RESUMO
In order to improve the angle measurement performance of a coprime linear array, this paper proposes a novel direction-of-arrival (DOA) estimation algorithm for a coprime linear array based on the multiple invariance estimation of signal parameters via rotational invariance techniques (MI-ESPRIT) and a lookup table method. The proposed algorithm does not require a spatial spectrum search and uses a lookup table to solve ambiguity, which reduces the computational complexity. To fully use the subarray elements, the DOA estimation precision is higher compared with existing algorithms. Moreover, the algorithm avoids the matching error when multiple signals exist by using the relationship between the signal subspace of two subarrays. Simulation results verify the effectiveness of the proposed algorithm.
RESUMO
Dyeing wastewater in various industries poses a great threat to the environment. Montmorillonite (MT) is widely used in wastewater treatment because of its abundant reserves and strong exchange capacity. However, natural MT has low affinity for organic pollutants and needs to be organically modified. In order to improve the adsorption capacity of MT to cationic dyes [Congo red (CR)], using ionic liquid [1-hexadecyl-3-methylimidazolium chloride (C16MImCl)] as organic modifier, the optimal preparation process of C16MImCl/MT was determined by response surface methodology. The C16MImCl/MT was comprehensively characterized by utilizing the techniques of XRD, FTIR, TG, BET, SEM, and molecular dynamics simulation. All the research results showed that C16MImCl is successfully inserted into the layers of MT, and the basal interplanar spacing and average pore size of MT are obviously increased. The C16MImCl/MT is a mesoporous material, which shows strong adsorption capacity for CR, and its CR unit adsorption capacity (CRUAC) could reach 940.200 mg/g, which is about three times that of magnetic graphene oxide and bentonite/expanded graphite.