Stochastic resonance has seen wide application in the physical sciences as a tool to understand weak signal amplification by noise. However, this apparently counterintuitive phenomenon does not appear to have been exploited as a tool to enhance vibrational energy harvesting. In this note we demonstrate that by adding periodic forcing to a vibrationally excited energy harvesting mechanism, the power available from the device is apparently enhanced over a mechanism without periodic forcing.In order to illustrate this novel effect, a conceptually simple, but plausible model of such a device is proposed to explore the use of stochastic resonance to enhance vibrational energy harvesting.

Abstract-Hemodynamic forces such as fluid shear stress have been shown to modulate the activity of an expanding family of genes involved in vessel wall homeostasis and the pathogenesis of vascular disease. We have investigated the effect of shear stress on tissue factor (TF) gene expression in human endothelial cells (ECs) and in a rat arterial model of occlusion. As measured by reverse transcriptase polymerase chain reaction, exposure of ECs to 1.5 N/m 2 shear stress resulted in a time-dependent induction of endogenous TF transcripts of over 5-fold. Transient transfection of TF promoter mutants into cultured ECs suggests the involvement of the transcription factor Egr-1 in mediating the response of the TF promoter to shear stress. To address the importance of flow induction of Egr-1 in vivo, we have established a flow-restricted rat arterial model and determined the level of expressed Egr-1 and TF at the site of restricted flow using immunohistochemistry. We report an increase in the level of Egr-1 and TF protein in ECs expressed at the site of restricted flow. Elevated expression of Egr-1 and TF is restricted to a highly localized area, as evidenced by the fact that no significant increase in level can be detected at arterial sites distal to the site of occlusion. These findings suggest a direct role for Egr-1 in flow-mediated induction of TF and further substantiate the importance of shear stress as a modulator of vascular endothelial gene function in vivo. Key Words: fluid shear stress Ⅲ tissue factor promoter Ⅲ Egr-1 transcription factor Ⅲ vascular endothelial cells E ndothelial cells (ECs) lining the inner surface of blood vessels are constantly exposed to blood flow. Locally disturbed flow at arterial curvatures or bifurcations is characterized by both low and high oscillatory wall shear stresses that are conveyed to the cell as both a change in pressure and a change in the stretch capacity of the EC lining. 1-3 As a consequence of the local perturbation in laminar shear stress, a number of genes have been identified whose promoter activity is positively or negatively regulated by shear stress (reviewed in References 4 to 8). Several cis-acting elements have been implicated in mediating shear modulation of gene expression, and the term shear stress responsive element (SSRE) was first proposed after the identification of the sequence GAGACC. 9 This SSRE was demonstrated to confer shear stress responsiveness on the platelet-derived growth factor (PDGF) B promoter, 9 a heterologous SV40 promoter, 10 and has since been located in a number of other promoters that have been shown to be shear stress responsive in ECs. 11 The GAGACC sequence binds nuclear factor B (NF-B) p50 -p65 heterodimers, and consistent with this observation, the wild-type HIV-1 LTR, but not an LTR lacking the NF-B binding site, was also shown to be responsive to shear stress. 5 Other transcription factors that have been shown to mediate shear stress activation of a promoter are AP1, 12,13 Sp1, 14 and Egr-1. 15 Recently, the transcription fa...

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The non-linear equations of motion of a #exible pipe conveying unsteadily #owing #uid are derived from the continuity and momentum equations of unsteady #ow. These partial di!erential equations are fully coupled through equilibrium of contact forces, the normal compatibility of velocity at the #uid} pipe interfaces, and the conservation of mass and momentum of the transient #uid. Poisson coupling between the pipe wall and #uid is also incorporated in the model. A combination of the "nite di!erence method and the method of characteristics is employed to extract displacements, hydrodynamic pressure and #ow velocities from the equations. A numerical example of a pipeline conveying #uid with a pulsating #ow is given and discussed.

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