1,704 research outputs found
Coulomb scattering of quantum dipoles in QED
We calculate the total scattering cross-section of a dynamical quantum
electrically neutral dipole in QED of the infinitely heavy charge and of the
infinitely heavy dipole in the leading order in electromagnetic coupling
constant.Comment: 7 pages, no figure
Exploiting Query Structure and Document Structure to Improve Document Retrieval Effectiveness
In this paper we present a systematic analysis of document
retrieval using unstructured and structured queries within
the score region algebra (SRA) structured retrieval framework. The behavior of di®erent retrieval models, namely
Boolean, tf.idf, GPX, language models, and Okapi, is tested
using the transparent SRA framework in our three-level structured retrieval system called TIJAH. The retrieval models are implemented along four elementary retrieval aspects: element and term selection, element score computation, score combination, and score propagation.
The analysis is performed on a numerous experiments
evaluated on TREC and CLEF collections, using manually
generated unstructured and structured queries. Unstructured queries range from the short title queries to long title
+ description + narrative queries. For generating structured
queries we exploit the knowledge of the document structure
and the content used to semantically describe or classify
documents. We show that such structured information can
be utilized in retrieval engines to give more precise answers to user queries then when using unstructured queries
Damped Lyman-alpha absorption from a nearby Low Surface Brightness galaxy
Ground-based & HST images of the nearby galaxy SBS 1543+593 (z=0.009) show it
to be a Low Surface Brightness (LSB) galaxy with a central surface brightness
of mu_B(0)=23.2 mag/arcsec-2 and scale length 0.9 h-1 kpc, values typical for
the local LSB galaxy population. The galaxy lies directly in front of the QSO
HS 1543+5921 (z=0.807); an HST STIS spectrum of the quasar reveals a damped
Lyman-alpha (DLA) line at the redshift of the interloper with an HI column
density of log N(HI) = 20.35, as well as several low-ionization metal lines
with strengths similar to those found in the Milky Way interstellar medium. Our
data show that LSB galaxies are certainly able to produce the DLA lines seen at
higher redshift, and fuels the speculation that LSB galaxies are a major
contributor to that population of absorbers.Comment: Submitted to A
Two distance-regular graphs
We construct two families of distance-regular graphs, namely the subgraph of
the dual polar graph of type B_3(q) induced on the vertices far from a fixed
point, and the subgraph of the dual polar graph of type D_4(q) induced on the
vertices far from a fixed edge. The latter is the extended bipartite double of
the former
Calculation of 1/m^3 terms in the total semileptonic width of D mesons.
We calculate the 1/ corrections in the inclusive semileptonic widths
of mesons. We show that these are due to the novel penguin type operators
that appear at this level in the transition operator. Taking into account the
nonperturbative corrections leads to the predicted value of the semileptonic
width significantly lower than the experimental value. The worsen the
situation or at the very least, within uncertainty, give small contribution. We
indicate possible ways out. It seems most probable that violations of duality
are noticeable in the energy range characteristic to the inclusive decays in
the charm family. Theoretically these deviations are related to divergence of
the high-order terms in the power expansion in the inverse heavy quark mass.Comment: Final version accepted for publication in Physical Review D (19
pages, 5 figures appended as two PS files at the end of the LATEX file
Vague element selection and query rewriting for XML retrieval
In this paper we present the extension of our prototype three-level database system (TIJAH) developed for struc-tured information retrieval. The extension is aimed at mod-eling vague search on XML elements. All three levels (con-ceptual, logical, and physical) of the TIJAH system are enhanced to support vague search concepts. The vague search is implemented as vague selection of XML elements using XML element name expansion lists and rewriting tech-niques. We test the performance of retrieval models us-ing automatically generated expansion lists and compared them with models that use manual ones. The goal is to find the best approach for structured information retrieval with vague structural constraints on element names expressed in the query. 1
Triggering the Formation of Halo Globular Clusters with Galaxy Outflows
We investigate the interactions of high-redshift galaxy outflows with
low-mass virialized (Tvir < 10,000K) clouds of primordial composition. While
atomic cooling allows star formation in larger primordial objects, such
"minihalos" are generally unable to form stars by themselves. However, the
large population of high-redshift starburst galaxies may have induced
widespread star formation in these objects, via shocks that caused intense
cooling both through nonequilibrium H2 formation and metal-line emission. Using
a simple analytic model, we show that the resulting star clusters naturally
reproduce three key features of the observed population of halo globular
clusters (GCs). First, the 10,000 K maximum virial temperature corresponds to
the ~ 10^6 solar mass upper limit on the stellar mass of GCs. Secondly, the
momentum imparted in such interactions is sufficient to strip the gas from its
associated dark matter halo, explaining why GCs do not reside in dark matter
potential wells. Finally, the mixing of ejected metals into the primordial gas
is able to explain the ~ 0.1 dex homogeneity of stellar metallicities within a
given GC, while at the same time allowing for a large spread in metallicity
between different clusters. To study this possibility in detail, we use a
simple 1D numerical model of turbulence transport to simulate mixing in
cloud-outflow interactions. We find that as the shock shears across the side of
the cloud, Kelvin-Helmholtz instabilities arise, which cause mixing of enriched
material into > 20% of the cloud. Such estimates ignore the likely presence of
large-scale vortices, however, which would further enhance turbulence
generation. Thus quantitative mixing predictions must await more detailed
numerical studies.Comment: 21 pages, 11 figures, Apj in pres
A Structural and Dynamical Study of Late-Type, Edge-On Galaxies: I. Sample Selection and Imaging Data
We present optical (B & R) and infrared (K_s) images and photometry for a
sample of 49 extremely late-type, edge-on disk galaxies selected from the Flat
Galaxy Catalog of Karenchentsev et al. (1993). Our sample was selected to
include galaxies with particularly large axial ratios, increading the
likelihood that the galaxies in the sample are truly edge-on. We have also
concentrated the sample on galaxies with low apparent surface brightness, in
order to increase the representation of intrinisically low surface brightness
galaxies. Finally, the sample was chosen to have no apprarent bulges or optical
warps so that the galaxies represent undisturbed, ``pure disk'' systems. The
resulting sample forms the basis for a much larger spectroscopic study designed
to place constraints on the physical quantities and processes which shape disk
galaxies. The imaging data presented in this paper has been painstakingly
reduced and calibrated to allow accurate surface photometry of features as
faint as 30 mag/sqr-arcsec in B and 29 mag/sqr-arcsec in R on scales larger
than 10 arcsec. Due to limitations in sky subtraction and flat fielding, the
infrared data can reach only to 22.5 mag/sqr-arcsec in K_s on comparable
scales. As part of this work, we have developed a new method for quantifying
the reliability of surface photometry, which provides useful diagnostics for
the presence of scattered light, optical emission from infrared cirrus, and
other sources of non-uniform sky backgrounds.Comment: scheduled to appear in the Astronomical Journal, LaTeX, 36 pages
including 7 pages of figures (fig 1-2,4). A low resolution version of Figure
3 is included in JPEG format; contours are seriously degraded. A full
resolution Postscript version of Figure 3 (10.6Mb,gzipped) is available
through anonymous ftp at
ftp://ftp.astro.washington.edu/pub/users/jd/FGC/dalcanton.f3.ps.g
From Participation to Interruption : Toward an ethics of stakeholder engagement, participation and partnership in corporate social responsibility and responsible innovation
Contrary to the tendency to harmony, consensus and alignment among stakeholders in most of the literature on participation and partnership in corporate social responsibility (CSR) and responsible innovation (RI) practices, in this chapter we ask which concept of participation and partnership is able to account for stakeholder engagement while acknowledging and appreciating their fundamentally different judgements, value frames and viewpoints. To this end, we reflect on a non-reductive and ethical approach to stakeholder engagement, collaboration and partnership, inspired by the philosophy of Emmanuel Levinas. We contrast a cognitive approach with an ethical approach to stakeholder engagement, collaboration and partnership, and explore four characteristics of this ethical approach. Based on the ethical approach to stakeholder engagement, collaboration and partnership, we also provide a three-stage framework for partnership formation in CSR and RI practices
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