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- 저자 : Nohmi, Motohiko (검색결과 6 건)
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Thresholds of Genotoxic and Non-Genotoxic Carcinogens
Takehiko Nohmi 한국독성학회 2018 Toxicological Research Vol.34 No.4
Exposure to chemical agents is an inevitable consequence of modern society; some of these agents are hazardous to human health. The effects of chemical carcinogens are of great concern in many countries, and international organizations, such as the World Health Organization, have established guidelines for the regulation of these chemicals. Carcinogens are currently categorized into two classes, genotoxic and non-genotoxic carcinogens, which are subject to different regulatory policies. Genotoxic carcinogens are chemicals that exert carcinogenicity via the induction of mutations. Owing to their DNA interaction properties, there is thought to be no safe exposure threshold or dose. Genotoxic carcinogens are regulated under the assumption that they pose a cancer risk for humans, even at very low doses. In contrast, non-genotoxic carcinogens, which induce cancer through mechanisms other than mutations, such as hormonal effects, cytotoxicity, cell proliferation, or epigenetic changes, are thought to have a safe exposure threshold or dose; thus, their use in society is permitted unless the exposure or intake level would exceed the threshold. Genotoxicity assays are an important method to distinguish the two classes of carcinogens. However, some carcinogens have negative results in in vitro bacterial mutation assays, but yield positive results in the in vivo transgenic rodent gene mutation assay. Non-DNA damage, such as spindle poison or topoisomerase inhibition, often leads to positive results in cytogenetic genotoxicity assays such as the chromosome aberration assay or the micronucleus assay. Therefore, mechanistic considerations of tumor induction, based on the results of the genotoxicity assays, are necessary to distinguish genotoxic and non-genotoxic carcinogens. In this review, the concept of threshold of toxicological concern is introduced and the potential risk from multiple exposures to low doses of genotoxic carcinogens is also discussed.
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Study of Cavitation Instabilities in Double-Suction Centrifugal Pump
Hatano, Shinya,Kang, Donghyuk,Kagawa, Shusaku,Nohmi, Motohiko,Yokota, Kazuhiko Korean Society for Fluid machinery 2014 International journal of fluid machinery and syste Vol.7 No.3
In double-suction centrifugal pumps, it was found that cavitation instabilities occur with vibration and a periodic chugging noise. The present study attempts to identify cavitation instabilities in the double-suction centrifugal pump by the experiment and Computational Fluid Dynamics (CFD). Cavitation instabilities in the tested pump were classified into three types of instabilities. The first one, in a range of cavitation number higher than breakdown cavitation number, is cavitation surge with a violent pressure oscillation. The second one, in a range of cavitation number higher than the cavitation number of cavitation surge, is considered to be rotating cavitation and causes the pressure oscillation due to the interaction of rotating cavitation with the impeller. Last one, in a range of cavitation number higher than the cavitation number of rotating cavitation, is considered to be a surge type instability.
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Study of Cavitation Instabilities in Double- Suction Centrifugal Pump
Shinya Hatano,Donghyuk Kang,Shusaku Kagawa,Motohiko Nohmi,Kazuhiko Yokota 한국유체기계학회 2014 International journal of fluid machinery and syste Vol.7 No.3
In double-suction centrifugal pumps, it was found that cavitation instabilities occur with vibration and a perio dic chugging noise. The present study attempts to identify cavitation instabilities in the double-suction centrifugal pump by the experiment and Computational Fluid Dynamics (CFD). Cavitation instabilities in the tested pump were classified into three types of instabilities. The first one, in a range of cavitation number higher than breakdown cavitation number, is cavitation surge with a violent pressure oscillation. The second one, in a range of cavitation number higher than the cavitation number of cavitation surge, is considered to be rotating cavitation and causes the pressure oscillation due to the interaction of rotating cavitation with the impeller. Last one, in a range of cavitation number higher than the cavitation number of rotating cavitation, is considered to be a surge type instability.
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Structural Analysis of STARS Satellite
Shunsuke Onishi,Tetsuo Yasaka,Masahiro Nohmi 한국항공우주학회 2008 한국항공우주학회 학술발표회 논문집 Vol.- No.-
This paper presents the structural analysis of STARS (Space Tethered Autonomous Robotic Satellite). STARS is a small satellite and will be launched in piggyback fashion by the Japanese launch vehicle H-2A in this fiscal year The STARS project is mainly carried out by Kagawa University, and Kyushu University is responsible for structural analysis. The satellite must satisfy the rocket's requirements in order to qualify for launch. This involves stiffness conditions and load conditions. The stiffness conditions require that the natural frequency of the satellite structure must be above a given frequency. In the load conditions. the following loads are considered: quasi-static, sinusoidal oscillation and random oscillation. It is necessary to analyze and perform experiments to satisfy these conditions. This paper presents the analysis of the natural frequencies, the quasi-static loads and the sinusoidal oscillations. The analysis uses the numerical simulation software ANSYS. Moreover, the paper explains the experiments performed: they are the surveying of the natural frequencies, the quasi-static loads, the sinusoidal oscillations and the random oscillations. The paper also compares the results of the analyses and the experiments in terms of the natural frequencies.
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Donghyuk Kang,Satoshi Yamazaki,Shusaku Kagawa,Byungjin An,Motohiko Nohmi,Kazuhiko Yokota 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.1
The present study investigated flow characteristics in the V-shaped region of the suction performance curve for a double-suction centrifugal pump based on the computational fluid dynamics (CFD). The V-shaped region in the time-averaged suction performance curve was simulated well. The CFD simulated the fluid oscillations due to cavitation surge and rotating cavitation well. The V-shaped region was observed in the absolute total pressure difference between the impeller inlet and outlet. The time histories showed that the cavity produced vorticity, resulting in an increase in a pressure loss, and a decrease in an impeller torque and an angular momentum flow rate. The time-averaged cavity volume, pressure loss between the impeller inlet and outlet, vorticity in the blade passage and impeller torque were examined. A Λ shape of a cavity volume curve caused a Λ shape of a vorticity curve, resulting in a Λ shape of a pressure loss curve and a V shape of an impeller torque curve. The Λ shape of the pressure loss curve and the V shape of the impeller torque curve caused the V shape of the suction performance curve.
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