22,657 research outputs found
The effect of stimulus duration on over-selectivity: evidence for the role of within-compound associations
The phenomenon whereby behaviour becomes controlled by one aspect of the environment at the expense of other aspects of the environment (stimulus over-selectivity) is widespread across many intellectual and developmental disabilities. However, the theoretical mechanisms underpinnings over-selectivity are not understood. Given similarities between over-selectivity and overshadowing, exploring over-selectivity using associative learning paradigms might allow better theoretical understanding of the phenomenon. Three experiments explored over-selectivity using a simultaneous discrimination task with typically developing participants undergoing a cognitively demanding task. Experiment 1 investigated whether stimulus duration effects found within the overshadowing literature also occurred in an over-selectivity paradigm, and demonstrated that greater over-selectivity was observed when stimuli were presented for short durations (2s and 5s) compared to longer durations (10s). Experiment 2 demonstrated that a post-training revaluation procedure resulted in retrospective revaluation for stimuli presented at shorter durations (2s) and mediated extinction for stimuli presented at longer durations (10s). Such results replicate findings from the overshadowing literature that have been interpreted in terms of within-compound associations while also supporting assumptions made by an extended comparator hypothesis. Experiment 3 uses an additional control condition to further demonstrate that the retrospective revaluation is a genuine revaluation effect. Additionally, the experiment provides further evidence for the within-compound association explanation of the results through manipulating the consistency with which elements of a compound were paired during training. Taken together, the findings highlight the necessity to consider the role of within-compound associations in over-selectivity, allowing for a better understanding of over-selectivity effects
High-resolution 3D weld toe stress analysis and ACPD method for weld toe fatigue crack initiation
Weld toe fatigue crack initiation is highly dependent on the local weld toe stress-concentrating geometry including any inherent flaws. These flaws are responsible for premature fatigue crack initiation (FCI) and must be minimised to maximise the fatigue life of a welded joint. In this work, a data-rich methodology has been developed to capture the true weld toe geometry and resulting local weld toe stress-field and relate this to the FCI life of a steel arc-welded joint. To obtain FCI lives, interrupted fatigue test was performed on the welded joint monitored by a novel multi-probe array of alternating current potential drop (ACPD) probes across the weld toe. This setup enabled the FCI sites to be located and the FCI life to be determined and gave an indication of early fatigue crack propagation rates. To understand fully the local weld toe stress-field, high-resolution (5 mu m) 3D linear-elastic finite element (FE) models were generated from X-ray micro-computed tomography (mu-CT) of each weld toe after fatigue testing. From these models, approximately 202 stress concentration factors (SCFs) were computed for every 1 mm of weld toe. These two novel methodologies successfully link to provide an assessment of the weld quality and this is correlated with the fatigue performance
Strong and weak semiclassical limits for some rough Hamiltonians
We present several results concerning the semiclassical limit of the time
dependent Schr\"odinger equation with potentials whose regularity doesn't
guarantee the uniqueness of the underlying classical flow. Different topologies
for the limit are considered and the situation where two bicharateristics can
be obtained out of the same initial point is emphasized
An isoperimetric problem for leaky loops and related mean-chord inequalities
We consider a class of Hamiltonians in with attractive
interaction supported by piecewise smooth loops of a fixed
length , formally given by with .
It is shown that the ground state of this operator is locally maximized by a
circular . We also conjecture that this property holds globally and
show that the problem is related to an interesting family of geometric
inequalities concerning mean values of chords of .Comment: LaTeX, 16 page
From bcc to fcc: interplay between oscillating long-range and repulsive short-range forces
This paper supplements and partly extends an earlier publication, Phys. Rev.
Lett. 95, 265501 (2005). In -dimensional continuous space we describe the
infinite volume ground state configurations (GSCs) of pair interactions \vfi
and \vfi+\psi, where \vfi is the inverse Fourier transform of a nonnegative
function vanishing outside the sphere of radius , and is any
nonnegative finite-range interaction of range , where
. In three dimensions the decay of \vfi can be as slow
as , and an interaction of asymptotic form
is among the examples. At a dimension-dependent
density the ground state of \vfi is a unique Bravais lattice, and
for higher densities it is continuously degenerate: any union of Bravais
lattices whose reciprocal lattice vectors are not shorter than is a GSC.
Adding decreases the ground state degeneracy which, nonetheless, remains
continuous in the open interval , where is the
close-packing density of hard balls of diameter . The ground state is
unique at both ends of the interval. In three dimensions this unique GSC is the
bcc lattice at and the fcc lattice at .Comment: Published versio
Adiabatically switched-on electrical bias in continuous systems, and the Landauer-Buttiker formula
Consider a three dimensional system which looks like a cross-connected pipe
system, i.e. a small sample coupled to a finite number of leads. We investigate
the current running through this system, in the linear response regime, when we
adiabatically turn on an electrical bias between leads. The main technical tool
is the use of a finite volume regularization, which allows us to define the
current coming out of a lead as the time derivative of its charge. We finally
prove that in virtually all physically interesting situations, the conductivity
tensor is given by a Landauer-B{\"u}ttiker type formula.Comment: 20 pages, submitte
Reply to "Comment on 'Quantization of FRW spacetimes in the presence of a cosmological constant and radiation'"
The Comment by Amore {\it et al.} [gr-qc/0611029] contains a valid criticism
of the numerical precision of the results reported in a recent paper of ours
[Phys. Rev. D {\bf 73}, 044022 (2006)], as well as fresh ideas on how to
characterize a quantum cosmological singularity. However, we argue that,
contrary to what is suggested in the Comment, the quantum cosmological models
we studied show hardly any sign of singular behavior.Comment: 4 pages, accepted by Physical Review
Generalized MICZ-Kepler Problems and Unitary Highest Weight Modules
For each integer , we demonstrate that a -dimensional
generalized MICZ-Kepler problem has an \mr{Spin}(2, 2n+2) dynamical symmetry
which extends the manifest \mr{Spin}(2n+1) symmetry. The Hilbert space of
bound states is shown to form a unitary highest weight \mr{Spin}(2,
2n+2)-module which occurs at the first reduction point in the
Enright-Howe-Wallach classification diagram for the unitary highest weight
modules. As a byproduct, we get a simple geometric realization for such a
unitary highest weight \mr{Spin}(2, 2n+2)-module.Comment: 27 pages, Refs. update
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