Search

Quantitative microstructural analysis was performed on Si3N4materials doped with 5 wt% Y2O3and 5 wt% Sc2O3as sintering aids. Two different processing routes were utilized to achieve complete densification : (i) gas-pressure sintering of Si3N4-starting powders (SSN) and (ii) post-sintering of reaction-bonded Si3N4(SRBSN). Apart from quantitative evaluation of grain diameter and aspect ratio of the matrix grains, the fracture toughness was determined. While the two Y2O3-doped materials (SSN, SRBSN) showed identical KIC-values, a large discrepancy in fracture toughness was found for the Sc2O3-doped Si3N4(ΔKIC= 5 MPa√m). SEM crack propagation studies and additional TEM interface characterization showed no signifïcant difference between these materials. Quantitative microstructure analysis, however, revealed a pronounced variation in grain diameter and aspect ratio after thermal treatment. A correlation between interface chemistry and both resulting microstructure and fracture resistance is discussed.

Abstract: The pressure dependence of the Lamb-Mössbauer factor of the spin crossover compound [Fe(2-pic-ND2)3]Cl2·EtOD(2-pic-ND2=2-picolylamine, deuterated at the−NH2 group) has been measured at pressures up to 1500 bar and at three temperatures (115.7, 146.7, 185.6 K) around the transition temperatureT t=135 K. The temperature dependence of the unit cell volume has been determined by X-ray diffraction. In the transition region (T=146.7 K), the pressure dependence of thef-factor shows an anomalous increase as compared to the dependence below and above the transition. The behaviour off(p, T), its anomaly and absolute value, can be consistently explained within a theoretical model which treats the compound as an isotropic elastic medium. The Poisson ratio of σ=0.4, the bulk modulusK (185.6 K)=1.26·1010 Nm−2, and the Grüneisen constant γG=3.1 were determined.

Not Available

Six healthy male volunteers, aged 21 to 31 years, participated in an 81-day study of the effect of dietary nitrogen level and the pattern of dietary amino acids on serum amino acids. Ten different formula diets were consumed, nitrogen being supplied from mixtures of synthetic l-amino acids. Results indicated that although serum amino acids are altered within 3 days after a change in diet, they do not reflect the particular amino acid pattern consumed. Variations in levels of serum amino acids were evident when the total amount of dietary nitrogen was shifted. When dietary nitrogen was lower, there were increases in nonessential amino acids, especially alanine, and decreases in essential amino acids, mainly those with branched chains.

Error-free demultiplexing of 40 4;Gbit/s channels out of a 160 4;Gbit/s optical time-division signal is demonstrated using four-wave mixing in a semiconductor optical amplifier.