• Journal of the Korean Data and Information Science Society
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• v.26 no.6
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• pp.1317-1325
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• 2015

There are two types of clinical research to figure out risk factor for disease using collected data. One is prospective study to approach the subjects from the present time and the other is retrospective study to find the risk factor using the subject's information in the past. Both approached and study design are different but the purpose of the two studies is to identify a significant difference between two groups and to find out what the variables to influence groups. Especially when comparing the two groups in clinical research, we have to look at the difference between the impact clinical variables by group while controlling the influence of the baseline characteristics variables such as age and sex. However, in the retrospective study, the difference of baseline characteristic variables can occur more frequently because the past records did not randomly assign subjects into two groups. In clinical data analysis use covariates to solve this problem. Typically, the analysis method using the analysis of covariance of variance, adjusted model, and propensity score matching method. This study is introduce the way of equality adjustment between groups data analysis using covariates in retrospective clinical studies and apply it to the recurrence of gastric cancer data.

• 월간산업보건
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• s.46
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• pp.16-20
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• 1992

• Journal of Periodontal and Implant Science
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• v.33 no.1
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• pp.37-47
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• 2003

• Journal of Korean Philosophical Society
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• v.105
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• pp.269-290
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• 2008

The purpose of this paper is to explore the possibility of backwards causation. For study, this paper was divided into four views as follows: The first view was sometimes suggested by the people such as M. Dummett who distinguished observers from behaviors. According to observers' view, backwards causation is impossible, whereas behaviors' view possible. However, in a real or genuine sense, it is incorrect for us to argue for impossibility of backwards causation from the observer aspect. The second view was supported by J. H. Schmidt. He analyzed the possibility of backwards causation in terms of macro and micro level analysis about the causal events. According to micro level analysis, backwards causation is possible, but macro level analysis impossible. Usually the latter makes the former something miraculous. Under the macro level analysis, backwards causation, at first, seems to be miraculous phenomena which belongs to the micro level analysis. The third view had to do with physical equation, and the fourth view physical phenomena, respectively. John Earman argued for the backwards causation by the transformation from Lorentz­-Dirac equation to a second-order integro-differential one in the field of electrodynamic acceleration. His argument was criticized because of his misunderstanding about the relationship between two equations. On the other hand, Phil Dowe defended a version of Reichenbach's own theory about the direction of causation founded on the fork asymmetrical causal relation. However his view was different from Reichenbach's because the former defended the backwards causation model of Bell phenomena in quantum mechanics. On the contrary, Reichenbach put stressed on the priority of cause in the causal process. Subjectivism has recently been defended by H. Price, under the label of perspectivism. According to him, in a certain sense causal asymmetry is not in the world, but is rather a product of our own asymmetric perspective on the world. He also suggested causal net, the symmetry of microphysics, and so on. As mentioned above, there are many kind of suggestions of backwards causation. However none of them replaced objectively the main streams of the direction of causal process. The main stream has been usually defended by pragmatical ground. That is, effects do not precede their causes although causes cannot be without their effects.

• Journal of Periodontal and Implant Science
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• v.39 no.1
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• pp.109-109
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• 2009

• 대한정형외과스포츠의학회:학술대회논문집
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• 2005.11a
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• pp.30-31
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• 2005

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.97-103
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• 2003

Numerical research has been done for the transverse jet behind a rearward-facings step in turbulent supersonic flow without chemical reaction. Purpose of transverse jet is to enhance mixing of the fuel in the combustor. Two-dimensional unsteady flowfields generated by slot injection into supersonic flow are numerically simulated with the Navier-Stokes equations with two-equation k-$\varepsilon$ turbulence model. Numerical method is used high-order upwind TVD scheme. Eight cases are computed for different slot momentum flux ratios and slot position at downstream of the step. The flow is very similar to the cavity flow, because the jet acts as an obstacle. The numerical results thus show the periodic phenomenon.

• 대한치주과학회:학술대회논문집
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• 2007.11a
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• pp.188-189
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• 2007

• Journal of the korean academy of Pediatric Dentistry
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• v.47 no.2
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• pp.140-147
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• 2020

This study analyzed the longevity of preformed metal crowns (PMCs) in first permanent molars and evaluated factors influencing their survival during a long-term follow-up period. In all, 115 first permanent molars treated with PMCs between June 2008 and June 2018 were retrospectively analyzed. The overall combined success rate for the study group was 84.3%. The 5-year survival rate was 82.8%. Multivariate Cox regression analyses identified distal cavities and mandibular PMC placement as risk factors for restoration failure. Careful placement of PMCs at the final try-in stage augments the longevity of the crown.

• Journal of radiological science and technology
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• v.34 no.4
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• pp.315-321
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• 2011

The goal of this study is to reduce patient exposure dose by providing image quality and radiation dose according to inspection methods. Volume Computed Tomography Dose Index(CTDIvol) and Dose Length Product(DLP) of prospective and retrospective ECG gating snapshot segment of Coronary CT angiography(CTA) were measured each snapshot segment methods. CT number, noise, uniformity, and resolution were also measured using phantom under the same condition of coronary CTA. The results showed that CT number, noise, uniformity and resolution are similar to each other. In terms of CTDIvol and DLP, however, measurement dose of prospective ECG gating snapshot segment was lower than the retrospective case by 37.5% and 40.3%. Therefore, it is highly recommended that in the coronary CTA, prospective ECG gating scan mode should be chosen to reduce patient dose.