Magnetic properties of Fe3O4 nanoparticles coated with oleic and dodecanoic acids

Magnetic nanoparticles (NP) of magnetite (Fe3O4) coated with oleic acid (OA) and dodecanoic acid (DA) were synthesized and investigated through Transmission Electron Microscopy (TEM),magnetization M, and ac magnetic susceptibility measurements. The OA coated samples were produced with different magnetic concentrations (78, 76, and 65%) and the DA sample with 63% of Fe3O4. Images from TEM indicate that the NP have a nearly spherical geometry and mean diameter ~ 5.5 nm. Magnetization measurements, performed in zero field cooled (ZFC) and field cooled (FC) processes under different external magnetic fields H, exhibited a maximum at a given temperature TB in the ZFC curves, which depends on the NP coating (OA or DA), magnetite concentration, and H. The temperature TB decreases monotonically with increasing H and, for a given H, the increase in the magnetite concentration results in an increase of TB. The observed behavior is related to the dipolar interaction (DI) between NP which seems to be an important mechanism in all samples studied. This is supported by the results of the ac magnetic susceptibility Xac measurements, where the temperature in which X' peaks for different frequencies follows the Vogel-Fulcher model, a feature commonly found in systems with dipolar interactions. Curves of H vs. TB/TB(H=0) for samples with different coatings and magnetite concentrations collapse into a universal curve, indicating that the qualitative magnetic behavior of the samples may be described by the NP themselves, instead of the coating or the strength of the dipolar interaction. Below TB, M vs. H curves show a coercive field (HC) that increases monotonically with decreasing temperature. The saturation magnetization (MS) follows the Bloch's law and values of MS at room temperature as high as 78 emu/g were estimated, a result corresponding to ~80% of the bulk value. The overlap of M/MS vs. H/T curves for a given sample and the low HC at high temperatures suggest superparamagnetic behavior in all samples studied. The overlap of M/MS vs. H curves at constant temperature for different samples indicates that the NP magnetization behavior is preserved, independently of the coating and magnetite concentration.Comment: 8 pages and 9 figure

Nonsingular solutions of Hitchin's equations for noncompact gauge groups

We consider a general ansatz for solving the 2-dimensional Hitchin's equations, which arise as dimensional reduction of the 4-dimensional self-dual Yang-Mills equations, with remarkable integrability properties. We focus on the case when the gauge group G is given by a real form of SL(2,C). For G=SO(2,1), the resulting field equations are shown to reduce to either the Liouville, elliptic sinh-Gordon or elliptic sine-Gordon equations. As opposed to the compact case, given by G=SU(2), the field equations associated with the noncompact group SO(2,1) are shown to have smooth real solutions with nonsingular action densities, which are furthermore localized in some sense. We conclude by discussing some particular solutions, defined on R^2, S^2 and T^2, that come out of this ansatz.Comment: 12 pages, 3 figures. To appear in Nonlinearit

Determination of pesticides in water by liquid chromatography-(Electrospray Ionization)-mass spectrometry (LC-ESI-MS).

A method for determination of a selected group of pesticides in water (tap and ground water) was developed using liquid chromatography-(electrospray ionization)-mass spectrometry (LC-ESI-MS). The pesticides dimethoate, carbaryl, simazine, atrazine, ametryne, tebuthiuron, diuron and linuron were isolated using liquid-liquid extraction with dichloromethane and analyzed on a reversed phase column, C-18, with gradient elution at flow rate of 1 mL. min-1. Recoveries ranged from 89% to 112% (R.S.D. <_10%) for tap water and from 76% to 98% (R.S.D <_ 6%) for ground water. The enrichment procedure, followed by use of the selected ion monitoring (SIM) mode gave quantification limits low enough to reach the international legislation level of 0.1 µg.L-1, with a 500-fold preconcentration. The method developed is practical, efficient and reliable for the determination of the selected group of pesticides in the water samples. Um método para a determinação de um grupo selecionado de resíduos de pesticidas em água (de torneira e subterrânea) foi desenvolvido usando cromatografia líquida-ionização electrospray-espectrometria de massas (LC-ESI-MS). Os pesticidas dimetoato, carbaril, simazina, atrazina, ametrina, tebutiuron, diuron e linuron foram isolados usando extração líquido-líquido com diclorometano e analisados em uma coluna de fase reversa, C-18, com eluição gradiente a uma vazão de 1 mL/min. Foram obtidas recuperações de 89 a 112% (RSD <_10%) para água de torneira e 76 a 98% (RSD <_ 6%) para água subterrânea. O procedimento de enriquecimento, seguido pelo uso do monitoramento seletivo de íons (SIM) forneceu limites de quantificação baixos o suficiente para atingir a legislação internacional (Comunidade Européia) que é de 0,1 µg/L. O método desenvolvido é prático, eficiente e confiável para a determinação do grupo selecionado dos pesticidas em amostras de água

The upper critical field in superconducting MgB_2

The upper critical field Hc2(T) of sintered pellets of the recently discovered MgB_2 superconductor was investigated in magnetic fields up to 16 T. The upper critical field of the major fraction of the investigated sample was determined from ac susceptibility and resistance data and was found to increase up to Hc2(0) = 13 T at T = 0 corresponding to a coherence length of 5.0 nm. A small fraction of the sample exhibits higher upper critical fields which were measured both resistively and by dc magnetization measurements. The temperature dependence of the upper critical field, Hc2(T), shows a positive curvature near Tc and at intermediate temperatures. This positive curvature of Hc2(T) is similar to that found for the borocarbides YNi_2B_2C and LuNi_2B_2C indicating that MgB_2 is in the clean limit.Comment: 8 pages with 4 figure

Calorons, Nahm's equations on S^1 and bundles over P^1xP^1

The moduli space of solutions to Nahm's equations of rank (k,k+j) on the circle, and hence, of SU(2) calorons of charge (k,j), is shown to be equivalent to the moduli of holomorphic rank 2 bundles on P^1xP^1 trivialized at infinity with c_2=k and equipped with a flag of degree j along P^1x{0}. An explicit matrix description of these spaces is given by a monad constructio

Efeito de duas intensidades de colheita de madeira na estrutura de uma floresta natural na região de Paragominas, Pará.

Foram estudadas as mudanças na estrutura de 108ha de uma floresta primária submetida a duas intensidades de colheita de madeira, na Fazenda Rio Capim, pertencente à Cikel Brasil Verde Madeiras Ltda., no município de Paragominas, Pará. Os dados foram coletados, em dois períodos (2003, antes da exploração, e 2004, após a exploração) em 36 parcelas permanentes quadradas de 0,25ha, estabelecidas aleatoriamente na área, sendo12 em floresta não-explorada: Testemunha - T0; 12 em floresta explorada com colheita apenas do fuste comercial das árvores: Tratamento - T1; e 12 em floresta explorada com colheita do fuste e dos resíduos lenhosos: Tratamento - T2. Em 2003 foram registrados 4469 indivíduos com DAP > 10cm, nas 36 parcelas amostradas (9ha). Sete meses após a exploração (2004), foram observados na área 4531 indivíduos com DAP > 10cm, sendo 4330 vivos. Lecythis idatimon, Poecilanthe effusa, Rinorea flavescens, Eschweilera grandiflora, Eschweilera pedicellata, Inga sp., Protium spp., Vouacapoua americana, Guatteria poeppigiana e Eschweilera coriacea foram as dez espécies mais importantes, tanto antes como após a exploração. A estrutura da floresta, tanto no T1 como no T2, sofreu alterações significantes devido à exploração a que foi submetida. Entretanto, não foram verificadas diferenças significativas entre os três tratamentos, sugerindo que com a intensidade de exploração aplicada, mais a retirada adicional dos resíduos, a floresta manteve as características semelhantes à floresta original, apesar do menor estoque de árvores adultas de espécies comerciais. Recomendam-se estudos sobre a regeneração natural (DAP < 10cm), silvicultura pós-colheita e crescimento da floresta

Assessment of the Impact of Potential Tetracycline Exposure on the Phenotype of Aedes aegypti OX513A: Implications for Field Use

Aedes aegypti is the primary vector of dengue fever, a viral disease which has an estimated incidence of 390 million infections annually. Conventional vector control methods have been unable to curb the transmission of the disease. We have previously reported a novel method of vector control using a tetracycline repressible self-limiting strain of Ae. aegypti OX513A which has achieved >90% suppression of wild populations.We investigated the impact of tetracycline and its analogues on the phenotype of OX513A from the perspective of possible routes and levels of environmental exposure. We determined the minimum concentration of tetracycline and its analogues that will allow an increased survivorship and found these to be greater than the maximum concentration of tetracyclines found in known Ae. aegypti breeding sites and their surrounding areas. Furthermore, we determined that OX513A parents fed tetracycline are unable to pre-load their progeny with sufficient antidote to increase their survivorship. Finally, we studied the changes in concentration of tetracycline in the mass production rearing water of OX513A and the developing insect.Together, these studies demonstrate that potential routes of exposure of OX513A individuals to tetracycline and its analogues in the environment are not expected to increase the survivorship of OX513A

Prevalência de doenças crônicas autorrelatadas em indivíduos acima de 40 anos em São Paulo, Brasil: estudo Platino

Few studies have been conducted to determine the prevalence of chronic diseases and its impact in individuals aged 40 years or over in Brazil. The objective of this study is to evaluate the prevalence of some common chronic diseases in the Brazilian subgroup assessed by the PLATINO study using a self-reported survey. A total of 918 individuals (55% women) with a mean age of 54.6 ± 10.9 years were evaluated. The most prevalent diseases were obesity (62.5%), hypertension (39.2%) and gastritis (30.9%). We conclude from this study that there is a high prevalence of chronic diseases in the population over 40 years of age: 88% of the population suffers from a minimum of one disease and 26% of the sample suffers from at least three diseases. We also observed that the number of comorbidities increases with age.Poucos estudos foram desenvolvidos para determinar a prevalência de doenças crônicas e suas associações em indivíduos com mais de 40 anos de idade no Brasil. O objetivo deste trabalho foi avaliar a prevalência de algumas doenças crônicas altamente prevalentes no país, de modo autorreferido, avaliadas no Estudo PLATINO em São Paulo, em uma amostra de base populacional. Novecentos e dezoito indivíduos (55% mulheres) com média de idade de 54,6 ± 10,9 anos foram avaliados. As três doenças mais prevalentes foram obesidade (62,5%), hipertensão (39,2%) e gastrite (30,9%). Há uma alta prevalência de doenças crônicas na população acima de 40 anos: 88% da amostra apresentaram pelo menos uma doença e 26%, pelo menos, três doenças; e o número de doenças apresentava tendência a aumentar com a idade.Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Universidade Federal de São Paulo (UNIFESP)Lar Escola São FranciscoUniversidade Federal de Pelotas Faculdade de MedicinaInstituto Nacional de Enfermedades RespiratoriasUNIFESPSciEL

Quality of life as a prognostic marker in pulmonary arterial hypertension

Background: Improvement in quality of life together with better survival are the ultimate goals in the treatment of pulmonary arterial hypertension (PAH) patients. the objective of this study was to evaluate the health-related quality of life (HRQL) of pulmonary arterial hypertension (PAH) patients with the SF-36 generic questionnaire and to identify the prognostic implication of this assessment.Methods: Fifty-four consecutive newly diagnosed PAH patients (WHO classification group I) in a single PAH reference center were included. Patients were evaluated at baseline for clinical and hemodynamic parameters, and they subsequently received first-line therapy with either an endothelin receptor antagonist or a phosphodiesterase-5 inhibitor. After 16 weeks of specific PAH therapy, all patients were re-evaluated using a 6MWT and a SF 36 questionnaire, and then they were followed up for at least 36 months.Results: After treatment, the patients demonstrated an improved 6MWT (414 +/- 124 m vs. 440 +/- 113 m, p = 0.001). Specific PAH therapy also improved the HRQL scores.Patients with a baseline Physical Component Score (PCS) higher than 32 had a better survival rate than those who had a score under 32 (p = 0.04). Similarly, patients with a PCS of at least a 38 after the 16 week therapy period had a better survival rate when compared with those who did not achieve this value (p = 0.016). Unlike the absolute PCS values, the post-treatment PCS variability was unable to predict better survival rates (p = 0.58).Conclusions: Our findings suggest that HRQL is associated with prognosis in PAH. Furthermore, achieving pre-determined PCS scores might represent a specific goal to be reached in treatment-to-target strategies.Univ São Paulo, Sch Med, Pulm Dept, Inst Heart, BR-05403000 São Paulo, BrazilUniversidade Federal de São Paulo, Rheumatol Dept, São Paulo, BrazilUniversidade Federal de São Paulo, Rheumatol Dept, São Paulo, BrazilWeb of Scienc