4,323 research outputs found
Magnetic and superconducting instabilities in the periodic Anderson model: an RPA stud
We study the magnetic and superconducting instabilities of the periodic
Anderson model with infinite Coulomb repulsion U in the random phase
approximation. The Neel temperature and the superconducting critical
temperature are obtained as functions of electronic density (chemical pressure)
and hybridization V (pressure). It is found that close to the region where the
system exhibits magnetic order the critical temperature T_c is much smaller
than the Neel temperature, in qualitative agreement with some T_N/T_c ratios
found for some heavy-fermion materials. In our study, all the magnetic and
superconducting physical behaviour of the system has its origin in the
fluctuating boson fields implementing the infinite on-site Coulomb repulsion
among the f-electrons.Comment: 9 pages, 2 figure
Caracterização de acessos e híbridos de maracujazeiro por meio de descritores morfológicos.
Objetivou-se por meio deste trabalho a caracterização morfológica de híbridos interespecíficos e acessos de maracujazeiro do banco de germoplasma de maracujá da Embrapa Mandioca e Fruticultura (BAG-Maracujá). Foram caracterizados 79 híbridos interespecíficos (P. edulis x P. setacea) e sete acessos do BAG-Maracujá. Para a caracterização foram utilizados 22 descritores quantitativos e 32 qualitativos, sendo 21 referentes à parte foliar e 33 referentes à flor. Os dados foram submetidos à análise de diversidade utilizando-se como medida de dissimilaridade a distância de Gower e método de agrupamento UPGMA. A análise de cluster derivada dos dados morfológicos permitiu verificar uma ampla variabilidade genética entre os acessos e os híbridos de maracujazeiro avaliados. O coeficiente de correlação cofenético foi de 0,93, indicando um bom ajuste entre o dendrograma e a matriz de distância original. De modo geral, não houve um agrupamento com base nos grupos de cruzamentos realizados, o que pode ser justificado pelo fato de envolver apenas duas espécies nos cruzamentos interespecíficos. De maneira geral, há variabilidade nos acessos e híbridos avaliados, e estas informações podem ser úteis no direcionamento de cruzamentos visando obtenção de híbridos intra e interespecíficos
Local Moment Formation in the Periodic Anderson Model with Superconducting Correlations
We study local moment formation in the presence of superconducting
correlations among the f-electrons in the periodic Anderson model. Local
moments form if the Coulomb interaction U>U_cr. We find that U_cr is
considerably stronger in the presence of superconducting correlations than in
the non-superconducting system. Our study is done for various values of the
f-level energy and electronic density. The smallest critical U_cr values occur
for the case where the number of f- electrons per site is equal to one. In the
presence of d-wave superconducting correlations we find that local moment
formation presents a quantum phase transition as function of pressure. This
quantum phase transition separates a region where local moments and d-wave
superconductivity coexist from another region characterized by a
superconducting ground state with no local moments. We discuss the possible
relevance of these results to experimental studies of the competition between
magnetic order and superconductivity in CeCu_2Si_2.Comment: 4 pages. accepted for publication in Phys. Rev.
The Highly Miniaturised Radiation Monitor
We present the design and preliminary calibration results of a novel highly
miniaturised particle radiation monitor (HMRM) for spacecraft use. The HMRM
device comprises a telescopic configuration of active pixel sensors enclosed in
a titanium shield, with an estimated total mass of 52 g and volume of 15
cm. The monitor is intended to provide real-time dosimetry and
identification of energetic charged particles in fluxes of up to 10
cm s (omnidirectional). Achieving this capability with such a
small instrument could open new prospects for radiation detection in space.Comment: 17 pages, 15 figure
Prevalence and Causes of Cognitive Impairment and Dementia in a Population-Based Cohort From Northern Portugal
Background:
Vascular disease may play an important role in the epidemiology of dementia in countries with high stroke incidence, such as Portugal.
Objective:
To assess the prevalence and etiology of cognitive impairment in a population-based cohort from Portugal.
Methods:
Individuals ≥55 years (n = 730) from the EPIPorto cohort were assessed using the Mini-Mental State Examination and the Montreal Cognitive Assessment. Those scoring below the age-/education-adjusted cutoff points were further evaluated to identify dementia or mild cognitive impairment (MCI) and to define its most common causes.
Results:
Thirty-six cases of MCI/dementia were identified, corresponding to adjusted prevalences of 4.1% for MCI and 1.3% for dementia. The most common cause of MCI/dementia was vascular (52.8%), followed by Alzheimer’s disease (36.1%).
Conclusion:
These findings highlight the importance of vascular cognitive impairment in the epidemiology of dementia in Portugal and carry an important public health message regarding its prevention and management, possibly extending to other countries with a high-stroke burden.The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research project was financed by the Programa Operacional Competitividade e Internacionalização (POCI) (POCI-01-0145-FEDER-016867), the Programa Operacional Regional do Norte 2014/2020 (NORTE 2020) (NORTE-01-0145-FEDER-000003) and by the Fundação para a Ciência e a Tecnologia, in the context of the Epidemiology Research Unit—Instituto de Saúde Pública da Universidade do Porto (EPIUnit) (POCI-01-0145-FEDER-006862; FCT UID/DTP/04750/2013), and the PhD Grant SFRH/BD/119390/2016 (Natália Araújo), co-funded by the FCT and the POCH/FSE Program
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