Norm inequalities related to the arithmetic–geometric mean inequalities for positive semidefinite matrices

In this paper, we propose three new matrix versions of the arithmetic–geometric mean inequality for unitarily invariant norms, which stem from the fact that the Heinz mean of two positive real numbers interpolates between the geometric and arithmetic means of these numbers. Related trace inequalities are also presented.     

Single crystal growth of La2(SO4)3 · 9 D2O

Single crystals of La₂(SO₄)₃ · 9 D₂O were grown from saturated D₂O solutions. According to X-ray diffraction measurements, the crystals have a hexagonal structure with unit cell parameters a = 10.996 Å and c = 8.077 Å (space group C–P6₃/m). Several physical properties were also determined (density, refractive indices, dielectric constants, specific heat, coefficient of linear expansion, microhardness).     

Des anomalies observées dans l'etude par effet Raman de La2(SO4)3. 9H2O monocristallin en fonction de la temperature

In this paper we present some new results obtained by Raman spectrometry in La₂(SO₄)₂. 9H₂O single crystal. Several particular structural and dynamic properties as well as the anomalies observed near 260 K are reported.     

A study on the structural phase transitions of ferroelastic [N(CH3)4]2CuCl4 from microhardness measurements

Measurements of Vickers microhardness (MHv) as a function of temperature has been carried out on [N(CH₃)₄]₂CuCl₄ single crystals. The suitability of this technique for the determination of transition temperatures in the paraelastic-incommensurate→ferroelastic (commensurate) phase transitions sequence is shown.     

Foaming behavior,cellular structure and physical properties of polybenzoxazine foams

In this paper, polymer foams based on a benzoxazine resin have been successfully prepared using azodicarbonamide (ADC) as a chemical blowing agent and have been characterized regarding their foaming behavior, cellular structure, and physical properties. The effect of the ADC on the curing process of the resin was analyzed using differential scanning calorimetry and blowing agent decomposition was followed by thermogravitmetric analysis (TGA). The characterization of the cellular structure of the foamed samples was done using scanning electron microscopy. The mechanical properties of the foams were determined using compression tests and the thermal conductivity was assessed using the transient plane source method. The results indicated that the curing process and gas release took place in a similar time interval. The foams showed an isotropic cellular structure with relative densities in the range 0.35–0.60, and showed compressive strengths and compressive moduli in the range of 10–70 MPa and 400–1100 MPa, respectively. Thermal conductivities were in the range of 0.06–0.12 W m^?1K^?1. The findings in this paper demonstrate the possibility of producing polybenzoxazine foams using a simple process in which curing and foaming take place simultaneously. In addition, the mechanical characterization of these materials indicates that they are suitable for structural applications. Copyright © 2011 John Wiley & Sons, Ltd.     

Etude de la relaxation dipolaire dans le Ce2(S04)3·9H2O(9D2O) monocristallin

We report in this article the resolution of TSDC (Thermally Stimulated Depolarization Current) spectra and the relaxation parameters of Ce₂(SO₄)₃· 9H₂O(9D₂O) single crystals, for two typical orientations parallel and perpendicular to C₆, symmetry axes The TSDC peaks obtained show a nonDebye type of behavior Calculation of the dipolar relaxation parameters was achieved by fitting the experimental curves to a general order kinetic equation This method allows us to describe the nonDebye-type of behavior of the TSDC peaks on the basis of dipolar interactions during the relaxation process The three different kinds of electric dipoles leading to the three experimentally observed TSDC peaks are ascribed to three different configurations of hydrogen bonds.     

Sensors based on double-decker rare earth phthalocyanines

Phthalocyanines are interesting materials for sensing applications because their physicochemical properties are susceptible to be modified by the presence of certain molecules. Among the large family of the phthalocyanines, the sensing properties of double-decker phthalocyanines (which are sandwich-type complexes where a lanthanide metal is co-ordinated with two phthalocyanine rings) are of special interest due to their unique physicochemical properties. Their high intrinsic semiconductivity and their rich electrochemical and electrochromic behaviour, facilitate enormously the measurement of the changes in the physicochemical properties caused by the environment. In spite of their remarkable sensing behaviour, bisphthalocyanines have not been so extensively studied as sensitive materials as the parent monophthalocyanine compounds. This is due to the difficulty of the synthesis and purification processes, and to the fact that these compounds are not commercially available. In this paper, the sensing devices constructed using rare earth bisphthalocyanines are revised (including sensors foe electronic noses and electronic tongues) and their advantages discussed.     

Dynamic Mechanical Behavior of PP/PET/MAPP Blends Filled with Glass Beads

PP/PET/MAPP blends have been filled with 50 wt% of glass beads. The orientation of the PP crystalline phase, the crystallization behavior and the dynamic mechanical response of these materials have been analyzed. The dynamic mechanical response is strongly affected by the presence of the glass beads, being possible to detect the effect of PET and MAPP on the storage modulus and loss factor values. Moreover, the alpha relaxation of the composites is visibly affected by thermal treatments.     

Thermal expansion of crosslinked closed-cell polyethylene foams

An experimental study on the thermal expansion of a collection of crosslinked low-density polyethylene (LDPE) foams with closed-cell structure is presented. The thermal characterization of these materials, the relationships between the linear thermal expansion coefficient and the structure of the foams, and the determination of the variables that can modify the thermal properties of these products are the goals of this work. The experimental results show that the linear thermal expansion coefficient decreases when the density of the foamed material increases. The gas expansion inside the cells is a mechanism that should be taken into account. Moreover, the thermal expansion also depends on the cellular structure. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2587–2596, 1998     

Measuring the time evolution of the gas pressure in closed cell polyolefin foams produced by compression moulding

The evolution with time of the gas pressure in the cells of low density closed cell polyolefin based foams has been measured using a method that combines mechanical testing and modelling of the compressive response. The results have proved that foam blocks produced by compression moulding present a sub-atmospheric, non-constant gas pressure after production, the increase of pressure with time being a very slow process. In fact, it has been shown that this process has not finished 200 days after production. In addition, it has been also shown that the cooling of the foam during production affects the pressure distribution within the foam.