RESUMO
Beryllium is a vital alkaline-earth metal for plasma physics, space science, and nuclear technology. Unfortunately, its accurate phase diagram is clouded by many controversial results, even though solid beryllium can only exist with hcp or bcc crystalline structures. Herein, we offer a simple quantum-statistical solution to the above problem. Our core idea is to develop the moment expansion technique to determine the Helmholtz free energy under extreme conditions. This strategy helps elucidate the underlying correlation among symmetric characteristics, vibrational excitations, and physical stabilities. In particular, our analyses reveal that the appearance of anharmonic effects forcefully straightens up the hcp-bcc boundary. This phenomenon explains why it has been difficult to detect bcc signatures via diamond-anvil-cell measurements. Besides, we modify the work-heat equivalence principle to quickly obtain the high-pressure melting profile from the room-temperature equation of state. The hcp-bcc-liquid triple point of beryllium is found at 165 GPa and 4559 K. Our theoretical findings agree excellently with cutting-edge ab initio simulations adopting the phonon quasiparticle method and the thermodynamic integration. Finally, we consider the principal Hugoniot curve and its secondary branches to explore the behaviors of beryllium under shock compression. Our predictions would be advantageous for designing inertial-confinement-fusion experiments.
RESUMO
Vacancies are prevalent point defects in crystals, but their thermal responses are elusive. Herein, we formulate a simple theoretical model to shed light on the vacancy evolution during heating. Vibrational excitations are thoroughly investigated via moment recurrence techniques in quantum statistical mechanics. On that basis, we carry out numerical analyses for Ag, Cu, and Ni with the Sutton-Chen many-body potential. Our results reveal that the well-known Arrhenius law is insufficient to describe the proliferation of vacancies. Specifically, anharmonic effects lead to a strong nonlinearity in the Gibbs energy of vacancy formation. Our physical picture is well supported by previous simulations and experiments.
RESUMO
Purpose. To investigate the knowledge, attitude, and practice of surgeons toward introducing novel surgical techniques in Egypt, Palestine, and Vietnam. Summary Background Data. Despite the recent advances in modern surgical care and its role in advancing the quality and the length of lives, surgery in the developing world has stagnated or even regressed. Methods. A survey was undertaken among the surgeons in 9 hospitals belonging to the 3 countries. Questions were categorized into knowledge, attitude, and practice questions. Meta-analyses were performed to estimate the event rate and compare between knowledge and practice, senior and junior surgeons. Results. A total of 244 responses, with a response rate of 79.7%, were included in the analysis. Regarding knowledge and attitude, the results were satisfactory except that only 55.8% of surgeons appraised their level of education and 43.3% wanted to earn money from the novel procedure. There was a significant difference between knowledge and practice regarding getting informed consent from the patients (P = .024), discussing the novelty of the procedure (P < .001), discussing the alternative procedures (P < .001), discussing the surgeons' experience and level of skills (P < .001), discussing the risk of the new procedure (P < .001), and monitoring the outcomes after the new procedure (P < .001). Conclusions. Most surgeons have sufficient knowledge and are motivated regarding adopting novel surgical techniques in order to provide the best care for the patients. However, there was a gap between knowledge and practice. Training programs and evidence-based guidelines regarding the introduction of novel surgical techniques are needed to overcome these challenges.
