241 research outputs found
Finite size effects on transport coefficients for models of atomic wires coupled to phonons
We consider models of quasi-1-d, planar atomic wires consisting of several,
laterally coupled rows of atoms, with mutually non-interacting electrons. This
electronic wire system is coupled to phonons, corresponding, e.g., to some
substrate. We aim at computing diffusion coefficients in dependence on the wire
widths and the lateral coupling. To this end we firstly construct a numerically
manageable linear collision term for the dynamics of the electronic occupation
numbers by following a certain projection operator approach. By means of this
collision term we set up a linear Boltzmann equation. A formula for extracting
diffusion coefficients from such Boltzmann equations is given. We find in the
regime of a few atomic rows and intermediate lateral coupling a significant and
non-trivial dependence of the diffusion coefficient on both, the width and the
lateral coupling. These results, in principle, suggest the possible
applicability of such atomic wires as electronic devices, such as, e.g.,
switches.Comment: 9 pages, 5 figures, accepted for publication in Eur. Phys. J.
Phosphodiesterase type 4 anchoring regulates cAMP signaling to Popeye domain-containing proteins.
Cyclic AMP is a ubiquitous second messenger used to transduce intracellular signals from a variety of Gs-coupled receptors. Compartmentalisation of protein intermediates within the cAMP signaling pathway underpins receptor-specific responses. The cAMP effector proteins protein-kinase A and EPAC are found in complexes that also contain phosphodiesterases whose presence ensures a coordinated cellular response to receptor activation events. Popeye domain containing (POPDC) proteins are the most recent class of cAMP effectors to be identified and have crucial roles in cardiac pacemaking and conduction. We report the first observation that POPDC proteins exist in complexes with members of the PDE4 family in cardiac myocytes. We show that POPDC1 preferentially binds the PDE4A sub-family via a specificity motif in the PDE4 UCR1 region and that PDE4s bind to the Popeye domain of POPDC1 in a region known to be susceptible to a mutation that causes human disease. Using a cell-permeable disruptor peptide that displaces the POPDC1-PDE4 complex we show that PDE4 activity localized to POPDC1 modulates cycle length of spontaneous Ca2+ transients firing in intact mouse sinoatrial nodes
Mechanisms explaining transitions between tonic and phasic firing in neuronal populations as predicted by a low dimensional firing rate model
Several firing patterns experimentally observed in neural populations have
been successfully correlated to animal behavior. Population bursting, hereby
regarded as a period of high firing rate followed by a period of quiescence, is
typically observed in groups of neurons during behavior. Biophysical
membrane-potential models of single cell bursting involve at least three
equations. Extending such models to study the collective behavior of neural
populations involves thousands of equations and can be very expensive
computationally. For this reason, low dimensional population models that
capture biophysical aspects of networks are needed.
\noindent The present paper uses a firing-rate model to study mechanisms that
trigger and stop transitions between tonic and phasic population firing. These
mechanisms are captured through a two-dimensional system, which can potentially
be extended to include interactions between different areas of the nervous
system with a small number of equations. The typical behavior of midbrain
dopaminergic neurons in the rodent is used as an example to illustrate and
interpret our results.
\noindent The model presented here can be used as a building block to study
interactions between networks of neurons. This theoretical approach may help
contextualize and understand the factors involved in regulating burst firing in
populations and how it may modulate distinct aspects of behavior.Comment: 25 pages (including references and appendices); 12 figures uploaded
as separate file
Quantitative trait loci analysis reveals a correlation between the ratio of sucrose/raffinose family oligosaccharides and seed vigour in Medicago truncatula
Seed vigour is important for successful establishment and high yield, especially under suboptimal environmental conditions. In legumes, raffinose oligosaccharide family (RFO) sugars have been proposed as an easily available energy reserve for seedling establishment. In this study, we investigated whether the composition or amount of soluble sugars (sucrose and RFO) is part of the genetic determinants of seed vigour of Medicago truncatula using two recombinant inbred line (RIL) populations. Quantitative trait loci (QTL) mapping for germination rate, hypocotyl and radicle growth under water deficit and nutritional stress, seed weight and soluble sugar content was performed using RIL populations LR1 and LR4. Seven of the 12 chromosomal regions containing QTL for germination rate or post-germinative radicle growth under optimal or stress conditions co-located with Suc/RFO QTL. A significant negative correlation was also found between seed vigour traits and Suc/RFO. In addition, one QTL that explained 80% of the variation in the ratio stachyose/verbascose co-located with a stachyose synthase gene whose expression profile in the parental lines could explain the variation in oligosaccharide composition. The correlation and co-location of Suc/RFO ratio with germination and radicle growth QTL suggest that an increased Suc/RFO ratio in seeds of M. truncatula might negatively affect seed vigour
Sonication is superior to scraping for retrieval of bacteria in biofilm on titanium and steel surfaces in vitro
Background and purpose Low-virulence implant infections are characterized by bacterial colonization of the implant with subsequent biofilm formation. In these cases, soft tissue biopsies often prove to be culture negative. Consequently, detachment of the causative adherent bacteria is crucial for correct microbiological diagnosis. Using an in vitro model, we compared 4 methods of biofilm sampling from metal surfaces
Persistent cAMP-Signals Triggered by Internalized G-Protein–Coupled Receptors
Real-time monitoring of G-protein-coupled receptor (GPCR) signaling in native cells suggests that the receptor for thyroid stimulating hormone remains active after internalization, challenging the current model for GPCR signaling
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