9,101 research outputs found
Phonographic neighbors, not orthographic neighbors, determine word naming latencies
The orthographic neighborhood size (N) of a word—the number of words that can be formed from that word by replacing one letter with another in its place—has been found to have facilitatory effects in word naming. The orthographic neighborhood hypothesis attributes this facilitation to interactive effects. A phonographic neighborhood hypothesis, in contrast, attributes the effect to lexical print-sound conversion. According to the phonographic neighborhood hypothesis, phonographic neighbors (words differing in one letter and one phoneme, e.g., stove and stone) should facilitate naming, and other orthographic neighbors (e.g., stove and shove) should not. The predictions of these two hypotheses are tested. Unique facilitatory phonographic N effects were found in four sets of word naming mega-study data, along with an absence of facilitatory orthographic N effects. These results implicate print-sound conversion—based on consistent phonology—in neighborhood effects rather than word-letter feedback
Methods of testing and diagnosing model error : dual and single route cascaded models of reading aloud
Models of visual word recognition have been assessed by both factorial and regression approaches. Factorial approaches tend to provide a relatively weak test of models, and regression approaches give little indication of the sources of models’ mispredictions, especially when parameters are not optimal. A new alternative method, involving regression on model error, combines these two approaches with parameter optimization. The method is illustrated with respect to the dual route cascaded model of reading aloud. In contrast to previous investigations, this method provides clear evidence that there are parameter-independent problems with the model, and identifies two specific sources of misprediction made by model
Xenon in Mercury-Manganese Stars
Previous studies of elemental abundances in Mercury-Manganese (HgMn) stars
have occasionally reported the presence of lines of the ionized rare noble gas
Xe II, especially in a few of the hottest stars with Teff ~ 13000--15000 K. A
new study of this element has been undertaken using observations from Lick
Observatory's Hamilton Echelle Spectrograph. In this work, the spectrum
synthesis program UCLSYN has been used to undertake abundance analysis assuming
LTE. We find that in the Smith & Dworetsky sample of HgMn stars, Xe is vastly
over-abundant in 21 of 22 HgMn stars studied, by factors of 3.1--4.8 dex. There
does not appear to be a significant correlation of Xe abundance with Teff. A
comparison sample of normal late B stars shows no sign of Xe II lines that
could be detected, consistent with the expected weakness of lines at normal
abundance. The main reason for the previous lack of widespread detection in
HgMn stars is probably due to the strongest lines being at longer wavelengths
than the photographic blue. The lines used in this work were 4603.03A, 4844.33A
and 5292.22A.Comment: 8 pages, 4 figures. Accepted by Monthly Notices of the Royal
Astronomical Society, 8 January 200
Magnetic field, chemical composition and line profile variability of the peculiar eclipsing binary star AR Aur
AR Aur is the only eclipsing binary known to contain a HgMn star, making it
an ideal case for a detailed study of the HgMn phenomenon. HgMn stars are a
poorly understood class of chemically peculiar stars, which have traditionally
been thought not to possess significant magnetic fields. However, the recent
discovery of line profile variability in some HgMn stars, apparently
attributable to surface abundance patches, has brought this belief into
question. In this paper we investigate the chemical abundances, line profile
variability, and magnetic field of the primary and secondary of the AR Aur
system, using a series of high resolution spectropolarimetric observations. We
find the primary is indeed a HgMn star, and present the most precise abundances
yet determined for this star. We find the secondary is a weak Am star, and is
possibly still on the pre-main sequence. Line profile variability was observed
in a range of lines in the primary, and is attributed to inhomogeneous surface
distributions of some elements. No magnetic field was detected in any
observation of either stars, with an upper limit on the longitudinal magnetic
field in both stars of 100 G. Modeling of the phase-resolve longitudinal field
measurements leads to a 3 sigma upper limit on any dipole surface magnetic
field of about 400 G.Comment: Accepted for publication in MNRAS, 11 pages, 9 figure
The HgMn Binary Star Phi Herculis: Detection and Properties of the Secondary and Revision of the Elemental Abundances of the Primary
Observations of the Mercury-Manganese star Phi Herculis with the Navy
Prototype Optical Interferometer (NPOI) conclusively reveal the previously
unseen companion in this single-lined binary system. The NPOI data were used to
predict a spectral type of A8V for the secondary star Phi Her B. This
prediction was subsequently confirmed by spectroscopic observations obtained at
the Dominion Astrophysical Observatory. Phi Her B is rotating at 50 +/-3
km/sec, in contrast to the 8 km/sec lines of Phi Her A. Recognizing the lines
from the secondary permits one to separate them from those of the primary. The
abundance analysis of Phi Her A shows an abundance pattern similar to those of
other HgMn stars with Al being very underabundant and Sc, Cr, Mn, Zn, Ga, Sr,
Y, Zr, Ba, Ce, and Hg being very overabundant.Comment: Accepted to ApJ, 45 pages, 11 figure
Peculiar Motions in the Region of the Ursa Major Supercluster of Galaxies
We have investigated the peculiar motions of clusters of galaxies in the Ursa
Major (UMa) supercluster and its neighborhood. Based on SDSS (Sloan Digital Sky
Survey) data, we have compiled a sample of early-type galaxies and used their
fundamental plane to determine the cluster distances and peculiar velocities.
The samples of early-type galaxies in the central regions (within R_200) of 12
UMa clusters of galaxies, in three main subsystems of the supercluster -- the
filamentary structures connecting the clusters, and in nine clusters from the
nearest UMa neighborhood have similar parameters. The fairly high overdensity
(3 by the galaxy number and 15 by the cluster number) suggests that the
supercluster as a whole is gravitationally bound, while no significant peculiar
motions have been found: the peculiar velocities do not exceed the measurement
errors by more than a factor of 1.5-2. The mean random peculiar velocities of
clusters and the systematic deviations from the overall Hubble expansion in the
supercluster are consistent with theoretical estimates. For the possible
approach of the three UMa subsystems to be confirmed, the measurement accuracy
must be increased by a factor of 2-3.Comment: 21 pages, 4 tables, 7 figure
Temporally ordered collective creep and dynamic transition in the charge-density-wave conductor NbSe3
We have observed an unusual form of creep at low temperatures in the
charge-density-wave (CDW) conductor NbSe. This creep develops when CDW
motion becomes limited by thermally-activated phase advance past individual
impurities, demonstrating the importance of local pinning and related
short-length-scale dynamics. Unlike in vortex lattices, elastic collective
dynamics on longer length scales results in temporally ordered motion and a
finite threshold field. A first-order dynamic phase transition from creep to
high-velocity sliding produces "switching" in the velocity-field
characteristic.Comment: 4 pages, 4 eps figures; minor clarifications To be published in Phys.
Rev. Let
The magnetic Bp star 36 Lyncis, I. Magnetic and photospheric properties
This paper reports the photospheric, magnetic and circumstellar gas
characteristics of the magnetic B8p star 36 Lyncis (HD 79158). Using archival
data and new polarised and unpolarised high-resolution spectra, we redetermine
the basic physical properties, the rotational period and the geometry of the
magnetic field, and the photospheric abundances of various elements.}{Based on
magnetic and spectroscopic measurements, we infer an improved rotational period
of d. We determine a current epoch of the longitudinal
magnetic field positive extremum (HJD 2452246.033), and provide constraints on
the geometry of the dipole magnetic field (i\geq 56\degr, G, unconstrained). We redetermine the effective
temperature and surface gravity using the optical and UV energy distributions,
optical photometry and Balmer line profiles ( K,
), and based on the Hipparcos parallax we redetermine the
luminosity, mass, radius and true rotational speed ( \kms). We
measure photospheric abundances for 21 elements using optical and UV spectra,
and constrain the presence of vertical stratification of these elements. We
perform preliminary Doppler Imaging of the surface distribution of Fe, finding
that Fe is distributed in a patchy belt near the rotational equator. Most
remarkably, we confirm strong variations of the H line core which we
interpret as due to occultations of the star by magnetically-confined
circumstellar gas.Comment: Accepted by Astronomy and Astrophysic
An Interacting Two-Fluid Scenario for Dark Energy in FRW Universe
We study the evolution of the dark energy parameter within the scope of a
spatially flat and isotropic Friedmann-Robertson-Walker (FRW) model filled with
barotropic fluid and dark energy. To obtain the deterministic solution we
choose the scale factor which yields a time dependent
deceleration parameter (DP). In doing so we consider the case minimally coupled
with dark energy to the perfect fluid as well as direct interaction with it.Comment: 11 pages, accepted for publication in Chinese Physics Letters. Unlike
the previous version the new one contains the time depending deceleration
paramete
The stellar population histories of early-type galaxies. III. The Coma Cluster
We present stellar population parameters of twelve early-type galaxies (ETGs)
in the Coma Cluster based on spectra obtained using the Low Resolution Imaging
Spectrograph on the Keck II Telescope. Our data allow us to examine in detail
the zero-point and scatter in their stellar population properties. Our ETGs
have SSP-equivalent ages of on average 5-8 Gyr with the models used here, with
the oldest galaxies having ages of ~10 Gyr old. This average age is identical
to the mean age of field ETGs. Our ETGs span a large range in velocity
dispersion but are consistent with being drawn from a population with a single
age. Specifically, ten of the twelve ETGs are consistent within their formal
errors of having the same age, 5.2+/-0.2 Gyr, over a factor of more than 750 in
mass. We therefore find no evidence for downsizing of the stellar populations
of ETGs in the core of the Coma Cluster. We suggest that Coma Cluster ETGs may
have formed the majority of their mass at high redshifts but suffered small but
detectable star formation events at z~0.1-0.3. Previous detections of
'downsizing' from stellar populations of local ETGs may not reflect the same
downsizing seen in lookback studies of RSGs, as the young ages of the local
ETGs represent only a small fraction of their total masses. (abridged)Comment: 49 pages, 20 figures (19 EPS, 1 JPEG). MNRAS, in press. For version
with full resolution of Fig. 1 see
http://www.astro.rug.nl/~sctrager/coma.pdf; for Table 2, see
http://www.astro.rug.nl/~sctrager/coma_table2.pdf; for Table B3, see
http://www.astro.rug.nl/~sctrager/coma_tableB3.pd
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