Formation of nanocrystalline phases during thermal decomposition of amorphous Ni-P alloys by isothermal annealing

The microstructure and the average grain size were investigated by x-ray diffraction and transmission electron microscopy for nanocrystalline (n) Ni-P alloys with 18, 19, and 22 at.% P. A detailed study of the nanocrystalline states obtained along different heat treatment routes has been performed: (1) a-->ni by isothermal annealing of the melt-quenched amorphous (a) Ni-P alloys; (2) ni-->nii by isothermal annealing of the nanocrystalline ni state; (3) ni-->nii by linear heating of the ni state. The heats evolved during the structural transformations were determined by differential scanning calorimetry. From these studies, a scheme of the structural transformations and their energetics was constructed, which also includes previous results on phases obtained by linear heating of the as-quenched amorphous state of the same alloys. Grain boundary energies also have been estimated. In some cases it was necessary to assume a variation of the specific grain boundary energy during the phase transformation to understand the enthalpy and microstructure changes during the different heat treatments.     

Quantification of adenovirus particles

A physical method for quantification of the adenovirus was tested. It implies a centrifugation of the clarified or chloroform- (or freon-) treated crude virus suspension (0.5 ml) in a gentle sucrose gradient, following the analysis in a sensitive UV flow photometer and calculation of virus mass. The result (micrograms/ml) is obtained after about 1 h. The sensitivity of detection at wavelength 254 nm, 278 nm and 226 nm was compared. Virus yield of several serotypes from monolayer cultures of FL-cells was determined in a range of < 0.1 to 7 micrograms/ml. The ratio of infectious to physically complete virus (about the 770S component), the influence of freezing and thawing, storing at 4 degrees C and the effectiveness of concentration steps were also determined. There was no significant difference between the sucrose density gradient method (sedimentation rate) and the density equilibrium ultracentrifugation in a CsCl gradient.     

矾土瓷——一种新型高电压高强度的绝缘材料

使用经筛选的专用粘土原料和不同种类、不同用量的熔剂 ,并使用作为新型氧化铝基质的矾土 ,就可开发出一种高 Al2 O3 的新型优质瓷。这种瓷具有良好的强度 ,特别是它的长期性能 ,还降低了制造成本。因此 ,新型矾土瓷的发展前景广阔。     

Effects of shear bands in glassy alloy ribbons on some magnetic properties

Metallic glasses deformed in an inhomogeneous manner show degradation of structure-sensitive soft magnetic properties. Ribbons of different magnetostriction have been magnetically measured in the as-cast and in the cold-rolled state. Subsequent isochronal annealing and retesting indicates that recovery of magnetic properties may be rationalized on the basis of competition between stress relief and incipient crystallization, both of which occur during annealing. The minimum coercivity to which an inhomogeneously deformed sample may be annealed is limited primarily by magnetostriction and thermal stability of a particular metallic glass. Stress relaxation and Curie temperature measurements suggest the creation of free volume during the formation of shear bands.     

Configuration interaction calculations of annihilation rates for positronic complexes of alkali hydrides

Ab initio multireference single- and double-excitation configuration interaction (MRD-CI) wave functions have been employed to compute the annihilation rates (AR) of positronic molecular complexes of four alkali hydrides. The first step in these calculations is the evaluation of integrals of the two-particle Dirac delta function δ₊₋ over pairs of electronic and positronic basis functions. MRD-CI wave functions calculated with the same basis are then employed to obtain expectation values of the δ₊₋ operator (Z_eff), which in turn are proportional to the corresponding annihilation rates (AR) of the associated many-particle states. The importance of removing near-linear dependencies in the basis sets employed is stressed as well as the advisability of placing diffuse (small-exponent) functions in the basis only at the most electronegative center of the molecule. A tendency to underestimate the Z_eff values is noted because of the impracticality of including sufficiently high-l basis functions in the basis for general molecular systems. However, comparison with the relatively accurate values for the four-electron e⁺LiH complex obtained by Quantum Monte-Carlo (QMC) and other methods indicates that the fractional error is nearly constant over a large range of internuclear distance, consistent with the expectation that missing correlation effects in the MRD-CI treatment are predominantly atomic in nature. A scaling procedure based on the asymptotic δ₊₋ value, which is the same for all four alkali hydrides, is then shown to produce good agreement with the QMC AR data for e⁺LiH. The same procedure has been applied to the δ₊₋ values for the positronic complexes of the heavier alkali hydrides for which no other theoretical results are available. Trends in the variation of the AR results with bond distance are discussed.