295 research outputs found
Comportamiento dieléctrico de materiales compuestos reforzados con Ground Tire Rubber (GTR)
La masiva fabricaciĂłn de neumáticos y la dificultad para su eliminaciĂłn o almacenamiento constituye un grave problema medioambiental. En la actualidad, se utilizan diversos mĂ©todos para el reciclaje de neumáticos, como la trituraciĂłn mecánica, en la que se separa el caucho vulcanizado del acero y las fibras, utilizándose este caucho en numerosas aplicaciones como pavimentos, aislantes, calzados, etc.Con el presente estudio se pretende dar una nueva salida a los neumáticos fuera de uso (GTR), demostrándose su utilidad como dielĂ©ctricos. Para ello, se ha combinado GTR con policloruro de vinilo (PVC), obteniendo un material compuesto de matriz polimĂ©rica reforzado con GTR. Se ha caracterizado el comportamiento dielĂ©ctrico paralas diversas mezclas del PVC con GTR (desde el 0% al 70% de GTR), en un rango de temperaturas que varĂa desde los 30ÂşC hasta los 130ÂşC, y con unas frecuencias desde 1·10-2 Hz, hasta 1·107 Hz. Los ensayos elĂ©ctricos han permitido el análisis de la permitividad, la resistividad, el factor de pĂ©rdidas dielĂ©ctricas y los mĂłdulos de relajaciĂłn (Arrhenius). Se ha comprobado como todas estas propiedades aumentan a bajas temperaturas (30ÂşC). Asimismo, tambiĂ©n se observa que la evoluciĂłn de estos parámetros varĂa significativamente en funciĂłn de la frecuencia y la temperatura
Characterization of different Arundo donax L. Clones from the Mediterranean region
The present study assessed the behaviour of a tour ecotypes of Arundo donax L. (giant reed) as a perennial rhizomatous grass with an increasing interest due to its high biomass production and great s adaptability to stress conditions. In this study we perform a molecular, physiological and biomass characterization in greenhouse conditions on four mediterranean ecotypes. Not large significant differences were found in physiological and biomass parameters. However, it was possible to observe large differences in the chromosome count for the four ecotypes. In this way, we detected different number of chromosomes for each ecotype (98 to 122), but surprisingly, no correlation was observad between their chromosomes number and their physiological and biomass responses
Efecto de pretratamientos desvulcanizantes y de aditivos en materiales compuestos con matriz de HDPE y neumáticos fuera de uso
La gestiĂłn de los neumáticos al final de su ciclo de vidaprecisa soluciones para potenciar su reutilizaciĂłn y reciclado.Un paso previo consiste en la pulverizaciĂłn de losneumáticos por parte de empresas especializadas. La incorporaciĂłnde este granulado como refuerzo en matricestermoplásticas se ha propuesto como mĂ©todo de valorizaciĂłndel polvo de neumático. Este sistema se ve limitadopor la incompatibilidad entre matriz y refuerzo. Recientemente,un nuevo polvo de neumático, denominado comercialmente “desvulcanizado” ha aparecido en el mercado.En este artĂculo se comparan materiales compuestosformulados con polvo de neumático desvulcanizado conlos obtenidos con el mismo material sin tratamiento enmatriz de polietileno de alta densidad. TambiĂ©n se estudiael efecto de distintos mĂ©todos de mezclado, del uso deaditivos dispersantes y del tamaño de partĂcula
Coercivity enhancement in exchange biased systems driven by interfacial magnetic frustration
We report the temperature and cooling field dependence of the coercivity of exchange biased MnF2/Fe bilayers. When the antiferromagnetic surface is in a state of maximum magnetic frustration and the net exchange bias is zero, we observe a strong enhancement of the coercivity, which is proportional to the exchange coupling between the layers. Hence, the coercivity can be tuned in a reproducible and repeatable fashion in the same sample. We propose that a frustrated interface provides local energy minima which effectively pin the propagating domain walls in the ferromagnet, leading to an enhanced coercivity
Two-stage magnetization reversal in exchange biased bilayers
MnF2/Fe bilayers exhibit asymmetric magnetization reversal that occurs by coherent rotation on one side of the loop and by nucleation and propagation of domain walls on the other side of the loop. Here, we show by polarized neutron reflectometry, magnetization, and magnetotransport measurements that for samples with good crystalline "quality" the rotation is a two-stage process, due to coherent rotation to a stable state perpendicular to the cooling field direction. The result is remarkably asymmetrically shaped hysteresis loops
Size effects in the magnetic behaviour of TbAl_2 milled alloys
The study of the magnetic properties depending upon mechanical milling of the
ferromagnetic polycrystalline TbAl_2 material is reported. The Rietveld
analysis of the X-ray diffraction data reveals a decrease of the grain size
down to 14 nm and -0.15 % of variation of the lattice parameter, after 300
hours of milling time. Irreversibility in the zero field cooled - field cooled
(ZFC-FC) DC-susceptibility and clear peaks in the AC susceptibility between 5
and 300 K show that the long-range ferromagnetic structure is inhibited in
favour of a disordered spin arrangement below 45 K. This glassy behaviour is
also deduced from the variation of the irreversibility transition with the
field (H^{2/3}) and frequency. The magnetization process of the bulk TbAl_2 is
governed by domain wall thermal activation processes. By contrast, in the
milled samples, cluster-glass properties arise as a result of cooperative
interactions due to the substitutional disorder. The interactions are also
influenced by the nanograin structure of the milled alloys, showing a variation
of coercivity with the grain size, below the crossover between the multi- and
single-domain behaviours.Comment: 23 pages, 11 figures, to appear in J. Phys.: Condens. Ma
Erratum to: The impact of common co-morbidities (as measured using the Charlson index) on hip fracture risk in elderly men: a population-based cohort study
Antiferromagnetic spintronics
Antiferromagnetic materials are magnetic inside, however, the direction of
their ordered microscopic moments alternates between individual atomic sites.
The resulting zero net magnetic moment makes magnetism in antiferromagnets
invisible on the outside. It also implies that if information was stored in
antiferromagnetic moments it would be insensitive to disturbing external
magnetic fields, and the antiferromagnetic element would not affect
magnetically its neighbors no matter how densely the elements were arranged in
a device. The intrinsic high frequencies of antiferromagnetic dynamics
represent another property that makes antiferromagnets distinct from
ferromagnets. The outstanding question is how to efficiently manipulate and
detect the magnetic state of an antiferromagnet. In this article we give an
overview of recent works addressing this question. We also review studies
looking at merits of antiferromagnetic spintronics from a more general
perspective of spin-ransport, magnetization dynamics, and materials research,
and give a brief outlook of future research and applications of
antiferromagnetic spintronics.Comment: 13 pages, 7 figure
Marker-assisted introgression of the salinity tolerance locus Saltol in temperate japonica rice
Background Rice is one of the most salt sensitive crops at seedling, early vegetative and reproductive stages. Varieties
with salinity tolerance at seedling stage promote an efficient growth at early stages in salt affected soils, leading
to healthy vegetative growth that protects crop yield. Saltol major QTL confers capacity to young rice plants growing
under salt condition by maintaining a low Na+/
K+ molar ratio in the shoots.
Results Marker-assisted backcross (MABC) procedure was adopted to transfer Saltol locus conferring salt tolerance
at seedling stage from donor indica IR64-Saltol to two temperate japonica varieties, Vialone Nano and Onice. Forward
and background selections were accomplished using polymorphic KASP markers and a final evaluation of genetic
background recovery of the selected lines was conducted using 15,580 SNP markers obtained from Genotyping by
Sequencing. Three MABC generations followed by two selfing, allowed the identification of introgression lines achieving
a recovery of the recurrent parent (RP) genome up to 100% (based on KASP markers) or 98.97% (based on GBS).
Lines with highest RP genome recovery (RPGR) were evaluated for agronomical-phenological traits in field under nonsalinized
conditions. VN1, VN4, O1 lines were selected considering the agronomic evaluations and the RPGR% results
as the most interesting for commercial exploitation. A physiological characterization was conducted by evaluating
salt tolerance under hydroponic conditions. The selected lines showed lower standard evaluation system (SES) scores:
62% of VN4, and 57% of O1 plants reaching SES 3 or SES 5 respectively, while only 40% of Vialone Nano and 25% of
Onice plants recorded scores from 3 to 5, respectively. VN1, VN4 and O1 showed a reduced electrolyte leakage values,
and limited negative effects on relative water content and shoot/root fresh weight ratio.
Conclusion The Saltol locus was successfully transferred to two elite varieties by MABC in a time frame of three years.
The application of background selection until BC3F3
allowed the selection of lines with a RPGR up to 98.97%. Physiological
evaluations for the selected lines indicate an improved salinity tolerance at seedling stage. The results supported
the effectiveness of the Saltol locus in temperate japonica and of the MABC procedure for recovering of the RP
favorable traits
Bone Mineral Changes in Spine and Proximal Femur in Individual Obese Women after Laparoscopic Sleeve Gastrectomy: A Short-Term Study
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