Molekulardynamische Untersuchungen heterogener Keimbildung

Heterogeneous nucleation phenomena, in particular the condensation of vapors in presence of a substrate, are studied by molecular dynamics simulations. The simulations reported to this date have paid little attention to the description on the substrate. Here the dynamics of the vapor phase and the surface are simultaneously treated. Two cases are studied: the condensation of argon and the condensation of platinum on polyethylene films. The fundamental difference between both systems is the relative strength of the adsorbate-substrate interactions. The United Atom Method is used to represent the interactions of methyl groups within the polymer. The properties of polyethylene in the bulk phase such as the glass transition temperature, the density and the formation of gauche defects in the crystalline phase can be well described with this model. The interactions between argon atoms can be well represented by the Lennard Jones potential. The Embedded Atom Method is used to describe interactions between platinum atoms since many body effects, important in metals, can be incorporated with a computation requirement similar to pair potentials. Cross interactions between different types of atoms and groups are here approximated by the Lennard Jones potential with Lorentz-Berthelot combining parameters. The aim of this investigation is to describe the dynamics of heterogeneous nucleation and to establish the variables which control the growth and structure formation of clusters on the surface, the nucleation rates, and possible modifications of the substrate during condensation. For this purpose, different conditions of the saturation of the vapor phase and temperature of the substrate were simulated in each of the systems studied. Stationary nucleation rates in vapor phase and on the surface are obtained from cluster size statistics using the method of Yasuoka and Matsumoto. Different growth mechanisms were observed in for the simulated systems. Argon tends to condense on the surface as two-dimensional islands which finally coalesce as layers on the polymer surface. Consistent with this type of growth the condensation in the regime of low saturated and undersaturated vapors can be explained by a two- dimensional model within the frame of the classical nucleation theory. Platinum clusters condense as three-dimensional islands and partially wet the polymer surface. For the first time the embedding of metal atoms and metal clusters growth into a polymer substrate, as observed in experiments, is attained by large-scale molecular simulations. Depending on their sizes, the platinum clusters can diffuse into the polymer matrix even at temperatures lower than the glass transition of the polymer. The routines used for the simulation and analysis have been specially developed for the systems studied. Among them are NpT and NVT ensemble molecular dynamics simulations for the preparation and equilibration of thin polymer films, simulations of condensation of argon and platinum on polyethylene films. Furthermore routines developed for the analysis of simulation results include the calculation of a) radial distribution functions, torsion angle distributions and density profiles for the characterization of polymers, b) algorithms for the recognition of clusters in bulk and on a surface and c) routines for the visualization of the performed simulations

Carbon Nanotubes: Molecular and Electronic Properties of Regular and Defective Structures

In this chapter, we describe how structural parameters affect the reactivity of single-walled carbon nanotubes through global reactivity descriptors obtained by the DFT methods (B3LYP/6-31G(d) with real frequencies in all cases). First, we investigate regular armchair, chiral, and zigzag nanotubes with bumpy defects (five- and seven-membered rings), finding that regular and defective zigzag nanotubes exhibit the greater conductive ability, reactivity, and capacity of nanotubes to be reduced. The bumpy defects favor those properties with greater intensity in chiral nanotubes. We also investigate how the properties of armchair nanotubes change in the presence of bumpy, haeckelite, Stone-Wales, and zipper defects, and we found that armchair nanotubes with zipper defects show greater reactivity and better conducting abilities enhanced by nitrogen doping and longer nanotubes. In addition, for armchair nanotubes containing bumpy defects, our results reveal, considering B3LYP-D3 correction, that bumpy defects confer a greater ability to physically adsorb hydrogen, with adsorption energies of 0.32 eV/adsorbed H2. That value is considered ideal for the reversible adsorption of hydrogen at room temperature and low pressures and therefore favorable for use as a clean energy source. These results contribute to the future design of novel useful materials based in carbon nanotubes

Kinetics of rapid growth and melting of Al 50 Ni 50 alloying crystals: phase field theory versus atomistic simulations revisited *

A revised study of the growth and melting of crystals in congruently melting Al 50 Ni 50 alloy is carried out by molecular dynamics (MDs) and phase field (PF) methods. An embedded atom method (EAM) potential of Purja Pun and Mishin (2009 Phil. Mag. 89 3245) is used to estimate the material’s properties (density, enthalpy, and self-diffusion) of the B2 crystalline and liquid phases of the alloy. Using the same EAM potential, the melting temperature, density, and diffusion coefficient become well comparable with experimental data in contrast with previous works where other potentials were used. In the new revision of MD data, the kinetics of melting and solidification are quantitatively evaluated by the ‘crystal-liquid interface velocity–undercooling’ relationship exhibiting the well-known bell-shaped kinetic curve. The traveling wave solution of the kinetic PF model as well as the hodograph equation of the solid-liquid interface quantitatively describe the ‘velocity–undercooling’ relationship obtained in the MD simulation in the whole range of investigated temperatures for melting and growth of Al 50 Ni 50 crystals

Geometría y proporción en el oratorio mozárabe de San Miguel de Celanova

La pequeña iglesia mozárabe de San Miguel de Celanova se analiza en planta y alzado descubriendo el uso de proporciones aureas, cambios técnicos en la obra de cantería y la utilización de los sistemas de medida árabe y romano. Estas características indican la existencia de una dirección de obra inicial procedente de Al-Andalus y una gran permeabilidad de la frontera a las preocupaciones matemáticas cordobesas del siglo X.In this paper we analize the mozarabic little church called Saint Miguel of Celanova. We find the use of golden number in the plan and the elevation. The builders utilized arabian and roman measurigs, and changed thechnicals solutions during the construction. These characteristics lead to an inicial builder from Al-Andalus in addition one can conclude a permeability of the border to the novelties of cordoban mathematics at X century.peerReviewe

Semi-Decoupled Second-Order Consistency Correction for Smoothed Particle Hydrodynamics

We present an approximate second-order consistent smoothed particle hydrodynamics method which uses the 1D solutions to approximate the 2D second order derivatives. The numerical tests of the analytic functions show that the method is exact for regular arrangements of interpolation points, while in the disordered areas the accuracy is lower than the exact solution of the second-order consistent modified smoothed particle hydrodynamics, but still better that the standard version or the so-called decoupled finite particle method. We applied the new model to the flow of a fluid around a circular solid obstacle and found that the use of a corrected semi-decoupled second-order consistent SPH gives better accuracy for lower resolutions allowing for a more efficient numerical model and also easier to extend to 3D

RELaTED Project: New Developments on Ultra-Low Temperature District Heating Networks

District heating networks deliver around 13% of the heating energy in the EU, being considered as a key element of the progressive decarbonization of Europe. The H2020 REnewable Low TEmperature District project (RELaTED) seeks to contribute to the energy decarbonization of these infrastructures through the development and demonstration of the following concepts: reduction in network temperature down to 50 °C, integration of renewable energies and waste heat sources with a novel substation concept, and improvement on building-integrated solar thermal systems. The coupling of renewable thermal sources with ultra-low temperature district heating (DH) allows for a bidirectional energy flow, using the DH as both thermal storage in periods of production surplus and a back-up heating source during consumption peaks. The ultra-low temperature enables the integration of a wide range of energy sources such as waste heat from industry. Furthermore, RELaTED also develops concepts concerning district heating-connected reversible heat pump systems that allow to reach adequate thermal levels for domestic hot water as well as the use of the network for district cooling with high performance. These developments will be demonstrated in four locations: Estonia, Serbia, Denmark, and Spain.This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 768567. This publication reflects only the authors’ views and neither the Agency nor the Commission are responsible for any use that may be made of the information contained therein

Local perceptions on social-ecological dynamics in Latin America in three community-based natural resource management systems

Several examples of community-based natural resource management in Latin American social-ecological systems exist in which communities control the management of common-pool resources. Understanding community perceptions of the performance of these systems is essential to involve communities in sustainable management strategies. In this analysis of three areas in Colombia, Mexico, and Argentina, we analyzed the local perceptions of the social and environmental challenges faced by these social-ecological systems and how these challenges and drivers affect their resilience. To do this, we combined prospective structural analysis to unravel stakeholders’ perceptions of each system’s functioning along with network analysis to assess resilience. We identified external variables as the most influential variables in the Colombian and Argentine cases. In the Mexican case, larger influence is exerted by internal variables, particularly those linked to the governance system. The case study analysis revealed that the community-based natural resource management approach needs external support and recognition to work effectively. In the Argentine and Colombian cases, megaprojects were perceived as controllers with medium or strong influence but low dependence. The use of ancestral knowledge (Colombia), the history of land use (Mexico), and the history of the artisanal fishery (Argentina) were all perceived as common challenges to communitybased natural resource management. In terms of social-ecological resilience, framed within the three-dimensional model of the adaptive cycle, all three social-ecological systems were considered to be highly connected and resilient but with different degrees of capacity or cumulative potential

Tree-ring distinctness, dating potential and climatic sensitivity of laurel forest tree species in Tenerife Island

Producción CientíficaMacaronesian laurel forests are the only remnants of a subtropical palaeoecosystem dominant during the Tertiary in Europe and northern Africa. These biodiverse ecosystems are restricted to cloudy and temperate insular environments in the North Atlantic Ocean. Due to their reduced distribution area, these forests are particularly vulnerable to anthropogenic disturbances and changes in climatic conditions. The assessment of laurel forest trees’ response to climate variation by dendrochronological methods is limited because it was assumed that the lack of marked seasonality would prevent the formation of distinct annual tree rings. The aims of this study were to identify the presence of annual growth rings and to assess the dendrochronological potential of the most representative tree species from laurel forests in Tenerife, Canary Islands. We sampled increment cores from 498 trees of 12 species in two well-preserved forests in Tenerife Island. We evaluated tree-ring boundary distinctness, dating potential, and sensitivity of tree-ring growth to climate and, particularly, to drought occurrence. Eight species showed clear tree-ring boundaries, but synchronic annual tree rings and robust tree-ring chronologies were only obtained for Laurus novocanariensis, Ilex perado subsp. platyphylla, Persea indica and Picconia excelsa, a third of the studied species. Tree-ring width depended on water balance and drought occurrence, showing sharp reductions in growth in the face of decreased water availability, a response that was consistent among species and sites. Inter-annual tree-ring width variation was directly dependent on rainfall input in the humid period, from previous October to current April. The four negative pointer years 1995, 1999, 2008 and 2012 corresponded to severe drought events in the study area. This study gives the first assessment of dendrochronological potential and tree-ring climate sensitivity of tree species from the Tenerife laurel forest, which opens new research avenues for dendroecological studies in Macaronesian laurel forests.Ministerio de Ciencia, Innovación y Universidades (projects PID2019-109906RA-I00, PID2020-118444GA-100 and PID2019-106908RA-I00/AEI/10.13039/501100011033)Ministerio de Ciencia, Innovación y Universidades (predoctoral contract PRE2018-084106)Ministerio de Economía, Industria y Competitividad (project CGL2017-87309-P and postdoctoral grant IJC2019-040571-I)Junta de Castilla y León (projects VA113G19 and IR2020-1-UVA08)Universidad de Valladolid (predoctoral contract 113-2019PREUVA22)Comunidad de Madrid (project S2018/EMT-4338