This study reports the behavior of the Ni20Cr alloy in molten nitrate salts. Its behavior was evaluated in the eutectic mixture called Solar Salt (binary salt) and in a ternary mixture (90% Solar Salt and 10% lanthanum nitrate). The addition of lanthanum nitrate was performed to determine if the presence of the La3+ cation could act as a corrosion inhibitor. Through mass loss and potentiodynamic polarization studies, the effects of both electrolytes on the corrosion resistance of the alloy at 300, 400, and 500 °C and at exposure times of 250, 500, 750, and 1000 h were determined. The results showed an increase in the corrosivity of the ternary salt, due to a decrease in its melting point and an increase in the concentration of nitrate ions. However, it was observed that the La3+ cations formed a protective layer (La2O3) on the alloy surface. In both corrosive media, the Ni20Cr alloy showed excellent corrosion resistance, due to its ability to form protective layers of Cr2O3, NiO, and NiCr2O4, in addition to the presence of a layer of La2O3 in the case of the ternary salt. 相似文献
This paper is concerned with the modeling of wheels within the framework of finite element-based dynamic analysis of nonlinear, flexible multibody systems. The overall approach to the modeling of wheels is broken into four distinct parts: a purely kinematic part describing the configuration of the wheel and contacting plane, a unilateral contact condition giving rise to a contact force, the friction forces associated with rolling and/or sliding, and a model of the deformations in the wheel tire. The formulation of these various aspects of the problem involves a combination of holonomic and non-holonomic constraints enforced via the Lagrange multiplier technique. This work is developed within the framework of energy-preserving and decaying time integration schemes that provide unconditional stability for nonlinear, flexible multibody systems involving wheels. Strategies for dealing with the transitions from rolling to sliding and vice-versa are discussed and are found to be more efficient than the use of a continuous friction law. Numerical examples are presented that demonstrate the efficiency and accuracy of the proposed approach. 相似文献
In areas that require high performance components, such as the automotive, aeronautics and aerospace industries, optimization of the dynamic behavior of structures is sought through different approaches, such as the design of materials specific to the application, for instance through structural topology optimization. The bi-directional evolutionary structural optimization (BESO) method, in particular, has been used for the simultaneous design of hierarchical structures, which means that the structural domain consists not only of the macrostructure but also of the microstructural topology of the materials employed. The purpose of this work is to apply the BESO method to solve two-dimensional multiscale problems in order to minimize the response of structures subjected to forced vibrations in a given frequency range. The homogenization method is applied to integrate the different scales of the problem. In particular, the material interpolation model for two materials is used. The BESO method is applied to different cases of optimization, in macroscale, microscale, and multiscale structural domains. Numerical examples are presented to validate the optimization and demonstrate the potential of this approach. The numerical examples show that the multiscale bi-material topology optimization method implemented here is able to produce structures and microstructures for optimization of the frequency domain response, satisfying prescribed volume constraints.
Morphoanatomical analysis of seeds contributes to knowledge of the development of seedlings and identification of species, as well as supporting conservation studies. The conservation of the species belonging to the Passiflora genus is crucial due to of the threats to the genetic resources of these species. Thus, the objective of this study was to morphoanatomically characterize Passiflora seeds, verify possible injuries to the tissues after cryopreservation and thus contribute to the conservation strategies of the species of this genus. Initially, seeds of Passiflora coccinea, P. edulis, P. gibertii, P. maliformis, P. morifolia, P. setacea, P. suberosa, and P. tenuifila collected from the Passion Fruit Active Germplasm Bank of the Embrapa Cassava and Fruits research unit (Embrapa Mandioca e Fruticultura) were analyzed. Then, their length, width and thickness, shape of the base and tip, and ornamentations present on the body and edge of the seeds were evaluated. The seeds of the species were placed in cryotubes and immersed in liquid nitrogen to assess possible cryoinjuries. The tegument and tissues of the seeds were examined by scanning electron microscopy. The seeds had varied biometric data, with average values of 4.63 mm for length, 3.28 mm for width, and 1.51 mm for thickness. Six ornamentation types were observed: reticulate for the species P. coccinea; finely reticulate for P. edulis; foveolate reticulate for P. gibertii and P. setacea; alveolate reticulate for P. maliformis and P. tenuifila; coarsely reticulate for P. morifolia; and falsifoveolate reticulate for P. suberosa. Some seeds suffered tegument cracks due to the freezing in liquid nitrogen, but without physiological damages to the embryo and endosperm. The cryopreservation of the seeds in the presence of the tegument significantly reduced the cryoinjuries caused to the embryo. Cryopreservation can be promising for long-term conservation of passion fruit seeds. 相似文献
Video content consumption is currently dominating the mix of traffic observed in Internet service provider (ISP) networks. The distribution of that content is usually performed by means of content delivery network (CDN) caches storing and delivering multimedia. The advent of virtualization is calling attention to the CDN providers as a use case for virtualizing the cache function. In parallel, there is a trend for sharing network infrastructures as a way of reducing deployment costs by ISPs. Then, an interesting scenario emerges when considering the possibility of sharing virtualized cache functions among ISPs which are sharing a common physical infrastructure, mostly considering that those ISPs offer similar video content catalogs to end users. Furthermore, when deciding to share the caches among ISPs, it is interesting to understand the impacts due to limiting the storage capacity at the edge sites. This paper investigates through simulations the potential efficiencies that can be achieved when sharing a virtual cache function if compared with the classical approach of independent virtual caches operated per ISP, as well as the implications of limiting the storage capacity of the caches at the edge. 相似文献
Undoubtedly, Industry 4.0 in the energy sector improves the conditions for automation, generation and distribution of energy, increasing the rate of electric vehicle manufacturing in recent years. As a result, more grid-connected charging infrastructures are being installed, whose charging stations (CSs) can follow standardized architectures, such as the one proposed by the open charge point protocol (OCPP). The most recent version of this protocol is v.2.0.1, which includes new security measures at device and communication level to cover those security issues identified in previous versions. Therefore, this paper analyzes OCPP-v2.0.1 to determine whether the new functions may still be susceptible to specific cyber and physical threats, and especially when CSs may be connected to microgrids. To formalize the study, we first adapted the well-known threat analysis methodology, STRIDE, to identify and classify threats in terms of control and energy, and subsequently we combine it with DREAD for risk assessment. The analyses indicate that, although OCPP-v2.0.1 has evolved, potential security risks still remain, requiring greater protection in the future.
Currently, biodiesel is pointed out worldwide as the main alternative in the complementation and substitution of petrochemical diesel. However, the current industrial route of synthesis of this biofuel depends on the cost of raw materials (which are also destined for food purposes) and the expense of the production process. Aiming to remedy this obstacle, the use of solid, sustainable, low-cost, efficient, and reusable catalysts in residual raw materials, such as waste cooking oils, has been highlighted as a promising alternative. This work focused on studying the influence of the glycerin content used in the preparation by wet impregnation of catalyst calcium diglyceroxide in the efficiency of transesterification of waste cooking oil. The catalyst was synthesized from CaO from chicken eggshell, raw glycerin co-product from biodiesel, and methanol. The transesterification reactions were performed using 120 g of frying residual oil, methanol: oil molar rate of 6:1, constant shaking, and reaction temperature of 63 ± 1°C for 180 min. The catalyst material synthesized with residual glycerin was active for four reactions (without reactivation of its sites) with high percentages of efficiency of 96.13, 96.85, 95.93, and 91.65, respectively. It was noted that the glycerol purity correlated with changes in the structural morphology of the final compound, as well as changes in the leaching rate, acidity index, water content, and ester content of the blends. It was found that adding 15% water to the lipid material correlated with an increase in ester content (99%) in the synthesized biodiesel. 相似文献
In this paper, a novel approach to train control systems based on virtual coupling is presented. Virtual coupling is a concept that has evolved from platooning of vehicles and allows to reduce the distance and headway between trains without constructing new lines while ensuring safe operation. With this objective in mind, we propose a decentralized robust model predictive control (MPC) framework for a virtually coupled train set based on a min–max approach. Unlike the nominal MPC, robust MPC is designed to consider external undetermined disturbances and errors to improve robustness in real-world applications. Therefore, in this study, we present the formulation of a robust MPC based on solving a finite-horizon optimization problem with bounded uncertainties. The bounds consider resistive modeling errors, positioning errors, communication delays, and a possible adhesion loss of up to 10%. We then performed four simulations to compare the behavior of the robust MPC with the equivalent nominal MPC. In these simulations, we simulated a metro line, main line, and high-speed line. The simulations also analyzed the behavior of the robust MPC under the considered perturbations and different communication delays. The results show that the robust MPC ensures safer operation than nominal MPC in subways, conventional lines, and high-speed lines. Future research can focus on centralized MPC and artificial intelligence. 相似文献