This research was conducted in laboratory to investigate an alternative for Cr removal from an electroplating wastewater using the electro-chemical precipitation (ECP) process. The ECP unit, operated in the bipolar mode, had six steel plates including the anode and cathode and was supplied with DC power. The electroplating wastewater used in the experiments contained Cr concentrations in the range of 570-2100 mg/l. The Cr removal efficiencies in the bipolar ECP units were higher than 99% and the Cr concentrations in the treated effluent were less than 0.5 mg/l. The acceptable conditions of the bipolar ECP unit treating the electroplating wastewater were found to be: I - 1.0 amp (or i - 6.70 amp/m2) and initial pH (pHi) of 4.5. At these acceptable conditions, the electric power and steel electrode plate consumptions were 20.0 kWh/m3 and 1.1-2.8 kg-Fe/kg Cr removed, respectively. X-ray fluorescence and X-ray diffractometric analysis performed on the precipitated sludge revealed the main compounds to be maghemite (Fe2O3) and chromite (FeCr2O4). The percent Fe2O3 and FeCr2O4 contents of the dried ECP sludge were 68% and 25%, respectively. From the mass balance analysis, the percent of Cr removal by precipitation in the ECP unit and adsorption on the ECP sludge were 85.1 and 14.8%, respectively.

Abstract-In this paper, we derive bounds to the channel capacity of orthogonal frequency division multiplexing (OFDM) systems over the underwater (UW) acoustic fading channel as a function of the distance between the transmitter and the receiver. The upper bound is obtained under perfect channel state information (CSI) at the receiver. The lower bound is obtained assuming the input is drawn from phase-shift keying (PSK) constellation which results in non-Gaussian distribution of the output signal and no CSI. The reduction from the upper bound is due to limited mutual information that can be conveyed by PSK constellation and the linear minimum mean square prediction error. Our UW channel deviates from the wide sense stationary and uncorrelated scattering (WSSUS) model commonly used for small bandwidths. We incorporate frequency-dependent path loss due to the acoustic propagation into each arrival path between the transmitter and the receiver. This leads the UW channel to be modeled as a frequency-dependent doubly spread fading channel characterized by the wide sense stationary and correlated scattering (WSS-non-US) fading assumption. Both Rayleigh and Ricean fading assumptions are investigated in our model. Results from the model show a gap between the upper and lower bounds which depends not only on the ranges and shape of the scattering function of the UW channel but also on the distance between the transmitter and the receiver. Our model for the scattering function was suggested by Rescheduled Acoustic Communications Experiment (RACE08) experimental data, leading to a multilag autoregressive (AR-) model for the fading.Index Terms-Doubly spread fading channels, linear minimum mean square error, orthogonal frequency division multiplexing (OFDM), underwater acoustic communications, underwater acoustic propagation, wideband channel capacity.

Single-carrier frequency-domain equalization (SC-FDE) is a promising technique for coherent underwater acoustic communications. The method has a lower peak-to-average power ratio than orthogonal frequency-division multiplexing (OFDM) and is more resistant to frequency offset. In this work, SC-FDE performance is evaluated using data collected during the 2009 Cooperative Array Performance Experiment (CAPEx09) that took place near Seattle, WA, USA. CAPEx09 had two densely populated vertical receiving arrays and a highly refractive environment, features that make it suitable for examining issues related to sensor positioning in range and depth. Two-channel equalization results show only a weak dependence on the spacing between the two sensors. Communications performance is interpreted in terms of relevant propagation physics, including acoustic ducting and rough surface scattering. The implications for undersea acoustic networks are discussed.Index Terms-Refraction, rough surface scattering, single-carrier frequency-domain equalization (SC-FDE), underwater acoustic communications.

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These studies demonstrate that significant performance improvement over the RC stimulation is obtained without additional testing or training samples to compensate for low P300 amplitude at high flash rate. We show that our proposed stimulation is more robust to reduced signal strength due to the increased flash rate than the RC stimulation.

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