Low-Temperature Devices     

McWhorter  Alan L. 《Education, IRE Transactions on》1960,3(4):137-141

The basic operating principles of three low-temperature devices the maser, the cryotron, and the cryosar are discussed. In masers the process of stimulated emission of radiation is used to produce an extremely low noise amplifier, with all practical solid state masers thus far employing the electron spins in paramagnetic salts. The cryotron and the cryosar are both primarily intended for computer applications. The former utilizes the phenomenon of superconductivity and its quenching in magnetic fields; the latter uses impact ionization of impurities in semiconductors.  相似文献   

The role of instructional variables in conceptual change in high school physics topics     

Cynthia R. Hynd  J. Yevette McWhorter  Virginia L. Phares  C. William Suttles 《科学教学研究杂志》1994,31(9):933-946

This study was conducted to determine the effect of three variables on conceptual change in physics. Ninth and 10th-grade students who, despite instruction, still held nonscientific intuitive ideas about the motion of objects participated in viewing a demonstration, engaged in student-to-student discussion, and/or read a refutational text about Newton's laws of motion. Students (N = 310) were randomly assigned within classes to eight groups representing combinations of the three activities and participated in pretesting, instruction, and posttesting. Posttest results revealed that reading the refutational text helped students change their intuitive ideas to scientific ones, while seeing a demonstration affected how students interacted with group and text on some measures. Discussing ideas in a group did not lead to significant learning of scientific notions but, rather, caused students to be less influenced by either the demonstration or the text.  相似文献