ESR and XRD investigation of effects induced by gamma radiation on PVA-TiO2 membranes

The effects of gamma radiation on the local structure of PVA membranes containing TiO₂ were investigated by ESR and XRD methods. An intense ESR signal is observed after irradiation at 16 KGy dose. This signal appears only for irradiated samples and it is associated with the breaking of the polymeric chain, followed by local reorganization of the polymeric segments and the apparition of the unpaired electrons and free radicals. The intensity of the signal decreases with the concentration of TiO₂, indicating a shielding effect of the dopand. That the modification of local order of the polymeric chains has been modified after irradiation is confirmed by XRD method.     

Non-linear equity portfolio variance reduction under a mean–variance framework—A delta–gamma approach

To examine the variance reduction from portfolios with both primary and derivative assets we develop a mean–variance Markovitz portfolio management problem. By invoking the delta–gamma approximation we reduce the problem to a well-posed quadratic programming problem. From a practitioner’s perspective, the primary goal is to understand the benefits of adding derivative securities to portfolios of primary assets. Our numerical experiments quantify this variance reduction from sample equity portfolios to mixed portfolios (containing both equities and equity derivatives).     

MTD-ADJ: A multiconformational minimal topologic difference for determining bioactive conformers using adjusted biological activities

The active conformation is part of a conformational mixture with experimental activity Yexp, and is used in QSAR studies to extract more information regarding the ligand-receptor interaction. To reflect the relative amount () of the active conformation, we adjust Yexp : Yadj = Yexp - log . We establish a quantitative structure-activity relationship (QSAR) between Yadj and 3D conformational characteristics for the acetylcholinesterase (AChE) hydrolysis rates of 25 acetic esters. The 3D-QSAR model was obtained using the adjusted multiconformational minimal steric/topologic difference (MTD-ADJ) method, optimizing the receptor map based on Yadj for each conformer. Yadj was updated during each step of the optimization process. and Yadj are based on the Boltzmann distribution calculated using AM1 (MOPAC 6.0) relative energies of the COSMIC 90 derived conformers. The MTD-ADJ results are: (i) the 3D-QSAR models obtained by this procedure have significant statistical parameters and are similar to the unadjusted (MTD-MC, using Yexp) models; (ii) the selected bioactive conformations are extended, occupy cavity vertices and, for the same structures, have the same MTD value; and (iii) the optimized conformational map of the neutral ligands obtained from the MTD-ADJ model fits well in the active site of the crystallographic structure of AChE (from Torpedo californica). We propose a neutral ligands binding site model for AchE. Our results show that MTD-ADJ, which can be implemented in any 3D-QSAR method, is capable of providing additional information regarding the active conformations, and can be used to gain further insight into the ligand-receptor models for which no structural data are available.     

Validation of protein structural models using THz spectroscopy: a promising approach to solve three-dimensional structures

Terahertz (THz) spectroscopy is a promising technique for the study of protein structure and internal flexibility. Here, we used THz spectroscopy and molecular modeling for bovine serum albumin (BSA) structure investigation. BSA molecule was built using homology modeling methods and 30 different more relaxed models were obtained by molecular dynamics simulations of the hydrated protein. As the experimental and simulated THz spectra are linear, we compared them by comparing the slopes of the lines that fit them. Six BSA structures had slope values in the range given by the slope of the experimental spectrum $\pm $  0.2 and a total of sixteen BSA structures had slope values in the 0.6 interval near the experimental slope value. BSA average structures were calculated over the six and the sixteen identified BSA molecules. Based on the similarity with the crystal structure of BSA, we validated the average structure calculated over the sixteen BSA conformations. The comparison with the crystal structure showed that the structure validated using THz spectroscopy is a coarse model of BSA, as its root-mean-square deviation relative to the crystal structure is 1.9 Å. The regions from our model that present the highest deviation from the crystal structure are exterior loops. The results presented here show that using THz spectroscopy and molecular modeling is a promising approach to determine the structure of proteins.     

Influence of the heat treatment conditions on the formation of CuFe2O4 from mechanical milled precursors oxides

Stoichiometric mixture of CuO and ??-Fe₂O₃ milled in air up to 30?h was subjected to different heat treatments. The evolution of the heat treated milled powders was investigated by X-ray diffraction (XRD). The CuFe₂O₄ was partially obtained by milling, the material consisting in a mixture of phases. By applying different heat treatments in air and in vacuum, for 2?C6?h, in 500?C800?°C temperature range the phases composition of the milled samples is changed. A heat treatment at 500?°C in vacuum favours the formation of delafossite (CuFeO₂) and tenorite (CuO) phases. If the same heat treatment is made in air, the CuFe₂O₄ phase formation with a cubic structure is favoured. Differential scanning calorimetry (DSC) investigation realised in Ar atmosphere revealed two large exothermic peaks. The first one is associated with the formation of the delafossite and tenorite phases and the second one with the formation of CuFe₂O₄. The XRD patterns of the samples subjected to the DSC measurements present maxima corresponding to the delafossite and cuprospinel (CuFe₂O₄) phases. For the heat treatment at 600?°C in air the phases present in the sample are the same as for the annealing performed at 500?°C: CuFe₂O₄, ??-Fe₂O₃ and CuO. The heat treatment in air at 800?°C leads to the complete reaction between the different phases and the formation of CuFe₂O₄ phase in whole the sample volume. The CuFe₂O₄ ferrite crystallises after this heat treatment in two crystal systems: cubic and tetragonal.     

The Effect of UV-Irradiation on Poly(vinyl alcohol) Composites with Bacterial Cellulose

The development of biodegradable packaging materials, especially from renewable resources is a constant preoccupation of nowadays, because of the environmental problems caused by synthetic polymers. The combination of cellulose with other polymeric materials could be an ecologic alternative and a way to use renewable resources for food packaging. Bacterial cellulose which is produced by microbial fermentation is also a promising material which can be used not only in biomedical application, but also as food packaging material. In this research different composite films between poly(vinyl alcohol)-bacterial cellulose (PVA-BC) were obtained by casting method. The obtained films were UV irradiated for different periods of times from 1 to 10 hours, using a mercury lamp, Philips TUV-30, emitting light mainly at 254 nm. Changes in FT-IR spectra before and after UV irradiation and the modification of transparency and of the swelling characteristics of the films were observed. As it was expected the composites materials are sensitive at UV exposure.     

Improvement in Radiation Stability of EPDM by Efficient Antioxidants

This paper analyses the stabilization effect induced by the presence of several compounds with antioxidant features (oleanolic acid, quercetin, capsaicin, metallic selenium and rosemary extract). The investigation are carried out for different additive concentrations (0, 0.25, 0.50 and 1% w/w), as well as for pairs of metallic selenium with the other four compounds. For antirad contribution to the delaying of radiochemical oxidation, modified and pristine EPDM samples were irradiated in GAMMATOR machinery provided with ¹³⁷Cs source. While dose rate is 0.4 kGy.h⁻¹, the total doses were 0, 10, 20 and 30 kGy, which are specific for radiosterilization. The results are obtained by application of two complementary techniques: isothermal chemiluminescence (180 °C) and FT-IR spectroscopy. From chemiluminescence determinations oxidation induction times and rate of oxidation were calculated as the main kinetic characteristics depicting the progress in the oxidative degradation of polymer substrate. FT-IR spectroscopy allows us to evaluate the evolution of hydroxyl and carbonyl accumulations.     

Numerical approximation of the Smagorinsky model by a two-level method

A two-level method for discretizing the Smagorinsky model for the numerical simulation of turbulent flows is proposed. In the two-level algorithm, the solution to the fully nonlinear coarse mesh problem is utilized in a single-step linear fine mesh problem. When modeling parameters are chosen appropriately, the error in the two-level algorithm is comparable to the error in solving the fully nonlinear problem on the fine mesh. We provide an a priori error estimate for the two-level method, which yields appropriate scalings between the coarse and fine mesh-sizes (H and h, respectively), and the radius of the spatial filter used in the Smagorinsky model (δ). In addition, we provide an algorithm in which a coarse mesh correction is performed to further enhance the accuracy. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Improvement of thermal stability of EPDM by radiation cross-linking for space applications

Journal of Thermal Analysis and Calorimetry - The investigation of radiation effects on ethylene–propylene–diene terpolymer (EPDM) loaded with trifunctional monomer (trimethylolpropane...     

Thermal stability of gamma-irradiated polyurethane/POSS hybrid materials

Through temperature-programmed pyrolysis, the physicochemical properties of Pteria martensii (PM) before and after calcination are investigated. Our results show that the mass loss is 11.02% from room temperature to 600 °C with an average mass loss rate of 0.19% per min. The decomposition of organics coupling with the phase transition of calcium carbonate from aragonite to calcite occurs in the range of 367.4–423.0 °C, as confirmed by X-ray diffraction and Fourier transform infrared spectroscopy analyses. The decomposition pores and channels are changed forming complex porous structures. The surface of sample shows a much rougher fracture, with higher C, O and N element concentrations. At the stage of decomposition and phase transition of organics, the average activation energy value is 118.78 kJ mol^?1. This study provides valuable information on the calcination process and calcined PM for use in medicines.