Stability results for the approximation of weakly coupled wave equations

In this Note, we consider the approximation of two coupled wave equations with internal damping. Our goal is to damp the spurious high frequency modes by introducing numerical viscosity terms in the approximation scheme. With these viscosity terms, we show the exponential or polynomial decay of the discrete scheme when the continuous problem has such a decay (since the spectrum of the spatial operator associated with the undamped system satisfies the generalized gap condition).     

Comparison of fullerene and large argon clusters for the molecular depth profiling of amino acid multilayers

A major challenge regarding the characterization of multilayer films is to perform high-resolution molecular depth profiling of, in particular, organic materials. This experimental work compares the performance of C₆₀ ⁺ and Ar₁₇₀₀ ⁺ for the depth profiling of model multilayer organic films. In particular, the conditions under which the original interface widths (depth resolution) were preserved were investigated as a function of the sputtering energy. The multilayer samples consisted of three thin δ-layers (~8 nm) of the amino acid tyrosine embedded between four thicker layers (~93 nm) of the amino acid phenylalanine, all evaporated on to a silicon substrate under high vacuum. When C₆₀ ⁺ was used for sputtering, the interface quality degraded with depth through an increase of the apparent width and a decay of the signal intensity. Due to the continuous sputtering yield decline with increasing the C₆₀ ⁺ dose, the second and third δ-layers were shifted with respect to the first one; this deterioration was more pronounced at 10 keV, when the third δ-layer, and a fortiori the silicon substrate, could not be reached even after prolonged sputtering. When large argon clusters, Ar₁₇₀₀ ⁺, were used for sputtering, a stable molecular signal and constant sputtering yield were achieved throughout the erosion process. The depth resolution parameters calculated for all δ-layers were very similar irrespective of the impact energy. The experimental interface widths of approximately 10 nm were barely larger than the theoretical thickness of 8 nm for the evaporated δ-layers.

EMI shielding and microwave absorption behavior of Au‐MWCNT/polyaniline nanocomposites

Electrically conducting Au‐multiwalled carbon nanotube/polyaniline (Au‐MWCNT/PANi) nanocomposites were synthesized by two different ways: (1) by direct mixing of MWCNT/PANi and Au nanoparticles (Au‐MWCNT/PANi‐1) and (2) by in situ polymerization of aniline in the presence of both MWCNTs and Au nanoparticles (Au‐MWCNT/PANi‐2). The higher electrical conductivity of Au‐MWCNT/PANi‐2 compared with the other samples (PANi, MWCNT/PANi, Au‐MWCNT/PANi‐1) is supported by the red shifts of the UV‐vis bands (polaron/bipolaron), the high value of the –NH+= stretch peak (Fourier transform infrared spectroscopy studies), the high % crystallinity (X‐ray diffraction analysis) and more uniform dispersion of the Au NPs in the material. The performance of the samples in electromagnetic interference (EMI) shielding and microwave absorption was studied in the X‐band (8–12 GHz). For all the samples, absorption was the dominant factor contributing toward the EMI shielding. Au‐MWCNT/PANi‐2 showed the best performance with a total shielding effectiveness of ?16 dB [averaged over the X‐band (GHz)] and a minimum reflection loss of ?56.5 dB. The higher dielectric properties resulting from the heterogeneities because of the presence of nanofillers and the high electrical conductivity lead to the increased EMI shielding and microwave absorption. The results show the significance of both Au nanoparticles and method of synthesis on the EMI shielding performance of MWCNT/PANi composites. Copyright © 2016 John Wiley & Sons, Ltd.     

A Stable Integrated Photoelectrochemical Reactor for H2 Production from Water Attains a Solar-to-Hydrogen Efficiency of 18 % at 15 Suns and 13 % at 207 Suns

The major challenge in solar water splitting to H₂ and O₂ is in making a stable and affordable system for large-scale applications. We have designed, fabricated, and tested a photoelectrochemical reactor characterized as follows: 1) it comprises an integrated device to reduce the balance of the system cost, 2) it utilizes concentrated sunlight to reduce the photoabsorber cost, and 3) it employs and alkaline electrolyte to reduce catalyst cost and eliminate external thermal management needs. The system consists of an III-V-based photovoltaic cell integrated with Ni foil as an O₂ evolution catalyst that also protects the cell from corrosion. At low light concentration, without the use of optical lenses, the solar-to-hydrogen (STH) efficiency was 18.3 %, while at high light concentration (up to 207 suns) with the use of optical lenses, the STH efficiency was 13 %. Catalytic tests conducted for over 100 hours at 100–200 suns showed no sign of degradation nor deviation from product stoichiometry (H₂/O₂=2). Further tests projected a system stability of years.     

Stabilisation faible interne locale de système élastique de Bresse

In [1], Alabau-Boussouira et al. (2011) studied the exponential and polynomial stability of the Bresse system with one globally distributed dissipation law. In this Note, our goal is to extend the results from Alabau-Boussouira et al. (2011) [1], by taking into consideration the important case when the dissipation law is locally distributed and to improve the polynomial energy decay rate. We then study the energy decay rate of the Bresse system with one locally internal distributed dissipation law acting on the equation about the shear angle displacement. Under the equal speed wave propagation condition, we show that the system is exponentially stable. On the contrary, we establish a new polynomial energy decay rate.     

Metal-assisted SIMS and cluster ion bombardment for ion yield enhancement

In addition to structural information, a detailed knowledge of the local chemical environment proves to be of ever greater importance, for example for the development of new types of materials as well as for specific modifications of surfaces and interfaces in multiple fields of materials science or various biomedical and chemical applications. But the ongoing miniaturization and therefore reduction of the amount of material available for analysis constitute a challenge to the detection limits of analytical methods. In the case of time-of-flight secondary ion mass spectrometry (TOF-SIMS), several methods of secondary ion yield enhancement have been proposed. This paper focuses on the investigation of the effects of two of these methods, metal-assisted SIMS and polyatomic primary ion bombardment. For this purpose, thicker layers of polystyrene (PS), both pristine and metallized with different amounts of gold, were analyzed using monoatomic (Ar⁺, Ga⁺, Xe⁺, Bi⁺) and polyatomic (SF₅⁺, Bi₃⁺, C₆₀⁺) primary ions. It was found that polyatomic ions generally induce a significant increase of the secondary ion yield. On the other hand, with gold deposition, a yield enhancement can only be detected for monoatomic ion bombardment.     

Antioxidant Properties of Hydrogen Gas Attenuates Oxidative Stress in Airway Epithelial Cells

Oxidative stress plays a crucial role in the development of airway diseases. Recently, hydrogen (H₂) gas has been explored for its antioxidant properties. This study investigated the role of H₂ gas in oxidative stress-induced alveolar and bronchial airway injury, where A549 and NCI-H292 cells were stimulated with hydrogen peroxide (H₂O₂) and lipopolysaccharide (LPS) in vitro. Results show that time-dependent administration of 2% H₂ gas recovered the cells from oxidative stress. Various indicators including reactive oxygen species (ROS), nitric oxide (NO), antioxidant enzymes (catalase, glutathione peroxidase), intracellular calcium, and mitogen-activated protein kinase (MAPK) signaling pathway were examined to analyze the redox profile. The viability of A549 and NCI-H292 cells and the activity of antioxidant enzymes were reduced following induction by H₂O₂ and LPS but were later recovered using H₂ gas. Additionally, the levels of oxidative stress markers, including ROS and NO, were elevated upon induction but were attenuated after treatment with H₂ gas. Furthermore, H₂ gas suppressed oxidative stress-induced MAPK activation and maintained calcium homeostasis. This study suggests that H₂ gas can rescue airway epithelial cells from H₂O₂ and LPS-induced oxidative stress and may be a potential intervention for airway diseases.     

Optically pure beta-substituted beta-hydroxy aspartates as glutamate transporter blockers

A short asymmetric synthesis of optically pure beta-substituted beta-hydroxy aspartates is described. The key step is an aldol reaction between a glycine enolate derived from an oxazinone intermediate used as chiral auxiliary and various alpha-keto esters. Excellent diastereomeric excesses are obtained.     

FT-IR spectral imaging of blood vessels reveals protein secondary structure deviations induced by tumor growth

Vascular basement membrane remodeling is involved in tumor angiogenesis to enable tumor invasion and growth. FT-IR spectral imaging was used to determine changes in tumor blood vessels to reveal protein secondary structure in Rag-gamma immuno-deficient mice sacrificed 14 and 21 days after subcutaneous glioma implantation. For the oldest blood capillaries (diameter >20 microns), tumor growth induced a decrease in triple-helix content (1638 cm(-1); -7.3%; P < 0.05) and an increase in beta turns (1666 and 1615 cm(-1); +4%; P < 0.01). These protein-structure alterations, mainly from type IV collagen, reflected the high angiogenic stress of growing tumors. We propose to use these molecular markers of vascular basement membrane protein alterations for gradation of solid tumors by FT-IR spectral imaging.