Spatio-temporal patterns in a mechanical model for mesenchymal morphogenesis

We present an in-depth study of spatio-temporal patterns in a simplified version of a mechanical model for pattern formation in mesenchymal morphogenesis. We briefly motivate the derivation of the model and show how to choose realistic boundary conditions to make the system well-posed. We firstly consider one-dimensional patterns and carry out a nonlinear perturbation analysis for the case where the uniform steady state is linearly unstable to a single mode. In two-dimensions, we show that if the displacement field in the model is represented as a sum of orthogonal parts, then the model can be decomposed into two sub-models, only one of which is capable of generating pattern. We thus focus on this particular sub-model. We present a nonlinear analysis of spatio-temporal patterns exhibited by the sub-model on a square domain and discuss mode interaction. Our analysis shows that when a two-dimensional mode number admits two or more degenerate mode pairs, the solution of the full nonlinear system of partial differential equations is a mixed mode solution in which all the degenerate mode pairs are represented in a frequency locked oscillation

System thermal-hydraulic modelling of the phénix dissymmetric test benchmark

Phénix is a French pool-type sodium-cooled prototype reactor; before the definitive shutdown, occurred in 2009, a final set of experimental tests are carried out in order to increase the knowledge on the operation and the safety aspect of the pool-type liquid metal-cooled reactors. One of the experiments was the Dissymmetric End-of-Life Test which was selected for the validation benchmark activity in the frame of SESAME project. The computer code validation plays a key role in the safety assessment of the innovative nuclear reactors and the Phénix dissymmetric test provides useful experimental data to verify the computer codes capability in the asymmetric thermal-hydraulic behaviour into a pool-type liquid metal-cooled reactor. This paper shows the comparison of the outcomes obtained with six different System Thermal-Hydraulic (STH) codes: RELAP5-3D©, SPECTRA, ATHLET, SAS4A/SASSYS-1, ASTEC-Na and CATHARE. The nodalization scheme of the reactor was individually achieved by the participants; during the development of the thermal-hydraulic model, the pool nodalization methodology had a special attention in order to investigate the capability of the STH codes to reproduce the dissymmetric effects which occur in each loop and into pools, caused by the azimuthal asymmetry of the boundary conditions. The modelling methodology of the participants is discussed and the main results are compared in this paper to obtain useful guide lines for the future modelling of innovative liquid metal pool-type reactors

Nanomosaic Network for the Detection of Proteins Without Direct Electrical Contact

A nanomosaic network of metallic nanoparticles for the detection of ultralow concentrations of proteins is reported, which uses two planar microelectrodes embedded in a microchip that permit generation of capacitive coupling to the nanomosaic system without the need for direct electrical contact with the channel. By tailoring the microchannel surface using a sandwich configuration of polyethylene terephthalate/gold nanoparticles/poly(L-lysine), the surface charge can be modified following biomolecular interactions and monitored using a noncontact admittance technique. This nanodevice system behaves like a tunable capacitor and can be employed for the detection of any kind of molecule. The femtomolar detection of an anionic protein, such as b- lactoglobulin in phosphatebuffered saline medium, is taken as an example

Antioxidant Redox Sensors Based on DNA Modified Carbon Screen-Printed Electrodes

Antioxidant redox sensors based on DNA modified carbon screen-printed electrodes were developed. The carbon ink was doped with TiO2 nanoparticles, onto which double- strand DNA was adsorbed. A redox mediator, namely, tris- 2,2′-bipyridine ruthenium(II) [Ru(bpy)32+] was electro- oxidized on the electrode surface to subsequently oxidize both the adsorbed ds-DNA and the antioxidants in solu- tion. The resulting oxidation damage of the adsorbed ds- DNA was then detected by square wave voltammetry in a second solution containing only Ru(bpy)3Cl2 at a low con- centration (μM). A kinetic model was developed to study the protecting role of antioxidants in aqueous solutions. The electrochemical sensor has been applied to evaluate the redox antioxidant capacity of different molecules

Electrochemical evidence of catalysis of oxygen reduction at the polarized liquid–liquid interface by tetraphenylporphyrin monoacid and diacid

Cyclic voltammetry is used to study the role of 5,10,15,20-tetraphenyl-21H,23H-porphine (H2TPP) in the reduction of molecular oxygen by decamethylferrocene (DMFc) at the polarized water|1,2-dichloroethane (DCE) interface. It is shown that this rather slow reaction proceeds remarkably faster in the presence of tetraphenylporphyrin monoacid (H3TPP+) and diacid (H4TPP2+), which are formed in DCE by the successive transfer of two protons from the acidified aqueous phase. A mechanism is proposed, which includes the formation of adduct between H3TPP+ or H4TPP2+ and O2 that is followed by electron transfer from DMFc to the adduct leading to the observed production of DMFc+ and to the regeneration of H2TPP or H3TPP+, respectively

Random division of an interval

The well-known relation between random division of an interval and the Poisson process is interpreted as a Laplace transformation. With the use of this interpretation a number of (in part known) results is derived very easily

Adsorption and photoreactivity of CdSe nanoparticles at liquid|liquid interfaces

The voltage induced assembly and photoreactivity of cadmium selenide (CdSe) nanoparticles protected by mercaptosuccinic acid are studied at the polarisable interface between water and 1,2-dichloroethane electrolyte solutions. Cyclic voltammograms and admittance measurements show an increase of the interface excess charge associated with the adsorption of CdSe nanoparticles as the Galvani potential difference is tuned to negative values with respect to the potential in the organic phase. Within the potential range where the nanoparticles are adsorbed, band-gap illumination leads to heterogeneous electron transfer from CdSe nanoparticles to electron acceptors located in the organic phase. The interfacial Galvani potential difference plays an important role in these phenomena, as it affects the interfacial density of the nanoparticles, as well as the driving force for the electron transfer. The photocurrent efficiency also strongly depends on the formal redox potential of the electron acceptor, indicating that the heterogeneous photoreaction is kinetically controlled. The interfacial electron transfer occurs via depopulation of the deep trap states in the band gap. Analysis of the photocurrent transient responses reveals that the magnitude of the instantaneous photocurrent upon illumination is determined by the kinetics of heterogeneous electron transfer, while photogenerated holes are swiftly captured by species present in the aqueous phase. The photocurrent decay upon constant illumination is associated with the diffusion of the acceptor to the interfacial region. From the phenomenological point of view, the photoelectrochemical behaviour of CdSe nanoparticles can be compared to a self-assembled ultrathin p-type semiconductor photoelectrode

In-source photocatalytic reduction of disulfide bonds during laser desorption ionization

A photosensitive plate based on sintered TiO2 nanoparticles has been developed to carry out in-source photo-induced reductions for cleavage of disulfide bridges using glucose as a hole scavenger during laser desorption ionization

Electroacoustic miniaturized DNA-biosensor

A micrometer-sized electroacoustic DNA-biosensor was developed. The device included a thin semi-crystalline polyethylene terephthalate (PET) dielectric layer with two Ag microband electrodes on one side and a DNA thiol-labeled monolayer adsorbed on a gold surface on the other. A resonance wave was observed at 29 MHz with a network analyzer, upon AC voltage application between the two Ag electrodes, corresponding to electromechanical coupling induced by molecular dipoles of the PET polymer chain in the dielectric layer. It was found that the device size and geometry were well adapted to detect DNA hybridization, by measuring the capacity of the resonance response evolution: hybridization induced polarization of the dielectric material that affected the electromechanical coupling established in the dielectric layer. The 0.2 mm2 sensor sensitive area allows detection in small volumes and still has higher detection levels for bioanalytical applications, the non-contact configuration adopted avoids electric faradic reactions that may damage biosensor sensitive layers, and finally, PET is a costless raw material, easy to process and well adapted for large scale production. The well-balanced technological and economic advantages of this kind of device make it a good candidate for biochip integration

Specific On-Plate Enrichment of Phosphorylated Peptides for Direct MALDI-TOF MS Analysis

An on-plate specific enrichment method is presented for the direct analysis of peptides phosphorylation. An array of sintered TiO2 nanoparticle spots was prepared on a stainless steel plate to provide porous substrate with a very large specific surface and durable functions. These spots were used to selectively capture phosphorylated peptides from peptide mixtures, and the immobilized phosphopeptides could then be analyzed directly by MALDI MS after washing away the nonphos- phorylated peptides