Group Size Effect on the Success of Wolves Hunting

Social foraging shows unexpected features such as the existence of a group size threshold to accomplish a successful hunt. Above this threshold, additional individuals do not increase the probability of capturing the prey. Recent direct observations of wolves in Yellowstone Park show that the group size threshold when hunting its most formidable prey, bison, is nearly three times greater than when hunting elk, a prey that is considerably less challenging to capture than bison. These observations provide empirical support to a computational particle model of group hunting which was previously shown to be effective in explaining why hunting success peaks at apparently small pack sizes when hunting elk. The model is based on considering two critical distances between wolves and prey: the minimal safe distance at which wolves stand from the prey, and the avoidance distance at which wolves move away from each other when they approach the prey. The minimal safe distance is longer when the prey is more dangerous to hunt. We show that the model explains effectively that the group size threshold is greater when the minimal safe distance is longer. Although both distances are longer when the prey is more dangerous, they contribute oppositely to the value of the group size threshold: the group size threshold is smaller when the avoidance distance is longer. This unexpected mechanism gives rise to a global increase of the group size threshold when considering bison with respect to elk, but other prey more dangerous than elk can lead to specific critical distances that can give rise to the same group size threshold. Our results show that the computational model can guide further research on group size effects, suggesting that more experimental observations should be obtained for other kind of prey as e.g. moose.Comment: 20 pages, 4 figures, 8 references. Other author's papers can be downloaded at http://www.denys-dutykh.com

Intervención basada en la orientación temporal. Consumo de alcohol y percepción del riesgo en adolescentes

Alcohol consumption is a prevalent risky behaviour in adolescence. A way of prevention is to obtain information about the cognitive components involved, such as Temporal Perspective (TP), which refers to the tendency to be oriented towards the past, the present or the future. The aim of this study was to analyze the relationship between TP, risk perception and alcohol consumption (Study 1) and to determine whether an intervention programme based on emphasizing a Future orientation can reduce alcohol consumption and increase risk perception (Study 2). Seventy-five adolescents participated in the study. Results showed that a bias toward the Present can enhance the probability of incurring in risk behaviours, while a Future orientation might act as a protective factor. Half of the adolescents took part in the intervention programme, and their risk perception increased, suggesting that TP can be a tool to minimize the probability of incurring in risk behaviours.Consumir alcohol es una conducta de riesgo frecuente en adolescentes. Una forma de prevención es obtener información sobre los componentes cognitivos involucrados, como la Perspectiva Temporal (PT), referida a la tendencia a orientarse hacia el pasado, el presente o el futuro. El objetivo del estudio fue analizar la relación entre PT, percepción de riesgo y consumo de alcohol (Estudio 1) y determinar si un programa de intervención basado en enfatizar una orientación Futura reduciría el consumo de alcohol y aumentaría la percepción de riesgo (Estudio 2). Setenta y cinco adolescentes participaron en el estudio. Los resultados mostraron que un sesgo hacia el presente aumentaría la probabilidad de incurrir en conductas de riesgo y una orientación futura actuaría como factor protector. La mitad de los adolescentes participó en la intervención y su percepción de riesgo aumentó, sugiriendo que la PT podría minimizar la probabilidad de incurrir en conductas de riesgo

A note on computing Murphy-Topel corrected variances in a heckprobit model with endogeneity in Stata

We outline a fairly simple method to obtain in Stata Murphy-Topel corrected variances for a two-step estimation of a heckprobit model with endogeneity in the main equation. The procedure utilizes the score option and the powerful matrix tool accum in Stata and builds on previous works by Hardin (2002) and Hole (2006)

ENTREPRENEURSHIP IN LATIN AMERICA DURING THE 21st CENTURY

This paper aims to provide an brief overview of Entrepreneurship during the last decade in three of the most representative economies of Latin America. With this objective, the relationship of different variables that pertain to both entrepreneurship and the elements that, according to the literature, are individual-level determinants of it (such as attitude, social norms and the perceived ability to develop individual action itself) are explored over time. The period analyzed is 2001-2012 for the cases of Brazil, Argentina and Mexico with indicators from the Global Entrepreneurship Monitor (GEM). The data show that for all selected countries, the perceived desirability, specifically the dimension of the social value given to the entrepreneurial activity, is positively and significantly associated with both the initiation of new business and the intent to undertake them. Looking at each country in particular, this important association persisted with at least one dimension of entrepreneurship (either the activity or the intention). The variable on perceived feasibility for conducting business is more strongly associated with entrepreneurship in the case of Brazil, in contrast to the cases of Argentina and Mexico where it, in general, does not reflect statistical significance

A note on computing Murphy-Topel corrected variances in a heckprobit model with endogeneity in Stata

We outline a fairly simple method to obtain in Stata Murphy-Topel corrected variances for a two-step estimation of a heckprobit model with endogeneity in the main equation. The procedure utilizes the score option and the powerful matrix tool accum in Stata and builds on previous works by Hardin (2002) and Hole (2006)

Búsqueda de víctimas de avalancha mediante quadricóptero

Los accidentes por aludes son noticia frecuente, en ocasiones costando vidas humanas, por ello los montañeros portan consigo el dispositivo ARVA, que emite una señal pulsada de 457KHz de campo magnético. A partir de esta señal es posible localizar a la víctima sepultada bajo la nieve, proceso que actualmente es llevado a cabo por equipos de búsqueda especializados. Esta tarea de búsqueda realizada hasta la fecha manualmente, conlleva un tiempo que puede resultar crítico en la supervivencia de la víctima. Este trabajo tiene como objetivo la sustitución del personal de búsqueda por un dron encargado de localizar la señal del ARVA. Se trata de una prueba de concepto del sistema electrónico capaz de la recepción de las líneas de campo magnético cercano generadas por un dispositivo ARVA y su seguimiento. Para ello se ha creado y diseñado el sistema completo partiendo de dos antenas de ferrita para captar la señal de campo y obteniendo como salida la señal PWM conectada al autopiloto del dron, controlando el giro del mismo. Se ha diseñado y producido las placas receptoras, que acondicionan la señal y su posterior procesamiento en una placa comercial (BeagleBone) obteniendo la información necesaria, modulo y ángulo, de la línea de flujo magnético, permitiendo así su seguimiento por el dron. Para la realización de este Trabajo Fin de Grado se realizó: el análisis de la búsqueda de victimas de aludes, análisis del entorno electromagnético, diseño electrónico del dispositivo receptor, simulación de las etapas, diseño y fabricación de la PCB, puesta en marcha de las placas, programación en tiempo real del programa de lectura y procesado de la señal, generación de la señal PWM y finalmente se han realizado las pruebas del prototipo en laboratorio

Unbalancing Zur (FurB)-mediated homeostasis in Anabaena sp. PCC7120: Consequences on metal trafficking, heterocyst development and biofilm formation

Zinc is required for the activity of many enzymes and plays an essential role in gene regulation and redox homeostasis. In Anabaena (Nostoc) sp. PCC7120, the genes involved in zinc uptake and transport are controlled by the metalloregulator Zur (FurB). Comparative transcriptomics of a zur mutant (Δzur) with the parent strain unveiled unexpected links between zinc homeostasis and other metabolic pathways. A notable increase in the transcription of numerous desiccation tolerance-related genes, including genes involved in the synthesis of trehalose and the transference of saccharide moieties, among many others, was detected. Biofilm formation analysis under static conditions revealed a reduced capacity of Δzur filaments to form biofilms compared to the parent strain, and such capacity was enhanced when Zur was overexpressed. Furthermore, microscopy analysis revealed that zur expression is required for the correct formation of the envelope polysaccharide layer in the heterocyst, as Δzur cells showed reduced staining with alcian blue compared to Anabaena sp. PCC7120. We suggest that Zur is an important regulator of the enzymes involved in the synthesis and transport of the envelope polysaccharide layer, influencing heterocyst development and biofilm formation, both relevant processes for cell division and interaction with substrates in its ecological niche

Application of an ELISA test using Schistosoma bovis adult worm antigens in travellers and immigrants from a schistosomiasis endemic area and its correlation with clinical findings

[EN] We have recently evaluated an ELISA for the diagnosis of human schistosomiasis using S. bovis adult worm antigens (AWA Sb), showing a sensitivity of 94% and a specificity of 97% for patients diagnosed by egg detection. Nevertheless, the comparison of this AWA Sb ELISA with direct parasitological findings as the gold standard could introduce a Selection bias, due to the well-known lack of sensitivity of direct methods in the detection of acute schistosomiasis and of low burden infections. The objective of the present work is to compare it with parasitological methods and commercial indirect haemagglutination test using S. mansoni antigens (WA Sm IHA) in 254 immigrants and travellers with different clinical settings; in addition, to find specific bands in the EITB of different phases of schistosomiasis. The AWA Sb ELISA showed 72% of seropositivity in patients with Katayama fever, while patients with eosinophilia and genito-urinary complaints showed 27% and 93%, respectively. The diagnosis yield was globally higher than direct egg detection or WA Sm IHA test with regard to the clinical setting. Finally, the utilization of EITB with S. bovis AWA permits the confirmation of diagnosis in chronic and acute phases of the disease

Assessment of the SmMIT-LAMP technique for the molecular detection of Schistosoma mansoni DNA in urine samples

Background: Human schistosomiasis, is one of the most common parasitic diseases worldwide. Parasitological and serological techniques have different shortcomings to control this illness. Therefore, the development of new diagnostic methods to detect infection in acute phase is required. Loop-mediated isothermal amplification technique (LAMP) could be a good choice. Methodology / Results: Firstly, experimental model was used to obtain urine samples from mice infected with cercariae of S. mansoni. The samples were collected weekly from week 0 to 8th post-infection. Finally, SmMIT-LAMP technique was performed to analyse urine samples DNA of S. mansoni was detected since 3rd week post-infection, Conclusions / Significance: We have detected, for the first time in acute phase, DNA of the S. mansoni in urine samples of infected mice, using a simple, rapid, inexpensive, and potentially applicable method to the diagnosis of schistosomiasis in endemic areas.Antecedentes: La esquistosomosis humana, es una de las enfermedades parasitarias más frecuentes en todo el mundo. Su principal problema reside en el control de la enfermedad debido a las limitaciones de las técnicas parasitológicas y serológicas. Por ello, es necesario el desarrollo de nuevos métodos de diagnóstico capaces de detectar la infección en fase aguda. Un enfoque prometedor es la técnica de amplificación isotérmica de ácidos nucleicos tipo LAMP (Loop-mediated isothermal amplification). Metodología / Resultados: Se utilizó un modelo murino de Schistosoma mansoni para obtener muestras de orina a partir de ratones infectados con cercarias de S. mansoni. Las muestras se recogieron semanalmente desde la semana 0 hasta la semana 8ª después de la infección. Posteriormente se realizó al análisis de las muestras de orina mediante la técnica SmMIT-LAMP, consiguiendo detectar ADN de S. mansoni desde la 3ª semana post-infección (p.i). Conclusiones / Importancia: Hemos logrado, por primera vez la detección de ADN de S. mansoni en muestras de orina en fase aguda de la infección producida por S. mansoni mediante un método molecular sencillo, rápido, económico y potencialmente aplicable en zonas endémicas