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Objective:To evaluate the effect of visual input on static balance function, by assessing the posture control of young healthy subjects with eyes open and closed using the plantar pressure analysis technique.Methods:A total of sixty-six young, healthy adults were recruited in the study. They were instructed to stand at a fixed position on the FreeMed plantar pressure analysis test board. The subject's pelvis was swung in four directions including front, back, left and right, to make their foot pressure evenly distributed. The pressure data of the soles was recorded in eyes open and closed states for 30 seconds, respectively. The collected data was processed using the Freestep plantar pressure analysis system. The ball length, ellipse area, average velocity, average X, average Y, ellipse tilt angle, ellipse eccentricity, maximum swing, minimum swing, and total plantar load, forefoot load, and hind foot load of the left and right lower limbs were obtained.Results:There were significant differences in the ellipse area (P< 0.05), the average Y(P< 0.001) and the maximum swing (P< 0.001) of the subjects in the two states of eyes open and closed. Compared with eyes open condition, the ellipse area decreased, the average Y decreased, and the maximum swing increased during eyes closed condition. According to the scatter plot distribution of center of pressure (COP), it was found that the COP distribution was more concentrated with the eyes open than that with eyes closed. Comparing the two conditions (eyes open and eyes closed), the subjects'left foot forefoot load (P< 0.001), right foot forefoot load (P< 0.001), left foot hind foot load (P< 0.001) and right foot hind foot load (P< 0.001) were significantly different. Compared with the eyes open, the left-foot forefoot load and the right-foot forefoot load increased both, while the left-foot hind foot load and the right-foot hind foot load decreased. In the comparison of the two status of the left lower limb and the right lower limb, the subject's overall load on the left foot in the eyes open state was reduced compared with the right lower limb (P=0.030); the overall load on the left foot was also lower than that on the right side in eyes closed. The difference of the lower limbs decreased was statistically significant (P=0.021). In the comparison of the forefoot and hind foot in eyes open and closed, the hind foot load was significantly greater than the forefoot load (P< 0.001).Conclusion:The findings of this experiment indicated that normal young subjects could adjust the balance function under different visual input status by changing the ellipse area and swing amplitude. The kinematics and dynamics parameters analyzed by plantar pressure analysis can be used for quantitative and clinical evaluation of static balance function.

Taking a deep-water exploration well of natural gas located in the Qiongdongnan Basin in the South China Sea as an example, the hydrate risks of the well under operational conditions during drilling and testing processes were analyzed, and the corresponding hydrate prevention solutions were presented and verified by lab experiments and field application. Based on the predicted gas hydrate equilibrium curves and the calculated wellbore pressure-temperature fields, the hydrate risks were analyzed. The maximum sub-cooling temperature is 6.5 °C during normal drilling with a small hydrate stability zone in the wellbore; when the drilling or testing stops, the hydrate stability zone in the wellbore becomes larger and the maximum sub-cooling temperatures are 19 °C and 23 °C respectively; the maximum sub-cooling temperature at the beginning of testing is no more than that when testing stops; when the tested production rate of natural gas increases, the hydrate stability zone in the wellbore decreases or even disappears if the gas rate is more than 25×104 m3/d. The designed hydrate prevention solutions include: adding sodium chloride and ethylene glycol into drilling fluid during normal drilling and when drilling stops; adding calcium chloride/potassium formate and ethylene glycol into testing fluid; applying downhole methyl alcohol injection when the production rate of natural gas is lower than 25×104 m3/d; filling the testing string with testing fluid when the test shuts down for a long time. Lab experiments and field operations have indicated that all the designed solutions can meet the requirements of hydrate prevention. Key words: gas hydrate, drilling fluid, wellbore temperature, sub-cooling temperature, hydrate inhibitor, deep water drilling