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Owing to the special planar structure and very high resistivity, Z-type hexaferrites possess the high initial permeability and cut-off frequency, indicating great application potential in high-frequency devices. Strontium Co2Z hexaferrites (Sr3Co2Fe24O41) were successfully prepared by the sol–gel method and calcined at the different temperatures from 1175∘C to 1250∘C. The influence of the calcined temperatures on the microstructure, phase structures, magnetic properties and microwave absorption behavior of all samples was investigated in detail. All results indicated that strontium hexaferrites go through the M-, Y-, Z-, and W-phase transformation process from 1175∘C to 1250∘C, and S-1200 (calcined at 1200∘C) is confirmed to be Co2Z-type hexaferrites. S-1200 showed the highest imaginary permeability while the imaginary permittivity of all samples is close to zero, indicating the excellent microwave adsorption behavior of strontium Co2Z hexaferrites. The reflection loss results indicate that S-1200 exhibits the best microwave absorption performance with the RL value of −32.4 dB for 4.0 mm thickness at 4.72 GHz, according to the impedance matching and quarter-wavelength theory.

The derivation of a universal formula for the variance-covariance component estimation is discussed. The formula is derived adopting the universal functional model (the condition adjustment with unknown parameters and constraints among the parameters),and is based on the maximum likelihood principle. The derived formula in this paper can be applied to all adjustment models for estimating variance-covariance components, which expands the formulas given by K. Kubik (1970)and K. R. Koch (1986).Besides, it is proved that the estimator given in this paper is equivalent to that of Helmert type and best quadratic unbiased estimation (BQUE).

Genetic variability of the nontranscribed spacer (NTS) region within ribosomal DNA repeating units in the various subspecies of Mus musculus was determined. Mice belonging to several laboratory mouse strains were examined by means of Southern blot hybridization with a mouse ribosomal DNA probe. This probe encompasses the 3' end of the 28S ribosomal RNA (rRNA) gene and the following spacer. Restriction enzyme digestions of the liver DNAs from various wild mice revealed that each of the subspecies has a unique pattern in the spacer encompassing a distance approximately 10 kb downstream from the ribosomal gene. These restriction patterns permit the classification of mouse subspecies and also provide insights into the origin of the laboratory mouse strains.