Características clínicas de los pacientes con insuficiencia cardiaca en un servicio de medicina interna.

Características clínicas de los pacientes con insuficiencia cardiaca en un servicio de medicina interna. 

Unconventional superconductivity in the nickel-chalcogenide superconductor, TlNi2_2Se2_2

We present the results of a study of the vortex lattice (VL) of the nickel chalcogenide superconductor TlNi2Se2, using small angle neutron scattering. This superconductor has the same crystal symmetry as the iron arsenide materials. Previous work points to it being a two-gap superconductor, with an unknown pairing mechanism. No structural transitions in the vortex lattice are seen in the phase diagram, arguing against d-wave gap symmetry. Empirical fits of the temperature-dependence of the form factor and penetration depth rule out a simple s-wave model, supporting the presence of nodes in the gap function. The variation of the VL opening angle with field is consistent with earlier reports of of multiple gaps

Magnetic structure and spin dynamics of quasi-one-dimensional spin-chain antiferromagnet BaCo2V2O8

We report a neutron diffraction and muon spin relaxation muSR study of static and dynamical magnetic properties of BaCo2V2O8, a quasi-one-dimensional spin-chain system. A proposed model for the antiferromagnetic structure includes: a propagation vector k_AF = (0, 0, 1), independent of external magnetic fields for fields below a critical value H_c(T). The ordered moments, of 2.18 \mu_B per Co ion, are aligned along the crystallographic c-axis. Within the screw chains, along the c axis, the moments are arranged antiferromagnetically. In the basal planes the spins are arranged ferromagnetically (forming zig-zags paths) along one of the axis and antiferromagnetically along the other. The temperature dependence of the sub-lattice magnetization is consistent with the expectations of the 3D Ising model. A similar behavior is observed for the internal static fields at different muon stopping sites. Muon time spectra measured at weak longitudinal fields and temperatures much higher than T_N can be well described using a single muon site with an exponential muon spin relaxation that gradually changes into an stretched exponential on approaching T_N. The temperature-induced changes of the relaxation suggest that the Co fluctuations dramatically slow down and the system becomes less homogeneous as it approaches the antiferromagnetic state.Comment: 7 pages, 9 figure

Influence of the Fermi Surface Morphology on the Magnetic Field-Driven Vortex Lattice Structure Transitions in YBa2_{2}Cu3_{3}O7−δ:δ=_{7-\delta}:\delta=0, 0.15

We report small-angle neutron scattering measurements of the vortex lattice (VL) structure in single crystals of the lightly underdoped cuprate superconductor YBa2Cu3O6.85. At 2 K, and for fields of up to 16 T applied parallel to the crystal c-axis, we observe a sequence of field-driven and first-order transitions between different VL structures. By rotating the field away from the c-axis, we observe each structure transition to shift to either higher or lower field dependent on whether the field is rotated towards the [100] or [010] direction. We use this latter observation to argue that the Fermi surface morphology must play a key role in the mechanisms that drive the VL structure transitions. Furthermore, we show this interpretation is compatible with analogous results obtained previously on lightly overdoped YBa2Cu3O7. In that material, it has long-been suggested that the high field VL structure transition is driven by the nodal gap anisotropy. In contrast, the results and discussion presented here bring into question the role, if any, of a nodal gap anisotropy on the VL structure transitions in both YBa2Cu3O6.85 and YBa2Cu3O7

Magnetic nano-fluctuations in a frustrated magnet

Frustrated systems exhibit remarkable properties due to the high degeneracy of their ground states. Stabilised by competing interactions, a rich diversity of typically nanometre-sized phase structures appear in polymer and colloidal systems, while the surface of ice pre-melts due to geometrically frustrated interactions. Atomic spin systems where magnetic interactions are frustrated by lattice geometry provide a fruitful source of emergent phenomena, such as fractionalised excitations analogous to magnetic monopoles. The degeneracy inherent in frustrated systems may prevail all the way down to absolute zero temperature, or it may be lifted by small perturbations or entropic effects. In the geometrically frustrated Ising--like magnet Ca3Co2O6, we follow the temporal and spatial evolution of nanoscale magnetic fluctuations firmly embedded inside the spin--density--wave magnetic structure. These fluctuations are a signature of a competing ferrimagnetic phase with an incommensurability that is different from, but determined by the host. As the temperature is lowered, the fluctuations slow down into a super-paramagnetic regime of stable spatiotemporal nano-structures

Switching of magnetic domains reveals evidence for spatially inhomogeneous superconductivity

The interplay of magnetic and charge fluctuations can lead to quantum phases with exceptional electronic properties. A case in point is magnetically-driven superconductivity, where magnetic correlations fundamentally affect the underlying symmetry and generate new physical properties. The superconducting wave-function in most known magnetic superconductors does not break translational symmetry. However, it has been predicted that modulated triplet p-wave superconductivity occurs in singlet d-wave superconductors with spin-density wave (SDW) order. Here we report evidence for the presence of a spatially inhomogeneous p-wave Cooper pair-density wave (PDW) in CeCoIn5. We show that the SDW domains can be switched completely by a tiny change of the magnetic field direction, which is naturally explained by the presence of triplet superconductivity. Further, the Q-phase emerges in a common magneto-superconducting quantum critical point. The Q-phase of CeCoIn5 thus represents an example where spatially modulated superconductivity is associated with SDW order

Validación de un cuestionario sobre el estilo de vida de médicos especialistas antes y durante la pandemia COVID-19

Introduction. Isolation and social distancing strategies to control the COVID-19 pandemic probably had a negative impact on physicians’ lifestyles. Objective. To design and validate a questionnaire to assess physicians’ lifestyle before and during the pandemic. Methods. We carried out a psychometric study. A total of 204 medical specialists from a national hospital in Lima-Peru were admitted to the study and answered the questionnaire virtually. Results. Content validity was carried out with a committee of experts, with a Cochran’s Q of 7 and p of 0.50. In the relevance, representativeness and clarity of the items, the global Aiken’s V was 0.97. The pilot test showed adequate reliability (Cronbach’s alpha 0.842). For construct validity, overall sample adequacy was assessed by Bartlett’s test of sphericity, before (X2=4235.75, p<0.01) and during (X2=4328, p<0.01) the pandemic. In addition, the Kaiser-Meyer-Olkin (KMO) test had an overall value before and during the pandemic of 0.78 and 0.76 respectively. Exploratory Factor Analysis structured five domains. Factor loadings (polychoric correlations and Oblimin rotation) were estimated, and the correlation between domains was adequate. Confirmatory Factor Analysis indicated adequate model fit. Conclusion. The instrument shows adequate psychometric properties, so it can be considered as a useful, valid, and reliable instrument to assess the lifestyle of physicians before and during the COVID-19 pandemic.Introducción. Las estrategias de aislamiento y distanciamiento social para controlar la pandemia COVID-19, pudieron tener repercusón negativa en el estilo de vida de los médicos. Objetivo. Diseñar y validar un cuestionario para evaluar el estilo de vida de los médicos antes y durante la pandemia. Métodos. Estudio psicométrico. Se admitieron a 204 médicos especialistas de un hospital nacional de Lima-Perú, que respondieron virtualmente el cuestionario. Resultados. Se realizó la validez del contenido con un comité de expertos, con resultado de Q de Cochran de 7 y valor p de 0,50. En la relevancia, representatividad y claridad de los ítems la V de Aiken global fue de  0,97. La prueba piloto demostró una  confiabilidad adecuada (alfa de Cronbach 0,842). Para la validez del constructo, se evaluó la adecuación muestral global por medio de la prueba de esfericidad de Bartlett, antes (X2=4235,75, p<0,01) y durante (X2=4328, p<0,01) la pandemia. Además la prueba de Kaiser-Meyer-Olkin (KMO) tuvo un valor global antes y durante la pandemia de 0,78 y 0,76 respectivamente. El análisis factorial exploratorio estructuró cinco dominios. Se estimaron las cargas factoriales (correlaciones policoricas y rotación de Oblimin), y la correlación entre los dominios fue adecuada. El análisis factorial confirmatorio indicó un adecuado ajuste del modelo. Conclusión. El instrumento mostró propiedades psicométricas adecuadas, por lo que se puede considerar como un instrumento útil, válido y fiable para evaluar el estilo de vida de los médicos antes y durante la pandemia COVID-19