A stronger impossibility for fully online matching

We revisit the fully online matching model (Huang et al., 2020), an extension of the classic online matching model due to Karp, Vazirani, and Vazirani (1990), which has recently received a lot of attention (Huang et al., 2019, 2020), partly due to applications in ride-sharing platforms. It has been shown that the fully online version is harder than the classic version for which the achievable competitive ratio is at most 0.6317, rather than precisely 1 - 1/e approximate to 0.6321. We introduce two new ideas to the construction. By optimizing the parameters of the modified construction numerically, we obtain an improved impossibility result of 0.6297. Like the previous bound, the new bound even holds for fractional (rather than randomized) algorithms on bipartite graphs. (C) 2021 Elsevier B.V. All rights reserved

Species delimitation and phylogenetic relationships in a genus of African weakly-electric fishes (Osteoglossiformes, Mormyridae, Campylomormyrus)

African weakly-electric fishes (Mormyridae) are able to communicate through species-specific electric signals; this feature might have favoured the evolutionary radiation observed in this family (over 200 species) by acting as an effective pre-zygotic isolation mechanism. In the present study we used mitochondrial (cytb) and nuclear (rps7, scn4aa) markers in order to reconstruct a species-phylogeny and identify species boundaries for the genus Campylomormyrus, by applying inference methods based on the multispecies coalescent model. Additionally, we employed 16 microsatellite markers, landmark-based morphometric measurements, and electro-physiological analyses as independent lines of evidence to the results obtained from the sequence data. The results show that groups that are morphologically different are also significantly divergent at the genetic level, whereas morphologically similar groups, displaying dissimilar electric signals, do not show enough genetic diversity to be considered separate species. Furthermore, the data confirm the presence of a yet undescribed species within the genus Campylomormyrus

Alcohol and tobacco use and heart rate reactivity to a psychosocial stressor in an adolescent population

Background: Few studies have investigated physiological stress (re)activity in relation to substance use, especially in adolescents. Using substances is one way to stimulate physiological arousal, therefore inherent hypo-arousal may be associated with substance use in adolescents. The purpose of this study was to examine the relation of autonomic nervous system (ANS) activity with alcohol and tobacco use in adolescents. Methods: ANS activity and perceived stress during a social stress procedure were examined in relation to substance use. 275 Dutch adolescents from a general population study provided complete data. Heart rate was recorded continuously during a pre-task rest period, a stressful task period and a post-task recovery period. Alcohol and tobacco use were self-reported. Results: Adolescents who consumed a medium and high number of alcoholic drinks per week (more than two) exhibited lower heart rates during the entire stress procedure as compared to those who consumed a low number of alcoholic drinks. Adolescents who smoked every day portrayed blunted heart rate reactivity to stress as compared to adolescents who smoked less frequently or not at all. Perceived stress was not related to alcohol or tobacco use. Conclusions: Overall lower heart rate in adolescents who drank more and blunted heart rate reactivity to stress in those who used tobacco every day may indicate inherent hypo-arousal of the ANS system in those vulnerable to use substances more often. These adolescents may actively seek out substances in order to achieve a more normalized state of arousal