Gongcheng Kexue Yu Jishu/Advanced Engineering Science

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.

Chloride erosion is the most important factor affecting the corrosion of steel bars in the marine environment, salt lakes and saline soil areas. Therefore, timely and accurate grasp of the distribution of chloride ions inside reinforced concrete structures is of great significance to the durability evaluation, protection and repair of reinforced concrete structures under severe environmental conditions. In this paper, a solid Mn/MnO2 reference electrode for concrete with compact structure and stable performance is prepared by physical powder compaction method. The results show that the loading pressure is an important parameter that affects the strength and density of the Mn/MnO2 electrode prepared by the tablet method. When preparing Mn/MnO2 electrodes, the loading pressure needs to be controlled, and the recommended loading pressure is 96 MPa. The electrode must be activated before use. The response time of the activated Mn/MnO2 electrode is less than 60 s, and the stability, reproducibility and anti-polarization performance are good. When the Mn/MnO2 electrode works in the temperature range of 5~65 °C, the electrode potential is linearly related to the temperature. When the Mn/MnO2 electrode works in the pH range of 8.36~13.00, the electrode potential remains constant. Therefore, if the Mn/MnO2 electrode prepared by this method is used as the reference electrode of the chloride ion sensor to be buried in concrete, the temperature inside the concrete must be tested and corrected at the same time. Keywords: reference electrode; powder compaction method; performance characterization; influencing factors.