3,662 research outputs found
Giant circular dichroism of a molecule in a region of strong plasmon resonances between two neighboring gold nanocrystals
We report on giant circular dichroism (CD) of a molecule inserted into a
plasmonic hot spot. Naturally occurring molecules and biomolecules have
typically CD signals in the UV range, whereas plasmonic nanocrystals exhibit
strong plasmon resonances in the visible spectral interval. Therefore,
excitations of chiral molecules and plasmon resonances are typically
off-resonant. Nevertheless, we demonstrate theoretically that it is possible to
create strongly-enhanced molecular CD utilizing the plasmons. This task is
doubly challenging since it requires both creation and enhancement of the
molecular CD in the visible region. We demonstrate this effect within the model
which incorporates a chiral molecule and a plasmonic dimer. The associated
mechanism of plasmonic CD comes from the Coulomb interaction which is greatly
amplified in a plasmonic hot spot.Comment: Manuscript: 4+pages, 4 figures; Supplemental_Material: 10 pages, 7
figure
On Convergence Properties of Shannon Entropy
Convergence properties of Shannon Entropy are studied. In the differential
setting, it is shown that weak convergence of probability measures, or
convergence in distribution, is not enough for convergence of the associated
differential entropies. A general result for the desired differential entropy
convergence is provided, taking into account both compactly and uncompactly
supported densities. Convergence of differential entropy is also characterized
in terms of the Kullback-Liebler discriminant for densities with fairly general
supports, and it is shown that convergence in variation of probability measures
guarantees such convergence under an appropriate boundedness condition on the
densities involved. Results for the discrete setting are also provided,
allowing for infinitely supported probability measures, by taking advantage of
the equivalence between weak convergence and convergence in variation in this
setting.Comment: Submitted to IEEE Transactions on Information Theor
Challenges to Promoting Social Inclusion of the Extreme Poor: Evidence from a Large-Scale Experiment in Colombia
We evaluate the large scale pilot of an innovative and major welfare intervention in Colom-
bia, which combines homes visits by trained social workers to households in extreme poverty
with preferential access to social programs. We use a randomized control trial and a very rich
dataset collected as part of the evaluation to identify program impacts on the knowledge and
take-up of social programs and the labor supply of targeted households. We find no consistent
impact of the program on these outcomes, possibly because the way the pilot was implemented
resulted in very light treatment in terms of home visits. Importantly, administrative data in-
dicates that the program has been rolled out nationally in a very similar fashion, suggesting
that this major national program is likely to fail in making a significant contribution to re-
ducing extreme poverty. We suggest that the program should undergo substantial reforms,
which in turn should be evaluated
Paired emitter-detector diode detection with dual wavelength monitoring for enhanced sensitivity to transition metals in ion chromatography with post-column reaction
The combination of post-column derivatisation and visible detection are regularly employed in ion chromatography (IC) to detect poorly absorbing species. Although this mode is often highly sensitive, one disadvantage is the increase in repeating baseline artifacts associated with out-of-sync pumping systems. The work presented here will demonstrate the use of a second generation design paired emitter-detector diode (PEDD-II) detection mode offering enhanced sensitivity to transition metals in IC by markedly reducing this problem and also by improving signal noise. First generation designs demonstrated the use of a single integrated PEDD detector cell as a simple, small (15 x 5 mm), highly sensitive, low cost photometric detector for the detection of metals in ion chromatography (IC). The basic principle of this detection mode lies in the employment of two linear light emitting diodes (LEDs), one operating in normal mode as a light source and the other in reverse bias serving as a light detector.
The second generation PEDD-II design showed increased sensitivity for Mn(II)- and Co(II)-2-(pyridylazo) resorcinol (PAR) complexes as a result of two simultaneously acquiring detection cells - one analytical PEDD cell and one reference PEDD cell. Therefore, the PEDD-II employs two wavelengths whereby one monitors the analyte reaction product and the second monitors a wavelength close to the isosbestic point. The optimum LED wavelength to be used for the analytical cell was investigated to maximise peak response. The fabrication process for both the analytical and reference PEDD cells was validated by determining the reproducibility of detectors within a batch. The reproducibility and sensitivity of the PEDD-II detector was then investigated using signals obtained from both intra- and inter-day chromatograms
A new species in the major malaria vector complex sheds light on reticulated species evolution
Complexes of closely related species provide key insights into the rapid and independent evolution of adaptive traits. Here, we described and studied Anopheles fontenillei sp.n., a new species in the Anopheles gambiae complex that we recently discovered in the forested areas of Gabon, Central Africa. Our analysis placed the new taxon in the phylogenetic tree of the An. gambiae complex, revealing important introgression events with other members of the complex. Particularly, we detected recent introgression, with Anopheles gambiae and Anopheles coluzzii, of genes directly involved in vectorial capacity. Moreover, genome analysis of the new species allowed us to clarify the evolutionary history of the 3La inversion. Overall, An. fontenillei sp.n. analysis improved our understanding of the relationship between species within the An. gambiae complex, and provided insight into the evolution of vectorial capacity traits that are relevant for the successful control of malaria in Africa
Homogenization and enhancement for the G-equation
We consider the so-called G-equation, a level set Hamilton-Jacobi equation,
used as a sharp interface model for flame propagation, perturbed by an
oscillatory advection in a spatio-temporal periodic environment. Assuming that
the advection has suitably small spatial divergence, we prove that, as the size
of the oscillations diminishes, the solutions homogenize (average out) and
converge to the solution of an effective anisotropic first-order
(spatio-temporal homogeneous) level set equation. Moreover we obtain a rate of
convergence and show that, under certain conditions, the averaging enhances the
velocity of the underlying front. We also prove that, at scale one, the level
sets of the solutions of the oscillatory problem converge, at long times, to
the Wulff shape associated with the effective Hamiltonian. Finally we also
consider advection depending on position at the integral scale
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