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Personalized quality of service （QoS） prediction is crucial for developing high-quality cloud service system.However, the traditional collaborative filtering method, based on centralized training, presents challenges in protecting user privacy.In order to effectively protect user privacy while obtaining highly accurate prediction effect, a distributed user privacy adjustable personalized QoS prediction model for cloud services （DUPPA） was proposed.The model adopted a “server-multi-user” architecture, in which the server coordinated multiple users, handled multiple users’ requests for uploading model gradients and downloading global model, and maintained global model parameters.To further protect user privacy, a user privacy adjustment strategy was proposed to balance privacy and prediction accuracy by adjusting the initialization proportion of local model parameters and gradient upload proportion.In the local model initialization stage, the user calculated the difference matrix between the local model and the global model, and selected the global model parameters corresponding to the larger elements in the difference matrix to initialize the local model parameters.In the gradient upload stage, the user can select some important gradients to upload to the server to meet the privacy protection requirements of different application scenarios.To evaluate the privacy degree of DUPPA, a data reconstruction attack method was proposed for the distributed matrix factorization model gradient sharing scheme.The experimental results show that when DUPPA sets the gradient upload proportion to 0.1 and the local model parameter initialization proportion to 0.5, the predicted MAE and RMSE are reduced by 1.27% and 0.91%, respectively, compared with the traditional centralized matrix factorization model.Besides, when DUPPA sets the gradient upload proportion to 0.1, the privacy degree is 5 times higher than when the gradient upload proportion is 1.And when DUPPA sets the local model parameter initialization proportion to 0.5, the privacy degree is 3.44 times higher than when the local model parameter initialization proportion is 1.

BACKGROUND The injection of nanoscale zero valent iron particles (nZVI) into groundwater has been recently developed as an in-situ groundwater remediation technology. Most researches focused on how to remove a single type pollutant and the related mechanism. However, cases on the coexisting multiple pollutants in groundwater should not be ignored. OBJECTIVES To synthesize the bentonite-supported nanoscale Fe/Ni bimetals(B-Fe/Ni), in order to remove typical pollutants of trichloroethylene (TCE) and hexavalent chromium[Cr(Ⅵ)] which exhibit high reactivity and are more stable to remediate contaminated water. Also, to assess the performance of B-Fe/Ni on the removal of coexisting TCE and Cr(Ⅵ) and to determine the reaction mechanism. METHODS B-Fe/Ni was synthesized by one-step method and the batch experiments were conducted on the removal of TCE coexisted with different concentration of Cr(Ⅵ) by B-Fe/Ni. The samples of B-Fe/Ni were characterized before and after the reaction, and the contents of TCE and Cr(Ⅵ) were also monitored. RESULTS B-Fe/Ni can efficiently remediate Cr(Ⅵ) and TCE in water. B-Fe/Ni (1 g/L) could completely remove Cr(Ⅵ) (50 mg/L) in 2 h in the presence of coexisting TCE (0.1 mmol/L). However, the degradation rate of TCE by B-Fe/Ni was decreased with increased initial concentration of Cr(Ⅵ) (0, 10, 30, 50 mg/L). According to TEM-EDS and XPS for B-Fe/Ni before and after reaction, it is shown that Fe-Cr co-precipitation from the fast interaction of B-Fe/Ni with Cr(Ⅵ) occupied the reactive sites on the surface of B-Fe/Ni, mitigating the degradation of TCE. According to the final products of TCE degradation, it is shown that TCE was completely dechlorinated. CONCLUSIONS B-Fe/Ni is suitable for the remediation of groundwater combined pollution. In practical applications, it is necessary to consider the mutual influence of multiple pollutants and select the appropriate reagent dosage and injection method. The proposed method has important theoretical significance and application for the development of ZVI repair technology.

Powder solid sampling atomic emission spectrometry is a simple sample pretreatment method with high sensitivity, low detection limit, and little environmental pollution. This method has been applied to the simultaneous analysis of trace Ag, B and Sn in geochemical samples. However, the serious matrix effect limits the application of this method. Based on the Scanning Electron Microscopy (SEM) technique, the differences in the composition of the reaction products at different times for specific formulations and different samples was compared. Combined with the evaporation curve to reverse the reaction process, a carrier buffer suitable for different types of geochemical samples was developed. In order to realize the improvement of the arc burning process, K2S2O7 and NaF were used as flux during preparing carrier buffer to catalytically decompose the matrix. Synergizing with PTFE and sedimentation S promotes rapid evaporation of analyzed elements in various forms. The formation of Al2O3-SiO2-CaO-BaO mutual melt lowers the Tammann temperature and can absorb matrix oxides in-situ, suppressing the interferences. Compared with the available method, the sensitivity increased by 1.2 times, and the precision, accuracy and detection limit are superior to a number of geochemical survey specifications.

Nanoscale zero-valent iron (nZVI) is a newly developed method for in-situ remediation of groundwater in recent years. To overcome easy oxidation and aggregation, modification on nZVI is widely adopted. In addition, the ubiquitous natural organic matters (NOM) in water also affect the scatter and reaction activity of nZVI. Therefore, it is of significance to study the aggregation effect of different kinds of nZVI in water by in-situ measurement method. Besides commercial nZVI (RNIP), normal nZVI, carboxymethyl cellulose coated nZVI (C-nZVI) and bentonite supported nZVI (B-nZVI) was synthesized. Nano particle size/Zeta potential analyzer based on the Dynamic Light Scattering (DLS) technique, Transmission Electron Microscope (TEM) and UV-Vis spectrum of sedimentation were employed to characterize the aggregation behavior of above four types of nZVI in the presence or absence of humic acid (HA), a representative NOM. The results showed that the dispersion stability of C-nZVI and B-nZVI was improved significantly after modification and the aggregation precipation was suppressed. And size distribution of aggregates stabilizes at below 1000 nm. Humic acid adsorbed onto the surface of nanoparticles, which can increase the electrostatic force to prevent aggregation of nZVI. The effect of HA on B-nZVI is most obvious for B-nZVI aggregates with diameters below 100 nm and the sedimentation was very slow, indicating the dispersion performed the best among all kinds of nZVI. It can be concluded that the combination of DLS technique and TEM to characterize nanoparticles is a valuable approach for more comprehensive information.