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The interfacial properties of epoxy composites reinforced with a single, plasma-treated fibre of either poly(p-phenyleneterephthalamide) (PPTA) or poly(p-phenylenebenzobisoxazole) (PBO) have been investigated with a focus on evaluating the effect of two non-oxidative (He and N2) microwave plasma treatments on interfacial adhesion properties. Tensile testing of single filaments revealed that their tensile strength does not diminish with the plasma treatments, despite the fact that their surface properties have been both physically and chemically modified. Interfacial characterisation by Raman spectroscopy indicated that the quality of adhesion was substantially enhanced following exposure of the fibres to microwave plasma treatment in either pure helium or pure nitrogen flows for just one minute. Such improvement was higher than that attained when O2 was used for blowing the plasma, under the same operational conditions. Moreover, no swelling effect was observed by AFM after exposure of the He or N2 plasma-treated fibres to ambient conditions for as much as 24 h.

The effect of nitrogen and oxygen plasma surface treatments on the compressive strength of PBO fibers has been studied. To this end, the nucleation and propagation of compression-induced kink bands was carefully monitored by means of in situ bending tests inside a scanning electron microscope. The micromechanisms of deformation were identical irrespective of fiber surface condition (either as-received or modified by plasma) but the critical stress necessary to induce irreversible damage in compression in the nitrogen-plasma treated fibers was 40% higher than in the as-received fibers. This improvement occurred without any reduction in the fiber tensile properties. The source of this behavior is discussed in the light of the morphological and chemical changes induced by the plasma treatments on the fiber surface, as studied by AFM and XPS. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

A combination of 57Fe-Mossbauer spectroscopy and X-ray Powder Diffraction analysis has been employed to study modifications in chemical and mechanical stability occurring in a cordierite burner aged under combustion conditions which simulate the working of domestic boilers. Mossbauer study shows that Fe is distributed into the structural sites of the cordierite lattice as Fe2+ and Fe3+ ions located mostly at octahedral sites. Ferric oxide impurities, mainly hematite, are also present in the starting cordierite material accounting for ≅40% of the total iron phases. From Mossbauer and X-ray diffraction data it can be deduced that, under the combustion conditions used, new crystalline phases were formed, some of the substitutional Fe3+ ions existing in the cordierite lattice were reduced to Fe2+, and ferric oxides underwent a sintering process which results in hematite with higher particle size. All these findings were detected in the burner zone located in the proximity of the flame and were related to possible chemical reactions which might explain the observed deterioration of the burner material.

Metabolic syndrome (MetS) is considered an independent risk factor for developing cardiovascular disease. It is well known that the prevalence of metabolic disorders have increased in pediatric HIV-infected children. The objective of this study is to assess the prevalence and characteristics of MetS in HIV-infected children and adolescents in Spain.A cross-sectional multicenter study in 152 patients from the pediatric cohort of the Spanish AIDS Research Network (CoRISpe) was performed. MetS was defined according to the new International Diabetes Federation (IDF) diagnostic criteria and the modified National Cholesterol Education Program Adult Treatment Panel III (NCEP-ATP III) criteria. Measurements included anthropometry, waist circumference, blood pressure, fasting lipids, glucose and insulin and lipodystrophy assessment. Demographic, clinical, immunological, virological and antiretroviral therapy data were obtained from the Network database.An abnormally low high-density lipoprotein-cholesterol level was the most prevalent disturbance (21.05%) found. Three patients met IDF criteria for MetS (1.97%), and MetS was significantly associated with lipohypertrophy (P=0.029) in the analysis. When the modified NCEP-ATP III criteria were used, the prevalence of MetS was 5.92% (9 patients), and MetS was significantly associated with Tanner stage ≥2 (P=0.041), lipohypertrophy (P=0.001) and higher Z scores for weight and body mass index (P=0.002 and P0.001). Insulin resistance was observed in 17 patients (11.18%) and was associated with MetS (as per the modified NCEP-ATP III criteria) (P=0.03) and lower high-density lipoprotein-cholesterol values (P=0.036).The prevalence of MetS in our cohort was 1.97% or 5.92%, depending on the diagnostic criteria used. MetS should be actively assessed, particularly in children who show lipohypertrophy.

Two Fe–Ce catalysts were prepared by wet impregnation of Ce onto iron oxyhydroxide (FeOOH) and hematite iron oxide (α-Fe2O3), respectively. Their performance in the Fischer–Tropsch (FT) synthesis was investigated and compared with that obtained with a Ce-free α-Fe2O3 catalyst. It was observed that the behavior of the different catalysts changed along the course of the FT reaction. The catalysts were tested for different periods of time, carefully passivated, recovered from the reactor and characterized by different techniques. The FT activity of the Ce-loaded and Ce-free catalysts decreased initially, but at a certain point the catalytic activity started to increase. The time needed to reach this inflection point depended on the catalyst composition, being shorter for the Ce-promoted catalysts. The catalytic activity of the Ce-free catalyst increased when the Fe3C species were transformed into χ-Fe2.5C, which are suggested to be the carbide phase present when polymerized carbon species (Cβ) are formed. The addition of Ce to the iron oxyhydroxide developed solids with a higher BET surface area. Besides, these samples displayed a higher FT activity at long time-on-stream (TOS). Moreover, Ce addition also facilitated the formation of the Cβ species previous to the evolution of Fe3C into χ-Fe2.5C, and therefore, promoted the FT synthesis reaction.

Scanning tunneling microscopy (STM) and noncontact tapping mode atomic force microscopy (AFM) have been employed to study on a local scale the structural and, for the first time, the chemical changes of carbon black (CB) particles following plasma oxidation. STM imaging of the pristine, untreated particles revealed a relatively ordered structure of tiny crystallites with a few amorphous regions. After plasma treatment, the crystallites were no longer observed and the CB particle surface exhibited a noticeable and ubiquitous increase in atomic-scale disorder. Phase contrast images obtained with noncontact tapping mode AFM indicated that the untreated CB particles were essentially hydrophobic as a pristine basal surface of graphite, but with occasional hydrophilic patches. By contrast, their plasma-treated counterparts displayed enhanced hydrophilicity as a result of the introduction of oxygen onto the CB surface, the presence of which was evidenced by X-ray photoelectron spectroscopy, but most significantly, such enhancement was observed to be quite uniform at a local scale of individual particles. The possibility of investigating on a very local scale the chemical behavior of oxidized CB particles should be useful for the control and optimization of their dispersion properties in different systems.

10 pages (final publisher version), 23 pages (attached post-print version)., Two different types of ancient bricks (12th to 14th centuries) collected from historical buildings of Toledo (Spain) were characterised by optical microscopy, scanning electron microscopy/energy-dispersive X-ray spectrometers (SEM/EDS), electron probe microanalysis (EM), X-ray diffraction (XRD), differential thermal analysis (DTA) and 57Fe-Mössbauer spectroscopy. Physical properties such as water absorption and suction, porosity, density and compression strength were also determined. Several minerals found in the brick matrix, such as garnet, let us infer raw material sources; calcite, dolomite, illite and neoformed gehlenite and diopside phases, on temperature reached in firing; secondary calcite, on first cooling scenarios; and manganese micronodules, on late pollution environments. XRD and DTA of original and refired samples supply information about firing temperatures. Additional data on firing conditions and type of the original clay are provided by the Mössbauer study. Physical properties of both types of bricks were compared and correlated with raw materials and fabric and firing technology employed. The physicochemical characterisation of these bricks provides valuable data for restoration purposes to formulate new specific bricks using neighbouring raw materials., The authors are especially indebted to Josefo Bedoya, technician of the Museo de Ciencias Naturales (Madrid), who took the beautiful SEM microphotographs for this work and was killed in a car accident during the preparation of this manuscript. We are also grateful to Carlos Sánchez (Faculty of Chemistry Sciences, Ciudad Real) for the XRD analyses. The Spanish project MCYT IFD 1997-0561 and agreement CICYT-JCCM (2002) supported the work.

In this paper we address the question of how telecommunications affect economic growth, by estimating the effect of direct investment in telecommunications infrastructures on aggregate output, employment, and investment in Spain. In contrast with previous studies, the problem is analyzed in a dynamic multivariate framework which allows for explicit consideration of feedbacks among all the variables. We find significant effects of the investment in infrastructures of telecommunications on aggregate output, employment and investment which extend for several years. This might justify a policy for stimulating investment in this sector.

The objective of this paper is to evaluate the short- and long-term effects of public investment in infrastructure on aggregate output, labour and capital formation in the private sector. The problem is analysed in a dynamic multivariate framework, which allows for explicit consideration of feedback among all the variables. This approach generalizes the current literature, which relies on a single-equation model to estimate production functions and implicitly assumes the absence of feedback relationships. For the Spanish economy, our results suggest positive long-term effects of public investment on the private sector variables.

This article estimates how demographic changes in the composition of the labor force affect the unemployment rate in the United States. In addition to the effect from changes in the weights of the individual groups composing the total, the impact of compositional changes on the individual unemployment rates is estimated by using a dummy-variables model and incorporated into the estimate on the overall unemployment rate. The results suggest that the incorporation of the latter effect is significant. Indedd, the estimates presented in this article are almost twice as high as those provided by the fixed-weight method used in previous studies.