Styrene Butadiene Rubber/Epoxidized Natural Rubber (SBR/ENR50) Nanocomposites Containing Nanoclay and Carbon Black as Fillers for Application in Tire-Tread Compounds

Nanocomposite vulcunizates based on a SBR/ENR50 (50/50%wt) rubber blend containing nanoclay (5 or 10 phr) with and without carbon black (CB 20 phr) were prepared by melt blending in an internal mixer. The compound containing 35 phr carbon black (only) was prepared as a reference sample. Microstructure of nanocomposite samples was investigated by using X-ray diffraction (XRD), melt rheo-mechanical spectroscopy (RMS), and scanning electron microscopy (SEM). The XRD patterns revealed that the distance between the clay layers were increased by adding CB to the nanocomposite samples; they caused better diffusion of chains between the layers and resulted in an intercalated structure. The RMS results also indicated the formation of the filler-filler networks. SEM images of fracture surfaces showed the presence of much roughness in the samples containing both nanoclay and CB compared to the other samples. The results obtained from application of the Flory–Rhener equation showed a high crosslink density for the sample with 10 phr nanoclay and 20 phr CB. Dynamic mechanical behavior, mechanical properties, and abrasion resistance of the nanocomposites were evaluated. The results indicated that the sample containing 10 phr nanoclay and 20 phr CB had an increased dynamic elastic modulus, reduced maximum loss factor (tanδ)_max,, and an improved tensile strength and abrasion resistance compared to the reference sample. Also, this sample showed the lowest maximum loss factor, at 50–60°C, so it can be a candidate for tire-tread application.     

Simultaneous kinetic–spectrophotometric determination of mycophenolate mofetil and mycophenolic acid based on complexation with Fe(III) using chemometric techniques

Determination of pharmaceutical analytes has been subjected to many investigations, especially in transplantations in which accurate and precise detection of drugs is of importance. In this study, a simple and fast complexation reaction has been employed for simultaneous kinetic–spectrophotometric determination of two immunosuppressant drugs, mycophenolate mofetil and its active metabolite mycophenolic acid, which is based on the reaction between drugs and Fe(III) ions in the presence of sodium dodecyl sulfate as anionic surfactant by standard addition method. The effect of influential parameters including type of surfactant, concentration of Fe(III) ions and pH of the solution on the complexation reaction has been studied, and SDS was chosen as suitable surfactant, while reaction proceeds with 0.1 M Fe(III) at pH 4. Multivariate curve resolution-alternating least squares has been employed for analyzing the multiset data obtained from augmentation of resulting standard addition matrices. Values for limit of detection of method have been calculated as 4.88 and 1.62 µg mL^?1 for mycophenolic acid and mycophenolate mofetil, respectively, and Beer’s law is obeyed over the concentration ranges 10–200 µg mL^?1 for MPM and 50–250 µg mL^?1 for MPA. The proposed method was successfully applied for determination of drugs in plasma serum samples. The accuracy and reliability of the method was further ascertained by recovery studies via standard addition procedure.     

Chemo‐selective reduction of nitro and nitrile compounds using Ni nanoparticles immobilized on hyperbranched polymer‐functionalized magnetic nanoparticles

The nitro and nitrile groups in aromatic and aliphatic compounds containing various reducible substituents such as carboxylic acid, ketone, aldehyde and halogen are selectively reduced to the corresponding amines in water as a green solvent with excellent yields by employing NaBH₄ in the presence of Fe₃O₄@PAMAM/Ni(0)‐b‐PEG nanocatalyst. The morphology and structural features of the catalyst were characterized using various microscopic and spectroscopic techniques. The designed catalyst system because of it being covered with hydrophilic polymers is soluble in a wide range of solvents (e.g. water and ethanol) and suitable for immobilizing and stabilizing Ni nanoparticles in aqueous mediums. In addition, the catalyst can be easily recovered from a reaction mixture by applying an external magnetic field and can be reused up to six runs without significant loss of activity.     

GESPECOR: A versatile tool in gamma-ray spectrometry

GESPECOR is a Monte Carlo based software developed for the computation of efficiency, of matrix effects and of coincidence summing effects in gamma-ray spectrometry. GESPECOR can be applied to coaxial and well-type HPGe or to Ge(Li) detectors and to various types of sources, including point, cylindrical, and spherical sources or Marinelli beakers. In this paper the structure of GESPECOR is presented and the procedures applied are described. The uncertainty of the results computed by GESPECOR is carefully analyzed. The analysis shows that GESPECOR is able to provide results with a well defined uncertainty, in a user friendly WINDOWS environment.     

3-D transient analytical solution based on Green’s function to temperature field in friction stir welding

Friction stir welding (FSW) is a relatively modern welding process, which not only provides the advantages offered by fusion welding methods, but also improves mechanical properties as well as metallurgical transformations due to the pure solid-state joining of metals. The FSW process is composed of three main stages; penetrating or preheating stage, welding stage and cooling stage. The thermal history and cooling rate during and after the FSW process are decisive factors, which dictate the weld characteristics. In the current paper, a novel transient analytical solution based on the Green’s function method is established to obtain the three-dimensional temperature field in the welding stage by considering the FSW tool as a circular heat source moving in a finite rectangular plate with cooling surface and non-uniform and non-homogeneous boundary and initial conditions. The effect of penetrating/preheating stage is also taken into account by considering the temperature field induced by the preheating stage to be the non-uniform initial condition for the welding stage. Similarly, cooling rate can be calculated in the cooling stage. Furthermore, the simulation of the FSW process via FEM commercial software showed that the analytical and the numerical results are in good agreement, which validates the accuracy of the developed analytical solution.     

Quantification of magnetic resonance spectroscopy signals with lineshape estimation

Quantification of magnetic resonance spectroscopy (MRS) signals is required for providing metabolite concentrations of the tissue under investigation. For estimating these concentrations several biochemical and acquisition conditions need to be taken into account. It is still a challenge to obtain reliable concentrations, as experimental conditions may have a detrimental effect on the spectral quality. The lineshape of MRS signals is affected, for instance, by inhomogeneities of the static magnetic field arising from imperfect shimming and tissue heterogeneities. To handle this type of distortions, we propose an extension of the self‐deconvolution method, where a common lineshape is estimated and a robust method with local regression is included to improve the smoothing of the estimated damping (or lineshape) function. This common lineshape is imposed in the metabolite quantification method and the spectral parameters (amplitude, frequency, damping and phase corrections) are obtained via nonlinear least squares. In this study, we considered distorted simulated, in vitro and in vivo rat brain signals which were lineshape corrected and quantitative results were compared in all three cases. Copyright © 2011 John Wiley & Sons, Ltd.     

Mesopore structure of microcrystalline cellulose tablets characterized by nitrogen adsorption and SEM: the influence on water-induced ionic conduction

Tablets of microcrystalline cellulose were formed at different compaction pressures and physical properties, such as pore size distribution, surface area, and pore surface fractality, were extracted from N2 adsorption isotherms. These properties were compared to previously published data on the water-induced ionic conductivity of the tablets. The conduction process was shown to follow a percolation model with a percolation exponent of 2 and a porosity percolation threshold of approximately 0.1. The critical pore diameter for facilitated charge transport was shown to be in the 5-20 nm range. When the network of pores with a diameter in this interval is reduced to the point where it no longer forms a continuous passageway throughout the compact, the conduction process is dominated by charge transport on the surfaces of individual microfibrils mainly situated in the bulk of fibril aggregates. A fractal analysis of nitrogen adsorption isotherms showed that the dominant interface forces during adsorption is attributed to surface tensions between the gas and the adsorbed liquid phase. The extracted fractal dimension of the analyzed pore surfaces remained unaffected by the densification process at low compaction pressures (< approximately 200 MPa). At increased densification, however, pore-surface structures smaller than approximately 100 nm become smoother as the fractal dimension decreases from approximately 2.5 at high porosities to approximately 2.3 for the densest tablets under study.     

One‐Pot,Three‐Component Condensation Reaction in Water: An Efficient and Improved Procedure for the Synthesis of Pyran Annulated Heterocyclic Systems

Environmentally friendly three‐component condensation reactions of an activated C‐H acid, an aldehyde, and alkyl nitriles to afford the corresponding pyran annulated heterocyclic systems in water in good yields, avoiding the addition of any catalyst, are reported.     

Characterization of the physical–mechanical properties of dental resin composites reinforced with novel micro-nano hybrid silica particles: An optimization study

Abstract

In the study, dental composites of color A2 using Bis-GMA/UDMA/TEGDMA resins (ratios 70/10/20), and silica filler (70%wt, 75%wt, and 80%wt) which is a hybrid of two silica types in nano and micro dimensions were made using two different photoinitiators namely BAPO and camphorquinone. The optimum photoinitiator was selected based on the mechanical tests results after which the composites were subjected to the following tests: FTIR to evaluate polymerization degree, microhardness test, UTM, and SEM micrographs were taken to analyze the surface fracture of samples. The results of photoinitiator selection (flexural strength test) is 36.54?MPa, 37.62?MPa, and 75.08?MPa for BAPO?+?camphorquinone, camphorquinone, and BAPO respectively. The results show that the BAPO photoinitiator exhibits better results over camphorquinone and also BAPO/camphorquinone initiator systems. Then after choosing the photoinitiator system composites with different filler contents show higher mechanical strength than existing dental composites. The results of the mechanical tests for the composites with different filler contents synthesized after initiator system selection were significantly higher than the values specified in ISO 4049:2009 (102?MPa over 80?MPa). FTIR results indicate that the degree of conversion in these composite is 25.41%, 37.68, and 40.94% for composites with different filler amounts.     

Separable nonlinear least squares fitting with linear bound constraints and its application in magnetic resonance spectroscopy data quantification

An application in magnetic resonance spectroscopy quantification models a signal as a linear combination of nonlinear functions. It leads to a separable nonlinear least squares fitting problem, with linear bound constraints on some variables. The variable projection (VARPRO) technique can be applied to this problem, but needs to be adapted in several respects. If only the nonlinear variables are subject to constraints, then the Levenberg–Marquardt minimization algorithm that is classically used by the VARPRO method should be replaced with a version that can incorporate those constraints. If some of the linear variables are also constrained, then they cannot be projected out via a closed-form expression as is the case for the classical VARPRO technique. We show how quadratic programming problems can be solved instead, and we provide details on efficient function and approximate Jacobian evaluations for the inequality constrained VARPRO method.