10,767 research outputs found
Giant magnetic anisotropy at nanoscale: overcoming the superparamagnetic limit
It has been recently observed for palladium and gold nanoparticles, that the
magnetic moment at constant applied field does not change with temperature over
the range comprised between 5 and 300 K. These samples with size smaller than
2.5 nm exhibit remanence up to room temperature. The permanent magnetism for so
small samples up to so high temperatures has been explained as due to blocking
of local magnetic moment by giant magnetic anisotropies. In this report we
show, by analysing the anisotropy of thiol capped gold films, that the orbital
momentum induced at the surface conduction electrons is crucial to understand
the observed giant anisotropy. The orbital motion is driven by localised charge
and/or spin through spin orbit interaction, that reaches extremely high values
at the surfaces. The induced orbital moment gives rise to an effective field of
the order of 103 T that is responsible of the giant anisotropy.Comment: 15 pages, 2 figures, submitted to PR
Doping and temperature dependence of Mn 3d states in A-site ordered manganites
We present a systematic study of the electronic structure in A-site ordered
manganites as function of doping and temperature. The energy dependencies
observed with soft x-ray resonant diffraction (SXRD) at the Mn L_{2,3} edges
are compared with structural investigations using neutron powder diffraction as
well as with cluster calculations. The crystal structures obtained with neutron
powder diffraction reflect the various orbital and charge ordered phases and
show an increase of the Mn-O-Mn bond angle as function of doping and
temperature. Cluster calculations show that the observed spectral changes in
SXRD as a function of doping are more pronounced than expected from an increase
in bandwitdh due to the increase in Mn-O-Mn bond angle, and are best described
by holes that are distributed at the neighbouring oxygen ions. These holes are
not directly added to the Mn 3d shell, but centered at the Mn site. In
contrast, the spectral changes in SXRD as function of temperature are best
described by an increase of magnetic correlations. This demonstrates the strong
correlations between orbitals and magnetic moments of the 3d states
La producción científica española en cirugía ortopédica y traumatología: su presencia en una base de datos internacional
Una manera de evaluar la calidad de la investigación desarrollada en un país es
estudiar su presencia en una base de datos bibliográfica internacional. Se han analizado el número y el factor de impacto de los trabajos producidos por España en Cirugía Ortopédica y
Traumatología que han sido recogidos por Science Citation Index durante los años 1986 a
1989. De un total de 12706 documentos que se habían originado en nuestro país, sólo 41
(0,3%) pertenecían al área temática referida, siendo 34 artículos y siete comunicaciones a
congresos. El factor de impacto medio ha sido de 1,2 y el número medio de autores, 4. Nuestro
país se encuadra dentro de los países con baja actividad y baja atracción en Cirugía Ortopé-
dica y Traumatología. Estos hallazgos confirman, además de su escasa presencia en un índice
bibliográfico internacional, el reducido valor que los autores extranjeros asignan a nuestra
producción científica.The study of the presence in an international bibliographic data-base seems to
be a suitable assessment of the quality of the research developed in a country. In this paper we analize the number and the impact-factor of the works produced in Spain in the field of orthopaedic surgery and traumatology which have been included in the Science Citation Index
from 1986 to 1989. Out of 12706 documents produced in our country, only 41 (0,3%) corresponded
to the field of orthopaedics. There were 34 articles and 7 congress contributions.
The mean impact factor was 1,2 and the average of authors was 4. From these date, Spain can
be considered to have low research activity and low atraction of the publications on orthopaedic
surgery and traumatology. Apart from the scarce presence in an international citation, these
findings confirm the limited value that international authors fine to our scientific production
in this area
Cotilo recubierto con hidroxiapatita de la artroplastia Omnifit: resultados a medio plazo
Las cúpulas acetabulares roscadas han mostrado malos resultados en períodos
medios de evolución. Aunque la sujeción inmediata es excelente, con el paso del tiempo
se ha comprobado la ausencia de fijación, mostrando un alto porcentaje de movilizaciones.
Una alternativa para evitar esos fracasos es el recubrimiento de estos cotilos con
hidroxiapatita. Hemos revisado clínica y radiográficamente 36 casos de artroplastias
Omnifit con cotilo roscado y recubierto de hidroxiapatita, con un tiempo medio de seguimiento
de 58 meses. Diez pacientes presentaban dolor en región inguinal. Sólo el 63,9% de
los cotilos se encontraban radiográficamente integrados, habiendo sufrido una clara movilización
seis que precisaron cirugía de revisión acetabular; otros siete mostraban signos
radiológicos de probable inestabilidad.
El recubrimiento con hidroxiapatita no asegura una buena fijación en los cotilos roscados
Omnifit por lo que recomendamos componentes acetabulares implantados a presión
con posibilidad de sujeción adicional con tornillos.The threaded acetabular cups have shown mid-term bad results. Though
the immediate fixation is excellent, as time goes by it has been proven the absence of fixation,
appearing a high percentage of mobilizations. An alternative to avoid those failures
is the hydroxyapatite coated implant. We have analysed clinically and radiographically
36 cases of Omnifit arthroplasties with cup threaded and coated with hydroxyapatite
with an average time of follow-up of 58 months. Ten patients had pain in the hip. Only
63.9% of the acetabular cups were found to be radiographically integrated, six having suffered
a clear mobilization requiring surgical review. Seven showed radiological signs of
probable instability. The hydroxytapatite coatings does not assure a good fixation in the
Omnifit threaded cups, therefore we recommend press fit acetabular components with
the possibility of additional fixation with screws
Some results on the eigenfunctions of the quantum trigonometric Calogero-Sutherland model related to the Lie algebra E6
The quantum trigonometric Calogero-Sutherland models related to Lie algebras
admit a parametrization in which the dynamical variables are the characters of
the fundamental representations of the algebra. We develop here this approach
for the case of the exceptional Lie algebra E6.Comment: 17 pages, no figure
Extended WKB method, resonances and supersymmetric radial barriers
Semiclassical approximations are implemented in the calculation of position
and width of low energy resonances for radial barriers. The numerical
integrations are delimited by t/T<<8, with t the period of a classical particle
in the barrier trap and T the resonance lifetime. These energies are used in
the construction of `haired' short range potentials as the supersymmetric
partners of a given radial barrier. The new potentials could be useful in the
study of the transient phenomena which give rise to the Moshinsky's diffraction
in time.Comment: 12 pages, 4 figures, 3 table
Reaction Dynamics for the Systems 7Be,8B + 208Pb at Coulomb Barrier Energies
In this contribution we describe the first results obtained for the investigation of
the elastic scattering process in the reactions induced by the Radioactive Ion Beams 7Be and
8B on a 208Pb target at Coulomb barrier energies. The experimental data were analyzed within
the framework of the optical model in order to extract the total reaction cross section. The
comparison with data available in literature for reactions induced on 208Pb by light ions in the
mass range A = 6-8 shows that the loosely-bound 8B has the largest reactivity
Ensayo de fertilización foliar sobre regenerado de pino rodeno en Cuéllar (Segovia)
El regenerado de Pinus pinaster Ait. en la tierra de pinares segoviana presenta frecuentemente, en estado de monte bravo, un desarrollo deficiente de la guía y de las ramas del tercio superior de la copa. El objetivo del presente estudio es tratar de determinar si este deficiente desarrollo está relacionado con alguna carencia nutricional. Para ello se realiza un ensayo de fertilización foliar y se analiza su influencia sobre la Longitud de las acículas y la Longitud de los ramillos desarrollados en el periodo vegetativo siguiente a la fertilización. Se consideran cuatro localizaciones diferentes y tres tratamientos distintos (Testigo, T, sin fertilización; fertilización simple, F; y fertilización doble, FF)
- …