The Nagoya cosmic-ray muon spectrometer 3, part 2: Track detector

The twelve wide gap spark chambers were utilized as the track detectors of the Nagoya cosmic-ray muon spectrometer not only to obtain the precise locations of particles, but also to get some information about the correspondences between segments of trajectories. The area of each chamber is 150 x 70 sq cm and the width of a gap is 5 cm. The gas used is He at the atmospheric pressure. Each three pairs of them are placed on both sides of the deflection magnet. All images of sparks for each event are projected through the mirror system and recorded by two cameras stereoscopically. The mean detection efficiency of each chamber is 95 + or - 2% and the spacial resolution (jitter and drift) obtained from the prototype-experiment is 0.12 mm. Maximum detectable momentum of the spectrometer is estimated at about 10 TeV/c taking into account these characteristics together with the effects of the energy loss and multiple Coulomb scattering of muons in the iron magnet

Selective production of metallic carbon nanotubes

In this report, we discuss whether the optimal electric field to promote the growth of armchair- type nanotubes (metallic character) evaluated using the previous Huckel-Poisson method can be applied at the tip of a nanotube in a realistic system. Setting the cross-section of a nanotube and the external field by the sheath, we estimate an effective area at the sheath edge. Since the electric charge distribution in a nanotube caused by the external electric field was determined in our previous study, we obtained the electric field distribution out of a nanotube by solving the Poisson equation and clarified the structure of the electric field lines. By determining the effective area, we show the optimal interval of the catalyst metal, which is necessary to selectively grow the metallic nanotubes. When nanotubes grow thickly during the initial stage of growth, a strong electric field cannot be applied to the tips of the tubes. As a tube grows and the tube length increases, we found that the optimal electric field decreased. To maintain the chemical activity at the tip, the sheath electric field must be decreased. We estimated the decreasing rate of the sheath field to the tube length.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France

Improvement of solar cycle prediction: Plateau of solar axial dipole moment

Aims. We report the small temporal variation of the axial dipole moment near the solar minimum and its application to the solar cycle prediction by the surface flux transport (SFT) model. Methods. We measure the axial dipole moment using the photospheric synoptic magnetogram observed by the Wilcox Solar Observatory (WSO), the ESA/NASA Solar and Heliospheric Observatory Michelson Doppler Imager (MDI), and the NASA Solar Dynamics Observatory Helioseismic and Magnetic Imager (HMI). We also use the surface flux transport model for the interpretation and prediction of the observed axial dipole moment. Results. We find that the observed axial dipole moment becomes approximately constant during the period of several years before each cycle minimum, which we call the axial dipole moment plateau. The cross-equatorial magnetic flux transport is found to be small during the period, although the significant number of sunspots are still emerging. The results indicates that the newly emerged magnetic flux does not contributes to the build up of the axial dipole moment near the end of each cycle. This is confirmed by showing that the time variation of the observed axial dipole moment agrees well with that predicted by the SFT model without introducing new emergence of magnetic flux. These results allows us to predict the axial dipole moment in Cycle 24/25 minimum using the SFT model without introducing new flux emergence. The predicted axial dipole moment of Cycle 24/25 minimum is 60--80 percent of Cycle 23/24 minimum, which suggests the amplitude of Cycle 25 even weaker than the current Cycle 24. Conclusions. The plateau of the solar axial dipole moment is an important feature for the longer prediction of the solar cycle based on the SFT model.Comment: 5 pages, 3 figures, accepted for publication in A&A Lette

Heat conduction of single-walled carbon nanotube isotope-superlattice structures: A molecular dynamics study

Heat conduction of single-walled carbon nanotubes (SWNTs) isotope-superlattice is investigated by means of classical molecular dynamics simulations. Superlattice structures were formed by alternately connecting SWNTs with different masses. On varying the superlattice period, the critical value with minimum effective thermal conductivity was identified, where dominant physics switches from zone-folding effect to thermal boundary resistance of lattice interface. The crossover mechanism is explained with the energy density spectra where zone-folding effects can be clearly observed. The results suggest that the critical superlattice period thickness depends on the mean free path distribution of diffusive-ballistic phonons. The reduction of the thermal conductivity with superlattice structures beats that of the one-dimensional alloy structure, though the minimum thermal conductivity is still slightly higher than the value obtained by two-dimensional random mixing of isotopes.Comment: 7 Pages, 5 figures, accepted to Phys. Rev.

Semiconductor-enriched single wall carbon nanotube networks applied to field effect transistors

Substantial progress on field effect transistors "FETs" consisting of semiconducting single wall carbon nanotubes "s-SWNTs" without detectable traces of metallic nanotubes and impurities is reported. Nearly perfect removal of metallic nanotubes is confirmed by optical absorption, Raman measurements, and electrical measurements. This outstanding result was made possible in particular by ultracentrifugation (150 000 g) of solutions prepared from SWNT powders using polyfluorene as an extracting agent in toluene. Such s-SWNTs processable solutions were applied to realize FET, embodying randomly or preferentially oriented nanotube networks prepared by spin coating or dielectrophoresis. Devices exhibit stable p-type semiconductor behavior in air with very promising characteristics. The on-off current ratio is 10^5, the on-current level is around 10 $\mu$A, and the estimated hole mobility is larger than 2 cm2 / V s

A novel type of proximity focusing RICH counter with multiple refractive index aerogel radiator

A proximity focusing ring imaging Cherenkov detector, with the radiator consisting of two or more aerogel layers of different refractive indices, has been tested in 1-4 GeV/c pion beams at KEK. Essentially, a multiple refractive index aerogel radiator allows for an increase in Cherenkov photon yield on account of the increase in overall radiator thickness, while avoiding the simultaneous degradation in single photon angular resolution associated with the increased uncertainty of the emission point. With the refractive index of consecutive layers suitably increasing in the downstream direction, one may achieve overlapping of the Cherenkov rings from a single charged particle. In the opposite case of decreasing refractive index, one may obtain well separated rings. In the former combination an approximately 40% increase in photon yield is accompanied with just a minor degradation in single photon angular resolution. The impact of this improvement on the pion/kaon separation at the upgraded Belle detector is discussed.Comment: submitted to Nucl. Instr. Meth.

Modelisation of transition and noble metal vicinal surfaces: energetics, vibrations and stability

The energetics of transition and noble metal (Rh, Pd, Cu) vicinal surfaces, i.e., surface energy, step energy, kink energy and electronic interactions between steps, is studied at 0K from electronic structure calculations in the tight-binding approximation using a {\it s, p} and {\it d} valence orbital basis set. Then, the surface phonon spectra of copper are investigated in the harmonic approximation with the help of a semi-empirical inter-atomic potential. This allows to derive the contribution of phonons at finite temperatures to the step free energy and to the interactions between steps. The last part is devoted to the stability of vicinal surfaces relative to faceting with special attention to the domain of orientations (100)-(111). Semi-empirical potentials are shown to be not realistic enough to give a reliable answer to this problem. The results derived from electronic structure calculations predict a variety of behaviors and, in particular, a possible faceting into two other vicinal orientations. Finally, temperature effects are discussed. Comparisons are made with other theoretical works and available experiments

Semi-conservative reduced speed of sound technique for low Mach number flows with large density variations

The reduced speed of sound technique (RSST) has been used for efficient simulation of low Mach number flows in solar and stellar convection zones. The basic RSST equations are hyperbolic, and are suitable for parallel computation by domain decomposition. The application of RSST is limited to cases where density perturbations are much smaller than the background density. In addition, non-conservative variables are required to be evolved using this method, which is not suitable in cases where discontinuities like shock waves co-exist in a single numerical domain. In this study, we suggest a new semi-conservative formulation of the RSST that can be applied to low Mach number flows with large density variations. We derive the wave speed of the original and newly suggested methods to clarify that these methods can reduce the speed of sound without affecting the entropy wave. The equations are implemented using the finite volume method. Several numerical tests are carried out to verify the suggested methods. The analysis and numerical results show that the original RSST is not applicable when mass density variations are large. In contrast, the newly suggested methods are found to be efficient in such cases. We also suggest variants of the RSST that conserve momentum in the machine precision. The newly suggested variants are formulated as semi-conservative equations, which reduce to the conservative form of the Euler equations when the speed of sound is not reduced. This property is advantageous when both high and low Mach number regions are included in the numerical domain. The newly suggested forms of RSST can be applied to a wider range of low Mach number flows.Comment: 12 pages, 10 figures, accepted for publication in Astronomy & Astrophysic

Fat transforms ascorbic acid from inhibiting to promoting acid-catalysed N-nitrosation

<b>Background</b>: The major potential site of acid nitrosation is the proximal stomach, an anatomical site prone to a rising incidence of metaplasia and adenocarcinoma. Nitrite, a pre-carcinogen present in saliva, can be converted to nitrosating species and N-nitroso compounds by acidification at low gastric pH in the presence of thiocyanate. <b>Aims</b>: To assess the effect of lipid and ascorbic acid on the nitrosative chemistry under conditions simulating the human proximal stomach. <b>Methods</b>: The nitrosative chemistry was modelled in vitro by measuring the nitrosation of four secondary amines under conditions simulating the proximal stomach. The N-nitrosamines formed were measured by gas chromatography–ion-trap tandem mass spectrometry, while nitric oxide and oxygen levels were measured amperometrically. <b>Results</b>: In absence of lipid, nitrosative stress was inhibited by ascorbic acid through conversion of nitrosating species to nitric oxide. Addition of ascorbic acid reduced the amount of N-nitrosodimethylamine formed by fivefold, N-nitrosomorpholine by .1000-fold, and totally prevented the formation of N-nitrosodiethylamine and N-nitrosopiperidine. In contrast, when 10% lipid was present, ascorbic acid increased the amount of Nnitrosodimethylamine, N-nitrosodiethylamine and N-nitrosopiperidine formed by approximately 8-, 60- and 140-fold, respectively, compared with absence of ascorbic acid. <b>Conclusion</b>: The presence of lipid converts ascorbic acid from inhibiting to promoting acid nitrosation. This may be explained by nitric oxide, formed by ascorbic acid in the aqueous phase, being able to regenerate nitrosating species by reacting with oxygen in the lipid phase