Sunghyuk Im

Adjustable, rapidly switching microfluidic gradient generation using focused travelling surface acoustic waves

We demonstrate a simple device to generate chemical concentration gradients in a microfluidic channel using focused travelling surface acoustic waves (F-TSAW). A pair of curved interdigitated metal electrodes deposited on the surface of a piezoelectric (LiNbO3) substrate disseminate high frequency sound waves when actuated by an alternating current source. The F-TSAW produces chaotic acoustic streaming flow upon its interaction with the fluid inside a microfluidic channel, which mixes confluent streams of chemicals in a controlled fashion for an adjustable and rapidly switching gradient generation.

Delamination crack originating from transverse cracking in cross-ply composite laminates under extension

Abstract Based upon the Stroh formalism for anisotropic elastic materials and upon the method of eigenfunction expansion, the stress redistribution due to delamination cracks originating from transverse cracking is examined from [90/0], and [0/90], laminates under extension. The structure of the solution, in the form of a series expansion, is determined from the eigenvalue equation resulting from appropriate near-field conditions. To complete the solution, use is made of a boundary collocation technique in conjunction with the eigenfunction series that includes a large number of terms, enough to represent the elastic state throughout the appropriate domain concerned. The fracture mechanics parameters, such as stress intensity factors and energy release rates, are calculated and the major characteristics of stress distribution are discussed. The stability of delamination cracks is examined for varying ratios of ply thickness in terms of the energy release rate.

Photosynthesis of cyanobacteria in a miniaturized optofluidic waveguide platform

We investigated the effect of increasing the optical penetration length, inside polydimethylsiloxane (PDMS)-based photobioreactors (PBRs), upon the photosynthetic cell growth of cyanobacteria. A thin layer of Teflon amorphous fluoropolymer (Teflon AF) was applied inside the PDMS-based PBRs to prevent light loss at the solid–liquid interface. The Teflon AF layer, with a refractive index (nTeflon = 1.31) lower than PDMS (nPDMS = 1.442) and higher than the culture medium (nmedium = 1.332), constructed the light waveguide in the PBRs via the total internal reflection. Such a combination of refractive indices led to the prevention of light loss at the interface. The cell growth rate and the optical cell density were measured periodically for 5 days under different light power and Teflon AF-coating conditions. The local or global auto-fluorescence signal and the optical density at 450 nm wavelength (OD450) were measured in parallel by a fluorescence microscope and a micro plate reader, respectively. The optofluidic waveguide-based PBR improved the photosynthetic cell growth up to ∼9% compared to a regular PBR.

Experimental Study of Moderator Circulation in CANDU6 Calandria Tank

As a CANDU6 reactor has a high pressure primary cooling system and an independently cooled moderator system, the moderator in the calandria would act as a supplementary heat sink during a loss of coolant accident (LOCA) if the primary cooling and emergency coolant injection systems fail to remove the decay heat from the fuel. For the safety concern it is required to predict the 3-dimensional velocity and temperature distribution of moderator fluid to confirm the effectiveness of moderator heat sink.Korea Atomic Energy Research Institute (KAERI) is carrying out a scaled-down moderator test program to simulate the CANDU6 moderator circulation phenomena during steady state operation and accident conditions. This research program includes the construction of the Moderator Circulation Test (MCT) facility, production of the validation data for self-reliant CFD tools, and development of optical measurement system using the Particle Image Velocimetry (PIV). In the present work the PIV technique is used to measure the velocity distributions in the scaled moderator tank of MCT under iso-thermal test conditions. The preliminary PIV measurement data are obtained and compared with CFX code predictions.Copyright