Shunting effect on resistance measurements in visceral smooth muscle tissue

An electrical network is presented as a model of the electrical connections between cells in a cross section of visceral smooth muscle. Methods of operational calculus are used to analyze the network and to determine the effect of parallel paths on measured resistances between the nodes. The analysis of the model suggests that actual resistances between two adjacent cells if they are isolated from the other cells in the cross section could be three times the values measured when the cells are interconnected with the parallel fibers. It is felt that the analysis presented makes possible a more accurate interpretation of electrical measurements of intercellular resistance by providing an estimate of the shunting effect of the current paths through parallel cells.     

Predicting human visuomotor behaviour in a driving task

The sequential deployment of gaze to regions of interest is an integral part of human visual function. Owing to its central importance, decades of research have focused on predicting gaze locations, but there has been relatively little formal attempt to predict the temporal aspects of gaze deployment in natural multi-tasking situations. We approach this problem by decomposing complex visual behaviour into individual task modules that require independent sources of visual information for control, in order to model human gaze deployment on different task-relevant objects. We introduce a softmax barrier model for gaze selection that uses two key elements: a priority parameter that represents task importance per module, and noise estimates that allow modules to represent uncertainty about the state of task-relevant visual information. Comparisons with human gaze data gathered in a virtual driving environment show that the model closely approximates human performance.     

A model model: a commentary on DiFrancesco and Noble (1985) ‘A model of cardiac electrical activity incorporating ionic pumps and concentration changes’

This paper summarizes the advances made by the DiFrancesco and Noble (DFN) model of cardiac cellular electrophysiology, which was published in Philosophical Transactions B in 1985. This model was developed at a time when the introduction of new techniques and provision of experimental data had resulted in an explosion of knowledge about the cellular and biophysical properties of the heart. It advanced the cardiac modelling field from a period when computer models considered only the voltage-dependent channels in the surface membrane. In particular, it included a consideration of changes of both intra- and extracellular ionic concentrations. In this paper, we summarize the most important contributions of the DiFrancesco and Noble paper. We also describe how computer modelling has developed subsequently with the extension from the single cell to the whole heart as well as its use in understanding disease and predicting the effects of pharmaceutical interventions. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.     

Female-committed infanticide followed by juvenile-enacted cannibalism in wild white-faced capuchins

Primates - On 5 February 2021, we observed the first instance of female-committed infanticide followed by cannibalism in a long-studied (> 35 years) population of wild...     

Making remote sense of biodiversity: What grassland characteristics make spectral diversity a good proxy for taxonomic diversity?

Aim

The spectral variability hypothesis (SVH) predicts that spectral diversity, defined as the variability of radiation reflected from vegetation, increases with biodiversity. While confirmation of this hypothesis would pave the path for use of remote sensing to monitor biodiversity, support in herbaceous ecosystems is mixed. Methodological aspects related to scale have been the predominant explanation for the mixed support, yet biological characteristics that vary among herbaceous systems may also affect the strength of the relationship. Therefore, we examined the influence of three biological characteristics on the relationship between spectral and taxonomic diversity: vegetation density, spatial species turnover and invasion by non-native species. We aimed to understand when and why spectral diversity may serve as an indicator of taxonomic diversity and be useful for monitoring.

Location

Continental U.S.A.

Time Period

Peak greenness in 2017.

Major Taxa Studied

Grassland and herbaceous ecosystems.

Methods

For nine herbaceous sites in the National Ecological Observatory Network, we calculated taxonomic diversity from field surveys of 20 m × 20 m plots and derived spectral diversity for those same plots from airborne hyperspectral imagery with a spatial resolution of 1 m. The strength of the taxonomic diversity–spectral diversity relationship at each site was subsequently assessed against measurements of vegetation density, spatial species turnover and invasion.

Results

We found a significant relationship between taxonomic and spectral diversity at some, but not all, sites. Spectral diversity was more strongly related to taxonomic diversity in sites with high species turnover and low invasion, but vegetation density had no effect on the relationship.

Main Conclusions

Using spectral diversity as a proxy for taxonomic diversity in grasslands is possible in some circumstances but should not just be assumed based on the SVH. It is important to understand the biological characteristics of a community prior to considering spectral diversity to monitor taxonomic diversity.     

Radiolabelling of the monate moiety in the study of pseudomonic acid biosynthesis

Abstract Monic acid A was isolated from a Pseudomonas fluorescens fermentation in which pseudomonic acid A (PA) was the principal secondary metabolite. [3-¹⁴C]3-Hydroxy-3-methyl-glutaric acid (HMG) given early in the idiophase radiolabelled PA (1.1% incorporation), confirming experimentally the putative direct involvement of HMG in the biosynthesis of PA, but contributed relatively insignificant radiolabel to the monic acid extracted from the broth at the end of the fermentation. Ethionine inhibited (80%) PA biosynthesis and correspondingly reduced incorporation of [¹⁴C]HMG. In contrast, ethionine increased incorporation of [methyl-¹⁴C]methionine into PA and enhanced specific radioactivity of the antibiotic 8-fold. Ethionine inhibition of secondary metabolite methylations did not divert pseudomonate biosynthesis to give unusual analogues, implying that methylation of a putative pentaketide precursor of the monate moiety forms a vital intermediate of the pseudomonate pathway, but caused a new [¹⁴C]HMG-derived polar metabolite of biosynthetic interest to become evident.