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Synthesis & Properties of Nd-doped Glass-ceramics in the SiO2-CaO-MgO System from Sol-gel Method Used as Solid Lasers
,
M.Sc. Thesis
Sharif University of Technology
;
Hamnabard, Zohreh
(Supervisor)
;
Nemati, Ali
(Supervisor)
Abstract
In this study, SiO2-CaO-MgO galsses and glass-ceramic powder doped with Nd3+ were synthesized with sol-gel method. Tetraethylorthosilicate (TEOS), Ca(NO3)2.4H2O, Mg(NO3)2.6H2O, Nd(NO3)3.6H2O, ethanol, distilled water, and HNO3 were used as starting materials. The synthesized powder’s properties were examined with STA, XRD, DRS, PL, FTIR and SEM analysis. From XRD patterns of glass samples, the role of dopant was introduced as intermediate oxide in glass matrix. The XRD patterns of glass-ceramic samples indicated that the bredigite and akermanite crystals were formed in glass matrix. The band gap energy of samples were calculated from DRS analysis and were seen with increasing the dopant...
Structural aspects and the conduction mechanism of Ln(Ba 2-xPrx)Cu3O7+δ (Ln = Tm, Lu)
, Article Physica Status Solidi (B) Basic Research ; Volume 244, Issue 9 , 2007 , Pages 3211-3222 ; 03701972 (ISSN) ; Akhavan, M ; Sharif University of Technology
2007
Abstract
TmBa2_xPrxCu3O7+δ and LuBa2_xPrxCu3O7+δ samples with 0.0 < x ≤ 1.0 have been prepared by a solid-state reaction technique. The occurrence of the orthorhombic to tetragonal phase transition, increasing of oxygen content with the increase of Pr doping, and the existence of solubility limit in both systems confirm the correct substitution of Pr at Ba sites. The solubility limit for Pr in the Lu-based samples is less than 0.7, which is less than x = 0.90 for the Tm-based samples. The Tc depression versus doping content in both systems shows that depression of superconductivity by Pr at Ba sites is mostly due to the hole-filling/localization effects. Also, in the Tm-based system, the...
Tilted-Lorentz symmetry
, Article Iranian Journal of Physics Research ; Volume 19, Issue 4 , Winter , 2020 , Pages 831-834 ; Sharif University of Technology
Isfahan University of Technology
2020
Abstract
Dirac cone can be tilted in condensed matter setting. As a result of tilt, the Lorentz symmetry is reduced to what we call tilted-Lorentz symmetry. In this paper, we derive the tilted-Lorentz transformations that leave a world with tilted Dirac cone invariant. © 2020, Isfahan University of Technology. All rights reserved
Unleashing the potentials of dynamism for page allocation strategies in SSDs
, Article SIGMETRICS 2014 - Proceedings of the 2014 ACM SIGMETRICS International Conference on Measurement and Modeling of Computer Systems ; 2014 , pp. 551-552 ; ISBN: 9781450327893 ; Arjomand, M ; Sarbazi-Azad, H ; Sharif University of Technology
Abstract
In Solid-State Drives (SSDs) with tens of ash chips and highly parallel architecture, we can speed up I/O operations by well-utilizing resources during page allocation. Propos- als already exist for using static page allocation which does not balance the IO load and its efficiency depends on access address patterns. To our best knowledge, there have been no research thus far to show what happens if one or more internal resources can be freely allocated regardless of the request address. This paper explores the possibility of using different degrees of dynamism in page allocation and iden- tifies key design opportunities that they present to improve SSD's characteristics
Xylanase production under solid state fermentation by aspergillus niger
, Article International Journal of Engineering, Transactions B: Applications ; Volume 24, Issue 3 , March , 2011 , Pages 197-208 ; 1728-144X (ISSN) ; Alemzadeh, I ; Khanahmadi, M ; Roostaazad, R ; Sharif University of Technology
Materials and Energy Research Center
2011
Abstract
Central composite orthogonal design was applied to quantify relations of xylanase production, loss of dry matter and change of pH with four critical variables during solid state fermentation of a mixture of wheat bran and wheat straw on which Aspergillus niger CCUG 33991 was cultivated. The studied variables included the percentage of wheat straw, wheat bran, temperature, moisture content, and fermentation time. The second-order quadratic model predicted the xylanase activity at a suitable set of conditions namely 29°C, 55% moisture content, and 50 hours of fermentation to be 1465 U/g of fermented dry matter which differed less than 6% from measured value at this set of conditions....
On the Al/Cu Dissimilar Joints Produced Through Simple Cold Compression
, Article Transactions of the Indian Institute of Metals ; Volume 68, Issue 5 , October , 2015 , Pages 991-998 ; 09722815 (ISSN) ; Ghasemi, A ; Pouraliakbar, H ; Jandaghi, M. R ; Sharif University of Technology
Springer India
2015
Abstract
Dissimilar Al/Cu joints were produced through simple cold compression technique. The influence of different reductions (40, 53 and 66 %) on the joint strength was studied. Also, the effect of heat treatment on the joints’ mechanical characteristics was investigated using a modified miniature shear test. Microscopical examinations by means of optical and scanning electron microscopes were conducted and results confirmed that acceptable joints produced through 53 and 66 % deformations. According to the shear test results, it was revealed that post-weld heat treatment influenced the joint’s strength and caused strength enhancement in the samples which were not subjected to annealing prior to...
Vanadium dioxide-anchored porous carbon nanofibers as a Na+ intercalation pseudocapacitance material for development of flexible and super light electrochemical energy storage systems
, Article Applied Materials Today ; Volume 10 , 2018 , Pages 72-85 ; 23529407 (ISSN) ; Shahrokhian, S ; Sharif University of Technology
Elsevier Ltd
2018
Abstract
The development of a flexible binder free electrode based on 3D vanadium dioxide (VO2) nano-architectures has materialized as an effective strategy for fabrication of advanced wearable, portable, and stretchable electronic devices. However, most of the stretchable energy storage devices based on VO2 suffer from a relatively low operating voltage, high weight, low specific capacitance, and thus low energy density. Here, a novel binder free supercapacitor electrode composed of hierarchical VO2 nanosheet arrays grown on porous carbon nanofibers (VO2@PCNFs) is designed using a simple hydrothermal method followed by annealing treatment. The electrochemical evaluation confirmed that the energy...
Influence of different nitrogen sources on amount of chitosan production by Aspergillus niger in solid state fermentation
, Article Iranian Journal of Chemistry and Chemical Engineering ; Volume 27, Issue 1 , 2008 , Pages 47-52 ; 10219986 (ISSN) ; Yaghmaei, S ; Beigi, S. M ; Sharif University of Technology
2008
Abstract
In this study the effect of different nitrogen source substrates on the amount of chitosan production by Aspergillus niger was investigated. A. niger PTCC 5012 from the Persian Type Culture Collection (PTCC) was grown on soy bean, corn seed and canola residues at 30 °C for specified cultivation days under sterilized conditions. Chitosan was extracted from the fungal mycelia using hot alkaline and acid treatment. The results were shown that soy bean residue at moisture of 37% and 8.4 ± 0.26 % of nitrogen content produced the highest amount of chitosan (17.053 ± 0.95 g/kg of dry substrate), after 12 days of incubation. Corn seed residue produced very low amount of chitosan (1.9 ± 0.4 % of...
Flux dynamics in-Ln(Ba2-xPrx)Cu3O 7+δ (Ln = Tm, Lu)
, Article Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers ; Volume 45, Issue 2 A , 2006 , Pages 742-751 ; 00214922 (ISSN) ; Akhavan, M ; Sharif University of Technology
2006
Abstract
Single-phase Tm(Ba2-xPrx)Cu3O 7+δ and Lu(Ba2-xPrx)Cu3O 7+δ compounds with Pr content 0.0 ≤ x ≤ 1.0 have been prepared by solid-state reaction technique. The oxygen content of our samples is more than 7. X-ray diffraction (XRD) patterns demonstrate an orthorhombic to tetragonal transition with an increase in Pr content in both systems. For each system, a solubility limit exists for substitution of Pr at the Ba site. The intergrain region investigated by the thermally activated flux creep (TAFC) and Ambegaokar-Halperin (AH) models, show that the pinning energy decreases with increasing Pr content; it also decreases in each sample with increasing magnetic field as a power-law relation. The...
Thermal entanglement of spins in an inhomogeneous magnetic field
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Volume 71, Issue 2 , 2005 ; 10502947 (ISSN) ; Karimipour, V ; Sharif University of Technology
American Physical Society
2005
Abstract
We study the effect of inhomogeneities in the magnetic field on the thermal entanglement of a two-spin system. We show that in the ferromagnetic case a very small inhomogeneity is capable of producing large values of thermal entanglement. This shows that the absence of entanglement in the ferromagnetic Heisenberg system is highly unstable against inhomogeneity of magnetic fields, which is inevitably present in any solid state realization of qubits. © 2005 The American Physical Society
Investigating the use of cooling surfaces in solid-state fermentation tray bioreactors: Modelling and experimentation
, Article Journal of Chemical Technology and Biotechnology ; Volume 79, Issue 11 , 2004 , Pages 1228-1242 ; 02682575 (ISSN) ; Roostaazad, R ; Safekordi, A ; Bozorgmehri, R ; Mitchell, D. A ; Sharif University of Technology
2004
Abstract
The effect of wall cooling in tray-type solid-state fermenters was investigated by cultivation of Aspergillus niger ATCC 10 864 on wheat bran. Temperature, moisture, pH and glucoamylase activity in the bed were monitored. Application of the heat exchanger plate reduced the overall water loss but increased the heterogeneity of moisture distribution in the bed. Moisture content increased markedly close to the heat transfer plate while the upper regions of the bed dried out. The thermal conductivity of the bed was measured to be 0.19 Wm-1 K-1. At these conditions and depending on the air flow rate, 58-82% of the metabolic heat was removed via conduction towards the plate. A mathematical model...
Thermo-mechanical modeling of hot forging process
, Article Journal of Engineering Materials and Technology ; Volume 126, Issue 4 , 2004 , Pages 406-412 ; 00944289 (ISSN) ; Sharif University of Technology
American Society of Mechanical Engineers(ASME)
2004
Abstract
In the present study, a mathematical model has been developed to evaluate temperature and strain fields as well as dynamic and static microstructural changes during the nonisothermal forging process. To do so, a finite element analysis and a microstructural model based on Bergstrom's model have been coupled for predicting temperature history, velocity and strain fields as well as phase transformations within the metal during and after hot forging. To verify the results of the model, theoretical predictions for loadstroke behavior and austenite grain size have been compared with experimental results for two grades of steel
Design Tradeoffs of SSD Implementations on Reconfigurable Devices and ASICs
, M.Sc. Thesis Sharif University of Technology ; Asadi, Hossein (Supervisor)
Abstract
Solid-State Drives (SSDs) are replaced to a great portion of Hard Disk Drives (HDDs) in personal computers, servers, and supercomputers due to their high reliability, shock resistance, low power consumption, and high performance. SSDs utilize either NAND or NOR flash chips in the drive backend logic to persistently store user data. Since NAND/NOR flash chips incur from limited number of write endurance and high write/erase operation latency, they use a controller called Flash Translation Layer (FTL) to alleviate these limitations. As the performance of commercially off-the-shelf (COTS) SSDs is tuned for few mainstream applications, COTS SSDs provide limited throughput for variety of...
A High-Level SSD Performance Estimation Model based on Workload Features
, M.Sc. Thesis Sharif University of Technology ; Asadi, Hossein (Supervisor)
Abstract
With increases in amount of data being processed and generated, the need for highperformance data storage systems is essential. These systems must keep up with request throughputs as high as millions of requests per second. Solid-State Drives (SSD) lack mechanical parts and have lower read and write latency. SSDs have key differences with traditional spinning drives in having a fixed read/write granularity, erase before write and requiring wear-leveling and garbage collection operations. These operations have significant impact on drive performance and also frequency of these operations depends on the workload characteristics, such as randomness. In this thesis, a high-level estimator of SSD...
Improved charge collection efficiency of hollow sphere/nanoparticle composite TiO 2 electrodes for solid state dye sensitized solar cells
, Article Current Applied Physics ; Volume 13, Issue 2 , March , 2013 , Pages 371-376 ; 15671739 (ISSN) ; Mohammadpour, R ; Irajizad, A ; Taghavinia, N ; Dadgostar, S ; Samadpour, M ; Tajabadi, F ; Sharif University of Technology
2013
Abstract
The photoanodes of solid state dye sensitized solar cells (ss-DSCs) embedded with different contents of TiO 2 hollow spheres (HSs) were prepared and the photovoltaic performances were systematically characterized. TiO 2 hollow spheres were synthesized by a facile sacrificial templating method, grounded and added in different ratios to TiO 2 nanoparticle (NP) paste, from which composite HS/NP electrodes were fabricated. The composite photoanodes include hollow spheres of 300-700 nm with enhanced light scattering characteristics in visible range which leads to improved light absorption in conventional thin film electrodes of ss-DSC. By optimizing the amount of HSs in the paste, 40% improvement...
Hybrid Raid: A solution for enhancing the reliability of SSD-based raids
, Article IEEE Transactions on Multi-Scale Computing Systems ; Volume 3, Issue 3 , 2017 , Pages 181-182 ; 23327766 (ISSN) ; Miremadi, S. G ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2017
Abstract
The failure probability in SSDs increases when the number of Program/Erase (P/E) cycles increases. Traditionally, a group of SSDs are protected with parity disks, called SSD-based RAID. It has been shown that the reliability of RAIDs depends on the distribution of parities among SSDs. There are two main policies to distribute parities among SSDs in RAIDs, i.e., evenly and unevenly. By distributing parities evenly, all SSDs would wear out with the same rate, causing simultaneous failures of SSDs. By distributing parities unevenly, one of the SSDs in RAID may fail much earlier than the others. Both these two drawbacks, i.e., the simultaneous failures of SSDs and the rapid first failure of one...
ReCA: An efficient reconfigurable cache architecture for storage systems with online workload characterization
, Article IEEE Transactions on Parallel and Distributed Systems ; Volume 29, Issue 7 , 2018 , Pages 1605-1620 ; 10459219 (ISSN) ; Ebrahimi, S ; Asadi, H ; Sharif University of Technology
IEEE Computer Society
2018
Abstract
In recent years, Solid-State Drives (SSDs) have gained tremendous attention in computing and storage systems due to significant performance improvement over Hard Disk Drives (HDDs). The cost per capacity of SSDs, however, prevents them from entirely replacing HDDs in such systems. One approach to effectively take advantage of SSDs is to use them as a caching layer to store performance critical data blocks in order to reduce the number of accesses to HDD-based disk subsystem. Due to characteristics of Flash-based SSDs such as limited write endurance and long latency on write operations, employing caching algorithms at the Operating System (OS) level necessitates to take such characteristics...
Advanced binder-free electrode based on core–shell nanostructures of mesoporous Co3V2O8-Ni3V2O8 thin layers@porous carbon nanofibers for high-performance and flexible all-solid-state supercapacitors
, Article Chemical Engineering Journal ; Volume 341 , 2018 , Pages 10-26 ; 13858947 (ISSN) ; Shahrokhian, S ; Sharif University of Technology
Elsevier B.V
2018
Abstract
The development of thin layer structures on flexible current collectors has become as an effective strategy for preparing advanced portable and wearable power sources. Herein, a flexible and efficient electrode was fabricated based on electrospun porous carbon nanofibers (PCNFs) substrate with elaborately designed thin layer Co3V2O8-Ni3V2O8 core–shell nanostructures (Co3V2O8-Ni3V2O8 TLs@PCNFs). The resulting free-standing Co3V2O8-Ni3V2O8 TLs@PCNFs composite was used directly as a flexible electrode in three electrode system for supercapacitor studies without the need for utilization of either binder or metal-based current collector. The unique thin layer structure of Co3V2O8-Ni3V2O8...
Solid state fermentation for production of chitosan by aspergillus niger
, Article International Journal of Engineering, Transactions B: Applications ; Volume 22, Issue 1 , 2009 , Pages 1-6 ; 1728-144X (ISSN) ; Razavi, J ; Yaghmaei, S ; Sharif University of Technology
Materials and Energy Research Center
2009
Abstract
The effect of Solid State Fermentation (SSF) on Chitosan production by A. niger was investigated. A. niger BBRC 20004 from Biochemical and Bioenvironmental Research Centre of Sharif University of Technology (Tehran, Iran), was grown on corn residue. Chitosan was extracted from the fungal mycelia using hot alkaline and acid treatment. A. niger was incubated for 12 days on corn residue with moisture content of 35 % and 1.12 % of nitrogen. The Chitosan was obtained and 10.9 g/kg of Urea dry residue was added in various amounts to the medium in order to evaluate the effect of the nitrogen concentration in the production of Chitosan. The highest amount of Chitosan obtained by 6.5 g of urea after...
Can erasure codes damage reliability in SSD-based storage systems?
, Article IEEE Transactions on Emerging Topics in Computing ; Volume 7, Issue 3 , 2019 , Pages 435-446 ; 21686750 (ISSN) ; Safaei, B ; Miremadi, S. G ; Sharif University of Technology
IEEE Computer Society
2019
Abstract
Erasure codes are applied in storage systems including both Hard Disk Drive (HDD) and Solid State Disk (SSD) to protect arrays of disks against failures. Applying these codes in SSD-based systems incurs additional number of Program/Erase (P/E) cycles on each disk, which may accelerate the wear-out of disks. This means that while erasure codes improve reliability of SSD-based systems, they impose a side-effect that may degrade reliability as the number of P/E cycles increases. This paper investigates the benefit and side-effect of erasure codes on reliability of SSD-based systems. The investigation attempts to find out the parameters which improve/damage reliability. This study has been...