We consider the constraints on the fraction of dark matter in the universe in the form of primordial black holes taking into account the crucial role of accretion which may change both their mass and ...mass function. We show that accretion may drastically weaken the constraints at the present epoch for primordial black holes with masses larger than a few solar masses.
The LIGO/Virgo Collaboration has recently observed GW190521, the first binary black hole merger with at least the primary component mass in the mass gap predicted by the pair-instability supernova ...theory. This observation disfavors the standard stellar-origin formation scenario for the heavier black hole, motivating alternative hypotheses. We show that GW190521 cannot be explained within the primordial black hole (PBH) scenario if PBHs do not accrete during their cosmological evolution, since this would require an abundance which is already in tension with current constraints. On the other hand, GW190521 may have a primordial origin if PBHs accrete efficiently before the reionization epoch.
Canceling a pending movement is a hallmark of voluntary behavioral control because it allows us to quickly adapt to unattended changes either in the external environment or in our thoughts. The ...countermanding paradigm allows the study of inhibitory processes of motor acts by requiring the subject to withhold planned movements in response to an infrequent stop-signal. At present the neural processes underlying the inhibitory control of arm movements are mostly unknown. We recorded the activity of single units in the rostral and caudal portion of the dorsal premotor cortex (PMd) of monkeys trained in a countermanding reaching task. We found that among neurons with a movement-preparatory activity, about one-third exhibit a modulation before the behavioral estimate of the time it takes to cancel a planned movement. Hence these neurons exhibit a pattern of activity suggesting that PMd plays a critical role in the brain networks involved in the control of arm movement initiation and suppression.
This article reports major land use changes in India’s worst badland incised area. India, being an agriculture dependent economy, suffers a great economic loss to badlands. Strategically, it is ...important to know the state-of-the-art status on the dynamics of badlands. Furthermore, it is equally important to assess the processes and factors which contribute most towards it. This study, therefore, assesses the dynamics of badlands that have occurred from 1971 to 2010 using CORONA and GeoEye-1 satellite images. The study design includes 24 study plots of 1 km
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each, covering all the dimensions of the study area. Change detection analysis which was also verified on ground revealed that the areas covered by badlands are reducing at a greater rate than badland encroachment. Badlands were reduced by 20 % in the last ca. 40 years. Factors influencing the reduction of badlands cover were studied using a logistic regression model. Five factors found to significantly influencing the reduction in badlands area are (1) distance to Chambal River, (2) distance to river channels, (3) distance to settlement, (4) slope and (5) Contributing Area. The fitted model was validated using receiver operating characteristic (ROC) curve. This study failed to find a model with good discriminative power for badland encroachment. The statistical evidence in the light of field studies indicated that badlands in populated areas are increasingly transformed into cropland.
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•Monkeys were trained to perform a transitive inference task.•Performance was modulated by the degree of difficulty in comparing the pairs of items.•Lower degrees of difficulty ...favored target location encoding in DLPFC and PMd.•Encoding of target location occurred earlier in DLPFC than in PMd.
Several studies have reported similar neural modulations between brain areas of the frontal cortex, such as the dorsolateral prefrontal (DLPFC) and the premotor dorsal (PMd) cortex, in tasks requiring encoding of the abstract rules for selecting the proper action. Here we compared the neuronal modulation of the DLPFC and PMd of monkeys trained to choose the higher rank from a pair of abstract images (target item), selected from an arbitrarily rank-ordered set (A > B > C > D > E > F) in the context of a transitive inference task. Once acquired by trial-and-error, the ordinal relationship between pairs of adjacent images (i.e., A > B; B > C; C > D; D > E; E > F), monkeys were tested in indicating the ordinal relation between items of the list not paired during learning. During these decisions, we observed that the choice accuracy increased and the reaction time decreased as the rank difference between the compared items enhanced. This result is in line with the hypothesis that after learning, the monkeys built an abstract mental representation of the ranked items, where rank comparisons correspond to the items’ position comparison on this representation. In both brain areas, we observed higher neuronal activity when the target item appeared in a specific location on the screen with respect to the opposite position and that this difference was particularly enhanced at lower degrees of difficulty. By comparing the time evolution of the activity of the two areas, we observed that the neural encoding of target item spatial position occurred earlier in the DLPFC than in the PMd.
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