Studies of a mathematical model for generating rhythmic behavior with a simple brain

The rhythmic behavior of feeding in the pond snail, Lymnaea stagnalis can be described computationally by a model describing its central pattern generator network (CPG). The model includes coupled Hodgkin-Huxley type nonlinear ordinary differential equations describing four neurons connected by both inhibitory and excitatory synapses. We studied the system’s dependence on current parameters to generate periodic behavior. We also considered the effect of eliminating specific connections from the network. In addition, experiments on the biological system were used to motivate application of the model in Parkinson’s disease

Space use by foragers consuming renewable resources

We study a simple model of a forager as a walk that modifies a relaxing substrate. Within it simplicity, this provides an insight on a number of relevant and non-intuitive facts. Even without memory of the good places to feed and no explicit cost of moving, we observe the emergence of a finite home range. We characterize the walks and the use of resources in several statistical ways, involving the behavior of the average used fraction of the system, the length of the cycles followed by the walkers, and the frequency of visits to plants. Preliminary results on population effects are explored by means of a system of two non directly interacting animals. Properties of the overlap of home ranges show the existence of a set of parameters that provides the best utilization of the shared resource

Simulación numérica de la convección mixta de gases en tubos verticales incluyendo inversiones del flujo

Este estudio paramétrico trata la influencia de la convección mixta en el desarrollo simultáneo de la velocidad y la temperatura de un gas con propiedades constantes, desplazándose por una tubería circular en posición vertical. Entretanto, la velocidad y la temperatura se consideran uniformes a la entrada de la región de intercambio térmico permaneciendo la pared del tubo isotérmica. La hipótesis más relevante utilizada en este análisis es la aproximación de Boussinesq para la densidad en el término de flotación, en tanto que el resto de las propiedades termofisicas permanecen invariantes con la temperatura. El sistema de ecuaciones en derivadas parciales altamente acoplado que gobierna el citado problema (conservación de masa, cantidad de movimiento y energía) se resuelve numéricamente mediante el método de los volúmenes de control. Un grupo selecto de gráficos ilustra la influencia de la convección natural sobre la convección forzada: ascendente con enfriamiento y ascendente con calentamiento. Además, se presentan curvas ilustrativas que ponen de manifiesto las inversiones del flujo en ambos casos. Este aspecto constituye un aporte innovador del presente trabajo.Peer Reviewe

Antioxidant activity of alkyl gallates and glycosyl alkyl gallates in fish oil in water emulsions: Relevance of their surface active properties and of the type of emulsifier

The antioxidant activity of gallic acid and a series of alkyl gallates (C4-C18) and glycosylated alkyl gallates (C4-C18) on fish oil-in-water emulsions was studied. Three types of emulsifiers, lecithin, Tween-20 and sodium dodecyl sulphate (SDS) were tested. A nonlinear behavior of the antioxidant activity of alkyl gallates when increasing alkyl chain length was observed for emulsions prepared with lecithin. Medium-size alkyl gallates (C6-C12) were the best antioxidants. In contrast, for emulsions prepared with Tween-20, the antioxidants seem to follow the polar paradox. Glucosyl alkyl gallates were shown previously to be better surfactants than alkyl gallates. Nevertheless, they exhibited a worse antioxidant capacity than their corresponding alkyl gallates, in emulsions prepared with lecithin or Tween-20, indicating the greater relevance of having three OH groups at the polar head in comparison with having improved surfactant properties but just a di-ortho phenolic structure in the antioxidant

The Use Of Peer Tutoring To Improve The Passing Rates In Mathematics Placement Exams Of Engineering Students: A Success Story

This paper describes a highly successful peer tutoring program that has resulted in an improvement in the passing rates of mathematics placement exams from 16% to 42%, on average. Statistical analyses were conducted using a Chi-Squared (X2) test for independence and the results were statistically significant (p-value much less than 0.05). These encouraging results suggest that this type of initiative should be institutionalized at the end of the grant period that funds it. The paper describes the structure of the program, the conditions of the university in which it is being implemented, the details of the statistical analyses, and its impact in engineering education. This model may easily be replicated in academic institutions with similar conditions.

Towards Portability of Models for Predicting Students’ Final Performance in University Courses Starting from Moodle Logs

Predicting students’ academic performance is one of the older challenges faced by the educational scientific community. However, most of the research carried out in this area has focused on obtaining the best accuracy models for their specific single courses and only a few works have tried to discover under which circumstances a prediction model built on a source course can be used in other different but similar courses. Our motivation in this work is to study the portability of models obtained directly from Moodle logs of 24 university courses. The proposed method intends to check if grouping similar courses by the degree or the similar level of usage of activities provided by the Moodle logs, and if the use of numerical or categorical attributes affect in the portability of the prediction models. We have carried out two experiments by executing the well-known classification algorithm over all the datasets of the courses in order to obtain decision tree models and to test their portability to the other courses by comparing the obtained accuracy and loss of accuracy evaluation measures. The results obtained show that it is only feasible to directly transfer predictive models or apply them to different courses with an acceptable accuracy and without losing portability under some circumstances

Behavior of early warnings near the critical temperature in the two-dimensional Ising model

Among the properties that are common to complex systems, the presence of critical thresholds in the dynamics of the system is one of the most important. Recently, there has been interest in the universalities that occur in the behavior of systems near critical points. These universal properties make it possible to estimate how far a system is from a critical threshold. Several early-warning signals have been reported in time series representing systems near catastrophic shifts. The proper understanding of these early-warnings may allow the prediction and perhaps control of these dramatic shifts in a wide variety of systems. In this paper we analyze this universal behavior for a system that is a paradigm of phase transitions, the Ising model. We study the behavior of the early-warning signals and the way the temporal correlations of the system increase when the system is near the critical point.Comment: 20 pages, 8 figures, Submitted to PLOS ONE on Oct. 20th 2014. PONE-D-14-4718