• Progress in Superconductivity
• /
• v.9 no.2
• /
• pp.193-198
• /
• 2008

We fabricated BSCCO-2212(2212) bulk superconductors by using a casting process and evaluated the superconducting properties. The effects of annealing conditions on microstructure and critical properties were studied. It was found that the homogeneous and uniform microstructure improved the critical properties and the microstructures of ingot and annealed rods were different with the size of 2212 rod and tube. The critical current($I_c$) of rods increased with increasing annealing time, probably due to increased grain size of 2212. Annealing time of the highest $I_c$ for the smaller rod(diameter of 10 mm) was shorter(150 hr) than that of the larger rod(diameter of 16 mm, 400 hr). This size effect seems to be related to different grain sizes of the intermediate phases such as 2201 and secondary phases in the ingot. In addition, we fabricated 2212 tubes from the rod by removing the center region which contained inhomogeneous microstructures. The $I_c$ of 2212 tube with the outer diameter of 16 mm and the thickness of 2 mm was measured to 844 A, which corresponds to the critical current density of $1017\;A/cm^2$ at 77 K.

• Journal of Trauma and Injury
• /
• v.32 no.3
• /
• pp.150-156
• /
• 2019

Purpose: To determine whether a peripherally inserted central catheter (PICC) meets the goals of a low infection rate and long-term use in trauma patients. Methods: From January 2016 to June 2018, the medical records of patients who underwent central venous catheterization at a level I trauma center were retrospectively reviewed. Data collected included age, sex, injury severity score, site of catheterization, place of catheterization (intensive care unit [ICU], emergency department, or general ward), type of catheter, length of hospital stay during catheterization, types of cultured bacteria, time to development of central line-associated bloodstream infection (CLABSI), and complications. Results: During the study period, 333 central vein catheters (CVC) were inserted with a total of 2,626 catheter-days and 97 PICCs were placed with a total of 2,227 catheter-days. The CLABSI rate was significantly lower in the PICC group when the analysis was limited to patients for whom the catheter was changed for the first time in the ICU after CVC insertion in the ER with similar indication and catheter insertion times (18.6 vs. 10.3/1,000 catheter-days, respectively, p<0.05). The median duration of catheter use was significantly longer in the PICC group than in the CVC group (16 vs. 6 days, respectively, p<0.05). Conclusions: The study results showed that the duration of catheter use was longer and the infection rate were lower in the PICC group than in the CVC group, suggesting that PICC is a safe and reliable alternative to conventional CVC.

• Journal of Trauma and Injury
• /
• v.35 no.1
• /
• pp.25-33
• /
• 2022

Purpose: The scoring system for traumatic liver injury (SSTLI) was developed in 2015 to predict mortality in patients with polytraumatic liver injury. This study aimed to validate the SSTLI as a prognostic factor in patients with polytrauma and liver injury through a generalized estimating equation analysis. Methods: The medical records of 521 patients with traumatic liver injury from January 2015 to December 2019 were reviewed. The primary outcome variable was in-hospital mortality. All the risk factors were analyzed using multivariate logistic regression analysis. The SSTLI has five clinical measures (age, Injury Severity Score, serum total bilirubin level, prothrombin time, and creatinine level) chosen based on their predictive power. Each measure is scored as 0-1 (age and Injury Severity Score) or 0-3 (serum total bilirubin level, prothrombin time, and creatinine level). The SSTLI score corresponds to the total points for each item (0-11 points). Results: The areas under the curve of the SSTLI to predict mortality on post-traumatic days 0, 1, 3, and 5 were 0.736, 0.783, 0.830, and 0.824, respectively. A very good to excellent positive correlation was observed between the probability of mortality and the SSTLI score (γ=0.997, P<0.001). A value of 5 points was used as the threshold to distinguish low-risk (<5) from high-risk (≥5) patients. Multivariate analysis using the generalized estimating equation in the logistic regression model indicated that the SSTLI score was an independent predictor of mortality (odds ratio, 1.027; 95% confidence interval, 1.018-1.036; P<0.001). Conclusions: The SSTLI was verified to predict mortality in patients with polytrauma and liver injury. A score of ≥5 on the SSTLI indicated a high-risk of post-traumatic mortality.

• Bulletin of the Korean Mathematical Society
• /
• v.50 no.1
• /
• pp.105-116
• /
• 2013

In this paper, we consider the positive solution to a Cauchy problem in $\mathbb{B}^N$ of the fast diffusive equation: ${\mid}x{\mid}^mu_t={div}(\mid{\nabla}u{\mid}^{p-2}{\nabla}u)+{\mid}x{\mid}^nu^q$, with nontrivial, nonnegative initial data. Here $\frac{2N+m}{N+m+1}$ < $p$ < 2, $q$ > 1 and 0 < $m{\leq}n$ < $qm+N(q-1)$. We prove that $q_c=p-1{\frac{p+n}{N+m}}$ is the critical Fujita exponent. That is, if 1 < $q{\leq}q_c$, then every positive solution blows up in finite time, but for $q$ > $q_c$, there exist both global and non-global solutions to the problem.

• Journal of Biosystems Engineering
• /
• v.16 no.4
• /
• pp.346-354
• /
• 1991

Turning behavior of tractor-trailer system was studied to guide the tractor and trailer. Based upon kinematic relationship between the tractor and the trailer, a mathematical model was developed and analyzed by computer simulation. A field test was carried out to verify the mathematical model. Following conclusions were drawn from this study. 1. A mathematical model and a simulation program for turning behavior of tractor-trailer system were developed. 2. The results of the field tests showed that the RMS errors were less than 0.33m and the mathematical model based upon kinematic relationship can be used for mapping guidance system for tractor and trailer. 3. As the steering angle was increased, the turning radius was decreased. When the tractor travelled at the low speed, the travel speed of the tractor did not affect turning radius but did affect running time and stability for steering. 4. When the tractor travelled under the critical velocity, the towed trailer followed smoothly. When the the tractor travelled faster than the critical velocity, the towed trailer oscillated. The critical velocity was determined from the specification of the tractor and the trailer.

• Progress in Superconductivity and Cryogenics
• /
• v.20 no.1
• /
• pp.1-10
• /
• 2018

The improvement of critical current properties of $REBa_2Cu_3O_{7-x}$ (REBCO) coated conductors by introducing artificial pinning centers (APCs) is examined with respect to the field-angle anisotropy, high-field performance and relaxation property with time. Nano-rods along the c-axis introduced by PLD method and isotropic nano-particles introduced by TFA-MOD method are treated. The theoretical analysis is also shown to understand the effect of APCs quantitatively. The effects of superconducting layer thickness that influences the high-field performance and relaxation property are also discussed. It is shown that the upper critical field, which is another important factor to determine the high-field property, can be improved by introduction of APCs through electron scattering at interfaces with the superconducting matrix. The optimum critical current property can be obtained by properly designing the morphology and number density of APCs and the superconducting layer thickness.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.29 no.1
• /
• pp.86-93
• /
• 2015

Globally, wind power development is experiencing dramatic growth and wind power penetration levels are increasing. Wind generation is highly variable in time and space and it doesn't guarantee the system reliability and secure system operation. As wind power capacity becomes a significant portion of total generation capacity, the reliability assessment for wind power are therefore needed. At present, this operational reliability assessment is focusing on a generation adequacy perspective and does not consider transmission reliability issues. In this paper, we propose the critical transmission operating constraint prediction(CTOCP) system with high wind power penetration to enhance transmission reliability.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.19 no.6
• /
• pp.1351-1362
• /
• 1995

A method to estimate the torsional critical speed for practical rotors has been developed in this study. First, the rotor with a uniform shaft segment is modeled for undamped torsional motion analysis, while satisfying all the boundary conditions. This eventually generates governing equations for the torsional critical speeds of the system. The set of governing equations has the form of a sparse and banded matrix. The elements of banded matrix can be arranged in partitions, which correspond to the specific boundary of the rotor. This permits an automatic generation of the system matrix using a computer. In order to calculate the determinant generated by the simultaneous equations, which leads to the torsional critical speed, a recurring numerical algorithm for a (3*4) sub-matrix has been used. This numerical algorithm practically examines successive (3*4) sub-matrix, one at a time, instead of treating a huge matrix. The output of the program provides the mode shapes with continuous curves. The method has been implemented to three rotors given as examples : a simple rotor, Prohl's rotor, and Macmillan rotor.

• Journal of computational fluids engineering
• /
• v.10 no.3 s.30
• /
• pp.70-76
• /
• 2005

A two-layer incompressible time-accurate Euler solver is applied to analyze flow fields around a submerged body moving at a critical speed near a pycnocline. Discontinuities in the dependent variables across the material interface are captured without any dissipation or oscillation using the ghost fluid method on an unstructured grid. It is shown that the material interlace has significant effects on forces acting on a submerged body moving near a pycnocline regardless of the small difference in densities of two layers. Contrary to the shallow water waves, a submerged body can reach a critical speed at very low Froude number due to the small difference in the densities of the two layers.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2005.05a
• /
• pp.107-112
• /
• 2005

Renovation of existing sports facilities or construction of temporary ones for international complex games requires a wide variety of hundreds of sub construction projects to be awarded at the same time but there are few precedents required regarding the study of tendering process required in such cases. As award of construction contracts to build sports facilities for various international complex games is a critical determinant of fate of international complex games in the initial phase, it is very critical that adequate construction tendering process bedetermined. This research is aimed to study tendering cases for renovation or construction of critical international sports facilities to enhance efficiency of facility construction and define most reasonable tendering approach to satisfy schedule constraints often associated with international complex games and contribute to improvement of international competitiveness of their host cities and propose a direction for further development. This study also provides inputs to subsequent sports events of comparable scale to minimize trial and error.