300 research outputs found
Time-resolved photoluminescence of n-doped SrTiO_3
Following the recent surge of interest in n-doped strontium titanate as a
possible blue light emitter, a time-resolved photoluminescence analysis was
performed on nominally pure, Nb-doped and oxygen-deficient single-crystal
SrTiO3 samples. The doping-effects on both the electronic states involved in
the transition and the decay mechanism are respectively analyzed by comparing
the spectral and dynamic features and the yields of the emission. Our
time-resolved analysis, besides shedding some light on the basic recombination
mechanisms acting in these materials, sets the intrinsic bandwidth limit of the
proposed blue light emitting optoelectronic devices made of Ti-based
perovskites heterostructures in the GHz range
Pancharatnam-Berry phase optical elements for wavefront shaping in the visible domain: switchable helical modes generation
We report the realization of a Pancharatnam-Berry phase optical element [Z.
Bomzon, G. Biener, V. Kleiner, and E. Hasman, Opt. Lett. \textbf{27}, 1141
(2002)] for wavefront shaping working in the visible spectral domain, based on
patterned liquid crystal technology. This device generates helical modes of
visible light with the possibility of electro-optically switching between
opposite helicities by controlling the handedness of the input circular
polarization. By cascading this approach, fast switching among multiple
wavefront helicities can be achieved, with potential applications to
multi-state optical information encoding. The approach demonstrated here can be
generalized to other polarization-controlled devices for wavefront shaping,
such as switchable lenses, beam-splitters, and holographic elements
Direct effects of fermented cow's milk product with Lactobacillus paracasei CBA L74 on human enterocytes
Cow's milk fermented with Lactobacillus paracasei CBA L74 (FM-CBAL74) exerts a preventive effect against infectious diseases in children. We evaluated if this effect is at least in part related to a direct modulation of non-immune and immune defence mechanisms in human enterocytes. Human enterocytes (Caco-2) were stimulated for 48 h with FM-CBAL74 at different concentrations. Cell growth was assessed by colorimetric assay; cell differentiation (assessed by lactase expression), tight junction proteins (zonula occludens1 and occludin), mucin 2, and toll-like receptor (TRL) pathways were analysed by real-time PCR; innate immunity peptide synthesis, beta-defensin-2 (HBD-2) and cathelicidin (LL-37) were evaluated by ELISA. Mucus layer thickness was analysed by histochemistry. FMCBA L74 stimulated cell growth and differentiation, tight junction proteins and mucin 2 expression, and mucus layer thickness in a dose-dependent fashion. A significant stimulation of HBD-2 and LL-37 synthesis, associated with a modulation of TLR pathway, was also observed. FM-CBAL74 regulates non-immune and immune defence mechanisms through a direct interaction with the enterocytes. These effects could be involved in the preventive action against infectious diseases demonstrated by this fermented product in children
Thermodynamic formalism for dissipative quantum walks
We consider the dynamical properties of dissipative continuous-time quantum
walks on directed graphs. Using a large-deviation approach we construct a
thermodynamic formalism allowing us to define a dynamical order parameter, and
to identify transitions between dynamical regimes. For a particular class of
dissipative quantum walks we propose a quantum generalization of the the
classical PageRank vector, used to rank the importance of nodes in a directed
graph. We also provide an example where one can characterize the dynamical
transition from an effective classical random walk to a dissipative quantum
walk as a thermodynamic crossover between distinct dynamical regimes.Comment: 8 page
On the variability of HD 170699 - a possible COROT target
We present the analysis of the variability of HD 170699, a COROT star showing
the characteristics of a non evolutionary Delta Scuti star with high rotational
velocity. There is a clear period of 10.45 c/d with 5.29 mmag amplitude in the
y filter. From the data, it can be seen that the star shows multi-periodicity
and it is necessary to add more frequencies to adjust the observationsComment: To appear in RevMexAA(SC) in Proceedings of XII Reunion Regional
Latinoamericana de la UAI held in Isla Margarita, Venezuela, October 22-26,
200
Polar catastrophe and electronic reconstructions at the LaAlO3/SrTiO3 interface: evidence from optical second harmonic generation
The so-called "polar catastrophe", a sudden electronic reconstruction taking
place to compensate for the interfacial ionic polar discontinuity, is currently
considered as a likely factor to explain the surprising conductivity of the
interface between the insulators LaAlO3 and SrTiO3. We applied optical second
harmonic generation, a technique that a priori can detect both mobile and
localized interfacial electrons, to investigating the electronic polar
reconstructions taking place at the interface. As the LaAlO3 film thickness is
increased, we identify two abrupt electronic rearrangements: the first takes
place at a thickness of 3 unit cells, in the insulating state; the second
occurs at a thickness of 4-6 unit cells, i.e., just above the threshold for
which the samples become conducting. Two possible physical scenarios behind
these observations are proposed. The first is based on an electronic transfer
into localized electronic states at the interface that acts as a precursor of
the conductivity onset. In the second scenario, the signal variations are
attributed to the strong ionic relaxations taking place in the LaAlO3 layer
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