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.

Antitumor effects in vitro and in vivo and mechanisms of protection against melanoma B16F10-Nex2 cells by fastuosain, a cysteine proteinase from Bromelia fastuosa

In the present work, the antitumor effect of fastuosain, a cysteine proteinase from Bromelia fastuosa, was investigated. In the intravenous model of lung colonization in C57Bl/6 mice, fastuosain and bromelain injected intraperitoneally were protective, and very few nodules of B16F10-Nex2 melanoma cells were detected. Tumor cells treated with fastuosain showed reduced expression of CD44 and decreased invasion through Matrigel, lost their cytoplasmic extensions and substrate adherence, and became round and detached, forming strongly bound cell clusters in suspension. Peritoneal cells recruited and activated by fastuosain treatment ( mainly monocytic cells and lymphocytes) migrated to the lung, where pulmonary melanoma metastases grew. Adoptive transference of peritoneal cells recruited by fastuosain had no protective effect against lung metastases in recipient mice. Treatment of green fluorescent protein - chimeric animals with fastuosain did not change the number of cells that migrated to the lung, compared to PBS-injected control mice, but the number of positive major histocompatibility complex class II cells increased with fastuosain treatment. Murine antibodies against fastuosain, bromelain, and cathepsins B and L cross-reacted in ELISA and recognized surface and cytoplasmic components expressed on B16F10-Nex2 cells. Anti-fastuosain antibodies were cytotoxic/lytic to B16F10-Nex2 cells. Antitumor effects of fastuosain involve mainly the direct effect of the enzyme and elicitation of protective antibodies.

NONLOCAL EFFECTS IN THE NUCLEUS-NUCLEUS FUSION CROSS-SECTION

Effects of the nonlocality of factorizable potentials are taken into account in the calculation of nucleus-nucleus fusion cross section through an effective mass approach. This cross section makes use of the tunneling factor calculated for the nonlocal barrier, without the explicit introduction of any result coming from coupled channel calculation, besides the approximations of Hill-Wheeler and Wong. Its new expression embodies the nonlocal effects in a factor which redefines the local potential barrier curvature. Applications to different systems, namely O-16 + Co-59, O-16,O-18 + Ni-58,Ni-60,Ni-64, and O-16,O-18 + Cu-63,Cu-65 are presented, where the nonlocal range is treated as a free parameter.

Compositeness effects in the anomalous weak-magnetic moment of leptons

We investigate the effects induced by excited leptons, at the one-loop level, in the anomalous magnetic and weak-magnetic form factors of the leptons. In particular, we compute their contributions to the weak-magnetic moment of the tau lepton, which can be measured on the Z peak, and we compare it with the contributions to g(mu) - 2, measured at low energies.

Crotoxin-induced behavioral effects in rats

Crotoxin is the major component of Crotalus durissus terrificus venom. In view of the presence of high-affinity specific binding sites for crotoxin in the brain, the objective of this work was to investigate whether crotoxin induces behavioral effects in the open-field and hole-board tests. Adult male Wistar rats (180-220 g) treated with crotoxin, 100, 250 and 500 mu g/kg, ip, administered 2 h before the test, presented statistically significant behavioral alterations (ANOVA for one-way classification complemented with Dunnet test, P<0.05). In the open-field test, 250 and 500 mu g/kg of crotoxin increased freezing (from 3.22 sec to 10.75 sec and 11.2 sec) and grooming (from 13.44 sec to 22.75 sec and 21.22 sec) and decreased ambulation (from 64.8 to 39.38 and 45.8). The dose of 500 mu g/kg also decreased rearing (from 24.9 to 17.5). In the hole-board test, 500 mu g/kg of crotoxin decreased head-dip count (from 6.33 to 4.00). All the crotoxin-induced behavioral effects were antagonized by an anxiolytic dose of diazepam (1.5 mg/kg, ip, 30 min before the tests). These results show that crotoxin reduced open-field activity and exploratory behavior as well. We suggest that these effects express an increased emotional state induced by this toxin.

Exchange and crystal field effects in the ESR spectra of Eu(2+) in LaB(6)

Electron spin resonance of Eu(2+) (4f(7), S=7/2) in a La hexaboride (LaB(6)) single crystal shows a single anisotropic Dysonian resonance. From the observed negative g shift of the resonance, it is inferred that the Eu(2+) ions are covalent exchange coupled to the B 2p-like host conduction electrons. From the anisotropy of the spectra (linewidth and field for resonance), we found that the S ground state of Eu(2+) ions experience a cubic crystal field of a negative fourth order crystal field parameter (CFP), b(4)=-11.5(2.0) Oe, in agreement with the negative fourth order CFP, A(4), found for the non-S ground state R hexaborides. These results support covalency as the dominant contribution to the fourth order CFP for the whole R hexaboride family.

Exchange interaction effects in the ESR spectra of Eu2+ in LaB6

The electron spin resonance (ESR) spectra of Eu2+ (4f(7), S = 7/2) in LaB6 single crystal show a single Dysonian resonance for the localized Eu2+ magnetic moments. It is shown that the Eu2+ ions are covalent exchange coupled to the (B) 2p-like host conduction electrons. (c) 2007 Elsevier B.V. All rights reserved.

Photo-induced effects in Ge25Ga10S65 glasses studied by XPS and XAS

The present paper focuses on the structural, electronic, and compositional properties of Ge25Ga10S65 glasses before and after UV illumination in air using X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) techniques. The XPS Ge 3d spectra reveal the existence of Ge-O bonds in the surface region of illuminated glass. In the case of this sample, XAS O K-edge spectra showed the formation of an enriched region of oxygen atoms in the glass bulk, indicating a different bonding structure of oxygen at the surface and in the bulk of the glass. Moreover, the structural changes that occur after UV illumination in the glass sample are identified as the formation of a homogeneous germanium oxide surface layer followed by an intermediary Ge25Ga10S65-yOz subsurface region. (c) 2005 Elsevier B.V. All rights reserved.

Quantitative estimates of time-averaging in terebratulid brachiopod shell accumulations from a modern tropical shelf

Quantitative estimates of time-averaging in marine shell accumulations available to date are limited primarily to aragonitic mollusk shells. We assessed time-averaging in Holocene assemblages of calcitic brachiopod shells by direct dating of individual specimens of the terebratulid brachiopod Bouchardia rosea. The data were collected from exceptional (brachiopod-rich) shell assemblages, occurring surficially on a tropical mixed carbonate-siliciclastic shelf (the Southeast Brazilian Bight, SW Atlantic), a setting that provides a good climatic and environmental analog for many Paleozoic brachiopod shell beds of North America and Europe. A total of 82 individual brachiopod shells, collected from four shallow (5-25 m) nearshore (<2.5 km from the shore) localities, were dated by using amino acid racemization (D-alloisoleucine/L-isoleucine value) calibrated with five AMS-radiocarbon dates (r(2) = 0.933). This is the first study to demonstrate that amino acid racemization methods can provide accurate and precise ages for individual shells of calcitic brachiopods.The dated shells vary in age from modern to 3000 years, with a standard deviation of 690 years. The age distribution is strongly right-skewed: the young shells dominate the dated specimens and older shells are increasingly less common. However, the four localities display significant differences in the range of time-averaging and the form of the age distribution. The dated shells vary notably in the quality of preservation, but there is no significant correlation between taphonomic condition and age, either for individual shells or at assemblage level.These results demonstrate that fossil brachiopods may show considerable time-averaging, but the scale and nature of that mixing may vary greatly among sites. Moreover, taphonomic condition is not a reliable indicator of pre-burial history of individual brachiopod shells or the scale of temporal mixing within the entire assemblage. The results obtained for brachiopods are strikingly similar to results previously documented for mollusks and suggest that differences in mineralogy and shell microstructure are unlikely to be the primary factors controlling the nature and scale of time-averaging. Environmental factors and local fluctuations in populations of shell-producing organisms are more likely to be the principal determinants of time-averaging in marine benthic shelly assemblages. The long-term survival of brachiopod shells is incongruent with the rapid shell destruction observed in taphonomic experiments. The results support the taphonomic model that shells remain protected below (but perhaps near) the surface through their early taphonomic history. They may be brought back up to the surface intermittently by bioturbation and physical reworking, but only for short periods of time. This model explains the striking similarities in time-averaging among different types of organisms and the lack of correlation between time-since-death and shell taphonomy.

Many-body effects in wide parabolic AlGaAs quantum wells

Photoluminescence measurements at different temperatures have been performed to investigate the optical response of a two-dimensional electron gas in n-type wide parabolic quantum wells. A series of samples with different well widths in the range of 1000-3000 A was analyzed. Many-body effects, usually observed in the recombination process of a two-dimensional electron gas, appear as a strong enhancement in the photoluminescence spectra at the Fermi level at low temperature only in the thinnest parabolic quantum wells. The suppression of the many-body effect in the thicker quantum wells was attributed to the decrease of the overlap between the wavefunctions of the photocreated holes and the two-dimensional electrons belonging to the highest occupied electron subband. (C) 2007 American Institute of Physics.

Exchange narrowing effects in the EPR linewidth of Gd diluted in Ce compounds

Anomalous thermal behavior on the EPR linewidths of Gd impurities diluted in Cc compounds has been observed. In metals, the local magnetic moment EPR linewidth, Delta H, is expected to increase linearly with the temperature. In contrast, in CexLa1-xOs2 the Gd EPR spectra show a nonlinear increase. In this work, the mechanisms that are responsible for the thermal behavior of the EPR lines in CexLa1-xOs2 are examined. We show that the exchange interaction between the local magnetic moments and the conduction electrons are responsible for the narrowing of the spectra at low temperatures. At high temperatures, the contribution to the linewidth of the exchange interaction between the local magnetic moments and the Ce ions has an exponential dependence on the excitation energy of the intermediate valent ions. A complete fitting of the EPR spectra for powdered samples is obtained, (C) 1998 American Institute of Physics. [S0021-8979(98)39911-9].

SURFACE EFFECTS IN THE HYDROGEN EVOLUTION REACTION ON NI-ZN ALLOY ELECTRODES IN ALKALINE-SOLUTIONS

Hydrogen evolution reaction was studied on Ni-Zn (25% of Ni before leaching) in 1 M NaOH at 25 degrees C. These electrodes were characterized by very low Tafel slopes of 67 mV dec(-1). Other techniques used included potential and current pulse, potential relaxation in an open circuit, and ac impedance spectroscopy. Analysis of the experimental results led to the conclusion that hydrogen adsorption in the surface layers was responsible for the observed behavior. Influence of the oxidation of the electrode surface and the addition of poisons, thiourea and cyanides, were also studied. These processes inhibit the hydrogen absorption and restore ''normal'' Tafel slopes. Kinetic parameters of the hydrogen evolution reaction were determined.

Upconversion luminescence and thermal effects in terbium-ytterbium codoped fluorogermanate glass-ceramic

Cooperative energy transfer upconversion luminescence is investigated in Tb(3+)/Yb(3+)-codoped PbGeO(3)-PbF(2)-CdF(2) glass-ceramic and its precursor glass under resonant and off resonance infrared excitation. Bright UV-visible emission signals around 384, 415, 438 nm, and 473-490, 545, 587, and 623 nm are identified as due to the (5)D(3)((5)G(6))->(7)F(1) (J=6,5,4) and (5)D(4)->(7)F(1) (J=6,5,4,3) transitions, respectively, and readily observed. The results indicate that cooperative energy transfer between ytterbium and terbium. ions followed by excited state absorption are the dominant upconversion excitation mechanisms involved. Comparison of the upconversion process in a glass-ceramic sample and its glassy precursor revealed that the former present much higher upconversion efficiency. The dependence of the upconversion emission upon pump power, temperature, and doping content is also examined.