142 research outputs found
Desarrollo de psoriasis durante el tratamiento con Abatacept en artritis reumatoidea
Abatacept es el primer agente biológico aprobado para el tratamiento de la Artritis Reumatoidea (AR) que actúa inhibiendo la co-estimulación de linfocitos T.
Si bien se ha reportado su eficacia en psoriasis y artritis psoriásica, existen casos de psoriasis inducida por el fármaco como así también reactivación de las lesiones en pacientes previamente enfermos.
Una mujer con antecedentes de AR en tratamiento con Abatacept endovenoso presentó máculas eritemato-escamosas y pruriginosas en toda la superficie corporal, clínica e histológicamente compatibles con psoriasis. La suspensión del tratamiento con Abatacept, ocasionó la desaparición de las lesiones cutáneas.
Más de 4 años después se encuentra en tratamiento con Rituximab sin haber vuelto a presentar compromiso cutáneo
Effects of domain walls on hole motion in the two-dimensional t-J model at finite temperature
The t-J model on the square lattice, close to the t-J_z limit, is studied by
quantum Monte Carlo techniques at finite temperature and in the underdoped
regime. A variant of the Hoshen-Koppelman algorithm was implemented to identify
the antiferromagnetic domains on each Trotter slice. The results show that the
model presents at high enough temperature finite antiferromagnetic (AF) domains
which collapse at lower temperatures into a single ordered AF state. While
there are domains, holes would tend to preferentially move along the domain
walls. In this case, there are indications of hole pairing starting at a
relatively high temperature. At lower temperatures, when the whole system
becomes essentially fully AF ordered, at least in finite clusters, holes would
likely tend to move within phase separated regions. The crossover between both
states moves down in temperature as doping increases and/or as the off-diagonal
exchange increases. The possibility of hole motion along AF domain walls at
zero temperature in the fully isotropic t-J is discussed.Comment: final version, to appear in Physical Review
Hole-hole correlations in the limit of the Hubbard model and the stability of the Nagaoka state
We use exact diagonalisation in order to study the infinite - limit of
the two dimensional Hubbard model. As well as looking at single-particle
correlations, such as , we also study {\it N-particle correlation
functions} which compare the relative positions of {\it all} the particles in
different models. In particular we study 16 and 18-site clusters and compare
the charge correlations in the Hubbard model with those of spinless fermions
and hard-core bosons. We find that although low densities of holes favour a
`locally-ferromagnetic' fermionic description, the correlations at larger
densities resemble those of pure hard-core bosons surprisingly well .Comment: 15 pages, REVTE
Magnetic field effects and magnetic anisotropy in lightly doped La_{2-x}Sr_xCuO_4
The effects of the application of a magnetic field on the diagonal stripe
spin-glass phase is studied in lightly doped La_{2-x}Sr_xCuO_4 (x=0.014 and
0.024). With increasing magnetic field, the magnetic elastic intensity at the
diagonal incommensurate (DIC) positions (1,\pm\epsilon,0) decreases as opposed
to the increase seen in superconducting samples. This diminution in intensity
with increasing magnetic field originates from a spin reorientation transition,
which is driven by the antisymmetric exchange term in the spin Hamiltonian. On
the other hand, the transition temperature, the incommensurability, and the
peak width of the diagonal incommensurate correlations are not changed with
magnetic field. This result suggests that the magnetic correlations are
determined primarily by the charge disproportionation and that the geometry of
the diagonal incommensurate magnetism is also determined by effects, that is,
stripe formation which are not purely magnetic in origin. The
Dzyaloshinskii-Moriya antisymmetric exchange is nevertheless important in
determining the local spin structure in the DIC stripe phase.Comment: 7 pages, 5 figures, to appear in Phys. Rev.
Boosting the activity of transition metal carbides towards methane activation by nanostructuring
The interaction of methane with pristine surfaces of bulk MoC and Mo2C is known to be weak. In contrast, a series of X-ray photoelectron spectroscopy (XPS) experiments, combined with thermal desorption mass spectroscopy (TDS), for MoCy (y = 0.5-1.3) nanoparticles supported on Au(111)¿which is completely inert towards CH4¿show that these systems adsorb and dissociate CH4 at room temperature and low CH4 partial pressure. This industrially-relevant finding has been further investigated with accurate density functional theory (DFT) based calculations on a variety of MoCy supported model systems. The DFT calculations reveal that the MoCy/Au(111) systems can feature low C-H bond scission energy barriers, smaller than the CH4 adsorption energy. Our theoretical results for bulk surfaces of Mo2C and MoC show that a simple Brønsted-Evans-Polanyi (BEP) relationship holds for C-H bond scission on these systems. However, this is not the case for methane activation on the MoCy nanoparticles as a consequence of their unique electronic and chemical properties. The discovery that supported molybdenum carbide nanoparticles are able to activate methane at room temperature paves the road towards the design of a new family of active carbide catalysts for methane activation and valorisation, with important implications in climate change mitigation and carbon cycle closure
Thermodynamic and thermoelectric properties of high-temperature cuprate superconductors in the stripe phase
We examine the thermodynamic and thermoelectric properties in the stripe
phase of high-Tc cuprates, by using the finite-temperature Lanczos technique
for the t-J model with a potential that stabilizes vertical charge stripes.
When the stripe potential is turned on, the entropy is suppressed as a
consequence of the formation of one-dimensional charge stripes accompanied by
an enhancement of antiferromagnetic spin correlation in the spin domains. The
stripe formation leads also to weak temperature dependence of the chemical
potential, leading to the suppression of the thermoelectric power. The
suppression of the entropy and thermoelectric power is consistent with
experimental data in the stripe phase of La_{1.6-x}Nd_{0.4}Sr_xCuO_4.Comment: REVTeX4, 4 pages, 4 figures, to appear in Phys.Rev.B Rapid Comm
A complex case of interaction between lizard and plants. The dead horse arum (Dracunculus muscivorus) and the Balearic lizard (Podarcis lilfordi)
Census. Recenser et identifier les manuscrits par langue et par pays La rencontre internationale « Census », du 12 au 13 octobre 2017, réunit de nombreux experts européens, du monde universitaire et des bibliothèques, pour réfléchir aux pratiques actuelles de recensement des manuscrits au sein des bases de données de référence et au sein des catalogues en ligne de bibliothèques. Ce partage d’expériences est l’occasion de mettre en lumière les nouveaux enjeux de recherche et les améliorations ..
Hole dynamics and photoemission in a t-J model for SrCu_2(BO_3)_2
The motion of a single hole in a t-J model for the two-dimensional spin-gap
compound SrCu_2(BO_3)_2 is investigated. The undoped Heisenberg model for this
system has an exact dimer eigenstate and shows a phase transition between a
dimerized and a Neel phase at a certain ratio of the magnetic couplings. We
calculate the photoemission spectrum in the disordered phase using a
generalized spin-polaron picture. By varying the inter-dimer hopping parameters
we find a cross-over between a narrow quasiparticle band regime known from
other strongly correlated systems and free-fermion behavior. The hole motion in
the Neel-ordered phase is also briefly considered.Comment: 4 pages, 3 fig
Spin polarons in triangular antiferromagnets
The motion of a single hole in a 2D triangular antiferromagnet is
investigated using the t-J model. The one-hole states are described by strings
of spin deviations around the hole. Using projection technique the one-hole
spectral function is calculated. For large J/t we find low-lying
quasiparticle-like bands which are well separated from an incoherent background
by a gap of order J. However, for small J/t this gap vanishes and the spectrum
becomes broad over an energy range of several t. The results are compared with
SCBA calculations and numerical data.Comment: 4 pages, 6 figs, to be publish in PR
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