Sharif Digital Repository

Hand in hand with the flourish of the biodiesel industry, glycerol (GLY) as an inconvenient by-product has generated environmental and sustainability concerns. Devising measures for efficient transformation of GLY into value-added products is a promising solution. In this contribution, the transformation of GLY to lactic acid (LA) as a valuable chemical was investigated in a continuous process for industrial applications. In this regard, a catalytic method using heterogeneous Cu nanoparticles in NaOH solution was studied in a microreactor by a CFD simulation. A seven-inlet micromixer comprising an optimized mixing unit was incorporated for uniform distribution of the species. The effects of... 

This study provides a stochastic dynamic programming model with a Markov chain that explicitly focuses on the customer as well as a new model for valuing the customers in the banking industry. The proposed framework calculates individual customer’s lifetime value dynamically. The study follows a stochastic dynamic programming model that is based on the Markov chain. The deduced findings are illustrated with supplementary context from an outstanding case study. The findings underline the importance of the stochastic model for calculating customer lifetime value based on customer behavior. The presented framework provides a beneficial way for future research and valuable insight for allocating... 

Relative novelty and wide functionality of ionic liquids (ILs) have led to a surge in the studies devoted to experimental determination of their physicochemical properties. Systematic collection and analysis of the available data and development of predictive models to address the extreme diversity of IL systems are of great value in this regard. In the present work, the significance of speed of sound in ILs and their mixtures was outlined and related theoretical concepts were surveyed. A comprehensive database was utilized for the construction of predictive models based on least square support vector machine. By constructing four different models, the influence of temperature, molecular... 

Twitter as one of the most important microblogging online social networks has attracted more than 200 million users in recent years. Although there have been several attempts on characterizing the Twitter by using incomplete sampled data, they have not been very successful to estimate the characteristics of the whole network. In this paper, we characterize Twitter by sampling from its social graph and user behaviors through a random walk based sampling technique called Respondent-Driven Sampling (RDS). To the best of our knowledge, for the first time RDS method and its estimator are used in order to obtain uniform unbiased estimation of several key structural and behavioral properties of... 

Periodic cycles of flood and drought are aggravated by global warming, thereby inducing critical desiccation cracks in soils. However, the estimation and prevention of crack propagation is imperfect due to the imprecise field measurements and the underlying soil uncertainties. To address these issues, this study presents an alternative framework to assess the probability of crack propagation. Thus, a series of Monte Carlo sampling (MCS) and Gaussian random fields are employed to quantify the associated uncertainties. The results suggest that matric suction has a governing effect in the course of crack propagation and induces cracking particularly at shallow depths. Crack propagation tends to... 

This paper presents experimental results on the fatigue properties of Al-matrix nanocomposites prepared by the friction stir processing (FSP) technique. An Al-Mg alloy (AA5052) with different amounts (∼2 and 3.5 vol%) of pre-placed TiO2 nanoparticles were FSPed up to 6 passes to attain homogenous dispersion of nano-metric inclusions. Microstructural studies by electron microscopic and electron back scattering diffraction (EBSD) techniques showed that nano-metric Al3Ti (50 nm), TiO2 (30 nm), and MgO (50 nm) particles were distributed throughout a fine-grained Al matrix (<2 μm). Consequently, a significant improvement in the tensile strength and hardness was attained. Uniaxial... 

Like many of the world's large-scale terminal lakes, the Urmia saltwater lake in northwestern Iran is undergoing a process of desiccation. The anticipated economic, social, environmental and health consequences of this are daunting. We set out to examine the policies that have been designed in response to the lake crisis in the past twenty years. We focus on the set of measures proposed by the Urmia Lake Restoration Program (ULRP) and explain why their impact on water savings are overstated while the potentially most effective measures are abandoned. We then discuss the various social, institutional and political factors that have led to this state of affairs. Identifying and understanding... 

Prediction of thermal crack propagation in desiccated soils is imperfect due to the obscure field measurements, modeling approximations, and the underlying soil uncertainties. To address these issues, a probabilistic framework is developed to quantify the uncertainties and enhance the crack estimation reliability. Hence, the uncertainties associated with the soil properties, including the tensile strength, matric suction, Poisson's ratio, elastic modulus and suction ratio are associated in a probabilistic model. Then, the probabilistic model is utilized with the improved Monte Carlo simulation to calculate the failure probability due to the exceedance of the crack propagation. Furthermore,...