42,754 research outputs found
Children's suggestibility in relation to their understanding about sources of knowledge
In the experiments reported here, children chose either to maintain their initial belief about an object's identity or to accept the experimenter's contradicting suggestion. Both 3â to 4âyearâolds and 4â to 5âyearâolds were good at accepting the suggestion only when the experimenter was better informed than they were (implicit source monitoring). They were less accurate at recalling both their own and the experimenter's information access (explicit recall of experience), though they performed well above chance. Children were least accurate at reporting whether their final belief was based on what they were told or on what they experienced directly (explicit source monitoring). Contrasting results emerged when children decided between contradictory suggestions from two differentially informed adults: Threeâ to 4âyearâolds were more accurate at reporting the knowledge source of the adult they believed than at deciding which suggestion was reliable. Decision making in this observation task may require reflective understanding akin to that required for explicit source judgments when the child participates in the task
A Spectropolarimetric Atlas of Seyfert 1 Galaxies
We present optical spectropolarimetry of the nuclei of 36 Seyfert 1 galaxies,
obtained with the William Herschel and the Anglo-Australian Telescopes from
1996 to 1999. In 20 of these, the optical emission from the active nucleus is
intrinsically polarized. We have measured a significant level of polarization
in a further 7 objects but these may be heavily contaminated by Galactic
interstellar polarization. The intrinsically polarized Seyfert 1s exhibit a
variety of characteristics, with the average polarization ranging from < 0.5 to
5 per cent and many showing variations in both the degree and position angle of
polarization across the broad H alpha emission line. We identify a small group
of Seyfert 1s that exhibit polarization properties similar to those of Seyfert
2 galaxies in which polarized broad-lines have been discovered. These objects
represent direct observational evidence that a Seyfert 2-like far-field polar
scattering region is also present in Seyfert 1s. Several other objects have
features that can be explained in terms of equatorial scattering of line
emission from a rotating disk. We propose that much of the diversity in the
polarization properties of Seyfert galaxies can be understood in terms of a
model involving both equatorial and polar scattering, the relative importance
of the two geometries as sources of polarized light being determined
principally by the inclination of the system axis to the line-of-sight.Comment: Accepted for publication in MNRAS (28 pages, 25 figures
Effects of T=0 two body matrix elements on M1 and Gamow-Teller transitions: isospin decomposition
We perform calculations for M1 transitions and allowed Gamow Teller (GT)
transitions in the even-even Titanium isotopes - Ti, Ti, and
Ti. We first do calculations with the FPD6 interaction. Then to study
the effect of T=0 matrix elements on the M1 and GT rates we introduce a second
interaction in which all the T=0 matrix elements are set equal to zero and a
third in which all the T=0 matrix elements are set to a constant. For the
latter two interactions the T=1 matrix elements are the same as for FPD6. We
are thus able to study the effects of the fluctuating T=0 matrix elements on M1
and GT rates
X ray spectra of X Per
The cosmic X-ray spectroscopy experiment on OSO-8 observed X Per for twenty days during two observations in Feb. 1976 and Feb. 1977. The spectrum of X Per varies in phase with its 13.9 min period, hardening significantly at X-ray minimum. Unlike other X-ray binary pulsar spectra, X Per's spectra do not exhibit iron line emission or strong absorption features. The data show no evidence for a 22 hour periodicity in the X-ray intensity of X Per. These results indicate that the X-ray emission from X Per may be originating from a neutron star in a low density region far from the optically identified Be star
A 4.8 hour periodicity in the spectra of Cyg X-3
The X-ray spectra from three observations of the X-ray binary Cyg X-3 by the cosmic X-ray spectroscopy experiment on OSO can be represented by power-law continua with strong iron line emission. Comparisons of spectra taken within the same observation at various phases of the 4.8 hour period reveal a relative excess of low energy X-ray emission near zero phase (i.e. the minimum) of the 4.8 hour modulation. In addition, the centroid of the line emission is observed to vary in phase with the 4.8 hour cycle. The possibility of persistent thermal X-ray emission from material surrounding the binary system is introduced in an effort to account for the observed effects
Investigation of microwave transitions and nonlinear magneto-optical rotation in anti-relaxation-coated cells
Using laser optical pumping, widths and frequency shifts are determined for
microwave transitions between ground-state hyperfine components of Rb
and Rb atoms contained in vapor cells with alkane anti-relaxation
coatings. The results are compared with data on Zeeman relaxation obtained in
nonlinear magneto-optical rotation (NMOR) experiments, a comparison important
for quantitative understanding of spin-relaxation mechanisms in coated cells.
By comparing cells manufactured over a forty-year period we demonstrate the
long-term stability of coated cells, an important property for atomic clocks
and magnetometers
Heisenberg models and a particular isotropic model
The Heisenberg model, a quantum mechanical analogue of the Ising model, has a
large ground state degeneracy, due to the symmetry generated by the total spin.
This symmetry is also responsible for degeneracies in the rest of the spectrum.
We discuss the global structure of the spectrum of Heisenberg models with
arbitrary couplings, using group theoretical methods. The Hilbert space breaks
up in blocks characterized by the quantum numbers of the total spin, and
, and each block is shown to constitute the representation space of an
explicitly given irreducible representation of the symmetric group ,
consisting of permutations of the spins in the system.
In the second part of the paper we consider, as a concrete application, the
model where each spin is coupled to all the other spins with equal strength.
Its partition function is written as a single integral, elucidating its
-dependence. This provides a useful framework for studying finite size
effects. We give explicit results for the heat capacity, revealing interesting
behavior just around the phase transition.Comment: 16 pages LaTeX, one of the 2 figures included as a postscript file.
Oxford preprint OUTP-93-18S, to be published in Phys. Rev.
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