The roles of various plasma agents in the inactivation of bacteria have recently been investigated. However, up to now, the effect of the charged particles on the inactivation of bacteria is not well understood. In this paper, an atmospheric pressure plasma jet device, which generates a cold plasma plume carrying a peak current of 300 mA, is used to investigate the role of the charged particles in the inactivation process. It is found that the charged particles play a minor role in the inactivation process when He/N2(3%) is used as working gas. On the other hand, when He/O2(3%) is used, the charged particles are expected to play an important role in the inactivation of bacteria. Further analysis shows that the negative ions O2− might be the charged particles that are playing the role. Besides, it is found that the active species, including O, O3, and metastable state O2∗, can play a crucial role in the inactivation of the bacteria. However, the excited He∗, N2 C Π3u, and N2+ B Σ2u+ have no significant direct effect on the inactivation of bacteria. It is also concluded that heat and UV play no or minor role in the inactivation process.
Impacts of Various Boundary Conditions on Beam Vibrations Ye Tao In real life, boundary conditions of most structural members are neither totally fixed nor completely free. It is crucial to study the effect of boundary conditions on beam vibrations. This thesis focuses on deriving analytical solutions to natural frequencies and mode shapes for Euler-Bernoulli Beams and Timoshenko Beams with various boundary conditions under free vibrations. In addition, Green's function method is employed to solve the close-form expression of deflection curves for forced vibrations of Euler-Bernoulli Beams and Timoshenko Beams. A direct and general beam model is set up with two different vertical spring constraints 1 , 2 and two different rotational spring constraints 1 , 2 attached at the ends of the beam. These end constraints can represent various combinations of boundary conditions of the beam by varying the spring constraints. A general solution for the Timoshenko beam with this various boundary conditions is derived, and to the best of our knowledge, this solution is not available in the literature. Numerical examples are presented to illustrate the effects of the end constraints on the natural frequencies and mode shapes between Euler-Bernoulli beams and Timoshenko beam. The results show that Euler-Bernoulli beams have higher natural frequencies than Timoshenko beams at different modes. The ratio of the natural frequencies for Timoshenko beams to the natural frequency for Euler-Bernoulli beams decreases at higher modes. Natural frequencies at lower modes are more sensitive to boundary constraints than natural frequencies at higher modes. iii ACKNOWLEGEMENTS I would like to express my gratitude and appreciation to everyone who helped to make this thesis possible.
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