Understanding the Effect of Balance of Plant Contaminants On PEMFCS Performance: Models, Mechanisms, Functional Group

This dissertation considers contamination of a proton exchange membrane fuel cell (PEMC) that may result from chemicals that leach from balance of plant (BOP) materials. Both model predictions and experimental data are presented. The model is used to predict the cathode contamination impact on the Pt/C electrode and the membrane assuming no transport of contaminant from cathode to anode. The model prediction accounts for the contamination mechanisms such as adsorption, ion-exchange, absorption and three sources of voltage (i.e., performance) loss. The simple 2-D time-dependent model is developed by considering well known chemical engineering concepts of Langmuir adsorption, partition coefficients, plug flow reactors (PFRs), and dimensionless analysis. The three important dimensionless groups that result from the analysis are the Da (contamination reaction rate), fÕ (capacity ratio), and ,,C (coverage ratio). For the experiments, selected model compounds were identified in leachate solutions during the screening of off-the-shelf BOP materials. Ex-situ studies using a rotating disk electrode and a membrane conductivity device allow the preparation of isotherms based on functionality and fundamental mechanisms. The isotherms for each mechanism provide a quantitative effect of coverage by these compounds. The in-situ data obtained from segmented cell experiments is also reported. The comparison of the model predictions with in-situ experiment data shows consistent predicted coverage and performance loss. The prediction results for different species that drive the contamination mechanisms agree with experimentally determined voltage losses for each mechanism. The voltage loss for the ionomer by an ion-exchange mechanism shows the slowest contamination rate but the greatest performance loss relative to other mechanisms (i.e., adsorption/absorption). That is, voltage losses by ion-exchange continued with feed contaminant until the cell totally lost the performance. In addition, the maximum coverage by contaminants with absorption and adsorption mechanisms is determined by the leachate concentration. Finally, the tolerance limit for the each mechanism is provided from the predictions allows for the establishment of qualification standards for BOP materials

Half-Wave Dipolar Metal-Semiconductor Laser

Nano-scale lasers harnessing metallic plasmons hold promise across physical sciences and industrial applications. Plasmons are categorized as surface plasmon polaritons (SPP) and localized surface plasmons (LSP). While SPP has gained popularity for nano-lasers by fitting a few cycles of SPP waves into resonators, achieving LSP lasing in single nanoparticles remains an elusive goal. Here, we highlight the equivalence of LSP and SPP within resonant systems and present lasers oscillating in the lowest-order LSP or, equivalently, half-cycle SPP. This diffraction-limited dipolar emitter is realized through strong coupling of plasmonic oscillation in gold and dielectric resonance in high-gain III-V semiconductor in the near infrared away from surface plasmon frequencies. The resulting single-mode stimulated emission peak exhibits linewidth Q factors over 50 at room temperature, with wide tunability spanning from 1190 to 1460 nm determined by resonator sizes ranging from 190 to 280 nm. A semiconductor laser model elucidates the temporal and spectral buildup dynamics under optical pumping. Notably, linewidth Q values surpassing 250 are attained from higher-order, isolated laser particles within live biological cells. These results offer fresh perspectives in nanophotonics and indicate promising opportunities for multiplexed biological applications

Laser Particle Stimulated Emission Microscopy

We introduce an optical microscopy technique that utilizes micro- or nanolasers embedded in a sample as imaging probes. The narrow spectra and nonlinear power dependence of stimulated emission from the laser particles yield optical sectioning, subdiffraction resolution, and low out-of-focus background. A proof of concept is demonstrated using perovskite nanowires.National Science Foundation (U.S.) (Grant ECCS-1505569)National Institutes of Health (U.S.) (Grants DP1EB024242 and P41EB015903)Massachusetts General Hospital. Research Scholar Award Progra

Effects of Aerobic Exercise Intensity on Post-exercise Blood Pressure and Cardiovascular Function in Prehypertensive Men in Their 30s

PURPOSE Blood pressure (BP) in hypertensive individuals is reduced by the accumulation of post-exercise hypotension (PEH) induced by a long period of training. This study aimed to investigate the effects of intensity of two different aerobic exercises with identical energy expenditure on post-exercise blood pressure and cardiovascular function in prehypertensive men. METHODS Eleven prehypertensive men in their 30s participated in two trials repeatedly. In the first trial, the exercise was moderate in intensity and continuous (MICE) with 70% of VO2max, and the exercise in the second trial was high-intensity interval exercise (HIIE) with 50% and 90% of VO2max. Each exercise was performed for 30 min, and the variables related to BP and cardiovascular function were measured at certain times for 1 hr during the recovery phase. RESULTS Our main findings are as follows: (1) Systolic blood pressure was significantly lower at 30 and 45 min of recovery time than the baseline in the HIIE trial, and systolic blood pressure was significantly lower in the HIIE trial than the MICE trial at 10, 15, and 30 min of recovery time. (2) The rate pressure product was significantly higher in the HIIE trial than the MICE trial at 15, 30, 45, and 60 min of recovery time. (3) The heart rate was significantly higher in the HIIE trial than the MICE trial at 15, 30, 45, and 60 min of recovery time. (4) Stroke volume was significantly lower in the HIIE trial than the MICE trial at 30 min of recovery time. (5) Cardiac output was significantly higher in the HIIE trial than the MICE trial at 15 min of recovery phase. (6) Total vascular conductance was significantly higher in the HIIE trial than the MICE trial at 15 and 30 min of recovery phase. (7) Total peripheral resistance was significantly lower in the HIIE trial than the MICE trial at 15 and 30 min of recovery phase. CONCLUSIONS The HIIE shows a higher cardiovascular stress than MICE; however, HIIE contributes to the augmentation of PEH and improvement of cardiovascular function. Therefore, HIIE rather than MICE should be suggested in BP control and enhancement of cardiovascular function in prehypertensive males

Sub-fingerprint masking for a robust audio fingerprinting system in a real-noise environment for portable consumer devices

author's final draftThe robustness of audio fingerprinting system in a noisy environment is a principal challenge in the area of content-based music retrieval, especially for use in portable consumer devices. Our new audio fingerprint method using sub-fingerprint masking based on the predominant pitch extraction dramatically increases the accuracy of the audio fingerprinting system in a noisy environment, while requiring much less computing power for matching, compared to the expanded hash table lookup method, where the searching complexity increases by the factor of 33 times the degree of expansion.This research was supported by Konkuk University