8,925 research outputs found
Normal mere exposure effect with impaired recognition in Alzheimer’s disease.
We investigated the mere exposure effect and the explicit memory in Alzheimer’s disease (AD) patients and elderly control subjects, using unfamiliar faces. During the exposure phase, the subjects estimated the age of briefly flashed faces. The mere exposure effect was examined by presenting pairs of faces (old and new) and asking participants to select the face they liked. The participants were then presented with a forced-choice explicit recognition task. Controls subjects exhibited above-chance preference and recognition scores for old faces. The AD patients also showed the mere exposure effect but no explicit recognition. These results suggest that the processes involved in the mere exposure effect are preserved in AD patients despite their impaired explicit recognition. The results are discussed in terms of Seamon et al.’s proposal (1995) that processes involved in the mere exposure effect are equivalent to those subserving perceptual priming. These processes would depend on extrastriate areas which are relatively preserved in AD patients
Observation of Stueckelberg oscillations in dipole-dipole interactions
We have observed Stueckelberg oscillations in the dipole-dipole interaction
between Rydberg atoms with an externally applied radio-frequency field. The
oscillating RF field brings the interaction between cold Rydberg atoms in two
separated volumes into resonance. We observe multi-photon transitions when
varying the amplitude of the RF-field and the static electric field offset. The
angular momentum states we use show a quadratic Stark shift, which leads to a
fundamentally different behavior than linearly shifting states. Both cases are
studied theoretically using the Floquet approach and are compared. The
amplitude of the sidebands, related to the interaction strength, is given by
the Bessel function in the linearly shifting case and by the generalized Bessel
function in the quadratically shifting case. The oscillatory behavior of both
functions corresponds to Stueckelberg oscillations, an interference effect
described by the semi-classical Landau-Zener-Stueckelberg model. The
measurements prove coherent dipole-dipole interaction during at least 0.6
micro-seconds
On the normality of Higgins commutators
In a semi-abelian context, we study the condition (NH) asking that Higgins
commutators of normal subobjects are normal subobjects. We provide examples of
categories that do or do not satisfy this property. We focus on the
relationship with the "Smith is Huq" condition (SH) and characterise those
semi-abelian categories in which both (NH) and (SH) hold in terms of reflection
and preservation properties of the change of base functors of the fibration of
points.Comment: 15 pages; final published versio
Breeding drought tolerant cowpea: constraints, accomplishments, and future prospects
This review presents an overview of accomplishments on different aspects of cowpea breeding for drought tolerance. Furthermore it provides options to enhance the genetic potential of the crop by minimizing yield loss due to drought stress. Recent efforts have focused on the genetic dissection of drought tolerance through identification of markers defining quantitative trait loci (QTL) with effects on specific traits related to drought tolerance. Others have studied the relationship of the drought response and yield components, morphological traits and physiological parameters. To our knowledge, QTLs with effects on drought tolerance have not yet been identified in cowpea. The main reason is that very few researchers are working on drought tolerance in cowpea. Some other reasons might be related to the complex nature of the drought stress response, and partly to the difficulties associated with reliable and reproducible measurements of a single trait linked to specific molecular markers to be used for marker assisted breeding. Despite the fact that extensive research has been conducted on the screening aspects for drought tolerance in cowpea only very few¿like the `wooden box¿ technique¿have been successfully used to select parental genotypes exhibiting different mechanisms of drought tolerance. Field and pot testing of these genotypes demonstrated a close correspondence between drought tolerance at seedling and reproductive stages. Some researchers selected a variety of candidate genes and used differential screening methods to identify cDNAs from genes that may underlie different drought tolerance pathways in cowpea. Reverse genetic analysis still needs to be done to confirm the functions of these genes in cowpea. Understanding the genetics of drought tolerance and identification of DNA markers linked to QTLs, with a clear path towards localizing chromosomal regions or candidate genes involved in drought tolerance will help cowpea breeders to develop improved varieties that combine drought tolerance with other desired traits using marker assisted selection
Unstable coronal loops : numerical simulations with predicted observational signatures
We present numerical studies of the nonlinear, resistive magnetohydrodynamic
(MHD) evolution of coronal loops. For these simulations we assume that the
loops carry no net current, as might be expected if the loop had evolved due to
vortex flows. Furthermore the initial equilibrium is taken to be a cylindrical
flux tube with line-tied ends. For a given amount of twist in the magnetic
field it is well known that once such a loop exceeds a critical length it
becomes unstableto ideal MHD instabilities. The early evolution of these
instabilities generates large current concentrations. Firstly we show that
these current concentrations are consistent with the formation of a current
sheet. Magnetic reconnection can only occur in the vicinity of these current
concentrations and we therefore couple the resistivity to the local current
density. This has the advantage of avoiding resistive diffusion in regions
where it should be negligible. We demonstrate the importance of this procedure
by comparison with simulations based on a uniform resistivity. From our
numerical experiments we are able to estimate some observational signatures for
unstable coronal loops. These signatures include: the timescale of the loop
brightening; the temperature increase; the energy released and the predicted
observable flow speeds. Finally we discuss to what extent these observational
signatures are consistent with the properties of transient brightening loops.Comment: 13 pages, 9 figure
Radio-frequency driven dipole-dipole interactions in spatially separated volumes
Radio-frequency (rf) fields in the MHz range are used to induce resonant
energy transfer between cold Rydberg atoms in spatially separated volumes.
After laser preparation of the Rydberg atoms, dipole-dipole coupling excites
the 49s atoms in one cylinder to the 49p state while the 41d atoms in the
second cylinder are transferred down to the 42p state. The energy exchanged
between the atoms in this process is 33 GHz. An external rf-field brings this
energy transfer into resonance. The strength of the interaction has been
investigated as a function of amplitude (0-1 V/cm) and frequency (1-30 MHz) of
the rf-field and as a function of a static field offset. Multi-photon
transitions up to fifth order as well as selection rules prohibiting the
process at certain fields have been observed. The width of the resonances has
been reduced compared to earlier results by switching off external magnetic
fields of the magneto-optical trap, making sub-MHz spectroscopy possible. All
features are well reproduced by theoretical calculations taking the strong
ac-Stark shift due to the rf-field into account
The importance of heterogeneity in large-scale replications
In a large-scale replication effort, Klein et al. (2018, https://doi.org/10.1177/2515245918810225) investigate the variation in replicability and effect size across many different samples and settings. The authors concluded that, for any given effect being studied, heterogeneity across samples and settings does not explain failures to replicate. In the current commentary, we argue that the heterogeneity observed indeed has implications for replication failures, as well as for statistical power and theory development. We argue that psychological scientific research questions should be contextualized—considering how historical, political, or cultural circumstances might affect study results. We discuss how a perspectivist approach to psychological science is a fruitful way for designing research that aims to explain effect size heterogeneity.</p
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