88 research outputs found
A comprehensive examination of the local- and long-range structure of Sb6O13 pyrochlore oxide
The crystal structure of the Sb6O13 oxide, exhibiting a defect pyrochlore crystal structure with atomic vacancies, has been studied using a complete set of state-of-the-art techniques. The degree of antimony disproportionation in Sb3+ and Sb5+ valence states has been directly determined around 36% and 64%, respectively, using X-ray absorption near edge structure (XANES). These findings are in excellent agreement with our Rietveld analysis of synchrotron X-ray (SXRD) and neutron powder diffraction (NPD) results. Moreover, the highly distorted Sb3+ coordination due to its lone electron pair has been critically revisited. The bonding distances and coordination of Sb3+ and Sb5+ species closely agree with an extensive dynamic and crystallographic determination using the Extended X-ray Absorption Fine Structure (EXAFS) technique. Most importantly, the specific local disorder of the two distinctive Sb ions has been crosschecked monitoring their unusual Debye–Waller factors.Fil: Mayer, Sergio Federico. Instituto de Ciencia de Materiales de Madrid; España. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Nanociencia y Nanotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rodrigues, Joao Elias. Universidade de Sao Paulo; Brasil. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Marini, C.. CELLS–ALBA Synchrotron; EspañaFil: Fernández-Díaz, M.T.. Institut Laue Langevin; FranciaFil: Falcón, H.. Universidad Tecnológica Nacional. Facultad Regional Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Tecnología Química. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación y Tecnología Química; ArgentinaFil: Asensio, M. C.. Consejo Superior de Investigaciones Científicas; España. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Alonso, J. A.. Instituto de Ciencia de Materiales de Madrid; Españ
A comprehensive examination of the local- and long-range structure of Sb6O13 pyrochlore oxide
The crystal structure of the Sb6O13 oxide, exhibiting a defect pyrochlore crystal structure with atomic vacancies, has been studied using a complete set of state-of-the-art techniques. The degree of antimony disproportionation in Sb3+ and Sb5+ valence states has been directly determined around 36% and 64%, respectively, using X-ray absorption near edge structure (XANES). These findings are in excellent agreement with our Rietveld analysis of synchrotron X-ray (SXRD) and neutron powder diffraction (NPD) results. Moreover, the highly distorted Sb3+ coordination due to its lone electron pair has been critically revisited. The bonding distances and coordination of Sb3+ and Sb5+ species closely agree with an extensive dynamic and crystallographic determination using the Extended X-ray Absorption Fine Structure (EXAFS) technique. Most importantly, the specific local disorder of the two distinctive Sb ions has been crosschecked monitoring their unusual Debye–Waller factors.Fil: Mayer, Sergio Federico. Instituto de Ciencia de Materiales de Madrid; España. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Nanociencia y Nanotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Rodrigues, Joao Elias. Universidade de Sao Paulo; Brasil. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Marini, C.. CELLS–ALBA Synchrotron; EspañaFil: Fernández-Díaz, M.T.. Institut Laue Langevin; FranciaFil: Falcón, H.. Universidad Tecnológica Nacional. Facultad Regional Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Tecnología Química. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación y Tecnología Química; ArgentinaFil: Asensio, M. C.. Consejo Superior de Investigaciones Científicas; España. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Alonso, J. A.. Instituto de Ciencia de Materiales de Madrid; Españ
Microscopic transition potential: Determination of and coupling constants
A transition potential, based on an effective
quark-quark interaction and a constituent quark cluster model for baryons, is
derived in the Born-Oppenheimer approach. The potential shows significant
differences with respect to those obtained by a direct scaling of the
nucleon-nucleon interaction. From its asymptotic behavior we extract the values
of and coupling constants in a
particular coupling schemeComment: 15 eps figures, Accepted for publication in Phys. Rev.
Essential Role of the Cooperative Lattice Distortion in the Charge, Orbital and Spin Ordering in doped Manganites
The role of lattice distortion in the charge, orbital and spin ordering in
half doped manganites has been investigated. For fixed magnetic ordering, we
show that the cooperative lattice distortion stabilize the experimentally
observed ordering even when the strong on-site electronic correlation is taken
into account. Furthermore, without invoking the magnetic interactions, the
cooperative lattice distortion alone may lead to the correct charge and orbital
ordering including the charge stacking effect, and the magnetic ordering can be
the consequence of such a charge and orbital ordering. We propose that the
cooperative nature of the lattice distortion is essential to understand the
complicated charge, orbital and spin ordering observed in doped manganites.Comment: 5 pages,4 figure
Effects of Boson Dispersion in Fermion-Boson Coupled Systems
We study the nonlinear feedback in a fermion-boson system using an extension
of dynamical mean-field theory and the quantum Monte Carlo method. In the
perturbative regimes (weak-coupling and atomic limits) the effective
interaction among fermions increases as the width of the boson dispersion
increases. In the strong coupling regime away from the anti-adiabatic limit,
the effective interaction decreases as we increase the width of the boson
dispersion. This behavior is closely related with complete softening of the
boson field. We elucidate the parameters that control this nonperturbative
region where fluctuations of the dispersive bosons enhance the delocalization
of fermions.Comment: 14 pages RevTeX including 12 PS figure
Inhomogeneous Magnetism in La-doped CaMnO3. (II) Mesoscopic Phase Separation due to Lattice-coupled FM Interactions
A detailed investigation of mesoscopic magnetic and crystallographic phase
separation in Ca(1-x)La(x)MnO3, 0.00<=x<=0.20, is reported. Neutron powder
diffraction and DC-magnetization techniques have been used to isolate the
different roles played by electrons doped into the eg level as a function of
their concentration x. The presence of multiple low-temperature magnetic and
crystallographic phases within individual polycrystalline samples is argued to
be an intrinsic feature of the system that follows from the shifting balance
between competing FM and AFM interactions as a function of temperature. FM
double-exchange interactions associated with doped eg electrons are favored
over competing AFM interactions at higher temperatures, and couple more
strongly with the lattice via orbital polarization. These FM interactions
thereby play a privileged role, even at low eg electron concentrations, by
virtue of structural modifications induced above the AFM transition
temperatures.Comment: 8 pages, 7 figure
k=0Magnetic Structure and Absence of Ferroelectricity in SmFeO3
SmFeO3 has attracted considerable attention very recently due to the reported
multiferroic properties above room-temperature. We have performed powder and
single crystal neutron diffraction as well as complementary polarization
dependent soft X-ray absorption spectroscopy measurements on floating-zone
grown SmFeO3 single crystals in order to determine its magnetic structure. We
found a k=0 G-type collinear antiferromagnetic structure that is not compatible
with inverse Dzyaloshinskii-Moriya interaction driven ferroelectricity. While
the structural data reveals a clear sign for magneto-elastic coupling at the
N\'eel-temperature of ~675 K, the dielectric measurements remain silent as far
as ferroelectricity is concerned
Charge disproportionation in YNiO : ESR and susceptibility study
We present a study of the magnetic properties of YNiO in the
paramagnetic range, above and below the metal-insulator (MI) transition. The dc
susceptibility, (measured up to 1000 K) is a decreasing function of
T for 150 K (the N\'{e}el temperature) and we observe two different
Curie-Weiss regimes corresponding to the metallic and insulator phases. In the
metallic phase, this behaviour seems to be associated with the small ionic
radius of Y% . The value of the Curie constant for T T allows
us to discard the possibility of Ni localization. An electron spin
resonance (ESR) spectrum is visible in the insulator phase and only a fraction
of the Ni ions contributes to this resonance. We explain the ESR and behaviour for T T in terms of charge disproportionation of
the type 2Ni Ni+Ni that is compatible with the
previously observed structural transition across T.Comment: 10 pages, 4 figures, submitted to Phys. Rev.
Do Religious Factors Influence the Attitude Toward Organ Donation Among Medical Students? A Spanish Multicenter Study
Introduction
Religious factors have conditioned the attitude toward organ donation and transplantation (ODT) since the beginning of transplantation, despite the fact that most religions are in favor of transplantation.
Objective
To assess the impact of religious beliefs of medical students on their attitude toward ODT.
Method
Population under study: Medical students in Spanish universities. Study sample: Stratified by geographical area and academic course. Assessment instrument: Attitude ODT questionnaire PCID-DTO-Ríos, anonymous and self-administered.
Results
Of all students, 42% (n = 3907) declare themselves atheists or agnostics. The remaining 58% (n = 5368) declare themselves to be religious, the majority being Catholic (55%, n = 5102). Of the rest, 0.2% are Muslims (n = 8), 0.1% Protestants (n = 1), and the remaining 2.7% (n = 257) indicate other religious doctrines but do not want to specify it. Regarding their attitude toward ODT, those who consider themselves atheists or agnostics have a more favorable attitude than those who consider themselves religious (84% versus 76%; P < .001). Among those who follow some kind of religion, Catholics are more in favor of ODT than non-Catholics (77% vs 64%, P < .001). Note that among the religious, only 57% (n = 3050) know which religion is in favor of transplantation, while 22% (n = 1,152) consider that it has not been pronounced on the matter, 13% (n = 723) think the religion is against donation, and the remaining 8% (n = 443) do not know.
Conclusion
The religion professed by medical students conditions their attitude toward donation, with the atheists and agnostics being more in favor of donation.Sin financiación0.784 JCR (2019) Q4, 155/158 Immunology, 191/210 Surgery, 24/24 Transplantation0.363 SJR (2019) Q3, 254/451 Surgery, 27/41 TransplantationNo data IDR 2019UE
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