Composition,preparation procedure and physical properties of linear homogeneous polyurethanes for membranes

Linear polyurethanes (PUs) were prepared in solution in two steps. In the first step, toluene‐diisocyanate (TDI) 80:20 (T) was reacted with a short‐chain poly(oxypropylene) diol (V) to obtain prepolymers characterized by various ratios of R = [T]°/[V]°. In the second step, the prepolymers were reacted with the extender 1,4‐cyclohexanedimethanol (E) with various extension ratios R_E = (R ? 1)[V]°/[E]°. The PU properties were analyzed by various techniques. In particular, the molecular weights determined by gel permeation chromatography (GPC), the thermal properties such as glass transition temperature T_g and specific heat variation ΔC_p measured by differential scanning calorimetry (DSC), the chemical composition of the PUs and the various types of hydrogen bonds present in the polymers evidenced by Fourier‐transform infrared (FTIR) spectroscopy, the monophasic structure evidenced by small‐angle X‐ray scattering (SAXS), and the existence of only one T_g confirmed that these PUs were linear, amorphous and monophasic. Positron annihilation lifetime spectroscopy (PALS) analysis showed that the mean volume of the nanoholes increased with increasing temperature, but was not dependent on the composition, as expected for a monophasic system. A stoichiometric semi‐empirical model was proposed that relates the PU blocks' micro‐composition to the R and R_E macro‐parameters, chosen for the synthesis. The polymer assumes various expressions of the general formula X? [(TV)_k? (TE)_n]_m? X for different values of the R and R_E ratios. The micro‐parameters k and m have a direct connection with the experimental mean molecular weights of the prepolymer and the polymer, respectively: n depends only on R. The model could foresee the density of hydrogen bonds and distinguished the bonds connected to either V or E, which could be shown by FTIR analysis. This paper shows that, when using stereo‐irregular diols and blends of 2,4‐ and 2,6‐TDI, non‐stereoregular PUs are obtained. If low‐molecular‐weight diols are used and R < 3.3, it is quite improbable that the PU blocks separate into macrophases and therefore monophasic amorphous PUs are obtained. Monophasic PUs can be useful for applications such as in the field of membrane gas and vapour separation. Copyright © 2005 Society of Chemical Industry     

Multivariate data analysis of some xenobiotic trace metals in mussels from the Gulf of Trieste

Summary The concentration of Cd, Hg and Pb in the soft part of mussels has been studied by means of bi-and multi-variate statistical approaches. In particular, the principal component analysis has been applied to study the association among these toxic metals in mussels sampled from the gulf of Trieste, which is a critical area as far as mercury pollution is concerned.

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Mehrdimensionale Analyse der Daten einiger xenobiotischer Spurenmetalle in Miesmuscheln aus dem Golf von Triest

Zusammenfassung Der Gehalt von Cd, Hg und Pb in Miesmuschelfleisch wurde nach einer statistischen mehrdimensionalen Analyse untersucht. Besonders wurde die Hauptkomponentenanalyse zum Studium der Assoziationen dieser toxischen Metalle in Miesmuscheln angewandt. Die Miesmuschelproben stammten aus dem Golf von Triest, ein kritisches Gebiet für Quecksilberverunreinigungen.

     

Training family psychologists: The family studies program at Georgia State University.

Describes the Family Studies Program, which has a 2-phased clinical practica format that combines theory and practice. The format is not fixed but will change as knowledge in the field increases. (3 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of Frequency Selective Surfaces at Millimeter Wave Band Using the Hertz Vector Potential Method

In this work, the Hertz vector potential method was used to obtain the dyadic Green’s function components for frequency selective surfaces (FSS) on an anisotropic layer. The considered structures are composed by periodic arrays of conducting crossed dipole and rectangular patch elements. Results of reflected power were obtained by using the moment method. Curves for the reflected power versus frequency are presented as function of the structural parameters, assuming x, y, and z orientation for the optical axis in the anisotropic substrate.     

Fractal coupled theory of drilling and wear

Drilling perforations and tool wear are intimately and mutually connected by fracture propagations at different size-scales. To study this interaction phenomenon, we propose an ad hoc developed fractal coupled theory. Describing the two processes in terms of drilling and wear velocities, the theory is able to predict the relation between these two quantities. The result is represented by a power law between wear and drilling velocities with exponent comprised between 2/3 and 3/2. Some experimental tests on different materials like mortar, concrete and reinforced concrete have also been performed. Theoretical predictions and experimental results agree satisfactorily.     

Rearing influences on tonic immobility in three-day-old chicks (Gallus gallus).

Subjected 86 3-day-old White Leghorn chicks, reared either socially or in isolation in large or small boxes, to tonic immobility by a ventral restraint induction procedure. Test boxes were identical to rearing boxes or differed only in size. Incidence and duration of immobility were reliably enhanced by social and high-density rearing, but similarity of test and rearing boxes had no effect. A high negative correlation between vocalization rate and duration of eye closure was obtained. Results are discussed in terms of the optimizing induction procedure in relation to early righting behavior. Qualitatively different stages of immobility are defined. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Respiratory quotient changes in full term newborn infants within 30 hours from birth before start of milk feeding

Over the period of a year I have systematically recorded any episodes of continuing medical education (CME) that I have attended, and reflect on the effectiveness of this system in terms of whether it has achieved its objective, that is, has my behaviour changed, and whether the existence of the need to record CME has influenced this effect. I consider which aspects of CME have been most beneficial. I conclude that the proposed level of CME is readily achievable, useful, but costly. The way in which I learn most or best is in preparing presentations or teaching sessions. There has been some debate on the usefulness of keeping a record of CME to which I would like to add my opinion. I also recommend the form of record keeping I have used as an impetus to reflection and research on the topic of education received, as this reinforces and enhances the educational experience.     

A boundary element formulation for the inverse elastostatics problem (iesp) of flaw detection

A boundary integral formulation is presented for the detection of flaws in planar structural members from the displacement measurements given at some boundary locations and the applied loading. Such inverse problems usually start with an initial guess for the flaw location and size and proceed towards the final configuration in a sequence of iterative steps. A finite element formulation will require a remeshing of the object corresponding to the revised flaw configuration in each iteration making the procedure computationally expensive and cumbersome. No such remeshing is required for the boundary element approach. The inverse problem is written as an optimization problem with the objective function being the sum of the squares of the differences between the measured displacements and the computed displacements for the assumed flaw configuration. The geometric condition that the flaw lies within the domain of the object is imposed using the internal penalty function approach in which the objective function is augmented by the constraint using a penalty parameter. A first-order regularization procedure is also implemented to modify the objective function in order to minimize the numerical fluctuations that may be caused in the numerical procedure due to errors in the experimental measurements for displacements. The flaw configuration is defined in terms of geometric parameters and the sensitivities with respect to these parameters are obtained in the boundary element framework using the implicit differentiation approach. A series of numerical examples involving the detection of circular and elliptical flaws of various sizes and orientations are solved using the present approach. Good predictions of the flaw shape and location are obtained.