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Determination of the critical velocity of a straight wing with a high aspect ratio

Thanh Le Thi

International Journal of Applied Mechanics and Engineering

2023

Vol. 28, no. 1

105--117

An aerodynamic problem on an air flow around a large aspect ratio rectangular wing is investigated in this study. According to the theory of Vlasov, the wing is considered to be a thin rod. External loads are assumed to be proportional to the airfoil angle of attack related to the dimensionless coefficient of the lift and the pitching moment coefficient. These coefficients depend on the airfoil parameters and the Mach number M and are determined by experimental measurements for subsonic and supersonic velocities. In this case, to define the unstable cases of the wing, one bases on the Lyapunov stability theory. Equations of bending and torsional free vibrations have resulted. Based on the analysis of natural frequencies (eigenfrequencies), it is possible to determine the changing positions of the real part and the imaginary part of the characteristic equation solution. These positions can cause instabilities for the wing such as torsional divergence and flutter.

Zastosowanie procesu Boscha do plazmowego trawienia krzemu

Góra K., Kozłowski A.

Materiały Elektroniczne

2011

T. 39, nr 2

31-34

W pracy opisano wielostopniowy proces plazmowy powszechnie znany jako proces Boscha. Składa się on z wielokrotnie powtarzanych sekwencji kroków trawienia i pasywacji. Dzięki temu można otrzymać w krzemie bardzo głębokie struktury o wysokim współczynniku kształtu. Proces zaimplementowano na urządzeniu Alcatel 601E. Końcowym efektem opracowanej procedury jest wytrawiony profil o wysokim współczynniku kształtu, pionowych ścianach i gładkiej powierzchni.

This paper reports on two step time multiplexed plasma etch process, widely known as a Bosch process. The Bosch process was implemented on Alcatel 601E plasma reactor. On the basis of this patented process we created the procedure to achieve high aspect ratio submicron trenches in silicon. A deep silicon etching Bosch process in ICP reactive ion plasma reactor was based on SF6/C4F8 chemistry. Process consists of two alternating etching and deposition cycles. In thirst step, SF6 a very effective source of F* radicals is responsible for etching. In second step C4F8 gas creates polymers layer that protect side wall from lateral etching. This technique consisting of series alternating etch and deposition cycles(each lasts only a few seconds) produces high aspect ratio features. The etch rate and thickness of deposition layer are controlled by gas flow and cycle time, respectively. Created recipe can be used to etch silicon high aspect ratio features with smooth vertical walls.