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1. Exploiting Fine-grained Dimming with Improved LiFi Throughput

   https://doi.org/10.1145/3643814  

   Zhang, Xiao; Mariani, James; Xiao, Li; Mutka, Matt W (May 2024, ACM Transactions on Sensor Networks)

   Optical wireless communication (OWC) shows great potential due to its broad spectrum and the exceptional intensity switching speed of LEDs. Under poor conditions, most OWC systems switch from complex and more error prone high-order modulation schemes to more robust On-Off Keying (OOK) modulation defined in the IEEE OWC standard. This paper presents LiFOD, a high-speed indoor OOK-based OWC system with fine-grained dimming support. While ensuring fine-grained dimming, LiFOD remarkably achieves robust communication at up to 400 Kbps at a distance of 6 meters. This is the first time that the data rate has improved via OWC dimming in comparison to the previous approaches that consider trading off dimming and communication. LiFOD makes two key technical contributions. First, LiFOD utilizes Compensation Symbols (CS) as a reliable side-channel to represent bit patterns dynamically and improve throughput. We firstly design greedy-based bit pattern mining. Then we propose 2D feature enhancement via YOLO model for real-time bit pattern mining. Second, LiFOD synchronously redesigns optical symbols and CS relocation schemes for fine-grained dimming and robust decoding. Experiments on low-cost Beaglebone prototypes with commercial LED lamps and the photodiode (PD) demonstrate that LiFOD significantly outperforms the state-of-the-art system with 2.1× throughput on the SIGCOMM17 data-trace. 

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2. Sliding Mode Control of an Array of Three Oscillating Water Column Wave Energy Converters to Optimize Electrical Power

   Mario E. Magaña, Danielle R. (September 2019, Proceedings of the European Wave and Tidal Energy Conference)

   This paper presents a complete mathematical model of an array of three oscillating water column (OWC) wave energy converters (WECs) and the design of a direct generator torque control strategy using a sliding mode control (SMC) to maximize the output power of doubly-fed induction generators (DFIGs) attached to bi-radial turbines that are driven by the oscillating motion of the air inside the OWC tubes. The performance of the proposed control strategy is evaluated in irregular waves scenarios and different angles of arrival of the wave front. 

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3. Hierarchical control of a park of floating oscillating water column wave energy converters

   Gaebele, Daniel T; Magana, Mario E (September 2021, Proceedings of the European Wave and Tidal Energy Conference)

   null (Ed.)

   —Ocean wave energy is a renewable energy which remains costly for large-scale electricity generation. Although the oscillating water column (OWC) wave energy converter (WEC) is a promising device type with a rectifying air turbine and generator which convert alternating airflow induced by the water motion into kinetic energy then to electric energy, there are still several challenges to overcome to achieve commercial energy production. A first step is deploying multiple devices close to each other in WEC parks, to save cost associated with mooring lines and power transmission cables and a second step is applying control at each stage of energy conversion to increase the electric energy output of the devices and ensure a safe operation. Herein, we first present a state-space model of a park of seven hydrodynamically interacting floating OWC WECs in all degrees of freedom with nonlinear PTO dynamics and a shared, quasi-static mooring model. The electric power flow is modeled by considering the conversion losses from the AC generators over a DC link, including a storage unit to the grid connection. Secondly, the OWC WEC park is expressed from a higher hierarchical level as an automaton driven by discrete events. Finally, we use a standard supervisory control approach to enable different local control schemes to ensure a save operation of the individual WEC and the park. The supervisor has good adaptability potential for different WECs and the incorporation of safety mechanisms. 

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4. On the Capacity of Intensity-Modulation Direct-Detection Gaussian Optical Wireless Communication Channels: A Tutorial

   https://doi.org/10.1109/COMST.2021.3120087  

   Chaaban, A. (January 2022, IEEE Communications surveys and tutorials)

   Optical wireless communication (OWC) using intensity-modulation and direct-detection (IM/DD) has a channel model which possesses unique features, due to the constraints imposed on the channel input. The aim of this tutorial is to overview results on the capacity of IM/DD channels with input-independent Gaussian noise as a model of OWC channels. It provides the reader with an entry point to the topic, and highlights some major contributions in this area. It begins with a discussion on channel models and how this IM/DD Gaussian channel model comes about, in addition to an explanation of input constraints. Then, it discusses the capacity of the single-input single-output channel, its computation, and capacity bounds and asymptotic capacity results. Then, it extends the discussion to the multiple-input multiple-output setup, and reviews capacity bounds for this channel model. Finally, it discusses multi-user channels modelled as a broadcast channel (downlink) or a multiple-access channel (uplink), with their associated capacity bounds. 

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5. Nucleation in a liquid droplet

   https://doi.org/10.1039/D0CP00559B  

   Yang, Fuqian (May 2020, Physical Chemistry Chemical Physics)

   null (Ed.)

   The droplet-based microreactors in microfluidic systems have been used to synthesize nanocrystals of a variety of metals and semiconductors, which involves the nucleation and growth processes. Considering the limited numbers of solvent atoms and solute atoms/particles in a stationary droplet, we derive analytical expressions of the changes of the Gibbs free energy and the Helmholtz free energy for the concurrent formation of multiple microclusters of the same size in the liquid droplet. Both the changes of the Gibbs free energy and the Helmholtz free energy are dependent on the ratio of the number of microclusters to the solvent atoms and the interface energy between the solution and the microclusters. Using the change of the free energy, which is an approximation of the Gibbs free energy and the Helmholtz free energy, we obtain the critical nucleation number of the solute atoms/particles in the microclusters for the concurrent nucleation of multiple nuclei of the same size. The critical nucleation number of the solute atoms/particles is dependent on the ratio of the number of nuclei in the droplet to the solvent atoms, and the maximum change of the free energy for the concurrent nucleation of multiple nuclei of the same size increases with the increase of the ratio of the number of the nuclei in the droplet to the number of the solvent atoms. 

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