Two-Particle-Self-Consistent Approach for the Hubbard Model

Even at weak to intermediate coupling, the Hubbard model poses a formidable challenge. In two dimensions in particular, standard methods such as the Random Phase Approximation are no longer valid since they predict a finite temperature antiferromagnetic phase transition prohibited by the Mermin-Wagner theorem. The Two-Particle-Self-Consistent (TPSC) approach satisfies that theorem as well as particle conservation, the Pauli principle, the local moment and local charge sum rules. The self-energy formula does not assume a Migdal theorem. There is consistency between one- and two-particle quantities. Internal accuracy checks allow one to test the limits of validity of TPSC. Here I present a pedagogical review of TPSC along with a short summary of existing results and two case studies: a) the opening of a pseudogap in two dimensions when the correlation length is larger than the thermal de Broglie wavelength, and b) the conditions for the appearance of d-wave superconductivity in the two-dimensional Hubbard model.Comment: Chapter in "Theoretical methods for Strongly Correlated Systems", Edited by A. Avella and F. Mancini, Springer Verlag, (2011) 55 pages. Misprint in Eq.(23) corrected (thanks D. Bergeron

Debriefing to improve outcomes from critical illness : a systematic review and meta-analysis

Purpose Intensive care clinicians play a central role in the co-ordination and treatment of patients that develop life-threatening emergencies. This review evaluates the effect of debriefing after life-threatening emergencies and considers the implications for intensive care training and practice. Methods Studies were identified by searching electronic databases, citation tracking, and contact with subject specialists. Studies evaluating the effect of debriefing after life-threatening emergencies on clinician performance (process) and/or patient outcomes were eligible for inclusion. Study quality was assessed and summarised using the GRADE system. Results The search identified 2,720 studies. After detailed review, 27 studies were included of which 20 supported the use of debriefing. Debriefing was viewed positively (n = 3), improved learning (n = 1), enhanced non-technical performance (n = 4) and technical performance (n = 16), and improved patient outcomes (n = 2). Four cardiac arrest studies were suitable for meta-analysis. This found evidence of improved resuscitation process outcomes [compression fraction (mean difference 6.80, 95 % CI 4.19–9.40, p < 0.001)] and short-term patient outcome [return of spontaneous circulation (OR 1.46, 95 % CI 1.01–2.13, p = 0.05)]. There was no effect on survival to hospital discharge (OR 0.80, 95 % CI 0.38–1.67, p = 0.55). Conclusions This review supports the use of structured debriefing as an educational strategy to improve clinician knowledge and skill acquisition and implementation of those skills in practice. However, the effect of debriefing on long-term patient outcomes is uncertain. There remains a need for further high-quality research, which seeks to identify the optimal method for debriefing delivery and effect on patient outcomes