• Journal of applied mathematics & informatics
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• v.41 no.5
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• pp.1085-1102
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• 2023

In this study the magneto hydrodynamic (MHD) micro polar fluid flow of a viscous incompressible fluid past a porous medium in the presence of chemical reaction is considered. This work is devoted to investigate the Soret effect and Electromagnetic radiation effect and analyze analytically. In the energy equation the applied magnetic field strength and in the concentration equation the Soret effect are incorporated. The basic PDE (partial differential equations) are reduced to ODE (ordinary differential equations) using non dimensional variables. Then the analytical solution of the dimensionless equations are found using perturbation technique. The features of the fluid flow parameters are analyzed, discussed and explained graphically. The graphical solutions are found using MATLAB R2019b. Skin friction coefficient at the wall, Couple stress coefficient at the plate and the local surface heat flux are also thoroughly examined. Overall, this study sheds light on the complex interplay between physical parameters in the behavior of MHD micro-polar fluid past a porous medium in the presence of chemical reaction.

• Journal of the Korean Society for Precision Engineering
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• v.29 no.5
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• pp.572-577
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• 2012

Recently porous polymer has widely been applied to packaging, heat isolation, and sound absorption in various fields from the electrics to the automobiles industry. A lot of micro porosities inside foamed polymer provide lower heat conduction and lighter weight than non-porous polymer, because they involve gas or air during foaming process. In this paper experimental approaches of the UV laser micro machining behavior for Expanded Polypropylene (EPP) foamed polymer materials, which have different expansion rates, were investigated. From these results, the ablation phenomena were finally observed that the ablation is depended upon stronger photo-chemical than photo-thermal effect. This study will also help us to understand interaction between UV laser beam and porous polymer.

• Bulletin of the Korean Chemical Society
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• v.31 no.8
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• pp.2223-2227
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• 2010

Reaction of [(bpy)Pd]$(PF_6)_2$ (bpy = 2,2'-bipyridine) with racemic bis(isonicotinoyl)-1,1'-bi-2-naphtholate (L) in acetone, and followed by addition of chloroform and solvent evaporation allows to form amorphous micro-bowl morphology consisting of $[(bpy)PdL]_2(PF_6)_4$ without any template or additive. In contrast, the reaction and recrystallization in acetone for 1 week produce parallel-piped single crystals consisting of $[(bpy)_3Pd_3({\mu}_3-HPO_4)_2](PF_6)_2$. The formations of micro-bowl and parallel-piped single crystal morphologies appear to be primarily associated with the kinetic and thermodynamic control, respectively. The formation of micro-bowls may be attributed to eruption of organic solvents. Cosolvent effects and chemical properties on the formation of micro-bowl morphology have been observed.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.21 no.3
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• pp.355-361
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• 2012

Though a micro pump is a crucial element in miniaturized bio-fluidic systems or drug delivery systems, it has some intrinsic disadvantages such as backward flow, pulsation of flow, low repeatability and producibility, and high cost. To overcome these limitation, a PZT disc actuated micro pump including a novel ring-shaped multi-flap check valve is introduced. To enhance the performance of the micro pump, the static behaviour of flap valve module and the micro fluidic behavior of fluids are numerically modelled and analyzed. As results of the numerical analysis, the optimal dimension and configuration of the ring-shaped multi flap valve are $1{\times}0.05$ mm and 2 (inlet side)${\times}1$ (outlet side) type. The obtained maximum flow rates and flow resolution are about 90 ml/min and 30 ${\mu}l$/stroke respectively.

• Journal of the Korean institute of surface engineering
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• v.46 no.1
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• pp.22-28
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• 2013

$WS_2$ particles were added to micro-diamond blades with Cu/Sn binding metal as lubricants to improve cutting efficiency. It was found in previous works that the added $WS_2$ lubricant could reduce remarkably the momentary energy consumption during dicing tests but increased wear rate slightly owing to weak bonding between lubricant particles and bond metals. In the present work, the surface of $WS_2$ lubricant particles were etched for activating the surface of $WS_2$ particles that provide even distribution of particles during powder mixing process and improvement of wetting at the interfaces between $WS_2$ particles and molten Cu/Sn bond metals during pressurized sintering so that could provide the improved strength of micro-blades and result in extended life. Chipping behavior of workpiece with the types of micro-blades including $WS_2$ were compared because it is important in semiconductor and micro-packaging industries to control average roughness and straightness of sliced surface which is closely related with quality.

• Korean journal of applied entomology
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• v.32 no.3
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• pp.354-371
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• 1993

Behavior of adult females of the smoky brown cockroach was observed for 10-15 days continuously by using computer and the automatic sensoring system. Under the light condition of l2L~ 12D, individual variations were generally higher and the periodicity appeared less in terms of the presence time at the micro-habitats and the locomotory activity. The smoky brown cockroach appeared 20.42, 11.50, 6.31 and 2.66 % in a day in averages respectively at the shelter and the places for other individuals, feeding and drinking. It stayed 20.29 % in a day at the shelter when food, water, and other individuals were not supplied. Visiting rates were higher at the feeding and dnnking places than at. the ot.her micro-habitats. The degree of t.he locomotory activity was relatively lower when food, water, and other individuals were not supplied t.han when they were supplied. The Pnncipal Component Analysis (PCA) on the presence at the micro-habitats showed that. t.he presence pattern for each mdividual appeared differently (Q mode) while the differem time zones were grouped to the photophase and scotophase (R mode). When food, water, and other individuals were supplied the degree of grouping was higher at the shelter than at the places for feeding and drinking. When the act.ivityand the presence time at the different micro-habitats were jointly analyzed by PCA, the achvity of the female smoky brown cockroach appeared in relation with the presence time ( %) at the places for feeding and other individuals.

• Journal of Power System Engineering
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• v.17 no.6
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• pp.122-129
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• 2013

The microstructure and deformation behavior in 22Cr-0.2N micro-duplex stainless steels with various Ni and Mn contents were compared using by OM, TEM, and XRD. The 22Cr-0.2N duplex stainless steel plates were fabricated and hot rolled, followed by annealing treatment at the temperature range of $1,000-1,100^{\circ}C$. All the samples showed the common strain hardening behaviour during the tensile test at a room temperature. The steels tested at the temperatures of $-30^{\circ}C$ or $-50^{\circ}C$ showed a distinct inflection point in the stress-strain curves, which should be resulted from the formation of strain-induced martensite(SIM) of austenite phase. This was confirmed by TEM observations. The onset strain of a inflection point in a stress-strain curve should be depended up the value of $M_d30$. With the decrease of the tensile test temperature, the inflection point appeared earlier, and the strength and fracture strain were higher. The tensile behaviour was discussed from the point of austenite stability of the micro-duplex stainless steels with the different Ni and Mn content.

• Tribology and Lubricants
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• v.24 no.1
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• pp.27-33
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• 2008

A micro-impression creep machine was designed and developed, adopting a small punch in diameter of 150 um, displacement gage with an accuracy of sub-${\mu}m$ scale, and load-cell with an accuracy of mN scale in order to investigate creep behavior of small solder ball in diameter of less than 1 mm. Creep behavior of lead-free solder ball(Sn-3.0Ag-0.5Cu) in diameter of $760\;{\mu}m$ was investigated in the stress range of $8{\sim}60\;MPa$ and at $303\;K{\sim}393\;K$. The applied load became decreased slightly and continuously in the creep rate of $10^{-4}/s$ range during the current experiments. Also, the machine frame was so sensitive to the environmental temperature that nm scaled displacement recording was unstable according to the change in environmental temperature.

• Journal of the Korean Society for Precision Engineering
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• v.32 no.6
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• pp.577-585
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• 2015

We fabricated multi-scale such as macro-, micro-, and multi-scale wrinkles by using repetitive volume dividing (RVD) method and thermal curing process. Also wrinkle surface was modified with coating of a self-assembled monolayer (SAM). We measured the contact angle of each wrinkled surface, and observed the behavior of droplets on sloping surface. Through experimental study, we found out that the contact angle was much higher in case of multi-scale and SAM coated wrinkles. And micro-scale wrinkle showed a high contact angle comparing with that of macro-scale wrinkle. Dynamic behaviors of a water droplet like sliding velocity on diverse wrinkled surfaces were dependent on their static contact angles. These results showed that hydro-dynamic characteristics were changed depending on the wrinkle structure and the material forming the wrinkle. These dynamic characteristics can be utilized in bio-chip, microfluidics, and many others in order to control easily chemical reactivity.

• Transactions of Materials Processing
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• v.20 no.7
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• pp.518-523
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• 2011

The three dimensional geometries of an aluminum open cell foam before and after uniaxial compressive loading were investigated using the X-ray micro CT(computed tomography). Aluminum 6101-T6 open cell foams of 10, 20, 40 ppi (pore per inch) were considered in this work. After the serial sectioning CT images of aluminum foams were obtained from non-destructive X-ray images, the exact 3D structure were reproduced and visualized with commercial image processing program. The relative density ratio was around the 7.0 to 9.0 range, the unit cells showed anisotropic shapes having the different dimensional ratios of 1.1 to 1.3 between the rise and the transverse directions. The yield stress increased with the relative density ratio and the volumetric strain increased proportionally with compressive strain. The plateau stress in the compressive stress-strain curve was caused by the buckling of ligaments.