Sharif Digital Repository

SnO2-CuO is one the most promising systems for detection of detrimental H2S gas. Although previous experimental research has suggested a sulfidation reaction to explain selectivity toward H2S, little is known about the origin of change of electrical response of this system by changing the H2S gas concentration. In this study the relation between sensing response of continuous SnO2-CuO bilayer thin film and H2S gas concentration is computed based on changeability of chemical composition of covellite CuxS. For this purpose, chemical activity of sulfur as a function of atomic fraction in covellite copper sulfide is estimated using Gibbs energies of formation and chemical thermodynamics. By... 

Resistive sensors composed of SnO2 and CuO, are known to be highly efficient in detection of detrimental H2S gas in terms of sensitivity, selectivity and speed. Recently, dependency of electrical response of the sensor toward H2S gas concentration has been related to the selective mechanism (formation of CuS) by a theoretical model. Another important factor in design of gas sensors is the working temperature which so far has not been explicitly explained for H2S sensing process of SnO2-CuO system. In present study, origin of this temperature for SnO2-CuO thin bilayer based on the selective mechanism has been theoretically interpreted. For this purpose, Poisson, Laplace and continuity... 

This study presents a steady-state Markov chain model to predict the long-term probability of drought conditions. The research aims to propose a rigorous framework for statistical analysis of drought characteristics and its trends over time for a large area of aquifers and plains in Iran. For this purpose, two meteorological indicators called the Standardized Precipitation Index (SPI), and the Groundwater Resource Index (GRI) are examined. The groundwater drought study includes more than 26,000 wells in about 600 meteorological stations over 20 years being surveyed daily. This study discusses the spatial interpolation of drought steady-state probabilities based on recorded SPI and GRI data... 

Metal-oxide gas sensors are widely used for detection of detrimental H2S gas. Among them, SnO2-CuO system has been proved to be an excellent candidate. The previous theoretical 2D thin bilayer model was able to explain some aspects of H2S sensing performance of this promising system. However, experimental researches have indicated that response values for this system are very diverse and various SnO2-CuO multicomponent heterostructures such as rods, wires and particles have much higher response than their thin bilayer counterparts. Understanding the reason behind this differences would help fabrication of optimized sensor element. However, the previous model cannot address this issue mainly... 

In this study, a new mathematical programming approach for solving the joint timetabling and train stop planning problem in a railway line with double-track segments is proposed. This research aims to design an optimized train timetable subject to the station- capacity and time-dependent dwell time constraints. The objective function is to maximize the railway infrastructure capacity by minimizing the schedule makespan. The problem is formulated as a particular case of blocking permutation flexible flow shop scheduling model with dynamic time window constraints. Due to the combinatorial nature of the problem, heuristic algorithm and bound tightening methods are proposed that generate...