Sharif Digital Repository

Partially-observed network data collected by link-tracing based sampling methods is often being studied to obtain the characteristics of a large complex network. However, little attention has been paid to sampling from directed networks such as WWW and Peer-to-Peer networks. In this paper, we propose a novel two-step (sampling/estimation) framework to measure nodal characteristics which can be defined by an average target function in an arbitrary directed network. To this end, we propose a personalized PageRank-based algorithm to visit and sample nodes. This algorithm only uses already visited nodes as local information without any prior knowledge about the latent structure of the network.... 

In the past 10 years Iran has been emerging as a major car producer in the world. However, due to delays in economic reforms, Iranian car exports have not increased as much as production. This paper presents a first estimation of the Iranian export potential in the car industry. Based on new theoretical developments of the gravity equation, an empirical bilateral trade model is proposed. It includes sectoral variables (car production, import tariffs), as well as other original variables, such as expectations and hysteresis. We then develop a dataset which includes the 40 major car-exporting countries in the world, 34 importing countries, a 10-year time period as well as four car production... 

This paper investigates the causal relationship between financial development and economic growth in Libya during the period 1970–2016, providing new insights from a resource-dependent economy. The empirical results vary with estimation methodology and model specification, but indicate no long-run relationship between financial intermediation and nonhydrocarbon output growth. The OLS estimation shows that financial development has a statistically significant negative effect on real nonhydrocarbon GDP per capita growth. However, both the VAR- and ARDL-based estimations present statistically insignificant results, albeit still attaching a negative coefficient to financial intermediation. It... 

This paper theoretically and experimentally investigates the exchange flow due to temperature differences between open water and a canopy of aquatic plants. A numerical model is used to study the interfacial shape, frontal velocity and total volumetric exchange, and their dependence on a dimensionless vegetation drag parameter. The numerical predictions are consistent with the laboratory measurements. There is a short initial period in which the force balance is between buoyancy and inertia, followed by drag-dominated flow for which there is a balance between buoyancy and drag forces. After the initial stage, the gravity current propagating into the canopy takes a triangular shape whereas... 

Partially-observed data collected by sampling methods is often being studied to obtain the characteristics of information diffusion networks. However, these methods usually do not consider the behavior of diffusion process. In this paper, we propose a novel two-step (sampling/estimation) measurement framework by utilizing the diffusion process characteristics. To this end, we propose a link-tracing based sampling design which uses the infection times as local information without any knowledge about the latent structure of diffusion network. To correct the bias of sampled data, we introduce three estimators for different categories, link-based, node-based, and cascade-based. To the best of... 

During recent years, active learning has evolved into a popular paradigm for utilizing user's feedback to improve accuracy of learning algorithms. Active learning works by selecting the most informative sample among unlabeled data and querying the label of that point from user. Many different methods such as uncertainty sampling and minimum risk sampling have been utilized to select the most informative sample in active learning. Although many active learning algorithms have been proposed so far, most of them work with binary or multi-class classification problems and therefore can not be applied to problems in which only samples from one class as well as a set of unlabeled data are... 

Most of the methods developed for efficiency estimation of distillation columns were based on the empirical mass transfer and hydraulic relations correlated to laboratory data. Therefore, these methods cannot estimate efficiency of industrial columns with sufficient accuracy. In this paper, a new and applicable method was developed for calculation of efficiency (and mass and heat transfer coefficients) of distillation columns containing structured packings. This method has potential advantages; e.g., it can calculate efficiency without using any empirical mass transfer and hydraulic correlations and models, and without the need to estimate the operational and hydraulic parameters of column.... 

In contrast to the findings of simple rational expectations permanent income hypothesis models, empirical studies show that income changes can help predict consumption change. This is dubbed as excess sensitivity in the macroeconomic literature. We use Iranian household data to investigate the excess sensitivity using civil servant status as a proxy for borrowing constraints. We observe that the excess sensitivity is different among different panels. Much less excess sensitivity is observed for government employees who have better access to finance due to the structure of the labour market and banking system in Iran. Our proxy variable to divide data, which is the working status of the head... 

The hydraulic efficiency of sedimentation basins is reduced by short-circuiting, circulation zones and bottom particleladen jets. Baffles are used to improve the sediment tank performance. In this study, laboratory experiments were used to examine the hydrodynamics of several baffle configurations. An accompanying numerical analysis was performed based on the 2-D Reynolds-averaged Navier-Stokes equations along with the k-ε turbulence closure model. The numerical model was supplemented with the volume-of-fluid technique, and the advection-diffusion equation to simulate the dynamics of particle-laden flow. Model predictions compared well with the experimental data. An empirical function was... 

This paper presents an innovative hybrid approach for the estimation of the solar global radiation. New prediction equations were developed for the global radiation using an integrated search method of genetic programming (GP) and simulated annealing (SA), called GP/SA. The solar radiation was formulated in terms of several climatological and meteorological parameters. Comprehensive databases containing monthly data collected for 6 years in two cities of Iran were used to develop GP/SA-based models. Separate models were established for each city. The generalization of the models was verified using a separate testing database. A sensitivity analysis was conducted to investigate the... 

In this paper the predictive equations for collapse assessment of shear links used in eccentric braced frames are developed. An extensive database including results of over 70 cyclic tests on steel wide flange shear links is collected and the structural parameters governing the hysteresis behavior are calibrated using a simplified numerical model. The methodology of calibration is to minimize the discrepancy between the experimental hysteresis loops and the corresponding numerical results using Particle Swarm Optimization (PSO) algorithm. The objective function of PSO algorithm is minimized by iterating parameters that govern the hysteresis behavior of the numerical model. Stepwise... 

Wheel wear is one of the major costs in railway tracks consisting of sharp curves. In this paper, wear behavior of S1002 profiles of wheels in the "Southern Line" of Iran's railway, which consists of a large number of distinct and/or consecutive sharp curves, is studied using the field data measuring technique. Based on wear behavior analysis of all wheels, an optimal wagon maintenance technique called the "first and second limits" is suggested to minimize the wagon's cost per traveled distance. The results show that: 1) A severe wheel flange wear occurs for all wheels in comparison to the wheel tread wear in normal tracks; 2) A wagon's detachment for repair of critical wheels on its four... 

Displacement-based assessment procedures require as input reliable estimates of the deformation capacity of all structural elements. For unreinforced masonry (URM) walls, current design codes specify the in-plane deformation capacity as empirical equations of interstory drift. National codes differ with regard to the parameters that are considered in these empirical drift capacity equations, but the inhomogeneity of datasets on URM wall tests renders it difficult to validate the hypotheses with the currently available experimental data. This paper contributes to the future development of such empirical relationships by investigating the sensitivity of the drift capacity to the shear span,... 

Dynamic compaction (DC) is a common soil improvement technique, used extensively worldwide. DC treatment design is usually based upon empirical relations and past experience. The common problem with all empirical relations is oversimplification of the mechanisms, and the use of parameters that are highly dependent on engineering judgement. In this paper, a developed finite-element code is used for modelling the impact behaviour of dry and moist sandy soil. The code is verified against the results of centrifuge tests. Then the validity of the popular Menard empirical relation for determination of improvement depth in DC design is investigated. The effect of initial relative density, tamper... 

An axial load-transfer analysis for energy piles is presented in this study that incorporates empirical models for estimating the side shear resistance and end bearing capacity in rock along with associated normalized stress-displacement curves. The analysis was calibrated using results from field experiments involving monotonic heating of three 15.2 m-long energy piles in sandstone. Analyses of the field experiments indicates that poor cleanout of the excavations led to an end restraint smaller than that expected for a clean excavation in sandstone. Specifically, end bearing parameters representative of cohesionless sand were necessary to match the load-transfer analysis to the field... 

This paper develops a model for estimating unsignalized intersection delays which can be applied to traffic assignment (TA) models. Current unsignalized intersection delay models have been developed mostly for operational purposes, and demand detailed geometric data and complicated procedures to estimate delay. These difficulties result in unsignalized intersection delays being ignored or assumed as a constant in TA models. Video and vehicle license plate number recognition methods are used to collect traffic volume data and to measure delays during peak and off-peak traffic periods at four unsignalized intersections in the city of Tehran, Iran. Data on geometric design elements are measured... 

In the last years, an appreciable effort has been directed toward developing empirical models to link the relative permeability of gas condensate reservoirs to the interfacial tension and velocity as well as saturation. However, these models suffer from non-universality and uncertainties in setting the tuning parameters. In order to alleviate the aforesaid infirmities in this study, comprehensive modeling was carried out by employing numerous smart computer-aided algorithms including Support Vector Regression (SVR), Least Square Support Vector Machine (LSSVM), Extreme Learning Machine (ELM), Multilayer Perceptron (MLP), Group Method of Data Handling (GMDH), and Gene Expression Programming...