299 research outputs found
Highly tunable low-threshold optical parametric oscillation in radially poled whispering gallery resonators
Whispering gallery resonators (WGR's), based on total internal reflection,
possess high quality factors in a broad spectral range. Thus, nonlinear optical
processes in such cavities are ideally suited for the generation of broadband
or tunable electromagnetic radiation. Experimentally and theoretically, we
investigate the tunability of optical parametric oscillation in a radially
structured WGR made of lithium niobate. With a 1.04 /mum pump wave, the signal
and idler waves are tuned from 1.78 to 2.5 \mum - including the point of
degeneracy - by varying the temperature between 20 and 62 {\deg}C. A weak
off-centering of the radial domain structure extends considerably the tuning
capabilities. The oscillation threshold lies in the mW-power range.Comment: 4 pages, 5 figure
Adsorption of 2,2 '-dithiodipyridine as a tool for the assembly of silver nanoparticles
Silver nanostructured thin films stabilized by 2,2â-dithiodipyridine (2dtpy) were prepared. The Ag nanoparticles
were obtained by treating the complex [Ag(2dtpy)]NO3 with NaBH4 in a methanolâtoluene mixture. The films
were transferred to borosilicate glass slips by a dip-coating method and were found to consist of Ag
nanoparticles possibly linked via 2dtpy molecules. Surface-enhanced Raman scattering (SERS) studies have
offered the possibility of investigating the adsorption modes of 2dtpy at the Ag nanoparticle surfaces in the
fil
Semences et séquences génétiques en open source ? Expériences récentes et stratégies futures
Le concept d'open source appliquĂ© aux semences vĂ©gĂ©tales a un avenir prometteur. Ce concept inverse la logique du systĂšme de propriĂ©tĂ© intellectuelle pour une ressource renouvelable que l'on rend disponible en la sortant du domaine exclusif de la propriĂ©tĂ© intellectuelle. Aujourd'hui, les instruments juridiques font encore dĂ©faut pour Ă©tablir un cadre lĂ©gal complet. Toutefois, le concept d'open source, que l'on pourrait traduire ici par licence libre et ouverte, engendre au fil du temps une masse critique d'utilisateurs et de soutiens qui entraĂźne une lĂ©gitimitĂ© sociale grandissante. Ă terme, cette lĂ©gitimitĂ© pourrait renforcer le pouvoir juridique. L'extension future Ă d'autres matĂ©riels dans diffĂ©rents contextes doit ĂȘtre rĂ©flĂ©chie en s'appuyant sur les expĂ©riences actuelles de semences sous licences libres et ouvertes conduites aux Ătats-Unis, en Europe et en Afrique
Synthesis of CdS and CdSe nanocrystallites using a novel single-molecule precursors approach
The synthesis of CdS and CdSe nanocrystallites using the thermolysis of several dithioor
diselenocarbamato complexes of cadmium in trioctylphosphine oxide (TOPO) is reported.
The nanodispersed materials obtained show quantum size effects in their optical spectra
and exhibit near band-edge luminescence. The influence of experimental parameters on
the properties of the nanocrystallites is discussed. HRTEM images of these materials show
well-defined, crystalline nanosized particles. Standard size fractionation procedures can
be performed in order to narrow the size dispersion of the samples. The TOPO-capped CdS
and CdSe nanocrystallites and simple organic bridging ligands, such as 2,2Âą-bipyrimidine,
are used as the starting materials for the preparation of novel nanocomposites. The optical
properties shown by these new nanocomposites are compared with those of the starting
nanodispersed materials
First measurement of the Gerasimov-Drell-Hearn integral for Hydrogen from 200 to 800 MeV
A direct measurement of the helicity dependence of the total photoabsorption
cross section on the proton was carried out at MAMI (Mainz) in the energy range
200 < E_gamma < 800 MeV. The experiment used a 4 detection system, a
circularly polarized tagged photon beam and a frozen spin target.
The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward
spin polarizability determined from the data are 226 \pm 5 (stat)\pm
12(sys) \mu b and -187 \pm 8 (stat)\pm 10(sys)10^{-6} fm^4, respectively, for
200 < E_\gamma < 800 MeV.Comment: 6 pages, 3 figures, 3 table
Quantum dots coordinated with conjugated organic ligands: new nanomaterials with novel photophysics
CdSe quantum dots functionalized with oligo-(phenylene vinylene) (OPV) ligands (CdSe-OPV nanostructures) represent a new class of composite nanomaterials with significantly modified photophysics relative to bulk blends or isolated components. Single-molecule spectroscopy on these species have revealed novel photophysics such as enhanced energy transfer, spectral stability, and strongly modified excited state lifetimes and blinking statistics. Here, we review the role of ligands in quantum dot applications and summarize some of our recent efforts probing energy and charge transfer in hybrid CdSe-OPV composite nanostructures
The VIMOS Public Extragalactic Redshift Survey (VIPERS): from the galaxy clustering ratio measured at
We use a sample of about 22,000 galaxies at from the VIPERS
PDR-1 catalogue, to constrain the cosmological model through a measurement of
the galaxy {\it clustering ratio} . This statistic has favourable
properties, being defined as the ratio of two quantities characterizing the
smoothed density field in spheres of given radius : the value of its
correlation function on a multiple of this scale, , and its variance
. For sufficiently large values of , this is a universal
number, capturing 2-point clustering information independently of the linear
bias and linear redshift-space distortions of the specific galaxy tracers. In
this paper we discuss in detail how to extend the application of
to quasi-linear scales and how to control and remove observational selection
effects which are typical of redshift surveys as VIPERS. We verify the accuracy
and efficiency of these procedures using mock catalogues that match the survey
selection process. These results evidence the robustness of to
non-linearities and observational effects, which is related to its very
definition as a ratio of quantities that are similarly affected.
We measure . In addition to the great
precision achieved on our estimation of using VIPERS PDR-1, this
result is remarkable because it appears to be in good agreement with a recent
estimate , obtained applying the same technique to the SDSS-LRG
catalogue. It, therefore, suports the robustness of the present analysis.
Moreover, the combination of these two measurements at and provides us with a very precise estimate
which highlights the great consistency between our estimation and other
cosmological probes such as BAOs, CMB and Supernovae.Comment: 18 pages, 17 figures, accepted for publication in A&A, references
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