Relaxation dynamics of metallic systems in the liquid/glass transition region

Peer ReviewedPostprint (published version

Relaxation dynamics of Fe55Cr10Mo14C15B6 metallic glass explored by mechanical spectroscopy and calorimetry measurements

In this work, the mechanical relaxation dynamics of Fe55Cr10Mo14C15B6 metallic glass is explored by mechanical spectroscopy. The temperature-dependent loss modulus E″(T) shows the features of β relaxation well below glass transition temperature Tg. This β relaxation can be well described in the framework of anelastic theory by a thermal activated process with activation energy of 165 kJ mol−1. Structural relaxation, also known as physical aging, has a large effect on the glass properties. The activation energy spectrum of structural relaxation is characterized by differential scanning calorimetry measuring the heat flow difference between as-quenched and relaxed states. The obtained energy spectrum is well described by a lognormal distribution with maximum probability activation energy of 176 kJ mol−1. The obtained activation energy of structural relaxation is similar to that of β relaxation observed from mechanical spectroscopy. Both values are also close to the Johari–Goldstein β relaxation estimated by the empirical rule Eβ = 26RTg.Peer ReviewedPostprint (author's final draft

Phonon dispersion relation of metallic glasses

Experimental data on the phase sound speed of metallic glasses show anomalies in the terahertz range, reflecting an underlying complex behavior of their phonon dispersion spectrum not yet explained. We determine the phonon dispersion curve of metallic glasses by means of massive molecular dynamics simulations, allowing us to obtain the low-q region behavior with unprecedented detail. Results confirm that the sound speed is constant below the THz range, down to the macroscopic limit. On the contrary, a hardening of the sound speed, more notable in the transverse case, is found in the THz range. This behavior is modeled in terms of a relaxation model. The model gives quantitative agreement and allows us to determine a new threshold frequency ¿h, at the end of the boson-peak region. Above ¿h the shear modulus increases dramatically, reflecting the end of the amorphous-like acoustic propagation region characterized by the excess density of vibrational states.Peer ReviewedPostprint (author's final draft

Temporal evolution of the domain structure in a Poisson-Voronoi nucleation and growth transformation. Results for one and three dimensions

The distribution of spatial domain structures originated during one and three dimensional Poisson-Voronoi transformations are computed analytically extending the recently obtained re- sults for the two dimensional case. The presented method gives a full description of the developed microstructure and is valid for tessellations of any dimensionality. The temporal and spatial depen- dences of the domain structure are completely discriminated and separated, showing the existence of geometric configurations independent of time. A single computation of the probability distribution of these geometric configurations allows us to calculate the total free-boundary and size probabil- ity distributions at any desired time. The obtained results show full agreement with stochastic simulations and reproduce completely the previously existing partial results. A discussion about the potential applications of the method to the calculation of other geometrical properties and the characteristics of the final static structure leading to a gamma distribution of sizes is also presented

Root Zone Respiration on Hydroponically Grown Wheat Plant Systems

Root respiration is a biological phenomenon that controls plant growth and physiological development during a plant's lifespan. This process is dependent on the availability of oxygen in the system where the plant is located. In hydroponic systems, where plants are submerged in a solution containing vital nutrients but no type of soil, the availability of oxygen arises from the dissolved oxygen concentration in the solution. This oxygen concentration is dependent on the , gas-liquid interface formed on the upper surface of the liquid, as given by Henry's Law, depending on pressure and temperature conditions. Respiration rates of the plants rise as biomass and root zone increase with age. The respiration rate of Apogee wheat plants (Triticum aestivum) was measured as a function of light intensity (catalytic for photosynthesis) and CO2 concentration to determine their effect on respiration rates. To determine their effects on respiration rate and plant growth microbial communities were introduced into the system, by Innoculum. Surfactants were introduced, simulating gray-water usage in space, as another factor to determine their effect on chemical oxygen demand of microbials and on respiration rates of the plants. It is expected to see small effects from changes in CO2 concentration or light levels, and to see root respiration decrease in an exponential manner with plant age and microbial activity

Phase-field modelling of microstructural evolution in primary crystallization

One of the main routes to obtain nanostructured materials is through the primary crystallization of metallic glasses. In such transformations, crystallites with a different composition than the amorphous precursor grow with a diffusion-controlled regime. Particle growth is slowed and eventually halted by the impingement between the concentration gradients of surrounding particles. Primary crystallization kinetics is not well described by the KJMA equation, and this fact was generally ascribed to both the soft-impingement effect and the non-random nucleation. However, recent phase-field simulations showed that the underlying physical reason is the change in the local diffusion properties of the amorphous precursor due to the variation of the composition during the transformation. The kinetics of primary crystallization is thus well described by considering a diffusion coefficient of the slowest diffusing species dependent on the local concentration. The nanostructure developed in such transformations is a key point to explain the macroscopic properties of these materials. In this work the grain size distributions obtained in realistic phase-field simulations of transformations with continuous nucleation and both constant and variable diffusion coefficient are presented. The obtained distributions are analyzed and the physical mechanisms responsible of their different features are recognized

Nuevas perspectivas de la gobernanza Privada: un análisis desde las prácticas de Responsabilidad social y ambiental de las Empresas en Colombia

The investments on social and environmental responsibility in Colombia have generated a new perspective for private governance in terms of sustainability. To understand this phenomenon, we analyze sustainability reports, financial statements and management reports provided by a successful case of sustainability in Colombia. This would be with the purpose of assessing whether or not such policies constitute a potential political instrument to advance in government regulations; otherwise policies would curtail to management strategy with repercussions on corporate image and financial performance for reporting companies. The testing of our research hypotheses concluded that the execution of sustainability reports in Colombia is a recent practice, despite the existence of a normative framework established since the 1991 Constitution. The foregoing may acknowledge that actual importance is due to investments on social innovation and a new approach of private governance, as a response for economic dynamics and political advances in Colombia

Análisis bibliométrico y sistémico de la relación entre la gestión y el carbono

[EN] This paper aims to present a bibliometric and systemic analysis of the Bibliographic Portfolio (BP) jointly examining the literature related to topics like “Greenhouse gas,” mainly carbon, and “Management,” as published in databases data such as Web of Science and Scopus in the field of economic and social sciences. The Knowledge and Constructivist Development Process methodology —Proknow-C— was used to establish the final portfolio and through the VosViewer program were mapped the various groups or relationships between the studied literature. The paper presents the theoretical and methodological aspects focusing on the areas and countries of study and highlighting the most relevant authors to have researched this particular topic. We use this constructivist model to describe the measurement variables and synthesize the concepts most used in these studies in order to propose new focal points and thematic approaches that could be developed further in the future.[ES] Este trabajo tiene como objetivo presentar un análisis bibliométrico y sistémico del Portafolio Bibliográfico (PB) examinando conjuntamente la literatura relacionada con temas como “Gas de efecto invernadero”, principalmente el carbono, y “Gestión”, según lo publicado en bases de datos como Web of Science y Scopus, en el campo de las ciencias económicas y sociales. Se empleó la metodología del Proceso de Desarrollo del Conocimiento y Constructivismo—Proknow-C— para establecer el portafolio final y a través del programa VosViewer se mapearon los diversos grupos o relaciones entre la literatura estudiada. El trabajo presenta los aspectos teóricos y metodológicos centrándose en las áreas, países de estudio y el reconocimiento de los autores más relevantes que han investigado este tema en particular. A partir de este modelo constructivista, se describen las variables de medición y se sintetizan los conceptos más utilizados en estos estudios, con el fin de proponer nuevos enfoques temáticos que puedan desarrollarse en el futuro.This document was produced thanks to the fact that Yenny Naranjo Tuesta was a beneficiary of the “Colombia Científica - Pasaporte a la Ciencia Program of ICETEX” in the foco – país of Society, which financed her doctoral studies. The authors would like to thank the anonymous reviewers for their comments, which have considerably improved this documen

Nuevas localidades alicantinas de Carduncellus dianius Webb

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Plastic deformation induced anisotropy in metallic glasses: A molecular dynamics study

The atomic structure of a Cu13Ni34Pd53 metallic glass was studied by molecular dynamics simulation at different temperatures along a shear deformation cycle. A simulation box of 1 million atoms was deformed in the x axis and then the original orthogonal shape was recovered. Directional pair distribution functions were computed in the coordinate planes and some significant directions along the shear deformation cycle. No anisotropy was found in the initial state, while post-deformation anisotropy was revealed by significant differences of the partial pair distribution functions. The analysis of atomic environments concluded that the remnant anisotropy remains constrained into the shear plane. Low temperature samples showed remnant anisotropy after the full shear sample, while close to the glass transition the anisotropy induced by the initial shear process is removed by the subsequent recovery process.Peer ReviewedPostprint (published version