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1. The tracking detector of the FASER experiment

   https://doi.org/10.1016/j.nima.2022.166825  

   Abreu, Henso; Antel, Claire; Ariga, Akitaka; Ariga, Tomoko; Bernlochner, Florian; Boeckh, Tobias; Boyd, Jamie; Brenner, Lydia; Cadoux, Franck; Casper, David W.; et al (July 2022, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment)
2. Ultrasound Tracking of the Acoustically Actuated Microswimmer

   https://doi.org/10.1109/TBME.2019.2902523  

   Chen, Qiyang; Liu, Fang-Wei; Xiao, Zunding; Sharma, Nitin; Cho, Sung Kwon; Kim, Kang (March 2019, IEEE Transactions on Biomedical Engineering)

   Objective: The purpose of this paper is to demonstrate the ultrasound tracking strategy for the acoustically actuated bubble-based microswimmer. Methods: The ultrasound tracking performance is evaluated by comparing the tracking results with the camera tracking. A benchtop experiment is conducted to capture the motion of two types of microswimmers by synchronized ultrasound and camera systems. A laboratory developed tracking algorithm is utilized to estimate the trajectory for both tracking methods. Results: The trajectory reconstructed from ultrasound tracking method compares well with the conventional camera tracking, exhibiting a high accuracy and robustness for three different types of moving trajectories. Conclusion: Ultrasound tracking is an accurate and reliable approach to track the motion of the acoustically actuated microswimmers. Significance: Ultrasound imaging is a promising candidate for noninvasively tracking the motion of microswimmers inside body in biomedical applications and may further promote the real-time control strategy for the microswimmers. 

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3. Tracking exceptional points above the lasing threshold

   https://doi.org/10.1038/s41467-023-43874-z  

   Ji, Kaiwen; Zhong, Qi; Ge, Li; Beaudoin, Gregoire; Sagnes, Isabelle; Raineri, Fabrice; El-Ganainy, Ramy; Yacomotti, Alejandro M. (December 2023, Nature Communications)

   Abstract Recent studies on exceptional points (EPs) in non-Hermitian optical systems have revealed unique traits, including unidirectional invisibility, chiral mode switching and laser self-termination. In systems featuring gain/loss components, EPs are commonly accessed below the lasing threshold, i.e., in the linear regime. In this work, we experimentally demonstrate that EP singularities in coupled semiconductor nanolasers can be accessed above the lasing threshold, where they become branch points of a nonlinear dynamical system. Contrary to the common belief that unavoidable cavity detuning impedes the formation of EPs, here we demonstrate that such detuning is necessary for compensating the carrier-induced frequency shift, hence restoring the EP. Furthermore, we find that the pump imbalance at lasing EPs varies with the total pump power, enabling their continuous tracking. This work uncovers the unstable nature of EPs above laser threshold in coupled semiconductor lasers, offering promising opportunities for the realization of self-pulsing nanolaser devices and frequency combs. 

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4. Source tracking microplastics in the freshwater environment

   Farhenfeld, N.L.; Arbuckle-Kiel, G.; Naderi Beni, N.; Bartelt-Hunt, S.L. (February 2019, TrAC Trends in analytical chemistry)
5. Acoustic Float Tracking with the Kalman Smoother

   https://doi.org/10.1175/JTECH-D-21-0063.1  

   Chamberlain, Paul; Cornuelle, Bruce; Talley, Lynne D; Speer, Kevin; Hancock, Cathrine; Riser, Stephen (July 2022, Journal of Atmospheric and Oceanic Technology)

   Abstract Acoustically-tracked subsurface floats provide insights into ocean complexity and were first deployed over 60 years ago. A standard tracking method uses a Least-Squares algorithm to estimate float trajectories based on acoustic ranging from moored sound sources. However, infrequent or imperfect data challenge such estimates, and Least-Squares algorithms are vulnerable to non-Gaussian errors. Acoustic tracking is currently the only feasible strategy for recovering float positions in the sea ice region, a focus of this study. Acoustic records recovered from under-ice floats frequently lack continuous sound source coverage. This is because environmental factors such as surface sound channels and rough sea ice attenuate acoustic signals, while operational considerations make polar sound sources expensive and difficult to deploy. Here we present a Kalman Smoother approach that, by including some estimates of float behavior, extends tracking to situations with more challenging data sets. The Kalman Smoother constructs dynamically constrained, error-minimized float tracks and variance ellipses using all possible position data. This algorithm outperforms the Least-Squares approach and a Kalman Filter in numerical experiments. The Kalman Smoother is applied to previously-tracked floats from the southeast Pacific (DIMES experiment), and the results are compared with existing trajectories constructed using the Least- Squares algorithm. The Kalman Smoother is also used to reconstruct the trajectories of a set of previously untracked, acoustically-enabled Argo floats in the Weddell Sea. 

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