2,543 research outputs found
Magnetism of two-dimensional defects in Pd: stacking faults, twin boundaries and surfaces
Careful first-principles density functional calculations reveal the
importance of hexagonal versus cubic stacking of closed packed planes of Pd as
far as local magnetic properties are concerned. We find that, contrary to the
stable face centered cubic phase, which is paramagnetic, the hexagonal
close-packed phase of Pd is ferromagnetic with a magnetic moment of 0.35
/atom. Our results show that two-dimensional defects with local hcp
stacking, like twin boundaries and stacking faults, in the otherwise fcc Pd
structure, increase the magnetic susceptibility. The (111) surface also
increases the magnetic susceptibility and it becomes ferromagnetic in
combination with an individual stacking fault or twin boundary close to it. On
the contrary, we find that the (100) surface decreases the tendency to
ferromagnetism. The results are consistent with the magnetic moment recently
observed in small Pd nanoparticles, with a large surface area and a high
concentration of two-dimensional stacking defects.Comment: 8 pages, 10 figure
Light emission, light detection and strain sensing with nanocrystalline graphene
Graphene is of increasing interest for optoelectronic applications exploiting
light detection, light emission and light modulation. Intrinsically light
matter interaction in graphene is of a broadband type. However by integrating
graphene into optical micro cavities also narrow band light emitters and
detectors have been demonstrated. The devices benefit from the transparency,
conductivity and processability of the atomically thin material. To this end we
explore in this work the feasibility of replacing graphene by nanocrystalline
graphene, a material which can be grown on dielectric surfaces without catalyst
by graphitization of polymeric films. We have studied the formation of
nanocrystalline graphene on various substrates and under different
graphitization conditions. The samples were characterized by resistance,
optical transmission, Raman, X-ray photoelectron spectroscopy, atomic force
microscopy and electron microscopy measurements. The conducting and transparent
wafer-scale material with nanometer grain size was also patterned and
integrated into devices for studying light-matter interaction. The measurements
show that nanocrystalline graphene can be exploited as an incandescent emitter
and bolometric detector similar to crystalline graphene. Moreover the material
exhibits piezoresistive behavior which makes nanocrystalline graphene
interesting for transparent strain sensors
Stability and electronic structure of M-DNA: Role of metal position
We investigate, by first-principles density-functional calculations, fragments and periodic helices of CG- and AT-DNA, modified by incorporation of Zn2+ cations. We study the relative stability of different binding sites for the metal ions as well as different methods of charge neutralization. We find that binding the Zn cation to the N(7) atom of guanine or adenine leads always to lower energies than substitution of an imino proton between two H-bonded bases. Also, neutralizing with OH- groups bonded to Zn2 + is more stable than removing protons from the phosphate groups. Contrarily to common wisdom, we find that planarity of the base pairs is not an essential factor of stability, and that nonplanar base pairs can also be stacked effectively. Finally, we find that the most stable CG and AT helices, with Zn2+ bonded to N(7) atoms and neutralized by OH- ions, have wide band gaps of more than 2 eV, and we conclude that they are poor candidates for electronic conductionThis work has been supported by Brazilian agencies: Fapemig, CNPq, and Ministerio da Ciencia e Tecnologia; by Grants FIS2009-12712, MAT2010-20843-C02-01, and CSD2007-00050 of the Spanish Ministry of Science and Innovation; and by European Grant EU(FP6-029192
Acurácia do Timed Up and Go Test para rastrear risco de quedas em idosos da comunidade
Objective: To determine the accuracy of the Timed Up and Go Test (TUGT) for screening the risk of falls among community-dwelling elderly individuals. Method: This is a prospective cohort study with a randomly by lots without reposition sample stratified by proportional partition in relation to gender involving 63 community-dwelling elderly individuals. Elderly individuals who reported having Parkinson's disease, a history of transitory ischemic attack, stroke and with a Mini Mental State Exam lower than the expected for the education level, were on a wheelchair and that reported a single fall in the previous six months were excluded. The TUGT, a mobility test, was the measure of interested and the occurrence of falls was the outcome. The performance of basic activities of daily living (ADL) and instrumental activities of daily living (IADL) was determined through the Older American Resources and Services, and the socio-demographic and clinical data were determined through the use of additional questionnaires. Receiver Operating Characteristic Curves were used to analyze the sensitivity and specificity of the TUGT. Results: Elderly individuals who fell had greater difficulties in ADL and IADL (p<0.01) and a slower performance on the TUGT (p=0.02). No differences were found in socio-demographic and clinical characteristics between fallers and non- fallers. Considering the different sensitivity and specificity, the best predictive value for discriminating elderly individuals who fell was 12.47 seconds [(RR= 3.2) 95% CI: 1.3- 7.7]. Conclusions: The TUGT proved to be an accurate measure for screening the risk of falls among elderly individuals. Although different from that reported in the international literature, the 12.47 second cutoff point seems to be a better predictive value for Brazilian elderly individuals.OBJETIVO: Determinar a acurácia do Timed Up and Go Test (TUGT) para rastrear risco de quedas em idosos da comunidade. \ud
MÉTODO: Trata-se de um estudo de coorte prospectivo com amostra sorteada aleatoriamente, sem reposição e estratificada por partilha proporcional em relação ao sexo de 63 idosos da comunidade. ExcluÃram-se idosos com doença de Parkinson, ataque isquêmico transitório, acidente vascular encefálico, Miniexame do Estado Mental inferior ao considerado normal de acordo com a escolaridade, movimentação exclusiva por cadeira de rodas e relato de uma queda nos seis meses anteriores à primeira entrevista. O TUGT, um teste de mobilidade, foi a medida testada, e o desfecho, a ocorrência de queda. Mensuraram-se atividades básicas (ABVD) e instrumentais de vida diária (AIVD) pela Older American Resources and Services e dados sociodemográficos e clÃnicos por questionário complementar. Para analisar a sensibilidade e a especificidade do TUGT, utilizou-se a Receiver Operating Characteristic Curves (ROC). \ud
RESULTADOS: Os idosos que caÃram tinham maior dificuldade na execução de ABVD e AIVD (p<0,01) e desempenho mais lento no TUGT (p=0,02). Quanto à s caracterÃsticas sociodemográficas e clÃnicas, não houve diferença entre idosos que caÃram e os que não caÃram. Considerando as diferentes sensibilidades, especificidades e razões de verossimilhança, o melhor valor preditivo para discriminar idosos que caÃram foi 12,47 segundos [(RR=3,2) IC95%: 1,3-7,7]. CONCLUSÃO: O TUGT é acurado para rastrear risco de quedas em idosos. O cut-off de 12,47 segundos, embora diferente da literatura internacional, parece ser um melhor valor preditivo para idosos brasileiros
High incidence of acquiring methicillin-resistant <i>Staphylococcus aureus</i> in Brazilian children with Atopic Dermatitis and associated risk factors
BACKGROUND: Methicillin-resistant Staphylococcus aureus (MRSA) colonization in Atopic Dermatitis (AD) patients can contribute to worsening their clinical condition. OBJECTIVE: A cohort study was carried out to determine the incidence of MRSA acquisition and its risk factors in AD children. METHODS: Patients with AD (2 months-14 years old) were followed up for about 1 year at a reference center for AD treatment in Rio de Janeiro, Brazil, from September 2011 to February 2014. Nasal swabs from patients and contacts were collected every 2 months. The SCORAD system assessed the severity of the AD. S. aureus isolates were evaluated to determine the methicillin resistance and the clonal lineages. RESULTS: Among 117 AD patients, 97 (82.9%) were already colonized with S. aureus and 26 (22.2%) had MRSA at the first evaluation. The incidence of MRSA acquisition in the cohort study was 27.47% (n = 25). The SCORAD assessments were: mild (46.15%), moderate (37.36%) or severe (16.48%). Risk factors were: colonized MRSA contacts (HR = 2.27; 95% CI: 1.16-7.54), use of cyclosporine (HR = 5.84; 95% CI: 1.70-19.98), moderate or severe AD (HR = 3.26; 95% CI: 1.13-9.37). Protective factors were: availability of running water (HR = 0.21; 95% CI: 0.049-0.96) and use of antihistamines (HR = 0.21; 95% IC: 0.64-0.75). MRSA isolates carried the SCCmec type IV and most of them were typed as USA800/ST5. CONCLUSIONS: The high incidence of MRSA acquisition found among AD patients and the risk factors associated show that an effective surveillance of MRSA colonization in these patients is needed
Accuracy of Timed Up and Go Test for screening risk of falls among community-dwelling elderly
Desempenho de pacientes esquizofrênicos no Stroop Color Word Test e responsividade eletrodérmica após administração aguda de canabidiol (CBD)
OBJECTIVE: The last decade has seen increasing evidence of dysfunctions in the endogenous cannabinoid system in schizophrenia and of its relationship with the typical cognitive impairment of the disorder. Studies in animal models, healthy volunteers, and psychotic patients clearly suggest an antipsychotic-like effect of cannabidiol. This study investigated the effects of cannabidiol on selective attention in 28 schizophrenic patients using the Stroop Color Word Test and on these patients' electrodermal responsiveness to auditive stimuli. METHOD: The subjects attended two experimental sessions, the first one without the administration of drugs. In the second session the subjects were divided into three groups that received either a single dose of cannabidiol 300mg or cannabidiol 600mg or placebo. RESULTS: The three groups did not differ significantly with respect to electrodermal measures in the two experimental sessions. When the first and second sessions were compared improved performance was found in all three groups, with patients who received placebo and cannabidiol 300mg performing better than those who received cannabidiol 600mg. CONCLUSION: The single, acute administration of cannabidiol seems to have no beneficial effects on the performance of schizophrenic patients in the Stroop Color Word Test, although the hypothesis that chronic administration may lead to improvement cannot be disregarded.OBJETIVO: Descobertas relativas a possÃveis disfunções do sistema canabinóide endógeno na esquizofrenia e sua relação com o prejuÃzo cognitivo caracterÃstico da doença têm aumentado durante a última década. Estudos com modelos animais, voluntários saudáveis e pacientes psicóticos sugerem claramente que o canabidiol possui efeitos antipsicóticos. Este estudo investigou os efeitos do canabidiol sobre a atenção seletiva por meio do Stroop Color Word Test e a responsividade eletrodérmica a estÃmulos auditivos em 28 pacientes com esquizofrenia. MÉTODO: Duas sessões experimentais foram realizadas, a primeira sem a administração de drogas. Na segunda sessão, os sujeitos foram divididos em três grupos que receberam dose única de canabidiol 300mg, canabidiol 600mg ou placebo. RESULTADOS: Os três grupos não diferiram significativamente no que se refere à s medidas eletrodérmicas nas duas sessões experimentais. Os três grupos apresentaram melhora da primeira para a segunda avaliação, com os grupos placebo e canabidiol 300mg superiores ao grupo canabidiol 600mg. CONCLUSÃO: A administração aguda de canabidiol em dose única parece não ter efeitos benéficos sobre o desempenho de pacientes com esquizofrenia no Stroop Color Word Test, embora estes dados não sejam suficientes para refutar a hipótese de que a administração continuada de canabidiol possa resultar em melhora no funcionamento cognitivo em esquizofrenia
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