1,946 research outputs found
Primed to be inflexible: the influence of set size on cognitive flexibility during childhood
One of the hallmarks of human cognition is cognitive flexibility, the ability to adapt thoughts and behaviors according to changing task demands. Previous research has suggested that the number of different exemplars that must be processed within a task (the set size) can influence an individual’s ability to switch flexibly between different tasks. This paper provides evidence that when tasks have a small set size, children’s cognitive flexibility is impaired compared to when tasks have a large set size. This paper also offers insights into the mechanism by which this effect comes about. Understanding how set size interacts with task-switching informs the debate regarding the relative contributions of bottom-up priming and top-down control processes in the development of cognitive flexibility. We tested two accounts for the relationship between set size and cognitive flexibility: the (bottom-up) Stimulus-Task Priming account and the (top-down) Rule Representation account. Our findings offered support for the Stimulus-Task Priming account, but not for the Rule Representation account. They suggest that children are susceptible to bottom-up priming caused by stimulus repetition, and that this priming can impair their ability to switch between tasks. These findings make important theoretical and practical contributions to the executive function literature: Theoretically, they show that the basic features of a task exert a significant influence on children’s ability to flexibly shift between tasks through bottom-up priming effects. Practically, they suggest that children’s cognitive flexibility may have been underestimated relative to adults’, as paradigms used with children typically have a smaller set size than those used with adults. These findings also have applications in education, where they have the potential to inform teaching in key areas where cognitive flexibility is required, such as mathematics and literacy
A Complex Chemical Potential: Signature of Decay in a Bose-Einstein Condensate
We explore the zero-temperature statics of an atomic Bose-Einstein condensate
in which a Feshbach resonance creates a coupling to a second condensate
component of quasi-bound molecules. Using a variational procedure to find the
equation of state, the appearance of this binding is manifest in a collapsing
ground state, where only the molecular condensate is present up to some
critical density. Further, an excited state is seen to reproduce the usual
low-density atomic condensate behavior in this system, but the molecular
component is found to produce an underlying decay, quantified by the imaginary
part of the chemical potential. Most importantly, the unique decay rate
dependencies on density () and on scattering length () can be measured in experimental tests of this theory.Comment: 4 pages, 1 figur
12.2-GHz methanol maser MMB follow-up catalogue - II. Longitude range 186 to 330 degrees
We present the second portion of a catalogue of 12.2-GHz methanol masers
detected towards 6.7-GHz methanol masers observed in the unbiased Methanol
Multibeam (MMB) Survey. Using the Parkes radio telescope we have targeted all
207 6.7-GHz methanol masers in the longitude range 186 to 330 degrees for
12.2-GHz counterparts. We report the detection of 83 12.2-GHz methanol masers,
and one additional source which we suspect is thermal emission, equating to a
detection rate of 40 per cent. Of the 83 maser detections, 39 are reported here
for the first time. We discuss source properties, including variability and
highlight a number of unusual sources. We present a list of 45 candidates that
are likely to harbor methanol masers in the 107.0-GHz transition.Comment: Accepted MNRAS 19 July 201
Multi-transition study and new detections of class II methanol masers
We have used the ATNF Mopra antenna and the SEST antenna to search in the
directions of several class II methanol maser sources for emission from six
methanol transitions in the frequency range 85-115 GHz. The transitions were
selected from excitation studies as potential maser candidates. Methanol
emission at one or more frequencies was detected from five of the maser
sources, as well as from Orion KL. Although the lines are weak, we find
evidence of maser origin for three new lines in G345.01+1.79, and possibly one
new line in G9.62+0.20.
The observations, together with published maser observations at other
frequencies, are compared with methanol maser modelling for G345.01+1.79 and
NGC6334F. We find that the majority of observations in both sources are
consistent with a warm dust (175 K) pumping model at hydrogen density ~10^6
cm^-3 and methanol column density ~5 x 10^17 cm^-2. The substantial differences
between the maser spectra in the two sources can be attributed to the geometry
of the maser region.Comment: 13 pages, 6 figures, Accepted for publication in MNRA
VLBI study of maser kinematics in high-mass SFRs. II. G23.01-0.41
The present paper focuses on the high-mass star-forming region G23.01-0.41.
Methods: Using the VLBA and the EVN arrays, we conducted phase-referenced
observations of the three most powerful maser species in G23.01-0.41: H2O at
22.2 GHz (4 epochs), CH3OH at 6.7 GHz (3 epochs), and OH at 1.665 GHz (1
epoch). In addition, we performed high-resolution (> 0".1), high-sensitivity (<
0.1 mJy) VLA observations of the radio continuum emission from the HMC at 1.3
and 3.6 cm. Results: We have detected H2O, CH3OH, and OH maser emission
clustered within 2000 AU from the center of a flattened HMC, oriented SE-NW,
from which emerges a massive 12CO outflow, elongated NE-SW, extended up to the
pc-scale. Although the three maser species show a clearly different spatial and
velocity distribution and sample distinct environments around the massive YSO,
the spatial symmetry and velocity field of each maser specie can be explained
in terms of expansion from a common center, which possibly denotes the position
of the YSO driving the maser motion. Water masers trace both a fast shock (up
to 50 km/s) closer to the YSO, powered by a wide-angle wind, and a slower (20
km/s) bipolar jet, at the base of the large-scale outflow. Since the compact
free-free emission is found offset from the putative location of the YSO along
a direction consistent with that of the maser jet axis, we interpret the radio
continuum in terms of a thermal jet. The velocity field of methanol masers can
be explained in terms of a composition of slow (4 km/s in amplitude) motions of
radial expansion and rotation about an axis approximately parallel to the maser
jet. Finally, the distribution of line of sight velocities of the hydroxyl
masers suggests that they can trace gas less dense (n(H2) < 10^6 cm^-3) and
more distant from the YSO than that traced by the water and methanol masers,
which is expanding toward the observer. (Abridged)Comment: 23 pages, 8 figures, 4 tables, accepted by Astronomy and Astrophysic
12.2-GHz methanol maser MMB follow-up catalogue - I. Longitude range 330 to 10 degrees
We present a catalogue of 12.2-GHz methanol masers detected towards 6.7-GHz
methanol masers observed in the unbiased Methanol Multibeam (MMB) survey in the
longitude range 330\circ (through 360\circ) to 10\circ. This is the first
portion of the catalogue which, when complete, will encompass all of the MMB
detections. We report the detection of 184 12.2-GHz sources towards 400 6.7-GHz
methanol maser targets, equating to a detection rate of 46 per cent. Of the 184
12.2-GHz detections, 117 are reported here for the first time. We draw
attention to a number of 'special' sources, particularly those with emission at
12.2-GHz stronger than their 6.7-GHz counterpart and conclude that these
unusual sources are not associated with a specific evolutionary stage.Comment: accepted to MNRAS 21 Dec 201
First Interferometric Images of the 36 GHz Methanol Masers in the DR21 Complex
Class I methanol masers are believed to be produced in the shock-excited
environment around star-forming regions. Many authors have argued that the
appearance of various subsets of class I masers may be indicative of specific
evolutionary stages of star formation or excitation conditions. Until recently,
however, no major interferometer was capable of imaging the important 36 GHz
transition. We report on Expanded Very Large Array observations of the 36 GHz
methanol masers and Submillimeter Array observations of the 229 GHz methanol
masers in DR21(OH), DR21N, and DR21W. The distribution of 36 GHz masers in the
outflow of DR21(OH) is similar to that of the other class I methanol
transitions, with numerous multitransition spatial overlaps. At the site of the
main continuum source in DR21(OH), class I masers at 36 and 229 GHz are found
in virtual overlap with class II 6.7 GHz masers. To the south of the outflow,
the 36 GHz masers are scattered over a large region but usually do not appear
coincident with 44 GHz masers. In DR21W we detect an "S-curve" signature in
Stokes V that implies a large value of the magnetic field strength if
interpreted as due to Zeeman splitting, suggesting either that class I masers
may exist at higher densities than previously believed or that the direct
Zeeman interpretation of S-curve Stokes V profiles in class I masers may be
incorrect. We find a diverse variety of different maser phenomena in these
sources, suggestive of differing physical conditions among them.Comment: 8 pages, accepted for publication in Ap
Two-channel Kondo model as a generalized one-dimensional inverse square long-range Haldane-Shastry spin model
Majorana fermion representations of the algebra associated with spin, charge,
and flavor currents have been used to transform the two-channel Kondo
Hamiltonian. Using a path integral formulation, we derive a reduced effective
action with long-range impurity spin-spin interactions at different imaginary
times. In the semiclassical limit, it is equivalent to a one-dimensional
Heisenberg spin chain with two-spin, three-spin, etc. long-range interactions,
as a generalization of the inverse-square long-range Haldane-Shastry spin
model. In this representation the elementary excitations are "semions", and the
non-Fermi-liquid low-energy properties of the two-channel Kondo model are
recovered.Comment: 4 pages, no figure, to be published in J. Phys.: Condens. Matter,
200
Magnetically Robust Non-Fermi Liquid Behavior in Heavy Fermion Systems with f^2-Configuration: Competition between Crystalline-Electric-Field and Kondo-Yosida Singlets
We study a magnetic field effect on the Non-Fermi Liquid (NFL) which arises
around the quantum critical point (QCP) due to the competition between the
f^2-crystalline-electric-field singlet and the Kondo-Yosida singlet states by
using the numerical renormalization ground method. We show the characteristic
temperature T_F^*, corresponding to a peak of a specific heat, is not affected
by the magnetic field up to H_z^* which is determined by the distance from the
QCP or characteristic energy scales of each singlet states. As a result, in the
vicinity of QCP, there are parameter regions where the NFL is robust against
the magnetic field, at an observable temperature range T > T_F^*, up to H_z^*
which is far larger than T_F^* and less than min(T_{K2}, $Delta).Comment: 8 pages, 9 figur
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