220 research outputs found
Direct evidence of nuclear spin waves in NdCuO by high-resolution neutron-spin-echo spectroscopy
We investigated the dispersion of nuclear spin waves in NdCuO by
using neutron spin-echo spectroscopy at millikelvin temperatures. Our results
show unambiguously the existence of dispersion of nuclear spin waves in
NdCuO at T = 30 mK. A fit of the dispersion data with the spin wave
dispersion formula gave the Suhl-Nakamura interaction range to be of the order
of 10 {\AA}
J-NSE: Neutron spin echo spectrometer
Neutron Spin-Echo (NSE) spectroscopy is well known as the only neutron scattering technique that achieves energy resolution of several neV. By using the spin precession of polarized neutrons in magnetic field one can measure tiny velocity changes of the individual neutron during the scattering process. Contrary to other inelastic neutron scattering techniques, NSE measures the intermediate scattering function S(Q,t) in reciprocal space and time directly. The Neutron Spin-Echo spectrometer J-NSE, operated by JCNS, Forschungszentrum Jülich at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching, covers a time range (2 ps to 200 ns) on length scales accessible by small angle scattering technique. Along with conventional NSE spectroscopy that allows bulk measurements in transmission mode, J-NSE offers a new possibility - gracing incidence spin echo spectroscopy (GINSENS), developed to be used as "push-button" option in order to resolve the depth dependent near surface dynamics
Inelastic Neutron Scattering Analysis with Time-Dependent Gaussian-Field Models
Converting neutron scattering data to real-space time-dependent structures
can only be achieved through suitable models, which is particularly challenging
for geometrically disordered structures. We address this problem by introducing
time-dependent clipped Gaussian field models. General expressions are derived
for all space- and time-correlation functions relevant to coherent inelastic
neutron scattering, for multiphase systems and arbitrary scattering contrasts.
Various dynamic models are introduced that enable one to add time-dependence to
any given spatial statistics, as captured e.g. by small-angle scattering. In a
first approach, the Gaussian field is decomposed into localised waves that are
allowed to fluctuate in time or to move, either ballistically or diffusively.
In a second approach, a dispersion relation is used to make the spectral
components of the field time-dependent. The various models lead to
qualitatively different dynamics, which can be discriminated by neutron
scattering. The methods of the paper are illustrated with oil/water
microemulsion studied by small-angle scattering and neutron spin-echo. All
available data - in both film and bulk contrasts, over the entire range of
and - are analyzed jointly with a single model. The analysis points to
static large-scale structure of the oil and water domains, while the interfaces
are subject to thermal fluctuations. The fluctuations have an amplitude around
6 nm and contribute to 30 % of the total interface area.Comment: The following article has been accepted by Journal of Chemical
Physics. After it is published, it will be found at
https://aip.scitation.org/journal/jcp
Tunable viscosity modification with diluted particles: When particles decrease the viscosity of complex fluids
While spherical particles are the most studied viscosity modifiers, they are
well known only to increase viscosities, in particular at low concentrations.
Extended studies and theories on non-spherical particles find a more
complicated behavior, but still a steady increase. Involving platelets in
combination with complex fluids displays an even more complex scenario that we
analyze experimentally and theoretically as a function of platelet diameter, to
find the underlying concepts. Using a broad toolbox of different techniques we
were able to decrease the viscosity of crude oils although solid particles were
added. This apparent contradiction could lead to a wider range of applications.Comment: 13+7 pages, 6+7 figure
Influence of Ibuprofen on Phospholipid Membranes
Basic understanding of biological membranes is of paramount importance as
these membranes comprise the very building blocks of life itself. Cells depend
in their function on a range of properties of the membrane, which are important
for the stability and function of the cell, information and nutrient transport,
waste disposal and finally the admission of drugs into the cell and also the
deflection of bacteria and viruses.
We have investigated the influence of ibuprofen on the structure and dynamics
of L-alpha-phosphatidylcholine (SoyPC) membranes by means of grazing incidence
small-angle neutron scattering (GISANS), neutron reflectometry and grazing
incidence neutron spin echo spectroscopy (GINSES). From the results of these
experiments we were able to determine that ibuprofen induces a two-step
structuring behavior in the SoyPC films, where the structure evolves from the
purely lamellar phase for pure SoyPC over a superposition of two hexagonal
phases to a purely hexago- nal phase at high concentrations. Additionally,
introduction of ibuprofen stiffens the membranes. This behavior may be
instrumental in explaining the toxic behavior of ibuprofen in long-term
application.Comment: -Improved indexing in Fig. 4e) -changed concentrations to mol%
-improved arguments, however conclusions stay unchange
La multifonctionnalité de l'agriculture : un concept d'avenir ?
International audienceLa multifonctionnalité de l'agriculture : un concept d'avenir ? Etude par Luc Bodiguel chargé de recherche, UMR CNRS 3128, Droit et changement social (DCS)chargé d'enseignement à la faculté de droit de Nantes et d'Angers Accès au sommaire Comment comprendre aujourd'hui le concept de multifonctionnalité de l'agriculture ? Les réformes française et communautaire sont-elles venues lui donner un véritable contenu juridique ? Une autre portée politique ? Ou, au contraire, la multifonctionnalité de l'agriculture est-elle restée au stade théorique, au concept, voire, at -elle été dépassée par d'autres concepts plus influents, plus opérationnels ou plus à la mode ? Enfin, à quoi peut bien encore servir le concept de multifonctionnalité de l'agriculture d'un point de vue politique et juridique ? Afin de tenter de répondre à ces questions, Luc Bodiguel nous propose d'observer tout d'abord les fondements et règles de droit qui peuvent aujourd'hui être liés au concept de multifonctionnalité pour ensuite s'interroger sur l'avenir du concept au vu du droit français, communautaire et de l'organisation mondiale du commerce
Fractal diffusion in high temperature polymer electrolyte fuel cell membranes
© 2018 Author(s). The performance of fuel cells depends largely on the proton diffusion in the proton conducting membrane, the core of a fuel cell. High temperature polymer electrolyte fuel cells are based on a polymer membrane swollen with phosphoric acid as the electrolyte, where proton conduction takes place. We studied the proton diffusion in such membranes with neutron scattering techniques which are especially sensitive to the proton contribution. Time of flight spectroscopy and backscattering spectroscopy have been combined to cover a broad dynamic range. In order to selectively observe the diffusion of protons potentially contributing to the ion conductivity, two samples were prepared, where in one of the samples the phosphoric acid was used with hydrogen replaced by deuterium. The scattering data from the two samples were subtracted in a suitable way after measurement. Thereby subdiffusive behavior of the proton diffusion has been observed and interpreted in terms of a model of fractal diffusion. For this purpose, a scattering function for fractal diffusion has been developed. The fractal diffusion dimension dw and the Hausdorff dimension df have been determined on the length scales covered in the neutron scattering experiments
Inner structure and dynamics of microgels with low and medium crosslinker content prepared via surfactant-free precipitation polymerization and continuous monomer feeding approach
The preparation of poly(N-isopropylacrylamide) microgels via classical precipitation polymerization (batch method) and a continuous monomer feeding approach (feeding method) leads to different internal crosslinker distributions, i.e., from core–shell-like to a more homogeneous one. The internal structure and dynamics of these microgels with low and medium crosslinker concentrations are studied with dynamic light scattering and small-angle neutron scattering in a wide q-range below and above the volume phase transition temperature. The influence of the preparation method, and crosslinker and initiator concentration on the internal structure of the microgels is investigated. In contrast to the classical conception where polymer microgels possess a core–shell structure with the averaged internal polymer density distribution within the core part, a detailed view of the internal inhomogeneities of the PNIPAM microgels and the presence of internal domains even above the volume phase transition temperature, when polymer microgels are in the deswollen state, are presented. The correlation between initiator concentration and the size of internal domains that appear inside the microgel with temperature increase is demonstrated. Moreover, the influence of internal inhomogeneities on the dynamics of the batch- and feeding-microgels studied with neutron spin-echo spectroscopy is reported.TU Berlin, Open-Access-Mittel - 201
Slow Dynamics in Complex Fluids: Neutron Spin Echo Spectroscopy, Small-angle Neutron Scattering and Neutron Spin-Echo Spectroscopy for Structure and Dynamics of Soft Condensed Matter Workshop
- …