An Analysis of \pi\pi-Scattering Phase Shift and Existence of \sigma(555) particle

In most of the Nambu:Jona-Lasinio(NJL)-type models, realizing the hidden chiral symmetry, the existence of a scalar particle \sigma is needed with a mass m_\sigma=2 m_q, as a partner of the Nambu-Goldstone boson \pi. However, the results of many analyses on \pi\pi phase-shift thus far made have been negative for its existence. In this paper we re-analyze the phase-shift, applying a new method, the interfering amplitude method, which treats the T-matrix directly and describes multi-resonances in conformity with the unitarity. As a result, the existence of \sigma has been strongly suggested from the behavior of the \pi\pi-->\pi\pi phase shift between the \pi\pi- and the KK- thresholds, with mass = 553.3 +- 0.5_{st} MeV and width= 242.6 +- 1.2_{st} MeV. The most crucial point in our analysis is the introduction of a negative background phase, possibly reflecting a ``repulsive core" in \pi\pi interactions. The properties of f_0(980) are also investigated from data including those over the KK threshold. Its mass is obtained as 993.2 +- 6.5_{st} +- 6.9_{sys} MeV. Its width is about a hundred MeV, although this depends largely on the treatment of the elasticity and the \pi\pi-->KK phase shift, both of which may have large experimental uncertainties.Comment: 22 pages, Latex with Prog. Theor. Phys. format PTPTEX.sty, 4 EPS figure

pi^0 pi^0 Scattering Amplitudes and Phase Shifts Obtained by the pi^- P Charge Exchange Process

The results of the analysis of the pi^0 pi^0 scattering amplitudes obtained with pi^- P charge exchange reaction, pi^- P --> pi^0 pi^0 n, data at 9 GeV/c are presented. The pi^0 pi^0 scattering amplitudes show clear f_0(1370) and f_2(1270) signals in the S and D waves, respectively. The pi^0 pi^0 scattering phase shifts have been obtained below Kbar K threshold and been analyzed by the Interfering Amplitude method with introduction of negative background phases. The results show a S wave resonance, sigma. Its Breit-Wigner parameters are in good agreement with those of our previous analysis on the pi^+ pi^- phase shift data.Comment: 4 pages, 4 figures. Proceedings of the int. conf. Hadron'99 at Beijing, Aug. 1999. Presented for the collaboration of A.M.Ma, K.Takamatsu, M.Y.Ishida, S.Ishida, T.Ishida, T. Tsuru and H. Shimizu, and the E135 collaboration. For our activities on sigma, visit http://amaterasu.kek.jp/sigm

Determination of Reactivity and Neutron Flux Using Modified Neural Network for HTGR

Nuclear kinetic calculations based on point kinetic model have been generally applied as the standard method for neutronics codes. As the central control rod (C-CR) withdrawal test has demonstrated in a prismatic core type high-temperature gas-cooled reactor (HTGR) named High Temperature Engineering Test Reactor (HTTR), the transient calculation of kinetic parameter, reactivity, and neutron fluxes, requires a new method to shorten calculation-process time. Development of neural network method was applied to point kinetic model as the necessity of real-time calculation that could work in parallel with the digital reactivity meter. The combination of Time Delayed Neural Network (TDNN) and Jordan Recurrent Neural Network (Jordan RNN) named TD-Jordan RNN was the result of the modeling approach. The application of TD-Jordan RNN with adequate learning, tested offline, determined results accurately even when signal inputs were noisy. Furthermore, the preprocessing for neural network input utilized noise reduction as one of the equations to transform two of twelve time-delayed inputs into power corrected inputs

THE EFFECTS OF A MARATHON RACE ON RUNNING ECONOMY AND LEG MUSCULAR STRENGTH AND POWER

INTRODUCTION: Previous studies have reported that running economy as well as leg muscular strength and power decrease after a marathon race(Nicol et al., 1991 ; Chevrolet et al. 1993). However, the relationship between the change in running economy and the change in muscular strength and power is still unclear. Therefore, the purpose of this study was to examine the effects of a marathon race on running economy, as well as leg muscular strength and power. Relationships among race performance, decrease in running economy and decrease in leg muscular strength and power were also investigated. METHODS: Thirteen healthy males performed treadmill running (200 m/min., 3 min.), isometric knee extension (3s), counter-movement-jump and 5-series-jumps 3-1 day(s) before (PRE) and immediately after (POST) participating in either the 1996 or 1997 "Tsukuba marathon race (42.195 km) ". RESULTS: 1) Mean race time of the marathon was 2 hours 57 minutes 39 seconds. Average running speed during the latter half of the race was significantly lower than the former half . 2) In comparison to PRE, oxygen consumption during treadmill running in POST increased significantly while maximal strength of isometric knee extension, jumping height of counter-movement-jump and jumping height of 5-series-jumps decreased significantly . 3) There were no relationships between percent change ((Post-Pre)/Pre x 100) in oxygen consumption during treadmill running and percent change in leg muscular strength and power. 4) There was a significant correlation between percent change ((Latter- Former)/Former x 100) in running speed during the race and percent change in jumping height of counter-movement-jump (r=0.541). However, no significant relationship was observed between percent change in running speed and percent change in running economy. CONCLUSION: Running a marathon race decreases both running economy and muscular strength and power but these seem to be caused by different mechanisms. The decrease in leg muscular strength and power during the marathon race seems have been an influence on the decrease in running speed during the latter half of the race. REFERENCES Chevrolet et al. (1993) Med. Sci. Sports Exerc. 25:501-507. Nicol et al. (1991) Scand. J. Sports Med. 1:195-204

Field Detection of Microcracks to Define the Nucleation Stage of Earthquake Occurrence

Main shocks of natural earthquakes are known to be accompanied by preshocks which evolve following the modified Ohmori’s law in average over many samples. Individual preshock activity, however, is far less systematic for predictive purposes. On the other hand, the microcracks in laboratory rock experiments are always preceded to final rupture. And, previous investigations of field acoustic emissions showed that the activity increases prominently before and after the main shock. But there is no detection of any phenomena to identify the nucleation stage. Here we show that a special underground electric field measurement could detect microcracks. Pulse-like variations were classified into three groups (A, B, C) by frequency. The B-type is suggested to define the nucleation period: activity increases sharply following the modified Omori’s law before the main shock and there is no activity afterward. The B-type is subgrouped into three types possibly corresponding to crack-rupture modes. The variations are supposed to be induced by crack occurrence through electrokinetic effects in the elastic-porous medium. The detection distance is suggested to be several orders larger than that of the acoustic emission due to the effective smallness of dissipation rate, and the waveform can be used to infer the rupture mode