195 research outputs found
Intrinsic and extrinsic geometries of a tidally deformed black hole
A description of the event horizon of a perturbed Schwarzschild black hole is
provided in terms of the intrinsic and extrinsic geometries of the null
hypersurface. This description relies on a Gauss-Codazzi theory of null
hypersurfaces embedded in spacetime, which extends the standard theory of
spacelike and timelike hypersurfaces involving the first and second fundamental
forms. We show that the intrinsic geometry of the event horizon is invariant
under a reparameterization of the null generators, and that the extrinsic
geometry depends on the parameterization. Stated differently, we show that
while the extrinsic geometry depends on the choice of gauge, the intrinsic
geometry is gauge invariant. We apply the formalism to solutions to the vacuum
field equations that describe a tidally deformed black hole. In a first
instance we consider a slowly-varying, quadrupolar tidal field imposed on the
black hole, and in a second instance we examine the tide raised during a close
parabolic encounter between the black hole and a small orbiting body.Comment: 27 pages, 4 figure
The Effect of Flipped Instruction on Special Education Preservice Teachers\u27 Perceptions
This study analyzes the flipped instruction model used in three special education educator preparation courses to examine which components preservice teachers perceived most contributed to their content knowledge, motivation, and engagement (n=50). Weekly pre-class asynchronous assignments included the use of educational technology tools such as an interactive e-textbook site, Perusall, and online academic activities such as Khan Academy to strengthen their content knowledge. This allowed more time for a student-centered approach during synchronous instruction to incorporate tools such as Nearpod, Pear Deck, Flipgrid and digital badges to strength-en their motivation and engagement. Data were collected through a post-course survey; results indicate that preservice teachers perceived this model was motivating, engaging, and contributed significantly to their content knowledge. They also identified hands-on activities during class as a significant component of their learning. This article discusses the project, limitations, and implications for future flipped instruction research in special education educator preparation programs
Effect of Vehicle on the Nasal Absorption of Epinephrine During Cardiopulmonary Resuscitation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90174/1/j.1875-9114.1996.tb03030.x.pd
Sensitivity Analysis for Multidisciplinary Systems (SAMS)
This report describes the research conducted under an interagency collaboration agreement between the Aerospace Systems Directorate of the Air Force Research Laboratory (AFRL/RQ) and the Computational AeroSciences Branch of NASA Langley (NASA LaRC). Both organizations have a long-term goal of developing a modular computational system for coupling fluids and structures to enable both analysis and optimization of aerospace vehicles. Ultimately, the system should support multiple solvers within the fluid and structure domains to allow the best combination for the task at hand, as well as to allow for institutional preferences of specific software components. Towards this goal, the current research was focused on enhancing the existing modal aeroelastic analysis in the NASA FUN3D (Fully-UNstructured three-dimensional CFD (Computational Fluid Dynamics) code) software (Biedron et al. 2018), as well as developing new aeroelastic analysis and optimization capabilities based on a non-linear finite-element method. The methods and enhancements described in this document pertain to FUN3D Version 13.4
Planetary Construction Zones in Occultation: Discovery of an Extrasolar Ring System Transiting a Young Sun-like Star and Future Prospects for Detecting Eclipses by Circumsecondary and Circumplanetary Disks
The large relative sizes of circumstellar and circumplanetary
disks imply that they might be seen in eclipse in stellar light curves. We
estimate that a survey of ~10^4 young (~10 Myr old) post-accretion pre-MS stars
monitored for ~10 years should yield at least a few deep eclipses from
circumplanetary disks and disks surrounding low mass companion stars. We
present photometric and spectroscopic data for a pre-MS K5 star (1SWASP
J140747.93-394542.6), a newly discovered ~0.9 Msun member of the ~16 Myr-old
Upper Cen-Lup subgroup of Sco-Cen at a kinematic distance of 128 pc. SuperWASP
and ASAS light curves for this star show a remarkably long, deep, and complex
eclipse event centered on 29 April 2007. At least 5 multi-day dimming events of
>0.5 mag are identified, with a >3.3 mag deep eclipse bracketed by two pairs of
~1 mag eclipses symmetrically occurring +-12 days and +-26 days before and
after. Hence, significant dimming of the star was taking place on and off over
at least a ~54 day period in 2007, and a strong >1 mag dimming event occurred
over a ~12 day span. We place a firm lower limit on the period of 850 days
(i.e. the orbital radius of the eclipser must be >1.7 AU and orbital velocity
must be <22 km/s). The shape of the light curve is similar to the lop-sided
eclipses of the Be star EE Cep. We suspect that this new star is being eclipsed
by a low-mass object orbited by a dense inner disk, girded by at least 3 dusty
rings of lower optical depth. Between these rings are at least two annuli of
near-zero optical depth (i.e. gaps), possibly cleared out by planets or moons,
depending on the nature of the secondary. For possible periods in the range
2.33-200 yr, the estimated total ring mass is ~8-0.4 Mmoon (if the rings have
optical opacity similar to Saturn's rings), and the edge of the outermost
detected ring has orbital radius ~0.4-0.09 AU.Comment: Astronomical Journal, in press, 13 figure
The compositional and evolutionary logic of metabolism
Metabolism displays striking and robust regularities in the forms of
modularity and hierarchy, whose composition may be compactly described. This
renders metabolic architecture comprehensible as a system, and suggests the
order in which layers of that system emerged. Metabolism also serves as the
foundation in other hierarchies, at least up to cellular integration including
bioenergetics and molecular replication, and trophic ecology. The
recapitulation of patterns first seen in metabolism, in these higher levels,
suggests metabolism as a source of causation or constraint on many forms of
organization in the biosphere.
We identify as modules widely reused subsets of chemicals, reactions, or
functions, each with a conserved internal structure. At the small molecule
substrate level, module boundaries are generally associated with the most
complex reaction mechanisms and the most conserved enzymes. Cofactors form a
structurally and functionally distinctive control layer over the small-molecule
substrate. Complex cofactors are often used at module boundaries of the
substrate level, while simpler ones participate in widely used reactions.
Cofactor functions thus act as "keys" that incorporate classes of organic
reactions within biochemistry.
The same modules that organize the compositional diversity of metabolism are
argued to have governed long-term evolution. Early evolution of core
metabolism, especially carbon-fixation, appears to have required few
innovations among a small number of conserved modules, to produce adaptations
to simple biogeochemical changes of environment. We demonstrate these features
of metabolism at several levels of hierarchy, beginning with the small-molecule
substrate and network architecture, continuing with cofactors and key conserved
reactions, and culminating in the aggregation of multiple diverse physical and
biochemical processes in cells.Comment: 56 pages, 28 figure
'To live and die [for] Dixie': Irish civilians and the Confederate States of America
Around 20,000 Irishmen served in the Confederate army in the Civil War. As a result, they left behind, in various Southern towns and cities, large numbers of friends, family, and community leaders. As with native-born Confederates, Irish civilian support was crucial to Irish participation in the Confederate military effort. Also, Irish civilians served in various supporting roles: in factories and hospitals, on railroads and diplomatic missions, and as boosters for the cause. They also, however, suffered in bombardments, sieges, and the blockade. Usually poorer than their native neighbours, they could not afford to become 'refugees' and move away from the centres of conflict. This essay, based on research from manuscript collections, contemporary newspapers, British Consular records, and Federal military records, will examine the role of Irish civilians in the Confederacy, and assess the role this activity had on their integration into Southern communities. It will also look at Irish civilians in the defeat of the Confederacy, particularly when they came under Union occupation. Initial research shows that Irish civilians were not as upset as other whites in the South about Union victory. They welcomed a return to normalcy, and often 'collaborated' with Union authorities. Also, Irish desertion rates in the Confederate army were particularly high, and I will attempt to gauge whether Irish civilians played a role in this. All of the research in this paper will thus be put in the context of the Drew Gilpin Faust/Gary Gallagher debate on the influence of the Confederate homefront on military performance. By studying the Irish civilian experience one can assess how strong the Confederate national experiment was. Was it a nation without a nationalism
Taking into account sensory knowledge: the case of geo-techologies for children with visual impairments
This paper argues for designing geo-technologies supporting non-visual sensory knowledge. Sensory knowledge refers to the implicit and explicit knowledge guiding our uses of our senses to understand the world. To support our argument, we build on an 18 months field-study on geography classes for primary school children with visual impairments. Our findings show (1) a paradox in the use of non-visual sensory knowledge: described as fundamental to the geography curriculum, it is mostly kept out of school; (2) that accessible geo-technologies in the literature mainly focus on substituting vision with another modality, rather than enabling teachers to build on children's experiences; (3) the importance of the hearing sense in learning about space. We then introduce a probe, a wrist-worn device enabling children to record audio cues during field-trips. By giving importance to children's hearing skills, it modified existing practices and actors' opinions on non-visual sensory knowledge. We conclude by reflecting on design implications, and the role of technologies in valuing diverse ways of understanding the world
The Effective Temperature Scale of Galactic Red Supergiants: Cool, But Not As Cool As We Thought
We use moderate-resolution optical spectrophotometry and the new MARCS
stellar atmosphere models to determine the effective temperatures of 74
Galactic red supergiants. From these we find a new effective temperature scale
that is significantly warmer than those in the literature. We show that this
temperature scale, along with the newly derived bolometric corrections, gives
much better agreement between our red supergiants and stellar evolutionary
tracks. This agreement provides an independent verification of our new
temperature scale. The combination of effective temperature and bolometric
luminosities allows us to calculate stellar radii; the coolest and most
luminous stars have radii of roughly 1500 solar radii (7 AU), in excellent
accordance with the largest stellar radii predicted from current evolutionary
theory. We find that similar results are obtained for the effective
temperatures and bolometric luminosities using only the de-reddened V-K colors,
providing a powerful demonstration of the self-consistency of the MARCS models.Comment: 32 pages, 16 figures; Accepted by the Astrophysical Journa
Lensing in the Blue II: Estimating the Sensitivity of Stratospheric Balloons to Weak Gravitational Lensing
The Superpressure Balloon-borne Imaging Telescope (SuperBIT) is a
diffraction-limited, wide-field, 0.5 m, near-infrared to near-ultraviolet
observatory designed to exploit the stratosphere's space-like conditions.
SuperBIT's 2023 science flight will deliver deep, blue imaging of galaxy
clusters for gravitational lensing analysis. In preparation, we have developed
a weak lensing measurement pipeline with modern algorithms for PSF
characterization, shape measurement, and shear calibration. We validate our
pipeline and forecast SuperBIT survey properties with simulated galaxy cluster
observations in SuperBIT's near-UV and blue bandpasses. We predict imaging
depth, galaxy number (source) density, and redshift distribution for
observations in SuperBIT's three bluest filters; the effect of lensing sample
selections is also considered. We find that in three hours of on-sky
integration, SuperBIT can attain a depth of b = 26 mag and a total source
density exceeding 40 galaxies per square arcminute. Even with the application
of lensing-analysis catalog selections, we find b-band source densities between
25 and 30 galaxies per square arcminute with a median redshift of z = 1.1. Our
analysis confirms SuperBIT's capability for weak gravitational lensing
measurements in the blue.Comment: Submitted to Astronomical Journa
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