The corneal biomechanical changes after SMILE and LASIK refractive surgery were compared based on finite element analysis

The three-dimensional (3D) finite element model of human eye was established, and the intraocular pressure (IOP) was loaded to simulate refractive surgery. The biomechanical properties of human cornea after SMILE and LASIK surgery were studied from the stress, strain and induced wavefront aberration. Our results showed that SMILE had less impact on the biomechanics, having less stress and strain changes than LASIK. However, the stress and strain of the cornea increased with the increase of the diopter and were concentrated in the central region. We also investigated the changes in wavefront aberrations of the cornea after surgery, and the results indicated that the defocus and vertical commotion were significantly affected by SMILE and LASIK surgery, while the remaining aberrations were approximately unchanged. In conclusion, both SMILE and LASIK sergury procedures changed the postoperative corneal biomechanics, but SMILE had less impact on the biomechanics of corneal

Simulation of Optical Coherence Elastography in Agar Based on Finite Element Analysis

The finite element method is used to simulate the optical coherent elastic imaging in Agar. The shear wave velocity in Agar was measured by ARF-OCE system, and then the Agar model was established by finite element method, and then the shear wave velocity in Agar model was measured. The shear wave velocity in experiment and finite element simulation were compared and analyzed. The shear wave velocity obtained in the experiment is 2.50 m/s, and the range of shear wave velocity obtained in the finite element simulation is 2.4802m/s, and the average wave velocity is 2.5167m/s. The finite element method can express tissue elasticity directly and clearly, and it plays a great guiding role in corneal elastography

Research on the Influencing Factors of Air-puff Test after SMILE Based on Finite Element Analysis

The three-dimensional finite element model of the postoperative whole human eye after small incision lenticule extraction (SMILE) surgery and the axisymmetric air-puff model were established, the influencing factors in the Air-puff test were explored from the displacement nephogram on anterior corneal surface. Our results showed that the maximum depression displacement was positively correlated with the corrected diopter when the peak pressure of ejection and air-puff center location were constant, but the highest concavity radius of concave curvature was negatively correlated with the corrected diopter. At the same time, we also found that when the decentration of air-puff center position was 1mm, the maximum depression displacement of the anterior corneal surface was reduced by 8.3% under the condition of constant correction diopter and peak air-puff pressure, compared with the maximum depression displacement of the anterior corneal surface when the decentration of air-puff center position was 0 mm. In conclusion, the corrected diopter and decentration of air-puff position have an important effect on the results of air-puff test after SMILE

Effects of intraocular pressure and aspheric transition zone ablation profile on corneal biomechanics after conventional refractive surgery

Our Purpose is to study the effects of intraocular pressure (IOP) and aspheric transition zone (ATZ) on corneal biomechanics after pure hyperopia correction by using the finite element analysis (FEA). The values of IOP were changed, and 1-5# aspheric transition zones were designed in 1-5D hyperopia correction model. Simulate and calculate the wavefront aberration, stress and vertex displacement of cornea. The results show that with the increase of IOP and diopter, defocus increases positively and sphere increases negatively. Diopter and IOP have slight influence on coma. At 22mmHg, the maximum value of defocus was 1.367mm at 5D-1#, and the maximum value of sphere was -0.32mm at 5D-5#. IOP and diopter have great influence on the stress in the marginal region of the anterior corneal surface, and 1D-1 # has the maximum value at 22mmHg. With the increase of IOP and diopter, the vertex displacement of posterior corneal surface increased. The ATZ ablation profile has little effects on the wavefront aberration and displacement. We can draw a conclusion that refractive surgery destroys the physiological structure of cornea and has a great influence on the biomechanical properties of cornea. IOP plays an important role in maintaining the physiological structure of cornea

Analysis of the Electrical and Thermal Properties for Magnetic Fe3O4-Coated SiC-Filled Epoxy Composites.

Orderly arranged Silicon carbide (SiC)/epoxy (EP) composites were fabricated. SiC was made magnetically responsive by decorating the surface with iron oxide (Fe3O4) nanoparticles. Three treatment methods, including without magnetization, pre-magnetization and curing magnetization, were used to prepare SiC/EP composites with different filler distributions. Compared with unmodified SiC, magnetic SiC with core-shell structure was conducive to improve the breakdown strength of SiC/EP composites and the maximum enhancement rate was 20.86%. Among the three treatment methods, SiC/EP composites prepared in the curing-magnetization case had better comprehensive properties. Under the action of magnetic field, magnetic SiC were orderly oriented along the direction of an external field, thereby forming SiC chains. The magnetic alignment of SiC restricted the movement of EP macromolecules or polar groups to some extent, resulting in the decrease in the dielectric constant and dielectric loss. The SiC chains are equivalent to heat flow channels, which can improve the heat transfer efficiency, and the maximum improvement rate was 23.6%. The results prove that the orderly arrangement of SiC had a favorable effect on dielectric properties and thermal conductivity of SiC/EP composites. For future applications, the orderly arranged SiC/EP composites have potential for fabricating insulation materials in the power electronic device packaging field

Research on the Compound Optimization Method of the Electrical and Thermal Properties of SiC/EP Composite Insulating Material.

In this paper, in order to improve the electrical and thermal properties of SiC/EP composites, the methods of compounding different crystalline SiC and micro-nano SiC particles are used to optimize them. Under different compound ratios, the thermal conductivity and breakdown voltage parameters of the composite material were investigated. It was found that for the SiC/EP composite materials of different crystal types of SiC, when the ratio of α and β silicon carbide is 1:1, the electrical performance of the composite material is the best, and the breakdown strength can be increased by more than 10% compared with the composite material filled with single crystal particles. For micro-nano compound SiC/EP composites, different total filling amounts of SiC correspond to different optimal ratios of micro/nano particles. At the optimal ratio, the introduction of nanoparticles can increase the breakdown strength of the composite material by more than 10%. Compared with the compound of different crystalline SiC, the advantage is that the introduction of a small amount of nanoparticles can play a strong role in enhancing the break-down field strength. For the filled composite materials, the thermal conductivity mainly depends on whether an effective heat conduction channel can be constructed. Through experiments and finite element simulation calculations, it is found that the filler shape and particle size have a greater impact on the thermal conductivity of the composite material, when the filler shape is rounder, the composite material can more effectively construct the heat conduction channel

Network traffic characteristics of hyperscale data centers in the era of cloud applications

We present the network architecture of Alibaba Cloud DCs and investigate their traffic characteristics based on statistical data and captured traces. The statistical coarse-grained data are in the granularity of one minute, while the captured traces are fine-grained data that are in the granularity of one packet. We study the traffic features from the perspective of a macroscopic view, network performance, and microscopic view. The results report that the average utilization ratio of spine switches is stable when the observation time period reaches one day and the intra-ToR traffic ratio is in the range of 2%-10%. By mapping the folded-Clos topology to a tree topology and considering logical switching planes, we obtain the traffic matrix among pods from the average port utilization ratio. As we further investigate the perspective of network performance and the microscopic view, we find that there is no cell loss happening as the normalized queue speed Q_s is lower than 0.4. The normalized queue speed Q_s is defined as the total bytes of a queue sent in 1 s divided by 100 Gb, which reflects the packet sending speed of the queue. The observed maximum buffer size for one port conforms with the calculated maximum buffer occupation of 2.8 MB. By analyzing the captured traces, we find that the packet length is subject to a trimodal distribution. Under a time granularity of 10 ms, the instant bandwidth of one ToR port could reach 96 Gb/s at an average load of around 0.2 under a maximum link bandwidth of 100 Gb/s.</p

Dead-Time Correction Applied for Extended Flux-Based Sensorless Control of Assisted PMSMs in Electric Vehicles

Sensorless control technology of PMSMs is of great importance for safety and reliability in electric vehicles. Among all existing methods, only the extended flux-based method has great performance over all speed range. However, the accuracy and reliability of the extended flux rotor position observer are greatly affected by the dead-time effect. In this paper, the extended flux-based observer is adopted to develop a sensorless control system. The influence of dead-time effect on the observer is analyzed and a dead-time correction method is specially designed to guarantee the reliability of the whole control system. A comparison of estimation precision among the extended flux-based method, the electromotive force (EMF)-based method and the high frequency signal injection method is given by simulations. The performance of the proposed sensorless control system is verified by experiments. The experimental results show that the proposed extended flux-based sensorless control system with dead-time correction has satisfactory performance over full speed range in both loaded and non-loaded situations. The estimation error of rotor speed is within 4% in all working conditions. The dead-time correction method improves the reliability of the control system effectively