Quantum critical point in the spin glass-antiferromagnetism competition in Kondo-lattice systems

A theory is proposed to describe the competition among antiferromagnetism (AF), spin glass (SG) and Kondo effect. The model describes two Kondo sublattices with an intrasite Kondo interaction strength $J_{K}$ and an interlattice quantum Ising interaction in the presence of a transverse field $\Gamma$. The interlattice coupling is a random Gaussian distributed variable (with average $-2J_0/N$ and variance $32 J^{2}/N$) while the $\Gamma$ field is introduced as a quantum mechanism to produce spin flipping. The path integral formalism is used to study this fermionic problem where the spin operators are represented by bilinear combinations of Grassmann fields. The disorder is treated within the framework of the replica trick. The free energy and the order parameters of the problem are obtained by using the static ansatz and by choosing both $J_0/J$ and $\Gamma/J \approx (J_k/J)^2$ to allow, as previously, a better comparison with the experimental findings. The results indicate the presence of a SG solution at low $J_K/J$ and for temperature $T<T_{f}$ ($T_{f}$ is the freezing temperature). When $J_K/J$ is increased, a mixed phase AF+SG appears, then an AF solution and finally a Kondo state is obtained for high values of $J_{K}/J$. Moreover, the behaviors of the freezing and Neel temperatures are also affected by the relationship between $J_{K}$ and the transverse field $\Gamma$. The first one presents a slight decrease while the second one decreases towards a Quantum Critical Point (QCP). The obtained phase diagram has the same sequence as the experimental one for $Ce_{2}Au_{1-x}Co_{x}Si_{3}$, if $J_{K}$ is assumed to increase with $x$, and in addition, it also shows a qualitative agreement concerning the behavior of the freezing and the Neel temperatures.Comment: 11 pages, 3 figures, accepted for publication in J. Phys.

Avaliação da eficiência do tratamento preservante em moirões de Eucalyptus dunnii pelo método de substituição de seiva.

Organizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso

Comportamento do Angiostrongylus costaricensis em planorbídeos

Some terrestrial mollusks are natural hosts of Angiostrongylus costaricensis. In the laboratory, this nematode can be maintained in certain planorbids, which are aquatic mollusks and intermediate hosts of Schistosoma mansoni. Mollusks can be infected with Angiostrongylus costaricensis by ingestion of or active penetration by the first-stage larvae. In this work we assessed the ability of Biomphalaria glabrata to attract first-stage larvae of A. costaricensis. Movement of the nematode larvae towards the mollusks was observed after 15 min, 30 min and 1 h. B. glabrata did not attract the first-stage larvae of A. costaricensis in any of the three intervals. The susceptibility of two populations of Biomphalaria tenagophila to infection by A. costaricensis was also determined. One population was genetically selected for the susceptibility to S. mansoni while the other was not. Third-stage larvae were recovered from the snails 30 days after exposure of the two populations to 120 first-stage larvae. All the mollusks were infected. However, a significantly higher number of third-stage larvae were recovered in mollusks not genetically selected.Alguns moluscos terrestres são hospedeiros naturais do Angiostrongylus costaricensis. No laboratório, esse nematódeo pode ser mantido em planorbídeos, que são moluscos aquáticos e hospedeiros intermediários do Schistosoma mansoni. Os moluscos podem ser infectados com A. costaricensis por ingestão ou por penetração ativa de larvas de primeiro estágio. Neste trabalho, testamos a habilidade de Biomphalaria glabrata em atrair larvas de primeiro estágio de A. costaricensis. A movimentação das larvas do nematódeo em direção aos moluscos foi observada após 15 minutos, 30 minutos e 1 hora. B. glabrata não atraiu as larvas de primeiro estágio de A. costaricensis nos três intervalos de tempo. Verificamos também a suscetibilidade de duas populações de Biomphalaria tenagophila à infecção por A. costaricensis. Uma população era selecionada geneticamente para a susceptibilidade ao S. mansoni, enquanto a outra não o era. Larvas de terceiro estágio foram recuperadas dos moluscos 30 dias após a exposição das duas populações a 120 larvas de primeiro estágio. Todos os moluscos estavam infectados. Entretanto, um número significativamente maior de larvas de terceiro estágio foi recuperado em moluscos não geneticamente selecionados.19920

Transient ischemic attacks in rural and urban northern Portugal: incidence and short-term prognosis

Abstract BACKGROUND AND PURPOSE: There are no community-based studies on the incidence of transient ischemic attacks (TIAs) in Portugal. This study was designed to determine TIA incidence and the risk of stroke occurrence in rural and urban populations in northern Portugal. METHODS: All suspected first-ever TIAs occurring between October 1998 and September 2000 in 18,677 residents in a rural municipality and 86,023 living in the city of Porto were entered into a population-based registry. Standard definitions and comprehensive sources of information were used for identification of patients who were followed up at 3 and 12 months after the TIA. RESULTS: During a 24-month period, 141 patients with a first-ever TIA were registered, 36 in rural and 104 in urban areas. The vascular territory was carotid in 66.7% of the patients, vertebrobasilar in 29.1%, and undetermined in 4.3%. The overall crude annual incidence rate per 1000 was 0.67 (95% CI, 0.45 to 1.04), 0.61 (95% CI, 0.38 to 1.01) for rural, and 0.96 (95% CI, 0.43 to 2.33) for urban populations. The risk of stroke within the first 7 days of the index event was 12.8% (95% CI, 7.3 to 18.3), reaching 21.4% (95% CI, 14.6 to 28.1) at 1 year. Three factors were associated with stroke occurrence within 120 days after TIA: patients' age > or =65 years and an episode in the carotid distribution lasting > or =3 hours. CONCLUSIONS: The incidence of TIA in northern Portugal, particularly in rural populations, ranks among the highest reported in community-based studies, following closely the stroke incidence trend (ACINrpc). Early recognition of TIA by patients and physicians is crucial for effective stroke prevention

Teaching Laminar-flow reactors: From experimentation to CFD simulation

An integrated chemical engineering lab experiment is described in this paper. It makes use of a laminar-flow tubular reactor (LFTR) through consecutive lab sessions. In a first session (not described here), the pseudo first-order kinetic constant for the reaction between crystal violet and sodium hydroxide is determined at different temperatures in a batch reactor. Then a tracer experiment is used to characterize the flow, pattern in the LFTR, and finally the steady-state conversion of crystal violet in the reactor is measured. For computing the theoretical reactor conversion, students must use the previously collected kinetic and tracer data, in a concept-integration exercise. A computational fluid dynamics (CFD) code (Fluent) is also used to simulate both the tracer and the isothermal reaction experiments performed in the LFTR. A very good agreement is obtained between experimental and simulated results and both only differ slightly from the theoretical predictions. The use of the CFD program is particularly noteworthy. For instance, transient simulations allow a very nice visualization of the tracer concentration front evolution, while the steady-state profiles along the axial position provide a good perspective of how reactant concentration varies within the reactor

Solid wood treated by plasma jet.

Editado por Luiz Henrique Capparelli Mattoso, Alcides Leão e Elisabete Frollini

Photoassociative ionization of Na inside a storage ring

Motivated by recent interest in low dimensional arrays of atoms, we experimentally investigated the way cold collisional processes are affected by the geometry of the considered atomic sample. More specifically, we studied the case of photoassociative ionization (PAI) both in a storage ring where collision is more unidirectional in character and in a trap with clear undefinition of collision axis. First, creating a ring shaped trap (atomotron) we investigated two-color PAI dependence with intensity and polarization of a probing laser. The intensity dependence of the PAI rate was also measured in a magneto-optical trap presenting equivalent temperature and density conditions. Indeed, the results show that in the ring trap, the value of the PAI rate constant is much lower and does not show evidences of saturation, unlike in the case of the 3D-MOT. Cold atomic collisions in storage ring may represent new possibilities for study.Comment: 5 pages, 5 figures; Accepted by Optics Communicatio

Aplicação de métodos quimiométricos em análises não-destrutivas de Eucalyptus grandis.

Este trabalho teve como objetivo a construção de uma curva de calibração utilizando a espectroscopia no infravermelho próximo (NIR) para predição de propriedades físicas como densidade básica, retratibilidade radial, longitudinal e tangencial e anisotropia de contração de amostras de Eucalyptus grandis. A partir de análise matemática multivariada dos resultados observou-se que existe correlação estatística, de acordo com o modelo proposto, com as propriedades retratibilidade radial e longitudinal