First-principles study of the ferroelectric properties of SrTaO2N/SrTiO3 interfaces.

First-principles calculations based on density-functional theory in the pseudo-potential approach have been performed for the total energy, crystal structure and cell polarization for SrTaO2N/SrTiO3 heterostructures. Different heterojunctions were analyzed in terms of the termination atoms at the interface plane, and periodic or non-periodic stacking in the perpendicular direction. The calculations show that the SrTaO2N layer is compressed along the ab-plane, while the SrTiO3 is elongated, thus favoring the formation of P4mm local environment on both sides of the interface, leading to net macroscopic polarization. The analysis of the local polarization as a function of the distance to the interface, for each individual unit cell was found to depend on the presence of a N or an O atom at the interface, and also on the asymmetric and not uniform c-axis deformation due to the induced strain in the ab-plane. The resulting total polarization in the periodic array was ≈0.54 C m-2, which makes this type of arrangement suitable for microelectronic applications.

Clinical, epidemiologic, and virologic features of dengue in the 1998 epidemic in Nicaragua.

From July to December 1998, a hospital- and health center-based surveillance system for dengue was established at selected sites in Nicaragua to better define the epidemiology of this disease. Demographic and clinical information as well as clinical laboratory results were obtained, and virus isolation, reverse transcriptase-polymerase chain reaction, and serologic assays were performed. World Health Organization criteria were used to classify disease severity; however, a number of patients presented with signs of shock in the absence of thrombocytopenia or hemoconcentration. Therefore, a new category was designated as "dengue with signs associated with shock" (DSAS). Of 1,027 patients enrolled in the study, 614 (60%) were laboratory-confirmed as positive cases; of these, 268 (44%) were classified as dengue fever (DF); 267 (43%) as DF with hemorrhagic manifestations (DFHem); 40 (7%) as dengue hemorrhagic fever (DHF); 20 (3%) as dengue shock syndrome (DSS); and 17 (3%) as DSAS. Interestingly, secondary infection was not significantly correlated with DHF/DSS, in contrast to previous studies in Southeast Asia. DEN-3 was responsible for the majority of cases, with a minority due to DEN-2; both serotypes contributed to severe disease. As evidenced by the analysis of this epidemic, the epidemiology of dengue can differ according to geographic region and viral serotype.

[Freezing of gait unresponsive to dopaminergic stimulation in patients with severe Parkinsonism]. / Bloqueos de la marcha sin respuesta al estímulo dopaminérgico con apomorfina en pacientes parkinsonianos graves.

INTRODUCTION: Freezing of gait unresponsive to dopaminergic stimulation in patients with severe Parkinsonism. The freezing of gait episodes (FOG) normally appear during the off period and generally improve with dopaminergic stimulus, at the same time as improving other Parkinsonian symptoms. PATIENTS AND METHODS: We report a group of 10 patients with severe Parkinson's disease. All patients suffered motor fluctuations, dyskinesias and episodes of FOG during the on and off state. The patients received a subcutaneous apomorphine bolus, without other dopaminergic medication; an effective dose of apomorphine was considered as one that induced a reduction of at least a 60% in the UPDRS motor scale. RESULTS: The baseline motor UPDRS was 61.3 +/- 4.7, which dropped to 21 +/- 4.3 after the apomorphine injection. The mean dose of apomorphine was 5.5 mg (3-7 mg). The bolus of apomorphine improved the parameters of the gait related to bradykinesia and the tapping tests of the limbs, but the episodes of FOG did not vary significantly between the off and on state. CONCLUSIONS: We present a group of 10 patients with freezing of gait episodes that did not improve with treatment and persisted during the on period induced by dopaminergic stimulus with apomorphine.