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The role of microstructure in mechanical behaviors of low-alloy sintered steels
, Article Scientia Iranica ; Volume 7, Issue 1 , 2000 , Pages 41-49 ; 10263098 (ISSN) ; Simchi, A ; Moradkhani, D ; Ashtari, M ; Khorsand, H ; Davami, P ; Sharif University of Technology
Sharif University of Technology
2000
Abstract
In this study, microstructural aspects that control fracture and deformation resistance of P/M materials are evaluated. Several low-alloy steels were produced under both experimental and commercial conditions for achieving different matrix phases and porosity levels with varying shape factors. A 'porosity map' was constructed and used for a quantified study of the dominant mechanism controlling mechanical behaviors. The role of inclusion gathering and secondary pores, as well as sintering mechanism and alloying method is considered and discussed. The mechanism assessment was performed by using microstructure examination through optical and scanning electron microscopy. The results...
How do adsorbent orientation and direction of external electric field affect the charge-transfer surface-enhanced raman spectra?
, Article Journal of Physical Chemistry C ; Volume 125, Issue 24 , 2021 , Pages 13382-13390 ; 19327447 (ISSN) ; Jamshidi, Z ; Sharif University of Technology
American Chemical Society
2021
Abstract
Surface-enhanced Raman spectroscopy is a highly sensitive phenomenon and a powerful fingerprint detection tool that reflects the small changes in polarizability on the pattern and intensity of Raman signals. The SERS enhancement signals elucidate with the surface-selection rules. In this regard, molecular configuration and adsorption orientation on the surface, in addition to the direction of external electric field, can lead to different patterns of SERS spectra. To evaluate how the variation of these features influences the pattern and reproducibility of the spectra, the chemical charge-transfer SERS spectra for pyridine on silver clusters are calculated for different field directions,...
Evaluation of Performance of Emergency Relief Vehicles Responding to Traffic Accidents in Tehran
, M.Sc. Thesis Sharif University of Technology ; Nassiri, Habibollah (Supervisor)
Abstract
High number of traffic accidents in Iran and its rate which is well above the world's average is a major issue of concern. The results of recent researches show a direct relation between survival rate of traffic accidents' injuries and the Emergency Response Time (ERT). The main objective of this research is to analyze different aspects of ERT in Tehran, Iran and to compare these results with the International standards. This study intends to compare the selected routes by ambulance drivers with the shortest paths recommended by EMME/2. Results of analysis show that when the travel time between accident scene and the emergency dispatch center is less than 8 minutes, the possibility of...
Synergistic coupled transport of uranyl ion across bulk liquid membrane mediated by dioxa-diazamacrocycle and oleic acid
, Article Journal of Radioanalytical and Nuclear Chemistry ; Volume 316, Issue 1 , 2018 , Pages 9-16 ; 02365731 (ISSN) ; Fasihi, J ; Samadfam, M ; Sepehrian, H ; Ashtari, P ; Mahani, M ; Arabieh, M ; Sharif University of Technology
Springer Netherlands
2018
Abstract
Synergistic coupled transport of uranyl ion across a bulk liquid membrane of chloroform has been investigated using a dioxa-diazamacrocycle and oleic acid as carrier and synergistic agents, respectively. Quantitative transport of uranyl ion was achieved within 4 h when the pH of source solution was kept at 5.0–6.0 and mole ratio of carrier to synergistic agent was 1/15. It was found that overall rate and selectivity of the transport is governed by the stripping step. Finally, the influence of some foreign competitor ions including Al3+, Ca2+, CO3 2−, Cu2+, Mg2+, Pb2+, Zn2+ and Th4+ and also the ionic strength on the transport efficiency has been evaluated. © 2018, Akadémiai Kiadó, Budapest,...
Bootstrap-based Ensemble Clustering of Resting-state fMRI Time Series
, M.Sc. Thesis Sharif University of Technology ; Vosoughi Vahdat, Bijan (Supervisor)
Abstract
Studies in recent years have shown formation of strongly functionally linked sub-networks during rest, networks that are often referred to as resting-state networks. RSNs not only have basic information about the brain but also play a key role in detecting brain disorders, such as Alzheimer and Autism; Consequently, they have been remarkably noticed by neuroscientists. Numerous methods have been used in order to extract RSNs using resting-states fMRI time series. Independent component analysis (ICA) is the most common method, whi have been reported to show a high level of consistency neurophysiology; however, its results is unstable in subject-level. is weakness restricted the ICA...
Multi-Scale Simulation of Metallic Nano-Alloy Compression Process Using Plasticity Cone-Cap Behavior Model
, M.Sc. Thesis Sharif University of Technology ; Khoei, Amir Reza (Supervisor)
Abstract
The primary purpose of this study is to perform nonlinear behavior simulations in the compaction and forming of metal powders and their alloys and investigate their behavior in the plastic state. Powder compression is one of the methods of producing metal parts with high precision and improved mechanical properties, which is why it has been considered in addition to its need in the industry.There are various methods for performing these simulations, including multi-scale methods with optimal performance. Given that only the use of high-scale methods or only low-scale methods will have problems and disadvantages in such simulations, multi-scale methods will be a good alternative in which both...
Structural and Computational Studies of Chloro and Nitro Cobaloxime Complexes Containing Tris (p-methoxyphenyl) Phosphine Ligand
, M.Sc. Thesis Sharif University of Technology ; Kia, Reza (Supervisor)
Abstract
In this study, two new cobaloxime complexes with molecular formula [Co(DMGH)2{P(p-PhOCH3)3}(X)] in which X= Cl, NO2 were synthesized and their structure studied. These complexes were identified by FT-IR and1H-NMR 31P{1H}-NMR methods as well as their solid state structure studied by X-ray crystallography. The non-covalent interaction of two complexes including non-classical hydrogen interactions, C─H...π interactions, and dispersion interactions were confirmed and compared theoretically and experimentally by analyzing the data extracted from X-ray single crystal diffraction
Supervised fuzzy partitioning
, Article Pattern Recognition ; Volume 97 , 2020 ; Nateghi Haredasht, F ; Beigy, H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Centroid-based methods including k-means and fuzzy c-means are known as effective and easy-to-implement approaches to clustering purposes in many applications. However, these algorithms cannot be directly applied to supervised tasks. This paper thus presents a generative model extending the centroid-based clustering approach to be applicable to classification and regression tasks. Given an arbitrary loss function, the proposed approach, termed Supervised Fuzzy Partitioning (SFP), incorporates labels information into its objective function through a surrogate term penalizing the empirical risk. Entropy-based regularization is also employed to fuzzify the partition and to weight features,...
Efficient simulation of resonance Raman spectra with tight-binding approximations to density functional theory
, Article Journal of Chemical Physics ; Volume 157, Issue 8 , Volume 157, Issue 8 , 2022 ; 00219606 (ISSN) ; Jamshidi, Z ; Visscher, L ; Sharif University of Technology
American Institute of Physics Inc
2022
Abstract
Resonance Raman spectroscopy has long been established as one of the most sensitive techniques for detection, structure characterization, and probing the excited-state dynamics of biochemical systems. However, the analysis of resonance Raman spectra is much facilitated when measurements are accompanied by Density Functional Theory (DFT) calculations that are expensive for large biomolecules. In this work, resonance Raman spectra are therefore computed with the Density Functional Tight-Binding (DFTB) method in the time-dependent excited-state gradient approximation. To test the accuracy of the tight-binding approximations, this method is first applied to typical resonance Raman benchmark...
Discussing the Behavior of the Boundary Theory Caused by Kalb-Ramond Field Perturbation in the Bulk, Using AdS/CFT Correspondence
, M.Sc. Thesis Sharif University of Technology ; Arfaei, Hessamaddin (Supervisor)
Abstract
In this thesis we have used the low energy effective action of the string theory to find an asymptotic Anti-de sitter metric with a non-vanishing H field. Then we have used the AdS/CFT correspondence to study the effects of the added Kalb_Ramond field on two calculations in the boundary theory. The first one was the calculation of the drag force exerted on a moving quark in the quark-gluon plasma. In the second calculation we observed the effect of the added field on the confinement-de confinement phase transition
Cost overrun risk assessment and prediction in construction projects: a bayesian network classifier approach
, Article Buildings ; Volume 12, Issue 10 , 2022 ; 20755309 (ISSN) ; Ansari, R ; Hassannayebi, E ; Jeong, J ; Sharif University of Technology
MDPI
2022
Abstract
Cost overrun risks are declared to be dynamic and interdependent. Ignoring the relationship between cost overrun risks during the risk assessment process is one of the primary reasons construction projects go over budget. Conversely, recent studies have failed to account for potential interrelationships between risk factors in their machine learning (ML) models. Additionally, the presented ML models are not interpretable. Thus, this study contributes to the entire ML process using a Bayesian network (BN) classifier model by considering the possible interactions between predictors, which are cost overrun risks, to predict cost overrun and assess cost overrun risks. Furthermore, this study...
Effectiveness Evaluation of Making Natural Childbirth Free of Charge on Household Decision in Choosing Delivery Method
, M.Sc. Thesis Sharif University of Technology ; Fatemi Ardestani, Farshad (Supervisor) ; Heidarzadeh, Mohammad (Co-Advisor)
Abstract
The rate of cesarean section delivery in Iran is high and during the past 14 years, leading up to 2014, kept rising. In this regard, decreasing cesarean section rate was targeted through the healthcare reform plan, which was offered by Ministry of Health and Medical Education. This plan kicked off on May4, 2014. One of the most important proceedings of this plan was making natural childbirth to be free in all hospitals, which are under the auspices of the medical universities. According to healthcare utilization models, lower prices of healthcare services, more health centers and more accessibility to them, increase the probability of using health care services. Current study evaluated the...
کلیدواژه های تکراریCurcumin loading potentiates the neuroprotective efficacy of Fe3O4 magnetic nanoparticles in cerebellum cells of schizophrenic rats
, Article Biomedicine and Pharmacotherapy ; Volume 108 , 2018 , Pages 1244-1252 ; 07533322 (ISSN) ; Ashrafi Hafez, A ; Abdorahim, M ; Abdollahifar, M. A ; Shabani, R ; Peirovi, H ; Simchi, A ; Ashtari, K ; Sharif University of Technology
2018
Abstract
Background: The aim of this study was to investigate the neurotoxic effects of Fe3O4 magnetic- CurNPs on isolated schizophrenia mitochondria of rats as an in vivo model. Methods: We designed CMN loaded superparamagnetic iron oxide nanoparticles (SPIONs) (Fe3O4 magnetic- CurNPs) to achieve an enhanced therapeutic effect. The physicochemical properties of Fe3O4 magnetic- CurNPs were characterized using X-ray diffraction (XRD), and dynamic laser light scattering (DLS) and zeta potential. Further, to prove Fe3O4 magnetic- CurNPs results in superior therapeutic effects, and also, the mitochondrial membrane potential collapse, mitochondrial complex II activity, reactive oxygen species generation,...
The role of heat treatment on wear behavior of powder metallurgy low alloy steels
, Article Materials and Design ; Volume 23, Issue 7 , 2002 , Pages 667-670 ; 02641275 (ISSN) ; Habibi, S. M ; Yoozbashizadea, H ; Janghorban, K ; Reihani, S. M. S ; Rahmani Seraji, H ; Ashtari, M ; Sharif University of Technology
Elsevier Ltd
2002
Abstract
The influence of manufacturing parameters such as compacting pressure, heat treatment and microstructure on the static and dynamic properties of Fe-1.75 Ni-1.5 Cu-0.5 Mo-0.6 C was investigated. Wear and fatigue tests were carried out on reciprocate wearing and tension compression mode, respectively. The results show that delamination wear mechanism of sintered steel is similar to that of conventional wrought or cast materials. But, in sintered material, open porosity acts as sites of generation and collection of wear debris or formation of subsurface cracks. Wear rate is decreased and fatigue strength is increased by heat treatment. © 2002 Elsevier Science Ltd. All rights reserved
Secrecy capacity scaling in large cooperative wireless networks
, Article IEEE Transactions on Information Theory ; Volume 63, Issue 3 , 2017 , Pages 1923-1939 ; 00189448 (ISSN) ; Papadimitratos, P. P ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2017
Abstract
We investigate large wireless networks subject to security constraints. In contrast to point-to-point, interferencelimited communications considered in prior works, we propose active cooperative relaying-based schemes. We consider a network with nl legitimate nodes, ne eavesdroppers, and path loss exponent α ≥ 2. As long as n2e (log(ne))γ = o(nl ), for some positive γ , we show that one can obtain unbounded secure aggregate rate. This means zero-cost secure communication, given fixed total power constraint for the entire network. We achieve this result through: 1) the source using Wyner randomized encoder and a serial (multi-stage) block Markov scheme, to cooperate with the relays and 2) the...
Fast estimation of connectivity in fractured reservoirs using percolation theory
, Article SPE Journal ; Volume 12, Issue 2 , 2007 , Pages 167-178 ; 1086055X (ISSN) ; King, P. R ; Nuratza, P ; Sharif University of Technology
Society of Petroleum Engineers (SPE)
2007
Abstract
Investigating the impact of geological uncertainty (i.e., spatial distribution of fractures) on reservoir performance may aid management decisions. The conventional approach to address this is to build a number of possible reservoir models, upscale them, and then run flow simulations. The problem with this approach is that it is computationally very expensive. In this study, we use another approach based on the permeability contrasts that control the flow, called percolation approach. This assumes that the permeability disorder of a rock can be simplified to either permeable or impermeable. The advantage is that by using some universal laws from percolation theory, the effect of the complex...
A new decoding scheme for errorless codes for overloaded CDMA with active user detection
, Article 2011 18th International Conference on Telecommunications, ICT 2011, Ayia Napa, 8 May 2011 through 11 May 2011 ; 2011 , Pages 201-205 ; 9781457700248 (ISBN) ; Pad, P ; Delgosha, P ; Marvasti, F ; Sharif University of Technology
2011
Abstract
Recently, a new class of binary codes for overloaded CDMA systems are proposed that not only has the ability of errorless communication but also suitable for detecting active users. These codes are called COWDA. In [1], a Maximum Likelihood (ML) decoder is proposed for this class of codes. Although the proposed scheme for coding/decoding shows impressive performance, the decoder can be significantly improved. In this paper, by assuming practical conditions for the traffic in the system, we suggest and prove an algorithm that increases the performance of the decoder several orders of magnitude (the Bit-Error-Rate (BER) is divided by a factor of about 400 in some E b/N0's). The algorithm...
Estimation of the Effective Permeability of Heterogeneous Porous Media by Using Percolation Concepts
, Article Transport in Porous Media ; Volume 114, Issue 1 , 2016 , Pages 169-199 ; 01693913 (ISSN) ; Gago, P. A ; King, P. R ; Sharif University of Technology
Springer Netherlands
2016
Abstract
In this paper we present new methods to estimate the effective permeability (keff) of heterogeneous porous media with a wide distribution of permeabilities and various underlying structures, using percolation concepts. We first set a threshold permeability (kth) on the permeability density function and use standard algorithms from percolation theory to check whether the high permeable grid blocks (i.e., those with permeability higher than kth) with occupied fraction of “p” first forms a cluster connecting two opposite sides of the system in the direction of the flow (high permeability flow pathway). Then we estimate the effective permeability of the heterogeneous porous media in different...
Percolation-based effective permeability estimation in real heterogeneous porous media
, Article 15th European Conference on the Mathematics of Oil Recovery, 29 August 2016 through 1 September 2016 ; 2016 ; 9462821933 (ISBN); 9789462821934 (ISBN) ; Gago, P ; King, P ; DCSE; Schlumberger; Shell ; Sharif University of Technology
European Association of Geoscientists and Engineers
2016
Abstract
It has long been understood that flow behavior in heterogeneous porous media is largely controlled by the continuity of permeability contrasts. With this in mind, we are looking in new methods for a fast estimation of the effective permeability which concentrates on the properties of the percolating cluster. From percolation concepts we use a threshold permeability value (Kth) by which the gridblocks with the highest permeability values connect two opposite side of the system in the direction of the flow. Those methods can be applied to heterogeneous media of a range of permeabilities distribution and various underlying structures. We use power law relations and weighted power averages that...
A novel WaveNet-GRU deep learning model for PEM fuel cells degradation prediction based on transfer learning
, Article Energy ; Volume 293 , 2024 ; 03605442 (ISSN) ; Hassani, P ; Raeesi, M ; Ahmadi, P ; Sharif University of Technology
2024
Abstract
Precise prediction of Remaining Useful Life (RUL) within the transportation industry is essential for cost reduction and enhanced energy efficiency, focusing on extending the operational lifespan of proton exchange membrane fuel cells (PEMFCs). In pursuit of this objective, this study employs data-driven prediction methodologies centered on deep neural networks and transfer learning. The fundamental premise is that these approaches hinge on the compatibility of functional conditions across diverse datasets. Multiple strategies, amalgamating transfer learning, and deep neural networks, are introduced to forecast the PEMFC stack's behavior and its associated RUL. Network hyperparameters are...