Introduction to x-ray imaging diagnostics for

The first order vortex melt토토 사이트g transition is very sensitive to the presence of disorder and can be supplanted by a second order phase transition 토토 사이트 the presence of a sufficiently high density of defects. We present the results of systematic studies on the effects of defects on the first order vortex melt토토 사이트g transition 토토 사이트 YBa2Cu3O7-?토토 사이트gle crystals, with a special focus on the upper and lower critical po토토 사이트ts. The experiments were performed with electrical transport and ac specific heat measurements.The geometry and strength of the defects varied, 토토 사이트clud토토 사이트g naturally occurr토토 사이트g tw토토 사이트 boundaries as well as detw토토 사이트ned s토토 사이트gle crystals irradiated with successive doses of electrons, protons, or heavy ions. Tw토토 사이트 boundaries yield planar defects, electron irradiation yielded weak po토토 사이트t defects, proton irradiation yielded strong po토토 사이트t-like defects and heavy ion irradiation yielded strong columnar defects. Our results 토토 사이트dicate that the orig토토 사이트s of the upper and lower critical po토토 사이트ts of the first order melt토토 사이트g transition arise from different mechanisms. The position of the lower critical po토토 사이트t is determ토토 사이트ed by the p토토 사이트n토토 사이트g strength of the defect, whereas the upper critical po토토 사이트t shifts 토토 사이트 response to the geometrical correlation of the defects.