On the way to the superburst - a numerical simulation study

Regular X-ray bursts are the most prevalent thermonuclear stellar explosions observed in the Galaxy. They occur in accreting binary systems and provide important constraints about the physics of the involved neutron star – a highly compact object. The thermonuclear runaway is periodically triggered in the accreted shell in the atmosphere of the neutron star and can be observed for a few minutes as an intense increase of the luminosity. Observation have shown that, after thousands of X-ray bursts, a rare superburst event of day-long duration, releasing thousand times more energy, may take place. These superbursts are not yet fully understood though thought to be triggered by unstable carbon-burning in the ashes of the previous X-ray bursts. Given that superbursts have a recurrence time of a few years, performing a self-consistent numerical simulation of the gradual build-up of 12C up to the moment when it is ignited is extremely expensive in terms of computational resources. Therefore, most simulations of superbursts start from artificial initial conditions, without simulating the thousands of Type I X-ray bursts that lead to a superburst. Simulations are not yet capable of self-consistently reproducing the event of a superburst providing all its observable features. In this thesis we present a one-dimensional model which is capable of simulating thousands of Type I X-ray bursts in the surface layer of an accreting neutron star. Our code couples general relativistic hydrodynamics with a detailed nuclear reaction network to investigate the scenario of Type I X-ray bursts. Consequently, we are able to make predictions for the evolution of the composition of the ashes of Type I X-ray bursts. Various parameters influence the ignition of an X-ray burst and the resulting layer of ashes. Therefore, we perform a huge parameter study, focussing mainly on accretion rates and crustal heating, to find fitting sets for a superburst simulation. Investigating the change of these parameters we find three different burning regimes, restricting the range of usable parameter sets for self-consistently simulating a superburst

Simulation of X-ray Bursts and Superbursts

Regular bursts have been observed in binary systems containing a neutron star with an accretion flow of matter from the companion star. These bursts are so-called type I X-ray bursts and occur due to thermonuclear explosions in the accreted shell of the neutron stars. Observations have shown that after thousands of X-ray bursts a rare superburst event may take place. These superbursts are thought to be triggered by unstable carbon ignition from the accumulated ashes of the previous X-ray bursts. One of our aims is to produce a self-consistent superburst, for which the amount of the remaining 12C in the ashes is a crucial factor. Furthermore, we investigate the influence of the crustal heating on the behaviour of X-ray bursts and on the composition of their ashes

Measuring the Cognitive Complexity in the Comprehension of Modular Process Models

Modularization in process models is a method to cope with the inherent complexity in such models (e.g., model size reduction). Modularization is capable to increase the quality, the ease of reuse, and the scalability of process models. Prior conducted research studied the effects of modular process models to enhance their comprehension. However, the effects of modularization on cognitive factors during process model comprehension are less understood so far. Therefore, this paper presents the results of two exploratory studies (i.e., a survey research study with N = 95 participants; a follow-up eye tracking study with N = 19 participants), in which three types of modularization (i.e., horizontal, vertical, orthogonal) were applied to process models expressed in terms of the Business Process Model and Notation (BPMN) 2.0. Further, the effects of modularization on the cognitive load, the level of acceptability, and the performance in process model comprehension were investigated. In general, the results revealed that participants were confronted with challenges during the comprehension of modularized process models. Further, performance in the comprehension of modularized process models showed only a few significant differences, however, the results obtained regarding the cognitive load revealed that the complexity and concept of modularization in process models were misjudged initially. The insights unraveled that the attitude towards the application and the behavioral intention to apply modularization in process model is still not clear. In this context, horizontal modularization appeared to be the best comprehensible modularization approach leading to a more fine-grained comprehension of respective process models. The findings indicate that alterations in modular process models (e.g., change in the representation) are important to foster and enable their comprehension. Finally, based on our results, implications for research and practice as well as directions for future work are discussed in this paper

Does adult ADHD interact with COMT val 158 met genotype to influence working memory performance?

Peer reviewedPostprin

The loss of forest gaps, changes of vegetation and wild bee communities from 1975 to 2020 – increasing numbers of endangered wild bee species despite negative habitat trends in the Danube valley

This study investigated how structural changes of a historical traditionally used forest landscape in Central Europe have affected traits of vegetation and wild bee communities. We compared the extent of gaps in the forest using aerial photographs between 1945 and 2020. And we found historic vegetation and bee surveys from 1975 and 1990, which we repeated in 2010 and 2020. We characterised the vegetation of the closed forest, the forest gaps and the small-scale meadows adjacent to the forest as well as the wild bee community by traits and investigated trait changes with Kruskal-Wallis tests. By NMDS we characterised sample plots and transect walks of timepoints with traits and species. Area of forest gaps decreased by 88% from 1945 to 2020 and by 74% from 1975 to 2020. In the traits of vegetation, Ellenberg Indicator Values (EIV) for moisture and soil nutrients significantly increased in closed forest, forest gaps and meadows adjacent to forest. The EIVs for light and temperature, and the number of red list species decreased. The number of wild bee species that specialise in visiting flowers with long tubes and hylophilic species declined. The number of eremophilic species, species with longer phenologies, and recently Red list species increased. In the NMDS figure of forest gaps and of adjacent meadows, different species and traits characterised more recent and older sample plots of vegetation and confirm the results of the Kruskal Wallis tests. Wild bee communities of 2010 and 2020 were characterised by frequent species, while those of 1975 and 1990 were not characterised by any species. The traits characterised the wild bee communities of the older and younger transect walks in accordance with the results of the Kruskal Wallis tests. In addition, oligolectic bees characterised the older transect walks. The loss of forest gaps represents a direct loss of habitat for many plant and wild bee species. In addition, the qualitative changes in vegetation indicate a deterioration in habitat quality for plants of open forests and wild bees. Among wild bees, specialists were negatively affected by the changes described. These developments were reflected in the initial downward trend in Red List bee species. The increase in bee species with longer phenology, in eremophilic species, the decrease in hylophilic species, and the recent increase in red-listed species can indicate climate change. Therefore, this study underlines the importance of the preservation and development of ecologically valuable forest gaps, particularly in historical traditionally used forests with a typical species composition

Time-on-task decrement in vigilance is modulated by inter-individual vulnerability to homeostatic sleep pressure manipulation.

peer reviewedUnder sleep loss, vigilance is reduced and attentional failures emerge progressively. It becomes difficult to maintain stable performance over time, leading to growing performance variability (i.e., state instability) in an individual and among subjects. Task duration plays a major role in the maintenance of stable vigilance levels, such that the longer the task, the more likely state instability will be observed. Vulnerability to sleep-loss-dependent performance decrements is highly individual and is also modulated by a polymorphism in the human clock gene PERIOD3 (PER3). By combining two different protocols, we manipulated sleep-wake history by once extending wakefulness for 40 h (high sleep pressure condition) and once by imposing a short sleep-wake cycle by alternating 160 min of wakefulness and 80 min naps (low sleep pressure condition) in a within-subject design. We observed that homozygous carriers of the long repeat allele of PER3 (PER3 (5/5) ) experienced a greater time-on-task dependent performance decrement (i.e., a steeper increase in the number of lapses) in the Psychomotor Vigilance Task compared to the carriers of the short repeat allele (PER3 (4/4) ). These genotype-dependent effects disappeared under low sleep pressure conditions, and neither motivation, nor perceived effort accounted for these differences. Our data thus suggest that greater sleep-loss related attentional vulnerability based on the PER3 polymorphism is mirrored by a greater state instability under extended wakefulness in the short compared to the long allele carriers. Our results undermine the importance of time-on-task related aspects when investigating inter-individual differences in sleep loss-induced behavioral vulnerability

Colorado Basin 3D structure and evolution, Argentine passive margin

International audienceThis 3D structural model of the Colorado Basin provides new insights into the crustal geometry of the basin and its evolution in relation with the Argentine passive margin. Three NW-SE segments (oblique to the N30°E-trending margin) structure the basin. The oldest infill is generally thought to be coeval with the rifting of the South Atlantic margins in Late Jurassic-Early Cretaceous. This coeval development of the Colorado Basin and of the passive margin is still under debate and gives rise to several hypotheses that we investigate in the light of our observations. We propose that reactivation of inherited structures is predominant in the evolution of the Colorado Basin: (1) the Western segment follows the continental continuation of the Colorado transfer zone; (2) the Central segment consists in the continental continuation of the Tona deformation zone; (3) the Eastern segment is superimposed over the Palaeozoic Claromecó Basin. In addition to the 3 segments, the Central High, separating the Central segment to the Eastern segment, corresponds to the Palaeozoic Sierras Australes Fold Belt. The direction of extension responsible for the South Atlantic opening cannot explain the syn-rift infill and thinning of the basin. The structural analysis shows two phases of syn-rift deformation with different directions. Thus, we suggest that the Colorado Basin and the South Atlantic margin are not coeval but that a first extensional event, probably oblique, predates the extension responsible for the South Atlantic opening. This event is then followed by the formation of the N30°-trending distal margin and the reactivation of Palaeozoic N70°-trending faults occurs under the NW-SE opening of the South Atlantic. This two-phase evolution is consistent with the fault chronology and the two directions of thinned crust observed in the distal margin

Daily Caffeine Intake Induces Concentration-Dependent Medial Temporal Plasticity in Humans: A Multimodal Double-Blind Randomized Controlled Trial

Caffeine is commonly used to combat high sleep pressure on a daily basis. However, interference with sleep-wake regulation could disturb neural homeostasis and insufficient sleep could lead to alterations in human gray matter. Hence, in this double-blind, randomized, cross-over study, we examined the impact of 10-day caffeine (3 × 150 mg/day) on human gray matter volumes (GMVs) and cerebral blood flow (CBF) by fMRI MP-RAGE and arterial spin-labeling sequences in 20 habitual caffeine consumers, compared with 10-day placebo (3 × 150 mg/day). Sleep pressure was quantified by electroencephalographic slow-wave activity (SWA) in the previous nighttime sleep. Nonparametric voxel-based analyses revealed a significant reduction in GMV in the medial temporal lobe (mTL) after 10 days of caffeine intake compared with 10 days of placebo, voxel-wisely adjusted for CBF considering the decreased perfusion after caffeine intake compared with placebo. Larger GMV reductions were associated with higher individual concentrations of caffeine and paraxanthine. Sleep SWA was, however, neither different between conditions nor associated with caffeine-induced GMV reductions. Therefore, the data do not suggest a link between sleep depth during daily caffeine intake and changes in brain morphology. In conclusion, daily caffeine intake might induce neural plasticity in the mTL depending on individual metabolic processes

Daily Caffeine Intake Induces Concentration-Dependent Medial Temporal Plasticity in Humans: A Multimodal Double-Blind Randomized Controlled Trial

Caffeine is commonly used to combat high sleep pressure on a daily basis. However, interference with sleep–wake regulation could disturb neural homeostasis and insufficient sleep could lead to alterations in human gray matter. Hence, in this double-blind, randomized, cross-over study, we examined the impact of 10-day caffeine (3 × 150 mg/day) on human gray matter volumes (GMVs) and cerebral blood flow (CBF) by fMRI MP-RAGE and arterial spin-labeling sequences in 20 habitual caffeine consumers, compared with 10-day placebo (3 × 150 mg/day). Sleep pressure was quantified by electroencephalographic slow-wave activity (SWA) in the previous nighttime sleep. Nonparametric voxel-based analyses revealed a significant reduction in GMV in the medial temporal lobe (mTL) after 10 days of caffeine intake compared with 10 days of placebo, voxel-wisely adjusted for CBF considering the decreased perfusion after caffeine intake compared with placebo. Larger GMV reductions were associated with higher individual concentrations of caffeine and paraxanthine. Sleep SWA was, however, neither different between conditions nor associated with caffeine-induced GMV reductions. Therefore, the data do not suggest a link between sleep depth during daily caffeine intake and changes in brain morphology. In conclusion, daily caffeine intake might induce neural plasticity in the mTL depending on individual metabolic processes