Total energy calculation of high pressure selenium: The origin of incommensurate modulations in Se-IV and the instability of proposed Se-II

We present calculation of the high pressure crystal structures in selenium, including rational approximants to the recently reported incommensurate phases. We show how the incommensurate phases can be intuitively explained in terms of imaginary phonon frequencies arising from Kohn anomalies in the putative undistorted phase. We also find inconsistencies between the calculated and experimental Se-II phase - the calculations show it to be a metastable metal while the experiment finds a stable semiconductor. We propose that the experimentally reported structure is probably in error.Comment: 4 pages 4 figure

Two-band second moment model and an interatomic potential for caesium

A semi-empirical formalism is presented for deriving interatomic potentials for materials such as caesium or cerium which exhibit volume collapse phase transitions. It is based on the Finnis-Sinclair second moment tight binding approach, but incorporates two independent bands on each atom. The potential is cast in a form suitable for large-scale molecular dynamics, the computational cost being the evaluation of short ranged pair potentials. Parameters for a model potential for caesium are derived and tested

Origin of complex crystal structures of elements at pressure

We present a unifying theory for the observed complex structures of the sp-bonded elements under pressure based on nearly free electron picture (NFE). In the intermediate pressure regime the dominant contribution to crystal structure arises from Fermi-surface Brillouin zone (FSBZ) interactions - structures which allow this are favoured. This simple theory explains the observed crystal structures, transport properties, the evolution of internal and unit cell parameters with pressure. We illustrate it with experimental data for these elements and ab initio calculation for Li.Comment: 4 pages 5 figure

Non-inferiority of retrospective data collection for assessing perioperative morbidity

Background. Postoperative morbidity has immediate and delayed consequences for surgical patients, including excess risk of premature death. Capturing these data objectively and routinely in large electronic databases using tools such as the Postoperative Morbidity Survey (POMS) would offer tremendous clinical and translational potential. However, POMS has thus far only utilised prospective data collection by research staff. We hypothesised that retrospective data collection from routinely collated hospital data from paper and electronic charts, medical and nursing notes was non-inferior to prospective data collection requiring research staff capturing POMS-defined morbidity in real-time.Methods. Morbidity was recorded by a trained investigator as defined by POMS prospectively on postoperative days 3 and 7. Separately, an independent investigator blinded to prospectively acquired data retrospectively assessed the same patients’ morbidity as defined by POMS criteria, using medical charts, nursing summaries and electronic data. Equivalence was accepted when the confidence limits for both modes of data collection fell completely inside the equivalence bounds, with the maximum equivalence difference (i.e., the largest value of the difference in sensitivities deemed to reach a conclusion of equivalence) set a priori at 0.2. Differences for confidence limits between retrospective and prospective data collection were based on Nam’s RMLE method. The relationship between morbidity on postoperative day 3 as recorded by each data collection method on time to become morbidity free and length of hospital stay was compared using the log-rank test.Results. POMS data from 85 patients undergoing elective or emergency surgery were analyzed. At postoperative day 3, POMS-defined morbidity was similar regardless of whether data were collected prospectively or retrospectively (95% CI [−0.13–0.013]; p < 0.001). Non-inferiority for sensitivity was observed for all other POMS domains and timepoints. Time to become morbidity free Kaplan–Meier plots were indistinguishable between POMS obtained prospectively or retrospectively (hazard ratio: 1.09 (95% CI [0.76–1.57]); p = 0.33, log rank test). Similarly, the mode of data collection did not alter the association between early postoperative morbidity on postoperative day 3 and delayed hospital discharge.Conclusions. Postoperative morbidity as defined by the Post Operative Morbidity Survey can be assessed retrospectively. These data may therefore be easily captured using electronic patient record systems, thereby expanding the potential for bioinformatics approaches to generate new clinical and translational insights into recovery from surgery

The Relationship Between Stride Rates, Lengths and Body Size and their Affect on Elite Triathletes’ Running Performance During Competition

Previous research has suggested that a degree of predictability exists in the relationship between self-selected running stride rates (SR) and stride lengths (SL) with measures of body size such as mass, height and limb lengths. Significant correlations have also been revealed between these body size measures and performance and between SL and performance. However, there is also evidence to suggest that triathlon performance may be related to maintaining a longer SL during the final run. Hence, the aim of this investigation was to examine whether there was any relationship between SR and SL, with body masses and heights of senior elite triathletes during the run stage of a triathlon. The SRs and SLs of 37 male senior elite Triathlon World Championships competitors were analysed via videography and Video Expert II Coach. These values were correlated with the athletes’ body masses and heights (p\u3c0.01). The results indicated a limited relationship between height and mass with SR in the early stages of the run. However, a significant, positive correlation existed between SL and height at all points from 3 km to the end of the run. Those triathletes who were taller used longer strides. Further research is warranted to examine the effects of cycling on the subsequent run discipline during triathlon and if body size and shape of triathletes have evolved as the young sport of triathlon develops