Abstract:The sources of groundwater pollution and the influence of Three Gorges Reservoir on the downstream of the Yangtze River is analyzed based on spatial and temporal distribution of flow rate, geological structures of the Three Gorges Reservoir area, and regional water balance. The analysis result shows that there are deep fault structures and underground river systems in Three Gorges Reservoir area, through which the reservoir leakage may be recharged to the downstream areas or other outside basins. Therefore, pollution sources of groundwater in the lower reaches of the Yangtze River include not only upstream pollution, mining industry pollution, agricultural pollution, domestic and industrial solid waste pollution, but also the recharge of upstream polluted water through deep channels. Upstream protection should be taken into priority for thd groundwater pollution control in lower reaches.

Abstract:In order to explore the correlation between phosphorus and iron in the sediment-water interface, by the indoor cultivation of situ sediment column, this study used the micro interface analysis technology and the interstitial water collection technology of high resolution balance type(HR - Peeper), and designed three stages(7, 21 and 35 days after adding the Chironomus larva), to explore the transfer mechanism of phosphorus in the sediment-water interface system under the oxidative coupling of Chironomus larva disturbance and iron in aerobic environment. The results show: the disturbance of Chironomus larva increased the penetration depth and E_h of oxygen in sediments, and the disturbance was most intense on the 21st day; the disturbance reduced the concentration of Solubility Reactive Phosphorus(SRP)with maximum 58% and Soluble Fe(Ⅱ)with maximum 44% in the interstitial water of three stages; SRP and Soluble Fe(Ⅱ)were also highly correlated on days 7 and 21. It can be seen that the change of P in the sediment caused by the disturbing action of Chironomus larva is controlled by the oxidation adsorption of Fe.

Abstract:In order to reveal the indicating significance of magnetic susceptibility of river floodplain sediments, the magnetic susceptibility has been determined by using 3 river floodplain sediment cores of 100 cm at the lower reaches of the Yangtze River between Zhenjiang and Yangzhou. It can be found that: the magnetic susceptibility of old river floodplain sediment core SY7 ranges from 12. 11×10^-8 m³/kg to 30. 60×10^-8 m³/kg, for the average in 20. 79×10^-8 m³/kg; the magnetic susceptibilities of SY5 and Z2 in the modern river floodplain sediments are obviously larger, the highest average value of SY5 is 123. 20×10^-8 m³/kg, and the modern river floodplain’s magnetic susceptibility is 5-6 times of old river floodplain sediments. Heavy metal pollution in the river floodplain sediments of the study area was compared with the background values of stream sediments in the Yangtze River basin, and the heavy metal pollution in Cu, Ni and Cr was more serious. Meanwhile, the pollution of newly formed river floodplain was more severe than that of old river floodplain. Simple and rapid determination of magnetic susceptibility can be used as one of important means for diagnosing heavy metal pollution in floodplain sediments.

Abstract:Taking the Herong station as an example, this work analyzes the swing range of the water level and flow rate by the systematical method. The result shows that there is a certain law in distributions of axial swings for the flood-peak water level and the corresponding flow rate under the impact of flood fluctuations. This law gets stronger when the relationship of water level and flow rate is closer to the flood peak. Meanwhile, the water level forms a regular series with the axis, which can establish the relationship between the flood-peak water level and the corresponding flow rate, and that between the water level and the flow conversion model of the flood peak. This study effectively solves the bottleneck of flood level forecasting under the impact of flood fluctuations on the relationship between water level and flow rate, for meeting the requirement of flood control.

Abstract:Using the digital dam construction technology, considering the spatial difference of the constitutive model parameters caused by the spatial difference of the actual dam construction quality, a three-dimensional precise finite element model is built by estimating and valuing each element of the model. Then, a core rock-fill dam is taken as an example to analyze the influence of two possible construction schedule appearances on the dam structure behaviors. These appearances are designed to fill up to the flood-control elevation before flood season under the condition of construction schedule lagging. The result shows that the different construction appearances mainly affect the horizontal displacement, and have little effect on vertical displacement and stress. Therefore, it can provide guidance for planning the filling schedule of dam during the actual construction.

Abstract:By the uniaxial compressive strength test in laboratory, the mechanical properties of the cemented sand and gravel(CSG)material were investigated under the conditions that cement contents were 40 kg/m³, 60 kg/m³, 80 kg/m³, and 100 kg/m³, respectively. Experimental results show that as the increase of cement content, the elastic modulus and compressive strength gradually increase, and their mechanical properties gradually evolve from those similar to rockfill materials to those similar to RCC. In order to study the failure mechanism of material, the lattice discrete particle method(LDPM)was used to establish a meso-scale model, and the crack propagation behavior under the uniaxial compression was simulated. The curves fit well with the experimental data. In addition, from the cloud diagram of crack opening, there are almost no cracks in the elastic stage. After the axial stress reaches the compressive strength value, the crack gradually initiates and expands, finally forms multiple fractures parallel to the pressure direction, and causes damage to the specimen. The cracks mainly extend along the interfacial layer between mortar and aggregate, while the aggregate is not broken at all. The results show that the formation and developing mechanism of meso-crack of CSG material can be effectively simulated by the LDPM.

Abstract:In order to study the deterioration law of the bond performance of adhesive-concrete interface, the deterioration tests of adhesive-concrete specimens were designed under the environments of freshwater, coupling of freshwaters and sustain load, and freeze-thaw cycles. Considering two kinds of concrete strengths and two kinds of adhesive in the tests, a total of 100 sandwiched beam specimens containing adhesive-concrete interface were prepared. After the deterioration treatment, the specimens were experimented by four-point bending test, and the failure load, failure mode and load-displacement curves at different time were measured. Based on test results, the deterioration law of bond performance of the adhesive-concrete interface was analyzed. The test results showed that the influence of freshwater environment on the adhesive-concrete interface was negligible, the deterioration effect under coupled environment of freshwater and sustain load was more significant, and the ultimate load capacity of specimens decreased by 41. 2% after 42 days. Besides, the deterioration effect of freeze-thaw cycles was not significant after 25-times cycles, but the ultimate load capacity of the specimens decreased by 28. 3% after 50-times cycles. The failure mode of specimens under various deterioration conditions was adhesive-concrete mixed failure, and the load-displacement curves showed that this kind of failure was brittle failure.

Abstract:Four typical plants are chosen to analyze the reinforcing mechanism of plant root and form a simplified calculation method of shear strength for root-permeated soils. A uniform function for the area-depth distribution of plant was proposed based on these four typical plants. The relationship of tensile strength and root diameter, correlation of plant height to sectional area of root trunk at ground surface, and that of sectional area of root trunk at ground surface to maximum vertical depth from the surface were statistically analyzed. Then, reinforcing mechanism of root-permeated soil was explained based on the reinforcement principle. A simple method to calculate the shear strength of root-permeated soil was proposed according to a uniform function for the correlation of reduced shear strength to depth. The shear strength of root-permeated soil can be directly calculated from the tensile strength of roots and the distribution of root area to depth. At last, the feasibility of proposed method was validated by existing data.

Abstract:Based on the analysis of reasons for the poor reinforcement effect and the limited strength growth of dredged soil foundation with a high viscosity content after the conventional vacuum preloading, large scale model tests of graded loading vacuum preloading and conventional vacuum preloading are carried out, and the influence and advantage of graded vacuum preloading in the consolidation and deformation of convective clay are discussed. The results show that: the dredged fill mud is in a muddy mixture state with obvious fluidity, and the staged loading vacuum preloading adopts the initial small vacuum load and lasts for a long time. It is beneficial to slow down the prematurely accumulation and consolidation of soil around the drainage plate, and can give the full drainage and consolidation time to soil far from the drainage plate, which is beneficial to the improvement of the whole soil. The power consumption is only 60. 8% of the conventional vacuum preloading, thus it has high practical applicability and economic benefits.

Abstract:In order to effectively describe the acceleration stage of rock creep and consider the compacting closure effect of rock fissures, a fractured plastic element is added to the model based on the fractional calculus theory. Then, a nonlinear creep model with five elements is established by introducing a variable section dashpot and a plastic element into a nonlinear visco-plastic body in parallel. The creep constitutive equation of this model is deduced, and the creep parameters are determined by fitting the data of rock creep test. The results show that the model can well describe three stages of rock creep, and it is reasonable and feasible.

Abstract:In order to reduce the logic overhead caused by the full scan method in the FPGA-based fault injection attack emulation, this study proposes a partial scan based method for the simultaneous control of circuit states, i. e. , setting the values of all flip-flops in the circuit at any time, to emulate the fault injection attack. This emulation allows the early security assessment of integrated circuits during the design phase. Meanwhile, the method abstracts the circuit as a graph, extends the balanced-structure based partial scan method to select flip-flops, and then adds enable signals to achieve simultaneous control of all flip-flops. In addition, based on circuit logic, the SAT satisfiability algorithm is used to generate fault test vectors to be injected. The experimental results show that compared with the full scan, the proposed method reduces the number of scanning flip-flops by 28. 04% on average, which reduces the logic overhead in the hardware emulation of fault injection attack at the cost of adding a small number of input ports.

Abstract:Aiming at the key problems of single-stage LC resonant electric-field coupled underwater power transfer(ECPT)system with low output power, small resonance capacity and large frequency drift, a more suitable wireless power transfer system in seawater environment is designed. The system is based on the CLC-S tuning network, which combines the advantages of high efficiency and high frequency of the class E amplifier, and achieves a large power output. The capacitance value of the coupling mechanism in seawater environment was solved by Maxwell finite element simulation software. Through the experiment of underwater coupling mechanism, the influence law of load quality factor Q and normalized frequency μ on underwater wireless power transfer system is analyzed. The experimental results provide an important reference for the design of underwater ECPT systems in the future.

Abstract:Aiming at the sensitivity of most users’consumption habits to the geographical location and the "long tail effect" in the recommendation process, a collaborative filtering algorithm is proposed combining the location information and the item popularity. In this study, two improvements are made to the conventional collaborative filtering algorithm. At first, a new calculating method of user similarity based on the geographic location is proposed by combining the preference of user interest and the position preference. Then, in predicting, the recommended expectations of the popular items and the long-tailed items are reasonably adjusted by introducing the popularity of goods weight. The Foursquare data set is used as the experimental data set in this work, and experiments are compared with related algorithms. The experimental results show that the improved algorithm can effectively improve the precision and the diversity of the recommended results.

Abstract:In order to solve the planning and design problems of the microgrid demonstration project, a set of simulation systems for microgrid capacity planning and operation based on Matlab has been developed in this study for the microgrid capacity planning and operation. Different from the traditional implementation of simulation software, the system can support the environment programming of multi-application strategy for the microgrid, and realize the functions of raw data analysis, distributed configuration of power capacity, energy storage system planning, and system operation simulation, etc. It also has high application adaptability and simulation precision. The application result of the Tibet Nyima Microgrid Project shows that the planning simulation system can well simulate the microgrid’s actual running effect, and provide useful analysis as well as calculation for the power planning of microgrid in early stage.