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Objective: To study on medium-term results after aortic valve replacement surgery for aortic stenosis (AS) at 108 Military Central Hospital. Subject and method: 67 patients with AS received aortic artificial valves replacement. The results collected at the time of 3, 6, 12, 24, 36 and 48 months include: NYHA class, echocardiography (LVEDd, LVEDs, AVA, mean PG), Sokolow-Lyon, PPM and complications. Evaluation is based on the criteria of the Vietnam National Heart Association and the Guidelines of the ACC/AHA. Result: NYHA 1 was increased (76.1%) and NYHA 2 - 3 was 23.9% with p0.05). Sokolow-Lyon index < 35mm after surgery > 90%, mid-term echocardiography AVA about 1.6cm², LVEF > 60%, mean PG < 20mmHg, LVEDd and LVEDs within normal limits. Hemorrhagic complications, stuck aortic valve (≤ 3.8%), fuite paraprosthetiques did not appear after 6 months. Conclusion: The medium-term outcome after aortic valve replacement for aortic stenosis has good clinical and subclinical improvement and the rate of medium-term complications is low.

Objective: To evaluate the results of endovascular surgery to treat aortic disease at 108 Military Central Hospital. Subject and method: We conducted a prospective descriptive study of 69 patients undergoing stent graft at 108 Military Central Hospital from 12/2016 to 03/2021. Result: Endpoints: Technical success rate 100% (n = 69); Survival: n = 65 (94.2%); Target vessel patency: n = 67 (97.1%); Re-intervention n = 0 (0%); 30-day in-hospital mortality: n = 3 (4.3%), Endoleak: n = 2 (2.8%), spinal cord ischemia: n = 2 (2.8%), Stroke: n = 2 (2.8%), Infection: n = 1 (1.4%). Conclusion: Endovascular repair to treat aortic disease is a safe and highly effective method. The procedure should be considered in the Hybrid operation room and performed by cardiovascular surgeon- interventional cardiologist.

Conventional transmission systems utilize either high voltage ac (HVAC), operating at 50 or 60 Hz, or high voltage dc (HVDC) to transfer bulk power. The HVAC system is designed to operate at a high voltage level to reduce losses and increase bulk power transfer. This method is limited, however, by the constraints of installed transmission overhead lines, such as voltage level and power transfer capability. In contrast, the HVDC system can handle a large amount of power on the transmission line by utilizing dc current instead of ac. While the HVDC system has no limitation in transmission line length for power transfer, it does however, require a high initial cost for converter stations and specialized protection systems. Additionally, the HVDC system is a point-to-point connection, and thus not flexible for multi-terminal connection. The low frequency ac (LFAC) transmission system, first introduced in 2000, is another solution for bulk power transmission that inherits advantages from both high voltage ac and high voltage dc systems. The primary advantage of LFAC transmission is that by operating the system at a frequency lower than 50 or 60 Hz, the transmission line reactance can be significantly reduced, thus extending power capacity. Further advantages include multi-terminal connections, distance protection using alternating-current based circuit breakers, and improving power transfer capability close to that of an HVDC system. This dissertation investigates the benefits of an LFAC system in terms of power transfer capability and voltage stability. First, the steady-state performances of the transmission line under low frequency range are investigated, including the skin effect to see any possible changes in transmission line model. More importantly, the power transfer capability, and voltage profiles during no-load and full-load conditions are examined. Next, the system voltage stability under low frequency operations is studied in detail to analyze how the low frequency operation helps improve a power system stability. Furthermore, the system modeling, protection, and hardware platform to test the low frequency ac transmission are studied deeply. A new grid synchronization configuration to interface a low frequency system with a 60 Hz ac system is also proposed. Moreover, a fast and robust fault detection mechanism based on the second-order generalized-integrator (SOGI) grid synchronization technique is to develop and work properly in a low frequency system. Last but not least, a small-scaled transmission and distribution system is built to verify the basic performances of a power system at a low frequency operations.

A series of 1-g shaking table model tests were carried out to study the behavior of pile groups embedded in sloping ground subjected to lateral flow of liquefied soil. Two different configurations of pile groups: large (6×6 and 11×11) and small (3×3), were considered. The models were subjected to the liquefaction-induced large ground deformation to investigate the effect of several parameters on the response of pile groups and mechanism of lateral flow. These parameters comprise amplitude, frequency, and direction of input motion; density and slope of ground; and the thickness of non-liquefiable layer at the surface. The outcome of this parametric study reveals the importance of above mentioned factors which should be taken into account for analysis and design purposes. In addition, the results from the experiments clearly illustrate that in sloping ground configuration, both front (in upstream) and rear (in downstream) row piles receive greater lateral forces than middle row piles. This finding is attributed to the distribution of soil motion (displacement and velocity) of the liquefied soil in the model. As a result, installation of additional pile rows in front and behind an existing pile foundation can be considered as an effective retrofitting technique. Finally, soil-pile interaction was evaluated by running experiments with different pile spacings, and reliability of the JRA 2002 design manual in estimation of liquefaction-induced lateral force on piles is evaluated.