高强耐磨Cu—Ni—Sn合金的研究

研究了多种成分的Cu-Ni-Sn-X合金350℃下时效3h的力学性能。结果表明：加入微量的Fe和Mn后,合金既有较高的强度和硬度,又有比较好的塑性。X射线衍射分析表明CuNiSn系合金时效会析出γ相和Ni3Sn相,γ相使合金的强度大大增加,但Ni3Sn相会使合金的塑性显著降低。CuNiSn系合金的强化主要来源于固溶强化、加工硬化和Spinodal析出强化。     

The microstructural details of β-Sn precipitation in a 5Sn-95Pb solder alloy

Solders of Pb-rich compositions, such as 5Sn-95Pb, are commonly used in electronic packaging applications, and this demanding use necessitates that the microstructure-property-processing relationships of the solder be understood fully. In this study, the microstructure of 5Sn-95Pb solder was characterized using a variety of metallographic techniques. The effect of cooling rate on the precipitation of β-Sn from supersaturated α-Pb was determined. On slow cooling, β-Sn precipitates discontinuously with resultant β-Sn lamella alternating with the α-Pb. Upon rapid cooling, the β-Sn precipitates with a nominally homogeneous distribution. These discrete precipitates were found to have a platelike shape with a (111)_Pb habit plane and an orientation relationship of (111)_Pb‖(010)_Sn and [011]_Pb‖ [001]_Sn. Regions of the β-Sn precipitates that curved away from this habit plane formed ledges. Upon heating, the precipitates were found to dissolvevia a ledge mechanism. Prolonged aging of both the fast and slow cooled 5Sn-95Pb resulted in a coarsening of the β-Sn precipitates with a resultant decrease in strength. Furthermore, the strength of the aged alloy was observed to be independent of cooling rate. D.R. FREAR, formerly Graduate Research Assistant, Lawrence Berkeley Laboratory     

Hydrophobicity and flexibility of alpha A- and alpha B-crystallin are different

Since the discovery that the lens protein alpha-crystallin is also found in non-lenticular tissues and can function as a chaperone, relatively little attention has been paid to differences in properties between alpha A- and alpha B-crystallin, which form mixed aggregates in the lens but have so far never been found together in other tissues. In this study hydrophobicity and flexibility, properties that are thought to be relevant for chaperone function, are compared for alpha A- and alpha B-crystallin. Hydrophobicity was monitored from sodium dodecylsulphate polyacrylamide gel electrophoresis in the absence and presence of (methyl-substituted) ureas. Flexibilities were calculated from primary structures. Based on literature data also some other properties are compared. The results indicate significant difference in hydrophobicity profile, flexibility of the terminal parts and stability of alpha A- and alpha B-crystallin.     

G-Protein-dependent facilitation of neuronal alpha1A, alpha1B, and alpha1E Ca channels

Modulation of neuronal voltage-gated Ca channels has important implications for synaptic function. To investigate the mechanisms of Ca channel modulation, we compared the G-protein-dependent facilitation of three neuronal Ca channels. alpha1A, alpha1B, or alpha1E subunits were transiently coexpressed with alpha2-deltab and beta3 subunits in HEK293 cells, and whole-cell currents were recorded. After intracellular dialysis with GTPgammaS, strongly depolarized conditioning pulses facilitated currents mediated by each Ca channel type. The magnitude of facilitation depended on current density, with low-density currents being most strongly facilitated and high-density currents often lacking facilitation. Facilitating depolarizations speeded channel activation approximately 1.7-fold for alpha1A and alpha1B and increased current amplitudes by the same proportion, demonstrating equivalent facilitation of G-protein-inhibited alpha1A and alpha1B channels. Inactivation typically obscured facilitation of alpha1E current amplitudes, but the activation kinetics of alpha1E currents showed consistent and pronounced G-protein-dependent facilitation. The onset and decay of facilitation had the same kinetics for alpha1A, alpha1B, and alpha1E, suggesting that Gbeta gamma dimers dissociate from and reassociate with these Ca channels at very similar rates. To investigate the structural basis for N-type Ca channel modulation, we expressed a mutant of alpha1B missing large segments of the II-III loop and C terminus. This deletion mutant exhibited undiminished G-protein-dependent facilitation, demonstrating that a Gbeta gamma interaction site recently identified within the C terminus of alpha1E is not required for modulation of alpha1B.