PVC membrane and coated graphite potentiometric sensors based on Et4todit for selective determination of samarium(III)

Solution studies on the binding properties of 4,5,6,7-tetrathiocino[1,2-b:3,4-b']diimidazolyl-1,3,8,10-tetraethyl-2,9-dithione (Et(4)todit) toward a number of cationic species including some lanthanide ions revealed the occurrence of a selective 1:1 complexation of the ligand with Sm(3+) ion. Consequently, Et(4)todit was used as a suitable neutral ionophore for the preparation of novel polymeric membrane (PME) and coated graphite (CGE) Sm(3+)-selective electrodes. The electrodes exhibit a Nernstian behavior for Sm(3+) ions over wide concentration ranges (1.0 x 10(-5)-1.0 x 10(-1) M for PME and 1.0 x 10(-7)-1.0 x 10(-1) M for CGE) and very low limits of detection (8.0 x 10(-6) M for PME and 1.6 x 10(-8) M for CGE). The proposed potentiometric sensors manifest advantages of relatively fast response, and, most importantly, good selectivities relative to wide variety of other cations, including other lanthanide ions. The selectivity behavior of the proposed Sm(3+)-selective electrodes revealed a great improvement compared to the best previously reported electrode for samarium(III) ion. The potentiometric responses of the electrodes are independent of the pH of the test solution in the pH range 4.0-6.5. The electrodes were successfully applied to the recovery of Sm(3+) ion from tap water samples and also, as an indicator electrode, in potentiometric titration of samarium(III) ions.     

Rheology-morphology relationships in nylon 6/liquid-crystalline polymer blends

Extrusion measurements have been carried out on blends of nylon 6 and a liquid-crystalline copolyesteramide (LCP). The flow curves at low temperature show a behavior similar to that of pure LCP with a rapid rise of the viscosity at low shear rates. At high shear rates the viscosity is lower than that for each of the two components. This minimum has been attributed to the lack of interactions between the two phases and to the formation of fibrils of the LCP phase. The SEM analysis shows, indeed, that fibrils of the LCP phase are produced in the convergent flow at the inlet of the capillary at high shear rates. These fibrils are lost during the flow in the long capillary.     

A study of polycarbonate-liquid crystal polymer blends

The morphology and the thermal and mechanical properties of blends of bisphenol-A polycarbonate (PC) with a wholly aromatic liquid crystal copolyester-amide (Vectra-B of Hoechst-Celanese) are discussed with reference to the conditions used for their preparation. The blends made by extrusion behave as mixtures of incompatible polymers: the dispersed liquid crystalline phase is more or less oriented in the extrusion direction and acts as a reinforcing filler for the PC matrix. The behaviour of the blends prepared in a batch mixer depends strongly on mixing time. A slight decrease in the mechanical properties (especially tensile strength and elongation) accompanies the morphological changes associated with a progressive improvement in the compatibility of the two polymers, which finally leads to an apparently homogeneous material after 45 min mixing at 290°C and 150 rpm. These effects are interpreted in terms of chemical interactions taking place between the two components of the blends.     

Crystallization behavior of polyphenylene sulfide in blends with a liquid crystalline polymer

Blends of polyphenylene sulfide (PPS) with a commercial, wholly aromatic, liquid crystal copolyesteramide (Vectra-B950) have been prepared by meltblending. The crystallization behavior of neat and blended PPS has been studied by differential scanning calorimetry (DSC), under both non-isothermal and isothermal conditions. It has been found that blending PPS with Vectra-B leads to an increase of the temperature of non-isothermal crystallization and to a pronounced acceleration of the isothermal crystallization, without any reduction of the degree of crystallinity. All these effects have been found to occur independent of the Vectra-B concentration, within the investigated range (2 to 20%, w/w). The results have been interpreted in terms of an incrased nucleation density of the blends, probably due to heterogeneous substances, initially present in the Vectra-B bulk, which dissolve to saturation in the PPS phase, during melt-blending.     

MRI appearances in amoebic granulomatous hepatitis: a case report

Amoebiasis is a common cause of liver disease usually presenting as single large or multiple smaller abscesses. Cases with granulomatous hepatitis have rarely been described. We report the case of a 7-year-old girl with amoebic granulomatous hepatitis in which multiple liver abscesses were demonstrated by MRI. A total of 14 abscesses were identified, ranging from 5 mm to 3 cm in diameter. The largest lesions appeared to T2-weighted images as heterogeneous, low-intensity areas surrounded by a double-layered wall, the inner layer of which was hyperintense and the outer layer hypointense. These signs, which have never been described in classic amoebic abscess, represent, we believe, a pattern of hepatic granulomatous amoebiasis lesions. We suggest that MRI should always be performed in cases of amoebic infection.     

Magic Angle Spinning-Cross Polarization 13C NMR of crosslinked unsaturated polyester resins

Summary Magic Angle Spinning-Cross Polarization (MAS-CP) ¹³C NMR spectra of four different unsatured resins reticulated with styrene have been measured.Styrene crosslinks may be constituted essentially by dyads or may consist in (styrene) microdomains (n2), depending mainly upon the molar ratio of maleic acid residues in the original unsaturated polyester to styrene.Also in the case of solid unsaturated resins the MAS-CP ¹³CNMR technique promises to allow structural insights only very difficultly obtainable by more classical indirect means.     

A meshless method for axi‐symmetric poroelastic simulations: numerical study

A meshless model, based on the meshless local Petrov–Galerkin (MLPG) approach, is developed and implemented for the solution of axi‐symmetric poroelastic problems. The solution accuracy and the code performance are investigated on a realistic application concerning the prediction of land subsidence above a deep compacting reservoir. The analysis addresses several numerical issues, including the parametric selection of the optimal size of the local sub‐domains for the weak form and the nodal supports, the appropriate integration rule, and the linear system solver. The results show that MLPG can be more accurate than the standard finite element (FE) method on coarse discretizations, with its superiority decreasing as the nodal resolution increases. This is due to both a slower convergence rate and a progressively higher computational cost compared to FE. These drawbacks can be partially mitigated by improving the efficiency of the numerical integration and the system solver with the aid of projection techniques based on Krylov subspace methods. The outcome of the present analysis supports the development of coupled methods where a limited number of MLPG nodes are used to locally improve a FE solution. Copyright © 2006 John Wiley & Sons, Ltd.     

A system for securing push-based distribution of XML documents

Push-based systems for distributing information through Internet are today becoming more and more popular and widely used. The widespread use of such systems raises non trivial security concerns. In particular, confidentiality, integrity and authenticity of the distributed data must be ensured. To cope with such issues, we describe here a system for securing push distribution of XML documents, which adopts digital signature and encryption techniques to ensure the above mentioned properties and allows the specification of both signature and access control policies. We also describe the implementation of the proposed system and present an extensive performance evaluation of its main components.     

Peak Response of a Nonlinear Beam

A model for estimating the peak dynamic response distribution of a nonlinear beam, based on a special class of non-Gaussian stochastic processes, is proposed in this paper. It is shown that the stochastic response of a cantilever beam with geometrically nonlinear behavior can be accurately calibrated with translation processes. Different models to describe the significant bimodal features in the marginal probability density functions of the response time histories are proposed. Finally, two of these models are used to estimate the response peak value distributions and the results are compared. This comparison demonstrates the effects of inaccurate models for the parent response processes on the peaks estimation.