Nonstandard finite difference schemes for general linear delay differential systems

This paper deals with the construction of non‐standard finite difference methods for coupled linear delay differential systems in the general case of non‐commuting matrix coefficients. Based on an expression for the exact solution of the continuous initial value vector delay problem, a family of non‐standard numerical methods of increasing orders is defined. Numerical examples show that the new proposed numerical methods preserve the stability properties of the exact solutions. This work extends previous results for delay systems with commuting matrix coefficients, allowing the use of the new numerical non‐standard methods in more general problems.M.A.C. and F.R. acknowledge funding by Ministerio de Economía y Competitividad grant number CGL2017-89804-R

How to translate results from auctions to procurements

The translation of statements from auctions to procurements is not always straightforward. We define a duality relationship between them and provide the appropriate transformations needed for establishing it. Additionally, we prove that affiliation is preserved under these transformations and establish the linkage principle for procurements.Suggestions from V. Krishna are appreciated. Financial support from MCI (SEJ2007/04339/001) is gratefully acknowledgedPublicad

The board of directors and international decision-making

This paper develops a view of how specific elements of the directors' human and social capital can enhance a company's international performance. We have taken the view that the board is an active participant in the firm’s management, and we have therefore set out and tested a number of arguments related to the board’s role in the adoption of international decisions. Specifically, our results point to the need to incorporate board members with high levels of education and international background with ability to learn and process information and to help international decision-making. As shown by our results, a high level of external connectivity of directors could have negative repercussions for internationalization since they limit the time spent on the board and therefore reduces the cohesion and trust inside the board. The implications of this research, therefore, are important for both executives and academics, as it helps to know what attributes contribute to the board’s effectiveness in such a way as to positively affect the internationalization of the firm

Citocompatibilidad de tejidos cardiacos humanos decelularizados con detergentes

La insuficiencia cardíaca (IC) es una patología de mal pronóstico muy prevalente en todo el mundo, con más de 20 millones de afectados a nivel global, estimándose que aproximadamente el 50% de los pacientes habrán fallecido en los siguientes 5 años tras el diagnóstico. El trasplante cardíaco (TC) es el tratamiento definitivo en la fase final de la enfermedad pero su aplicación está limitada por la escasez de donantes. Los dispositivos de asistencia ventricular son una alternativa al TC pero tampoco están exentos de complicaciones. El diseño de tejidos bioartificiales que puedan reparar o sustituir miocardio dañado es una opción terapeútica teórica en estos pacientes. En el año 2008 Ott y Taylor demostraron que es posible obtener una matriz extracelular tridimensional decelularizada (MECd) de un corazón completo de rata mediante la perfusión anterógrada de detergentes a través del sistema vascular del órgano. La matriz acelular resultante conserva la estructura tridimensional así como los componentes extracelulares del órgano. Otros investigadores han reproducido estos resultados en varios modelos murinos y de cerdo. Con estos precedentes formulamos la hipótesis de que la decelularización con detergentes iónicos (Dodecil Sulfato de Sodio, SDS) aplicada a tejidos cardíacos humanos permite crear matrices extracelulares decelularizadas que constituyen un armazón tridimensional, perfundible y citocompatible donde es posible la supervivencia y ordenación de células maduras y la supervivencia, ordenación y maduración de células progenitoras..

Energy Efficiency in Public Lighting Systems Friendly to the Environment and Protected Areas

Solid-state lighting technology, such as LED devices, is critical to improving energy efficiency in street lighting systems. In Ecuador, government policies have established the obligation to exclusively use LED systems starting in 2023, except in special projects. Ecuador, known for its vast biodiversity, protects its national parks, which are rich in flora, fauna and natural resources, through international institutions and agreements such as UNESCO, CBD and CITES. Although reducing electrical consumption usually measures energy efficiency, this article goes further. It considers aspects such as the correlated color temperature in the lighting design of protected areas, light pollution and the decrease in energy quality due to harmonic distortion. Measurements of the electromagnetic spectrum of the light sources were made in an area in the Galápagos National Park of Ecuador, revealing highly correlated color temperatures that can affect ecosystem cycles. In addition, the investigation detected levels of light pollution increasing the night sky brightness and a notable presence of harmonic distortion in the electrical grid. Using simulations to predict the behavior of these variables offers an efficient option to help preserve protected environments and the quality of energy supply while promoting energy savings.The APC was funded by University of Alicante Research Groups Grants (VIGROB23-162)

Enantiomeric separation of prothioconazole and prothioconazole-desthio by capillary electrophoresis. Degradation studies in environmental simples

In this work, two analytical methodologies by Capillary Electrophoresis were developed. The first one enabled the rapid and cost-effective enantioseparation of prothioconazole and was applied to the analysis of prothioconazole-based commercial agrochemical formulations. The second methodology enabled the simultaneous enantioseparation of prothioconazole and its metabolite prothioconazole-desthio and was applied to degradation studies of both compounds in soil and sand samples. The influence of several experimental variables was investigated to develop both methodologies. The separation of prothioconazole enantiomers was achieved in 4.5 min with a resolution of 2.8 employing a neutral cyclodextrin (heptakis(2,3,6-tri-O-methyl)-?-cyclodextrin). Given the nature of prothioconazole-desthio, a neutral cyclodextrin cannot be used for its chiral separation. For this reason, the simultaneous enantioseparation of prothioconazole and prothioconazole-desthio was achieved in 5.5 min with resolution values of 1.9 and 8.2, respectively, using a negatively charged cyclodextrin (sulfated-?-cyclodextrin). The analytical characteristics of the developed methodologies were evaluated and both methods showed good performance to be applied to the quantitation of the enantiomers of prothioconazole in commercial agrochemical formulations (LOD 0.7 mg L-1) and to carry out degradation studies for both compounds in environmental matrices (LODs lower than 0.9 and 1.3 mg L-1 for prothioconazole and prothioconazole-desthio enantiomers, respectively). The recovery values obtained were in the range between 94-104 % for the agrochemical formulations, between 96-99 % for the sand samples and between 97-100 % for the soil samples

Resource mobilization levels and the configuration of the alliance portfolio

Alliance Portfolio Configuration (APC) conditions access to network resources, however, not all access to partner resources is finally mobilized by the firm. Our paper contributes to the understanding of alliance portfolio performance by examining how an acceptable configuration of the alliance portfolio will be conditioned by the level of resource mobilization that the firm really achieves. A variance-based structural equation modelling (Partial Least Squares) has been applied to a sample from the Top International Airlines database. Results from the data analysis show that the Level of Network Resource Mobilization (LNRM) (a) fully mediate the effect of alliance portfolio configuration on the operating performance; and (b) partially mediate this effect on financial performance of airlines

Delay Effects on Plant Stability and Symmetry-Breaking Pattern Formation in a Klausmeier-Gray-Scott Model of Semiarid Vegetation

The Klausmeier–Gray–Scott model of vegetation dynamics consists of a system of two partial differential equations relating plant growth and soil water. It is capable of reproducing the characteristic spatial patterns of vegetation found in plant ecosystems under water limitations. Recently, a discrete delay was incorporated into this model to account for the lag between water infiltration into the soil and the following water uptake by plants. In this work, we consider a more ecologically realistic distributed delay to relate plant growth and soil water availability and analyse the effects of different delay types on the dynamics of both mean-field and spatial Klausmeier–Gray–Scott models. We consider distributed delays based on Gamma kernels and use the so-called linear chain trick to analyse the stability of the uniformly vegetated equilibrium. It is shown that the presence of delays can lead to the loss of stability in the constant equilibrium and to a reduction of the parameter region where steady-state vegetation patterns can arise through symmetry-breaking by diffusion-driven instability. However, these effects depend on the type of delay, and they are absent for distributed delays with weak kernels when vegetation mortality is low.This research was funded by “MCIN/AEI/10.13039/501100011033 (Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación) grant number PID2021-125517OB-I00” and “Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital, Generalitat Valenciana grant number CIPROM/2021/001”. I. Medjhadi and F.Z. Lachachi were supported by national grants from the Algerian Ministry of Higher Education and Scientific Research