A Dipole on the Sky: Predictions for Hypervelocity Stars from the Large Magellanic Cloud

We predict the distribution of hypervelocity stars (HVSs) ejected from the Large Magellanic Cloud (LMC), under the assumption that the dwarf galaxy hosts a central massive black hole (MBH). For the majority of stars ejected from the LMC the orbital velocity of the LMC has contributed a significant fraction of their galactic rest frame velocity, leading to a dipole density distribution on the sky. We quantify the dipole using spherical harmonic analysis and contrast with the monopole expected for HVSs ejected from the Galactic Center. There is a tendril in the density distribution that leads the LMC which is coincident with the well-known and unexplained clustering of HVSs in the constellations of Leo and Sextans. Our model is falsifiable, since it predicts that Gaia will reveal a large density of HVSs in the southern hemisphere.Comment: 6 pages, ApJ (Letters), in pres

The orbit of the Cepheid AW Per

An orbit for the classical Cepheid AW Per was derived. Phase residuals from the light curve are consistent with the light-time effect from the orbit. The companion was studied using IUE spectra. The flux distribution from 1300 to 1700 A is unusual, probably an extreme PbSi star, comparable to a B7V or B8V star. The flux of the composite spectrum from 1200 A through V is well matched by F7Ib and B8V standard stars with Delta M(sub upsilon) = 3(m) multiplied by 1. The mass function from the orbit indicates that the mass of the Cepheid must be greater that 4.7 solar mass if it is the more massive component. A B7V to B8V companion is compatible with the 1 sigma lower limit (3.5 solar mass) from the mass function. This implies that the Cepheid has the same mass, but the large magnitude difference rules this out. It is likely that the companion is itself a binary

Hypervelocity runaways from the Large Magellanic Cloud

We explore the possibility that the observed population of Galactic hypervelocity stars (HVSs) originate as runaway stars from the Large Magellanic Cloud (LMC). Pairing a binary evolution code with an N-body simulation of the interaction of the LMC with the Milky Way, we predict the spatial distribution and kinematics of an LMC runaway population. We find that runaway stars from the LMC can contribute Galactic HVSs at a rate of $3 \times 10^{-6}\;\mathrm{yr}^{-1}$. This is composed of stars at different points of stellar evolution, ranging from the main-sequence to those at the tip of the asymptotic giant branch. We find that the known B-type HVSs have kinematics which are consistent with an LMC origin. There is an additional population of hypervelocity white dwarfs whose progenitors were massive runaway stars. Runaways which are even more massive will themselves go supernova, producing a remnant whose velocity will be modulated by a supernova kick. This latter scenario has some exotic consequences, such as pulsars and supernovae far from star-forming regions, and a small rate of microlensing from compact sources around the halo of the LMC.Comment: MNRAS, in pres

Source Separation, Frequency Dynamics and Lighting Dependency of Electrophosphenes in Human Vision

Exposure to electromagnetic fields (EMF) can produce illusory perceptions of light referred to as phosphenes. Various exposure guidelines around the world use phosphene perception as an indicator that environmental EMF may be affecting the central nervous system, however many of them are based on low quality legacy literature. While exposure guidelines should consider all commonly encountered ambient lighting conditions, there are no studies examining electrophosphenes in commonly encountered mesopic (i.e., dim) lighting conditions. As a result, conclusions drawn from these guidelines may not be reliable or encompass all plausible EMF exposure conditions. Additionally, the roles of the retina and visual cortex in electrophosphene generation have not yet been adequately separated. Given the importance of understanding the effects of EMF exposure on human health, it is crucial to investigate the factors that affect sensitivity to phosphenes in a rigorous and systematic manner. This thesis examined the effects of transcranial electrical stimulation (tES) using different electrode placements, stimulation parameters, and ambient lighting conditions on phosphene detection thresholds using a large sample size, as well as robust experimental and analytical techniques. Detection thresholds across the three experiments (presented in Chapters 2 – 4) showed that up to 74% less current had to be applied to induce phosphenes in mesopic conditions compared to well-lit and dark conditions, indicating that existing guidelines have used relatively insensitive scenarios to determine safe levels of EMF exposure. Lower phosphene detection thresholds in frontal montages suggested that the retina was the most likely source of tES-induced phosphenes. However, the double dissociation analysis in Chapter 3 showed that additional stimulation over the visual cortex lowered the current strength required to induce phosphenes by stimulation near the retina (from 130.7 μA to 87.5 μA). It appears then that electrical stimulation over the cortex can facilitate phosphene detection. Chapter 4 showed that phosphenes were more readily perceived when stimulation was set to specific frequencies in each of the dark (10 Hz), mesopic (16 Hz) and well-lit (20 Hz) conditions. Frequency dependence in these well-lit and dark conditions was in-line with: 1) previously reported dominant electroencephalograph (EEG) frequency bands in the cortex; and 2) sensitivity to stimulation found in rod and cone photoreceptors in the retina. All three experiments found that stimulation at 16 Hz produced the strongest electrophosphenes in mesopic conditions. While this does not align with any known EEG frequency response in the visual cortex, it closely aligns with the rod-cone phase delay mechanism found in the retina at 15 Hz, suggesting that the frequency component of tES-induced phosphenes may be driven by the frequency dynamics of retinal photoreceptors. Overall, the findings of this thesis indicate that exposure guidelines for EMF need to consider mesopic lighting if they intend to encompass all plausible exposure scenarios. Additionally, tES over the visual cortex can influence phosphene perception. Finally, ambient lighting conditions strongly affect the frequency dynamics and current strength required for tES to produce phosphenes

A quantitative study of the relationship between faith formation opportunities and the religiosity of lay educators in Catholic secondary schools

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A Realist Ethnography of Nuclear Security Officer Culture

This realist ethnography describes the heretofore unexamined culture of commercial nuclear power security officers over a one-year period from an active participant observer’s perspective. Data include field notes taken during observations at various sites and 15 interviews with security leaders working at or who had recently worked at 12 different commercial nuclear power plants and had previously worked at a dozen other commercial nuclear power plants, thus representing a broad overview of the commercial nuclear security culture. The data also include more than 58 unclassified documents from these sites, industry organizations, and regulatory agencies. An analysis of the data reveals 16 key themes that are characteristic of the nuclear security officer culture. The study describes how, although safety and security are of paramount concern at a commercial nuclear plant, the cultures of security workers and safety workers differ significantly. Not only is the nuclear security officer culture different from that of the safety culture at the same plant, but it often conflicts with it in its attitudes, goals, procedures, supervision, and job satisfaction. The commercial nuclear security officer culture is unique in many ways, including the isolation of security officers— institutionally, physically, and socially—from the other plant workers; their working conditions and benefits; their need to work oftentimes long, boring, unpredictable shifts and carry heavy equipment to remote sites; and their responsibility to respond immediately and, if necessary, with deadly force, even putting their lives on the line. iii Supplementing the data analysis, and in keeping with a realistic ethnography, are a series of vignettes describing the typical day in a nuclear security officer’s life. The study also points out differences between the commercial nuclear security culture and that of the private non-nuclear security cultures. The study concludes with recommendations for improving the commercial nuclear security officer culture and for future research into a culture we know little about but whose members are invested with one of the greatest responsibilities in our country—protecting us from potential acts of terrorism perpetrated on nuclear plants and the resultant exposure to the effects of nuclear waste, which can last for generations

Dirac and non-Dirac conditions in the 2-potential theory of magnetic charge

We investigate the Cabbibo-Ferrari, two potential approach to magnetic charge coupled to two different complex scalar fields, $\Phi_1$ and $\Phi_2$, each having different electric and magnetic charges. The scalar field, $\Phi_1$, is assumed to have a spontaneous symmetry breaking self interaction potential which gives a mass to the "magnetic" gauge potential and "magnetic" photon, while the other "electric" gauge potential and "electric" photon remain massless. The magnetic photon is hidden until one reaches energies of the order of the magnetic photon rest mass. The second scalar field, $\Phi _2$, is required in order to make the theory non-trivial. With only one field one can always use a duality rotation to rotate away either the electric or magnetic charge, and thus decouple either the associated electric or magnetic photon. In analyzing this system of two scalar fields in the Cabbibo-Ferrari approach we perform several duality and gauge transformations, which require introducing non-Dirac conditions on the initial electric and magnetic charges. We also find that due to the symmetry breaking the usual Dirac condition is altered to include the mass of the magnetic photon. We discuss the implications of these various conditions on the charges.Comment: revtex 9 pages, 1 figure, to be published EPJ