Advances in the Study of Nitrogen and Phosphorus Removal Mechanisms in Constructed Wetlands

Constructed wetlands are wastewater treatment ecosystems composed of substrata, plants, microorganisms and water. We summarize herein recent research findings about nitrogen and phosphorus removal mechanisms in wastewater treated by constructed wetlands and the influencing factors, such as substrata, plants, microorganisms, hydraulic loads, temperature and dissolved oxygen. To increase the nitrogen and phosphorus removal efficiency and extend the fields of constructed wetland application, nitrogen and phosphorus removal mechanisms, influencing factors and techniques must be studied intensively in the future.     

Analytical computation of uniform load deflection for a shock absorber throttle slice

We present a method for computing annular slice deflection. The physical model of throttle slice was built. The equation for deformation under a uniform load was deduced by using a deflection differential equation for throttle slice and boundary condition, which was convenient for theory analysis and engineering application. Equation correctness was validated by comparing the approximated result in the existing technology. We subsequently studied the rules of different loads, structure parameters, and material characteristics of throttle slice influence on the deformation at any radius. The equation and conclusions can serve as references for accurately designing shock absorber throttle valves.     

Numerical simulation of the mechanism of atypical dynamic phenomena in mines

An atypical dynamic phenomenon of mines, including its action forms and definition, were put forward, based on the mining accident at the Furong Mining Group Company in Sichuan, P. R. China. The mechanism of the atypical dynamic phenomenon was revealed by analyzing rock stress distribution, calculating the first and cycle broken distance of each thick and hard roof, and analyzing the balance structure of broken rock based on the three dimensional finite element software. The first stratum of the bent, sunken, aged strip was influenced by the geological conformation and the coal mining activity. This created the first break of the key stratum and led to the atypical dynamic phenomenon. We show that the key factors affecting the phenomena are the roof and floor structures, surrounding rock, and initial stress and rock burst tendency of the key stratum.     

养猪常见问题解答

1猪粪便发黑就是饲料消毒得好吗？ 高铜对仔猪有促生长作用（对生长肥育猪不明显）,许多饲料厂在猪饲料中添加了高铜（以硫酸铜的形式）。硫酸铜在猪体内经过化学变化后成为黑色的氧化铜,因而粪便也表现为黑色,所以粪便发黑并不能表明饲料消毒得好,只能表明饲料中添加了高铜。高铜只对仔猪有促生长作用,生长猪添加量过高不仅无益,还会对环境造成污染,不易提倡。     

采用16S rDNA鉴定甜瓜细菌性叶斑病菌

从甘肃河西、新疆阿勒泰甜瓜上分离获得的2株致病细菌,通过16S rDNA序列测定以及序列同源性比较,结合病原菌落培养性状、菌体形态观察和革兰氏染色反应等,初步确定当地甜瓜细菌性叶斑病菌为丁香假单胞杆菌[Pseudomonas syringae pv.lachrymans (Smith et Bryan) Young et al.]     

Effects of magnesium stress and temperature on the crowth and photosynthetic character of cucumber seedlings

The effects of magnesium stress on the growth and photosynthetic character of cucumber seedlings are studied at various temperatures using artificial climate box. This is done to investigate the functional mechanism of magnesium in cucumbers. The results show that at low temperature, magnesium stress evidently inhibits plant growth, while at suitable temperatures it decreases the plant diameter, total number of leaves, leaf area, and dry weight of the above ground parts, and increases the plant height and root/shoot ratio. Excessive magnesium promotes below ground cucumber growth. The value of chlorphyl A/chlorophyl B (Chla/Chlb) increases more under conditions of magnesium deficiency than under magnesium excess. The Chla, Chlb and Cxc content decreases when magnesium is deficient, increase when excessive magnesium exists at suitable temperatures, but decreases if excessive magnesium exists at low temperatures. Pn and Gs decrease under magnesium stress, and are at the lowest level when excessive magnesium exists at low temperatures. The effects of magnesium stress on Ci, WUE, Tr and Ls vary at different magnesium concentrations and temperatures. The main factor limiting photosynthesis of cucumber seedlings is non stomata factor when magnesium is deficient, but is a stomata factor if there is excessive magnesium.     

Characteristics and Fitting Model of Structure Plane in Layered Rock Mass

In order to study the compressive failure characteristics of layered rock mass and build the corresponding theoretical model, the fast lagrangian method was adopted to address numerical simulation of the layered rock mass under tri axial compression. The relationship between compressive strength and inclination of structure plane was analyzed, and a theoretical model was proposed to describe their relationship. The test data from the foreign references were described by the theoretical model and the relationship between loading velocity and the compressive strength was analyzed. It was shown that, the fitting model can well describe the strength characteristics of stratified rock mass, which was validated by the numerical test and laboratory test. And the compressive strength of rock mass increased linearly with the increase of loading velocity.      

Stability of various height waste dumps based on nonlinear strength criterion

Coal mining waste dumps are representative artificial accumulations of bulky rock and soil material. Certain factors make these dumps possess characteristics such as self organized criticality, nonlinear shear strength of the waste accumulation. We discusse the main waste dump characteristics and subsequently produced numerical simulations of the stability of waste dumps of various heights using the Fast Lagrangian Analysis of Continua and based on the Hoek Brown nonlinear strength criterion. The simulation calculation results show that the stability is a dynamic evolving process corresponding to increasing waste dump height. Safety factors, based on a nonlinear rule, vary with the waste dump height. Theoretical analysis and calculated outcomes reveal a progressive failure rule of waste dumps, and all indicate the methods we put forward are reasonable.     

Stability analysis method for perilous rock by fracture mechanics

Perilous rock is a type of geological disaster in mountainous areas. Research concerning perilous rock ruptures focuses on the expanding of control fissures in perilous rock under load action. Taking the control fissure in perilous rock as one crevice in a sample, a method employing fracture mechanics is established to calculate the union fracture strength factor along the rupture orientation at the terminus of a control fissure in perilous rock. The union fracture strength factor is a function of both the first and second type fracture strength factors. We define the ratio between the fracture tendency of rock and the union fracture strength factor as the stability coefficient of perilous rock. Further, it simplifies the rupture mechanism of sliding, falling, and toppling perilous rock as pressure shear and tension shear ruptures. We establish methods for calculating the first and second type fracture strength factors. The applications show that the stability status identified by the method is more reasonable and sensitive.     

Application of a Particle Swarm Optimization Algorithm in Truss Structure Optimal Design

The particle swarm optimization (PSO) algorithm developed in recent years is a stochastic optimization algorithm based on swarm intelligence. It possesses advantages such as being a simple concept, ease of implementation and low resource occupation. The PSO algorithm was adopted to solve the problem of size optimization of truss structures with stress and displacement constraints. We present the basic principle of the original PSO algorithm in detail, and then introduce a constriction coefficient to modify it. Moreover, reasonable values of the coefficients are proposed for the modified PSO algorithm. Several classical problems are solved using the modified PSO algorithm, and the results compared with those using traditional optimization algorithms and genetic algorithms. Numerical results show that the modified PSO algorithm has good convergence and stability, and can be applied to the size optimization of truss structures.