Sound transmission loss of multi-layered infinite micro-perforated plates.

In this paper, the sound transmission loss (STL) of multi-layered infinite micro-perforated plates (MPPs) is studied. A prediction model for the STL of the multi-layered infinite MPPs is developed, where each MPP may or may not have a perforation, and the number of MPPs is arbitrary. When the frequency of interest is well below the critical frequency of the plate such that the effect of flexural vibration can be neglected compared to that of the inertia term, the mass is replaced by an equivalent complex mass. For numerical examples, single-, double- and triple-layered MPPs are studied. As the perforation ratio increases, the magnitude of the equivalent complex mass decreases rapidly, which in turn results in a decrease of the STL. It is observed that for very small perforation ratios, the mass-spring resonance frequencies in double- and triple-layered MPPs move toward a higher frequency as the perforation ratios increase. In addition, the dips at the resonance frequencies become blunt with increases in the perforation ratios due to the artificial damping induced by micro-perforations. It is also found that at a high frequency, the STL shows dips regardless of the perforation ratios when the wavenumber and air gap depths satisfy certain conditions.

Development of a Fault Monitoring Technique for Wind Turbines Using a Hidden Markov Model.

Regular inspection for the maintenance of the wind turbines is difficult because of their remote locations. For this reason, condition monitoring systems (CMSs) are typically installed to monitor their health condition. The purpose of this study is to propose a fault detection algorithm for the mechanical parts of the wind turbine. To this end, long-term vibration data were collected over two years by a CMS installed on a 3 MW wind turbine. The vibration distribution at a specific rotating speed of main shaft is approximated by the Weibull distribution and its cumulative distribution function is utilized for determining the threshold levels that indicate impending failure of mechanical parts. A Hidden Markov model (HMM) is employed to propose the statistical fault detection algorithm in the time domain and the method whereby the input sequence for HMM is extracted is also introduced by considering the threshold levels and the correlation between the signals. Finally, it was demonstrated that the proposed HMM algorithm achieved a greater than 95% detection success rate by using the long-term signals.

Sound transmission loss of double plates with an air cavity between them in a rigid duct.

In this paper, the sound transmission loss (STL) of thin double plates with an air cavity between them in a rigid duct is considered using an analytical approach. The vibration motion of the plate and sound pressure field are expanded in terms of an infinite series of the modal functions. Under the plane wave condition, a low frequency solution is derived by including the first few symmetric modes. It is determined that the peak frequencies of the double plates coincide with those of each single plate. When the two plates are identical, the STL becomes zero at the natural frequencies of the single plate. However, when the two plates are not identical, the STL is always greater than zero. The location and amplitude of the dips are investigated using an approximate solution when the cavity depth is very small. It is observed that dividing the single plate into two plates with an air cavity in between degrades the STL in the low frequency range, while the equivalent surface mass density is preserved. However, when the cavity depth is not small, the STL of the single plate can be smaller than that of the double plates.

Dynamin II involves in cell migration and actin formation of NIH3T3 cells.

It was previously reported that in Ras transformed NIH3T3 cells, dynamin II acts as an intermediate messenger in the Ras signal transduction pathway leading to membrane ruffling and cell migration. However, these results do not provide sufficient evidence of a relationship between dynamin II and the Ras signal transduction pathway leading to membrane ruffling and cell migration. The results showed that a dynamin II association with myosin II as a signaling molecule is involved in NIH3T3 cell migration through the Ras/PI3K signaling pathway, and is associated with the p85 subunit of PI3K. Confocal microscopy also revealed co-localization between dynamin II and paxillin after PDGF stimulation. In addition, immunofluorescence results showed that dynamin II was colocalized with the actin filament. After stimulating the NIH3T3 cells with PDGF and treating them with an actin inhibitor, such as Cytochalasin D, it was observed that dynamin II with the myosin II complex inhibited binding to the actin. Therefore, dynamin II is localized in focal adhesion when cell migration is triggered and binds to the actin filament component, suggesting that it is a good candidate nanomolecule to regulate the cell attachment and migration to the materials such as implants etc.

A theoretical model to predict the low-frequency sound absorption of a helmholtz resonator array.

A theoretical method based on mutual radiation impedance is proposed to compute the sound absorption performance of a Helmholtz resonator array in the low-frequency range. Any configuration of resonator arrangement can be allowed in the method, while all the resonators may or may not be identical. Comparisons of the theoretical predictions with those done by the past studies or experiments show that the present method can accurately predict the absorption performance in more general cases.