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Objective To assess the differential diagnostic performance of spectral characteristic parameters of radio-frequency （RF） signal time series based on ultrasonic RF flow for benign and malignant breast lesions. Methods Two dimensional B-mode ultrasound images and RF data of 137 breast lesions were collected. All ultrasonic RF data were quantitatively analyzed with a software developed by our laboratory for ultrasonic RF time series analysis. Finally，nine spectral characteristic parameters were obtained，including SMR fractal dimension，Higuchi fractal dimension，slope，intercept，mid-band fit，S1，S2，S3，and S4. All of the 116 breast lesions were pathologically diagnosed. 86 lesions were confirmed to be malignant，30 lesions were benign and 21 lesions were diagnosed as benign after follow-up. The sensitivity，specificity，accuracy，positive and negative predictive values of individual parameter of RF time series spectral characteristic parameters and combined parameters of regression models were calculated，as well as Logistic regression model was established. The receiver operating characteristic （ROC） curve and the area under ROC curve （AUC） were obtained to evaluate the differential diagnostic values of these parameters for benign and malignant breast lesions. Results Multivariate regression analysis showed that the parameters finally included into the Logistic model were Higuchi fractal dimension，S2，and S4. The highest sensitivity，specificity，accuracy，positive and negative predictive values of RF time series spectral characteristic parameters in the diagnosis of breast lesions were 90.7% （S2） and 92.2% （Higuchi fractal dimension，S4），86.1% （regression model），93.9% （S4） and 79.6% （regression model），respectively. The AUCs could reach up to 0.910 （S4） and 0.930 （regression model），and there was no statistical significance between them （P > 0.05）. Conclusions The characteristic parameters of RF signal time series based on ultrasonic RF flow provide quantitative data on the sub-resolution tissue microstructure in terms of physical properties，which yields high differential diagnostic efficiency for benign and malignant breast lesions.

Sintered rare-earth permanent magnets (for example, [Sm.sub.2][Co.sub.17], Sm[Co.sub.5], and [Nd.sub.2][Fe.sub.14]B magnets) are quite brittle and easily crack in the course of fabrication, machining, and application. Here, we report on an investigation of fracture behavior and mechanical characteristics of sintered rare-earth permanent magnets and discuss the origin of rare-earth magnet brittleness. We studied three groups of bending specimens with different orientations, cut from the same block of magnet. The bending strength was measured. The fracture surfaces were carefully observed by scanning electron microscopy and showed that the fracture behavior and bending strength of sintered rare-earth permanent magnets obviously exhibit anisotropy. Sintered Sm-Co magnets tend to cleavage fracture in the close-packed (0001) plane or in the (10[bar.1]1) plane. The fracture mechanism of sintered [Nd.sub.2][Fe.sub.14]B magnet appears to be mainly intergranular fracture. Our analysis indicates that the anisotropy of fracture behavior and mechanical strength of sintered rare-earth magnets is caused by the strong crystal-structure anisotropy and grain texture created by magnetic field alignment during the fabrication process. Index Terms--Anisotropy, fracture behavior, mechanical strength, rare-earth permanent magnets.