Optimization of the leak conductance in the squid giant axon

We report on a theoretical study showing that the leak conductance density, \GL, in the squid giant axon appears to be optimal for the action potential firing frequency. More precisely, the standard assumption that the leak current is composed of chloride ions leads to the result that the experimental value for \GL is very close to the optimal value in the Hodgkin-Huxley model which minimizes the absolute refractory period of the action potential, thereby maximizing the maximum firing frequency under stimulation by sharp, brief input current spikes to one end of the axon. The measured value of \GL also appears to be close to optimal for the frequency of repetitive firing caused by a constant current input to one end of the axon, especially when temperature variations are taken into account. If, by contrast, the leak current is assumed to be composed of separate voltage-independent sodium and potassium currents, then these optimizations are not observed.Comment: 9 pages; 9 figures; accepted for publication in Physical Review

The demand for crop genetic resources: international use of the U.S. National Plant Germplasm System

In contrast to a perception that ex situ collections of germplasm are rarely used, this empirical case study reveals large quantities of germplasm samples distributed by the U.S. National Germplasm System to many types of scientific institutions located in numerous countries around the world. Distributions favor developing countries in several ways including the numbers of samples shipped, utilization rates in crop breeding programs, and the secondary benefits brought about through sharing this germplasm with other scientists. Expected future demand is also greater among scientists in developing countries. These findings underscore the importance to global science and technology of retaining such resources in the public domain.Germplasm resources, Plant Research., Germplasm conservation., Germplasm resources, Plant International cooperation. ,

Instability of synchronized motion in nonlocally coupled neural oscillators

We study nonlocally coupled Hodgkin-Huxley equations with excitatory and inhibitory synaptic coupling. We investigate the linear stability of the synchronized solution, and find numerically various nonuniform oscillatory states such as chimera states, wavy states, clustering states, and spatiotemporal chaos as a result of the instability.Comment: 8 pages, 9 figure

A collaborative tool for mobilizing knowledge in agrobiodiversity and the interface with climate change: the Platform for Agrobiodiversity Research

Poster presented at 2nd ANAFE International Symposium. Lilongwe (Malawi), Jul 200

First evidence of multiple populations along the AGB from Str\"omgren photometry

Spectroscopic studies have demonstrated that nearly all Galactic globular clusters (GCs) harbour multiple stellar populations with different chemical compositions. Moreover, colour-magnitude diagrams based exclusively on Str\"omgrem photometry have allowed us to identify and characterise multiple populations along the RGB of a large number of clusters. In this paper we show for the first time that Str\"omgren photometry is also very effcient at identifying multiple populations along the AGB, and demonstrate that the AGB of M3, M92, NGC362, NGC1851, and NGC6752 are not consistent with a single stellar population. We also provide a catalogue of RGB and AGB stars photometrically identified in these clusters for further spectroscopic follow-up studies.We combined photometry and elemental abundances from the literature for RGB and AGB stars in NGC6752 where the presence of multiple populations along the AGB has been widely debated. We find that, while the MS, SGB, and RGB host three stellar populations with different helium and light element abundances, only two populations of AGB stars are present in the cluster. These results are consistent with standard evolutionary theory.Comment: 9 pages, 3 figures, 1 table in the main article, 3 tables in the appendix of which 2 tables containing coordinates and photometry of photometrically identified RGB and AGB star