Molecular weight dependence and stereoselective chain cleavage during the early stages of the isotactic polypropylene pyrolysis

The comparative study on the pyrolysis of two Polypropylene samples, with a similar high isotactic character but quite distinct molecular weights, reveals a significant difference in their thermal performances. The detailed qualitative analysis of the parameters, which are expected to govern the thermal degradation, leads to reasonably assume a main role of the molecular weight in their relative early stabilities. Furthermore, the correlation found between the sharp initial build-up of the Eact and the selective cleavage of isotactic stereosequences in both samples, suggests the relevance of the stereoregular length into the energy required for chain scissionThe authors acknowledge the financial support of project MAT2016-79869-C2-1-P (AEI/FEDER, UE), as well as the kindly assistance of Repsol for the supply of samples.Peer reviewe

Astrobiological field campaign to a volcanosedimentary mars analogue methane producing subsurface protected ecosystem: Imuruk Lake (Alaska)

Viking missions reported adverse conditions for life in Mars surface. High hydrogen signal obtained by Mars orbiters has increased the interest in subsurface prospection as putative protected Mars environment with life potential. Permafrost has attracted considerable interest from an astrobiological point of view due to the recently reported results from the Mars exploration rovers. Considerable studies have been developed on extreme ecosystems and permafrost in particular, to evaluate the possibility of life on Mars and to test specific automated life detection instruments for space missions. The biodiversity of permafrost located on the Bering Land Bridge National Preserve has been studied as an example of subsurface protected niche of astrobiological interest. Different conventional (enrichment and isolation) and molecular ecology techniques (cloning, fluorescence >in situ> probe hybridization, FISH) have been used for isolation and bacterial identification.The expedition to Imuruk Lake was supported by Centro de Astrobiologia-INTA (Spain). The laboratory experimental procedures were supported by Grant AYA 2010–2013 “Desarrollo de Tecnología para la identificación de vida de forma automática” from the Spanish Government.Peer Reviewe

Little-Parks effect governed by magnetic nanostructures with out-of-plane magnetization

Little-Parks effect names the oscillations in the superconducting critical temperature as a function of the magnetic field. This effect is related to the geometry of the sample. In this work, we show that this effect can be enhanced and manipulated by the inclusion of magnetic nanostructures with perpendicular magnetization. These magnetic nanodots generate stray fields with enough strength to produce superconducting vortex-antivortex pairs. So that, the L-P effect deviation from the usual geometrical constrictions is due to the interplay between local magnetic stray fields and superconducting vortices. Moreover, we compare our results with a low-stray field sample (i.e. with the dots in magnetic vortex state) showing how the enhancement of the L-P effect can be explained by an increment of the effective size of the nanodots

Breaking the configurational anisotropy in Fe single crystal nanomagnets

In this work, we improve the ability to tailor the switching mechanism in nanomagnets by introducing an additional, highly controlled source of anisotropy: magnetocrystalline anisotropy. We analyze the vortex dynamics in single crystal Fe nanotriangles with different orientations of the crystalline axes. By experimental studies and simulation, we show that the angular dependence of the vortex annihilation field springs from the convolution of the crystalline and configurational anisotropies. In contrast, the remanence and the nucleation field present a much simpler behavior controlled by the existence of a single symmetry axis when shape and crystalline orientation are taken into account

Variation of ultimate properties in extruded iPP-mesoporous silica nanocomposites by effect of iPP confinement within the mesostructures

Nanocomposites based on isotactic polypropylene (iPP) and mesoporous silica particles of either MCM-41 or SBA-15 were prepared by melt extrusion. The effect of the silica incorporated into an iPP matrix was firstly detected in the degradation behavior and in the rheological response of the resultant composites. Both were ascribed, in principle, to variations in the inclusion of iPP chains within these two mesostructures, with well different pore size. DSC experiments did not provide information on the existence of confinement in the iPP-MCM-41 materials, whereas a small endotherm, located at about 100 °C and attributed to the melting of confined crystallites, is clearly observed in the iPP-SBA-15 composites. Real-time variable-temperature Small Angle X-ray Scattering (SAXS) experiments with synchrotron radiation turned out to be crucial to finding the presence of iPP within MCM-41 pores. From these measurements, precise information was also deduced on the influence of the MCM-41 on iPP long spacing since overlapping does not occur between most probable iPP long spacing peak with the characteristic diffractions from the MCM-41 hexagonal nanostructure in comparison with existing superposition in SBA-15-based materials.Fil: Barranco García, Rosa. Instituto en Ciencia y Tecnología de Polímeros; EspañaFil: Gómez Elvira, José M.. Instituto en Ciencia y Tecnología de Polímeros; EspañaFil: Ressia, Jorge Aníbal. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Quinzani, Lidia Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Valles, Enrique Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Planta Piloto de Ingeniería Química. Universidad Nacional del Sur. Planta Piloto de Ingeniería Química; ArgentinaFil: Pérez, Ernesto. Instituto en Ciencia y Tecnología de Polímeros; EspañaFil: Cerrada, María L.. Instituto en Ciencia y Tecnología de Polímeros; Españ

Topologically protected superconducting ratchet effect generated by spin-ice nanomagnets

We have designed, fabricated and tested a robust superconducting ratchet device based on topologically frustrated spin ice nanomagnets. The device is made of a magnetic Co honeycomb array embedded in a superconducting Nb film. This device is based on three simple mechanisms: (i) the topology of the Co honeycomb array frustrates in-plane magnetic configurations in the array yielding a distribution of magnetic charges which can be ordered or disordered with in-plane magnetic fields, following spin ice rules; (ii) the local vertex magnetization, which consists of a magnetic half vortex with two charged magnetic Neel walls; (iii) the interaction between superconducting vortices and the asymmetric potentials provided by the Neel walls. The combination of these elements leads to a superconducting ratchet effect. Thus, superconducting vortices driven by alternating forces and moving on magnetic half vortices generate a unidirectional net vortex flow. This ratchet effect is independent of the distribution of magnetic charges in the array

Realization of macroscopic ratchet effect based on nonperiodic and uneven potentials

Ratchet devices allow turning an ac input signal into a dc output signal. A ratchet device is set by moving particles driven by zero averages forces on asymmetric potentials. Hybrid nanostructures combining artificially fabricated spin ice nanomagnet arrays with superconducting films have been identified as a good choice to develop ratchet nanodevices. In the current device, the asymmetric potentials are provided by charged Neel walls located in the vertices of spin ice magnetic honeycomb array, whereas the role of moving particles is played by superconducting vortices. We have experimentally obtained ratchet effect for different spin ice I configurations and for vortex lattice moving parallel or perpendicular to magnetic easy axes. Remarkably, the ratchet magnitudes are similar in all the experimental runs; i. e. different spin ice I configurations and in both relevant directions of the vortex lattice motion. We have simulated the interplay between vortex motion directions and a single asymmetric potential. It turns out vortices interact with uneven asymmetric potentials, since they move with trajectories crossing charged Neel walls with different orientations. Moreover, we have found out the asymmetric pair potentials which generate the local ratchet effect. In this rocking ratchet the particles (vortices) on the move are interacting each other (vortex lattice); therefore, the ratchet local effect turns into a global macroscopic effect. In summary, this ratchet device benefits from interacting particles moving in robust and topological protected type I spin ice landscapes

Foro de debate: seguridad de las alternativas a la transfusión alogénica en el paciente quirúrgico y/o crítico

Estos últimos años han aparecido alertas de seguridad, no siempre bien sustentadas, que cuestionan el uso de algunas alternativas farmacológicas a la transfusión de sangre alogénica y/o lo restringen en indicaciones establecidas. Asistimos también a la preconización de otras alternativas, incluyendo productos hemáticos y fármacos antifibrinolíticos, sin que haya una base científica sólida que lo justifique. Por iniciativa del Grupo de Estudios Multidisciplinares sobre Autotransfusión y del Anemia Working Group Espana¿ se reunió a un panel multidisciplinar de 23 expertos del área de cuidados de la salud en un foro de debate para: 1) analizar las diferentes alertas de seguridad en torno a ciertas alternativas a la transfusión; 2) estudiar los antecedentes que las han propiciado, la evidencia que las sustentan y las consecuencias que conllevan para la práctica clínica, y 3) emitir una valoración argumentada de la seguridad de cada alternativa a la transfusión cuestionada, según el uso clínico de la misma. Los integrantes del foro mantuvieron contactos por vía telemática y una reunión presencial en la que presentaron y discutieron las conclusiones sobre cada uno de los elementos examinados. Se elaboró un primer documento que fue sometido a 4 rondas de revisión y actualización hasta alcanzar un consenso, unánime en la mayoría de los casos. Presentamos la versión final del documento, aprobada por todos los miembros del panel, esperando sea de utilidad para nuestros colegas