arXiv subjects

Michael Famiano

Publications and source records attributed to Michael Famiano.

6 recordsLinked to original sources

arXiv2022

Evolution of Urca Pairs in the Crusts of Highly Magnetized Neutron Stars

We report on the effects of strong magnetic fields on neutrino emission in the modified Urca process. We show that the effect of Landau levels on the various Urca pairs affects the neutrino emission spectrum and leads to an angular asymmetry in the neutrino emission. For low magnetic fields the Landau levels have almost no effect on the cooling. However, as the field strength increases, the electron chemical potential increases resulting in a lower density at which Urca pairs can exist. For intermediate field strength there is an interesting interference between the Landau level distribution and the Fermi distribution. For high enough field strength, the entire electron energy spectrum is eventually confined to single Landau level producing dramatic spikes in the emission spectrum.

astro-ph.HE↗

arXiv2020

Nuclear Reaction Screening, Weak Interactions, and r-Process Nucleosynthesis in High Magnetic Fields

Coulomb screening and weak interactions in a hot, magnetized plasma are investigated. Coulomb screening is evaluated in a relativistic thermal plasma in which electrons and positrons are in equilibrium. In addition to temperature effects, effects on weak screening from a strong external magnetic field are evaluated. In high fields, the electron transverse momentum components are quantized into Landau levels. The characteristic plasma screening length at high temperatures and at high magnetic fields is explored. In addition to changes to the screening length, changes in weak interaction rates are estimated. It is found that high fields can result in increased $β$-decay rates as the electron and positron spectra are dominated by Landau levels. Finally, the effects studied here are evaluated in a simple r-process model. It is found that relativistic Coulomb screening has a small effect on the final abundance distribution. While changes in weak interaction rates in strong magnetic fields can have an effect on the r-process evolution and abundance distribution, the field strength required to have a significant effect may be larger than what is currently thought to be typical of the r-process environment in collapsar jets or neutron star mergers. If r-process sites exist in fields $\gtrsim 10^{14}$ G effects from fields on weak decays could be significant.

astro-ph.HE↗

arXiv2020

Plastic Scintillation Detectors for Time-of-Flight Mass Measurements

Fast timing detectors are an essential element in the experimental setup for time-of-flight (ToF) mass measurements of unstable nuclei. We have upgraded the scintillator detectors used in experiments at the National Superconducting Cyclotron Laboratory (NSCL) by increasing the number of photomultiplier tubes that read out their light signals to four per detector, and characterized them in a test experiment with $^{48}$Ca beam at the NSCL. The new detectors achieved a time resolution ($σ$) of 7.5 ps. We systematically investigated different factors that affect their timing performance. In addition, we evaluated the ability of positioning the hitting points on the scintillator using the timing information and obtained a resolution ($σ$) below 1 mm for well-defined beam spots.

physics.ins-det↗

arXiv2013

Explaining the Sr and Ba Scatter in Extremely Metal-Poor Stars

Compilations of abundances of Strontium and Barium in extremely metal-poor stars show that an apparent cutoff is observed for [Sr/Ba] at [Fe/H]$<$-3.6 and large fluctuations for [Fe/H]$>$-3.6 with a clear upper bound depending on metallicity. We study the factors that place upper limits on the logarithmic ratio [Sr/Ba]. A model is developed in which the collapses of type II supernovae are found to reproduce many of the features seen in the data. This model is consistent with galactic chemical evolution constraints of light-element enrichment in metal-poor stars. Effects of turbulence in an explosive site have also been simulated, and are found to be important in explaining the large scatter observed in the [Sr/Ba] data.

astro-ph.SR↗

arXiv2011

The r-Process in Metal Poor Stars and Black Hole Formation

Nucleosynthesis of heavy nuclei in metal-poor stars is generally thought to occur via the r-process because the r-process is a primary process that would have operated early in the Galaxy's history. This idea is strongly supported by the fact that the abundance pattern in many metal-poor stars matches well the inferred Solar r-process abundance pattern in the mass range between the second and third r-process abundance peaks. Nevertheless, a significant number of metal-poor stars do not share this standard r-process template. In this Letter we suggest that the nuclides observed in many of these stars are produced by the r-process, but that it is prevented from running to completion in more massive stars by collapse to black holes before the r-process is completed, creating a "truncated r-process," or "tr-process." We find that the observed fraction of tr-process stars is qualitatively what one would expect from the initial mass function, and that an apparent sharp truncation observed at around mass 160 could result from a combination of collapses to black holes and the difficulty of observing the higher mass rare earths. We test the tr-process hypothesis with r-process calculations that are terminated before all r-process trajectories have been ejected. We find qualitative agreement between observation and theory when black hole collapse and observational realities are taken into account.

astro-ph.SR↗

arXiv2006

Promoting Instructional Change via Co-Teaching

Physics Education Research (PER) has made significant progress in developing knowledge about teaching and learning as well as effective instructional strategies based on this knowledge. Disseminating knowledge and strategies to other faculty, however, has proven difficult. Coteaching is a promising and cost-effective alternative to traditional professional development that may be applicable in many situations. In this article, we discuss the theoretical background of co-teaching and describe our initial experience with co-teaching. A new instructor (MF) cotaught with an instructor experienced in PER-based reforms (CH). The pair worked within the scaffolding of the course structure typically used by the experienced instructor and met regularly to discuss instructional decisions. An outsider (AB) conducted separate interviews with each instructor at the beginning, middle, and end of the semester and observed several class sessions. Classroom observations show an immediate use of PER-based instructional practices by the new instructor. Interviews show a significant shift in the new instructor's beliefs about teaching and intentions towards future use of the PER-based instructional approaches.

physics.ed-ph↗