Chemical enrichment

The ocean is host to a variety and quantity of inorganic raw materials equal to or surpassiag the resources of these materials available on land. Inorganic raw materials are defined here as any mineral deposit found ia the marine environment. The mineral resources are classified generally as iadustrial minerals, mineral sands, phosphorites, metalliferous oxides, metalliferous sulfides, and dissolved minerals and iaclude geothermal resources, precious corals, and some algae. The resources are mosdy unconsoHdated, consoHdated, or fluid materials which are chemically enriched ia certain elements and are found ia or upon the seabeds of the continental shelves and ocean basias. These may be classified according to the environment and form ia which they occur (Table 1) and with few exceptions are similar to traditional mineral deposits on land. 

For the samples of high C concentrations, obtained by a chemical enrichment of coaly shales, the technique was developed, which uses in addition the CK analytical line intensity to correct interelernent effects. The application of this correction allowed to reduce errors in determining the studied element concentrations up to an acceptable level. The cai bon content was determined over the range 1 to 100 %. 

Fig. 1. Left panel Demonstration that SNela have contributed to the chemical enrichment for stars that are kinematically selected to trace the thick disk (i.e. knee in the trend for [O/Fe]). Figure taken from [4], Thick disk stars are represented by filled symbols (circles from [4] and triangles from [16]), thin disk by open symbols (circles from [4] and triangles from [16]), and halo stars by (from [16]). Right panel Shows the kF-velocity as a function of [Fe/H] for stars kinematically selected to be thin (open circles) or thick (filled circles) disk stars. Data taken from [3] and Bensby et al. submitted. This plot establishes that metal-rich stars can also have high velocities perpendicular to the plane (sometimes taken as an evidence for the star to belong to the thick disk)...

Heavy Elements and Chemical Enrichment in Globular Clusters... 

Abstract. We present preliminary results of an extensive low and high-resolution ESO-VLT spectroscopic survey of Subgiant stars in the stellar system uj Centauri. Basing on infrared Ca II triplet lines we derived metallicities and radial velocities for more than 110 stars belonging to different stellar populations of the system. The most metal rich component, the SGB-a, appears to have metallicity [Fe/H] -0.5. Moreover, SGB-a stars have been found to stray from the dynamical behaviour of the bulk population. Such evidence adds new puzzling questions on the formation and the chemical enrichment history of this stellar system. 

The growing scenario for the Bulge is pointing toward an early formation and a rapid chemical enrichment, as for the Galactic Halo but possibly at higher star formation rate. 

Future work [7] will include a modeling of phase-space variations of a elements in galaxy halos and their satellites, using the chemical enrichment code of [10]. 

Abstract. We have studied the effects of an hypothetical initial generation made only of very massive stars (M > 100M , pair-creation SNe) on the chemical and photometric evolution of spheroidal systems. We found that the effects of Population III stars on the chemical enrichment is negligible if only one or two generations of such stars occurred, whereas they produce quite different results from the standard models if they continuously formed for a period not shorter than 0.1 Gyr. In this case, the results produced are at variance with the main observational constraints of ellipticals such as the average [< a/Fe > ] ratio in stars and the color-magnitude diagram. 

In this work, a detailed kinetic model for the Fischer-Tropsch synthesis (FTS) has been developed. Based on the analysis of the literature data concerning the FT reaction mechanism and on the results we obtained from chemical enrichment experiments, we have first defined a detailed FT mechanism for a cobalt-based catalyst, explaining the synthesis of each product through the evolution of adsorbed reaction intermediates. Moreover, appropriate rate laws have been attributed to each reaction step and the resulting kinetic scheme fitted to a comprehensive set of FT data describing the effect of process conditions on catalyst activity and selectivity in the range of process conditions typical of industrial operations. 

Middle-sized stars, between about 1 and 8 M , undergo complicated mixing processes and mass loss in advanced stages of evolution, culminating in the ejection of a planetary nebula while the core becomes a white dwarf. Such stars are important sources of fresh carbon, nitrogen and heavy elements formed by the slow neutron capture (s-) process (see Chapter 6). Finally, small stars below 1 M have lifetimes comparable to the age of the Universe and contribute little to chemical enrichment or gas recycling and merely serve to lock up material. 

Stellar evolution has consequences in the development of luminosity and colours of stellar populations, as well as chemical enrichment. Boissier and Prantzos (1999) have produced a more-or-less classical model of the evolution of the Milky Way, making a detailed study of this aspect, known as chemo-photometric evolution , using an IMF similar to the Kroupa-Scalo function in Chapter 7 this detail is significant because the Salpeter(O.l) function often used has a smaller contribution from stars of around solar mass which dominate the light at late times. The chemical evolution results are combined with metallicity-dependent stellar isochrones, synthetic stellar spectra by Lejeune et al. (1997) and a detailed treatment of extinction by dust. Some of their results are shown in Fig. 8.39. 

Pagel, B.E.J. 2002, in R. Fusco-Femiano F. Matteucci (eds.), Chemical Enrichment of Intracluster and Intergalactic Medium, ASP Conf. Series, 253,489. 

Chemical enrichment and class fractionation procedures vary from laboratory to laboratory. Thus, no universal method for further enrichment and fractionation exists. However, the following provides some specific examples of commonly used... 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

Although the release of large numbers of these highly chemically enriched particles may have profound health and environmental consequences, the published literature contains virtually no data characterizing the distribution, physical properties, chemical composition, and source terms of a broad range of important primary pollutants emitted in submicrometer particles. 

Chemical enrichment of aerosols. In Figure 4 we plot the relative concentrations of W, V, U, and As in particles collected in stack and at the ESP outlet location with the 8-stage impactors vs equivalent aerodynamic diameter (d5o). 

We have further applied these techniques to investigate the chemical modification of aerosols by a modern flue-gas desulfurization system. This study confirms our earlier work with a high-energy Venturi wet scrubber system, in which we observed high chemical enrichment of aerosols from evaporative processes. 

We can attempt to apply the same type of model to the H2S data, however there are two additional unknown factors involved. First, we do not have a measurement of the sea surface concentrations of H2S. Second, the piston velocity of H2S is enhanced by a chemical enrichment factor which, in laboratory studies, increases the transfer rate over that expected for the unionized species alone. Balls and Liss (5Q) demonstrated that at seawater pH the HS- present in solution contributes significantly to the total transport of H S across the interface. Since the degree of enrichment is not known under field conditions, we have assumed (as an upper limit) that the transfer occurs as if all of the labile sulfide (including HS ana weakly complexed sulfide) was present as H2S. In this case, the piston velocity of H2S would be the same as that of Radon for a given wind velocity, with a small correction (a factor of 1.14) for the estimated diffusivity difference. If we then specify the piston velocity and OH concentration we could calculate the concentration of H2S in the surface waters. Using the input conditions from model run B from Figure 4a (OH = 5 x 106 molecules/cm3, Vd = 3.1 m/day) yields a sea surface sulfide concentration of approximately 0.1 nM. Figure S illustrates the diurnal profile of atmospheric H2S which results from these calculations. 

Abstract Supernovae are a prominent component of modern astrophysics. They are responsible for a major part of the chemical enrichment in the universe and the main recycling mechanism in galaxies. The physics of these explosions is fairly well, although not completely, understood. 

Keywords Supernovae explosion physics chemical enrichment... 

Stimulated by these studies, samples of primitive meteorites were inspected by neutron multiplicity counting. In the Allende meteorite available in large quantities, a weak fission activity at the 1014 g/g level was reported [71-73] but could not be chemically enriched [74-76]. 

In conclusion, this is the poison paradox chemicals have useful and beneficial effects but under different conditions the same chemicals can be harmful. Some chemicals can cure our ailments, improve our mood, or make our food taste better others can be used to make valuable products such as brightly coloured paints, parts of computers, or cars, and many kinds of plastic or flame-resistant clothes. There is a multitude of ways in which chemicals enrich our society, yet at the same time, if they are misused or used without respect, they can be hazardous. When a person takes or is given a dose of a drug that is too high, or is exposed to a concentration of a chemical that is too high (say in an industrial accident), adverse consequences inevitably foUow. As Paracelsus commented centuries ago All substances are poisons there is none that is not a poison. The right dose differentiates a poison from a remedy ... 

Peridotite fertilization may also result from the fractional solidihcation of exotic (deep-seated) melts inhltrated in wall rocks of translithospheric magma conduits. This process was hrst described in composite mantle xenoliths (Wilshire and Shervais, 1975 Gurney and Harte, 1980 Irving, 1980 Wilshire et al., 1980 Boivin, 1982 Harte, 1983 Harte et al, 1993 Menzies et ah, 1987), where it is referred to as modal metasomatism when new (generally hydrous) minerals are precipitated (Dawson, 1984 Kempton, 1987), or Fe-Ti metasomatism (Menzies et al., 1987) when the attention is focused on chemical enrichment. In contrast with ultramafic xenoliths, the tectonically emplaced and oceanic peridotites contain only sparse rock types attributable to mantle metasomatism by deep-seated melts. Examples of wall-rock, modal, and Fe-Ti metasomatism were nevertheless described in IP orogenic Iherzolites, notably in the Pyrenees (Fabrics et al., 1989 Bodinier et al., 1988, 1990, 2003 McPherson et al., 1996 Woodland et al., 1996). 

Most of the orogenic spinel Lherzolites also contain small amounts of amphibole ( 1 %) textu-rally equilibrated with the peridotite minerals. These amphiboles have been ascribed to the infiltration of melts/fluids in mantle conditions (Fabries et al., 1991), but their presence is not associated with noticeable chemical enrichments (Vannucci et al., 1995). A possible explanation is that the liquid/rock ratio was so low that the fluid composition was buffered by the LREE-depleted composition of the peridotites. Alternatively, these amphiboles might represent the products of a late crystallization stage during fertilization of the peridotites by LREE-depleted basaltic melts. 

However, a few examples of metasomatism and chemical enrichment by alkaline, deep-seated melts have been described, notably in the St. Paul s Island oceanic peridotites, in the Atlantic Ocean (Roden et al., 1984) and in the Lherz orogenic massif and neighboring massifs such as Caussou, in the Eastern Pyrenees (Fabries et al., 1989 Bodinier et al., 1988, 1990). 

However, the information conveyed by mantle xenoliths indicates that stable subcontinental lithosphere is dominated by refractory peridotites which are enriched in HIE and LREE and have often acquired an enriched isotopic signature as a result of time integration of their chemical enrichment (see Chapter 2.05). Therefore, an alternative to the porous-flow model is to consider that the harzburgite layers represent strips of lithospheric peridotites embedded into more fertile material derived from the asthenospheric mantle (e.g., the Lherz massif, Eigure 30). In this scheme, the and Sr/ Sr versus... 

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