1,600 research outputs found
The Isgur-Wise function in a relativistic model for system
We use the Dirac equation with a ``(asymptotically free) Coulomb + (Lorentz
scalar) linear '' potential to estimate the light quark wavefunction for mesons in the limit . We use these wavefunctions to
calculate the Isgur-Wise function for orbital and radial
ground states in the phenomenologically interesting range . We find a simple expression for the zero-recoil slope, , where is the energy eigenvalue
of the light quark, which can be identified with the parameter
of the Heavy Quark Effective Theory. This result implies an upper bound of
for the slope . Also, because for a very light quark the size of the meson is determined mainly by the
``confining'' term in the potential , the shape of
is seen to be mostly sensitive to the dimensionless
ratio . We present results for the ranges of
parameters , and
light quark masses and compare to existing
experimental data and other theoretical estimates. Fits to the data give:
,
and [ARGUS
'93]; , and
[CLEO '93]; ${\bar\Lambda_{u,d}}^2/Comment: 22 pages, Latex, 4 figures (not included) available by fax or via
email upon reques
Using Part-of-Speech N-grams for Sensitive-Text Classification
Freedom of Information legislations in many western democ-
racies, including the United Kingdom (UK) and the United
States of America (USA), state that citizens have typically
the right to access government documents. However, certain
sensitive information is exempt from release into the pub-
lic domain. For example, in the UK, FOIA Exemption 27
(International Relations) excludes the release of Informa-
tion that might damage the interests of the UK abroad.
Therefore, the process of reviewing government documents
for sensitivity is essential to determine if a document must
be redacted before it is archived, or closed until the infor-
mation is no longer sensitive. With the increased volume of
digital government documents in recent years, there is a need
for new tools to assist the digital sensitivity review process.
Therefore, in this paper we propose an automatic approach
for identifying sensitive text in documents by measuring the
amount of sensitivity in sequences of text. Using government
documents reviewed by trained sensitivity reviewers, we fo-
cus on an aspect of FOIA Exemption 27 which can have a
major impact on international relations, namely information
supplied in con�dence. We show that our approach leads to
markedly increased recall of sensitive text, while achieving
a very high level of precision, when compared to a baseline
that has been shown to be e�ective at identifying sensitive
text in other domains
Changing Ionization Conditions in SDSS Galaxies with AGN as a Function of Environment from Pairs to Clusters
We study how AGN activity changes across environments from galaxy pairs to
clusters using galaxies with from the Sloan Digital Sky
Survey (SDSS). Using a refined technique, we apply a continuous measure of AGN
activity, characteristic of the ionization state of the narrow-line emitting
gas. Changes in key emission-line ratios ([NII]/H,
[OIII]/H) between different samples allow us to disentangle
different environmental effects while removing contamination. We confirm that
galaxy interactions enhance AGN activity. However, conditions in the central
regions of clusters are inhospitable for AGN activity even if galaxies are in
pairs. These results can be explained through models of gas dynamics in which
pair interactions stimulate the transfer of gas to the nucleus and clusters
suppress gas availability for accretion onto the central black hole.Comment: Accepted for publication in Ap
Recovering 3D structural properties of galaxies from SDSS-like photometry
Because of the 3D nature of galaxies, an algorithm for constructing spatial
density distribution models of galaxies on the basis of galaxy images has many
advantages over surface density distribution approximations. We present a
method for deriving spatial structure and overall parameters of galaxies from
images and estimate its accuracy and derived parameter degeneracies on a sample
of idealised model galaxies. The test galaxies consist of a disc-like component
and a spheroidal component with varying proportions and properties. Both
components are assumed to be axially symmetric and coplanar. We simulate these
test galaxies as if observed in the SDSS project through ugriz filters, thus
gaining a set of realistically imperfect images of galaxies with known
intrinsic properties. These artificial SDSS galaxies were thereafter remodelled
by approximating the surface brightness distribution with a 2D projection of a
bulge+disc spatial distribution model and the restored parameters were compared
to the initial ones. Down to the r-band limiting magnitude 18, errors of the
restored integral luminosities and colour indices remain within 0.05 mag and
errors of the luminosities of individual components within 0.2 mag. Accuracy of
the restored bulge-to-disc ratios (B/D) is within 40% in most cases, and
becomes worse for galaxies with low B/D, but the general balance between bulges
and discs is not shifted systematically. Assuming that the intrinsic disc axial
ratio is < 0.3, the inclination angles can be estimated with errors < 5deg for
most of the galaxies with B/D < 2 and with errors < 15deg up to B/D = 6. Errors
of the recovered sizes of the galactic components are below 10% in most cases.
In general, models of disc components are more accurate than models of
spheroidal components for geometrical reasons.Comment: 15 pages, 13 figures, accepted for publication in RA
The KMOS^3D Survey: design, first results, and the evolution of galaxy kinematics from 0.7<z<2.7
We present the KMOS^3D survey, a new integral field survey of over 600
galaxies at 0.7<z<2.7 using KMOS at the Very Large Telescope (VLT). The KMOS^3D
survey utilizes synergies with multi-wavelength ground and space-based surveys
to trace the evolution of spatially-resolved kinematics and star formation from
a homogeneous sample over 5 Gyrs of cosmic history. Targets, drawn from a
mass-selected parent sample from the 3D-HST survey, cover the star
formation-stellar mass () and rest-frame planes uniformly. We
describe the selection of targets, the observations, and the data reduction. In
the first year of data we detect Halpha emission in 191
Msun galaxies at z=0.7-1.1 and z=1.9-2.7. In
the current sample 83% of the resolved galaxies are rotation-dominated,
determined from a continuous velocity gradient and , implying
that the star-forming 'main sequence' (MS) is primarily composed of rotating
galaxies at both redshift regimes. When considering additional stricter
criteria, the Halpha kinematic maps indicate at least ~70% of the resolved
galaxies are disk-like systems. Our high-quality KMOS data confirm the elevated
velocity dispersions reported in previous IFS studies at z>0.7. For
rotation-dominated disks, the average intrinsic velocity dispersion decreases
by a factor of two from 50 km/s at z~2.3 to 25 km/s at z~0.9 while the
rotational velocities at the two redshifts are comparable. Combined with
existing results spanning z~0-3, disk velocity dispersions follow an
approximate (1+z) evolution that is consistent with the dependence of velocity
dispersion on gas fractions predicted by marginally-stable disk theory.Comment: 20 pages, 11 figures, 1 Appendix; Accepted to ApJ November 2
Quenched QCD at finite density
Simulations of quenched at relatively small but {\it nonzero} chemical
potential on lattices indicate that the nucleon
screening mass decreases linearly as increases predicting a critical
chemical potential of one third the nucleon mass, , by extrapolation.
The meson spectrum does not change as increases over the same range, from
zero to . Past studies of quenched lattice QCD have suggested that
there is phase transition at . We provide alternative
explanations for these results, and find a number of technical reasons why
standard lattice simulation techniques suffer from greatly enhanced
fluctuations and finite size effects for ranging from to
. We find evidence for such problems in our simulations, and suggest
that they can be surmounted by improved measurement techniques.Comment: 23 pages, Revte
Compact to extended Lyman- emitters in MAGPI: strong blue peak emission at
We report the discovery of three double-peaked Lyman- emitters (LAEs)
exhibiting strong blue peak emission at 2.9 4.8, in the
VLT/MUSE data obtained as part of the Middle Ages Galaxy Properties with
Integral Field Spectroscopy (MAGPI) survey. These strong blue peak systems
provide a unique window into the scattering of Lyman- photons by
neutral hydrogen (HI), suggesting gas inflows along the line-of-sight and low
HI column density. Two of them at and are spatially extended
halos with their core regions clearly exhibiting stronger blue peak emissions
than the red peak. However, spatial variations in the peak ratio and peak
separation are evident over kpc () and kpc
() regions in these extended halos. Notably, these systems do not fall
in the regime of Lyman- blobs or nebulae. To the best of our knowledge,
such a Lyman- halo with a dominant blue core has not been observed
previously. In contrast, the LAE at is a compact system spanning a
kpc region and stands as the highest-redshift strong blue peak
emitter ever detected. The peak separation of the bright cores in these three
systems ranges from to km/s. The observed
overall trend of decreasing peak separation with increasing radius is supposed
to be controlled by HI column density and gas covering fraction. Based on
various estimations, in contrast to the compact LAE, our halos are found to be
good candidates for LyC leakers. These findings shed light on the complex
interplay between Lyman- emission, gas kinematics, and ionising
radiation properties, offering valuable insights into the evolution and nature
of high-redshift galaxies.Comment: 2 Figures, 1 Table, accepted for A&A Letter
Nonlinear spectral calculus and super-expanders
Nonlinear spectral gaps with respect to uniformly convex normed spaces are
shown to satisfy a spectral calculus inequality that establishes their decay
along Cesaro averages. Nonlinear spectral gaps of graphs are also shown to
behave sub-multiplicatively under zigzag products. These results yield a
combinatorial construction of super-expanders, i.e., a sequence of 3-regular
graphs that does not admit a coarse embedding into any uniformly convex normed
space.Comment: Typos fixed based on referee comments. Some of the results of this
paper were announced in arXiv:0910.2041. The corresponding parts of
arXiv:0910.2041 are subsumed by the current pape
What explains the uneven take-up of ISO 14001 at the global level?: a panel-data analysis
Since its release in the mid-1990s, close to 37 000 facilities have been certified to ISO 14001, the international voluntary standard for environmental management systems. Yet, despite claims that the standard can be readily adapted to very different corporate and geographic settings, its take-up has been highly geographically variable. This paper contributes to a growing body of work concerned with explaining the uneven diffusion of ISO 14001 at the global level. Drawing from the existing theoretical and empirical literature we develop a series of hypotheses about how various economic, market, and regulatory factors influence the national count of ISO 14001 certifications. These hypotheses are then tested using econometric estimation techniques with data for a panel of 142 developed and developing countries. We find that per capita ISO 14001 counts are positively correlated with income per capita, stock of foreign direct investment, exports of goods and services to Europe and Japan, and pressure from civil society. Conversely, productivity and levels of state intervention are negatively correlated. The paper finishes by offering a number of recommendations to policymakers concerned with accelerating the diffusion of voluntary environmental standards
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