4,023 research outputs found
HIIphot: Automated Photometry of HII Regions Applied to M51
We have developed a robust, automated method, hereafter designated HIIphot,
which enables accurate photometric characterization of HII regions while
permitting genuine adaptivity to irregular source morphology. HIIphot utilizes
object-recognition techniques to make a first guess at the shapes of all
sources then allows for departure from such idealized ``seeds'' through an
iterative growing procedure. Photometric corrections for spatially coincident
diffuse emission are derived from a low-order surface fit to the background
after exclusion of all detected sources. We present results for the
well-studied, nearby spiral M51 in which 1229 HII regions are detected above
the 5-sigma level. A simple, weighted power-law fit to the measured H-alpha
luminosity function (HII LF) above log L_H-alpha = 37.6 gives alpha =
-1.75+/-0.06, despite a conspicuous break in the HII LF observed near L_H-alpha
= 10^38.9. Our best- fit slope is marginally steeper than measured by Rand
(1992), perhaps reflecting our increased sensitivity at low luminosities and to
notably diffuse objects. HII regions located in interarm gaps are
preferentially less luminous than counterparts which constitute M51's
grand-design spiral arms and are best fit with a power-law slope of alpha =
-1.96+/-0.15. We assign arm/interarm status for HII regions based upon the
varying surface brightness of diffuse emission as a function of position
throughout the image. Using our measurement of the integrated flux contributed
by resolved HII regions in M51, we estimate the diffuse fraction to be
approximately 0.45 -- in agreement with the determination of Greenawalt et al.
(1998). Automated processing of degraded datasets is undertaken to gauge
systematic effects associated with limiting spatial resolution and sensitivity.Comment: 41 pages, 14 figures, Postscript version with high-resolution figures
at ftp://ftp.aoc.nrao.edu/staff/dthilker/preprint
Asymptotic information leakage under one-try attacks
We study the asymptotic behaviour of (a) information leakage and (b) adversary’s error probability in information hiding systems modelled as noisy channels. Specifically, we assume the attacker can make a single guess after observing n independent executions of the system, throughout which the secret information is kept fixed. We show that the asymptotic behaviour of quantities (a) and (b) can be determined in a simple way from the channel matrix. Moreover, simple and tight bounds on them as functions of n show that the convergence is exponential. We also discuss feasible methods to evaluate the rate of convergence. Our results cover both the Bayesian case, where a prior probability distribution on the secrets is assumed known to the attacker, and the maximum-likelihood case, where the attacker does not know such distribution. In the Bayesian case, we identify the distributions that maximize the leakage. We consider both the min-entropy setting studied by Smith and the additive form recently proposed by Braun et al., and show the two forms do agree asymptotically. Next, we extend these results to a more sophisticated eavesdropping scenario, where the attacker can perform a (noisy) observation at each state of the computation and the systems are modelled as hidden Markov models
Exploring Processing of Affective Lexical Semantics in the Visual and Auditory Modalities
While research on affective word processing in adults witnesses increasing
interest, the present paper looks at another group of participants that have
been neglected so far: pupils (age range: 6–12 years). Introducing a variant
of the Berlin Affective Wordlist (BAWL) especially adapted for children of
that age group, the “kidBAWL,” we examined to what extent pupils process
affective lexical semantics similarly to adults. In three experiments using
rating and valence decision tasks in both the visual and auditory modality, it
was established that children show the two ubiquitous phenomena observed in
adults with emotional word material: the asymmetric U-shaped function relating
valence to arousal ratings, and the inversely U-shaped function relating
response times to valence decision latencies. The results for both modalities
show large structural similarities between pupil and adult data (taken from
previous studies) indicating that in the present age range, the affective
lexicon and the dynamic interplay between language and emotion is already
well-developed. Differential effects show that younger children tend to choose
less extreme ratings than older children and that rating latencies decrease
with age. Overall, our study should help to develop more realistic models of
word recognition and reading that include affective processes and offer a
methodology for exploring the roots of pleasant literary experiences and ludic
reading
A Half-Megasecond Chandra Observation of the Oxygen-Rich Supernova Remnant G292.0+1.8
We report on our initial analysis of a deep 510 ks observation of the
Galactic oxygen-rich supernova remnant (SNR) G292.0+1.8 with the {\it Chandra
X-ray Observatory}. Our new {\it Chandra} ACIS-I observation has a larger field
of view and an order of magnitude deeper exposure than the previous {\it
Chandra} observation, which allows us to cover the entire SNR and to detect new
metal-rich ejecta features. We find a highly non-uniform distribution of
thermodynamic conditions of the X-ray emitting hot gas that correlates well
with the optical [O {\small III}] emission, suggesting the possibility that the
originating supernova explosion of G292.0+1.8 was itself asymmetric. We also
reveal spectacular substructures of a torus, a jet, and an extended central
compact nebula all associated with the embedded pulsar J11245916.Comment: 10 pages including 1 table and 2 figures (both figures are color),
accepted by ApJ Letter
Tonoplast Sugar Transporters (SbTSTs) Putatively Control Sucrose Accumulation in Sweet Sorghum Stems
Carbohydrates are differentially partitioned in sweet versus grain sorghums. While the latter preferentially accumulate starch in the grain, the former primarily store large amounts of sucrose in the stem. Previous work determined that neither sucrose metabolizing enzymes nor changes in Sucrose transporter (SUT) gene expression accounted for the carbohydrate partitioning differences. Recently, 2 additional classes of sucrose transport proteins, Tonoplast Sugar Transporters (TSTs) and SWEETs, were identified; thus, we examined whether their expression tracked sucrose accumulation in sweet sorghum stems. We determined 2 TSTs were differentially expressed in sweet vs. grain sorghum stems, likely underlying the massive difference in sucrose accumulation. A model illustrating potential roles for different classes of sugar transport proteins in sorghum sugar partitioning is discussed
Tonoplast Sugar Transporters (SbTSTs) Putatively Control Sucrose Accumulation in Sweet Sorghum Stems
Carbohydrates are differentially partitioned in sweet versus grain sorghums. While the latter preferentially accumulate starch in the grain, the former primarily store large amounts of sucrose in the stem. Previous work determined that neither sucrose metabolizing enzymes nor changes in Sucrose transporter (SUT) gene expression accounted for the carbohydrate partitioning differences. Recently, 2 additional classes of sucrose transport proteins, Tonoplast Sugar Transporters (TSTs) and SWEETs, were identified; thus, we examined whether their expression tracked sucrose accumulation in sweet sorghum stems. We determined 2 TSTs were differentially expressed in sweet vs. grain sorghum stems, likely underlying the massive difference in sucrose accumulation. A model illustrating potential roles for different classes of sugar transport proteins in sorghum sugar partitioning is discussed
Presentations of Wess-Zumino-Witten Fusion Rings
The fusion rings of Wess-Zumino-Witten models are re-examined. Attention is
drawn to the difference between fusion rings over Z (which are often of greater
importance in applications) and fusion algebras over C. Complete proofs are
given characterising the fusion algebras (over C) of the SU(r+1) and Sp(2r)
models in terms of the fusion potentials, and it is shown that the analagous
potentials cannot describe the fusion algebras of the other models. This
explains why no other representation-theoretic fusion potentials have been
found.
Instead, explicit generators are then constructed for general WZW fusion
rings (over Z). The Jacobi-Trudy identity and its Sp(2r) analogue are used to
derive the known fusion potentials. This formalism is then extended to the WZW
models over the spin groups of odd rank, and explicit presentations of the
corresponding fusion rings are given. The analogues of the Jacobi-Trudy
identity for the spinor representations (for all ranks) are derived for this
purpose, and may be of independent interest.Comment: 32 pages, 3 figures, added references, minor additions to text. To be
published in Rev. Math. Phy
Study Abroad for Preservice Teachers: A Critical Literature Review with Considerations for Research and Practice
This article applies a postcolonial analytical framework to critically review empirical literature on study abroad for preservice teachers (PSTs). Our systematic search of scholarly databases identified 47 empirical studies of study abroad programs for PSTs in the 2000-2019 time period. Our analysis of these 47 studies is driven by the objectives to (a) understand geographic patterns in study abroad of PSTs, (b) examine the topics, conceptual frames, and implementation of study abroad of PSTs, (c) explore how study abroad for PSTs is currently being conceptualized and studied, and (d) critically analyze how these geographic patterns and study abroad programmatic and research trends are situated within broader North-South relations (Major & Santoro, 2016). Using geovisualizations we illustrate patterns in the countries of origin of PSTs and the countries in which they study abroad. We find that the majority of PSTs are from the United States and are traveling to countries in the North. When examining the content and programming of study abroad, we find many programs focus on cultivating professional skills for PSTs such as language fluency for foreign language teachers and intercultural competence. After establishing these patterns, we pay particular attention to the 23 studies in our sample that examine PSTs traveling to regions in the Global South. We conclude by offering considerations for future research and highlighting practices for program design that encourage PSTs to reflect upon global power differentials and complexities
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