underwater explosion mechanism a summary of the numerical methods used for propagation of explosion waves in water is introduced and finally a preferable method is proposed for modeling the phenomenon. Based on such considerations numerical results using multipurpose commercial codes are successfully compared with empirical relations.