流体动压轴承主轴系统的动态特性实验研究

选用螺旋槽轴承代替球轴承 ,建立了螺旋槽轴承主轴系统模拟试验台 ,研究了螺旋槽轴承主轴系统的动态特性 ,并考察了载荷、速度、轴承间隙以及润滑剂等对其动态特性的影响 .结果表明 :随着转速提高 ,螺旋槽轴承主轴系统的径向和轴向不可重复误差 ( N RRO)均减小 ;载荷对主轴的径向动态特性影响很小 ,但对其轴向动态特性影响较大 ,随着载荷增大 ,轴向 N RRO逐渐减小 ;主轴的径向和轴向 N RRO均随轴向间隙减小而减小 ;随着润滑剂粘度增大 ,主轴径向 NRRO逐渐减小 ,而轴向 NRRO受润滑剂的影响不明显 ;润滑剂粘度越大 ,主轴所消耗的功率越大     

Real figure of two-dimensional spin-echo NMR spectra for a homonuclear two-spin system in rotating solids

Two-dimensional (2D) spin-echo NMR experiments have been carried out on polycrystalline [2,3-¹³C₂]-alanine under magic-angle sample spinning (MAS) conditions, so that two unusual resonance lines emerged along the F₁ axis (Kuwahara, D., Nakai, T., Ashida, J., and Miyajima, S., 1999, Chem. Phys. Lett., 305, 35). To examine the spectral structure observed in the F₁ direction more closely the 2D NMR experiment was undertaken using a sufficiently small t_l increment, yielding many more resonance lines on a spectrum sliced along the F₁ axis. The line distribution had a very unique and interesting structure. To elucidate the line positions theoretically, the signal for the 2D spin-echo experiment performed with any t₁ increment was calculated analytically for a homonuclear two-spin-1/2 system undergoing MAS. Virtually six resonance lines (exactly 12 resonance lines) occurred on a spectrum sliced along the F₁ axis. In addition, it was demonstrated that the intensities of some resonance lines were largely dependent on the dipolar interaction.     

Influences of chemical modifications on the mechanical strength of cellulose beads

Spherical cellulose beads having narrow particle-size distribution were prepared by the coagulation/regeneration method for small viscose droplets formed by centrifugal force in an acid bath. The influences of chemical modifications on mechanical strengths such as the hydraulic property and compressive strength were investigated, together with the effects on crystallinity, particle size and degree of swelling. Cross-linking with epichlorohydrin and substitution of hydroxyl groups in cellulose with diethylaminoethyl, carboxymethyl and cyanoethyl groups were studied. No remarkable differences were found in X-ray diffraction patterns for the cellulose beads after the chemical modification. The substitution promoted swelling of the beads and decreased the mechanical strength, probably by scission of intermolecular and/or intramolecular hydrogen bonds in cellulose. However, the cross-linking retarded the cellulose beads from swelling effectively. The beads were made significantly ha rder by the substitution, and this hardening effect competed with the softening effect of the swelling. Moreover, it was suggested that the simple compression test was useful for the prediction of the hydraulic property of the cellulose beads in the column operation. 0969--0239 © 1998 Blackie Academic & Professional