718 research outputs found
Heavy ion beam lifetimes at relativistic and ultrarelativistic colliders
The effects of higher order corrections in ultra-relativistic nuclear
collisions are considered. It is found that higher order contributions are
small at low energy, large at intermediate energy and small again at very high
energy. An explanation for this effect is given. This means that the
Weizsacker-Williams formula is a good approximation to use in calculating cross
sections and beam lifetimes at energies relevant to RHIC and LHC.Comment: 10 pages, 2 tables, 4 figure
The Nystrom plus Correction Method for Solving Bound State Equations in Momentum Space
A new method is presented for solving the momentum-space Schrodinger equation
with a linear potential. The Lande-subtracted momentum space integral equation
can be transformed into a matrix equation by the Nystrom method. The method
produces only approximate eigenvalues in the cases of singular potentials such
as the linear potential. The eigenvalues generated by the Nystrom method can be
improved by calculating the numerical errors and adding the appropriate
corrections. The end results are more accurate eigenvalues than those generated
by the basis function method. The method is also shown to work for a
relativistic equation such as the Thompson equation.Comment: Revtex, 21 pages, 4 tables, to be published in Physical Review
Evaluation of an interview skills training package for adolescents with speech, language and communication needs
BACKGROUND & AIMS: We evaluated a structured intervention programme aimed at preparing adolescents with developmental language disorders for job interviews. Our primary outcome measures included change in ratings of verbal and nonâverbal social communication behaviours evident during mock interviews.
METHODS & PROCEDURES:
In study 1, 12 participants, aged 17â19 years, from a specialist sixthâform college completed the intervention and two mock interviews, one preâ and one postâintervention. In study 2, 34 participants, aged 17â19 years, completed a modified intervention programme and three mock interviews, one at baseline (included to control for possible practise effects), one preâ and one postâintervention. In both studies, interviews were video recorded and social communication behaviours were coded by independent assessors blind to interview time, participant diagnosis and therapy content. A repeatedâmeasures design was employed to measure change in communication behaviours.
OUTCOMES & RESULTS:
In study 1, a significant increase in the number of âpositiveâ verbal and nonâverbal social communication behaviours was observed from preâ to postâintervention. However, there was no significant change in the number of ânegativeâ behaviours (i.e., fidgeting, irrelevant remarks). In study 2, there were no significant changes in verbal behaviours, but significant group differences (though wide individual variation) in both positive and negative nonâverbal social communication behaviours.
CONCLUSIONS & IMPLICATIONS:
Our findings suggest that training specific social communication skills that are important for interview success, and consistently reinforcing those behaviours during therapy practice, can increase the use of those skills in an interview setting, though in this heterogeneous population there was considerable variation in therapy outcome. The skills of the interviewer were identified as a potential source of variation in outcome, and a target for future research and practice
Figurative language comprehension in individuals with autism spectrum disorder: A meta-analytic review
We present a meta-analysis of studies that compare figurative language comprehension in individuals with autism spectrum disorder and in typically developing controls who were matched based on chronological age or/and language ability. A total of 41 studies and 45 independent effect sizes were included based on predetermined inclusion criteria. Group matching strategy, age, types of figurative language, and cross-linguistic differences were examined as predictors that might explain heterogeneity in effect sizes. Overall, individuals with autism spectrum disorder showed poorer comprehension of figurative language than their typically developing peers (Hedgesâ g = â0.57). A meta-regression analysis showed that group matching strategy and types of figurative language were significantly related to differences in effect sizes, whereas chronological age and cross-linguistic differences were not. Differences between the autism spectrum disorder and typically developing groups were small and nonsignificant when the groups were matched based on the language ability. Metaphors were more difficult to comprehend for individuals with autism spectrum disorder compared with typically developing controls than were irony and sarcasm. Our findings highlight the critical role of core language skills in figurative language comprehension. Interventions and educational programmes designed to improve social communication skills in individuals with autism spectrum disorder may beneficially target core language skills in addition to social skills
A Quantum-Mechanical Equivalent-Photon Spectrum for Heavy-Ion Physics
In a previous paper, we calculated the fully quantum-mechanical cross section
for electromagnetic excitation during peripheral heavy-ion collisions. Here, we
examine the sensitivity of that cross section to the detailed structure of the
projectile and target nuclei. At the transition energies relevant to nuclear
physics, we find the cross section to be weakly dependent on the projectile
charge radius, and to be sensitive to only the leading momentum-transfer
dependence of the target transition form factors. We exploit these facts to
derive a quantum-mechanical ``equivalent-photon spectrum'' valid in the
long-wavelength limit. This improved spectrum includes the effects of
projectile size, the finite longitudinal momentum transfer required by
kinematics, and the response of the target nucleus to the off-shell photon.Comment: 19 pages, 5 figure
Another exact inflationary solution
A new closed-form inflationary solution is given for a hyperbolic interaction
potential. The method used to arrive at this solution is outlined as it appears
possible to generate additional sets of equations which satisfy the model. In
addition a new form of decaying cosmological constant is presented.Comment: 10 pages, 0 figure
The new two-image gravitational lens system CLASS B2319+051
We report the discovery of a new two-image gravitational lens system from the
Cosmic Lens All-Sky Survey, CLASS B2319+051. Radio imaging with the Very Large
Array (VLA) and Multi-Element Radio-Linked Interferometer Network (MERLIN)
shows two compact components with a flux density ratio of 5:1, separated by
1.36 arcsec. Observations with the Very Long Baseline Array (VLBA) resolve each
of the radio components into a pair of parity-reversed subcomponents. Hubble
Space Telescope (HST) observations with the Near-Infrared Camera and
Multi-Object Spectrometer (NICMOS) show a bright elliptical galaxy (G1)
coincident with the radio position, and a second irregular galaxy (G2) 3.4
arcsec to the northwest. Previous spectroscopic studies have indicated that
these galaxies are at different redshifts: z(G1) = 0.624, z(G2) = 0.588.
Infrared counterparts to the lensed radio components are not detected in the
NICMOS image, and the source redshift has not yet been determined. Preliminary
mass modeling based on the VLBA subcomponent data indicates that the lensing
potential includes a strong external shear contribution. A VLA monitoring
program is currently being undertaken to measure the differential time delay.Comment: 16 pages, 7 figs, several typos corrected, AJ in press (August 2001
CLASS B2108+213: A new wide separation gravitational lens system
We present observations of CLASS B2108+213, the widest separation
gravitational lens system discovered by the Cosmic Lens All-Sky Survey. Radio
imaging using the VLA at 8.46 GHz and MERLIN at 5 GHz shows two compact
components separated by 4.56 arcsec with a faint third component in between
which we believe is emission from a lensing galaxy. 5-GHz VLBA observations
reveal milliarcsecond-scale structure in the two lensed images that is
consistent with gravitational lensing. Optical emission from the two lensed
images and two lensing galaxies within the Einstein radius is detected in
Hubble Space Telescope imaging. Furthermore, an optical gravitational arc,
associated with the strongest lensed component, has been detected. Surrounding
the system are a number of faint galaxies which may help explain the wide image
separation. A plausible mass distribution model for CLASS B2108+213 is also
presented.Comment: 9 pages, 8 figures, accepted for publication in MNRA
Disentangling Baryons and Dark Matter in the Spiral Gravitational Lens B1933+503
Measuring the relative mass contributions of luminous and dark matter in
spiral galaxies is important for understanding their formation and evolution.
The combination of a galaxy rotation curve and strong lensing is a powerful way
to break the disk-halo degeneracy that is inherent in each of the methods
individually. We present an analysis of the 10-image radio spiral lens
B1933+503 at z_l=0.755, incorporating (1) new global VLBI observations, (2) new
adaptive-optics assisted K-band imaging, (3) new spectroscopic observations for
the lens galaxy rotation curve and the source redshift. We construct a
three-dimensionally axisymmetric mass distribution with 3 components: an
exponential profile for the disk, a point mass for the bulge, and an NFW
profile for the halo. The mass model is simultaneously fitted to the kinematics
and the lensing data. The NFW halo needs to be oblate with a flattening of
a/c=0.33^{+0.07}_{-0.05} to be consistent with the radio data. This suggests
that baryons are effective at making the halos oblate near the center. The
lensing and kinematics analysis probe the inner ~10 kpc of the galaxy, and we
obtain a lower limit on the halo scale radius of 16 kpc (95% CI). The dark
matter mass fraction inside a sphere with a radius of 2.2 disk scale lengths is
f_{DM,2.2}=0.43^{+0.10}_{-0.09}. The contribution of the disk to the total
circular velocity at 2.2 disk scale lengths is 0.76^{+0.05}_{-0.06}, suggesting
that the disk is marginally submaximal. The stellar mass of the disk from our
modeling is log_{10}(M_{*}/M_{sun}) = 11.06^{+0.09}_{-0.11} assuming that the
cold gas contributes ~20% to the total disk mass. In comparison to the stellar
masses estimated from stellar population synthesis models, the stellar initial
mass function of Chabrier is preferred to that of Salpeter by a probability
factor of 7.2.Comment: 16 pages, 13 figures, minor revisions based on referee's comments,
accepted for publication in Ap
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