The aim of the present work is to investigate the ability of commercial natural bentonite (untreated) (NB) to remove silver ions from aqueous solution. Specific surface area of the sample was determined as a result of N 2 adsorption-desorption at 77 K using BET method. X-ray powder diffraction (XRD) was used to characterize the (NB). Towards this aim, batch adsorption experiments were carried out and the effect of various parameters on this removal process has been investigated. The effects of pH, adsorption time, silver ion concentration, bentonite doses, Temperature and the NB treatment (calcinations and washing) on the adsorption process were examined. The optimum pH for adsorption was found to be 4-8. It was found that NB treatment has a substantial effect on the metal uptake. In adsorption studies, residual silver ions concentration reached equilibrium in a short duration of 15 min. The paper discusses the thermodynamic parameters of the adsorption (the Gibbs free energy, entropy, and enthalpy). Adsorption of Ag + on NB appeared to follow Langmuir isotherm. Our results demonstrate that the adsorption process was spontaneous and endothermic under natural conditions. Additionally, a pseudo-second-order rate model was adopted to describe the kinetics of adsorption. In desorption experiment, an approximately (15%) desorption yield was obtained for silver ions.
We address the problem of designing a transmit beampattern for multiple-input multiple-output (MIMO) radar considering co-existence with wireless communication systems. The designed beampattern is able to manage the transmit energy in spatial directions as well as in spectral frequency bands of interest by minimizing the deviation of the designed beampattern versus a desired one under a spectral constraint as well as the constant modulus constraint. While unconstrained beampattern design is straightforward, a key open challenge is jointly enforcing the spectral constraint in addition to the constant modulus constraint on the radar waveform. A new approach is proposed in our work, which involves solving a sequence of constrained quadratic programs such that constant modulus is achieved at convergence. Further, we show that each problem in the sequence has a closed form solution leading to analytical tractability. We evaluate the proposed beampattern with interference control (BIC) algorithm against the state-ofthe-art MIMO beampattern design techniques and show that BIC achieves closeness to an idealized beampattern along with desired spectral shaping.
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