1,376 research outputs found
Optical Stark Effect and Dressed Excitonic States in a Mn-doped Quantum Dot
We report on the observation of spin dependent optically dressed states and
optical Stark effect on an individual Mn spin in a semiconductor quantum dot.
The vacuum-to-exciton or the exciton-to-biexciton transitions in a Mn-doped
quantum dot are optically dressed by a strong laser field and the resulting
spectral signature is measured in photoluminescence. We demonstrate that the
energy of any spin state of a Mn atom can be independently tuned using the
optical Stark effect induced by a control laser. High resolution spectroscopy
reveals a power, polarization and detuning dependent Autler-Townes splitting of
each optical transition of the Mn-doped quantum dot. This experiment
demonstrates a complete optical resonant control of the exciton-Mn system
Secoviridae: a proposed family of plant viruses within the order Picornavirales that combines the families Sequiviridae and Comoviridae, the unassigned genera Cheravirus and Sadwavirus, and the proposed genus Torradovirus
The order Picornavirales includes several plant viruses that are currently classified into the families Comoviridae (genera Comovirus, Fabavirus and Nepovirus) and Sequiviridae (genera Sequivirus and Waikavirus) and into the unassigned genera Cheravirus and Sadwavirus. These viruses share properties in common with other picornavirales (particle structure, positive-strand RNA genome with a polyprotein expression strategy, a common replication block including type III helicase, a 3C-like cysteine proteinase and type I RNA-dependent RNA polymerase). However, they also share unique properties that distinguish them from other picornavirales. They infect plants and use specialized proteins or protein domains to move through their host. In phylogenetic analysis based on their replication proteins, these viruses form a separate distinct lineage within the picornavirales branch. To recognize these common properties at the taxonomic level, we propose to create a new family termed “Secoviridae” to include the genera Comovirus, Fabavirus, Nepovirus, Cheravirus, Sadwavirus, Sequivirus and Waikavirus. Two newly discovered plant viruses share common properties with members of the proposed family Secoviridae but have distinct specific genomic organizations. In phylogenetic reconstructions, they form a separate sub-branch within the Secoviridae lineage. We propose to create a new genus termed Torradovirus (type species, Tomato torrado virus) and to assign this genus to the proposed family Secoviridae
Quantum network coding for quantum repeaters
This paper considers quantum network coding, which is a recent technique that
enables quantum information to be sent on complex networks at higher rates than
by using straightforward routing strategies. Kobayashi et al. have recently
showed the potential of this technique by demonstrating how any classical
network coding protocol gives rise to a quantum network coding protocol. They
nevertheless primarily focused on an abstract model, in which quantum resource
such as quantum registers can be freely introduced at each node. In this work,
we present a protocol for quantum network coding under weaker (and more
practical) assumptions: our new protocol works even for quantum networks where
adjacent nodes initially share one EPR-pair but cannot add any quantum
registers or send any quantum information. A typically example of networks
satisfying this assumption is {\emph{quantum repeater networks}}, which are
promising candidates for the implementation of large scale quantum networks.
Our results thus show, for the first time, that quantum network coding
techniques can increase the transmission rate in such quantum networks as well.Comment: 9 pages, 11figure
Electron-nuclei spin dynamics in II-VI semiconductor quantum dots
We report on the dynamics of optically induced nuclear spin polarization in
individual CdTe/ZnTe quantum dots loaded with one electron by modulation
doping. The fine structure of the hot trion (charged exciton with an
electron in the -shell) is identified in photoluminescence excitation
spectra. A negative polarisation rate of the photoluminescence, optical pumping
of the resident electron and the built-up of dynamic nuclear spin polarisation
(DNSP) are observed in time-resolved optical pumping experiments when the
quantum dot is excited at higher energy than the hot trion triplet state. The
time and magnetic field dependence of the polarisation rate of the
emission allows to probe the dynamics of formation of the DNSP in the optical
pumping regime. We demonstrate using time-resolved measurements that the
creation of a DNSP at B=0T efficiently prevents longitudinal spin relaxation of
the electron caused by fluctuations of the nuclear spin bath. The DNSP is built
in the microsecond range at high excitation intensity. A relaxation time of the
DNSP in about 10 microseconds is observed at and significantly increases
under a magnetic field of a few milli-Tesla. We discuss mechanisms responsible
for the fast initialisation and relaxation of the diluted nuclear spins in this
system
Packing and Hausdorff measures of stable trees
In this paper we discuss Hausdorff and packing measures of random continuous
trees called stable trees. Stable trees form a specific class of L\'evy trees
(introduced by Le Gall and Le Jan in 1998) that contains Aldous's continuum
random tree (1991) which corresponds to the Brownian case. We provide results
for the whole stable trees and for their level sets that are the sets of points
situated at a given distance from the root. We first show that there is no
exact packing measure for levels sets. We also prove that non-Brownian stable
trees and their level sets have no exact Hausdorff measure with regularly
varying gauge function, which continues previous results from a joint work with
J-F Le Gall (2006).Comment: 40 page
A four-season prospective study of muscle strain reoccurrences in a professional football club
The aim of this investigation was to characterise muscle strain reinjuries and examine their impact on playing resources in a professional football club. Muscle strains and reoccurrences were prospectively diagnosed over four seasons in first-team players (n = 46). Altogether, 188 muscle strains were diagnosed with 44 (23.4%) of these classed as reinjuries, leading to an incidence of 1.32 strain reoccurrences per 1,000 hours exposure (95% Confidence Interval [CI], 0.93–1.71). The incidence of recurrent strains was higher in match-play compared with training (4.51, 95% CI, 2.30–6.72 vs 0.94, 95% CI, 0.59–1.29). Altogether, 50.0% of players sustained at least 1 reoccurrence of a muscle strain, leading to approximately 3 days lost and 0.4 matches missed per player per season. The incidence of recurrent strains was highest in centre-forwards (2.15, 95% CI, 1.06–3.24), peaked in May (3.78, 95% CI, 0.47–7.09), and mostly affected the hamstrings (38.6% of all reoccurrences). Mean layoff for nonreoccurrences and recurrences was similar: ∼7.5 days. These results provide greater insight into the extent of the problem of recurrent muscle strains in professional football
Ion-exchange purification and structural characterization of five sulfated fucoidans from brown algae
Fucoidans are a diverse class of sulfated polysaccharides integral to the cell wall of brown algae, and due to their various bioactivities, they are potential drugs. Standardized work with fucoidans is required for structure-function studies, but remains challenging since available fucoidan preparations are often contaminated with other algal compounds. Additionally, fucoidans are structurally diverse depending on species and season, urging the need for standardized purification protocols. Here, we use ion-exchange chromatography to purify different fucoidans and found a high structural diversity between fucoidans. Ion-exchange chromatography efficiently removes the polysaccharides alginate and laminarin and other contaminants such as proteins and phlorotannins across a broad range of fucoidans from major brown algal orders including Ectocarpales, Laminariales and Fucales. By monomer composition, linkage analysis and NMR characterization, we identified galacturonic acid, glucuronic acid and O-acetylation as new structural features of certain fucoidans and provided a novel structure of fucoidan from Durvillaea potatorum with alpha-1,3-linked fucose backbone and beta-1,6 and beta-1,3 galactose branches. This study emphasizes the use of standardized ion-exchange chromatography to obtain defined fucoidans for subsequent molecular studies
EFFECTS OF MAGNETIC AND NON MAGNETIC LAYER THICKNESS ON GIANT MAGNETORESISTANCE IN (NiFeCo/Cu) MULTILAYERS
This paper presents a study of the magnetoresistance (MR) in the layered magnetic structure (NiFeCo/Cu). The effect of the magnetic (m) and non magnetic (nm) layer thickness (tm , tnm) and the composition of the magnetic layer has been discussed in the framework of the Johnson-Camley semiclassical approach, which is based on the Boltzmann transport equation. Our results are compared with the experiments and seem to show good agreement. Indeed, three main features of the MR are reproduced: (i) Presence of MR peak at tmmax which vary with the magnetic layer composition, (ii) A MR decrease with non magnetic layer thickness tnm, (iii) The increasing magnitude of MR ratio with increasing Co content.This paper presents a study of the magnetoresistance (MR) in the layered magnetic structure (NiFeCo/Cu). The effect of the magnetic (m) and non magnetic (nm) layer thickness (tm , tnm) and the composition of the magnetic layer has been discussed in the framework of the Johnson-Camley semiclassical approach, which is based on the Boltzmann transport equation. Our results are compared with the experiments and seem to show good agreement. Indeed, three main features of the MR are reproduced: (i) Presence of MR peak at tmmax which vary with the magnetic layer composition, (ii) A MR decrease with non magnetic layer thickness tnm, (iii) The increasing magnitude of MR ratio with increasing Co content
Universal fluctuations in the support of the random walk
A random walk starts from the origin of a d-dimensional lattice. The
occupation number n(x,t) equals unity if after t steps site x has been visited
by the walk, and zero otherwise. We study translationally invariant sums M(t)
of observables defined locally on the field of occupation numbers. Examples are
the number S(t) of visited sites; the area E(t) of the (appropriately defined)
surface of the set of visited sites; and, in dimension d=3, the Euler index of
this surface. In d > 3, the averages (t) all increase linearly with t as
t-->infinity. We show that in d=3, to leading order in an asymptotic expansion
in t, the deviations from average Delta M(t)= M(t)-(t) are, up to a
normalization, all identical to a single "universal" random variable. This
result resembles an earlier one in dimension d=2; we show that this
universality breaks down for d>3.Comment: 17 pages, LaTeX, 2 figures include
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