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The aim of this study was to investigate the effect of low-level laser therapy (LLLT) on short-term and long-term joint pain, synovitis, anabolic, and catabolic factors in the cartilage of a rabbit model with progressive osteoarthritis (OA) induced by anterior cruciate ligament transection (ACLT). A total of 160 New Zealand white rabbits were randomly assigned into two groups (ACLT group and LLLT group). All rabbits received ACLT surgery, and 2-, 4-, 6-, and 8-week treatment after the surgery, with 20 rabbits being tested biweekly over every study period. The LLLT group received LLLT with a helium-neon (He-Ne) laser (830 nm) of 1.5 J/cm(2) three times per week, and the ACLT group received placebo LLLT with the equipment switched off. Long-term and short-term pain was tested via weight-bearing asymmetry; synovitis was assessed histologically; and knee joint cartilage was evaluated by gross morphology, histology, and gene expression analysis of anabolic and catabolic factors. The histological assessment of pain and synovitis showed that at least 6-week intermittent irradiation of LLLT could relief knee pain and control synovium inflammation. Gross morphologic inspection and histological evaluation showed that 6 weeks of LLLT could decrease cartilage damage of medical femoral condyle and 8 weeks of LLLT could decrease cartilage damage of medical and lateral femoral condyles and medical tibial plateau. Gene expression analysis revealed two results: At least 6 weeks of LLLT could decrease production of catabolic factors, for example, interleukin 1β (IL-1β), inducible nitric oxide synthase (iNOS), and MMP-3, and slow down the loss of anabolic factors, mainly TIMP-1. Eight weeks of LLLT treatment could slow down the loss of collagen II, aggrecan, and anabolic factors, mainly transforming growth factor beta (TGF-β). The study suggests that LLLT plays a protective role against cartilage degradation and synovitis in rabbits with progressive OA by virtue of the regulation of catabolic and anabolic factors in the cartilage.

Numerical simulations of the elastohydrodynamic lubrication (EHL) have been conducted by many researchers, in which the entrainment velocity is usually parallel to one of the axes of Hertzian contact ellipse. However, in some engineering applications, such as the counterformal contacts in spiral bevel and hypoid gears, entraining velocity vector may have an oblique angle that could possibly influence the lubrication characteristics significantly. Also, a vast majority of gears operate in mixed EHL mode in which the rough surface asperity contacts and lubricant films coexist. These gears are key elements widely used for transmitting significant power in various types of vehicles and engineering machinery. Therefore, model development for the mixed EHL in elliptical contacts with an arbitrary entrainment angle is of great importance. In the present paper, a recently developed mixed EHL model is modified to consider the effect of arbitrary entraining velocity angle, and the model is validated by comparing its results with available experimental data and previous numerical analyses found in literature. Based on this, numerical simulations are conducted to systematically study the influence of entrainment angle on lubricant film thickness in wide ranges of speed, load, and contact ellipticity. The obtained results cover the entire lubrication spectrum from thick-film and thin-film lubrication all the way down to mixed and boundary lubrication. In addition, minimum film thickness prediction formula is also developed through curve-fitting of the numerical results.

Spiral bevel and hypoid gears are key components widely used for transmitting significant power in various types of vehicles and engineering machineries. In reality, these gear surfaces are quite rough with three-dimensional (3D) topography that may significantly influence the lubrication formation and breakdown as well as components failures. Previous spiral bevel and hypoid gears lubrication studies, however, were limited mostly to cases under the full-film lubrication condition with smooth surfaces. In the present study, a comprehensive analysis for gearing geometry, kinematics, mixed lubrication performance, and friction and interfacial flash temperature in spiral bevel and hypoid gears is developed based on a recently developed mixed elastohydrodynamic lubrication (EHL) model that is capable of handling practical cases with 3D machined roughness under severe operating conditions and considering the effect of arbitrary entrainment angle. Obtained results from sample cases show that the simulation model developed can be used as an engineering tool for spiral bevel and hypoid gears design optimization and strength prediction.

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Large deformation control of deep soft rock roadways has been a major problem in mining activities worldwide. This paper considers the supporting problem related to large deformation of a deep soft rock roadway in Chao'hua coal mine. The discrete element simulation method (UDEC software) is adopted to simulate a tailgate of panel 31041 in Chao'hua coal mine. The failure patterns of unsupported and primary supported roadway are simulated, and these reveal the characteristics of deformation, stress and crack propagation. The excavation of roadway leads to high deviator stress, which exceeds the peak strength of shallow surrounding rock and causes it to enter the post-failure stage. Tensile failures then initiate and develop around the roadway, which causes the fragmentation, dilation and separation of shallow surrounding rock. The compressive capacity of the primary support system is low, which results in serious contraction in the full section of the roadway. An improved control scheme is put forward for the support of a tailgate. The underground test results confirm that the improved support system effectively controlled large deformation of the surrounding rocks, which can provide references for support in the design of roadways excavated in deep soft stratum.

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