Quantifying the nonlinear mode competition in the flow over an open cavity at medium Reynolds number

Our purpose is to quantify the rate of intermittency of nonlinearly competing modes, in a dominantly mode-switching scenario. What is the rate of presence of each mode? Can they simultaneously appear in, or disappear from the signal? The study is done in the context of open flows, exhibiting self-sustained oscillations, where air is here flowing over an open cavity. Reynolds numbers are of the order of 14,000. Velocity measurements downstream of the cavity are based on a laser Doppler velocimetry technique. We propose two methods to estimate the rate of presence of each mode: one based on a complex demodulation technique, the other on the distribution of the state vectors in the phase portrait of the signal.     

On the star-discrepancy of generalized Hammersley sequences in two dimensions

From a previous study in one dimension, precise estimates are deduced for the star discrepancy of some generalized Hammersley sequences in two dimensions, giving the lower constants presently known; also general bounds are obtained, and it is shown that these bounds are reached by the usual Hammersley sequences.     

Complex aggregation patterns in drying nanocolloidal suspensions: size matters when it comes to the thermomechanical stability of nanoparticle-based structures

We report the results of a model study on the interrelation among the occurrence of complex aggregation patterns in drying nanofluids, the size of the constitutive nanoparticles (NPs), and the drying temperature, which is a critical issue in the genesis of complex drying patterns that was never systematically reported before. We show that one can achieve fine control over the occurrence and topological features of these drying-mediated complex structures through the combination of the particle size, the drying temperature, and the substrate surface energy. Most importantly, we show that a transition in the occurrence of the patterns appears with the temperature and the particle size, which accounts for the size dependence of the thermomechanical stability of the aggregates in the nanoscale range. Using simple phenomenological and scaling considerations, we showed that the thermomechanical stability of the aggregates was underpinned by physical quantities that scale with the size of the NPs (R) either as R(-2) or R(-3). These insights into the size-dependent dissipation mechanisms in nanoclusters should help in designing NPs-based structures with tailored thermomechanical and environmental stability and hence with an optimized morphological stability that guarantees their long-term functional properties.     

Electrochromatography in cyclic olefin copolymer microchips: A step towards field portable analysis

In order to develop a portable and disposable instrument for on-site analysis of neutral compounds, a lauryl methacrylate monolith has been synthesized into a cyclic olefin copolymer microdevice for reversed-phase electrochromatography purposes. This monolith was tested in capillary to evaluate electrochromatographic performances in terms of electroosmotic flow (EOF) mobility, retention and efficiency prior to its transfer into the microfluidic device. The produced monolithic bed exhibited a good run-to-run repeatability, column-to-column reproducibility and batch-to-batch reproducibility, with relative standard deviation (RSD) values below 9% for EOF mobility, retention factors and heights of theoretical plate. The electrochromatographic performances of the monolith were optimized by reducing irradiation time. Photopolymerization time of 10 min was found to be the best process in order to obtain a robust, retentive and efficient system. The on-chip performances of this monolith were evaluated in detail for the reversed-phase electrochromatographic separation of polycyclic aromatic hydrocarbons, with plate heights reaching down to 15 μm when working at optimal velocity. Aiming at the maximum simplification of instrumental fabrication and operation, a direct injection from a 2 μL droplet was compared with more conventional dynamic injection process.     

Upper Bound on the Density of Ruelle Resonances for Anosov Flows

Using a semiclassical approach we show that the spectrum of a smooth Anosov vector field V on a compact manifold is discrete (in suitable anisotropic Sobolev spaces) and then we provide an upper bound for the density of eigenvalues of the operator (−i)V, called Ruelle resonances, close to the real axis and for large real parts.     

A Hot‐Segment‐Based Approach for the Design of Cross‐Amyloid Interaction Surface Mimics as Inhibitors of Amyloid Self‐Assembly

The design of inhibitors of protein–protein interactions mediating amyloid self‐assembly is a major challenge mainly due to the dynamic nature of the involved structures and interfaces. Interactions of amyloidogenic polypeptides with other proteins are important modulators of self‐assembly. Here we present a hot‐segment‐linking approach to design a series of mimics of the IAPP cross‐amyloid interaction surface with Aβ (ISMs) as nanomolar inhibitors of amyloidogenesis and cytotoxicity of Aβ, IAPP, or both polypeptides. The nature of the linker determines ISM structure and inhibitory function including both potency and target selectivity. Importantly, ISMs effectively suppress both self‐ and cross‐seeded IAPP self‐assembly. Our results provide a novel class of highly potent peptide leads for targeting protein aggregation in Alzheimer’s disease, type 2 diabetes, or both diseases and a chemical approach to inhibit amyloid self‐assembly and pathogenic interactions of other proteins as well.     

Comparative studies of nontoxic and toxic amyloids interacting with membrane models at the air-water interface

Many in vitro studies have pointed out the interaction between amyloids and membranes, and their potential involvement in amyloid toxicity. In a previous study, we generated a yeast toxic mutant (M8) of the harmless model amyloid protein HET-s((218-289)). In this study, we compared the self-assembling process of the nontoxic wild-type (WT) and toxic (M8) protein at the air-water interface and in interaction with various phospholipid monolayers (DOPE, DOPC, DOPI, DOPS and DOPG). We first demonstrate using ellipsometry measurements and polarization-modulated infrared reflection absorption spectroscopy (PMIRRAS) that the air-water interface promotes and modifies the assembly of WT since an amyloid-like film was instantaneously formed at the interface with an antiparallel β-sheet structuration instead of the parallel β-sheet commonly observed for amyloid fibers generated in solution. The toxic mutant (M8) behaves in a similar manner at the air-water interface or in bulk, with a fast self-assembling and an antiparallel β-sheet organization. The transmission electron microscopy (TEM) images established the fibrillous morphology of the protein films formed at the air-water interface. Second, we demonstrate for the first time that the main driving force between this particular fungus amyloid and membrane interaction is based on electrostatic interactions with negatively charged phospholipids (DOPG, DOPI, DOPS). Interestingly, the toxic mutant (M8) clearly induces perturbations of the negatively charged phospholipid monolayers, leading to a massive surface aggregation, whereas the nontoxic (WT) exhibits a slight effect on the membrane models. This study allows concluding that the toxicity of the M8 mutant could be due to its high propensity to interact with membranes.