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Absorption and scattering are the main problems affecting the transmission of large capacity information data in underwater visible light communication system(UVLC). To address these problems, we propose the imaging multiple input multiple output (MIMO) system for the underwater communication in this paper. Furthermore, the proposed system uses imaging lens to separate the light signal resulting in that decreasing disturbance of the proposed system is better than that of non-imaging MIMO. In this paper, the spatial correlation caused by imaging lens structure of underwater visible light imaging MIMO communication channel is analyzed. In addition, the influence of the spatial position for transmitting and receiving ends of the imaging system such as light-emitting diode (LED) light source array spacing, and the distance between LED and photodiode (PD) on spatial correlation are modeled. Moreover, the imaging MIMO channel capacities under different channel conditions are derived. The upper bounds of channel capacities under different spatial correlations are solved by equal power allocation method and water injection power allocation method. Finally, the simulation results show that the imaging MIMO system achieves a 12 dB gain at the same bit error rate (BER) compared to the non-imaging MIMO system. Furthermore, the capacity and BER performance of the proposed system are the best in the case of the weakest spatial correlation, and the performance is greatly improved as the spatial correlation becomes weaker.

The meniscus is a meniscus-shaped fibrocartilage tissue located between the femur and tibia，it is mainly composed of meniscus cells and related extracellular matrix.The synovial limbus area of the knee joint capsule near the meniscus is divided into red areas with rich blood vessels and white areas with less blood supply according to the distribution of blood vessels,there is a transition zone called the red and white zone between the two;Red zone has better self-repair ability,The injury in this area can be treated by conservative treatment or surgical suture;Once the white area of the meniscus is torn and involves the free edge area,It is often necessary to partially remove the damaged meniscus.When most of the entire meniscus is severely torn and involved,not only the course of the disease is very long, but it cannot be repaired by sutures,Often a subtotal or total meniscus resection is required,whether it is a partial meniscus resection, a subtotal meniscus resection or a complete resection.In the later period, it may cause quadriceps atrophy and osteoarthritis (OA）.OA is a refractory multi-system disease,involve the patient’s peripheral joints,it has high disability and teratogenicity, and is very harmful to human health.Chondrocyte pyrolysis, degradation, and inflammation play a vital role in the destruction of OA articular cartilage and chondrocyte apoptosis.Meniscus stem cells have strong proliferation and differentiation ability,has become one of the hot spots in the field of meniscus repair,this article studies the role of meniscal stem cells in the development of OA.

Film cooling represents one of most advanced technologies that facilitate the operation of gas turbine blades in today’s high-thrust-to-weight-ratio gas engines. The accuracy of the film cooling holes in a turbine blade is of central importance to cooling performance. However, in all the state-of-the-art methods known for producing turbine blades with drilled holes, complexity in the manufacturing processes will inevitably cause unwanted consequences such as non-uniform deformation of turbine blades and fixture layouts, and resisting motions and deflections of workpieces during drilling. These manufacturing issues will cause deviations in the geometrical and positional parameters of drilled holes. In this paper, we propose a systematic methodology to establish an improved parameterized model for drilled cooling holes on turbine blades. The non-uniform deformation of turbine blades, including the wall thickness and shrinkage distribution, was established by deformation decoupling analysis; the surface error generated before and after machining was obtained using locating error analysis and finite element analysis (FEA). An accurate model for film cooling holes can be established by considering the process-induced deviations in geometry and positioning. The applicability of the proposed methods is validated using numerical simulation data and experimental results.

In femtosecond laser helical drilling, the laser focus moves downward into the workpiece as material is removed, which is one of the main features used to improve the processing efficiency. Numerical modeling is the primary method used to study this process. To reduce the spatial scale of the numerical model, the influence of the helical trajectory was not considered in this study. Instead, the influences of the pulse interval and the downward velocity of the laser focus on the ablation process during deep-hole processing with multi-pulse femtosecond laser ablation were explored, and the existing two-temperature model was adapted. We used the critical-point phase separation model to describe the material ablation process with a femtosecond laser. Using a copper workpiece, we simulated an ablation process in which multiple pulses from a femtosecond laser were focused onto the workpiece and the focus moved into the workpiece at a constant speed. We used the finite element method to determine the variation in the electron and lattice temperatures, as well as the ablation depth under different pulse intervals with the focus moving downward at different velocities. The results demonstrate that the pulse interval is an important factor affecting the ablation depth during multi-pulse femtosecond laser ablation. As the pulse interval increased, the ablation depth first increased and then decreased. The laser ablation efficiency was highest when the pulse interval was 200 ps. The downward velocity of the laser focus determined the defocusing distance during laser processing. We obtained a high processing efficiency when a reasonable downward velocity was adopted to maintain the defocusing distance within approximately 50 nm.

Film cooling is one of most developed technologies which enhance the gas turbine blades operation in today’s high-thrust-to-weight-ratio gas engines. The determination of the accurate cooling holes of turbine blades is of vital importance to improving the cooling performance. However, in all current methods for manufacturing drilled cooling holes on turbine blades, the complexity of the production processes will ineluctably cause unexpected consequences such as the deformation of the turbomachinery parts, the locating error caused by fixture layouts. These issues will cause deviations in the geometry and position of the drilled holes. In this paper, a methodology is proposed to analyze the deviation and to establish an improved geometric model of drilled cooling holes with accurate positional and geometrical parameters on turbine blades. The discontinuous deformation, including the non-uniform wall thickness and shrinkage distribution, was established by deformation characteristics decoupling analysis; the surface error generated by locating error was obtained using locating error analysis. An accurate model for film cooling holes can be established by considering the process-induced deviations in geometry and positioning. The relevance of the proposed method is verified using numerical and experimental results.

The paper proposes an analytical model, which deals with the throughput of 802.11 DCF in presence of hidden nodes under saturation condition. Different scenarios are used in simulation to validate it, and the results show that the model is fairly accurate.