An algorithmic discrete gradient field and the cohomology algebra of configuration spaces of two points on complete graphs

We introduce an algorithm that constructs a discrete gradient field on any simplicial complex. We show that, in all situations, the gradient field is maximal possible and, in a number of cases, optimal. We make a thorough analysis of the resulting gradient field in the case of Munkres' discrete model for $\text{Conf}(K_m,2)$, the configuration space of ordered pairs of non-colliding particles on the complete graph $K_m$ on $m$ vertices. Together with the use of Forman's discrete Morse theory, this allows us to describe in full the cohomology $R$-algebra $H^*(\text{Conf}(K_m,2);R)$ for any commutative unital ring $R$. As an application we prove that, although $\text{Conf}(K_m,2)$ is outside the "stable" regime, all its topological complexities are maximal possible when $m\geq4$.Comment: 29 pages, 18 figure

Observation of a continuous interior crisis in the Hindmarsh-Rose neuron model.

Interior crises are understood as discontinuous changes of the size of a chaotic attractor that occur when an unstable periodic orbit collides with the chaotic attractor. We present here numerical evidence and theoretical reasoning which prove the existence of a chaos-chaos transition in which the change of the attractor size is sudden but continuous. This occurs in the Hindmarsh¿Rose model of a neuron, at the transition point between the bursting and spiking dynamics, which are two different dynamic behaviors that this system is able to present. Moreover, besides the change in attractor size, other significant properties of the system undergoing the transitions do change in a relevant qualitative way. The mechanism for such transition is understood in terms of a simple one-dimensional map whose dynamics undergoes a crossover between two different universal behavior

Validación de los procesos de determinación de estándares de interpretación (EE) para pruebas de rendimiento educativo

En este trabajo se presenta una revisión del estado de la cuestión acerca de los métodos para desarrollar procesos de validación de la determinación de Estándares en pruebas de rendimiento educativo. Se analiza el concepto de Validez de los Estándares, así como estrategias de validación, y algunos indicadores de juicio

Relationships among main soil properties and three N availability indices.

A biological (aerobic incubation for 3 and 6 weeks) and a chemical method [successive extractions with cold 0.1 (H1-N) and 0.5 M HCl (H2-N)] were applied to 21 soils to determine: a) the potentially mineralizable-N; b) the most useful soil variables for predicting soil N availability; and c) their usefulness for predicting N uptake by a greenhouse wheat crop. At t=3, both net N mineralized (NNM) and net N mineralization rate (NNMR) were correlated: a) positively with SOM- and CEC-related variables; and b) positively with soil δ 15N and negatively with soil pH, suggesting that Nmineralization, dominated by nitrification, is associated with NO3 --N losses and soil acidification. At t=6, all previously discussed variables were important for NNM, but not for NNMR, mainly controlled by the available-P content. The importance of H1-N increased with N2-inputs and decreased with NO3 - losses and soil-N. Relationships of H1-N and H2-N with soil CEC and texture showed the strong relations among nutrients content, biological activity and N mineralization, as well as the recalcitrance of clay-bounded SOM. Soil total-N correlations with wheat-N in absolute amount (positive) and as percentage of soil-N (negative) showed an important supply of available-N by N-rich soils, despite their slow N turnover. The best regression models for wheat-N always included 1-2 main available nutrients. The percentage of soil N exported to plant biomass was negatively correlated with noncrystalline Al compounds and soil δ 15N. Mineralized-N and wheat-N pools did not share many correlations with soil properties and seemed to come from different sources; consequently, the former pool, which only explained a quarter of wheat-N variance, was not more useful than soil total-N for predicting it. Only a positive correlation with soil total-N was shared by wheat-N and hydrolysable-N, highlighting that the latter N pools are mainly unrelated. Nevertheless, half of wheat-N variation was explained by its negative relationship with the percentage of soil-N as (H1+H2)-N; a possible explanation is that chemically labile N is also biologically labile, being cumulated because of a limiting factor for microbial N mineralization or plant growth and emerging as a good predictor for wheat-N uptake.Peer reviewe

Reliability analysis for systems with large hydro resources in a deregulated electric power market

This work describes a procedure that determines the optimal allocation for the yearly energy resulting from random water inflows to the different subperiods of a year so that the expected benefits are maximized. Its main idea is to distribute the energy stored in reservoirs in each period into two parts: one is directly sold in the energy market, while the other is made available to cover any unplanned outages of thermal units. The method proposed fulfills two objectives, to distribute the hydro energy optimally according to economic criteria and to assess the impact of new market rules on the reliability of an electric system. The procedure will be illustrated by an example based on the Spanish generating system.This work was supported by the Project PB-98-0728 of the Ministerio de Educación, Cultura y Deporte, Spain.Publicad

Seismic behavior of medium and high strength concrete buildings

Current concrete technology has made higher concrete grades more affordable to mid and high-rise buildings; hence its use has been increasing in the late years as it allows for smaller cross-sections, reduction of the structure’s weight, improve durability, among other benefits. However, it is known that brittleness of plain concrete increases with the strength; therefore, some national codes have limited the concrete’s strength in high seismic zones. In this paper, the seismic behavior of a 10 storey dual frame-wall building, designed with concrete grades C30, C60 and C90 is studied in order to assess the advantages and disadvantages of this material and investigate the effects of high concrete strength on the seismic behavior of buildings. In total, three models were studied. Furthermore, a comparison between Force-Based-Design (FBD) and Displacement-Based-Design (DBD) methodologies is made. DBD showed advantages in determining the adequate design ductility and the distribution of forces between frame and wall. The structures are designed according to Eurocode 8 for seismic design high ductility structures. To assess the seismic performance of the building, pushover analyses were made according to the Eurocode 8 (N2 method) in order to determine the performance point. It is observed that adequate design could accommodate concrete’s reduction of ductility. Needed confinement levels can objectively be defined for different concrete strength. Some benefits of the overall increase of strength are highlighted in the paper. The C90 building showed adequate response, although changes on the failure mode were observedPostprint (published version

Evaluación criterial: determinación de estándares de interpretación (EE) para pruebas de rendimiento educativo

En este trabajo se presenta una revisión del estado de la cuestión acerca de los métodos para determinar estándares en pruebas de referencia criterial. Se analiza el concepto de estándar, sus componentes y los problemas implicados en las tareas de juicio en estos métodos. Se revisan los procedimientos para diseñar descriptores de estándares y los métodos para identificar puntuaciones de corte

Análisis de la mortalidad en pacientes con fracturas subcapitales de cadera

El objetivo del presente trabajo es realizar un estudio analítico restrospectivo de la mortalidad de una serie de 528 fracturas subcapitales de cadera en 523 pacientes tratados en nuestro centro mediante prótesis cérvico-cefálica cementada durante el periodo de 1978-1986. De estos 523 pacientes, 190 (36%) habían fallecido en el momento de realizar el estudio. Hemos analizado la mortalidad hospitalaria, 47 casos (9%) y 6 meses después de la intervención, 104 (20%). Se han demostrado como factores de alto riesgo: edad superior a 85 años, presentar tres o más enfermedades asociadas, complicaciones generales en el postoperatorio (escaras, tromboembolismo pulmonar, infarto agudo de miocardio, neumonía, etc.) complicaciones locales como la luxación de la prótesis y finalmente, una demora en la intervención superior a 6 días.We report a retrospective study analyzing the mortality of 528 femoral neck fractures in 523 patients treated with Thompson or Cathcart prosthesis during the period 1978-1986. The hospital mortality was 9% (47 cases) and 20% (104 cases) the mortality and six-months after surgery. High risk factors, were found to be: age more than 85 years-old, three o more preoperative illness, postoperative general complications (Pulmonar tromboembolism, Acute myocardial infarction, sores, pneumonia), dislocation of the prosthesis and a more than 6 days delay surgery