This place: Conversations with the provost about leadership and change

Professor Heather Corcoran invited faculty members across Washington University to interview Provost Edward S. Macias about key issues in higher education, including diversity and interdisciplinary research, as he concluded 25 years of leadership to the university. This book, published in 2013, is an archive of the interviews.https://openscholarship.wustl.edu/books/1008/thumbnail.jp

Sensitivity of the Cherenkov Telescope Array to spectral signatures of hadronic PeVatrons with application to Galactic Supernova Remnants

The local Cosmic Ray (CR) energy spectrum exhibits a spectral softening at energies around 3 PeV. Sources which are capable of accelerating hadrons to such energies are called hadronic PeVatrons. However, hadronic PeVatrons have not yet been firmly identified within the Galaxy. Several source classes, including Galactic Supernova Remnants (SNRs), have been proposed as PeVatron candidates. The potential to search for hadronic PeVatrons with the Cherenkov Telescope Array (CTA) is assessed. The focus is on the usage of very high energy Υ-ray spectral signatures for the identification of PeVatrons. Assuming that SNRs can accelerate CRs up to knee energies, the number of Galactic SNRs which can be identified as PeVatrons with CTA is estimated within a model for the evolution of SNRs. Additionally, the potential of a follow-up observation strategy under moonlight conditions for PeVatron searches is investigated. Statistical methods for the identification of PeVatrons are introduced, and realistic Monte-Carlo simulations of the response of the CTA observatory to the emission spectra from hadronic PeVatrons are performed. Based on simulations of a simplified model for the evolution for SNRs, the detection of a Υ-ray signal from in average 9 Galactic PeVatron SNRs is expected to result from the scan of the Galactic plane with CTA after 10 h of exposure. CTA is also shown to have excellent potential to confirm these sources as PeVatrons in deep observations wit ο(100) hours of exposure per source

High resolution observations of the outer disk around T Cha: the view from ALMA

T Cha is a young star surrounded by a transitional disk with signatures of planet formation. We have obtained high-resolution and high-sensitivity ALMA observations of T Cha in the ${\rm CO}(3$--$2)$, ${\rm ^{13}CO}(3$--$2)$, and ${\rm CS}(7$--$6)$ emission lines to reveal the spatial distribution of the gaseous disk around the star. In order to study the dust within the disk we have also obtained continuum images at 850$\mu$m from the line-free channels. We have spatially resolved the outer disk around T Cha. Using the CO(3-2) emission we derive a radius of $\sim$230 AU. We also report the detection of the $^{13}$CO(3-2) and the CS(7-8) molecular emissions, which show smaller radii than the CO(3-2) detection. The continuum observations at 850$\mu$m allow the spatial resolution of the dusty disk, which shows two emission bumps separated by $\sim$40AU, consistent with the presence of a dust gap in the inner regions of the disk, and an outer radius of $\sim$80AU. Therefore, T Cha is surrounded by a compact dusty disk and a larger and more diffuse gaseous disk, as previously observed in other young stars. The continuum intensity profiles are different at both sides of the disk suggesting possible dust asymmetries. We derive an inclination of i(deg)=67$\pm$5, and a position angle of PA (deg)= 113$\pm$6, for both the gas and dust disks. The comparison of the ALMA data with radiative transfer models shows that the gas and dust components can only be simultaneously reproduced when we include a tapered edge prescription for the surface density profile. The best model suggests that most of the disk mass is placed within a radius of $R<$ 50AU. Finally, we derive a dynamical mass for the central object of $M_{*}$=1.5$\pm$0.2M$_{\odot}$, comparable to the one estimated with evolutionary models for an age of $\sim$10Myr.Comment: 5 pages, 5 figures, accepted for publication in A&A Letter

Limits to differences in active and passive charges

We explore consequences of a hypothetical difference between active charges, which generate electric fields, and passive charges, which respond to them. A confrontation to experiments using atoms, molecules, or macroscopic matter yields limits on their fractional difference at levels down to 10^-21, which at the same time corresponds to an experimental confirmation of Newtons third law.Comment: 6 pages Revtex. To appear in Phys. Rev.

Investigating the impact of ageing and thermal management of a fuel cell system on energy management strategies

This paper studies the impact of two significant aspects, namely fuel cell (FC) degradation and thermal management, over the performance of an optimal and a rule-based energy management strategy (EMS) in a fuel cell hybrid electric vehicle (FCHEV). To do so, firstly, a vehicle's model is developed in simulation environment for a low-speed FCHEV composed of a FC stack and a battery pack. Subsequently, deterministic dynamic programming (DP), as an optimal strategy, and bounded load following strategy (BLFS), as a common rule-based strategy, are utilized to minimize the hydrogen consumption while respecting the operating constraints of the power sources. The performance of the EMSs is assessed at different scenarios. The first objective is to clarify the effect of FC stack degradation on the performance of the vehicle. In this regard, each EMS determines the required current from the FC stack for two FCs with different levels of degradation. The second objective is to evaluate the thermal management contribution to improving the performance of the new FC compared to the considered cases in scenario one. In this respect, each strategy deals with determining two control variables (FC current and cooling fan duty cycle). The results of this study indicate that negligence of adapting to the PEMFC health state, as the PEMFC gets aged, can increase the hydrogen consumption up to 24.8% in DP and 12.1% in BLFS. Moreover, the integration of temperature dimension into the EMS can diminish the hydrogen consumption by 4.1% and 5.3% in DP and BLFS respectively. © 2020 Elsevier Lt

A Novel Use of Light Guides and Wavelength Shifting Plates for the Detection of Scintillation Photons in Large Liquid Argon Detectors

Scintillation light generated as charged particles traverse large liquid argon detectors adds valuable information to studies of weakly-interacting particles. This paper uses both laboratory measurements and cosmic ray data from the Blanche dewar facility at Fermilab to characterize the efficiency of the photon detector technology developed at Indiana University for the single phase far detector of DUNE. The efficiency of this technology was found to be 0.48% at the readout end when the detector components were characterized with laboratory measurements. A second determination of the efficiency using cosmic ray tracks is in reasonable agreement with the laboratory determination. The agreement of these two efficiency determinations supports the result that minimum ionizing muons generate ${\mathcal N}_{phot} = 40,000$ photons/MeV as they cross the LAr volume.Comment: Accepted version (without final editorial corrections

Radioactive Decay Studies of Nuclei Produced from Bombardment by Intermediate-Energy Neutrons

This work was supported by National Science Foundation Grant PHY 76-84033 and Indiana Universit

The role of morphological evolution and prey specialization in adaptive radiations: The spider genus Dysdera in the Canary Islands

Non peer reviewe