Stress effects on stability and diffusion behavior of sulfur impurity in nickel: A first-principles study

A systematic investigation regarding the effect of stress on the stability and diffusion behavior of S impurity in Ni was carried out via first-principles methods. A comparison of the formation energy of S in Ni indicated that S more easily forms as a solution atom with increasing S concentration in Ni supercells, but the binding energy showed that as the concentration of S that dissolved into Ni increased, the structure became less stable. The diffusion barrier via the octahedral-tetrahedral-octahedral site path was always lower than that via the octahedral-octahedral site path. The diffusion barrier of single S decreased with increase in tensile stress. S diffusion accelerated under applied tensile stress, which was disadvantageous in suppressing S retention in Ni. These results implied that even at a low concentration, dissolved S still had a tendency of precipitating from the Ni matrix, to further increase the stability of the system. (C) 2014 Elsevier B. V. All rights reserved

Transport Processes in Hydrating Cementitious Coating Systems

Concrete is currently the most widely used material in construction field. A good performance of concrete structures is required for reaching the designed service life. However, the initial scatter in the quality of concrete is unavoidable in practice, possibly resulting from improper design, poor execution, or deterioration due to stresses during the service life of concrete structures (e.g. external load, stress induced by temperature, drying shrinkage or ingress of chemical substances, etc.). A cementitious coating can be used to protect low quality concrete structures against the ingress of aggressive substances, like CO2 and chloride ions, and to extend the service life of the reinforced concrete structures.Materials and Environmen

Inorganic powder encapsulated in brittle polymer particles for self-healing cement-based materials

Many types of healing agents have been investigated. These agents are processed in different ways, such as adhesive polymer in capsules or hollow fibre glasses, bacteria in porous aggregates and geo-materials directly incorporated in the cementbased materials. In this study, sodium silicate powder is encapsulated in polystyrene particles (polystyrene particle containing sodium silicate is defined as PS particle in short). The PS particles remain intact in the cement-based matrix before cracking. If water or moisture is available, the healing agent can be released into the crack provided that the crack passes through the PS particles. The dissolved sodium silicate reacts with calcium hydroxide in the matrix, and the healing products (C-S-H gel) can form in the crack. Furthermore, compared to the reference, for the cracked specimens with polystyrene particles, the recovery of flexural stiffness can be observed. Different sizes and mass fractions, i.e. sodium silicate / cement ratios, of PS particles used in engineered cementitious composite (ECC) mixture are studied to see their influence on mechanical properties as well as their healing efficiency. When the mass fraction of polystyrene particles is 4% of cement and the polystyrene particles have a proper slender shape, the ECC show good results in terms of flexural strength, flexural deflection capacity and recovery of mechanical properties. Therefore, encapsulation of healing agent in polystyrene could be regarded as a promising way for realising self-healing of cement-based materials.Structural EngineeringCivil Engineering and Geoscience

Numerical Study on Chloride Ingress in Cement-Based Coating Systems and Service Life Assessment

Chloride-induced corrosion is a critical issue for RC structures. Cement-based coatings can be used to protect concrete structures with unsatisfactory quality against chloride ingress. To evaluate the effectiveness of the coatings to extend the service life of coated concrete structures, the evolution of the chloride profile in the coated concrete structures should be determined. This paper investigated the mechanism of chloride ingress into coated concrete structures (i.e., coatings made of cement paste and concrete substrate). A numerical tool is proposed for calculating the chloride profiles in the coated concrete structures. A parametric study investigated the influence of several factors on the chloride ingress: the water:cement (w:c) ratio of the coating, the thickness of the coating, and early or late application of the coating. A preliminary cost analysis of coating materials was carried out. The results showed that the effectiveness of the coatings increased with coating thickness at a drastic increase of material cost; the effectiveness of the coatings increased with the decrease of the w:c ratio at a moderate increase of material cost. In order to extend the service life of the substrate, a coating with a low w:c ratio is recommended, and the coating thickness should be designed depending on the requirements. Moreover, the exposure history of the substrate before application of the coating also has an influence on the effectiveness of the coating. To protect an existing concrete structure exposed to a chloride environment against rapid chloride ingress, it is preferable to apply a coating as early as possible, because the effectiveness of the coating is reduced by late application.Accepted Author ManuscriptMaterials and Environmen

What role an agent could play at home?: Exploring the social roles of smart home system based on a content analysis

Smart home systems not only serve users to fulfill pragmatic goals, but also ‘live with’ users. Despite the conceptual possibilities, it still remains unclear whether and what social roles current smart home systems are intended by the companies. In this paper, we report a retrospective study on 15 selected smart home systems (SHSs) on current market. We used content analysis to identify themes and categories of function, personality and social role of these SHSs, and also explore the connections among them. Four representative social roles were identified: instrument, lobby boy, assistant and family member. Four related personalities were found: competent, helpful, trustworthy, and caring. Results of this study revealed an overview of current social roles that smart home system plays as well as the personalities they exhibit.Design Aesthetic

Characterization and comparison of capillary pore structures of digital cement pastes

More and more studies are based on digital microstructures of cement pastes obtained either by numerical modelling or by experiments. A comprehensive understanding of the their pore structures, therefore, becomes significant. In this study, the pore structure of a virtual cement paste (HYMO-1d) generated by cement hydration model HYMOSTRUC 3D is characterized. The pore structure of HYMO-1d is compared to the one of CT-1d that is reconstructed by using X-ray computed tomography technique (CT scan). Both HYMO-1d and CT-1d have the same porosity. Various parameters are taken into account, viz., the specific surface area, the pore size distribution (PSD), the connectivity and the tortuosity of water-filled pores. Regarding the PSD, two concepts (i.e., the “continuous PSD” and the “PSD by MIP simulation”) are adopted. The “continuous PSD” is believed to be a “realistic” PSD; while the “PSD by MIP simulation” is affected by the “throat” and “ink bottle” pores. The results show that HYMO-1d and CT-1d exhibit a similar curve of “continuous PSD”, but distinct curves of “PSD by MIP simulation” and different specific surface areas. A lower complexity of the pore structure of HYMO-1d is indicated by a higher tortuosity of water-filled pores with reference to CT-1d. This study indicates that the comparison of pore structures between the digital microstructures should be based on multiple parameters. It also gives an insight into further studies on digital microstructures, i.e. transport properties of unsaturated materials.Else Kooi LaboratoryMaterials and Environmen

Interlinkages between human agency, water use efficiency and sustainable food production

Efficient use of water and nutrients in crop production are critical for sustainable water and crop production systems. Understanding the role of humans in ensuring water and nutrient use efficiency is therefore an important ingredient of sustainable development. Crop production functions are often defined either as functions of water and nutrient deficiency or are based on economic production theory that conceptualizes production as a result of economic activities that take in inputs such as water, capital and labor and produce crop biomass as output. This paper fills a gap by consistently treating water and nutrient use and human agency in crop production, thus providing a better understanding of the role humans play in crop production. Uptake of water and nutrients are two dominant biophysical processes of crop growth while human agency, including irrigation machine power, land-preparing machine power and human labor force, determine limits of water and nutrient resources that are accessible to crops. Two crops, i.e., winter wheat and rice, which account for the majority of food crop production are considered in a rapidly developing region of the world, Jiangsu Province, China, that is witnessing the phenomenon of rural to urban migration. Its production is modeled in two steps. First water and nutrient efficiencies, defined as the ratios of observed uptake to quantities applied, are modeled as functions of labor and machine power (representing human agency). In the second step, crop yields are modeled as functions of water and nutrient efficiencies multiplied by amounts of water and fertilizers applied. As a result, crop production is predicted by first simulating water and nutrient uptake efficiencies and then determining yield as a function of water and nutrients that are actually taken up by crops. Results show that modeled relationship between water use efficiency and human agency explains 68% of observed variance for wheat and 49% for rice. The modeled relationship between nutrient use efficiency and human agency explains 49% of the variance for wheat and 56% for rice. The modeled relationships between yields and actual uptakes in the second step explain even higher percentages of observed the variance: 73% for wheat and 84% for rice. Leave-one-out cross validation of yield predictions shows that relative errors are on average within 5% of the observed yields, reinforcing the robustness of the estimated relationship and of conceptualizing crop production as a composite function of bio-physical mechanism and human agency. Interpretations based on the model reveal that after 2005, mechanization gradually led to less labor being used relative to machinery to achieve same levels of water use efficiency. Labor and irrigation equipment, on the other hand, were found to be complimentary inputs to water use efficiency. While the results suggest interventions targeting machinery are most instrumental in increasing wheat productivity, they may exasperate rural – urban migration. Policy strategies for alleviating rural-urban migration while ensuring regional food security can nonetheless be devised where appropriate data are available.Accepted Author ManuscriptWater Resource

Simulation of moisture transport in hydrating cement-based overlay systems

Drying of cement-based overlay systems is a critical issue, because it causes differential shrinkage between the overlay material and the concrete substrate and may induce cracking or debonding of the overlay material. In this paper the mechanisms of moisture transport in hydrating cement-based overlay systems are studied. A model is proposed for simulating the moisture transport. A parameter study has been conducted to quantitatively investigate the influence of the thickness of the overlay material and the curing conditions on hydration of the overlay materials. The evolution of the moisture profile in the overlay system and the development of the degree of hydration (DOH) of the overlay material have been calculated. The change of water content in the overlay material is investigated, in terms of the water absorbed by the substrate, the water consumed by hydration of the overlay material and the water evaporated to the environment. The simulation results show that the water evaporation is a dominant factor that causes water loss of the overlay material, while the water absorption by the substrate plays only a minor role. Moist curing is much more effective than sealed curing (e.g. by using sealing agent) for hydration of the overlay material. The DOH of the overlay material is significantly increased with longer moist curing. Under the same curing condition (e.g. moist curing + drying), thinner overlay materials are more vulnerable to water loss and exhibit a lower DOH. It suggests that for proper hydration of cement-based overlay materials, moist curing is recommended rather than applying a sealing agent.Materials and Environmen

Robust Lane Detection through Self Pre-training with Masked Sequential Autoencoders and Fine-tuning with Customized PolyLoss

Lane detection is crucial for vehicle localization which makes it the foundation for automated driving and many intelligent and advanced driving assistant systems. Available vision-based lane detection methods do not make full use of the valuable features and aggregate contextual information, especially the interrelationships between lane lines and other regions of the images in continuous frames. To fill this research gap and upgrade lane detection performance, this paper proposes a pipeline consisting of self pre-training with masked sequential autoencoders and fine-tuning with customized PolyLoss for the end-to-end neural network models using multi-continuous image frames. The masked sequential autoencoders are adopted to pretrain the neural network models with reconstructing the missing pixels from a random masked image as the objective. Then, in the fine-tuning segmentation phase where lane detection segmentation is performed, the continuous image frames are served as the inputs, and the pre-trained model weights are transferred and further updated using the backpropagation mechanism with customized PolyLoss calculating the weighted errors between the output lane detection results and the labeled ground truth. Extensive experiment results demonstrate that, with the proposed pipeline, the lane detection model performance on both normal and challenging scenes can be advanced beyond the state-of-the art results, while the training time can be substantially shortened.Transport and Plannin

Fast rotor loss calculations in fractional-slot permanent magnet machines

Permanent magnet machines with fractional slot windings are popular because of their shorter end windings, low cost and ease of manufacturing. On the other hand, fractional slot machines have higher eddy current losses in the rotor magnets and sleeve. An accurate calculation of these losses usually involves a time-stepped finite-element analysis with moving rotor, which is time consuming. This paper compares different methods of evaluating these losses using finite element analysis based on their time-cost. The models are mainly divided into two types: time-domain and frequency-domain models. The paper proposes an equivalent frequency-domain analysis in the stator frame for rotor loss calculations, using the Lorentz force term. This method yields similar results to the time-stepped finite element model with a significant time saving. The time saving can be significant in a machine optimization study.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care   Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Transport Engineering and LogisticsDC systems, Energy conversion & Storag