• Journal of the Korean Society of Clothing and Textiles
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• v.37 no.8
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• pp.1060-1074
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• 2013

This study measured and analyzed pressure at each measurement part of imported compression stockings sold in Korea to provide basic information to establish a pressure standard and grade ranking. This study used 40 medical compression stockings imported from 6 countries. Pressure measurements were taken at 11 points: front side and back side of ankle, end-point of the gastrocnemius muscle, front, inner side, back, and outer side of calf, back side of below knew girth, inner side, and outer side of mid-thigh girth, and inner side of thigh girth. AMI 3037-10 and AMI 3037-2 were used for measurements taken inside an environmental chamber at a temperature of $21^{\circ}C$ and a relative humidity (RH) of 65%. For the measurements, 11 air pack sensors were attached to a wooden model leg (Hohenstein) and three measurements were taken at each measurement point in three minutes. The average of these measurements was used for analysis. The findings of this study were as follows. As for the front side of the ankle, of the 40 products, 14 products (6 USA, 2 Swiss, 3 Italian, and 2 Taiwanese) were within the pressure range indicated on the product label; however, no German products fell within the pressure range. A total of 8 products (5 USA, 1 Swiss, 1 Italian, and 1 German) were gradient compression type; however, no Japanese or Taiwanese product were of this type. The majority of products had the highest pressure at the end-point of the gastrocnemius muscle. Only 3 products, 1 USA (Jobst Opaque 30-40mmHg), 1 Swiss (Sigvaris Cotton 34-46mmHg) and 1 Italian (Jobstocking 25-32mmHg), had measurements that met the indicated standard pressure, were a gradient compression type, and met the overall standard for compression stockings.

• Steel and Composite Structures
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• v.49 no.4
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• pp.361-380
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• 2023

A size dependent bending behavior of piezoelectrical flexoelectric layered perforated functionally graded (FG) composite nanobeam rested on an elastic foundation is investigated analytically. The composite beam is composed of regularly cutout FG core and two piezoelectric face sheets. The material characteristics is graded through the core thickness by power law function. Regular squared cutout perforation pattern is considered and closed forms of the equivalent stiffness parameters are derived. The modified nonlocal strain gradient elasticity theory is employed to incorporate the microstructure as well as nonlocality effects into governing equations. The Winkler as well as the Pasternak elastic foundation models are employed to simulate the substrate medium. The Hamiltonian approach is adopted to derive the governing equilibrium equation including piezoelectric and flexoelectric effects. Analytical solution methodology is developed to derive closed forms for the size dependent electromechanical as well as mechanical bending profiles. The model is verified by comparing the obtained results with the available corresponding results in the literature. To demonstrate the applicability of the developed procedure, parametric studies are performed to explore influences of gradation index, elastic medium parameters, flexoelectric and piezoelectric parameters, geometrical and peroration parameters, and material parameters on the size dependent bending behavior of piezoelectrically layered PFG nanobeams. Results obtained revealed the significant effects both the flexoelectric and piezoelectric parameters on the bending behavior of the piezoelectric composite nanobeams. These parameters could be controlled to improve the size dependent electromechanical as well as mechanical behaviors. The obtained results and the developed procedure are helpful for design and manufacturing of MEMS and NEMS.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.383-387
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• 1998

The vacuum-Bridgman equipment for large size diameter (4 inch more over) crystal growth was organized simply and the $CaF_2$ single crystal which was grown in the conditions of growth rate of 2mm/hr, freezing temperature gradient of $12^{\circ}C$/cm, have analyzed to keep excellent properties. Using Mo thermal reflector of umbrella shape, it could be eliminated the formation of polycrystalline. The preferential growth direction was (111) and the calculated lattice parameter was $5.460 \AA$ by XRD peaks. The secondary phases, also, was not formed by means of powder-XRD analysis. The value of EPD is $1.4{\times}10^4 \textrm{cm}^{-2}$ and the optical quality, which is the transmittance is 91% up in UV region, is suitable for optical components of UV applications.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.103-103
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• 2009

As the size of containership increased over 14,000TEU, thick steel plate with high strength has been used. The plate thickness increased over 70mm and yield strength of the steel plate was around $47kg_f/mm^2$. Many researchers reported that the thick welded plate has low crack arrest toughness. They noticed the crack arrest ability is dependent on the plate thickness. In other words, brittle crack propagates straightly along the welded line and make abrupt fracture in the thick plate which causes low $K_{ca}$. In this study, the other factors, especially welding heat input, to cause low crack arrest toughness was investigated for thick steel plate welds. EH grade steel plates were used in this study and 50 to 80 thick plates were tested to confirm thickness sensitivity. Electro gas welding (EGW) and flux cored arc welding (FCAW) were adopted to prepare the welded joints. Temperature gradient ESSO test was performed to measure $K_{ca}$ values with the variation of welding variables. As a result of this study, regardless of plate thickness, welding heat input to cause welding residual stress around crack path is a key factor to control the brittle crack propagation in welded joints.

• Steel and Composite Structures
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• v.19 no.6
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• pp.1549-1560
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• 2015

This paper presents the characterization of fatigue crack in the A283 Grade C steel using the MMM method by identifying the effects of magnetic flux leakage towards the crack growth rate, da/dN, and crack length. The previous and current research on the relation between MMM parameters and fatigue crack effect is still unclear and requires specific analysis to validate that. This method is considered to be a passive magnetic method among other Non-Destructive Testing (NDT) methods. The tension-tension fatigue test was conducted with a testing frequency of 10 Hz with 4 kN loaded, meanwhile the MMM response signals were captured using a MMM instrument. A correlation between the crack growth rate and magnetic flux leakage produces a sigmoid shape curve with a constant values which present the gradient, m value is in the ranges of 1.4357 to 4.0506, and the y-intercept, log C in the ranges of $4{\times}10^{-7}$ to 0.0303. Moreover, a linear relation was obtained between the crack length and magnetic flux leakage which present the R-Squared values is at 0.830 to 0.978. Therefore, MMM method has their own capability to investigate and characterize the fatigue crack effects as a main source of fracture mechanism for ferrous-based materials.

• Investigative Magnetic Resonance Imaging
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• v.1 no.1
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• pp.119-124
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• 1997

Purpose: To assess the utility of magnetic resonance(MR) cerebral blood volume (CBV) map in the evaluation of brain tumors. Materials and Methods: We performed perfusion MR imaing preoperatively in the consecutive IS patients with intracranial masses(3 meningiomas, 2 glioblastoma multiformes, 3 low grade gliomas, 1 lymphoma, 1 germinoma, 1 neurocytoma, 1 metastasis, 2 abscesses, 1 radionecrosis). The average age of the patients was 42 years (22yr -68yr), composed of 10 males and S females. All MR images were obtained at l.ST imager(Signa, CE Medical Systems, Milwaukee, Wisconsin). The regional CBV map was obtained on the theoretical basis of susceptibility difference induced by first pass circulation of contrast media. (contrast media: IScc of gadopentate dimeglumine, about 2ml/sec by hand, starting at 10 second after first baseline scan). For each patient, a total of 480 images (6 slices, 80 images/slice in 160 sec) were obtained by using gradient echo(CE) single shot echo-planar image(EPI) sequence (TR 2000ms, TE SOms, flip angle $90^{\circ}$, FOV $240{\times}240mm,{\;}matrix{\;}128{\times}128$, slice-thick/gap S/2.S). After data collection, the raw data were transferred to CE workstation and rCBV maps were generated from the numerical integration of ${\Delta}R2^{*} on a voxel by voxel basis, with home made software (${\Delta}R2^{*}=-ln (S/SO)/TE). For easy visual interpretation, relative RCB color coding with reference to the normal white matter was applied and color rCBV maps were obtained. The findings of perfusion MR image were retrospectively correlated with Cd-enhanced images with focus on the degree and extent of perfusion and contrast enhancement. Results: Two cases of glioblastoma multiforme with rim enhancement on Cd-enhanced Tl weighted image showed increased perfusion in the peripheral rim and decreased perfusion in the central necrosis portion. The low grade gliomas appeared as a low perfusion area with poorly defined margin. In 2 cases of brain abscess, the degree of perfusion was similar to that of the normal white matter in the peripheral enhancing rim and was low in the central portion. All meningiomas showed diffuse homogeneous increased perfusion of moderate or high degree. One each of lymphoma and germinoma showed homogenously decreased perfusion with well defined margin. The central neurocytoma showed multifocal increased perfusion areas of moderate or high degree. A few nodules of the multiple metastasis showed increased perfusion of moderate degree. One radionecrosis revealed multiple foci of increased perfusion within the area of decreased perfusion. Conclusion: The rCBV map appears to correlate well with the perfusion state of brain tumor, and may be helpful in discrimination between low grade and high grade gliomas. The further study is needed to clarify the role of perfusion MR image in the evaluation of brain tumor.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.7
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• pp.779-793
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• 2023

Intensive and long-term aquaculture activities in Korea have generated considerable amounts of organic matter, deteriorating the sedimentary environment and ecosystem. The Korean government enacted the Fishery Management Act to preserve and manage the environment of fish farms. Based on this, a fisheries environment assessment has been conducted on fish cage farms since 2014, necessitating the development of a scientific and objective evaluation method suitable for the domestic environment. Therefore, a benthic health index (BHI) was developed using the relationship between benthic polychaete communities and organic matter, a major source of pollution in fish farms. In this study, the development process and calculation method of the BHI have been introduced. The BHI was calculated by classifying 225 species of polychaetes appearing in domestic coastal and aquaculture areas into four groups by linking the concentration gradient of the total organic carbon in the sediment and the distributional characteristics of each species and assigning differential weights to each group. Using BHI, the benthic fauna communities were assigned to one of the four ecological classes (Grade 1: Normal, Grade 2: Slightly polluted, Grade 3: Moderately polluted, and Grade 4: Heavily polluted). The application of the developed index in the field enabled effective evaluation of the Korean environment, being relatively more accurate and less affected by the season compared with the existing evaluation methods like the diversity index or AZTI's Marine Biotic Index developed overseas. In addition, using BHI will be useful in the environmental management of fish farms, as the environment can be graded in quantified figures.

• Journal of The Geomorphological Association of Korea
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• v.18 no.2
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• pp.65-80
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• 2011

This is to find out geomorphological environment of optimum location for the object of dwelling site of Bronze Age (hereinafter called dwelling site) of total 177 unit confirmed in Yongducheon basin and Onyangcheon basin (hereinafter called investigation-object basin) in Asan-si Chungnam. To do this, hill of investigation-object basin where dwelling sites were confirmed was divided into 11 units of hillslope geomorphological and this was combined with the grade of 5 units of gradient and again subdivided into total 55 units of micro-landforms of Hillslope. Based on this, in the viewpoint of 'gradient of each of micro-landforms' analyzed 'number of dwelling sites' and 'dwelling site distribution density (unit: number of dwelling sites/1000m2)'. As the result, the optimum geomorphological environment where dwelling sites were located was largely confirmed be 5 units(① semi-gentle slope land of crest slope ②gentle slope land of crest slope ③ slope of upper sideslope ④ flat land of crest slope ⑤ flat land of crest flat). It is thought that this analysis data will be used in the future as basic data for the study of predicting distribution of dwelling sites in Bronze Age which might have been buried in the investigation-object basin.

• Journal of the Korean School Mathematics Society
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• v.10 no.2
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• pp.187-206
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• 2007

The purpose of this study is to know what is the difficulties that mathematics underachievers are suffering from the area of mathematical function and how to overcome this difficulties. For this study, we have selected two mathematics underachievers and carried out the inspection. The mathematics underachievers have undergone the difficulties of understanding mathematical problems, the difficulties from the deficit of prerequisite and basic learning, the difficulties of finding the answer typically and the difficulties of classifying an algebraic symbol, the difficulties of calculating the gradient of the straight line passing through two points.

• Journal of Industrial Technology
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• v.20 no.A
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• pp.169-178
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• 2000

The 4-point bending tests have been performed In order to estimate the effect of TIG-dressing on fatigue strength and fatigue characteristics quantitatively for non load-carrying fillet welded joints subjected to pure bending. As a result of fatigue tests, fatigue strengths of as-welded specimens have satisfied the grade of fatigue strength prescribed in specifications of korea, AASHTO and JSSC. Fatigue strength at 2 million cycles of TIG-dressing specimens have increased compared with as-welded specimens. As the result of beachmark tests, fatigue cracks occurred at several points, where the radius of curvature and flank angle in the weld bead toes were low, and grew as semi-elliptical cracks, then approached to fracture. As a result of finite element analysis, stress concentration factor in weld bead toes has closely related to the flank angle and radius of curvature, and between these, the radius of curvature has more largely affected in stress concentration factor than flank angle. As a result of fracture mechanics approaches, the crack correction factor of test specimens has largely affected on stress gradient correction factor in case a/t is below 0.4. From the relations between stress intensity factor range estimated from FEM analysis and fatigue crack growth rate, fatigue life has been correctly calculated.