Overcoming parasitic reactions occurring in carbonaceous Seawater Battery cathodes and their mechanisms

School of Energy and Chemical Engineering (Battery Science and Technology)Rechargeable seawater batteries (SWBs) have recently been investigated as a potential candidate for future energy storage systems, owing to their cost-effectiveness and environmentally friendly properties derived from the use of naturally abundant seawater as a catholyte. However, the fundamental understanding of the cathode reactions in SWBs is not yet fully elucidatedhence, an investigation of their mechanisms is imperative for future development. Herein, parasitic cathode reactions other than the previously identified oxygen evolution/reduction reactions (OERs/ORRs) are identified for the first time using activated carbon cloth (ACC) as the cathode current collector. In this study, carbon fibers of the current collector were observed to undergo cathode side-reactions such as fiber-fracturing carbon corrosion during charging and surface-insulating CaCO3 precipitation via carbon dioxide capture during discharging, both resulting in cathode performance failure. Moreover, carbon corrosion was determined to be the dominant factor behind performance degradation under normal charge???discharge cycling conditions in comparison to CaCO3 precipitation, which was found to be a reversible phenomenon during the operation of the SWB. These results provide insight for future work into enhancing the longevity of SWBs by identifying carbon corrosion as the main cathode performance degradation mechanism. Owing to these findings, an alternative cathode which exceeds the performance and cycle stability of the previously investigated ACC was found. An activated carbon fiber (ACF) cathode with a larger degree of graphitization than the ACC was found to resist carbon corrosion. Characterization and comparison of the level of carbon disorder in the ACC and ACF was done, elucidating the origin of the difference in carbon corrosion resistance.ope

Learning Terrain-Aware Kinodynamic Model for Autonomous Off-Road Rally Driving With Model Predictive Path Integral Control

High-speed autonomous driving in off-road environments has immense potential for various applications, but it also presents challenges due to the complexity of vehicle-terrain interactions. In such environments, it is crucial for the vehicle to predict its motion and adjust its controls proactively in response to environmental changes, such as variations in terrain elevation. To this end, we propose a method for learning terrain-aware kinodynamic model which is conditioned on both proprioceptive and exteroceptive information. The proposed model generates reliable predictions of 6-degree-of-freedom motion and can even estimate contact interactions without requiring ground truth force data during training. This enables the design of a safe and robust model predictive controller through appropriate cost function design which penalizes sampled trajectories with unstable motion, unsafe interactions, and high levels of uncertainty derived from the model. We demonstrate the effectiveness of our approach through experiments on a simulated off-road track, showing that our proposed model-controller pair outperforms the baseline and ensures robust high-speed driving performance without control failure.Comment: Accepted to IEEE Robotics and Automation Letters (and ICRA 2024). Our video can be found at https://youtu.be/VXf_prNQnJo Project page : https://sites.google.com/view/terrainawarekinody

Optofluidic Lasers and Their Bio-Sensing Applications

Novel optofluidic ring resonator (OFRR) lasers resolving problems of existing lasers have been demonstrated and DNA melting analysis taking advantages of the OFRR laser is suggested. The OFRR laser fabricated on a polymer chip utilizes two optically coupled ring resonators in different sizes in order to address an intrinsic multi-mode emission of the ring resonator laser. A single-mode emission is obtained by Vernier effect and the wavelength is tunable by modifying the refractive index of the gain medium. A quasi-droplet OFRR laser is developed based on a micro-bubble filled with liquid gain medium. Due to the sub-micron wall thickness, the micro-bubble mimics a droplet in air that has 3-dimensional optical confinement, extremely high Q-factor and versatility of handling liquids of different refractive index. The laser using Rhodamine 6G in methanol has low lasing thresholds and dye concentration. Furthermore, it enables repetitive interrogation and easy directional laser emission out-coupling without evaporation or size/shape variations. Microdroplets in carrier fluid are delivered to the capillary OFRR downstream and laser emission is obtained. The laser can conveniently be coupled into an optical fiber and lasing threshold 6 times lower than the state-of-art is achieved. An efficient FRET lasing is also demonstrated making the OFRR droplet laser an attractive platform of bio/chemical sensing with small sample volume. In last, a highly specific intracavity DNA melting analysis scheme utilizing the optofluidic laser is proposed. The laser optically amplifies the small yet intrinsic thermal dynamic difference between the target and the single-base-mismatched DNA, resulting in a differential signal that is orders of magnitude greater than with fluorescence-based methods. In particular, the existence of a phase transition between the stimulated laser emission and fluorescence enables accurate determination of the DNA transition temperature difference. Furthermore, the high differential signal in the intracavity detection allows for scanning of the laser excitation at a fixed temperature to distinguish two DNA sequences, which provides another means for rapid DNA analysis. The intracavity DNA detection leads to novel optofluidic devices that enable rapid and simple analysis of DNAs with long sequences.PhDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/102452/1/wonslee_1.pd

Smooth Model Predictive Path Integral Control without Smoothing

We present a sampling-based control approach that can generate smooth actions for general nonlinear systems without external smoothing algorithms. Model Predictive Path Integral (MPPI) control has been utilized in numerous robotic applications due to its appealing characteristics to solve non-convex optimization problems. However, the stochastic nature of sampling-based methods can cause significant chattering in the resulting commands. Chattering becomes more prominent in cases where the environment changes rapidly, possibly even causing the MPPI to diverge. To address this issue, we propose a method that seamlessly combines MPPI with an input-lifting strategy. In addition, we introduce a new action cost to smooth control sequence during trajectory rollouts while preserving the information theoretic interpretation of MPPI, which was derived from non-affine dynamics. We validate our method in two nonlinear control tasks with neural network dynamics: a pendulum swing-up task and a challenging autonomous driving task. The experimental results demonstrate that our method outperforms the MPPI baselines with additionally applied smoothing algorithms.Comment: Accepted to IEEE Robotics and Automation Letters (and IROS 2022). Our video can be found at https://youtu.be/ibIks6ExGw

Optofluidic ring resonator laser with an edible liquid laser gain medium

We demonstrate a biocompatible optofluidic laser with an edible liquid laser gain medium, made of riboflavin dissolved in water. The proposed laser platform is based on a pulled-glass-capillary optofluidic ring resonator (OFRR) with a high Q-factor, resulting in a lasing threshold comparable to that of conventional organic dye lasers that are mostly harmful, despite the relatively low quantum yield of the riboflavin. The proposed biocompatible laser can be realized by not only a capillary OFRR, but also by an optical-fiber-based OFRR that offers improved mechanical stability, and is promising technology for application to in vivo bio-sensing

Accurate Distance Estimation between Things: A Self-correcting Approach

This paper suggests a method to measure the physical distance between an IoT device (a Thing) and a mobile device (also a Thing) using BLE (Bluetooth Low-Energy profile) interfaces with smaller distance errors. BLE is a well-known technology for the low-power connectivity and suitable for IoT devices as well as for the proximity with the range of several meters. Apple has already adopted the technique and enhanced it to provide subdivided proximity range levels. However, as it is also a variation of RSS-based distance estimation, Apple's iBeacon could only provide immediate, near or far status but not a real and accurate distance. To provide more accurate distance using BLE, this paper introduces additional self-correcting beacon to calibrate the reference distance and mitigate errors from environmental factors. By adopting self-correcting beacon for measuring the distance, the average distance error shows less than 10% within the range of 1.5 meters. Some considerations are presented to extend the range to be able to get more accurate distances

A quasi-droplet optofluidic ring resonator laser using a micro-bubble

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98697/1/ApplPhysLett_99_091102.pd

Age-specific associations between serum cholesterol levels and suicidal behaviors in patients with depressive disorders: A naturalistic prospective observational cohort study

IntroductionThis study investigated the effects of total cholesterol levels on prevalent, and incident suicidal behaviors according to age group (<60 vs. ≥60 years) in depressed patients.MethodsConsecutive outpatients with depressive disorders who visited the Chonnam National University Hospital between March 2012 and April 2017 were recruited. Among 1,262 patients assessed at baseline, 1,094 agreed to blood sampling for measurement of serum total cholesterol levels. Among the patients, 884 completed the 12-week acute treatment phase and were followed up at least once during the 12-month continuation treatment phase. Suicidal behaviors assessed at baseline included baseline suicidal severity; behaviors assessed at the 1-year follow-up included increased suicidal severity and fatal/non-fatal suicide attempts. Associations of baseline total cholesterol levels with the above-mentioned suicidal behaviors were analyzed using logistic regression models after adjustment for relevant covariates.ResultsOf 1,094 depressed patients, 753 (68.8%) were women. The mean (SD) age of patients was 57.0 (14.9) years. Lower total cholesterol levels (87–161 mg/dl) were associated with increased suicidal severity (Linear Wald = 4.478, p < 0.05) and fatal/non-fatal suicide attempt (Linear Wald = 7.490, p < 0.01) in patients <60 years of age. U-shaped associations between total cholesterol levels and 1-year follow-up suicidal outcomes (increased suicidal severity, Quadratic Wald = 6.299, p < 0.05; fatal/non-fatal suicide attempt, Quadratic Wald = 5.697, p < 0.05) were observed in patients ≥60 years of age.ConclusionsThese findings suggest that differential consideration of serum total cholesterol levels according to age group may have clinical utility for predicting suicidality in patients with depressive disorders. However, because our research participants came from a single-hospital, the generalizability of our findings may be limited