Phase diagram for a single flexible Stockmayer polymer at zero field

The equilibrium conformations of a flexible permanent magnetic chain that consists of a sequence of linked magnetic colloidal nanoparticles with short-ranged Lennard-Jones attractive interactions (Stockmayer polymer) are thoroughly analysed via Langevin dynamics simulations. A tentative phase diagram is presented for a chain of length $N=100$. The phase diagram exhibits several unusual conformational phases when compared with the non-magnetic chains. These phases are characterised by a large degree of conformational anisotropy, and consist of closed chains, helicoidal-like states, partially collapsed states, and very compact disordered states. The phase diagram contains several interesting features like the existence of at least two 'triple points'

Régimen hídrico de los suelos en zonas acarcavadas. Algunos ejemplos en la cuenca experimental de Petrer. Alicante.

[Resumen] La humedad del suelo determina la actividad biológica, los procesos físicos y químicos, y la hidrología de los suelos. Así, los procesos de erosión, sus tasas, y las formas terrestres dependen indirectamente del régimen hídrico de los suelos. A pesar de ello, son poco conocidas las variaciones espaciales y la evolución temporal de la humedad del suelo y la influencia que sobre ella ejerce la vegetación. El desconocimiento del régimen hídrico de los suelos y de los procesos de erosión es aún más patente en aquellos ambientes con escaso aprovechamiento agrícola y forestal como son las zonas acarcavadas o badlands. Mediante el muestreo periódico de la humedad del suelo (método gravimétrico) en distintos puntos de una ladera se comprobó que la humedad del suelo es muy variable espacial y temporalmente. Este comportamiento se debe a que la vegetación favorece mayores contenidos de agua en el suelo frente a zonas desnudas donde la evaporación es muy rápida. El régimen hídrico de los suelos en los badlands reduce las posibilidades de revegetación natural por la rápida pérdida de humedad tras las lluvias.[Abstract] The soil moisture determines the biological activity, the physical and chemical processes and the soil hydrology. Therefore, the erosion processes, its rates, and the landforms relates indirectly to the soil water regime. Even though, little is known on the spatial variability and temporal evolution of the soil moisture and the influence of vegetation. The ignorance of the soil water regime and the erosional processes is still more obvious on the environments with scarce agricultural and forestry use as the gullied landscape or badlands. By means of a periodical sampling of soil moisture (gravimmetric method) in different sites of a slope is found that the soil moisture is very variable spatially and temporally. This behaviour is due to the vegetation, which favours greater soil moisture content than on the bare zone where the evaporation is very fasto The soil water regime on the badlands reduces the vegetation recovery possibilities because the quick soil dissecation after the rains

Simulations of the Magneto-rotational Instability in Core-Collapse Supernovae

We assess the importance of the magneto-rotational instability in core-collapse supernovae by an analysis of the growth rates of unstable modes in typical post-collapse systems and by numerical simulations of simplified models. The interplay of differential rotation and thermal stratification defines different instability regimes which we confirm in our simulations. We investigate the termination of the growth of the MRI by parasitic instabilities, establish scaling laws characterising the termination amplitude, and study the long-term evolution of the saturated turbulent state.Comment: 6 pages, 1 figure. To appear in Proceedings of 4th International Conference on Numerical Modeling of Space Plasma Flows (Chamonix 2009

Suspensions of supracolloidal magnetic polymers: self-assembly properties from computer simulations

We study self-assembly in suspensions of supracolloidal polymer-like structures made of crosslinked magnetic particles. Inspired by self-assembly motifs observed for dipolar hard spheres, we focus on four different topologies of the polymer-like structures: linear chains, rings, Y-shaped and X-shaped polymers. We show how the presence of the crosslinkers, the number of beads in the polymer and the magnetic interparticle interaction affect the structure of the suspension. It turns out that for the same set of parameters, the rings are the least active in assembling larger structures, whereas the system of Y- and especially X-like magnetic polymers tend to form very large loose aggregates

Managing soil nitrate with cover crops and buffer strips in Sicilian vineyards

When soil nitrate levels are low, plants suffer nitrogen (N) deficiency but when the levels are excessive, soil nitrates can pollute surface and subsurface waters. Strategies to reduce the nitrate pollution are necessary to reach a sustainable use of resources such as soil, water and plant. Buffer strips and cover crops can contribute to the management of soil nitrates, but little is known of their effectiveness in semiarid vineyards plantations. The research was carried out in the south coast of Sicily (Italy) to evaluate nitrate trends in a vineyard managed both conventionally and using two different cover crops (Triticum durum and Vicia sativa cover crop). A 10 m-wide buffer strip was seeded with Lolium perenne at the bottom of the vineyard. Soil nitrate was measured monthly and nitrate movement was monitored by application of a 15N tracer to a narrow strip between the bottom of vineyard and the buffer and non-buffer strips. Lolium perenne biomass yield in the buffer strips and its isotopic nitrogen content were monitored. Vicia sativa cover crop management contributed with an excess of nitrogen, and the soil management determined the nitrogen content at the buffer areas. A 6 m buffer strip reduced the nitrate by 42% with and by 46% with a 9 m buffer strip. Thanks to catch crops, farmers can manage the N content and its distribution into the soil over the year, can reduced fertilizer wastage and reduce N pollution of surface and groundwater. © 2013 Author(s)

Erosionabilidad del suelo a lo largo del gradiente climático Coll de Rates - Benidorm, Alicante

[Resumen] Se estudia la influencia del clima sobre la erosionabilidad de los suelos mediante la cuantificación de la estabilidad de los agregados por medio del test de Emerson, por impactos de gotas (CNO y TOI) y por ultrasonidos (UD) a lo largo del gradiente climático Coll de Rates-Benidorm. En todos los suelos estudiados la estabilidad de los agregados es muy elevada, lo que hace difícil encontrar diferencias apreciables entre zonas de estudio. Las distintas historias de uso del suelo (incendios, pastoreo, explotación de la biomasa, etc.) ha dado lugar a la inexistencia de la influencia del clima sobre la erosionabilidad de los suelos.[Abstract] The influence of climate on soil erodibility is studied by means of aggregate stability measurements with the Emerson, drop impacts· (CNO y TOI) and ultrasound (UD) tests along the Coll de Rates-Benidorm climatological gradient. The soils have a very high aggregate stability, and this is the reason why there are not clear differences between study zones. The different past land uses (forest fire, grazing, wood exploitation, etc./) have induced the non existence of the influence of climate on soil erodibility

The contribution of mulches to control high soil erosion rates in vineyards in Eastern Spain

Soil erosion take place in degraded ecosystem where the lack of vegetation, drought, erodible parent material and deforestation take place (Borelli et al., 2013; Haregeweyn et al., 2013; Zhao et al., 2013). Agriculture management developed new landscapes (Ore and Bruins, 2012) and use to trigger non-sustainable soil erosion rates (Zema et al., 2012). High erosion rates were measured in agriculture land (Cerdà et al., 2009), but it is also possible to develop managements that will control the soil and water losses, such as organic amendments (Marqués et al., 2005), plant cover (Marqués et al., 2007) and geotextiles (Giménez Morera et al., 2010). The most successful management to restore the structural stability and the biological activity of the agriculture soil has been the organic mulches (García Orenes et al; 2009; 2010; 2012). The straw mulch is also very successful on bare fire affected soil (Robichaud et al., 2013a; 2013b), which also contributes to a more stable soil moisture content (García-Moreno et al., 2013). The objective of this research is to determine the impact of two mulches: wheat straw and chipped branches, on the soil erosion rates in a rainfed vineyard in Eastern Spain. The research site is located in the Les Alcusses Valley within the Moixent municipality. The Mean annual temperature is 13 ºC, and the mean annual rainfall 455 mm. Soil are sandy loam, and are developed at the foot-slope of a Cretaceous limestone range, the Serra Grossa range. The soils use to be ploughed and the features of soil erosion are found after each thunderstorm. Rills are removed by ploughing. Thirty rainfall simulation experiments were carried out in summer 2011 during the summer drought period. The simulated rainfall lasted during 1 hour at a 45 mmh-1 intensity on 1 m2 plots (Cerdà and Doerr, 2010; Cerdà and Jurgensen 2011). Ten experiments were carried out on the control plots (ploughed), 10 on straw mulch covered plots, and 10 on chipped branches covered soil. The results show that the soil erosion is reduced by 10 on straw mulch covered soils and by 4 on chipped branches covered soil. Acknowledgements The research projects GL2008-02879/BTE, LEDDRA 243857 and RECARE supported this research

El efecto de la escala sobre los procesos de escorrentía superficial

[Resumen] En una pequeña cuenca bajo explotación de dehesa se investiga la generación de escorrentía superficial a distintas escalas. Ello incluye experimentos con lluvia simulada en microparcelas, mediciones del flujo superficial en eventos en 17 parcelas abiertas y una parcela. cerrada, y la producción de caudal de la cuenca y una subcuenca. Los coeficientes de escorrentía de las escalas consideradas se agrupan en dos conjuntos: valores bajos para la cuenca y subcuenca, y valores altos a escala de pedón y ladera. Los resultados demuestran que gran parte de la escorrentía producida en las vertientes se infiltra después en las zonas coluviales y fondos de valle. Además indican la importancia de estudiar varias escalas para entender los procesos hidrológicos que operan en cuencas.[Abstract] In a small catchment under the so-called dehesa landuse system, the production of surface runoff is investigated at different scales. This includes experiments with simulated rainfal1 at micro-plots, event-based measurements of overland flow at 17 open plots and 1 closed plot, and discharge production of the catchment and subcatchment. The runoff coefficients of the considered scales form two groups, with low values for the catchment and sub-catchment and high values for the microplots and hillslope plots. The results show that large part of runoff produced at the slopes is infiltrated afterwards at colluvial sites and the valley floors.Furthemore, they indicate the importance of studying at various scales in order to understand the hydrological processes operating in catchment