1,720,962 research outputs found
Prediction of vibrational energy distribution in the thin plate at high-frequency bands by using the ray tracing method
No full textAt high frequencies, one is interested in both the energy distribution and the energy flow of connected vibrating structures. The prediction of time- and space-integrated energy quantity has been usually performed by the statistical energy analysis (SEA), whereas the vibration conduction analysis (VCA) was suggested for calculating the time-averaged spatial energy distribution in structures. However, the VCA has not been useful due to inaccuracies in predicting the energy distribution and estimating the vibration transmission through structural joints. In this article, the ray tracing method (RTM) for high-frequency plate flexural vibration is suggested for solving the foregoing problems. The ray tube concept is adopted For describing the emanating circular wave and the governing relationships are derived for incident, reflected, and transmitted ray tubes at the coupled boundaries. The proposed RTM is applied to the prediction of the time-averaged vibration distribution in a single square panel and two line-coupled square plates, In addition, a four-panel array is investigated for the performance of the proposed RTM in analyzing the vibration transmission characteristics by panel joints. The results reveal that an improved prediction of spatial energy distribution can be obtained compared with SEA and VCA. It is also noted that the performance of the RTM is very similar to that of the wave intensity analysis (WIA) although RTM results seems to be slightly better. (C) 2001 Academic Press
Time accurate finite difference method for performance prediction of a silencer with mean flow and nonlinear incident wave
No full textTransmission losses of various reactive silencers are predicted, using a time accurate finite difference method. The numerical scheme is the 3rd order upwind scheme for axisymmetric Euler equations. Main advantage of the present method is that it can simulate linear and nonlinear wave propagation phenomena in a flow field directly with minimum numerical oscillation errors. The special treatments of incident wave condition, i.e. multiple harmonics of the transparent acoustic condition are applied to the transmission loss prediction for calculation efficiency. For the validation of the present approach, circular expansion chamber silencers without mean flow and an exponential pipe with mean flow are simulated in case of linear incident wave. The computed transmission losses have quite good agreements with those of the others. The nonlinear incident wave case is also investigated to check the usefulness of this method. The periodic N wave is clearly captured without numerical oscillation errors, and the insertion losses of two different incident frequencies are compared
High Frequency vibration in Structures: Comparison of SEA, Energy, Conduction, Ray Tracing Models
No full textHeat inducible expression of the CDC70 gene under the control of heat shock element in Saccharomyces cerevisiae
No full textIn order to express the CDC70 gene of Saccharomyces cerevisiae by heat shock, we have designed heat inducibe hybrid promoters using the Drosophila melanogaster heat shock elements (HSEs), A 220-bp-long upstream fragment of the D. melanogaster hsp70 gene comprised of four HSEs was placed upstream of the putative proximal TATA box of the CDC70 gene, Hybrid promoters containing different fusion joints were tested for their ability to drive the CDC70 gene expression by heat shock The results showed that the HSEs of D, melanogaster conferred the heat-induced CDC70 gene expression, but the heat inducibility was much lower than that in D. melanogaster
Formulation and validation of boundary conditions at a branched junction for nonlinear waves
No full textA numerical model is presented for the calculation of nonlinear waves through the branched junctions in a gas transmission pipe system. In the one-dimensional time domain analysis of the wave dynamics. the behaviour of the nonlinear waves is determined by quasi-steady boundary conditions at junctions in a pipe system. The quasi-steady treatment through the junction yields a system of nonlinear balance equations. The iterative solution procedure of the system of nonlinear equations causes the problems of divergence and multiple solutions. In order to overcome the difficulties, a new set of quasi-linear balance equations is formulated without a sacrifice of accuracy. The present model, therefore, requires a non-iterative solution procedure that results in a unique solution and a smaller computational effort. Thompson's boundary condition is used at each pipe. A new time-derivative form of balance equations, based Thompson' boundary condition, gives a set of linear algebraic equations for the balance equations. When implementing the new time-derivative form of the balance equations, corrected terms are added numerically. The present numerical model is implemented and tested for the calculation of behaviour of nonlinear waves in a branched pipe and the calculation of sound attenuation of a Helmholtz resonator and the prediction of radiated orifice noise of an internal combustion engine. Calculation results show good agreements with previous iterative calculations and measurement data. (c) 2006 Published by Elsevier Ltd
Characteristics of back-illuminated visible-blind UV photodetector based on AlxGa1-xN p-i-n photodiodes
No full textIn this work, we reported the growth, fabrication and characterization of an AlxGa1-xN heteroepitaxial back-illuminated visible-blind UV photodetector designed for flip-chip mounting. This device was grown on one side of a polished sapphire substrate using a low-temperature A1N buffer layer created by six-pocket multi-wafer system metalorganic chemical vapor deposition (MOCVD) with a vertical reactor. In order to obtain the wavelength of the visible-blind region, the AlxGa1-xN layer was grown under various conditions of growth time and gas flow rate, after optimizing the AIN buffer layer. This device consisted of a 1.3 mu m thick Al0.15Ga0.85N "window layer", a 0.16 pm thick Al0.08Ga0.92N i-layer, a 0.46 mu m thick Al0.08Ga0.92N p-layer, a 0.1 mu m thick GaN p-layer, followed by a 30 nm GaN:Mg p(+)-contact layer. All of the device processing was completed using standard semiconductor processing techniques that included photolithography, metallization and etching. In this device, the zero-bias peak responsivity was found around 0.052 A/W at 340 nm, corresponding to an external quantum efficiency of 19%. The rise and fall time of the photoresponse was 20.8 ns. Moreover, this device exhibits a low dark current density of 17 pA/cm(2) at zero-bias. (c) 2004 Elsevier B.V. All rights reserved
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