Statistical physics and stromatolite growth: new perspectives on an ancient dilemma

This paper outlines our recent attempts to model the growth and form of microbialites from the perspective of the statistical physics of evolving surfaces. Microbialites arise from the environmental interactions of microbial communities (microbial mats). The mats evolve over time to form internally laminated organosedimentary structures (stromatolites). Modern day stromatolites exist in only a few locations, whereas ancient stromatolitic microbialites were the only form of life for much of the Earth's history. They existed in a wide variety of growth forms, ranging from almost perfect cones to branched columnar structures. The coniform structures are central to the heated debate on the oldest evidence of life. We proposed a biotic model which considers the relationship between upward growth of a phototropic or phototactic biofilm and mineral accretion normal to the surface. These processes are sufficient to account for the growth and form of many ancient stromatolities. These include domical stromatolites and coniform structures with thickened apical zones typical of Conophyton. More angular coniform structures, similar to the stromatolites claimed as the oldest macroscopic evidence of life, form when the photic effects dominate over mineral accretion.Comment: 8 pages, 3 figures. To be published in Proceedings of StatPhys-Taiwan 2004: Biologically Motivated Statistical Physics and Related Problems, 22-26 June 200

Frequency of Parathyroid Hormone Assessment in the Evaluation of Hypercalcemia. A Comparison Between Patients With and Without a History of Malignancy in a 20-year Dataset of 20,954 Patients

Background: The purpose of this study was to evaluate whether a prior diagnosis of malignancy affected the assessment of parathyroid hormone (PTH) in hypercalcemic patients and whether the rate of this assessment changed over time. Methods: A retrospective cohort study was designed that included adult patients with hypercalcemia with and without a history of malignancy between January 1, 2000 and December 31, 2019 in the Marshfield Clinic Health System (MCHS). The overall and annual rates of PTH assessment in each group was determined. In patients with a PTH assessment, duration of time and number of elevated serum calcium levels between the first documentation of hypercalcemia and the assessment of PTH were recorded, as was the degree of hypercalcemia. Results: Approximately a quarter (23%) of the patients in each group had a PTH assessment. The rate of PTH assessment initially increased over time but later declined significantly. Although a more severe degree of hypercalcemia predicted a greater probability of PTH assessment, the rate of assessment declined with all degrees of hypercalcemia in the last 5 years. While most patients who had a PTH assessed did so within a few months of the first documentation of hypercalcemia, less than half (40%) had a delay of more than 2 years before a PTH level was drawn. Conclusion: This lack of appropriate and timely assessment may have significant health consequences in both groups of patients. Better education of providers about the appropriate and timely assessment of PTH in the evaluation of hypercalcemia is urgently needed.Scopu

A new high-resolution chitinozoan composite standard for the East Baltic Lower Silurian succession based on numerical analysis

The chitinozoan successions (zonation) in the Llandovery and Wenlock deposits, accumulated along the northern shelf edge of the Livonian Basin, an embayment of the Palaeobaltic sea, is studied and used for time-rock correlation of the area. Analysis of the ranges of 180 taxa from 44 sections (41 of them well-sections) by graphic correlation revealed largely compatible successions of taxa as well as local stratigraphic gaps in both shelf and basin sections. Alternatives to graphic methods also produced composite standards based on stratigraphic relationships (below, co-occurring, or above) of taxonomic ranges and considered as palaeontological time scales (composites) similar to zonal schemes. We constructed such a scale using the DISTR algorithm to analyse the distribution of 84 taxa and recognized 41 datum planes. This scale includes the traditional regional and global chitinozoan zones and the associated chronological standards (including regional stages). The BioGraph and DISTR algorithms were used to study diversity changes, and to illustrate patterns of originations and extinctions of the chitinozoans. Correlation plots between composite standard and particular sections reveal variations in sedimentary rock accumulation patterns, supporting the results of sequence stratigraphic analysis of the study interval