Use of dialkyldithiocarbamato complexes of bismuth(III) for the preparation of nano- and microsized Bi2S3 particles and the X-ray crystal structures of [Bi{S2CN(CH3)(C6H13)}(3)] and [Bi{S2CN(CH3)(C6H13)}(3)(C12H8N2)]

A range of bismuth(III) dithiocarbamato complexes were prepared and characterized. The X-ray crystal structures of the compounds [Bi{S2CN(CH3)(C6H13)}3] (1) and [Bi{S2CN(CH3)- (C6H13)}3(C12H8N2)] (2) are reported. The preparation of Bi2S3 particulates using a wet chemical method and involving the thermalysis of Bi(III) dialkyldithiocarbamato complexes is described. The influence of several experimental parameters on the optical and morphological properties of the Bi2S3 powders was investigated. Nanosized Bi2S3 colloids were obtained having long-term stability and showing a blue shift on the optical band edge; the presence of particles exhibiting quantum size effects is discussed. Morphological welldefined Bi2S3 particles were obtained in which the fiber-type morphology is prevalent.FCT - POCTI/1999/CTM/ 3545

Spin Josephson effect in ferromagnet/ferromagnet tunnel junctions

We consider the tunnel spin current between two ferromagnetic metals from a perspective similar to the one used in superconductor/superconductor tunnel junctions. We use fundamental arguments to derive a Josephson-like spin tunnel current $I_J^{\rm spin}\propto\sin(\theta_1-\theta_2)$. Here the phases are associated with the planar contribution to the magnetization, $\sim e^{i\theta}$. The crucial step in our analysis is the fact that the $z$-component of the spin is canonically conjugate to the phase of the planar contribution: $[\theta,S^z]=i$. This is analogous to the commutation relation $[\phi,N]=i$ in superconductors, where $\phi$ is the phase associated to the superconducting order parameter and $N$ is the Cooper pair number operator. We briefly discuss the experimental consequences of our theoretical analysis.Comment: LaTex, seven pages, no figures; version to appear in Europhys. Lett.; in order to make room for a more extended microscopic analysis, the phenomenological discussion contained in v2 was remove

The superconducting phase transition and gauge dependence

The gauge dependence of the renormalization group functions of the Ginzburg-Landau model is investigated. The analysis is done by means of the Ward-Takahashi identities. After defining the local superconducting order parameter, it is shown that its exponent $\beta$ is in fact gauge independent. This happens because in $d=3$ the Landau gauge is the only gauge having a physical meaning, a property not shared by the four-dimensional model where any gauge choice is possible. The analysis is done in both the context of the $\epsilon$-expansion and in the fixed dimension approach. It is pointed out the differences that arise in both of these approaches concerning the gauge dependence.Comment: RevTex, 3 pages, no figures; accepted for publication in PRB; this paper is a short version of cond-mat/990527

Interference and complementarity for two-photon hybrid entangled states

In this work we generate two-photon hybrid entangled states (HES), where the polarization of one photon is entangled with the transverse spatial degree of freedom of the second photon. The photon pair is created by parametric down-conversion in a polarization-entangled state. A birefringent double-slit couples the polarization and spatial degrees of freedom of these photons and finally, suitable spatial and polarization projections generate the HES. We investigate some interesting aspects of the two-photon hybrid interference, and present this study in the context of the complementarity relation that exists between the visibilities of the one- and two-photon interference patterns.Comment: 10 pages, 4 figures. Accepted in Physical Review

Permanent Junctional Reciprocating Tachycardia: an Incessant Tachycardia in Children

A taquicardia juncional recíproca permanente é uma forma de taquicardia supraventricular de reentrada pouco comum, embora constitua a causa mais frequente de taquicardia incessante em crianças. O seu carácter permanente causa disfunção ventricular esquerda e miocardiopatia dilatada e é de difícil controlo terapêutico. Objectivo: Rever as características clínicas mais significativas desta arritmia, a sua evolução e as opções terapêuticas actuais. Métodos: estudo retrospectivo, analisando a forma de apresentação e evolução, com particular relevo para a resposta à terapêutica farmacológica e alternativas terapêuticas. Doentes: Grupo de 5 doentes com o diagnóstico de taquicardia juncional recíproca permanente. Resultados: As crianças estudadas tinham idades compreendidas entre os 14 dias e os 12 anos. Três encontravam-se assintomáticas. O primeiro ecocardiograma demonstrou dilatação do ventrículo esquerdo e diminuição da fracção de encurtamento em uma das crianças. A terapêutica farmacológica foi inicialmente eficaz em todos os casos. Ao longo do seguimento (0,2-4,5 anos) a arritmia tornou-se refractária em um dos casos, pelo que se procedeu a ablação da via anómala por radiofrequência. Conclusões: A taquicardia juncional recíproca permanente tem diversas formas de apresentação. A terapêutica farmacológica é recomendada, mas tem carácter transitório. A ablação por radiofrequência é o tratamento definitivo, estando condicionada pela idade dos doentes

Sotalol in the Treatment of Fetal Tachyarrhythmia

A taquicardia fetal é uma situação rara, que, quando mantida coloca em risco a vida do feto. O modo de tratamento não é consensual, existindo várias modalidades farmacológicas. O objectivo deste estudo foi avaliar a eficácia e segurança do sotalol no tratamento de taquicardias fetais. Material e métodos: Estudo retrospectivo, com base nos registos de consulta e entrevista às mães dos fetos com taquicardia supraventricular, referenciados ao Serviço de Cardiologia Pediátrica do Hospital de Santa Marta, durante um período de dez anos. Resultados: Foram diagnosticados oito fetos com taquicardia supraventricular, dos quais seis foram tratados com sotalol. A idade média de gestação na apresentação foi de 30 semanas. Nenhum feto apresentava cardiopatia estrutural, em dois verificou-se hidropisia fetal e outro apresentou hidrocefalia. A taquicardia era supraventricular em todos, sendo em dois por flutter auricular. Em todos os casos, excepto um, houve conversão a ritmo sinusal, não se registando efeitos secundários nas mães nem mortalidade fetal. No período neonatal em três crianças foram registados episódios de taquicardia supraventricular paroxística. Conclusão: O sotalol mostrou-se seguro e eficaz no tratamento das taquicardias fetais, mas, dada a pequenez da amostra, outros estudos mais alargados são necessários para se tirarem conclusões válidas

Magnetic monopoles and superinsulation in Josephson junction arrays

Electric-magnetic duality or S-duality, extending the symmetry of Maxwell's equations by including the symmetry between Noether electric charges and topological magnetic monopoles, is one of the most fundamental concepts of modern physics. In two-dimensional systems harboring Cooper pairs, S-duality manifests in the emergence of superinsulation, a state dual to superconductivity, which exhibits an infinite resistance at finite temperatures. The mechanism behind this infinite resistance is the linear charge confinement by a magnetic monopole plasma. This plasma constricts electric field lines connecting the charge-anti-charge pairs into electric strings, in analogy to quarks within hadrons. Yet the origin of the monopole plasma remains an open question. Here we consider a two-dimensional Josephson junction array (JJA) and reveal that the magnetic monopole plasma arises as quantum instantons, thus establishing the underlying mechanism of superinsulation as two-dimensional quantum tunneling events. We calculate the string tension and the dimension of an electric pion determining the minimal size of a system capable of hosting superinsulation. Our findings pave the way for study of fundamental S-duality in desktop experiments on JJA and superconducting films.Comment: 10 pages, 1 figur

Effect of different treatments on swine carcasses surface contamination with Salmonella Typhimurium

Salmonella is worldwide related to the most cases of food poisoning in humans. The meat contamination may occur from direct or indirect sources during the slaughter and pork processing