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Guo Y.,Tianjin University of Technology | Ma W.,Tianjin University of Technology | Zhang F.,Materials and Aerospace Engineering | Zhang F.,Wanger Institute for Sustainable Energy Research
Journal of Materials Science: Materials in Electronics | Year: 2016

In this work Pb(Sb1/2Nb1/2)O3–Pb(Ni1/3Nb2/3)O3–Pb(Zr, Ti)O3 (PSN–PNN–PZT) ceramics were prepared by a conventional mixed oxide method. The morphotropic phase boundaries (MPBs) of yPSN–0.3PNN–(0.7 − y)PZT (y = 0, 0.005, 0.01, 0.015 and 0.02) ceramics with a variable PSN were investigated. The MPB compositions, possessing high performances, were identified using X-ray diffraction and further confirmed by their piezoelectric/dielectric properties. The MPBs shifted to a PT-rich region as PSN increased. The optimal electric properties of 0.015PSN–0.3PNN–0.685PZT were found to be d33 = 660pC/N, kp = 0.68, ε33 T/ε0 = 4279, tan δ = 1.56 % for the MPB composition. The remanent polarizations and poling strain gradually increased and then decreased as the PSN content increased. The remanent polarizations (Pr) and poling strains of 0.015PSN–0.3PNN–0.685PZT ceramics at MPB were 33.5 μC/cm2 and 0.39 %, respectively. Furthermore, the electrical performances were also related to the cooling speed in the poling process, where the poling field was 3 kV/mm, the poling temperature was 120 °C and the poling time was 15 min. © 2015, Springer Science+Business Media New York. Source


Sengupta D.,University of California at San Diego | Kahn A.M.,University of California at San Diego | Burns J.C.,University of California at San Diego | Sankaran S.,University of California at San Diego | And 2 more authors.
Biomechanics and Modeling in Mechanobiology | Year: 2012

Kawasaki Disease (KD) is the leading cause of acquired pediatric heart disease. A subset of KD patients develops aneurysms in the coronary arteries, leading to increased risk of thrombosis and myocardial infarction. Currently, there are limited clinical data to guide the management of these patients, and the hemodynamic effects of these aneurysms are unknown.We applied patient-specific modeling to systematically quantify hemodynamics and wall shear stress in coronary arteries with aneurysms caused by KD. We modeled the hemodynamics in the aneurysms using anatomic data obtained by multi-detector computed tomography (CT) in a 10-year-old male subject who suffered KD at age 3 years. The altered hemodynamics were compared to that of a reconstructed normal coronary anatomy using our subject as the model. Computer simulations using a robust finite element framework were used to quantify time-varying shear stresses and particle trajectories in the coronary arteries. We accounted for the cardiac contractility and the microcirculation using physiologic downstream boundary conditions.The presence of aneurysms in the proximal coronary artery leads to flow recirculation, reduced wall shear stress within the aneurysm, and high wall shear stress gradients at the neck of the aneurysm. The wall shear stress in the KD subject (2.95-3.81 dynes/sq cm) was an order of magnitude lower than the normal control model (17.10-27.15 dynes/sq cm). Particle residence times were significantly higher, taking 5 cardiac cycles to fully clear from the aneurysmal regions in the KD subject compared to only 1.3 cardiac cycles from the corresponding regions of the normal model. In this novel quantitative study of hemodynamics in coronary aneurysms caused by KD, we documented markedly abnormal flow patterns that are associated with increased risk of thrombosis. This methodology has the potential to provide further insights into the effects of aneurysms in KD and to help risk stratify patients for appropriate medical and surgical interventions. © Springer-Verlag 2011. Source


Osorio A.F.,Materials and Aerospace Engineering | Kassab A.J.,Materials and Aerospace Engineering | Divo E.A.,University of Central Florida | Argueta-Morales R.,Congenital Heart Institute at Arnold Palmer Hospital | DeCampli W.M.,Congenital Heart Institute at Arnold Palmer Hospital
ASME International Mechanical Engineering Congress and Exposition, Proceedings | Year: 2010

Presently, mechanical support is the most promising alternative to cardiac transplantation. Ventricular Assist Devices (VADs) were originally used to provide mechanical circulatory support in patients waiting planned heart transplantation ("bridge-to-transplantation" therapy). The success of short-term bridge devices led to clinical trials evaluating the clinical suitability of long-term support ("destination" therapy) with left ventricular assist devices (LVADs). The first larger-scale, randomized trial that tested long-term support with a LVAD reported a 44% reduction in the risk of stroke or death in patients with a LVAD. In spite of the success of LVADs as bridge-to-transplantation and long-term support. Patients carrying these devices are still at risk of several adverse events. The most devastating complication is caused by embolization of thrombi formed within the LVAD or inside the heart into the brain. Prevention of thrombi formation is attempted through anticoagulation management and by improving LVADs design; however there is still significant occurrence of thromboembolic events in patients. Investigators have reported that the incidence of thromboembolic cerebral events ranges from 14% to 47% over a period of 6-12 months. An alternative method to reduce the incidence of cerebral embolization has been proposed by one of the co-authors, namely William DeCampli M.D., Ph.D. The hypothesis is that it is possible to minimize the number of thrombi flowing into the carotid arteries by an optimal placement of the LVAD outflow conduit, and/or the addition of aortic bypass connecting the ascending aorta (AO) and the innominate artery (IA), or left carotid artery (LCA). This paper presents the computational fluid dynamics (CFD) analysis of the aortic arch hemodynamics using a representative geometry of the human aortic arch and an alternative aortic bypass. The alternative aortic bypass is intended to reduce thrombi flow incidence into the carotid arteries in patients with LVAD implants with the aim to reduce thromboembolisms. In order to study the trajectory of the thrombi within the aortic arch, a Lagrangian particle-tracking model is coupled to the CFD model. Results are presented in the form of percentage of thrombi flowing to the carotid arteries as a function of LVAD conduit placement and aortic bypass implantation, revealing promising improvement. Copyright © 2010 by ASME. Source


Wang C.,Materials and Aerospace Engineering | Wang C.,Wanger Institute for Sustainable Energy Research | Sawicki M.,Materials and Aerospace Engineering | Sawicki M.,Wanger Institute for Sustainable Energy Research | And 3 more authors.
Journal of the Electrochemical Society | Year: 2015

Na3MnCO3PO4 with a potential to deliver two-electron transfer reactions per formula via Mn2+/Mn3+ and Mn3+/Mn4+ redox reactions and a high theoretical capacity (191 mAh/g) can play an important role in Na-ion batteries. This study investigates the dependence of the electrochemical performance of Na3MnCO3PO4-based sodium-ion batteries on processing, structural defects and ionic conductivity. Na3MnCO3PO4 has been synthesized via hydrothermal process under various conditions with and without subsequent high-energy ball milling. Particle sizes, structural defects and ionic conductivity have been studied as a function of processing conditions. It is found that Na3MnCO3PO4 nanoparticles (20 nm in diameter) can be produced from hydrothermal synthesis, but the reaction time is critical in obtaining nanoparticles. Nanoparticles exhibit a higher ionic conductivity than agglomerated particles. Further, structural defects also have a strong influence on ionic conductivity which, in turn, affects the charge/discharge capacities of the Na3MnCO3PO4-based sodium-ion batteries. These results provide guidelines for rational design and synthesis of high capacity Na3MnCO3PO4 for Na-ion batteries in the near future. © The Author(s) 2015. Source


Woodburn D.A.,University of Central Florida | Wu T.,University of Central Florida | Chow L.,Materials and Aerospace Engineering | Leland Q.,Air Force Research Lab | And 6 more authors.
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition | Year: 2010

All-electric aircraft is a high priority goal in the avionics community. Both increased reliability and efficiency are the promised implications of this move. But, thermal management has become a significant issue that must be resolved before reaching this goal. Advanced analysis technologies such as finite element method and intelligent control systems such as field oriented control are being used to better understand the source of the heat and to eliminate as much of it as possible. This paper addresses the motivation behind all-electric aircraft and gives an overview of some of the considerations in cooling, simulation and modeling, and control, with an example of one control scheme which is being developed. © 2010 by the American Institute of Aeronautics and Astronautics, Inc. Source

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