Sharif Digital Repository

The seasonal fluctuations in economics variables relate to the different behavior of economic agents across different seasons. In past, seasonality has been viewed as a redundant feature that needs to be removed from data before economic analysis. From 1988, modeling seasonality has become the major concern of many economists; moreover, it was seen that many economic analysis and forecasts could be flawed if seasonality is ignored. In the present research, periodic times series approach is used for the first time in modeling the seasonality feature of the housing market. Regarding the importance of the housing sector in economy from micro and macroeconomic points of view, using a more... 

Time series of asset returns display specific regularities such as bell-shaped distribution, leptokurticity and volatility clustering. Economists have made continuous efforts to develop models that explain these patterns and can be used to predict the return and the risk of holding an asset. These efforts can be classified into 3 eras: Bachelier Era (1900-1960) in which the random walk model was developed for speculative prices. Mandelbrot Era (1960-1980) in which the normality assumption was replaced with the Pareto-Levy family of distributions which are flexible enough to justify leptokurticity and infinite variance. And finally, the Dynamic Volatility era in which the focus was on... 

In order to better understand the performance of the Iranian health insurance industry, household decisions to purchase private health insurance are analyzed using a two-stage (Heckman) model on Survey of Family Income and Expenditure data. Probit and OLS regressions are used to examine the factors influencing the probability and amount of private health insurance purchased. Generally, factors affecting the probability of having insurance also influence the amount of insurance coverage purchased. The results show the importance of some demographics on the insurance decision, particularly age, gender and marital status. Socio-economic factors such as education, income, employment sector,... 

This paper decomposes the saving rate into cohort, age and year effects. This objective is accomplished by constructing a pseudo-panel that amalgamates nineteen consecutive, cross-sectional Household Income and Expenditure Surveys from 1991 to 2009. To construct year-of-birth cohorts with consistent composition over time, analyses are limited to those born between 1926 and 1975. Results reveal that those belonging to younger cohorts save a higher fraction of their income relative to their predecessors at the same age. Moreover, the increase in the saving rate can not be explained by the significant decline in household size or rise in educational attainment among younger cohorts. Closer... 

Fine-grained image classification is image classification where the considered classes are all sub-classes of a certain, more general class. In this setting of the problem, the classes are visually very similar to each other, such that an unskilled human cannot discriminate between them. In this case, proposed methods for the ordinary image classification problem do not obtain good classification accuracy. So proposing new methods for solving this problem is necessary. In this thesis two new methods, based on recent advances in deep learning are proposed for solving the fine-grained image classification problem. First by improving several parts of one of the recent proposed methods for this... 

This investigation is intended to assess the behavior of SCBFs in the presence of typical brace members, which buckles in compression, and BRBs joining by yielding elements. While braces play a role in providing stiffness for structure, central yielding elements will act as energy-absorbing fuses. In this frame type, energy dissipation will mainly be undertaken by BRBs and yielding elements. The mentioned yielding elements do this by initiating plastic hinges in each corner of the central frame. As it is clear, designing a structure that includes the stated lateral-load-resisting system necessitates seismic performance parameters to be evaluated. Hence, by pursuing the FEMA P695 methodology,... 

Asphaltenedeposition is a major problem during natural depletion and EOR processes due to formation damage issues. It is necessary to reveal asphaltene deposition mechanisms and its effective parameters to prepare an acceptable prevention strategy. Therefore, different natural depletion and EOR experiments must performed on core samples. In this research, Effect of CO2 injection on asphaltene deposition phenomena has been surveyed. Two carbonate core samples and one sandstone core sample was used in experiments. The oil used in these experiments was recombinedoilfrom one of Iranian offshore oilfield.In order to estimate permeability reduction during experiment, injection of oil and CO2 was... 

Among probable hazards in chemical industries: vapor cloud explosion (VCE) is one of the worst and most destructive ones. More than half of the major process inci¬dents, according to the statistics, are VCEs. VCE causes the most serious consequences; therefore, it attracts many attentions to itself. Accordingly, plenty of researches have been done for the purpose of protection against VCE effects. All efforts in this field can be categorized in two different main activities; firstly, prescribing safety distances between groups of hazardous equipment and vulnerable areas, secondly, using facilities which reinforce vulnerable areas against explosion blasts. Regardless to which category is... 

There are different well-established strategies for making a process plant inherently safer. The benefits of applying these strategies on reducing the overall risk inside a plant are obvious. However, some of these changes are rejected many times because they appear to be too costly. But if the effects of applying inherently safer design strategies are investigated not only on the processing costs of a plant but also on the potential accident costs, the decision would in fact be different. In this paper an optimization procedure is proposed which integrates both processing and accident costs for different design schemes. In this procedure, some of the design variables are chosen with regard... 

Today, Quantitative Risk Assessment (QRA) has become an efficient tool in decision making for safety and process experts. To assess the risk of any accident scenario, it is necessary that the probability of that event be determined in addition to estimating the probable consequences. Event tree and fault tree analysis are known to be the standard tools for calculating the frequency of incident outcomes.
In this research, a new method based on Markov chin and Fuzzy theory is presented to estimate the occurrence probability of events. A one of important parameter which has sufficient effect on probability of incident frequency, is inspection and maintenance interval. in this research... 

Inherently safer design is the new approach to maximize the overall safety of a process plant. This approach suggests some risk reduction strategies to be implemented in the early stages of design. There are different well-established strategies for making a process plant inherently safer. The benefits of applying these strategies on reducing the overall risk inside a plant are obvious. However, some of these changes are rejected many times because they appear to be too costly. But if the effects of applying inherently safer design strategies are investigated not only on the processing costs of a plant but also on the potential accident costs, the decision would in fact be different. In this... 

This study estimates a hedonic model for the price of housing in the city of Tehran. Using 1340 observations from the eighth region of the city as a sample and applying geographically weighted regression, the study shows that hedonic price function regardless of space variation in house price, leads to spatial autocorrelation in the error term of the model. Thus geographically weighted regression method can deal with this problem and is able to explain more than 76% of the variation in housing prices. Additionally, almost all three structural (floor area, kind of housing appearance and type of houses), environmental (distance from nearest hospital, park, school, health club and mosque) and... 

In order to measure poverty, researchers used to consider only the income and the financial aspect of poverty; however, further research has revealed that income in itself cannot be a proper and comprehensive index for measuring poverty, and other factors such as education, health, occupation, personal characteristics, cultural activities, political activities, etc. are also significant in determining the poverty index. Based on the information acquired from "household expenditure-income survey", this study tries to take into account all the factors affecting the poverty index, in four dimensions of economic well-being, capability, political participation and cultural participation. Poverty... 

Fire is the most likely type of process accident which occurs in industrial plants. Among all different types of fire, pool fire is the most frequent one, so there are extensive researches done about pool fire. One of the research areas that has drawn a lot of attention in recent years, is pool fire modeling. Results obtained from fire modeling are quite applicable in different fields of safety engineering such as Quantitative Risk Assessment (QRA) or fire proofing studies of process equipment. But fire modeling is an inherently complex process. Because there are several aspects involved such as multi-phase flow, turbulent mixing, combustion and different mechanisms of heat transfer. This... 

Methane conversion into higher hydrocarbons has been investigated by non-thermal plasma. The most important advantages of utilizing this type of plasma are atmospheric pressure and ambient temperature of the operating system. In order to prepare non-thermal plasma, a spark discharge reactor has been used with the main prospect of acetylene production. Other components such as hydrogen, ethylene and ethane are also formed in the process as by-products. By optimizing the affecting parameters on methane conversion and products selectivity, maximum methane conversion of 83.2% is obtained. Acetylene yield varies between 25%-63% with input gas flow rate, voltage, frequency and discharge volume.... 

The continual deterioration and insufficient strength of reinforced concrete (RC) structures has been a vital problem in the field of civil engineering such an extent that traditional methods of strengthening found to be inconvenient. Nowadays by increasing demands for retrofitting of structures, it necessitates the application of efficient, inexpensive and unobtrusive methods of strengthening. Common way on retrofitting was to use of steel plates externally bonded to RC members. Although this technique has proven to be reasonably effective, it has several distinct disadvantages such as susceptibility of the steel plates to corrode and the excessive weight of steel plates when used in... 

The release of toxic materials causes tragic accidents every year. There are various techniques in order to mitigate the release effect of these materials such as Application of air jets, steam curtains and water curtains. In this study first, previous works are reviewed in order to select the best technique for the mitigation of heavy toxic gas release. Then CFD modeling is used to simulate this technique.
A field situation in which chlorine gas was released upwind of water spray was simulated using the open-source software FDS (Fire Dynamic Simulator), a CFD model. Only mechanical effects of water sprays are considered; hence the effect of absorbtion is neglected. Finally tha... 

Domino accidents are one types of incidents that lead to irreparable damage to industrial units. Since the consequences of such incidents are far more than the first level incident, consideration of this issue and the provision of appropriate strategies for identifying and evaluating this type of incident is very important. Major efforts have been made in the area of process safety is in risk assessment and identify possible scenarios and their probability of occurrence, and have not addressed the financial consequences of an incident. In this research, an algorithm has been developed to estimate the financial losses incurred with an industrial unit due to a domino incident and various...