Sharif Digital Repository

Despite brilliant properties of glass ionomer cement (GIC), its weak mechanical property poses an obstacle for its use in medical applications. The present research aims to formulate hydroxyapatite/yttria-stabilized zirconia (HA/YSZ) in the composition of GIC to enhance mechanical properties and to improve fluoride release of GIC. HA/YSZ was synthesized via a sol-gel method and characterized by applying X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photo-emission spectroscopy (XPS) and simultaneous thermal analysis (STA) along with transmission electron microscopy (TEM) methods. The synthesized nanocomposite was mixed with GIC at a fixed composition of 5.... 

In this paper the projected gradient method is applied as an effective gradient-based topology optimization algorithm in order to direct energy propagation through the desired region of composites microstructure. Rayleigh Damping model is also used in order to take the effect of internal damping mechanisms into account and thus, to fill in the gap between the designed layouts and those in reality. The success of the proposed algorithm is illustrated through several numerical experiments by revealing a set of various designed optimal layouts besides their corresponding energy distributions  

In this work, the evolution of the local structure in Cu50-Zr50 bulk metallic glass during glass formation was studied by molecular dynamics simulation. The pair distribution function and Voronoi analysis were adopted to characterize local structures in this alloy. The stability of icosahedral clusters and the role of other local clusters in the formation of icosahedra were evaluated. It was found that the (0,2,8,2) polyhedron is not only the dominant cluster in this alloy, but also the most prone cluster to convert into an icosahedron in the course of cooling. Moreover, it acts as an intermediate state during the icosahedron formation. The onset of stability of icosahedra emerges at the... 

The effect of temperature on the short-range order (SRO) structures, deformation mechanisms and failure modes of metallic glasses (MGs) is of fundamental importance for their practical applications. However, due to lack of direct structural information at the atomistic level from experiments and the absence of previous molecular dynamics (MD) simulations to reproduce experimental observations over a wide range of temperature, this issue has not been well understood. Here, by carefully constructing the atomistic models of Cu64Zr36 and Fe80W20 MGs, we are able to reproduce the major deformation modes observed experimentally, i.e. single shear banding (SB) at low temperatures, multiple... 

Background/Objectives: In this paper by utilizing frequency tracking electrical loads are shared on voltage source converters and then by applying a proposed-supplementary control system, frequency changes during changing electrical loads inside network is omitted. Methods/Statistical Analysis: Using decentralized control in Microgrids and sharing loads on power generation units respect to their nominal capacity are unavoidable approaches to have stable and operational network. Droop control in load sharing is known as practical and significant solution. In droop control, units output frequency, changes proportional to output active power that is not preferable. Simulation results in PSCAD... 

In this work, the evolution of the local structure in Cu50–Zr50 bulk metallic glass during glass formation was studied by molecular dynamics simulation. The pair distribution function and Voronoi analysis were adopted to characterize local structures in this alloy. The stability of icosahedral clusters and the role of other local clusters in the formation of icosahedra were evaluated. It was found that the (0,2,8,2) polyhedron is not only the dominant cluster in this alloy, but also the most prone cluster to convert into an icosahedron in the course of cooling. Moreover, it acts as an intermediate state during the icosahedron formation. The onset of stability of icosahedra emerges at the... 

Interface engineering of solar cell device is a prominent strategy to improve the device performance. Herein, we synthesize reduced-graphene scaffold (rGS) by using a new and simple chemical approach. In this regard, we synthesize a hollow structure of graphene and then fabricate a three-dimensional scaffold of graphene with a superior surface area using electrophoretic process. We employ this scaffold as an interface layer between the electron transfer and absorber layers in perovskite solar cell. The characterization tests and photovoltaic results show that rGS improves the carrier transportation, yielding a 27% improvement in device performance as compared to conventional device. Finally,... 

Fabrication of organohalide perovskite materials on the top of ZnO nanoparticles (NPs) has some beneficial advantages such as room temperature processing; however, the perovskite is not stable on ZnO NPs layer during the annealing process. In fact, there are only a few reports about the fabrication of perovskite solar cells on ZnO NPs layer. Herein, the decomposition mechanism of CH3NH3PbI3 perovskite materials on ZnO is reported, and it is found that the perovskite film on the top of the ZnO layer is converted into PbI2 during the annealing process due to the existence of hydroxide groups on the surface of the ZnO NPs. Depending on the annealing temperature, the reaction rate and the... 

The atomic structure of metallic glasses (MGs) plays an important role in their physical and mechanical properties. Numerous molecular dynamics (MD) simulations have been performed to reveal the structure of MGs at the atomic scale. However, the cooling rates utilized in most of the MD simulations (usually on the order of 109-1012 K/s) are too high to allow the structure to relax into the actual structures. In this study, we performed long-term pressurized sub-Tg annealing for up to 1 μs using MD simulation to systematically study the structure evolution of Cu50Zr50 MG. We find that from relaxation to rejuvenation, structural excitation of MGs and transition during sub-Tg annealing depend on... 

In this work, the effect of strain rate on the ductility, intermediate temperature brittleness and fracture surface of Zr-based BMG over a wide range of temperatures from 0.1 Tg to near Tg, has been systematically investigated. The results showed two remarkable ductile to brittle transition at low cryogenic and intermediate temperatures. At low temperatures, below 0.4 Tg, the activation of diffusion mediated phenomena is negligible and the combined effects of strain rate and temperature contribute to the plasticity of material by changing the STZ volume, hence the possibility of forming multiple shear bands. At the temperature range from 0.4 Tg to the temperature at which the intermediate... 

Self-expandable stents are widely used to restore blood flow in a diseased artery segment by keeping the artery open after angioplasty. Despite the prevalent use of conventional crystalline metallic alloys, for example, nitinol, to construct self-expandable stents, new biomaterials such as bulk metallic glasses (BMGs) are being actively pursued to improve stent performance. Here, we conducted a series of analyses including finite element analysis and molecular dynamics simulations to investigate the feasibility of using a prototypical Zr-based BMG for self-expandable stent applications. We model stent crimping of several designs for different percutaneous applications. Our results indicate... 

In this work, a novel and facile synthesis process to fabricate single crystalline organometal halide perovskite nanowires has been successfully developed. Nanowires were grown in a high density ordered array from metal nanoclusters inside anodic aluminum oxide templates using a non-catalytic chemical vapor deposition method. Specifically, perovskite NWs were grown as a result of the reaction between methylammonium iodide (MAI) and the Pb/Sn (Pb or Sn) metal in anodic aluminum oxide templates under optimal conditions. The characterization results show that there is a reaction zone at the interface between the perovskite material and metal, at the bottom of the anodic aluminum oxide... 

This paper presents solid-state ligand exchange of spin-coated colloidal lead sulfide quantum dot (PbS QD) films by methylammonium iodide (MAI) and integration of them in depleted heterojunction solar (DHS) devices having an antireflecting (AR) nanocone plastic structure. Time-resolved photoluminescence measurements determine a shorter lifetime of the charge carries on a semiconductor (TiO2) electron transfer layer for the MAI-passivated QD films as compared with those with long-chain aliphatic or short thiol ligands. Consequently, the DHS device yields improved power conversion efficiency (>125%) relative to oleic-acid-passivated PbS QD films. Using anodized aluminum oxide templates, an... 

Previous studies have shown that a small variation in the chemical composition of metallic glasses (MGs) can drastically alter their strength and ductility. However, the underlying structural origin and atomistic mechanisms remain unclear. Using large-scale molecular dynamics simulations, we studied the effect of chemical composition and affinity on the microstructure and deformation behaviour of Zr50Ni50 − xAlx MG by varying the value of x in the range of 5 ≤ x ≤ 25 (at.%). We show that an increase in x is able to strengthen and embrittle the material. In particular, a ductile (homogeneous deformation) to brittle (shear banding) transition occurs at x ~ 15. To reveal the structural origin,... 

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... 

According to recent studies, Cu–Zr and Ni–Zr binary alloying systems are very similar based on known glass-forming ability criteria, however, they exhibit significant difference in glass-forming ability in practice. In this work, local atomic structures of Cu–Zr and Ni–Zr metallic glasses are studied by molecular dynamics simulation to explain the source of mentioned difference. The total and partial distribution functions, coordination number and voronoi analysis are utilized to characterize the local atomic structures around Zr, Ni and Cu atoms. It was found that the local environment around Zr atoms is almost similar in both systems. The difference in the atomic structure in these systems... 

In the present work, the mechanical properties, in particular, the Poisson's ratio of four two-dimensional silica structures, called here α,β,γ and δ are studied by means of molecular dynamics simulations. The α structure has been synthesized experimentally and the others have been reported as the most stable low-energy structures that reveal in-plane negative Poisson's ratio based on the first principles calculations. Among these structures, β-silica exhibits the largest in-plane negative Poisson's ratio which is 2–4 times higher than penta-graphene. Our results illustrate that the classical molecular dynamics simulation reproduces results in agreement with those of the first principles... 

The improvement of the quality of the hole transporting layer (HTL) plays a key role in the fabrication of highly efficient and stable perovskite solar cells (PSCs). Here, we used rubrene as a surface treatment agent on top of a spiro HTL. We found that rubrene can cover the pinholes of the spiro layer and provide an excellent contact layer for planar PSCs. Based on this modification, mobile gold ions from the metal electrode are prevented from diffusing through the HTL hindering the degradation of PSCs. The optimized device shows a maximum power conversion efficiency (PCE) of 19.87% and a 79% fill factor (FF), which are higher than the 17.98% PCE and 72% FF of the reference device. In... 

Interfacial studies and band alignment engineering on the electron transport layer (ETL) play a key role for fabrication of high-performance perovskite solar cells (PSCs). Here, an amorphous layer of SnO2 (a-SnO2) between the TiO2 ETL and the perovskite absorber is inserted and the charge transport properties of the device are studied. The double-layer structure of TiO2 compact layer (c-TiO2) and a-SnO2 ETL leads to modification of interface energetics, resulting in improved charge collection and decreased carrier recombination in PSCs. The optimized device based on a-SnO2/c-TiO2 ETL shows a maximum power conversion efficiency (PCE) of 21.4% as compared to 19.33% for c-TiO2 based device.... 

According to previous studies on the fracture surface morphologies of bulk metallic glasses, the stable crack growth region width and vein pattern size increase with the plasticity at room temperature. In the present work, the fracture surface morphologies of Ti- and Zr-based bulk metallic glasses bent over a wide temperature range (0.1–0.8 glass transition temperature) are systematically analyzed. According to our finding, the stable crack growth region width increases while the vein pattern size decreases as the ductility improves by varying temperature. This observation is in contrast to the common thought that the ductility is proportional to the stable crack growth region width and vein...