520 research outputs found
Antiferromagnetic S=1/2 Heisenberg Chain and the Two-flavor Massless Schwinger Model
An antiferromagnetic S=1/2 Heisenberg chain is mapped to the two-flavor
massless Schwinger model at \theta=\pi. The electromagnetic coupling constant
and velocity of light in the Schwinger model are determined in terms of the
Heisenberg coupling and lattice spacing in the spin chain system.Comment: 3 pages. LaTex2
Distraction from pain and executive functioning: an experimental investigation of the role of inhibition, task switching and working memory
Although many studies have investigated the effectiveness of distraction as a method of pain control, the cognitive processes by which attentional re-direction is achieved, remain unclear. In this study the role of executive functioning abilities (inhibition, task switching and working memory) in the effectiveness of distraction is investigated. We hypothesized that the effectiveness of distraction in terms of pain reduction would be larger in participants with better executive functioning abilities. Ninety-one undergraduate students first performed executive functioning tasks, and subsequently participated in a cold pressor task (CPT). Participants were randomly assigned to (1) a distraction group, in which an attention-demanding tone-detection task was performed during the CPT, or (2) a control group, in which no distraction task was performed. Participants in the distraction group reported significantly less pain during the CPT, but the pain experience was not influenced by executive functioning abilities. However, the performance on the distraction task improved with better inhibition abilities, indicating that inhibition abilities might be important in focussing on a task despite the pain
The ARIEL Instrument Control Unit design for the M4 Mission Selection Review of the ESA's Cosmic Vision Program
The Atmospheric Remote-sensing Infrared Exoplanet Large-survey mission
(ARIEL) is one of the three present candidates for the ESA M4 (the fourth
medium mission) launch opportunity. The proposed Payload will perform a large
unbiased spectroscopic survey from space concerning the nature of exoplanets
atmospheres and their interiors to determine the key factors affecting the
formation and evolution of planetary systems. ARIEL will observe a large number
(>500) of warm and hot transiting gas giants, Neptunes and super-Earths around
a wide range of host star types, targeting planets hotter than 600 K to take
advantage of their well-mixed atmospheres. It will exploit primary and
secondary transits spectroscopy in the 1.2-8 um spectral range and broad-band
photometry in the optical and Near IR (NIR). The main instrument of the ARIEL
Payload is the IR Spectrometer (AIRS) providing low-resolution spectroscopy in
two IR channels: Channel 0 (CH0) for the 1.95-3.90 um band and Channel 1 (CH1)
for the 3.90-7.80 um range. It is located at the intermediate focal plane of
the telescope and common optical system and it hosts two IR sensors and two
cold front-end electronics (CFEE) for detectors readout, a well defined process
calibrated for the selected target brightness and driven by the Payload's
Instrument Control Unit (ICU).Comment: Experimental Astronomy, Special Issue on ARIEL, (2017
Role of low-frequency vibrations on sound propagation in glasses at intermediate temperature
We report measurements of the temperature dependence of the sound attenuation and the fractional change in sound velocity for the glass (G) and orientational-glass (OG) phases of polymorphic ethanol. Strikingly similar behaviors are found for both phases despite the OG's underlying crystal (bcc) lattice. Such similarity, which is also revealed in dielectric spectroscopy and inelastic neutron scattering measurements, suggests whole molecule small-angle librations as a common microscopic origin for a wide variety of "glassy" phenomena.Dirección General de Investigación CientÃfica y Técnica PB95-0075-C03-0
Quasi-two-dimensional hole ordering and dimerized state in the CuO2-chain layers in Sr14Cu24O41
Neutron scattering experiments have been performed on
SrCuO which consists of both chains and ladders of copper
ions. We observed that the magnetic excitations from the CuO chain have two
branches and that both branches are weakly dispersive along the and
axes. The - dispersion relation as well as the intensities can be
reasonably described by a random phase approximation with intradimer coupling
between next-nearest-neighbor copper spins =11 meV, interdimer coupling
along the c axis =0.75 meV, and interdimer coupling along the a axis
=0.75 meV. The dimer configuration indicates a quasi-two-dimensional hole
ordering, resulting in an ordering of magnetic Cu with spin-1/2 and
nonmagnetic Cu, which forms the Zhang-Rice singlet. We have also studied the
effect of Ca substitution for Sr on the dimer and the hole ordering.Comment: 7 pages, Revtex, 10 figures, Submitted to Phys. Rev.
Electron transport in coupled chains of interacting fermions with impurities
We study the low-temperature transport of a doped two-chain ladder system of
interacting fermions in the presence of a barrier or of a low concentration of
impurities. Above a certain value of the interaction, the conductance is
suppressed, like for a single chain, despite the presence of dominant
superconducting correlations. There is, however, a region of repulsive
interaction where perfect transmission across the barrier occurs unlike the
single-chain case. We provide a possible explanation for the temperature
maximum of the resistivity in the normal state of \srca.Comment: 4 pages, 2 figures, to be published in Phys. Rev. Let
Stability of the Haldane phase in anisotropic magnetic ladders
We have considered the properties of anisotropic two-leg ladder models with
S=1/2 or S=1 spins on the rungs, using White's density matrix renormalization
group method. We have generalized the method by taking into account the
symmetries of the model in order to reduce the dimensions of the matrix to be
diagonalized, thereby making possible to consider more states. The boundaries
in the parameter space of the extended region, where the Haldane phase exists,
are estimated.Comment: 19 pages, 5 figure
Two-magnon Raman scattering in spin-ladder geometries and the ratio of rung and leg exchange constants
We discuss ways in which the ratio of exchange constants along the rungs and
legs of a spin-ladder material influences the two-magnon Raman scattering
spectra and hence can be determined from it. We show that within the
Fleury-Loudon-Elliott approach, the Raman line-shape does not change with
polarization geometries. This lineshape is well known to be difficult to
calculate accurately from theory. However, the Raman scattering intensities do
vary with polarization geometries, which are easy to calculate. With some
assumptions about the Raman scattering Hamiltonian, the latter can be used to
estimate the ratio of exchange constants. We apply these results to Sugai's
recent measurements of Raman scattering from spin-ladder materials such as
LaCaCuO and SrCuO.Comment: 5 pages, revtex. Latest version focuses on ladder materials, with a
detailed examination of the role of Heisenberg-like coupling constants which
appear in the Fleury-Loudon-Elliott scattering operator but are rarely
discussed in the literatur
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