415 research outputs found
Influence of the multipole order of the source on the decay of an inertial wave beam in a rotating fluid
We analyze theoretically and experimentally the far-field viscous decay of a
two-dimensional inertial wave beam emitted by a harmonic line source in a
rotating fluid. By identifying the relevant conserved quantities along the wave
beam, we show how the beam structure and decay exponent are governed by the
multipole order of the source. Two wavemakers are considered experimentally, a
pulsating and an oscillating cylinder, aiming to produce a monopole and a
dipole source, respectively. The relevant conserved quantity which
discriminates between these two sources is the instantaneous flowrate along the
wave beam, which is non-zero for the monopole and zero for the dipole. For each
source the beam structure and decay exponent, measured using particle image
velocimetry, are in good agreement with the predictions
Temperature dependence of exciton recombination in semiconducting single-wall carbon nanotubes
We study the excitonic recombination dynamics in an ensemble of (9,4)
semiconducting single-wall carbon nanotubes by high sensitivity time-resolved
photo-luminescence experiments. Measurements from cryogenic to room temperature
allow us to identify two main contributions to the recombination dynamics. The
initial fast decay is temperature independent and is attributed to the presence
of small residual bundles that create external non-radiative relaxation
channels. The slow component shows a strong temperature dependence and is
dominated by non-radiative processes down to 40 K. We propose a quantitative
phenomenological modeling of the variations of the integrated photoluminescence
intensity over the whole temperature range. We show that the luminescence
properties of carbon nanotubes at room temperature are not affected by the
dark/bright excitonic state coupling
Ultra-coherent single photon source
We present a novel type of single photon source in solid state, based on the
coherent laser light scattering by a single InAs quantum dot. We demonstrate
that the coherence of the emitted single photons is tailored by the resonant
excitation with a spectral linewidth below the radiative limit. Our
ultra-coherent source opens the way for integrated quantum devices dedicated to
the generation of single photons with high degrees of indistinguishability
Exploiting one-dimensional exciton-phonon coupling for tunable and efficient single-photon generation with a carbon nanotube
Condensed-matter emitters offer enriched cavity quantum electrodynamical
effects due to the coupling to external degrees of freedom. In the case of
carbon nanotubes a very peculiar coupling between localized excitons and the
one-dimensional acoustic phonon modes can be achieved, which gives rise to
pronounced phonon wings in the luminescence spectrum. By coupling an individual
nanotube to a tunable optical micro-cavity, we show that this peculiar
exciton-phonon coupling is a valuable resource to enlarge the tuning range of
the single-photon source while keeping an excellent exciton-photon coupling
efficiency and spectral purity. Using the unique flexibility of our scanning
fiber cavity, we are able to measure the efficiency spectrum of the very same
nanotube in the Purcell regime for several mode volumes. Whereas this
efficiency spectrum looks very much like the free-space luminescence spectrum
when the Purcell factor is small (large mode volume), we show that the
deformation of this spectrum at lower mode volumes can be traced back to the
strength of the exciton-photon coupling. It shows an enhanced efficiency on the
red wing that arises from the asymmetry of the incoherent energy exchange
processes between the exciton and the cavity. This allows us to obtain a tuning
range up to several hundred times the spectral width of the source
Neutrophil Elastase Activity Imaging: Recent Approaches in the Design and Applications of Activity-Based Probes and Substrate-Based Probes
International audienceThe last few decades of protease research has con rmed that a number of important biological processes are strictly dependent on proteolysis. Neutrophil elastase (NE) is a critical protease in immune response and host defense mechanisms in both physiological and disease-associated conditions. Particularly, NE has been identi ed as a promising biomarker for early diagnosis of lung in ammation. Recent studies have shown an increasing interest in developing methods for NE activity imaging both in vitro and in vivo. Unlike anatomical imaging modalities, functional molecular imaging, including enzymatic activities, enables disease detection at a very early stage and thus constitutes a much more accurate approach. When combined with advanced imaging technologies, opportunities arise for measuring imbalanced proteolytic activities with unprecedented details. Such technologies consist in building the highest resolved and sensitive instruments as well as the most speci c probes based either on peptide substrates or on covalent inhibitors. is review outlines strengths and weaknesses of these technologies and discuss their applications to investigate NE activity as biomarker of pulmonary in ammatory diseases by imaging
The Branding Effect of Contracts
In his case study of the MasterCard IPO and its predecessor piece on the Google IPO, Victor Fleischer claims to find evidence of a branding effect of legal infrastructure. The branding effect is not aimed at reducing the potential for opportunism by a counterparty to a contract, but rather at increasing the attractiveness of a product to present and future users or improving the image of a company in the eyes of regulators, judges, and juries. In this essay commenting on Fleischer\u27s work, I endorse the notion that deal structures have branding effects and position Fleischer\u27s work within a larger stream of scholarship that focuses on the substantive terms of contracts rather than on contract doctrine or dispute resolution in various contractual settings. In addition, I offer a few refinements to Fleischer\u27s notion of branding effect
Unifying the low-temperature photoluminescence spectra of carbon nanotubes: the role of acoustic phonon confinement
At low temperature the photoluminescence of single-wall carbon nanotubes show
a large variety of spectral profiles ranging from ultra narrow lines in
suspended nanotubes to broad and asymmetrical line-shapes that puzzle the
current interpretation in terms of exciton-phonon coupling. Here, we present a
complete set of photoluminescence profiles in matrix embedded nanotubes
including unprecedented narrow emission lines. We demonstrate that the
diversity of the low-temperature luminescence profiles in nanotubes originates
in tiny modifications of their low-energy acoustic phonon modes. When low
energy modes are locally suppressed, a sharp photoluminescence line as narrow
as 0.7 meV is restored. Furthermore, multi-peak luminescence profiles with
specific temperature dependence show the presence of confined phonon modes
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