2,427 research outputs found
Phonological Priming In Young Children Who Stutter: Holistic Versus Incremental Processing
Purpose: To investigate the holistic versus incremental phonological encoding processes of young children who stutter (CWS; N = 26) and age- and gender-matched children who do not stutter (CWNS; N = 26) via a picture-naming auditory priming paradigm. Method: Children named pictures during 3 auditory priming conditions: neutral, holistic, and incremental. Speech reaction time (SRT) was measured from the onset of picture presentation to the onset of participant response. Results: CWNS shifted from being significantly faster in the holistic priming condition to being significantly faster in the incremental priming condition from 3 to 5 years of age. In contrast, the majority of 3- and 5-year-old CWS continued to exhibit faster SRT in the holistic than the incremental condition. Conclusion: CWS are delayed in making the developmental shift in phonological encoding from holistic to incremental processing, a delay that may contribute to their difficulties establishing fluent speech.Communication Sciences and Disorder
Multicolour Optical Imaging of IR-Warm Seyfert Galaxies. V. Morphologies and Interactions. Challenging the Orientation Model
This paper is the last in a series, investigating the optical properties of a
sample of mid-IR Warm Seyfert galaxies and of a control sample of mid-IR cold
galaxies. In the present paper we parametrize the morphologies and interaction
properties of the host galaxies and combine these with the major conclusions in
our previous papers. Our results confirm that nuclear activity is linked to
galactic interactions. We suggest an alternative view for the simple
orientation-obscuration model postulated for Seyfert types 1 and 2, that takes
into account the time evolution of their environmental and morphological
properties. Within this view, an evolutionary link between starburst-dominated
and AGN-dominated IR emission is also suggested, to account for the
observational discriminator (mid-IR excess) between our Warm and Cold samples.Comment: 24 pages, including 6 figures and 3 tables (figure 5 included as
independent file), Submitted to Ap
Active Galactic Nuclei in Void Regions
We present a comprehensive study of accretion activity in the most underdense
environments in the universe, the voids, based on the SDSS DR2 data. Based on
investigations of multiple void regions, we show that AGN's occurrence rate and
properties differ from those in walls. AGN are more common in voids than in
walls, but only among moderately luminous and massive galaxies (M_r < -20, log
M_*/M_sun < 10.5), and this enhancement is more pronounced for the weakly
accreting systems (i.e., L_[O III] < 10^39 erg/s). Void AGN hosted by
moderately massive and luminous galaxies are accreting at equal or lower rates
than their wall counterparts, show less obscuration than in walls, and
similarly aged stellar populations. The very few void AGN in massive bright
hosts accrete more strongly, are more obscured, and are associated with younger
stellar emission than wall AGN. Thus, accretion strength is probably connected
to the availability of fuel supply, and accretion and star-formation co-evolve
and rely on the same source of fuel. Nearest neighbor statistics indicate that
the weak accretion activity (LINER-like) is not influenced by the local
environment. However, H IIs, Seyferts, and Transition objects prefer more
grouped small scale structures, indicating that the rate at which galaxies
interact with each other affects their activity. These trends support a
potential H II -> Seyfert/Transition Object -> LINER evolutionary sequence that
we show is apparent in many properties of actively line-emitting galaxies, in
both voids and walls. The subtle differences between void and wall AGN might be
explained by a longer, less disturbed duty cycle of these systems in voids.Comment: 19 pages, 7 figures (1 color); to appear in ApJ, submitted on May 11,
200
On the Green's Function of the almost-Mathieu Operator
The square tight-binding model in a magnetic field leads to the
almost-Mathieu operator which, for rational fields, reduces to a
matrix depending on the components , of the wave vector in the
magnetic Brillouinzone. We calculate the corresponding Green's function without
explicit knowledge of eigenvalues and eigenfunctions and obtain analytical
expressions for the diagonal and the first off-diagonal elements; the results
which are consistent with the zero magnetic field case can be used to calculate
several quantities of physical interest (e. g. the density of states over the
entire spectrum, impurity levels in a magnetic field).Comment: 9 pages, 3 figures corrected some minor errors and typo
Orbits of quantum states and geometry of Bloch vectors for -level systems
Physical constraints such as positivity endow the set of quantum states with
a rich geometry if the system dimension is greater than two. To shed some light
on the complicated structure of the set of quantum states, we consider a
stratification with strata given by unitary orbit manifolds, which can be
identified with flag manifolds. The results are applied to study the geometry
of the coherence vector for n-level quantum systems. It is shown that the
unitary orbits can be naturally identified with spheres in R^{n^2-1} only for
n=2. In higher dimensions the coherence vector only defines a non-surjective
embedding into a closed ball. A detailed analysis of the three-level case is
presented. Finally, a refined stratification in terms of symplectic orbits is
considered.Comment: 15 pages LaTeX, 3 figures, reformatted, slightly modified version,
corrected eq.(3), to appear in J. Physics
Circumnuclear stellar population, morphology and environment of Seyfert 2 galaxies: an evolutionary scenario
We investigate the relation between the characteristics of the circumnuclear
stellar population and both the galaxy morphology and the presence of close
companions for a sample of 35 Seyfert 2 nuclei. Fifteen galaxies present
unambiguous signatures of recent episodes of star formation within 300
pc from the nucleus. When we relate this property with the Hubble type of the
host galaxy, we find that the incidence of recent circumnuclear star formation
increases along the Hubble sequence, and seems to be larger than in non-Seyfert
galaxies for the early Hubble types S0 and Sa, but similar to that in
non-Seyfert galaxies for later Hubble types. Both in early-type and late-type
Seyferts, the presence of recent star-formation is related to the galaxy
morphology in the inner few kiloparsecs, as observed in HST images through the
filter F606W by Malkan et al., who has assigned a late ``inner Hubble type'' to
most Seyfert 2s with recent nuclear star-formation. This new classification is
due to the presence of dust lanes and spiral structures in the inner region.
The presence of recent star formation in Seyfert 2 nuclei is also related to
interactions: among the 13 galaxies of the sample with close companions or in
mergers, 9 have recent star formation in the nucleus. These correlations
between the presence of companions, inner morphology and the incidence of
recent star formation suggest an evolutionary scenario in which the interaction
is responsible for sending gas inwards which both feeds the AGN and triggers
star-formation. The starburst then fades with time and the composite Seyfert 2
+ Starburst nucleus evolves to a ``pure'' Seyfert 2 nucleus with an old stellar
population.Comment: 12 pages, 6 figures, 2 table
Gapped optical excitations from gapless phases: imperfect nesting in unconventional density waves
We consider the effect of imperfect nesting in quasi-one-dimensional
unconventional density waves in the case, when the imperfect nesting and the
gap depends on the same wavevector component.
The phase diagram is very similar to that in a conventional density wave. The
density of states is highly asymmetric with respect to the Fermi energy.
The optical conductivity at T=0 remains unchanged for small deviations from
perfect nesting. For higher imperfect nesting parameter, an optical gap opens,
and considerable amount of spectral weight is transferred to higher
frequencies. This makes the optical response of our system very similar to that
of a conventional density wave. Qualitatively similar results are expected in
d-density waves.Comment: 8 pages, 7 figure
Generalized Euler Angle Paramterization for SU(N)
In a previous paper (math-ph/0202002) an Euler angle parameterization for
SU(4) was given. Here we present the derivation of a generalized Euler angle
parameterization for SU(N). The formula for the calculation of the Haar measure
for SU(N) as well as its relation to Marinov's volume formula for SU(N) will
also be derived. As an example of this parameterization's usefulness, the
density matrix parameterization and invariant volume element for a
qubit/qutrit, three qubit and two three-state systems, also known as two qutrit
systems, will also be given.Comment: 36 pages, no figures; added qubit/qutrit work, corrected minor
definition problems and clarified Haar measure derivation. To be published in
J. Phys. A: Math. and Ge
Recommended from our members
Review of Androgenic Anabolic Steroid Use
An area that has been overlooked within personnel security evaluations is employee use of androgenic-anabolic steroids (AAS). Current drug testing within the federal government does not include testing for anabolic steroids, and the difficulties to implement such testing protocols-not to mention the cost involved-make AAS testing highly improbable. The basis of this report is to bring to the forefront the damage that anabolic steroids can cause from both a physical and a psychological standpoint. Most individuals who use AASs do so to increase their muscle mass because they wish to gain some type of competitive edge during athletic competition or they wish to enhance their physical features for self-satisfaction and self-esteem (i.e., body building). Security officers are one group of men who often take high doses of anabolic steroids, according to the Second Report of the Senate Standing Committee (1990). The negative psychological characteristics for AAS use is extensive and includes prominent hostility, aggressiveness, irritability, euphoria, grandiose beliefs, hyperactivity, reckless behavior, increased sexual appetite, unpredictability, poor impulse control, mood fluctuations, and insomnia. The drug may invoke a sense of power and invincibility (Leckman and Scahill, 1990). Depressive symptoms, such as anhedonia, fatigue, impaired concentration, decreased libido, and even suicidality (Pope and Katz, 1992) have been noted with steroid withdrawal. It appears that long-term users of AAS experience similar characteristics as other substance abusers (i.e., craving, dependence, and withdrawal symptoms)
Some exact non-vacuum Bianchi VI0 and VII0 instantons
We report some new exact instantons in general relativity. These solutions
are K\"ahler and fall into the symmetry classes of Bianchi types VI0 and VII0,
with matter content of a stiff fluid. The qualitative behaviour of the
solutions is presented, and we compare it to the known results of the
corresponding self-dual Bianchi solutions. We also give axisymmetric Bianchi
VII0 solutions with an electromagnetic field.Comment: latex, 15 pages with 3 eps figure
- …