ABSTRACT
Deformation at high strain rates often results in high stresses on many engineering materials, potentially leading to catastrophic failure without proper design. High-strain-rate mechanical testing is thus needed to improve the design of future structural materials for a wide range of applications. Although several high-strain-rate mechanical testing techniques have been developed to provide a fundamental understanding of material responses and microstructural evolution under high-strain-rate deformation conditions, these tests are often very time consuming and costly. In this work, we utilize a high-strain-rate nanoindentation testing technique and system in combination with transmission electron microscopy to reveal the deformation mechanisms and dislocation substructures that evolve in pure metals from low (10-2 s-1) to very high indentation strain rates (104 s-1), using face-centered cubic aluminum and body-centered cubic molybdenum as model materials. The results help to establish the conditions under which micro- and macro-scale tests can be compared with validity and also provide a promising pathway that could lead to accelerated high-strain-rate testing at substantially reduced costs.
ABSTRACT
Obstructive sleep apnea (OSA) is an under-recognized yet highly prevalent disease that has major implications to cardiovascular health. Pulmonary hypertension (pH) is less common but none the less a fatal condition. The association of OSA and PH is a known but not well understood phenomenon. Furthermore, the relationship appears to be bi-directional with limited understanding of the mechanism(s) driving the processes. PH in OSA has real time consequences as it has been shown to increase mortality. Limited data suggests that treatment with continuous positive pressure therapy may be beneficial and reduce pulmonary pressure. In this review, we discuss current data on prevalence of PH in OSA and vice versa. We also explore the pathophysiology of this relationship and a proposed mechanism for their connection. Finally, we address the treatment of OSA with CPAP and its impact on pulmonary pressures. Gaps in knowledge and future research potential are illustrated and discoursed.
