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- 저자 : Kazuaki Okamoto (검색결과 5 건)
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Tayyaba Mateen,Kazuaki Okamoto,Sun-Lin Chung,Kuo-Lung Wang,Hao-Yang Lee,Shuhei Abe,Yuji Mita,Hafiz U. Rehman,Masaru Terabayashi,Hiroshi Yamamoto 한국지질과학협의회 2019 Geosciences Journal Vol.23 No.6
U-Pb-Hf isotopes of zircons from the granitic intrusive rocks in the Iwakuni area of southwest Japan are determined by LA-ICP-MS analysis. The Gamano Granodiorite belonging to the Older Ryoke Granites of the Ryoke Belt yielded U-Pb mean age of 92.3 ± 2.6 Ma (MSWD = 1.8). The Namera Granite belonging to the Younger Ryoke Granites of the Ryoke Belt yielded U-Pb mean age of 106.3 ± 1.6 Ma (MSWD = 2.3). The Shimokuhara Granite belonging to the Hiroshima Granites of the San-yo Belt yielded U-Pb mean age of 103.8 ± 1.5 Ma (MSWD = 0.32). A granite porphyry sample taken from about 15 m thick dike discordantly intruded into pelitic schist of the Ryoke metamorphic rocks yielded U-Pb mean age of 92.5 ± 1.6 Ma (MSWD = 0.63). Hf isotope data, obtained from the same dated zircon grains, show initial 176Hf/177Hf isotopic ratios referred to as “εHf(t)” generally ranging between –4.8 and +1.1 except an anomalously low value (–15.0) from an inherited core. The εHf(t) values, calculated with average crustal 176Lu/177Hf ratio of 0.015, correspond to Hf isotope crustal model ages between 1474 to 1087 Ma (Mesoproterozoic). The Gamano Graodiorite has long been regarded to be a syn-tectonic intrusion, but the zircon ages and εHf(t) values are similar to those of the post-tectonic granite porphyry dike. The results of this study together with available U-Pb zircon ages of granitic rocks in the Iwakuni area reported elsewhere reveal that the order of emplacement indicated by the U-Pb zircon ages are much discrepant with the traditional classification, the Older Ryoke, the Younger Ryoke. It is better to refrain from the use of “Older” and “Younger” for the collective names of the granitic intrusive bodies.
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Seok, Young Mi,Azam, Mohammed Ali,Okamoto, Yasuo,Sato, Atsushi,Yoshioka, Kazuaki,Maeda, Masataka,Kim, InKyeom,Takuwa, Yoh Ovid Technologies Wolters Kluwer -American Heart A 2010 Hypertension Vol.56 No.5
<P>Rho-mediated inhibition of myosin light chain (MLC) phosphatase (MLCP), together with Ca2+-dependent MLC kinase activation, constitutes the major signaling mechanisms for vascular smooth muscle contraction. We recently unveiled the involvement of Ca2+-induced, phosphoinositide 3-kinase (PI3K) class II alpha isoform (PI3K-C2 alpha)-dependent Rho activation and resultant Rho kinase-dependent MLCP suppression in membrane depolarization- and receptor agonist-induced contraction. It is unknown whether Ca2+ - and PI3K-C2 alpha-dependent regulation of MLCP is altered in vascular smooth muscle of hypertensive animals and is involved in hypertension. Therefore, we studied the role of the Ca2+-PI3K-C2 alpha-Rho-MLCP pathway in spontaneously hypertensive rats (SHRs). PI3K-C2 alpha was readily detected in various vascular beds of Wistar-Kyoto rats and activated by high KCl. High KCl also stimulated vascular Rho activity and phosphorylation of the MLCP regulatory subunit MYPT1 at Thr(853) in a PI3K inhibitor wortmannin-sensitive manner. In mesenteric and other vessels of SHRs at the hypertensive but not the prehypertensive stage, the activity of PI3K-C2 alpha but not class I PI3K p110 alpha was elevated with concomitant rises of Rho activity and Thr(853)-phosphorylation of MYPT1, as compared with normotensive controls. Infusion of the Ca2+ channel antagonist nicardipine reduced blood pressure with suppression of vascular activity of PI3K-C2 alpha-Rho and phosphorylation of MYPT1 in hypertensive SHRs. Infusion of wortmannin lowered blood pressure with inhibition of PI3K-C2 alpha-Rho activities and MYPT1 phosphorylation in hypertensive SHRs. These observations suggest that an increased activity of the Ca2+-PI3K-C2 alpha-Rho signaling pathway with resultant augmented MLCP suppression contributes to hypertension in SHRs. The Ca2+- and PI3K-C2 alpha-dependent Rho stimulation in vascular smooth muscle may be a novel, promising target for treating hypertension. (Hypertension. 2010;56:934-941.)</P>
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Study aerosol-cloud interaction phenomena from satellite remote sensing and climate modeling
Nakajima, Teruyuki,Higurashi, Akiko,Kawamoto, Kazuaki,Okamoto, Hajime,Takemura, Toshihiko,Kuroda, Shunsuke 대한원격탐사학회 1999 International Symposium on Remote Sensing Vol.15 No.1
We have analyzed AVHRR global data set for obtaining aerosol and cloud microphysical parameters, i. e., optical thickness and size index of particle polydispersions. From the results, it is found that the cloud optical thickness increases with increasing aerosol column number, which seems to be caused mainly by decreasing cloud particle radius. The cloud liquid water path was observed to be relatively constant without a significant dependence on the aerosol number. Further comparison of the satellite results with a general circulation model simulation.
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Detrital zircon evidence for the antiquity of Taiwan
Ching-Ying Lan,Tadashi Usuki,Kuo-Lung Wang,Tzen-Fu Yui,Kazuaki Okamoto,Yuan-Hsi Lee,Takafumi Hirata,Yoshitaka Kon,Yuji Orihashi,Juhn G. Liou,Chun-Sun Lee 한국지질과학협의회 2009 Geosciences Journal Vol.13 No.3
In-situ U–Pb geochronology and Hf isotopic studies of zircons from the Pre-Tertiary basement complex and Eocene rocks of the Central Range of Taiwan were carried out to elucidate the history of detrital zircons older than 2.3 Ga. Zircons from the eastern Backbone Range and Eastern Central Range show Paleoproterozoic to late Neoarchean ages (2.3 –³2.5 Ga), whereas those from the Hsuehshan Range yield Neoarchean to Mesoarchean ages (2.6–3.2 Ga). The εHf(T) for the Paleoproterozoic to late Neoarchean zircons varies from –7.4 to +5.1, implying both juvenile crustal growth and reworking of old crusts. This dual origin could extend back to Mesoarchean–Paleoarchean (3.0–3.4 Ga) based on Hf isotopic model ages. Consistent but narrower εHf(T) values and Hf crustal model ages for zircons from Taiwan compared to Cathaysia suggest a possible common origin for these zircons, although Taiwan has a generally younger crustal evolution history than SE China.
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Tadashi Usuki,Ching-Ying Lan,Tzen-Fu Yui,Yoshiyuki Iizuka,Van Tich Vu,Tuan Anh Tran,Kazuaki Okamoto,Joseph L. Wooden,Juhn G. Liou 한국지질과학협의회 2009 Geosciences Journal Vol.13 No.3
To constrain the timing of collisional event in the Indochina block, SHRIMP U–Pb dating and REE analyses of zircon were carried out for two paragneiss samples of the Kham Duc Complex, central Vietnam. Both samples contain kyanite, staurolite, and zoisite as relics from an early metamorphic stage (M1), and biotite and sillimanite as major minerals constituting the foliation formed during the late metamorphic stage (M2). The change in mineral assemblages indicates a clockwise P-T path composed of a high- or medium-P + low-T stage (M1) and a subsequent low-P + high-T stage (M2). The U−Pb concordia ages of zircon rims are 447 ± 6 Ma and 452 ± 6 Ma for the two samples, respectively. These results are distinctly different from the available Ar–Ar mineral ages of 254–225 Ma. Following the clockwise P-T path and phase equilibrium analyses of the Complex, we suggest that the zircon rims were formed near peak temperatures during the decompression. The ~450 Ma zircon rim thus gives the minimum age constraint for a possible crustal thickening event during Early Paleozoic, whereas the reported Permo-Triassic Ar–Ar ages would result from an Indosinian overprint. This Early Paleozoic event is most likely related to a collisional orogeny between the Indochina and South China blocks. Late Neoproterozoic to Neoarchean ages are recorded from detrital zircon cores of the Kham Duc Complex, the Kontum Massif and Truong Son Belt, suggesting that their protoliths might have derived from sediments at the Gondwana margin.
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