A square-well model for the structural and thermodynamic properties of simple colloidal systems

A model for the radial distribution function $g(r)$ of a square-well fluid of variable width previously proposed [S. B. Yuste and A. Santos, J. Chem. Phys. {\bf 101}, 2355 (1994)] is revisited and simplified. The model provides an explicit expression for the Laplace transform of $rg(r)$, the coefficients being given as explicit functions of the density, the temperature, and the interaction range. In the limits corresponding to hard spheres and sticky hard spheres the model reduces to the analytical solutions of the Percus-Yevick equation for those potentials. The results can be useful to describe in a fully analytical way the structural and thermodynamic behavior of colloidal suspensions modeled as hard-core particles with a short-range attraction. Comparison with computer simulation data shows a general good agreement, even for relatively wide wells.Comment: 23 pages, 10 figures; Figs. 4 and 5 changed, Fig. 6 new; to be published in J. Chem. Phy

Heat capacity of square-well fluids of variable width

We have obtained by Monte Carlo NVT simulations the constant-volume excess heat capacity of square-well fluids for several temperatures, densities and potential widths. Heat capacity is a thermodynamic property much more sensitive to the accuracy of a theory than other thermodynamic quantities, such as the compressibility factor. This is illustrated by comparing the reported simulation data for the heat capacity with the theoretical predictions given by the Barker-Henderson perturbation theory as well as with those given by a non-perturbative theoretical model based on Baxter's solution of the Percus-Yevick integral equation for sticky hard spheres. Both theories give accurate predictions for the equation of state. By contrast, it is found that the Barker-Henderson theory strongly underestimates the excess heat capacity for low to moderate temperatures, whereas a much better agreement between theory and simulation is achieved with the non-perturbative theoretical model, particularly for small well widths, although the accuracy of the latter worsens for high densities and low temperatures, as the well width increases.Comment: 11 pages, 4 figures; figures now include additional perturbation data; to be published in Mol. Phy

- A COMPUTATIONAL APPROACH TO THE FUNDAMENTAL THEOREM OF ASSET PRICING IN A SINGLE-PERIOD MARKET.

In this paper we provide a new approach to the Fundamental Theorem of As-set Pricing. The proofof this result is usually based on Projection (Separation) Theorems and is far more intuitive. Ourapproach follow the relation between the projection problem an equivalent least squares problem.More precisely, we will use and iterative procedure in order to obtain solutions of a bounded leastsquare problem. This solutions will give, under some conditions, either the state price vector orthe arbitrage opportunity of the problem under consideration.Asset Pricing; Arbitrage; Mathematical Finance

La reacción frente a una crisis generalizada: Un enfoque teórico al consumo de recursos en las empresas familiares

Research to date has shown that companies can accumulate resources over those strictly needed in order to overcome the uncertainty associated to a crisis. But the usage, redeployment, or consumption of this excess of resources when facing an adverse environment is yet underexplored. As suggested by the literature, the condition of family business can exert an important effect in such behaviour. This paper proposes a theoretical framework, focused on family business, about how firms manage the different slack resources when facing a general crisis. We make a call on family business scholars to leverage our propositions and the existing literature on slack resources to develop a guidance for family owners when facing an economic downturn.Las investigaciones realizadas hasta la fecha han demostrado que las empresas pueden acumular recursos por encima de los estrictamente necesarios para superar la incertidumbre asociada a una crisis. Pero la utilización, redistribución o consumo de este exceso de recursos cuando se enfrentan a un entorno adverso está todavía poco explorada. Como sugiere la literatura, la condición de empresa familiar puede ejercer un efecto importante en dicho comportamiento. Este trabajo propone un marco teórico, centrado en la empresa familiar, sobre cómo las empresas gestionan los diferentes recursos slack cuando se enfrentan a una crisis. En este sentido, se plantea la necesidad de que los investigadores en el campo de la empresa familiar aprovechen nuestras propuestas, y la literatura existente sobre los recursos slack, para desarrollar una guía que facilite la toma de decisiones en las empresas familiares cuando se enfrentan a una recesión económica

¿Para qué acumulas? Gestionar los recursos no utilizados ante una recesión económica generalizada

Research to date has shown that a company can accumulate slack resources for a variety of reasons. But how do managers use this excess of resources in a general economic crisis? This study aims to ascertain how companies apply these resources when faced with a financial crisis and economic meltdown, in order to provide answers to the underexplored questions regarding the ways in which firms consume their slack resources. Through the analysis of a sample of 449 Spanish industrial companies during the 2006-2017period, and the application of Latent Growth Modelling, the evolution of the different slack and performance indicators is observed for the identification of disparate behaviour between companies with high and lowinitial endowments of slack resources. The results also show that each type of slack serves a differentpurpose and, therefore, their consumption or use shows clear divergences.Las investigaciones realizadas hasta la fecha han demostrado que una empresa puede acumular un exceso de recursos por diversas razones. Pero, ¿cómo utilizan los directivos este exceso de recursos en una crisis económica generalizada? Este estudio pretende averiguar cómo aplican las empresas estos recursos cuando se enfrentan a una crisis financiera y a un colapso económico, con el fin de dar respuesta a las cuestiones poco exploradas sobre las formas en que las empresas consumen sus recursos holgados. Mediante el análisis de una muestra de 449 empresas industriales españolas durante el periodo 2006-2017, y la aplicación de la Modelización Latente del Crecimiento, se observa la evolución de los distintos indicadores de holgura y rendimiento para la identificación de comportamientos dispares entre empresas con altas y bajas dotaciones iniciales de recursos de holgura. Los resultados también muestran que cada tipo de holgura sirve a un propósito diferente y, por tanto, su consumo o utilización muestra claras divergencias

Learning about knowledge: A complex network approach

This article describes an approach to modeling knowledge acquisition in terms of walks along complex networks. Each subset of knowledge is represented as a node, and relations between such knowledge are expressed as edges. Two types of edges are considered, corresponding to free and conditional transitions. The latter case implies that a node can only be reached after visiting previously a set of nodes (the required conditions). The process of knowledge acquisition can then be simulated by considering the number of nodes visited as a single agent moves along the network, starting from its lowest layer. It is shown that hierarchical networks, i.e. networks composed of successive interconnected layers, arise naturally as a consequence of compositions of the prerequisite relationships between the nodes. In order to avoid deadlocks, i.e. unreachable nodes, the subnetwork in each layer is assumed to be a connected component. Several configurations of such hierarchical knowledge networks are simulated and the performance of the moving agent quantified in terms of the percentage of visited nodes after each movement. The Barab\'asi-Albert and random models are considered for the layer and interconnecting subnetworks. Although all subnetworks in each realization have the same number of nodes, several interconnectivities, defined by the average node degree of the interconnection networks, have been considered. Two visiting strategies are investigated: random choice among the existing edges and preferential choice to so far untracked edges. A series of interesting results are obtained, including the identification of a series of plateaux of knowledge stagnation in the case of the preferential movements strategy in presence of conditional edges.Comment: 18 pages, 19 figure

Occurrence of Cryptosporidium and Giardia in raw and finished drinking water in north-eastern Spain

This paper collects the first large-sample-size study on the presence of Cryptosporidium oocysts and Giardia cysts in drinking water plants at the 20 most populated towns in Aragón (north-eastern Spain). Samples of influent raw water and effluent finished water were collected from each plant during different seasons and processed according to USEPA Method 1623. Cryptosporidium oocysts and Giardia cysts were detected in samples collected from 55% and 70% plants, respectively, with nine plants being positive for both protozoa and only four plants being negative over the study period. Both parasites were identified in the raw water throughout the year, with a lower frequency in autumn and a peak in winter, at a mean concentration of 67 ± 38 oocysts per 100 l and 125 ± 241 cysts per 100 l. The turbidity of raw water was not related to the presence or concentration of (oo)cysts, and the (oo)cyst removal efficiency was not related to the type of water treatment. One or both pathogens were identified in the finished water in 7 out of 11 plants with a conventional treatment process (coagulation, flocculation, sedimentation, filtration, and disinfection processes) compared to 4 out of 9 plants that did not apply one of the pre-chlorination treatment steps. Protozoa were detected in the finished water of positive plants at a mean concentration of 88 ± 55 oocysts per 100 l and 37 ± 41 cysts per 100 l, and most of them excluded propidium iodide so were considered potentially viable. The ubiquity of these parasites in the drinking water sources and the inefficiency of conventional water treatment in reducing/inactivating them may present a serious public health issue in this geographical area