• Journal of Chest Surgery
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• v.33 no.10
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• pp.777-784
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• 2000

Congenital aortic stenosis in children is characterized by "excessive" left ventricular hypertrophy with reduced left ventricular systolic wall stress that allows for supernormal ejection performance. We hypothesized that left ventricular wall stress was decreased immediately after surgical correction of pure congenital aortic stenosis. Also measuring postoperative left ventricular wall stress was a useful noninvasive measurement that allowed direct assessment for oxygen consumption of myocardium than measuring the peak systolic pressure gradient between ascending aorta and left ventricle for the assessment of surgical results. Material and Method: Between September 1993 and August 1999, 8 patients with isolated congenital aortic stenosis who underwent surgical correction at Yonsei cardiovascular center were evaluated. There were 6 male and 2 female patients ranging in age from 2 to 11 years(mean age, 10 years). Combined Hemodynamic-Ultrasonic method was used for studying left ventricular wall stress. We compared the wall stress peak systolic pressure gradient and ejection fraction preoperatively and postoperatively. Result: After surgical correction peak aortic gradient fell from 58.4${\pm}$17.6, to 23.7${\pm}$17.7 mmHg(p=0.018) and left ventricular ejection fraction decreased but it is not statistically significant. In the consideration of some factors that influence left ventricular end-systolic wall stress excluding one patient who underwent reoperation for restenosis of left ventricular outflow tract left ventricular end-systolic pressure and left ventricular end-systolic dimension were fell from 170.6${\pm}$24.3 to 143.7${\pm}$27.1 mmHg and from 1.78${\pm}$0.4 to 1.76${\pm}$0.4 cm respectively and left ventricular posterior wall thickness was increased from 1.10${\pm}$0.2, to 1.27${\pm}$0.3cm but it was not statistically singificant whereas left ventricular end-systolic wall stress fell from 79.2${\pm}$24.9 to 57.1${\pm}$27.6 kdynes/cm2(p=0.018) in 7 patients. For one patient who underwent reoperation peak aortic gradient fell from 83.0 to 59.7 mmHg whereas left ventricular end-systolic wall stress increased from 67.2 to 97.0 kdynes/cm2 The intervals did not change significnatly. Conclusion ; We believe that probably some factors that are related to left ventricular geometry influenced the decreased left ventricular wall stress immediately after surgical correction of isolated congenital aortic stenosis. Left ventricular wall stress is a noninvasive measurement and can allow for more direct assesment than measuring peak aortic gradient particularly in consideration of the stress and oxygen consumption of the myocardium therefore we can conclude it is a useful measurement for postoperative assessment of congenital aortic stenosis.

• Investigative Magnetic Resonance Imaging
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• v.4 no.1
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• pp.20-26
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• 2000

Gradient moment nulling techniques require the introduction of an additional gradient on each axis for each order of motion correction to be applied. The additional gradients introduce new constraints on the sequence design and increase the demands on the gradient system. The purpose of this paper is to demonstrate techniques for optimization of gradient echo gradient moment nulling sequences within the constraints of the gradient hardware. Flow compensated pulse sequences were designed and implemented on a clinical magnetic resonance imaging system. The design of the gradient moment nulling sequences requires the solution of a linear system of equations. A Mathematica package was developed that interactively solves the gradient moment nulling problem. The package allows the physicist to specify the desired order of motion compensation and the duration of the gradients in the sequence with different gradient envelopes. The gradient echo sequences with first, second, and third order motion compensation were implemented with minimum echo time. The sequences were optimized to take full advantage of the capabilities of the gradient hardware. The sequences were used to generate images of phantoms and human brains. The optimized sequences were found to have better motion compensation than comparable standard sequences.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.191-201
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• 2006

New design equations for calculating the lateral-torsional buck ling moment resistances of stepped I-section beams with/without continuous lateral top-flange bracing subjected to a point load, a series of point loads, and a uniformly distributed load, are suggested based on the results of elastic finite-element analyses. The new equations presented in this study are compared with the current moment gradient modifiers presented by other researchers and specifications. Although the study paper presents mainly stepped-beam cases subjected to a point load and a uniformly distributed load. The proposed equations include the length-to-height ratio effects for stepped beams with continuous lateral top-flange bracing. The new moment gradient correction factors could be easily used to calculate the lateral-torsional buckling moment resistance of stepped I-beams.

• Proceedings of the Acoustical Society of Korea Conference
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• 1994.06a
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• pp.746-751
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• 1994

The four-terminal transmission matrix method has been widely used to estimate the insertion-loss. However, the predictins using the equations in the four-terminal transmission matrix method do not reflect a practical phenomenon accurately, In this paper, the correction method to derive the insertion-loss for a constant sound pressure source is presented. The method of correction to the four-terminal transmission matrix method was proposed by rewriting the real and imaginary parts as they depend solely on the flow velocity. Then the result was compensated for by adding the component of the temperature gradient.

• Structural Engineering and Mechanics
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• v.66 no.6
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• pp.693-701
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• 2018

This paper develops a nonlocal strain gradient plate model for vibration analysis of graphene sheets under thermal environments. For more accurate analysis of graphene sheets, the proposed theory contains two scale parameters related to the nonlocal and strain gradient effects. Graphene sheet is modeled via a two-variable shear deformation plate theory needless of shear correction factors. Governing equations of a nonlocal strain gradient graphene sheet on elastic substrate are derived via Hamilton's principle. Differential quadrature method (DQM) is implemented to solve the governing equations for different boundary conditions. Effects of different factors such as temperature rise, nonlocal parameter, length scale parameter, elastic foundation and aspect ratio on vibration characteristics a graphene sheets are studied. It is seen that vibration frequencies and critical buckling temperatures become larger and smaller with increase of strain gradient and nonlocal parameter, respectively.

• Journal of the Korean Magnetic Resonance Society
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• v.24 no.3
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• pp.66-69
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• 2020

In ultra-low field magnetic resonance imaging (ULF-MRI), the strength of a static magnetic field can be comparable to that of gradient field. On that occasion, the gradient field is accompanied by concomitant gradient field, which yields distortion and blurring artifacts on MR images. Here, we focused on the distortion artifact and derived the equations capable of correcting it. Its usefulness was confirmed through the corrections in both simulated and experimental images. This solution will be effective for acquiring more accurate images in low and/or ultra-low magnetic fields.

• Journal of the Korean Mathematical Society
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• v.38 no.3
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• pp.683-695
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• 2001

In this paper we are concerned with theoretical properties of gap functions for the extended variational inequality problem (EVI) in a general Banach space. We will present a correction of a recent result of Chen et. al. without assuming the convexity of the given function Ω. Using this correction, we will discuss the continuity and the differentiability of a gap function, and compute its gradient formula under tow particular situations in a general Banach space. Our results can be regarded as infinite dimensional generalizations of the well-known results of Fukushima, and Zhu and Marcotte with soem modifications.

• Journal of Industrial Technology
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• v.19
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• pp.269-278
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• 1999

When a variety of repeated loads are given, most steel structures failed in much lower level of loads than static failure loads. In addition, bridge always includes the internal defects or discontinuities. from these, fatigue cracks initiates and can lead to sudden failure. Thus, in this study, tensile specimens by the cover plate shapes were used as the test specimens. The fatigue test was performed by constant amplitude fatigue loading and beach mark. From the results of this study, each specimen's fatigue section was observed. in addition, stress intensity factor at crack tip was calculated by using the Green's function which applied to discontinuous section where causing stress concentration. Therefore, the fatigue life of structural detail was investigated by adopting the theories of fracture mechanics. each specimen's crack shape is a semi-elliptical surface crack or center crack sheet, stress gradient correction factor, Fg is the most subjective of all stress intensity correction factors and fatigue life should be predicted by previous proposed function and finite element analysis.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.10a
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• pp.48-48
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• 1998

• Bulletin of the Korean Chemical Society
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• v.16 no.10
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• pp.991-994
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• 1995