Large‐scale extrusion processing and characterization of hybrid nylon‐6/SiO2 nanocomposites

Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide‐6 (PA‐6) is achieved using a twin‐screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6 kg h^?1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA‐6 showed higher amounts of γ‐phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E‐modulus increased from 2.7 to 3.9 GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E′ and E″) increased and tan δ decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd.     

Monitoring stabilizing procedures of archaeological iron using electrochemical impedance spectroscopy

A methodology for monitoring washing procedures applied to stabilize archaeological iron is described. It is based on the combination of voltammetry of microparticles (VMP) with electrochemical impedance spectroscopy (EIS). A semi-empirical approach is used where the impedances at low and high frequencies were related with the fraction areas of passive and corrosion layers generated during the stabilizing treatment, the thickness, and the porosity of the corrosion layer. The variation of such parameters with the time of washing was determined from EIS data for four types of desalination procedures using concentrated NaOH and/or Na₂SO₃ aqueous solutions on archaeological iron artifacts. After 2 months of treatment, EIS data indicate that an essentially identical “stable” state was attained in all cases, as confirmed by the formation of a passive magnetite layer identified in VMP measurements while the rate of variation of corroded surface and porosity at short washing times varied significantly from one stabilization procedure to another.     

Improved Thermal and Reusability Properties of Xylanase by Genipin Cross-Linking to Magnetic Chitosan Particles

Enzymes are gradually increasingly preferred over chemical processes, but commercial enzyme applications remain limited due to their low stability and low product recovery, so the application of an immobilization technique is required for repeated use. The aims of this work were to produce stable enzyme complexes of cross-linked xylanase on magnetic chitosan, to describe some characteristics of these complexes, and to evaluate the thermal stability of the immobilized enzyme and its reusability. A xylanase was cross-linked to magnetite particles prepared by in situ co-precipitation of iron salts in a chitosan template. The effect of temperature, pH, kinetic parameters, and reusability on free and immobilized xylanase was evaluated. Magnetization, morphology, size, structural change, and thermal behavior of immobilized enzyme were described. 1.0?±?0.1 μg of xylanase was immobilized per milligram of superparamagnetic chitosan nanoparticles via covalent bonds formed with genipin. Immobilized xylanase showed thermal, pH, and catalytic velocity improvement compared to the free enzyme and can be reused three times. Heterogeneous aggregates of 254 nm were obtained after enzyme immobilization. The immobilization protocol used in this work was successful in retaining enzyme thermal stability and could be important in using natural compounds such as Fe₃O₄@Chitosan@Xylanase in the harsh temperature condition of relevant industries.

     

Determination of Phenolic Compounds and the Antioxidant Capacity of Ximenia parviflora Benth. var. parviflora (Olacaceae) Fruit by High-Performance Liquid Chromatography with Diode Array Detection

The total phenolic and flavonoid content, phenolic composition, and in vitro antioxidant capacity of ethanolic extracts of Ximenia parviflora Benth. var. parviflora fruits collected at Zinaparo, Michoacan (in central Mexico) were determined. Fruit extracts present a high scavenging activity of 2,2-diphenyl-1-picrylhydrazyl and 2,2′-azino-bis[3-ethylbenzothiazoline-6-sulfonic acid] radicals (71.49?±?0.11% and 85.00?±?1.29% inhibition, respectively). The four phenolic compounds identified in fruit extracts by high-performance liquid chromatography with diode array detection were gallic acid, chlorogenic acid, caffeic acid, and quercetin. X. parviflora fruits may be used as a starting material for the extraction of high value antioxidant phenolic compounds with potential applications in the pharmaceutical and dietary supplement industries.     

Regularization Parameter Selection in Total Variation Based Image Denoising

A new approach of selecting the regularization parameter in a multiscale total variation model is proposed. The method is combined with a primal–dual algorithm to get a new iteration method for noise removal. Numerical results illustrate significant improvement over other popular methods. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Prediction and realisation of high mobility and degenerate p-type conductivity in CaCuP thin films

Phosphides are interesting candidates for hole transport materials and p-type transparent conducting applications, capable of achieving greater valence band dispersion than their oxide counterparts due to the higher lying energy and increased size of the P 3p orbital. After computational identification of the indirect-gap semiconductor CaCuP as a promising candidate, we now report reactive sputter deposition of phase-pure p-type CaCuP thin films. Their intrinsic hole concentration and hole mobility exceed 1 × 10²⁰ cm⁻³ and 35 cm² V⁻¹ s⁻¹ at room temperature, respectively. Transport calculations indicate potential for even higher mobilities. Copper vacancies are identified as the main source of conductivity, displaying markedly different behaviour compared to typical p-type transparent conductors, leading to improved electronic properties. The optical transparency of CaCuP films is lower than expected from first principles calculations of phonon-mediated indirect transitions. This discrepancy could be partly attributed to crystalline imperfections within the films, increasing the strength of indirect transitions. We determine the transparent conductor figure of merit of CaCuP films as a function of composition, revealing links between stoichiometry, crystalline quality, and opto-electronic properties. These findings provide a promising initial assessment of the viability of CaCuP as a p-type transparent contact.

We synthesize air-stable, p-type CaCuP thin films with high hole concentration and high hole mobility as potential p-type transparent conductors. We study their optoelectronic properties in detail by advanced experimental and computational methods.     

Determination and quantification of phenolic compounds in methanolic extracts of Solanum ferrugineum (Solanaceae) fruits by HPLC-DAD and HPLC/ESI-MS/TOF

Solanum ferrugineum Jacq. is a wild species that in previous analysis reported a significant antioxidant capacity. The aim of our research was to determine total phenolic content (TPC) and total flavonoid content (TFC), and the phenolic composition by HPLC-DAD and HPLC/ESI-MS/TOF of methanolic extracts of S. ferrugineum fruits, collected from Paredones, Jiquilpan, and Fray Dominguez, Pajuacarán in the Mexican state of Michoacán. TPC and TFC were determined by the spectrophotometric Folin–Ciocalteu reagent and the AlCl₃ method, respectively. TPC in S. ferrugineum fruit [31.41?±?0.91?mg gallic acid equivalent/g dry tissue (DT)] was similar to those reported for Turkey berry (Solanum torvum Sw.) and eggplant (Solanum melongena L.) fruits. The TFC values of S. ferrugineum fruits (29.14?±?4.99?mg catechin equivalent /g DT) corresponded to 80.24% of the TPC. Eight phenolic compounds (PC) were identified by HPLC analysis. The main PC identified in S. ferrugineum fruits were chlorogenic acid, caffeic acid, p-coumaric acid, gallic acid, quercetin, and kaempferol. S. ferrugineum fruits could be used as a starting material for the extraction of high-value PC with potential applications.     

Curves having one place at infinity and linear systems on rational surfaces

Denoting by L_d(m₀,m₁,…,m_r) the linear system of plane curves of degree d passing through r+1 generic points p₀,p₁,…,p_r of the projective plane with multiplicity m_i (or larger) at each p_i, we prove the Harbourne-Hirschowitz Conjecture for linear systems L_d(m₀,m₁,…,m_r) determined by a wide family of systems of multiplicities and arbitrary degree d. Moreover, we provide an algorithm for computing a bound for the regularity of an arbitrary system , and we give its exact value when is in the above family. To do that, we prove an H¹-vanishing theorem for line bundles on surfaces associated with some pencils “at infinity”.     

Antinociceptive Synergism of Pomegranate Peel Extract and Acetylsalicylic Acid in an Animal Pain Model

Several modern drugs, which are derived from traditional herbal medicine are used in contemporary pharmacotherapy. Currently, the study of drug–plant interactions in pain has increased in recent years, looking for greater efficacy of the drug and reduce side effects. The antinociception induced by intragastric co-administration of the combination of pomegranate peel extract (PoPEx) and acetylsalicylic acid (ASA) was assessed using the isobolographic analysis in formalin test (nociceptive and inflammatory pain). The effective dose that produced 30% of antinociception (ED₃₀) was calculated for both drugs from the logarithmic dose–response curves, subsequently generating a curve with the combination on fixed proportions (1:1) of PoPEx and ASA. Through isobolographic analysis, this experimental ED₃₀ was compared with the calculated theoretical additive ED₃₀. The result was a synergistic interaction, the experimental ED₃₀ was significantly smaller (p < 0.05) than the theoretical ED₃₀. The antinociceptive mechanism of the PoPEx-ASA combination involves the l-Arginine/NO/cGMP pathway, antioxidant capacity, and high content of total phenols. These findings suggest that an interaction between PoPEx and ASA could be a novel treatment for inflammatory and nociceptive pain, also diminish the secondary reactions of ASA.     

Evaluation codes defined by finite families of plane valuations at infinity

We construct evaluation codes given by weight functions defined over polynomial rings in m ≥ 2 indeterminates. These weight functions are determined by sets of m?1 weight functions over polynomial rings in two indeterminates defined by plane valuations at infinity. Well-suited families in totally ordered commutative groups are an important tool in our procedure.