• 호남수학학술지
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• 제43권3호
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• pp.453-463
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• 2021

In this study, tubular surfaces that play an important role in technological designs in various branches are examined for the case of the base curve is not satisfying the fundamental theorem of the differential geometry. In order to give an alternative perspective to the researches on tubular surfaces, the modified orthogonal frame is used in this study. Firstly, the relationships between the Serret-Frenet frame and the modified orthogonal frame are summarized. Then the definitions of the tubular surfaces, some theorems, and results are given. Moreover, the fundamental forms, the mean curvature, and the Gaussian curvature of the tubular surface are calculated according to the modified orthogonal frame. Finally, the properties of parameter curves of the tubular surface with modified orthogonal frame are expressed and the tubular surface is drawn according to the Frenet frame and the modified orthogonal frame.

• Kyungpook Mathematical Journal
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• 제62권3호
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• pp.497-507
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• 2022

In this study, we define tubular surfaces in Pseudo Galilean 3-space as type-1 or type-2. Using the X(s, t) position vectors of the surfaces and G(s, t) Gaussian transformations, we obtain equations for the two types of tubular surfaces that satisfy the conditions ∆X(s, t) = 0, ∆X(s, t) = AX(s, t), ∆X(s, t) = λX(s, t), ∆X(s, t) = ∆G(s, t), ∆G(s, t) = 0, ∆G(s, t) = AG(s, t) and ∆G(s, t) = λG(s, t).

• 대한수학회보
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• 제61권2호
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• pp.401-419
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• 2024

Let K, H, K_II and H_II be the Gaussian curvature, the mean curvature, the second Gaussian curvature and the second mean curvature of a timelike tubular surface T_γ(α) with the radius γ along a timelike curve α(s) in Minkowski 3-space E³₁. We prove that T_γ(α) must be a (K, H)-Weingarten surface and a (K, H)-linear Weingarten surface. We also show that T_γ(α) is (X, Y)-Weingarten type if and only if its central curve is a circle or a helix, where (X, Y) ∈ {(K, K_II), (K, H_II), (H, K_II), (H, H_II), (K_II , H_II)}. Furthermore, we prove that there exist no timelike tubular surfaces of (X, Y)-linear Weingarten type, (X, Y, Z)-linear Weingarten type and (K, H, K_II, H_II)-linear Weingarten type along a timelike curve in E³₁, where (X, Y, Z) ∈ {(K, H, K_II), (K, H, H_II), (K, K_II, H_II), (H, K_II, H_II)}.

• Corrosion Science and Technology
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• 제14권6호
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• pp.267-272
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• 2015

The performance of three tubular materials (C-90, L-80, and N-80) was evaluated in a synthetic brine inoculated with sulfate-reducing bacteria (SRB) in the absence and presence of biocides. A flow loop was used in the evaluation of the three alloys. Morphological examination of the alloy surfaces after exposure to SRB and after biocide treatment was performed by scanning electron microscopy (SEM) to determine the nature of any localized corrosion. The SE images of the coupon samples showed a marked difference between the biocide-treated and untreated samples. Small pits were observed on the ultrasonically cleaned surfaces of the three alloys after exposure to SRB. The biocide treatment reduced the number of SRB on the surfaces of the alloys. Results indicated that C-90 and L-80 alloys exhibited better MIC resistance than N-80 under the conditions used in this study.

• Kyungpook Mathematical Journal
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• 제60권2호
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• pp.361-373
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• 2020

In this paper, we define admissible canal surfaces with isotropic radius vectors in pseudo-Galilean 3-spaces and we obtaine their position vectors. We also attain some important results by considering their Gauss and mean curvatures.

• Kyungpook Mathematical Journal
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• 제57권2호
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• pp.319-326
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• 2017

In this paper, we defined the admissible canal surfaces with isotropic radious vector in Galilean 3-spaces an we obtained their position vectors. Also we gave some important results by using their Gauss and mean curvatures.

• Korean Chemical Engineering Research
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• 제62권2호
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• pp.191-199
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• 2024

A study was conducted on a tubular heat exchanger to improve its heat transfer rate by using a novel baffle plate design with discontinuous swirling patterns. The design consisted of perforated baffle plates with rectangular air deflectors positioned at varying angles. The tubes in the heat exchanger were arranged in a consistent alignment with the airflow direction and exposed to a uniform heat flux on their surfaces. Each baffle plate included sixteen deflectors inclined at the same angle and arranged in a clockwise pattern. This arrangement induced a swirling motion of the air inside a circular duct where the heated tubes were located, leading to increased turbulence and improved heat transfer on the tube surfaces. The spacing between the baffle plates was adjusted at different pitch ratios, and the Reynolds number was controlled within a range of 16,000 to 29,000. The effects of pitch ratios and inclination angles on the heat exchanger's performance were analyzed. The results indicated that using a baffle plate with rectangular deflectors inclined at 30° and a pitch ratio of 1.2 resulted in an average increase of 1.29 in the thermal enhancement factor.

• 한국임상수의학회지
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• 제8권2호
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• pp.143-146
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• 1991

Renal cyst was detected in a mongrel dog aged 3 months old. The most prominent clinical abnormalities were vomiting, loss of appetite, depression, abdominal swelling and lethargy. Gross appearances included ascites and bilaterally irregular capsular surfaces of the kidneys. Characteristic microscopical findings were various sized cysts formation, shrunken glomeruli with hypercellularity, connective tissue porliferation in the interstitum, tubular dilatation and sligth leukocytic infiltration. The cause. of the renal disorder in a mongrel dog could not be determined.

• 대한치과보존학회:학술대회논문집
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• 대한치과보존학회 2003년도 제120회 추계학술대회 제 5차 한ㆍ일 치과보존학회 공동학술대회
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• pp.624-624
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• 2003

I. Objectives The purpose of this study was to investigate the ultrastructure of sclerotic dentin of non-carious cervical lesions after acid etching. II. Materials and methods Teeth with non-carious cervical lesions were collected and dentinal surfaces were acid etched with 35% phosphoric acid. The micromorphological features of peritubular dentin and intra-tubular calcific structure were observed with scanning electron microscope.(omitted)

• Steel and Composite Structures
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• 제27권5호
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• pp.577-598
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• 2018

The imperfect steel-concrete interface bonding is an important deficiency of the concrete-filled double skin tubular (CFDST) columns that led to separating concrete and steel surfaces under lateral loads and triggering buckling failure of the columns. To improve this issue, it is proposed in this study to use longitudinal and transverse steel stiffeners in CFDST columns. CFDST columns with different patterns of stiffeners embedded in the interior or exterior surfaces of the inner or outer tubes were analyzed under constant axial force and reversed cyclic loading. In the finite element modeling, the confinement effects of both inner and outer tubes on the compressive strength of concrete as well as the effect of discrete crack for concrete fracture were incorporated which give a realistic prediction of the seismic behavior of CFDST columns. Lateral strength, stiffness, ductility and energy absorption are evaluated based on the hysteresis loops. The results indicated that the stiffeners had determinant role on improving pinching behavior resulting from the outer tube's local buckling and opening/closing of the major tensile crack of concrete. The lateral strength, initial stiffness and energy absorption capacity of longitudinally stiffened columns with fixed-free end condition were increased by as much as 17%, 20% and 70%, respectively. The energy dissipation was accentuated up to 107% for fixed-guided end condition. The use of transverse stiffeners at the base of columns increased energy dissipation up to 35%. Axial load ratio, hollow ratio and concrete strength affecting the initial stiffness and lateral strength, had negligible effect of the energy dissipation of the columns. It was also found that the longitudinal stiffeners and transverse stiffeners have, respectively, negative and positive effects on ductility of CFDST columns. The conclusions, drawn from this study, can in turn, lead to the suggestion of some guidelines for the design of CFDST columns.