70 research outputs found
ADHD patients fail to maintain task goals in face of subliminally and consciously induced cognitive conflicts
Background. Attention deficit hyperactivity disorder (ADHD) patients have been reported to display deficits in action control processes. While it is known that subliminally and consciously induced conflicts interact and conjointly modulate action control in healthy subjects, this has never been investigated for ADHD.
Method. We investigated the (potential) interaction of subliminally and consciously triggered response conflicts in children with ADHD and matched healthy controls using neuropsychological methods (event-related potentials; ERPs) to identify the involved cognitive sub-processes.
Results. Unlike healthy controls, ADHD patients showed no interaction of subliminally and consciously triggered response conflicts. Instead, they only showed additive effects as their behavioural performance (accuracy) was equally impaired by each conflict and they showed no signs of task-goal shielding even in cases of low conflict load. Of note, this difference between ADHD and controls was not rooted in early bottom-up attentional stimulus processing as reflected by the P1 and N1 ERPs. Instead, ADHD showed either no or reversed modulations of conflict-related processes and response selection as reflected by the N2 and P3 ERPs.
Conclusion. There are fundamental differences in the architecture of cognitive control which might be of use for future diagnostic procedures. Unlike healthy controls, ADHD patients do not seem to be endowed with a threshold which allows them to maintain high behavioural performance in the face of low conflict load. ADHD patients seem to lack sufficient top-down attentional resources to maintain correct response selection in the face of conflicts by shielding the response selection process from response tendencies evoked by any kind of distractor
Digital modulation of the nickel valence state in a cuprate-nickelate heterostructure
Layer-by-layer oxide molecular beam epitaxy has been used to synthesize
cuprate-nickelate multilayer structures of composition
(LaCuO)/LaO/(LaNiO). In a combined experimental and
theoretical study, we show that these structures allow a clean separation of
dopant and doped layers. Specifically, the LaO layer separating cuprate and
nickelate blocks provides an additional charge that, according to density
functional theory calculations, is predominantly accommodated in the
interfacial nickelate layers. This is reflected in an elongation of bond
distances and changes in valence state, as observed by scanning transmission
electron microscopy and x-ray absorption spectroscopy. Moreover, the predicted
charge disproportionation in the nickelate interface layers leads to a
thickness-dependent metal-to-insulator transition for , as observed in
electrical transport measurements. The results exemplify the perspectives of
charge transfer in metal-oxide multilayers to induce doping without introducing
chemical and structural disorder
Tunable Charge and Spin Order in PrNiO Thin Films and Superlattices
We have used polarized Raman scattering to probe lattice vibrations and
charge ordering in 12 nm thick, epitaxially strained PrNiO films, and in
superlattices of PrNiO with the band-insulator PrAlO. A carefully
adjusted confocal geometry was used to eliminate the substrate contribution to
the Raman spectra. In films and superlattices under tensile strain, which
undergo a metal-insulator transition upon cooling, the Raman spectra reveal
phonon modes characteristic of charge ordering. These anomalous phonons do not
appear in compressively strained films, which remain metallic at all
temperatures. For superlattices under compressive strain, the Raman spectra
show no evidence of anomalous phonons indicative of charge ordering, while
complementary resonant x-ray scattering experiments reveal antiferromagnetic
order associated with a modest increase in resistivity upon cooling. This
confirms theoretical predictions of a spin density wave phase driven by spatial
confinement of the conduction electrons.Comment: PRL, in pres
Quantitative determination of bond order and lattice distortions in nickel oxide heterostructures by resonant x-ray scattering
We present a combined study of Ni -edge resonant x-ray scattering and
density functional calculations to probe and distinguish electronically driven
ordering and lattice distortions in nickelate heterostructures. We demonstrate
that due to the low crystal symmetry, contributions from structural distortions
can contribute significantly to the energy-dependent Bragg peak intensities of
a bond-ordered NdNiO reference film. For a LaNiO-LaAlO superlattice
that exhibits magnetic order, we establish a rigorous upper bound on the
bond-order parameter. We thus conclusively confirm predictions of a dominant
spin density wave order parameter in metallic nickelates with a
quasi-two-dimensional electronic structure
Long-range charge density wave proximity effect at cuprate-manganate interfaces
The interplay between charge density waves (CDWs) and high-temperature
superconductivity is currently under intense investigation. Experimental
research on this issue is difficult because CDW formation in bulk copper-oxides
is strongly influenced by random disorder, and a long-range-ordered CDW state
in high magnetic fields is difficult to access with spectroscopic and
diffraction probes. Here we use resonant x-ray scattering in zero magnetic
field to show that interfaces with the metallic ferromagnet
LaCaMnO greatly enhance CDW formation in the optimally
doped high-temperature superconductor YBaCuO (), and that this effect persists over several tens of nm. The wavevector
of the incommensurate CDW serves as an internal calibration standard of the
charge carrier concentration, which allows us to rule out any significant
influence of oxygen non-stoichiometry, and to attribute the observed phenomenon
to a genuine electronic proximity effect. Long-range proximity effects induced
by heterointerfaces thus offer a powerful method to stabilize the charge
density wave state in the cuprates, and more generally, to manipulate the
interplay between different collective phenomena in metal oxides.Comment: modified version published in Nature Material
Plastic Optical Fiber Technology for Reliable Home Networking: Overview and Results of the EU Project POF-ALL
The rising performance of broadband connections for residential users, particularly in conjunction with fiber to the home, will present a new challenge for telecom operators in the short and medium terms: how to deliver the high bit rate digital signals with high quality-of-service to all consumer devices scattered inside the building of final users? Among the many different solutions for the home network, we review in this article the use of polymer optical fibers for short-reach and high-capacity optical communications for residential customer premises. POF is an easy-to-install, low-cost, and eye-safe solution for these networks, with the potential of being future-proof. In this article the state of the art in POF technology is presented by summarizing significant results achieved in the European project POF-ALL. Data transmission rates of more than 1 Gb/s over 50+ m and 100 Mb/s over 200+ m of standard step-index POF have been show
Transfer of Magnetic Order and Anisotropy through Epitaxial Integration of 3d and 4f Spin Systems
Resonant x ray scattering at the Dy M 5 and Ni L 3 absorption edges was used to probe the temperature and magnetic field dependence of magnetic order in epitaxial LaNiO3 DyScO3 superlattices. For superlattices with 2 unit cell thick LaNiO3 layers, a commensurate spiral state develops in the Ni spin system below 100 K. Upon cooling below T ind 18 K, Dy Ni exchange interactions across the LaNiO3 DyScO3 interfaces induce collinear magnetic order of interfacial Dy moments as well as a reorientation of the Ni spins to a direction dictated by the strong magnetocrystalline anisotropy of Dy. This transition is reversible by an external magnetic field of 3 T. Tailored exchange interactions between rare earth and transition metal ions thus open up new perspectives for the manipulation of spin structures in metal oxide heterostructures and device
Doping dependent charge order correlations in electron-doped cuprates
Understanding the interplay between charge order (CO) and other phenomena
(e.g. pseudogap, antiferromagnetism, and superconductivity) is one of the
central questions in the cuprate high-temperature superconductors. The
discovery that similar forms of CO exist in both hole- and electron-doped
cuprates opened a path to determine what subset of the CO phenomenology is
universal to all the cuprates. Here, we use resonant x-ray scattering to
measure the charge order correlations in electron-doped cuprates (La2-xCexCuO4
and Nd2-xCexCuO4) and their relationship to antiferromagnetism, pseudogap, and
superconductivity. Detailed measurements of Nd2-xCexCuO4 show that CO is
present in the x = 0.059 to 0.166 range, and that its doping dependent
wavevector is consistent with the separation between straight segments of the
Fermi surface. The CO onset temperature is highest between x = 0.106 and 0.166,
but decreases at lower doping levels, indicating that it is not tied to the
appearance of antiferromagnetic correlations or the pseudogap. Near optimal
doping, where the CO wavevector is also consistent with a previously observed
phonon anomaly, measurements of the CO below and above the superconducting
transition temperature, or in a magnetic field, show that the CO is insensitive
to superconductivity. Overall these findings indicate that, while verified in
the electron-doped cuprates, material-dependent details determine whether the
CO correlations acquire sufficient strength to compete for the ground state of
the cuprates.Comment: Supplementary information available upon reques
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