Microstructural characterization of creep anisotropy at 673 K in the M5® alloy

Zirconium alloy tubing is used in pressurized water nuclear reactors in order to prevent fissile material from leaking into the coolant. It can be the first safety wall of nuclear fuel, and is submitted to complex thermomechanical loadings. In consequence, new Nb-modified alloys, such as the M5® alloy, and fine numerical models are being developed to guarantee a better and longer mechanical integrity of these tubes. To identify the physical mechanisms that could be considered in such models, an experimental approach, combining creep tests with electron backscattered diffraction and Transmission electron microscopy investigations, was carried out.Tubular specimens were submitted to multiaxial creep tests at a temperature of 673 K. Seven ratios between the axial and hoop applied stresses were investigated. It enabled a macroscopic evidence of the creep anisotropy. Besides, EBSD analyses on a mesoscopic-sized non deformed area led to the characterization of the variation of the average Schmid factor with the direction of loading. Finally, TEM observations were done on seven crept samples, corresponding to the seven directions of loading tested mechanically. The variations of the different parameters investigated (activated slip systems, dislocation densities, curvatures of the dislocations) can be seen as the effects of the creep anisotropy at a microscopic scale. The correlation between results is then discussed in a multiscale frame.     

DETONATION CLASSIFICATION FROM ACOUSTIC SIGNATURE WITH THE RESTRICTED BOLTZMANN MACHINE

We compare the recently proposed Discriminative Restricted Boltzmann Machine (DRBM) to the classical Support Vector Machine (SVM) on a challenging classification task consisting in identifying weapon classes from audio signals. The three weapon classes considered in this work (mortar, rocket, and rocket‐propelled grenade), are difficult to reliably classify with standard techniques because they tend to have similar acoustic signatures. In addition, specificities of the data available in this study make it challenging to rigorously compare classifiers, and we address methodological issues arising from this situation. Experiments show good classification accuracy that could make these techniques suitable for fielding on autonomous devices. DRBMs appear to yield better accuracy than SVMs, and are less sensitive to the choice of signal preprocessing and model hyperparameters. This last property is especially appealing in such a task where the lack of data makes model validation difficult.     

Discovery of Heterocyclic Nonacetamide Synaptic Vesicle Protein 2A (SV2A) Ligands with Single‐Digit Nanomolar Potency: Opening Avenues towards the First SV2A Positron Emission Tomography (PET) Ligands

The role of the synaptic vesicle protein 2A (SV2A) protein, target of the antiepileptic drug levetiracetam, is still mostly unknown. Considering its potential to provide in vivo functional insights into the role of SV2A in epileptic patients, the development of an SV2A positron emission tomography (PET) tracer has been undertaken. Using a 3D pharmacophore model based on close analogues of levetiracetam, we report the rationale design of three heterocyclic non‐acetamide lead compounds, UCB‐A, UCB‐H and UCB‐J, the first single‐digit nanomolar SV2A ligands with suitable properties for development as PET tracers.     

Superparamagnetic Ag@Co‐Nanocomposites on Granulated Cation Exchange Polymeric Matrices with Enhanced Antibacterial Activity for the Environmentally Safe Purification of Water

Cation exchange polymeric matrices are widely used in water treatment protocols to reduce the mineral content of hard waters, even for human consumption. However, they are not antibacterial and flowing bacteria can be trapped in their structures and proliferate, thus acting as microbial contamination sources. Here, Ag@Co‐nanoparticles (Ag@Co‐NPs) with a low‐cost superparamagnetic Co⁰‐core and an antibacterial Ag‐shell are synthesized on granulated cation exchange polymeric matrices under soft reaction conditions. The presence of these NPs provides the final nanocomposite (NC) with additional functionalities (superparamagnetism and antibacterial activity) making it ideal for water purification applications. Ag@Co‐NPs are synthesized in situ on four cation exchange polymeric matrices containing either strong (sulfonic) or weak (carboxylic) acid functional groups homogeneously distributed (C‐type) or concentrated on an external shell (SST‐type) by the intermatrix synthesis (IMS) method. The NCs are characterized (metal content, NP size and distribution, metal oxidative state, and metal release) and evaluated for water purification applications.     

The X-prolyl dipeptidyl-peptidase PepX of Streptococcus thermophilus initially described as intracellular is also responsible for peptidase extracellular activity

This study addresses the hypothesis that the extracellular cell-associated X-prolyl dipeptidyl-peptidase activity initially described in Streptococcus thermophilus could be attributable to the intracellular X-prolyl dipeptidyl-peptidase PepX. For this purpose, a PepX-negative mutant of S. thermophilus LMD-9 was constructed by interrupting the pepX gene and named LMD-9-ΔpepX. When cultivated, the S. thermophilus LMD-9 wild type strain grew more rapidly than its ΔpepX mutant counterpart. Thus, the growth rate of the LMD-9-ΔpepX strain was reduced by a factor of 1.5 and 1.6 in milk and LM17 medium (M17 medium supplemented with 2% lactose), respectively. The negative effect of the PepX inactivation on the hydrolysis of β-casomorphin-7 was also observed. Indeed, when incubated with this peptide, the LMD-9-ΔpepX mutant cells were unable to hydrolyze it, whereas this peptide was completely degraded by the S. thermophilus LMD-9 wild type cells. This hydrolysis was not due to leakage of intracellular PepX, as no peptide hydrolysis was highlighted in cell-free filtrate of wild type strain. Therefore, based on these results, it can be presumed that though lacking an export signal, the intracellular PepX might have accessed the β-casomorphin-7 externally, perhaps via its galactose-binding domain-like fold, this domain being known to help enzymes bind to several proteins and substrates. Therefore, the identification of novel distinctive features of the proteolytic system of S. thermophilus will further enhance its credibility as a starter in milk fermentation.     

Immobilization of aloin encapsulated into liposomes in Layer-by-layer films for transdermal drug delivery

Layer-by-layer (LbL) films have been exploited in drug delivery systems that may be used in the form of patches, but the encapsulation of poor water soluble drugs and their release with a controlled rate are still major challenges to be faced. In this paper, we demonstrate the controlled release of aloin (barbaloin), an important component of the widely used Aloe vera, encapsulated into liposomes and immobilized in LbL films with a polyelectrolyte. With a systematic study using fluorescence spectroscopy of aloin release from solutions and from LbL films with different phospholipid liposomes, we inferred that optimized release was achieved with aloin incorporated into palmitoyl oleyl phosphatidyl glycerol (POPG) or dipalmitoyl phosphatidyl glycerol (DPPG) liposomes immobilized in LbL films. Significantly, with this optimized system aloin was almost completely released within 30 h, with a small release rate at the end, which followed a sharp release in the first 5 h. Upon comparing the rates of the distinct systems, we conclude that the main factors controlling the release are the electrostatic interactions involving the negatively charged phospholipids. Because these interactions can be tuned in LbL films, the approach used here opens the way for new drug delivery systems to be developed with fine control of the drug release.     

Automatic multiple sclerosis lesion detection in brain MRI by FLAIR thresholding

Magnetic resonance imaging (MRI) is frequently used to detect and segment multiple sclerosis lesions due to the detailed and rich information provided. We present a modified expectation-maximisation algorithm to segment brain tissues (white matter, grey matter, and cerebro-spinal fluid) as well as a partial volume class containing fluid and grey matter. This algorithm provides an initial segmentation in which lesions are not separated from tissue, thus a second step is needed to find them. This second step involves the thresholding of the FLAIR image, followed by a regionwise refinement to discard false detections. To evaluate the proposal, we used a database with 45 cases comprising 1.5T imaging data from three different hospitals with different scanner machines and with a variable lesion load per case. The results for our database point out to a higher accuracy when compared to two of the best state-of-the-art approaches.     

Competing topological phases in few-layer graphene

We investigate the effect of spin-orbit coupling on the band structure of graphene-based two-dimensional Dirac fermion gases in the quantum Hall regime. Taking monolayer graphene as our first candidate, we show that a quantum phase transition between two distinct topological states—the quantum Hall and the quantum spin Hall phases—can be driven by simply tuning the Fermi level with a gate voltage. This transition is characterized by the existence of a chiral spin-polarized edge state propagating along the interface separating the two topological phases. We then apply our analysis to the more difficult case of bilayer graphene. Unlike in monolayer graphene, spin-orbit coupling by itself has indeed been predicted to be unsuccessful in driving bilayer graphene into a topological phase, due to the existence of an even number of pairs of spin-polarized edge states. While we show that this remains the case in the quantum Hall regime, we point out that by additionally breaking the layer inversion symmetry, a non-trivial quantum spin Hall phase can re-emerge in bilayer graphene at low energy. We consider two different symmetry-breaking mechanisms: inducing spin-orbit coupling only in the upper layer, and applying a perpendicular electric field. In both cases, the presence at low energy of an odd number of pairs of edge states can be driven by an exchange field. The related situation in trilayer graphene is also discussed.