278 research outputs found
An economic approach to collective management of endemic animal diseases
The control of animal diseases is an issue of particular interest in animal production chains. Because of their direct impact on production, animal diseases generate income shortfalls for farmers. In some cases, diseases may also have lead to human health problems and undermine market access conditions. Because of these potential negative impacts, some diseases are regulated. But for many communicable diseases, much latitude is given to individual control of the disease by farmers. In the case of a communicable disease, individual management therefore generates an externality, as individual decisions have an impact on the level of risk exposure of other farms to the disease. Thus, the collective result of individual management may differ from the collective expectations. This gap can be reduced by collective actions. The aim of this paper is to provide a conceptual framework for the study of collective management of animal diseases, which will provide management tools to collective managers of animal health. The development of this conceptual framework rests on three steps. We first discuss the means to model the individual decisions of farmer in regard to animal diseases. Then it should take into account the interaction between the epidemiology of the disease and the individual decisions of farmers, by the coupling of epidemiologic and economic models. Finally, collective management tools are introduced in these models in order to test incentives schemes for horizontal coordination. Finally, collective actions are introduced in these models, in order to test devices for horizontal coordination (management of prevalence between farms).Animal health economics - Micro modelling – Bio-economic modelling - endemic animal diseases, Animal health economics, Micro modelling, Bio-economic modelling, endemic animal diseases, Livestock Production/Industries,
Quantum dot-cavity strong-coupling regime measured through coherent reflection spectroscopy in a very high-Q micropillar
We report on the coherent reflection spectroscopy of a high-quality factor
micropillar, in the strong coupling regime with a single InGaAs annealed
quantum dot. The absolute reflectivity measurement is used to study the
characteristics of our device at low and high excitation power. The strong
coupling is obtained with a g=16 \mueV coupling strength in a 7.3\mum diameter
micropillar, with a cavity spectral width kappa=20.5 \mueV (Q=65 000). The
factor of merit of the strong-coupling regime, 4g/kappa=3, is the current
state-of-the-art for a quantum dot-micropillar system
Nuclear spin physics in quantum dots: an optical investigation
The mesoscopic spin system formed by the 10E4-10E6 nuclear spins in a
semiconductor quantum dot offers a unique setting for the study of many-body
spin physics in the condensed matter. The dynamics of this system and its
coupling to electron spins is fundamentally different from its bulk
counter-part as well as that of atoms due to increased fluctuations that result
from reduced dimensions. In recent years, the interest in studying quantum dot
nuclear spin systems and their coupling to confined electron spins has been
fueled by its direct implication for possible applications of such systems in
quantum information processing as well as by the fascinating nonlinear
(quantum-)dynamics of the coupled electron-nuclear spin system. In this
article, we review experimental work performed over the last decades in
studying this mesoscopic,coupled electron-nuclear spin system and discuss how
optical addressing of electron spins can be exploited to manipulate and
read-out quantum dot nuclei. We discuss how such techniques have been applied
in quantum dots to efficiently establish a non-zero mean nuclear spin
polarization and, most recently, were used to reduce fluctuations of the
average quantum dot nuclear spin orientation. Both results in turn have
important implications for the preservation of electron spin coherence in
quantum dots, which we discuss. We conclude by speculating how this recently
gained understanding of the quantum dot nuclear spin system could in the future
enable experimental observation of quantum-mechanical signatures or possible
collective behavior of mesoscopic nuclear spin ensembles.Comment: 61 pages, 45 figures, updated reference list, corrected typographical
error
Dynamic nuclear polarization of a single charge-tunable InAs/GaAs quantum dot
We report on the dynamic nuclear polarization of a single charge-tunable
self-assembled InAs/GaAs quantum dot in a longitudinal magnetic field of
0.2T. The hyperfine interaction between the optically oriented electron
and nuclei spins leads to the polarization of the quantum dot nuclei measured
by the Overhauser-shift of the singly-charged excitons ( and ).
When going from to , we observe a reversal of this shift which
reflects the average electron spin optically written down in the quantum dot
either in the state or in the final state of recombination. We
discuss a theoretical model which indicates an efficient depolarization
mechanism for the nuclei limiting their polarization to ~10%.Comment: 4+ pages, 3 figure
Optical pumping and non-destructive readout of a single magnetic impurity spin in an InAs/GaAs quantum dot
We report on the resonant optical pumping of the |\pm1> spin states of a
single Mn dopant in an InAs/GaAs quantum dot embedded itself in a charge
tuneable device. The experiment relies on a "W" scheme of transitions reached
when a suitable longitudinal magnetic field is applied. The optical pumping is
achieved via the resonant excitation of the central {\Lambda} system at the
neutral exciton X0 energy. For a specific gate voltage, the red-shifted
photoluminescence of the charged exciton X- is observed, which allows
non-destructive readout of the spin polarization. An arbitrary spin preparation
in the |+1> or |-1> state characterized by a polarization near or above 50% is
evidenced.Comment: 11 pages, 3 figure
Hyperfine interaction in InAs/GaAs self-assembled quantum dots : dynamical nuclear polarization versus spin relaxation
We report on the influence of hyperfine interaction on the optical
orientation of singly charged excitons X+ and X- in self-assembled InAs/GaAs
quantum dots. All measurements were carried out on individual quantum dots
studied by micro-photoluminescence at low temperature. We show that the
hyperfine interaction leads to an effective partial spin relaxation, under
50kHz modulated excitation polarization, which becomes however strongly
inhibited under steady optical pumping conditions because of dynamical nuclear
polarization. This optically created magnetic-like nuclear field can become
very strong (up to ~4 T) when it is generated in the direction opposite to a
longitudinally applied field, and exhibits then a bistability regime. This
effect is very well described by a theoretical model derived in a perturbative
approach, which reveals the key role played by the energy cost of an electron
spin flip in the total magnetic field. Eventually, we emphasize the
similarities and differences between X+ and X- trions with respect to the
hyperfine interaction, which turn out to be in perfect agreement with the
theoretical description.Comment: 10 pages, 5 figure
Structure-based prediction of BRAF mutation classes using machine-learning approaches.
The BRAF kinase is attracting a lot of attention in oncology as alterations of its amino acid sequence can constitutively activate the MAP kinase signaling pathway, potentially contributing to the malignant transformation of the cell but at the same time rendering it sensitive to targeted therapy. Several pathologic BRAF variants were grouped in three different classes (I, II and III) based on their effects on the protein activity and pathway. Discerning the class of a BRAF mutation permits to adapt the treatment proposed to the patient. However, this information is lacking new and experimentally uncharacterized BRAF mutations detected in a patient biopsy. To overcome this issue, we developed a new in silico tool based on machine learning approaches to predict the potential class of a BRAF missense variant. As class I only involves missense mutations of Val600, we focused on the mutations of classes II and III, which are more diverse and challenging to predict. Using a logistic regression model and features including structural information, we were able to predict the classes of known mutations with an accuracy of 90%. This new and fast predictive tool will help oncologists to tackle potential pathogenic BRAF mutations and to propose the most appropriate treatment for their patients
Immune cell extravasation in an organ-on-chip to model lung inflammation.
Acute respiratory distress syndrome (ARDS) is a severe lung condition with high mortality and various causes, including lung infection. No specific treatment is currently available and more research aimed at better understanding the pathophysiology of ARDS is needed. Most lung-on-chip models that aim at mimicking the air-blood barrier are designed with a horizontal barrier through which immune cells can migrate vertically, making it challenging to visualize and investigate their migration. In addition, these models often lack a barrier of natural protein-derived extracellular matrix (ECM) suitable for live cell imaging to investigate ECM-dependent migration of immune cells as seen in ARDS. This study reports a novel inflammation-on-chip model with live cell imaging of immune cell extravasation and migration during lung inflammation. The three-channel perfusable inflammation-on-chip system mimics the lung endothelial barrier, the ECM environment and the (inflamed) lung epithelial barrier. A chemotactic gradient was established across the ECM hydrogel, leading to the migration of immune cells through the endothelial barrier. We found that immune cell extravasation depends on the presence of an endothelial barrier, on the ECM density and stiffness, and on the flow profile. In particular, bidirectional flow, broadly used in association with rocking platforms, was found to importantly delay extravasation of immune cells in contrast to unidirectional flow. Extravasation was increased in the presence of lung epithelial tissue. This model is currently used to study inflammation-induced immune cell migration but can be used to study infection-induced immune cell migration under different conditions, such as ECM composition, density and stiffness, type of infectious agents used, and the presence of organ-specific cell types
Controlling the polarization eigenstate of a quantum dot exciton with light
We demonstrate optical control of the polarization eigenstates of a neutral
quantum dot exciton without any external fields. By varying the excitation
power of a circularly polarized laser in micro-photoluminescence experiments on
individual InGaAs quantum dots we control the magnitude and direction of an
effective internal magnetic field created via optical pumping of nuclear spins.
The adjustable nuclear magnetic field allows us to tune the linear and circular
polarization degree of the neutral exciton emission. The quantum dot can thus
act as a tunable light polarization converter.Comment: 5 pages, 3 figure
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