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A Lacerda

Publications and source records attributed to A Lacerda.

At least 19 recordsLinked to original sources
PubMed2006

Bose-Einstein condensation of S = 1 nickel spin degrees of freedom in NiCl2-4SC(NH2)2.

It has recently been suggested that the organic compound NiCl2-4SC(NH2)2 (DTN) undergoes field-induced Bose-Einstein condensation (BEC) of the Ni spin degrees of freedom. The Ni S = 1 spins exhibit three-dimensional XY antiferromagnetism above a critical field H(c1) approximately 2 T. The spin fluid can be described as a gas of hard-core bosons where the field-induced antiferromagnetic transition corresponds to Bose-Einstein condensation. We have determined the spin Hamiltonian of DTN using inelastic neutron diffraction measurements, and we have studied the high-field phase diagram by means of specific heat and magnetocaloric effect measurements. Our results show that the field-temperature phase boundary approaches a power-law H - H(c1) proportional variant T(alpha)(c) near the quantum critical point, with an exponent that is consistent with the 3D BEC universal value of alpha = 1.5.

Journal Article↗
PubMed2005

Quantum critical 5f electrons avoid singularities in U(Ru,Rh)2Si2.

We present specific heat measurements of 4% Rh-doped URu2Si2 at magnetic fields around the proposed metamagnetic transition field H(m) approximately 34 T, revealing striking similarities to the isotructural Ce analog CeRu2Si2 for H>H(m). This suggests that strongly renormalized hybridized-band models apply equally well to both systems. The vanishing bandwidths as H-->H(m) are consistent with a quantum-critical point close to H(m). The existence of a phase transition into an ordered phase in the vicinity of H(m) for 4% Rh-doped URu2Si2, but not for CeRu2Si2, is consistent with a stronger superexchange in the case of the U 5f system. Irreversible processes at the transition indicate a strong coupling of the 5f orbitals to the lattice, most suggestive of electric quadrupolar order.

Journal Article↗
PubMed2001

Choroid plexus tumours: a surgically treated series.

Choroid plexus tumours-carcinomas and papillomas are rare, especially in adults, and they pose some problems in their diagnosis and management. We have reviewed a series of nine cases from our institution surgically treated during the last 18 years. Their clinical charts, neuroradiological examinations, surgical technique, neuropathology and follow-up were analysed. In only one case total removal proved to be impossible, but even in cases of total removal recurrence appeared in two cases (one carcinoma and one papilloma). Morbility is especially associated with posterior fossa tumours. These rare tumours are managed surgically. They are usually associated with hydrocephalus, and it is difficult to forecast whether or not permanent CSF drainage will be required. A long-term follow-up is needed in patients with this type of tumour.

Adolescent↗
PubMed1995

[The imaging of malignant pancreatic tumors].

Malignant neoplasias of the pancreas include various histological types with imaging characteristics and behaviour which allows them to be distinguished from one another in a good percentage of situations. However, differentiation is not always possible without resorting to anatomo-pathological techniques, differential diagnosis with benign lesions being a great challenge to imaging, with particular reference to the inflammatory masses. Adenocarcinoma makes up about 95% of pancreatic neoplasias and is one of the great causes of death by cancer in developed countries. The imaging techniques applied in the diagnosis and staging of the principal tumours of the pancreas are very diversified, including innocuous means such as ultrasound, invasive methods using angiographic techniques or the recourse to endoscopic means to endocavity assessment. The use of each of these techniques depends essentially on the type of tumor to be studied, the correct and complete knowledge of the possibilities and limitations of each one, becomes fundamental in what concerns the rational application of means in the imaging of the pancreas.

Adenocarcinoma↗