223 research outputs found
Measurement of the complex Faraday angle in thin-film metals and high temperature superconductors
A sensitive polarization modulation technique uses photoelastic modulation
and hetrodyne detection to simultaneously measure the Faraday rotation and
induced ellipticity in light transmitted by semiconducting and metallic
samples. The frequencies measured are in the mid-infrared and correspond to the
spectral lines of a CO2 laser. The measured temperature range is continuous and
extends from 35 to 330K. Measured samples include GaAs and Si substrates, gold
and copper films, and YBCO and BSCCO high temperature superconductors.Comment: 12 pages of text, 6 figures, fixed typos in formulas, added figur
Magneto-optical evidence for a gapped Fermi surface in underdoped YBa2Cu3O6+x
The infrared (900-1100 cm-1) Faraday rotation and circular dichroism are
measured in the normal state of underdoped High Tc superconductors and used to
study the magneto-transport. YBa2Cu3O6+x thin films are investigated in the
temperature range 10-300 K in magnetic fields up to 8 Tesla and as a function
of oxygen concentration. A dramatic increase of the Hall frequency is observed
for underdoped samples which is not consistent with the approach to a Mott
transition but is consistent with a partial gapping of the Fermi surface as
predicted in charge density wave models.Comment: 14 pages, 4 figure
Optical Conductivity and Hall Coefficient in High-Tc Superconductors: Significant Role of Current Vertex Corrections
We study AC conductivities in high-Tc cuprates, which offer us significant
information to reveal the true electronic ground states. Based on the
fluctuation-exchange (FLEX) approximation, current vertex corrections (CVC's)
are correctly taken into account to satisfy the conservation laws. We find the
significant role of the CVC's on the optical Hall conductivity in the presence
of strong antiferromagnetic (AF) fluctuations. This fact leads to the failure
of the relaxation time approximation (RTA). As a result, experimental highly
unusual behaviors, (i) prominent frequency and temperature dependences of the
optical Hall coefficient, and (ii) simple Drude form of the optical Hall andge
for wide range of frequencies, are satisfactorily reproduced. In conclusion,
both DC and AC transport phenomena in (slightly under-doped) high-Tc cuprates
can be explained comprehensively in terms of nearly AF Fermi liquid, if one
take the CVC's into account.Comment: 5 page
In situ relationships between microbiota and potential pathobiota in Arabidopsis thaliana.
A current challenge in microbial pathogenesis is to identify biological control agents that may prevent and/or limit host invasion by microbial pathogens. In natura, hosts are often infected by multiple pathogens. However, most of the current studies have been performed under laboratory controlled conditions and by taking into account the interaction between a single commensal species and a single pathogenic species. The next step is therefore to explore the relationships between host-microbial communities (microbiota) and microbial members with potential pathogenic behavior (pathobiota) in a realistic ecological context. In the present study, we investigated such relationships within root-associated and leaf-associated bacterial communities of 163 ecologically contrasted Arabidopsis thaliana populations sampled across two seasons in southwest of France. In agreement with the theory of the invasion paradox, we observed a significant humped-back relationship between microbiota and pathobiota α-diversity that was robust between both seasons and plant organs. In most populations, we also observed a strong dynamics of microbiota composition between seasons. Accordingly, the potential pathobiota composition was explained by combinations of season-specific microbiota operational taxonomic units. This result suggests that the potential biomarkers controlling pathogen\u27s invasion are highly dynamic
Strong, Ultra-narrow Peaks of Longitudinal and Hall Resistances in the Regime of Breakdown of the Quantum Hall Effect
With unusually slow and high-resolution sweeps of magnetic field, strong,
ultra-narrow (width down to ) resistance peaks are observed in
the regime of breakdown of the quantum Hall effect. The peaks are dependent on
the directions and even the history of magnetic field sweeps, indicating the
involvement of a very slow physical process. Such a process and the sharp peaks
are, however, not predicted by existing theories. We also find a clear
connection between the resistance peaks and nuclear spin polarization.Comment: 5 pages with 3 figures. To appear in PR
SPHERE: the exoplanet imager for the Very Large Telescope
Observations of circumstellar environments to look for the direct signal of
exoplanets and the scattered light from disks has significant instrumental
implications. In the past 15 years, major developments in adaptive optics,
coronagraphy, optical manufacturing, wavefront sensing and data processing,
together with a consistent global system analysis have enabled a new generation
of high-contrast imagers and spectrographs on large ground-based telescopes
with much better performance. One of the most productive is the
Spectro-Polarimetic High contrast imager for Exoplanets REsearch (SPHERE)
designed and built for the ESO Very Large Telescope (VLT) in Chile. SPHERE
includes an extreme adaptive optics system, a highly stable common path
interface, several types of coronagraphs and three science instruments. Two of
them, the Integral Field Spectrograph (IFS) and the Infra-Red Dual-band Imager
and Spectrograph (IRDIS), are designed to efficiently cover the near-infrared
(NIR) range in a single observation for efficient young planet search. The
third one, ZIMPOL, is designed for visible (VIR) polarimetric observation to
look for the reflected light of exoplanets and the light scattered by debris
disks. This suite of three science instruments enables to study circumstellar
environments at unprecedented angular resolution both in the visible and the
near-infrared. In this work, we present the complete instrument and its on-sky
performance after 4 years of operations at the VLT.Comment: Final version accepted for publication in A&
Does spatial locative comprehension predict landmark-based navigation?
In the present study we investigated the role of spatial locative comprehension in learning and retrieving pathways when landmarks were available and when they were absent in a sample of typically developing 6- to 11-year-old children. Our results show that the more proficient children are in understanding spatial locatives the more they are able to learn pathways, retrieve them after a delay and represent them on a map when landmarks are present in the environment. These findings suggest that spatial language is crucial when individuals rely on sequences of landmarks to drive their navigation towards a given goal but that it is not involved when navigational representations based on the geometrical shape of the environment or the coding of body movements are sufficient for memorizing and recalling short pathways
Supported ionic liquid silica nanoparticles (SILnPs) as an efficient and recyclable heterogeneous catalyst for the dehydration of fructose to 5-hydroxymethylfurfural
Supported ionic liquid nanoparticles (SILnPs) having particle size ranging from 293 ± 2 to 610 ±
11 nm have been prepared by immobilization of ionic liquid, 1-(tri-ethoxy silyl-propyl)-
3-methyl-imidazolium hydrogen sulfate (IL-HSO4) on the surface of silica nanoparticles. The
catalytic activity of the prepared SILnPs was investigated for the dehydration of fructose to
5-hydroxymethylfurfural (HMF) in the presence of dimethylsulfoxide (DMSO) as a solvent. The
reaction temperature and amount of catalyst have been optimized for dehydration of fructose over
SILnPs using experimental design leading to 99.9% fructose conversion and 63.0% HMF yield
using silica SILnPs (d = 610 ± 11) nm at 130.0 ◦C in 30 min reaction time. The SILnPs catalysts
developed in this study present improved performances over other zeolites and strong acid ion
exchange resin catalysts, and they have been efficiently and very easily recycled over seven times
without any significant loss in fructose conversion and HMF yield
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