Nickel Mixing in the Outer Layers of SN 1987A

Supernova 1987A remains the most well-observed and well-studied supernova to date. Observations produced excellent broad-band photometric and spectroscopic coverage over a wide wavelength range at all epochs. Here, we focus on the very early spectroscopic observations. Only recently have numerical models been of sufficient detail to accurately explain the observed spectra. In SN 1987A, good agreement has been found between observed and synthetic spectra for day one, but by day four, the predicted Balmer lines become much weaker than the observed lines. We present the results of work based on a radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE spectra generated from this model by the general radiation transfer code PHOENIX strongly support the theory that significant mixing of nickel into the outer envelope is required to maintain strong Balmer lines. Preliminary results suggest a lower limit to the average nickel mass of 1.0 \times 10^{-5} solar masses is required above 5000 \kmps by day four. PHOENIX models thus have the potential to be a sensitive probe for nickel mixing in the outer layers of a supernova.Comment: 16 pages, 7 figures, ApJ, v556 2001 (in press

How Difficult Can It Be? Creating an Integrated Network Among Library Stakeholders to Promote Electronic Access

Tracking electronic access is a major challenge for libraries that cannot be ignored. Vast quantities of electronic resources continue to be acquired, and libraries continue to seek a way to keep up with the evolving electronic resource ecosystem. Libraries are immersed in monitoring electronic resources for access performance, features, functionality, completeness of content, and usage. Publishers, providers, and vendors are immersed in their innovative business models. Users are immersed in their research needs. With these immersion silos, there is a lack of communication between stakeholders that creates an unsustainable ecosystem. Currently, stakeholders are creating piecemeal patches that partially address access problems rather than an integrated effort of the whole community to incorporate interconnected solutions. These patches are not solving the problems. They are focusing on the symptoms, but not treating the cause. Why? The electronic access ecosystem is constantly in a state of flux. The system was simpler in times past. In this digital age, the creation, dissemination, and use of data is dynamic. It is vital to the success of the electronic access ecosystem that there be interplay between all the stakeholders. One stakeholder cannot successfully manage electronic access by itself. There needs to be a concerted effort among all stakeholders for monitoring, identifying, and addressing electronic access issues. These relationships are complex. What’s hindering the communication between stakeholders? What are we doing wrong and how can it be fixed? This problem can’t be fixed overnight, but must be carefully orchestrated. Libraries need to take the lead in the development of integrated networks. This presentation will address some of the networking problems that plague stakeholders and provide suggestions for improved networking integration. Audience participation will be sought for sharing problems and suggestions

The stellar populations of spiral disks.II Measuring and modeling the radial distribution of absorption spectral indices

The radial distributions of the Mg2 and Fe5270 Lick spectral indices have been measured to large radial distances on the disks of NGC 4303 and NGC 4535 using an imaging technique based on interference filters. These data, added to those of NGC 4321 previously published in Paper I of this series are used to constraint chemical (multiphase) evolutionary models for these galaxies. Because the integrated light of a stellar disk is a time average over the history of the galaxy weighted by the star formation rate, these constraints complement the information on chemical gradients provided by the study of HII regions which, by themselves, can only provide the alpha-elements abundance accumulate over the life of the galaxy. The agreement between the observations and the model predictions shown here lends confidence to the models which are then used to describe the time evolution of galaxy parameters such as star formation rates, chemical gradients, and gradients in the mean age of the stellar population.Comment: to be published in Astrophysical Journa

Optical sum in Nearly Antiferromagnetic Fermi Liquid Model

We calculate the optical sum (OS) and the kinetic energy (KE) for a tight binding band in the Nearly Antiferromagnetic Fermi Liquid (NAFFL) model which has had some success in describing the electronic structure of the high $T_c$ cuprates. The interactions among electrons due to the exchange of spin fluctuations profoundly change the probability of occupation $(n_{{\bf k},\sigma})$ of states of momentum {\bf k} and spin $\sigma$ which is the central quantity in the calculations of OS and KE. Normal and superconducting states are considered as a function of temperature. Both integrals are found to depend importantly on interactions and an independent electron model is inadequate.Comment: 9 Pages, 5 Figures Accepted for publication in Phys. Rev.

Walls talk: Microbial biogeography of homes spanning urbanization.

Westernization has propelled changes in urbanization and architecture, altering our exposure to the outdoor environment from that experienced during most of human evolution. These changes might affect the developmental exposure of infants to bacteria, immune development, and human microbiome diversity. Contemporary urban humans spend most of their time indoors, and little is known about the microbes associated with different designs of the built environment and their interaction with the human immune system. This study addresses the associations between architectural design and the microbial biogeography of households across a gradient of urbanization in South America. Urbanization was associated with households' increased isolation from outdoor environments, with additional indoor space isolation by walls. Microbes from house walls and floors segregate by location, and urban indoor walls contain human bacterial markers of space use. Urbanized spaces uniquely increase the content of human-associated microbes-which could increase transmission of potential pathogens-and decrease exposure to the environmental microbes with which humans have coevolved

Helium Emission in the Type Ic SN 1999cq

We present the first unambiguous detection of helium emission lines in spectra of Type Ic supernovae (SNe Ic). The presence of He I lines, with full width at half maximum ~ 2000 km/s, and the distinct absence of any other intermediate-width emission (e.g., Halpha), implies that the ejecta of SN Ic 1999cq are interacting with dense circumstellar material composed of almost pure helium. This strengthens the argument that the progenitors of SNe Ic are core-collapse events in stars that have lost both their hydrogen and helium envelopes, either through a dense wind or mass-transfer to a companion. In this way, SN 1999cq is similar to supernovae such as SN 1987K and SN 1993J that helped firmly establish a physical connection between Type Ib and Type II supernovae. The light curve of SN 1999cq is very fast, with an extremely rapid rise followed by a quick decline. SN 1999cq is also found to exhibit a high level of emission at blue wavelengths (< 5500 A), likely resulting from either an unusually large amount of iron and iron-group element emission or uncharacteristically low reddening compared with other SNe Ic.Comment: 17 pages (AASTeX V5.0), 4 figures, accepted for publication in the Astronomical Journa

Effect of anisotropy on universal transport in unconventional superconductors

We investigate the universal electronic transport for a mixed $d_{x^2-y^2}$+s-wave superconductor in the presence of an anisotropic elliptical Fermi surface. Similar to the universal low-temperature transport predicted in a $d_{x^2-y^2}$-wave superconductor with a circular Fermi surface, anisotropic universal features are found in the low-temperature microwave conductivity, and thermal conductivity in the anisotropic system. The effects of anisotropy on the penetration depth, impurity induced $T_c$ suppression, and the zero-frequency density of states are also considered. While a small amount of anisotropy can lead to a strong suppression of the effective scattering rate and hence the density of states at zero frequency, experimental data suggests that large effects are restored by a negative $s$-component gap admixture.Comment: 8 page