A Polyhedral Description of Kernels

postprin

Active optical clock based on four-level quantum system

Active optical clock, a new conception of atomic clock, has been proposed recently. In this report, we propose a scheme of active optical clock based on four-level quantum system. The final accuracy and stability of two-level quantum system are limited by second-order Doppler shift of thermal atomic beam. To three-level quantum system, they are mainly limited by light shift of pumping laser field. These limitations can be avoided effectively by applying the scheme proposed here. Rubidium atom four-level quantum system, as a typical example, is discussed in this paper. The population inversion between $6S_{1/2}$ and $5P_{3/2}$ states can be built up at a time scale of $10^{-6}$s. With the mechanism of active optical clock, in which the cavity mode linewidth is much wider than that of the laser gain profile, it can output a laser with quantum-limited linewidth narrower than 1 Hz in theory. An experimental configuration is designed to realize this active optical clock.Comment: 5 page

Effects of volumetric energy density on melting modes, printability, microstructures, and mechanical properties of laser powder bed fusion (L-PBF) printed pure nickel

Volumetric energy density (VED) is a fundamental criterion for the laser powder bed fusion (L-PBF) process, influencing various forming characteristics. This study employed L-PBF to print pure nickel (Ni) using different VEDs across various melting modes. The thermodynamics in the different melt pools, obtained microstructural features, and tensile properties were characterized and investigated. The results reveal a higher likelihood of keyhole mode melt pool formation than the conduction mode due to the peak temperature exceeding 3005 K. The larger size and slower cooling rate of the keyhole mode melt pool facilitate the formation of cellular subgrains in the central zone and the overall grain coarsening. Compared to the conduction mode, the microstructure in the keyhole mode exhibits a higher dislocation density and a distinct distribution pattern for each type of dislocation. Unlike the L-PBF of commercial Ni alloys, where alloy element distribution significantly impacts tensile performance, the tensile performance of L-PBF Ni is governed by the interaction between grain morphology, dislocation density and distribution

Mean-field theory of the spin-Peierls systems: Application to CuGeO3

A mean-field theory of the spin Peierls systems based on the two dimensional dimerized Heisenberg model is proposed by introducing an alternating bond order parameter. Improvements with respect to previous mean-field results are found in the one-dimensional limit for the ground state and the gap energies. In two dimensions, the analysis of the competition between antiferromagnetic long range order and the spin-Peierls ordering is given as a function of the coupling constants. We show that the lowest energy gap to be observed does not have a singlet-triplet character in agreement with the low temperature thermodynamic properties of CuGeO3.Comment: 3 Revtex pages. Submitted to Rapid Comm. Figures available upon reques

Heavy Quarkonium Potential Model and the 1P1{}^1P_1 State of Charmonium

A theoretical explanation of the observed splittings among the P~states of charmonium is given with the use of a nonsingular potential model for heavy quarkonia. We also show that the recently observed mass difference between the center of gravity of the ${}^3P_J$ states and the ${}^1P_1$ state of $c\bar{c}$ does not provide a direct test of the color hyperfine interaction in heavy quarkonia. Our theoretical value for the mass of the ${}^1P_1$ state is in agreement with the experimental result, and its E1 transition width is 341.8~keV. The mass of the $\eta_c'$ state is predicted to be 3622.3~MeV.Comment: 15 page REVTEX documen