6,802 research outputs found
Recommended from our members
Reversible intercalation of methyl viologen as a dicationic charge carrier in aqueous batteries.
The interactions between charge carriers and electrode structures represent one of the most important considerations in the search for new energy storage devices. Currently, ionic bonding dominates the battery chemistry. Here we report the reversible insertion of a large molecular dication, methyl viologen, into the crystal structure of an aromatic solid electrode, 3,4,9,10-perylenetetracarboxylic dianhydride. This is the largest insertion charge carrier when non-solvated ever reported for batteries; surprisingly, the kinetic properties of the (de)insertion of methyl viologen are excellent with 60% of capacity retained when the current rate is increased from 100 mA g-1 to 2000 mA g-1. Characterization reveals that the insertion of methyl viologen causes phase transformation of the organic host, and embodies guest-host chemical bonding. First-principles density functional theory calculations suggest strong guest-host interaction beyond the pure ionic bonding, where a large extent of covalency may exist. This study extends the boundary of battery chemistry to large molecular ions as charge carriers and also highlights the electrochemical assembly of a supramolecular system
The electrophysiology of the betacell based on single transmembrane protein characteristics
The electrophysiology of betacells is at the origin of insulin secretion.
Betacells exhibit a complex behaviour upon stimulation with glucose including
repeated and uninterrupted bursting. Mathematical modelling is most suitable to
improve knowledge about the function of various transmembrane currents provided
the model is based on reliable data. This is the first attempt to build a
mathematical model for the betacell-electrophysiology in a bottom-up approach
which relies on single protein conductivity data. The results of previous
whole-cell-based models are reconsidered. The full simulation including all
prominent transmembrane proteins in betacells is used to provide a functional
interpretation of their role in betacell-bursting and an updated vantage point
of betacell-electrophysiology. As a result of a number of in silico knock-out-
and block-experiments the novel model makes some unexpected predictions:
Single-channel conductivity data imply that calcium-gated potassium currents
are rather small. Thus, their role in burst interruption has to be revisited.
An alternative role in high calcium level oscillations is proposed and an
alternative burst interruption model is presented. It also turns out that
sodium currents are more relevant than expected so far. Experiments are
proposed to verify these predictions.Comment: 28 pages, 5 figures, 54 references, 14 pages supplementary materia
On the impact of capillarity for strength at the nanoscale
The interior of nanoscale crystals experiences stress that compensates the
capillary forces and that can be large, in the order of 1 GPa. Various studies
have speculated on whether and how this surface-induced stress affects the
stability and plasticity of small crystals. Yet, experiments have so far failed
to discriminate between the surface contribution and other, bulk-related size
effects. In order to clarify the issue, we study the variation of the flow
stress of a nanomaterial while distinctly different variations of the two
capillary parameters surface tension and surface stress are imposed under
control of an applied electric potential. Our theory qualifies the suggested
impact of as not forceful and instead predicts a
significant contribution of the surface energy, as measured by the
. The predictions for the combined potential- and
size dependence of the flow stress are quantitatively supported by the
experiment. Previous suggestions, favoring the surface stress as the relevant
capillary parameter, are not consistent with the experiment
Factors Affecting the Electrochemical Responses of Metal Complexes at Pyrolytic Graphite Electrodes Coated with Films of Poly(4-Vinylpyridine)
Electrochemical responses from the reduction of RuIII (edta) coordinatedto films of high molecular weight poly(4-vinylpyridine) on pyrolytic graphiteelectrodes were studied as functions of film thickness, temperature, supportingelectrolyte composition, and solvent. Responses at filmed electrodes from metalcomplexes that do not coordinate to the films were also examined. With filmsthicker than ca. 1000Ă…, the current responses are limited by the rates of molecularmotions within the films. Penetration of counterions, segmental motion ofsections of the polymer chains, and juxtapositioning of pairs of attached metalcomplexes to facilitate intercomplex electron transfer within the film or combinationsof the three are suggested as likely current limiting processes
National Educators' Workshop: Update 1989 Standard Experiments in Engineering Materials Science and Technology
Presented here is a collection of experiments presented and demonstrated at the National Educators' Workshop: Update 89, held October 17 to 19, 1989 at the National Aeronautics and Space Administration, Hampton, Virginia. The experiments related to the nature and properties of engineering materials and provided information to assist in teaching about materials in the education community
- …