7,296 research outputs found
Sprachgebrauch und Sprachbewusstsein: Implikationen der empirischen Linguistik für die Sprachtheorie
Get PDFAn experimental study on the pressure dependence of viscosity in silicate melts
No full textThe effect of pressure on melt viscosity was investigated for five compositions along the join An(CaAl2Si2O8)–Di(CaMgSi2O6) and four alkali silicates containing lithium, sodium, and potassium in constant ratio of ∼ 1:1:1, but alkali-silica ratios are varying. The experiments were performed in an internally heated gas pressure vessel at pressures from 50 to 400 MPa in the viscosity range from 108 to 1011.5 Pa⋅s using parallel plate viscometry. The polymerized An composition shows a negative pressure dependence of viscosity while the other, more depolymerized compositions of the join An–Di have neutral to positive pressure coefficients. The alkali silicates display neutral to slightly positive pressure coefficients for melt viscosity. These findings in the high viscosity range of 108–1011 Pa⋅s, where pressure appears to be more efficient than in low viscous melts at high temperature, are consistent with previous results on the viscosity of polymerized to depolymerized melts in the system NaAlSi3O8–CaMgSi2O6 by Behrens and Schulze [ H. Behrens and F. Schulze, Am. Mineral. 88, 1351 (2003) ]. Thus we confirm that the sign of the pressure coefficient for viscosity is mainly related to the degree of melt polymerization in silicate and aluminosilicate melts.DFG Grant n.°BE1720/9Published044504-142.3. TTC - Laboratori di chimica e fisica delle rocceJCR Journalope
Viscosity of pantelleritic and alkali-silicate melts: Effect of Fe redox state and Na/(Na+K) ratio
No full textThe viscosity of two series of synthetic alkali silicates, corresponding to Al-bearing pantelleritic and Al-free tri-silicate compositions, has been investigated as a function of temperature, iron redox and Na/(Na + K) ratio. Low temperature (708–1000 K) viscosities were determined by the micropenetration technique in the 109.6 to 1013.6 Pa s range. The effect of Fe2 +/Fetot, from 0.15 to 0.86, was explored for [Na/(Na + K)] ratios from 0 to 1. The results demonstrate a strong decrease of viscosity with the replacement of Na for K in both the Al-bearing and Al-free compositions. In the Al-bearing pantelleritic glasses (Ebu) the viscosity as well as the activation energy for viscous flow decrease with an increase of Fe2 +/Fetot from 0.15 to 0.76. In contrast, no measurable changes in viscosity occur in the Al-free tri-silicate glasses (NFS and KFS) as Fe2 +/Fetot ratio varies from 0.15 to 0.86. The comparison of the pantelleritic glasses with peralkaline compositions from the literature stresses the strong influence of iron redox on the overall viscosity of such melts. This suggests that the contribution of iron species should be accounted for in the calculation of agpaitic index (AI) if magma Fe3 + contents are known.
One peculiarity of peralkaline magmas is the excess of alkali to alumina, which generally results in lower viscosities of pantelleritic liquids compared with more common metaluminous rhyolites and exerts a primary control of the rheological behaviour of these melts.
Our new viscosity data, combined with existing literature, allow more accurate constraints on the nature and eruption of the pantelleritic magmas. Moreover, the present experimental study can be used to improve the viscosity models that mostly do not take in consideration parameters as iron redox in the viscosity prediction
Dynamic Phase Diagram of a Nonionic Surfactant Lamellar Phase
No full textThe dynamic phase diagram of triethylene glycol dodecyl ether (C12E3) in D2O was determined for 40, 50, and 60 wt % of surfactant. The shear flow effect on the nonionic lamellar phase was investigated as a function of temperature and concentration. The transition from planar lamellae (L-alpha)-to-multilamellar vesicles (MLVs) was characterized by means of rheology, rheo-small-angle neutron and light scattering. New insight into the nature of the transition region between L-alpha and the MLVs state is provided. A disorder-order transition was also observed by SANS. This is attributed to a transition from disordered MLVs to a close-packed array of MLV's with slightly higher order than before. Moreover flow instability was observed in the shear-thickening regime at 40 degrees C
CO line emission from galaxies in the Epoch of Reionization
No full textWe study the CO line luminosity (LCO), the shape of the CO spectral line energy distribution (SLED), and the value of the CO-to-H2 conversion factor in galaxies in the Epoch of Reionization (EoR). For this aim, we construct a model that simultaneously takes into account the radiative transfer and the clumpy structure of giant molecular clouds (GMCs) where the CO lines are excited. We then use it to post-process state-of-the-art zoomed, high resolution (30 pc), cosmological simulation of a main-sequence (M* ≈ 1010M⊙, SFR ≈ 100M⊙ yr-1) galaxy, 'Althæa', at z ≈ 6.We find that the CO emission traces the inner molecular disc (r ≈ 0.5 kpc) of Althæa with the peak of the CO surface brightness co-located with that of the [C II] 158 μm emission. Its LCO(1-0) = 104.85 L⊙ is comparable to that observed in local galaxies with similar stellar mass. The high (Σgas ≈ 220M⊙ pc-2) gas surface density in Althæa, its large Mach number (M≈ 30) and the warm kinetic temperature (Tk ≈ 45 K) of GMCs yield a CO SLED peaked at the CO(7-6) transition, i.e. at relatively high-J and a CO-to-H2 conversion factor αCO ≈ 1.5M⊙(K km s-1 pc2)-1 lower than that of the Milky Way. The Atacama Large Millimeter/submillimeter Array observing time required to detect (resolve) at 5σ the CO(7-6) line from galaxies similar to Althæa is ≈13 h (≈38 h)
MBE grown GaAs on GaAs (001): UHV X-ray diffraction measurements
No full textMBE grown gallium arsenide crystals with (001) orientation were investigated with a three-crystal X-ray diffractometer under UHV conditions. In the region of total external reflection (Q<0.3AA-1) no Kiessig fringes occur and hence no electron density difference between the substrate and the MBE layer exists. In the tails of the 004 Bragg reflection, modulations are observed. They are ascribed to a phase shift at the substrate-layer interface originating from a misfit parallel to the surface normal or a thin intermediate layer. The method can be applied to other thin film systems like oxidized or buried layers
Viscosity of flux-rich pegmatitic melts
No full textViscosity experiments were conducted with two flux-rich pegmatitic melts PEG0 and PEG2. The Li2O, F, B2O3 and P2O5 contents of these melts were 1.04, 4.06, 2.30 and 1.68 and 1.68, 5.46, 2.75 and 2.46 wt%, respectively. The water contents varied from dry to 9. 04 wt% H2O. The viscosity was determined in internally heated gas pressure vessels using the falling sphere method in the temperature range 873-1,373 K at 200 and 320 MPa pressure. At 1,073 K, the viscosity of water-rich (~9 wt% H2O) melts is in the range of 3-60 Pa s, depending on the melt composition. Extrapolations to lower temperature assuming an Arrhenian behavior indicate that highly fluxed pegmatite melts may reach viscosities of ~30 Pa s at 773 K. However, this value is a minimum estimation considering the strongly non-Arrhenian behavior of hydrous silicate melts. The experimentally determined melt viscosities are lower than the prediction of current models taking compositional parameters into account. Thus, these models need to be improved to predict accurately the viscosity of flux-rich water bearing melts. The data also indicate that Li influences significantly the melt viscosity. Decreasing the molar Al/(Na + K + Li) ratio results in a strong viscosity decrease, and highly fluxed melts with low Al/(Na + K + Li) ratios (~0. 8) have a rheological behavior which is very close to that of supercritical fluids. © 2010 Springer-Verlag
Aqueous Humor Concentrations of Topically Administered Caspofungin in Rabbits
No full textBackground: The echinocandin caspofungin (CAS) is a novel antifungal drug with fungicidal in vitro activity against all Candida spp., which are the most frequent cause of fungal keratitis. Penetration of CAS through the cornea into the aqueous humor after topical administration was investigated. Methods: A CAS solution with a concentration of 7 mg/ml was applied onto each rabbit's cornea. Drug application after corneal epithelium abrasion was processed in different time intervals: single application with aqueous humor sampling after 1 and 2 h. In addition, after continuous application of CAS every 30 min, aqueous humor concentrations of CAS after 1, 2 and 5 h were analyzed by liquid-chromatography tandem mass spectrometry. Results: Topical administration of CAS without corneal epithelium abrasion resulted in no detectable amounts of the drug in the aqueous humor. However, with corneal abrasion, after a single application, levels of 2.16 +/- 1.57 mu g/ml (n = 6) were reached after 1 h and then decreased to 1.76 +/- 0.88 mu g/ml (n = 2) after 2 h. After serial application every 30 min, the following intracameral levels of CAS were detected: after 1 h, 2.11 +/- 1.09 mu g/ml (n = 6); after 2 h, 4.94 +/- 1.80 mu g/ml (n = 5), and after 5 h, 3.45 +/- 2.11 mu g/ml (n = 6). Conclusion: In the aqueous humor, therapeutic drug levels can be reached that cover the MICs of most fungi after epithelial abrasion. To achieve a sustained high level of CAS as an effective antifungal therapy for corneal keratitis, CAS should be administered topically every 30 min after removal of the corneal epithelium. Copyright (C) 2008 S. Karger AG, BaselBMBF-NBL
Aqueous humor concentration of voriconazole after topical administration in rabbits
No full textObjectives Voriconazol is a triazole antifungal drug with in vitro fungicidal activity against all Candida spp., Fusarium spp. and Aspergillus spp. which are frequent causes of fungal keratitis depending on geographic location. We investigated the penetration of voriconazole through the cornea into the aqueous humor (AH) after topical administration. Methods A 1% voriconazole solution was applied onto each rabbit's cornea. Topical drug application was processed at different time intervals: single drug application with AH sampling after 30 min, 1 h, 2 h, 3 h and 6 h. In addition, we evaluated AH samples after repeated topical application of voriconazole every 30 min after 1, 2, 4 and 6 h. Furthermore, after repeated drug application every hour, we analyzed voriconazole concentration after 2, 3, 4 and 6 h. All samples were analyzed by high-performance liquid chromatography (HPLC)-UV. Results A single application showed a maximum peak in AH of 3.58 mu g/ml (N=9) after 30 min. Within 3 h the concentration decreased to 0.04 mu g/ml (N=11). Application of voriconazole every half an hour revealed a peak value of 6.73 mu g/ml (N=10) after 2 h; after 4 h the value decreased to 6.19 mu g/ml (N=10) and was constant after 6 h (6.12 mu g/ml, N=6). When administrated every hour, only lower AH concentrations of voriconazole were reached with a maximum level of 2,06 mu g/ml (N=8) after four hours. Conclusion In AH, therapeutic drug levels that cover the minimum inhibitory concentrations (MIC) of most fungi can be reached. To achieve a sustained high level of voriconazole as an effective antifungal therapy for corneal keratitis, voriconazole should be topically administered every 30 min
Welding and Lung Cancer in a Pooled Analysis of Case-Control Studies
No full textThe Cancer de Pulmón en Asturias Study was supported by the Instituto Universitario de Oncología, Universidad de Oviedo, Asturias, the Fondo de Investigación Sanitaria, and the Ciber de Epidemiología y Salud Pública, SpainKendzia, B., Behrens, T., Jöckel, K.-H., Siemiatycki, J., Kromhout, H., Vermeulen, R., Peters, S., Gelder, R.V., Olsson, A., Brüske, I., Wichmann, H.-E., Stücker, I., Guida, F., Tardón, A., Merletti, F., Mirabelli, D., Richiardi, L., Pohlabeln, H., Ahrens, W., Landi, M.T., Caporaso, N., Consonni, D., Zaridze, D., Szeszenia-Dabrowska, N., Lissowska, J., Gustavsson, P., Marcus, M., Fabianova, E., Mannetje, A., Pearce, N., Tse, L.A., Yu, I.T.-S., Rudnai, P., Bencko, V., Janout, V., Mates, D., Foretova, L., Forastiere, F., McLaughlin, J., Demers, P., Bueno-De-Mesquita, B., Boffetta, P., Schüz, J., Straif, K., Pesch, B., Brüning, T
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