Pilot Reduction Using Spatial and Temporal Correlation in Massive MIMO-OFDM Systems

Wireless Personal Communications - In MIMO-OFDM systems, the base station sends pilot signals for channel estimation at receivers. Since the number of pilots is proportional to the number of...     

Novel interactions of caffeic acid with different hemoglobins: Effects on discoloration and lipid oxidation in different washed muscles

Caffeic acid (CA) accelerated methemoglobin (Hb) formation at pH 5.8 and 25 °C. This was attributed to electron donation from CA to liganded O₂ in Hb. CA inhibited hemin dissociation from metHb. Pig Hb remained mostly as oxyHb and did not promote lipid oxidation in washed cod muscle (WCM) nor washed turkey muscle (WTM) during iced storage at pH 5.8. Conversely, perch Hb rapidly was converted to metHb and readily promoted lipid oxidation based on lipid peroxide and hexanal formation. CA strongly inhibited perch Hb-mediated lipid oxidation during storage. Once metHb formation occurred in WCM, CA appeared to maintain the heme protein as metHb during the remainder of iced storage. CA may have become bound to perch Hb based on filtration analysis. CA facilitated the transfer of perch Hb (but not pig Hb) from the aqueous phase to the insoluble components of WCM. Collectively, these results suggest that CA inhibited Hb-mediated lipid oxidation by various mechanisms not related to inhibition of metHb formation.     

Comparison of influences of NaCl and CaCl2 on the corrosion of 11% and 17% Cr ferritic stainless steels during cyclic corrosion test

During the drying stage of the cyclic corrosion test on ferritic stainless steels in the NaCl environment, the current abruptly increased and then decreased to nearly zero, indicating that pits are initiated as the salt concentration is increased, which are then repassivated when the surface is completely dry. During the wet stage, the current remained high, suggesting that pits mainly propagate during the wet stage. In contrast, in the cyclic corrosion test in the CaCl₂ environment, the current was highest during the drying stage, indicating that the electrolyte is not completely dried and corrosion mainly propagates during the drying stage.     

Pinhole formation in PEMFC membrane after electrochemical degradation and wet/dry cycling test

During the operation of a PEMFC, the polymer membrane is degraded by electrochemical reactions and mechanical stresses. We investigated the effects of repeated electrochemical and mechanical degradations in a membrane. For mechanical degradation, the membrane and MEA were repeatedly subjected to wet/dry cycles; for electrochemical degradation, the cell was operated under open-circuit voltage (OCV)/low-humidity conditions. The repeated wet/dry cycles led to a decrease in the mechanical strength of the membrane. When the MEA was degraded electrochemically, repeated wet/dry cycling resulted in the formation of pinholes in the membrane. In the case of different MEAs that were first degraded electrochemically, the extents of their hydrogen crossover currents increased due to repeated wet/dry cycling being different. Therefore, these results indicated that the membrane durability could be evaluated by these methods of repeated electrochemical degradation and wet/dry cycles.     

Examining the effects of velocity ratio of the pressurized flow to the main inlet flow on coagulants dispersion in pump diffusion mixer

This study was conducted to evaluate the ratio of the pressurized flow to the main inlet flow, which has been considered one of the most important parameters for operating the pump diffusion mixer (PDM). Computational fluid dynamics (CFD) simulation was employed to evaluate the conventional operation rule of PDM and to propose a supplementary operating parameter and criterion. Test simulation of CFD was carried out for the 21 cases of flow ratio in a full scale PDM. The values of local velocity gradient were calculated in each case to analyze the simulation results in more detail. A wet test was conducted to verify CFD simulation results, which measures the factual coagulant dispersion distribution at a distance of 5.4 m from deflector. From results of both CFD simulation and wet test, the flow ratio was adequate as an operating parameter or criterion; also, the velocity ratio (dimensionless) of the pressurized flow to the main inlet was useful in predicting the performance of PDM. In addition, the injected coagulant could be dispersed evenly in overall cross section on the condition that the velocity ratio is at least over 20.     

A health management algorithm for composite train carbody based on FEM/FBG hybrid method

In this study, a health management program for a composite train carbody was developed using the acquired strain distributions from fiber Bragg grating (FBG) sensor arrays. To determine appropriate locations for the FBG sensors, a finite element analysis (FEA) was executed. In this FEA, a FE model of the Korean tilting train (TTX) was used as a representative composite carbody train. The FEA results of various derailment situations and high speed operation on curved track were used as the database of each deformation case. In the last step, the health management program was produced using LabVIEW software. In this post-processing algorithm, the method of least squares was used to determine the difference between the FEA results and the acquired strains. This program shows the estimated deformations and plots of the acquired strains, as well as displaying an emergency indicator when necessary, all through post-processing of the strains. Finally, this FEM/FBG hybrid method was verified by several simulations using the reproductive sensor data.     

Degradation behavior of Ni-YSZ anode-supported solid oxide fuel cell (SOFC) as a function of H2S concentration

This study investigated the effect of H₂S concentration (5, 10 and 50 ppm) on the degradation and performance of Ni-YSZ anode supported solid oxide fuel cells. When supplied with hydrogen fuel containing H₂S, the cell voltage dropped rapidly, and with increasing H₂S concentration, voltage drop % increased (due to higher sulfur coverage on the Ni surface) and saturated more rapidly. A high concentration (50 ppm) of H₂S led to an additional, slow rate voltage loss. In all cases, cell performance did not completely recover even after being supplied with H₂S-free hydrogen fuel, because of the incomplete desorption of sulfur from the Ni surface. After the performance tests, nickel sulfides were detected on the Ni surface by Raman spectra, which were produced by the reaction of the remaining adsorbed sulfur with Ni during the cooling process. This indicates that the formation of nickel sulfides was not responsible for the secondary voltage drop. SEM/EDS analyses combined with FIB revealed that the reason for the additional 2^nd drop was Ni oxidation; at a high sulfur coverage ratio (50 ppm), the outer layer of the Ni particle was oxidized by oxygen ions transported from the electrolyte. This indicates that H₂S concentration as well as current density is a critical factor for Ni oxidation, and gives rise to the second voltage drop (irreversible cell degradation). The present work showed that the degradation behavior and phenomenon can differ significantly depending on the concentration of H₂S, i.e., permanent changes may or may not occur on the anode (such as Ni oxidation) depending upon H₂S concentration.     

CdS-sensitized TiO2 in phenazopyridine photo-degradation: Catalyst efficiency,stability and feasibility assessment

Mineralization of phenazopyridine, 1, in water, under solar-simulator radiation was efficiently achieved using nanoparticle CdS-sensitized rutile TiO₂, TiO₂/CdS, 2, as photo-catalysts. Despite that, 2 showed two main drawbacks. Firstly, the system was difficult to recover by simple filtration, and demanded centrifugation. Secondly, the sensitizer CdS showed relatively high tendency to leach out hazardous Cd²⁺ ions under photo-degradation reaction conditions. In an attempt to solve out such difficulties, 2 was supported onto sand surface. The sand/TiO₂/CdS system, 3, was easier to recover but showed slightly lower catalytic activity compared to 2. On the other hand, the support failed to prevent leaching of Cd²⁺. This indicates limited future applicability of CdS-sensitized TiO₂ photo-catalyst systems, in solar-based water purification strategies, unless leaching out tendency is completely prevented.