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Hardening and overaging Mechanisms in an Au-Ag-Cu-Pd alloy with In additions
Geon-Hoo Jeon,Yong Hoon Kwon,Hyo-Joung Seol,Hyung-Il Kim
Gold Bulletin , 2008, DOI: 10.1007/BF03214879
Abstract: Hardening and overaging mechanisms were examined in a semi-precious Au Ag Cu Pd dental alloy with small amounts of In, Zn and Ir. The alloy showed maximum age-hardenability at the aging temperature of 400°C. The hardness value increased to reach the maximum value, and then decreased continuously with aging time. In the early stage of aging process, the matrix of the single α0 phase separated into the α1 and AuCu I phases, and the fine InPd-based precipitates containing Zn and Cu formed at the grain boundaries. During further aging, the grain boundary precipitates grew toward the grain interior. In overaged specimens, the original matrix was replaced by the coarse lamellar structure composed of the AuCu I phase containing Pd and Zn and the Ag Au-based α1 phase of Cu-, Pdand Zn-depleted. The hardness increase in the early stage of aging process was caused by the nucleation of the InPd-based phase and the AuCu I phase in the ga0 matrix; this introduced significant lattice strains into the interface with the matrix. The hardness decrease in the latter stage of aging process was caused by the formation and coarsening of the lamellar structure composed of the α1 phase and the AuCu I phase. The minor constituent, In formed InPd-based grain boundary precipitates prior to the lamellar structure formation of α1 and AuCu I.
Age-hardenability and related microstructural changes during and after phase transformation in an Au-Ag-Cu-based dental alloy
Kim, Hyung-Il;Kim, Tae-Wan;Kim, Young-Oh;Cho, Su-Yeon;Lee, Gwang-Young;Kwon, Yong Hoon;Seol, Hyo-Joung;
Materials Research , 2013, DOI: 10.1590/S1516-14392012005000169
Abstract: the aim of this study was to clarify how the microstructural changes during and after phase transformation determine the age-hardenability of an au-ag-cu-based dental alloy. the rapid increase in hardness in the initial stage was the result of rapid atomic diffusion by spinodal decomposition into metastable ag-rich' and cu-rich' phases. the constant hardening after apparent initial hardening was the result of a subsequent transformation of the metastable ag-rich' and cu-rich' phases to the stable ag-rich α1phase and aucu i phase through the metastable aucu i' phase. during the increase in hardness, fine block-like structure with high coherency formed in the grain interior, which changed to a fine cross-hatched structure. a relatively coarse lamellar structure composed of ag-rich α1and aucu i phases grew from the grain boundaries, initiating softening before the grain interior reached its maximum hardness. as a result, the spinodal decomposition attributed to rapid hardening by forming the fine block-like structure, and the subsequent ordering into aucu i, which is a famous hardening mechanism, weakened its hardening effect by accelerating the lamellar-forming grain boundary reaction.
Age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental Au–Ag–Cu–Pd–Zn alloy
Sang-Hwa Lee,In-Sook Lim,Mi-Hyang Cho,Ae-Ri Pyo,Yong Hoon Kwon,Hyo-Joung Seol,Hyung-Il Kim
Gold Bulletin , 2011, DOI: 10.1007/s13404-011-0021-x
Abstract: The age-hardening and overaging mechanisms related to the metastable phase formation by the decomposition of Ag and Cu in a dental casting gold alloy composed of 56Au–25Ag–11.8Cu–5Pd–1.7Zn–0.4Pt–0.1Ir (wt.%) were elucidated by characterizing the age-hardening behaviour, phase transformations, changes in microstructure and changes in element distribution. The fast and apparent increase in hardness at the initial stage of the aging process at 400°C was caused by the nucleation and growth of the metastable Ag–Au-rich phase and the Cu–Au-rich phase by the miscibility limit of Ag and Cu. The transformation of the metastable Ag–Au-rich phase into the stable Ag–Au-rich phase progressed concurrently with the ordering of the Cu–Au-rich phase into the AuCu I phase through the metastable state, which resulted in the subsequent increase in hardness. The further increase in hardness was restrained before complete decomposition of the parent α0 phase due to the initiation of the lamellar-forming grain boundary reaction. The progress of the lamellar-forming grain boundary reaction was not directly connected with the phase transformation of the metastable phases into the final product phases. The heterogeneous expansion of the lamellar structure from the grain boundary caused greater softening than the subsequent further coarsening of the lamellar structure. The lamellar structure was composed of the Ag–Au-rich layer which was Cu-, Pd- and Zn-depleted and the AuCu I layer containing Pd and Zn.
Age-hardening by grain interior and grain boundary precipitation in an Au-Ag-Pt-Zn-In alloy for multipurpose dental use
Joo-Hee Park,Mi-Hyang Cho,Mi-Gyoung Park,Yong Hoon Kwon,Hyung-Il Kim,Hyo-Joung Seol
Gold Bulletin , 2010, DOI: 10.1007/BF03215001
Abstract: The complex precipitation mechanisms related to the age-hardening of Cu-free Au-Ag-Pt-Zn-In alloy for multipurpose dental use was studied by means of hardness test, X-ray diffraction (XRD) studies, field emission scanning electron microscopic (FE-SEM) observations, energy dispersive spectrometer (EDS) analysis, and electron probe microanalysis (EPMA). The early diffusion and then clustering of the In-concentrated phase in the grain interior, together with the early diffusion and then ordering of the PtZn phase in the grain boundary, introduced the internal strains in the Au-Ag-rich α1 matrix, resulting in the hardening process. As the Au-Ag-rich α 1 ’ and PtZn β lamellarforming grain boundary reaction progressed, the phase boundaries between the solute-depleted face-centered cubic (FCC) α 1 ’ matrix and the face-centered tetragonal (FCT) PtZn β precipitate reduced, resulting in softening. In the particlelike structures composed of the major Pt-Au-rich α2 phase and the minor Pt-Zn-rich α3 phase, the separation of In and Zn progressed producing the In-increased Pt-Au-rich α 2 ’ phase and the Zn-increased PtZn α3′ phase with aging time without restraining the softening. The miscibility limit by complex systems of Au-Pt, Ag-Pt, Au-In and In-Zn resulted in the phase transformation and related microstructural changes.
Age-hardening by miscibility limit in a multi-purpose dental gold alloy containing platinum
Hyo-Joung Seol,Joo-Hee Park,Ri-Mo Ku,Mi-Gyoung Park,Yong Hoon Kwon,Hyung-Il Kim
Gold Bulletin , 2010, DOI: 10.1007/BF03214965
Abstract: This study examined the age-hardening by miscibility limit in a multi-purpose dental gold alloy containing platinum. The hardness increased rapidly in the initial stage of the aging process, reached the maximum value, then decreased continuously with aging time. The significant hardness increase resulted from the heterogeneous precipitation of the Pt-rich β phase from the grain boundary of the Au-rich α1 matrix due to the miscibility limit of Au-Pt system. With increasing aging time, the fine Pt-rich β precipitates covered almost the whole matrix, and by further aging, the precipitates grew coarse. The microstructural coarsening reduced the interface between the Au-rich α1 matrix and the Pt-rich β precipitates, which released the lattice strains between the two phases, resulting in a softening effect. In the later stage of aging process, the Au-containing Pt3In particle-like structure was transformed into the Au-depleted particle-like structure containing relatively large amounts of Cu resulting from the overlapping miscibility limit of both Au-Pt and Ag-Cu systems, which was responsible for the slow decreasing rate in hardness in the later stage of aging.
Age-hardening characteristics of a dental low-carat gold alloy with dual hardener system of In and Cu
Hyo-Joung Seol,Seong-Woo Kweon,Su-Yeon Cho,Gwang-Young Lee,Yong Hoon Kwon,Hyung-Il Kim
Gold Bulletin , 2011, DOI: 10.1007/s13404-011-0034-5
Abstract: The age-hardening characteristics of a dental low carat gold alloy with a dual hardener system of indium (In) and Cu (33.9 Au–26.2 Ag–20.28 Cu–9.8 Pd–7.8 In–2 Zn (at%)) were examined by observing the age hardenability and related phase transformation, microstructural changes and elemental distribution during the aging process at 400°C. The dual hardener system by the use of both In and Cu provided more powerful hardening effect compared to a single-hardener system of In or Cu, without the formation of a AuCu type ordered phase. The alloy showed apparent initial hardening, which was attributed to the pre-precipitation or zone formation by the help of quenched in excess vacancies. During the constant increase in hardness, the single parent phase separated into three phases, Au–Ag-based phase, Au–Cu-based phase containing Pd and In, and InPd-based phase, through a metastable state. Indium which was added as one of the hardeners induced initial grain boundary precipitation, followed by an expansion of the lamellar structure, which was responsible for softening. The alternative lamellar structure was composed of a Cu-rich layer (Au–Cu-based phase containing Pd and In) and an Ag-rich layer (Au–Ag-based phase) replaced partly by the InPd-based phase. Separation of the Ag-rich layer from the Cu-rich layer is based on the miscibility limit of Ag and Cu due to their eutectic property.
Valproic acid inhibits neural progenitor cell death by activation of NF-κB signaling pathway and up-regulation of Bcl-XL
Hyo Go, Jung Seo, Ki Kim, So Han, Pitna Kim, Young Kang, Seol Han, Chan Shin, Kwang Ko
Journal of Biomedical Science , 2011, DOI: 10.1186/1423-0127-18-48
Abstract: Apoptosis occurs in not only neuron but also in NPCs and neuroblast. When growth and survival signals such as EGF or LIF are removed, apoptosis is activated as well as the induction of differentiation. To investigate the regulation of cell death during developmental stage, it is essential to investigate the regulation of apoptosis of NPCs.Neural progenitor cells were cultured from E14 embryonic brains of Sprague-Dawley rats. For in vivo VPA animal model, pregnant rats were treated with VPA (400 mg/kg S.C.) diluted with normal saline at E12. To analyze the cell death, we performed PI staining and PARP and caspase-3 cleavage assay. Expression level of proteins was investigated by Western blot and immunocytochemical assays. The level of mRNA expression was investigated by RT-PCR. Interaction of Bcl-XL gene promoter and NF-κB p65 was investigated by ChIP assay.In this study, FACS analysis, PI staining and PARP and caspase-3 cleavage assay showed that VPA protects cultured NPCs from cell death after growth factor withdrawal both in basal and staurosporine- or hydrogen peroxide-stimulated conditions. The protective effect of prenatally injected VPA was also observed in E16 embryonic brain. Treatment of VPA decreased the level of IκBα and increased the nuclear translocation of NF-κB, which subsequently enhanced expression of anti-apoptotic protein Bcl-XL.To the best of our knowledge, this is the first report to indicate the reduced death of NPCs by VPA at developmentally critical periods through the degradation of IκBα and the activation of NF-κB signaling. The reduced NPCs death might underlie the neurodevelopmental defects collectively called fetal valproate syndrome, which shows symptoms such as mental retardation and autism-like behavior.The importance of cell death for normal brain morphogenesis in the developing nervous system has been acknowledged since the beginning of modern neuroscience era [1,2]. Programmed cell death is a normal and physiological process to all
Carbon Sequestration and Nitrogen Transformation in Soil Cooperated with Organic Composts and Biochar during Corn (Zea mays) Cultivation  [PDF]
Joung Du Shin
Journal of Agricultural Chemistry and Environment (JACEN) , 2015, DOI: 10.4236/jacen.2015.44010
Abstract: Background: Objectives of this study were to investigate changes of soil carbon contents and to evaluate N mineralization and nitrification rates in soils cooperated with organic composts and biochar during the 2nd year corn cultivation. Methods and Results: For the experiment, the soil texture used in this study was clay loam. Application rates of chemical fertilizer were 480-150- 260 kg/ha (N-P2O5-K2O) as recommended amount after soil test. Biochar application was 0.2% to soil weight. The soil samples were periodically taken at every 15-day interval during corn cultivation periods. The treatments were consisted of cow compost (CC), pig compost (PC), swine digestate from aerobic digestion system (AD), and their biochar cooperation. TC contents in treatments cooperated with biochar at harvesting stages were ranged from 0.96% to 1.24%, and its CC applied plot was highest at 1.24%. It was observed that TC contents with biochar treatments were higher than the compost treatment only. Therefore, it was observed to be carbon sequestration into corn field cooperated with biochar. For nitrogen transformation in soil cooperated with organic composts and biochar, net mineralization rates were dramatically decreased at 44 days after sowing, but nitrification rates were abruptly increased at 73 days after sowing. For N mineralization and nitrification rates, it was shown that they were generally low in the soil cooperated with biochar as compared to the only application plots of different organic composts. Also, it was observed to be highest in the application plot of pig compost manure. Conclusion: Overall, application of biochar in the cropland could be an important role for mitigation of greenhouse gas as well as carbon sequestration.
Prenatal exposure of ethanol induces increased glutamatergic neuronal differentiation of neural progenitor cells
Ki Kim, Hyo Go, Hae Bak, Chang Choi, Inha Choi, Pitna Kim, Seol-Heui Han, So Han, Chan Shin, Kwang Ko
Journal of Biomedical Science , 2010, DOI: 10.1186/1423-0127-17-85
Abstract: Neural progenitor cells were cultured from E14 embryo brain of Sprague-Dawley rat. Pregnant mice and rats were treated with ethanol (2 or 4 g/kg/day) diluted with normal saline from E7 to E16 for in vivo FASD animal models. Expression level of proteins was investigated by western blot analysis and immunocytochemical assays. MTT was used for cell viability. Proliferative activity of NPCs was identified by BrdU incorporation, immunocytochemistry and FACS analysis.Reduced proliferation of NPCs by ethanol was demonstrated using BrdU incorporation, immunocytochemistry and FACS analysis. In addition, ethanol induced the imbalance between glutamatergic and GABAergic neuronal differentiation via transient increase in the expression of Pax6, Ngn2 and NeuroD with concomitant decrease in the expression of Mash1. Similar pattern of expression of those transcription factors was observed using an in vivo model of FASD as well as the increased expression of PSD-95 and decreased expression of GAD67.These results suggest that ethanol induces hyper-differentiation of glutamatergic neuron through Pax6 pathway, which may underlie the hyper-excitability phenotype such as hyperactivity or seizure susceptibility in FASD patients.Fetal alcohol spectrum disorder (FASD) is a spectrum of mental and physical disorders associated with prenatal exposure to alcohol during pregnancy, which affects one in every 100 live births in United states and Europe [1]. Ethanol has well-known teratogenic effects by mechanisms including induction of apoptosis and inhibition of proliferation, migration, differentiation, and other cellular functions during developmental period [2-5]. In addition, ethanol exposure influences membrane-associated receptor signaling pathways [6], cell adhesion [7,8], and the binding of transcription factors [9].The central nervous system is the main organ affected by FAS [10-13], and neurological symptoms include mental retardation, learning disabilities and ADHD-like symptoms such
Peripheral Afferent Mechanisms Underlying Acupuncture Inhibition of Cocaine Behavioral Effects in Rats
Seol Ah Kim, Bong Hyo Lee, Jong Han Bae, Kwang Joong Kim, Scott C. Steffensen, Yeon-Hee Ryu, Joong Woo Leem, Chae Ha Yang, Hee Young Kim
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0081018
Abstract: Administration of cocaine increases locomotor activity by enhancing dopamine transmission. To explore the peripheral mechanisms underlying acupuncture treatment for drug addiction, we developed a novel mechanical acupuncture instrument (MAI) for objective mechanical stimulation. The aim of this study was to evaluate whether acupuncture inhibition of cocaine-induced locomotor activity is mediated through specific peripheral nerves, the afferents from superficial or deep tissues, or specific groups of nerve fibers. Mechanical stimulation of acupuncture point HT7 with MAI suppressed cocaine-induced locomotor activity in a stimulus time-dependent manner, which was blocked by severing the ulnar nerve or by local anesthesia. Suppression of cocaine-induced locomotor activity was elicited after HT7 stimulation at frequencies of either 50 (for Meissner corpuscles) or 200 (for Pacinian corpuscles) Hz and was not affected by block of C/Aδ-fibers in the ulnar nerve with resiniferatoxin, nor generated by direct stimulation of C/Aδ-fiber afferents with capsaicin. These findings suggest that HT7 inhibition of cocaine-induced locomotor activity is mediated by A-fiber activation of ulnar nerve that originates in superficial and deep tissue.
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