117,612 research outputs found
A Critical Analysis of the Hand and Othmer-Tobias Correlations
No full textCarniti, P., Cori, L. and Ragaini, V., 1978. A Critical Analysis of the Hand and Othmer-Tobias Correlations. Fluid Phase Equilibria, 2: 39-47. The Hand (H) and Othmer-Tobias (OT) correlations are extensively analyzed on 83 aqueous and 26 non-aqueous ternary systems. Twenty solutropic systems are also included. 65% and 58% of the systems give a linear correlation coefficient greater than 0.99 for H and OT respectively. An analysis of the sensitivity to systematic or random errors demonstrates the H correlation to be highly insensitive. A remarkable insensitivity, although not completly for some systematic errors, is also demonstrated for the OT correlation. However there is sufficient proof that they are both unsuitable as a check of experimental data, even though they are used for this purpose. The relation, not necessarily linear, derived from the H correlation, log(x32/x22) vs. log(x31/x11) is useful in locating the plait point
Studio di una malacofauna pliocenica raccolta in loc. Valle S. Giovanni-Suese (Comune di Collesalvetti-Li). Nota preliminare.
No full textIl genere Schizaster nel Miocene maltese
No full textThe genus Schizaster in the Miocene of the Maltese islands. We have examined some specie of the genus Schizaster from the «Globigerine Limestone» of Maltese islands (Malta and Gozo).
The taxonomic study make use of biometrical and biometrical-statistical methods based on analysis of the following linear measurements: the specimen lenght (L), the anterolateral ambulacra lenght (aa), the posterolateral ambulacra lenght (ap) and of the index from these obtained. We have carried out our bivariate analysis by scatter diagrams reporting the reduced major axis of every sample
Co/SiO2 for Fischer-Tropsch Synthesis: comparison among different preparation methods
No full textAn extensive sludy of different preparation methods for Co/SiO2 catalysis is reported in the present paper. In addition to the conventional impregnation, other more innovative methods are tested together with the sol-gel process, methods involving the use of ultrasound and of particular metal precursors or solvents. The prepared samples are fully characterized and tested in the CO hydrogenation
Ruthenium complexes with polymeric alpha-diimine containing poly [aryliminoacenaphthene] fragments
No full textalpha-diimine/Ru, Pd and Ni complexes are very active homogeneous catalysts for several reactions. In particular bis(arylimino)acenaphthene (Ar-BIAN) compounds have been widely studied in polymerizations and reactions involving the use of carbon monoxide. We developed a method for the synthesis of oligomeric Ar-BIAN (oligo-BIAN) from acenaphthenequinone and 4,4'-methylenedianiline and for their use as building blocks in polyamide synthesis (poly-BIAN).
Such polymeric Schiff bases could be useful both for developing a heterogenized catalyst and for developing multi-nuclear organometallic species that are known to be good catalysts in olefins polymerization reactions.
The investigation of the reaction between [Ru(CO)3Cl2(THF)] and the synthesized macromolecular Schiff bases showed different coordination modes of the poly-BIAN with respect to the oligo-BIAN and the non-polymeric tolyl BIAN, with the oxygen
atom of the terephthaloyl connecting unit becoming the actual binding site in the former case
Warm-water mollusc assemblages from northern Chile (Mejellones Penisula): new evidence for permanent El Niño-like conditions during the Pliocene warmth?
No full textThough results have been controversial, understanding the tropical Pacific climatic state during the Pliocene warm interval (ca. 4.5-3.0 Ma) is crucial if insight is to be gained into the dynamic processes of present and future global warming. In the multi-proxy effort to reconstruct ancient climates, a critical role can be played by palaeoclimatic evidence provided by the spatial and temporal distribution of temperature-sensitive marine molluscs. Shallow-water strata of the Mejillones Peninsula, northern Chile (23°S), contain dense faunal assemblages in which molluscs exclusive to, or characteristic of, Pliocene deposits (Chlamys simpsoni, Chlamys vidali, Chorus blainvillei, Concholepas nodosa, Fusinus remondi, Herminespina mirabilis) coexist with surprisingly abundant and varied populations of extant warm-water species (Bulla punctulata, Cerithium stercusmuscarum, Olivella sp., Turbo cf. fluctuosus, Anomia peruviana, Argopecten ventricosus, Donax peruvianus, Dosinia ponderosa, Mexicardia procera, Undulostrea megodon), most of which have their current southern zoogeographic limit at 6°S. These tropical elements are reliable indicators of nearshore marine conditions and their abundant occurrence implies that: (i) sea surface temperatures (SST) along the northern Chile coast were at least 2°C warmer in the mid-Pliocene than at present; (ii) these very different conditions lasted long enough to allow stable colonization of the area. Such a significantly warmer SST pattern strongly resembles general climatic conditions accompanying modern El Niño events, when warm tropical waters propagate southward along the western margin of South America; this supports the existence in this area of persistently El Niño-like conditions during the mid-Pliocene
Kinetic of esterification of diluted acetic acid with pure 2-ethyl-1-hexanol
No full textThe esterification of diluted acetic acid with pure 2-ethyl-1-hexanol is a purification process, involving a liquid-liquid-solid catalyst system, where streams of water containing small amount of acid are purified and the acetic acid is converted to a high commercial value ester at the same time. This process has been studied in a wide range of acetic acid (AA) concentration (6-15%, w/w). A maximum final conversion of 67% can be reached at 372 K. A mathematical model is here proposed: this takes into account all the diffusional and reactive steps between the aqueous and organic phases and from the latter into the pores of the solid catalyst. The relative importance of the different steps is fully discussed
Shell structure, taphonomy, and mode of life of a Pleistocene ostreid from Ecuador.
No full textCrassostrea specimens recognized in the Pleistocene sediments of Ecuador represent the first fossil thick-shelled species of this genus in the Pacific South America. The specimens come from the Pleistocene Jama Formation exposed along the coastal cliffs of central Ecuador in the Esmeraldas-Caraquez Basin. The middle stratigraphie unit of this formation (the Punta Ballena Member) is about 100 m thick and composed of eight superposed, unconformity-bounded depositional sequences (PB1/PB8) with a highfrequency cyclicity (40 ky The Crassostrea specimens collected in the middle of the PB5 fining-upward sequence may belong to a new species of this genus. The oyster concentration is a lens-shaped bank up to 60-70 cm thick and a few meters long where thick-shelled, large-sized, and elongated individuals in general good state of preservation are embedded in a soft, muddy to fine-grained sandy matrix. They display a high degree of packing and locally a bioclast-supported biofabric. Some specimens consist of disarticulated valves oriented both convex-up and convex-down whereas conjoined shells are predominant in number and arranged with different orientations from nearly horizontal to oblique. A few complete shells show a vertical position with the commissural plane more or less perpendicular to the bottom and the ligamental area pointing downwards. Fragmentation and abrasion are scarce, signs of encrustation and bioerosion are rare and occur only on the external surface of few valves. SEM investigation on the shell micro structure points out a thin outer prismatic layer composed of compact, closely joined calcific prisms, irregularly polygonal in section and obliquely or nearly perpendicular oriented to the outer surface (regular simply prismatic, RSP The underlying shell shows alternating thin and thick layers. The thin layers consist of continued sheets oriented nearly parallel or oblique to the valve surface and arranged as "tiles of a roof (regularly foliated, RF) whereas the thick layers display a severely re-crystallized structure originally composed of parallel/ subparallel calcific blades interconnected by smaller calcific leaflets. The large amount of void spaces interlocked between blades and leaflets accounts for the original "chalky" appearance of the porous structure (crossed lamellar, CL The elongated and flat shape of the valves along with the elongate and triangular shape of the ligamental area are typical morphological attributes of the "secondary soft-bottom dwellers" with vertical life posture. Porous chalky deposits have been interpreted as an adaptive strategy to prevent the sinking in the soft bottom, but they may have been also used as a mechanism to increase shell thickness deterring prédation by fully marine organisms. We infer that individuals lived as seminfaunal with a vertical posture of life within a soft bottom of shallow-water environments (lower shoreface to inner shelf) and interested by dislodging, before or after death, due to storm-induced wave/current action
Tectonic controls on sequence stacking pattern and along-strike architecture in the Pleistocene Mejillones Formation, northern Chile: implications for sequence stratigraphic models.
No full textIn the Mejillones Formation, a shallow-marine Pleistocene succession of northern Chile, the cyclic stratigraphic record is the result of the complex interaction of regional uplift, glacio-eustasy, local tectonics, sediment supply, and sedimentary processes. Stratal geometries, characteristics of sedimentary facies, and nature of sequence-bounding unconformities have been investigated to evaluate the influence of: (i) intrabasinal, short-term normal faulting on both along-strike variations in sequence architecture and genetic complexity of key stratal surfaces; and (ii) long-term regional uplift on sequence stacking pattern. The stratigraphic succession, dissected by small-displacement (few meters) normal faults striking obliquely with respect to the palaeo-shoreline trends, displays systematic variations in sequence architecture and the nature of bounding surfaces across them. Indeed, depending on position with respect to the fault plane, two basic types of internal organisation can be recognised in the examined shallow-marine, almost clastic-starved sequence. Within grabens it consists of a siliciclastic-rich transgressive systems tract (TST), which is bounded beneath by a transgressively modified, Glossifungites-demarcated sequence boundary (SB/RS), overlain by a mollusc-bearing falling-stage systems tract (FSST). The erosional downlap surface that separates the TST from the FSST is the regressive surface of marine erosion (RSME). On the footwall crests the combination of marine regressive erosion, during falls in relative sea-level, and uplift has resulted in complete removal of the sediments of the TST from these sites, leading to the formation of a tectonically enhanced basal unconformity composed of the RSME superimposed onto the previous SB/RS (SB/RS/RSME). The prominent lateral change in component units (systems tracts) and nature of bounding surfaces within the studied sequence is directly related to the presence of normal faults and indicates that fault activity had a major impact on the sequence stratigraphic evolution of the Mejillones Formation, enhancing subsidence within the grabens and promoting unconformities in the horsts. Overall, the Mejillones Formation records a long-term sea-level fall driven by the contemporaneous regional uplift, punctuated by repeated, high-frequency eustatic sea-level changes. The effect of this superimposition was that glacio-eustatic sequences were displaced progressively downward and basinward and stacked in a distinct downstepping, tectonically enhanced falling-stage sequence set, which reflects basin-wide loss in accommodation space. The sequence set is underlain by a composite RSME that becomes progressively younger basinward and is made up by the lateral and down-dip connection of a series of lower-rank sequence boundaries including hanging-wall SB/RSs and footwall SB/RS/RSMEs of successive sequences
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