2,795 research outputs found
Disturbances in the spontaneous attribution of social meaning in schizophrenia
Background. Schizophrenia patients show disturbances on a range of tasks that assess mentalizing or 'Theory of Mind' (ToM). However, these tasks are often developmentally inappropriate, make large demands on verbal abilities and explicit problem-solving skills, and involve after-the-fact reflection as opposed to spontaneous mentalizing.
Method. To address these limitations, 55 clinically stable schizophrenia out-patients and 44 healthy controls completed a validated Animations Task designed to assess spontaneous attributions of social meaning to ambiguous
abstract visual stimuli. In this paradigm, 12 animations depict two geometric shapes' interacting' with each other in three conditions: (1) ToM interactions that elicit attributions of mental states to the agents, (2) Goal-Directed (GO) interactions that elicit attributions of simple actions, and (3) Random scenes in which no interaction occurs. Verbal
descriptions of each animation are rated for the degree of Intentionality attributed to the agents and for accuracy.
Results. Patients had lower Intentionality ratings than controls for ToM and GO scenes but the groups did not significantly differ for Random scenes. The descriptions of the patients less closely matched the situations intended by the developers of the task. Within the schizophrenia group, performance on the Animations Task showed minimal
associations with clinical symptoms.
Conclusions. Patients demonstrated disturbances in the spontaneous attribution of mental states to abstract visual stimuli that normally evoke such attributions. Hence, in addition to previously established impairment on mentalizing tasks that require logical inferences about others' mental states, individuals with schizophrenia show disturbances in implicit aspects of mentalizing
The Distance of the First Overtone RR Lyrae Variables in the MACHO LMC Database: A New Method to Correct for the Effects of Crowding
Previous studies have indicated that many of the RR Lyrae variables in the
LMC have properties similar to the ones in the Galactic globular cluster M3.
Assuming that the M3 RR Lyrae variables follow the same relationships among
period, temperature, amplitude and Fourier phase parameter phi31 as their LMC
counterparts, we have used the M3 phi31-logP relation to identify the M3-like
unevolved first overtone RR Lyrae variables in 16 fields near the LMC bar. The
temperatures of these variables were calculated from the M3 logP-logTe relation
so that the extinction could be derived for each star separately. Since blended
stars have lower amplitudes for a given period, the period amplitude relation
should be a useful tool for identifying which stars are affected by crowding.
We find that the low amplitude stars are brighter. We remove them from the
sample and derive an LMC distance modulus 18.49+/-0.11.Comment: 30 pages, 7 figures, accepted for publication in the Astronomical
Journa
Apparent superluminal advancement of a single photon far beyond its coherence length
We present experimental results relative to superluminal propagation based on
a single photon traversing an optical system, called 4f-system, which acts
singularly on the photon's spectral component phases. A single photon is
created by a CW laser light down{conversion process. The introduction of a
linear spectral phase function will lead to the shift of the photon peak far
beyond the coherence length of the photon itself (an apparent superluminal
propagation of the photon). Superluminal group velocity detection is done by
interferometric measurement of the temporal shifted photon with its correlated
untouched reference. The observed superluminal photon propagation complies with
causality. The operation of the optical system allows to enlighten the origin
of the apparent superluminal photon velocity. The experiment foresees a
superluminal effect with single photon wavepackets.Comment: 11 pages, 2 figure
Carbon sp chains in graphene nanoholes
Nowadays sp carbon chains terminated by graphene or graphitic-like carbon are
synthesized routinely in several nanotech labs.
We propose an ab-initio study of such carbon-only materials, by computing
their structure and stability, as well as their electronic, vibrational and
magnetic properties.
We adopt a fair compromise of microscopic realism with a certain level of
idealization in the model configurations, and predict a number of properties
susceptible to comparison with experiment.Comment: 34 pages, 27 figure
A Dispersion Operator for Geometric Semantic Genetic Programming
Recent advances in geometric semantic genetic programming (GSGP) have shown that the results obtained by these methods can outperform those obtained by classical genetic programming algorithms, in particular in the context of symbolic regression. However, there are still many open issues on how to improve their search mechanism. One of these issues is how to get around the fact that the GSGP crossover operator cannot generate solutions that are placed outside the convex hull formed by the individuals of the current population. Although the mutation operator alleviates this problem, we cannot guarantee it will find promising regions of the search space within feasible computational time. In this direction, this paper proposes a new geometric dispersion operator that uses multiplicative factors to move individuals to less dense areas of the search space around the target solution before applying semantic genetic operators. Experiments in sixteen datasets show that the results obtained by the proposed operator are statistically significantly better than those produced by GSGP and that the operator does indeed spread the solutions around the target solution
How well do self-supervised models transfer to medical imaging?
Self-supervised learning approaches have seen success transferring between similar medical imaging datasets, however there has been no large scale attempt to compare the transferability of self-supervised models against each other on medical images. In this study, we compare the generalisability of seven self-supervised models, two of which were trained in-domain, against supervised baselines across eight different medical datasets. We find that ImageNet pretrained self-supervised models are more generalisable than their supervised counterparts, scoring up to 10% better on medical classification tasks. The two in-domain pretrained models outperformed other models by over 20% on in-domain tasks, however they suffered significant loss of accuracy on all other tasks. Our investigation of the feature representations suggests that this trend may be due to the models learning to focus too heavily on specific areas
The Rise of the s-Process in the Galaxy
From newly-obtained high-resolution, high signal-to-noise ratio spectra the
abundances of the elements La and Eu have been determined over the stellar
metallicity range -3<[Fe/H]<+0.3 in 159 giant and dwarf stars. Lanthanum is
predominantly made by the s-process in the solar system, while Eu owes most of
its solar system abundance to the r-process. The changing ratio of these
elements in stars over a wide metallicity range traces the changing
contributions of these two processes to the Galactic abundance mix. Large
s-process abundances can be the result of mass transfer from very evolved
stars, so to identify these cases, we also report carbon abundances in our
metal-poor stars. Results indicate that the s-process may be active as early as
[Fe/H]=-2.6, alalthough we also find that some stars as metal-rich as [Fe/H]=-1
show no strong indication of s-process enrichment. There is a significant
spread in the level of s-process enrichment even at solar metallicity.Comment: 64 pages, 15 figures; ApJ 2004 in pres
Galaxy populations in the Antlia cluster. I. Photometric properties of early-type galaxies
We present the first colour-magnitude relation (CMR) of early-type galaxies
in the central region of the Antlia cluster, obtained from CCD wide-field
photometry in the Washington photometric system. Integrated (C -T1) colours, T1
magnitudes, and effective radii have been measured for 93 galaxies (i.e. the
largest galaxies sample in the Washington system till now) from the FS90
catalogue (Ferguson & Sandage 1990). Membership of 37 objects can be confirmed
through new radial velocities and data collected from the literature. The
resulting colour-magnitude diagram shows that early-type FS90 galaxies that are
spectroscopically confirmed Antlia members or that were considered as definite
members by FS90, follow a well defined CMR (sigma_(C -T1) ~ 0.07 mag) that
spans 9 magnitudes in brightness with no apparent change of slope. This
relation is very tight for the whole magnitude range but S0 galaxies show a
larger dispersion, apparently due to a separation of ellipticals and S0s.
Antlia displays a slope of -13.6 in a T1 vs. (C -T1) diagram, in agreement with
results for clusters like Fornax, Virgo, Perseus and Coma, which are
dynamically different to Antlia. This fact might indicate that the build up of
the CMR in cluster of galaxies is more related to galaxies internal processes
than to the influence of the environment. Interpreting the CMR as a
luminosity-metallicity relation of old stellar systems, the metallicities of
the Antlia galaxies define a global relation down to Mv ~ -13. We also find,
for early-type dwarfs, no clear relation between luminosity and effective
radius, indicating a nearly constant mean effective radius of ~ 1 kpc. This
value is also found in several samples of dwarf galaxies in Virgo and Coma.Comment: 13 pages, 6 figures. Accepted for publication in MNRA
Empirically Constrained Color-Temperature Relations. II. uvby
(Abriged) A new grid of theoretical color indices for the Stromgren uvby
photometric system has been derived from MARCS model atmospheres and SSG
synthetic spectra for cool dwarf and giant stars. At warmer temperatures this
grid has been supplemented with the synthetic uvby colors from recent Kurucz
atmospheric models without overshooting. Our transformations appear to
reproduce the observed colors of extremely metal-poor turnoff and giant stars
(i.e., [Fe/H]<-2). Due to a number of assumptions made in the synthetic color
calculations, however, our color-temperature relations for cool stars fail to
provide a suitable match to the uvby photometry of both cluster and field stars
having [Fe/H]>-2. To overcome this problem, the theoretical indices at
intermediate and high metallicities have been corrected using a set of color
calibrations based on field stars having accurate IRFM temperature estimates
and spectroscopic [Fe/H] values. Encouragingly, isochrones that employ the
transformations derived in this study are able to reproduce the observed CMDs
(involving u-v, v-b, and b-y colors) for a number of open and globular clusters
(including M92, M67, the Hyades, and 47Tuc) rather well. Moreover, our
interpretations of such data are very similar, if not identical, with those
given by VandenBerg & Clem (2003, AJ, 126, 778) from a consideration of BV(RI)c
observations for the same clusters. In the present investigation, we have also
analyzed the observed Stromgren photometry for the classic Population II
subdwarfs, compared our "final" (b-y)-Teff relationship with those derived
empirically in a number of recent studies, and examined in some detail the
dependence of the m1 index on [Fe/H].Comment: 70 pages, 26 figures. Accepted for publication in AJ (Feb 2004).
Postscript version with high resolution figures and complete Table 3
available at http://astrowww.phys.uvic.ca/~jclem/uvb
On the Use of Blanketed Atmospheres as Boundary Conditions for Stellar Evolutionary Models
Stellar models have been computed for stars having [Fe/H] = 0.0 and -2.0 to
determine the effects of using boundary conditions derived from the latest
MARCS model atmospheres. The latter were fitted to the interior models at both
the photosphere and at tau = 100, and at least for the 0.8-1.0 solar mass stars
considered here, the resultant evolutionary tracks were found to be nearly
independent of the chosen fitting point. Particular care was taken to treat the
entire star as consistently as possible; i.e., both the interior and atmosphere
codes assumed the same abundances and the same treatment of convection. Tracks
were also computed using either the classical gray T(tau,T_eff) relation or
that derived by Krishna Swamy (1966) to derive the boundary pressure. The
latter predict warmer giant branches (by ~150 K) at solar abundances than those
based on gray or MARCS atmospheres, which happens to be in good agreement with
the inferred temperatures of giants in the open cluster M67 from the latest
(V-K)-T_eff relations. Most of the calculations assumed Z=0.0125 (Asplund et
al.), though a few models were computed for Z=0.0165 (Grevesse & Sauval) to
determine the dependence of the tracks on Z_\odot. Grids of "scaled solar,
differentially corrected" (SDC) atmospheres were also computed to try to
improve upon theoretical MARCS models. When they were used as boundary
conditions, the resultant tracks agreed very well with those based on a
standard scaled-solar (e.g., Krishna Swamy) T(tau,T_eff) relation,
independently of the assumed metal abundance. Fits of isochrones to the C-M
diagram of the [Fe/H] = -2 globular cluster M68 were examined, as was the
possibility that the mixing-length parameter varies with stellar parameters.Comment: 54 pages, including 20 figures and 3 tables; accepted (July 2007) for
publication in the Astrophysical Journa
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