Sharif Digital Repository

SiBNC nanofibers were synthesized through the polymeric route by a one-pot synthesis approach. DMTA (dichloroboryl methyl trichlorosilyl amine) polymer was selected as pre-ceramic for SiBNC, which was shaped into nanofibers by electrospinning. Then, the nanofibers were cured in an inert atmosphere in order to obtain the final ceramic. By changing the curing atmosphere, the compound of final ceramic has been manipulated. In addition, the ceramic yield of DMTA as a preceramic was increased in the nitrogen atmosphere. The effects of applied voltage, solution concentration, and feeding rate on the morphology of final electrospun ceramic nanofibers were also investigated. Final ceramic remains... 

Discrete-time Markov Chains (MCs) and Markov Decision Processes (MDPs) are two standard formalisms in system analysis. Their main associated quantitative objectives are hitting probabilities, discounted sum, and mean payoff. Although there are many techniques for computing these objectives in general MCs/MDPs, they have not been thoroughly studied in terms of parameterized algorithms, particularly when treewidth is used as the parameter. This is in sharp contrast to qualitative objectives for MCs, MDPs and graph games, for which treewidth-based algorithms yield significant complexity improvements. In this work, we show that treewidth can also be used to obtain faster algorithms for the... 

In this paper, we first analyze a real storage system consisting of 72 SSDs utilizing either Hardware RAID (HW-RAID) or Software RAID (SW-RAID), and show that SW-RAID is up to 7× faster. We then reveal that with an increasing number of SSDs, the limited I/O parallelism in SAS controllers and multi-enclosure handshaking overheads cause a significant performance drop, minimizing the total I/O Per Second (IOPS) of a 144-SSD system to less than a single SSD. Second, we disclose the most important architectural parameters that affect a large-scale storage system. Third, we propose a framework that models a large-scale storage system and estimates the system IOPS and system resource usage for... 

Activities conducted in this study can be divided into two general sections: synthesis and analysis and identifies the properties. A geopolymeric cement production process includes two steps of thermal activation and alkaline activation. Geopolymers are cementitious materials synthesized by a polycondensation reaction between an aluminate and silicate. The geopolymeric structures of the products were investigated by Fourier transform infrared spectroscopy (FTIR), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). XRD results showed that there are no significant differences between the XRD patterns of geopolymers and metakaolin. The structure of the geopolymer is typically... 

Bi-objective optimization of a multi-product multi-period three-echelon supply-chain-network problem is aimed in this paper. The network consists of manufacturing plants, distribution centers (DCs), and customer nodes. To bring the problem closer to reality, the majority of the parameters in this network including fixed and variable costs, customer demand, available production time, set-up and production times, all are considered stochastic. The goal is to determine the quantities of the products produced by the manufacturing plants in different periods, the number and locations of the warehouses, the quantities of products transported between the supply chain entities, the inventory of... 

Bi-objective optimization of a multi-product multi-period three-echelon supply chain network consisting of manufacturing plants, distribution centers (DCs) each with uncertain services, and customer nodes is aimed in this paper. The two objectives are minimization of the total cost while maximizing the average number of products dispatched to customers. The decision variables are: (1) the number and the locations of reliable DCs in the network, (2) the optimum number of items produced by plants, (3) the optimum quantity of transported products, (4) the optimum inventory of products at DCs and plants, and (5) the optimum shortage quantity of the customer nodes. The problem is first formulated... 

We consider the fundamental problem of reachability analysis over imperative programs with real variables. Previous works that tackle reachability are either unable to handle programs consisting of general loops (e.g. symbolic execution), or lack completeness guarantees (e.g. abstract interpretation), or are not automated (e.g. incorrectness logic). In contrast, we propose a novel approach for reachability analysis that can handle general and complex loops, is complete, and can be entirely automated for a wide family of programs. Through the notion of Inductive Reachability Witnesses (IRWs), our approach extends ideas from both invariant generation and termination to reachability analysis.... 

The rupturing process of a membrane, located between two fluids at the center of a three-dimensional channel, is numerically investigated. The smoothed particle hydrodynamics (SPH) and the finite element method (FEM) are used, respectively, for modeling the fluid and solid phases. A range of pressure differences and membrane thicknesses are studied and two different rupturing processes are identified. These processes differ in the time scale of the rupture, the location of the rupture initiation, the level of destruction and the driving mechanism. © 2019 by the authors  

Excessive energy consumption is one of the serious problems of large cities in Iran. In order to avoid unreasonable growth in energy use as well as conservation of natural resources, more attention should be paid to energy consumption patterns in metropolitan cities. Accordingly, the current study aims at analyzing energy demand and its related pollutants in the household sector in Tehran Metropolitan. The study includes a discussion of past trends and future scenarios to reduce greenhouse gas emissions in this sector. Using LEAP software and according to Iran's long-term development policies, energy demand and its greenhouse gas emissions were evaluated based on a baseline scenario within a... 

Electrochemical sensing performance of two-dimensional hexagonal boron nitride (2D h-BN) has traditionally been suppressed by their intrinsic electrical insulation and deficient electron transportation mechanism. However, the excellent electrocatalytic activity, high specific surface area, N- and B-active edges, structural defects, adjustable band gap through interaction with other nanomaterials, and chemical functionalization, makes 2D h-BN ideal for many sensing applications. Therefore, finding a pathway to modulate the electronic properties of 2D h-BN while the intrinsic characteristics are well preserved, will evolve a new generation of highly sensitive and selective electrochemical... 

Let G be a graph with v vertices. If there exists a collection of list of colors S1, S1,..., Sv on its vertices, each of size k, such that there exists a unique proper coloring for G from this list of colors, then G is called a uniquely k-list colorable graph. In this note we present a uniquely 3-list colorable, planar and K4-free Graph. It is a counterexample for a conjecture by Ch. Eslahchi, M. Ghebleh and H. Hajiabolhassan [3]  

Improvement of mechanical properties and microstructure of 2024 aluminum alloy by performing a severe plastic deformation method, called multidirectional forging (MDF), and heat treatment was the aim of this research. In this work, the effects of different heat treatments such as annealing, solid solution, peak ageing and over ageing before MDF on mechanical properties and microstructure of the alloy were studied. Microstructure evolution during severe plastic deformation was considerably affected by the precipitates and non-shearable particles. On the other hand, the severe plastic deformation had different effects on precipitates in the microstructure. Fragmentation, scattering and... 

Using mixed method research the current study has analyzed Iranian researchers' information searching behavior on the Web. Based on extracted concepts, the model of their information searching behavior was revealed. Forty-four participants, including academic staff from universities and research centers were recruited for this study selected by purposive sampling. Data were gathered from questionnaires including ten questions and semi-structured interview. Each participant's memos were analyzed using grounded theory methods adapted from Strauss & Corbin (1998). Results showed that the main objectives of subjects were doing a research, writing a paper, studying, doing assignments, downloading... 

Purpose - The aim of this paper is to look at the relationship between research in Iranian medical universities, together with their Web Impact Factor (WIF). Design/methodology/approach - The Altavista search engine was chosen because of its advanced search facilities for counting links and having a wider scope of academic web sites than other search engines. It was searched for determining the number of pages, in-links and self-links of 42 web sites of Iranian medical universities. The Web Impact Factor (WIF) was calculated by two formulas and the relationship between the two grades of universities (WIF and ISI) was calculated by using the Spearman's correlation coefficient. Findings -... 

Improvement of mechanical properties and microstructure of 2024 aluminum alloy by performing a severe plastic deformation method, called multidirectional forging (MDF), and heat treatment was the aim of this research. In this work, the effects of different heat treatments such as annealing, solid solution, peak ageing and over ageing before MDF on mechanical properties and microstructure of the alloy were studied. Microstructure evolution during severe plastic deformation was considerably affected by the precipitates and non-shearable particles. On the other hand, the severe plastic deformation had different effects on precipitates in the microstructure. Fragmentation, scattering and... 

Evaluation of workers’ body posture in workstations is a prerequisite to estimate spinal loads and assess risk of injury for the subsequent design of preventive interventions. The Microsoft Kinect™ sensor is, in this regard, advantageous over the traditional skin-marker-based optical motion capture systems for being marker-less, portable, cost-effective, and easy-to-use in real workplaces. While several studies have demonstrated the validity/reliability of the Kinect for posture measurements especially during gait trials, its capability to adequately drive a detailed spine musculoskeletal model for injury risk assessments remains to be investigated. Lumbosacral (L5-S1) load predictions of a... 

Asphalt binders are known to exhibit an inherent ability to repair damage. Such self-healing potentially affects the fatigue damage performance of bituminous materials. There are contradicting findings about the effects of aging and polymer modification on healing. The effectiveness of rejuvenating agents also has not been sufficiently addressed. In the present study, three healing indices have been defined to provide a more complete representation with which to quantify the healing potential of binders. These indices have been defined using damage characteristic curves derived from interrupted linear amplitude sweep tests. Initial healing (IH) describes the immediate reduction in the damage...