36,340 research outputs found
The attainable superconducting Tc in a model of phase coherence by percolation
The onset of macroscopic phase coherence in superconducting cuprates is
considered to be determined by random percolation between mesoscopic
Jahn-Teller pairs, stripes or clusters. The model is found to predict the onset
of superconductivity near 6% doping, maximum Tc near 15% doping and Tc= T* at
optimum doping, and accounts for the destruction of superconductivity by Zn
doping near 7%. The model also predicts a relation between the pairing
(pseudogap) energy and Tc in terms of experimentally measurable quantities.Comment: 3 pages + 3 postscript figure
Global Facilitation of Attended Features Is Obligatory and Restricts Divided Attention
Peer reviewedPublisher PD
Nuclear Medium Modifications of Hadrons from Generalized Parton Distributions
We study the structure of generalized parton distributions in spin 0 nuclei
within a microscopic approach for nuclear dynamics. GPDs can be used on one
side as tools to unravel the deep inelastic transverse structure of nuclei in
terms of both transverse spatial and transverse momentum degrees of freedom. On
the other, one can obtain information on GPDs themselves by observing how they
become modified in the nuclear environment. We derive the structure of the
nuclear deeply virtual Compton scattering tensor and generalized parton
distributions at leading order in in a field-theoretical framework. The
nuclear generalized parton distributions are calculated using a two step
process -- the convolution approach -- where the scattering process happens
from a quark inside a nucleon, itself inside a nucleus, disregarding final
state interactions with both the nuclear and nucleon debris. We point out that
details of the nuclear long range interactions such as two-body currents, can
be disregarded compared to the deep inelastic induced modifications of the
bound GPDs. We show how the pattern of nuclear modifications predicted, and in
particular the deviations of off-shell effects from the longitudinal
convolution provide clear signals to be sought in experimental measurements.
Finally, we find interesting relationships by studying Mellin moments in
nuclei: in particular we predict the -dependence for the -term of GPDs
within a microscopic approach, and the behavior with of the total momentum
carried by quarks in a nucleus. The latter provides an important element for
the evaluation of nuclear hadronization phenomena which are vital for
interpreting current and future data at RHIC, HERMES and Jefferson Lab.Comment: 29 pages, 10 figure
Determination of anisotropic dipole moments in self-assembled quantum dots using Rabi oscillations
By investigating the polarization-dependent Rabi oscillations using
photoluminescence spectroscopy, we determined the respective transition dipole
moments of the two excited excitonic states |Ex> and |Ey> of a single
self-assembled quantum dot that are nondegenerate due to shape anisotropy. We
find that the ratio of the two dipole moments is close to the physical
elongation ratio of the quantum dot.Comment: 11 pages, 2 figures, MS Word generated PDF fil
Estimation of the surface-d to bulk-s Crossover in the Macroscopic Superconducting Wavefunction in Cuprates
The concept of a surface d- and bulk s-symmetry in cuprate superconductors is
applied to recent small-angle neutron-scattering results. These show a change
of hexagonal to square vortex lattice as a function of the magnetic field along
the c-axis. Identifying the hexagonal lattice with s- and the square with
d-symmetry, the crossover distance from the surface d to the bulk s
perpendicular to the c-axis is estimated to be 35 nm for LSCO and roughly 7 nm
for YBCO, both at optimum doping. The crossover along the c-axis has to be of
only a few layers distance to reconcile tunneling, photoemission and pulsed
femtosecond reflectivity experiments. These estimates are compatible with
m-rotation, NMR and other experiments.Comment: 6 pages, 2 figure
Temperature dependence of trapped magnetic field in MgB2 bulk superconductor
Based on DC magnetization measurements, the temperature dependencies of the
trapped magnetic field have been calculated for two MgB2 samples prepared by
two different techniques: the high-pressure sintering and the hot pressing.
Experimentally measured trapped field values for the first sample coincide
remarkably well with calculated ones in the whole temperature range. This
proves, from one side, the validity of the introduced calculation approach, and
demonstrates, from another side, the great prospects of the hot pressing
technology for large scale superconducting applications of the MgB2.Comment: 3 pages, 3 figures, submitted to AP
Buried heterostructure vertical-cavity surface-emitting laser with semiconductor mirrors
We report a buried heterostructure vertical-cavity surface-emitting laser
fabricated by epitaxial regrowth over an InGaAs quantum well gain medium. The
regrowth technique enables microscale lateral confinement that preserves a high
cavity quality factor (loaded 4000) and eliminates parasitic
charging effects found in existing approaches. Under optimal spectral overlap
between gain medium and cavity mode (achieved here at = 40 K) lasing was
obtained with an incident optical power as low as = 10 mW
( = 808 nm). The laser linewidth was found to be 3
GHz at 5
What pops out in positional priming of pop-out: insights from event-related EEG lateralizations
It is well established that, in visual pop-out search, reaction time (RT) performance is influenced by cross-trial repetitions versus changes of target-defining attributes. One instance of this is referred to as “positional priming of pop-out” (pPoP; Maljkovic and Nakayama, 1996). In positional PoP paradigms, the processing of the current target is examined depending on whether it occurs at the previous target or a previous distractor location, relative to a previously empty location (“neutral” baseline), permitting target facilitation and distractor inhibition to be dissociated. The present study combined RT measures with specific sensory- and motor-driven event-related lateralizations to track the time course of four distinct processing levels as a function of the target’s position across consecutive trials. The results showed that, relative to targets at previous target and “neutral” locations, the appearance of a target at a previous distractor location was associated with a delayed build-up of the posterior contralateral negativity wave, indicating that distractor positions are suppressed at early stages of visual processing. By contrast, presentation of a target at a previous target, relative to “neutral” and distractor locations, modulated the elicitation of the subsequent stimulus-locked lateralized readiness potential wave, indicating that post-selective response selection is facilitated if the target occurred at the same position as on the previous trial. Overall, the results of present study provide electrophysiological evidence for the idea that target location priming (RT benefits) does not originate from an enhanced coding of target saliency at repeated (target) locations; instead, they arise (near-) exclusively from processing levels subsequent to focal-attentional target selection
- …