• ALGAE
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• 제39권2호
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• pp.109-127
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• 2024

High production and efficient harvesting of microalgae containing high omega-3 levels are critical concerns for industrial use. Aeration can elevate production of some microalgae by providing CO₂ and O₂. However, it may lower the production of others by generating shear stress, causing severe cell damage. The mixotrophic dinoflagellate Gymnodinium smaydae is a new, promising microalga for omega-3 fatty acid production owing to its high docosahexaenoic acid content, and determining optimal conditions and methods for high omega-3 fatty acid production and efficient harvest using G. smaydae is crucial for its commercial utilization. Therefore, to determine whether continuous aeration is required, we measured densities of G. smaydae and the dinoflagellate prey Heterocapsa rotundata in a 100-L semi-continuous cultivation system under no aeration and continuous aeration conditions daily for 9 days. Furthermore, to determine the optimal conditions for harvesting through centrifugation, different rotational speeds of the continuous centrifuge and different flow rates of the pump injecting G. smaydae + H. rotundata cells into the centrifuge were tested. Under continuous aeration, G. smaydae production gradually decreased; however, without aeration, the production remained stable. Harvesting efficiency and the dry weights of omega-3 fatty acids of G. smaydae + H. rotundata cells at a rotational speed of 16,000 rpm were significantly higher than those at 2,000-8,000 rpm. However, these parameters did not significantly differ at injection pump flow rates of 1.0-4.0 L min^-1. The results of the present study provide a basis for optimized production and harvest conditions for G. smaydae and other microalgae.

• Journal of the Microelectronics and Packaging Society
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• 제24권1호
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• pp.83-90
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• 2017

In this paper, we evaluated the solderability of thin electroless nickel-electroless palladium-immersion gold (ENEPIG) plating layer for fine-pitch package applications. Firstly, the wetting behavior, interfacial reactions, and mechanical reliability of a Sn-3.0Ag-0.5Cu (SAC305) solder alloy on a thin ENEPIG coated substrate were evaluated. In the wetting test, maximum wetting force increased with increasing immersion time, and the wetting force remained a constant value after 5 s immersion time. In the initial soldering reaction, $(Cu,Ni)_6Sn_5$ intermetallic compound (IMC) and P-rich Ni layer formed at the SAC305/ENEPIG interface. After a prolonged reaction, the P-rich Ni layer was destroyed, and $(Cu,Ni)_3Sn$ IMC formed underneath the destroyed P-rich Ni layer. In the high-speed shear test, the percentage of brittle fracture increased with increasing shear speed.

• Membrane Journal
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• 제13권2호
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• pp.88-100
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• 2003

A change of filtrate flux in Taylor vortex flow filtration was investigated experimentally by rotating speed of inner cellulose ester membrane cylinder (average pore size: 1.2 ${\mu}m$), slurry concentration, and particle size. The filtrate flux was a direct proportion relation with TMP, but an inverse relation with resistances. A change of cake resistance with time was examined by rotating speed, slurry concentration, and particle size. Initial resistance increased dramatically as raising slurry concentration, and the pseudo-steady state was maintained at high resistance value. However, times to reach the pseudo-steady state did not depend on slurry concentration. The resistance was larger as smaller particle size, because possibility of pore blocking inside membrane could be higher and shear effect should be lower as smaller particle size. A model equation suggested in this study was composed of particle deposition and removal terms, and could confirm well experimental data using average values of experimental coefficients.

• Tribology and Lubricants
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• 제30권6호
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• pp.337-342
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• 2014

The reduction of drag torque is an important research issue in terms of improving transmission efficiency. Drag torque in a wet clutch occurs because of the viscous drag generated by the transmission fluid in a narrow gap (clearance) between the friction plate and a separate plate. The objective of this paper is to observe the effects of the friction plate area and the clearance on the drag torque using finite element simulation. The two-phase flow of air and oil fluid is considered and modeled for the simulation. The simulation analysis reveals that as the rotational speed increases, the drag torque generally increases to a critical point and then decreases sharply at a high speed regime. The clearance between the two plates plays an important role in controlling drag torque peak. An increase in the clearance causes a decrease in shear stress; thus, the drag torque also decreases according to Newton's law of viscosity. An observation of the effect of the area of contact between transmission fluid and friction plate shows that the drag torque increases with the contact area. The flow vectors inside the flow channel present clear evidence that the velocity of the fluid flows is faster with a larger friction plate, that is, in the case of a larger contact area. Therefore, the optimum size of the friction plate should be determined carefully, considering both the clutch performance and drag reduction. It is expected that the results from this study can be very useful as a database for clutch design and to predict the drag torque for the initial design with respect to various clutch parameters.

• Structural Engineering and Mechanics
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• 제84권4호
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• pp.489-502
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• 2022

This paper is aimed at developing an optimization-based Finite Element model updating approach for structural damage identification and quantification. A modal flexibility-based error function is introduced, which uses modal assurance criterion to formulate the updating problem as an optimization problem. Because of the inexplicit input/output relationship between the candidate solutions and the error function's output, a robust and efficient optimization algorithm should be employed to evaluate the solution domain and find the global extremum with high speed and accuracy. This paper proposes a new multi-stage Selective Particle Swarm Optimization (SPSO) algorithm to solve the optimization problem. The proposed multi-stage strategy not only fixes the premature convergence of the original Particle Swarm Optimization (PSO) algorithm, but also increases the speed of the search stage and reduces the corresponding computational costs, without changing or adding extra terms to the algorithm's formulation. Solving the introduced objective function with the proposed multi-stage SPSO leads to a smart feedback-wise and self-adjusting damage detection method, which can effectively assess the health of the structural systems. The performance and precision of the proposed method are verified and benchmarked against the original PSO and some of its most popular variants, including SPSO, DPSO, APSO, and MSPSO. For this purpose, two numerical examples of complex civil engineering structures under different damage patterns are studied. Comparative studies are also carried out to evaluate the performance of the proposed method in the presence of measurement errors. Moreover, the robustness and accuracy of the method are validated by assessing the health of a six-story shear-type building structure tested on a shake table. The obtained results introduced the proposed method as an effective and robust damage detection method even if the first few vibration modes are utilized to form the objective function.

• Journal of the korean academy of Pediatric Dentistry
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• 제34권4호
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• pp.569-578
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• 2007

This study was performed to compare the shear bond strength of self etching system and two bottle bonding system with or without laser preparation. Group I was prepared with high speed rotary instrument and $Prompt^{TM}$ L-$Pop^{TM}$, group II with Er:YAG laser and $Prompt^{TM}$ L-$Pop^{TM}$, group III with Er:YAG laser, 37% phosphoric acid and Single bond, group IV with Er:YAG laser and Single bond and group V with high speed, etching and Single bond. And also observation of the prepared and etched dentin surface were performed under scanning electro-microscope. The possibility of clinical application of laser preparation which might have an advantage to reduce pain for children with less unfavorable noise were evaluated. The results obtained are as follows; 1. Group V showed significantly higher bond strength than other groups. And group IV showed significantly lower bond strength than other groups. 2. There was no significant difference between group I and group III. 3. Group II showed significantly lower bond strength than group I, III, V, but showed significantly higher bond strength than group IV. 4. Under scanning electro-microscope, laser-preparated dentin surface showed high irregularity and no smear layer. The surface showed less irregularities and more exposed dentinal tubules with etching. Laser preparation has many advantages over conventional tooth preparation. But this method showed lower resin bonding strength. Laser preparated tooth surface differed from the conventionally preparated tooth surface. More researches are needed on suitable methods for laser preparated dentin surface.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.371-372
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• 2002

It is well known that red blood cells (RBCs) are suffered from chronic stresses in systemic circulation. The objective of this study is to clarify the effect of the aging of RBCs on rheological properties and hemolysis. Initially, RBCs age fractionation was performed by using a high-speed centrifugation (15[min] at 1500[G]), then young and aged RBCs were suspended in plasma to adjust the hematocrit level of 40[%]. After this pretreatment, the viscosity was measured by using a capillary type and a cone-plate type viscometers, respectively, and the hemolysis test was carried out by a seesaw type shaker. Results from these experiments showed that the viscosity of the aged RBCs measured by the capillary viscometer was increased by 10[%] as compared with that of the young RBCs. Under the condition of all shear zones, the viscosity of the aged RBCs was increased in case of using the cone-plate type viscometer. And the hemolytic level was increased twice as the aging. The data obtained in this study indicated that the ability of aggregation of RBCs was increased and the deformability of RBCs membrane got lower with the aging. Furthermore, it was exhibited that the fragility of RBCs ’ membrane was increased with the aging.

• Journal of Welding and Joining
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• 제34권3호
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• pp.6-11
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• 2016

Joining Al/Fe dissimilar metals is becoming a subject of special interest in the assembly of automotive parts as a trade-off between the weight lightening and the cost reduction. Although various studies have been introduced to join Al alloy with the steel sheet by fusion welding, weak joint strength and galvanic corrosion still remained as problems to be solved. As a solid state welding, friction stir welding has been preferred to fusion welding processes in the dissimilar metal joints. This study investigated friction stir spot welding (FSSW) of Al alloy to the thin steel sheet with a thickness of 0.65 mm. The conventional FSSW is a stationary spot welding process but new approach adopted an additional circumferential movement in company with high speed tool rotation. A full factorial experimental design was implemented, and the main and interaction effects of parameters were analysed on the failure load in the tensile shear test. The direction and radius of rotation were statistically significant parameters and these two parameters affected the joint width and the shape of the hook.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 한국추진공학회 2005년도 제24회 춘계학술대회논문집
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• pp.329-333
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• 2005

Total temperature distribution in high speed fee & wall jet regions was investigated using the total temperature probe. For the free jet, the distance of probe from the nozzle exit is changed in the range of 1, 2, 4 and 6 times o nozzle exit diameter. Energy separation phenomenon was observed on shear layer between jet and ambient. In wall jet region, impinging plate was fixed at Z/D=2 and total temperature distribution has been measured for various radial distance($R/D=1.25\sim2.0$). Energy separation phenomenon was found at wall jet boundary and near wall, and was compared with measured adiabatic wall temperature value.

• Transactions of the Korean Society of Automotive Engineers
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• 제7권9호
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• pp.182-194
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• 1999

Occupant injury in rear end impact is rapidly becoming one of the most aggravating traffic safety problems with high human suffering and societal costs. Although rear end impact occurs at relatively low speed , it may cause permanent disability due to neck injuries resulting from an abrupt moment, shear force , and tension/compression force at the occipital condyles. The analysis is performed for a combined occupant-eat model response, using the SAFE(Safety Analysis for occupant crash Environment) computer program. The computational results are verified by those from sled tests. A parameter study is conducted for many physical and mechanical properties. Seat design has been performed based on the design of experiment process with respect to five parameters; seat-back upholstery stiffness, torsional stiffness of the seat-back. An orthogonal array is selected from the parameter study. A good design has been found from the analysis results based on the orthogonal array. The results show that reductions of stiffness in seat-back upholstery and joint are the most effective for preventing neck injuries.