8,077 research outputs found
Nuclear gas dynamics in Arp 220 - sub-kiloparsec scale atomic hydrogen disks
We present new, high angular resolution (~0.22") MERLIN observations of
neutral hydrogen (HI) absorption and 21-cm radio continuum emission across the
central ~900 parsecs of the ultraluminous infrared galaxy, Arp220. Spatially
resolved HI absorption is detected against the morphologically complex and
extended 21-cm radio continuum emission, consistent with two counterrotating
disks of neutral hydrogen, with a small bridge of gas connecting the two.
We propose a merger model in which the two nuclei represent the galaxy cores
which have survived the initial encounter and are now in the final stages of
merging, similar to conclusions drawn from previous CO studies (Sakamoto,
Scoville & Yun 1999). However, we suggest that instead of being coplanar with
the main CO disk (in which the eastern nucleus is embedded), the western
nucleus lies above it and, as suggested by bridge of HI connecting the two
nuclei, will soon complete its final merger with the main disk. We suggest that
the collection of radio supernovae (RSN) detected in VLBA studies in the more
compact western nucleus represent the second burst of star formation associated
with this final merger stage and that free-free absorption due to ionised gas
in the bulge-like component can account for the observed RSN distribution.
(Abridged)Comment: 26 pages including 8 figures and 1 table; accepted for publication in
Ap
Chandra Observations of Extended X-ray Emission in Arp 220
We resolve the extended X-ray emission from the prototypical ultraluminous
infrared galaxy Arp 220. Extended, faint edge-brightened, soft X-ray lobes
outside the optical galaxy are observed to a distance of 10 to 15 kpc on each
side of the nuclear region. Bright plumes inside the optical isophotes coincide
with the optical line emission and extend 11 kpc from end to end across the
nucleus. The data for the plumes cannot be fit by a single temperature plasma,
and display a range of temperatures from 0.2 to 1 keV. The plumes emerge from
bright, diffuse circumnuclear emission in the inner 3 kpc centered on the
Halpha peak, which is displaced from the radio nuclei. There is a close
morphological correspondence between the Halpha and soft X-ray emission on all
spatial scales. We interpret the plumes as a starburst-driven superwind, and
discuss two interpretations of the emission from the lobes in the context of
simulations of the merger dynamics of Arp 220.Comment: Accepted for publication in ApJ; see also astro-ph/0208477 (Paper 1
Excitations in confined helium
We design models for helium in matrices like aerogel, Vycor or Geltech from a
manifestly microscopic point of view. For that purpose, we calculate the
dynamic structure function of 4He on Si substrates and between two Si walls as
a function of energy, momentum transfer, and the scattering angle. The
angle--averaged results are in good agreement with the neutron scattering data;
the remaining differences can be attributed to the simplified model used here
for the complex pore structure of the materials. A focus of the present work is
the detailed identification of coexisting layer modes and bulk--like
excitations, and, in the case of thick films, ripplon excitations. Involving
essentially two--dimensional motion of atoms, the layer modes are sensitive to
the scattering angle.Comment: Phys. Rev. B (2003, in press
Quantum sticking, scattering and transmission of 4He atoms from superfluid 4He surfaces
We develop a microscopic theory of the scattering, transmission, and sticking
of 4He atoms impinging on a superfluid 4He slab at near normal incidence, and
inelastic neutron scattering from the slab. The theory includes coupling
between different modes and allows for inelastic processes. We find a number of
essential aspects that must be observed in a physically meaningful and reliable
theory of atom transmission and scattering; all are connected with
multiparticle scattering, particularly the possibility of energy loss. These
processes are (a) the coupling to low-lying (surface) excitations
(ripplons/third sound) which is manifested in a finite imaginary part of the
self energy, and (b) the reduction of the strength of the excitation in the
maxon/roton region
Over the River and Through the Woods
Twenty-eight year old Nick, an Italian single guy from New Jersey, gets the professional career offer of a lifetime … on the opposite coast from his family. Nick’s traditional Italian grandparents, Frank and Aida and Nunzio and Emma, do their level best to keep their beloved grandson home with them on the East Coast, while a job as a marketing executive calls him to Seattle. Will Nick abandon family to pursue a glamorous and exciting career move, the opportunity he has hoped for? His grandparents wonder if he would stay in New Jersey if he fell in love with a hometown girl. And so the lovely — and single — Caitlin O’Hare is brought in as bait. But will their scheme work? This comedy by contemporary playwright Joe DiPietro is sure to resonate with audience members from university students (soon to face the same career decisions themselves) to extended family members (who have either wrestled with these same choices themselves or have struggled to release those they love to pursue their own dreams). Themes of family, professional goals, tradition, and romance are all presented in a way that reminds us to celebrate the everyday gifts of our lives.https://digitalcommons.cedarville.edu/theatre_productions/1008/thumbnail.jp
Probabilistic Model Checking for Energy Analysis in Software Product Lines
In a software product line (SPL), a collection of software products is
defined by their commonalities in terms of features rather than explicitly
specifying all products one-by-one. Several verification techniques were
adapted to establish temporal properties of SPLs. Symbolic and family-based
model checking have been proven to be successful for tackling the combinatorial
blow-up arising when reasoning about several feature combinations. However,
most formal verification approaches for SPLs presented in the literature focus
on the static SPLs, where the features of a product are fixed and cannot be
changed during runtime. This is in contrast to dynamic SPLs, allowing to adapt
feature combinations of a product dynamically after deployment. The main
contribution of the paper is a compositional modeling framework for dynamic
SPLs, which supports probabilistic and nondeterministic choices and allows for
quantitative analysis. We specify the feature changes during runtime within an
automata-based coordination component, enabling to reason over strategies how
to trigger dynamic feature changes for optimizing various quantitative
objectives, e.g., energy or monetary costs and reliability. For our framework
there is a natural and conceptually simple translation into the input language
of the prominent probabilistic model checker PRISM. This facilitates the
application of PRISM's powerful symbolic engine to the operational behavior of
dynamic SPLs and their family-based analysis against various quantitative
queries. We demonstrate feasibility of our approach by a case study issuing an
energy-aware bonding network device.Comment: 14 pages, 11 figure
How to Complete an Interactive Configuration Process?
When configuring customizable software, it is useful to provide interactive
tool-support that ensures that the configuration does not breach given
constraints.
But, when is a configuration complete and how can the tool help the user to
complete it?
We formalize this problem and relate it to concepts from non-monotonic
reasoning well researched in Artificial Intelligence. The results are
interesting for both practitioners and theoreticians. Practitioners will find a
technique facilitating an interactive configuration process and experiments
supporting feasibility of the approach. Theoreticians will find links between
well-known formal concepts and a concrete practical application.Comment: to appear in SOFSEM 201
Submillimeter Observations of the Ultraluminous BAL Quasar APM 08279+5255
With an inferred bolometric luminosity of 5\times10^{15}{\rm \lsun}, the
recently identified z=3.87, broad absorption line quasar APM 08279+5255 is
apparently the most luminous object currently known. As half of its prodigious
emission occurs in the infrared, APM 08279+5255 also represents the most
extreme example of an Ultraluminous Infrared Galaxy. Here, we present new
submillimeter observations of this phenomenal object; while indicating that a
vast quantity of dust is present, these data prove to be incompatible with
current models of emission mechanisms and reprocessing in ultraluminous
systems. The influence of gravitational lensing upon these models is considered
and we find that while the emission from the central continuum emitting region
may be significantly enhanced, lensing induced magnification cannot easily
reconcile the models with observations. We conclude that further modeling,
including the effects of any differential magnification is required to explain
the observed emission from APM 08279+5255.Comment: 12 Pages with Two figures. Accepted for publication in the
Astrophysical Journal Letter
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