1,641 research outputs found
Microsaccades and Visual-Spatial Working Memory
Observers performed working memory tasks at varying retinal eccentricities, fixating centrally while microsaccade rates and directions were monitored. We show that microsaccades generate no interference in a working memory task, indicating that spatial working memory is at least partially insulated from oculomotor activity. Intervening tasks during the memory interval affected memory as well as microsaccade patterns. Average microsaccade rate peaks after appearance of a fixation cross at the start of a trial, and dips at cue onset and offset. Direction of stimuli in choice tasks did not influence micro-saccade direction, however. Poorer memory accuracy for locations at greater retinal eccentricity calls for revising ideas of short-term spatial representations to include retinotopic or allocentric code
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Visual vs. Spatial Contributions to Microsaccades and Visual-Spatial Working Memory
Microsaccade rates and directions were monitored while observers performed a visual working memory task at varying retinal eccentricities. We show that microsaccades generate no interference in a working memory task, indicating that spatial working memory is at least partially insulated from oculomotor activity. Intervening tasks during the memory interval affected microsaccade patterns; microsaccade frequency was consistently higher during concurrent spatial tapping (no visual component) than during exposure to dynamic visual noise (no task). Average microsaccade rate peaked after appearance of a fixation cross at the start of a trial, and dipped at cue onset and offset, consistent with previous results. Direction of stimuli in choice tasks did not influence microsaccade direction,however
Microscopic analysis of multipole susceptibility of actinide dioxides: A scenario of multipole ordering in AmO
By evaluating multipole susceptibility of a seven-orbital impurity Anderson
model with the use of a numerical renormalization group method, we discuss
possible multipole states of actinide dioxides at low temperatures. In
particular, here we point out a possible scenario for multipole ordering in
americium dioxide. For Am ion with five electrons, it is considered
that the ground state is doublet and the first excited state is
quartet, but we remark that the ground state is easily
converted due to the competition between spin-orbit coupling and Coulomb
interactions. Then, we find that the quartet can be the ground
state of AmO even for the same crystalline electric field potential. In the
case of quartet ground state, the numerical results suggest that
high-order multipoles such as quadrupole and octupole can be relevant to
AmO.Comment: 8 pages, 4 figures. To appear in Phys. Rev.
Probabilistic Analysis of Power Network Susceptibility to GICs
As reliance on power networks has increased over the last century, the risk
of damage from geomagnetically induced currents (GICs) has become a concern to
utilities. The current state of the art in GIC modelling requires significant
geophysical modelling and a theoretically derived network response, but has
limited empirical validation. In this work, we introduce a probabilistic
engineering step between the measured geomagnetic field and GICs, without
needing data about the power system topology or the ground conductivity
profiles. The resulting empirical ensembles are used to analyse the TVA network
(south-eastern USA) in terms of peak and cumulative exposure to 5 moderate to
intense geomagnetic storms. Multiple nodes are ranked according to
susceptibility and the measured response of the total TVA network is further
calibrated to existing extreme value models. The probabilistic engineering step
presented can complement present approaches, being particularly useful for risk
assessment of existing transformers and power systems.Comment: 6 pages, 7 figures, accepted for PMAPS 202
MendelVar:gene prioritization at GWAS loci using phenotypic enrichment of Mendelian disease genes
The Universlity Class of Monopole Condensation in Non-Compact, Quenched Lattice QED
Finite size scaling studies of monopole condensation in noncompact quenched
lattice indicate an authentic second order phase transition lying in the
universality class of four dimensional percolation. Since the upper critical
dimension of percolation is six, the measured critical indices are far from
mean-field values. We propose a simple set of ratios as the exact critical
indices for this transition. The implication of these results for critical
points in Abelian gauge theories are discussed.Comment: ILL-(TH)-92-6, CERN-TH.6515/92, 10 pages, no figures available as PS
fil
Improvement in the modelling of geomagnetically induced currents in Southern Africa
One of the consequences of the geomagnetic storms resulting from adverse space weather is the induction of geomagnetically induced currents (GICs) in power lines. The GICs that flow in a power transmission network are driven by the induced electric field at the Earth's surface. The electric field, in turn, is affected by the changing magnetic field during a magnetic storm. These GICs can cause extensive and expensive damage to transformers in the power transmission system. Understanding the behaviour of the magnetic field during a magnetic storm is a crucial step in modelling and predicting the electric field and ultimately the GICs in a power transmission network. We present a brief overview of the present status of GIC modelling in southern Africa and then discuss whether it is sufficient to use geomagnetic data from a single magnetic observatory alone to model GICs over the subcontinent. A geomagnetic interpolation method is proposed to improve the modelling of GICs in southern Africa. This improved model is one step closer to our being able to predict GICs accurately in the subcontinent, which will enable power distribution companies to take the necessary precautions to minimize possible transformer damage
Double Parton Scattering Singularity in One-Loop Integrals
We present a detailed study of the double parton scattering (DPS)
singularity, which is a specific type of Landau singularity that can occur in
certain one-loop graphs in theories with massless particles. A simple formula
for the DPS singular part of a four-point diagram with arbitrary
internal/external particles is derived in terms of the transverse momentum
integral of a product of light cone wavefunctions with tree-level matrix
elements. This is used to reproduce and explain some results for DPS
singularities in box integrals that have been obtained using traditional loop
integration techniques. The formula can be straightforwardly generalised to
calculate the DPS singularity in loops with an arbitrary number of external
particles. We use the generalised version to explain why the specific MHV and
NMHV six-photon amplitudes often studied by the NLO multileg community are not
divergent at the DPS singular point, and point out that whilst all NMHV
amplitudes are always finite, certain MHV amplitudes do contain a DPS
divergence. It is shown that our framework for calculating DPS divergences in
loop diagrams is entirely consistent with the `two-parton GPD' framework of
Diehl and Schafer for calculating proton-proton DPS cross sections, but is
inconsistent with the `double PDF' framework of Snigirev.Comment: 29 pages, 8 figures. Minor corrections and clarifications added.
Version accepted for publication in JHE
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