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126 results on '"Kimura, Kazutaka"'

1. 3D Radiation-Hydrodynamic Simulations Resolving Interior of Rapidly Accreting Primordial Protostar

Author

Kimura, Kazutaka, Hosokawa, Takashi, Sugimura, Kazuyuki, and Fukushima, Hajime

Subjects
Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics
Abstract

Direct collapse of supermassive stars is a possible pathway to form supermassive black hole seeds at high redshifts. Whereas previous three-dimensional (3D) simulations demonstrate that supermassive stars form via rapid mass accretion, those resolving the stellar interior have been limited. We here report 3D radiation-hydrodynamic (RHD) simulations following the evolution of rapidly accreting protostars resolving the stellar interior. We use an adaptive mesh refinement code with our newly developed RHD solver employing an explicit M1 closure method. We follow the early evolution until the stellar mass reaches $\sim 10~M_\odot$ from two different initial configurations of spherical and turbulent clouds. We demonstrate that, in both the cases, a swollen protostar whose radius is $100\mathrm{-}1000~R_\odot$ appears, as predicted by the stellar evolution calculations. Its effective temperature remains a few thousand Kelvin, and the radiative feedback by ionizing photons is too weak to disturb the accretion flow up to the epoch examined in this work. In the turbulent case, the protostar rotates rapidly at more than 0.4 times the Keplerian velocity owing to the angular momentum provided by the initial turbulence. The protostar approximates an oblate spheroid, and its equatorial radius is more than twice the polar radius. Our results suggest that we need to consider the rapid stellar rotation to elucidate the realistic 3D protostellar evolution in the supermassive star formation., Comment: 9 pages, 5 figures, accepted to ApJ

Published
2023
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2. Growth of Massive Disk and Early Disk Fragmentation in the Primordial Star Formation

Author

Kimura, Kazutaka, Hosokawa, Takashi, and Sugimura, Kazuyuki

Subjects
Astrophysics - Astrophysics of Galaxies, Astrophysics - Solar and Stellar Astrophysics
Abstract

Recent high-resolution simulations demonstrate that disks around primordial protostars easily fragment in the accretion phase before the protostars accrete less than a solar mass. To understand why the gravitational instability generally causes the fragmentation so early, we develop a one-dimensional (1D) non-steady model of the circumstellar disk that takes the mass supply from an accretion envelope into account. We also compare the model results to a three-dimensional (3D) numerical simulation performed with a code employing the adaptive mesh refinement. Our model shows that the self-gravitating disk, through which the Toomre $Q$ parameter is nearly constant at $Q \sim 1$, gradually spreads as the disk is fed by the gas infalling from the envelope. We further find that the accretion rate onto the star is an order of magnitude smaller than the mass supply rate onto the disk. This discrepancy makes the disk more massive than the protostar in an early evolutionary stage. Most of the infalling gas is used to extend the outer part of the self-gravitating disk rather than transferred inward toward the star through the disk. We find that similar evolution also occurs in the 3D simulation, where the disk becomes three times more massive than the star before the first fragmentation occurs. Our 1D disk model well explains the evolution of the disk-to-star mass ratio observed in the simulation. We argue that the formation of such a massive disk leads to the early disk fragmentation., Comment: 22 pages, 14 figures, accepted for publication in ApJ

Published
2020
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14. 3D Radiation-hydrodynamic Simulations Resolving Interior of Rapidly Accreting Primordial Protostar

Author

30413967, Kimura, Kazutaka, Hosokawa, Takashi, Sugimura, Kazuyuki, Fukushima, Hajime, 30413967, Kimura, Kazutaka, Hosokawa, Takashi, Sugimura, Kazuyuki, and Fukushima, Hajime

Abstract

Direct collapse of supermassive stars is a possible pathway to form supermassive black hole seeds at high redshifts. Whereas previous three-dimensional (3D) simulations demonstrate that supermassive stars form via rapid mass accretion, those resolving the stellar interior have been limited. Here, we report 3D radiation-hydrodynamic (RHD) simulations following the evolution of rapidly accreting protostars resolving the stellar interior. We use an adaptive mesh refinement code with our newly developed RHD solver employing an explicit M1 closure method. We follow the early evolution until the stellar mass reaches ∼10 M⊙ from two different initial configurations of spherical and turbulent clouds. We demonstrate that, in both cases, a swollen protostar whose radius is 100–1000 R⊙ appears, as predicted by the stellar evolution calculations. Its effective temperature remains a few thousand Kelvin, and the radiative feedback by ionizing photons is too weak to disturb the accretion flow up to the epoch examined in this work. In the turbulent case, the protostar rotates rapidly at more than 0.4 times the Keplerian velocity owing to the angular momentum provided by the initial turbulence. The protostar approximates an oblate spheroid, and its equatorial radius is more than twice the polar radius. Our results suggest that we need to consider the rapid stellar rotation to elucidate the realistic 3D protostellar evolution in the supermassive star formation.

Published
2023

20. Low serum creatine kinase level is associated with poor prognosis in patients with hepatocellular carcinoma: A retrospective single‑center study.

Author

Matsumoto, Yu, Otsuka, Yuichiro, Okada, Rei, Ito, Yuko, Kimura, Kazutaka, Ishii, Jun, Maeda, Tetsuya, Tsuchiya, Masaru, Funahashi, Kimihiko, and Shimada, Hideaki

Subjects
RECEIVER operating characteristic curves, CANCER prognosis, CREATINE kinase, PATIENTS, OVERALL survival
Abstract

Previous studies have reported low serum creatine kinase (s-CK) levels as a poor prognostic factor in various cancers. However, there have been no reports on its significance in hepatocellular carcinoma. The present study aimed to evaluate the association of the preoperative s-CK levels with clinicopathologic features and their prognostic impact on survival in patients with hepatocellular carcinoma. This retrospective study included 163 patients with hepatocellular carcinoma (127 male and 36 female patients; median age, 69 years) who underwent radical liver resection between January 2004 and December 2021. A cutoff preoperative s-CK level of 91 U/l determined by receiver operating characteristic curve analysis was used to evaluate the significance of s-CK in predicting overall and recurrence-free survival. In addition, the prognostic impact of s-CK was evaluated using univariate and multivariate analysis. s-CK level was not associated with clinicopathologic factors. Overall survival and recurrence-free survival of the low s-CK group were significantly worse compared with the high s-CK group (P=0.043 and P=0.029, respectively). By multivariate analysis, low s-CK was an independent risk factor for poor overall survival and recurrence-free survival (P=0.019 and P=0.014, respectively). This trend was the same for male patients, but no significant difference was observed for female patients. Low preoperative s-CK level might be a poor prognostic biomarker in patients with hepatocellular carcinoma. [ABSTRACT FROM AUTHOR]

Published
2024
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22. Feasibility of totally laparoscopic hemi-hepatectomies for liver tumor, with consideration of correspondence for difficult cases

Author

Otsuka, Yuichiro, primary, Ito, Yuko, additional, Matsumoto, Yu, additional, Kimura, Kazutaka, additional, Kajiwara, Yoji, additional, Okubo, Kazunori, additional, Tsuchiya, Masaru, additional, Okada, Rei, additional, Ishii, Jun, additional, Maeda, Tetsuya, additional, Funahashi, Kimihiko, additional, and Kaneko, Hironori, additional

Published
2021
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24. Laparoscopic Suture Rectopexy for Treatment of Refractory Full-Thickness Rectal Prolapse in 5 Patients Aged 90-100 Years

Author

Funahashi, Kimihiko, Kurihara, Akiharu, Ushigome, Mitsunori, Kagami, Satoru, Suzuki, Takayuki, Koda, Takamaru, Kimura, Kazutaka, Koike Junichi, Shiokawa, Hiroyuki, Imamura, Shigeki, Miura, Yasuyuki, and Kaneko, Tomoaki

Subjects
laparoscopic suture rectopexy, refractory full-thickness rectal prolapse, very elderly
Abstract

Case Report, Full-thickness rectal prolapse (FTRP) is common among elderly adults and greatly impairs quality of life. We report successful use of laparoscopic suture rectopexy to treat FTRP in 5 patients aged 90-100 years. The median age of patients was 92 years (range, 90-100 years). Three of the 5 patients had recurrent FTRP that was previously managed by a transperineal procedure. All patients had massive protrusion of the rectal wall (range 50-150 mm), and FTRP greatly adversely affected quality of life. No severe comorbidities were noted in any patient preoperatively. All patients had an American Society of Anesthesiologists physical status classification of II. Laparoscopic suture rectopexy for all patients was selected after consultation with anesthesiologists. Although there were no deaths, medical complications were observed in 3 patients: 2 developed mild heart failure (Clavien-Dindo classification, grade I) and one had AU20aspiration pneumonitis (Clavien-Dindo classification, grade III). There were no complications associated with laparoscopic suture rectopexy. All patients were able to return home after surgery. Our experience suggests that laparoscopic suture rectopexy without resection is beneficial for selected patients older than 90 years who are active and in good general health. However, when treating very elderly patients, cautious evaluation of operative risks and careful perioperative management are required in order to avoid surgical complications.

Published
2017

33. Usefulness of Transrectal Ultrasonography for a Patient with Coexisting Rectal-Anal Varices and Internal Hemorrhoids

Author

Kurihara, Natsuko, primary, Funahashi, Kimihiko, additional, Kimura, Kazutaka, additional, Kurihara, Akiharu, additional, Koike, Junichi, additional, Shiokawa, Hiroyuki, additional, Ushigome, Mitsunori, additional, Kaneko, Tomoaki, additional, Kagami, Satoru, additional, Koda, Takamaru, additional, Goto, Mayu, additional, and Nagashima, Yasuo, additional

Published
2018
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47. Development of a 10 Kg-class Micro Satellite for the Observation of Sprites and Atmospheric Lightning Events(WSANE2006)

Author

Yoshida, Kazuya, Takahashi, Yukihiro, Nakanishi, Hiroki, Shoji, Yasuhiro, Horichi, Takafumi, Kimura, Kazutaka, Ueda, Shinya, Hayashi, Tomonao, Yokoyama, Koji, Hosokawa, Shigeru, and Masumoto, Yoshinari

Abstract

Lightning discharges are full of mystery although they are frequently observed atmospheric luminous phenomena. In these 20 years, unidentified phenomena related to lightning discharges have been discovered. One is 'Transient Luminous Event (TLS)', which is a huge luminous phenomenon above thunderclouds. Another is 'Terrestrial Gamma-ray Flash (TGF)', which seems generated by lightning discharges. Many observations and studies have revealed the details of the phenomena until today, but their structures and mechanisms have not been fully understood yet. To investigate the structure of TLEs and the generation mechanism of TGFs, an observation satellite named Sprite-Sat is developed by a joint team of Tohoku University and Chiba Institute of Technology, Japan. The satellite is designed in the shape of a 30cm cube in launching configuration, and weighs no more than 30kg. The function is specialized for the observation of TLEs and TGFs. The launching date of the satellite is targeted in 2008. The satellite will contribute a lot for the science of Earth's atmospheric luminous events including gamma-ray flushes.

Published
2006

48. Comparison of the clinical significance of single cuff-based arterial stiffness parameters with that of the commonly used parameters.

Author

Komatsu, Shunsuke, Tomiyama, Hirofumi, Kimura, Kazutaka, Matsumoto, Chisa, Shiina, Kazuki, and Yamashina, Akira

Abstract

Background We examined the following: (1) whether the new simple markers related to the arterial stiffness/central hemodynamics [i.e. arterial pressure-volume index (API) and arterial velocity pulse index (AVI)] are clinically interchangeable with the commonly used markers [brachial-ankle pulse wave velocity (baPWV) and radial augmentation index (rAI)]; (2) whether the new simple markers reflect vascular damage as reliably as the commonly used markers; (3) which cardiovascular risk factors are reflected by these new simple markers. Methods API, AVI, baPWV, and rAI were measured simultaneously in consecutive patients admitted for the management of cardiovascular disease and/or cardiovascular risk factors ( n = 322). Results The API was correlated with the baPWV ( R = 0.492, p < 0.001) and the AVI correlated with the rAI ( R = 0.462, p < 0.001). The API, AVI, baPWV, and rAI were higher in the patients admitted for coronary angiography (CAG group: n = 152) than in those admitted for reasons other than coronary angiography (nonCAG group: n = 170). After adjustments for confounding factors, only the AVI was found to be higher in the CAG group than in the nonCAG group. Multivariate linear regression analysis revealed that age and the systolic blood pressure were independently associated with the API and AVI after adjustments. Conclusion In patients with cardiovascular diseases or cardiovascular risk factors, the new simple markers and the commonly used markers are not interchangeable for assessing vascular damage and/or cardiovascular risk. Further study is proposed to examine whether AVI is higher in subjects with cardiovascular disease than in those without a history of cardiovascular disease. Similar to the case for the commonly used markers, age and the blood pressure significantly influenced both the new markers; therefore, age and the blood pressure need to be taken into account while interpreting the changes in these new simple markers. [ABSTRACT FROM AUTHOR]

Published
2017
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