Absolute thickness measurement of pyrolytic graphite spheroids by STEM-EELS.

This paper studies the absolute thickness measurement of pyrolytic graphite spheroids (GSs) by using STEM-EELS mode with log-ratio method and Kramers-Kroning (K-K) method, taking the measured thickness from TEM image as reference that is the diameter of GSs ranging from 60 to 250nm. The effect of collection semi-angle (ß) on thickness measurement has been investigated. It is found that in general the thickness obtained by K-K analysis with surface effect corrected shows the best accuracy, followed by K-K sum rule and then log-ratio method for the three different collection semi-angles of 12.4, 17.3 and 21.1mrad applied. Of these angles, the smallest one gives an overestimated result and the largest one gives an underestimated result, whereas between the two, the angle of 17.3mrad that is about 2x convergence semi-angle (9.0mrad) is identified as more appropriate for K-K analysis. The surface-scattering correction, inelastic mean free path of GS and effect of refractive index n on thickness measurement for different ß angles are also investigated. Moreover, the optical property deduced from the data collected at the center of graphite spheroid, which is related to its microstructure, is characterized by K-K analysis.

[Utility of texture analysis of magnetic resonance imaging in differential diagnosis of common pediatric cerebellar tumors in children].

OBJECTIVE: To analyze magnetic resonance images of the posterior cranial fossa tumors, and evaluate the texture characteristics of three kinds of children's posterior cranial fossa tumors by support vector machine (SVM). METHODS: From May 2008 to August 2015, a total of 76 patients with children's posterior cranial fossa tumors in First Affiliated Hospital of Zhengzhou University were retrospectively analyzed, texture analysis was performed on the three types of tumors. RESULTS: The 5 texture parameters extracted from the gray level co-occurrence matrix had at least 3 parameters which had statistically significant difference between the two different classes of data sets (P<0.05). For all kinds of data sets, the variance parameters of gray value of ROI region had statistically significant differences.The accuracy rate of SVM test in the remarkable difference of the ependymomas and medulloblastomas, the ependymomas and astrocytomas and the medulloblastomas and astrocytomas was 86.15%±4.16%, 73.63%±5.82% and 74.32%±5.85%, respectively. CONCLUSION: The analysis of texture features can provide more quantitative information which could provide a new thought and method for the differential diagnosis of tumors in the posterior cranial fossa.

Purification of Xenopus transcription factor IIIA and 5 S RNA from 7 S ribonucleoprotein particle by ammonium sulfate precipitation.

A simple and efficient method for purifying Xenopus transcription factor IIIA from the 7 S particle has been developed by taking advantage of the differential solubilities of the protein factor and 5 S RNA in ammonium sulfate solution. Conditions under which ammonium sulfate dissociates the 7 S particle and selectively precipitates factor IIIA while the 5 S RNA moiety remains in the supernatant were found. The method simultaneously purifies, in a nondestructive manner, both factor IIIA and 5 S RNA in high yield. Purification proceeds through several ammonium sulfate precipitations of the 7 S particle. Factor IIIA obtained by this method contains no detectable RNA and is highly active as judged by DNase I footprinting and in vitro transcription of the 5 S RNA gene, as well as reconstitution with 5 S RNA to form the 7 S particle. The molar extinction coefficients of factor IIIA at 205 and 280 nm were determined from the ultraviolet absorption spectra measured with the purified protein.