Loading...
Search for:
orders-of-magnitude
0.006 seconds
Total 44 records
Hybrid anisotropic pentamode mechanical metamaterial produced by additive manufacturing technique
, Article Applied Physics Letters ; Volume 117, Issue 6 , 2020 ; Movahhedy, M. R ; Shishkovsky, I ; Hedayati, R ; Sharif University of Technology
American Institute of Physics Inc
2020
Abstract
Pentamode metamaterials are a type of extremal designer metamaterials, which are able to demonstrate extremely high rigidity in one direction and extremely high compliance in other directions. Pentamodes can, therefore, be considered as building blocks of exotic materials with any arbitrarily selected thermodynamically admissible elasticity tensor. The pentamode lattices can then be envisioned to be combined to construct intermediate extremal materials, such as quadramodes, trimodes, and bimodes. In this study, we constructed several primary types of anisotropic pentamode lattices (with midpoint positioning of 10%, 15%, 20%, 25%, 30%, 35%, and 42% of the main unit cell diagonal) and then...
Compensation of nonlinearity impairments in coherent optical OFDM systems using multiple optical phase conjugate modules
, Article Journal of Optical Communications and Networking ; Vol. 6, Issue 6 , June , 2014 , pp. 549-558 ; ISSN: 19430620 ; Sharif University of Technology
Abstract
In this paper, we propose utilizing multiple optical phase conjugate (OPC) modules along fiber spans, in order to improve the performance of coherent optical orthogonal frequency division multiplexing (CO-OFDM) communication systems in long-haul fiber-optic channels. The role of OPC in CO-OFDM systems is investigated by formulating the four-wave mixing (FWM) process generated along a CO-OFDM with two and three OPCs. Analytical results reveal that increasing the number of OPC modules reduces the average FWM power along the transmission link and as a result mitigates the degrading effect of interaction between amplified spontaneous emission noise and FWM. The proposed schemes have also been...
Effect of chemical substitution on the morphology and optical properties of Bi1-xCaxFeO3 films grown by pulsed-laser deposition
, Article Journal of Materials Science: Materials in Electronics ; Volume 24, Issue 1 , 2013 , Pages 248-252 ; 09574522 (ISSN) ; Mahdavi, S. M ; Nemati, A ; Sharif University of Technology
2013
Abstract
The morphological characteristics as well the optical properties of Ca-doped BiFeO3 films grown by pulsed-laser deposition technique have been investigated. AFM images revealed that calcium has a radical effect on the surface features of BiFeO3 films. By utilizing spectrophotometer, transmission behaviour of the films was investigated. Local IV characteristics of the films disclosed about three orders of magnitude enhancement concerning electrical conductivity through Ca doping. X-ray photoelectron spectroscopy results revealed that Ca can reduce the valence state of iron in the compound
Efficient algorithms to accurately compute derating factors of digital circuits
, Article Microelectronics Reliability ; Volume 52, Issue 6 , June , 2012 , Pages 1215-1226 ; 00262714 (ISSN) ; Tahoori, M. B ; Fazeli, M ; Miremadi, S. G ; Sharif University of Technology
2012
Abstract
Fast, accurate, and detailed Soft Error Rate (SER) estimation of digital circuits is essential for cost-efficient reliable design. A major step to accurately estimate a circuit SER is the computation of failure probability, which requires the computation of three derating factors, namely logical, electrical, and timing derating. The unified treatment of these derating factors is crucial to obtain accurate failure probability. Existing SER estimation techniques are either unscalable to large circuits or inaccurate due to lack of unified treatment of all derating factors. In this paper, we present fast and efficient algorithms to estimate SERs of circuit components in the presence of single...
Extreme bendability of DNA double helix due to bending asymmetry
, Article Journal of Chemical Physics ; Volume 143, Issue 10 , 2015 ; 00219606 (ISSN) ; Eslami Mossallam, B ; Naderi, S ; Ejtehadi, M. R ; Sharif University of Technology
American Institute of Physics Inc
2015
Abstract
Experimental data of the DNA cyclization (J-factor) at short length scales exceed the theoretical expectation based on the wormlike chain (WLC) model by several orders of magnitude. Here, we propose that asymmetric bending rigidity of the double helix in the groove direction can be responsible for extreme bendability of DNA at short length scales and it also facilitates DNA loop formation at these lengths. To account for the bending asymmetry, we consider the asymmetric elastic rod (AER) model which has been introduced and parametrized in an earlier study [B. Eslami-Mossallam and M. R. Ejtehadi, Phys. Rev. E 80, 011919 (2009)]. Exploiting a coarse grained representation of the DNA molecule...
Polynomial chaos expansions for uncertainty propagation and moment independent sensitivity analysis of seawater intrusion simulations
, Article Journal of Hydrology ; Volume 520 , January , 2015 , Pages 101-122 ; 00221694 (ISSN) ; Ataie Ashtiani, B ; Simmons, C. T ; Sharif University of Technology
Elsevier
2015
Abstract
Real world models of seawater intrusion (SWI) require high computational efforts. This creates computational difficulties for the uncertainty propagation (UP) analysis of these models due the need for repeated numerical simulations in order to adequately capture the underlying statistics that describe the uncertainty in model outputs. Moreover, despite the obvious advantages of moment-independent global sensitivity analysis (SA) methods, these methods have rarely been employed for SWI and other complex groundwater models. The reason is that moment-independent global SA methods involve repeated UP analysis which further becomes computationally demanding. This study proposes the use of...
Identification of fluid dynamics in forced gravity drainage using dimensionless groups
, Article Transport in Porous Media ; Volume 83, Issue 3 , July , 2010 , Pages 725-740 ; 01693913 (ISSN) ; Kharrat, R ; Pooladi Darvish, M ; Ghotbi, C ; Sharif University of Technology
2010
Abstract
A number of forced gravity drainage experiments have been conducted using a wide range of the physical and operational parameters, wherein the type, length, and permeability of the porous medium as well as oil viscosity and injection rate were varied. Results indicate that an increase in the Bond number has a positive effect on oil recovery whereas the capillary number has an opposite effect. These trends were observed over a two-order of magnitude change in the value of the dimensionless groups. Furthermore, it was found that use of each number alone is insufficient to obtain a satisfactory correlation with recovery. A combined dimensionless group is proposed, which combines the effect of...
Two-Phase Low-Energy N-Modular Redundancy for Hard Real-Time Multi-Core Systems
, Article IEEE Transactions on Parallel and Distributed Systems ; Volume 27, Issue 5 , 2016 , Pages 1497-1510 ; 10459219 (ISSN) ; Ejlali, A ; Al-Hashimi, B. M ; Sharif University of Technology
IEEE Computer Society
2016
Abstract
This paper proposes an N-modular redundancy (NMR) technique with low energy-overhead for hard real-time multi-core systems. NMR is well-suited for multi-core platforms as they provide multiple processing units and low-overhead communication for voting. However, it can impose considerable energy overhead and hence its energy overhead must be controlled, which is the primary consideration of this paper. For this purpose the system operation can be divided into two phases: indispensable phase and on-demand phase. In the indispensable phase only half-plus-one copies for each task are executed. When no fault occurs during this phase, the results must be identical and hence the remaining copies...
OPTIMAS: overwrite purging through in-execution memory address snooping to improve lifetime of NVM-based scratchpad memories
, Article IEEE Transactions on Device and Materials Reliability ; Volume 17, Issue 3 , 2017 , Pages 481-489 ; 15304388 (ISSN) ; Farbeh, H ; Miremadi, S. G ; Sharif University of Technology
Abstract
SRAM-based scratchpad memories (SPMs) used in embedded systems impose high leakage power. Designing SPMs based on non-volatile memories (NVMs) were proposed as NVMs have negligible leakage power. The main problem of utilizing NVMs across the SPM is their limited number of write cycles (endurance). This problem threatens the reliability of NVM-based SPMs. To alleviate the problem of limited endurance in NVM-based SPMs, this paper proposes a method, called overwrite purging through in-execution memory address snooping (OPTIMAS). The main idea behind the proposed method is to control the lifetime of NVM-based SPMs, directly by a hardware unit, outside of the SPM mapping algorithm. This idea...
On the design of graphene oxide nanosheets membranes for water desalination
, Article Desalination ; Volume 422 , 2017 , Pages 83-90 ; 00119164 (ISSN) ; Tavakoli, R ; Sharif University of Technology
Elsevier B.V
2017
Abstract
According to current researches, graphene oxide (GO) membranes show promising desalination properties due to ease of synthesis, low production cost, and high efficiency. There are several experimental works to study ionic sieving properties of GO membranes. However, it is difficult to characterize atomistic mechanism of water permeation and ion rejection by experimental approaches. On the other hand, there exist a few reports in which the atomistic picture of water permeation across GO membranes is investigated by means of molecular dynamics (MD) simulation. In the present work, in addition to water desalination, the atomic scale mechanism of ion rejection is studied using large scale MD...
Reverse time migration by Krylov subspace reduced order modeling
, Article Journal of Applied Geophysics ; Volume 151 , April , 2018 , Pages 298-308 ; 09269851 (ISSN) ; Javaherian, A ; Shomali, Z. H ; Dehghani Firouz Abadi, R ; Gholamy, S. A ; Sharif University of Technology
Elsevier B.V
2018
Abstract
Imaging is a key step in seismic data processing. To date, a myriad of advanced pre-stack depth migration approaches have been developed; however, reverse time migration (RTM) is still considered as the high-end imaging algorithm. The main limitations associated with the performance cost of reverse time migration are the intensive computation of the forward and backward simulations, time consumption, and memory allocation related to imaging condition. Based on the reduced order modeling, we proposed an algorithm, which can be adapted to all the aforementioned factors. Our proposed method benefit from Krylov subspaces method to compute certain mode shapes of the velocity model computed by as...
Molecular simulation of protein dynamics in nanopores. II. Diffusion
, Article Journal of Chemical Physics ; Volume 130, Issue 8 , 2009 ; 00219606 (ISSN) ; Tabar, M.R.R ; Sahimi, M ; Sharif University of Technology
2009
Abstract
A novel combination of discontinuous molecular dynamics and the Langevin equation, together with an intermediate-resolution model of proteins, is used to carry out long (several microsecond) simulations in order to study transport of proteins in nanopores. We simulated single-domain proteins with the α-helical native structure. Both attractive and repulsive interaction potentials between the proteins and the pores' walls are considered. The diffusivity D of the proteins is computed not only under the bulk conditions but also as a function of their "length" (the number of the amino-acid groups), temperature T, pore size, and interaction potentials with the walls. Compared with the...
A mechanistic study of emulsion flooding for mobility control in the presence of fatty acids: Effect of chain length
, Article Fuel ; Volume 276 , 2020 ; Suleymani, M ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
Emulsion flooding is a promising method for enhanced oil recovery (EOR). The static and dynamic behavior of the emulsions is greatly influenced by the nature of the applied surfactant. In this work, the effect of fatty acids, as natural surface-active agents, and their chain length on the emulsion behavior was investigated in both bulk and porous media. A panel of the fatty acids with different chain lengths (6 < C < 18) was applied at constant concentration and pH. Upon the static stability tests, emulsion stability at the optimum value of chain length (C14) was increased by two orders of magnitude. Under the optimal condition, the hydrogen bonding between dissociated and undissociated...
Hydrogenated graphene oxide (H-G-SiO2) Janus structure: Experimental and computational study of strong piezo-electricity response
, Article Journal of Physics D: Applied Physics ; Volume 53, Issue 17 , 2020 ; Alidoosti, M ; Hosseinzadeh, A ; Seyyedi, S. M. S ; Elahi, M ; Pourfath, M ; Mohajerzadeh, S ; Sharif University of Technology
Institute of Physics Publishing
2020
Abstract
We have investigated the piezoelectric response of the hydrogenated graphene oxide (H-G-SiO2) stacks both experimentally and theoretically. The piezoresponse force microscopy method and density-functional theory (DFT) calculations were used to study the piezoresponse effect of this structure from both experimental and computational point of views. A mono-layer graphene, made by chemical vapour deposition method, is deposited on Si/SiO2 substrate and its surface is then functionalized with hydrogen atoms. The vertical piezoresponse, observed by piezoresponse force microscopy, is measured to be about 2146 pC N-1, that is comparable to the reported state of the art piezoelectric materials such...
STAIR: high reliable STT-MRAM aware multi-level I/O cache architecture by adaptive ECC allocation
, Article 2020 Design, Automation and Test in Europe Conference and Exhibition, DATE 2020, 9 March 2020 through 13 March 2020 ; 2020 , Pages 1484-1489 ; Cheshmikhani, E ; Asadi, H ; ACM Special Interest Group on Design Automation (SIGDA); et al.; European Design and Automation Association (EDAA); European Electronic Chips and Systems Design Initiative (ECSI); IEEE Council on Electronic Design Automation (CEDA); SEMI Strategic Technology Community and Electronic System Design Alliance (ESD Alliance) ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2020
Abstract
Hybrid Multi-Level Cache Architectures (HCAs) are promising solutions for the growing need of high-performance and cost-efficient data storage systems. HCAs employ a high endurable memory as the first-level cache and a Solid-State Drive (SSD) as the second-level cache. Spin-Transfer Torque Magnetic RAM (STT-MRAM) is one of the most promising candidates for the first-level cache of HCAs because of its high endurance and DRAM-comparable performance along with non-volatility. However, STT-MRAM faces with three major reliability challenges named Read Disturbance, Write Failure, and Retention Failure. To provide a reliable HCA, the reliability challenges of STT-MRAM should be carefully addressed....
A modeling framework for reliability of erasure codes in SSD arrays
, Article IEEE Transactions on Computers ; Volume 69, Issue 5 , May , 2020 , Pages 649-665 ; Ahmadian, S ; Asadi, H ; Sharif University of Technology
IEEE Computer Society
2020
Abstract
Emergence of Solid-State Drives (SSDs) have evolved the data storage industry where they are rapidly replacing Hard Disk Drives (HDDs) due to their superiority in performance and power. Meanwhile, SSDs have reliability issues due to bit errors, bad blocks, and bad chips. To help reliability, Redundant Array of Independent Disks (RAID) configurations, originally proposed to increase both performance and reliability of HDDs, are also applied to SSD arrays. However, the conventional reliability models of HDD RAID cannot be intactly applied to SSD arrays, as the nature of failures in SSDs are totally different from HDDs. Previous studies on the reliability of SSD arrays are based on the...
Super-fast discharge of phase change materials by using an intermediate boiling fluid
, Article International Communications in Heat and Mass Transfer ; Volume 115 , 2020 ; Mohammadi, O ; Rahgozar, I ; Shafii, M. B ; Ahmadi, M. H ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
The low thermal conductivity of phase change materials (PCM) results in the slowdown in the discharging process of PCM which limits the usability of these materials in the field of Thermal Energy Storage (TES). In this research, an innovative solution is proposed to significantly accelerate the solidification speed, up to two orders of magnitude greater than conventional methods. Using acetone as the intermediate boiling fluid (IBF), the paraffin discharge rate as a phase-change material is significantly improved which is known as super-fast discharge (SFD) in this article. In this method, liquid acetone takes the heat by boiling in liquid paraffin and causes it to solidify. As the liquid...
Symmetry enhanced spin-Nernst effect in honeycomb antiferromagnetic transition metal trichalcogenide monolayers
, Article Physical Review B ; Volume 103, Issue 1 , 2021 ; 24699950 (ISSN) ; Hamdi, M ; Haddadi, F ; Khavasi, A ; Sadeghi, A ; Mohseni, S. M ; Sharif University of Technology
American Physical Society
2021
Abstract
We investigate systematically the spin-Nernst effect in Néel and zigzag ordered honeycomb antiferromagnets. Monolayers of transition-metal trichalcogenides, MnPSe3, MnPS3, and VPS3 show an antiferromagnetic Néel order while CrSiTe3, NiPS3, and NiPSe3 show an antiferromagnetic zigzag order. We extract the exchange and Dzyaloshinskii-Moriya interaction parameters from ab initio calculations. Using these parameters, we predict that the spin-Nernst coefficient is at least two orders of magnitude larger in zigzag compared to the Néel ordered antiferromagnets. We find that this enhancement relies on the large band splitting due to the symmetry of magnetic configuration in the zigzag order. Our...
Simultaneous use of physical and chemical dispersants for electrical conductivity enhancement in polyamide 6/carbon nanotube/conductive carbon black hybrid nanocomposites
, Article Polymer-Plastics Technology and Materials ; 2021 ; 25740881 (ISSN) ; Jahanaray, B ; Pircheraghi, G ; Bagheri, R ; Sharif University of Technology
Taylor and Francis Ltd
2021
Abstract
Polyamide 6 (PA6)/carbon nanotube (CNT)/conductive carbon black (CCB) nanocomposites with the incorporation of physical and chemical dispersants were prepared via melt blending method to examine the synergistic enhancement of electrical conductivity. Investigation of modified CNT with octadecyl triphenyl phosphonium chloride (OTPC-CNT) as physical dispersant was performed by Fourier transform infrared, nuclear magnetic resonance, Raman spectroscopy, and thermogravimetric analysis. Morphological, electrical, rheological, and mechanical properties of PA6/CNT/CCB nanocomposites were examined by field emission scanning electron microscopy, transmission electron microscopy, digital insulation...
Polyvinylcarbazole as an efficient interfacial modifier for low-cost perovskite solar cells with CuInS2/Carbon hole-collecting electrode
, Article Solar RRL ; Volume 5, Issue 7 , 2021 ; 2367198X (ISSN) ; Behrouznejad, F ; Forouzandeh, M ; Khosroshahi, R ; Darbari, S ; Zhan, Y ; Taghavinia, N ; Sharif University of Technology
John Wiley and Sons Inc
2021
Abstract
Different polymers have been already introduced for passivating the interfacial defects at the interface of perovskite and the organic hole transport material, meanwhile as an environmental barrier in perovskite solar cells (PSCs). Herein, polyvinylcarbazole (PVK) compared to polymethylmethacrylate (PMMA) at the interface of the perovskite (Cs0.05(MA0.83FA0.17)0.95Pb(Br0.17I0.83)3) layer and CuInS2/carbon as a low-cost inorganic hole-collecting electrode are investigated. By suppressing interfacial recombination using PMMA and PVK, saturation current density (in dark current) decreases one order of magnitude from 7.9 × 10−10 to 4.0 × 10−11 mA cm−2 by adding PMMA and two orders of magnitude...