An asynchronous variational integrator for the phase field approach to dynamic fracture

The phase field approach is widely used to model fracture behaviors due to the absence of the need to track the crack topology and the ability to predict crack nucleation and branching. In this work, the asynchronous variational integrator (AVI) is adapted for the phase field approach of dynamic brittle fracture. The AVI is derived from Hamilton's principle and allows each element in the mesh to have its own local time step that may be different from others'. While the displacement field is explicitly updated, the phase field is implicitly solved, with upper and lower bounds strictly and conveniently enforced. In particular, two important variants of the phase field approach, the AT1 and AT2 models, are equally easily implemented. Several benchmark problems are used to study the performances of both the AT1 and AT2 models, and the results show that the AVI for the phase field approach significantly speeds up the computational efficiency and successfully captures the complicated dynamic fracture behavior.     

LBAA: A novel load balancing mechanism in cloud environments using ant colony optimization and artificial bee colony algorithms

Recently, cloud computing has been recognized as an effective paradigm for offering an on-demand platform, software services, and an efficient infrastructure to cloud clients. Due to the exponential growth of cloud tasks and the rapidly increasing number of cloud users, scheduling and balancing these tasks among involved heterogeneous virtual machines becomes an Non-deterministic Polynomial hard (NP-hard) optimization problem considering significant constraints, such as high rate of resource usage, low scheduling time, and low implementation cost. Therefore, various meta-heuristic algorithms have been widely used to tackle the issue. The current paper proposes a novel load balancing mechanism using the ant colony optimization and artificial bee colony algorithms, called LBAA, which aims to balance the load division among systems in data centers. The simulation outcomes confirm that our algorithm outperforms previous works regarding response time, imbalance degree, makespan, and resource utilization up to 25%, 15%, 12%, and 10%, respectively.     

Deposition Patterns of Evaporating Sodium Alginate Sessile Droplets Cross-Linked by Calcium Chloride

Controllable patterning of bio-compatible polymers in the presence of a cross-linker in evaporating bi-dispersed colloidal drops is of critical importance in functional coatings, bioprinting, and food packaging. This study investigates the effect of calcium chloride and sodium alginate concentration on the evaporative deposition and elemental distribution of dried-out patterns. Different concentrations of alginate and salt in aqueous solutions are deposited on clean glass substrates to gain a deeper understanding of the final structures. Overall, the results indicate that changing the concentrations of sodium alginate and calcium chloride can significantly alter the elemental distribution and deposition uniformity of the final patterns. The modifications in relative concentration alter the physicochemical characteristics of the solution, resulting in significant changes in the pinning time and contact angle of the droplets that correspond to the alteration of the colloidal size and concentration, ultimately resulting in significant differences in deposition patterns. The dried-out patterns are categorized based on their structures and mechanisms (crystallization, sedimentation, and adsorption) controlling the evaporative deposition, and then justified based on the competitive effects of cross-linking, crystallization, and evaporation-driven flows. Using scanning electron microscopy and energy-dispersive X-ray spectroscopy, the elemental distribution of dried-out patterns is also mapped to substantiate the discussion made.     

Pore-network modelling of combined molecular diffusion and gravity drainage mechanisms in a porous matrix block: The competitive role of driving forces

A large part of the world's hydrocarbon resources are located in fractured reservoirs, and mass transfer phenomena play a crucial role in enhanced hydrocarbon recovery from these reservoirs. Pore-network models have been widely used to study kinetic and pore-scale micro-mechanisms. Molecular diffusion involves mass transfer and liquid–vapour phase change and can be simulated by a modified invasion percolation model. Despite the existence of separate pore-scale studies on molecular diffusion and gravity drainage, no articles have been published that evaluate the combined effect of both mechanisms. This study investigates the competitive roles of the two phenomena and the effective factors controlling each mechanism with the aid of pore-network models. According to the results obtained, gravity drainage and molecular diffusion would have a synergic effect when they are simultaneously active. Although for a single-component liquid system, there would be a capillary holdup residual saturation in the pure gravity drainage process (between 11% and 14% for the evaluated cases) and a slow and lengthy evaporation in pure molecular diffusion (between 47% and 57% longer for the cases under study), our investigation revealed that when the two mechanisms coexist, a faster process with no residual liquid is expected. Our findings clarify that when the system is strongly gravity dominated, the liquid body remains integrated, gas–liquid contact recedes in a piston-like manner, and three-stage liquid desaturation is observed. Furthermore, highly clustered liquid saturation is observed in strongly capillary-dominated systems, and the liquid desaturation curve in a capillary-dominated model has two distinguishable stages. The competitive contribution of gravity drainage and molecular diffusion as the main driving forces of liquid extraction from a single-block model is quantified for the entire period of desaturation. Depending on the dominance of the production mechanisms, the process is either gravity-assisted molecular diffusion or diffusion-assisted gravity drainage.     

Neurocognitive evidence for test equity in an academic listening assessment

Behaviormetrika - The present study explored the potential of a new neurocognitive approach to test equity which integrates evidence from eye-tracking and functional near-infrared spectroscopy with...     

Thermodynamic and economic evaluation and optimization of the applicability of integrating an innovative multi-heat recovery with a dual-flash binary geothermal power plant

Clean Technologies and Environmental Policy - Generally, a stand-alone flash-binary geothermal power plant loses most of its input energy, so its efficiency declines accordingly. Its overall...     

Efficient Coupling in Transverse Strip Metal-Insulator-Metal Structure on Silicon-on-Insulator Layer Stack

Silicon - This article presents a new directional coupling between two transverse strip metal-insulator-metal (TS-MIM) waveguides on silicon-on-insulator (SOI) platform at 1.55 μm...     

Novel isocyanate-based matrix resins for high temperature composite applications

Polyoxazolidone composites were prepared from polymeric isocyanate (PAPI 901) and epoxides (Epon 828 and DEN 431) in the presence of an oxazolidone-forming catalyst, triphenylantimony iodide. The effects of isocyanate to epoxide equivalent ratio, type of epoxide, and amount of fiberglass reinforcement on the composite properties were studied as well as the effects of post-curing temperature and time. Increasing the fiberglass content of the polyoxazolidone composites resulted in an improvement of the thermal and mechanical strength properties. The heat deflection temperature of all polyoxazolidones was > 250°C. The retention of the tensile strength at 150°C was excellent, ∼90% or higher. Polyoxazolidone composites based on DEN 431 at 1.2 isocyanate to epoxide equivalent ratio with 70 wt.% of fiberglass and post-cured at 150°C for 48 h exhibited the best properties. According to the results of DMA, TMA and DSC, the maximum operating temperature for polyoxazolidone composites is around 200°C. The TGA data showed that the decomposition temperature was ∼330°C.     

Functionally Graded AA7075 Components Produced via Hot Stamping: A Novel Process Design Inspired from Analysis of Microstructure and Mechanical Properties

Herein, functionally graded AA7075 components manufactured via hot stamping are investigated by focusing on the effect of different process variables on localized microstructure evolution. To realize gradation through stamping, an active tool is designed and applied. The design of experiments allows to assess the impact of transfer time from the furnace to the tool, quenching time in the tool, and final quenching media. Related characteristics of mechanical properties throughout the hat-shaped profile are assessed via hardness and tensile tests. As expected, the sections of the samples formed in the cooled part of the tool are characterized by higher mechanical strength following subsequent aging, while sections formed in the heated part exhibit higher ductility. Moreover, the microstructural analysis reveals that fine precipitates with minimum interparticle distances only form in the cooled section of the samples. Increasing the tool temperature at the heated side to 350 °C results in the formation of coarse precipitates in the grain interior and along the grain boundaries. A sharp gradient in terms of microstructural and mechanical properties is found between these conditions. After reducing the transfer time, an increased volume fraction of fine precipitates leads to further improvements in hardness and mechanical strengths.