103 research outputs found
Hyperfine interaction in cobalt by high-resolution neutron spectroscopy
We have investigated the ferromagnetic phase transition of elemental Co by
high-resolution neutron backscattering spectroscopy. We monitored the splitting
of the nuclear levels by the hyperfine field at the Co nucleus. The energy of
this hyperfine splitting is identified as the order parameter of the
ferromagnetic phase transition. By measuring the temperature dependence of the
energy we determined the critical exponent and the
ferromagnetic Curie temperature of ~K. The present result
of the critical exponent agrees better with the predicted value (0.367) of the
3-dimensional Heisenberg model than that determined previously by NMR
SPHERES: Backscattering spectrometer
SPHERES (SPectrometer for High Energy RESolution), operated by JCNS, Forschungszentrum Jülich, is a third-generation neutron backscattering spectrometer with focussing optics and a phase-space-transform chopper. It enables the investigation of atomic and molecular dynamics with an energy resolution of about 0.65 μeV in a dynamic range of ± 31 μeV
Spin correlations in the extended kagome system YBaCo3FeO7
The transition metal based oxide YBaCo3FeO7 is structurally related to the
mineral Swedenborgite SbNaBe4O7, a polar non-centrosymmetric crystal system.
The magnetic Co3Fe sublattice consists of a tetrahedral network containing
kagome-like layers with trigonal interlayer sites. This geometry causes
frustration effects for magnetic ordering, which were investigated by
magnetization measurements, M\"ossbauer spectroscopy, polarized neutron
diffraction, and neutron spectroscopy. Magnetization measurement and neutron
diffraction do not show long range ordering even at low temperature (1 K)
although a strong antiferromagnetic coupling (~2000 K) is deduced from the
magnetic susceptibility. Below 590 K, we observe two features, a spontaneous
weak anisotropic magnetization hysteresis along the polar crystallographic axis
and a hyperfine field on the Fe kagome sites, whereas the Fe spins on the
interlayer sites remain idle. Below ~50 K, the onset of a hyperfine field shows
the development of moments static on the M\"ossbauer time scale also for the Fe
interlayer sites. Simultaneously, an increase of spin correlations is found by
polarized neutron diffraction. The relaxation part of the dynamic response has
been further investigated by high-resolution neutron spectroscopy, which
reveals that the spin correlations start to freeze in below ~50 K. Monte Carlo
simulations show that the neutron scattering results at lower temperatures are
compatible with a recent proposal that the particular geometric frustration in
the Swedenborgite structure promotes quasi one dimensional partial order.Comment: 13 pages, 7 figure
Experimental investigation of fast electron transport in solid density matter: Recent results from a new technique of X-ray energy-encoded 2D imaging
AbstractThe development activity of a new experimental technique for the study of the fast electron transport in high density matter is reported. This new diagnostic tool enables the X-ray 2D imaging of ultrahigh intensity laser plasmas with simultaneous spectral resolution in a very large energy range to be obtained. Results from recent experiments are discussed, in which the electron propagation in multilayer targets was studied by using the Kα. In particular, results highlighting the role of anisotropic Bremsstrahlung are reported, for the sake of the explanation of the capabilities of the new diagnostics. A discussion of a test experiment conceived to extend the technique to a single-shot operation is finally given
Proyecto Vainica: valoración e intervención nutricional e insuficiencia cardiaca
Desde el comienzo del milenio diversos estudios muestran la “paradoja de la obesidad en pacientes con insuficiencia cardiaca”. Existe una epidemiología inversa: la obesidad predispone para desarrollar enfermedades cardiovasculares e insuficiencia cardiaca, pero un índice de masa corporal elevado mejora la supervivencia a dos y cinco años. Esta paradoja se ha extendido con posterioridad, a otras enfermedades de carácter crónico y ha sido un tema controvertido en la comunidad científica. Posteriormente, diversos estudios han ido migrando la orientación, relacionando el pronóstico no con el índice de masa corporal en sí, sino con el estado nutricional y el adelgazamiento no intencionado. De modo que el foco de interés está ahora en el estado nutricional de los pacientes y no en su índice de masa corporal. El peso –y por tanto el índice de masa corporal- es un parámetro cambiante en los pacientes con insuficiencia cardiaca, ya que por la naturaleza de su patología, pueden presentar un volumen hídrico aumentado y son susceptibles a descompensaciones edemo-asciticas. Los episodios de descompensación son habitualmente tratados con diuréticos, con el objetivo de eliminar el exceso de líquido, lo que hace que el peso fluctúe rápidamente, a expensas de la reducción del exceso de volumen hídrico. No existe consenso o marcador universalmente aceptado para definir la malnutrición. Por ello, coexisten múltiples métodos de cribado y valoración nutricional. No destacándose ninguno como “gold estándar”..
Simulation-guided optimization of small-angle analyzer geometry in the neutron backscattering spectrometer SPHERES
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