@article{suo_govind_gu_dayton_jing_2019, title={Dynamic assessment of dual-frequency microbubble-mediated sonothrombolysis in vitro}, volume={125}, ISSN={["1089-7550"]}, DOI={10.1063/1.5083908}, abstractNote={Optimizing the use of high intensity focused ultrasound (HIFU) for recanalization of occluded blood vessels is an actively researched area. This yields an alternative therapy to the use of thrombolytic drugs in the treatment of ischemic stroke. HIFU treatment, used in conjunction with microbubbles (MBs) in the fluid stream, serves to augment the dissipation of the blood clot. In this study, using an in vitro approach, we implement a flow system to simulate the dynamic dispersion of blood clots using single-frequency focused ultrasound (SFFU) and dual-frequency focused ultrasound (DFFU). The effects of permutations of acoustic power and driving frequency (SFFU vs. DFFU) on the rate of disintegration and site-specific lytic action are quantified under the influence of fluid akin to that in a blood vessel, for specific microbubble concentrations. It is found that dual-frequency excitation in general produces a faster rate of clot dissipation in comparison to single-frequency excitation, and this observation is corroborated by cavitation signal detection. Our observations indicate that accelerated thrombolysis may be realized by the inertial cavitation threshold of DFFU being lower than that of SFFU. Furthermore, the thrombolytic effect with variance in microbubble concentration is studied for a fixed acoustic power. The efficacy of DFFU is not found to vary appreciably with an increase in microbubble concentration from 108 MBs/ml to 109 MBs/ml, possibly due to acoustic shadowing induced at increased concentrations.}, number={8}, journal={JOURNAL OF APPLIED PHYSICS}, author={Suo, Dingjie and Govind, Bala and Gu, Juanjuan and Dayton, Paul A. and Jing, Yun}, year={2019}, month={Feb} }
 @article{suo_govind_zhang_jing_2018, title={Numerical investigation of the inertial cavitation threshold under multi-frequency ultrasound}, volume={41}, ISSN={["1873-2828"]}, DOI={10.1016/j.ultsonch.2017.10.004}, abstractNote={Through the introduction of multi-frequency sonication in High Intensity Focused Ultrasound (HIFU), enhancement of efficiency has been noted in several applications including thrombolysis, tissue ablation, sonochemistry, and sonoluminescence. One key experimental observation is that multi-frequency ultrasound can help lower the inertial cavitation threshold, thereby improving the power efficiency. However, this has not been well corroborated by the theory. In this paper, a numerical investigation on the inertial cavitation threshold of microbubbles (MBs) under multi-frequency ultrasound irradiation is conducted. The relationships between the cavitation threshold and MB size at various frequencies and in different media are investigated. The results of single-, dual and triple frequency sonication show reduced inertial cavitation thresholds by introducing additional frequencies which is consistent with previous experimental work. In addition, no significant difference is observed between dual frequency sonication with various frequency differences. This study, not only reaffirms the benefit of using multi-frequency ultrasound for various applications, but also provides a possible route for optimizing ultrasound excitations for initiating inertial cavitation.}, journal={ULTRASONICS SONOCHEMISTRY}, author={Suo, Dingjie and Govind, Bala and Zhang, Shengqi and Jing, Yun}, year={2018}, month={Mar}, pages={419–426} }
 @article{govind_2017, title={Increasing the operational capability of a horizontal axis wind turbine by its integration with a vertical axis wind turbine}, volume={199}, ISSN={["1872-9118"]}, DOI={10.1016/j.apenergy.2017.04.070}, abstractNote={A major difficulty encountered by a horizontal axis wind turbine is the limit of aerodynamic torque that it can withstand at high wind speeds. A novel strategy is proposed to improve the operational capability of a prototype scale system by increasing its rated wind speed for power generation. This is achieved by integrating its drivetrain with that of a vertical axis wind turbine supported on a common tower. Excess torque is transferred from the horizontal axis rotor to the vertical axis rotor’s drivetrain by coupling them using a continuously variable transmission. In this article, firstly, the concepts of motion transfer that facilitate this combined operation are discussed. A combination of a 12-kW horizontal axis rotor and a 10-kW vertical axis wind turbine is studied to estimate the increased benefit of increments in rated wind speed. Performance of this hybrid system is predicted at potential wind sites and is shown to exceed the standalone mechanical power output of both subsystems under different wind regimes. The critical criterion of the system’s aerodynamic feasibility is then investigated. Turbulence modelling is performed for a configuration which involves a combination of the NREL Phase VI rotor and a NACA 0021 profiled vertical axis H-rotor. A 3-D simulation, using a validated k-ω (Shear Stress Transport) computational fluid dynamics model helps confirm the ability of both turbines to operate aerodynamically independent of each other. Further, by this methodology, a safe clearance between the two rotors is pre-determined. Analysis of turbulent flow scenarios reveals the characteristic effects of aerodynamic torque ripple experienced by the vertical axis wind turbine and its impact on combined power output. Parameters outlined in this article will be of assistance in the practical implementation of the integrated axes wind turbine.}, journal={APPLIED ENERGY}, author={Govind, Bala}, year={2017}, month={Aug}, pages={479–494} }