• Journal of The Korean Astronomical Society
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• v.54 no.3
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• pp.103-112
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• 2021

The intracluster medium (ICM) is expected to experience on average about three passages of weak shocks with low sonic Mach numbers, M ≲ 3, during the formation of galaxy clusters. Both protons and electrons could be accelerated to become high energy cosmic rays (CRs) at such ICM shocks via diffusive shock acceleration (DSA). We examine the effects of DSA by multiple shocks on the spectrum of accelerated CRs by including in situ injection/acceleration at each shock, followed by repeated re-acceleration at successive shocks in the test-particle regime. For simplicity, the accelerated particles are assumed to undergo adiabatic decompression without energy loss and escape from the system, before they encounter subsequent shocks. We show that in general the CR spectrum is flattened by multiple shock passages, compared to a single episode of DSA, and that the acceleration efficiency increases with successive shock passages. However, the decompression due to the expansion of shocks into the cluster outskirts may reduce the amplification and flattening of the CR spectrum by multiple shock passages. The final CR spectrum behind the last shock is determined by the accumulated effects of repeated re-acceleration by all previous shocks, but it is relatively insensitive to the ordering of the shock Mach numbers. Thus multiple passages of shocks may cause the slope of the CR spectrum to deviate from the canonical DSA power-law slope of the current shock.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.3
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• pp.31-40
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• 2020

The structure and dynamics of multiple shock waves are studied numerically using a finite volume solver for a model with nozzle exit Mach number of 1.75. At first, the shock variation based on images were analyzed using a Matlab program then later to the wall static pressure variation. The amplitude and frequency variation for multiple shock waves are analyzed. The cross-correlation between the shock location suggests that the first and the second shocks are well correlated while the other shocks show a phase lag in the oscillation characteristics. The rms values of pressure fluctuations are maximum at the shock locations while the other parts in the flow exhibit a lower value os standard deviation.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.21 no.1
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• pp.65-68
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• 1999

Multiple facial trauma patient should be carefully treated because of severe bleeding on extraoral and intraoral wound, possibilty of airway obstruction and hypovolemic shock. Hypovolemic shock may be divided to hemorrhagic shock and non-hemorrhagic shock. Also hemorrhagic shock is divided to mild, moderate and severe shock according to the degree of blood volume depletion. Mild shock occurs in blood loss of less than 20% of blood volume and moderate shock does in blood loss of 20-40% of blood volume. And Severe shock occurs in blood loss of more than 40% of blood volume. The goal of emergency care of trauma patient is that respiration and perfusion should be recovered to satisfactory level and that normal vital sign is maintained. We reported the case of multiple facial trauma patient with severe bleeding and hopovolemic shock and metabolic acidosis who was treated with adequate supply of fluid transfusion, intubation, tracheostomy and emergency operation.

• Journal of Periodontal and Implant Science
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• v.33 no.4
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• pp.555-562
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• 2003

The present study has been performed to evaluate Porphyromonas gingivalis (P.gingivalis) heat shock protein(HSP)60 as a candidate vaccine to inhibit multiple bacteria-induced alveolar bone loss. Rats were immunized with P.gingivalis HSP60 and experimental alveolar bone loss was induced by infection with multiple periodonto -pathogenic bacteria. Post-immune rat anti-P.gingivalis HSP IgG levels were significantly elevated and have demonstrated highly significant inverse relationship with the amount of alveolar bone loss induced by multiple bacteria. Results from PCR detection of subgingival bacterial plaque indicated that the vaccine successfully eradicated the multiple pathogenic species. We concluded that P.gingivalis HSP60 could potentially be developed as a vaccine to inhibit periodontal disease induced by multiple pathogenic bacteria.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.39-44
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• 2000

Two-dimensional Navier-Stokes codes are used to simulate the shock tunnel in Konkuk university. In order to design experiments in impulse facilities properly and to interpret data from such facilities, it is necessary to understand how the flow approaches steady state. This is done by determining the transient flow field and flow establishment time around a given model. This will be accomplished by developing appropriate CFD codes which solve the Navier-Stokes equations, and simulating the starting process and resulting unsteady viscous flow phenomena. The starting process in a shock tunnel consists of multiple shock interactions and contact discontinuities, which are difficult to solve with the classical shock capturing schemes. A recently developed high resolution scheme is adapted for resolving the unsteady phenomena of those multiple shock interactions and contact surfaces during the starting process. The bifurcation phenomenon due to the interactions of the reflected shock from the end of the shock tube with the boundary layer generated by the incident shock becomes of particular interest. By comparing with the experiment results, the accuracy of the numerical analysis is validated and it is demonstrated that the properties which can hardly be obtained through the experiment can be estimated.

• The Korean Journal of Applied Statistics
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• v.27 no.7
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• pp.1097-1114
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• 2014

Multiple-life policies pay a benefit on the first death or the last death among the group of lives. In practice, the future lifetime random variable of policy holders has been considered to be independent, but it is more rational to take into account the correlations among the policy holders. In this paper, the Gaussian copula is applied to re ect the correlations among policy holders and then to diversify the common shock of the multiple life policies which follows an exponential distribution. Five case studies demonstrate its usefulness of using copula in calculating the premiums of the multiple-life policies including the common shock.

• Journal of Power System Engineering
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• v.15 no.4
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• pp.11-18
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• 2011

A Shock absorber is one of the most important components in vehicle suspension systems. In general, many repeated analyses are required for the design of a shock absorber to satisfy the suspension characteristics of a specific automobile, like fluid flow analysis and mechanical analysis. The purpose of this study is to develop a fast design tool for shock absorber designers. One of the efficient solutions for this can be an empirical design method considering phenomenological effects from the shock absorber design variables. In order to extract the shock absorber's experimental characteristics, we used Taguchi method. This method showed that which design variables have major effects for the shock absorber's damping characteristics. This empirical design method also showed the direction of the design changes to satisfy the designer's intension.

• International Journal of Precision Engineering and Manufacturing
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• v.3 no.1
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• pp.57-65
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• 2002

Pneumatic cylinder is widely used fur mechanical handling systems. Often, the impact occurs at the both ends points of pneumatic cylinder and generates the destructive shock with in the structural operating members of the machine or equipment. To reduce the damage of system, therefore, shock absorbing devices are required. Cushioning of pneumatic cylinders at one or both ends of piston stroke is used to reduce the shock and vibration. The cylinder body have to withstand under conditions of high velocity and load. In this research pneumatic cushioning cylinder moving tests have been conducted for different load mass and supply pressure. The velocity of pneumatic cylinder actuation system which is set vertically with multiple orifice cushion sleeve is controled with the meter-in/out control system. This study examines the dynamic characteristics of pneumatic cylinder which are used as cushion devices. It turns out that the cushion pressure is mainly a function of the external load rather than the supply pressure. The cushion region characteristics was also revealed in the meter-in control system.

• Journal of Korean society of Dental Hygiene
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• v.23 no.4
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• pp.251-260
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• 2023

Objectives: This study aimed to provide basic data for the development of clinical practice-related education program by analyzing the effects of grit, job satisfaction, and retention intention on transition shock of new dental hygienists. Methods: From April 19 to July 4, 2022, the data was collected from 200 new dental hygienists working for dental hospitals/clinics. Using the SPSS Statistics ver. 22.0, this study was conducted the t-test, one-way ANOVA, Pearson's correlation analysis, and multiple regression analysis. Results: There were positive correlations between grit, job satisfaction, and retention intention, a negative correlation between grit and transition shock, a positive correlation between job satisfaction and retention intention, a negative correlation between job satisfaction and transition shock. and a negative correlation between retention intention and transition shock. As the factors affecting transition shock, lower pay and main performance of medical cooperation work increased transition shock. When job satisfaction and retention intention were higher, transition shock decreased. Conclusions: In order to reduce transition shock of new dental hygienists, it would be necessary to operate clinical practice-related training program, and also to establish a training environment similar to the clinical site/context/situation similar to clinical context/situation.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.23-28
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• 1999

In this paper we study numerically the shock-vortex interaction in the shear layer generated by moving shock waves above and below a flat plate. The faster normal shock is diffracted at the tip of the flat plate, producing a starting vortex. The slower normal shock below the flat plate arrives soon later to run across the vortex and make interaction. The two shocks are merged together and reflected back at the closed end of the shock tube to impinge on the shear layer developing multiple vortexlets. The computational simulation based on Euler and Navier-Stokes equations shows good prediction.