Development of Spherical Ultrasonic Motor for Critical Environment

In recent years, due to advances in science technology, space satellites have made progress. So, the presence of space debris has become problem in the world because they may collide each other. In our study, we have developed Spherical Ultrasonic Motor (SUSM) for space use with 3 DOF to drive the satellite thruster and resolve it. We aim that the satellites enter the atmosphere when the satellites reached the end of life, and SUSM controls thrusters when they inject for the directional control. We have made experiments of measuring torque, durability and lifetime. It shows that the torque and lifetime meets target value. But durability does not meet target value. To resolve it, we have applied stator lining materials and shifted frequency with 0.4kHz from resonant frequency and we have shown that it meets durability required specifications

Lattice study of meson correlators in the epsilon-regime of two-flavor QCD

We calculate mesonic two-point functions in the epsilon-regime of two-flavor QCD on the lattice with exact chiral symmetry. We use gauge configurations of size 16^3 32 at the lattice spacing a \sim 0.11 fm generated with dynamical overlap fermions. The sea quark mass is fixed at \sim 3 MeV and the valence quark mass is varied in the range 1-4 MeV, both of which are in the epsilon-regime. We find a good consistency with the expectations from the next-to-leading order calculation in the epsilon-expansion of (partially quenched) chiral perturbation theory. From a fit we obtain the pion decay constant F=87.3(5.6) MeV and the chiral condensate Sigma^{MS}=[239.8(4.0) MeV ]^3 up to next-to-next-to-leading order contributions.Comment: 20 pages, 12 figures, final version to appear in PR

Determination of the chiral condensate from 2+1-flavor lattice QCD

We perform a precise calculation of the chiral condensate in QCD using lattice QCD with 2+1 flavors of dynamical overlap quarks. Up and down quark masses cover a range between 3 and 100 MeV on a 16^3x48 lattice at a lattice spacing around 0.11 fm. At the lightest sea quark mass, the finite volume system on the lattice is in the epsilon-regime. By matching the low-lying eigenvalue spectrum of the Dirac operator with the prediction of chiral perturbation theory at the next-to-leading order, we determine the chiral condensate in 2+1-flavor QCD with strange quark mass fixed at its physical value as Sigma (MS-bar at 2 GeV) = [242(04)(^+19_-18}) MeV}]^3, where the errors are statistical and systematic, respectively.Comment: 4 pages, 3 figures, errors in table 1 and fig.3 corrected. Published in PR

Strong coupling constant from vacuum polarization functions in three-flavor lattice QCD with dynamical overlap fermions

We determine the strong coupling constant $\alpha_s$ from a lattice calculation of vacuum polarization functions (VPF) in three-flavor QCD with dynamical overlap fermions. Fitting lattice data of VPF to the continuum perturbative formula including the operator product expansion, we extract the QCD scale parameter $\Lambda_{\overline{MS}}^{(3)}$. At the $Z$ boson mass scale, we obtain $\alpha_s^{(5)}(M_Z)=0.1181(3)(^{+14}_{-12})$, where the first error is statistical and the second is our estimate of various systematic uncertainties.Comment: 15 pages, 7 figures, references updated. After correction of error in code, final value is changed, see Erratum Phys.Rev.D89,099903 (2014