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Search Results: 1 - 10 of 150073 matches for " H. Nakayama "
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Large-Eddy Simulation on turbulent flow and plume dispersion over a 2-dimensional hill
H. Nakayama ,H. Nagai
Advances in Science and Research (ASR) , 2010, DOI: 10.5194/asr-4-71-2010
Abstract: The dispersion analysis of airborne contaminants including radioactive substances from industrial or nuclear facilities is an important issue for air quality maintenance and safety assessment. In Japan, many nuclear power plants are located at complex coastal terrains. In these cases, terrain effects on the turbulent flow and plume dispersion should be investigated. In this study, we perform Large-Eddy Simulation (LES) of turbulent flow and plume dispersion over a 2-dimensional hill flow and investigate the characteristics of mean and fluctuating concentrations.
Analyzing $η'$ Photoproduction Data on the Proton at Energies of 1.5--2.3 GeV
K. Nakayama,H. Haberzettl
Physics , 2005,
Abstract: A combined analysis of the existing data on the reactions $\gamma p \to p \eta^\prime $ and $pp \to pp\eta^\prime $, based on a relativistic meson exchange model of hadronic interactions, is presented.
Analyzing eta' photoproduction data on the proton at energies of 1.5--2.3 GeV
K. Nakayama,H. Haberzettl
Physics , 2005, DOI: 10.1103/PhysRevC.73.045211
Abstract: The recent high-precision data for the reaction $\gamma p\to p\eta'$ at photon energies in the range 1.5--2.3 GeV obtained by the CLAS collaboration at the Jefferson Laboratory have been analyzed within an extended version of the photoproduction model developed previously by the authors based on a relativistic meson-exchange model of hadronic interactions [Phys. Rev. C \textbf{69}, 065212 (2004)]. The $\eta'$ photoproduction can be described quite well over the entire energy range of available data by considering $S_{11}$, $P_{11}$, $P_{13}$, and $D_{13}$ resonances, in addition to the $t$-channel mesonic currents. The observed angular distribution is due to the interference between the $t$-channel and the nucleon $s$- and $u$-channel resonance contributions. The $j=3/2$ resonances are required to reproduce some of the details of the measured angular distribution. For the resonances considered, our analysis yields mass values compatible with those advocated by the Particle Data Group. We emphasize, however, that cross-section data alone are unable to pin down the resonance parameters and it is shown that the beam and/or target asymmetries impose more stringent constraints on these parameter values. It is found that the nucleonic current is relatively small and that the $NN\eta^\prime$ coupling constant is not expected to be much larger than 2.
Interaction current in $p p \to p p γ$
K. Nakayama,H. Haberzettl
Physics , 2009, DOI: 10.1103/PhysRevC.80.051001
Abstract: The nucleon-nucleon bremsstrahlung reaction is investigated based on a fully gauge-invariant relativistic meson-exchange model approach. In order to account consistently for the complicated part of the interaction current (which at present is too demanding to be calculated explicitly), a generalized contact current is introduced following the approach of Haberzettl, Nakayama, and Krewald [Phys. Rev. C74, 045202 (2006)]. The contact interaction current is constructed phenomenologically such that the resulting full bremsstrahlung amplitude satisfies the generalized Ward-Takahashi identity. The formalism is applied to describe the high-precision proton-proton bremsstrahlung data at 190 MeV obtained at KVI [H. Huisman et al., Phys. Rev. C65, 031001(R) (2002)]. The present results show good agreement with the data, thus removing the longstanding discrepancy between the theoretical predictions and experimental data. The present investigation, therefore, points to the importance of properly taking into account the interaction current for this reaction.
Gauge-invariant formulation of $N N \to N N γ$
H. Haberzettl,K. Nakayama
Physics , 2010, DOI: 10.1103/PhysRevC.85.064001
Abstract: A complete, rigorous relativistic field-theory formulation of the nucleon-nucleon (NN) bremsstrahlung reaction is presented. The resulting amplitude is unitary as a matter of course and it is gauge invariant, i.e., it satisfies a generalized Ward-Takahashi identity. The novel feature of this approach is the consistent microscopic implementation of local gauge invariance across all interaction mechanisms of the hadronic systems, thus serving as a constraint for all subprocesses. The formalism is quite readily adapted to approximations and thus can be applied even in cases where the microscopic dynamical structure of the underlying interacting hadronic systems is either not known in detail or too complex to be treated in detail. We point out how the interaction currents resulting from the photon being attached to nucleon-nucleon-meson vertices can be treated by phenomenological four-point contact currents that preserve gauge invariance. In an advance application of the present formalism [K. Nakayama and H. Haberzettl, PRC 80, 051001(R) (2009)], such interaction currents were found to contribute significantly in explaining experimental data. In addition, we provide a scheme that permits the approximate treatment of current contributions resulting from pieces of the NN interaction that cannot be incorporated exactly. In each case, the approximation procedure ensures gauge invariance of the entire bremsstrahlung amplitude. We also discuss the necessary modifications when taking into account baryonic states other than the nucleon N; in detail, we consider the $Delta(1232)$ resonance by incorporating the couplings of the $NN$ to the $N\Delta$ and $\Delta\Delta$ systems, and the $\gamma N \to \Delta$ transitions. We apply the formalism to the 280-MeV bremsstrahlung data from TRIUMF [PRD 41, 2689 (1990)] incorporating $\gamma N\Delta$ transition currents and find good agreement with the data.
Consistent analysis of the reaction $γp \to p η^\prime$ and $pp \to ppη^\prime$
K. Nakayama,H. Haberzettl
Physics , 2004, DOI: 10.1103/PhysRevC.69.065212
Abstract: The production of $\eta'$ mesons in the reactions $\gamma p\to p\eta'$ and $pp\to pp\eta'$ is described consistently within a relativistic meson exchange model of hadronic interactions. The photoproduction can be described quite well over the entire energy range of available data by considering an $S_{11}$ and a $P_{11}$ resonance, in addition to the $t$-channel mesonic current. The observed angular distribution is due to the interference between the $t$-channel and the nucleon resonance $s$- and $u$-channel contributions. Our analysis yields positions close to 1650 MeV and 1870 MeV for the $S_{11}$ and $P_{11}$ resonances, respectively. We argue that, at present, identifying these states with the known $S_{11}(1650)$ resonance and the missing $P_{11}$ resonance predicted at 1880 MeV, respectively, would be premature. It is found that the nucleonic current is relatively small and that the $NN\eta^\prime$ coupling constant cannot be much larger than $g_{NN\eta^\prime}=3$. As for the $p p \to p p \eta^\prime$ reaction, different current contributions are constrained by a combined analysis of this and the photoproduction reaction. Difficulties to simultaneously account for the 47-MeV and 144-MeV angular distributions measured by the COSY-11 and DISTO collaborations, respectively, are addressed.
Large-eddy simulation of plume dispersion within regular arrays of cubic buildings
H. Nakayama, K. Jurcakova,H. Nagai
Advances in Science and Research (ASR) , 2011, DOI: 10.5194/asr-6-79-2011
Abstract: There is a potential problem that hazardous and flammable materials are accidentally or intentionally released within populated urban areas. For the assessment of human health hazard from toxic substances, the existence of high concentration peaks in a plume should be considered. For the safety analysis of flammable gas, certain critical threshold levels should be evaluated. Therefore, in such a situation, not only average levels but also instantaneous magnitudes of concentration should be accurately predicted. In this study, we perform Large-Eddy Simulation (LES) of plume dispersion within regular arrays of cubic buildings with large obstacle densities and investigate the influence of the building arrangement on the characteristics of mean and fluctuating concentrations.
Large-Eddy Simulation of plume dispersion within various actual urban areas
H. Nakayama, K. Jurcakova,H. Nagai
Advances in Science and Research (ASR) , 2013, DOI: 10.5194/asr-10-33-2013
Abstract: Plume dispersion of hazardous materials within urban area resulting from accidental or intentional releases is of great concern to public health. Many researchers have developed local-scale atmospheric dispersion models using building-resolving computational fluid dynamics. However, an important issue is encountered when determining a reasonable domain size of the computational model in order to capture concentration distribution patterns influenced by urban surface geometries. In this study, we carried out Large-Eddy Simulations (LES) of plume dispersion within various urban areas with a wide range of obstacle density and building height variability. The difference of centerline mean and r.m.s. concentration distributions among various complex urban surface geometries becomes small for downwind distances from the point source greater than 1.0 km. From these results, it can be concluded that a length of a computational model should be at least 1.0 km from a point source.
Detecting Incomplete Learners in a Blended Learning Environment Among Japanese University Students
Minoru Nakayama,H. Kanazawa,H. Yamamoto
International Journal of Emerging Technologies in Learning (iJET) , 2009, DOI: 10.3991/ijet.v4i1.659
Abstract: To examine the feasibility of identifying incomplete participants who had not eventually completed a course in a blended learning environment using current learning behavioral data, access log data of complete and incomplete participants were analyzed. There is a significant difference between the two sets, and the number of accesses correlates with the final test score. Discrimination analysis was conducted using several variables across the learning process, and the ratio of those taking part in online tests was significant. Discrimination performance improved in relation to the number of accesses. The estimation performance was determined for two disparate courses in order to detect incomplete participants.
Aproveitamento de um fosfato natural parcialmente solubilizado pelo sorgo sacarino em condi??es de casa de vegeta??o: I. Latossolo vermelho amarelo
Nakayama, L.H. I.;Malavolta, E.;
Anais da Escola Superior de Agricultura Luiz de Queiroz , 1983, DOI: 10.1590/S0071-12761983000200007
Abstract: the usefulness of a rock phosphat from araxá, mg, brasil, partially acidulated with sulfuric acid (faps) was studied, rock phosphate (fa), gafsa phosphate (fg), and simple superphosphate (sps) being used for comparison. there successive crops were employed in order to assess the residual value, both in presence an in the absence of liming. the analyses of data obtained allowed for the following conclusions to be drawn: the efficiency of faps in relation to that of sps decreased from the first to the third crop, reaching 70% as general ave rage; in the presence of liming, however, the efficiency did not decrease so much, 80-90% being obtained; fg gave results equivalent to those obtained with sps; liming decreased the relative efficiency of the rock phosphates, especially that of fa which fell from circa 50% to 40%; available p content in the soil was increased as consequence of varions treatments including faps plus lime; faps acted as a source of p, ca, and s; its performance in closer to that of sps than to that of the original fa.
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