Background/purpose The aim of this study was to explore the presence and variability of oral Candida in adolescents before and during treatment with fixed orthodontic appliances. Materials and methods A total of 50 patients aged 10–18 years old were randomly selected for this study. Microorganism samples were obtained prior to and after orthodontic treatment and identified by culture methods. Molecular biology techniques were used to investigate the samples further and the effect of the orthodontic appliance on oral pathogenic yeasts was studied longitudinally. Results The percentage of patients with candidiasis and the total number of colony-forming units significantly increased 2 months after orthodontic treatment. Changes in the type of oral candidiasis prior to and after treatment were significant. Conclusion Fixed orthodontic appliances can influence the growth of oral pathogenic yeasts among adolescents.

ASP (alkali-surfactant-polymer) flooding improves recovery rate dramatically. However, scaling problem happens in artificial lift systems and causes pump sticking in sucker rod pumps and the average pump running time decrease from 500 days to 37 days. By analyzing the constituents and characteristics of scales from ASP production wells and experimenting with simulating produced liquid, characteristics and mechanism of silicon containing scale forming are researched. The results show that Ca2+, Mg2+, Al3+, polyacrylamide, surfactant and silicon influence the ASP scales structures and forming processes. The ASP scales have the characteristics of absorbing and sticking. Basing on describing of scaling characteristics, mechanisms and the pump structures, the reasons for pump sticking are analyzed. Pump sticking which caused by scaling between the plunger and barrel occurs when the sucker rod pump is sucking, hot water is circulating or the pump is stopping. When the well is shut down, one major reason of pump sticking is scale particles set down, stick and pack in the anti-sand groove. When a great deal of hot water is circulating in the well bore, liquid viscosity lowers and scale particles set down speed increases also. The slow-dissolved solid scale-inhibitor SY-2 and anti-scale pump with long plunger-short barrel are developed and applied in field. Through these methods applications, the pump running time have been prolonged and good results have been achieved. Introduction ASP flooding technology improves recovery rate dramatically 1. However, alkali in ASP solution reacts with both formation fluids and mineralogical components such as kaolinite, montmorillonite and feldspar, from which silicon and aluminum components are soluted into fluids 2. With the fluids flowing and surrounding condition changing gradually, scale forming in artificial lift wells, which causes pump sticking in sucker rod pumps and the work over periods decrease. For example, without any anti-scale methods after scaling, the average work over periods are 37 days in sucker rod pump wells in a test area of Daqing oilfield, which influence the production and cause low commercial effectiveness. Silicon scale forming characteristics of ASP flooding Analysis of scale samples The typical scale samples from the field are analyzed. The well-consolidated scales are flake-shaped macroscopically and scale layers are fline vertically. The scales from oil well are not a single composition. They consist of silicon scale, carbonate scale and organic impurities. Silicon exists as silicate or SiO2, Ca2+, Mg2+ exist as carbonate. Fe exists as its oxide or sulfide or carbonate. Na and K are adsorbed on the surface of scale as soluble salts. Water is not the ingredient of the scale but it exists as absorbed water or crystal water. The characteristic functional group of HPAM such as CO-, -CH2-, -CONH2 exists in the scale, but the content of HPAM can't be quantificationally tested by Amylum-Cadmium Iodide method. Influencing factors of silicon scale formation Considering the field conditions, Na2SiO3 solution and mineralized water are made up to different simulating produced water. It is described as bellow. The temperature, correlative ion concentration, pH is changed, and the influences of these factors to scale formation are given as following. The first is silicon-only solution. The second is Si, Ca2+ and Mg2+ solution.

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Natural fractures in tight sandstone formation play a significant role in fracture network generation during hydraulic fracturing. This work presents an experimental model of tight sandstone with closed cemented preexisting fractures. The influence of closed cemented fractures’ (CCF) directions on the propagation behavior of hydraulic fracture (HF) is studied based on the hydraulic fracturing experiment. A field-scaled numerical model used to simulate the propagation of HF is established based on the flow-stress-damage (FSD) coupled method. This model contains the discrete fracture network (DFN) generated by the Monte-Carlo method and is used to investigate the effects of CCFs’ distribution, CCFs’ strength, and in-situ stress anisotropy, injection rate, and fluid viscosity on the propagation behavior of fracture network. The results show that the distribution direction of CCFs is critical for the formation of complex HFs. When the angle between the horizontal maximum principal stress direction and the CCFs is in the range of 30° to 60°, the HF network is the most complex. There are many kinds of compound fracture propagation patterns, such as crossing, branching, and deflection. The increase of CCFs’ strength is not conducive to the generation of branched and deflected fractures. When the in-situ stress difference ranges from 3 MPa to 6 MPa, the HF network’s complexity and propagation range can be guaranteed simultaneously. The increase in the injection rate will promote the formation of the complex HF network. The proper increase of fracturing fluid viscosity can promote HF’s propagation. However, when the viscosity is too high, the complex HFs only appear around the wellbore. The research results can provide new insights for the hydraulic fracturing optimization design of naturally fractured tight sandstone formation.