Introduction to x-ray imaging diagnostics for

The first order vortex melting transition is very sensitive to the presence of disorder and can be supplanted by a second order phase transition in the presence of a sufficiently high density of 토토 사이트 순위. We present the results of systematic studies on the effects of 토토 사이트 순위 on the first order vortex melting transition in YBa2Cu3O7-?ingle crystals, with a special focus on the upper and lower critical points. The experiments were performed with electrical transport and ac specific heat measurements.The geometry and strength of the 토토 사이트 순위 varied, including naturally occurring twin boundaries as well as detwinned single crystals irradiated with successive doses of electrons, protons, or heavy ions. Twin boundaries yield planar 토토 사이트 순위, electron irradiation yielded weak point 토토 사이트 순위, proton irradiation yielded strong point-like 토토 사이트 순위 and heavy ion irradiation yielded strong columnar 토토 사이트 순위. Our results indicate that the origins of the upper and lower critical points of the first order melting transition arise from different mechanisms. The position of the lower critical point is determined by the pinning strength of the defect, whereas the upper critical point shifts in response to the geometrical correlation of the 토토 사이트 순위.