Sharif Digital Repository

This paper is an endeavour to give an alternative definition for sustainable development (SD). It reviews the previous works in this area, and finds common grounds of these works, namely dynamism and quantification of the system. The paper then discusses dynamic stability and relates it to the concept of sustainability. It constructs an analogy between sustainability objectives and dynamic stability. The discussion continues to introduce chaos as one inherent characteristic of socio-economic systems because of their nonlinear behaviour. A new definition of SD is then proposed. It is applied to the dynamic models that describe the inter-relationships of environmental, economic and social... 

Manual material handling (MMH) tasks were evaluated and compared under different lifting conditions. For the theoretical evaluations, a two-dimensional sagittally symmetric human-body model was established to compute the moment and joint load time histories for MMH tasks for a variety of different lift specifications and constraints such as lifting durations, loads, and modes. Nonlinear control techniques and genetic algorithms were utilized in the optimizations to explore optimal lifting patterns. Since the kinetic measures such as joint moments are vital metrics in the assessment of the likelihood of injury, the simulation results obtained may be compared using these metrics for each lift... 

Computational investigations on the gas phase SN2 reactions of X ions (X-=OH-,F-,Cl-,Br-, and I-) with fluoroethane and 2-fluoroethanol (β-hydroxyl ethyl fluoride) were performed by using MPW1K, M06 and CCSD(T) methods with a range of basis sets including 66-311++G**, TZVP, aug-cc-pVDZ and SDD. To better understand the nature of the corresponding intermolecular interactions, we performed natural bond orbital (NBO) analysis and Bader's quantum theory of atoms in molecules (QTAIM). In our calculations, we took into account two possible pathways for these reactions, i.e. SN2 reactions of 2-fluoroethanol. In path(i), β-hydroxyl group participates in hydrogen bonding... 

Hydrogen bonding effects of protic solvents, apart from bulk properties, on the reaction rate of the cycloaddition of cylopentadiene and vinyl acetate in the presence of water and methanol in the gas phase were investigated. The results showed that methanol increases the reaction rate in the gas phase more than the water. This is attributed to the stronger hydrogen bonding effect of methanol in this phase. Ab initio and semi-empirical calculations show that methanol stabilizes the transition state of the reaction more than water. This arises from two different origins, distribution of charge and geometry of the hydrogen bond. Copyright © 2002 John Wiley & Sons, Ltd  

This paper addresses the first-order extension of the Lighthill–Whitham– Richards (LWR) macroscopic traffic flow model. Although previous studies have focused on the fluid aspect of traffic flow, none have addressed the sensitivity of drivers to the number of free spaces within a certain distance ahead of the subject driver. To incorporate driver behavior, we used the number of free spaces ahead of subject drivers and their sensitivity to the number of free spaces within a certain distance ahead. The resulting model is a convection-diffusion model. By computing Einstein's diffusion equation and comparing it with the diffusion coefficient in the extended model, a theoretical relation for the... 

In the present paper, several experimental and theoretical studies conducted on the thermal conductivity of nanofluids are represented and investigated. Based on the reviewed studies, various factors affect thermal conductivity of nanofluids such as temperature, the shape of nanoparticles, concentration and etc. Results indicated the increase in temperature and concentration of nanoparticles usually leads to the higher thermal conductivity of nanofluids. In addition, it is concluded that there are some novel approaches in order to obtain nanofluids with more appropriate thermal properties including using binary fluids as the base fluid or utilizing hybrid nanofluids. © 2018 Elsevier B.V  

This paper addresses the first-order extension of the Lighthill–Whitham– Richards (LWR) macroscopic traffic flow model. Although previous studies have focused on the fluid aspect of traffic flow, none have addressed the sensitivity of drivers to the number of free spaces within a certain distance ahead of the subject driver. To incorporate driver behavior, we used the number of free spaces ahead of subject drivers and their sensitivity to the number of free spaces within a certain distance ahead. The resulting model is a convection-diffusion model. By computing Einstein's diffusion equation and comparing it with the diffusion coefficient in the extended model, a theoretical relation for the... 

In this study, a well-known Computational Fluid Dynamics software, so-called Fire Dynamics Simulator (FDS), has been used to simulate multiple ethanol pool fire scenarios. Influences and reciprocal impacts in terms of dynamics and growth of the pool fires have been investigated. Heat release rates temperature and flame shapes have been monitored as the main outputs of the simulations. Based on the simulation results, it can be concluded that the amounts of mass burning rate, the radiation energy and the pool fire flame height were significantly higher in multiple pool fires, when compared with the theoretical values obtained by the mere summation of single pool fires. Furthermore, the... 

This paper presents a novel model for designing a reliable network of facilities in closed-loop supply chain under uncertainty. For this purpose, a bi-objective mathematical programming formulation is developed which minimizes the total costs and the expected transportation costs after failures of facilities of a logistics network. To solve the model, a new hybrid solution methodology is introduced by combining robust optimization approach, queuing theory and fuzzy multi-objective programming. Computational experiments are provided for a number of test problems using a realistic network instance  

Over the last decades quota violations have become a norm for OPEC countries. However, the academic literature on OPEC focuses more on its production behavior than on analyzing the quota allocation process or characterizing quota violation patterns. This paper offers a theoretical model with empirical evidence to explain OPEC members’ incentives for abiding or violating quotas. We first offer a cartel model with a quota allocation rule and an endogenous capacity choice. The model highlights the trade-off between building spare capacity to bargain for a higher legitimate quota versus risking quota violation punishment. Using the quarterly data from 1995 to 2007, we empirically support the... 

Balance theory proposed by Heider for the first time modeled triplet interaction in a signed network, stating that relationships between two people, friendship or enmity, is dependent on a third person. The Hamiltonian of this model has an implicit assumption that all triads are independent, meaning that the type of each triad, being balanced or imbalanced, determined apart from the state of other triads. This independence forces the network to have completely balanced final states. However, there exists evidence indicating that real networks are partially balanced, raising the question of what is the mechanism preventing the system to be perfectly balanced. Our suggestion is to consider a... 

The theoretical model developed in this article predicts that collaboration with top-funded scientists positively affects the number of scientific publications of an individual scientist. Having combined data on funding and publication of Quebec scientists, this article empirically tests the theoretical predictions. This article examines numerous definitions of top-funded scientists as those in the top 10 per cent, or top 5 per cent in terms of total funding, funding from the public sector, and funding from the private sector. The results show that collaborating with such top-funded scientists has a positive effect on a scientist's number of publications, hence confirming our theoretical... 

In this paper, the Conley index theory is used to examine the Poincaré index of an isolated invariant set. Some limiting conditions on a critical point of a planar vector field are obtained to be an isolated invariant set. As a result, the existence of infinitely many homoclinic orbits for a critical point with the Poincaré index greater than one is shown. © Sharif University of Technology  

Although GAN-based methods have received many achievements in the last few years, they have not been entirely successful in generating discrete data. The most crucial challenge of these methods is the difficulty of passing the gradient from the discriminator to the generator when the generator outputs are discrete. Despite the fact that several attempts have been made to alleviate this problem, none of the existing GAN-based methods have improved the performance of text generation compared with the maximum likelihood approach in terms of both the quality and the diversity. In this paper, we proposed a new framework for generating discrete data by an adversarial approach in which there is no... 

Theoretical study of arrays of graphene ribbons is currently of high interest due to its potential application in beam splitters, absorbers, and polarizers. In this paper, an analytical method is presented for diffraction analysis of graphene ribbon arrays. Previous analytical studies were carried out in the regime where the lateral separation between the ribbons is much smaller than the wavelength of the incident wave. As such, they cannot be used to calculate the reflection coefficients of higher diffracted orders. In contrast, the method proposed here can predict the electromagnetic response of graphene ribbon arrays even when the array constant is larger than the wavelength. To reach our... 

Complicated sedimentary processes control the spatial distribution of geological heterogeneities. This serves to make the nature of the fluid flow in the hydrocarbon reservoirs immensely complex. Proper modeling of these heterogeneities and evaluation of their connectivity are crucial and affects all aspects of fluid flow. Since the natural variability of heterogeneity occurs in a myriad of length scales, accurate modeling of the rock type connectivity requires a very fine scheme, which is computationally very expensive. Hence, this makes other alternative methods such as the percolation approach attractive and necessary. The percolation approach considers the hypothesis that a reservoir can... 

The connectivity of high conductivity pathways in geological formations depend on the spatial distribution of geological heterogeneities that may appear on various length scales. Appropriate modeling of this is crucial within in hydrology and petroleum systems. The approach taken in this study is to use percolation theory to quantify the connectivity, hydraulic conductivity, and breakthrough time behavior between an injector and a producer within such systems. In particular, a three-dimensional overlapping sandbody model is considered which assumes that the geological formation can be split into either conductive flow units (i. e., good sands) or non-conductive units (i. e., poor sands). The... 

One of the most important operating parameters which affects the performance and efficiency of active solar stills is brine depth. In all of the previous experimental or theoretical studies, effects of water depth were investigated during only the first 24-hour period (or even shorter periods) of the operation of active solar stills. In other words, only the first day was taken into account. However, the production of an active solar still depends on several parameters such as brine temperature at sunrise (initial temperature), which are all affected by the depth variation after the first day of operation. However, the present research experimentally investigates the long-term effects of...