Frequency-invariant robust adaptive beamforming based on interference covariance matrix reconstruction

Consider the problems of frequency-invariant beampattern optimization and robustness in broadband beamforming.Firstly,a global optimization algorithm,which is based on phase compensation of the array manifolds,is used to construct the frequency-invariant beampattern.Compared with some methods presented recently,the proposed algorithm is not only available to get the global optimal solution,but also simple for physical realization.Meanwhile,a robust adaptive broadband beamforming algorithm is also derived by reconstructing the covariance matrix.The essence of the proposed algorithm is to estimate the space-frequency spectrum using Capon estimator firstly,then integrate over a region separated from the desired signal direction to reconstruct the interference-plus-noise covariance matrix,and finally caleulate the adaptive beamformer weights with the reconstructed matrix.The design of beamformer is formulated as a convex optimization problem to be solved.Simulation results show that the performance of the proposed algorithm is almost always close to the optimal value across a wide range of signal to noise ratios.

Determination of N-nitrosodimethylamine in drinking water by UPLC-MS/MS

The method for detecting N-nitrosodimethylamine （NDMA） in drinking water using ultra performance liquid chromatography （UPLC） coupled with tandem mass spectrometry （MS/MS） was improved by optimizing the clean-up procedure to remove the matrix interference in pretreatment process, and was then applied to a survey of NDMA in both raw and finished water samples from five water treatment plants in South China. The NDMA concentrations ranged from 4.7 to 15.1 ng/L in raw water samples, and from 4.68 to 46.9 ng/L in finished water. The NDMA concentration in raw water was found to be related with nitrite concentration, and during the treatment, the NDMA concentration increased following ozonation but decreased after subsequent activated carbon treatment.

Development of an Indirect Competitive ELISA Based on Polyclonal Antibody for the Detection of Diethylstilbestrol in Water Samples

An indirect competitive enzyme-linked immunosorbent assay （icELISA） based on polyclonal antibody for the estrogen diethylstilbestrol （DES） was developed. With this aim, two different haptens mono-O-3-carboxypropyldiethylstilbestrol （DES-CP） and mono-O-carboxymethyldiethylstilbestrol （DES-CM） with carboxylic group that preserve the molecular structure character of diethylstilbestrol were synthesized. The haptens were conjugated with the carder proteins bovine serum albumin （BSA） by mixed-anhydride method for immunogen and conjugated with ovalbumin （OVA） by active ester method for coating antigen. Polyclonal antibodies for diethylstilbestrol were raised by immunizing mice with immune antigen DES-CP-BSA. Under optimized system, the lowest limit of detection （LLD） of diethylstilbestrol was 0.01 ng/mL, and IC50= 1.02 ng/mL. Its analogs were tested and no obvious cross-reactivity was found to anti-diethylstilbestrol antibody. DES-fortified water samples were determined by simple dilution to diminish the matrix effect. The comparison between the amount of DES estimated by ELISA and the amount added indicates good agreement for all water samples tested, with mean recovery values ranging from 86% to 120.2%.

Tip-assisted ambient electric arc ionization mass spectrometry for rapid detection of trace organophosphorus pesticides in strawberry

In this study,an ambient mass spectrometry(AMS)based method was developed for rapid detection of organophosphorus pesticides in strawberry.This method combines an electric arc and a microsyringe tip to realize tip-assisted ambient electric arc ionization(TAAEAI).A high-voltage electric arc can be applied to the microsyringe tip to generate an electric field,which results in corona discharge at the microsyringe tip.The juiced strawberry sample loaded on the tip could be directly ionized with TAAEAI and then analyzed by a mass spectrometer.TAAEAI-MS was successfully applied to analyze 6 organophosphorus pesticides in three strawberry samples.Malathion and profenofos were detected from the investigated strawberry samples.This method could quantitatively determine the contents of organophosphorus pesticides in strawberry with high reproducibility,high precision,and high sensitivity.Sample matrices did not interfere with the pesticide analysis.The recoveries of organophosphorus pesticides spiked in strawberry samples varied between 82.6%and 116%with relative standard deviations(RSDs)less than 9.2%.The limits of detection(LODs)varied between 0.0124µg/g and 0.0245µg/g,while the limits of quantification(LOQs)varied between 0.0413µg/g and 0.0817µg/g.The coefficients of determination(R2)of the method were determined to be>0.995.The method established here may have potential application in the detection of organophosphorus pesticides in vegetables and fruits.