Microstructure and electric properties of a SnO2 based varistor

High non-linear J x E electrical characteristic (alpha=41) were obtained in the Nb2O5 and Cr2O3 doped CoO highly densified SnO2 ceramics. X-ray diffraction analysis showed that these ceramics are apparently single phase. Electrical properties and microstructure are highly dependent on the Cr2O3 concentration and on the sintering temperature. Excess of Cr2O3 leads to porous ceramics destroying the material's electrical characteristics probably due to precipitation of second phase of CoCr2O4 Dopant segregation and/or solid solution formation at the grain boundaries can be responsible for the formation of the electrical barriers which originate the varistor behaviour. (C) 1998 Elsevier B.V. Limited and Techna S.r.l. All rights reserved.

Efficient energy upconversion emission in Tm3+/Yb3+-codoped TeO2-based optical glasses excited at 1.064 mu m

Efficient energy upconversion of cw radiation at 1.064 mum into blue, red, and near infrared emission in Tm3+-doped Yb3+-sensitized 60TeO(2)-10GeO(2)-10K(2)O-10Li(2)O-10Nb(2)O(5) glasses is reported. Intense blue upconversion luminescence at 485 nm corresponding to the Tm3+ (1)G(4)--> H-3(6) transition with a measured absolute power of 0.1 muW for 800 mW excitation power at room temperature is observed. The experimental results also revealed a sevenfold enhancement in the upconversion efficiency when the sample was heated from room temperature to 235 degreesC yielding 0.7 muW of blue absolute fluorescence power for 800 mW pump power. High brightness emission around 800 nm (F-3(4)--> H-3(6)) in addition to a less intense 655 nm ((1)G(4)--> H-3(4) and F-3(2,3)--> H-3(6)) fluorescence is also recorded. The energy upconversion excitation mechanism for thulium emitting levels is assigned to multiphonon-assisted anti-Stokes excitation of the ytterbium-sensitizer followed by multiphonon-assisted sequential energy-transfer processes. (C) 2001 American Institute of Physics.

Acquired resistance of horses to Amblyomma cajennense (Fabricius, 1787) ticks

Acquired immunity of horses to larvae, nymphs and adults of the Amblyomma cajennense tick was evaluated through three consecutive experimental infestations of tick-bite naive hosts. Data from these infestations were compared to those from field-sensitized horses and donkeys. It was observed that tick-bite naive horses developed a low level of resistance after two infestations as shown by a significant decrease in larval yield and a tendency for lower engorged weight of nymphs during third infestation. Ticks fed on field-sensitized horses had a similar biological performance to that observed on the third infestation of tick-bite naive horses but the mean engorged nymph weight was significantly lower than that of the first infestation from tick-bite naive horses. Donkeys presented the strongest resistance with significantly lower engorged weights of all instars and of the egg mass compared to the first infestation of tick-bite naive horses. Donkeys also displayed a significantly higher resistance than field-sensitized horses as demonstrated by significantly lower egg mass weights. Overall these results indicate that donkeys but not horses maintain a strong resistance to A. cajennense ticks. The importance of these findings in relation to vectoring of tick-borne diseases is discussed. (C) 2003 Elsevier B.V. All rights reserved.

Imbalance of IL-2, IFN-gamma and IL-10 secretion in the immunosuppression associated with human paracoccidioidomycosis

Patients with paracoccidioidomycosis (PCM) display a certain degree of immunecompromise characterized by lymphocyte hyporesponsiveness to the main Paracoccidioides brasiliensis antigen (gp43). To determine whether cytokines are involved in this state, we evaluated the secretion of IL-2, IL-10 and IFN-gamma by peripheral blood mononuclear cells (PBMC) from patients with the acute (AF) and chronic (CF) forms of PCM and from healthy, P. brasiliensis-sensitized subjects. gp43-stimulated PBMC from healthy subjects produced substantial amounts of IL-2, IFN-gamma and IL-10, whereas PBMC from AF and CF patients produced low levels of IL-2 and IFN-gamma but substantial amounts of IL-10, Phytohaemagglutinin-induced cytokine secretion was comparable among AF and CF patients and healthy subjects, suggesting integrity of non-specific cellular immune mechanisms in PCM. gp43-pulsed adherent cells, but not non-adherent cells, mere the main source of IL-10, Moreover, IL-2 and IFN-gamma secretion correlated inversely with the amount of specific antibodies produced by patients and healthy subjects. Our results suggest that the imbalance in cytokine production of patients with PCM plays a role in the gp43-hyporesponsiveness and the marked (non-protective) antibody production of these patients. (C) 2001 Academic Press.

Plasma nitriding of sintered AISI 316L at several temperatures

Samples of sintered AISI 316L stainless steel were plasma nitrided in a mixture of H-2-20% N-2, for 3 or 4 h. The treatment temperature was selected in 400-550 degreesC interval, in steps of 50 degreesC. X-ray diffraction (glancing angle geometry-GAXRD), conversion electron Mossbauer spectroscopy (CEMS), optical microscopy and Vickers microhardness were used as analytical techniques. For T greater than or equal to 500 degreesC and t = 4 h, a 40-mum layer is formed. The GAXRD results showed a transformation of the austenite gamma phase to the martensite in the sinterization process and showed as well, that the gamma' (Fe4N) phase is the predominant nitride besides small amounts of epsilon-Fe2N, gamma(N) CrN, Cr2O3 and the fcc nitrogen supersatured solid phase gamma(N). The CrN phase seems to decrease with temperature while the gamma(N) phase fraction is almost less than or equal to10%, independently on the temperature. The CEMS results indicated that while the gamma(N) fraction decreases with temperature of plasma nitriding, the gamma' fraction increases proportionally. (C) 2003 Elsevier B.V. All rights reserved.

GRANULOMATOUS REACTION IN THE HAMSTER-CHEEK POUCH INDUCED BY KILLED PARACOCCIDIOIDES-BRASILIENSIS

We have studied the role of Paracoccidioides brasiliensis viability in the morphology of paracoccidioidomycotic granulomas in the hamster cheek pouch, an immunologically privileged site. Naive (N = 75) and previously sensitized (N = 50) two-month old male hamsters (Mesocricetus auratus) were inoculated into the pouch with 5 x 10(5) live or heat- or formalin-killed fungi. Previously sensitized animals presented a positive footpad test and immunodiffusion demonstrable antibodies (titer 1/32), at the time of sacrifice; naive animals were always negative for those immunological tests. The histological results showed that, like viable P. brasiliensis, killed fungi evoke typical epithelioid granulomas in 100% of animals, even in the absence of immunodiffusion or footpad test detectable immune response. The granulomas elicited by killed fungi were devoid of giant cells or a mononuclear cell halo, suggesting that live proliferating fungi or their products may be involved in these events.

Er3+-doped germanate glasses for active waveguides prepared by Ag+/K+ <-> Na+ ion-exchange

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Effect of atmosphere on the electrical properties of TiO2-SnO2 varistor systems

This work illustrates the advancement of research on TiO2-based electroceramics. In this work will be presented that the addition of different dopants, as well as thermal treatments at oxidizing and inert atmosphere, influences of the densification, the mean grain size and the electrical properties of the TiO2-based varistor ceramics. Dopants like Ta2O5, Nb2O5, and Cr2O3 have an especial role in the barrier formation at the grain boundary in the TiO2 varistors, increasing the nonlinear coefficient and decreasing the breakdown electric field. The influence of Cr'(Ti) is to increase the O' and O'(2) adsorption at the grain boundary interface and to promote a decrease in the conductivity by donating electrons to O-2 adsorbed at the grain boundary. In this paper, TiO2 and (Sn,Ti)O-2-based studies of polycrystalline ceramics, which show a non-linear I-V electrical response typical of low voltage varistor systems are also presented. All these systems are potentially promising for varistor applications. (C) 2004 Kluwer Academic Publishers.

Cytostatic in vitro Effects of DTCM-Glutarimide on Bladder Carcinoma Cells

Bladder cancer is a common malignancy worldwide. Despite the increased use of cisplatin-based combination therapy, the outcomes for patients with advanced disease remain poor. Recently, altered activation of the PI3K/Akt/mTOR pathway has been associated with reduced patient survival and advanced stage of bladder cancer, making its upstream or downstream components attractive targets for therapeutic intervention. In the present study, we showed that treatment with DTCM-glutaramide, a piperidine that targets PDK1, results in reduced proliferation, diminished cell migration and G1 arrest in 5637 and T24 bladder carcinoma cells. Conversely, no apoptosis, necrosis or autophagy were detected after treatment, suggesting that reduced cell numbers in vitro are a result of diminished proliferation rather than cell death. Furthermore previous exposure to 10 mu g/ml DTCM-glutarimide sensitized both cell lines to ionizing radiation. Although more studies are needed to corroborate our findings, our results indicate that PDK1 may be useful as a therapeutic target to prevent progression and abnormal tissue dissemination of urothelial carcinomas.

Obesity enhances eosinophilic inflammation in a murine model of allergic asthma

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cr3+ and Cr4+ luminescence in glass ceramic silica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Pulmonary paracoccidioidomycosis in immunized mice

Paracoccidioidomycosis was induced in immunized (IM) and non-immunized (NI) mice. The histopathology, the number of fungi in the lungs, the cellular (footpad test - FPT and macrophage inhibition factor assay - MIF) and humoral (immunodiffusion test) immune response were investigated serially postinfection. In the IM mice, at days 1 and 3, there was intense and predominant macrophagic-lymphocytic alveolitis with loose granulomatous reaction; at day 30, inflammation was mild. In the NI group, up to day 3, the lesions were focal; later there was formation of extensive epithelioid granuloma. The number of fungi in IM mice were always smaller than those of NI group. Immunization alone induced positive FPT and MIF indices with low titer of antibody. After infection, there was a significant decrease of the FPT indices in the IM group, which we interpreted as desensitization due to trapping of sensitized lymphocytes in the lungs. In conclusion, (1) The lesional pattern of pulmonary paracoccidioidomycosis in IM mice was similar to that of a hypersensitivity pneumonitis. This reaction was probably effective in reducing the extension of the infection and decrease the number of fungi. (2) In this model, pulmonary resistance against P. brasiliensis seems to be related to local and systemic delayed-type hypersensitivity reaction. © 1992 Kluwer Academic Publishers.

Lithium-lanthanum double chromates

Synthesis and crystallographic data are reported for low and high temperature forms of LiLa(CrO4)2. The compounds are closely related to lamellar rare earth phosphates and arsenates of sodium and to RbLu(CrO4)2. Lattice parameters of the orthorhombic (low temperature) and monoclinic (high temperature) forms are given. The low temperature form is moisture sensitive and Li+ ions are easily displaced by protons. Thermal decomposition takes place at 250 °C and results in the formation of LiCrO2, LaCrO4, LaCrO3 and Cr2O3. © 1993.

Triplet carbonyls: from photophysics to biochemistry

Triplet carbonyls can be generated not only from the thermal cleavage of dioxetanes, but also enzymatically from appropriate substrates. The excited species can phosphoresce with an intensity depending upon the extent of shielding from deactivating oxygen collisions, react and also transfer energy, thus promoting sensitized emission and sensitized photochemistry. © 1994.

Pre-resonant Raman effect of CrO2- 4 in a metasilicate glass

Pre-resonant Raman effect of chromate ion, CrO2- 4, was observed in a metasilicate glass with molar composition 2Na2O · 1CaO · 3SiO2 containing 1.0 wt% of Cr2O3. Raman spectra were measured by the conventional 90° scattering geometry and by the microprobe Raman spectroscopic techniques. The presence of chromate ions in the glass is favoured by the glass composition and oxidizing conditions during the glass melting, and they are responsible for optical absorption bands at 370 and 250 nm. Raman spectrum of the undoped glass presents bands at 625, 860 and 980 cm-1, and the presence of chromate ions gives rise to additional bands at 365, 850 and a shoulder at 890 cm-1. An enhancement of the 850 cm-1 Raman band is observed with decreasing laser exciting wavelength. The exciting frequency dependence of the intensity of this band is discussed in terms of theoretical models given in the literature.