What You Don\u27t Know About Motivational Laptop Stickers

Mental health problems are on the rise among young adults in the U.S. (Kingkade, 2016). At the same time, today’s U.S. young adults are significantly more invested than their older counterparts in portraying themselves as “positive” (self-confident, easy-going, and happy; Berenson et al., 2018). Although many have begun to speculate that these two trends may be linked (e.g., Fagan, 2017), little empirical research on this issue exists

The effects of a background potential in star cluster evolution: a delay in the relaxation time-scale and runaway collision processes

Runaway stellar collisions in dense star clusters are invoked to explain the presence of very massive stars or blue stragglers in the center of those systems. This process has also been explored for the first star clusters in the Universe and shown to yield stars that may collapse at some points into an intermediate mass black hole. Although the early evolution of star clusters requires the explicit modeling of the gas out of which the stars form, these calculations would be extremely time-consuming and often the effects of the gas can be accurately treated by including a background potential to account for the extra gravitational force. We apply this approximation to model the early evolution of the first dense star clusters formed in the Universe by performing $N$-body simulations, our goal is to understand how the additional gravitational force affects the growth of a very massive star through stellar mergers in the central parts of the star cluster. Our results show that the background potential increases the velocities of the stars, causing an overall delay in the evolution of the clusters and in the runaway growth of a massive star at the center. The population of binary stars is lower due to the increased kinetic energy of the stars, initially reducing the number of stellar collisions, and we show that relaxation processes are also affected. Despite these effects, the external potential enhances the mass of the merger product by a factor $\sim$2 if the collisions are maintained for long times.Comment: 16 pages. Accepted for publication in Astronomy and Astrophysic

The physical origin of super-competitive accretion during the formation of the first supermassive black holes

Numerical simulations have shown the occurence of a scenario termed ''super-competitive accretion'', a term that describes a situation where only the central few objects grow supermassive while a larger number of stars compete for the reservoir, with significant accretion flows of $\gtrsim0.1$ M$_\odot$ yr$^{-1}$. This scenario particularly implies that the presence of fragmentation will not necessarily impeed the formation of a central massive object. We here explore this phenomenon using analytical estimates for growth via collisions and accretion, considering accretion due to self-gravity as well as Bondi-Hoyle accretion. Particularly, we explore under what conditions the accretion onto the central massive object breaks down, and derive a criterion that depends on the mass of the most massive object and the mass in fragments. For compact clusters with sizes about $0.1$~pc, we further find that the mass growth by collisions is comparable to the growth via accretion. Our results are validated through the comparison with numerical simulations, and we overall conclude that super-competitive accretion is a valid mechanism for the formation of very massive objects in the early Universe.Comment: 9 pages, 5 figures. Accepted for publication in MNRA

La gobernabilidad en el uso del agua en Guandacol, La Rioja, Argentina

Guandacol is a village in the Felipe Varela department, located on the west of the province of La Rioja (Argentina), 44 kilometers north of Villa Unión city, on route 40, which leads south to the province of San Juan. Guandacol is nestled in the Andean foothill valley of the same name at 1,050 meters above sea level.Those who have studied the region claim that Guandacol is related to the ethnic group of the Capayanes, who spoke the Cacan.There are three tributaries to the waterway in Guandacol: the Troya, Flecha and Guandacol rivers. Their waters have represented the ancient essential resource given by the gods to the people of Guandacol. In this context, the waterway has been a magnet that determined a dwelling place for the people, while it has also meant the very source of life, from the germinating seed up to the ripe fruit.The aim of this text is to review the waterway from the ethno-historical point of view, as well as the indissoluble and unquestionable relationship between the use of water as a resource and the vital mark it has always been for the natives. This relationship surpasses the oversimplification of merely using water as a resource.Guandacol es una localidad del Departamento Felipe Varela, ubicado en  el  extremo oeste  de la Provincia de La Rioja (Argentina) y a 44 kilómetros hacia el Norte  de la ciudad de Villa Unión, sobre la Ruta 40 que comunica hacia el Sur con la Provincia de San Juan. Está enclavado en el valle homónimo pre cordillerano a 1.050 metros de altura sobre el nivel del mar.Quienes han estudiado la región afirman que Guandacol está relacionado al  grupo étnico llamado los Capayanes que usaban la lengua Cacana.La travesía del agua en Guandacol está representada en tres afluentes principales que comprendelos ríos de la Troya, la Flecha y Guandacol,  aguas que fueron el recurso esencial entregado por los dioses a los Guandacoles. El agua en este contexto actuó como una fuerza imantada que determinó el lugar de residencia, y cada derrame volumétrico de ella, esparcido por la tierra se constituyó en fuente de vida para mantenerla, desde el mismo momento de hacer germinar la semilla hasta consumir el fruto de la planta.Se procura en este texto repasar un recorrido etnohistórico asociado a la travesía del agua y la indisociable e indiscutible relación entre el uso como recurso y la impronta vital que implica este elemento para el habitante nativo, la cual excede el simplismo involucrado en la lógica de utilización de la misma

Weather radar for urban hydrological applications: lessons learnt and research needs identified from 4 pilot catchments in North-West Europe

International audienceThis study investigates the impact of rainfall estimates of different spatial resolutions on the hydraulic outputs of the models of four of the EU RainGain project’s pilot locations (the Cranbrook catchment (UK), the Herent catchment (Belgium), the Morée-Sausset catchment (France) and the Kralingen District (The Netherlands)). Two storm events, one convective and one stratiform, measured by a polarimetric X-band radar located in Cabauw (The Netherlands) were selected for analysis. The original radar estimates, at 100 m and 1 min resolutions, were aggregated to a spatial resolution of 1000 m. These estimates were then applied to the high-resolution semi-distributed hydraulic models of the four urban catchments, all of which have similar size (between 5 and 8 km2), but different morphological, hydrological and hydraulic characteristics. When doing so, methodologies for standardising rainfall inputs and making results comparable were implemented. The response of the different catchments to rainfall inputs of varying spatial resolution is analysed in the light of model configuration, catchment and storm characteristics. Rather surprisingly, the results show that for the two events under consideration the spatial resolution (i.e. 100 m vs 1000 m) of rainfall inputs does not have a significant influence on the outputs of urban drainage models. The present study will soon be extended to more storms as well as model structures and resolutions, with the final aim of identifying critical spatial-temporal resolutions for urban catchment modelling in relation to catchment and storm event characteristics

Global instability by runaway collisions in nuclear stellar clusters: Numerical tests of a route for massive black hole formation

The centers of galaxies host nuclear stellar clusters, supermassive black holes, or both, but the origin of this dichotomy is still a mystery. Nuclear stellar clusters are the densest stellar system of the Universe, so they are ideal places for runaway collisions to occur. In these dense clusters it is possible that global instability occurs, triggered by collisions and mergers forming a massive black hole. Here we test a new mechanism to form massive black holes through runaway stellar collisions in nuclear stellar clusters, performing N-body simulations using the code nbody6++gpu. Our idealized models show that there is a critical mass where collisions become very efficient making it possible to form massive black holes in nuclear stellar clusters. The most massive objects reach masses of the order of $10^4-10^5\rm~ M_\odot$. We find that our highest black hole formation efficiency is up to $50\%$ of the stellar mass at the end of the simulation. In real astrophysical systems, the critical mass scale for this transition is expected to occur in stellar clusters of $10^7-10^9\rm~M_\odot$, implying the formation of quite massive central objects.Comment: 11 pages, 6 figure

Spatial and temporal variation in population dynamics of Andean frogs: Effects of forest disturbance and evidence for declines

AbstractBiodiversity loss is a global phenomenon that can result in the collapse of food webs and critical ecosystem services. Amphibian population decline over the last century is a notable case of species loss because amphibians survived the last four major extinction events in global history, their current rate of extinction is unprecedented, and their rate of extinction is greater than that for most other taxonomic groups. Despite the severity of this conservation problem and its relevance to the study of global biodiversity loss, major knowledge gaps remain for many of the most threatened species and regions in the world. Rigorous estimates of population parameters are lacking for many amphibian species in the Neotropics. The goal of our study was to determine how the demography of seven species of the genus Pristimantis varied over time and space in two cloud forests in the Ecuadorian Andes. We completed a long term capture–mark–recapture study to estimate abundance, survival, and population growth rates in two cloud forests in the Ecuadorian Andes; from 2002 to 2009 at Yanayacu in the Eastern Cordillera and from 2002 to 2003 at Cashca Totoras in the Western Cordillera. Our results showed seasonal and annual variation in population parameters by species and sex. P. bicantus experienced significant reductions in abundance over the course of our study. Abundance, apparent survival, and population growth rates were lower in disturbed than in primary or mature secondary forest. The results of our study raise concerns for the population status of understudied amphibian groups and provide insights into the population dynamics of Neotropical amphibians