Magnesium isotope ratio measurements by negative thermal ionisation mass spectrometry using molecular fluoride ions

A new technique for accurate Mg isotope ratio measurements has been developed with MgF₂ as sample compound. With the help of a fluorinating agent negatively charged MgF₃ molecular ions were formed in the ion source of a thermal ionisation mass spectrometer. An evaporation study has been performed and the results clearly show that Mg is evaporated from the filament as MgF₂ molecules. The MgF₂ technique has been applied in the certification of a candidate ²⁶Mg-enriched Spike Isotope Reference Material. The result from this new technique has been compared with results obtained for the same material using ICP-MS.     

Time resolved fluorescence and anisotropy of 1-pyrene butyric acid and pyranine as probes of solvent organization in sucrose solutions

The microenvironment of solute-solvent interactions in aqueous sucrose solutions, ranging from 0 to 80 wt% in concentration, was investigated using time resolved fluorescence techniques. The fluorescence lifetimes and rotational correlation times of the trace fluorescent probes, PBA (1-pyrene butyric acid) and pyranine (trisodium 8-hydroxy-1,3,6-pyrenetrisulfonate), were measured in sucrose solutions. The behavior of the fluorescence lifetimes and the increase in the rotational correlation times with increasing sucrose concentration provided no evidence for the formation of water exclusive solute clusters in the metastable solutions. Instead, the results indicated the formation of a network of hydrogen bonding interactions between dispersed sucrose molecules.     

Electrochemical Measurements of Optogenetically Stimulated Quantal Amine Release from Single Nerve Cell Varicosities in Drosophila Larvae

The nerve terminals found in the body wall of Drosophila melanogaster larvae are readily accessible to experimental manipulation. We used the light‐activated ion channel, channelrhodopsin‐2, which is expressed by genetic manipulation in Type II varicosities to study octopamine release in Drosophila. We report the development of a method to measure neurotransmitter release from exocytosis events at individual varicosities in the Drosophila larval system by amperometry. A microelectrode was placed in a region of the muscle containing a varicosity and held at a potential sufficient to oxidize octopamine and the terminal stimulated by blue light. Optical stimulation of Type II boutons evokes exocytosis of octopamine, which is detected through oxidization at the electrode surface. We observe 22700±4200 molecules of octopamine released per vesicle. This system provides a genetically accessible platform to study the regulation of amine release at an intact synapse.     

Homotopical Morita theory for corings

A coring (A,C) consists of an algebra A in a symmetric monoidal category and a coalgebra C in the monoidal category of A-bimodules. Corings and their comodules arise naturally in the study of Hopf–Galois extensions and descent theory, as well as in the study of Hopf algebroids. In this paper, we address the question of when two corings (A,C) and (B,D) in a symmetric monoidal model category V are homotopically Morita equivalent, i.e., when their respective categories of comodules V _A ^C and V _B ^D are Quillen equivalent. As an illustration of the general theory, we examine homotopical Morita theory for corings in the category of chain complexes over a commutative ring.     

Hunting French ducks in a noisy environment

We consider the effect of Gaussian white noise on fast–slow dynamical systems with one fast and two slow variables, containing a folded node singularity. In the absence of noise, these systems are known to display mixed-mode oscillations, consisting of alternating large- and small-amplitude oscillations. We quantify the effect of noise and obtain critical noise intensities beyond which the small-amplitude oscillations become hidden by fluctuations. Furthermore we prove that the noise can cause sample paths to jump away from so-called canard solutions with high probability before deterministic orbits do. This early-jump mechanism can drastically influence the local and global dynamics of the system by changing the mixed-mode patterns.