Quantum Yield Calculations for Strongly Absorbing Chromophores

This article demonstrates that a commonly-made assumption in quantum yield calculations may produce errors of up to 25% in extreme cases and can be corrected by a simple modification to the analysis.Comment: 3 pages, 2 figures. Accepted by Journal of Fluorescenc

Implementing Silicon Nanoribbon Field-Effect Transistors as Arrays for Multiple Ion Detection

Ionic gradients play a crucial role in the physiology of the human body, ranging from metabolism in cells to muscle contractions or brain activities. To monitor these ions, inexpensive, label-free chemical sensing devices are needed. Field-effect transistors (FETs) based on silicon (Si) nanowires or nanoribbons (NRs) have a great potential as future biochemical sensors as they allow for the integration in microscopic devices at low production costs. Integrating NRs in dense arrays on a single chip expands the field of applications to implantable electrodes or multifunctional chemical sensing platforms. Ideally, such a platform is capable of detecting numerous species in a complex analyte. Here, we demonstrate the basis for simultaneous sodium and fluoride ion detection with a single sensor chip consisting of arrays of gold-coated SiNR FETs. A microfluidic system with individual channels allows modifying the NR surfaces with self-assembled monolayers of two types of ion receptors sensitive to sodium and fluoride ions. The functionalization procedure results in a differential setup having active fluoride-and sodium-sensitive NRs together with bare gold control NRs on the same chip. Comparing functionalized NRs with control NRs allows the compensation of non-specific contributions from changes in the background electrolyte concentration and reveals the response to the targeted species

"Active surfaces" as Possible Functional Systems in Detection and Chemical (Bio) Reactivity

This article presents design strategies to demonstrate approaches to generate functionalized surfaces which have the potential for application in molecular systems; sensing and chemical reactivity applications are exemplified. Some applications are proven, while others are still under active investigation. Adaptation and extension of our strategies will lead to interfacing of different type of surfaces, specific interactions at a molecular level, and possible exchange of signals/cargoes between them. Optimization of the present approaches from each of five research groups within the NCCR will be directed towards expanding the types of functional surfaces and the properties that they exhibit

Rab27a and Rab27b control different steps of the exosome secretion pathway

Exosomes are secreted membrane vesicles that share structural and biochemical characteristics with intraluminal vesicles of multivesicular endosomes (MVEs). Exosomes could be involved in intercellular communication and in the pathogenesis of infectious and degenerative diseases. The molecular mechanisms of exosome biogenesis and secretion are, however, poorly understood. Using an RNA interference (RNAi) screen, we identified five Rab GTPases that promote exosome secretion in HeLa cells. Among these, Rab27a and Rab27b were found to function in MVE docking at the plasma membrane. The size of MVEs was strongly increased by Rab27a silencing, whereas MVEs were redistributed towards the perinuclear region upon Rab27b silencing. Thus, the two Rab27 isoforms have different roles in the exosomal pathway. In addition, silencing two known Rab27 effectors, Slp4 (also known as SYTL4, synaptotagmin-like 4) and Slac2b (also known as EXPH5, exophilin 5), inhibited exosome secretion and phenocopied silencing of Rab27a and Rab27b, respectively. Our results therefore strengthen the link between MVEs and exosomes, and introduce ways of manipulating exosome secretion in vivo

Mise en oeuvre expérimentale d’impacts basse vitesse sur matériau énergétique

Les matériaux énergétiques présentent un caractère sensible aux sollicitations mécaniques, chimiques ou thermiques « faibles », dont l’origine est probablement liée à un endommagement microstructural progressif du matériau. La butalite analysée dans le cadre de notre étude est un propergol composite, constitué de grains de perchlorate d’ammonium et d’une matrice polymérique de type PBHT. Pour décrire la réponse thermomécanique sous faible choc de ce matériau à l’échelle mésoscopique, nous réalisons des essais d’impacts basse vitesse à la tour de chute, sous différentes  configurations expérimentales, en couplant un enregistrement par caméra rapide à une analyse ante et post mortem de l’échantillon par microtomographie X..

Cdc42 controls the dilation of the exocytotic fusion pore by regulating membrane tension.

Membrane fusion underlies multiple processes, including exocytosis of hormones and neurotransmitters. Membrane fusion starts with the formation of a narrow fusion pore. Radial expansion of this pore completes the process and allows fast release of secretory compounds, but this step remains poorly understood. Here we show that inhibiting the expression of the small GTPase Cdc42 or preventing its activation with a dominant negative Cdc42 construct in human neuroendocrine cells impaired the release process by compromising fusion pore enlargement. Consequently the mode of vesicle exocytosis was shifted from full-collapse fusion to kiss-and-run. Remarkably, Cdc42-knockdown cells showed reduced membrane tension, and the artificial increase of membrane tension restored fusion pore enlargement. Moreover, inhibiting the motor protein myosin II by blebbistatin decreased membrane tension, as well as fusion pore dilation. We conclude that membrane tension is the driving force for fusion pore dilation and that Cdc42 is a key regulator of this force.journal articleresearch support, non-u.s. gov't2014 Oct 152014 08 20importe

IODP expedition 347: Baltic Sea basin paleoenvironment and biosphere

The Integrated Ocean Drilling Program (IODP) expedition 347 cored sediments from different settings of the Baltic Sea covering the last glacial-interglacial cycle. The main aim was to study the geological development of the Baltic Sea in relation to the extreme climate variability of the region with changing ice cover and major shifts in temperature, salinity, and biological communities. Using the Greatship Manisha as a European Consortium for Ocean Research Drilling (ECORD) mission-specific platform, we recovered 1.6 km of core from nine sites of which four were additionally cored for microbiology. The sites covered the gateway to the North Sea and Atlantic Ocean, several sub-basins in the southern Baltic Sea, a deep basin in the central Baltic Sea, and a river estuary in the north. The waxing and waning of the Scandinavian ice sheet has profoundly affected the Baltic Sea sediments. During theWeichselian, progressing glaciers reshaped the submarine landscape and displaced sedimentary deposits from earlier Quaternary time. As the glaciers retreated they left a complex pattern of till, sand, and lacustrine clay, which in the basins has since been covered by a thick deposit of Holocene, organic-rich clay. Due to the stratified water column of the brackish Baltic Sea and the recurrent and widespread anoxia, the deeper basins harbor laminated sediments that provide a unique opportunity for high-resolution chronological studies. The Baltic Sea is a eutrophic intra-continental sea that is strongly impacted by terrestrial runoff and nutrient fluxes. The Holocene deposits are recorded today to be up to 50m deep and geochemically affected by diagenetic alterations driven by organic matter degradation. Many of the cored sequences were highly supersaturated with respect to methane, which caused strong degassing upon core recovery. The depth distributions of conservative sea water ions still reflected the transition at the end of the last glaciation from fresh-water clays to Holocene brackish mud. High-resolution sampling and analyses of interstitial water chemistry revealed the intensive mineralization and zonation of the predominant biogeochemical processes. Quantification of microbial cells in the sediments yielded some of the highest cell densities yet recorded by scientific drilling

A finite-strain model for an explosive simulant

On propose un modèle de comportement isotherme en transformations finies pour l'équivalent inerte d'un explosif. Il décrit les processus dissipatifs correspondant à deux mécanismes différents dont l'un est plastique avec dilatance et l'autre est de type viscoélastique. Ce modèle est ensuite implanté dans le code EPIC-2 et utilisé pour simuler des expériences d'impact de plaques.An isothermal finite strain constitutive modelling for the mechanical behaviour of an explosive simulant is presented. It accounts for two different dissipative processes including dilatational plasticity and a complementary viscous mechanism (viscoelastic-like). This model is implemented into the EPIC-2 hydrocode and used to simulate plate impact experiments