Saving fourth generation and baryon number by living long

Recent studies of precision electroweak observables have led to the conclusion that a fourth generation is highly constrained. However, we point out that a long-lived fourth generation can reopen a large portion of the parameter space. In addition, it preserves baryon and lepton asymmetries against sphaleron erasure even if B−L=0. It opens up the possibility of exact B−L symmetry and hence Dirac neutrinos. The fourth generation can be observed at the LHC with unique signatures of long-lived particles in the near future.     

Lattice Dynamical Calculations of Trans and Cis Polyacetylene

Lattice dynamical calculations of the lattice modes for both trans and cis polyacetylene were performed. Using rigid body approximation for the chain we obtained all 8 lattice frequencies and modes of motion for both trans and cis polyacetylene. The frequencies concerned with Raman active lattice modes are presented for the first time. We also performed far infrared transmission measurements of undoped trans and cis polyacetylene and confirmed the results obtained by Bechtold et al. Comparison of the lattice frequencies obtained by lattice dynamical calculations with the results obtained by far infrared measurement and inelastic neutron scattering is discussed.     

Direct search coding algorithm with reduction in computing time by simultaneous selection rule

An optimized encoding algorithm is required to produce high-quality computer-generated holograms (CGHs). For such a purpose, I have proposed that the use of the direct search algorithm (DSA) is effective for encoding the amplitude and phase in the Lohmann-type CGH. However, it takes much computation time to obtain an optimum solution by the DSA. To solve this problem, I have newly found that the simultaneous direct search algorithm (SDSA) is greatly effective for shortening the computation time for encoding the Lohmann-type CGH. As a result, the evaluation value of the reconstructed image for the SDSA is the same as that of 0.992 for the DSA. The computation time for the SDSA is drastically shortened from 3575 to 55 s for the DSA.     

Enhancement of stability and accuracy of the moving particle semi-implicit method

As a Lagrangian gridless particle method, the MPS (Moving Particle Semi-implicit) method has been proven useful in a wide range of engineering applications. Up to now, most of MPS applications have been limited to problems with compressive stress states. This paper investigates the performance and stability of MPS method in simulation of more general hydrodynamic problems, including those characterized by tensile stresses or by changes in the stress states. It is shown that MPS-based simulations are prone to become destabilized in presence of attractive interparticle forces. This instability appears to be similar to the so-called tensile instability in SPH method. Two new modifications, namely, a modified Poisson Pressure Equation and a corrective matrix for pressure gradient model, are proposed to resolve this shortcoming. These two new modifications together with two previously proposed improvements are shown to stabilize and enhance the performance of MPS method.     

Energy structure of Er-2O center in GaAs:Er,O studied by high magnetic field photoluminescence measurement

We perform photoluminescence measurement of GaAs:Er,O under a pulsed magnetic field up to 60 T and succeed to obtain the magnetic field dependence of three main photoluminescence peaks. We also estimate the energy splitting of states ⁴I_15/2 and ⁴I_13/2 using the crystal field theory. Theoretically calculated energy differences between the lowest state of J= and the lowest three states of J= are in good agreement with experimentally obtained energy of three main PL peaks. We discuss the local configuration around the luminescent Er-2O center. By using parameters in the crystal field calculation, our analysis suggest that not only O²⁻ sites but also As³⁻ sites adjacent to Er³⁺ ion are displaced from their original lattice positions.