The role of vacancies, impurities and crystal structure in the magnetic properties of TiO₂

We present an ab initio study of pure and doped TiO₂ in the rutile and anatase phases. The main purpose of this work is to determine the role played by different defects and different crystal structures in the appearance of magnetic order. The calculations were performed for varying impurity and vacancy concentrations in both TiO₂ structures. For Co impurities the local magnetic moment remained almost independent of the concentration and distribution while for Cu this is not the case, there is magnetism for low concentrations that disappears for the higher ones. Impurity–impurity interactions in both structures favor linear ordering of them. Magnetism in undoped samples appears for certain vacancy concentrations and structural strain.Facultad de Ciencias ExactasInstituto de Física La Plat

Study of the relation between oxygen vacancies and ferromagnetism in Fe-doped TiO2 nano-powders

In this work, we present an experimental and theoretical study of structural and magnetic properties of Fe doped rutile TiO2 nanopowders. We show that Fe-doping induces the formation of oxygen vacancies in the first-sphere coordination of iron ions, which are in +2 and +3 oxidation states. We found that Fe ions form dimers that share one oxygen vacancy in the case of Fe3+ and two oxygen vacancies in the case of Fe2+. The saturation magnetization is almost independent of iron concentration and slightly increases with the relative fraction of Fe2+. Ab initio calculations show that two Fe ions sharing an oxygen vacancy are coupled ferromagnetically, forming a bound magnetic polaron (BMP), but two neighbor BMPs are aligned antiparallel to each other. Extra electron doping plays a fundamental role mediating the magnetic coupling between the ferromagnetic entities: carriers, possibly concentrated at grain boundaries, mediate between the BMP to produce ferromagnetic alignment.Fil: Mudarra Navarro, Azucena Marisol. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: RodrÍguez Torres, Claudia Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Bilovol, Vitaliy. Universidad de Buenos Aires. Facultad de Ingeniería. Departamento de Física. Laboratorio de Sólidos Amorfos; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Cabrera, Alejandra Fabiana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Errico, Leonardo Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional del Noroeste de la Provincia de Buenos Aires; ArgentinaFil: Weissmann, Mariana Dorotea. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Meningoencefalite chagásica: relato de caso de doença recentemente incluida como indicativa de AIDS no Brasil

Recently, reactivation of Chagas disease (meningoencephalitis and/or myocarditis) was included in the list of AIDS-defining illnesses in Brazil. We report a case of a 52-year-old patient with no history of previous disease who presented acute meningoencephalitis. Direct examination of blood and cerebrospinal fluid (CSF) showed Trypanosoma cruzi. CSF culture confirmed the diagnosis. Serological assays for T. cruzi and human immunodeficiency virus (HIV) were positive. Despite treatment with benznidazol and supportive measures, the patient died 24 hours after hospital admission. In endemic areas, reactivation of Chagas disease should always be considered in the differential diagnosis of meningoencephalitis among HIV-infected patients, and its presence is indicative of AIDS.Recentemente, a reagudização da doença de Chagas (meningoencefalite e/ou miocardite) foi incluída na lista de doenças indicativas de aids no Brasil. Os autores relatam o caso de um paciente de 52 anos de idade, natural de área rural da Bahia e procedente de uma área urbana de São Paulo, sem história de doenças prévias e que apresentou meningoencefalite aguda. As sorologias e pesquisas parasitológicas diretas no sangue e no liquido cefalorraquideano (LCR) demonstraram presença de Trypanosoma cruzi, confirmando-se o diagnóstico mediante cultura do LCR. O teste rápido assim como os ELISA e Western Blot diagnosticaram infecção pelo vírus da imunodeficiência humana (HIV). Apesar do tratamento com benzonidazole e as medidas de suporte, o paciente faleceu 24 horas depois da admissão hospitalar. Em áreas endêmicas, a reagudização da doença de Chagas deve ser sempre considerada no diagnóstico diferencial das meningoencefalites e sua presença em pacientes com infecção pelo HIV é indicativa de aids

The role of vacancies, impurities and crystal structure in the magnetic properties of TiO2

We present an ab initio study of pure and doped TiO2 in the rutile and anatase phases. The main purpose of this work is to determine the role played by different defects and different crystal structures in the appearance of magnetic order. The calculations were performed for varying impurity and vacancy concentrations in both TiO2 structures. For Co impurities the local magnetic moment remained almost independent of the concentration and distribution while for Cu this is not the case, there is magnetism for low concentrations that disappears for the higher ones. Impurity-impurity interactions in both structures favor linear ordering of them. Magnetism in un-doped samples appears for certain vacancy concentrations and structural strain.Comment: 6 pages, 4 figures, 2 tables. Accepted for publication in Physica B, in pres

Management of infection by the Zika virus

A panel of national experts was convened by the Brazilian Infectious Diseases Society in order to organize the national recommendations for the management of zika virus infection. The focus of this document is the diagnosis, both clinical and laboratorial, and appropriate treatment of the diverse manifestations of this infection, ranging from acute mild disease to Guillain-Barré syndrome and also microcephaly and congenital malformations.1

Detection of plasma viral DNA in individuals with chronic hepatitis B virus infection coinfected with human immunodeficiency virus and under antiretroviral therapy: frequency and associated factors

INTRODUÇÃO: A terapia antirretroviral (TARV) determinou diminuição da incidência de aids e da mortalidade em pessoas vivendo com o vírus da imunodeficiência humana (HIV). Outras comorbidades assumiram, consequentemente, maior relevância no cuidado integral a esses indivíduos. Destaca-se, nesse contexto, a infecção crônica pelo vírus da hepatite B (VHB), dada a influência negativa que a infecção pelo HIV tem sobre a história natural da infecção pelo VHB nos coinfectados. Sabendo-se que medicamentos antirretrovirais podem também inibir a replicação do VHB, justifica-se analisar o impacto da TARV no manejo da hepatite B nessa população. OBJETIVOS: Verificar a frequência de detecção do ácido desoxirribonucleico (DNA) do VHB entre indivíduos coinfectados pelo HIV em uso de antirretrovirais e fatores associados. MÉTODOS: Em estudo transversal de uma série de casos, acompanhada no Serviço de Extensão ao Atendimento de Pacientes HIV/Aids da Divisão de Moléstias Infecciosas e Parasitárias do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, avaliaram-se pacientes com coinfecção HIV/VHB, idade acima de 18 anos e em uso de TARV por mais de seis meses, que passaram em consulta no ano de 2015. Não houve critério de exclusão. Coletaram-se dados sociodemográficos, de exposição ao HIV e VHB, clínico-laboratoriais e de avaliação da fibrose hepática por meio de entrevistas, revisão de prontuários e exames complementares. A viremia pelo VHB foi aferida por reação em cadeia pela polimerase quantitativa em tempo real. Nos casos em que se detectou DNA do VHB em concentração superior a 900 UI/mL, realizou-se sequenciamento para genotipagem viral e identificação de mutações conferidoras de resistência aos antivirais. RESULTADOS: Em 2015, 2 946 pessoas vivendo com HIV foram atendidas no serviço, sendo 83 elegíveis para o estudo, das quais 56 puderam ser avaliadas. Viremia pelo VHB foi identificada em 16 (28,6%) delas (IC 95%: 18,0-41,3%), sendo que todas faziam uso de lamivudina e tenofovir no momento da inclusão no estudo. Mostraram-se diretamente associadas à viremia pelo VHB: escolaridade mais baixa (p = 0,015), valores mais elevados da relação normalizada internacional (RNI) (p = 0,045), antecedente de doença definidora de aids [OR: 3,43 (IC 95%: 1,10-11,50); p = 0,040] e detecção sérica de AgHBe [OR: 6,60 (IC 95%: 1,84-23,6); p = 0,003]. Em contraste, a última contagem de linfócitos T CD4+ acima de 500 células/mm3 nos 365 dias prévios à inclusão no estudo [OR: 0,18 (IC 95%: 0,04-0,71); p = 0,016] e a detecção sérica de anti-HBe [OR: 0,21 (IC 95%: 0,04-0,99); p = 0,043] mostraram-se inversamente associados à ocorrência de viremia pelo VHB. Nos quatro pacientes que apresentaram carga plasmática do VHB superior a 900 UI/mL, verificou-se predominantemente infecção pelo genótipo A1 (75%). Nesses indivíduos foram identificadas mutações capazes de conferir resistência total à lamivudina e parcial ao entecavir. CONCLUSÕES: Mesmo em uso de TARV, porcentagem significativa dos pacientes coinfectados pelo HIV permanece com viremia do VHB. A caracterização dos fatores associados a esse desfecho pode orientar os profissionais no manejo mais apropriado desses indivíduosINTRODUCTION: Antiretroviral therapy (ART) has decreased the incidence of acquired immunodeficiency syndrome (AIDS) and mortality rate of people infected with human immunodeficiency virus (HIV). Other comorbidities have, therefore, gained more relevance in the comprehensive care provided to these individuals. In this context, we highlight chronic infection with hepatitis B virus (HBV) because HIV coinfection is known to have a negative influence on the natural history of HBV infection. Given that antiretroviral drugs may also inhibit HBV replication, it is important to analyze the impact of ART on the management of hepatitis B in this population. OBJECTIVES: To verify the frequency of HBV-DNA among HIV-coinfected individuals under ART and its associated factors. METHODS: In this cross-sectional study, we evaluated a series of HIV/HBV-coinfected cases, followed up at the HIV outpatient clinic affiliated to Hospital das Clínicas University of São Paulo Medical School. Patients aged over 18, who were under ART for more than 6 months and had a medical consultation at the clinic in 2015 were included in the study. There was no exclusion criterion. We collected socio-demographic data, information about exposure to HIV and HBV and findings of clinical assessment, laboratory tests and evaluation of liver fibrosis by means of interviews and chart reviews. HBVDNA was measured by quantitative real-time polymerase chain reaction. In cases who had HBV-DNA detected in concentrations above 900 IU/mL, additional HBV genome sequencing for viral genotyping and identification of drug resistance-conferring mutations was conducted. RESULTS: In 2015, 2946 people living with HIV attended medical consultations at the clinic. Out of 83 who were eligible for the study, 56 could be evaluated. HBV-DNA was detected in 16 (28.6%) (95% CI: 18.0-41.3%), all of whom were receiving lamivudine and tenofovir treatment. In bivariate analysis, HBV-DNA was associated with lower education (p = 0.015), higher international normalized ratios (INR) (p = 0.045), history of an AIDS-defining illness [OR: 3.43 (95% CI: 1.10-11.50); p = 0.040] and HBeAg detection in serum [OR: 6.60 (95% CI: 1.84-23.6); p = 0.003]. In contrast, the last CD4+ T-lymphocyte count above 500 cells/mm3 in the 365 days prior to inclusion in the study [OR: 0.18 (95% CI: 0.04-0.71); p = 0.016] and detection of anti-HBe in serum [OR: 0.21 (95% CI: 0.04-0.99); p = 0.043] were negatively associated with the occurrence of HBV viremia. In the 4 patients with HBV-DNA concentrations above 900 IU/mL, HBV subgenotype A1 was predominant (75%). In these individuals we detected drug resistanceconferring mutations associated with total resistance to lamivudine and partial resistance to entecavir. CONCLUSIONS: Though under ART, a significant proportion of HIV/HBV-coinfected individuals present HBV viremia. The characterization of factors that are associated with this finding may guide professionals to provide the most appropriate management to these individual

Effect of low dimensionality and encapsulation on the magnetic and hyperfine properties of iron nanowires

Ab initio calculations were performed for a very thin iron nanowire, both free-standing and enclosed in a carbon nanotube with the same size and structure of available experiments. Our interest was to study the effects of low dimensionality and the influence of the Fe–C interaction on the magnetic and hypefine properties of these systems. Our main finding was that the interfacial region between the nanowire and the carbon nanotube is of fundamental importance, as an iron atom close to the carbon atoms has a magnetic moment and a local hyperfine field very different from that at the surface of a free-standing iron nanowire. In fact, the properties of the calculated iron nanowire, of only 1 nm in diameter, when encapsulated inside a carbon nanotube result close to those of bulk iron.Fil: Weissmann, Mariana Dorotea. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Errico, Leonardo Antonio. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional del Noroeste de la Provincia de Buenos Aires; Argentin

<i>Ab initio</i> study of ferromagnetism induced by magnetic impurities in rutile TiO₂

Using the first-principles density-functional approach, magnetic properties of Mn-, Fe-, Co-, and Ni-doped rutile TiO₂ were investigated for two different impurity concentrations (25% and 6.25%). Calculations were performed with the Full-Potential Linearized-Augmented Plane Waves (FLAPW) method, assuming that the magnetic impurities substitutionally replace the Ti ions. Our results show that the systems (with the exception of Ni-doped TiO₂) are ferromagnetic. We also found that polarization mainly occurs at the impurity sites, and the magnetic moments of the impurities are independent of the impurity concentration.Facultad de Ciencias Exacta

Ab initio study of the ferromagnetic response, local structure, and hyperfine properties of Fe-doped SnO2

We present here an ab initio study of the structural, magnetic, and hyperfine properties of Fe-doped rutile SnO2 for different concentrations and distributions of the Fe atoms and oxygen vacancies in the SnO2 host. The calculated results are compared with experimental ones obtained by Mössbauer spectroscopy and X-ray absorption techniques. This comparison enables us to characterize the local structure around Fe atoms and to identify the different hyperfine interactions that are observed in samples prepared by different methods. It is concluded that oxygen vacancies are fundamental for the ferromagnetic response of Fe-doped SnO2. The ab initio calculations show that two Fe ions sharing an oxygen vacancy are coupled ferromagnetically, forming a bound magnetic polaron (BMP), and that two neighbor BMPs are aligned antiparallel to each other. Electron doping plays a fundamental role mediating the magnetic coupling between the BMP inducing ferromagnetic alignment between the BMPs.Fil: Mudarra Navarro, Azucena Marisol. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; ArgentinaFil: RodrÍguez Torres, Claudia Elena. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Cabrera, Alejandra Fabiana. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; ArgentinaFil: Weissmann, Mariana Dorotea. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Nomura, K.. University of Tokyo; JapónFil: Errico, Leonardo Antonio. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Departamento de Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

<i>Ab Initio</i> Study of the Ferromagnetic Response, Local Structure, and Hyperfine Properties of Fe-Doped SnO₂

We present here an ab initio study of the structural, magnetic, and hyperfine properties of Fe-doped rutile SnO2 for different concentrations and distributions of the Fe atoms and oxygen vacancies in the SnO2 host. The calculated results are compared with experimental ones obtained by Mössbauer spectroscopy and X-ray absorption techniques. This comparison enables us to characterize the local structure around Fe atoms and to identify the different hyperfine interactions that are observed in samples prepared by different methods. It is concluded that oxygen vacancies are fundamental for the ferromagnetic response of Fe-doped SnO2. The ab initio calculations show that two Fe ions sharing an oxygen vacancy are coupled ferromagnetically, forming a bound magnetic polaron (BMP), and that two neighbor BMPs are aligned antiparallel to each other. Electron doping plays a fundamental role mediating the magnetic coupling between the BMP inducing ferromagnetic alignment between the BMPs.Facultad de Ciencias ExactasInstituto de Física La Plat