Search NASA⌕ Search

Engineering topics

Li, Z.

Publications and source records attributed to Li, Z..

94 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Thermal expansion of the cubic (3C) polytype of SiC

Thermal expansion of the cubic beta or (3C) polytype of SiC was measured from 20 to 1000 C by the X-ray-diffraction technique. Over that temperature range, the coefficient of thermal expansion can be expressed by a second-order polynomial. It increases continuously from about 3.2 x 10 to the -6th/C at room temperature to 5.1 x 10 to the -6th/C at 1000 C, with an average value of 4.45 x 10 to the -6th/C between room temperature and 1000 C. This trend is compared with other published results and is discussed in terms of structural contributions to the thermal expansion.

Li, Z.↗
NASA NTRS1986

Thermal expansion of the hexagonal (4H) polytype of SiC

The principal axial coefficients of thermal expansion, alpha(11) and alpha(33), of the (4H) polytype of hexagonal alpha SiC have been determined by X-ray diffraction measurements in the temperature range 20-1000 C. Alpha(11) and alpha(33), derived from the lattice parameter measurements, were expressed as the second-order polynomials in temperature. Alpha(11) was found to be larger than alpha(33) over the entire temperature range, with a thermal expansion anisotropy factor A increasing from 0.04 at room temperature to 0.11 at 1000 C. The thermal expansion results for the (4H) structure were compared with previously published results for the cubic (3C) and the hexagonal (6H) SiC polytypes.

Li, Z.↗
NASA NTRS1986

Conditioned invariant subspaces, disturbance decoupling and solutions of rational matrix equations

Conditioned invariant subspaces are introduced both in terms of output injection and in terms of state estimation. Various properties of these subspaces are explored and the problem of disturbance decoupling by output injection (OIP) is defined. It is then shown that OIP is equivalent to the problem of disturbance decoupled estimation as introduced in Willems (1982) and Willems and Commault (1980). Both solvability conditions and a description of solutions for a class of rational matrix equations of the form X(s)M(s) = Q(s) on several ways are given in state-space form. Finally, the problem of output stabilization with respect to a disturbance is briefly addressed.

Li, Z.↗