4,704 research outputs found
A Religious Pacifist Looks at Abortion
From the standpoint of the religious pacifist, Professor Zahn sees elementary human rights beginning at the moment of conception marking the beginning of the individual\u27s life process, and argues against abortion from this point
Self-intersecting fuzzy extra dimensions from squashed coadjoint orbits in SYM and matrix models
We find new vacuum solutions of super-Yang-Mills with totally
anti-symmetric cubic soft SUSY breaking terms, or equivalently solutions of the
IKKT matrix model of type with flux
terms. The solutions can be understood in terms of 4- and 6- dimensional fuzzy
branes in extra dimensions, describing self-intersecting
projections of compact flag manifolds of . The 6-dimensional solutions
provide a 6-fold covering of the internal space near the origin, while the
4-dimensional branes have a triple self-intersections spanning all 6 internal
directions. The solutions have lower energy than the trivial vacuum, and we
prove that there are no negative modes. The massless modes are identified
explicitly. In particular there are chiral fermionic zero modes, linking the
coincident sheets with opposite flux at the origin. They have a
family symmetry, originating from the Weyl group rotations.Comment: 28+8 pages, 2 figures. V2: improved discussion, published versio
A Robust Measure of Tidal Circularization in Coeval Binary Populations: The solar-type spectroscopic Binary Population in The Open Cluster M35
We present a new homogeneous sample of 32 spectroscopic binary orbits in the
young (~ 150 Myr) main-sequence open cluster M35. The distribution of orbital
eccentricity vs. orbital period (e-log(P)) displays a distinct transition from
eccentric to circular orbits at an orbital period of ~ 10 days. The transition
is due to tidal circularization of the closest binaries. The population of
binary orbits in M35 provide a significantly improved constraint on the rate of
tidal circularization at an age of 150 Myr. We propose a new and more robust
diagnostic of the degree of tidal circularization in a binary population based
on a functional fit to the e-log(P) distribution. We call this new measure the
tidal circularization period. The tidal circularization period of a binary
population represents the orbital period at which a binary orbit with the most
frequent initial orbital eccentricity circularizes (defined as e = 0.01) at the
age of the population. We determine the tidal circularizationperiod for M35 as
well as for 7 additional binary populations spanning ages from the pre
main-sequence (~ 3 Myr) to late main-sequence (~ 10 Gyr), and use Monte Carlo
error analysis to determine the uncertainties on the derived circularization
periods. We conclude that current theories of tidal circularization cannot
account for the distribution of tidal circularization periods with population
age.Comment: 37 pages, 9 figures, to be published in The Astrophysical Journal,
February 200
X-ray Emission from the Weak-lined T Tauri Binary System KH 15D
The unique eclipsing, weak-lined T Tauri star KH 15D has been detected as an
X-ray source in a 95.7 ks exposure from the Chandra X-ray Observatory archives.
A maximum X-ray luminosity of 1.5 x 10^{29} erg s is derived in the
0.5--8 keV band, corresponding to L_{X}/L_bol = 7.5 x 10^{-5}. Comparison with
samples of stars of similar effective temperature in NGC 2264 and in the Orion
Nebula Cluster shows that this is about an order of magnitude low for a typical
star of its mass and age. We argue that the relatively low luminosity cannot be
attributed to absorption along the line of sight but implies a real deficiency
in X-ray production. Possible causes for this are considered in the context of
a recently proposed eccentric binary model for KH 15D. In particular, we note
that the visible component rotates rather slowly for a weak-lined T Tauri star
and has possibly been pseudosynchronized by tidal interaction with the primary
near periastron
The isotope composition of water vapour: A powerful tool to study transport and chemistry of middle atmospheric water vapour
International audienceA one-dimensional chemistry model is applied to study the stable hydrogen (D) and stable oxygen isotope (17O, 18O) composition of water vapour in stratosphere and mesosphere. The stable isotope ratios of tropospheric H2O are determined by "physical'' fractionation effects, i.e. phase changes, diffusion processes, and mixing of air masses. Due to these processes water vapour entering the stratosphere (i) is mass-dependently fractionated (MDF), i.e. shifts in the isotope ratio 17O/16O are ~0.52 times of those of 18O/16O and (ii) shows isotope shifts in D/H, which are ~5 times of those in 18O/16O. In stratosphere and mesosphere "chemical'' fractionation, that are the oxidation of methane, re-cycling of H2O via the HOx family, and isotope exchange reactions are shown to considerably enhance the isotope ratios in the imported tropospheric H2O. Enrichments relative to the isotope ratios at the tropopause are used to derive the partitioning of tropospheric (unmodified), re-cycled and in situ generated H2O. The model reasonably predicts overall increases of the stable isotope ratios in H2O by ~23% for D/H, ~8.5% for 17O/16O, and ~14% for 18O/16O. The17O/16O and 18O/16O ratios in H2O are shown to be a measure of the partitioning of HOx that receives its O atom either from the reservoirs O2 or O3. In the entire middle atmosphere, MDF O2 is the major donator of oxygen atoms incorporated in OH and HO2 and thus in H2O. It is demonstrated that in the stratosphere mass-independent fractionation (MIF) in O3 in a first step is transferred to the NOx family and only in a second step to HOx and H2O. In contrast to CO2, O(1D) only plays a minor role in this MIF transfer. The major uncertainty in our calculation arises from the many badly quantified isotope exchange reactions and kinetic isotope fractionation factors
Sector Models - A Toolkit for Teaching General Relativity. Part 1: Curved Spaces and Spacetimes
Teaching the general theory of relativity to high school or undergraduate
students must be based on an approach that is conceptual rather than
mathematical. In this paper we present such an approach that requires no more
than elementary mathematics. The central idea of this introduction to general
relativity is the use of so-called sector models. Sector models describe curved
spaces the Regge calculus way by subdivision into blocks with euclidean
geometry. This procedure is similar to the approximation of a curved surface by
flat triangles. We outline a workshop for high school and undergraduate
students that introduces the notion of curved space by means of sector models
of black holes. We further describe the extension to sector models of curved
spacetimes. The spacetime models are suitable for learners with a basic
knowledge of special relativity. For online teaching materials, see
http://www.spacetimetravel.org .
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F\"ur die Vermittlung der Allgemeinen Relativit\"atstheorie in der Schule, im
Grund- oder im Nebenfachstudium besteht das Anliegen, eine fachlich
befriedigende Darstellung zu geben, die nicht mehr als Schulmathematik
voraussetzt. Wir stellen in diesem Beitrag einen solchen Zugang vor. Das
zentrale Werkzeug unserer Einf\"uhrung sind sogenannte Sektormodelle, die
gekr\"ummte R\"aume im Sinne des Regge-Kalk\"uls durch eine Zerlegung in
kleine, ungekr\"ummte Sektoren beschreiben, \"ahnlich der Triangulierung einer
gekr\"ummten Fl\"ache. Wir schildern einen Workshop f\"ur Sch\"uler/innen und
Studierende, in dem gekr\"ummte R\"aume anhand von Sektormodellen Schwarzer
L\"ocher eingef\"uhrt werden. Wir beschreiben ferner die Erweiterung auf
Sektormodelle gekr\"ummter Raumzeiten. Raumzeitliche Sektormodelle setzen
Grundkenntnisse der Speziellen Relativit\"atstheorie voraus. Online-Materialien
unter http://www.tempolimit-lichtgeschwindigkeit.de .Comment: bilingual: English version 18 pages, 9 figures, for associated movies
see http://www.spacetimetravel.org/sectormodels1/sectormodels1.html. German
version 19 pages, 9 figures, for associated movies see
http://www.tempolimit-lichtgeschwindigkeit.de/sectormodels1/sectormodels1.htm
Tidal dissipation in rotating giant planets
[Abridged] Tides may play an important role in determining the observed
distributions of mass, orbital period, and eccentricity of the extrasolar
planets. In addition, tidal interactions between giant planets in the solar
system and their moons are thought to be responsible for the orbital migration
of the satellites, leading to their capture into resonant configurations. We
treat the underlying fluid dynamical problem with the aim of determining the
efficiency of tidal dissipation in gaseous giant planets. In cases of interest,
the tidal forcing frequencies are comparable to the spin frequency of the
planet but small compared to its dynamical frequency. We therefore study the
linearized response of a slowly and possibly differentially rotating planet to
low-frequency tidal forcing. Convective regions of the planet support inertial
waves, while any radiative regions support generalized Hough waves. We present
illustrative numerical calculations of the tidal dissipation rate and argue
that inertial waves provide a natural avenue for efficient tidal dissipation in
most cases of interest. The resulting value of Q depends in a highly erratic
way on the forcing frequency, but we provide evidence that the relevant
frequency-averaged dissipation rate may be asymptotically independent of the
viscosity in the limit of small Ekman number. In short-period extrasolar
planets, if the stellar irradiation of the planet leads to the formation of a
radiative outer layer that supports generalized Hough modes, the tidal
dissipation rate can be enhanced through the excitation and damping of these
waves. These dissipative mechanisms offer a promising explanation of the
historical evolution and current state of the Galilean satellites as well as
the observed circularization of the orbits of short-period extrasolar planets.Comment: 74 pages, 12 figures, submitted to The Astrophysical Journa
Gravity Survey of the Serpent Mound Area, Southern Ohio
Author Institution: Department of Geology, The Ohio State University, Columbus, Ohio 43210Over most of south-central Ohio, the sedimentary Paleozoic rocks exposed at the surface are relatively flat-lying, but in the Serpent Mound area of Highland and Adams Counties they show a circular feature, four miles in diameter, in which the rocks are complexly faulted. This structure has not yet been satisfactorily explained; two of the hypotheses proposed to explain its origin are 1) that it was caused by a "cryptovolcanic" event and 2) that it is an "astrobleme," produced by the impact of a meteoritic body. These two possible mechanisms might be distinguished by the attendant differences in the density variations produced: the cryptovolcanic structure could be associated with large lateral variations in density at the level of the basement rocks, while the meteoritic impact could produce shatter zones and brecciated layers, and small reductions in density in the rock lying closer to the surface. A closely-spaced network of gravity stations extending beyond the limits of the surface expression of the ring structure shows no gravity anomaly pattern that can be related to the surface features. Supporters of the astrobleme hypothesis are more likely to find this evidence useful than are the cryptovolcanists
How to Find More Supernovae with Less Work: Object Classification Techniques for Difference Imaging
We present the results of applying new object classification techniques to
difference images in the context of the Nearby Supernova Factory supernova
search. Most current supernova searches subtract reference images from new
images, identify objects in these difference images, and apply simple threshold
cuts on parameters such as statistical significance, shape, and motion to
reject objects such as cosmic rays, asteroids, and subtraction artifacts.
Although most static objects subtract cleanly, even a very low false positive
detection rate can lead to hundreds of non-supernova candidates which must be
vetted by human inspection before triggering additional followup. In comparison
to simple threshold cuts, more sophisticated methods such as Boosted Decision
Trees, Random Forests, and Support Vector Machines provide dramatically better
object discrimination. At the Nearby Supernova Factory, we reduced the number
of non-supernova candidates by a factor of 10 while increasing our supernova
identification efficiency. Methods such as these will be crucial for
maintaining a reasonable false positive rate in the automated transient alert
pipelines of upcoming projects such as PanSTARRS and LSST.Comment: 25 pages; 6 figures; submitted to Ap
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