Characterization of a Large-Scale Nondoped YBa2Cu3O7−x Superconductor Prepared by Plastic Forming Without High-Pressure Molding

A slurry containing YBa₂Cu₃O_{7− x} particles and a fine YBa₂Cu₃(OH) _x colloid solution was prepared, and a large-scale bulk YBa₂Cu₃O_{7− x} superconductor (about 50 mm × 35 mm × 2 mm) was produced by plastic forming without high-pressure molding. The samples molded from the slurry were dried and then fired at 1223 K in air. X-ray diffraction data indicated that the samples had the characteristic orthorhombic YBa₂Cu₃O_{7− x} structure. Measurements of electrical resistance were carried out between 300 and 50 K by the standard four-probe DC electrical measurement. The samples began superconducting at an onset temperature around 92 K, and the full-transition temperature (critical temperature) ( T _c) was 88.7±1.4 K. The critical current density ( J _c) measured at 77 K was about 440 A/cm², the value of J _c was improved by the heat treatment under an oxygen atmosphere, and J _c=1.6 × 10³ A/cm² was observed. Under the magnetic field (B=1 T), the sample held its superconductivity, and demonstrated that this method can be used to produce the magnetic shielding used in magnetic resonance imaging diagnosis.     

Detection of a new crosslinking and properties of liquid polysulfide polymer

Polysulfide polymer was found in the 19th century. At present, this polymer consists of the repetition of disulfide linkage and diethyl formal and has SH terminals. This liquid polymer (LP) is cured by lead dioxide. We studied polysulfide polymerization and elastomeric mechanical properties of cured LP. The condition of polymerization greatly influenced its elastomeric mechanical properties. These phenomena could not be explained from the point of residual unreacted chlorine or produced OH terminals. We found that additional crosslinking sites are produced during polymerization besides crosslinking agents trichloropropane (TCP) by using the Insensitive Nuclei Enhanced by Polarization Transfer (INEPT) method. We proposed their chemical structures and reaction scheme of their formation. TCP and also these additional crosslinking sites influence the modulus of cured LP. The sum of the intensity of their crosslinking sites by ¹³C‐NMR had good correlation with 300% modulus of cured LP. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 59–66, 1999     

Scattering of fast protons on densely stepped surfaces of ionic crystals

The surfaces of KCl crystals were sputtered by irradiation with 5 keV electrons (500 μA/m²), in order to create a high density of surface steps. Energy loss distributions of 550 keV protons at glancing angle incidence scattered from the (001) surface were then measured for random (100 mrad off 〈100〉 direction) and surface-channeling (〈100〉 direction) conditions. The surfaces were examined using atomic force microscope (AFM) in air. The measured energy spectra of protons were compared with those calculated by computer simulation. For random incidence, the fraction of the projectiles which penetrate through the surface increases with increasing dose of electron-irradiation. These protons pass through the steps both at the entrance and the exit. For the case of channeling incidence, this fraction decreases with increasing electron-irradiation dose in the dose range from 10¹⁹ m⁻² to 10²⁰ m⁻², because the projectiles do not necessarily pass through the surface steps. AFM observations show that there are many steps of several to several tens of monolayers' height on the surface for samples irradiated with doses of more than 1 × 10²⁰ m⁻².     

Narrative Development in Bilingual Kindergarteners: Can Arthur Help?

This study examined the effects of the children's TV program Arthur on the development of narrative skills over an academic year for Spanish-speaking English-language learners. In October, February, and June of their kindergarten year, children were asked to tell a story, in English, prompted by 3 pictures. Before the 2nd and 3rd assessments, half of the 108 children were randomly assigned to view Arthur 3 times a week during school hours, and the other half, which formed the control group, viewed the children's program Between the Lions on the same schedule. Individual growth modeling analysis showed that children who viewed Arthur had steeper growth trajectories than those who viewed Between the Lions. Boys displayed better English narrative skills than girls but no difference in narrative growth rate. The results suggest that certain educational TV programs can assist in some aspects of the language development of bilingual children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)