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Water Present (water + present)
Selected AbstractsDiffusion-controlled growth of wollastonite rims between quartz and calcite: comparison between nature and experimentJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2002R. Milke Abstract Growth rates of wollastonite reaction rims between quartz and calcite were experimentally determined at 0.1 and 1 GPa and temperatures from 850 to 1200 °C. Rim growth follows a parabolic rate law indicating that this reaction is diffusion-controlled. From the rate constants, the D,,-values of the rate-limiting species were derived, i.e. the product of grain boundary diffusion coefficient D, and the effective grain boundary width, ,. In dry runs at 0.1 GPa, wollastonite grew exclusively on quartz surfaces. From volume considerations it is inferred that (D,CaO,)/(D,SiO2,),1.33, and that SiO2 diffusion controls rim growth. D,SiO2, increases from about 10,25 to 10,23 m3 s,1 as temperature increases from 850 to 1000 °C, yielding an apparent activation energy of 330±36 kJ mol,1. In runs at 1 GPa, performed in a piston-cylinder apparatus, there were always small amounts of water present. Here, wollastonite rims always overgrew calcite. Rims around calcite grains in quartz matrix are porous and their growth rates are controlled by a complex diffusion-advection mechanism. Rim growth on matrix calcite around quartz grains is controlled by grain boundary diffusion, but it is not clear whether CaO or SiO2 diffusion is rate-limiting. D,, increases from about 10,21 to 10,20 m3 s,1 as temperature increases from 1100 to 1200 °C. D,SiO2, or D,CaO, in rims on calcite is c. 10 times larger than D,SiO2, in dry rims at the same temperature. Growth structures of the experimentally produced rims are very similar to contact-metamorphic wollastonite rims between metachert bands and limestone in the Bufa del Diente aureole, Mexico, whereby noninfiltrated metacherts correspond to dry and brine-infiltrated metacherts to water-bearing experiments. However, the observed diffusivities were 4 to 5 orders of magnitude larger during contact-metamorphism as compared to our experimental results. [source] Aqueous versus non-aqueous salt delivery strategies to enhance oral bioavailability of a mitogen-activated protein kinase-activated protein kinase (MK-2) inhibitor in ratsJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 1 2009Po-Chang Chiang Abstract A potent pyridine-containing MK2 inhibitor has recently been internally discovered. In pre-clinical dosing, the low solubility of the neutral form limited oral bioavailability and dose escalation in toxicity studies. A mesylate salt was developed as part of a formulation strategy to enhance both oral bioavailability and dose escalation orally in pre-clinical rat studies. Several non-aqueous systems were used to deliver the mesylate salt, which resulted in varied oral bioavailability. It was found that administration of an aqueous chaser immediately after dosing drastically increased the oral bioavailability of the salt. This finding implies that the quantity of water present in vivo is an important consideration when evaluating salts of free bases with low aqueous solubility in pre-clinical in vivo rat models where limited aqueous vehicle may be presented. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:248,256, 2009 [source] Cooperative interaction of n -butylammonium ion with 1,3-alternate tetrapropoxycalix [4]arene: NMR and theoretical studyMAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2008Jaroslav K Abstract The interaction of 1,3-alternate tetrapropoxycalix[4]arene (1) with n -butylammonium ion (2) in CD2Cl2 was examined using 1H, 13C and 14N NMR spectroscopy and DFT (density functional theory) calculations. NMR shows that 1 forms with 2 an equimolecular hydrogen-bonded complex with the equilibrium constant 5.91 × 103 l/mol at 296 K. The structure of the complex can be shown to be asymmetric at 203 K, with 2 interacting by hydrogen bonds with the two ethereal oxygen atoms of one half of 1 and with the , system of the other half, but is rapidly averaged to an apparent C4h symmetry by chemical exchange at higher temperatures. Using two related but independent techniques based on transverse and rotating-frame proton relaxation, it is shown that only an intermolecular exchange of 2 between the bound and free states takes place, in contrast to previously studied interaction of 1 with H3O+. Its correlation time is 0.169 ms. It is shown by DFT calculations that such swift exchange is not possible without a cooperative interaction of both 2 and 1 with several molecules of water present. Similarities and contrasts between the exchange processes of 2 and H3O+ bound to 1 are discussed, in particular with respect to the apparent quantum tunneling of the latter inside the molecule of the complex. Copyright © 2008 John Wiley & Sons, Ltd. [source] Development of graphene layers by reduction of graphite fluoride C2F surfacePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11-12 2009A. V. Okotrub Abstract We studied a possibility of reduction of the surface of graphite fluoride obtained by fluorination of highly oriented pyrolytic graphite (HOPG) by a gaseous mixture of BrF3 and Br2. X-ray diffraction (XRD) revealed a layered structure of the fluorinated product being a second-stage intercalate due to a presence of bromine molecules between the fluorinated graphite layers. Scanning tunneling microscopy and spectroscopy showed that the "old" surface of graphite fluoride (exposed to the ambient air) has the graphite-like structure, while the fresh cleaved surface is non-conductive. Therefore, the outer layers of graphite fluoride can be reduced by water present in the laboratory atmosphere. The sample was treated by H2O vapor to confirm that. The reduction was controlled by Raman spectroscopy using intensity of the 1360 and 1580,cm,1 bands. The energy dependent photoelectron spectroscopy was used for estimation of thickness of the reduction layer, which was found, does not exceed 2,3 graphite layers. The obtained results indicate the possibility of synthesis of graphene layers on dielectric fluorinated graphite matrix. [source] Selective Capture of Water Using Microporous Adsorbents To Increase the Lifetime of LubricantsCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 3 2009Eng-Poh Ng Abstract Long live lubricants: The selective capture of water from lubricants using nanosized microporous aluminophosphate (AEI) and aluminosilicate materials was studied. Nearly 98,% of the moisture was removed from the lubricating oil under ambient conditions, resulting in a significant improvement in the lubricating service lifetime. Moreover, both the lubricant and the microporous sorbents can be recovered and reused. The selective capture of water from lubricants using nanosized microporous aluminophosphate and aluminosilicate materials was studied with an aim to increase the lifetime of the lubricating mineral oil. The amount of water present in oxidized lubricating oil before and after treatment with microporous materials was studied by FTIR spectroscopy and determined quantitatively using the Karl Fischer titration method. Nanosized aluminophosphate revealed a high selectivity for water without adsorbing other additives, in contrast to nanosized aluminosilicates which also adsorb polar oxidation products and ionic additives. About 98,% of the initial moisture could be removed from the lubricating oil under ambient conditions, resulting in a significant improvement in the lubricating service lifetime. Moreover, no by-products are formed during the process and both the lubricant and the sorbents can be recovered and reused, thus the method is environmentally friendly. [source] Zoogeography of the southern African ascidian faunaJOURNAL OF BIOGEOGRAPHY, Issue 12 2004Carmen Primo Abstract Aim, To describe the biogeography of the ascidian fauna of southern Africa, to compare the results obtained with those reported for other fauna and flora of the same region, and to speculate about the origin of ascidians in the region. Location, Southern Africa extending over 4000 km from Mossāmedes (15° S,12° E) to Inhaca Island (26°30, S,33° E), including Vema Seamount (31°40, S,8 °20, E), Amsterdam-Saint Paul Islands (38° S,77°30, E) and the Tristan-Gough Islands (38° S,12°20, W). Methods, We constructed a presence/absence matrix of 168 species for 26 biogeographical divisions, 21 classical biogeographical regions described by Briggs (Marine zoogeography, McGraw-Hill, New York, 1974) and five provinces within the southern African region. We considered the following limits and divisions into provinces for the southern African region: Namibia, Namaqua, Agulhas and Natal as proposed by Branch et al. (Two oceans. A guide to the marine life of southern Africa, David Philip Publishers, 1994), and the West Wind Drift Islands province (WWD) according to Briggs (Global biogeography, Elsevier Health Sciences, Amsterdam, 1995). To examine the biogeographical structure, species and divisions were classified using cluster analysis (based on UPGMA as the aggregation algorithm) with the Bray,Curtis index of similarity. This classification was combined with MDS ordination. Main conclusions, Four main groups were obtained from the analysis of affinities among species: (1) species present in the WWD, separated by a high percentage of endemisms and a low number of species with a southern African distribution. Moreover, in the light of the species distribution and the results of further analysis, which revealed that they are completely separated and not at all related to the southern African region, it appears that there are no close relationships among the different islands and seamounts of the West Wind Drift Island province. This province was therefore removed from the remaining analyses; (2) species with a wide distribution; (3) species of colder waters present in Namaqua and Agulhas provinces, a transitional temperate area in which gradual mixing and replacement of species negate previous hypotheses on the existence of a marked distributional break at Cape of Good Hope; (4) species of warmer waters related to Natal province. The classification into biogeographical components was dominated by the endemic (47%), Indo-Pacific (25%) and cosmopolitan (13%) components. The analysis of affinities among biogeographical areas separated Namibia from the rest of the southern African provinces and showed that it was related to some extent to the Antarctic region because of the cold-temperate character of the province and the low sampling effort; Namaqua, Agulhas and Natal were grouped together and found to be closely related to the Indo-West Pacific region. In general, our results were consistent with those obtained for other southern African marine invertebrates. The frequency distribution of solitary/colonial strategies among provinces confirmed the domination of colonial organisms in tropical regions and solitary organisms in colder regions. Finally, we speculate that the southern African ascidian fauna mainly comprises Indo-Pacific, Antarctic and eastern Atlantic ascidians. [source] | ||||||||||