Gongcheng Kexue Yu Jishu/Advanced Engineering Science

Nowadays, there is an interest in fully applying on the reaction solution, such as desulfurization by pyrolusite or leaching pyrolusite with sulfur dioxide, for the purpose of controlling air pollution and the recovery of manganese salt. However, some researchers aimed at studying on the technological problem that there was a byproduct of S2O6 2- ,which debase the main product of MnSO4 from the desulfurization solution. In the present work, a large amount of Na2SO4 was prepared by the low temperature pyrolysis of Na2S2O6, which was acquired as the precursor by MnS2O6 that was carbonated by the carbonization reagent (NaHCO3). During the thermal decomposition process of Na2S2O6·2H2O, the reaction products and the temperatures of the key steps of reaction processes were investigated and both of the reaction mechanisms and the kinetic parameters were deduced. The thermal decomposition experiments showed that 255 ℃ was the optimum temperature for the preparation of Na2SO4 by the thermal decomposition of Na2S2O6, which underwent two steps including dehydration and desulfurization. The characterization results of X-ray diffraction (XRD) and Ion chromatography (IC) showed that the decomposition product was the pure and single phase cubic sodium sulfate. The thermal decomposition process of Na2S2O6 was characterized by thermo-gravimetric analysis and differential scanning calorimetry analysis (TG-DSC), in which the activation energies (Ea) of dehydration and desulfurization were calculated by the combining Kissinger differential method and the Coats-Redfern integral method, respectively. The processes of dehydration and desulfurization of Na2S2O6·2H2O were controlled by phase boundary reaction model fitting shrinking sphere equation with the Ea of 14.75～18.11 kJ/mol for dehydration and 132.61～137.18 kJ/mol for desulfurization. SO2 was observed as the main decomposition gas. Finally, the reaction equations were demonstrated combined with the chemical analysis method. Based on realizing the resource recovery, this technology of the thermal decomposition of Na2S2O6·2H2O is feasible and used to avoid the acidic wastewater problem within the liquid-phase method, from which decomposition gas could reacted with sodium bicarbonate again during the process of thermal decomposition.

With the advent of the era of big data, the problem of information overload has become particularly serious. The recommendation system can provide personalized recommendation services for users by analyzing users' basic information and users' behavior information. How to push information accurately and efficiently has become an urgent issue in the era of big data. Based on the Alternating Least Squares (ALS) collaborative filtering recommendation algorithm, this paper reduces the loss of the invisible factor item attribute information by merging the similarity of the item on the loss function. At the same time, the cold start strategy is introduced into the model to complete the recommendation. The algorithm is implemented on the Spark distributed platform and single node by using the Movie Lens dataset published by the GroupLens Lab. The experiment results show that the proposed recommendation algorithm can preferably alleviate the data sparsity problem compared with the traditional recommendation algorithm. Moreover, the algorithm improves the accuracy of recommendation and the efficiency of calculation.

The experimental study investigates the takeoff characteristics of lower jet trajectory from the dovetail-shaped flip bucket under different inlet conditions. The experiment analyzes the influences of velocity and water depth on lower takeoff characteristics, especially the variation of takeoff angle of lower jet trajectory. The following items are addressed 1) relationship between takeoff angle of lower jet trajectory and inlet velocity as well as inlet water depth 2) characteristics of the takeoff angle as a function of changes of inlet Fr0 3) the empirical formulas for calculating takeoff angle of lower jet trajectory. The results indicate that the effects of inlet conditions are significant on lower takeoff characteristics. Additionally, with the established empirical formulas, the calculated values of horizontal distance of lower nappe profile are in good agreement with the experimental data.

Geopolymer is a novel binding material produced from the reaction of fly ash with an alkaline solution. In Geopolymer mortar, Portland cement is not utilized at all. In this research, the influence of various parameters on the short term engineering properties of fresh and hardened low-calcium fly ash-based geopolymer mortar were studied. Tests were carried out on 70.71 × 70.71 × 70.71 mm cube geopolymer mortar specimens. The test results revealed that as the concentration of alkaline activator increases, the compressive strength of geopolymer mortar also increases. Study showed that higher mixing temperature and higher curing temperature exhibited higher compressive strength in early stages and still develop with longer curing. When the samples were mixed at room temperature, the compressive strength was low at an early stage, but gradually increased and finally, had as high strength.The mass ratio of activator/fly ash of 0.416 produced the highest 28 days compressive strength for the specimen.

The ultra wide bandwidth nature of ground penetrating radar antenna has made a raw data acquired with the tool prone to unwanted noise and hence low signal to noise ratio. Quantitative interpretation of the data is desirable for radar image quality enhancement. This study used multiresolution analysis to process radar image at different levels of decomposition. Daubechie wavelets family was used to decompose the image into 4-different levels of details. Level 3 diagonal details and level 4 horizontal details provide a noise-free visualization of the subsurface discontinuities. This led to the detection of buried utility and unique identification of its spatial location. The depth of the buried utility was estimated based on the image scale. The work demonstrates the effectiveness of Daubechie wavelet transform analysis as yet another technique of utility survey data acquired with GPR.