114 research outputs found
Charge ordering and dielectric properties in the near half-doped Pr0.79Na0.21MnO3 perovskite
[Abstract] The Pr0.79Na0.21MnO3 perovskite has been prepared in polycrystalline form by a ceramic method. We have carried out its structural characterization by synchrotron X-ray powder diffraction (SXRPD) at room temperature and at 150 K (T<TCO). In the charge ordering (CO) state, the SXRPD data can be refined both on the basis of the site-centred model and the bond-centred model proposed for half-doped manganites, without a clear advantage of one model over the other. From the dielectric point of view, at the CO temperature this manganite shows a maximum in the dielectric constant whose origin is intrinsic, and cannot be attributed to the presence of extrinsic factors. We relate this dielectric behaviour to the formation of polar entities at the temperature of charge condensation, due to an asymmetric charge distribution intermediate between site-centred and bond-centred type.Xunta de Galicia; PGIDIT06PXB103298PRMinisterio de Educación y Ciencia; Project FEDER MAT 2004-0513
Studies on the power factor of (Ba,Sr)Co2+xRu4−xO11 compounds
[Abstract] We have prepared polycrystalline single-phase ACo2+xRu4−xO11 (A = Sr, Ba; 0 ≤ x ≤ 0.5) using the ceramic method and we have studied their structure, electrical resistivity and Seebeck coefficient, in order to estimate their power factor (P.F.). These layered compounds show values of electrical resistivity of the order of 10−5 Ωm and their Seebeck coefficients are positive and range from 1 μV K−1 (T = 100 K) to 20 μV K−1 (T = 450 K). The maximum power factor at room temperature is displayed by BaCo2Ru4O11 (P.F.: 0.20 μW K−2 cm−1), value that is comparable to that shown by compounds such as SrRuO3 and Sr6Co5O15.Ministerio de Ciencia e Innovación; Project FEDER MAT 2007-6669
IR characterization of Ln2−xSrxCoO4 (x≥1; Ln=La, Nd) oxides
[Abstract] We have recorded the FTIR spectra of powder samples of Ln2−xSrxCoO4 (Ln=La, Nd) at room temperature. We have identified the infrared active modes (3A2u+4Eu), and analyzed how they change as a function of Ln and the Sr doping. We correlate the obtained results with structural data obtained from powder X-ray diffraction studies and with the electronic properties displayed by these samples
Sarcomas primarios de hueso: estudio por citometría estática mediante análisis digital de imagen
Se presenta un estudio morfométrico y densitométrico mediante análisis digital
de imagen de una serie de 50 tumores óseos malignos (32 osteosarcomas, 12 condrosarcomas
y 6 histiocitomas fibrosos malignos de hueso), con el fin de evaluar la utilidad
de la técnica para establecer el grado y el pronóstico de estas neoplasias. Las variables
morfométricas y la disposición de la cromatina guardan una estrecha relación con el grado
histológico (Spearman; p < 0,05) y muestran diferencias estadísticamente significativas
entre los tumores considerados de alto y bajo grado en base a su presentación y evolución
clínica. La ploidía estimada por densitometría óptica se comporta como un factor pronóstico
independiente en el análisis multivariante de la serie de tumores de alto grado (COX;
p < 0,001). La citometría estática, aunque más lenta e imprecisa que la citometría de flujo
en la determinación de los picos de ploidía, permite analizar el modelo de cromatina y
contribuye objetivamente al establecimiento del grado biológico de los tumores óseos.A densitometry and morphometric assessment by static image cytometry of
50 malignant bone tumors (32 osteosarcomas, 12 chondrosarcomas, and 6 malignant fibrous
histiocytomas of bone) was performed in order to assess the validity of the technic
in the pathobiological and prognostic evaluation of these neoplasms. A strong correlation
between the morphometric features, cromatine distribution and histologic grade was
found (Spearman; p < 0.05). These parameters are also statistically different for hight and
low grade tumors in clinical staging. The stimation of DNA ploidy by optic densitometry
is a significant prognostic factor in the multivariant analysis for the high grade tumors
(COX; p < 0.001). Although Flow cytometry is a better procedure to evaluate DNA ploidy
peaks, our study reveals static image cytometry as a useful technic for determine the
cromatine model and objective assessment of the biological grade of bone neoplasms
Multiferroic behavior in the new double-perovskite LuMnCoO
We present a new member of the multiferroic oxides, LuMnCoO, which we
have investigated using X-ray diffraction, neutron diffraction, specific heat,
magnetization, electric polarization, and dielectric constant measurements.
This material possesses an electric polarization strongly coupled to a net
magnetization below 35 K, despite the antiferromagnetic ordering of the Mn and Co spins in an configuration along the c-direction. We discuss the magnetic order
in terms of a condensation of domain boundaries between and
ferromagnetic domains, with each domain boundary
producing a net electric polarization due to spatial inversion symmetry
breaking. In an applied magnetic field the domain boundaries slide, controlling
the size of the net magnetization, electric polarization, and magnetoelectric
coupling
Atypical magnetic behavior in the incommensurate hybrid perovskite
A plethora of temperature induced phase transitions have been observed in
compounds, where M is Co(II) or Ni(II). Among them, the
nickel compound exhibits a combination of magnetic and nuclear
incommensurabil-ity below N\'eel temperature. Despite the fact that the
zero-field behavior has been previously addressed, here we study in depth the
macroscopic magnetic behavior of this compound to unveil the origin of the
atypical magnetic response found in it and in its parent family of formate
perovskites. In particular, they show a puzzling magnetization reversal in the
curves measured starting from low temperatures, after cooling under zero field.
The first atypical phenomena is the im-possibility of reaching zero
magnetization, even by nullifying the applied external field and even
compensating it for the influence earth's magnetic field. Relatively large
magnetic fields are needed to switch the magnetization from negative to
positive values or vice versa, which is compatible with a soft-ferromagnetic
system. The atypical path found in its first magnetization curve and hysteresis
loop at low temperatures is the most noticeable feature. The magnetization
curve switches from more than 1200 Oe from the first magnetization loop to the
subsequent magnetization loops. A feature that cannot be explained using a
model based on unbalanced pair of domains. As a result, we decipher this
behavior in light of the incommensurate structure of this material. We propose,
in particular, that the applied magnetic field induces a mag-netic phase
transition from a magnetically incommensurate structure to a magnetically
commensurate structure.Comment: 9 pages, 7 figures, 1 tabl
Risk of Trypanosoma cruzi infection among travellers visiting friends and relatives to continental Latin America
Factors de risc mèdic; Serologia; Malaltia de ChagasFactores de riesgo médicos; Serología; Enfermedad de ChagasMedical risk factors; Serology; Chagas diseaseBackground
Chagas disease (CD) is regarded as a possible risk for travellers to endemic areas of continental Latin America (LA). The aim of the study is to determine the risk of Trypanosoma cruzi (TC) infection among travellers to CD endemic areas and to identify risk factors for acquiring TC infection.
Methods/Principal finding
We designed a multicenter cross-sectional study among travellers in Spain (Badalona, Barcelona and Madrid). All available adults with laboratory confirmed proof of absence of TC infection from January 2012 to December 2015 were contacted. Participants referring a trip to LA after the negative TC screening were offered to participate. We performed a standardized questionnaire of travel related factors and measurement of TC antibodies in serum. A total of 971 participants with baseline negative TC serology were selected from the microbiology records. After excluding participants not meeting inclusion criteria, eighty participants were selected. Sixty three (78.8%) were female, and the median age was 38 (IQR 34–47) years. The reason to travel was visiting friends and relatives in 98.8% of the participants. The median duration of travel was 40 (IQR 30–60) days, with 4911 participants-day of exposure. Seventy seven cases (96.25%) participants had two negative TC serology tests after the travel, two cases (2.5%) had discordant serology results (considered false positive results) and one case was infected before travelling to LA. According to our data, the upper limit of the 95% confidence interval of the incidence rate of TC acquisition in travellers is 0.8 per 1000 participant-days.
Conclusions/Significance
Among 79 non-CD travellers to TC endemic areas, we found no cases of newly acquired TC infection. The incidence rate of TC acquisition in travellers to endemic countries is less than or equal to 0.8 per 1000 traveller-days.ASM was supported by a postdoctoral grant “Juan Rodés” (JE18/00022) from the Instituto de Salud Carlos III (www.isciii.es) through the Spanish Ministry of economy and competitiveness. The funders had no role in study design data collection and analysis, decision to publish, or preparation of the manuscript
Anomalous and Colossal Thermal Expansion, Photoluminescence, and Dielectric Properties in Lead Halide-Layered Perovskites With Cyclohexylammonium and Cyclopentylammonium Cations
[Abstract] A detailed study of lead halide-layered perovskites with general formula A2PbX4 (where A is cyclohexylammonium (CHA) or cyclopentylammonium (CPA) cation and X is Cl− or Br− anion) is presented. Using variable temperature synchrotron X-ray powder diffraction, we observe that these compounds exhibit diverse crystal structures above room temperature. Very interestingly, we report some unconventional thermomechanical responses such as uniaxial negative thermal expansion and colossal positive thermal expansion in a perpendicular direction. For the polymorphs of (CHA)2PbBr4, the volumetric thermal expansion coefficient is among the highest reported for any extended inorganic crystalline solid, reaching 480 MK−1. The phase transitions are confirmed by calorimetry and dielectric measurements, where the dielectric versus temperature curves show anomalies related with the order-disorder phase transitions. In addition, these compounds exhibit a broad photoluminescence (PL) emission with a large Stokes shift, which is related with an exciton PL emission.This work was financially supported by the Ministerio de Ciencia e Innovación (MICINN) and EU-ERDF under the projects MAT2017-86453-R and PDC2021-121076-I00. We thank Alba synchrotron for the provision of beamtime at BL04-MSPD beamline (experiment 2019023280). We also thank prof. Dr. R. Artiaga and Dr. J.J. López-Beceiro (University of A Coruña) for assistance during DSC measurements. J.M.B.G. thanks Xunta de Galicia for a postdoctoral fellowshi
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