Sharif Digital Repository

In this research, the effects of nano-sized MgO in Al2O 3-SiC composites were investigated. The overall changes in the density and mechanical properties of sintered samples (hardness, bending strength and toughness) were evaluated. After mixing, drying and uniaxial compaction of the powders, they were first heat-treated at low temperature in an electric furnace to remove any residuals. They were then heat-treated at high temperature (1700 °C) inside a graphite furnace in argon atmosphere for sintering (at normal and high pressure). The content of MgO in the Al 2O3-10 vol% SiC composite was 0, 500, 1000, and 1500 ppm. Thefracture toughness(KIC)of sintered composite with 10... 

Solid oxide fuel cells (SOFCs) are rapidly becoming recognized as a new alternative to traditional energy conversion systems because of their high energy efficiency. From an ecological perspective, this environmentally friendly technology, which produces clean energy, is likely to be implemented more frequently in the future. However, the current SOFC technology still cannot meet the demands of commercial applications due to temperature constraints and high cost. To develop a marketable SOFC, suppliers have tended to reduce the operating temperatures by a few hundred degrees. The overall trend for SOFC materials is to reduce their service temperature of electrolyte. Meanwhile, it is... 

Nanocars have been proposed to transport nanomaterials on the surface. Study of the mechanism of the motion of nanocars has attracted a lot of interests due to the potential ability of these nano-vehicles in the construction of nanostructures with bottom-up approach. Using molecular dynamics simulations, we study the motion of two nano-vehicles named “Nanocar” and “Nanotruck” on hexagonal boron-nitride monolayer. The obtained results reveals that, boron-nitride is an appropriate option to obtain higher mobility of nanocars compared with metal substrates. Considering different temperatures reveals that nanocars start to move on the BN at 200 K, while long range motions are observed at 400 K... 

Ultrathin MoS2-MoO3-x heterojunction nanosheets with unique features were introduced as biocompatible, non-cytotoxic, and visible light-sensitive stimulator layers for the controlled differentiation of human neural progenitor cells (hNPCs) into nervous lineages. hNPC differentiation was also investigated on reduced graphene oxide (rGO)-containing scaffolds, that is, rGO and rGO/MoS2-MoO3-x nanosheets. In darkness, hNPC differentiation into neurons increased on MoS2-MoO3-x by a factor of 2.7 due to the excellent biophysical cues and further increased on rGO/MoS2-MoO3-x by a factor of 4.4 due to a synergistic effect induced by the rGO. The MoO3-x domains with antioxidant activity and LSPR... 

Al2O3-SiC composite ceramics were prepared by pressureless sintering with and without the addition of MgO, TiO2 and Y2O3 as sintering aids. The effects of these compositional variables on final density and hardness were investigated. In the present article at first α-Al2O3 and β-SiC nano powders have been synthesized by sol-gel method separately by using AlCl 3, TEOS and saccharose as precursors. Pressureless sintering was carried out in nitrogen atmosphere at 1600 °C and 1630 °C. The addition of 5 vol.% SiC to Al2O3 hindered densification. In contrast, the addition of nano MgO and nano TiO2 to Al 2O3-5 vol.% SiC composites improved densification but Y2O3 did not have positive effect on... 

SiC Ceramic was joined to itself using active brazing alloys, like Ti in shape of sheet filler of Ag-cu and Ti-6AI-4V. This operation occurred in an inert gas furnace. Interfacial microstructure was studied with scanning electron microscopy and X-Ray diffraction. Variation of Electrical Specific Resistance measured by 4 pin astute multimeter and strength of these joints was measured by fracture shear loading. This joint happened at 900°C and upper temperature with 90 minutes and upper time. Electrical specific resistance goes up with the joint in low temperature and time but this variation is very little. The microstructure showed excellent bonding at the interfaces. The data showed also... 

Hydroxyapatite is the most important bio ceramic, due to its structure and chemical composition which is similar to bone. Since feeble fracture toughness, brittleness and low tensile strength have restricted their use, for overcoming this problem, they were often used as a secondary component. HAp-Al2O3 nano-composite powder combined the benefits of biocompatibility of HAp and high strength of Al2O3. When HAp-Al2O3 nano-composite powders were sintered at a higher temperature than 1100- 1200°C, HAp was decomposed and converted to the second phase of TCP, due to the formation of calcium aluminate increasing decomposition speed of HAp to TCP at higher degree than 1100-1200°C temperatures;... 

The original version of this article unfortunately contained a mistake. The presentation of Eq. 1,2, and 3 was incorrect.The correct versions are given below. The original article has been corrected. (Formula Presented.) (1) (Formula Presented.) (2) (Formula Presented.) (3). © 2018, Springer-Verlag GmbH Germany, part of Springer Nature  

In this study, PZT-PCN ceramic was made via sol–gel seeding method and effects of conventional sintering (CS) as well as two-step sintering (TSS) were investigated on microstructure, phase formation, density, dielectric and piezoelectric properties. First, high quality powder was achieved by seeding method in which the mixture of Co3O4 and Nb2O5 powder was added to the prepared PZT sol to form PZT-PCN gel. After drying and calcination, pyrochlore free PZT-PCN powder was synthesized. Second, CS and TSS were applied to achieve dense ceramic. The optimum temperature used for 2 h of conventional sintering was obtained at 1150 °C; finally, undesired ZrO2 phase formed in CS procedure was removed... 

The growing number of spine diseases and surgeries has resulted in advancements in equipment and implants. On the other hand, given the uniqueness of the anatomy of the spine, particularly in terms of mechanical characteristics, selecting the type of implant is critical. In addition to high biocompatibility and superelasticity, the implant utilized in the spine needs properties like strength, fatigue resistance, and elastic modulus close to the bone, which is found in nitinol. NiTi alloy lumbar-like samples were prepared by sintering and mechanical braiding method. The mechanical properties study revealed that the elastic modulus of the sample was 3.5 GPa, and the compressive strength at 6 %... 

Conductive self -electrical stimuli bioactive scaffolds could be used the potential for peripheral nerve regeneration with the maximum efficiency. To produce such conductive self-electrical stimuli bioactive scaffolds, chopped spun piezoelectric nanofibers of polyvinylidene fluoride/mesoporous silica nanoparticle (PVDF/MCM41) are prepared and incorporated in gellan/polyaniline/graphene (gellan/PAG) nanocomposites which have been previously prepared by incorporation of polyaniline/graphene (PAG) nanoparticles in gellan gel at 80 °C. Highly conductive binary doped polyaniline/graphene nanoparticles are prepared by chemical oxidative polymerization of aniline monomer using in-suite... 

Ceramic-matrix composites containing TiC-TiN have been used in a variety of application because of their superior properties such as high hardness, good wear resistance and high chemical stability. In this research, effect of coke and coke/calcium beds in synthesis of Al2O3-Ti(C, N) composites using alumino-carbothermic reduction ofTiO2 has been investigated. Al, TiO2 and active carbon with additives of extra carbon and NaCl and without additives, in separate procedures, have been mixed. Afterwards, mixtures were pressed and synthesized in 1200°C for 4hrs, in coke and coke/calcium beds, separately. Al2O3-Ti(C,N) composite was synthesized in ternary system of Al-TiO2-C with excess carbon and... 

In this paper, we present design and implementation of TCvisor, a new trusted hypervisor. To this end, TCvisor provides a secure storage with different isolated view per user by using para-passthrough and combined key. In this regard, virtualization technology of processors has been used for complete isolation from operating system. By combining TPM base key, user's password and geo function key, TCvisor provides a secure storage in an environment with split data. We have applied feature wise security analysis TCvisor's secure storage from software system layers point then we have compared performance of TCvisor to selected candidates of existing layers  

A new method for guiding the motion of fullerene and fullerene-based nanocars is introduced in this paper. The effects of non-flat substrates on the motion of C60, a nanocar and a nanotruck are investigated at different conditions and temperatures. Their behavior is studied using two different approaches: analyzing the variation in potential energy and conducting all-atom classical molecular dynamics simulations. This paper proposes that the use of a stepped substrate will make their motion more predictable and controllable. The results of the simulations show that C60 stays on the top side of the step and cannot jump over the step at temperatures of 400 K and lower. However, at temperatures... 

The rotational and translational motions of nanocars and nanotrucks as well as their motion regimes at different temperatures are investigated. In recent years, few similar types of molecular machines have been simulated. In contrast to previous studies, which have used the Rigid-Body Molecular Dynamics (RBMD) method, an all-atom model and classic atomistic dynamics have been employed in this paper to achieve better accuracy. Our results demonstrated that the exibility of the chassis and its attachment to the gold surface played an important role in the motion of a nanocar. In fact, a heavier and more exible nanocar chassis reduces its speed compared to a nanotruck. In addition, the results... 

Pharmaceutical drug Research and Development (R&D) outsourcing to contract research organizations (CROs) has experienced a significant growth in recent decades and the trend is expected to continue. A key question for CROs and firms in similar environments is which projects should be included in the firm's portfolio of projects. As a distinctive contribution to the literature this paper develops and evaluates a business support tool to help a CRO decide on clinical R&D project opportunities and revise its portfolio of R&D projects given the existing constraints, and financial and resource capabilities. A new mathematical programming model in the form of a capital budgeting problem is... 

In the present article, α-Al2O3 nano powder was synthesized by a simple aqueous sol-gel method by using AlCl3 as precursor. It was shown that the gel calcined at 1000°C, 1100 °Cand 1200 °Cresulted in the formation of a crystalline ?-Al2O3 nano powder. In continue TEOS and saccharose was used to prepare SiO2 xerogels containing carbon nano particles. The conversion of the gel to β-SiC nano powders was accomplished by carbothermal reduction at 1500°Cfor 1 h in argon atmosphere. In second pace alumina matrix composites with nano particles of 5 vol% SiC were prepared with the addition of TiO 2 as sintering aid and densified by pressureless sintering method at 1600°Cand 1630°C for 2 h in nitrogen... 

In this paper we have studied the motion of a nanocar and nanotruck on gold substrate using the classical molecular dynamics method. Analyzing the motion regime of the nanocar at different temperatures is one of the main goals of this paper. In the past years, similar molecules such as Trimmer, Z-car and nanotruck have been simulated by Konyukhov and Akimov. To increase the modeling accuracy in this paper we have used classical molecular dynamics contrary to previous works which used a rigid body molecular dynamics method. The result of our simulations were compared qualitatively to the experimental tests performed by Zhang et al. [12]. There was a good agreement between the results achieved... 

In the previous years, a few types of nanocars have been built with the promising potential to transport other molecules, to provide bottom-up assembly, or to perform other mechanical tasks. In this study, we propose a method to convert the diffusive displacement of nanocars to a guided motion in a desired path by adding some impurity atoms in the substrate. We investigated the motion of C60 as well as the nanotruck and the nanocar on a flat gold substrate containing silver contamination and conversely a silver substrate containing gold contamination at the different temperatures. The results showed that silver impurity on the gold substrate act as a repellent obstacle in the path of C60... 

In this research study, a comparative evaluation of the additional impact of nanometer-sized tetravalent oxides [Zirconia (ZrO2), Titania (TiO2), and Silica (SiO2)] on the properties and performance of Doloma-Magnesia (MgO-CaO) ceramic refractories, with an emphasis on their hydration resistance improvement, has been done. For this purpose, from 0 to 2.5 wt% ZrO2, TiO2, and SiO2 nanometer-sized particles have been added to the Doloma-Magnesia compositions. After formulation and mixing of the starting materials, the pressed samples (at 150 MPa) were tempered (at 250 °C for 12 h) and fired in a shuttle furnace (at 1650 °C for 3 h). The physical, mechanical, and thermo-mechanical properties of...