Cooperation in costly-access environments

Understanding cooperative behavior in biological and social systems constitutes a scientific challenge, being the object of intense research over the past decades. Many mechanisms have been proposed to explain the presence and persistence of cooperation in those systems, showing that there is no unique explanation, as different scenarios have different possible driving forces. In this paper, we propose a model to study situations in which voluntary participation involves an access cost to the cooperative interaction, besides the cost associated with cooperation. The proposed costly-access prisoner’s dilemma (PD), a symmetric donation game with voluntary and costly participation, breaks the symmetry between abstainers and participants of the voluntary PD. A mean-field approach shows that, in well-mixed populations, the dynamic always leads the system to abstention. However, depending on the return parameter, numerical simulations in structured populations display an alternating behavior between mono-strategic, multi-stable, and coexistence phases. This behavior is fully explained through a theoretical analysis of the strategic motifs, the transitions being determined by the change in stability of those motifs

Residual Forage and Animal Performance from a Kikuyo Pasture under Mixed Grazing and Supplementation

Five grazing strategies were compared: grazing by ewes only and mixed grazing (ewes + heifers), in mixed grazing heifers received no supplement or one of three supplements. Ruminal undegradable protein (RUP) varied among supplement: 4.25, 9.11 and 9.13%, the supplement with the highest RUP included protected methionine. All supplements were 21% crude protein and 3.0 Mcal/kg of metabolizable energy. Grazing was on kikuyu, ratio was 30 kg of ewe per 100 kg of heifer in the mixed grazing treatments. Experimental grazing lasted 84 days. Variables measured were residual forage, proline content in residual forage and liveweight gains per animal and per hectare. Experimental design was a completely random with two replicates. Residual forage was the highest (P\u3c 0.05) in mixed grazing and RUP in supplement was above 4.25%. The highest (P\u3c 0.05) proline content was found in grazing by ewes only, 52% above the proline content found in mixed grazing without supplement, when heifers received supplement proline content decreased (P\u3c 0.05) further. Grazing by ewes only and mixed grazing with heifersreceiving the highest RUP in supplement showed the highest (P\u3c 0.05) daily liveweight gain per ewe of 134 g. Mixed grazing in which heifers received no supplement gave a 100% increase (P\u3c 0.05) in liveweight gain per hectare compared to grazing by ewes only. In mixed grazing offering a supplement with 9.13% RUP and protected methionine gave both the highest liveweight gains per animal and per hectare. It was concluded that mixed grazing allowed a lower stress level on kikuyu due to defoliation and a higher liveweight gain per hectare than grazing by ewes only

Rectification of electronic heat current by a hybrid thermal diode

We report the realization of an ultra-efficient low-temperature hybrid heat current rectifier, thermal counterpart of the well-known electric diode. Our design is based on a tunnel junction between two different elements: a normal metal and a superconducting island. Electronic heat current asymmetry in the structure arises from large mismatch between the thermal properties of these two. We demonstrate experimentally temperature differences exceeding $60$ mK between the forward and reverse thermal bias configurations. Our device offers a remarkably large heat rectification ratio up to $\sim 140$ and allows its prompt implementation in true solid-state thermal nanocircuits and general-purpose electronic applications requiring energy harvesting or thermal management and isolation at the nanoscale.Comment: 8 pages, 6 color figure

Nuevos registros de Vespidae (Hymenoptera: Vespoidea) para la región de la Orinoquía colombiana

We analyzed 72 specimens from the Arauca (71) and Casanare (1) departments in the Orinoco region of Colombia. The specimens belong to 10 genera and 18 species of vespid wasps. Four species are reported for the first time for the region and 14 are new records for the Arauca department. There is a likely new record of Stenodynerus cf. australis for the Neotropical region.Analizamos 72 especímenes colectados de los departamentos de Arauca (71) y Casanare (1) en la región de la Orinoquía. Estos pertenecen a 10 géneros y 18 especies de avispas. Cuatro especies son nuevos registros para la región y 14 son nuevas para el departamento de Arauca. Hay también un posible nuevo registro de Stenodyneus cf. australis para la región Neotropical

Combined use of vacuum assisted device and dermal monolayer substitutes

Artículo previamente publicado en Cirugia Plástica Iberolatinoamericana Vol. 36 - Nº 4. 2010 / Pag. 321-326El método de elección para la cobertura de algunos defectos cutáneos es el autoinjerto de piel parcial; sin embargo, sufre retracciones que pueden adquirir gran relevancia sobre áreas especiales. Diferentes autores han intentado evitar estos déficits funcionales mediante la interposición de matrices de regeneración dérmica monocapa e injerto en un solo tiempo quirúrgico. Diseñamos un estudio para comparar la tasa de integración de los injertos sobre una matriz monocapa con y sin la aplicación de terapia de vacío tipo VAC® sobre ellos. Se aleatorizaron 20 pacientes con defectos cutáneos sobre áreas especiales en 2 grupos. Recogimos los datos epidemiológicos y la etiología del defecto (quemadura aguda, secuelas de quemadura o defectos secundarios a extracción de colgajo fasciocutáneo). En 10 casos (Grupo I) se aplicó matriz dérmica monocapa Matriderm ® más un injerto cutáneo de piel parcial, realizando un cambio de vendaje a los 7 días y luego cada 3- 4 días hasta su estabilización. En otros 10 pacientes (Grupo II), tras realizar el mismo protocolo quirúrgico se aplicó VAC ® durante una semana y se cambió hasta la estabilización del injerto. La evaluación del prendimiento del injerto y su estabilidad la realizó un observador ciego. Se recogieron todas las complicaciones surgidas en el postoperatorio hasta 3 meses después de la estabilidad del injerto. Comprobamos la homogeneidad de ambos grupos para las variables epidemiológicas de los pacientes, así como para la etiología de los defectos. La media de tiempo hasta el prendimiento fue de 17,6 ± 8 días, de forma global con una tasa de complicaciones del 20%. Al estratificar en 2 grupos encontramos que las diferencias en la tasa de complicaciones no eran estadísticamente significativas. El tiempo hasta el prendimiento era de 21,4 ± 9 días en el grupo I, frente a 13,9 ± 4 días en el grupo II. Estas diferencias sí eran estadísticamente significativas. Como conclusión, la aplicación de matrices de regeneración dérmica monocapa es segura, con una tasa de prendimiento de los injertos sobre ella del 85%. El uso del VAC ® sobre las láminas monocapa de dermis sintética acorta el tiempo de integración de las mismas y el prendimiento de los injertos sobre ellas, con una tasa de complicaciones similarSplit thickness autografts are the gold standard for wound coverage. However, scars and retractions are frequent after skin grafts, and would be severe over special regions. Different authors avoid these complications using a dermal substitute interposed between the wound and the skin graft in the first surgical time. A prospective study was designed to evaluate the split thickness skin graft uptake time over a monolayer matrix, with and without a vacuum assisted therapy device (VAC®). Twenty patients with a full thickness wound over a special region were randomized between 2 groups. Epidemiological data and wound etiology (acute burn, burn sequelae or donor site after a fasciocutaneous flap raised) were collected. Matriderm ® (mono layer dermal substitute) and a split thickness skin graft was applied over 10 cases (Group I). The dressing was changed after 7 days, and every 3-4 days until the skin graft was uptake and stable. Another 10 cases were treated with the same surgical strategy (Group II). After surgery, a vacuum assisted therapy device (VAC®) was applied until the graft was uptake. The skin graft evaluation was done by a blind observer. All complications were reported until 3 months after the skin graft was stable. The homogeneity between groups was assessed. Averaged uptake time was 17, 6 ± 8 days, and the total complication rate was 20%. Statistically differences were not found between the 2 groups for the complication rate. The uptake time was 21,4 ± 9 days in the Group I and 13,9 ± 4 days in the Group II. These differences was statically significative. As a conclusion, the use of monolayer dermal substitutes is safe, with skin graft uptake rate of 85%. Time for skin graft uptake over a monolayer dermal matrix is shorter using a VAC ® device over the skin graft, with similar complication rat

Effect of Impulsivity Traits on Food Choice within a Nudging Intervention

Food choices are often driven by impulsive tendencies rather than rational consideration. Some individuals may find it more difficult resisting impulses related to unhealthy food choices, and low self-control and high impulsivity have been suggested to be linked to these behaviors. Recent shifts have been made towards developing strategies that target automatic processes of decision-making and focus on adjusting the environment, referred to as nudging interventions. Therefore, the purpose of this study was to investigate the effect of impulsivity traits on food choices within a nudging intervention (increased perceived variety). A total of 83 adults participated in an experimental study consisting of a self-service intelligent buffet. Impulsivity traits were measured using the UPPS-P impulsivity scale. General linear models were fitted to evaluate the effect of the five impulsivity traits on the difference of salad consumption (g) between the control and intervention situations. Results showed that impulsivity does not affect food choices in this nudging situation, suggesting that nudging works independently of the participant’s impulsivity score. Results also showed a significantly higher consumption of salad in the nudging versus the control setting (17.6 g, p < 0.05), suggesting that nudging interventions can be effective in significantly increasing total vegetable consumption across the whole impulsivity scale

Ac magnetic susceptibility of a molecular magnet submonolayer directly patterned onto a microSQUID sensor

We report the controlled integration, via Dip Pen Nanolithography, of monolayer dots of ferritin-based CoO nanoparticles (12 Bohr magnetons) into the most sensitive areas of a microSQUID sensor. The nearly optimum flux coupling between these nanomagnets and the microSQUID improves the achievable sensitivity by a factor 100, enabling us to measure the linear susceptibility of the molecular array down to very low temperatures (13 mK). This method opens the possibility of applying ac susceptibility experiments to characterize two-dimensional arrays of single molecule magnets within a wide range of temperatures and frequencies.Comment: 4 pages 3 figure

Integral field spectroscopy of type-II QSOs at z=0.3-0.4

We present and analyse integral-field observations of six type-II QSOs with z=0.3-0.4, selected from the Sloan Digital Sky Survey (SDSS). Two of our sample are found to be surrounded by a nebula of warm ionized gas, with the largest nebula extending across 8" (40 kpc). Some regions of the extended nebulae show kinematics that are consistent with gravitational motion, while other regions show relatively perturbed kinematics: velocity shifts and line widths too large to be readily explained by gravitational motion. We propose that a ~20 kpc x20 kpc outflow is present in one of the galaxies. Possible mechanisms for triggering the outflow are discussed. In this object, we also find evidence for ionization both by shocks and the radiation field of the AGN.Comment: 6 pages, 5 figures, accepted by MNRAS Letter

New Physics effects in the flavor-changing neutral couplings of the Top quark

We survey the flavor-changing neutral couplings (FCNC) of the top quark predicted by some extensions of the Standard Model: THDM, SUSY, L-R symmetric, TC2, 331, and models with extra quarks. Since the expected sensitivity of the LHC and ILC for the tcV (V=\gamma,g,Z) and tcH couplings is of order of a few percent, we emphasize the importance of any new physics effect that gives a prediction for these FCNC couplings within this limit. We also review the constraints imposed on these couplings from low-energy precision measurements.Comment: 19 pages, 7 figures. Accepted as a review paper in Int. J. of Mod. Phys.

Caracterización de tormentas locales severas en Camagüey, archipiélago cubano

Ponencia presentada en: 1er Encuentro sobre Meteorología y Atmósfera de Canarias, celebrado en el Puerto de la Cruz, los días 12,13 y 14 de noviembre de 2003. El encuentro estuvo organizado por el Centro Meteorológico Territorial en Canarias Occidental, con la colaboración del Observatorio Atmosférico de Izaña y del Grupo de Física de la Atmósfera de la Facultad de Física (Universidad de La Laguna)Se presentan las variables más informativas del estudio de 25 eventos severos estudiados con vista a perfeccionar los indicadores radáricos de Tormentas Locales Severas ocurridas en el archipiélago cubano, destacándose para tales fines la altura de la reflectividad máxima vertical, la densidad VIL, el VIL, la altura del tope y la reflectividad máxima horizontal