Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions

We review the most important experimental results from the first three years of nucleus-nucleus collision studies at RHIC, with emphasis on results from the STAR experiment, and we assess their interpretation and comparison to theory. The theory-experiment comparison suggests that central Au+Au collisions at RHIC produce dense, rapidly thermalizing matter characterized by: (1) initial energy densities above the critical values predicted by lattice QCD for establishment of a Quark-Gluon Plasma (QGP); (2) nearly ideal fluid flow, marked by constituent interactions of very short mean free path, established most probably at a stage preceding hadron formation; and (3) opacity to jets. Many of the observations are consistent with models incorporating QGP formation in the early collision stages, and have not found ready explanation in a hadronic framework. However, the measurements themselves do not yet establish unequivocal evidence for a transition to this new form of matter. The theoretical treatment of the collision evolution, despite impressive successes, invokes a suite of distinct models, degrees of freedom and assumptions of as yet unknown quantitative consequence. We pose a set of important open questions, and suggest additional measurements, at least some of which should be addressed in order to establish a compelling basis to conclude definitively that thermalized, deconfined quark-gluon matter has been produced at RHIC.Comment: 101 pages, 37 figures; revised version to Nucl. Phys.

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Ductility exhaustion mechanisms in thermally exposed thin sheets of a near-β titanium alloy

This study examines the effects of thermal exposure in air environment on the plastic elongation of thin sheets of Ti-15Mo-2.7Nb-3Al-0.2Si (Timetal-21S) alloy. Specimens with thicknesses of 0.12, 0.39, and 1.0 mm were exposed in air environment to temperatures ranging from 482 ° C to 693 °C. Tensile tests conducted on these specimens at room temperature show a reduction of plastic elongation proportional to the thermal exposure parameters, time and temperature. Furthermore, a change in the failure mode into a quasi-brittle fracture was observed in the near-surface region. The depth of this region depends on both exposure time and temperature. The kinetics of embrittlement is studied through theoretical considerations of gas diffusion into metal. This approach shows that two distinct embrittlement mechanisms operate in this alloy. The characteristics of each of these mechanisms depend on the corresponding temperature range. At temperatures higher than 545 °C, the embrittlement activation energy is 41.2 kcal·mol -1, indicating that the embrittlement process is governed by an enhanced diffusion of oxygen into Timetal-21S. Below this transitional temperature, the embrittlement activation energy approaches zero, a characteristic of slow kinetics transformation. The effects of solid-solution hardening, precipitation-hardening mechanisms, and alloying-element partitioning on ductility exhaustion processes are analyzed and discussed