10,603 research outputs found
Parent-child relationships and dyadic friendship experiences as predictors of behavior problems in early adolescence
This study focused on support and conflict in parent–child relationships and dyadic
friendships as predictors of behavior problems in early adolescence (n¼182;
M age¼12.9 years, 51% female, 45% African American, 74% two-parent homes).
Support and conflict in one relationship context were hypothesized to moderate the
effects of experiences in the other relationship context. Adolescent-reported antisocial
behavior was low when either parent–child relationships or friendships were low in
conflict, and adolescent-reported depressed mood was low when either friendship
conflict was low or parental support was high. Parent-reported antisocial behavior
was high when high levels of conflict were reported in either parent–child or friendship
relationships and adolescent-reported depressed mood was high when either parental or
friendship support was low. Associations appear to be similar for boys and girls as no
interactions involving gender were significant.
Fresh-Register Automata
What is a basic automata-theoretic model of computation with names and fresh-name generation? We introduce Fresh-Register Automata (FRA), a new class of automata which operate on an infinite alphabet of names and use a finite number of registers to store fresh names, and to compare incoming names with previously stored ones. These finite machines extend Kaminski and Francez’s Finite-Memory Automata by being able to recognise globally fresh inputs, that is, names fresh in the whole current run. We exam-ine the expressivity of FRA’s both from the aspect of accepted languages and of bisimulation equivalence. We establish primary properties and connections between automata of this kind, and an-swer key decidability questions. As a demonstrating example, we express the theory of the pi-calculus in FRA’s and characterise bisimulation equivalence by an appropriate, and decidable in the finitary case, notion in these automata
The Magellan Adaptive Secondary VisAO Camera: Diffraction- Limited Broadband Visible Imaging and 20mas Fiber Array IFS
The Magellan Adaptive Secondary AO system, scheduled for first light in the
fall of 2011, will be able to simultaneously perform diffraction limited AO
science in both the mid-IR, using the BLINC/MIRAC4 10\{mu}m camera, and in the
visible using our novel VisAO camera. The VisAO camera will be able to operate
as either an imager, using a CCD47 with 8.5 mas pixels, or as an IFS, using a
custom fiber array at the focal plane with 20 mas elements in its highest
resolution mode. In imaging mode, the VisAO camera will have a full suite of
filters, coronagraphic focal plane occulting spots, and SDI prism/filters. The
imaging mode should provide ~20% mean Strehl diffraction-limited images over
the band 0.5-1.0 \{mu}m. In IFS mode, the VisAO instrument will provide R~1,800
spectra over the band 0.6-1.05 \{mu}m. Our unprecedented 20 mas spatially
resolved visible spectra would be the highest spatial resolution achieved to
date, either from the ground or in space. We also present lab results from our
recently fabricated advanced triplet Atmospheric Dispersion Corrector (ADC) and
the design of our novel wide-field acquisition and active optics lens. The
advanced ADC is designed to perform 58% better than conventional doublet ADCs
and is one of the enabling technologies that will allow us to achieve broadband
(0.5-1.0\{mu}m) diffraction limited imaging and wavefront sensing in the
visible.Comment: Proceedings of the SPIE, 2010, Vol. 7736, 77362
Resolving the H-alpha-emitting Region in the Wind of Eta Carinae
The massive evolved star Eta Carinae is the most luminous star in the Milky
Way and has the highest steady wind mass-loss rate of any known star. Radiative
transfer models of the spectrum by Hillier et al. predict that H-alpha is
mostly emitted in regions of the wind at radii of 6 to 60 AU from the star (2.5
to 25 mas at 2.35 kpc). We present diffraction-limited images (FWHM ~25 mas)
with Magellan adaptive optics in two epochs, showing that Eta Carinae
consistently appears ~2.5 to 3 mas wider in H-alpha emission compared to the
adjacent 643 nm continuum. This implies that the H-alpha line-forming region
may have a characteristic emitting radius of 12 mas or ~30 AU, in very good
agreement with the Hillier stellar-wind model. This provides direct
confirmation that the physical wind parameters of that model are roughly
correct, including the mass-loss rate of 10^-3 M_sun/yr, plus the clumping
factor, and the terminal velocity. Comparison of the H-alpha images
(ellipticity and PA) to the continuum images reveals no significant asymmetries
at H-alpha. Hence, any asymmetry induced by a companion or by the primary's
rotation do not strongly influence the global H-alpha emission in the outer
wind.Comment: Published in ApJ
PG 1700+518 Revisited: Adaptive Optics Imaging and a Revised Starburst Age for the Companion
We present the results of adaptive-optics imaging of the z=0.2923 QSO PG
1700+518 in the J and H bands. The extension to the north of the QSO is clearly
seen to be a discrete companion with a well-defined tidal tail, rather than a
feature associated with the host galaxy of PG 1700+518 itself. On the other
hand, an extension to the southwest of the QSO (seen best in deeper, but
lower-resolution, optical images) does likely comprise tidal material from the
host galaxy. The SED derived from images in J, H, and two non-standard optical
bands indicates the presence of dust intermixed with the stellar component. We
use our previously reported Keck spectrum of the companion, the SED found from
the imaging data, and updated spectral-synthesis models to constrain the
stellar populations in the companion and to redetermine the age of the
starburst. While our best-fit age of 0.085 Gyr is nearly the same as our
earlier determination, the fit of the new models is considerably better. This
age is found to be remarkably robust with respect to different assumptions
about the nature of the older stellar component and the effects of dust.Comment: 11 pages; includes two eps figures. Latex (AASTEX). Two additional
figures in gif format. Postscript version including all figs. (424 kb) can be
obtained from http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
ApJ. Letter
Weighted-density approximation for general nonuniform fluid mixtures
In order to construct a general density-functional theory for nonuniform
fluid mixtures, we propose an extension to multicomponent systems of the
weighted-density approximation (WDA) of Curtin and Ashcroft [Phys. Rev. A 32,
2909 (1985)]. This extension corrects a deficiency in a similar extension
proposed earlier by Denton and Ashcroft [Phys. Rev. A 42, 7312 (1990)], in that
that functional cannot be applied to the multi-component nonuniform fluid
systems with spatially varying composition, such as solid-fluid interfaces. As
a test of the accuracy of our new functional, we apply it to the calculation of
the freezing phase diagram of a binary hard-sphere fluid, and compare the
results to simulation and the Denton-Ashcroft extension.Comment: 4 pages, 4 figures, to appear in Phys. Rev. E as Brief Repor
Measurement of Temporal Correlations of the Overhauser Field in a Double Quantum Dot
In quantum dots made from materials with nonzero nuclear spins, hyperfine
coupling creates a fluctuating effective Zeeman field (Overhauser field) felt
by electrons, which can be a dominant source of spin qubit decoherence. We
characterize the spectral properties of the fluctuating Overhauser field in a
GaAs double quantum dot by measuring correlation functions and power spectra of
the rate of singlet-triplet mixing of two separated electrons. Away from zero
field, spectral weight is concentrated below 10 Hz, with 1/f^2 dependence on
frequency, f. This is consistent with a model of nuclear spin diffusion, and
indicates that decoherence can be largely suppressed by echo techniques.Comment: related papers available at http://marcuslab.harvard.ed
Providing Self-Aware Systems with Reflexivity
We propose a new type of self-aware systems inspired by ideas from
higher-order theories of consciousness. First, we discussed the crucial
distinction between introspection and reflexion. Then, we focus on
computational reflexion as a mechanism by which a computer program can inspect
its own code at every stage of the computation. Finally, we provide a formal
definition and a proof-of-concept implementation of computational reflexion,
viewed as an enriched form of program interpretation and a way to dynamically
"augment" a computational process.Comment: 12 pages plus bibliography, appendices with code description, code of
the proof-of-concept implementation, and examples of executio
Effect of Exchange Interaction on Spin Dephasing in a Double Quantum Dot
We measure singlet-triplet dephasing in a two-electron double quantum dot in
the presence of an exchange interaction which can be electrically tuned from
much smaller to much larger than the hyperfine energy. Saturation of dephasing
and damped oscillations of the spin correlator as a function of time are
observed when the two interaction strengths are comparable. Both features of
the data are compared with predictions from a quasistatic model of the
hyperfine field.Comment: see related papers at http://marcuslab.harvard.ed
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