Sharif Digital Repository

The effects of SiO 2 and K 2O were investigated on the glass forming ability (GFA) and structural characteristics of CaOTiO 2P 2O 5 system. Differential thermal analyzer (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), FT-IR and 31P magic angle spinning NMR methods were applied for characterizations of the system. Unwanted crystallization in the initial three components base glass composition was observed by adding SiO 2 and crystalline phases such as TiP 2O 7, rutile (TiO 2) and cristobalite (SiO 2) were formed in it. The results showed that K 2O prevents crystallization of glasses and promotes the formation of glass. FT-IR and X-ray diffraction showed that the addition... 

Glass-ceramic composites in the SiO2-CaO-MgO-(Na2O) system, reinforced with 5, 10 and 20 wt.% aluminum titanate were synthesized by pressureless sintering. Optimum sintering temperatures with maximum relative density were determined for each composition. The composites were fired above the crystallization peak temperature of glass-ceramic. Mechanical properties of glass-ceramic and sintered composites, such as fracture toughness, flexural strength and Vickers microhardness, were investigated. The sintered composites were characterized by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD). The results showed that the composite containing 10... 

A novel electrochemical sensor for clonazepam (CLNP) was fabricated based on immobilizing cellulose nanofibers/carbon nanoparticles (CNFs/CNPs) nanocomposite on glassy carbon electrode (CNFs/CNPs/GCE). The combination of CNFs and CNPs produced a novel kind of structurally uniform and electro-analytically active nanocomposite. The surface morphology of CNFs/CNPs layer deposited onto glassy carbon electrode was characterized by scanning electron microscopy. The results of the voltammetric investigations showed a considerable enhancement in the cathodic peak current of CLNP (up to 60 times) on the surface of CNFs/CNPs/GCE relative to the bare GCE. Under the optimal conditions, the modified... 

Both natural montmorilonite (CN) and organically modified montmorilonite (CB) improved significantly the mechanical performance of novolac phenolic resin (PF)/woven glass-fiber (GF) composites due to their nanodispersion and good interfacial interaction with the matrix. It was revealed that the incorporation of 2.5 wt% of the clays enhances the elastic modulus up to 38% for CN and 43% for CB. Aging of PF/GF composites at various aqueous solutions, i.e. water, brine and acidic environments, increased stiffness of the composite (∼100-250% increase in elastic modulus) due to possible secondary crosslinking caused by water molecules and hydroxyl groups of PF resin. However, aging led to the... 

For the first time graphene nanosheets and carbon nanospheres/chitosan (GNS-CNS/CS) based nanocomposite film modified electrode was used for the electro-oxidation of mebendazole (MD). MD is a benzimidazole drug that is used to treat human infections caused by parasitic worms. MD causes slow immobilization and death of the worms by selectively and irreversibly blocking uptake of glucose. The electrochemical behavior of MD at GNS-CNS/CS modified glassy carbon electrode has been investigated using cyclic and differential pulse voltammetry in aqueous media at different pHs. The prepared electrode showed an excellent electrochemical activity toward the electro-oxidation of MD leading to a... 

In this work, a series of solvent- and water-injection scenarios were conducted on horizontal five-spot glass micromodels that were saturated initially with heavy oil. Sandstone and limestone rock look-alike and network patterns with different pore structures were used in the experiments. The results show that the ultimate oil recovery of a water-alternating-solvent (WAS) scheme was greater than that of a simultaneously water-alternating-solvent (SWAS) scheme, and the efficiency of a solvent-soak scheme also offers a greater recovery. Likewise, the WAS scheme resulted in greater oil recovery when compared with continuous solvent injection (CSI), with the same amount of solvent consumption.... 

This work presents results from two sets of experiments conducted to study, in pore level, the role of fracture aperture and tilt angle on the stability of liquid bridges and the shape of a front during free gravity drainage process. Glass micromodels of two different aperture sizes were used to monitor the mechanism of gravity drainage of air-crude oil system, rotating around a bottom corner to create different tilting angles. Oil content within the matrix blocks was determined as a function of time using a series of images obtained during the experiments, from which net drainage rate from the upper and lower matrix blocks is calculated. Liquid bridges are more frequent but less stable at... 

As a selective estrogen receptor modulator, raloxifene (RXF) prevent of osteoporosis in postmenopausal women by estrogenic actions on bone and decreases the risk of invasive breast cancer by anti-estrogenic actions on the breast and uterus tissue. However, RXF may increase the risk of blood clots, including deep vein thrombosis and pulmonary embolism. For the first time glassy carbon electrode modified with a thin film of melamine/carbon nanoparticles (CNPs/Mela) was constructed and used for the sensitive voltammetric determination of RXF. In comparison with unmodified electrode, the presence of the CNPs/Mela film resulted in a remarkable increase in the peak currents and sharpness of the... 

Finemet soft magnetic alloy has been in the focus of interest in the last years due to its high saturation magnetization, high permeability and low core loss. The great quantity of papers has been devoted to the study of its structural and magnetic properties, confirms this claim. This paper reviews the different researches performed on Finemet up to now. The criteria that should be satisfied in order to have the high glass forming ability in an alloy and also the techniques applied for production of Finemet ribbons, powders and bulk samples have been explained. In addition, the mechanism of devitrification, nanocrystallization and magnetic softness in this applicable magnetic alloy has been... 

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... 

Bond durability of FRP bars and concrete is an important issue to the overall integrity and long-term performance of a strengthening structure. This paper examines the bond durability of GFRP bars embedded in different types of concrete (Normal, self-compacting, light weight, and high strength) exposed to aggressive environments, namely, sea water, alkaline, and acid. A total of 132 specimens were tested in direct pull-out. The development lengths of both control and conditioned specimens were obtained and compared to the current standards. The results revealed bond strength reductions of 0–21% for the light weight, 1–16% for the normal, 5–9% for the high strength, and 4–12% for the... 

In the present study, a 3D porous graphene-carbon nanotube (G-CNT) network is successfully constructed on the surface of glassy carbon electrode (GCE) by electrochemical co-deposition from a concentrated graphene dispersion. The large accessible surface area provided by the interpenetrated graphene backbone in one hand and the enhanced electrical conductivity of the 3D network by incorporating CNTs on the other hand, dramatically improved the electrochemical performance of GCE in determination of Methotrexate (MTX) as an important electroactive drug compound. Under the optimum conditions, the electrode modification led to a significant increase in the anodic peak current (∼25 times) along... 

A side coupled integrated spaced sequence (SCISSOR) of Silicon or Chalcogenide glass microrings of different diameter are considered as a wide-band Raman amplifier. Because the two-photon absorption (TPA) losses in Chalcogenide glass are less than that of Silicon, it is shown that Chalcogenide microrings are suitable for wide-band Raman amplifier in the telecommunication bandwidth (1.5 μm). The Lagrange unknown multiplier method is employed to minimize the gain ripple of the amplifier versus the pump and system parameters. Crown Copyright © 2008  

In this work, the magnetic and transport properties of micro and nanometer-sized samples of La0.9Ba0.1MnO3 manganite have been studied. The temperature variation of ac susceptibility of the nanometer-sized sample shows one transition at high temperature (265 K). On the contrary, the ac susceptibility of the micrometer-sized sample shows two transitions with a high-temperature transition occurring at 240 K and low-temperature transition around 100 K. The high-temperature transition corresponds to the paramagnetic-ferromagnetic (PM–FM) transition (Tc) and is independent of frequency, while the low-temperature transition is frequency-dependent and shifts toward high temperatures by increasing... 

In this paper, the interaction between various window specifications and different climate conditions is investigated. For this purpose, simultaneous effects of several aspects including glazing system, glass type, filling gas, glass thickness, window frame fraction, and interior shading are considered under three different climatic conditions. To evaluate the energy performance of various considered alternatives, the energy simulation of a base case building is evaluated in a computer environment. Using the validated model, the energy analysis is quantitatively performed, and cost-benefit analyses from the viewpoints of both residents and government are carried out based on the domestic and... 

This study addresses the issue of using recycled materials to obtain low-cost structural products for practical applications. Through the use and re-extrusion of virgin high-density polyethylene (HDPE), the effects of the degradation level of HDPE as a matrix phase on its mechanical properties and the mechanical performance of composites produced with the degraded polyethylene have been examined. The degradation level of HDPE caused by reextrusion has been evaluated by the measurement of the melt flow index and mechanical properties of virgin and degraded HDPEs. The results indicate that the modulus and strength of HDPE significantly increase with the addition of polypropylene filled with 30...