Mechanism of antireflux procedures in treating sliding hiatal hernia

Objective To investigate the mechanism of antireflux procedures in treating sliding hiatal hernia and the effectiveness of the method of cardia position by clock to evaluate the outcome of antireflux procedures. Methods From 1992 to 2008,136 patients with sliding hiatal hernia underwent transabdominal antireflux surgery:

Three-dimensional Finite Element Analysis of the Mechanical Stress on Root from Orthodontic Tooth Movement by Sliding Mechanics

In order to study mechanical stress on root from orthodontic tooth movement by sliding mechanics, a 3-dimensional finite element model incorporating all layers of a human mandibular dental arch with orthodontic appliance has been developed to simulate mechanical stress on root from the orthodontic tooth movement. Simulated orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis was applied to the crown of the teeth. The finite element analysis showed when orthodontic forces were applied to the tooth, the stress was mainly concentrated at the neck of the tooth decreasing uniformly to the apex and crown. The highest stress on the root was 0.621 N/mm^2 for cervical margin of the canine, and 0.114 N/mm^2 for apical region of the canine. The top of canine crown showed the largest amount of displacement （2.417 μm）, while the lowest amount of displacement was located at the apical region of canine （0.043 μm）. In conclusion, this model might enable one to simulate orthodontic tooth movements clinically. Sliding force at 2 N is ideal to ensure the bodily orthodontic tooth movement. The highest stress concentration in the roots was always localized at the cervical margin when orthodontic force of 2 N at 0, 30 and 45 degree from the horizontal axis, so there may be the same risk of root resorption when orthodontic force of 2 N at 0, 30 and 45 degree was used in clinic cases.

Stability analysis of concrete gravity dam on complicated foundation with multiple slide planes

A key problem in gravity dam design is providing enough stability to prevent slide, and the difficulty increases if there are several weak structural planes in the dam foundation. Overload and material weakening were taken into account, and a .finite difference strength reserve method with partial safety factors based on the reliability method was developed and used to study the anti-slide stability of a concrete gravity dam on a complicated foundation with multiple slide planes. Possible slide paths were obtained, and the stability of the foundation with possible failure planes was evaluated through analysis of the stress distribution characteristics. The results reveal the mechanism and process of sliding due to weak structural planes and their deformations, and provide a reference for anti-slide stability analysis of gravity dams in complicated geological conditions.

Effect of mechanical degradation of laminated elastomeric bearings and shear keys upon seismic behaviors of small-to-medium-span highway bridges in transverse direction

Laminated elastomeric bearings have been widely used for small-to-medium-span highway bridges in China, in which concrete shear keys are set transversely to prohibit large girder displacement. To evaluate bridge seismic responses more accurately, proper analytical models of bearings and shear keys should be developed. Based on a series of cyclic loading experiments and analyses, rational analytical models of laminated elastomeric bearings and shear keys, which can consider mechanical degradation, were developed. The effect of the mechanical degradation was investigated by examining the seismic response of a small-to-medium-span bridge in the transverse direction under a wide range of peak ground accelerations（PGA）. The damage mechanism for small-to-medium-span highway bridges was determined, which can explain the seismic damage investigation during earthquakes in recent years. The experimental results show that the mechanical properties of laminated elastomeric bearings will degrade due to friction sliding, but the degree of decrease is dependent upon the influencing parameters. It can be concluded that the mechanical degradation of laminated elastomeric bearings and shear keys play an important role in the seismic response of bridges. The degradation of mechanical properties of laminated elastomeric bearings and shear keys should be included to evaluate more precise bridge seismic performance.

Effects of Al on Microstructure and High-Temperature Wear Properties of Austenitic Heat-Resistant Steel

Microstructure and high-temperature dry sliding wear at 600 ~C in ambient air of austenitic heat-resistant steel ZG40Cr25Ni20 with different contents （mass percent） of AI （0 to 7.10~） have been investigated. The results show that microstructures of 4.68% and 7.10% A1 addition content consist of the matrix and reinforcement of inter- metallic compound y＇ and carbide, while microstructures of ZG40Cr25Ni20 without A1 and with A1 of 1.68% are ab- sent of y＇. Higher wear resistance than the original ZG40Cr25Ni20 alloy is achieved in alloys with higher content of A1 under the same high-temperature wear test condition. The wear rates of Fe-25Cr-20Ni-7.10A1 and Fe-25Cr-20Ni- 4.68A1 are only 20.83% and 45.83% of that of Fe-25Cr-20Ni, respectively. Heat-resistant steels with higher con- tents of AI （4.72% and 7.10%） have higher hardness than those with lower contents of AI （1.68% and 0）. Wear mechanisms of ZG40Cr25Ni20 are considered as severe plough plastic deformation and slight adhesive. However, wear mechanisms of Fe-25Cr-20Ni 4.68A1 are light micro-cutting and oxidation-wear, while that of Fe-25Cr-20Ni- 7. 10A1 are severe adhesive transfer and oxidation-wear_