Zigzag persistence for coral reef resilience using a stochastic spatial model

A complex interplay between species governs the evolution of spatial patterns in ecology. An open problem in the biological sciences is characterizing spatio-temporal data and understanding how changes at the local scale affect global dynamics/behaviour. Here, we extend a well-studied temporal mathematical model of coral reef dynamics to include stochastic and spatial interactions and generate data to study different ecological scenarios. We present descriptors to characterize patterns in heterogeneous spatio-temporal data surpassing spatially averaged measures. We apply these descriptors to simulated coral data and demonstrate the utility of two topological data analysis techniques-persistent homology and zigzag persistence-for characterizing mechanisms of reef resilience. We show that the introduction of local competition between species leads to the appearance of coral clusters in the reef. We use our analyses to distinguish temporal dynamics stemming from different initial configurations of coral, showing that the neighbourhood composition of coral sites determines their long-term survival. Using zigzag persistence, we determine which spatial configurations protect coral from extinction in different environments. Finally, we apply this toolkit of multi-scale methods to empirical coral reef data, which distinguish spatio-temporal reef dynamics in different locations, and demonstrate the applicability to a range of datasets.

Severity of oEsophageal Anastomotic Leak in patients after oesophagectomy: the SEAL score

Background

Anastomotic leak (AL) is a common but severe complication after oesophagectomy. It is unknown how to determine the severity of AL objectively at diagnosis. Determining leak severity may guide treatment decisions and improve future research. This study aimed to identify leak-related prognostic factors for mortality, and to develop a Severity of oEsophageal Anastomotic Leak (SEAL) score.

Methods

This international, retrospective cohort study in 71 centres worldwide included patients with AL after oesophagectomy between 2011 and 2019. The primary endpoint was 90-day mortality. Leak-related prognostic factors were identified after adjusting for confounders and were included in multivariable logistic regression to develop the SEAL score. Four classes of leak severity (mild, moderate, severe, and critical) were defined based on the risk of 90-day mortality, and the score was validated internally.

Results

Some 1509 patients with AL were included and the 90-day mortality rate was 11.7 per cent. Twelve leak-related prognostic factors were included in the SEAL score. The score showed good calibration and discrimination (c-index 0.77, 95 per cent c.i. 0.73 to 0.81). Higher classes of leak severity graded by the SEAL score were associated with a significant increase in duration of ICU stay, healing time, Comprehensive Complication Index score, and Esophagectomy Complications Consensus Group classification.

Conclusion

The SEAL score grades leak severity into four classes by combining 12 leak-related predictors and can be used to the assess severity of AL after oesophagectomy.

Understanding how porosity gradients can make a better filter using homogenization theory

Filters whose porosity decreases with depth are often more efficient at removing solute from a fluid than filters with a uniform porosity. We investigate this phenomenon via an extension of homogenization theory that accounts for a macroscale variation in microstructure. In the first stage of the paper, we homogenize the problems of flow through a filter with a near-periodic microstructure and of solute transport owing to advection, diffusion and filter adsorption. In the second stage, we use the computationally efficient homogenized equations to investigate and quantify why porosity gradients can improve filter efficiency. We find that a porosity gradient has a much larger effect on the uniformity of adsorption than it does on the total adsorption. This allows us to understand how a decreasing porosity can lead to a greater filter efficiency, by lowering the risk of localized blocking while maintaining the rate of total contaminant removal.

Temperature dependence of electric transport in few-layer graphene under large charge doping induced by electrochemical gating

The temperature dependence of electric transport properties of single-layer and few-layer graphene at large charge doping is of great interest both for the study of the scattering processes dominating the conductivity at different temperatures and in view of the theoretically predicted possibility to reach the superconducting state in such extreme conditions. Here we present the results obtained in 3-, 4- and 5-layer graphene devices down to 3.5 K, where a large surface charge density up to about 6.8·10¹⁴ cm⁻² has been reached by employing a novel polymer electrolyte solution for the electrochemical gating. In contrast with recent results obtained in single-layer graphene, the temperature dependence of the sheet resistance between 20 K and 280 K shows a low-temperature dominance of a T² component – that can be associated with electron-electron scattering – and, at about 100 K, a crossover to the classic electron-phonon regime. Unexpectedly, this crossover does not show any dependence on the induced charge density, i.e. on the large tuning of the Fermi energy.

Mechanical bowel preparation and antibiotic prophylaxis in colorectal surgery: use by and opinions of Spanish surgeons

OBJECTIVE

Antibiotic prophylaxis (AP) and mechanical bowel preparation (MBP) previous to surgery have classically been regarded as important in colorectal surgery. The latter has recently been questioned. We evaluated opinion of Spanish surgeons about the use of these measures.

METHOD

E-mail survey among all members of Spanish Coloproctologic Associations.

RESULTS

Of 413 participants in the survey, 131 (31.7%) responded; 87% of surgeons used cathartics (70%), enemas (2%) or both (28%) for MBP. MBP was used 60% in right colon surgery, 90% in left colon and 99% in rectal surgery. Surgeons with more case load or those who specialized in colorectal surgery used significantly less MBP; 60% of the surgeons thought that MBP made surgery easier and reduced contamination; 35% thought that it decreased wound infection (WI) and 17% thought that it prevented anastomotic leaks. For 77%, it was regarded as useful or very useful. AP was used by 99.3% of surgeons including systemic alone in 86.2% and combined with oral in 16.8%. The first dose was given 2 h before surgery by 20.2% of the surgeons, at the anaesthetic induction by 78.3% and postoperatively by 1.5%; 43% used single dose only, 44.5% extended to 24 h and 12.5% for two or more days; 95% thought that AP reduced WI and 96% considered that it was useful.

CONCLUSION

There is general agreement on AP. MBP remained a common practice among Spanish colorectal surgeons except for right colonic resection. Surgeons with more case load and specialization used it significantly less.

Análisis de las áreas de mejora del control de la hipertensión arterial en Atención Primaria

BACKGROUND AND OBJECTIVES

Most hypertensive patients do not have their blood pressure (BP) under control. This study aims to evaluate Primary Care physicians' management of hypertension by analyzing the four main areas proposed by experts to improve BP control.

MATERIAL AND METHODS

From February to May 2003 a questionnaire was completed by 195 Primary Care physicians from 33 Primary Care centers of Madrid, Spain. Four aspects of clinical practice were examined: a) knowledge of hypertension guidelines and objectives; b) diagnosis and follow-up of patients; c) hypertension treatment, and d) drug compliance.

RESULTS

Guidelines were followed by 90.6% of the physicians. Twenty six percent of the physicians perceived that guideline objectives are too strict and only 32% identified systolic BP as the component that provides more risk. Only 14% used automatic devices to measure BP while 89% still use the mercury sphygmomanometer. Diuretics were included among the 3 most used antihypertensive drugs by 94% of the physicians, ACEI by 91%, beta blockers by 62% and combinations only by 24%. Eighty eight percent believed that more than 40% of their patients have their BP under control and 53% felt that less than 20% of their patients were non-compliant with antihypertensive treatment.

CONCLUSIONS

Hypertension management among Primary Care physicians showed some deficiencies in the 4 analyzed areas. Thus, perception of excessively rigorous guideline objectives, underrating of systolic BP, underuse of automatic devices and drug associations, and the overestimation of BP control and therapeutic compliance are specific areas that should be modified to improve BP control.