Metastable states influence on the magnetic behavior of the triangular lattice: Application to the spin-chain compound Ca3Co2O6

It is known that the spin-chain compound Ca3Co2O6 exhibits very interesting plateaus in the magnetization as a function of the magnetic field at low temperatures. The origin of them is still controversial. In this paper we study the thermal behavior of this compound with a single-flip Monte Carlo simulation on a triangular lattice and demonstrate the decisive influence of metastable states in the splitting of the ferrimagnetic 1/3 plateau below 10 K. We consider the [Co2O6]n chains as giant magnetic moments described by large Ising spins on planar clusters with open boundary conditions. With this simple frozen-moment model we obtain stepped magnetization curves which agree quite well with the experimental results for different sweeping rates. We describe particularly the out-of-equilibrium states that split the low-temperature 1/3 plateau into three steps. They relax thermally to the 1/3 plateau, which has long-range order at the equilibrium. Such states are further analyzed with snapshots unveiling a domain-wall structure that is responsible for the observed behavior of the 1/3 plateau. A comparison is also given of the exact results in small triangular clusters with our Monte Carlo results, providing further support for our thermal description of this compound.Comment: 8 pages, 11 figures, submitted to PR

Evaluation of the performance of single-walled carbon nanohorns in capillary electrophoresis

II Encuentro sobre nanociencia y nanotecnología de investigadores y tecnólogos de la Universidad de Córdoba. NANOUC

Modeling displaced squeezed number states in waveguide arrays

We present an exact analytical solution for a one-dimensional zigzag waveguide array with first and second neighbor interactions. It is found that the waveguide system possess a classical analog to the displaced squeezed number states. The exact solution was compared directly with the numerical solution showing a perfect agreement between both results. The implication of a linear index of refraction changing as a function of the site number is also studied. In this case, we show that the first neighbor interaction strongly influences the periodicity of Bloch oscillations.Comment: 15 pages, 9 figure

An Embedded-Sensor Approach for Concrete Resistivity Measurement in On-Site Corrosion Monitoring: Cell Constants Determination

[EN] The concrete electrical resistivity is a prominent parameter in structural health monitoring, since, along with corrosion potential, it provides relevant qualitative diagnosis of the reinforcement corrosion. This study proposes a simple expression to reliable determine resistivity from the concrete electrical resistance (R-E) provided by the corrosion sensor of the Integrated Network of Sensors for Smart Corrosion Monitoring (INESSCOM) we have developed. The novelty here is that distinct from common resistivity sensors, the cell constants obtained by the proposed expression are intended to be valid for any sensor implementation scenario. This was ensured by studying most significant geometrical features of the sensor in a wide set of calibration solutions. This embedded-sensor approach is intended to be applicable for R-E measurements obtained both using potential step voltammetry (PSV, used in the INESSCOM sensor for corrosion rate measurement) and alternating current methods. In this regard, we present a simple protocol to reliably determine R-E, and therefore resistivity, from PSV measurements. It consists in adding a very short potentiostatic pulse to the original technique. In this way, we are able to easy monitor resistivity along with corrosion rate through a single sensor, an advantage which is not usual in structural health monitoring.This research was funded by the pre-doctoral scholarship granted to Jose Enrique Ramon Zamora by the Spanish Ministry of Science and Innovation, grant number FPU13/00911. Funding was also provided by the Spanish Ministry of Economy and Competitiveness under the national program for research, development and innovation geared to societal challenges; project number BIA2016-78460-C3-3-R. The research activity reported in this paper has been partially possible thanks to the project Voltammetric Electronic Tongue for Durability Control in Concrete funded by the Universitat Politecnica de Valencia, project number SP20180245.Ramón, JE.; Martínez, I.; Gandía-Romero, JM.; Soto Camino, J. (2021). An Embedded-Sensor Approach for Concrete Resistivity Measurement in On-Site Corrosion Monitoring: Cell Constants Determination. Sensors. 21(7):1-23. https://doi.org/10.3390/s21072481S12321

Performance and challenges in the value chain of the Anadara tuberculosa bivalve mollusk in Ecuador

The bivalve mollusk, Anadara tuberculosa (Black Shell, in Spanish Concha Prieta), is found on America’s Pacific coast, where it is harvested for subsistence and commercial markets. This paper aims to diagnose the performance of the black shell’s value chain. We also identify several challenges that must be addressed to improve the sustainability of the black shell fishery in Ecuador. The applied methodology was quantitative and descriptive. Its design was non-experimental, field, cross-sectional and ex post facto. The investigation was carried out from January to October 2019 in the Jambelí archipelago, El Oro province, Ecuador. The study population consisted of 565 individuals, shellfish collectors, shellfish associations managers, traders, and restaurants from the A. tuberculosa production chain. The sample size was estimated at 222 informants. The type of sampling used was probabilistic, random, stratified, and with proportional allocation, with an effective participation rate of those selected of approximately 80%. The questionnaire was applied personally through the structured survey method, in writing, in the work area, and with their consent. The performance of the value chain was diagnosed in the dimensions of productivity, competitiveness, and quality of life, reaching a 75.1% index, a result that indicates that the value chain has a moderate to good performance level. The competitiveness dimension reached the highest performance, followed by productivity. Quality of life was the dimension with the lowest performance. The value chain can be improved if the following challenges are met: (1) Restoration of the mangrove ecosystem, (2) Promotion of low-intensity shellfish aquaculture, (3) Good sanitary management and purification, (4) Promotion of value-focused ventures, (5) Strengthening of organizations and agreements for the use and custody of mangroves, and (6) Strengthening of institutions that contribute to the advancement of these challenge

Stainless Steel Voltammetric Sensor to Monitor Variations in Oxygen and Humidity Availability in Reinforcement Concrete Structures

[EN] The present work presents the results obtained with a stainless steel (SS) voltammetric sensor to detect variations in humidity (H2O) and oxygen (O2) availability in concretes. First, studies in solution were run by preparing several solutions to represent the different conditions that can be found in concrete pores. Second, the sensor's response was studied by varying O2 availability by argon or synthetic air bubbling. Then concrete conditions with different degrees of carbonation were simulated using solutions with a pH between 13 and 8.45. After characterization in solution, a study by means of concrete samples with several water/cement ratios (0.6, 0.5 and 0.4) was performed, in which sensors were embedded and studied under different O2 and H2O saturation conditions. The obtained results revealed that with the voltagram, it is possible to evaluate O2 availability variation from the slopes of the lines identified logarithmically in the voltagram for the obtained cathodic sweeping. All the results obtained with the sensor were correlated/validated by standard assays to characterize porosity in hardened concretes.The authors would like to express their gratitude to the Spanish Ministry of Science and Innovation for the pre-doctoral scholarship granted to Ana Martinez Ibernon (FPU 16/00723). To the Universitat Politecnica de Valencia for the financial support in the project "Ayudas a Primeros Proyectos de Investigacion (PAID-06-18): Lengua Electronica Voltametrica para el control de durabilidad en hormigones, SP20180245"Martínez-Ibernón, A.; Lliso-Ferrando, JR.; Gandía-Romero, JM.; Soto Camino, J. (2021). Stainless Steel Voltammetric Sensor to Monitor Variations in Oxygen and Humidity Availability in Reinforcement Concrete Structures. Sensors. 21(8):1-21. https://doi.org/10.3390/s21082851S12121

Alternative analysis to perturbation theory

We develop an alternative approach to time independent perturbation theory in non-relativistic quantum mechanics. The method developed has the advantage to provide in one operation the correction to the energy and to the wave function, additionally we can analyze the time evolution of the system. To verify our results, we apply our method to the harmonic oscillator perturbed by a quadratic potential. An alternative form of the Dyson series, in matrix form instead of integral form, is also obtained.Comment: 12 pages, no figure

A Computer Simulation Model of Knowledge Management in Small and Medium Agri-Food Enterprises

 System dynamics is an appropriate tool to build management models due to its ease of application in solving unstructured problems. In the twenty-first century the sustainability of organizations is influenced by the way it manages its knowledge. In this sense, knowledge management (KM) represents a strategy that contributes to improving the production supply chain (SC) of the agri-food industry (AFI). The objective of this research is to develop a computer model to simulate the effect of KM on the production of AFI. The methodology applied was that of the system dynamics by using the Vensim PLE ® v. 5.10 software, whose determining indicators were selected through an empirical study of KM in the SC of precooked corn flour industry in Venezuela. The study concluded that the balanced implementation of KM practices in the strategic dimension and in the functional dimension achieved an increase in production through the stabilization of the system. Further evaluation of the methodology developed in other agro-industrial environments is recommended