The aging of asphalt pavements leads to less flexible asphalt mixtures that are prone to cracking and spalling. In this study, the relationship between lab and field aging was evaluated based on both theoretical asphalt aging models and practical asphalt and asphalt mixture performance tests. The results show that the corresponding field aging duration calculated using the mixture testing, especially the cracking test, is more conservative than the traditional aging models or binder rheological measurements. 5 and 12 days appear to simulate 16 and 38 years of field aging (in New Hampshire) for the top 12.5 mm pavement, respectively, based on the asphalt binder test results. In contrast, the theoretical aging model considers climatic conditions and suggests that 5 and 12 days simulate in-field aging of 6.2 and 15.0 years, respectively. The asphalt mixture test results indicate that the laboratory aging conditions simulate minimal field aging durations. This is because the damage to the asphalt pavement structure caused by climatic conditions and traffic loads is fully considered. This could be very useful for designing a more reliable and durable pavement incorporating intricate field conditions.

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Sintered nano-silver die-attach materials have been widely used in high-power electronics packaging because of their high thermal and electrical conductivities. In this study, we characterized the tensile properties of sintered nano-silver particles over a range of strain rates and temperatures, and established the constitutive models. First, 50 nm nano-silver particles were sintered at 275 °C for 50 min as test samples, and their tensile tests were conducted under a dynamic thermomechanical analyzer (DMA Q800) and an IBTC 300SL in-situ mechanical test system respectively with different strain rates and ambient temperatures. Then, both Anand and variable-order fractional models (VoFM) were adopted to analyze the obtained stress-strain data and we studied their fitting accuracy and applicability. The results showed that: (1) The Young's modulus of the sintered nano-silver particles decreased with increasing temperature. In addition, the tensile strengths declined under lower strain rates and higher temperature conditions; (2) both the Anand model and VoFM characterized the tensile stress-strain properties of the sintered nano-silver material well. Compared to the Anand model, the VoFM utilized a simpler formula with fewer parameters and higher precision.@en

In high-power electronics packaging, nano-silver sintering technology has been widely applied due to its excellent electrical and thermal conductivity and its low-temperature packaging and high-temperature operation. In this study, 50-nm nano-silver particles are sintered at 275°C for 50 min and placed under a dynamic thermomechanical analyzer (DMA Q800) with three strain rates (0.001%s-1, 0.01%s-1, and 0.1%s-1) and seven ambient temperatures (-40°C, 0°C, 25°C, 60°C, 120°C, 150°C, and 185°C). Both the variable-order fractional constitutive model and Anand model are adopted to characterize the tensile behaviors of sintered nano-silver particles. The results show that (1) the tensile strength of sintered nano-silver particle samples declines under the lower strain rate and higher temperature; and (2) both the variable-order fractional model and Anand model can well represent the tensile mechanical properties of sintered nano-silver. According to the root mean square error (RMSE) calculation, the fitting accuracy of the variable-order fractional model is slightly better than that of the Anand model. Furthermore, the variable-order fractional model involves fewer parameters, which makes it easier to fit than the Anand model.

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This paper introduces a novel technique to design the level of service (LOS) for facilities or sub spaces of buildings for the purpose of evacuation planning. LOS is a standard qualitative indicator used to describe flow characteristics in a pedestrian environment. Some evacuation planners use LOS to help determine the network parameters when solving evacuation planning problems by the network flow approach. However, there is currently limited research into the optimization of the LOS parameters themselves to construct more efficient evacuation networks. In this paper the authors used a genetic algorithm optimization approach to determine LOS for facilities to improve the evacuation performance of building networks. Each individual chromosome containing a LOS design represents a fully defined evacuation network that can be solved. The fitness of each network is measured by minimum clearance time, which is calculated by the Capacity Constrained Route Planner (CCRP) approach. A comparative computational test in a hypothetical three-story building shows that the evacuation network under the optimized LOS design has a roughly 11% less minimum clearance time compared to the network under the original LOS design. Sensitivity analysis is also included, focusing on how the population size and the building layout influence the LOS design. In addition, an additional computational test for a twelve-deck cruise ship shows that the approach is scalable to solve more complex evacuation networks. The proposed approach has the potential to provide better LOS assignments for facilities for the government officials to develop effective emergency management strategies.

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