1,176 research outputs found
A versatile dual spot laser scanning confocal microscopy system for advanced fluorescence correlation spectroscopy analysis in living cell
A fluorescence correlation spectroscopy (FCS) system based on two independent
measurement volumes is presented. The optical setup and data acquisition
hardware are detailed, as well as a complete protocol to control the location,
size and shape of the measurement volumes. A method that allows to monitor
independently the excitation and collection efficiency distribution is
proposed. Finally, a few examples of measurements that exploit the two spots in
static and/or scanning schemes, are reported.Comment: Accepted for publication in Review of Scientific Instrumen
Harmonised Principles for Public Participation in Quality Assurance of Integrated Water Resources Modelling
The main purpose of public participation in integrated water resources modelling is to improve decision-making by ensuring that decisions are soundly based on shared knowledge, experience and scientific evidence. The present paper describes stakeholder involvement in the modelling process. The point of departure is the guidelines for quality assurance for `scientific` water resources modelling developed under the EU research project HarmoniQuA, which has developed a computer based Modelling Support Tool (MoST) to provide a user-friendly guidance and a quality assurance framework that aim for enhancing the credibility of river basin modelling. MoST prescribes interaction, which is a form of participation above consultation but below engagement of stakeholders and the public in the early phases of the modelling cycle and under review tasks throughout the process. MoST is a flexible tool which supports different types of users and facilitates interaction between modeller, manager and stakeholders. The perspective of using MoST for engagement of stakeholders e.g. higher level participation throughout the modelling process as part of integrated water resource management is evaluate
Geometrical effects on the optical properties of quantum dots doped with a single magnetic atom
The emission spectra of individual self-assembled quantum dots containing a
single magnetic Mn atom differ strongly from dot to dot. The differences are
explained by the influence of the system geometry, specifically the in-plane
asymmetry of the quantum dot and the position of the Mn atom. Depending on both
these parameters, one has different characteristic emission features which
either reveal or hide the spin state of the magnetic atom. The observed
behavior in both zero field and under magnetic field can be explained
quantitatively by the interplay between the exciton-manganese exchange
interaction (dependent on the Mn position) and the anisotropic part of the
electron-hole exchange interaction (related to the asymmetry of the quantum
dot).Comment: 5 pages, 5 figures, to be published in Phys. Rev. Let
Matter Mixing in Aspherical Core-collapse Supernovae: Three-dimensional Simulations with Single Star and Binary Merger Progenitor Models for SN 1987A
We perform three-dimensional hydrodynamic simulations of aspherical core-collapse supernovae focusing on the matter mixing in SN 1987A. The impacts of four progenitor (pre-supernova) models and parameterized aspherical explosions are investigated. The four pre-supernova models include a blue supergiant (BSG) model based on a slow merger scenario developed recently for the progenitor of SN 1987A (Urushibata et al. 2018). The others are a BSG model based on a single star evolution and two red supergiant (RSG) models. Among the investigated explosion (simulation) models, a model with the binary merger progenitor model and with an asymmetric bipolar-like explosion, which invokes a jetlike explosion, best reproduces constraints on the mass of high velocity Ni, as inferred from the observed [Fe II] line profiles. The advantage of the binary merger progenitor model for the matter mixing is the flat and less extended profile of the C+O core and the helium layer, which may be characterized by the small helium core mass. From the best explosion model, the direction of the bipolar explosion axis (the strongest explosion direction), the neutron star (NS) kick velocity, and its direction are predicted. Other related implications and future prospects are also given
p-Type doping of II-VI heterostructures from surface states: application to ferromagnetic CdMnTe quantum wells
We present a study of p-type doping of CdTe and CdMnTe quantum
wells from surface states. We show that this method is as efficient as usual
modulation doping with nitrogen acceptors, and leads to hole densities
exceeding cm. Surface doping was successfully applied
to obtain carrier-induced ferromagnetism in a CdMnTe quantum well.
The observed temperature dependence of photoluminescence spectra, and the
critical temperature, correspond well to those previously reported for
ferromagnetic quantum wells doped with nitrogen.Comment: 4 figure
Optical-fiber-microsphere for remote fluorescence correlation spectroscopy
International audienceFluorescence correlation spectroscopy (FCS) is a versatile method that would greatly benefit to remote optical-fiber fluorescence sensors. However, the current state-of-the-art struggles with high background and low detection sensitivities that prevent the extension of fiber-based FCS down to the single-molecule level. Here we report the use of an optical fiber combined with a latex microsphere to perform FCS analysis. The sensitivity of the technique is demonstrated at the single molecule level thanks to a photonic nanojet effect. This offers new opportunities for reducing the bulky microscope setup and extending FCS to remote or in vivo applications
Discrete complex analysis on planar quad-graphs
We develop a linear theory of discrete complex analysis on general
quad-graphs, continuing and extending previous work of Duffin, Mercat, Kenyon,
Chelkak and Smirnov on discrete complex analysis on rhombic quad-graphs. Our
approach based on the medial graph yields more instructive proofs of discrete
analogs of several classical theorems and even new results. We provide discrete
counterparts of fundamental concepts in complex analysis such as holomorphic
functions, derivatives, the Laplacian, and exterior calculus. Also, we discuss
discrete versions of important basic theorems such as Green's identities and
Cauchy's integral formulae. For the first time, we discretize Green's first
identity and Cauchy's integral formula for the derivative of a holomorphic
function. In this paper, we focus on planar quad-graphs, but we would like to
mention that many notions and theorems can be adapted to discrete Riemann
surfaces in a straightforward way.
In the case of planar parallelogram-graphs with bounded interior angles and
bounded ratio of side lengths, we construct a discrete Green's function and
discrete Cauchy's kernels with asymptotics comparable to the smooth case.
Further restricting to the integer lattice of a two-dimensional skew coordinate
system yields appropriate discrete Cauchy's integral formulae for higher order
derivatives.Comment: 49 pages, 8 figure
Light and electric field control of ferromagnetism in magnetic quantum structures
A strong influence of illumination and electric bias on the Curie temperature
and saturation value of the magnetization is demonstrated for semiconductor
structures containing a modulation-doped p-type Cd0.96Mn0.04Te quantum well
placed in various built-in electric fields. It is shown that both light beam
and bias voltage generate an isothermal and reversible cross-over between the
paramagnetic and ferromagnetic phases, in the way that is predetermined by the
structure design. The observed behavior is in quantitative agreement with the
expectations for systems, in which ferromagnetic interactions are mediated by
the weakly disordered two-dimensional hole liquid.Comment: 4 pages and 3 figure
Excitonic giant Zeeman effect in GaN:Mn^3+
We describe a direct observation of the excitonic giant Zeeman splitting in
(Ga,Mn)N, a wide-gap III-V diluted magnetic semiconductor. Reflectivity and
absorption spectra measured at low temperatures display the A and B excitons,
with a shift under magnetic field due to s,p-d exchange interactions. Using an
excitonic model, we determine the difference of exchange integrals between
Mn^3+ and free carriers in GaN, N_0(alpha-beta)=-1.2 +/- 0.2 eV. Assuming a
reasonable value of alpha, this implies a positive sign of beta which
corresponds to a rarely observed ferromagnetic interaction between the magnetic
ions and the holes.Comment: 4 pages, 4 figure
Ferromagnetic (Ga,Mn)N epilayers versus antiferromagnetic GaMnN clusters
Mn-doped wurtzite GaN epilayers have been grown by nitrogen plasma-assisted
molecular beam epitaxy. Correlated SIMS, structural and magnetic measurements
show that the incorporation of Mn strongly depends on the conditions of the
growth. Hysteresis loops which persist at high temperature do not appear to be
correlated to the presence of Mn. Samples with up to 2% Mn are purely
substitutional GaMnN epilayers, and exhibit paramagnetic
properties. At higher Mn contents, precipitates are formed which are identified
as GaMnN clusters by x-ray diffraction and absorption: this induces a
decrease of the paramagnetic magnetisation. Samples co-doped with enough Mg
exhibit a new feature: a ferromagnetic component is observed up to
K, which cannot be related to superparamagnetism of unresolved magnetic
precipitates.Comment: Revised versio
- …