This paper presents exact density, velocity components, and temperature solutions for collisionless gas flows over a cylinder or a sphere. Possible real applications may include collisionless gas flows over a hot wire inside a vacuum chamber and rarefied gas flows around an aerosol at very high altitude. At any point off the cylinder or the sphere, the local velocity distribution function consists of two pieces of Maxwellian distribution functions: one for the freestream, which is characterized by the freestream density n 0 , temperature T 0 , and velocity U 0 ; the other is characterized by density at the wall n w and wall temperature T w , where n w is not constant at different surface locations. Directly integrating the distribution functions leads to the detailed flowfield solutions; the solutions are complex but exact. We performed numerical simulations with the direct simulation Monte Carlo method to validate these exact solutions. In general, the exact analytical and numerical results are virtually identical.

No abstract

No abstract

Impulse noise (IN) is the main cause of performance degradation in high-speed power line communication systems. Traditional methods mainly focus on manually setting a fixed blanking threshold to mitigate the corresponding IN. However, the fixed threshold cannot adapt to the time-varying IN efficiently. To solve this problem, an adaptive IN-mitigation system is proposed based on orthogonal frequency division multiplexing in a time-varying IN channel. The characteristics of IN are preevaluated by the method of moment estimation. Moreover, the adaptive threshold is efficiently solved in closed form according to the IN characteristics. In addition, an adaptive iterative IN-mitigation block is designed to leverage the performance of the receiver. For the number of iterations, a look-up table is constructed according to the IN characteristics. The experimental results show that the proposed method achieves performance balance in weak, moderate, and heavy IN environments simultaneously. It is noted that the bit error rate significantly decreases with an increment in E b /N 0 .

No abstract