Characteristics of a CW HF chemical-laser calculated from a simplified two-dimensional model

A two-dimensional simplified model of an HF chemical laser is introduced. Using an implicit finite difference scheme, the solution of two adjacent parallel streams with diffusion mixing and chemical reaction is generated. A contour of mixing and reaction boundary is obtained without presupposition. The distribution of the HF(v) concentrations, gas temperature and the optical small signal gain (alpha sub V, J) on the flowing plane (X, Y) are presented. Compared with the solution solved directly from a set of Navier-Stokes equations, the results of these two methods agree with each other qualitatively. The influences of the different velocity, temperature (T sub 0) and composition of the two streams on the small signal gain after the nozzle exit are investigated. It is interesting that for larger J with a fixed v, the peaks of alpha sub v-T sub 0 profiles move towards higher T sub 0. The computing method is simple and only a short computing time is needed.

Resonant frequencies and quality factors for optical equilateral triangle resonators calculated by FDTD technique and the Pade approximation

The mode wavelength and quality factor (Q-factor) for resonant modes in optical equilateral triangle resonators (ETR's) are calculated by the finite-difference time-domain (FDTD) technique and the Pade approximation, For an ETR with the side length of 3 mu m and the refractive index of 3.2, we get the mode wavelength interval of about 70 nm and the Q-factor of the fundamental mode over 10(3), The results show that the ETR is suitable to realize single-mode operation, and that the radiation loss in the corner regions of ETR is rather low, In addition, the numerical results of the mode wavelength agree very well with our analytical formula.

CALCULATED ELECTRONIC AND MAGNETIC-STRUCTURES OF THE NEW TERNARY RARE-EARTH IRON NITRIDE ND2FE17N3

The electronic and magnetic structures of Nd2Fe17 and Nd2Fe17N3 have been calculated using the first-principle, spin-polarized orthogonalized linear combination of atomic orbitals method. Comparative studies of the two materials reveal important effects of the nitrogen atoms (at 9e site) on the electronic and magnetic structures. Results are presented for the total density of states, site-projected partial density of states and the spin magnetic moments on four nonequivalent Fe sites. The highest magnetic moments are found to be located on the 6c site for Nd2Fe17 and on the 9d site for Nd2Fe17N3, in agreement with the neutron and Mossbauer experiments. The variation trends of the magnetic moments on different Fe sites are discussed in terms of the separation between Fe and N atoms. Compared with Nd2Fe17, an increase in the exchange splitting of the Fe d band is found in Nd2Fe17N3, which accounts for its higher Curie temperature as observed in experiments. The calculated results show that the nitrogen atoms are charge acceptors in these compounds.