Microstructure characterization of high-pressure induced texture in fully densified zirconium diboride ceramics

Fully dense oriented monolithic zirconium diboride (ZrB₂) ceramics with <0001> fiber texture were fabricated using high-pressure spark plasma sintering. The <0001> fiber texture is proposed to be triggered by grain rotation, as (0001) <$11\overline{2}0$> basal $⟨a⟩$ slip of ZrB₂ was activated during sintering. The high temperature, uniaxial high pressure, and uniform starting particles play a vital role in the texture formation of ZrB₂ ceramics. The result provides visible evidence for the occurrence of plastic deformation during high-pressure-assisted sintering.     

A Portmanteau Test for Smooth Transition Autoregressive Models

This article investigates a portmanteau test statistic for checking model adequacy of smooth transition autoregressive (STAR) models. The asymptotic distribution of residual autocorrelations and the least-squares estimators are also derived. Hence, the correct asymptotic standard errors for residual autocorrelations are also obtained facilitating model diagnostic checking. Through the graphical display of the simulation results concerning the size and power, for commonly used nominal sizes ($\le 0.1$), the portmanteau test appears to be more advantageous than the Lagrange multiplier tests in checking serial independence for the errors of STAR models.