RESPIRATORY RESPONSES IN A BRAZILIAN MILLIPEDE, PSEUDONANNOLENE-TRICOLOR, TO DECLINING OXYGEN PRESSURES

Oxygen uptake and the influence of declining oxygen pressures (Po2's) were examined in a Brazilian spirostreptid millipede, Pseudonannolene tricolor. The data were obtained in a Warburg respirometer at 25-degrees-C from both male and female animals, sexually inactive, in the intermolt stage, and fasting for 24 h. In a sudden exposure to a decreased Po2 the millipedes regulated respiration down to at least 71 mmHg O2. From a Po2 of 35 mmHg O2 downward the animals started to show oxyconformity. When the millipedes were exposed to a stepwise declining Po2 the results indicated only conformation. After exposure to hypoxia, P. tricolor showed a pattern of underrepayment on return to normoxia, but larger millipedes accumulated more O2 debt than smaller ones.

An ab initio study of oxygen vacancies and doping process of Nb and Cr atoms on TiO2 (110) surface models

We theoretically investigated how the formation of oxygen vacancies and the addition of niobium and chromium atoms as dopants modify the varistor properties of TiO2. The calculations were carried out at the HF level using a contracted basis set, developed by Huzinaga et al.. to represent the atomic centers on the (110) surface for the large (TiO2)(15) cluster model. The change of the values for the net atomic charges and band gap after oxygen vacancy formation and the presence of dopants in the lattice are analyzed and discussed. It is shown that the formation of oxygen vacancies decreases the band gap while an opposite effect is found when dopants are located in the reduced surface. The theoretical results are compared with available experimental data. A plausible explanation of the varistor behavior of this system is proposed. (C) 1997 John Wiley & Sons, Inc.

Oxygen mobility and structural phase transformation in Bi2Sr2CaCu2O8+delta measured by anelastic spectroscopy

One of the most studied ceramic superconductors for application has been, undoubtedly, Bi2Sr2CaCu2O8+delta. Although being a multiphasic material, it has proved to have great advantages compared to other ceramic systems. Measurements of the elastic energy loss and modulus (anelastic spectroscopy) as a function of temperature call distinguish among different atomic jumps that occur inside the various phases or at different local ordering. In this paper, mechanical loss spectra of Bi2Sr2CaCu2O8+delta bar shaped samples, made by a conventional method, have been measured between 80 and 600 K, using a torsion pendulum operating in frequencies below 50 Hz, for samples annealed in vacuum up to 600 K. Possible relaxation mechanisms are proposed to explain the origin of the mechanical-loss peaks observed 300 and 500 K. (C) 2004 Elsevier B.V. All rights reserved.

Metal-insulator transitions and magnetic ordered states in oxygen-depleted manganites

The use of AC/DC magnetic susceptibility and impedance measurements to detect oxygen depletion effects in La0.7Ca0.3MnO3 +/-delta and NiMn2O4+delta spinel-type compounds is reported. For the NiMn2O4, for which no Mn4+ was found, three superposed Debye relaxations were observed in the range 260-180 K. Otherwise, in La0.7Ca0.3MnO3, the argon annealed has contributed to a decrease in T-C, but the amount of Mn4+ is still too high to allow the observation of a relaxation in this frequency window. (c) 2006 Elsevier B.V. All rights reserved.

STUDIES ON THE RELATIONSHIP BETWEEN THE PATHOGENICITY OF PARACOCCIDIOIDES-BRASILIENSIS IN MICE AND ITS GROWTH-RATE UNDER DIFFERENT OXYGEN ATMOSPHERES

We performed comparative studies of the pathogenicity of six strains of Paracoccidioides brasiliensis (Bt-9, Bt-4, Pb-9, Pb-18, Bt-7 and B-1183) for young adult male ddY mice and growth rate of each strain under different oxygen atmospheres (aerobic, micro-aerobic and anaerobic atmospheres) at 37-degrees-C. 10(6) units of yeast cells were intravenously injected into each mouse. The pathogenicity of each isolate was determined by a scoring system based on organ culture and histopathological findings. The growth rates under different oxygen atmospheres were determined by a scoring system in which 300 fungal units per strain were counted. The strain Bt-9 showed the greatest pathogenicity, followed by Bt-4. Pb-9 and Pb-18 had on intermediate rank of pathogenicity. Bt-7 and B-1183 were the least pathogenic of the strains tested. Except for strain Bt-7 all strains showed an excellent growth under an aerobic atmosphere. Bt-4 and Bt-9 also showed excellent growth under a micro-aerobic atmosphere, followed by Pb-9, whereas the growth of Pb-18, Bt-7 and B-1183 was limited. There was a correlation between the growth rate under a micro-aerobic atmosphere and the pathogenicity of a strain. The growth rate of P. brasiliensis under a micro-aerobic atmosphere strongly correlated to its pathogenicity.

Evaporative water loss and oxygen uptake in two casque-headed tree frogs, Aparasphenodon brunoi and Corythomantis greeningi (Anura, Hylidae)

Evaporative water loss (EWL) and oxygen uptake ((V) over dot o(2)) was measured in two species of tree frogs with cranial co-ossification, Aparasphenodon brunoi and Corythomantis greeningi. Both species use their head to seal the entrance of bromeliads, tree holes or rocky crevices used as shelters. EWL was significantly reduced in sheltered individuals of both species as compared with those exposed nude to desiccation. EWL per unit area through the head surface was significantly lower than the body skin for A. brunoi but not for C., greeningi. EWL per unit surface area through C. greeningi body skin was about 50% that of A. brunoi, indicating a less permeable skin in the former species. The relationship between cranial coossification and EWL is discussed. ((V) over dot o(2)) in A. brunoi was comparable with other anurans of similar size, whereas in C. greeningi, it was lower than predicted from body mass. Moreover, ((V) over dot o(2)), in C. greeningi showed less sensitivity to temperature increase than in A. brunoi. C. greeningi occurs in a drier environment than A. brunoi, and this appears to be reflected in their EWL and ((V) over dot o(2)) characteristics. (C) 1997 Elsevier B.V.

Internal friction measurements in Nb-0.3wt.%Ti containing oxygen

Internal friction measurements were made in the Nb-Ti alloy containing 0.3 wt. % of Ti, doped with various quantities of oxygen (0.04 to 0.08 wt. %) utilizing a torsion pendulum. These measurements were performed in the temperature range of 300 K to 700 K with the oscillation frequency about 1.0 Hz. The experimental results showed relaxation peaks due the stress induced ordering of oxygen atom and pairs of oxygen atom around the niobium atoms (metallic matrix) and around titanium atoms (substitutional solute).

Oxygen stoichiometry effects in spinel-type NiMn2O4-delta samples

We report the effects of oxygen stoichiometry in the structure and magnetic response of spinel-type NiMn2O4-delta polycrystalline samples controlled by heat-treatments in different atmospheric conditions.The post-annealed samples were analyzed by Scanning Electron Microscopy associated to X-ray Energy Dispersion Spectrometry, X-ray Photoelectron Spectroscopy and AC/DC magnetic measurements.Results indicate that the oxygen stoichiometry highly influences the magnetic interactions between the ferromagnetic, and antiferromagnetic sublattices in these compounds due to the presence of manganese in three possible valence states. (c) 2005 Elsevier Ltd. All rights reserved.

Oxygen-uptake in snakes - is there a reduction in fossorial species

Oxygen uptake of the fossorial blind snake (Typhlops reticulatus) and the semifossorial coral snake (Micrurus ibiboboca) was measured at 20 and 30 degrees C. Oxygen uptake of blind snakes was within the normal range, whereas oxygen uptake of coral snakes was in the lower end of values reported for snakes. The results do not support the hypothesis of reduced oxygen uptake in fossorial reptiles.

ONTOGENIC VARIATION OF OXYGEN-UPTAKE IN THE PITVIPER BOTHROPS MOOJENI (SERPENTES, VIPERIDAE)

The scaling of oxygen uptake was measured along the ontogeny, in the neotropical pitviper Bothrops moojeni. Allometric relationship between oxygen uptake and body mass, quantified for juveniles, sub-adults and adults, showed the same mass coefficient and exponent. The uniformity of mass constants along ontogeny suggests that B. moojeni is energetically homomorphic. Variation in mass seem to be the sole determinant of oxygen uptake, and structural modifications have no effect on the metabolic rate. Applications of the homomorphism principle to assess variations in mass coefficient and exponent for intraspecific analysis of metabolism in reptiles are discussed. B. moojeni had an oxygen consumption in the range reported for viperids, but lower than that for colubrid snakes of similar size. Possible causative reasons for this pattern is discussed.

CIRCADIAN OSCILLATORY PATTERNS OF OXYGEN-UPTAKE IN INDIVIDUAL WORKERS OF THE ANT CAMPONOTUS-RUFIPES

Respiratory rates of individual workers of Camponotus rufipes Fabricius (Hymenoptera: Formicidae) were measured at 25-degrees-C and LD 12:12 h (lights on 06.00 hours), DL 12:12 h (lights on 18.00 hours), LL (850 lux) and DD (red light, 20-30 lux), using the micro-Warburg technique. Worker ants were collected from natural nest during the winter of 1987 in a woodland park in the region of Rio Claro, São Paulo, Brazil. The respiration of ants showed a circadian rhythm with acrophase ranging from 20 h 41 min to 01 h 18 min and from 10 h 32 min to 12 h 22 min at LD and DD, respectively. In constant darkness the rhythmometric variables were similar to those presented by ants kept at LD 12:12 h. Under constant light no circadian rhythm in the respiration rates was found. A reduction in the amplitude was observed, indicating an inhibitory effect of this light regime on the respiration process.

REACTIVE OXYGEN GENERATION BY AZOMETHINE-H - A NEW ANTIMALARIAL DRUG

Superoxide radical (O-2(-)) is a free radical that may be involved in various toxic processes. Cu-Zn superoxide dismutase catalyzes the dismutation of the superoxide free radical and protects cells from oxidative damage. A rat bioassay validated for the identification of the toxic effects of azomethine H revealed increased serum activities of amylase, alanine transaminase, and alkaline phosphatase. The lipoperoxide and bilirubin concentrations were also increased in animals that received azomethine H (1 g/kg) from ascorbic or hydrochloric acid solutions. Azomethine H increased Cu-Zn superoxide dismutase activity. This elevation of Cu-Zn superoxide dismutase activity was highest on the 7th day and was at levels comparable with those of control rats from day 60 onwards. Superoxide is an important intermediate in the action and toxicity of azomethine H.

Cation-oxygen interaction and oxygen stability in CaCu3Ti4O12 and CdCu3Ti4O12 lattices

The cubic perovskite related material CaCu3Ti4O12 has attracted a great deal of attention due to the high values of the static dielectric constant, of order 104, approximately constant in the temperature range 100-600 K. The substitution of Ca by Cd results in a similar temperature dependence but a static dielectric constant more than one order of magnitude lower. A theoretical electronic structure study is performed on CaCu3Ti4O12 (CCTO) and CdCu3Ti4O12 (CdCTO) using a tight binding with overlap method. Although the calculations are performed in a paramagnetic configuration, excellent agreement with experiment was found for the calculated band gap of CCTO. In spite of the fact that the band structures of both systems look practically the same, a significant difference is found in the calculated bond strength of Ca-O and Cd-O pairs, driven by the presence of Ti, with Ca-O interaction in CCTO loosened with respect to Cd-O interaction in the cadmium compound. It is suggested that O vacancies are more easily formed in CCTO, this being related to the lower electronegativity of Ca as compared to Cd. The formation of oxygen vacancies could be the origin of the difference in the static dielectric constant of the two compounds.