• Journal of Animal Reproduction and Biotechnology
• /
• v.35 no.1
• /
• pp.58-64
• /
• 2020

This present study was conducted to investigate protective effect of discontinuous Percoll gradient containing alpha-linolenic acid (ALA) before freezing process on viability, acrosome damage, mitochondrial activity, and oxidative stress of frozen-thawed boar spermatozoa. The separation of spermatozoa by discontinuous Percoll gradient was performed by different concentration of Percoll solution (45/90%) containing ALA combined with bovine serum albumin (BSA), and collected sperm in each Percoll layer was cryopreserved. To evaluate viability, acrosome damage, mitochondrial activity, and reactive oxygen species (ROS) level of frozen-thawed sperm, flow cytometry was used. Morphological abnormalities were observed under light microscope. In results, viability of sperm from 90% Percoll layer was higher than control and 45% Percoll group (p < 0.05). Separated sperm in 90% Percoll layer had lower acrosome damage and morphological abnormalities than control as well as viability, whereas 45% Percoll group was higher (p < 0.05). Similar with acrosome damage and abnormalities, mitochondrial activity was slightly enhanced and the population of live sperm with high ROS level was decreased by 90% Percoll separation, however, there was no significant difference. Supplementation of 3 ng/mL ALA into Percoll solution increased sperm viability and decreased population of live sperm with high ROS compared to control (p < 0.05). In conclusion, discontinuous Percoll gradient before freezing process could improve efficiency of cryopreservation of boar sperm through selection of sperm with high freezing resistance, and supplement of ALA during Percoll gradient might contribute suppression of ROS generation via stabilizing of plasma membrane during cryopreservation.

• Clinical and Experimental Reproductive Medicine
• /
• v.21 no.3
• /
• pp.261-266
• /
• 1994

Semen preparation for Assisted Reproductive Technology(ART) involves the separation of the motile sperm from non-motile, dead sperm, cellular debris and seminal fluid. The aim of this study is to compare the motile sperm recovery rate and motility index of different sperm preparation method(swim-up method, 80% isotonic continuous percoll method, two-layer discontinuous percoll method, mini-percoll method). In Mini-Percoll method, pellets from patients were suspended in 0.3ml of medium and layerd on a discontinuous percoll gradient consisting of 0.3ml each of 50, 70, 95% isotonic percoll. All semen samples are divided into normal and subnormal sperm group(oligo-, astheno-, oligoasthenozoospermia). Especially, we evaluated the effect of mini-percoll method in subnormal sperm group. In normal sperm group, mini-percoll method and two layer discontinuous percoll method (40%/80%) allowed increasing of motile sperm recovery rate. But motility index was higher in swimup method than the other methods. In subnormal sperm group, mini-percoll method has advantages as compare with the other methods in motile sperm recovery rate and motility index. These results suggest that modified mini-percoll method could be certainly a valuable tool in some cases of severe male factor sperm.

• Communications of the Korean Mathematical Society
• /
• v.13 no.2
• /
• pp.345-358
• /
• 1998

Let (p/q,n) denote the orbifold with its underlying space $S^3$ and a rational knot or link p/q as its singular set with a cyclic isotropy group of order n. In this paper we shall show the geometrical realization for the case (7/3,n) for all $n \geq 3$.

• Journal of the Korean Society for Heat Treatment
• /
• v.31 no.5
• /
• pp.231-236
• /
• 2018

The purpose of this study was to investigate the microstructural characteristics and hardness distribution of AZ91 magnesium alloy furnace-cooled to room temperature after solution treatment, and to compare the results with those of as-cast condition. The as-cast alloy showed a partially divorced eutectic ${\beta}(Mg_{17}Al_{12})$ phase and discontinuous precipitates (DPs) with a lamellar morphology, while only DPs were observed in the furnace-cooled alloy. The DPs in the furnace-cooled AZ91 alloy had various apparent interlamellar spacings, which would be ascribed to the different transformation temperatures during the furnace cooling. The average hardness for the furnace-cooled alloy is similar to that for the as-cast alloy. It is interesting to note that the hardness values of the furnace-cooled alloy were distributed over a narrower range than those of the as-cast alloy. This is likely to be caused by the relatively more homogeneous microstructure of the furnace-cooled alloy in comparison with the ascast one.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.11 no.1
• /
• pp.572-583
• /
• 2019

This paper aims to assess the applicability of the Runge Kutta Discontinuous Galerkin-Direct Ghost Fluid Method to the internal explosion inside a water-filled tube, which previously was studied by many researchers in separate works. Once the explosive charge located at the inner center of the water-filled tube explodes, the tube wall is subjected to an extremely high intensity fluid loading and deformed. The deformation causes a modification of the field of fluid flow in the region near the water-structure interface so that has substantial influence on the response of the structure. To connect the structure and the fluid, valid data exchanges along the interface are essential. Classical fluid structure interaction simulations usually employ a matched meshing scheme which discretizes the fluid and structure domains using a single mesh density. The computational cost of fluid structure interaction simulations is usually governed by the structure because the size of time step may be determined by the density of structure mesh. The finer mesh density, the better solution, but more expensive computational cost. To reduce such computational cost, a non-matched meshing scheme which allows for different mesh densities is employed. The coupled numerical approach of this paper has fewer difficulties in the implementation and computation, compared to gas dynamics based approach which requires complicated analytical manipulations. It can also be applied to wider compressible, inviscid fluid flow analyses often found in underwater explosion events.

• 한국터널공학회:학술대회논문집
• /
• 2005.04a
• /
• pp.348-358
• /
• 2005

Although the evaluation of the mechanical properties and behavior of discontinuous rock masses is very important for the design of underground openings, it has always been considered the most difficult problem. One of the difficulties in describing the rock mass behavior is assigning the appropriate constitutive model. This limitation may be overcome with the progress in discrete element software such as PFC, which does not need the user to prescribe a constitutive model for rock mass. Instead, the micro-scale properties of the intact rock and joints are defined and the macro-scale response results from those properties and the geometry of the problem. In this paper, a $30m{\times}30m{\times}30m$ jointed rock mass of road tunnel site was analyzed. A discrete fracture network was developed from the joint geometry obtained from core logging and surface survey. Using the discontinuities geometry from the DFN model, PFC simulations were carried out, starting with the intact rock and systematically adding the joints and the stress-strain response was recorded for each case. With the stress-strain response curves, the mechanical properties of discontinuous rock masses were determined and compared to the results of empirical methods such as RMR, Q and GSI. The values of Young's modulus, Poisson's ratio and peak strength are almost similar from PFC model and Empirical methods. As expected, the presence of joints had a pronounced effect on mechanical properties of the rock mass. More importantly, the mechanical response of the PFC model was not determined by a user specified constitutive model.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.2
• /
• pp.159-165
• /
• 2015

Motion control schemes are generally classified into three categories (point stabilization, trajectory tracking, and path following). This paper deals with the problem which is associated with the initial deployment of a group of Unmanned Surface Vehicle (USVs) and corresponding point stabilization. To keep the formation of a group of USVs, it is necessary to set the relationship between each vehicle. A forcing functions such as potential fields are designed to keep the formation and a graph Laplacian is used to represent the connectivity between vehicle. In case of fixed topology of the graph representing the communication between the vehicles, the graph Laplacian is assumed constant. However the graph topologies are allowed to change as the vehicles move, and the system dynamics become discontinuous in nature because the graph Laplacian changes as time passes. To check the stability in the stage of deployment, the system is modeled with Kronecker algebra notation. Filippov's calculus of differential equations with discontinuous right hand sides is then used to formally characterize the behavior of USVs. The stability of the system is analyzed with Lyapunov's stability theory and LaSalle's invariance principle, and the validity is shown by checking the variation of state norm.

• The Journal of Korean Medicine
• /
• v.21 no.3
• /
• pp.88-98
• /
• 2000

Objectives : This study was carried out to evaluate the effect of Boyanghwano-tang Extracts on Reversible Forebrain Ischemia in Mongolian Gerbils. Methods : The water content of cerebral edema and the morphologicalㆍneurocytochemistrical change of neuron in MG were implemented to conduct this study. Results : The change rate of water content by ischemia in the normal group was 78.90% on the third day and 79.12% on the seventh day after an attack of ischemia. The rate in the control group was 80.34% and 81.72%. In the sample group the rate was 79.85% and 80.97%. This is a significant result. According to the result of the optical microscopic examination, the cells seen to be continuous and systematic in the pyramidal cells of hippocampus were changed into discontinuous and unsystematic forms in the control group. But compared with the control group, the cells were less damaged in the sample group. Conclusions : The data shows that the effect of Boyanghwano-tang Extracts on Reversible Forebrain Ischemia in MG is a significant result.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2010.09b
• /
• pp.96-103
• /
• 2010

This paper presents of effect of tunneling on pile group of being operated bridge using Three-dimensional numerical modeling to study the effect of coordination of tunneling location under discontinuous group pile. In order to find idealistic tunneling location that causes settlement, change of stress on the piles and movement of soil at a minimum, a fully coupled 3D finite element model is adopted. The study contains pile settlement, axial force on each piles in the group, axial displacement of piles and soil behaviour caused by tunneling. Based on the result some insights into the pile behavior due to tunneling obtained from numerical analysis were mentioned and discussed.

• Bulletin of the Korean Space Science Society
• /
• 2003.10a
• /
• pp.41-41
• /
• 2003

Satellite formation flying is currently an active area of research in the aerospace engineering. There are many categories for this research such as the determination of initial conditions, formation keeping, configuration and reconfiguration. In this study, a tracking controller using sliding mode techniques is designed to control a satellite for the satellite formation flying. In general, Hill's equations are used to describe the relative motion of the follower satellite with respect to the leader satellite. But, the modified Hill's equations considering J2 perturbation were used for the design of sliding mode controller. Sliding mode control law causes the chattering phenomenon because it is a discontinuous control. Dead-zone was used to avoid the chattering. The Extended Kalman filter was applied to estimate the state vector based on the measurements of relative distance and velocity between two satellites.