ALBERT

Description: Calculations of synthetic spectropolarimetry are one means to test multidimensional explosion models for Type Ia supernovae. In a recent paper, we demonstrated that the violent merger of a 1.1 and 0.9 M white dwarf binary system is too asymmetric to explain the low polarization levels commonly observed in normal Type Ia supernovae. Here, we present polarization simulations for two alternative scenarios: the sub-Chandrasekhar mass double-detonation and the Chandrasekhar mass delayed-detonation model. Specifically, we study a 2D double-detonation model and a 3D delayed-detonation model, and calculate polarization spectra for multiple observer orientations in both cases. We find modest polarization levels (〈1 per cent) for both explosion models. Polarization in the continuum peaks at ~0.1–0.3 per cent and decreases after maximum light, in excellent agreement with spectropolarimetric data of normal Type Ia supernovae. Higher degrees of polarization are found across individual spectral lines. In particular, the synthetic Si ii 6355 profiles are polarized at levels that match remarkably well the values observed in normal Type Ia supernovae, while the low degrees of polarization predicted across the O i 7774 region are consistent with the non-detection of this feature in current data. We conclude that our models can reproduce many of the characteristics of both flux and polarization spectra for well-studied Type Ia supernovae, such as SN 2001el and SN 2012fr. However, the two models considered here cannot account for the unusually high level of polarization observed in extreme cases such as SN 2004dt.

Description: Ocean acidification is an escalating environmental issue and associated changes in the ocean carbonate system have implications for many calcifying organisms. The present study followed the growth of Sepia officinalis from early-stage embryos, through hatching, to 7-week-old juveniles. Responses of cuttlefish to elevated p CO 2 (hypercapnia) were investigated to test the impacts of near-future and extreme ocean acidification conditions on growth, developmental time, oxygen consumption, and yolk utilization as proxies for individual fitness. We further examined gross morphological characteristics of the internal calcareous cuttlebone to determine whether embryonically secreted shell lamellae are impacted by environmental hypercapnia. Embryonic growth was reduced and hatching delayed under elevated p CO 2 , both at environmentally relevant levels (0.14 kPa p CO 2 similar to predicted ocean conditions in 2100) and extreme conditions (0.40 kPa p CO 2 ). Comparing various metrics from control and intermediate treatments generally showed no significant difference in experimental measurements. Yet, results from the high p CO 2 treatment showed significant changes compared with controls and revealed a consistent general trend across the three treatment levels. The proportion of animal mass contributed by the cuttlebone increased in both elevated p CO 2 treatments. Gross cuttlebone morphology was affected under such conditions and cuttlebones of hypercapnic individuals were proportionally shorter. Embryonic shell morphology was maintained consistently in all treatments, despite compounding hypercapnia in the perivitelline fluid; however, post-hatching, hypercapnic animals developed denser cuttlebone laminae in shorter cuttlebones. Juvenile cuttlefish in acidified environments thus experience lower growth and yet increased calcification of their internal shell. The results of this study support recent findings that early cuttlefish life stages are more vulnerable towards hypercapnia than juveniles and adults, which may have negative repercussions on the biological fitness of cuttlefish hatchlings in future oceans.

Description: SUMMARY Since its beginning in acoustics, the Time-Reversal method (hereafter referred as TR) has been explored by different studies to locate and characterize seismic sources in elastic media. But few authors have proposed an analytical analysis of the method, especially in the case of an elastic medium and for a finite body such as the Earth. In this paper, we use a normal mode approach (for general 3-D case and degenerate modes in 1-D reference model) to investigate the convergence properties of the TR method. We first investigate a three-point problem, with two fixed points which are the source and the receiver and a third one corresponding to a changing observation point. We extend the problem of a single channel TR experiment to a multiple channel and multiple station TR experiment. We show as well how this problem relates to the retrieval of Green’s function with a multiple source cross-correlation and also the differences between TR method and cross-correlation techniques. Since most of the noise sources are located close to the surface of the Earth, we show that the time derivative of the cross-correlation of long-period seismograms with multiple sources at the surface is different from the Green’s function. Next, we show the importance of a correct surface-area weighting of the signal resent by the stations according to a Voronoi tessellation of the Earth surface. We use arguments based on the stationary phase approximation to argue that phase-information is more important than amplitude information for getting a good focusing in TR experiment. Finally, by using linear relationships between the time-reversed displacement (resp. strain wavefields) and the components of a vector force source (resp. a moment tensor source), we show how to retrieve force (or moment tensor components) of any long period tectonic or environmental sources by time reversal.

Description: The positions of nucleosomes across the genome influence several cellular processes, including gene transcription. However, our understanding of the factors dictating where nucleosomes are located and how this affects gene regulation is still limited. Here, we perform an extensive in vivo study to investigate the influence of the neighboring chromatin structure on local nucleosome positioning and gene expression. Using truncated versions of the Saccharomyces cerevisiae URA3 gene, we show that nucleosome positions in the URA3 promoter are at least partly determined by the local DNA sequence, with so-called ‘antinucleosomal elements’ like poly(dA:dT) tracts being key determinants of nucleosome positions. In addition, we show that changes in the nucleosome positions in the URA3 promoter strongly affect the promoter activity. Most interestingly, in addition to demonstrating the effect of the local DNA sequence, our study provides novel in vivo evidence that nucleosome positions are also affected by the position of neighboring nucleosomes. Nucleosome structure may therefore be an important selective force for conservation of gene order on a chromosome, because relocating a gene to another genomic position (where the positions of neighboring nucleosomes are different from the original locus) can have dramatic consequences for the gene's nucleosome structure and thus its expression.

Description: We show that the X-ray line flux of the Mn Kα line at 5.9 keV from the decay of 55 Fe is a promising diagnostic to distinguish between Type Ia supernova (SN Ia) explosion models. Using radiation transport calculations, we compute the line flux for two three-dimensional explosion models: a near-Chandrasekhar mass delayed detonation and a violent merger of two (1.1 and 0.9 M ) white dwarfs. Both models are based on solar metallicity zero-age main-sequence progenitors. Due to explosive nuclear burning at higher density, the delayed-detonation model synthesizes ~3.5 times more radioactive 55 Fe than the merger model. As a result, we find that the peak Mn Kα line flux of the delayed-detonation model exceeds that of the merger model by a factor of ~4.5. Since in both models the 5.9-keV X-ray flux peaks five to six years after the explosion, a single measurement of the X-ray line emission at this time can place a constraint on the explosion physics that is complementary to those derived from earlier phase optical spectra or light curves. We perform detector simulations of current and future X-ray telescopes to investigate the possibilities of detecting the X-ray line at 5.9 keV. Of the currently existing telescopes, XMM – Newton /pn is the best instrument for close (1–2 Mpc), non-background limited SNe Ia because of its large effective area. Due to its low instrumental background, Chandra /ACIS is currently the best choice for SNe Ia at distances above ~2 Mpc. For the delayed-detonation scenario, a line detection is feasible with Chandra up to ~3 Mpc for an exposure time of 10 6 s. We find that it should be possible with currently existing X-ray instruments (with exposure times 5 10 5 s) to detect both of our models at sufficiently high S/N to distinguish between them for hypothetical events within the Local Group. The prospects for detection will be better with future missions. For example, the proposed Athena /X-IFU instrument could detect our delayed-detonation model out to a distance of ~5 Mpc. This would make it possible to study future events occurring during its operational life at distances comparable to those of the recent supernovae SN 2011fe (~6.4 Mpc) and SN 2014J (~3.5 Mpc).

Description: To understand how ocean acidification (OA) influences sediment microbial communities, naturally CO 2 -rich sites are increasingly being used as OA analogues. However, the characterization of these naturally CO 2 -rich sites is often limited to OA-related variables, neglecting additional environmental variables that may confound OA effects. Here, we used an extensive array of sediment and bottom water parameters to evaluate pH effects on sediment microbial communities at hydrothermal CO 2 seeps in Papua New Guinea. The geochemical composition of the sediment pore water showed variations in the hydrothermal signature at seep sites with comparable pH, allowing the identification of sites that may better represent future OA scenarios. At these sites, we detected a 60% shift in the microbial community composition compared with reference sites, mostly related to increases in Chloroflexi sequences. pH was among the factors significantly, yet not mainly, explaining changes in microbial community composition. pH variation may therefore often not be the primary cause of microbial changes when sampling is done along complex environmental gradients. Thus, we recommend an ecosystem approach when assessing OA effects on sediment microbial communities under natural conditions. This will enable a more reliable quantification of OA effects via a reduction of potential confounding effects.

Description: Policy makers around the world recognize the potentially harmful consequences of trademark counterfeiting and copyright piracy. Indeed, many countries have recently initiated policy reforms to strengthen the enforcement of intellectual property rights (IPR). Further, minimum standards of enforcement have been incorporated in many international treaties, especially trade agreements. This emphasis on enforcement raises basic questions about the actual impacts of IP rights infringement, which differ across the types of IPR and economic sectors. We review the academic literature and other studies in the public domain to evaluate what has been learned about these socioeconomic effects, with an emphasis on developing countries where possible. We also identify important gaps in our understanding of the consequences of counterfeiting and piracy and develop recommendations on how governments might collect data and conduct studies to better inform IPR enforcement policy.

Description: We analyse the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) – the Double Focusing Mass Spectrometer data between 2014 August and 2016 February to examine the effect of seasonal variations on the four major species within the coma of 67P/Churyumov-Gerasimenko (H 2 O, CO 2 , CO, and O 2 ), resulting from the tilt in the orientation of the comet's spin axis. Using a numerical data inversion, we derive the non-uniform activity distribution at the surface of the nucleus for these species, suggesting that the activity distribution at the surface of the nucleus has not significantly been changed and that the differences observed in the coma are solely due to the variations in illumination conditions. A three-dimensional Direct Simulation Monte Carlo model is applied where the boundary conditions are computed with a coupling of the surface activity distributions and the local illumination. The model is able to reproduce the evolution of the densities observed by ROSINA including the changes happening at equinox. While O 2 stays correlated with H 2 O as it was before equinox, CO 2 and CO, which had a poor correlation with respect to H 2 O pre-equinox, also became well correlated with H 2 O post-equinox. The integration of the densities from the model along the line of sight results in column densities directly comparable to the VIRTIS-H observations. Also, the evolution of the volatiles’ production rates is derived from the coma model showing a steepening in the production rate curves after equinox. The model/data comparison suggests that the seasonal effects result in the Northern hemisphere of 67P's nucleus being more processed with a layered structure while the Southern hemisphere constantly exposes new material.