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1. A dual-bladder buoyancy engine for a cephalopod-inspired AUV

   Sholl, N.; Mohseni, K. (May 2019, Proceedings of the IEEE International Conference on Robotics and Automation (ICRA))

   This paper presents a nonlinear, backstepping depth and pitch controller for a dual-bladder buoyancy engine actuated by gear pumps. Flow-rate feedback is obtained using a custom flow sensor comprised of a differential pressure sensor and a small, 3D-printed attachment. The controller is simulated using a model of the CephaloBot, our in-house developed autonomous underwater vehicle (AUV). Its depth control capability is also experimentally validated using a single-bladder buoyancy engine on-board a smaller-scale test cylinder. Lyapunov stability analysis shows global, asymptotic stability, which is exhibited in our simulation. Our experiments verify that this buoyancy engine is a feasible and effective depth controller for AUVs. 

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2. Static Stability and Swim Bladder Volume in the Bluegill Sunfish ( Lepomis macrochirus )

   https://doi.org/10.1093/iob/obad005  

   Fath, M. A.; Nguyen, S. V.; Donahue, J.; McMenamin, S. K.; Tytell, E. D. (February 2023, Integrative Organismal Biology)

   Synopsis Static stability is a property inherent to every organism. More stable bodies benefit from a lower energy cost associated with maintaining a desired orientation, while less stable bodies can be more maneuverable. The static stability of a fish is determined by the relative locations of its center of mass (COM) and center of buoyancy (COB), which may change with changes in swim bladder volume. We hypothesized, however, that fish would benefit from consistent static stability, and predicted that changes in swim bladder volume would not alter the overall pattern of COM and COB locations. We used micro-computed tomography to estimate the locations of the COM and COB in bluegill sunfish (Lepomis macrochirus). Using this technique, we were able to find a small but significant difference between the location of the COM and COB for a given orientation. We found that the swim bladder can change shape within the body cavity, changing relative locations of the COM and COB. At one extreme, the COB is located 0.441 ± 0.007 BL from the snout and 0.190 ± 0.010 BL from the ventral surface of the pelvic girdle, and that the COM is 0.0030 ± 0.0020 BL posterior and 0.0006 ± 0.0005 BL ventral to the COB, a pattern that causes a nose-up pitching torque. At the other extreme, the COM is anterior and dorsal to the COB, a pattern that causes the opposite torque. These changes in location seems to be caused by changes in the shape and centroid location of the swim bladder within the body: The centroid of the swim bladder is located significantly more posteriorly in fish oriented head-down. The air in the bladder “rises” while heavier tissues “sink,” driving a change in tissue distribution and changing the location of the COM relative to the COB. Supporting our hypothesis, we found no correlation between swim bladder volume and the distance between the COM and COB. We conclude that bluegill are statically unstable, requiring them to expend energy constantly to maintain their normal orientation, but that the pitch angle of the body could alter the relative locations of COM and COB, changing their static stability. 

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3. Peptide-Mediated Targeting Mesoporous Silica Nanoparticles: A Novel Tool for Fighting Bladder Cancer

   Sweeney, Sean K; Luo, Yi; O'Donnell, Michael A; Assouline, Jose G (February 2017, Journal of biomedical nanotechnology)

   Transitional cell carcinoma of the bladder is particularly devastating due to its high rate of recurrence and difficulty in retention of treatments within the bladder. Current cystoscopic approaches to detect and stage the tumor are limited by the penetrative depth of the cystoscope light source, and intravesical dyes that highlight tumors for surgical resection are non-specific. To address the needs for improved specificity in tumor detection and follow-up, we report on a novel technology relying on the engineered core of mesoporous silica (MSN) with surface modifications that generate contrast in fluorescence and magnetic resonance imaging (MRI). The particle surface was further functionalized to include a bladder cancer cell specific peptide, Cyc6, identified via phage display. This peptide possesses nanomolar specificity for bladder cancer cells and homology across multiple species including mouse, canine, and human. Our study takes advantage of its target expression in bladder tumor which is not expressed in normal bladder wall. When functionalized to MSN, the Cyc6 improved binding efficiency and specificity for bladder cancer cells in vitro. In an in vivo model, MSN instilled into bladders of tumor-bearing mice enhanced T 1- and T 2-weighted MRI signals, improving the detection of the tumor boundaries. These findings support the notion that our targeted nanomaterial presents new options for early detection and eventual therapeutic intervention. Ultimately, the combination of real-time and repeated MRI evaluation of the tumors enhanced by nanoparticle contrast have the potential for translation into human clinical studies for tumor staging, therapeutic monitoring, and drug delivery. 

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4. A Hybrid PID Design for Asymptotic Stabilization with Intermittent Measurements

   https://doi.org/10.1109/CDC.2018.8619150  

   Lavell, Daniel; Phillips, Sean; Sanfelice, Ricardo G. (December 2018, 2018 IEEE Conference on Decision and Control)

   In this paper, we propose a modeling and design technique for a proportional-integral-derivative (PID) controller in the presence of aperiodic intermittent sensor measurements. Using classical control design methods, PID controllers can be designed when measurements are available periodically, at discrete time instances, or continuously. Unfortunately, such design do not apply when measurements are available intermittently. Using the hybrid inclusions framework, we model the continuous-time plant to control, the mechanism triggering intermittent measurements, and a hybrid PID control law defining a hybrid closed-loop system. We provide sufficient conditions for uniform global asymptotic stability using Lyapunov set stability methods. These sufficient conditions are used for the design of the gains of the hybrid PID controller. Also, we propose relaxed sufficient conditions to provide a computationally tractable design method leveraging a polytopic embedding approach. The results are illustrated via numerical examples. 

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5. Modeling and Numerical Simulation of a Buoyancy Controlled Ocean Current Turbine

   https://doi.org/10.36688/imej.4.47-58  

   Hasankhani, Arezoo; VanZwieten, James; Tang, Yufei; Dunlap, Broc; De Luera, Alexandra; Sultan, Cornel; Xiros, Nikolaos (July 2021, International Marine Energy Journal)

   Increased global renewable power demands and the high energy density of ocean currents have motivated the development of ocean current turbines (OCTs). These compliantly mooring systems will maintain desired near-surface operating depths using variable buoyancy, lifting surface, sub-sea winches, and/or surface buoys. This paper presents a complete numerical simulation of a 700 kW variable buoyancy controlled OCT that includes detailed turbine system, inflow, actuator (i.e., generator and variable buoyancy), sensor, and fault models. Simulation predictions of OCT performance are made for normal, hurricane, and fault scenarios. Results suggest this OCT can operate between depths of 38 m to 329 m for all homogeneous flow speeds between 1.0-2.5 m/s. Fault scenarios show that rotor braking results in a rapid vertical OCT system assent and that blade pitch faults create power fluctuations apparent in the frequency domain. Finally, simulated OCT operations in measured ocean currents (i.e., normal and hurricane conditions) quantify power statistics and system behavior typical and extreme conditions. 

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