Yun Hak Kim

Mathematical model and experimental validation of surface profile of a workpiece in round–oval–round pass sequence

Abstract A reliable analytical model that determines the surface profile of a workpiece (material) in round–oval–round pass sequence has been established. The surface profile of an outgoing workpiece is computed by using the linear interpolation of the radius of curvature of an incoming workpiece and that of roll groove to the roll axis direction. The validity of the surface profile model has been examined by hot rod rolling experiment with the roll gap and the design of oval groove changed. The surface profile and cross sectional area of a workpiece predicted by the new model were in agreement with those obtained experimentally.

A study of the application of upper bound method to the CONFORM process

Abstract This paper is concerned with the calculation of the powers required in the steady-state CONFORM process. For this goal, similarity is applied to the CONFORM process for an equivalent side extrusion process, to which the upper bound method is used to derive the equation for calculating the powers. Even though the global flow characteristics between the real and the simplified processes are not similar, the calculated results for both processes show good agreement. Furthermore, FEM simulation is carried out using the DEFORM commercial program in order to verify the theoretical results.

A study on optimal design for CONFORM process

Abstract In this paper, we investigated the effects of several significant process parameters on the process characteristics in the CONFORM process, such as material flow, defect occurrence, temperature and effective strain distributions, using DEFORM commercial FEM code. Since there are many parameters governing the process, it is not so easy to obtain an optimal combination of process parameters. Therefore, here, according to the parametric investigation of general forming methods, we carried out numerous numerical simulations and suggest a qualitative guide for the optimal CONFORM process.

Mechanical stretch increases MMP-2 production in vascular smooth muscle cells via activation of PDGFR-β/Akt signaling pathway.

Increased blood pressure, leading to mechanical stress on vascular smooth muscle cells (VSMC), is a known risk factor for vascular remodeling via increased activity of matrix metalloproteinase (MMP) within the vascular wall. This study aimed to identify cell surface mechanoreceptors and intracellular signaling pathways that influence VSMC to produce MMP in response to mechanical stretch (MS). When VSMC was stimulated with MS (0–10% strain, 60 cycles/min), both production and gelatinolytic activity of MMP-2, but not MMP-9, were increased in a force-dependent manner. MS-enhanced MMP-2 expression and activity were inhibited by molecular inhibition of Akt using Akt siRNA as well as by PI3K/Akt inhibitors, LY293002 and AI, but not by MAPK inhibitors such as PD98059, SP600125 and SB203580. MS also increased Akt phosphorylation in VSMC, which was attenuated by AG1295, a PDGF receptor (PDGFR) inhibitor, but not by inhibitors for other receptor tyrosine kinase including EGF, IGF, and FGF receptors. Although MS activated PDGFR-α as well as PDGFR-β in VSMC, MS-induced Akt phosphorylation was inhibited by molecular deletion of PDGFR-β using siRNA, but not by inhibition of PDGFR-α. Collectively, our data indicate that MS induces MMP-2 production in VSMC via activation of Akt pathway, that is mediated by activation of PDGFR-β signaling pathways.

Approximate analysis of roll force in a round–oval–round pass rolling sequence

Abstract This paper presents a semi-analytical method for the prediction of roll force in the oval–round (or round–oval) pass rolling sequence most commonly employed in present continuous rod (or bar) mills. Introduced here is the concept of a weak plane-strain deformation taking into account the deformation characteristics of the workpiece (material) in the roll grooves when the equation for the roll force is formulated. The flow stress (deformation resistance) of the workpiece is characterized by Shida’s constitutive equation. Hot rod rolling experiments were conducted to examine the proposed semi-analytical method. The results reveal that using the weak plane-strain deformation condition is appropriate in solving three-dimensional problems, where it is often necessary to reduce the cost of computation by simplification. For low plain-carbon steel, the roll forces predicted are in good agreement with those obtained experimentally with the rolling temperature changed (800–1100°C).

Resistin derived from diabetic perivascular adipose tissue up‐regulates vascular expression of osteopontin via the AP‐1 signalling pathway

Perivascular adipose tissue (PVAT) is implicated in the development of vascular diseases; however, the roles of PVAT on OPN expression in diabetic vasculature remain to be determined. This study investigated the role of adipokines derived from diabetic PVAT in regulating the vascular expression of OPN and explored the mechanisms involved. Aortic sections of ob/ob and high‐fat diet (HFD)‐induced obese (DIO) mice showed an increased expression of OPN, which was paralleled by increased amounts of PVAT characterized by enlargement of adipocytes. In the earlier phase of HFD feeding, macrophage infiltration was mainly localized to the area of PVAT at which adipocytes were enlarged, suggesting a potential link of activated adipocytes to macrophage infiltration. PVAT sections of ob/ob and DIO mice revealed a significantly greater number of macrophages with increased expression of adipokines, including resistin and visfatin. The distribution of resistin in PVAT mostly co‐localized with macrophages, while visfatin was expressed in macrophages and other cells. In in vitro studies, OPN expression in vascular smooth muscle cells (VSMCs) co‐cultured with PVAT of DIO mice was significantly increased, which was attenuated by a resistin‐neutralizing antibody. Likewise, resistin up‐regulated expression of OPN mRNA and protein in cultured VSMCs and the pivotal role of AP‐1 in resistin‐induced OPN transcription was demonstrated. Resistin produced by PVAT plays a pivotal role in the up‐regulated expression of OPN in the diabetic vasculature via a signalling pathway that involves activation of AP‐1.

PAF enhances MMP-2 production in rat aortic VSMCs via a β-arrestin2-dependent ERK signaling pathway

Platelet-activating factor (PAF), 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, is a potent phospholipid mediator and has been reported to be localized in atherosclerotic plaque. However, its role in the progression of atherosclerosis remains unclear. In the present study, we investigated the role of PAF in the production of matrix metalloproteinase (MMP) in primary vascular smooth muscle cells (VSMCs). When rat aortic primary VSMCs were stimulated with PAF (1 nmol/l), the expressions of MMP-2 mRNA and protein, but not of MMP-9, were significantly increased, and these upregulations were markedly attenuated by inhibiting extracellular signal-regulated kinases (ERKs) using molecular and pharmacological inhibitors, but not by using inhibitors of p38 mitogen-activated protein kinase or c-Jun N-terminal kinase. Likewise, ERK phosphorylation was markedly enhanced in PAF-stimulated VSMCs, and this was attenuated by WEB2086, but not by EGF receptor inhibitor, demonstrating the specificity of PAF receptor (PAFR) in PAF-induced ERK phosphorylation. In immunofluorescence studies, β-arrestin2 in PAF-stimulated VSMCs colocalized with PAFR and phosphorylated ERK (P-ERK). Coimmunoprecipitation results suggest that β-arrestin2-bound PAFRs existed as a complex with P-ERK. In addition, PAF-induced ERK phosphorylation and MMP-2 production were significantly attenuated by β-arrestin2 depletion. Taken together, the study shows that PAF enhances MMP-2 production in VSMCs via a β-arrestin2-dependent ERK signaling pathway.

5-Lipoxygenase plays a pivotal role in endothelial adhesion of monocytes via an increased expression of Mac-1

AIMS 5-Lipoxygenase (5-LO) is known to participate in the pathogenesis of atherosclerosis; however, the underlying mechanisms are unclear. Thus, this study investigated the molecular mechanisms responsible for 5-LO expression in monocytes as well as the role of 5-LO in monocyte adhesion to the vascular endothelium, which is a key early event in macrophage foam cell formation. METHODS AND RESULTS An en face immunohistochemistry of endothelial surfaces revealed a marked increase in monocyte adhesion to the aortic endothelium in wild-type (WT) mice treated with lipopolysaccharide (LPS), which was significantly attenuated in 5-LO((-/-)) mice. Likewise, the adhesion capacity of primary monocytes isolated from LPS-treated WT mice was higher than those of monocytes from 5-LO((-/-)) mice. In in vitro study, LPS increased monocyte adhesion to endothelial cells with an enhanced Mac-1 expression. These were attenuated by a 5-LO inhibitor, MK886, as well as by molecular depletion of 5-LO in monocytes. Furthermore, LPS-induced Mac-1 expression on monocytes was significantly inhibited by pre-treatment with U-75302, a BLT1-receptor antagonist, suggesting a pivotal role of 5-LO-derived leukotrienes. In promoter activity analysis and chromatin immunoprecipitation assays to identify transcription factors involved in 5-LO expression, both NF-κB and Sp1 played central roles to increase 5-LO expression in LPS-treated monocytes. CONCLUSION 5-LO expression in monocytes is modulated via NF-κB and Sp1 signalling pathways, and 5-LO plays a pivotal role in LPS-mediated monocyte adhesion to the vascular endothelium through an increased expression of Mac-1 on monocytes.

Dental image replacement on cone beam computed tomography with three-dimensional optical scanning of a dental cast, occlusal bite, or bite tray impression

The goal of the present study was to compare the accuracy of dental image replacement on a cone beam computed tomography (CBCT) image using digital image data from three-dimensional (3D) optical scanning of a dental cast, occlusal bite, and bite tray impression. A Bracket Typodont dental model was used. CBCT of the dental model was performed and the data were converted to stereolithography (STL) format. Three experimental materials, a dental cast, occlusal bite, and bite tray impression, were optically scanned in 3D. STL files converted from the CBCT of the Typodont model and the 3D optical-scanned STL files of the study materials were image-registered. The error range of each methodology was measured and compared with a 3D optical scan of the Typodont. For the three materials, the smallest error observed was 0.099±0.114mm (mean error±standard deviation) for registering the 3D optical scan image of the dental cast onto the CBCT dental image. Although producing a dental cast can be laborious, the study results indicate that it is the preferred method. In addition, an occlusal bite is recommended when bite impression materials are used.

Experimental investigation of the forming parameters of the rotational upset forging process

Abstract In a conventional upset forging, the presence of friction at the tool–workpiece interface not only increases the forging pressure and force, but also leads to non-homogeneity of deformation. In this study, to solve the above problems, a parametric study is presented on a new rotational upset forging process. Twisting torque can change the harmful effect of friction into a useful effect. Experiments were carried out to generate data of forming parameters, which are the friction factor, the sliding factor, the punch velocity and the geometry of the billets, on the rotational upset forging process. Comparing with the conventional upset forging process, the rotational upset forging process reduces both the forming load and bulging. The deformation of rotational upset forging is more uniformly distributed and its total deformation is greater than that of conventional upset forging for the same reduction of height.