1,593 research outputs found
Electron correlation effects in a wide channel from the quantum Hall edge states
The spatial behavior of Landau levels (LLs) for the quantum Hall
regime at the edge of a wide channel is studied in a self-consistent way by
using a generalized local density approximation proposed here. Both exchange
interaction and strong electron correlations, due to edge states, are taken
into account. They essentially modify the spatial behavior of the occupied
lowest spin-up LL in comparison with that of the lowest spin-down LL, which is
totally empty. The contrast in the spatial behavior can be attributed to a
different effective one-electron lateral confining potentials for the
spin-split LLs. Many-body effects on the spatially inhomogeneous spin-splitting
are calculated within the screened Hartree-Fock approximation. It is shown
that, far from the edges, the maximum activation energy is dominated by the gap
between the Fermi level and the bottom of the spin-down LL, because the gap
between the Fermi level and the spin-up LL is much larger. In other words, the
maximum activation energy in the bulk of the channel corresponds to a highly
asymmetric position of the Fermi level within the gap between spin-down and
spin-up LLs in the bulk. We have also studied the renormalization of the
edge-state group velocity due to electron correlations. The results of the
present theory are in line with those suggested and reported by experiments on
high quality samples.Comment: 9 pages, 4 figure
Correlations, inhomogeneous screening, and suppression of spin-splitting in quantum wires at strong magnetic fields
A self-consistent treatment of exchange and correlation interactions in a
quantum wire (QW) subject to a strong perpendicular magnetic field is presented
using a modified local-density approximation (MLDA). The influence of many-body
interactions on the spin-splitting between the two lowest Landau levels (LLs)
is calculated within the screened Hartree-Fock approximation (SHFA), for
filling factor \nu=1, and the strong spatial dependence of the screening
properties of electrons is taken into account. In comparison with the
Hartree-Fock result, the spatial behavior of the occupied LL in a QW is
strongly modified when correlations are included. Correlations caused by
screening at the edges strongly suppress the exchange splitting and smoothen
the energy dispersion at the edges. The theory accounts well for the
experimentally observed strong suppression of the spin-splitting pertinent to
the \nu=1 quantum Hall effect (QHE) state as well as the destruction of this
state in long, quasi-ballistic GaAlAs/GaAs QWs.Comment: Text 23 pages in Latex/Revtex/preprint format, 6 Postscript figures,
submitted to Physical Review
Evolution of magnetic and microstructural properties of thick sputtered NdFeB films with processing temperature
Ta (100 nm) / NdFeB (5 m) / Ta (100 nm) films have been deposited onto
Si substrates using triode sputtering (deposition rate ~ 18 m/h). A 2-step
procedure was used : deposition at temperatures up to 400 C followed by ex-situ
annealing at higher temperatures. Post-deposition annealing temperatures above
650 C are needed to develop high values of coercivity. The duration of the
annealing time is more critical in anisotropic samples deposited onto heated
substrates than in isotropic samples deposited at lower temperatures. For a
given set of annealing conditions (750 C/ 10'), high heating rates (≥
2000 C / h) favour high coercivity in both isotropic and anisotropic films. The
shape and size of Nd2Fe14B grains depend strongly on the heating rate
Timing of therapeutic hypothermia for inborn and outborn infants with neonatal encephalopathy
Therapeutic hypothermia is now the standard of care for infants with moderate to severe hypoxic ischaemic encephalopathy. Sixty-three infants received therapeutic hypothermia at Cork University Maternity Hospital (CUMH) from 2010-2014. Median gestational age was 40 weeks. Eighteen (29%) infants were Sarnat grade 3, 41(65%) grade 2 and 4(6%) grade 1. Nineteen outborn infants arrived in CUMH at a median (IQR) age of 310 (270, 420) minutes. Four (21%) outborn infants were within the target temperature range on arrival. Median (IQR) time (minutes) from birth to achieve target temperature was 136 (90, 195) for inborn and 300 (240, 360) for outborn infants (p <.01). Overall, 35 (56%) infants had electrical seizures, 42 (74%) had a normal MRI at a median (IQR) age of 7(6,9) days and the median(IQR) length of stay was 9 (7,11) days. Although no difference in seizures or MRI findings was seen, passive cooling does not achieve consistent temperature control for outborn infants
A WXW Motif Is Required for the Anticancer Activity of the TAT-RasGAP317-326 Peptide.
TAT-RasGAP317-326, a cell-permeable 10-amino acid-long peptide derived from the N2 fragment of p120 Ras GTPase-activating protein (RasGAP), sensitizes tumor cells to apoptosis induced by various anticancer therapies. This RasGAP-derived peptide, by targeting the deleted in liver cancer-1 (DLC1) tumor suppressor, also hampers cell migration and invasion by promoting cell adherence and by inhibiting cell movement. Here, we systematically investigated the role of each amino acid within the RasGAP317-326 sequence for the anticancer activities of TAT-RasGAP317-326. We report here that the first three amino acids of this sequence, tryptophan, methionine, and tryptophan (WMW), are necessary and sufficient to sensitize cancer cells to cisplatin-induced apoptosis and to reduce cell migration. The WMW motif was found to be critical for the binding of fragment N2 to DLC1. These results define the interaction mode between the active anticancer sequence of RasGAP and DLC1. This knowledge will facilitate the design of small molecules bearing the tumor-sensitizing and antimetastatic activities of TAT-RasGAP317-326
Microscopic description of the surface dipole plasmon in large Na_N clusters (950 < N < 12050)
Fully microscopic RPA/LDA calculations of the dipole plasmon for very large
neutral and charged sodium clusters, Na_N^Z+, in the size range 950
< N < 12050 are presented for the first time. 60 different sizes are
considered altogether, which allows for an in-depth investigation of the
asymptotic behavior of both the width and the position of the plasmon.Comment: Latex/Revtex, 4 pages with 4 Postscript figures, accepted for
publication in Physical Review
Hydrodynamic theory of an electron gas
The generalised hydrodynamic theory of an electron gas, which does not rely
on an assumption of a local equilibrium, is derived as the long-wave limit of a
kinetic equation. Apart from the common hydrodynamics variables the theory
includes the tensor fields of the higher moments of the distribution function.
In contrast to the Bloch hydrodynamics, the theory leads to the correct plasmon
dispersion and in the low frequency limit recovers the Navies-Stocks
hydrodynamics. The linear approximation to the generalised hydrodynamics is
closely related to the theory of highly viscous fluids.Comment: 4 pages, revte
Negative Consequences of Substance Use in European University Students: Results from Project SNIPE
Background: University students are a risk group for heavy substance use and the experience of various potentially severe negative substance use consequences which may impact on their health, social, and academic functioning. Whilst the experience of negative consequences of substance use is well understood in North American student samples, there is little data on these experiences in European students. In order to develop effective harm prevention and reduction interventions for students’ substance use, there needs to be an understanding of the types of consequences experienced in European student samples. Objectives: The aim of the study was to investigate the prevalence and predictors of the experience of negative substance use-related consequences amongst university students in 7 European countries. Methods: University students (n = 4,482) in Belgium, Denmark, Germany, the Slovak Republic, Spain, Turkey, and the UK completed an online survey of their substance use behaviours and the experience of associated negative consequences. Results: European students reported that experiencing a hangover or illness, missing class, being short of money, and experiencing memory loss were the most commonly experienced negative consequences of substance use. Not living with other students and using alcohol, cannabis, sedatives, and cocaine were also associated with higher odds of experiencing these negative consequences. Conclusions: In contrast to North American data, European university students tended to experience consequences that are associated with lower level health risks rather than more severe consequences (e.g., drink-driving and physical injury). Harm prevention and reduction interventions for students should be targeted towards those consequences that are most salient to the target group to ensure feedback is relevant and potentially more effective in changing students’ substance use behaviours
Intrinsic somatosensory feedback supports motor control and learning to operate artificial body parts
Objective Considerable resources are being invested to enhance the control and usability of artificial limbs through the delivery of unnatural forms of somatosensory feedback. Here, we investigated whether intrinsic somatosensory information from the body part(s) remotely controlling an artificial limb can be leveraged by the motor system to support control and skill learning. Approach In a placebo-controlled design, we used local anaesthetic to attenuate somatosensory inputs to the big toes while participants learned to operate through pressure sensors a toe-controlled and hand-worn robotic extra finger. Motor learning outcomes were compared against a control group who received sham anaesthetic and quantified in three different task scenarios: while operating in isolation from, in synchronous coordination, and collaboration with, the biological fingers. Main results Both groups were able to learn to operate the robotic extra finger, presumably due to abundance of visual feedback and other relevant sensory cues. Importantly, the availability of displaced somatosensory cues from the distal bodily controllers facilitated the acquisition of isolated robotic finger movements, the retention and transfer of synchronous hand-robot coordination skills, and performance under cognitive load. Motor performance was not impaired by toes anaesthesia when tasks involved close collaboration with the biological fingers, indicating that the motor system can close the sensory feedback gap by dynamically integrating task-intrinsic somatosensory signals from multiple, and even distal, body- parts. Significance Together, our findings demonstrate that there are multiple natural avenues to provide intrinsic surrogate somatosensory information to support motor control of an artificial body part, beyond artificial stimulation
Solution of the Schr\"odinger Equation for Quantum Dot Lattices with Coulomb Interaction between the Dots
The Schr\"odinger equation for quantum dot lattices with non-cubic,
non-Bravais lattices built up from elliptical dots is investigated. The Coulomb
interaction between the dots is considered in dipole approximation. Then only
the center of mass (c.m.) coordinates of different dots couple with each other.
This c.m. subsystem can be solved exactly and provides magneto- phonon like
collective excitations. The inter-dot interaction is involved only through a
single interaction parameter. The relative coordinates of individual dots form
decoupled subsystems giving rise to intra-dot excitations. As an example, the
latter are calculated exactly for two-electron dots.
Emphasis is layed on qualitative effects like: i) Influence of the magnetic
field on the lattice instability due to inter-dot interaction, ii) Closing of
the gap between the lower and the upper c.m. mode at B=0 for elliptical dots
due to dot interaction, and iii) Kinks in the single dot excitation energies
(versus magnetic field) due to change of ground state angular momentum. It is
shown that for obtaining striking qualitative effects one should go beyond
simple cubic lattices with spherical dots. We also prove a more general version
of the Kohn Theorem for quantum dot lattices. It is shown that for observing
effects of electron- electron interaction between the dots in FIR spectra
(breaking Kohn's Theorem) one has to consider dot lattices with at least two
dot species with different confinement tensors.Comment: 11 figures included as ps-file
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