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Search Results: 1 - 10 of 149964 matches for " H. Nakai "
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Substorm-associated large-scale magnetic field changes in the magnetotail: a prerequisite for "magnetotail deflation" events
H. Nakai,Y. Kamide
Annales Geophysicae (ANGEO) , 2003,
Abstract: An attempt is made to search for a critical condition in the lobe magnetic field to initiate large-scale magnetic field changes associated with substorm expansions. Using data from ISEE-1 for 1978, sudden decreases in the lobe magnetic field accompanied by magnetic field dipolarizations are identified. In this study, such events are designated as the magnetotail deflation. The magnetic field component parallel to the equatorial plane, BE , is normalized to a fixed geocentric distance, BEN , and is corrected for the compression effect of the solar wind dynamic pres-sure, BENC . It is shown that the BENC value just prior to a magnetotail deflation correlates well with the Dst index; BENC = 37.5 - 0.217 Dst0, where Dst0 denotes the Dst value corrected for the solar wind dynamic pressure. This regression function appears to delineate the upper limit of BENC values, when they are sorted by the Dst0 index. On the basis of this finding it is suggested that a prerequisite condition for magnetotail deflations must exist in the magnetosphere. Key words. Magnetospheric physics (magnetotail; current systems; storms and substorms)
Effects of Cooking Fuels on Acute Respiratory Infections in Children in Tanzania
James H. Kilabuko,Satoshi Nakai
International Journal of Environmental Research and Public Health , 2007, DOI: 10.3390/ijerph200704040003
Abstract: Biomass fuels, charcoal and kerosene are the most used cooking fuels in Tanzania. Biomass fuel use has been linked to Acute Respiratory Infections (ARI) in children. It is not clear whether the use of charcoal and kerosene has health advantage over biomass fuels. In this study, the effects of biomass fuels, charcoal/kerosene on ARI in children under five years old in Tanzania are quantified and compared based on data from Tanzania Demographic and Health survey conducted between 2004 and 2005. Approximately 85% and 15% of children were from biomass fuels and charcoal/kerosene using homes respectively. Average ARI prevalence was about 11%. The prevalence of ARI across various fuel types used for cooking did not vary much from the national prevalence. Odds ratio for ARI, adjusting for child’s sex, age and place of residence; mother’s education, mother’s age at child birth and household living standard, indicated that the effect of biomass fuels on ARI is the same as the effect of charcoal/kerosene (OR 1.01; 95% CI: 0.78-1.42). The findings suggest that to achieve meaningful reduction of ARI prevalence in Tanzania, a shift from the use of biomass fuels, charcoal and kerosene for cooking to clean fuels such as gas and electricity may be essential. Further studies, however, are needed for concrete policy recommendation.
Air Quality and Acute Respiratory Illness in Biomass Fuel using homes in Bagamoyo, Tanzania
James H. Kilabuko,Hidieki Matsuki,Satoshi Nakai
International Journal of Environmental Research and Public Health , 2007, DOI: 10.3390/ijerph2007010007
Abstract: Respiratory Diseases are public health concern worldwide. The diseases have been associated with air pollution especially indoor air pollution from biomass fuel burning in developing countries. However, researches on pollution levels and on association of respiratory diseases with biomass fuel pollution are limited. A study was therefore undertaken to characterize the levels of pollutants in biomass fuel using homes and examine the association between biomass fuel smoke exposure and Acute Respiratory Infection (ARI) disease in Nianjema village in Bagamoyo, Tanzania. Pollution was assessed by measuring PM10, NO2, and CO concentrations in kitchen, living room and outdoors. ARI prevalence was assessed by use of questionnaire which gathered health information for all family members under the study. Results showed that PM10, NO2, and CO concentrations were highest in the kitchen and lowest outdoors. Kitchen concentrations were highest in the kitchen located in the living room for all pollutants except CO. Family size didn’t have effect on the levels measured in kitchens. Overall ARI prevalence for cooks and children under age 5 making up the exposed group was 54.67% with odds ratio (OR) of 5.5; 95% CI 3.6 to 8.5 when compared with unexposed men and non-regular women cooks. Results of this study suggest an association between respiratory diseases and exposure to domestic biomass fuel smoke, but further studies with improved design are needed to confirm the association.
Evidence for s-wave superconductivity with antiferromagnetic fluctuations in filled skutterudite LaFe$_{4}$P$_{12}$: $^{139}$La and $^{31}$P-NMR studies
Y. Nakai,K. Ishida,D. Kikuchi,H. Sugawara,H. Sato
Physics , 2005, DOI: 10.1143/JPSJ.74.3370
Abstract: We have performed $^{139}$La,$^{31}$P-NMR studies on a filled skutterudite superconductor LaFe$_{4}$P$_{12}$ with a critical temperature $T_c=4.1$ K. In the normal state, the presence of antiferromagnetic (AFM) fluctuations at finite wave vectors is suggested from the relation between the nuclear spin-lattice relaxation rate $1/T_1$ and the Knight shift. In the superconducting (SC) state, the distinct coherence peak was observed just below $T_c$, and is easily suppressed by the applied field. An exponential decrease of $1/T_1$ was observed, suggestive of the isotropic superconducting gap with $2\Delta/k_{\rm B}T_c =3.8$. Besides, we observed the decrease of the Knight shift, indicative of the singlet-pair formation below $T_c$. These results are clear evidence that LaFe$_{4}$P$_{12}$ is a rare s-wave superconductor with significant AFM fluctuations.
The Apsidal Antialignment of the HD 82943 System
Ji Jianghui,H. Kinoshita,Liu Lin,Li Guangyu,H. Nakai
Physics , 2003, DOI: 10.1023/A:1026193724121
Abstract: We perform numerical simulations to explore the dynamical evolution of the HD 82943 planetary system. By simulating diverse planetary configurations, we find two mechanisms of stabilizing the system: the 2:1 mean motion resonance between the two planets can act as the first mechanism for all stable orbits. The second mechanism is a dynamical antialignment of the apsidal lines of the orbiting planets, which implies that the difference of the periastron longitudes $\theta_{3}$ librates about $180^{\circ}$ in the simulations. We also use a semi-analytical model to explain the numerical results for the system under study.
The Stability Analysis of the HD 82943 and HD 37124 Planetary Systems
Ji Jianghui,H. Kinoshita,Liu Lin,Li Guangyu,H. Nakai
Physics , 2002,
Abstract: We carry out numerical simulations to explore the dynamical evolution of the HD 82943 and HD 37124 planetary systems,which both have two Jupiter-like planets. By simulating various planetary configurations in the neighborhood of the fitting orbits, we find three mechanisms to maintain the stability of these systems: For HD 82943,we find that the 2:1 mean motion resonance can act as the first mechanism for all the stable orbits. The second mechanism is the alignment of the periastron of the two planets of HD 82943 system. In the paper,we show one case is simultaneously maintained by the two mechanisms. Additionally,we also use the corresponding analytical models successfully to explain the different numerical results for the system. The third mechanism is the Kozai resonance which takes place in the mutual highly orbits of HD 37124. In the simulations,we discover that the argument of periastron $\omega$ of the inner planet librates about $90^{\circ}$ or $270^{\circ}$ for the whole time span. The Kozai mechanism can explain the stable configuration of large eccentricity of the inner planet.
Mantle-derived xenoliths with hotspot type helium in Cenozoic alkali, basalt, northwestern Kyushu, Japan
H. Sumino,K. Nagao,K. Notsu,S. Nakai
Chinese Science Bulletin , 1998, DOI: 10.1007/BF02891587
Molecular gas observations and enhanced massive star formation efficiencies in M100
J. H. Knapen,J. E. Beckman,J. Cepa,N. Nakai
Physics , 1995,
Abstract: We present new J=1-0 12-CO observations along the northern spiral arm of the grand-design spiral galaxy M100 (NGC 4321), and study the distribution of molecular hydrogen as derived from these observations, comparing the new data with a set of data points on the southern arm published previously. We compare these measurements on both spiral arms and on the interarm regions with observations of the atomic and ionized hydrogen components. We determine massive star formation efficiency parameters, defined as the ratio of H alpha luminosity to total gas mass, along the arms and compare the values to those in the interarm regions adjacent to the arms. We find that these parameters in the spiral arms are on average a factor of 3 higher than outside the arms, a clear indication of triggering of the star formation in the spiral arms. We discuss possible mechanisms for this triggering, and conclude that a density wave system is probably responsible for it. We discuss several possible systematical effects in some detail, and infer that the conclusions on triggering are sound. We specifically discuss the possible effects of extinction in H alpha, or a non-standard CO to H_2 conversion factor (X), and find that our conclusions on the enhancement of the efficiencies in the arms are reinforced rather than weakened by these considerations. A simple star forming scheme involving threshold densities for gravitational collapse is discussed for NGC 4321, and comparison is made with M51. We find that the gas between the arms is generally stable against gravitational collapse whereas the gas in the arms is not, possibly leading to the observed arm-interarm differences in efficiency, but also note that these results, unlike the others obtained in this paper, do depend critically on the assumed value for the conversion factor.
LDA + Negative U Solves a Puzzle of too Large Calculated Magnetic Moment in Iron-based Superconductor LaFeAsO_{1-x}F_x
H. Nakamura,N. Hayashi,N. Nakai,M. Machida
Physics , 2008,
Abstract: A puzzle in the iron-based superconductor LaFeAsO_{1-x}F_x is that the magnetic moment obtained by first-principle electronic structure calculations is unexpectedly much larger than the experimentally observed one. For example, the calculated value is ~ 2.0 \mu_B in the mother compound, while it is ~ 0.3 \mu_B in experiments. We find that the puzzle is solved within the framework LDA + U by expanding the U value into a slightly negative range. We show U dependence of the obtained magnetic moment in both the undoped x=0.0 and doped x = 0.125. These results reveal that the magnetic moment is drastically reduced when entering to the slightly negative range of U. Moreover, the negative U well explains other measurement data, e.g., lattice constants and electronic DOS at the Fermi level. We discuss possible origins of the negative U in these compounds.
Effective Vector Meson Masses in a Cutoff Field Theory
K. Sakamoto,M. Nakai,H. Kouno,A. Hasegawa,M. Nakano
Physics , 1999, DOI: 10.1142/S0218301300000106
Abstract: Based on quantum hadrodynamics with a finite cutoff, the effective masses of vector mesons(\omega, \rho) in nuclear medium are calculated. We use a low-energy effective Lagrangian which is obtained by integrating high-energy quantum fluctuations. Although we use an artificial cutoff, the cutoff-dependence can be removed order by order. It is shown that there is a strong correlation between the effective \omega -meson mass and the effective nucleon mass at the normal density. It is also found that the effective \rho-meson mass m_\rho^* decreases as density increases. The rate of the decrease becomes smaller at high density. As a result, at the normal density, the m^*_\rho/m_\rho is 0.85 \sim 0.95.
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