The critical layers of waves in parallel shear flow are generally classified into three kinds: viscosity critical layer, nonlinear critical layer, and non-steady critical layer.

平行切变流的临界层一般分为三类：粘性临界层、非线性临界层和非定常临界层。

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An experimental study on the laminar boundary layer instability and transition was carried out in a flat-plate boundary layer by means of controllable heat pulsing introduced into the critical layer.

本文用可控热脉冲输入临界层的方法研究了平板层流边界层的稳定性与转捩。

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The application server is a critical component in multi-tenancy at the application and infrastructure layer, because multi-tenancy affects installation, configuration, and application code.

应用服务器是应用程序和基础架构层多租户的关键部件，因为多租户会影响安装、配置和应用程序代码。

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Buy why wait until something goes wrong to add this critical layer of independent protection?

FORBES: 10 Tips To Improve Family Office Investing

The second critical step is putting a layer of analytics (historical, predictive, prescriptive) to make it actionable.

FORBES: More Data, More Dollars?

Airport directors, pilots and others in the aviation sector have argued that stripping away an extra layer of safety during the most critical stages of flight will elevate risks and at the very least slow years of progress that made the U.S. aviation network the safest in the world.

NPR: FAA To Close 149 Air Traffic Towers Under Cuts