Profile of biological characterizations and clinical application of corneal stem/progenitor cells

Corneal stem/progenitor cells are typical adult stem/progenitor cells.The human cornea covers the front of the eyeball,which protects the eye from the outside environment while allowing vision.The location and function demand the cornea to maintain its transparency and to continuously renew its epithelial surface by replacing injured or aged cells through a rapid turnover process in which corneal stem/progenitor cells play an important role.Corneal stem/progenitor cells include mainly corneal epithelial stem cells,corneal endothelial cell progenitors and corneal stromal stem cells.Since the discovery of corneal epithelial stem cells(also known as limbal stem cells)in 1971,an increasing number of markers for corneal stem/progenitor cells have been proposed,but there is no consensus regarding the definitive markers for them.Therefore,the identification,isolation and cultivation of these cells remain challenging without a unified approach.In this review,we systematically introduce the profile of biological characterizations,such as anatomy,characteristics,isolation,cultivation and molecular markers,and clinical applications of the three categories of corneal stem/progenitor cells.

Experimental study on airfoil flow separation control via an air-supplement plasma synthetic jet

An air-supplement plasma synthetic jet(PSJ)actuator increases the air supplemental volume in the recovery stage and improves the jet energy by attaching a check valve to the chamber of a conventional actuator.To explore the flow control effect and mechanism of the air-supplement actuator,via particle image velocimetry experiments in a low-speed wind tunnel,the flow field and boundary layer characteristics of a two-dimensional airfoil surface under different actuation states were compared for different attack angles and jet orifices.The experimental results show that,compared with the conventional actuation state,the jet energy of the air-supplement PSJ is higher and the indirect mixing effect of the counter-vortex sequence produced by the jet-mainstream interaction is stronger.Furthermore,the boundary layer mixing effect is better,which can further suppress flow separation and improve the critical flow separation attack angle.Moreover,increasing the jet momentum coefficient can enhance the flow control effect.The findings of this study could provide guidance for the flow control application of air-supplement PSJs.

Active flow control of S-duct by plasma synthetic jet

Flow separation and secondary flow in the S-duct of an aircraft engine cause severe pressure loss and airflow distortion at the outlet,lowering engine performance.Herein,a serial two-electrode plasma synthetic jet(PSJ)actuator array is used to actively control the flow field in the duct and improve its characteristics.The results show that the PSJ significantly increases the wall pressure recovery coefficient,suppresses flow separation,and improves the outlet pressure distortion.The primary and secondary orders of the influencing factors are as follows:control position>jet momentum coefficient>excitation frequency>jet configuration.The best jet control position is near the separation location,and the best jet configuration is the‘Λ’configuration.The higher the jet momentum coefficient and excitation frequency,the better the flow control.The wall pressure coefficient increases by up to 127.8%,and the outlet steady pressure distortion index decreases by 9.15%.The control mechanism is the direct energy injection into the flow boundary layer through a high-speed jet and the indirect control effect of the induced streamwise vortex.On the one hand,the PSJ suppresses flow separation by improving the ability of the boundary layer to resist the inverse pressure gradient.On the other hand,it reduces pressure distortion by decreasing the intensity of the secondary flow and weakening the backflow.This study thus provides a new technology for the active control of the flow-field characteristics in an S-duct and has significance for guiding the application of synthetic jet technology in S-ducts.