Hysteresis in vibrated granular media

Some general dynamical properties of models for compaction of granular media based on master equations are analyzed. In particular, a one-dimensional lattice model with short-ranged dynamical constraints is considered. The stationary state is consistent with Edward's theory of powders. The system is submitted to processes in which the tapping strength is monotonically increased and decreased. In such processes the behavior of the model resembles the reversible–irreversible branches which have been recently observed in experiments. This behavior is understood in terms of the general dynamical properties of the model, and related to the hysteresis cycles exhibited by structural glasses in thermal cycles. The existence of a “normal” solution, i.e., a special solution of the master equation which is monotonically approached by all the other solutions, plays a fundamental role in the understanding of the hysteresis effects.Dirección General de Investigación Científica y Técnica (Spain) through Grant No. PB98-112

Strong nonexponential relaxation and memory effects in a fluid with nonlinear drag

We analyze the dynamical evolution of a fluid with nonlinear drag, for which binary collisions are elastic, described at the kinetic level by the Enskog-Fokker-Planck equation. This model system, rooted in the theory of nonlinear Brownian motion, displays a really complex behavior when quenched to low temperatures. Its glassy response is controlled by a long-lived nonequilibrium state, independent of the degree of nonlinearity and also of the Brownian-Brownian collisions rate. The latter property entails that this behavior persists in the collisionless case, where the fluid is described by the nonlinear Fokker-Planck equation. The observed response, which includes nonexponential, algebraic, relaxation, and strong memory effects, presents scaling properties: the time evolution of the temperature—for both relaxation and memory effects—falls onto a master curve, regardless of the details of the experiment. To account for the observed behavior in simulations, it is necessary to develop an extended Sonine approximation for the kinetic equation—which considers not only the fourth cumulant but also the sixth one.FEDER/Ministerio de Ciencia e Innovación–Agencia Estatal de Investigación (Spain) Project No. PGC2018-093998-B-I00FPU programme Grant No. FPU2019-411

Strong nonexponential relaxation and memory effects in a fluid with nonlinear drag

We analyze the dynamical evolution of a fluid with nonlinear drag, for which binary collisions are elastic, described at the kinetic level by the Enskog-Fokker-Planck equation. This model system, rooted in the theory of nonlinear Brownian motion, displays a really complex behavior when quenched to low temperatures. Its glassy response is controlled by a long-lived nonequilibrium state, independent of the degree of nonlinearity and also of the Brownian-Brownian collisions rate. The latter property entails that this behavior persists in the collisionless case, where the fluid is described by the nonlinear Fokker-Planck equation. The observed response, which includes nonexponential, algebraic, relaxation, and strong memory effects, presents scaling properties: the time evolution of the temperature—for both relaxation and memory effects—falls onto a master curve, regardless of the details of the experiment. To account for the observed behavior in simulations, it is necessary to develop an extended Sonine approximation for the kinetic equation—which considers not only the fourth cumulant but also the sixth one.FEDER/Ministerio de Ciencia e Innovación–Agencia Estatal de Investigación (Spain) Project No. PGC2018-093998-B-I00FPU programme Grant No. FPU2019-411

Glassy behavior in a simple model with entropy barriers

We study the dynamical behavior of a system with a variable number of particles n. The empty state n=0 is the ground state, while all the other states n>0 are degenerate in energy. In equilibrium, the mean number of particles is equal to unity, independently of the temperature. The static properties are the same as for the Backgammon model recently proposed by Ritort [Phys. Rev. Lett. 75, 1190 (1995)], while a variation of the kinetics is considered. The elementary dynamical processes are the arrival and departure of a particle. The rate of the departure process is constant, while the arrival rate is obtained from the detailed balance condition. Thus, there is no energy barrier separating the ground state n=0. Nevertheless, glassy behavior appears due to the presence of effective entropy barriers. At low temperatures, the response functions are shown to obey φ(t)≃exp[-(t/τ)γ]. In thermal cycles of cooling and reheating from low temperatures, the system shows hysteresis, which follows from the trend of the system to approach the normal curve characterizing the heating program.Dirección General de Investigación Científica y Técnica (Spain) through Grant No. PB96-0534

Chrome Layer Thickness Modelling in a Hard Chromium Plating Process Using a Hybrid PSO/ RBF–SVM–Based Model

The purpose of chromium plating is the creation of a hard and wear-resistant layer of chromium over a metallic surface. The principal feature of chromium plating is its endurance in the face of the wear and corrosion. This industrial process has a vast range of applications in many different areas. In the performance of this process, some difficulties can be found. Some of the most common are melt deposition, milky white chromium deposition, rough or sandy chromium deposition and lack of toughness of the layer or wear and lack of thickness of the layer deposited. This study builds a novel nonparametric method relied on the statistical machine learning that employs a hybrid support vector machines (SVMs) model for the hard chromium layer thickness forecast. The SVM hyperparameters optimization was made with the help of the Particle Swarm Optimizer (PSO). The outcomes indicate that PSO/SVM–based model together with radial basis function (RBF) kernel has permitted to foretell the thickness of the chromium layer created in this industrial process satisfactorily. Thus, two kinds of outcomes have been obtained: firstly, this model permits to determine the ranking of relevance of the seven independent input variables investigated in this industrial process. Finally, the high achievement and lack of complexity of the model indicate that the PSO/SVM method is very interesting compared to other conventional foretelling techniques, since a coefficient of determination of 0.9952 is acquired

Aging in the one-dimensional Ising model with Glauber dynamics

We study the zero-temperature limit of the one-dimensional Ising model with nearest-neighbor interactions and Glauber dynamics. An exact evolution equation is derived for the spin-spin two-time correlation functions following an instantaneous quench from equilibrium at low temperature. In the limit of long waiting times the correlations become independent of the distance and reduce to the autocorrelation function, which exhibits aging, i.e. it decays over a time which scale with the waiting time.Dirección General de Investigación Científica y Técnica PB96-053

Gamma-flatness and Bishop-Phelps-Bollobas type theorems for operators

[EN] The Bishop-Phelps-Bollobas property deals with simultaneous approximation of an operator T and a vector x at which T nearly attains its norm by an operator T-o and a vector x(o), respectively, such that T-o attains its norm at x(o). In this note we extend the already known results about the Bishop-Phelps Bollobas property for Asplund operators to a wider class of Banach spaces and to a wider class of operators. Instead of proving a BPB-type theorem for each space separately we isolate two main notions: Gamma-flat operators and Banach spaces with ACK(rho) structure. In particular, we prove a general BPB-type theorem for Gamma-flat operators acting to a space with ACK(rho) structure and show that uniform algebras and spaces with the property beta have ACK(rho) structure. We also study the stability of the ACK(rho) structure under some natural Banach space theory operations. As a consequence, we discover many new examples of spaces Y such that the Bishop-Phelps-Bollobas property for Asplund operators is valid for all pairs of the form (X, Y).The research of the first, second and third authors was partially supported by MINECO grant MTM2014-57838-C2-1-P and Fundacion Seneca, Region de Murcia grant 19368/PI/14. The research of the third author is done in frames of Ukrainian Ministry of Science and Education Research Program 0115U000481. The research of the fourth author has been partially performed during her stay in University of Murcia in frames of Erasmus+ program. We thank the referee for his/her suggestions that helped to improve the original manuscript.Cascales Salinas, B.; Guirao Sánchez, AJ.; Kadets, V.; Soloviova, M. (2018). Gamma-flatness and Bishop-Phelps-Bollobas type theorems for operators. Journal of Functional Analysis. 274(3):863-888. https://doi.org/10.1016/j.jfa.2017.10.020S863888274

Mantos inducidos por microbialitas en sedimentos siliciclásticos plio-cuaternarios? del NO de Iberia

Microbial mats are organo-sedimentary deposits formed by bacteria that trap or synthesize certain chemical elements. This type of activity gives rise to the formation of lamellar and/or columnar bioconstructions (stromatolites) and/or concentric structures (oncolites and thrombolites). The study of microbial mats used to be restricted mainly to marine and coastal environments related to the formation of ancient carbonate sediments (Palaeozoic/Proterozoic), and/or extreme conditions in hypersaline environments. However, in recent years, the presence of these forms has been identified in continental siliciclastic rocks and sediments with a temporal distribution that reaches into modern times. In this study, several levels of ferruginous crusts associated with microbial activity are found, interspersed in a Cenozoic deposit located in the province of Zamora. This deposit consists of concentric, laminated iron structures filled with silt, interspersed throughout a clayey-silt layer of variegated colors which shows signs of bioturbation and desiccation due to fluid escape. These findings allow the inference of the sedimentary and climatic conditions responsible for the growth and preservation of microbial mats in the siliciclastic sediments of the north-western edge of the Duero BasinLos mantos microbiales constituyen depósitos organosedimentarios formados por bacterias que atrapan o sintetizan determinados elementos químicos. Este tipo de actividad da lugar a la formación de estructuras laminares y/o columnares (estromatolitos) y/o concéntricas (oncolitos y trombolitos). Su estudio, por tanto, quedaba reducido principalmente a ambientes marinos y litorales relacionados con la formación de sedimentos carbonatados de edad muy antigua (Paleozoico/ Proterozoico), y/o condiciones extremas en ambientes hipersalinos. Sin embargo, en los últimos años, se ha identificado la presencia de estas formas en rocas y sedimentos de afinidad continental y carácter siliciclástico, que se extienden temporalmente hasta la actualidad. En este estudio, se presenta el hallazgo de varios niveles de costras ferruginosas asociadas a la actividad microbiana, intercalados en un depósito cenozoico de la provincia de Zamora. Se trata de una serie de niveles caracterizados por la presencia de capas ferruginosas laminadas y concéntricas, constituidas por limos que aparecen en el techo y muro de un nivel arcilloso-limoso de colores abigarrados y signos de bioturbación y desecación por escape de fluidos. Este singular hallazgo permite establecer las condiciones sedimentarias y climáticas responsables del crecimiento y conservación de mantos microbianos en sedimentos siliciclásticos del borde noroccidental de la cuenca del Duer

Remediation of Potential Toxic Elements from Wastes and Soils: Analysis and Energy Prospects

[EN] The aim of this study is to evaluate the application of the main hazardous waste management techniques in mining operations and in dumping sites being conscious of the inter-linkages and inter-compartment of the contaminated soils and sediments. For this purpose, a systematic review of the literature on the reduction or elimination of different potential toxic elements was carried out, focusing on As, Cd and Hg as main current contaminant agents. Selected techniques are feasible according to several European countries’ directives, especially in Spain. In the case of arsenic, we verified that there exists a main line that is based on the use of iron minerals and its derivatives. It is important to determine its speciation since As (III) is more toxic and mobile than As (V). For cadmium (II), we observed a certain predominance of the use of biotic techniques, compared to a variety of others. Finally, in mercury case, treatments include a phytoremediation technique using Limnocharis flava and the use of a new natural adsorbent: a modified nanobiocomposite hydrogel. The use of biological treatments is increasingly being studied because they are environmentally friendly, efficient and highly viable in both process and energy terms. The study of techniques for the removal of potential toxic elements should be performed with a focus on the simultaneous removal of several metals, since in nature they do not appear in isolation. Moreover, we found that energy analysis constitutes a limiting factor in relation to the feasibility of these techniques.SIUniversidad de Leó

The effects of scale-up and coal-biomass blending on supercritical coal oxy-combustion power plants

[EN] Carbon Capture and Storage (CCS) with biomass is called to be one of the most important technologies to reduce the climate change all over the world. In addition, supercritical pulverized coal plants have been pointed out as interesting power installations because its high efficiency. In this work, the effects of plants scaling and biomass-coal co-firing level on net present value (NPV), cost of energy (COE) and cost of CO2 avoided (CCA) have been studied on a supercritical pulverized combusting coal/biomass blends. Aspen Plus© was used to implement technical simulations. Finally, the main factors affecting plants viability were identified by a sensitivity analysis. The results obtained revealed that the use of biomass reduces the NPV in (-0.23,-1.75) M€/MWe, and increases the COE by (0.007,0.263) M€/MWe. However, plant scaling was found to be a more important factor, by reaching an impact of 4.32M€/MWe on NPV variation in best case. The reduction of oxy-plants viability by biomass using as raw material could be compensated by an increasing of the designed scale-up. Finally, 300 MWe power plants with 40-50% biomass co-firing level were identified as a compromise solution between economy and risk, improving in this way the interest for potential investmentSIThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Authors thanks the assistance of University of Oviedo (Spain) Chemical Engineering Department in the implementation of the technical simulations of this stud