Hyun Jung Kim

Examination of ratiometric laser induced fluorescence thermometry for microscale spatial measurement resolution

Ratiometric laser induced fluorescence (LIF) thermometry technique has been quantitatively examined for its capability for a microscale field-of-view. The goal of the study is to quantitatively examine the measurement accuracy of the ratiometric LIF technique at sub-millimeter and micron scales for its potential use as a microscale temperature mapping tool. Measurements have been made for the steady temperature fields established by thermal buoyancy inside 1-mm wide closed test cell with low Grashof–Prandtl numbers (86 < GrwPr < 301), and the detailed measured data have been compared with the well-known predictions. The smallest measurement resolution could be achieved being equivalent to the CCD pixel size of 4.7 lm in the present experiment, but with large data uncertainties. The measurement uncertainties show persistent improvement to better than ±1 � C when measurement resolution is equivalent to 76 lm.

Iron chelation-induced senescence-like growth arrest in hepatocyte cell lines: association of transforming growth factor beta1 (TGF-beta1)-mediated p27Kip1 expression.

Iron is essential for cellular proliferation in all organisms. When deprived of iron, the growth of cells is invariably inhibited. However, the mechanism involved remains largely unclear. In the present study, we have observed that subcytotoxic concentrations of desferroxamine mesylate (DFO), an iron chelator, specifically inhibited the transition from G1 to S-phase of Chang cells, a hepatocyte cell line. This was accompanied by the appearance of senescent biomarkers, such as enlarged and flattened cell morphology, senescence-associated beta-galactosidase activity and reduced expression of poly(ADP-ribose) polymerase. Concomitantly, p27Kip1 (where Kip is kinase-inhibitory protein) was induced markedly, whereas other negative cell-cycle regulators, such as p21Cip1 (where Cip is cyclin-dependent kinase-interacting protein), p15INK4B and p16INK4A (where INK is inhibitors of cyclin-dependent kinase 4), were not, implying its association in the G1 arrest. Furthermore, the induction of p27Kip1 was accompanied by an increased level of transforming growth factor beta1 (TGF-beta1) mRNA. When neutralized with an anti-(TGF-beta1) antibody, p27Kip1 induction was completely abolished, indicating that TGF-beta1 is the major inducer of p27Kip1. Finally, DFO-induced senescence-like arrest was found to be independent of p53, since cell-cycle arrest was still observed with two p53-negative cell lines, Huh7 and Hep3B cells. In conclusion, DFO induced senescence-like G1 arrest in hepatocyte cell lines and this was associated with the induction of p27Kip1 through TGF-beta1, but was independent of p53.

Gas foaming fabrication of porous biphasic calcium phosphate for bone regeneration

For reconstruction of bone defects resulting from the treatment of bone fractures or tumors or for the reconstruction of bone tissues following the surgery of organs or the like, biomaterials, including metals, polymers and ceramics, have been used. In this study, among ceramic materials, biphasic calcium phosphate (BCP) consisting of hydroxyapatite having excellent bioactivity and osteoconductivity, and β-tricalcium phosphate having high biodegradability, were mixed at a ratio of 60:40, which is suitable for new bone formation. To manufacture porous BCP scaffold, which has interconnected pores and is suitable for tissue regeneration and reconstruction, a polyurethane foaming (gas foaming) fabrication was applied to manufacture a bone scaffold satisfying various functional requirements. As the results, bone scaffolds having a pore size ranging from 300 μm to 800 μm and a porosity ranging from 75% to 85% could be manufactured using this process. In in vitro and in vivo animal tests, it was confirmed that the scaffold manufactured in this study can be effectively used as a bone scaffold, which is biocompatible and has the ability to induce bone differentiation and regeneration.

Hybrid scaffolds composed of hyaluronic acid and collagen for cartilage regeneration

Hybrid scaffolds composed of hyaluronic acid (HA) and collagen was prepared and evaluated for cartilage regeneration. The hybrid scaffolds prepared by adding 0.1, 0.3 or 0.5 wt.% collagen to HA had a three-dimensional structure with interconnected pores and showed an increase in tensile strength with increasing collagen concentration. The degradation period of the hybrid scaffolds in vitro increased with increasing collagen concentration and that the cell growth in the hybrid scaffolds increased with increasing collagen concentration for 2 weeks of cell culture. After the hybrid scaffolds with different collagen concentrations were implanted into cartilage defects of rabbit ears for 6 months, the GAG concentration of the hybrid scaffolds was higher than the HA scaffold itself, suggesting that cartilage tissue was easily formed in the collagen-containing scaffolds although the GAG concentration in the hybrid scaffolds decreased with increasing collagen concentration. Therefore, it is concluded that the collagen- containing porous scaffolds can be effectively used for cartilage regeneration.

Wide Range Parametric Study for the Pool Boiling of Nano-fluids with a Circular Plate Heater

The characteristics of boiling and critical heat flux (CHF) behavior of nano-fluids with alumina and silver nano-particles suspended in de-ionized water (pure water) were studied with circular plate heaters in the present study. Enhancements of CHF in nano-fluids in the wide range of particle sizes and concentrations were compared with those in pure water. Also, the effects of the particle deposition on CHF enhancement were investigated. All experiments were performed at the atmospheric pressure condition. The results show that the measured boiling curves in nano-fluids were shifted to the right and CHF were significantly enhanced for different nano-particle sizes and concentrations. The CHF of nano-fluids was increased as the size of the nano-particles decreased. On the other hand, nano-particle concentration value showing the maximum CHF had a critical value. In each pool boiling experiment of nano-fluids, nano-particles were deposited on the heater surface. Assuming that this phenomenon caused the CHF enhancement, pool boiling experiments of pure water were carried out with these nano-particle deposited heaters. The results of these tests were similar to those of the test of the nano-fluids for the CHF enhancement. The main cause of CHF enhancement was found to be the change of the heater surface structure. In order to analyze boiling phenomena of pure water and Al2O3 nano-fluids, boiling process was visualized by using a high speed camera.

A Study on the Development of Measurement Techniques for Thermal Flows in MEMS

A review on advanced flow visualization techniques is presented particularly for applications to micro scale heat and mass transport measurements. Challenges, development and applications of micro scale visualization techniques are discussed for the study of heating/evaporating thin films, a heated micro channel, and a thermopneumatic micro pump. The developed methods are (1) Molecular Tagging Fluorescence Velocimetry (MTFV) using 10-nm caged seeding molecules (2) Micro Particle Velocimetry (MPIV) and (3) Ratiometric Laser Induced Fluorescence (LIF) for micro-resolution thermometry. These three methods are totally non-intrusive techniques and would be useful to investigate the temperature and flow characteristics in MEMS. Each of these techniques is discussed in three-fold: (1) its operating principle and operation, (2) its application and measurement results, and (3) its future challenges.

Perceived Need and Use of Child Mental Health Services in Korea

This study examined the degree of perceived need and use of child mental health services in Korea, as well as the factors associated therewith. The sample consisted of 3,477 children aged 8–13xa0years. Overall, 10.4% of the parents demonstrated a perceived need for mental health services regarding their children’s emotional or behavioral problems, while 1.9% used mental health services. Although the perceived need for mental health services is high, only a small proportion of children receive them. Whether a child receives mental health care is influenced by the child’s psychopathology, especially when social and/or thought problems exist.

Thermal and Flow Characteristics of Evaporating Capillary Pore Flows Ranging from 10-mm to 10-μm Diameter

Flow and thermal characteristics are studied for capillary pore cavities with free surfaces ranging from 10-mm to 10-μm diameter. Also the effect of micro gravity is investigated. A standard finite volume method (FVM), in association with the well-established boundaryfitted coordinate transformation (BFCT), is used to numerically solve the governing equations for primitive scalar variables of velocity components, pressure and temperature. Calculation results show that the convection-driven circulation and the thermocapillary phoresis effect dominate the flow and thermal fields of larger pores, bigger than 1.0-mm diameter. With decreasing pore diameter, the flow circulation diminishes and the interfacial evaporation dominates to establish nearly stratified flow patterns parallel to the pore wall. Micro-scale capillary pores, less than 1.0-mm diameter, show no flow circulation with almost horizontally stratified temperature fields. Micro gravity condition shifts this transition which is from convection-driven to interfacial flow dominated flow regime to bigger pore diameter.

Measurements of Temperature and Flow Fields with Sub-Millimeter Spatial Resolution Using Two-Color Laser Induced Fluorescence (LIF) and Micro-Particle Image Velocimetry (PIV)

Comprehensive measurements for velocity and temperature fields have been conducted. A Micro PIV 2-color LIF system have been setup to measure the buoyancy driven fields in a 1-mm heated channel with low Grashof-Prandtl numbers [86<GγωPγ< 301] Fluorescence microscopy is combmed with an MPIV system to obtain enough intensity images and clear pictures from nano-scale fluorescence particles The spatial resolution of the Micro PIV system is 75μm by 67 μm and error due to Brownian motion is estimated 1.05% Temperature measurements have achieved the 4 7 μm spatial resolution with relatively large data uncertainties the present experiment. The measurement uncertainties have been decreased down to less than ±1.0 C° when measurement resolution is equivalent to 76 μm Measured velocity and temperature fields will be compared with numerical results to examine the feasibility of development as a diagnostic technique

Fabrication and Performance Investigation of Surface Temperature Sensor Using Fluorescent Nanoporous Thin Film II

We present a non-invasive technique to the measure temperature distribution in nano-sized porous thin films by means of the two-color laser-induced fluorescence (2-LIF) of rhodamine B. The fluorescence induced by the green line of a mercury lamp with the makeup of optical filters was measured on two separate color bands. They can be selected for their strong difference in the temperature sensitivity of the fluorescence quantum yield. This technique allows for absolute temperature measurements by determining the relative intensities on two adequate spectral bands of the same dye. To measure temperature fields, Silica (SiO2) nanoporous structure with 1-um thickness was constructed on a cover glass, and fluorescent dye was absorbed into these porous thin films. The calibration curves of the fluorescence intensity versus temperature were measured in a temperature range of , and visualization and measurement of the temperature field were performed by taking the intensity distributions from the specimen for the temperature field.