Contributions of Microgravity Test Results to the Design of Spacecraft Fire Safety Systems

Experiments conducted in spacecraft and drop towers show that thin-sheet materials have reduced flammability ranges and flame-spread rates under quiescent low-gravity environments (microgravity) as compared to normal gravity. Furthermore, low-gravity flames may be suppressed more easily by atmospheric dilution or decreasing atmospheric total pressure than their normal-gravity counterparts. The addition of a ventilating air flow to the low-gravity flame zone, however, can greatly enhance the flammability range and flame spread. These results, along with observations of flame and smoke characteristics useful for microgravity fire-detection 'signatures', promise to be of considerable value to spacecraft fire-safety designs. The paper summarizes the fire detection and suppression techniques proposed for the Space Station Freedom and discusses both the application of low-gravity combustion knowledge to improve fire protection and the critical needs for further research

Local Observables in a Landscape of Infrared Gauge Modes

Cosmological local observables are at best statistically determined by the fundamental theory describing inflation. When the scalar inflaton is coupled uniformly to a collection of subdominant massless gauge vectors, rotational invariance is obeyed locally. However, the statistical isotropy of fluctuations is spontaneously broken by gauge modes whose wavelength exceed our causal horizon. This leads to a landscape picture where primordial correlators depend on the position of the observer. We compute the stochastic corrections to the curvature power spectrum, show the existence of a new local observable (the shape of the quadrupole), and constrain the theory using Planck limits.Comment: 5 pages, 3 figures, v2: minor updates, matches version published in Physics Letters

Risks, designs, and research for fire safety in spacecraft

Current fire protection for spacecraft relies mainly on fire prevention through the use of nonflammable materials and strict storage controls of other materials. The Shuttle also has smoke detectors and fire extinguishers, using technology similar to aircraft practices. While experience has shown that the current fire protection is adequate, future improvements in fire safety technology to meet the challenges of long duration space missions, such as the Space Station Freedom, are essential. All spacecraft fire protection systems, however, must deal with the unusual combustion characteristics and operational problems in the low gravity environment. The features of low gravity combustion that affect spacecraft fire safety, and the issues in fire protection for Freedom that must be addressed eventually to provide effective and conservative fire protection systems are discussed

The Incidence of Debris Disks at 24 {\mu}m and 670 Myr

We use Spitzer Space Telescope 24 {\mu}m data to search for debris disks among 122 AFGKM stars from the \sim 670 Myr clusters Hyades, Coma Ber, and Praesepe, utilizing a number of advances in data reduction and determining the intrinsic colors of main sequence stars. For our sample, the 1{\sigma} dispersion about the main sequence V-K, K-[24] locus is approximately 3.1%. We identify seven debris disks at 10% or more (\geq 3{\sigma} confidence level) above the expected K-[24] for purely photospheric emission. The incidence of excesses of 10% or greater in our sample at this age is 5.7 +3.1/-1.7%. Combining with results from the literature, the rate is 7.8 +4.2/-2.1% for early- type (B9 - F4) stars and 2.7 +3.3/-1.7% for solar-like (F5 - K9) stars. Our primary sample has strict criteria for inclusion to allow comparison with other work; when we relax these criteria, three additional debris disks are detected. They are all around stars of solar-like type and hence reinforce our conclusion that disks around such stars are still relatively common at 670 Myr and are similar to the rate around early-type stars. The apparently small difference in decay rates between early-type and solar-like stars is inconsistent with the first order theoretical predictions that the later type stellar disks would decay an order of magnitude more quickly than the earlier type ones.Comment: 26 pages, 3 figures, accepted for publication in Ap

Origins of Extragalactic Cosmic Ray Nuclei by Contracting Alignment Patterns induced in the Galactic Magnetic Field

We present a novel approach to search for origins of ultra-high energy cosmic rays. These particles are likely nuclei that initiate extensive air showers in the Earth's atmosphere. In large-area observatories, the particle arrival directions are measured together with their energies and the atmospheric depth at which their showers maximize. The depths provide rough measures of the nuclear charges. In a simultaneous fit to all observed cosmic rays we use the galactic magnetic field as a mass spectrometer and adapt the nuclear charges such that their extragalactic arrival directions are concentrated in as few directions as possible. Using different simulated examples we show that, with the measurements on Earth, reconstruction of extragalactic source directions is possible. In particular, we show in an astrophysical scenario that source directions can be reconstructed even within a substantial isotropic background.Comment: 14 pages, 15 figure

The Use of Exempla from Cicero to Pliny the Younger

This dissertation expands our picture of Roman exemplarity by focusing on exempla as they are used to construct arguments. In contrast to recent studies of the practice, instead of focusing on repeatedly cited instances in a series of different texts, my argument centers on repeated patterns in which authors deploy exempla. I suggest that Roman exemplarity constructs a mode of moral and practical reasoning that conditions its users to repeat a pattern of imbuing and responding to meaning in the exempla they select for themselves. I focus on texts that present themselves as dealing directly with contemporary society: in particular forensic oratory, epistolography and satire. Cicero and Pliny the Younger provide the central anchors for my discussion. The chapters of this dissertation frame and supplement the current discussion by exploring several of the most prominent uses of exempla. The first chapter builds on Quintilian\u27s discussion of exemplary comparison to demonstrate the malleable nature of moral arguments based in comparisons between narratives. The second chapter focuses on exempla featuring nameless figures which consequently emphasize patterns of action rather than the authority of the actor. Such exempla display close connections with declamations and fables, creating a triangle of relationships through which factual and fictional narratives influence one another. In my third chapter, I demonstrate that exempla which claim to illustrate how things are provide a powerful means to forestall judgment or obscure status distinctions. The final chapter explores the frequently superficial deployment of exempla as emblems: where anonymous exempla emphasize actions as opposed to actors, exempla deployed as emblems foreground the status and authority of the actor while downplaying the narrative details of the action. Exemplarity provides a useful window onto the patterns of Roman moralism

Gerasim\u27s Compassion in Tolstoy\u27s The Death of Ivan Ilyich

In this article on Gerasim, from Tolstoy\u27s The Death of Ivan Ilyich, David Urban examines this character\u27s example of compassion in the face of his master\u27s terminal illness. Urban suggests that all humans would do well to follow Gerasim\u27s example, especially in light of everyone\u27s mortality

Blow-up of waves on singular spacetimes with generic spatial metrics

We study the asymptotic behaviour of solutions to the linear wave equation on cosmological spacetimes with Big Bang singularities and show that appropriately rescaled waves converge against a blow-up profile. Our class of spacetimes includes Friedman-Lema\^itre-Robertson-Walker (FLRW) spacetimes with negative sectional curvature that solve the Einstein equations in presence of a perfect irrotational fluid with $p=(\gamma-1)\rho$. As such, these results are closely related to the still open problem of past nonlinear stability of such FLRW spacetimes within the Einstein scalar field equations. In contrast to earlier works, our results hold for spatial metrics of arbitrary geometry, hence indicating that the matter blow-up in the aforementioned problem is not dependent on spatial geometry. Additionally, we use the energy estimates derived in the proof in order to formulate open conditions on the initial data that ensure a non-trivial blow-up profile, for initial data sufficiently close to the Big Bang singularity and with less harsh assumptions for $\gamma<2$.Comment: 24 pages. This version now includes a pointwise blow-up condition for $\gamma=2$ and discuss its strengths and weaknesses compared to other conditions, along with various minor improvements, especially in the references. Version as published in Letters in Mathematical Physic

The effect of international subsidiaries on voluntary disclosure - evidence from natural disasters

This paper documents that managers of multinational companies adjust voluntary disclosure after significant events at international subsidiaries. We show an increase in the likelihood and frequency of management forecasts following natural disasters in regions where companies operate subsidiaries. The exogenous and staggered nature of natural disasters as well as our research design choices substantially raise the hurdle for alternative explanations of our result. Further analyses suggest that the effect is particularly strong for companies that rely on equity financing. Our paper contributes to the nascent literature on transmission effects within international business groups