Sharif Digital Repository

In recent years, one of the important and challenging issues that has drawn many engineers’ attention is the system reliability. Generally, the possibility of the system’s satisfactory performance under specified operating conditions, for a given period of time, is defined as the System Reliability. Analytical and Simulation methods are two main reliability techniques. In the Analytical technique, mathematical models with some simplification are applied, whereas the Simulation technique utilizes significant number of experiments which are extremely costly and time-consuming. In spite of carrying out analytical methods for proving results, simulation is carried out in different analyses... 

The use of public transportation in metropolises has developed due to the increase in the population and the need for within-city transportation. Among public transportation service, the use of city subways has attracted more public interest due to its speed, safety, and matching with the environment. Also, one solution for reducing the between-city transit distances,decreasing the accidents and above all, saving the time of the travel is building tunnels and underground lines. Design and construction of underground structures (tunnels),in comparison with surfacestructures, has more complex conditions and considerations that require special studies. One challenging problem fortunnel... 

Since the discovery of nanomaterials, the nanotubes have found special considerations. The high strength beside the low density, have attracted the interest of the scientists and engineers. Nowadays, one of the common methods to produce composites with high specific strength is to utilize of the nanotubes in the matrix of lightweight metals and alloys such as magnesium and aluminum. Recent researches indicate that very limited focus has been given to the production and properties of the magnesium - carbon nanotube composites and their workability. In this research, magnesium alloy - carbon nanotube composite is produced by casting method and its strength and workability are investigated as... 

The continous growth of wireless networks, the increasing numbers of users and devices, along with the demand for higher data rates have intensified the frequency band limitations as the communication medium. In search for more efficient methods to use this limited resource, the cognitive radio approach that allocates the local unused frequency bands to potential users has attracted considerable attension.
A fundamental and unseperable part of any cognitive radio system is its need to search, detect and understand the surrounding frequency spectrum. Although various methods have been already propose to overcome the challenges of this domain, simpler and more reliable methods are still in... 

Methiocarb [3,5-dimethyl-4-(methylthio) phenyl methylcarbamate] is an N-methylcarbamate with neurotoxic action. Because carbamate pesticides are acetylcholinesterase inhibitors, they are considered to be carcinogens and mutagens. Methiocarb pesticide is widely used throughout the world particularly effective as fungicides, insecticide and bird repellent. To prevent its harmful effects on animals, humans, and the environment, it is of crucial importance to develop simple and sensitive methods for in-situ detection of methiocarb. This research describes a simple and low-cost method for on-site monitoring of methiocarb insecticide. Gold nanoparticles (AuNPs) aggregation caused by methiocarb,... 

This study seeks to identify the characteristics of pricing behavior in Iran's economy at the producer level. For the first time, this research utilizes Iranian producer price quote microdata from the industrial sector, which is used to construct the Producer Price Index (PPI). Using this new data, five facts about Iran's economy can be inferred: 1) On average, the frequency of price changes each quarter is about 52%, and the average implied duration of prices is 1.6 quarters. 2) There is no significant difference in the price stickiness between producer and consumer prices. 3) Firms' decisions to change or not change prices are more influenced by producer inflation, while their decisions on... 

Hydrogen bonding is an important weak interaction encountered in gas, liquid, as well as solid phases. The hydrogen bond plays a very vital role in many life processes and is one of the most frequently used terms in chemistry and biology.
Polyols or polyhydric alcohols are, strictly speaking, simply organic chemicals containing more than two hydroxyl groups. Each hydroxyl is attached to separate carbon atoms of an aliphatic skeleton.They may also contain ester, ether, amide, acrylic, metal, metalloid and other functionalities; along with hydroxyl groups. Polyols are obtained from many plant and animal sources and are synthesized by a variety of methods. Among important properties of... 

Photonic lattices can provide an inexpensive and fine tools to investigate some common phenomena in condensed matter physics, quantum optics, relativistic mechanics,atomic and molecular physics. These phenomena contain Anderson localization,Bloch oscillation, Dynamic localization, coherent and squeezed states, Relativistic Dirac equation, Rabi oscillation, ... .In this thesis, it was investigated three worthy phenomena of them, which at first are introduced in condensed matter physics for electronic systems, in photonic lattices. These phenomena are as follow: Transverse localization of light wave, Bloch oscillation and dynamic localization of light. It was also simulate classically, the... 

The increasing utilization of silver nanoparticles (Ag-NPs) in industrial and consumer products has raised concern to wastewater treatment utilities, due to its antimicrobial activity. In this research, recovery of silver nanoparticles from wastewater via using activated carbon and convert it into usable nanoparticles is presented. real waste of silver nanoparticles have been used and activated carbon as adsorbent has a high absorption recovery for silver. Under the optimized experimental parameters e.g. pH, temperature, time of process, and amount of activated carbon, an absorption maximum was achieved and over than 99% of silver nanoparticles can be removed from wastewater. After the... 

The growing use of nanomaterials leads to causing harm to the aquatic environment resulting in a demand for effective methods to remove these nanomaterials from aquatic environment. On the other hand, the high cost of raw materials used for the production of noble metal nanomaterial limits their use or requires the development of recycling and recovery methods. In this study, we found that citrate capped gold nanoparticles (cit-AuNPs) could be removed effectively from waste water using aluminum chloride (AlCl3) coagulant. The effect of pH, of coagulant concentration, and alkalinity on the performance of this coagulant was investigated. It has... 

There is a growing interest in developing high-performance sensors monitoring fungicides, due to their broadly usage and their adverse effects on humans and wildlife. In the present study, a colorimetric probe has been proposed for detection of prothioconazole based on aggregation of unmodified silver nanoparticles (AgNPs). Under optimized condition, linear relationships between the concentration of prothioconazole and the absorbance ratio of A500/A395 were found over the range of 0.01 µg. mL-1 to 0.4 µg. mL-1 with Detection limit as low as 1.7 ng. mL-1. Furthermore, AgNPs color change from yellow to pink-orange in presence of prothioconazole, indicates highly sensitive naked-eye...