Novae -The study of the reactive flow

There is a wide consensus in the astrophysics community that the mechanism underlying the observed Classical Nova eruptions is a surface thermonuclear runaway. We start this short review with the main observational facts that lead to the theoretical model of a thermonuclear runaway that takes place in an accreted hydrogen rich envelope placed on top of a cool degenerate core of a white dwarf. According to the theory, the accreted envelope becomes unstable to convection days to weeks prior to the runaway. During the extreme stages of the runaway itself, when the burning is most efficient, the envelope is fully convective. Therefore, the elements processed under such extreme conditions are lifted to the outermost regions of the star. A significant fraction of the envelope is ejected during the outburst. The complicated combination of hydrodynamic instabilities and explosive hydrogen burning, close to the surface of the star, gives us a unique opportunity to study this complex reactive flow. The range of core masses, core temperatures and accretion rates introduce a whole range of burning temperatures and densities. Following the description of the "standard" cases, we then focus on rare, but still possible, portions of the relevant parameter space, in which "breakout" of the traditional CNO cycle can occur and lead to heavy element enrichment patterns caused only by breakout burning. We conclude our review with the main challenges that nova theorists face today, with special emphasis on problems related to the nucleosynthesis issues.Comment: Proceedings of: Nuclear Physics in Astrophysics-V,Eilat,April,201

The Sensitivity of Multidimensional Nova Calculations to the Outer Boundary Conditions

Multidimensional reactive flow models of accreted hydrogen rich envelopes on top of degenerate cold white dwarfs are very effective tools for the study of critical, non spherically symmetric, behaviors during the early stages of nova outbursts. Such models can shed light both on the mechanism responsible for the heavy element enrichment observed to characterize nova envelope matter and on the role of perturbations during the early stages of ignition of the runaway. The complexity of convective reactive flow in multi-dimensions makes the computational model itself complex and sensitive to the details of the numerics. In this study, we demonstrate that the imposed outer boundary condition can have a dramatic effect on the solution. Several commonly used choices for the outer boundary conditions are examined. It is shown that the solutions obtained from Lagrangian simulations, where the envelope is allowed to expand and mass is being conserved, are consistent with spherically symmetric solutions. In Eulerian schemes which utilize an outer boundary condition of free outflow, the outburst can be artificially quenched.Comment: 12 Pages 3 figures; Accepted for publication in the Astrophysical Journa

Reordering contigs of draft genomes using the Mauve Aligner

Summary: Mauve Contig Mover provides a new method for proposing the relative order of contigs that make up a draft genome based on comparison to a complete or draft reference genome. A novel application of the Mauve aligner and viewer provides an automated reordering algorithm coupled with a powerful drill-down display allowing detailed exploration of results

Kohlenstoffspeicherung in Feuchtgebieten Ost-Afrikas

Feuchtgebiete/Auengebiete spielen seit der Sesshaftigkeit des Menschen eine wichtige Rolle in der Nahrungsmittelproduktion. Besonders in Zeiten steigender Bevölkerungszahlnen können derzeit ungenutzte Flächen schnell und einfach in fruchtbare Ackerflächen umgewandelt werden. In Zwei typischen Feuchtgebieten Ost-Afrikas, einem ungenutzten Inland-Valley (Uganda) und einem Überschwemmungsgebiet mit Reisanbau des Kilombero-Stroms (Tansania), haben wir in jeweils drei Positionen unterschiedlicher Wasserüberstauung den derzeitigen Zustand der C-Speicherung erfasst. Dafür wurden mittels Dichtefraktionierung die Leichte Fraktion (LF), die gebundene partikuläre organische Substanz (oPOM) und die mineralische Fraktion (Min) voneinander getrennt. Die Untersuchung soll den Status-Quo der C-Speicherung nach hydrologischer Position und eine mögliche Dynamik der Umsetzung bei Nutzungsänderung beschreiben. Erste Ergebnisse für den Standort Uganda zeigen, dass im Oberboden (0-30cm) etwa 25% des TOC in der LF und der oPOM zu finden sind. Dabei nimmt der Gehalt mit zunehmender Überstauung zu. Im Unterboden (30-100cm) zeigt sich bei viel geringeren Anteilen ein gegenläufiger Trend. Für den Standort Tansania zeigen erste Untersuchungen, dass die TOC-Gehalte insgesamt viel geringer sind als in Uganda. Zudem ist der Kohlenstoff hier überwiegend in der mineralisch assoziierten Fraktion zu finden. Die bisher vorliegenden Ergebnisse zeigen, dass auch in den inneren sommerfeuchten Tropen Ost-Afrikas zunehmende Überstauung negativ mit dem Abbau der organischen Substanz korreliert. Zudem zeigen Regionen mit einer hohen landwirtschaftlichen Nutzung eine geringe C-Speicherung

Logarithmically Slow Expansion of Hot Bubbles in Gases

We report logarithmically slow expansion of hot bubbles in gases in the process of cooling. A model problem first solved, when the temperature has compact support. Then temperature profile decaying exponentially at large distances is considered. The periphery of the bubble is shown to remain essentially static ("glassy") in the process of cooling until it is taken over by a logarithmically slowly expanding "core". An analytical solution to the problem is obtained by matched asymptotic expansion. This problem gives an example of how logarithmic corrections enter dynamic scaling.Comment: 4 pages, 1 figur

Thinking strategically about assessment

Drawing upon the literature on strategy formulation in organisations, this paper argues for a focus on strategy as process. It relates this to the need to think strategically about assessment, a need engendered by resource pressures, developments in learning and the demands of external stakeholders. It is argued that in practice assessment strategies are often formed at the level of practice, but that this produces contradiction and confusion at higher levels. Such tensions cannot be managed away, but they can be reflected on and mitigated. The paper suggests a framework for the construction of assessment strategies at different levels of an institution. However, the main conclusion is that the process of constructing such strategies should be an opportunity for learning and reflection, rather than one of compliance

Long-term effectiveness of a digital therapeutic intervention for smoking cessation: a randomized controlled trial

Introduction: The present study evaluated the long-term effectiveness of Quit Genius (QG), an extended digital smoking cessation intervention. Methods: Participants were adult smokers (N=556) recruited between January and November of 2019 via social media and referrals from primary care practices who were given nicotine replacement therapy and randomly assigned to Quit Genius (QG) (n=277), a cognitive behavioral therapy (CBT) based digital intervention or Very Brief Advice (VBA) (n=279), a face-to-face control intervention. Primary analyses (N=530), by intention-to-treat, compared QG and VBA on biochemically verified continuous 7-day abstinence at 4, 26, and 52 weeks post-quit date. Secondary outcomes included sustained abstinence, quit attempts, self-efficacy and mental well-being. Results: Seven-day point prevalence abstinence from weeks 4 through 52 ranged from 27% to nearly 45% among those who received QG, and from 13% to 29% for those in VBA. Continuous 7-day abstinence at 26 and 52 weeks occurred in 27.2% and 22.6% of QG participants, respectively, relative to 16.6% and 13.2% of VBA participants; QG participants were more likely to remain abstinent than those in VBA (Relative Risk [RR]= 1.71, 95% CI 1.17-2.50; p=0.005). Conclusions: This study provides evidence for the long-term effectiveness of an extended digital therapeutic intervention. Implications The long-term effectiveness of digital smoking cessation interventions has not been well-studied. This study established the long-term effectiveness of an extended CBT-based intervention; results may inform implementation of scalable, cost-effective approaches to smoking cessation in the health system