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  • Author: N. Wei x
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Abstract

Bioactive glass particles andweak scaffolds have been used to heal small contained bone defects but an unmet challenge is the development of bioactive glass implants with the requisite mechanical reliability and in vivo performance to heal structural bone defects. Inadequate mechanical strength and a brittle mechanical response have been key concerns in the use of bioactive glass scaffolds in structural bone repair. Recent research has shown the capacity to create strong porous bioactive glass scaffolds and the ability of these scaffolds to heal segmental bone defects in small and large rodents at a rate comparable to autogenous bone grafts. Loading these strong porous scaffolds with bone morphogenetic protein-2 can significantly enhance their ability to regenerate bone. Recentwork has also shown that coating the external surface of strong porous scaffolds with an adherent biodegradable polymer can dramatically improve their load-bearing capacity in flexural loading and their work of fracture (a measure of toughness). These tough and strong bioactive glass-polymer composites with an internal architecture conducive to bone infiltration could provide optimal synthetic implants for structural bone repair.

Abstract

In this study, we have determined the combined effect of pressure and temperature on the compressional-wave velocity (V P) of Ne up to 53 GPa and 1100 K using Brillouin scattering in externally heated diamond-anvil cells. The phase transition from the supercritical fluid to solid phase was observed to cause a 10.5–11% jump in V P, and the magnitude in the V P contrast across the phase transition increases with temperature. In addition, we have observed an abnormal reduced increase rate of V P with pressure in the supercritical Ne fluid at both 800 and 1100 K before the transition to the solid phase. V P of the solid Ne exhibits a nonlinear increase with pressure at all the investigated temperatures. The elevating temperature was noted to cause an apparent reduction in V P, yet the reduction in V P caused by increasing temperature dramatically decreases at higher pressures. At 20 GPa, increasing temperature by 100 K can lower the V P of Ne by 2.4%. Yet elevating temperature by 100 K can only reduce the V P by 0.4% at 50 GPa. We further compare V P of Ne to that of other rare gases, including Ar, Kr, and Xe. At 300 K, V P of Ne shows a stronger dependence on pressure than both Kr and Xe. Moreover, increasing temperature can produce a greater reduction in V P of Ne than that of Ar below 50 GPa. Our measured V P of Ne is also useful for understanding the velocity structure of giant planets, such as Jupiter.

Abstract

Bioactive glasses have attractive characteristics as a scaffold material for healing bone defects but their brittle mechanical response, particularly in bending, is a concern. Recent studies have shown that coating the external surface of strong porous bioactive glass (13-93) scaffolds with an adherent biodegradable polymer layer can significantly improve their load-bearing capacity andwork of fracture, resulting in a non-brittle mechanical response. In the present study, finite element modeling (FEM) was used to analyze the mechanical response in four-point bending of composites composed of a porous glass scaffold and an adherent polymer surface layer. The glass scaffold with a cylindrical geometry (diameter = 4.2 mm; porosity = 20%) was composed of randomly arranged unidirectional fibers (diameter 200-700 μm) thatwere bonded at their contact points. The thickness of the polymer layer was 500 μm. By analyzing the stresses in the individual glass fibers, the simulations can account for the main trends in the observed mechanical response of practical composites with a similar architecture composed of a bioactive glass (13-93) scaffold and an adherent polylactic acid surface layer. These FEM simulations could play a useful role in designing bioactive glass composites with improved mechanical properties.

Abstract

Mass evacuation of urban areas due to hurricanes is a critical problem in emergency management that requires extensive basic and applied research. Previous research uses agent-based models to simulate individual vehicle and driver behavior, and is limited mostly to a small study area due to the complexity of the models and the computational time needed. To better understand evacuation behavior, simulating the evacuation traffic in a larger region is needed. This paper develops a two-level regional disaster evacuation model by coupling two agent-based models. The first model uses each census block centroid, weighted with its corresponding number of vehicles, as an agent to simulate the local road network traffic. The second model, developed on the platform of a commercial software program called VISSIM, treats each vehicle as an agent to simulate the interstate highway traffic. This two-level agent-based model was used to simulate hurricane evacuation traffic in New Orleans. Validation results with the real Hurricane Katrina’s evacuation data confirm that the proposed model performs well in terms of high model accuracy (i.e., close agreement between the real and simulated traffic patterns) and short model running time. The modeling results show that the average root-mean-square error (RMSE) for the three major evacuation directions was 347.58. Under a simultaneous evacuation strategy, and with 240,251 vehicles in 17,744 agents (census blocks), it would take at least 46.3 hours to evacuate all residents from the New Orleans metropolitan area. This two-level modeling approach could serve as a practical tool for evaluating mass evacuation strategies in New Orleans and other similar urban areas.

Abstract

First-principles calculations are performed to study the structural and elastic properties, sound velocities, and Debye temperature of rocksalt-structured copper monochloride (CuCl) and copper monobromide (CuBr). The structural parameters, elastic constants, longitudinal, transverse, and average elastic wave velocities, and the Debye temperature in the pressure range 10–20 GPa are successfully predicted and analysed. The variation of the elastic constants and bulk modulus as a function of pressure is found to be non-linear for CuCl and almost linear for CuBr. Based on the obtained values of the elastic constants, the bulk modulus, the isotropic shear modulus, Young’s modulus, Poisson’s ratio, and Pugh’s ratio of the aggregate materials are also investigated. The analysis of Poisson’s and Pugh’s ratios shows that these materials become ductile for pressures in the range 10–20 GPa. The evolution of the longitudinal sound velocity under pressure indicates the hardening of the corresponding phonons in both materials.