Sharif Digital Repository

The use of active modes of travel in school trips has sharply declined for a number of reasons, some of which are rooted in urban design, location of schools, and parental reservations. Thus, policy makers are keen to find practical ways to promote active modes of travel, particularly walking. This study was an effort to determine a tolerable walking distance for school trips and identify factors that made walking trips more reasonable for students. In the vein of understanding the tolerable walking distance, a two-step framework encompassing a random utility method and a hazard-based model was introduced. This framework was applied to a set of data that were collected from middle and high... 

In the present work, mesoporous nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by using a low-cost and unique set of precursors (camphor and urea). The CVD method at 1000 °C was used with different camphor/urea ratios, and Co-Mo/MgO nanocatalyst was utilized as growth catalyst. Application of mesoporous N-CNTs in selective oxidation of H2S was studied experimentally and N-CNTs interactions with H2S was also investigated using DFT calculations. The as-synthesized N-CNTs were characterized using FTIR, FE-SEM, elemental analysis, X-ray diffraction (XRD), XPS and nitrogen adsorption/desorption. The N-CNT2 sample with urea to camphor ratio (U/C) of 1 showed the highest sulfur yield at... 

The activity and travel patterns of people with disabilities are generally distinct, as their activities are more dependent on others due to their special physical condition. This paper elaborates on the patterns of regular out-of-home activities (i.e. for different trip purposes) of disabled persons along with the way that they are accompanied to perform the activities. Household Travel Tracker Survey data collected by the Chicago Metropolitan Agency for Planning is used to develop new travel models. Two multinomial logit models are estimated to explore the influential variables and elaborate the consequences of ignoring their inter-dependency. From the influential parameters perspective,... 

Selective oxidation of H2S to elemental sulfur is a low cost and highly efficient process for sulfur removal from H2S-containing hydrocarbon streams in medium scale (i.e. 0.2–10 ton sulfur/day) for environmental protection and prevention of emitting toxic gases to the atmosphere. In this research, in order to prepare a highly active and selective nanocatalyst for selective oxidation of hydrogen sulfide, for the first time, molybdenum oxides were loaded uniformly over nitrogen- doped carbon nanotubes through incipient wetness impregnation. Different metal loadings including 5, 10, and 15 wt% Mo were considered in the synthesis procedure to achieve the optimized performance and provide... 

A considerable shift has occurred in mode choice behaviour and escort pattern of students for their school trips around the world during the last few decades. This shift towards using more non-active modes has undesirable consequences, including physical inactivity among students, traffic jams during peak hours, and adverse environmental impacts. Hence, understanding the behaviour of decision-makers with regard to the mode choice and escorting pattern selection is crucial for controlling the trend of the shift and promoting active modes. This study is the first effort to mathematically model the mode choice and accompaniment pattern selection by parents for the school trip of students, in a... 

Travel time is an uncertain variable with inherited uncertainty for many reasons, such as measurement error, perception error, and temporal aggregation variation impacts. Many researchers have considered travel time as an exact value for different limitations, including models’ restrictions and being unaware of the travel time distribution. However, previous studies have shown that standard logit and probit models can result in biased estimations with uncertain variables or variables with errors (EIV). Nevertheless, limited evidence is available on the magnitude of this bias and the impact of the uncertain variable distribution on the estimated parameters. In this paper, we use a... 

This paper points out an application of the "two-echelon single-period product (newsboy) problem," in which within a limited budget the final product and the raw materials are purchased before the start of the selling period and depending on the demand, the raw materials may be transformed into the finished product during the period. The objective of this problem is to find the order quantities of both the raw materials and the final product at the beginning of the period such that the expected profit is maximized. A new model is first developed for this problem and then a Lagrangian method is proposed to solve it. Finally, a numerical example is given to illustrate the application of the... 

A new multi-objective intermodal hub-location-allocation problem is modeled in this paper in which both the origin and the destination hub facilities are modeled as an M/M/m queuing system. The problem is being formulated as a constrained bi-objective optimization model to minimize the total costs as well as minimizing the total system time. A small-size problem is solved on the GAMS software to validate the accuracy of the proposed model. As the problem becomes strictly NP-hard, an MOIWO algorithm with an efficient chromosome structure and a fuzzy dominance method is proposed to solve large-scale problems. Since there is no benchmark available in the literature, an NSGA-II and an NRGA are... 

The vehicle routing problem (VRP) is one of the most complicated optimization mathematical models; the school bus routing problem (SBRP) is an important and practical branch of this problem. Because the number of variables and equations is vast, finding the exact solution for this problem under real conditions is difficult; only heuristic and metaheuristic algorithms can be used to solve it. Recently, the ejection chain method (ECM) has been introduced as a heuristic algorithm that efficiently finds a new neighbor solution. In a case study in developing countries, efficiency of several heuristic algorithms including ECM along with one metaheuristic algorithm-tabu search algorithm (TSA)-is... 

Phase Change Memory (PCM) is an emerging memory technology that has the capability to address the growing demand for memory capacity and bridge the gap between the main memory and the secondary storage. As a resistive memory, PCM is able to store data based on its resistance values. The wide resistance range of PCM makes it possible to store even multiple bits per cell (MLC) rather than a single bit per cell (SLC). Unfortunately, PCM cells suffer from short lifetime. That means PCM cells could tolerate a limited number of write operations, and afterward they tend to permanently stick at a constant value. Limited lifetime is an issue related to PCM memory; hence, in recent years, many studies... 

Phase Change Memory (PCM) is one of the most promising candidates to be used at the main memory level of the memory hierarchy due to poor scalability, considerable leakage power, and high cost/bit of DRAM. PCM is a new resistive memory that is capable of storing data based on resistance values. The wide resistance range of PCM allows for storing multiple bits per cell (MLC) rather than a single bit per cell (SLC). Unfortunately, higher density of MLC PCM comes at the expense of longer read/write latency, higher soft error rate, higher energy consumption, and earlier wearout compared to the SLC PCM. Some studies suggest removing the most error-prone level to mitigate soft error and write... 

A new multi-objective intermodal hub-location-allocation problem is modeled in this paper in which both the origin and the destination hub facilities are modeled as an M/M/m queuing system. The problem is being formulated as a constrained bi-objective optimization model to minimize the total costs as well as minimizing the total system time. A small-size problem is solved on the GAMS software to validate the accuracy of the proposed model. As the problem becomes strictly NP-hard, an MOIWO algorithm with an efficient chromosome structure and a fuzzy dominance method is proposed to solve large-scale problems. Since there is no benchmark available in the literature, an NSGA-II and an NRGA are... 

Connected and autonomous vehicles (CAVs) have the potential to drastically change the structure of future cities and regions. Researchers predict different outcomes to result from the emergence of CAV technology. While some see their potential as amounting to a complete overhaul of the transport system, others predict the technology will be slow to be adopted and may face competition from other mobility options such as drones. Therefore, the future can be viewed along a spectrum, ranging from no CAVs to a fully driverless transport system. This paper presents an overview of the past attempts on studying CAVs and their impacts to provide a comprehensive view about possible futures with CAVs.... 

Persian handwritten digit recognition has attracted some interests in the research community by introduction of large Hoda dataset. In this paper, the well-known random forest (RF) and convolutional neural network (CNN) algorithms are investigated for Persian handwritten digit recognition on the Hoda dataset. Using the Hoda dataset as a standard testbed, we have performed some experiments with different preprocessing steps, feature types, and baselines. It is then shown that RFs and CNNs perform competitively with the state-of-the-art methods on this dataset, while CNNs being the fastest if appropriate hardware is available  

Two-dimensional mesoporous carbon nitride and its highly efficient nanorod framework were prepared via hard-templating method. The obtained materials were fully characterized. The results showed that the samples structural ordering and morphology were similar to those of the parent silica templates; they had large pore volumes as well as high surface area structures. Carbon nitride carbocatalysts were used for H2S selective oxidation. The catalytic tests were carried out at 190, 210 and 230 °C in a fixed bed reactor. The obtained selectivity values for mesoporous carbon nitride rod and mesoporous carbon nitride toward elemental sulfur at 190 °C were 88.8% and 83%, respectively. Both samples... 

This study deals with an experimental investigation on the thermal performance of a mechanical wet cooling tower with counter flow arrangement by using multi-walled carbon nanotubes (MWNTs) and nanoporous graphene nanofluids. Stable nanofluids were prepared through two-step procedure by using water with properties taken from a working cooling tower in the South of Iran. Zeta potential revealed suitable stability of MWNTs and nanoporous graphene nanofluids. Thermal and rheological properties of the nanofluids were investigated. It was found that thermal conductivity increases by 20% and 16% at 45°C for MWNTs and nanoporous graphene nanofluids, respectively. The increase in density and... 

In this study, we have used a low temperature plasma, produced by a DC magnetron sputtering device, for decolorizing of denim fabrics, and the effect of using different gases such as Argon and Oxygen as the discharge medium have been investigated. The results obtained under equal periods of time have been compared and the effect of washing on the treated denims has been reported. © 2006 Elsevier B.V. All rights reserved