Sharif Digital Repository

How does retirement plane affect retirement decision? This paper uses the data of 24,000 retirees of oil industry of Iran between 1996 and 2016 to answer the question. We calculate Accrual, Option Value, and Peak Value to evaluate retirement behavior. These variables calculate the difference between utility of retirement in the current year and some time in the future. Theoretically we expect that higher values in these variables lower the probability of retirement. We use two types of probabilistic models, linear and non-linear. In the linear model we run a pooled OLS and in the non-linear model we use a Probit model to estimate the effect of the variables above on the retirement... 

Virtual Reality technologies and its related standards and tools, will play a remarkable role in our future digital life. Development of that topic will be definitely dependent on availability of a reliable, precise and low-cost video quality assessment method. In recent years, there was a significant amount of research works on 360 videos, notably among them are new video quality metrics. Unfortunately in terms of correlation to subjective scores, they are still far from ideal especially with respect to previous performances in regular video domain. In this research we focused on desiging a full-reference 360-video quality assessment method. First, we extracted 2D viewport videos from the... 

In economic literature, there are two major theories about population distribution; One perspective gives geography a central role, and the second one emphasizes path dependency. In this study, we investigate the Iran-Iraq war as an exogenous shock to the population of Iranian cities to answer the basic question of which theory best explains the population distribution. The Iran-Iraq war began in 1980, with Iraq invasion of Iran's western borders. Some border cities of Iran were captured at the beginning of the war and forced migration was inflicted on their population. non-captured cities near the western border were repeatedly targeted by artillery, airstrike and missile attacks, yet they... 

Investigation stability of chatter vibration is of great importance in machining processes. Finding frequency response function (FRF) at the tool tip is an effective method to predict stable machining regions. Commonly, the tool tip FRF is obtained using experimental modal analysis but this approach is often time consuming and requires expertise. In addition, changing tool or holder requires modal test which is a disadvantage, consequently modeling methods are of interest for researchers. Moreover, optimum design of machine tool is another benefit of modeling method. Also, in machining with flexible or micro tools in which experimental tests can not be performed, modeling methods would be... 

High-quality online services demand reliable and fast packet delivery at the network layer. However, clear evidence documents the existence of compromised routers in the ISP and enterprise networks, threatening network availability and reliability. A compromised router can stealthily drop, modify, inject, or delay packets in the forwarding path to launch Denial-of-Service, surveillance, man-in-the-middle attacks, etc. So researches tried to create intrusion detection methods to identify adversarial routers and switches. To this end, data-plane fault localization (FL) aims to identify faulty links and is an effective means of achieving high network availability. FL protocols use... 

Bubble collapse is a two-phase problem whose numerical simulation has many important applications in science and technology. In hydrodynamics systems (pumps, ship propellers, …), bubbles form due to cavitation. These bubbles grow and collapse These bubbles grow and collapse farther downstream and their energy destroys the surrounding walls. In medical sciences, the shear force caused by collapse of a bubble can be used to destroy adipose tissues in arteries. The small scales time in this phenomenon, as well as the compressibility of the flow in bubble collapse, are interesting challenges researchers face. The present thesis targets are two-dimensional numerical simulation of bubble collapse... 

Power harvesters are used to generate energy for electronic devices. These electrical energy generators consist of three main parts: energy source, power electronic converter and energy storage. In order to minimize some of the weaknesses of these devices, including low power density and low reliability, the hybrid power harvesting method can be utilized. In this thesis, we design and build a hybrid energy harvester considering the advantages of simultaneous usage of solar and thermal energies for a wearable sensor, focusing on "efficiency enhancement" and "availability improvement". In the designed device, both solar and thermal energy harvesting units operate independently. In the solar... 

With the advancement of technology, the volume of network traffic has also increased dramatically. The optical network, as the main part of the backbone communication system, plays a significant role in the transmission of network traffic. Due to the limited network resources, an efficient resource allocation in optical networks is required to increase network performance and reduce costs. To solve resource allocation optimization problems, an effective tool is needed to provide a suitable solution in a reasonable time. Resource allocation problems are usually developed on a graph, which is derived from network topology or other properties of the network. As a result, graph-based tools seem to... 

Uranium conversion process is one of the most important stages in nuclear fuel cycle. The Uranium Conversion Facilities (UFC) of Iran is located in Isfahan. In this plant, the Yellowcake (impure uranium oxide, U3O8) is converted to Uranium hexa-fluoride, UF6. During the process, considerable amounts of uranium-containing liquid waste are generated. This liquid waste was collected in evaporation pools inside the UCF Plant. In the course of time, a thick layer of precipitated salt form in bottom of the pools which are collected and stored in drums inside a building. This solid waste contains uranium at concentration levels much higher than that permitted for land disposal of the waste.... 

Weexaminetherelationshipbetweenfamilysizeandchildreneducationaloutcomes. Using a 2 percent sample of Iran Populaion Census 2011, we construct a sample of school age children. Estimation using unrestricted OLS with controls shows an inverse-U relationship between family size and educational outcomes; children educational performance improves significantly as their number increases form 1 to 2, but for families with 3 or more children, increasing the number of childern deteriorates educational outcomes  

The main goal of this research is to reduce aircraft design cycle period, by reducing the necessary number of design cycle iterations. The Design cycle period is one of the main characteristics of the design process and design cycle iterations play a major role in the design cycle period. To achieve the above mentioned goal, we present a mathematical model of iterations for the aircraft design process. This model describes the design coupled tasks as a discrete-linear time invariant dynamic system. This model also helps identify tasks which are the most important for generating iterations. This new method basically helps break information cycles that create iterations among important tasks.... 

One of the most powerful means to increase thermal efficiency in gas turbines is to increase the turbine inlet temperature. However, due to metallurgical limitations, the turbine blades need to be cooled constantly. Thus, film cooling of blades has shown to be the most efficient way. In this study, a three-dimensional film cooling problem at jet Reynolds number of 4700 are investigated, using RANS approach and three different turbulence models, namely (Wilcox), SST(Shear Stress Transport), and the new model. A fine non-uniform staggered grid and a SIMPLE based finite volume method were used. Film cooling simulation results, including mean velocity components and turbulent kinetic energy... 

Sharply bent DNA plays an important role in many biological processes such as gene regulation, DNA replication and recombination. DNA cyclization experiments are well suited to study of sharply bent DNA, because they are sensitive to strongly bent conformations. Results of these experiments show that short length DNA molecules are more flexible than predicted by elastic rod model. Therefore, based on these experiments, the elastic rod model is not a suitable model for explaining elastic behavior of DNA at small lengths, although it can explain DNA elasticity at large length scales. Recently, it has been shown that a new model called asymmetric elastic rod model can explain high flexibility... 

The aim of this research was an investigation, development, and application of low- dimensional proper orthogonal decomposition (POD) method for simulation of unsteady flow around bodies. Since analytical methods have low accuracy and limitations and also experimental methods have other problems, researchers usually use computational approaches, which mostly do not have acceptable efficiency and speeds of computations (especially in 3-D unsteady flows). On the other hand, the idea of application of reduced order modelling, which orginally comes from control theories and structural analysis, have attracted many researchers in recent years. In this research, we also used POD for reduced order... 

Considering the annual growth in the air traffic, new challenges arise; one of which is the appropriate level of automation that needs to be brought into the picture. This research focuses on the characteristics of a high level automation device, such as level 6 and upper, which could be used onboard a transport for traffic conflict prevention. The main objective behind such a device is to help ground controllers in crowded airspaces. In this work, we discuss the abilities of a new algorithm to resolve a general conflict in the absence of ground based ATC centers. The proposed algorithm considers the Earth rotation as well as general wind patterns. Mathematically, it is based on real-time... 

Soil-structure interaction has significant effect on dynamic behavior of the super structure. This effect is usually investigated in two separate parts, i.e., the Kinematic Interaction effect and the Inertial Interaction effect. The first modifies the input ground motion to the foundation as a result of difference in soil and foundation stiffness. The later, i.e., the II effect, introduces the effect of soil flexibility and radiation of waves into the supporting medium on the response of the structure. These effects are usually considered by introducing a replacement oscillator with modified natural period and damping ratio subjected... 

Atomic force microscope (AFM) has a significant capability of imaging surface topography on an atomic scale. It is also widely used for Nanolithography in MEMS/NEMS (micro/nanoelectromechanical systems). Conventional AFMs consist of a cantilever with a sharp conical or pyramidal tip located at the free end of the cantilever that plays an important role in AFM measurements. Scanning across a surface, AFM interacts with the sample surface through its tip. Although the dynamic behavior of the AFM cantilever is complicated, the researchers have been interested in studying AFM dynamic behavior because it has a great influence on the surface imaging process. The imaging rate and contrast of... 

The main objective of all managers of the economic organizations, manufacturing and industrial companies and service providers is to take steps toward improvement and effective use of different resources like workforce, capital, materials, energy and information. To attain the desired productivity, managers have to observe requirements such as establishment of a working organizational structure, effective implementation methods, safe equipment and tools, balanced working atmosphere and qualified human force as the most important factor. Therefore productivity culture should be publicized throughout the organization, and human force should be considered as the main component of this process.... 

In this work we simulate SIRS1 model on homogeneous networks by means of simulation, then we drove meanfield equations for this model and compared the solution of these equations to the simulations results on the network. To obtain a new model closer to the reality, we modified the SIRS model and introduce history to the convenient model. After simulation of this model we redrove the equations with history and found that this model can show bifurcation so we found the phase diagram for this model. And in the last part we introduced history to a meanfield model with pair approximation and drove the equations and try to solve
them numerically.
 

The  aim  of  this  work  is  to  investigate  some  theoretical  models  developed  in  recent years for describing electronic correlation and apply them to some special problems  and  metallicity  and  insulating  behavior  of  one  type  of  paramagnetic  systems. One  of  the  vast‐applied  and  effective  routines  for  investigating  the  strongly  correlated electron systems is Dynamical Mean Field Theory (DMFT). In the first part,  the  equations  of  DMFT  are  solved  on  nearly  real  frequency  axis  with  a  effective and more reliable solver a little parameter γ above the real axis. This approach  appears  fine  structures  that  can’t  be  captured  with  the ...