Catalytic Hydrogenation of the Sweet Principles of Stevia rebaudiana,Rebaudioside B,Rebaudioside C,and Rebaudioside D and Sensory Evaluation of Their Reduced Derivatives

Catalytic hydrogenation of rebaudioside B, rebaudioside C, and rebaudioside D; the three ent-kaurane diterpene glycosides isolated from Stevia rebaudiana was carried out using Pd(OH)₂. Reduction of steviol glycosides was performed using straightforward synthetic chemistry with the catalyst Pd(OH)₂ and structures of the corresponding dihydro derivatives were characterized on the basis of 1D and 2D nuclear magnetic resonance (NMR) spectral data indicating that all are novel compounds being reported for the first time. Also, the taste properties of all reduced compounds were evaluated against their corresponding original steviol glycosides and sucrose.     

Zinc interstitial as a universal microscopic origin for the electrical degradation of ZnO-based varistors under the combined DC and temperature condition

The electrical degradation of four different commercial ZnO-based varistors under the combined DC bias and high temperature condition was investigated with XRD, SEM, I–V, impulse current measurement, and dielectric spectroscopy, respectively. Contrary to the negligible structural changes, the electrical properties vary significantly after the degradation from sample to sample. Those deviations could not be completely ascribed to the differences in fabrication, but instead be consistently explained in terms of the intrinsic defect structure of ZnO ceramics. With a detailed analysis of their dielectric spectra in broad temperature and frequency ranges, it was found that zinc interstitial is the main intrinsic defect species responsible for the observed electrical degradation and its density could be used as a “universal” microscopic parameter to characterize the macroscopic electrical degradation. In addition, depending on the conduction mechanism, the role taken by Zn_i also differs correspondingly.