92 research outputs found
What is the valence of a correlated solid? The double life of delta-plutonium
Plutonium displays phase transitions with enormous volume differences among
its phases and both its Pauli like magnetic susceptibility and resistivity are
an order of magnitude larger than those of simple metals. Curium is also highly
resistive but its susceptibility is Curie-like at high temperatures and orders
antiferromagnetically at low temperatures. The anomalous properties of the late
actinides stem from the competition between the itinerancy and localization of
its f electrons, which makes the late actinides elemental strongly correlated
materials. A central problem in this field is to understand the mechanism by
which these materials resolve these conflicting tendencies. In this letter we
identify the electronic mechanisms responsible for the anomalous behaviour of
late actinides. We revisit the concept of valence using theoretical approach
that treats magnetism, Kondo screening, atomic multiplet effects, spin orbit
coupling and crystal field splitting on the same footing. Plutonium is found to
be in a rare mixed valent state, namely its ground state is a superposition of
two distinct valencies. Curium settles in a single valence magnetically ordered
state at low temperatures. The f7 atomic configuration of Curium is contrasted
with the multiple configuration manifolds present in Plutonium ground state
which we characterize by a valence histogram. The balance between the Kondo
screening and magnetism is determined by the competition between spin orbit
coupling and the strength of atomic multiplets which is in turn regulated by
the degree of itinerancy. The approach presented here, highlights the
electronic origin of the bonding anomalies in plutonium and can be applied to
predict generalized valences and the presence or absence of magnetism in other
compounds starting from first principles.Comment: 2 figures, 1 tabl
Prognostic model to predict postoperative acute kidney injury in patients undergoing major gastrointestinal surgery based on a national prospective observational cohort study.
Background: Acute illness, existing co-morbidities and surgical stress response can all contribute to postoperative acute kidney injury (AKI) in patients undergoing major gastrointestinal surgery. The aim of this study was prospectively to develop a pragmatic prognostic model to stratify patients according to risk of developing AKI after major gastrointestinal surgery. Methods: This prospective multicentre cohort study included consecutive adults undergoing elective or emergency gastrointestinal resection, liver resection or stoma reversal in 2-week blocks over a continuous 3-month period. The primary outcome was the rate of AKI within 7 days of surgery. Bootstrap stability was used to select clinically plausible risk factors into the model. Internal model validation was carried out by bootstrap validation. Results: A total of 4544 patients were included across 173 centres in the UK and Ireland. The overall rate of AKI was 14·2 per cent (646 of 4544) and the 30-day mortality rate was 1·8 per cent (84 of 4544). Stage 1 AKI was significantly associated with 30-day mortality (unadjusted odds ratio 7·61, 95 per cent c.i. 4·49 to 12·90; P < 0·001), with increasing odds of death with each AKI stage. Six variables were selected for inclusion in the prognostic model: age, sex, ASA grade, preoperative estimated glomerular filtration rate, planned open surgery and preoperative use of either an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. Internal validation demonstrated good model discrimination (c-statistic 0·65). Discussion: Following major gastrointestinal surgery, AKI occurred in one in seven patients. This preoperative prognostic model identified patients at high risk of postoperative AKI. Validation in an independent data set is required to ensure generalizability
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