Acoustical inverse problems regularization: Direct definition of filter factors using Signal-to-Noise Ratio

Acoustic imaging aims at localization and characterization of sound sources using microphone arrays. In this paper a new regularization method for acoustic imaging by inverse approach is proposed. The method first relies on the singular value decomposition of the plant matrix and on the projection of the measured data on the corresponding singular vectors. In place of regularization using classical methods such as truncated singular value decomposition and Tikhonov regularization, the proposed method involves the direct definition of the filter factors on the basis of a thresholding operation, defined from the estimated measurement noise. The thresholding operation is achieved using modified filter functions. The originality of the approach is to propose the definition of a filter factor which provides more damping to the singular components dominated by noise than that given by the Tikhonov filter. This has the advantage of potentially simplifying the selection of the best regularization amount in inverse problems. Theoretical results show that this method is comparatively more accurate than Tikhonov regularization and truncated singular value decomposition.     

Pressure- and temperature-induced association of arborescent polystyrene-graft-poly(ethylene oxide) copolymers at the air-water interface

The influence of surface pressure and subphase temperature on the association of arborescent polystyrene- graft-poly(ethylene oxide) (PS- g-PEO) copolymers at the air-water interface was investigated using the Langmuir balance and atomic force microscopy (AFM) techniques. These dendritic molecules form stable condensed monolayers with surface compressional moduli >250 mN/m. The variation in film thickness observed as a function of surface pressure suggests that at low surface pressures (gaslike phase) the PEO chains remain adsorbed at the air-water interface. At higher surface pressures (condensed phase), the PEO chains partially desorb into the subphase and adopt a more brushlike conformation. Large islandlike clusters with a broad size distribution were observed for samples with PEO contents of up to 15% by weight. In contrast, copolymers with PEO contents of 22-43% displayed enhanced side-by-side association into ribbonlike superstructures upon compression. The same effect was observed even in the absence of compression when the subphase temperature was increased from 12 to 27 degrees C. The temperature-induced association was attributed to increased van der Waals attractive forces between the PS cores relative to the steric repulsive forces between PEO chains in the coronas because the solvent quality for the PEO segments decreased at higher temperatures. The restricted number of superstructures observed for arborescent copolymers as compared with linear- and star-branched PS-PEO block copolymers is attributed to the enhanced structural rigidity of the molecules due to branching.     

Stability of Plasma Treated Non-vulcanized Polybutadiene Surfaces: Role of Plasma Parameters and Influence of Additives

Surface modification studies of non-vulcanized BR elastomers (butadiene rubber) by low-pressure air plasma treatment and the effect on ageing and adhesion performances are presented in this paper. In particular, the influence of discharge power and distance from the glow discharge, and impact of antioxidant molecules in the BR formulation were examined. To characterize the changes to the BR surface, XPS spectroscopy, contact angle measurements, AFM nanoindentation experiments and tack measurements were utilized. Oxidation and crosslinking were the main mechanisms observed on the polymer chains regardless of the plasma conditions used. Beyond a certain threshold of plasma energy (in our case, discharge power of ~60 W and exposure time of ~30 s), a steady state was reached irrespective of the distance from the glow discharge. The presence of antioxidant molecules considerably reduced crosslinking phenomena while maintaining oxidation processes on polymer chains and increasing the nitrogen content in the near surface region. The mechanisms responsible for these differences have been identified. Interestingly, the COOH/C=O ratio changed according to the balance between oxidation and crosslinking. The hydrophobic recovery rate was mainly driven by temperature-dependent dynamics and varied according to the degree of crosslinking in the surface region. It was found to be lower in air atmosphere in the presence of antioxidant molecules. Finally, the presence of antioxidant molecules in the BR formulation allowed the adhesion performances after plasma exposure to significantly increase.     

Complete 1H and 13C NMR assignments for two new monodesmoside saponins from Pentaclethra macroloba (Willd.) Kuntze

A detailed NMR study and full assignments of the 1H and 13C spectral data for two novel triterpenoid saponins isolated from the stem bark of Pentaclethra macroloba (Willd.) Kuntze are described. Their structures were established using a combination of 1D and 2D NMR techniques including 1H,1H-COSY, TOCSY, NOESY, gs-HMQC and gs-HMBC, and also electrospray ionization mass spectrometry and chemical methods. The structures were established as 3beta-O-([O-beta-D-glucopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(1-->4)-O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)]-[O-beta-D-glucopyranosyl-(1-->3)-O-beta-D-glucopyranosyl-(1-->4)])-alpha-L-arabinopyranosylhederagenin (1) and 3beta-O-)[O-beta-D-glucopyranosyl-(1-->2)-O-beta-D-glucopyranosyl-(1-->4)-O-beta-D-glucopyranosyl-(1-->3)-O-alpha-L-rhamnopyranosyl-(1-->2)]-[O-beta-D-glucopyranosyl-(1-->3)-O-beta-D-glucopyranosyl-(1-->4)])-alpha-L-arabinopyranosyloleanolic acid (2).     

PTV-LV-GC/MS/MS as screening and complementary method to HRMS for the monitoring of dioxin levels in food and feed

Recent developments in trapping efficiency inside ion trap mass spectrometer permitted to lower instrument detection limit (IDL). An IDL of 200 fg μl⁻¹ injected with a signal-to-noise ratio of 5:1 for tetrachlorodibenzo-p-dioxin (TCDD) was obtained by gas chromatography coupled to a quadrupole ion storage mass spectrometer in tandem mode (GC/MS/MS). Coupling large volume programmable temperature vaporizer (PTV-LV) injection to GC/MS/MS provides an alternative and complementary method to classical splitless-GC injection connected to high-resolution mass spectrometry (splitless-GC/HRMS) method for dioxin monitoring in food and feed.

An injection volume of 10 μl was found to be the best compromise between the sensitivity requirements and the robustness required for a high throughput method. PTV-LV-GC/MS/MS and Splitless-GC/HRMS were compared by performing analysis on five different matrices such as beef fat, yolk eggs, milk powder, animal feed and serum samples covering a concentration range of two orders of magnitude (i.e. 0.2–25 ng WHO-TEQ kg⁻¹). An analysis of variance (ANOVA) was carried out. Fisher tests pointed out that the method effect for all the 2,3,7,8 congeners was not significant, indicating that the null hypothesis (H₀: μ₁=μ₂=…=μ_n) was not rejected. Moreover, the interaction effects between methods and matrices were not significant for most of the 2,3,7,8 congeners. However, three congeners (2,3,7,8-TCDF; 1,2,3,4,7,8-HxCDD and 1,2,3,4,6,7,8-HpCDD) were characterized by P-values lower than the significance level (=0.05). In toxic equivalence (TEQ), the study showed that no significant bias was observed between the two methods. Consequently, PTV-LV-GC/MS/MS is an attractive technique and can be used as a cost effective complementary method to HRMS for dioxin levels monitoring in food and feed.     

Polypropylene/Cellulosic Fiber Composites Chemical Treatment of the Cellulose Assuming Compatibilization Between the Two Materials

Abstract

The present work deals with the realization of composites with a polypropylene (PP) matrix and cellulosic fibers as reinforcement. In order to achieve a good adhesion with the PP matrix, the modification of different cellulosic fibers has been performed with various chemical functions: carboxylic anhydrides, isocyanates, vinylsulfone, and chlorotriazine systems. All these compatibilizing agents carry an alkyl chain or a PP chain. Grafting is evidenced by infrared and ESCA spectroscopies, and the grafting rates for the different chemicals are determined by microweighing measurements. Modification of the surface characteristics is followed by wettability tests and inverse gas chromatography. Determination of the water sorption isotherm for the treated fibers shows an important decrease in water regain in the case of isocyanate treatments in swelling medium. Enhancement of adhesion between fibers and the matrix is demonstrated by mechanical tests: the interfacial shear stress obtained by the microbond test increases by 70% for cellulosic fibers treated with maleated PP. This may be the result of entanglements between PP chains, but for macrocomposites the effect is much more limited due to the predominance of external factors during development of the composite.     

Nanocomposite materials from latex and cellulose whiskers

Composite materials were processed by casting a mixture of aqueous suspensions of latex and microfibrils. These microfibrils, or whiskers, are extracted from a sea animal and are monocrystals of cellulose, with an aspect ratio around 100 and an average diameter of 20 nm. It has been found that the mechanical properties (shear modulus) are increased by more than two orders of magnitude in the rubbery state of the polymeric matrix, when the whisker content was 6% (w/w). This very large effect is discussed on the basis of different types of mechanical models and it is concluded that these whiskers form a rigid network, probably linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.     

Acid-Catalyzed E-Ring Expansion and Isomerization of 3-Acetylbetulin: Synthesis of Cytotoxic Anhydrobetulin Saponins

22(17 → 28)abeo-Lupene derivatives 5a and 6a were obtained after the acid-catalyzed E-ring expansion of 3-acetylbetulin (1a). Glycosylation of these dehydrated triterpenoids using Schmidt's trichloroacetimidate sugar donors in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf) provided the new anhydrobetulin saponins 7b–7e in which the terminal olefin C-20(29) isomerizes to form a C-19 tetrasubstituted alkene. The preliminary cytotoxic evaluation revealed that saponins 7b–7d exhibited a moderate cytotoxic activity against A549, DLD-1, and WS1 human cell lines with IC₅₀ ranging from 22 to 49 μM.     

In vitro determination of the release kinetics of peptides and free amino acids during the digestion of food proteins

The kinetics of peptide release during in vitro digestion of 4 protein sources (casein, cod protein, soy protein, and gluten) were investigated. Samples were sequentially hydrolyzed with pepsin (30 min) and pancreatin (2, 4, or 6 h) in a dialysis cell with continuous removal of digestion products. Nondialyzed digests were fractionated by ion-exchange chromatography and ultrafiltration. Animal proteins were digested at a greater rate than plant proteins. Target amino acids of specific enzymes appeared more rapidly in the dialyzed fractions when compared to other amino acids. Throughout the hydrolysis, nondialyzed digests contained a higher proportion of peptide mixtures with basic-neutral properties. Except for gluten, peptide fractions with molecular weights that exceeded 10 kDa (basic-neutral, BN > 10) were rapidly hydrolyzed during the first 2 h of pancreatin digestion. The kinetics of release and the composition of peptide fractions were different when the protein sources were compared. The analysis of amino acids revealed that threonine and proline proportions were relatively high in BN > 10 and in peptide fractions with molecular weight between 10-1 kDa (BN 10-1), while tyrosine, phenylalanine, lysine, and arginine predominated in the low molecular weight (<1 kDa) fractions. More resistant peptides were generally rich in proline and glutamic acid. The role of in vitro digestion assays in dietary protein quality evaluation is discussed.