Late Light Curves of Normal Type Ia Supernovae

We present late-epoch optical photometry (BVRI) of seven normal/super-luminous Type Ia supernovae: SN 2000E, SN 2000ce, SN 2000cx, SN 2001C, SN 2001V, SN 2001bg, SN 2001dp. The photometry of these objects was obtained using a template subtraction method to eliminate galaxy light contamination during aperture photometry. We show the optical light curves of these supernovae out to epochs of up to ~640 days after the explosion of the supernova. We show a linear decline in these data during the epoch of 200-500 days after explosion with the decline rate in the B,V,& R bands equal to about 1.4 mag/100 days, but the decline rate of the I-band is much shallower at 0.94 mag/100 days.Comment: 33 pages, 11 figures, Accepted for publication in The Astronomical Journa

Estimating Animal Abundance Using Noninvasive DNA Sampling: Promise and Pitfalls

Advances in molecular biology offer promise to the study of demographic characteristics of rare or hard-re-capture species, because individuals can now be identified through noninvasive sampling such as fecal collection or hair snags. However, individual genotyping using such methods currently leads to a novel problem that we call a shadow effect, because some animals not captured previously are believed to be recaptures due to their DNA profile being an indistinguishable shadow of previously captured animals. We evaluate the impact of the shadow effect on the two methods most commonly used in applied population ecology to estimate the size of closed populations: Lincoln-Petersen and multiple-recapture estimators in program CAPTURE. We find that the shadow effect can cause a negative bias in the estimates of both the number of different animals and the number of different genotypes. Furthermore, with Lincoln-Petersen estimators, the shadow effect can cause estimated confidence intervals to decrease even as bias increases. Because the bias arises from heterogeneity in apparent capture probabilities for animals with genetic shadows vs. those without, a model in program CAPTURE that is robust to capture heterogeneity (Mh-jackknife) does not underestimate the number of genotypes in the population and only slightly underestimates the rotal number of individuals As the shadow effect increases, CAPTURE is better able to correctly identify heterogeneity in capture probability and to pick Mh-jackknife, so that the higher levels of shadow effect have less bias than medium levels. The shadow effect will occur in all estimates of demographic rates (including survival) that use DNA sampling to determine individual identity, but it can be minimized by increasing the number of individual loci sampled

Late-time emission of type Ia supernovae: optical and near-infrared observations of SN 2001el

We present optical and near-infrared light curves of SN 2001el from 310 to 445 days past maximum light, obtained with the Very Large Telescope. The late-time optical (UBVRI) light curves decay in a nearly linear fashion with decay time scales of 1.43\pm0.14, 1.43\pm0.06, 1.48\pm0.06, 1.45\pm0.07, and 1.03\pm0.07 magnitudes (per hundred days) in the U, B, V, R and I bands, respectively. In contrast, in the near-infrared (JHKs) bands the time evolution of the flux appears to be nearly constant at these epochs. We measure decline rates (per hundred days) of 0.19\pm0.10 and 0.17\pm0.11 magnitudes in the J and H bands, respectively. We construct a UVOIR light curve, and find that the late-time luminosity has a decay time scale nearly consistent with complete depostion of positron kinetic energy. The late-time light curves of the normal type Ia SN 2001el demonstrate the increased importance of the near-infrared contribution. This was previously observed in the peculiar SN 2000cx, and the results for SN 2001el thus ensure that the conclusions previously based on a single peculiar event are applicable to normal type Ia supernovae. The measured late-time UVOIR decline rate suggests that a majority of the positrons are trapped within the ejecta. This results does not favor the predictions of a weak and/or radially combed magnetic field configuration.Comment: 4 pages with 2 figures plus 7 tables. Accepted for publication in A&A letter. Constructive comments welcome

Analysing the impact of compaction of soil aggregates using X-ray microtomography and water flow simulations

Soil aggregates are structural units of soil, which create complex pore systems controlling gas and water storage and fluxes in soil. Aggregates can be destroyed during swelling and shrinking or by external forces like mechanical compaction and yet, the knowledge of how physical impact alters aggregate structure remains limited. The aim of the study was to quantify the impact of compaction on macroaggregates, mainly on the pore size distribution and water flow. In this study, aggregates (2–5 mm) were collected by dry sieving in grassland of the Fuchsenbigl–Marchfeld Critical Zone Observatory (Austria). The structural alterations of these soil aggregates under controlled compaction were investigated with a non-invasive 3D X-ray microtomography (XMT). The detailed changes in pore size distribution between aggregates (interpores, diameter >90 μm) and within the aggregates (intrapores, diameter ≤90 μm) in pre- and post-compacted soils were revealed at two soil moisture (9.3% and 18.3% w/w) and two bulk density increments (0.28 and 0.71 g cm−3 from the initial values). The soil permeability was simulated using lattice Boltzmann method (LBM) based on 3D images. Soil compaction significantly reduced total pores volume and the proportion of interpores volume and surface area, while total pore surface area and the proportion of intrapores volume and surface area increased. The increases in soil moisture tended to reduce the effects of compaction on interpores and intrapores, while the high compaction increment drastically changed the pore size distribution. The aggregate compaction decreased water penetration potential due to the increase of small intra-aggregate pores and cavities as demonstrated by LBM. Notably, the LBM results showed a significant linear correlation between the water flow rate and bulk density of soil aggregates and predicted that the water flow could be reduced by up to 97–99% at bulk density of ≥1.6 g cm−3 with soil water content of 18.3% w/w. Thus, a combination of imaging and modelling provided new insights on the compaction effects on aggregates, underpinning the importance of protecting soil structure from mechanical compaction to minimise environmental impacts of soil compaction and maintain water infiltration and percolation in arable soils

A circle map in a human heart

A circle is divided into two regions, a black one and a white one. Successive iterates of an invertible nonlinear circle map generate a symbolic string indicating whether each iterate is in the black or white region. A number of remarkable properties of the symbolic sequences are described. These properties were previously described for a linear circle map corresponding to a rigid rotation in the "gaps and steps" problem. These results have direct application to a cardiac arrhythmia, parasystole, that results from the competition between two pacemakers in the heart, one in the sinus mode and the other in the ventricles. The theoretical results are directly applicable to a clinical case of a young man who had frequent extra heartbeats

Annihilation emission from young supernova remnants

A promising source of the positrons that contribute through annihilation to the diffuse Galactic 511keV emission is the beta-decay of unstable nuclei like 56Ni and 44Ti synthesised by massive stars and supernovae. Although a large fraction of these positrons annihilate in the ejecta of SNe/SNRs, no point-source of annihilation radiation appears in the INTEGRAL/SPI map of the 511keV emission. We exploit the absence of detectable annihilation emission from young local SNe/SNRs to derive constraints on the transport of MeV positrons inside SN/SNR ejecta and their escape into the CSM/ISM, both aspects being crucial to the understanding of the observed Galactic 511keV emission. We simulated 511keV lightcurves resulting from the annihilation of the decay positrons of 56Ni and 44Ti in SNe/SNRs and their surroundings using a simple model. We computed specific 511keV lightcurves for Cas A, Tycho, Kepler, SN1006, G1.9+0.3 and SN1987A, and compared these to the upper-limits derived from INTEGRAL/SPI observations. The predicted 511keV signals from positrons annihilating in the ejecta are below the sensitivity of the SPI instrument by several orders of magnitude, but the predicted 511keV signals for positrons escaping the ejecta and annihilating in the surrounding medium allowed to derive upper-limits on the positron escape fraction of ~13% for Cas A, ~12% for Tycho, ~30% for Kepler and ~33% for SN1006. The transport of ~MeV positrons inside SNe/SNRs cannot be constrained from current observations of the 511keV emission from these objects, but the limits obtained on their escape fraction are consistent with a nucleosynthesis origin of the positrons that give rise to the diffuse Galactic 511keV emission.Comment: 15 pages, 11 figures, accepted for publication in A&