Black Hole Thermodynamics and Statistical Mechanics

We have known for more than thirty years that black holes behave as thermodynamic systems, radiating as black bodies with characteristic temperatures and entropies. This behavior is not only interesting in its own right; it could also, through a statistical mechanical description, cast light on some of the deep problems of quantizing gravity. In these lectures, I review what we currently know about black hole thermodynamics and statistical mechanics, suggest a rather speculative "universal" characterization of the underlying states, and describe some key open questions.Comment: 35 pages, Springer macros; for the Proceedings of the 4th Aegean Summer School on Black Hole

Effect of pH and oxygen on stress corrosion cracking of stainless steel in reactor moderator service

Intergranular cracking of Type 304 stainless steel outlet nozzles in reactor moderator service prompted a broad program of laboratory studies to determine the cause of the failures. It was demonstrated that sensitized and pickled Type 304 stainless steel is extremely susceptible to both intergranular and transgranular chloride stress corrosion cracking in hot water of pH 4.5 to 5.0 which contains as little as 2 ppM chloride ion. Although the chloride content of moderator is only about 0.01--0.03 ppM, it was concluded that chloride concentrations sufficient to cause cracking occurred on the nozzle surfaces, either very gradually or as a result of a system change. This conclusion was substantiated later when chlorides were shown to be concentrated in a film of aluminum oxide (from fuel cladding corrosion) deposited on the moderator side of a failed nozzle. Circumstantial evidence suggested that initiation of moderator pH (pD) control with nitric acid and oxygen caused or contributed to cracking of the nozzles. Therefore, in recent laboratory work the effects of pH and oxygen concentration on cracking of sensitized and pickled Type 304 stainless steel were investigated. The effects of nitrate and sulfate ion concentrations were also investigated. Results of these laboratory investigations are summarized in this report. Changes in the moderator system caused by pD control and the possible effects on cracking are also discussed. 7 refs., 4 figs., 4 tabs

The Role of Moisture and Hydrogen in Hot-Salt Cracking of Titanium Alloys

This study investigated the role of moisture and hydrogen in the stress corrosion cracking of Ti-8Al-1Mo-1V exposed to hot chloride salts. The adsorption and retention of moisture during the application of salt deposits and subsequent heating, and the extent of HCl and hydrogen generation during corrosion were studied using radiotracer techniques and mass spectrographic analysis of volatile corrosion products

The dislocation mechanism of stress corrosion embrittlement in Ti-6Al-2Sn-4Zr-6Mo

An observation of the dislocation mechanisms operating below a naturally initiated hot-salt stress corrosion crack is presented, suggesting how hydrogen may contribute to embrittlement. The observations are consistent with the hydrogen-enhanced localized plasticity mechanism. Dislocation activity has been investigated through post-mortem examination of thin foils prepared by focused ion beam milling, lifted directly from the fracture surface. The results are in agreement with the existing studies, suggesting that hydrogen enhances dislocation motion. It is found that the presence of hydrogen in (solid) solution results in dislocation motion on slip systems that would not normally be expected to be active. A rationale is presented regarding the interplay of dislocation density and the hydrogen diffusion length

Transverse-mode dynamics in vertical-cavity surface-emitting lasers with optical feedback

We study the transverse-mode dynamics of vertical-cavity surface-emitting lasers with weak optical feedback. We use a model that takes into account the spatial dependence of the transverse modes and of two carrier density profiles, associated with confined carriers in the quantum well region of the laser and unconfined carriers in the barrier region. Optical feedback is included as in the Lang-Kobayashi model. We find that for adequate parameter values antiphase dynamics occurs. As the injection current varies, the antiphase dynamics is destroyed through a sequence of periodic mixed states leading to in-phase dynamics. In these mixed states there are time intervals in which the modes are in phase, followed by time intervals in which they are in antiphase. We study the origin of the antiphase dynamics, assessing the role of the different spatial profiles. We show that the competition between the different profiles leads to the observed antiphase behavior. 5555 2002 The American Physical Society.SCOPUS: ar.jSCOPUS: ar.jinfo:eu-repo/semantics/publishe