1,864 research outputs found
An Extraordinary Scattered Broad Emission Line in a Type 2 QSO
An infrared-selected, narrow-line QSO has been found to exhibit an
extraordinarily broad Halpha emission line in polarized light. Both the extreme
width (35,000 km/sec full-width at zero intensity) and 3,000 km/sec redshift of
the line centroid with respect to the systemic velocity suggest emission in a
deep gravitational potential. An extremely red polarized continuum and partial
scattering of the narrow lines at a position angle common to the broad-line
emission imply extensive obscuration, with few unimpeded lines of sight to the
nucleus.Comment: 4 pages, 1 figure, to appear in the Astrophysical Journal Letter
Flavour symmetry breaking in the kaon parton distribution amplitude
We compute the kaon's valence-quark (twist-two parton) distribution amplitude
(PDA) by projecting its Poincare'-covariant Bethe-Salpeter wave-function onto
the light-front. At a scale \zeta=2GeV, the PDA is a broad, concave and
asymmetric function, whose peak is shifted 12-16% away from its position in
QCD's conformal limit. These features are a clear expression of
SU(3)-flavour-symmetry breaking. They show that the heavier quark in the kaon
carries more of the bound-state's momentum than the lighter quark and also that
emergent phenomena in QCD modulate the magnitude of flavour-symmetry breaking:
it is markedly smaller than one might expect based on the difference between
light-quark current masses. Our results add to a body of evidence which
indicates that at any energy scale accessible with existing or foreseeable
facilities, a reliable guide to the interpretation of experiment requires the
use of such nonperturbatively broadened PDAs in leading-order, leading-twist
formulae for hard exclusive processes instead of the asymptotic PDA associated
with QCD's conformal limit. We illustrate this via the ratio of kaon and pion
electromagnetic form factors: using our nonperturbative PDAs in the appropriate
formulae, at spacelike-, which compares
satisfactorily with the value of inferred in annihilation
at .Comment: 7 pages, 2 figures, 3 table
Impact of the developmental appropriateness of teacher guidance strategies on kindergarten childrenâs interpersonal relations
This initial study explored the social behaviors of kindergarten children in two classrooms (one developmentally appropriate, one developmentally inappropriate) where the teacher used either positive or negative guidance strategies. Six pairs of kindergartners-three dyads (boy-boy, girl-girl, boy-girl) from a classroom in which the teacher used positive guidance strategies and three from a classroom where the teacher used negative guidance strategies-were observed while playing in a researcher-designed play center. Observations over a three-month period revealed an increase in positive social behaviors among children from the positive guidance classroom and a decrease in positive social behaviors among children from the negative guidance classroom. Implications are discussed. © 2007 by the Association for Childhood Education International
Elastic and transition form factors of the \Delta(1232)
Predictions obtained with a confining, symmetry-preserving treatment of a
vector-vector contact interaction at leading-order in a widely used truncation
of QCD's Dyson-Schwinger equations are presented for \Delta and \Omega baryon
elastic form factors and the \gamma N -> \Delta transition form factors. This
simple framework produces results that are practically indistinguishable from
the best otherwise available, an outcome which highlights that the key to
describing many features of baryons and unifying them with the properties of
mesons is a veracious expression of dynamical chiral symmetry breaking in the
hadron bound-state problem. The following specific results are of particular
interest. The \Delta elastic form factors are very sensitive to m_\Delta.
Hence, given that the parameters which define extant simulations of
lattice-regularised QCD produce \Delta-resonance masses that are very large,
the form factors obtained therewith are a poor guide to properties of the
\Delta(1232). Considering the \Delta-baryon's quadrupole moment, whilst all
computations produce a negative value, the conflict between theoretical
predictions entails that it is currently impossible to reach a sound conclusion
on the nature of the \Delta-baryon's deformation in the infinite momentum
frame. Results for analogous properties of the \Omega baryon are less
contentious. In connection with the N->\Delta transition, the Ash-convention
magnetic transition form factor falls faster than the neutron's magnetic form
factor and nonzero values for the associated quadrupole ratios reveal the
impact of quark orbital angular momentum within the nucleon and \Delta; and,
furthermore, these quadrupole ratios do slowly approach their anticipated
asymptotic limits.Comment: 30 pages, 10 figures, 5 table
Optical Spectropolarimetry of Quasi-Stellar Objects Discovered by the Two-Micron All Sky Survey
Highly polarized QSOs discovered in the Two-Micron All Sky Survey (2MASS)
have been observed to determine the source(s) of optical polarization in this
near-infrared color-selected sample. Broad emission lines are observed in the
polarized flux spectra of most objects, and the polarization of the lines is at
about the same level and position angle as the continuum. Generally, the
continuum is bluer and the broad-line Balmer decrement is smaller in polarized
light than for the spectrum of total flux. Narrow emission lines are much less
polarized than the broad lines and continuum for all polarized objects. These
properties favor scattering by material close to a partially obscured and
reddened active nucleus, but exterior to the regions producing the broad-line
emission, as the source of polarized flux in 2MASS QSOs. The largely
unpolarized narrow-line features require that the electrons or dust polarizing
the light be located at distances from the nucleus not much greater than the
extent of the narrow emission-line region. In addition to known
high-polarization objects, four 2MASS QSOs with AGN spectral types of 1.9 and 2
were observed to search for hidden broad emission-line regions. Broad lines
were detected in polarized light for two of these objects, and the polarizing
mechanism appears to be the same for these objects as for the highly polarized
QSOs in the sample that readily show broad emission lines in their spectra. The
observations also show that starlight from the host galaxy contributes a
significant amount of optical flux, especially for the narrow-line objects, and
support the suggestion that many 2MASS QSOs are measured to have low
polarization simply because of dilution of the polarized AGN light by the host
galaxy.Comment: 27 pages; 3 tables; 8 figures; Accepted for publication in The
Astrophysical Journal (Part 1
Spatial and visual discrimination reversals in adult and geriatric rats exposed during gestation to methylmercury and nâ3 polyunsaturated fatty acids
Fish contain essential long chain polyunsaturated fatty acids (PUFAs), particularly docosahexaenoic acid (DHA), an omega-3 (or n-3) PUFA, but are also the main source of exposure to methylmercury (MeHg), a potent developmental neurotoxicant. Since n-3 PUFAs support neural development and function, benefits deriving from a diet rich in n-3s have been hypothesized to protect against deleterious effects of gestational MeHg exposure. To determine whether protection occurs at the behavioral level, female Long-Evans rats were exposed, in utero, to 0, 0.5, or 5 ppm of Hg as MeHg via drinking water, approximating exposures of 0, 40, and 400 ÎŒg Hg/kg/day and producing 0, 0.29, and 5.50 ppm of total Hg in the brains of siblings at birth. They also received pre- and postnatal exposure to one of two diets, both based on the AIN-93 semipurified formulation. A âfish-oilâ diet was high in, and a âcoconut-oilâ diet was devoid of, DHA. Diets were approximately equal in α-linolenic acid and n-6 PUFAs. As adults, the rats were first assessed with a spatial discrimination reversal (SDR) procedure and later with a visual (nonspatial) discrimination reversal (VDR) procedure. MeHg increased the number of errors to criterion for both SDR and VDR during the first reversal, but effects were smaller or nonexistent on the original discrimination and on later reversals. No such MeHg-related deficits were seen when the rats were retested on SDR after two years of age. These results are consistent with previous reports and hypotheses that gestational MeHg exposure produces perseverative responding. No interactions between Diet and MeHg were found, suggesting that n-3 PUFAs do not guard against these behavioral effects. Brain Hg concentrations did not differ between the diets, either. In geriatric rats, failures to respond were less common and response latencies were shorter for rats fed the fish oil diet, suggesting that exposure to a diet rich in n-3s may lessen the impact of age-related declines in response initiation
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