Geometry of Triple Junctions during Grain Boundary Premelting.

Grain boundaries (GBs) whose energy is larger than twice the energy of the solid-liquid interface exhibit the premelting phenomenon, for which an atomically thin liquid layer develops at temperatures slightly below the bulk melting temperature. Premelting can have a severe impact on the structural integrity of a polycrystalline material and on the mechanical high-temperature properties, also in the context of crack formation during the very last stages of solidification. The triple junction between a dry GB and the two solid-liquid interfaces of a liquid layer propagating along the GB cannot be defined from macroscopic continuum properties and surface tension equilibria in terms of Young's law. We show how incorporating atomistic scale physics using a disjoining potential regularizes the state of the triple junction and yields an equilibrium with a well-defined microscopic contact angle. We support this finding by dynamical simulations using a multiphase field model with obstacle potential for both purely kinetic and diffusive conditions. Generally, our results should provide insights on the dynamics of GB phase transitions, of which the complex phenomena associated with liquid metal embrittlement are an example.

Dynamics of grain boundary premelting.

The mechanical strength of a polycrystalline material can be drastically weakened by a phenomenon known as grain boundary (GB) premelting that takes place, owing to the so-called disjoining potential, when the dry GB free energy [Formula: see text] exceeds twice the free energy of the solid-liquid interface [Formula: see text]. While previous studies of GB premelting are all limited to equilibrium conditions, we use a multi-phase field model to analyze premelting dynamics by simulating the steady-state growth of a liquid layer along a dry GB in an insulated channel and the evolution of a pre-melted polycrystalline microstructure. In both cases, our results reveal the crucial influence of the disjoining potential. A dry GB transforms into a pre-melted state for a grain-size-dependent temperature interval around [Formula: see text], such that a critical overheating of the dry GBs over [Formula: see text] should be exceeded for the classical melting process to take place, the liquid layer to achieve a macroscopic width, and the disjoining potential to vanish. Our simulations suggest a steady-state velocity for this transformation proportional to [Formula: see text]. Concerning the poly-crystalline evolution, we find unusual grain morphologies and dynamics, deriving from the existence of a pre-melted polycrystalline equilibrium that we evidence. We are then able to identify the regime in which, due to the separation of the involved length scales, the dynamics corresponds to the same curvature-driven dynamics as for dry GBs, but with enhanced mobility.

Interplay between α(Ti) nucleation and growth during peritectic solidification investigated by phase-field simulations.

The properties of modern TiAl-based alloys with aluminum contents around 45 at.% critically depend on the as solidified α(Ti) grain structure. Commonly, a rather coarse grain structure is obtained if α(Ti) forms via the peritectic reaction '[Formula: see text]'. Phase-field simulations have been applied to perform a case study of grain structure formation during the early peritectic growth under unidirectional growth conditions. In the absence of foreign nucleation sites, the peritectic α(Ti) phase nucleates on the dendritic surface of the properitectic ß(Ti) phase. For typical values of the critical nucleation undercooling, coarse structures with large elongated grains are reproduced. A delicate interplay between nucleation and growth is predicted for reduced values of the critical undercooling. In this case, the alloy composition is found to play an additional role. An effective grain refinement by frequent nucleation is obtained, if potent nucleants can reduce the critical undercooling below the local growth undercooling. Complementary Scheil calculations and Bridgman experiments show that in situ precipitation of TiB(2) particles can be controlled by adequate boron addition. Both, numerical predictions and experiments confirm that these particles can act as effective nucleation agents and significantly reduce the grain size of α(Ti).

Screening for cytotoxic activity of extracts and isolated alkaloids from bulbs of Hippeastrum vittatum.

The dichloromethane and n-butanol extracts obtained from fresh bulbs of Hippeastrum vittatum (Amaryllidaceae), collected in Southern Brazil, were evaluated for their cytotoxic activity in vitro against five human cell lines (HT29 colon adenocarcinoma, H460 non-small cell lung carcinoma, RXF393 renal cell carcinoma, MCF7 breast cancer, and OVCAR3 epithelial ovarian cancer), using the sulphorhodamine B assay. Both extracts showed potential antiproliferative activity. From CH(2)Cl(2) fraction, three alkaloids were isolated: lycorine, vittatine and montanine. The two last compounds were submitted to the antiproliferative assay and the highest level of cytotoxicity was found for the alkaloid montanine.

Caracterización química de los aceites esenciales y extractos de especies mesoamericanas del género piper como nuevos recursos aromáticos / Chemical characterization of essencial oils and extracts Mesoamerican species of the genus piper as new resources aromatic

La familia Piperaceae comprnde 14 gneros y aproximadamente 700 especies, que están distribuidas en las zonas tropicales y subtropicales del mundo. En Guatemala se describen aproximadamente 88 especies de Piper distribuidas en diferentes regiones del país, de las cuales se encuentra muy poca información química y farmacológica. El presente estudio contribuye al estudio químico de las especies aromáticas más importantes del género Piper en Guatemala. Se identificaron 16 especies en tres departamentos de Guatemala: en Suchitepequez se encontraron cuatro especies (Piper umbellatum, P. oradendrum, P. patulum y P. jacquemontianum); en Alta Verapaz se encontraron 8 especies...

Potentiation of nitric oxide synthase expression by superoxide in interleukin 1 beta-stimulated rat mesangial cells.

Exposure of mesangial cells to superoxide, generated by the hypoxanthine/xanthine oxidase system or by the redox cycler 2,3-dimethoxy-1,4-naphthoquinone caused a concentration-dependent amplification of interleukin (IL)-1beta-stimulated nitrite production. The effect of superoxide was accompanied by an increase in inducible nitric oxide synthase (iNOS) protein and iNOS mRNA levels. Incubation of mesangial cells with superoxide alone did not induce iNOS expression. To elucidate whether the increase of iNOS expression is due to transcriptional upregulation we fused a 4.5-kb genomic iNOS fragment that contains the transcriptional start site of the rat iNOS gene to a luciferase reporter gene. In transient transfection studies, superoxide caused a 10-fold augmentation of iNOS promoter activity in IL-1beta-challenged mesangial cells. Our data identify superoxide as a co-stimulatory factor amplifying cytokine-induced iNOS gene expression and subsequent nitric oxide (NO) synthesis.

Restricting smoking at the University of Köln, Germany: a case study.

The effects of a new policy limiting smoking to separate, designated areas in School of Education buildings at the University of Köln, Germany, were analyzed. Although the majority (77%) of the 1,223 students surveyed did not expect the changed policy to affect their smoking habits, approximately 28% of the men and 30% of the women said they were smoking less at the university after the change went into effect. Ninety-one percent of the nonsmoking students and 68% of the smokers supported the new policy. Smoking rates among Köln students are not significantly different from those of the adult German population, where 34% of the women and 41% of the men are smokers. The findings in this study indicate that such a policy change may result in a net decrease in amount smoked and could be a successful intervention in countries where smoking rates are traditionally higher than they are in the United States.

Interactions between bilirubin and reactive oxygen species in liver microsomes and in human neutrophil granulocytes.

Bilirubin protects polyunsaturated fatty acids from lipid peroxidation, thus preventing damage by reactive oxygen species to cell membranes and proteins. On the other hand, such reactive oxygen species may contribute to the degradation and elimination of bilirubin. We therefore examined the interactions between bilirubin and reactive oxygen species. Bilirubin is decomposed in microsomes via a NADPH-independent process. This reaction appears to be mediated by H2O2 or by the hydroxyl radical since it is stimulated by exogenous H2O2 and by cytochrome P450 inducers, which increase H2O2 production in microsomes, and is inhibited by the hydroxyl radical scavenger sodium benzoate. These results suggest that cytochrome P450 may act as a peroxidase or as a Fenton catalyst in bilirubin degradation. On the other hand, bilirubin inhibits the NADPH consumption of microsomes as well as the NADPH oxidase activity of human neutrophil granulocytes and the resulting superoxide formation in these cells. This effect on superoxide concentration may be partially due to direct interaction between superoxide and bilirubin, since bilirubin reduces the superoxide concentration in a xanthine oxidase system. Bilirubin degradation is inhibited by superoxide dismutase suggesting that bilirubin may be oxidized in this system by the superoxide radical. The bilirubin-induced reduction in superoxide concentration in the supernatant of granulocytes suggests that hyperbilirubinemia may compromise immune function.

On the cardiac contractile, biochemical and electrophysiological effects of cantharidin, a phosphatase inhibitor.

Cantharidin concentration dependently increased the force of contraction in isolated guinea pig papillary muscles (1-100 microM). The positive inotropic effect is accompanied by a reduction in time to peak tension and relaxation time. Cantharidin did not exert a positive chronotropic effect in spontaneously beating right atria. L-type calcium channel currents of guinea pig cardiomyocytes were moderately increased by cantharidin (by about 20%), both at the whole-cell level (2 mM Ca2+) and at the single channel level (70 mM Ba2+). There was a correspondingly small increment of single channel availability. Additionally, a larger proportion of single-channel sweeps displayed high open probability-gating (so-called mode 2-gating). Cantharidin inhibited both type 1 and type 2A phosphatase activity in phosphatases purified from guinea pig ventricles [IC50 2.70 (2.06-3.53) and 0.13 (0.05-0.34) microM, n = 5-6, with 95% confidence intervals, respectively]. In isolated [32P]-labeled guinea pig ventricular cardiomyocytes, cantharidin (10 microM) increased the phosphorylation state of phospholamban (to 210% of control), the inhibitory subunit of troponin (to 155% of control), C-protein (to 156% control) and various additional proteins. It is concluded that the effects of cantharidin are likely mediated by increasing the phosphorylation state of several regulatory proteins. Furthermore, cantharidin might be an economical tool to investigate the function of phosphatases in model organ systems.