Papers by Keyword: Stability

Abstract: As a drug product for vitreous replacement, the stability of polydimethylsiloxane (PDMS) during storage is very necessary. PDMS must be stable both chemically and physically during the storage process according to WHO standards. This is necessary to maintain security and regulate the drug supply. Our research shows that low-and medium-viscosity PDMS produced from low-grade octamethylcyclotetrasiloxane (D4) monomer have good stability and storage for 15 months. The optimal time for stability and storage of this PDMS is 5 months. Changes in viscosity values occur due to a very slow chain growth from 5 until 15 months. However, a longer assessment time and other tests are needed to complete the material stability information.

Abstract: The stability of dispersed nanoparticles in the base fluid has always been one of the most important challenges in using nanofluids as a coolant in heat transfer applications in different industries such as modern electronic equipment, heat exchangers, solar technologies, etc. In the present study, the dynamic light scattering (DLS) method is used to obtain the particle size distribution of Al₂O₃-ZnO dispersed in DI water. After adjusting the optical arrangement and designing the DLS setup, the correlation curves are plotted by analyzing the detected signals of the experiments. Then, a decay rate is derived by fitting an exponential function to the correlation curve to get the particle size distribution by using the Stoke-Einstein equation. In order to investigate the stability of Al₂O₃-ZnO water-based nanofluid, the particle size distribution profiles are studied several times. In addition, the stability of Al₂O₃-ZnO-CNT hybrid nanofluid is followed by absorbance measurements using a UV-Vis spectrophotometer. Moreover, the thermal conductivity coefficient and electrical conductivity of the Al₂O₃-ZnO hybrid nanofluid with and without CNT particles are determined by utilizing KD2 Pro and PCT-407 devices, respectively. The results showed that the peak in the particle size distribution curve for Al₂O₃-ZnO hybrid nanofluid shifted from 476 nm to 128 nm after 5 days. Furthermore, the inclusion of carbon nanotubes increased the stability of zinc oxide particles in the nanofluid. In addition, by adding carbon nanotubes in a ratio of 1:1:0.5 to Al₂O₃-ZnO nanofluid and forming 0.05 wt.% hybrid nanofluid, the thermal conductivity coefficient was enhanced by 30% in comparison with deionized water, while a 0.05 wt.% hybrid nanofluid without CNT particles improved the thermal conductivity by 19%. Although the electrical conductivity increased by adding nanoparticles to the base fluid, it didn’t change significantly for nanofluids containing CNTs compared to nanofluids without CNT particles.

Abstract: Reduced glutathione (GSH) is incorporated in polymeric wound dressings to prevent oxidative stress-induced cellular damage and the development of chronic wounds. The present study investigates the influence of polyvinyl alcohol (PVA), polyethylene oxide (PEO), and PVA/PEO blend polymeric solutions on the stability of GSH during the preparations or storage. The stability was studied in three concentrations which were 3%, 5% and 8%, after sometimes between 0 to 7 days. The level of GSH achieved the highest electron donor activity at day 7 in 8% PVA/PEO (95.42%) and 8% PVA (94.27%) solutions, whereas GSH activity decreased when incorporated with PEO solutions. Such a decrease in the GSH activity due to PEO being less water-resistant and hydrolytic degradation susceptibility could expose the GSH to an aqueous environment and lead to the loss of GSH activity. In conclusion, a higher concentration of polymer and less-water resistant polymers can shield the GSH from an aqueous environment and maintain its stability in the polymer solutions used in wound dressing applications.

Abstract: The article is devoted to the description of analytical and structural methods used in the design to avoid progressive collapse of buildings and structures in the case of extreme influences. Three directions are described to avoid the process of development of local to global destruction. The concept realized in the LIRA-SAPR software, which is aimed at automating analysis for progressive collapse in quasi-static and dynamic formulations, including linear and nonlinear analysis taking into account the dynamic factor, is also substantiated. The purpose of the analysis is to design structures for various purposes, which in addition to accident-free performance of functions during the specified period of operation, in case of an accident due to natural and man-made phenomena (defects in production technology, explosions, impacts), as well as other causes not provided for by the conditions of normal operation, would cause minimal damage to people and the environment.

Abstract: In this paper, BaO-ZnO-TiO₂-SiO₂ is used as the research system of high refractive index glass, and IR, XRD and DTA are used to study the structure, thermal behavior, crystallization and chemical stability of different glasses when Al₂O₃ gradually replaces CaO. The results show that when Al₂O₃ replaces CaO, the glass still has an amorphous structure. With the increase of Al₂O₃ content, the glass structure first becomes tight, and then due to the formation of [AlO₆], the glass network becomes loose, and the glass density peaks with the increase of Al₂O₃ content. DTA analysis showed that with the increase of Al₂O₃ content, the devitrification trend of the glass increased during the cooling process, the crystallization peak moved to the low temperature direction, and the exothermic effect weakened, indicating that the surface crystallization trend of the glass increased and the overall crystallization became weaker. The results show that the density, refractive index and water resistance of glass microspheres containing only CaO are the best, but the crystallization of glass is obvious during heat treatment.

Abstract: The electrolytic production of aluminium starts after the completion of the cathode lining and the baking process. After that, the cell start-up period is followed by the early operating period. During the early operating period, the following parameters (cell voltage, metal height, electrolyte height, cryolite ratio, electrolyte temperature, and ledge formation) were measured and investigated. The required times for these parameters to reach the steady-state have been investigated. The cell voltage, metal height, electrolyte height, cryolite ratio, and electrolyte temperature were stabilized after 35, 25, 24, 86, and 45 days, respectively from cell start-up. These cells took four months to form a stable ledge at a thickness of 10 cm. Also, the thermal behavior of the sidewall carbon blocks was studied during the early operating period by inserting twenty thermocouples at these locations in three prebaked cells. The cell instability during the early operation period for these cells was illustrated.

Abstract: The size-dependent bending and static stability characteristics of nanobeams made of bi-directional functionally graded materials (2D-FGMs) under different boundary conditions are comprehensively investigated. Based on the modified couple stress theory and surface elasticity theory, the size-dependent model is formulated for 2D-FG Euler-Bernoulli beam. The material properties of the beam smoothly change along both the axial and thickness directions according to power-law distribution. The continuous spatial variations of the single material length scale parameter and the three surface constants are incorporated to describe the effects of microstructure and surface energy, respectively. This model accounts for the axial and transverse displacements, the exact position of the physical neutral plane, and Poisson’s effect. To obtain the static response of the present model, Ritz method is employed by approximating the axial and transverse displacements in terms of polynomial forms. Different boundary conditions, i.e., Simply-simply (S-S), Clamped-clamped (C-C), Clamped-simply (C-S), and Clamped-free (C-F), are considered and satisfied by adding auxiliary functions to the displacement functions. Numerical results with various cases of boundary conditions are performed with an insight to explore the effects of gradient indices in thickness and length directions, surface energy, material length scale parameter, slenderness ratio, and thickness on the static deflection and buckling responses of 2D-FG nanobeams. Results disclose that, the material properties, the surface energy, and microstructure effects have a significant effect on the bending, and buckling responses of 2D-FG nanobeams. Hence, this study can be helpful in the design and optimization of 2D-FG nanobeams in bending and buckling responses.

Abstract: One of the most common asphalt concrete pavement distresses is low temperature cracking, also known as thermal cracking. Characterizations of low temperature cracking and formulation for pavement design have taken a lot of effort. Asphalt binder has viscoelastic behaviour, so asphalt mixture behaviour changes as the temperature changes. At high and low temperatures, the asphalt binder shows viscoelastic plastic behaviour and elastic behaviour. Low temperature cracks that grow day by day due to the movement of vehicles are the most significant pavement cracks caused by cold climates. It needs early and premature repairs to build and expand low temperature cracks. The aim of this research is to perform Low Temperature Cracking analysis of asphalt materials (laboratory and analytical assessment), in light of the latest update of binder cracking temperature. The role of basic material properties in low-temperature cracking was studied in this work. As a result, statistical analysis in the cohesive failure condition revealed that the asphalt mixture aggregate's free energy was ineffective in this cohesion failure. Fly ash had been used in the other type of asphalt mixture. It was proven that the addition of fly ash as an additive can improves the low temperature resistance of the asphalt mix. The binder with 60/70 penetration grade was used. The different amount of fly ash (0%, 1%, 3% and 5%) was added to the asphalt mixture. Marshall Stability and flow, resilient modulus and dynamic creep were carried out to investigate the mechanisms of cracking at low temperature. From the results obtained, there are significant effect comes from the addition of the fly ash. The result show that the addition of 5% fly ash produce the best outcomes for the density, stability, stiffness, resilient modulus and dynamic creep. Thus, it can conclude that the existence of fly ash in the mixture is able to enhance the mechanical performance of the AC14 dense-graded asphalt.

Abstract: Due to its rough surface texture, Stone Mastic Asphalt (SMA) can create great qualities, such as good skid resistance and better visibility during rainy days, as well as optimal light reflection. The service life of SMA, on the other hand, reduces owing to a rapid increase in traffic loads, heavy traffic, and environmental conditions. TiO₂'s stable qualities and optimal content can help to improve the performance of modified asphalt at a reasonable cost and with low filler content. This study explores the effect of nano titanium on the performance of stone mastic asphalt. Virgin bitumen is modified with 2% and 4% of nano titanium by bitumen weight. The physical properties of the bitumen are accessed by carrying tests such as penetration tests, softening points, and ductility. The results show that the modified bitumen samples of 2% Nano-TiO2 powder content for bituminous tests have enhanced hardness, consistency, and ductility. While for the performance tests for the SMA samples are abrasion, Marshall stability, resilient modulus, and dynamic creep. Overall, 2% Nano-TiO₂ powder content has been determined for the optimum content and best performance, where it provides high stability, strength and enhances stiffness effectiveness, which can improve SMA performance. However, the findings show lack of awareness and research is a factor that does not receive special consideration from the industry or the government. Therefore, the sharing of ideas and technology for each continuous research is needed to improve construction quality.

Abstract: The paper considers principles of creating promising memristive structures based on composite oxides with agglomerates of nanoparticles. The proposed functional nanomaterial is promising for the formation of a composite structure of a memristor, consisting of two electrodes based on one or more nanoscale layers of metal oxides, which are separated by an active medium so that an insulating layer is applied between the electrodes at the periphery of the active medium region. A conductive layer is formed on top of the insulating layer, which is connected to the negative rail, which prevents leakage of negative oxygen ions through the insulating layer. The authors considered in detail technological process of integral production, which forms the necessary vertical profile of the memristive structure ensuring its greatest stability and repeatability of parameters. The implementation of a hardware-software complex for monitoring and diagnosing a memristive structure is proposed. As a result of the research, an original technical solution was created, which ensures formation of memristive structures with a high efficiency of impact on negative oxygen ions, which are charge carriers in this structure, which ensures their high productivity and stability of parameters.