6,024 research outputs found
Modelling food storage management in ants: mechanisms and social implications.
According to the complementary learning systems (CLS) account of word learning, novel words are rapidly acquired (learning system 1), but slowly integrated into the mental lexicon (learning system 2). This two-step learning process has been shown to apply to novel word forms. In this study, we investigated whether novel word meanings are also gradually integrated after acquisition by measuring the extent to which newly learned words were able to prime semantically related words at two different time points. In addition, we investigated whether modality at study modulates this integration process. Sixty-four adult participants studied novel words together with written or spoken definitions. These words did not prime semantically related words directly following study, but did so after a 24-hour delay. This significant increase in the magnitude of the priming effect suggests that semantic integration occurs over time. Overall, words that were studied with a written definition showed larger priming effects, suggesting greater integration for the written study modality. Although the process of integration, reflected as an increase in the priming effect over time, did not significantly differ between study modalities, words studied with a written definition showed the most prominent positive effect after a 24-hour delay. Our data suggest that semantic integration requires time, and that studying in written format benefits semantic integration more than studying in spoken format. These findings are discussed in light of the CLS theory of word learning
Terahertz response of dipolar impurities in polar liquids: On anomalous dielectric absorption of protein solutions
A theory of radiation absorption by dielectric mixtures is presented. The
coarse-grained formulation is based on the wavevector-dependent correlation
functions of molecular dipoles of the host polar liquid and a density-density
structure factor of the positions of the solutes. A nonlinear dependence of the
absorption coefficient on the solute concentration is predicted and originates
from the mutual polarization of the liquid surrounding the solutes by the
collective field of the solute dipoles aligned along the radiation field. The
theory is applied to terahertz absorption of hydrated saccharides and proteins.
While the theory gives an excellent account of the observations for saccharides
without additional assumptions and fitting parameters, experimental absorption
coefficient of protein solutions significantly exceeds theoretical calculations
within standard dielectric models and shows a peak against the protein
concentration. A substantial polarization of protein's hydration shell is
required to explain the differences between standard theories and experiment.
When the correlation function of the total dipole moment of the protein with
its hydration shell from numerical simulations is used in the present
analytical model an absorption peak similar to that seen is experiment is
obtained. The result is sensitive to the specifics of protein-protein
interactions in solution. Numerical testing of the theory requires the
combination of terahertz dielectric and small-angle scattering measurements.Comment: 11 p
Pressure-temperature Phase Diagram of Polycrystalline UCoGe Studied by Resistivity Measurement
Recently, coexistence of ferromagnetism (T_Curie = 2.8K) and
superconductivity (T_sc = 0.8K) has been reported in UCoGe, a compound close to
a ferromagnetic instability at ambient pressure P. Here we present resistivity
measurements under pressure on a UCoGe polycrystal. The phase diagram obtained
from resistivity measurements on a polycrystalline sample is found to be
qualitatively different to those of all other ferromagnetic superconductors. By
applying high pressure, ferromagnetism is suppressed at a rate of 1.4 K/GPa. No
indication of ferromagnetic order has been observed above P ~ 1GPa. The
resistive superconducting transition is, however, quite stable in temperature
and persists up to the highest measured pressure of about 2.4GPa.
Superconductivity would therefore appear also in the paramagnetic phase.
However, the appearance of superconductivity seems to change at a
characteristic pressure P* ~ 0.8GPa. Close to a ferromagnetic instability, the
homogeneity of the sample can influence strongly the electronic and magnetic
properties and therefore bulk phase transitions may differ from the
determination by resistivity measurements.Comment: 4 pages, 4 figures, submitted to J. Phys. Soc. Jp
Testing Hardy nonlocality proof with genuine energy-time entanglement
We show two experimental realizations of Hardy ladder test of quantum
nonlocality using energy-time correlated photons, following the scheme proposed
by A. Cabello \emph{et al.} [Phys. Rev. Lett. \textbf{102}, 040401 (2009)].
Unlike, previous energy-time Bell experiments, these tests require precise
tailored nonmaximally entangled states. One of them is equivalent to the
two-setting two-outcome Bell test requiring a minimum detection efficiency. The
reported experiments are still affected by the locality and detection
loopholes, but are free of the post-selection loophole of previous energy-time
and time-bin Bell tests.Comment: 5 pages, revtex4, 6 figure
In situ observations of "cold trap" dehydration in the western tropical Pacific
International audienceWater vapor sonde observations were conducted at Bandung, Indonesia (6.90 S, 107.60 E) and Tarawa, Kiribati (1.35 N, 172.91 E) in December 2003 to examine the efficiency of the "cold trap'' dehydration in the tropical tropopause layer (TTL). Trajectory analysis based on bundles of trajectories suggest that the modification of air parcels' identity due to irreversible mixing by the branching-out and merging-in of nearby trajectories is found to be an important factor, in addition to the routes air parcels are supposed to follow, for interpreting the water vapor concentrations observed by radiosondes in the TTL. Clear correspondence between the observed water vapor concentration and the estimated temperature history of air parcels is found showing that dry air parcels are exposed to low temperatures while humid air parcels do not experience cold conditions during advection, in support of the "cold trap'' hypothesis. It is suggested that the observed air parcel retained the water vapor by roughly twice as much as the minimum saturation mixing ratio after its passage through the "cold trap,'' although appreciable uncertainties remain
Stress acts cumulatively to precipitate Alzheimer’s disease-like tau pathology and cognitive deficits
Stressful life experiences are likely tiological factors in sporadic forms of Alzheimer’s disease (AD). Many AD patients hypersecrete glucocorticoids (GCs), and their GC levels correlate with the rate of cognitive impairment and extent of neuronal atrophy. Severity of cognitive deficits in AD correlates strongly with levels of perphosphorylated forms of the cytoskeletal protein TAU, an essential mediator of the actions of amyloid Beta (ABeta ), another molecule with a key pathogenic role in AD. Our objective was to investigate the sequential interrelationships between these various pathogenic elements, in particular with respect to the mechanisms through which
stress might precipitate cognitive decline. We thus examined whether stress, through the mediation of GCs, influences TAU hyperphosphorylation, a critical and early event in the cascade of processes leading to AD pathology. Results from healthy, wild-type, middle-aged rats show that chronic stress and GC induce abnormal hyperphosphorylation of TAU in the hippocampus and prefrontal cortex (PFC),
with contemporaneous impairments of hippocampus- and PFC-dependent behaviors. Exogenous GC potentiated the ability of centrally infused ABeta to induce hyperphosphorylation of TAU epitopes associated with AD and cytoplasmic accumulation of TAU, while previous
exposure to stress aggravated the biochemical and behavioral effects of GC in ABeta-infused animals. Thus, lifetime stress/GC exposure may have a cumulative impact on the onset and progress of AD pathology, with TAU hyperphosphorylation serving to transduce the negative
effects of stress and GC on cognition.Marie Curie Training FellowshipsEU CRESCENDO Consortium contract FP6-018652University College, London.Max Planck Society and European Union (EU) German-Portuguese Luso-Alemas Program and the EU CRESCENDO Consortium (Contract FP6-018652).German-Portuguese Luso-Alemas Progra
TDP1 deficiency sensitizes human cells to base damage via distinct topoisomerase I and PARP mechanisms with potential applications for cancer therapy
Base damage and topoisomerase I (Top1)-linked DNA breaks are abundant forms of endogenous DNA breakage, contributing to hereditary ataxia and underlying the cytotoxicity of a wide range of anti-cancer agents. Despite their frequency, the overlapping mechanisms that repair these forms of DNA breakage are largely unknown. Here, we report that depletion of Tyrosyl DNA phosphodiesterase 1 (TDP1) sensitizes human cells to alkylation damage and the additional depletion of apurinic/apyrimidinic endonuclease I (APE1) confers hypersensitivity above that observed for TDP1 or APE1 depletion alone. Quantification of DNA breaks and clonogenic survival assays confirm a role for TDP1 in response to base damage, independently of APE1. The hypersensitivity to alkylation damage is partly restored by depletion of Top1, illustrating that alkylating agents can trigger cytotoxic Top1-breaks. Although inhibition of PARP activity does not sensitize TDP1-deficient cells to Top1 poisons, it confers increased sensitivity to alkylation damage, highlighting partially overlapping roles for PARP and TDP1 in response to genotoxic challenge. Finally, we demonstrate that cancer cells in which TDP1 is inherently deficient are hypersensitive to alkylation damage and that TDP1 depletion sensitizes glioblastoma-resistant cancer cells to the alkylating agent temozolomide
Planform selection in two-layer Benard-Marangoni convection
Benard-Marangoni convection in a system of two superimposed liquids is
investigated theoretically. Extending previous studies the complete
hydrodynamics of both layers is treated and buoyancy is consistently taken into
account. The planform selection problem between rolls, squares and hexagons is
investigated by explicitly calculating the coefficients of an appropriate
amplitude equation from the parameters of the fluids. The results are compared
with recent experiments on two-layer systems in which squares at onset have
been reported.Comment: 17 pages, 7 figures, oscillatory instability included, typos
corrected, references adde
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