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In this work, we study several closely related problems involving chains, conveyor belts, and rockets, which are described and solved without the application of infinitesimal calculus, or even the concept of mathematical limit. On one hand, the novelty lies not in the problems themselves, but in the method used for their solution, which brings them down from more advanced courses of engineering studies to the ambit of early-stage students. On the other hand, they shed new light on old questions and give teachers the chance to discuss subtle matters on energy conservation that have led to some controversy in the recent past.

We introduce the basics of the Monte Carlo method that allows computing areas and definite integrals, by means of the generation of long sequences of random numbers. The areas of some nontrivial shapes are computed, showing the convergence towards their exact values. The application of the method to the computation of definite integrals is also given, showing an important example of the kinematics of a particle under the action of an arbitrary time-dependent force.

This manuscript describes an implementation of scripts of code aimed at reducing the influence of artifacts, specifically focused on ocular artifacts, in the measurement and processing of electroencephalogram (EEG) signals. This process is of importance because it benefits the analysis and study of long trial samples when the appearance of ocular artifacts cannot be avoided by simply discarding trials. The implementations provided to the reader illustrate, with slight modifications, previously proposed methods aimed at the partial or complete elimination of EEG channels or components obtained after independent component analysis (ICA) of EEG signals. These channels or components are those that resemble the electro-oculogram (EOG) signals in which artifacts are detected. In addition to the description of each of the provided functions, examples of utilization and illustrative figures will be included to show the expected results and processing pipeline. [ABSTRACT FROM AUTHOR]

Why do leaders of organizations cooperate with players with whom they may never transact again? Such transactions can involve the incentives to exploit the other party because these interactions are not recurrent or embedded in networks. Yet, in a market economy, organizational actors learn to cooperate with strangers; otherwise, they risk closure from new ideas and business opportunities outside of their local community. With a large random sample of CEOs of manufacturing firms in the Yangzi River Delta region of China, we measured social norms using vignettes that describe hypothetical situations illustrating the social mechanisms of norm enforcement in respondents' local communities. Several years later, in a laboratory-in-the-field experiment, we asked the same participants to play a one-shot Prisoner's Dilemma (PD) game with a complete stranger. Our findings suggest that belief in the reliability of robust norm enforcement is positively associated with a higher probability of cooperation with strangers. To our knowledge, this mixed-method study is the first to explore the relationship between social norms and cooperation with strangers using a large sample of leaders of organizations outside the environment of the laboratory. Finally, to explore the generalizability of our behavioral findings, we experimentally manipulated norm vignettes and study the PD game in online experiments with managers in the Yangzi River Delta region. History: This paper has been accepted for the Organization Science Special Issue on Experiments in Organizational Theory. Funding: V. Nee gratefully acknowledges funding for research from the John Templeton Foundation (2005-2009 and 2015-2018), and from the College of Arts and Sciences at Cornell University. H. Holm thanks the Jan Wallander's and Tom Hedelius' Foundation for funding lab-in-the-field behavioral game. Supplemental Material: The online appendix is available at https://doi.org/10.1287/orsc.2021.1521. [ABSTRACT FROM AUTHOR]

Abstract Background While air pollution exposures have been linked to cardiovascular outcomes, the contribution from acute gas and particle traffic-related pollutants remains unclear. Using a panel study design with repeated measures, we examined associations between personal exposures to traffic-related air pollutants in Mexico City and changes in heart rate variability (HRV) in a population of researchers aged 22 to 56 years. Methods Participants were monitored for approximately 9.5 hours for eight days while operating a mobile laboratory van designed to characterize traffic pollutants while driving in traffic and “chasing” diesel buses. We examined the association between HRV parameters (standard deviation of normal-to-normal intervals (SDNN), power in high frequency (HF) and low frequency (LF), and the LF/HF ratio) and the 5-minute maximum (or average in the case of PM2.5) and 30-, 60-, and 90-minute moving averages of air pollutants (PM2.5, O3, CO, CO2, NO2, NOx, and formaldehyde) using single- and two-pollutant linear mixed-effects models. Results Short-term exposure to traffic-related emissions was associated with statistically significant acute changes in HRV. Gaseous pollutants – particularly ozone – were associated with reductions in time and frequency domain components (α = 0.05), while significant positive associations were observed between PM2.5 and SDNN, HF, and LF. For ozone and formaldehyde, negative associations typically increased in magnitude and significance with increasing averaging periods. The associations for CO, CO2, NO2, and NOx were similar with statistically significant associations observed for SDNN, but not HF or LF. In contrast, PM2.5 increased these HRV parameters. Conclusions Results revealed an association between traffic-related PM exposures and acute changes in HRV in a middle-aged population when PM exposures were relatively low (14 μg/m3) and demonstrate heterogeneity in the effects of different pollutants, with declines in HRV – especially HF – with ozone and formaldehyde exposures, and increases in HRV with PM2.5 exposure. Given that exposure to traffic-related emissions is associated with increased risk of cardiovascular morbidity and mortality, understanding the mechanisms by which traffic-related emissions can cause cardiovascular disease has significant public health relevance.

Here, we explore conservation of momentum for variable-mass systems by means of two systems: a stalled boat in a lagoon and the propulsion of a rocket. He manages to throw the stones with a speed of I v i SB 0 sb = 4.0 m/s. The mass of the boat and its original load is I M i = 150 kg. The situation in which the rocket continuously dumps mass corresponds to the limit case I m i SB 0 sb -> 0, while I n i -> to maintain the validity of the condition I nm i SB 0 sb = I M i SB E sb . [Extracted from the article]

In exchange for extrafloral nectar, ants deter herbivores from the plants decreasing the herbivore damage, and increasing plant performance in terms of growth and survival. Plants of different sexes may exhibit differences in the investment of resources for defence, thereby differentially decreasing the amount of energy available to other physiological processes. In this context, little is known about sex‐related differences in the outcome of ant–plant interactions in plants bearing extrafloral nectaries (EFNs).In the present study, we conducted ant‐exclusion experiments in the field to test for sex‐related differences in the outcome of ant–plant interactions in vegetative and reproductive buds of Opuntia robusta in individuals of different sexes in two populations: trioecious and dioecious. We applied tanglefoot to some plant and others were allowed ant access, and measured herbivory, relative growth rates and survival probabilities of buds during the growing season when EFNs are active. We counted the number of ants foraging in EFNs of flowers and cladodes of different sexes. We hypothesized that differences in resource investment to defence between sexes change the outcome of ant–plant interactions in terms of the number of ants foraging on EFNs, herbivory, growth, and survival probabilities.Our results suggest sex‐specific strategies in the investment of resources for defence mediated by EFNs in O. robusta, wherein males, females and hermaphrodites from both populations respond differentially to ant presence and herbivores. These sex‐related differences affected the outcome of the ant–plant interactions, influencing changes in number of ants foraging on EFNs, and the resulting herbivory, growth and survival of flowers and cladodes among the different sexes and among populations. Our results suggest that the maintenance of EFNs in O. robusta is costly, reflecting some trade‐offs between growth/survival and defence. Buds visited by ants tended to grow slowly and survive worse in the trioecious population; in the dioecious population they grew slower but survived better. Overall, a greater number of ants visiting EFNs was related to lower herbivore damage, greater growth and survival of flowers and cladodes. Our study underscores the importance of considering plant sex in the outcome of ant–plant interactions. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

A growing body of research investigates how changes in weather shape individual choices about migration, yet highly variable results continue to challenge our understanding of the weather-migration nexus. We use a data-driven approach to identify which weather variables best predicted migration decisions of 54,986 individuals originating in Mexico between 1989 and 2016. Using supervised machine learning, we fit random forests to model migration choices based on individual, household, and community attributes in training data (three-fourths of the sample) from the Mexican Migration Project. We aggregated 36 annual weather variables at the community level and applied k-fold cross-validation to evaluate which models best predicted migration decisions. The top performing models were then applied to the test data (one-fourth of our sample). Three weather variables consistently out-performed others across models: minimum temperature during day, maximum temperature at night, and 'growing degree days' – the number of days with optimal growth temperatures for corn (the major crop for most communities). Our results demonstrate that weather is related to individual choices about migration and illustrate the utility of using principled variable selection which revealed that both customized (growing degree days for a particular crop) and generic (max-min temperatures) metrics can be predictive of migration behaviors. [ABSTRACT FROM AUTHOR]

El modelo depredador-presa de Goodwin predice ciclos en el sentido del reloj en el plano empleo-distribución. Se presenta evidencia cualitativa de comportamiento no lineal para una muestra de 67 países, algunos con ciclos como los de Goodwin. Los centros estimados yacen por fuera de los ciclos observados. El tipo de ciclo (en el sentido del reloj, contrario o atípico) parece relacionarse con el tipo de capitalismo del país. Economías con capitalismo de mercado o europeo, y las economías en transición no presentan ciclos de demanda; los países en desarrollo con capitalismo mediterráneo no presentan ciclos de Goodwin.