Detailed analysis of dynamic mechanical properties of TPU nanocomposite: The role of the interfaces

Organo-modified layered silicates (OMLSs) can largely improve mechanical properties of Thermoplastic polyurethanes (TPUs) as well as affect their microdomain morphology. Nanocomposite TPU containing OMLSs were prepared by melt blending at different concentrations. The addition of OMLS has both induced variation in enthalpy of melting of hard and soft phases, and influenced the glass transition temperature of soft domains, as result of the microdomain phase segregation measured by means of fourier transform infrared spectroscopy (FT-IR). Small angle X-ray scattering (SAXS) analysis has shown that the mean distance between hard domains was mostly unaffected by the filler. However, its distribution broadened with the increasing concentration of the OMLSs, resulting in increased extent of the hard domain interface. The storage modulus of TPU nanocomposites incremented with the silicate content, while the dynamic strain scan tests showed pronounced non linear viscoelastic behavior. The analysis of morphological data obtained by SAXS and FT-IR measurements were correlated to thermal and dynamic mechanical properties of TPU samples suggesting a crucial role of the soft domains interface. The storage modulus and loss tangent of TPU nanocomposites were found to increase with the increasing of the interface area of soft domains with both hard domains and OMLS stacks.     

Indoor air quality: validation and setting up quality control for determination of anions and cations in particulate matter

In recent years, the indoor air quality has been studied more frequently due to an increasing concern within the scientific community on the effects of indoor air quality upon health. The indoor air quality studies of schools have a large impact in both health and educational performance of children since they constitute a sensitive group with higher risk than adults, particularly vulnerable to pollutants due to their undeveloped airways. A total of 14 basic schools located in Lisbon city, Portugal, were selected for sampling the total particulate matter (TPM) by passive deposition into polycarbonate filters and to assess the indoor air quality. Compared to automatic samplers, this passive sampling method represents an easier and cheaper way to assess several indoor air quality environments with no interference in the classroom activities. The procedure was performed on four different campaigns during 2009–2010. The filter loads were measured by gravimetry with a 0.1-μg sensitivity balance and, afterwards, the TPM water-soluble ions content was assessed by ionic chromatography (Cl⁻, NO₃ ⁻, PO₄ ³⁻ and SO₄ ²⁻); flame absorption (Na⁺, K⁺, Mg²⁺ and Ca²⁺). The performance characteristics of the methods, namely specificity, limit of detection, limit of quantification, working range, precision and trueness were evaluated. Measurement uncertainty was expressed in terms of precision and trueness. Precision under intralaboratory reproducibility conditions was estimated from triplicate analysis. The trueness component was estimated in terms of overall recovery using the reference material SPS-NUTR WW2 Batch 107, from Spectrapure Standards, Oslo, Norway, for anions and the certified reference material CRM 1643e, from NIST, Gaithersburg, MD for cations. Measurement uncertainty of the results obtained with the methods described in this work fulfilled the relative differences (RD) defined by the anion−cation balance in the extraction solutions of the particulate matter. Target RD values were defined: RD < 0.05.     

Physicochemical characterization and cytotoxic activity evaluation of hydroxymethylferrocene:β-cyclodextrin inclusion complex

An inclusion complex of hydroxymethylferrocene (FeMeOH) with β-cyclodextrin (β-CD) was prepared in the solid state by different techniques such as physical mixture, coprecipitation, kneading and freeze-drying. The formation of the inclusion complex was confirmed by X-ray Powder Diffractometry and Fourier Transform-Infrared spectroscopy. In aqueous solution, the 1:1 stoichiometry was established by a Job plot. The inclusion complex formation was also investigated by NMR and the stability constant (Kb) of the complex was determined to be 478 M?1, which is in agreement with that obtained with UV-Vis tritation (Kb = 541.3 M?1). The phase solubility study showed a diagram classified as Bs type and that the solubility of FeMeOH was slightly increased in the presence of β-CD. Furthermore, utilizing phase solubility diagram data, the Kb was estimated to be equal to 528.0 M?1. The cytotoxic activity of FeMeOH and its complexation product with β-CD was determined using the MTT-assay on MDA-MB-231 cell line, showing that the inclusion complex has a higher capability of inhibiting cell growth compared to that of pure FeMeOH.     

Solution enthalpies of hydroxylic compounds

Solution enthalpies of adamantan-1-ol, 2-methyl- butan-2-ol, and 3-methylbutan-1-ol have been measured at 298.15 K, in a set of 16 protogenic and non-protogenic solvents. The identification and quantification of solvent effects on the solution processes under study were performed using quantitative-structure property relationships. The results are discussed in terms of solute–solvent–solvent interactions and also in terms of the influence of compound’s size and position of its hydroxyl group.     

Comparative chemical composition and antioxidant activity of Calamintha nepeta (L.) Savi subsp. glandulosa (Req.) Nyman and Calamintha grandiflora (L.) Moench (Labiatae)

The two studied Calamintha species showed different polyphenolic content and sterol composition. Calamintha grandiflora possessed twice the polyphenolic content of Calamintha nepeta subsp. glandulosa, while the latter contained a higher number of sterols. Among them, stigmast-5-en-3β-ol was found to be the major constituent. The methanolic extract of C. grandiflora was more potent than the C. nepeta subsp. glandulosa methanolic extract in a DPPH assay, while the activity of the C. grandiflora EtOAc fraction was weaker than its C. nepeta subsp. glandulosa counterpart. Fractions of C. nepeta subsp. glandulosa showed higher activity using a β-carotene bleaching test. The petrol ether fraction of C. grandiflora showed significant inhibition of NO production.     

A compactness result for differentiable functions with an application to boundary value problems

We characterize the relative compactness of subsets of the space ${\mathcal{BC}^m([0,+\infty [;E)}$ of bounded and m-differentiable functions defined on [0, +∞[ with values in a Banach space E. Moreover, we apply this characterization to prove the existence of solutions of a boundary value problem in Banach spaces.     

A Jacobi–Davidson type method with a correction equation tailored for integral operators

We propose two iterative numerical methods for eigenvalue computations of large dimensional problems arising from finite approximations of integral operators, and describe their parallel implementation. A matrix representation of the problem on a space of moderate dimension, defined from an infinite dimensional one, is computed along with its eigenpairs. These are taken as initial approximations and iteratively refined, by means of a correction equation based on the reduced resolvent operator and performed on the moderate size space, to enhance their quality. Each refinement step requires the prolongation of the correction equation solution back to a higher dimensional space, defined from the infinite dimensional one. This approach is particularly adapted for the computation of eigenpair approximations of integral operators, where prolongation and restriction matrices can be easily built making a bridge between coarser and finer discretizations. We propose two methods that apply a Jacobi–Davidson like correction: Multipower Defect-Correction (MPDC), which uses a single-vector scheme, if the eigenvalues to refine are simple, and Rayleigh–Ritz Defect-Correction (RRDC), which is based on a projection onto an expanding subspace. Their main advantage lies in the fact that the correction equation is performed on a smaller space while for general solvers it is done on the higher dimensional one. We discuss implementation and parallelization details, using the PETSc and SLEPc packages. Also, numerical results on an astrophysics application, whose mathematical model involves a weakly singular integral operator, are presented.     

Asymptotically radial solutions in expanding annular domains

In this paper we consider the problem

$\left\{\begin{array}{ll}-\Delta u=u^{p}\quad {\rm in}\, \Omega_R,\\ u=0 \quad \quad \quad {\rm on}\, \partial\Omega_R,\quad\quad\quad (0.1)\end{array}\right.$

where p > 1 and Ω _R is a smooth bounded domain with a hole which is diffeomorphic to an annulus and expands as \({R \longrightarrow \infty}\). The main goal of the paper is to prove, for large R, the existence of a positive solution to (0.1) which is close to the positive radial solution in the corresponding diffeomorphic annulus. The proof relies on a careful analysis of the spectrum of the linearized operator at the radial solution as well as on a delicate analysis of the nondegeneracy of suitable approximating solutions.

     

A nonexistence theorem for an equation with critical Sobolev exponent in the half space

In this paper we prove the nonexistence of positive solutions of the equation-Δu=u^2*-1 inR ₊ ^N with certain homogeneous mixed boundary conditions. The proof is based on a monotonicity theorem obtained using the moving plane methods and some recent results of Berestycki and Nirenberg (see [BN]). The nonexistence theorem is applied to improve a result of [GP] on the characterization of the critical levels of a functional related to some nonlinear elliptic problem with critical Sobolev exponent and mixed boundary conditions.