• Macromolecular Research
• /
• v.12 no.1
• /
• pp.127-133
• /
• 2004

We have studied the surface micelle formation of polystyrene-b-poly(2-vinyl pyridine) (PS-b-P2VP) at the air-water interface. A series of four PS-b-P2VPs were synthesized by anionic polymerization, keeping the PS block length constant (28 kg/㏖) and varying the P2VP block length (1, 11, 28, or 59 kg/㏖). The surface pressure-area ($\pi$-A) isotherms were measured and the surface morphology was studied by atomic force microscopy (AFM) after Langmuir-Blodgett film deposition onto silicon wafers. At low surface pressure, the hydrophobic PS blocks aggregate to form pancake-like micelle cores and the hydrophilic P2VP block chains spread on the water surface to form a corona-like monolayer. The surface area occupied by a block copolymer is proportional to the molecular weight of the P2VP block and identical to the surface area occupied by a homo-P2VP. It indicates that the entire surface is covered by the P2VP monolayer and the PS micelle cores lie on the P2VP monolayer. As the surface pressure is increased, the $\pi$-A isotherm shows a transition region where the surface pressure does not change much with the film compression. In this transition region, which displays high compressibility, the P2VP blocks restructure from the monolayer and spread at the air-water interface. After the transition, the Langmuir film becomes much less compressible. In this high-surface-pressure regime, the PS cores cover practically the entire surface area, as observed by AFM and the limiting area of the film. All the diblock copolymers formed circular micelles, except for the block copolymer having a very short P2VP block (1 kg/㏖), which formed large, non-uniform PS aggregates. By mixing with the block copolymer having a longer P2VP block (11 kg/㏖), we observed rod-shaped micelles, which indicates that the morphology of the surfaces micelles can be controlled by adjusting the average composition of block copolymers.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.10a
• /
• pp.386-390
• /
• 2003

As a trial of application of hydrostatic pressure in micro fomring, burr-free punching has been conducted by means of hydro-mechanical procedure. Even though it is in beginning stage, result of the hydro-mechanical punching is promising. Hydrostatic pressure helps delay fracture initiation and makes it possible to get clean shearing surface. Without any burr on both side of sheet, smooth holes are archived as intended. To verify the significance of hydro-mechanical punching, conventional punching is performed under similar conditions and relatively larger portion of fracture surface is detected in the punching hole. Despite the quality of sidewall is not good enough, it might be possible to make the hole shaped upright, reduce the roll-over radius and minimize the fracture surface by optimizing process parameters.

• Selected Papers of The Society of Naval Architects of Korea
• /
• v.2 no.1
• /
• pp.140-155
• /
• 1994

The hydrodynamic problem is treated here when a pressurized bag is submerged partially in the water and the end points of it oscillate. SES(Surface Effect Ship) has a bag filled with pressurized air at the stern in order to prevent the air leakage, and the pitch motion of SES is largely affected by the hydrodynamic force of the bag. The shape of a bag can be determined with the pressure difference between inside and outside. Once the hydrodynamic pressure is given, the shape of a bag can be obtained, however in order to calculate the hydrodynamic pressure we should know the shape change of the bag, and vice versa. Therefore the type of boundary condition on the surface of a bag is a moving boundary like a free surface boundary. The present paper describes the formulation of this problem and treats a linearized problem. The computations of the radiation problem for an oscillating bag are shown in comparison with the case that the bag is treated as a rigid body. The hydrodynamic forces are calculated for various values of the pressure inside the bag and the submerged depth.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2001.11b
• /
• pp.1078-1082
• /
• 2001

An alternative formulation of the Helmholtz integral equation is derived to express the pressure field explicitly in terms of the velocity vector of a radiating surface. This formulation, derived for arbitrary sources, is similar in form to the Rayleigh's formula for planar sources. Because the pressure field is expressed explicitly as a surface integral of the particle velocity, which can be implemented numerically using standard Gaussian quadratures, there is no need to use Boundary element method to solve a set of simultaneous equations for the surface pressure at the discretized nodes. Furthermore the non-uniqueness problem inherent in methods based on Helmholtz integral equation is avoided. Validation of this formulation is demonstrated for some simple geometries.

• Korean Journal of Metals and Materials
• /
• v.48 no.3
• /
• pp.241-247
• /
• 2010

In order to develop the vacuum distillation process of magnesium alloy scrap, a fundamental study on the evaporation behavior of magnesium alloy (AM50) scrap melt was carried out. Melt temperature, pressure, reaction time, and initial specific surface area of melt were considered as experimental variables. The evaporation rate of magnesium increased with the increase of melt temperature and initial specific surface area of melt, and with the decrease of the pressure. The activation energy of magnesium evaporation reaction calculated by an Arrhenius plot decreased with the decrease of the pressure and with the increase of the initial specific surface area of melt. An empirical equation was derived for the evaporation rate of magnesium from AM50 alloy melt.

• Journal of the Korean Society of Visualization
• /
• v.21 no.1
• /
• pp.31-39
• /
• 2023

Sloshing of the fluid having a free surface produces an impact force on a tank wall subjected to external excitation. This paper investigates the effect of cylindrical structures in a rectangular sloshing tank under translational harmonic excitations. By varying the number of installed cylinders in the tank, the characteristics of the free-surface deformation is experimentally observed, and the peak pressure on the tank wall is extracted by threshold values. To predict the peak pressure, the numerical simulation is also conducted using smoothed particle hydrodynamics (SPH), and the peak values are compared with the experimental results. Furthermore, pressure and velocity fields in the tank and free-surface shape are analyzed at the moment of impact.

• Journal of Hydrogen and New Energy
• /
• v.8 no.2
• /
• pp.79-90
• /
• 1997

Extensive work has been done on investigating the inner cell pressure characteristics of sealed type Ni-MH battery in which Zr-Ti-Mn-V-Ni alloy is used as anode. The inner cell pressure of this type Ni-MH battery much more increases with the charge/discharge cycling than that of the other type Ni-MH battery where commercialized $AB_5$ type alloy is used as anode. The increase of inner cell pressure in the sealed type Ni/MH battery using Zr-Ti-Mn-V-Ni alloy system is mainly due to the accumulation of oxygen gas during charge/discharge cycling. The accumulation of oxygen gas arises mainly due to the low rate of oxygen recombination on the MH electrode surface during charge/discharge cycling. The difference of oxygen recombination rate between $AB_5$ type electrode and Zr-Ti-Mn-V-Ni electrode is caused by the difference of electrode reaction surface area resulting from different particle size after their activation and the difference of surface catalytic activity for oxygen recombination reaction, respectively. After EIS analysis, it is identified that the surface catalytic activity affects much more dominantly on the oxygen recombination reaction than the reaction surface area does. In order to suppress the inner cell pressure of Ni-MH battery where Zr-Ti-Mn-V-Ni is used as anode, it is suggested that the surface catalytic activity for oxygen recombination should be improved.

• Journal of the Korean Society of Physical Medicine
• /
• v.10 no.3
• /
• pp.19-27
• /
• 2015

PURPOSE: This study aimed to investigate the effects of pressure sense perception training (PSPT) on various surfaces on the somatosensory system, balance, and walking ability in chronic stroke patients. METHODS: Thirty patients with stroke participated in this study and were randomly assigned to one of three groups; group 1 received the general physical therapy and the PSPT on a stable surface, group 2 received the general physical therapy and the PSPT on an unstable surface, and group 3 received the general physical therapy alone. Participants in group 1 and group 2 underwent 30 min/session, 3 days per week, for 4 weeks. Pressure error (PE) was used to evaluate changes of proprioception. The Balancia, Functional reach test (FRT), and Timed Up and Go (TUG) were used to assess the balance ability, and the 10m Walking Test (10-MWT) was used to assess walking ability. RESULTS: Experimental groups (group 1 and group 2) showed significant differences in PE, FRT, TUG, and 10-MWT compared to the control group (p <0.05). Group 2 (PSPT on an unstable surface) was significantly different in PE, FRT, and 10-MWT from group 1 (p <0.05). No significant differences were observed for other measures. CONCLUSION: Pressure sense perception training on an unstable surface might be a significantly more effective method for improving somatosensory function, balance, and walking ability, than PSPT on a stable surface.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.39 no.8
• /
• pp.735-743
• /
• 2011

In this study, the distribution of surface pressure was measured in a steady state on a turbine blade which was moved the injected region and receded the stagnation region using a linear cascade apparatus. Axial-type blades were used and the blade chord was 200mm. The rectangular nozzle was applied and its size was $200mm{\times}200mm$. The experiment was done at $3{\times}10^5$ of Reynolds number based on the chord. The surface pressures on the blade were measured at three different nozzle angles of $58^{\circ}$, $65^{\circ}$ and $72^{\circ}$ for off-design performance test. In addition, three different solidities of 1.25, 1.38 and 1.67 were applied. From the results, the low solidity caused the low pressure on the blade suction surface at entering region and the reverse rotating force was generated at the low nozzle angle. The positive incidence also made the pressure lower on the suction surface at entering region.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.1
• /
• pp.1-8
• /
• 2003

The heat transfer and flow measurements on a cylindrical pedestal mounted on a flat surface with a turbulent impinging jet were made. The experiments were made for the jet Reynolds number of Re = 23,000, the dimensionless nozzle-to-surface distance of L/d = 2~10, the dimensionless pedestal height of H/D = 0~1.5. Measurements of the surface temperature and the Nusselt number distributions on the plate surface were made using liquid crystal and shroud-transient technique. Flow measurements involve smoke flow visualization and the wall pressure coefficient. The results show that the wall pressure coefficient sharply decreases along the upper surface of the pedestal. However, the pressure increases when the fluid escapes from the pedestal and then collides on the plate surface. The secondary maxima in the Nusselt numbers occur in the region of 1.0 $\leq$ r/d $\leq$ 1.9. Their values for the case of H/D = 0.5 are maximum 80% higher than those for other cases. The formation of the secondary maxima may be attributed to the reattachment of flow on the plate surface which was separated at the edge of the pedestal.